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[Question] [ This hypothetical organism would: * Be able to control a host using neurostimulus * Inhabit the space near the host's brain * Be rather large, so it would have to disguise its body in an attempt to match a human body part. Maybe it would approximate hair as best it could? Signs that a host has this parasite could include: * Chemical imbalance of the host such as orange pigmentation of the skin * Irrationality or lack of temperament * Misperception of own body as an error of the neurostimulus, ex. "I have big hands, I have the biggest hands" * Disregard of common sense or common morals * A sudden or unexpected change in political power as the parasite makes its way to a position of power Is this plausible? Could an alien parasite really work in these ways, or be present on a human host disguised within the population? [Answer] ## Toxoplasma Gondii [![enter image description here](https://i.stack.imgur.com/QisRF.jpg)](https://i.stack.imgur.com/QisRF.jpg) The organism [toxoplasma gondii](https://en.wikipedia.org/wiki/Toxoplasma_gondii) is well known to do almost exactly what you are wondering about. This is not fiction—it is actually a scientific fact on Earth now (except the organism is not considered to be of extraterrestrial origin.) Its most notable characteristics are * its propensity for causing the host to be attracted to predators, such as [mice being attracted to cats](http://www.livescience.com/56529-strange-facts-about-toxoplasma-gondii-parasite.html) and [chimpanzees being attracted to leopards](http://blogs.discovermagazine.com/d-brief/2016/02/15/chimps-predator-t-gondii-leopard/#.WAbmEnj3arX) * causing the host to be attracted to what would ordinarily be considered negative experiences, such as [fear, pain and danger](https://www.google.com/search?num=100&safe=off&client=safari&hl=en-us&ei=Q-gGWPDwDcvherXmhvAE&q=toxoplasma%20gondii%20sexual%20attraction&oq=toxoplasma%20gondii%20sexual%20attraction&gs_l=mobile-gws-serp.3...25189.25368.1.26544.2.2.0.0.0.0.123.208.1j1.2.0....0...1c.1.64.mobile-gws-serp..0.0.0.2Py3MLWDR8Y). This could explain BDSM behavior, loving scary movies, daredevils, etc. So far no concrete evidence has been found that t. gondii effects human behavior, even though [half of the world's population is thought to be infected, up to 95% in certain populations](https://en.wikipedia.org/wiki/Toxoplasmosis). However, there is [speculation it could effect human behavior](https://www.google.com/search?num=100&safe=off&client=safari&hl=en-us&ei=e-cGWOHONsLZe4T0vvAP&q=toxoplasma%20gondii%20in%20humans%20behavior&oq=toxoplasma%20gondii%20in%20h&gs_l=mobile-gws-serp.1.1.0l5.2133.5428.0.6797.6.6.0.3.3.0.154.632.0j5.5.0....0...1c.1.64.mobile-gws-serp..1.5.348...35i39k1j0i20k1.JEc11BNMjxk), perhaps even causing [schizophrenia and other mental illnesses](https://www.google.com/search?num=100&safe=off&client=safari&hl=en-us&ei=hOcGWJOlFcTbeeLeqqgF&q=toxoplasma%20gondii%20schizophrenia&oq=toxoplasma%20gondii%20sch&gs_l=mobile-gws-serp.1.0.0l2j0i22i30k1l3.2739.6183.0.7410.22.22.0.0.0.0.360.3087.4j14j2j1.21.0....0...1c.1.64.mobile-gws-serp..14.8.969...35i39k1j0i67k1j0i20k1.aN6kyj_bmmk). I feel this type of organism could very well already be doing what you are asking about: BDSM, extreme sports, suicide bombings, schizophrenia, bipolar, etc., as well as unwillingness to agree to peace in the Middle East. ## Zombie organisms There are a few organisms, some microscopic, some macroscopic, that cause [real zombie behavior](http://mentalfloss.com/article/53290/5-real-life-zombies): *1. Ophiocordyceps unilateralis*** [![enter image description here](https://i.stack.imgur.com/u63Nw.png)](https://i.stack.imgur.com/u63Nw.png) > > When a spore of Ophiocordyceps unilateralis meets an ant, things get very weird and very bad for the ant very quickly. The spore germinates and enters the ant’s body through holes in its exoskeleton. The fungus then starts to grow inside the ant’s body, absorbing soft tissue while leaving vital organs intact, for the ant must remain alive and fully functional for a while longer to be of real use to the fungus. > > > When O. unilateralis reaches the autumn of its short life and is ready to sporulate and make way for a new generation, its long, branching filaments grow into the ant’s brain. The fungus produces chemicals that poison the ant’s brain and cause it to become transportation to the fungus’ birthing ground—and its own hearse. The ant, no longer in control of its own body, leaves its colony, climbs a plant, and clamps its mandibles around a leaf at the top, fastening it to its grave. There, new life springs into the world, right out of the ant’s head. Now out in the open, the fruiting bodies of the fungus mature and burst, releasing clusters of spore capsules into the air. As they descend, these capsules explode, spreading spores like confetti over the ground. The spores infect other ants, continuing the fungus’ bizarre life cycle. The whole ordeal, from one infection to the next, can take as little as two weeks. > > > *2. Hymenoepimecis argyraphaga*** [![enter image description here](https://i.stack.imgur.com/hW0aQ.png)](https://i.stack.imgur.com/hW0aQ.png) > > Normally, the web of an orb weaver spider is where bugs meet their untimely death and become spider snacks. Using an arsenal of toxins and mind-altering chemicals, though, the parasitic wasp Hymenoepimecis argyraphaga turns the spider into a slave and a meal, and its web into a safe haven. The female wasp paralyzes the spider with a sting and then lays her egg on its abdomen. When the egg hatches, the larva lives on the spider and sucks hemolymph (kind of the arthropod version of blood) from its body for nourishment. > > > A few weeks later, the larva is ready to move on to the next stage of its life cycle, and injects the spider with a chemical (as yet unidentified) that alters its behavior. The next time the zombie spider builds a web, it repeats the first few steps over and over again instead of going through all the regular steps, resulting in a web that’s just a few heavily-reinforced anchor threads and a small center section. Then the spider crawls to the center of the web and sits there complacently. The larva molts, kills the only companion it has ever known, sucks any remaining useful bits out from its corpse, and discards it. Then it builds its cocoon on a web custom-built for the job. A few weeks later, the adult wasp emerges and flies away, and the cycle starts over. > > > 3. Jewel Wasp [![enter image description here](https://i.stack.imgur.com/Wo5Xb.png)](https://i.stack.imgur.com/Wo5Xb.png) > > Like H. Argyaphaga, the Emerald Cockroach (or Jewel) Wasp is free-living as an adult, but starts life inside a host. As their name suggests, these wasps use cockroaches as living nurseries for their little bundles of joy. When a female wasp is ready to lay her eggs, she swoops in, lands on a roach’s back and plunges her stinger into its midsection. The roach’s legs buckle and it tumbles to the ground, unable to flee or fight back for a short while. This buys the wasp time to play brain surgeon. She slides her stinger through the roach’s head and into its brain, slowly probing until she hits just the right spot. The venom she releases this time doesn’t paralyze the roach; it can move its legs again, but not of its own accord. When the momma wasp grasps its antennae and starts moving, it follows her like an obedient puppy. She leads the roach to her burrow, where she lays her egg on its abdomen and then leaves. All the roach can do is sit and wait. Soon the egg hatches and the larva emerges. It chews into the roach’s abdomen and wriggles inside, where it lives for a week, devouring the roach’s organs the whole while. It forms a pupa and emerges as a full-grown adult a few weeks later, bursting forth from the roach and leaving it buried in the burrow. > > > *4. Glyptapanteles* Wasps** [![enter image description here](https://i.stack.imgur.com/H0GBl.jpg)](https://i.stack.imgur.com/H0GBl.jpg) > > The females of the genus Glyptapanteles lay scores of eggs inside caterpillars, and the larva squirm out a short time later to spin their cocoons. It seems like the caterpillar gets off a little easier than those poor roaches and spiders, but its work isn’t done yet. A few of the larva actually stay behind inside the caterpillar and give up their chance to pupate and mature, for the good of their siblings. They take control of their host’s body, and force it to stand guard over the cocoons. The caterpillar waits motionless, unless a potential predator comes too close to the pupae, in which case it thrashes violently at the visitor to drive it away. By the time the adult wasps emerge, the caterpillar, which hasn’t eaten during its guard duty, dies from starvation. > > > 5. The parasitic hairworm [![enter image description here](https://i.stack.imgur.com/RkDpt.jpg)](https://i.stack.imgur.com/RkDpt.jpg) > > The parasitic hairworm grows up on land—specifically, inside a grasshopper or a cricket—but is aquatic as an adult. To make the transition to water, it forces its host to take it for a swim. The worm pumps the insect full of proteins (which may mimic ones that the host produces on its own) that sabotage its central nervous system and compels it to leap into the nearest body of water. The host drowns and the adult worm, three to four times longer than the corpse it once called home, wriggles out and swims away in search of a mate. The babies they make will infest the water until they're guzzled down by a host they can call their own. > > > ## Conclusion Since these real-life parasitic organisms have the ability to control both the host's consciousness and physiology, even in complex ways, I think it is very plausible another organism could do so to the extent you describe. [Answer] Well, this is so hypothetical, you can't really say no. There are tons and tons of difficulties with achieving this, and some of them are very technical to an extent unnecessary for the general question. So many Ways All the details you suggest could well be one of the ways such an alien could work. It would need to get around the issue of its DNA (if it even uses DNA and not PNA or such) allowing it to work with earth creatures, and humans specifically, to an extent so natural that they are not immediately noticed as behaving uncannily and weird. It has to override parts of the brain's function without ruining the brain's function and control in various areas, you can't suppress the subject's ability to control their blood flow and organs. Conscious Host? Some of the things you suggest make it sound like the host is conscious and in control to an extent (or allowed to be) and isn't aware of the parasite. That perhaps your creature cannot control the human brain fully and cannot pose as a human on its own, so it has to manipulate and trick the host. This sounds very interesting, and I think it adds plausibility to the idea. This implies the alien is able to do some pretty good brainwashing/hypnosis via its parasitic connection, and that does raise questions as to how it works so well with the host's brain without them freaking out so much something goes wrong (like they get a heart attack). You can get around that by such means as sneaking up to and paralyzing a host into a coma before attachment, or a tiny parasitic egg learning how to control the host for a long time before asserting proper control. Conclusion Again, there is little way to say if it is possible, you can only make it plausible and consider what is technically possible, the more technical you get the more technical the information you need. At maximum technicality, you would literally design an alien creature capable of this, and so there is never need to get close to that far. I think this is a good concept. I hope this was helpful. [Answer] Is this from <https://www.rottentomatoes.com/tv/braindead/s01/> ? :) Or from that bad bad book : <https://www.goodreads.com/book/show/13641105-parasite?ac=1&from_search=true> ? The series is fun, in reality to control a person's mind it means to know how it functions and basically we even don't know to much on the brain to use it, so the alien organism must be very knowledgeable, more than human race, to be able to control our brain and through it the body. Next, to control the culture/politics ... it means the organism is not only some parasite that somehow, let say it grew with our race as a symbiont and adapted to our .. brain?!, but has a large conscious brain that can understand our language and all... [Answer] If youre interested in more ideas of how to create your story/world with a parasite, look at the anime 'parasyte' <https://en.wikipedia.org/wiki/Parasyte> Its about a boy who got infected by a parasite, but that parasite couldnt infect his whole body, unlike other parasites. I think it handles the scenario moderately well. [Answer] It isn't easy to design a parasite that could directly mind control a host organism to compel it toward specific actions - brains are extremely complicated and differ from one individual to the next, and parasites are typically not the most intelligent of organisms. There are a lot of parasites that manipulate the behavior of simpler animals, but they usually do this by hijacking a natural instinct that the host has already. This is harder to do with organisms that learn most of their behavior through experience (such as humans). However, a lot of human emotional responses are controlled by simple chemical triggers, and any parasite that could produce said chemicals could easily modify the mood and behavior of its host. A parasite could make its host more or less prone to anger, compassion, self-restraint, fear, and risk-taking. Pick any drug and a parasite can replicate its effects. The problem is that humans are very good at detecting abnormal behaviors and socially rejecting people who display abnormal behaviors, perhaps because it is a likely indicator of parasites. So developing a parasite that can make its host better at attaining social dominance could be very tricky. It would have to be subtle enough to fall beneath the radar of most people, while at the same time have enough of an impact to actually make a difference. One possibility is that the parasite could inhibit serotonin, the chemical that is responsible for feelings of contentment. People who have a serotonin deficiency can be prone to risk-taking, aggression, and sociopathy. They are never satisfied. Oxytocin is another chemical that could be affected by a parasite. This chemical is associated with trust, compassion, love, generosity, morality, and a great number of behaviors human society calls "good". By inhibiting it, a parasite could basically turn a person into their "evil" counterpart. So basically, a parasite that inhibits serotonin and oxytocin could turn a person into an uncaring, unsatisfiable, amoral, risk-loving sociopath. If it infected someone who was already smart enough to manipulate people - or someone who had already attained social acceptance and fame before they were infected - it could very turn them into a very dangerous individual indeed. ]
[Question] [ One of the things that affects the color of the sky is the wavelengths of light that the star emits, like the image in [this question](https://worldbuilding.stackexchange.com/questions/48867/sky-color-of-an-alien-world). Here is the image again: [![enter image description here](https://i.stack.imgur.com/wA8GN.jpg)](https://i.stack.imgur.com/wA8GN.jpg) If you are standing on a circumbinary planet with an earth-like atmosphere orbiting a binary star system containing one star from the left side of that image and one star from the right side, would the sky appear different colors depending on which star was currently visible? If not, what sort of atmospheric conditions would make it possible? For the purposes of this question, I am counting different shades of the same hue as the same color, i.e. light blue and dark blue don't count as "different colors". [Answer] Yes, because: Here on Earth you see a wide range of colours in the sky depending on time of day, cloud cover, dust etc. as the atmosphere absorbs and scatters different frequencies of the generally yellow light from our Sun. If your planet orbits a very blue star you won't expect to see the reds you get here at sunrise and sunset. If it orbits a very red star, you will never see a blue sky as you just won't get light at those wavelengths. So: Assuming a similar atmosphere to our own, when your red star is in the sky you will have an overall red sky, with the blue star in the sky you will have a blue sky. With both you will have variation. The interesting times will be at or around sunset and sunrise as the light from one appears or disappears and is attenuated through atmosphere. [Answer] I agree with Rory's answer, particularly about the exaggerated variations at sunrise and sunset. I just want to add that if both suns set or rise at the same time, you won't see those variations. Both suns will set/rise at the same time daily only if the planet is orbiting close to 90 degrees off of the plane of the ecliptic, or the binary stars are orbiting each other 90 degrees off the plane of the ecliptic. For a normal planet orbiting within the plane of the ecliptic, this will sort of happen at the poles: the suns will appear to drop below the horizon at the same time with the passage of seasons. [Answer] If you want to build a calendar to determine what the sky will look like throughout the year you'll need to know a few things. 1. The orbital periods of the stars to each other. This will determine the relative positions of each star in the sky. 2. The distance of your stars from each other as well as there size. If the distances between your stars are great enough than as they move around their size relative to each other will vary in relation to your planet. 3. The Incline of the orbit of your planet. what maters is the relative position to the orbital plane of your stars. The more out of sync it is with that plane the more vertical variation will be observed over the year. One thing to keep in mind is the possibility of eclipses. If your orbital period lines up with the stellar plane this can happen all year round. If the planet orbits at an incline then it will have a two windows every year during which an eclipse can happen. Depending on the relative size of each star partial eclipses will allow for the light of the further star to pass over the other and according to Einstein the light of the further star will be refracted inward. [Answer] Probably not much. The colour of stars isn't that variable. A red giant is reddish white. A blue giant is bluish white. Even a red dwarf is a dark orange. Your eye has maximum sensitivity in the green. [![Spectral temp class](https://i.stack.imgur.com/X6bKA.png)](https://i.stack.imgur.com/X6bKA.png) In addition your eye adjusts to changes in illumination. That's why in a room lit by tungsten lighting you don't notice that the world looks like a photograph shot through a Holsum bread wrapper. Tungsten light corresponds to about 2700 K which is cooler than a red dwarf Most people don't notice it, except that things that in daylight are a vibrant blue or green in tungsten lighting look a lot darker. Take a look at a house plant. Your eye adjusts because your brain remembers what the houseplant is supposed to look like. You can have interesting discussions about fabric colours. If you haven't seen a clothes article in daylight, it's sometimes hard to say what colour it is lit by tungsten. The blue of our present sky is mostly raleigh scattering. This is roughly linear with frequency, so higher frequncies get scattered more. The average is the blue we see. A blue sky at 90 degrees from the sun has a colour temperature of 12,000. This corresponds to a stellar class B or A Yet if you look at something lit only by the northern sky, it looks more or less normal. (Artists like northern light because it's fairly constant over the day.) A red star would mean less blue in the light so it would be shifted further away from the blue. However I suspect that it would mostly appear just to be darker. If you get dust in the air you get a more pronounced difference. Dust being larger than air molecules scatter more, and also absorb more. See the copper coloured sun when you have forest fire upwind. But with dust the scattering is more uniform with frequency. The sky will be a smeared out version of the colour of the star. You will also get interesting shadow effects. If both stars are in the sky, you will have two shadows. The shadow of the red star is illuminated by the blue one, and vice versa. You can get a bit of the feel of this by going out on a sunny winter day. Compare where the sun hits the snow to a place where the snow is lit only by blue sky. The snow shadows are quite blue compared to the sunlit snow. This can be very pronounced in photographs. ]
[Question] [ I have a society of merpeople that have developed sonar in order to hunt, gather resources, and in some instances communicate. They use organically created weaponry (sharpened coral, animal incisor daggers, turtle shell shields, etc.) and live in woven seaweed fortresses. A rift has been created, and the society has split, leaving two groups of merpeople about to head into war over the organic and natural resources (Prime seaweed for building, excellent coral flexibility in this area, the water currents funnel the fish juuuust right, etc.). I was thinking on how to beef up those defenses, when I hit a block. My merpeople live ~150 meters down, and although they can utilize photosynthesis, it is not a necessity to them. Most of their structures are either built in as part of a kelp forest, or spread out into a hut city of sorts. There is a stigma about caves in their world being cursed by the god of water, so holing up (in some cases literally), is out of the question. They have the ability to burrow, but mining through stone is only done for the rich and the powerful due to its difficulty, and so is not commonly done. Digging is easily done provided the ground is soft enough for a coral shovel to penetrate. If they have sonar, then there would never be a surprise attack that would gain the advantage on the enemy, and directional warfare would probably be akin to space warfare, in that an attack could come from any direction. My flaw was in first thinking about the defenses, but I couldn't come up with a reason to not create essentially a bubble of seaweed or shells (think the part in 300 where they have the shield turtle), and just go on with their daily lives using sonar to say, "Oh hey, the enemy is over there". My question is thus: How would warfare be conducted in an underwater environment? Is there a way to gain the upper hand at the start of a battle? I'm looking for something like an attack of some sort (blitzkrieg, sneak attack, etc.), but intelligence, espionage, and sabotage might work as well, provided the actual reason for the wars (resources) would remain usable. [Answer] While sonar is better at penetrating water than light is, it doesn't give the user a perfect picture of their environment. If the surrounding area has trees, reefs, or coral, those will all make it difficult to detect a passing enemy using sonar in the same way that hills or forests can stop people from seeing approaching enemies in our air-based environments. Even without dense kelp forests, the sort of long sea grasses that are common in areas like the Mediterranean Sea would effectively obscure merfolk crawling through them close to the sea floor. Even schools of fish or pods of whales could be used as cover from sonar, effectively forming moving shields blocking sonar from imaging what's behind them. Alternately, blocking sonar is as simple as stopping sound waves from reflecting off of you. Armor made of soft-bodied creatures like sponges or something similar might be sufficient to hide the wearer from someone searching for them with sonar, or at least diminish the reflected sound wave to the point where it sounds like something much smaller than a merfolk. [Answer] Don't trick the technology, trick the user Sonar like all forms of wave detection is open to interpretation by the operator. Case in point, modern submarines and stealth craft do not completely mask their signature, but reduce it to the point where the signature appears to be something innocuous. Given your merpeople don't have stealth technology, they could use an opposite technique. Instead of trying to appear as a fish, they can build some larger movable cover and appear as a whale or a squid, that way a squad of MerSoldiers, appears as a single large entity instead of many man-sized entities, leading to unskilled sentries to dismiss it. Bad Communication Kills The United States had detected the Japanese Naval Air Squadrons plenty of miles out before Pearl Harbor. Why then did the US not respond? Communication mix-ups from higher sources indicated that an American Bomber wing was due to arrive, but said bomber wing was delayed. Only when the fighters got into visual range did everyone realize their goof up. Subterfuge can still work in this situation if you don't want to use the previous idea. Some false missives, a killed off messenger, and you have a massacre on your hands. [Answer] I can think of a few methods that circumvent sonar sentries or are general of use in warfare. * Underwater drums or trumpets for distraction. * Herd innocent fish to block accurate sonar images. * Bait and lure sharks to confuse. Any aggressive and/or poisonous fish would do. * Tame a whale to use as underwater 'elephant'. * Dolphin squads for light cavalry. * Orca squads with nets for heavy cavalry. * Sneak along the ocean floor and attack key targets from behind. Inspiration can be found from generals like Alexander the Great, Caesar, Lu Tzu, Napoleon, and often underwater versions can be envisioned. Confusion to the enemy! ]
[Question] [ I'm trying to create a continent where desert areas are as maximal and fertile coastal areas as minimal as possible. I've been trying to find some tools to help me with this, but I've only been able to find Geoff's Climate Cookbook. Unfortunately, Geoff's has it backwards. The Cookbook wants me to have a predefined map and then it helps me define the climates for that map. But I wanted to draw a map that would fit the climates I have in mind, not the other way around. In short, I wanted to know how to draw a map of a continent that has a particular preponderance for a particular climate, namely hot deserts. The mountains, latitudes, winds, everything should be drawn to make as much hot deserts as possible. Are there any resources that would help me do this? Please, bear in mind that I have absolutely no scientific knowledge regarding climates, so it should be an easy-to-understand resource. [Answer] I'm going to give you some guidelines that will give you the result you want. I'm assuming that your planet is very much earth-like. If it's not the case, you can specify the differences so I can modify the answer later. Maybe it's not going to have any consequences though. * The regions located close to 30° north and south tend to be dry because, in the general atmospheric circulation, it is where the air is sucked back toward the land from the higher atmosphere. That air contains very little moisture. * I just said that it tends to be dry but in fact, it's not always the case. Large landmasses became so hot in summer that a low pressure system may form, which is what we could call a monsoon. That monsoon can bring a lot of rain even if it's just for a short period of time. * But the good thing is that not all low pressure systems will bring rain. For example, the Sahara is dry all year long despite having a low pressure system overland in summer. There are two things that can cause this dryness. 1. A lack of a nearby ocean: although a low pressure system is favorable to precipitations, it need to gather the moisture from somewhere. The Sahara usually receive winds coming from the central part of Africa and from Arabia (in summer) so the winds are completely dry because of this. The situation is different in Asia where the winds can pick up the evaporating water from the ocean before dropping it on the continent. 2. Mountains: Imagine if there was a tall mountain range in eastern China running north to south. In summer, the land became really hot. The winds converge to this low pressure system but the mountains will block all the moisture. The eastern coast would be a tropical rainforest, very rainy in summer and drier in winter and the west would be a desert. The mountains would need to be about 3000-4000m tall if you really want to block all the moisture (the effect of altitude on the precipitations is negligible if you go higher than that). The direction of the winds is generally from east to west near the equator and the poles, but from west to east in mid latitudes. Again, the monsoon is a reversal of the direction of the winds and can happen both in summer and in winter if the landmass is hot/cold enough (example is the Siberian high forming over Mongolia in the winter). Lastly, the driest desert on Earth, the Atacama (with some places receiving an average of 1mm or precipitation per year) is located on the west coast and it's not a coincidence. First, that part of South America is too small to have any monsoon season. Secondly, the western coasts is generally where the cold currents flow. The Humboldt current takes the water from the Southern Ocean back to the equator. This coldness is responsible for the high pressure systems forming in the area, which are generally dry. Also, colder water and colder winds transport less moisture than hotter ones. * To summarize, you need to make sure that you desert receive winds not from the oceans but form the interior of the continent. If it's from the ocean, it need to be on the west coast close to 30° or blocked by a mountain range. ]
[Question] [ TL;DR: suggest human traits of mind/society that one should (a) tweak (b) leave well alone, in order to generate an alien worldview that allows a novel length tale to be told purely from perspective of said aliens but at the same time permit human readers to identify with and care about the characters. This is a bio-chemistry free question. Background: I have a setting based on a super earth with 4-10 times earths surface area, some oceans and plant life and animals and stuff. The ecology will be sufficently different to earth's oxygen based environment that it'll seem nice and alien (my critters breathe hydrogen), but not like a Venus-hell-hole alien, the weather will be nice(-ish) and there will be a solid surface to walk on. This should afford a suitably wide potential for an epic xenofiction world (I say potential because more than likely I'm way off having the skill to pull it off). By epic I mean large in scale in terms of time span, geography, numbers of characters and events. Anyway, this setting has no humans, but lets assume it does have human readers; its important to hang onto the reader through to the end of at least one book and maybe more. This is not a short story format, where one often finds xenofiction. What it can and will feature is the struggle to survive against alien nature, ones own worst alien instincts and against the unwanted attentions of other members of ones alien race. It may feature some physical intra-species conflict but war and violence ought not to be the main thrust of the narrative. It would feature stuff like love, childbirth/rearing/being a child, family, competition, economics etc etc to the extent that the species exhibits such characteristics. I am willing to consider a range of readerships (e.g. Young Adult, Mainstream, Adult, Sci-Fi nuts, Fantasy nuts) but I would like to keep it as broad as possible and do not intend to employ any magic devices or powers in the setting. The setting's tech level will range from stone-age equivalent tech through to early Renaissance. Question Restatement * What aspect of human psychology (and by extension human myth archtypes etc) would you suggest changing in order to fulfil my goals above? How might they be altered? * What aspect do you suggest I do not alter? * And most importantly because this is a world-building forum, what overall 'look and feel' do your suggested changes and non-changes generate that can be woven into a large scale alien setting? Suggestions that generate the right kind of skew from human POV and which generate nice plot devices with the minimum alterations to the human mind are likely to be the most useful. If you have a particular readership in mind when making a suggestion please state who you are aiming at. By all means cite existing works but please outline the psychology changes that were involved and whether the story worked for you. TL;DR: existing questions This [WB.SE question](https://worldbuilding.stackexchange.com/questions/420/creating-convincingly-alien-viewpoints/531#531)is an excellent question and set of answers but it seems to me that the OP still had in mind to write from a human viewpoint at least for part of the book. My requirements are more restrictive. [Answer] It may be too glib, but maybe make the aliens egg-layers, and base your "alien" expressions of emotion on birds. Some birds are remarkably intelligent and social, yet are about as far from human as we're able to empathize with. Others are almost completely asocial: well-adjusted autists? Personally I think we underestimate birds. A small bird's brain must clock far faster than ours; flight with small flapping wings must require conscious control ten or more times faster than humans are capable of. Does a bird's four-year lifespan feel subjectively like forty or eighty to the bird? If so, a bird's day is nearly a week long, subjectively, and winter is a truly terrible thing. There's another idea: a different rate of consciousness. There's a girl who decided to feed her neighbourhood crows. The crows are reciprocating, saying thank-you as best they can. That's very advanced thinking. <http://www.bbc.co.uk/news/magazine-31604026> [Answer] We have one criterion already which pretty much dictates a certain set of psychological traits: Stone Age to Renaissance technological development. It might not seem much, but this criterion dictates quite a lot about a being's psychology. It is not really possible to move beyond the stone age without sociability. In order to develop renaissance-level technology, these beings must co-operate with one-another, which means some sort of communication, leading to social grooming (of whatever variety) in order to defuse conflicts which may lead to violence or avoidance. However, the definition of 'social grooming' can be quite broad. Humans mostly make small-talk, but can also have sex. Dogs sniff each-others' backsides. Cats sniff noses. Bonobos have sex. Chimpanzees and many monkeys literally groom each-other (hence the term 'social grooming'). Whatever form you choose for your protagonists' social grooming, it must exist, and your story will likely be better for you knowing what it is and how they do it. Secondly, these beings must be able to comprehend and practise economic principles. Without this, they will either over-consume to the point where they starve themselves and suffer a major population crash, or will not have sufficient motivation to better themselves with improved technology at the other extreme, that of frugality. There are exceptions, of course. You may have a species that is unable to practise birth-control for whatever reason, and therefore undergoes periodic population crashes as resources are exhausted and fought over (consider the Moties from [The Mote in God's Eye](https://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye)), yet are still able to develop technology. However, as it is stated that warfare is not the prime focus (of the story nor, we can presume, the society), this is unlikely - hence our presumption of knowledge and practise of economic principles, as well as a certain degree of birth-control, either natural-biological or artificial. Another option is that the protagonist species is itself predated upon by a physically superior carnivore species, thus providing natural population control, but this option becomes less relevant as technology improves, unless the species is an [r-strategist](https://en.wikipedia.org/wiki/R/K_selection_theory), and expects to lose a lot of offspring. All things considered (though coming from the bias of a K-selected species, namely humans), K-selected species are more likely to produce civilisations, yet the converse is not impossible. However, a r-selected species would likely be less sympathetic to a human audience. Who would sympathise with characters who give birth to whole broods of offspring, then basically neglect them, not lifting a manipulatory appendage to prevent them from being eaten by a variety of eager predators, until they grew up enough to become worthy of inclusion in society? It may be possible to make said scenario sympathetic, but the life-story of K-selected species would inherently be more sympathetic to us. The question mentions love. This may or may not be a necessity, and too much may be worse than none at all. It is possible to have a perfectly well-functioning technological society without love, where reproduction takes place on some schedule or in response to some environmental trigger, and the operative emotion during reproductive events is lust. In biological terms, love binds breeding members together in order to provide for offspring, and can be expected to occur primarily in K-strategists. However, why is too much love bad? In species where pair-bonding is for life, the bonds between partners are so strong that they instinctively reject other members of their own species, reducing the likelihood that sufficient co-operation could be mustered to establish a technological society. It isn't impossible, just unlikely. Now, to warfare. It may not be the primary focus of the intended story, but it is all too likely to exist in a species with an appetite for resources and technology. Warfare typically takes place in response to competition for limited resources, though in humans at least, it can also take place in response to competing ideologies. It is possible to design a species that would not consider fighting for beliefs, but the strict limitations of economics dictates that some form of conflict or drama will occur in response to an insufficient supply of resources, whether that is some form of competition for those resources or a concession within the society that the resources are unattainable in the desired quantities, and the compromises that must be made to reduce the demand for them to sustainable and equitable levels. However, a species that has the drive to develop technology is quite likely a species that is willing to fight over resources if not also their beliefs. It has been shown from human history that warfare has been a major impetus in the development of technology - in those areas where conflict is rare, technology tends to be simpler than where conflict is frequent. However, while warfare need not be the focus of a story, a good story should acknowledge that it exists and consider the impacts of warfare on the non-combatant protagonists. Additionally, while it was not stated in the question, I should point out that warfare tends to be concentrated to areas with many natural boundaries between regions; social groups form where movement and communication is easiest, and conflict occurs across natural boundaries where the society on the other side is 'not like us' in some - or many - respects. Places with wide-open plains tend to be more peaceful than places with many natural barriers, leading to a technological disparity in favour of the societies who are more frequently in conflict with one-another. Given these guidelines, if a question was to be asked with a more specific set of personality traits, I would have a better chance of designing a biology to fit it. [Answer] A dash of [Blue/Orange](http://tvtropes.org/pmwiki/pmwiki.php/Main/BlueAndOrangeMorality) morality for the win! Blue/orange morality is an excellent way to get some really weird behaviors from aliens but the danger is that it's also easy to make them too alien which will fail the "novel length story" requirement. My favorite example of Blue/Orange morales comes from Eve Online where space ship pilots will kill each other, for fun, with nukes because they can. Instant cloning with no memory loss on death enables this kind of "play". Areas of Psychology to Explore: In general, the problem with altering many of the below traits in this alien will cause them to appear to be mentally ill to a casual human reader. While there is an audience for wacked-out alien psych, it's a smaller audience than for aliens with more human characteristics. Some aspects don't need to be completely alien, just borrow from the habits of life on earth to get some really weird options. For example, you could tell a story about an alien that is born from an egg and must be completely self-sufficient immediately. * Violence - This could be used in moderation. Reading graphic descriptions of violence would be exhausting to a human reader, even if the alien depicted thrives on violence. * Sexuality/Reproduction - Exploring this aspect will depend on the audience. Probably not appropriate for a children's book. In general, you'll need to be careful with this area since human sexuality touches so many different aspects of psyche that it would be easy to design an alien with horrifying sexual tendencies. For example, reading about an alien that mimics the black widow spider females post-coitus meal of her mate might be difficult to read. * Authority - This could be played with a ton though it will need to be combined with another aspect in order to be truly alien. Humans range from the megalomanical dominator type to willing abject slaves. Between those two extremes there are many nuances to be explored. * Concept of Self - Perhaps an alien with no concept of self. I'm not sure how you'd portray this but it could be interesting. * Concept of [Other](https://en.wikipedia.org/wiki/Other) - This may play into the 'empathy' aspect listed below. If a creature has no concept of 'self' or 'other'...that'd be curious to read about. * Concept of Family - Lots of variation possible here. Humans have a wide variety of family types so a really strange family arrangement by your aliens won't be too difficult to read about. * Relationship between parent and child - Lots of variation possible here too. * Empathy - Lots of variation possible though it's super easy to create a psychopathic or sociopathic alien. * Cooperation with others - Lots of variation possible. * Relationship with Environment - Lots of variation possible. * Industry/Commodities/Commerce - Lots of variation possible. * Alteration/Inversion of Maslow's Hiearchy of needs...leading to aliens that feed on experiences and must work their way up to food and shelter. That'd be so weird! Manipulation of any of these dimensions of human personality can easily be alien if not downright horrifying. Be careful or it will be very easy to alienate your audience. [Answer] This has already been done (by Niven, i think?) but it might inspire other ideas: Birds use birdsong as a form of combat. The birds with the stronger bird songs get the mates and drive away competitors. A member of a bird race comes to Earth. Their singing is so beautiful that they are treated as celebrities: given gifts, fawned over and otherwise pampered. That individual then goes back to his home world, believing that he conquered an entire planet with his song. So, in general, observe animal behaviors and think how they would interact with sentience. The readers should be able to understand animal behaviors and should have a touchstone so they can relate to the characters. ]
[Question] [ I have made my billions here in the present day, and I'd like to have a permanent underwater settlement. It is about as useless as the [Mars One](http://en.wikipedia.org/wiki/Mars_One) mission (yes, I went there), but some people may come and go as they like or can afford to. This is fully pressurized and connection with the outside world is similar to a space station, whereby airlocks and submersibles connect you to the outside world, but at this location there's still some light and warmth. This is only a depth of 50m in the tropics - pretty far away from the island nation of [Nauru](http://en.wikipedia.org/wiki/Nauru), so not a lot nearby. Plopped right on the ocean floor, and yeah, I got my environmental permits. I'd like to house 1,000 people, of which 1/4 are research-related (6 months rotating), 1/2 are tourists (1 month, rotating), and the remaining are staff and I have even received express interest in full-time retirees to live 'on board'. So there has to be additional space for study, leisure, housing, etc. What are my opportunities and constraints for construction, power, water, wastewater, communications, transport, air, trash, etc.? I'm not interested in cost, but a magnitude of order would be helpful. Any other ideas are helpful, particularly design considerations. [Answer] Someone is trying to do something like this on a [smaller scale](http://www.poseidonresorts.com). But you could do better. Construction Thankfully 50 meters isn't all that far down, so while it will take some heavy duty construction, it won't take Rapture level technology. Power You could use a few different renewable power technologies. Wind is easy. [Tidal power](http://en.wikipedia.org/wiki/Tidal_power) might be an option if there is land somewhat close. Biogas could be generated on site. There has been work on using algae to [produce fuel](http://www.wikipedia.org/wiki/Algae_fuel). Hydrogen could be produced by electrolysing water from the Water Recovery System to produce oxygen and hydrogen. Water Desalination, evaporation, and recycling are going to be your best options. Desalination and evaporation could be combined with the power generation if you go with biogas or algae fuel. Keeping it self contained like the ISS will help as then you'll only need to replace a little instead of a lot. Wastewater Use the same methods used on the [ISS](http://www.wikipedia.org/wiki/ISS_ECLSS#Water_recovery_systems). You want to replace as little water as possible. Communications Having a radio buoy would be an easy way, and could easily include satellite too. Just raise it on a wire, pull it down in really bad weather. Keep spares. Transport Submersible would be one good option, but you could have a floating platform with a elevator tube as well. This would allow easier coming and going, and help with communication and air. Plus it would give you a place to dock boats. Air Similar to the ISS again. Electrolysis from the water reclamation system, pulled from the surface, or recycled in a green house. Trash This would be the hardest one. You'd want to remove as much of it as possible before it got to your city. No extra packaging, make as many things as possible biodegradable so they can be composted, recycle as much as you can. Food A few greenhouses are going to be important for food, fuel (algea), air, water filtration, sanity, etc. I'm sure fish will be another big part. Probably import some stuff, but you'd want to be as self sufficient as possible. Windows If you can't have windows then what's the point If being under water in the first place? Pressure is an issue though. As WhatRoughBeast points out, big windows are probably impractical, though with the right laminated materials and with enough thickness it's probably doable. The other option is to have smaller windows, but more of them. The window on this is designed to go down to 300m: ![underwater vehicle](https://i.stack.imgur.com/jYvuR.jpg) So you get a lot of them and put them all over. Being stuck in a tin can 50m under water without being able to look out for any length off time would be a horrible vacation. [Answer] ## Communication Seawater is [highly resistive](http://users.tpg.com.au/users/ldbutler/Underwater_Communication.pdf) to radio waves at the frequencies we usually use them. (see page 7, section Sea Water.) However, at lower frequencies, 10-30 kHz, it is entirely possible. Unfortunately, [this frequency allocation chart](http://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf) shows that the entire 10-30 kHz range is occupied. You'd be interfering with other signals, if you're using the same systems. However, you could set things up in your world so that the 10-30 kHz range is completely empty, at which point you can put radio communications from your city in it. Your other option, since you're not that far underwater, is to build a big antenna extending above the surface, which you could then assign any frequency to since air conducts radio transmissions. The alternative, which you can use for many of these sections, is a tunnel leading out that takes you to the surface. ## Transport Transport around your city is not a problem - since you're pressurising the whole area, you can just use regular methods of transport. To get in and out of your city, your setup of airlocks and submersibles is sufficient, but you might want to consider big submersibles for that many people. The alternative, as I alluded to, is to use your communications tunnel to move people as well. ## Power This answer is going to get very boring very quickly if I just keep saying "use the tunnel". However, you could do, just run a big cable down it. The alternative, which is slightly more interesting, is to build an [osmotic power plant](http://en.wikipedia.org/wiki/Osmotic_power) or salinity gradient power plant, which uses osmosis between and fresh water source and a saline water source to create power. Assuming you also have a desalination plant set up for water, you have both required water types. ## Air Run a pair of tubes up to the surface and stick big pumps on both of them. One of them should pull air out of the underwater dome and one should put air from outside back into it. You could also add some filters if you want really clean air - this might also work as a health centre where people with weak immune systems could come to because you've cleaned the air. Just make sure you decontaminate every visitor. ## Waste You need transport for this, basically. The simple solution is to take bags of waste out on every submersible trip and bring in supplies. You could also have some fun by installing a flexible tube leading to the surface and putting some targets around on the surface... trash bag shooting becomes your new sport. Shoot them with air pressure. For waste water, do what every country does with their waste water already: recycle it. Clean it out, filter it, sanitize it, and put it back into the fresh water system. (If this disgusts you, don't worry - you're drinking the water that someone flushed down the toilet a month or two ago.) You can dump the remaining solid waste into the sea. Again, if you protest violently against this, countries already do it and have done for a very long time. --- See also eharper256's comment below this post explaining some alternatives. [Answer] You've got a big air supply problem. Underwater habitats are normally pressurized to ambient but that's got some big headaches: The lesser problem is the rapture of the deep. Everyone is going to go around a bit drunk all the time. The real problem, though, is the oxygen. Your ambient pressure at that depth is 87 psi. \* 21% oxygen in ambient air = 18.27 psi of oxygen. Your safety limit for this is only 3 hours. You're going to need a fancy atmosphere plant--use an oxygen concentrator to pull some of the oxygen out of the air before you pump it into your dome. Also, decompression from saturation at this depth takes 39 hours if it's done continuously and in practice it will take 2 1/2 days as it's not normally done during sleeping time. The alternative is to maintain the habitat at surface pressure but that makes for big hassles going in and out to the surrounding water--the main reason for an underwater habitat is the free passage between the living space and the outside. There's a reason the previous attempts in this direction have been set shallower! [Answer] Have a look at how submarines work, that should give you a good idea. In a flight of fancy I am going to, with my limited knowledge speculate what might be required. You should address power since most other things can be solved by conventional means when that is satisfied. If you have power you have artificial light that you can use to grow food and scrub the atmosphere of CO2. Biological waste can be incinerated with heat to release CO2 for the plants. The minerals can be recovered from the ash. Desalinating water is a solved problem so I am not even going to address that. For power you have two options that are not very far fetched, geothermal in the form of hydrothermal vents and nuclear. With hydrothermal vents your location is bound, with nuclear it is not. In both cases you could use conventional methods of power generation. Heat $\to$ steam $\to$ electricity. Nuclear can be done the way that submarines work, so that is solved. I am not sure if self-sufficiency is feasible with nuclear, since you require enriched uranium. That being said, fuel by weigh is minuscule compared to coal. To be clear, the ocean is abundant with uranium, just not the type you can use for a nuclear reactor. [Answer] Dome needs to be highly strong to support 50m of water, density a ton per metre cubed. That's 50 tonnes of pressure on every square metre of dome. Fortunately, dome is a strong shape and should support the weight if you make it reasonably thick - maybe some inches to a foot. You can just use pipes for most of the other problems. Waste, air, water, can be taken in and out using pipes. People need the submersibels but thats the only thing they'd be used for. [Answer] # Material You need thick glass or some other material to support 50 tonnes on every square meter. Thickness depends on how safe you want the settlement to be: thicker glass is less likely to fail under extreme conditions. # Transport You can just use the same method of transport to get everything, waste, water, food, supplies, people, in and out. I suggest just using big submersibles: if you have enough capacity, you can get a good load of people and all the other necessities in or out in one load. ]
[Question] [ Especially like the sandy Sahara. I read a little and found said desert lost its lushness from a change in Earth's tilt. Are there other reasons? [Answer] It is correct that equatorial areas typically are hotter due to greater exposure to the sun. However, that doesn't directly impact rainfall. There are very wet areas at the same latitude as the Sahara, like Thailand and central/south America. There are other factors, like forestation, but the simplest overview is to say deserts are based on air currents. Rainfall is determined by how moist the air over a region is. Air over oceans, especially hot air, becomes saturated with water. When this air blows over land masses, it results in rain. Typically, mountains are involved as well, as mountains can block cloud movement and create temperature differences which prevent moisture from moving beyond them. If you look at a chart of wind currents, [like this one](http://studyofplace.terc.edu/images/M2_A3_S02_wind_currents.jpg), you'll notice that deserts lack moist air currents (those that have been over oceans recently), and that jungles typically have direct winds blowing on them from the coast. This is why it is possible to have deserts directly on coastlines: if the wind moves away from the land, it has no impact on moisture. It is also worth pointing out the direction the air currents move in depends on which side of the equator you are on. On a normal map, above the equator they move clockwise, and below counter-clockwise. This is heavily impacted by land masses, but is a general rule. Such is caused by the planet's rotation. Not every point on the Earth's surface rotates with the same angular velocity. Effectively, equatorial areas move faster and polar areas slower. [Answer] One of the best articles I've found on this topic can be read [here](http://education-portal.com/academy/lesson/desert-biomes-facts-climate-locations.html#lesson). From the article: > > The location of deserts is dependent on two factors, latitude and global wind patterns. > > > Latitude has an impact because of the temperature gradient across the Earth. Most deserts lie between 15' and 35' latitude. Looking at a map of rainforests will reveal that most rainforests also lie between these latitudes. Rainforests (and mountains) are what create deserts. Warm, damp air rises off oceans, carrying lots of moisture. This moisture is deposited in the rainforests, until the air has no more left. At this point, the air is very dry. The next region it passes over (until it passes over ocean again) will be a desert, receiving very little rainfall. Wind patterns are important because they are what make the damp air move. Most deserts are between the Northeastern and Southeastern trade winds belts. These two air currents carry the air over land, where it loses moisture, then creating a desert further on. # Desert Qualification > > Generally, a desert is defined as an area that receives less than 10 inches, or 25 centimeters, of precipitation a year. > > > Emphasis mine. Precipitation is emphasised because it can come in the form of either rain or snow. Deserts that mainly get rain are hot deserts, deserts that mainly receive snow are cold deserts. Another defining factor for a desert is temperature swings. Because the air in a desert is so dry, there is nothing to hang onto the heat it receives in the day, so the temperature drop is quite large. [Answer] In the Köppen climate classification, there are 3 different kind of deserts: Hot desert, Cold desert and the Polar climate. The last one is not always a desert regarding precipitations but it is too cold for the vegetation, so I'll include it in the deserts. A desert can receive some rain and can even have some vegetation. A desert is classified as a place where the evaporation rate is much greater than the precipitations. Hot places require more rain to keep them from turning into a desert. Near the equator, almost 2 m of annual precipitations are required to keep the climate classified as wet. While other places like Siberia would require possibly less than 100 mm of annual precipitation. To figure out where the deserts are, it is important to understand the wind circulation. It is rainy where the air pressure is low and dry where the air pressure is high. Low pressure areas are drawing the surrounding air masses toward them with all the humidity it contains. But the high pressure zones are drawing the air form the higher part of the atmosphere. This air is not always cold but it is dry. Theoretically, the two places that are mostly high pressure are the subtropical ridges (near 30 degrees of latitudes) and at the poles. This is why the Sahara and the Antarctica are desert despite being surrounded by the sea at some places like Saudi Arabia. This is where you will find the hot desert and the polar climate near the poles. Of course the landmasses will influence on the pressure. Large continent become hotter in the summer and create larger low pressure zones. On the opposite, Siberia is very cold in winter and thus creates a very high pressure area. In the Northern hemisphere , the high pressure area is not over the pole but over eastern Siberia. That is also why India is not a big desert. Since Asia become very hot is drive precipitation toward the land. Some places are deserts even if the air pressure is low and we should expect some precipitations. It usually happen when the rain is blocked by the mountains like in Lima, Peru. Deserts that are located at higher altitudes or at latitudes over 35-40 are mostly cold deserts. The most important characteristic of these deserts is that they are always located deep inland or near mountains that are blocking the winds. They are much drier than the hot deserts as they barely receive any rain. Normally at these latitudes, the quantity of precipitation require to have a wet climate is not that high. You don't find a lot of deserts near the sea for example. If it is near the sea, the winds are blocked by mountains. ]
