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[Question] [ For my story I have an alien species who are detrivore. They are also an intelligent species on par with humans. But many people have pointed out to me that intelligent detrivores don't work, because their diets don't support a large brain or a large body. My question is therefore whether intelligent detrivores that are human sized could exist on a planet with the following characteristics: * super sized fauna being super common (for average size think titanosaur) * most fauna having super inefficient digestive systems so that their waste is rich in calories * detritus covering the floors of almost all the land on the planet [Answer] ## The answer is: Possible, but contrive Let's face it, detrivore is **not** a good option for the kind of energy needed to support a large brain / body ratio. By the time they eat, their food have already pass through at least 2, probably more trophic level (plant => herbivore => carnivore (continue for more carnivores)). Combine that with the fact that what the detritivore eat is waste (ie. not as good as the organism itself, and laden with substances that is at least harmful to the excreting organism), there is not much left for them to pick over here. On the other hand, a big, well-developed nervous system is an important foundation for intelligence. Enter the [slime mold](https://www.nature.com/news/how-brainless-slime-molds-redefine-intelligence-1.11811), eater of various organic scrap, and surprisingly intelligent (not human level though). They can solve mazes, choose healthy foods, and plan ahead of time (so at the very least, they are smarter than me :o). Currently still under study, so we don't quite know how they do those things yet, but I think being a collection of multi-nuclei cell with capability for cooperation as a colony play a big part in it. Another thing you might want to know about intelligence is why the organism develop it in the first place. Plant can gain lots of energy from the sun, which means they only need to be smart enough to search for light, water, and nutrients and out-compete other plant for it, so they don't need much intelligence. On the other end of the spectrum, carnivore need to compete with both their prey, and other carnivores of the same trophic level or above it, so they tend to be more clever. The only main challenge for detrivore are environmental conditions and predators, so not a lot to go on here (even the slime molds above only become multicellular if the condition are harsh, which affect everyone). The good news is intelligence reward having more intelligence, so as long as you make the first step, things are looking up from there. So sure, if the planet you are imagining is ridiculously abundant, but only in a few specific spots, and harsh in everywhere else, with energetic sun to support a lot of energy going through different energy level, but damaging in places without plantlife (not impossible), **and** somehow the carnivores don't develop intelligence first (that will be a problem), then yeah, you can have an intelligent detrivore that's as smart as human (their expression of it will be different though), but bigger in size, and probably composed of many less intelligent smaller organism that might bail if the condition become too plentiful though. There is a simple, hand-wavey solution to those problem by just making the detritivore organism have extremely different metabolism than the rest of the biosphere, so that a normal, plentiful, temperate environment for everyone else is a harsh place with bountiful spots to them, and somehow their vital nutrients are indigestible to everything else. But then you have to explain why they are the odd one out in the entire biosphere. **Additional information:** There is an inherent problem with the intelligent detrivore though, depend on their tech-level in your story. If they have advance enough to overcome other flora and fauna of you world, then there is a good chance that they won't **stay** detrivore, but develop agriculture and animal domestication, and eventually become omnivore (like us) instead. Therefore take their intended culture into account before you make the species. [Answer] If you stick with your idea of huge mega-fauna with vastly inefficient digestive systems to provide the nutrition then it might just be possible... As mentioned in the other answers intelligence requires a reason to evolve and eating faeces doesn't exactly require a huge amount. But if you consider that most of the herbivores are colossal giants then it makes sense that carnivores may have a hard time feeding on them. Even more so if you make them somewhat toxic (let's say they feed off a plant that's toxic but they are immune to it and the toxins build up in their bodies). So your intelligent detrivore is specially evolved to maximise the now safe calorific content of these beasts waste, and as such are the perfect target for carnivores. The detrivores then evolve intelligence to evade their predators. I'm imagining they might be a long lived but less numerous species so you don't need quite so much waste to sustain the population and there is a drive for each individual to survive which leads to the development of intelligence. And if you say their digestive system has evolved to only be able to process the waste from your megafauna (or the rest of the possible food on the planet is highly toxic in some way) then they can stay detrivores past the point where intelligence might make them carnivores or omnivores. [Answer] Intelligence only evolves if it is needed. I can't really imagine detrivores needing intelligence to hunt down their food, and that's what intelligence is for. But intelligence is also easier to evolve if communication between a group of individuals is needed for daily survival, again, I cannot imagine they would need to utilize teamwork if their food just lay there "covering the floors of almost all the land on the planet". They would probably jut evolve a shell for defences and stick to the ground because they don't really need to work for their food. So even if they have all the nutrition required to evolve a big brain, it would be much more efficient not to have one, which means intelligence in this species would not naturally evolve. **ETA months later:** I'm surprised I haven't thought of this first but human diet also contains excrement. This food item is called "wine" or "beer" or, indeed, any fermented beverage or food. Although humans are not evolved to make much use of alcohol, it contains a lot of calories - as evidenced by its use as biofuel. The yeast or some sort of bacteria that consume sugars like yeast would need to live inside the bowels of your super-sized fauna and the droppings would need to be at least gelatinous for this to work. I'm no biologist though, so not sure how realistic this would be. [Answer] While intelligent detrivores are not impossible, it may be improbable. One way I can think of to support your idea is to have the plant life or the fauna or both, excrete waste products that are actually highly beneficial to your detrivores and chemically alters their intelligence and consciousness over time to improve and expand it. Like magic mushrooms but increases your IQ, EQ etc. Hope this gives you a germ of an idea on how to proceed. [Answer] The only way I can guess it can work is a particular combination of **high solar energy** and a **full symbiotic cycle**. Too much light: This planet receives an awfull amount of energy and thus anything living under the sun must be sturdy to survive it. Plants are bold and with a rich soil and lots of umidity even the grass of this planet looks like a tree. Those big tree-grass are food for species of big scarabs like insects, they sawrn like a plague and eat like termites (maybe even using bacteria to digest de celulosi) but they life cycle is short. They eat a lot and die full off eggs but not before tranforming a big area of grass in bug-poo. The slime-mold-intelligent detrivore will come at night, maybe pouring from subterran to avoid the sun light. They will feast in the sugar rich bug-poo and bug-corpses but symbiotic nurture the bug eggs. After million years the slime mold start to become more smart and develops a efficient bug farming. They can start to develop grass plantations to feed the scarab-cattle. From farming follows all the traits of a cvilization. [Answer] I've read that there are kinds of trees that harbor ants who protect the tree. In the extreme case the tree provides places for the ants to nest, and feeding stations. Also there are trees that are "intentionally" hollow, to provide places for bats etc to live in relative safety, and the bats spending their days inside the tree naturally excrete there which provides minerals the tree needs. You could combine those ideas, directly or not. Giant herbivore. It nurtures a colony of intelligent human-size detrivores who protect it in various ways, and it feeds them. They can ride the herbivore and it gives them various kinds of protection also. Rabbits etc excrete their partially-digested food and eat it again. This herbivore could feed that -- or part of it -- to its commensals. Giant plant. It harbors giant birds that bring it minerals. The birds need lots of energy to fly, and they strip out the easiest-to-digest parts from their food, and dump the rest inside the tree. The intelligent detrivores care for the plant and the birds (and might sometimes kill or drive off a bird that behaves wrong). They eat the food which the birds haven't digested, and perhaps ferment it further to get the digested cellulose etc. This doesn't seem completely plausible to me. I'm imagining flying elephants that carry lots of elephant shit home. But consider panda bears that eat lots of bamboo they can't digest well.... Still pandas don't have to fly carrying the excess weight. Something like this seems possible but not the default. Now I'm imagining these creatures thinking about space travel, and the necessity to take their trees and elephant-birds with them.... ]
[Question] [ I have a species of ambush predators that are going to be sentient space-farers one day. But to get them on that path I need them to evolve hands, which will lead to tools, and so on. They come from a world of wide open grasslands, mountainous regions and canyons, no large forests. The predators themselves are built roughly like tigers, they lack a tail, and instead they have several long flat antenna growing off their heads that they use to entangle prey after jumping onto it in order to bring it down. What can I introduce to their grassland environment to help them develop dexterous grasping hands? I can give more information on both the world and predators as needed. [Answer] As others have mentioned, the basic food web needs to change. Felines pouncing on game don't really require hands so much as claws to hold and pin. Reasons this setup could require hands: 1. The feline is (slowly) forced towards omnivory and/or out of the apex predator spot. Specifically, food that requires preparation or overcoming some passive barrier of some kind. If you can just get the nutrients from biting something, the big brains and dexterous hands won't develop. Look at scavengers like rats or raccoons. 2. Bipedality becomes useful in addition to another mitigating factor. The grasses become too tall and thick, or the prey evolves some way to totally avoid detection from ground-level might point towards bipedality, but that bipedality might only need tiny T-rex arms. You'd need some reason to use those now-freed-from-walking digits. Complex social requirements? A longer onboarding process for young? Taking down prey suddenly requires eye-gouging ala Three Stooges? 3. Tool use. Prey starts using burrows that require you to use a stick to get them out. Lean times has the felines start eating bugs like termites where obtaining them at a distance is the best way to avoid being bitten by the whole mound. Prey develops some armor that outdoes the felines' bite strength or teeth sharpness, requiring the use of a rock to break it open. [Answer] > > What would it take to make this “Big cat” species evolve hands? > > > There would have to be an *advantage* to having hands. Say... if they **dwelled in the trees**. Not just climbing up *big* trees and laying on big lower branches for napping and scanning, but actually *living* up there, jumping from branch to branch and tree to tree, where opposable thumbs really useful for grasping. Of course, there aren't dense forests (where hands are needed for leaping -- and grasping) from tree to tree in the grasslands. That's why there aren't any hand-grasping creatures except man in the African Savannah or the American Great Plains. But where did man evolve from? The trees. [Answer] **[Polydaktyly](https://en.wikipedia.org/wiki/Polydactyl_cat)** (having additional toes on each foot, including opposing "thumbs") is a mutation that occurs naturally in cats and it is speculated that polydaktyly was evolutionary advantageous for ship cats (it is frequent in cat populations founded by ship cats at many places of the world). So it is not too far fetched that a big cat evolves some kind of "hand". [Answer] You already mentioned that they jump on their prey and then bring it down. Have you ever tried to grapple with someone without using your thumbs? It's hard. Even with the antennticles, that might be your evolutionary pressure right there. Also, my house cat "grips" things between her paws all the time. And at least here on Earth in the real world, it's easy for most species to adapt extra digits when needed. [Answer] The hands would appear when the brain requires them. To have a need for hands, the animal would need to handle small objects. Thus, I can suggest several ways for you. First, obvious, is a gradual decline of prey that you can leap upon, with the increase of prey that you can just pick up. Cats gradually turn from carnivores to insectivores, may be rodent eaters. Then hands will evolve for the ease of picking, the use of tools in form of sticks for digging, so on. Another, more fantastic. Introduce a plant to your world, that has fruits that are deadly poisonous to touch. It may be like a chestnut with deadly spikes, or it may contain the poison inside and the hit makes it to burst open. You carnivores learned to pick those objects and hurl them at their prey. More agile ones are better hunters, so agility with small items increase. ]
[Question] [ A group of space criminals collectively known as the Butchers is gathering enough power to be considered as a serious threat. Although they are nowhere near as powerful as the two major space empires, they are large, heavily armed, and able to be a serious thorn in the sides of the two major space empires. The Butchers are composed of four separate groups. 1. Pirates raid other ships that are already in space. They prefer convoys that are already in deep space, and are very adept at capturing valuable ships, repairing them, and either reselling them or using them themselves. 2. Raiders are similar to pirates, but instead of attacking ships, raiders attack settlements. There they take supplies, weaponry, food, water, and anything else they want. 3. Outlaws are people or groups that are wanted by either of the other space empires and have decided to live outside of the law. They live with very few rules and tend to be excessively violent. 4. Slavers either buy captives from the other three, or directly attack ships or settlements on their own to capture people. They turn their captives into slaves for use or sale. All four groups are ruled by the Butcher King, a former general from one of the space empires that was removed from command because of his extreme brutality. He is personally motivated by his hatred for the rest of civilization, and uses the Butchers to harass the less protected elements of each empire, while also attempting to cause tensions between the two to escalate until full scale war breaks out. The question here is what holds this group of criminals together? Obviously the threat of violence from the rest of the group would be effective, but it seems like that alone would fall far short of keeping this group unified enough to be a serious threat to two technologically and numerically superior foes. If it helps the Butchers have access to faster-than-light travel, drones, and AI, but all of it is at least slightly inferior to their more civilized counterparts. [Answer] ## Fuel As you know, Liquid MacGuffinium (LMg) is the main source of fuel for all space travel in the galaxy. Now, in the space empires, the production and sale of LMg is highly controlled and regulated (after all, if you had enough raw MacGuffinium in one place you could blow up an entire planet). To refine and produce such an important resource requires an entire supply chain for extraction, purification, refining, and acid purging, in order to create the safe, fuel that spaceships need. Rumor has it, that the Butcher King has a fully functioning, albeit less safe LMg production facility hidden in the asteroid belt of some far off system. This production facility is no doubt heavily guarded by the Butcher King's loyal former legion, and indeed that is where you can find his massive dreadnaught. Word is, even if some daring crew could gain control of the station, they wouldn't be able to run it. The only refinery engineers out there that know how to operate a facility like that are either part of the Imperial Navy or loyal to the Butcher King. Thieves, pirates, raiders and vagabounds must either (dangerously) outfit their ships to run on raw MacGuffinium, spend all of their time raiding heavily defended LMg transports, or buy it from the Butcher King. ## Fear The Butcher King watches all. His eyes and ears are everywhere, and he suffers no traitors. The word is out: the Butcher King always gets his cut. The evidence of those who hid their scores from the King are plain to see. There's the husk of the mighty pirate dreadnaught that was cut in half from space, orbiting that planet like a ghastly moon. Outside of the trading port, there lay a massive pile of heads from the last Raider crew who didn't pay the King his due. Turn in your crew and you will be rewarded by the Butcher King. Defy him and he'll send every Outlaw, Bounty Hunter, Assassin, and Saboteur in the sector after you. Or sometimes he'll just "accidentally" leak your ship's location to the nearest Imperial Cruiser. ## Loyalty The Butcher King? Oh man, he's the greatest. When you hear him talk, it makes the Butchers feel like they're not the scum of the galaxy. The empire might look down on bounty hunters and scavengers but the Butcher King? He protects them. He loves them unconditionally. He takes the people cast out by the empires and gives them a home. He knows the Empire, inside and out, used to run one of their legions. He knows that the butchers are destined for greatness. He's going to lead the butchers out of this forgotten sector of the galaxy and one day, the butchers are going to take back what's rightfully theirs. [Answer] **Technology** If these assorted raiders are using advanced gear like faster than light, AI and drones they must have access to a relatively high level of technology. Maybe the Butcher King has monopolised the best minds in the sector or simply owns all the power plants and resources. Even if the bulk of the technology is stolen from the empires he could have all the best mechanics to repurpose it for bandit use. **Tribe** The raiders could be unified by a shared ideology, ethnicity or religion. Their common codes could encourage unity or they could simply be so badly treated by the other tribes and civilizations in the area that sticking together and playing nice is the only way to survive. **Friends in High Places** Made less likely by the Butcher King's zealous hatred of the empires but still possible. Maybe some faction within one of the more advanced civilizations has an interest in keeping the Butcher King in place. He could form a handy buffer zone between the two power blocs or be tricked/persuaded into attacking their rivals. This could work in various ways. They could be directly liasing with the Butcher King or one of his high-ranking lieutenants. Alternatively they might be manipulating him behind the scenes by tricks of espionage or implanted agents. [Answer] Humans are social creatures, that much is for certain. We tend to cluster into groups so we can do more than we ever could alone. With criminal organizations, the goal is usually to make as much money as possible. What you've got here is a combination of star mob and space pirates. Let's take a look at each group in specific: ## Pirates Groups like the pirates would be motivated by the next haul. They'd be inseparable from their crew, but only loosely bound to the butchers in general. Maybe some sort of guild system could be in place, where only those who have sworn fealty are allowed into 'safe' ports where the empires can't get them. ## Raiders They'd probably work just the same as the pirates. Historic pirates generally did what they wanted, whether it was terrorizing sea ports or taking ships at sea. There would be significant overlap between the pirates and the raiders. In the interest of character development, the raiders would have a much more Nordic air to them, while the pirates would be buccaneer-y. ## Outlaws Go watch the entirety of Firefly. Do it. Now. OK, now then... Take note of the way that the Captain acts. This is pretty typical of the Outlaws. They're not in this for the gold or the glory. Outlaws want to do what they want, and be left alone otherwise. They'll submit to guild membership if it makes them safer, but don't expect them to show up to war parties. ## Slavers These guys need people, both as customers and merchandise. I expect that they'd be the richest of the butchers, and that they would manage the stations and coordinate everything. They're sociable, but they have a drug lord type of cruelty that keeps them ruthless. (as a joke, they should probably execute anybody named Ruth. Gotta stay ruthless!) All together, the guild is what keeps them functioning. The guild provides safety and is, essentially, a step-in for society. For a price, the guild would provide everything a criminal could need: safe ports, entertainment, fuel, entertainment, quality fences (picket and otherwise,) entertainment, shopping, entertainment, alcohol, and entertainment. In the end, the utility of the guild is why the guild exists. Welcome to economics 101, class. Textbooks can be bought in the bookstore, or rented in the library. [Answer] **Give them Freedom** The major space empires are dystopias where people have no freedom at all. Your butcher provides freedom which all the pirates and raiders want. Once they have experienced freedom, they will never want to return to the space empires again. **Give them a cause** similar to the one above. The butchers could be fighting for a greater cause; freedom, liberty or whatever from the space empires. Perhaps they could be a cult, brainwashed into following the Butcher King. Or, they are part of a rebellion, fighting against the tyranny of the space empires. [Answer] The easiest reason is the Butcher King is the fence or controls the fences/ pirate trading port. Without a means to sell ill-gotten goods and buy illegal gear and repairing and refueling ships, the butchers would have a very hard time operating. The Butcher King could quite easily an unknown face and well connected in legal society. He pays bribes for information to feed jobs back to raiders and bribes for authorities to turn a blind eye. Every so often he sells out people who displease him in return for police favors and keeps the worst excesses under control so authorities don't try too hard to shut them down. The butcher also does tit for tat favors attacking the other side so both sides can claim their hands are clean while kneecapping their opposition. ]
[Question] [ Maneouvrability is a potentially significant advantage in almost any battle. But, the maneouvrability of a spacecraft with inhabitants is limited by the inhabitants's tolerance to accelerational forces. Humans generally can't tolerate high g-forces for a long time. Even to horizontal g-forces, which are more tolerable than vertical g-forces, untrained humans can tolerate 20 g for less than 10 seconds, to 10 g for 1 minute, and 6 g for 10 minutes (Source : [Wikipedia](https://en.wikipedia.org/wiki/G-force#Horizontal)). The limits for trained humans may be higher, but not much higher. Considering that, I put forth a system, where most battleships are remotely controlled from specialised control ships, where the crew are. A crew member sits in front of a computer, controlling what he is in charge of. He sees what he needs to see, and not too much else (e.g. a gunner sees his field of fire, whereas the admiral sees the entire battlefield). Obviously, in such a system, the most valuable targets would be the control ships, much like the generals were in historical battles. The loss of a control ship means that all the ships controlled from it lose some degree of control (not necessarily all control, since the other control ships can take it over; but they only have basic control such as "move there", "fire the forward guns", "self-destruct", etc.). The loss of all control ships means that the battle is lost. Because of that, control ships are generally the most well-shielded. Details on FTL travel: * Ships can travel to the battle site faster than light but can only battle at subluminal speeds. * Faster-than-light travel is done through "hyperspace" and has a 15 minute recharge time, ship time (after emerging from hyperspace, ships need 15 minutes before being able to activate FTL again) * FTL travel speeds vary from 10,000 to 40,000 times the speed of light, with the average being 20,000 *c*. * A ship retains its direction of movement when entering hyperspace, and upon leaving hyperspace its speed reverts to the speed before the FTL travel. For example, if a ship travels at 0.001 *c* and enters the hyperspace, upon leaving it its speed would be 0.001 *c*. Corollary : If a battleship were to travel FTL in a direction it's not heading towards, it either uses the subluminal propulsion system to adjust its direction then actiivate FTL, or activate FTL first, emerge in a relatively safe location, adjust its direction while waiting the 15 minutes, and activate FTL. * A control ship *can* travel FTL, but if it's not travelling FTL, its acceleration is limited by the crew's tolerance. * FTL communication without FTL travel is available, but the transmission and reception facilities needed is too large to be put in a ship. Such faclities are generally built on planets. Therefore, ships in a battlefield communicate at no more than *c*. Details on combat capabilities: * Ships only battle (fire guns, launch fighters, etc.) at subluminal speeds. Guns *can* be fired in hyperspace, but why waste ammunition? * Battles are conducted at a range of about 1,000 km ("close quarters") to 300,000 km ("long range"). * Battleships and control ships have shields; shields deplete as energy (including kinetic energy but not including the $E=mc^2$ mass-energy) is thrown to it. * Shields stop only incoming projectiles etc.; shots from inside are practically unaffected. * A ship generally can take 20,000 hits from "standard-issue" guns (which are the most numerous of the guns), a large battleship can take 30,000, a control ship can take 40,000. Missiles are about 10 times more effective, but 20 times fewer. Battleship main armaments can take down a control ship with only 40 hits. A control ship can usually be destroyed with a 200 MT of TNT weapon. * Most of the weapons used are subluminal; projectiles travel at around 20,000 m/s. My question: > > How far **from the other ships** would the control ships be located? What distance is a good compromise between response time and safety? > > > Edits: * The ships travel as fast as needed (and tolerable, for control ships). Remember, this is space, there's no atmosphere to slow you down. So acceleration is more important. Control ships are usually capped at 1 g, but can accelerate to 6 g for a short time. Other ships can reach 100 g on average, with the range being 40 g (heavy battleships) to 250 g (fast, small ships). Fighters can reach 400 g. * Control ships are about 750 m long, heavy battleships 1,500 m to 2,000 m, fast cruisers 500 m. * Let's say communications technology has developed to the point the equipment is resistant to being disabled, and that communications can't be intercepted nor faked (one side can't control an enemy ship). * You can't just disguise a control ship as a controlled ship; sensors are available which can detect shield strength. * A shield **extends to hyperspace** forming an "umbrella". Trying to emerge on **or near** a shielded ship results in prompt, utter destruction of the attacking ship, and little damage to the attacked ship almost regardless of the previous speed of the attacker. (But yes, if the ship's shield is down, an FTL attack can take down the ship.) The umbrella is about 15-20 km in diameter. * If a fighter starts from zero speed and uses all its fuel to accelerate in a straight line, it can reach 5 MT of TNT equivalent. * **Fighters can't travel FTL.** The smallest ships which can are about 300 m in length. * Each crew computer has a toggle for "automatic mode", in which it takes general orders (such as "fire at that ship every 10 seconds") and executes them automatically. But, the operator can override it or disable it altogether. [Answer] ## Time Light travels at 300,000 km/s. In the largest battles, you'd want to station your control ships on the edge of the fighting. Let's say that each one is responsible for controlling ships in a sphere with radius 150,000 km. This means that if a fighter detects something and needs to avoid it, it has to send a signal to the control ship (which will take half a second). Someone on that ship needs to make a decision; let's say they make an evasive maneuver within one second. The signal then takes a half second to travel back to the fighter. This adds an extra second - which can be critical with projectiles and ships traveling so fast. You said projectiles can travel at 20 km/s; if a ship can send a guided missile of sorts at that speed from 10 km away, it will hit the target in half a second - and the control ship won't have been able to do anything. Most shots will likely be fired at closer ranges, which gives even less time to react. That's also bad enough, but having a control ship half a light-second away makes thinks worse. You need to reduce the distance of the control ships *drastically*. Ideally, transmission should happen both ways in less than half a second, maybe less. So that puts you maybe four times closer to the ships - and also puts you in range of enemy attackers. I would say that, in terms of timing alone, you'd want to be **less than 40,000 km away** from the section of the battle you're controlling. ## How to attack a control ship Say an enemy fighter can travel, in battle, at a kilometer each second. That means that it would take 40,000 seconds traveling at that speed to reach the control ship, from the thick of the fighting. That is, give or take, half a day. Even if you increase this by a factor of ten, it would take an hour. That's not feasible. You'd be detected long in advance and destroyed with ease. You can't surprise the control ships. The alternative? Jump through hyperspace. On an attack run, a fighter picks up speed, then jumps to about 10 km away from a control ship. If their pre-jump speed was 1 km/s, they've got 10 seconds to start their attack, and the control ship has 10 seconds to respond. If the fighter does things just right, and aims properly, they'll be able to get in a strafing run or two. A big problem could be suicide attacks. Increase your speed to 10 km/s pre-jump and aim just for the center of the control ship, the bridge, the engines, or the communications structures. Assuming you did it right, you'll hit your target in 1 second, and the control ship won't have time to move away. So, how do you guard against these? I don't have great ideas here. You could have the control ship be constantly moving, but it can't turn too quickly - it's got humans aboard! It's defending against an attacker that has the ultimate element of surprise, and can be there in an instant, once the shields are knocked down. So here's the problem: **The enemy will always bring the battle to the control ship.** They might try an attack plan like the following: * If there's a different primary attack target - a flagship, a moon base, a space station - send one quarter of the fleet to that target. * Send another quarter of the fleet to attack the control ship and bring down the shields. * Once the shields are down, use data from the ships already there to let the other half of the fleet know the control ship's position and velocity. * Take it down via suicide attacks (or by jumping to hyperspace and launching a missile when the attackers come out). ## Mitigation Like I said before, you can't guard against this sort of a strategy too well. You have to hope you can keep your shields up long enough to fend off the attackers (or if the control ships are on the offensive, hit your targets). Now, I said I didn't have great ideas about how to fight this. But I have a couple: * **Use redundancy.** Have each fighter be able to be controlled by two control ships. One control ship will take on additional fighters if another is hit. * **Jump to hyperspace.** You can do this once every 15 minutes. In a pinch, do this as a last resort . . . assuming you can't be tracked this way. * **Give the fighters some AI.** This is a good option, if you have the tech. It can have basic functions - evasive actions, some weaponry control, etc. Also, you could have intermediate-level ships have the ability to command fighters in the near vicinity. --- ### A note on communications structures Every large enough sci-fi vessel has some sort of vulnerability, buried deep down (according to tropes, at least). Barring that, there's some critical part of its infrastructure that needs to be protected. For the Death Star, it was a womp-rat sized target in a trench; for the second Death Star, it was the shield generator on a moon below. The thing is, you don't need to destroy a control ship entirely. You just need to knock out its communications arrays. It doesn't matter if it still has weapons or fighters; *it can't control the rest of the fleet if it can't transmit data*. This means you need additional layers of shielding, just for those sections. The alternative to shielding, of course, is to remove the control ship far from the battle. But as I wrote before, that makes it ineffective. [Answer] > > How far from the other ships would the control ships be located? What > distance is a good compromise between response time and safety? > > > @HDE 226868 is right: if they can, [the enemy will always bring the battle to the control ship](https://worldbuilding.stackexchange.com/questions/102240/remotely-controlled-battle-starships/102241#102241). A control ship close enough for effective realtime subluminal communication will be quickly detected and hit by remotely controlled attacks jumping FTL to the site of the control ship. Not really suicide attacks if they are remote controlled. Side note: subluminal communication is presumably electromagnetic lightspeed radiation of some sort. This cannot be faked (per OP) but can be easily interfered with by massive noise generators. Although that would cut both ways. My proposition: **Pony Express.** Your FTL communication requires stuff too big to put on ships. But your ships can go FTL. If vehicles can move faster than light, send your communications on the vehicles. A relay of small jumping vessels can bring communications near the site of the battle, recharge the FTL and then jump back with fresh updates from the front. Around a battle at any given time would be a large number of droneships (none concentrated in any one spot) which blink into space in the vicinity of the fight and transmit communication to the nearby drone fighters. After recharging they pick up communication from the fighting drones just before blinking back. There would be enough of these to make communication continuous. With more you could also make communication redundant. With the FTL pony relay, your control ships can be arbitrarily far away. They cannot be traced unless you can track the FTL pony ships somehow when they return. --- A seemingly clever trick would be to put a locator beacon on one of the returning ponies and detect its signal when it blinked out of FTL near the command ship. Some slick scifi: the locator beacon is detected and destroyers are sent to the vicinity of the locator beacon. There is nothing there but an long-abandoned planetary base. Someone had come up with the same idea some decades before and when no signal was received from the locator, decided that it did not work. But it did work. Light is just slow. [Answer] I would consider a beacon system, in which a small beacon floats relatively closer to the battle and uses radar cloaking tech to stay out of view. The pilots of starfighters would be stationed here, and the commanding officers would stay on control ships on the outskirts, as they don't require split second reaction time. With the beacons, the starfighter pilots are close to the fighters so the commands take almost no time to transmit. [Answer] Since your remote crew essentially operate the ship as though they were there, we can model the effects of round-trip comm latency as an online game. We'll presume open space with noise not a factor, and hardware effects on latency negligible. Distances are the sum of distance between the command ship to the remote ship and the remote ship to the enemy (due to sensor latency) **1500km**: 10ms Latency. Ace range, crews can operate ship as if in person. Human reflex limits are bottleneck. Probably favoured by your ace gunners etc. Weapons within 75secs of command ship. **2795km**: Fighter kill range. Assuming a fighter the weight of a space shuttle (~75 metric tonnes) a fighter can accelerate to 105km/s and 200MT of energy within 26.5 seconds and covering this range. Your command ship should probably be able to swat a target moving at speed in a straight line from at least this far. **7500km**: 50ms Latency. Optimal range, where most people can react. Past this point performance starts to decline. **15000km**: 100ms Latency. Outer limits of FPS play. Maximum range for gunners, past this point fire control needs to be turned over to automatic systems. **18000km**: Outer limits of standard weapons. Assuming 20km/s is a limit for relative velocity (ie. Aiming breaks down past here) past this point a ship can hyperspace quicker than weapons can reach it. **75000km**: 500ms latency. Outer limits of third person (say, racing) play. Maximum range for pilots, past this point is autopilot land. **150000km**: 1000ms latency. Outer limits of RTS play. Maximum range for tactical control, past this point it's likely only broad strategic control will be practical. This all, of course, goes out the window if c-fractal hyperspace missiles (kamikaze fighters) are in play. I'd suggest tuning the details of your hyperspace system to prevent such a strategy from being effective. (Maybe you crash into the shield from anything more than N seconds away, making point defence easy? Jumps are predictable? Your call) To answer the question, about 18000km from the battle would be the safe distance, but would be operationally impractical since a closer command ship would have better performance and outfight your fleet. Optimal engagement range would place the command ships somewhere between 7500-15000km from the 'front'. They would need to manoeuvre somewhat since they're still 'in range' but their attendant fleets would have a significant advantage against an opposing command ship staging a remote attack. Bomber command ships and other ships commanding vessels with simple fire control may be able to work out to a good 75000km though the bombers would be pretty vulnerable - though effective if the opposing fleet is tied up. [Answer] # Use AI compounded with remote control. As said in user\_194421's answer, the battle area is generally too large for light-speed communications to be effective at controlling craft, as there will be a noticeable and possibly life-threatening delay. The solution is to use less commands. With sufficient technology, an AI can be developed that runs the ship (i.e. directly interfaces with maneuvering and weapons systems), but also takes a higher-level objective from control ships. These "objectives" could be like "Kill enemy ships", "Destroy something" or perhaps just "Patrol the area". The delay will not be as critical as all immediate decisions are being executed onboard. [Answer] **The problem with shields, in this context** You need to reconcile the Star Trek transporter dilemma wherein having shields up prevents certain high density data signal data transfers, such as transporters. At the end of the day, since the field units are limited to non-FTL communications, they are going to be limited to radio signals. They can be encrypted, they can be intercepted, they can be jammed, they can be drowned out by radiation surges or a strong enough magnetic field, like from a planet or sheild generators. So shields up or continue transmitting? I imagine that a lot of strategy in this universe will revolve around communication drones to help extend your control network and reduce the visibility of your command ship's EM signature, decoy drones that send out a similar EM signature to a transmitting command ship, and signal jamming / electronic warfare. Unfortunately, ECM is going to evolve at the same pace that your communications technology does - and in this kind of strategic paradigm there's a strong incentive for it to evolve faster. It sounds like the best investment a defending planet or space station could make is in high-power jamming in fact. ]
[Question] [ Could a structure similar to that shown in the image below inspired by Roger Dean’s “Close to the edge” actually exist in nature? If not could it be constructed artificially and if so how? Assume the two bodies of water obscured by the mountain on the right terminate in waterfalls and that the waterfalls run constantly at high volume. [![Close to the edge](https://i.stack.imgur.com/O9OxT.jpg)](https://i.stack.imgur.com/O9OxT.jpg) [Answer] Yes, this is strictly a matter of size. You need a massive influx of water from rain, which is proportional to the surface (goes roughly with the radius squared), while the waterfalls outflux is proportional to the circumference of the plateau. When the radius is large enough, you can get enough water to feed all the waterfalls. In nature however you'll get *some* waterfalls to erode faster than the others, lowering the water level, so that you don't really get a continuous range of waterfalls; given long enough, "there will be only one". So you need a maintenance mechanism that counteracts the erosive effect (which for waterfalls is huge - I heard that the Garganta del Diablo falls back half a meter every year, or something like that). You could posit some kind of reef coral able to grow and counteract the erosion; the coral cannot live outside the water, and it thrives at the brim due to the influx of oxygen and food particles, so it only reaches up to the brim, reinforcing it. Also possibly imperceptibly raising it over the centuries, so that the plateau slowly becomes a "cup". The effect is self-limiting, because if the coral grows too much, the waterfall slows down, oxygen and food become scarcer, the coral begins to die and the "waterfall-less" area crumbles, restoring the waterfall at that point. # Taking a rain check We cannot have too large a plateau because we need to get humid winds all over it, and there are no plausible mechanisms that allow this on a Earth-sized planet, constantly and for very long distances. Also, as @Braydon correctly pointed out, if we have a moon, or the same strong winds that feed rain to the plateau, they'll start interacting with the water surface and disrupt the waterfalls. So let's try to come up with a size estimate for the plateau. It needs a *lot* of rain. On Earth a plausible "lot of rain" (monsonic rain) is around 120mm/die in multiple daily or nightly showers (I witnessed a 250mm/hour downpour and was quite shocked, but survived). A [waterfall rate](https://en.wikipedia.org/wiki/List_of_waterfalls_by_flow_rate) like Niagara is 2500 cubic meters per second over 1200 meters of aperture. Let's approximate it to F = 2 cubic meter per second per meter of aperture. The available water daily rate is 12cm, approximated in P = 1/8 cubic meter per square meter. Every eight square meters of surface we have, give us one cubic meter each day and no more. One day contains 86400 seconds, so every meter of the circumference requires F\*86400 m3 of water, which means we need F/P\*86400 m2 of surface to sustain each meter of circumference. So it must be true that (imagining the plateau as circular) surface $\pi r^2$ is F/P\*86400 times the circumference $2\pi r$. With F=2 and P=1/8, F/P is 16. $\pi r^2 = F/P\*2\*86400\pi r$ means a minimum radius of r = 2764800 m, or 2800 km, and a surface of 24 million square kilometers - more than three times the size of Australia. In short, $r = 17280\*F/P$ with r in kilometers, F in cubic meters per meter of aperture, and P as centimeters of rain per day. By reducing F or increasing P, the surface can be reduced. For example halving the flow to half of that of Niagara, F = 1 m3/s per meter, the surface is reduced by a factor 4. A [still respectable waterfall](https://it.wikipedia.org/wiki/Cascata_delle_Marmore#/media/File:Cascatemarmore.jpg) is about 0.3 m3 per meter, and this would allow us to reduce the radius by a factor of six (the surface by about forty times), to "only" 470 km. Remaining with the original figure of 2800 km, there would be another thing that's not really going to fly - where is the rain coming *from*? That precipitation rate is an average, but it's not likely that in the center of the plateau, 2800 km from the border, there's a significant inflow of humid air; all rain brought by the wind ought to have fallen in the first 2800 km, and actually one has to wonder what the clouds and the winds at the border must look like. Actually, it stands to reason that if the wind need to arrive 2800 km inland in one day, it has to travel at almost hurricane speed, *always*. So we're talking about a planetary-sized permanent hurricane - something like the [Great Red Spot](https://en.wikipedia.org/wiki/Great_Red_Spot) on Jupiter. The same formulas work if we suppose that there's constant heavy rainfall near the border and more bearable weather further inland, provided the average rate stays the same. Which means, the drier the center, the more abysmal the conditions on the boundary. [Answer] This is very similar to the OPs other question [How to form a world with steep sided very high plateaus and very deep depressions](https://worldbuilding.stackexchange.com/questions/92281/how-to-form-a-world-with-steep-sided-very-high-plateaus-and-very-deep-depression) except not exactly the same. So I suppose it should remain different so someone does not say OP is asking too much at once. The answer again is **yes; [tepuis](https://worldbuilding.stackexchange.com/questions/92281/how-to-form-a-world-with-steep-sided-very-high-plateaus-and-very-deep-depression/92289#92289)**. [Angel Falls](https://www.beautifulworld.com/south-america/venezuela/angel-falls) is the highest waterfall in the world and comes off of one of the high tepuis. [![angel falls](https://i.stack.imgur.com/vBWoM.jpg)](https://i.stack.imgur.com/vBWoM.jpg) There is not a spring up there. The tops of tepuis get a lot of rain. If you had a really big one it could be enough rain to get a near circumferential waterfall. I suspect over time though the water would find the path of least resistance and you would wind up with one big waterfall. Although waterfalls can be very wide. This [Chutes Wagenia](https://translate.google.com/translate?sl=fr&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fchute-wagenia.webs.com&edit-text=) (not on a tepui!) is 4500 feet across; well over a mile. [![chutes wagenia waterfall](https://i.stack.imgur.com/DZtDz.jpg)](https://i.stack.imgur.com/DZtDz.jpg) [Answer] As mentioned by slarty in the comments of another answer, this could be managed through siphoning from a higher reservoir. This was mentioned as an artificial method, but siphons are also expected to form [naturally](https://en.wikipedia.org/wiki/Rhythmic_spring#Theory). Although it would take some stretches for a large enough one to both form naturally and be made of hard enough rock to not be very quickly eroded by such a high flow rate. Possibly a [tuya](https://en.wikipedia.org/wiki/Tuya) would provide a good solution. Solid igneous rock would resist erosion and may justifiably have a series of lava tubes for the siphon. Glaciation would also lead to deep valleys which might justifiably be dammed up [naturally](https://en.wikipedia.org/wiki/Landslide_dam), leading to the required high reservoir for input. This natural damming could also justify this waterfall being geologically recent so the erosion is not as much of an issue. [Answer] No, it can't appear in nature because there is no addition of new water, and as the water falls off at the water falls, it is not replenished. The only way to achieve this would be with a colossal pump under the lake pushing up massive quantities of water, basically making it a colossal fountain. If you want something naturally occurring and similar, the most similar scenario would be that it has a higher cliff face on one edge from which more water pours down, replenishing the waterfalls. You would also likely need to town back the water falls. ]
[Question] [ **Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers. --- You are asking questions about a story set in a world instead of about building a world. For more information, see [Why is my question "Too Story Based" and how do I get it opened?](https://worldbuilding.meta.stackexchange.com/q/3300/49). Closed 6 years ago. [Improve this question](/posts/84684/edit) So, I have run into a bit of a problem. You see, I am currently creating a magic system for a second fantasy world I'm working on, and I am unable to figure out how to solve some of the problems posed by how the system itself functions. My question is: If a magic user has to enter into a dream-state, meaning they have to be asleep to use their magic, how would they protect themselves from harm? A few notes on how the system works: * These magic users, called Dreamers, are able to enter the "dreamworld" and shape reality around them when they are asleep. * They use powdered magic crystals called dreamdust to fall asleep whenever they need to use their powers. * When they are in the dreamworld, they inhabit a "spirit" body separate from their own. * Dreamers can "possess" golems made of dreamdust crystals using their spirit bodies, but do not always have access to these due to them being expensive and difficult to produce. * A Dreamer who is unusually powerful can control their physical body as well as their spirit bodies at the same time while awake, but magic users capable of this are extremely rare. * Lastly, Dreamers are responsible in most places for fighting the "nightmares", which are basically demons that inhabit the dreamworld. Sorry for the information overload, but basically my question boils down to this: considering the factors listed above, how would a Dreamer defend their physical bodies while they are asleep without using their spirit forms to guard themselves? [Answer] ### Locks How do you protect yourself while you sleep now? Most people lock their doors and windows. At the advanced end, you might have a security system that calls the police in case of break-in. ### Hide You may be able to locate your sleeping place where no one can find it. ### Guards If dreamers are protecting normal people while dreaming, won't normal people be willing to protect the dreamers? ### Share Perhaps one dreamer can't afford guards, great locks, or even a secret hideaway. So group together. One or two dreamers might animate golems or their own physical bodies and hang back to protect the underground lair in the volcano. The others can be out fighting the nightmares. [Answer] Mages are usually pretty defenseless anyway, I don't see how being asleep changes much. If anything, they will be less of a target and possibly safer anyway. So really you are asking how do weak, defenseless mages protect themselves. And the answer is always the same: Lots of big tough friends. [Answer] Perhaps they have some creature from the dreamworld defend them? Something that comes through when they go in, like a familiar or an elemental. A simpler solution would be to simply have hired guards. Would a protective spell work? Perhaps something illusionary to hide them or some sort of force-field. Perhaps it is widely known in this world that disturbing (or killing) a Dreamer wakes them or causes rifts between the physical world and the dreamworld. This could have hazardous consequences for everyone involved, such as 'dream monsters' coming through, or surges of violent energy. [Answer] The most obvious solution is to have guards protecting the magic user while he's asleep. Or have him only use magic in a secure room. Alternatively he you could find some way to use their powers against anyone who might try to harm the physical body without knowing more details on how their powers work I can't keep you much of a suggestion but perhaps they can somehow produce their own version of nightmares and use them to attack anyone trying to hurt their sleeping body. [Answer] **Fear of the Dreamers' Pact** Ordinary folk are terrified of harming any Dreamer when they are asleep, because they fear revenge. All Dreamers, good or evil, participate in a common Pact, that an attack on any of them is an attack on all of them, if such an attacker dare make his move while his victim dreams. Fear of this arrangement has led to a reality where nobody has dared harm a sleeping Dreamer for hundreds of years. It is unthinkable. If such an attack were to occur, every Dreamer would be obligated to respond, whether the attacker be friend or foe, even if it were to split their family, or even if it were to unite old enemies. [Answer] **A psychic works together** It's unmentioned in your description so I write some preconditions here: * Spirits from dreamworld are invisible to normal people. But there could be some d evices or talented ones who can communicate with spirits. * *Nightmares* can also alter the real world and harm citizens in this manner. (So dreamers need an efficient way to protect or warn them.) * In the spirit state dreamers' vision is dim and limited because they're literally dreaming. (So they need someone to inform them how is everything going on.) And this powerful magic may be equally dangerous, If you don't stay concentrated you may lost connection to the mundane world and wandering in dreamworld for eternity. A psychic has no power to actually deal with a spiritual entity but he can grasp the whole picture of current situation and tell the dreamer what happened or what to do, and vice versa. Basically, psychic is there to make sure nothing's going wrong and dreamer's here make things done. ]
[Question] [ Imagine a terrestrial creature with a sail on its back, like a [Spinosaurus](https://en.wikipedia.org/wiki/Spinosaurus) or [Dimetrodon](https://en.wikipedia.org/wiki/Dimetrodon). Would it be possible to use this sail as a lung for oxygen exchange with the air? [Answer] Lungs are basically a gas exchanger. To breath you need a large surface area (75 m² for a human, according [Wikipedia](https://en.wikipedia.org/wiki/Pulmonary_alveolus)) to exchange this gas, for a human. If you supposed that the greater is the animal is, the more surface he needs, its sails need to be monstrous. Especially an animal the size of a Spinosaurus or Dimetrodon. The other issue is the movement. An animal with a very large sail couldn't move easily by standard means (I mean legs). It can't be a carnivore because of this, as it couldn't run after a prey. In this case I see three maybe plausible solution: * a very peaceful and massive grass eater with a giant sail (more or less, like a stegosaurus). It doesn't need to move fast nor think, so it reduces the oxygen consumption * a swordfish like reptile, living in the desert, sailing on the sand with its sail. The wind provides it with speed so that it could hunt. The surface of the sail allows it to capture the dew to drink. As it doesn't move by itself, it doesn't need much oxygen and could even have a really giant sail. * an hippopotamus like animals, living in symbiosis with a single leave fern or tree providing the hippopotamus energy, sun protection and vital gas when the hippo provides mobility and nutriments to the giant sail like leave. In this case the hippo could even sail on a river and even an ocean, navigating like a boat with its leave-sail. To recap: I think this kind of animal isn't really possible for a known life form on Earth, but with some kind of exotic cases it may be plausible. You could think about moving trees or maybe chlorophyll fed butterflies, too. [Answer] Short answer: it's plausible, but you'll want to look into the details of [cutaneous respiration](https://en.wikipedia.org/wiki/Cutaneous_respiration). You'll need to address the three constraints of ventilation, diffusion, and convection, as well as finding a way to keep the surface responsible for diffusion moist. An insect modeled on a Dimetrodon, with the sale covered in structures like very tiny alveoli, seems like your best bet. I think that with some creativity, this could be made believable. [Answer] Technically [book lungs](https://en.wikipedia.org/wiki/Book_lung) are external lungs and can be found in numerous existing creatures such as spiders, crabs and other crustaceans. There is a size-limit in how big a creature could get while possessing book lungs, however. [Answer] Pretty vulnerable place to have an organ like that I would think, but possible. Lots of sea worms have exposed gills on their backs yet survive. It's unlikely to have evolved on earth, because creatures with lungs here usually (always?) have rib cages protecting them. But there is no physical reason I think of that that organ couldn't be anywhere on the body. It's essential to life so I'd expect it to be protected in some way. The sail could also work a different way instead of lungs. Lungs are not the only gas exchange system that has evolved on earth or even the most common. It could collect oxygen from the air by absorbing it through special pores or something. It would take some fancy physical mechanics to circulate the gases, but it's perfectly doable. [Answer] This structure would be good for a small floating air-breathing creature, as, assuming it has ways of staying stable, there would be very little chance of the sail becoming submerged, and therefore the creature would be near-immune to drowning ]
[Question] [ I'd like a gravity room on my space vessel for long space stays to avoid osteoporosis. They would spend a few hours each day in this room, reading or doing paper work, to maintain bone-mass. I'm imagining a chamber (it doesn't need to be large) where the astronauts stand against a wall as the room rotates, like [the classic carnival ride](https://en.wikipedia.org/wiki/Gravitron). [![Picture of Gravity Carnival Ride](https://i.stack.imgur.com/5UbPs.png)](https://i.stack.imgur.com/5UbPs.png) Image By Lzcracker - Own work, CC BY-SA 3.0, <https://commons.wikimedia.org/w/index.php?curid=4531120> I imagine that I would need some kind of counter-weight (spinning in the opposite direction) to maintain net-zero rotational momentum. My question is whether a room like this is feasible on a spacecraft that would be built today. Or whether I'm overlooking some other factors that would make this undesirable. Edit: I am imagining a very small centrifuge. Not large enough to run around in (as in 2001 or the Martian). [Answer] ## It's possible... As the other answers suggest, your science and reasoning are sound. Such a room, if spun at the right rate, could simulate gravity, and perhaps negate some of the effects of prolonged exposure to microgravity. This is also fully possible with modern technology. ## But for what it actually does, no one will pay for it. ### Expensive to fuel Moving a pound of material into orbit costs on average between 2,000 and 20,000 dollars. To keep this room spinning relative to the rest of the station, you would need to constantly burn fuel (or sacrifice most of your solar input). Electricity is valuable, and fuel costs too much to move up, so such an endeavor may not be accepted. The difference between this approach and entire stations that spin is that the "one-room" approach involves friction. The friction between the spinning room and the rest of the station will slow it down, requiring more motion to combat, and thus more fuel. Meanwhile, if you **spin the entire ship**, it will keep spinning unless acted upon by another force - requiring significantly less energy. ### Expensive to build As noted above, moving mass into space is expensive. I'm not going to make any assumptions about the size of this room but if you want something large I wish you luck finding an investor. It's just cheaper to move the whole station. ### Not very effective * A few hours each day will not help significantly. Spending the rest of their hours without gravity will reverse most of the positive changes you make, if not all. * Bone density is lost in space because bones no longer need to stay strong enough to fight gravity; that material is better used elsewhere. By lying on their **backs,** or with their backs to the wall, bones will act as if humans are sleeping; there is not much work that they need to do, so density will not increase by much. * Other problems, such as impaired vision, occur in space because internal fluid is not restrained by gravity. By pulling from the front of the individual to the back, you will simply change where the fluid pools - in the back - and drain it from the wrong places - as opposed to pulling it down from the brain. * Bed sores will occur from astronauts constantly lying down (as opposed to standing up produced by upright motion). ## Consider spinning the whole ship, indefinitely, and having people stand upright. [Answer] While the idea of having artificial gravity is sound, there are several issues with the idea of having a room or "Hamster wheel" for artificial gravity inside your spaceship: 1. It is heavy. The cost of bring ing objects or even inert mass into orbit is enormous, and will be so for the foreseeable future (even with SpaceX). A separate rotating structure isn't just the wheel, but the bearings and support structure, motors to spin and despin it, rotating slip joints and seals, slip rings for passage of electrical power and data etc. You will also need a set of flywheels or perhaps another ring spinning in the opposite direction to cancel out torques, and possibly some sort of counterweight system so your moving around in the room won't destabilize the system. 2. It is complex. Looking at the list of items in 1 above, this thing is going to be a maintenance hog and nightmare for your crew to keep going. Just ensuring the flow of electricity and data to the rotating cabin is going to be difficult enough, much less airlocks, pressure seals and so on. 3. It is dangerous. Can you imagine if your slip ring has to transmit kilowatts of energy, either by design or because of an accident? What happens if the wheel becomes unbalanced? Will the vibrations damage important systems on your ship? is there some means to brake the system in an emergency and deal with the sudden change in rotational energy? 4. It isn't healthy. If your room is too small, the corals force of the rotation could induce nausea and disorient the people inside. The calculations can be found on the ever helpful [Atomic Rockets](http://www.projectrho.com/public_html/rocket/artificialgrav.php) site. In general terms, rotating at faster than 7RPM can cause problems for the people inside. Either the room has to be unreasonably large or you will have to settle for less than one "G" if you rotate the room more slowly. While Atomic Rockets has lots of caveats, much of this has to do with training and also with gradually upping or reducing the rotational speed. This may or may not be practical. However, there is a solution: turn the entire spaceship into the centrifuge. No slip joints or moving parts, the ship can spin at any arbitrary rate and the "room" is the size of the entire habitat portion. This fan art version of the "Hermes" from the novel "[The Martian](http://rads.stackoverflow.com/amzn/click/0804139024)" shows how its done: [![enter image description here](https://i.stack.imgur.com/0UDKx.jpg)](https://i.stack.imgur.com/0UDKx.jpg) [![enter image description here](https://i.stack.imgur.com/XlpQc.jpg)](https://i.stack.imgur.com/XlpQc.jpg) The nuclear reactor is facing the viewer in this picture, and the habitat is on the far end of the boom. The ion engines are in the centre of the boom, and can be rotated to provide course adjustments and corrections. A .gif of the ship in rotation is [here](http://francisdrakex.deviantart.com/art/Hermes-Rotate-564814706) So by some clever design, you can make the entire ship rotate and provide the crew with 100% gravity inside the crew quarters for as long as you like. Rotating the ship and despinning do have issues (and you need to take this slowly in order to prevent over stressing the central truss), but overall, this is a much more robust solution than a spinning room inside the ship. [Answer] The concept is certainly workable, and is being actively investigated by a number of different groups. It's also been depicted in science fiction many, many times. A recent high-profile proposal for a vessel using such a system was the [Nautilus X](https://en.wikipedia.org/wiki/Nautilus-X), a proposed multi-role spaceship that would use a centrifuge to provide around 0.5 - 0.6 g for the crew. A version of the same concept was also tried on [Gemini 11](https://en.wikipedia.org/wiki/Gemini_11). The crew capsule and its Agena target vehicle were connected by a tether and spun around their common centre. The experiment was not a total success, for various reasons, but they did generate a small amount of artificial gravity. To my knowledge, nobody has actually flown another mission to test the concept in space, despite many proposals. The Soviets experimented extensively with centrifuges as a habitat on Earth, but never in orbit. A module called the [Centrifuge Accommodation Module](https://en.wikipedia.org/wiki/Centrifuge_Accommodations_Module) was partially built for the ISS, but was cancelled before completion. [Answer] Generally speaking, the idea should be workable. For 2016, the problem is that we don't have many spacecraft or space stations, and those were launched in many small parts. Assembling this room in orbit would be difficult. * Something similar was shown in the movie 2001. * Variant: The spacecraft has two (or four) pods rotating on arms. The *Leonov* from *2010* or some Earth Force ships from *Babylon 5*. * Variant: The spacecraft has a ring rather than separate pods. [Answer] It doesn't really make much sense to have only a room. If you can build it it would be better for it to represent all (or almost all) of the living space available. If the room available is limited for any reason then you could still have a very small centrifuge, maybe divided in a few bunks, so that people can rest there and maybe sleep. The reasons such a space would be used for sleeping and resting are two: first if the centrifuge is small, moving inside is difficult and you will experience different levels of acceleration within you body and also a very strong coriolis effect every time you turn around; second, sleeping in space is actually very difficult! Astronauts on the ISS can hardly sleep a few hours, so if you have a gravity room available only at times sleeping in there is one of the best thing you can do probably. Oh, also, if the space is limited better do something in there that requires limited movements and room. ]
[Question] [ Okay, I know I'm posting a really implausible question, please be understanding.... Many years ago, a powerful mage went mad (occupational hazard; one *does* encounter eldritch horrors and reality-altering magic when one is a powerful mage responsible for keeping the world safe), harnessed the powers of the eldritch horrors he slain, and corrupted the world's mana, permanently altering our *food.* Each and every single food you can think of-Black Forest cake, sour gummi worms, hardboiled eggs, carrots-has gained adorable eyes, simple mouths, and primitive limbs (for examples of creatures with these traits, look at Kirby or Shopkins, the inspiration for this question). Furthermore, each of these food items has gained both unique personalities and 'cultural' traits, along with the ability to speak (which comes with rudimentary-think caveman-intelligence). Food heals or reproduces by expending energy, which comes from the corrupted mana of the planet itself. For example, two hamburgers, side by side, release a bolt of energy that collides between them and *poof!* A baby-size hamburger appears. The two "parents" then have halved energy and must wait a certain amount of time before they can have another "child." Furthermore, food items can merge. For example, flour, eggs, sugar, butter, and milk fuse into a cake (and without baking soda, since I just can't count that as actual food...). This cake will have the combined intelligence and traits of the ingredients that came together to make it, making it a superfood (the food equivalent of superhuman). Each food has instinctive awareness of merging and reproduction from the get-go, but they can't do either until they mature. This takes the same amount of time as recharging for a "parent." Additionally, food does not need to eat and heals damage (or loss of mass, like when a cake is cut into slices) over time. One example would be that candy tends to dissolve in water; so if living candy is exposed to water, and isn't completely dissolved, it can gradually restore mass. Since energy is going into regeneration, the candy will be weaker and slower during this time. This principle makes any cold food (like ice cream) weak but generally unmelting when exposed to heat (say, room temperature, or a hot car, NOT a blowtorch). Finally, food can grow (or heal) by absorbing other members of their kind or their ingredients; carrots can grow by absorbing carrots, while cakes have the alternate option of absorbing flour, eggs, butter, sugar, or milk to grow. Growing causes a proportional increase in intelligence. As for when animal/plant matter becomes food for the purposes of this question: as soon as fruit is fully formed, it becomes food and comes off. Once vegetables (like a carrot or head of lettuce) are fully formed, they become food. Animal carcasses and so forth are not meat until they are prepared; for birds, this means being plucked, beheaded, and cooked, for snails and insects, this means being cooked, and for fish, they have to be either cooked, made into sushi, or cooked and canned (as for sardines). For those interested (like Nzall), bulk food LIFE is simple. Take a scoop from a bag of flour, and that scoop is alive as well, but less powerful and intelligent than the entire bag. The bag then has a slight dip in power and intelligence. My question is simple but complex: **How Will This Impact Mankind's Interaction With Food?** As always I appreciate your input, and your feedback. If this question is too opinion-based, or needs additional information, I would greatly appreciate advice on fixing it. EDIT: Thanks everyone, your answers were all very helpful and I'll be using pieces of each and every one. **EDIT 2: Clarification** 1. Yes, the food feels pain-*emotional* pain, a sense of loss, whenever they lose part of themself. Exposing food to it's weakness-like heat for ice cream or water for bread-causes it physical and emotional anguish. 2. Where is the energy over time coming from? Eldritch monstrosities, things like Chthulhu, have an Aura of Discord. They generate chaotic (AKA magical) energy that the living food draws off of. [Answer] **Food cannot be stored in the home.** So everything we eat is alive? Well guess what, that's already true. The cow you had for dinner was alive! Okay I admit it's not quite the same. But now the world has changed so, not only does the cow in the meadow walk and talk, but also the steak on you plate was still walking and talking as you gobbled it down. The same for the milk and eggs that would be in your fridge and the fruit in the fruit bowl. I say *would* because fridges and fruit bowls no longer exist. Food cannot be stored in the home any easier than storing a live cow. All food must be treated as though it was livestock, in the age before meat preservation was invented. That means it cannot be stored and must be eaten immediately after it is *slaughtered*. Meaning if you want some meat you go to the market square where someone has just slaughtered an animal, with a mind to immediately butchering and selling off the pieces for consumption *that day*. That means most meals are now eaten outside the home in large facilities. I presume the crops and livestock behave same as normal. It is transported from the fields to special facilities and only at the last second is it rendered into *food*. Then it is prepared in industrial size pressure cookers, with reinforced walls to prevent the ingredients escaping. Then it is served and eaten immediately. [Answer] **Breaking News!! PETA finally loses it and declares war on mankind, starves to death before doing anything.** Okay, so that may be pushing it... they'd probably starve before declaring war. I don't think the overall relationship between us and our food would change all that much just because food is cute now (have you seen a baby cow? cute as can be... [also delicious apparently](https://en.wikipedia.org/wiki/Veal), can't really say as I've never had it to my knowledge). There would inevitably be those who now shy away from cooking for themselves and end up contributing to the sudden restaurant boom. The most major impact this event will have is perhaps a vast increase in price due to the inadvertent creation of perpetual-motion/self-sustaining food. Buy it once and so long as you don't eat it all? Boom, food for life. So that pretty much ends global hunger. Oh, and the vast majority of farmers/ranchers/etc... going out of business because nobody needs *extra* food now. Though, with food now able to reproduce, maybe they'll all have new jobs as food wranglers. Imagine trying to corral a herd of tacos. [Answer] <https://en.wikipedia.org/wiki/The_Magic_Pudding> [![magic pudding](https://i.stack.imgur.com/UPwsr.jpg)](https://i.stack.imgur.com/UPwsr.jpg) > > Wanting to see the world and unable to live with his uncle anymore, > Bunyip Bluegum the koala sets out on his travels, taking only a > walking stick. At about lunchtime, feeling more than slightly peckish, > he meets Bill Barnacle the sailor and Sam Sawnoff the penguin who are > eating a pudding. The pudding is a magic one which, no matter how much > one eats it, always reforms into a whole pudding again. He is called > Albert, has thin arms and legs and is a bad-tempered, ill-mannered > so-and-so into the bargain. His only pleasure is being eaten and on > his insistence, Bill and Sam invite Bunyip to join them for lunch. > > > The interactions will be one of songs (many), battling persons who come to claim delectable living food, racing to catch the fleet footed food as it tries to run away (out of principle; it likes to be eaten) and also three-stooges style comedic violence. > > One of the great advantages of being a professional Puddin'-owner,' > said Sam Sawnoff, 'is that songs at breakfast are always encouraged. > None of the ordinary breakfast rules, such as scowling while eating, > and saying the porridge is as stiff as glue and the eggs are as tough > as leather, are observed. Instead, songs, roars of laughter, and > boisterous jests are the order of the day. For example, this sort of > thing,' added Sam, doing a rapid back-flap and landing with a thump on > Bill's head. As Bill was unprepared for this act of boisterous humour, > his face was pushed into the Puddin' with great violence, and the > gravy was splashed in his eye. > > > <http://www.gutenberg.org/files/23625/23625-h/23625-h.htm> [Answer] ## There will be war against food If the food have primitive inteligence, it would try to preserve itself from being eaten, spoiled or dissolved (candy would try to climb out from puddle, for example.) Home food would try to escape to wild, to keep itself alive. And cake can simply absorb berries to became berry-cake, so it would survive there rather than be eaten by wild food. And it would increase its inteligency too. There is also lot of food in wild already, just think of fruits, insects, honey ... and if it have ability to multiply without eating, it would eventually fill all the space and then start spreading to human-occupied places, at least forced by pressure of the mass itself. (And with capability of self-healing it would not degraded to soil, but lives heathy forever.) But we have already too much of food in storages, gardens etc. etc. so there would be conflicts much earlier, when loose food start massively overtaking cities, villages and such. The overfoodation (= overpopulation of food) will grow exponentially and unregulated would cover Earth in layers after layers of food, until the monstrosity would collapsed into itself just by gravity force. So humans would be forced to solve that thread by force and long lasting fight over all the globe. Also it could destroy the ecosystem easily - cooked rice does not dissolve in watter, so it would be able hunt sea for raw fish and octopuses and sharks to create sushi, sashimi and all kind of such superfood. (If flour and milk and eggs is able mix itself and cook to cake, then rice should be able mix itself with fish and make sushi. Also note, that "living suschi" <https://en.wikipedia.org/wiki/Ikizukuri> is made of still living seafood, therefore it could came "superfood of rice" ) --- ## Foodibalism It is well documented canibalism ( <https://en.wikipedia.org/wiki/Human_cannibalism> ) in times of famine at many times, some only 90 years old ( <https://en.wikipedia.org/wiki/Holodomor#Cannibalism> ). So regardless its eyes, limbs, inteligecy and ability to argue, people will eat the food anyway - as there will be no other food, than food - and it is more simple eat protesting cake, than to kill a fellow human, cook it and then eat protesting coocked fellow human. [Answer] **"How will this impact mankind's interaction with food?"** In many, many ways. Given that food is now intelligent, it will presumably begin to actively avoid permanent destruction. Especially so given that they possess ape-like (caveman) intelligence. I don't know how motile a living cake is, but we could see foods attempting to flee distribution centers, pantries, etc. And they may decide to form some sort of army or active armed resistance to inflict casualties and fatalities on the human population (aka their predators). This could very well end up a serious threat, given that food itself is undying, regenerates, and does not need to ingest energy in the way ordinary living things do. A kitchen or pantry will almost certainly turn into a sort of prison but for food. Where the goal is no longer to preserve and organize meals, but simply to keep them contained. This is of course a losing proposition: The biggest issue is one of physics. Two food items can 'zap' another food item of similar type and form into existence. This expends some sort of energy within the food items. But the food items can and will regenerate this energy. Where, exactly, does this energy come from? The food items are, effectively, creating mass out of a regenerating nothing. They can use this ability to burst through any barrier, overrun any population center, turn our planet into some horrific cakeworld, etc. Or, if we could reason with or permanently subdue them, we could use this ability to generate an infinity of almost any element (or, you know, food) one could reasonably expect to find in food, such as Hydrogen or Potassium. A cake covered in platinum shavings is still a cake, is it not? All in all, things would get incredibly strange incredibly quickly. ]
[Question] [ Now I know this is a very weird and impossible question, there is clearly no civilization on Venus. But for the sake of the story I'm cooking up in my head, Venus remains habitable and develops life alongside Earth. Now the details of how Venus doesn't turn into a hell world is moot and respectfully, not what I'm asking about. But I will give a simple description of the environment of this version of Venus as I think it does matter. Essentially Venus in my story is a place old science fiction writers centuries ago imagined Venus to be a tropical, warm and misty "paradise planet". I like to imagine Venus shrouded in clouds although not to the extent in our world, but enough to obscure *some* surface features. The intelligent species will be named Venusians for simplicity sake and be similar to humans in appearance and appendages etc. *(Also for simplicity sake)*. Now my question is given these simple parameters, (*and assuming Venusians develop technology alongside humans and are only 5-10 years behind*) When would humanity be able to realize there is an intelligent species on Venus? Would it be before the Space Race? during? after? And when I say "when" I mean what time period/ year. [Answer] Assuming your version of Venus is still cloaked in dense cloud cover even though it has a breathable atmosphere? **With the invention of radio, in particular **VHF radio****. This is because Earth's atmosphere (and by extension Venus's) is transparent to VHF frequencies so radio emissions from Earth in that band range would be detectable from Venus if they were broadcast in the right general direction and of course vice vera. From memory Marconi started experimenting with VHF radio waves for long range communication use late in the 19th century. So given your Venusians are a decade or so behind us historically our radio operators would probably start detecting their signals sometime in the 1910's or 20's perhaps 30s at the latest. (Of course their own early pioneers in radio at that time might also detect our broadcasts which in turn would probably spur on them a bit to try and perfect the technology so that might save a year or two of their schedule. If they chose not to respond? They might well end up being aware of us before we are aware of them!) Note: I say the 'latest' because given the development of optical spectroscopy and interferometers and their use in astronomy started earlier than this it's possible astronomers might have realized Venus had an Earth like atmosphere and therefore life might exist on it's surface sooner than that. That wouldn't of course prove your Venusians existed but it would lead to intense scientific interest in the planet. [Answer] Martian canals were [described](https://en.wikipedia.org/wiki/Martian_canals) in 1877. As we know now, the descriptions were wrong. Over the next century, this was gradually shown. Part of that was showing the lack of water in the spectrographic analysis of the atmosphere in the early 1900s, which lacked water vapor. So one data point would be when the Venus civilization did build structures larger than a 'canal,' and the other when they did pollute their atmosphere enough to show up in spectroscopy. For the latter, one would have to consider that mankind would be judging habitable planets based on a sample of two -- we were polluting our atmosphere, they are polluting theirs, people might dispute that it is anthropogenic. Gut feeling, there would be a **dispute** from the 1870s onwards, to be settled in the 1910s or 1920s. [Answer] I would imagine that some form of radio telescope would be needed to detect the faint radio signals from early Venusians radio. In all likelihood the first signals would be missed as the signals would be too weak and the early radio astronomers would have so much to look out. That could easily go on for a decade or two into the 1940's and 1950's before someone found it. For example pulsars weren't discovered until 1967, I suspect they could have been detected earlier, but nobody thought to look or didn't have quite the right kit or funding. So chance would play a leading role. Just because something can be detected does not mean that something will be detected, although as time goes on the chance of discovery increases as the radio astronomy infrastructure builds. [Answer] They would know about us long before we knew about them due to our lesser cloud cover and architecture. If their tech was close to ours, we'd both know via radio waves long before either had spaceships. I would think we'd know at least by the birth of civilisation although we'd attribute it to gods or something. We'd have pretty good proof shortly after decent telescopes and conclusive proof after radio. This is assuming the Venusians didn't attempt some sort of signaling themselves. All it would take is some meglomaniac mobilising a few million slaves and writing his name with stones across a desert or something. [Answer] > > I like to imagine Venus shrouded in clouds although not to the extent in our world, but enough to obscure some surface features. > > > If Venus had an atmosphere just like the Earth's, it would need to have considerably more cloud coverage than Earth to keep it inhabitable, so as to reflect more radiation into space than Earth does. That would obscure some surface features, but wouldn't obscure the whole surface. Humanity would have two ways to detect a civilization on Venus: visible light and radio signals. Visible light detection could happen as early as Galileo's time, but would more likely happen in the early 1900's. That's supposing their technology evolves at the same pace as ours. We would have the combination of very good telescopes on Earth and electric lights becoming a thing on Venus, illuminating cities by night. Failing that, we could possibly detect nukes being detonated on the night side around the 1940's. As for radio, any signals either side sent that could reach the other would be picked up. That might happen around the 1940's, when "moonbouncing" became a thing. Moonbouncing is a technique which uses the Moon as mirror to send microwave or radio signals over vast distances. A good moonbouncing antenna and some FAFO (the scientific approach better known as ***F...*** er, ***F***rolic ***A***round and ***F***ind ***O***ut) and you could pick some conversation from the Venusians, or even an actual invitation to chat from them. [Answer] Your tropical Venus is lush and green, since its flora evolved under the light of the same sun as ours. Like Earth's civilizations, your Venusian civilizations will need to clear a lot of land for farming and timber (if they want to keep just a decade behind our progress). Tragically, this means your untouched paradise will be scarred by swaths of deforestation. As long as the cloud cover on your version of Venus is not thick enough to obscure the contrast between green and brown, Earthlings will be pretty suspicious as soon as their telescopes can resolve some of the brown patches. Or, if you want to extrapolate, the Venusians leave their dense forests alone. Humanity's intellects, vast and cool and unsympathetic, regard this Venus with envious eyes, and slowly and surely draw their plans against the Venusians. They attack in bipods, but underestimate the resilience of the forest that protects its planet. Previously, I had included an image illustrating how the forest would attack a bipod. Perhaps I should have included a warning for any readers who harbor imperial sympathies. ]
[Question] [ In my dream I have been chased by a plane which had chainsaw blades instead of wings. That woke up my inner worldbuilder and instead being terrified, I started to wonder if something is even possible. So I summon you, my fellow Worldbuilders to help me with this: **Design an airplane which uses chainsaws to propel itself** * No magic * Ideally it should use only chainsaw to lift and steer * Should be able to carry at least one person * Ideally, the saws itself should be also capable to cut something without damaging the plane * End goal is to this plane being able to cut a person in half without crashing and/or damaging itself Yes, the plane itself serves for a horror story, so worst case scenario, I could always use some magic and/or handwavium, but still ... Is it possible to have a plane like that? [Answer] No, this will unfortunately (?) not work as advertised. The basic problem is lift. There are three basic ways I can see a chainsaw mechanism generating lift, and all have insurmountable issues. One is basically using the mechanism of the saw itself to *push* air down with, effectively, little scoops instead of teeth. This might work in water, which is a lot heavier (paddle steamers use this to travel *forward* rather than upward), but with air the volume you'd need to push down would far exceed your available power. The second, somewhat more practical, is to turn each individual tooth of the chainsaw into a wing, which generates lift as it turns. This is basically how helicopters work, except that their blades only go around in a circle instead of in a pill shape. The problem here is that even if you could get it to work (and the connection of the teeth to the "hub" seems *very* suspect) it will look and act much more like a helicopter blade than a chainsaw: the "teeth" will be long and thin, and rotating extremely quickly. Trying to saw through things will put immense torque on the teeth and probably break them. The third option is to taper the profile of the teeth and saw such that the saw itself is a wing. This approach will generate lift, but has issues of its own. One is that the edge of the wing, where the teeth are, is normally where the control surfaces are. Having a bunch of fixed, moving slats in your wing is going to lead to some *profoundly* odd handling characteristics. It will not fly even remotely like a normal plane. More problematic to the wing approach is that chainsaws are not designed to saw through things at full speed, the way you see in zombie movies. They're designed to be pushed with slow, constant pressure like any circular saw. (Think of a table saw: you don't throw boards at it, you push them gradually into it.) Any practical design will have a stall speed that's far faster than its safe chainsawing speed; if it's going fast enough to generate lift, it won't be able to cut through objects fast enough and will become stuck or will fling objects away at high speed. A vehicle that both flies and chainsaws may be possible (though probably not practical) but a single mechanism that both generates lift and is a usable saw at the same time is not. [Answer] A plane won't be able to do it because wings are not meant to take the shock of an impact. You would also be risking a lot by trying to mow down a person: you'd have to fly too low and you risk bits ending up in the turbines. If you ever read news about what birds do to airplanes, you'll see that never ends well for the plane. However! Did you know that drones are not vegan friendly? No, seriously! Nowadays anyone can buy a drone, and given the idiotic nature of humans, there is always someone being hit by a drone by accident somewhere in the world. In order not to kill nor injure people too much, drone makers try and use shapes and materials that will hurt as little as possible. Tests are usually done by getting the blades on a track and accelerating them against a target which is usually pork, to simulate a blade hitting human flesh. If there is too much damage, the blade gets redesigned and retested. ![Take that, vegan drone operators!](https://i.stack.imgur.com/A8LLb.jpg) Notice that the industry has to make an actual effort to make drones harmless. All you need to do to make them deadly is being lax and using cheaper materials. You may now think that this doesn't live up to the question because drones are small and won't seat a pilot. Wrong! A company called Ehang is working on pilotable drones: ![Science!](https://i.stack.imgur.com/h9ZIr.jpg) You could take most of the housing out to make it more personal: ![SCIENCE!](https://i.stack.imgur.com/cN8XO.jpg) Or even use a bathtub, to turn horror into trash horror: ![SCIENCEGASM!](https://i.stack.imgur.com/5Tk7s.jpg) All you need now is for the blades to be replaced with curved chainsaws; Shape the chainsaws so that they are curved like helicopter blades and fly towards your targets. Don't forget to wear a helmet and follow safety procedures! [Answer] Perhaps the magnus effect might get you close enough to sci-fi plausible here. It says basically that an object spinning in a fluid generates a force perpendicular to the axis of rotation. So basically something like this [model airplane that uses KFC buckets for wings](https://www.youtube.com/watch?v=K6geOms33Dk), just put little chainsaw teeth on the cylinder-wing-things. [Answer] # This can work To fly you fundamentally need two things, lift and thrust. The chainsaw only adds one more consideration which is cutting speed. ### Lift Many of the answers so far have focused on the "chain" part of a chainsaw and have completely forgotten that a chainsaw is made up of a bar and a chain. If we utilise both this is much simpler. To get the lift with chainsaw is fairly simple. We design a specially shaped chainsaw bar that can serve as an airfoil. Basically this will look more like mounting a chain to the edge of a actual aircraft wing because that's what shape we need for the lift. ### Thrust Thrust can be provided by a traditional airplane engine and propeller. If we use a strong enough one it will also be able to power the chainsaws without the need for a second engine. Too me your description sounds like an old spitfire or similar with chainsaw blades on the wings. This should fit perfectly. ### Cutting Speed Getting a plane in the air with a cutting chain on the front edge of each wing in the easy part. The hard part is staying in the air while cutting. As others have said traditional chainsaws are designed to cut slowly with constant pressure. However it is possible to design a tooth pattern to increase cutting speed. This involves making the cutting edge thinner (less material to cut) and increasing the aggression of the cutting angle (deeper cuts). In traditional saw this would raise the stall-point and cause the blade to catch. However as can be seen with competition hot-saws used in timbersports, if we add a bigger engine (usually a 250-400cc motorcycle engine) we can cut faster. In our case we already have a thumping huge jet engine we can power our saw off. Combine the massive power with the aggressive tooth pattern and we should be able to reduce the drag from cutting enough to keep us airborn. All that increase in power and cutting speed increases the stress on the chain though. So it is likely we will need to make it out of something stronger than steel. There are a number of light weight high strength materials out there. Using one of these will help to reduce weight as well as prevent the chain from breaking. ## Conclusion Yes, absolutely we *can* build a plane with chainsaw for wings. And yes we can make it be able to cut through tree, people and hoards of zombies while remaining airborn. We have the technology, we can build it. [Answer] This does not fulfill the requirements, but: It is certainly possible to build airplanes, helicopters, gyrocopters, airships, hovercraft, and other air vehicles that have payload capacity, the ability to lift more weight than the necessary mechanisms that make it fly, weight devoted to crew, passengers, cargo, weapons, etc. Therefore it is easy to build an aircraft that uses some of that payload capacity for attached chainsaws. Those attached chainsaws would have to work very fast if they could cut through items at the aircraft's normal speeds, so I suggest a plane that can fly as slow as a Wright flyer or other early airplane, and maybe hover almost motionless, that has super speed chainsaws attached. This does not fulfill the condition that the chainsaw be part of what drives the aircraft, but other answers show that would be impractical, and even a chainsaw that works at flying speeds would be a major technological development. So maybe you will have to be satisfied with a relatively normal, though unusually slow and low flying, aircraft that has highly advanced super speed chainsaws attached. ]
[Question] [ It's the Olympics, and it'll be one the world won't soon forget. The sprinters are in position on the starting blocks, the signal is given and the runners are off! However, one man gives off a fart so huge that it significantly boosts his acceleration. This mother of all farts propels him all the way to a first-place finish and a trophy on a pedestal. Cue a training montage flashback where our protagonist learns the art of fine muscular control in a remote mountaintop monastery. My question is this: **is it mechanically viable for a male athlete weighing approximately 80kg to use rapid anal gas expulsion (AKA flatulence) as a form of assisted take off or even as a [nitro boost](https://tvtropes.org/pmwiki/pmwiki.php/Main/NitroBoost)?** Main problems with this idea that I've identified: * Fart propulsion might have too low a thrust-to-weight ratio for this purpose * The human body might not be able to store enough gas for this purpose [Answer] I don't think it is viable. If you want to propel the athlete of mass m to certain velocity v starting from rest, you need to provide a momentum $P = m\_a \cdot \delta v\_a$. The same momentum has to be given to the expelled gases. The average bowels should be around 10 meters long, and let's assume they have an homogeneous radius of 1 cm, it means the available volume of gas is about 10 liters, accounting for a mass of about 6 grams, if we assume it is fully made of methane. It follows that, to speed jump the athlete at 10 m/s that gas would need to be expelled at $\delta v\_g = m\_a \cdot \delta v\_a /m\_g = 80 \cdot 10 /{6 \cdot 10^{-3}}= 130 \ km/s$. Though I am not aware of any scientific study on the topic (if it exists, please submit it to IgNobel award committee), I am fairly confident that would be sufficient to blast away the athlete's lower body. For additional reference, the SP2B 28 mm, a WWII cannon, had a muzzle velocity of 1.4 km/s, while conventional gaseous intestinal emissions have been [measured](http://mistupid.com/facts/page070.htm) at 0.003 km/s (credits @Mołot for the last reference). **Addendum** One can object that it could be possible to increase the momentum of the ejecta by choosing a denser medium. Let's pick water, as it is convenient to assume that whatever is in the intestine is water based: 10 liters of water would weight 10 kg, so the discharge would need to happen at "just" 80 m/s. Still way faster than a conventional emission. [Answer] Your scenario would not work, flatulence of this magnitude would not be possible. However swimmers can do something similar in competition. Except not farting for a jet assist, but filling their bowels with gas and holding it in. This gives their bodies a fraction more buoyancy enabling them to swim just a tiny bit faster. [Answer] L.Dutch had alreary given you the physical reason why it would not work. I'll focus on the biological. For it to be possible, the guy would need a propellant like gas or diesel. We are talkung about acceleration like the [famous jet bike from Jackass](https://youtu.be/rIcOI1WqGtM). Besides being too hard to control (neither that bike nor you have thrust vector control) the anus of the runner would probably explode from the pressure. Supposing the guy has an artificial anus that is made of steel, there is still the problem of expelling the gas in force. You would need a lot force in the intestines. That would draw blood to them, and hence away from the legs, which goes counter what he wants to do. Also, if you want to feel the discomfort the athelete would feel just by trying to run with gas, go eat half a pound of mexican beans then do a sprint. Remember to bring a roll of toilet paper to the exercize. [Answer] You made reference to a 'nitro boost' in your question. If this takes precedence over the concept of the flatulence creating some form of 'jet' effect, then maybe we have something to explore. I have read the question carefully, and I do not read anything in it that specifically relates to the jet propulsion effects. Rather, it seems to be able to be interpreted as relating to any effects on the maximization of energy creation and utilization. Nitrous oxide does not in itself combust. What it does, when used in engines, is to provide more oxygen (the oxide part) for combustion. The gas decomposes at gas engine temperatures into nitrogen and oxygen. (Injecting pure oxygen would give a similar but perhaps more hazardous and difficult to control boost in combustion). So, given that: 1. many farts are methane gas. 2. increased oxygen intake adds to human performance. 3. the flatulence results in a reduction in air pressure in the intestines. 4. the Bernoulli effect uses air flow to compound air flow. 5. the lungs would be the benefactor of this increased or enhanced air flow, as they are in the same air pathway as the intestines. 6. Olympic sprints are determined by hundredths of a second difference in timing. 7. the flatulence would lead to an expansion of the methane gas 8. methane is lighter than air, and the sprinters' shorts would fill with methane, making the runner ever so slightly lighter (but counter to the relationship to Nitrous Oxide, which is heavier than air). 9. the expelled methane would change the air flow dynamics, if even so briefly, behind the sprinter. 10. even a misplaced seam in the uniform of a sprinter could make the difference between winning and second place. If we are looking for a performance boost in terms of hundredths of a second, I think we have enough factors that could make this question a good candidate for a Mythbusters Episode. And, of course, it does fit with their overall theme. [Answer] Maybe a competitive advantage could be gained on the swimmers in the lanes immediately to the right and left of the subject. Say if they ate nothing but White Castle with double onions for 3 days prior to the event, when those swimmers to the immediate right and left turn their heads for a quick gulp of air...if all they get is a gulp of White Castle exhaust...that might at least provide a competitive boost ]
[Question] [ It's modern day, and aliens travel to Earth (cloaked so that no one is aware of them). They send huge robots down to a town or city and manage to kill everyone there, apart from a single survivor. This survivor manages to make it to another town, where the first thing he does is run to the police station to tell everyone there that he has witnessed the destruction of the town/city and managed to escape. However, everyone looks at him as if he is crazy. They say "if that had happened we would have heard about it!" **So what would be the best way for the aliens to ensure word isn't spread about the destruction of this town/city?** **Conditions:** * The aliens have **almost omnipotent powers** with their advanced technology compared to ours. They can do things such as cloaking, holograms, blocking satellite/radio/internet communication and anything else you can think of that technology can do now or in the future. However, they cannot erase memories to make everyone think that the town/city never existed. * The ruse only needs to go on for approximately 24-48 hours, after which time they have already destroyed a number of smaller towns/cities in order to make bases for themselves where the towns/cities once stood. After this time they will drop the stealth tactics and branch out from these bases to attempt to subjugate the human race. * They have studied Earth for a while and understand our technology limits and humans themselves, so they wouldn't leave any means to be discovered by accident, until they're ready to reveal themselves. **Considerations:** 1. What would be the best way for the aliens to make sure no one has noticed these towns/cities have been destroyed? They will have to take into consideration people who live there all of a sudden not communicating with out of town friends/family, people who would drive through after the town is destroyed potentially walking into the ruins. 2. What size towns/cities would be big enough to have bases of operations but small enough to not attract attention to the general population? Could it happen to a small city or would it have to be small villages? What countries could they be in that it would go unnoticed? 3. How would they subvert things such as satellites noticing this has happened? --- **To clarify:** Perhaps I put too much information into the question, so I will summarize what I am asking. **If you had infinite technology, how would you conceal the fact you have captured a town and all of its people without alerting anyone for 1-2 days?** It's OK if people start to suspect something is wrong (like a friend going to voicemail who usually picks up), but without anyone jumping to the conclusion that the planet is being invaded. [Answer] 3) Satellites: easy to fool with an image perpetuated from just before the attack. Project it above the site so the satellites perceive it as the actual surface. Only has to last 24-48 hours. They may want to spend 24 hours hovering to take a full noon-to-noon cycle to cover the night changes in artificial lighting. 2) Choice of country can make all the difference. The more wired the country, the more mobile the population, the more outsiders will notice the lack of Facebook updates or be more likely to drive to through. It has to be off regular rail or air service, only a weekly or biweekly at best. Of course, villages are easier. But I think you want the largest place they can get away with, right? Otherwise they could avoid destructions and set up in the middle of uninhabited nowhere at leisure. So what are the human facilities they need out of the village/town that they can't get at some deserted lake in northern Canada? How is a rural village in Nigeria or a small town in the Philippines any better? 1) Timing is critical. If it's a ski resort, don't hit on a February weekend. Look for when it is most deserted, with the fewest outsiders coming in. Not on a convention weekend. Major cities and capitals are off the list. I'm seeing a seaside resort in off season, still cold if not snowy, and a major storm (blizzard, sleet, rain) may have knocked out communications normally in the area. This question is going to take people from all over piling on with their suggestions of a good town in their area that suits the shopping list. This could probably be best as a separate question: this is my set-up; what towns in your knowledge would you suggest? Otherwise, you get to invent a place. Some small towns get most of their traffic on weekends, with the weeks isolated. Some act as bedroom communities, with lots of commuting on the weekdays but people stay home and mow the lawns on the weekend. Do you have a positive or negative preference in continents or countries for the setting? Like, you just don't think you can handle the cultural differences of setting this in the USA or Mongolia or wherever? Obviously, this target must be within fleeing distance of the second town where the survivor goes. On foot, maybe thirty miles in two days (assuming he isn't an ultra-marathoner). On horse, maybe seventy miles if he got a good one. On bicycle? Moped? Motorcycle? What will he find to use? > > However, everyone looks at him as if he is crazy. They say "if that had happened we would have heard about it!" > > > At which he tells them to call someone there. Frankly, if destruction of communications is the first step he tells them about, there isn't any reason they would have heard about it. Hmm. The aliens also need to keep the sky above the town lit. Neighboring places might wonder at the sudden lack of light pollution, especially on a cloudy night. Hilly/mountainous terrain is the aliens' friend. At this, I suggest the aliens create a major rainstorm over the larger area a couple days before to keep humans inside on the weekend, busy pumping out their basements, swearing at localized flooding, not looking at the sky, not wanting to drive anywhere unnecessarily, and blaming any communications or other blackouts on the weather. Hope this helped! [Answer] So the aliens sneak into town as quietly as possible. They have personal cloaking, as well as cloaking on their mothership. They go house to house, quietly unlocking the doors, and throw in knockout gas to subdue the people inside. Knockout darts are used for people that are out and about. After the occupants are knocked out they scan their brains and digitize their personality and memories, then kill them. They tap into all the communication lines, but leave all the infrastructure alone. All the street lights work, lights are on in some of the homes but not enough to be weird, etc. Anyone arriving at the town is allowed in, and when they stop and get out of their vehicles they are surouned by cloaked aliens, knocked out and digitized. When the lone survivor gets to the neighboring town he runs to the police station and tells the officer on duty that everyone is dead. The officer calls the police station of the captured city, and gets one of the digitized police officers on the phone who assures him that there are no aliens and everything is quiet. The survivor leaves the police station, calls one of his friends who he saw killed, and the digitized version answers the phone, wondering why he's being called at that time of night, and answering all questions naturally. Now the survivor is doubting his own sanity. The weirdest thing is that his one friend who NEVER answers his phone or responds to text messages is suddenly responding promptly. Bonus if he's able to convince one of the digitized personalities that they are dead, and then use them as an ally against the aliens... [Answer] **Coordinated attack on whole country** Example: Czech republic (I love attacking my own country) With unlimited tech, it should be easy to attack all people in given country. You just program attack bots. And if you choose proper time of such attack, which should be 4 AM (source: I worked at Telco and at this time all major releases were done), you will have easy job locating the people. Also if someone managed to escape, they will be really not trustworthy because they managed to escape from some party, so most probably they will be under influence of alcohol (imagine someone shouting at 4:30 AM to police that whole country was attacked by aliens. The police will most probably look them up and buy some more time for aliens) After such attack, you are only left with tourists and people passing by. Easy to fool them. **Problem with unlimited tech** Say I have programmable kill bots. And I have loads of time and really advanced technology... What stops me from sending 8 billion of them in one huge coordinated attack? [Answer] Another classic approach: Set up some plausible situation where nobody would wonder about what he's seeing. Simple example: Spread the news (spoofed TV, Internet, ...) that some industrial accident happenend at the town, which both destroyed communication infrastructure and made complete quarantine necessary for a day or two. Now if someone claims there are aliens at work, every well-informed person will tell him - that he's crazy and that what's really going on is what was on the news. This could work for a single town or city, but of course not so well if a couple of those accidents happened all over the country at about the same time... [Answer] With advanced technology, a convincing simulation should be possible. Redirect all communications to the simulation and those outside the town would feel like they still are in touch. The simulation would be good enough to reproduce the responses of individuals that once lived in the town, so that the character that survived would have the surreal experience of phoning a friend or relative that he knows is dead. The alien base would replicate the structures and electro-magnetic signature of the town so that light, radio, financial transactions, etc. are still continuing as normal. The surviving character would then be challenged to prove to outsiders (and maybe to insiders, the AI simulations themselves) that it is a simulation. If the ruse only needs to last 48 hours, then things like airplane or bus traffic could work on a "roach motel" model: travellers can check in but they never check out. Anyone who makes it to the town is destroyed and the simulation takes up their communication with the outside world (they can still call their family and let them know they are delayed in this town). Sub-plots could include the fact that grandma suddenly knows how to work her phone a whole lot better, or that the town is trying to lure certain strategic individuals to travel there so they can be destroyed or captured. [Answer] I have a town in mind that could be a great candidate for this total destruction that would go unnoticed for a week. I lived in this town so like the aliens I have studied it and think it is a good town to destroy for a base. But a bit of a paradox comes up. Why would they take over a town? What benefit does a destroyed town have for them over a isolated spot? It does not seem they benefit from taking over a city. A town or city seems to have a higher risk of discovery then an uninhabited spot, just a thought. The town I have in mind is [Ely Nevada](http://www.bing.com/search?q=ely%20nevada&form=PRSNRT&mkt=en-us&refig=4c870e0d3dec4febb022b69c2a53734b&filters=ufn%3A%22ely%20nevada%22%20sid%3A%22c142ea82-3192-f340-d508-7c8c6a1245e6%22&qs=MB&pq=ely%20nv&sc=8-6&sp=1&cvid=4c870e0d3dec4febb022b69c2a53734b). The link is to search result of Ely. Ely is a small isolated town, with a small population of about 5000 people. It is a town at high altitude, 6400 feet. The town is at the intersection of two highways, NV 93 and Highway 50. In all directions it is 80 to 160 miles to the next gas. It is over two hundred miles to the nearest Walmart. If the aliens need super low priced shopping the are out of luck. Ely has very little trade. It has a mine that truckloads of ore are moved out of daily. Businesses that have deliveries like a super market, McDonalds and of course package type stuff like postal. It also has an Internet trunk line (backbone) routed through town. The roads have very little traffic, I would speculate hundreds of cars and trucks each day, not much more. Tourist trade is light, mostly hunters in season and people just passing through on their way to someplace else. There is only one scheduled flight in each day, which is often cancelled because no one is flying in. (Ely airport has the highest per passenger flight subsidy in the nation, over $3000 per passenger.) A weather event like a snow storm would bring traffic coming in and out of town to a standstill. Add as a consequence of that event a power outage, that puts cell phone service down and knocks out the internet and you have enough diversion to keep outside suspicion down to a very reasonable level. Outsiders might get suspicious, but it is not likely that suspicion would gain enough momentum for investigation to verify something is wrong within your time frame of 48 hours. The people that might be the people that raise the invasion by aliens flag, would be the crews coming to repair the lines, and clear the roads, would put off coming until the storm mostly passed. In Ely the highway station that keeps all the snow plows is located in Ely, so not much out side help would be coming in. Same is true for power. Nobody will be coming in force from the outside. There is no chance of someone getting out on foot, it is simply too far to the next town. Even a motorized escape by land would be difficult. A snow mobile would not have the hundred plus mile range needed to get to the next town, and since the next town in all directions is at least two thousand feet lower, it is likely they will run out of snow to trek even if they had range. Most other vehicles would have a difficult time getting out cross country. At any rate the trip cross country in snow would be very long, twelve hours more or less. Word might get out from a ham radio hobbyist with a generator. Even if the Aliens were discovered in a matter of hours, it would still be a matter of days before anything but an airstrike could be mounted to remove the aliens. It would be a good bet that the Aliens would be able to defend against any kind of conventional air attack. All the major airbases, Nellis at Las Vegas, Indian Springs, and Hill AFB near Salt lake, are hundreds of miles away. Even an emergency air response would take awhile. Ground response, the army would take days if not weeks to mount and deploy to the area. Even modern armies do not move at highway speeds. The army would be very exposed on the long highways they would be coming in on, making attacking the convoys easy for the aliens. Aliens could take and hold Ely easily. Aliens would have plenty of time to mount a defensive posture before any kind of force could be bought to bare. [Answer] Do the people have to be killed at the moment of invasion? Instead, one evening everyone in the sleepy town/city goes to bed, except the protagonist who is outside the city limits indulging his vice/exploring/doing some science (pick something that fits their character). Then the aliens transport the entire town to a habitable planet somewhere nearby. This transportation is not traumatic nor is it particularly noticeable, except to our poor protagonist who was not in the transport zone. The aliens, having supremely advanced technology, set it up so the foreign town is still connected to the rest of the world somehow, and set up a projection (or a duplicated town) in the space left by the old town - this projection could even be a live video feed of the real city if aerial reconnaissance is an issue). Now there is no difficulty, and depending on how crazy you are willing to let the protagonist feel, cops could call the city and get that cities police station reporting everything is fine. Once the aliens are ready to drop the veil they can easily annihilate the other city(s) (or leave them alone if wiping out humanity is not the primary goal). The one remaining issue would be anyone wanting to leave town - but either you use your handy-dandy teleportation technology to allow that temporarily (again...best used if you want your protagonist feeling crazy), or you have tragic accidents befall the towns folk. If the town is isolated enough (one road in/out), you only have to "blow out the bridge" or similar and it practically takes care of itself. [Answer] The large robots from the initial post could be the clean up crew. Nano technology is interesting... Drop self-replicating geocentric nanobots into the drinking water or via an air delivery system, and the bodies could dispose of themselves. The large robots would simply be used for the construction of the base. Think of it as A.T.O.M. nanobots meet drones, with an alien omnipotent evil spin. [Answer] # Control the weather. In places where inclement weather occurs, your Aliens create the weather system. In Florida, a Cat 4 Hurricane rolls through. Not big enough to require evacuation, but enough to bring down communications. Nobody knows why the weather forecaster can't connect with the satellites! The devastation from the hurricane prevents emergency access through, and also masks the devastation from attacking and killing people. One overly cautious person, however, has a very deep, old storm shelter. The aliens could have detected it, but didn't think they needed to look that deep. When she/he finally stumbles past the wreckage and tells the emergency vehicles that everyone is gone, they don't believe him. A Cat4? And this is Florida: they know how to handle hurricanes! A day later, a really bad snow-storm is ripping through Germany and... [Answer] If it's done quietly why would anyone have heard of it? You don't need vast alien tech to accomplish this. How about method that could be used (albeit quite expensive) with human tech: Infiltrate the town. Release a colorless, odorless gas that is a mild sedative--the intent is **not** to knock people out, but rather make them tired. Slowly pump up the dose until everyone goes to sleep of what they think is their own free will. People without something essential to do will go take a nap, this will reduce the demand on others with more essential jobs so they'll be freed up to take a nap and so on. [Answer] The aliens could scan a town over a couple of days and play back the activity as a hologram. Any vehicles leaving the town could be projected as a hologram out to a distance determined to be out of range of observation by people arriving. In the mean time the area scanned would be incinerated to a depth of +/- 500 meters. Any vehicles entering the town would be instantly added to the hologram showing their movement to a side street to prevent further observation by those outside the edge of the hologram. The vehicles entering the town would obviously plummet to the bottom. Any telecommunications errors would be handled by their respective services i.e. subscriber could not be found to we are experiencing technical difficulties at this time. The aliens would have the choice of letting the people incinerate with the rest of the town or to teleport them to the mother ship to probe to their hearts content. [Answer] Make an even bigger, more interesting, more conventional looking disaster somewhere else. For instance, drop a meteor on a major city, or start a tsunami that floods a coast with a large population. Have a good reason for the disaster to explain dropped communications to your new home base town, and have a way to sweep up stragglers who might stumble upon your new construction. [Answer] It is probably not very hard to keep the ruse up unless people already suspect something fishy is going on. If you call your friend in the next town and he doesn't pick up the phone, then "oh no, aliens must've invaded and killed him" is probably not going to be your first thought. And honestly; can you be *absolutely sure* that the next town over is still there? What are you basing it on? Most likely on the fact that you've not yet heard anything that would suggest it isn't. And if you heard such a thing, it would probably be because a news station would tell you, right? So really, to keep the ruse going for 24/48 hours, you only need to do two basic things: ## 1) kill all people who get direct visual confirmation of trouble Yeah, that's anyone who sees what is going on. Whether a traveller, or an aircraft passing over close enough, or whatever. Since you can't mess around with what people see, you just need to terminate their ability to communicate it. You'll have to be fairly quick and might want to drop something that cuts connection to common communication methods (ie; disrupt the local internet and phone system) ## 2) make electronic systems pretend that the town is still there For starters, scan the local area internet and try to replicate their social and other media. Facebooks continue to update, news outlets still post news, maybe even text messages still get a basic response. Doesn't have to be super accurate, just not obviously fake. The harder part is fooling some of the other systems in place. If you take down an aircraft, you'll have to feed data into flight control to make it appear to still be there. Then you redirect the plane into the ocean after a while. Before anyone figures out where the plane really disappeared, the 48 hours will be up. Likewise, you'll need to fool any active satellite feeds of the area (if they exist) and you need to make sure you don't trigger any other warning systems (seismographs going funky because you bring down the kill-o-bot might cause a lot of unanswered phonecalls, for example) But once you do that, you basically have no information coming out to make people doubt that something is wrong. You can easily keep that going for a day or two, since that's a very short amount of time. (Assuming you pick your target somewhat wisely. This will not work if you make an entire metropolis disappear, but it will work for many small villages.) So to **TL;DR**: * kill anyone who figures it out visually * keep outputting the electronic signals of the location * nobody will get suspicious for the first few days [Answer] Assuming that your aliens have some significant powers, there are some better options than just shutting down communications to one town. Assuming that these aliens have the power to do so, it would make more sense to start taking out communications infrastructure to the point where it doesn't seem unusual for this town to have suddenly disappear. One option that occurred to me was to either induce a large solar storm, or to wait for one to occur naturally. Solar storms tend to knock out everything from communications satellites to the power grid, and so losing communication with a large area is still conceivable. Obviously, people will know that something is happening, but most rational people would blame it on a more scientific explanation than aliens. [Answer] The clarification really helps. Assuming even mildly advanced technology, knocking out a town without anyone noticing is trivial. You just kill everyone in their sleep during night, that's it. Maybe one or two late night phone calls will be interrupted, but that won't raise a general alarm. Communication is the key, of course. However, in many parts of the world, occasional failures in the communication networks are still so common that a 1-2 day black-out would not cause a national alarm. That's why knocking out a town is much easier than knocking out a city (and it makes it much more believable that there's just one survivor). Depending on what exactly you mean by "without anyone knowing", however, the #1 secret trick to covering up pretty much anything is **plausible deniability**. Knock out the town and inject fake data that a blizzard or flood or hurricane or whatever the common local desaster is has knocked out all the communication lines (even mobile phone networks ultimately go into cables). That way, people know that something is up, but they don't know the whole town has been knocked out. If that satisfies your definition of "without anyone knowing", it's the easiest way with the least amount of handwaving. ]
[Question] [ I have a civilization in my story structured around the idea of worshiping the sun(s) as gods. The Church is the ruling body of this interstellar civilization and ensures that the "Blessings of the Gods" (technology) are only operated by Priests and the Chosen Few. Anyone caught violating the Blessings of the Gods by daring to disassemble, examine, or question their operation is immediately put to death for having the hubris to believe they could understand the Gods' power. In this way, anything more complicated than a pocket communicator or simple power bike can only be operated by a member of the Church, keeping the normal populace in check and reliant on the Church for the continuation of their way of life. Access to the Divine Heart (fusion power), Protectors from the Great Void (spacecraft), and Portals of the Gods (computer networks/internet) are strictly controlled by the Priesthood. That's the easy part. **The hard part is, how do I keep the Priests themselves from knowing how their technology works, while still letting them a) operate, b) repair, and c) build it?** The technology itself was designed many thousands of years past by a now long-dead, more secular, previous iteration of this civilization. Further R&D by the Priesthood is unnecessary, but they need to be able to repair existing Prayer Vessels (deep-space comms) and build new Fists of the Almighty (laser guns). The trick is that the Priests believe in the Divinity of the Stars just as much as the populace: to them, their operation of these Holy Devices is a god-given right, not the result of superior technological understanding. How can I impose some social rule strong enough to keep a curious Priest from disassembling a Star Shard (light bulb) one day and figuring out how it works? There are two explanations I'd like to avoid using: * They don't do it because faith. I'm looking for a way to keep some of the more skeptical priests in check; faith is enough to keep most in line but I'm looking to scare the outliers here. * They don't do it because the original designers made the technology un-understandable. This seems like a cop-out to me, and doesn't fit with the story of the previous civilization. [Answer] This might actually be easier than you think. Just use a list of instructions for every 'build' or 'operation' and a checklist for every 'repair'. In point of fact, we're already doing this. In Australia, we have a bakery franchise called Baker's Delight. You don't have to be a baker to buy into it; they give you a set of instructions (and all the tools) to bake a range of different bread products. They're great! Lovely bread all the time, consistently made. My father (who was a baker by trade) once showed me a minor defect in a bun, and said something like 'it wasn't proved enough' but I don't know enough about bread for it to matter to me and as far as I was concerned, it tasted just fine. The point being, you don't have to know 'why' if you know 'how'. I've also seen this in office environments all the time. People follow blindly a list of instructions for producing a (say) monthly report that was designed by the person who sat in the role 3 people ago. The current person doesn't know that the data has been moved and they've been using old archived data for the last 2 years, and his or her manager has been making decisions on this without realising. The beauty of instructions and checklists is that they're ideal for lazy people; and there's a LOT of lazy people out there. Not always by character, some people are just plain busy and don't have time to investigate further. Sure, you're going to get the odd curious soul out there who's going to want to poke around with the process and experiment a little bit, but a crippling workload will crush that out of most of them soon enough. If you catch someone playing with the formula, just double their output quota for the year. Ultimately, you're going to get some people finding out what's really in the kool-aid and that will have to be managed, but by having everything done by rote and rewarding adherence to the instruction list (and punishing curiosity with more work) the vast majority of your clerical (no pun intended) workforce will fall into line. [Answer] It seems to me that by the time technology reaches this level, it will primarily be all 'black box' technology. Even our modern technology is pretty much indecipherable by even engineers, it is so miniaturized. It takes microscopes approaching electron microscopes to be able to reverse engineer our integrated circuits. Add to this, our reliance on lithium ion batteries for energy. Take a lithium ion battery apart, or even try to, pretty much means an instant hot, intense fire if not an explosion. I would expect that, at this high level of technology, power sources would be fully integrated with the circuitry, the way they are integrating lithium ion batteries right into the circuit boards today. Combine these, and you don't need the ***threat*** of death, it would pretty much be automatic. Remove the protective coverings, and the energy store of the device goes 'phytzzz' in sparkensenbominsenflamesenzen. So the people, including the priests, have an innate fear of what is inside. That 'there be dangers herein' would not be hard to convince people thereof. 'Repair by authorized personnel only' would be more than just an idle warning. And even if they ***did*** get them apart safely the insides would just be solid black masses of technology. Let's face it, even computers of today reveal absolutely nothing about their function. The innards just sit there, no obvious physical changes to reveal function. Remove all of the labels on the chips, and one has absolutely no idea of what the circuitry does until it is hooked up to inputs and outputs. A cob light is pretty much just layers of stuff that somehow emits light. Absolutely no movement that can be seen. So how do these devices get repaired? Probably they do not. There would be 'no user-serviceable parts inside'. Swap out components. Replace, not repair. No one does board-level repairs on our technology today. If it doesn't work, trash it. Okay, how do they get replaced? I suggest that their manufacture would be completely automated. Not just robots, but micro-robots. 3D printers on steroids. Put in the raw materials, and the automatic control systems print out the product, completely finished. All circuitry, layers, connections, components automatically built up, layer by layer. The assemblers just feed in the raw materials, and take out the final product. They don't need to know anything about how it works, any more than an assembler on a smart phone line needs to know how the smart phone works. Everything is automatically controlled by computers, and the programs would all be embedded. Inaccessible. No re-programming allowed. The original programmers would have 'burned' the 'programs' into the 'chips', and future 'upgrades' would have been by swap-outs of the 'chips'. The 3D printers automatically embed the 'code' when they print the device, 'hard-wired' into the 'circuitry'. Everything is in air quotes, because it would probably not look anything like our technology, but would be quantum computers, quantum effects, quantum memory, quantum technology that we have no terminology for. Everything is a black box in a black box surrounded by a black box, manufactured and assembled in a black box by completely automated black boxes. Even if someone could *see* what the 3D printer is doing, they would never comprehend *why* it was doing it. Even today, we can see a smart phone being assembled, without having any idea of how the components work together. It is not *deliberately* making the technology unknowable, it is an artifact of *how* it is manufactured. It sounds like your civilization has not advanced in technology for thousands of years - it pretty much seems like they have completely forgotten what is inside the black boxes. And opening one up would be inherently really, really dangerous. [Answer] I have spent some time in extremely impoverished 3rd world nations and the mindset towards technology in such places is pretty much to consider it as magic already. If you are poor and desperate you stop thinking about things that don't put food in your belly. You aren't making plans for the future, you are farming because if you don't you will starve. The struggle for daily survival consumes your entire waking life and to ponder how those airplanes overhead are able to fly never even occurs to you. They just do, everybody knows that, what good would knowing how do you? It doesn't fill the hole in your belly or get those crops planted. It doesn't keep your aggressive and dangerous neighbors away. It doesn't make the rain fall sooner. So it doesn't matter. Illiteracy is also a massive shove in the direction of making tech into a superstition. If they cant read even if they wanted to learn how that airplane works they wouldn't be able to. If the majority of people's time is spent scrabbling for the most basic life necessities (food, water, shelter, and security) they tend to naturally not even worry about how learning how to read, let alone studying engineering, physics, and tech. The fact that our present culture is populated by literate people all heavily educated in how the world around them works is really a monument to how much free time and extra resources we have. In ages past only a very very tiny portion of the population could read and write, it was such an exclusive talent for a while that it practically put somebody into a different caste during the medieval ages. If You take our modern free time and surplus of material wealth away and in a generation they might not be worshiping tech, but they will certainly have abandoned trying to figure it out. Keep it that way for a century or two and suddenly its pretty easy for whoever wants to manipulate the people to essentially tell them whatever they want the people to believe. [Answer] Something I have not seen yet is the point about how dangerous a lot of that technology is. Many humans are reckless in our use of guns, cars, and many other things. If these things are new to us though, we tend to be careful and not use them too much. To be a priest is to have proven yourself to be capable of handling that danger, much like a police officer proves to those who hire them that they are worthy of the badge or a Knight their position. They are the ones who get taught how to handle the dangerous stuff, and the more distinguished ones among them can go farther in and learn how to do the more complicated making and repairing of the dangerous stuff. The intricate aspects would and probably should be handled by factories that maintain themselves, as kinds of [Black Boxes](https://en.wikipedia.org/wiki/Black_box). A space faring civilization is likely to have some factories that are almost fully automated that survived, and the Priests just do the rituals that request of the factory to turn raw materials they put in into the finished products. The factories kick out people that are in the assembly line because they are obstructions endangering themselves and the machines, so the Priests can never learn how to build from scratch, but basic repairs could be learned by trial and error plus reverse engineering. Those who do so are the bravest of priests who sacrificed themselves to learn how to tame the machines when they go out of control so that others could do so without dying. After decades of this, while they don't know everything about the black boxes that are the automated factories, they would certainly have learned how to do basic repairs. The vast record of individuals dying while using the devices would scare away non priests, because everyone knows that if you don't know what your doing, your probably going to get killed by it, especially since countless experts who dedicated their lives to it have been killed by them. The only thing remaining would be to do something similar for the communications arrays and computers. Both of those use electricity to dangerous levels. They say the 2 things on a computer you should never mess with are the Power supply and the Monitor. If its not widespread, you could easily convince the masses through rumors that they too are dangerous and have killed priests investigating how they work. They also are super complicated, so much so that priests who spend their lives studying them only know part of how they work and what they do, which is true even of modern day individuals. No common layman would ever want to mess with a strange device that can kill them and is so complicated that they could only learn a few basic things without a teacher. Priests only teach other priests, so an average person would be much like an elderly person today who has never used a phone or computer trying to figure one out without someone to help them. This kind of method also lets you limit what tech is available, stripping out modern conveniences that you don't want on the basis that there are no factories that build them or their components. Sure the Priests could build the guns from the components with a guide, but if no factory exists to build the fundamental parts for washing machines, they are probably out of luck. With all that, and a bit of hand waving that the story went in a specific way, its very realistic to believe that most of the population knows from rumors and stories from Preists themselves about how dangerous and complicated technology is. Most people will be afraid of it, many who try to understand it will kill themselves on accident, and most of it is otherwise restricted to Priests. Those who do make it or are interested may be try to or be invited to become priests. Thus, any talent or desire to understand tech will steadily remove itself from the villages to become priests or die trying. [Answer] If you think about it, cows and chicken perfectly satisfy your requirements. Create alive evolving technologies and you are done. We had no idea how they work until recently (and still largely don't). We know how to make them reproduce though. > > Anyone caught violating the Blessings of the Gods by daring to disassemble, examine, or question their operation is immediately put to death for having the hubris to believe they could understand the Gods' power. > > > I think that's exactly how anatomy studies were treated not too long ago [Answer] In the future every machine may be able to communicate through means which would seem magical even to us. Interstellar, FTL communication provided by microscopical components may be ubiquitous in machines and you can handwave the technical explanations (no one questions those in Star Wars/Star Trek as well). So, supposing your machines are connected to a sci-fi network, some [IoT](https://en.wikipedia.org/wiki/Internet_of_things) may be just what you need. It could work in the following ways - you can even combine them as you see fit: * **Megalomaniacal AI:** there is an AI connected to every device and it either thinks it is a god, or is impersonating one or more gods (suggested read: Count Zero). In order to use machines, one must worship the gods - hence the need for a priesthood. Diffetent rituals may be needed for different levels and modes of access to technology. * **Fragile things:** machines need the network in order to function well, and the comms circuitry is very fragile. Trying to disassemble a machine is a sure way to break the comms, and then you brick the device. * **Stupid bug:** the machines used to be more helpful and would answer all technical questions, or at least point to manuals and documentations. However after civilization fell long ago, machines suffered from a bug similar to the [Year 2000 Problem](https://en.wikipedia.org/wiki/Year_2000_problem). They flipped their calendars from year 9,999 (or 99,999, or 999,999) to a negative year at some point and this caused an astronomical quantity of bugs. Questioning a machine, or failing to recite a set of commands in a long-dead language and in a very specific order (which could be seen as a form of prayer) will cause a device to crash and/or reboot. * **Strong DRM:** machines were built by governments or corporations that did not want them reverse engineered. Any detected attempt will cause the machine to brick on purpose. The civilization that built them this way is gone, but the DRM measures are still in place. Last but not least, using any machine may require authentication and authorization. Thus the rituals of innitiation are actually a long-held secret of how to create a user account, and the high clergy may be able to deauthorize a church member until they attone for their mistakes. This works well regardless of how much understand and faith the priesthood has when it comes to the ways that the machines work. --- Last but not least, I cannot help but think of Blur's 2112 while typing this. The song is not part of an answer per se, but I think the tone of the story connects very well to the question and helped me think about the suggestions above. > > We are the Priests of the Temples of Syrinx > > Our great computers fill the hallowed halls > > We are the Priests, of the Temples of Syrinx > > All the gifts of life are held within our walls > > > ]
[Question] [ I was recently reading an medieval heroic fantasy book and I was disturbed by the usage of the metric system. Distances, heights were expressed in meters and it reminded me advanced civilization and French Revolution. Maybe metric system is not the best unit system if we had to stay consistent in a medieval fantasy world. It sounds like an anachronism to me. I'm building a medieval world which has sparse cities, villages and primitive commercial trades. What would be a realistic unit system? [Answer] Back in the middle age each city had its own system of measures, usually based on the human body. Inch, arm, palm, span, foot were used to measure distances, for example. Normally in the market square there was some sort of reference sample for lenght and volume (at least), which would come in handy when foreign merchants came to sell their goods and for paying taxes in nature. If you stick to those, it should sound realistic for those times. [Answer] You've already got a nice collection of [links](http://www.everingham.com/family/data2/rec0034.html) in the comments and in answers to get you started. Measurements during this time were not consistent from place to place, however, traders did do conversions, letting buyers know how a general measurement which was used more widely, stacked up against the local measure. There are many complaints based on measurements in the annals of law during this time because of the inconsistency. In fact, a person selling cloth might even have their own measuring stick (which might just be a single, flat stick) that they might use as a measure, telling customers that each of those is a unit, with the varying cost attached. About 1200 or so because of the rize of Medieval fairs, more interest in consistent measurement, mandated by local rulers became more prevalent. So, at the Troyens Hot Fair in Champagne for example, they mandated that all merchants use a standard of measure that they imposed. The Champagne ell (2 feet 6 inches) was the standard and was checked against the iron bar wielded by the Keeper of the Fair. The fairs in that region were popular enough, with enough goods coming through, that this method of measurement spread to other regions in France and Belgium. But this doesn't mean that an ell in France was the same as an ell in Germany or England. There were literally hundreds of thousands of measurement units, and in less regulated places this could even vary from shop to shop. England, perhaps because of its isolation, kept the Medieval system the longest. America's current measurement system of pounds and feet and gallons--is actually closer to that old Medieval system than the Metric system is, at least in terms of what the measurements were. While there were provincial measurement systems in England, the places that traded the most were the ones that set the standard. So, London would actually send out measures of bronze or brass to the provincial towns to basically let them know what the standard was. They would then "copy" those and send them out to other villages which wanted them. By copy, I mean that they would counterweight something else, such as sand in a container of equal measure. Unfortunately, these copies and copies of copies were not always accurate (because means of measurement were not always that good). So a pound in one place might not be quite the same in another. (Jokes could come from this--like a town known for their pound being short, if the word spreads, can become a saying-- people might know that a Jameston pound will always come up shorter than a London pound). Standards were reissued in the hopes of keeping things consistent, but until Elizabeth I in 1588, a uniform system in England was not well imposed. (Okay, there was an effort in 1496 as well). If you are starting from scratch, I would use the American system as the guide, because it's the closest thing we have in modern times to what the systems were like then, rather than the metric system. [Answer] I've got an interesting view on this as a Canadian, but I'm thinking not only will you see multiple systems, you will see multiple mixed systems. The best unit system to represent medieval would be arbitrary, inconsistent, and vary from city to city and person to person. If you ask a Canadian how much they weigh or how tall you are, most likely you'll get a pound and foot/inches answer. I buy my potatoes in 10 pound bags, price my meat out per pound, and I know my cars fuel efficiency in miles per gallon. Proximity to US tends to keep these terms alive. Ask me to measure a distance that's not my height, I'll answer in meters...I drive Km/h and buy litres of fuel...and in that very same grocery store, I buy deli meat in grams, beverages in litres, and (perhap most ironic considering it's sitting beside the 10lbs bag of potatoes) my fruits and veggies are priced per Kilo. Well except berries that are back to pint. To go a bit further...my Grandma's recipe book continues several entrees that actively list 1lbs of butter, 2 cups of sugar, and 0.5 liters of oil. Mixed measuring units is a part of life here, and I'm sure you're medieval land would realistically see people struggling with multiple measurements. It can get to the point of absurd too...If you ask weather, my dad will tell you degrees F. Any other topic will be in Celcius. The only consistent might come through in distances...though even then it's pretty arbitrary. If a town is a 30 minute horseback journey, that time (30 mins) can work as a valid distance measurement. Albeit this isn't accurate as speeds of travel aren't consistent, but it does function. [Answer] Beyond that, use measurements based on the human body. Hands high, feet high, arm's, thumb-length, paces, days (walking) journey. These seem archaic, yet modern people don't need to memorize strange units; they can grasp the distances by looking at their body. These values will vary from place to place, and some places might use feet and others arm-spans and others paces. Another option is to use yards, which are basically meters. For things like time, if hours/minutes are too "modern", you could replace time with "bells" instead of hours, with each "bell" being some fraction (say 1/4) of a day-length (one bell at dawn, one at noon, and one half-way in between, similar for the afternoon) or 1/4 of a night-length (so 8 bells/day, thus 1 bell every 3 modern hours at the equinox, but it varies with the time of year). Without lots of clocks, mearing time in hours/minutes makes little sense. [Answer] [Wikipedia](https://en.wikipedia.org/wiki/Medieval_weights_and_measures#English_System) has a list of many unit systems that were used in medieval times. Those were basically units based on a natural object, like a plant or a length of a foot for example, or based on a reference object (a rod of some sorts). The first variant makes it easier to have it available for everyone, but the second variant is more precise (for the one who have the reference). [Answer] Some ancient empires were surprisingly good at enforcing a single measurement standard across their realm. Later local systems were often build upon such prior systems or were the result of increasingly deviating copies of copies of reference measures. Preexisting or imported systems were often adapted to fit the predominant one with simple integer ratios. ## Length The most general units of length are usually related to approximate measures of the human body. * *Ell, inch*: The width or length of fingers, hands and arms or the span between two of them is common in artisan and other manual work. * *Foot, yard*: The length of a foot (with shoe) or a (double) step is more likely in anything working in or on the ground (farming, military, architecture). * *Mile, league*: The distance that can be traveled either without rest (either on foot or on horseback) or within a standard time unit (part of a day) will often be the largest one defined. In naval cultures, it is more likely to be defined in relation to the circumference of the planet, e.g. 1 nautical mile = 1 equatorial minute of arc. While different domains will prefer different units they are quite likely made to relate by simple integer ratios. The relations may look arbitrary, e.g. 12:3:22, because of this and sometimes two units will have a fractional relationship with each other because they relate to a common base by different primes, e.g. 1 palm = 3 inches = 4 fingers. Note that 1 foot is 12 inches less for the convenient factors (2, 3, 4, 6) but more because 3 + 4 + 5 = 12: a triangle with these sides has a square angle (9 + 16 = 25) and this is a useful property of measuring devices in construction. It would be unusual but not unthinkable to have an actual consistent system, e.g. with generalized dozenal relationships between units. ## Area Small area measurements do not have a dedicated unit. People would specify them by the dimensions of edges or the radius. Land area (i.e. hundreds of square meters) is measured for different purposes. Their historic relevance will determine the local prevalence of units. * *Acre*: agricultural workload. A popular unit is the area that can be plowed in a day or half-day with the technology available when it was defined. This may be normalized to the rectangle made by two length units, e.g. 1 rood = 1 furlong × 1 rod. Such units may depend on the local soil and topography. * *Rood*: agricultural resources. Another, smaller unit useful to Farmers is one that can be measured with simple tools and relates to the amount of either seed required for or crops harvested from this area. That means it will be aligned with a unit of weight or capacity, e.g. the area that needs one bushel of barley seed. * *Hide*: military taxation. For administrative purposes, especially in serfdom cultures, there will probably be a unit that is the area of land necessary to provide for one horseback knight or something similar. It may be a simple multiple of one of the agricultural units. ## Volume Wet and dry measures will probably have different, though possibly related units. Most of them will be derived from standardized measuring containers or casks, which may in turn be aligned with the respective weight (like 1 liter of water weighing 1 kilogram) at least for the base size (e.g. tun and ton). More often, the calibrated containers are specified by their inner dimensions. You can either have three length values for a cuboid or two for a cylinder: height and either radius, diameter or circumference of the base. π is probably assumed to equal 3+1/7. Other capacity units are usually derived by halving and doubling the base iteratively. Some steps on this idealized scale may not have canonic names, e.g. there is no half-gallon measure in English. During the course of history the system may get further distorted for one reason or another, so occasionally there will be a factor of 3 or 5, rarely 7, between units. * *Pint*: The size of a drinking glass is a general purpose wet measure. * *Gallon*: * *Bushel*: The amount of harvest a single person can carry cash be a useful base in agricultural ## Weight Weight and mass are not distinguished. Very often, small weights directly correspond to the amount of gold or silver (originally) minted into coins of the same name. A *pound* will usually be the maximum unit for this, while it is the minimum unit useful for other applications, e.g. in agriculture or mining. Multiple subsystems may coexist, e.g. Troy vs. Avoirdupois, or just differ in subdivisions, e.g. Troy=Apothecary ounce but the former divided into 20 pennyweights and the latter into 8 drachms or 24 scruples. Subdivisions are less likely to be binary than capacity measures are, i.e. prime factors 3 and 5 are more likely to occur. [Answer] In medieval times, travel was not easy. Even if there was a standard, it would be difficult to share that standard. The natural order of things would be to make copies of copies, allowing error to creep in. Or unscrupulous sellers could shave a little off the measuring stick and sell less product for the same money. Further, what's the point of standardizing? If you're happy to buy a bag of weasel dust for X quatloos, do you care if the bag contains 5 kilograms? Or do you care that it was about the same size as last time? Finally, the expectation and need of day-to-day precision of medieval life was quite different than it is today. ]