[Question] [ It seems that people who live at very high altitudes have demonstrably "thicker" blood, highly concentrated with red blood cells to overcome the low concentration of oxygen in the air. Moving between extremes of altitude apparently needs to be done gradually for the same reason. Assuming a biology largely similar to humans: Two (or more) humanoid species, in many ways biologically similar/compatible. One species lives almost exclusively in an isolated location at a very high altitude. One or more other species live in a variety of environments. Is it plausible for species A to survive as such a height that members of species B were guaranteed not to survive in? Phrased differently, is it possible for a species to live in a habitat so extreme as to be radically socially isolating? [Answer] The simple answer is yes, however the more complicated answer is no. The yes: If a species is adapted to one extreme environment then that often renders them unable to function effectively at another. [Sky Islands](http://en.wikipedia.org/wiki/Sky_island) for example have isolated species that only survive on them. If this hypothetical species were adapted to an altitude where humans cannot survive then that species would also find lower altitudes hard for them to live in. There would be little or no contact between the two species. But the No: Many animals, and humans in particular, are very adaptable. We can adjust our clothing, use tools, fire, buildings, etc to survive in a vast range of conditions. Conditions so extreme that they are absolutely impossible for the non-adapted to survive in would be unlikely to support much life in the first place. What would be far more likely is that the high altitude dwellers have a strong advantage there, but visitors from below can survive for at least a while. [Answer] ## Yes but not separated by altitude I agree with Tim B that mammal in general and humans in particular are very versatile. But one exception would be water. In an appropriate environment it probably wouldn't take long for human to evolve as marine animal.Not to the same level as Dolphin, of course, but to the same level than sea otter, why not. To help the process, you could make this specie specific to the Caspian sea. With a water salinity merely matching human biology. To give you an idea, the polar bear ([Ursus maritimus](https://en.wikipedia.org/wiki/Polar_bear))"diverged" from brown bear about [150 000 years ago](https://en.wikipedia.org/wiki/Polar_bear#Taxonomy_and_evolution) (quote/unquote "diverged" because they can interbreed. They don't do it much because they are socially isolated) Now, it wouldn't be really socially isolating. Normal human can not live this way, but they can ride a boat and Homo Maritimus can walk on firm ground. EDIT2: polar and brown bear diverged about 150 000 years ago [Answer] I could imagine it happening. Suppose we have a mutation: It improves the ability to function with low levels of oxygen but the flip side of this is that the system becomes very vulnerable to too much oxygen--for much lower levels of "too much". When you get one copy of the gene you don't function quite as well at any altitude but you can function at a higher altitude than those who don't have it at all. If you get two copies you can function at even higher altitudes but the lowlands become lethal with prolonged exposure. (Think of humans--we can function between about 2 and 10 psi of oxygen, with prolonged exposure to pressure outside this range causing serious problems or death.) Those who get two copies have a niche they can live in that starts out without competition and since everyone up there has two copies it now breeds true. You have your separated population and thus they will in time diverge. [Answer] Around the world, many high altitude populations adapt by having higher concentrations of red blood cells, which allows them to better make use of the limited oxygen at those altitudes. While some populations may be more prone to do this, it is mostly a process of acclimation. Spending several weeks at heights will let your body adapt and produce extra red blood cells. It Tibet, however, they have a genetic mutation related to genes that appear to better balance anaerobic and aerobic metabolism processes. It appears to do this in a way that is more optimal for the low-oxygen environment of high altitude. Recent immigrants from lower altitudes get headaches, tire easily, and have lower birthrates and higher child mortality than the native population. To directly relate this to your question, it would not be too much of a stretch to have a low altitude population have a mutation that exacerbates oxygen deprevation (perhaps they can no longer adapt by producing the extra red blood cells). The high altitude population might have another mutation that they cannot long survive higher concentrations of oxygen. [Answer] Yes, it kind of already happens There is a point on high mountains where humans cannot permanently live at that altitude because there is not enough oxygen for them to live there long-term. They can only go there short periods of time, bring oxygen with them, or die. However, birds have been observed living at these altitudes with little problem, and [bar-headed geese](https://en.wikipedia.org/wiki/Bar-headed_goose) frequently migrate at altitudes of 20,000+ feet with little to no difficulty. These animals exhibit few to no ill effects of living at lower latitudes. Bar-headed geese and other birds are not sapient but the same might apply to a sapient, humanoid bird. Bird lungs (and saurischian dinosaur lungs, based on features indicative of a bird-like respiratory system on the bones) can function comfortably at much lower concentrations of oxygen than mammals can. ]
[Question] [ Note: This question assumes an earth-like biology. Could a microbe (probably virus) be created that transformed humans into plants? What I mean by this is that the microbe would take human cells, and slowly, over time, transform them into plant cells. Like the new plant would retain a human like shape, and possibly be a new species of plant, i.e. a human plant. The human (i.e. the human's consciousness) would die in the process, but before the human died he/she would start having plant like tendencies. These would include being attracted to sunlight, drinking lots of water, and eating less food. These new tendencies would lead to the human being a suitable place for a plant to grow, when it eventually created roots and killed its human host. There would be a short stage where both the human and the plant were alive, likely during this stage, the human would not be able to move (lower body would be plant like), and quite possibly would be insane. So, could such a microbe exist under earth-like biology? And would there be multiple variants of the microbe, with each variant producing a different kind of plant? [Answer] In principle, host cells can be changed quite significantly by a virus. A very common unwanted change triggered by viruses is cancer. [The Wikipedia article on Viral transformation discusses some details](http://en.wikipedia.org/wiki/Viral_transformation) The biggest problem with a viral replication mechanism for a complex living thing, such as a plant, would be delivering enough DNA to describe the new form. Most plants have far too much DNA needed to describe then that would fit inside a simple virus. DNA would need to describe the chemicals needed to overcome the host's immune system and transform/develop the new organism, although that is probably no more than would be required to define the growth of a plant from scratch - at least this virus/plant would have a physical scaffold. In numbers, the most complex known viral particles are [known as "Megavirus"](http://en.wikipedia.org/wiki/Megavirus) and can contain over a million base pairs of DNA. Whilst [a relatively simple plant has 135 million base pairs](http://en.wikipedia.org/wiki/Arabidopsis_thaliana). If you can hand-wave this discrepancy, and the unlikely natural lifecycle of this organism, then I think that on the purely physical and chemical level, this is feasible. If you extend this to other microbes, I think the nearest real-world example might be Anthax, [which essentially changes a complex creature into goo](http://www.ph.ucla.edu/epi/bioter/anthraxlifecycle.html), ready to be taken up again by another creature. Not quite the build you are looking for, but if you imagine perhaps a symbiosis between Anthrax and a plant which benefits from the extra nutrients and could produce very small spores that hitched a ride alongside, you might have a pathway to a single rather nasty plant/microbe parasite. Add a little sci-fi or handwaving to make the transform a little more grotesque and/or whilst alive, and you could get very close to your imagined parasite. In terms of altering mental state, there is a [well known fungus that infects ants](http://en.wikipedia.org/wiki/Ophiocordyceps_unilateralis) and makes them climb up high to get the best spread of spores later. There are also other parasites that appear to take over their host's behaviour, although this is most likely by working with existing drives and behaviours to the parasite's advantage, as opposed to a wholesale transform. [Answer] Speculations aside, transformation into plant is possible at the cell level if the cell swallows and retains another photosynthetic organism that becomes useful. This can happen for a single cell, or some simple multi-cellular organism. Initially this is just infection, later genetic transformation may happen, moving photosynthetic genes into the host genome. This is how plants actually originated. Not a transformation by virus; a whole working machine of photosynthesis have been swallowed as food but ... stayed operational! An infection that makes the skin green and photosynthetic, and is not deadly, and immune system does not fight? If this is a science fiction, who knows... However human likely cannot survive with existing habits feeding just on sunlight. The skin area is not sufficient. If evolution would press on surviving on light only, various adaptations to use less energy and add the surface should occur. Move less, drop the body temperature by ten degrees at least and maybe more and bigger ears? [Answer] Rather than changing the DNA of an existing cell and further having it change into a rather different cell, it could replace the cells one by one. A plant, growing vegitatively, consumes a host cell and replaces it with one of its own that is sort-of useful in the same tissue, preserving the life of the host so it continues to use its animal abilities to gather food and find shelter, and prevent a sudden rotting body from being consumed by decay bacteria and carrion feeders. Ultimatly it could be symbiotic like a lichen. Plant cells have much much more DNA, so let them do the work rather than somehow morphing an existing cell. A cell can replicate. Break down the other into raw material and then use the substance to make your daughter. From an observer's point of view, it doesn't matter if the cell is changed gradually while still working the whole time, or completely taken apart and rebuilt. To transform rather than just rotting in the normal way, maybe the plant infiltrates the cell and eats it from the inside, and keeping the old tissue function like a guest operating system in a virtual machine. Note that plant cells are different from animal cells. They have cell walls and various architectural differences. Now if this transformer germ is engineered nanotechnology, then it could have a well planned program stored compactly in the DNA, and use a robust communications network between cells and download new code. ]
[Question] [ The Question of the [Tunnel through a Planet](https://worldbuilding.stackexchange.com/q/612/122) grinds my mind. How could you dig a Hole through the fluid mantle of a planet? Would your walls not constantly break and collapse on you after the 15-20 km of the crust? Would it be a straight, spiraled one or something totally different? [Answer] You have several problems here, let's assume the logistical ones are all solved (as they already are for long distance tunnels) and just focus on the engineering ones. You have six problems with a tunnel through the magma: * Making the hole * Temperature * Pressure * Leaks * Seismic activity * Currents Making the hole Actually making the hole is easier in the liquid area, assuming you can exert sufficient force you can just push the liquid mantle out of the way and it will flow. The problem is stopping it from filling back in again. Temperature The mantle has a temperature ranging from 500°C to 4000°C. (Some research suggests the core may even reach 6000°C). Even Tungsten melts at those temperatures. Diamond will melt at around 4000°C so might survive if you made the tunnel out of pure Diamond, but that's at atmospheric pressure. Increase the pressure and even Diamond melts before you reach the core, bringing us on to our next problem. Pressure You are talking 140GPa (Gigapascals) of pressure. That's 10,000,000 times atmospheric pressure. The walls of the tunnel would need to be incredibly strong to withstand the pressure, or the interior of the tunnel would need to be pressurized to the same level which would make travel through the tunnel problematic to say the least. Leaks At those temperatures and pressures even a tiny leak would quickly become catastrophic and you could well lose the entire tunnel. Seismic activity The tunnel would be vulnerable to shocks and quakes in the upper areas before it reaches the mantle itself. These forces would act to deform, twist, or even sheer straight through the tunnel. Currents The mantle is flowing, the lava is moving. This movement would try to carry your tunnel along with it. That would provide a lot of stress into the already stressed material and again would cause the tunnel to flex and move as the mantle flowed around it. ## Conclusion It's not possible with any current scientific ability to dig a tunnel through an earth-like planet. A smaller planet with a cooler core would be a different matter. The materials science needed is incredible, and most likely physically impossible. The development of force fields and other non-material reinforcement might make it possible in the far future but such concepts are speculative at best. [Answer] I fear that conventional science may fail you here. It is not technically possible, for instance, to actually "drill" through a liquid, for instance. (To say nothing of the incredible heat and pressure encountered in this scenario.) However, this is the Worldbuilding SE not the Geophysics SE. Which means if we need to "drill" through the mantle of a planet, we just need to make it plausible in-universe. I'm going to assume that, for this, you are in a generic soft science fiction universe. This gives you some options: ## Force Fields Generated and focused walls of force could be used to "simply" push the molten rock and metal out of a path through the mantle. A setup like this would likely involve a series of generators down the center of the cavity to reinforce the tunnel. This process should take incredible amounts of energy to make it plausible. (Whether that is done as a trivial matter by an ultra-tech civilization or as a titanic undertaking by lesser civilization is up to the author/designer) A tunnel like this might actually flex in order to resist any currents in the molten sea of the mantle. ## Magma Ships If the goal is simply to travel through and/or harvest the liquid material of the mantle, an advanced vehicle (properly shielded) could "swim" through the liquid like it was an ocean. This solution would still need a hole drilled through the crust in order to deploy these craft. I could go on really, the possibilities are endless. The important thing here is to know the problems with what you're trying to do, and then how to overcome those issues in a reasonable manner. [Answer] Like Tim B, I will assume that logistics are solved, and deal purely with the walls of the tunnel. Supposing that the walls are made of diamond and it is available in practically unlimited quantities. Diamond begins to transition from molten liquid form to forming solid chunks at 11 million atmospheres (<http://news.discovery.com/space/alien-life-exoplanets/diamond-oceans-jupiter-uranus1.htm>). Suppose that the tunnel walls were to be a thickness of diamond such that at least temporarily a solid inner core could be maintained while the outer edges of the walls melt. For example, 100 metres thickness of diamond. We now "merely" need the solution to two issues: 1. Cooling of the tunnel: We have already assumed that logistics are solved, so this is merely a matter of large scale cooling or perhaps a new geothermal power solution. 2. Loss of diamond to melting: The more challenging issue. Diamond from the outer wall will disperse in the molten core material. Diamond will have to be continuously synthesized at the inner wall and slowly migrate to the outer wall. As crazy as that might sound, living organisms create similar structures through a continuous cycle of interior growth and exterior loss. [Answer] A few out-there ideas, sci-fi concepts included: Spinning the planet, along its axis: Although only possible pole to pole, spin the planet fast enough to reduce pressure - although this would only work really by destroying most of the planet. A wonder material made by nanobots, and designed by AI: We may not know the answer, but put a good smart AI onto the task and it may yet find a solution, even a brute force one such as using untold nanobots to continually mine, cool, and create support structures, using a wonder-material. Wormhole: Although wormholes are theorised to exist, but are extremely small and last only for fractions of time, there may yet be technology to be invented that allows for longer lasting, larger wormholes. This could bypass the magma completely. Anti-gravity: If someone can create a repelling force, pushing away heavy objects, it may be possible to maintain a hole using many repelling anti-gravity generators. Again, to-be-invented. All-in-all, pretty hard stuff to invent yet. Makes going around the planet that much more attractive. [Answer] Drop a small black hole at your feet. If it falls straight, it will fall through to the center of the earth and go all the way (almost to the other side of the world) and then fall back to the center of the earth and will repeat this many times until it settles at the center. I'm ignoring the rotation of the earth which will complicate things. The black hole will gobble up magma and leave a tunnel behind. The tunnel will unfortunately quickly refill. Of course, the filling tunnel is the least of your problems. It won't take long for the whole earth to be gobbled up. ]
[Question] [ The world is an infinite plane with an Earth-like surface. It has an atmosphere, but it has finite height Because of this, and how fields work, this should give us the same gravity all the way up, which has implications for light; all light that leaves the atmosphere will eventually turn around and hit the ground, as no matter how high it travels up, it will still be under the same gravity, and so it must eventually be turned around and fall back to the ground. And due to the atmosphere's finite height, it stands a decent chance of reaching the ground again This raises the question of what that would actually look like. Specifically, what images would these falling beams form when seen by the human eye? [Answer] # Rainbow skies, happy times The world described would seem to be a dark world, since any Sun would have fallen to the ground far, far away. It would seem to be a doomed world, with all heat energy going up and coming back, like the heat death of the universe brought to a human scale, with tribes huddled around geologic deposits. But that's not the way I want to go, so... * The sky is a vast and lovely aurora. Whatever bizarre physics or gods made this world, they left behind a little gas far, far above the world. It falls without limit and lands as powerful cosmic rays. These particles strike the atmosphere and light up the planet. * We can calculate how far light goes before it has to come back. Every kilogram of light has a potential energy of 9.8 m/(s^2) times however many meters high, times 1 kg. Every kilogram of light has (3E8 m/s)^2 of total energy. So by the time it gets to about 1E16 m (1 trillion kilometers) high, the light is redshifted to nothing and has to either fall back down or disappear. (comparing black holes, this distance might be halved for reasons I don't understand but might have to do with both the light and the spacetime being pulled by gravity) We know light bends in gravity, so unless it goes perfectly up, I'm betting it falls back down. This adds a steady "Earthshine" glow to the background. * But ... it'll keep accumulating energy until it roasts? Nope. I'm going to say that the planet, nay plane has a special trick to dump heat energy, because otherwise it isn't 'Earthlike' and that goes against the premise. My favorite is neutrino pair production - sending 3/2 kT of energy out on every single neutrino. Do that and you can have cooling spots somewhere that are keeping the planet at a steady temperature. Putting this all together, the skies have brilliant rainbow aurorae stronger than Earth's, but this shares the light with a constant muddled background of Earthshine. The aurorae dominate where the currents of space are stronger, and the Earthshine can be tracked back in an arc to some far-distant horizon. If you look very closely, perhaps the outlines of continents can be made out in that background light, to the degree that they can be from a trillion kilometers away. [Answer] # Frame challenge: Atmospheric collapse You have an infinite plane with infinite matter, initially evenly distributed with an initial density of an earth-like atmosphere, or about 2-3 x 10^25 particles per m^3. That matter has mass, and that mass has gravitational pull. Molecular clouds with a density of a mere 3\10^8 particles/m^3 are considered stellar nurseries, and we're exceeding that by seventeen orders of magnitude. [Answer] (this answer assumes the thickness of the plane is about 1 Earth radius, that is about 12,000km, according to the link HDE 226868 provided in the comments, there will be 9.81g everywhere, on either side of the plane)* ## Paradise for a few weeks.. then it gets perforated, again and again So how would the sky look, at first.. Depends on the atmosphere the gods arranged for your infinite flat world. Suppose the weather will be stable, suppose some Earthly gods were involved in the creation and you'll have oxygen, water, blue sky and sunshine. A week after creation (see calculation below) the inhabitants would notice their plane starts to warm up.. End of paradise will come soon.. Every 96 days, your sun will impact and perforate the plane There are no stable orbits around the plane. Everything will fall.. When would the sun arrive ? [![enter image description here](https://i.stack.imgur.com/PGTRB.png)](https://i.stack.imgur.com/PGTRB.png) This formula works, until light speed is reached. Fillin the values, suppose the sun 1 AE away from you, that is 149,597,870,700 meters. If you multiply that by 9.81 your sun won't reach light speed. So invert the formula, enter s = 1AE = 149,597,870,700 meters in t square s / 0.5 g = 30,581,039,755, square root of that is 180,000 seconds, which is 48 days. Your sun will crash the plane and perforate it, proceeding its path through the plane and coming back again. After another 12 weeks, the sun will return and perforate your plane again, from the other side. This can be prepared for, inhabitants could survive this: suppose your plane is infinite, the sun would arrive perpendicular, leave perpendicular and travel back through the same hole. Any place within 1AE of that point needs to be evacuated. Maybe it is advisable for the gods, to create a suitable hole in the plane, beforehand.. Blue shift Your plane will now have a (local) "day night cycle" of 96 Earth days followed by a night of 96 Earth days, the sun oscillating through the plane. Not only your sun, the whole sky accelerates toward you. This will cause the sky to be full of blue stars at night. Instead of red shift (expanding) your universe will show blue shift. .. it goes into ultraviolet shift, your sky will get dark When your plane has existed for a few months, the surrounding stars will start to approach with the speed of light. Remote stars and planets will reach your plane at light speed eventually, so you won't see them arriving. Their blue shift becomes an ultraviolet shift. after that.. color oscillates, red-blue shifts alternate: purple skies ? Disasters keep reoccurring, every few years the stars will return to your plane, perforating it.. and it will be quite difficult for the gods, to predict where these impacts will take place, to prepare holes for it. Suppose these gods are omnipotent, they could prepare holes in your plane for every star and black hole in your local galaxy.. The end.. After some 3 million years, the first neighbouring galaxies will start to collide.. and slowly, everything in the cosmos would come to rest on your plane. Oscillations would stop and every celestial object will come to rest in a hole, somewhere in your infinite plane. For black holes, these perforations will be giant. Light years of your plane will simply vanish. The inhabitants will have to move.. euuhm.. away from these perforations. ========== NOTES about paths of light I think locally emitted lights would not behave differently than light on earth, that is Horizontal light rays travel horizontal until out of sight Eventually, a horizontally directed light would reach the ground.. question is when and would that happen in sight ? I think not, with g=9.81 G the path of the light would not differ from Earth. Vertical light rays travel very far away There would not be any relevant effect. The light will travel against an infinite gravitational pullback and as Mike Serfas pointed out, the light will travel a trillion kilometers, until it comes to a standstill and fall back (?? I have to hand-waive this actually). But whatever happens, the distance is beyond any visible range, so the returning light will be so weak it can only be seen by Hubble. [Answer] What is up there? Can the light hit it? You discuss light leaving the atmosphere then turning around and hitting the ground. If it must turn around to hit the ground I take that the ground is the source of light. OK; glowy ground. That will make for a sweet anime. /It has an atmosphere, but it has finite height/ It is not the atmosphere that has finite height but the plane or dimension itself because /all light that leaves the atmosphere will eventually turn around and hit the ground/. It is possible to leave the atmosphere. I take from this that the boundary of this plane is some distance above the glowy ground and the atmosphere. The question I have is the nature and position of this boundary. If the boundary is so far away that light leaving the ground never hits it before turning around, it does not seem relevant to the question of light. If this boundary is close enough to the ground that light leaving the ground hits it before the light can turn around, then what it looks like depends on how the boundary works - whether it emits light, reflects light, absorbs light etc. [Answer] ### It Seems Like Your Describing An Infinite Mirror All of the light gets turned around, eventually. Depending on the height of your atmosphere, and the size of the dust and other particulates in it, this light gets scattered to a varying degree - blue first, then other colors. It may be impossible to clearly see the ground reflected above them, but maybe some larger structures like mountains and forests can be dimly seen reflected in the sky. But when the light comes back down, it is absorbed by the ground. Since the universe ends at the “sky”, it would seem that all new light comes from the ground. Maybe that’s your intent. Or, maybe this is a one-way mirror, and new light from beyond can enter the system. And some sort of heat balance takes the excess energy and dumps it on the other side of the Earth, or an effectively infinite (for the time frame of your story) heat sink in a cold core. ]
[Question] [ House cats are among the oldest domestic animals on Earth. They basically followed domestication of cereals in the Middle East; mice infiltrated human habitation to eat the stored grain, and cats came in to eat the mice. To this day, house cats behave, unlike other domestic animals, as though they are guests who came in of their own volition. I'm writing about a world that can be considered an alternate Earth, where there is a civilization rising in an area whose biome is a mixture of prehistoric Europe and America. It turns out this biome does still contain a wild cereal that seems suitable for domestication: <https://en.wikipedia.org/wiki/Aegilops> But it does not have house cats for when mice start eating the stored grain; it has the American bobcat, but that is not suitable for domestication. So what to do about mice? Maybe they need to invent mousetraps early, though will mousetraps work in a grain storage building where the bait will be swamped by the local abundance of food? Or: ferrets are native to Europe and America, and they eat mice! And they have been domesticated. But reading about ferrets, everyone talks about their use for hunting rabbits, but there doesn't seem to be a whole lot of discussion about their value in eating mice. Is that because ferrets have some disadvantage that I'm not aware of? Or is it just that this job in our world was already being satisfactorily done by cats, and ferrets would be valued for it in the absence of house cats? [Answer] You want genets! [![genet](https://i.stack.imgur.com/4rF1B.jpg)](https://i.stack.imgur.com/4rF1B.jpg) <https://petpress.net/10-legal-exotic-pets-that-are-not-dangerous/> <https://en.wikipedia.org/wiki/Common_genet> > > It was brought to the Mediterranean region from Maghreb as a > semi-domestic animal about 1,000 to 1,500 years ago. It spread from > the Iberian Peninsula to the Balearic Islands and southern France.[9] > In Italy, individuals were sighted in mountainous areas in the > Piedmont region and in the Aosta Valley. Individuals sighted in > Switzerland, Germany and the Netherlands are considered to have > escaped or been released from captivity.[10] > > > Genets are not felids or mustellids but viverrids - mongoose family. I read that the genet came to Europe with the Moors and was favored by them for its mouse and rat killing abilities. It has largely been displaced by housecats but some people still keep genets as pets. They are much more beautiful than ferrets and their semi-arboreal nature would be great for a fiction. ]
[Question] [ When a planet is under seige, obviously its airports, missile silos, and launch sites are the first targets of bombardment, to prevent a counterattack. It thus seems that submarines, which can fire missiles and then submerge and swim away, and only have to resupply at a port every few years, are the logical choice for anti space defense. If the attacked spacecraft survived and quickly aimed its lasers and railguns at the submarine, how deep would a submarine, with modern military hull thickness, have to submerge to prevent destruction by the spacecraft's 100 gigawatt laser? Would double or single hulled submarines be more effective at stopping laser damage? How deep would a submarine have to be to survive the spacecraft's other weapon, a "rods from the gods" type attack with a 1 ton 10 meter long pointed titanium projectile railgunned at it at 5000 m/s? [Answer] Lets assume for this consideration that your spaceship can detect the exact location of the attacking submarine within a few seconds after the attack is launched. Rod of the gods The spaceship will be in an orbit of at least a few hundred kilometers, if not much higher. So even with an instant counterattack the submarine gets more than a minute to dive and move. As titanium is roundabout 4.5times as dense as water your rod will loose its full impulse within 45 meters into water. I can't find exact speeds for diving down but there are proven stories about submarines diving up more than 300 meters within two minutes, so I think your submarine has more than enough time to dive deep enough and far enough for not beeing hit at all. Laser As the speed of light is a little bit higher than 5000m/s it would be possible to hit the submarine, just looking for the speed. The problem here is the refraction of our atmosphere. Even with an absolutely clear sky much energy of the laser will be lost when reaching the surface for most of the possible wavelengths. Some clouds in the sky -> even for the few optimised wavelengths a high degree of laserlight is scattered away. If our submarine beginns to dive instantly after firing their own weapons the spaceship has no time to take a good position before firing back so there occurs another problem: the high reflection-factor of light transfering from air to water under less then 90°. As the sea-surface is in motion all the time a high level of light gets reflected by just centimeters of water. Furthermore the cooling-effects of water help the submarine to survive laser impact a few seconds more. Thereby I conclude that your submarine could be save with just a few securitymeassures against laser (highly reflective hull, attacking from a sharp angle and such). Edit: added some details for the laser-attack and corrected some writing mistakes. [Answer] I think the key obstacles are submarine detection from space and spaceship detection from underwater. * Most submarine detection systems today are sound-based, and they rely on receivers [in the water](https://en.wikipedia.org/wiki/Sonar). Even aircraft (which are in the atmosphere) drop [sonobuoys](https://en.wikipedia.org/wiki/Sonobuoy). * There are some non-sound systems, like [MAD](https://en.wikipedia.org/wiki/Magnetic_anomaly_detector), but they are short-ranged. * Some things are possible from orbit, e.g. [wake detection and thermal signatures](https://www.defence.gov.au/adc/adfj/Documents/issue_127/127_1997_Nov_Dec.pdf). Regarding the specific attacks, consider that [nuclear depth charges](https://en.wikipedia.org/wiki/Nuclear_depth_bomb) were retired. Wikipedia says that homing torpedoes were better, I guess there was also a hesitation/revulsion to employ nuclear weapons in that role. (What good is an ASW weapon when you have to phone the White House for each shot?) I expect that the efficiency considerations will apply to the KE and laser attacks as well. [Answer] Modern SSNs don't necessarily need to come to periscope depth to fire. It's possible to pop out encapsulated missiles that only launch AFTER the launching sub cleared datum. While currently they are only used for AGM's on SSKNs, there are no reasons why they couldn't also be applied to VLS tubes, or even apply them to ICBM tubes, albeit a new gen of missiles will probably need to be designed for ICBMs or VLS tubes. Basically, the capsule will "hang" just under the surface until it is time to launch, then it'll pop up, and launch, even hang vertically in the water. [Answer] # God Rod Analysis ## Facts: * Dropping anything from orbit produces 31mj/kg. * A telephone pole sized mass of tungsten weighs slightly less than 13 metric tons. * 31mj \* 13000kg ~= 400GJ. That's around 100 tons of TNT (1/10th of one kiloton). * It takes an object dropped from orbit around 15 minutes to reach the surface of Earth. * 100 pounds of TNT has a kill radius of 3-4 meters, and a disable radius of 8-10 meters on a modern hull. * To maintain the necessary energy density over a larger radius, the energy must increase by the cube of the radius. So while a tungsten light pole traveling at 10 times the speed of sound has 1000 times more energy than a depth charge, it won't have anything like 1000 times the blast radius. More like 5 times the disable radius. * One can expect a sci fi sub to be significantly more durable than a modern one, further reducing the disable radius. ## Evaluation: With a 15 minute lead time, a dropped God Rod is unlikely to land anywhere near its target. Even with the effective kill radius of 100 tons of TNT, it's extremely unlikely that a kinetic weapon will threaten a submarine. OTOH, a dropped rod might be relatively subtle until it really got moving. A fired rod might drastically reduce that time and increase the impact energy. If it comes out of a mass driver at relativistic speed, the warning time shrinks drastically while the impact energy skyrockets. So dropping stuff on a sub isn't going to work. Shooting at it could be just fine. ]
[Question] [ I'm writing a fictional story where non-primate mammals (and marsupials) evolved into different species of humanoids which roamed the earth. In my world humanoids have evolved from animals such as bears , sloths and koalas including extinct animals such as Chalicotheres. I'm wondering what evolutionary pressures could lead to the rise of such species. ![enter image description here](https://i.stack.imgur.com/VfmWF.jpg) [Answer] Feasible Primates evolved from a non-primate precursor, according to scientists, around 65 million years ago. So, there's nothing preventing the body structure of humanoids from arising given the right set of influences into a humanoid shape. The real question is why humans are human shaped. And the answer is intelligence. Humans were designed with intelligence in mind. Being bipedal with thin but flexible fingers isn't an advantage unless you can do something better with the arms than if they were feet, like use and make simple tools or manipulate the environment to your advantage. Bears, for instance, derive an advantage from having four powerful limbs for movement, so if you want to have them become a humanoid, you need to give them a reason to use arms - and that's intelligence. [Answer] Evolution is a combination of random mutation and natural selection. In our case, we exist because one of our ancestors had a mutation that caused the lumbar curve, i.e. where the lower spine curves the wrong way. That allowed standing and walking upright, which made it easy to see over tall grasses (a relatively recent development itself on an evolutionary scale) and use hands for carrying tools or weapons instead of walking, which in turn drove increased intelligence to better make/use said tools and weapons, all of which were huge selection benefits. Many other, lesser mutations refined that new form over time into what we are now, but that was the key. Our primate ancestors were a bit smarter than other mammals, but nothing else really set them apart—or does so today, if you exclude us. If the same mutation happened in other mammals, you could easily get other bipeds, and they would likely evolve higher intelligence as a result just like we did. Convergent evolution to where they all appeared "humanoid" probably depends on how strictly you define the term. [Answer] So there’s according to Wikipedia 12 theories on why humans became bipedal, I remember there being more. Anyways here’s a nice explanation for reasons to give your species human-like bipedalism: <https://en.m.wikipedia.org/wiki/Bipedalism#Evolution_of_human_bipedalism> The problem you’re gonna run in to is that a lot of these problems we might have evolved towards bipedalism to fix are just things primates sorta suck at but other animals have better solutions for, like defense or travel, or they’re things that require a ton of specialized primate abilities to make into a good solution (like we were good at reaching for branches. Which may work for koalas but not sheep). The one thing I could see working is introducing a very deadly predator in the food chain that’s proportionally more intimidated by large-sized creatures. It is a cheap way to make yourself appear significantly bigger. Also based on that picture your animal has fingers, low facial prognathism, a butt, ability to use tools, non-rhiperian nose, and maybe a chin and maybe permanently enlarged breasts which are all pretty unusual physical traits it’ll take a lot more working to evolve if you wanna use them. ]
[Question] [ Specifics: the magical ability is genetic, very rare (about one in ten thousand people will be born with it), and no mage can be too strong (no destroying mountains, drying lakes etc.). Also, the nature of magical spells is fundamentally different from any technology or natural phenomena (i.e. laser beams or lightning), even if the effects can be similar. In other words, think Harry Potter kind of magic (not literally, but close enough). But there is a third group of people, who have a genetic ability to resist any magical effect (be it physical or mental). Their numbers are approximately the same as for people with magic. In other aspects, they are normal, with no special abilities. Let's call the groups mundanes, mages and insulars (the third group). Some of the effects: * Mages would find it very hard to harm insulars with magic (some ways are still possible - for example, setting fire to a house would kill an insular if the magical fire causes an ordinary one. Dropping a large stone on them should work as well); * Mages would find it hard (almost impossible) to help insulars with magic. For example, no magical healing would work on them, be it spells or potions; no teleportation, etc; * Insulars would probably benefit more from living in mundane society, however the mage society wouldn't be able to hide from them with mental magic - they will see through any such disguise. So to hide from insulars, mages would have to completely separate themselves from the mundane society. * Mundanes who know and fear magic would either want to employ insulars to search for and fight mages, or hate and fear them as well, becasue insulars are better protected. --- Question: In a modern setting with total population about the same size and the same level of technology/medicine, how would the three groups coexist realistically? We assume that around Middle Ages everyone knew about magic, or at least suspected. [Answer] Due to Insulars, Mages wouldn't be able to hide and create a separate society like in Harry Potter, so it could go a number of ways: 1) Insulars band together and control everything by twisting mundanes into fearing Mages. They could easily convince mundanes this is true by a few examples (like mundane rulers in the past being influenced by a mage) and then proving mages can't manipulate them thus "proving" that they should lead. In this case, Mages might be hunted by mundanes and Insulars much like vampires, Werewolves, etc. are in those types of fantasy. 2) The ingenuity of mundanes (much like regular human history just add some extra elements) allows them to create an egalitarian society where all three have their place. Insulars would probably work in conjunction with Mages and mundanes to manage the criminal Mage population like a special police. It's quite likely that Mages would have a slight economic advantage due to their abilities, however, it would be kept in check by insulars who make sure they don't exploit (not all exploitation is necessarily criminal) the mundanes and society as a whole similar to say anti-monopoly laws we have in place now. 3) Mages rule via systematically eliminating the Insulars as they're born by exploiting their weakness to the mundane. This is the least likely outcome as older Insulars would (hopefully) have found a way to prevent this though this could be an interesting story since you could the insulars and mundanes would rise up against the Mages (though then this could lead to the first case and unlikely the second.) [Answer] Keep in mind that these ideas are from a tabletop Game Master (mainly D&D), writer of fiction, fantasy, and voracious reader. A few notes of observation. In a world of mages, the mages would be able to tell who has magic and who is mundane. Those who possess the insular quality would be "blanks" to them. Just as the "mundanes" would fear magic, those who are insulars would be feared by those who control magics, as they would be wildcards in the equation for whatever schemes they have. Another thing I would note is that the mages wouldn't really know the populations of both mundanes and insualars. Why? Because in the medieval era there wouldn't be testing everyone to determine if they are mage, mundane, or insular. People would probably find out accidentally what their skills are and seek likeminded people to be with. Or in the case of insulars, simple disappear into mundane society and only when circumstances arise that would cause them to showcase these special talents, they would come to the forefront. A third thing I would probably have in effect is that certain insulars can, with sheer force of will lower their resistance - but this would be a special individual such as the main protagonist. The benefit to doing so would allow them to be affected by magic(s) they wanted to, while still having resistances to the magic(s) they didn't think would do them good. [Answer] I recon the most important factor in this is the power of the mages. If one mage can easily fight off a village of mundanes, there's not that much need to hide. If they risk considerable injury when taking on an angry mob with torches and pitchforks, they might want to hide their magic. ### If the mages are powerful The mages can just enslave everyone, and the Insulars would potentially be leaders of a rebellion, or strong agents. But the Mages could easily pressure the Mundanes to get rid of an annoying Insular (either mind control them, or threaten to harm them or people they care for). Or if the Mages are even more powerful, they'll likely behave somewhat like the Greek Gods, living on a mountain, seeing humanity more as a pet or a game. Much like we see birds or similar critters. ### If the mages are not powerful The mages would therefore be in hiding. They'll generally try to lead a relatively normal life, probably with a significant amount of 'luck' where convenient. Or they might live a nomadic life, enjoying their powers and the world, moving on if people get suspicious. Generally people take a lot of convincing to believe something new, so Mages can probably stay in one place for quite some time. Insulars would likely be the first to notice something odd. But, they might just shrug it off as something they imagined. There might even be a thriving mage community (like in Harry Potter). Insulars would obviously notice various signs. Most that speak up would likely end up in some asylum, that is, until one manages to undeniably expose the Mage community. [Answer] If technology developed alongside magic, I can see a world where Insulars and Mages coexist. In this case, magic just provides alternative solutions to problems (need to get somewhere: fly or drive; need to hurt someone from a distance: zap with spell or shoot with gun). In this case magic can make quick, one off changes to the world but would not benefit from economies of scale. You might be able to summon an item but summoning 100,000 items would be harder than tooling a factory to produce them. Unless Mages are prevented from using technology, Insulars are going to have a distinct disadvantage. If a Mage can carry a gun, the Insular isn't much more of a threat than a Mundane. Insulars would have to relay on the slower healing times of real medicine. However, Insulars would make great cops and first responders. If some idiot Mage summoned demon, send in the Insulars. If some mage is growing senile, give them an Insular caregiver (who will not get turned into a toad). [Answer] Given the amount of insulors there are it is still possible for magic to remain hidden from the General Public as long as they take some precautions Picture Harry Potter but slightly more cautious, more like the American magic Society in the Harry Potter prequel. The Magicians who have good much more involved in the mundane world wear hats in the early days they would have their agents seduce and marry into royal families. Or become leaders of religious institutions. And more modern times they might install double agents in both law enforcement and politics. The main goal of these people would be to keep magic hidden from insulors. This doesn't mean that they necessarily have to kill any insulators they find ( in extreme cases it might come to that) it could be as simple as is discrediting them or blackmailing them should they try to reveal the existence of magic. If they persist then they can get some doctor to brand them as insane. Then they can rave about magical they want it will just make them look more insane. Also remember that just because magic can't influence the minds of insulors doesn't mean they can't influence the minds of anyone they talk to. How dangerous would an insulator really be if you could make anyone he talked about magic to forget the conversation that had about magic with them. Doing magic in public would be highly illegal. Wizards be trained not to rely on their mind wiping spells since those won't work on insulator instead showing ways to conceal spell work so if they do get caught the insulor won't be tell for certain who cast a spell only that a spell was cast. In this system most insulors probably never encounter Magic and those that did would live on the fringes of society it'd be that weird conspiracy theories or that end of the world nuts. [Answer] They would coexist in the way that mages would be good or bad aiding people or using them. Moguls would be everything on the spectrum and people who can't be affected would become criminal masterlord that magic trick won't work on or successful businessman that can resist magic in handling or negotiations. Source: Your mind trick won't work on me - Jabba the Hut. Jedi mind tricks don't work on me, im Toydarian. - Watto the Toydarian Nom, nom, nom delicious nutrients - Ysalamirs of Myrkr ]
[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. In [A World Out of Time](http://rads.stackoverflow.com/amzn/click/0345336968), per [Schlock Mercenary](http://www.schlockmercenary.com/2003-08-03), Earth is moved to a new home by lighting a fusion candle. The fusion candle idea is discussed in the Schlock quote: > > Building a gas-giant colony ship is not as difficult as it looks. > > > 1. Build a fusion candle. It's called a "candle" because you're going to burn it at both ends. The center section houses a set of intakes that slurp up gas giant atmosphere and funnel it to the fusion reactors at each end. > 2. Shove one end deep down inside the gas giant, and light it up. It keeps the candle aloft, hovering on a pillar of flame. > 3. Light up the other end, which now spits thrusting fire to the sky. > Steer with small lateral thrusters that move the candle from one place to another on the gas giant. Steer very carefully, and signal your turns well in advance. This is a big vehicle. > 4. Balance your thrusting ends with exactness. You don't want to crash your candle into the core of the giant, or send it careening off into a burningly elliptical orbit. > 5. When the giant leaves your system, it will take its moons with it. This is gravity working for you. Put your colonists on the moons. > 6. For safety's sake, the moons should orbit perpendicular to the direction of travel. Otherwise your candle burns them up. > 7. They should also rotate in the same plane, with one pole always illuminated by your candle (think "portable sunlight") > 8. The other pole absorbing the impact of whatever interstellar debris you should hit (think "don't build houses on this side") > > > But the logistics are mind-boggling. It seems things would get tricky piloting Jupiter to catch earth (but not impossible) - the maneuvers for [getting into orbit](https://worldbuilding.stackexchange.com/questions/12203/how-to-enter-the-orbit-of-a-gas-giant) seem basic, but the candle needs to be rotated pretty fast to not burn the earth (going out of the [ecliptic](https://en.wikipedia.org/wiki/Ecliptic), I'd imagine). So my question revolves on the possibility of getting Earth to Jupiter instead. Rockets, explosions, throwing the moon like a baseball towards the sun - whatever it takes to get over there. Given the [rocket equation's](https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation) thirst for mass, how much of an Earth is left over by the time we get into orbit around Jupiter? Is it habitable? *Main Question:* Is this idea plausible or will we be forced to pilot Jupiter to pickup Earth like a hobo jumping on a moving train? I'll assume a [Hohmann transfer orbit](https://en.wikipedia.org/wiki/Hohmann_transfer_orbit), with methane-oxygen combustion to start, but who am I kidding? This is saving the Earth. If you want to [Rich Purnell](http://www.imdb.com/character/ch0513031/) a couple of Venus Flybys to save the planet, go for it. If you want to light up a fusion candle on earth that slurps up the ocean, go for it. If you want to light all the nuclear bombs in the world on one side of a really big metal plate, go for it. Throw the moon into the sun and be propelled backwards? Go for it. The Earth will be grateful you did - I'm just looking for plausible solutions. Of course, the other logistics of having Earth orbit Jupiter (Tidal forces, radiation) - is bad, but that's another question. [Answer] ## Asteroid flybys ### Description 1. Use a convenient asteroid of small mass, pick one already close (in $\Delta V$ terms) to one of Jupiter's Lagrange point. [Asteroid Hektor](https://en.wikipedia.org/wiki/624_Hektor) is a good candidate. It's already in Jupiter's L4 point and masses about $1 \cdot 10^{19} kg$ 2. Put a solar power stations in several spots on the body. 3. Plant [mass driver/railgun/coilgun](https://en.wikipedia.org/wiki/Mass_driver) on its surface so that the recoil of at least one of them points through the body's center of mass & connect them to your solar panel farms. [![Mass driver layout](https://i.stack.imgur.com/hy4EE.jpg)](https://i.stack.imgur.com/hy4EE.jpg) 4. Even distribute the other railgun/coilguns around the body to provide for maneuvering. 5. Begin launching materials in such a way that you begin moving your asteroid (and you can also launch those materials to where they are needed - so you get a twofer). 6. Now steer that body through the nearest [Lagrange point](https://en.wikipedia.org/wiki/Lagrangian_point) so you can begin using the [Interplanetary Transportation Network.](https://en.wikipedia.org/wiki/Interplanetary_Transport_Network) (see references). [![Interplanetary Transportation Network](https://i.stack.imgur.com/oPZO4.jpg)](https://i.stack.imgur.com/oPZO4.jpg) > > The Interplanetary Transport Network (ITN)[1](https://i.stack.imgur.com/hy4EE.jpg) is a collection of > gravitationally determined pathways through the Solar System that > require very little energy for an object to follow. The ITN makes > particular use of Lagrange points as locations where trajectories > through space are redirected using little or no energy. These points > have the peculiar property of allowing objects to orbit around them, > despite lacking an object to orbit. While they use little energy, the > transport can take a very long time. > > > 7. You will arrange for the small asteroid to begin a very long series of alternate flybys between Jupiter and a large asteroid. 8. On one end of the orbit, the asteroid flyby will transfer some momentum between the small asteroid and the large one. 9. On the other end of the orbit, the asteroid flyby will transfer some momentum between the small asteroid and Jupiter. 10. Each of these flybys will mimic a purely elastic momentum transfer ($m\_{asteroid} \cdot \Delta v\_{asteroid} = m\_J \cdot \Delta v\_J$ collision, but the net result is that you are transferring momentum between the target and Jupiter by way of your small asteroid. The goal is to get the large asteroid to its nearest (in terms of $\Delta V$) Lagrange point so it enters the Interplanetary Transportation Network too. You will repeat the above steps only the Earth will be the target of movement. Rather than moving the Earth into the Interplanetary Transportation Network, you will gradually increase the orbital radius of the Earth until you get it to the desired location. Warning, although we could start doing this sort of Solar System Engineering now, it will likely take thousands of years to complete the operation. ### Calculations Basically we're performing momentum transfer interactions (modeled as collisions). We get one complete round trip momentum transfer exchange for every round trip between Jupiter, the target, and back to Jupiter. Because the orbit phase (where the object is in its orbit around the sun) will constantly change and that for most exchanges, the asteroid will have to complete a whole orbit of the Sun before it gets another chance to interact. Assumptions: * Approximate the time it takes to complete a single momentum exchange as the time it takes to complete an elliptical orbit with perihelion at Earth's orbit and aphelion at Jupiter's [(5.2 years)](http://www.calctool.org/CALC/phys/astronomy/planet_orbit). * Asteroid we use to transfer momentum is Vesta * $M\_{Vesta} = 2.6 \cdot 10^{20}$ * $M\_{Earth} = 5.9 \cdot 10^{24}$ * $M\_{Jupiter} = 1.9 \cdot 10^{27}$ * Max $\Delta V$ from Jupiter encounter is $35 \frac{km}{sec}$ but realistically we'll be lucky to get $10 \frac{km}{s}$ * Max $\Delta V$ from Earth encounter is about $10 \frac{km}{sec}$ So the momentum transfer from each encounter will be about the same and it equals: $$ m\_{Jupiter} \cdot \Delta V\_{Jupiter} = m\_{Earth} \cdot \Delta V\_{Earth} = m\_{Vesta} \cdot \Delta V\_{Vesta} $$ So each interaction will give the following $\Delta V$: * $\Delta V\_{Vesta} = 10 \frac{km}{sec}$ * $\Delta V\_{Earth} = 4.4 \cdot 10^{-4} \frac{km}{sec}$ * $\Delta V\_{Jupiter} = 1.37 \cdot 10^{-6} \frac{km}{sec}$ [$\Delta V$ required to raise Earth to Jupiter's orbit $= 3.4 \frac{km}{sec}$.](http://www.projectrho.com/public_html/rocket/appmissiontable.php#id--Erik_Max_Francis%27_Mission_Tables--Delta_V_Required_for_Travel_Using_Hohmann_Orbits--Solar_System) Divide the $\Delta V$ requirement by the amount of $\Delta V$ provided by a single interaction: $$N\_{interactions} = \frac{\Delta V\_{required}}{\Delta V\_{Interaction}} = \frac{3.4}{4.4 \cdot 10^{-4}} = 7,624 interactions$$ Vesta flybys of Earth. At an average of 5.2 years per flyby, this will take you $$7,624 \times 5.2 = 39,648 years$$ But you can significantly accelerate the process by using more than one asteroid to transfer momentum. Related discussion on [how to move planets using asteroid flybys.](http://forum.kerbalspaceprogram.com/index.php?/topic/86127-moving-a-planet/&page=2) [Answer] As usual for me, I am substituting ancient wisdom for hard science... How do you eat an elephant? One bite at a time. Start by building a planetoid in Jupiter's orbit using materials from the asteroid belt and the existing moons. That should give you a reasonable core for your "captured earth". Now start shipping your favorite parts of Earth to Jupiter, in whatever quantities your technology allows. As each new part arrives, add it to your planetoid, building it up like a layer cake. Keep this up until there is nothing left on Earth worth saving. Whether your extra-planetary exports include all the humans is up to you, but you will want to take at least one mating pair of each major animal species. More would probably be better. The final step is to edit the history books, so that in a few generations, everyone thinks that your now-earth-sized planetoid IS the original Earth. Problem solved! Earth now orbits Jupiter. ]
[Question] [ I'm working on a planet wherein the dominant species isn't humanoid (in this case, mantids.) However, I'm unsure as to whether or not it'd make more logical sense for the dominant species to be comprised of a single species of mantis, or multiple species of mantises. Mantises, after all, are an order, not a species. There are thousands of mantis species, and hundreds of genera. I know that humans are classified as a single species with multiple races/ethnic groups. Would that be how the mantis planet would develop, or would it make more sense for it to be comprised of multiple mantis genera or species? [Answer] As you said humans are one species. But we also have the other great apes, Chimpanzees, Gorillas, orangutans, etc. We also have other farther monkey species. Though there were several other homids that got wiped out, such as Neanderthal and Denisova, who died out with some cross breeding. So either they died out or were absorbed depending on interpretation. So you'd more likely have something like that. species that are 'similar' but not the same. You might even still have some of species that are separate branches, maybe there was enough separation that one didn't dominate and wipe out the others (yet). If each one was locked on a continent, it is possible that there might be multiple species. But you'd have to keep them mostly separate for a long time. [Answer] ## No A niche is an [N-dimensional hypervolume](https://en.wikipedia.org/wiki/Ecological_niche#Hutchinsonian_niche) the dimensions are spatial as well as environmental variables and resources. Species compete when they overlap the overlapping hyperspace is ceded to one or the other or divided up. If the niches overlap completely or by too much one of the species goes extinct. (or you get symbiosis) On Earth there is a kind of old world monkey that is such a generalist that it's niche literally overlaps with that of every bit of macro life on the planet. This could be a special case and on Mantvald the mantids species are all specialists with non-overlapping niches. Some only eat [Craykits](https://3.bp.blogspot.com/-AxkMCKw_toU/VqeU5YgXkRI/AAAAAAAACHg/dS1_ni__h1c/s640/crayket.png) others are Vegetarians, fisher-mantids etc. If there is no competition between the species then there is no reason for them to compete with each other. There is a paradox that emerges that on the individual level a crayket-eater would have less to fear from a fisher-mantid than from his own species as there is no resource to fight over. If you mantid's niches are non-overlapping there is no reason that there cannot be any number of sentient species especially if sentience is an ancestral trait. I.e. the common ancestor was sentient. [Answer] If you looking at a technologically advanced species, one thing you need to consider is the significant difference between the physical evolution and the technological evolution. The differences between these makes it possible that two sapient species could evolve at the same time. As a species, Homo sapiens came into being [200-500 thousand years ago](https://en.wikipedia.org/wiki/Timeline_of_human_evolution). This means that if you had a time machine and brought a young child from then to our time, they would be able to fit into modern society1. We know that agriculture has been around for [at least 10 thousand years](https://en.wikipedia.org/wiki/History_of_agriculture). So it took over 90% of our existence as a species so far in order to develop agriculture. Agriculture has allowed us to live in much larger groups. Living in large groups, we have the ability to systematically destroy any threat that consists of only small groups. This is why reaching the milestone of agriculture means dominance over non-agricultural threats. So now, what about that window of 190 thousand years? What if another species capable of developing technology evolved during that period? It would be a race to develop agriculture, with the winner being the species that developed it first. This means that it is very unlikely that there could be multiple dominant species unless the two species did not have to compete with each other. Consider the dog. According to the first result of a quick Google search, [there are around half a billion dogs in the world](https://www.psychologytoday.com/blog/canine-corner/201209/how-many-dogs-are-there-in-the-world). Most people would agree that they are not dominant, but dogs are clearly doing well as a species without any level of technology at all. They were able to attain this status by being capable of things that we can't do and helping us. Over time, dogs have been bred to emphasize the traits that we find useful. One result of this is that most dogs have been bred to be more obedient. As such, dogs have proliferated by not even trying to be the dominant species anymore. So what needs to happen to have multiple dominant species? They can't be in competition, or else the first to agriculture will likely wipe out the other. Also, they should be of roughly the same level of intelligence, with other features to distinguish between them. For example, suppose one species is stronger and the other is quicker. This would allow for interesting ways that the two species could work together—predators against which the stronger species has a distinct advantage, and others against which the quicker species has the advantage. Another possibility is, as others have mentioned, physical separation. Suppose that instead of being different races, Africans and Europeans had been separate species. By the time of the "Age of Discovery", European society had advanced enough to no longer be immediately concerned about survival. The Europeans would likely have still chosen the slave trade over extermination. The slave trade may have lasted longer with the Africans being a different species, but as society continued to progress it would still be eliminated. It still would not have been enough time for intelligence to be bred out of the African species, allowing them to join the European species as dominant. 1. Assuming that the child did not have mental disability due to malnutrition during their mother's pregnancy, diseases that we no longer have to worry about, etc. [Answer] Humans have been fighting for resources for 10's of thousands of years. Some homids are known to be lost to history. This fighting is still going on today. However one could easy argue that we are getting more similar as we cross breed. Also our technology is reducing the radical responses to our visual and cultural differences. So to answer the question ... If the mantids could not interbreed then over a long time the most adaptable/advanced group of mantids would dominate the most habitable regions of their planet leading to enslavement / extinction of the weaker/less adaptable groups. This may leave mantid groups acting like horses or bullocks or maybe like pets cats dogs? If however they could interbreed then there would more assimilation's into the most adaptable/advanced/numerable group of mantids leading to that group's dominance. ]
[Question] [ Perhaps you've flown in a plane on an especially cloudy day when all you can see are clouds beneath and above you. It's a beautiful sight, strata'd white all around. So what if the plane were flying on Jupiter instead and enjoying the cloud strata there? There's a couple of assumptions here: 1. There are floating colonies for the planes to fly between. 2. Getting metals to supply an aviation industry is economical. 3. Fueling these airplanes is also economical. Assume that the plane can be built or delivered into Jupiter's gravity well without difficulty. At what altitude would this plane likely fly and how would it differ from modern airliners in terms of shape? If it's possible, try to minimize pressure differences between the cabin and surrounding atmosphere since more strength equals more weight. The propulsion systems are likely to be very different so I'm not worried about that part yet, though if you have thoughts to share on that then go ahead and include it. [Answer] It seems to me that the trick is to go deeper into Jupiter to get denser atmosphere, not to try to climb to reduce gravitational pull. Requiring lift to equal gravitational pull, we are concerned with: $${{Sv^2}\over m} \sim {g\over \rho}$$ Where $S$ is the wing surface area, $v$ the speed, $m$ the aircraft mass, $g$ gravity and $\rho$ density. This basically states what you would expect: more gravity makes it harder to fly, and higher pressure makes it easier. For the Jovian atmosphere, See for example [Wikipedia](https://en.wikipedia.org/wiki/Atmosphere_of_Jupiter). Jupiter does not really have a surface, at least until you get deep down the the metallic hydrogen core. > > "the pressure level of 10 bars, at an altitude of about 90 km below > the 1 bar with a temperature of around 340 K, is commonly treated as > the base of the troposphere" > > > Noting that the radius of Jupiter is over 70,000 km, this altitude will still effectively have the same gravity as the 1 bar level, i.e. around 2.5g. With 10x the pressure and much the same temperature as Earth, but a hydrogen composition, overall atmospheric density will still be lower by around a third. So at that altitude, you've got your work cut out. However, it seems to me do-able; not unlike flying at earth gravity at 0.25 atmospheres, which is around 50,000ft. However, it is not the same as flying at 50,000 ft here: remember the pressure is 10x higher. This will have implications on the structural engineering. Alternatively, if one keeps going deeper, behaviour may become more like that of a submarine in a liquid: build a pressure vessel that has neutral buoyancy. Follow up remark. The main problem with flying is that there is nowhere to land. The "aircraft" will need to sustain "flight" indefinitely or descend to a level where it is neutrally buoyant. [Answer] Something other answers don't seem to have mentioned yet: Jupiter has some pretty wild winds. The red spot you see in pictures is a storm that is literally the size of the Earth. So, I feel like the important question here is not whether you could design a craft that can move about in Jupiter's atmosphere, but whether it can stay stable. From this article I found after typing in "Jupiter winds" on google: > > Jupiter has bands of wind and jet streams that crisscross along the surface of the planet and rotate at different speeds — sometimes differing by up to 220 miles per hour (100 meters per second). Many thought these streams might just exist on the planet’s exterior, a bit like the winds on Earth. But now, researchers think the jet streams actually stretch deep within the planet > > > Link: <https://www.theverge.com/2018/3/7/17085462/nasa-juno-spacecraft-jupiter-fluids-winds> [Answer] Overall: I would say that powered flight is at the outside edge of feasible on Jupiter. How would you design a aircraft for Jupiter? 1) Dirigible using heated hydrogen for lift. While you could manage buoyancy, the end result would be not usable. Not sure how your floating cities are supposed to work, but even using the unobtanium for lift still has a problem. Landing these may be impossible due to high wind velocity (350 kph being common). If the cities are allowed to move with the air currents you still have problems controlling flight in the intervening space to avoid being blown off course. Due to the size of Jupiter balloon flight will be very slow to cover significant fractions of the planetary circumference. 2) Airplane. You need a lift / air-frame mass ratio greater then 2.5 to keep aloft and carry cargo. A heavy lift plane C-5 Galaxy has a maximum take-off weight of 769,000 lbs and dry weight of 380,00 pounds a ratio of 2.02 : 1 -- s, A 747-400 is 2.22:1, Airbus A310-300F is also 2.21:1 So, given a little more attention to better materials, etc. a lift ratio over 2.5 is likely feasible (though a bit expensive), not that the net cargo capacity will likely be fairly poor. You still have a pretty marginal design though. Is there anything you can do? Yes, assist the plane at take and landing just like they do on an aircraft carrier. It may expensive, but it is cheaper than building sky bridges. What about fuel? For a hydrogen atmosphere, you need to carry an oxidizer. But you have a real problem, the weight is really working against you. Burning hydrocarbons on earth, you carry only a small mass fraction of the end products of combustion. Both C02 and H2O are mostly oxygen by weight, so you get most of the mass from the atmosphere. And on earth a 2.2 lift ratio allows you to carry a lot fuel (perhaps 30 tons or so) and still carry a reasonable amount of cargo. On Jupiter, the physics and chemistry are both working against you pretty hard. Maybe it is time to make a nuclear air plane. The US air-force wanted some of these in the days before ICBM so that they keep planes in flight for weeks at a time. The nuclear plant that they liked used a molten salt reactor -- no heavy pressure containment vessel, and other advantages made this look at least feasible. A 747 requires about 90 MW for takeoff, about 45 MW for cruising -- this is small compared to a commercial nuclear plant. Anyway, [GE built a small (2.5 MW) molten salt reactor for testing](http://www.realclearscience.com/blog/2014/07/why_not_nuclear-powered_aircraft.html) and it was generally considered viable. Unfortunately I could not find any data re: the mass of this experimental reactor. They actually flew the reactor around, though they did not use it to operate the plane. Also for those keeping their fingers crossed, Lockheed Martin claims to have a [small fusion reactor available in a 100 MW prototype by 2025.](http://aviationweek.com/technology/skunk-works-reveals-compact-fusion-reactor-details) The only size claim I've seen is mentioned in the article in that it would fit on a truck. So, I would say that powered flight is at the outside edge of feasible on Jupiter. Larger designs in particular may be feasible as a nuclear plant does not necessarily scale up in a linear manner. Given the large size of Jupiter, airplanes would certainly be very desirable to reduce transportation times. Finally, some things that would be desirable for flight on Jupiter-- speed of sound would be roughly 3 times that of earth normal atmosphere (at the same temperature) because the molecules are very light, and the viscosity. Hydrogen has less than half the viscosity of air though helium is slightly higher than air, the overall mix should be a little less than half of air. So you get to cruise a lot faster for the same energy consumption. [Answer] Usable aircraft on Jupiter are very, very unlikely. Per [this fact sheet from NASA](http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html), an atmospheric pressure of 1 bar occurs at an equatorial radius of about 71 km, but the local gravity is about 2.5 $g$s. At this altitude, the atmospheric density is about .13 that of Earth, and local temperature is about -108 °C. In order to get the local gravity down to 1 g, it is necessary to rise to an altitude of $$h = 71 \text{ km} \times\sqrt{2.5} = 112 \text{ km}$$ As it happens, this occurs at an atmospheric pressure of 0.1 bar and a temperature of -161 °C. Ignoring temperature effects, this suggests that the density of the Jovian atmosphere at 0.1 bar will be about .013 that of Earth at sea level. As a comparison, ![](https://upload.wikimedia.org/wikipedia/commons/d/de/Atmosphere_model.png) shows a similar density occurring at about 90 km for terrestrial atmosphere. Since the NASA boundary for outer space is 100 km, it's hard to see how any aircraft, be it lighter or heavier than air, could function. The atmosphere is just too thin at altitudes with reasonable gravity. [Answer] There is no reason why a craft can't move through a fluid by using that fluid as reaction mass and using fluid dynamics to have shapes that are harder or easier to pass through the fluid in various orientations. That covers swimming as well as flying, and the appearance of whatever works for the chosen pressure, gravity, and other fluid properties might be something you would characterise as something else again. A basic glider shape will have a gliding effect. Add enough power and anything can fly, regardless of aerodynamics. Between the two is a practical design. For plausible SF ideas on the craft, you need to be more specific regarding the depth (outside pressure and composition) and range of operating environments. A previous answer assumed near-vacuum. I'd be more likely to envision high density, all, the way down to supercritical state. [Answer] you could fly a specially designed airplane on jupiter, but it would not be like one that flies on earth. Altitude is a matter of design, does it float on some limit of density? or use principles of lift? A bladder of less dense gas would float, but would need to be strong enough to not be crushed. This is not really a question of 'can' but rather 'what parameters need to be determined for a plane to fly?' As your question asks this, I would proffer: * A more rounded or spherical shape, possibly like an egg, to better distribute the forces on the hull. * Rigid delta wings, like a B2 Stealth, instead of protruding bird like wings like an airliner. * Propulsion would likely be rocket engines to gain the force needed to move in the atmospheric soup. ]
[Question] [ The government of Futurestan has finally decided to hear the voice of her people. It would seem that [the protriotors](https://worldbuilding.stackexchange.com/questions/18771/the-new-rioters-weapon-of-choice) access to malware, EMP-otovs, and weaponized angry glaring (and thermite. Lots of thermite) caused enough of a thorn in the government's side and generated enough of a presence that the government couldn't censor the media fast enough. Well, and there was that whole "the internet gaining sentience" thing. Either way the government has sat down to listen to their grievances, the biggest of which being a lack of toilets. Yes it would seem that the expensive and expansive process of carbon harvesting from waste and an expensive and expansive population have put a huge amount of stress on restroom facilities (this is the side of overpopulation that the media won't cover). But the government of Futurestan, along with its allied nations The Democratic People's Republic of the After Times and the United States of the Far Far Away, have managed to concoct a brilliant plan. Put them in space!!! Using dubious information obtained from the post-sentient internet (he prefers to be called Bob), they have learned that with a population density of New York (a legendary city from the before times) they could fit ~7 billion people into an area the size of the nation-state of Texas. Ignoring the cost of such a venture (a lot) and the difficulty of accomplishing such a task (high), the governments still ignore the most basic of problems with such a venture. ### Problem The government policy on who gets to go up in the space station, known as the Space Station, isn't so much a policy as it is "let's just sort of cram people in". Doing this with 8 or 9 people would be a problem, let alone ~7 billion. As long as you look sort of healthy and signed a waiver about explosive decompression, you were in. ### Question Assuming Space Station to be a scaled up (present day) New York inside a hermetically sealed box flying around in low Earth orbit (or whatever is a reasonable orbit so as not to interfere with cable television and the alignment of the moon), what would be the major problems faced by its citizens? ### Assumables: You can also assume that: 1. food and supplies are delivered at regular intervals in a quantity that would allow everyone on the station to lead a middle class lifestyle 2. there are enough jobs for everyone 3. there are enough toilets 4. this is physically possible 5. demographic information is similar to present day NYC for all intents and purposes, there just happens to be ~7 billion people rather than 8.4 million If you assume more things please state what you are assuming please. [Answer] Heat A space station of 7 billion people will need to get rid of the waste heat somehow. Vacuum is a fantastic insulator. Let's set a lower bound on the amount of heat that will need to be removed from the Space Station for 7 billion people. An [average resting adult male](http://www.engineeringtoolbox.com/metabolic-heat-persons-d_706.html) generates 100 watts of heat, multiply by 7 billion people and we have heat budget of 700 billion watts. Were this on earth and waste heat can simply be dumped "outside", it would take 142.1 million 1.5 ton AC units hooked up to colossal radiation panels to move that much heat and maintain a livable temperature. (The radiation panels are needed because there is no conduction or convection in space to get rid of the heat. It must be radiated away by IR radiation.) This is the minimum threshold for heat and does not include anyone who is exercising nor the waste heat generated by electronics or equipment, nor heat absorption from solar energy. Economic Incentives Why go up there in the first place? Access to a toilet might be a good reason but the [hedonistic treadmill](https://en.wikipedia.org/wiki/Hedonic_treadmill) will soon turn that luxury into a boring feature. Providing economic incentives to stay on the Space Station will need to be devised in the form of a manufacturing and/or services economy. It's reasonable that a civilization capable of building a space habitat for 7 billion people can also manipulate the orbit of asteroids to provide raw materials for manufacturing. Biological Disincentives Without artificial gravity (not stated in the OP) then the inhabitant's bodies will begin to [degrade fairly quickly](http://www.space.com/23017-weightlessness.html). Long term exposure to zero gravity may eventually preclude any chance of return to earth....though maybe that's the point? Making a station that spins shouldn't be too hard in the case we have a non-malevolent government. Bah! We're putting [7 billion people in orbit.](https://what-if.xkcd.com/7/) So many technological problems have been solved at this point that we can basically do whatever the hell we want. Feeding the population Reliance on ground based food deliveries is a recipes for disaster. A shipment will be missed. Support will probably, eventually disappear for reasons of political, economic, or ecological viability. Feeding 7 billion people takes tremendous amounts of resources. Getting that much food into orbit requires highly sophisticated techniques for production, shipping and transferal to orbit. [Answer] Heat as Green very excellently explained. Biological but not so much: I think those issues can be solved except that food, water and waste transfer would affect... Economics too as Green said but even more so: What is this station producing that it can trade with the rest of the world to an extent that it could fund itself and its 7 billion people? Food, air and water for 7 billion people being lifted off the Earth every day! Surely it isn't able to grow and recycle that much; We struggle to manage that now with the entire Earth at our disposal. If it doesn't achieve parity then it is a drain on Earth and probably an enormous one. That would make it a constant worry that Earth might cut back or even cut off support. ("Sorry guys, we really do want to keep sending you food we just don't have any left to spare. We feel really terrible about it. Bob bless.") That leads onto what I think would be the biggest existential problem: Vulnerability The Space Station would be utterly at the mercy of Earth and its political trends. One stroke of a pen and all 7 billion people will be starving or suffocating within weeks. This could be a president or a union or the effects of dissident rebels. Furthermore, the Earth's atmosphere is a very effective shield against small asteroids and cosmic rays. The Space Station won't have that luxury. Cosmic rays might be well shielded against but that could be very expensive (and therefore economized on). Asteroids are a different matter though: A moderately-sized (1 to 10m) asteroid moving at a few 10,000 miles per hour will likely cause enormous damage to the station - possibly killing millions. A medium-large asteroid (10 to 100m) would be like an atom bomb and might destroy it completely. The Earth is regularly struck by small meteorites. It is likely the Space Station would be too. Such strikes would clatter the entire structure. Such ringing thuds would signal a few thousand or million people have just died. They would be regular reminders that "The Big One" could come at any moment and then they would all be dead. People going stir crazy from these ever-present threats and the general isolation/entrapment would be a serious problem. There's vulnerability to sabotage too (perhaps from one of these crazies or some other fanatic): Air, water, power, food, orbital stability, etc. systems could all be catastrophically compromised if someone had the will to do so (unless very clever and careful safeguards were put in place). Earth withdrawing or scaling back its support will be the biggest threat though because I think it would be inevitable. Some Numbers Average mass of a person 80.7kg, x7 billion = 565 million tonnes of people The ISS mass is 370 tonnes and can accommodate 6 people, so 61.7 tonnes per person, x7 billion = 432 billion tonnes. The whole station would have a mass of at least a tenth that: 43 billion tonnes. (Water usage in the western world is at least 100 litres per person per day, x7 billion = 700 million tonnes of water per day. This would surely be recycled though but the machinery to recycle that much water on a daily basis would be impressive indeed.) Average food consumption in the US: 1 tonne per year. Say a tenth of that = 0.3kg per day, x7 billion = 2 million tonnes of food per day. To deliver that by chemical rocket would be very deleterious to Earth's atmosphere. You're building a 43 billion tonne space station and transporting 565 million tonnes of people up to it and then 2 million tonnes of food every day. A space elevator would be the only option. But the elevator would then be a very serious single point of failure; Any malfunction in the elevator (including, Bob forbid, a breakage) could quickly spell extinction to those on board. Conclusion If the Space Station cannot achieve self-sufficiency (at least its own food) it would start to look very much like an orbiting death camp. [Answer] With the technology to put 7 billion people into space, there is no particular need to cram them all into a space structure the size of Texas. Larger ones are not only safer and more pleasant for the occupants, but also have sufficient land area to grow food and have somewhat natural ecological cycles to ensure their continued operation independent of the Earth. This is important since (as pointed out) the Earth might not be a dependable supplier for these colonists, and if the population pressure on Earth is so great that everyone has run out of toilets, then the citizens and politicians on Earth might prefer to spend their resources on other things than feeding a space colony. To give you some idea, the Island Three concept of Gerald K O'Neil would be 5 miles (8.0 km) in diameter and 20 miles (32 km) long; a McKendree cylinder is designed to be 460 km (290 mi) in radius and 4600 km (2900 mi) in length, containing 13 million square kilometers (5.1 million square miles) of living space, nearly as much land area as that of Russia, while the larges conceivable structure is a Bishop Ring, 1,000 km (620 mi) in radius and 500 km (310 mi) in width, containing 3 million square kilometers (1.2 million square miles) of living space, comparable to the area of India. (data cribbed from Wikipedia) Multiple colonies can be built from materials extracted from asteroids, as well as mined from the Moon, the various moons of the Gas Giant planets and even Mercury. Solar energy is plentiful out to the orbit of Mars, so solar mirrors and solar panels can be scaled to provide sufficient light to grow crops, enjoy life inside and generate sufficient electrical power. Heat rejection and keeping the life support systems closed are the two main technological issues of a space colony of any size. For the most part, larger radiators provide the cooling, and since we are in an environment where delivering 7 billion people into orbit isn't an issue, keeping the life support system(s) topped up with supplies and raw material should not be an issue; asteroids are prime sources of metals, silicon and carbon compounds; the moon Europa has 3X the water as all the oceans of Earth combined, and nitrogen can be scooped from the moon Titan. If we want to have abundant spec travel (and can hand wave 3He Fusion), then fuel for millions of years of spec travel can be extracted from the atmosphere of Saturn and Uranus. The big social issue will have to do with population. Each colony will have limits to how many people can be aboard (life support, available crop "land" and heat rejection define the limits), so colony structures might start out relatively empty. As the population naturally grows, a new structure might be started, and the existing colony becomes crowded in the mean time (fewer toilets) until the new colony is finished and the life support started, then the population of the first colony crashes as people move out to the new colony. A secondary social issue might be the development of a clan or tribal mentality if the colony structures are designed with multiple "bubbles" or chambers to prevent any individual event from catastrophically destroying the colony or killing all aboard. "Stay safe in your bubble" might become a watch word, and people interact between bubbles via a network system of some sort. Real interaction become rare and the bubbles become more insular in nature and isolationist. Of course since each space colony is also an independent "world" of its own, there may also be balkanization between the various polities in space, which will allow Earth or the most competitive colony to divide and conquer the various "nations" in space. Lastly, since a space colony can conceivably be designed to pack people in a compact 3D structure (without gravity, or variable gravity if there are multiple levels in the rotating structure), then social and political structures will have to be designed to allow for efficient functioning of large numbers of people in a very small space (Manhattan at noon rather than the average NYC population density). You might have a billion people in a rather small asteroid under this arrangement, rather than them spread out like nomads on the pre contact Great Plains (which would imply other, rather different social, economic and political structures). ]
[Question] [ Lets say there is a fire on a zero-g space station (no efforts have been made to give gravity to the structure and it's far enough away from any planet/sun that gravity is negligible). It is contained and does not breach any of the structure itself (so ignore the vacuum elements here). For simplicity, lets assume it's a candle sitting in the middle of a contained room (no air is entering and air circulation is minimal). Assume 'air' has the standard earth like composition. 2 part question: 1. Heat rises on Earth as the hot air is significantly less dense than cool air. A flickering flame flickers upwards for the same reason. However in a zero-g environemnt, there really is no up. So what does a zero-g flame visually look like? 2. Heat rising also fuels the fire by dragging in more oxygen as the hot air rises giving room for new oxygen rich air to move in behind it. Without this cycle, to fuel itself and without some other mechanism to cycle the air, how long would a fire feasibly burn for? Would it consume all the oxygen in a room before burning out, or would it simply consume the oxygen in the immediate area around the flame and burn itself out before the oxygen in the room is fully consumed? And an extention to #2 - would it be possible that the fire would sit in a state where it's ready to ignite the second enough oxygen was present (or very slowly burn as the remaining oxygen in the room diffuses)? [Answer] Without gravity to constrain the flames and give us the "lighter"/"heavier" aspects of "hot air is lighter than cold air", there are no convection currents (at least not the "upward" ones we're familiar with) to give the flame its familiar flame shape; the result is that the flame burns in a sphere. These literal fireballs have even been observed to exist without visible fuel or ignition source, and have confounded experts in combustion. Here's a [really cool video](http://youtu.be/9zdD7lfB0Fs) of exactly this. A side-effect of this fact is that with the flames burning in literally all directions, rather than being pulled down toward its fuel, it burns slower in micro-gravity than it does under "normal" gravity. You do end up with a low-pressure zone as the hot air expands, which pulls in more oxygen to keep the flames going (strictly speaking, "convection currents", just not "upward" as we're used to), so it may actually burn far more efficiently as it slowly consumes its fuel (this last bit is my own speculation on my completely non-expert review of what I could find on the subject). To answer the second part of your question: Yes, in exactly the same way the same situation can happen here on Earth. Basically you have to have something hot enough to combust, but held in a state where there's not enough oxygen to actually do so; the moment you add that oxygen, however, you get what firefighters call a [backdraft](http://en.wikipedia.org/wiki/Backdraft) and/or [flashover](http://en.wikipedia.org/wiki/Flashover). This type of situation could easily exist in e.g. a sealed (or mostly-sealed) storage room after a slow-burning fireball goes unnoticed and consumes the oxygen in the room, but lingers as a hot ember until someone opens the door and lets the heated air rush out, replaced by the cooler, oxygen-rich air the poor sap has just turned loose. (There are other ways to get the same effect, this is just one example that occurs to me off the top of my head. Read up on backdrafts and flashovers to learn more and adapt the situation to your needs.) [Answer] First, [this](http://www.youtube.com/watch?v=Q58-la_yAB4) is what fire looks like in micro-gravity: (what we often mistakenly call zero-g) Secondly, air will still be sucked towards the flame via the pressure difference created by the fire consuming the local oxygen, but the flame will not be as hot without the effects provided by gravity. (Note how pale the flame is in the above video.) Disclaimer: I am not a scientist, and I may have grossly misused several of the above terms. ]
[Question] [ Any curved space is approximately Euclidean on small enough scales, so for a sufficiently large characteristic length (significantly larger than the radius of the smallest real stars) the answer is obviously "yes". But what about more extreme cases? Say, if the characteristic length is 1km? That's large enough that you drop humans into such a universe and they'd survive, but small enough to seriously screw up the geometry of a planet--or a star. A hyperbolic sphere has much more volume, thus much more mass packed closely together, than a Euclidean sphere of equal radius... but the force of gravity also decreases much more quickly with distance, so it's not obvious that results in equivalent pressures for either equal mass or equal radius; and for a given core pressure, there will be a much larger radiative surface, which will totally screw with the equilibrium temperature and gravity-radiation pressure balance. So, yeah. Do stars work in strongly curved hyperbolic space? [Answer] I think sphennings is more or less correct, but just wanted to expound on their answer with a few more quantitative comparisons. As a warning this will involve some fairly advanced math in the middle section, but I'll end with a few plots that should be parseable even if you're not well versed in the math. # The Gritty Math First off, we have to define how exactly gravity is going to work in hyperbolic space-- I assume we want something that works exactly the same as the gravity you're used to in flat space in the limit that curvature goes to zero. Luckily, general relativity provides a pretty straightforward way to calculate this by just assuming that our metric obeys so called [hyperspherical coordinates](https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric#Hyperspherical_coordinates) and using linearized gravity in the non-relativistic limit: $$g\_{\mu\nu} = g^{(0)}\_{\mu \nu} + g^{(1)}\_{\mu \nu}$$ with $$ \|g^{(0)}\_{\mu \nu}\| \gg \|g^{(1)}\_{\mu \nu}\| $$ and $$ g^{(0)}\_{\mu \nu} = \begin{bmatrix} -1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & S^2(r) & 0\\ 0 & 0 & 0 &S^2(r)sin^2(\theta) \\ \end{bmatrix} \quad $$ Where $$ S(r) = \sqrt{\|k\|}^{-1} sinh(\sqrt{\|k\|}r)$$ and our coordinates $(t,r,\theta,\phi)$ give the time, distance to origin along the shortest path, and polar and azimuthal coordinates for this path with respect to its intersection at the origin. You have to be a little careful with how you think about $\phi$ and $\theta$ because the standard euclidean definitions get messed up-- traveling north 1 mile and then west 1 mile is no longer the same as traveling west 1 mile and then north 1 mile! Meanwhile, $k < 0$ has units of length$^{-2}$ and is a measure of how curved the space is-- as $k \to 0$, it becomes Euclidean. As $\sqrt{\|k\|}^{-1}$ approaches the length scale of physical processes, it will start to affect them in a way that changes them significantly from the Euclidean result. We shall see that as sphennings says, the first major impact this has is on density, not nuclear processes directly. Now this is fine and dandy but unfortunately, I'm too lazy to deal with all the requisite Christoffel symbols and geodesic equations right now so instead I'm going to wildly wave my hands in the air and say that what we want is the following field equation, which based off a few quick calculations I made seems to be reasonable: $$\frac{1}{\sqrt{\|g^{(0)}\|}}\partial\_i (\sqrt{\|g^{(0)}\|}g\_{(0)}^{ij}\partial\_j \Phi) = 4\pi G \rho$$ Where $G$ is the gravitational constant, $\rho$ is mass density, and $\Phi$ is the gravitational potential that gives rise to gravitational acceleration like so: $$\mathbf{a} = -\nabla \Phi$$ Why this equation? Well, the operator in the top equation is known as the [Laplace-Beltrami operator](https://en.wikipedia.org/wiki/Laplace%E2%80%93Beltrami_operator) and is basically an extension of the well known Laplacian operator to funkier geometries. And if you replace it with the Laplacian, you get $\nabla^2 \Phi = 4 \pi G \rho$-- which is exactly the formula for the Newtonian gravitational potential in Euclidean space. Now let's try to use this a bit more, by assuming our solution is spherically symmetric-- then our equations become: $$\frac{1}{S^2(r)}\partial\_r (S^2(r) \partial\_r \Phi) = 4\pi G \rho$$ $$a\_r = -\partial\_r \Phi$$ Note that if $S(r)=r$, this is exactly the same as what we expect from Newtonian mechanics-- and indeed, if the $k\to 0$ limit is taken, this is what $S$ reduces to. Now, if you haven't already, you should check out [this answer](https://worldbuilding.stackexchange.com/questions/209444/is-there-a-mathematical-way-to-calculate-the-density-volume-etc-of-a-planet-ju/209532?noredirect=1#comment647552_209532) of mine, which details the process you can use to find the radius of a planet given it's mass by leveraging the gravitation field equation and hydrostatic equilibrium. I'll spare the gory details, but it's relatively straightforward to show that we can use pretty much the same equations as in that answer, only the $r^2$'s occurring in them should be replaced with $S^2(r)$. The result is basically what many were speculating-- the hyperbolic curvature of space leads your gaussian spherical surfaces growing extremely quickly in surface area so that the gravitational field is less strong than you would get for the same packing in Euclidean space. In math-ier words, we can show that $$a\_r(r) = -\frac{4\pi G}{S^2(r)} \int\_0^{r} S^2(r')\rho(r')dr'$$ so if $S$ is an extremely fast growing function of $r$, the evaluation of it at $r$ will outpace the average of it over the density profile and the gravitational acceleration will go down. If you really like math, this argument could probably be made more formal with some well-justified restrictions on $\rho$ and [Jensen's inequality](https://en.wikipedia.org/wiki/Jensen%27s_inequality). # Fun Plots If none of that made any sense to you, fret not-- this section should be more understandable. As I said, the net result is that for a given amount of mass, it's more difficult to pack it densely in hyperbolic space. Since nuclear processes that power fusion require very high densities, this means that a very hyperbolic universe, especially one that's expanding quickly, will have more difficulty forming stars. That being said, I'm neglecting thermal effects here so it's possible that those will play a large role for stars undergoing fusion. These next few plots are calculated using the program from my other answer modified for hyperbolic space for a planet made of 30% iron, 70% silicates with a mass of $6 \times 10^{24} kg$-- you may recognize this as Earth. For this, I have varied $k$ a bit and you can see how more negative values lead to a smaller yet less dense planet given the same mass. Although keep in mind the planet is only small if you tunnel straight through it-- if you walk along the surface it will still seem big! [![enter image description here](https://i.stack.imgur.com/JNjtt.png)](https://i.stack.imgur.com/JNjtt.png) [![enter image description here](https://i.stack.imgur.com/667Yi.png)](https://i.stack.imgur.com/667Yi.png) I would include more extreme plots here but unfortunately my code has been running into numerical gremlins which is why I did a planet density profile instead of a star. However, there should be enough stuff here for you to play around with it on your own if you wish! [Answer] My back of envelop wild guess is that in a hyperbolic universe it would be harder to pack things close enough to sustain fusion. It's not the amount of mass within a given radius that causes hydrogen to fuse it's the likelihood of colliding with another hydrogen atom. In a hyperbolic universe you can fit far more stuff within a given radius without packing it any tighter. This would reduce the likelihood of collisions, and fusion events. Since you can pack more stuff in a given radius without packing it tighter, if you continue down this barely-scientific vein it would be easier to form a black hole. I'll leave analyzing the interaction between harder-to-pack-tightness, easier-to-get-closeness and curvature, as an exercise for readers with far more math and physics chops than I have. ]
[Question] [ I've seen [Which is easier to develop: a piston prop engine or a jet engine?](https://worldbuilding.stackexchange.com/questions/168295/which-is-easier-to-develop-a-piston-prop-engine-or-a-jet-engine) and my own [Effects of ~10atm pressure on engine design](https://worldbuilding.stackexchange.com/questions/146862/effects-of-10atm-pressure-on-engine-design) neither of which answers this. Would different atmospheric density, composition, etc. ever be able to achieve this? Are there conditions under which no practical aircraft could reach the speed at which jets are a significant advantage in the first place? PS. And not conditions where rockets have an advantage over both. [Answer] Low oxygen atmosphere or really rough terrain 1. Low oxygen atmosphere Jet engines need at least some oxygen to operate. As [the answers here](https://aviation.stackexchange.com/questions/10034/if-jets-carried-pure-o2-to-use-for-combustion-would-they-be-more-efficient) illustrate, they don't need much oxygen, but there's a point where the atmosphere has so little oxygen that a jet engine can't operate efficiently. The "combustion" part of the diagram below will peter out. [![Schematic of turbofan engine](https://i.stack.imgur.com/nJlD3.png)](https://i.stack.imgur.com/nJlD3.png) On Earth, propeller-driven aircraft also operate using combustion engines, either a jet engine (turboprop) or traditional internal combustion. Obviously, they would also be affected by a lack of oxygen. You basically have two options: either bring your own oxygen (i.e. use a rocket) or find another way to power the propeller. There are projects at various stages of development to [use electricity to power planes](https://en.wikipedia.org/wiki/Electric_aircraft). 2. Really rough terrain You don't see many jet aircraft in the backcountry of Alaska (though [there are exceptions](https://arstechnica.com/cars/2018/08/one-man-designed-and-built-the-ultimate-bush-plane/)). If you want a reasonably priced plane that can carry passengers and freight through small dirt airstrips, you're going to want a prop. They're easier to repair, cheaper to operate, and less susceptible to foreign object debris. More broadly, you should think about the missions you want aircraft to accomplish in your world. If most aviation is regional and consists of ferrying goods and passengers over short distances in rough terrain, a prop is a natural fit. Supersonic travel across oceans would require more in-story explanation for why you're not using a jet. [Answer] The primary advantage of a propeller is that it is more efficient than a jet engine. Moving large masses of air slowly is simply more efficient than moving small masses of air quickly. In other applications we see helicopters are far more fuel efficient in hover than a Harrier "jump jet", or propeller driven ships more efficient than pump jets or other forms of water jet propulsion. In fact, you might even wonder why use a jet engine at all, given these factors, but most users who have other considerations like speed, the need for a very compact powerplant, silence in operation (pump jets) and so on find these considerations have far greater priority than fuel efficiency. [![enter image description here](https://i.stack.imgur.com/zc4MK.jpg)](https://i.stack.imgur.com/zc4MK.jpg) GE 36 Unducted Fan prototype Unfortunatly I can no longer find the link outlining performance, but back in the 1990's there was experimentation with something called an "unducted fan", which was a form of turboprop which dispensed with the usual gearbox and used the turbine to drive the unducted fan blades with minimal speed reduction. While this was extremely noisy (the main reason that it was never adopted), there were great gains in fuel efficiency, and the large area that the unducted fan could "grab" when running gave the plane far superior performance in things like short field take off. The Soviet Union and now Russia have done more development work on unducted fan engines (they have far less stringent requirements for noise reduction, and most of their engines seem to be used on military transports) [![enter image description here](https://i.stack.imgur.com/SmIyy.jpg)](https://i.stack.imgur.com/SmIyy.jpg) Antonov AN-70 prototype [![enter image description here](https://i.stack.imgur.com/Fo8v3.jpg)](https://i.stack.imgur.com/Fo8v3.jpg) Progress D-27 Propfan engine So the primary advantages of propellers is their efficiency (within the correct flight regime - no propeller can power a supersonic aircraft, for example) and greater performance in certain aspects, like short field take off. The power plant is actually irrelevant, model aircraft are powered by rubber bands, two stroke ["glow plug"](https://www.rc-airplane-world.com/glow-plugs-for-rc.html) engines and electric motors, while most common propeller driven aircraft are powered by piston or turbine engines. A [steam engine](https://www.flyingmag.com/blogs/fly-wire/steam-powered-airplane-anyone/) for propeller aircraft was developed in the 1930's, the Germans used [diesel engines](https://en.wikipedia.org/wiki/Junkers_Jumo_205) for a period during that time as well, and any other motive power source, like a [Stirling engine](https://deepresource.wordpress.com/2019/03/17/stirling-motor-for-flying/) could be used as well. ]
[Question] [ On an Earth-like planet, an intelligent species evolved in symbiosis with another species that lives in their digestive system and act as the microbial gut flora in humans do. What implementations of macro-scale creatures (such as insects or something similar) would allow them to take over as much of the functionality in their host's digestive system as possible? [Answer] > > (...) instead of having bacteria and enzymes break down foood, it would be a lot of small insects or insect-like things living inside of a creature's stomach (...) > > > The stomach is a very harsh environment for most bacteria. Usually when something manages to live there, it's Heliobacter pylori, which gives you stomach ulcers. Some worms pass through the stomach alive, but practically always in some egg or larval stage where they are protected against the acid. They mature somewhere else, usually the bowels or liver. The one place in the human digestive system where multicellular lice can thrive without damaging the host (too much) is the intestines. Insects could live there, going in and out by yes exactly that passage. When we lose our gut flora, we get diarhea, which is not nice. In an environment where there is no such flora, land vertebrates could develop a symbiotic relationship with insects that enter their intestines and eat or remove the feces. Good candidates for this are non-flying eusocial insects such as ants and termites (the latter build their homes out of excrement anyway), or dung beetles. If you don't like the idea and really want a stomach replacement... Imagine an animal whose stomach is innefective as a species trait. The function of the dtomsch is to break stuff at a molecular level, mostly protheins. Insects could either visit or live in that creature's stomach, eating stuff and... Well... Leaving out very aminoacid rich feces. The insects provide the breakdown otherwise given by a stomach, while the host provides shelter and a toilet. [Answer] # Intestinal worms > > Intestinal worms are properly called “helminths,” which most > dictionaries will tell you are parasites. Exploiting their hosts, > draining resources, sucking the life out of the body – that’s what > parasites do, by definition...Helminths have been a part of the > ecosystem of the body for so many millions of years that they have > become an integral part of that system. Mutualistic helminths help > regulate immune function, stimulating our body to build regulatory > networks of immune cells that decrease general inflammation without > hurting our immune system’s ability to respond to danger. In addition, > these helminths produce their own array of anti-inflammatory molecules > and give our immune systems much needed exercise, all of which > decreases inflammation. ([ref](http://theconversation.com/they-might-sound-gross-but-intestinal-worms-can-actually-be-good-for-you-49868)) > > > Our existing Earth systems are not quite what you're looking for. [Some worms](https://www.britannica.com/animal/worm) (the kind that change into moths and butterflies) are insects, though helminths are not. You could change this for your story. [Intestinal worms have their own microflora](https://www.livescience.com/62026-parasitic-worms-gut-bacteria.html) so even if the worms do not take over the jobs of gut bacteria, they could (in an alien ecosystem) be a necessary intermediary. > > It's a Russian nesting doll of sorts: Parasitic bugs that live in the > human gut have their own set of gut bugs inside their intestines... > "We were amazed to find that whipworms have their own distinct > microflora" and — similar to humans — that the bacteria appear to aid > in the parasite's health...The bacteria inside the parasite's > intestine appear to be necessary for its growth...What's more, > whipworms appear to be able to alter the gut bacteria of their human > hosts to aid in their own survival. ([ref](https://www.livescience.com/62026-parasitic-worms-gut-bacteria.html)) > > > If you really want an insect, create an insect worm that only goes through metamorphosis after leaving its host. Or expand your label of "insect" to include worms. Multiple species of worms on Earth are already adapted for the gut of higher animals so it would not be a stretch to create a species that fits your other needs. [Answer] Symbiosis means living together. There are different types of symbiosis: (1) mutualism - both organisms benefit; (2) commensalism in which one organism benefits from the interaction and the other is unaffected by the interaction; (3) amensalism in which one organism is harmed by the interaction but the other organism is not affected (no benefit); and (4) parasitism in which one organism is harmed and the other benefits. Predation is sometimes also considered a symbiotic relationship. Mutualism and parasitism are all possible symbiotic relationships that would work for your scenario. If your sentient symbiont imparted some evolutionary advantage to its host insect then the relationship would be mutualism. If the symbiont simply used the insect as an intermediate host for its larvae and took sustenance from it without providing any advantage then that relationship would be parasitic. It seems difficult to me to come up with a situation that would make the evolution of a sentient mutualistic organism. Obviously there are extant examples in science fiction (DS9's Trills) but you will have to think this through very carefully to make it believable. You have to imagine the conditions that would warrant the evolution of the symbiosis first. Actually that WILL BE the hardest part, I think. After that you can use a basic Parasitology textbook from your local library as a starting point for coming up with a design for the details of your sentient symbiont be it a mutualist or parasite. The text can give you numerous examples of parasite life cycles and interactions with hosts. All of this would need to be worked out closely to be convincing. Certainly there are a plethora of life cycles, physiologies, and morphologies that could be taken from examples here on Earth. Those details could make your stories interesting. I hope this helps. ]
[Question] [ This is part of a series of questions about biological hydraulics, the fist one being [here](https://worldbuilding.stackexchange.com/questions/111528/would-biological-hydraulics-be-worth-evolving-in-tetrapods). My tetrapods have hydraulics in the thighs of their hind legs. To push or pull fluid from closed chambers in the legs, muscles are going to contract either in the legs themselves or the abdomen. As hydraulic fluid, I am thinking of using either blood or lymph from the circulatory or lymphatic system, as both are closed. Alternatively, there could be a reservoir for the sole purpose of storing hydraulic fluid, but I am unsure over the efficiency with this. All of them have the following in common: * Four chambered heart * Warm blood * A closed circulatory and a separate closed lymphatic-like system * A two chambered lymphatic heart-like organ below the true heart to pump lymph * Small, rigid lungs with a unidirectional pattern of breathing * Four respiratory airsacs * Endoskeleton with four limbs, a skull, and one to two tails Arthropods and some other invertebrates do use their hemolymph to push themselves, but I am unsure of whether this will change for vertebrates with complex hearts and closed circulatory systems. [Answer] The fluid would need to be able to be moved quickly, without additional "side effects" like blood pressure loss, sudden changes in white blood cell levels or such. Therefore, use a dedicated liquid, possibly evolved from synovial fluid (the "grease" secreted in our joints that makes them move smoothly). It may be just water (with some mineral salts to retain body-neutral pH) which can be used for sustenance when required - dehydration would reduce mobility, but should be easily avoided. While bladders are a fairly common solution, they aren't optimal for moving liquid quickly and under pressure. I'd suggest a specific tissue that is a mix of skeletal muscle and Corpus Spongiosum, a spongy tissue that can fill with liquid. The muscle could squeeze the organ ejecting the liquid at a quite high pressure on demand, or relax and absorb any influx. And instead of one centralized reservoir, multiple smaller ones distributed over the body could support whatever "hydraulic actuators" you design. That way damaging one of these doesn't completely cripple the creature but just restricts this particular joint/actuator. (breaking any hydraulic element in a hydraulic system/machine causes the whole thing to stop, with loss of pressure. Not something welcome in animals!) [Answer] Alas, I don't think it's a worthwhile trait. It was recently found that Blue Fin Tuna fish have a biological analog of a canonical hydraulic system. The muscles pressurize the liquid, which helps change the fins’ shape and position for swimming and maneuvering control during hunting. the researchers who found this confirmed it was indeed lymph fluid. However this is on a much smaller scale and moving a lot less pressure then what you need it to do. And also not a Tetrapod, Willk presented another creature that uses hydraulics, but both of these live underwater. This is most likely because they need the extra water pressure to allow these fine control units to utilise the hydraulic pressure. (Yes this is an assumption, but stay with me.) Realistically if it was worth doing then we probably would have seen it happen more often. Evolution means adapting to survive (at its most basic level; please don't shout at me for this simplification) if they were more efficient then they would be used, but the pressure required to have a noticeable effect when compared to conventional muscle structures are really quite high, then you'd need an organic material that is capable of holding that pressure so that it can be used. The only real benefit to being stronger is fighting, every example of life we have (which being only earth is actually massive and quite limited at the same time) shows that the ones that survive are usually the ones that have exerted the least energy to do so, or at least been the most efficient about it. Therefore if it was efficient then we would see it more often. I know This doesn't answer you question, but hopefully it might help. [Answer] Perhaps you could use something similar to what spiders use to extend their legs? > > “A remarkable and effective hydraulic mechanism is found in the legs of spiders, which have muscles to flex the joints but none to extend them. Spiders stretch their legs by pumping fluid into them. When a spider gets ready to jump, it generates, for a fraction of a second, excess pressure of up to 60 percent of an atmosphere. The legs extend in order to accommodate more fluid.” (Tributsch 1984:59) > > > <https://asknature.org/strategy/legs-use-hydraulics/#.Ww2rOEgvzAQ> [Answer] Store the fluid in the leg. The leg has chambers. You can adjust chamber size with muscles to expel fluid to adjacent chambers (contract muscles with valve open) or increase leg rigidity (contract muscle against closed valve). Fluid can be moved among the various leg chambers to achieve any desired combination of rigidity / movement / rotation. Leg fluid chambers are closed off from the rest of the body as well as from each other. The loss of one leg to a predator will not cause exsanguination from contiguous fluid filled body spaces. The loss of a leg segment will render the leg shorter but with the valve leading to the lost segment closed, the rest of the leg can still function to some degree. ]