[Question] [ **Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers. --- This question does not appear to be about worldbuilding, within the scope defined in the [help center](https://worldbuilding.stackexchange.com/help). Closed 7 years ago. [Improve this question](/posts/31712/edit) Due to *\*cough\* hmrnrnrmrn rmrmr \*cough*\*, some humans are born with two heads. This has been happening for at least as long as humans have been making cave paintings and it seems to be nothing to worry about (unless you don't get along with your bodymate, in which case you should contact a trained psychologist and refrain from fighting or biting yourself until an appointment is available). They have two heads (no connection between the brains), a Y-shaped oesophagus and wind-pipe, a slightly larger chest to contain their marginally larger heart, lungs, veins and arteries to handle their increased oxygen requirements and (anecdotally at least) a tremendous appetite. However, as they could not be proven to be anything other than than human, further testing and experimentation hasn't been legally or ethically possible. What other, if any, biological differences would two-headed humans show in order to operate just as efficiently and easily as single-headed humans? --EDIT-- (From comment by OP) @MontyWild Most of them can't tell because they generally don't disagree and coordinating movement becomes subconscious, but those that do fight claim they are both in control and that being shouted at and punched by yourself is too distracting to concentrate on which head is doing what [Answer] There is a real-life case of almost-exactly what you are asking about. [Abigail and Brittany Hensel](https://en.wikipedia.org/wiki/Abby_and_Brittany_Hensel) are a pair of *dicephalic parapagus* conjoined twins. They each have an individual head, but share a single body beneath, though there is some duplication of organs above the waist (for example, two hearts and three lungs). They each control and feel one side of their conjoined body, but because they grew up that way, they are very coordinated -- able to ride a bike, drive a car, and play piano, for example. At least in the real world (and this may be different in your scenario), conjoinment is an abnormal condition -- i.e. it's not a programmed genetic trait -- so the biological specifics are randomly unique to each case. As a result, most cases end up with various health conditions, and many don't survive infanthood. So far, for the Hensels, this doesn't seem to be an issue, as they are doing quite well. There is quite a lot of information about them on line, but here is a decent article that gives a summary, and some additional details: <http://www.buzzfeed.com/moonc/everything-about-conjoined-twins-abby-and-brittan-a1kb> [![enter image description here](https://i.stack.imgur.com/pJ4h8.jpg)](https://i.stack.imgur.com/pJ4h8.jpg) [![enter image description here](https://i.stack.imgur.com/A2Q95.jpg)](https://i.stack.imgur.com/A2Q95.jpg) [Answer] If there is no connection between the brains, then one of them is probably useless to the body. That also means that this useless head cannot control the body. If the two heads can control the body somehow, they can sleep in different times, keeping the body active all the time, which would be extremely necessary since eating more than usual humans means they will also have to gather more food. If the two brains studied and learned different things from one another, they can complement each others knowledge to a more intelligent being. In both cases the other head serves as an additional opinion to ask for anytime you need. [Answer] One big problem would be how such humans are born. Major problem and major limit for human development is the size of the head and how it can pass through birthing canal. I assume that Hensel twins were born by C-section. Which is fine in developed world, but not so much in natural habitat in stone age. So main problem in your world is not how such humans will live, but how they can be born. **Without advanced medical care, they cannot be born,** and unresolved pregnancy would kill the mother. So **such trait cannot "evolve" naturally** - any gene increasing chance of two heads would be eliminated by darwinian pressure. [Answer] As I remember, there is one other case of a two headed adult. The story is that in early 17th century France (roughly time of the Three Musketeers) A two headed sideshow freak killed a man. He was not executed because they didn't know which head was guilty and they didn't want to execute an innocent person. I doubt that they would have been born by C section that early, so presumably they survived a natural birth. Added October 15, 2019. Here is another case of adult two headed humans. Giacomo and Givovanni Battista Tocci were born between 1875 and 1877 and retired from their career as a circus freak in 1897; reports differ on how long they lived afterwards. <https://en.wikipedia.org/wiki/Giacomo_and_Giovanni_Battista_Tocci> Wikipedia lists 11 examples of two headed humans born between 2000 and 2014 and doesn't say that all of them died, so some of them might also still be alive. <https://en.wikipedia.org/wiki/Polycephaly#List_of_recent_occurrences> ]
[Question] [ In the Terminator movies, time travellers arrive naked and then steal clothes and other items from the locals. In my society this is also true. However they can carry some things internally in the same way that drug smugglers do. There is only so much that they can carry. When they arrive, they have to unload the cargo via bowel movements so they can't carry anything sharp or excessively bulky. Time travel is a closely guarded secret and the exclusive property of a guild. Members of the guild become rich by trading with people in other times. **Questions** 1. Given the problems of internal concealment, what can they trade for the most profit? 2. How can they return their earnings to their own time? 3. Should they visit the past or the future? Which is better for trading purposes? How will past and future trading differ? Note that they must be careful not to change the past too dramatically or they will stop themselves from ever being born. [Answer] ## Knowledge. * **The Market** knowing when the market is going to tank or soar. * **Locations** of minerals and other resources (Sutter's Mill anyone?). * **Materials** imagine bringing fiberglass to the Vikings * **Engineering** * **Inventions** (maybe Thomas Edison was a time traveler?) * **Trends** When styles and trends were likely to take off (hula-hoops to clothing, maybe the inventor of the Frisbee was a time traveler?). * **Music** What sort of music will become trendy (maybe the Beatles were time travelers?). * **History** being on the "right side" of political events * **Weather** (know to plant corn in a year when the corn harvest will be abysmal, know to pull up the stakes of your New Orleans operations before Katrina strikes - Maybe Forest Gump was a time traveler?). * **Insurance** (know which people and items you should not be insuring)! * Knowing the future value of things (there have been times and places when people traded gold for salt, there have been other times and places that sold platinum for less than silver because platinum was a waste product of silver refining). * **Land** (which land will become valuable and when it will happen). ***Edit 10/16/2015:*** Added from the comments: * **Numbers** memorize several sets of winning lottery numbers * **History** knowing when to be "out of town" when human disasters will occur like Hiroshima 1945 and NYC 9/11 [Answer] My very first thought was drugs. Not just because of the method of transportation, but also because if you live in a time period where say, opium is used as a cure-all, you could totally take it forward to a time where it's illegal and sell it at a premium. Maybe even historical artifacts that are in better condition than the versions they'd have in the future. (Check it out, world's first mass-produced sim card as it looked the day after it came out!) [Answer] # Labor savings In mining, surveys must be conducted to discover the locations of ore deposits and such. Write your time travel laws such that the following can occur: 1. Time traveler Alice appears in the year 1800 on August 5, promises Bob the miner that she'll bring back his survey results for \$1000. 2. Bob agrees, and spends \$50,000 on a survey to find the best place to mine coal. The survey is completed in 1810. 3. Alice memorizes the survey results. Alice travels back to 1800 on August 6, and sells Bob the results. Bob has saved \$49k and Alice has profited $1k. This technique for bringing memorizable information back in time could have a number of applications, including: * Mad Scientist support - want the results of a 5 year experiment in 5 minutes? * Accident prevention - want to know the week before a lethal accident blows up your fireworks factory? These time travelers could one day even become required by the insurance company. * Wartime strategy - better hope both sides don't have one! Due to the risk of paradoxes, this industry may grow to become highly regulated. Presumably the Guild will handle this regulation, and dispose of rogues before they go rogue. [Answer] Well, instead of bio-bags (which I like), how about small containers like Tupperware or ziplock backs under the skin? The 'zipper' could be concealed, but easily opened. Would at least be easier than the drug smuggling approach. Really, if time travel is possible, extras dimensional containers aren't that implausible. (Like bags of holding in Dungeons and Dragons). Also, things need not be material, to be valuable. How much would someone pay for a vial of fresh, refrigerated, dinosaur blood? Or a Dodo bird egg? Or DNA of the 'missing link'? If amnesiacs can be created (fool proof drugs to erase short term memory) then rich people could pay a million dollars for five minutes with Jesus of Nazareth. Or Napoleon. Or King Arthur. Just try to get them when they aren't going to be busy (scout ahead, then go back and get them during their down time.) Might be a minor plot, when someone kidnaps a visitor from the past, and have to find them in 5 hours- that's the limit of the amnesiac. [Answer] The problem with becoming rich from this is the butterfly effect. This effect would easily prevent you from going back in time let's say to 1980 and buy stocks in Apple. On a smaller scale buying chicken from a local grocery store may eventually lead to the bankruptcy of Apple because the guy from the grocery store founded a rival company. [Answer] How to carry very valuable items back in time within your bod? Interesting question. Forget diamonds and gold. Give me an iPhone and send me back to the 1980's. Transferring either small technology *or* information back to the past would be far more valuable than any single item made of a precious substance. Think of how much we would pay today for the cure to cancer or cold fusion. I'm pretty confident I could swallow a micro SD easily, and if you know anything about micro SD cards it's pretty easy to mock up a card reader. That's a lot of information you can transport, here's a few ideas; 1. Medical breakthroughs 2. Technology specs 3. Government political (de)classified information 4. Knowledge of future events - earthquake mitigation etc. So go to the past. Once you have the money, buy something that will never get devalued. Land is probably a good shout; or a material that becomes more highly valued in your present (rare earth metals might be a nice on). [Answer] ## How to make money Data. With access to the knowledge of the future, governments and large companies would happily buy research that is yet to be done. Do you have an issue with the bootstrap paradox? Imagine going to Google today and giving them all of the information about their mistakes and dead-ends in the future, what makes them successful etc. > > You know what a learning experience is? A learning experience is one of those things that says, "You know that thing you just did? Don't do that -- Douglas Adams. > > > Imagine a learning experience without having done "that thing you just did". Imagine going back to the 1920-1930s and giving some nation of your choice all of the future science and research on atomic weapons. Imagine how many people would pay to publish the general theory of relativity before Einstein even published the special theory. Transfer all of this information on a memory card inside a small smartphone and write it up by hand. Alternatively, the traveller can post on here asking for advice on how they could print files with technology from previous decades and devices that can fit into one's anus - it wouldn't be the strangest question to be answered here! ## How to keep the money with you The problem then is what happens to the money you earn, and how you would take it back. My answer is that you don't. Use modern day knowledge to build a condition-preserving bunker, in the past, in a permanently-remote location. Use your money from trades to buy famous pieces of art, original pressings of books/records, a model-T Ford hand signed by the man himself, with zero miles on the clock. Get back to the future, open the bunker and report the find (Donate 60% to a small town museum) to remove suspicion. The rest will make you billions. You will be revered amongst 'normies' as an adventurer, an Indiana Jones-like character. You can pay off some companions to make some other "discoveries" to remove all media attention from yourself. You can plant stories in the past to hint of such bunkers, with sufficient mystery surrounding them to make them unfindable. This storyline sounds like a hell of a lot of fun. [Answer] Work in the crematorium of a prison that executes prisoners. When a body is about to be disposed of, because no family will claim it, use the skin-bag to store your gold or platinum in for transport. (Dispose of the meat and bones in the usual way so as not to arouse suspicion.) When you transport yourself, make sure to set it so you get there 30 seconds or so before the skin, to make sure you are alone and no one sees you. If someone does, make sure they approach you and have them standing in the EXACT spot the cargo materializes, vaporizing the witness in the process. [Answer] While there are already very good answers, especially about trading information, I would also mention one more possibility that is not yet covered. Since this kind of time-travel requires for the transported object to possess a living exterior, it should be possible, with that level of science anyway, to create bio-bags. It could be an artificial non-sentient lifeform with a big cavity inside that could be filled with objects. There are big possibilities opening with that approach, depending on what you want to have in your plot - for example, the lifeform could be in need of nutrition, and keeping it alive and fed up during the journey may give an additional point of concern for the characters. Or it could go rogue. Or a big enough bio-bag can be used to send a spaceship in time... However, if you postulate the need of a living exterior for the time travel, I would reasonably ask "why so?". Back in the days when the Terminator movies were made, it was enough just to postulate this. Today's minds are already more hungry for knowledge and reasonability. I still question myself, what could be the technical reason for the limitation in Terminator.. and why did not they use bio-bags to send more stuff when the terminator itself is essentially a bio-bag for the robot? [Answer] I think the most important information to trade would be intelligence on enemy time-travellers. Your model of time travel is quite important. How are paradoxes resolved? Is this overwrite style, whatever can be changed already has been (like time crimes),or coexisting multiple timelines whenever a new branch is created? [Answer] When the PS2 came out in Japan about 6 weeks ahead of the USA, people would pay 2,000 dollars for a Japanese PS2 that only cost 700-800 dollars there. It WOULD be possible to surgically implant these in the intestinal cavity. I'm not saying it wouldn't hurt. When the PS3 came out, people sold their PS2s for as little as 5 dollars 2,000 dollars from 5 dollars is pretty good. (What is the fuel cost of a time jump?) Around 1995-1996 the earthquakes and flooding that destroyed the manufacture of SIMMs for computer memory in Malaysia. The price went up from a thousand-fold for memory already on the shelves. It took years to recover partially. Then another series of floods wiped out production again. Sticks of RAM in body cavities would be easier than surgery for a complete game system. Sierra Leonne, the diamond fields. Can you timejump from outdoors in the open? or do you need a large device? I do not require a device, I prefer to grab the merchandise and jump from a high place before transporting myself, people assume I am dead and don't look for me. I have been thinking about the diamond fields for a while now but have not tried it yet. If anyone speaks the language there and can assist me, I can comfortably carry 3-4 small-average sized individuals along on each jump with me. leave a msg here, I will check back next time I am in this century. Yours truly, -D.B. Cooper. [Answer] Strange answer but bare with me... forget the idea that what you change in the past will change the future as misunderstanding both the past and the future. What you do in the past has already happened in the future that you came from. I will try very hard here not to spoil the latest episode of Doctor Who... I will spoil a Star Trek movie, however, on the basis that its a throwaway line. Think, if you will, that when you go into the past you enter a timeline that is fixed in your time. By giving the secret to transparent aluminium to someone so that you can build your whale tank you are actually giving the inventor of that material the idea that they had in the past. To quote Scotty: "Why? How do we know he didn't invent the thing?" By going into the past and "changing" something all you have done is complete the circle. Scotty does not change history at all by giving the formula to someone in the past, he simply makes the past happen. Now expand this to your time travelers' guild, or "time lords" as we might call them (*knowing wink*). That the guild is rich, is powerful, or even has the time travelling ability in the first place is due to them "changing" time or rather being a part of the past. Nothing that they do has any effect above bringing the past in line with the future. [Answer] If Bitcoin is still around, they could simply create a brainwallet and memorize it. They could then find a cheap smartphone, install a bitcoin app, and start spending their bitcoin, assuming the bitcoins have already been mined by the date at which they arrive. [Answer] The human body is capable of becoming quite large. People have grown so fat as to become immovable, except by crane. Such a large person could have parts of their body fat replaced with storage containers. They could work in a team with a skinnier, more mobile time traveller, bringing large artifacts with them. Presumably there would be future tech that would allow such body modifications to be simple and reversible. [Answer] **Arnold had plenty to trade!** [![arnold in the buff](https://i.stack.imgur.com/KXVBw.jpg)](https://i.stack.imgur.com/KXVBw.jpg) > > Honestly, though, Arnie never really did it for me. As a horny gay > ’80s kid, The Terminator was all about Michael Biehn, who has a > similar nude scene. Ah, Michael Biehn… ::sigh:: Come with me if you > want to live, indeed! > > > <https://fleshandboners.com/arnold-schwarzenegger-nude/> So too your future people. Forget about smuggling drugs or remembering winners at the dog track. Your time travelers work at the oldest profession and they are good at what they do. As regards where and when - they go to times and places where there is a safe and lucrative market for their services and these are well mapped out. The past is easier as regards earnings because they can convert it to gold, hide it then retrieve it when they return to their own time. ]
[Question] [ One of the early events in my story involves a 2x2 mile section of a suburban town that is encased in invisible walls 100 feet (30m) high and perpetually subjected to heavy rain at a rate of about an inch an hour. It will keep filling up with water until it goes over the 100 foot (30m) walls roughly 50 days later, and from then on it will become a massive four-directional waterfall that, I suspect, will start carving massive rivers and radically altering the landscape. The specifics of what that would look like are a question for another day, however. Right now what I want to know is when, if ever, the water flowing out of that flooded suburb will be drinkable. Given that nearly the entire planet has been subjected to frequently-dangerous supernatural ordeals like this one, modern society has entirely collapsed, and smaller communities need to figure out how to survive without things like advanced plumbing infrastructure. Living near such a huge source of water would be an incredibly valuable asset... if it were drinkable. [But when I asked questions about how quickly said suburban deathtrap would start flooding](https://worldbuilding.stackexchange.com/questions/200254/how-quickly-would-an-inch-per-hour-of-rain-flood-an-enclosed-2x2-mile-area), several people brought up something that had completely slipped my mind: the sheer amount of pollution that would get into that flood water due to the suburb it's built on and render it completely undrinkable. **If a 2x2 mile section of a modern American suburb were encased in 100ft (30m) high walls and flooded, how long would it take before the water flowing out over those walls would no longer be too contaminated and polluted to drink?** [Answer] ## Not as much pollution as you think The reservoir is filling so quickly, draining from the top, and the area exposed to the suburbs is so small relative to the volume that it just cannot contaminate it quickly enough to matter at the top of the water column. The "box" is acting like a giant settling tank, so very few particles will even make it to the top. If you boil the water it will be completely drinkable. Even without boiling the water will be safe by most survival standards. There is just too much water compared to the amount of contaminants. Remember, we have reservoirs that literally contain flooded towns. Only in the very beginning when there is a lot of sediment and contaminants relative to the amount of water will it be dangerous. You are looking at 300,000,000 cubic meters of water. That is more than most reservoirs hold. For scale, NY's largest reservoir, New Croton Reservoir, hold 70,000,000 cubic meters. All of the reservoirs in NY state's combined only hold 2,000,000,000 cubic meters of water. 4 square miles of suburbs just cannot supply enough contaminants in a few weeks of being submersed in essentially still water. Keep in mind this is a survival situation. Minor impurities that may have long terms effects in 40 years are irrelevant. A suburb just cannot supply enough chemical contaminants in such a short time scale, so you only have to worry about biological contaminants, hence boiling. Even without boiling the risks involved are small, the influx of fresh water is just too fast. Would I want to drink it today? Not for long. Would I drink it in a post apocalyptic/survival setting? Absolutely. Once you settle into rebuilding a civilization and years start going by, you may want to start actually purifying it, because things inside will start failing and breaking down, but even then the water coming out of your box will be cleaner than most reservoirs. The refresh rate on the water is outstanding, and the shape minimizes the migration of contaminants. Your water is clean by most pre-industrial standards and tolerable by modern ones. Eventually the contaminants from the suburbs will be exhausted and in a few hundred years you have the cleanest water on the planet. Again many real reservoirs contains submerged towns. Monument City, Indiana was filled in 1965 submerging an entire town. NY contains dozens of flooded towns in its reservoirs, Ashokan Reservoir alone contains at least four towns flooded in their entirety. Keep in mind water in real reservoirs is flowing because it is coming in from rivers not magic rain so it is also far better at destroying and thus exposing stuff in the towns. [Answer] **That which can float, will soon float to the sides** and eventually go over the waterfall. (your barrier is spilling 20.43 cubic meters of water per hour, per meterlength of outside wall.) And yes, even at a mere 2x2 miles it will be subject to a bit of tides, a lot of wind-driven waves, and will slosh over the sides instead of just gently dribbling. Note that this will include most of the noxious chemicals we use, such as oil, gasoline, etc. **That which wants to sink, will sink** and settle on the bottom. The only problem will be **anything that dissolves in the water**, either once-off or via continuous contamination (like **rotting organics**) And *these* will be continuously diluted by the influx of pure water. I expect that the water will be fine as soon as all the organics have finished rotting, so give it maybe 6 months. This will also allow any rapid pollutant releases to deplete themselves. For example, gas tank of automobiles. But for many, many years the water will have a slight sheen of oil on it, as the many machines and devices and storage tanks and containers rust through and gradually release their oily residue. The water will not be *undrinkable*, but it will not be a fresh mountain stream! --- later comment: Remember that we are looking at a 100ft deep container, completely full, with rainwater falling on top at a rate that would have filled the container in 50 days. If using full mixing and only dilution to get rid of pollutants, we would only be halving the concentration every 25 days. But because both the inlet (rainfall) and outlet(spillage over the edges) occurs at the very top of this reservoir, and there is no force *at all* to cause internal turnover currents, there will be *very little* mixing of the water. Mostly what will go over the edge is newly fallen rainwater, and anything that floats in the water. Dissolved contamination, even without any source of replenishment, will dilute at a rate of something *less* (possibly much less) than halving every 25 days. [Answer] Some math: 25mm/m2/h and about 10km2 area leads to approximately 70 m3/s of water. Not even close to large rivers, but it is a decent stream. Approx 1/100 of Danube. Population density varies, taking a reasonably high estimate of 1k/km2: 10k people, each with 100l of problems. 5k cars, each with 100l of problems. 5k "misc" (homes and whatnot), each with 100l of problems, and you end up with 20 m3 of issues. Now, threshold for pollution greatly depends on source. I can't be bothered to find thresholds for all sources of problems, so I took the first number I found: 50 ppm = 50 mg/l threshold (EU threshold for nitrates). This means water is "clean" as soon as outflow of problematic stuff is below 3.5 l/s. With 20 m3, even constant linear outflow of problems (the worst case estimate) would give you mere hours to have stuff below that threshold. Even estimating 10 times as many pollutants will have the water clean enough in less than a day. So, we can ignore suburbs. Pollution is negligible with that amount of water flow. EDIT: we can most likely also ignore rainwater problems. With that amount of rain, it will be essentially pure water falling down. You are still going to need approximately 30 tons/day of generic pollutants to make water problematic for drinking. (so, to make water undrinkable you need specific pollutants that have way lower threshold of causing problems. Generic post-apocalyptic pollution will not do) [Answer] At the start, all the gasoline from underground tanks at filling stations, all the motor oil and similar substances from cars, all the contents of sewage treatment and septic systems, plus things like pesticides from garden stores and the like will wind up mixed into the water. It'll be a veritable stew of coliform bacteria and chemical pollutants (not to mention all the drowned residents and their pets adding to the mix). By the time the water is twenty or so feet deep, however, there'll be enough dilution that chemical pollutants will become nearly negligible and, as noted in another answer, boiling will be sufficient. Assuming there's no fresh sewage or bodies going into the Fish Tank, it should be safe enough to drink without boiling in a matter of months -- the worst of the pollutants will have either washed out soon after the water starts to overflow the invisible wall, or settled to the bottom of the new "lake", leaving what's left almost completely rain water. Given the rate of rainfall, the water inside the Fish Tank will be purer than most surface water ca. 2021 within a year (likely less). [Answer] You would have to include what kind of and level of toxins were frequent in the suburb, account for erosion, how fast is the water churning ? How is it leaking out ? Is the water remaining muddy ? Is new sediment being introduced at all (which it sounds like it is not). What kind of air pollution may be nearby (consider acid rain), and also what kind of potentially parasite microorganisms were present to begin with that might be reproducing from preexisting waterways or soil layers that are now thriving or being introduced by some other means. The question is kind of complex, so the answer will spark more questions. In brief it may be that the soil pollutants will settle in a layer of silt within a month or two, but if there are harmful critters in the water, or if there were high levels of pesticides etc that were water solubale, then you may be SOL. In the wild we tend to filter and/or treat water for a reason, there are many parasites and pollutants that make us very sick. Near springs and head waters wit natural aquifers the water is less polluted, but the idea of a crystal lake is not realistic these days and what you are describing sounds sort of like a manmade lake in an area flooded, which contained ridiculous amounts of modern pesticides herbicides gasoline, and other pollutants and trash. There might be a breakdown of garbage and trash by natural bacteria which help things alongs and some contagions might very well die in the water, which were aerobic. Just some thoughts. [Answer] [Water treatment plants](https://en.wikipedia.org/wiki/Water_purification) daily process rain water coming from the surfaces of urban area > > The goals of the treatment are to remove unwanted constituents in the water and to make it safe to drink or fit for a specific purpose in industry or medical applications. Widely varied techniques are available to remove contaminants like fine solids, micro-organisms and some dissolved inorganic and organic materials, or environmental persistent pharmaceutical pollutants. The choice of method will depend on the quality of the water being treated, the cost of the treatment process and the quality standards expected of the processed water. > > > The processes which are carried out are: 1. Pretreatment 2. Coagulation and flocculation 3. Sedimentation 4. Dissolved air flotation 5. Filtration 6. Removal of ions and other dissolved substances 7. Disinfection If the water is simply kept still, only step 3 would happen naturally at a significant rate, and the growth of bacteria and algae in the water would just make the problem worse. It would take years at best to make the water drinkable without any intervention. ]
[Question] [ An alien race was rubbed the wrong way by humans being humans and decided that humankind has to go. However, unlike many other science fiction stories, they do not intend to give the humans even a semblance of a sporting chance by sending their equivalent of an invasion force. These aliens are capable of manipulating the [fundamental interactions](https://en.m.wikipedia.org/wiki/Fundamental_interaction) and instead have decided on using gravity as their tool. Before humanity can realise the gravity of their situation, the aliens will flip a switch, at which point the strength of Earth's gravitational pull will be multiplied by 10 without any alteration of mass for a period of 24 hours. So for instance a person weighing 60kg will suddenly become 600kg with no prior warning and no other change. After this 24 hour period, Earth's gravity will return to its prior normal level of 1G. Is this sufficient to guarantee the extinction of the human race? Will this also end all life as we know it on Earth? [Answer] <https://en.wikipedia.org/wiki/G-force#Human_tolerance> According to Wikipedia, 16g for a minute are already deadly. For a day 10g are very much lethal for humans, as well as for any large animal. Insects, bacteria will fare better, as may various marine life. [Answer] In addition to other effects, there is atmospheric compression to consider. With gravity increased by a factor of 10, the atmospheric pressure at sea level will become (about) 10 times greater, and the altitude at which air becomes unbreathable will drop by (about) a factor of 10. It's well-known that prolonged exposure on Mt Everest is not survivable, so let's put 30,000 feet as a killer altitude. With 10 times the gravity, the same air density will now be found at 3,000 feet, and anybody much above this will be in big trouble. The altitude limit is not exactly a factor of 10, though. At scales of 3000 feet the earth is not a uniform sphere. Higher-altitude areas will have no lower-altitude areas at all, so the death zone will be somewhat higher than a simple calculation indicates. I'd put a rough estimate for the 30,000 foot equivalent at about 4,000 feet. Fortunately (if you're looking for good news), a x10 increase in atmospheric pressure is not quite enough to produce lethal oxygen toxicity in most people. [Answer] a very very small chance of **no** Thanks to the corrections given by the moderators, the most viable answer that "some" humans will survive is if they take a trip to space before the gravity alteration occured. That's the only chance some humans might have survived... [Answer] Humanity and life will die, that is for sure, but maybe not because of the g-force *alone*. As AlexP pointed out in the comments of the original post : > > The small problem is that the force pulling the Earth towards the Sun will also increase by a factor of ten, with very unhappy consequences for Earth's orbit... > > > **Temperature** While a day might not be enough to make Earth plunge into the sun with such force, the orbit will be off-course by **a lot**. I have no idea how to do the calculation, but I'm convinced usual users might know how to prove it. Anyway, the Earth orbit is in a very small spot where the temperature is balanced, having a span of temperature of -30ish°C in the coldest places in winter to 40ish°C in hot places on summer. This relatively small span of temperature allows fauna & flora to adapt to winter and be reborn / wake-up in spring. Having a larger orbit because of the 24h gravitational shift will increase this temperature span, and thus killing every life being that can't adapt enough. [![enter image description here](https://i.stack.imgur.com/qRyyB.png)](https://i.stack.imgur.com/qRyyB.png) EDIT : As pointed out by ThisIsMe, this schematic is wrong in its naming. Instead of Summer and Winter (which is influenced by the inclinaison of Earth and NOT by the distance to the Sun), let's call them "Hot phase" and "Cold phase". There is a 25ish°C temperature gap between the 2 seasons in continental contries as is, imagine the temperature gap now that summer and winter are so far appart from what they were. **The moon** Even if Earth won't pludge into the sun because of the distance between them and the short duration, the moon will plundge into Earth (can't prove it once again, but I'm pretty sure being pulled during a full revolution will drag it down). And even if I'm mistaken and the moon doesn't crash, it will at least pass very close to Earth, generating some big waves. **Conclusion** If the goal is just to destroy humanity, yes, it's a good way to do it (for the most part, some could escape), but if aliens plan to colonise Earth afterward, that's a big no. [Answer] Extinction is almost certainly inevitable. In another answer, I addressed the effects of atmospheric compression. I failed to extend the analysis to the interior. With a 10x increase in gravitational attraction, the apparent weight of the entire planet will increase by at least a factor of 10, as will the pressures at any given (proportional) depth. With increasing pressure, density increases, so the planet will become smaller. Exactly how much is going to depend on the depth of the rock involved, and the exact composition. I'm not willing to do the effort required to determine the exact pressure/density relationship of rock at these pressures (it's rather an obscure field) so let's take a target density increase of 100% overall. In this case, the volume of the earth will decrease by 50%, which means the radius of the earth will decrease by about 20%. Note that this will decrease the area of the earth by about 30%, but the surface material density will not increase at all (relatively speaking). This means that the earth's crust will massively wrinkle, with essentially a complete destruction of all surface features. Worse, the transition from 100% to 80% radius (about 800 miles) will essentially occur in freefall, at least the early stages. This will have two effects: first, everything on the surface will be pulverized by the equivalent of a fall of several hundred miles at 10 times the current gravitational acceleration. Second, the kinetic energy released by the impact will liquefy the crust into an incandescent mass of molten rock. The energy released by the fall of 1 kg 100 km in a 10g field is about 1 MJ, which is enough to raise granite or basalt by more than 1000 degrees K. Since 100 km is about 60 miles, a 20% radius reduction (800 miles) will produce temperatures more than 10 times as great. When 24 hours is up, the reverse (rebound) effect will occur, with the reduced-area crust ripped apart as the area of the earth increases by 45%. The crust will redistribute over a fairly short period, even if it has cooled to the point of solidifying in the 24-hour grace period - which simply isn't going to happen. Granted, the 100% density increase is fuzzy at best, but two things should be kept in mind: 1) Since the earth becomes significantly smaller, the pressure increase becomes even greater, since gravitational attraction gets greater as distance to the point of attraction (the center of the earth, in this case) decreases. This will increase the amount of density enhancement. 2) Given the catastrophic nature of the results, even if the density does not increase as much, the effects will remain catastrophic. [Answer] Since it is a given that these aliens can manipulate gravity however they like: Would not be easier just to 'switch off' gravity entirely? [Answer] If I was the head of Aliens I d rather invert gravity to -1G and happily watch those humans fly into space. [Answer] Not sure why this bounty hasn't been rewarded yet but perhaps it is because the answers are not direct enough, so I will give it a shot. Q1) "Is this sufficient to guarantee the extinction of the human race?" A1) No, based on your question, you have not detailed if the aliens have accounted for dependencies such as: "Is all of humanity currently on the Earth?" how could they eliminate all human life by only targeting the planet if not all of human life currently exists on the planet? However, increasing the gravity by a factor of 10 would most definitely kill all human life on the planet assuming that humans have no way of altering gravity on their own. The human body can withstand roughly 40 g's: A man named John Stapp demonstrated a human can withstand 46.2 g's for just an instance. I say 40 g's for the average human (probably an overestimate) because the average human has no training as John Stapp did. The Earth's gravitational field push's on the surface at 9.8 m/sec^2 == 1 g, 9.8x10 = 98, 98 >> 40. Q2) Will this also end all life as we know it on Earth? A2) No, there are many organisms on this Earth which could withstand 98 g's or greater for 24 hours, humans just aren't one of them. Hope that helps! [Answer] Nope, they will all die, except for those in space. However, if they are in orbit the orbit may become destabilized and they could die from atmospheric reentry or hurtling into space. ]
[Question] [ Imagine a world full of islands. No continents, just average-sized islands. There are so many islands, that it would look a bit like this from space: [![enter image description here](https://i.stack.imgur.com/EEuIi.png)](https://i.stack.imgur.com/EEuIi.png) Now, imagine that the sea is very, very deep. I'm talking like, a few kilometers deep. In a way that if you are on a beach walking towards the ocean, instead of the water slowly getting deeper, it's a sudden a drop of many kilometers. Now, imagine that there's no ocean at all. The surface of the planet is covered in humongous pillars. Those pillars (aka. the islands) are habitable; some have even lakes in them. The atmosphere is breathable, it rains all over the planet, somehow. But there is no life in there. Its conditions are too insane for life to have evolved there, but humans could live on top of the pillars with relative ease. What could possibly explain the existence of such a bizarre world? [Answer] The closest feature we have on our planet that gets close to appear like this is the Giant's Causeway. [![Giant's Causeway](https://i.stack.imgur.com/AaFnA.jpg)](https://i.stack.imgur.com/AaFnA.jpg) To obtain this you need to have magma intruding a rock, then cooling down to form the pillars, and the surrounding rocks being eroded away. But you want it made on scales like El Capitan: [![enter image description here](https://i.stack.imgur.com/pFGWn.jpg)](https://i.stack.imgur.com/pFGWn.jpg) With the right combination of factor (gravity, volcanic activity) you might achieve this, I mean, we have a 20 km high mountain on Mars... Nevertheless this is hardly stable over geological times: gravity always asks its toll, and will slowly pull down the pillars. [Answer] 1. A supernova explodes. Hurtling away is a molten blob of mixed elements. 2. As it slowly cools, the component elements stratify. The silicate mix slowly crystalizes, forming long needle-like spines protruding circumferentially. [![needle crystals](https://i.stack.imgur.com/jdshg.jpg)](https://i.stack.imgur.com/jdshg.jpg) <http://www.rockhounds.com/tucson_show/reports/tucson2001/p3.shtml> 3. Water comes from space, deposited little by little from comets and ice meteors. The space crystal is covered with water so that only the tips of each needle protrude. Some are submerged completely. Some come out of the water thousands of meters straight up. Some remain fairly sharp at the tip but others have fractured off flat at the top. Or you could have them (almost) all fractured across just over water level - which I think might be an ominous sign that something energetic enough to break off the crystals happens here from time to time. On earth, life was in the oceans for a billion years before it colonized the land. So too on your world - the oceans are full of life. That life provides your breathable atmosphere. Also narrative energy: some of the life forms might be large and dangerous. [Answer] Another approach, inspired by the description as "like islands with the oceans gone": * Cover the world with a shallow ocean. * Build coral reefs. * Create an organism that builds up atolls just a bit higher than sea level. * Gradually raise the sea level so that the atolls get built up higher in response. (perhaps a one-time reaction to a wandering planet brings a cascade of ice comets to the inner planets, or an ice cap melts.) * After the ocean is deep enough, new reefs and atolls can't get started, but existing ones can keep getting taller as the oceans rise. * Remove the mechanism that adds water to the planet; in time the oceans will evaporate. * Leave just enough ocean in the deeper parts that there is a weather cycle bringing enough water to the pillars for life. * over time the former ocean bottoms will get their own ecosystem but the soil will be salty enough that it won't be a productive one. * you will need a mechanism for cycling biomass onto the pillar tops. Guano from deep flying birds should cover most of that. [Answer] Does it have to be naturally occurring? It's an art planet. Humanity stumbles upon this bizarre planet and formulate a slew of potential natural causes for its landscape, but none hold up to serious modelling. The only hypothesis that doesn't fall apart is that someone, at some ancient long-forgotten point in history, created it. The question of how and to what ends is a continual debate among thinkers of your world, but so far none have come upon a satisfactory answer. Perhaps they just made it to prove that they could. Regardless, they're long gone and you can now find regular terrestrial humans squatting atop these monuments to their precursors' greatness. [Answer] I was going to suggest columnar jointed igneous deposits too but the end result you're looking for doesn't allow for their initial formation, let alone the differential erosion needed to leave them so isolated. I'd suggest that the only way such a planet might exist would be as the result of some esoteric form of warfare; if you used something like Niven's [Treatymaker](http://larryniven.wikia.com/wiki/Wunderland_Treatymaker) that ionises matter in the immediate area of impact, the material ejected by an ionisation weapon will re-condense in areas away from the direct fire zone. If large numbers of such weapons were fired on a single world the re-condensation zones could be few and small enough to form your high pillars of rock. Such pillars will be inherently unstable and quickly (geologically speaking) decay under the combined effects of gravity and erosion, the thicker the pillar the longer this will take so the large ones may last long enough for colonisation. Some notes: such weaponry, if used on a global scale, would pretty well sterilise any planet. There would be strange effects on the overall sea-level/landmass balance of the world in question, such that the planet may appear far wetter afterwards than before. The seas of such a world could be either stripped of or enriched in salts by such an event depending on the way different compounds and elements condense out after the blast. ]
[Question] [ What I'm thinking about is simply an animal,any with a protective bony-like shell covering its eyes. The shell must be openable for clear vision but when closed the animal still has the ability to see through the shell with roughly good visual definition. These plates are transparent only to its own species but is not made of glass, other animals and humans see the shell completely black. Can this be done without magic ? ![enter image description here](https://i.stack.imgur.com/MD2cC.jpg) [Answer] I think this could be entirely possible. First things first, there is a somewhat similar technique already widely available in the animal world; the [nictitating membrane](https://en.wikipedia.org/wiki/Nictitating_membrane). [![bird of prey with nictitating membrane](https://i.stack.imgur.com/dViRP.jpg)](https://i.stack.imgur.com/dViRP.jpg) This is basically a third eyelid that is transparent and protects the eye while still allowing vision. What you want is pretty much a supercharged version of this, so it shouldn't be too unlikely. The biggest issue is having a strong enough bone like substance that would still be transparent (unfortunately I doubt it's possible to make a [one way mirror](https://en.wikipedia.org/wiki/One-way_mirror) organically) but nature to the rescue again! [![ghost shrimp](https://i.stack.imgur.com/54Rqv.jpg)](https://i.stack.imgur.com/54Rqv.jpg) This is a ghost shrimp. Now shrimp aren't exactly tough, but their shells are made of a chitin like substance, so it should be entirely possible to have a tougher but still transparent version like the ghost shrimp. There are also insects with transparent shells like the [tortoise shell beetle](https://www.google.co.uk/search?q=Tortoise%20Shell%20Beetle&source=lnms&tbm=isch&sa=X&ved=0ahUKEwienpmdr_TZAhXjBsAKHX3VDlUQ_AUICygC&biw=1517&bih=718). So a chitin face plate is what your creature will want. The final piece of the puzzle is why. What could cause such an adaption to evolve and become commonplace? Fortunately that has an answer too. Many animals (snakes and skunks come to mind) have defence mechanisms that involve spraying their attacker with a particularly corrosive or noxious substance. This is most often aimed at the eyes as this will cause the most damage and allow the animal to escape. Now imagine your proto creature lived in an area rich in such creatures. Those who could withstand the attack long enough to kill their prey would thrive and so the armoured eye plating would become commonplace and stronger. [Answer] I'm thinking about [barreleyes](https://en.wikipedia.org/wiki/Barreleye). They are fish that have their eyes **inside** their heads. On top of that, pun non intended, their heads are transparent. Look at them. The eyes are the green domes. Yes, they are pointing up. ![Do a barrel roll!](https://i.stack.imgur.com/XFtpY.jpg) ![So cute!](https://i.stack.imgur.com/ZvwT5.jpg) Your creature could have flaps of soft tissue to cover its eyes. The soft tissue would be opaque for visible light, but transparent to infrared or ultraviolet. And if you think soft tissue is not good protection, just remember that bowels and stomaches don't usually get destroyed when people take a punch to the abdomen. Sharks roll their eyes when biting, and sperm whales retract their eyes ([seriously!](https://en.wikipedia.org/wiki/Sperm_whale#Eyes_and_vision)) when hunting. Your creature (or its ancestors) might have evolved the flaps so as not to go blind when doing something potentially dangerous with their faces too. That would explain why they have the flaps, rather than a permanent structure always covering their eyes. [Answer] The bone needs to be somewhere when it's folded away from the eyes, and in your picture, the only way it can fold is in the middle. That completely eliminates binocular vision, and in fact creates *double* vision. Other problems: 1. They'd be prone to damage when open. 2. There needs to be room on the face for the opening and closing muscles. In all likelihood, the armored flaps would stay closed all the time. (That would be bad if your creature is a predator, since they require good eyesight.) [Answer] Some scarabs have transparent elytra, if you're looking for an actual retractable mask-like structure then this might be more suitable than nictitating membranes over individual eyes. This seems to fit your drawing slightly more accurately. [![enter image description here](https://i.stack.imgur.com/Jak3c.jpg)](https://i.stack.imgur.com/Jak3c.jpg) ]
[Question] [ There have been questions of the validity of combat mechs and the shape of police robots before, but the general consensus is that the main reason for a mech to be humanoid is to appear less threatening to the people they are defending. But realistically, if mechs are to be used by authoritative forces, it is likely that the military will come to the party first, while the local police will be fashionably late. In a combat environment, the idea of having your combat mech honestly seems laughable, current designs suggest drones are superior in almost every imaginable way. There seems to be little to no advantage, at least to me, as to why military robots would be humanoid. My current thoughts are that perhaps for X reason, it is cheaper, but frankly adding X anywhere on its own in a hard science fiction story is asking for trouble. Is there any logical reason as to why the military would make humanoid combat droids? If there is a reason, what would be the most realistic reason? [Answer] ## Genesis of the robot soldier: Humanoid shapes are pretty hard to make with current robotics. However, depending on the way the robots came to be, it might still be easier to keep the basic humanoid shape than to go the way of simplifying the design. One train that might lead to humanoid robots could be: 1. Starting at basic human soldiers, they get aditional body armor to keep ahead of the weapon developments 2. As we armor them up, at some point (pretty soon actually) a critical point is reached, where aditional armor slows the soldiers down more than it protects them. 3. As a way to increase mobility again, servomotors are added to the joints to help in moving the bulk - and add more armor again. Let's call this "Power Assisted Armor" - or Powerarmor for short. 4. The steps 2 & 3 are repeated several times, until the armor with all its motors and structural integrity just stands on its own, only lacking the human to control it most times. 5. Step in some engineer that manages to simulate said human operator by recording the soldiers movement commands in the Powerarmor and then sending them into the armor directly, maybe simply by putting a relay in one 'operator' armor and having the others just repeat what they are told. An early application would be to just remove the soldier from the field and have them control the remote operated Powerarmor from some command bunker, where the operators wear some sort of dummy in suspension with a screen. Safe and sound warfare with humans at the controls is achieved. 6. The next logical step is to trim down the bulk of the remote operated Powerarmor again, as now it is just a shell and it doesn't need to be armored so much anymore. The result might look more humanoid, but some designs might add the weaponry right into the cavities, like having a gun in the arm and the ammo stored in the torso under the relay equipment. 7. Since training remote operators takes lots of time and remote operation is prone to being attacked by ECM (Electronic Counter Measures), development might go towards autonomous Powerarmor, which would be just a fancy term for nothing short of an armed, humanoid robot. 8. Starting here, everything is just refinement of the already existing systems - increased autonomy, possibly filing on the look to look less machinelike and maybe even the addition of synthskin to create infiltration models. ## Benefits of Robots over all: Indifferent of their shape, there are certainly benefits that give robots an edge: * Robots are not alive. Loosing a bunch in the battlefield or sending them into hazardous areas to do stuff you don't want to give to people (nuclear waste disposal, bomb defusing, handling chemicals) is pretty standard today, but you don't actually need to be humanoid to do that. * With an all-time perfect morale and their possibly better-than-human response times and almost 24/7 battle readyness, they could easily form the backbone of striketeams. * Skipping over a system for the robots to speak and adding a little bomb to destroy any data storeage and radio equipment could make the information about them safe in case they fall into enemy hands, either by capture or damage. ## Benefits of the humanoid shape Now, as we have a probable way to get to humanoid robots, what benefits does it have? * Humanoid shapes are familiar. As such, people will interact with them a bit easier on a personal basis. A police robot with a face and a humanoid makeup will be asked for help much easier, people will open the door to a delivery robot with a face more happily and they might be much more comfortable with a humanoid teller robot or barkeep than with some arms and a camera that stick out of the wall. Getting commands from a humanoid robot soldier with a gun might look less threatening to the civillian population. * The world is made for humans. Most tools and items require a human hand to perate them well, so giving robots at least humanoid hands cuts down the development time of specialized equipment to 0. Still, humanoid hands are not the most perfect tools, we are just used to make stuff good for them. At least the military could just phase out the old weapons that the robot soldiers don't use anymore over the reserve battalions and cut down the need to keep up two sets of weapons (robot weapons vs. human ones) * Robots could be made without a sense of self preservation, making them perfect for attacks like the "human wave" where the army just marches on despite having massive losses. Having an unstoppable army of suposedly humans walking up on you however is wrecking havoc with the morale of the adversary side: Soldiers expect enemies to die if they shoot them or if they walk upon mines and then the rest taking a detour or going to cover. They do not expect them to just continiue the march despite loosing an arm or the soldiers next to them falling. ## Demands for different shapes Now, what are the caveats that might demand non-humanoid robots? * There are actually shorter ways to robots with battle capabilities, but those are not humanoid! Tracks instead of legs would be a pretty standard thing if the way to robots was not from Powerarmor, but from armored vehicles - which would mean to go via automated to miniaturize tanks. This way would forgo quite much of the humanoid aspect for increased 'battle value'. * Humanoid shapes are prone to hazards such as tripping and a quite high center of mass. A human just stays upright because he has a very very precise tilting sensor in his inner ear, which is at least one potence more accurate than those in modern phones (and which reacts with nausea to a shaking floor). Doing something that can do the same is a serious feat of engineering, which might lead to short robots with big feet. + For some rewuirements the humanoid shape might be a hindrance! If you want a fast robot, two legs are not a good solution. Four legs or wheels would be a much more stable and faster solution. If you want a strong arm, arms with internal motors are a bad solution, as the best solution would be to use external hydraulic systems to get the best leverage. * Military doesn't care how something looks, as long as it is effective. They might choose a simple, tracked variant ofer a fully humanoid one because it is simpler to repair. They might demand stuff that makes a humanoid shape hard to uphold, like jumpjets. * Having the weapons being inoperable with human hands would actually be a benefit in military terms, as that would make them inoperable in the hands of enemy troups. In civil unrest/wars and guerillia warfare quite a lot of weapons that the "rebel" side uses comes from the "governement" side's stocks. # Alternate Origins However, there are also organisations that might clearly prefer humanoid builds, which could be part of the reason why the military adopts just more sturdy models of these branches: * Intelligence Agencies. Using a robot spy might need a much more sophisticated machine than the military, but deep cover agents with perfect morale and hard encoded integrity to some rules would cross out double agents. * Storefronts. A shop that is operated by a friendly robot pal in a humanoid shape could be open 24/7 with just one payment for the robot clerk and much less personnel. * Police. As said, having some basic trust (which does come with humanoid shape and features) is needed for policework. * Correction facilities. Sending in robots to pacify inmates could save the live of wardens. * Caretakers. Having a humanoid shape is much needed here, as it will reduce the fighting of the people getting taken care of against being 'handled by a machine'. These robots could serve as some kind of "reserve pool", if they have a similar set of capabilities than the military robots, just needing a different set of commands and the toys of a soldier. [Answer] I can think of one reason. If your infantry makes use of powered exoskeletons, someone is likely to think 'wait, do we need to have the human in there all the time?'. It could start with exoskeletons or powered armor capable of autonomous use, with specialized autonomous variants being developed from that. You'd have some perks like them potentially being able to use a variety of tools, vehicles and weapons, but the main reason you'd be doing it is you already have an assembly line putting out what are in essence humanoid robots. [Answer] Firstly, humanoid robots are considerably more expensive than simpler, more narrowly purposed devices, such as you suggest with drones. The trade-offs for upright gait make evolutionary sense - saving calories while walking in order to reserve those calories for higher consciousness - but not robotic sense. Slithering for example is much simpler; a few parts repeated, attached together, simple algorithm, done deal. Helicopter (quad/hex et al) drones seem to be the sweet spot for utility vs versatility at short range, i.e. hovering, vertical take-off and landing and quick reorientation and maneuverability - vis a vis dragonflies, such that they have survived millions of years. With humans/humanoids the entire equation is different. We evolved large brains and in short order, on evolutionary time scales, have placed ourselves on a path for opting to rid ourselves of our cumbersome, but narrowly advantageous, calorie conserving frames, to go further into the mental spaces, augmenting our brains, storing them, understanding them better. The laughable thing to me is that brains seemed to have evolve for the very purpose of becoming bigger brains. Secondly, mechs are even more complicated and expensive that humanoid robots because they not only have to emulate what a humanoid robot can do, but then they must incorporate a user interface into the equation so that using them is not an uncontrollable affair. The bounding and the jostling and the controlling of the mech must be such that the whole system behaves in a way that is natural to human movement. Otherwise, by requiring the user to work harder than they otherwise would than by simply being deployed on foot, then the proposition becomes too risky, i.e. it equates to throwing a poorly functioning and very expensive piece of equipment and a highly trained soldier along with that expense into a situation where positive results are less likely. So no, in a combat situation, I would say that terminators and other humanoid robots, including mechs are pure fantasy. ### Edit To clarify the distinction between mechs and augmentative devices such as the exoskelton. A Mech is a fully armored and equipped combat device where as the primary focus of exoskeleton devices is for aiding in ground deployment, e.g. such as helping to carry equipment. Other options such as mechanical mules are included as alternatives to the exoskeleton. The maneuverability and agility necessary in full engagement are the issues which limit the practicability of mechs and increase the requirements and complications for making them feasible. [Answer] As you wrote, specialized robots like drones, autonomous tanks etc. are superiour in almost every way. However, I could think of two reasons why a military force might use humanoid robots: * These robots could use existing tools and vehicles made for humans. If they are smart enough, they could just get into any car, tank or helicopter and use them for their mission. * To hide the fact that they are robots. They could fore example move through enemy cities as spies. If they get caught, you could just *turn them off* without any ethical debates and also without blackmailing attempts. [Answer] I think such combat robots might be usefull. Let's consider why. **Firstly**, today we're using **flying combat drones** that are really effecient to supplant conventional aircrafts. They can sustain much higher speed, because you don't have to care about a human suffering from g forces inside your drone. **Nonetheless**, even if they're pretty efficient they have the same problem all aircrafts got. When you're fighting in **higly dense area**, like forests, mountains, towns, these sort of drones tends to be less adapted. Secondly, you might think then "Eyh let's **use flying drones with propellers**, these would act like helicopters and works perfectly". Helicopters are far more adapted to urban environment for sure. Nonetheless that's the kind of hard to maintain equipement, I can't find my source anymore but I read somewhere on world building SE that helicopters had a ton of drawbacks preventing armies from having hundreds of thousands of these instead of using trucks. On top of that, even with no drawbacks, you're not going to fight inside **buildings** with such drones. And you definitely can't do it either in **forests**. So then another solution is using drones with **wheels/tracks or perhaps many legs**, but not humanoid shaped with two legs and two arms. Wheels and tracks ? Not adapted to **difficult terrains** too. Many legs ? Means more cost, will be more stable and more efficient than two legs robots. At least, robots with legs would have that advantages animals and humans got to move on almost every kind of terrain. But then why **giving arms**/heads/eveyrthing that defines a human shape to a robot ? Well perhaps for military it's no use at first, in combat situation a robot do not need arms, it can have turret mounted weapons most likely and accessories to supplant arms, it does not need a head either, or not the same one we human got. But outside of fighting ? Don't your drones have any other goal than just to fight ? A soldier does not fight each second of his life. He need to do things that could require arms, like building stuff (fortifications most likely), or transporting supplies, or doing some maintenance tasks, even help the civilians (don't forget today's armies are often used to provide assistance to civilians in case of natural disaster)s. **Last** point for me would be : **Civilian use and war economy**. If the army is producing drones for it's own purposes, it is very likely **the civilian industry will produce drones to**. If they are enough advanced, people would really like to have a robot with which they can talk and live. And I guess everyone likes more to live with something that mimics living beings (so cats or dogs, or even human-shaped robots) than with weirds robots looking like a tank. **Would you like to talk to a tank in your dinning room** ? If yes, then you're really hardcore sir ! But anyway this is not the point. If drones are produced by the civilian economy, esthetics factors (like humanoid shaped robots) needs to be taken into account for customers, thus **having humanoid like robots makes sense.** And when war will break out, all the robots produced by the civilian industry would make **perfect second hand drones to use as military stuff**. They'll just need to be refitted a little, like adding a new shape with a bit of armor, creating some programms to teach them how to fire, and give them small fire arms and here you are, **cheap robots fighters** coming from the **civilian industry** without any need to heavily convert your civilian factories into **military factories**. Easy isn't it ? Even easier than converting cars factories into tank factories. It would most likely give a **great advantage** in the case of a total war, to have at once a **full stock of ready-to-be-converted robots**. The best is, before any war breaks, the country using such method **would be considered pretty weak** "Eyh look at them they have such a **small army**, they are **no threat to us**." And then the war breaks, and millions of civilians robots are turned into fellow fearless soldiers, ready to fight for the mother/father - land. [Answer] Humanoid robots for military use would have several advantages: As humans sized and shaped robots, they are already the right shape to interact with the "human" environment. Humanoid robots will be able to open doors, drive cars off the road, pick up and manipulate tools and other objects in the local environment because they will be able to do what every person can do. Specialist combat robots will be able to fight in their environments and use their weapons, sensors and tools far more effectively, but in the chaotic environment of urban combat, a general purpose machine might be more useful. A "gunship" robot might have to expend ammunition shooting through doors or blasting a stalled car off the road when such actions are not necessary or even counter productive. Human shaped robots might be able to interact with the local population more effectively as well. While the idea of dealing with mechanical men might be strange or even abhorrent to the local population, they are still programmed to respond to and interact with humans. A human robot who makes a friendly wave, or holds out a cell phone for the person to take and talk to a "real" human on the other end is much easier to respond to than an anonymous box with a remote weapons mount and a manipulator arm that rolls up to you on a set of tracks. Human robots will also be a strong signal of intent. It won't take long for the local population to realize that *we* send robots into high danger areas ahead of human troops, with the expectation they can take fire without taking casualties, and using their robotic sensors and weapons, respond faster and far more accurately than any human. One could imagine a robot soldier responding to an attack by an enemy squad. Outside observers hear an irregular burst of fire and find all the enemy soldiers dead with a single gunshot wound. The robot aims and fires so fast that the observer hears what sounds like a burst of automatic fire, but the robot is actually taking single aimed shots at each target. After a few of these encounters, the appearance of robot soldiers will cause the local population to either hide, or expel the insurgents hiding in their midst. (A negative possibility is they decide to come out and fight, but this would require a very strong indoctrination of the local population, on the level of the Imperial Japanese government preparing the civilian population to fight the Allied invasion of the Home Islands with bamboo spears!). The technical demands of creating a humanoid robot for combat are very high, so many of the tasks of combat will be devolved to specialist robots. IT is much more likely there will be a human solder in the field, but surrounded by robotic devices to assist and protect him instead. ]
[Question] [ In my alternate history, during the Islamic golden age (in this case, 9th century Arabia - present day Oman), my characters are building a series of glass towers. They are like lighthouses traversing from present-day Muscat to Niswah; 6 towers, one every five miles (total 30 mile journey). For aesthetic purposes, they want to make them out of glass with minimal stone support. [![enter image description here](https://i.stack.imgur.com/brUzc.png)](https://i.stack.imgur.com/brUzc.png) I'd like the six towers to be glass, and about 10 stories high; imitation of Western lighthouses. The foundation is sandstone *jebloon* (or little rocky mountains). **What will the requirements and limitations be? Where should stone supports be?** There are no issues with security, or storms, and the engineers have been given the best engineering literature from North Africa to the Levant and Arabia (imagine they have access to the sum of the Islamic renaissance, for this question). [![enter image description here](https://i.stack.imgur.com/Q5eqd.jpg)](https://i.stack.imgur.com/Q5eqd.jpg) [Answer] **You could do it, but you'd want to build your lighthouse out of small glass blocks.** Glass, even the sorts of glass available in the Renaissance, has a much higher compressive strength than brick. Something on the order of 1 GPa to brick's 7 to 70 MPa. Even substances like basalt and granite have lower compressive strength than glass, with strengths in the range of 100MPa or so. This means that a glass tower, build in a similar manner to a regular brick tower, will have no problem supporting its own weight. Unfortunately, glass is liable to fracture and propagates cracks extremely well. If you want to build a tower out of it, you should use short, stout glass bricks instead of large panes. If you want your tower to look glass-like, you should look into [dry stacking](https://en.wikipedia.org/wiki/Dry_stone) techniques, in which irregular, but closely fitted, blocks are stacked into walls without the use of mortar. Also unfortunately, glass is far more difficult to work with than stone because of its tendency to fracture and crack. In addition to the cost of glass, which will be much higher than the cost of similar stone, your towers will take an order of magnitude more effort to build. In short, your glass towers won't need any stone support, but they'll be incredibly expensive to construct. [Answer] A [lighthouse](http://www.bellrock.org.uk/lighthouse/lighthouse_stats.htm) contains around 2000 tonnes material ( 2 million kg ) Creating glass takes [up to 35 MJ per kg](http://www.lowtechmagazine.com/what-is-the-embodied-energy-of-materials.html) The discovery of Arabian mineral oil for fuel didn't happen until the 20th century. Charcoal gives [30 MJ per kg](https://en.wikipedia.org/wiki/Energy_content_of_biofuel). You get 3 tons wood per acre, and around [40% charcoal yield](http://opensourceecology.org/wiki/Biomass_to_Fuel), so 1.2 tons per acre. So each lighthouse requires felling about 2000 acres of forest. Six towers is 12,000 acres of woodland. Not absurdly impossible - 36,000 tonnes of hardwood could have been 60 warships and some navies were bigger than that - but possibly significant given the location isn't very wooded. Trying to build one huge ship in the 16th century [cost Scotland much of its oak forests](https://books.google.co.uk/books?id=h9JTAAAAcAAJ&lpg=PA107&ots=BMTnRJogjV&dq=scotlands%20forests%20navy%20james&pg=PA108#v=onepage&q=scotlands%20forests%20navy%20james&f=false), though of course there's a difference in yield of wood good enough for ships vs wood good enough for charcoal. Your tower builder may go down in history as a great feller. Solar power is around 1 kW/m², so 1 m² running for 10 hours per day gives 36 MJ, enough to create 1 kg of glass. So with a perfect solar furnace you would need 12 million square-metre days to create the towers, about 8 acres running for a year. Efficiency is probably [at best 1%](http://www.tvu.com/PSolarFurn.html) with the available materials, so 800 acre-years of mirrors. A square metre of 0.5 mm bronze would weigh about 4kg and require [42 MJ/kg](https://en.wikipedia.org/wiki/Embodied_energy), so 800 acres of mirrors is 13 million kg or another 500 million MJ energy on top of the 450 million MJ for the glass. One square metre produces energy to create 0.01\*36/(4\*42) = 0.002 square metres of mirror per day; at 0.2% growth per day it would take 8.5 years to get to 800 acres, five years if you start with 10 acres and so on. There's probably a formula for the shortest time based growing enough mirrors vs. using them for the glass. You also could use thinner bronze, but then need wood or something to support it, so still be dependent on felling trees. ]
[Question] [ For this scenario, imagine your classical habitable tidally locked planet: hot desert on one side, frigid wasteland on the other, and the only thing that is good is in the twilight zone. Now, assume that the planet evolves life. How would life on the planet sleep? [Answer] Different forms of sleep exist - there's a great radiolab episode about this, link below. <https://www.wnycstudios.org/podcasts/radiolab/episodes/91528-sleep> So, some main things. First of all, sleep isn't dependent on a day night cycle, it just takes advantage of it. Other survival concerns can take precedent over an animal's sleep cycle. Predation is a big one, but animals like dolphins also need to worry about problems like drowning. The solution that many animals seem to have embraced is partial sleep, where the brain will power down some sections while keeping others running. The majority of animals do this, often literally sleeping with one eye open so that, if a predator does show up, that portion of the brain can sound the alarm, wake up the rest of the brain and find a way to stay alive. Fish sleep while a part of their nervous system keeps them swimming, making sure that they can still breath and helping them to avoid predators. Sleep as humans and many other mammals experience it, with the whole body going entirely unconscious, turns out to be the exception rather than the rule. So, for life evolving on a planet with no real day/night cycle, sleep in phases seems to be the most obvious direction to go in. There are many ways this could work, but one method would be bodies with redundancies. Bicameral brains, working in shifts where one half rests while the other functions, seems like a clear option. Decentralized intelligence, where the nervous system is spread out across the body and different parts can get away with micro-sleep while the rest of the body compensates, is another. Social and Eusocial behavior also adapts for this. Herd or hive mentality could have some individuals in a group sleep while others protect them, switching off as need be, or potentially not at all. For smaller, insect-like creatures, it wouldn't be unthinkable to imagine drones that never sleep protecting a hive until they die of exhaustion while the queen gets the sleep cycles she needs to keep up the hive and produce more temporary drones. It is most likely that, to an outside observer, animals on this planet would not appear to sleep. Many would have adapted to give the impression, especially to would be predators, that they are always ready, always awake and aware. However, close attention would show this for a ruse, and probably various predators and parasites would have evolved to take advantage of whatever patterns there are to the partial sleep that these creatures would use. But nature is full of exceptions. There is an oppurtunity here for something really fun - you know how many birds have evolved mating signals based around intentional disadvantages, like bright coloration or big heavy tails? What if there was a creature - probably some kind of megafauna - that broadcast its fitness to potential mates by going into full blown REM sleep? Like, look at me, I'm so amazing, I can literally stop moving for hours at a time in direct sunlight and nobody can kill me, don't you want my genes? The one doing the selecting would then nestle down and fall asleep next to the individual they found, and some kind of pheromone signalling system would kick in so that their sleep cycles synchronize and they both wake up at the same time, and that's how they select their mates. [Answer] Even for a tidally-locked body, [libration](https://en.m.wikipedia.org/wiki/Libration) would occur, in effect, the body would rock back and forth, slightly changing the direction toward which the sunlight side of the planet faces on a regular cycle. This would cause regular periods of light and darkness or twilight around the twilight zone. It is entirely possible that life forms would evolve to take advantage of their preferred light levels, and might sleep through the other part of the libration cycle. It is also entirely possible that if sleep is necessary for the life forms on this world, they might synchronize to some other regular cycle, whether astronomical or local, or they might have an entirely arbitrary sleep-wake cycle. [Answer] **Sleep in Short Periods** Modern humans sleep for a single period during the night and wake during the day. Some cultures incorporate a nap in the middle of the day. Historically This is because (a) we have bad night vision and (b) have no predators. For many animals this is not the case. Some animals are nocturnal. They sleep during the day and are active at night. Some animals are crepuscular. They sleep during the day and night and are active at dusk. Some animals sleep in shifts throughout the night and day while the others keep a look out. Some animals never fully sleep. They put half their brain into a rest mode and then swap over after a while. Some animals live in caves and never see the light of day. Some animals have burrows where they hide as well as sleep. Some animals just sleep on their feet standing in big herds in the open. All of these animals have different sleep schedules. The only pattern is that there is no pattern. It is believable that Earth-like animals in a permanent twilight would still sleep. The main difference is there can no longer be any coordination between predators and prey. For example many predators hunt by sight, and potential prey animals get an advantage by being active at night. In a world with day and night and rabbits and cats, the rabbits sleep for one long period in their burrows during the night, and are active during the day when there are fewer cats around. In a twilight world with only rabbits and cats, I predict the rabbits sleep in shorter bursts. When the herd spots a cat they all flee underground and sleep for an hour. Then they come out when the danger has passed. [Answer] # They would have daily migrations In your twilight zone they likely would separate out the day and night by simply finding a shady spot behind a mountain or in a valley, and move to the lit areas during their active period. **What is a day?** Consider that if we follow the current theory of how our life evolved, the idea of a day was a late development. Your planet's first life may have never even known the sun or the surface, and instead began by getting their energy from radioactive decay [like these *Desulfotomaculum* bacteria on earth do, two miles under ground](https://www.newscientist.com/article/dn10336-gold-mine-holds-life-untouched-by-the-sun/#:%7E:text=The%20first%20known%20organisms%20that,to%20create%20food%20for%20themselves.). Even though your planet does not have a clearly defined day and night, there will always be some subtle variations in the surface climate which a living organism can take advantage of. It could be some eccentricity in the orbit, or it may be a pair of satellites creating a wobble, or it may be the subtle resonant librations of the planet. But in the end, life is not going to do well in a perfectly static environment, because that environment will quickly devolve through entropy. Fortunately, the universe is messy and doesn't really make perfectly static systems. It's probably not helpful to compare the concepts of "sleep" as we know it on earth to your life forms, because everything here has had the benefit of a very clearly defined diurnal cycle. We work the way we do because we grew up where we did. The metabolisms in the higher life on your planet would not recognize periods similar to our own, but instead, there would be some other cyclic energy flow that would trigger an active period, and a rest period—a circadian clock set by the planet. It would be reasonable to assume your life began just feeding off radioactivity deep in the planet's crust at first, and as it got pushed higher, it found some sort of energy cycle that it could leverage to drive higher metabolic rates in small bursts. Let's assume for now it was some seasonal change caused by eccentricity in the orbit. It may also be a much dimmer star than our sun, so your goldilocks zone is much closer. [It is even possible to have your entire orbit happen in one earth day](https://worldbuilding.stackexchange.com/questions/160405/what-star-can-give-an-earth-like-planet-a-1-day-year) while keeping an earth-like climate. So you can imagine any arbitrary cycle, and any arbitrary cause for it; but what your life will need is to have these cycles of higher and lower energy density, and a more rapid energy cycle will allow your mechanisms of evolution to work more quickly on successful adaptations. At any rate, your lowest life forms need to locate this certain cycle to reach up for the surface. That will promote the more advanced forms, allowing multicellular life which can share resources and coordinate energy spending. Once these median forms find their way to the surface, they need to come up with some form of locomotion. Your planet's energy cycles need to have a large enough variation for them to store energy for bursts of activity. On earth, this likely happened in the seas, because water was so easy to push yourself through with very little energy. The clusters of multiple cells could all push together, and with a small amount of effort, they were into a new area of fresh energy. Your life soon gets good enough at having its cells work together, that it becomes the first energy hunter. It figures this out by coming across some sort of sensory input, where a source of energy triggers something in one cell. On earth, maybe one of the first ways we found energy was by cells that reacted to sunlight: rudimentary eyes. It can determine where energy might be around it before it touches it; it no longer has to wait for energy to be delivered by the planet's natural cycles. This upper-middle organism now has the tools to control its own fate. It can spend energy in larger bursts using some of the cells (we call them muscles), it can deliver energy to some cells that are good at locating energy (sensory cells and nerves), and it can store energy reserves in case the natural energy cycles get interrupted (fat reserves). It is not long now, if the right random mutation happens by, before it also starts hardening some cells to give it more leverage and mobility—it discovers a skeleton frame. As soon as these parts are together, and the organism can move itself around to find energy, and it has been set into a cyclic pattern of spending and conserving energy; then the adaptations which will win out will be those which choose a scheme of "hunting" and "resting" that times itself well with the planet's natural circadian rhythms. It is now that the organism has become fixed into a "day" and "night" scheme. Through all of this, there has been a common theme that thermodynamics will not allow it to forget. It must have one period that offers it a chance to take energy in, and one period that it is allowed to metabolize the energy it collected. That second period is what we on earth refer to as "sleep." For your planet, the life will not have these low energy periods come to it like our nights do; so only the ones who can move themselves to the night will be able to overpower the entropy of a nearly static energy level. This higher organisms can no longer get by on the weak energy from the planet's circadian rhythms that powered your early life. Perfectly stationary organisms like many terrestrial plants may not do well on your planet. Instead, the producers on your planet will need to happen across their own [nyctinasty](https://en.wikipedia.org/wiki/Nyctinasty) solutions which create their own high and low energy periods, likely by opening up to energy in their "day," and sealing up their mass in some bark or shell when they need to metabolize. Very early on, it would need to look much like modern flowering plants. This leaves the more energetic life forms to use their mobility to migrate daily into the hunting grounds of the daylight-side of your twilight zone, and then return to the darker side, or perhaps a cave or the shade of a mountain, to sleep. [Answer] Many people would have no great difficulty sleeping in a wide range of situations. I'm one of them. There is no reason to think that the normal sleep mode could not be like this. I used to have trouble getting to sleep. 30 mins to one hour to more was not unknown. **THEN** we had a 8 weeks premature daughter, my wife could not breast feed her and was permanently exhausted - after a while we found that she had easily curable pernicious anaemia. I had to bottle feed my daughter twice a night. She would stop sucking with the teat in her mouth. If I removed the teat and she would cry continuously. Feed faster she would not. I was writing up a Master's thesis during the evenings and working full time. Sleep I needed. After a while my body "learned" how to fall asleep in under 5 mintues, anywhere under almost any conditions. That was about 40 years ago. The fast drop off to sleep ability has never left me. I'd rather bright light was not shining on my face. Loud noise is Ok - sudden bursts may annoy. I have slept under a grand piano in a Hong Kong hotel lobby. On consulting trips to China when a quick nap helps a lot, I have slept in hidden niches under conference tables, under a stairwell, and various other interesting places. Your creatures should be able to do likewise :-) [Answer] > > How would life on the planet sleep? > > > Why would you necessarily assume that life needs to sleep at all? "Sleep" is something that higher animal life on Earth do (and no one knows why); if life evolved independently on your planet, why would you necessarily assume it would get the same trait? Now, for story reasons, you might want to assume that they do - that's your choice. However, assuming that your life has no need for sleep is an equally valid choice. [Answer] Simple: You have sleeping time be determined by when exhaustion sets in and whether the location is safe rather than light levels. ]
[Question] [ An ancient kingdom covers a several rivers in a desert basin all converging on a central, hypersaline, lake. Because of its central location, and the importance of the salt, the lake has important religious and cultural significance. In particular, an island in the middle of the lake. I thought about making the island the capital of said kingdom as a fusion of civil and religious power, but I ran into trouble of the feasibility of it. How would one get sufficient amount of water into middle of the lake? * In war time. A capital that can withstand siege would be ideal - especially that it is very hard to assault, and a central location allows them to project force through 'army in being'. * In peace time. Just as Rome was largely unprotected during its Empire, during a golden age, the capital might have been moved there for symbolic reasons. The closest thing I come up with was either shipping it (probably too labor expensive in the Bronze Age for anything but the palace of the god king) or create a juicy plant which either is farmed on the lake or on land (but probably hypersaline lakes are too salty and I don't know how much farmland would need to be used). Does Bronze Age civilization have the means to obtain water for a large city in the middle of the hypersaline lake and, if yes, how would they obtain it? [Answer] Water is an essential resource, especially in bronze age. You can't have a city without supplying it, that's why the first civilization have arisen next to big rivers (Gange, Yang-Tze, Nile, Tigris and Euphrates). In your case the hyper-saline lake looks like a nasty environment even for a tribe. If you however want to have a city there, a way to have fresh water is to have an underground aquifer, more or less like in the North of the Sahara desert. A rather simple well could provide access to the fresh water and thus allow a city to sustain itself there. However, such a city would massively rely on external supplies of food, since farming in an hyper-saline lake is out of question. [Answer] Your lacustrine island is pretty much akin to a marine one in terms of salinity, so it will have access to fresh water in the same way that maritime islands do. Rainfall over the island will create fresh groundwater that floats above the hypersaline waters due to being significantly less dense. In hydrology, this is known as a [freshwater lens](https://en.wikipedia.org/wiki/Lens_(hydrology)). [Answer] > > how would they obtain it > > > Probably the same way the Romans did it: with arched stone aqueducts. (There's nothing particularly complex about them. If you can build a big stone pyramid, you can build an aqueduct...) Stone aqueducts this early aren't historically accurate, but... close enough. After all, the Henge Builders hewed hard stone and moved it long distances, and historical **fiction**, is, after all fiction! [![enter image description here](https://i.stack.imgur.com/BapTQ.jpg)](https://i.stack.imgur.com/BapTQ.jpg) [Answer] Actually this has reminded me of a very interesting culture. The Aztecs built a huge city on an island in the middle of a lake, albeit a freshwater lake. The island was connected to the surrounding land by long floating bridges, and keep in mind that Aztecs didn't smelt iron and used bronze as your question outlines. This island city was their capital as well, called Tenochtitlan. They farmed crops on this lake with *floating gardens*. Now for applying this tactic with your hyper saline lake, as L.Dutch said, forget about it. There are no halophile crops even remotely worth harvesting. With the Aztecs island city, there were also a myriad of other small islands surrounding it, all interconnected with each other through a series of floating bridges. What I suggest is have a central hypersaline lake which would be surrounding by small town-islands that contain wells/underground aquifers for water to be transported quickly and easily between these towns and the main city, and for crops to be grown somewhat near the lake, but not close enough to damage the crops. The crops will then be transported through this bridge network throughout the islands. In preparation for war or just as a precaution, grain stores will be made as to keep themselves self-sufficient for the time needed. If under siege, simply destroy the floating bridges. The enemy will attempt to starve you out, but if the empire is large, simply ask for assistance from your myriad city states and conquered territories. Animals can be farmed on the town-islands and capital city with ease. Hopefully this answers everything! \*If the rivers are freshwater and not hypersaline, simply grow crops there and transport them through the bridge network [Answer] # Solar stills. Basically, they would build a cone of glass over a section of the saltwater lake, allowing sunlight into the water to heat it up and cause the water to begin to evaporate. The top of the cone would be connected to copper or bronze tubing to a shaft that's dug into the ground at an angle, where the water begins to condense and collect, with a different shaft that's been dug straight down to form a well, where the condensed water can be collected. The [Wikipedia article on them](https://en.wikipedia.org/wiki/Solar_still) has a nice image depicting such a structure, though I can't directly include it in this answer because its filetype is incompatible with StackExchange's image functionality. Apparently similar devices were constructed by Stone Age Native American tribes, though they used wood and leaves to construct theirs, since they lived in a climate where dews condensed naturally overnight, so they just needed to construct a device to capture this water, rather than one that generated it. ]
[Question] [ **Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers. --- You are asking questions about a story set in a world instead of about building a world. For more information, see [Why is my question "Too Story Based" and how do I get it opened?](https://worldbuilding.meta.stackexchange.com/q/3300/49). Closed 1 year ago. [Improve this question](/posts/31197/edit) **The Situation** After 4 years being a baron, the empire that you are sharing a border with decides to declare war to your suzerain. It will take at least a year for them to muster their whole army and knock on the doors. You, the Baron has one year to prepare for war. The rest of the country refuses to help you due to the elitism of country's nobility. The royal family can't help you without showing favoritism and tells you that this is a trial on how well you handle the situation. Furthermore, the nobility have decided to protect the second line of defense instead of your barony. The nobility sees you as a social climber who knows nothing and they prefer to leave you to the enemy. They see this as an occasion where you can prove yourself (how useful you can be). They will barely supply you with anything but trading activities remain open. Your task is to delay the enemy at all cost since the country has little knowledge of war logistic. but no one said you cant stop them. The adversary, the empire, is a regional dominant power that can muster more than a million professional soldiers of its own, 4 million levies and another 2 million mixed of professional and levy soldiers from its vast vassal states. Economy wise, they can maintain a standing army indefinitely. They also deploy land battleships with no gunpowder but with numerous ballistas and formidable magicians that serves as the battleship's main weapon. The empire is not festered by corruption and uses divide and conquer tactics to subjugate adversaries. The baron's country is protected by mountain ranges and known for its formidable and numerous dragon knights, wyvern riders and griffin knights. The country also has many magic knight orders and a well equipped professional army of 100,000 with an additional 400,000 levy that can be called upon but the levies are very poorly equipped. They also possess the most talented magicians in the continent and are prepared to go to war at a moment's notice. Not that they will count by they must be considered to the decision as it might be, sooner or later they might be your enemies. THey are very much united under the current royal family and can't be bribed by anything. **The design objective** You have a year to prepare but the snowy winter will last for 2 months at least, which will impede your preparation for war. You have to design something that will stop the enemy on its tracks, deter them from invading. Or if anything fails, destroy the invading army. However, if you totally destroy the invading army, the other foreign powers might seize this moment of weakness to attack. You need to sink the empire's army morale to stop them in their tracks when by using your deterrent. Unfortunately you don't have reputation enough to scare the enemy. But you have a resource that no one has, you are from modern day Earth. Using that resource to full strength you realize that "Peace through Superior Firepower" fits your taste and need as diplomatic approach will either tell you to die or betray. You come up with 3 designs of weapons that can be used as deterrent. 1. A flying ship or an airship - You've been constructing one for over a year ever since you have discovered how to make it float! But the workforce is not skilled enough to construct this wonder in time unless you dedicate all your resources there. You will need at least two for a complete military effectiveness or so you think. Logistics and maintenance of this will be very troublesome but it will be worth the trouble. 2. A Super-Gun - You know how gun works, you have mass produced it for your standing forces. The thing is, how to make a gun or in this case cannon scary enough for any threats/diplomatic relations that they'll be thinking twice before knocking on your doors again. You have a dwarven clan from the mountains that will work for you to create this cannon, but still unless you concentrate your resources on this work, it will not be completed before the war. Not to mention that you haven't tested the design and you are not even sure that you have enough resources to maintain it. 3. Prism tower Spellarms - Your fortress has the tallest tower in the known world. You can see everything in the horizon, including the invading army and the nobility army. You can cover your front, rear and flanks with these spellarms. But you've just begun studying runecrafting effect for light. You don't know how to weaponize light but you have the power issue solved because you still have a tortoise behemoth heart that you got from your adventure. You are confident that you can weaponize light but the question is will you be able to weaponize it before the imperial army knocks on your doors? To top it off it is only limited to your territory alone. **Resources** Food - You have plenty. You also have several refrigerated and vacuum warehouses: you can withstand a siege of few years, give or take. Mineral - You have a lot since your territory is surrounded by mountains: gold, silver, copper, brass, iron and other metals. Not to mention, the discovery of an all temperature super conductor and crystalline metal that when heated makes things float. You are definitely loaded with resources but you don't have enough people to utilize the output of your mines/foundry to full effect. Manpower - due to abundant food and work, many peasants have been relocated to your barony. However they are not enough to start your wartime manufacturing without suffering the consequences in few weeks. You have dwarven mountain clans that resides in your territory that can be coerced to work for your projects, but you need to focus on one project alone due to manpower constraints. In addition you have bought slaves to supplement your lack of manpower. Army - You have an army of 7000 mixed troops ranging from gunpowder troops which numbers 3000, 2000 troops of well armored militia which was thought of team work and 1000 troops of skirmishers that uses lever action crossbows. Additionally, you have 1000 troops for 227 mixed battery of mortars, howitzers and cannons. These troops are better equipped than both king/queendom and imperial elite soldiers. Their morale is high and they know how to follow orders. However against the empire's million army, they probably will count for something but not victory. You simply don't have enough body to throw at the imperial army even if you enlist all of your people. Weapons and armor - With the introduction of gunpowder weaponry, you are bound to be superior to anything you face except numbers. The introduction of new ways of manufacturing steels and other refined metals, the ease of manufacturing armor, weapons and other war and industrial components allowed you to deploy a professional army. Your weapons are better, sharper and harder than anyone in the world except spell arms and of course your gun powder weaponry, your armor is lighter, stronger and easy to procure allowing you to deploy armored troops, remotely detonated mines that can be deployed in preparation for any conflict. and lastly, your artillery batteries that allows you to pound enemies at extreme ranges with good to acceptable accuracy. **Rare/Talent resources** Magician - Just one and her main magic strength lies in healing, alchemy and runecrafting. Yourself - you can use magic, which is limited to time-space manipulation, rune crafting and spellarms. To top it off you are a very rare male magician albeit weak but with very rare magic. Various UAV - You have brought things from modern Earth. One of it are surveillance UAV. It will be very useful for real time intel gathering and leading artillery fire to the right place at the right time. Your pet tyrannosaurus rex - She is intelligent short of making conversations with you. she is as big as a house and loves you like her mother. Tri-Heart of Behemoth Tortoise - The still beating heart of a titanic monster you faced. Capable of generating huge amounts of mana indefinitely. Shells of Behemoth Tortoise - The shell of the Tortoise you have slain a while ago. Amazingly stronger than any thing you know and super magic resistant than dragon scales. Bones of Behemoth Tortoise - Surprisingly soft and brittle but has many uses apart from potion ingredients like can be used to ultra focus glass and make it stronger, mixed with metal to be very heat and kinetic resistant and when mixed with mercury, can be a deadly odorless aerosol. A very large diamond - The size of a lion head. Your magician said that a very small diamond the size of a child's nail is capable of storing huge amounts of energy. Dragon Heart - A still beating dragon heart that you manage to acquire after killing your first dragon. You realize that the mana that this heart pumps can be converted to electricity. **Objective** With the resources you have, you must achieve the following from any of the 3 designs. * Deter ANYONE from threatening your position * Be able to do the "Speak softly, carry the big stick" diplomatic approach * Stop the imperial army on their tracks without totally decimating them * prove your usefulness to the royal family. * Not be threatened by the elite nobility of the kingdom * positive future prospect in terms of economy, military and politics for your territory. Which of the three designs will be the best deterrent? [Answer] Well, it all has to do with RATE of FIRE. Does your airship have capabilities equivalent to the [US AF AC-130](https://en.wikipedia.org/wiki/Lockheed_AC-130), which is capable of blowing to smithereens a football-field's worth of enemy combatants every second? Most importantly can you blow enemy flyers out of the sky before they get within range? Does your [Big Bertha-like](https://en.wikipedia.org/wiki/Schwerer_Gustav) mega-canon fire at 200 km ranges and leave a 100 meter crater where the enemy general's HQ tent used to be? And then can fire again, a minute later? If it can be this precise and accurate, Big Bertha is the way to go. Does your Spellarm tower have the capability of sustained fire? Is it a ray of death, dancing merily amidst the burning or panicked and fleeing soldiers of the enemy camp? Does lifting one's head above the trenches for a single second leave a charred stump where the soldier's head used to be? Spellarm towers it is. Given equal rates of fire (casualties per second) the Airship has the advantage of mobility, and the disadvantage of being within line of sight. Perhaps it can be disabled by enemy mages? Given equal rates of fire, the Big Bertha has the advantage of causing utter horror out of the blue, with no possible defense. Especially given the massed troop formations common in medieval-tech armies, this should be horrifying to enemy leaders. However, this comes with significant supply issues (must have a steady supply of 1,000-7,000 kg high-explosive rounds. Some of these are about the size of a passenger car. Not an easy ask for a rencently medieval tool-kit. Given equal rates of fire, the ray-towers would make a traditional siege of your capitol virtually impossible, since any open structures in line of sight would be vulnerable, the most common medieval construction materials are either flammable (wood and hides), can be melted through (iron), or cannot be produced in sufficient quantities fast enough to shelter a million-man army (porcelains and baked clay). However, they are obviously immobile, so no offensive capabilities and no use beyond direct line of sight. The enemy might be seizing your mines and killing your peons, if it's around the nearby mountain, you're helpless to do anything. All in all, if all solutions had similar killing power (casualties per second), I'd go for the airship. If you are in a defensive mind-set and worried about sieges, the light-towers will help. If you just want to rain death upon enemies within a 50 mile range and have the industrial chops to supply the shells it needs, definitely go for the mega-cannon. [Answer] The three options shift the power too heavily for peace to be maintained even if victory is achieved. No king will allow a province within his kingdom to have a WMD which he himself can't control (otherwise what stops you from claiming the throne yourself?!). And no empire will want a neighbor that can assert such power. The best option for the Baron seems to be to declare Independence from the crown and declare a Swiss-style neutrality. The mountains provide a natural boarder so territorial disputes are unlikely. If trade routes close to the kingdom, then the Empire provides a new avenue. Given time, the new country could provide a pivotal trade route. [Answer] This is going to become an "update after receiving new information" answer, I have the feeling... So... lets put aside the logistics necessary to provide 21 million meals a day without the technology for eatable energy bars and Cola. **One Airship**? Seriously? They may take some pounding, but as soon as a lucky fireball hits it or one of that dragon-riders get cocky, its two years of development reduced to a flying target. It would need to fly at an altitude no enemy could reach, which would it make next to impossible to hit anything at the ground level if you cant shell them with HE-Artillery from up there. Maybe it can do so, but as soon as it will go down to dock at your city, its target practice for any long-range weaponry. Or imagine a bad wind blows it away from its supply-range... Still, hoping a SINGLE super unit will provide you with an argument to not get attacked is pretty optimistic. All it needs is a silent assassin who torch that thing during peace-time. **Super Cannon**? That does remind me of some WW2 Weapons. Railway-Gun Dora and Superheavy Mortar Karl. When these cuties did hit something, all that remained was a huge crater. But reloading one of these was a task that took hours. Needless to say, that the barrels did wore out pretty fast. And Accuracy? What is this? Your super cannon should be able to hit the enemy capital from its deploying position to make any difference. Load it with some chemical agent that does burn as soon as someone put water on it and that could at least land a pretty lucky hit. And no wall from that time would resist a concrete shell with a mass of several 100 kg or even a ton. But... even this would be an impressive weapon, it's still one. Lose it, and you are a nasty piece of rubble your million man army enemy will eat for lunch. Well, he could do this anyway, knowing that you could land at best a dozen hits, which have a good chance to do no damage at all, during the first days of the war. **Death Ray of Doom** That sounds like that... uh... Archimedes Fire? There was one old geek who may have build the first laser in history using big lenses. That would be a pretty useful weapon, but all your enemy needs to do is employing sappers. Or magic. An earth wall in front of every enemy camp and all you can do is baking earthenware. They could even employ mirrors and welcome home dear death ray. **Other suggestions**? What you need is something that's not a single super advantage. You said there is one year to plan ahead? Send out commandos and mine all bridges that lead to your realm from your million man enemy's point. When things got hot, blow one up and tell em that you can do this with every bridge you want. Okay, not the best plan, but your only hope is to find something that can stop the enemy supply train without being a glass cannon type; what may fit more to that other question. [Answer] On how I read this, the Baron stands there with roundabout 10.000 men and 227 gunpowder artillery. The Kingdom with about 700.000 Men plus various Knight (also winged Knight on monstrous Mounts) will refuse to help even through Feudal pact? **Big Edit! More Time to think and more tactics (old answer in Spoiler)** 1. Your feudal Lord refuses help, which he must provide. Therefore call a council of all lords of the king to point out that matter AND that there will be a massive invasion against your fief, which belongs to the kingdom. If the king refuses again he will risk losing support from the other lords, as they will conclude, that the king is willing to sacrifice any fief only to not get involved in that war. That thought will be incorrect as I can't believe that the Empire will stop its steamrolling after the fief of the baron (of this story). 2. Use the landscape to your advantage! The country itself is protected by mountain ranges, therefore the empire army has to use valleys and passes. Prepare them with mines, explosive charges and find out which the enemy uses first. The empire will probably take only one route despite its size and capability of using every pass to your fief. (The empire will be cocky through its tremendous army size of 7 million troops) When the army is in a pass decimate the first ranks with continuous fire with gunpowder and when ammo gets low, set off the charges to collapse the pass trapping some enemy troops and cut off reinforcements. Repeat that strategy. I suppose that the empire does not even know about gunpowder and the gunpowder weaponry, therefore the troop will be terrified by them, as with every thunder explosions and death follow (which may be very unlike to magic attacks). 3. Attack the supply routes! Use the skirmisher (or even the airship when built) to avoid the main force and attack their supplies. An armies morale stands and falls with rations. Even worse if the commanders of the empire consist mostly out of spoiled noblemen. They will insist on their luxus rations while the troops starve. Definite morale killer and a call for desertion. Therefore the empire will halt its invasion if casualties get too high (4 times your troop size may suffice or 10 times). There won't be a need to utterly destroy the empire army as they risk to be torn apart by neighbors if they waste their 7 million men in that "insignificant" invasion. On the superweapons: Deathray: As I understand it the prism tower works like a magic laser cannon. There I see the possibility that if it is magic it may be canceled by enemy mages. On the other hand, it is an impressive option, as it can kill everything in the line of sight (therefore I suppose everything in your fief). I personally go for the Airship (or two or three if possible) using it to attack supply lines or rain death from above in the valley-battles. This works best if the airship flies high enough to prevent counterattacks from the ground. Then your enemy has to face a "weapon" that can attack and transport troop independent to roads ignoring water and mountains. A strategic nightmare in a medieval setting, as armies have to move to a degree on roads. So here you go I hope this version is even clearer. PS: The grammatic errors can be corrected as I could write this more easily in German than English. > > ! > Point 1 as MakorDal: > Force a council as the feudal pact goes both ways. Your Lord has to protect you as you have to offer support in his affairs. > Additionally, if he lets your barony be squished by that tremendous enemy, there will be very little chances stopping them. > > Reason: > > The barony is protected by mountains. This will ensure you a bonus fighting on your land, providing possibilities of entrapping that huge army (which will move and react slowly) in passages, enabling you to rain death upon them. > > Point 2: > > A single Superweapon may help, but put you in Danger to be on your own alone, as your feudal lord may force you to hand it over or expel you to conquer you. > > My suggestion: > > -Enforce help of your feudal lord (by enforcing the feudal pact) here the airship may help greatly. With his support rally his complete army and use the winged knights to terrorize the support lines. There is the saying "an army cannot fight on empty stomach" a huge army fails as its support lines do. > -Hit and Run tactics against commanders. In medieval armies, the troops rely heavily on commanding officers, without them even trained troops may falter if faced against special odds (entrapping in passages, mines, or even a superweapon like the laser) > > On the superweapons: > > Airship: > > the IMHO best of the 3 as it is versatile, but only in more than one vehicle > > Supercannon: > > Useful to rain death from afar, but only as its location is secured (as this monster with push itself into the ground, see the Sturmtiger tank of WW2, it's mortar pushed it so far into the ground, that after three shots, it could no longer move) > > Deathray: > > second best, as some ray of death is not only deadly but also terrorizing. Best option for "talk softly and carry a big stick". > > > > [Answer] The way I see it, the biggest threat that you face is a prolonged siege. You could never defeat an army ten times the size of your own without a massive positional advantage, no matter how well equipped your army is. Your troops would all die of starvation before you manage to defeat half of their army. With that many troops, they can besiege your city indefinitely, particularly if they have good supply chains to keep their army fed. However, those numbers will not count for a thing when you're inside your city walls: there is only a finite amount of space that they can attack from. The only advantage that will offer them is fresh troops, but they won't survive long enough to battle you if you have such superior firepower. So if you won't meet them in open combat, and they cannot penetrate your city (particularly if you use that Behemoth Tortoise shell to reinforce your city gates against battering rams), then their only chance is to starve you out. They will take their vast army and surround your city, making sure that no one can leave and no one can enter. All whilst having the benefit of free run of your country, as you will be sat behind the city walls unable to leave. So, which of your weapons can break the siege the fastest? The super-guns can repel any attacks on your city walls, but considering your army already has guns that can have the edge on your enemies, having better ones will not offer you too much of an advantage. If they have superior range from the city walls, the army can just move further away out of range and keep on waiting. Probably the worst option of the three. The airships could be very useful in a prolonged siege. They could help to resupply your city, and also harry the enemy supply lines so that *their* army begins to starve. The logistics of keeping millions of soldiers well-fed and in fighting condition is very difficult, so any disruption to that is a benefit. You could easily wait out the siege with this strategy, as eventually the senate/nobility of the attacker's country will realize that they're being plunged into debt by funding a war that is being dragged out for far too long. The army will get called home, and you will have succeeded in your mission. The problem with this is that whilst you are waiting for the army to leave, enemy soldiers will be left to pillage your country, especially if they're sitting around bored and hungry thanks to you making sure they are ill-stocked with your airships. So you would win, but at a great cost. In addition, if you were going to use the airships to attack the army, they would need to stay well out of the range of the ballistae, magicians and other siege weaponry that the enemy has. If you only have 2 airships, you cannot afford to lose one, so would need to be extra careful. This means that any weapons you could use from them would be out of range, and anything you could drop on them would be from too great a height, they would simply move out of the way. So airships would would ensure victory, but we can do better. The best thing that you can do is to build your mega death-ray tower. You can fire at the waiting army from a great range, which they will not be able to avoid. Wherever the army is stationed whilst besieging your city, they will be constantly being attacked. Let's say that the beams of death are only able to attack a dozen or so people at a time, and it can only fire one charge per day as it requires energy from the sun to be stored within the giant diamond, you will only be killing a handful of people at a time. This is a drop in the ocean in terms of numbers for the enemy. The advantage you have is that the enemy army don't have any idea *which* dozen people will be incinerated. You fire into their ranks indiscriminately, and they will be constantly on edge, never knowing from one day to the next who will survive. Add onto this attacking them occasionally with the chemical weapons that you possess manufactured from the Behemoth Tortoise bones, and this adds in an extra element of concern for them. You may still only kill a couple of hundred of them at a time, but they will constantly be in fear of their eyeballs melting in their skull. Then you can send out small strike teams on night time raids to attack individual encampments. Your men and women know your country better than they ever could, so they can sneak upon the enemy in darkness, and before they can react to the slaughter, your people will have returned behind the city walls, ensuring that no other encampments will ever sleep soundly at night. Trying to keep order within the ranks of the enemy army will become a nightmare. They will all be on edge, sleep deprived, in fear of death and missing home. And once the horror stories reach others throughout the army, and the families back home, there will be more deserters of their army than you could ever hope to defeat with any of the weaponry you can build. Therefore, using guerrilla tactics and terrorism, you can allow their army to defeat themselves using the prism tower. [Answer] The feodal contract goes both way : you help your sire, he protects you. In this case, by throwing you to the wolves, he has already betrayed you. You know it. He knows it. All of his vassals know it. You build the Airship... get it to his capital and force him to held a conclave of the high lords of the realm. (Most kingdom had poweful nobles whose power rivaled the ruler, especialy if they banded together.) If it's not possible, join the Empire. [Answer] Either surrender, or play Moscow. These are your only 2 real options. If your overlord won't support you, a single weapon isn't going to do much against an overwhelming opponent. Classically, what has worked is lots of cheap weapons that cause disproportionate damage (e.g., fireships vs Spanish Armada). If delaying the enemy is all you want to do, destroy all means of crossing the mountains, or at least make it extremely difficult. You won't STOP a determined invader, you will make them wonder if it's worth it. Your only chance of VICTORY is to starve them out (Moscow). Destroy the passes, withdraw all food and supplies behind your capital, damage the roads, destroy signposts, leave incorrect maps and wait for winter. If possible, use raiders to attack their supplies and foraging parties. Your ruler is not to be trusted, as he has already proved. A doomsday weapon will result in demands to hand it over followed by another war, assassins or simply by you being told to report to court, ALONE. Edit: On re-reading the question, you have massive technological superiority already. It makes far more sense to focus build up your army instead on doomsday weapons. Save those for the next war. [Answer] mines. lots of mines. not the fanciest option, but it can do the job better than your weapon. 1. great chance of success since your country is surrounded by mountain, and the enemy have land-ship to move around, it quite safe to say the invasion route will be pretty much fixed. that mean the enemy will have to walk pass your traps if they want to advance. 2. easy to carry well, much easier than carry a big cannon. that allow you to plant them in unexpected place, like a bridge inside enemy's territory, a supply storage, etc.. also, since you dont need many people to plant a mine, you could send many team to simply littering the country with land mines. 3. hard to avoid without any metal detector, the only way to find mine is either: a. dig up every road ahead and b. send a guy to "check". if they choose a. , you can always re-mine a clear route and they will have to dig it up again. if they choose b. , mix anti-personnel mine with anti-landship one and let them figure out themselve. 4. multipurpose when not busy blowing up people and things, mine can be used for many other purposes. they can be used to creat landslide or avalanche, to make boulder to block a road etc. 5. and the most important.. losing a few mines dont have any significant setback for you, while losing your single superweapon is an instant gameover. heck, if your can place your plant behind the 2nd line of defense, then you can keep going even after your barony has been overruned. on the noteside: i think the best detention is to focus in the enemy's most pride unit, or the costliest one. if their land ship is the symbol of power, then focus in destroy them. it's not only demoralize, but also make the war become less cost-effective. also, the object should focus in weaken the enemy and make them vulnerable again other empires, rather than in defeat or stop them on track; just show them that whatever they got from you is not worth the risk for it. [Answer] Considering given three options and objectives, they seem to be more about way of playing your cards than actual hand you have. As for weaponry, to not mimic already given answers, there is one more interesting trick to the Prism tower, which may make it more appealing. When firing high energy ray with right frequency you may bounce it from higher levels of atmosphere drastically increasing it's range and allowing you to smite any target. If you don't want to abandon idea of laser you can still use plasma mirroring (needs very short laser impulses lasting femtoseconds) to achieve the same. Whether your protagonist is able to kill all the intruders or just dozen of them, with that trick he may be able turn rulership (and/or capital) of enemy into fine dust and come victorious without overkill. Moreover even if he'll die (even just temporary and only in general opinion) before the news will make it to the army as they will plunder his land (possibly even start further invasion if flow of information will be too slow, question if mages cannot send such an important messages), it's still technical win. What's more important it will probably appeal to the court as it wouldn't make him look dangerous and the king will be obliged to honor his bravery and luck (which will be the more generous, the less destruction will be caused upon king's country). Effectively it may cover most of your points, except domain devastation and loss of the subjects already under his rule. However it would be probably the best scenario which includes actual attack of an imperial army and virtually no support from other nobles. For plasma mirroring option, it makes quite terrifying idea of stationary offense. One that will need only solid surfaces to perform extended range attack. Also brutal power of impulse needed to create plasma mirror may be directed even from aerial object like balloons with some solid attachments. What's even more fascinating, with precise control over laser it will be possible to adjust plasma mirror to reflect the beam in expected direction, which will effectively force enemy army to hide under mirrors, allow for attacks on supplies and affect enemy morale. The beauty of this solution connects with facts that ceiling mirrors can become artillery targets, or beam may be changed into some other radiation, like microwaves or X-rays (which should prove more effective as mages may not know how it works). Mark that the real problem will start IF your character will WIN the actual battle, against the odds sourcing from significant difference in numbers. Why would that happen? Even if he would try really hard, with magic on both sides (guessing from disproportions imperials may mobilize much more mages) chances are very low. In world that studied magic, most probably both military and civilian geomancers would likely have some spells useful for mining (e.g. to make underground passages below walls), securing passage thorough swamps and creating one. Whether they would find any underground explosives, they would make sure to sink potential mines and/or seal them in rocks which would slow the army. Eventually they obviously have detection spells for detection of mineral ores which would make their task trivial. Also probably there are spells used for scouting and hiding. To make the point, as long as protagonist will not use unthinkable (by imperial standards) or imperial army is not lead by incompetent idiots/rushed by arrogant dreadful ruler/never actually fought/has no exploitable beliefs, it is very unlikely that your protagonist will actually deter invaders. If mages are able to assure great harvests, probably they are also able to reconstruct destroyed bridges, at last when working together. Then objectives would not be achieved with battle but during it's aftermath. Device able to destroy such an army would be surely branded as doomsday weapon, as it sounds like Prism Tower magic is uncommon to protagonist's world. To lessen the fear of his power he'll most probably have to lie about output or activity of the Tower (like claiming it's power source exploded or creator of the spell died heroically to power it as nobody could prove you wrong without "power source" or knowing the inventor) and other parties will likely try to get closer to him to know what the truth is and use gained position to own benefit. All of the world powers will try to secure control over the Weapon. Depending on protagonist's relations with royalty he may be pardoned, but no ruler would allow for his subjects to posses doomsday device even if for greatest friend. Even if they would make an exception, they still would have to react on issue or risk showing supposedly weakness in eyes of nobles. Exact reaction of the king and his court will heavily depend on circumstances you create. Saying so, your protagonist would make a bothersome royal friend. As the one who defended the country from sure doom may easily be viewed as a war hero and better candidate for crown than a coward king (as ruler would be surely called behind his back in such a case at least by a few new "friends" of protagonist), so probably your protagonist would be forced (with differing courtesy) to marry into royalty or declare own rule over his domain as neutral (which probably nobody would deny at this point, mind the doomsday device) which will bring him into area of international politics. In case of political marriage your protagonist would cover most of goals, except for avoiding decimation of invading army and being drawn into court politics which I presume is not something he wishes for. Assuming your Prism Tower will provide enough kill rate, your protagonist should expect that he will be threatened by mages as they are probably the only ones who can destroy his tower. For the finishing touch, even if your protagonist would declare independent rule over his domain, he would be pestered by agents of other countries till his death/assassination/moment somebody else reinvents Prism Tower (which may be proved impossible due to need of immensely powerful mana input from Tri-Heart and gathering of sunlight). I hope it answers intention behind this question. [Answer] I'm going to ignore any diplomatic moves and focus totally on the weaponry/innovations that could be sufficiently called a 'big stick'. It's difficult to say if these are effective without knowing more about the magic system but the effects of raw mana on an unprotected body would seem to be devastating (as they generally tend to be in fantasy), with mutation, mutilation or just getting exploded being the main effect. I quite like the idea of the cannon, though it's a mechanical nightmare and might not really function, I think it's ability to be protected vs it's range (and it's disregard for line of sight) could make it a potent weapon. Here's the plan: Create two, smaller lighter cannons with a focus on muzzle velocity instead of direct payload size. This might not be needed, wouldn't mind feedback. I just don't think one basket is the best egg carrier. Empty the massive diamond and shatter it into >child head size bits (I assume child's head is an imperialist measurement state like hogs head). Create shells for these new cannons with a large amount of your discovered hover metal within them. Charge the diamond with the tri-heart and find a reliable solution to break them (perhaps a fragment of tortoise shell). Load it all into your new cannon rounds. With the tip of shell pushing against the highly charged mana diamond. Perhaps seal with bits of tortoise shell to prevent magical discharge or interception by enemy magicians. Perhaps perhaps, place a rune of seeking or some such on the shell to assist with target allocation (or any other handy resistance, smiting or penetration rune). Load your new Diamond Fire shells into your cannons and conduct some range testing with your UAV to confirm hits and gauge range. When fired, the gunpowder and friction of the discharge should hear the projectile to possibly hundreds of degrees (depending on power composition). This will cause an already fast projectile to gain altitude very quickly and easily, vastly increasing the range on the device (especially if rifled or flight fitted). When impacting, the tortoise shell fragment with shatter the diamond, causing a catastrophic mana containment failure which in turn should (hopefully) remove a large section of map as well as any people unlucky enough to be within X m/km (I was angling for a magical Nuke). The UAV sighting of high profile targets as well as any magical guidance that can be included would make this a fearsome weapon. The accuracy and power of which should only require one or two shots to bring serious political discussion to the table. [Answer] As far as a deterrent is concerned, your flying ship is the best bet. Here's why - To deter your enemy you must conclusively prove that you have the means to utterly destroy them if they try to attack you. It's not enough to be able to withstand a siege or be unbeatable, they'll keep trying to find ways to beat you unless they are sufficiently afraid of a decisive attack by you. Below is the comparison - 1. Prism tower - It's primarily a defensive weapon. Your enemies can keep their armies out of range and there's nothing you can do. They'll keep testing it and will eventually find ways to sabotage/block it. 2. The big gun - It can work as an offensive weapon but that'll require taking it out of your walls. Then hauling it all over the place is too risky. You can potentially use your space/time magic to move it quickly but you can't hide it. The enemy will eventually capture it and try to use it against you. If you keep it inside, then it's worse than the prism tower. 3. Flying ship - This is the most versatile of all. It can attack, defend and work as transport/supply. Armor it with the tortoise shell, use your space/time magic to move it instantaneously, arm it with your explosives and it'll become something that can attack anywhere without enemy being able to touch it. Now go kill a small but well defended village deep inside enemy territory or kill the enemy generals if they deploy and make it clear that the next target could be enemy's Capitol. How it works - 1. Tortoise shell & Mage's alchemy/rune crafting for defense - I'm assuming this tortoise shell is basically vibranium (nothing can break it), so no enemy attacks can penetrate it. Your Mage remains onboard to ensure any other type of damages are immediately repaired and runes are working as expected. The enemy can just watch in despair as their most powerful attacks are either unable to reach or deflected. 2. Your space/time magic for travel - You manipulate the time/space around it so that it covers more distance in less time. Simply contracting the space between the ship and its destination may achieve it. Now you can arrive pretty much unnoticed wherever you want. Travel as high as possible and then drop down to deliver the payload accurately and then fly back up again. Then "appear" 50 miles south in a matter of minutes and do the same trick again. You may or may not be able to do this over the Capitol but they don't know that. Also, you can potentially create smaller versions of the prism tower to install on your ship. You can use that prism tower for aiming from very high up above the clouds before dropping the bombs! 3. Bigger bombs for shock and awe - You have the technology to create bombs that the enemy has never seen before and you have a delivery method that no enemy can counter/block. Use your drones intelligently to keep track of enemy movements pretty much everywhere at all times. You can effectively destroy the entirety of enemy leadership in one blow with careful surveillance and planning. 4. Preemptive strikes and warning strikes - if things flare up, you can either decimate a strongly fortified enemy base well inside enemy's territory to demonstrate your secret super weapon or wait for them to deploy and then kill the entire leadership of the army. You're effectively telling them that next will be their king's palace. That'll force them to stop and reconsider. They'll still try by less overt means but that's a different question. [Answer] **TL;DR -- Get the airship, yo** I like this detailed scenario! Let's dig in... **Assumptions** * You mentioned the enemy has powerful land forces, but didn't list any air units for him. Assuming he has none. * Assuming your guns are primitive muskets; take 30 seconds to reload **First Approach -- Wind** Have you *talked* with the Empire guys? Why do they want to invade anyway? First move should be to find out what they want; it might be possible to dissuade them, or figure out a way for them to get their objectives without fighting. Really, a large empire should be *happy* to have a strong mountain border... one less thing for them to worry about. They might want a simple border adjustment ... put the border halfway through the passes so they can have forts, too. We could work with this. They might want access to something which is in your territory ... trade routes, diamond mines, or the like. If this is what they want, you may be able to buy them off with tribute. King will be annoyed, but he's got precious little moral high ground. They might want to annex your barony or your whole kingdom. If they just want your barony, maybe you can make a deal, become an Imperial governor, and have those million men protecting *you*! ;D Might be an ambitious prince or general wants to gain reknown for internal political reasons. Could you ... guide him to attack someone else? Okay, 'nuffa dat. Let's assume they are hell-bent on conquering the entire Kingdom. **Second Approach -- Ether** Per above, they seem to lack aerial units. You might be able to stage aerial raids into their turf with dragons and airship. Disrupt their supply depots. Destroy bridges on roads leading toward your land. Try to delay them until winter, when it becomes impossible to move troops through the mountains. You're showing them that you have weapons that they just can't answer. You strike, then fade away like a ghost. Might be enough to stop the invasion, or delay it long enough for your King to wise up and send support, or heck, the horse may learn to sing. **Third Approach -- Earth** Your best asset is that mountain range. There are a limited number of passes they can use to attack you, meaning that (a) they have to funnel through that area, and (b) they can't overwhelm you with a full-border attack. Fortify your passes. Get your dwarves to build successive defensive walls every mile or so. Make it prohibitively expensive to carry through to your fat, helpless lowlands. Drop bombs on clustered troops from air assets. Make sure to contest the high ground above the passes. Your men can roll rocks down on the foe. With enough magic/gunpowder you may be able to provoke avalanches! *Stopping them in the passes is your best hope of victory.* Try real hard here. If they do make it to the lowlands, the sunk-cost fallacy will drag things out longer than you'd like. **Fourth Approach -- Water** We've just seen how you do well at bottleneck locations. Find more. You'd be surprised how few stretches of land are suitable for moving huge armies. If the Imperials break through to the lowlands, contest fords and stretches between forests/swamps. Do not engage in set-piece battle; you'll lose. You are the water; you dance away from their embrace. Bleed them at every bottleneck, then flow away. Consider training dragoons (ride to battle, dismount to fight, ride away). Not dragons, dragoons. ;D Don't forget to engage your contingency plans; you want to evacuate as many civilians (and their livestock and food) as possible *well* in front of the enemy advance. Leave nothing valuable behind. Especially food. Leave mounted units behind enemy lines; their job is to harass communications and disrupt supply trains. **This is critical. If the enemy can't feed his army, he must leave or surrender.** Remember, you have total control of the air. You can find supply caravans. You can watch the maneuvers of his army. This is a huge advantage. Also ... focus on his landships. You want them dead before the next phase. **Fifth Approach -- Fire** Let's say the enemy grinds through all this. Maybe they get lucky and shoot down your airship. They debouche into the plains near your baronial capital. You're about to teach them a new concept. It's called ... *rate of fire*. It's way easier/faster to train a musketman than an archer. Every footsoldier you have is a rifleman. Group your men into 4 sections, each of which fires in a coordinated volley while the others reload. If you have 10,000 soldiers left, you send a volley of 2500 bullets every (30/4) 7.5 seconds. This has an unsalubrious effect on massed infantry. I don't think any non-gunpowder army can take this for long without breaking. **Sixth Approach -- Defeat** Let's say it still doesn't work. The enemy is disciplined enough to soak up the ruinous casualties and routs your men. Take your survivors and flee to the kingdom proper, leaving the battered enemy in a foodless wasteland. If practical, make one last attempt to blow the passes. You've had observers with you, so word of your savage defense has spread. You've sent tutors to all your allies, teaching them the secrets of gunpowder. Your defense has given the rest of the kingdom time to mobilize and assimilate the lessons of the fighting. Remember you are just one barony in a much larger kingdom. You have a lot of friends. Friends with guns. And they are pissed. Time for the counterattack. But hey, that's another day. [Answer] Contrary to most answers, so far, I think this is going to be *easy*. First off, **being surrounded by mountains is already an insanely awesome defensive advantage**. Mountain passes make it so that a few determined defenders can swing way above their weight class. Factor in that your army is better-equipped (more magic and gunpowder,) has night vision scouts (UAV's,) and you probably don't even need a super weapon to defend your territory. But, you can build a superweapon, so why not? My #1 choice depends on the details of your mountain passes. ***IF*** there is a location you could put the giant cannon so that it could hit all major mountain passes, then go with the cannon. You don't have to spend energy on mobility, so it'll probably be stronger. If not, then go with the airship. Your strategy: position decently-sized forces at mountain passes, use UAV's to identify enemy incursions, and then use the super weapon to annihilate them once they've fed a few thousand troops in. Finally, maintain a mobile reserve and remain vigilant for the use of minor passes and commando infiltrations over otherwise impassable terrain. Even if the enemy actually punches through, you can still contain them by obliterating their supply trains and reinforcements with the super weapon and then crushing the troops trapped within your realm. Goals met: * deter anyone = how about "defeat anyone"? No one can beat you. * speak softly = your advantage evaporates outside of your mountain passes, so nobody is going to feel overly-threatened * stop the army without decimating them = mountain passes will restrict the number of enemy troops that can invade at any one time (get blown up by your super weapon at one time), so you're good here * prove your usefulness = You'll win, so I hope that's enough here * not be threatened by the elite nobility = it will be harder, but the mountains should serve you well even against similarly-equipped forces * positive future prospect = maintaining one airship/cannon won't be too expensive, and you should be able to find at least one trustworthy person to captain it without worrying about a coup. Historially, the weakness of mountain pass defenders is the fact that their own country and allies neglect to reinforce and resupply them or the enemy goes around them. Since you are surrounded by mountains and appear to be quite stable and dedicated, these weaknesses are not yours. [Answer] I tentatively suggest that you can at least hold them off as long as you like. > > you can use magic, which is limited to time-space manipulation. > > > A gradual increase in the local gravity field as they approach will render their efforts more and more wasteful to the point where they cannot continue further. Calibrate this to a desired 'distance from capital', then unleash with a mix of the other answers people might come up with? ...I reckon the approach would exhaust them long before then. To compliment, you can sweep them with microwaves (as light) from the top of the tower using the big diamond-thing and some sort of modulating setup. (details elusive). Amplify accordingly using various tortoise body-parts and they will be sufficiently deterred long after the burning sensation stops them even facing front. The deterrent may emerge on its own after a wasted generation of approaching forces realise they've become sterile. [Answer] Airship. Everyone is looking at it wrong. An airship or two is not going to be enough to be militarily effective given the size of the forces. While it could do nasty things to ground troops it can't be in enough places to win the war. What it can do is fly high and bombard enemy cities. Fly over their capital, toss out a big load of stones, along with a note (many copies to be sure they actually get one) "If you do not immediately cease your attack upon my nation your cities will be put to the torch one by one. You have no weapon that can reach high enough to harm this airship and we have supply caches sufficient to burn your empire to the ground even if our lands should fall." ]
[Question] [ An ancient human like civilization exists on a planet like our own but warmer, with more deserts and smaller oceans. Climate change is forcing the daytime temperature slowly upwards. What measures might such a civilization take to protect itself from the increasing heat and roughly what sort of temperature would be survivable long term? I understand what ancient civilizations did historicaly, but I'm more interested in different approaches that might be used at higher temperatures. They have access to fresh water in deep wells refreshed by an aquifer charged by rain fall in a distant and inaccessible area. They are also near to the sea. The crops they grow have a similar heat resistance to the most heat resistant plants that grow in our desert regions. They are trapped in their current location by oceans and mountains so they can’t escape. **Edit** Clarification concerning "ancient", "human like" and "civilization" This ancient civilization has no high tech, the human like beings only differ in insignificant ways from real humans. The answer can be based on any ancient human civilization prior to 400AD, but in the absence of any compelling reason otherwise I suggest the ancient Egyptians would be suitable. But their motivations would be more directed towards surviving in a warming environment than pyramid building. [Answer] Two of my favorites for this scenario. **Dig.** Fresno is pretty close to what you describe. This guy Forestiere bought land sight unseen thinking he would grow fruit and nut trees but on getting there realized it was worthless. So he dug. When he got low enough, he planted the trees. [![Forestiere underground gardens](https://i.stack.imgur.com/8ZAXt.jpg)](https://i.stack.imgur.com/8ZAXt.jpg) > > Take a tour off hwy 99 and visit fresno's best kept secret > •A > hand-built network of underground rooms, courtyards and passageways > reminiscent of the ancient catacombs. > •Unique fruit producing trees, > shrubs, and vines growing underground - some over 90 years old! > > •Ancient Roman architecture - arches, vaults and stone-built walls. > > •Underground micro-climates - temperature variations of 10 to 30 > > degrees! •Underground home of Sicilian visionary and self-taught > artist/builder Baldassare Forestiere. > > > <http://www.undergroundgardens.com/> --- **Qanats.** <https://en.wikipedia.org/wiki/Qanat> The qanats are really excellent. They are ancient long distance underground waterways. Maybe when you state in OP that your people are getting water from distant rain and you are aware of the practices of ancient civilizations, you know about the qanats. A think I think is really neat about them is that in addition to watering your plants, if you build over a qanat it can cool your house; air in the qanat is cool and you can pull it up into your house with the updraft from tall chimney. From linked Wikipedia. [![qanat cooling house](https://i.stack.imgur.com/GTeP3.png)](https://i.stack.imgur.com/GTeP3.png) --- **Saltwater canals.** [![Amsterdam map](https://i.stack.imgur.com/99G81.jpg)](https://i.stack.imgur.com/99G81.jpg) Water can locally reduce temperatures. This is why fountains are in public squares in hot places. Your folks are near the sea. I propose that surface saltwater canals could run through the communal areas of their cities. This would cool things a lot and could be useful for transportation too. These could be connected to an estuary and so the water would flow back and forth according to the tides, or just be directly contiguous like Amsterdam, above. The moving water would absorb heat. One could have windpowered saltwater fountains as well for extra heat absorption. Having moving, nondrinkable water coming thru the city would also be good for sanitary reasons. I cannot think of an example of a desert city with canals like this - if someone knows one please link it up or feel free to edit this answer and add a screenshot. [Answer] Much depends on *how much* fresh water they can harvest, either by wells or by desalinating sea water. To keep reasonably cool in hot climate needs a lot of water, to drink, in the first place, but also to cool down other things (animals and plants) less heat resilient. Human body can resist very high temperatures (up to 60°C and more, for shorter periods) with enough drinking water, but "useful" animal and plants have a narrower range. Humans and animals can also resort to bury into caves (just 20m underground temperature is almost independent from outside heat), but that is not the case for plants needing light to thrive. Being an "ancient" civilization it doesn't (supposedly) have access to means to pull cold water from some hundred meter undersea (close to 4°C), so they should resort to keep wet some large overhead cloth; evaporation can lower temperature under it more than 10°C, which may be enough... but will require a lot of water (using sea water is dangerous for salt accumulation which won't be healthy for plants). [Answer] Heavy clay structures, with thick walls and deep windows to limit heat transfer ([adobe](https://en.wikipedia.org/wiki/Adobe)). Water cooled structures: a large water reservoir on the roof, covered from direct sunlight put open to evaporation, connected to pipes in the walls. Would require a lot of energy pumping, but also doubles as a gravity based running water supply. [Building inside a rock formation](https://en.wikipedia.org/wiki/Petra). [Optimizing location to minimise heat transfer](https://en.wikipedia.org/wiki/Feng_shui) [Answer] Taking from David Eddings' Dagashi, they might keep talking to a minimum to preserve moisture, possibly developing a sign language. Are there large animals in your desert? Some might find a way to make a boat if the bones are large enough to make a frame and cover that with skin. That would be one way to escape. (Or if some areas have just enough trees to make a Polynesian-style ship.) If slavery exists, the wealthy would probably have human-powered fans akin to slave owners in the American antebellum South. [Answer] The limit for long term exposure is that the wet bulb temperature has to be lower than their body temperature. Otherwise you can't discard the heat. Animals with a higher normal temp can tolerate a higher temperature. You can get some help by spending days underground, and doing your work during the night. [Answer] Further to the answer above quoting the [Forestiere Underground Gardens](http://www.undergroundgardens.com/), caves have often been used this way throughout history. In some cases people used existing caves, but it was a natural step to engineer complete underground settlements, taking advantage of the thermal mass of the rock to moderate temperatures. The many cave systems in [Cappadocia](https://en.wikipedia.org/wiki/Cappadocia) are a perfect example of this, where entire villages were built primarily underground. Cappadocia only had the houses underground, of course. The Forestiere Underground Gardens adds an extra element to this by also moving agriculture at least partially into the underground domain as well. ]