[Question] [ I'm inspired by the comments discussion on a (now deleted) question by XandarTheZenon. We're preconditioned to think in terms of a 2-sex lifeform, which is natural with diploid genetic material, and sexes that specialize with different reproductive strategies. This often leads to species that have sexual dimorphism. (At the very least, the sex organs are dimorphic.) But that's not alien enough. Why else would an animal-like species have different body plans within one species? In particular, it would not have the male/female division that Earth macrofauna life has. Reproduction could have a different number of sexes, or at least doesn't have the same kind of division where one partner invests most of the energy and sustenance and the other is non-essential to development, with different body plans and behavior evolving from that original source of difference. How can an alien species have more than one body plan (and behavioral traits to match) yet individuals of all types are needed to make a family? A human biologist would not find it immediately obvious that these are the same species at all. But there's a sound reason why there are different forms and furthermore they are all necessary as part of a family unit, rather than just being different lifestyles. [Answer] The more social a species is, the more beneficial polymorphism becomes. A good example for extreme social polymorphism would be termites. Not only do they have the queen/male/worker division found in ants and bees, some species have many different kinds of specialized soldiers, ranging from melee fighters with big mandibles, guards with oversized heads that act as living doors, acid-spewing ranged attackers, and exploding chemical kamikaze bombers. Workers can include foragers, tower builders, diggers, nurses that take care of the children, grooms that tend to the king and queen, and farmers that cultivate fungi. Some species can have over 10 distinct castes! A [eusocial](https://en.wikipedia.org/wiki/Eusociality) intelligent alien species might have even more specialists — a scientist caste, a military strategist caste, a communications caste, a data entry caste... Really, any specialized jobs we have as humans could potentially lead to a specialized caste in such a species. Polymorphism can also allow different members of a less-social species to specialize in different lifestyles (consuming different kinds of foods, for instance) in order to minimize competition. However, this situation is often unstable in an evolutionary sense — unless it is the male and female morphs diverging into different lifestyles but coming back together to reproduce, it will often result in the morphs diverging into separate species. Reproduction rarely requires more than two sexes. The main function of sexual reproduction is to recombine DNA, which you get just fine from two sexes. The minor benefit you get from adding another DNA source in the mix generally doesn't outweigh the complexity of having to arrange a threesome every time you want to reproduce. That doesn't mean it can't happen, but there's a good reason why on Earth at least, one to two sexes is the norm. [Answer] 3 different members needed for reproduction Perhaps not exactly 3 genders, but here on Earth we have many examples of 3 different organic entities needed for a successful reproduction: for example, the wasps of the genus Glyptapanteles, whose females inject their eggs into living caterpillars. There you need for the reproduction a male wasp, a female wasp, and a third entity that performs the incubation and feeds the babies (the caterpillar). Yes, this is a dramatic example (the caterpillar dies), but it is not so bizarre to think of an alien species needing 3 elements to be involved in the reproduction process: two of them providing the ADN (or its equivalent) and the third one only providing the incubation (hopefully without being damaged in the process). In that case, you could have the same species but with 3 different specialized functions: the male, the female, and the carrier, and you would not be able to create a baby without any of them. ]
[Question] [ From a science-fiction development perspective I am looking for some plausible answer for the following: What conditions (the more permanent, the better) would make for a bronze sky? All the better, could we be currently creating those conditions? For instance, the sky is typically blue based on the current conditions of our atmosphere and light. What conditions would make orange/brown appearance more prominent? Dull, lacking life. Technically, a reddish-orange color would be acceptable too. Either the sun itself or degenerate (or even natural) conditions can contribute to this. [Answer] Turns out this is happening- right now, on this planet, in reality. All you need is some smog. This photo from Beijing last year looks rather bronze-ish to orange-ish I think. [![enter image description here](https://i.stack.imgur.com/d3PK4.jpg)](https://i.stack.imgur.com/d3PK4.jpg) ([image source](http://www.isciencetimes.com/articles/6696/20140117/beijing-smog-televised-sunrise-tiananmen-square-china.htm): International Science Times) [Answer] Dust/fines in the atmosphere would be able to do it. [Mars has a reddish sky](https://en.wikipedia.org/wiki/Mars_surface_color#Red_skies_on_Mars) because of this. The reason is that the dust particles in the atmosphere absorb sunlight in the 0.4-0.6 µm range, giving it a red tint. Could we do it? It would be harder on Earth, as the moisture in the air would collect around the dust and come down as rain. You might get it to work for a little while, especially if it was super fine dust (fines) up really really high, but our weather would clear it up again before to long. [Answer] The simplest way to achieve this is just have the planet in orbit around a cooler (redder) star than our sun. You can adjust the orbit to still be in the habitable band and the incoming red light would color the whole sky that way. The next best solution would probably to have much less water and a lot of iron oxide on the planet. Vast arid areas would cause dust to be picked up in the wind and colour the entire sky. This would clear sometimes and at other times be a full-on sandstorm. ]
[Question] [ In analogy with a skydiver, a culture has developed an extreme sport called "tornado-surfing". Essentially, a thrillseeker hunts down supercells that might create tornadoes and lets themselves be sucked in by one. The goal is to stay airborne as long as possible while surviving the winds and debris. The ultimate thrill is surviving an F5, the strongest tornado possible. Obviously, this requires specialized gear and probably a supporting team. What would someone surfing a tornado use to protect themselves, both against the extreme winds, the debris flying around in the tornado and the inevitable landing? [Answer] I imagine this would be like using a [wingsuit](https://en.wikipedia.org/wiki/Wingsuit_flying) with the addition of: * GPS tracking (once in the suit & one in the helmet) * Full helmet & enhanced neck support * Oxygen tank (integrates with the helmet) to keep breathing in those high speed winds In the near future the helmet would be upgraded to one with a HUD which displays realtime tracking of dangerous debris (through a colour scale) based upon the expected fly path. The debris would be tracked by mobile ground stations (SUV with some serious radar capabilities). The landing would be the trickiest part. They could go for: * Riding it out (to set a duration records) * Aim for the eye when an suited shelter is available in it (with a parachute or crushable landing) * Take a short dip in it and then release a balloon to be [air lifted](https://www.youtube.com/watch?v=tFnJGt-uYlw) out of it. [Answer] To be able to surf/survive a tornado, you must be able to have the consistency of tank but light enough for a human to carry. I'm going to assume this extreme sport always gets you in trouble or puts the surfer in the worst case scenario. Here are the essentials every tornado surfer will have. First and most important every surfer needs a parachute. Of course this can't just be any parachute since normal material can be shredded by debris flying at over 200 MPH. That's why this parachute is made and engineered to work using [Cuban Fiber](http://indefinitelywild.gizmodo.com/how-the-lightest-strongest-outdoors-fabric-is-designed-1601176186), a lightweight fiber that's stronger than steel. Of course the bag concealing will also be made of the same material. (This could also be used to be "wings" on the suite like in @Ahriman answer). Now of course you want something to protect your body from all this debris also! Lucking there is a [new class of magnesium-alloy](http://motherboard.vice.com/read/one-of-the-strongest-lightest-metals-ever-made-is-less-dense-than-water) that is one of the strongest metals ever produced that is less dense than water! So this lightweight solution of body armor will be perfect to stack on. In this suite will have to be small oxygen tanks like in @Ahriman answer. These will be small enough to just last the duration of the ride, nothing huge like when scuba diving. The surfer can't get suffocated from the wind! (try putting your head out the window going down the highway, even that's tough to breath!) Of course under the armor would need to be some extreme cushioning like [Sorbothane](http://www.sorbothane.com/what-types-of-materials-are-best-for-shock-absorption.aspx), which can help protect from fire and such also, and probably a neck brace and sorts like that for impacts. (Human bodies are too squishy). Possible facts - Anything over 12m/s is pretty dangerous when falling. The sudden stop is what kills. So here are some techniques [to survive a fall](http://www.wikihow.com/Survive-a-Long-Fall). Scenario 1 (Launched High & possibly far) This is the best scenario a tornado surfer would want to be in. This gives the person plenty of time to react to what is going and will allow them to use their parachute to float down safely. Assuming projectiles don't come from the tornado and snag the parachute, it will become an easy ride. If the parachute does get grabbed, the wings on the suite can slow the descent hopefully to safe speed. Scenario 2 (Launched low & and fast) Coming out of the bottom part of the tornado, launched like a human missile, only hopes and prayers will help you here. The surfer is now faced with great danger, tons of things to collide with. Only the protective gear will save them now. Hoping the body armor can withstand colliding or being pushed through walls and cars or slammed into metal structures. And the cushioning underneath can absorb the impact! Scenario 3 (Launched midrange) Any experienced good surfer will be able to react using their body suit to glide out and possible up depending the wind. From there they can get their parachute deployed to slow their decent. Even though this would be a rough landing, they will survive to surf again! Scenario 4 (Anything slow) High up, mid range is no problem for these guys at low speed. It's like surfing a 4 foot wave in the ocean for professional water surfers. Low range is where it still can be dangerous, but with the proper gear and the perfect falling techniques, these guys have come into much worse! All in all this is not a sport for the fearful, also not a sport for the unhealthy. This is a high class high energy, highly dangerous sport that only few and brave and (stupid?) every attempt. [Answer] Body armor and a parachute to compensate for the added weight. The extreme athlete needs an assistant who pilots the two-seat jet into proximity of the funnel, up near the cloud level. At the critical moment, the athlete ejects and once clear of the plane, opens the parachute. If everything is timed perfectly, the athlete gets spun around in the heights where debris is less common, then floats down to earth when the funnel abates. If things go wrong... that is what the armor is for. ...and the second, backup parachute. Landing is an issue, if the parachutes fail, so the faint-at-heart only surf water spouts. [Answer] I agree with wingsuit for flying, and body armor for protection. For landing (or debris emergencies), I propose personal airbags. We already have "airbag vests" for motorcyclists (google them). you will need a bigger version, with mutliple airbags, like what Mars Exploration Rover and Mars Pathfinder used for their landing. The idea is to form a ball 3-5 meters in diameter around the surfer. There is a nontrivual issue of when and how to trigger the airbags. Surfer can be knocked out. Parachutes have emergency trigger based on altitude, but I suspect it will not work well in a tornado (which involve lots of pressure differences). Ground crew might not be able to track the surfer, or might be disabled by the tornado. So I propose that airbags are triggered by a dead-man switch: surfer holds down a button down when he goes in, and when he released it, the airbags are deployed. You can also allow remote activation by ground crew (who monitor the position of the surfer by triangulating his beacon). You can also have an GPS unit that triggers the airbags once surfer goes below certain altitude, or is heading towards earth. But I am not sure if GPS is fast enough. ]
[Question] [ So I heard about this thing on vsauce a while ago, where scientists use this thing called “acoustic levitation”. They use ultrasonic frequencies to levitate various substances, for use of studying their properties in an isolated environment. But I had a thought: if sound can push against gravity and cause objects to levitate, could it possibly push against an object, sending it away from the source of the sound? To be more specific, could ultrasound speakers be installed in the ceiling of a spaceship, and push its occupants towards the floor, simulating gravity? Would this work? And what would be the possible side effects on the human body? [Answer] Gravity acts on every atom of the body equally. Sound pressure decreases with distance and can only act on the exterior of objects. This would result in someone's head experience more force than their feet. Plus the downward force would be applied to the parts of the body that face up -- tops of feet, shoulders, boobs, top of the head. Assuming your speaker is a multitude of point sources, all very close together, and to produce a uniform force in one direction then if the sides of a person (left v. right or front v. back) didn't have constant and equal area then they would experience unequal forces as they moved about. And humans generally have more surface area in the back, then the front. The long and the short is that I think your space explorers would have difficulty walking around without practice, and they'd have really bad headaches from the ultrasonic noise bombarding their heads. Unless they wore styrofoam hats to absorb the sounds waves, then everyone would make fun of them for looking like dorks. I think your idea is good, but instead of sound maybe wind like from a laminar flow that sources from the ceiling and leaves through holes in the floor. Get the same effect without the headaches, and your hair has that just blown out look all the time. ]
[Question] [ I want to write about men out doing whaling and fishing with the type of technology similar to that of early 1700s boating. They are going to have a blunderbuss, use old harpoon fishing, sail boats made of wood etc. However, I don't know as much about this subject as I would like to. Where could I learn more about how the men on the boat worked, what they did, how they whaled, etc? [Answer] ## Use Moby-Dick There was an American author, [Herman Melville](https://en.wikipedia.org/wiki/Herman_Melville), who, sometime around the middle of the 19th century, wrote a thousand pages book about whaling. While this is 1850 instead of 1750, the characters live and work aboard a ship, the [Pequod](https://en.wikipedia.org/wiki/Pequod_(Moby-Dick)), which is described as "a ship of the old school", "long seasoned and weather-stained in the typhoons and calms of all four oceans". Since it is unlikely that the readers will know the difference, if there is any difference, between the whalers of 1750 and those of 1800, I believe that [Moby-Dick](https://en.wikipedia.org/wiki/Moby-Dick) would do very well indeed. [![Queequeg](https://upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Queequeg.JPG/290px-Queequeg.JPG)](https://en.wikipedia.org/wiki/Moby-Dick#/media/File:Queequeg.JPG) [![Final Chase](https://upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Moby_Dick_final_chase.jpg/305px-Moby_Dick_final_chase.jpg)](https://en.wikipedia.org/wiki/Moby-Dick#/media/File:Moby_Dick_final_chase.jpg) An artists impression of the boats and whalers described in Moby-Dick. (Pictures from Wikimedia, public domain.) For those readers who don't have a personal acquaintance with Moby-Dick: Melville likes to engage in long and loving descriptions of technology, processes, and culture. One can safely use Moby-Dick as a guide on how to hunt sperm whales. One can safely use [White Jacket](https://en.wikipedia.org/wiki/White-Jacket) as a guide to the life aboard an early 19th century warship. While Moby-Dick is notorious for dedicating a whole chapter to the description of the harpoon line, White Jacket has an equally entertaining description of mast and spar technology. ## But wait there’s more There is an entire site, [The Plough Boy Anthology](https://mysite.du.edu/%7Ettyler/ploughboy/pbeditions.htm), dedicated to 19th century American whaling; I would recommend Thomas Beale’s [Natural History of the Sperm Whale](https://mysite.du.edu/%7Ettyler/ploughboy/bealenew.htm), London, 1839. Containing: Its anatomy and physiology – Food – Spermaceti – Ambergris – Rise and progress of the fishery –Chase and capture – "Cutting in" and "trying out" – Description of the ships, boats, men, and instruments used in the attack; with an account of its favourite places of resort. [![Boats attacking whales](https://i.stack.imgur.com/qtE8V.jpg)](https://i.stack.imgur.com/qtE8V.jpg) (source: [mysite.du.edu](https://mysite.du.edu/%7Ettyler/ploughboy/boats%20attacking.jpg)) Boats attacking whales, from the Natural History of the Sperm Whale by Thomas Beale, 1839, available at the [Plough Boy Anthology](https://mysite.du.edu/%7Ettyler/ploughboy/pbeditions.htm). [Answer] The Wikipedia article on the subject of sailing ships battle tactics is quite elaborate and detailed - definitely check it out : <https://en.wikipedia.org/wiki/Sailing_ship_tactics> Do note this concerns mostly battle tactics. For specific tasks such as whalinh you might want to check out other articles. [Answer] Wind and water haven't changed This means that you can hop on a modern sail-boat, and learn some things about 17th century sailing. Even on a dingy you can learn the difference between tacking upwind and running downwind. After a couple weeks you'll learn to see the pattern of wind upon the water and be able to predict when a gust will come. If you're even more dedicated, it turns out there are even 'tours' for sailing tall-ships: <http://www.maybe-sailing.com/> Why do this as opposed to just reading? There's a big difference between reading about the amount of force on a ships sail and realising that even a square meter or two of cloth can exert more force than any human can hold.... But some things have changed Things like navigation, and the sail-rigs of the ships. For finding what these differences are, I'd suggest reading books, both fiction (As AlexP suggests) and non-fiction. If you live in a country settled via ships (Eg America, Australia, New Zealand) you can probably go to your local library and find first-hand accounts of the voyage written by the settlers who spent at least a month or two onboard those ships. Many of these diaries aren't publicly available online, so tracking those down will probably require some legwork. Finally, here's a video from sailing a square-rigged ship: <https://www.youtube.com/watch?v=96cRjLkIKlE> ]
[Question] [ I am trying to construct a standing stone calendar for my world Jasmi, located at latitude 53.8 degrees South. To do this, I need the hour angle of moonrise and moonset for my world. The problem is that I have no idea how to calculate the hour angle of the Earth's moon, much less the hour angle of an exoplanet's moon from that planet. Given planetary obliquity 14.92 degrees, local solar time of 24.02 Earth hours, and a lunar orbital period of 32.002 Earth days, how can I find the hour angle h0, or the angle of moonrise and moonset, for each of the four phases from a latitude of 53.8 degrees South? Is this possible or do I need more information? ETA: To make it easier on all of us, I've made the descending node of my moon occur at new moon and the ascending node occur at full moon. [Answer] ## I'm a geographer, not an astronomer, so there's your grain of salt. If all you need is the hour angle, then you could just substitute the moon for the sun in this equation you posted here: [How do I calculate solar altitude and hour angle from the surface of another planet?](https://worldbuilding.stackexchange.com/questions/105990/how-do-i-calculate-solar-altitude-and-hour-angle-from-the-surface-of-another-pla) ...But as you've posted here: <https://astronomy.stackexchange.com/questions/25352/how-do-i-calculate-the-hour-angle-of-a-planets-moon-from-a-point-on-that-planet> what you're really after is > > a standing stone calendar that'll accurately denote where to look for my planet's moon at its four major phases > > > And that's not something the hour angle can tell you. The tl;dr is that 1. your full moons will not be in the same places every month; 2. the hour angle seems to only give you you degrees longitude; 3. and you'll also need a predictor of latitude to tell where they are. The long version is that this is due to a combination of two reasons. ## First of all... You have exactly 20 lunar months for one solar year (640.04 days around the sun / 32.002 days around the planet). You're going to have exactly twenty new moons, twenty full moons, etc throughout your year. And that's fine. You also have 768.68804 solar hours per lunar month (24.02 times 32.002). This is also fine, but *that .68804 is important.* I'll get back to it near the end. ## Secondly... More importantly, your moon's orbital inclination is 9.92 degrees off the ecliptic in relation to a planet whose axial tilt is 14.92 degrees (for reference, our moon has an inclination of 5.145 degrees in relation to Earth's 23.5 degree axial tilt). And that's also fine. So, assuming your planet and moon have the same dimensions as Earth and our Moon, here's a not-to-scale diagram of what your system will look like if we assume your moon reaches its highest *latitude* in the northern sky on the same day as the northern summer solstice. [![enter image description here](https://i.stack.imgur.com/JhgTl.jpg)](https://i.stack.imgur.com/JhgTl.jpg) And here's a closeup of your planet on that hypothetical day. The upper red line denotes the highest northern *latitude* that will, from their perspective, see the moon as directly overhead. [![enter image description here](https://i.stack.imgur.com/D6zx8.jpg)](https://i.stack.imgur.com/D6zx8.jpg) Now, let's both flip the planet and reflect the moon's orbital inclination 9.92 degrees below the pink line so that your moon reaches its highest *latitude* in the southern sky during the southern summer solstice. In this case, it's the *lower* red line that is the highest southern *latitude* that will see the moon as directly overhead. [![enter image description here](https://i.stack.imgur.com/0ybR8.jpg)](https://i.stack.imgur.com/0ybR8.jpg) ## By these powers combined... *The result of these two things is that your moon is going to create a sinusoidal path, like the ones described here:* <https://www.youtube.com/watch?v=JyfEffMrglI> Because of the .68804 hours (which is about 41 minutes, 19 seconds) each apogee and perigee of your moon will occur not quite 10 degrees, *15 minutes* of longitude away from the previous one. This creates the overlapping wave pattern in the video posted above. And that sinusoidal path means that all twenty of your full moons will rise at different latitudes on the horizon *between those two red lines* over the course of the year, similar to how the sun rises at different points between the Tropics of Cancer and Capricorn over the course of a year here on Earth. --- This isn't to say that you can't make your calendar. But to the best of my knowledge, the sin waves used in the equation for hour angles describe the longitudinal motion of a celestial body over a planet, and you'll need something to describe the latitudinal motion as well. ]
[Question] [ Imagine an earth-like planet on which gravity is reduced by 20%-30% every 15 months. The low-grav-effect should start slowly, reaching its peak/bottom of round about 0.7 g after 6 weeks and should slowly diminish again for another 6 weeks, so that it lasts for 3 months in total. The effect exists since the emergence of the planet.The planet itself is located in our galaxy, but much nearer to the center. Which astronomical or cosmological event would explain such an effect? (It preferably should be visible to observers from the planet´s surface.) This is serving for fictional worldbuilding. But I want the most scientific approach possible and only stretch or ignore empirical data, where absolutely necessary to fulfill my conceptions, in order to make the whole story function. For example: The 20%-30% grav-relief is only guessing. What I want is a considerable effect on intelligent lifeforms on the planet, so that they could think about the effect like a fifth season, with all of it´s implications. [Answer] Binary planet <http://farm1.staticflickr.com/164/358228043_d07837333f_z.jpg?zz=1>[![binary planet](https://i.stack.imgur.com/JnPXq.jpg)](https://i.stack.imgur.com/JnPXq.jpg) Our own moon has enough gravity to tug up a bulge in the ocean, producing tides. But what if our planet's partner were even bigger? If the partner were as big or even bigger than the planet in question, its gravity could be felt by people on the ground. When overhead it would pull on objects to some degree, effectively making them lighter. When on the far side its pull would be additive to that of the planet, making things heavier. One would need to work jiggery pokery with the masses, distances and velocities of these 2 planets such that the orbital period was as requested by the OP and the mass of the companion planet was correct to make the 20%-30% decrease when overhead. The OP did not ask for a 20-30% increase in gravity also but that is what she gets. As regards noticeable, a giant planet sized satellite would be noticeable to people on the planet's surface. I am sure basketball season would be timed for when it is high in the sky. --- ADDENDUM from comments > > I'm trying to crunch the numbers for this scenario, and I'm failing to > get any "sane" results - may be an error with my calculations, though > - @Will (or anyone else, for that matter), would you mind suggesting distance and mass for the satellite that produces the 20-30% reduction > in perceived surface gravity (let's ignore the seasonality of the > effect for simplicity)? – G0BLiN 2 days ago > > > OK @G0BLiN with your tricky to spell username. Math is not my strong suit. But there are calculators to help. I used this one. <https://www.omnicalculator.com/physics/gravitational-force> First: Earth Plugging in my own 100 kg weight standing at Earths radius 6371 (6371 km from the center of mass) I get: [![earth gravity](https://i.stack.imgur.com/y4sj6.jpg)](https://i.stack.imgur.com/y4sj6.jpg) 981.7 N / 100 kg = 9.8 m/s2 which is Earths surface gravity. Looks good. Now let us consider Jupiter at 317 Earth masses and radius 69911 km. How far off the surface can on object in orbit exist? [Metis](https://en.wikipedia.org/wiki/Metis_(moon)) is the closest moon of Jupiter, orbiting at 128,000 km. 128000 + 69911 = 197911 km from Jupiter’s center of mass. [![enter image description here](https://i.stack.imgur.com/0nYIF.jpg)](https://i.stack.imgur.com/0nYIF.jpg) 322.5 N / 100 kg = 3.2 m/s2. Which is about a third of Earth’s gravity. So: if I were standing on Earth’s surface looking at Jupiter 197911 km overhead, I would be lifted up by Jupiter with a force of 30% of Earth’s own pull. I would feel 30% lighter. On the far side of Earth I have the diameter of the Earth between us too; if it is 12742 then the force is 2.8 N in addition to the 9.8 of earth. A problem: to orbit as closely as Metis does a body must move very fast. It is falling towards Jupiter at a good clip and it has to reliably miss. A fix: the Earth in this scenario orbits in a highly [elliptical orbit.](https://en.wikipedia.org/wiki/Elliptic_orbit) [![elliptical orbit](https://i.stack.imgur.com/OTK8u.gif)](https://i.stack.imgur.com/OTK8u.gif) Ha! Gifs work on WB stack! This can address the periodicity also – for much of the 18 month orbit the Earthlike body is at some distance from its large Jupiteresque partner. It swoops close for the specified period in the OP during which the proximity allows the above described gravity reduction due to the large partner. [Answer] Exiting an unusually dense dark matter field. This is, essentially, equivalent to decreasing the planet's mass, as suggested by Luke's answer, but it's a reasonably plausible mechanism, especially in a science fiction context. Cold dark matter would tend to increase in density around concentrations of normal baryonic matter. If the background density of dark matter is already fairly high, this could produce a noticeable increase in the total mass hanging around in the interior of a planet, thus increasing its gravity. Note, however, that this would not generically be a static blob of dark matter that's gravitationally bound to the planet--it's a dynamic structure, more of an event than a thing, consisting of whatever dark matter particles happen to passing through the planet at any given time, like a standing wave in a stream where water bulges as it flows over a submerged rock. Thus, if the planet moves out of the background dark matter cloud, or if the cloud itself moves, this standing wave of extra mass would disperse, and the planet's gravity would decrease. There are all kinds of ways to make that periodic. Maybe the cloud is associated with the planet's sun, and the planet has an eccentric orbit that periodically takes it closer to the middle (denser) part of the cloud and then out towards the (thinner) edges. Maybe the cloud itself regularly expands and contracts (which could happen if each individual particle of the dark matter cloud is on a highly eccentric solar orbit, and they all have similar phases), thus periodically changing the background density where the planet orbits. Maybe there's a coherent cloud of dark matter orbiting the same sun like another (very large and diffuse!) planet which periodically intersects the baryonic planet. And so forth--I'm sure you can come up with lots more possibilities for periodically varying the dark matter density surrounding the planet. Unfortunately, this sort of thing, by definition, would not be (directly) visible to the inhabitants! But it's the only option I can think of that could be stable over geologic timescales and wouldn't kill everyone on the surface. [Answer] The strength of a gravity field is given by (G \* m) / r^2. To decrease the strength of the gravity field, you can decrease m, the mass of the planet, increase r, the distance from the center of the planet, or decrease G, the gravitational constant. # Decrease mass of planet Your planet is some how loosing mass without loosing size. Where is it going? Who is taking it? How are the people on the surface surviving the process? These are questions you'd have to answer. # Increase the distance from the center Your planet is getting bigger without changing mass. I can't imagine how this happens. Someone is inflating a planet sized balloon inside the planet? # The gravitational constant is diminishing We named it constant because it's not known to change. That being said, we don't know why it should be at the value it apparently is, so we have no idea what might cause it to change. If the change isn't local to the planet, then everything in the solar system gets farther away as their orbits are no longer stable. Eventually things start flying away into interstellar space to freeze in darkness forever. If the strength of the gravitational field isn't decreasing, then maybe there is a force that counteracts it. I suggest: centrifugal force (I know it's not a real force, but it seem lit it is to anyone on the surface of the planet) # Centrifugal force If you planet is spinning ever faster and faster, then people near the equator would experience lower and lower gravity. People near the poles will not experience the same thing nearly as strongly. If the Earth reaches a speed where the equator is moving at orbital velocity (about 1 rotation every 90 minutes) then people living there would experience 0 gravity. If the earth speeds up any more than that, then it will break apart and everyone on earth will die. [Answer] As cosmological event I think the flyby of a very large astronomical object can cause this kind of effect. But then your problem will be that its strong gravity will induce very strong tidal effects which will make all other effects you required pretty useless. [Answer] I believe that any significant change to a planets gravity as described by the OP would inherently result in a destabilizing orbit (which eventually means crashing or flying off somewhere). That being said I'm going to play with the fringes of physics. I propose your planet orbits a blackhole that periodically produces Gravitational waves, which I think if you are close enough to the source would have a perceivable effect on gravity. As we have learned from the science of Interstellar its possible to have a habitable world near a blackhole. This is sort of handwavium answer because gravitational waves and their effects aren't fully understood let alone what would be the conditions needed to have the right balance of not getting ripped to pieces while receiving enough em radiation to support life. ]
[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 1 year ago. [Improve this question](/posts/52440/edit) So Murlocs. I'm referencing Murlocs from World of Warcraft since I never actually found any other novels or games that have them. Described as a bipedal, amphibious, intelligent, aggressive[Still capable of negotiations] race residing along coastlines, lakeshores, and riverbeds. Murlocs have * bulbous bodies * large mouths filled with sharp fangs * Slime-coated skin * height of around 3-6feet[but are usually hunched down] How might they have evolved? [Anatomically Correct Series](http://meta.worldbuilding.stackexchange.com/questions/2797/anatomically-correct-series/2798#2798) [MURLOCS](http://wowwiki.wikia.com/wiki/Murloc) [![Murloc](https://i.stack.imgur.com/fy1YL.jpg)](https://i.stack.imgur.com/fy1YL.jpg) [Answer] Murlocs are basically carnivorous frog so you can start from here. Initially, you have frogs in an environment with mixed water and land but with little amount of bugs, so classical frog hunting method of capturing bugs with theirs tongues and switch to hunting like small predator and evolve to a jaw with small teeth. Next, murlocs begin to need to hunt bigger prey due to a lack of small comestible prey. In order to be able to kill taller animals, murlocs are forced to hunt in group, thus developing communications abilities and improved intelligence. Over time, murlocs grow bigger due to better feeding, this increase in size allow a better brain, that lead to increased intelligence and therefore better hunting tactics that allow to kill bigger prey improving the available food, continuing the cycle. Eventually, murlocs reach the limit in size of 3-6feet due to the available prey. ]
[Question] [ Suppose we have a binary star system and a planet at the L4 or L5 point of the orbit of one of the stars around the other. The planet is thus illuminated by the two stars from the same distance and the angle between the stars is about 60 degrees. If the planet is tidally locked, it will be constantly illuminated by two non-moving stars. Is this possible? [Answer] I saw a reference once that indicated the magic ratio for the L4 / L5 points to remain stable, is 9 / 1 (primary / secondary). As long as your world was less than 1/9 of the mass of the smaller star, it could remain in a stable orbit in the secondary's L4 / L5 points. Whether this allows the planet a habitable temperature depends upon the specifics of the orbital parameters. For instance, use a G2 start (like our Sun) and a barely fusing M9 dwarf as the secondary. Place the secondary a little further out than Earth's orbit and Voila, you have a habitable planet. Tidal forces between your planet and the primary at those distances would less than the Solar tides the Earth experiences. The tidal forces between the Earth and the secondary would be even smaller. So the planet would not be tidally locked. Of course many different configurations could be used. However, you wouldn't want the tidal forces too get too strong or you'd end up with a planet tidally locked to not just one star but too. Or maybe that is what you want :) [Answer] Sorry, due to only being able to edit comments for 5 minutes (it took me longer than that to even complete the comment) when I decided to split the comment into an answer they got messed up. If smaller sun must have a mass 25 times smaller than the larger one then I kind of assume one would be brighter than the other since they are at the same distance. I don't know that much about suns. I do know that having one 25 times larger than another is not problem, but I don't know if somehow a smaller sun can give off the same amount of light as a larger one. Anixx didn't say if that was important. If it were me, I would find two suns that would work, then place them so that the planet had the right climate and calculate what kind of orbit they had. Lather rinse repeat. It might also be possible to have two suns that orbit each other so closely that they almost exchange atmospheres and have the planet orbit both of them. I'm not sure how the tidal lock would work, but intuitively, I figure the planet could lock to the barycenter. Again, these things are fairly easily calculated and it gives more freedom for the types of suns. Hope this helps. [Answer] The Langrangian points L4 and L5 are stable, but not very stable. When the two binary stars and the planet\* are the only non-negligible masses in the vicinity and the mass of the planet is very small compared to that of the stars, then the configuration would be stable. But add any disturbing factors, like additional planets and moons, and the whole configuration will become unstable. In our solar system, many planets have small asteroids at their L4 and L5 points, but the majority of them are only temporary because the gravity influence by other planets soon knocks them out of their orbits. For further reading, I recommend [the Wikipedia article Trojan (astronomy)](https://en.wikipedia.org/wiki/Trojan_%28astronomy%29). Regarding tidal locking: It's unlikely. For tidal locking to happen, the satellite must be not perfectly spherical. It only works because different points of the satellite experience different gravity and due to the uneven form this generates torque forcing the satellite to face the gravity source. The necessary gravity gradient only appears when the gravity source is very close compared to the irregularity of the planet. In the given configuration, the suns must be quite far away or they will bake the satellite (in our solar system, the only planet tidally locked to the sun is Mercury) or the satellite must be very irregular in shape (unlikely when it is large enough to have non-negligible gravity itself). For further reading, I recommend [the Wikipedia article on tidal locking](https://en.wikipedia.org/wiki/Tidal_locking). \*It's technically not a planet when it shares its orbit with a much larger mass ]
[Question] [ Much like how certain cultures have adapted to live at extremely high altitudes, what would be the evolutionary effects if humans today were taken to a planet with atmospheric pressure not unlike an early Earth? Think something oxygen-rich, about 4 bars of atmospheric pressure. The catch is that gravity is only 80% of Earth's gravity (think Venus' gravity compared to Earth). I understand that humans living in a lower-gravity, oxygen-rich world might adapt to become taller and more spindly on average compared to humans today, but I don't know what effects atmospheric pressure would have on that growth -- would they become taller but 'stronger' (i.e., denser bones) compared to people from Earth? I'm no scientist and so my attempts at researching this have confused me at best! Any ideas you could suggest would be very much appreciated. [Answer] Weight 80% Earth normal: Minor adaptions, less muscle mass needed, perhaps a little taller, maybe thinner bones. Heart has been mentioned, a smaller heart would likely suffice as the muscle demand is smaller. Hemoglobin can only carry so much oxygen so the amount of blood transport should be very similar ignoring the reduced oxygen demand of smaller muscles, blood viscosity would be unchanged, pressure required would be a bit less, so maybe circulation gets a little easier for 2 reasons. Atmospheric pressure 400% Earth normal: While this heavier atmosphere requires a greater pumping effort, it is also more oxygen rich so perhaps the amount of air pumped could be reduced. Since you pretty much assume a redesign based on optimal changes in a question like this you should expect a change to the response to carbon dioxide. Humans do not have oxygen sensors, they have CO2 sensors. The oxygen starvation sensation is actually a response to elevated CO2 levels. This is why inert gases are dangerous, you don't notice that oxygen is being reduced when displaced by the inert gas. So, either adjust the CO2 sensitivity response or waste energy pumping a lot of air just to keep CO2 level down. Not sure how much tolerance to increasd CO2 is really possible, so this may not really provide a useful optimization if you have to dump CO2 just as much as we do. Oxygen partial pressure 400% of Earth normal: No problem if you don't mind dying and a lot of painful and debilitating symptoms resulting from [oxygen toxicity.](https://en.wikipedia.org/wiki/Oxygen_toxicity) before you actually die. Well, that and some other problems too. In your scenario, you are breathing 0.84 bars worth of oxygen instead of the 0.21 bars we do. Within 90 minutes, many people would be having serious health problems (largely reversible if the source of the problem is corrected). But the long term effects are deeply wired into our biology because of the prevalence of free oxygen radicals, the hydroxyl ion would kill you as it damages vital system like kidneys, lungs, and every other organ since it degrades the lipids in every cell wall. Even bones are damaged by oxygen toxicity. The body has coping mechanisms for our oxygen levels, but there must be fundamental changes for your scenario. It is commonly held that the [oxygenation event a.k.a. oxygen catastrophe](https://en.wikipedia.org/wiki/Great_Oxygenation_Event) is responsible for a major extinction due to oxygen build up over a period a few few thousand to a few ten thousand years. I.e. you really would not have time to evolve sufficient coping mechanisms. Lack of animal life meant that free oxygen was not being removed quickly enough by non-biotic mechanisms to keep many anaerobic species viable. Now assuming humans arrived a few hundred million years after this, the oxygen coping mechanisms would necessarily be present in all animal life (otherwise you die before reproducing). You may not notice these changes (as they occur at the cellular level) but they would be significant and the body would have to spend a lot of resources on oxidation prevention and cleanup. Cleaning up oxidation damage is already expensive, this would be a dramatic change in resource usage. Probably more redundancy mechanisms as well as more aggressive cleanup methods would be needed. A higher rate of [apoptosis](https://en.wikipedia.org/wiki/Apoptosis) would also be a probable outcome. Higher animal forms may not have the margin of error needed to keep functioning -- i.e., sum of resources required for respiration, circulation, digestion, calculation, etc. could exceed the available resources given the added burden if the apoptosis burden increase is large. We operate on a much thinner margin than most people realize. In stressful times, the margins are even thinner. Pregnancy and lactation could be push child bearing into a very marginal outcome zone. Remember that childbirth used to be very dangerous for both the baby and the mother and will be again if would lose modern medicine. Even now, child-bearing is the 6th most common death among women 20-34 in the US. Perhaps men could share the burden by providing the milk giving the women a change to recover from pregnancy or start another pregnancy before the child is weaned. Lots of social adjustment, but think of this perhaps men could not go topless on the beach instead of women. Forest fires would also be a huge problem, once started they would be essentially impossible to put out unless you redesign the plant kingdom to be less flammable you will have mega fires. Plants contains an enzyme [RuBisCO](https://en.wikipedia.org/wiki/RuBisCO) that responds strongly to high oxygen levels and happens to be critical to photosynthesis. High oxygen levels can shut down photosynthesis. So you probably need to redesign plants even ignore the fire problem. RuBisCO is and very important and prevalent protein in plants. Designing around the RuBisCO issue may be very difficult. --- What about 4 bars atmosphere but only 0.3 bars oxygen? This is still a pretty rich oxygen environment, forest fires will still be an issue. 0.25 bars O2 is a better choice. So, you increase the inert gas mix correspondingly. N2 is considered an inert gas in this sense and it would presumably be very likely essentially the remainder of the atmosphere except for some argon, H20, CO2 and trace gases. For us humans, this presents the problem of [nitrogen narcosis](https://en.wikipedia.org/wiki/Nitrogen_narcosis). For 3.75 bars of N2 you only get relatively mild narcosis. I could not find any long-term exposure studies and since the clinical basis of inert gas narcosis is murky, I would prefer not to predict the effect of long-term exposure. Since artificial environments are required to induce narcosis I don't think there is much incentive to study long-term exposure. Since this is only mild level narcosis exposure, I would except that the adaptation would either be mild or non-existent. Maybe a little more computational power in the brain to compensate or scavenging mechanisms in nerve fibers or such-like. Reduced oxygen levels in hyperbaric environments is how we avoid oxygen toxicity. Such environments are often helium enriched since helium does not cause inert gas narcosis. It is hard to justify a rocky planet having high level of helium in the atmosphere as it is prone to reaching escape velocity. Your lower gravity would accelerate the helium loss, so you are probably stuck with the narcosis unless you could justify a large increase in neon levels. Neon either does not cause narcosis or it is simply considerably smaller effect compared to nitrogen. Xenon is actually worse than nitrogen, you can use an oxygen/xenon atmosphere to replace anesthesia. Xenon is too expensive for this to be practical and you would sound like a Go'auld too. I can't think of a good way to adapt our lungs, etc. to negate or strongly mitigate the oxygen toxicity problems along the lines commented upon by Ville Niemi. But supposing I'm missing something and it is reasonable, you still need to deal with the other issues with high O2 levels. So overall, 0.25 bars of O2 is probably the best solution - At least it does not cause any major problems that I can think of. Since it is also necessary to solve the other problems from high O2 levels, it seems a much more useful change than trying to make adaptive changes to compensate for oxygen toxicity in humans. Of course, we also reintroduce the pumping burden problem in full. Since people in good health can already handle this extra burden (though reports of fatigue and soreness are common at first), I would have to say this is not a big problem. A more muscular diaphragm seems pretty easy compared to other changes. [Answer] A lower gravity would rather imply a lesser atmospheric pressure, not greater, unless the planet has a huge atmosphere going thousands of miles above the surface. Greater atmospheric pressure would imply a much more powerful heart, as you would need to pump blood with more force to help it reach the extremities when you have a huge pressure all around your body. This is the most significant anatomical change. Another difference would be in the lungs. Since the atmosphere is oxygen-rich and high-pressure, probably a small lung-set would do. Maybe a single lung instead of two would suffice. Breathing rate might be slower than us (Earthly creatures). Due to excessive air drag, the muscles would probably be slightly stronger than us, to not be blown away by gusts of wind. Also, the eyes might have a protective covering on them (read [Ophthalmosaurus](https://en.wikipedia.org/wiki/Ophthalmosaurus) for detail). Interestingly, instead of eyes, ears could become the most acute sensory organs. Under high pressure, sound tends to travel farther and faster, allowing for a sound-oriented creature. Not saying or implying that vision would become useless, but hearing would be much more enhanced than here on Earth. I cannot say how bones or skin would be affected. ]
[Question] [ Sometimes when building a world, and in particular since Tolkien, one may wish to create original languages for the inhabitants. There are some information around the site about the creation of conlang, but @knave made a [good summary](https://medium.com/universe-factory/conlangs-for-non-linguists-827b1e566779) on our blog. From there, we learn that one of the first step is to decide on the phonemes of the new language. However in the world creation steps, it is likely that we define the [climate](https://worldbuilding.stackexchange.com/questions/1353/creating-a-realistic-world-map-currents-precipitation-and-climate?lq=1) and [geography](http://meta.worldbuilding.stackexchange.com/questions/2594/creating-a-realistic-world-series) of the world before populating it. I was thus wondering whether the climate or geography had some influence in the phoneme used in a given region. Are colder countries more prone to use guttural sounds? Etc. [Answer] I can't remember what to search for to find the article again, but I found a neat article on the tonal languages, such as Chinese, which depend on the pitch of the vowels to convey meaning. They found that all such languages were found in equatorial regions. They postulated that the tonal languages may depend on reasonable climates and high humidity, because those are conditions which make it easier to maintain the level of vocal chord health required to continuously create such changing pitches. [Answer] There are some theories. Ejectives are predominantly found in languages at high altitudes (e.g. Caucasus). Does lower air pressure help the pronunciation of ejective consonants? Maybe. See [Everett C (2013) Evidence for Direct Geographic Influences on Linguistic Sounds: The Case of Ejectives. PLoS ONE 8(6): e65275](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0065275). (This one is a speculation) If you have a climate that facilitates survival of abandoned children or groups of children (say, pre-teens in a jungle whose parents are lost or dead) with not quite mature language, they, after they grow up, will pass a mangled and heavily modified version of the language to their children, and languages will diverge quickly. In a hostile climate (e.g. the Arctic), survival without you community is impossible and the language will be passed relatively unchanged. Now, compare the linguistic diversity of Subsaharan Africa or Brazil (thousands of widely diverse languages) with that of the Arctic - historically, there is Inuit and related Yupik... and that's about all. [Answer] Language is not inherited biologically. It is a cultural phenomenon, it is inherited through culture. The climate of an area has very little to do with the language spoken in that area. What counts is the history of the region, who conquered it last, what was their cultural level, how many people they brought in and so on. Languages, at least successful languages, do not remain fixed in the place they were born, like plants. They spread, they move, they evolve. English was born on a cold, foggy and rainy island; but it is now spoken in sunny California, and in parched Australia, and in frigid Alaska. French was born in the sweet heart of France, blessed by the mildest climate of all Europe; but it is now spoken from Montreal in Quebec, to Cayenne in French Guiana, to Brazzaville in Congo. Russian is spoken over an unimaginably large territory, from the Pontic Steppe in the south-west to the Siberian taiga in the north-east, comprising fertile plains, and unforgiving steppes, and rugged mountains and whatever have you. So here we are: three examples of languages spoken over every imaginable climate and geography. And what do those examples show? They show that the climate of a district is irrelevant when it comes to finding out what language is spoken there. What counts is its history. Consider the perfect example: Asia Minor, known as Anatolia nowadays. What languages are spoken in Asia Minor? Well, it all depends on when. There were the Anatolian languages, Hittite, and Luwian and Lycian and so on; and there was Phrygian; and there was Armenian. And we know that those languages were not autochthonous, for they are Indo-European languages, and we even have direct references in ancient Hittite texts to a previous language which had been replaced by Hittite. And then came the Greeks, and Asia Minor spoke Greek, a language quite unlike the languages it replaced. And then came the Turks, and nowadays Asia Minor speaks Turkish, a language utterly unlike Greek. So that, the supposed influence of the climate of Asia Minor becomes irrelevant when compared to the overwhelming importance of history. [Answer] Although scientifically I have little to offer, there is something I'd like to add here. Generally speaking our names for things start with what is around us, and we name things off of that afterwards. For example, guinea pigs are not pigs, koala bears are not bears, red pandas are not pandas. Or perhaps my favourite, the flying fox. We could have called it a giant bat, but then you can imagine the first time its name was used. "It was huge! Like a fox with wings!" I believe this also extends itself to naming simpler things. We have names for snow, frost, sleet. But there could be cultures that could never have seen snow, that may have a word for frost, but not snow, and hence call it "falling frost" instead. Our surroundings definitely change our language. A rainbow comes from the words rain and bows yet has existed long before mankind invented the word bow, so why that name? In Norwegian there is the term "stormskritt" which is literally "storm steps" but means something more like "progress by leaps and bounds". Why use the word "storm" at all? Well, I imagine it's because historically the people loved and feared storms, because they had a lot of them and lived by the sea. So it worked into the language. If storms weren't common in their climate, then those people probably wouldn't have used that phrase. Edit: I realise the question is specifically about the sounds of the languages, and therefore my answer doesn't offer much, except I would like to highlight: We re-use a lot of parts of words because they use something we already know that is easy to say. So I imagine if a climate makes a particular sound harder to make, that's the main impact I would expect. For example, in climates where keeping your mouth open could lose precious body heat, avoiding sticking your tongue out would make sense. Edit edit: Another thing to consider is sometimes we copy sounds of other things. Such as the cuckoo, or dik-dik. Since we then copy the noise that animal makes, we can re-use that. Such as cuckoo going from a bird sound to meaning 'bonkers'. A cuckoo lives in its own climate to survive, and therefore areas without that living creature would never develop that terminology because of that animal. Therefore, climate defined a piece of that language. [Answer] At least pitch of language depends on climate. I talked with lady who works in post office in village of [Verhneimbatsk](https://yandex.ru/maps/-/CCQ3mReKlD), we both talk the same language, but she talks like machine gun, at least 2 times faster than me. Probably, because it was winter, and there is ~ -40 degrees C (-40 F) at winter. [Answer] Language has nothing to do with the climate. Language depends on social and historical circumstances. The simplest example is that half of the world speaks English, although these people live in different climates. For example - in the hot climate of California, in the cold climate of Canada and in the mild climate of Great Britain, people speak English. ]
[Question] [ Apparently it is theoretically possible for a planet [to achieve a stable orbit](http://news.discovery.com/space/alien-life-exoplanets/black-hole-alien-life-110413.htm) around the [singularity](http://en.wikipedia.org/wiki/Gravitational_singularity) at the centre of a black hole within the [event horizon](http://en.wikipedia.org/wiki/Event_horizon#Event_horizon_of_a_black_hole). This means that life could hypothetically form inside a (presumably [supermassive](http://en.wikipedia.org/wiki/Supermassive_black_hole)) black hole. There are obviously many problems with this, but I suggest we ignore those for a while. What I'm interested in is how quickly (or slowly) time would pass for this planet taking into account [time dilation due to extreme gravity](http://en.wikipedia.org/wiki/Gravitational_time_dilation) and how much time this leaves for life to develop before this black hole explodes due to [Hawking radiation](http://en.wikipedia.org/wiki/Hawking_radiation). Any other unavoidable events that will eliminate all possibilities of life inside this black hole along with when they will take place would also be interesting. [Answer] # Original answer, preserved for posterity [Here's](http://arxiv.org/pdf/1103.6140v4.pdf) the paper. First, there are some important assumptions that the author - Vyacheslav Dokuchaev - made. Specifically, there are two scenarios: 1. The particles are charged and the black hole is not rotating. This is not helpful, because all the particles in a given object would have to be charged perfectly. This is not going to happen in an object even as small as a human. 2. The particles are uncharged and the black hole is rotating. Rotating black holes, described by the Kerr metric, can easily exist, and there's nothing that says that one body can't orbit a Kerr black hole. So one (or both) of these scenarios must be satisfied. Second, Dokuchaev mentions life only once outside the introduction, conservatively saying > > We hypothesize that civilizations of the third type (according to Kardashev scale [28]) may live safely inside the supermassive BHs in the galactic nuclei being invisible from the outside. > > > He alludes to life several other times throughout the paper, but barely touches on it. Discovery has really exaggerated the paper's implications: Dokuchaev really has only shown that particles can orbit inside the event horizon in certain conditions. And that's if the paper is entirely correct. The Discovery article mentions the evaluation of one other scientist, Dr. David Floyd. Floyd says that the paper raises interesting questions, but it also raises some problems; > > Astronomer Dr David Floyd from the Australian Astronomical Observatory and the University of Melbourne says even if the theory is correct, it would be impossible to know what is occurring beyond the event horizon of a black hole. > > > "At this point — and perhaps forever — we're restricted to making untestable assertions," says Floyd. > > > "As far as we know, matter would go into free fall, that is, it would all fall into this tiny infinitesimal point at the centre which forms the singularity." > > > Floyd says that one shortcoming of the paper is that it assumes radiation has no impact on orbits inside the black hole. > > > "It wouldn't take much to produce drag which would slow down the orbits described in Dokuchaev's paper, causing them to collapse onto the singularity". > > > And that's just talking about particles orbiting inside the black hole - not taking life into account! I don't think the paper gives a convincing argument at all. > > What I'm interested in is how quickly (or slowly) time would pass for this planet taking into account time dilation due to extreme gravity and how much time this leaves for life to develop before this black hole explodes due to Hawking radiation. > > > We can't use [a simple approximation](http://en.wikipedia.org/wiki/Gravitational_time_dilation#Outside_a_non-rotating_sphere) that would be used around Schwarzschild black holes, so we have to go to the Kerr metric. The formula for that is way too complicated to work with. Another problem with using time dilation inside the black hole is that you end up with a factor of $$\sqrt{-a}$$ where $a$ is less than 1. So we have a bit of a formula breakdown for non-rotating black holes. This may be the same for rotating black holes - impossible to calculate. For the time it takes for black holes to evaporate, I got $$4.63 \times 10^{104} \text{ seconds}$$ So they'll have a loooong time. [Wikipedia gives a much larger figure](http://en.wikipedia.org/wiki/Timeline_of_the_far_future), though the mass of the black hole is different. I really don't think that life could live here, though. --- # New answer That's the original answer. I want to rework it, because I was in a bit of a rush when I wrote it, and it could be better. So I'll mostly scrap that and start anew. I'll reuse some bits, though. Correct me if I'm wrong, but here's the setup: 1. The setting is a supermassive black hole, like the one at the center of our Milky Way, Sagittarius A\. 2. There is some sort of planet or other body orbiting inside the event horizon. 3. This body can presumably support life, illuminated by the surrounding radiation. You want to know: 1. The time dilation the planet would experience. 2. Whether or not life could develop before the black hole evaporates due to hawking radiation. 3. What could happen to jeopardize that life. Time dilation* For a non-rotating (i.e. Schwarzschild) black hole, the [formula for time dilation](http://en.wikipedia.org/wiki/Gravitational_time_dilation#Outside_a_non-rotating_sphere) is $$t+0=t\_f \sqrt{1-\frac{2GM}{rc^2}}=t\_f \sqrt{1-\frac{r\_0}{r}}$$ The issue for using this for an object within the event horizon is that the term $$\frac{r\_0}{r}>1$$ and so we get an imaginary number. For a rotating black hole, the equation is more complex, as shown [here](http://arxiv.org/pdf/1209.2113.pdf): $$\frac{dt}{d \tau}= \frac{1}{\Delta} \left[\left(r^2+a^2+\frac{2Ma^2}{r} \right) e - \frac{2Ma}{r}l\right]$$ where $a = J/M$, $\Delta = r^2-2Mr+a^2$ and $e$ and $l$ are constants. The calculations would take a while and depend quite a lot on the properties of the black hole. If we know $M$ - which we do - and we know the black hole's angular velocity, $\omega$, we should be able to figure it out. That would take a long time, though. Feel free to plug in some numbers and figure out how long you've got. [This](https://physics.ucsd.edu/students/courses/spring2014/physics161/book.pdf) and [this](https://www.physicsforums.com/threads/equation-for-time-dilation-of-body-in-orbit-around-kerr-black-hole.781691/) are also helpful. Hawking radiation There are a couple relevant formulas for [Hawking radiation](http://en.wikipedia.org/wiki/Hawking_radiation): the temperature of the black hole: $$T=\frac{\hbar c^3}{8 \pi G M k\_B} \approx \frac{1.227 \times 10^{23} \text{ K}}{M} \text{K}$$ the temperature of the emitted Hawking radiation: $$T\_H=\frac{\hbar c^3}{8 \pi G M k\_B}=T$$ the power emitted by the black hole: $$P=\frac{\hbar c^6}{15360 \pi G^2 M^2}$$ and the time it will take for the black hole to evaporate: $$t=\frac{5120 \pi G^2 M\_0^2}{\hbar c^4}$$ Doing the calculations shows that the temperature of the Hawking radiation is negligible, as is the power emitted. The time is on the order of $10^{100}$ years, perhaps a few magnitudes higher. That's for the outside world; the people inside will experience less time than that. If you could calculate that. . . But all is not lost! Black holes - and especially supermassive black holes - generally have accretion disks surrounding them containing hot gas, dust and plasma. As I explained [here](https://astronomy.stackexchange.com/questions/8413/what-is-the-temperature-of-an-accretion-disc-surrounding-a-supermassive-black-ho/8414#8414), [the formula](http://en.wikipedia.org/wiki/Hawking_radiation) for the temperature of the accretion disk is $$T(R)=\left[\frac{3GM \dot{M}}{8 \pi \sigma R^3} \left(1-\sqrt{\frac{R\_{\text{inner}}}{R}} \right) \right]^{\frac{1}{4}}$$ This will give you more energy than the Hawking radiation, and it will prolong the life of the black hole. Supermassive black holes are monsters; they can eat stars and gas clouds. It throws a wrench into your calculations, but it gives you hope for the life. Things that could destroy life It also fits into the category of "Any other unavoidable events that will eliminate all possibilities of life." In fact, all of the things in this category have to do with the black hole eating up something or merging with another black hole. The conditions here would be extreme - even more incredible gravitational forces, incredible temperatures, strong magnetic and electric fields. . . The one thing that could destroy this life would be an unfortunate encounter with matter coming into the black hole. [Answer] When you start asking about time dilation the important question is "Relative to what?" You don't say so I'm going to make some reasonable assumptions like "A planet well outside the event horizon but not vastly far away or moving vastly fast." In the same galaxy say. Likewise if we assume some basic commonsense assumptions about time, space and causality that I think your operating under, namely because everyone does, the answer to amount of time dilation the planet would experience is: "More than infinity." The more than infinity answer is the reason we have an event horizon in the first place. How long do you have to wait for light to escape from beneath the event horizon? More than an infinite period of time. IE it never will. Note that this doesn't apply to other objects inside the event horizon, near to the planet in question. They could still pass signals to each other so the sense of time passing that would make things like time dilation be sensible, as long as you restrict your question to "Close-by". The event horizon isn't like some sort of magical brick wall, a barrier where assumptions like "There is space, time and stuff on the other side" still hold true. Its the point where your fundamental commonsense notions of time, space, objectivity and relationship totally break down. Whats totally weird about it is where your standing matters. Outside the black hole the answer to the question "Whats going on inside the blackhole" the answer is The question is meaningless. Their is no possible relationship you can have with anything past the event horizon. And so you can never see anything "fall" past the event horizon. Time dilation will slow it down and down, the stream of photons from that object becoming a trickle and then on to a vastly rare occurrence until the black hole itself dissolves in a blast of hawking radiation. But even if the black hole didn't dissolve you could wait an infinite period of time and never see the object cross the horizon. But if your the observer falling into the blackhole their is no event horizon. You go straight past the point that the rest of the observable universe says isn't there. You can relate to stuff that fell in with you. Their is a sense that their is an inside the blackhole. But "outside" the blackhole starts to vanish. Red-shifted away to nothing. But as I said, this is in terms of "commonsense" notions of time and space. No one said you had to stick with those notions and people who study this stuff have come up with non-commonsense ways of describing it. [Answer] It cannot. Distribution of matter inside the black hole is symmetric agains the BH center (as if all its mass were in the center or along the surface). So there cannot be any structure inside. Otherwise it would be possible to transfer information from inside BH to the outside by moving mass bodies inside. > > Apparently it is theoretically possible for a planet to achieve a > stable orbit around the singularity at the centre of a black hole > within the event horizon. > > > No, even mathematically it is impossible. Not even close enough to the BH outside it. Inside ergosphere (which is outside the BH surface) the centrifufgal force is directed towards the BH center. So the faster you revolve around the BH the faster you fall. So any body orbiting BH will fall faster than a directly free falling body. [Answer] Going towards a black hole will eventually cause the direction towards the singularity to flip and become a timelike dimension. Since nobody has any clue as to the conversion ratio between space and time, it is unclear how much time an object inside a black hole has. Either way, attempting to imagine the inside of the black hole as if it were normal space is a mistake. Past the even horizon, no matter what you do, you will move towards the singularity. This is because past the event horizon it takes a speed higher than the speed of light in a vacuum to move outwards, so moving outwards becomes impossible. This makes the forward direction time-like. Probably, you could move up and down in what used to be the time-like dimension, so each spherical cut we can imagine making through a black hole event horizon is a slice through a multitude of time-like paths, rather than a time-like instant as it would be in normal space. Now if you ask me how that makese sense since black holes have a definite origin point in our spacetime perspective and will likely undergo Hawking radiation death in the impossibly distant future, I haven't a clue... [Answer] Ok, this does not include exact maths... for that, I leave you to physicists. First: Hawking Radiation would apparently not affect your black hole... it only matters for very small ones: > > This surprising new insight showed that there is still much to learn about black holes. However, Hawking's glow is completely irrelevant for any of the black holes known to exist in the Universe. For them, the temperature of the glow is almost zero and the energy loss is negligible. The time needed for the black holes to lose much of their mass is unimaginably long. However, if much smaller black holes ever existed in the Universe, then Hawking's findings would have been catastrophic. A black hole as massive as a cruise ship would disappear in a bright flash in less than a second. > > > [Source](http://hubblesite.org/explore_astronomy/black_holes/encyc_mod3_q10.html) Shortened because I did mess up the direction.... Space Travel would give them some serious challenges: send a ship closer to the black hole, or farther away from it, they would get into detectable time dilation differences very quickly... any manned mission would have to take that into account. It DOES provide them with neat possibilities for science, though. Need to do your calculations very quickly? Put up an automatic satellite to do computations further away from your friendly black hole. I am not 100% sure of how observability of far away objects works with time dilation, but sending something IN so you can watch thinks on it happen more slowly than they usually would sounds like a feasible scheme. Also, you could send out objects (or even people) you want to preserve further in... and bring them back when you want them, still relatively "fresh". [Answer] Life might develop inside (at least some) black holes without limitation. We know (and apparently can know) nothing about the internal structure of black holes in general. They're a mathematical construct we came up with to account for the fact that we can't imagine anything preserving the structure of a dying star once it's massive and degenerated enough to fuse its neutrons. All we know about the inside from the math is literally nothing. However, if you look into the debate surrounding the cosmological constant and the "shape" of the universe (open, flat, or closed), you will find that working scientists seem to believe that we live in a universe that is very near the boundary of "flatness", i.e. a universe with a maximum degree of expansion beyond which it will never expand. Flat and closed accounts of our universe look very much like black holes in the following sense: the Schwarzchild radius (the radius into which you'd have to pack all of the mass to make a black hole of it, 2GM/c^2) of the universe comes out equal to or larger than the radius of the observable universe. That means that if these cosmologists (those proposing flat and closed universe theories) are right, we currently live inside a black hole. Hence, it's absurd to suppose that being inside a black hole places some limitations on the development of life which we haven't considered. One important caveat: surely you've heard of dark matter and energy. Well, for our universe to be flat or closed it has to be made of MOSTLY dark matter and energy. So, if the dark energy stories turn out to be bullshit, we will discover ourselves in an open universe with no idea what the interiors of black holes are like. Your sub-questions about the time dilation within the black hole seem meaningless to me, there's simply no access to the outside of the black hole to allow for a comparison between interior and exterior frames of reference. [Answer] Here's a fun link (warning, it's old): (<http://jila.colorado.edu/~ajsh/insidebh/schw.html>) that shows what it's like to fall into a black hole. The video is short and has some artificial inlays to help you understand what's going on and it does explain the frame by frame what's happening. Basically, the premise is flaw because once inside the event horizen, you are now falling towards the singularity at a speed nearing the speed of light. Space is so warped by the gravity at this point that any object is now falling at an infinetly increasing near light speed (if you do get up to light speed, you can get out... if you haven't fallent too far... you just get faster and faster and approach it). You also have matter undergo speghettifacation, which is a lengthening and thinning of the object as it falls. Now, the link does helpfully show the points where you can keep an orbit. At 1.5 times the event horizen radius, orbit is possible with a degree of assistence and photons can maintain a stable orbit, essentually creating a weird effect where our perception of the stuff behind the black hole is warped around it. At 3+ times the Event Horizen Radius, an orbit is stable. Your confusion comes from the fact that Supermassive Black Holes a surpringly low average density in the volume of space inside the Event Horizen. The largest known black hole has a mass of 21 billion times that of our sun and an event horizen with a radius of 63 billion kilometers. Since the bulk of all that matter is contained in the singularity, there really isn't anything between the point of no return and the singularity to get in your way. For comparison, if our sun was to collapse into a black hole (it can't, too small) it would have an event horizen with a radius of 3 km. While Earth would be doomed, it would be from the lack of and heat provided by the sun, not the black hole. In fact, the mass of the sun hasn't gone anywhere and we would Earth and all the other planets et. al. would maintain their orbits. It's important to note we were never inside the event horizen to begin with. [Answer] Until the interior of the black hole experiences [heat death](http://en.wikipedia.org/wiki/Heat_death_of_the_universe). That time entirely depends on the size of the black hole, which has (as far as I'm aware) no theoretical limit - you can make it as big as you want, which means you can stick an entire galaxy or galaxy cluster inside of it to support your lifeforms, slowly spiraling inwards. Edit: removed the "our universe" reference as the article wasn't quite what I was originally thinking. ]
[Question] [ I am a big fan of of 'post-scarcity' societies, where we could, in theory not worry about basic needs such as food and shelter anymore, and instead focus on pursuit of 'greater' things that are our area of interest. The crucial stepping stone to that is the concept of basic income - that is everyone has enough to take care of food, drink, shelter, hygiene etc. This doesn't have to be money per se - just an entitlement for those resources. There are a few hurdles to make it work in practice. The policy that is absolutely the easiest to implement and has the most potential is simply giving people a small, fixed amount of money, regardless of whether they work or not. There have been some attempts at this in the real world. The most recent that I know was a referendum in Switzerland. One concern was massive inbound migration. Simply put Switzerland could probably afford fixed income for all its citizens but not for the whole world. There are actually cases of that policy working in 19th century villages in UK and another one in Canada and even more in Alaska. Do people have some ideas how to go about setting up such a system in Europe, where movement is generally unrestricted so it's hard to prevent people coming for the benefits. Could a solution be something in-lieu of fiat money (this smells of communism too much - great in theory but too much bureaucracy, which can lead to inefficient and unfair distribution in practice) or some policy so that only the original resident get the 100% benefits and as more people come, they get less and less (Ponzi scheme)? I'd love more examples of that already working somewhere I haven't heard of yet. [Answer] I think you'd need to move gently into something like this - you don't just say one day, "free money!". You introduce a minimal income, based on citizenship, residence for several years and previous payment of tax. Every year, if the economic health of the country/city/region permits you increase the payment and make a corresponding decrease in both the minimum wage, tax free allowance and welfare payments. Eventually you have no minimum wage, almost no welfare payments and no tax free allowance. The first paragraph and the bolded portion above is to ensure that this doesn't cripple the economy by removing too many low income workers overnight. Employers are going to have to adapt by, especially in low income jobs, treating employees better. We're all familiar with people working awful minimum wage jobs for awful people because they have to. Now any sufficiently mistreated employee can walk. [Answer] The simplest way I can see to do it is to give people "Citizenship". You have a citizenship scale where everyone starts at 0 and then accumulates points through contributing to society. Certain events would give automatic citizen points (for example born in country +1000, completing education +1000, further education +1000, each year worked and paying taxes +200, etc). Other actions (vandalism, antisocial behaviour, etc) would cause a reduction in citizen points. At 2000 citizen points or below the basic income would be 0, at 3000 points or above it would be full. There would be a linear scale between those points. This means that if someone is born in the country then as soon as they completes education they are already starting to be eligible. After working a few years or completing further education then they are receiving the full basic income. Immigrants though will be discouraged because they are starting from 0, that means they need to work for 5 to 15 years (depending on education level) before they qualify for the basic income. Additionally because there is no minimum wage and citizens have their wages on top of basic income immigrants have to work and pay taxes on a low wage for several years to qualify. This means that only those people who will work for it and deserve it can get it. [Answer] Richard Sennett wrote a book about this, called [The Culture of the New Capitalism](http://en.wikipedia.org/wiki/The_Culture_of_the_New_Capitalism), which covers politics, economics, sociology and psychology, and also the problem of setting a basic-income politic without resorting to socialist solutions. Sennet's proposal however is actually proposed to solve the problem of lack of experience and knowledge accumulation that capitalist culture is creating. Sennett sees the new capitalist culture as a culture that wastes resources and talents and favors adaptability against experience, but in doing so it destroys the human side of work and society, as it transforms the work not in a single task that should be accomplished well, but in a series of tasks to be carried out regardless of the consequences. For this new capitalism the best worker is not the best in his field, but one that can perform more tasks than others. A proposal to give back humanity to the worker is to establish a basic income for all. > > "In this way, the State, through taxes, would guarantee to everyone a minimum level of quality of life, but the Nanny-State will disappear. If you throw your money out the window, is your business. In addition, each receive the minimum income, regardless of whether or not he uses it, in this way, the test of need would disappear." > > > This socialist capitalism is essentially extreme liberalism, but it's same for everyone. Every citizen would be provided with a minimum income, which he can increase with his work. However it would not be desirable to live in a State that apply these policies, as every public service would be private. The basic income is based on the fact that the State no longer uses taxes to pay public services, but to give the minimum income to its citizens. Healthcare, law enforcement, firefighters, and other services of this kind would become private companies. The citizen can freely decide from which company buying the services, given that he has the money to do it, but of course those who have only the basic income will have a significantly worse quality of life of those who have a job. [Answer] The first thing that you need is a source of funding. For example, in [Alaska](http://en.wikipedia.org/wiki/Basic_income#Alaska), they are sharing the state's oil revenues. Obviously, that doesn't work in an area without a distinct revenue stream, and in Alaska is not enough for basic necessities. The most common proposals have funded a basic income out of general tax revenues, possibly offset by eliminating tax breaks. For example, in the United States, there are standard deductions that are applied to taxable income. Thus, income is only taxed above those amounts. Eliminating those deductions and further reducing some welfare programs could provide an income stream to pay for a basic income. A [previous question](https://worldbuilding.stackexchange.com/q/6899/2113) suggested using the seigniorage from our increasing money supply to fund a monthly payment. The challenge there is that of course we currently use that money for other things. Also, it's not that stable a funding source. In a post-scarcity society, funding should be relatively easy, as everything is plentiful and cheap. The problem there is that we aren't close to a post-scarcity society. In particular, labor is still expensive, as is the automation to replace it. A second issue is the possibility of migration from places without a basic income to places that do have it. The Alaskan solution to this is to limit the payments to just those who were a resident for the entire previous year. I.e. someone can move to Alaska to get the payment but must live there for at least a year before getting the first payment. A European country might want to establish systems of mutual benefit. For example, if France and Germany both have basic incomes, someone moving from France to Germany might get immediate payments. Whereas someone moving from a country without a basic income might not. Of course, that won't be a problem for the first country to pass something like this. The third issue is getting a system like this passed. Again, this should be simple in a post-scarcity society, as funding is not a problem and you don't really need limits on who is eligible. It's more difficult if your world is similar to ours, where resource limits are real and problematic. So the easy way to add this into a world is to make it post-scarcity. A more difficult path is to make it funded by taxes in a more current world. Will the Swiss be willing to vote for a VAT of 20-30% in exchange for a basic income? That's a pretty big increase from 8%. I suspect that that will be a bigger obstacle than a potential flood of immigrants. [Answer] How to get from here to a post scarcity society? I think you should avoid government-based solutions because of the inherent inefficiency of government-scale thinking. Corporations are also out for the same reason; too much red tape. So let's try it with a lean-startup mentality. The inventor of cold fusion invests startup funds to build an isolated town in an area with the basics, water and fertile land. A million applications for citizen ship come in and ten thousand are chosen. Each citizen is given a single room with a bed, a desk and a lamp. Three meals a day are provided along with medical care when needed. Nothing else is free. Now you have the basis for a post scarcity society. Nobody is going to starve or go without necessary health care. Everyone has a safe place to sleep. What happens next is up to human nature. If you want something more than the necessities, you work for it. All the classic jobs, from farm-hand to surgeon are available; nothing non-productive, no desk-jobs, and no bureaucrats. Any job which can be automated is automated, including the tracking of each citizen's "credit" balance. Citizens earn credits by working and spend them on luxuries not provided by the base economy. All credit motion between citizens generates taxation which allow "the state" to pay for food production, food preparation and medical care. Over time, as the internal economy grows, the cold-fusion inventor decreases her ongoing support of the society and if it continues to operate in the absence of external funding, then the experiment is a success. If everyone is satisfied with the basics and doesn't work, then no taxes are generated and the experiment fails. Interaction with the outside world is handled through the investor's company. Credits can be exchanged for goods from the outside (with a few exceptions, no guns, bombs, etc). A heavy tarrif is applied to all such purchases with the resulting funds being reinvested into the experiment. In the beginning, the investor would fund the conversion of credits to external products, but if the experiment succeeded, eventually citizens would be selling their creations (art, literature, technology) to the outside world, creating a balancing flow of external money being converted into credits. Notice that the base economy has no money. It is not a handout to be spend in any way the citizen wants. It is a fundamental fullfillment of the citizen's physical needs, food, water and safety. It is capitalizm with a safety net. That is the key to its success. ]
[Question] [ Picture, if you will, four planets sharing the exact same orbit and orbital speed, and separated by exactly same distance from each other. Each planet is the same size and roughly the same gravitational pull and are stable in this arrangement. No satellites and each has no axial tilt. If each world's surface and atmospheric features were similar, what could cause their evolutionary paths also to become very similar? [Answer] There are two concepts at play here. [Speciation](http://en.wikipedia.org/wiki/Speciation) and [Convergent evolution](http://en.wikipedia.org/wiki/Convergent_evolution). Speciation is the evolutionary process by which new biological species arise. I won't go deep into the details as the question asks how they can be similar but suffice to say that Speciation is the explanation as to why evolution can create difference branches even in identical situations, given this, and the fact that mutation is generally randomized, there is a statistically negligible chance the the same mutation would occur upon all the planets. Which brings us to my answer. The only way in which to ensure that evolution would be similar between the planets would be for someone to interfere with the genetic structure of the creatures on the planets. The only reason why its not impossible is because you asked for similar evolutionary paths. Can you imagine how difficult it would be to DNA sample every single insect, plant and creature on four planets to ensure they were all identical and then cull those that were not? An alternative non-evolutionary interference would be that the creatures do not reproduce but are instead grown and released into the ecosystem at a steady rate. But what about convergent evolution? This theory talks about the independent evolution of features, that is to say several different creatures developing the same kinds of abilities. Given our understanding of evolution (and constrained by my lesser understanding) it would be fair to say that you would still encounter inserts that appears to the casual observer to be doing similar things. Smaller lifeforms are so abundant and different that you would be hard pressed not to have something similar to ants, something similar to pollinators, etc. Plants would still be green (Assuming earth like condition, see [this question](https://worldbuilding.stackexchange.com/questions/720/what-environment-would-make-leaves-light-blue). I feel that generally you would still find the basic concepts, as survival of the fittest tends to mean that the most efficient way always wins out, so they would be common across all planets. Where you would start to encounter differences would be in the more complex life forms where you would notice changes. You would still find predators and prey, you would still find creatures that fly and creatures that swim in the seas. At this point, it all depends on how similar similar is as to if the answer is yes or no. [Answer] Since you are asking for similarity...there are only three options: Convergent evolution This answer here gives an excellent explanation of one way you could end up with similar life forms: <https://worldbuilding.stackexchange.com/a/2496/49> You can expect that animals similar to great cats, grazing beasts, fish, monkeys and birds to evolve on any planet. They may have differences but they would have more similarities than differences. They most certainly would not be the same species or able to crossbreed though. Cross planet transfer Some agency is allowing animals and plants to travel from one of the planets to the other. Whether this is weird alien technology or unusual astronomical phenomena a substantial amount of life must be passing from one planet to another. Consider just how divergent life just on two islands on earth can be and consider the divergences between different planets. Even if they all started off the same they would not remain the same! Tampering Some force is deliberately shaping the process. This is actually made more likely by the fact that the arrangement of four planets as described is highly unlikely to have formed by accident. [Answer] Adding a different explanations to the good existing answers: ## Common origin of life As you have not defined how life came to exist on these four planets, I offer the idea of a common origin: maybe at some point during the genesis of this star system two big bodies collided, at least one of which contained the first proto-life form which was the basis for all life on your planets. This event could either be the fundamental origin of the 4 planets - however it is unlikely, that any living thing would survive such an event. Alternatively it could just mean that the four planets where pelted by small meteorites which impregnated them with the first proto-life. From there on you would have evolutionary processes as described in the other answers, but at least based upon some common proto-ancestor. This could provide some basic guidelines, which might give the four different ecospheres a bit more similarity than completely separate origins of life. ]
[Question] [ Any form of FTL, including traversable wormholes, allows backwards time travel. (EDIT: I mean going backwards in coordinate time. We get to closed timelike curves later in the post.) My world has traversable wormholes, so I just bite the bullet and say yes, anyone with the ability to use wormholes can travel back in time as much as they like. For example, if you want to appear on the moon 1 second ago, you can set up wormholes to do that. How do we deal with time travel paradoxes then? Well, there is one rule about how the wormholes work. You can't arrange them into closed timelike curves. The moon example is fine, because even though you can go to the moon 1 second ago, it takes you at least 1.28 seconds to get back to Earth, so you can't actually change your own past using them. In fact, most things we think of as time travel just don't work; time travel is only allowed because physics demand it, but we take away its ability for you to influence your own past. What if you tried to make a wormhole that took you to the moon 2 seconds in the past? Well, if you tried to set up the wormholes to do that, the wormholes would just blow up. Quite violently in fact. All the wormholes are forced to obey the [Chronology protection conjecture](https://en.wikipedia.org/wiki/Chronology_protection_conjecture) in my world. If you try to arrange wormholes close to violating it, enough wormholes will blow up that the violation is never reached (usually more). Quoting from that Wikipedia article: > > Initial attempts to apply semiclassical gravity to the traversable wormhole time machine indicated that at exactly the moment that wormhole would first allow for closed timelike curves, quantum vacuum fluctuations build up and drive the energy density to infinity in the region of the wormholes. > > > Anyways, with those rules, humanity wants to take over the galaxy with these things, but without the wormholes blowing up. What is the most efficient solution to colonizing the galaxy with wormholes that obey Chronology protection? * There are currently wormholes that can take you from Earth to Alpha Centauri, 4.2 light years in the future. The goal is to build wormholes from Alpha Centauri to every other solar system in the galaxy (the government does not want people building all of these wormholes from Earth for alleged safety reasons). * Around Alpha Centauri, there is a machine that creates wormholes. At creation time, the mouths are created at almost the same point in spacetime, but after that can be separated and carried wherever. EDIT: The machine specifically can create [Ellis wormholes](https://en.wikipedia.org/wiki/Ellis_wormhole) (and Ellis drainholes). * The spaceships that carry the wormholes are traditional chemical rockets. However, they can go at great speeds because fuel and other resources can be delivered through the same wormhole it is tasked to carry. Also keep in mind that this means the wormholes will be time dilated significantly. In fact, that is a good thing, because it allows you to use the wormhole before its completed! * An end of one wormhole can traverse through another wormhole. * The only real restriction on how they are placed is that if they are arranged in such a way that they would form a [closed timelike curve](https://en.wikipedia.org/wiki/Closed_timelike_curve), they violently explode instead. However, it is also preferable for efficiency reasons to place them in orbits around things (because then the machine only needs to stabilize the wormhole, not levitate it). * Wormhole Inc. has access to the galaxy's finest time-dilated quantum super computers and are willing to spend years on mission planning, so you have time to find a solution. Cheaper and faster is better. EDIT: The question is how Wormhole Inc. can most efficiently distribute wormholes according to these rules, not how to change the rules to better accommodate Wormhole Inc. (although that is itself an interesting question). [Answer] The classic [Traversable Wormhole FAQ](https://www.aleph.se/Trans/Tech/Space-Time/wormholes.html) goes into wormhole networks in some detail. Essentially, a wormhole network defines an "Empire time" of mutually spacelike-separated points which have, thanks to the wormholes, a shared simultaneity. Creating such a thing without violating the CPC would require some amount of planning; the FAQ suggests sending probes containing wormholes at high sublight speeds, using them as "seeds" through which you send more probes branching off in different directions to fill the entire space. Creating a plan for this sort of staggered penetration shouldn't be too hard for your quantum supercomputers. The biggest problem I think you'd have is that, once you started off, pretty much everything would happen all at once. At high speeds, the amount of time dilation on the probe end of the wormhole would be significant, so you'd be able to go further and further in less and less time as the probes accelerate. Accelerating at 10g (and they could accelerate continuously, since you can pump fuel to them through the wormhole), in a year after launch your wormholes would be about 15 ly away; but only a year later, they'd be about 3000 light years away, and it'd only take 15 more months to get to the Andromeda galaxy. If you want to keep up a uniform probe density, you'll have to shoot more and more branch probes through more and more frequently as time goes on; either that, or throttle the acceleration based on the production rate for new wormholes. [Answer] The simplest solution is to assume that the 'laws of physics' including those pertaining to the creation of wormholes (WH) prevent anyone from using WH that violate the chronology protection conjecture (CPC). As as a result the CPC is no longer a conjecture but rather a fundamental principal of physics. You can even 'write' into the background of your story that experiments conducted with (mirco) wormholes shortly after their first 'discovery' proved conclusively that any attempt to violate causality using one caused the WH concerned to 'collapse' the instant any attempt is made to send information through it. It doesn't have to be a violent explosion either. The instant a particle or photon enters a micro-sized CPC violating WH it 'collapses' in on itself and/radiates out its (tiny) mass as sub-atomic particles. So if you assume every 'large'/traversal WH starts off life as a 'seed' or micro hole that has to be actively expanded from a quantum scale anomaly up into something useful over time there won't be a violent explosion because you can't grow a CPC violating WH. You can either shield it from a CPC event or 'grow it' but not both at once. This means the only WH you can 'grow' are ones that don't violate CPC. PS: and no-one would try such an experiment even if they could with a macro sized WH because the dam things are hugely expensive to build - requiring an investment in exotic matter/negative mass/upsidasium/ whatever to expand upwards in scale. It would be like risking blowing up the LHC just to reproduce the same results you would get with $1000 worth of equipment in any run of the mill science lab. [Answer] The network topology you want is a tree. Earth is the trunk. Branches split off at Alpha Centauri. Each branch may split into as many branches as it likes, but they cannot connect to other branches. What this means, practically, is that any world is allowed to send wormholes to any neighbouring solar systems that does not have any wormholes yet. But they are forbidden from sending wormholes to a system that is already connected to the network. Each system may have one uptime gate and as many downtime gates as they like. For ease of navigation, you can let systems assign network addresses simply by counting their wormholes. Earth's address is 1. Alpha Centauri's address is 1.1. Alpha Centauri's connections: Beta Centauri is 1.1.1, Proxima Centauri is 1.1.2. And so on. If you were at 1.1.2.6.2.5 and you wanted to get to 1.1.2.3.8.1 then you would immediately know that you have to go through the single uptime gate in each solar system until you get to 1.1.2 at Proxima Centauri, then follow the numbers downtime to 1.1.2.3, 1.1.2.3.8, 1.1.2.3.8.1. This network will put Alpha Centauri at the centre of more galactic trade routes and communication lines than any other system. After a few centuries it may start to feel like Alpha Centauri is the capital city of the galaxy and Earth is the quiet suburb on the capital city's fringes. [Answer] I am not sure there is a problem. No need to blow anything up. See EDIT at the end for a more formal explanation. Your assumption is that traversing a wormhole does not take as long as making the same trip by light speed. This is NOT a given. A wormhole between here and Alpha Centauri, for instance, could take 4.4 years to traverse, whether through a wormhole or the more scenic route traveling at the speed of light. Since wormholes are pure conjecture, time itself in a wormhole may not be (probably isn't) the same as time in normal space/time. I suppose it could be conjectured that, to the traveler, it may seem instantaneous. Wooops, in a blink of my eye, 4.4 years passed. But if you WANT to use wormholes, so that you can travle FTL, such that you can only go into the future to protect the Chronology protection conjecture (a neat concept) then design the physics such that, when you travel through a wormhole in the direction you came from (the return loop of the circle), it takes twice as long as the trip would have at light speed. That is, you end up taking a very slow boat throught the wormhole to come back home, on the return leg. Leave the calculations for the time lapse up to your physics, not us poor humans. It's your world, since you are playing around with the laws of relativity anyway, you get to modify the rules in whatever fashion you want. Warp time in a way that suits your story, and make your wormholes into reverse time machines. *EDIT* To clarify the 'reverse time machine' concept. If, for instance, I leave point A and go through a wormhole that actually takes less time to traverse than going the same distance the 'scenic' route to point B at cee, relative to the observer taking the scenic route at cee, it is true that I will arrive at the destination B before the light 'pulse' containing the information of my departure from A gets to B, so it might appear as if I arrived before I left. However, if I take the return trip (B to A), I will 'pass' that pulse of light in the opposite direction. I will NOT arrive back at the original destination A before the pulse of light is 'sent' from A, I will have passed that pulse of light in its journey. I will have 'caught up with time', and will still arrive back at my origin A after I first left. If I turned around and looked 'back' to B, yes I would have arrived back at my original point A before the information containing my departure from B arrived at A, but again if I returned back to B, I would pass that pulse of light (information) and still arrive back at B AFTER I left B. In fact, I could pass the pulse of light going from A to B of my first departure, again, going in the same direction, and arrive at B beore both pulses of information arrive at B (first and second departure from A). But at no 'time' would I have an opportunity to change the data in either pulse of light. The 'ripples' of information from A would still be contiguous in time, as they arrived at B. The history would not have changed. TL:DR That is, if you travel AWAY from the point that information is being transmited (originated) from at FTL, you are going one direction in 'time', ahead of the information travel. But if you travel back TOWARDS the origin of that information, you are traveling FORWARD in time again. You will always arrive at the origin A after the pulse of light was originally sent, relative to an observer at A. [Answer] It has been proven that, given that wormholes exist and they connect two regions of space instantly, you can hurt the Chronology already with a single wormhole. Check out this episode of Sean Carroll's Mindscape podcast where he explains a lot better than I could ever do: <https://www.preposterousuniverse.com/podcast/2020/11/23/124-solo-how-time-travel-could-and-should-work/> Here is a quote from the transcript. I really advise to take two hours during commute and listen to this podcast. snip Now, in fact, they later worked it down to just a single wormhole, and this is a little bit elaborate, but it’s worth explaining ’cause it’s just so cool. So, imagine one wormhole. Imagine we make a wormhole, don’t ask me how we make it, but we have these two spherical regions of space, the mouths of the wormhole, and you go in one, you instantly come out the other one, okay? And imagine that somehow, we can manipulate the mouths of the wormhole. We can basically put a tractor beam on and move one end of the wormhole around independently from the other one. So, this is the point, that there remains zero distance if you travel through the wormhole. You don’t actually traverse any distance going from one sphere to the other one, but from the point of view of someone outside, the two mouths of the wormhole could be very close, or they could be very far away. And so what Thorne and his friends say is, imagine that we move them, but we start them right next to each other so they’re very close, and we move one of them far away, and then we move it back. Okay? 1:22:25 SC: And they know the other one just stays constant, the other one stays put. This little thing that we just did, one mouth of the wormhole stays put, the other one moves out, let’s say close to the speed of light and then comes back, that should remind you of the twin paradox. If you put a clock on one wormhole and on the other one, the clock on the wormhole that stayed the same might know it reads an hour has passed. Well, let’s say this. Yeah, let’s say two hours have passed on the wormhole that stayed the same, on the mouth of the wormhole that stayed put, whereas the other one that went out and came back, its clock only reads one hour. Okay? So initially the two clocks, again, from the point of view of someone outside who’s watching all of these shenanigans, there’s two clocks, they both say noon, and then two hours passed from the point of view of the wormhole that stayed stationary, so its clock now says 2:00 PM, but the wormhole that went out and came back, its clock just as 1:00 PM. So they’re now out of sync by an hour. 1:23:28 SC: And you say, “Alright, that’s fine. Good special relativity, twin paradox. I get it.” But here’s the twist: When you look through the wormhole, you see what’s on the other side. You don’t see flashing lights, it’s not a subway, you see whatever is on the other side. It’s like a window, it’s like, you know, a telescope or something. You’re seeing through a view portal in space-time. And let’s imagine that our clocks are so arranged that you can see the clock on the other side, you can see the other wormhole’s clock, the other mouth of the wormhole’s clock, by looking through either sphere. So, when you’re moving, when the one wormhole is moving, it’s going out and coming back, what would I see if all along, I was looking through that wormhole at the stationary clock? Well, from the point of view of looking through the wormhole, nothing’s moving. There is still zero distance between the two mouths of the worm hole from the point of view of through the wormhole as opposed to outside. Outside the wormhole, the wormhole mouths are moving apart and then back together, but from looking through the wormhole, there’s always no change in distance whatsoever. 1:24:40 SC: And so you don’t see the other clock moving; you see it stationary. And therefore what you see is that clock ticking at one second per second, just like your clock. And that sounds paradoxical, because you say that, “Well, if I’m outside and I look at both clocks, one does a little twin paradox motion and goes forward one hour in time; one just days stationary and goes forward two hours, so now they’re out of sync,” but if, I instead of looking them from the outside, look through the wormhole, to borrow a phrase, they’re in sync. They both read the same time. So, once the wormhole that went out on a journey comes back, it says 1:00 PM, its friend that stayed behind says 2:00 PM, but when we look through the wormhole from the one that went out and came back to the other direction, we still see it saying 1:00 PM, ’cause it still has to say the same thing as the clock that was moving out and came back. 1:25:37 SC: And what that means is, I hope you followed this, I hope you bought everything I just said, what it means is if you go through the wormhole yourself from starting in the mouth that went out on its journey and came back and its clock says 1:00 PM, you come out the other wormhole not just in a different location in space, but also at a different moment in time compared to the point of view of the external observer. Since you are looking at the clock on the other side of the wormhole and it says 1:00 PM, you come out at 1:00 PM from the point of view of that wormhole mouth. So you have moved into the past from the point of view of the external observer. What the external observer sees is at 2:00 PM, you entered the wormhole, and at 1:00 PM, you exited. You exited before you left. And then you could hang around and there could be another copy of you that said hi to the copy of itself that went through the wormhole. An honest-to-goodness closed time-like curve that you made in a local region of space; you didn’t just put it into the universe from the start. snip Again, this is the link. Go there, take a look. <https://www.preposterousuniverse.com/podcast/2020/11/23/124-solo-how-time-travel-could-and-should-work/> [Answer] Wormholes Pairs Take a Lot of Time to Set up Suppose you want to create a wormhole pair between here and Andromeda. The only way is to take two nearby regions of space (which are already entangled with each other by virtue of being next to each other ) and push them apart until one reaches Andromeda and the other reaches here. The bridge takes 2.5 million years to build. Of course after the bridge is built we can pop back and forth between galaxies very quickly. But the long setup period prevents information being transmitted faster than the speed of light. This protects the chronology. ]
[Question] [ By that, I don’t mean what type of structures, I mean under which part of the Earth? It's an extremely densely populated nation. As densely populated as many major cities - think Hong Kong and more specifically the Kowloon at its prime. I’m struggling to think about where on our planet this place would be and roughly how big it would be. I need to know this for traveling distance purposes. For reference, Hong Kong is 2754 km2 with a population of 7.347 million people - that’s around 6500 people per square kilometer. Also, assume they have the tech to be able to build and maintain this space as this takes place a thousand or so years into the future. They have absolutely no contact with the outside world so it doesn’t necessarily have to be entirely under an inhabited continent but certainly off of the coast of one. [Answer] Well this its a very complicated scenario, the maximum amount of people for a city with a Kowloon kind of lifestyle would be huge, like stupendously huge, in an area the size of Delaware [you could fit all of the current human population](https://sploid.gizmodo.com/what-if-the-entire-worlds-population-lived-in-one-city-1787022943) so the amount of land its not an issue here, given that fact your real limitation would be how to feed all the resources taken by such city, basically we would take all the resources in the entire world just to feed such behemoth, and here I would have to ask, do you have hydroponic systems? does energy gets supplied by fusion reactors? if the answer to those its yes, we could discard any coastal areas due to inundations, the same for rivers and lakes (there are huge sources of underground water almost everywhere), same for agricultural lands or fossil fuels, fusion and hydroponics make such things irrelevant, hence we would have to search for rare earths like lithium and the high metal concentrations that the construction of such city would need for steel, currently the leader for rare earths its China, given that they have also a developing steel industry I would say that they are the perfect candidate. [Answer] You could go with deep caves like Krubera <https://www.gizmodo.com.au/2014/03/the-complete-map-to-earths-deepest-cave7208-feet-deep-8-miles-long/> or large caves like Hang Son Doong in Vietnam (just an example) <https://en.wikipedia.org/wiki/Hang_S%C6%A1n_%C4%90o%C3%B2ng> where the cave is quite large it has its own ecosystem. They can probably operate some form of clean energy such as a super refined nuclear fusion plant that is small and powerful enough to power your civilization. Another thing to note that in Australia, they have built underground dwellings (town) in Coober Pedy as they mine opal there (<https://en.wikipedia.org/wiki/Coober_Pedy>). Hope these examples give you a good idea where to build your underground place. [Answer] An analysis of most existing cave systems may yield your answer. Existing cave systems normally form in limestone rock, normally through erosion of hundreds of thousands of years caused by water. Some of the largest caves in the world, those in Borneo or Vietnam, are also tectonically formed too. Access to Hang Son Doong cave (the largest cave in the world, 5km long, 200m high and 150mm wide) is restricted, mainly because it is flooded much of the year and quite dangerous. However Deer cave in Malaysia (174m wide and 122m high) attracts 25k tourists a year. [![enter image description here](https://i.stack.imgur.com/nbhdy.jpg)](https://i.stack.imgur.com/nbhdy.jpg) I would suggest your underground cavern must therefore not be able to be flooded - therefore in a mountainside is the best location such as Deer Cave above, in a fairly elevated position above sea level, in a region of the world where tectonic forces are pushing land up (not down). The underground cavern must be in a relatively stable material (limestone is good) that is also able to be extended or worked on with little industrial effort. Finally to sustain your city you would need an energy source, and water source. Spring/river passages could serve this purpose, evidenced in most caves, requiring lots of rainfall - likely in tropical regions. My bet is your city should be in the tropical bands of the earth, in mountainous regions. ]