[Question] [ As I understand it, a massive battle with lots of bloodshed can cause pieces of land to become infertile, due to the amount of salt in the blood the land has to soak up. If this happened, **how long would it be until the land could support trees again?** I realize that the answer to this question is probably going to change with the scale of the battle, so I'm looking for some sort of equation that will allow me to calculate the time. Let me know if you need additional details. [Answer] Blood does not contain enough salt to stop plant growth, and in fact it is used as a fertilizer. Dried animal blood is sold as "Blood Meal" and deliberately added to gardens to help plant growth. During warfare "salting the earth" was used to deny the enemy use of an area for agriculture but that involved spreading actual salt in the area. There is not enough blood in even a large pile of corpses to have the same effect. So in other words - all plants would keep growing immediately. To look at the problem in more detail: The human body contains in total around 220g of sodium chloride. Of that however only 28g is dissolved into their bodily fluids and only 16g in their blood. The rest is bound up in flesh and organs. So in a worst case scenario a battle with ten thousand deaths would release a total of 2,200kg of salt. That sounds like a lot but most of this is going to be carried away by animals or consumed and the remainder is spread over a large area. If you take a worst case real scenario and say that a quarter of the salt in blood makes it into the environment then that is a release of 4g per person. The ten-thousand death battle has actually only released 40kg of salt into the ground. Again 40 bags of salt sounds like a lot but distribute it out over a huge battlefield big enough for ten thousand casualties and suddenly it is spread pretty thinly. For that many casualties the armies must have been far bigger than 20 thousand people on a side. And this is where it falls down, it is very hard to increase the concentration at any point because to get more blood you need more people. That in turn means a larger battlefield, which spreads the salt more evenly. In theory if you had some sort of massacre at a choke point you could have a localized concentration, but you are talking a very unlikely scenario. [Answer] The real question isn't about the bodies, since human remains would make good fertilizer. Rather the issue wold be the mechanism of death. If the battle took place in ancient times, with the proximate cause of death being through edged weapons or blunt force trauma, then plant growth would be able to take place right away. The main issue would be the bodies would cover the ground and prevent plant growth where they lay until the remains were fully decayed, or scavengers ate them. In most instances, the bodies were stripped of armour and valuables and then buried, which would facilitate plant growth even better since there would not be a large quantity of metals or other inorganic materials to interfere with plant growth. If the battle took place during the age of black powder warfare, the situation would be relatively similar, but there would be additional complications due to the quantities of inorganic materials embedded in the ground in the form of spent bullets and shells or pieces of shrapnel. Gnerally speaking, this would be localized in small areas, and if the water table was high, then lead and other compounds could leach into the groundwater and stunt some of the plant growth. The battlefields of the Western Front during the Great War of 1914-1918 would have a much different issue, as the ground was churned up by massive quantities of artillery focused on very small areas of ground. Not only will there be a lot of contamination of the soil, but the very structure of the soil will be changed. Explosive shells would turn the soil and bring clay and other materials from deep below the surface; materials which is missing much of the organic matter needed for plant growth. The natural drainage would also be disrupted or destroyed, making plant growth more difficult as well. Use of chemical munitions will add complications to the regrowth of vegetation as well, either directly or indirectly as animals and insects which are beneficial to plant growth avoid the contaminated areas. More modern warfare can have much more firepower, but the general trend has been to spread things out over a larger area through mechanization, as well as using more precise munitions to target things, so unless chemical munitions, nuclear weapons or biological warfare is unleashed, the effects of modern warfare on vegetation is very localized and diffused. ]
[Question] [ What attributes of a species (not space-faring) or culture could lead to reasons to not **want** or even imagine to develop near instant planetary-wide communication (Internet) technologies? The species can know about the possibility of near instant planetary-wide communication. Edit to clarify: For the purpose of this question "Internet" is only a way to achieve real time communication planetary-wide, for all the purposes and 99% of time Internet is "instant" and allow me to have real time planetary communication, the fact that is not yet 100% reliable is irrelevant. [Answer] Depending on what exactly you're going for, I can see a couple broad possibilities: **1. They already have an organic alternative, and no desire for privacy:** If they're already capable of something like telepathy, then it might not occur to them to invent actual communication technologies as their communication is already perfect. Even if the range of the power was only a mile, they could still pass messages along at the speed of thought from person to person. If they evolved with telepathy, then they probably wouldn't have the same concept of "private thoughts" as we do. **2. They don't have enough trust:** If they evolved in very small, social tribes/troops/herds/etc, and only trusted members within that very small circle (say, a dozen members or less), then they'd never feel the need to communicate with some stranger on the opposite side of the planet. They'd probably also not trust any other groups with their messages, so they wouldn't be willing to send data through routers not run by their own members, regardless. [Answer] One thing is that a free repository of information that could be accessed by any, including non humans (such as a machine scraping the internet) could be dangerous at the hands of a strong AI. So I can see societies becoming much stricter at only allowing humans to move through the web if it was feared that a machine scraping it with a sufficiently strong model of intelligence could use that information to harm us. [Answer] This is bordering on idea generation, which is discouraged here. Anyway: * Internet and instant communication are not the same. The *look and feel* of the internet depends on websites on servers which host content and millions of people with browsers on clients to read and add content. Things would look different if the message protocols were more restrictive, e.g. mail only. * The internet architecture allows clients and servers to hook up in an unplanned fashion. People who run TLDs are free to add domains, people who run domains are free to add servers. There could have been architectures which insist that every networked computer is registered and authentificated by a central authority. If there *was* such a scheme, nations would insist on running their own national nets. No more scammers from Nigeria, no more hackers from China, no more snoopers from the NSA. (Or fewer of them.) Assume a more paranoid cold war, and that no open architecture gets started. If all you have is mail protocols, something like dial-up with a 56k modem is enough. The home computer dials up to **one** mail server at some institution (big company, university, government) and those are on an orderly network. Somewhere some harried admins have a map with **all** the servers in the world, and try to manage the message flow. [Answer] > > What attributes of a species or culture could lead to reasons to not want or even imagine to develop near instant planetary-wide communication? > > > You are assuming that a *species* is social in the way we are as humans. That's a pretty hefty assumption. We've become social creatures because it gives us a huge evolutionary advantage as a species. Cooperation is perhaps the most important part of our survival, but that's not true of a lot of life on earth. Think of all the solitary hunters. Or things without brains. Possible attributes of a *culture* (this implies the species is social) wouldn't want planet-wide communication: * They have a different social structure where delegation of tasks is de-emphasized, such as a hunter-gatherer society. This means that the need to communicate to anyone beyond walking distance is almost non-existent. They have no need for it, so they never come up with the idea. * They live in an Eden-like environment and no longer need to rely on communication for survival. This change could be very gradual. * A past planet-wide catastrophe related to this kind of communication or its implementation makes the concept taboo. * It is a culture of bacteria in a lab. [Answer] The obvious answer was that the microchip was never invented... But let's say they had computers but still no Internet. **They didn't have a cold war** The dawn of the Internet was in the 1960s. The idea was to have a network of computers communicating with each other and withstand attack from their enemies. If one line of communication was bombed then many others could still be used. Without this threat, and an interest in Information Technology by the U.S. government/military, there would be no Internet. And I specify the *U.S.* because other countries didn't develop similar technologies (so it's quite easy to see why it wouldn't necessarily happen) Now of course, what brought the Internet to the civilians was the ability for educational institutes to share data between each other, but I can't really see them having developed the infrastructure required to facilitate the Internet without the groundwork first being laid by the military. I disagree with the posts about people's fear of loss of privacy, etc. The benefits of the Internet outweigh that fear, especially during the 1980s when transmitting data back and forth was not too much different from speaking to them on the telephone in terms of privacy loss. In a parallel, no one complains by the loss of privacy generated by fax machines... And unless you were living in a repressed society where such research was expressly forbidden, there would still be the interest amongst the people actually developing it (as opposed to people who feared it) that it would still get developed. [Answer] I think the key reason would have to be social. They didn't develop the internet for all the reasons that people take 'time out' now. * People ignoring each other and instead looking at phones. * The comments on YouTube/popular news sites. * Facebook/Twitter being overwhelming sources of pointless noise. * Personal privacy - Plenty of people don't "do" the internet because they don't want to share anything. * Surveillance fears - with ubiquitous comes unrivalled intelligence gathering capability. Some countries have enacted really harsh laws due to a 'bad experience' (e.g. Germany) which if enough did, might be sufficient to cripple a nascent internet. * Hounding/abusing people (see: Gamergate) - enough incidences might get people to wonder if it's actually worth it. I don't actually think it would take too much to 'tip the balance'. All it requires is a bit more privacy consciousness, a little more 'real world > virtual world' and a bit less narcissism to reduce the acceptability of selfies/status updates, etc. Now, we've gone too far down the road, and 'everyone' can see the value delivered by the internet. But there's still people who don't really "do" it, because they don't like it, fear it, or usage will put them at risk. [Answer] What I thought when seeing the question is the "High Castle" alternate reality were Germany and Japan prevailed in the second world war. I wouldn't think they would embrace the internet the way we know it today. They might very well develop the technology and use it on a limited basis for some military and business things, but for the average person the internet would be a mystery. Any planet that developed a society that leaned toward totalitarian would keep something like the Internet we know very limited. Wide spread open communication and totalitarian societies do not get along well. Ironically they would miss that great spying on the public tool that our current governments have taken full advantage of. (For our safety of course) [Answer] Internet as it formed at the brink of millenium is a fluke. I remember reading a tongue-in-cheek conspiracy article which argued that even if in the field of mathematic research we had two incompatible standards (Mathematica and Matlab at that time), it's improbable that a single earth-encompassing standard for communications would emerge. The zeitgeist, by the way, (surveillance, national three-strikes like laws, etc) is for the Internet to be torn onto semi-walled national webs, so value it while it lasts. Not that the most internet users will notice, as the internet for them means their social network site of choice. That aside, there are several variants you may want to consider. Imagine an internet **without anonymity** at all. You go in under your realname, you need to have your local authorities agreement to create a website (like what you need when you're opening a real-life establishment). Imagine South Korea's internet, just slightly exaggerated. This will make a drastically different web from what we know. For the cheap way out you might describe some oppressive government. However, realname policy worked quite fine in FidoNet, without any government oversight. Your aliens may hyperreact (from our point of view) to any slights (it's in their culture), so to curb any violence the disclosure of personally identifiable info is mandated by benevolent authorities or cultural consensus. Sure, this approach may not sit well with someone, but the practice of selling phones locked in for SIMs of a particular cellular operator also seems outlandish to plenty of non-US people. You may have the world-wide network operating on **different principles**. Imagine a world-wide network based on FTN technology. In fact, just dig into 90s, you'll see it. You have the throughput way lower, with all the synchs and mail-exchange times, your mail may take three hours to get to the other side of the planet, but it worked and it will work. You may have **different, hardly compatible networks** developed in different state-like entities. France had its own quite robust network Minitel in 80s (though in the beginning of 90s it was outdated by internet). You just need a strong not-invented-here bias for independent networks to survive. The internet won't be the way we perceive it now if only a **limited number of people** could access it (think Eternal September): * If you're cheap, again, you may go for an oppressive government repressing freedom-loving rubber-mask humans. * For a moderate variant let's imagine that access terminals just cost too much (think of ARPANet). * For a truly alien variant your extraterresterials may be just not that socializing. Imagine a civilization of city-states where people are just as interested in talking with other states as you are interested in delving into a zoning debate in some Indonesian province. Sure, you can, but what for? So, only a small share of population will use such a network, scientists, diplomats, xenophiliacs, this sort of people. They will shape their web in a very alien way. [Answer] **Religious prohibitions against information sharing or just plain anti-science** would be two of many reasons to not develop an Internet-like. In human history, religion and superstition were huge stumbling blocks that stood in the way of human progress for hundreds of years (and depending on who you talk to, still does today). There's a very long history of primitive cultures not wanting to have their photos taken (even the modern American Amish don't like [their pictures taken](http://www.amishnews.com/amisharticles/amishand%20photos.htm)). The Amish believe that pictures are "graven images" and prohibited by the [Second Commandment](https://en.wikipedia.org/wiki/Thou_shalt_not_make_unto_thee_any_graven_image). Other cultures believe that their virtue or souls are stolen when pictures are taken of them. So while a global information sharing apparatus doesn't necessarily mean that pictures of people will be shared, it's not a far stretch that some overly superstitious religious leader will condemn information sharing by this method in the strongest possible way. (Perhaps he is afraid of being exposed as a fraud, or is just afraid of change, or is worried that young people will do evil things if not watched very closely, or he's "thinking of the children".) [Answer] Inspired by colmde's answer ... Or, they **did** have a cold war. Which then turned hot. They've rebuilt civilisation amidst the wreckage. They have legends / poorly documented history containing two or three grains of truth and one grain of "Terminator" movie. These suggest that if computers are allowed to form networks, they will turn on their owners. The evidence is all around them, in the form of green glass lakes and residual radiation and fiber-optic cables everywhere that wasn't melted. If you want a back-story, this happened when their technology had advanced to where I expect ours will be ~2050-2100. All-out cyber-war by then will be as much a threat to civilisation as nukes are today, and the one might easily lead to the other. Alternatively, something not unlike Cylons are known to have existed. They were defeated, at great cost. No way is anyone going to risk re-creating them. (The back-history of "Dune" is not dissimilar. Or - shudder - the Blight in Vinge's "A Fire upon the Deep", lurking in latent form in every archive). [Answer] Suppose they come from a society that constantly resorts to war (much like ours does.) Rather than attempting to establish a world government with all of it's internal conflicts, the cultural paradigm is that prosperity is achieved through a balancing of power between insular factions. (this concept is thoroughly explored in the "Naruto" franchise.) Space exploration opens up new possibilities. You could colonise a large asteroid, attach thrusters, and sail away at close to the speed of light, and never face the threat of war with your own species again. It is a concept that has captured their imaginations. Instant communication defeats the intention of insulation. You would want colonists to be free of all political friction originating from the home world. [Answer] Maybe they don't have anything to share? Why would any animal on our planet want communication like that? It requires a desire for social networking or shared information or some kind of business. Not much else going on in our internet. A more darwinistic approach to live might be "don't depend, stay invariant, don't share, manage alone". [Answer] Paranoia over space aliens learning all their secrets and invading. Extreme sensitivity to electromagnetic radiation. (Cell phones cause instant cancer.) Shortages of key raw materials. Alien sabotage. Genius, love of learning and extreme NIH (not invented here). Everyone lives for centuries. If they read the latest mathematical or scientific theories, then it is like getting the answer to the daily crossword - it ruins all the fun. Everyone wants to be their own Newton - Gauss - Einstein - Watson - Crick - Von Braun. Everyone can run as fast as the Flash and talk as fast as an auction dickerer. It is so much better to talk to a person face-to-face anyway. Highly litigious people. The smallest bit of inaccuracy is punishable by {insert really bad outcome here}. [Answer] That your Aliens would use some form of communication is given, provided they aren't some symbiotic planet spanning organism, plasma or fungus. Yet even if those non-indivual Planetary organisms were to be populated by symbiotic parasites in order to maintain them, there would still be a form of communication between parasite and the host and between the parasites the self, the Planetary organism communicating the with itself, being a unity. How does this relate to the reasons for no Internet? By showing that if those Aliens were not to choose redundant decentralised network protocols to exchange their messages, the different factions would still exchange information, perhaps on a less open, less decentralised, and even low-level of technology. Post offices come to mind, messengers like mail-birds, and from smoke signs with little information to something more informative like a laser coded message aimed at the addresses receiver and waiting for his laser responder for reply. If the technology suffices to transmit the amount of Information your Aliens send around, then what comes around to them will be more of the same. New technologies might even be uncovered but deemed unnecessary as their advantages (for science?) would not justify the investments needed to convert to this level of technology over remaining at the old, time-proven standard. [Answer] How about this: They simply don't like internet. You would think why. Because they are different and they do not have to be like us. ]
[Question] [ The primary mechanism of “faster than light” travel in my story is via artificially formed wormholes that can be created to transport a craft to a reasonably precise location. Would the existence of the ability to create an artificial wormhole mean that time travel would also be possible, or even a side-effect of this method of travel? I’ve found seemingly conflicting information regarding this, so I would greatly appreciate someone’s help understanding the implications for this. [Answer] Be clear to distinguish two things: FTL effects and [non-simply-connected space](https://en.wikipedia.org/wiki/Simply_connected). Given a wormhole network subject to some chronology protection (see [Logan's answer on that subject](https://worldbuilding.stackexchange.com/a/245250/62341)) there isn't necessarily any actual FTL going on at all... everything is moving at or below the speed of light at all points, but space-time is no longer simply connected and you can travel take the shortcut between points A and B without exceeding C. There are a lot of restrictions that your protected wormholes have to comply with regarding the shape of your wormhole network (probably a tree rather than a grid) and how the wormhole mouths are deployed (you need to fly them to other stars at slower-than-light speeds), but so long as you follow them you'll be fine. *However.* Your wormholes, as described in your other question [If a civilization had the technology to create portals (wormholes) for FTL space travel, what physics favor their use for ships over small weapons?](https://worldbuilding.stackexchange.com/questions/245249/if-a-civilization-had-the-technology-to-create-portals-wormholes-for-ftl-space) would appear to violate causality: > > If a civilization had the technology to create wormholes for travel, why wouldn’t they use this technology to open wormholes right above their targets and launch a weapon through it? > > > Opening wormhole mouths at arbitrary points in space is Bad News. If you can open a wormhole between two points A and B in less time than it takes for light to travel from A to B, then what you've done is created an FTL transport and signalling system and suddenly All Bets Are Off, because relativity will have already come back and bitten you in your past light cone. The perils of superluminal signalling under relativity were described in the [tachyonic antitelephone](https://en.wikipedia.org/wiki/Tachyonic_antitelephone) thought experiment and I won't repeat it here, but it breaks causality. > > would that necessitate the existence of time travel? > > > Are you writing a hard-scifi setting that tries to keep as close as possible to physics as it is currently understood? Then yes, magically and instantaneously opening a wormhole at a distance means some form of time travel. If this interferes with your plans for your setting, then I can heartily recommend *not going the hard-scifi route*. Hyperspace and teleporters and ansibles are all nice things to have. If you need some or all of them, and don't want to worry about time travel, then *handwave them in*. No-one will mind. You can waffle a bit about preferred reference frames if you like, but I suspect that most people won't care very much. [Answer] No. It implies that you could try to set up a time travel loop, but not that you could succeed. The [Chronology Protection Conjecture](https://en.wikipedia.org/wiki/Chronology_protection_conjecture) suggests that, if you try to arrange a loop of wormhole paths which permits time travel, quantum field effects will result in at least one wormhole in the circuit collapsing before anything can actually traverse the circuit. So, just declare this conjecture about quantum gravity to be accurate in your universe, and you don't have to worry about wormhole time travel. The result is that you will end up establishing an effective standard reference frame for FTL travel artificially, based on how you construct your wormhole network, even though the universe does not come with any preferred frame built-in. It also implies that you will have to establish struct regulations on where wormhole-bearing ships can travel to avoid risk to other parts of the network, and militaries and terrorist groups could exploit attempted loop construction to probabilistically destroy other parts of the network. And if wormhole placement starts consistently failing at the edge of the expanding network, that's a good signal that you might be getting close to the edge of another expanding alien civilization which has established a different "Empire Frame" for their wormhole network. [Answer] The *mechanism* which makes faster than light travel possible is irrelevant. Whether FTL is achieved by means of warp fields, space distorsion, worm holes, subspace, hyperspace etc. *does not matter*. If a ship or a signal can travel from point A to point B faster than light would travel from point A to point B then the ship or the signal has travelled faster than light; this is all that matters. Whether faster than light travel, by whatever means, does or does not automatically imply time travel depends on the specific details of what exactly is meant by faster than light travel, and not on the mechanism of faster than light travel. In particular, *if* faster than light travel is only allowed with respect to a particular, fixed and universal [frame of reference](https://en.wikipedia.org/wiki/Frame_of_reference) *then* faster than light travel does not imply time travel. See [section 9.5.4](http://www.physicsguy.com/ftl/html/FTL_part4.html#subsec:specialframe) in the most excellent [*Relativity and FTL travel*](http://www.physicsguy.com/ftl/index.html) by Jason W. Hinson. For the curious: this is not a loophole in Einsteinian relativity. To the best of our knowledge, there is not and there cannot be such a thing as a fixed and universal frame of reference. (Mostly because there is no way that we know of to measure the time coordinate of an event so that any arbitrary observer will agree on it; plus, of course, the existence such a fixed and universal frame of reference is forbidden by the fundamental postulates of the theory of relativity.) But if such a fixed and universal frame of reference will be found to exist then all time-travel-related objections to faster than light travel will become solvable. As a bonus, physics will have to be rebuilt from the ground up, providing lifetime employment to generations of physicists. Win-win. The usual way of introducing such a fixed and universal frame of reference in the kind of science-fiction which is mostly soft but still attempts to be at least a tiny little bit hard is to assume the existence of a special field which extends $\rightarrow$uniformly$\leftarrow$ throughout the universe, and which is measurable so that anybody at any point and at any time can measure their velocity with respect to that field. But this is pure creative detail a.k.a. handwaving. [Answer] Both wormholes and time travel are hypothetical things. It is not established that either one of them actually do exist in real life. All mathematics, all science regarding them is *completely* speculative, not even remotely tested or (as of now) even testable in practice. Time travel requires that time is a true dimension like the three known spatial dimensions, but science has not found a single shred of evidence of its existence. Even [potentially existing retrocausality](https://en.wikipedia.org/wiki/Retrocausality) can be explained without it: it is just same causality as normal physical causality, only incorporating a lot more things from a lot broader area. No one has ever truly peeked even a fraction of second into the future or past to confirm that there is nothing more than the eternal now, the only moment whose existence we can be sure of. It is possible that there is no time dimension at all, and therefore there is no time travel either. Wormholes require that fabric of space can be manipulated in a way that two otherwise distinct locations are actually the same. This is a bit more plausible thing given that it can "be same" as [quantum entanglement](https://en.wikipedia.org/wiki/Quantum_entanglement), but at an enormously larger scale. However, still: quantum entanglement is a far cry from wormholes. So, if you incorporate either in your world, you are stepping outside of boundaries of hard science, and therefore you can define the rules as they suit your story. Or, to answer your question: wormholes can exist in a world where there is no time dimension. Connecting two locations, or making them identical, does not make it necessary to have any more dimensions apart from the three spatial ones. [Answer] I would say no, FTL travel does not necessarily imply time travel. Both ends of the wormhole are "moving" normally through time - forward through time. You are taking a shortcut, not actually moving faster than light. Therefore, causality won't be violated. ]
[Question] [ What I'm thinking for this question is that some kind of filter is put around the sun by aliens that prevents some kinds of solar energy from passing through but allows other types. Like if it stopped visible light but allowed UV. **Is there any way that the parts of light plants need for photosynthesis can be separated from visible light, allowing the plants to survive but preventing visible light from passing through?** I've tried to do my own research on this, but all I've found is that they require a nonspecific "light", and I'm not sure if this means specifically visible light or all kinds of light, such as UV. **For the question, assume that the barrier around the Earth can sort between different types of light, regardless of whether or not this makes any sense.** EDIT: Close voters, I understand my question may be slightly difficult to understand due to the nature of what I am asking, however reading the answers below should allow you to see what I am looking for, and show that there are others who understood the question even if you didn't. [Answer] TL;DR you are looking for this image: ![absortion spectrum](https://i.stack.imgur.com/WVIIk.jpg) As you can see, plants depend on those frequencies for photosynthesis. They can absorb some UV light ([wavelengths close to 400nm](https://en.wikipedia.org/wiki/Ultraviolet)), which we naturally can't see (except for some rare people who have no lens in their eyes), but that's not optimal. Plants living in such a world would evolve different pigments for photosynthesis. Life always finds a way. As for our own plants from Earth, many species might thrive, though I think most wouldn't. There is only one way to know, and I have neither the space, time, seeds, black light lamps, nor the soil to test it out. Food for thought: the ozone layer does not absorb UV light in wavelengths ranging from 315 to 400nm (see the link above), and by the graphic it seems that it is absorbed just as well as red light. [Answer] Plants can only use the frequencies of light that pass through the natural filter of Earth's atmosphere. Humans can see many of the comparatively few frequencies that Earth's atmosphere is transparent to. The Earth's atmosphere adsorbs Gamma Rays, X Rays, most ultraviolet rays, and many frequencies of radio waves. Earth's atmosphere is largely transparent to visible light that human eyes can see, a few neighboring ultraviolet frequencies, and many infrared frequencies, and in another part of the spectrum it is largely transparent to many frequencies of radio waves. > > Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with absorption peaks in violet-blue and red light. In red algae, the action spectrum is blue-green light, which allows these algae to use the blue end of the spectrum to grow in the deeper waters that filter out the longer wavelengths (red light) used by above ground green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms. > > > <https://en.wikipedia.org/wiki/Photosynthesis>[1](https://en.wikipedia.org/wiki/Photosynthesis) Since blue and violet light supports photosysthesis for many types of planets, some near ultraviolet frequencies probably also support photosynthesis for plants. I don't know if ultraviolet light alone would enough for plants to flourish if aliens cut off all visible light from Earth. But on an alien planet that didn't have an ozone layer for some reason, plants might have evolved to use many more ultraviolet frequencies that are blocked by Earth's atmosphere. Thus such a hypothetical alien planet might have plant life that survived having all light except for ultraviolet light blocked much better than Earth plants do. [Answer] Plants on earth require visible light. Animals have adapted to use the same light that is available after passing through Earth's atmosphere. On an alien planet, a different atmosphere could potentially have caused the evolution of different plants that utilize different wavelenths. But the aliens would would also have developed sight based on those wavelengths. So they could block out what we consider visible light, but they would be seeing on different spectrums. If I guess where you are going with this, I should also mention that real Astronomy analyzes radiation at every level. We are looking at visible light, infrared, radio waves, gamma particles, neutrinos, etc. so blocking your sun from one portion of the spectrum would not hide you. [Answer] Depending on *why* you want to block visible light, there is a possible solution, but it lies in the shield, not in the plants: If your reason is to prevent life from seeing space, your planetary shield could be fluorescent. It blocks visible light, but it absorbs UV light and discharges it (via fluorescence) as a fairly uniform glow of visible light on the inside of the shield. This means that the only evidence of "outside" you can see is when a suitably large shadow is cast on the shield (e.g. during a solar eclipse) (Quick note: Photosynthesis - and other processes, such as Vitamin D production in animals - required absorbing light. Colour requires *reflecting* light. So, if you take an RGB colour for your plant's leaves and invert it, then you get the visible colours that it absorbs - of course, not all of these are necessarily used for photosynthesis) [Answer] There is already a company in California doing this ([soliculture](http://www.soliculture.com/)), they are called "smart greenhouses" and use glass tinted magenta. They claim plants grow just as well in their green houses and have the potential to produce solar power as well. Take a look at this article detailing more about the idea. <https://newatlas.com/magenta-solar-greenhouses/52053/> you can also go to their corporate page. <http://www.soliculture.com/> ]
[Question] [ It's 2018. Dr. Evil tried to [rob a bank/destroy the city/take over the world] using a [unstoppable robot army/death ray/zombie ninja T-Rex]. Just when hope is lost, Superdude comes flying in with a timely one liner and vows to thwart Dr. Evil's nefarious plans. Naturally, this means a super powered fight in the downtown of a major city (and, importantly, lots of property damage). Lucky for the city's residents, due to our civil engineers, there is little interruption of service for most utilities, and life returns to normal relatively quickly. Lucky for the city's Supervillain insurance providers, these building techniques also result in minimal payouts. Given today's level of technology, **how would cities be built in response to frequent super powered battles?** * You can expect that in a large city (e.g., Chicago), a battle happens about once every five years * Super villains are difficult to draw away from the city (because cities provide a good supply of meat shields against heroes) * We maintain at least our current level of infrastructure * There aren't any super powers that can directly 'reset' an area after a battle * Super battles have been happening for long enough that most, if not all, structures in the city have been designed with them in mind [Answer] Have redundant infrastructures with no single points of failure, managed by simple failsafes. Avoid complexity (think BP gulf of mexico). A few city blocks can be leveled and the infrastructure under them destroyed, but disruption of service ends at a point just outside the area of total destruction. To cause a massive disruption, the entire city essentially needs to be demolished. Build with rugged but cheap modular units so they are resistant to damage but easily swapped out after the supers are done playing rough. My apartment got trashed, insurance covers replacement. The contractor comes in shortly after the event du jour, cleans up the mess, extracts the broken module (s) for recycling/repair, then inserts the replacement module (s) which can be brand new or recycled and refurbished. [Answer] Apart from redundancy as mentioned in other answers. Things would be built deeper into the ground and farther away. Skyscrapers would no longer be desirable, instead cities would be more spread out. * Deep supply-tunnels for electricity and water (with auto shutting-valves to seal off damaged parts) * vaults at every street-corner * Fast-lane subways to cover the increased distances Also, maybe there would be crumple zones around important/historical buildings so the super-fights had something to crash into (like guardrail on motorways for example) [Answer] It was the insurance companies that killed the high rise city block in the end. They refused to cover anything larger than 5 floors up and 3 down. City regulators settled on this count after extensive experience based on the speed with which a super powered fist fight could demolish city towers, and the amount of time it takes to evacuate a building. The few large towers that remained after the first decades of metahumans and other troublemakers throwing each other around, are largely abandoned, or slums and squats with nobody willing to take responsibility for them in such a risky environment. The city is now dominated by sprawling low rise, decentralised structures, sometimes the size of a city block, easily evacuated through large numbers of exits, and to bomb shelter grade basements able to contain the number of people expected to be in the building and the surrounding streets at any given moment. Any non-residential building of larger than two stories is required to provide shelter of this type to the general public in times of need. Larger companies have abandoned city centres entirely, choosing in favour of multiple campus-scale company towns where all staff can be accommodated. Schools are provided, and everything is a reasonably safe distance from any other equivalent facility, thus attempting to avoid the attractive vulnerability that the centralisation of large cities generates to generic supervillains. [Answer] Taking into account your last bullet point, buildings could be designed & built to descend below ground level during super-powered slugfests. Then raised above after the dust has settled. Big spaces below buildings, hydraulics, lots of electricity, and improved elevator machinery will do the trick. The citizenry will retreat to conveniently provided underground bunkers that will be fitted out like shopping malls with adequate wi-fi and telephony to enable business as usual to continue. Large TV screens will be mounted on the walls of corridors to let the bunkered populace to watch Superdude and Dr Evil slug it out. Once the battle is over, an all-clear will be sounded. The doors to the bunkers opened. City buildings will commence rising above ground level as their gigantic elevator machinery swings into action. Insurance corporation executives will breathe a collective sigh of relief. Dr Evil will be languishing in his favourite holding cell for the criminally super-powered. All this can be put down to the ingenuity of civil engineers, architects, city planners, and the generous contributions to fund these super-powered slugfest countermeasures from the insurance industry. [Answer] # Polycentric cities [Orange County](https://en.wikipedia.org/wiki/Orange_County,_California) in California is one big suburb that is actually, secretly, one big city. There are over three million people in the county, which makes it pretty big on its own. But the county is not very big, geographically. Those three million people are stuffed into just over 1000 km$^2$, which makes it surprisingly dense. For the same size area, OC has as many people as Miami or Washington DC. So it is basically a large city....except with no city center. But instead of having one city center, it has many. The three biggest downtowns are [Anaheim](https://en.wikipedia.org/wiki/Anaheim,_California), [Santa Ana](https://en.wikipedia.org/wiki/Santa_Ana,_California), and [Irvine](https://en.wikipedia.org/wiki/Irvine,_California). All three cities have a higher population density than any part of Houston, Atlanta, Phoenix or Detroit, to name a few other cities. [![Downtown Santa Ana, from silverliningrealty.com](https://i.stack.imgur.com/UfcAO.jpg)](https://i.stack.imgur.com/UfcAO.jpg) Downtown Santa Ana [![Downtown Irvine, from momentumrg.com](https://i.stack.imgur.com/cvmNX.jpg)](https://i.stack.imgur.com/cvmNX.jpg) Downtown Irvine But there is also [Irvine-Spectrum](https://en.wikipedia.org/wiki/Irvine_Spectrum), a huge outdoor shopping center surrounded by industry and business like [Blizzard's headquarters](http://us.blizzard.com/en-us/company/about/tours-faq.html). There is a tech hub around UC-Irvine; downtown [Costa Mesa](https://en.wikipedia.org/wiki/Costa_Mesa,_California); Disneyland in Anaheim; and Fullerton. And probably more. It is easy to destroy something new every five years, when there is a whole new downtown to destroy. By spreading out the job centers, you minimize the damage of any one fight, while still giving the superheroes some nice buildings to smash every once in a while. With the advancements in autonomous vehicles and the possible near-future of robot-Ubers, this sort of polycentric, auto-oriented city might be the future of cities. Already, places like Atlanta and Dallas (which are less dense than OC) are starting to grow to look a lot like it, with multiple job centers scattered around. [Answer] Your city is mostly underground and reinforced concrete was used very liberally in it's construction. Nothing is going to survive a direct hit, the objective is damage containment. Non-trivial structures will not take important damage from flying debris. Utilities are buried deep and instead of being laid out in very weird tree arrangements they are laid out like roads--any major line can take over for it's neighbors. Rather than traffic signals they have automated cutoffs that will disconnect damaged segments. Data protection is high on everyone's mind as physical destruction of information-bearing materials (not just hard drives--think contracts, identification documents etc) is much more common. This will be distributed--rather than internet service being a narrow pipe from a supplier it's going to be a fat pipe with much of the traffic being local. Instead of a 2tb backup drive, you buy a 2tbx10 cloud backup drive. It actually has 20tb of capacity but only 2tb of it is available. Once it's plugged in it communicates with those it can find. The 2tb of data you store on it is also encrypted and pushed to various other computers, they're doing the same thing and the remaining 18tb holds files from other people's systems. Data is only lost if all 10 copies are destroyed--and some of those copies are stored far enough away that's not likely. (Drives would be available in various redundancies--they simply accept as much as they push.) ]
[Question] [ So in my urban fantasy story, among other things, new fantasy races suddenly start appearing in the modern world via the system I outlined in this thread: [Reasons to voluntarily change into a fantasy race?](https://worldbuilding.stackexchange.com/questions/110352/reasons-to-voluntarily-change-into-a-fantasy-race) Long story short, for a variety of reasons, a bunch of humans have now willingly transformed into a new species, and this happens about half a dozen times over the course of two or so years. Now a few of these have features which would require specially modified clothing to fit them (different foot shapes, multiple arms, weird ears that things like sunglasses don't quite fit on), and I've been operating under the assumption that the opportunistic and profit-hungry industries of the world would be racing to put products on the market to cater to them. But it occurs to me that I don't have a good concept of how fast that would be. How long should I show these trans-species characters making due with homemade solutions before the free market starts marketing more professional clothes and accessories to accommodate their biology? What about the next times this happens? How much faster would the industry react to the *next* time a bunch of people suddenly decide to shapeshift into new creatures? **Edit: Just to give a clearer picture of the market share and profit opportunities, the current idea is that each of the first two transformations are taken by roughly 10-15% of the population (at least in America, where the story's set), while the remaining four get fewer takers at around 5% of the population each due to the changes being more extreme. By the end of year 2, humans will be 60-50% of the total population.** [Answer] Never under-estimate the entrepreneurial spirit. As soon as each new alternative form option becomes available and while the knowledge of its availability is still saturating into the general population, there will be entrepreneurs working on how to profit from this new trend. And since clothing needs are easier to predict than dietary or person-hygiene needs, these will be one of the first opportunities leped upon. YouTube will overflow with fashion show videos filled with affiliate links to small-scale clothiers. Etsy will need new categories for hand-crafted products for each new species. Ebay and Amazon will also pounce on each new market. As the pattern begins to emerge, lawyers will go proactive, crafting exclusive contracts with those scheduled to transform at the transition moment; offering monetary bonuses if the signer emerges in a new form. Then the major clothing companies who hired the lawyers can get a jump on everyone else as the new market emerges. Have no worry for clothing your new menagerie. As soon as each transformed person steps out in their new birthday suit, there will be merchants lining up to take their money. [Answer] It already exists. Mainstream media already has covered some standard fantasy races pretty extensively, so known human brands could obviously quickly offer designs for them, but it is expected that someone has already sketched up some clothes for anything you can imagine. This is an overlooked outgrowth of [rule 34](https://en.wikipedia.org/wiki/Rule_34_(Internet_meme))(not safe for work). People imagine all sorts of weird stuff all the time, but no body cares about it because it generally doesn't effect anything. If there were suddenly people looking to sell new kinds of clothes searches will turn up loads of stuff. You might get unlicensed Chinese knockoffs where the F-shirts face the wrong way produced the first week, but stylish prototypes of existing designs shouldn't be far behind. [Answer] The fashion industry *could* respond very fast – within days for an indie maker, or within months for a high-street store. But would they? It makes sense for *some* **indies** to get into it as a profitable niche market. But most will likely ignore the market, as it's probably going to be difficult to work with (I imagine there'll be a big learning curve on how to design t-shirts to fit over wings). **Boutique Designer Brands** might do some very expensive designer clothes, if it fits their aesthetic. But those things are way pricy. But **high-street stores**? Hahaha. They already don't serve a large chunk of the population – you have to fit the standard shapes. I believe the middle 80% is a typical claim, meaning about 1 in 5 people will struggle to find stuff that fits *properly* in high-street stores - of course, most people just settle for clothes that don't fit very well (I'm tall but slim, and have wide feet, so I wear t-shirts baggy to get the height, and shoes long to get the width. Big deal.) But if you've got wings or a tail, that's not going to work. That leaves the **chain specialist stores**, who cater for unusual body shapes (in the UK we've got Long Tall Sally (tall women), High & Mighty (tall/large guys), Bravissimo (big boobs)). So you'd likely get some new chains catering for these new body shapes. It'd start probably with an indie clothing maker who starts to specialise in trousers for tails, finds the market large enough to do it full time & then to subcontract the actual making to India. After running a store in Camden for a year & getting increasing online orders, they'd get a feel there's enough market to set up another store in Birmingham, then it'd grow from there. But it'd take quite a few years before there were many stores around. Now, with your edit, you're suggesting a very high uptake of modifications. That sounds *extremely* high. But ok. High street stores probably aren't going to deal with a 5-10% uptake, or they might offer a couple of designs just so they can claim to be 'inclusive'. Once it gets larger, they'll think about it, but they – and everyone else – is likely to be blown away by that speed of uptake of significant body modifications. [Answer] Behind the scene the markets work really fast. Entrepreneurs are looking for new opportunities all the time, and some types of clothes for fantasy races will come out even before anyone became this type of race. To give you an example from our world you can look at autonomous cars. They are still on testing and no one knows if or when they will come out to the public, but you won't believe how many startup companies already develop gadgets for them. [Answer] 6 months and the factories in china/asia will have the freighters going to the west full of them. You could see how long it takes for factories to adapt to new designs/trends and nowadays it is quite a short turnaround. If someone orders designs from them, like something practical to wear, then other such shops will start producing similar items - if your fantasy conversion is global then the timeframe will be even faster due to there being immediate market, at higher profit than normal clothing they export, in the vicinity of the clothing factories. I live in Thailand, I could if there was an opportunity find someone to make a new t-shirt shape, have one factory cut them from canvas, have someone print something fancy and edgy on them and have different locals sew them together. I could have a set to send off in a week. A lot of cheap t-shirt a lot of the production is fragmented a little bit like that, you can buy precut cloth canvas from one place, other people do printing, other sew it together, it's all a connected network and a lot of it isn't even big factories so it would be very flexible to providing odd shapes. I'd give it one year for the market to be saturated and not believe in a story where they would have to make do with homemade solutions past 6 months. It is also fairly simple and inexpensive to just buy clothing made just for you in Asia. I say inexpensive in western terms, but of course it's 25x more expensive than just buying a shirt at a market. For simple shoes it's not that much different either. If you can make a design for a crocs copy to fit their feet, it's a few months. [Answer] "different foot shapes" I think this would be hardest. There'll be sufficient home seamstresses to cut and sew cotton or wool into various shaped smocks, dresses and tunics to cover up pretty much any body. Long lasting footwear giving protection and support is another matter. Perhaps they have hooves that can be nailed up with metal 'horseshoes' ? Supportive underwear (thinking bras) may also prove challenging. And then you get into sanitation products, cleaning, cosmetics, contraceptives, medicines... ]
[Question] [ In the two latter periods of the Stone Age, the Mesolithic and the Neolithic, technology improved significantly. Their predecessors, the Paleolithic people, used roughly hewn flints as weaponry and tools, but the Mesolithic saw the wider use of more sophisticated implements, composed of wood, bone, antler and cordage as well as flints. Furthermore, the people of the Neolithic developed polished stone tools, among other things, which were more effective. So, what is the closest a Neolithic or ideally a Mesolithic person could get to making a sword? I say "what is the closest" because I presume that the main impediment would be how the stone weapons shatter on impact with another blade. Instead, could they perhaps fashion a weapon somewhere between a very long knife and a sword? Before I post this question, I'd like to ask a few things of you. If there are any errors in my question, or if there's something else impractical about this whole idea, by all means say so in the comments, but without any hate please. If you point it out to me, I'll edit it as soon as I can, and thus the crisis is resolved. Edit: So, I've gotten a few answers now about real Stone Age sword-like weapons, or clubs embedded with microliths. On that note, I'm going to take the question further and ask - **could Stone Age people build a sword that is essentially an elongated flint/bone, with one, thrusting blade?** [Answer] There are a few options I can think of. 1. [Macuahuitl.](https://en.wikipedia.org/wiki/Macuahuitl) A weapon used by the Aztecs (and others) which consisted of a wooden sword with the edges studded with obsidian (volcanic glass). Interestingly, these obsidian blades could be sharpened further than steel at the time, meaning they were sharper than the Spanish swords, although much more prone to edge damage. 2. [Shark-tooth swords.](https://en.wikipedia.org/wiki/Leiomano) Many island societies like the Hawaiians and Polynesians made flat wooden clubs studded with shark teeth. Many of these are also very sword-like in form. 3. [Mere.](https://en.wikipedia.org/wiki/Mere_(weapon)) Again similar to a club, but with an unbroken sharpened edge, is the Polynesian Mere constructed from a solid piece of polished jade. They have also been made from hardwood, whalebone and stone. As an alternative that I haven't seen in our cultures (doesn't mean it doesn't exist! I'm far from an expert) is a formed bone sword. If your people have megafauna available then they could conceivably carve a bladed weapon from bone. [Answer] Yes, this is a Mayan sword made of obsidian. Without hilt (probably wood) it is still 68 cm long (almost 27 inches), which makes it a sword and not a dagger. [![enter image description here](https://i.stack.imgur.com/FCol7.jpg)](https://i.stack.imgur.com/FCol7.jpg) You just need a huge piece of obsidian and a lot of patience. Flint was also used to make knives. But there were flintknapping blade cores 40 cm long, with a hilt they would fall in that intermediate area between long dagger and short sword: [![enter image description here](https://i.stack.imgur.com/Teo3b.jpg)](https://i.stack.imgur.com/Teo3b.jpg) The hilts could be made with bone and quite long: [![enter image description here](https://i.stack.imgur.com/wB8Hd.jpg)](https://i.stack.imgur.com/wB8Hd.jpg) Bone can also be sharpened, although it is only a piercing weapon: [![enter image description here](https://i.stack.imgur.com/P3xDY.jpg)](https://i.stack.imgur.com/P3xDY.jpg) Also check: <https://gizmodo.com/5994118/15-human-weapons-made-from-animal-weapons> [Answer] Surprisingly close. Aztecs had wooden swords with obsidian blades able to decapitate horses in one blow. They had no point though, so they could not be used for thrusting. [Answer] On the [wiki](https://en.wikipedia.org/wiki/Sickle) page for sickles is a nice stone age version, this should be easily extended to become a sword. There are much nicer versions of this seen on a Columbia university video of World History 8000 BCE - 1500 CE in one of the first videos. ]
[Question] [ The setting is medieval fantasy (for example, D&D) with *some* magic (although I would prefer solutions without magic). # "The majestic canyon city of Hurr, the gem of the Durr desert or whatever" [![City carved into canyon walls](https://i.stack.imgur.com/SsRfu.jpg)](https://i.stack.imgur.com/SsRfu.jpg) *(Example image. Source: [Pinterest](https://www.google.it/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0ahUKEwion6SW8evYAhUPmrQKHXzeBXIQjxwIAw&url=https%3A%2F%2Fwww.pinterest.com%2Fpin%2F443604632026938591%2F&psig=AOvVaw2hjKQe5UQrvEve2AlwP2B4&ust=1516721153088856))* The city is entirely built into the **"walls" of a canyon** (pretty much like the Grand Canyon) which has a flowing river on the bottom. Most of the buildings are on the side of the "cracks", but some can be constructed on the **flat top.** Suppose there are a **few entrances at ground level** (e.g. where the river gets larger and enters the plains outside). **Few to no buildings are built on the bottom**, most of those being infrastructure related to water (or walls and gates, in the outermost parts of the city). **Food** is gathered via hanging gardens and terraced farms inside the city. The city came to be because of the humongous quantity of valuable gems and materials present underground in the area. Obviously, this makes it a target for attacks. **So how could such a city effectively defend itself from sieges, with medieval-fantasy technology?** (*some* magic is acceptable, but I don't want stuff like "a wizard makes the city invisible to the outside") Technology level is comparable to that of D&D dwarfs, so something *a little steampunk-ish* is acceptable (e.g. they probably have huge dams to control the flow of water, and a good hydraulic system) **What are the biggest threats?** (I'm assuming water shortage and an "attack from above", although I'd say the latter would be pretty impractical) ## More information: The "canyon" would look like Mount Conner (Australia) from the outside: [![Mount Conner, Australia](https://i.stack.imgur.com/vl547.jpg)](https://i.stack.imgur.com/vl547.jpg) *([source](https://www.flickr.com/photos/nazgulhead/9634513681/))* that is why I say that getting a decently-sized army on top would be impractical at best. This could be the city's layout, approximately: [![Drawing of the city made with Paint](https://i.stack.imgur.com/BLzKP.png)](https://i.stack.imgur.com/BLzKP.png) (I know it looks awful, but I had to use Paint) The layout of the canyon itself in the image is random, it's just to give an idea. Dark gray area is "mountaintop" area, blue is the river, green is the plains outside. The mountain is connected to a taller mountain range, from which the river originates. I can see the city having many alternative escape routes for the water, so as to counter any outside attempt at flooding the city. The two lines in brown are the gates. Food is harvested from the terraced farms (both on top of the mountain and inside the canyon) and kept in underground granaries. I could see there being underground escape tunnels (that perhaps allow to bring food to the city undetected) [Answer] Defending this canyon city against Siege doesn't entirely work with standard military practices, but it is very do-able. You do have a lot of positive things going for you, so we'll start with those. The fact that you mentioned that it's in a desert and that this is a fantasy world helps. A lot. # Good Stuff ### Water supply Assuming you have a proper river in your canyon, not some mostly-dead stream, you have a water supply that is very hard to mess with. Because... 1. Once a river has dropped into a canyon, diverting it back out of the canyon is impossible. Any attempt to cut off your water supply would require them to travel all the way to wherever the river first drops into the canyon, then travel far enough up-stream that it won't just flow around your obstruction and drop back into the canyon anyway. 2. Poisoning an entire river is HARD. You need a constant, high-volume inflow of toxins, because the toxins keep getting washed away and diluted by the massive volume of water that is moving through there. It's not like a well, where you can toss some corpses in and call it a day. Historically, the city of Babylon was built straddling a river and took full advantage of the second point. It was taken after the Persians diverted the river and came in through the water grates. But as long as the canyon you're in is significantly longer than your city is...they're going to have a hard time plugging it up. That said, you want to divert some of that river down into some unused tunnels to serve as a back-up cistern. People have turned islands into peninsulas in the name of capturing a castle...so don't assume your river is invincible. ### Food Using D&D as an example here...there are entire civilizations in your typical fantasy setting that live completely underground and grow all of their food in the complete absence of sunlight (see: The Entire Underdark). If Dwarves can have vast cities that can feed themselves without ever seeing the sun, you can do the same. You really don't need to worry about running out of food at this point. So, don't just rely on your terrace farms...go talk to them dwarves and get your hands on subterranean crops. Make use of all those tunnels you dug out looking for valuables, and grow food. ### Stone Construction The buildings of your city aren't flammable. This is good. The walkways and stuff (detailed far below) may be...but that's fine, they're supposed to get destroyed in a siege. ### The Desert You mentioned that Hurr resides within the *desert* of Durr. Deserts are *phenomenal* natural defenses. Little rain means little plantlife means little animal life...which means that an invading force is going to have a hard time finding food. Additionally, if you in a hot (or cold) desert, the invading force has to worry about exposure to the elements. Heat Stroke will be a very real risk to them. Just getting an entire army to Hurr will be difficult, not to mention having to lug siege engines along with you (because there are no trees near Hurr apart from what may be growing down in the canyon). Thus, an invading army is only going to have what lives along the river as forage. They'll strip that bare pretty quickly. And, the bigger this desert is, the further they are going to have to travel to find provisions or ship them in. ### Encirclement is nearly impossible If this plateau/mountain is large enough to contain a massive canyon with a big city in it...it's huge. The enemy force is going to have a really hard time encircling the entire thing. If you have hidden passages that lead out of the mountain, you can probably come and go almost as you please. This continues to apply even if they take the top of the plateau. The more easily you can slip out of your city without being caught, the more easily you can sneak around and set all their stuff on fire. Or sneak in provisions. # Bad Stuff ### If they get on top the 'mountain,' your city is in trouble. And the mountain is *BIG* Standard medieval military doctrine is that being on high ground is better. You can see further, shoot further, drop stuff on your foes, etc. Gravity is working for you when you have the high-ground. Even if the canyon is in it's own little stand-alone plateau, you don't need to put a large army on top in order to cause some serious havoc. A double-line of archers firing down into the city would rapidly kill anyone exposed. And a tall canyon would result in the people on the floor of the canyon having an extremely hard time firing projectiles up at the top. You're going to have to defend the *entire mountain* as if it were walls. If enemies reach the top, they can attack your gates from above, or just skip past the gates and start attacking your city. All they need to do is get a small team up the cliffs somewhere you don't catch them, and they are going to wreak all manner of havoc. (Kill the crew of a few guard towers to provide a 'blind spot' for more troops to scale the wall. Get behind the gates and open them. Dress like your people and set fire to farms and poison cisterns. And so on.) And if they can 'take' the top of the plateau, they're going to start getting siege engines up there to fire down into your city. In short...your outer wall is *vast* and you have to defend the whole thing. If you can field enough troops to properly man the cliffs...then this place becomes massively defensible...but this mountain sounds huge. # Effects of the above ### Long-duration sieges favor the city Any attempt to starve you out is going to go poorly. To starve out a fortification, the attackers need to have enough provisions to outlast the defenders. Because of Hurr's location within the desert of Durr (and the existence of fantasy-style dwarf crops), the city must be mostly self-sufficient, and can keep a good sized chunk of back-up farms safely in tunnels accessible from within the city. So the attacker is sitting in a desert with a very limited ability to forage. They can forage along the river where it leaves your canyon, and that's about it. Meanwhile your city has spent the bulk of its existence living on what it can grow in the tunnels and along the river. They are not going to outlast you. Their only option is to assault the city. ### Physical Defenses 1. Set your gates back inside the mouth of the canyon a bit. This limits the angles from which your gates can be fired upon with siege weapons. Make sure there are towers either carved into the walls, or sitting on top of the edges of the canyon overlooking this little path leading to the front gate. If you can force enemies into a 3-sided death-box to assault your gate....they probably aren't taking that gate by storm. Make sure there are grates for water to get through...you'll need to defend these vigorously, as they are points of vulnerability. 2. You need to treat the outer cliffs of the mountain this canyon is carved into like walls. Build towers, man them, kill anyone who tries to come up the the side. If you can have your diggers work to 'smooth' the outside of the mountain to make it harder to climb, that is also good. 3. Routes from the lip of the canyon to the city should be destructible. If the enemy takes the plateau, you don't want them to be able to just walk their way down 4. Build entrances to buildings above 'ground level.' Build ramps, walkways, bridges, etc. to provide access to and from the floor of the canyon. You have lots of money from the precious ores and gems you're harvesting...import that wood. Don't have *too* many of these, though...you don't want to give the enemy too much in the way of combustibles to target. 5. Buildings should be interconnected inside the walls. Think fortress here...choke points are your friend. Try to tunnel under the river if you can dig deep enough, so the two sides of the city are connected. Choke points should be rigged so that you can cave them in if you're losing them. 6. Build important stuff like archer posts in narrow parts of the canyon. Typical anti-wall siege weapons (catapults/trebuchets) fire in a parabolic arc. A narrow stretch of the canyon will interfere with this arc and prevent topside-based weapons from hitting your buildings without a lot of work * Additionally, put really important stuff deeper inside the walls where outside projectiles can't hit. 7. Air vents, Air vents, Air vents. You have dwarvish-level digging tech: drill lots of tubes leading to random spots along the walls of the canyon so that smoke can get out and fresh air can get in if they collapse your entrances. Or, y'know...build fires in your entrances. Which is generally the best way to wipe out everything hiding in a cave 8. Route parts of the river into underground reservoirs. In case someone takes the canyon floor, you want a back-up supply of water. ### Tactics Your goal in defending this city is to draw this siege out as long as possible. The longer you make this drag on, the more enemies the desert will kill for you. Between the river and your fantasy-style dwarf farms, you're in good shape for a prolonged siege. Your walls (both the ones you made, and the walls of the mountain) should be defended in typical siege-style. Archers, boiling oil, the works. Your enemy is going to have a hard time building siege engines in a desert, and undermining is probably not happening against the very limited wall-area they can target. Any attempt to flood you out is limited by there being multiple water-exits from the canyon, and the fact that waiting for the entire canyon to fill with water would take a long time and, again, time favors the defender when you're in this situation. However, in a serious siege, the enemy is likely going to take the top of your mountain/plateau thing. It's just too big to fully defend, and someone is going to get troops past your defenses. Frankly...that's fine. Pull all your forces back *inside* the buildings and tunnels of the city. Do NOT under any circumstances attempt to defend the floor of the canyon. You've lost your 'walls;' any attempt to hold there will be a slaughter. On your way in, destroy the access ramps coming down from the cliffs and up from the floor. Now....the enemy gets to die in large numbers. In order to assault the buildings of your canyon city, they have to march into the canyon to assault the actual buildings. Sure, they can bombard you with any siege weapons they get up on top of the lip...but their targets will be limited by parabolic arcs and the difficulty of getting heavy siege equipment up on top of the mountain. Naturally, you should try to set those on fire whenever possible. Ultimately, to take a city, you have to take the buildings and deal with the people. And you guys are holed up with your supplementary dwarf-style food production and entire caves full of water. And any time their army comes down into the canyon, they are walking into a narrow space with enemies possessing the high-ground on both sides of them. Rain down arrowy death. If they do get inside, then we're on to tunnel warfare. Make good use of those choke points. Just plug em with corpses. Their best option for getting you out is to smoke you out...but that's what all the air-vents are for. They're going to have to go climbing around the walls of the canyon (likely while under fire from the other side of the canyon) trying to plug all the holes, or try to hit them all with siege engines and hope they collapse them, rather than just take a few layers off the outside. # Summary Trying to defend such a place in real life would be hard...because city-supporting underground crops don't exist, and the middle ages didn't have dwarven levels of digging technology (such as being able to bore breathing hole tunnels). IRL, once you take the top of the mountain...battle is over. They just cave in your entrances and let you starve of suffocate. Or they lob big piles of burning stuff at your entrances, smoke you all out, and either just let you burn, or pick you off when you come running out. A Plateau is wonderfully defensible if it is relatively small. Masada was, historically, one of the most invincible fortresses of all time. In no small part because it was built atop a plateau. But, said plateau was only 550m x 270m. Mount Conner is 3km by 1.2km...a vastly larger perimeter to defend. And to have such a canyon system with a full city inside it...yours is probably even bigger. Your enemy is going to have a hard time getting up there, but once they do your outer defenses are toast. And so, in terms of tactics...you plan for that. Try to keep them from taking the mountaintop, of course, but design the city such that trying to actually *invade* it forces them into a killbox. [Answer] > > The city is entirely built into the "walls" of a canyon (pretty much like the Great Canyon) which has a flowing river on the bottom. > > > I presume you mean the *Grand* Canyon ? > > Most of the buildings are on the side of the "cracks", but some can be constructed on the flat top. Suppose there are a few entrances at ground level (e.g. where the river gets larger and enters the plains outside). > > > There are four issues here : * The top will be the location of attacks and as you've effectively lost the high ground, which is a form of military suicide, you would need very strong defenses on top. But even these can be breached - static defenses are doomed in this sense as eventually any static defense can be breached. * If you station troops and fortifications on the top, you cannot give them direct access to the city itself. To do so would be to introduce weak spots, making the fortifications themselves locations ideal for attack. * Access to the river is very problematic. It allows your attacker two potential vectors (top and bottom) all along the city. This requires you to defend *both* top and bottom, splitting your forces. * They have mobility, you don't. Your defenses are limited by the construction of your external "facade". How many resources and men you can deploy is therefore limited. As your internal movements will be limited by corridor sizes and the need to move vertically by stairs ( a choke point for movement ) you have more difficulty that the attackers do in moving to a new point to enter. > > Few to no buildings are built on the bottom, most of those being infrastructure related to water (or walls and gates, in the outermost parts of the city). > > > They can attempt to undermine you on the bottom. This is exactly what it sounds like : they mine under your existing systems, perhaps by developing a beachhead at one the existing entrances. They can then tunnel and use that to deliberately undermine the structural integrity of the support for the levels above. This is a well established technique in ancient warfare. It becomes even more problematic for you if they can deploy any form of explosives (including magic). > > Food is gathered via hanging gardens and terraced farms inside the city. > > > Unless you have some very strange things happening (magic ??) you have gardens indoors without sunlight to grow things. That's a major problem. You can deploy these areas to the canyon walls (which will probably be in shade anyway) as they'll be easy targets for the enemy. As you're stuck inside you are in a siege situation. You cannot forage for food outside and must rely on stores inside. > > The city came to be because of the humongous quantity of valuable gems and materials present underground in the area. Obviously, this makes it a target for attacks. > > > If you have underground gems you have mines protected by fortifications. These are much simpler to defend in more conventional ways. The city is a source, perhaps, of manpower, but in a sense the manpower is irrelevant. You need to protect the primary asset and by keeping the manpower away from it in conventional towns you would create a potential militia force to help defend any mines, as well as themselves. One the manpower is trapped in your essentially underground city they loose any mobility to respond to attacks and become a burden to the defenders (e.g. your children are not a particularly useful fighting force, but they do require food and drink and protection). > > So how could such a city effectively defend itself from sieges, with medieval-fantasy technology? (some magic is acceptable, but I don't want stuff like "a wizard makes the city invisible to the outside") > > > Sieges against conventional and even highly fortified cities have been conducted throughout history and at best the defenders outlast the attackers, but typically at the cost of massive death by famine, death and disease. At worst (which is perhaps a better than 50% chance) the city defenses are breached and the entire population massacred. As you've given up the high ground your population already has a major problem for defense. I'd consider this a death trap, and if I was attacking I'd feel right pleased with the prospects for my endeavors. If I was defending I get the heck out as fast as possible - desertion is OK in my book and beats certain death by slow starvation any day. :-) > > Technology level is comparable to that of D&D dwarfs, so something a little steampunk-ish is acceptable (e.g. they probably have huge dams to control the flow of water, and a good hydraulic system) > > > I don't think "steampunk-ish" makes much difference. We've had major sieges of strong underground fortifications before and the attackers won. Think of the complex and actually well designed forts of the Maginot Line. These were successfully attacked and contrary to popular belief they were breached. The lesson from these systems is that even a well designed system with rapid internal transport systems can be breached and that once there is a breach along the line, you effectively split the defenders off into two smaller groups who cannot aid each other or seal the breach. This is another reason I'd be happier attacking than defending. And dams ? Not for long they wouldn't. What attacking army is going to leave you in control of those ? So those systems would probably become either useless to you or, worse, an actual weapon for the enemy. And dams imply flooding is possible, another significant vulnerability. You need underground rivers and reservoirs, not a dam. > > What are the biggest threats? (I'm assuming water shortage and an "attack from above", although I'd say the latter would be pretty impractical) > > > Attack from above is fabulous ! You have gravity working for you. In conventional sieges of castles and fortified walls you have to pass through a gauntlet of fire coming from *above* - stones, hot oil, any form of projectile. It's much harder to shoot up at them (generally requiring siege engines or the construction of elevated platforms to fire back from). And the attacker has to scale the walls somehow (or break them). All your attackers have to do is fall, maybe nothing more than a jump or descent by rope - fast, easy to reinforce, hard to prevent. Foot holds (breaches) are relatively easy to reinforce for the attacker, and relatively hard to retake for the defender. Defense after an (inevitable) breach would be a matter of using choke points and trying to prevent further breaches that make defense harder. As breaches can be multi-level your defenders cannot restrict what they have to defend to just e.g. a single level on top of a high wall. You have to be ready and able to tackle breaches everywhere ! No, I'll be the attacking general on this one, thanks. Also keep in mind that, as any siege progresses and food and conditions worsen, your city population may decide that they've had enough and would prefer life under the heal of the oppressor than e.g. no life at all. You can have a revolt internally and they could create a breach that the enemy can exploit. So in a sense you would be trapped and besieged both within and without. [Answer] When our great fathers and great mothers first built this city it wasn't to escape violent men. It was to escape the storms. Violent storms sweeping the sand along so fast that it will leave you blistered or worse. I've even heard of the winds flinging small stones through a horses head. They happen frequently, several times a month. At first the settlements in the canyon were small and spread out. But then we discovered the Red Beryls and our population grew. Our fathers and mothers where wise. They knew that the storms that drove us here would keep us safe from above. But we were still vulnerable to siege. So they stored large amounts of grain. in case our enemies blocked up the canyon entrance by the plains. We have listening post deep in the canyon wall were we mount large metal shields on the wall, so that if our enemies try to dig their way in, the vibrations will make the shields ring, and we will know where they are coming from bellow. Once before when I was just a lad we opened all our locks and dams releasing our all the water stored in our small lakes and ponds at once. We flooded our enemies away from the canyon mouth. But alas my people are growing lazy. Too much prosperity for so long has led to greed, and carelessness. Some worry about corruption in the city guard, and I've heard rumors of rats in our grain stores. The council of elders argues day by day about the most trivial of matters, and I worry that our enemies will find a way to break us from with in. [Answer] ### The weak point is the flat top I think that the weakest point is the flat top. If there were no buildings, nothing would prevent the assailants from trying to bore holes straight down. Then they could either go into the town, or drop bombs (incendiary bombs, oil lamps), or pump poisoning gases (even just smoke would do), or simply weaken the structure until everything collapses on the defenders. In a non-medieval yet steampunk-ish tech setting the assailants could use Thermite, and as long as they can provide fuel from above, it would continue to descend by mere gravity force. In a medieval setting, they could still try to smelt the rocks, one fireball at a time, or they could just manually dig. The Romans were quite good at digging under thick walls to make them collapse, and that was long before the middle ages. ### Coping with the possibility of disaster To prevent this disaster, they need fortifications on the flat top, or they need to make it inaccessible, for instance, if the town contained an island in the canyon, such that access was not granted unless someone would go through the city. Another possibility is to have pressurized steam running between the rock sheets of the flat top and the ceiling of the city. When a holes are dug, jets of overheated steam will come out, effectively preventing further access to what lies below. [Answer] # Attacking from the top is not practical How do you attack a stone wall with medieval or earlier technology? The answer is that you mine the wall. You dig under it, causing it to collapse from its own weight. Your city is basically the wall, itself. Given the picture above, some of the structures appear to be carved out of the solid rock *a la* south Indian rock temples: [![enter image description here](https://i.stack.imgur.com/OeqMl.jpg)](https://i.stack.imgur.com/OeqMl.jpg) or Petra in Jordan [![enter image description here](https://i.stack.imgur.com/AT4rV.jpg)](https://i.stack.imgur.com/AT4rV.jpg) How are you going to mine these pictured building? You are not. How else can you get in, other than from the front door? Well, you can't really dig from the top; that is solid rock and you'd be tunneling for months if not years. Basically, I argue that if the defensible buildings are built into the rockfaces, there is no good way to mine or tunnel into the building, because of the strength and thickness of the rocks involved. The most famous carving at Petra is the [Treasury](https://en.wikipedia.org/wiki/Al-Khazneh), which is about 40 meters high. The Grand Canyon has a depth up to 1800 meters. If you start 50 meters above the canyon floor and build up 250 meters (almost the height of the Empire State Building), then you still have just short of a mile of solid rock above you in the Grand Canyon. How are you going to dig through that? Catapults and trebuchets were around in this time period, but they threw relatively small rocks and weren't very useful for battering down walls. They were more useful for attempting to destroy emplacements on those walls in preparation for an assault. The rocks thrown by these machines were too small to do serious damage to a city built into a cliff. Now, decorative elements could be destroyed, but you never conquered a city by making it look ugly. Finally, there is the option of throwing boulders down onto the city from above. There are two difficulties here; first is that hitting anything is not trivial. Second is that the walls and city are one. In destroying the defensive fortifications you also destroy the city. The whole purpose of taking the city is to plunder its loot, or subject it to tribute. If you reduce the city to rubble, that isn't going to help your wealth generation. I argue that not only is hitting this city's vertical walls with a boulder dropped vertically hard, but also counterproductive. # Conclusion The city is extremely defensible. There is no easy access from below, no easy access from above, and it can be too high to scale with ladders. The walls are to strong to hit with catapults, and vertically built into a cliff-face they are too hard to hit with boulders, if you even wanted to do that. [Answer] I believe others have given good arguments why your city is unlikely to survive a direct military conflict without unsustainable defenses or magic. For a solution to a siege I'd direct you to Asimov's solution in the [Foundation Series](https://en.wikipedia.org/wiki/Foundation_series "Foundation Series"). The beginning of this story features a militarily indefensible, yet technologically advanced planet surrounded by 5 warring kingdoms, any one of which could easily annex the protagonists if they so chose. The solution offered is for the planet to become extremely rich in exports of technology, to the benefit of all factions. No faction is able to seize the planet without being immediately destroyed by the other four, as none have the capacity to manufacture themselves, and losing the technologies on offer to a single enemy would be military suicide. In that story the technology was nuclear power. The makeup of your city could allow for these to be the potentially magical or valuable nature of the gems and metals native to Durr, or the advanced and secretive industrial techniques your city developed to sustain itself in such an inhospitable setup. So long as the political situation in your fantasy realm remains relatively stable, Durr may not need to beat a siege. They can survive with efficient, unsustainable defenses (such as walling off the few entrances pictured) with scouts for early-warning, secure that other self-interested communities will break the siege themselves. A status quo like this may be doomed to eventually collapse, but that itself poses interesting narratives for your world. [Answer] ## Defend forward Your first advantage is height. Put sentry posts checking for possible enemy forces. If anything suspicious is seen, send your army to block their possible upward routes. With any luck they will be narrow enough to allow to face your enemy piecemeal, with the top position advantage. If the paths available are too wide, just fortify them. Even if you fail to defend the tops, making difficult its access will stop the arrival of supplies to the enemy, which is your long term goal. ## Starve your enemy If the previous point fails, fall back to the wall you have already built around the canyon. Here you have: * A disavantage, in that the design of your city is too lineal. That means that your walls will be relatively long and you may be lacking manpower to defend all of them. Good interior lines (to move reinforcements to wherever they are needed is must. * An advantage, as the enemy army will have trouble supplying themselves. No food grows on rocks, and water is down the canyon. Ensure that you do not need food stores near the enemy reach. Try to defend as much of the river as possible. If possible and needed, don't be shy to be ready to dam it to prevent your enemy access to water. If people dies, throw their bodies downriver towards the sections of the river they control. ## Defend your citadel Create a safe area, easy to defend. Water supply. Lots of room for people, food and other supplies. If everything else fails, burn anything that you cannot take with you and lock yourself in. Make entry as difficult as possible, exit as easy as you can without compromising entry. Wait for the enemy to discover that there are no supplies to plunder and that, if they want to get you, maybe they will run out of food first. ## Sneak out It is your home. You know every bend in the canyon, every cave. Which caves do have an alternative exit elsewhere in the zone. Or just dig some of these caves until you get alternative exits. Ensure that the entries have chokepoints, so if the enemy discovers them they can easily be defended. Keep the entries hidden, and guarded. Use them at night, to avoid the enemy detecting them. Use them to launch attacks against your enemy back, to smuggle supplies, to communicate with your allies. [Answer] **Desert crops are are vulnerable to fire** This is a fairly crude answer, but a simple approach would be to get a few hundred archers to shoot flaming arrows on the crops for a while, and once they're torched, you could conquer the cities *around* Hurr on which it would depend for food, and once you'd done that, Hurr would have no choice but to surrender or starve. This is assuming a foreign army can burn the crops, but they're in a dry environment, and fire is contagious, so I don't really see an issue with that part of it. I doubt Hurr's irrigation infrastructure would be sufficient for dousing the fires fast enough. Even if the archers can't reach the top of the mountain, just one raid (where you accept you'll lose everyone who takes part in it) to get the fire started would be sufficient. Especially if the raid can knock down some irrigation infrastructure too. This lowers the bar from *invading them successfully* to *sneaking a few guys past their defense once*. The only defense for this is either trying to keep reservoirs on top of the mountain for dousing (which would be hard, because it's in a desert), or not to let the invaders get close to the city, which is so difficult that it can barely be considered a defense. [Answer] To prevent attacks from on top change the outward appearance to something more like mount roraima this sits between Brazil, Venezula and Guyana. [![enter image description here](https://i.stack.imgur.com/ffS3V.jpg)](https://i.stack.imgur.com/ffS3V.jpg) There is only a single passageway up to the top and it's a full day trek and it's only wide enough for a single file line, it's hard to even cross another team coming up from the bottom. Also there is a water fall on the path, so if it's rained a bit in the last hour you have to wait. This would then mean that the only way in would be the river. This is much more defensible for the people. [Answer] A mesa, such as Mount Conner would be superbly defensible. The cliffs would be cut to make scaling them only possible by skilled rock climbers. On the top, I would have an array of ranged weapons to keep an attacking army as far as possible from the cliffs. As an attacker, the best option would be to encircle the mesa and starve you out. Even if you have sufficient crops to feed the entire population, you need water for irrigation. For that reason as attacker, you would divert the river, so it no longer flows through the mesa, but around it. Even if with underground water storage, that is going to run out eventually. Unless you can get water, the attacker eventually wins. The solution: An underground aqueduct. The aqueduct would connect with the river as far as feasibly possible away from the mesa. The underground storage would be constantly refilled from the aqueduct. With luck, you can outlast them. [Answer] [![enter image description here](https://i.stack.imgur.com/vl547.jpg)](https://i.stack.imgur.com/vl547.jpg) If the place looks like this then the attacking army is coming from outside, right? So unless they can fly they shouldn't be able to get in. They might have massive catapults that they can use to throw stuff over, but if the walls are high enough then that might not work either, not to mention that they couldn't see what they're hitting. Most of their shots could hit nothing. So they only have entrances/exits to worry about. If the conflicts center around those, the people on the inside just have to wait out the attackers. Whats that you say? Shouldn't it be the other way around? Wouldn't the attacking army just have to wait out the ones on the inside until they starve? Not if they have their own farms and livestock in there. It certainly looks big enough that they could do it. And they could have large caches of water too. Sure those would drain away sooner or later, but not so soon that they couldn't wait out the attackers. And there's rain to replenish that (I know its an arid place, but if they can trap the water one strong rainfall could last a long time), or wells, or an underground water source. Mountain climbing enemies could be kicked off the cliff side or squashed with avalanches or burning oils. In a sense the attackers are the ones trapped outside in an inhospitable desert. And the people inside could use their catapults to much greater advantage as they have the high ground. If the canyon city is self-sufficient they could hold out much longer than an attacking army might. Think the Fremen of Dune. Or even *Masada*, but better (and with a happier ending, no offense intended). ]
[Question] [ **Terraforming is the process of transforming a celestial body to become habitable by Earth-like life.** Even when I try to imagine an advanced civilization, the cost, time and complexity to terraform a planet seems like a real challenge. Terraforming Mars seems like an easy job compared to other planets and yet it would be a daunting task: * Mars's mass is much smaller than Earth's and it has no magnetic field. This means that there is nothing to stop the ultraviolet radiation and only a thin atmosphere. Less gravity makes it harder to have a thicker atmosphere. * Mars is cold, we would need to make it warmer possibly using the greenhouse effect but for this we need to add tons of gases on the planet. We would to take the gases form Earth or directly from Mars. Considering the quantity we produce on Earth and that it's only starting to warm up the climate, it would take a lot more to get Mars to have the same temperature as Earth. And it would take a lot of time. At least a century, because we have to warm it and make sure it stabilizes at the end. And I will stop there because it is not really the point of the question. **I make the assumption** that terraforming is really complicated. But I admit that maybe, in a distant future, (or in a distant science fiction future) advanced civilizations might have enough wealth and technology to consider terraforming a planet. The problem is that, with advanced space travel, they might be better to search for another planet, it would be much simpler in my point of view. Terraforming could be a solution for us since we have problems on Earth but it's not feasible right now. By the time it will becomes possible to do such wonders, space travel will be a better option. Finding a planet with less challenges might be easier. So, I'm trying to understand why in a lot of science fiction stories and games, civilizations would favor terraforming a planet instead of looking elsewhere. [Answer] The first reason off the top of my head is the time it would take to find a new world that is already habitable or easier to terraform, versus the time it would take to terraform a world that's close by. ## Habitable planets are not that easy to find Faster-than-light travel is a not a trivial problem and it may take much longer to solve than terraforming. Even if you *do* manage to achieve FTL travel, the speeds might not be ideal - at light speed, it can take a decade to reach a close-by star system only 10 light years away (a short distance by astronomical standards) and that's assuming that you have one that close that has habitable planets. If you're unlucky, even achieving many times the speed of light could still not be enough. In fiction, FTL travel tends to be extremely fast - moving between star systems is a matter of hours or days. At those speeds, it is indeed a preferable choice to terraforming because you can search hundreds of star systems in a time shorter than it would take to build a basic colony. An additional problem could be how much you can carry with your faster-than-light ship - if the cost is too high, perhaps terraforming is still cheaper despite the enormous cost. To colonize a planet you need thousands of people (44 thousand by 2013 estimates[[1](http://en.wikipedia.org/wiki/Generation_ship#Biology_and_society)]) and a lot of materials and resources. Perhaps you're not sure if it's actually habitable and you have to check first - that's extra time and resources. FTL drives are, at this moment, purely theoretical - we don't even know if they're possible and indeed in some fiction, there is no FTL. Terraforming on the other hand, while a huge engineering task that requires a lot more knowledge than we have, is almost certainly possible. ## Proximity Even if it's easy to travel to distant star systems in search of habitable planets, it's going to be *much* cheaper to move within one if you have that capability (unless you're using mass drivers and only make very few of them). By terraforming a planet that's close by, like Mars, you get a whole new planet where people can live and very close to the homeworld. That means it's going to be faster to develop it, trade is cheaper, people can move faster between planets etc. . Another advantage is that we've studied our own solar system enough and its planets as well. A new star system might have configurations we're not experienced with - you could have celestial phenomena that surprise you or geological phenomena that do the same. To put it in Earth terms: it might be hard to grow food in the desert that's next to your city, but you might still prefer working with it in order to expand *this* city instead of moving far away to found a new city. All of this of course depends on the relative energy and time costs of traveling astronomical distances, versus the engineering costs of transforming an entire planet. ## Prior establishment You might prefer to terraform a planet, not because it's cheaper, but because you *already* have colonies on it, but they have to live in habitats. If you, for example, colonize Mars before you have cheap FTL travel and by the time it's cheap enough to search for habitable planets there's already hundreds of millions of people living on Mars colonies, you can't just relocate all of them. You might find new worlds but eventually decide to terraform Mars as well, so that it's friendlier to human life. [Answer] Some terraforming could actually be fairly simple (as such things go). Mars is a weak candidate as it has low gravity and no magnetic field but you could still work with. Imagine creating a bunch of machines that go out to the asteroid belt and start looking for ice asteroids and redirecting them into Mars, rain ice asteroids down onto the surface and over time you increase the supply of water and atmospheric thickness and slightly increase the planet's mass. A better candidate would have a magnetic field and already have an atmosphere of some kind. In that case "all" you would need to do is seed it with appropriate genetically modified bacteria/fungus/plants/etc. Those lifeforms would the convert the atmosphere towards the one we wanted. A small team would monitor the process and seed it with updated terraforming species as needed for each stage of the process. As the environment starts to become more like we wanted early animal life could then be seeded as well and we build up an entire ecosystem from there. The process would take a long time (centuries probably) but not actually be very expensive when you consider the value of an entire new habitable world. [Answer] **Terraforming Technology Outpacing Space Travel Technology** Space travel is not an easy task. We've been at it for a little less than 70 years and still haven't broken out of our Ort Cloud, and as far as getting people off the surface of our planet, we haven't even made it to another one yet. And yet, we as a society are already considering the possibility of utilizing water sources (and other resources) on local celestial bodies to mine resources and even as habitable land. This is why scientists get really excited about finding sources of water on celestial bodies in our own solar system. And it's not as if we have no experience with terraforming - we regularly alter the water flow and construct habitable spaces out of the resources on our own planet. It's simply a matter of finding a planet or celestial body that would make a good candidate. (Mars is actually not all that promising in this regard, unless we can get its magnetic field up and running. The Dwarf Planet Ceres, and our own moon, are better candidates). [Answer] Terraforming in fiction is big in fiction for a couple of reasons it has only been recently that we have come to see how prolific planets are out there. What in general is considered even more rare is a planet with life already on it. The assumption is that most planets we will find are going to be barren whatever their makeup. On top of that if there is already life on a planet, who is on it? Even if the life was just crawling out of the oceans, doesn't mean that it would be good for humans and their crops and livestock. The indigenous life could be very dangerous on it's own, the predators, the plants, the microbes. Starting with a barren planet you don't have to worry about unknown effects of indigenous species, either they on you or you on them. [Answer] It would be nice to have biomass on a planet before you got there. As well as any target byproducts you might engineer them to make. I'd add that Deinococcus radiodurans can survive anywhere you can't engineer other bacteria to. So you're pretty much guaranteed to be able to just launch a can across the universe at any planet, even if you can't quite fly to it yet. If your lucky the locals may have evolved before you got there and be able to contribute to science with their "un-poisoned" paradigms. (Panspermia anyone?) [Answer] Planets are more resistant to the kinds of dangers that exist in space. It's played down in fiction but persistent radiation is a big problem in space, both just the ambient background radiation and peak events like solar storms. Hunkering down under a blanket of atmosphere gives lots of protection. If the planet has a magnetic field, all the better. Also, a planet scale biosphere could buffer a lot of manmade catastrophes like nukes, hacking, biological attacks, nano attacks, even run away robots. Anything in space will have a lot of people, in a small area, dependent utterly on a meshwork of tech to keep them alive. Hit the small area, contaminate it or wreck the life support and everybody dies. Conversely, on a planet, you could loose most or all of your tech and still survive in the biosphere. [Answer] You should (as an civilization) advanced enough to the point of "not to bothering the answer of the question". Such questions only relevant to civilizations like us / ours, (behind the point). Other civilizations "beyond to point" simply they do because they can. If you "on the point" (to see whether they can terraform a planet) terraform a planet... ]
[Question] [ In a medieval fantasy setting, if you had to regularly deal with transforming into a beast that's taller, stronger, and that have a much larger build overall than your frail priestess body, what would you wear that could actually withstand the transformation without the need of constant repair, and how would that work? I guess this is a problem usually solved with the "It's magic" card but this isn't really an option here. Either some unusually large robe or some padded clothing that would get squeezed but still hold would do the trick, but maybe someone could help me find a more elegant solution? Maybe some kind of belt/strap that would move to a second position if under pressure but I have no idea how that would even work. Well, I can't quite find a solution that I like right now so any insight would be welcome. [Answer] ### Some smart leather-working should save your priestess from flashing. This is so much easier with modern materials. Velcro or spandex would make this so much simpler. But, alas, medieval tech it is. For the chest, torso, waist, legs, and arms, you basically have an expanding cylinder - I'd build a flexible outfit out cotton or linen or hide that's much too large, and fold it back on itself, like this: [![enter image description here](https://i.stack.imgur.com/JTFFz.png)](https://i.stack.imgur.com/JTFFz.png) If the transformation is rare (warewolf once a month sorta thing), or the smaller being needs to be athletic and mobile, then a few sacrificial stitches could hold the garment taught on the smaller user, and then immediately give way when the transformation occurs. Those sacrificial stitches can be repaired in a few minutes by the small being after the change, they'd probably keep the needle and thread on them. However if the transformation is very common, and the small being doesn't need to do gymnastics, then a thin peice of rope wrapped around the outside, granny knotted and the ends tucked inside will do the trick. However, if the transformation is very common, and the small being needs to be extremely mobile, then you need something with two latching positions. Cut these two shapes out of leather: [![enter image description here](https://i.stack.imgur.com/Uuomt.png)](https://i.stack.imgur.com/Uuomt.png) The long peice of thonging with a circle in it attaches one side to the clothing, the other end hangs loose. The Double-T shape rolls up into a cylinder, with the T bits inside (which result in that part of the cylinder having smaller diameter, smaller than the circle). It's then stitched shut, and one end is attached to clothing. The leather is flexible and distorts under strain, but the circle in the leather thonging is held against the T bits under normal forces. When the character expands, the forces are much greater, and the leather distorts and travels to the next position. After they transform back, they pull the string hard and their clothing tightens, the circle then travels past the other T, and is then held taught again. [Answer] **It is ok for magic users to get naked first.** Witches get naked. True for salacious Frazetta witches but also true for creepy Goya witches. [![goya witches flight with some seriously tall hats](https://i.stack.imgur.com/oJUV9.jpg)](https://i.stack.imgur.com/oJUV9.jpg) <https://www.museodelprado.es/en/the-collection/art-work/witches-flight/5e44d19d-7cda-472b-b6d8-8868c599d252> There are a number of reasons this is how they are depicted. Taking off clothes means removing the self from civilization and public interaction. It is clearly a departure from any sort of Judeo-Christian norm. Taking off clothes harkens to fertility rites and older gods. It is an intimate act, a precursor to animal actions like procreation and childbirth, and butchering. It is a frightening act seen in a stranger who knows that she is watched - what does this stranger think is happening or will happen? And having her strip will give you time to write. What does she look like under her clothes? Is she talking? The scene where the priestess carefully removes her clothes and what she has underneath will be a scary and uncertain one for the reader. Where is this going? And when she changes into a beast, do not have her immediately attack. She can still speak, but she does not sound the same. And the reader will think "holy moly where the f\* is this going now??". [Answer] I would suggest pleated robes with wide sleeves. Pleats allow great expansion. The garment will be pleated everywhere, including sleeves, when a priestess is in her human form and will stretch when she transforms. If you have access to [natural rubber](https://www.wikiwand.com/en/Natural_rubber) or similar material you can use it to make necklines stretchable for a better look. Rubber would also work great for expandable belts. If you do not have rubber equivalent in your world belts can be knitted. [Ribbing](https://www.wikiwand.com/en/Ribbing_(knitting)) and lose knitting would provide significant stretch. The same as pleats, they will return to their original shape once the priestess returns to her human size. If the expected change in size if very significant, go for kimono-like robes made of pleated fabric with long sashes that would be removed before the transformation and tied again after. [Answer] Make garments of human, wolf or whatever skin, which retains enough genetic characteristics that simple contact with the wearer means the transformation spreads to the clothing. ]
[Question] [ The current world population is around 7 billion living people and 107 billion dead people. Since the population is increasing steadily and faster than ever, I was wondering if we could ever reach the turning point. Given the 'facts' from [this source](http://www.livescience.com/18336-human-population-dead-living-infographic.html) are fully correct, I am left with two questions: * How many years will have to pass for those living to exceed those dead on Earth (assuming we don't populate/colonize another planet). (This first question is purely asking about the math, excluding the question of the availability of food, housing and other resources). * Is it even remotely possible for the living population to exceed the dead population before we turn extinct or run out of space? (This one does take the lack of resources into account). [Answer] Like other answers said, it is not practically possible at this point for Earth to sustain a population greater than number of people already dead. Unless you assume that every woman on the Earth for some strange reason decide to give birth each one: ``` Number of women = 7 billions / 2 Number of dead people = 107 billions Children to give birth = (107)/(3.5) = 30.5 => 31 children. ``` So in the case that every woman now decide to give birth to 31 children (well in reality should be 40: we have to take into account people that would die in the meanwhile and keep a good error margin), and assuming (each pregnancy last 9 months) that in the middle of the process we will not end the available food (at some points we will have 60 billions people to feed and the Whole process would last 40 years), then yes it is theoretically possible. However there's no way we could do that in general: Assume that population keeps constantly doubling: in that case the **sum of dead people and living people would be almost the same**, but a double growth rate is not sustainable, at some point it will slow. To keep living population greater than dead population then you need a growth rate that is more than constant doubling ( x3, but also x2.1 is fine... or even x2.00001 and so on), and that is even less sustainable that a doubling growth rate. While in theory it is possible to exceed that limit for now (assuming enough resources), we will quickly reach a limit that will not allow us to exceed that again. When number of children a woman can give birth in a life will be lesser than ``` Sum of dead people / sum of living women ``` Then we will not be able to exceed that limit again. (well in theory we could do that in a hundred of years, assuming we can keep a exponential grow of population for so long). [Answer] # Not possible The primary reason is that population growth has already peaked. From the US Census Bureau: [![enter image description here](https://i.stack.imgur.com/Qfnbw.png)](https://i.stack.imgur.com/Qfnbw.png) Estimated growth is going to drop further. The UN [currently estimates](https://esa.un.org/unpd/wpp/publications/files/key_findings_wpp_2015.pdf) that population growth will top out at around 11 billion people in 2100. Given that world population is not likely to even get close to 100 billion +, it is very unlikely that human living population will exceed the dead. [Answer] Great question. This is one of the questions that my friends and I have asked at various points in our lives. (also: how long would it take for N monkey, typing randomly, to create Macbeth spontaneously?) The population data SEEMS wrong. Why? My suspicious arise because there is no mention of estimated lifespans or the rate of death in ancient populations. Let's try to fill in some of these and see where that gets us: Lifespan: let's estimate 40 years. (By this measure, Jesus was normal by actuarial standards) Death rate: if the lifespan is 40 years, then for every cohort of 1000 people, there would be 25 deaths per year (1000/40 = 25). Plug these numbers into a spreadsheet and see that a starting population of 5M in 8000 BC would grow to 5e192 by the year 1 AD. !!! SOMETHINGS WRONG HERE !!! Looking more closely, at a birth rate of 80 per 1000 per year (and a death rate of 25 per 1000 per year), 5M people would grow to 10M in 13 years. This is much higher than the flat line shown in all of these growth models. If you assume the rate of birth is steady at 80/1000, you need to jigger the death rate to over 79.48 to achieve the stated population of 300M by 1AD. I'm thinking that the number of births is too high: one would have to look at the model demographics to see if this is realistic: Assume an evenly-distributed cohort of 1000 persons, with ages ranging from 0 to 40. this places 25 people per age. Assume that the fertile years are from 15-40, etc. and you can really look at a more realistic model of populations. (for example, half of those born would not be able to give birth...) To sustain a lot of births and keep a slowly growing population, you need to have a lot of deaths. We need numbers like infant death rates and the risk of death during childbirth. If they are huge (79.48 / 1000), this can get you to 300 million by 1 AD on a smooth glide path. Doing so would require 47 billion people to be born in this span--a truly epic slaughter. (this might be the way that the referenced numbers were achieved) It is possible, though, to look at the rate of birth and death in primitive populations in the Amazon, New Guinea, or Kalahari tribesmen. I suspect that this would suggest birth rates at 50 per 1000 (I'm not asserting this--i'm probably wrong); It's probably not a good idea to gauge ancient birth rates from any data collected anywhere after 1800. Increasing urbanization, medical, food improvements, and access to petroleum-based energy added an artificial stimulus to growth rates that probably did not exist in earlier eras. With these numbers, it would only require 28 billion people to be born in this time. My suggestions are: (1) define a model that accounts for realistic birth behavior and more detailed methods of death. See what models suggest from this. (2) try to find some proxy for historical birth rates form archaeology or comparative anthropology. [Answer] The current population is sum(births) - sum(deaths) Not solving for 2017 plus Just how do those births and deaths need to relate for sum(deaths) = current population sum(births) - sum(deaths) > sum(deaths) sum(births) > 2 \* sum(deaths) plug in x \* deaths for births and solve a single fixed ratio for population to be sum(deaths) sum(x \* deaths) = 2 \* sum(deaths) x \* sum(deaths) = 2 \* sum(deaths) x = 2 so if the birth rate doubles the death rate then that is the balance point even if you more than doubled life expectancy would need to catch up in one life expectancy [Answer] The only way it can happen is with immortality plus a major jump in the available living space (space colonization in a major way, or else interstellar colonization if we already have major space colonization before immortality is developed.) Your question requires the answer to two unknowns in order to answer and thus there is no way to answer it. [Answer] Easy Answer: Zombies! Or some other mass resurrection. The math doesn't support it any other way, as has been pointed out in all of these other fine answers. Another possibility would be cloning on an enormous scale. The only problem with massive cloning is that it serves no purpose in the stated premise. If we can't leave the planet, Mother Earth will slap down the population growth one way or another. Either her or our own hubris will prevent growth of the living to surpass the dead. Remember that the planet is a closed system. Here is one way the living and the dead could reach population parity. If we had the means to store consciousness in a computer, and then archive everyone alive today. Then, as people die, the become activated in this new digital Elysium. Grant them rights and agency on par with those still in the "meat space". You would be then, in essence, granting immortality that maybe could work within the closed system of Earth without the great mother earth slap down. [Answer] Here we have 2 major points in life cycle, birth and death. Each life meets both points. More birth = more death (after life lasting cycle). **Conclusion** - we can never get equal or even get near to the dead population. **Exception** is if tomorrow women start giving birth to babies like pop corn. Lets say we have 7 billion people, and lets divide population this way (for example), 25% children, 25% men, 25% old folks, and 25% women. 25% from 7 billion is 1,750,000,000. To get the number of 107 billion living people, each woman need to breed **57.143** children during this life. Since more people would die till all of this women in labor meet their ends, number is slightly increasing to around **62** babies per woman. **Exception no. 2** is immortality. No need to write much about that. **Conclusion no. 2** - planet Earth is perfect in doing one thing, recycling. Every living being is recycled after death, and who knows how many other forms of life that brings. I'd say that number of living and dead is always the same, the only thing that is changing is people. (judging by the fact that we are all recycled) [Answer] Until about 6,000 years ago, the population of the living people in the world was 4, with none dead. Then Cain murdered Able, prior to the birth of Adam and Eve's third child [Seth around 3900BC](http://www.bibletruths.net/archives/btar199.htm). Given the longer life span of people in the early days of the world, the living probably out numbered the dead until about 2350BC when the great flood killed most of humanity. Related sister site question [Who was the second decedent of Adam to die?](https://christianity.stackexchange.com/questions/54323) [Answer] It probably already has. According to several books that I've read on lineage all modern humans can be traced back to one group of 500-3000 people who lived about 100,000 yrs. ago, meaning that apparently we've almost gone extinct before for whatever reason. Adding in things like the Black Death epidemic and the fact that it took until 1900 or so for the population of living humans to reach 1 billion, the total number of humans who've ever lived isn't nearly as great as you'd think. ]
[Question] [ Mounts are one of the coolest things about fantasy in my opinion. Riding around on raptors, dragons, elephants and even weirder things is one of the main draws to a lot of fantasy things. However, justifying dragons and unicorns can be tricky. So, inspired by the hours I've spent riding a parasaur on ARK, I have a question. What are the best alternatives to horses—or is there anything better? Drawing on animals that exist in the real world—even if they are extinct—what are the best animals to fulfill the transportation and haulage roles of horses? Answers should take feeding/housing into consideration, but domestication can take any length of time. The environment is a mix of dense, rain-forest jungle and open plains with minimal hills. Rivers and lakes are plentiful and river transportation could be a viable option if creatures allow it. [Answer] The best choices here are actually not going to be that exciting but there are many options around the globe for [transportation/pack animals](http://en.wikipedia.org/wiki/Pack_animal). Around the globe, you have camels, donkeys, llamas, oxen, reindeer, elephants and water buffaloes. Some potential options that I don't think have been done before are american bison, Elk, and moose. The idea of a rhinoceros is appealing though generally against their nature as they tend to be edgy...but a rhino cavalry charge would be fantastic. ![enter image description here](https://i.stack.imgur.com/Gt0m3.png) Generally speaking you are not going to be able to use predators as mounts, as cool an idea as it is their bodies are not able to support weight the way pack animals can. They are also designed to be agile where as pack animals while potentially fast are generally not terribly agile. If you want to make a tiger (for example) believable you would have to make it very rare, a special ranger loner type bond. If we get into dinosaurs its harder to say. Its somewhat realistic to believe we could have tamed some herbivores during the time of the dinosaurs but without knowing their behaviors the way we know living creatures its hard to say. [Answer] # Camels Where I lived in the UAE they were treated similarly - used as beasts of burden, transportation, but also there were regular endurance races and even beauty pageants! They're stronger, bigger, faster and nicer\*. They also produce a lot of very nutritious milk. This might not be the sexy answer you're looking for, but when you're riding a camel, it's pretty awesome and your feet are about where a horseback rider's head is, in height. \*- never assume, though, that it will be nice! [Answer] Depending on the weight of the rider or the load carried, an ostrich could make a good mount. I have only seen people ride them short distances though. <https://www.youtube.com/watch?v=plk35VYDKZE> They seem to be having trouble staying on, but an improved saddle might be all that is needed. The ostrich is an omnivore so finding food for it should be no problem. It can go without water for several days. The ostrich can swim. <https://www.youtube.com/watch?v=IuB0tqCKv1w> Although I haven't seen it, I am thinking that a pack of ostriches could pull a sled. > > During breeding season and sometimes during extreme rainless periods ostriches live in nomadic groups of five to 100 birds (led by a top hen) that often travel together with other grazing animals, > > > Birds are superior to mammals in some points: > > The ostrich utilizes its respiratory system via a costal pump for ventilation rather than a diaphragmatic pump as seen in most mammals. > Thus, they are able to use a series of air sacs connected to the lungs. The use of air sacs forms the basis for the three main avian respiratory characteristics: > > > Air is able to flow continuously in one direction through the lung, making it more efficient than the mammalian lung. > > > It provides birds with a large residual volume, allowing them to breathe much more slowly and deeply than a mammal of the same body mass. > > > It provides a large source of air that is used not only for gaseous exchange, but also for the transfer of heat by evaporation. > > > The maximum metabolic scope in an ostrich is seen to be at least 28 times greater than the BMR. Likewise, the daily energy turnover rate for an ostrich with access to free water is 12,700 kJ·d−1, equivalent to 0.26 ml O2 g−1 h−1. > > > Source: Wikipedia Ostrich Max Speed:50 mph Average Speed for 20+ miles:30 mph Estimated Marathon Time:45 minutes [Answer] I noticed this thread at the front page and could have sworn I gave an answer to it. It turns out, though, I only gave an answer to a similar question which can be found **[here.](https://worldbuilding.stackexchange.com/a/139290/58403)** In it I included some giraffids from the Miocene, which wouldn't exactly fit the bill for "realistic" (although the Pleistocene *Sivatherium* could hypothetically become a draft animal). Even though this post is over 3 years old and you may have already went through with your story, I'll see if I can answer anyway because what even are responsibilities? In order to have an alternate "horse", it needs to share these similarities: 1. It needs to be large and strong enough to ride and pull vehicles, or at least be feasibly bred to such a size later on (just like the real horse's history). 2. It must be *intelligent enough to train*. Sorry, rhinos and ostriches... 3. It must have the stamina to work for extended periods of time. 4. It must have a comparable speed and have a quick acceleration *to* that speed, matching the horse's effectiveness in battle. 5. A herding social structure is *not* vital to domestication, but will help immensely in becoming a substitute warhorse - the animal will instinctively charge with other mounted animals and be more likely to trust the rider's guidance. This is why donkeys are terrible in battle: they are much more solitary and self-reliant in the wild than horses. So basing off of your criteria and mine, I will boil down my other answer into a few specific animals that I think would be ideal (as well as adding some new information...so really, not much of a 'boiling down'). * **Zebras:** Okay, okay, I'm technically cheating here, but couldn't resist being cheeky. You said no horses, but never said anything about equines in general! Unlike the parroted words from *Guns, Germs and Steel* that you may often hear, this is actually more doable than you think. I'm actually working on a very long Quora answer about zebras which pooh-pooh's Diamond's claims on the subject; I'll be sure to link it when I'm done. To put it short, though, zebra "domestication" was much more successful than people remember (albeit low-intensity), went on for several decades before being replaced by more efficient horse medicine and modern vehicles, most zebra species share the exact same social structure as a horse, zebra behavior towards humans is little different from the [tarpan](https://en.wikipedia.org/wiki/Tarpan), and among all the species the most readily tamed animal was the now-extinct [quagga](https://en.wikipedia.org/wiki/Quagga), which would then have a temperament not unlike a domestic horse which is beyond impressive for a wild animal. So you could do it if you wanted. Of these, the ideal "horse" replacements would likely be one of the plains zebras; either the Burchell's Zebra or the quagga. The Grévy's zebra handles more like a donkey than the plains zebras. They all might be too close to horses for your liking, though! [![enter image description here](https://i.stack.imgur.com/EDwGC.jpg)](https://i.stack.imgur.com/EDwGC.jpg) A final note, horses and zebras are both capable of some light browsing and so could probably make it on the periphery of your jungle habitat, but may have nutritional deficiencies if they stay too long. * **Bovins:** My gut instinct go with some long-legged variant of domestic cattle, since this is of course the animal we know the most about. OTL, we have longhorns, which have a more cursorial build than other cattle and are popular to ride. Yaks could work, were it not for the fact that they aren't adapted well to your world's climate. And water buffalo are great alone in your jungles, but their wide feet would make for terrible long-distance runners. Cattle are well-adjusted to your world. They can handle a wider variety of feed than horses, and, being ruminants, can digest their food more efficiently which will be very helpful in the jungle. Alternatively, and if you wanted to spice things up, you could go with the [banteng](https://en.wikipedia.org/wiki/Banteng). They have the affinity for dense, wet tropical forests like the water buffalo, but have a build more like regular cattle which makes developing running breeds easier. They're only somewhat domesticated IOTL and so we have very little information to go on, which makes this risky for a 'realistic' mount because of the assumptions we have to make. But if you assume they're like cattle, which I don't think is too 'out there', then they would be quite ideal for your world. The biggest quip about bovins (but not other bovin**e**s) is that their backs tend to be very flat, leading to a rather more uncomfortable ride than a horse. Any long-term riders will be *very* bowlegged...but this could potentially be solved in ATL breeds. Addendum: Any kind of head-butting mount will have interesting implications in war, especially when faced with another head-butting animal... * **Camelids:** The dromedary camel, or a surviving *Hemiauchenia*. Camels can approach some horses in speed, but the fastest camel is still slower than the fastest horse, can't keep up their top speed for long and aren't as agile or quick to accelerate. The size of a camel can make cutting down people difficult, but doable with a lance or *long* sword. Camel archery is also feasible. Dromedaries are much more adaptable to hot, humid weather than Bactrians, but will still require ATL breeds to survive in actual *jungle*. *Hemiauchenia* has been found from Nebraska to Florida, so not only may it prove the most adaptable, but may also be the faster and more agile pick. Beware the giant llama. * **Antelope:** The giant eland would be the best pick for riding-type domestic antelope. I talk very favorably about eland domestication in [this post](https://worldbuilding.stackexchange.com/a/139300/58403). In 1924, Arthur Blayney Percival, member of the African Game Department, speaks highly of the eland's [speed and ability](https://books.google.com/books?id=Ilg0DwAAQBAJ&pg=PT208#v=onepage&q&f=false), at least for the cows (he may be talking about the common eland), and says they are ["easily trained to harness"](https://books.google.com/books?id=Ilg0DwAAQBAJ&pg=PT209#v=onepage&q&f=false). Harry Edgell, who lived in German East Africa and had been performing hybridization experiments on tame zebras, said that two elands in double harness ["trotted thirteen miles without a break"](https://books.google.com/books?id=06d8CgAAQBAJ&pg=PT149#v=onepage&q&f=false). Hugh Cholmondeley, 3rd Baron Delamere apparently had [similar success breaking in elands](https://books.google.com/books?id=ooM7AQAAMAAJ&pg=PA179#v=onepage&q&f=false), but I can't find a more direct source. Though the common eland is more...common in a farming context, both species are farmed and ranched. They're a safe bet. They can eat a wide variety of plant material and are hardy in dry areas, but might have some problems in densely forested areas. * **Deer:** Any large member of *Cervus canadensis*, though I'd go with the [Eastern elk](https://en.wikipedia.org/wiki/Eastern_elk) for their size and ubiquity. Reindeer would be the obvious answer if it weren't for the fact that they'd all die in your world. Compared to the eland, there isn't as much solid information on taming apart from [anecdotes and rumors](https://books.google.com/books?id=CH5cbqqXbyIC&pg=RA1-PA49#v=onepage&q&f=false). However, it's safe to assume that they're much the same as the smaller Rocky Mountain elk, which are easily tamed and are farmed today for meat and antlers. If you've ever had an elk burger at Fuddruckers, it was from a semi-domestic elk bred in captivity. There also exist at least two ambiguous photos of [a man riding an elk](https://i.redd.it/w5xg4qf1sybz.jpg), which may be Roosevelt elk from their size. Elk are highly adaptable generalists and can survive on the open grasslands, dense forests, hot, dry, humid, cold, whatever. They will eat almost anything and digest it [more efficiently than cattle](https://www.naelk.org/elk_facts.cfm). If you have a ridable breed, then I think these are the ones best equipped to handle all of your world's biomes. Unlike many bovines which headbutt and slowly back away for another impact, nearly all deer, elk included, fight by constantly pushing forward and lock antlers (exemplified well in [this video](https://www.youtube.com/watch?v=BMmmq77qahs)). Unless you're using cow elk, that would make for an interesting battle dynamic. [![enter image description here](https://i.stack.imgur.com/QD0D6.jpg)](https://i.stack.imgur.com/QD0D6.jpg) That's pretty much everything as far as "realistic" goes. To get more diverse animals we'd need to go back in time further than realism would allow, starting with pre-Interchange South American megafauna. Though who doesn't want to ride a terrorbird...assuming you can keep your balance and your limbs? It's hard to rank these animals from best to least suited because they're all so close together and have their benefits and drawbacks, However, we may not have to split the difference: you could have separate animals for open and forested terrain. Zebras, elands and dromedaries seem the best equipped for just the plains and light forest, cattle and potentially *Hemiauchenia* are excellent plains mounts that can handle incursions into the jungle, and banteng and elk are the best equipped for life in dense forests, though elk can thrive in nearly all of these biomes. For that reason, I'm really tempted to call elk the "winner" here, despite the lack of domestication data and a close match with more specialized animals. [Answer] Since we are on Worldbuilding SE, I would give an answer like: **HUMANS** Let's say You will mix two tribes that coexist: high, strong ppl with short ones, but more agile. If both tribe would work together in terms of warfare they may come into conclusion that it's far better to have 1 or 2 'strong' men plus 1 'agile' rider with bow than monts that needs to be fed and raised. More benefits? All of them (carriers and - let's say - archers) can think, don't really need to be steered, giving/receiving orders, they all can fight if dismounted, they can swim/crawl/climb/prowl/shoot/melee/sack/pillage/procreate. What we must face here is a story that would ligitimize all of this coexistence and all of the outcomes to their society. We may say that 'tall ones' must be slaves, but it would worsen this scenario in my opinion. Just think about all of positives. Negative sides are: limited (inferior to horses for example) speed and constitution, possible problems within society, role diversion due to different body build, and so on. I guess that the idea is worth of taking into consideration. [Answer] I would look back in history to the mega fauna of the Miocene and Pliocene. There are tons of large pack animals to choose from like: [Indricotheriinae](http://en.wikipedia.org/wiki/Indricotheriinae) Personally I think large canids and ursids would make more interesting choices. Canids may be a little more inclined to domestication than ursids, but ursids would probably be able to support more weight. Look for things like: [Epicyon](http://en.wikipedia.org/wiki/Epicyon) [Amphicyon Major](http://www.prehistoric-wildlife.com/species/a/amphicyon.html) [Arctotherium](http://en.wikipedia.org/wiki/Arctotherium) Even though these are obviously carnivores or at best omnivores, I would guess that some of them may be social enough to domesticate on a long enough timeline. [Answer] **I recommend the [Procoptodon](https://en.wikipedia.org/wiki/Procoptodon):** A giant cousin of [Skippy the Bush Kangaroo](https://www.imdb.com/title/tt0060025/). [![enter image description here](https://i.stack.imgur.com/YWQe3.jpg)](https://i.stack.imgur.com/YWQe3.jpg) *Attribution Wikipedia 2019 [Licence](https://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License)* > > a genus of giant short-faced kangaroo living in Australia during the > Pleistocene epoch. > > > Extinct now, but thought to have been around as recently as 18,000 years ago and quite suited to unkind terrain: > > Procoptodon goliah was mainly known for living in semiarid areas of > South Australia and New South Wales. These environments were harsh, > characterised by vast areas of treeless, wind-blown sand dunes. > > > Artist's impression of a mount and rider (note the stowaway): [![enter image description here](https://i.stack.imgur.com/lBJqj.jpg)](https://i.stack.imgur.com/lBJqj.jpg) *Attribution Survive-ark.com 2019* More than one theory about their locomotion exists - that they hopped like today's kangaroos or that they walked and ran in a fashion similar to humans, it's not currently certain. If their fighting style is anything like modern kangaroos, they would box and bounce up on their tales kicking and tearing with their rear claws velociraptor style. David Attenborough narrates a [Youtube clip](https://www.youtube.com/watch?v=WCcLMNcWZOc) of this. [Answer] This is a very interesting one to consider, but there is a good reason that humanity has trained different animals for similar tasks, and that's because different animals can be better suited to particular tasks, so there isn't a 'definitive' answer. A youtuber called ZooTier does great videos on this sort of stuff if you're interested. Horses are great due to their incredible stamina regeneration, their size and speed. Many horses are pretty good at running, and that's why humans like them. They can be used for war, transportation and recreation. Other animals, not so much. (note: Humans have actually outrun horses on occasion, google 'Man versus Horse Marathon', the conditions normally have to be hot however) You could cop out and say Camel, as they'd be the next optimal choice if horses went extinct, but I want something more interesting. [![enter image description here](https://i.stack.imgur.com/7KT2U.png)](https://i.stack.imgur.com/7KT2U.png) Ostriches are incredible animals for many reasons, and could definitely replace horses as mounts, and I believe would be just as effective. They've got everything a horse as got, perhaps just not as good. One, they can run long distances. Ostriches are good long distance runners and would be very effective at transportation. I'm not too sure what sort of pace they could keep over an extended period of time, but they could get the job done. Two, they can swim. I don't know how effective they are but I've seen pictures of Ostrich in the ocean, so they're known to be capable at swimming in deep water. I'm unsure as to whether they could support a human on their back if they were ridden however. They probably couldn't, as they only weigh about 120kg, so riders would dismount and guide through deep water, however they can get through shallow water. Three, they're quick. Ostriches can run faster than horses in a straight line, and they are also a lot more maneuverable. They can use their wings to change direction quickly which horses can't do. Four, they can fight front ways. Often in war, horses wouldn't charge into an object, like a large group of people. They just refuse to because they know they couldn't slow down before they hit it. Cavalry was more used at skimming groups down from the outside while the main forces were fighting. Although horses were trained to run people down presumably. Ostriches can fight (not effectively, but they're still scary), they can kick front ways and also peck if need be. I couldn't say I've seen this in action so we wouldn't know if they could effectively kill armoured people but if a rider was caught in the middle of enemies, an ostrich can attack front ways, horses on the other hand attack what is in front. Perhaps weaponizing an ostrich is a possibility. Five, they breed well. Ostriches can lay up to 10 eggs in a season, and as they'll be protected by humans, they'll have a greater likelihood of survival and hence they're replaceable. This could also mean they're farmed for the eggs, meat and feathers. Horses can only make meat. Six, they don't require as much food as horses. Being much smaller creatures, they can feed on more diverse food as they're omnivores, which means you can have more ostriches. Seven, they can be aggressive. Most Ostrich would attack humans rather than run from humans. I figure this is a similar aggressive mentality to Swans, and they're quite effective at essentially bluffing their strength, whereas horses would run most times, unless they couldn't. Disadvantages however are present... They're quite small in comparison to horses. They weigh 120kg whereas horses can weigh about 500kg, size matters in a fight and you'll feel a kick from a horse a lot more than a kick from an Ostrich. Similarly, this means they're weaker as well. They could be speared pretty easily whereas horses may fair better. However, strength in numbers, would you rather fight five ostriches or one horse? Bear in mind, you're armed. They can't be used for hauling goods. So they do not have the strength to pull wagons and such and never will. However as your question was pertaining to mounts, I figured this wouldn't matter as much. It's an interesting alternative to horses as mounts. It should be bore in mind that horses have been domesticated for a long time and as such have adapted to humanity. Had ostriches had the same amount of exposure and adaptation, they'd be a much more viable choice. [Answer] Well, Most of your predators are out. Do you really want to go into stressful situations in desolate areas where, not to put too fine a point on it, your ride might think you are dinner? We get away with it with dogs, only because they are pack predators. Lone predators like most great cats and bears might not be a great idea unless you can come up with some sort of un-breakable bond, and that would likely require some handwavium. Most options are probably going to require a long history of human interaction to make them viable So here are some that might work out, assuming breeding can take care of pushing characteristics to where we want them. **Pigs, Hogs, Swine, etc.** We always think of pigs as slow critters that are good for eating and not much else. This is so very wrong though. Pigs are smart. They are strong. They are Omnivorous, though they seem to prefer flora. Feral Hogs are a real problem in place like Texas because the tusks and size make them dangerous, they breed very rapidly, and they can tear up acres of farmland in nothing flat. So breed them to be a bit leaner, and maybe longer legged, and they will probably make decent mounts. They are pretty dangerous with those tusks, too. Hunting wild boar was a very dangerous pastime, in part because they are hard to kill. **Ostritch** Ok, it's been mentioned in at least 2 answers, but it's a viable transportation animal. You might need to adjust your thinking a bit. Take a pair of ostrich, harness them to a lightweight chariot and a normal human can get around. Smaller humans could ride one solo with a decent saddle as a messenger. **Moose** These will take a few thousand years of training an breeding to make them great mounts, But these would be great for northern climates. They are big, hardy animals. Elk might work too. They could be good in high, mountainous areas. Just keep in mind that mounts are generally beasts that can also be harnessed to pull as well. If you are looking to move people, a cart or wagon will serve with a wide variety of animals to pull. For a weapon of War, the chariot was the pinnacle for many centuries. Fodder is also a critical consideration. Your animal needs to be able to eat wherever you go, and if it grows there, great. If not, you have to haul it with you. Grasses and plants travel much better than meats, which is why predators aren't a great idea. The great part of the animals suggested here is that they all exist in the real world. [Answer] # Military T-Rex While you were inconvenient enough to specify "transportation and haulage" in your OP, I can't resist suggesting this for a specialty role - shock assault cavalry. They're certainly big enough to carry a rider, and at a pre-firearms tech level they would be unstoppable against infantry formations, and it wouldn't take many to be decisive. Just the possibility that the other side has them would be enough to justify the expense of having some yourself - sort of like nuclear weapons. Of course, breaking one to saddle would probably be a high-risk operation, but you did say that the humans are good at domestication. [Answer] Maybe large wolves/dogs? Pack mentality, and if large enough could support a rider. In addition wolves are long distance runners, and fast enough for warfare and hunting. Although you could possibly ride Sivatherium giganteum, the largest of extinct giraffids. [Answer] ## Oxen Pros 1. They are already domesticated, and were long before horses were. They are still ridden and used for haulage. 2. Their haulage capability has always been far greater than horses. they pull much heavier loads for longer periods of time. 3. They are easier to train than horses, for [basic training](https://www.record-bee.com/2017/02/17/oxen-vs-horses/) at least, becasue they are less excitable. 4. They handle foul weather better than horses. 5. they are easier to take care of than horses, there is a reason horses were a rich man's animal for a long time. 6. they are more "fuel" efficient than horses, that is you need less food per pound of haulage, one of the advantage of a ruminant. Cons 1. They are quite a bit slower than horses. 2. They have to be shod for long distance travel, although this may not be a issue with soft wet jungle soils. [![enter image description here](https://i.stack.imgur.com/3APuX.png)](https://i.stack.imgur.com/3APuX.png) [![enter image description here](https://i.stack.imgur.com/DXXFG.png)](https://i.stack.imgur.com/DXXFG.png) basically all this applies to water buffalo as well. [Answer] Well if you really want to be reductionist **Mules and Donkeys** ]
[Question] [ In my very lengthy story in the near future, there are some great 'Modern Marvels'. The next one I'm going to introduce might not be feasible, but if it is, I'd like to attach some numbers to it. The Secretary for Urban & Regional Development with the Federal Highway Administration have secured the funds to build a straight tunnel from New York City to Los Angeles, through the Earth. It is a near vacuum. Therefore the modernized high speed rail cars simply "fall" into the tunnel, accelerating continuously for the first half of the tunnel, then slowing down to almost a perfect stop at the other end. The only friction is that of the rolling coefficient, and perhaps what little air remains. Simply board your pressurized rail car, and go through the airlock. ![Map](https://i.stack.imgur.com/C4FtS.png "Map") (1) What is the deepest the tunnel goes? Is it in the crust still? (2) What is the length of the tunnel? On the great arc, they're about 4,000km apart, but the tunnel will be shorter. Bonus: Any ideas how fast a 'falling' train can get going? Should I add support from the train? High level figures and speculation fine, of course. [Answer] # Curved Tunnels It turns out that a longer path can actually be faster than the straight-line path. The fastest possible path in a uniformly dense Earth is a [hypocycloid](http://en.wikipedia.org/wiki/Hypocycloid). We can define this path parametrically as follows: $$ x = (R-r)\cos\theta + r\cos\left(\frac{r-R}{r}\theta\right) \\ y = (R-r)\sin\theta + r\sin\left(\frac{r-R}{r}\theta\right) $$ $R$ is the radius of the planet, and $r$ is the 'radius' of a single loop of the cycloid. $\theta$ goes from $0$ to $2\pi r/R$ over a single loop. For example, the case $R=1,\ r=0.1$ looks like this: ![enter image description here](https://i.stack.imgur.com/3GyIz.png) ## Geometric Properties We can integrate to find the length $S$ of a loop: $$ S = \int |d\vec{s}| = \int\_0^{2\pi r/R} \sqrt{\left(\frac{\partial x}{\partial\theta}\right)^2+\left(\frac{\partial y}{\partial\theta}\right)^2}d\theta \\ = \int\_0^{2\pi r/R} 2(R-r)\sqrt{\sin^2\left(\frac{R}{2r}\theta\right)}d\theta \\ = 8r(1-\frac r R) $$ The endpoint has coordinates: $$ x = R\cos\left(2\pi\frac r R\right) \qquad y = R\sin\left(2\pi\frac r R\right) $$ This means that the distance across the surface $d$ is: $$ d = R\times 2\pi\frac r R=2\pi r $$ ## Equations of Motion First, we calculate the distance $\rho$ from the center of the planet: $$ \rho^2 = x^2+y^2 \\ \rho^2 = 2r^2-2rR+R^2+2r(R-r)\cos\left(\frac R r\theta\right) \\ \rho^2 = R^2-2r(R-r)\left(1-\cos\left(\frac R r\theta\right)\right) $$ Then we calculate the velocity $v$ as a function of the rate of change of $\theta$: $$ v^2 = \dot x^2 + \dot y^2 \\ v^2 = 2(R-r)^2\left(1-\cos\left(\frac Rr\theta\right)\right)\dot\theta^2 $$ We can calculate the total energy of the train (per mass) as: $$ \frac{v^2}2 + \frac g{2R}\rho^2 $$ Where $g$ is the surface gravity of the planet. Plugging in our above expressions, adding the initial conditions $\theta=0,\ \dot\theta=0$, and solving for $\dot\theta$ gives us: $$ \dot\theta = \sqrt{\frac{gr}{R(R-r)}} $$ Therefore, the period of motion over one loop is: $$ T = \frac{\Delta\theta}{\dot\theta} = 2\pi\frac rR\sqrt{\frac{R(R-r)}{gr}} = 2\pi\sqrt{\frac{(R-r)r}{gR}} $$ For the Earth, this results in a curve like this: ![enter image description here](https://i.stack.imgur.com/1hJhg.png) You can see that the time reaches 42 minutes and 14 seconds for the limiting case of traveling to the other side of the Earth (where the cycloid degenerates to a straight line). We can divide the distance by this time to obtain an equivalent speed; that is, how fast you would have to go around the surface to make the same time: ![enter image description here](https://i.stack.imgur.com/MXUfL.png) In the through-the-Earth case, the speed reaches $\sqrt{gR}$, $7.9~\text{km}/\text{s}$. This happens to be the same as orbital speed, meaning that a surface-skimming satellite makes it to the other side at the same time as a straight-line gravity train. In the case of a New York to Los Angeles trip ($d=3914~\text{km}$): * The track length is $4500~\text{km}$ * The maximum depth is $1250~\text{km}$ * The equivalent surface speed is $2.6~\text{km}/\text{s}$ * The maximum speed is $4.7~\text{km}/\text{s}$ * The peak acceleration is $1.8~g$ + Acceleration is zero (free-fall) at both ends, and peaks in the center of the track. Peak value is $2~g$ for a very short track, and decreases linearly with length to $0~g$ (free-fall) for a through-the-Earth track. * The ratio $r/R$ is about $0.098$, meaning that the picture of the hypocycloid in the beginning is a pretty close approximation to the shape of this track. # Practical Problems * Such a tunnel is impossible to build, since no known material could withstand the heat and pressure in the mantle of the planet. * Any air friction or friction with the tunnel will slow the train down, and it will not be able to reach the other side without propulsion. [Answer] Assuming an Earth radius of 6378 km, an arc of 4000 km would represent about 36 degrees of arc, so the direct line between the points (i.e. the length of the tunnel) would be about 3935 km. Interestingly, if you assume Earth is uniform density (not actually true, but not a horrible approximation for this), the travel time for the train is the same between any two points on earth, [about 42 minutes](http://en.wikipedia.org/wiki/Gravity_train). The top speed depends on the points, and would take a bit of high school physics to work out (if someone wants to add it in the comments, I'll incorporate it into the answer.) Edit: I neglected to add that with the calculations above, the tunnel would extend about 300 km below the surface, which is about 10 times the thickness of the Earth's crust. Also to clarify, this is very infeasible with current engineering techniques. The depths, the attendant pressures, the friction, and other problems mean we seem to be quite a ways away from achieving this. [Answer] I came up with this same idea about 20 years ago as a thought experiment, and did calculations to arrive at the 42-minute travel time as well! But I want to point out that the tunnel does not need to be a straight line, especially since it would travel deeper than the earth's crust. You can have a 1000-foot drop (on a non-terrifying angle for the passengers) to get up to speed, and then travel "level" for most of the distance before ramping up at the end. And to avoid the rolling coefficient, I recommend maglev. ]