[Question] [ When looking at mammals and their heart rates one can find a [correlation between the lifespan of a mammal and their heart rate](https://biology.stackexchange.com/questions/20489/is-there-any-relationship-between-heartbeat-rate-and-life-span-of-an-animal). Namely most mammals seem to get [about 1 billion (the American one)](https://skeptics.stackexchange.com/questions/5701/does-every-species-get-around-a-billion-heartbeats-on-average) of heartbeats in their life (with some slight discrepancies). --- Now mammals, such as humans, use blood to transport oxygen. When they enter increased physical activity, e.g. running, their heart rate increases to transport more oxygen to organs and muscles. My idea is that if we can increase the oxygen transported by the blood we could decrease the heart rate necessary to transport enough oxygen, thus increasing life-expectancy as we have more beats left. A possible way to achieve that increase in oxygen transported in blood is to use [the hemoglobin of lugworms](http://www.hemarina.com/index.php?rub=hemoglobin_oxygen_carrier), which [can transport ~40 times as much oxygen as human hemoglobin](https://www.pri.org/stories/2017-07-31/lugworm-frequently-used-bait-could-save-human-lives). --- Q: Could this increase in oxygen-carrying-capacity in blood lead to a decreased heart rate and thus to an increased lifespan? Bonus: How many additional years could I get? [Answer] Probably not. This idea that heart-rate inversely correlates with life span, also called the [rate of living theory](https://en.wikipedia.org/wiki/Rate-of-living_theory) While some studies have showns a correlation between heart rate and life span, this doesn't imply a causal relationship. In fact it's more likely that heart rate and life span are both a function of the size of the animal. Larger animals having larger more efficient hearts that need to beat less. A [2007 study on the subject](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2288695/) found no correlation between metabolic rate and average life span birds and mammals. They concluded: > > Body Mass Is Likely Associated With Longevity due to Ecological Constraints > > > --- Of course in the degenerate case there definitely isn't a link between low heart rate and a longer lifespan, since with a heart rate of 0 a lifespan of 0 is likely. [Answer] There is a lot of work done in science to see if there is a correlation between heart rate and longevity, but as the previous answer shows, this is not held to be the case. The longevity of the heart though is only one thing that can kill you. Ironically enough, the molecule that seems to have the most to do with our ageing process is oxygen itself. In that sense, it's probably more likely that cumulative oxygen exposure is likely to kill you more than heart rate. But (I hear you all say), exercise makes our heart beat faster, gets us breathing harder, and generally makes us use MORE oxygen and is also supposed to be good for you, right? Well, exercise is good for us, but the truth is that anaerobic exercise is good for us because it actually causes a form of hypoxia; we're using energy faster than the oxygen in our system can be replaced to generate more energy within our system. It's only mild so it's not the life threatening form of hypoxia associated with suffocation and it's self tuning insofar as when we're exhausted we can't continue the exercise. One way that exercise increases our fitness is by acclimating us to less oxygen in our bodies. That means when we are not working as hard, we can go for longer on the same amount of oxygen. This is exemplified the most by high altitude African long distance runners who come down to sea level and higher atmospheric pressures and run marathons with higher saturations of oxygen than they're used to, allowing them to run for longer without getting as tired. Breathing excess oxygen generates what are called Free Radicals in our bodies, that can be harmful to our cellular structures. This is one of the reasons that anti-oxidants are touted as such a solution to the ageing process. They reduce free radicals out of our system and ensure that the amount of oxygen in our system is balanced a little better to our energy needs. So, instead of making hemoglobin more efficient, perhaps the secret to longevity is making it less efficient. If we can reduce oxygen levels to those that we use at rest during normal breathing, and use increased heart rate and breathing to increase our oxygen levels during exertion, then several things will happen. First, free radicals will be (radically) reduced. If we use all the oxygen we can absorb, then there's less of a chance of free radicals being present in our system. This means less overall damage to our bodies in normal day to day life. Second, there will be an upper limit on what exercise or physical exertion we can actually do. This is not so bad a thing as one might think. In the past, we had to exert ourselves to eat and get out of danger. We've changed our environment so much that we have machines helping us get food and no natural dangers to speak of. Sure, we won't be able to out run a bullet, but we can't now so in some respects nothing would change except that we would all be a little slower. Finally, our bodies would not age as fast because we're not processing as much oxygen (and carbohydrates) to produce energy. This is really one of those 'the light that burns half as bright burns half as long' situations. We know that oxygen causes ageing in our bodies, and we know that the animals that seem to be longest lived in our environment are those which are specialised to low oxygen environments, like the Naked Mole Rat (Underground) and the Bowhead Whale (DEEP underwater). All this said... It is important to note that a longer life is not necessarily a more fulfilling one. You'll be slower, doing less with your life (No one with lower oxygen absorption rates is climbing Everest for instance) and if all our tech dies one day, so do we. (But, that's arguably the case for most of us anyway if that happens.) Also, oxygen is not the only factor here. Assuming that we live longer with regular heart rate (say only 5% reduction in O2 absorption) then our heart has to beat more often. That may well end up one of the limiting factors. Not to mention mental disorders like Alzheimer's and Parkinson's disease. There are a range of things that could still kill us long before our cells naturally 'age'. When you get right down to it, the human body is a marvel of bio-engineering. It is staggeringly complex, and it is that very complexity that causes part of this problem. Natural ageing, either by oxygen processing or the breakdown of any of the other 'critical' processing systems like kidneys, liver, heart, brain; the list goes on. The one thing that is sure is that evolution has built a body that is capable of far more energy expenditure than is currently needed with our current technologies to survive. As such, in a technical society, dialing back our oxygen intake may slow us down and lengthen our lives. Is that a good thing? Ultimately, if the choice was made to us, it would be up to each one of us to decide for ourselves. [Answer] You are too focusing on heart rate. If blood had 40x capacity for oxygen it could extend lifespan in many ways (not related to heart rate), decreased heart rate would be just side effect (that would probably lower that capacity). Increased oxygen capacity would help in cases of heart and brain attacks where fast intervention is required. Looking at [mortality rates](https://en.wikipedia.org/wiki/List_of_causes_of_death_by_rate) , A1 (Coronary artery disease) and A2 (Brain stroke) categories contribute to 7,4% of deaths (if my calculations are right). Indirectly it would help with survivability in other categories too. On its own (without medical intervention) heart has some [regenerative abilities](http://nocamels.com/2013/05/researchers-stumble-upon-the-hearts-self-healing-ability/) so with better oxygen supply it could cope with damage better. [Answer] As a hypothetical feature of superhumanoid physiology, genetic manipulation, or a sci-fi explanation for improved longevity, yes. "Is this possible even if implausible?" Yes, it is possible. I'm not much of a mathematician, please forgive the loose mathematics to estimate an answer to "How much longer do they live?"\new info The original calculations have been redacted in light of newer findings. You could estimate based on the tool at the bottom of this post a decrease in estimated age of 3 years for an 8% decrease in VO2 max (I've heard it quoted 1%/year in various clubs). The average is quoted as 40 for fitness enthusiasts and 24 for the average person in fitness and health clubs. Age affects oxygen-carrying capacity moreso than the other way around, and not as a given/established causal relationship, only as a correlation. You could* in the name of fiction form an estimate from those numbers, like, say "if a 150yo wanted a fitness age of 34 with a 208 heart rate, they'd need 150-34=116/3=38.67, so 40\1.08^38.67=40^19.6, a VO2 max of around 784" but you see how quickly that got out of hand. That could be the equivalent of a human with an elephant or whale's oxygen-carrying capacity. The caveat to that is bigger isn't always better (think horses and cheetahs and dogs, which all have higher VO2 max than humans, with supportive anatomies for the levels they do have, and humans outlive all of them). I've never found a study that supported it, the dogs racing the Iditarod are said to be near 225 or 230 for VO2 max. ![https://www.sport-fitness-advisor.com/vo2max.html](https://i.stack.imgur.com/le1PH.jpg) In science!-based reality, no. \Partial edit, somewhat more plausible, but still limited to the entirety of thenstructure supporting it. You'd need something like Greed from FMA's body structure (not Brotherhood). <http://www.dailygalaxy.com/my_weblog/2010/11/sherpa-genetics-human-evolution-at-work.html> "Even at elevations of 14,000 feet above sea level or higher, where the atmosphere contains much less oxygen than at sea level, most Tibetans do not overproduce red blood cells..." Instead, they adapted to negate polycythemia, the body's response to oxygen deprivation (creating too many more red blood cells. <http://www.nature.com/articles/nature13408> In an environment in which scientists (biologists) had anticipated higher red blood cell count to facilitate greater efficiency in oxygen-carrying capacity, humanity had instead adapted by way of genetics and interbreeding to mitigate the effects of hypoxia. Human adaptation was thus primarily negating negatives (hypoxia & polycythemia) rather than bestowing positives (increased oxygenation, carrying capacity). Humanity adapts by nerfing environmental hazards moreso than outright buffing. sphennings made an excellent point, results of studies do not necessarily mean a causal relationship between heart rate and lifespan. Athletes are the best example for both forced inclinations in oxygen-carrying capacity (supplements) and natural inclination of lower resting heart rates & higher oxygen-carrying capacity. The base or resting heartrates of active individuals -- professional and elite athletes especially -- appears to inversely correlate with oxygen-carrying capacity measured as VO2 Max. ![https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767992/](https://i.stack.imgur.com/lmP6u.jpg) While this is estimated by scientists and doctors as the "common sense/advice" that healthy/fit individuals live longer, heart rate and oxygen-carrying capacity are -- I'm going to stop this here and finish the edit when I have a desktop in 4 days. As per the above information on athletic correlation, I found fitness.mercola.com/sites/fitness/archive/2014/11/07/amp/how-fitness-age-indicate-longevity.aspx to disprove where I was originally going (that despite fitness and healthiness plenty of athletes die earlier than comparatively less fit or healthy individuals) but the more I search the more similar articles, journals, and studies I find. <https://www.worldfitnesslevel.org/#/> This tool from the mercola article told me that despite my age, 34, and low VO2 max (31), my "real" count is actually <20 and about 59 for VO2 max. With the same max heart rate, it shows a loss of about 3 years & 8% VO2 max for picking the most sedentary choices. I tried with different info and it came out to be about the same. ]
[Question] [ I was wondering what is the smallest a terrestrial planet can be and maintain plate tectonics and generate a magnetic field, atleast to Earth's current age? [Answer] I have been browsing a few references on the subject and the parameters that are involved seem more numerous than just the size or mass of the planetary body. Examples in the Solar System are already contradictory with the mass parameter: while Mercury has a magnetic field (around 1% of Earth's, i.e [300 nT on the surface at equator](http://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact.html), vs. [30 µT on Earth surface](http://gji.oxfordjournals.org/content/183/3/1216) - those values are order of magnitude and vary from place to place), Venus has so to speak no inner magnetic field, all of its measured magnetic field likely coming from its ionosphere. Basically, the required conditions for a planet to have a magnetic field are a conductive liquid core layer, along with rotation and convective motions of that liquid layer. These convective motions are due to a cooling solid inner core. I did not find quantitative values regarding the minimum mass for such effects to appear, but Mars likely was around the limit, as [its core likely cooled to the point where no convection exists anymore](http://www.sciencedirect.com/science/article/pii/S0012821X02011263), either because its liquid core froze or its solid core is not hot enough to maintain the convectional motions. [Studies](http://www.sciencedirect.com/science/article/pii/S0032063311000742) tend to show that cataclysmic events such as planetary impacts may be benefactory for plate tectonics to begin, as they would weaker the uper layers of the planet. However, I also found [studies](http://onlinelibrary.wiley.com/doi/10.1029/2008JE003287/full) that [suggest](http://www.sciencedirect.com/science/article/pii/S0019103511000315) impacts may cripple the dynamo effect, i.e. the magnetic field... As well as [studies](http://www.sciencedirect.com/science/article/pii/S0012821X11004699) hinting the contrary, which really tends to show that no conclusion can really be drawn at the moment without further data. Sadly, due to the very [few known exoplanets](http://www.exoplanet.eu/diagrams/) that have a lower mass than Earth, research regarding magnetic fields mainly address heavier planetary bodies. Factors that are usually taken into account are [the temperature distribution along the planetary layers](http://www.sciencedirect.com/science/article/pii/S0019103511000595), the mass properties, the materials properties, the heat sources, incuding radioactive decay, and the presence of water, which is supposed to weaken the upper layers. This being said, [this research](http://www.sciencedirect.com/science/article/pii/S003206331300161X) for example has made computation for planetary objects being 0.1 and 0.5 Earth mass. They tend to indicate that 0.1 Earth mass planets would be very unlikely to present with plates tectonics at all; 0.5 Earth mass would strongly depend on material properties, 1 Earth mass would be most likely to present with plates tectonics, while the probability decreases again as mass increases. In conclusion, it seems that Earth is optimal regarding these factors, or maybe we lack other points of data and even a better understanding of what really is happening deep below our own feet. Objects smaller than Earth may have plates tectonics and a magnetic field, but not objects much smaller. [Answer] Plates move around because of convection in the mantle underneath them. That basically means they are floating on currents in the mantle. The mantle is liquid, though very very viscous, so as it flows hither and yon as it is heated by the core it rises then flows along the under surface of the crust then cools and sinks. There is friction between the bottom of the plate and the surface of the mantle (the asthenosphere). This is called basal drag. There are alternate theories that it is mantle plumes that are doing the moving (still transferred to the plates through basal drag) not convection current. So theoretically, you need a hot core with a liquid mantle differentiated from the core to have plate tectonics. Well that includes just all the large objects in the solar system. Venus, Mars, Mercury, Ganymede, Titan, Callisto, Io, Luna, and Europa should all be large enough to have differentiated silicate mantle above a metallic core. Obviously, since we know very little about the mantle and core that we are standing on, we know even less about the interiors of these distant objects. On the other hand, we haven't OBSERVED plate tectonics at work for sure on any of the other planets. * [Venus](http://www.es.ucsc.edu/~fnimmo/website/paper5.pdf) shows tectonic activity but not plate tectonics. Possible reasons include lack of water or higher viscosity of the Venusian mantle. * Mars had plate tectonics [early in its history](http://www.iflscience.com/space/mars-may-have-continental-crust-similar-earths/) that stopped, possibly due to cooling of the planet. Some recent evidence suggests it may have partial plates today, especially around on [Tharsis Rise](http://digitalcommons.csbsju.edu/cgi/viewcontent.cgi?article=1048&context=compass). * [Mercury and Luna's](http://www.lpi.usra.edu/education/explore/shaping_the_planets/tectonism.shtml) plate tectonics ceased 3.7 and 3 billion years ago, respectively. * Io has lots of volcanoes and is heated from tidal stretching from Jupiter, but [does not have](http://skywalker.cochise.edu/wellerr/students/io/project.htm) plate tectonics. * Europa has a structure fundamentally different from earth, since it has an ocean deeper than our crust. The ice sheets on the surface thus act like our crust, sliding over a liquid ocean instead of a mantle. Given that water is much less viscous than molten rock, it is no surprise that [Europa](http://www.space.com/27059-jupiter-moon-europa-plate-tectonics.html) is suspected to have plate tectonics. * Ganymede is kind of in the same boat as the Europa, and some think that has the same [ice plates over ocean](https://www.uwgb.edu/dutchs/GeolColBk/Ganymede0.HTM) thing going on...or that it used to in the past. * Callisto always gets ignored, and I can't find anything about it. I'm the third biggest moon, why do you ignore me. Just because I don't have volcanoes, oceans, or atmosphere. Sad Face :( * Titan may have a huge ocean like Europa and Ganymede, but I [can't find anyone](http://www.nasa.gov/mission_pages/cassini/multimedia/pia10654.html) who thinks that this causes plate tectonics. On to magnetic fields. This one is easier to summarize: * Venus's [magnetic field](https://en.wikipedia.org/wiki/Venus#Magnetic_field_and_core) is induced by interaction between atmosphere and solar wind, not due to its core, and is thus weak. Venus's slow rotation may prevent its core from making a field. * Mars may have had an [internal dynamo](http://www.space.dtu.dk/english/Research/Universe_and_Solar_System/magnetic_field) in the past, but no longer. * Mercury does have a [magnetic field](https://en.wikipedia.org/wiki/Mercury_%28planet%29#Magnetic_field_and_magnetosphere) due to its hot core. * Ganymede does have a self-generated [field](https://en.wikipedia.org/wiki/Ganymede_%28moon%29#Magnetosphere), in addition to the induced field from Jupiter due to its subsurface ocean. The self-generated field is probably generated the same way as Earth's, which makes you wonder what Ganymede is doing that Mars and Venus aren't. * [Titan](https://www.newscientist.com/article/dn14717-saturn-magnetises-its-moon-titan/) and [Europa](http://solarsystem.nasa.gov/europa/evidence.cfm) have induced magnetic fields from their salty oceans. Ganymede does too, in addition to its self-generated field. [Callisto](http://www.space.com/16448-callisto-facts-about-jupiters-dead-moon.html) is so ignored that we'll dump it in this category too. * [Luna](https://en.wikipedia.org/wiki/Magnetic_field_of_the_Moon) has a very weak magnetic field, and what is there might be caused by magnetization of moon rocks during large impact events. Conclusions: 1. Earth has both for sure 2. Objects as small as the Moon may have had plate tectonics in the past 3. Objects as small as Ganymede have magnetic fields to this day, for mysterious reasons. 4. A different sort of ice tectonics/induced magnetic field is possible on cold moons/planets with huge salty oceans, down to the size of Europa. 5. Lithospheric plate tectonics might have something to do with viscosity of the mantle, in which case a hotter mantle is better. 6. The way to preserve tectonics in a smaller body is to have tidal heating of a moon to keep the mantle nice and hot. Of course, that isn't working for Io, so I guess no one knows. So there you go, the answer is that there is no answer :) [Answer] According to NASA, the smallest planet they have discovered that functions like a planet, Tectonic plates, volcanoes etc is roughly the size of our moon. That's not to say there can't be smaller planets out there as such, though in this instance, the smallest recorded so far is Kepler 37-b As quoted from an article: > > A team of Danish astrophysicists has now made what may well be a sensational discovery. They have found the smallest planet that has ever been observed in orbit around a star other than our Sun. > > > With a radius of only 0.3 times that of the Earth, the planet orbits its host star once every 13 days. > > > Sadly however, it also states that due to the planet being so small, it cannot create enough gravity to maintain a sustainable atmosphere, meaning it wouldn't be able to harbour human life without machines, or terraformers etc. Sources - [Here](http://sciencenordic.com/nasa-spots-smallest-planet-ever) and [Here](http://www.nasa.gov/mission_pages/kepler/news/kepler-37b.html) Give a better understanding of the planets, so doing some background research yourself to gain a full understanding would be best if you wish to delve deeper. The planet isn't known to have a magnetic field, though it is assumed so. it could be considered terrestrial, though it's a far stretch. In terms of fiction, you could make the planet however small you wanted it. ]
[Question] [ I was thinking of writing a story and had the idea of having a society exist on the core of a gas planet. The core would be similar to earth with a breathable atmosphere similar to ours above it but still have the outer atmosphere of hydrogen and helium above it as these two gases are lighter than the mainly oxygen and nitrogen of the inner atmosphere and so the breathable atmosphere would sink down and allow the lifeforms on the planet's core to live. I was just wondering if this is possible at all in regards to science and its limitations or if this could never happen in real life. [Answer] Absolutely not. First off, "breathable atmosphere sinking to the bottom" is not a valid assumption because gas giants are solid on the inside, due to the pressure as Thucydides pointed out. Also, not only does Jupiter radiate more heat than it gets, Jupiter's core is hotter than the surface of the sun. [Answer] # No. Gas giants are not big planets with a huge atmosphere, they are an almost [failed star.](https://en.wikipedia.org/wiki/Brown_dwarf) It is the enormous pressure inside a Gas Giant that lets hydrogen to be found in metallic form. Liquid Metallic Hydrogen is some sort of [degenerated matter](https://en.wikipedia.org/wiki/Degenerate_matter) and the required pressure to form such type of Hydrogen is 25 Gpa($3.5\times 10^6$ psi). At that kind of pressure Oxygen becomes solid, so no breathable atmosphere made of oxygen in the deep layers of a Type-I Gas Giants. But how about the other types of gas giants? Turns out that are five of them in the [Surdasky's Gas Giant Classification](https://en.wikipedia.org/wiki/Sudarsky%27s_gas_giant_classification). In our solar system, we only have Type-I, which is the coldest. Type IV and V are what we call Hot Jupiters, to much close to their parent star and to hot for almost anything. There's also the fact that Liquid Metallic Hydrogen is really conductive. It's responsible for Jupiter's magnetosphere which is fourteen times strong that ours on Earth. And not a good factor for life. So, I guess that covers all basic facts of why not life can prosper inside a Gas Giant. The environment of and Gas Giant is simply to harsh to anything build up and later develop as life. Pressures, temperatures and constant electric currents also make impossible to life came from another place and make the Gas Giant his home. At least not in his core. Probably they will have more luck setting up a station in the atmosphere of a Type II, that are made of water vapor. [Answer] It might be possible, depending on the size. Per [this question](https://astronomy.stackexchange.com/questions/370/can-small-gas-planets-exist) on the astronomy exchange, smaller gas planets can exist. The minimum density it would need would be is related to it's distance from the star it orbits though. As mentioned in Zxu's answer, you wouldn't be able to pull off a gas giant due to issues with pressure. Alternatively, you could also have a planet with a solid core, but a tall and more opaque atmosphere which might give the appearance of a gas planet. You still wouldn't be able to get too large for the same reason. You also didn't specify if the inhabitants were on solid ground or not, so this may or may not be an option. ]
[Question] [ Our universe is incredibly young, relative to its total life span. How young? Well, it contains stars. Giant balls of readily fusing hydrogen and helium that give off a pleasant glow, suitable for igniting the formation of life forms on planets orbiting at optimal distances with healthy chemical compositions. About 100 trillion years from now, the universe will look very different. All hydrogen burning stars will have exhausted their fuel, and all pockets of free floating gasses large enough to form into new stars will have done so, and then those stars will have all run out of fuel. The only remaining stars in this future universe will be degenerate ones: white dwarfs, neutron stars, and black holes. The universe will have entered what's known as [the Degenerate Era.](https://en.wikipedia.org/wiki/Future_of_an_expanding_universe#Degenerate_Era) Assuming that there are chemically ideal planets for it to evolve on (these will stick around for a few hundred trillion more years after the stars have all burned away), could life evolve in such a universe? How would life in the Degenerate Era differ from life in the current universe? What is life? When considering the question of the evolution of life, we must first answer an important question: what is life? While there are many working definitions of life, here's a simple one that may work for the purpose of this question. In order to be considered "life", something must meet these four criteria: 1. Reproduce - Life must be able to reproduce in a manner which passes on the traits of the parent organism(s). 2. Grow - Life must consume matter and use this matter to grow in size. 3. React to stimuli - Life must be capable of reacting to external stimuli. 4. Metabolize - Life must be able to utilize chemicals and energy to change its structure and physical state. [Answer] There are several possibilities - actually, quite a few - for the development of life in the Degenerate Era. Some have potential; some don't. 1. The planet is a rogue planet. It has been proposed that [rogue planets could retain heat and support life](https://en.wikipedia.org/wiki/Rogue_planet#Retention_of_heat_in_interstellar_space) via geothermal energy from radioactive decay (see also [Stevenson (1999)](http://adsabs.harvard.edu/abs/1999Natur.400...32S)). However, it seems unlikely that a planet's core could remain "hot" for any time period of an order greater than billions of years (see [here](https://physics.stackexchange.com/a/80169/56299) and [here](https://physics.stackexchange.com/a/154514/56299), as well as [here](https://earthscience.stackexchange.com/a/2524/1399) and [here](https://en.wikipedia.org/wiki/Timeline_of_the_far_future#Future_of_the_Earth.2C_the_Solar_System_and_the_Universe), noting the disagreement between the latter two links). You would have to have a planet form in the degenerate era for this to be possible. I find this unlikely simply because most planets would likely have formed long before this time. These planets would then be generating minimal internal heat via radioactive decay, if any. 2. The planet gains energy from [tidal heating](https://en.wikipedia.org/wiki/Tidal_heating). [This answer](https://worldbuilding.stackexchange.com/a/27334/627) mentions it; indeed, it has been proposed as a potential mechanism for life on Europa, an the reason that its hypothetical subsurface ocean could exist. However, the tidal forces would have to be significant, meaning that the planet would have to be very close to the body it orbits, which could be dangerous. This might, though, be your best option. The heat produced by tidal heating is computed by $$q=\frac{63}{38}\frac{\rho n^5r^4e^2}{\mu Q}$$ where the important orbital components here are $r$ (distance to primary), $e$ (eccentricity) and $n$ ([mean motion](https://en.wikipedia.org/wiki/Mean_motion)). The equation makes it seem that $q\propto r^4$; however, given that $n\propto a^{-3/2}$, where $a$ is the semi-major axis, the heat generated drops off for orbits with greater semi-major axes, instead of increasing. 3. New stars form from collisions. [The Wikipedia article containing a section on the Degenerate Era](https://en.wikipedia.org/wiki/Future_of_an_expanding_universe#Degenerate_Era) notes that collisions between bodies (e.g. white dwarfs, brown dwarfs, etc.) can produce Type Ia supernovae, [carbon stars](https://en.wikipedia.org/wiki/Carbon_star), or even red dwarfs, if two brown dwarfs collide correctly. However, this does not mean that the star will be suitable for life. These cases make it unlikely that there will be a planet orbiting the resulting object. The odds of capturing a rogue planet are quite slim. Getting the planet into an orbit that could bring it inside the star's habitable zone is even harder. There are some reasons why I don't like the odds of life arising on a planet orbiting one of the degenerate objects you listed in your question1. * White dwarfs. These are actually the most benign of the three, insofar as there's not too much deadly radiation or extreme tidal forces hanging around, for the most part. The obvious problem is that white dwarfs may evolve to become [black dwarfs](https://en.wikipedia.org/wiki/Black_dwarf), and thus emit virtually no light. It has been estimated that black dwarfs will form on a timescale on the order of ~1015 years, possibly near the end of the Degenerate Era. The bigger problem is that the circumstellar habitable zone will be extremely tiny. [Agol (2011)](http://arxiv.org/pdf/1103.2791.pdf) estimates that it extends from ~0.005 AU to ~0.02 AU. You would need planets to be extremely close to the star. Putting aside the risk of tidal forces making the planets uninhabitable, this begs another question: How did the planets get so close to begin with? A Sun-like star would have expanded far, far beyond this during its [AGB phase](https://en.wikipedia.org/wiki/Asymptotic_giant_branch), meaning that (as Agol notes) the planets would have to form later on or migrate inwards. This may not be likely, but it is certainly possible: > > Formation mechanisms must be modeled to help motivate future surveys. For example, gravitational interactions of a planet and star with a third companion body may be responsible for creating hot Jupiters (Fabrycky & Tremaine 2007), which is also promising for moving distant planets around white dwarfs to $2a\_R\approx0.01\text{ AU}$, the tidal circularization radius (Ford & Rasio 2006). It is also possible that tidal disruption of a planet or a companion star will result in the formation of a disk which may cool and form planets (Guillochon et al. 2010), out of which a second generation of planets might form (Menou et al. 2001; Perets 2010; Hansen et al. 2009). > > > That said, planets might not survive this long. [Adams & Laughlin (1997)](http://arxiv.org/pdf/astro-ph/9701131v1.pdf) show that, assuming a number density of objects that is similar to the number density of stars in the galaxy today, a planet with a nearly circular orbit of radius $R$ would be disrupted on a timescale of $$\tau=1.3\times10^{15}\text{ years }\left(\frac{R}{1\text{ AU}}\right)^{-2}$$ Other similar problems arise when we consider that planetary systems with more than one planet are generally chaotic, as [matscienceman mentioned](https://worldbuilding.stackexchange.com/questions/37920/could-life-evolve-in-the-degenerate-era-of-the-universe#comment105949_37959). This could either help or hurt the chances of habitability, by making the planet better or worse for life through collisions or ejections. Additionally, planetary orbits will decay over time. This timescale depends on both the initial orbital radius of the planet and the mass of its parent star. * Neutron stars. You again have the issue of habitability. I wrote a lot about the issues specific to planets orbiting pulsars [here](https://astronomy.stackexchange.com/a/13340/2153). There are a couple main problems, neglecting the radiation (which would likely be emitted elsewhere, such as from the poles of the neutron star, and so be [mostly] harmless). The applicable one here is that the planets might have been captured, and would likely be orbiting far away from the neutron star - too far for them to get any benefits from tidal heating or light. However, this is not necessarily the case (see [Veras et al. (2011)](http://arxiv.org/pdf/1107.1239v1.pdf), [an article that cites it](http://news.nationalgeographic.com/news/2011/08/110805-planets-survive-supernovas-ejected-rogues-space-science/), [and an answer that cites that](https://worldbuilding.stackexchange.com/a/19001/627)). Other problems: + The neutron star could have an accretion disk, which could produce more radiation and in general make life unpleasant. + Neutron stars don't emit a lot of radiation conducive to life. * Black holes. Insert all of the issues that come with neutron stars, and then add more. By now, Worldbuilding Stack Exchange has beaten to death the idea of life on a planet orbiting a black hole. Issues include: + Tidal forces[[1]](https://worldbuilding.stackexchange.com/a/9640/627) + Radiation from an accretion disk (told you!)[[1]](https://worldbuilding.stackexchange.com/a/9640/627) + A fairly large magnetic field[[1]](https://worldbuilding.stackexchange.com/a/9640/627) + Minimal tidal heating at safe distances[[2]](https://worldbuilding.stackexchange.com/a/22802/627) + Plasma (mainly around supermassive black holes)[[3]](https://worldbuilding.stackexchange.com/a/36539/627)I could go on. As Serban Tanasa wrote in the first of those three answers, a planet orbiting a black hole would most likely be "a radiation swept molten rock horror." Even though the Degenerate Era will be an interesting place, it seems unlikely that life will find a planet enjoying stable enough conditions to be habitable. That said, [as DJMethaneMan said](https://worldbuilding.stackexchange.com/questions/37920/could-life-evolve-in-the-degenerate-era-of-the-universe/37959#comment106168_37959), there are most likely enough planets in the universe for all of these cases to successfully yield habitable conditions somewhere. --- 1 Let's assume that the planet wasn't captured. I've already mentioned the difficulties that arise with that scenario. [Answer] There is one little explored possibility for abundant life - the stellar remnants themselves. On their way towards black dwarfs, stars will inevitably pass through favourable temperature range, where chemistry is possible. First at upper atmosphere layers, then as the star cools down the "habitable zone" moves deeper and deeper, increasing in pressure, heated by still hot core which brings (via convection) needed heavier elements and chemical energy. White dwarfs are better candidates than red dwarfs, since the latter contain mostly hydrogen and helium, while the former stars burned through interesting elements, such as carbon and oxygen. Since there is still much hydrogen present, life will probably be based around $CH\_4$ and $H\_2$, not $CO\_2$. And it's dark, so life depends on chemical energy. Gravity is crushing and there is no definite solid surface (think of Superjupiters as fluffy light and immaterial gas balls in comparison), thus life would be probably floating (Jovian-like). With cooling down, it will move towards extreme pressures and exotic chemistry. [Answer] The degenerated era of the universe is the era in which no new stars will form and the present ones will burn out one by one and leaving only black hole behind (ok, that is simplicistic) Probably if a star like our Sun will form a couple of billion years before entering in the degenerated era, it can sustain life (more or less) as we know. Since our sun is not a star that has a very long life (about 15/20 billion years, compared with the trillion years of a red dwarfs), once the sun-like stars burn out, life as we know (or comparable with life as we know) will easily cease to exist, eventually leaving space to some more extreme forms of life, comparable to our extremophiles. At the end of the degenerated era, once the universe will enter in the black hole era, but probably much earlier, all life will probably cease to exist, if we exclude the possibility of some very extreme extremophiles that will adapt to live near a black hole findind some way to use the Hawking radiation to survive, but this is really very unlikely. [Answer] Life depends on energy to exist. One possibility is a rogue planet, hospitable to life, captured by a white or red dwarf star, in a tight orbit. Then, let's hope that the star remains luminous for time enough for life to evolve (or re-evolve, if it had life before). [Answer] Why wouldn't it? As long as the temperature and such is nice enough (which should be possible with a proper orbit), there's a lot more time for it to evolve - your typical degenerate-era star is going to remain in a fairly stable state for several trillion years (unlike our Sun, which only has a lifespan of less than ten billion years). It's the "temperature and such" thing that can be a problem (and perhaps anything in a sufficiently close orbit will receive too much hard radiation). I'm not enough of an astrophysicist to speculate further. That said, I agree with Freedo's comment - some civilization that evolves before the degenerate era will likely try to work for continuation of life into the future. A lovely setting based on that concept had been discussed a few years ago on AlternateHistory.com, named "Ten quintillion A.D." (search for it if you happen to be a member there). ]
[Question] [ As a tangent to [How "advanced" can a stone age society get?](https://worldbuilding.stackexchange.com/q/968/539), is there a way that simple electronics could be created by filling channels cut into rock with some form of conductive material? An organic substance derived from a plant, for instance, or a rare-earth element extracted from seawater. Assumptions: * Metal and metal-working are unknown or prohibitively rare * The society itself is quite advanced, and has been able to develop and produce simple computers using purely mechanical means. * Earth's plant and animal life. (No new hypothetical kinds of plants and animals, but more extreme species of earth organisms could be postulated) * The society knows how to selectively breed desired traits into plants and animals easily, allowing for more extremely specialized versions of current earth organisms. [Answer] I would suspect that they would go down the path of [Organic electronics](http://en.wikipedia.org/wiki/Organic_electronics). While metals are the easiest way to create circuits there are other ways available. It is also possible they could produce [biological circuits](http://en.wikipedia.org/wiki/Synthetic_biological_circuit) but unless they get lucky I think the organic based ones would be more likely, at least for starting. If they are really good at breeding micro-organisms they might come up with something that could be used in a circuit somehow. I think Star Trek had one episode centered around that. Almost forgot about [crystal circuits](http://en.wikipedia.org/wiki/Crystal_oscillator), which currently are used in primarily in time keeping devices, but I think it could be interesting to try and use them in a bigger role. Might get your glowing pillars that way! ;) [Answer] One of the epilogue MacGyver movies featured an ancient ruin that had primitive, steam powered computer. It used what were basically large stone punch cards, the different holes in the cards directing the steam to different conduits, with different effects. In theory, over time the technology could be improved and shrunken down, just like modern computers (though probably not quite as small). [Answer] Saltwater is a perfectly fine conductive material, for as long as you can keep it from drying out. Fill the stone channels with seawater, and refill every day or so. There's your circuit. (generation is a much harder problem, but OP clarified in a comment that it's out of scope) ]
[Question] [ I use the koppen-geiger climate maps a lot but I haven't found any for Pangaea. Would the climate zones be the same if the continents were in the Pangaea shape or is it something different? It would be helpful if there was a map or something of the Pangaea climate.[![](https://i.stack.imgur.com/d2VgV.jpg)](https://i.stack.imgur.com/d2VgV.jpg) I don't own the picture AT ALL (I found it on the web :) ) it just is the shape of Pangaea I've been thinking of working with. It's pretty close to the equator so I'd imagine most of the climate would be similar to central Africa but my main question is would the climates of various areas be similar to how they are now or just totally different because of the location. [Answer] [Here is a 2001 paper](http://www.ipgp.fr/~fluteau/UIA/articles/7_fluteau-pangea-climate.pdf) which used climate modelling to compare two reconstructions of Pangaea--there was still some question about the precise orientation of Laurussia and Gondwana in respect to each other--and the heights of mountains such as the Appalachians and the Variscan orogeny, and using the model to compare to the paleoclimates that can be seen in the geology. In the reconstruction the paper concluded was the more likely one, the supercontinent didn't form a near-circle because Gondwana was slightly closer to the equator and a bit further east than in the map you have. In any event, what paleoclimate data does show is that eastern Gondwana Australia on your map) had a warm temperate climate with a seasonal monsoon system. The far north and south of the supercontinent (Siberia, North China, and Antarctica on your map) had a cold temperate climate with large seasonal temperature swings. The western subtropics of both Laurussia and Gondwana (North and South America on your map) had extensive arid zones. Think present North Africa and you won't be far off the mark. It's known that arid conditions stretched from present-day Arizona all the way across to Nova Scotia and into Africa, so we're talking really big deserts. [Here](https://socratic.org/questions/what-was-the-climate-like-on-pangaea) is another climate reconstruction and they helpfully provide a relatively useful map of general climate zones. [![enter image description here](https://i.stack.imgur.com/ijzdb.jpg)](https://i.stack.imgur.com/ijzdb.jpg) [And another paper on Pangaean climate](https://www.jstor.org/stable/30081148?seq=1#page_scan_tab_contents) (focused on the breakdown of the monsoon). In fact, the monsoon was so important to Pangaean climate, [there's even a Wikipedia entry about it](https://en.wikipedia.org/wiki/Pangean_megamonsoon). [Here is a list of papers](https://www.researchgate.net/publication/230890352_Climate_of_the_Supercontinent_Pangea) that reference reconstructions of Pangaean climate. ]
[Question] [ Humans evolved in ancestral environments as semimigratory omnivores, which has embedded several things into our instinctive sense of wellness, aka "all is alright with the world", among them a preference of [living close to water](http://www2.tulane.edu/news/newwave/010912_ethiopia.cfm), [rolling hills](http://www.tandfonline.com/doi/abs/10.1080/01426397.2011.576884?scroll=top&needAccess=true&journalCode=clar20) with lots of green and sparse tree cover, an average tendency to exhibit weaknesses for certain foodgroups (such as meat and fructose), and experience cognitive biases and limitations generally steering them towards living in groups of 50-200 people. Let's assume for now these traits are preserved, i.e. we are dealing w/ Homo Sapiens Sapiens as we know and love it. Now, I want humans in space. Now, I want A LOT of humans in space. I want humans to infect the solar system and nearby galactic regions like a plague, like an unstoppable ever expanding Zerg creep. Now, complicating things, I'm also a firm believer that human lives ought to be happy as far as possible. Thus, each human in space will need a certain amount of mass to breathe, swim, play, socially interact, have sex and procreate, and raise disgustingly happy children in. Let's say we choose to build space habitats large enough to house a billion people each. Let's ignore to the extent possible things like the specific shape, rotational speed to maintain a livable gravity-like experience and so forth. Let us not focus of the need for ways to make up for mass loss to space for various reasons. How much mass, and how much mass per capita should I expect each of these habitats to take? --- Ah, but the question is now a bit broad. Let there be constraints. So, constraints. Humans need (for each of the following, you may assume that a technical infrastructure to support them is needed, with --and I am probably guessing wrong-- a 90%:10% mass ratio between infrastructure and the thing being supported): * air, * day-night cycle, * space and mass for lakes and rivers, * space and mass for trees so a layer of soil of at least 10 feet is probably required, * space and mass for rolling hills to wander around in, * space and mass for cute furry/scaly/feathery things to pet and/or eat (aka a biosphere), * space and mass for habitats to live in (caves, homes whatever) * lots of electricity, enough connectivity to maintain a rich verbal and cultural heritage (these folks live in the future, and are not primitive, although we would probably find them strange) * mechanical servants and tools to do some of the heavy work occasionally Humans also like to live in communities, let's say the aforementioned villages of 50-200 people, and assume about 3 miles (5km) or so between villages. Let's keep in mind (for the purpose of realism) that some small fraction might prefer solitude (so higher mass requirements) and that a significant fraction (5-99%) might actually prefer to live in denser communities of millions or billions of people, which means our village estimate should be a rather conservative (in the sense of being generous & expansive) estimate of the amount of mass needed. --- And yes, I know that being as a flesh-being in space is expensive. I know it's easier to colonize Antarctica and the Gobi desert, or the Mariana trench for that matter. You may safely assume that's all occurred, or that Earth is a pristine nature preserve or whatever. Remember, ever spreading plague of happy humans. --- And yes, I know the AIs and Uploads will probably take over, and that most intelligence in the universe in the future will likely be of the computronium rather then squishy fleshy brains variety, which would result in totally different mass requirements, I've read Age of Em too -- if it makes you happier, assume this is a pet-project of some trivial nostalgic fraction of the Uberminds. Let's just focus on the question at hand for now. [Answer] Speaking from experience, having 100'000 m2 per human is more than enough to be lost in any type of village or city or woods you would like to have. Also, 250 m2 per human is good enough for a relatively big city, and you can have different things in the city - trees, grass, water to swim, small forests/parks. 21'853 m2 per human is enough to host 7 billion people with different habits and appetites for territories, including water bodies, land used to grow food, cities, villages, roads, nuclear testing sites, deserts, etc - this is the average density of Earth's population at the moment. One of the significant uses of land is land to grow different crops and livestock, forests to use as the material source. According to this [source](http://www.fao.org/docrep/005/y4252e/y4252e06.htm), 11% of the land area is used for crop production. Different types of activities and plants require a different thickness of the ground. In my understanding forest requires the deepest of them all and forest takes about 1/3 of the available land according to this [source](http://data.worldbank.org/indicator/AG.LND.FRST.ZS). Grass requires the least thickness of them all (0.1m seems to be well enough). So if you assume about 1m thickness of soil on average it is not that big of a stretch. However, it depends on the technologies you have. So we speak about low-grade technology, which is called "no special technology at all". Requirements for soil, especially for food production, could be significantly reduced to essentially 0 soil with different types of aquaponics. The same goes for livestock - no soil requirements. Requirements for forests could be reduced if we do not use them too much for the production of different stuff and do not rely on them as CO2->O2 conversion as such conversion is doable with the same grass, algae, etc. - no soil required. So soil requirements could be cut in half just by changing the main contributors for CO2 conversion and ways to grow food or as a minimum the proportion of soil requirements could be reduced significantly. All that said, assuming 1m thick soil isn't a big stretch and the average density is about 2.5-3.5 ton per cubic meter. So if we really want to make everyone happy then about 60'000 tons per human is enough. That's for the matter wich has no structural input for the construction of the habitat itself. The mass of the habitat construction depends on the technologies you are using to build that habitat, and the sizes of it, as well a the approach you take to combine different parts of it. As an example: have a set of smaller habitats, which form a system with different climate zones, look and feel and which hosts 10-20 million inhabitants. These are connected in a bigger structure consisting of hundreds of them and hosting billions of people - this approach is cheaper in terms of the amount of construction material than a single big structure for reasons of safety as an example or reasons of protecting the external hull. Different materials and technologies could affect a number of materials you need for the construction itself. Using carbon nanotubes everywhere could significantly improve the situation with the required materials by reducing their amount. So if we take twice of what we need for the interior for the supporting structures of the habitat itself then we get about 200'000 tons per human. So this number is based on the average density of Earth's population, without significant improvements in land use, without considering optimizing landscape design, etc. If we take city norms, which a lot of people are ok with, then it seems those requirements are lower by 2 orders of magnitude. However, they will require the use of aquaponics and large-scale livestock keeping methods. [O'Neill, G. K: The Colonization of Space](http://www.nss.org/settlement/physicstoday.htm) contains interesting calculations for an O'Neil cylinder. And if I understand it correctly it assumes in general about 8 tons per square meter for the average material requirement for the cylinder. Here we have more than that, I assumed about 11 tons. So at the end you need to get some numbers for the average territory you assume as per human for the "to live a satisfying life", and it seems to be below of about 22'000 m2. However, who knows. Using materials with high strength (those CNT's) and technologies (like smart matter stuff, made of those CNT's as an example) could significantly lower the requirements by mass, significantly increase the surface produced with them and allow other optimizations like 0-soil for real plants (all of them - trees, grass, etc), almost massless mountains similar to the Everest, or even fake things like oceans, deserts, forests and other procedurally generated graphics, but made in 3d space of the smart matter. ]
[Question] [ I need an semi-organic structure large enough to fit a dense kasbah village on top, that protrudes from a shallow sea. additional info, maybe unimportant: planet orbits a red dwarf star tidally locked in the habitable zone, breathable atmosphere but unpleasant, located on the night or twilight side of the planet. Other than a large ice cap glacier on the night-side there aren't really any other land masses (maybe a sun-scorched area on the day-side, but not habitable). The sea is basically melt from the glacier, possibly too salty to support life? My vague idea is that a mining company bioengineered this thing to filter and collect some trace element from this remote planet. Its "cells" are chambers of fresh water, and it concentrates the mineral in it's outer "skin". Eventually, hundreds of years later after the structure matured, the concentrated mineral would have been harvested by grinding down the mountain – except for whatever reason the economics have changed, and that element is now unimportant or cheaply manufactured. The mining company went bust eons ago, and squatters moved in and drained the upper chambers to live inside. The structure naturally wicks moisture through it's skin, so the chambers will eventually refill with fresh water if they are not pumped out. The planet is a backwater off the main trade routes. Trade Syndicate Corporations control the small harbor, but most of the locals live in a semi-lawless kasbah, smuggling contraband or servicing space sailors. The farmers who live deep below might never associate with top-siders or off-worlders. Top-side is a slum of unhealthy people suffering from the atmosphere, but just under that in the highest cells are businesses, markets, tea houses, brothels, etc. I imagine large older cells each as big as a stadium honeycombing the top of the mountain. The native population would be a few hundred thousand, with an additional sailor/harbor population of about twenty thousand. Originally I was trying to make it be based on a vegetable, but now I'm leaning towards modeling it from a wart, as this seems to be more or less the structure I was imagining: a cluster of cells that push up to form a low protruding mountain, and also go deep underground. [![enter image description here](https://i.stack.imgur.com/hqjGA.jpg)](https://i.stack.imgur.com/hqjGA.jpg) I don't plan to delve into the science of how it was created, other than to casually mention that squatters moved in and over many generations repurposed the structure. The upper cells that are longest inhabited are probably "dead" now, but deeper underground cells still function and collect fresh water. The whole structure is haphazardly riddled with manmade tunnels and drainage pipes, something between an ant hill and a sewer world below, and on top a dense little kasbah city looking something like Shibam in Yemen. [![Shibam, Yemen](https://i.stack.imgur.com/jWIvV.jpg)](https://i.stack.imgur.com/jWIvV.jpg) I guess this is partly a reality check, but I'd also appreciate some practical ideas about how deep underground people could live and potentially have farms. Would pockets of CO₂ be a hazard? Is geothermal heat or pressure a problem (would they get the bends)? Should I go with this wart idea (I like it because it's revolting)? What else am I missing? [Answer] What you're describing could be basically a kind of coral, albeit with a couple of modifications. First off, coral would fulfill the first part of your requirements. Coral consists of a colony (of perhaps several million in the case of a reef) and both eat small organisms and gain energy from sunlight. What most people think of as coral is actually the secreted exoskeleton of the coral as it grows. It would build off of the seabed and make a reef. It isn't too much of a stretch to have the coral find a way to grow above water. The skeleton is created by siphoning carbonate and calcium from the water, creating limestone. This obviously wouldn't work above the water but you said the science wasn't really relevant and it may be better for your story to change what the structure is made of. To have spaces large enough to house people, it would have to be massive organisms as the space inside coral is large enough to enclose the coral polyp. The good news is that limestone doesn't really react with carbon dioxide so the structure will be fine with people in it. Coral is also porous so the gases may naturally filter out (but I'm not sure about this). As for going underground, the coral can eat into the bedrock in search of minerals or food, since the lack of sunlight removes the possibility of photosynthesis. The coral could become a terravore and eat the actual rock and earth. This could create underground space as the coral extends deeper into the earth. Pressure sickness and heating would have to be managed by the people living there, although it would be well insulated in the water and underground. To sum up, I think a type of coral would be a better fit than a 'wart' as it fits most of your requirements. * It can be bio-engineered and filters impurities from water (or air in your world) which you specified was its original purpose there * The coral would naturally form spaces within its structure (assuming giant coral organisms, spaces large enough for people) * It could extend up and down as required for your world * The coral leaves behind a skeletal structure even after its died whereas typical biological cells, such as those in a wart, do not. ]
[Question] [ Garden Fairies exist... But not in the way we thought. A strange form of life borrowing traits from insects and plants with a human-like appearance. This is a reality-check, is what I am about to suggest at all possible? What improvements need to be made to make it plausible. Aside: how these fairies evolved to be like they are is not important, as long as their present form is plausible. The fairies have elongated limbs (rather insectile but four limbs and one trunk/main body part, humanoid face) and large thin wings. This is to increase surface area to volume as they photosynthesise (have chloroplasts). The volume is further decreased by them not being taller than five centimetres. They must roughly conform, especially at a distance, to the general look of a european flower fairy They do not fly but due to their large wings (butterfly like proportions), small size and hollow bones (fairies are delicate) they can glide. (Mom I saw a tiny flying human in the garden!) I chose for them not to fly because I was worried it would be to energy intensive but it would be a bonus if they could. To supplement their diet I thought they could, much like aphids, drink plant sap. (Who said fairies love plants?). To do this successfully they would need a stylet like an aphid so maybe like scientists they kill aphids and use the aphid's stylets. Else they could have very thin fingers that can make a small hole which allows sap to gush out. If they use aphid's stylets, fairies would encounter hard times when aphids are sprayed to death (no more tools, no more sap). So they would love to sunbathe and would stay around plants. [Answer] Acquiring semi-hollow bones requires an intense evolutionary selection process, in combination with size selection[(1)](https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-016-2681-7). the lack of feathers makes the evolution of wings more improbable, but will still have evolved from the ability to glide. They would not be Tetrapods, as they would have six limbs (wings are limbs). The faeries would be Teleostomi[(2)](https://en.wikipedia.org/wiki/Teleostomi), alongside tetrapods and bony fish. So the faeries would be as closely related to us as bony fish are. This means that a large family of animals exist with six limbs, with varies levels of gliding capability for the middle limbs. These limbs may have evolved alongside the other limbs from different kinds of fins, and might originally have been used as guidance under water rather than thrust. Note that the fused arch (Synapsid[(3)](https://en.wikipedia.org/wiki/Synapsid)), evolved after the body plan of four legs. So there would need to be a significant amount of convergent evolution between tetrapods and our hexapods. Note that your faeries may eat algae. The seaslug Elysia chlorotica[(4)](https://en.wikipedia.org/wiki/Elysia_chlorotica) is able to make proteins necessary for photosynthesis through its ingestion of algae. The prime marker for intelligence in a species isn't absolute brainsize, but rather relative in size to the body. The crow family consists of incredibly smart birds, magpies are even considered to be self-aware[(5)](https://www.newscientist.com/article/dn14552-mirror-test-shows-magpies-arent-so-bird-brained/). It isn't impossible that the faeries would gain near-human intelligence, their heads would likely be a little larger relative to their bodies than with humans. It is unlikely that the faeries would have such distinctive noses as we have. We are omnivores, and the faeries wouldn't have one canines or incisors. Humans have excellent vision, whether the same would apply for faeries is doubtful. The level of convergent evolution you're expecting is extremely unlikely. That said, the high intelligence would likely lead to an ability to adapt tools. For crows this is the beak, for elephants the trunk, for bipedal hexapods, this would mean hands with thumbs. [Answer] # They're perfectly plausible There isn't much about your fairies that don't already exist in some other animal, at least in some form. The size is no issue at all: Many actual insects reach or even exceed the 5cm mark, and from the other side there are several mammals and a few birds which are no more than 5cm in length. The main issue would be intelligence, but this isn't much of a problem: Ants and bees are quite intelligent, and have almost all of the traits required for civilisation. Hence your fairies, which are both much larger and much more encephalized, should have more than enough brain space for sapience Aside from the size, most of their anatomy is just human anatomy, which obviously is plausible. On the wings: If they do not need to fly, then there are pretty much no real issues here. You could have regular leaves appended to the back, with some arteries and veins replacing the standard xylem system and a bit of cartilage or such to add support. These leaves could simply attach to the flesh of the back, with a layer of tougher connective tissue linking them to the backbone and the spine of the scapula. Photosynthesis also seems plausible enough. Using ants as a model for weight/energy consumption, your fairies would have an average power requirement of 18mW. With butterfly-type proportions, the wings/leaves would have an area of approximately 22cm^2 and will capture at most 1.35W of sunlight. At a 2% photosynthetic efficiency, this will provide a maximum of 27mW during the day. While this is a lot, it is not enough to keep the fairies 'fed' over night (especially given that they'll likely be doing things that are suboptimal for collecting light). Consuming sap could be a useful way of supplementing their diet. However, fairies are very large compared to other sap-sucking animals, even accounting for their photosynthesis. Coupled with the fact that sap is quite hard to digest, it seems like it would make sense for other food sources, such as nectar or honeydew, to be included in their diet. ]
[Question] [ In an old story of mine, there happened to be a species of humanoid who could produce a variety of mutants and hybrids from stolen and harvested DNA, sperm, and biological tissues. They would produce organic embryo-holding pillars, or eggs, or sacks to contain their countless highly differentiated young until they were fully developed, and hatched into whatever bizarre spawnling their given "scrunch" of DNA allowed. I found this grody form of mass spawning very fascinating and alien, and wondered if a body of perfectly sustained cultures really could reproduce anything from its dumpster of stolen DNA and tissues from foreign species. In hindsight, it was not a very realistic concept for a relatively-small-for-the-scenario humanoid to mass-spawn infantile creatures from thin air, sometimes in the dozens or hundreds. This had me thinking about the plausibility of a creature specifically built for "creature building" as a reproductive concept. Hypothetically, I am wondering what baseline type of creature(Be it a plant, insect, or jelly, or mammal, or some alien thing with the ability to do "X" with samples of organic tissue, and so on) would be best suited for this task instead of an over-sized humanoid. Currently, the guidelines for what such a creature would have at their disposal would be this: * The creature can incubate and preserve all forms of tissue, organic matter, DNA, cells, and so forth within itself- and its body can naturally 'feed' its samples no matter their complexity in order to keep them alive and of use without breaking them down into components that rob them of being from a different creature entirely. * It is thought that once this creature has a decently sized or reproductively geared sample, it can always replicate this sample and use it for spawning purposes.(Possibly, this could mean growing the creature from scratch, and harvesting its ...cough...fluids. Although that's yet to be a system I can currently imagine.) * The internals of this creature are directly capable of manipulating the growth and creation of cells, and can begin production of whatever is necessary to make certain fusions or growths of things to occur. * Its method of incubation for most creatures is universal, not only in method, but in compatibility with what it can grow. (Example: It will always grow a fetus in a sack on a pillar, but all fetuses will be able to safely grow under the given circumstances) * This creature cannot reproduce anything, even akin to itself, without use of its 'belly' of samples from other species. That means all children it has most similar to itself will be hybrids... or it will only have offspring that are of another genus. (To add to this point, we can safely assume this creauture can regenerate itself, or just simply does not completely die at all- preventing it from hitting extinction) TLDR; What is the best type of creature to act as a mass mutation-causing, clone-making baby machine? (I did not add 'reality-check' to this question due to how implausible or strange it seems. I do not know enough about this subject to understand how ludicrous the concept may be. I also would like to leave it open to scientifically impossible, but still somewhat more compatible concepts.) [Answer] So after some consideration, this is what I've come up with. [![anemone](https://i.stack.imgur.com/jLMgs.jpg)](https://i.stack.imgur.com/jLMgs.jpg) Sort of a [half plant half animal hybrid similar to a sea anemone](http://www.livescience.com/44243-sea-anemone-genome-analyzed.html). Maybe slightly more mobile like a sea slug. It would have a wide trunk, be 30 feet tall, and have a flaring top with tendrils that hang down. The tips of the tendrils would have stingers that would be used as defense and to immobilize prey for absorption of nutrients, but at the same time would sample anything they touched, taking cells to be cultured. Its trunk would be honeycombed with many small incubation chambers, where sampled cells would be placed so they can be cultured and grown. It lures creatures to itself using pheromones. When a creature comes to check it out, it stings them, taking a sample and delivering a powerful paralyzing agent, so it can then dissolve them down to their component chemicals. As it slowly moves across the landscape it absorbs all biological material it touches, using the nutrients to grow new things. Inside it has biological factories to break down and recombine the samples it takes into new forms. Once it finds a form that it deems to be viable, it creates a long arrow like spike in its cone snail like radula sac, injects the cultured cells into a bulb on the back, and spits it up, where air resistance takes over so the spike lands point first, and with the incubation bulb up high out of reach from predators. The spike puts down roots for water, and leaf like panels to turn sunlight into energy to feed the growing fetus. It also extends small hair like needles with the paralyzing agent inside as another layer of defense. The offspring matures in the sack until it is ready, and then the sack splits open to release it. The spike begins to liquefy, becoming a nutrient paste that the offspring can consume. The paste contains the same paralyzing agent, which the offspring is immune to. It eats the paste and any wild creatures that were paralyzed until it is able to survive on its own. [Answer] As a general rule of thumb, more complicated organisms change more gradually. Several previous Science Fiction authors like to use fungi for the role you are describing, particularly because of their ability to spread spores, adapt to new environments, and their diversity in function. ]
[Question] [ My question is mainly related to the impact on food production if the climate changes made agriculture more difficult in the state of California but also in the other American and Mexican states from both side of the border. Context: If you live in the United Sates, in Canada or possibly in other countries as well, you might have noticed all the food produced by this region while shopping in the grocery store. [They produce most of the fruits, vegetables and nuts that we eat](http://www.slate.com/articles/health_and_science/explainer/2013/07/california_grows_all_of_our_fruits_and_vegetables_what_would_we_eat_without.html): > > California produces a sizable majority of many American fruits, vegetables, and nuts: 99 percent of artichokes, 99 percent of walnuts, 97 percent of kiwis, 97 percent of plums, 95 percent of celery, 95 percent of garlic, 89 percent of cauliflower, 71 percent of spinach, and 69 percent of carrots. > > > The problem: The climate changes are making the [Hadley cell](http://en.wikipedia.org/wiki/Hadley_cell#Hadley_cell_expansion) larger. The northern limit of that cell is dry. Right now, California is affected by this dry pattern only during the summer. While winter are more humid due to the influence of the polar front. South of the border,in Mexico, we have Baja California. It is mostly a dry desert because it is always affected by a dry weather. My guess is that the expansion of the Hadley cell could lead to the desertification of southern California and other states along the border. * If the region suddenly became more arid, what would happen to the food production? * Could farmers adapt to the drier climate with different crops or different agricultural techniques? * Would the climate changes simply move the food production more to the north and could these states adapt to replace the lost production from the south? For more information about how climate works : [Creating a realistic world map - Currents, Precipitation and Climate](https://worldbuilding.stackexchange.com/questions/1353/creating-a-realistic-world-map-currents-precipitation-and-climate) [Answer] Won't comment on the weather patterns causing it...I think the Colorado river being drained prior to California is more likely: > > Food production > > > From what I know of California, is the majority of the crops there are already high heat and low water crops. Had the water flow from the Colorado river halted, I would assume we would first see a few years of failed crops and unusually low yields and the prices of a few items exclusive to California to shoot up (somewhat like we've seen in Turkey of recent with the Hazelnut wipeout almost eliminating Nutella production). Honestly, if you look at most of the crops, none of them are really native to the region and are there artificially because we have put them there and irrigated them so they could grow. Wine might be the most resilient just due to the amount of interest and wealth involved will ensure those grapes keep irrigated. We would see shortages and increased costs of particular fruits/veggies that are heavier on water consumption go up first, and the disappearance of a lot of these items on restaurant menu's across north america. I'm not sure if it'll ever fully fail, there is enough water coming downstream to California that even if it becomes much drier, irrigation will still happen. Reversely, there are certain crops that would thrive in these changes. Almond Tree's give their best yields in exceedingly dry hot summer and wet winters...so although certain crops that heavily rely on irrigation may start to falter, other harvests could potentially see some bumper crops and increased yields from these climate changes. > > Could farmers adapt to the drier climate with different crops or different agricultural techniques? > > > They've adapted to some pretty dry conditions already and I'm not sure how much further you can adapt...it's just a matter of getting water to those fields. My guess is the issue in the comments of the Colorado river being diverted prior to California would become a major political issue US wide and not just in California. > > Would the climate changes simply move the food production more to the north and could these states adapt to replace the lost production from the south? > > > I wouldn't say north...northern California is redwoods and the territory doesn't get much agriculture friendly north of that. I would suggest further inland...sadly this is basically saying we'd go further up the Colorado river and farm there instead. Arizona...Yuma county in particular...is already known as America's winter salad bowl. It produces the majority of the greens consumed in winter months across north America. None of this production is really native to Arizona, but the intense sunlight coupled with irrigation means we can grow pretty much anything there. [Answer] Even if California dried up completely,we would not suffer much more than slightly higher prices for the produce. Production will move to places where it is more profitable, and more imports will come in. Production processes will adapt, as with everything else. We already produce more than enough food as it is, and California is not the only place where food will grow. They could even survive significantly drier climate if farmers switched from flood irrigation to drip irrigation - that alone would save massive amounts of water (at the cost of investing in drip irrigation systems). ]
[Question] [ Related: * [How would a completely urbanized city-planet support its population?](https://worldbuilding.stackexchange.com/questions/810/how-would-a-completely-urbanized-city-planet-support-its-population) * [How a completely urbanized city-planet be maintained?](https://worldbuilding.stackexchange.com/questions/813/how-would-a-completely-urbanized-city-planet-be-maintained) * [How would the global environment of a completely urbanized city-planet be affected?](https://worldbuilding.stackexchange.com/questions/811/how-would-the-global-environment-of-a-completely-urbanized-city-planet-be-affect) It makes most sense that it is a natural end of rampant urbanization, but could a truly planetary city ever come into existence without the direct control of a single organizing body? If so, why would they decide that such a completely developed planet is best route for whatever their goals may be? If not, would the cost/difficulties/drawbacks of remaining/expanding on the burgeoning city-planet drive independent owners away? Is there any situation in which a single-city planet would be the logical development aside from the rule of extreme cool? [Answer] Lots of questions, but I'll try to answer: ## Forming without a Ruling Body A completely urbanized planet might be able to form without one ruling body. This would mean that the different countries on the planet would have to be very trusting of each other. Or at a point in war where you couldn't destroy each other's cities. In the Middle Ages, France and England were at war. Along one river in France, each country would build a castle, each on their own side of the river. Around these castles towns would form, the two enemy towns may be very near each, even though they were at war. Cities on an urbanized planet could form similarly. Even if both countries were at war, the cities could come up to the boundary line (or very close) if the technology or incentive was there not to attack. In the case of France and England, the river prevented a quick attack on the opposing town, meaning that the town would have time to flee to the castle and be protected. If the two countries were allies, then they might not object to building cities right up against each other. There would probably be a small boundary line, but this would be negligible to the size of the city. It might even be used as a park. ## Why Such a Planet is Good Cities provide great opportunities. They are the sources of jobs, because the jobs can find labor. They are the source of government, because the governors need a place to meet. If cities kept growing, with bigger corporations and bigger amounts of work, it could be economically beneficial. It might also be more efficient (more people in a smaller space), keeping scientists together so research could go on. It could also be politically useful, everyone in one place is easier to manage than having them scattered across the stars. These are all reasons to do this if you had the ability to travel to other habital planets. If you couldn't travel, a planet-wide city would merely provide you with enough space to house all your people. I don't see why there couldn't still be private landowners, it is just likely that a land owner would get a "cubic" plot, meaning that their land doesn't necessarily go up into the sky forever. This would make it easier to build large sky scrapers. ## Summary Your final section of the question asks why this could happen. I believe I have already answered that, but I will summarize. Such a planet might exist if there were a single government and the population needed a planet-wide city to provide enough space. Or it could exist if the government thought a large city to be economically or politically beneficial. Such a planet might exist if there were multiple governments and they were at peace. Each government would extend its city as far as possible, for the reasons above. Or if the planets were at war, a system were each side couldn't attack the other would allow for the reasons above to take over. [Answer] There really isn't a sound economic reason to create a city-planet. People need food, they need air and they need a place to put their waste. And while there are certainly ways to mitigate those needs without breaking the urban environment, they can't be fully taken care of that way. Not to mention the sheer vast expense; you have to cut down every forest, you need to flatten the tallest mountains, drain the oceans and fill the deepest ravines. And you need to build factories to replace the important functions all of those things perform. All of that is theoretically workable, but in order to sustain the population, you must clearly have space elevators or some other technology to lift vast amounts of material or personnel in and out of orbit. You must clearly have the ability to build vast space stations or to terraform other planets in the system to grow all of your food and dispose of your organic waste without entirely wasting it. You must clearly have the technology to survive in great comfort somewhere besides the clearly overcrowded and ludicrously expensive big city. It might be cheaper and more effective to just telecommute from your station in low earth orbit and fly a shuttle down when you need to be somewhere in person. Add to this that the main reason that people typically want to live in cities, that things will be close by to you, works less well on a planet-wide scale and the whole thing looks rather unfeasible. Living in space is just much, much cheaper. Religious or cultural reasons could maybe explain it, but it would require something fairly specific, strong, and well-tailored. [Answer] "Could a truly planetary city ever come into existence without the direct control of a single organizing body?" I think you would need some sort of governing, which is true of any city or country. In this case, it's possible that the planetary city could have started as multiple independent cities who each grew gigantically large. These "sub-cities" may still rule their own areas. However, there'd probably need to be some sort of organization to coordinate everything - possibly like the United Nations. "If so, why would they decide that such a completely developed planet is best route for whatever their goals may be?" Most cities grow naturally, and presumably this one would too. I doubt that anyone would decide, "Hey, let's turn the entire planet into an entire city!" What's more likely is that due to increased population and demand for land, the cities would slowly come to dominate the world. Obviously, food production would be an issue. Food would either have to be imported from other planets (feasibility would depend on the transportation technology) or grown under factory like conditions in giant (underground?) warehouses using growth lights and genetic engineering. If the city planet is part of a universal planetary system with ease of transportation, then it's likely that it could specialize in the sorts of goods and services that cities offer. It'd probably be a hub for many major industries. "If not, would the cost/difficulties/drawbacks of remaining/expanding on the burgeoning city-planet drive independent owners away?" I think this would depend on the goals as well as the costs. Depending on the technology of your set up, you could create it a number of different ways. For instance, if the city imports it's food from elsewhere, farmers would obviously migrate to other planets. Food would probably cost more, though, again, this depends on technology. Food grown under factory conditions might still be cheap. Habitable or desirable land would probably also become costly, and other people may find a greater quality of life on other planets (like some people know move from the city to the suburbs). "Is there any situation in which a single-city planet would be the logical development aside from the rule of extreme cool?" For a human civilization, I think the city would have to part of a large and efficient trading network. I don't know that it'd be logical for the entire planet to be a city. There's bound to be high mountains or deserts or tundra that's simply uninhabitable. For an alien situation, you could change the meaning of what we understand as "city." Maybe the aliens use organic life forms to construct their buildings, or maybe they all live underground and grow crops on the surface. [Answer] An urbanised world could happen many ways- extreme war pollutes the whole world but remaining civilisations have high resources stores- especially energy. There is no better to handle radioactive land than building over it- solid concrete is an excellent barrier. Aero- and hydroponics (and industry) expand over the world by simple necessity. Extreme Green governments lock up big swathes of land for nature and the other countries' people respond by uncontrolled urban-sprawl. The Green government collapse by starvation and the people and industries keep the sprawl going. Its sort of happening now. Needs a vast population to need to cover the world or most of the world locked up by ocean. This will need vast amounts of cheap energy and resources but as long you have the cheap energy then resources is not a problem- the Earth has vast amounts of aluminium and silicon in the crust- we'd just draw the resources from the ground. It would have vast amounts of waste heat. The pre-existing condition of cheap energy is the only thing that go against having independent/local owners as it need lots of money to get the economies of scale to produce. It would only limit it to many significant corporations to produce the energy- if those corporations aren't into excessive control preferring wanton demand instead then there isn't anything stopping the whole world being segmented. A whole urbanised world is the thing that one large government (authoritarian) wants- its so unwieldy. It was for a long time very difficult for large empires to have central control. China is as big as it gets and its not really centralised- its really multiple governments. Russia is of course bigger but its less nominally authoritarian than China. The Chinese government doesn't really China to be bigger- the parts might big enough to threaten the nominal central government. [Answer] I think that a city-planet would be hard to come up with as a solitary idea and convince different nations/worlds to cooperate in building it, since it would most likely be such a huge undertaking, it would have no precedent. Trading and travelling can be done without a huge construct like that, so there would be no reason to come up with the idea. However, people didn't come up with the idea of building each major city in history, it pretty much happens cumulatively. A possible, in my opinion, origin for such a city-planet would be one that circumvents the need for deliberate planning and cooperation, such as the following: ## In the beginning there was trade You have multiple worlds across lots of star systems with interstellar travel fast and practical enough for trade and casual travel (much like Star Wars, which had Coruscant). There are various space bases and trading posts across intermediate star systems, orbiting planets usually but sometimes oribiting the local star directly, due to practicality or choice by the owner to build it there. Trade routes pass more often through certain systems than others. In fact, at some relatively distant point in the past, most routes go through a specific star system with multiple bases due to how much trade and travel goes through it. The system is so popular because it stands between large clusters of star systems and thus it forms a convenient trade route to other large clusters due to low amounts of celestial bodies (asteroid fields etc.) and is the safe and common path for trade. The popularity of this system as a trade node and passage point attracts trade through itself from neighboring systems and alternative routes. ## Everyone puts their eggs in one basket As time goes on, the bases are going to naturally grow and expand - they might be privately owned and operated or operated by states, but it's irrelevant - their holders compete to attract more trade and travel through their own station/base. Some people work there, so there's some dwelling accomodations. Trade cooperation happens and some bases decide to merge for mutual profit - smaller owners can't compete, so they merge to stay in the market, larger owners subsidize trade through them and welcome the new additions to their own base, which gives them more capacity and a share of the profits of others. Considering that there's lots of different worlds moving in and out and a lot of transactions happening, as the bases coagulate into a single main one, there is political and social interest in regulating it. If it is such an important node to the entirety of a huge number of star systems and worlds, there is mutual interest to keep it running and grow it. So it grows in the same way as before. Private owners attach their own expansions, some for dwellings, some for shops, some for products, others for depots and craft maintenance. To keep everyone satisfied, a sort of representative body is established to handle administrative matters. Due to social structures on the worlds using the station, a cellular political structure, based on voting and station section hierarchies is established. ## The biggest space bar in the universe The station grows, until it is so massive, it's the size of a small moon. Give it a few thousand years and in the intermediate time, it has been slowly moved out of its parent planet's orbit (if it orbited a planet in the first place) and is now as big as an earth-like planet, orbiting the star of the system. It becomes the center of political and economical matters since it is effectively neutral ground and all trade routes go through it (or most at least). People are born and die on it, it has enough mass to have regular gravity on its surface (although by this point, generating and regulating gravity technologically is probably to be expected) and it is, for all practical purposes, considered a planet. ## Have you been reading the funny pages again kid? Assuming you have multiple worlds across multiple systems, the material isn't hard to find if there is enough mining. You don't need to strip planets clean - there's lots of ore and metals available on space rocks, clustered conveniently in asteroid fields. A bit of this from all the systems would easily allow for enough high quality material and mass to create a planet-sized body. And there you have it: Coruscant :P Noone needed to come up with it - it just happens given time, fast enough travel and enough star systems with their own trade structure. It has a hybrid government to manage it, slowly growing out of small practical needs. It was never the best idea out of many - it's just the best option now, since it's already there. ]
[Question] [ I'm building a soft sci-fi world where gravity works a bit differently: the acceleration due to gravity drops off at a rate much greater than our inverse-square; and the acceleration due to gravity "flips" and oscillates at regular intervals, becoming repulsive rather than attractive and vice versa (similar I guess to [MOND](https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics), but at smaller, planetary scales). The acceleration $g$ experienced by an object of negligible mass can be modeled with: $g\approx Se^{-\lambda du}\cos(du+\phi )$ where * $S$ - gravitational acceleration at a planetary surface1 (in $m/s^{2}$), * $\lambda$ - dimensionless decay constant (describes how gradual force drop-off is), * $d$ - distance from the surface in meters, * $u$ - scalar constant2 (converts meters to radian angle measure), * $\phi$ - phase angle, almost always zero and can be ignored. 1If you follow the math through, the gravitational forces below the surface oscillate with exponentially greater magnitudes, which would obviously rip a planet to bits. So, the formula is only good for gravity above the surface. Below, a different (and unimportant) set of rules apply. 2$u=0.5\pi /d\_0$, where $d\_0$ is the distance between two zero-g points or $1/2$ the cosine wavelength. $e^{-\lambda du}$ and $\cos(du)$ are dimensionless, leaving the result in the units of $m/s/s$. Multiplying the result by the object's mass gives force applied to the object, which may be positive or negative. Because this is Worldbuilding, a lot of these parameters are toggleable and don't (seem to) arise from fundamental interactions. This is okay, I think. I don't need to fully flesh out and justify why these constants are what I choose them to be (or even why gravity is different), I can simply tuck them away to a black corner and work with their output. --- There are some strange properties with this form of gravitation. Here's a graph: [![gravity graph2](https://i.stack.imgur.com/Trkw4.png)](https://i.stack.imgur.com/Trkw4.png) $\lambda =0.5, S=1$ As an object rises above the surface, gravitational acceleration drops until, at some distance $\pi /u$, acceleration becomes zero and inverts, turning repulsive. The force vectors point away from the planet surface and the object is accelerated away until it crosses the recurring zero-g point and begins decelerating. However, because the distance over which acceleration/deceleration occurs is constant and the magnitude of acceleration/deceleration always decreases, a non-propulsive object will always accelerate away from the planet--forever--once it has crossed the initial zero-g point above the planet's surface. To even approach the planet, an object must have some minimum "entry velocity." --- What do orbits look like? [![gravity graph 1](https://i.stack.imgur.com/ewb3e.jpg)](https://i.stack.imgur.com/ewb3e.jpg) Gravity oscillates between positive and negative, attractive and repulsive. (In the graph, attractive regions are solid.) Stable orbits seem to come in two varieties: orbits that remain solely inside attractive regions (largely circular), and orbits that oscillate between attractive and repulsive regions (largely sinusoidal). Highly elliptical orbits are impossible; if an object has enough orbital energy to cross more than one zero-g point, it'll be ejected from the system. Trajectories that nearly cross a second zero-g point are "critical." [![critical trajectory 1](https://i.stack.imgur.com/Z4eNp.jpg)](https://i.stack.imgur.com/Z4eNp.jpg) [![critical trajectory 2](https://i.stack.imgur.com/D9baF.jpg)](https://i.stack.imgur.com/D9baF.jpg) (Attractive regions in black, repulsive in dark grey. Paths traced w.r.t non-rotating body at the center.) Here we see an object (second image) on a critically oscillating trajectory, falling toward the planet though not having enough kinetic energy to overcome the repulsive region and being accelerated back out--though not great enough to enter the second repulsive region--ad infinitum. Tangential velocity seems almost independent of radial, meaning two objects can share an orbital region and yet have wildly different velocities compared to one another. Hence the thicker band of traced orbits (representing faster motion) within the larger, slower, more sparse trajectory. Stable orbits only exist inside attractive regions, where the force vectors point toward the planet. Circular trajectories in these regions can have wildly different orbital velocities due to the large gravity gradient. At the peak of the region, where the force vector is strongest, orbital velocity is highest, whereas to either side of the peak, velocities decrease and approach zero. Geosynchronous trajectories are not limited to the space of the zero-g regions, but may also oscillate between attractive and repulsive regions. On the planet surface, this would look like a satellite growing nearer and farther (in the same position or along a figure-eight path) throughout the day. [![few geosynchronous 1](https://i.stack.imgur.com/CrUsO.jpg)](https://i.stack.imgur.com/CrUsO.jpg) [![few geosynchronous 2](https://i.stack.imgur.com/VOWFO.jpg)](https://i.stack.imgur.com/VOWFO.jpg) Near the higher orbits are a few synchronous trajectories, almost "bouncing in place." --- What I'm having trouble with I think my trouble is mostly a mathematical one (I know about as much mathematics as an intermediate programmer should, but not enough to analyze and derive the equations I need to answer my own question, I guess). I'd like my travelers to explore such objects, and although the properties of this gravity system are magical, the travelers themselves are constrained by the [Tsiolkovsky rocket equation](https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation). What I need is a method for computing delta-v budgets respecting the modified gravity. Say my travelers wish to rocket off the planet to some altitude above the surface (suppose there's no atmosphere). They'd need a method to figure how much delta-v is required to get there (which likely involves slowing down at "there", as the repulsive regions will work to accelerate them out of the system), as well as how much delta-v they'd need to get back. Remember, the repulsive regions will assist them in getting off the planet (and maybe even a little with circularizing their orbit), but they'll be fighting those same regions on the way back down. Perhaps the problem put into simplest terms would be figuring out how much delta-v is required to move radially from one region--repulsive or attractive--to any other. I am not sure how tangential velocities would figure into the mix. For the sake of simplicity, we're only worried about coplanar changes in trajectory. [Answer] I think you'll need to re-formulate the vis-viva equations. Let's try that out and see what happens : ## Circular orbit : * $g = {{GM}\over r^2}$ * $v^2 = {{GM}\over r}$ $\rightarrow$ $v^2 = gr$ * $g\approx Se^{-\lambda du}\cos(du+\phi )$ Since $d$ is $r - R$, u is a frequency term, $S$ is ${{GM}\over R^2}$ and $\phi$ can be ignored, just going to substitute: * $g\approx {{GM}\over R^2}e^{-\lambda (r - R)u}\cos((r - R)u + 0)$ * $v^2 = [{{GM}\over R^2}e^{-\lambda (r - R)u}\cos((r - R)u + 0)] r$ Let's try it out! Using Earth for a reference (M = $5.9 \times 10^{24}$, R=6378km), trying it with the sinusoidal effects far away $u = {\pi \over R}$, and r being on the surface (6378km ~ 6,378,000m); I get 9.67 m/s/s for g, which is the same value I get just computing ${GM} \over r^2$. I get an orbital velocity of 7,855 m/s; which matches $\sqrt{{GM} \over R}$ If I move up into the sinusoidal effect at r = 1.5 R, g ~ 0 and v ~ 0, which is exactly what I'd expect. So, with a little more confidence, let's try applying this to... ## Elliptical orbit : * $v^2 = GM ({2 \over r} - {1 \over a})$ $\rightarrow$ $v^2 = ({2GM \over r} - {GM \over a})$ $\rightarrow$ $v^2 = ({2 g r} - {g r^2 \over a})$ * $g\approx {{GM}\over R^2}e^{-\lambda (r - R)u}\cos((r - R)u)$ * $v^2 = ({2 {{GM}\over R^2}e^{-\lambda (r - R)u}\cos((r - R)u) r} - {{{GM}\over R^2}e^{-\lambda (r - R)u}\cos((r - R)u) r^2 \over a})$ Testing again, still using Earth, and trying an elliptical orbit where the major axis is equal to R (a circular orbit) : 7,855 m/s ... just what I'd expect from a circular orbit. How about inside the sinusoidal effect at r = 1.5 R? v ~ 0 m/s; what I'd expect. ## Transfers : Boosting from a lower orbit $r\_1$ to a higher one $r\_2$ * $\Delta v\_1 = \sqrt{\mu \over r\_1} ( \sqrt{{2 r\_2} \over {r\_1 + r2}} - 1)$ $\rightarrow$ $\Delta v\_{1} = \sqrt{g r\_1} ( \sqrt{{2 r\_2} \over {r\_1 + r2}} - 1)$ * $\Delta v\_{1} = \sqrt{{({{GM}\over R^2}e^{-\lambda (r - R)u}\cos((r - R)u )}) r\_1} ( \sqrt{{2 r\_2} \over {r\_1 + r2}} - 1)$ And circularizing the new orbit * $\Delta v\_2 = \sqrt{\mu \over r\_2} ( 1 - \sqrt{ {2 r\_1} \over {r\_1 + r\_2}} )$ $\rightarrow$ $\Delta v\_{2} = \sqrt{g r\_2} ( 1 - \sqrt{ {2 r\_1} \over {r\_1 + r\_2}} )$ $\Delta v\_{2} = \sqrt{({{GM}\over R^2}e^{-\lambda (r - R)u}\cos((r - R)u)) r\_2} ( 1 - \sqrt{ {2 r\_1} \over {r\_1 + r\_2}} )$ ## Escape velocity : Can't just substitute the new g in here. * $ {1 \over 2}mv\_e^2 = \int{g \delta r}$ Borrowing BMFs excellent answer. $\int{g} = \dfrac{S\mathrm{e}^{-\lambda du}\left(\sin\left(du+\phi \right)-\lambda \cos\left(du+\phi \right)\right)}{\left(\lambda ^2+1\right)u}$ Substituting d and S, and dropping phi * $\int{g \delta r} = \dfrac{{{GM}\over R^2}\mathrm{e}^{-\lambda (r-R)u}\left(\sin\left((r-R)u \right)-\lambda \cos\left((r-R)u \right)\right)}{\left(\lambda ^2+1\right)u}$ Then, placing back into the escape velocity equation * $ {1 \over 2}mv\_e^2 = \dfrac{{{GM}\over R^2}\mathrm{e}^{-\lambda (r-R)u}\left(\sin\left((r-R)u \right)-\lambda \cos\left((r-R)u \right)\right)}{\left(\lambda ^2+1\right)u}$ Dropping m, and solving for $v\_e$ * $v\_e^2 = 2 [\dfrac{{{GM}\over R^2}\mathrm{e}^{-\lambda (r-R)u}\left(\sin\left((r-R)u \right)-\lambda \cos\left((r-R)u \right)\right)}{\left(\lambda ^2+1\right)u}]$ [Answer] I think I might be close to an answer, but I'm not entirely sure. At the very least, this may help someone towards a more complete answer. Originally, I thought to integrate my modified gravitational acceleration formula $g\approx Se^{-\lambda du}\cos(du+\phi )$ over the dimension $d$, which is distance in meters. I couldn't make sense of the return of that (I thought it might be useful for finding velocity), so I went ahead with this question, but now I think I have a little better of an understanding of what that result might've been. $\int g\approx Se^{-\lambda du}\cos(du+\phi ) dd = \dfrac{S\mathrm{e}^{-\lambda du}\left(\sin\left(du+\phi \right)-\lambda \cos\left(du+\phi \right)\right)}{\left(\lambda ^2+1\right)u}+v\_i$ $v\_i$ is the "initial velocity." When set to the minimum of the graph along the positive x-axis, the entire velocity graph lies above the x-axis, which I believe means that the minimum value is the "entry velocity" required of an object starting at infinity to reach $d=0$. [![acceleration over velocity](https://i.stack.imgur.com/iEx8b.png)](https://i.stack.imgur.com/iEx8b.png) The equation for gravitational acceleration in red (y-values bloated by a factor of 20,000 for visibility), the integration of that equation in blue. The graph of the integrated formula has a minimum value along the positive x-axis, which I interpreted as the minimum velocity required to approach the planet (assuming the integrated formula does represent instantaneous velocity). That minimum value exists on the graph at $d=d\_0$, where $d\_0$ is the distance in meters between two zero-g points (I think they're called inflection points). So, evaluating the integrated formula for $d=d\_0$ and shifting the graph up the y-axis by that amount, we should find a plot of the velocity of an object falling from infinity to the surface of the planet, the aforementioned "entry velocity." If the object has less than the entry velocity, then the object's velocity at the final zero-g point is negative, which I interpreted as the object not having enough energy to surpass it and being thrust back whence it came. Following the plot backward, we should find the minimum velocity for an object at each step required to fully escape the planet. That energy seems to be given to the object right after it surpasses the first zero-g point. ]
[Question] [ Let's consider an [O'Neill cylinder](https://en.wikipedia.org/wiki/O%27Neill_cylinder) with a radius of 3.2km and length of 20km. In the classic O'Neill design, we have three large axis-aligned windows in the shell, alternating between purlins of habitable surface. The windows provide light, and presumably affect thermal transfer considerably. Before we start things spinning, we pump the inner volume full of breathable air. I believe O'Neill proposed 1/2 atmosphere, 20% partial-pressure O and 30% N, but I don't have my copy of High Frontier handy at the moment. We'll assume that the designers of the habitat have set up the mirrors and cooling system needed to maintain as comfortable a shirt-sleeve environment as possible. We spin the cylinder at ~0.5rpm to produce 1g of centripetal acceleration on the inner surface, and then we wait for everything to reach some sort of equilibrium-ish state. The tangential velocity at the outer radius is ~630km/hr (nearly 400 miles/hour), whereas at the axis it's nil. Because the spin gravity is fictional, acceleration is only imparted to the atmosphere by frictional interactions with the inner surface of the cylinder. Let's assume it's not smooth, but populated with short buildings (probably two or three stories, max), small trees, people, etc. So, near the inner surface, you have the outer edge of a vortice of atmosphere spinning at ~400mph, and a relatively calm eye at the axis. There are a lot of oddities about this vortice though. I'm imagining it like a smoothie in a blender, except the whole blender is spinning, with paddles extending from the walls of the blender instead of a blade at one end. Because there's no true gravity, the air molecules are just hanging out in space until they interact with the inner surface and are imparted with a tangential velocity. The outer edge of the vortice will end up moving at roughly the same tangential velocity as the inner surface, so just like you don't notice the air in your car moving with you at 60mph, the residents shouldn't be bothered by super-hurricane-force winds. But if you consider how ballistic trajectories work in this system, I think there'll be the sensation of a steady "downward"/spinward breeze as the accelerated mass of air meets the curve of the ground. Then we have to consider thermal transfer and convection, but again, the gravity is fictional, so I'm not sure we can think about this system in the same way we'd think about atmosphere on Earth. Normally you would think of hot air rising, and cooler air sinking, but without real gravity, that goes out the window. Instead you have the frictional interaction at the outer edge of the atmosphere imparting linear velocities to masses of air. If the blender analogy applies, I think there's going to be some significant amount of pressure differential between axis and outer radius, but I have no idea how much. So because of the pressure differential, you'd still have warm air "rising" as the higher pressure system seeks a lower pressure environment, and I think you'd have masses of cooler air "sinking" back into the higher-pressure outer radius, with all the weird apparent deflections that you get in a rotating reference frame: anything moving in toward or out from the axis will appear to be deflected anti-spinward. Then there's the wind shear to account for: going from a theoretically-calm axis to 400mph winds at radius will be no joke. So between denser, cooler air masses deflecting anti-spinward as they make their way out from the axis, and that steady spinward breeze from frictional linear accelerations at the surface level, it definitely seems like we're going to at least have buffeting spinward and antispinward breezes at the surface. Unless I have any signs reversed in my very-provisional mental modeling! :) As for thermal inputs, you have radiative insolation through the windows, you have conductive heat transfer through the shell, and you have heat generated by the friction between atmosphere and the inner walls, buildings, trees, etc. (In [another question](https://worldbuilding.stackexchange.com/a/120637/40786) Carlos Zamora suggests convective systems developing between the windows and the land purlins, but he may not be taking the "blender effect" into consideration...) My question: what in the world is this crazy weather system going to be like, experientially, for shirtsleeve humans living on the surface? There's certainly going to be some crazy wind shear as you move from axis to radius (no human gliders in this scenario, I think, and no fluffy white clouds). I think the surface would be habitable, even if it might always be good kite-flying weather. The harder the science you can appeal to in the answer, the better, but I don't think anybody has actually studied this question with any amount of rigor, so I'll happily take flights of fancy and imagination as well. :D I've read all the discussions I could find about atmospheres in one of these contraptions. I see lots of suggestive hints, lots of questionable assumptions, but no clear answer: * [Prevailing winds on a rotating space habitat](https://worldbuilding.stackexchange.com/questions/119918/prevailing-winds-on-a-rotating-space-habitat) This is a very similar question, but encompasses everything from sealed cylinders to Ringworlds, and the drift of the conversation tends to a Ringworld scenario, whereas I'm interested solely in the much smaller O'Neill cylinder. Carlos Zamora provides a [fascinating answer](https://worldbuilding.stackexchange.com/a/120637/40786) outlining the pattern of convection from warm land to cold windows, with a stagnant hot zone at the axis, but I'm not sure that he's taking pressure differential and wind shear into consideration. * [What would happen to air flow and fires in an O'Neill cylinder?](https://worldbuilding.stackexchange.com/questions/148380/what-would-happen-to-air-flow-and-fires-in-an-oneill-cylinder) Another similar question, with an interesting answer about how smoke would propagate. However, that question is labelled `hard-science` and so doesn't get much help because of the lack of hard research. * [What conditions would make rain possible in an O'Neill Cylinder?](https://worldbuilding.stackexchange.com/questions/99149/what-conditions-would-make-rain-possible-in-an-oneill-cylinder) There's [a very suggestive comment](https://worldbuilding.stackexchange.com/questions/99149/what-conditions-would-make-rain-possible-in-an-oneill-cylinder#comment295615_99149) by Loren Pechtell that got me thinking about this. * [Radial variation of atmospheric pressure in rotating O'Neill cylinder-like ship?](https://space.stackexchange.com/q/31465/20474) This suggests that there wouldn't be much variation between the pressures at the axis and radius of an O'Neill cylinder. * [Can birds fly inside an O'Neill cylinder?](https://space.stackexchange.com/q/27665/20474) and also [Flying helicopters on Rama](https://scifi.stackexchange.com/q/73754) * [What would determine the interior temperature of a large space station?](https://space.stackexchange.com/q/5672/20474) Tangential (ha!) discussion of temperature management for a space colony. Summary: let the engineers figure it out. They'll be fine. Update: @Matthew makes a really good point about convection: it's just various densities of gas seeking an equilibrium. When I first was preparing the question, I was weirding myself out switching between the two reference frames and considering the transition from rest to spinning. As the habitat hits its target angular velocity and the contents come to equilibrium, velocities are transferred from walls to nearby gasses via friction, and then knock-on until everything near the walls is moving in a relatively orderly fashion along with the walls, so everything close to the walls is acting more or less as if they were under gravity, with convection currents and the whole nine yards. [Answer] Overall, you'll get convection and Coriolis effects from air movement just as you would on a rotating planetary surface. The biggest difference, relative to Coriolis, is that the axis of rotation is parallel to the ground and there's a big velocity difference over a relatively small height range. On Earth, the Coriolis effect on a strong updraft near the equator is negligible, because you're lifting the air perhaps a kilometer, with a starting radius of 6400 km and a rotation rate of 24 hours. In your O'Neill cylinder, you're lifting air a kilometer from a starting radius of 3.2 km, and a rotation rate of half a minute -- so as you note, there's roundly 200 km/hr difference in rotation speed from ground to 1 km altitude. So you have thousands of times the Coriolis effect you'd have on Earth. Will that produce tornadoes every time the ground gets a little warmer than the axis? Probably Not. Why? An updraft will never manage to build up enough momentum to turn into a (horizontal) whirlwind; it'll start turning spinward almost instantly. Instead, you'll get tiny eddies, surely nothing bigger than a minor dust devil (a meter or two diameter and a couple m/s or so rotation velocity), and to a person on the "ground" they may be perceptible only as a wind gust that blows your hair one way and your pants legs the other. In the end, air can still rise, so you can develop clouds and rain (assuming enough humidity and temperature differential over height) -- but you won't get violent Coriolis storms because there's too much Coriolis effect. [Answer] ## Yes, there will be wind shear, but it is irrelevant: On Earth, there is a 1656km/hr difference over a distance of 10,000 km between how fast the air is moving at the poles and how fast it moves at the equator. Because it is so spread out, the sheer is so minor that this coriolis effect is only noticeable at the global scale. On your O'Niell cylinder, you will have a 630km/hr difference in air velocities between the center and the perimeter, but that velocity difference is only spread out over 3.2 km. This means your coriolis effect is about 1200 times more pronounced as on Earth, but the nature of how an O'Niell cylinder works will make this added wind shear zero-out to the observer in most cases. The reason hurricane/tornado winds are so dangerous is not because they are fast, but because they are moving at a different speed than we are. Let's pretend you build a 1km tall tower inside of the O'Niell cylinder. The base will be moving at 630km/hr and the top will be moving around a smaller circle; so, it will only be moving at 433km/hr. Incidentally, the speed of the air at the ground will be about 630km/hr, and the air at at 1km will also be about 433km/hr; so, you will not experience in change in the air velocity relative to your own as you go up. The only entities inside the cylinder that will experience this sheer will be anything free floating that has yet to sync up with the cylinder's rotation. The only apparent wind you will get will be from what ever whether patterns are formed by the external heating and cooling of the cylinder resulting in updrafts across the gradient. [Answer] It really depends how hot the floor is. If the structure absorbs and transmits a lot of stellar energy inwards as heat at ground level then you're going to get a lot of convection and the thunderstorms etc... that go with it. If you introduce relatively little heat directly at ground level, but primarily heat the atmosphere from the top down, using what I think of as the "central filament" design (per Arthur C. Clarke's Rama), then you have a lot more control over the emission wavelength and it's interaction with the internal landscape and you can create less violent weather. [Answer] Thinking about blenders got me thinking about tornadoes. If we consider the largest recorded tornadoes, the [2013 El Reno tornado](https://en.wikipedia.org/wiki/2013_El_Reno_tornado) was 4.2 km wide with max wind speeds of 302 mph. An O'Neill Cylinder with those specifications only produces 0.4g acceleration. With an O'Neil cylinder we are literally talking about bottling up a supertornado and selling lots in the walls of the storm. ü§Ø Of course, because the lots and the people who live in them are moving with the storm, everything is hunky-dory. Maybe? By examining the [characteristics of tornadoes](https://en.wikipedia.org/wiki/Tornado#Characteristics) and [mesocyclones](https://en.wikipedia.org/wiki/Mesocyclone), we can start to make some interesting suppositions for the builder of these monstrosities. * Tornadoes emit sound: + high frequency ([Abdullah, 1966](https://web.archive.org/web/20170921230829/https://docs.lib.noaa.gov/rescue/mwr/094/mwr-094-04-0213.pdf)): atmospheric tornadoes have been described as making "a peculiar whining sound like the buzzing of a million bees", which is drowned out by a roar that begins when the tornado makes contact with the ground. + low frequency ([Bedard, 2005](https://journals.ametsoc.org/doi/full/10.1175/MWR-2851.1)): tornadoes produce identifiable inaudible infrasonic signatures * The pressure drops rapidly in the core of the tornado (as I suspected from the blender analogy). An individual [who gave an account](https://web.archive.org/web/20070309150026/http://docs.lib.noaa.gov/rescue/mwr/058/mwr-058-05-0205.pdf) of seeing the center of a relatively small tornado above his head reported a "strong gassy odor and it seemed I could not breathe". * Tornadoes emit electric signals and fields ([Leeman, 2008](https://www.sciencedirect.com/science/article/pii/S0169809508003165?via%3Dihub)) * [The same account](https://web.archive.org/web/20070309150026/http://docs.lib.noaa.gov/rescue/mwr/058/mwr-058-05-0205.pdf) describes the center as very still: "Everything was as still as death." * [The same account](https://web.archive.org/web/20070309150026/http://docs.lib.noaa.gov/rescue/mwr/058/mwr-058-05-0205.pdf) describes lightning(!) in the center: "the whole was made brilliantly visible by constant flashes of lightning which zigzagged from side to side", though Wikipedia notes that "Tornadic storms do not contain more lightning than other storms" (citation needed). The comparison is complicated, of course, since it's hard to separate out the effects from interactions between a tornado and the larger atmosphere. (It's easier to separate out effects from interactions with the ground, as plenty of tornadoes have been observed in mid-air, with distinct characteristics.) Update to clarify: As with anything regarding rotating reference frames, it's all about your perspective. The good news is that, as I mentioned, the residents are moving with the storm, so the inner surface experience is probably more along the lines of a blustery fall day. The danger of a tornado is in how the vortex interacts with stationary objects on the ground, i.e. in a different inertial reference frame. We've captured this vortex in a bottle, but it's still a vortex, so comparing to mid-air tornadoes is a useful exercise./Update The most important potential characteristics for a resident in the colony might be: * The bees. Is this sonic phenomenon inherent to the tornado itself, or is it an interaction w/ the external atmosphere? Some observers have connected the noise with the small sub-vortices that seem to be emitted from the outer edge of the main tornado vortex, so this may only be a feature of terrestrial tornadoes. Nobody knows, though, so this is still fair game for creative license. * The brown note. Infrasound emissions [can produce](https://en.wikipedia.org/wiki/Infrasound#Human_reactions) irritability, disturbed sleep, and fatigue. * The electric field. We already know that the colony acts as a giant Faraday cage, requiring exterior signals to be repeated inside. Would the noise inside put a damper on radio communication? Would a cell phone work? * The lightning(?!). Would the residents be subject to a constant light show at the axis? Hopefully this effect would be amenable to preventative engineering! Some very interesting non-obvious effects of the setting, useful to storytellers, but perhaps less useful to O'Neill and Bezos' idyllic visions. :) I'm also interested in the effects at the axis. Old stories about O'Neill cylinders are full of people flying with wings, etc. in the free fall at the center. One book I read even had a mountain at one end that you could climb up to the axis. Sounds like the flying might work, perhaps with oxygen, but don't stray too close to the 400mph walls of the vortex. And watch out for the lightning! ]
[Question] [ How can I predict the color of the sky based on the information provided? Atmospheric composition: * \| 2% Trace gases \| 58% Nitrogen \| 26% Oxygen \| 11% Argon \| 3% Carbon dioxide \| Average surface temperature: * 36 degrees Celsius Planetary rotation: * 34 hours Axial tilt: * 0 Info regarding of altitude, pressure, and atmospheric density: ``` altitude pressure density (meters) (atm) (kg/m^3) 0 17 10 1000 15.3 9 2000 13.8 8.1 3000 12.5 7.3 4000 11.3 6.6 5000 10.1 6 10000 6 3.6 15000 3.6 2.1 20000 2.2 1.3 30000 0.8 0.5 40000 0.3 0.2 50000 0.1 0.06 ``` Keep in mind, the type of star this world is orbiting is an F9V class star, only slightly above a G1V. [Answer] # Blue, but darker Earth's sky is blue due to [Rayleigh Scattering](https://worldbuilding.stackexchange.com/a/63962/23519). Rayleigh scattering redirects at an angle a percentage of incident light through a gas. The percentage of light reflected is proportion to $1/\lambda^4$, where lambda is the wavelength. That is, the shorter the wavelength, the more light is reflected. Violet light is most reflected, percentage-wise, but the purple section of the visible spectrum is small. So Blue light is the next most reflected, and since that portion of the visible spectrum is large, the sky is blue. For your atmosphere, the percentage of oxygen and argon are higher, but he percentage of nitrogen is lower. From Table 1 of [Shardanand and Rao, 1977](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770012747.pdf) here is a comparison of scattering cross section (in $10^{-27}\text{ cm}^{-2}$) for various atmospheric gasses at certain wavelengths (on the x-axis, in Angstroms): ``` Molecule 6328 5145 4880 4579 3638 O2 2.06 4.88 6.50 8.39 20.03 N2 2.24 5.61 7.26 10.38 23.82 Ar 2.08 5.46 7.24 10.13 23.00 CO2 7.28 17.25 23.00 29.60 70.70 CH4 5.26 12.44 16.59 21.40 51.10 ``` Notice how similar oxygen, nitrogen, and argon are to each other, as compared to carbon dioxide or methane. The relative rate at which the different wavelengths of light are scattered by your atmosphere will be almost the same as on Earth, so the color of the sky will be almost the same as on Earth. Your star will be putting out light in a spectrum very similar to that of our sun, so the highest magnitude wavelengths will be in the blue range, just as our Sun's are. See [here](https://worldbuilding.stackexchange.com/a/102636/23519) for more details. The final factor is the mass of the air column. The proportion of light both absorbed by the atmosphere and raleigh scattered is affected by the number of air molecules that a light wave encounters as it travels into the atmosphere. Without you giving a surface gravity, I can't exactly calculate the air column's mass, but from your pressure and density, the mass of the air column is something like 10 times as massive on Earth. Therefore, light will be that much more likely to be absorbed or scattered. This will make the sky a much darker shade of blue. But note, due to the same emission spectrum of the sun and the same scattering factors, that doesn't mean that the shade of blue is changed, just the brightness of the blue. The blue color will be the same shade, but darker. [Answer] It will stay blue. But what blue? [![enter image description here](https://i.stack.imgur.com/i94g7.png)](https://i.stack.imgur.com/i94g7.png) As stated, rayleigh scattering will be most deciding factor for [sky color](http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html). As your atmosphere has more volume and density, more carbon dioxide >> more scattering and more scattering for shorter wavelenghts. [Paper on color of the sky](http://file.scirp.org/pdf/ACS20120400011_46715429.pdf), it is more about our sky and how color changes as sun sets. But you can get some understanding from that. So blue light wavelenght will be moved to around 450-480nm, that gives us blue to pale blue. How much light makes it to surface? Is up to you, but it too will influence how dark your blue is. But it would be way more nicer if we make your density more in line with atmospheric pressure of 17 atm >> around twice your choise. That would give us pinkish sky or yellow with a lot of dust. ]