[Question] [ **Closed**. This question is [opinion-based](/help/closed-questions). It is not currently accepting answers. --- **Want to improve this question?** Update the question so it can be answered with facts and citations by [editing this post](/posts/239598/edit). Closed 1 year ago. The community reviewed whether to reopen this question last year and left it closed: > > Original close reason(s) were not resolved > > > [Improve this question](/posts/239598/edit) The first human stepped foot on the Moon in 1969. The first probe (Venera 3) landed on Venus in 1970 The first probe (Mars 3) landed on Mars in 1971. If Venus and Mars were habitable (they have liquid water, and are perfectly safe for "naked" humans except for the absence of food), the resources and effort to put more probes and humans on them would have surely been far greater. By what year would they have been colonized? [Answer] **1990.** The moon race was really the peak of the "space race" between America the Soviet Union. The Soviets putting something in orbit was A Big Deal, and America needed to not only answer that, but show they can do way more. Once on the moon, though, there simply wasn't much interest in continuing. The space race was basically over. But imagine if we had been looking at Venus and Mars, and they looked like they could be habitable, so we sent probes, and found out they were habitable. The space race would not have ended. Getting people (and military...mainly military, really) to lay claim to these planets would be absolute tip-top priority. Mustn't let the Soviets get there first! And the Soviets would do their best to try, because they mustn't let the Americans get there first! I think -- much like the moon landings -- the practicality or immediate value of doing such a thing would take a deep back seat to the idea that it *must* be done. I think you'd see America care a lot less about the spread of terrestrial Communism. It wouldn't have to fight in Korea or Vietnam. They'd be busy getting some rockets into space, and pouring loads of resources into that. Who needs this little bit of land in Southeast Asia when you can grab entire continents on Venus and Mars. **There [actually was a plan](https://www.history.nasa.gov/SP-4214/ch11-6.html), in 1969, to get people on Mars by the 80s**, including a 50-man earth-orbiting space station, but it was far more costly than the moon landings and the plan was not well received. But I think that would be a vastly different story if we knew they were fully habitable. **tl;dr** The space race would not only have not ended, but would have become a bigger budget item than anything else, and top priority for any country or alliance that could cobble together anything to send there, and in 1969 we felt like mid-1980s was a reasonable, if ambitious, target, to start landing people there. [Answer] **By what year would they have been colonized?** The answer to this question is heavily dependent on what resources we are able to find there. In this instance, Venus and Mars would obviously have the great benefit of an additional place that was safe for humans to live. You'd see the timeline start diverging mid century, where we're starting to get better observations of Venus and Mars. I'm going to make the assumption that you don't want drastic differences to the two planets - Venus still being obscured in mysterious clouds, and Mars still being primarily red. Going into the 1950s and 60s, we would have some awareness that there was liquid water on Mars - if there are large seas that is, we would probably be able to detect them via telescope. The point of real divergence happens when these respective probes land on the planets - Venera finds a lush rainforest. Viking finds a desert, but nonetheless, one that shows signs of life. From here the prediction begins to get fuzzy. In our real history, while significant fractions of the public protested the Moon landings as a distraction, many in the public were confident that we would soon be going to Mars, and were excited about this "inevitable" sci fi future. The problem is, getting to space is still pretty difficult. The tyranny of the rocket equation makes getting things and people into space expensive, and thus, in the 1970s, with the Vietnam war, an energy crisis, and unrest as we tried to figure out the aftermath of the civil rights movement, congress was very uninterested in exploring space. There is just as much of a likelihood that NASA could've gotten completely dissolved or just greatly diminished rather than what we got. What got NASA to keep moving was the promise of the space shuttle, a much cheaper, reliable craft to Earth orbit. After establishing this, we would build space stations, and cheaper architecture to return to the Moon, and truly establish an in-space economy. This however, was not to be. The shuttle was vastly more complex than NASA and its contractors had intended, and after the Challenger and Columbia disasters, it was solidified as having failed in its purpose. It did many great things, but had failed in its goals nonetheless. Flip flopping priorities from presidential administrations, and lack of interest from congress led to little progress in space until the 2000s. By this time, NASA couldn't really be killed off, because they were providing so many jobs around the country, but neither could they really progress, as a plethora of factors, mostly political, were holding them back. The thing that really changed the tide were the commercial companies. SpaceX, Rocket Lab, and many others coming onto the stage in the past twenty years really disrupted the industry and have lowered the cost. The true consequences of this I feel we'll only really see by the end of this decade. By decade's end, we will likely see at least one commercial space station, Axiom being the most likely, but we could have as many as three or four (starlab, orbital reef, Northrup Grumman station). Meanwhile, NASA is finally getting the political support necessary to return to the Moon, and SpaceX is gunning for Mars. I am personally more optimistic than some in my predictions - and thus I say that we will probably get people on Mars sometime after 2032, and I think it's very likely we will get there before 2050. The cost of spaceflight is decreasing dramatically, and with commercial space stations, the demand for human spaceflight will also increase, leading to more reliable and cheaper flights for people. Thus, while many engineering challenges lay in getting to Mars, it is for the most part a money problem. We could've tackled the engineering decades ago, I would say. But that money is important - and focus. The commercial companies have shown to be very adept in that regard. Unlike NASA's contractors, they cannot waste money for little development, or else they will go out of business. Now. Tangent on bringing up to speed the current state of today's spaceflight world, let's return to the original question - how would this be different in this new scenario? My unfortunate answer is probably not tremendously. The planets being discovered to be habitable would have an immediate effect of excitement in the public - life has been discovered on another planet. You'd probably see congress greenlight more funding for NASA to conduct science missions, especially sending their own missions to Venus. Actually getting there would be difficult. You'd still have the question many had then, and still today - why explore space when we have enough problems on Earth? This is an overblown feeling by the public being quite frank, considering that the average American pays about $30 a year to NASA in exchange for tons of jobs, scientific discoveries, and NASA developed technologies being spun off into ones useful for consumers. It honestly is quite up in the air. It all depends on if NASA could get the support behind it to get there faster. They might get trapped in a paralysis of sending many scientific probes, that though making many discoveries, would not be pushing things forward. Perhaps the commercial sector may spark into existence a bit faster. Whether it would have been as successful is a big question. SpaceX changed the whole paradigm because they wanted to do things quick and dirty. They wanted to break the monopoly that Boeing and Lockheed Martin had on space. Whether a similar company could have arisen a decade or more earlier is up in the air. What I am quite confident in is that SpaceX's iconic reusable boosters tech likely couldn't have come around too much earlier, as it requires pretty good computers controlling the descent. This would have a pretty big impact on the cost of space. It does not preclude other reusable tech coming about, like gliding boosters down to a runaway. Whatever the case, for your colonies to come about, you either need a world willing to drop buttloads of money, burning hundreds of millions to billions per launch, or find some way to make a rapid reusable rocket - and one that doesn't require extensive refurbishment like the space shuttle. The problem is that even if you find something valuable, like rare-earth materials on Mars, getting them back is so prohibitively expensive, it wouldn't be like how gold and spices pushed forward exploration five hundred years ago. It could sustain a colony after a great deal of time, after launch costs get lower, but as for pushing the first exploration closer, probably wouldn't do a lot. One possible idea is that the population scare, most prominent in the 70s (before improvements in agriculture showed we'd be able to feed a larger population) could perhaps prompt a movement to send people to Venus or Mars. This could bleed into political support for space, with congress giving some token support towards larger NASA budgets. Conclusion then for when we might see the first boots on Mars and Venus? As I said earlier, probably not too much different to our reality. These planets *would* be a lot more enticing, but many of the challenges are still there. If there were bigger changes, I could see us getting to Mars in the 2020s or even perhaps earlier, but it'd likely be rather ramshackle. How this pans out depends heavily on what decade it happens in, what the geopolitics are like, etc. You could come up with reasonable explanation for it happening in the 90s maybe, but not too much earlier I'd say. You might look at the alternate history show For All Mankind. Not *super* accurate, but gives enough explanation for a work of fiction. Venus would be more difficult, as presumably you want to return home on the early missions, and due to the larger gravity, would require a larger return rocket (which is already a difficult task with Mars exploration). I'm confident in saying then that we would probably see Venus happen later, but not extremely later. It depends on if there is competition between countries or companies who might want to take the "real first prize." **And by what year (if different) would those colonies become self-sufficient?** Oh boy. Self sufficiency. That is a tough question to answer. I'd venture a guess that it would be faster than with our real Mars and Venus. It would be slow going I'd say early on. Much more native flora and fauna would prompt a lot more scientific research before colonization could happen in earnest. It would likely lead to protests from the growing environmental movement, that "we're already screwing up our Earth do we need to screw up two more?" This is already a thing that a lot of people are saying in our world, and we don't even know if there's anything living out in our solar system. It would be much more pronounced in this world. There is also a lot of risks to consider with space originating diseases, astronauts quarantining after missions, and likely a good while before we'd start seeing people walking around on Venus or Mars without a space suit. It would be at least easier that they would only need something more similar to a hazmat suit, and not a full blown pressurized space suit. If the environments of these planets proved suitable to human life, if the protesting was managed in some way, then you'd likely start seeing colonization efforts arising. It would depend heavily on if you could grow food in the planets' native soil. Mars in real life has very toxic soil that would need to be heavily processed before use. This depends on if the life on these planets is carbon based, how similar it is to Earth, etc. If its carbon based, and there are ecosystems on the planets allowing breakdown of soil, we could perhaps grow food there - but that would likely only happen after years of astrobiologists studying this new life. Your early colonists would, for the most part be scientists. Commercial companies would probably start moving in next. There isn't much of value business wise on these planets still, but Mars would be a good stepping stone to the asteroid belt, where mining could be done. So I'd venture that Mars would not only be visited first, it would also grow faster. Venus would be a more desirable place to live probably, depending on how hot it is, but it wouldn't have much value beyond the science, unless we discover something valuable there. So yeah... this scenario gets into a ton of "what ifs." It allows you a lot of flexibility in coming up with reasons why something can happen earlier and still be plausible - perhaps "the spice must flow" on Mars. I'd probably make an upper limit that self sufficiency on both worlds would probably happen prior to 2100 (which I think could probably happen on Mars in our world) but technology could make that go faster, environmental concerns slow it down, or politics just not get its rear in gear. I can for sure say that this change to these two planets would really muddy up things. People will likely be more persuaded by the idea of becoming a multiplanetary species (a goal often spoken of by SpaceX) - obviously people get the idea of having insurance in case of the absolute worst of Earth facing extinction - but knowing that Venus and Mars are actually livable places would increase this allure a lot more. Most people interested in living on Mars today are... eclectic, lets say. It would be a difficult life, where we would need to spend centuries at least in protected bases or underground before we could have a world where we could breathe. This world though, would be much different. The environmental concerns though, are again a big factor in how this pans out. Today a lot of political discourse goes around about the impact Europeans had on the natives of the Americas - in the future it might be that future Martians and Venusians looking down upon their ancestors for tramping down the native creatures and plants. This has been a very, long response, but it is a scenario that prompts a lot of questions. You could take it in a number of ways, have many interesting stories to tell. You could investigate how we deal with being the stewards of another planet when we barely know how to manage our own. You could look at how this changes the culture and ambitions of people a thousand years from now. Maybe we care little about pursuing interstellar travel when we have three whole habitable worlds to contain humanity. I wish you luck as you study this. For further study, I recommend looking at stuff on space exploration (like from the youtube channels Scott Manley and Everyday Astronaut) and stuff on Astrobiology, like the work of Seth Shostak. [Answer] ## December 2022 Of course, humanity did not really *need* to take a 50-year break on manned space travel after 1971. We could be on Mars by now. The long pause happened in our world, because the main accomplishment, that was putting a human being on the moon, had been achieved. But private enterprise and governments saw little use for manned moon missions, the moon being a desolate and hostile environment place, without relevant resources. **Limits to Growth: serious incentive to proceed colonizing another planet** Now imagine bringing humans to Mars or Venus would be the new goal set. Why ? There was every reason to consider colonization: in this period (1972), the report [Limits to Growth](https://www.clubofrome.org/publication/the-limits-to-growth/) published by the Club of Rome: a limit on the further expansion of humanity on Earth and planetary resource use. There was a serious incentive. **Timeline 1972-2022, let's pick Mars** We reached the moon, but now, technology would be needed to colonize a near planet. A huge project. Governments world wide started to cooperate and invest in it. There were two options: Mars had been known for its deserts, but oxygen (16%) and plenty of water were detected, so there was every reason to assume Mars would be inhabitable. Venus could be, but it seemed somewhat uncomfortable to permanently live indoors.. and most water exists in a boiling state, requiring cooling equipment, that would be expensive. So.. Mars was picked. **Moon base, Mars expedition** The NASA, together with rising private space enterprise (yields were projected!) set out to build a moon base, which was finished in 1985. By 1992, the first astronauts set foot on Mars. They stayed there for a few weeks, with no need to wear a helmet. But they had to take food supplies, and when these supplies were exhausted, they were forced to return home. **Cargo ship** The current absence of food on mars implied agriculture had to be developed. Meanwhile, ESA and the Chinese enterprise Spactec had developed a cargo ship. By 1988, they finished the design, and a succesful test launch followed in 1994. The Spactec freighter, a one-way, fully robotic space ship, could transport and parachute fuel and tons of goods, which was needed to boot agriculture development on Mars.. In 1996, a Spactec ship was launched empty, and parked on the moon. Then fourty-eight Earth-Moon shuttle Missions followed it, each loaded with agriculture equipment, like tractors, plowers, seeds, soil, embryos of cattle and poultry, and tons of food. **Food production** In 2002, the Spactec freighter was fully loaded and launched from the moon, on its way to Mars. In 2004, a team of farm supervisors and technicians arrived on Mars, with the farming equipment ready for use. With the help of farm robots, they had food production up and running on Mars in 2018. **People** Volunteer colonizers [came in plenty](https://www.mars-one.com/): there was a long list of candidate colonizers. Anyone who would like to leave the planet subscribed to a website, submitted a short autobiography and experts in sociology, economy and behavioral psychology evaluated the candidates. One Spactec cargo ship named Pioneer III was modified to carry people. The ship left for the moon in 2018, arriving on Mars in 2021. The ship had 1600 colonizers on board. At this point, careful reconnaissance followed, the colonizers consuming their first Mars vegetables and meat. They celebrated Christmas on their new planet, with the first *home grown* Christmas meal in december 2022 and the original (and now famous!) Mars Beer. [Answer] Depends on what you count as "being colonized". A colony, in the traditional sense, has a few specific purposes: * Resource extraction * A place to move undesirable people to (overpopulation, criminals, ...) * Prestige (e.g. expanding a country's sphere of influence) Since space travel is incredibly resource intensive, you won't be able to move significant amounts of people between Earth and other planets, and this might even be a hard, physical limit. The same thing also limits the transport of resources. There is no point in extracting resources on Mars, if getting the resources back to Earth takes more resources than what fits on the transporter. This leaves prestige, which is worth something in the right political circumstances (e.g. the race to the moon, which wasn't actually about getting to the moon, but about proving that the USA/USSR is better than the other), but is probably not enough to warrant too much cost (as seen in the real world, where manned space travel to other planetoids quickly stopped once the prestige goal was reached). In the case of colonizing other planets, there is one additional reason: * Working as an ark, in case the Earth becomes inhabitable, so that humanity can still survive somewhere That's a mostly moot point. The dead on Earth will not care that there are a few people on Mars still living. Also, getting a few people to Mars and creating a self-sustaining advanced Civilization on a different planet, that can survive when no more supply ships from Earth arrive, that's something completely different. A settlement of 1000 people can easily be wiped out by a single disaster. So I fear, there wouldn't be much practical and financial motivation to actually create a colony on Mars. I'm sure we'd have a few people on Mars by now, but the Mars colony would be probably on the level of the ISS. A handful people, who are there "for science". [Answer] Not too much before present time. Interest in Mars has always been there, but only in the past 20 years (Spirit and Opportunity were in 2003) have we actually managed to get mobile robots on the ground there. And around 30 missions to Mars **failed**. It's not as easy as it seems. If Mars were habitable, interest would've been much higher, of course, and more effort would've been made, but why would technology have developed very differently? More funding and interest can accelerate things by a couple years, but the same way a Moon landing wasn't going to happen in 1945 no matter how much some Nazis would've wanted to escape Earth, colonizing Mars requires technology that we barely have today, even if all you need to bring is people, construction materials and agriculture foundations. [Answer] Depending on what was there. Another Earth (minus life)? Nobody would seriously care. We don't even "colonize" the shit out of "primitives" in the various parts of Earth, like in the past. Even if we do, it is because of ideology, not because we want more land. In that case, we would be only trying to send people there to show we can, not because we cared about that piece of ground. So, it would happen slightly faster than now, only because one-way trip makes some sense. But if people knew there was some valuable unobtainium out there in addition to a place to live, we would be SERIOUSLY trying to get some of that. Bonus points if that unobtainium can be only extracted/handled/transported by humans, probes/robots being too clumsy. In that scenario, it isn't too far-fetched that NASA would be given way more money to work with, which would seriously speed up the timeline of rocket development. Obviously, at a high cost to other areas of science - like how putting everyone on Manhattan project stopped or slowed down everything else. Now the important question is, when do we learn of this unobtainium? If we got to know with the first probes in 70s, then possible timeline is in 1980s. Under huge and likely unrealistic assumption that USSR would simply watch and let USA get hands on that, and not actively try to sabotage their efforts in various ways (having USA+USSR work together is too far fetched while I believe USSR wouldn't have a chance to win the race). If we learned that back in ~1950, that might bring timeline down to as short as 1970 - it would be a MUCH more worthy goal than merely getting some beeping chunk of metal in orbit. [Answer] ## Archean Eon, between 4.0 and 2.5 billion years ago The formation of the Earth is believed to have occurred about 4.54 billion years ago. Prokaryotic life originated not too long after, as early as 4.28 billion years ago. In their early histories, Earth and Venus likely had thinner atmospheres than they have today; Mars likely had a thicker atmosphere than today which may have been similar to early Earth's. These relatively thin early atmospheres, coupled by a preponderance of projectiles striking the Earth during the [Late Heavy Bombardment](https://en.wikipedia.org/wiki/Late_Heavy_Bombardment), 4.1 to 3.8 billion years ago, could very well have allowed meteorites seeded with prokaryotic life from Earth to arrive on Venus and Mars. [Over 53,000 Martian meteorites](https://en.wikipedia.org/wiki/List_of_Martian_meteorites) have been found peppered across OTL Earth. Today, Earth's relatively thicker atmosphere would make it less likely for Terran meteorites to land on Mars, but this may not have been the case ~4 billion years ago when the two planets had more similar atmospheric densities. Likewise, Venus's atmosphere today is almost 100x as massive as Earth's, making it extremely difficult for Venusian meteorites to escape - but, again, this may not have been true much closer to both planets' origin date. It's not unreasonable to imagine material being exchanged between all three planets in this era. If, unlike in OTL, environmental conditions on Venus and Mars had gone down a path more similar to that of Earth, then microbes on Terran meteorites might have been able to reproduce, flourish, and evolve on those planets. Over the eons of evolutionary time, entirely alien alternate trees of life could have evolved on Venus and Mars, eventually spreading into every ecological niche on those planets. Well... perhaps not *entirely* alien. For one thing, these separate Venusian and Martian trees of life would still have shared a common evolutionary ancestor with Earth life. Thus, we might expect it to also have some of the same properties as the [Last Universal Common Ancestor (LUCA)](https://en.wikipedia.org/wiki/Last_universal_common_ancestor) of life on Earth: its biology would be based on carbon and water, its genetic material would be DNA or RNA, its metabolism would use the same amino acids, it would share other aspects with Earth life such as enzymes, proteins, ribosomes, etc. And for another thing: "habitable" is, at the end of the day, relative. If by "habitable" we are assuming that the Venusian and Martian environments went down similar paths as Earth's environment, then via convergent evolution we might expect some traits to originate independently on Venus and Mars in parallel with traits of Earth life. For example, the abundance of energy arriving at all three planets from the Sun may have spurred the independent evolution of photosynthetic life - though most likely, the specific chemical pathways would differ drastically. Nevertheless, these commonalities put only very weak constraints on just how alien life on Venus and Mars could have gotten. At the very least, we might expect to see at least as much diversity *across* planets, as already exists *within* the single tree of life which evolved in OTL on Earth - and the amount of diversity we already see in the latter is staggering. Life on Venus and Mars would likely have evolved into categories which never existed in OTL - though, whether these categories would be practically relevant from a human perspective is uncertain. As for the prospect of sentient life: here I delve a bit more into personal subjective speculation. My take on it is that we tend to be guilty of highly anthropocentric thinking when it comes to speculating about nonhuman "sentient life". We see Earth life has having evolved according to a teleological progression, i.e. from the simplest single-celled life, through less to more complex organisms, and finally arriving at us, "sentient life". We see this history as a "progression", because it already happened so here on Earth; but from a pure evolutionary perspective, this is nonsense. Evolution has no "end goal"; it just happens. Thus there is really no good reason to imagine that Venusian or Martian life would happen to converge towards sentience. "Sentience" is, imho, a circularly-defined notion: humans are sentient, and sentient means "like humans". Venusian life could just as well end up "progressing" toward some other characteristic which, from our perspective, seems utterly arbitrary: sphericalness, bumpiness, symmetry, viscosity, anything at all. Martian life, as it increased in complexity, could end up "progressing" toward some other property, which while roughly analogous to our own sentience in a very loose sense, is something of which we cannot even conceive and for which we have no concepts. Human colonization of Venus and Mars in this timeline would likely be a rocky prospect. In the early days, most likely humans would need to live in sealed colony habitats ironically reminiscent of those in OTL, though the reason for such habitats would be different: there would be no telling how alien organisms which evolved on Venus and Mars might interact with our own Terran biology. For this reason, the early cost/benefit of extraterrestrial colonization would not be too much lower than in OTL; thus, the timescales on which it occurred might also end up being similar. Eventually, we would ascertain whether/if/where it was possible for us to interact with the native Venusian and Martian biospheres without danger to ourselves. This would likely be a pretty gradual process: after all, we still have only an incomplete picture of biology on Earth, and we would need to understand entirely new xenobiologies from the ground up. Considering our psychology, it would likely also be a process fraught with various tragic accidents and risky experiments - I imagine not a few people would end up just saying "screw it", and jumping out of the habitat, damn the consequences. The colonization process writ large would be replete with ethical conundrums and existential risks to humanity needing to be managed. If we subjectively judged Venusian or Martian life to be inconsequential and/or dangerous, we might simply try to sterilize it and substitute it with more familiar Earth organisms. Alternatively, research access to entirely new xenobiologies might spur medical, ecological, or other lines of research in a way that is simply not possible in OTL. Last, but not least: access to Venus and Mars would reshape and widen our conceptual understanding of exactly what "life" is, and of the myriad ways in which it can vary. While we would still be constrained by "solar-system-centric" thinking due to lack of referents apart from the genealogies of life originating among the inner planets, we would have access to larger & entirely new categories of knowledge which are not available to us in OTL. ]
[Question] [ Rivers of lava are a staple of fantasy. But in the real world, lava flows are usually very short-lived phenomenons caused by volcanic eruptions. Is there some plausible way on an otherwise earth-like world to have a naturally occuring river of lava which is several meters wide, several kilometers long and functions as a permanent geographical feature? With "permanent" I mean permanent enough that someone would draw it on a map which is still useful a couple decades later. [Answer] **It's not completely impossible, but it requires some unusual conditions.** First: The 'source' of your lava river is always going to be an active volcano, by definition, but volcanos don't always involve tall mountains. There are also [Shield Volcanos](https://en.wikipedia.org/wiki/Shield_volcano) which form relatively low, broad rises in the terrain where the lava pushes to the surface. It's important to note here that lava doesn't always come from the top of a volcanic mountain either. The heat and pressure come out through the path of least resistance and while the top of a volcanic mountain may be where the lava came out LAST time, subsequent eruptions are as likely as not to come out through cracks and newly opened fissures in the sides of the mountain. Second: You only get lava when an enormous amount of heat is rising up from the earth's mantle. Generally speaking this occurs in one of two cases: Either you have a 'hot spot' allowing that heat (and magma) to rise up through the middle of a continental plate like the one that's been continuously forming the Hawaiian Islands for the last few million years, OR you have a place where the continental plates are being pushed apart. Now, the biggest example of this is the huge volcanic rift that runs right down the middle of the Atlantic Ocean that's pushing Europe and Africa in one direction and the Americas in the other, but another good example is the [Great Rift Valley](https://en.wikipedia.org/wiki/East_African_Rift) in Africa that is currently in the process of breaking Somalia off from the rest of Africa and forming two new continental plates. Both of those examples have historically had occasions of very long-lasting continuous lava flows primarily because instead of going through cycles of cooling and heating where pressure builds up over centuries or millennia to a catastrophic eruption, these volcanoes have a continuous supply of lava constantly rising to surface. **So, all of that basically means the following.** To have a river of lava that persists for decades what you need is an area of continuous low-grade volcanic activity that's near the sea, to allow somewhere for all that lava to go instead of building up a big mountain right there. [Kilauea](https://en.wikipedia.org/wiki/K%C4%ABlauea) isn't venting lava like this right now, but it has done in the past, for decades at a time. You could also get a similar sort of condition from the African rift valley if Saudi Arabia weren't in the way holding the two plates together at the north end. The main thing is that it's not going to work if you want your river of lava to be out in the middle of a desert somewhere or something. It has to flow into the ocean, and it can't take very long to get there, or the lava will cool and it'll just start forming a big blobby mountain instead. [Answer] ## River No, Lake Yes you just can't have a steady state lava river, the shape of a river means the lava is cooling which means the river is getting smaller so even if you feed in more lava it follows a different path. Lava Lakes however are a real thing and steady state lava lakes can exist for centuries because the lava can circulate and get reheated as it cools. Although you will want a lake with some gas to keep the lava moving the most. Basically the lava will swell, spit, and sink constantly, this will also give you a nice roiling effect. Erta Ale for instance has been active for over a hundred years. [![enter image description here](https://i.stack.imgur.com/OGZut.jpg)](https://i.stack.imgur.com/OGZut.jpg) [![enter image description here](https://i.stack.imgur.com/XC7Xq.jpg)](https://i.stack.imgur.com/XC7Xq.jpg) Note: keep in mind a visual marker for "lava flows here" would be a perfectly valid thing to put on a map in a valley prone to lava flows, it just is not a indication of a permanent structure, as much as "this area is prone to lava flows" plan accordingly. [Answer] Not really. There have been tons of long lived lava flows in history, but they dramatically alter the land. Lava cools as it flows, creating layers of solid rock that build up. This happens on volcanic islands where the lava can flow into the ocean, expanding the size of the island. Lava flows exposed to air will cool and form a crust over them while the hotter lava continues to flow underneath. This can make really cool lava tubes, but prevents standing rivers from really being a thing for long. Your best bet is to have really, really fast flowing lava that has somewhere to go. So a tall volcano with a well established channel (maybe a lava tube with the roof caved in) that drains into an ocean could work well enough. Lava that cools never has time to form solid sheets / gets broken up by the turbulence and gets carried out to sea. Your island will have grown considerably in a decade though. [Answer] **River of molten metal.** This "river" does not actually flow - rather it is static. Within its impervious rocky banks, the molten iron comprising the river extends down to the mantle, and the conductivity of the metal means that the vast internal heat of the planet can keep the metal molten. Perhaps the metal is at this surface position because of an ancient meterorite impact, or maybe the molten metal has been squeezed up to the surface. This sidesteps the problem of continuous flow and offers a solution to produce continuous heat and permanence. Convection currents within the metal would make it stir and eddy. Parts of the surface that cool from contact with the air would sink down into the depths and be replaced by hotter metal from beneath. The molten metal is a good resource and there are industries along the banks that gather and process the molten iron into useful tools and building materials. [Answer] **Really Big Lopsided Eruption** Some time ago, the mountain got a lot bigger, and either had one side fall over at the beginning or evolved a channel to the side as it crumbled. Crucially, there must be significant height to drop lava at the end of its channel, or it will pile up and you won't have a channel anymore. The new lava pumped up from inside must be insulated on most sides in the mountain, with one big exit. Real world lava flows tend to form crusts if they slow down and cool, so your channel needs to have significant steepness. [Answer] As with all things worldbuilding and writing, it's just up to you to decide how much you want to bend reality or play with the rules. My personal route, in an otherwise earthly scenario, would be to say that the rock simply comes out of a volcano and travels until it solidifies, which could actually be a fair distance. Some applications of this would be playing with the idea that the reason the river continues is because people harvest the cooled rock and refine it/sell it. Or, if you really wanted to get creative, you could always say that the river somehow deposits back into the mantle, thus a technically never-ending cycle. ]
[Question] [ Take your typical Necromancer- able to raise/control/talk to corpses, summon/bind ghosts, wither an organism- things that revolve around 'death' as a theme, as opposed to manipulating life/death energy or just a specialisation of magic. Assuming that they don't have access to human corpses, what could the modern necromancer do to make money? What niche markets exist that a necromancer could fill? For the purposes of the answer, assume a ghost's memories fade over time, there is a generic, cave-like underworld where ghosts without 'anchors' get sucked to and necromancers can access and that necromancy is legal- but messing with a human corpse is still highly illegal. Necromancers are born as such and there is no way to 'create' a necromancer. While resurrection is impossible, they can bind a ghost into a human corpse- but this takes a lot of bureaucracy, weekly hour-long 'repairs' and generally only lasts about a year. The setting is 2015 with our tech levels. [Answer] There are all sorts of "services" that such a necromancer could provide. It depends really entirely on what they can do, and if they can bind ghosts to do their will, there is really quite a lot that can be done. 1. Summon ghost to pass information to and from the underworld. Maybe a murder took place, and they need to find out who it was. Find a necromancer! Only uncle Joe knew where the treasure was buried? Find a necromancer! Sentimental wife just wants to talk to her husband who has passed away? Find a necromancer! This alone would be enough to keep a necromancer well-fed. 2. Spying. Yes, seriously. It may not seem mystic and in fact, it may seem downright absurd, but why not? Ask a ghost to eavesdrop in a nearby castle.. find out how many soldiers they have, with what frequency they change shifts, do they get drunk often? Etc. Want to find out if your lover is cheating on you? Get a ghost to tag him. 3. Can ghosts haunt objects/places? If so, you can be hired to send a ghost to haunt these objects/places. It would be an excellent way to keep people away from something you possess. Similarly, a necromancer could presumably dispell the haunting of an object/place, which would be an equally valuable skill to have. 4. Create plagues. It would be an excellent weapon against an enemy castle. Hurl a couple vials containing these plagues and wipe out the castle without ever having set foot inside. Needless to say, if such a thing were possible, there would be a lot of plagues about, so presumably if a necromancer creates them, a necromancer can also create cures fairly easily, so this doubles as an antidote to plague manufacturer. 5. Expertise. Is the woman a witch or not? Necromancers would be considered the experts on this subject (despite being albeit a bit hypocritical to allow a necromancer but disallow a witch). A necromancer may honestly not even know how to tell, but this doesn't mean the people think that way, meaning a necromancer can still exploit these services in exchange for money. 6. Raise armies. No, they don't have access to corpses, but this doesn't mean that someone of power wouldn't try to befriend a necromancer in order to expand his armies. Usually laws are meant to keep the people in order, but kings and queens are above that order, so long as such things are kept somewhat discrete from the general public, and you had better believe that if a king or queen had a way of doubling his or her armies that he or she would do so. In that regard, having a necromancer, even one that has access to corpses, could be very useful, so long as his practices are kept from prying eyes and the general public. Hope that answers your question. [Answer] While Necromancers may not be allowed to mess with human corpses, they can work with animals and plants - and with live humans. Therefore: * Healing humans: A necromancer controls the energies of life, and may thus be able to perform feats of healing unavailable to the common herbalist. Reattach an arm? Stop gangrene? Anesthetize a patient before an operation, and then speed up healing? Easy, and possibly well-paying work. There may even be a corpse or two whose disappearance nobody will notice. * Reviving animals: Your pet died? No problem, the Necromancer will bring back your dearest companion. The horse/oxen requires too much maintenance? An undead beast may smell a bit worse, but will do its job just as well (that is not only useful for farmers, but of course also for armies). * Killing plants and insects: Getting rid of all the weed in the king's gardens may not be what the bright-eyed novice dreamed of when entering the necro-academy, but it does pay the bills. Destroying growth on large patches of land makes clearing more land for the ever-expanding kingdom a lot easier (though somewhat dangerous, because you shouldn't kill the microorganisms). Killing insects can require similar high levels of skill: While killing mosquitoes, or eliminating bed bugs may carry little risk of overdoing it, removing fleas from a pet means being really careful, otherwise you may have to throw in a revive for free. * Killing everything: Instead of the hard task of killing only some organisms but not others, the ability of the necromancer to purge life completely is highly regarded in the food industry: All you need is a airtight container for the food, and *sha-zam* it will not spoil for a long time, and suddenly, you can think about exporting milk from the vast necromancer-created pastures throughout the known world. Similarly, healers appreciate thoroughly sterilized equipment, and goods in warehouses keep a lot longer if there is no threat from mold and rats. In conclusion, while the fancy necromancers get to speak with the dead, solve crimes, and get featured in the news, there is plenty of mundane, but well-paying work for the aspiring necromancer. [Answer] Though technically covered by @Neil, but not explicitly mentioned: the easy answer is (private) detective/ coroner. The ability to communicate with corpses and or ghosts simplifies many police activities, mostly solving murders by getting a witness statement from the victim. The other necromancy could be useful for self-defense and subduing suspects by/without killing them. [Answer] As it is a lot of cheap labor (in terms of pay and sacrificability) it could be used in the army to mine dangerous, but lucrative material, and work with some that in the procedure would be too dangerous to living humans. Then he could sell those materials so cheap that it could end up in a monopoly, giving him great power near a nation/kingdom. ]
[Question] [ Could a war continue indefinitely? I see two parts to this question: ### Stability A war is often unstable, in that a slight advantage gained by one side makes them more likely to win further battles and gain further advantage. This positive feedback loop makes power swing to one side or the other, rather than remaining balanced. Is there a situation in which a war could be stable, so that a slight advantage gained would tend to lead back to balance preventing either side from winning? ### Persistence If a war is clearly balanced, it can lead to agreement by both sides to stop and negotiate instead. Similarly if neither side really wants war or escalation leaves both sides drained of resources then attacks might gradually diminish to the point that they stop altogether to be replaced by a stand off and eventual peace. Is there a situation in which a war could be sustained, so that the attacks do not tail off and no negotiation is possible? **Specifically I am interested in finding a situation where both these factors are present at once, to give a war that never ends.** --- To clarify, I am looking for any situations that would give the desired effect. Not necessarily attitudes of people and societies, but technological, geographical, seasonal or other situations that would create the dynamics I'm looking for. I'm asking the question because I don't know which of these will be the source of the answer. [Answer] Indefinitely is hard to say but for a long time yes. If for example the USSR hadn't had fiscal/food issues we would likely still be in the cold war - that's just a recent one. Further back in history, England and France had that "little spat", [The Hundred Years War](http://en.wikipedia.org/wiki/Hundred_Years%27_War) about who was the rightful rule for oh about 120 years. The likelihood of never ending is very low but for a long time yes. The requirements for a long war would be: * tactical/technical parity; the side(s) don't have to have anything like the same weapons but all put together they have to have similarity. (unless it is a guerrilla/terrorism based war in which case it is different but I don't think that's really what you're thinking of). It doesn't need to be similar at one specific point because the fortunes of war can sway back and forth as technological advancements happen; just in the long run analysis it has to be equivalent. This includes military leadership as well as the weapons/plans. * Strong public sentiment (for democracies)/Powerful leadership (for most non-democracies). Ideological support for the war (f.e. United States in the Cold War) or a highly controlled society (f.e. England/Hundred Years War). * lots of small incidents to keep feelings high but avoidance of major battles which could actually be decisive. (f.e. Cold War) * A lot of territory that can be lost/gained without finishing the war (f.e. Hundred Years war) [Answer] Have you read 1984 (Orwell)? > > Since about that time, war had been literally continuous, though strictly speaking it had not always been the same war. For several months during his childhood there had been confused street fighting in London itself, some of which he remembered vividly. But to trace out the history of the whole period, to say who was fighting whom at any given moment, would have been utterly impossible, since no written record, and no spoken word, ever made mention of any other alignment than the existing one. At this moment, for example, in 1984 (if it was 1984), Oceania was at war with Eurasia and in alliance with Eastasia. In no public or private utterance was it ever admitted that the three powers had at any time been grouped along different lines. Actually, as Winston well knew, it was only four years since Oceania had been at war with Eastasia and in alliance with Eurasia. But that was merely a piece of furtive knowledge, which he happened to possess because his memory was not satisfactorily under control. Officially the change of partners had never happened. Oceania was at war with Eurasia: therefore Oceania had always been at war with Eurasia. The enemy of the moment always represented absolute evil, and it followed that any past or future agreement with him was impossible. > > > **George Orwell (Nineteen Eighty-Four, 1949)** > > > Essentially, the three large powers are always fighting over large patches of contested ground by switching alliances whenever a side grows too powerful - an unspoken agreement to allow any side to win, so that they'd never have to share the spoils with their ally. Most (no?) wars have endured like the one in 1984 because the major sides do not change alliances repeatedly during the war. Stability is found by strong public support and the endurance of the megapowers. They cannot by starved off - they are too large, and the people are kept in a fervor for the endless fighting via propaganda and strict control. As a side effect, little actual innovation occurs which gives one of the three powers an advantage over the others: the governments don't really want the war to end, as it gives them reason to keep the people in control. Read 1984. Just read it. [Answer] **Three (or more) Sides** The easiest way to get a permanent war situation (where there is actual real fight) is to have three sides. If one side is clearly winning the other two team up to bring them down, but then a new side is winning so the alliances shift again. The situation is inherently unstable though so unless someone is acting to keep the war going by pulling strings behind the scenes eventually it will end. **MAD** In theory you could create a low level conflict if both sides have powerful weapons too powerful to use (Mutually Assured Destruction) but conflicting goals. The problem though with this theory is that while you can get low level skirmishes and conflicts and/or a cold war neither side is ever going to commit its full force and you're unlikely to ever see actual warfare. So depending on exactly what you are looking for in the permanent war MAD may or may not be helpful. **Asymmetric Conflict** If one side is waging an underground guerilla war then the conflict could potentially go on indefinitely. That does depend on the "dominant" power not being willing to just wipe everyone out to solve the problem though and again doesn't really give you the "armies in the field" experience. [Answer] There could exist a situation where warfare was a tradition, where the targets of warfare were pre-agreed, and were the only legitimate targets, and where the forces employed were of pre-agreed sizes. This is different to limited or total war, where each side is *trying* to bring the conflict to a close by military means. Such a situation may exist where warfare is a religious rite that victory would make impossible to perform further - the object is to fight, perhaps to achieve *personal* victories, not to achieve a *collective* victory. Another possibility is that the leaders of the warring parties each encourage unending war in order to maintain their grip on power and profits - in fact they have a secret agreement to never seek victory in order to maintain the status quo. I would imagine such leaders to be somewhat Stalinesque in their propensity to execute those who ask too many questions or cast doubts on the leaders' judgement. [Answer] Halderman's "The Forever War" used the following to quite convincing effect: 1. Space travel at near-light speed caused "time dilation"; soldiers could travel vast distances in a matter of weeks, but on Earth 100s of years would pass. 2. No possibility of communication between the sides due to language barrier. 3. No concrete objective. War was primarily about vengeance and propping up the economy. 4. Small scale and small political cost. While the expense was enormous due to the technologies required to wage a space war, the number of soldiers involved was quite small. No one on earth felt harmed or in any way impacted by the war, thus no one had any reason to stop it. 3 and 4 were the case in the author's experience in Vietnam, and still the case with modern wars today. [Answer] All the above are good answers, but I've got one more to add: ## Automation The only reason to ever end a war is because one or both sides have decided it's not worth continuing the fight. Generally they've lost too much, stand to lose more, or simply don't have the will or the resources to keep fighting. Very few nations are ok with losing, so from the standpoint of the losing side, every war *ought* to be permanent, at least until they aren't the losers anymore. But that logic gets undermined in the face of automation. If I've got a factory making death-bots and sending them to you, and you've got a factory making death-bots and sending them to me, but the two armies just meet in the middle and tear each other up before reaching either of us, that could continue forever with little change. If you start to get the upper-hand, I'll just build another factory to shore up my weakness, etc. But if I start to advance too far, your supply lines will shorten, giving you an advantage that could shift the war back toward "balance." So long as neither side changes tactics, such a scenario could continue forever. It could even outlive the civilizations that started it. [Answer] Actually the more warlike American Indian tribes were often in a state of low level permanent war with every other tribe except for a few allies. There are many examples of tribe A and Tribe B raiding each other for decades at a time. Research may find examples of permanent war conditions lasting for over a century. And other warrior societies may also have examples of war conditions lasting for decades or centuries. [Answer] I'm adding a second answer as it's quite different to my other one now I've thought about this a bit more. Again it may not be the situation you were envisaging but it is a scenario that gives near-permanent warfare and which would be innately stable. I can envisage another situation where you could have endless war, although again it might not be quite the sort of war you had in mind. The reason wars end is because they are between nations, between collectives. Those collectives assimilate or destroy other collectives and then continue, with the larger ones gradually or rapidly absorbing the smaller ones into themselves. If instead states were a more transient thing, with no concept of the state itself existing but instead were personality cults, that would change things a lot. Someone rises up to lead a tribe, or nation. He or she forms alliances, conquers smaller tribes, rises to glory. But then when that leader dies the empire fragments, with each part of the fragment following one of that leaders children. Some or all of those fragments may be allied at first but over time that would fade away, while at the same time tribes that weren't followers of the original leader would also remain and possibly be growing in power itself. Even if one leader is succeeded by only one child and the empire stays together that child will have further children (or die and cause a different type of succession struggle). Eventually a child will come along incapable of leading and at that point the empire will fall apart. The key thing though is that the individual is the focus, not the organisation. People group together following a charismatic or powerful war leader, but when that leadership is gone the organisation he built falls apart again. [Answer] I think you need several factors to align. You need the territory that each side controls to be roughly equal, but far enough apart that neither side can effectively adjust, reinforce, or take advantage of weaknesses that are exposed by attacks. Economies must be roughly equal and robust enough that it can maintain status through out the drawn out war, but not so much that either side can leverage enough to overwelm the other. Any outside forces are willing to mostly stay out of the conflict or are intent on seeing the conflict continue with out either side gaining an advantage. Ideally these forces would be able to destroy either of the warring people with little effort.(Think US and USSR when they toyed with Iran and Iraq in the 80's) The percieved greivance is so great that neither side is willing to tolarate a lasting peace. One situation I can see that fits this would be a war among some tribes that exist in an island chain otherwise secluded from the rest of the world. Weapons are mostly going to be wood and stone and there is not going to be a reliable source of metal that can support a continuously fought war for hundreds of years. The islands give the defensive advantage that would be needed to prevent gains that would result in a signifigant advantage and make it more difficult to hold on to any land that was conquered. And the travel betweeen the islands would take long enough that no advantage could be pressed with fresh troops. The remoteness of the islands will help keep outsiders from getting involved if they even know the islands exist. [Answer] (i am very sorry. I am writing from a different browser than usually, and this one has a German spelling correction, that messes with my writing. I am sorry for the many spelling and capitalization mistakes) Another historical example is the [Thirty years war](https://en.wikipedia.org/wiki/Thirty_Years%27_War). The war was started for religious and political reasons. In those days, most countries had a Standing army. So in the first years of the war, it just "went fine". No side could get a significant advantage. After a few years, the governments started Recruiting new soliders. In those days, a soldier would get a one-time-payment once they were hired, and regular payments afterwars, as well as (sometimes) a one-time-payment when he was dismissed. After another dozen years of war, economy in most countries involved was at a harsh low. The governments were pretty much bankrupt, only being able to continue to wage war because they would conquer and loot cities and use the loot to pay their armies. Often, soldiers were not paid for long times, leading to deserters and marauders. What arose was "the Monster of war", a "beast that keeps itself alive". If for example sweden and Austria would have wanted to go to peace, they would Need Money to pay their soldiers. Money that they didn't have anymore. So in order to make peace, the other Party would have needed to pay them some Money, so they could retire their armies. But the other parties were also bancrupt, and it would have been a BIG disgrace to admit that you actually couldn't pay that Money. You would need to pretent you could, but don't WANT to. So everyone waited for the tides of war to turn, so next time you negotiated for peace, you were in a better Position and could request Money from the other guys. Everyone wanted to go to peace, noone could afford to do so. Meanwhile, the soldiers were poorly equipped, starving, most often only being kept alive by looting the local farmers and villages. In those days, you couldn't fight during winter, so during the winter months, armies were sent to quarters. Now, a huge german City like Frankfurt hat 80-100k citizens. The armies were equally huge. No single City could Support a whole army, so in late fall, armies were disbanded and spread over a large area - preferably an area that belongs to your enemy, because in spring, everything edible, huntable, rapeable or forageable would be gone or dead. As you may easily imagine, after 30 years of war, the countries were barren and dead. So in order to Keep your army alive - you placed it in some neighbours land. Even if he didn't have anything to do with the war (yet). Also, those cities still had some wealth, that you could use to fuel the war... And so, the involved parties became more and more, forming a complex System of alliances, secret treaties and pacts, that basically ensured that no side would ever win. And then there was France. France profited from the other countries being at each others throat, and just continued changing alliances and Support whenever one Party was about to lose. THus, they acutally made sure the war continued. But why wasn't the war decided in battle? Because of the way warfare worked. In a battle, only around 10% of all soldiers who stopped fighting were actually dead. Many were wounded, not necessary gravely, but most had simply fled the battlefield. Breaking morale was the main thing that scattered armies. But later, they would Reform. And while the losses were harsh, there was an abundance of new soldiers to "recruit", and muskets were so simple, that you didn't require much training. So even after you won a battle, the very same army could try to fight you again only few weeks later. Also, the armies were so huge, that usually withdrawing from the field was easy for the commanders and high-ranking officers. So your command staff stayed alive for many many battles, and they were the only thing that, if lost,could have permanently scattered an army. The thirty years war is an excellent example of a war that couldn't be stopped anymore. You might take the "lessons learned" from that war, and try to fit them into the Scenario you have in mind. But the Basic mechanisms should be clear: * It's too expensive to stop the war * No side can gain a clear Advantage * You'd loose face by admitting defeat or financial difficulties * Ever growing battlefield, so new parties join the war, changing the tides of battle * Third parties wanting to keep the war alive. [Answer] Stability? It's simple. There must not be sufficient dissent in the countries to allow war to end, or there must be a system to prevent dissent from organizing. Perhaps at one extreme, you could use conspiracy theories where real dissenters are killed, and safe dissident groups are funded and controlled. Or use totalitarian oppression. Stalin and Mao killed an unbelievable number of their own people through starvation and oppression, and still were in charge. Persistence? That's a different issue. The intensity of war is the limitation. After WWI, [there were 40% fewer single French men per unmarried woman.](https://research.stlouisfed.org/wp/2015/2015-007.pdf) Obviously a society structured differently, with polygamy, high birth rates, and pensions for veterans could cope with the hazards of war better and longer. Modern technology allows for lower casualty rates, and [less men on the front line](https://en.wikipedia.org/wiki/Tooth-to-tail_ratio). The economic burden of war won't be too severe if the investment portion of GDP is sufficient to allow for economic growth. You asked a general question, so this is a general response. ]
[Question] [ Suppose that there was a tribe of nomadic mermaids whose lives were primarily centered around following pods of dolphins to eat. They live in the equivalent of the frigid antarctic seas. As they possess both lungs and gills, they can surface above the water or swim in the watery depths for hours on end without having to worry about drowning or suffocation. Their strong claws can easily chip through ice in a manner of minutes. This is where the ice plays in. In this setting, the mermaid cut floe or small icebergs away from the land and hollow holes in their sides. That is where they rest and temporarily store their food. I haven't made up a name for them yet, so I'll just call them trailers for the purposes of the question. Through the use of whale sinews, the trailers are tied to the titular pack animals, which transport the trailers to where the mermaids want them to go. I'd rather not have them ride the currents, because they wouldn't be able to make sails, and also because they wouldn't be able to float away from assailants very quickly. What real-life marine creature would be best suited as a pack animal? Keep in mind that their technology is medieval at best. [Answer] You're going to want to obtain some whales. Not only are they the largest mammals alive, they also have the largest muscles. Whales travel in pods, the equivalent of a "pack" of wolves. They're strong, and should be able to lug your iceberg-storage system around for you. They also breathe air, so they can take advantage of the holes your mermaids cut in the ice. Depending on the type of whale, they may not need you to provide a food source, as they could eat plankton while traveling. Alternatively, if you pick grey whales, they don't eat very much during migration, so if you're traveling between their migration locations that might be a benefit. If you choose Orcas, they can hunt their own food and provide defense against sharks at the same time (Orcas are known to eat manta rays, hammerhead sharks, seals, sea lions, and baleen whales). I can't imagine your floating icebergs being heavier than a man made boat, but [here's some footage](https://www.youtube.com/watch?v=flC5eztQo2M) of a whale pulling a boat. If your mermaids can cut the icebergs to have less drag that could be helpful as well. [Answer] [Greenland shark](https://en.wikipedia.org/wiki/Greenland_shark). [![Greenland shark](https://i.stack.imgur.com/kwaYw.jpg)](https://i.stack.imgur.com/kwaYw.jpg) <https://dougperrine.photoshelter.com/image/I0000T2B0QCOMFiE> > > The Greenland shark is one of the largest living species of shark, > with dimensions comparable to those of the great white shark. > Greenland sharks grow to 6.4 m (21 ft) and 1,000 kg (2,200 lb), and > possibly up to 7.3 m (24 ft) and more than 1,400 kg (3,100 lb). Most > Greenland sharks observed have been around 2.44–4.8 m (8.0–15.7 ft) > long and weigh up to 400 kg (880 lb). > > > The Greenland shark is known to be a scavenger, and is attracted by > the smell of rotting meat in the water. The sharks have frequently > been observed gathering around fishing boats. It also scavenges on > seals. > > > Greenland sharks seem more like pack animals to me. Big, slow, tough, strong, stupid. They like it ice cold. They live for centuries, getting gradually bigger and bigger. They eat carrion and waste which should be easy for the merfolk to provide. Bonus: glowing creatures live on their eyes. [Answer] [Tuna](https://en.wikipedia.org/wiki/Tuna) -- powerful swimmers, top speed nearly 40 mph, weight more than half a ton each, known to swim with dolphins already; warm-blooded (one of the only fish species that is), some species near the arctic (e.g. 60 degrees); maximum age 10-50 years (depending on species); vulnerable/threatened/endangered by human fishing. With modern climate they're being found around Greenland. [Answer] 1. I'd go with turtles. True, the RL ones are tropical; but in a fantasy setting already rife with mermaids, adding arctic turtles would be a minor edit. You can make them as large as you want, or have teams of smaller turtles (like huskies pulling sleds) harnessed to a single trailer---driving them would be a complex skill that the natives start learning as toddlers. Turtles have the disadvantage of needing air, but to have surface-traveling trailers you need open water anyway. And turtles can stay submerged for longer than dolphins or whales. They are non-aggressive and they eat jellyfish mostly, which are everywhere. And they have the ability to crawl onto land, albeit as clumsily as their mermaid owners. 2. Of RL animals, I would go with @Willk's Greenland shark, because it is a scavenger (easy to keep fed with scraps) and because it needs no air. It seems dangerous at first glance, but that's no worse than the huskies Inuits use. And like most sharks it has a super-keen sense of smell, which would be very valuable in tracking dolphins or whatever. 3. Finally, an off-the wall idea: giant squid. No need for sinew-rope harnesses---just tether the trailer to the pair of long tentacles, and away you go! It eats fish, but tends to be a deep diver---that behavior would have to be de-trained. Attach a skin air-bladder to the squid, like the Inuit did to harpooned game? 4. And BTW, the Vikings used leather sails, so there is no problem with sail material, really. [Answer] Most likely, whales. They live in pods with a leader, so they have the herd instinct of other domesticated pack animals such as a horse or cow. All land based animals who have been trained as pack animals have that herd instinct... they're used to taking orders, so transferring that from the pack leader to a human isn't that great a leap. Whatever aquatic creature you choose, you do have to train it to haul packs where you want them, and they need a fair amount of endurance. Herbivores tend to have more endurance than predators with a pack instinct, who are more sprinters. The less advanced creatures who don't have a herd or pack instinct, like sharks, probably won't make good pack animals for the same reason alligators aren't used as pack animals... they don't have the intellect, temperament or instinct for domestication. Not used to taking orders from a pack leader. Also, alligators tend to eat anyone who tries to domesticate them, which could dampen enthusiasm for the endeavor. [Answer] Whales. There are several of them living in the Antartic zone. They are incredibly strong, some could even feed on planktons on the move, and after they die the oil in them could be used by the tribe. [Answer] Squids. No need for ropes and things as they have it built-in. Many species can camouflage quite well, so the chance of a post robbery is reduced. [Answer] I assume you are thinking of a storyline for a book. This mermaid-world is fictional,so why not invent a pack animal? I assume Nomadic Mermaids were inspired by the mermaids of legend. Those mermaids of legend were inspired by various forms of oceanic creatures,so the Nomadic Mermaids' pack animals can be inspired by real life animals. You will need to invent an animal which could live in the your antarctic equivalent condtions. Draw your inspiration from real oceanic animals. This will depend upon the similarity of your "Antarctic equivalent" to the real life conditions of antarctica. The animal should be endothermic.You can count on endotherms. It should,when in the wild untamed state, swim just below the water's surface. It should be a social, easily domesicated animal. The just-below-the surface behavior is the hardest part to invent. Consider the natural history of this animal. It needs to have exhibited a similar behavior,pre-domestication. Invent an ecosystem. This just below the surface swimming might be a feeding behavior. You have to work at this. I think a whale-like endotherm that has historicaly eaten something from just under the ice floes would be a good candidate for your pack animals. [Answer] Somewhat difficult to justify given that your mermaid prey on them but how about dolphins? They lack the size and raw muscle power of whales and giant squid but are highly social, pack animals with an extremely high level of intelligence. If your mermaids could train enough of them to work together they could probably meet your criteria. ]
[Question] [ Self-explanatory. I have a planet-eating entity moving slowly across the solar system towards Earth and I wanna know how long it would take for us to notice its presence once it starts consuming Pluto (assuming we had no prior warning or knowledge of its existence). [Answer] ## Within Two Days *After* Pluto is Eaten I want to clarify a point that I'm not sure other answers are giving here, which is that **we have a really, really hard time seeing Pluto**. It's literally [easier to look at another galaxy](http://www.planetary.org/blogs/emily-lakdawalla/2013/02141014-hubble-galaxy-pluto.html) than that planet, even from the Hubble telescope. Here is the [best picture](http://www.space.com/17784-best-pluto-photo-from-earth-picture.html) that I could find from a large terrestrial telescope: [![Pluto, Observed from the Gemini Observatory in Hawaii](https://i.stack.imgur.com/HWFIx.jpg)](https://i.stack.imgur.com/HWFIx.jpg) Of course, observatories aren't looking at Pluto much because there's frankly not much to see. So instead we rely on amateurs to track it day-to-day, with this [being a good result](http://earthsky.org/space/how-to-see-pluto-in-the-night-sky): [![A Good Image of Pluto from an Amateur Telescope](https://i.stack.imgur.com/J8dow.jpg)](https://i.stack.imgur.com/J8dow.jpg) So basically we rely on amateurs seeing a dot to know it's there most of the time. If a being approached it that wasn't enormously larger the dot might look a bit bigger, but we would have no idea that it was eating Pluto. Even when it was done, presumably the beast would be at least the size of pluto so we would assume the dot we saw in its place WAS Pluto. Now once the Pluto-dot disappears because the monster moved away from where Pluto should have been, or once it starts coming closer and we see the dot getting noticeably larger, we're going to say something is happening. Of course it's going to take a day or two of "odd" observation reports coming in before a big telescope is re-oriented in that direction (doing so will disrupt the observations it is currently taking and so involves a lot of bureaucracy). Given the astronomical distances involved however — and the fact that even Jupiter is small compared to a distant galaxy — we aren't going to actually know WHAT happened until that sucker gets pretty close. Depending on size it may have to be about as close as Saturn or closer before we could get any real definition. ## EDIT / Update Note that if the planet-eater is MUCH larger than Pluto we would see that SOMETHING was different because we would see a much larger dot. We would know that SOMETHING was happening, but still would have no idea what. Exactly how close it would have to be before we could identify what was happening would be a function of the size of the creature, which is unstated. Keep this image in mind though: [![Relative Planet Sizes](https://i.stack.imgur.com/Mxzwq.jpg)](https://i.stack.imgur.com/Mxzwq.jpg) Something the size of Earth could easily swallow Pluto and still not be properly visible even if it were as close as Saturn. I like to use Saturn as an example because we can get a pretty good picture of it from Earth... as in decent resolution, clear images. But it's also MANY, MANY times larger than Earth. So be sure to adjust the distance away that we can properly see it to its size. Unless your monster is large enough to eat giants like Neptune or Uranus I think you'd be safe saying we couldn't get a clear enough image to understand the threat until it was as close as / closer than Jupiter. If it is on the scale of gas giants though, then by the time it hits Saturn's distance we can probably tell you the color of its eyes. [Answer] It will take a minimum of 4 hours because of the speed of light. Since it can be observed by amature astronomers it will be noticed pretty much right away. Worst case scenario would be if the sun was occluding Pluto it might be unobservable for a month or so. [Answer] Months at most, I think. Such an entity would be big enough for its gravity to perturbate Pluto's orbit before eating it, and the perturbation would be picked up by instrumentation in Earth. The astronomy community would point telescopes to Pluto, find the entity, and sound the alert. [Answer] Something that hasn't been mentioned is the [New Horizons](http://pluto.jhuapl.edu/) probe. It's out near Pluto right now. It passed Pluto last year and as of this writing is 500 million km away. Could it have noticed? The answer is "it depends". If it had happened last year while New Horizons was actively observing Pluto during its flyby we'd know immediately. [During its approach and flyby](https://en.wikipedia.org/wiki/New_Horizons#Pluto_approach) starting January 2015 New Horizons was taking photographs in many spectrums. If there was a chunk missing from Pluto it would see it. How quickly it would see it depends on how big the chunk was. The first low resolution photographs would arrive in about five hours (the fastest they can with the speed of light). Ultimately in July 2015 New Horizons mapped Pluto at a resolution of about 1 mile per pixel with certain areas as fine as 50 m per pixel. If there was evidence of Pluto being gnawed on within those resolution ranges, New Horizons would have seen it. But New Horizons is done observing Pluto and has moved 500 million km past it. Now it's observing [Kuiper Belt Objects](https://en.wikipedia.org/wiki/Kuiper_belt) beyond Pluto. If your planet eater showed up now it wouldn't see it. But it might *feel* it. It depends on how *massive your planet eater is*. The gravity from a very massive planet eater, significantly more massive than Pluto, arriving at Pluto now would very slightly pull New Horizons off course. How much depends on how massive. The smaller the anomaly the longer it would take to be noticed. Even then the conclusion would not be "there's something eating Pluto" but it would be chalked up to something out in the Kuiper Belt, perhaps evidence for [Planet X](https://en.wikipedia.org/wiki/Planet_X). [Answer] The way your entity consumes Pluto could be the key here. The (essentially hard sf) novel [Eater](https://en.wikipedia.org/wiki/Eater_%28novel%29) by Gregory Benford has a similar premise: a sentient black hole starts doing something similar, and is first spotted as a result of the resulting flares of radiation. This would be much easier to spot than the absence of Pluto, which as other posters have noted is difficult to see at the best of times. ]
[Question] [ In the world I'm working on, magic has been Sufficiently Analyzed, and has been turned into a well-defined science. It takes the place of much of technology (why invent the forklift, when a magically-augmented human is just as strong, and far more agile?). It does, however, have two limitations: 1. It can only be cast on a willing subject. You can't cast a spell on an inanimate object, and animals that can be trained to accept spells are rare. 2. It's subject to conservation of energy. Given those limitations, which would you use for heavy physical labor (eg. pulling a plow or a freight wagon): an augmented human, or a horse? The human is at least as strong as the horse, so which has a greater capacity to do work? [Answer] ## Horses, always horses **It boils down to economic factor:** Why do we replace humans with machines? Sometimes the first version of the machine can do less work than trained human. So why do we do it? **Because in most cases horses and machines cost you less** Take this example: Augmented human asks for an hour of *really hard work* one piece of gold. For same amount of work, in same conditions, an hour of horsepower cost you half a piece. We have winner! Plus, you have benefit with horses: They do not require salary raises, they do not want to go on holiday, they do not have desire to go home to be with family... So in nutshell: If hour of horsepower cost you same or less than hour of augmented human work, you will use horses. In our world, people went to the machines for simple reason, that machines and horses cost you less. If you want to have lot of augmented people, their work has to cost less than cost of owning a horse. **It does not mean augmented people do not exist,** they would be minority and working in fields/professions where you cannot use horses (or machines). Augmented people would be real professionals in your world [Answer] You need to look at the social factors as well. Are you looking at a modern world with a middle class and people expecting a decent daily wage or a highly stratified feudal society with mages/lords at the top and everyone else basically [serfs](https://en.wikipedia.org/wiki/Serfdom). If it's the former then it's one person with a team of horses. Simply a matter of cost. If the latter then peasants are cheap and don't need paying. Remember that serfdom wasn't abolished in Europe until the mid 19th Century. --- Considering a "modern" society, non-feudal with mid 18thC tech what you want are [mules](https://en.wikipedia.org/wiki/Mule). > > Mules are "more patient, sure-footed, hardy and long-lived than horses, and they are considered less obstinate, faster, and more intelligent than donkeys. > > > They're also cheaper to run as they'll eat less than a horse of equivalent size. We don't tend to breed them so much these days but they were a staple of long distance transport for [thousands of years](http://columbiadailyherald.com/sections/lifestyles/mule-day/mules-mankind-share-common-history-modern-world.html). > > Mules have been deliberately bred by humans since the Book of Genesis was first put down on parchment. The Hittites thought Mules to be more valuable than a chariot horse, and the mule was the favored mount of the Kings of Israel in biblical times. The exact origin of the first mule is unknown, but we do know that the mule was deliberately bred by man in ancient times. > > > On plains wagon trains that used mules instead of horses, they could travel 30 miles a day, while wagon trains with horses or oxen could only average about five miles per day. In the west, stage coaches preferred mules over horses because large mules could travel at 5-6 mph over flat dry land for hours, but a horse would give out long before a mule would. > > > Mules every time. [Answer] I see a scenario where **magic-augumented humans would do all the work**: Magic analysis started thousands years ago before Neolith, when humans were homo sapiens, but they were exclusively hunter-gatherer tribes - they didn't know agriculture, didn't domesticated any animals. If they started to grow plants and already had some basic spells, maybe it wouldn't *make sense* for them to domesticate horses/oxen; they preferred to enhance their magical abilities because it was more fun. And so the "magic revolution" went along the agricultural revolution, they fueled each other. You suggest 18th-century level in comments. If each farmer can afford his fields being plowed, I think such civilization is perfectly achievable economically. You need to watch your language though, idioms like "to hold one's horses" or "put the cart before the horse" or comparisons like "horseshoe shape" would be out of universe. Side note: Maybe they didn't also domesticate chickens, pigs, etc - a potential for ongoing evolution toward vegan world scenario; in 17th-18th century mass hunting might become uneconomical and fell out of favor. [Answer] In a comment I asked: > > "**animals that can be trained to accept spells are rare.**" - I think this point is easy to misinterpret in a variety of ways. For instance, is it the type of animal that can be trained which is rare? (Horses, but not Cows, Deer, or Zebra) Is it the difficulty of training particular types of animals? (anybody can train their dog to sit. To train a dog for much fancier things can require a smart dog and a lot of work - but people would probably do that much work for magic horses) Or is there some individual trait for some animals, or "Magic-proneness" any type of animal could have? > > > I believe this, along with the cost of manpower, is what will ultimately drive the decision. Why? Because unless magical-acceptance is completely random, we will find a way to make them "not-so-rare". * **Certain types of animals**: Horses would presumably be one of them. Horses would be used all the way. * **Training is difficult**: New occupation of magical horse-training emerges. Horses would be preferred, but only available in locations with horse-trainers. Certain traits are easier for training, and are breedable (next point). * **Animals require some kind of trait or intelligence which isn't random**: Horse breeding takes place, just like it did in the past. At first, humans are more used. But as more horses are bred which are capable of magic, they become cheaper and more available. * **Completely random - magical horses will always be rare for magical reasons, magical horses are only for the incredibly rich**: Depends on local cost - which is more costly, magic or basic horse? Look to the next section: --- Consider the following for each physical labor situation: 1. How many humans/magic horses/normal horses would you need? 2. How many of each could you possibly purchase/hire, and supply? (*food, gear, etc.*) How expensive are the supplies? 3. Can you effectively run that many at once or watch over that many? How many men would you need to hire to supervise? (*or do they not even need to be worked or watched?*) 4. After figuring out the cost of multiple compositions of humans+horses, Weight the decision more-or-less towards whichever method requires less direct work for the land-owner. [Answer] I agree with Pavel - horses, in general. For me, primarily, due to psychological reasons. If the work really is purely physical as per your example of pulling heavy loads, then most people are going to find it extremely boring. You aren't going to get many of your willing subjects to begin with, and how long will they remain willing? Breaking rocks was used as a punishment - why would people choose to do similar unless you are willing to pay them a lot more than the equivalent of horsefeed? A couple of caveats: You could of course get over these objections with user16295's social factors - scarcity of food so people HAVE to be willing, for example; also playing with the concept of "willing" - bonded labourers might be considered "willing" to pay off their debt? Either of these could actually make humans cheaper than a horse, which could be a very valuable beast, e.g. for non-magical transport. [Answer] Whatever is cheaper Your version of magic may include conservation of energy (???), but any type of free-market system (that is, there's no law saying what you must use) will lean on conservation of profit. If the protag's in an area, there's going to be leaning on whatever is in large abundance - If the area is like Venice, you're going to leaning largely on water travel. If you're in an area where you can hire an augmented 'running man' cheaper than purchasing and maintaining a horse, camel, mule or dog team, you will. There are also externalities to consider - If you're in a city or urban environment, do you want to deal with domesticated animal waste? Where are the animals kept when not being used? If you're in a rural environment, how does the environment impact an augmented person? Rain, Heat, et cetera? (I'm thinking of the story of the British trying to use the Irish for Slave labor, but they couldn't take the heat in colonies, which led to the slave trade to Africa) Are you advancing the plot in some manner? Is this a debate that the characters are experiencing, or the society as a whole is discussing? Are the augmented humans actually willing (skilled worker) or brainwashed to be willing (serf/slave)? Will there be a progression of enchantment, where today's work animals or augmented people pulling wagons will be replaced by self-pulling wagons? [Answer] I didn't see this addressed in any of the other answers, but essentially it boils down to: # Whatever is most cost effective for the job As @PavelJanicek gets at, horses will always be cheaper. # But! Horses aren't very clever and are not very good at adapting to rapidly changing work conditions. They're good for jobs where an increased amount of brute force has a linear increase in work produced. Humans on the other hand, augmented, magical, or otherwise, can handle rapidly shifting conditions where the "goal" is an abstract concept and which *flexibility and creativity* is more important than sheer power. You know that thing about monkeys and typewriters? Well, we don't employ an infinite number of monkeys because while individually they're paid peanuts, and the produced result is quantitatively very high, the quality is rather poor: it takes almost as much work *from an intelligent human* to sift through the crap (pardon the pun) in order to find those works of Shakespeare than it would be to just employ the human in *writing it in the first place.* As an added benefit, you save the cost of an infinite number of peanuts. # Ergo... Your augmented humans would be used in scenarios where their brains are more important than their brawn: the ability to identify strangers, perceive threats and dangers, or perform delicate manipulation (even with the strength of a horse, human fingers are a *tad* more nimble than hooves). Search and rescue would be a good example: collapsed buildings, avalanche zones, etc. but by no means the *only* place. Factory machinine might also be a good place. Lots of strength, requiring less energy keeping the forges hot (because the guy can just bend metal bars with his bare hands) along with all of the creative ingenuity the human mind can bring to bear. But as a general rule, any job that can be performed better by merely increasing the employee's strength will go to the horse. That's why even though in the real world we've replaced horses and humans with increasingly complex machines, but we've not had the unemployment crisis that laying off all of those unskilled workers would logically represent: instead they find jobs that the machines *can't yet do* such as *keeping the machines oiled.* [Answer] Sorry to go against the premise, but you would use a forklift. It requires 10J of energy to lift 1 kg by 1 m. To, say, pump 100 L of water from a river to an adjacent house (3 metres above river level), roughly what a family would use in a day would require 3 kJ, which would require the wizard to eat 500 grams of rice to provide the energy. This is quite a lot of energy just to cover one task that technology currently does, and is if you live very close to a water source. There are limits to how much we can eat, just based on some physical limitations on how fast we can breakdown food. We would not be able to compete with technology running on fossil fuels or renewables because of the energy requirements. Technology will always be better than magic that obeys conservation of energy. [Answer] A horse because it cannot think and plan a up rising to get out of servitude. Even with magic humans still have the ability to problem solve on a higher level than all other animals. The hoarse will keep pulling with a carrot in front of there face. A monkey as show in this video can comprehend a difference in equality of life. Monkey on the left is paid in cucumber and the right grapes. <https://i.imgur.com/KRHGrCN.jpg> [Answer] I would have to go with a human on this one. Think about it, if you use a horse, you have to feed the horse and the human used to get the horse to do something and you have to pay the human to work with the horse. The human you get to drive the horse needs some knowledge on how to properly get the horse to do what you want it to do which means you can't hire unskilled labor. You also have to build and or pay for housing for the horse... pay for grooming... pay for medical care... the list goes on. If you could get a human to do the same thing, just hire an unskilled worker, cast your mojo on him/her and hand him/her a quadruple size bowl of cheap porridge. The work will be done better because a human has more precision doing things manually than they do driving an animal to do things, and you eliminate 100% of the many costs associated with the horse. Just in case it wasn't obvious, the energy that I am proposing the human use to get around the conservation of energy bit is the calories in the extra large bowl of porridge. So the human would get the requisite energy much the same way as the horse would, by consuming food. In fact, if you wanted to go really cheap you could always cast a ruminant stomach spell on the human and feed him/her hay... but you might end up with some disgruntled employees. [Answer] Thinking outside-the-box... if magic is cheap, instead of a human or horse why not conjure an obedient troll or giant and dismiss him at the end of the work day? You wouldn't have to pay out money or oats then. ]
[Question] [ I am creating a world in which a society exists that is heavily inspired that ancient [Sparta](https://en.wikipedia.org/wiki/Sparta), specifically with a focus on [Spartiates](https://en.wikipedia.org/wiki/Spartiate) and their military education, the [agoge](https://en.wikipedia.org/wiki/Agoge). A character in the story is trying to change the life perspective of a group of male Spartiates, who were trained from a very young age to fight in military battles, through competitive sports, specifically [Basketball](https://en.wikipedia.org/wiki/Basketball). **Therefore I am looking for information about the effect of competitive sports on the psychology of teenagers with extreme levels of aggression potential with the goal of reducing said aggression potential.** Can I integrate these teenagers into today's society after working with them and introducing them to Basketball? There are a few differences between the agoge and the training these teenagers went through: * Kids are trained in all sorts of martial arts. * Military training started at the age of 3. * They were trained 16 hours a day, 7 days a week. * Each Spartiate has killed at least 5 kids - some of which have been close friends. * All Spartiates have average intelligence. * All Spartiates are able to read and write. The teenagers in this specific group are between 15 and 19 years old. I would like to paint these teenagers as veteran warriors who did not learn how to smile, born in a world where love did not exist and their sole purpose is to kill or die. Why Basketball? The protagonist is the coach of a Basketball team, which means that he knows a lot about the sport. The teenagers will listen to the coach as if he was any other instructor they have had over the course of their military education. **Would introducing these teenagers to Basketball be a suitable way to reduce their aggression potential in the long run to an acceptable level for today's society?** [Answer] ### The Power of Sports is useful, But Overstated I am a combat veteran of two wars and I found competitive sports useful to provide a distraction and work off excess anxiety and restlessness, but frankly there never was an Oscar worthy moment where the power of sportsmanship and football suddenly made all my problems go away. Military indoctrination, mental conditioning, and war trauma just really don't go away because you magically channel it all into a sports team. It's really just a pleasant distraction for a while that serves as a constructive way to burn off some negativity in a positive manner. I understand the misconception, too. Most people have never been in a military unit, undergone any formal military training, or gone to war. The closest most people ever get to having a regimented and competitive lifestyle like that is sports, so it's only natural to think that if one could just channel themselves into sports that it only stands to reason that they would just be putting said conditioning and experience to good use and get over it. There are surface similarities, but a sports team and a military unit are worlds apart. Nothing the vast majority of civilians have experienced ever comes close to what being in war is like, so it's understandable that they don't understand the nature of combat, so I will give you a bit of an eye into the military mind and maybe you can form some more accurate conclusions from it. ### They Will NOT Listen to the Coach If he is a Civilian We have a near racial slur for you people. *Civvies*, or *civs*. A *Civ* is a soft, naive and docile thing that doesn't really understand hardship, sacrifice, dedication, or brotherhood. They either fear us, or are trying to get our attention by pretending to "get" us. When you are a vet hearing most civvies talk about the military is kind of like asking a 6 year old to explain what they think college is like. When you show up for a therapy session or for psychological counseling or even get treatments for a past wound and the person is a civvie it's pretty disappointing. You know one of a few things will happen. They will often come across as patronizing and simpering by trying to impress you with how much they "get it." Another thing they do is try so hard to tiptoe around the elephant in the room that it becomes annoying and awkward. Finding out that the person you are meeting with is a combat veteran is a huge relief, because you can both communicate on the same wavelength. There is a mutual respect there as well as a shared experience. It is my advice that your coach be a retired very senior ranking enlisted man, who has extensive combat and military history. They will respect, resonate, and trust him more. He's not a "dumb civvie" talking about things he's never done or seen. He's one of them, he doesn't have to pretend he "gets it." It's just instinctively understood that he does without him having to undermine his own authority by being patronizing or offering advice on matters he doesn't have experience with. Being a previous senior staff NCO also generates a lot of respect because first, he's been a grunt foot slogger just like them who worked his way through the ranks just like they hope to do some day. It shouldn't be an officer, because the enlisted/officer relationship is too formal and would get in the way of the mentor-ship relationship. ### It Should be Built on a Military Style Training Regimen One of the reasons that sports might NOT appeal to somebody like this is because they lack weight. In the military nothing you do is pointless. It may seem that way sometimes, but the point is ALWAYS to learn some valuable skill, mindset, or achieve a better physical condition. When every action of your life is planned to make you better at your job and increase your survival depends on your ability to perform this job when you get back to the civilian world it's kind of weird. "Wow, these people really get worked up over something so stupid." When I run 8 miles it's because I need to make sure that I can locate, close with, and destroy my enemy. When I lift weights it's so I can carry a wounded brother better, or get a machine gun into position that saves my squad. "These people just do it because they want to put a ball into a basket better. How stupid and pointless." In the military as a combatant you do not just have a job, you have a purpose for existing. It is your sole purpose in life to either be winning wars, or training to win wars. These guys are going to just turn away from a purpose they were literally bred and born to fulfill to toss a ball? Not unless the training of it resonates. To do so it has to feel familiar. ### There Will be no Magic "Oscar Moment" I was not subjected to military conditioning until I was an adult, and I was a volunteer. I still have issues with a lot of stuff, including a recurring smoldering disdain for the often petty and trivial things that people always seem to get so worked up over. I suffer from an inability to feel much pity for much of anyone. In war weakness gets one or their brothers killed. Weakness is a sin and when somebody is trying to make me sympathize with them I often instead feel an irrational disgust and hatred instead. These are all issues I still deal with years later. These guys were conditioned from *birth*. They are going to have it even a lot worse than I do. It was never a choice for them, and they have very very little context to compare any of their experiences to that are not military in nature. Expecting them to suddenly be okay after winning a championship or something is just irrational. You need to set realistic expectations for these young men to achieve. They will probably never be totally alright. They can only really hope to learn healthy coping mechanisms and try to manage their symptoms. There will always be a disconnect there and there will always need to be a willful internal struggle to try to use the experience for good. It's been several years and I still sometimes have trouble. It's not about "getting over it" so much as learning to live with it. ### Keep Them Separate from Normal Kids Back to the civvies thing, except imagine somebody who has spent 15 to 19 years training to kill getting into a fist fight with a normal athletic, but mentally soft jock whose biggest claim to toughness is a few bloody noses and puffy lips in schoolyard scuffles. These spartan kids aren't really kids, they're honed killers. They are people to whom death is a suitable conflict resolution strategy. They're literally going to rip even your biggest "toughest" teen jock or bully apart. I'm talking broken bones, possible brain damage or all out death here. Introducing them to normal kids is going to be a very slow and gradual process that doesn't begin until well towards the end of the program once the members have demonstrated a clear and obvious improvement. ### Summary The sports are ultimately just going to be one tool among many that are used to ease these guys into a normal life. Don't expect all of them to make it, and even possibly expect some of them to actually wish to return to their old life, maybe even possibly do so. Hell, I actually *miss* Afghanistan and Iraq. I had a very simple and clearly defined purpose there and an easily quantified value and place within the hierarchy. I miss my brothers and I miss being so focused and having everything so clearly defined and understood. I imagine that at least a few of these kids will not see themselves as liberated and maybe even want to go back. The Sports Regimen could be a useful part of the recovery process, but it's not going to be the only one by far. ]
[Question] [ I'm trying to imagine mystery setting when amateur astronomer stumbles upon a torrent which contains a 3D map of the Milky Way galaxy. The map contains all large objects: star systems, **planets**, nebulae, black holes. Is there a way with our current knowledge to check is the map real or just an object of someone's imagination? [Answer] **Just look at the sky1** Your *protagonist* is an astronomer (albeit an amateur one). He'll most certainly have access to a telescope or similar apparatus that allows him to start verifying the positions of certain stars or clusters relative to earth. From there it is just a process of elimination, the more star locations they can verify using these methods, the higher the probability becomes that the map is \*real. On the other hand, *anyone*2 else will be able to do the same, so this method only allows you to garner a certain amount of proof. Still, thanks to exact coordinates of stars, it becomes almost trivial to look out for certain electromagnetic-wave-patterns that would confirm3 the coordinates to be *valid*. 1you silly you... 2~~well not really anyone, but at least astronomers and people with lots of money/time~~ yes, **anyone** - because [star charts are a thing now](http://news.nationalgeographic.com/2016/09/gaia-milky-way-maps-billion-stars-atlas-space-science/)(thanks to at @Zxyrra for that phantastic bit of information) 3well not really confirm, more like telling you that the chances of there being something like a star are higher than lightsecond to the relative left of that source [Answer] ## It's completely possible: We've already made a map As of September, we have a [fairly accurate map](http://news.nationalgeographic.com/2016/09/gaia-milky-way-maps-billion-stars-atlas-space-science/) of our galaxy. By measuring the parallaxes of distant objects, we know the relative locations of about 400 million stars. The satellite which gathered this information, called Gaia, also found [billions](http://www.cosmos.esa.int/web/gaia) of other potential objects. Most if not all of the data recorded, including the map your character needs for comparison, is [open to the public](http://www.cosmos.esa.int/web/gaia/gaia-data). After some comparison, it should be clear that the file they found is or is not accurate. [Answer] Zxyrra's approach of comparing to a publicly-available, trusted map has a flaw: the person faking the map could have downloaded the same map you're comparing against, then added the planets by making that data up. All the data that exists on both maps would be the same. That'd be pretty obvious (different maps should *not* be exactly the same, there are surely mistakes in both). A more clever forger would of course introduce some errors, and move things a little within the error bars, etc. Of course, all of this will need to be done by computers—not like you can eyeball two maps of the galaxy and say if they're the same. So both the forger and especially the person checking need to be skilled. Checking for forgery essentially will involve outsmarting the forger: find some signature left by the algorithm the forger used to generate the new data. There is another, easier way that doesn't require outsmarting the forger: wait. Astronomers are, fairly routinely, announcing newly discovered planets. You can check new discoveries against your map—any that agree with your map and occurred after you downloaded the map are evidence the map is true; any the disagree with your map are evidence it isn't (or at least is incomplete). [Answer] Find an object on the map that is unknown but is within the detection capabilities of the best telescopes but no others. Point one at it. Since the big scopes have good records as to where they have been pointed you can rule out prior human knowledge. While this doesn't prove the map to be accurate it does prove it to be of alien origin. [Answer] ## Information theory 101: Either you know something, or you don't. The map can be falsified (proved false) if it describes something physically impossible or extremely improbable. However, a sufficiently motivated forger can avoid this by running physical simulations of the map and verifying that it is physically stable over the short-to-intermediate term (which is exactly what you would do to check for these physical impossibilities in the first place). Otherwise, it's a matter of comparing the map to reality. The problem with that is twofold: 1. Some aspects of reality are already known, to both you and any sufficiently well-motivated forger. Because you already know these things, a genuine map tells you nothing interesting about them, and a good forgery will contain them anyway. 2. Some aspects of reality are unknown, to both you and any forger. Because you do not know these things, you cannot use them to verify the map. If you need to know whether the map is real based on the same set of information as the forger has, you are out of luck. You could wait for more aspects of reality to become known (i.e. for more stars and exoplanets to be discovered), or perhaps use nonpublic information depending on who you work for (e.g. the military?), but the above dilemma continues to hold: Everything which is learned is now known, so the map can no longer provide new information about it. And that's assuming that science follows a straight line from unknown to truth without passing through falsehood, which is unrealistic. It would perhaps be more accurate to say that there is a continuum between (1) and (2), and it's often difficult to know exactly where you are on that continuum. It's possible that a genuine map might disagree even with supposed "known facts," if our understanding is badly incorrect. Perhaps, after enough new stars and exoplanets have been discovered, and the map has agreed with these discoveries sufficiently often, you will conclude that the map is genuine, rejecting the possibility that a forger managed to guess all those discoveries by chance alone. But how often is "sufficiently often" and how many discoveries does this take? To answer that, we ([usually](https://en.wikipedia.org/wiki/Bayesian_statistics)\*) use statistical significance testing. Basically, you imagine (or simulate) numerous forgers creating numerous fake maps, and try to figure out what fraction of those fakes happen to look at least as realistic as the map you actually have. If this number (called the *p-value*) is very small, you can argue that it's unreasonable to continue believing the map is a forgery. Your definition of "very small" (the *significance level*) will depend on what (if anything) you plan to do with the map once you know it's genuine. If you're going to launch a generation ship at an exoplanet, you will probably be a lot more cautious than if you're going to point a space telescope at an interesting area of the sky for a few days. If you don't plan on doing anything in particular with the map, perhaps you should ask yourself why you care about its accuracy in the first place. That reason will inform your choice of significance level. If all that is a bit hard to follow, here's the short version: You can wait for some more celestial bodies to be discovered by astronomers, compare the newly-discovered objects to those in the map, and use that to prove the map is (probably) real. But if you do that, you won't be able to use the map right away, and by the time you are able to use it, it will be partially redundant to the newly-discovered information. \* This link included for completeness; you can completely ignore it if it doesn't make sense to you. [Answer] Does the OP have any idea of hat a 3D map of our galaxy showing all the stars and planets would be like? There are at least 100,000,000,000 stars in our galaxy and possibly a few times that many. And a large percentage of them have planets so there are billions of planets in the galaxy. And how could you show everything to scale on a map? In our solar system the eight planets have average distances from the Sun of 57,909,000 to 4,500,000,000 kilometers - Neptune is 77.708 times as distant as Mercury. A light year is 9,460,700,000,000,000 kilometers. The nearest star is Alpha Centauri about 4.30 light years away, or 2,100.33 times as far as Neptune. The diameter of the galactic disc is about 100,000 to 120,000 light years, or about 23,255.813 to 27,906.9 times the distance to Alpha Centauri, or about 48,844,854 to 58,613,699 times the distance of Neptune. So your map should be a gigantic computer database with all the information and the ability to display 3D maps of selected objects. The way to check its accuracy would be to find out what astronomical projects are looking for objects in the galaxy and planning to do so in the near future. You will want to have a computer program to automatically record all announcements of discoveries of objects in our galaxy and automatically check against the data base. If you want to prove to others that you have a accurate database you will want to search the data base for relatively small group of objects that are being currently searched for. For example there are only a few hundred star systems within a few tens of light years from Earth. Finding them all is important to getting a good unbiased sample of the stars in this part of the galaxy. So you can make a list of all star systems within 30 light years of Earth that have not yet been found to be that close and publish their distances and when astronomers check them and find you are correct that will convince many that you do have an accurate database. ]
[Question] [ I've hit a wall in my tale of humans attempting to escape [the Singularity](https://worldbuilding.stackexchange.com/questions/6340/the-challenge-of-controlling-a-powerful-ai) or a [fate worse than death](https://worldbuilding.stackexchange.com/questions/6550/humans-as-pets) by running off into the depths of space. And I only have myself and my accursed hard sci-fi leanings to blame. ![enter image description here](https://i.stack.imgur.com/rZBpb.jpg) First of all, [my habitats leak like a sieve](http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110012997.pdf), even before getting battered by micrometeorites, leaving my 'survivalist' fanatics gasping for air and dying faster than a gecko's libido on a [Russian lizard sex satellite](http://www.csmonitor.com/Science/2014/0903/Russia-s-zero-g-lizard-mating-experiment-ends-badly). Furthermore, as the poor fools stumbled around my spinning cylinders, [the maths suggests that they would made them wobble](https://physics.stackexchange.com/questions/149080/throwing-a-ball-in-a-rotating-space-station?rq=1) so much that their tears of despair [would falling sideways](http://www.spacefuture.com/archive/artificial_gravity_and_the_architecture_of_orbital_habitats.shtml) and my glorious cylinder-habitats (above) now have to look like ugly [stumpy tires](http://settlement.arc.nasa.gov/Kalpana/KalpanaOne2007.pdf) (below). But forget aesthetics, it's the air loss I'm most concerned about. ![enter image description here](https://i.stack.imgur.com/4uksl.jpg) **Does anybody know of a long-term non-planetary habitat model in space that seems actually sustainable?** I'm talking wall materials, docking ports, EVA ports, the occasional window (if needed, it can be windowless), etc. Would giant hollowed out space rocks fare any better? Where to put my flesh-human holdouts? Tech level can be a tad higher than current, but should be plausible given (late) 21st century standards. Remember, these are regular unaugumented humans escaping the impending techo-singularity event on Earth, sometime in the second half of the 21st. [Answer] Alright. So this is a multi-stage project. First, we head to the asteroid belt. There we alter the orbit of a ton of asteroids with useful properties (water, metals, etc) and send them off towards Venus. They don't have to be exact, or quick, we're just looking to supply ourselves over the long-term here. Think minor alterations that will put the asteroids near 10, 100, or 1,000 years from now. Now we pick a couple of decent-sized asteroids to jump-start our project, put those on shorter orbits and head to Venus to start constructing our habitats. And now we have a two-step plan to mitigate air loss. **Self-healing water shielding** The idea here is that you have a two-layered hull, with 1-2 meters of water in between. That's enough to cut down [almost entirely](https://space.stackexchange.com/questions/1336/what-thickness-depth-of-water-would-be-required-to-provide-radiation-shielding-i) on radiation. But a secondary benefit for us is it also helps us keep our air supply intact by reducing leakage. Air won't go through as easily. The water also helps absorb and protect against micro-meteorites - what you do is mix some sort of replaceable fiber in with the water. Then when your outer hull is pierced, as you lose water the fibers will tend to bunch up against the hole, acting similar to how human blood cells clot to prevent bleeding. The water will alternately boil/freeze but should eventually stabilize. We can keep it from freezing by picking an orbit that always keeps us in sunlight, and we can circulate the water by painting the outside various shades between black and white, ensuring uneven heating. Maintenance will be tricky. Eventually enough small impacts will build up to the point where we want to entirely replace the outer hull. Probably the best way to do this would be to temporarily evacuate, drain the water shielding, replace the outer hull, then pump the water back in. We could make the outer hull out of something like fabric to make replacement easier, rather than metals - it will hold its shape due to the water pressure, so doesn't need to be a solid. Alternatively we could have all our habitats be somewhat temporary, and just replace them before the likelihood of failure gets too high. Water shielding is a known idea, but with current tech it's not feasible to get enough water into space to make it useful. Thankfully we went to the Asteroid Belt first, since plenty of those will have some water. **Harvesting Carbon Dioxide** The fact is that there's no way with current tech to totally prevent air loss. You're always going to lose some whenever you use an air lock, and there will be some leakage no matter what. So our way around that is to replace it, and that brings us to why we're around [Venus](http://en.wikipedia.org/wiki/Atmosphere_of_Venus#Composition) - we're going to get our air supply from it. Obviously to keep ourselves alive, we need huge greenhouses to provide food, and eat carbon dioxide and give us that oxygen. So every once in a while we'll hop into our giant gas harvester (space ship with a big balloon attached?), go a little bit into Venus's atmosphere and fill our bag. Then we can slowly filter that into our greenhouses, where the plants will eat the CO2 and give us yummy oxygen. [Answer] **Stick yourself in a rock and hope for the best.** That's literally the best approach. It's a bit more elegant than that sentence might make you think, but it's something. I'll tell it like a story. > > You're strapped into the transfer shuttle, nervously waiting to enter your future home. You'll be sharing it with hundreds of others, but it's a home nonetheless. Making the habitat communal was the only feasible way. Putting small groups of people in smaller habitats means it's harder to get from one dwelling to the other. Smaller habitats also mean lower gravity. Although there's low gravity in the habitat you're going to, it's weaker still on smaller habitats. > > > You're going to an asteroid - specifically, [Vesta](https://en.wikipedia.org/wiki/4_Vesta). It's over 500 kilometers long - enough to fit have a dozen cities, and then some. However, most of it is uninhabited. At the moment, only 500 souls live on one end, though the capacity may go up to 1,500. Some of the other space is used for mining, and the center is solid. The two opposite ends are connected on the surface with a special railroad; shuttle flights between the ends are too difficult, and maneuvers are tricky. The reason the center of the asteroid is never going to be hollowed out is that the planners wanted the center of gravity to stay in the same place, so it would continue to move semi-normally. > > > The shuttle gets closer and closer to what seems to be a tiny opening on one end. It's a door about 20 feet high and 30 wide - barely enough for the shuttle to get in (Vesta is in the main belt; a larger ship, on its way to a mission to the outer planets, dropped you off near the belt, and a shuttle docked with it and took you to the asteroid. Specialized flights are way too expensive, even with groups the size of yours - 20.). > > > Now the shuttle is inside, and it's landing. As the engines power down, you walk down the boarding ramp and are greeted by a friendly man who would seem more in place at a department store as a salesman. You and your 19 companions follow him as he shows you around. > > > After telling you all the preliminary details that you learned before you left Earth, he gets to the details you didn't know. "We're going to go deeper into the asteroid," he says. "At the moment, we're as close to the surface as you'll be for a while." You all walk to a rather large room - which is an elevator - and descend. > > > The feeling is astonishing. You'd spent months in zero gravity, but now your stomach does a belly flop. After you landed, your boots became magnetically linked to the floor with each step, a vain attempt at simulating gravity. In the elevator, there are no magnets under the floor, and were it not for the railings your guide has wisely pointed out, all 19 of you might flutter around the elevator. > > > Your guide smirks then gets on with his information. "We're currently going over 10 kilometers down into the asteroid," he says. "Can anyone tell me why?" Nobody can - which he knew - which gives him a smug feeling of superiority. You're impatient, though, and wait for him to tell you. > > > "There are a few reasons," he says. "The first is to protect you all from [cosmic rays](https://en.wikipedia.org/wiki/Cosmic_ray). If you stood on the surface of the asteroid, you'd be hit with a lot. Sure, 10 kilometers of protection may be overkill, but the engineers needed the structure to be strong. > > > "A second reason is UV light. On Earth, you had the ozone layer. Here, there's nothing of the kind. Again, 10 kilometers is overkill, but there are reasons for that. > > > "The engineers also wanted to watch out for collisions with other asteroids. Here in the Asteroid Belt, the density of asteroids per a given volume is surprisingly low. However, collisions are possible. Vesta is one of the biggest ones - that's why it was chosen - but a hit could cause damage. 10 kilometers should be enough to protect it from anything short of a direct hit." > > > Finally, the guide shuts up, and you wait for the next hour to pass. It feels like you're going slower than a snail, but you're going faster than that. It feels like an eternity has passed before you reach your destination. > > > "Come on," the guide says. "I'll show you around." You all hurry after him, and he starts to talk. "As we pass along this corridor, we're going towards the central area. It's built like a giant bubble - just an enormous cavern carved into the asteroid. There's a twin-ish area on the opposite side for mining. However, we left some parts of the asteroid inside the cavern intact, for support. You travel along from one part to another via ziptracks." > > > Ziptracks? What are those? Then you enter the cavern. It's about one kilometer across - it's *huge*! You look around, up and down, and you see people floating about. Most are on tethers, attached to something nearby, but some are attached to small carts on ropes - carbon nanotube-based tracks, someone whispers - that traverse the cavern. > > > On the walls, there are people and dwellings. You think you see gardens and buildings. There's no gravity - save for some magnetic boot tracks - but it's so amazing. You could get used to this, you think. > > > Some credit goes to [celtschk](https://worldbuilding.stackexchange.com/questions/4740/motivations-for-interstellar-colonizations/4741#4741), for inspiring this format. --- # Update I kind of have to agree with [Vincent's comment](https://worldbuilding.stackexchange.com/questions/7364/how-to-mimimize-air-loss-in-space-based-cities#comment24053_7364): > > most answers are now outdated > > > Mine certainly is, now that the question has been edited. I'll keep the above part because I like it (shamelessly praising my own work), but I'll write up what's basically a new answer. **Protection from micrometeorites and cosmic rays** Without proper protection, your poor guys are not only going to be stumbling around but getting seriously ill from cosmic rays coming in. We're pretty shielded here on Earth, but in outer space, all bets are off. [These](https://space.stackexchange.com/questions/4132/what-happens-if-an-astronaut-is-hit-by-a-tiny-micrometeorite/4134#4134) [two](https://physics.stackexchange.com/questions/159960/light-speed-travel-precautions/159965#159965) answers discuss the types of shielding that are used in space stations and the ISS. The most important type is the Whipple bumper, which is detailed [here](http://www.nap.edu/openbook.php?record_id=5532&page=29) along with the other two main types. It uses a metal plate to slow down high-speed incoming particles, such as micrometeorites. I now know what I didn't know back when I first wrote this answer: You don't need a whole lot of rock to stop radiation. After all, enough layers of Whipple bumpers can stop some micrometeorites, and cosmic rays can be [blocked easily enough](https://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays#Shielding) The same goes for UV radiation. I don't know how much shielding you'd need, but it sure wouldn't be a lot. I was exaggerating it in my original answer when I said 10 kilometers (and that was also for support purposes). So your space station doesn't have to have really thick walls to protect the people inside. **Air** The best way to avoid all those nasty, complicated air filtration systems is to make your space station have a bona fide weather system. If we're going for the hollow-asteroid approach - which seems to be our best shot - [it could have weather inside it](https://worldbuilding.stackexchange.com/questions/6949/how-big-must-a-building-spaceship-be-to-create-an-indoor-weather-system?lq=1). You'll need to plant plants to help the O2 be regenerated. You then run into the problem of generating enough light for them. I'd line the outside of the asteroid with solar panels, and use the electricity to light artificial lights so the plants can grow. In addition to getting oxygen, you can also harvest food. [Answer] Run to Europa and dig in! Set up a temporary settlement on top of the ice but immediately start drilling. If you can reach the water, great! Lower your colony ships down through the ice and turn them into submarines. The external pressure against the hull will keep the atmosphere in and you can harvest additional oxygen either from the water or from the thin atmosphere above the ice. You might even find some water-born deuterium for the fusion reactors so your survivalists can keep the lights on and grow some food. If you can't reach the water, get as far as you can, then bury the colony ships in the holes you've dug and then melt the ice in above you. That will give you additional insulation which may also serve to keep the atmosphere inside. Then it is just a matter of waiting till the singularity evolves some compassion so you can move back home where it's warm. [Answer] If you are running away from a potentially soon to be out-of-control AI complex on Earth, going to Venus or even Jupiter might not be far away enough. Since you stated 21st century technology, your habitats are not going to be perfectly sealed, so you need to be somewhere where you can refresh your air and water. Depending on the technology level, you might have to stick to the outer Oort cloud, or if you've some serious Joules to spare, consider a cryogenic inertial escape to a nearby Brown Dwarf, just to be out of immediate range. You can use the protodisk or the frozen planets in the Brown Dwarf system to replenish your losses, and you'll need a fusion power reactor and the ability to build all the spare parts and a basic industrial infrastructure from scratch. From the safe distance of the Oort cloud or the nearby Brown Dwarf, you can assess the danger posed by the emergent AI civilization, and make a decision on whether to run even farther, stay in place or return home. As to the air-loss, it's a trivial problem (since you can replenish losses) compared to the more difficult problems of maintaining a biosphere to feed your people, and having an all-around industrial capability with only a few thousand people on board. [Answer] **Vent waste gasses from an outer shell** The easiest way to avoid losing your precious atmosphere is to lose some other gasses instead. Build your city in the form of two concentric spheres, with all of your inhabited areas in the inner sphere and all of your industry in the outer sphere. Make sure your industry releases gaseous waste, ideally waste that isn't too toxic since little bits of it will escape into your city from time to time. Now, reduce the air pressure of your city to less than the pressure of the toxic atmosphere your factories are producing in the second sphere. Bleed off any excess waste your factories produce into space. **How does this work?** Essentially, you'll be taking advantage of the fact that gasses like to move from high pressure areas to lower pressure areas. Since your atmosphere is now surrounded by a high pressure area, if you have any small leaks in your habitable area, the result will be little bits of exhaust leaking in, rather than your air leaking out. You can patch any holes that form and scrub your atmosphere of pollutants on a regular basis (which you'll need to do anyways) to keep the exhaust from making your atmosphere toxic and your set! The only thing you'll need to do is periodically resupply your space city with fuel. Luckily, things like hydrocarbons and ammonia are fairly easy to come by in space. Titan, for example, has [more oil than Earth.](http://www.space.com/4968-titan-oil-earth.html) So long as your industry is based partially on burning such materials, you can use the exhaust from your factories to keep your precious atmosphere from running away. [Answer] *First off, nice title ;)* **I'd like to suggest a highly unusual mode of transportation, the Leviathan.** Gregory Benford's book, *Beyond Infinity*, described a potential world where life and evolution never quit, and generated spectacular creatures which coexisted in a galactic ecosystem. In this ecosystem is the Leviathan, an unimaginably massive living creature which travels the emptiness of space in search of food. The Leviathan has a strong advantage over nearly all other forms of transit: it is alive. It flexes and adjusts and adapts to stresses. It is also intelligent (to a point where we, as a reader, are left wondering just how vastly intelligent it might be). It just might be your ticket. You just have to wait a few billion years for it to evolve.... ... or do you? [Answer] Hollowing out asteroids is a rather common idea for generating a large enclosed space in space for a large number of humans that can withstand a decent amount of pounding from space junk. [Here](https://worldbuilding.stackexchange.com/questions/377/asteroid-as-a-generation-ship) I asked about an asteroid being used as a Generation ship. I thought the idea would be easier than trying to build great protection around the whole thing or the need to have extremely powerful shields trying to protect you. ]
[Question] [ **Captain's Log** For some time we have been monitoring broadcasts from a planet that calls itself "Earth". We have noticed that it is fond of placing short documentaries in slots between the regular programs. They call these documentaries, "adverts". Often there appear to be some creatures that are bred purely to be eaten. Many, e.g. "sheep" and "cows" appear to be limited in intelligence as would be hoped. However a few species have remarkable skills. For example there are those called "biscuits" or "cookies". We know from the short documentaries that many of these are capable of conversing and even other activities such as playing music. See examples below. That sentient or even living beings should be eaten seems unethical but there are other mysteries. These creatures arrive at humans' homes packed densely in cartons or packets. How do they breathe? A greater mystery, how and why do they develop such amazing skills in such a short time? **Question** Why do humans invest so much time in training these creatures to speak, play music etc. only to eat them alive almost immediately? --- Documentary 1. <https://youtu.be/08LzhobYj-8> Documentary 2. <https://www.youtube.com/watch?v=p2wy_YyHucI> [Answer] Ultimately, the answer comes down to breeding. No, not thát kind of breeding! I mean the kind that results in **Making More Biscuits!** You see, the entire life span of any biscuit species is long and complex and, oddly enough, requires a trip through one of a small number of domesticated species' digestive tracts. Mostly humans, but also dogs and cats, in the case of a smaller number of biscuit species. You see, any kind of biscuit begins life as a seed called "corn", and there are several variants that can ultimately become biscuits, the most populous kind being "wheat". After the seed matures, it enters a sort of larval stage called "flour" where all the corns amalgamate into a kind of mega colony where they await further development. The flour stage can last from several weeks to several months or even years. But once activated, by the consumption of certain sugars & fats, the larval flour moistens, thickens and matures into its pupal stage called "dough", and it is from the dough that individual biscuits mature in a very hot envronment. After this intense period of maturation, the adult biscuits emerge, and after a time of intense courtship, make use of their curiously evolved mimicry (the ability to "talk" and make "music" in the fashion of humans) which endears the humans to them to such an extent that they can hardly put the packet of biscuits down before gobbling the whole sweet lot! This is actually precisely what the adult biscuits' goal is, to be eaten by humans! Because it's the humans whose wastes (their own as well as their animals') that will fertilise the next generation! Biscuits have apparently achieved this curious symbiosis after millennia of careful breeding of a species capable of engaging in agriculture. It's further thought that the very brains of the humans have in some curious way been modified such that they have become willing & complicit partners in the suicidal reproductive cycle of the biscuit. As a matter of clarification: it has been brought to the Commission's attention that human farmers do not (or rather rarely) use human excrement to fertilise their crops. Biscuits are well aware of this, as a matter of fact. If they specialised in passing through the intestines of cows and sheep and so forth, biscuits wouldn't get very far on account of cows and pigs can't cook. What they've come to depend on is a creature just bright enough to engage in agriculture, but yet just dim enough to not question the eating of a sentient species. [Answer] I presume it's because these 'human beings' are actually non-sentient creatures that are taken over by a collective consciousness that manifests itself as 'biscuits' in order to be consumed. This theory explains: 1. Why cookies make themselves attractive — through song, dance, sweetening, and witty repartee — and why they package themselves for ready consumptions, so that they can settle into a host 2. Why human beings do not express any notable intellectual capacities until they reach the age where they can begin consuming biscuits (around age one to two) 3. Why human beings at the height of their biscuit-eating activity — ages six to ten — reach peak intelligence for the species. See supplementary footage "Home Alone", "Home Alone 2", and similar. N.B. I will not weigh in on the McClaren/Dreyfus dispute over whether the eponymous 'Cookie Monster' is a collective cognitive archetype or an ancestral memory of a previous species used by cookies before they chose humans as a vector for consciousness, but point out its relevance to this discussion. [Answer] It's an honor for cookies to be eaten for humans. They train hard for their sub-species (or "brand") to be chosen by humans. Sometime humans shot the documentaries with a particular brand, and the cookies do their best so that humans eat a maximum of cookies from this brand. In turn, human grow (or "produce") a lot of cookies from this brand. If a brand is not often chosen, humans end the brand, so working hard as a cookie for its brand to be chosen hence grown is also a Darwinian winning strategy. Humans are just cold-hearted and dominant, so they pick the most entertaining species (among other criteria). They spend time and energy to train cookies for entertaining purpose. They just have some resources to spend on entertainment. ]
[Question] [ **Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers. --- This question does not appear to be about **worldbuilding**, within the scope defined in the [help center](https://worldbuilding.stackexchange.com/help). Closed 3 years ago. [Improve this question](/posts/64333/edit) Would it be feasible to construct a weapon silencer with modern day 3-D printers and available materials? If so, what might the lifespan be? Is there any chance of creating a durable device or is it disposable at best? [Answer] # Yes, it is feasible to construct a silencer Here are a [pair](https://3dprint.com/52245/3d-printed-plastic-silencer/) of [3-d printed](https://3dprint.com/56493/metal-3d-printed-gun-silencer/) silencers. The first is plastic, the second is metal. # Yes, you can take a durable device, but the work is in progress First off, it is feasible to make an [AR-15 lower receiver](http://arstechnica.com/tech-policy/2013/03/download-this-gun-3d-printed-semi-automatic-fires-over-600-rounds/) in a 3-d printer that lasts around 1,000 rounds. That isn't great, but the lower receiver is the part that takes the brunt of the explosion force of the cartridge. Here is a [list](https://en.wikipedia.org/wiki/List_of_3D_printed_weapons_and_parts) of various 3-d printed gun parts. A silencer doesn't take the mechanical stresses that a lower receiver does, but will be subject to plenty of heat. The plastic silencer is pretty much a one or two shot deal before it starts to melt from heat. The metal one, though, with some engineering should be able to last at least as long as a lower receiver. Its worth keeping in mind, that this is very much a brand new technology. As you can see by the spacing on those articles, these 3-d printed weapons have only been viable in the last couple years. I would expect significant improvements in the near future as more try-and-fail experimentation is carried out. [Answer] # Metal 3D printing Since you can do [3D printing in metal](https://en.wikipedia.org/wiki/Direct_metal_laser_sintering), the short answer is: yes, you can make a firearms **suppressor** (pet peeve: you cannot make a gun be **silent**, only **suppressed**) with a metal 3D printer. There may some issue about how well a 3D printer can do the threads for the suppressor, but that is nothing that cannot be solved by having a fixed threader available for polishing up. As for a **plastic** 3D printed suppressor... well, that is probably **possible** but unless you want it to fly apart on the first shot it probably needs to be made quite thick and sturdy. [Answer] People talking about metal and plastic printers, but what about resin ones? Well, [here](https://www.youtube.com/watch?v=ekDs60QxmNE) you can see an AMAZING person do it, and it works really well. Can't say much about durabillity tough, it is a really new field. But the cool thing is resin printers are pricier than plastic ones, but WAY WAY WAY cheaper than metal ones. And everyone with a bit of engeneering and much magverism can do it in your backyard, so if you need to your characters do a makeshift silenpressor (i loved the term my dear Deolater) is the best choice. ]
[Question] [ For the sake of simplicity, my species is similar to humans but far more advanced. We will also assume that they live in a solar system similar to ours, and that they are advanced enough that they can 'catch' an asteroid and land on it. These people wish to create a research base which orbits the sun, not the earth. To do so, they are planning to build a base on an asteroid. Assuming this asteroid has a similar orbit to the one shown below, what would this research station look like? [![Asteroid orbit](https://i.stack.imgur.com/3E2Wo.jpg)](https://i.stack.imgur.com/3E2Wo.jpg) People would be transported to the base on rockets, and to get back to 'earth' they would eject a pod while the asteroid is travelling towards the planet and drift back home (again, assuming very advanced technology). The asteroid they have chosen is large (about 900-1000 km diameter) and is made from a combination of carbon compounds, iron and magnesium silicates, nickel, igneous rock, and ice (all in abundance). Its gravitational field strength is around 1/32 of earth's. With an orbit like above, the speeds and temperatures on the surface would be difficult to deal with. Assuming my race of sentients can land on an asteroid like Ceres, with an orbit similar to Phaethon, what would their asteroid base look like? How would it be operated and what sort of systems would it use? They need to be self-sufficient (produce food) and be able to survive both extremes of the asteroid's orbit. Assume advanced technology, but nothing unrealistic (no time travel, teleportation, or artificial gravity please) [Answer] Some consideration has to be made abut the composition of the asteroid. If it is a solid mass, then you will essentially be tunnelling into it like the NORAD bunker in Cheyenne Mountain. However, current theory suggests that asteroids are loose piles of rubble with lots of spaces in between, so the interior of the asteroid is almost like a sponge. A very large asteroid such as you describe could have a very interesting composition. Some of the data from Ceres seems to suggest there is a lot of water trapped inside. Regardless of the composition, once you have burrowed inside, you will have very little gravity. Creatures evolved on a planet would prefer some simulation of gravity, both for health and comfort, and because it makes working easier (tools don't float away, for example). So the space inside should be cleared enough to build a rotating space station that provides a gravitational simulation. This concept can be expanded to create what is known as a [Gravity Balloon](http://www.scifiideas.com/science-2/colonizing-asteroid-cores/). The concept is explained in detail at the link, but the explanation is simple. A large enough space is found or excavated, lined with an airtight membrane and filled with air. Tension cables are strung along the interior, and rotating structures strung along like beads to provide the living space where a simulation of gravity is created. [![enter image description here](https://i.stack.imgur.com/6HcOE.png)](https://i.stack.imgur.com/6HcOE.png) *The rotating structure everyone lives in* This illustration would be for a very ambitious colony, an external mirror transfers sunlight into the interior and the small black dots are rotating structures 500m in length to give you an idea of scale: [![enter image description here](https://i.stack.imgur.com/MwKIF.png)](https://i.stack.imgur.com/MwKIF.png) Most of the other details of day to day operations can be gleaned from sites like [Atomic Rockets](http://www.projectrho.com/public_html/rocket/index.php), and many of the other posters have mentioned many of the factors needed to operate in space. [Answer] # Underground base The base will need to be underground to provide protection from radiation. Even just being in Earth orbit is a [major radiation hazard when the solar wind is heavy.](https://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays) The reason we do not fry here on the ground is because the Earth's magnetic field and its atmosphere protect us. [![enter image description here](https://i.stack.imgur.com/ikl4H.jpg)](https://i.stack.imgur.com/ikl4H.jpg) *These pretty lights are where the atmosphere blocks particles that would otherwise kill you through severe radiation poisoning* Your asteroid has no atmosphere and no magnetic field worth speaking of, and it goes into the very "stormy" regions of the solar system, right next to the Sun. By the look of that diagram, it even passes close enough to touch [the corona](https://en.wikipedia.org/wiki/Corona). **This means the radiation hazard is extreme. If this base is sweeping that close to the Sun, they will need very heavy radiation shields.** Best way to do that would be to 1) bore down into the asteroid, since stone and metal-rich minerals protect very well, and 2) place the water tanks between themselves and the Sun. [Water is an excellent radiation shield](https://what-if.xkcd.com/29/). [![enter image description here](https://i.stack.imgur.com/VQf8v.png)](https://i.stack.imgur.com/VQf8v.png) *The major danger of taking a swim in a nuclear fuel pool is that the guards will be very cross with you for contaminating the ultra-pure water in the pool, you filthy thing you* **So the main distinguishing feature of your base is that it needs to be underground.** All work sites related to this base will need to be underground as well, or be shielded, or have radiation hardened bunkers nearby where people can go when things get "hot". This was a concern on the [Apollo missions](https://en.wikipedia.org/wiki/Apollo_program) when — on the later, long duration [J-type missions](https://en.wikipedia.org/wiki/List_of_Apollo_mission_types) — the astronauts went for long treks on the [Lunar Rover](https://en.wikipedia.org/wiki/Lunar_Roving_Vehicle). NASA was very nervously watching the Sun for activity, because if the Sun had flared, Mission Control would have needed to recall the astronauts and have them take shelter in the [Lunar Module](https://en.wikipedia.org/wiki/Apollo_Lunar_Module) to protect them from the resulting radiation. With this I would expect the base to have one or several dedicated [tunnel boring machines](https://en.wikipedia.org/wiki/Tunnel_boring_machine) in operation. # Energy Fusion reactors. Someone else suggested solar panels but I digress on that. Solar panels are extremely heavy compared to the power they give, and when you travel in space, you want to keep things as light as possible compared to the amount of "usefulness" they provide. If your heroes are "far more advanced" than us, then just assume they have mastered fusion instead. Energy is probably a non-issue. [![enter image description here](https://i.stack.imgur.com/LhJPi.jpg)](https://i.stack.imgur.com/LhJPi.jpg) *Bring your [handy fusion reactor](https://en.wikipedia.org/wiki/Polywell), and energy will not be an issue. Plus you have a very sci-fi looking element of your futuristic base. ([Source](http://www.emc2fusion.org/))* # Water, air ~~This will need to be brought, or — if they bring an extra fusion reactor — they can break apart materials on the asteroid to form these on site. Hydrogen is everywhere in the universe, and so is Oxygen. You just need **energy** to break apart minerals and molecules to form the right stuff.~~ **After the edit to the question:** If there is ice on the asteroid, this is a non-issue. Use the fusion reactors to melt and purify the ice for water; use electrolysis to make Oxygen from the water. Purification and re-circulation of waste water / waste air will probably be necessary. # Food Expect that to need to be stockpiled. Unless of course — like air and water — you expect to be able to manufacture that on site. But unless your heroes have Star Trek type replicators it will probably be quite boring food... rather simple nutritional pastes and fluids, simple sugars. Do note that this makes for a nice plot element when the transport from Earth comes with the good stuff... steak, juice, drinks. Also note that during the perihelion (passage closest to the Sun), no transports can come... the radiation is too heavy. And there is probably very little work to do during perihelion since they have to huddle in the radiation proofed areas of the base, sucking on their protein pastes and mineral-supplements. [Answer] (First answer ever here, I'm not sure to be specific enough) Survival will be hard. Asteroids having no atmosphere, your base should be able to resist very high temperatures, nothing stopping the energy from the sun they orbit around to get directly to your base. You would also need some heavy energy-absorption systems and ventilation if you do not want your base to hold some human barbecue. Those conditions are necessary only if you want an orbit similar to Phaethon, which passes [very close to the sun](http://www.thelivingmoon.com/43ancients/04images/Asteroids/Phaethon_orbit.jpg) at some point. Assuming very advanced technology, they could build some kind of railway building very quickly, in order to dodge going close to the sun. It would automatically adapt to get to the opposite face when it goes near the sun, and facing the sun when it is far enough. Detection systems like antennas or anything could do this positionning decision trick. About the look of your building ... It is all up to you. The only restriction I would give you is to make it as flat as possible. The composition of your asteroid makes me feel like a huge building will have a rough time getting solid foundations, and the speeds there will be tremendous for it to bear. A maximum of one floor, maybe ? I don't know, but make it kind of flat. In my vision, it would greatly ressemble [houses from Dragon Ball Z ?](http://vignette2.wikia.nocookie.net/dragonball/images/9/95/900.png/revision/latest?cb=20110219010425) This way, you'll divide the weight of your building throughout the asteroid's surface, and won't have to think about very deep structures. For the deployment, you have advanced technology. Automatic building deployment could be a thing, as [it already exists](http://www.rapidbuiltshelters.com/) in some extend. You could improve it to make automatic foundation digging (careful, not too deep) and room-repartition deployment. It lands, it deploys, humans can come and go. **EDIT** Energy is not a problem, you have the Sun. Solar panels will absorb the energy for you and feed the electrical system. So you have power to keep your food nice and cold, until it is consumed. I doubt any prey for humans would live there naturally. You would have to transport it from your "main planet". I think lyophilized food will allow you to transport a lot of food, so you can limit your transport cost. Your base should plan some kind of landing field, so you can get both humans and supply to come (and go) to your base. If they want to go back to base, there are numerous solutions. A small number of humans may be able to go for it through escape pods, be it classical propulsion or heavy-calculated launch through space to Earth. If you want to leave entirely, the building would have, **of course**, some "zipping" functionnality (as you deployed them). Call the Earth, tell them you are all planning to leave. Send the equipment first, then most of scientists, then a space ship could come and take back the building and the few engineers staying. [Answer] Wait wait wait... While resources and stuff has been addressed already (I'm voting for fusion reactor btw.... I wonder if you can grab/soak/inhale new fusion material while drifting through suns corona...) something just spoke of in a comment @Dan Bryant and @Euphoric is pretty vital to the whole story. ## Rendezvous with the asteroid so... I do not know what kind of future advanced technology your civilization does own, but if they cannot offer vessel that has a deltaV of... huh... * remove earth-velocicy (30km/s) * correct ascending node and perihelion (about 5km/s?) * rendezvous burning (5km/s?) * and back: remove orbital speed of base-asteroid at earth' semi-major-axis (hm... 5km/s?) * gain earth orbit velocity (30km/s) * break to decent back to earth (7km/s, while here much aerobraking can be done) means about 80km/s deltaV... ehm, deltaV is the total change of speed of a spcecraft provided by its engines (and fuel niveau). Okay, these are estimates beyond any calculation, so maybe the real number is even bigger. Thats pretty insane. The only useful alternative would be a Hohnmann-Transfer to the asteroids aphelion and than a braking burn, which would be quite fuel efficient. Still, thats beyond today capabilities, and even if you could do this, you only have a narrow timeframe every year when the transfer would be most efficient (I would guess when the earth is at the suns other side). So as long as your spacecraft arn't capable of these stunts, please go for a more relaxed asteroid. ## Cooling Okay... half the distance of Mercury? Did you bring some insane cooling radiators with you? Don't think a lump of rock will keep you cool enough when coming this close to sun. While you will have the energy to fuel this, you need some real batshit engineered apparatus to get rid of excess heat. Cooling Doesn't sound so fancy, but without an atmosphere to carry away heat, all you have is blackbody-radiation, which need huge surfaces to work properly. Surfaces that shold not point to the bright, warm thingy that will cover up half of the visible sky. So no asteroid rotation or the cooling apparatus needs to be even more interesting. ## Station keeping Last but not least - you are passing through suns most outer part of atmosphere... A T M O S P H E R E. every time you are at the closest point, you will loose some momentum due to friction. When not accelerating the whole asteroid one day in future even the best heat-radiators won't keep you cool any more. So... yeah, there are plenty of cute asteroids out there which don't require such an effort to went to. if there isn't any really fine stuff located at that heap of stone and metal, leave it be alone. ## Plane Shift That's the second edit about something I forgot in the beginning: That astroid needs to be at a pretty inclined plane compared to these of the other planets; because he is passing at least four other celestial bodys during his orbit (which are all in the (way) > 10e22kg mass range) all of them would be able to throw him into the sun or make him a runaway when he comes inside their sphere of influence. Or just plain crash (which is highly unlikely but still an valid option). What does this mean? Not only you need to arrange with that eccentric orbit, you need to adjust to a probably insane inclined plane, which is even less of a pleasure to compute. --- EDiT: I have to admit, the latest comments made me think... advanced technology *may* be able to convert even the heat gained by the close distance to sun into thrust... just funnel this to a point where some kind of expanding propellant is stored. Hell, you could get thrust by applying microwave laser to your most retrograde part of that rock; the surface melting and subliming away will provide forward momentum (but how much... and one day our asteroid will be... used). The skyhook... wiki says you get about 3.5km/s in theory. Still missing 60km/s. This comes down to pure math. Which I'm not good at. If you employ a mass-driver for spaceships you might be off better. If your spaceship can use any form of an ion drive (or something similar) than reaction mass (and ship mass difference between dry and wet) would be a negligible problem, but you need aeons to apply the thrust. I'm still for an asteroid in a much nicer orbit ;) [Answer] I'm going with the simple idea, that there wouldn't be a base in an asteroid at all unless it served another purpose than just 'research'. That purpose could be anything from surveillance, where the asteroid might be span to produce 'gravity', to a military installation with a mass driver, to a factory that produced high tensile strength cable and lowers it onto planets for a relatively mobile space elevator / counterweight in one. whereby the base would stay in a stable geostationary orbit for a time. Much of the equipment on board would depend on the purpose of this asteroid base. I mean, what does an asteroid base in a fairly erratic orbit provide that the ISS cannot do in the real world? I don't see any logical reason why any 'intelligent' species would just build a base in an asteroid with such an orbit. Unless the goal is to obfuscate their goals they'd capture it and put it into a more stable orbit, probably mine it for raw resources. Food's easy: multi-level robotic greenhouses. Water is easy, they already have ice. Radiation protection comes from the thickness of the rock and some extra gold foil around the viewing areas. For power, I'd assume that this species would already have solar panels in orbit, and can laser the energy into the base. No weather, no day night cycle, affordable and infinite. Heck, maybe the asteroid base is a maintenance station for the species' new dyson swarm. Gravity is trickier, either spinning it or constantly accelerating it, either one provides problems that are fairly intuitive. Controlling the asteroid shouldn't be too hard, solar sails are surprisingly effective (both cost and usability), and can even be designed to allow for tacking and beating toward the sun. Keeping that orbit would only help if the goal is to: Survey something inconspicuously. Attack something unexpectedly. Maybe the base is nothing but a giant flywheel, and your species is moving it into a more stable orbit in order to: Turn this base into a counterweight for a space elevator. Mining for rare metals space-based construction of solar panels other goals, like tourism, are equally applicable to either one, but a more steady orbit would help people arrive and leave. ]
[Question] [ In most representations of mermaid cities, they either live in implausible magical palaces, or in some more or less elaborate cave systems. Assuming the only difference with our world is the presence of the mermaids (so no magic), and that those follow the typical image of lower part fish, upper part humanoids. That they have brains and intelligence similar to the *homo sapiens sapiens*. We can imagine that much in the same way that we spread over the lands, they did over the oceans, from the tropics to the arctic, etc. I am curious, assuming that the main steps of their technological development is somewhat parallel to ours, how their city would realistically look at the dawn of the 20th Century? They face some challenges different than ours, namely that digging is harder and they have stronger currents. I would be interested to know about the different architectures for different geographical areas, but I am primarily interested in the moderate waters of the North-Atlantic Ocean (roughly between the USA and Europe). [Answer] I will derive my solution by comparing to real-world precedents, and analyzing how these might be adapted by merfolk. (TL;DR: Rock domes.) **Why do humans have houses?** * *Shelter from the elements.* As mentioned in another answer, houses provide protection from storms and from extremes in heat and cold. This may be less important to merfolk, but not entirely absent. * *Shelter from predators.* As much as we once feared the dire-wolf and smilodon, merfolk likely had the same issue with sharks and orcas. * *Privacy.* Humans feel the need to perform acts of ablution, elimination, and procreation away from the eyes of other humans. Let us assume merfolk have the same sense of modesty, so this is a factor. * *Security.* Humans like to accumulate stuff. They attach value to it, and want to keep other humans from readily taking it away. Again, let's assume merfolk have also developed this sense of ownership. **What do humans make houses from?** * *Wood.* We can eliminate this as not available to merfolk. Even if they salvaged wood from sunken ships and fallen trees which washed down flooded rivers, it would be in poor condition for use in construction. * *Mud/ Adobe.* Another thing we can eliminate. When baked on land, it is rain proof, but against total immersion it would break down and drift away quickly. * *Woven Vegetation (thatch).* This is plausible, I'm imagining kelp. In fact, sea otters wrap themselves in kelp when sleeping. Primitive merfolk might have copied this and expanded on it. * *Animal Hides.* I don't have any way to back this up, but my gut tells me it is not possible to tan leather when surrounded by salt water. As fun as it is to think of a merman making shark leather, we must eliminate this one too. * *Bones.* Generally not sufficient to make an entire house, but like humans, merfolk probably put bone to good use in tools, decorations, and so on. Bone is better preserved in the ocean than on land, also. * *Metals.* Deteriorates in salt water, so nope. * *Glass.* I'm not sure about merfolk's ability to make glass, so I'm just going to punt this one away. * *Rock.* This is my pick, especially coral rock. Collect it, stack it, and soon you have yourself a nice structure. Mortar is not an option (see adobe above), but it could be reinforced with the kelp-thatch the ancestors used. **What shape are human houses?** * *Tepee/ Yurt.* The central timbers lean together to support each other and the surrounding skins. Since we have eliminated these materials, we also eliminate these shapes. * *Cube-Like.* Some human ancestors seemed to heavily favor straight lines and things that were perfectly horizontal and vertical and met at exact right angles. I won't rule this out for merfolk, but I like the next option better, given that merfolk live in a three dimensions and need no concept of "floor." * *Domes/ Igloos:* The weight of the bricks (whether rock or snow) is mutually and evenly distributed, resulting in a sturdy structure. Domes also use space very efficiently. There just *must* be a Buckminster Fuller amongst the merfolk. **How do we put all of this together?** Most merfolk dwellings consist of overlapping dome-shaped modules. Each module is built from pieces of coral and other rock. Where needed, the coral is held together with by mats of woven seaweed, particularly kelp. They have doors with locks. They don't have what a human would call a "window," since any opening is just another door. The doors might be made of single flat rocks, or perhaps bone. Each door also has curtains, to retain privacy even when left open to let fresh water circulate through. Depending on the fashion sense of the owner, the curtain could just be a simple collection of plant leaves, or strings of shells and small bones. It isn't clear whether they need any variant of HVAC. As mentioned above, fresh water will circulate if you just leave a few doors open when the current is just right. Whether they have furnaces and how they work could be the subject of a whole other question here. Larger buildings like office complexes or shopping malls are just larger domes with larger numbers of inter-locking modules. They locate their cities in the places that offer the best conditions, just like humans. That means mild climate, access to resources, and plenty of open build-able spaces. I suspect areas adjacent to- but not directly on- large reefs would be attractive to them. [Answer] As a RPG-writer, I've stumbled with how would my mermaids culture and architecture look for humans. Well, unless your mermaids and your humans are isolated, some things will follow, but the more important one is: **Mermaids won't live in deep waters** As a human-sized fish-mammal hybrid, mermaids are *not* adapted to living in deep water conditions. They will probably live around beaches, and maybe a bit off the coast, but never on deep, empty ocean. The human body that makes their upper torso doesn't support deep-sea living for long without heavy equipment, and evolution can only take you so far as adaptation goes without making them look like whales or sea-lions. The sea can be really cold, so they will need shallower, warmer waters to thrive. Also, in literature, at least, mermaids go with some frequency to the surface to interact with the surface in a way or another. Don't think of them like the mermaids from the Disney movies or as friends of Aquaman. They are likely to spend a lot of time on land trading, gathering stuff from the beaches, getting sun-baths, luring sailors to eat them alive... mermaid stuff. They are half-human, and they can breath air. They will probably love the warm sun on their skin, the taste of fresh coconuts, or some freshly-cut palmito with their fish. They will love to look to the sky at full moon, and will probably love to sing in the beach, around a fire. You can't sing really well underwater. I believe that mermaids would start more tribal than humans, at first, like Amazonian or African tribes that develop a bit away from the main bodies of civilization. They will probably be more carnivorous than anything else, since fish is a way better source of fundamental nutrients for mammals of their size than kelp - I imagine their diet being similar to those of dolphins. Since building stuff underwater is hard, mermaids will probably be stuck with living in caves or some rudimentary rock-houses for a while. That's it, until they see what land-dwellers built. At the moment the mermaid scouts bring the notice of the majestic human cities near the coast, I believe mermaids will take a great deal of interest on those strange, two-legged creatures and the stuff they build. Their leaders will want those majestic buildings, too, and will, sooner or later, do what humans do best - imitate them. They will try to simulate what they see on the coast, with their vision on how should things work on their culture. They will probably build hybrid constructions on relatively shallow water, with some parts over and some parts under water. However, this type of building needs materials that are really hard to get underwater, so they will probably need to buy them from land-dwellers. To make that work, your mermaids will need some economical advantage over humans - something that only they can get, it's expensive, and that humans *really want*. That way, they can buy the materials and hire the work they need to build their coastal palaces, which will be built using granite and similar materials, and adorned with gold and gemstones. Mermaids like some bling, too. Those buildings will probably be made to be used by mermaids, with some capabilities for humans to cross. There is no good to have a sublime palace if you can't show it off to the other people. Mermaids will probably *love* wide open spaces, with tons of glass panes for light to shine in, probably emulating how the sun shines through the water. If they do have multi-store buildings over-water, they will use columns of water which connect pools in different floors to go up and down. Those columns could be partially sealed off to prevent water spill, and some crafty use of wind-powered water pumps will make sure the water stays on level everywhere. The use of hybrid buildings will make a lot of things that are harder underwater way easier. Medical care, for example. If blood spills on land, it goes down to the ground and stays there. If it spills underwater, it goes everywhere, mixing with water and making things really messy. Metalworking and leather working simply don't happen underwater, and so your mermaids will want some surface area to work with those the same way humans do. Also, electricity and water can go messy really fast, so they will probably be way more wary of electrical power than humans are. If they adopt it, it probably will be restricted to the surface areas of their dwellings, and will not, for obvious reasons, extend to their underwater areas except on some really, really controlled settings for essential stuff - mostly illumination and heating. So, in essence, instead of deep-water cities, they will probably build coastal, resort-like cities adapted both for them and for humans, which they will probably be contacting often. Their cities will probably be build from the beach towards the sea, and will extend for a while until the water gets too deep to build or too cold to live in. As a side-note, don't be afraid to build a less-advanced culture for your mermaids. Their problems and environments are different, and so will be their development. Think of how Hawaii was before the arrival of the foreign people, and how it is now. Seems as a good way to go with your mermaids, I think. Most important of all, don't let their fish-tails be something restrictive. On the contrary, use them to boost their capabilities, and let them roam the land and the sea in ways that we humans can only dream of. Don't shackle them to the bottom of the ocean. Their voices deserve to be heard, their songs deserve to be listened, and their belies deserve to be full of sailor-meat! [Answer] Architecture is a means of providing for a need. For humans, the primary reasons for housing of any kind are shelter, as in shelter from the rain, shelter from the cold, and protection against large predators. Over time, obviously, housing became more and more complex. Since you assume your mermaids are pretty similar to homo sapiens, you can assume that their needs will be quite similar, although you will have to account for the absence of legs, and the somewhat wetter environment. Two things spring to mind there: Mermaids have no need for stairs, and they don't need (much) scaffolding. So, building vertically is easier under the sea than it is on land, although the currents create much stronger lateral forces than the wind does above the surface, which reduces the benefits somewhat. Something else is important: Human propulsion typically happens with an upright human, while a mermaid, given the water density, will typically travel more or less horizontally, even for short distances. that means, passages can be much lower, but need to be wider to allow for turning. Finally, a floor is of much lesser importance for mermaids than for us. The only thing one should expect to be truly similar is that a building typically will have an outer shell of walls and roof, to keep out the currents, and predators as well as pests. You should expect windows, but doors will be shaped differently, especially they don't need to be as high as ours, again because of travel in a horizontal attitude. You will most likely have means of storing your things, which means chests, cupboards and such, but far less shelves. And after that, everything else will most likely be left to personal taste. [Answer] Interestingly, I'd think that much aquatic architecture would attempt to build *down* as well as up. The oceans are full of caves, caverns, and bottomless chasms: these should provide both protection from predators and enemies and a great three-dimensional foundation on which to build your city. With this in mind, I'd like to think that many buildings would be supported by a series of ropes. This would make it easy to add new buildings to an existing structure, or move buildings to other structures with minimal demolition. As mentioned in other answers, things like stairs and doors become mostly useless underwater, so what might seem to us to be a confused interconnected mass of buildings might end up making a lot of sense to merfolk. For instance, big ropes supporting some of the city's largest and heaviest structures may be used as an analogue to highways, while smaller ropes help serve as landmarks when navigating more suburban areas. If electricity gets introduced, it shouldn't be hard to attach wires to the ropes to connect all buildings to the power grid. The problem I can see with this kind of city is sanitation. Without a rigid structure upon which to lay your piping, it may be difficult to keep things properly plumbed. Though now I'm wondering if our concept of plumbing would even work underwater; maybe they just use outhouses. [Answer] While the building construction aspect is covered, if truly mirroring the dawn of the 20th century then the city planning would be happening at the point where the car was replacing the horse and buggy for us. Roads weren't paved, sidewalks when available were wood and to keep you out of the mud and horse-poop. Where big cities had plumbing in the downtown core and sewage systems, but the power grid was generally not yet there. If you are really going to mirror that, you may want to consider what the mer-folk used for draft animals, what they farmed and how they contained livestock that moves in three dimensions. And most marine life tends to fall within a fairly narrow band of water depth to meet their light / temperature requirements. Are your mermen top-of-ocean dwellers? Or deep-sea creatures? [Answer] Mermaids and merman in my story would preferably live closer to the surface because as with all mammals, they need oxygen. So their houses would be built by adapting the coves and caves underwater to reach their sheltering desires. No need for floors and they would make good use of underwater plants. As they do not want to draw attention from Humans, their buildings would be a bit hidden. I like the bone idea too. ]
[Question] [ The [Hollow Earth](http://en.wikipedia.org/wiki/Hollow_Earth) theory is/was a pseudoscientific idea that our world is actually on the inside of a large sphere. The "sky" points inward towards the center, where the "Sun" (a light source) is, while the "ground" points outward. Let's assume that we have a planet the size of Earth, except that it is a hollow Earth. In reality, it's simply an Earth-sized cavity inside a larger body, notably, some sort of artificial megastructure. I had assumed that said megastructure was spherical, but clearly I should have stated it explicitly, so I'll do so now. The structure will have spherical symmetry and be as uniform as possible. Is it possible to put a moon inside the sphere - somewhere between the central light source and the "ground" - and have it move in an "orbit" around the center? Would the moon crash into the ground, or would it be stable? I'm almost positive that the moon can't be as big as Earth's moon, but I don't know a reasonable size. I'm fine with anything bigger than, say, [Janus](http://en.wikipedia.org/wiki/Janus_(moon)) or [Epimetheus](http://en.wikipedia.org/wiki/Epimetheus_(moon)). --- Bonus question (not necessary to answer): Is the setup possible if the hollow Earth is non-spherical, i.e. ellipsoidal? [Answer] # No. Bodies composed of known materials the size of the Earth and Moon are in ["hydrostatic equilibrium"](https://en.wikipedia.org/wiki/Hydrostatic_equilibrium), > > This occurs when external forces such as gravity are balanced by a > pressure gradient force.[1] For instance, the pressure-gradient force > prevents gravity from collapsing Earth's atmosphere into a thin, dense > shell, whereas gravity prevents the pressure gradient force from > diffusing the atmosphere into space. > > > Hydrostatic equilibrium is the current distinguishing criterion > between dwarf planets and small Solar System bodies, and has other > roles in astrophysics and planetary geology. This qualification > typically means that the object is symmetrically rounded into a > spheroid or ellipsoid shape, where any irregular surface features are > due to a relatively thin solid crust. There are 31 observationally > confirmed such objects (apart from the Sun), sometimes called > planemos,[2] in the Solar System, seven more[3] that are virtually > certain, and a hundred or so more that are likely. > > > What this means in your case is that the strength of the materials is insufficient to support the mass above them. So they flow like molten plastic/liquid and fill all voids. So in your Scenario the "Earth" outer shell would collapse under its mutual gravitation. The strength of materials required to prevent this from happening would be quite high and I don't have the time to perform the necessary calculations for you. [Answer] It's not possible without active intervention. The sphere's gravity is zero on the inside. So there is no force acting on the moon from the sphere. This would allow the moon to orbit a mass at the center of the planet. However any perturbation of the sphere would not be transmitted to the moon. Hence nothing prevents the moon, and whatever it is that is in the center for the moon to orbit, to pick up velocity relative to the sphere. [Answer] Certainly - [the sphere's gravity at the inside will be zero](https://en.wikipedia.org/wiki/Shell_theorem), so the composition and thickness of the crust is irrelevant. The moon has to orbit the central light source, and the mass of the light source should be much bigger than the moon's, and you'd better keep vacuum in the cavity (since there is no gravity, you cannot expect the air to stick close to the crust). Other than that, it's possible. [Answer] **Not without artificial gravity or some other outside source.** Your mega structure large enough to have an earth sized pocket is going to have a lot of mass. Something that big is going to need futuristic materials and technologies to keep from collapsing. Anything on the inside of the sphere is going to be drawn toward the center of the structure. If the sphere is off center then everything will be pulled toward one side. If it's in the center of the structure then things would just fall off the surface toward the "sky", unless... To get gravity on the inside surface of a sphere without artificial gravity it needs to be spinning, meaning the structure needs to be spinning around the sphere, or a mechanism needs to be spinning the earth size sphere independently of the structure. Spinning the whole structure is not a good idea, since if you have 1g at the surface of the sphere, you'll have even more the further out you go. Angular Velocity: 0.0118 rotations/minute Earth Radius: 3959 miles Gravities: 1g Radius: 5000 miles Gravities: 1.26g Radius: 8000 miles Gravities: 2g Stress on the structure would be increased exponentially the further out from the center of gravity you get. If you just spin the sphere independently you still need super materials like [ringworld scrith](http://larryniven.wikia.com/wiki/Scrith) and you better hope it's really well balanced. So you'll have to pick your magic: Artificial gravity or impossible building materials. Edit: Without artificial gravity you'd need a gravity point source in the center to orbit a moon around, since centripetal force wouldn't work to orbit inside a sphere. Any variations in mass in the outside structure would tend to destablize the system, similar to the three body problem, requiring constant corrections to keep the moon from crashing. **With artificial gravity, getting a moon to do anything you want is easy.** [Answer] You're describing a [Dyson Sphere](https://en.wikipedia.org/wiki/Dyson_sphere). It is theoretically possible to still have orbital bodies inside the sphere in their orbit around the sun. Assuming we live on the inside of the Dyson shell and can process the entirety of the sun's output without frying, we wouldn't have a moon since the only orbital bodies are the planets further in and the Sun. There's no center of gravity for a moon to orbit around, since the Dyson sphere's center of gravity is the sun itself. That doesn't stop the Venus or Mercury from having moons of their own. [Answer] I will answer your bonus question: If the hollow earth is oblate or prolate spheroidal, and the two body system of moon and light source remains in the plane on which the cross section of the hollow earth is still circular, then stable orbits will exist as they would otherwise by symmetry. For a more complicated case, I expect nothing but a series of rather intense numerical simulations could determine the answer to whether there exist any periodic orbits at all. [Answer] Yes, but you need: * a *very* dense central light source, and this density is in contrast with what we know about sufficiently powerful energy sources, i.e. nuclear fusion. Of course you could go with an artificial light source, such as a degenerate matter sphere which reflects light beamed from the inside of the shell. * some next-to-uncompressible material with which to build the shell, *or* some mechanical means of counteracting the gravity of the inner sphere and preventing it from making the outer shell collapse (the late [Paul Birch](https://en.wikipedia.org/wiki/Paul_Birch_%28writer%29) suggested a network of rails where heavy carriages would travel at orbital velocities, thus exterting an outward pressure capable of counteracting gravity. Of course, this leaves us with the problem of energizing the network itself. * some way of keeping the outer shell centered on the light source. The net force exerted by the shell on the central sphere would be zero, which means there's nothing to stop small perturbations to make the central sphere drift against the shell (it's the same reason Niven's Ringworld has stabilizing engines) * the internal volume should be kept in vacuum, or the Moon's orbit would quickly degrade. If the perturbations are small enough, it could be feasible to stabilize the shell (and maybe the moon too) using the pressure of the light being beamed from the shell to the "Sun". However, the central volume would be uninhabitable, as gravity would push towards the "Sun" and the whole cavity would be in vacuum. People on the inside of the shell would need to receive light through thick, airtight glass floors. [Answer] A mass at the centre and a uniform superstructure of sufficient mass such that the gravitational attraction on any body between the central mass and the superstructure by the central mass equal the attraction due to the superstructure in that direction. There's your answer. ;) Think of gravity as a set of elastic ropes. The one rope pulling a "moon" towards the central must be balanced by ropes extending from the superstructure in every direction. Calculating these forces will be an infinite series, as the rest of the superstructure will also exert a gravitational attraction towards a moon in between. It is doable, but obviously nothing could live there, unless you build a set of biospheres along the superstructure. Tidal forces will be a major concern, as will Coriolis forces is the superstructure is spinning. The poles might be liveable; the equator, between the moon-based tides and the structure's own spin, would be like the inside of a washing machine. ]
[Question] [ No, not [that one](http://en.wikipedia.org/wiki/USS_Enterprise_(NCC-1701)). [This one](http://en.wikipedia.org/wiki/USS_Enterprise_(CVN-65)). ![USS Enterprise pic: courtesy Wikipedia/US Navy](https://i.stack.imgur.com/dXYRH.jpg) I want to see the USS Enterprise fly, but I'm curious how it would be accomplished in any realistic fashion. Now, the world I'm building that needs a flying Enterprise has some advantages that might help us. Gravity is at 0.6 Earth Standard, and the atmosphere is considerably more dense. (Let's say 50% more) * How could this be done in the field? (using scavenged parts not necessarily only from the Enterprise herself) * How could it be done with the benefit of a full shipyard? (with the full technological and industrial might of the US Navy) > > Note that I am aware of the relation between gravity and atmospheric > density. This world gleefully ignores it for... *reasons*. > > > [Answer] > > **edit: This answer arrives at the wrong conclusion because I made > a mistake in my calculation of the craft's mass in Newtons. Spoiler > alert: you can't make it fly this way. The rest > of the analysis stands however, as far as I know. See the end of the post and the comments for details.** > > > Lets crunch some numbers: * We can use displacement to figure out its mass: + The Enterprise has a displacement of `94,781 tonnes`[[1](http://en.wikipedia.org/wiki/USS_Enterprise_%28CVN-65%29)] at sea-level gravity on Earth, which gives it a weight of 56,900 tonnes at .6g gravity. * While less gravity would normally mean *less* density in the atmosphere, we'll go with the prescribed +50% density from the question. While that would make the air heavier, since the carrier is immersed in the atmospheric fluid, the forces cancel out (especially during flight - but it might have a bit of trouble trying to disengage the water surface - we'll disregard it for now). ## Lifting it up There are two obvious ways to lift an aircraft carrier-sized object in the air - one is using a standard airship approach (stick it under a huge balloon) and the other would be a VTOL approach[[7](http://en.wikipedia.org/wiki/VTOL)]. Since others have answered on the airship case, I'll stick with the VTOL - I think it's preferable since: 1. You want to modify an existing craft to fly 2. You'd want to maintain the same functionality, thus you want to reuse the same facilities and structures as much as possible Making an airship is probably a lot simpler however - VTOL is more complicated and costly, but it's damn cool. * The Enterprise has 8 reactors, giving a total of `210 MW`[[1](http://en.wikipedia.org/wiki/USS_Enterprise_%28CVN-65%29)] of power. + The Avengers carrier resembles a Fan-in-Wing setup[[8](http://en.wikipedia.org/wiki/Powered_lift#Fan-in-wing)] and this seems viable as an option for such a craft + Thrust vectoring would be an option, but it doesn't give us enough control to use downward-facing engines to move forward fast. + Although ideally we'd be able to use all fans to lift and move, the requirement for stability here is high - the carrier, unlike a helicopter or plane, can't pitch at all (doing so might cause people and planes to roll off - real carriers tie planes to the deck, but there's still a very small margin for pitching here). This means we'll have to use separate fans to control altitude and translate. ![quadcopter](https://mikeshouts.com/wp-content/uploads/2013/02/Air-Hogs-Elite-Helix-X4-Radio-Control-Quadcopter.jpg) Lets see if our reactors have enough power to lift the carrier: * Since we're reusing existing reactors and the Enterprise used them for propulsion as well, we'll assume we have no fuel capacity and we can't use jet engines. That means we're using helicopter mechanics pretty much. * We need to generate thrust higher than its weight in order to lift it up, which means over `560 KN` of thrust (**edit: this is incorrect, I was off by 1000 because of a mistake in my units, it's actually `560 MN`. See end of this answer.**). Using this propeller thrust equation[[14](http://quadcopterproject.wordpress.com/static-thrust-calculation/)] and assuming: + air density at `150%` + `45 MW` used per propeller + fan diameter equal to the width of the craft: `80m` we get: `((pi/2)⋅(80)^2⋅(1.225⋅1.5)⋅(45e6)^2)^(1/3) =` `3.34 MN` assuming I haven't made a horrible mistake in the calculations. That gives us a single fan capable of lifting the carrier with a TWR of almost 6:1. We can't use a single fan though, so we'll split it between two, each with a diameter of 50m, for altitude, which gives us a total of `4.89 MN`. We have to place these so that their thrust vector aligns with the center of mass of the craft, so probably near the middle. So far we're using 90 MW, so we have room for our propulsion propellers. If we have two of them, mounted in the back-side, `10m` in diameter each and pumping `25 MW` to each of them, we get `565 KN` of thrust for each, which is enough to move the craft easily (TWR of 2:1). ## Summing up That's a total of about `9.8 MN` upwards thrust and `1.13 MN` of forwards thrust at `140 MW` of power, which is 2/3 of our capacity. We haven't factored in the weight of the propellers yet so lets do that. Extrapolating from the size of the GE90 jet engine[[15](http://en.wikipedia.org/wiki/General_Electric_GE90)] which is the largest one yet, we arrive at a weight of `110 kN` for each of the `50m` fans and `22 kN` for each of the `10m` fans. Adjusting for the lower gravity and summing, that's a total of about `160 kN` of extra weight due to the fans. At our `720 kN` of mass and accounting for all the engines, we have a TWR upwards of `13.6` and forwards of `1.57`. This means we'll rise very fast and have a high maximum altitude but will move forwards relatively slowly. These calculations aren't exact (obviously) and I'm not an expert on this kind of thing, but it seems that, if you're willing to deal with the extra engineering challenge of making it a VTOL, it *should* be possible at a lower gravity and higher air density. You could of course adjust the sizes to make better use of your power, but it depends on what you want to favor - flying or moving fast. > > Demitri has found a horrible mistake I made. My original calculation > of the mass of the craft in Newtons was off by 3 orders of magnitude (1000) > which means everything after that is pretty much invalid. The engines > would have to be about 100 times more powerful, even under lower gravity > and higher atmospheric density to allow this craft to fly. > Not sure what to do with the answer except note that the conclusion is > incorrect. I'll leave it as it is so the overall post isn't confusing. > > > According to Demitri's corrections, with the correct mass of $558 MN$ for the carrier, the power required to lift it is $172 GW$, which far exceeds the capacity of the carrier's reactors. > > > [Answer] Of course there is always The Avenger's flying carrier (which is ridiculously impractical but should be mentioned). ![Flying Aircraft Carrier](https://i.stack.imgur.com/jX0LY.jpg) Moving away from fantasy towards reality then actually there have been some serious real-world investigations along these lines. <http://en.wikipedia.org/wiki/Airborne_aircraft_carrier> > > USS Akron (ZRS-4) and USS Macon (ZRS-5) were two rigid airships built for scouting duties for the U.S. Navy and operational between 1931 and 1933. > > > Following experiments with launching and recovering small aeroplanes using the USS Los Angeles (ZR-3), the USA designed the Akron and Macon with internal hangars able to house a number of Curtiss F9C Sparrowhawk biplane fighters. The fighters were launched and recovered using a "trapeze" mechanism > > > ![USS Akron in Flight](https://i.stack.imgur.com/mgG7e.jpg) This leads us to our first point, the carrier will be slow moving and extremely heavy so it would not lend itself to heavier-than-air flight. However airships are excellent for lifting large loads at slower speeds. They also do not disrupt the airflow around themselves so would be better for landing and taking off from. **In earth conditions:** The USS Enterprise weighs 94,780 tons. 1000 cubic feet of helium can lift 65.82 lbs. So we need 2 879 975 000 cubic feet of helium. The carrier itself is 2106 feet long and 1522 feet wide so if we make the balloon the same size as the carrier that gives us a helium balloon 2106 feet long, 1522 feet wide and 900 feet high That's a damn big balloon! There's no complete blocker on building it though, it would be expensive, slow, and vulnerable but it certainly could be done if enough money was thrown at it. **In our hypothetical world** The gravity is 0.6 earth standard, that will make the same change to the weight: The USS Enterprise now weighs 56,868 tons. The atmospheric density is hard to calculate for as the helium will also be compressed more if the pressure rises. Lets say the atmosphere has earth pressure but increased density. In that case Helium has 50% more effective lifting power and 1000 cubic feet of helium can now lift 98.73lbs. So we now need 1,151,990 cubic feet of helium. That now gives us a helium balloon 2106 feet long, 1522 feet wide and 359 feet high As you can see the altered conditions of your world make things much easier. **But what about the weight of the ballon?** The weight of the lifting gas itself is already included in the buoyancy figures so can be discounted. The balloon structure itself will have a noticeable weight but it will still be a tiny fraction of the weight of the aircraft carrier so while it would need to be allowed for if someone were designing this for real it will not make large changes to these figures which are illustrative anyway. [Answer] Yes, an airship version of the USS Enterprise is practical. It would be several times the size of the Hindenburg but well within reach of modern technology. The main constraints would be: * Weight. Without a 100% rebuild, the USS Enterprise is far too heavy to make a good gondola design. You would need a staggering amount of lifting gas. Not impossible though, and modern airship designs incorporate aerodynamic improvements, which you could take advantage of by using the copious electrical power from the nuclear reactor to propel it (think 100+ modern jet engines) * Aircraft operations. Assuming it carries the USS Enterprise's full complement of aircraft, a substantial part of it must be dedicated to aircraft operations. If you replaced the Enterprise's flight deck with a gigantic Zeppelin structure, you could operate from a runway on top, or change your aircraft to support cradle launch (this was done with biplanes, not sure if it would work for modern jet fighters) * Power. A large part of your weight budget has to go to the nuclear reactor and jet fuel for the aircraft. * Crew accommodation. not a problem if you keep most of the original structure intact. * Operations - You would need massive new mooring facilities around the world for maintenance. Obviously the airship route requires the support of a full shipyard, including a lot of facilities custom designed for the project. All of it well in reach of current technology, if a little expensive. EDIT: With the increased density and reduced gravity, the proposed airship would be about 3 times longer than the proposed US Army heavy lift cargo airship, so manoeuvrability and docking should not be too bad: ![US Army heavy lift cargo airship](https://i.stack.imgur.com/rgTYE.jpg) [Answer] You would have to change the power supply. The reactor on the CVN-65 is water cooled using around 50gpm. [SOURCE](http://water.epa.gov/lawsregs/lawsguidance/cwa/vessel/unds/upload/2006_08_10_oceans_regulatory_unds_surfacebilge_SVBCHAR03_draft.pdf) This works because the carrier is sitting on literally a sea of coolant. This allows the carrier to replenish cool water and expel waste heat quickly and easily with out having to maintain a large reserve of coolant on board. The need for the coolant would make nuclear power a poor choice for a large air ship like this. Now if you have something like a [ZPM](http://stargate.wikia.com/wiki/Zero_Point_Module) you could make the types of changes that would be needed to make the Enterprise airworthy. Another issue is going to be keeping lift. Lets assume that 250knots would be sufficient for lift to keep the ship airborne. That is going to make the flight deck incredibly hazardous. Anything over 50-60 knots is probably going to be unmanageable for both aircraft landing and taking off, and crew working on the deck. So you are going to need a hover capability. This would allow the ship to go into near stationary mode for deck work then resume normal flight speeds. You will also need to make the control tower able to drop into the deck for flight speed mode. Something more interesting for full speed launches might be to drop the planes more like bombs allowing the planes to accellerate to flight speed after they have been dropped. This would allow for a much more rapid deployment of a squadron as well. [Answer] So you want to write that a crafty crew in dire need made thier ship to fly. I think it is doable in 3 steps. 1. They cut off the upper deck from the hull, reinforce it to be able to withstand weight, and mount all the equipment they would need in flight on the deck or under it. Modern ship can literally be peeled like an egg, as hull is not the integral part. 2. They sew a lot of ballons from I don't know what material. They provide heating to the balloons. 3. They tie balloons to the deck and get themselves something of a big flying raft. 4. They are lucky to have appropriate winds. Now, to the problems. * In big modern ships, all fixtures on the top are connected not to the desk, but to the internal structure. They will have to re-weld it all to the desk. * Energy. Not only electricity, ship has a network of pipes, supplying pressurised steam for all systems. * A shot from main weapon literally makes a battleship to shake and move in the water sideways. In case of flying, in will rock violently. After all, I think, it is doable, but building several small zeppelins from ship's parts would be easier and more effective. P.S. How happens that your planet has lighter gravity but thicker atmosphere? I though these things are connected. This although means that locals will invent balloon-flying nearly as early as sailing, which means they may end up with elaborate ships. They can literally jump from cliffs with umbrellas! [Answer] I did a funny calculation that I want to share. Let's take a ship called *"Oasis of the Seas"* as example. Its gross tonnage is 225,282. We can estimate it's cargo volume as GT/0.32 = 700 000 m3 = 700 000 000 litres. One litre of helium on Earth can lift 1 gramm of weight besides itself. In your condition + heating let's say it is 4 gramms. 2800 000 000 gramms make *2 800 tonns of lifted weight*. This much lift will the crew get, if they fill cargo volume with hot balloons. Unfortunately, "Oasis of the seas" weights 100,000 tonns. But crew will have fun. Switching to hydrogen will double the lifting power, but remove the fun. ]
[Question] [ In a Sci-Fi setting, if there is a vast amount of non-humanoid intelligent life in the universe, like perhaps 20 or 30 species, would this make 4 or 5 species that look similar to each other, or similar to humans more believable? [Answer] ## The default humanoid is more believable than you think A lifeform does not have to be humanoid to be intelligent, but being generally humanoid helps a LOT with tool use. On Earth, we have a few species of cephalopods, cetaceans, and avians that evolved advanced intelligence well before our human ancestors did, but they don't have the body plans to form an advanced civilization; so, their intelligence seems to have capped at about where hominids were in the early stone age, while humanoids were able to keep going. ### Features you should consider for all of your aliens are: 1. Bilateral symmetry appears to be universally advantageous for complex organisms. There are very few examples of non-bilateral life on Earth that is more advanced than a starfish; so, assume this to be common elsewhere too. It also means that all of the below assertions should assume an even number of arms, legs, etc. Though throwing in 1 or 2 radially symmetrical races, or bilateral races with a central appendage creating an odd number could be believable too. 2. If you live in an aquatic environment, you can be smart, but never develop fire which means you will never develop chemistry, metallurgy, or ceramics or any of the other things that helped humans get out of the stone age. This means that nearly all of your aliens should be terrestrial or amphibious, and come from an oxygen rich planet. 3. If you don't have something like fingers, then you will be very dexterity limited in your tool use. Again, this caps you at a very primitive state. So, all of your aliens should have something like hands with multiple fingers. Something more tentacle like works too, but don't give them suckers because those require an aquatic environment to form a good seal. 4. If you have less than 2 arms, you will have a hard time manipulating objects against each-other. If you have more than 2 primary arms, then your arms will be strength limited compared to your size. Cleaving and hammering require a lot of force. Trying to strike with shoulders that are not perpendicular to your target means you rely on kenosis instead of momentum to drive the terminal impact. For this reason, most of your aliens should have 2 main, bilateral arms, plus maybe 2-4 smaller arms or arms that second as feet. More than 6 arms with no fingers might happen too, where the arms work together for grasping, but expect such an animal to require some kind of adaptation that allows it to perform very swift "snapping" actions with its hands to overcome the single shoulder limitation issue, or for all the arms to emerge from more or less the same part of the body. 5. If you can't see what your hands are doing, it limits your ability to use tools. So most aliens should have eyes (or comparable sensory organs) that can comfortably visualize whatever your alien is touching. A vision-like sense is also very helpful for developing reading and writing though not absolutely necessary. These organs should usually be in a head containing the brain and all of your other major sensory organs since this improves processing and reaction time by putting them all closer to the brain. This is seen in nearly all complex life forms; so, assume aliens will be similar. Secondary neural ganglions may exist throughout the rest of the body to improve motor control like an octopus does, but the actually sensory processing and executive thought parts of the nervous system should be in a head. 6. If you can't be motile while carrying a heavy load, then this limits your ability to use large tools and to construct buildings, or even to gather fuel for a fire. This is where the upright body plan of the humanoid really shines because humans can carry things very well. In fact humans can carry a load much farther than any of our Hominidae relatives despite being the proportionally weakest member of in the family. Centaur or Naga-like body plans may work well too. This will make body types without skeletons of any sort much more rare though because an upright body plan requires structure. 7. Avoid really good natural defenses. A tiger or a chameleon would have very little reason stop and make a spear, even if they could. So body designs that are just a little bit helpless without weapons and tools puts the evolutionary pressure on to develop weapon and tool use. Don't get me wrong: claws, fangs, venom, and active camouflage are are perfectly reasonable adaptations to have... just don't make them too perfect of versions of these adaptations. ### Areas where you should see a lot of variance: 1. Elder Races. While all of the above rules will apply to civilized races that have only been around for a little while like humans. Advanced civilizations that have existed for evolutionary timescales are more likely to break the rules. Once a civilization develops the ideas of separation of labor, welfare, automation, cybernetics, and gene-manipulation, genetic features that once would have been selected against may prove beneficial in unexpected ways. An alien adapted to sit in front of a computer all day may survive famines and plagues better than if they can naturally walk. An alien that relies on cybernetic augmentation might be more likely to survive their surgical adaptation if they are born with diminutive or missing appendages. An alien that lives its life interfacing with neurojacking technologies might become more fit without the distractions of natural vision, hearing, etc. Genetic augmentation might lead to a sort of polymorphic caste system where everyone's body is specialized to the task they are born for... So, many things we typically see as disabilities could become a future specie's adaptations causing one or more of the above rules to get thrown out the window all together... though I would still expect in most cases some vestigial elements of their humanoid evolution: like eyes that can't see, ears that can't hear, etc. 2. Color and skin type. Fur, feather, scales, shells, exoskeletons, and others will all be evolved to deal with each alien's native environment and ancestral lineage. So, any choice is as believable as another. That said, remember that any alien that does not see in the visual light spectrum will likely be black, white, or clear skinned if it comes from a planet where being seen by human like eyes is a not issue. Or the inverse, they could be very ornately patterned (like parrots) if they live where only themselves and few other animals can see in the visible light spectrum. 3. Sensory Organs. Human eyes, ears, mouths, and noses don't even look that much like some other mammals, much less animals in general. Alien sensory organs may be shaped very differently than humans, and even work by other mechanisms all together, but still plan to slap most of them into a head, and have some analogue for sight and feeling because they need to be able to have a good sense of what they are working on when tooling. 4. Digestive organs. While it should be true that your aliens will typically have a way to consume food and expel waste, the organs for this can come in all shapes an sizes and these have no bearing on how smart or tool using your alien can be. Some aliens may throw up their waste instead of having a specialized anus. Some may have sideways mouths, mandibles, proboscis, fangs, tusks, beaks, etc. Some might even be primary producers and need to sit in a tanning bed or a nutrient bath to "eat"... though I expect this to be more rare due to the energy requirements of being a tool user. 5. Legs and Feet. While hands are a pretty specific requirement, there is a lot more room for variance with the feet. This part of the body could be pretty much any number of legs with any number of joints. It could even be serpentine or something completely alien. As long as your alien can move around while holding something kind of heavy, its bottom section should be fine. 6. Size. The human brain is far from the most size efficient an organic brain can be. Even using Earth base biology, a bird brain the size of an orange could out-perform the human brain; so, expect some aliens to be as small as a medium sized dog whereas others could be the size of an elephant. 7. Reproductive Methods. Most aliens should have some kind of sexual reproduction because this is necessary for animals with longer life cycles to evolve at any reasonable rate. That said, sex organs come in all shapes and sizes; so, even if two aliens look almost identical, from the waist up, their methods of insemination and gestation could be completely incompatible. Don't do more than 2 genders though. It is a bad trope because it automatically puts a species at a terrible competitive disadvantage making it one of the least believable alien characteristics you typically see in sci-fi. Most aliens should be a form of hermaphrodite or bi-gendered with some being asexual. 8. Lifespan. While this may not change how an alien looks, I think it's worth bringing up. Most of your aliens should probably have a natural lifespan of at least 30 years to give them time to learn science and then apply it for long enough before dying to make the learning worth while. That said, there are exceptions that could make certain aliens live much shorter lives. You could have an alpha phenotype that lives a long time and does all the learning and science and stuff while most members of the species are just dumb worker/slave phenotypes that live much shorter lives. In this case, the alpha phenotype may not be humanoid at all. Or you could have an advanced system of genetic memory such that a member of a species might only live for a short while, but it has memories going back 100 generations. Or a third exception would be a hive mind where each member lives a short while, but the higher level thinking of the species is actually an emergent intelligence caused by the interactions of many smaller, weaker, minds. ### Conclusion While all these rules do not mean that the default should be exactly humanoid, it does mean that every advanced civilization should have a lot of common features with humanoids. Considering the specifications above, I think making ~25% of your aliens truly humanoid (2 arms, 2 legs, phalanges, etc.) is a good idea, but most of your advanced aliens should be "effectively" humanoid in terms of what their body plans can get accomplished, even if they get there by different means. In short, your universe probably has thousands of intelligent races, but only the 20 or 30 with good body plans and environments will develop past the stone age. So what they see as 1-in-4 intelligent races being humanoid is actually more like a 1 in 1000 kind of thing... it just takes a lot more than intelligence to cross the threshold into forming an advanced civilization. The OP said in comments on another question "In my world, the whole plot is 'its a mystery' with the humanoid species all trying to put forward their own theories for why it is" actually works well with this because there will be a lot of debate about what constitutes intelligent life. Here on Earth, we can't decide if a whale is more or less smart than a human, and we've lived along side them for thousands of years; so, any alien that does not have a strong interest in xenobiology will likely dismiss most intelligent life forms as simple animals. So, while the Xyphlonians might claim there is no mystery because only 1 in a million sentient being are humanoids because they have a very broad idea of intelligence, the Droxians might say that there is no mystery because the Droxians are the only intelligent species in the whole universe because even those other animals that can make spaceships can't comprehend some manner of thinking that is uniquely Droxian; so, they are just animals that make stuff no different than beavers or ants. The "mystery" only exists for those in the middle like us Humans that find space flight to be something special. In reality, it's just a very specific niche; so, convergent evolution will play a big part in what it takes to fill that niche. As for 25% of your races being not just humanoid, but mistakable for human... that is far less believable since coloration, skin type, size, etc. will likely vary too much for this. If this is a needed element in your story, then these races should all have a single progenerate race. So, if for example, Neanderthals developed space flight about 40,000 years ago, colonized 3 other worlds, and then their civilization collapsed, then you could have humans find other very human like races out there. But it would be obvious from the other 3 worlds' fossil records that they did not evolve on their own planets; so, making it a mysterious thing would be less believable. The other way to go would be to make them mistakable only to non-humanoid aliens. An average human might mistake a cuttlefish for an octopus despite thier glaring differences just because most of us lack a deep familiarity with cephalopods. Likewise a Gronkian might have a really hard time telling humanoids apart if humanoids are a thing he's only ever seen a few times in his high-school biology class 10 years ago. [Answer] # Maybe In order to make something believable you must give a reason. In this case I think the standard two arms two legs one head model is believable to develop again for the reason that the conditions are similar. So in your world with both humanoid and non humanoid species, it helps to have the humanoids come from Earthlike planets and the non humanoids come from more exotic worlds. Exactly where you draw the line at *exotic* I leave to your imagination. [Answer] There is a large range between "having a vaguely humanoid body plan" and "looking like a human with pointy ears." I do not think it likely that we will find any of the latter. Neanderthals and modern humans diverged less than a million years ago and Neanderthals would look more different from us than Vulcans do. The Na'vi from the Avatar movies are perhaps believable as a species that evolved from a common ancestor a couple of million years ago, but even then, they are more attractive to us than is realistic. A completely different evolutionary history going back to the beginning of life has such a large space of options to choose from that looking like tweaked humans is incredibly unlikely. I think a valid rule of thumb is, if a human can play the character without completely hiding their face and their proportions, then the alien is not alien enough to be realistic. [Answer] I am assuming you are following humans in your story. Space is vast, travelling between planets is not easy or pleasant. Also changing between worlds is always challenging as different worlds have different atmospheric conditions and gravity. Members of a species will not be able to visit most of the habitable worlds as even presence of a simple gas could be toxic let alone temperature, humidity, gravity, oxygen percentage, atmospheric pressure, food source, etc... Even when they are compatible it will still be unpleasant. Additionally, even if you forget about speciesism, it is not feasible for a human major (99%+) world to accommodate for say tentacled bird-like species that require specialized places to eat and live. Thus, most of your aliens stay in a few compatible worlds. Even when they travel, they choose to go somewhere similar. In the end, you will have a few types of humanoid aliens in a world that could realistically be travelled by humans. ]
[Question] [ A friend of mine was telling me about a story where a man clear cut a diverse ecosystem of plants in an area similar to size and shape of a small caldera (not necessarily a caldera itself). Eventually, he noticed other plants were sprouting up that no one has ever seen before, as they were ancient seeds dormant beneath the surface waiting for the perfect conditions to sprout. I've searched the internet for this story or something like it, and can't seem to find it. All I found out is that some people have grown some plants from ancient seeds. --- I was thinking if this were to happen on a large scale, globally speaking, I wonder if it could set the perfect conditions for ancient seeds to grow. Example, like some seeds of megaflora from the Mesozoic period buried deep within subsoil. With the proper amount of churning up of topsoil and subsoil, and the decimation of preexisting plant life, I'm fascinated with the idea of some prehistoric giant trees growing after the earth is fallow for a few centuries after such an event. [![giant trees](https://i.stack.imgur.com/1QkTZ.jpg)](https://i.stack.imgur.com/1QkTZ.jpg) *Picture shown for reference. Taken from [this](http://www.renegadetribune.com/giant-trees-days-yore/) site. Although a similar topic, does not reflect the nature of this post.* --- ## Edit: For clarification, this question is posted in search for a more descriptive support to the background of a world in which this scenario did happen - a purely *fictional* world. Not necessarily relating to seeds from a specific prehistoric time period, but ancient nonetheless. As though it *could* happen... perhaps? [Answer] The [oldest seed germinated](https://news.nationalgeographic.com/news/2012/02/120221-oldest-seeds-regenerated-plants-science/) is around 32,000 years old. > > The mature and immature seeds, which had been entirely encased in ice, were unearthed from 124 feet (38 meters) below the permafrost, surrounded by layers that included mammoth, bison, and woolly rhinoceros bones. > > > The mature seeds had been damaged—perhaps by the squirrel itself, to prevent them from germinating in the burrow. But some of the immature seeds retained viable plant material. > > > The team extracted that tissue from the frozen seeds, placed it in vials, and successfully germinated the plants, according to a new study. The plants—identical to each other but with different flower shapes from modern S. stenophylla—grew, flowered, and, after a year, created seeds of their own. > > > As you can see, this required the scientists direct intervention to trigger germination. The previous record holder was a 2000 year old [Judean Date Palm](https://en.wikipedia.org/wiki/Judean_date_palm) recovered from Masada which only needed appropriate conditions to germinate. So it's not entirely improbable, but preservation of organic materials on that timescale is a complex game. Seeds must not have the conditions to germinate, but equally not have the conditions to decay. Masada is high and dry, Siberia is permafrost, both suitable environments for long term preservation. Merely clearing the ground is not likely to trigger growth, but a [good fire](https://en.wikipedia.org/wiki/Fire_ecology) might. [Answer] # Plants There is a whole [wikipedia](https://en.wikipedia.org/wiki/Oldest_viable_seed) page for this! The oldest mature seed that grew into a plant on its own was a date palm excavated from Masada (which has its own [wiki page](https://en.wikipedia.org/wiki/Judean_date_palm#Germination_of_2000-year-old_seed) too!). The seed would be about 2000 years old, and it germinated in 2005. With some scientific help, a [campion](https://en.wikipedia.org/wiki/Silene_stenophylla) seed buried by squirrel about 31800 years ago had its embryo extracted by scientists and germinated *in vitro*. This plant in turn was viable and produced its own offspring. # Fungus Viable fungal spores were found [underneath a glacier](https://books.google.com/books?id=IFD4_VFRDdUC&pg=PA392&lpg=PA392&dq=oldest%20viable%20fungal%20spore&source=bl&ots=s_jVpdmim7&sig=aXJi2S5gN3Z29ukEepIXOkMsHjk&hl=en&sa=X&ved=0ahUKEwi-27n1hqjZAhUQ7WMKHe9HATIQ6AEIMjAC#v=onepage&q=oldest%20viable%20fungal%20spore&f=false) in Greenland. The ice immediately above the fungus was 140,000 years old, but it is not certain that the fungus itself is this old. The same reference suggest that a freeze dried fungal spore would be viable indefinitely. The limiting factor would likely be radiation damage to the spore. So long as the sport was buried deep enough to be protected from all ionizing radiation (and there wasn't enough uranium and thorium in the surrounding soil to irradiate it), a fungal spore that dried out and froze in a desert tundra might last millions of years. # Conclusion Thousands of years, definitely, so long as the envioroment is suitable. Keep in mind Masada, Siberia, and Greenland are all deserts. You can't have a seed survive where there is liquid water; bacteria will literally eat it alive. Given the proper freeze drying conditions, millions of years is possible. [Answer] my example is only on the scale of 100 years or so but in wisconsin where previously there had been grain fields turned pine forests (for lumber) the state tried restoring prairie, they clear cut the forest and before they could plant a mix of prairie seeds the prairie regrew itself. they studied the species and found some that they hadn't thought to include. going along with the other responders, id say a viable mechanism for bringing these seeds out is maybe an earthquake? a sudden split and upwelling of a landmass sends seeds spewing out down the meltwater channels and all along the rivers odd, old plants start appearing... ]
[Question] [ The idea of a collective consciousness (Or Anthill) is pretty simple: instead of cells you have small sentient animal that make up a larger creature. This is different from a hive mind in that the individuals of a hive mind are all sapient, but in a only the collective is. When I tend to think of this species, I struggle with how they would appear. Unlike with an angel, a centaur or a merperson, I lack both the inner anatomy and outer form for what they would look like. I literally am starting from the barebone scratch of a creature. This has made me ask, what would an anthill species look like? What would their biology be? [Answer] # The anthill would be an aquatic monster. *At first they were only ants, then the flood came. It was huge, immense. Actually, the whole continent seemed to dive underwater. There was nowhere to go and most land animals died. But ants don't die, they never die. That was hundreds of millions of years ago, the ants never got back to the solid ground. They adapted, changed, coordinated more than ever.* *Emphasized text should not necessarily be taken seriously.* ## Skeleton *The first anthills could not have survived without physical integrity. Air was still needed, so some ants became the anthill. First as an unorganized raft, then as more and more usefull backbones and limbs.* Bone ants are champions of gripping. Able to connect with each other in an extremely firm way, they form tubular structures (similar to those of the cytoskeleton of a cell) that can stretch from a few centimeters to several meters. The interior of the tubes is reserved for "nervous" transmissions. The rest of the colony moves (and stays) on the anthill by grabbing the multiple handles the bone ants can provide. The joints are more complex, some ants are specialized into sliding joints and some other ants are specialized into providing lubrication and maintenance. ## Peripheric nervous system *As the food started to need effort (at first it was just eating the cadavers of those that can't survive into water), ants quickly needed to adapt. They needed to coordinate, quickly.* As stated before, the peripheric nervous system (PNS) goes inside the bones. Inside the tubes are extremely elongated ants that most of the times stretch as long as the bone does. Their nerves are actually directly connected to the joint-ants. The joint-ant has several nerves (and so several different way to activate), the main functions being: * Controlling the joint rigidity * Activating/relaxing the muscles * Propagating back senses/pain We now need to talk about... ## Muscles *Food isn't always looking for you. Sometimes, you have to look for it. As in the water, ants could no longer go away from the colony, the colony had to move.* Compared to skeleton ants, muscle-ants are tiny. When a skeleton ant is usually 5mm long, a muscle-ant can rarely get to 0.5mm. Good thing there is a lot of them. Muscle-ants don't transmit much chemical signal in the muscle process (they do in the building and repairing processes however). They mostly grip an ant before them and another behind them. They are mostly programmed to imitate on their behind-grip what happened to their front-grip. The delay caused by the "grip-transmission" gives the anthill a very flexible movement, adapted to swimming. Muscles constantly transmit how "hard" they find the stretching to be, signaling back the effort needed. Tendon-ants are more complex, as they receive pheromone orders from the joints, initiate the grip with the muscles and maintain themselves within the joint. The latter is actually done thanks to their deformed antennas: they are stretched around the joint, at the same time ensuring reception of signals and physical connection. Tendon themselves are about 2mm long and there is a lot of them on each side of the joint. Two of their legs are big in order to grip the bones, the other four are able to grip up to 30 muscles each. ## Senses (and more on the PNS) *Moving is fine, and the colonies soon started following plankton gradients. But predators arose and the ants had bigger fish to hunt. Earing them was the key.* Throughout the skeleton, sensor-ants monitor chemicals (smell, taste) and mechanical (touch, sound) inputs as well as some other informations (heat, bubble presence, light-level). These various senses are transmitted to the joints by [courier ant](https://worldbuilding.stackexchange.com/questions/45184/is-the-idea-of-a-collective-consciousness-realistic) that are constantly going through the bones. Each sensor is therefore connected to the two joints of its bone, allowing to approximately pinpoint the epicenter of the signals. Places that need a lot of precision simply have smaller bones, or, in very specific cases, directly connected joints. Sensor information is first locally used by the joints. But let's see exactly how muscle activation works. There are actually a lot of nerves just to activate one muscle, way more than for usual animals. They encode parameters for a big function, that function being mainly "how much grip to do with respect to the various senses, grip difficulty and your position in the skeleton tree". This allows each node to be reactive while being centrally controlled. ## Feeding of ants *The ants where now one, more than ever, they had to rely on each other to live. How could those proto-bones and proto-muscles be allowed to look for food?* Food is transported from the central digestive system to the limbs through simple worker ants. Bone and nerves having actually their mouths constantly connected to another ant's behind, the whole bone manages to feed itself through sharing. Muscles, having a varying distance between each other, had to develop a different strategy. They made a friend! One very specific zooplankton has learned to live within the anthill at high concentrations. Good for the muscle ants, because the zooplankton learned to go by himself inside the tiny hard-workers belly and even pre-digest itself. Not that the plankton evolved to be stupid: being a prized guest in such a beauty has its perks. ## Skin *What good is motion if you can't push water? For water movement and for the first time, ants needed surface.* Skin has a structure comparable to that of the bones, except it does not cycle on itself. The structure is weaker, and more flexible than bones. Dead ants are used as glue between skin-ants to augment impermeability. Note that the colony is not covered in skin, it is only found where the anthill needs propulsion. ## Eating and digesting *Where does the food come from? How could small ant eat big fishes? My mom told me no ant could eat me, but I never believed her. I know better.* A colony doesn't really have a mouth. More like a waterlock between the exterior and their stomach. Outside the waterlock are lots of grabbing tentacles that push the food inside the hole. Remember the "some joints are directly linked together"? Tentacles. The stomach itself is a big pocket. The "skin" ants glue themselves together (and to the bones) to provide a waterproof containment. Inside the stomach are the digesting ants. Former warriors made into highly chemically corrosive assailants and former workers cutting big pieces and transporting it to the exterior of the stomach. The non-edible materials are themselves used as cement and gravel to the glue surrounding the stomach. ## Ant renewal *I tried to think about some joke about the Queen of the UK, but I found nothing worth it. Hey, have you noticed make less sense each chapter? Yeah, it's almost 4 am for me.* Right next to the stomach is the queen. The queen's job as not changed much since the colony still needs egg producing. What's interesting though is that eggs are quickly moved out of the queen's chamber and placed where the final ant should be. A special pheromone as been developed to say "here's a new bone/muscle/nerve/other, make him hatch in the right spot". The need for ants is inferred through the analysis of the quality of food, muscular and bone input (or absence thereof, indicating a fracture) and some other and more obscure signals (of course it's more complex than that, it's alive!) ## Reproduction *If the colony could not multiply, it could not evolve, and adapt, and survive. Anthills had to reproduce or be screwed. Am I a bad person? I'm not even ashamed.* Young future-queens are put at the farthest end of limbs and males have to go through the whole colony if they want to reproduce. Hijacking on their path workers and other ants. Only those with the material to perfectly communicate with the rest of the ants can get to transmit their genes. Once impregnated, the now-queen hijacks nearby bone ants and detaches itself and its deserters to form a new entity. The first step of gestation is to create a proto-stomach and a chamber for the queen. Interestingly, the future stomach is also the gestating entity's placenta. The hijacked ants having the signals from the mother colony, the baby can rely on its parent for food and shelter for a while. That is, until it has limbs too big to stay in the stomach. They then go out through the mouth-hole and the colony effectively becomes independent, killing the original renegades in the process of developing its own immune system. Interestingly, some male ants may be able to impregnate females from other hills, providing there is direct physical contact between the two. ## Central nervous system *The central nervous system is mainly required because fluid mechanics is weird. Like, super weird. Seriously, non-linear stuff.* The central nervous system (CNS) is a hive in itself. From birth until final death, it continuously grows. The neuron-ants have extremely small bodies and extremely long antennas. Each of their eight antennas (limbs were replaced) can reach up to a meter, effectively going through the whole brain, they basically work as axons. Neuron ants have some sort of hair that mimics the function of dendrites. The CNS and the stomach are stuck together through special extra-strong links that can transmit the best possible food. The queen's chamber is stuck on that "neck". ## General morphology *This is either a text about the ant's history or something silly.* Colonies take very various shapes. From far enough, they look like black skeletal sharks. However, the oldest colonies often stop having a regular (or even symmetrical) shape. This is only possible when the colony is old, because younger colonies can maintain a regular pattern and only the biggest and well-trained brains can handle a complex asymmetric body. *You've read through all of that text? Wow. I wouldn't.* [Answer] ## The Anthill Would be More of an Ant Pile [![Quite literally a pile](https://i.stack.imgur.com/EG1c0.jpg)](https://i.stack.imgur.com/EG1c0.jpg) --- As a living organism that needs to hunt, move and grow, remaining in one place would not be very good. The best solution is to act in a similar manner to army ants. Instead of always moving in a direction, they would move as a pile. The primary part of this pile would act as the anthill, with specialized ants guarding the outside. This caste would act as both the Immune system and skin, their best defense would be a combination of formic acid and [trap jaws](https://en.wikipedia.org/wiki/Odontomachus). The Soldier Caste would also be present in the limbs (see further down) and in small numbers inside of the pile itself. They would be the most expendable of all castes and also the most common. The Soldier also takes on the task of telling the difference between friend and foe. Another caste similar to this would be the Drones, they would basically work as an extension of sight; while all of the ants would attribute to sight (giving Anthills 360 degree spherical vision), Drones would allow the Anthill to find food and predators much quicker. Inside of this pile you would see a lot of odd grouping of different castes acting as different organs. The workers would act as the dirt on the diagram below. [![enter image description here](https://i.stack.imgur.com/RrYTt.jpg)](https://i.stack.imgur.com/RrYTt.jpg) **The Queen; The Circulatory, Immune and Reproductive System** The Queen would serve three human purposes; The Spleen, The Bone Marrow and the Reproductive system. * By laying eggs, she would be making members of castes, Doing this she works as the Spleen and the Bone Marrow. If the larva is a Drone, a Soldier or a Biter, then she made members of the Immune system acting as the bone marrow. If the larva is any other caste; Worker, Courier, etc then she has made members of the Circulatory system acting as the spleen. If she produces a queen, then the new queen will slowly bud off forming a new anthill, acting as the reproductive system (see the Reproduction System). **The Farms, Digestion** Ants as a species have been [farming](https://en.wikipedia.org/wiki/Ant%E2%80%93fungus_mutualism) for over 50 million years. It is completely possible that a part of the digestive system would be a Farmer caste. Using aphid droppings or a kind of Fungus as food. This farming would have be the equivalent to fat storage in humans; the food produced would be used in case of lack of outside food. An interesting idea here is for ants to [cultivate bioluminescent fungi](https://en.wikipedia.org/wiki/List_of_bioluminescent_fungi) in order to [make themselves glow](http://www.smithsonianmag.com/science-nature/these-rainbow-colored-transparent-ants-are-what-they-eat-25521112/?no-ist). The stomach as a digestive organ would not exist. It would be more akin to fat, since each ants would digest on its own, the stomach would only store food until an ant gets hungry. **The Reproductive System** Anthills would be a hermaphrodite species, able to act as both Male and Female. The female half produces Queens when resources are plenty and they have a mate to keep it alive. The male half provides the Queen with a place to grow while it is weak. When the Queen produces a Queen (due to a high amount of resources available to the larva) The new Queen (or Princess) will fly into the Anthills mate where it will act similar to marsupial mammals. When inside the 'Father', it will be protected and provided with a breeding male to create a combination of genetic material. The new Queen starts to make its own ants, a specialized caste is needed ([The Soldier Caste](https://worldbuilding.stackexchange.com/questions/45279/how-do-members-of-a-collective-consciousness-separate-themselves-from-another), see below) to tell that the Princess is not an intruder and alert other ants of this difference. As the Princess' ants grow in amount, she will start to bud off and eventually become her own Queen of a new Anthill. **Soldiers, The Immune System** [![enter image description here](https://i.stack.imgur.com/nd7kv.png)](https://i.stack.imgur.com/nd7kv.png) As said above the Soldier Caste is the most important of all castes, they would be built to prevent disease from spreading by catching it and abandoning the pile, like a sick dog. Also the dumbest caste, they are weaker in all but 2 regards (in which they are ahead by a wide margin); Fighting and Smelling. 1. They are are extremely powerful, using the 2 best weapons an individual ant has: [Trap jaws](https://en.wikipedia.org/wiki/Odontomachus) and [Formic acid](https://en.wikipedia.org/wiki/Formic_acid). Trap Jaws, as seen above, work as razor sharp biological mousetraps delivering a very powerful bite. Formic acid is the simplest carboxylic acid, most commonly found in ant venom. 2. Their defensive skills are matched only by their sense of smell. They can smell the difference between friendly things, such as other random anthills and enemies, such as predators or anthills with intent to harm and then transmit a scent to the rest of the colony with instructions to treat them as a friend or foe. **The Nervous System** Information and coordination works via pheromones and shared stomach contents between Ants, with no central controller, this is the primary difference between an animal and a collective. A specific caste, [the Courier](https://worldbuilding.stackexchange.com/questions/45184/is-the-idea-of-a-collective-consciousness-realistic), specializing in sending messages directly to distant reaches rather than diffusing slowly through the population allows for the collective Anthill to think. These can relay messages from one organ to another, directly and quickly. Like an octopus, the Anthill has distributive intelligence, Couriers are found in every part of the pile. Couriers are not like nerve tissue, they are nerve tissue. The Couriers work by using pheromones, which in turn rely on the hardest sense to duplicate; smell. These pheromones work much like electrical energy in the human brain, though not as efficient, they replace intelligence for a better rounded creature. **Growth and Death** The only factor that limits an Anthills growth is the amount of resources available to it. Similar to a cell, where at a certain size the food will not be able to reach the nucleus, size is a factor for Anthills. If the anthill becomes to large it will need to not only always eat, but be on a food source. Unlike most Earthern animals, age and size have no similarity or connection in Anthills. After a new Anthill buds off, it will technically be fully grown, though the will still age. An Anthill will likely be considered 'fully grown' when it is able to reproduce (though cultural reasons may change this) When it comes to aging, wounds and disease, Anthills are practically immortal. The Queen simply replaces herself as the spleen when she nears death, Wounds are not a problem due to the Anthills lack of blood and disease only kills an individual ant. Of course these are generalizations and they do have exceptions. For example, the Anthill has a very high metabolism and thus is very susceptible to starvation, especially in a community. Aging also has its limits, as (unless you go with the self reproducing method) the Anthill needs a mate to prevent dying of old age within [30 years](https://biology.stackexchange.com/questions/2785/why-do-ants-live-so-long), also even assuming the Anthill can endless provide itself with a new queen memory would be fading quickly after 100+ years considering smell is its primary source of memory. Wounds are an Anthills strongest immunity, the only way to kill an Anthill with wounds is to 1; kill the queen or 2; kill all the ants. Saying an Anthill is immune to disease is a stretch, because if the disease is contagious and the first ant to catch it spreads it before leaving, then the Anthill is like any other animal with disease. **Feeding** Emerging from the Central pile are "limbs" (I use the term loosely, a better name would be Chains) consisting of primarily Soldiers with a few Couriers. these will protrude from the central pile for many different reasons. [![enter image description here](https://i.stack.imgur.com/vsGcv.jpg)](https://i.stack.imgur.com/vsGcv.jpg) 1. To meet a predator early on, same reason you put an army outside the castle. By fighting the enemy from a distance, you decrease the odds of damage to the central pile. 2. Hunting. If it takes less energy to drag the prey to the central pile than to move the pile (which, unless it weights equal to or more than the pile, it is) then it makes more sense to drag the prey. 3. On of the biggest advantages to a collective over monobodied animals is their ability to spread out and search as a group. For example, if the Pile is starving they can send multiple chains in random directions, follow the one that finds food and let the others die. [Answer] Does the Portuguese Man O' War (also known as Blue Bottle jellyfish) ring a bell? This organism may be simple, but it is a real-world example of an 'ant-hill' organism. It may not look it, but the Man O' War is actually four polyps joined and dependent of each-other, each with different roles: * the sail (the tell-tail 'blue bottle') propels and suspends the 'individual'on the waves * the tentacles, protection and capturing of food * digestion * and of course the last polyp is responsible for reproduction Though a more amorphous form could be possible, (ant pile as you stated) each component organism could be extremely specialized and the product of their cooperation could look quite synthetic or mechanical, like the Man O' War. Of course, given enough time and specialization these component organisms could reach a point where a border cannot or is difficult to be drawn between them, essentially creating a true individual. As for each role specifically, the cells of multi-cellular organisms would be a perfect example. reproduction, digestion and physical function (tentacles and sail) already exist, so other organ-organisms could very well exist. Heart components could be numerous along the body, with its main component being a strong muscle to pump nutrients. The 'blood' vessels could be individuals with structures much like xylem and phloem, passing on nutrients in a chain and dispersing a portion outward to surrounding organisms (perhaps in this case the heart organism isn't needed?). Specialized components with a non-soluble layer on one side could make up the ant-hill's skin. Digestive organisms could specialize in different substances, probably making the ant-hill immune to many toxins. Specialized tentacles could provide mobility on land (a fully formed leg seems unrealistic), although perhaps land dwelling organisms would be immobile, being subterranean or even a parasite, though this kind of organism would thrive in the ocean, where a form is easier to keep and there are easier modes of mobility. Optic and other senses could be specialized by one organism, and there is the potential for a simple neural system between smaller 'neuron organisms'. [Answer] Alternatively for a simpler consciousness, I'd like to take two key aspects of the largest organism on Earth, [Armillaria solidipes](https://en.wikipedia.org/wiki/Armillaria_solidipes), Which is a clonal colony of many mushroom parts that grow together and eat decaying trees. 1) Being clonal every part of the fungus performs the same role. This makes each bit is expendable. Having uniform bodies simplifies the collective consciousness, and prevents a single point of failure. 2) Parasites have easy rules of engagement. Connecting to hosts and sapping their energy to grow allows for a simple form of spreading. Since a collective consciousness has many moving parts, allowing them to follow basic rules simplifies the required communication between individuals. The key to this creature would be it must be simple enough and not specialized so that the need for sharing one mind is evident. If some individuals are too specialized, it may seem less plausible that they share the same thoughts. Visually I would expect these to look like a small spherical object with legs, similar to an [Opiliones](https://en.wikipedia.org/wiki/Opiliones). Communication would best be done through some sort of radio wave, so that signals could be passed between nodes without need for contact. Having some sort of electromagnetic antenna would make this possible. [Answer] How about the creatures are small parasites. They evolved the ability to interface with neurons in a simple way. They can detect pulses on a nerve and they can send pulses onto a nerve. They use an organ called a synaptic interface to do this. This same organ can send and receive pulses from the organs of another parasite. Now we have a creature that can form a neural net AND a creature that can plug into the nervous systems of other creatures. So, each parasite is non-conscious, non-sentient. It is acting only on instinctive programming. However, consciousness is emergent when a huge (trillions) number of these parasites interface with each other (following simple rules). Further, this emergent consciousness can trap and link into the nervous system of other standard animals, taking it over and using it for locomotion, etc. So the anthill animal could be a tumor-like blob, a blood infection, a film on the ground or water, or a pile of mold or algae, just about anything where sufficient numbers of small parasites can make physical contact and organize. Then, any larger creature that is unfortunate enough to stumble into the colony, or host the colony, would be subject to being interfaced to the colony. The result of such might be different and might change over time as the size of the colonies net increases and the depth of the infection/interface with the host/captured animal increases. In this case, your question about internal anatomy could be answered thus: the anthill creature is a colony of identical parasites that do show an internal organized structure, similar to a human brain in analogy, which is the result of the individuals responding to simple environmental stimulie. The host animal's internal workings are its own, with the exception that its nervous system has been compromised at one or more interface sites by the colony. I'm sorry this is not as clear as I hoped it would be. The important point in my story is that the individual "ants" are dumb as bricks. Only their ability and tendency to form large networks allows for intelligence and/or consciousness to emerge. And if they decide to all scatter, they can crawl away to the four points of the compass. Each individual will be unchanged, but the consciousness that had developed will poof out of existence, never to be recreated exactly the same again, even if the same individuals all crawl back together again. [Answer] Georgia Tech researched that ants will bunch up together <http://antlab.gatech.edu/antlab/The_Ant_Raft.html> So perhaps a collective consciousness would look a little like this [![enter image description here](https://i.stack.imgur.com/tuoaN.png)](https://i.stack.imgur.com/tuoaN.png) ]
[Question] [ Let's say Earth suffered some technological catastrophe and the planet is now entirely or almost entirely only water and at today's commercial technological level. Putting aside the reasons and consequences of the apocalypse, people now live exclusively on ships, specifically big tanker/oil ships, that which concerns me is if linking/joining/tying a lot of such ships together is a good idea? I have been told it won't be such a good idea due to storms, but I want to know are there any potential benefits to such an action, as this allows people to be closer together and dramatically decreases travel time between ships (keep in mind - post catastrophe, no land, etc.). Also is it better for ships to be long or short when faced with a heavy storm? [Answer] Your question's title: **"Is building giant ship-cities in a water world a good idea?"** demands an answer that's sort of orthogonal to the actual question you elaborate, and to the answers you've gotten so far. This rogue answer: **Creatively, it's a brilliant idea.** In terms of storytelling potential you have amazing scope if you can get this right. * In terms of **contextual humans-vs-nature stress,** this amps up the storytelling tension. The sea can *always* provide plot-driving difficulties and drama. I've been there personally: I was a working sailor (submarine, tugboat, and bluewater sailboat.) Scary things can happen in a big hurry. On the other hand, sometimes trouble can take a long time to build. When a big storm is coming, you have time to wait and worry and doublecheck and trice everything down... and then watch it start to happen. This is some of the best dramatic tension you can get. * When it comes to **human-vs-human conflict** (not just in the obvious sense of physical combat, but social, political, psychological, and familial competition and antagonism), your opportunities are huge. You have people doing the best they can in a tough situation. You have individuals of piratical mindset. You have possible conflict for scarce resources. After all, protagonist/antagonist conflict is the heart of just about any story. * As a **beautiful, harsh, and dramatic setting,** the image of rafted vessels out at sea, establishing a survival society when the land has become unavailable, is really a great one. The sea is both beautiful and terrible, and ships in the kind of situation you describe have a haunting power all their own. There. A powerful, beautiful creative concept. Just so we're clear. :-) Now, **to, you know, actually answer the question you're asking...** --- Previous answers have done a pretty good job of **considering practicalities.** I'll add my US$0.02 on some of these: * @PeterMaisar: > > "And of course with no dry docks and no repair facilities it will be only a matter of time until your ship will sink, one after another." > > > This is an extremely important consideration. Until you've seen it at work, it's hard to grasp just how incredibly corrosive salt water is to steel. Since we're talking steel ships here, **it's very hard to see how this concept of building your infrastructure out of tankers and aircraft carriers would be sustainable.** You *could* posit some kind of [floating dry dock](http://en.wikipedia.org/wiki/Dry_dock#Floating) that would be a part of your flotilla/raft/floating city, but that's got a couple of severe drawbacks. + First, it's a **terribly difficult engineering problem.** All of these big ships are built and refitted in huge-ass shoreside [graving docks](http://en.wikipedia.org/wiki/Dry_dock#Graving). **A floating dock big enough to accommodate these huge ship hulls is not very practical:** - It has to **be *even bigger* than the ships it services;** - It will probably have **major [seakeeping](http://en.wikipedia.org/wiki/Seakeeping) issues.** Large oceanic waves would create twisting stresses on the comparatively fragile hulls characteristic of floating drydocks. Making them big enough to accommodate huge ships will make them fail and break up in short order. + Second - and most fundamentally important - **floating drydocks only kick the can down the road, because they themselves are subject to rust.** This is perhaps some virtuous Worldbiolding.SE bait. Hopefully some of the good people here will want to come up with some good answers. **However, until this one is solved, the entire project is doable only in the short run.** Of course, if that's OK for your storytelling purposes, it becomes a feature not a bug. :-) MOAR DRAMA is good. * @CortAmmon: > > **Well rafted ships survive better** > > Rafting does two important things. One is that it decreases the distance any boat can travel before smashing into another boat. This is counterintuitive, but it works like leaning into a punch in boxing. It decreases the distance the other boat has to accelerate before it hits you. Your boat will be peppered with smaller hits, but hopefully avoid a fellow boat being smashed into you. > > > Yes, absolutely. A good description. However, it's not all fair skies and following seas. **Rafts are good for big waves, *up to a point:*** A raft of vessels has one huge advantage compared to single hulls when the waves start getting big: **A raft is flexible.** you can have a raft that covers *acres* and it will conform to the surfaces of even immense waves. That said, there's a limit: **If the steepness of the wave face exceeds the working tolerances of the vessel-to-vessel flexibility of the raft, there would be a catastrophic failure.** I'm not conversant enough with naval engineering to make any suggestions about how that limit is computed; but it seems likely that gales and hurricanes would exceed the integrity of big ships rafted together, no matter how cleverly it was done. And then, there's also the occasional [Rogue wave](http://en.wikipedia.org/wiki/Rogue_wave) to worry about... really, rafts *of large vessels* in the open ocean would not survive too well, over time. **Rafts are awful for big waves:** The other thing about rafts, which can be a huge disadvantage in a heavy seaway, is that **they cannot maneuver as a unit.** What this means is that the ability to turn your bow into the wind/waves is no longer there when you're rafted. Each vessel is going to have to take the waves however they come: + bow-on (good), + dead astern (not too bad), + off the bow or on the quarter (worst forces on the cabling joining adjacent ships), or + on the beam (very bad.)Another concern: an independent ship under way has the option, not just of maneuvering to put the bow into the wind, but of turning to **run before the storm**. If you've got a 90 knot wind, and your vessel can make 10 knots, then running downwind you are only dealing with an 80 knot wind. That might not sound like much, but it's actually a pretty big deal in terms of moderating the forces on your vessel. (Note that *this may not be good:* sometimes running downwind in a storm will change the way the waves stress your hull in a bad way. Still, any ship captain will tell you that it's a good thing to have the option...) --- All in all, I'm starting to have serious concerns about the feasibility of your idea. I think that the fundamental creative vision is (as mentioned above) pretty wonderful. However, **strictly interpreted, your particular scenario - lots of very large ships rafted together - seems unworkable.** There are some things you could do to fix it from the standpoint of practical shipbuilding and seamanship, **if** you're willing to relax some of your requirements. For example: ### Raft dedicated components rather than big ships It's not at all hard to devise **modular floating structures that would raft together nicely.** Because they wouldn't have the initial design constraints as independently operable ships, they could be incredibly superior for rafting purposes. * Really, these could be **little more than floats with strong frameworks.** Probably with decking or other minimal superstructure. * You could raft them together to create very rugged floating docks, even ones that sprawl out over a lot of area. **It would be possible to dock smaller vessels at such a raft;** and therefore possible to have the tankers and such keeping station (or remotely ingeniously moored), with small craft going to and fro. This would leave the big ships free to move away and operate independently in the event of a storm. This would preserve that particular conceptual element (of which I remain very fond.) * They could be built of a range of **materials that wouldn't be as vulnerable to rust** as steel hulls. * **They could, and should, be small.** They would accordingly not require the same massive drydocking capabilities as preexisting tankers/aircraft carriers/container ships. * This would make an excellent **at-sea rendezvous/port for inexpensive small sailing vessels.** ### Consider semi-submersible large vessels/structures [Semi-submersible](http://en.wikipedia.org/wiki/Semi-submersible) hull design is capable of amazing stability in high seas. This is achieved by having all significant buoyancy in the craft concentrated in underwater pontoons. The buoyancy provided by the pontoons remains the same when big waves pass overhead: submerged is submerged. The pontoons are joined to a free-standing superstructure that remains above the water's surface at all times. Superstructure and pontoons are joined by strong struts that * do not show much net buoyancy change as the waves pass among them; * do not provide much of a surface for waves to break against, minimizing wave impact and the dynamic stress of wave action against the vessel. I have personally seen this principle in action. Working on a [submarine](http://en.wikipedia.org/wiki/USS_Dolphin_%28AGSS-555%29) doing scientific experiments with [FLIP](http://en.wikipedia.org/wiki/RP_FLIP), I was lucky enough to see FLIP holding dead still in heavy seas. ("Lucky" in relative terms. *We*, diesel-electric and therefore operating on the surface most of the time, were rolling all over the damn place.) There's a bit of footage in [this video](https://www.youtube.com/watch?v=3hYafJIr1B4) starting at around 3:40. Yes, it really was like that: FLIP holding stock still in big swells. Made a believer out of me. :-) --- ## Yes, you can do this, sort of. You need to make at least the following changes to your premise: **Don't raft big ships together in open ocean.** Have them together as a flotilla, working together, acting as motherships for smaller working vessels. **Treat the oil-tanker floating city/colony as a temporary thing,** working towards something that can be sustained over time. That in itself could be a dramatic decades-long process. A set of modular rafting floats, with some semi-submersible vessels at the center, could, over the long term, be the kind of floating city that you are asking about. I hope? [Answer] Better starter floating city than tanker would be nuclear-powered aircraft carrier. It already has living quarters for some 5-6K people and own electricity. You are right, storms would break any chains/links between such linked boats. In storm you want to face towards waves, and any jerk from other boat to side could be deadly. Longer ships with higher deck (farther from the water) like aircraft carrier should be able able to deal with storm better than ships like tanker with less above-water supersturucture. You point nose of the ship toward waves to split them, you don't want to get wave from one side. And you can also build fields to grow some potatoes on that huge deck. After thinking some more: with no land, hurricanes would be devastating, and waves they whip would circle the globe multiple times with no shores to stop them. So [rogue waves](http://en.wikipedia.org/wiki/Rogue_wave) would be more common, and much more devastating. Just fair warning. And of course with no dry docks and no repair facilities it will be only a matter of time until your ship will sink, one after another. You can build dry land using artificial reefs - [biorock](http://en.wikipedia.org/wiki/Biorock) - artificial coral reef in shallow seas like [Saya de Malha Bank](http://en.wikipedia.org/wiki/Saya_de_Malha_Bank): "bank covers an area of 40,808 km2 with depths from 17 to 29 m" [Answer] Two questions to answer: **Large ships fare better in heavy weather** The thing which sinks a ship is not the height of the waves, but how the waves act on the ship. The larger you are, the more you can ignore small waves, and the more you are in a position to be able to right yourself afterwards. Life on a carrier is surprisingly smooth because there's just so much mass damping out the waves, and so much length averaging out the small waves. Captains are taught to turn the bow into a wave if reasonable, because it makes their boat effectively longer, and thus more stable versus that wave. **Well rafted ships survive better** Rafting does two important things. One is that it decreases the distance any boat can travel before smashing into another boat. This is counterintuitive, but it works like leaning into a punch in boxing. It decreases the distance the other boat has to accelerate before it hits you. Your boat will be peppered with smaller hits, but hopefully avoid a fellow boat being smashed into you. I don't have any google research to defend this, but I think a raft could also act much like a larger hull, providing extra stability. A wave which might be sufficient to capsize a single vessel might be held upright by its fellow boats. However, I am less certain of whether this affects the edges. **The major advantage of rafting is sticking together** A powerful storm at sea is well beyond anything we land lubbers can comprehend. When a storm like that comes your way, you *will* yield to it. Storms like this can tear fleets asunder and scatter them across hundreds of square miles, if not thousands. Reconvening could be a monumental effort. This was a much larger issue before GPS and radio, but it's still an issue for a city that needs to be interdependent to survive. [Answer] There's a big unknown in the specification "entirely or almost entirely only water" of the planet and that is: the depth of this water. I'd argue that with a low depth (say a few hundred meters or so) it is both feasible and useful to build sturdy constructions founded firmly on the ground and with a height well above any major waves to be encountered (the issue of large waves and never slowing winds are covered in the other answers). Those structures could be the size of reasonable large cities. An example of this type of structures made with todays technology are fixed platform oil rigs. As a sidenote: a variety of oil platform types, e.g. offshore platforms, semi-submersible platform and large gravity-based structure could give valuable insights with respect to the question ([see Wikipedia](http://en.wikipedia.org/wiki/Oil_platform)). If the depth of the water prohibits such structures it's also conceivable to build submerged structures that at least do not have to face the issues of monster-waves and hurricanes. This of course comes at a high additional engineering cost. However since mining of raw materials will most likely have to be done at sea floor this field might develop faster than now. Also maintaining "today's commercial technological level" if living only aboard some ships will be quite a challenge, e.g. putting a semiconductor fab and its whole supply chain on ships... ]
[Question] [ I am currently brainstorming the history and logistics of the dragon species in my urban fantasy story about immortal mythical creatures. The way I currently envision them, dragons have their stereotypical signature hoards of treasure because they essentially use gold like solar panels: the celestial energies of the earth can either be dangerous to a magical creature or be harnessed for magical sustenance depending on their wavelength, which changes depending on what solid or liquid substance it most recently and predominantly passed through. In dragons' cases, they can absorb the planet's energy most effectively when it's recently passed through a large amount of gold. Furthermore, in my setting, all mythical creatures were once humans who were subject to an extremely rare, spontaneous magical transformation that magically activated them and turned them into their own species, which could then reproduce with humans and override mundane human DNA (incidentally, yes, dragons are capable of shapeshifting back into a human form for this and other purposes). So it stands to reason that the ex-human who became the progenitor of the dragon species already had a hoard of gold while they were human, otherwise they wouldn't last long enough to breed when they became a dragon. So now I'm wondering what that implies about how old the dragon species could be. **Given what we know about the history of the development of human technology and culture, what is the absolute earliest that a human being could have amassed a pile of golden treasure, big enough for a human to lie down in, that could have become the first dragon hoard?** [Answer] **A Very Long Time Ago** Our gold hoarding incipient dragon (let's call him Thag. Ask Gary Larson how Thag's ancestor of the same name famously died.) doesn't need a mine. Thag barely needs agriculture. He might even be a pure hunter gatherer in the right environment. The environment Thag requires: * Good shelter (caves or simple huts) * Abundant game (perhaps along the migratory route of multiple species that migrate at different times) * Abundant food plants (naturally growing and perhaps early agriculture) * Good enough climate (so the humans there don't need a migratory lifestyle) * A river * Hills up river (As Yosemite Sam said, ”there's gold in them thar hills”) Having a fixed place to stay allows critical changes from a wandering society. The biggest is the accumulation of items beyong what can be carried. As this happens, the concept of **mine** over **ours** has a chance to begin expanding from a tiny handful of personal items all the way to dragons with vaste hoards (and their modern equivalents, the multi billionaires). So, for a cave (or mud hut) man, Thag and his tribe are living far better than most other humans of this time. But wait, I said the gold was in the hills. Poor Thag's career as the first greedy gold hugger is over before it began. Thag is smart, but he's never even seen gold yet and doesn't own any mining tool even as good as a modern garden spade. Poor Thag will die never knowing what he missed, except for a few little details. Much of the massive amount of gold deposited in the hills is metallic gold (dust, flakes, nuggets). No chemical processing needed. On a geologic time scale, rivers are incredibly powerful mining machines. One day Thag was spearing fish in the river when something caught his eye. He knelt down, sifting through the pebbles on the bottom and pulled up a pea-sized piece of gold. Had Thag been a common human (or protohuman) from our world, he might have kept it just to show others the odd shiny rock. Thag wasn't from our world. Thag didn't want to show his rock to anyone. The feeling of touching the gold gave him a desire he had no words for. Thag took a long walk away from where he and the others lived, stopping and marvelling at the tiny lump of gold every so often. After much thought, Thag realized two things. He needed to live just a little apart from the others (privacy was not yet a concept in his group), and he had to got more of these amazing rocks. Thag became a model worker in his group. He got up early to hunt, fish, and harvest. He helped out with all other tasks at a speed that amazed others. Beyond this and living a little apart from the others, his only other noticeable quirk was always disappeared upriver for at least an hour each day. Late each night Thag would pull aside an animal skin and fall back on his growing pile of gold. Finally, 5 years after Thag was surprised by that first tiny piece of gold, his gold hoard gave him an even bigger surprise. Thag isn't sure how long ago this happened. He thinks maybe 15 to 20 thousand years ago. Currently, he goes by the name Thaddeus Morgan IV. Thaddeus owns Golden Rivers Mining, the largest gold mining and processing conglomerate in the world. [Answer] Below the hills of Bulgaria, down in ancient tombs, we have found the earliest gold artifacts, dating back to between 4700 and 4200 BC. Slumbering deeper under the ground, the Sakdrisi site is found. The oldest gold mining site in the world, from approximately 3rd and 4th millennium BC. So around 7000 years ago would be the earliest plausible date from our knowledge if this world is strictly based on earth, or bronze age civilization. If your dragon is not, in fact Bulgarian, anywhere after the 3rd century is where gold becomes more and more common. [Answer] ## Anytime you want Other answers have mentioned that humans in our world started mining and collecting gold ~7000 years ago. However, since in your world, there is a rare mutation that forks magical species from humans, technological history could play out differently. What if there was a race of King Midases in 200,000BC? Or super-miner dwarves in 1,000,000BC? Also, what about some sort of "Golden Goose" species that eats rocks and deposits metal droppings? [Answer] **Does it have to be pure?** If not, just go lay at the pile of gold ore in the ruins of the mountain that was split apart by yesterday's earthquake. All necessary elements precede humanity and even mammals. You can set this as early as you'd like. Mystical reverence for the Earthquake and/or for the the Ruins optional. ]
[Question] [ # Background The Apocalypse came on Tuesday, and no one was ready. For us soft city folk, survival was mostly a matter of luck. If you fell in with the right group of people with the right skills and the right equipment, you had a chance to make it. It certainly didn't help that the Tuesday in question was right before winter. After four bleak months of violence and starvation, spring found us with 30 other families in a well protected valley in the Virginia Piedmont. By fall, things were looking up. The reason we fought so hard for the valley is that it is filled with apple orchards. Potatoes and pumpkins are also surprisingly easy to farm. Best of all, some pigs must have escaped from a nearby farm because they multiplied like no one's business in the hills to the south. By fall they were all trying to find their way into the orchard for windfall fruit and we were practically tripping on bacon every time you went for a walk outside. Since things are doing better, it is time to think about the future. We have a decent collection of vehicles in the valley, and the scavengers from the old populations centers near the coast are happy to trade a near endless supply of parts (and tires!) for bacon and cider. There were four gas stations in the valley before that Tuesday, so we have nearly 100,000 gallons of gas on hand. That can go a long way at 25 miles per gallon; and we've found a lot of other abandoned gas stations in the mountains with gas still in the ground that we can raid for future use. # Question The truck we use the most for scouting and long distance trade is a [2007 Toyota Tacoma](https://en.wikipedia.org/wiki/Toyota_Tacoma#Second_generation_(August_2004%E2%80%93August_2015)) with a stick shift and an [inline four](https://en.wikipedia.org/wiki/Toyota_TR_engine#2TR-FE). We have a pretty big stockpile of parts already and a maintenance manual. We figure we have at least 10 years of gas on hand, more potentially hidden away, and we can [cut that with alcohol](https://mythresults.com/moonshiner-myths) to make it last a lot longer. What we are really worried about is consumable fluids. The truck will need them, and if they get used up in a decade or so, the scavengers might not be able to trade us more. Which fluids are going to give out first? Which ones can we run without? Which ones will we be able to make a substitute for? * Motor Oil: 0W-20 or 5W-20 is recommended * Brake fluid * Power steering fluid * Manual transmission/transfer case/differential lube: 75W-90 to 90W-90 * Coolant/Anti-freeze * Windshield wiper fluid (maybe we can make do without this one) Assume 20,000 miles per year of driving in rough conditions; mostly on (obviously un-maintained) roads but some of it off-roading. Temperature conditions are summers in the 90s (F) and humid, and winters down to 20 F and occasionally lower. --- Unlike the questions [here](https://worldbuilding.stackexchange.com/questions/895/automobiles-after-the-apocalypse) and [here](https://worldbuilding.stackexchange.com/questions/81560/for-how-long-after-an-apocalypse-would-modern-cars-remain-usable), this question deals specifically with fluids and lubricants, which is not addressed in either of those question or their answers. [Answer] When you look at this list of fluids, they basically break down to one of two categories; 1. Oil Based Lubricant 2. Ethelene-Glycol or similar The oil based lubricant may be [easier than you think](https://www.grainews.ca/2010/05/03/turn-animal-fat-into-engine-oil/) because you have all the pigs around. That means that your engine oil, grease, and even manual transmission fluid are probably okay if you know what you're doing and don't mind the fact that you'll be reducing the life of your car somewhat (but, hey? What else is it going to do?). As for the power steering, engine coolant, wiper fluids, and brake fluid, they're all some form of ethelene (or propylene) glycol - either for hydraulics or temperature regulation. These are REALLY toxic chemicals as it turns out and a quick search tells me that I don't want a more detailed search on how to make these chemicals in my ISP's metadata against my name. BUT, if you have a chemist within your family group, it's *possible*, though unlikely, that your combination of pig fat engine oil and fruit crops may be able to supply a small amount of these fluids for your needs. I'll admit that chemistry is not really my thing and perhaps there's others on the site that have a more detailed answer to this but this is at least where I'd start. I don't know for sure, but I think that if you have enough pigs and forego the streaky bacon for short cut only, you can at least generate SOME motor oil and the hydraulic / temperature fluids (in my experience at least) usually last for a while in any event; at least long enough to figure out whether or not you can synthesise the fluids you need from what you have. [Answer] **You don't tell us the nature of the apocalypse, so let's assume the majority of buildings and infrasctructure are in place** Oil lasts almost forever. Conventional oil does separate with time, but give it a good shake and you're back in business. It also coagulates with enough time... but that's a very long time. The number of Walmarts, hardware stores, automotive stores, etc. that exist are so many that you may have several lifetime's worth of supply. Honestly, you'll have oil long after you have gasoline, which decays with time. Ditto for brake and power steering fluid. Radiators really only need water unless you're traveling in very cold climates. Obviously, radiator fluid helps in really hot climates, but you can just carry more water. But, in the cold, water freezes, which can lock up your engine 'till spring. As I recall, some trucking companies in the far north will run their motors for weeks or months because restarting them is a grade-A pain in the tuckus. And this all assumes that you don't make use of refineries, [which exist in a number of locations throughout the U.S.](https://www.google.com/maps/search/oil+refineries/@46.2166613,-104.0091705,4z) *In many U.S. locations, survivors might have more trouble finding water than they would oil simply because you need so much more of it. An individual may need a gallon of drinking water a day and more for cleanliness... but a car in good condition may only need two quarts of oil a year.* **The real problem is whether or not your survivors across the land figured out that they can burn motor oil like heating fuel. If they did, you might find yourself stuck in warmer climates.** How fast oil survives the need for heat depends on the number of survivors, where they are, and whether or not there's anything more convenient around... like firewood or those big, honking propane tanks at regional distribution centers. But, people tend to think along the lines of simplest-solution-to-success, so they may disassemble their vacant neighbor's house before they lug propane tanks from miles away. And yet, if you think about it, if enough of the population died fast enough, there would be an enormous amount of a variety of fuels for a very long time. A "Mad Max" style of apocalypse requires destruction of buildings and infrastructure, which you didn't describe in your question. If you update your question, my answer may need to change. ***EDIT: Anticipated Answer: All of the fluids your vehicle needs save gasoline are available in such enormous quantities all over the U.S. that they will NEVER be your limiting factor unless your story has provided a reason for their consumption at a faster rate (e.g., used as heating oil). Under the conditions you've stated, they will last long beyond your vehicle's access to gasoline.*** If you want a mathematical analysis, you will need to provide the consumption rates for all these fluids. Of course, unless your Tacoma is a beater, the consuption rates for all these fluids will be ***so low*** that you can stockpile everything you need for a lifetime in a day — unless there's something else demanding the resource, which you have not specified. [Answer] You can run an engine with animal or plant oil instead of car oil, no problem. You can kind of get away even without power steering, wiper fluids (do you really need that post apocalypse?), and brake fluid if you use really old cars or retrofit existing cars with parts from old cars. Most post apocalypse cars would have non assisted steering wheels and brake, they d probably just use water as engine coolant and overheat easily. But you can't run a car without gasoline. Gasoline is highly volatile, it evaporates at room temperature. Gasoline stored in the tanks of fuel stations will go bad in a few month, possibly faster without proper monitoring and maintenance. You can add fuel stabilizer to extend gasoline lifetime to about 12-15 months. Within a few years all of the pre apocalypse gasoline will be unusable. <http://edition.cnn.com/2008/LIVING/wayoflife/04/09/aa.bad.gas/> You could try to run very old simple diesel engine with alcohol though. So really the limiting factor would be the metallic parts themselves. Eventually all pre Apocalypse parts will be so old that they ll be unusable. You d need a pretty bad ass smith to be able to manufacture replacement parts let alone an engine. [Answer] The reason this wasn't mentioned in the previous post apocalypse vehicle questions is that lubricating grease and oils are a very old concept and relatively easy to reproduce in perpetuity. Between animal fats, like lard or whale oil, and vegetable fats, peanut oil, olive oil or otherwise, you should be able to come up with a selection of weights of oil and grease that will comfortably do the jobs you need. While it may not be the 10W-40 that you're after, it'll be close enough and good enough to do the job and keep you on the road for a good few more years. Whales have a selection of different weights of oil, depending on what you manage to catch. If you're not in a coastal position where you can go whaling, pig fat will do nicely for a heavy grease, and peanut or olive oil can be used for lighter oils. The reason I always recommend finding an old diesel vehicle at this point is that [any oil of approximately the right weight can also be burned as a diesel fuel substitute](http://ready4itall.org/step-by-step-guide-to-making-fuel-from-animal-fat/) and the cruder old vehicles are much less sensitive to fuel quality. They often had fuel pre-heaters which allows a greater margin for error on fuel. [Answer] What you might want is a wood gassifier (a pretty simple device that converts dry biomass into vapours and gasses suitable for use in a car, they were used in WW2 during oil shortages and are still perfectly build-able today.) Your car might have a lower top-speed but that's not going be a horrendous problem. This way you don't need motor oil, just literally any plant matter (the enormous amount of paper in our landfill will work aswell). If there isn't ANY plant matter you have bigger problems than getting your car running. Such devices could eliminate your use of fuel or simply supplement it. The same devices can also be used when not powering your cars to produce many useful chemicals such as turpentine, tar, ethylene, sulphuric acid, cooking gas and even bio-fuel for the rest of your cars <https://en.wikipedia.org/wiki/Pyrolysis> which would all be immensely useful (especially if you have a chemist or chemical engineer with you (even a hobbyist with access to scavenged books on the subject.)). Other answers have all already done a good job explaining how to provide other lubricants, hydraulic fluids and anti-freezes however I will say this in case your assorted animal-oils fail or you simply don't want to bother with processing lard (remeber every person working in the oil factory is one who isn't on the pumkin farms.): if hydraulic fluid proves problematic your cars in-built braking system is not a requirement, it could be gutted and a simpler fluid-less brake could be set up in it's place it won't be as responsive as a proper brake and perhaps a bit more awkward to use but since you won't be driving though traffic that shouldn't be a problem. (this could range from a device as simple as "Oi doug, drop the plank of wood with all the weights on tied to the back of the car" To a system almost passable as a modern brake. Running your cars significantly below their maximum performance will increase their life-span and fuel efficiency. You won't be making any trans-continental trips (probably) so driving everywhere at 35 or 40 mph will significantly reduce the number of problems that will arise from engine heat, wear-and-tear, Etc... (given the quality of roads a several years without maintenance you'll probably want to go slowly anyway.) You can simply drive without power-steering fluid which, since you won't have much traffic to worry about, won't be too dangerous. Especially if you take my advice and go slowly. There is no need for anti-freeze if your simply keep your car warm. Yes anti-freeze is easy to produce, but so is fire and simply keeping your car in garage or shed next to a small fire (the fire is inside the garage, which has a hole in the roof) could constantly keep it above freezing and would only need to done in winter times. This "hot room" could be expanded to include space for humans (provided they don't mind sleeping next to, or in, cars). There is of course no danger of the car freezing-up when in normal operation. You can definitely do without windshield wiper-fluid, soapy water and bucket should be more than enough. Indeed if you are willing to accept significant performance losses (which you should be, given it's the end of the world and all) you can easily run your cars indefinitely (at least till you all die of dysentery or have so many disendants they have no problem building whole cars of their own). [Answer] Your truck, is screwed, but don't worry you can do better. So as other have pointed out, in the US at least, your not going to have a hard time finding oil. You don't need Power steering and any liquid will work for power breaks, same for the transmission. Some are WAY better then others, but, for example water will work (it will also ware the parts out much faster), but even a simple gas station will have enough oils to keep you going. Antifreeze is a joke if your not in a winter climate. In the summer or hot, dry areas use water and just carry an extra gallon or two. Hell you can even piss in the radiator (after it cools). Again shortens the life, but who cares. Wiper fluid is just water. Now your main problem is going to be parts and fuel. You say you raided an auto zone or two so your good on parts, so we will ignore that one. Fuel is going to, be an issue. If you keep gas moving it will last around 5 years. If you let it sit still you get maybe 5 months. You can add some things to it to help, but at the 1 year point fuel is going to be pointless unless your really maintaining it. In addition to which your truck is going to rust through, fall apart and other issues no too long after that. What are you doing to do when it's computer fails? Your best bet is to use that truck to head to a junk yard or used car lot and get a < 1970s truck or car. One with a corroborator, rack and pinion steering and no anti-lock breaks. They will be very easy to maintain. In addition they use such "standard" parts that you can make things from almost anything work. There's almost no electrics so batteries aren't even needed. Get a manual and you can push start it. ]
[Question] [ Fantasy settings frequently include giants or dragons or similar creatures with human-like or superior intelligence who are also much larger than humans, and weigh many tons. If our giants or dragons live in or near human-majority settlements, they need vastly more living space to achieve the same quality of life, and all land is claimed by one nation or other, so gaining living space is a matter of buying it, renting it or taking it by force. The other obstacle to their participation in human society is the high cost of consumables. Let's say that in fantasy biology land, their energy use is proportional to the square of their height. A 5m giant needs approximately 12,500 food calories per day at a minimum, and one doing physical labour could easily consume 25,000 calories per day. A 10m dragon doing physical labour could consume 100,000 calories per day. This is extended to most things they need to buy, which are huge, and so require more labour and materials to produce. * Because Magic, for the purpose of this question, they don't fall foul of the square-cube law. Their bones and muscles are proportionally stronger and more efficient than those of humans. * Despite their large size and high energy consumption, they have no particular issues with thermoregulation, although they generally prefer colder climes. * They have no inherent magical abilities other than this. * Unlike in many works, they have no more propensity towards good or evil than humans. * Their lifespans and birth rates are proportionally adjusted with their height. 5m giants live two and a half times longer than humans, but give birth two and a half times less often. * Their populations are low. Humans outnumber them fifty to one. * They are no more or less intelligent than humans, but their long lifespans mean they are able eventually gain more skills and knowledge. * Their prehistoric population densities were low, due to the large amount of land required to support their hunter-gatherer lifestyle. By the time humans and giants realised that they were both intelligent, their populations were roughly colocated. Because of this, human civilisation grew around their small isolated tribes, and the notion of land ownership was impressed upon them as they were unable to practically control enough territory to form independent nations without human collaboration. In a preindustrial society, what roles could these creatures take to cover their humungous living expenses? How badly would they be hit by industrialisation? This [question](https://worldbuilding.stackexchange.com/questions/30228/how-does-one-design-a-city-meant-for-creatures-of-greatly-varying-sizes) considers architecture, but not economy, so is only partially relevant here. [Answer] ## Craftsmen Craftsgiants Any merchant, baker, or book-keeper isn't going to find that being significantly taller than the average human benefits them in any way. Being a 5m tall farmer isn't going to be much better than being a 1.5m tall farmer after the invention of the ox driven plough, either. However, there are a few medieval professions where such stature and strength would be very useful and demand high compensation: trade skills like masonry and carpentry. Building large buildings can be an enormously skill intensive and potentially dangerous undertaking. For example, [here is a video of a barn being raised by a group or Amish men](https://www.youtube.com/watch?v=AsTB0HnM6WM). Notice how, especially in the early stages, many men have to push the exterior walls up in sections, and hold it in place with ropes until one or two men are able to climb up and fasten it to other pieces of the structure. Just having one or two giants to help with the initial framing work could save a carpenter's guild many man hours and potential accidents. Masonry work could also benefit from such a strong and tall member of the workforce. Giants (assuming 5m height as described in the OP) essentially function as autonomous [cranes](https://en.wikipedia.org/wiki/Crane_(machine)). Such work wouldn't make Giants noblemen, but being sought-after craftsmen they would be members of the middle class, rather than serfs. Whether it is economically feasible only depends on whether their usefulness outweighs the cost of employing them. If a giant is about 3x as tall as the average human, then a comparable living space would be about 3x as wide and 3x as long (and 3x as high); then, since only width-by-length matters when buying plots of land, a 9x sized plot of land would be needed for a giant's home. Furthermore, if a working giant has a 25,000 calorie diet compared to a working human's 2,500 then the grocer's bill would be approximately 10x as costly as the average human's. From these numbers, a giant needs to *do the work of 10 men* to pay the bills. This number doesn't appear to be difficult to achieve in my opinion (particularly not if their ability to increase the efficiency of the work group can be properly understood/quantified). Consumer goods like beds and furniture would probably fall into similar 9x-10x cost multipliers if you apply the same approximations, or at worst 27x if you now measure WxLxH, which again isn't horrible if you're getting paid at 10x the going rate; even if beds and furniture cost 27x that may not be so horrible to a giant with an extended lifespan to pay off a larger mortgage. --- ## Dragons Dragons, on the other hand, may be harder to place depending on their physical abilities. If they are as manually adept as we tool-using opposable-thumb-weilding humans, then they could also find work in construction. However, the efficiency boost of a dragon or two complimenting an all-human workforce might not scale as well as it does for a few giants, and thus it could be difficult to compensate their 40x caloric needs in all but the largest of big-city construction crews. However, if dragons can breath fire or have other similar magical abilities, then they might find specialized work that is particularly suited to their natural talents. A large scale blacksmith's shop might find that paying one dragon to stoke their fires could be significantly less expensive than buying all of the wood and charcoal they need each day (and so too for potters and glass-makers). If a dragon doesn't want such a monotonous job blowing fire into hearths all day, they could do quite well (independently) making and selling charcoal to humans, which burns cleaner and hotter than wood (both for the blacksmiths and for home stoves). [Answer] ## Independence (...?) You are completely correct that larger creatures will need more space, food, etc. to survive. It is likely that as a result, they may simply settle in different locations than humans or other species, with a lower population density, to manage their own natural resources. In other words, they own a couple kingdoms too, in which they account for these problems accordingly. --- ## Manual labor These creatures may (will?) be stronger than the average person. While they may require more food, they can do many construction tasks with much more efficiency than humans, whether it's building roads, diverting rivers, or digging military fortifications. ## Military potential If mythical creatures are stronger, they may be very practical weapons! Imagine the money any king would pay to have giants and dragons at his disposal on the battlefield or during a siege. ## Culture-based artistry Just like how some Americans get Chinese character tattoos, or like to order from Italian restaurants, there may be a demand for cultural variation. Dragons, giants, and the likes may be able to sell their own culture related wares to offer a different experience than that which humans normally receive - assuming the demand is sufficiently high and people aren't racist. ## Trade Similarly to the above, larger creatures may just briefly foray into human territory to trade goods. Perhaps giant country has giant trees, while the dragons' mountains have diamonds and sapphires, ready to sell. This could provide them the money to settle permanently in their trading outposts. [Answer] My first thought is that such a race would actually become "nobles" of a sort, superior to human beings by virtue of their strength, intelligence (by proxy), and longevity. The high demands of their lifestyles could be supported by providing "protection" to cities in exchange for tributes which could come in the form of money, goods, or even other services. Look to Terry Pratchett's "Guards! Guards!" for an example of how a dragon came to become king, albeit very briefly. Given that their roles in this society are mostly aristocratic, I doubt that industrialization would hurt them much in the short term - in fact it might improve their lives for a while as their human subjects become more productive and therefore able to provide them with better goods and services. However, as technology continues to improve, the humans may start to wonder if they really need to remain subservient to a "noble race" and instead begin to rebel against the ruling class (this is on the assumption that the giants get complacent with their positions and become rather unkind rulers). [Answer] I'd say it depends a good bit on the specific creature in question, since the nature of their needs and their capabilities would guide how they interacted with the society around them. So, 25,000 calories is a lot, sure, but manageable. Similarly, 100,000 is quite a bit, but it's not insurmountable. As an analog, horses performing moderate work use [about 25,000 calories a day](http://www.dayvillesupply.com/hay-and-horse-feed/calorie-needs.html). So each working giant literally eats as much as a horse, and each dragon eats enough for three or four. That's certainly feasible, provided that the creatures are able to get the bulk of their calories from grains, root vegetables and other bulk carbohydrates (much like humans). On the other hand, if, say, the dragons are obligate carnivores (like ten-meter long cats) then that gets expensive very quickly -- 100,000 food calories is in the ballpark of 70kg of meat per day. If dragons are going through a goat or sheep per day of hard labor, or a cow every three-four days or so, that would quickly become a strain on the surrounding area, unless said dragons were actually idle most of the time. As far as what Giants might do to earn their keep, what springs to mind at first would be heavy manual labor or construction, where, much like the horses they eat like, their productivity would make them more than worth the upkeep. Dragons or similar flying creatures could act as couriers or traders, carrying news and wares from location to location faster, further, and more securely (because who wants to pick a fight with a dragon?) than ground-based methods. They might also find work in more skilled fields. For example, a giant might find work as a blacksmith or other metalworker, where their strength would be an asset. Or an educated dragon or giant might find work as a clerk or tax collector. If a local lord has a dragon managing his books, few are going to try and cheat on their taxes! Similarly, they might find themselves in other knowledge-based positions like apothecaries, seneschals, or scribes. Since the populace at large is likely to be illiterate, long-lived giants with good memories could serve as historians or skalds, maintaining an oral history through stories and epics. Similarly, since they are more likely to become educated given their longer lives, they might become employed as educators in turn. All that said, I can also see different non-human sub-economies forming, though possibly only unofficially. If giants primarily employ other giants, and are only purchasing goods from giant producers, and that commerce is all kept within the giant community, then the impact of the scale difference between them and the humans is minimized. This does assume that on some level the giants have the means to support themselves indepenedently (e.g. giant farmers with giant-sized farms and herds, etc.). So I'd expect you'd see giant enclaves or dragon enclaves or whatever within the human society, rather than a random lone dragon on its own. When they have to start "importing" goods or services from humans, then they might lose out, and this would need to be balanced by "exporting" their own goods or labor back to the humans, much like a nation trades with its neighbors and has to deal with exchange rates and so on. Zxyrra mentioned military potential, and mercenary work could certainly be a lucrative profession for giants or dragons. Siege engines are expensive and complicated to build, so having giants hurling boulders or swinging battering rams would be useful. And dragons would be a complete game-changer, effectively providing an air force long before they were possible in the real world. So the services of both groups would be in high demand, and I can even picture, say, notable individuals or the heads of clans or communities receiving overtures or bids from both sides of a conflict for their services. Practically (and a bit cynically), I think that sort of strength alone will also help keep giants and dragons supported. Not necessarily as "nobility" per se, but local rulers may find that it's easier and cheaper to just make sure the dragons, giants, or what-have-you have a steady food supply, lest they be forced to turn to more *disruptive* means of support. Because while the humans *could* rally their army to slay the foul beast, it's probably easiest to just make sure things never get to that point in the first place. [Answer] They might form a mutually beneficial relationship. The Giants must gather a large portions of food. Humans must protect themselves from other humans as well as other Giants who might see them as food since they are equally as intelligent as humans and they have the ability to communicate they could easily begin striking some sort of deal. A giant or maybe a couple Giants would protect humans from other Giants and their own kind, in exchange the human this would give them a portion of the food and other resources as they gathered, not unlike a feudal Lord. As more and more people seek out a Giant or Giants for protection cities and Empires begin to grow around them. Soon conflicts among humans inevitably lead to a conflict among giants and vice versa. Overtime instead the Giants might become Godlike figures the gifts of resources might become a religious sacrifices, a whole priesthood could develop around the Giants. The priest job would be to and guard the Giant from Assassin's coming from rival Empires as well as doctors to treat the Giant in case of injury or illness. Of course any type of mutually beneficial relationship would require that giant populations stay relatively low when compared to the human population unwanted Giants could be exiled to keep the system in balance. ]
[Question] [ I'm thinking about using this as a sort of meta explanation for how Orcs (and possibly other things as well) are different than humans (in muscularity), but I'm not entirely sure what the result of this would be. What would be the expected appearance of a humanoid race with a suppressed myostatin gene? (Includes Men, Women, and Children) * (Bonus points for -accurate- picture examples, but explanations and approximations are perfectly valid as well.) The [Belgian Blue Cow](https://en.wikipedia.org/wiki/Belgian_Blue) is a notable example of such a mutation, and a helpful starting point for determining answers. Thanks! [Answer] A deficiency in myostatin can and does occur [in humans](https://en.wikipedia.org/wiki/Myostatin#In_humans). Take, for example, [a German boy](http://www.nbcnews.com/id/5278028/ns/health-genetics/t/genetic-mutationturns-tot-superboy/#.WQc2_WeHekk) who could lift 7-lb. weights with arms extended when he was 5 years old. You can find an image of him when he was a few months old in the article. Since his identity was not revealed, current images are likely hard to find. (Also, I don't want to be put on another watch list for trying to find them...) Researchers have expressed health concerns in the boy's future due to his increased muscle mass. (Warning: paywall ahead) [Research](http://rd.springer.com/article/10.1007/s11914-013-0160-5) shows that a reduction in myostatin may also cause an increase in bone formation. Additionally, animal breeds with a myostatin deficiency have [reproduction, dietary, and care issues](https://en.wikipedia.org/wiki/Myostatin#Double_muscled_cattle) relating to their increased muscle mass. Humanoids with a myostatin deficiency would be bulkier through increased muscle and bone mass, but I would also anticipate them being fewer in number, due to all the special concerns that apply. It's important to note that most breeds with a myostatin deficiency mutation have been engineered or selectively bred specifically for that trait, such as the Belgian Blue. This may be because nature cannot normally support such a creature due to the health concerns, especially as they apply towards reproduction. [Answer] From <http://journals.plos.org/plosgenetics/articleid=10.1371/journal.pgen.0030079> [![enter image description here](https://i.stack.imgur.com/TQqEP.jpg)](https://i.stack.imgur.com/TQqEP.jpg) This one is nice because you can see the difference between the +/+ wild type, the mh/+ heterozygote and the double mutant. But my favorite picture of the myostatin mutant whippets is this one. [![enter image description here](https://i.stack.imgur.com/J64iJ.jpg)](https://i.stack.imgur.com/J64iJ.jpg) because they both look like good dogs. [Answer] I am the first female to score a rushing touchdown in a male high-school varsity football game. I was 4'11" 130 lbs and even a starter my junior year as a fullback and outside linebacker. I thought the girls from softball were being too girly when they couldn't bench their weight or leg press around 300lb like me. I didn't realize it was me that was extremely different and they were not just being girly. This became an issue because myostatin affects muscles and the heart is a muscle. My heart disease is hypertrophic cardiomyopathy. I would max PT tests in Jrotc and lacked flexibility in the sit reach test. I lacked flexibility. My calves are still huge and I have active duty spinal cord injury and I haven't worked out in 10+ years. The problem with lacking the ability to get around the calf muscles just tighten. So they are making my toes point. I must stretch and massage them every day. I have to put a toe on a step and slightly lower the ball of my foot down to stretch the tendon. I am not sure if it's an rh negative birth defect. I have all of those symptoms too, extra rib, vertebrae, no wisdom teeth kind of stuff. My mother is rh negative and she is the same but her muscles were not as extreme as mine. But she never did actual body building with a football team like me. But it's painful and possibly a short life, coincidently that is often the results of early genetic altering. I thought rh neg alien link is an interesting topic. If so I'm a damn alien lol ]
[Question] [ **UPDATE!!!! - FINISHED THE SCULPT :D** [![I went with the tall towering dessert structures and used that to finish of the creature and i think it blends well](https://i.stack.imgur.com/bk4lR.jpg)](https://i.stack.imgur.com/bk4lR.jpg) [**UPDATE**: Much Much bigger response and feedback than i anticipated, I am hugely greatful and overwhelmed by the ideas and the help, I will keep the thread going and reply with updates and will respond to each of the questions, agan huge thank you, is really helping me get a good grip on what direction im going in with the design] I'm curious to see if there is any real world examples of a huge spider colony or crab colony on land. If not, I'd like to see if there is any form of examples in popular science fiction films. What I am looking to do is create a society of species which looks like this: [![Tester](https://i.stack.imgur.com/2SXfj.jpg)](https://i.stack.imgur.com/2SXfj.jpg) Does anyone have any ideas? [Answer] I would like to know how 'humanoid' they are, since it will affect whether they are ok with things like beauty or design or they would keep it based on its natural instinct despite they may have grasp complex logical thought. Another thing is arachnid and crabs share almost nothing alike about their nest, so it may need two answers. I will go with arachnid type first,some of their real counterparts had made a structure like this one below. [![enter image description here](https://i.stack.imgur.com/XZfcV.jpg)](https://i.stack.imgur.com/XZfcV.jpg) While another type of bagworm moth had made a hybrid structure with branches that they glued with their natural secrement [![enter image description here](https://i.stack.imgur.com/JUNyA.jpg)](https://i.stack.imgur.com/JUNyA.jpg) So I think,a structure in resemblance like these (below without the need of our normal floors) will be expected even on their early age of civilization. [![enter image description here](https://i.stack.imgur.com/szlga.jpg)](https://i.stack.imgur.com/szlga.jpg) And for the Crabs, I agree that it would be like Geonosis from starwars from the global view of their cities. Since we can draw from their nest of their real counterpart that have been found. [![enter image description here](https://i.stack.imgur.com/PKmHa.jpg)](https://i.stack.imgur.com/PKmHa.jpg) Its easy to imagine that their structures involved hollowed sands stucture with many 'chimneys' like structure protruding from it. [Answer] I see two characteristics in your alien's form that at least hint at what sorts of architecture they might develop: 1. They have exoskeletons, so (except for eyes and sensor stalks), they interact with the material world as rigid objects, with limited degrees of geometric freedom -- resulting (I'm pretty sure) in only hinge-like joints, no ball/sockets; no thumb joint that can move in two independent angles WRT the base. (Those tentacle-looking things around the mouth don't seem very crustacean/arachnid-like to me.) 2. They have lots of limbs (relative to humans) and thus probably good climbers, as are some crabs, such as the Coconut Crab. [![http://cdn2.theinertia.com/wp-content/uploads/2014/03/giant_coconut_crab_02.jpg](https://i.stack.imgur.com/LjGgL.jpg)](https://i.stack.imgur.com/LjGgL.jpg) How might these characteristics impact their architecture? 1. Probably not much need/desire for soft surfaces (carpeting, couches or beds as we know them.) 2. Possibly very three-dimensional living/working structures; I'm imagining a lattice structure, or something like a kid's jungle gym. --- Side thought: of more interest to me would be this question: What sorts of tools would an intelligent crustacean design for use with its claws? [Answer] Expanding upon what @John answered, wide doors are a necessity; additionally, because their legs are to the sides of their bodies, they will need wider hallways and such as well. Until hydraulics are invented (for a slow-closing door), there would probably be few actual hinged doors, as they would be awkward to close behind oneself, and if the doors were not hung perfectly evenly, the door would try to close on their legs. For most dwellings, I would envision heavy or beaded curtains as interior doors, and sliding doors for the exterior (a primitive form would just be wood/stone/etc slabs with an indented "track" for them to slide in). Regarding general architecture, since this species is likely adept at climbing due to their physiology, their society would likely start building vertically (multiple floors etc) as soon as the stone age, where dwellings might consist simply of holes carved into a cliff face, one on top of the other. This early adoption of vertical structures would allow them to quickly learn how to build load-bearing supports, and you would likely see arches and pillars featuring prominently in the architecture, and these supports would be the place for architects and even societies in general to express and distinguish themselves. The species might tolerate lower ceilings than we generally do to conserve space and materials, since they require a greater floor space to have human-equivalent activities. A family of four of these creatures (assuming human height and proportionate leg span as per your render) eating dinner together would not be comfortable in what we'd consider a moderate-sized dining room of maybe 11x15 feet. Space could also be saved on stairwells for multiple levels, as you could just have holes between the levels with rough wall surfaces to assist climbing (consecutive holes would not be vertically aligned though, to reduce the risk of injury in case of a fall). Outdoor "climb walls" would probably be more prevalent than outdoor stairs are for us, as it would provide easy access to the upper floors of a structure from outside. There may still be indoor holes/climb walls so they don't have to go out in the elements to go between floors (as well as for security/etc), but outdoor alternatives might seem more appealing. As mentioned by @John, floor surfaces should be coarse and/or soft. Depending on the technology level, loose gravel might make an ideal floor surface for a primitive race, and this might evolve to mortared gravel to create a bumpy surface with rough spaces in between, while eliminating the issue of gravel getting pushed around/kicked up/thrown by children or miscreants. Chairs would not have backs; cheaper or more primitive chairs would simply be pedestals to rest their abdomens on, while more advanced chairs would be curved on the sides, and possibly slightly curved up toward the front to provide support to the upper abdomen and "hip" region (the part that resembles a pelvic bone). On the topic of furnishings, tables would be smaller relative to the room size than we're used to, because a large table in the middle of the room can easily prove unwieldy to navigate around. For this reason you might see tables situated against the walls more often than in the center of the room. [Answer] When designing your creatures' architecture, there are two things you've got to consider, regardless of species: 1. Why do they need this architecture? 2. What materials do they have available? Because both of these factors will have a huge impact on design. Beings living in a tropical jungle don't need worry about winter. Your buildings would need to keep the rain off your head, help you avoid predators (treehouse?), and store things, but keeping warm might not be as important. In a desert, rain isn't a huge concern, while sandstorms and shade are (so maybe an underground burrow is ideal). And so on. As far as materials go, spider-people would have it easy. As TrEs-2b already pointed out, spider silk is incredibly strong, versatile, and cheap for the spider to obtain. It's reasonable that a spider person could build an entire home out of webbing. Crabs would have a trickier time. They would likely need to depend on many of the same materials humans would use: Wood, mud, stone, animal hides/bones, etc. Depending on their dexterity, and using just these types of materials, crab homes would probably look similar to shelters a human could build. To be more fantastical, one possibility might be to introduce giant mollusks whose shells could be utilized like hermit crabs do. Or perhaps the exoskeletons crabs shed periodically could serve as a useful material as well. Note: I'm assuming these crab/spiders are at a primitive/stone age technological level. If they're much more advanced, then the question becomes very broad. If the architecture isn't purely pragmatic, you've got a lot of freedom in how you can get it to look (just look at how much our modern architecture can vary). [Answer] Just based on what we can see, wide doors, and it does not look they would be able to use a door handle without the legs getting in the way, so doors might open up or they might use their feet to open and close them. Hard points are not good on a flat hard surface, so they would sliding all over a tile floor. So floors should be soft or pitted. [Answer] Many arachnids spin webs, which relative to size are much, much stronger than steel. If such a creature became smart enough to build homes (which I'm assuming is because they're sapient), then perhaps they would build a structure like the [Edible nest Swiftlet](https://en.wikipedia.org/wiki/Edible-nest_swiftlet%C3%A9), which makes its nest out of its own spit. Surely an igloo like structure or something akin to it, but made of silk, possibly able to survive natural disasters with ease. Even if it's destroyed, one can easily be rebuilt by a group of these arachnids. As for the decor of these homes, I imagine they would lack windows, as to keep the occupant cool (unless the area is windy, then windows would be common). [Spider webs](http://www.icr.org/article/masterful-design-spider-webs/) would likely be incorporated, from web hammocks replacing beds, to web bags and nets replacing cabinets. I imagine that their doors would be simple strands of webbing to ''keep out'' animals and that they may even have small webs over their house to catch snacks, like the old fashion TV antennae. [![enter image description here](https://i.stack.imgur.com/ZDrzk.png)](https://i.stack.imgur.com/ZDrzk.png) [![enter image description here](https://i.stack.imgur.com/YOhuJ.png)](https://i.stack.imgur.com/YOhuJ.png) ]
[Question] [ Goal: **Achieve a society where the average person is a creative and/or analytical and/or strategic genius and/or physically phenomenal (as measured by our current standards, of course).** Steps: 1. Start with a regular extant human society. It can be the United States, North Korea, Sudan, Singapore, anywhere really. 2. Introduce a (set of) mutation factor(s). It can be a policy change, a scientific breakthrough, a long-term shift in reproductive behavior, or something else you might think relevant. This should be reasoned, reasonable (in the sense that non-insane people would be willing to do it), and strategically viable (it does not go against basic fundamental incentive structures, making people avoid or obviate it somehow). 3. Explain how the set of mutation factors gains traction and why you think it would result in a society of ubermen. Notes: I don't think an answer of the type "Just genetically engineer everybody, duh" will satisfy my answer acceptance condition. How would you know what mutations to induce? Can genius be genetically coded, even? Same for "Make the schools better", since the US spends (by world standards) a fortune on its pupils and has mediocre outcomes. [Answer] Some physiological aspects of humans are controlled by one or few genes (say eye color). Other aspects (like height) might be controlled by 100s or 1000s of genes. Some scientists think that human intelligence may be [controlled by 10,000 genes](http://www.businessinsider.com/superintelligent-humans-with-iq-of-1000-2014-10). Each of them contributing a small amount to a person's over all intelligence. We have not yet identified all of these genes and what side effects the "smart" version of the gene might induce. The article I referenced above suggests that if we switched all of these genes to their "smart" setting, we might engineer a human with a 1000 IQ (100$ \sigma $ above average - genius IQ being about 4$ \sigma $ above average). The steps required to perform this engineering are: 1. Identify all (or most) of the genes influencing intelligence. 2. Identify the side-effects (especially the negative ones) associated with the "smart" setting. 3. Figure out if we can counteract negative effects with other settings. Without unsavory testing on human subjects, this is going to take quite a long time. [Answer] The "real life" example of this is the Ashkenazi Jewish population, where a small population was self selected for intelligence. Historically, Jews were often restricted to what jobs they could hold, so the few positions open to them like accounting and trade generally depended on having and using intelligence. More successful bankers, traders and accountants would have more children, building the cycle. Since the Jewish population was also generally insular for both religious and social reasons, outbreeding was not encouraged. As a result, the Ashkenazi Jewish population is generally both "smarter" than the median intelligence level, but also more prone to various inheritable genetic disorders. The population of Ashkenazi Jews is above the median, but I suspect that this is neither far enough or large enough to be the "society of Genii" that you are looking for. This sort of program takes centuries to implement, and the inbreeding also results in many problems. While it is possible (if not ethical) to do something similar today, I doubt we have the required knowledge to ensure that we actually achieve the genius population desired, and at the same time, avoid the problems of inbreeding. The possible out would be to run multiple programs, and occasionally outbreed between the various gene pools. Of course the risk there is that you end up diluting the desired genetic enhancements at the same time you reduce the risks of genetic disorders. [Answer] I think the answer here is selective reproduction...combined with a whole bunch of other things. Technologically you could introduce gene modification but with modern technology that is still pretty dicey as far as knowing what in the hell we are doing. Selective reproduction is a tried and true method to promote certain traits and/or behaviors. That being said, humans can be obstinate when comes to silly things like *self-determination* and *making babies*. **Ingrates** the lot of them. A lot of different things will need to happen for this program to be accepted by the general population...people like to have sex after all...I am sure that comes as a great surprise. **I can think of two reasonable scenarios...** 1. This is the easier route. A smaller group of individuals that volunteer could create and inhabit a controlled settlement supported by the state. * This would create a small class of elite * You would need to introduce new external individuals with each generation to avoid inbreeding deficiencies becoming a problem. * These people could potentially be allowed to exist in normal society but secretly be a part of this experiment. There is the potential for 'contamination' as even smart people have libidos. * Do no select solely for intelligence. There are those infuriating individuals out there who are both intelligent and physically above average...go for both, last thing you want is your super-geniuses ending up looking like this:![enter image description here](https://i.stack.imgur.com/DoguT.jpg) 2. Large scale nationalized program. The larger the nation the more difficult this will be and the more the program will be violated, no matter the consequences. You could either go the strait up dictatorial mandate route with punishments and forced compliance, or you could go the directive with incentives route. * For this to succeed you either need a government with incredible oversight powers both for information gathering and enforcement...I really don't think this is feasible in the end, or far better you get people to voluntarily play. * You could require mass sterilization...not going to make you popular but it would be effective. This seems to me to be the only realistic way this program could be forced. You can't stop people having sex without some sort of technimagic, so don't...just make sure only intelligent people can breed. * A good old fashioned external threat doesn't hurt here. You can get away with a lot more crazy when people are scared. Some threat that we have time to breed several generations while waiting for seems odd though...maybe global warming or the sun going nova. I won't bother going into the moral implications of dictating compliance **Notes:** Nature and Nurture. Never forget the importance of nurture, creating your ubermen is one thing...but they need to be educated...I think of the scene of spock as a child on vulcan in the more recent Trek movie. Don't forget about creativity and introducing new ideas. Group think is bad, and intelligence without creativity is more limited in its possibilities than the alternative. In the end...you get Nietzsche fighting Superman while holding an eagle and a snake...*[if you don't get why Nietzsche is relevant, click here](http://en.wikipedia.org/wiki/%C3%9Cbermensch)* ![enter image description here](https://i.stack.imgur.com/6hOtV.jpg) Which is so awesome I don't even have the words to describe it... [Answer] I think a good first step if you want geniuses would be to build a system for finding, recognizing, and using genius. Currently the system is based on the people themselves having the motivation to develop and use their abilities. This works just fine for normal intelligent people, who are what the economy is built for, but not so much for actual genius. A smart person will figure out an ingenious way to make lots of money. To a genius it will be obvious he can get the same end result by wasting less of the money he already gets. Sure you could use those millions to do something fun, but it is much faster to spend the time making those millions would take to do something fun and free. Fundamentally incentive systems are built to affect the way people think and a genius **thinks different** just enough that the incentive systems are less effective than they are for merely very smart people who for most jobs perform just as well. Very few jobs are built to require a genius to do fully. Geniuses are simply too rare. This means that the very smart almost always have a competitive advantage. So you would start a system to recognize potential geniuses, regardless of social background and personal motivation, at an early age. Then a system to develop and use that genius for something useful enough to justify the expense. Genius level intelligence is fairly rare and whatever testing system you have could also recognize the very smart and motivated special talents for optimizing the educational system for them so the cost would probably be fairly low. The simplest use for the geniuses would be to push them to government think tanks and then use those think tanks to support research, development, and strategic planning. Now that you have a stock of male geniuses you can fairly easily make them have lots of children. Such human breeding projects are generally seen as unethical, but this kind of positive selection is about the least controversial (and most likely to work) form of eugenics possible. Just raise them to be sexually promiscuous and supply lots of fertile women with generous child support contracts. No real need to force anyone to do anything or try to plan anything. This should result in the frequency of genius gradually increasing in the population. The process would be slow, but that would be a benefit. Our society and economy is not really built for genius. A process that takes generations but is exponential is probably optimal. Transition to society and economy that **is** built for genius is another issue. I don't think anyone knows what it would look like. Best leave that as an issue to be solved by all those geniuses you are generating. [Answer] The society of geniuses would be easy to accomplish, simply prohibit idiots from reproducing. Suppose you have to be licensed to have children, and in order to obtain a license you have to earn citizenship in society, which is accomplished by obtaining a degree in some field of study. Unlicensed reproduction is prohibited, and individuals with bad genes, or who are genetically inferior in intelligence or physicality based on a predetermined threshold of standards are sterilized. They are allowed to exist in society, but are prevented from watering down the gene pool with their weak genes. You're basically talking about an arian race, but instead of mass genocides based on phenotypes or ethnicity, you're letting those with genetically inferior intelligence and genetic disabilities live their lives without passing on their inferior traits. There may be some flexibility in the laws for cases similar to Steven Hawking, who has a debilitating physical disability, but a vastly superior intellect, in which case he would be allowed to reproduce, but his gametes would be screened or genetically modified to remove the physical disabilities. [Answer] Simple eugenics should do it. Give everyone an IQ test at age 13 and eliminate the bottom 50%. You take care of the genetic factors, and you give everyone an incentive to try harder at school. Obviously such a society would be hell. [Answer] The first question is does this exist actually ? Well, more or less. For example, if you take some very hyped place whose population merely consist of rich people (like, in some extend, Gstaad in Switzerland), the average person tends to be an athelete, a genius or have any other capability which make easier for him to be rich (of course there is very rich idiots, but the average should be more "genial" than the overall average ; and there is poor geniuses). So one possibility is to first have a country populated mainly by very rich people. The idea is in fact not to "produce" (by genetic ingeneering or whatever) talented people in your country, but to "pump" geniuses from all around the world into your country. How do you achieve it ? You have to be very restrictive on immigration and offer high avantages to talented people, such as * Very high quality of life * Low taxes (to attract rich people) * Stimulating environment (the Silicon Valley "pumps" smart people partly because of that) Then you have to wait and destroy any other place which tends to do the same thing as you. You can also immagine to expulse or kill people being not talented enough (but it can make some of your talented people to leave your country). Of course, that strategy may force you to have a quite low population as you basically do not increase the number of talented people in the world (at first). Afterwards, the genetical part of the process should be natural. A final note however : talented people, as you want them, may be not willing to do the dirty necessary stuff in your society (like cleaning the floor). Particulary if in any other country, due to their talent, they will not have to do it. Therefore you will need less talented people to do the job, still excluding them from the society. That is a problem you can solve by having a "two chambers" country, one with the geniuses, the other with the low qualified servants. Well in fact that also already more or less exists... ]
[Question] [ By request, these are the two previous questions in this "series": [Low Voltage Lightning and Alien Nitrogen](https://worldbuilding.stackexchange.com/questions/88956/low-voltage-lightning-and-alien-nitrogen) [How To Make Lightning](https://worldbuilding.stackexchange.com/questions/90263/how-to-make-lightning) I recently asked a question about lightning storms on planets. One of the answers mentioned the idea of lightning between planets, and whilst I don't think that itself is feasible, I am going for a "Pirates of the Caribbean IN SPACE!" kind of feel to it and there's nothing better in a pirate story than stormy weather but I do want to stick to REAL science as much as possible. Some of the more detailed answers to my planetary lightning question suggested that dust, sandstorms, and ash could be used to generate lightning. Would a nebula, possibly artificial in nature, could be dense enough to create sparks in a vacuum? Is there an easier way to create "space storms" by natural or artificial means? If you come up with a decent estimate for density I'd also, ideally, like some sort of idea of what this would look like. Would you be able to see through it like a thick fog? Or would it be so dense that you couldn't see your own hand? The idea of a space battle surrounded by lightning and compounded by the inability to see, is very appealing to me but as I've said, I want this to be as real as possible. Maths is appreciated but not required. Thanks for reading. [Answer] **PULSAR STAR** You could make your battle rage near a pulsar star, this things burst insane amounts of radiation, lasers and deadly rays. Make it spin inside a nebula and the interaction with the dust could provide something that could emulate a "storm" <https://en.wikipedia.org/wiki/Pulsar#/media/File:Chandra-crab.jpg> **GAS GIANT** Hunt the pirate ships inside a gas giant and you will have the perfect storm and even more things to worry about that only the enemy batteries. <https://en.wikipedia.org/wiki/Saturn#/media/File:Rotatingsaturnhexagon.gif> [Answer] There is such a thing as "space weather", and satellite operators are constantly aware of this. The Sun releases a massive amount of energy every second in the form of radiation across the spectrum, as well as charged particles (the solar wind) and the occasional large bursts of matter and energy in the form of solar flares. [![enter image description here](https://i.stack.imgur.com/3RwOu.jpg)](https://i.stack.imgur.com/3RwOu.jpg) *Basic elements of space weather* The interactions between all this energy and the magnetic fields and atmospheres of the planets is the "space weather" which can do everything from scramble communications signals to damaging electronic circuits in spacecraft to heating the upper atmosphere and creating extra drag on objects in Low Earth Orbit. While actually pretty amazing in ts own right, the vast scale of the events and the fact that much of this happens in vacuum or the very rarefied upper atmosphere means it is also subtle and not generally visible to the human eye, the aurora being one of the few exceptions to this. Understanding how space weather works gives us a way to get the sort of "space weather" the OP is asking for. Things like hurricanes, thunderstorms, tornadoes etc. require massive amounts of matter in addition to energy. In free space this is difficult to achieve, but there are places which can be tapped. Molecular clouds, dust clouds and nebula exist which have a much greater concentration of matter than normal in space. While this is often enough to block the light of distant stars for astronomers on Earth, it is still dense as a matter of degree, the material is still far less dense than the upper atmosphere of Earth. [![enter image description here](https://i.stack.imgur.com/Gi4Fu.jpg)](https://i.stack.imgur.com/Gi4Fu.jpg) *The Eagle Nebula* Even higher density of matter can be found near stars, ranging from the nebula released by red giant stars as they go through their death throes (being near a Supernova as it implodes is an entirely different story, and "weather" doesn't even begin to describe the event). Newly forming stars have dense clouds of dust and gas, which will eventually form planetary systems. While much denser than molecular clouds in free space, they still are not going to be as dense as the atmosphere of Earth, except in localized knots where protoplanets are forming. [![enter image description here](https://i.stack.imgur.com/gLQ4z.jpg)](https://i.stack.imgur.com/gLQ4z.jpg) *Artists impression of a protoplanetary disc* Finally, the highest density of materials are probably to be found in the accretion disc of a black hole. Once again, we have other effects, including the immense tidal effects of the black hole itself, the radiation environment of the disc as it is accelerated and heated by the black hole and weird relativistic effects like "frame dragging", which affect the flow of time in the region. [![enter image description here](https://i.stack.imgur.com/4SdJw.jpg)](https://i.stack.imgur.com/4SdJw.jpg) *Accretion disc as depicted in the movie "Interstellar"* The conditions of space are far different from what we experience here on Earth, so extrapolating weather the way we understand it isn't going to be correct. You can play with these environments and probably come up with interesting space based effects which are much different from what we see here on Earth. [Answer] Lightning between dust particles requires friction or some other way to build up a static charge. A nebula is probably too dispersed to generate enough friction to make lightning except right after the nova that creates it and at that point, there's enough bad stuff going on that I doubt that any stray static electricity is going to matter. The accretion disk of a black hole might have enough stuff moving at different speeds to create lightning. Again there will be other stuff to worry about but the lightning won't be as overshadowed as it would in a nova. ]
[Question] [ An abandoned outpost from a long extinct race is discovered. It can easily be repaired and would make an ideal location for a colony, however it has been breached and any usable air has been long lost to space. The outpost has its own power systems that we are capable of turning back on and using, however there is no method on the station to create a breathable environment for humans. It's quite the journey and a colony ship would need to be in transit for more than a decade to reach its destination. If a colony ship was dispatched to this location, what would it need to bring to generate enough Earth-like air for the population to breathe and use? My first idea was solid ammonia and liquid oxygen… Burn the ammonia and let it release its nitrogen along with water. Use electrolysis to recover some of the oxygen back as required (or leave it as usable water). The issues here: * Way too high of a oxygen to nitrogen ratio… as nice as ammonia is for this, the nitrogen content is relatively low and is created at a 3:1 ratio with oxygen. * Need to carry too much liquid oxygen. It would be nice if one chemical compound can be released instead of two separate ones… also not a fan of storing high pressure gas on a long trek colony ship * Too much hydrogen… there are a few uses for it (water/fuel), however the ratio of nitrogen to hydrogen is too low and an excess of hydrogen is created in trying to get Earth-like conditions. Assume any chemical compound can be reasonably manufactured. Liquid gasses require high pressure and have some degree of danger in space transport… solid compounds preferred, but not an end all. What would you take on your colony ship to create an Earth-like atmosphere in as little amount as storage space possible and as safely as possible? It is preferable to bring the material on the ship as opposed to trying to harvest it. The tech level on the propulsion systems is limited and the speed to get there depends on some gravitational slingshotting to get it up to speed already, so there isn't the opportunity to stop to harvest anything and then re accelerate. [Answer] Per your question, it sounds like you preferred something that was not a pure oxygen atmosphere. In that case, nitrous oxide ($N\_2O$) might be an a good match. At 1 atmos. pressure it becomes liquid at -88.5 °C solid at -90.9 °C easily maintained at a 10 year trip in space. On arrival, $N\_2O$ could be easily decomposed into $O\_2$ and $N\_2$. I am not aware of any stable compound that has a ratio closer to the N/O ratio of earth's air. The atmos. pressure in your station would only be 60% of "normal" but that might be acceptable. [Answer] Ammonium nitrate melts at 169 C, and leaves no residue when heated: $$ \text{NH}\_4\text{NO}\_3 → \text{N}\_2\text{O} + 2\text{H}\_2\text{O} $$ Like Gary says $\text{N}\_2\text{O}$ can be decomposed into nitrogen and oxygen. But for the reality check, hydrogen, nitrogen and oxygen are very common elements. The colony ship is bound to find some compounds they could extract it from, although it takes longer. [Answer] People in an enclosed environment don't need anything but oxygen. While it's toxic at high *partial* pressures, you can account for this by having a lower ambient air pressure than what exists on Earth. For example, an atmosphere with a pressure of .2 bar will have enough oxygen for people to breathe, but won't be toxic. Issues with flammability are also tackled by reducing partial pressure, since it is what determines reaction rates in a gas. Reducing partial pressure will also reduce the structural loads on your habitat, making it easier to patch holes and reducing the rate of air loss if there are any small breaches. If you don't like liquid oxygen, there's another convenient way to transport it: liquid ozone. Ozone has a higher boiling point than oxygen by about 20 degrees, and is also 50% denser than oxygen. It also self-oxidizes, so you can burn it to produce energy, with the byproduct being oxygen. The downside is that anything that's a strong enough oxidizer that you can burn it to produce another strong oxidizer is *a really good oxidizer* which means that a tank of liquid ozone laying around needs to be treated really carefully, or it will explode, even without anything else to burn, because ozone *will burn itself*. But hey, lower volume for storage and free energy if you treat it right. [Answer] There are several sustances that can use to generate your atmosphere. Sice they are quite large, right now I'll post only one of them and when I have more time I'll post the other ones. You will note that this answer is quite large. That is because I also explain how to produce the sustance, and how to produce the sustances which produce it (maybe that information could be useful for someone who is willing to manufacturate the compound instead of bring it from Earth). If you aren't looking for that, only read up to **production** title (without include it), In order words, only read the first quarter/fifth of the post. Also note, that the most important part of my answer is under the tile **usage**. Finally, if someone have any question, ask in comment. I'll do my best to address the problem. Good luck reading! # [Nitrous Oxide](https://en.wikipedia.org/wiki/Nitrous_oxide) $\text{N}\_2\text{O}$ (Or [ammonium nitrate](https://en.wikipedia.org/wiki/Ammonium_nitrate) $\text{NH}\_4\text{NO}\_3$) $\begin{array}{|c|c} \hline \text{Molar Mass} & 44.013 \text{g/mol} & \\ \text{Density} & 1.977 \text{g/L (gas)} \\ \text{Melting Point} & −90.86 \text{°C} \\ \text{Boiling point} & −88.48 \text{°C} \\ \text{Price} & \text{¿?} \\ \hline \end{array}$ Or ammonium nitrate, see on industrial production. **Introduction:** Commonly know as laughing gas or nitrous. At room temperature, it is a colorless non-flammable gas, with a slight metallic scent and taste, and faint, sweet odour. At elevated temperatures, nitrous oxide is a powerful oxidizer similar to molecular oxygen. **Uses:** Futhermore build an atmosphere, you can use nitrous oxide in several ways. * Recreational (due to euphoric effects upon inhaling). * Anaesthetic and pain reducing on surgery and dentistry. (At 50% concentration can be administred by non-professional people) * Rocket propellants (used as an oxidizer). Can be use also as a monopropellant rocket with a catalyst. * Motor racing to increase the power output of engines. **Advantages:** * It's non-toxic. (Long-exposure and abuse can produce vitamin B12 defficiency...) * It's stable at room temperature -making easy to store and carry on flight-. * **It's possible to decomposed readily to from breathing air.** * It has high density and low storage pressure (when maintained at low tempertarue). That enable it to be highly competitive with stored high-pressure gas systems. ## **Storage:** This can be storaged in 20-25 bars tanks at -20 °C or in high pressure tanks at 45-60 bars. ## **Usage:** In the presence of a **heated catalyst**, $\text{N}\_2\text{O}$ will decompose exothermically into $\text{N}\_2$ and $\text{O}\_2$, at a temperature of approximately **577 °C** (this even produce energy!). $$2\text{N}\_2\text{O} \Rightarrow 2\text{N}\_2 + \text{O}\_2 + 82 \text{ kJ/mol}$$ $\begin{array}{|c|c|c|c|c} \hline \text{Examples} & \text{N}\_2\text{O} & \text{N}\_2 & \text{O}\_2 & \text{Energy}\\ \hline \text{by Mass} & 1,000\text{g} & 636.48\text{g} \text{ }(63.64\text{%}) & 363.51\text{g} \text{ }(36.35\text{%}) & 1,863.08\text{ kJ}\\ \text{by Volume} & 1,000\text{cm}^3 & 1,006.33\text{cm} \text{ }(100.63\text{%}) & 502.92\text{cm}^3 \text{ }(50.29\text{%}) & 3,683.32\text{ kJ}\\ \hline \end{array}$ With nitrous oxide you can build and atmosphere of: $\begin{array}{|cc|r|cc|r|} \hline \text{Chemical} & \text{gr/mol} & \text{Percentage} & \text{Mol Fractal} & \text{Mol} & \text{Partial Pressure} \\ \hline \text{N}\_2 & 28.0134 & 63.65\text{%} & 2.272 & 0.666 & 67.550 \text{ kPa} \\ \text{O}\_2 & 31.9988 & 36.35\text{%} & 1.135 & 0.333 & 33.775 \text{ kPa} \\ \hline \text{Total} & 60.0122 & 100.00\text{%} & 3.408 & 1.000 & 101.325\* \text{ kPa} \\ \hline \end{array}$ 101.325 kPa = 1 atm Okey... that is... fine. * **A bit high oxygen value:** Humans need around **21 kPa** of oxygen to "work" properly, you will have **33.775 kPa**, your people wouldn't suffer [hyperoxia](https://en.wikipedia.org/wiki/Hyperoxia). Hyperoxia is produced when oxygen is above **50 kPa** [it becomes toxic](https://en.wikipedia.org/wiki/Oxygen_toxicity). You will survive, but I *think* (complete and subjetive personal opinion) your crew will need a few days to adapt their lungs after stop coughing. Also, (again, my opinion) they will suffer some slightly diseases or deficiencies after some years. + You can *improve* that **reducing the overall pressure** from $101.325\text{ kPa} \rightarrow 63\text{ kPa}$. So you will have $42\text{ kPa N}\_2$ and $21\text{ kPa O}\_2$. Good! Also, reduce the overall pressure has an advantage: if there is a damage in the ship/station's hull, air will scape slowler from it, giving more time from crew to fix it. Also, because of the large heat release, the catalytic action rapidly becomes secondary, as thermal autodecomposition becomes dominant (that means you don't need to store much catalyst). Its catalyst can be any of this (I think): (Note that I don't know about catalysts and their usages) * [**Rhodium**](https://en.wikipedia.org/wiki/Rhodium): ($ 72.66/g). Density 12.41 g/cm3. * [**Cobalt**](https://en.wikipedia.org/wiki/Cobalt): ($ 81.50/kg). Density 8.90 g/cm3. * [**Platinum**](https://en.wikipedia.org/wiki/Platinum): ($ 28.56/g). Density 21.45 g/cm3. Strong. * [**Palladium**](https://en.wikipedia.org/wiki/Palladium): ($ 31.85/g). Density 12.023 g/cm3 * [**Cobalt**](https://en.wikipedia.org/wiki/Cobalt): ($ 81.50/kg). Density 8.90 g/cm3. * [**Copper**](https://en.wikipedia.org/wiki/Copper): ($ 7.20/kg). Density 8.96 g/cm3. Weak. * [**Cerium**](https://en.wikipedia.org/wiki/Cerium): ($ 5.51/kg). Density 6.770 g/cm3. Weak. * [**Iron**](https://en.wikipedia.org/wiki/Iron): ($ 71/t for ore). Density 7.874 g/cm3. Weak. * [**Nickel**](https://en.wikipedia.org/wiki/Nickel): ($ 15.24/t). Density 8.908 g/cm3. Weak. Prices from <http://www.infomine.com> (except cerium). I add density in the list because maybe it could be important for an space ship. Catalyst taken from [physicsforums.com](https://www.physicsforums.com/threads/catalytic-decomposition-of-nitrous-oxide.119242/). ## **Production:** Nitrous oxide can be produced by two ways, the industrial way and the laboratoy way. I have already asked on [Chemistry SE](https://chemistry.stackexchange.com/a/98512/44581) which is the difference between an "industrial" method and a "laboratory" method (Saldy, the used removes its answer, I'm not sure why). ### **Industrial production:** Nitrous oxide is prepared on an industrial scale by careful heating of [ammonium nitrate](https://en.wikipedia.org/wiki/Ammonium_nitrate) at about 250 ºC, which decomposes into nitrous oxide and water vapour. Amonium nitrate density 1.725 g/cm3. The addition of various [phosphate](https://en.wikipedia.org/wiki/Phosphate) salts favours formation of a purer gas at slightly lower temperatures. This reaction may be difficult to control, resulting in detonation. [![enter image description here](https://i.stack.imgur.com/z7H6r.png)](https://i.stack.imgur.com/z7H6r.png) $$\text{NH}\_4\text{NO}\_3\text{ (solid)} + 36\text{ kJ/mol} \Rightarrow 2\text{H}\_2\text{O} \text{ (gas)} + \text{N}\_2\text{O} \text{ (gas)}$$ $\begin{array}{|c|c|c|c|} \hline \text{Examples} & \text{NH}\_4\text{NO}\_3 & \text{H}\_2\text{O} & \text{N}\_2\text{O} & \text{Energy}\\ \hline \text{Mass} & 1,000\text{g} & 549.86\text{g} \text{ } (54.98\text{%}) & 450.14\text{g} \text{ } (45.01\text{%}) & -449.75\text{ kJ}\\ \text{Volume} & 1,000\text{cm}^3 & 636.57\text{cm}^3 \text{ } (63.65\text{%)} & 260.95\text{cm}^3 \text{ } (26.09\text{%}) & -775.83\text{ kJ}\\ \hline \end{array}$ That means that produce nitrous oxide also produce water to drink, yeah! But, what if we use water to produce more oxygen with electrolisys?: $$\text{H}\_2\text{O} + 241.8\text{ kJ/mol} \Rightarrow \text{H}\_2 + \frac{1}{2}\text{O}\_2$$ $\begin{array}{|c|c|c|c|} \hline \text{Examples} & \text{NH}\_4\text{NO}\_3 & \text{O}\_2 & \text{N}\_2 & \text{H}\_2 & \text{Energy}\\ \hline \text{Mass} & 1,000\text{g} & 599.65\text{g} \text{ } (59.96\text{%)} & 349.97\text{g} \text{ } (34.99\text{%)} & 50.36\text{g} \text{ } (5.03\text{%)} & 5.46\text{ MJ}\\ \text{Volume} & 1,000\text{cm}^3 & 723.86\text{cm}^3 \text{ } (72.38\text{%)} & 482.73\text{cm}^3 \text{ } (48.27\text{%)} & 966.49\text{cm}^3 \text{ } (96.64\text{%)} & 9.43\text{ MJ}\\ \hline \end{array}$ $$\text{NH}\_4\text{NO}\_3\text{ (solid)} + 437.6\text{ kJ/mol} \Rightarrow \text{N}\_2 \text{ (gas)} + 2\text{H}\_2 \text{ (gas)} + 1\frac{1}{2}\text{O}\_2 \text{ (gas)}$$ What do you want to do with all the hydrogen is your problem, not mine (may I suggest nuclear fussion). With that you can make this atmosphere: $\begin{array}{|cc|r|cc|r|} \hline \text{Chemical} & \text{gr/mol} & \text{Percentage} & \text{Mol Fractal} & \text{Mol} & \text{Partial Pressure} \\ \hline \text{N}\_2 & 28.0134 & 36.85\text{%} & 1.315 & 0.4 & 40.530 \text{ kPa} \\ \text{O}\_2 & 31.9988 & 63.15\text{%} & 1.973 & 0.6 & 60.795 \text{ kPa} \\ \hline \text{Total} & 60.0122 & 100.00\text{%} & 3.288 & 1.000 & 101.325\* \text{ kPa} \\ \hline \end{array}$ 101.325 kPa = 1 atm Okey... that is... lethal. * **High oxygen value:** Humans need around **21 kPa** of oxygen to "work" properly, you will have **60.795 kPa**, your people would suffer [hyperoxia](https://en.wikipedia.org/wiki/Hyperoxia). Hyperoxia is produced when oxygen is above **50 kPa** [it becomes toxic](https://en.wikipedia.org/wiki/Oxygen_toxicity). You won't survive mora than 1 or 2 days (maybe less). In [this answer](https://worldbuilding.stackexchange.com/a/84125/35041) I talk of hyperoxia symptoms (also, there is a cute image). + You can fix that **reducing the overall pressure** from $101.325\text{ kPa} \rightarrow 35\text{ kPa}$. So you will have $14\text{ kPa of N}\_2$ and $21\text{ kPa of O}\_2$. Good! But now the question is: Where can I find ammonium nitrate? > > Ammonium nitrate is a white crystal solid and is highly soluble in water. It is predominantly used in agriculture as a high-nitrogen fertilizer. Its other major use is as a component of explosive mixtures used in mining, quarrying, and civil construction. > > > **Harverst of [ammonium nitrate](https://en.wikipedia.org/wiki/Ammonium_nitrate):** $\text{NH}\_4\text{NO}3$ $\begin{array}{|c|c} \hline \text{Molar Mass} & 80.043 \text{g/mol} & \\ \text{Density} & 1.725 \text{g/cm}^3\text{ (solid)} \\ \text{Melting Point} & 169.6 \text{°C} \\ \text{Boiling point} & 210 \text{°C} \\ \text{Price} & \text{USD } 180-400/\text{ton} \\ \hline \end{array}$ > > Ammonium nitrate is found as a natural mineral (gwihabaite) [...] often as a crust on the ground and/or in conjunction with other nitrate, iodate, and halide minerals. > > > **Production of ammonium:** You can also produce it in several ways, but I will talk about a way because the anothers needs limestones, which currently is not avariable on space, or some components that end falling on a circular reference so quckly. The produciton entails the [acid-base reaction](https://en.wikipedia.org/wiki/Acid%E2%80%93base_reaction) of [ammonia](https://en.wikipedia.org/wiki/Ammonia) with [nitric acid](https://en.wikipedia.org/wiki/Nitric_acid) $$\text{HNO}\_3+\text{NH}\_3 \Rightarrow \text{NH}\_4\text{NO}\_3$$ $\begin{array}{|c|c|c|c|} \hline \text{Examples} & \text{HNO}\_3 & \text{NH}\_3 & \text{NH}\_4\text{NO}\_3\\ \hline \text{by Mass} & 787.20\text{g} & 212.77\text{g} & 1,000\text{g} \\ \text{by Volume} & 897.56\text{cm}\_3 & 502.78\text{cm}\_3\text{ (gas)} & 1,000\text{cm}\_3 \\ \text{"} & \text{"} & 0.53\text{cm}\_3\text{ (liquid)} & \text{"}\\ \text{"} & \text{"} & 0.44\text{cm}\_3\text{ (solid)} & \text{"}\\ \hline \end{array}$ > > Ammonia is used in its [anhydrous](https://en.wikipedia.org/wiki/Anhydrous) form (i.e., gas form) and the nitric acid is concentrated. This reaction is violent owing to its highly exothermic nature. > > > **Ammonia:** $\text{NH}\_3$ $\begin{array}{|c|c} \hline \text{Molar Mass} & 17.031 \text{g/mol} & \\ \text{Density} & 0.73 \text{g/L (gas)} \\ \text{"} & 681.9 \text{g/L (liquid)} \\ \text{"} & 817 \text{g/cm}^3\text{ (solid)} \\ \text{Melting Point} & −77.73 \text{°C} \\ \text{Boiling point} & −33.34 \text{°C} \\ \text{Price} & \text{USD } 400/\text{ton?} \\ \hline \end{array}$ Sadly, I couldn't find a way to produce ammonia that: * Doesn't fall into a circular reference. * It isn't made on volcanic region (because there aren't volcanoes on space). * Doesn't use coal (there isn't on space). * Doesn't use quicklime (I don't think there are quicklime asteroids). * Doesn't consume hydrogen (because that need water) nor nitrogen (because that is only harvested from the atmosphere...). **Maybe** this could be useful: > > [...] ammonia was obtained by the [dry distillation](https://en.wikipedia.org/wiki/Dry_distillation) of nitrogenous vegetable and animal waste products, including camel [dung](https://en.wikipedia.org/wiki/Manure), where it was distilled by the reduction of [nitrous acid](https://en.wikipedia.org/wiki/Nitrous_acid) and [nitrites](https://en.wikipedia.org/wiki/Nitrite) with hydrogen; > > > And nitrous acid can be made with nitrine and water, and nitrine... not sure (some ways are circular references, other one are too strange for me). **Nitric Acid:** $\text{HNO}\_3$ $\begin{array}{|c|c} \hline \text{Molar Mass} & 63.01 \text{g/mol} & \\ \text{Density} & 1.5129 \text{g/L (liquid)} \\ \text{Melting Point} & −42 \text{°C} \\ \text{Boiling point} & 83 \text{°C} \\ \text{Price} & \text{USD ~} 300 \text{-} 375/\text{ton (68% pure)} \\ \hline \end{array}$ Nitric acid is made by reaction of nitrogen dioxide (NO2) with water: $$3\text{NO}\_2 + \text{H}\_2\text{O} \Rightarrow 2\text{HNO}\_3 + \text{NO}$$ Normally, the [nitric oxide](https://en.wikipedia.org/wiki/Nitric_oxide) (NO) produced by the reaction is reoxidized by the oxygen in air to produce additional nitrogen dioxide $2\text{NO} + \text{O}\_2 → 2\text{NO}\_2$... maybe a way to dispatch the oxygen spares? Sadly, the nitrogen dioxide is made with oxygen and nitrogen (which is found on Earth atmosphere). The other way to make nitric acid is with [Hydrogen peroxide](https://en.wikipedia.org/wiki/Hydrogen_peroxide) and nitrogen dioxide, or with ammonia and oxygen, but produce hydrogen peroxide it too complex and both ways fall on a circular reference. Another way could be with [Dinitrogen pentoxide](https://en.wikipedia.org/wiki/Dinitrogen_pentoxide) and water, but as you guessed, produce dinitrogen pentoxide make a circular reference. ### **Laboratory Production** There are several ways to archive this on a lab: * I won't talk about the production with urea, nitric acid and sulfuric acid because artifial urea is pointless (use ammonia) and sulfuric acid use oxygen and sulfur, so is also pointless. * [Ostwal process](https://en.wikipedia.org/wiki/Ostwald_process) (Direct oxidation of ammonia with a manganese dioxide-bismuth oxide catalyst) is also pointless because an oxidation obiously need oxygen. * Hydroxylammonium chloride reaction with sodium nitrite can't be used because the first compound is very difficult to get (organic). * Treating $\text{HNO}\_3$ with $\text{SnCl}\_2$ and $\text{HCl}$ can't be used because we can't harvest $\text{SnCl}\_2$. * Hyponitrous acid descomposition can't be used because it's difficult to produce (we need silver hyponitrite). So our last alternative is the heating of a mixture of [sodium nitrate](https://en.wikipedia.org/wiki/Sodium_nitrate) and [ammonium sulfate](https://en.wikipedia.org/wiki/Ammonium_sulfate): $$2\text{NaNO}\_3 + (\text{NH}\_4)\_2\text{SO}\_4 \Rightarrow \text{Na}\_2\text{SO}\_4 + 2\text{N}\_2\text{O}+4\text{H}\_2\text{O}$$ **Sodium nitrate:**$\text{NaNO}\_3$ $\begin{array}{|c|c} \hline \text{Molar Mass} & 84.9947 \text{g/mol} & \\ \text{Density} & 2.257 \text{g/L (solid)} \\ \text{Melting Point} & 308 \text{°C} \\ \text{Boiling point} & 380 \text{°C} \\ \text{Price} & \text{USD ~} 100 \text{-} 300/\text{ton} \\ \hline \end{array}$ Sodium nitrate can be harvest from [Caliche](https://en.wikipedia.org/wiki/Caliche) rocks (I don't think it's avariable on asteroids. Additionally it can be syntethised by **a lot of ways**: Sodium nitrate is synthesized industrially by neutralizing nitric acid with [sodium carbonate](https://en.wikipedia.org/wiki/Sodium_carbonate): $$2\text{HNO}\_3 + \text{Na}\_2\text{CO}\_3 \Rightarrow 2 \text{NaNO}\_3 + \text{H}\_2\text{O} + \text{CO}\_2$$ Or with [sodium bicarbonate](https://en.wikipedia.org/wiki/Sodium_bicarbonate): $$\text{HNO}\_3 + \text{NaHCO}\_3 \Rightarrow \text{NaNO}\_3 + \text{H}\_2\text{O} + \text{CO}\_2$$ Or even with [sodium hydroxide](https://en.wikipedia.org/wiki/Sodium_hydroxide) (very exothermic) (Also note that sodium hydroixe is made with [Chloralkali process](https://en.wikipedia.org/wiki/Chloralkali_process) which need sea water... or with sodium carbonate and calcium hydroxide making it pointless): $$2\text{HNO}\_3 + \text{NaOH} \Rightarrow \text{NaNO}\_3 + \text{H}\_2\text{O}$$ Or just sodium reacting with nitric acid (violent reaction): $$2\text{HNO}\_3 + 2 \text{Na} \Rightarrow 2\text{NaNO}\_3 + \text{H}\_2$$ **Sodium carbonate:** $\text{Na}\_2\text{CO}\_3$ $\begin{array}{|c|c} \hline \text{Molar Mass} & 105.9888 \text{g/mol} & \\ \text{Density} & 2.54 \text{g/L (solid)} \\ \text{Melting Point} & 851 \text{°C} \\ \text{Price} & \text{USD ~} 100 \text{-} 280/\text{ton} \\ \hline \end{array}$ This can be hasvert from [Natron](https://en.wikipedia.org/wiki/Natron), again a rock. * You could produce sodium carbonate with the [Leblanc process](https://en.wikipedia.org/wiki/Sodium_carbonate#Leblanc_process)... which use salt, sulfuric acid, coal... and limestone. * Or the [Solvay process](https://en.wikipedia.org/wiki/Sodium_carbonate#Solvay_process) which use ammonia... and limestone. * Or even the [Hou process](https://en.wikipedia.org/wiki/Sodium_carbonate#Hou's_process) which use ammonia and [sodium chloride](https://en.wikipedia.org/wiki/Brine) (sea salt). **Sodium bicarbonate:** $\text{NaHCO}\_3$ $\begin{array}{|c|c} \hline \text{Molar Mass} & 84.0066 \text{g/mol} & \\ \text{Density} & 2.20 \text{g/L (solid)} \\ \text{Melting Point} & 50 \text{°C} \\ \text{Price} & \text{USD ~} 200 \text{-} 300/\text{ton} \\ \hline \end{array}$ It can be harvest from deposits of [nahcolite](https://en.wikipedia.org/wiki/Nahcolite) carbonate mineral. Sadly it's produced: * Using the [Solvay process](https://en.wikipedia.org/wiki/Sodium_bicarbonate#Production) which use sodium chloride, ammonia and carbon dioxide making a circular reference. * Also it can me made with carbon dioxide and sodium hydroxide, again making a circular reference. * But, it can also be made with the ore [trona](https://en.wikipedia.org/wiki/Trona) dissolved in water and treated with carbon dioxide. $$\text{Na}\_2\text{CO}\_3 + \text{CO}\_2 + \text{H}\_2\text{O} \Rightarrow 2 \text{NaHCO}\_3$$ [Answer] This will be my second post to this quesiton. My first one was [this one](https://worldbuilding.stackexchange.com/a/115687/35041). Here I'll put more nitrogen and oxygen derivates. # [Dinitrogen Pentoxide](https://en.wikipedia.org/wiki/Dinitrogen_pentoxide) $\text{N}\_2\text{O}\_5$ (AKA: Nitrogen Pentoxide) $\begin{array}{|c|c} \hline \text{Molar Mass} & 108.01 \text{g/mol} & \\ \text{Density} & 1.642 \text{g/L (gas)} \\ \text{Melting Point} & 41 \text{°C} \\ \text{Boiling point} & 47 \text{°C} \\ \text{Price} & \text{¿?} \\ \hline \end{array}$ **Introduction:** Also known as nitrogen pentoxide, N2O5 is one of the binary nitrogen oxides, a family of compounds that only contain nitrogen and oxygen. It is an unstable and potentially dangerous oxidizer. **Storage:** Despite its unstability it can be safestly stored a 8 °C and hide from sunlight. Also, at room temperature it's solid, which means it doesn't need pressurised tanks. **Usage:** Dinitrogen Petoxide exists as colourless crystals that sublime slightly above room temperature. The salt eventually decomposes at room temperature into $\text{NO}\_2$ and $\text{O}\_2$. $$2\text{N}\_2\text{O}\_5 \Rightarrow 4\text{NO}\_2 + \text{O}\_2$$ $\begin{array}{|c|c|c|c|} \hline \text{Examples} & \text{N}\_2\text{O}\_5 & \text{NO}\_2 & \text{O}\_2 \\ \hline \text{by Mass} & 1,000\text{g} & 851.87\text{g} \text{ }(85.18\text{%}) & 148.12\text{g} \text{ }(14.81\text{%})\\ \text{by Volume} & 1,000\text{cm}^3 & 744.03\text{cm} \text{ }(74.40\text{%}) & 170.20\text{cm}^3 \text{ }(17.02\text{%})\\ \hline \end{array}$ And nitrogen dioxide can be also broken for more oxygen. (Note that if you didn't want the O2 from the first reaction you could use instead [dinitrogen tetroxide](https://en.wikipedia.org/wiki/Dinitrogen_tetroxide)). At 150 °C, $\text{NO}\_2$ decomposes with release of oxygen via an endothermic process: $$2\text{NO}\_2 + 14\text{ kJ/mol} \Rightarrow 2\text{NO} + \text{O}\_2$$ And nitrogen oxide can be also broken for even more oxygen. Since the heat of formation of ·NO is endothermic, NO can be decomposed to the elements exothermically. Catalytic converters in cars exploit this reaction. See [my first post](https://worldbuilding.stackexchange.com/a/115687/35041) for a list of materials which can be used as catalysers. $$2\text{NO} \Rightarrow \text{O}\_2 + \text{N}\_2 + 91.29\text{ kJ/mol}$$ So the overal reaction would be: $$2\text{N}\_2\text{O}\_5 + 14\text{ kJ/mol} \Rightarrow 5\text{O}\_2 + 2\text{N}\_2 + 91.29 \text{ kJ/mol} \text{ (Net: }77.29\text{ kJ/mol)}$$ $\begin{array}{|c|c|c|c|} \hline \text{Examples} & \text{N}\_2\text{O}\_5 & \text{O}\_2 & \text{N}\_2 & \text{Energy}\\ \hline \text{by Mass} & 1,000\text{g} & 740.64\text{g} \text{ }(74.06\text{%}) & 259.35\text{g} \text{ }(25.93\text{%}) & 715.58\text{ kJ}\\ \text{by Volume} & 1,000\text{cm}^3 & 851.04\text{cm} \text{ }(85.10\text{%}) & 340.53\text{cm}^3 \text{ }(34.05\text{%}) & 1,174.98\text{ kJ}\\ \hline \end{array}$ Which all this stuff we can build an atmosphere of: $\begin{array}{|cc|r|cc|r|} \hline \text{Chemical} & \text{gr/mol} & \text{Percentage} & \text{Mol Fractal} & \text{Mol} & \text{Partial Pressure} \\ \hline \text{N}\_2 & 28.0134 & 25.94\text{%} & 0.925 & 0.285 & 28.950 \text{ kPa} \\ \text{O}\_2 & 31.9988 & 74.06\text{%} & 2.314 & 0.714 & 72.325 \text{ kPa} \\ \hline \text{Total} & 60.0122 & 100.00\text{%} & 3.239 & 1.000 & 101.325\* \text{ kPa} \\ \hline \end{array}$ 101.325 kPa = 1 atm * **Lethal oxygen value:** Humans need around **21 kPa** of oxygen to "work" properly, you will have **72.325 kPa**, your people will suffer [hyperoxia](https://en.wikipedia.org/wiki/Hyperoxia). Hyperoxia is produced when oxygen is above **50 kPa** [it becomes toxic](https://en.wikipedia.org/wiki/Oxygen_toxicity). You won't survive mora than 1 or 2 days (maybe less). In [this answer](https://worldbuilding.stackexchange.com/a/84125/35041) I talk of hyperoxia symptoms (also, there is a cute image). + You can fix that **reducing the overall pressure** from $101.325\text{ kPa} \rightarrow 29.4\text{ kPa}$. So you will have $8\text{ kPa N}\_2$ and $21\text{ kPa O}\_2$. Good! Also, reduce the overall pressure has an advantage: if there is a damage in the ship/station's hull, air will scape slowler from it, giving more time from crew to fix it. > > Another path to proxide oxygen is mixing dinitrogen pentoxide with water to produce [nitric acid](https://en.wikipedia.org/wiki/Nitric_acid). But there is no point doing this as explained bellow. > > $$\text{N}\_2\text{O}\_5 + \text{H}\_2\text{O} \Rightarrow 2\text{HNO}\_3$$ > > With sunlight and heat you could produce [nitrogen dioxide](https://en.wikipedia.org/wiki/Nitrogen_dioxide) and water from nitric acid, the same sustance used in the first path to get oxygen. > > $$4\text{HNO}\_3 \Rightarrow 2\text{H}\_2\text{O} + 4\text{NO}\_2 + \text{O}\_2$$ > > The water works a catalyst because it's recovered: > > $$2\text{N}\_2\text{O}\_5 + 2\text{H}\_2\text{O} \Rightarrow 2\text{H}\_2\text{O} + 4\text{NO}\_2 + \text{O}\_2$$ > > This path is worthless because it produce the same as the path before, but I had to show you. > > > # **[Dinitrogen Tetraoxide](https://en.wikipedia.org/wiki/Dinitrogen_tetroxide)** $\text{N}\_2\text{O}\_4$ $\begin{array}{|c|c} \hline \text{Molar Mass} & 92.011 \text{g/mol} & \\ \text{Density} & 1.44246 \text{g/L (gas)} \\ \text{Melting Point} & -11.2 \text{°C} \\ \text{Boiling point} & 21.69 \text{°C} \\ \text{Price} & \text{¿?} \\ \hline \end{array}$ $$\text{N}\_2\text{O}\_4 + 57.23 \text{ kJ/mol} \rightleftharpoons 2\text{NO}\_2$$ Overall: $$\text{N}\_2\text{O}\_4 + 71,23\text{ kJ/mol} \Rightarrow 2\text{O}\_2 + \text{N}\_2 + 91.26\text{ kJ/mol} \text{ (Net: }20.03\text{ kJ/mol)}$$ $\begin{array}{|c|c|c|c|} \hline \text{Examples} & \text{N}\_2\text{O}\_4 & \text{O}\_2 & \text{N}\_2 & \text{Energy}\\ \hline \text{by Mass} & 1,000\text{g} & 695.54\text{g} \text{ }(69.55\text{%}) & 304.45\text{g} \text{ }(30.44\text{%}) & 217.69\text{ kJ}\\ \text{by Volume} & 1,000\text{cm}^3 & 702.09\text{cm} \text{ }(70.20\text{%}) & 351.16\text{cm}^3 \text{ }(35.11\text{%}) & 314.01\text{ kJ}\\ \hline \end{array}$ Which produce an atmosphere of: $\begin{array}{|cc|r|cc|r|} \hline \text{Chemical} & \text{gr/mol} & \text{Percentage} & \text{Mol Fractal} & \text{Mol} & \text{Partial Pressure} \\ \hline \text{N}\_2 & 28.0134 & 30.45\text{%} & 1.086 & 0.666 & 33.775 \text{ kPa} \\ \text{O}\_2 & 31.9988 & 69.55\text{%} & 2.173 & 0.333 & 67.550 \text{ kPa} \\ \hline \text{Total} & 60.0122 & 100.00\text{%} & 3.259 & 1.000 & 101.325 \text{ kPa} \\ \hline \end{array}$ * **Keeps being lethal due high oxygen value**: + You can fix that **reducing the overall pressure** from $101.325\text{ kPa} \rightarrow 31\text{ kPa}$. So you will have $10.5\text{ kPa N}\_2$ and $21\text{ kPa O}\_2$. Good! > > Also, dinitrogen tetraoxide has serveral unuseful paths where water is catalizer (in one of them even oxygen is a catalizer): > $$\text{N}\_2\text{O}\_4 + \text{H}\_2\text{O} \Rightarrow \text{HNO}\_2 + \text{HNO}\_3$$ > > Subpaths: > > > • $2\text{HNO}\_2 \Rightarrow \text{NO}\_2 + \text{NO} + \text{H}\_2\text{O}$ > > • $3\text{HNO}\_2 \Rightarrow \text{HNO}\_3 + 2\text{NO} + \text{H}\_2\text{O}$ > > • $2\text{HNO}\_2 + \text{O}\_2 \Rightarrow 2\text{HNO}\_3$ > > > > The last two path also have: $4\text{HNO}\_3 \Rightarrow 2\text{H}\_2\text{O} + 4\text{NO}\_2 + \text{O}\_2$. > > > Then, $\text{NO}\_2$ and $\text{NO}$ can be broken as seen above on the post. > > > # **[Nitrogen dioxide](https://en.wikipedia.org/wiki/Nitrogen_dioxide)** $\text{NO}\_2$ And **[Nitrogen oxide](https://en.wikipedia.org/wiki/Nitric_oxide)** $\text{NO}$ You've already learn how to break them above! Also the $\text{NO}\_2$ oxygen and nitrogen production, and even the atmospheric composition are exactly the same as with dinitrogen tetraoxide. The only difference is that it doesn't need energy to break down. $\begin{array}{|c|cc|} \hline \text{} & \text{NO}\_2 & \text{NO}\\ \hline \text{Molar Mass} & 46.0055 \text{g/mol} & 30.01 \text{g/mol}\\ \text{Density} & 1.88 \text{g/L (gas)} & 1.3402 \text{g/L (gas)}\\ \text{Melting Point} & -11.2 \text{°C} & -164 \text{°C}\\ \text{Boiling point} & 21.69 \text{°C} & -152 \text{°C}\\ \text{Price} & \text{USD}7-8\text{/kg} & \text{USD}1.48-2.95\text{/kg}\\ \hline \end{array}$ But with nitrogen oxide: $\begin{array}{|c|c|c|c|} \hline \text{Examples} & \text{NO}\_2 & \text{O}\_2 & \text{N}\_2 \\ \hline \text{by Mass} & 1,000\text{g} & 533.13\text{g} \text{ }(53.31\text{%}) & 466.73\text{g} \text{ }(46.67\text{%})\\ \text{by Volume} & 1,000\text{cm}^3 & 500.00\text{cm}^3 \text{ }(50\text{%}) & 500.17\text{cm}^3 \text{ }(50.01\text{%})\\ \hline \end{array}$ $\begin{array}{|cc|r|cc|r|} \hline \text{Chemical} & \text{gr/mol} & \text{Percentage} & \text{Mol Fractal} & \text{Mol} & \text{Partial Pressure} \\ \hline \text{N}\_2 & 28.0134 & 46.68\text{%} & 1.666 & 0.5 & 50.663 \text{ kPa} \\ \text{O}\_2 & 31.9988 & 53.32\text{%} & 1.666 & 0.5 & 50.663 \text{ kPa} \\ \hline \text{Total} & 60.0122 & 100.00\text{%} & 3.32 & 1.0 & 101.325 \text{ kPa} \\ \hline \end{array}$ * **Keeps being lethal due high oxygen value**: + You can fix that **reducing the overall pressure** from $101.325\text{ kPa} \rightarrow 31\text{ kPa}$. So you will have $21\text{ kPa N}\_2$ and $21\text{ kPa O}\_2$. Good! # **[Dinitrogen Trioxide](https://en.wikipedia.org/wiki/Dinitrogen_trioxide)** $\text{N}\_2\text{O}\_3$ $\begin{array}{|c|c} \hline \text{Molar Mass} & 76.01 \text{g/mol} & \\ \text{Density} & 1.447 \text{g/L (liquid)} \\ \text{"} & 1.783 \text{g/L (gas)} \\ \text{Melting Point} & -107 \text{°C} \\ \text{Boiling point} & 3.5 \text{°C} \\ \text{Price} & \text{¿?} \\ \hline \end{array}$ It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C. This process is reversible so it produce that: $$\text{N}\_2\text{O}\_3 \rightleftharpoons \text{NO} + \text{NO}\_2$$ Using the process learned above: $$2\text{N}\_2\text{O}\_3 + 14\text{ kJ/mol} \Rightarrow 3\text{O}\_2 + 2\text{N}\_2 + 91.29\text{ kJ/mol} \text{ (Net: }77.29\text{ kJ/mol)}$$ $\begin{array}{|c|c|c|c|} \hline \text{Examples} & \text{N}\_2\text{O}\_5 & \text{NO}\_2 & \text{O}\_2 \\ \hline \text{by Mass} & 1,000\text{g} & 631.47\text{g} \text{ }(63.14\text{%}) & 368.54\text{g} \text{ }(36.85\text{%})\\ \text{by Volume} & 1,000\text{cm}^3\text{gas} & 639.42\text{cm} \text{ }(63.94\text{%}) & 429.42\text{cm}^3 \text{ }(42.94\text{%})\\ \text{by Volume} & 1,000\text{cm}^3\text{liquid} & 787.90\text{cm} \text{ }(78.79\text{%}) & 525.44\text{cm}^3 \text{ }(52.54\text{%})\\ \hline \end{array}$ Which produces this atmosphere: $\begin{array}{|cc|r|cc|r|} \hline \text{Chemical} & \text{gr/mol} & \text{Percentage} & \text{Mol Fractal} & \text{Mol} & \text{Partial Pressure} \\ \hline \text{N}\_2 & 28.0134 & 36.85\text{%} & 1.315 & 0.4 & 40.530 \text{ kPa} \\ \text{O}\_2 & 31.9988 & 63.15\text{%} & 1.973 & 0.6 & 60.795 \text{ kPa} \\ \hline \text{Total} & 60.0122 & 100.00\text{%} & 3.288 & 1.0 & 101.325 \text{ kPa} \\ \hline \end{array}$ * **Keeps being lethal due high oxygen value**: + You can fix that **reducing the overall pressure** from $101.325\text{ kPa} \rightarrow 35\text{ kPa}$. So you will have $14\text{ kPa N}\_2$ and $21\text{ kPa O}\_2$. Good! # **Production:** Sadly, the only way to produce all this usances use the same compounds that they produce or with other very difficult to get, that means a circular reference. So you must bring it from Earth. [Answer] I am kind a fan of a low presure pure oxygen environment which already mentioned. So you may use solidified oxygen. In the space there is no need to active cooling. You may keep it with simple insulation and a reflective wrapping from radiant heat sources (like sun) and from the rest of your spaceship. In fact in the failed Apollo 13 misson there is a malfunctioning "heater" that keeps oxygen from solidification. Or You may use **hydrogen peroxide** H2O2. It's a liquid under the room temprature. You may even transport it in the solid form (it's melting point is very close to water-ice). For safety reasons it is usually mixed with water. It's also used as a propellant in the rockets and the jetpacks. With the silver catalyst, H2O2 very rapidly breaks up (bursts) to water vapour and a oxygen. Personal Jetpacks used this reaction for a propulsion. ]
[Question] [ I'm inventing a constructed world for a personal exercise in writing, and I was wondering if a theoretical cube shaped planet could have a moon. Is that physically possible? I am going on the assumption that the planet is artificial, and I intend on it being a rogue planet. [Answer] It should be possible for a moon to orbit a hypothetical cubic planet. It is true that if the moon were orbiting extremely close to the planet, weird things would be happening with gravity that would influence the orbit. However, I believe there would be a distance such that a stable orbit could be achieved. There are at least a couple reasons I believe it is possible for a moon to be in a stable orbit around a hypothetical cubic planet: 1. I envision a stable situation where the planet and moon could be tidally locked with each other (e.g. one side constantly facing each other) in orbit: (see <http://en.wikipedia.org/wiki/Tidal_locking>). This way, the varying gravity of the corners would not be impacting the orbit much. The moon is tidally locked with the earth, for example (although the earth is not tidally locked with the moon). Pluto and Charon are tidally locked with each other in this manner though. 2. Another example is the Rosetta orbiter which is in orbit around a comet. This comet is far from being round, and the Rosetta orbiter is currently in orbit around it (imagine the comet being the planet and the orbiter being the moon). Granted, the comet is not cubic, but it is an example of something orbiting something else that is not quite round. Here is a picture of comet 67P/Churyumov–Gerasimenko (67P), which Rosetta is orbiting: <http://www.jpl.nasa.gov/images/rosetta/20141210/pia18899-16.jpg>![enter image description here](https://i.stack.imgur.com/2TG64.jpg) More about the Rosetta mission can be gathered here: <http://en.wikipedia.org/wiki/Rosetta_%28spacecraft%29> Note: It was pointed out that Rosetta is not necessarily in a "true orbit" around the comet, so this might not be a valid example. However, as @ilinamorato mentioned, asteroids (which usually aren't round) often do orbit one another. [Answer] **A definite yes for small low-orbit and high-orbit satellites as long as the cube does not rotate. Large moons far away should be fine** The question was answered in the 2012 Physics International paper: "[The Gravity Field of a Cube](http://www.thescipub.com/abstract/10.3844/pisp.2012.50.57)". (Available for free) The authors found stable orbits for a tiny moon or space probe to circle the cube. The gravity field of a cube is only distorted close to the cube and with a large moon you can presumably have a situation like the Pluto-Charon system where they each orbit a common center of mass, so cubeness shouldn't be a problem in that case. (Though I can't prove it :) The authors also provide us with great background material for writing a sci-fi story, such as how a lake on a cube will look, and what to do if you colonize the world: ![enter image description here](https://i.stack.imgur.com/bp1BZ.png) Paper citation: Consider now a hypothetical cube 12,000×12,000×12,000 km3, approximately the size of the Earth, with the same volume of water and atmosphere as found on the Earth, then we would approximately half fill each face with water and have an atmosphere approximately 100 km thick similar to what is assumed for the atmosphere on the Earth before reaching space. In this case then the corners and the edges of the cube, would be like vast mountain ranges several thousand km high, with their tips extending out into free space. It would therefore be very difficult to cross these mountain ranges and hence we would have six nearly independent habitable zones on each face. There would presumably be permanent snow on the sides of these vast mountain ranges and people would live around the edges of the oceans on each face in a fairly narrow habitable zone only about 100 km wide as the cube faces rise rapidly through the atmosphere. Unfortunately climbing the approximately 3000 km high corners does not result in an improved view because the surface is still fiat in any observed direction. However the corners, being in free space, would be very suitable for launching satellites. One would also have approximately sqrt(2) x 6000 km of downhill ski run from each corner, down to the centre of each face. In order to have a day night cycle we would also need the cube to be rotating. The sun would rise almost instantaneously over the face of a cube however, so that each face would need to be a single time zone and thus the cube as a whole would require four separate time zones, assuming the planet was rotating about the centre of an upper and lower face. The north and south faces in this case would be permanently frozen as they would receive no sunlight except that striking the oceans extending away from the surface of the cube, so there might be a permanent pool of liquid water at the two poles. Launching low orbit satellites around this cube needs special care in order to avoid certain orbital resonances that would create significant variations in the orbit. [Answer] Possible, yes. You can think of a cube-shaped planet as an ordinary spherical or ellipsoid planet, simply one with eight massive, three-sided, pyramid-shaped mountains protruding from it, equidistant from one another, connected by ridges. As long as your satellite doesn't hit one of those mountains, it can orbit just fine. Now, how stable will that orbit be? If you assume that the orbit is caused by rotational motion constrained by a gravity well, the orbit will be as stable as the gravity well is. Since a gravity well is a "depression" in space-time caused by the mass of the object, you can compare the gravity well of a spherical vs. a cubical body in space by placing a ball and a block onto a rubber sheet held taut (or a very heavy such body onto a well-tucked-in bedspread). You'll notice that while the gravity well is much sharper to begin with, it soon becomes semi-circular. So depending upon the proximity of your satellite to your planet, the orbit will be more or less stable. If it is close, it will be drawn in more closely as it orbits the vertices or ridges, and flung further out as it travels over a flat plane; if it is further from the planet, those fluctuations will be diminished. Irregular objects with satellites in stable orbits are far from uncommon. Asteroids, for instance, commonly orbit about one another. Similarly, as Jonathan has noted, the recent *Rosetta* mission features a man-made orbiter which is maintaining an orbit around a comet by tracing its path about the comet's nucleus. [Answer] Yes, once the orbit of the moon is far enough the shape of the planet is largely irrelevant. The orbit of the moon is not going to be as regular as it would be with a sphere but that is generally not an issue. The exception is if the plane of the moons orbit and the plane of rotation of the planet are different or the rotation of the planet is irregular. Also the sun would have effects on the moons orbit and in theory unless the planet is tidally locked the effects became chaotic and can disrupt the moons orbit. In practice, you can simply give the moon a far orbit and assume the effects are negligible for the duration of your story. Also, while this was not asked, I see no reason why an artificial planet cannot be shaped like a cube. Stability depends on the shape of the gravity field. The shape of the gravity field depends on the shape and density profile of the object. On an artificial planet those are both decided by builders. I'd assume that under some dirt and stone there would be a cube shaped structural frame of high density metal. The rest of the planet, the core of it would be some sort of low density silicate. Surface gravity would become from the high density metal near the surface, while the silicate would provide static pressure to keep the cube from collapsing. That said a planet like this would be much less stable than natural planets. Specifically, and relevant to the question, the planet would be vulnerable to tidal forces. A small far moon that does not cause significant tides should be fine. You'd still need a solution to tidal stresses from the sun. But the question was just about the moon, and the answer is that a moon that is far and small enough not to cause noticeable tides would work. And note that the builders might have been satisfied with a million year stable period, and ignored the possibility of the planet falling apart after 10 million years or so. "Warranty expired. No refund. Go ho... away." [Answer] This is not a good answer. I am inclined to delete it, but for now, I suggest reading Abulafia's answer and the paper he links to, and Jonathan's answer. So, I'm putting aside my instinctive feelings towards the concept of a constructed cubic planet here... Your question regarding can X have a satellite Y can be answered by the question: what shape is the gravity well in spacetime that is made by X? Y doesn't care what shape X is. It will just fall along the well made in spacetime by X. Now, if that well has 'corners' on it because of the geometric shape of X, and Y runs into one of those corners, then something odd will happen... Without crunching any numbers on it, I would suggest that a satellite wouldn't be possible, there wouldn't be a stable orbit. Think about what it would be like to stand on an edge of the planet, stepping over onto an adjacent face... Nope, feels like weird maths happening right there. But this is a constructed planet, right? So... Perhaps the cubic shape doesn't correspond to density, so the edges and vertices of the planet do not present a greater mass to the centre than a point in the middle of a face. If it was made to create a spherical dent in spacetime, then a satellite could orbit it. Of course, standing on the surface of the planet would be strange, as close to vertices, gravity would pull you down at an angle to the surface. Though walking across a flat surface, it would feel steeper and steeper the closer you got to an edge. But it still wouldn't be a planet, as planets by definition have reached hydrostatic equilibrium (ie they have a round shape). Making it a rogue planet doesn't really change anything... You've really just invented a massive spacecraft with a shape like a Borg craft. [Answer] In 1998 I drew a wooden space station for a cubical Earth. ![enter image description here](https://i.stack.imgur.com/bTA2Z.jpg) ([Full size](http://www.dlugosz.com/POV/texsat/texsat.jpg) link) If you really want to go crazy, the cube is the least of it. Play around with other things in your setting, too. If a planet is cube, does that mean that spacetime is warped so the shape it settles into (shaped gravity generators)? Then, the round orbital mechanics would not be applicable, or a problem. Make the orbit a [hamiltonian path](https://www.wikipedia.org/wiki/Hamiltonian_path) over the corners! How about warped space so that close to the surface you can't perceive the cubeness and it seems flat, but connected like a spread-open box. Even light turns the corners. They would seem to be on a flat world, but the sky would look odd. Later large-scale measurements would allow the inhabitants to discover the true topology. Later still they use a fleet of hamiltonian satellites to build their GPS system. Move over, Rincewind. ]
[Question] [ Okay, so based on some quick research, there don't appear to be any real-life cases in genetics of "circular dominance" where, for example, allele A is dominant to allele B, B is dominant to C and C is dominant to A, sort of like a genetic game of rock-paper-scissors. However, what I'm wondering is whether there's any reason such a system would be impractical/implausible. Can anyone share any insights on that? As a side note, I'm also curious to whether the prevalence of the different versions of the trait controlled by such a gene could reasonably remain skewed in favor of one form. (Drawing from the previous example, say, the phenotype that results from an BB or BC genotype being considerably more common in the population of the species than the other two manifestations of the trait.) Added Details: The species in question is diploid, so at most a given individual will have two of the three alleles, so three-way interaction in a given individual isn't an issue. In the particular case of the setting I'm working on the A-phenotype individuals are baseline 'normal' members of the species, B-phenotype individuals have a supernatural ability that causes them to be almost impossible to kill by violence (they die, but regenerate nearby good as new), but which makes them reckless and often outright adrenaline junkies, and C-phenotype individuals have a capabilities that make them superior combatants, but gives them a physical dependency on the flesh of other members of their species. Phenotype C is often discriminated against, but not outright killed on sight, because the B phenotype provides a source of flesh without anyone getting permanently hurt. [Answer] # Gene regulating protein with differing binding site: Your gene produces a protein that up-regulates the expression of other genes. Each allele has a slightly different binding site, and thus causes the other genes to be regulated differently. The three versions of the protein compete for overlapping but slightly different binding sites on the regulated gene. Site (a) binds the A protein, is a weak binding site but highly up-regulates the gene. Site (c) binding up-regulates modestly, but is a tight binding site for C and the binding site overlaps with (a). Site (b) binds B and is also a strong binding site but only weakly upregulates the gene. The (b) site overlaps the (c) site, but not the (a) site. * AA results in high protein production and the A phenotype * AB results in high protein production from (a) binding, and the contribution of (b) is insignificant. This results in the A phenotype * BB gives a low level of expression and the B phenotype. * BC causes the (b) and (c) sites to competitively inhibit each other, so the net result is overall low expression and the B phenotype. * CC causes intermediate expression of the gene and the C phenotype. * AC causes competition for the (a) and (c) sites. Since the binding to the (a) site is weak, and any successful expression from (a) binding effectively reverses the effects of the competition, the overall expression level is intermediate and results in the C phenotype. [![enter image description here](https://i.stack.imgur.com/AH1Hv.png)](https://i.stack.imgur.com/AH1Hv.png) There are additional similar regulatory schemes that will have similar results. The addition of tissue or developmental cofactors would allow the genes to have significantly different effects so the phenotypes you want are at least plausible (if we handwave the whole "superpower" thing). [Answer] **Plausibility**: There is no reason why such a system couldn't work in principle. [DWKraus's answer](https://worldbuilding.stackexchange.com/a/236572/98856) outlines one way, and I outline another way below. So if it can work in principle, why couldn't you find any examples? One reason might be that there are simpler ways of getting three different phenotypes from a single locus, which might therefore be more likely to evolve in the first place. For example, the alternative mating strategies among male *Uta stansburiana* lizards—which themselves follow a rock-paper-scissors dynamic—are controlled by a [single locus](https://en.wikipedia.org/w/index.php?title=Common_side-blotched_lizard&oldid=1097507348#Physiology) with alleles *o*, *b*, and *y*, where *o* is dominant to both *b* and *y* and *y* is dominant to *b*. Hence the orange phenotype is either *oo*, *ob* or *oy*, the yellow phenotype is either *yy* or *yb* and the blue phenotype is *bb* only. (Phenotypically, orange beats blue, blue beats yellow, and yellow beats orange, due to the alternative behaviours exhibited by males of each colour.) So just to be clear, having three different phenotypes, even if they themselves exist in a rock-paper-scissors nontransitive relationship in terms of competitive fitness, does not require any nontransitive dominance relationship at the genetic level. **Skew**: There is no reason why such a genetic architecture would necessarily prevent one phenotype from being more common than the others. Let's say the alleles are called *R*, *P*, and *S*. Suppose that both *RR* and *RS* individuals are phenotypically "Rock", *PP* and *PR* individuals are phenotypically "Paper" and *SS* and *SP* individuals are phenotypically "Scissors". Any combination of "Rock", "Paper", and "Scissors" individuals is possible with such a setup; this is trivial since we can just stipulate that, at a given time, X% of individuals are *RR*, Y% are *PP*, and Z% = 100% - X% - Y% are *SS*. But more generally, if we assume random mating between types, there are two degrees of freedom in the system (the proportion of alleles at the locus that are *R* and the proportion that are *P*, with the remaining proportion all being *S*) and these two degrees of freedom are sufficient to produce any combination of X%, Y%, and Z% = 100% - X% - Y% as outlined above. The question then is whether any given proportion of the three phenotypes in the population can be maintained stably, particularly in the case where the different phenotypes mate with each other and hence heterozygotes are common. If the proportions are being maintained by negative frequency-dependent selection, such that, for example, the fitness of phenotype-"Rock" individuals is higher than average when there are fewer than some optimal proportion of "Rock" individuals (whether that be 33% or anything else), and the fitness of phenotype-"Rock" individuals is lower than average when there are more than the optimal proportion of "Rock" individuals, this leads to a stable maintenance of that optimum frequency. That's because, provided there is at least one homozygote in the population (in this case *RR*), the average "Rock" individual is more likely to pass on the *R* allele than any other allele (since they are either *RR* or *RS*), so if the frequency of "Rock"-phenotype individuals is below its optimum, the result is that the transmission of *R* alleles increases above the average transmission of other alleles. Similarly for *P* and *S*, therefore, a stable mix of phenotypes can be maintained. Note that, in order for an intermediate mix of phenotypes to be stable, you still have to explain what leads to the negative frequency-dependent selection in your population. Or maybe the three types live somewhat separately, so they aren't competing fully for the same resources. # Biochemical rock-paper-scissors There is a number of ways of getting nontransitive dominance among three possible alleles at a diploid locus, so as to resemble the rock-paper-scissors game. I think the most fun way is just to follow the logic of rock-paper-scissors itself! In other words, let's call the three alleles *R*, *P*, and *S*. They are translated into proteins Rock, Paper, and Scissors, respectively. Each of these proteins has an active site, which does the actual work of producing the alternative phenotype. Hence, homozygous individuals (*RR*, *PP*, or *SS*) have the phenotype corresponding to the allele they are homozygous for. Each protein also has a secondary site, which plays some role in interaction with other proteins. In *PR* heterozygotes, Paper's secondary site binds to Rock's active site. This blocks Rock's active site from doing any work, while leaving Paper's active site exposed on the outside of the Paper-Rock [dimer](https://en.wikipedia.org/wiki/Protein_dimer). Paper covers Rock. (If Paper is at least as highly expressed as Rock in heterozygotes, then all Rocks could be covered by a Paper.) In *RS* heterozygotes, Rock's secondary site allows it to act as a kind of [chaperone](https://en.wikipedia.org/wiki/Chaperone_(protein)) causing Scissors to fold up into an inactive, mangled mess that can't unfold itself. Rock is unchanged by this interaction and remains free to do other work via its active site. Rock breaks Scissors. In *SP* heterozygotes, Scissors' secondary site [cleaves](https://en.wikipedia.org/wiki/Proteolysis) Paper into an inactive form. Scissors is unchanged by this interaction, and remains free to do its own thing. Scissors cuts Paper. Paper cannot cover Scissors because it only binds to Rock's active site, not Scissors'; and Rock can't break Paper, nor can Scissors cut Rock, because these interactions are specific to the very different shapes of the three proteins. [Answer] **I up voted L.Dutch's answer and you should too, but let's look at this in a different way** Let's assume alleles A, B, and C lead to traits that are valuable for survival *for different reasons.1* In other words, your rock-paper-scissors genetics game becomes unusually *environmentally biased.* I wholly agree with L.Dutch's assessment of the problem should A, B, and C appear together, meaning the body becomes susceptible to a tragic weakness because the recessiveness of the alleles are constantly exerting themselves. Or, on the flip-side, none appear at all in which case the poor soul is dead and the condition never passed on. But in the case where the environment favors A, B, or C, that resolves the rock-paper-scissors problem2 while allowing the other two alleles to remain subdued or dormant. **But this means there is an impracticality... and it's not a bad one IMO** It means that migration is *minimized* because there are environments where, for example, C can't be. Your circular dependency would result in three very separate races of people. Which also suggests that A and B folks can't easily breed because each generation spent apart reinforces the dependency on the associated allele, right? It's almost like blood types where (for example and not necessarily a specific issue) allele A people can't give blood to B people because it would kill them. And so on. --- 1 *Reasons that I'm not going to hazard here. That's your job.* 2 *Call it JBH's "magnet under the roulette wheel" method of genetic selection.* [Answer] It seems reasonable to suggest this could exist, even if we know of no real life examples. Within an organism there are long chains of chemical reactions which more or less terminate with the final chemical affecting the reactions of the first chemicals. They are self regulating. Systems in biochemistry already do this in principle. # Cycling Phenotypes Outside of the organism you must consider the species. Perhaps a generations long cycle of sorts could utilize such a genetic scheme. As suggested elsewhere, any cycle in the species must be in response to the cycles in its environment, so this cannot exist alone. My first thought is that competing species *both* use the scheme. A prey evolves, the predator evolves in response. This action could lead to *more* environmental stability if your genetic scheme evolved in somehow. Predator phenotype A is well suited to hunt prey phenotype A, but not so well prey phenotype B. Predator phenotype B hunts prey phenotype B well, but not prey phenotype C. And so on down however many links you want. The effect would be a species that cycles through phenotypes. Honestly, I could see this totally existing in real life life, especially among insects, and the only reason we haven't noticed is that it would take a decades long study to show it exists. # Phenotypes for the Super-organism Between species and organism is what some have called a super-organism. The typical beehive is a great example. Rather than depending on haploid and diploid schemes to produce drones and workers, your proposed genetic scheme produces the phenotypes the super-organism needs. I envision that this would not be a queen-type super-organism, but that most individuals within the super-organism reproduce regularly. Just like the biochemical chains that we know exist, the presence of the final link in the "phenotypes chain" is recessive to the first. The needed phenotypes are self-regulated. # Opinion on using these in story The first solution has the problem of being a very long lived cycle. There wouldn't be many phenotypes sharing their existence with others. I have a hard time seeing how that might create an interesting story. The only thing that would make sense is some kind of commentary about how sons are and should be different from their fathers, yet, ironically nothing is new and old things that used to work can still work today. The second solution allows you to have all the phenotypes coexisting. That kind of stuff certainly makes for exciting scifi. However, from a realistic perspective, the chain nature of the scheme makes every single phenotype a well tuned vital necessity to the super-organism's survival. One blip in any phenotype affects the whole chain for many cycles. We see this same problem in biochemistry, and it can take years to reset those systems and bring people back into health. Compared to the haploid/diploid scheme that honeybees use, this phenotype chain seems a good deal more delicate. There's also a fundamental difference that might stand out to your readers. In biochemistry these chains are a function of consumption. They are all metabolism; the processes by which healthy tissue is maintained so as to consume more energy. The final products do affect the first products, but there are waste products all along the way. In genetics, replication is the only function of consequence. It's not a metabolism. [Answer] > > for example, allele A is dominant to allele B, B is dominant to C and C is dominant to A, sort of like a genetic game of rock-paper-scissors. However, what I'm wondering is whether there's any reason such a system would be impractical/implausible. > > > Let's say that an individual has A, B and C together. None of them would be expressed, due to it being recessive to another. The individual would therefore lack a gene. We are then left with two options: * If the gene is not needed for the survival of the individual, it will be removed because keeping it it's a waste of resources. * If the gene is needed for the survival of the individual, then they will be dead and unable to transmit the feature to their posterity. ]
[Question] [ Before we begin, I know full-well that the answer changes based on the time-period, size of the estate, number of people being taken care of, amount of money available, and so forth. **A correct answer would be able to give a [resident:staff] ratio or an accurate algorithm/formula to give an easily adjustable answer for needs beyond my own, both solutions offering a simplified break-down of what roles would be held by the staff.** # What is the minimum number of staff members of each role (butler, maid, cook, groundskeeper, etc.) to keep a Medieval estate running smoothly? --- ## The following should be assumed. * We are in the European late medieval period (where female staff were now more common than previously in case this makes a difference) * Use the modern-day United Kingdom area as a basis for any regional specifications if necessary * The estate is actively in-use * The estate is of sufficient size to house 100 people in separate rooms * Of those residents, assume 50 are men and 50 are women (for the sake of simplicity) and all are equal parts owners of the estate (despite that concept being an anachronism) [Meaning: There are 50 lords and 50 ladies of the estate.] * The staff live on-site in shared rooms equipped to house the minimum number of staff, the number of staff per shared room being within-reason for the time * The estate has the standard luxuries like a ballroom and so forth * The estate has formal gardens, but no farmland of its own * Neither money nor resources to finance/support this are an issue * No military force (such as knights) is necessary * There is no surrounding town, but that is not to say you cannot get to a town if you were to travel a short while by carriage --- ## Staff Roles to consider (*Thanks to Alex P. for suggesting some staff I would never have thought of, and this list is mostly pulled from him/his source.*) Grooms, Maids, Butlers, Cooking Staff, Stable-Hands, Maintenance Staff, Sewers (Servers), Steward (Overseer), Gardeners/Groundskeepers, Cleaning Staff, Carriage Drivers, Secretaries, and Couriers. *I am listing what appear to be the most necessary roles for the core functionality of an estate. That said, an answer that excludes staff from these roles or includes unlisted staff is not inherently an incorrect answer as long as you show a reason for your assessment. I may be wrong in my assumption that all these staff roles are necessary or that only these roles are necessary and this list is subject to adjustment. Please, do not downvote others on the basis of included/excluded roles alone.* --- ## Requirements for a correct answer * Gives a ratio of [Residents:Staff], algorithm, or formula with a breakdown of necessary staff roles by numbers * Should not include any of the following: magic, modern/futuristic technology, demons/supernatural elements, MacGuffins, 7-headed chartreuse ostriches with naturally occurring lizard skin hats, and so on. *I just want an as-close-as-possible to real-life view without consideration of these things.* --- > > I understand that some of the details I've given would be improbable/impossible from a real-world historical perspective, but I just want an as accurate as possible answer that can be easily worked with. If this question is presently unanswerable or unclear, please leave a comment saying how I can narrow this down and I will narrow it down in my next edit. > > > - > > Alex P answered an earlier version of this question and his answer will be evaluated to reflect that. > > > [Answer] First of all, let's start with a rough *classification* of the people living in the palace: 1. The gentlepersons for the use of whom the palace is run. The question gives their number as one hundred. 2. The personal servants of the gentlepersons, of appropriate sex -- grooms for the gentlemen, maids for the gentlewomen. They number *at least* as many, but some of the gentlepersons will also have secretaries, aides, and so on. The personal servants of the gentlepersons are not counted among house personnel; they use the services of the house personnel. So up to this point we have some 250 people who live in the palace. 3. The actual *staff* of the palace: butlers, cooks (and undercooks, and scullery maids), cleaning personnel, washerwomen, ushers, servers, footmen, stable boys, couriers, carriage drivers, gardeners and so on. Some of them (especially senior perosnnel) will also have families. By and large the palace staff will be about the same number as the gentlepersons and personal servants put together, maybe somewhat (but not much) less, maybe (even probably) more. So up to this point we have some 450 to 600 people living in the palace. 4. Optionally, depending on local customs and necessities, protection personnel, that is, men at arms. The everhelpful [Elizabethan.org](http://elizabethan.org/compendium/index.html) provides a digital copy of the [*Book of Orders and Rules*](http://elizabethan.org/book-of-orders-and-rules/index.html) written by Lord Anthony Maria Browne, 2nd Viscount Montague, in 1595, for the *"better direction and government of my household and family, together with the several duties and charges appertaining to mine officers and other servants"*. This fine piece late 16th century gentlemanly thinking lists 37 distinct roles (most of them for a single person, some for multiple persons), for what was a single-family household: and it includes mainly *male* staff, his lordship leaving the administration of most of the female staff to her ladyship: > > *1. Steward of the Household. 2. Comptroller. 3. High steward of the Courts. 4. Auditor. 5. General Receiver. 6. Solicitor. 7. Other principal officers. 8. Secretary. 9. Gentlemen Ushers. 10. Carver. 11. Sewer (server). 12. Gentlemen of the Chamber. 13. Gentlemen of Horse. 14. Gentlemen waiters. 15. Marshall of the Hall. 16. Clerk of the Kitchen. 17. Yeomen of the Great Chamber. 18. Usher of the Hall. 19. Chief cook. 20. Yeomen of the chamber. 21. Clerk of the Officer's Chambers. 22. Yeoman of the Horse. 23. Yeoman of the Cellar. 24. Yeoman of the Ewery. 25. Yeoman of the Pantry. 26. Yeoman of the Buttery. 27. Yeoman of the Wardrobe. 28. Yeoman waiters. 29. Second cook, and the rest. 30. Porter. 31. Granator. 32. Bailiff. 33. Baker. 34. Brewer. 35. Grooms of the Great Chamber. 36. Almoner. 37. Scullery man.* > > > The same web site gives an example of a larger household, namely the [Earl of Hertford](https://en.wikipedia.org/wiki/Edward_Seymour,_1st_Earl_of_Hertford)'s embassy to Brussels. It included: * *"20 Knights, 2 barons, and 7 gentlemen, plus their servants to a total of 90."* This gives a ratio of 1:2 for gentlepersons to personal servants. * *"And in the earl's personal train: 2 chaplains, 1 steward, 1 secretary, 1 gentleman of the horse, 2 gentlemen ushers, 1 harbinger, 1 master of carriages, 1 surgeon, 1 physician, 1 apothecary, 8 musicians, 8 trumpeters, 6 footmen, 10 lackeys, 6 pages, 3 wardrobers, 16 gentlemen waiters, 30 yeoman waiters, 30 kitchen, buttery, & pantry staff, 4 gentlemen of the chamber."* Overall, this example shows the 30 gentlepersons lived with 60 personal servants and 133 staff. ]
[Question] [ I am trying to write a sci-fi setting in a not so distant future in which analog signal (brainwaves, in this case) processing is one of the main points of the plot and pretty much required to explain some of the mechanics going on in the universe. Thing is, analog to digital conversion is expensive, and it may compress data into an easier to handle finite set of values that would, in exchange, make it drop some information in the process. This is something I don't want since some of the mechanics required to develop the plot require subtle differences in a person's brainwaves (in this case, used as some sort of biometric key). This last part can be avoidable by just throwing more resources at a regular digital computer, but that's lazy and something I don't want, as an analog computer could allow for more interesting details and implications. Just how viable would it be for the world to go back to analog? In the past, we had analog computers, but we changed to digital because apparently they weren't designed with programmability in mind (as in, they were like ASICs) and soon digital became better than analog so there was no reason to try to improve a deprecated technology. Likewise, most of our telecommunication devices operate on waves and analog signals, but they are translated to digital at some point of the process (ie. the modem) and lose all the properties an analog signal has. DARPA tried to build an analog "cellular neuronal network" CPU (project UPSIDE) for computer vision back in 2012, but there is not much information about it. Apparently, it allows for much faster speeds at a lower energy cost, at the expense of some errors from time to time and what has been described as requiring a much different way of tackling problems. Problem is, it says nothing about how programmable it is (which it apparently is, but it doesn't mention if it's Turing complete by itself or not). In addition, it seems to be a hybrid analog-digital computer, which is the concept I initially thought about including in my story. **In the future, could we see the following things? How superior would they be to their digital counterparts? Would they have any limitations?** * Purely analog CPU (could they run the programs we run today? As in, would they still be usable as a PC?) * Hybrid analog-digital CPU, where they complement each other depending on the problem at hand * Analog RAM/storage. May be digital-analog or purely analog. Could it be made persistent, like with memristors? How would this work, anyway? * Truly analog telecommunications. I know they are impractical due to possible signal noise, but let's assume we have a reliable solution to compensate that, such as algorithms capable of discerning the real signal * Holographic CPU? Both digital and analog. I know a digital optical CPU is viable in theory, but I have no idea about analog; I assume it could operate on light frequency/color or something. * Analog-oriented programming languages. How different would they be from the programming languages we use today if any? Could a uniform analog-digital language exist, where a smart compiler decides whether to use the analog CPU or the digital CPU in a fashion similar to what hUMA compiler optimizations already do? Mind you that while this setting isn't supposed to be hard sci-fi at all, it isn't fantasy science either. Whatever the answers are, they should be at least remotely viable in reality, and more specifically, doable within the following 70 years or less, although computer science could always do some breakthroughs. No suspension of disbelief should be required to enjoy the setting, even if you were somewhat knowledgeable about the field. *Note: I guess you could draw some parallels from analog computing to quantum computing since both seem to work best (or only) on probabilistic algorithms instead of deterministic, but this is not about quantum. Quantum technology exists in this setting, but it's extremely rare and only used in some specific contexts, not to mention most of it is extremely experimental and the general public is oblivious about the existence of the somewhat viable prototypes.* --- **Edit:** to be more specific, the context and use cases of this technology are that user input is now handled through some sort of a matrix of electrodes implanted into the brain, capable of reading the user's brain activity/thoughts. The software handling the output of this matrix already tries to transform brain activity into some sort of "universal brain language" that covers up the differences between human brains, but still requires an analog/real numbers/wave signal for fine precision (not as in error-free, but as in descriptive) and high throughput. Analog signals were chosen because the brain can easily recover from small errors and discrepancies and because it is more similar to the way the human brain works, but due to limitations of the feedback system, "lag" and slow transmissions is something that you would generally not want to get in your wetware, which is why digital signals were discarded: the electrodes array requires a continuous stream of data, so buffering and processing something to compress it and send it over the network would make the brain "halt" waiting for the next signal, essentially damaging your psyche on the long run (think of becoming deprived of your senses or getting mind-frozen in place every two seconds, which is what the digital transmission could do, compared to seeing some static in your viewport every few seconds, which is what you could get when on analog). This is also the reason computers perform operations on their continuous output analog stream concurrently, to reduce the time the user waits for a reply. It is also the reason all algorithms that directly read from the user wave are also concurrent: it is better to update the wave late than to halt it until the answer is processed. In addition, due to the nature of the brain, a thought or sequence of thoughts can be read and predicted as it is being formed, but can't be confirmed until it is fully formed. This detail is extremely important, as the plot device is based around this fact. Think of the exchange of information between a computer and a human as a regular conversation between two humans (it would be more like telepathy, but for simplicity's sake, let's assume they are just speaking). 1. *Computer is just patiently nodding as the human talks to it, representing continuous feedback* 2. Human: Del... 3. Computer predictions: I am 85% sure Human is going to ask me about deleting something. 4. Human: Delete... 5. Computer thinks: Deletion command confirmed. 6. Human: Delete file... 7. Computer predictions: I am 70% sure Human will ask to delete a single file. I am 30% unsure about Human asking me to delete a whole filesystem instead. 8. Human: Delete file /home/myUser/delt... 9. Computer thinks: File deletion confirmed. 52 files fulfilling the FILEPATH=/home/myUser/delt\* criteria detected. 10. Human: Delete file /home/myUser/delta.bwave 11. Computer thinks: Filepath detected. Request for the deletion of file /home/myUser/delta.bwave confirmed. Initiating deletion. 12. *Computer continues nodding for a fraction of a second before replying* 13. Computer: File successfully deleted. What really happened here is that the user made a request for the deletion of a specific file. As the user formed its sentence, the computer already started doing all the necessary preparations for its execution, much in the way we humans converse: we can identify a word by its lexeme before the word is completely formed, so we can more or less guess what will come next, but we can't completely understand the full implications of this word until we hear all the morphemes (if any). Likewise, we can try to make a wild guess about which word may come next and try to understand what the other person is trying to tell us, but we will not be sure about the specifics until the whole sentence is complete. Likewise, a single sentence might throw some light into the context of the topic at hand, etc. After the user's request was completed, the object vanished from the user's viewport in a fraction of a second. This point is extremely important because the hackers of the future will attempt to trick the machine into doing something else (or just bring it to a halt) by surprising it with some sort of "punchline" capable of surprising it. Since security programs are concurrent, they can't really understand the full scope of the user's actions until it's already too late. Think of it like setting up a trap for the enemy king in chess over several turns: most of the "illogical" movements made earlier start to make sense the moment your king is killed. The paragraph talking about cranes was actually talking about birds and not boxes, but the computer could have never seen that coming since it mostly operates on sentences and not contexts as big as a paragraph or small text; generally, the precision of its predictions are drastically reduced the bigger the scope is, although it can still operate in bigger schemes if specifically programmed to do so. To identify what the user's trying to say, modern CPU incorporates a neuronal network that allows the OS to retroactively make some sense of words after hearing a string of letters. More often than not this is abstracted from userland programs through the use of libraries and APIs, although they may get access to the wavestream depending on their permissions. The "biometric authentication" system I mentioned before actually operates on big segments of the stream. Since the automatic conversion to "universal brain language" reduces (not removes!) the variance between user brains, trying to identify a user by these differences alone is impossible (not to mention that the, although small but random, noise the line may have, such a level of detail would be impossible). This is why the user authentication software operates on a larger set of thoughts: it detects the approximate state of mind of the user (excited, angry, relaxed, etc) and "mannerisms" they may have. This is more or less the equivalent of the accent a person may have or stylometric analysis of their texts: it identifies them with a high degree of precision, but it's not infallible. Hackers may again try to disguise themselves as the system operator of a device by using meditation techniques to appear as if they were thinking like the legitimate user of said computer. This "universal brain language" I talk about would be more or less like any human language (such as English). It encodes information so everyone can understand it, but it's not digital because the way you speak it may say something more about your message than what the language can express. That means, in the conversation example, the user may be thinking of deleting as symbol A with modifying factor B, while the software translates it to symbol X with modifying factor Y (which may be equal to B, although I haven't thought of that yet. I don't think it actually matters). The modifying factor is what tells the computer that you didn't just think of deleting, but that it also seems to sound as if the user was somewhat distressed or angry: it is analog metadata that would be difficult to translate to digital without butchering its meaning. Here is where the CPU's neuronal networks try to take a guess about what does this metadata mean, much in the same way a human would try to guess what does that tone of voice mean; it may be easier to guess when the modifying factor is stronger. What I originally meant with this question is: **how could the CPU process this brainwave?** Could some technology directly operate on this wave through the use of analog operation programs or would convert to digital be required for all cases? Mind you that the CPU has a digital coprocessor that can process those problems where the analog computer can't process that well, although communication between these two may be slightly slower in the same fashion memory to on-die cache transfers are slow. **Could the analog CPU be a universal Turing machine, independently of how practical that could be?** Alternatively, if this isn't the case, **would analog emulation on a digital CPU (emulated neuronal network simulations, like a partial brain simulation) be the only way to tackle this problem?** In addition, **could information about a wave be persistently stored somewhere? Could said stored wave be actually stored as a wave and not as a "parametrization" of a wave?** [Answer] I very much enjoy playing with this topic, so I'm going to turn the question on its head. **Every computer made today is a hybrid analog/digital computer you just might not know it!** Modern clock speeds are so blindingly fast that we find ourselves doing analog signal conditioning in the middle of our supposedly digital equipment. Modern memory subsystems use analog techniques to crank as many digital bits through the pipe as they can. Physical traces along boards are routed to be the same length as other wires on the bus, and are structures line analog transmission lines on the CB. CPUs regularly have to be concerned with the rise of parasitic capacitance between its logic elements, limiting the "fanout" of one output to multiple inputs. Gigabit Ethernet actually relies on analog superposition of voltages to achieve its extreme speeds. Analog appears everywhere in computing, so its clearly not the hardware we're talking about when we discuss analog vs. digital. I think the more important distinction in the analog vs. digital world is found in our models of said computer subsystems. It's not that a CPU doesn't have mixed analog/digital on it, but rather the fact that we *model* our CPUs as though they were purely digital that really matters. We like to pretend our CPUs are perfect digital structures when we write thousands of lines of code to be executed on it. **The gap between analog and digital is in the minds of the developers more than it is in the actual hardware.** The hardware manufacturers embraced the analog part of their job a long time ago. **Accordingly, the viability of "analog" computing would be stoutly seated on the desire of programmers to answer questions which are best handled in analog.** Once the desire is there, the hardware manufacturers will happily expose analog behavior to them. Then the slow grind towards making *useful* analog behaviors would begin (this is where that DARPA effort fits in). So when is an analog model useful? The most important answer I can think of is meta-stability. Digital circuits really like to resolve to either a true or false state for every bit of information. In fact, if you give a half-way voltage to many digital logic circuits, you can actually enter trippy metastable states where the circuit can actually cease to behave as intended for an arbitrary amount of time after the half-way voltage has been resolved. At the hardware level, we spend a great deal of time preventing our logic circuits from ever "seeing" the metastable points as the voltages swing from low to high, typically using "clocking" to do so. Where would this be useful? One thing you mentioned was energy. Analog computing *can* be more energy efficient than digital because it can tailor its signal-to-noise ratios to the moment. Consider a digital number, in binary, 100001. This is the number 33 in decimal. If noise corrupts the leftmost bit, it becomes 000001, which is 1 in decimal. If noise corrupts the rightmost bit, it becomes 100000, which is 32 in decimal. In some situations, the difference in semantic meaning of 33 and 32 is pretty minimal, and you might be willing to accept some error in the rightmost bit, in exchange for being more efficient. You may be less willing to accept error in the leftmost bit, which changes 33 into 1. However, if that 33 is in an equation, say perhaps 33 - 32, suddenly that subtraction makes all of the bits important. The difference between a 1 or a 0 from that subtraction could be a very big deal! Digital models cannot implement such decision making, because they would have to admit an analog model underneath to do so. Meanwhile, your mind has no problem being an inch off when waving your hand left to right saying goodbye to someone, and then cranking up the precision to write something legibly. This would be very powerful if you were dealing with highly intricate parallel operations. Right now, if two processes try to write different values to the same location, they must be "deconflicted." One must win, and the other must lose. The process happens in a blink of an eye, far faster than either process was aware of. However, what if your two processes wanted to be smarter, and actually talk through their differences to determine what the final result could be. This would be a natural operation in an analog computer. In a digital computer, we have to go through many hoops to make that happen (and typically we just choose to fix the "race case" in its entirety and move on). One final point of metastability is its ability to be still. A circuit sitting in its metastable state can be ready to spring to life at the slightest sensation. Doing this in digital is hard, because the gaps between low and high signals are so large. We typically have to custom tailor digital circuits to pass these rapid fire signals, while an analog computer might handle them intrinsically on all signals. If a computer stops, it has to stop in a fixed state. Computation ceases. An analog computer can instead decrease the energy consumption more and more, driving towards a balanced state, while never actually stopping. Then, when the computer is resumed, it may have actually accomplished something while stopped! [Answer] In the future you might have a breakthrough in developing analog computers which emulate [the features and efficiency of a human brain](http://www.extremetech.com/extreme/185984-the-human-brains-remarkably-low-power-consumption-and-how-computers-might-mimic-its-efficiency). Much like today how a digital computer is paired with a specialized [GPU](https://en.wikipedia.org/wiki/Graphics_processing_unit) for graphics, the analog brain would have a digital CPU co-processor to handle the things digital computers are good at. In essence, you'd have a thing which could do the things humans are good at (pattern matching, estimation) which can reference a thing computers are good at (very fast, very precise math). Imagine a robot which could not only debate politics, but while doing so be performing the research and statistics necessary to weigh their decisions. You can exploit two features of analog vs digital computing in your world: heat and precision vs accuracy. And build around our decades long failure to achieve AI using digital computing, something we've felt we're on the cusp of since the 60s. I imagine a world where, as computers get more and more integrated into everyday life, machines with human-like thinking becomes more and more important and analog computers are better at that. Human brains differ from digital computers in a few key ways. Digital computers have to be designed, understood and built by humans, and humans like simple, orderly things. The human brain has evolved over hundreds of millions of years of trial and error and have no such restraint. As a result, human brains can do things in surprising ways. Digital computers are built by humans to be *simple*, they combine many, many of a few basic parts in novel ways. Human brains are very, very, very *complex* using thousands of specialized neurons each doing multiple specialized tasks and being reused and recombined in surprising ways. The result is a digital brain is predictable and precise, but at a cost of flexibility and efficiency, while a human brain is unpredictable and sloppy, but very flexible and very efficient. Your future society will need a reason to transition from precision and predictability to flexibility and efficiency. Digital computing does one thing really well: it very precisely, very predictably, and very quickly calculates *a certain subset of problems*. For other problems it will be appallingly slow. It will do exactly what you tell it to calculate and that's *all it will do*. And, as we all know, digital computers have a very hard time learning or dealing with anything new. As we all know it's very easy for even good AI to carry on a convincing conversation. The human brain, an analog computer, is sometimes very precise ([hitting a baseball](https://www.youtube.com/watch?v=KhpKr1YvyRM)), sometimes very sloppy (math and statistics), sometimes very fast (baseball and estimation), sometimes very slow (precise math), but it's going to give you an answer. And it can solve some problems much, much faster and more reliably than a computer can, for example computer vision, path finding problems, and pattern matching. It does it all very, very, very efficiently and *it can handle them all*. It is a truly general purpose computer. The same brain that can hit a fastball can do calculus, hold a conversation, run over obstacles, and cook a meal. The human brain is extremely efficient and we're nowhere close to emulate what it's capable of. Take, for example, the [Human Brain Project](https://www.humanbrainproject.eu/). Professor Steve Furber of the University of Manchester has this to say on his attempt, [SpinNNaker](http://apt.cs.manchester.ac.uk/projects/SpiNNaker/project/). > > With 1,000,000 [ARM] cores we only get to about 1% of the scale of the human brain. > > > The [ARM968](https://en.wikipedia.org/wiki/ARM9) they're using is not exactly top of the line, the [Nintendo DSi](https://en.wikipedia.org/wiki/Nintendo_DSi) uses one at 133Mhz, but speaks to how important parallelism and heat management is in modern computing and how bad we are at it. Here's a few of [Computerphile](https://www.youtube.com/channel/UC9-y-6csu5WGm29I7JiwpnA) videos on the subject. * [Silicon Brain](https://www.youtube.com/watch?v=2e06C-yUwlc) about the SpiNNaker. * [The Deadly Stamp Collector](https://www.youtube.com/watch?v=tcdVC4e6EV4) about innocently rampant AI. * [The Singularity & Friendly AI](https://www.youtube.com/watch?v=uA9mxq3gneE). * [AI Safety](https://www.youtube.com/watch?v=IB1OvoCNnWY) which speaks to why you'd need an AI that understands human values. [Answer] I actually worked on analog[ue] computers in my "gap year", around 1968, at Redifon (the industrial arm of Rediffusion, a cable company avant-le-lettre). I guess these were (at that time) pretty much state-of-the-art, but they were not that of which a [silk purse](https://en.wiktionary.org/wiki/make_a_silk_purse_of_a_sow's_ear) is made. I can't find images, but programming entailed plugging cables into a patchboard of about 100cm x 80cm, with maybe 50 x 40 sockets. A complete problem might involve 100-400 cables (think [this](https://i.stack.imgur.com/tXXjF.jpg)) not to mention several dozen pages of notes. Once you had a program working, it gave real-time answers to variations in inputs or parameters, with a speed and accuracy which the digital world only managed around 2000 (30 years later!) Debugging was one problem (there was no way to trace variables); and stability was another: if one of the op-amps (JFET inputs, bipolar outputs) went unstable then the entire computer became what we called a "Christmas tree" with all overload lamps flashing. So your questions: `analog CPU`: forget it. `hybrid CPU`: no idea. `analog/RAM storage`: theoretically possible with [super]-capacitors but not very practical. `Analog-oriented programming languages`: I really cannot see a bridge between wires on a patch-panel and the modern concept of programming. In your story, if you want to parallel real life, you would be better off to use analog-to-digital converters and have as many bits as you need to capture the finest emotions. [Answer] They have been tried before and they are worse than digital. MOSFET VS BJT So the core component of cpus and memory are electrical switches called transistors. There are two main types digital MOSFET transistors and analog Bipolar junction transistors. The reason computers are digital is because MOSFETS are much better. Analog circuits are only use when the circuit has to be analog. MOSFETS are more power effect since they only consume power when they 'switch' BJTs use power when ever the machine is on. MOSFETS can be made much smaller with out introducing errors because they have smaller leak currents. This means you can get 100s or 1000s of MOSFETS for the same power space and heat of a BJT. * analog CPU and RAM attempts were made using multilevel logic they were less effective then just more digital * there are hybrid analog digital processors, they usually take analog input convert to digital process it then convert back to analog output. Check out micro-controllers like the arduino. * current computers simulate analog numbers with floating point numbers and have special digital processors for simulating floating point operations. If analog processors got better they might replace floating point units in current cpus. In theory an analog data point contains an infinite amount of information if it can be measured with infinite precision, its 1.23245... volts the decimal digits in theory go on forever. But we can never use those points because there is random unpredictable noise. A huge part of the Electrical Engineering field is trying to cope with noise. Since the noise makes some of the the information use able, why not just start with a smaller less noisy data set. Information theory shows removing random noise from a signal is a really hard problem unless you already know the original signal. Optical is cool but is still 1000x too large and 1000x too slow to compete with standard cpus. I should just put this in perspective a current cpu has around 3 billion transistors that switch over a billion times per second, a major design concern is electrons have to have enough time to cross the chip between switches and sine they only move at the speed of light they only cover an inch or two in that time. The whole thing can cost under thirty bucks. Its hard to compete with that. [Answer] It might be worth considering what nature has done. "There's nothing new under the sun" isn't true but isn't very far off either. So digital computing seems to have come first. DNA, RNA, stop codons, an escape codon, epigenetic labelling, error detection and correction mechanisms inside every cell. It seems to have all the characteristics of a digital system. A one-base (bit) error can have no impact, or can completely change the organism (result). And then hybrid systems evolved. Nerves and neural networks. Brains. We do not fully understand them. A single neuron accepts many analogue-ish inputs from other neurons and seems to generate something like a weighted sum of its inputs. If that sum passes a threshold the neuron "fires". The cell is bistable, binary, firing or not. The weights are modified by the firing of connected neurons. And in a brain neurons are elements of an absolutely enormous network. Synapses, the connections between a neuron's output and another neuron's input, are complex molecular systems. Not simple analogue. Thermal-noisy. Possibly, more quantum-magical than merely noisy. Beware anyone who says single synapses are simple and well understood. What is missing, are pure analogue systems without hysteresis. Nature's systems, if they react to analogue inputs, always seem designed with trigger thresholds that are greater to cause them to turn on than to turn off. Not unlike a plain ordinary electric switch. No halfway. Pure analogue computers? Gut feeling, not useful except for very restricted problem domains. Hybrids, brains intrinsically superior to digital CPUs? Open question. [Answer] I remember this example from a long ago article in Scientific American because it was so completely counter intuitive (On the Spaghetti Computer and other Analog Gadgets for Problem Solving," in the Computer Recreations Column (1984) <http://www.scientificamerican.com/article/computer-recreations-1984-06/>). Analogue computing can be, in many instances, faster than digital computing, but apparently only in the actual processing. Input and output required a lot of work and could be time consuming. The example given was a "spaghetti computer". If each strand of uncooked spaghetti was cut to a different length corresponding to inputs, in theory you could make a computer by assembling the lengths of spaghetti in you hand corresponding to the inputs and slamming the bundle "end on" into the counter. The answer would be derived from the pattern of high and low spaghetti ends sticking up from the other end of your hand from the counter. So you will have spent minutes or hours cutting and assembling the lengths of your spaghetti computer, and may have to spend some time looking at the "output" to understand the answer, but the actual act of "computation" takes the fraction of a second to slam the spaghetti bundle on the ground. While this seems a bit pointless (and scaling up to solve really big problems with a "Super Spaghetti Analogue Gadget" will also be difficult and messy, until you boil it down for the post computational dinner party), analogue computers are potentially viable for solving NP complete problems that would lock up digital computers for eons. So the real crux of the matter is what sorts of problems are being solved for that require the special attributes of an Analogue computer. Unless you are trying to solve for some sort of NP complete problem or avoiding the "halting problem" of a Turing machine, digital computers have been refined to a very high degree of power and accuracy. The only other huge advantage of an analogue machine comes from the fact that most examples I have ever heard of are essentially mechanical or electrochemical in nature, so they will not be affected by power spikes, EMP and other environmental factors which can disrupt digital computers. [Answer] Not answering all your points, but... **Analog CPU running the programs we run today**, no (as already answered). Analog computers were not designed for step-wise sequential operations; they were designed to solve specific classes of largely mathematical problems. **Hybrid**, sure... no reason a digital computer couldn't be interfaced to an analog computer, though there may not be a lot of benefit in doing so. **Analog RAM**... maybe not such a great idea. For example, storing a quantity as a charge can work, until it leaks down and the value you read out is not the same as the value you stored. Pretty much any other concept you might think of for analog storage would be vulnerable to distortion or loss of the stored information. Analog ROM on the other hand is totally practical - the good ol' phonograph master. **Totally analog communication** - totally practical. That's how we did things up until the 1970s for voice and up to at least the 1990s for video. Even digital data originally went down the wire as analog tones. [Answer] I'd like to take a different tack: In an analog general purpose computer... how do you make a NAND gate? The reason general purpose computers are so flexible is the fact that every single piece of the logic inside can be created from a single element: the NAND gate. Inverted And. This provides functional completeness... any and all other logic functions can be built with just NAND gates. Now, you can easily make more space and power efficient gates to do those other logic functions... but the key is that everything can be boiled down from one concept, and from that concept everything else can be built. So what's the analog equivalent of a NAND gate? I could imagine a merging between analog and digital circuits; we do this kind of stuff all the time. You've got a sound card... that's what it does. Old timey video cards used to output analog signals for video. Wifi has to translate between electromagnetic waves and digital signals. A layer of analog circuits would filter data, which could then be processed blazingly fast on a digital general purpose computer. The power of the future seems to be the merging of analog and digital, embracing the strengths of both and cancelling out each other's problems. We solve problems in different ways... but Google's assistant voice recognition is amazingly accurate these days. Sure, it uses a massive database of records to identify speech, instead of using a finger sized wad of meat... but that's playing to digital computing's strengths. Processing billions of pieces of data in a blink of an eye. [Answer] Yes it is possible to design a CPU that is 100% analog. 3d imaging isn't that hard. What is hard is convincing people that the fact that they believe everything they've been told about analog computers is exactly why no one has managed to create a full fledged analog CPU in the commercial sector. It's laziness and incompetence. 3d imaging can basically already be done. If you just look at some of the old analog video boards that would be able to "skew" and "stretch" broadcast images in the old days at tv news stations, that's basically it. A simple polygon would just need a few extra inputs and options to skew it properly, and then add more polygons to the screen. It's that simple. Except you can have a high resolution image and you wouldn't be worried about pixels, and it would be really cheap. There's an old example of a analog computer running a physics car/terrain simulation on youtube. It's 2d but then again, it's basically just a stock analog CPU. Here it is but it doesn't show the actual car, wheels or road in this one. <https://www.youtube.com/watch?v=AEJtajaRj_s> [Answer] Analog computers are vastly more power efficient, and are slowly gaining more attention as machine learning matures. <https://ieeexplore.ieee.org/document/8490883> <https://phys.org/news/2018-06-future-ai-hardware-based-analog.html> "Analog techniques, involving continuously variable signals rather than binary 0s and 1s, have inherent limits on their precision—which is why modern computers are generally digital computers. However, AI researchers have begun to realize that their DNN models still work well even when digital precision is reduced to levels that would be far too low for almost any other computer application. Thus, for DNNs, it's possible that maybe analog computation could also work. However, until now, no one had conclusively proven that such analog approaches could do the same job as today's software running on conventional digital hardware. That is, can DNNs really be trained to equivalently high accuracies with these techniques? There is little point to being faster or more energy-efficient in training a DNN if the resulting classification accuracies are always going to be unacceptably low. In our paper, we describe how analog non-volatile memories (NVM) can efficiently accelerate the "backpropagation" algorithm at the heart of many recent AI advances. These memories allow the "multiply-accumulate" operations used throughout these algorithms to be parallelized in the analog domain, at the location of weight data, using underlying physics. Instead of large circuits to multiply and add digital numbers together, we simply pass a small current through a resistor into a wire, and then connect many such wires together to let the currents build up. This lets us perform many calculations at the same time, rather than one after the other. And instead of shipping digital data on long journeys between digital memory chips and processing chips, we can perform all the computation inside the analog memory chip." [Answer] ### Storage With analog computers you wouldn't be able to reliably store information, since you would always change the analog signal upon measurement or just because there was a little bit of noise, not mentioning that you'd need to invent a way to store it in the first place. The reason we use digital signals is because you can have, for example, either 0V or 1V and if the voltage deviates a little bit then the system still recognizes as the correct one. However in your question you ask for an analog system that can notice subtle differences in a person's brainwaves. ### Solution What you are after is an [expansion card](https://en.wikipedia.org/wiki/Expansion_card) which would take care of the analog information and find a way to store it perfectly in digital form (for example it could recognize every simple wave that composes a complicated wave and store those which would be easily stored). You could even introduce this expansion card with a cool name like **Brain Card** and never actually explain how it works (or give a simple explanation like I just did), just that people buy it and use it to store their brainwaves with 100% accuracy. ]
[Question] [ Details: A culture of dryads has a strange death tradition. When a dryad dies there's usually a medic, or better say a "shaman" that rips a strange looking organ or gland off their head. The gland, shiny and the size of a hand, is then grafted into a tree. After several centuries the tree is able to finally release a fully grown child using only the gland from the old dead dryad and minerals from the ground. The dryad will have most of their memories intact after being reborn. I'm not asking if this is realistic, or plausible. I'm asking if the "gland" or any organ can force the tree to get the needed minerals off the ground and slowly build a humanoid child over the course of centuries. Why this question? I wanted to make dryads immortal while avoiding over overpopulation and other problems related to immortality by allowing them to die and come back as the same entity but younger after some centuries. Question: Can humanoids be born (reborn) from a tree? [Answer] For various values of "dryad" this is entirely possible. Look into [agrobacterium tumefaciens](https://en.wikipedia.org/wiki/Agrobacterium_tumefaciens) for inspiration. Those bacteria alter the DNA of their host plant to create a tumorous growth. Look into [gall wasps](https://en.wikipedia.org/wiki/Gall_wasp) for an example of induced growth that has to do with growth vectors/plant hormones and possibly RNA/DNA viruses - this growth is much more structured than that effected by agrobacterium. So inducing a plant to grow some new organ, that is fed and protected by the plant, while inside a new dryad ripens - absolutely possible. It would need some genetic vector (see the bacterium, but also many viruses), some chemical coaxing (which could easily be done by an entity as big as a hand) and the plant would be clay, waiting to be shaped. [Answer] **Sure...** One would assume that the symbiotic relationship between dryad and tree evolved (or was magically/divinely created) that way. Therefore, it's not just *any* tree this will work with, but a specific tree. This is actually a good thing for your story because limited resources are always useful as crisis-creators during the story. Given that the symbiotic relationship exists, the tree's genetics are wired to react to the presence of the gland. One could say the gland injects a protein into the tree to trigger the genetic response. At that point, the tree starts drawing nutrients as it always does, both from the ground and from sunlight (very appropriate for a dryad). The gland metamorphosises into a cocoon, which in turn metamorphosises into a new dryad. This is also useful to your story as the dryads likely have a hereditary disposition to defend/protect the cocoons. In the due course of time, the cocoon unwraps to release a newborn dryad and then falls like any other leaf. [Answer] Possibly. Trees grow flowers and fruits, so if somehow the tree was altered where the instead of flowers and fruit, it grew embryos and had a sac to hold them until they matured. [Answer] Most parasitic or symbiotic lifeforms work this way: the host provides resources for the lifeforms to grow an reproduce. *Mistletoe* is a simple example of nutrient extraction of the host tree. On a more impressive scale, *Toxoplasma* make infected mice and rats behave in ways that make them easy prey for cats – the later being the hosts where *Toxoplasma* will reproduce itself. Once nutrients are available, the process of transforming them into a complex lifeforms is nearly routine, as we all went through this process starting from a single cell. Centuries seems a long time, but the biology of Dryads and their hosting trees is speculative at best, so who knows? A side question would be if the relations between dryad and tree is purely parasitic or symbiotic. Hosting growing dryads may benefit to the tree, as other dryads may take car of it and protect it from predators or diseases. ]
[Question] [ Suppose a species of obligate carnivores had convergently evolved human-level intelligence and body plan. How would this affect their agriculture/food production, and would it lower their maximum population [Answer] Before asking such questions, you should provide as much information about the physiology of your species as possible. Even tiny differences can be very important. Obligate carnivores include species as diverse as tarsiers and lions! That being said, I will offer some guesses. ## Settlement Your people have no direct incentive to discover agriculture. Though it has recently been disputed, it has long been assumed that settlement was mainly driven by the discovery of agriculture. If we subscribe to this theory, your people may never form an urban culture. They might favour smaller social groups, even very small ones. Other cultural aspects intimately tied to settlement will also be impacted. I am especially thinking about stone architecture and sophisticated professional specialisation. If your typical community never exceeded a certain size, everyone will be an allrounder. Technical skills might advance much slower than in our history. That of course only applies on average. Such a society should experience industrialisation much later than ours. Due to the lesser degree of specialisation, it might also feature less trade, but that effect might be balanced by a migratory life style, i.e. going from place to place one always finds some good that is rare elsewhere. If you reduce industry and possibly trade your interest in financial services should be minimal. Even money might come up late, not to speak of banks. Of course, your people might discover agriculture as a way to feed domestic animals. Yet I think it's bound to happen much later than in our society. Unless you introduce special dependencies upon a herbivore (extreme example: symbiosis)! Alternatively, settlement might arise from the need for defensibility. Either against other predators, or hostile groups from the same species (see last point). If you make your species weaker you give it incentive to form groups, settlements or alliances with other species, thus softening many aspects of the above description. Weakness is clearly relative! Think of the [Krogan](http://masseffect.wikia.com/wiki/Krogan) on their dangerous home world. ## Hunter Priorities Given number one, and assuming a difference in phenotypes similar to humans, where one gender makes better hunters, the other gender is expected to occupy a significantly lower position and be strongly dependent upon the first. Harems are thus likely. Of course gender might not affect hunting prowess. Lionesses are fabulous hunters. You have given us too little information. ## Energy efficiency It is inefficient to convert plants to meat and then eat them. Assuming roughly human physiology, your people will need more land per capita. This, like the first point, suggests smaller groups. ## Social behaviour If your people are dependent upon nobody but their hunting partners, they might well be indifferent towards random members of the species and hostilities might be especially pronounced. Even the likelihood of cannibalism might be higher. If the social development happens to take this path, warrior archetypes will gain prestige along with hunters. Religions will, when they form, reflect those preferences. We should not expect to see harvest gods and gods of fertility will also be of secondary importance. Edit 3 years later: As correctly aluded to in the comments, in 2019/20 we often hear that most of our assumptions about alpha males, hierarchy, infighting in packs … are wrong and based upon our observing animals in captivity as opposed to natural packs/families. This was unknown to me in 2016. According to what I hear in 2020, for a pack of wolves it is typical to consist of parents, cubs and the cubs from the previous season. Therefore I have removed the speculations in the previous edition. [Answer] There are few human societies, where people have to be carnivores - because agriculture is nearly impossible, only hunting, gathering and fishing. For example, [Chukchi people](https://en.wikipedia.org/wiki/Chukchi_people). [![Chukchi people](https://i.stack.imgur.com/GzgaR.jpg)](https://i.stack.imgur.com/GzgaR.jpg) I think you can model your society on existent human societies that live in polar regions. Shortly, they count people from southern regions who perform agriculture as lesser beings, and themselves - as apex predators and pinnacle of evolution. [Answer] The way I have heard it stated before, one of the best potential analogues for a sedentary society of obligate carnivores would be many of the cultures of Greece, the Levant, etc. These cultures were largely based around sheep-rearing, though it is not a perfect analogy as they did also plant crops (e.g., olives) and eat vegetable matter in their diet. Believe it or not, a society of carnivores would probably be *less* likely to engage in wide-scale warfare and aggressive behavior than one of omnivores or herbivores. This is because to carnivores, any declaration of war has a high opportunity cost. It takes a lot of time and effort to raise meat to a point where it is viable to harvest, and mobilizing your society to go to war means you have large numbers of people not tending the flocks (and therefore potentially losing head of livestock, fewer people to maintain the herds, fewer people to help butcher livestock during the harvest for winter, etc.) You see this a lot in decision-making in warfare in sheep-herding cultures, there is often a lot of handwringing in historical or near-historical accounts about getting back to tend the flocks before harvest. Any declaration of war has a much greater risk of reducing the harvest for the year, beyond the normal risks of war on the economy of any species. You see this in non-sapient species as well. Carnivores, as a rule of thumb, are cowards who will not pick a fight unless they think they can win and will often abandon the attack if they lose the element of surprise. The reason for this is simple cost-effectiveness, if they can't win easily and get wounded in the process, that severely restricts their ability to find food and survive. Herbivores, on the other hand, can afford to be very aggressive (and tend to be more aggressive than carnivores), as if they get injured they can simply eat plants (which don't run away) until they heal from their injury. They are also more likely to get in fights because they live in larger groups and hence often adopt aggressive behaviors to find mates, etc. This is why in Africa hippos, elephants, and cape buffalo are often more dangerous than lions, hyenas, and leopards. Carnivore fights in general tend towards posturing and a few half-hearted swipes before one individual runs away than real or even ritualized combat that you see in herbivores. Livestock raising is also a lot more labor-intensive than planting crops because, well, crops don't wander off, you don't have to keep the herds moving to greener pastures, you are more likely to get diseases from your livestock, etc. Yes, issues with raising plants like crop rotation and pest protection are things, but they mostly involve the same plot of land that you can easily keep track of. Population density would be a lot lower. A carnivore takes ten times the amount of plant matter to feed than a herbivore as general practice, because it has to go through a middleman of livestock first. This can be seen analogously in human societies, the invention of widely edible grains (corn, wheat, rice, etc.) allowed human populations to balloon and population densities to skyrocket in many areas, whereas a hunter-gatherer diet of meat and whatever fruits and wild plants you could find is much less cost-efficient and exists at much lower densities. Even herding livestock or acting as nomads, the density of a carnivore species would be a lot lower than most human societies. **tl;dr: carnivores would be surprisingly passive, watch out for the herbivores** [Answer] What you describe in your question looks very close to a human society, with the difference that people just eat meat and that they evolved from carnivores instead of primates. Then the most simple answer is that such a human-like society would evolve to produce meat in the most efficient way (just as our human societies evolved to produce our mixed origen food as efficiently as possible), and the obvious way to produce food is husbandry. Then the main difference we could expect is that all available land would be used to produce food for domestic animals to produce meat. Since feeding animals with edible plants to get meat is a lot less efficient than just eating the edible plants, we could expect population to be lower than in our world - I would say 5 to 10 times lower, since that is the range for efficiency ratio usually given. Hunting could have been the most important way to get food in past times just as humans were hunter-gatherers for millennia but in a historical stage similar to ours hunting should be as marginal as a way of life as hunter-gathering is for present day humans. [Answer] They would start as nomadic hunters but as soon as they figure out that meats can be dried and stored for future use, a carnivore variety of agriculture revolution would begin. More efficient mechanisms for drying and long term storage of meats would be devised which would result in more specialized occupations and eventually settlements. People in the properly maintained settlements would be well fed and safe. After that, it's a slow but definite tread towards villages, towns, cities, newer discoveries/inventions and so on. Not very different from our world but with lower population density, and therefore lower total population size. [Answer] violence would be likely be less of a problem, social animals with deadly biological weapons usually evolve showy ritual like non-violent fighting because it's too easy to kill each other. expect eating to be more ritualized, eating order is important to predators. otherwise not that much different than omnivores. Morals would not be that different assuming they are K strategists.Although they would be far more likely to have an estrus period unlike humans. [Answer] Contrary to what many people think, we humans actually have more in common with the digestive system of a lion than we do of a deer (or even a bear). It is possible that a carnivorous race would also eat things besides meats. In the wild here on Earth, wolves, for example, actually eat berries and fruit. And researchers have learned that wolves can eat plants, although they can't eat just plants forever. They have to consume meat for proteins. If they are feline, then they can eat some plants, but they have to have meat in their diets as cats get essential proteins and vitamins from meat: <http://feline-nutrition.org/answers/answers-what-exactly-is-an-qobligate-carnivoreq> In other words, it depends on whether they are an obligate carnivore or not, however, in your question you say they are. It is also possible that deities of hunting would hold high importance in such a society as well as deities of life, since if there is a drought or famine, then the people would believe that the god of life was angry or sick. Hunting trophies would hold great significance in this society as it would bring great honor to the possessors of such trophies. Another key thing that is possible is that the society would be highly spiritual believing in the importance of life. This might be confusing but if you take a look at certain societies and cultures in history (Native American cultures for example), a society of hunters may actually give respect to the life of others, making the murder of another sentient being a serious crime (unless done in self-defense). Of course, it might be difficult to explain to a society of obligate carnivores that their prey are sentient! [Answer] I can see a carnivore society initially developing similarly to Mongols or Native Americans, with a nomadic culture and most food being dried or freshly caught. There would be two different outlooks on religion, with one being religions that suppress hostile urges and the other glorifying them. However, with no knowledge of the terrain they live in this is very difficult. Here are three different scenarios. Jungle-Prey is abundant, and as a result animal husbandry is never really a thing. Since many jungle creatures are deadly, they build great stone ziggurats housing entire tribes Plains-Prey is abundant, but not overflowing. They build a society of villages and hordes of horsemen, with possible Romanesque features. Basically medieval England plus Mongols plus Rome. Tundra-??? ]
[Question] [ Some science-fiction books I've read (including more than a few by Ray Bradbury) have men from Earth living on Mars, walking around outside of enclosures. I know that this is currently not realistic, because Mars' atmosphere is [too thin to support human life](https://scifi.stackexchange.com/a/11166)1. Let's ignore temperature in this question, and just look at oxygen and pressure. **Problems with atmosphere on Mars:** * **Oxygen levels are too low** (no breathable air) * **Pressure is too low** (critical body liquids will boil away) So, my question is: **what can we do to Mars to give it a survivable atmosphere?** Could we just add (a lot) more oxygen or something so that we don't have to live on Mars in pods? In the interest of keeping this question within reasonable limits, let's limit this to current + slightly advanced technology (stuff we don't have yet but is almost certainly possible). ( *monetary cost is of no consequence* ) --- 1 *I googled to find a good source for that assumption of mine, but wasn't expecting a SE result!* [Answer] Oxygen is easy -- import/manufacture more and fill your atmosphere with it. The hard part will be in getting the atmosphere to begin with; if you can do that, the rest is just details. But here's the problem with a Martian atmosphere: Gravity. More specifically, Mars doesn't have enough of it. Martian surface gravity is $3.711\;\mathrm{m/s^2}$; that's only a hair under 38% of Earth's $9.78\;\mathrm{m/s^2}$. If you were to take Earth's entire atmosphere and transplant it onto Mars, it would quite simply weigh less, and you'd end up with a surface pressure of approximately 38 kilopascals (compared to Earth's ~100 kPa)1. At that pressure, water would boil at 75C at the surface (versus 100C here on Earth). So you'd have to keep the A/C cranked pretty high just to keep your oceans from boiling off! I can't speak to the other effects of such a low pressure (you're going to have all the effects of acute "altitude sickness" until you acclimate, if you even can acclimate to an Earth-equivalent altitude of ~25,000 ft...), though it seems to me that that would be extremely uncomfortable, to say the least. But there's an even bigger problem: Mars doesn't have enough gravity to keep that atmosphere. Mars' low atmospheric density is not merely a random happenstance; gassses have a tendency to float away. This is even true of planetary atmosphere, which [can escape into space](http://en.wikipedia.org/wiki/Atmospheric_escape). Mars is simply physically incapable of sustaining Earth's atmosphere, so your 38 kPa atmosphere is going to get even lower, which will drop your boiling point lower still; eventually you're going to end up right back where you started, with a 600 P surface pressure. (Note that I believe it will take a very, *very* long time to get back to this point, but you will lose a lot of atmosphere quite quickly, with the losses slowing down as there's less to lose.) Is there any way to make Mars livable at all? You'd pretty much have to construct a solid bubble, or some kind of protective shell at least, around the planet to stop the outgassing. And probably have to make it a pressure vessel so you can actually artificially pressurize the planet just like you would a spacecraft. If cost is truly no object, this could certainly be done, except that I'm pretty sure it's out of reach of modern science -- I don't think we have materials, let alone construction methods, capable of building something on this scale, even ignoring the airlocks necessary for spacecraft to reach the surface. And the raw materials! Even ignoring how much money you spend, you're going to have a *very* hard time just getting the materials to build something of this scale! You'd be much better off just building luxurious domes around your Martian colonies: same result, but on a scale that's at least marginally feasible. **Edit:** TimB in the comments below points out Venus, which has about 91% of Earth's gravity, yet a surface atmospheric pressure of around 92 *times* that of Earth (9.2 MPa)! I don't know what allows Venus to hold onto that much atmosphere, however I suspect the reason is that Venus' atmosphere is primarily composed of much heavier elements than Earth's; for example, Earth's atmosphere is nearly 80% nitrogen, which has a molar mass of about 14 g/mol, whereas Venus' is over 96% carbon dioxide with a molar mass over 44 g/mol -- more than 3 times as heavy, and composing 1.2 times as much of the atmosphere! Which brings up the possibility that if you could find a gas that's safe for humans to breath (and mixes fine with the oxygen) but weighs significantly more than nitrogen, you could potentially solve the problem of obtaining a higher atmospheric pressure by simply creating a heavier atmosphere! --- 1 There's a significant caveat here, and that's that I could not find any direct corroboration of my assumption that surface pressure would change in direct proportion to surface gravity. However, planets are not pressure vessels; what you feel as "air pressure" is literally the weight of the atmosphere above you being pulled down by gravity onto you. Thus I believe it is a more than reasonable assumption that 38% gravity means 38% air pressure. On the other hand, with less pressure, the gasses will spread out further, which means the outer reaches will get further away and be affected by the inverse-square law; the upshot of this is that my numbers may be *too high*, making this even *worse* for plausibility! [Answer] Money is no object? How about time? Simple answer, throw a bunch of [stuff] at Mars. Send out automated probes to every hunk of free matter in range, and ion-drive it towards impact with Mars; ie: planetoids and comets. First one to bulk up Mars gravity (so you're not wasting your time), and the second to get water down there, which you crack and turn into atmosphere. The hydrogen will escape (like it does here on Earth), and eventually you'll have more free oxygen available. Problem? You're probably going to make a mess of things. But, since Mars doesn't have a molten core - and you want one of those so you can get a magnetic field - this may be on your path of things that should get done anyways. You need to make sure you hit it right, so you don't tear off a Moon (like Earth's). [Answer] I was playing around with this idea for a while too, and I discovered a very simple solution to creating and retaining a fully pressurized, breathable atmosphere on Mars: [Para-terraforming](http://terraforming.wikia.com/wiki/Paraterraforming). Rather than converting the entire surface of the planet into an earth like world, you would build capped off "habitable zones" that are covered by a super-durable, transparent ceiling. For instance, you could create massive cities and landscapes under huge graphene domes. Or you can convert Mars's valleys (like the Valles Marinaris) into lush green belts, while the area around them remains dry, depressurized, and barren like before. Aside from the airlocks, and the occasional small leak, the atmosphere would remain contained underneath the ceiling. Plus, if it's made out of the right materials, a paraterraformed ceiling could also act as a shield against solar and cosmic rays, further protecting those that live inside them. The best part is that the faint patterned outline of the ceiling against the sky would look awesome on a sci-fi landscape. Just look: [![A parraterraformed valley](https://i.stack.imgur.com/xXu6J.jpg)](https://i.stack.imgur.com/xXu6J.jpg) [![A parraterraformed dome](https://i.stack.imgur.com/aak1n.jpg)](https://i.stack.imgur.com/aak1n.jpg) [Answer] The claims that Mars doesn't have enough gravity to hold a decent atmosphere and that without a magnetic field the solar wind will strip it away are true. BUT they are also not relevant. The time frames necessary to appreciably strip away a newly terraformed Martian atmosphere will be tens of thousands to millions of years. That's plenty of time for a civilization to find ways to either protect the existing atmosphere or to replenish it. The fastest way to raise the atmospheric pressure on mars is to put greenhouse gasses in the air. Chloro fluorocarbons produced from martian soil or manufactured in space might be a good approach. Of course the chemistry and energy needs will be enormous. Also last I heard Mars doesn't have enough volitiles locked in the soil and frozen in the polar caps to make an appreciable atmosphere. Do some research on that before committing to long term terraforming of Mars. [![enter image description here](https://i.stack.imgur.com/ge5bz.jpg)](https://i.stack.imgur.com/ge5bz.jpg) [Answer] Those others have mentioned that gravity would be required to allow Mars to have a Earth like atmosphere, there is another factor to take into account. The electromagnetic field and solar winds. For a number of reasons, (size, internal structure, etc.) Mars has a much less dense electromagnetic field than Earth. Without a strong field to slow and deflect solar winds, the atmosphere would be blasted off, even if gravity were enough to otherwise support it. So if you wanted to terraform Mars, you would need either a physical or EM barrier to keep the sun from blowing your new atmosphere away. [Answer] This might not be an exact answer to what your looking for. In the short term, para terraforming, <https://en.wikipedia.org/wiki/Terraforming#Paraterraforming> seems to be the way to go, but with the conditions on Mars as they are, I believe the safest and longest enduring solution would be to build underground caverns. This will not only 1) help with preventing the atmosphere generated leaking of into space, 2) but it will also help with the radiation issue that comes with Mars not having a strong and stable electromagnetic field, 3) as well as, depending on your depth, create a more stable temperature due to geothermal gradients. <https://en.wikipedia.org/wiki/Geothermal_gradient> 4) in addition, subsurface terraformed landscapes will be protected from bolide impacts, which are less likely to burn up in the atmosphere, 5) and the dust storms and high winds that sweep across mars. [Answer] The highest proportion of gas in the martian atmosphear seems to be Co2.There for if we could plant fast growing trees such as Laylandi, they would absorb the CO2 and produce O2, ie oxygen. Add hydrogen and you have water. Plant grass and the atmosphear should grow. The gravity problem should be addressed next. Manufacture Micro magnets? How do you increase a planet's gravity? We already know there is liquid water on Mars. A photo released in error shows a large puddle. How about NASA (Never-A-Strait-Answer!) comes clean and gets the world public behind the project? ]
[Question] [ On Earth, photosynthetic organisms require additional nutrients to survive; in addition to "feeding" off of sunlight, plants respire and absorb water from the ground in order to grow. However, the Earth is a closed system chemically speaking, so fundamentally all chemical resources are recycled through the biosphere. Would it be possible for this process to take place within a single organism, such that the only input the creature needed was sunlight to provide energy for its chemical processes? [Answer] Using some limits from other answers - I will restrict myself by saying the creature must grow, be conscious, reproduce, and eventually die. It is my own opinion that this would be *possible* - though I do not believe such a creature would ever actually evolve in the real universe. It requires many unique complex processes and requirements because of its niche environment(*space*), and to reach this complexity, there should be less complex organisms which it could evolve from. This is a problem because there isn't really another similar environment that would easily provide some sort of evolution "cross-over", though I could be wrong. The only input to the system is sunlight, so the creature needs all other materials to be carried with it. This will have an impact on all the biological processes of the creature. The creature I imagine is actually quite close to [@Envite's answer](https://worldbuilding.stackexchange.com/a/4013/2138) when I think about it. The creature starts with being born. It has a bunch of "working materials" around it at the start - this is because of its parent. Other than that, there is only the emptiness of space and sunlight. The creature consumes the material and starts to grow - using the sunlight as its source of fuel. It could be a complex creature, capable of great thought (*though it has nobody to teach it anything*) or it could be a very simple creature. Eventually, it has consumed all the material. It self-replicates its child, probably into an egg form, and as it dies it releases (bacteria/chemicals/whatever) that it created during its lifetime which turn it into usable material once again. The shell of the egg protects it from the bacteria, and the bacteria dies. Then the child is born and the cycle begins again. [Answer] If the creature needs to grow and reproduce, a matter is required to build the new parts. Just energy itself is not enough. Because of that, plants need minerals and nitrogen from the soil and also take oxygen, carbon and hydrogen from the surrounding air. If no growth or reproduction is required, a living (= running typical metabolism of the living organism, capable of regeneration and possibly limited growth with expense of some other part dying and decomposing) system can be self-contained. A single usual plant would probably survive in a closed system with enough sunlight, sufficient initial amount of water and minerals and some bacteria and fungi to convert the dead parts into usable minerals. [Answer] Planet Earth as a whole (as stated in the [Gaia Theory](http://en.wikipedia.org/wiki/Gaia_hypothesis) in its stronger form) is a living being that lives by feeding only solar energy, and keeping all other resources in a closed circuit, gravity bound. So answer is **yes**. [Answer] This strongly depends on your definition of "Life". The most common definition is the **biological-life** in which living systems always depend on nucleic acides. > > Since there is no unequivocal definition of life, **the current understanding is descriptive**. Life is considered a characteristic of something that exhibits all or most of the following traits .. (click link for further information) - [Wikipedia - Life/Definition](http://en.wikipedia.org/wiki/Life#Definitions) > > > There are [theories](http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry) of lifeforms which do not depend on carbon (As we do). But while reading these theories, you'll notice that those who set up these theories, tried to recreate life as we know on different chemistry but did't really looked "how life else could work". For example, I remember this one episode (Dont know the #, sry) of Star Trek - The next generation in which they met a giant crystal which was floating in space. This crystal had some kind of consciousness and had to consume energy to stay alive. In the episode the creature consumed the warp-field or something, not sure. But you see the point I guess. **I** do not think life has to be 'biological' as we know. My personal definition of life, which doesn't really go against the common one (due there is none), is that living things have these: * consciousness (doesn't mean awareness of themself, but can) * ability to consume and create things ( as like metabolism ) * ability to replicate under specific circumstances According to this and [Abiogenesis](http://en.wikipedia.org/wiki/Abiogenesis) in theory life could develop almost everywhere. The point why it does not is the razerblade problem. Try to stack several razerblades on each other,... they'll collapse. Just under rare circumstances it's possible that they do not, and that's probably the point of life. We already found amino acids on asteroids, so this concept is not that hypotetical, even if it's not proven at the point. Another point: If you look at the lowest developed animals or bacteria we know, like [Trichoplax](http://en.wikipedia.org/wiki/Trichoplax) (which btw is different than any other animal we know), you will find structures and metabolism which are really basic and oftn don't need atmosphere to work. So the atmosphere itself is not the problem, the pressure isn't either due a evolution in space-low pressure literally evovles with this pressure. A lack of nutrient isn't probable too. Look at corals and other sessility animals you'll see that they do not, or almost not, need any nutrients to "stay alive" but to grow and replicate. This principe supports life in areas where almost no nutrients exist like in space. (Even in space, there are particles which could be consumed). **So, if you accept this definitions, nothing stops you from creating any fictional form of life which fit's this requierements.** And as always, stay plausible and keep causality up. **EDIT:** Life only depending on light is implausible. Just as said before, your lifeform must create matter out of light wich seems to be impossible. But as I said, even in space there are atoms and molecules which could be used as nutrients, even if they're very rare. This means your direct question must be answered with **NO**, but with a slight change it is possible. [Answer] You need to define what you mean by creature. If you want your creature to be considered living, then you still need to define what this means. There is currently no universally accepted definition of life. However most definitions require the ability to grow and reproduce. Unless your creature can transform light into mass it would be unable to fulfill this criteria. [Answer] I think it would be possible for such an organism to *survive* based solely on sunlight, especially for short periods, but not to reproduce or grow. I could imagine, for example, a highly efficient engineered organism which used sunlight to break apart its own waste products to continue metabolizing slowly over long periods of time. Such an organism would probably take the form of a hemispherical pressure vessel to withstand the vacuum of space, and even then, would need to have a very low density. I say 'engineered' because such an organism wouldn't really be able to evolve naturally. Even the densest clouds of gas in space only have densities of around 10^6 molecules per cubic centimeter, compared to 10^19 molecules per cubic centimeter for air. Space is too sparse and too cold to create the kinds of conditions under which enough chemical reactions are happening to build even the most basic of life forms. I could imagine, however, circumstances in which such a life-form comes to exist. Perhaps some advanced civilization needs a solution to clean up huge spills of organic chemicals in space. A simple life form could be engineered to slowly drift through the spills, consuming the chemicals to reproduce. The life forms could then be collected at a later point in time to reclaim the lost resources, at the point where the cloud is becoming to sparse and diffuse to sustain them. Even in this scenario, their metabolisms would be exceedingly slow, since a gas cloud in space would diffuse out to a low density fairly quickly, based on the internal pressure of the cloud. [Answer] As this is a question for world-building, it sounds like what you are seeking is if such a creature were *plausible*, given the science we know. Your story or world can work by different rules, but assuming biology and physics as we understand them, like many of the other answers here, I'd have to say it's implausible to think a creature could live on sunlight alone. That said, a creature could power its life, growth, reproduction, etc primarily from sunlight. To get the extra mass it would have to feed, in some sense, on materials floating in space along with it. Perhaps consuming others of it's kind, or raw materials like gas for volatiles. Ultimately, it's a question of chemistry. Breaking and forming chemical bonds produce energy for organisms to live. Even earth plants don't "eat" sunlight directly, they use the photons to drive chemical reactions via photo-synthesis. So, assuming you have some material to work with, the question seems more to be "how big / what kind of life" could fuel its biological processes purely by sunlight. For that, you can turn to physics. Decide how close to what kind of star your beastie lives, figure out its cross-sectional area facing the star, and you can determine how much energy it could absorb. That's your budget. Compare to some terrestrial plants to get a sense of what's a "reasonable" size, and go from there. But ultimately, it's your world. If you need or want a biological system capable of self contained nuclear fusion, go for it! The law of dramatic necessity should trump everything else. [Answer] It depends a lot on what you call a creature. With a bit of stretching you could consider a star a creature (any of the bigger stars in any case): * It's born * It gathers more materials to grow (using gravity) * It changes during lifetime * At its death, it creates the seeds for new stars: disruptions moving through space that can spawn new stars if they meet the right conditions (sufficient concentrations of matter) Now stars are (at the very least on an emotional level) very different from what we would consider life. So you could imagine a creature like a star, but with more consciousness. Like some kind of feedback system where it can detect matter (detectable by gravitation) and potentially jettison some mass to move in the direction of the matter (jettison at high speeds to love a minimal amount of mass for maximum propulsion). It would make it kinda like a giant space amoeba. However, defining the sensory system, feedback loops (decision making basically) and propulsion is essential. That definition would define when your creature is alive and when it's dead and how it reacts. Alternatively, sidestep evolution and steal from Asimov :D. Intelligent lifeforms engineer lifeform for space. You could envision a solar powered lifeform that would only replicate when it finds enough materials. It would probably have to hunt for new materials to occasionally repair itself though. Since it's engineered, it could be made in conditions that are extremely unlikely to happen randomly. Think of an extremely complicated robot. Be scared of however created it though... [Answer] Yes it is possible for living creature to depend on only sunlight. Physicists were able to create molecules that are [made up of light](http://www.wired.co.uk/news/archive/2013-09/28/photonic-molecules). So if the creature is made up of this photonic molecules then it may use the light from the sun as material for its biological process. If the creature was to be made up of regular molecules it might use light energy to drive its living process but for the materials it may depend on other particles that are emitted by the sun from solar winds or it might have a way to convert energy into matter. [Answer] Earth is not a closed system, even ignoring solar (and other) energy impacting it and heat leeching out. There's a constant stream of gas drifting out into space. It's a trickly, but it's there. There's also a constant stream of matter entering the system. Asteroid impacts, solar wind (which are charged particles), etc. etc. And of course every time we shoot a rocket into space, that's tons of material leaving the system as well. In space, your creature would be pelted with such stuff all the time. From dust motes and single gas molecules that fill the vacuum of space to asteroid and comet sized rocks, it will get hit by matter. If it can absorb and use that matter, that can allow it to grow. Combined with efficient use of impacting electro magnetic energy, who knows what may evolve. But given the environment, it probably won't look anything like life as we know it :) [Answer] Life in its simplest form might be just information. It was once thought of as an inseparable part of either matter or energy and that whatever ever else happens to the information after it travels beyond the event horizon of a black hole would also be lost to this universe along with the matter or energy. Stephen Hawking once was of this opinion. However, he is now of the opinion that the information is sort of stripped off and smeared all over an infinitely large hyper space that is the boundary of the Schwarzschild radius. This information would be expressed in quantum states that may indeed be still coupled to other particles on our side of the boundary. So the real question is, can life be totally destroyed, and it appears that the answer is no. [Answer] A creature could survive solely off sunlight, but it would not be "alive" according to the standard definition of life. The ability to grow, reproduce, and evolve are considered requirements for an object to be considered "alive". Growth requires matter in addition to energy, and reproduction requires growth, otherwise each new generation will be smaller than the last. Since the question specifies that the creature survives "solely off sunlight", there is no net mass increase. (In theory an organism could collect molecules and dust from the surrounding space, but this would be a *very* slow process.) Since this creature cannot reproduce, it cannot evolve, at least not in the standard biological sense of the word. Any space-dwelling organism must have either been created by another being or evolved in a circumstance that *did* allow it to grow and reproduce. That being said, as long as it is able to retain 100% of its matter (or alternatively gather as much matter from the surrounding medium as it loses), it can potentially *behave* like a living organism. Observation, reaction, and even thought do not technically require new matter to occur, only energy (animals on Earth gain their energy by eating food but that energy originally came from the sun). A moving, self-regulating, *thinking*, immortal being could survive indefinately in orbit around a star. (It couldn't use rockets, but movement could be accomplished by tilting 'solar sails'). However, it couldn't grow or reproduce, so it wouldn't be considered "alive" according to the standard scientific definition. It could be argued that the planet Earth is itself such an 'organism', as it is a functionally closed system as far as matter is concerned (the amount it has acquired from meteors, comets, and atmospheric gas exchange is negligable and irrelevant to life's survival) but supports life (and intelligence!) from sunlight alone. ]
[Question] [ I'm writing a story taking place in the semi-recent aftermath of a period of Human-Dragon warfare. The main character falls into a pit used during this period by dragons to trap/store/dump prey (humans). For aesthetic purposes I'd like there to still be recognizable human bones, possibly still bits of flesh. My question is how long would it take for bones to become brittle, to the point they would snap when stepped on without crumbling and would there still be any flesh? Also could a snapped bone become a dagger of sorts? One time use only, just to help the MC get out of the pit. The warfare period lasted for some time (still deciding just how long), so it's likely there would be remains from a range of years. Also for context, since I know that climate and other factors affect decomp, the environment is somewhat humid with a mild range of temperatures. The pit itself is in a forest, dug into the mud, probably largely clay in nature, and roughly 15 feet deep. Rain is not uncommon in the region, but the pit is largely sheltered from rainfall by trees. Flooding is obviously a consideration with these parameters, but whether it's the dry season or the pit is somehow protected from flooding, at the point the MC is in the pit there is no standing water. [Answer] I am not an expert, but if the practice of digging up monk bones after they die says something then I would say that in 7 years max, your human would not have a single bit of flesh on him. Now you said that the soil is full of clay which is a great preserver of bones, so for bone to snap like poorly made ceramics it would take over 50 years minimum. You can still use the bone for a weapon even after a lot of time has passed only that your knife would become more of a one use weapon as the years fly by. [Answer] In the kind of environment you're describing, I'd argue that the bones of the previous victims could be there for up to a century depending on the details of the environment. [Bones are not as long-lasting as some people think](https://www.scienceabc.com/humans/skeleton-mystery-dont-bones-decay-decompose.html) under less than ideal conditions, and the link attached goes into some good detail about the variances in how long bones will last in the environment, and some of the causes of them breaking down. As for the fleshy bits, I'd expect, especially in a cool dark pit, that insect life in particular would have made short work of most of it and I wouldn't expect any of it to survive more than a year. But the bones might be there for much longer, especially if you have kept a lot of the moisture out of the pit (which isn't likely just from tree cover). Also, a permanent lack of moisture would decrease overall decay and also make it harder for microbial life or insects to survive in the environment as well, further limiting the rate of decay. Given what you describe however, I'd imagine that the pit is *relatively* dry, meaning that it gets wet enough to support a healthy colony of microbial life and insects, meaning that your flesh would likely be gone inside a year, but the bones could last considerably longer although unlikely to last more than a few decades. In point of fact, the longer they are there, the more likely they are to go brittle and not make good daggers and the like. So, if the bones are an important feature of your hero's escape plan by fashioning weapons, I'd throw him in the pit no more than 5 years after the last victim, just in case. [Answer] Your best bet for a relatively long preservation time is to have the pit dug into an old riverbed (or on a river floodplain), this gives a silty clay-rich topsoil over layers of sand and gravel, making for a reasonably damp environment in the rainy parts of the year but the good drainage that will keep the hole from waterlogging. Complete drying for several weeks in the summer months will be important to retard plant growth in and around the pit or the trees will reclaim the open ground it represents within a decade. The sand layers in the pit wall will also make the pit slightly easier, though by no means simple, to climb out of. It should have been slightly undercut in it's original construction to hamper would be escapees, this will eventually collapse but that can take years. Some of the best preserved bone available to the protagonist will be that buried in the mud in the bottom of the pit, particularly the arm bones. The arms will have had to [disarticulate](https://en.wikipedia.org/wiki/Disarticulation) from the skeleton before being buried, this will happen due in part to decomposition but mainly because of insect scavenging so they'll be almost fleshless and reasonably dry when they go into the mud. Said mud will be largely composed of clay washed down from the topsoil and will form an [anaerobic](https://en.wikipedia.org/wiki/Anaerobic) environment that will slow further decay of anything buried in it. Anaerobic environments like lake beds and bog sediments have been known to preserve bone for literally tens of thousands of years under the right conditions. The leg bones buried with the flesh on will be subject to greater decay as the flesh supplies moisture, salt and bacterial decay enzymes to the environment around them in the ground but they'll be a so-so second best. The dry rip cages, vertebra and skulls left on or close to the surface will be brittle and crack when stepped on while the buried material will be wetter and can be carefully dried and used for makeshift weapons but any weapon made of bone will be fragile compared to an equivalent in wood, stone, or especially metal. [Answer] I imagine your pit can behave a bit like a mix between a [peat bog](https://en.wikipedia.org/wiki/Bog_body) and a [Lagerstätte](https://en.wikipedia.org/wiki/Lagerst%C3%A4tte), both known for anoxic conditions allowing for very slow decomposition. For your pit to have some of the same characteristics, these conditions have to be met to some extent: * It has to be permanently water logged. Clay is an effective water barrier. * The water needs to be completely still. The dragons have abandoned it, but so must scavengers and other larger organisms. No big floods. * Temperature has to be 'moderate'. Low temperature slows down all biological/chemical processes, including decomposition * The soil has a low pH, that is, at least slightly acidic. This is most commonly associated with peat bogs and coniferous forests, which again are most commonly associated with higher latitudes or altitudes. Densely packed spruce will be better for this than than a more open pine forest. Unless you need extremely slow decomposition rates not all of these has to be met to the tee. As this pit was used actively for many years before it was abandoned you can adjust these parameters so that you have a vertical gradient of decomposition. Say the water level has varied somewhat, so only the lower part of the pit has been permanently water logged, then the surface remains will be mostly bare brittle bones, but as you dig down a meter or so bones, flesh, skin, most things except the very softest parts, like the eyes, will be well preserved. Be careful though. As the main condition for this is an anoxic environment, there won't be much oxygen for your trapped human. Carbon dioxide, methane and hydrogen sulphide will dominate, especially as they thrash about disturbing the muddy, rotten goo, releasing pockets of trapped gas. [Answer] Decay rates for human cadavres is well studied. Based on your description the bones will not last long. Forests are just about the worst conditions for bone preservation. A few months to a few years at best. Flesh in particular will be gone in weeks or months. A pit in a forest will alternate between wet and dry and leaf litter will turn it acidic, wet, and aerobic, these are some of the worst conditions for preserving bone. I would not expect any identifiable bone to last more than a few years. Bone will be both mostly destroyed and become unusable for tools within a few months. the Climate matters, I assume mild means warm, warm conditions result in faster decay, while cold conditions will prolong it so it depends on your definition of "mild". Forests are really bad places for bone preservation, and the organisms in them often actively destroy exposed bone for the calcium. I would not expect to find anything identifiable within a few months to a few years (depending on what you call identifiable (that is Bob vs that is human). Of course if they are in a forest, they can also have fallen branches for tools. If there are a continuous supply of remains being dumped in the hole there will be a plentiful supply of scavengers and their predators which could provide the hazard you are looking for but will also speed up decomposition. Letting the pit stay partially full of water will help slow down decomposition, or allowing for a more temperate climate will as well. [Source](https://link.springer.com/article/10.1007/s00114-006-0159-1) [Source](https://www.sciencedirect.com/science/article/pii/S0379073810002720) [![enter image description here](https://i.stack.imgur.com/06H7C.jpg)](https://i.stack.imgur.com/06H7C.jpg) ]
[Question] [ Assuming that human civilization in the future will spread from earth into the galaxy, how long would it take for the human population to exceed one trillion (10¹²)? I doubt this is possible if humans remain on Earth, and it may require humans to colonize exoplanets, depending on how many planets in our Solar System are suitable for colonization. Edit: since a timeframe is hard to estimate, let me modify the question to ask "what is required for the population to exceed 1 trillion?" [Answer] **Not as long as you might think** It depends on the assumptions you're willing to make. * With the world population growing at a vigorous **2%** per year, there would be a trillion people alive in around the year 2260. The fastest human population has ever grown in recent history was 2.2% per year in the early sixties. This type of scenario would correspond to a **strongly pronatalist policy** by the powers-that-be, perhaps going as far as **banning birth control** and mandating early marriage. * With the world population growing at a more moderate **1%** per year, there would be a trillion people alive in around the year 2500. This rate is about **where we are currently**. As the population ages and becomes more urban, most demographers think the population growth rate will slow even further. From an overall perspective, many industrial democracies in fact have strongly negative growth rates if you exclude immigration. However, there are **fast-growing subpopulations** with strong pronatalist proclivities that will become dominant if current growth rates are maintained. * With the world population growing at a glacial **0.1%** per year, you wouldn't reach a trillion until almost the year 7000. This would be a slow growth scenario, and the one that gives mankind the most time to adapt. Perhaps a society where aging has been cured and very few people choose to have children at a particular given point might look like this. The energy and food requirements of such a host would be far beyond our current technologies, and might require extensive industrialization and agriculturalization of space. Imagine that view: a billion miles of space-farms, their bright green glittering against the dark sky, surrounding Earth like a gigantic set of Saturn-like rings. The plants within are made of organic material harvested from Titan, and are powered by the abundant 24h/day inflow of solar energy. A dense mesh of thousands of massive space elevators carry food to Earth and 'fertilizer' from Earth. If you're not limiting yourself to Earth, but allow for space farming habitats, space industries and even extraterrestrial colonies, the cosmic resources available in the solar system can easily support a trillion people. To give a simple example, ***the energy output from the sun is so enormous, that if all of it were captured, each one of the trillion people would have 100 times as much energy as all of today's humanity combined.*** We have all the organic volatiles we could ever need on Titan, oceans of it, metals in the asteroid belt, quadrillions upon quadrillions of tons. Our solar system's resources are literally on cosmic scale. ## Can we house everyone on Earth? A trillion people sounds like a lot. Nonetheless, humans are pretty small and Earth is pretty large. Plus its nice to have the air already here, not leaking into space, a magnetosphere, comfortable 1g gravitation ready made, all that good stuff. So Earth is pretty damn convenient. Let's see how much space they would take. If we use the density of a place like Mumbai, India, (30,000 people/sq.km) and extrapolate from there, you could fit a trillion people in [an arcology](http://en.wikipedia.org/wiki/Arcology) covering about 23% of Earth's land area. That's about the area of Earth's deserts. So **with a trillion people on it most of Earth could be a lush unspoiled garden**... Moreover, since such an arcology whould presumably be multilevel, each individual could have a vastly larger living area than a current resident of Mumbai. So we can definitely fit a trillion people on Earth, but Earth alone probably does not have the energy resources to feed them and meet all of their future needs. [Answer] NASA in 2005 published a report that stated if we were to take all the Earth orbit crossing asteroids and the asteroids in the Asteroid Belt, and process them for materials we could build living space equal to 30,000 X the land area of Earth(58 million sq. miles)and be able to house a half a quadrillion people at half the current population/sq. mile we now have. Think Stanford torus, O'Neil cylinder, McKendree cylinder. If we tear apart all the planets, comets, asteroid we could build enough habitat for 2 quadrillion people. We don't need to find planets around nearby stars. We just need the material. This link <http://www.science20.com/robert_inventor/blog/asteroid_resources_could_create_space_habs_trillions_land_area_thousand_earths-116541> tells how that future might come about. No, we don't have the tech to build space habitat equal to 58 million sq. miles, but I believe we have the tech to build 100,000 sq. mile torus or cylinders. NASA is considering a 1g component(a rotating assemblage) to the next space station. That would be the beginning of humankinds conquest of the Solar System, and nothing like what we have now. There is a point in our species future when we might consider the resources in the Earth too valuable(equal to 20,000 earths of living space) to remain a habitat for only the richest 10-20 billion people in the Solar System. There are 3 things pushing the future, zombie apocalypse not being one of these. They are: 1.) humans conquering space(here and around at least nearby stars) 2.) everlasting health/youth(stopping aging in the 11-14 yr. old range because aging would be far easier to control then) 3.) becoming one with our tech(cyborgism, not borg) nothing obvious more like super advances on the cellular level. Replacing cell parts with far advanced cellular machinery. Here are more Links on the subject of population: <http://blog.nss.org/?cat=35also> and here <http://www.ignorancedenied.com/threads/8479-The-Wealth-Of-Ages?p=56390> All we lack as a species is imagination! There are 520 stars within a 100lys of Earth if only half are suitable for development we could increase the human species to 260 quadrillion people! If all those star systems are suitable for development(meaning: lacking intelligent life) we could use the resources to support a half a quintillion eternally young humans/cyborgs with open ended lifespans! All we lack is imagination! Make it so .. After thought: there are 600 million star systems within 5000lys( <http://www.atlasoftheuniverse.com/5000lys.html> ) of Earth if 10% are suitable for future development they would support 60 sextillion human/cyborg inhabitants, and we can add 60 sextillion for every additional 10% we find useful. [Answer] I don't accept *either* of your premises that 1) Humanity will spread from the Solar System or that 2) that it isn't possible to have 1E12 people on Earth. I encourage you to do some simple math. Solar irradience at the surface is about 1000 W/m². The Earth shadows the Sun over an area of about 1.3E14 m². This gives us about 1.3E17 Watts per year (without pollution and clouds, together they will reduce that considerably). According to Wikipedia Global Power Consumption was (estimated) 1.2E13 Watts in 2013. Say this is for 7½ billion people, or ~1650 Watts per person per year. That is about 1% of what's available to us on Earth *from the Sun*. OK, say we need to increase per capita power consumption by a factor of 5, so we're using 5% of impinging solar energy, ok so lets limit it to the visible spectrum, and that's 20% - for a trillion people. Yeah, the planet would be drastically different. It couldn't support 1 trillion peeps and all its current flora and fauna, but then again we've got fission power and geothermal power now (along with a little tidal power) and who knows about fusion. I do agree that 1 terapeeps would be a daunting challenge, and perhaps isn't possible, but perhaps it is... [Answer] Most predictions that was made [were wrong](https://en.wikipedia.org/wiki/World_population). Scientists missed when we reached 6 billions, they were wrong about 7 billon border and current predictions are different. The population [growth](https://en.wikipedia.org/wiki/Total_fertility_rate) was different in different periods and there are many factors (and some of them are very new) so it's not possible to make good prediction --- Your second question, *what is required to exceed 1 trillion* has simple answer: **we don't know**. Optimist could say *just let us some time and we could solve all current problems and reach this line*. Pessimist could say *we'll meet with more and more complex problems and sometime problem become big enough to almost destroy humanitity and fall back to reptilies.* Note that although dinosaurs became extinct, reptilies in whole are alive and don't pretend both for extincting and be dominating [Answer] Humans balance out at 10 billion populate for earth size planet. Humans will reach this number around 2050. Minimum distance between stars is about 1ly. Humans use .10c travel speed. Let's say 22 stars are within a 1ly radius of any other star. Population start should be around 10,000. Population Growth is generally between 2 and 5% per year, let's just assume 5%. We have all these set for minimum time... and the resulting number should be fairly low... First 1t/10b = 100, so 100 planets is all you need to support this. This means that no ship has to leave 2 light years from Earth and max travel time is 20 years. That being the case we can just say we start in 2050 with 10b, wait a decade and start counting from there... even though the 10 year lag is useless because we can alway just colonize the planets, moons, asteroids around us and that is more than enough space to do that. and in the next hundred or so year construction projects will be fairly cheap... The most expensive part is launching human bodies, soil, and land materials up... after the first few decades we can rapidly expand and transofrm the whole solar system into very large colony colony station-ship-bases 2060 : 10000010000 2061 : 10500010500 2062 : 11025011025 2063 : 11576261576 2064 : 12155074654 2065 : 12762828386 2066 : 13400969805 2067 : 14071018295 2068 : 14774569209 2069 : 15513297669 2070 : 16288962552 2071 : 17103410679 2072 : 17958581212 2073 : 18856510272 2074 : 19799335785 2075 : 20789302574 2076 : 21828767702 2077 : 22920206087 2078 : 24066216391 2079 : 25269527210 2080 : 26533003570 2081 : 27859653748 2082 : 29252636435 2083 : 30715268256 2084 : 32251031668 2085 : 33863583251 2086 : 35556762413 2087 : 37334600533 2088 : 39201330559 2089 : 41161397086 2090 : 43219466940 2091 : 45380440287 2092 : 47649462301 2093 : 50031935416 2094 : 52533532186 2095 : 55160208795 2096 : 57918219234 2097 : 60814130195 2098 : 63854836704 2099 : 67047578539 2100 : 70399957465 2101 : 73919955338 2102 : 77615953104 2103 : 81496750759 2104 : 85571588296 2105 : 89850167710 2106 : 94342676095 2107 : 99059809899 2108 : 104012800393 2109 : 109213440412 2110 : 114674112432 2111 : 120407818053 2112 : 126428208955 2113 : 132749619402 2114 : 139387100372 2115 : 146356455390 2116 : 153674278159 2117 : 161357992066 2118 : 169425891669 2119 : 177897186252 2120 : 186792045564 2121 : 196131647842 2122 : 205938230234 2123 : 216235141745 2124 : 227046898832 2125 : 238399243773 2126 : 250319205961 2127 : 262835166259 2128 : 275976924571 2129 : 289775770799 2130 : 304264559338 2131 : 319477787304 2132 : 335451676669 2133 : 352224260502 2134 : 369835473527 2135 : 388327247203 2136 : 407743609563 2137 : 428130790041 2138 : 449537329543 2139 : 472014196020 2140 : 495614905821 2141 : 520395651112 2142 : 546415433667 2143 : 573736205350 2144 : 602423015617 2145 : 632544166397 2146 : 664171374716 2147 : 697379943451 2148 : 732248940623 2149 : 768861387654 2150 : 807304457036 2151 : 847669679887 2152 : 890053163881 2153 : 934555822075 2154 : 981283613178 2155 : 1030347793836 So basically 130 years under the quickest situation Adjusting for the 2% growth rate it's 275 years. ]
[Question] [ In the very near future, humans (somehow) travel to a distant planet - and discover aliens who turn out to be uncannily like us. Their appearance is, to put it bluntly, freakish, but they *are* humanoid bipeds, and their life cycles, family structures, and basic needs are all reminiscent of human biology, albeit with the occasional surprising quirks. Their civilizations appear - at least at first glance - to have technologies, religions and political institutions analogous to bronze and late stone age cultures from the ancient Near East. It is not immediately obvious at first contact whether the differences run deep or are best said to be merely contingent. Naturally, the very first thing the humans conclude is that these strange creatures are a veritable goldmine for the social sciences, and so they drop in teams of socio-cultural anthropologists (and perhaps also a scattering of psychologists, sociologists, economists, etc,) to do field research. The aliens prove very accommodating to all this... at least for now. **Given current academic practices, how do these anthropologists first go about it?** Most especially, what are the major questions to ask, and models to test? What is the likely order of priorities, and what (aside from the blunt fact of meeting aliens, anxiety over whether contact is even desirable, and excitement no longer having only one species to study) is most likely to generate controversy or excitement? **Edited Note:** I recognize that dropping in an "away team" is not wise or realistic, but take the question scenario as written. [Answer] Actually, I wouldn't be 'dropping in' a team of xenoanthropologists; the first step in their scientific process would be 'observation', and preferably in an environment that precludes interaction (and therefore potential contamination of the culture). Your anthropologists, and the rest of your scientists bar a special field team which I'll get to later, should be in orbit with absolutely no contact with this race. You use drones and stealthed sensors to pick up all the information you need, and then its shared with a team up top. That team will include linguists, psychologists, economists, anthropologists, etc., all of which contribute theory in their discipline to a more complete picture of how this race lives today. Unfortunately, these teams won't have access to the one dimension of data that we take for granted here on Earth; time. In other words, they'll see *current* practice, but won't know how it formed or what aspects of their culture are new, what parts come from ancient sources or practices, etc. A really simple example of this is that many of us who are in our 50s now were raised with parents who strictly told us to 'eat everything on our plate' at mealtimes. None of us knew why at the time, but our parents were almost pathological about it. That's because they were raised by parents who had grown up during the depression, and their parents had told them to eat everything on their plate knowing it might be the last meal they get for a while. They learnt the habit because of the emotional intensity of *their* parents, and passed it on with some intensity, which is only now starting to die away as a parenting practice in some quarters. So, when your anthropologists see children being chastised for what looks like a minor transgression, is that because of something in the environment now, or something that happened historically? Enter the one field team you need; archaeologists. Your drones and satellites need to be capable of deep scans, and they need to find remote, preferably uninhabited areas where there are remains in the ground of cities, burial sites etc. that can be excavated and studied. This field work should be done without interaction with the locals, and fills that missing dimension of historical perspective for your anthropologists. The practical upshot of all this is that the way your anthropologists would begin their studies is observation; either from an orbital platform with remote feeds, or from inside some form of duck blind, but the ONE thing they wouldn't do is interact with the culture. That would effectively contaminate the site and make many of their subsequent observations invalid. [Answer] # The scientists are excited that they have a "natural experiment" and a species with ZERO shared ancestry to humans Tim B II did a great job explaining your first question: "What is the likely order of priorities" (observation! without contaminating! and the need for archaeologists to put that observation into perspective). Much later down the line you can send in anthropologists to ask why the do certain behaviours and to run controlled studies (like they do here on earth). I'll answer your second question "and what is most likely to generate controversy or excitement." As a biologist who studies animal and human behaviour, the answer is: you have a [natural experiment](https://en.wikipedia.org/wiki/Natural_experiment) with no contamination from shared ancestry, allowing you to make causal inferences about behaviour and culture. In the sciences there are two major ways you can carry out research: observational (i.e. field research) and controlled (i.e. lab research). Field research is great because you see super real behaviours but cant control for anything (e.g. you may think island societies do x because of y but you didn't control for z which is the actual cause). Lab research is great because you control for everything but sometimes you've made it so controlled/sterile that the behaviours you are seeing aren't natural so don't actually tell you that much (e.g. you do research on parental effects of x on a behaviour but your subjects don't have access to y which is necessary for creating the natural behaviour). Having a completely separate group of animals or humans is a great "natural control" (a kind of [natural experiment](https://en.wikipedia.org/wiki/Natural_experiment)) meaning you can get the benefits of both field and lab research. For example you want to see the effects that living underground and eating insects has on a vertebrate. You can look at moles and say "they have super tiny eyes, so living underground must cause small eyes" but you can't prove that because what if the ancestor of moles had tiny eyes for some other reason before it moved underground, and you thats why moles have small eyes. Enter the Marsupial mole: this mole is a marsupial, so it is super unrelated to the placental moles BUT they look almost identical. Looking at both moles we can now say that evolving small eyes is probably a result living underground and not just that both moles had ancestors with small eyes (that both moles look so alike is because of [convergent evolution](https://en.wikipedia.org/wiki/Convergent_evolution)) To understand behaviour, "natural experiments" are great: you don't have to intervene in the subjects lives (good for ethics, and especially good in your scenario of not wanting to disturb the aliens), you get natural behaviours, you can often control for shared ancestry (yay your aliens have ZERO shared ancestry), you can often control for certain variables (e.g. you can show that smoking causes cancer by looking at countries with different smoking rates - hopefully other variables, like city density, diet, pollution levels etc, are controlled for naturally in your "experiment". Your planet likely has a lot of differences to earth (that you are now controlling for) but enough similarities to result in similar behaviours/social structures) The behavioural biologists and anthropologists are very excited to have this other species to double check (and form new theories) on the origins of all sorts of behaviours and the effects of all sorts of environmental and social pressures on behaviour and culture. In fact every sub-field of biology is salivating at the thought of this find (and hopefully loads of other plants and animals on the planet) [Answer] ## Interviews with minimal impact In addition to the great answer by Tim B II, they might want to interview individuals. Pretty much the only reasonable way to achieve that while minimizing the impact on their society and possible contamination of their practices would be the "alien abduction" sci-fi trope. I.e. they'd want to interview a selection of people, but they'd want to do that by abducting them without anyone knowing about it, and after the interview returning them right back to where they were - after pumping them full of amnesiac drugs so that they don't know what happened and don't know what questions were asked. [Answer] It is interesting to think about what 'contamination' means in this context. What are we trying to avoid? At some point we are going to say 'Hello". At that point we have decided what we think our contamination is going to be but not knowing what it's ongoing effect will be. We then have just made our friendship with them conditional on them. That's not fair to them. So just waltz in (carefully) and say 'Hello' up front (leave the guns behind and be ready to withdraw if they resent our presence). Behind the 'experts' will be the greed of mankind hoping to strip them of their resources. Think Conquistadors! EDIT: 'Given current academic practices, how do these anthropologists first go about it?': There are none as they apply to Humans not Aliens. To 'Drop in teams' would result in 'contamination' and skew results. The first step would be to find some authority within the race to negotiate (hence Hello being the first phase of meeting them). 'Most especially, what are the major questions to ask, and models to test?': Ask them: "We would like to understand your Race and if you agree could we invite you to study us." That is the phase in which a go/no-go is determined and answers the OP's last multi-question paragraph. I did not use the term 'looting' and what is being asked is rather an open question and therefore IMO a thought provoking response. It is not possible to provide an answer that doesn't require clarification due to the nature of the OP's request. The question interests me because I am writing a Sci-Fi novel which deals with some Aliens who arrive in Human Space and need help. I hope that clarifies things somewhat! Thanks. ]
[Question] [ So I'm writing a story that has a species that's immune to being burned or suffering any kind of ill effect from being heated, functionally regardless of the temperature (I'm not planning on tossing these dudes into a sun at any point in the story). This is being accomplished by a species-wide magic/boon-thing and has been a common facet of their lives since pre-history. At the time of writing, I'm just using this to have them be great overland traders because they can treat deserts like mildly-more inconvenient plains. Oh, and an excuse for members of this race to like literally scalding tea. In case it is relevant, any harmful amount of heat they experience is ejected from their skins (technically scales, but that's probably not relevant) without affecting them in any way. They can feel hot to the touch, but not suffer any effects of being hot, so to speak. Losing heat, like being in a snowstorm without coverings, will kill them at the same rate as humans. Other species in this setting do not have this heat immunity trait. **Is anyone aware of any ramifications of this trait I am missing?** I'm looking for any consequence of being fireproof that might shape their culture, be it militarily, economically, socially or religiously. And **Is this species, with human-level intelligence and physical ability, over-powered?** [Answer] **They would probably be larger or at least thicker** Being larger makes you less vulnerable to cold and more vulnerable to heat due to heat being generated by volume (cubic) and shed by area (quadratic). With magical heat dissipation, the balance would be much higher, so you'd expect body mass to grow and them to become thicker and more muscular. **Better endurance** Overheating is a major factor in getting tired from aerobic exercise. These people would not suffer from that. They could over distance easily outrun horses and cavalry. They'd also be able to outrun humans which is actually harder over long distances. **Resistant to hot places** These people would be well suited to places where humans need to take a siesta during the hottest time, which is lots of prime territory, not just those deserts. It might also cover places such as forges or deep mines. Lots of crafts would benefit from workers who are not distracted by the heat. **Resistant to arid conditions** Lots of our water need goes toward removing excess heat to keep body temperature even. Your people do not need to do this and would have lower water requirements. Using water to shed heat also consumes energy and electrolytes, so they'd probably need less food as well, especially if they have a thicker or larger body that retains heat better. This would make people better able to cross deserts or oceans or have high population densities. **What this means** I basically think you have reinvented the dwarves but with scales and magic. And without the obsession with living underground or being isolationist. Probably overpowered? Your people would not only have an edge in long-distance travel over deserts and oceans, they would also have an edge in melee combat due to superior endurance, making weapons and armor because of not being bothered by the heat and endurance, and in population density because of reduced water and possibly food requirements. They'd also have a general edge on productivity over humans in many climate types that generally have high agricultural productivity and very rich and valuable flora. [Answer] The single biggest problem that I see with your model is food. Not all deserts are hot. Take Antarctica, for instance. Almost no precipitation. You have access to water there, but it's either locked in ice or it's salty (from the ocean) Also (most importantly) nothing grows there. The species you're describing is almost the reverse of a penguin. Antarctica gets a lot of breeding colonies of penguins because of the absence of predators. Interestingly enough, Flamingos do something similar, [nesting in soda lakes](http://www.bbc.co.uk/nature/20271751) because the caustic nature of the lake means no natural predators. In each case, you either need to find food (and water) you can process in that location (be the *local* apex predator) or you need to venture out of that environment to find yourself (and in the case of penguins, your family) sufficient sustenance. Your species would probably do exactly the same thing. Being able to live in the middle of a desert means that you'd have major towns out there for things like breeding and security, but the food and water issue would have to be resolved. This is not so much an issue if you have an active trader culture as getting resources to and from the towns wouldn't be any larger a problem than it is for us today (How much food actually gets *grown* in New York, for example?). But, your people need something to *trade* for it. What is their industry? Personally, I'd go for [glass manufacture](https://en.wikipedia.org/wiki/History_of_glass). You already live around heaps of sand, you're less susceptible to heat stress and it's a commodity that would be in high demand in your world. So; with that in mind, your culture is very protective of its young. Most other species have probably never seen a young member of your species. They're artistic in nature, and have a canny sense for trade. They're curious, insightful, and probably more technologists than spiritualists. That is not to say that they wouldn't have religious proclivities, it just means that as a whole, their creativity is primarily directed to industry because without that, they would have to risk the safety of their children to migrate closer to food sources. Also, good trading ability means that their math skills would grow, and that also helps them with things like science and technology. All this said; they lack the natural resources that we take for granted. They're not in mountains (so lack the experience that leads to metallurgy), there'd be no practical reason to engage in mining for that reason as well, they don't have access to wood, bone, or even much stone which would lead to the creative resourcefulness that we assume a group like this would need. This is all the more reason why they would have a technology that focuses on the production of glass; it's the one thing they can manufacture in abundance and you'd probably find that they'd have built an entire culture and technology around it. Glass huts, even. This is a group that would by definition probably be both culturally and technologically narrow until they had regular contact with other species, not because they are unintelligent, but because their intelligence hasn't been exposed to other environments where it can be expanded on a regular basis. The key thing to state in summary about your species is that this specialisation they have (if you look at penguins, flamingos and others with similar traits) would be used to evade predators and enemies in the first instance and any other consideration (even the ones I list in this answer) are largely speculation. [Answer] One component you mention is that they like scalding tea, which indicates that the heat immunity is not only in their skin but a part of themselves. You also indicate they shed heat through their skin that then becomes hot to the touch (although they themselves do not feel it). This leads to some interesting possibilities: * **Hand to hand fighting/wrestling/jiu jitsu** They can ingest heat and exude it through their skin. In a fight they BECOME a weapon. With a touch they can scald the skin of other species. A bear hug could literally kill someone. Engaging in non-weapon combat would bring an entire host of problems for other species on your world. * **Weapon choices/styles** As above, their exothermic capabilities would invite them to carry sources of heat they could ingest and then use in conductive weapons. Think chain whips that would bind and sear their prey/enemies at the same time. * **Uncomfortable for other species** Being stuck in a room with many of these people in a hot climate would be unbearable for other species. Your species is heat immune, and so their body is converting the outside temperature to an internally comfortable one. They exude that heat back in a concentrated fashion into the room around them. This would in turn raise the temperature of the room and exacerbate the cycle. A sauna, for example, would possibly become scalding for other creatures if stuck too long with a few of these individuals. * **They are "heat conductive"** They can transfer heat from one medium to another. Much of this (and the above items too) would depend on the ratio of heat loss from the ingestion to the expulsion through their scales but they could in theory "swallow" fire and then use it to boil water. Or ingest other extreme heat sources and precisely etch glass using a finger. * **Inventing portable heat** Due to the uses above they would probably keep portable heat sources (magical or otherwise) handy at all times. It has many many uses in the wider world. This also would probably have shaped them spending time inventing portable heat sources that we humans have not invented (or didn't event until much later). If I think of other similar uses I'll update but this is the general idea... In answer to your second question I would argue that they would only be "over powered" if other species haven't been allowed to adapt to them. For all of the answers provided, other creatures/species would have found ways to negate/nullify those advantages. If they hadn't, they would have been eliminated long ago either through evolution, war, or attrition of resources. Humanity as a species is invariably adaptable. We might nullify one advantage with the maxim that you "always wear leather when fighting a Lizard" or (as has been mentioned in another answer) humans may be hunting your species for their hides. Assuming that the ecosystem is balanced, then other creatures would have found a balance with your species over time. [Answer] There's going to be a large amount of stuff made from human (alien) skin, if this trait is endemic to their bodies instead of the magical effect only happening to whole and living beings. Even if it's the latter case, then there will be a concerted push to replicate this trait in other materials. This material is a miracle, absorbing heat from both sides but only transmitting it away on the outside. You can take advantage of this to create one-way heat barriers, which would drastically impact the shape of society. At the bare minimum a tent or cloak of this material would block out head from the Sun, keeping the inside nice and cool even in baking-hot Summer days. [Answer] **No need to wear clothes in hot climates.** If you don't get sunburn or heatstroke then there is no need for sunhats, sunglasses or desert clothing. They might still wear clothes for modesty reasons (if they have a nudity taboo) or to show status (only royalty wear purple) or for fashion reasons (darling, *everyone's* wearing top hats this season). **They can wear winter clothes in hot climates.** The flip side of the above is that they can also wear tons and tons of clothes in hot climates without any ill effect - they could wear their favourite polar bear skin coat in the middle of the Sahara. **Other species are not immune to heat/fire.** If they ever get into conflict with other species, fire will be a weapon. They can blithely set fire to an opponent's forest/city and use that fire as part of their tactics. Perhaps their soldiers can flank the enemy by travelling through the forest fire, or try to drive the enemy into the fire? Your species' clothes and weapons may not be immune to the heat, and the soldiers themselves will still have to cope with breathing in smoke and being squished by falling debris. They'll be immune to castle defenders pouring boiling water on them, wizards casting fireballs, troops armed with flamethrowers and so on. **They won't burn themselves when cooking, firing pottery, doing blacksmithing, working in a foundry, etc.** Humans require all sorts of protective clothing - these guys can just grab hot metal and other things with their bare hands. Of course, they could still ruin their ordinary clothing by dangling sleeves in the fire or having sparks catch it alight, so perhaps they do blacksmithing and stoking the fires for a kiln in the nude? **They be in demand as firefighters.** Other species may want a few in their fire brigade, to send into burning buildings as a rescue team. See above about smoke inhalation and collapsing debris. **They'll be in demand as miners.** Deep mines are uncomfortably hot. Your species doesn't care. (I don't know what your technology level is and if anyone in your world can dig deep enough for this to be a problem for humans). [Answer] Assuming their body temp regulation is a constant process, they would be extremely vulnerable to infection. Ejecting excess body heat would essentially eliminate what we know as fevers. The human body raises its temperature as a reaction to infection to kill off bacteria. Without that defense mechanism, your fireproof reptilians would be easily overtaken by disease. This has multiple cultural impacts: * They would learn to place a high value on cleanliness. * Food and water would be customarily heated to very high temperatures to sterilize them (another excuse for scalding tea). * They would seek out extreme heat. With no adverse effects, being in extremely hot environments would only serve as a hindrance to potential pathogens. * Especially as traveling traders, they would likely keep their entire bodies covered at all times, particularly their hands and faces. * In general, they would avoid interacting with strangers who may pass disease to them. * Any religion they have could hold the extreme heating of food and drink as well as head and hand coverings as a central practice. That said, this is not a necessity. You could easily rationalize it away as their body being able to do the same thing, it just has much more control than the human body. On the other hand, this weakness would integrate well with the idea of these creatures being hunted for their skins. For that to be practical, you could say the skin is a sort of one-way heat barrier; any internal heat above a certain point just leaves the body. As a side note, it would be awesome to see a group of soldiers who run into battle with clothes soaked in oil and set themselves on fire. Think Viking beserkers, except far more terrifying. This has been mentioned before, but economically, they could be renowned metalworkers/glassworkers. Being able to manipulate molten materials with their bare hands gives them far more control than any human could get. It'd fit well with your idea of traveling merchants; they would both create and sell the most intricate and luxurious items in the world. If they get along well with other species, the other species would likely not develop any kind of metalworking of their own. Seeing as this trait extends to prehistory, they could either dominate other species by learning to make metal weapons first or have other species depend on them for metal tools and weapons themselves. ]
[Question] [ **This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information. I know this question has been asked in similar places, but I'm after a specific part of the problem. Assuming the following: * Perfectly flat, infinite world * Earth's atmosphere * Sun directly overhead of the viewer, no matter the time or location * No obstacles How far could a human see in all directions, before atmospheric refraction or other phenomena washed out any visible objects (i.e., mountains)? All the answers I've seen so far have been set on Earth, and that is the very thing I'm trying to avoid. I'm tagging this with hard science, because the numbers matter to me. [Answer] Here's a first-order approximation based on a fundamental limit: diffraction and angular resolution. How far someone can see of course depends on the size of the object they're looking at, because the main limitation we have is one of angular size. The issue comes down [to something called the Rayleigh criterion](http://astronomy.swin.edu.au/cosmos/R/Rayleigh+Criterion), which is a limitation telescopes have to deal with - and it has nothing to do with the medium light is traveling through. Any circular opening will produce a diffraction pattern, with peaks and troughs of intensity. The best angular resolution you can get depends on how far apart the two inner peaks are. If the aperture of your telescope (or eye) is $D$, and you're observing at a wavelength $\lambda$, then your angular resolution is $$\theta\approx1.22\frac{\lambda}{D}$$ [For a human eye, $D\approx9\text{ mm}$ when pupils are maximally dilated](https://physics.stackexchange.com/a/122790/56299), so even if you're observing at really red (and therefore long) optical wavelengths - say, $\lambda\approx700\text{ nm}$ - then you can achieve an angular resolution of $\theta\approx9.5\times10^{-5}$ radians. If the size of an object is $h$, then the distance at which your eye can resolve $h$ is $d\approx h/\theta$. If we choose $h=2\text{ m}$ (roughly human-sized), then $d\approx21\text{ km}$. We can repeat the calculation for a bluer object (say $\lambda=300\text{ nm}$), and we get $d\approx49\text{ km}$. Is this a reasonable model? I've made the assumption here that we're dealing with a [diffraction-limited system](https://en.wikipedia.org/wiki/Diffraction-limited_system). Any astronomer can tell you that in reality, if you're looking through several kilometers of air, your resolution is actually going to *seeing-limited* - that is, limited by turbulence and other atmospheric disturbances. Attenuation due to scattering and absorption is going to be a problem. That's why I call this a first-order approximation. Calculating scattering and optical depth is, I think, beyond what I can easily do. Taking atmospheric effects into account will reduce the numbers I have here - and the amount of reduction depends on the atmospheric conditions. So consider this an extreme upper limit. [Answer] The World Trade Center on a clear, sunny day used to report 40-mile visibility. On less pristine days, visibility could be much less including foggy days where they were less than a few feet. On that best of days, you are not likely to see many details at that distance, only the larger objects are discernible. Different people with different eyes will resolve those macro objects in different ways. The **first** challenge is in giving your eyes a tool that resolves what you are seeing at any distance you might want to view objects on your flat world. The **second** is the elimination of all objects/conditions that would impact the ability to see the maximum distance possible. You indicated in your question, there were no objects to interfere. Atmospheric conditions would be the single obstruction that affected your viewing distance. No matter what distance, you would assume a theoretical clear day that allowed you to eliminate those conditions from the equation. Any object anywhere on the line you are viewing would also, in effect, end your line of sight on that line. If objects were an issue, the World Trade Center had a fantastic viewing range on clear days, it was partially due to height which overcame some of the Earth's curvature (an "object"). Your flat world viewing distance would be enhanced by a viewing platform that could eliminate any objects from obscuring your long range views. The required height of your platform would depend on the distance those objects were placed on your plane. Basic triangle math would determine how tall that platform would need to be based on how tall the objects on your plane were. The **third** challenge is the speed of light... if you have optics that enhance your ability to view at any distance, you have no obstructions, and light from the furthest distances can get to your optics, you theoretically should be able to see an infinite distance. Each star we can see on a clear night exhibits this view of infinity quite well... while we can't see the details of those stars, we basically can see light-years. With the right optic, theoretically we could see the planets orbiting those stars. Your flat-world under optimum viewing conditions would have similar results. Final note, you would have to introduce some object into your world, at some distance, so that you would have something to look at over that infinite distance. [Answer] I took this panorama photo in the Oklahoma panhandle, one of the flattest places on Earth. It is 180 degrees (that's the same highway stretching in both directions). It was shot with an iPhone SE, whose aperture pupil is 1.86mm, smaller than what HDE226868 lists as a bound for the human pupil (therefore the human eye would do better on his limit calculations). It is 37 km to the horizon. Clear day. Beautiful color. In one sense, you can see a whole lot of nothing -- no cars, buildings, people -- for kilometers. But if you zoom in on this image, you will see details on the horizon that will give you a real feel for what you can resolve. Below is a low-res thumbnail. The high-res image is [here](https://drive.google.com/open?id=1Yo4lnTimBCSSPufe1ownwMzZn-AqyUTh). [![Oklahoma panhandle - flat land](https://i.stack.imgur.com/s3ukL.jpg)](https://i.stack.imgur.com/s3ukL.jpg) HDE226868's reply provides you a theoretical basis for estimation. I figured an experimental basis might be useful as well. [Answer] Firstly, [Rayleigh scattering](https://en.wikipedia.org/wiki/Rayleigh_scattering), which effectively redirects a small portion of light as it travels through a perfectly clean atmosphere. In a pure nitrogen atmosphere at [STP](https://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure), the light you get out of a regular green laser (wavelength 532nm) will have a Rayleigh scattering [cross section](https://en.wikipedia.org/wiki/Cross_section_(physics)) $\sigma$ of about [5.1x10-31m2](https://pdfs.semanticscholar.org/ff2f/95b7c9dd7a8d29b31cc390a617de253839a6.pdf). You might expect to find about 2x1025 nitrogen molecules per cubic metre. Given an initial beam intensity of $\Phi\_0$ that travels through $z$ metres of this nitrogen atmosphere with particle density $n$, the intesity of the beam as it leaves $\Phi$ is defined as $\Phi = \Phi\_0e^{-n\sigma z}$ This means that a beam of that passes through 1m of that nitrogen atmosphere, 99.99898% will carry on in the direction it was travelling and the rest will be scattered in a random direction. Once that beam of light has passed through approximately 450km, only 1% of the light will have been unscattered. This has two important effects. Firstly, things that are a very long way away will appear fainter, as some of the light travelling from them will be scattered away and will never reach your eyes (or whatever you are doing your looking with). The second is that the Rayleigh scattering cross section is inversely proportional to the fourth power of the light's wavelength: shorter wavelength (eg. bluer) light is scattered more strongly than longer wavelength (eg. redder) light. This means that things will be fainter *and* redder. A similar effect occurs in astronomy, whereby distant objects behind clouds of gas and dust [appear redder](https://en.wikipedia.org/wiki/Extinction_(astronomy)#Interstellar_reddening), even in the absense of any redshift effects, because the bluer parts of their spectrum are scattered away. Computing the exact effects here is awkward, at least in part because the definitions I've found for computing Rayleigh scattering cross sections totally disagree with actual measurements of cross sections, so whatever I'm doing I'm clearly doing it wrong. Nonetheless, it seems clear that even in extremely clean air lines of sight of over 100km aren't going to show you much. [Here's an example from the real world](https://www.flickr.com/photos/lattaj/6896706847), with a 90 mile view. --- When the stuff in the way of the light is large compared to the wavelength of that light, you can't use the Rayleigh approximation any more and you need to think about [Mie scattering](https://en.wikipedia.org/wiki/Mie_scattering), which is a bit more challenging. Cloud, fog, mist, smoke, soot, ash, dust... all these things cause Mie scattering. Mie scattering from large particles is mostly wavelength independent (which is why clouds are whiteish or greyish) though shorter wavelength light tends to get scattered more. Actually working out the contribution of Mie scattering is a) *really hard* and b) requires making a lot of assumptions about the nature of your atmosphere ("Earthlike" has a vast amount of variation), so I'm simply not going to do it. Instead, I'll steal a table from [chapter 15 of Vision and Acquisition](http://www.simulatedvision.co.uk/V&A_Chap15.pdf) (available in its entirety for free [here](http://www.simulatedvision.co.uk/page184.html)). [![Ratio of aerosol scattering to Rayleigh scattering](https://i.stack.imgur.com/jdHWC.png)](https://i.stack.imgur.com/jdHWC.png) Mie scattering tends to be more biased towards scattering in the direction the light was originally travelling, so it won't make things dark so much as make them blurry and faded... effectively, distant objects just disappear into a featureless "haze". You can see that the effects of this sort of scattering can be profound. Precisely quantifying it is *very* hard, but it is worth noting that with the best eyes in the world you can't "see through" this haze... the light travelling towards you from a distant object has been bounced around and blurred enough that the details are no longer there to resolve. HDE 226868's answer points out that the resolving power of the human eye is limited but artificial aids can help... this should show that they'll only take you so far, and the best visible-light telescope in the world isn't going to help you. YOu need to use longer-wavelength things, like infrared or radar to help you here. --- I'd like to say more on atmospheric distortion (for instance, I think you might see a slight bending effect that makes it look like you're in a very broad, shallow dish instead of on a flat plane) and thermal distortion is also going to ruin seeing things at a distance, but everything is just entirely too hard. Sorry about that! [Answer] I also wanted to know the answer to this question; searching online has given me answers from 10 miles, to 350 miles. I went through and did the Rayleigh Scattering calculation for an Earthlike atmosphere at STP that contains no dust, pollution, or condensation. For every mile visible light travels (I used 500 nm light) 98.404% would pass through unscattered; I then translated this into an image and I would say objects totally fade into blue obscurity within a range of 250 miles, at which point only 1.8% of the original light would reach your eyes unscattered, even less should there be literally any dust in the air[![Rayleigh Test and High Contrast Key](https://i.stack.imgur.com/xcdPm.png)](https://i.stack.imgur.com/xcdPm.png) ]
[Question] [ In my world, I am attempting to design a primitive organism to be the ancestor of life on an artificial planet with all chemicals necessary for life. I want the organism to be as small as possible (say 50 nanometers in diameter). Is such a small size possible? [Answer] 50 nanometers is awfully small. In fact, this is on the same order as [many viruses](https://en.wikipedia.org/wiki/Virus#Structure), which can be 20-300 nm in size; to a first order approximation, this figure seems a good fit for [Cort Ammon's estimate of 16-18 nm DNA strands](https://worldbuilding.stackexchange.com/a/36614/29). Some viruses are smaller along one dimension, but larger along others; Wikipedia mentions that some filoviruses can be 80x1400 nm in size. In contrast, [bacteria](https://en.wikipedia.org/wiki/Bacterium#Morphology) are usually in the 500-5000 nm (0.5-5.0 µm) size range. While [the issue of whether a virus constitutes life is as of yet undecided](https://en.wikipedia.org/wiki/Virus#Life_properties), there is little doubt that [bacteria can be considered to be life](https://en.wikipedia.org/wiki/Bacterium#Bioluminescence). Hence, the boundary for true life, at least in an Earth-like environment, appears to fall **somewhere in the 300 to 500 nm range,** which is about one order of magnitude larger than what you are aiming for. It is possible that some extreme biology and evolutionary pressure might be able to support living organisms smaller than Earth bacteria, but I find it highly doubtful that it would be able to reduce the minimum viable size of an organism by such a large fraction. There is also no real evolutionary benefit that I can see to becoming that much smaller, hence very limited evolutionary pressure in that direction. If the limiting factor is indeed DNA base pair size and the number of nucleotides needed, then you may need some completely different biochemistry to make a significantly smaller organism viable. Based on discussion in the answers to [Why would life on a different planet use DNA?](https://worldbuilding.stackexchange.com/q/99223/29), it's likely that life would settle on DNA or at least [RNA](https://en.wikipedia.org/wiki/Ribonucleic_acid), so DNA strand size could be one factor establishing a lower limit for the size of life even on a completely different planet. At the very least, again to a first order approximation, any living organism must be large enough to support some form of procreation, even if that is done by cell division. Even cell division would appear to need the cell to be well above its minimum viable size before the division. Because they co-opt existing cells, viruses do not have that size constraint, and in fact would appear to have an evolutionary advantage to being smaller (less things to go wrong leading to higher probability of success). You may also want to compare [Are there organisms with fewer than 1000 neurons?](https://biology.stackexchange.com/q/57594/1206) on the Biology Stack Exchange, which appears to be peripherally related. [Answer] There's some precedent for it. [Spiegelman's Monster](https://en.wikipedia.org/wiki/Spiegelman%27s_Monster) is a self-replicating strand of RNA, which they eventually got down to 48-54 nucleotides. I don't have the conversion from RNA nucleotides to length, but if I pretend that was 48-54 base pairs of DNA, we can use DNA's length of 340pm per base pair to arrive at a 16-18nm long strand. It's an open question whether you can say much about our actual abiogenesis from studying Spiegelman's monster, but it's at least a point suggesting its not impossible. [Answer] That all depends on whether or not you consider viruses to be living things or not. Typically, viruses **are far** smaller than other living organisms. For example, [Wikipedia](https://en.wikipedia.org/wiki/Smallest_organisms#Viruses) tells us that > > The smallest double stranded DNA viruses are the hepadnaviruses such > as Hepatitis B, at 3.2 kb and 42 nm; parvoviruses have smaller > capsids, at 18-26 nm, but larger genomes, at 5 kb. > > > If you don't consider viruses organisms, then the same Wikipedia page tells us > > Prasinophyte algae of the genus Ostreococcus are the smallest > free-living eukaryote. The single cell of an Ostreococcus measures > only 0.8 μm across. The smallest genome of any Eukaryote is Guillardia > theta with a genome size of only 551 Kilobases. > > > If you're looking for an actual animal-like organism, here you go (from the same Wikipedia article) > > The smallest crustacean, and indeed the smallest arthropod is the > tantulocarid Stygotantulus stocki, at a length of only 94 µm (0.0037 > in). > > > [Answer] Absolutely. Most of the size of organisms comes from their need to compete with other organisms and survive a range of hostile environments. Your ancestor, however, doesn't need to compete with anything but itself and can be seeded into the most welcoming of environments. Evolution will handle the rest. Consider this: the original forms of life on Earth *must* have been vastly smaller and simpler than today's life (due to the simple mathematics of what can plausibly have arisen by mere chance). In fact, they were likely a few molecules co-operating together ([ref](http://rsob.royalsocietypublishing.org/content/3/3/120190)) and between there and modern life there must have been innumerable intermediate forms that transition the range of size between a handful of small molecules and the smallest extant cells. The minimum size of modern life is thus an extremely poor guide to the possible size of an artificially generated seed life. [Answer] One famous example of a potentially biological organism which is smaller than any of the examples listed is surprisingly Martian in origin. The meteorite **[ALH84001](https://en.wikipedia.org/wiki/Allan_Hills_84001)** is known for its fossils, which were [thought by NASA scientists](http://science.sciencemag.org/content/273/5277/924) to be potentially fossilised Martian microorganisms. [![enter image description here](https://i.stack.imgur.com/horUQm.jpg)](https://i.stack.imgur.com/horUQ.jpg) The long rod-shaped structures were analysed by electron microscopy, and they found internal structures that resembled terrestrial bacterial precipitates. While it is disputed whether these are truly biological deposits as opposed to chemically or physically formed structures, if these objects are truly Martian microorganisms, their extremely small size (20-100nm diameter) potentially fits the range of sizes specified in the question. [Answer] Similar to what @si42 said, it depends on **how you define organism**. You can take as example the [model of abiogenesis](https://www.youtube.com/watch?v=U6QYDdgP9eg) (origin of life from non-living matter) proposed by the Nobel biologist Jack Szostak. The model was CONFIRMED to be possible and capable of originate life. That it actually did it on Earth or some other place is another question. The model works with **replicating micelles and vesicles**, [one of the papers](http://molbio.mgh.harvard.edu/szostakweb/publications/Szostak_pdfs/Budin_et_al_2012_JACS.pdf) says: > > We tested the concentration dependence of the micelle to > vesicle ratio independently by measuring the turbidity of vesicle > solutions that had been extruded to 50 nm to eliminate > spurious effects due to variation in vesicle size. > > > I did not read the entire paper, but I think that we can assume that they were of 50 nm or less. ]
[Question] [ This is part of the [Anatomically Correct Series](https://worldbuilding.meta.stackexchange.com/questions/2797/anatomically-correct-series/2798#2798). I've been wondering how an anatomically correct [pegasus](https://en.wikipedia.org/wiki/Pegasus) could evolve. ### Pegasus characteristics *They are pretty obvious, but just in case:* * Horse size and form * Wings * Being able to fly and gallop ### My questions As in the *anatomically correct creatures* series, I follow a line of questions about possibilities: * Is it possible? * How would they evolve? * Would it be possible to ride one? [Answer] # Weight vs. Wing length The approach I'll follow to decide if the Pegasus is possible is to analyze the Weight vs. Wing length. The first problem I have is to find a good enough data source. In the past (old version of this answer) I had used third party analysis based on Wikipedia data. This time I'll get a better data source and work estimation by myself. ## Extracting the data The data source I found is the information published by the [British Trust for Ornithology](https://www.bto.org/). In order to extract the data, I've created a [custom software](https://gist.github.com/theraot/e743751f0b4c8817e4991d09fd8b794a). Using that software I got the [raw data](https://gist.github.com/theraot/06166665f279a6a04440fad2434cfc21) that I will be working on. In order to process the data, I used an [online spreadsheet](https://docs.google.com/spreadsheets/d/17bl-xobu8CHLv-4Wt2rP3jz_8UqXw99AR-9H4fK-Z-c/edit?usp=sharing). The extracted data, once curated (removed entries with not enough data) consists of 540 data points corresponding to averages of weight and wing length. This data came from multiple measurements of the individuals per species. I'm disregarding the distribution of those values and only using the average. Note: if you want to compile the software you need a C# compiler and my libraries available from [nuget](https://www.nuget.org/packages/Theraot.Core/). ## Processing the data Once curated, I did the following plot of the data: [![Plot](https://i.stack.imgur.com/wCbT6.png)](https://i.stack.imgur.com/wCbT6.png) *Plot Weight (?) vs. Wing length (mm)* In the plot we can see that some of the data points lay very close to the horizontal (wing length) axis. The rest of the data points seem to follow growing curves. Actually the data is wrong, turns out some data is in kg and other in g (my software doesn't read the units) - after fixing the unit we have the following plot: [![Plot](https://i.stack.imgur.com/KrmNN.png)](https://i.stack.imgur.com/KrmNN.png) *Plot Weight (g) vs. Wing length (mm)* My next step was to plot the natural logarithm of the values for the same data points. The result is as follows: [![Log plot](https://i.stack.imgur.com/39NnU.png)](https://i.stack.imgur.com/39NnU.png) *Plot Ln(Weight(g)) vs. Ln(Wing length(mm))* In this plot we can see that a linear function seems to be a good enough approximation. Remember that the wings are at least as big as needed, and not as big as too increase Weight to a point that impedes flight. So, it is expected that for each Weight value, there actually exists a range of plausible wing sizes (the original plot supports that idea too). --- ## Adjust to a linear function [![Plot with linear approximation](https://i.stack.imgur.com/UNJzZ.png)](https://i.stack.imgur.com/UNJzZ.png) *Plot of the first cluster + approximation to a line* In the plot the added line follows the equation: $$Ln(Weight(g)) = \frac{1640}{1379}Ln(Wing length(m)) - \frac{2102}{2167}$$ *Oops... that's the wrong way around - of course, I have weight in the vertical - let me fix it:* $$Ln(Wing length(m)) = \frac{1379}{1640}Ln(Weight(g)) + \frac{7357}{9020}$$ Keep in mind that we are working with the natural logarithms. --- Of course, the wings add weight to the animal. So using the weight of the animal without wings is inaccurate. But it should be noted that due to the estimation method, this value is somewhere near the middle of the range of valid wing lengths. Thus, I’ll consider this method to be good enough. In case of doubt, BTO defines [Wing Length](https://www.bto.org/about-birds/birdfacts/about-birdfacts/biometrics) as follows: > > **Wing Length** > > > Maximum flattened chord measured on live birds, this measurement will be greater than that of the natural, resting wing, or of measurements taken from museum skins (see Svensson (1992) for details). > > > Also, it is a measurement of a single wing; it should not be confused with wingspan. --- # Horse computing ## Subject 1: Thumbelina [![Thumbelina on the left a dog on the right](https://i.stack.imgur.com/1Cl6y.jpg)](https://i.stack.imgur.com/1Cl6y.jpg) *Thumbelina compared to a dog.* [Thumbelina, the world smallest horse](http://www.dailymail.co.uk/news/article-409317/Meet-Thumbelina-worlds-smallest-horse.html) has 26Kg. So we have: $$ Weight = 26Kg $$ But we need grams, so: $$ Weight = 26000g $$ Next we need the natural logarithm in order to feed it into the function we found: $$ Ln(Weight (g)) = Ln(26000) $$ We compute [Ln(26000)](https://www.wolframalpha.com/input/?i=Ln(26000)): $$ Ln(Weight (g)) = 10.165851... $$ Plug it in the function: $$Ln(Wing length(mm)) = \frac{1379}{1640}10.165851... + \frac{7357}{9020}$$ Compute [that](https://www.wolframalpha.com/input/?i=%5Cfrac%7B1379%7D%7B1640%7DLn(26000)+%2B+%5Cfrac%7B7357%7D%7B9020%7D) and we have: $$Ln(Wing length(mm)) = 9.363625... $$ Now we get the [wing length](https://www.wolframalpha.com/input/?i=e%5E%7B%5Cfrac%7B1379%7D%7B1640%7DLn(26000)+%2B+%5Cfrac%7B7357%7D%7B9020%7D%7D): $$e^{Ln(Wing length(mm))} = e^{9.363625...} $$ $$ => $$ $$Wing length = 11656.574347... mm $$ $$ => $$ $$Wing length = 11.656574... m $$ So, we have Wing length of **11.65 m (38.22 feet)**. **That's HUGE for poor Thumbelina!** --- ## Other subjects I'll be using data from the paper [Estimating a horse’s weight](http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0008/109988/estimating-a-horses-weight.pdf) from the Department of Primary Industries of Australia. *Subject 2: Anatomically Correct (Flying) Pony* The large pony has 360kg. [Wolfram|Alphing](https://www.wolframalpha.com/input/?i=e%5E%7B%5Cfrac%7B1379%7D%7B1640%7DLn(360000)+%2B+%5Cfrac%7B7357%7D%7B9020%7D%7D) we get: 106.233559... m (348.535 feet) Ok, that's ridiculous. --- # Evolution Before we consider the case of riding the animal, we need to consider that the non-ridden modes of locomotion would have evolve naturally, and then for it to be ridden it would require domestication. In particular breeders would select the stronger animals for reproduction in order to make offspring strong enough for carrying a human. ## The Six-limbs problem As with Anatomically Correct Angels, we run into the problem of six-limbed mammals. There are no examples in nature, and there reason to believe that the DNA structure doesn't support it※ - of course, a different structure could also evolve. ※: Researchers have created [mutated fruit flies that have legs where they should have antennas](https://www.theguardian.com/science/2013/aug/18/fruit-flies-embryology-hox-genes). This was done by swapping portions of DNA, this suggests that there is a limited number of locations where you can insert limbs in the DNA. It is also worthy to look at the lore: [![Bellerophon on Pegasus spears the Chimera, on an Attic red-figure epinetron, 425–420 BC](https://i.stack.imgur.com/aEcTF.jpg)](https://i.stack.imgur.com/aEcTF.jpg) *Bellerophon on Pegasus spears the Chimera, on an Attic red-figure epinetron, 425–420 BC* The depiction above gives some insight on the six-limb problem as we can imagine the wings as ramifications of the frontal legs. I also want to note on the wing aspect ratio, that different wing aspect ratios are characteristic of different flight styles: [![Wing aspect ratio](https://i.stack.imgur.com/L47yU.png)](https://i.stack.imgur.com/L47yU.png) *Examples of Wing aspect ratio* If Pegasus is used for battle, it probably has high agility as to avoid attacks and approach the target from different angles. So, a wing with similar proportion to the crow depicted above example is expected. # Conclusion **Giving wings to horses result in exaggerated size** There is no way around it, if want something that resembles a Pegasus, you need to evolve the horse to have less mass. Similarly to the Anatomically Correct Angel, the Anatomically Correct Pegasus needs to have thinner bones... The Anatomically Correct Pegasus has two solutions: It can fly but you can't ride it because the bones are too weak to support a human. You can ride it, but it can't fly, the wings are only an ornamental vestige kept by the breeders. [Answer] I found good points in all the answers so far. I disagree with the ones that say it's not possible, though. I say it's possible. I believe that, as always is the case with the anatomically correct series, people are taking a very stiff aproach when it comes to mysthical beasts. In this case, people would like to see an [*Equus ferus*](https://en.wikipedia.org/wiki/Horse) with bird wings attached to it, obviously leading to problems related to weight. [![The horn is optional](https://i.stack.imgur.com/nMxrN.png)](https://i.stack.imgur.com/nMxrN.png) (Unicorn horn entirely optional) I'd like to take a different approach. I'd like to base the feasibility of my pegasus, henceforth known as the *Hippopterus quadratocubus*, on three pillars: * There have been really big critters flying on Earth before. I present you [*Quetzalcoatlus northropi*](https://en.wikipedia.org/wiki/Quetzalcoatlus) and *Quetzalcoatlus sp.*: [![Dragons!](https://i.stack.imgur.com/IBzAG.png)](https://i.stack.imgur.com/IBzAG.png) Weight estimates vary, but the bigger guy in the pic above could probably reach 200 kg and still fly like a vulture. * You don't need the wings to be homologous to other limbs. See [the real life dragons (non Komodo ones), also known as gliding lizards](https://en.wikipedia.org/wiki/Draco_(genus)). As the wiki says: > > The ribs and their connecting membrane may be extended to create a wing > > > [![So cute](https://i.stack.imgur.com/RInsL.jpg)](https://i.stack.imgur.com/RInsL.jpg) * It is believed that [mammals evolved from reptiles](https://en.wikipedia.org/wiki/Evolution_of_mammals), so if we stretch our suspension of disbelief enough, then a mammal species could evolve to have traits that in our real world have only ever been perceived in reptiles, extinc or extanct. With these three points in mind, imagine if you will a genus of mammals that branched off from the Equidae family a few million years ago. These beasts were originally very small, and at some point developed the following characteristics: * Their ribs are articulated, with the first articulation close to the vertebral column. They fold a couple times before enveloping the torso, and they don't support the structure of the thorax. They can open up like wings. A thick hide membrance, called a [patagium](https://en.wikipedia.org/wiki/Patagium), connects them. All in all their wings will resemble something between the wing of an eagle and the wing of a vulture. * A smaller, secondary patagium connects their legs, from the ankle up, to the ribs when they open up. The secondary patagium only serves to add to surface area during flight. Yes, our pegasus is going to fly with its legs spread open to the sides. * To make up for the loss of the bone ribs, a secondary set of hard, cartilagenous ribs has replaced them as the supporting structure for the thorax. * The *Hippopterus* has about the body size as an adult horse, but due to lighter bones and organs its weight is about 80 kilograms. Compare with [the 380 to 1,000 kilograms provided by Google](https://www.google.com.br/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=adult%20horse%20weight), and you see it's quite light when compared to an *Equus ferus*. The *Hippopterus* also looks very skinny, like an undernourished greyhound or whippet. * Last but not least, the wingspan. It is a little more than that of the *Quetzalcoatlus sp.*, the smalled of the two in the diagram above. Small Quetz has around 5,5 meters of wingspan. I'm eyeballing a 6 to 6.2 meters wingspan. This should give it about the same weight to wing surface ratio as the smaller Quetzacoatlus. So, all in all... Our flying horse has a very bizarre appearance. It will probably fly by soaring over thermal currents. It can flap its wings but cannot sustain powered flight for more than a few seconds. It can, however, glide for miles once it reaches a high enough altitude. It probably evolved this method of flight as a succesful migration strategy. Weighting less than an adult ostrich, it is probable that a human would only be able to ride it while it walks, but not while flying. The *Hippopterus* would also be a very bad ride, and would neither tolerate nor withstand a human sitting on it for long periods. So, to summarize: * Horse size and form: check * Wings: check * Being able to fly and gallop: check * Is it possible? Yes. * How would they evolve? As an offset of the Equidae, developing both [*Draco*](https://en.wikipedia.org/wiki/Draco_(genus)) and [*Azhdarchidae*](https://en.wikipedia.org/wiki/Azhdarchidae) reptilian characteristics. * It would be possible to ride one? Only on land, only for a very short while, and you'd probably be in for a very rough ride. If you want a flying ride that badly you'd probably do better by getting a [microlight](https://en.wikipedia.org/wiki/Ultralight_aviation). [Answer] **No, Pegasuses are Not Possible** Ah, the Anatomically Correct series - where we all learn that just because you can draw something doesn’t mean it would work. **The Primary Issue: Wingspan** First let's start with the size of horses. Per [Wikipedia](https://en.wikipedia.org/wiki/Horse), "Light riding horses usually range in height from 14 to 16 hands (56 to 64 inches, 142 to 163 cm) and can weigh from 380 to 550 kilograms (840 to 1,210 lb)". So let's say our horse is on the lighter side, at 380kg/840lbs. Next let's consider the necessary wing size. As outlined in [this academic paper](https://ocw.mit.edu/courses/materials-science-and-engineering/3-a26-freshman-seminar-the-nature-of-engineering-fall-2005/projects/flght_of_brdv2ed.pdf) on the topic of wing size to speed physics, let's use the equation: W/S = 0.38v^2 Where; W = Weight (Newtons) per Wing S = Surface Area of the Wing (square meters) V = Velocity (Meters per Second) **Note:** This equation assumes air density at sea level. So how fast should this horse fly? Traditionally a Pegasus has demonstrated a speed faster than a running human, so let's go with that. The fastest human speed is [12.4m/s](https://en.wikipedia.org/wiki/Footspeed), so we'll go with 12.5m/s just to edge it out. Result: **The resulting surface area of the wings must be at least 23.84 square meters per wing.** Compared to the human in a hang glider above, which has a surface area less than 11.9 square meters... for both "wings" put together! **This probably puts wing length in the area of 10 meters (33 feet) to a side.** Now imagine a horse dragging a 10 meter (33 foot) wing on each side while it tries to gallop! **NOTE:** The wingspan would actually have to be larger, to additionally account for the weight of the wings themselves! [Answer] # No - Not Possible Is my call. The largest known flying bird (living or extinct) appears to be [Pelagornis sandersi](http://www.livescience.com/46679-largest-flying-bird-discovered.html) This bird had a wing-span of some 20-24ft (up to 7.3 metres) and weighed something between 50 and 90lb (22-40 kilos) The average horse weighs something between from 380 to 550 kilograms (840 to 1,210 lb). For a good sized Pegasus, let's take the larger of the two to make it rideable. So that's over 10 times the weight of the largest bird. How big are those wings going to be, and how massive will the muscles that drive them have to be? And muscles aren't the lightest of tissue types. Then there's the bones to support those wings and the muscles that drive them. And how much larger will those wings have to be to support a rider...? It's all too much for reality as far as I can see. [Answer] Well adding onto all the answers here. It should be noted that a horse is HEAVY. Its stability and speed on land come because of its weight and anatomy. Imagine a horse, light as a feather, with hollow bones and zolatific wings! [Answer] To prevent the need from having obscenely large wings, I will choose a relatively light horse breed for our pegasus. The Spanish mustang weighs 365 kg and is 120 cm tall. The pegasus's bones should be hollow, allowing for a 10% reduction in mass, so our pegasus now weighs 328.5 kg. A horse is not normally going to have six limbs, so there has to be some handwaiving there. Based on the wings of a Ruppell's vulture, our pegasus should have a wingspan of 15.88 m, a wing area of 36.02 m^2, and a wing loading of 9.12 kg/m^2. That is 15.88 m *minimum*. If it were to have the wings of a black kite, its wingspan would be 31.28 m and its wing area would be 125.14 m^2. That is a *102 foot* wingspan and a *1,347 square foot* wing area. [Answer] Yes of course. Its a pegasus not just a horse. For the same body length a average bird weighs four times less than a mammal. And they are mythologically carnivorous with sharp teeth. Which makes their guts weigh less and they can obtain 50-90% more energy for a given assimilation of biomass. At 20 meters per second a horse can easily take off from a dead run, and at 80-100kg the light bone structure and gut weight (probably unable to take off immediately after eating) yield a modest wingspan of only 4-5 meters, with their elegant wings folded they are only about twice their body length of 2.5 meters. Fish and large mammals whose spines are broken from a four footed pronk from above or who are herded off of cliffs or into deep water where they are easily struck provide most of their diet, though they are omnivores, only high energy food items appeal to them. As for riding it - only if you are very small and light, less than 50kg, and generally only for short distances. Scouting and infiltrating i imagine would be their only use i wae. [Answer] Lots of talk about wing size here, but it isn't about size it's about LIFT. A 747-400 weighs about 300 metric tons (total weight, so includes the wings) and has a wing area of about 525m squared each (1050m squared in total). So in really simple terms as a ratio that's 3.5m squared wing area per metric ton (1050 divided by 300). A horse weighs anywhere between about 400kg and 1000kg, so let's go in at 1000kg (one metric ton) which we'll assume includes the rider too. By the above, we need 3.5m squared wing area, so each wing is 1.75m squared. Easy! (yes, I'm ignoring about a million points in relation to power to weight, take off speed, aerodynamics to name but a very few...but then again a Pegasus is a mythical animal so I may as well be mythical with my logic and maths!) ]
[Question] [ I am interested in the concept of a chitin *endo*skeleton (rather than exoskeleton). In the role of a humanoid internal structural skeletal system, how would chitin compare to bone? Would it be as strong? More flexible, or less so? Would it resist breakage better, or be more susceptible to fracture? Perhaps heavier, or lighter? [Answer] * Faster healing. [Chitin has a direct effect on Human health](http://onlinelibrary.wiley.com/doi/10.1002/pat.1280/epdf?r3_referer=wol&tracking_action=preview_click&show_checkout=1&purchase_referrer=en.wikipedia.org&purchase_site_license=LICENSE_DENIED_NO_CUSTOMER). * Lighter skeleton. oOr bone takes 30%–40% the weight of a healthy non-obese adult. * Our caloric intake would need to be bigger cause chitin consumes more energy. * We would be more fragile, as bone gathers minerals over time to become stronger. * Less age related handicaps, because bones after a certain age start to lose all the minerals, deform, bend and become thinner. * The skeleton would be more flexible which means impacts would be more physically painful but less destructive and deadly. A punch in the chest will hurt more but the hit would be almost completely absorbed by the rib cage and the surface of skin instead of your internal organs, like lungs and heart. **Obviously this only if chitin is supported by other proteins like resilin, otherwise it would be as rigid and fragile as glass** Minor effects would be higher risks of cancer due to faster regeneration, and losing a lot of teeth. Chitin, being more flexible, would allow for a tooth to fall more easily in case of incidents. Just like sharks we would change about 30'000 or more teeth during our lifetime. ]
[Question] [ So at some point in the future, humans have small colonies on the Moon, on Mars and many space stations in orbit of all the planets in the solar system. Everything is going great until one day something happens on Earth that sparks a global nuclear war. The USA, Russia, China, India, Pakistan, UK, France, Israel and North Korea shoot off all their missiles and nuke the world. Most of humanity on Earth is wiped out and the entire surface is irradiated. So how long until the humans who live off-world could return to earth and safely (without the need for rad suits or other preventative measures) begin farming again? **Parameters for the question:** * Assume 2016 level nuclear weapon capability when the war happens. * No large scale terraforming capability. * Don't worry about the space colonies' survivability without the earth. * Don't worry about what started the war. * Don't worry about any survivors on surface of the earth. * All defences against the warheads making groundfall are ineffective. All nukes hit their targets, every continent is targeted with basically 100% coverage. * Not looking for a super exact answer, just a general best case/worst scenario...is it like 5 years, 10 years, 1000 years, 10000 years? NOTE: People seems to stuck on the fact that this nuclear event isn't possible. My question doesn't care about that, in my scenario just assume this happens, that there are enough missiles with 2016 tech to devastate the entire habitable surface of the earth. How long before the Earth is safe and radiation free so that humans can live there again? [Answer] ## Probably about 5-10 years minimum Fallout would not be a major long-term problem, the timescale on which radiation due to fallout would present a serious danger would be less than 5 years. See [this article](http://www.bmartin.cc/pubs/82cab/) which says: > > Radioactive material which takes longer than 24 hours to return to earth is called delayed or global fallout. Some of the delayed fallout remains in the troposphere (see Figure 1) for days, weeks or months. This tropospheric fallout usually returns to earth within ten or 15 deg of latitude of the original explosion, mostly by being incorporated in raindrops as they are formed. The clouds of nuclear explosions larger than about one megatonne penetrate partially or wholly into the stratosphere, and deposit fission products there, which become stratospheric fallout. Since the stratosphere has no rain formation and is less turbulent than the troposphere, radioactive particles in the stratosphere can take months or years to return to earth. During this time the particles can move to any part of the globe. > > > By the time stratospheric fallout reaches the earth, its radioactivity is greatly reduced. For example, after one year, the time typically required for any sizable amount of fission products to move from the northern to the southern stratosphere, the rate of decay will be less than a hundred thousandth of what it was one hour after the blast. It is for this reason that stratospheric fallout does not have the potential to cause widespread and immediate sickness or death. > > > According to recent climate modeling, the big problems which could delay a return in your scenario would be: 1. [Nuclear winter](http://en.wikipedia.org/wiki/Nuclear_winter) due to smoke particles remaining in the upper atmosphere for years, which would cool and darken the world enough to make growing crops difficult for several years after 2. Destruction of a lot of the ozone in the [ozone layer](http://en.wikipedia.org/wiki/Ozone_layer), which would greatly increase the amount of dangerous ultraviolet radiation from the Sun that reached the surface, harmful to both people and crops. ## Nuclear winter Climate scientist Alan Robuck has done a lot of research on the effects of nuclear war, and has posted a large number of links to papers and articles on the subject on [this page](http://climate.envsci.rutgers.edu/nuclear/). He also has a good review article from 2010 online [here](http://climate.envsci.rutgers.edu/pdf/WiresClimateChangeNW.pdf). One point he notes on p. 420 of that article is that the nuclear winter effects would be exacerbated by the fact that cities and industrial facilities would likely be targeted, as opposed to the more uniform spread you seem to suggest in your question (which would make less sense politically and would have less damaging effects). If these areas are targeted it should produce an especially large amount of soot and smoke: > > Megacities have developed in India and Pakistan and other developing countries, providing tremendous amounts of fuel for potential fires. Following the flash of light comes the blast wave (like thunder following lightning) which will break apart many structures and blow out the flames, but crumpled structures burn more easily and fires would be reignited by burning embers and elec- trical sparks. Imagine how easily a house would burn with open gas lines or a filling station with gas pumps knocked over. In fact, there are many flammable sources of fuel for fires in cities, including buildings and their contents, trees, and even asphalt. Modern materials, such as plastics, not only burn with a sooty smoke, but also produce high levels of toxic chemicals. ... The climatic effects of the use of nuclear weapons depend on the amount of smoke they would generate, and this depends on the targets. Nuclear targeting plans call for not only cities to be targeted, but also industrial facilities such as oil refineries and wells. Forests around military targets would also provide fuel. All these targets together would produce clouds of black sooty smoke, which rise into the atmosphere. > > > Most of the modeling has investigated the effects of smaller-scale nuclear conflicts, like a nuclear war between India and Pakistan, but we can at least use the results of these studies as a sort of lower bound on what would happen in your scenario. And at least one recent study has modeled a global nuclear war with the full arsenal, the 2007 paper ["Nuclear winter revisited with a modern climate model and current nuclear arsenals: still catastrophic consequences"](http://climate.envsci.rutgers.edu/pdf/RobockNW2006JD008235.pdf). This study used a preexisting [global circulation model](https://en.wikipedia.org/wiki/General_Circulation_Model), [Model E](http://www.giss.nasa.gov/tools/modelE/) from the NASA Goddard Institute for Space Studies, which is [mainly used](http://data.giss.nasa.gov/modelE/) for climate issues unrelated to nuclear winter, like modeling global warming along with past climate change. The authors of the paper note on p. 3 that "This climate model has been tested extensively in global warming experiments [Hansen et al., 2005; Schmidt et al., 2006] and to examine the effects of volcanic eruptions on climate. The climate model (with a mixed-layer ocean) does an excellent job of modeling the climatic response to the 1783 Laki [Oman et al., 2006b] and the 1912 Katmai [Oman et al., 2005] volcanic eruptions." The paper estimates that about 150 teragrams of smoke would be released in a full nuclear conflict. As discussed on p. 6, the effects on global temperature would be dramatic for several years after, and even after 10 years they'd be comparable to temperatures in the last ice age (though of course there were warmer areas where farming would have been possible back then): > > A global average surface cooling of –7 °C to –8 °C persists for years, and after a decade the cooling is still –4 °C (Fig. 2). Considering that the global average cooling at the depth of the last ice age 18,000 yr ago was about –5 °C, this would be a climate change unprecedented in speed and amplitude in the history of the human race. The temperature changes are largest over land … Cooling of more than –20 °C occurs over large areas of North America and of more than –30 °C over much of Eurasia, including all agricultural regions. > > > The 2010 article had a graph of the temperature change observed in the model from the above 2007 paper, given a nuclear war in 2006, with the full-scale war releasing 150 Tg of smoke shown in brown: [![enter image description here](https://i.stack.imgur.com/TTB2T.jpg)](https://i.stack.imgur.com/TTB2T.jpg) Robuck also notes in the article that even in the case of a much more limited nuclear exchange which only put 5 Tg of smoke into the atmosphere, after 10 years the global temperature would still be 0.5 °C cooler than before, which is a bigger deal than it might sound: > > even after 10 years the temperature would still be 0.5 °C colder than normal. These numbers might not seem like much, but even during the Little Ice Age, global temperatures were only about 0.5 °C below normal. Every once in a while large volcanic eruptions produce temporary cooling for a year or two. The largest of the past 500 years, the 1815 Tambora eruption in Indonesia, produced global cooling of about 0.5 °C for a year. Year 1816 became known as the ‘Year Without a Summer’ or ‘18 hundred and froze to death’. There were crop-killing frosts every month of the summer in New England. The price of grain skyrocketed, the price of livestock plummeted as farmers sold the animals they could not feed, and a mass migration westward from the US East Coast across the Appalachians to the Midwest began. In Europe, widespread famines occurred ... A nuclear war could trigger declines in yield nearly everywhere at once, with strong impacts on the global agricultural trading system. > > > As for the question of farming after a global nuclear war, he says on p. 423: > > Not only would it be **virtually impossible to grow food for 4–5 years after a 150-Mt nuclear holocaust,** but it would also be impossible to obtain food from other countries. > > > And on that page and the next he discusses some of the reasons farming would become so difficult in the aftermath: > > There are many ways that agriculture is vulnerable to nuclear winter. The cold and the dark alone are sufficient to kill many crops. Superimposed on the average cooling would be large variations. During the summer of 1816 in New England, there were killing frosts in each summer month.30 Only 1 day with the temperatures below freezing is enough to kill rice crops. Colder temperatures mean shorter growing seasons, and also slower maturation of crops; the combination results in much lower yields. Most of the grains that are grown in midlatitudes, such as corn, are actually of tropical origin, and will only grow in summer-like conditions. For example, a study done in Canada shows that with summer temperatures only 3 °C below normal, spring wheat production would halt.8 Insufficient precipitation would also make agriculture difficult. > > > Finally, p. 5 shows a large drop in global precipitation, down to about 45% of its current value in years 2-4 for the 150 Tg case (the black line with open circles in the top graph): [![enter image description here](https://i.stack.imgur.com/OZmne.jpg)](https://i.stack.imgur.com/OZmne.jpg) ## Ozone layer Unfortunately the 2007 paper which models global nuclear war didn't model ozone loss, and just noted other studies had found "global ozone loss is likely". I couldn't find any recent papers modeling the effects of a global nuclear war on ozone, but [this paper from 2008](http://www.pnas.org/content/105/14/5307.full) deals with a more limited nuclear exchange that puts 5 Tg of smoke into the upper atmosphere, with these results: > > We calculate large losses in total (column) ozone that persist for years after the soot input. The global mean ozone column remains depleted by 20–25% for 5 years after the injection (Fig. 1). Catalytic destruction during the transport of air poleward compounds ozone loss at high latitudes. Throughout the first 5 years, total ozone depletions are 25–45% at midlatitudes and 50–70% at northern high latitudes. > > > In the discussion section they talk about biological consequences: > > Conclusive evidence shows that increased UV-B radiation damages aquatic ecosystems, including amphibians, shrimp, fish, and phytoplankton (13). The effects of sunlight on the biota are quantified as a product of the sun's spectrum at the Earth's surface and the action spectra for biologically damaging processes, such as erythema, carcinogenesis, and photoinhibition. An analysis of biological sensitivity to UV spectral changes concluded that a 40% ozone column depletion at 45°N – as computed here – would increase DNA damage (believed related to carcinogenesis) by 213%, and plant damage (e.g., photoinhibition) by 132% relative to normal conditions (14). The smallest ozone column losses are predicted to occur in the tropics, where self-healing limits depletion to ≈10% during the first 3–4 years. Although we found no studies of biological impacts of ozone loss in the tropics, the midlatitude analysis concludes that a 10% column loss would increase DNA damage by ≈28% (12, 14). Ozone losses at midlatitudes point to DNA effects in the range of 150% for five years or more. The biological implications should be further investigated. > > > Similarly, [this paper from 2014](http://climate.envsci.rutgers.edu/pdf/MillsNWeft224.pdf) also models a limited exchange adding 5 Tg of smoke to the air. As summarized in the paper's abstract: > > Our calculations show that global ozone losses of 20%–50% over populated areas, levels unprecedented in human history, would accompany the coldest average surface temperatures in the last 1000 years. We calculate summer enhancements in UV indices of 30% – 80% over midlatitudes, sug- gesting widespread damage to human health, agriculture, and terrestrial and aquatic ecosystems. Killing frosts would reduce growing seasons by 10 – 40 days per year for 5 years. Surface temperatures would be reduced for more than 25 years due to thermal inertia and albedo effects in the ocean and expanded sea ice. The combined cooling and enhanced UV would put significant pressures on global food supplies and could trigger a global nuclear famine. > > > More details on the ozone loss on p. 168: > > As in Mills et al. [2008], we calculate massive ozone loss as a consequence of these extreme stratospheric temperatures (Figure 8). Consistent with that work, we calculate a global average column ozone loss of 20%–25% persisting from the second through the fifth year after the nuclear war, and recovering to 8% column loss at the end of 10 years. Throughout the first 5 years, column ozone is reduced by 30%–40% at midlatitudes and by 50%–60% at northern high latitudes. > > > Pages 172-174 discuss the effects of increased ultraviolet radiation from ozone loss on plants and animals: > > Pierazzo et al. [2010] reviewed literature considering the effects of large and prolonged increases in UV-B radiation, similar to those we calculate, on living organisms, including agriculture and marine ecosystems. General effects on terrestrial plants have been found to include reduced height, shoot mass, and foliage area [Caldwell et al., 2007]. Walbot [1999] found the DNA damage to maize crops from 33% ozone depletion to accumulate proportionally to exposure time, being passed to successive generations, and destabilizing genetic lines. Research indicates that UV-B exposure may alter the susceptibility of plants to attack by insects, alter nutrient cycling in soils (including nitrogen fixation by cyanobacteria), and shift competitive balances among species [Caldwell et al., 1998; Solheim et al., 2002; Mpoloka, 2008]. > > > The ozone depletion we calculate could also damage aquatic ecosystems, which supply more than 30% of the animal protein consumed by humans. Häder et al. [1995] estimate that 16% ozone depletion could reduce phytoplankton, the basis of the marine food chain, by 5%, resulting in a loss of 7 million tons of fish harvest per year. They also report that elevated UV levels damage the early developmental stages of fish, shrimp, crab, amphibians, and other animals. The combined effects of elevated UV levels alone on terrestrial agriculture and marine ecosystems could put significant pressures on global food security. > > > The ozone loss would persist for a decade at the same time that growing seasons would be reduced by killing frosts, and regional precipitation patterns would shift. The combination of years of killing frosts, reductions in needed precipitation, and prolonged enhancement of UV radiation, in addition to impacts on fisheries because of temperature and salinity changes, could exert significant pressures on food sup- plies across many regions of the globe. As the January to May 2008 global rice crisis demonstrated, even relatively small food price pressures can be amplified by political reactions, such as the fearful restrictions on food exports implemented by India and Vietnam, followed by Egypt, Pakistan, and Brazil, which pro- duced severe shortages in the Philippines, Africa, and Latin America [Slayton, 2009]. It is conceivable that the global pressures on food supplies from a regional nuclear conflict could, directly or via ensuing panic, significantly degrade global food security or even produce a global nuclear famine. > > > And remember, both the studies above deal with the 5 Tg of smoke scenario, a full-scale nuclear war was predicted to put about 30 times that much smoke into the upper atmosphere, presumably having a significantly larger effect on the ozone layer. [Answer] ## 0 seconds The entire world's nuclear arsenal could hardly make the entire planet uninhabitable. [There are presently about 15,000 nuclear warheads](http://www.icanw.org/the-facts/nuclear-arsenals/), let's say with an average yield of 100kt. Only about 4,000 of these are at any reasonable level of deployment readiness, and the reliability of the carrying missiles is less than 100%. Let's guesstimate that the average warhead is about 100 kg, to which you have to add the displaced mass of irradiated soil in a ground burst (most nukes are programmed to be airbursts though to maximize blast damage). > > Most of the radiation hazard from nuclear bursts comes from short-lived radionuclides external to the body; these are generally confined to the locality downwind of the weapon burst point. This radiation hazard comes from radioactive fission fragments with half-lives of seconds to a few months, and from soil and other materials in the vicinity of the burst made radioactive by the intense neutron flux. > [Source](http://www.atomicarchive.com/Effects/effects17.shtml) > > > With 100kt average yield, the damage radius is about 3km or about 15 sq km. Multiply times 4000. That's 60,000 sq. km. Enough to devastate most of the metropolitan areas on the planet and blast most of the military bases off the map, but the earth is 149 million sq. km (just the landmass). That's a tiny percentage. Even with intense fallout clouds, it still does not add up to enough material to render the entire planet unihabitable. Remember, the Earth is big. Actually, it is likely that more radioactive debris would enter the atmosphere from the failure of cooling bays in nuclear power plants after the attack If you really, really want to make the planet uninhabitable, you either need a massive, massive arms race, or [**better bombs**](https://en.wikipedia.org/wiki/Antimatter_weapon). --- Edit Re **nuclear winter**: The kinetic energy of the impactor that killed off the dinosaurs [was in the range](http://arxiv.org/abs/1403.6391) from 1.3e24 J to 5.8e25 J, whereas a single nuke outputs about 420e12J, 10-12 orders of magnitude less. Again, considering that most detonations are going to be airburst for maximum surface damage, the amount of dust put out by 4,000 nukes is still going to be, on energetic considerations alone, at least 1 million times less than that impactor. [Answer] To clear somewhat: > > let's say with an average yield of 100kt > > > Actually, average yield nowadays is closer to 350-500 kilotons for ICBM RV's. Very few >1 megaton yield systems remain in stockpiles, I'm not sure if any of those are in ready stockpile / active service tho. As such, it's most probable that they would not have chance to be used in a global exchange scenario. > > Most of humanity on Earth is wiped out and the entire surface is irradiated. > > ... every continent is targeted with basically 100% coverage. > > > With current stockpiles it would be problematic. What is considered "most is wiped out"? Even hitting all of population centers at peak time, you will not wipe out most of humanity in one prompt strike. At most you can count for 40-70% prompt casualties within any given city, and that is assuming use of more than one warhead per city, to maximise overpressure / thermal exposure (and then, you will hit even less population centers) - human body is actually more resistant to overpressure than concrete buildings, unless you are in a collapsing building, hit by debris or thrown against something that causes actual damage to you. Thermal damage depends on fireball having line of sight to you for first few seconds (low kiloton) to a minute (high several megatons yield) after detonation. The long term radiological effect will be strongly dependent on whether or not detonations are ground bursts (so you can have highest fallout, but, again, it's on the expense of prompt effects of overpressure area, and thermal exposure because the fireball will be occluded by terrain / buildings). Actual fallout plumes can be very large - for example, 1 megaton weapon detonating in Paris will easily cause serious radiological hazard as far as London, provided that wind is steady and correct (and any rain on the way will lessen the range, on the expense of localised depositing of fallout). As stated above - current stockpiles can wipe out largest cities, and military but they are not enough to be an instant global doomsday device. ]
[Question] [ I've got an image in my head of a world where it's just normal that the star is black with a golden halo around it - in other words, where the planet is in a state of perpetual solar eclipse. Are there any mechanisms that could lead to this occurring naturally? It seems like a tidally-locked moon around a tidally-locked planet could produce such an effect, but I might be misunderstanding the dynamics of such an arrangement. And if that would do it, is there anything preventing such a system from developing naturally? [Answer] What you are describing is an annular eclipse, where the moon is not quite as big (visually) as the star it eclipses. This is not possible. First off. An eclipse is a localized phenomenon. The parallax of being in different places on the planet looking at the star and the moon will give them different relative positions. To eliminate this problem, the "moon" would have to be closer to the star than to the planet and almost as big as the star. A global total solar eclipse is possible, if you are on a moon being eclipsed by the planet it orbits. The planet is bigger than the moon and casts a bigger shadow that the moon can fit entirely within. This won't give you the ring of light that an annular eclipse does though. If the planet has an atmosphere, then you might be able to see it lit up like a ring shaped sunset. That's why the moon is red when eclipsed by Earth. Making that permanent though isn't going to work. Tidal locking is about the rotation of a body about its axis, not its movement though its orbit. The moon is locked to Earth which means we see the same face of. You can't make the orbit of the moon around the planet the same duration as the orbit of the planet around its star (which is what you are probably trying to get at with your double tide lock idea) The moon would be so far away, it wouldn't be in orbit around the planet any more and certainly wouldn't be close enough to cause an annular eclipse. To get something at a fixed position with respect to the star would require positioning at a Lagrange point. Either L1 or L2. These can be thought of as "orbits with periods equal to the orbit of the planet" but it's a bit more complicated and only two points work, not the whole orbit. Those points are directly in line with the star though so that might seem it would work. L1 is between the planet and its star. If something were that big enough to block the star, you'd get a permanent eclipse, until it drifted away which would eventually happen as L1 is unstable. L2 is on the far side of the planet so you might be able to get a planetoid (not exactly a moon or a planet) to sit there, although it's again unstable so the planetoid would drift away from the point eventually. Earth Sun L1 and L2 are about $1.5\times10^6\rm{\,km}$ from Earth. When it's causing an annular eclipse, the Moon is about $4.0\times10^5\,\rm{km}$ from Earth. Moving the moon out that far would reduce it's angular size by a factor of $3.75$ so we'd have to scale up its radius by the same amount to keep it visually the same. That would make it slightly larger than Earth! Even if it weren't for the instability of L1, it would need an incredibly low density to avoid disrupting the whole system. Conversely you could do something like put Jupiter at $0.93\,\rm{AU}$ then put Earth at Jupiter-Sun L2 ($1\,\rm{AU}$ from the sun), Jupiter would be about 50 arc minutes in radius (if I did the math right). This would be a bit less than twice the angular size of the sun at that distance. You might see a bit of light around the edges of Jupiter diffracting through its atmosphere. This would be subject to parallax variation, but not as much as with an annular eclipse. You have the basic problem of stability though. Earth might stay at L2 for a little while, but it would drift away without something holding it in place. It would end up as a moon of Jupiter, crashing into Jupiter or being flung out of the solar system. [Answer] As the impossibility of such a set-up is already stated by @smithkm, we have to look into other ways to make the effect you present possible. A possible naturally occurring thing that would permanently block the star is a ring system or very thick asteroid belt closer to the star than the planet. A view may then look something like this: [![cloud](https://i.stack.imgur.com/nzG3B.png)](https://i.stack.imgur.com/nzG3B.png) Not exactly a halo, but rather two thin slices. [Answer] **Note: My original answer was incorrect; tidal locking would not produce such a scenario. For an excellent explanation of why this is the case, see smithkm's answer. I want to leave in some notes regarding what would happen if there *was* somehow an object between the planet and the star. Not, though, that such a scenario is essentially impossible.** There would be some interesting effects due to this arrangement: 1. **Tides would be incredible - and not-existent.** Tides are caused by the various alignments of the Sun, Moon and Earth. Tidal bulges are the result, and can vary depending upon their location relative to the Sun and Moon. This arrangement would mean that the moon is forever on one side of the planet, and so the tidal bulges are forever like the spring tides shown [here](http://oceanservice.noaa.gov/education/kits/tides/media/tide06a_450.gif): [![enter image description here](https://i.stack.imgur.com/HyGo2.gif)](https://i.stack.imgur.com/HyGo2.gif) 2. **No change in the time of day.** Well, this actually applies to *any* planet tidally locked to a star. One hemisphere would always be in sunlight, and one hemisphere would always be in shadow. It would be the same on the moon. One side would have a blazing view of the star, while the other would have a nice view of the planet. 3. **You could build a space elevator to the moon.** I asked about [building a space elevator between doubly tidally locked bodies](https://space.stackexchange.com/questions/5193/space-elevator-between-doubly-tidally-locked-bodies) on Space Exploration a while ago, and the answers seem to apply here. As HopDavid and aramis said, it's possible but not very feasible. Still, it would provide an interesting form of transportation, and a handy one. All you need is hundreds of thousands of kilometers of carbon nanotubes and a lot of luck. [Answer] There is one possibility for this to occur, but it can only happen around a certain star. As you can see from [this answer](https://physics.stackexchange.com/questions/350805/seeing-something-from-only-one-angle-means-you-have-only-seen-what-of-its-su/350814#350814), > > Consider a neutron star. If the radius falls below 1.76 times the Schwarzschild radius for its mass, then due to the General Relativistic bending of light in curved space, then all of the surface is visible, when viewed from any direction > > > Any planet orbiting close to the neutron star will therefore be in the path of the light coming from the surface, obscuring it and generating an eclipse, and if the proportions and distance are in the proper range it might be well noticeable. I guess it will hardly looks constantly like a perfect halo, but still it will be a shadow. [Answer] I have one suggestion but that lies in more artificial/fantastical possibility: Not quite tidally locked, but using a similar concept... given a star, a planet and a satellite (i.e. lunar body or otherwise). The planet and the satellite are both surrounded by some sort of gas/construct that holds them together and dampens any movement relative to each other, this whole system (planet+satellite+stabiliser) is tidally locked with the star, the planet or satellite being at the far side and recieving the permanent eclipse effect. Essentially the planet and satellite act as one larger body that is tidally locked. As for if this idea is naturally possible? I suspect not, otherwise very unlikely. ]
[Question] [ The fantasy creature I am imagining (planning a short story or two around) satisfies the following analogy: > > Human is to Chimpanzee as "This Thing" is to Badger. > > > That is, the creature has a clear relationship to badgers, such as similar anatomy and behavioral inclinations. But it has also become much more highly evolved and sentient: i.e. tool use, its own religions/mythologies, sophisticated language both written and oral, a structured society with organized government, etc... I want this creature to retain a clear affinity for burrowing and living underground, eating tubers and worms found underground, making a living extracting minerals from the ground, artwork that relies on things like roots and clay, and so on. Thus it needs to still have digging claws, although it may use picks and shovels for larger and more difficult digging. At the same time, it needs to be able to hold a paper and pencil, make intricate carvings, use needle and thread, and indeed to swing those same picks and shovels. How would evolution handle this? I can accept very broad explanations, I prefer to paint my world with a wide stroke, if not with a broom. [Answer] Well a badger getting a thumb isn't hard to envision, racoons basically have thumbs, and claws. It's a little harder thinking about large digging claws with hands, but only a little. I would expect that the claws would actually become very useful and versatile tools in all their work. It would also affect the direction of their artistic areas. Finger painting would likely be out but carving would be a HUGE area of artistic endeavor. Pen and Paper? What ever for? Scratch your orders into a piece of wood. No need for writing utensils when you always carry one with you! Pencils are a pretty modern invention, and chalk like stuff was used, but what would be the need with claws? On top of that, early pens were quills dipped in ink, a clean well manicured claw would be even better, and in medieval times the manicured claw could be a 'symbol' of profession or status as one you can read/write. [Answer] The tools you mention need thumbs because they were created by creatures that have thumbs. I suppose that if a creature was intellect enough to use tools it would craft in a way to fit its anatomy. For small things like a pen or a needle it could use its claws like chop sticks, and for the more heavy tools it may have crafted them like gloves or extensions of its arms, or even make them in a way that you would need both hands to operate them. [Answer] The fine motor skills necessary for operating tools are difficult when your finger/claw ratios are as low as a badger's. Even with opposable thumbs, a badger's fingers aren't long enough to allow it to grasp an object (at least not in the way that a human grasps something, with fingers completely encircling it). Their claws may be able to encircle an object but with no joints in the claws, their control over it would be poor. For a badger-like species to evolve to the point where they would be likely to create and use hand tools, it's likely that you would see their fingers get longer and their claws get shorter. They would still be able to dig, but not as effectively. This would presumably be offset by their ability to use tools that are even more effective than claws. A badger-based species could also retain their claws *culturally* instead of biologically. Their physical claws could have evolved down to the point of being purely ornamental, but the species could traditionally fashion their tools to *resemble* claws. For example: instead of using a shovel, they could use a glove with large steel digging claws attached to it. This would merge the two worlds, giving them the traditional digging claws while treating them like a tool (that is, they can use them when appropriate, and not be burdened by them otherwise). [Answer] Possible evolutionary pressures (some of all could be acting simultaneously): * You need to dig through harder ground to get to better area. Opposable thumb allows you to wield a digging stick that is far superior to your claws * Holding a digging stick allows you to preserve your claws, making you fitter overall * Your ancestors developed ability to walk between two patches of soft diggable ground. Same reason fish developed lungs and other land-based adaptations. The claws make it easy to see why erect gait developed instead of 4-legged one (plus, being erect helps you see predators further), and that's pretty much leading to same evolutionary territory as Homo Erectus had for developing opposable thumb. See summary here: <http://www.ruf.rice.edu/~kemmer/Evol/opposablethumb.html> [Answer] You see, they could very easily have thumbs and claws, as raccoons have both thumbs and claws. Besides, look at the Diamond Dogs from My Little Pony. They live and dig underground, and have both thumbs and claws. But this comes at the cost that your creature's fingers would have to be even longer then the claws so it can grab things. Also, I would suggest that your creature to have arms much longer and much more muscular then it's legs, to burrow better. ]
[Question] [ > > **Defining what is a super intelligent civilization:** An industrial civilization > that invest on scientific progress and that builds and manipulates > computers, robots and nano-machines, has efficient automatized > communications and understand and manipulates physics and chemistry to > a level that they can efficiently create and study natural and novel > materials and improve their own biology, ecology and environment. > > > In a deep ocean planet with no solid surface outside water, if an intelligent industrial civilization evolves living on the deep ocean floor, at which tech stage they would start to study astronomy or try space exploration? How would they understand the universe before discovering the atmosphere? And after discovering atmosphere? And after discovering outer space? Further if the planet has an additional global ice cover with some kilometers in thickness separating the ocean from the atmosphere, how do this change the evolution of the civilization on the planet? And, if the planet has a thick and opaque atmosphere, how could this still further complicate the scenarios with and without the global ice cover? Could any of those possibilities result in a super intelligent civilization that thinks that all the universe corresponds to their own planet or they would always figure out that this is not the case before becoming a super intelligent? Or could this simply prevent them from becoming super intelligent to start with? If they become super intelligent, how hard would be for they to figure out that the universe is not limited to their own planet (if ever possible)? I am asking this question thinking specifically about what would happen if in the deep oceans floor of Europa or some other icy moon in the Solar System (though they do not possesses thick atmospheres), an intelligent tech civilization was living without knowing the existence of Earth. But this could also be applied to some extra-solar planets or moons. *[This is my first question in this community, so if there is any problems in its format, please provide me feedback and let me edit it before voting to close this question]* [Answer] **Water Worlds, probability and life** I have had similar thoughts as yours, specially for the case of a Europa or Enceladus type world, which is starting to seem the most likely type of planets for having liquid water. Think our Solar System, there is one Planet with liquid water on surface, one which had in past (Mars), however undersea oceans are almost certain in Enceladus and Europa and possible in several other bodies Ganymede, Callisto, Ceres, Titan and probably others. The lack of Sun light would certainly hinder development of life but I don't think it could be discarded. The aparent significantly higher probability of planets with water available in underground oceans migh somewhat compensate the less likely formation of life because of missing sunlight. It is interesting the other answer that mentions that more advanced lifeforms having developed on land inspite of it being much later than ocean life, not sure if that could be extrapolated to other worlds since I wouldn't be sure why that has happened. Ocean life certainly is not in bad shape and there are probably more species at sea that at land. Just seems that the stage they have evolved is in most cases sufficient for survival in that environment without having needed to develop into intelligent beings. **Alien Ocean civilizations** I would make a difference between an ocean civilization in an ocean in contact with an atmosphere vs one under a layer of ice. In the first case the civilization would eventualy reach the surface, and investigate the exterior, how much it could initially learn might depend on how deep they originaly evolved and presence or not of significant cloud cover in the atmosphere. **Under Ice Ocean Civs** Some of what applies in this case probably aplies also to previous case if the civilization where deep enough to make light absent. In these Europa-type worlds: * There would be no sunlight anywhere. * Therefore vision might not evolve or only in species evolving simultaneously some type of bioluminiscence, competing with other systems as sonar smell or others to interact with the world. * Lack of light and vision would make astronomy unknown for long stages of civilization development. * Maybe even the absence of paterns found in astronomy might slightly slow develoment of math vs other sciences. A civilization as we know would probably be sedentarious, this would make it unlikely at first to develop among species living in the open ocean, I speculate if such civilization apeared it would be either at the sea floor on at the sea top, in contact with the ice cover. Current speculation on posibility of hot vents in Europa at the sea floor might make a bottom civilization seem more likely, but maybe a "Top" civilization would be possible too if the life mass is enough for large animals living far from rocky bottom (or maybe the top could be chemically active in some way too.) Things in our evolution that we take for granted might take a different course of events, even knowing the world is round would probably not be known until the civilization expands enough to reach itself on the other end. For all this civilization knows they would just as likely think that the ceiling extends indefinately, something that would be possible to continue believing even well after they knew the world was round and therefore that the floor is finite and their world has a "center". I think this civilization would probably need to be at least at tech levels similar to ours or at minimum mid 20th century levels to even start speculating of the posibility of the world having an outer limit. This knowledge would probably be obtained from theoretical models, probably modeling pressures and gravitation. Gravitation, and Newton laws in general would probably take much longer to be accurately undestood, as on Earth these where modeled with important inputs from astronomy and observation of planets. Other chances are detecting the Sun by some type of radiation penetrating the ice and ocean in levels detectable to some science instrument. From then curiosity would eventualy lead to this new Field of Science (Astronomy). Even then much would be theorical and even debated until finaly being able to breach the ice cover. Considering that even in present Humans can reach the moon and other planets with probes, but still haven't made holes as deep as might be requiered by a civilization in Europa to reach outside the ice cover (and they would be drilling against gravity!) - maybe there could be a significantly developed civilization that knows little of the universe out of the ocean. Hey maybe there is a mega civilization now on Europa that is as advanced as us or more but has not developed technology or science to breach the ice cover yet. [Answer] I don't think there's a biological objection that you couldn't dispense with with a little research and a little hand waving. The food chain would be based on geo-thermal vents instead of sunlight, but that's manageable. It's also a good excuse for having sedentary (rather than nomadic) creatures who can build up material wealth and bennefit from things like specialization and science. The key difference would be having technology that works in liquid rather than gas; there's room for lots fun creativity and characterization. Instead of electricity for storing energy and doing computation you could have extensions of biological processes (like [biocomputers](http://en.wikipedia.org/wiki/Biocomputer)). Building becomes much easier, because you can make things buoyant rather than having to hold them up; [inflatable structures](http://inflate.co.uk/) are very natural. Communication is less of an issue because sound propagates so well in liquid, so radio and telescopes are much less useful (perhaps why your underwater intelligence isn't so great at astronomy). One stumbling block is not being able to burn fuel the usual kinds of fuel (wood, coal, oil, etc.), so you'll have to find a different exothermic chemical reaction or rely on a process like artificial [cellular respiration](http://en.wikipedia.org/wiki/Cellular_respiration) instead. Alternatively, if there are enough radioactive isotopes around you could get heat by mixing the right minerals together. Once you've got technology rolling (through bio-tech or primitive nuclear), getting through the ice or the atmosphere is only a matter of time and curiosity. [Answer] I would say most intelligence comes with a level of curiosity. Without curiosity and a need to know, what good is intelligence? So my guess like humans they would keep asking "Why: and "what if" Have a thick cloud that obscures the night sky? Questions like "what is hiding in up there?" would inspire checking out the clouds. A flying creature to observe might bring about this question earlier than without. Now their world view might be very different and what they believe is possible, we believed earth was the center of the universe, they won't even know about the 'universe'. So once someone successfully gets above the blinding atmosphere there would be a violent shift in the world view. Similar to having an ocean world covered in ice. while they might progress farther in many ways and remain ignorant of the universe outside, eventually someone would ask "How deep is the Ice?" and like on Europa "where does the water go?" when it squirts out. Not having an atmosphere would significantly retard the water life moving out, because they would be much more likely to die in a surfacing attempt before they could bring back any reports of what is out there. [Answer] > > Could any of those possibilities result in a super intelligent > civilization that thinks that all the universe corresponds to their > own planet or they would always figure out that this is not the case > before becoming a super intelligent? Or could this simply prevent them > from becoming super intelligent to start with? If they become > super-intelligent, how hard would be for they to figure out that the > universe is not limited to their own planet (if ever possible)? > > > The unfortunately boring answer is that life as we know it will not develop to near human levels, let alone beyond. As it exists on earth, complex life (beyond little crustaceans anyway) can't survive the pressure and temperatures at extreme depths (talking in the mile plus depth range). For example a complex circulatory system would collapse, and lungs or the marine equivalent would be unable to fill with air. In shallower depths complex live can obviously thrive, mammals even. Marine life has existed on earth for significantly longer than life on land and in many ways does not necessitate (to the degree required for land based animals) the degree of evolution that life on land does. Water movement and the ability to manipulate your surroundings is less valuable in a world where, for example, you can't throw a rock as a weapon. Considering the head start time line wise if an intelligent species were likely to develop in water it would have. > > In a deep ocean planet with no solid surface outside water, if an > intelligent industrial civilization evolves living on the deep ocean > floor, at which tech stage they would start to study astronomy or try > space exploration? How would they understand the universe before > discovering the atmosphere? And after discovering atmosphere? And > after discovering outer space? > > > Now, given that you can come up with a reason for there to be complex, intelligent life on this world here is how I would see things happening. Tech stages would essentially be similar to ours with a few additional requirements of course. * Going up: Simply travelling to the surface let alone space would likely require some sort of environment suit. * Underwater electricity: This is hard, we can do it today sure but with technology developed in the air...simple things like wrapping lines in rubber. Tapping and controlling electricity is hard enough but doing it in an environment like this makes it much more complex. * Collecting natural resources...mining becomes harder, transportation on the other hand would be less energy intensive. * There are more but these are the kinds of things you need to explain...or at least consider. > > Further if the planet has an additional global ice cover with some > kilometers in thickness separating the ocean from the atmosphere, how > do this change the evolution of the civilization on the planet? > And, if the planet has a thick and opaque atmosphere, how could this > still further complicate the scenarios with and without the global ice > cover? > > > Given that life develops to the levels we are talking in the first place these don't really make things much different other than it will take more time for the species to colonize and explore their entire planet. So yes given that a humanoid species developed (intelligence wise...their anatomy would still be very different). It would be a matter of time until they looked to the stars. This of course depending on them having the natural resources to do so. [Answer] Such a being may not even have vision, which would be another serious obstacle to studying astronomy. I will assume that this obstacle is surmountable, either by actual vision or by technological means (ie humans have developed tools to allow detection of phenomena not detectable to personal senses). Such exploration would go in stages. Exploring the lower pressures above them would involve some methods of surviving such (lack of) pressure. However, this technology would be fairly linear up to water/air barrier, where it would have a bit of a steep curve and then back to fairly linear. A shell of ice would result in a delay, but given enough time, explorers could figure out a way to penetrate it. Even prior to penetrating such a shell, there might be theories of some external bodies, depending on any detectable tidal effects and their understanding of gravity. Essentially, given enough time, the civilization could develop astronomy. Whether the civilization would last long enough would be a great topic to explore and a good source of drama. [Answer] The thing with all of this is... You people do not seem to understand what evolving in the depths of the sea would be like. If intelligent life(Comparable to us humans) were to somehow develop in pressure such as 700 miles deep, they would not have bone structure and lungs as we do or even known aquatic life. Their anatomy would probably seem impossible; Jelly fish like anatomy; Anatomy that would be able to adjust to going even deeper than 700 miles. With living conditions such as their's(Low sources of known energy to live off of), they might live on unknown energy sources that have not been discovered because of our limited technology in going into the extreme depths of the ocean. Considering the amount of possibilities we humans came into existence the way we did, I would say it is completely possible for life in the extreme depths of the ocean with unknown habitats, and living conditions that would be almost completely different to ours with the pressure difference, to develop intelligence comparable to ours. [Answer] Judging by the evolutionary trends we have seen on our own planet, you cannot have human-level intelligence evolving deep under an ocean. **A Summary Of Evolutionary History Of Earth's Aquatic Life Forms** prokaryotes (very simple, single celled organisms) appeared 3.8 billion years ago eukaryoted (advanced, but still single celled organisms) appeared 2.5 billion years ago primitive multicellular organisms appeared 800 - 900 million years ago sponges apeared some 600 million years ago pikaia, myllokunmingia and other primitive chordates appeared 540 million years ago first true fish (class agnatha) appeared 520 million years ago placoderms, sharks, acanthodes and other jawed fish appeared ~460 - 430 million years ago transition of fish to amphibians began ~420 million years go And that's it. The End. That's how far evolution went in the oceans. From the time of first amphibians some 420 million years ago up to the rise of modern man 0.2 million years ago, all the evolution regarding intelligent life forms has happened on land. Amphibians are smarter than fish. Reptiles are quite the more smarter than fish. Birds are very much smarter than fish. And it won't be a comparison matching a fish's intelligence with a non-primate mammal's (let alone a human's) Our great great great greatttttttttt ancestors left water and settled on land some 420 million years ago. Their evolution took a very long and winding path that led to a myriad of terrestrial life forms. And look where fish went! They are still at the same intelligence level they were 420 million years ago. So IF there is life in the oceans on some water-planet (a planet with no solid surface and basically a giant ocean floating in the space), you can only expect to find fish there. Nothing smarter. **Further Hindrances** Having a sheet of ice over the water surface (and you are saying it's thickness is in MILES) would totally throw the possibility of photosynthesis out of the window. No photosynthesis means no oxygen. No oxygen means slow, pathetic type of respiration and metabolism. Slow metabolism means your deep-ocean creatures would be limited to simple prokaryotes at most. They can't even evolve into eukaryotes, because eukaryotes had aerobic (using oxygen) respiration and their energy consumption was much more than prokaryotes (simple, sulphur eating cells). So I don't think you can get truly intelligent (comparable to mammalian intelligence level) creatures on a planet that has no solid crust. I'm sorry, but if you want to put intelligent creatures in the oceans, you will either have to solely rely on hand-waving everything we have known about evolutionary science so far. OR you can have your creatures evolve on land and then RETURN to water (such as cetaceans -dolphins and whales- which are mammals). Then only you can have a very very veryyyyyyyyy narrow possibility that some of their lineages could evolve into forms which are the intelligence level of an ape or monkey. [Answer] **Knowledge about the universe from under the ice shell** Given in the ocean of Europe you have an intelligent life form. What would they know of the world? * They would be able to measure the topography of the downside of that shell as is their heaven. * They would be able to measure the chemical compounds of that shell and observe the changes within. * They will most likely realize the volcanic activities which blow water up and bring new elements in which are not from their world. * They will realize and measure the tidal effects which are caused by Jupiter without knowing anything about Jupiter at first. * They might be able to calculate the heat budget of their world - how much comes from below, how much comes from above and in which periods. I am convinced if you have an intelligent species down there which is able of higher mathematics and measuring those things and have some kind of curiousity about the world they live in they should be able to get a conception of: * what is a planet based on their home. * what is gravity * gravitational forces outside the shell which cannot come from their planet therefore the existence of at least one other source of gravitation outside their own world * temperature differentials between inside the shell and outside the shell * material components of the outer side of the shell While it might be quite unlikely for them to ever be able to leave the ocean as they would need to penetrate the shell they might have a conception of at least two celestial bodys - their own they live on and one other which is producing the gravitational force resulting in tidal activity of the ocean. [Answer] I believe this is as much an exploration of evolution in general as it is about deep sea life. Any species that evolves has the potential to continue to evolve, stagnate, or perish - or all three. When a species finally evolves to a survival stage, a place where it has access to resources that perpetuate it, food, shelter and defense, it has to have impetus to evolve further. Hence, stagnation is possible. When a lifeform chooses to continue to evolve, it may or may not decide to evolve it's intelligence. It may simply evolve to be more prolific, as in most species. Biology becomes less relevant than the creativity and motivation of a species to further evolve intelligence. There is a point when humans reached this stage, and it is in modern times. There are bursts of genius that humanity has reached, but subsided from, then reached again. I believe even crystalline life could evolve to intelligence (given enough time) of genius level, especially for the impetus of immobility. It would want to move if it couldn't, and once it did, it would have an extreme burst of creativity, and motivation. I believe in the great depths of Earth's oceans, there is a high possibility of life on the precipice of evolving greater intelligence simply because of the impetus to survive such extreme environments. Because of the vast expanse of the ocean floor, and the tremendous amount of resources compared to another planet, it's possible for an entire advanced civilization to remain completely unnoticed by humanity, by choice. Life itself should have been impossible on Earth, given the primordial conditions of extremely volatile systems like tide, lack of oxygen, volcanism, and poisons present. Yet, we are here for some not-completely-understood reason. As for the highly radioactive moons around the gas giants, there is a remote possibility, but only if in their environments, there is a safe area for life. This could be where the hyper-huge tidal effects of the gas giants don't resurface the sub-ice-ocean floors on a regular basis. I wrote a book, [The Virtual Resort](http://www.lulu.com/shop/rene-saucedo/the-augmented-reality-resort/ebook/product-21975162.html), that details the evolution of an alien species on a water world, and studied the possibilities in detail. ]
[Question] [ In my story, which should be taken entirely seriously, mankind encounters a region of space occupied mostly by giant exo-householdobjects. That is, planet sized kettles, saucers, teacups, cutlery, etc. There is even a giant Russell Hobbs branded teapot, because this is how serious a story it is. They orbit around perfectly ordinary stars of various sizes. The protagonists are going to spend a significant amount of time stuck on a giant banana while observing a solar system with many such objects. They are mostly incredibly impractical people - philosophers, theologians and so on - with a small cohort of ships engineers and tradesmen, as well as a rapacious mine manager called Lobelia who only cares about the giant silverware. They're very well supplied with everything they could want except the means to get offworld. **Leave aside the problem of gravity trying to make the banana into a sphere** - assume that either the banana is mostly made of a nearly infinitely strong material when you drill much beneath the peel, or better still, that gravity is excluded from operating within it and only begins at the surface (albeit with all the mass of the banana still contributing). With a sunlike star, what combination of orbital distance and rotational motion can make this pungent, ethyne laced world in the sweet spot of being inhabitable but periodically very uncomfortable or dangerous? I'm specifically interested in: 1. and main) What problems are generated by rotation of the banana and what if any rotational motions are amenable to life at least over a few square kilometres while still being a damned nuisance? So, it needs a few square kilometres that have sort-of earth temperatures and pressures. I'll say -20 to 80 deg C temperature, and 0.3 to 3 bar pressure, with possible intermittent exceptions. I'm guessing depending on the axis of rotation, there are going to be areas that are uninhabitably hot/cold. I'd like to place their town in the middle of the banana on the concave side, unless there are any serious objections or better suggestions. For obvious reasons, answers need only stand up to limited scrutiny. Orbiting fruit worlds and kettles raise such serious theological, philosophical and anthropological problems that the eggheads that are on it are only going to notice that their lives are in danger when the engineers are banging on their doors warning of the impending 30 day shadow that will cause temperatures to drop to dangerously low levels and they need to put their entire libraries in buggies or local flying craft and relocate. I welcome anyone raising problems relating to atmospheric composition or ground instability that are likely to arise as the banana ripens, although I am not short of ideas in this department...unlike, you know, how these people can survive for 20s without freezing or burning or being thrown off the surface. [Answer] ## Not much fruit flies like a banana The colonists from apple and orange worlds may have figured that the banana world offered a similar experience, with lower gravity. The center of the concave side is drawn by gravity to the middle of the "cylinder" of the banana, but the ends pull it away a bit. Rapid rotation of the banana around the axis of this cylinder brings gravity to virtually nothing by centrifugal force, providing a wonderful 'habited space' environment for those who miss the zero gravity aboard ship. Despite the low gravity, it's still the lowest point on the banana, so all the "stuff" that is to be found (such as water) tends to accumulate there. Problem is, after a while the tidal forces from nearby pineapples and lawnmowers, combined with the sloshing of fluid that built up in the concave ocean, *changes* the rotation axis to match the largest moment of inertia, namely end over end like a boomerang. This causes everything that was casually suspended to start crushing to the 'ground'. I'll suppose the end-over-end rotation isn't so extreme as to pull large amounts of material from the tips of the banana, though any space-suited climbers who reach those heights before slipping on the banana peel may not be coming back. The end-over-end phase lasts longer, so I suppose they can build a new city on banana firma, but eventually the axis might shift back by chance (chaotic rotation, I mean) and then the gravity cuts out again. With this rapid of a rotation around any axis, there should be no Long Nights, and if the banana is the right distance from the sun, temperatures should be within some reasonable range. Note: [Veritasium](https://www.veritasium.com/videos/2019/9/19/the-bizarre-behavior-of-rotating-bodies-explained) has a nice video about a similar effect, which is certainly fun to watch. But I don't want to figure out the intermediate axis of rotation of a hypothetical banana, so I'm going to add additional handwaving regarding sloshing oceans and chaotic rotation caused by interactions with other orbiting bodies. [Answer] # Banana will not be a stable shape As soon as you place enough banana matter in banana shape in the banana system, gravity will start to work. Banana will contract and get denser, forming a roughly spherical planetoid that is mostly consisting of superheated banana mush. As the chemical separation of heavy and lighter elements happens, the core of the banana mush will become a core of solid graphite, surrounded by a carbon-potassium melt suspending green diamonds before we get to a somewhat softer dried banana mush layer, over which is the decomposing banana peel and the air. What started out as a giant banana, turned into just another planet with banana properties. Possibly habitable, if in the goldilocks zone. # Stable banana wouldn't be inhabitable either To live on the banana with 1 g, the banana will have the very same diameter as earth, but be roughly estimated to be a cylinder. a $42\*10^6$ km long cylinder. $$F=G\frac {M\_1 M\_2}{R^2}\to g=G\frac {M\_P}{R^2}$$ $$M\_P=\rho\_{Banana}V=\rho\_{Banana} \pi R^2\*l$$ $$g=G\frac {\rho\_{Banana} \pi R^2\*l}{R^2}=\pi G \rho\_{Banana} l$$ $$\frac g {\pi G \rho\_{Banana}}=l$$ $$l=42922688156 m$$ However, there is a BAD thing: the gravity does always point to the center of the Banana. This means at the end of the banana, the gravity pulls you almost parallel to the surface and only in a very narrow band around the center of the Banana life is possible *at all*. Also, due to the bend of the banana, the calculation doesn't even hold true for the whole equator... gravity will be totally messy. There might be two small zones where there is 1g pointing down into the ground roughly orthogonal, but in general, unless the banana is almost straight, gravity will be pointing in wonky angles towards the banana on the outside curve and there will be no gravity at all on the inside curve of the banana. This is because the inside of the banana curve can be solved using the basis of the [shell theorem](https://en.wikipedia.org/wiki/Shell_theorem) - and so there will be much less banana gravity on the inside curve. And no compensation. Any curve of the banana complicates things a lot too: no matter how you align the banana, spinning at any speed will create hyper extreme weather: the tips will be either *both* be much closer to the sun and scorch, or leave goldilocks on the other end and freeze. Due to the length, this deadly zone will be some 50% of the banana, 25% of either end. Even then, the equator of the banana will not inhabitable, as it undergoes something like 120 °C summers and -100 °C winters from moving to the edges of the goldilocks one, but much less than the banana tips. In total, there will be *not a single spot* on the banana world, that suffices with your dictate unless your Banana takes the banana mush route and the banana shape is discarded for the sanest banana sphere (see above), a [hollow banana ice cream ball](https://en.wikipedia.org/wiki/Hollow_Earth) or at least be peeled and stacked with copious amounts of banana ice cream and whipped cream as well as a topping cherry for a banana split world, which has an oblong ovaloid shape overall. #### PSA: There are exactly 42 Banana in this text. [Answer] Pay attention to what other answers say about gravity. [433 Eros](https://en.wikipedia.org/wiki/433_Eros) is a "fat banana" shaped asteroid. The number in its name means it's the 433rd asteroid we ever discovered. From the wiki: > > Surface gravity depends on the distance from a spot on the surface to the center of a body's mass. Eros's surface gravity varies greatly because Eros is not a sphere but an elongated peanut-shaped object. > > > That said, 433 Eros has a mass of about 1/10,000,000 that of our Moon. Supposing you made it much more massive, enough that a person could walk over it without achieving escape velocity, how would it feel? To answer that, I will suggest that you familiarize yourself with a videogame called Kerbal Space Program. It is a space program simulator, not perfect, but VERY realistic and intense in physics. It presents you with a fictional stellar system, and it happens to have a couple natural satellites which are not perfectly spheroidal. The smaller one, [Gilly](https://wiki.kerbalspaceprogram.com/wiki/Gilly), is actually a captured asteroid. From the KSP Wiki: > > Gilly's odd shape and fast rotation give the surface near the peaks an apparent velocity near 5 m/s. > > > Also, from playing the game, I can tell you that from anywhere you stand on Gilly it seems like you are on midway through a mountain. But a banana-shaped world would feel different. Anyone living in a banana world that rotates as fast as the Earth will notice this. The surface of the Earth has a linear speed of 460m/s due to rotation - we don't feel it because everything is moving at the same speed. But think of a banana shaped world as an Earth like world with two gigantic mountains, one on each side. If the mountains are at the equator, and they are as tall as the altitude of a geosynchronous orbit, they will each be ~35,000 km high - about 5 times as long as the Earth is thick - and their linear speed will be around 3 km/s, which is 6.6x faster than the speed of Earth's surface on the Equator. The faster speed combined with the lower gravity means that people closer to the tips who are not tethered to the ground will fall off into space in a fraction of a second. Since gravity is stronger in the middle, that's the only place where you will find an atmosphere. Since you have two mountains as thick as the Earth stuck into that atmosphere, you will have such turbulence that the whole world will be permanently ravaged by off-the-scale hurricanes. Tides will also be really extreme around those mountains. And each mountain will also block sunlight for a whole hemisphere until it's about noon on that mountain, so the world will be colder than Earth. The world will always be on the edge of inhabitability because of these features. [Answer] Forget gravity and habitable zones and atmospheric composition - your banana planet probably lacks a magnetic field (unless it has a rotating metal core or field-generating device), so stellar+cosmic radiation and CMEs are major concerns. Not only do they hurt people, but they also destroy/remove atmosphere. [Answer] # Ripened banana-planet-matter is denser One comment by YowaneHaku mentioned fixing gravitational effects by concentrating the mass at the center and saying the extremities are hollow. That's pretty arbitrary, but there's a way to make it fit with the very serious premise. Bananas often ripen from one end, and this one happens to be ripened from the "bottom" (part furthest from the stem). And for some reason, the ripened part of the banana is 100x denser than the green parts. This means the banana rotates about its bottom (whether end-over-end or longitudinally or oscillating between the two), but more importantly for the castananaways, it means that gravity near the bottom of the banana points almost directly into the banana. Atmosphere will accumulate there as well. Trying to reach the green parts of the banana would be like climbing a vertical cliff face. As for why the ripe part of the banana is more massive, whether the banana is continuing to ripen or was "always" in this state, whether the "bottom" of the banana is actually the "top" because of how bananas grow on trees, and whether they should be worried about the ambient ethylene gas their biologist is ranting about - those are matters for the philosophers and theologists to ponder over a nice, filling teaspoon of compressed banana. [Answer] To start with, I suggest watching the Veritassium video on the rotation of wing-nuts: <https://www.youtube.com/watch?v=1VPfZ_XzisU> Basically, you need to pick whether your banana rotates around its smallest or largest axis. If it rotates across the intermediate one, it'll flip back and forth. For weather patterns, you might want to consider Jinx, the Easter Egg planet, as envisioned by Larry Niven: <https://news.larryniven.net/concordance/content.asp?page=The%20Origin%20of%20Jinx> The reason for it is different (and just as wrong as your giant banana), but it identifies that the air and water would naturally attempt to pool around the equator. Th actually happens with Earth, too, but it's due to rotational momentum, and the difference is about 50 feet. This suggests that, even with even gravity across the surface of the banana, rotation would pull the air and water to the tips and the convex middle. Humans could survive in a ring around the convex extremity, but the air would probably leak off of it at the points. More magic needed to keep it in place, I guess. [Answer] ### Donuts and banana-phones This question reminded me of [this other one about torus-shaped donut-shaped planets](https://worldbuilding.stackexchange.com/questions/6465/what-would-the-problems-with-consequences-of-a-torus-shaped-planet-be). Amazingly enough, a donut-shaped planet is stable under the right (albeit extraordinary) circumstances. One of the webpages linked from there, <https://itzhakts.wordpress.com/2014/02/05/torus-earth/> , even offers fancy graphics about the strength of the gravity field of such a theoretical toroidal donut-shaped planet: [![gravitational field of toroidal planet](https://i.stack.imgur.com/zfp2Q.png)](https://i.stack.imgur.com/zfp2Q.png) The general idea is that such a planet spins fairly quickly (for the mass required for earth-like gravity, the figures vary between 2- and 4-hour-long days): the centrifugal force keeps the system in equilibrium. But, you want to live on a banana. Not a banana-filled donut covered in sprinkles. And a donut is not shaped like a banana. **But**, we can use a banana to approximate a **section** of the donut. The only thing needed would be some kind of "counterweight" in order to position the center of rotation of the banana so that the radius of curvature of the banana kinda sorta matches the radius of rotation. Therefore I bring to you: the banana-phone binary planetary system: [![bananaphone binary system](https://i.stack.imgur.com/JjHTb.png)](https://i.stack.imgur.com/JjHTb.png) The banana is not floating alone in space but, rather, the banana-phone behaves as one body: its mass distribution *kinda sorta* approximates that of an ideal torus donut, and both the banana and the phone rotate around the center of mass of the banana-phone at the same rate to provide 2- to 4-hour long days. Of course, the phone can be replaced by other object(s), but they should be massive enough to shift the center of gravity of the system. However, the more you deviate from a generally-donut-shaped mass, the more you'll have to hand-wave. I'll point out that there can be a small moon (a coin?) bobbing up and down through the center, and that daily phone eclipses are going to be a thing to people on the inward side of the banana. > > I welcome anyone raising problems relating to atmospheric composition or ground instability that are likely to arise as the banana ripens, > > > Since the gravity is stronger at the thicker parts of the banana, and weaker at the tips, the banana would be sloooowly squished. After all, the system would be pushing itself into a state of lower energy trying to achieve hydrostatic equilibrium. In other words: it would slowly turn into a donut. I can imagine pulp-quakes as the thicker parts are squished by their own weight and pulp is expelled through both rupturing tips. Note that the atmosphere, if any, would envelop the whole system and not just the banana. The banana tips would be a hazard zone of high atmospheric pressures and unstable expelled pulp. Other than that, I recommend reading through to the write-ups of donut-shaped planets linked before. ]
[Question] [ I am making a science fiction computer game where you can travel between planets. I would like the planets all to have some kind of differing materials. Now I have no idea about which kind of "materials" exist. I know an element is defined by the number of protons and the only thing that can change then are isotopes. But a lot of planets would probably also have compound materials. And now I don't understand, do I just have universal freedom to say (while staying reasonable realistic), you have found material XYZ on this planet, it behaves like steel but is twice as light? And can something like plastics be just found on a planet? (And is plastic something special we humans have discovered and other races would likely not have discovered it, but maybe some other group of materials which behave very differently?) So to make it short: While staying reasonably realistic, what are the kinds of materials I would expect to find on other planets and how much would they differ from what we have on earth? I don't need to tell the player: The element you found has this and that chemical formula; I just want a rough idea of what is possible and plausible. **EDIT**: Based on the comments I will specify my question. The player starts on some random planet. I want the player to be able to find materials. The important **properties** of these materials are: * How good are they for building houses * How good are they for building spaceships I will probably abstract all of that away into how hard, elastic and heavy they are and at which temperatures they differ in these properties. I need to communicate the finding of these materials to the player and here is my problem. On a different planet, is it plausible that the player will find for example an isotope of some material which has some differing properties? Will it be plausible that he finds some very new compound material that humans have never thought of? Or do the most planets look very similar in what they are made of to earth, such that the finding of new materials should be done with technology. I hope this clarifies my question a bit. [Answer] You have to set clear (in your mind first, then in the game) the difference between raw materials and processed materials. We don't mine plastics, we mine a raw material called oil and then process it to make plastics. We don't mine aluminum, we mine a raw material called bauxite and then process it to make aluminum. Raw material is what you will find on a planet, and you need the proper technology to harvest it. Then you need knowledge and other proper technology to process it for your purpose. Depending on the level of details you want to implement in the game you can give in more or less details. You can set a generic "mine" and according to the available technology you can process the ore to make steel or aluminum or gold, or you can set different mines each delivering different ores and thus different processed materials. [Answer] If other races do not too much upset the balance of your game, you can have alien traders on the planets you find. Sort of like the villagers in Minecraft. These gentle aliens have raw materials like lumber they take from forests, but also processed things like refined metals and made things like plastic. You can have these aliens offer anything the game requires. You can have different races of aliens and so be able to guess what sort of stuff they might have. From the gameplay standpoint, aliens also jazz up a planet because they have faces and character and variety (even if they are all basically Minecraft villagers). [Answer] **Yes, you can find unique things but most things will be the same** Since this is for a game, I am assuming by planet you mean something a human could actually walk around the surface of in a suit, so no gas giants or super cold ice balls. And I am restricting myself to planets and possibly moons, not everything in space, asteroids would be easier to min in many ways. **Things every planet will have.** **metals, glass (made from silica), and rocks**. Any planet even close to earth like gravity will have lots of these. It is what they are made of. they might find more of some materials but they will not find much in the way of different materials, the laws of physics are still the same. Something however might be much easier to find on some, some planets might be rich in rare earth elements and they find unique minerals produced with them. There minerals on earth with interesting properties that only exist in a single place on earth, caused by a unique combination of conditions. So it is possible they might find a planet with lots of naturally occuring superconductors or something like that. Yes they could find something humans had never thought of but such thing will occur on planets with very un-earth like conditions and be rare, how useful they will be is more or less random. **things unique to earth (or planets with life).** everything unique ot earth is a product of life. **Plastics, wood, rubber, petroleum**, etc are all products of life (or refined from products of life) so a fictional planet *with life* may have them or may not that is up to you and what you want the life on the planet to produce. A planet *without life* should not have them with the possible exception of petroleum, there are some very rare circumstances, like some moons, which produce hydrocarbons seas, and that only gives you petroleum. On the other hand planets with different life might well have completely different things produced by their life, wood might be unique to earth, milk and feathers will almost certainly be. Some planets might have life with iron teeth barbon fiber shells, or chitin trees. **The vast majority of unique materials you find will be products of local life forms**. I remember reading a story as a kid about an organism heavily poached in a galactic civilization becasue it produced a liquid that stayed a liquid even under hard vacuum and was used as spaceship lubricant. so it really comes down to what you want to build your houses out of and what you use to fuel your starships. A wooden house will not be possible on a planet devoid of life, but a house on such a planet does not make a lot of sense either. Plastic is only going to come from a planet with a manufacturing factory to produce it. Water will be your rarest resource, although some planets will be absolutely packed with it either as water or more likely as ice. As L.Dutch said there is a big difference between raw and manufactured materials that needs to be considered. [Answer] Most planets should contain most elements and most types of molecules should be found on most planets (methane is a hydrocarbon). The difference tends to be: which materials are found easily on the surface of the planet. 1. High tectonic/volcanic activity puts more gold, silver and heavy metals on the surface. 2. As has been pointed out, life gives larger molecules of many types (hydrocarbons, proteins, medical and poisonous molecules). 3. Water or past water gives salts and other molecules that are created when elements are dissolved in water. the presence of certain of these chemicals is why scientists are now convinced that Mars once had water. On any planet, you should have the building blocks for #2 and #3 types. So, the question is just how much work/energy needs to go into providing them. The #1 type are the tricky ones. If there is no tectonic activity at all, you might be SOL for those. There may be a few deposits from when the planet was still undergoing formation but you will have to find them. I recommend two parameters for your material availability: quantity and availability. Quantity is: how much is there to dig up or create. this one is pretty straight forward. Availability is: how difficult it is to mine / find / process. Maybe a 1 to 10 scale. 10 is: walk outside and pick it up off the ground. In some areas gold and diamonds like this. 9 would be: tales some work. Wood is like this. Unless you are in a desert, you can find it just about anywhere but you need to cut it down and then process it into the sizes that you need (for lumber) or into a form that will be useful (pulp for paper or charcoal). 1 would be: Yes you can do it but why? 0 would be: it isn't present at all or you can't obtain it for some reason (not allowed to mine radioactives and rare earth elements tend to come mixed with radioactive elements). Even the longest chain hydrocarbon can be created from carbon dioxide, water and some other commonly found elements. It is just that it takes a lot of energy to put the long chain molecules together and isn't worth it if you can get it from another source (and the transportation energy is less than the creation energy). [Answer] Materials you can find on a planets are all some mixtures or raw elements. Steel is an alloy $Fe\_3C$ plus some additives and other elements with varying content. Types of steel is exactly those additives and amount of $C$. You have mild steel, hard, carbon and so on. So you theoretically could have steel occurring naturally in some planet with slightly different proprieties due to process it was created in but it would still follow certain properties. Because you can't change mass of an atom. OR you can but it change the atom so instead of $Fe$ you end up with copper for example. and everything you will find on other planets, in our universe at least, will have the same atoms that ac the same way. And of course you can have different weight of processed materials. But not because the components are different but because you are on a different planet with different gravitational field. Everything what is on Mendeleev matrix you will find in other places of galaxy. With different quantity of course. Finding very new compound material that humans have never thought of is as possible as finding vein of Damascus steel occurring naturally on earth. ]
[Question] [ Got this idea from [Antarctica](http://legendmarielu.wikia.com/wiki/Antarctica) in the *Legend* series by Marie Lu Imagine that we've become so technologically advanced that every person, ages 3 and up, has an implant in their head that tracks everything you do. You get points or reputation when you do good things such as get a good grade on a test, do a good deed for someone, etc. and you lose points when you do bad things like cheat, lie, etc. Also, your points are visible to everyone else (through holograms that come with the implants) just like on SE. Also you are judged by how many points you have, but it does not necessarily determine how successful you will be. For government positions, it is elections, but people will be more likely to vote for you if you have more points. The implant doesn't punish/reward you for your thoughts. Bad things examples (I don't thing that the good things are very controversial) * Any type of crime (from today) * Not loyal to the government (this one's a bit controversial) * Getting a bad grade **How would society act differently? Would people work harder? What other things would change?** [Answer] So, basically, what you're saying is that people can gain/lose points, but the points don't actually matter? In that case, I would say people's point values would just be like another part of their resume: maybe employers worry about it, maybe they're just looking for someone with good interpersonal skills. You said points would factor into elections by swaying voters, but I'd think extramarital affairs or nonconformist religious views would be far more damaging to a candidate's chances of getting elected than a lower point value. Even more simply, supposedly people often pick candidates because they're taller than their opponents, or pick a car because it has the most cup holders: even with a definite point system saying how good someone is, people will still make irrational decisions based on criteria that really shouldn't matter. Not only that, but without a sophisticated means of discovering where the up/downvotes are coming from, it would be very easy to cheat. An entire business could spring up, with thousands of employees ready to upvote whoever can pay for the privilege, and downvote whoever has rich enemies. Unless there was an enormous amount of regulation, point values would become useless pretty fast. You could solve the above problem by only giving up/downvote privileges to appointed people (let's call them moderators), but this raises another potential problem: who gets to decide what's worth an upvote? If there are laws on such things, I'd think only really patriotic people would care about the point system, while others would chalk it up to propaganda and government regulation. If, on the other hand, points were handed out by individual choice, moderators or users would have way too much power, and the cheating I mentioned would become a huge problem. Keep in mind that in such a system, point values don't just let you do more on a Q&A site; points can earn you respect, which means power. Another potential problem is with age. Point values on SE usually correspond to seniority rather than virtue: the people with the highest scores have simply been around the longest. In the real world, we can already tell who's been around longest: they have grey hair and wrinkles. But honestly, for these reasons and others, I don't think the point values would matter all that much. Points are just an artificial representation of real-world attributes; if you really want to judge someone's character, you need to dig deeper. Anyone who *did* judge people based on their point value would be like someone who judged people based on their race, gender, economic background, and so on. But this answer leads to a somewhat contradictory conclusion: if you think I'm worth listening to because I have over 1000 rep, then you're doing it wrong. This is just what I think, and hopefully someone else can provide a better answer if you find this one lacking. [Answer] Your question has a tripping point: "Also, you are judged by how many points you have." The way that statement is implemented has far more of an effect than any other detail. For example, if there is a 50 point government sanctioned minimum to comment on an election, there will immediately be a market for cheap ways to quickly and artificially acquire 50 points. The ability to close a discussion at work (500pts) would be quickly farmed by everyone. I would also expect to see dirty things like gangs doing "run by"s where they quickly downvote someone's answers a few dozen times, just to ruin their reputation. On the other hand, if it is a social contract sort of thing, where everybody not only pays attention to points, but has a great interest in cultivating its validity, you have a situation like "honor" in feudal Japan. You seek to cultivate honor, and there are well accepted paths to take, but they're not always straight forward. SE seems to take a third approach. Points are fun, but there's not many places where they really interact with the world, so there is little incentive to break the system. Area 51 is pretty smart that way. --- If you think about it, what you've really done is create something that has both aspects of a currency and a free goods * It scores on a single dimensional metric scale. Someone who does one monumental task is given the same value/score as someone who does a bunch of small tasks. Someone who only does desirable tasks has the same value/score as someone who only does undesirable tasks (thank you moderators!). * It is freely creatable with little effort. As long as you've logged in, an upvote is virtually free. Compare this to currency, which is a scarcity economy -- in order to give a coin to someone you must lose a coin. Now, one solution to your system is that you are judged by your reputation, *but just barely.* When it is clear that reputation has little to nothing to do with how you want to interact with someone, people will ignore it. Remember, most people like to interact with people who aren't one dimensional. If you want your society to actually pay attention to these, a little feedback is needed: we're going to want a society which has an interest in these reputations being valuable. They're going to have to change their perceptions and actions to make this reputation system more valuable than it actually is. One of the first things I'd expect to see is dramatic clothing choices. Different groups are going to have different opinions on how reputation should be used. There's no way there will be agreement, so the best society can do is break into subcultures. Each subculture would have its own way of managing points. Clothing choices would be a natural augmentation to the point system to show which reputation group you belong to. Dress like a type A personality executive, and it's expected that you'll get 1k to 2k a day, or its a sign you're off your game. Suspend enough disbelief to give Tibetan monks VR implants and reputation, and they would treat it different. If you see someone in orange cloth with 8 or 9 rep, they are likely quite the pious soul. I'd be interested in seeing a Dali Lama like character in such a world. The world would naturally seek to give him many reputation points, and he would be too humble to not accept them. There might even be a giant ceremony where his fellow monks kindly downvote him so that his numbers don't get too high. ]
[Question] [ This is a submission for the [Anatomically Correct Series](https://worldbuilding.meta.stackexchange.com/questions/2797/anatomically-correct-series/2798#2798) ## How would you evolve a harpy? A harpy is defined [by Wikipedia](https://en.wikipedia.org/wiki/Harpy) as a flying creature with: * **Long, human hair** * **Human faces** * **Feathered bodies** * **Clawed feet** * **Bird wings and (sometimes) tail** From various mythology, they appear to be able to: * **Fly for a fairly long distance, (say a mile or two)** * **Live *on Earth,*** * **Eat human-digestible food** * **Speak like a scratchy-voiced human woman** * **Understand human language** There does not appear to be a discernible male of the species. ### Question: *How would evolution cause these creatures to come into existence?* [Answer] To me, it is clear we need to start with a bird and evolve human-like features, as opposed to vice-versa. I will start with a bird whose name already implies where we are going- the [harpy eagle](https://en.wikipedia.org/wiki/Harpy_eagle) (Harpia harpyja). To address your definition point-by-point: * Human hair - The double crest of this eagle hints at hair already. If it expands and becomes rougher over time, it might certainly look like human hair. * Human face - As I look at pictures, its already close. If the eagle's face moves toward that of its cousins, the [barn owls](https://en.wikipedia.org/wiki/Barn_owl), it might present a human-like appearance. * Feathered bodies- No change needed. * Clawed feet - Done. * Wings and tail - Got it. * Fly - Yep. * Live on Earth - Check. * Eat human food - Ok, we humans do not normally eat sloths and monkeys, but we're capable. Also, we do eat salads, which wouldn't be good for the eagle. Going from a strict carnivore to a more opportunistic feeding habit will take several generations, but it has happened in evolution before. * Speak/ understand human language- Borrowing from a comment, the eagle needs to learn from parrots, ravens, and similar birds. It will begin with mimicry, and evolve into full speech. As I score it we begin with 5-and-a-fraction out of 9, with the other 4 totally plausible given the right evolutionary pressures. --- Update: What are those evolutionary pressures? In a few words- habitat change or loss. As the creature is pushed further and further out of the rain forests of Central America, it must adapt to the different habitats it encounters. Hair: I see two possibilities, either climate or prey changes. As it expands its range, it comes into cooler zones and needs more thermal protection for its head. Alternatively, it begins eating something tougher, and needs the crest to be like a helmet- kind of the opposite of why vultures have no head feathers. Face: Same as the owls, to better see certain prey items, focus the sounds of prey into the ears, and move more stealthily when catching prey. Food: Its preferred foods are either absent or less easily located in the new habitats. Each generation adapts to eat a wider variety of things. Speech: Forced into ever closer and more frequent contact with humans, it realizes the advantages of being able to trick them and steal their scraps, not unlike crows already do. [Answer] I don't see a mechanism for evolving both hair and feathers. Maybe what you take to be hair is actually long stingy feathers, or feathers that further evolved to be hair-like. But why evolve a totally different covering on the head? Bald eagles have changed their head covering due to the way they feed. Having the environment presented to the head cause selection pressure is the general mechanism: maybe they get bits of stuff and gunk caught in it and it's advantageous to be able to comb it out, thus a simple strand rather than a complex shape. The human jaw goes *against* evolution. Birds evolved beaks after flight to save weight. The pictures also show mammalian breasts. Birds evolved different mechanisms (e.g. crop milk, or simple regurgitation) but they *might* have evolved the same solutions as mammals in the same way that mammals did. There are birds that are omnivorous, understand human speech, and form human speech. What could serve as the basis for the legend would be a flighted bird whose head became featherless (showing bare skin), eyes in a binocular arrangement, and beak retracted to leave a flat face. Perhaps the beak could be colored to resemble lips, All this would be due to the *diet* and manner of feeding. The bald face would be supplanted by top-head covering that still protects against the sun but is easy to rinse out, so more stingy. The stylized breasts in the drawings might be literal observations: circular target-like markings on the chest. These would be typical eye mimic spots to seem like a very large predator from a distance or glimpsed in the thicket. But human men got a different impression. Now given a naked flat face that sort-of resembled a human, might it then evolve to look more like a human face as a form of mimicry? A glimpse of what might be a human face, as opposed to a deer in the woods, is enough to make a hunter hesitate before taking a shot at something that moved. Other formidable beasts might fear humans and mimicking the part that other animals notice as being distinctive (and they pay attention to the predator's eyes) would let them spook other dangerous animals that they would otherwise fall prey to. ]
[Question] [ Well folks, 2015 has come and gone, and we still don't have widely-available [flying cars](http://backtothefuture.wikia.com/wiki/2015#Actuality). While there is some promising work being done on "flying cars", which are more like road-capable airplanes, it looks like we're a long way away from the type of flying cars I'm imagining from pop sci-fi. Thus, I'll abstain from using the "near-future" tag on this one. Okay, let's assume we're in a future Earth where flying cars are as ubiquitous as ground automobiles are today. Their price and the cost of operating them are comparable to today's autos as well. Also, flying cars are basically hover cars, and can be stationary in the air, or move fully in three dimensions, as you might expect a flying car to be able to do. To clarify, the bottom of the flying car must always be pointed down (unless you're pulling off some crazy car-chase maneuvers), and it can float up and down along a z-axis, move foward and backward as normal along a y-axis, or move left and right along an x-axis freely, without having to turn to point the front of the vehicle in that direction. However, it would move along the x-axis slowly, and do so by "banking" the vehicle. Also, while stationary, it can rotate to point the front of the car in any direction along a two-dimensional plane parallel to Earth's surface. The front of the vehicle can also tilt to an incline or decline of a limited amount, let's say by 25 degrees. And, for whatever reason, none of these flying cars are "self-driving". In some fictional futuristic worlds that contain these types of flying cars, you often will see traffic signs, signals, and [patterns](https://earthcrazy.files.wordpress.com/2014/09/jetsons-traffic-380x285.png) that hail back to modern-day Earth. You might see a normal [grid-pattern of cars in a city](http://screenrant.com/wp-content/uploads/Best-Movie-Car-Chases-Fifth-Element.jpg), but the grids stack up along a z-axis, and at each intersection, a stack of floating common traffic lights. You might even see a floating highway - a literal *high*way - that has floating [lane markers and exit signs](http://nerdunderground.net/wp-content/uploads/2015/08/Flying-delorean.jpg). This type of traffic management system has always seemed so contrived to me. There has to be a better way, especially considering that vehicles can move in three dimensions (or four if you're a specific DeLorean). However, I'm struggling with envisioning that better way. I suppose a future traffic system for flying cars would incorporate some degree of what a ground traffic system would look like today, with some of what today's air traffic control systems use as well. How could air traffic principles and ground traffic principles be combined in order to produce an effective traffic system for flying cars? [Answer] Real pilot here. Here are the air traffic management rules for what I shall call "Class V Airspace" : 1. Class V airspace generally only exists in the most congested urban areas of the United States, where normal air traffic procedures cannot sustain the high volume of VTOL traffic. Class V airspace generally consists of the region between 1000 and 3000 feet AGL. In more congested urban areas, Class V can exist between 1000 and 5000 feel AGL, with higher limits for airspeed in the region between 3000 and 5000 feet. Air Traffic above Class V airspace shall adhere to VFR or IFR flight rules, whatever that airspace is classified as, whether it be Class B, C, D or E. 2. Air Traffic inside of Class V airspace must travel between 100 and 150 knots, with altitude mapped to aircraft magnetic track such that at odd levels of 1000 feet (For example: at 1000, 3000, and 5000 feet) the aircraft must be traveling North (0 degrees). As the aircraft climbs (or descends), it must adjust its magnetic ground track heading to map to the altitude it is at, so that as it makes an ascending right-hand turn (or descending left-hand turn), its altitude is an even multiple of 1000 feet at the instant it is heading South (180 degrees). This allows the aircraft to make a standard 3-degree-per-second climbing turn at 1000 feet-per-minute while only conflicting with other aircraft either directly in-front or behind it. Aircraft must yield to conflicting aircraft in-front by passing on the right. 3. Air Traffic below 1000 feet and above 700 feet shall not exceed 100 knots, and shall yield right-of-way to any other aircraft on its right. 4. Air Traffic above 400 feet and below 700 feet AGL shall not exceed 50 knots. 5. Air Traffic below 400 feet shall not exceed 25 knots. 6. Landing aircraft have right-of-way over landed aircraft at vertipads. 7. In Class V airspace, separation is maintained using visual see-and-avoid techniques and ADS-B telemetry. Conflicts are handled using standard aeronautical right-of-way procedures. And there you go! It would probably take the rest of my night to provide the calculus of why this works and requires nothing more. In short, having access to the volume of air above even a large city far exceeds the traffic density that would have to exist to require a more complex management solution. Traffic congestion with automobiles is a result of their 1.5 dimensional nature: In a car, you can only move forward and possibly switch lanes. We like this as drivers because it make all the possible collision vectors collapse to only a few possible directions. Modern aircraft traffic rules somewhat also do the same thing. (See this [link](https://en.wikipedia.org/wiki/Flight_level) and this [link](http://www.lapeeraviation.com/odd-north-east/)). By mapping altitude to heading, we collapse the possible collision vectors to only ahead and behind. This method would work great for the average urban area. In areas where traffic density is much higher, it would make sense to have "climb" zones and "descent" zones where the mapping is still followed, but in addition only standard climbing or descending turns are allowed. Otherwise, aircraft are free to fly straight lines between points; getting to your desired heading only requires that you make a climbing/descending circle until your pointing where you want to go. The altitude mapping method works great for vehicles trying to get around, but how do we handle take-off and landing? This requires that we remove the mapping requirement for the regions where take-off and landing operations happen. To resolve the collision hazard, we restrict the cruising speed considerably. By restricting flying speed in the lower layer near the ground, any conflicts that could result in a collision will happen slow enough that either one or both pilots can react with ample room. The worst-case approach speed is 50 knots for a head-on situation below 400 feet, and 100 knots for the 400 to 700 foot region. Transitioning to the more busy and fast layer from the lower layers requires starting on a north heading as your aircraft passes through 1000 feet AGL. Aircraft climbing to this level will tend to align to north as they approach 1000 feet, at which point they must be traveling at least 100 knots and at most 150 knots. Thus, any conflicts are happening at 50 knots in-front or behind. In the case of aircraft transitioning to the slow layer from 1000 to 400 feet, the aircraft will deviate from North to various random headings. The possible conflict vectors expand to a field of regard of 360 degrees (a conflict can come from any direction), but by the time these aircraft have descended to 400 feet, they should only be traveling 25 knots, which again yields conflict velocities of only 50 knots. The most important feature of this approach is that the occupant(s) of the vehicle are in control, and have full proficiency and ability to make decisions based on what their instruments and eyes tell them. I've always been severely bothered by the various inventors and futurists that think that flying ought to be only handled by automated systems, with the occupants at their mercy. Flying is a talent and a freedom that the average person can master and should be able enjoy. [Answer] I made a computer program in my architecture university days to test this very hypothesis. As I discovered, the best system is a very simple one: **your direction is a direct linear relationship to your altitude.** I created a random series of tall buildings, and populated the whole sky at all altitudes with flying cars. After testing convoluted collision detection algorithms, 'streams', blocks, intersections and others, I have discovered that the most simplest solution is that as you ascend, you also turn clockwise. Everyone has the same direction at each altitude. It was amazing and wonderful to behold, because: * there were no collisions - at any given height, everyone goes the same direction. * all you need to watch is speed and who is in front of you - just like we do now on a freeway. * if you need to climb, you rotate clockwise as you move forward * if you need to descend, you rotate anticlockwise as you move forward * you can find your way to any point in space, by ascending to the right altitude, then making a 'b-line' to the point, then spiralling to the right altitude. Every point in the sky is accessible by you. * for obstacles (like a building) the flow will go around the obstacle, even this presents no crashes. For instance, if your path runs into a skyscraper, everyone descends or ascends (whichever the easiest) to change their direction around the obstacle, still within the rule, then ascends or descends when past the obstacle, following the original path. Easy. With a thousand cars, they all flowed around the buildings like water, with not a single collision. * NO TRAFFIC RULES, ie. no complicated things like 'give way to your right' or 'stop at intersections' or even 'look over your shoulder'. Simply follow the rule that your direction rotates with your height. * NO COMPLICATED TRAFFIC SYSTEM, no centralised authority needed, no need for communication between cars * it was crude, dumb and simple - just the thing that people can understand and is completely infallible. I cried out in joy after discovering the solution and thought 'yes this could work, if only someone could invent a flying car!'. [Answer] The best plan would not consist of highways, intersections, lights, signs, etc. Instead, a flight control system (like the FAA) would be the ideal system. Even assuming the cars are driven by humans, you could input the destination into the car, which then uses computers to log a flight plan. You then follow the flight plan. The real signals would be destination signs, Lets be honest - Walmart and Victoria's Secret look the same from above, but you goto them for different reasons. Parking and take-offs will need signals, indicating number of parking spaces available, what floor you can land on, etc. That's where the complexity will really lie. The open highway will be truly open, except in the mind of a computer. ]
[Question] [ Brown dwarf stars are cool. Both literally and figuratively; the temperature profile for cool brown dwarves runs somewhere between 225K and 600K. It's possible if not probable that there exist some brown dwarves at room temperature (≈300K or 80°F). With such a hospitable temperature, is it possible for humanoid life to survive around a brown dwarf? What if they lived within a pressurized station in the atmosphere? I'm mostly concerned here about gravity, atmospheric pressure, and temperature, not so much about atmospheric composition. **I'm also not particularly concerned with the *practicality* of such a situation.** Obviously the most practical way for life (as we understand it) to survive is on the surface of a rocky planet with atmosphere and water. Whether it's a good idea or not, these humanoids are forced to live here; I'm leaning toward some sort of forced emigration, scientific survey, or waypoint on a long but aborted journey. [Answer] This isn't that practical an idea. A brown dwarf doesn't have many appealing properties. Its low temperature is actually not a great thing. This means you can't get much energy out of it to support your society. You won't freeze or burn on the surface, but you have to create a habitat for yourself anyway, maintaining the temperature of which is not that big of a deal. Keeping a habitable temperature is really the least of worries for space societies, both making and disposing of heat is easy in space. You should be more worried about consumable things like air, food, water, and especially energy. There isn't really a surface to land on. Getting into the atmosphere of it will put you deep in the gravity well, and, as suggested by another answer, you can't just use rockets from the hydrogen *unless you have oxygen to combust with it*. Unfortunately, you had to bring all the oxygen you have and you're using that for breathing. If you want to allow for infinite resources (since you'll need to bring in everything required for life, including the energy) then yes, you could exist there. The question then becomes why would you want to? Perhaps for some kind of scientific mission where people actually need to be there. It would be a harsh outpost, I can't imagine volunteering for going. [Answer] You could easily liken a Jupiter to a Brown Dwarf. Jupiter has a massive amount of cosmic radiation compared to other planets we know of. A Brown Dwarf has immense gravity and the theoretical station you want would need to have a few very powerful rockets firing against the surface constantly to stop it from falling into the atmosphere. After that you would need a fuel source (possibly the hydrogen in the atmosphere?) and you would need to find the Goldilocks zone of the dwarf. As long as they were in this pressurized station and the rockets worked, you could within reason have something similar to what you described, although you would want to stay closer to the surface of the dwarf. [Answer] The most practical scenario would probably be a moon/planet(depending on how you classify it) orbiting the brown dwarf in a multiple star system where another star would provide your source of energy. [Answer] Sure. A planet rotating around it might be generating its own heat due to tidal forces against it. It might not be a large amount, but possibly enough for human made habitats to exist and function. Imagine the surface of Io or Europa. I would not be expecting it to be a particularly inviting environment. Nor would you expect to find Earth-like life developing there. [Answer] Regarding life in the atmosphere of cold brown dwarf: Buoyancy in the atmosphere (there is no surface) could be doable using heated balloons. However, carbon-based life, not to mention humanoids, requires plenty of heavier elements (like phosphorus and silicon) which would require **very** turbulent atmosphere to keep them available in the upper habitable layers, perhaps due to fast rotation? Or very unusual elements composition. Another question is source of energy as there's no photosynthesis available - perhaps from the atmospheric turbulencies (rather precarious) or these humanoids could be using nuclear energy but all known technology requires mining of heavier elements too. The immense gravity is problem of itself which may altogether preclude existence of human-sized humanoids breathing gaseous atmosphere. [Answer] From what I'm reading in the citations referenced below, this could only occur if the orbit of the object or platform used is extremely well controlled and the distance would need to move closer to the brown dwarf as time passes in order to maintain its habitability as the brown dwarf cooled. If you are actually referencing a surface type situation, you need to take into account that the mass of a brown dwarf is normally over 13 times that of Jupiter, but packed in a similar physical space. That would cause immense gravity and would very likely make habitability extremely inhospitable and unlikely by any life form that I know of at this time. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3612282/> <http://en.wikipedia.org/wiki/Brown_dwarf> ]
[Question] [ As human population continues to grow and need for raw resources grow, various nations and private organizations begin colonization efforts of our Solar System beyond the blue and green sphere we call home. For this question we are assuming that there have been no drastic changes to: * World cultures * World governments * World economies * Current human technologies So, while all of these can advance or shift, they are fundamentally comparable to what we have today, in late 2016. To this end, planet-wide terraforming, for example, is out of the question, and we're probably not crafting Dyson structures. *Colonization efforts are limited to what is remotely realistic through the filter of where we stand today, and will stand over the next handful of decades.* The question has two sides to it: * What planetary bodies would these colonization efforts realistically extend over (the first half dozen or so) * What order of colonization/approximate timespan is reasonable for these efforts? [Answer] The driving force for colonization will be to access some sort of valuable resources for the colonists to use. Most of the needs of the colonists can be broken into broad categories: 1. Energy, to allow them to do all their other activities 2. Water, to support life 3. Elements like Carbon, Hydrogen, Oxygen and Nitrogen in order to support life 4. Metals and rock for construction and shielding Luckily, modern space research has allowed us to discover that most of what we need is relatively close at hand. The Moon is the first place we'll go because it is quite close and has everything in categories 1,2 and 4. It is convenient to develop and refine techniques before taking the next big jump. The next easily available source of valuable resources is the NEO's (Near Earth Objects). These are much smaller and easier in terms of deltaV to reach than even the Moon, and collectively have all the major categories in abundance. Being very small, mining and accessing the resources requires that you learn how to operate in microgravity environments, but this experience will lay the foundations for moving to the asteroid belt, the Jovian Trojans and even (in the distant future) the Oort cloud. Unlike many space enthusiasts, I would actually give Mars a pass. As a planet it is too small to maintain a thick atmosphere, but large enough for gravity to become an issue with launching and so on. Energy is also an issue, since Mars is far enough from the Sum to make solar panels less efficient, so you would have to haul nuclear reactors there. The next major nexus of colonization will be Jupiter. The Jovian system has all the categories in abundance, with a powerful magnetosphere which can be mined for energy and 67 moons orbiting the planet itself. Europa alone has 3X the water as all the Earth's oceans combined. Because of the tremendous concentration of resources, it is entirely plausible that Jupiter becomes a civilization or nation on its own, a polity independent of Earth and quite capable of standing on its own. I can see a fork happening at this point in the timeline. Some projects like building giant lightsails for space development and interstellar flight, creating antimatter as a compact energy storage medium and so on will require settling Mercury. Mercury is very abundant in category 1 and 4, and will have to import its water and life supporting elements. In return, gigantic lasers can be used to beam power to deep space targets far beyond the limits where solar energy would be useful. Deep space colonies in Saturn would mostly be focused on the moon Titan, which has a thick nitrogen atmosphere, and the planet Uranus, which has the gravity field and radiation environment which allows for atmospheric mining, especially of 3He, which would be a valuable fuel for deep space colonies and spacecraft. Settling beyond might actually be a race between rising populations needing room and the building of a Dyson swarm around the Sun to harvest energy and create living space for trillions of sentient beings. You can see in a setting like this here will be a multitude of opportunities for trade (not every place haas all th elements needed for successful colonization), as well as some fairly well defined "zones" for separate cultures and civilizations to develop. From Mercury to the Asteroid belt will probably be the "Solar" zone, where cheap solar energy is the economic driver. Jupiter will be its own zone for the reasons described above. Deep space will be its own zone because of distance and the need to either import energy from Mercury or mine 3He from the atmosphere of Uranus. [Answer] # Moon first. It’s *close* and it offers a staging area for subsequent space industrial development. # Belt second Follow the money: people will prospect and mine the asteroids. An intermediate structure between moon industry and pure open-space structures would be to build out from Ceres and Vesta. Huge heavy industry of mining and refining! # Earth It's been pointed out that the Gobi Desert is more habitable than Mars and people could go there cheaply *now*. Why don't they? The technology of closed ecosystems and self-sustained cities that would allow people to live on Mars would also allow them to live in extreme environments on Earth, *first*. Areas without water or other resources are open just as much as Mars is, and the tech that’s not perfected yet will be applicable *here* because you can still go get more water etc. when you have to supplement the imperfect system. # from there, everywhere Once space technology is mature and life support systems are mature enough, they can go anywhere. So the local economy and politics at the time will dictate what comes next. ]
[Question] [ I have a work-in-progress scenario where an interstellar generation/ark/cryogenic ship has reached its destination, but there are no habitable planets. There's no turning back, and so now the colonists have to try and eke out a living in space and/or airless planetoids. At least initially, there is no suitable habitat to have farms, and not sustainable for the given population. Given there is plenty of energy available, a small amount of existing organic material to be recycled, and carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur and possibly other chemicals available to be gathered/extracted/mined, is it technically/realistically feasible to be able synthesise a constant life-sustaining completely nutritional (if not appetising) food/substance? I'm looking for something more Haber process rather than Star Trek replicator. The precise details of how this would work aren't too important; I just want to avoid a possible plot hole. [Answer] Yes, molecules can be made from scratch using primitive chemistry. Your plot will not be the general principal but in trying to identify and learn to synthesize every last vitamin needed. To make the set-up for your plot more believable, you can have an in-flight disaster destroy the planned capability and stores. They are left with primitive chemistry that they need to bootstrap from 19th century technology. Their redundancy and general salvage might come up with some nutritional algae and fungi if not a few herbs, but they find it is not a diverse enough diet to survive on. They need to synthesize things like vitamin C and who knows what else. Whether they've arrived at another star system or are still aboard the ship doesn't matter much but affects the details. I think such a story could be an interesting problem-solving SF if written by a chemist. It could have been an Asimov novel, had he not been taken from us prematurely. [Answer] How were the settlers anticipating feeding themselves? I would assume that seeds and farm animals would come along for the ride; even if the planets were habitable, there is no way to know what plants and animals live there, or if they are even edible; however, without the anticipated crop and ranch land, the animals and seeds have to be kept in cryo-storage until habitable domes are set up. That said, synthesizing food is possible, though not easy, and it's not a good long-term plan. The human body needs a lot of different nutrients to survive, and synthetic sources aren't always as good for you as natural ones. ## Water Without water, there's no point in synthesizing anything, because no one will live long enough to see it. Hopefully, the population has enough water to survive, and a way to recycle waste; there may occasionally be water to find in space, but there is no guarantee. If there's no water, then the population is dead. ## [Micronutrients](https://en.wikipedia.org/wiki/List_of_micronutrients) Micronutrients are required in small amounts; the inorganic nutrients would be easy to either find or synthesize: Boron, Cobalt, Chromium, Copper, Fluoride, Iodine, Iron, Manganese, Molybdenum, Selenium, and Zinc. Any of those not found locally could be even be pulled from parts of the ship; with requirements in the microgram to milligram range, supplies would last quite a while, and generally could be extracted from waste. Organic nutrients (vitamins A, B complex, C, D, E, K, and Carotenoids) are harder to make, but not impossible, especially if you have some basic building blocks and the right equipment. Certain vitamins (especially vitamin D) are created naturally in the body; other vitamins like C are quite easy to synthesize. Many of the B complex vitamins, however, would be fairly difficult to synthesize, and unfortunately are required for healthy living. Difficult, but not impossible. Luckily, the human body can go without many micronutrients for months, even years, with only minimal health impact. Small amounts of micronutrients, far below the recommended values, would be enough to sustain a population of adults for quite a while. Children, of course, should get as much as possible, as their developing bodies need more nutrients than adults. ## [Macronutrients](https://en.wikipedia.org/wiki/List_of_macronutrients) Macronutrients are needed in much greater amounts: carbohydrates, proteins, fats, fibers, and alcohols, the basic sources of calories, as well as essential structures like fatty acids. Of those, carbohydrates and alcohols are very easy to synthesize; both have simple structures that can be created in a lab, though it is much, much easier to distill them from organic sources like plants. Synthetic fiber is fairly easy to create as well, and only needed in low amounts, especially with a synthesized diet designed for minimal waste. Synthetic fats have fairly simple molecular chains and could be synthesized. Synthetic protein, however, has yet to be created in a lab, except by cloning - which, frankly, might be the best option. Cloned meat would be much easier to create than chemically-produced food, and the cloning process would use much, much less material. Assuming there are farm animals, samples could be taken from still-frozen creatures for cloning. ## Bacteria While bacteria isn't technically a nutrient, it is required to break down food into a digestible form. On Earth, helpful bacteria is easy to come by, but in space, in a sterile environment with no access to other living beings, it's possible for the bacteria in your gut to go extinct - especially if everyone takes any medication that kills off bacteria. I expect one of the biologists will be a "bacteria rancher", keeping a healthy population of gut bacteria in a maintainable way. Otherwise, all it takes is one round antibacterials to wreck your digestion process forever. ## Short term Many nutrients can be ignored for quite a while; not taking any vitamins for a week (or a month) won't kill you, though going for months on end will make you sick. Most people can go without food for a month without dying, and living on reduced calories for several months would have no lasting side effects apart from weight loss. Synthesized nutrients can replace "real" food for even longer, but be aware that synthetic sources of food often have reduced impacts - that is, eating natural vitamins from a plant will have more impact than synthetic vitamins. Frequent, mandatory checkups can help lessen any nutrient deficiencies. The best case is that the worldship anticipated a "ramp-up" period before the first crops came in, and kept a large stock of pill-form micronutrients and desiccated macronutrients to tide the settlers over. In that case, there would be enough to time clone protein and synthesize the other nutrients, and hopefully get some plants growing. Even basic fungus would be an enormous help towards synthesizing many nutrients. ## Long term While it may be possible to sustain a population indefinitely on cloned meat and synthetic vitamins, the population will begin to develop various diseases and disorders over time. They will need to focus on building a suitable long-term habitat; assuming they can find a planet with suitable gravity, they should be able to set up habitation domes within a few weeks, have viable gardens within a year. With enough room, in a few years they should have enough herd animals to start eating real meat. Life will still be tough, but at least they won't starve. [Answer] Yes it is ***theoretically*** possible to re-re-recycle the elements over and over again till infinity, provided that you have sufficient energy to invest in the process. However the process might take a long time to finish and may involve very complex procedures. The determining factors are these: * The extent of chemical labs available to the crew. * The amount of time available before the cycle of usage and production stabilizes. * The amount of chemicals available for initial consumption. * The amount of energy available for spending and the form in which they are available. Generally you want to have a limitless supply of electrical, thermal and light energy available. * The number of crew available for carrying out the synthesis. The more, the better. --- Edit to add: **1- How automated do you think this process could be made?** With our current technology, semi-automatic. It also depends on which ingredients are readily available from the environments and which have to be recycled. For example, consider a scenario where you get all the vital organic elements from the planet except oxygen. Here you will have to always wear a helmet (when out on the planet) and only breathe inside it. The coating of sodium peroxide on the inner sides of the helmets reacts with carbon dioxide and releases oxygen (while also turning sodium peroxide into sodium carbonate). You can never let even a tiny breathe waste away in the atmosphere of the planet as you can never get it back. You also have to consider the difficulties in collecting the products you want to recycle. For example, in the above scenario, since there is no oxygen on the planet, there is also no water. Which means that you have to have special types of urinals, which collect the urine and slowly evaporate them (only pure water evaporates, leaving salts as residue). Special condensers inside the mothership then condense water vapor back into drinkable water. All in all, how much automatic the process could be made, depends solely on the level of technology available and the type of elements/compounds you want to recycle. **2- Would it require a big factory, or would you think it could be reasonably portable (this is the "future")?** We do not know what level of tech would be available in "the future" so I can only answer the question as per my knowledge of the current technology. If you decide to make a big leap of technology in your work, feel free to do so. As a general rule in science fiction works, never go on in too much detail to make things look real and practical. Just state the general idea and a few hints on how things are done. Leave the rest on readers/viewers to imagine. Also, once again this depends on which compounds do you want to manufacture. For example, if you don't have freely available oxygen on the planet but have large bodies of water, you do not need to "recycle" your breaths (no need of those precarious helmets presented in the first answer). You can simply produce breathable oxygen by electrolyzing the water found on the planet (and surprisingly for most of us, water is surprisingly common on planets) which can be done comfortably and easily within a single room and can even be integrated inside the mothership's infrastructure. However if you want to produce nutritious food by recycling human digestive waste, this is going to take a really complex process which would probably require a small factory sized installation. **3- Or is this stretching the idea too far?** Read above. I suggest, you place most elements on the planet and only keep few as scarce. These could be calcium and phosphorous. For these you only have to recycle the dead bodies of the deceased people/animals and extract all these elements in their bodies. This would also make the plot somewhat catchy. **4- It'd be pretty bleak if everyone had to work on a production line.** Not really. Everybody could be on a production line for ... lets say ... 1 hour everyday. Make it a routine duty for everyone. Or ... you can divide the procedure so that some people have to work on recycling as their main duty, while others have to only work one hour per day and wear special suits which absorbs their sweat so as not to let any moisture go wasted (again, for oxygen depleted planets). [Answer] If you are traveling on a one way trip to some far off planet you make plans with the **expectation** that there WILL NOT be anything there to help immediately feed you and keep your power supplies going. What I'm saying is you are going to be sent with enough supplies to feed everyone for a reasonable time and enough supplies to start gardens and likely even livestock would be in cryofreeze to help start up a colony. So you will be bring seeds, and even bacteria needed to start producing a soil for plants to grow in, since even a habitable planet will still need these things. Most likely if most/everyone is frozen for the trip, then 'unfreezing' would be a regulated process. A few people at first to start. Maybe finding an asteroid to hollow out and terraform (with the help of robots) and then starting up a hydroponics lab in the ship to start growing fresh foods and producing needed bacteria and soils. as systems expand and more and more people are 'thawed' out to help out and continue expanding the livable spaces and generating foods, creating soils etc. Some of this stuff might have come along with ship. Maybe some good soil to begin with, some grass growing in a 'yard' etc. But there is no way anyone would travel with the expectation that when they get there they can all thaw out, disembark on a planet and start tilling the soil, let the cattle graze and start a western movie. [Answer] Non-biological food synthesis is likely to be an iffy proposition, if for no other reason than the issue of trace elements. You've mentioned the obvious elements: carbon, hydrogen, oxygen, nitrogen, sulphur, and phosphorous. You've left out a whole slew of others: sodium, chlorine, iodine, zinc, selenium, copper, molybdenum, chromium, calcium, iron, magnesium, bromine, manganese, silicon, nickel, boron and vanadium, at the least. See [here, for instance](https://en.wikipedia.org/wiki/Dietary_element). Management of these elements is likely to be tricky, since many of them are notably toxic in large quantities. Note that some elements seem to be needed in ng/kg quantities. Plus, the issue of bioavailability needs to be considered, especially since many of these require ingestion in certain classes of compounds, and may or may not be usable if not in the appropriate form. [Answer] In principle, yes. The [formose reaction](https://en.wikipedia.org/wiki/Formose_reaction) starts with formaldehyde (a simple molecule consisting of one carbon atom, one oxygen and two hydrogens) and produces an array of different sugars. Unfortunately the result is poisonous to eat, both because not all sugars are edible and possibly also because it still contains some formaldehyde, which is fairly nasty stuff by itself. However, with sufficient investment in chemical techniques this could probably be tamed to produce only a specific type of sugar, which could then by used as a starting point to synthesise more complex food molecules, such as larger carbohydrates, fatty acids and proteins. Again this assumes considerable investment in chemical expertise, but it's not far beyond what's achievable even with present technology, if there were sufficient reason to perfect it and make it safe. However, it may well be that it's cheaper and easier to just use bacteria instead. After all, a bacterium is already a machine that can break down existing organic material into its basic constituents and then (with the help of some energy) build them back up again into sugars, fats, proteins and carbohydrates. Doing all this chemically would be very expensive and it may well be hard to beat 4 billion years of evolution in terms of efficiency. (Though for the sake of a story, it's not completely implausible that you could.) ]
[Question] [ I envisioned this method of maintaining breathable oxygen. So each ship would have these gardens generating oxygen like the plants on Earth do. How plausible is this and how would it likely work? [Answer] The [Atomic Rockets Web Site](http://www.projectrho.com/public_html/rocket/) has all you could want and more about [Closed Ecological Systems](http://www.projectrho.com/public_html/rocket/lifesupport.php#id--Closed_Ecological_Systems). ![enter image description here](https://i.stack.imgur.com/Hm9PL.png) Selected quotes: > > Remember the fundamental rule of rocket design: **Every Gram Counts.** > > > and > > The main functions of a CELSS are: > > > 1 Turn astronaut's exhaled carbon dioxide into oxygen > > 2 Turn astronaut poop and table scraps into food > > 3 Turn astronaut pee and washing wastewater into drinkable water > > > The current lines of research focus on doing this the same way Terra's > ecosystem does: by using plants. In order to make the CELSS > hyper-efficient they have to use hyper-efficient plants. Which > explains the focus on algae. > > > and > > The advantage of algae is that it can theoretically form a closed > ecological cycle. This means that 6 liters of algae water, one human, > some equipment, and sunlight can keep the human supplied with food and > oxygen *forever.* > > > But there is **waaayyyy** more to this subject than the snippets I included. Please read that site for the details. **Which is better: Closed or Open Loop System?** Later on the page this resource indicates that closed-loop systems only make sense when you need environmental systems to last for a year or more. For times less than this, it takes less mass to just carry the inputs with you and dump the waste overboard. **A garden in space?** You could replace some or all of the algae with other plants, but your closed cycle ecological system will take more space, require more resources, and possess a very much higher mass. Similarly you could increase the mass of algae in the system and raise animals which ate it for nice variety in the diet (likely sea creatures able to share the algae tanks - crab, shrimp, fish, etc.). But as with replacing algae with trees, adding animal life decreases the mass efficiency of the system. For near-term (the next couple of hundred years) or possibly forever, space travel will require something less mass intensive to make space flight practical. [Answer] The [Biosphere 2](http://en.wikipedia.org/wiki/Biosphere_2) experiment was designed, in part, to answer this question (the term "Biosphere 1" being reserved for the planet Earth). It consisted of 3.14 acres of completely-enclosed, air-tight, land (including rainforest, wetlands, savannah, and desert), as well 8 individuals and a number of animals (including goats, chickens, and wild boar). Ultimately, the land was not able to sustain the necessary oxygen levels, which steadily dropped and eventually had to be artificially boosted. However, at least part of this oxygen loss was later found to be due to exposed cement portions of the structure absorbing oxygen from to air. Another atmospheric issue that was encountered was fluctuating CO2. It would drop during the daylight hours due to photosynthesis, and then rise again during the night. Occasionally, a CO2-scrubber had to be used. A later, second experiment (that included sealing the cement) was terminated prematurely due to some combination of personal, managerial, and financial issues. [Answer] > > "A single mature tree can absorb carbon dioxide at a rate of 48 > lbs./year and release enough oxygen back into the atmosphere to > support 2 human beings" > > > * *Arguments for Land Conservation: Documentation and Information Sources for Land Resources Protection* That being said, it becomes a matter of elementary math. Number of people / 2 = number of trees. However, the $O\_2:CO\_2$ ratio will be in constant flux, unless you keep lights on continuously. Also, you will have to water the trees. I would probably be easier to use a machine to produce oxygen. ]
[Question] [ In my own medieval fantasy setting, I have different countries that all have different populations. I admit that I have no idea of how many people should live in X or Y. Just using the numbers for the whole country is not really precise. I try to compare them to real medieval countries but I'm unsure of what is the best criteria to use. > > **Resources worth mentioning:** > > > * [Medieval demographics made easy](http://www222.pair.com/sjohn/blueroom/demog.htm) > * [Welsh Piper demographic guide](http://www.welshpiper.com/medieval-demographics) > > > (they are not wrong but they have limited informations.) > > > **[Historical Statistics of the World Economy: 1-2008 AD](http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCcQFjAB&url=http%3A%2F%2Fwww.ggdc.net%2Fmaddison%2FHistorical_Statistics%2Fhorizontal-file_02-2010.xls&ei=4_E5VM_cHZCNyASQy4HQCg&usg=AFQjCNFFKKZ1UysTOutlY4NsZF9qwdu2Hg&sig2=0iz29mi23oXQbCWHsaLHYQ&bvm=bv.77161500,d.aWw) by Angus Maddison and al.** > > > **[Data from the Worldmapper](http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCEQFjAA&url=http%3A%2F%2Fwww.worldmapper.org%2Fdata%2Fwithmap%2F8_worldmapper_data.xls&ei=aNdFVLaPGob6yATc9IHoDA&usg=AFQjCNHrQz9gJ_MEbAsHKbL1FoNu1xyA_g&sig2=-9_GZBs3JjvoNcBNSrPa2Q&bvm=bv.77880786,d.aWw) by the University of Sheffield** > > > **Clarifications:** * There is magic in the world but it's low magic. It mean people can't use it to farm. It would be a waste. * I'm trying to find numbers for a stable and sustainable population, not decimated, not starving or booming.This also mean that the land has been settled for quite some time. * About the available land: It is different everywhere and it clearly influences the population density of large area. But if we take a lot of different territories with different percentage of available land, we should have a average density. Then , we could apply a modifier depending if the land is flat or in the mountains. * Urbanization is another factor that will influence the density but it is not the most important. * Sedentary vs nomadic: I know that the population density is lower with nomadic people. There is a question about this [here](https://worldbuilding.stackexchange.com/questions/2928/what-is-the-difference-of-population-density-between-the-population-of-a-nomadic). **Hypothesis:** 1. The higher the temperature, the higher the population density as long as there is sufficient water to grow crops. 2. The higher the precipitations (or the water available) the higher the population density. Past a certain threshold, precipitations stops to have an impact on the population density. **So, I was wondering if there was a way to accurately estimate the population of a country in a middle age or renaissance era ?** [Answer] It really comes down to two factors: waterways and open land. **TL;DR: More waterways mean more cities and more people; more open land means more farmers and less people.** The above summary pretty much says it all, but I obviously have to expand on just where the connection lies. I think I can cite some pretty good examples to support my point, but if I've made any logical or (even worse) factual errors, I'd be obliged if anyone could point them out. --- Humans like to settle where there are good natural resources nearby that can aid them. If these resources are plentiful enough, more humans will move in. The settlement becomes a village, then a town, and finally a [city](https://en.wikipedia.org/wiki/City). What are these so-called "resources" that I've been talking about? Well, they can be a wide variety of things - open land, good sources of natural food and water, good ways for transportation, etc. One resource that combines all of these is a [waterway](https://en.wikipedia.org/wiki/Waterway). It could be a river, a stream, an ocean - anything you can dream up. What are the benefits of a waterway? Well, a waterway satisfies a few of humanity's simplest needs: 1. Food 2. Transportation 3. Agriculture **Food** The obvious thing that any marine environment can provide is a (fairly) good source of food. Fish, crab, lobster, eel, and a whole bunch of other delicacies. Rivers are particularly good because animals use them a lot to travel. [Salmon](https://en.wikipedia.org/wiki/Salmon) famously use them to get upstream to spawn. Crabs may live in the shallows. And there are other animals that like to *eat* these aquatic animals. Otters, bears, and a whole host of other carnivores. Herbivores, too, like to come to rivers to drink. If you live in the America Northeast, just think of the venison. . . There are, for the vegans, other options. Plants need water to live, and so if you're really out of food, you can always grab a few berries off a bush. But have your friend try them first. That could really save your life. . . Other plants, too (depending on the climate) may grow near rivers. **Transportation** Chances are, humans are going to need to go to other places outside the settlement - wars, trade, family reunions with the in-laws, etc. Waterways provide a great mode of transportation. You can't exactly use a boat in the middle of a plain, can you? If you're going downstream, you have a source of transportation that requires little effort. Upstream does require some effort (e.g. sails or rowers), but it's still an improvement over trekking miles and miles with a donkey and a cart. Rivers and oceans easily bolster trade. There's a reason that the term "[port](https://en.wikipedia.org/wiki/Port) city" is so ubiquitous. Back in the Middle Ages (and today), port cities were a dime (or shilling, rupee, guinea, yen, etc.) a dozen. Some of the bigger ones include London, Liverpool, Rotterdam, etc. More trade means a healthier economy, and more available resources. **Agriculture** Yep, waterways can help agriculture near cities. Even if land isn't directly near the river/ocean/whatever, canals can be built to help with irrigation. A farming economy an exist near an urban area, drawing people even closer to cities. This fell apart with the rise of suburbs, but the Middle Ages saw many serfs and peasants working and living near large population centers. --- Open land, however, also draws people. Sure, [Mesopotamia](https://en.wikipedia.org/wiki/Mesopotamia) was the poster child for settlements by the water, but it wouldn't have succeeded without agriculture - which resulted from a lot of open land. Plains are helpful, as are valleys - which are often created by glaciers, which eventually melt to become rivers. Wherever it is, open land draws people. There are primary uses for it: 1. Agriculture 2. Grazing and raising livestock **Agriculture** Okay, back to farming. It's hard to grow corn in the Himalayas. Just think about that sentence for a while. Crops are incredibly important to a civilization, and so humans will also settle where there is room to grow food. [The Three Sisters](https://en.wikipedia.org/wiki/Three_Sisters_(agriculture)) (corn, squash, and beans) were important to the indigenous people of North America. They could be grown in a variety of regions, from rocky New England to the sunny Midwest. Sure, they needed a certain climate to thrive in, but open land was another factor. Can you grow corn in the Rocky Mountains or in the eastern woodlands? I didn't think so. So open land definitely draws people. **Livestock** I hope that satisfied all the vegans out there, because they aren't going to like this next bit. The other good thing about open land is that animals like it, too. The [tribes of the North American plains](http://en.wikipedia.org/wiki/Plains_Indians) used it to their advantage by hunting buffalo. Later on, cattle ranchers drove out the tribes and used the land to raise cattle. Both groups were drawn by the allure of open land and the possibilities it held. Why waste your time staring at corn kernels when you can just go out and kill a buffalo? --- **How does this relate to you question?** I went off on quite a tangent there, and I did it to try to show how important waterways and open land are to civilizations. I emphasized them because the rest of my answer depends upon those two factors, and those two factors alone. **Calculating population** Here's the bit you have to wake up for. I'll start out by counting rural farmers and ranchers. In medieval Europe, many peasants worked as [serfs](https://en.wikipedia.org/wiki/Serfdom), working on a lord's land. In fact, a large portion of the population [lived in rural communities](https://en.wikipedia.org/wiki/Middle_Ages#High_Middle_Ages): > > The High Middle Ages saw an expansion of population. The estimated population of Europe grew from 35 to 80 million between 1000 and 1347, although the exact causes remain unclear: improved agricultural techniques, the decline of slaveholding, a more clement climate and the lack of invasion have all been suggested. As much as 90 per cent of the European population remained rural peasants. > > > This suggests about 8 million people living in "suburban" areas (i.e. small towns and villages) and cities. Let's say a lord owns $a$ acres of land. On each acre he might have $80$ [serfs working on it](http://www222.pair.com/sjohn/blueroom/demog.htm). So to calculate the population of a region, you would simply do $$a \text { acres} \times \frac{80 \text { serfs}}{\text { acre}}$$ Let's assume that all the open land in a region is used for this type of agriculture (which is likely the case). So you can simply use the above formula to calculate the population. What about cities? There's no easy formula for this; you'll just have to do estimation. You'll have more cities if 1. You country has a long coastline (or any coastline at all) 2. Your country has a lot of waterways So western China might not have a lot of cities, while eastern China will. I'd estimate perhaps 1.5 cities per major river, and 10 cities per length of the [east coast of the United States](https://en.wikipedia.org/wiki/East_Coast_of_the_United_States) (2,000 miles, give or take. From [here](http://www.europemaps.info/western-europe-medieval-city.html), > > The dimensions of the Western European cities were too small. Usually, their population numbers from 1000 up to 3-5 thousand people. Even in XIV-XV century, the cities with 20-30 thousand inhabitants were considered large. Only a few very large cities have a population of more than 80-100 thousand (Paris, Milan, Venice, Florence, Cordoba, Seville). > > > A region like Western Europe could, perhaps, have a half-dozen of these large cities, with perhaps 20 others of 5,000 people or more. Let's estimate a population of roughly 800,000 people in European cities during the High Middle Ages - 1% of Europe's population. --- **Summary** Contrary to what I had originally hypothesized, cities were not a huge part of the population of Europe; they held perhaps only a few percent of the population. Most people were rural farmers, living in densities of roughly 80 people per acre. If you know what fraction of your country is either arable land or land that can be made arable by magical means, you can figure out what the rural population is. From there, you can either use the rule of them that 90% of people were peasants, or simply sprinkle in a half-dozen 80-100,000-person cities per continent, with maybe 20 or so at 5,000 or more. [Answer] There are many variables involved when one seriously tries to model the cause and effect of populations, and there is no answer that can simply be expressed as something like: population = function of (climate, food-creation-technologies[x], medicine, land available, cultural effects[y], previous-population[age][gender][fertility][z]...) Not only is accurate population simulation very complex, but the population level in any area is caused by the actual history and its many details, starting with what the population was before the time you are interested in, what they actually do, etc. For example, looking at medieval England, there were great swings in population related to periodic famines and plagues. There are however some interesting immediate limits such as how much food, water, and shelter is available, and how predictable that is. So, especially for a fictional world, I would say it does make a lot of sense to try various views on what the limits might be on the population, especially in terms of where they get their food, and how much that can be based on the sources and labor available. I think a very reasonable and time-saving approach *would* be to go over to History.SE and ask about population demographics in a region/time you feel is similar to your setting. You might want to study what the contributing factors are, and adjust if your world is different. On the other hand, if you are making a simulation, then of course you will be interested in more of the actual cause and effect of the various details, rather than the resulting population and a description of conditions. Both simulation effects and historical populations are estimates. Historical estimates often have a wide range, and change as new theories or historians come and go. [Answer] **A possible answer:** Using the [Köppen classification](http://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classification) of climates, I did try to see if I could set a specific population density for each climate and I think I managed to get some numbers. The data for each area needed to be evaluated. For example: Jiangsu, Shangdong and Uttar Pradesh all have very high densities. This is mainly because they are very flat and almost all the space is used to grow food. That gives them a 20% or 30% bonus compared to other less fortunate regions with the same climate. Having a lot of data helps to figure where the marginal values are. My main sources are mentioned in the question and some of my other statistics include numbers form the game Victoria 2 of Paradox. The game studio made researches about the era and they try to be as accurate as possible. It's not foolproof but it's better than nothing. Using Madison numbers I see that the population was multiplied by 2 or 3 between 1500 and 1836. **Factors other than the climate to take in consideration:** * These values are the average and suppose a good deal of fertile land but also some areas unsuitable for farming. If the area is hilly, reduce the population density but increase it if it's mostly flat. * These values suppose that the country has enjoyed several decades of stability to allow the population to reach a certain level. The density is relatively high but sustainable. * Climates that have a dry summer will have lower population density because their crops have less water to grow. * The population from the Victorian era is 2 to 3 times higher than the population at the end of the medieval era. * High urbanization increase the population density. Maybe by 20%. * Non sedentary lifestyle usually mean a lower population density. Most temperate and humid climates are probably inhabited by sedentary people but nomadism is very common in arid, semi-arid climates and some cold climates. There, the possibilities are more limited for agriculture and the densities are low even with farming. The actual densities are between 10 or 100 times lower, I don't know exactly. * Trading: if a country is wealthy enough, he can import the food form elsewhere. **The results are classified by density of population per km2 in a decreasing order:** **30 to 40 :** BWh but the density fall around 0,2 without water * My main source of information was Egypt. Around 1500, the population was about 4 million people on a area of 1 000 000 km2. Since the population only live on 6% of the land, the real density is around 66 people per km2. But it's flat and very urbanized, so I lowered the values. This climate is the hottest and therefore can give a very good farming output with sufficient water. **30 to 35** : Cwa, Cfa, and BSh if water is available but 5 without water. * These areas include mostly regions of central and eastern China, but also Japan and some in Europe such as Montenegro. They pretty much all have high densities and are well developed and they tend to be pretty flat too. These are subtropical climates with almost no winters. Some areas can grow crops almost all year long. **20 to 25** : Cwb, Cfb, Dwa, Dfa * These two bunch of climates don't have much in common. Cb climates are well documented since it's the most common European climate. Thus, I just had to figure what the average was. Belgium and Italy have higher density because they are more urbanized. **15 to 20**: Am, Af, Aw * It is pretty much an estimation of the average. It is usually lower than that but never higher. **10 to 15**: Csa, Csb, Dwb, Dfb, Dsa, Dsb * Cs and Db had a lot of information and I managed to find information on Turkey regarding the Dsd climate. This is the average. **5 to 10**: Cwc, Cfc * I just have the numbers for Cfc but I extrapolated the results for Cwc. **4 to 6**: BSk * The cold steppes are usually pretty dry. Farming is possible but most of the population will be nomadic. if the population is only nomadic, divide the population by 10 or more. **0,5 to 1**: Dwc, Dfc, Dsc * These areas are not well suited for agriculture. The hottest parts might be acceptable for farming but the population is scattered. **0,25 to 0,5**: BWk * The cold desert is very dry and not suitable for farming except is some rare areas because rivers are also rare. **0,01**: Dwd, Dfd, Dsd and Ef (tundra) * Even nomads find that this is a harsh climate. Still some might live here. **0**: Ef (ice cap) * Nobody can live here because it's always frozen. ]
[Question] [ In the Carl Sagan novel *Contact* and the [1997 film of the book](http://en.wikipedia.org/wiki/Contact_(1997_US_film)), aliens from Vega have picked up TV pictures of Hitler opening the 1936 Olympics, which is depicted as the first TV signal powerful enough to reach the stars. The idea of aliens picking up our TV signals and learning human customs and languages from soap operas and commercials is well known enough to be a [comedy trope](http://tvtropes.org/pmwiki/pmwiki.php/Main/AliensStealCable). 1) How **plausible** is the basic idea that aliens might pick up Earth's TV or radio broadcasts in real life, assuming sentient technological aliens exist within the distance to which Earth's electromagnetic signals have penetrated? (That distance is a maximum of 79 light-years, if you agree with Sagan's view that the 1936 broadcasts were the first ones strong enough.) 2) Which types of broadcasts (in the sense of which **frequency** of EM radiation and type of signal modulation, amplitude or frequency) would pass through the atmosphere? My understanding is that TV and FM radio are the only realistic possibilities, as longwave radio is too weak and shortwave radio is bounced back by the ionosphere. 3) How **powerful** does the transmission have to be? [This piece by Brian Koberlein](https://briankoberlein.com/2015/02/19/e-t-phone-home/) expresses the view that a signal from earth would need a power of 110 MW to be picked up at the nearest star, Proxima Centauri, in order to be received about as well as we pick up the signals from Voyager I. UHF TV stations, he says, are limited to about 5MW, so the whole idea is unlikely. Do you agree? 4) Has humanity largely **stopped** sending signals that can be picked up by aliens? According to [Frank Drake](http://www.theguardian.com/science/2010/jan/27/aliens-cant-hear-us-astronomer), the astronomer behind the Drake Equation, since nowadays "most TV and radio programmes are transmitted from satellites that typically use only 75 watts and have aerials pointing toward Earth, rather than into space" it is no longer feasible for aliens to pick up our signals. So they'll get *The Twilight Zone* but not *Stargate*. 5) If they do get Earth TV, **whose** TV will it mostly be? I had assumed that the US output was dominant in the early part of the peak period for broadcasting power, as the signals that are most likely to be picked up are from the late 1950s to early 1980s, when America, as the richest large country, had the largest ownership of TV sets and the largest TV industry. In the comments to [this Worldbuilding SE answer](https://worldbuilding.stackexchange.com/a/18634/9207) Jorge Aldo disagrees. I have not been able to find good data about the historical spread of TV ownership and/or transmitter power across the world, so I might be wrong. And the answer might change if we look at FM radio rather than just TV. It is certain that latterly the amount of broadcasting in English has been equalled or surpassed by the amount in other languages such as Spanish and then Chinese. But would this be enough to counteract the effect in point (4)? 6) What **other factors** have I missed that might make aliens seeing our TV likely or unlikely? [Answer] Since my area of expertise is telecommunications, I think that I should first try to explain a little bit about how everything works, so that we can at least do some informed speculation about what the aliens could or could not receive and what they could make out of it. Do note that this answer is currently mostly about plausibility part. First concept that I'd like to introduce is antenna directivity. I'll start with visible light parallel before moving down the frequency axis into radio waves. Then, I'll try to explain how it allows us to compare power levels from different transmitters at different points. After that, I'll write a little bit about power spectral density and noise floor, which will allow us to compare the probabilities of detection of different types of modulations. Finally, I'll end this with a bit of my own speculation. So imagine that you take a lighter and you light it up. You'd get a small flame which would emit light, more or less equally in all directions. ![Lighter image from Wikipedia](https://i.stack.imgur.com/oR9jT.jpg) The radio version of that would be so called "isotropic point source", that is to say infinitely small antenna that radiates equally well in all directions. Such thing, of course doesn't exist, but is sort of useful in calculations, especially when we need to compare transmitters with different power levels and different antennas. Keep in mind that it would actually radiate equally well above itself as it would radiate below and to the sides. Here's an image of how its radiation pattern would look like: ![Diagram from website of PD0AC](https://i.stack.imgur.com/54Y6e.jpg) Then we have radiation patterns of different types of antennas. Here's a radiation pattern of a Yagi-Uda array that's commonly used for TV reception in some areas: ![Yagi radiation pattern from Cisco](https://i.stack.imgur.com/EWaY4.jpg) What this image shows us is that the antenna receives the best when the "long" front side of of the antenna and has very poor reception on the very short back side. In this particular case, we have a front-to-back radio of around 25 dB. When we convert that into linear units, that means that if the front side of the antenna is pointed towards our signal source, the signal would be received some 317 time more strongly compared to the case when the same signal was being received by the back side of the antenna. This brings us to the concept of "effective isotropic radiated power". So let's say that I have a transmitter that give out 5 W of power and that I have a receiver with an isotropic antenna, just for comparison's sake. I take my transmitter and connect it to one of my imaginary isotropic antennas, point the antenna towards the receiver and I measure EIRP of 5 W. Next, I take my Yagi antenna, from the previous example, I point it to the received antenna and do the measurement. I'd measure this way an EIRP of 158 watts. Quite a bit of difference we have there! But what if I don't point the front side of my Yagi antenna to receiver, but instead I point the side? Well from the radiation diagram we can see that on the sides, we have some -20 dB of gain, so that would give me 50 milliwatts at the sides of the antenna. There's also a concept of "effective radiated power". The difference between ERP and EIRP is that ERP assumes that the antenna is an ideal dipole antenna in free space which has gain of 2.15 dBi. That assumption is much more closer to realistic antenna systems than the isotropic antenna and is therefore often used in broadcast industry as a measurement unit for radiated power. So why is all of this antenna stuff important for reaching aliens? Well, the job of transmission system designers isn't to contact aliens (except when it is, but more on that later), it's to provide TV and radio to listeners, without interfering with other people doing the same thing. This means that the TV transmission antennas aren't usually going to have a radiation pattern that sends signal to the sky, they'll have a radiation pattern that tries to keep signal close to Earth. Also, the EIRP is going to be limited for safety and interference reasons. This doesn't mean that none of those many megawatts are going to reach space. They will, it's just that the power going out into space is going to be limited. Please keep in kind that someone needs to pay for all of that electricity consumed and that radio transmitters don't operate on 100% efficiency! There's a direct economical reason to keep your power as low as you can! Next, we have power spectral density. I think this is one point that I haven't seen discussed much in detection scenarios, but which I think is of extreme importance. Let's first take a look at the name itself: Power spectral density is a density. Density of what? Of power! Over what? Spectrum. So out units are watts per hertz. Remember power from the previous post? Well here we get to see how distributed it is across the bandwidth axis of our signal and how our modulation affects that. Here, I'll give a very, very rough comparison of PAL and DVB-T, used for television, FM from broadcast VHF radio (I wanted to do DAB, but couldn't find any realistic numbers) and one special FM Morse code signal. First, just to make calculations a bit easier and this very long answer a bit shorter, I'll assume that all modulations have a flat spectrum. This is more true for digital modulations and not so true for analog modulations. So let's start with PAL. Our channel, in UHF band, and I'm restricting myself to UHF band, since low parts of VHF band can have problems getting out of atmosphere, is around 8 MHz wide. There's also a version that's 6 MHz wide. So let's see the "idealized" power spectral density. For power levels, I'll just use some info from a local transmitter, so that we can get some real-life values. This transmitter, while it was transmitting PAL, had for one particular channel ERP of 250 kW. When we divide 250 kW by 8 MHz, we get 31.25 milliwatts per hertz of power spectral density. The same transmitter is now transmitting DVB-T channel with ERP of 25 kW. This gives us 3.125 milliwatts per hertz power spectral density. Much lower! The same transmitter is running an FM radio station at 15 kW. The bandwidth of the station is around 300 kHz, so this gives us PSD of around 500 milliwatts per hertz. Much higher than analog TV! Next, I'd like to mention the [Morse message](http://www.cplire.ru/html/ra&sr/irm/MIR-LENIN-SSSR.html). This was actually a test of an interplanetary radar, but it's here as an representative of so-called [Active SETI](https://en.wikipedia.org/wiki/Active_SETI). So they have frequency modulation with 62,5 Hz deviation and maximum input signal frequency of less than 1 Hz. I'll use 1 Hz for calculation. According to Carson's rule, we can get an estimate of bandwidth in which 98% of power of FM signal is contained. It gives us bandwidth of 125 Hz. ERP of transmission was 50 kW. This gives us PSD of 392 watts per hertz! Way higher than FM radio, but on the other hand, a test transmission and therefore not continuous. Now why did I go into this basic explanations about PSD? Well in order to detect that we have a signal, we first need a good enough signal to noise radio. Our noise could be coming from numerous sources, such as thermal noise, shot-noise etc. It is going to be a property of the receiver and it itself is also characterized by power spectral density. One common thing about receivers is that usually, we can easily affect their reception bandwidth. The lower reception bandwidth we have, the lower is our noise power at the receiver. In an ideal world, our receiver will have a filter matched to the bandwidth of our transited signal. So basically, this means that if our power is constant, it's going to be easier to detect a signal with lower bandwidth than a signal with higher bandwidth, as illustrated in this drawing: ![Signal PSD](https://i.stack.imgur.com/68Y8D.png) So basically, my idea is that the aliens, if they are going to detect out signals in the first place, are most likely to detect Active SETI attempts, if they happen to be looking for them at the moment. Otherwise, I think that FM radio has better chance of being picked up than TV. Furthermore, in an analog TV signal, not all components are transmitted with same power! Part of signal carrying color (chroma components) is usually weaker than part that carries black and white signal (luma). Also, depending on implementation, it might be possible to get audio signals from TV even if video reception is not possible. **EDIT1:** As a response to comment, let's say that we have a space ship in Earth's orbit with a TV transmitter on-board. Let's also say that our spaceship is pointing its antenna towards our listeners and is emitting the program with 5 MW of ERP and uses a 6 MHz wide channel. Let's say that we're transmitting at frequency of 430 MHz (not in TV band, but close by, chosen due to available data) and that our aliens built their own version of Arecibo with same specifications, that is to say 60,5 dBi gain on 430 MHz. Let us also say that noise floor is −106 dBm for our channel at the receiver. The Friis transmission equation goes something like this: Prx=Gtx*Grx*(λ/4πR)^2\*Ptx, where: Prx is the power at the receiver and should be -106 dBm, Gtx is the gain of transmitter antenna, Grx is the gain of the receiver antenna, Ptx is the power of the transmmitter, λ is the wavelength, R is the distance. From this equation, we should derive R and change it so that we take into account mixture of decibels and linear units. Do note that in our case, we have 5 MW of ERP, so in order to convert that to EIRP, we are going to use transmission antenna with gain of -2,15 dBi. Also note that the upper edge of our signal is at 436 MHz, which have wavelength of around 0.688 m. We divide everything with the antenna gains and transmit power and we take 10\*lg of everything to get to decibels. So we have: 10lg(Prx)-10lg(Ptx)-10lg(Grx)-10lg(Gtx)=20lg(λ/4πR) Now we put our numbers into that: 96.9897 dBm + 106 dBm +2,15 dBi -60,5 dBi=20lg(λ/4πR) Now we can use one of those handy Friis Transmission equation calculators and get a number for the range. Using [this](http://www.random-science-tools.com/electronics/friis.htm) one, I get range of 638 420 000 000 m, that's 638.42 Gm or 4,26 AU. That's very, very little! Even if we take much better values for system noise temperature, such as for example 100 K, or maybe even lower, we'll still have very low ranges. So for TV, we don't really have a big chance of having aliens receive a signal. For FM radio on the other hand, if we take a 100 kW ERP transmitter at 97 MHz, based on some USA limitations for power, and we imagine that the aliens have a 60,5 dBi gain antenna for FM with system temperature of 35 K we get a much nicer result of 5 349 800 000 000 m or 5,349 Tm or 35,76 AU. Still, it's quite short range. The range is much greater, but still not very sufficient to reach nearby star systems, assuming that system temperature is reasonable. **So TL;DR:** I do not believe that it is feasible that accidentally transmitted analog TV or radio signals would be able to reach a nearby star system in a reasonably-detectable state, but that depends also a lot on their detection capabilities. I do believe that aliens passing near the edges of our Solar system might be able to detect our transmissions. Also note that a 100 kW radio signal has longer range than 5 MW TV signal, so keep in mind that not everything is in transmitter power. It should be noted that for intentional active SETI signals, especially if digital, situation might be somewhat different. We'd have much higher powers, we'd have gains from error correction codes, assuming aliens can decode them. I also used signal to noise radio of 0 dB as the lower limit for analog system reception. In real life, it has been proven that decoding digital signals is possible at signal to noise rations a bit below 0 dB, so that could also make some impact. [Answer] I just saw a [presentation at SETI](http://www.seti.org/weeky-lecture/breakthrough-initiative-listen-and-megastructures-kic-8463) explained how near-future receiver arrays will be sensitive enough to pick up our aircraft radar from hundreds of lightyears. That's leakage of common use. We also have *interplanetary* radar that's occasionally beamed out. So to answer your question, look at the opposite end: what are SETI researchers expecting to be able to detect, modeling the situation of our own technological history? While radio is power-saving and subtle, radar by its nature must be bright enough to reflect off passive targets. So *much* more detectable. Here is a [press release](http://www.breakthroughinitiatives.org/News/1): > > # Unprecedented scope > > > The program will include a survey of the 1,000,000 closest stars to Earth. It will scan the center of our galaxy and the entire galactic plane. Beyond the Milky Way, it will listen for messages from the 100 closest galaxies. The telescopes used are exquisitely sensitive to long-distance signals, even of low or moderate power: > > > * If a civilization based around one of the 1,000 nearest stars transmits to us with the power of common aircraft radar, Breakthrough Listen telescopes could detect it. > * If a civilization transmits from the center of the Milky Way, with any more than 12 times the output of interplanetary radars we use to probe the Solar System, Breakthrough Listen telescopes could detect it. > * From a nearby star (25 trillion miles away), Breakthrough Listen’s optical search could detect a 100-watt laser (energy output of normal household light bulb). > > > ]
[Question] [ Suppose that there is a moon, orbiting a gas giant, and that gas giant is a rogue planet - it moves freely through the universe, unbound by the gravity of a star. This means that one, the moon will never see the light of day, and two, there will be no sun to warm it. But say that the processes of volcanism, convection and tidal heating do give it warmth. In that case, the moon could, potentially, be habitable, assuming other figures, statistics and technicalities were also appropriate for habitability. With no light - save for naturally occuring fires or volcanic eruptions - photosynthesis is impossible here. Chemosynthesis isn't really possible except in special locations, so to have something roughly similar to plants, a new process must be devised. We'll call that process kinetosynthesis - a method of autotrophy not seen on Earth. While photosynthesizers use chloroplasts to strip electrons from substances as water, kinetosynthesizers use piezoelectric crystals in their cells, such as quartz, to do the same thing, but with mechanical stress replacing sunlight. I'm no chemist, so I'll leave the process as vague as is for this question. These kinetotrophic plants would likely have a number of energy sources, so as to exploit vacant niches; namely wind, rain, tides, sound and pure stress. If this sunless moon was volcanically active, wind and rain could be present - volcanic hotspots create contrasting hot and cold areas for the air to move between, and volcanoes play a part in Earth's water cycle - were they in greater density, they could cause rain to occur. One possible problem with kinetosynthesis is the lack of energy that can be obtained - but perhaps the lower gravity, plus an oxygen-rich atmosphere (Which could be boosted significantly once kinetotrophic "Embryophytes" evolved, which in turn would be fuelled by the high volcanic activity), would decrease the energy usage of various organ systems, combined with drastic tides and fast winds - would make it more plausible. In the end, it's fair to say that we really don't know if kinetosynthesis would work. But, let's just say that it is here. Finally, onto my question: **If there were sessile, multicellular kinetoautotrophs, using piezoelectricity in the method described above, how would they be structured?** Let me explain a bit more. Earth plants, as we all know, have roots in the ground, a stem, and leaves. Stems are, in part, for growing taller than your peers, and thus get more light than them. How might kinetotrophs grow to recieve more energy than the surrounding ones? Leaves are for photosynthesis, mainly. Would kinetotrophs benefit from specialized kinetosynthesizing structures? Obviously, a plant that got energy from the tides would look different to one that got energy from the wind, and one that fed on rain would differ from one that fed on sound. For your answers, you can select any of the energy sources (Wind, rain, tide, sound, stress). If you consider this premise implausible, please say so. If you deem the question in need of editing, please say so too. [Answer] I'm going to take a crack at this one, as 'non-earthlike-energy for native life forms on exoplanets' is something that has interested me ever since I found out about the life here on earth, around volcanic vents under the sea, that use the earth's own heat for energy instead of the photosynthesis cycle (something widely considered to be impossible before its discovery). I may add more after I read other's answers for inspiration, but here's what I have off the top of my head (Disclaimer that I have no scientific experience to back any of this on, beyond entry level college biology class, and my own layman's 'research' prompted by my curiosity): **Stress**: I would expect this to be the most primitive form of life in this scenario, analogous to single-celled organisms here on Earth, and possibly the simplest of multicellular life. A fast spinning moon could allow single celled kinetoautotrophs to use the gravitational changes felt from the gravity of the planet, both in intensity and direction, as the source of the stress. The primary environmental factor they would need for this 'niche' would be a solid surface to live on, to provide a resistance force against the gravitational one. Evolution, from there in to multicellular organisms, could yield a structure similar to a sea sponge or moss clumps, spherical or semi-spherical except where in contact with irregularities in the surrounding surfaces, and with cells at the bottom adapted to take advantage of higher stressses (from the increased weight above them) at lower ranges of motion, while cells above adapted to lower stresses and higher ranges of motion. The next evolution would be more advanced structures on the bottom of organisms to grip the surface to prevent tipping over during growth, and thus avoiding ending up with the wrong specialized cells in the wrong orientations, and to extract nutrients more efficiently from the hard surface or any incidental liquid that might be present. Minor variations would exist for different climates. Wider and flatter in high wind areas or where flooding is a concern, taller and more conical in calmer areas. And that's where I think evolution would branch to adapt to more varied surfaces, and based on environmental conditions related to the other sources of energy, wind, rain, tides (sound adaptations come later). **Wind**: To me, this seems like the first natural adaptation to an alternate form of kinetic energy, simply due to the fact that it would be so wide-spread across the surface of the moon, regardless of the presence or absence of standing, flowing, or falling liquid, and especially if my assumption (mentioned in my section on stress energy) of a fast rotation speed is accepted since this rotation would also cause (relatively, compared to slower rotation speeds) more or less constant winds with and high average speeds for winds. Structural adaptations for this would vary widely, depending on surface, and also depending on prevailing wind conditions like speed (fast or slow) and consistency (steady or gusty). For broken surfaces (gravel, sand, soil, etc) root-like structures would be likely, to help keep from being blown over, and to provide a stable foundation to allow the possibility of more and greater vertical growth. For more unbroken solid surfaces, I would expect a horizontal variation of what is seen on wall-climbing vine plants, a network of 'branches' sent out from the base to seek out any of the relatively rare nooks and crannies that could be used for anchorage, and also to simply provide a wide base for support in the absence of significant or sufficient anchor points in the surface itself. Now, on to the energy collecting structures. Simpler forms of life would have structures that appear, superficially, like blades of grass, or a very short stem (stems with wide separation if multiple are present in a single organism) with a single leaf-like or fan-like (like an accordion-folding fan) structure at the end of each stem. The grass-like blades (more common in steady winds) could be air-foil shaped (think an airplane wing tipped up verticle) causing a bending motion (and subsequent stress for energy) in response to the wind, or have a cross section shaped like the letter "C" so that as wind fills the gap it will spill out of one side, causing a twisting motion (and subsequent stress for energy) before rebounding and catching more air which spills out the opposite side, oscillating it back and forth repeatedly (like a ribbon pulled semi-tight in stiff breeze). Fan structures (more common in areas with more calm air and intermittent stronger gusts or windstorms) could vary more widely, portions of a circle (nearly full circle, semi circle, quarter circle) for maximum surface area with minimal mass to take advantage of every slight change in the air movement in regions of low prevailing wind speeds and low intensity/frequency gusts and low intensity/frequency windstorms, to more exotic variations like very thin and fibrous webs (like dandelion fluff, but in any and all shapes) or a 'kite' with a horizontally oriented airfoil shape at the top of the stem to intentionally 'lift' and stretch the stem. More advanced varieties would evolve other ways to increase their surface area impacted by the wind, and increase strength (probably through thickness) of stem (trunk) and anchorage to withstand the compounded forces received by the additional impacted surface area. To do this, many would literally branch out like earth trees except that on earth optimum branching direction is perpendicular to the direction of sunlight (which averages to vertical from the surface of the earth, causing branching horizontally, causing plants to generally have a round shape when viewed from the top down) while optimal branching direction for wind gathering plants on this moon would be perpendicular to the prevailing wind direction, so they would generally branch north, south, and vertical, since prevailing wind direction would be either east to west, or west to east, depending on the direction of the rotation of the moon. So viewed from the top down, the branching plants would primarily look like long thin lines, slightly tapered at either end. Viewed from the north or south, they would again look long and thin, and tapered from top to bottom. Viewed from the east or west, they would most likely look like a rounded fan or semi-circle, or the very advanced ones might evolve strong enough anchors and trunks to make more significant vertical gains and look like a circle on the end of the stem/trunk. The advanced species that don't branch might evolve much wider bases perpendicular to the wind, and then fan out vertically, like giant versions of leaves. Others might send out long thin streaming threads from elevated branches to whip in the wind at the ends for maximum movement and energy gains. To compete with other organisms in the direct vicinity, any of these variations would likely use their base/root/anchor structures to seek out competition toward the prevailing wind direction, since any organism in 'front' of them (relative to wind direction) could block their source of energy, while organisms behind them would only be able to compete if they can also send something forward to 'attack' organisms. Once a competitor is identified, the organism behind would seek to either cut off the base or cover the face of the competitor. The most desirable reproduction strategies would be anything that sends offspring in the direction of the prevailing wind, so seeds in the air would be counterproductive, unless there is a band of suitable environment that is a complete circle around the moon (not likely). So budding up from anchors out in front of (though likely not directly in front of) the organism is a likely, creating colonies of organisms with members of a generation generally spread out north to south from each other, and members of newer generations in front of them, though staggered/offset north to south of the older generation behind them. **Rain**: This one is the one I think is the most interesting. A quick Google search got me estimates of up to about 14% of Earth's land area was once (pre-deforestation) covered by rain forest. Adjusted however you like for the total land area (as opposed to ocean) of this moon, and it's still a relatively rare thing, and the highest frequency I could find for rainy days per year was 243, in Belem, Brazil, in the Amazon rain forest. That's almost exactly 2 days out of 3, in the place where it rains the most frequently that I could find (not the highest amount of water volume, but the most reliable rain). This makes rain a very unreliable energy source (in general, on a the scale of the entire surface area of a moon[planetary? scale {but it's not a planet} moon-itary scale?]), except in the most ideal climates. So this type of life, with adaptations for this energy source, would likely be both relatively rare and relatively isolated. I see simple life forms evolving from the sponge-form or mossclump-form bu sending out horizontal (Like the branching of trees and plants on Earth spreading horizontally to catch the vertical [by average] sunlight) appendages from a ring near the half way point(ring) between their base and their peak to catch the energy from the vertical (again, average) falling rain. Somewhere near halfway between top and bottom is because too low and there is no room for downward flex after impact from the raindrops, and too high and it would be pointing straight up and there would not be room for enough appendages making it hard to have enough surface area to catch enough rain to be useful. In intermediately advanced life, the spongy/moss base evolves in to a more specialized root/anchor structure, which spreads out more efficiently, either by flattening like a disc, or by separating in to a more branching network, and the appendages become more specialized as well, some becoming dedicated support structures (stems/trunks), while others specialize at catching and using the rain energy by either increasing in number while thinning out (think very long thin stiff grass growing sideways instead of vertical), or by forming wider leaf-like shapes. The more advanced would combine the two, having very small fuzzy hairlike structure on their leaves that would react to the flowing of the rain off of the leave after impact, while the larger leaf structure focuses on harnessing the energy of the impact itself. The most advanced appendages would be even more highly specialized, forming funnel shapes (complete with openings at the bottom) with their largest leaves, and lining the inside surfaces with fine hairs, creating artificial currents at the bottoms of the funnels so that collected rain could provide longer term energy as it flows slowly through the end of the funnel even after the rain has stopped. Competition with local organisms would lead to both horizontal (cover up the neighboring organism) and vertical (get high enough that you can cover the neighboring organism) adaptations. These would likely be the only 'true' 'trees' on the planet, though the only thing that might encourage any significant height would be the low gravity on the moon. If the gravity is not enough of a factor, then even these trees would be relatively short compared to earth's trees. Being covered up by a competing organism could lead to special adaptations to catching residual rainfall coming off the leaves of the organisms above, such as extremely large individual leaves funneling in to relatively complex and efficient funneling systems. Unfortunately, nothing specific comes to mind for reproduction specializations for this energy form. **Tide**: I see two main methods here, sheer ocean surface level changes, and water flow changes like currents and waves. The adaptations for currents and waves are more likely to be more primitive than adaptations for ocean levels, because the immediate brute force of the waves are likely to have a more direct and immediately impactful influence on the sponge/moss close to the shoreline than a relatively calm and slow rise of the tide. The first adaptations would be the strongest anchoring system so far, to avoid being dislodged entirely and lost to the depths, and appendages to move with the flow of the waves and harvest energy from them. I see two main types of appendages forming here: the first is very stiff and strong, to take a beating from waves without breaking, while flexing just enough to create great internal stresses for energy collection. probably starting our as relatively straight spines like a sea urchin's, and later would be more complex lattices like fan coral but more flexible. The other would be VERY flexible, like fine strands of moss, or flowing kelp leaves, making use of movement by gathering less energy per movement, but making up for it by moving more often and in more directions. The most advanced species in this group take advantage of the tides directly. These are the ones that competed with the other wave dwellers originally, but got their start in the deeper side of the coastal waters and managed to survive despite being distanced from the most energetic areas of the waves nearer the shoreline. To avoid sinking too deep below the level where the wave movement wasn't sufficient, they developed gas filled bladders to keep their energy capturing appendages up nearer the surface where the wave energy is stronger. This increased pressure on their anchoring structures, leading to improved anchoring structures. This allowed access to increased depth while maintaining access to energy. This created a cycle of evolution, increased depth > increased bladder > increased anchoring > repeat. Eventually the depth achieved was so great, that sufficient wave energy was out of reach to support the nergy requirements of the stalk structure between the anchor and the energy capturing leaves. The next adaptation at this point was for the stalk structure itself to become an energy producer, from the stretch stress between anchor and gas bladder. Further adaptation moved this stress from secondary to primary, and the leaf structures become vestigial, or disappear entirely. At the same time, the anchor, stalk, and gas bladder all become exagerated until the most advanced species is an enormous bladder that floats on the surface of the ocean at low tide, and is mostly or completely submerged at high tide. This is connected to a very strong, thick, stalk which receives massive stress energy from the bladder pulling up and the anchor structure holding it down. Competition would be mostly based on surface area under the water, for anchor points, individual organisms would seek to cover as much of the available nooks and crannies within their reach, to ensure the best hold. I see no reason that reproduction in this oceanic environment would follow a pattern any different than earth's oceans, so budding/self-cloning, and releasing egg/sperm directly in to the water on regular cycles, are likely options regardless of the specific oceanic region or adaptation of the rest of the organisms body type. **Sound**: This would be the most advanced individual adaptation of any of the groups, and would apply to all of them, from the sponge/moss to the wind, rain, and tide, types. In other words, the adaptation wouldn't be specific to any of the groups, but any species within the group that has this adaptation would be the among the most advanced species in their respective groups. This mechanism actually exists in the animal kingdom on earth, and the human inner-ear is a good example. It has hair-like structures (an adaptation I already mentioned for other types) that convert movement from sound waves to electrical signals. The sponge and moss clump species could directly produce these hairlike structures externally, and the sponges could also have them inside the cavities that already existed in their more primitive relatives. Wind-specialists could incorporate them on their surfaces as well, and the most advanced would be the ones with ancestors that had already specialized to have a higher number of leaves/appendages with smaller surface structures, thus allowing their more advanced descendants the benefit of having more surface points from which to generate those hairlike structures. Rain-specialists would probably evolve this adaptation before the others, as the movement of liquid inside confined spaces is already part of their initial strategy, so this would just close the loop for them. Tidal-specialists could sprout those hairs from any part of their structures, since they are (almost) entirely submerged (almost) all their lives. The massive bladders of the deepest tidal species could have those hairs both inside and outside the bladders, to take advantage of sound both through air above (at low tide) and below. **my own group**: A hybrid type, not mentioned by the OP, seems likely to me. If it rains, and there are oceans, then there are almost certainly rivers that take the rain back to the ocean. Specialist species, hybrids(in form if not literally) between rain/wind/tidal, could anchor to the banks of rivers(easier to anchor on land, where water isn't trying to rush the seedling away from any anchor points), and reach appendages in to the current where they act like a combination of wave/wind energy collector appendages. Advanced variations could still use funnel forms like the rain collectors, but submerged. The Sound collecting hairs would not function on 'sound', specifically, while submerged as the current of the water would likely be universally more efficient than sound collection in this environment, but the surface structures could use them. [Answer] **There should be a part of the plant that, as much/as often as possible, is rhythmically moving.** Kinetosynthetic organisms would depend on relative motion between different parts of the their body, and their evolution would seek to maximize the amount of relative motion they obtain from the environment. I would expect your plants to end up looking like organic versions of machines that we have for harvesting energy from motion. Concept organisms that come to mind: ***Windmill plant***: "leaves" that are shaped such that they flap back and forth or make circular motions in the wind, at the top of a stalk that holds them up from the ground for better airflow. ***Wave-energy plant***: Attached to a shore/coast/riverbank with a floating part on the water, bobbing in the waves; kinetosynthesis occurs in the rhythmically bending stalk. (See here: <https://www.youtube.com/watch?v=GA_UgVm9bvU> ) ***Wave-energy carpet plant***: a floating carpet on wavy water (perhaps anchored with stalks to the river/ocean floor), with stretchy fibers above and below the floating volumes. As the carpet ripples in the waves, the stretchy fibers are rhythmically flexed. ***Wind/current energy grass***: simply a flexible blade/stem shaped so that it bends/twists in the wind (above water) or in the current (in a river). In general: for the plant to be viable, it needs a systematic source of rhythmic motion. What part moves? How does it maximize the motion? Final note: as these plants compete to capture motion out of the environment, they will slow/deaden the motion surrounding them. If enough wave-energy plants grow around a shoreline, they will eventually clog and deaden the wave motion there and reach an equilibrium where some are dying for lack of energy. (You could have predators/scavengers clear out the dead ones faster than they accumulate, though...how you manage your ecology is up to you!) Just keep in mind that plants will tend to congregate and saturate regions with high relative motion, like riverbanks or windy hilltops. [Answer] **Earth's photosynesizing plants come in all shapes and sizes** Which makes it difficult to predict what a kineteosynthesizing plant would look like. Earth's plants come in all densities, all configurations, all flexibility and rigidity. There are so many factors that go into estimating the evolution of plants that, IMO, this is a nearly impossible question to answer. *Nearly....* Energy or the resources to convert to energy must be obtained from somewhere. Earth's plants generally obtain said resources from two directions: the soil and the sun. Soil resources (water & chemicals) come through roots. Sugar comes from the chemical processes of photosynthesis, which requires sunlight. And that means capturing the sun. Whether through leaves or from the surface of stalks, sunlight impacts the plant, which enables the plant to convert soil resources into sugar for energy. **The kineteosynthesis idea is interesting, but what's the external resource it's using to create sugar?** Your plants will still have roots and still obtain most of their resources via soil. There's no sunlight (though there is some light generated from the planet's volcanism). As mentioned in my comments, there's plenty of chemical abundance in the atmosphere, so chemosynthesis is likely — but that's not your question, so we'll ignore it. That leaves vibration, caused by the volcanism. * A plant that lives in a high-vibration environment needs stability. That would suggest either very, very deep roots or a vast array of micro-roots such that the plant and the soil it depends on will stay in place. * Earth's plants survive high winds just fine, so I don't believe there would be a specific structure to help your plants survive high vibrations, but we could assume a thicker or more dense epidermis layer. I could imagine one of your plants adapting to its environment by incorporating the atmospheric ash with a thick ooze exuded from the epidermis resulting in a flexible but epoxy-like surface that protected it from the consequences of vibration. * We have a precedent for using piezoelectronics to generate electicity in the form of [vibration powered generators](https://en.wikipedia.org/wiki/Vibration-powered_generator#Piezoelectric_generators). The plant would need sheets of piezoelectric crystals that, basically, move back and forth like a speaker membrane. The motion causes electricity via the piezoelectric crystals which could replace sunlight as the glucose-creating catalyst. I can imagine flower petals taking on this role. **But in the end, the actual look of your plants is up to you** Earth has proven that plants can take on so great a variety of looks that it's quite literally impossible for us to tell you what your plants will look like. Honestly, they'll look like the plants we have other than they won't generally be green. Whether they have leaves will be dependant on your environment, whether or not flowers have color will be dpeendent on your ecology. It's horrifically complex. But, I've come up with three consequences of your world that would/could impact plant development: root structure, epidermis structure, and the membranes needed for electricity generation. You can take if from there. [Answer] Since kinetosynthesizing structures need to move, flex or stretch to produce energy, evolution would favor light and flexible structures that move at the slightest provocation. One possible branch of evolution would look like a fan coral and consist of very soft, lightweight branches that can all move individually. That way the plant catches the slightest movement of air or water around it and produces energy not only from the original current, but also from vortexes caused by its own shape. It has the disadvantage of being very vulnerable to strong currents. Those places with constant strong currents could be populated by plants shaped like long leaves of grass. Either seperate leaves grow directly out of the soil or some plants develop stronger, inflexible stems to lift their leaves above ground to catch more currents. If a current is strong enough to affect the whole length of the leaf, it will put it into a wave-like motion. Lots of movement, lots of energy harvested. But these are vulnerable to times of calm winds or currents and need a way to store excess energy. Tumbleweed could also produce piezoelectric energy by tumbling around. The spheric structure moves well at the slightest current, is resilient to too strong currents and beeing backed into a corner only increases the deformation and thereby energy production. You could even create a plant that can thrive without much of an atmosphere, as volcanic ashes rain down to the surface due to gravity alone. This one has very thin, lightweight leaves like overlong grass blades. They grow at a 45° angle upwards and form a slight curve. They are also covered with a dust repelling lotus-effect surface. The ashes constantly raining down from volcanoes accumulate on those leaves and bend them, producing energy. If a certain mass of ashes accumulated, it slips off the surface and the process starts all over again. Since the plant would be buried in ashes sooner or later, it must constantly grow longer, opening up a second opportunity to produce energy. The strong gravitational forces cause not only tidal heating, but also tidal deforming. A truely *long* blade of this pland might harvest energy from being stretched, bend and compressed by the ever shifting gravitational tides. [Answer] I'm almost certain this is nearly impossible, but in good faith I'll go with it on the small chance it isn't. Kineticsynthesizers would probably all take on flat, wide shapes. I'd imagine them starting out as colonies of single cell organisms that coat surfaces which eventually evolved into multicelled organisms with the same traits. Since the multicellular versions would produce more energy and have more chances at nutrients they would fair slightly better than their colonial counterparts. I imagine tidal versions pressed against cliffs would fair well, the compression of water and rock being a good medium for kinetic synthesis, and the nutrients from the water being good for growing. Tides probably wouldn't be regular on a drifter, but because pressure travels well through water sources like earthquakes and landslides would effect the water as well, plus possibly dump the chemicals life needs into it. A wind version could also grow on cliffs that are buffered by winds, but they could be scoured off by strong winds with particles so maybe not. I can't think of a scenario where sound or stress are consistent or loud enough for this to work. Rain may work, same with tides or wind, but I'm again not sure if the rain generates enough pressure, though there's a fair chance of it being consistent enough somewhere, though maybe you dont get rain on a planet with no sun for evaporation. Maybe occasionally. ]