[Question] [ I'm developing a silkworm that spins webs of a particular kind of "silk" and weaves thin, fragile webs. The magic part of this is that it also spins wind. The following addresses how this works and my question. # Info The silkworms "fold" breezes into the silk, basically funelling the wind into a handwaved sheath that surrounds the silk. The wind rushes freely through the unobtanium sheath, causing it to accelerate rapidly until it's really, really violent. Think a very strong dust devil/mini tornado. The webs are about 30 cm in diameter. To make matters worse, the worms fold hot and cold air into opposing ends of the single, closed loop of the web. As the winds move through the web, they dance past each other. But when the web is broken--it's fragile, remember--the sheath of wind also snaps. Then the winds, now moving very very fast, rush into a mini "tornado," encircling their helpless prey. Let us say a strong gale-force wind at 47–54 mph. The spinning wind sucks the air out of the vortex, which sucks the air out of the lungs of the prey. The prey falls unconcious and is slammed back and forth by the wind until the wind spins away. Then the creatures, summoned by the sound of the wind, come up to their prey and poison it before eating it. # My Question What's the best material that satisfies the following critera? * Fragile but tensile enough * Can be looped into a single, nonending piece * Economical for a creature to expend energy producing * Ensures that, e.g, the tree it's stuck against survives * Can be made hollow (tubes for support/strength and to make the webs easier to produce) Keeping in mind the winds released are * like a very strong dust devil/mini tornado. * strong gale-force winds at 47–54 mph. * and move in "mini-tornado" form. and the material needs to withstand the force of this wind across its surface --- Thank you to all in the [Sandbox](https://worldbuilding.meta.stackexchange.com/questions/6168/sandbox-for-proposed-questions) who helped me develop this question. --- Note: In accordance with [this meta post](https://worldbuilding.meta.stackexchange.com/questions/106/should-our-default-position-be-that-answers-should-be-science-logic-based-rath), please do not use magic as an answer (handwavium is reserved for the purposes of wind-weaving, and the magic sheath, not for the purposes of the material used. That's why this is tagged [science-based](/questions/tagged/science-based "show questions tagged 'science-based'"), not [magic](/questions/tagged/magic "show questions tagged 'magic'") [Answer] If you do want a vortex, then I think you need two layers of regular silk, opposite to each other and connected through their hubs by a perpendicular thread. The webs disconnect from the surroundings and spin (no pun intended) violently and in opposite directions when the axis string is broken. This will cause them to release the handwaved air contained in them, and when both masses mix, you will have your vortex. Most kinds of trees should be able to survive it with just a few leaves lost, maybe a branch gone, even if you do reach the gale force figure in the question. --- If you want to be realistic, though... A gale force wind is hardly obtainable biologically. The Mythbusters guys have [managed to sneeze at up to 39 mph](http://www.discovery.com/tv-shows/mythbusters/mythbusters-database/sneeze-travel-100-mph/). Real scientists, on the other hand, [have measured average speeds of 10 mph](https://biology.stackexchange.com/a/64062/41383). If you wish for a truly reallistic scenario without the vortex, a regular mix of silk and some mucus may do the trick. What the worm needs to do: dig a tunnel with two opposite openings. On one end, make a membrane of silk + mucus. The silk must be tense as a guitar string, and the mucus should make it airtight. This membrane will act as a drumhead. The other end of the hole should have an opening just small enough for the prey or the worm, whichever is largest, and the wall should be hard. Perhaps the worm is digging through a tree, for example. Or it may furnish the wall of this opening with rocks, sticks, and mucus. Next step, the worm pulls connects many thin threads to the drumhead wall and to random points inside of the tunnel. This can be done in a black widow web pattern. The important thing is that the threads should pull the drumhead towards the insde of the tunnel, with some force, but in a very delicate equilibrium. You will soon learn why. Last step, which is optional, is setting some bait along the tunnel. When unsuspecting prey comes inside and unwittingly cuts one thread, the drumhead wall will vibrate. With every few cycles of vibration, it will cut more and more threads, vibrating ever strongly, untill all threads are cut. It should then keep vibrating for some time and then stop, which is when the worm enters and does what it needs to do. Now for some science. Such vibrations will form a note, and the tunnel will act as a resonating chamber. If the wavelength of the note matches the length of the tunnel, you will have a [stationary wave](https://en.wikipedia.org/wiki/Standing_wave). Long story short, these are sound waves that do not move around, but rather just stay there. These things have nasty effects. Certain materials will vibrates without apparent cause. On humans, [even a considerably weak standing wave can have the following effects:](https://neuroresearchproject.com/2013/02/19/1289/) * Severe middle ear pain * Persistent eye watering * Respiratory difficulties * Sensations of fear including excessive perspiration and shivering From the same link: > > ‘Vibration of the body mostly affects the principal input ports, the eyes, and principal output means, hands and mouth.'(p. 287). > > > ‘Exposure to vibration often results in short-lived changes in various physiological parameters such as heart rate…At the onset of vibration exposure, increased muscle tension and initial hyperventilation have been observed.’ (p. 280). > > > If such effects can happen to humans in a very wide environment, imagine what a standing wave will do to a small insect. The vibration of their carapace would be extreme, and could mess up with their trachea and keep them from breathing for a moment, causing momentary stun. If you want to tune your silk/mucus drumhead... For a 10cm (~4 inches) long tunnel, you are looking for what would be approximately the A7 on a piano. I have calculated this using [this formula](http://www.softschools.com/formulas/physics/wavelength_formula/5/) and [this table](https://pages.mtu.edu/%7Esuits/notefreq432.html). --- All threads in both ideas can be made of regular silk like that of a spider. The threads which are supposed to break first will just be thinner. The threads that do not break first can be made as thick as human hair, or even all the way to the thickness of a couple sheets of regular printer paper. Even then, I expect that a gale force wind will break all the threads a little after the release of the air. ]
[Question] [ Sequel to [this question](https://worldbuilding.stackexchange.com/questions/95835/could-you-make-bat-wings-shaped-like-the-different-kinds-of-bird-wings). Basically, I've been designing an intelligent avian race based on bats. After reading through some of the answers for the linked question, I've decided that these bats will be a cross between our modern bats (such as the Flying Fox) and Anurognathid pterosaurs. I'm still going to call them 'Bats' just for convenience though. However, I've been pondering one key aspect to my design: I've been wanting to make these bats with another set of arms. This is mostly because, as an intelligent race, being capable of fine manipulation is an asset. My bats have thumbs like the Flying Fox and 2-3 non-webbed fingers. However, since many pterosaurs have long metacarpals in proportion to their fingers and thumbs I'm worried that these hands wont be as flexible. Additionally, bat feet don't seem to be as capable of fine manipulation like some bird feet are. So here's what I've been thinking: What if these bats had a small set of arms that could fold close to the body when flying? These arms don't just have to be for fine manipulation. Bats can catch small prey with their feet, but appear to be limited because of how their legs move up and down with their wings when they fly. If they had a set of arms that could move independently of the wings, they could probably more easily catch prey without throwing off the flight. Or, they might be able to. My main questions regarding this setup are: * What anatomical changes need to be made for this setup to work? and * Could a bat like this even fly? Edit: If it helps for answering, these bats would be among many species that evolved from a hexapodal ancestor. The world they come from is separate from our own world, so don't let the fact that we don't have hexapodal mammals on Earth limit you! [Answer] > > However, I've been pondering one key aspect to my design: I've been wanting to make these bats with another set of arms. > > > This is mostly because, as an intelligent race, being capable of fine manipulation is an asset. > > > I honestly don't understand why this means they have to have 6 appendages, adding a functional hand to the wrist of the wing would be more efficient but if that's your goal.... The key aspect is what Tim mentioned: > > The main problem would be fitting in another set of muscles - in the chest and new arms - which necessarily takes space away from the muscles used for flying. You'd be dealing with a different power-to-weight ratio, > > > Your bat would need larger wing spans and improved musculature. If basing this on terrestrial examples its going to be a meatier bat with wider wings. This doesn't necessarily dictate your end appearance. On your world organisms could have discovered a more efficient and powerful muscle equivalent which would be less weight but more power. Also its skeleton could be made from a lighter stronger substance thus saving weight. This is the inherent problem with trying to ask if a creature is realistic. The possibilities of evolution are only limited by physics, chemistry and imagination. I just wanted to clarify another point: > > Why not? Insects do just fine > > > Many of the mechanics used by insects do not scale well to larger organisms. A great deal of their abilities are only achievable because of their size with those constructs. If you scaled an ant to the size of a human, it would no longer be able to lift 10x its body weight. [Answer] If you are proposing an entirely alien world then there is nothing to stop this arrangement from occurring. In our world the [Cambrian explosion](https://en.wikipedia.org/wiki/Cambrian_explosion) generated a large number of different body plan types each of which would constitute distinct phyla today. The vagaries of specific conditions at the time and luck have given us the body plans and phyla we see today. So animals such as [Hallucigenia](https://en.wikipedia.org/wiki/Hallucigenia) are sadly absent. Two arms would not be very aerodynamic on a flying animal, so they should be capable of folding flat against the body as you suggest. You might want to think of some good reasons why arms and hands were indispensable to these creatures to ensure that they would be selected for. Perhaps the main issue that you face is ensuring that this creature is not too heavy to fly. There is a physical limitation on what wings are capable of. As well as all the normal animal bodily functions you also need to equip it with two legs, two wings, two arms and a head that is capable of supporting a brain that can develop intelligence. That’s quite a load, but given the ingenuity of nature I suspect it’s doable. [Answer] This creature would likely have evolved from a creature with a large heavy tail, in order to make the central pair of limbs into the wings. It is likely that such a creature would naturally stand hexapedally, and only raising the hands to do things. ]
[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 7 years ago. [Improve this question](/posts/64170/edit) Professor Y is trapped in a virtual reality. The VR is running on accelerated time to the point where he can live out millions of lifetimes in a real-life day, basically giving him immortality within the VR world. He also has godlike powers within the world, as he is a sysadmin. His goal is to escape. He has two options: 1. Use his sysadmin powers to terminate the world. However, because of the nature of the accident that trapped him, he is 99.9% certain this will kill him and anyone else who happens to also be trapped (he doesn't know how many others there are). 2. Wait for a very specific set of circumstances to be true, which will allow him to end the world safely and get everyone free. Y would obviously prefer #2. However, the circumstances required are exceptionally precise and rare; it requires a massive amount of random events to be just so. There is no risk of him missing the opportunity if it does pass, but if something doesn't work out, he has to wait several thousand virtual years for the system to do its regular reboot so he can try again. In fact, probably 90% or more of the iterations won't be anywhere close to having the necessary circumstances. Think of it like repeating human history until you get a world where the first man on the moon is named Jeff Bulliord and has three kids (one of them adopted), plus several dozen other such statements that must also be true. Y is aware of what the necessary circumstances are, and he can use his godly powers to try and push events in the needed directions, but he only has an average person's sense of the butterfly effect. Only once things get very close is it reasonable to expect his actions to to more good than harm. Otherwise, he's going to spend several million lifetimes sitting around waiting for the next iteration of the world to begin because this one didn't work out. Obviously, Professor Y isn't going to remember a lot of this. He's only human, and the system isn't going to help him remember things. I'm interested in how long it's going to take for him to forget the most important things, such as: * his name/who he is * his goal, or the reason behind his goal * the fact that he's a sysadmin in a rebooting virtual reality, and not an actual god in a cyclic world Additional notes prompted by comments: * Professor Y might have some godly powers, but if were to just throw them around on a whim he'd almost certainly mess up what he's waiting for (and possibly turn the world against him). He has to be more subtle. * Professor Y's persona in the world is ageless, though he can make it appear to age as necessary so he doesn't attract attention. He begins each world iteration just as he finished the previous one. * The system reboots at a predictable interval. Once rebooted, the starting state is exactly the same every time, but with a different randomization sequence; compared to the length of an iteration, it doesn't take long at all for the "new timeline" to become incomparably different than the previous one. Professor Y can't do anything about this. [Answer] ## Over 340 years worth of memories with lots of caveats The first caveat is that this is stored memories. Things not worth getting stored would be forgotten or more important things would overwrite them and memories can morph over time increasing or more likely decreasing the amount of space they are taking. [Scientific American](https://www.scientificamerican.com/article/what-is-the-memory-capacity/) had an article on the brain and its capacity. It estimates the brain could hold as much as 2.5 petabytes of information or 3 million hours of recorded TV (which higher grade video formats would be even less). Unfortunately there is no direct way to know how much memory our brains dedicate to a memory and it likely also varies by person. In order to make this answerable lets add a second caveat. Let say Professor Y's brain cannot exceed the quality of recorded TV or in other words a memory at that level would be a photographic memory. This allows the 3 million hours to become a lower bound number of 342 years. If Professor Y stores some really low res memories it will greatly exceed that. > > Otherwise, he's going to spend several million lifetimes sitting around waiting for the next iteration of the world to begin because this one didn't work out. > > > Now lets say a single life time was 70 years and I will take several million lifetimes as being two million lifetimes. that give 140 million years. At those number Professor Y would only be able to remember 0.000244% of a single cycle. At such low numbers Professor Y is not going to even remember the highlights. The only way Professor Y is going to remember the important items that you listed will be to use brain exercises to intentionally remember it. ## Millions of lifetimes in a real-life day I recommend cutting this figure back dramatically along with the length of a cycle. Civilization has only been around for a mere 200,000 years. With millions of lifetimes in a real-life day (140 million years), that is 7,000 times bigger. ### Brain has limited speed for storing data To borrow numbers from brain capacity the brain would need 833 MBs of space per hour of TV. If the Professor has an excellent memory his brain would need to be able to write to memory at 237 KB/s. However the VR is running millions of lifetimes in a real-life day or in other words 5.8 million times faster. The brain simply cannot store data at 1.3 TB/s. So I hope the VR has good exception handling since the brain is going to be throwing lots of file IO exceptions. This is very good news for Professor Y attempting to remember important items. Since his brain cannot keep up with the incoming data almost all of it is going to be lost before the brain can store it. Thus the brain will be kind of acting like it is in read only mode. ### Brain as a processor The brain also needs to process and respond to the input given to it from the VR. [According to this research paper](http://www.dynamicscience.com.au/tester/solutions1/biology/nervoussystem/responseresearch.html) humans auditory reaction time is 140-160 msec and visual reaction is 180-200 msec. Lets say the brain is directly hooked into the VR and given drugs that bypass most of the reaction time and get it down to 1 msec. That is still too slow for the VR. By the time the brain has processed an event and responded 5.8 million msec have passed in the VR or 96 minutes. Someone in the VR asks the Professor Y what his name is, they would have to wait 1.5 hours for him to respond. ### Brain needs calories for power Let say all the brain speeds got hand waved through a magic chip that causes the brain to go into awesome overdrive mode while in a VR setting. Brain needs fuel to operate, and it is quite an energy hog. According to [share care](https://www.sharecare.com/health/calories/brain-calories-at-rest) the brain uses about 20% of your total calories, or 400 calories of a 2,000 caloric diet. So if the brain's speed is upped by a thousand fold, guess what it is going to need? A thousand times more fuel. In this case it likely will need to be upped by a factor of a million, but lets go easy and say 100,000 fold increase. The brain would end up burning through 40 million calories of food in one day. Butter is a good source of calories coming in at 717 calories per 100 grams. In other words Professor Y's brain would need to burn 5,500 Kg (6 tons) of butter a day to keep up with the VR. [Answer] # Depersonalization The "forgetting" experience someone experiences being trapped in a continuously resetting virtual reality is probably less akin to amnesia, and rather more like depersonalization. In basic terms, it is the loss of the idea that your ideas and feelings belong to yourself. Depersonalization is used by states to encourage obedience in prisons etc. The main tactic is frequent, arbitrary changes of environment and cellmates. An inmate condemned to life in Gulag A becomes resigned to it, spends a week working out who's who, then finds they're being put on a bus to Gulag B. Hopefully none of us will find out what this is like, but you can read about it from people who do: Nelson Mandela: Long Walk to Freedom (1995), Aleksandr Solzhenitsyn: The First Circle (1968) or Denise Chong: Egg on Mao (2009). I expect being trapped in a virtual reality would be the same. It sounds like Professor Y has no power over himself whatsoever. Living for thousands of years while generations shuffle past around him, living through reboots and resets. Psychologically, being an inmate (politcal or otherwise) in a vast prison system is the closest real world scenario. Fortunately, while the psychological field's interest in this is lacking (although that's changing), there are first-hand accounts. # How long would it take? Psychologically-speaking, Professor Y is undeniably in a bad situation. In accounts from political prisons, people can forget their motivations and alliances on the first night. Apparently, just the expectation that a relocation will occur already packs quite a punch. The best example of this in Western (US, British, European) detainment facilities abroad, where inmates know that a short trip across the border can change all the rules (you'll find this stated in survivor accounts, I can't remember the reference). The main drivers of depersonalization are arbitrary changes in the environment and its occupants. How long Professor Y lasts would depend on how frequent the resets are. Then again, if the scope of the "randomization" is wide, he might not make it through the first one. ]
[Question] [ I might have a bit too much saltwater in my brain. I'd like to discuss (can you do that in this format?) the ideas of combative mermaids on land. If you saw my other questions, you saw me bring up Tactics Ogre Knight of Lodis as a cool inspiration for this. Bryan McClure had a good comment in this question thread: [Mermaids on Land?](https://worldbuilding.stackexchange.com/questions/58519/mermaids-on-land) The focus here is land combat, but sea combat may come up as it will effect mermaid military culture. Movement Crawl As was delved into in the linked question, mermaids aren't the most agile. Their crawling speed would be in the neighborhood of 5, 8, maybe 10mph. To compare, the average human runs (sprints?) at about 15mph. However, they need to use their arms to crawl like this, making it combat ineffective. They might be able to hold a weapon while doing this, at least. Crawling with one hand or even crawling backwards is probably possible, and you can use a weapon while doing this, but it would not be easy. Slither Mermaids could also move with just their tails, while their human upper-body is upright. However, this is much slower. Still, it will serve as a pretty stable platform for fighting, possibly more so than a human's stance. Quick Step: They could, in fact, curl up their tail, and make one "quick" "step". A little like a snake coiling before a big movement, but much less so. Sidewind Mermaids might also be able to do something a little like [this](https://www.youtube.com/watch?v=B3NbPUTD5qA), but again much less so. It does mean their sideways motion will be faster than their backward and forward motion, when moving with just their tail. Spring Due to their light weight, and presumably very strong tails, mermaids will likely have a very strong jump, where they can spring at you or into the air. That is, if they can get that energy shaped into a proper jump. This could be useful in a few ways. Roll Like people, mermaids could make use of a log roll. They might even be able to tumble forward or backwards, with some practice... possibly. This can be useful for quick, desperate, defensive motion. Spears These will likely be the most popular weapon with mermaids. They give them reach, which helps to make up for their lack of mobility, and are pretty useful underwater as well (so they'd have practice with them). They can also be thrown? Thrown I don't see why not. The mermaids have the upper body for it. While you can't get a run up, then might even be able to snap their bodies with the throw to give it a bit of extra velocity (so it might be more than a standing throw for a human, but less than a human with a run up?). Of course a mermaid would want more than one spear if they're going to be chucking them, and carrying around a bag of spears is rather cumbersome. Tail The tail itself is actually a reasonable weapon, for the mermaid. If they swat you in the back of the leg with this, you will fall down. If they smack you in the head with this, you will surely feel it. They can swing it around quickly, and will be rather erratic if panicked. I can imagine mermaids creating fight-book style techniques, where after parrying a certain blow, you come around and hit them with your tail Ranged Weapons Just about all ranged weapons should be fine, except ones like the crossbow that requires you to use your foot to load it. The issue is, mermaids will not have much underwater practice with ranged weapons. You can use a bow or crossbow underwater, at very short ranges. Some mermaids may have practice hunting near rivers, where they come out of the water with some ranged weapon then clock an animal who was taking a drink. Being submerged underwater will be tough on their bows, however, if they use those. Unless a mermaid commits a lot of effort into learning ranged weapons, it will be trouble, as they will not be used to the physics of projectiles. Physiology Posture Mermaids would be able to assume some postures not practical for humans. Mermaids are bottom heavy, their tail probably weighs a lot compared to the rest of their body. It will also be rather long/large. This means they have a solid foundation to lean from. Try leaning as far forward as you can, you'll notice your balance starting to give out. Bend in half like you're bowing to the King, and you can walk around and do stuff (like run into things) with reasonable balance; though taking a swing at someone would likely not go well. Mermaids can likely take these awkward postures easily. A mermaid might be able to lean so far, their body is close to horizontal by the time Reach Aside from the reach with the spear, Mermaids may have an amount of reach with their posture. For example, if they "coil" up and crouch down, it will be hard for a human swordsman to reach them as you have less reach down low. But then, when they need to, the mermaid could extend her entire body into a thrust. A small mermaid is probably about six feet long, others being longer still. As mentioned above with posture, the mermaid might be able to get close to horizontal, which gives them a much longer reach. A human can reach something like 3 to 5 feet if they really lean into it (dangerously). A six foot mermaid would have a reach of almost 8 feet! They may also be less endangered of overreaching, while doing that. What's more, due to how very low to the ground they'll be, to humans it'll feel more like 10 feet. This will make the mermaid with a spear the equivalent of melee artillery. It is also likely to make for a very strong thrust. One disadvantage to this reach, is it would take a moment for a mermaid to retract herself from this posture. For one thing, the amount of energy and mass involved, it's going to take a moment to fully stop (dissipate the energy) so you can start retracting. You wouldn't want to be thrusting like this constantly. As a point of interest, since mermaids are used to fighting vertically underwater, fighting horizontally likely won't seem unusual to them. Prone and "Standing" If you trip a human, it takes them a moment to re-orientate themselves and get up. Aside from the difficulties of how to trip a mermaid... they could swap between prone and "standing" positions quite easily. If they need to pick up loose change they dropped, easy. If you push them over, they can spring "back to their feet" like a wobbly man. Armour Armouring the lower parts of the mermaid's body is tricky, and normally mermaids would wear pretty limited armour underwater. You could combine armour with floats underwater, and take off the floats on land. They could wear chainmail skirts over their tails. The upper body can mostly be armoured as a humans can be. Of course, if the upper body is too armoured, certain postures will become difficult. Mermaids would likely wear some armour just so crawling around is less painful, possibly with a thick textile fitted to their tails to prevent chafing. But combat armour, as much as other people avoid it due to discomfort, mermaids would be far more concerned about that. They would already feel weighed down and uncomfortable on land. Shields Mermaids would not normally use shields underwater, as they are a pain to swim and maneuver with in water. They may try to learn their use on land, to make up for their limited mobility. Shields aren't difficult to learn the basics of, even if mermaids aren't skilled in their use it should be helpful. However, that is an extra thing to carry when travelling, so mermaids would likely not be keen on these by and large, except maybe bucklers. In case of armour and shield, of course, most mermaids would travel by raft, carriage or horse, so weight concerns are less of a problem. Important point: Since mermaids can make themselves very low to the ground, they could get complete coverage from a shield (as long as no one fires from the side, as that long tail is a target). Conclusion Mermaids are truly unorthodox enemies to face. Their oddities and advantages don't necessarily indicate they have equal ground with human fighters on land, but there is enough evidence to suggest they would not be completely helpless. Mermaids are very defensive fighters, using their reach to their advantage in a bid to scare off opposition. Ranged weapons are their bane, as mermaids aren't mobile, well armoured enough, nor skilled in ranged combat enough to contend with them. Still, mermaids can go prone, can move erratically, spring and roll as necessary, making them very unorthodox targets. Mermaids could launch surprise raids out of water, from sea or rivers, then retreat back in before reinforcements arrive. Question? So, what are your thoughts on mermaids? Anything in this that seems incorrect, or that you would like to add? I'm sorry that this isn't a straight question, but more of a reality check and a request for second opinions. We should consider taking this up to a chat room (I don't think I have privileges to make one, presently) to discuss it at length (I'd love to go into different types of thrusts and manoeuvres). [Answer] As far as armor goes they could use leather armor or maybe even armor created from the blubber of sea animals. ( Animal fat, especially blubber, can add a certain level of protection especially against projectile weapons). I agree that spears are probably the mermaids' preferred weapons. As for ranged weapons there is a crab that opens and shuts its front claws so fast that it causes a gust of water so powerful that it can kill certain sea creatures. I could see the mermaids using a similar type of weapon for underwater ranged combat and hunting. As for spears, years ago many ancient cultures carried two types of spear. First a single spear between 5 and 6 feet long for medium range combat, then they would also carry a pack of throwing spears ( 1 to 3 feet long used exclusively for throwing at targets). The smaller size made it easier to throw and allows you to carry more then one or two of them. A throwing spear might be a useful land ranged weapon. Also remember that the mermaids are capable of taming sea animals same way we are. If they could train their killer whales they could train them to fight the same way we train them to jump and do flips in the air. Killer whales such as these might be useful for land combat since unlike most whales they have the ability to beach themselves without significant harm. Also while it might be impractical while in water your mermaids should consider getting sheilds when they visit the land. Local merchants could make a killing off the selling shields to mermaids visiting from the sea. It also might be interesting to give the mermaid some type of natural defense against land humanoids. Maybe something hormonal that makes people not want to fight them. Or maybe you can go to the Odysseus route and said they have such beautiful voices that once they start to sing you can't think of anything else. [Answer] "Anything in this that seems incorrect..." This one: Physiology, Posture: I have only one major issue to consider. Center of mass of a human body will be on the upper body, usually somewhere above or around the belly, so to make valid the statement that merfolk are "bottom heavy", some extra-excessive bodymass is required down there, or very heavy training for tail use to counterbalance upper body work. Land Training: To wield combat on land is close to same difficult as to wield combat in water for humanoids (divers). Placing combat to land against land living creatures is a serious disadvantage, which is to be bridged via training, technology, or cunning. Throwing a weapon will be extremely different underwater, than on the surface, so merfolk are supposedly own much less expertise in this, and less competent in the field of firearms. So to make merfolk live to the presented expectations, they will need to put serious efforts to train themselves to land combat. This will call for secret training grounds! Some specialization might also come up similar to Spec Ops. Gears, armor: As Bryan McClure mentioned, most convenient would be if they use armor only when reaching surface, maybe owning skills to create makeshift armors. Merfolk are using shieldpieces most commonly with strings and straps, this would pretty well fit in their style. More resilient land combat armors typically take much time to fetch and apply on wielder if not being worn at patrol duty right at the moment. Tinkerings: Even if merfolk are not that science crazed as humans, they are still good at applying tricks and use underwater objects, creatures for their favor. If they turn out to have good tinkerers, they might figure out some pretty useful (even monumental) gadgets. Reverse Tidal Generators to raise the water level or make Assault Waves to unbalance land units near shores, Medusa Catapults, High Pressure Tubes (like firefighter hoses), Monsoon generators, poisonous creature grenades, "and much more". [Answer] In the odd occurrence of needing to remind the land lubbers that the sea is always a threat, I would suggest taming specific land creatures. Notably the ones that don't mind hanging out near/in water. Walrus - Slow but powerful Seals - Fairly fast, although probably not mountable, more like guard dogs Bears - I'm thinking polar bears mostly, but any bears near a coastline should work. Domesticate with meals of fish. Now you have a powerful land based mount. [Answer] Apologies if it's not done to answer old questions, but this one's quite interesting! Movement What movement mermaids would be capable of depends entirely on the anatomy of their tail. Do they propel themselves through the water with vertical up-down movements of their tail, or lateral side-to-side? Because of our historical spinal structure, most seaborne mammals use the up-down stroke, with limited movement side-to-side. For similar reasons, seaborne reptiles and fish use lateral motion with limited up-down movement. Neither of these options allow for particularly efficient movement on land, and depending on the length of their tail will make moving on land exceptionally difficult (think fish or stranded porpoise). If the tail is long enough, they should still be able to move about like seals or slither like snakes/naga (again, depending on which way their tail articulates). They will also need to have fins/flukes sufficiently shaped such that they don't get in the way (bare on the underside, not overly wide). This will make them less efficient swimmers, but it's necessary in order to make them capable of moving on land. Make no mistake, in order to look anything like mermaids they are going to be significantly disadvantaged compared to a human moving on land. Close Quarters Combat I think you're dead right that spears would be favoured as you can threaten a large area of space with a spear from a stationary position, whereas at least single combat with most other weapons would be significantly hampered by the lack of mobility. Spears are also fairly hydrodynamic so would function well underwater. It should be noted that this isn't a particularly great restriction. [Spears are fantastic weapons](https://www.youtube.com/watch?v=afqhBODc_8U). However, even with a spear, the lack of mobility will be a problem. They probably won't be able to turn as quickly as a human can dart around them, and they definitely won't be able to dart backwards and forwards to stop someone closing in on them. What this probably means is that merfolk will need to fight in close order in order to be successful. This again isn't such a bad thing as this is where the spear (in combination with a shield) really shines. Shields are a lot less hydrodynamic than spears so will probably be a later development (probably learnt from landlubbers), but will be a vital development in merfolk fighting tactics. The shieldwall/phalanx formation also plays into one of the few benefits to merfolk physiology on land: stability. Bipedal humans trade stability for endurance (and comparatively to merfolk; speed and agility). Due to the greater mass lower down (remember, the tail has to be long) and the greater area touchign the ground, a mer-warrior will be much harder to shift backwards, throw off balance, or knock down. As most combat between shieldwalls/phalanxes/pike formations tends to descend into a push-of-pike this will be a significant advantage. tl;dr Merfolk shieldwalls would be very difficult to defeat in close quarters. Ranged Combat I'm not wholly convinced that merfolk would be any good at ranged combat at all. Humans have specifically evolved to be very good at accurately throwing things. One of the reasons we tend to be weaker weight-for-weight than other animals is that we have a disproportionate amount of slow-twitch muscles, which allow us to very accurately adjust the trajectory of thrown objects. Even compared to Neanderthals, we are more adapted to throwing things. This, along with other adaptations to vision and co-ordination, directly translates through to our proficiency at ranged warfare. Merfolk, however, presumably evolved (I'm assuming they weren't magicked into existence) in a very, very different environment. It's very difficult to throw things underwater due to the drag both on your arm as you throw something and on the projectile itself. Bows don't function well, slings don't function well, atlatls don't function well, crossbows don't function well. The only thing that really works is spearguns, and they require the production of spring-steel which is at the very earliest late iron-age stuff. Furthermore, long-distance vision is difficult underwater. Especially so outside of clear tropical waters. What this adds up to is that merfolk are very unlikely to have the specific adaptations humans have to ranged combat. If they are capable of throwing, it is likely to be similar to chimpanzees (strong musculature, but comparably terrible aim). This would, however, free up merfolk upper body musculature to use more fast-twitch muscles so they'd likely be stronger than us for a given muscle mass. tl;dr Merfolk peltasts would be terrible, and archers likely non-existent. Cavalry Merfolk tails are not exactly suited to comfortably riding other animals. They're also not particularly suited to clambering and climbing. Thus, horses and other mounts are highly unlikely. Elephants with howdahs are more likely, but due to the climbing issue will be trickier than for people (although not insurmountable). Chariots are a possibility, but they don't appear to be as effective as individual riders. At least, they were largely phased out by the end of the bronze age. However, they would still be very useful to merfolk as they alleviate their manoeuvrability problems. tl;dr Merfolk cavalry will likely not be up to much in comparison to humans, but will still be useful for merfolk military tactics. Tactics Tactically, merfolk are somewhat similar to bronze-age Greece. Hoplite phalanxes (albeit less manoeuvrable than early greek hoplites) with chariot-borne nobility and limited ranged/cavalry support. They will likely evolve into later greek/diodachi tactics of bigger pike blocks, heavier armour and longer spears (but similar to the diodachi states, heavily relying on the strength of their phalanxes rather than the combined-arms approach of Alexander). While these are pretty solid battlefield tactics, they are vulnerable to disruption from rough terrain and a lack of flexibility. Given their screening troops would be of lower quality than human skirmishers and cavalry they would be vulnerable to the sort of tactics that the Thracians and Romans used successfully against greek hoplites and phalanxes. They may well pick up human mercenaries to fill these roles. tl;dr Merfolk are like bronze-age greeks, but more Logistics Here's where the merfolk start to fall down. Due to their slow and energy-intensive movement, their armies are going to be significantly less manoeuvrable on the logistical scale. Marching to and from engagements, intercepting rival armies, maintaining their supply lines. All of these are going to be a lot more difficult on land than for humans. They can probably use rivers to move troops fast, but they're restricted to where rivers flow to (and humans use boats for the same purpose, so it's not really an advantage other than in the time to construct fleets). They're also less able to use cavalry to alleviate this. They can use chariots, but it gets very expensive very quickly to be outfitting entire armies with chariots (even if you have ones that are closer to carts and can carry multiple merfolk). Historically, armies on foot have been able to travel about 15 miles per day. [Any army that has been able to significantly improve on that has met with considerable success](https://history.stackexchange.com/questions/8557/why-were-people-from-the-asian-steppes-able-to-militarily-dominate-europeans-on). This is one of the reasons that horse-borne steppe nomads found such significant success against a wide variety of foes. Given that it's physically much more energetic for merfolk to travel on land (human locomotion is very efficient, seals/snakes less so), I doubt that merfolk armies would be able to match the 15 miles-per-day that human armies can. It's reasonable to assume that a reduced ability to travel distance produces a roughly equivalent inverse effect as the increase in distance. Due to this, merfolk armies will be at a significant disadvantage in any arena where there is distance to be travelled over land. In conclusion/tl;dr On land, merfolk would likely fight in large phalanx/shieldwall blocks in order to negate their mobility disadvantage and maximise their stability advantage. They would have minimal ranged support, cavalry and skirmishing troops. This makes their formations very vulnerable, so they will likely hire mercenaries where possible. On campaign, they will have limited staying power away from shorelines and rivers and as such are tactically inflexible. A competent commander should be able to run rings around them in any reasonably matched land conflict. Rome meets post-Alexander successor states. ]
[Question] [ # Linked: [What would conditions on a methane world be like?](https://worldbuilding.stackexchange.com/questions/14312/what-would-the-conditions-on-a-methane-world-be-like?noredirect=1#comment34633_14312) # Question: As mentioned in the linked question, Titan is the second most likely world in the Solar System to harbor life. One of the answers also mentions that 'warm' days would cause the oceans to boil. Taking this into account, how would complex animal life evolve on a methane world and what common features would it evolve? Bonus to answer written using a single organism as an example and describing how it evolved its features and what they do to help it cope with its environment. [Answer] Alright, if we're assuming life formed in around the same timeline as on Earth, that means it would start with archaebacteria, or bacteria that don't have nuclei. Some of the bacteria that fall under this classification are INSANELY resistant to hardcore environments. From there evolution would take place. Let's assume some of these bacteria can absorb methane in a process similar to mitosis. Mitosis is the process of water going in and out of a cell to maintain cell structure and it helps in various other functions. So from here we're forced to look at the question of "How does it get energy?" A process similar to photosynthesis might work, using the intense sunlight as a source of raw energy and the extremely reactive chemicals and elements that would have to exist, especially methane, to produce a usable, working form like ADP and ATP. (Adenosine Diphosphate and Adenosine Triphosphate) It would most likely involve chlorine and fluorine. This is because chlorine and fluorine have pretty high energy outputs when mixed with Methane and react VIOLENTLY with light. So it would probably absorb the chemicals necessary and act as an autotrophe. (Produces energy on it's own) From there, basic evolution would occur. Eubacteria (Bacteria with nuclei) would form. Later, they would form multi-cellular organisms similar to fungi and plant life. Then once heterotrophes (Eats others for energy) started forming, they would probably absorb things lower than it in the food chain and use some kind of limiter to prevent too much energy from being expressed at once. Other elements would be used to form solid structures, such as shells or organ linings. Metals would be most likely bone structure, with lighter elements forming softer solids. It'd be the same as how calcium forms our bones. Genetics would probably occur using freons. Freons contain carbon and fluorine. Maybe methanol, formaldehyde, nitromethane, chloroform, or carbon tetrachloride would replace Adenine, Guanine, Cytosine, and Thymine. Transcription and translation (The process of writing RNA and the process of forming amino acids), occurring in similar way to ours. Mutations would occur in a similar fashion as well. Something interesting to note though, is that temperatures wouldn't matter to them, with all of the chemicals and elements found there having a high enough melting point where that is no longer a problem. If we approximate using the lifespan of life on Earth, it's now been about 3.8 billion years, with archaebacteria taking up about 1/3 of that time, eubacteria another 1/3, and plants about 1/6, with animals and heterotrophes taking up the rest. Hope you enjoyed this answer and found it interesting!! ^-^ All of the information involving methane can be found here in detail: <http://scifun.chem.wisc.edu/chemweek/methane/methane.html> ]
[Question] [ Closed. This question needs to be more [focused](/help/closed-questions). It is not currently accepting answers. --- Want to improve this question? Update the question so it focuses on one problem only by [editing this post](/posts/19/edit). Closed 9 years ago. [Improve this question](/posts/19/edit) In Worldbuilding, linguistica communication within and between cultures can greatly affect how the world is shaped. How does one make an invented language's aesthetic qualities sound authentic as regards the shapes of words, written patterns, and other phonemic relationships between dialects and related langauges? Relatedly, is there a some sort of boilerplate or template that beginners can use as a phonetic reference? [Answer] If you're just starting out, I would recommend selecting a number of phonemes (sounds) for each language to have, as well as rules for what sounds can be arranged in what ways (this video <https://www.youtube.com/watch?v=0h-gbeI0AFQ> can help with that). As far as making them sound authentic, one suggestion is: don't make all the languages have Indo-European syntax. The other videos on the channel I linked to talk about that some. For dialects, you could swap out one or two phonemes for similar ones, as well as having different words for a variety of things while keeping the syntax and grammar the same. The appendices of Lord of the Rings are always a great place to look for tips on constructing languages. ]
[Question] [ We occasionally get questions and answers that discuss how close to each other planets can be and still meet some criteria. For example, [this answer to the question ''Habitable'' planet close to a star](https://worldbuilding.stackexchange.com/a/151107/29). For the purposes of this question, I am not interested in answers discussing rogue planets which have been captured by the star. I am only interested in planets that form from a star's protoplanetary disk and remain gravitationally bound to that star. I am also not interested in co-orbiting planets, such as anything at another planet's [L4 or L5 point](https://solarsystem.nasa.gov/resources/754/what-is-a-lagrange-point/), or dual-planet pairs (not entirely unlike [our Pluto and Charon](https://en.wikipedia.org/wiki/Pluto#Satellites)). The planets I am talking about should each be in distinct orbits around the star, which differ in more than just phase. Quite simply, given what we know about planetary formation and material density in a star's protoplanetary disk, what is the smallest difference in orbital radius where distinct, rocky planets similar in size to Earth can plausibly form? I'm looking primarily for the formation of planets of similar total mass (let's say to within ±30% of Earth's mass), but bonus points if they can also plausibly have a similar composition (which, as also pointed out in a comment, I suspect is the easier part). I realize that the answer will to some extent depend on the orbital radius of the planet that is forming, since there's more distance to cover around a circle and thus at least the potential for more material to go around the farther from the focal point you are. Therefore, let's limit this to final planets' orbits with radii of 0.5 to 1.5 AU from the central star. For simplicity, it is acceptable to assume that all orbits in the resulting system are perfectly circular, though if you want to do proper elliptical orbits, then go ahead. The planets should ideally be able to hold together on their own over an astronomical timeframe. If you want to go down that rabbit hole, I suppose some such formed planets being ejected (or having their orbits changed to the point of, say, falling into the star) by perturbations from other planets could be acceptable, but it'd be a nice touch if the orbit is stable over the long term. [Answer] ### Planets will likely form in 2:1 resonances From [Zhu, et al., 2018](https://arxiv.org/pdf/1012.4395.pdf), simulations showed that multiple planet formation from a circumstellar dust cloud results very strongly in 2:1 planetary resonances, at least upon initial formations. > > In most cases, the planets are trapped into 2:1 resonances between > each pair of adjacent planets...Whenever the resonant angle librates > between the interval [-π,π] the planets are trapped in a 2:1 > resonance. The smaller the amplitude of libration, the deeper > resonance locking. > > > All exceptions to this resonance ended up causing one or the other proto-planet to be dispersed by gravitational interactions before it was fully formed. > > There are two cases, however, where planets experience a close > encounter and are gravitationally scattered. > > > Over their million years simulation, formations of three or more planets cause migration out of the original resonances, as we would expect. On the other hand, this model specifically deals with the formation of giant planets, so the possibility of smaller, more Earth-like planets exists. ### Notes I'll add more potential answers as (if) I find them. My review so far makes it seem unlikely that there is much settled science to be found in this area. [Answer] I am by no means an expert in planetary formation, but I actually think this boils down something called the Hill Sphere. For circular orbits, the radius of the Hill Sphere is given by $r\_H\approx a \sqrt[3]{\frac{m}{3M}}$. For Earth and the Sun, this equates to about 1.5 million km or around 0.01 AU. In developed systems the Hill Sphere is "the region in which an astronomical body dominates the attraction of sattelites." The upshot of this is that any body that forms within this radius would either become a satellite or be ejected. Whether it's reasonable that a second planet could form within this distance is determined by the properties of the protoplanetary disk, but if the conditions are right to form a pair of planets so close together, I'm fairly confident this is your absolute lower bound. [More information on the Hill Sphere from Wikipedia](https://en.wikipedia.org/wiki/Hill_sphere) [Answer] The planet Theia formed near or at the L4 or L5 Lagrange point of the Earth. I see that the OP rules out planets that are very close to each other. > > I am also not interested in co-orbiting planets, such as anything at > another planet's L4 or L5 point, or dual-planet pairs (not entirely > unlike our Pluto and Charon). > > > I am not sure why these are excluded. Planetary formation is planetary formation, so I am going to answer with the Theia example anyway. If two planets can form that close to each other it would seem to me to set the inner limit of how close to one another planets can possibly form. The linked wikipedia article states Charon is a big moon that was knocked off of Pluto by an ancient impact much as our own moon; not really relevant to the question of planet formation. Theia was an ancient planet the size of Mars which collided with and merged with Earth, in the process forming the moon. I here assert that Theia formed from the protoplanetary disk at the L4 or L5 point of the ancient Earth. Evidence. Prior to merging with the Earth, Theia is thought to have orbited at L4 or L5. <https://en.wikipedia.org/wiki/Theia_(planet)> > > Theia is thought to have orbited in the L4 or L5 configuration > presented by the Earth–Sun system, where it would tend to remain. In > that case, it would have grown, potentially to a size comparable to > Mars. Gravitational perturbations by Venus could have eventually put > it onto a collision course with the Earth.[7] > > > Theia hit Earth gently. It was not swooping in from distant reaches of the solar system. <https://en.wikipedia.org/wiki/Giant-impact_hypothesis> > > In astronomical terms, the impact would have been of moderate > velocity. Theia is thought to have struck the Earth at an oblique > angle when the Earth was nearly fully formed. Computer simulations of > this "late-impact" scenario suggest an impact angle of about 45° and > an initial impactor velocity below 4 km/s.[16] > > > That makes sense if it was only at L4 before impact and eventually had its orbit perturbed by Jupiter or Venus. [Earths Titanium Twin](https://www.nature.com/articles/ngeo1434) > > By contrast, Zhang et al.1 find that the Earth and the Moon are > identical in their titanium isotopic compositions within errors of > 0.0004% — almost the limit of detectability. This is not the first time the giant impact hypothesis has been challenged by isotopes. > During the past decade, similarities between lunar and terrestrial > rocks have been identified for oxygen6, silicon7, chromium8 and > tungsten9 isotopes. The latter three can be brought into accordance > with the latest giant impact simulations5, if one assumes that Theia > had a composition similar to Mars — possibly the only surviving > planetary embryo from which the larger terrestrial planets accreted10. > However, the oxygen isotopic compositions of terrestrial and lunar > rocks are so similar that, if Theia had a Mars-like composition, it > cannot have contributed more than a few per cent of material to the > Moon-forming disk6. Zhang et al. demonstrate that titanium isotopes > are similarly constraining. > > > The Earth and the Moon have the same isotopic composition. Where is the contribution from Theia? It is there. The Earth, the Moon and Theia all had the same composition. [On the origin and composition of Theia](https://www.sciencedirect.com/science/article/pii/S0019103514004175) > > If the FeO content of the Earth and the Moon is indeed inherited from > the proto-Earth and Theia, then by implication Theia must have had an > Earth-like isotopic composition (similar to enstatite chondrites, > aubrites or other Earth-like materials like NWA 5400). This is > possible if both the Earth and Theia, but not Mars, were part of an > early inner disk uniform reservoir (IDUR; Dauphas et al., 2014), or if > the inner disk region has been isotopically homogenized in the time > between the isolation of Mars from the disk and the Giant Impact that > formed the Moon. > > > From OP: > How close to each other can Earth-mass planets plausibly form from the > protoplanetary disk? > > > Theia formed right next to Earth from materials in the same region of the disk. The near-identical isotopic composition of the Earth and Moon precludes the possibility of Theia being some weird asteroid, or even Marslike in composition. Theia is formed of Earthlike materials. It formed closer to Earth than Mars is. I cannot see how two planets can form any closer than that. --- Nothing is going to form closer than the Lagrange points because it would fall into the planet. The example of Theia and Earth forming next to each other sets the minimum distance from one another that planets can form from the protoplanetary disk. ]
[Question] [ I'm envisioning a series of moons in orbit of a super-earth (ideal) or gas giant. If technically workable, the super-earth would have earthlike gravity, the mass and size aren't important. If it's too hard to make it terrestrial, I can use a gas giant. What is important are the moons: 7 earthlike. In addition, there are another 5, smaller, habitable moons/planetoids which themselves orbit the 7 primaries and have roughly earthlike levels of gravity, if not the same density and mass. Speaking of mass, I'd love to keep all of these moons as small as possible, while keeping earth gravity, but haven't worked out the math on that. I know that this could work in standard orbitals (though the number may be high), but I'd love to have the 7 operate in a horseshoe orbit, and I'm wondering how many objects can share an orbital by using horseshoe orbits. This is probably a bit complex, so just to recap: The Star: 'H' A central planet: 'N' 7 earthsized Primary moons & 5 orbiting Secondary moons: D&p V&r, W&i, E, A&z, L&s, F Can those moons, share a single, complex, horseshoe orbit? I'm thinking based on the sizes, that the primaries could simply be binary pairs with their secondaries. None of the primaries have more than one secondary, anyway, and it could help make the physics work. The original idea was simply to have them on different orbitals to the giant, or to have them in a stable ring, spaced out on the same orbital, alongside an asteroid belt, but the horseshoe concept may work better with other things that I won't get into here, and I'd love to know if that high a number is possible. There are 'magical' elements here, but I'd like to keep them out of the system structure as much as possible. Part of this concept is one original super-earth, which was fragmented into the moon system. I'm thinking maybe a civilization dragged a gas giant inner-system to create a brown dwarf, for a dyson sphere or something, and ended up failing spectacularly, and breaking a large terrestrial planet into fragments later captured by 'N'. I simply can't find any solar system modelling tools that are complex enough to handle this or tell me if there are stable solutions given the constraints. (P.S. if you know of a tool that can do that, I'd love to know). [Answer] Can those moons, share a single, complex, horseshoe orbit? Perhaps not as many as you describe, but the situation is plausible. Saturn's moons Janus and Epimetheus [share a horseshoe orbit](http://curious.astro.cornell.edu/about-us/59-our-solar-system/planets-and-dwarf-planets/moon/241-how-can-two-moons-of-saturn-share-the-same-orbit-intermediate). However, you will need to invoke some of the magic you describe. Earthlike moons means a massive planet, one that cannot be Earthlike because you require the high gravity to keep Earthlike moons in orbit. So, without the magic, you would be forced to give up the habitability of the planet. [Answer] Short answer: the gravitational relationships between this planet and moons will not be realistic. You'll have to make it work with either technology or magic. You might want to check out Pierson's Puppeteers from Laryy Niven's Known Space series. They've mechanically arranged five planets around a star; it's not quite the same as what you're describing, but you'll run into similar problems. <https://en.wikipedia.org/wiki/Pierson%27s_Puppeteers> <https://en.wikipedia.org/wiki/Klemperer_rosette> As the second link points out, these configurations are inherently unstable: > > ...any motion away from the perfect geometric configuration causes an oscillation, eventually leading to the disruption of the system (Klemperer's original article also states this fact). This is the case whether the center of the Rosette is in free space, or itself in orbit around a star. The short-form reason is that any perturbation destroys the symmetry, which increases the perturbation, which further damages the symmetry, and so on. > The longer explanation is that any tangential perturbation brings a body closer to one neighbor and further from another; the gravitational imbalance becomes greater towards the closer neighbor and less for the farther neighbor, pulling the perturbed object further towards its closer neighbor, amplifying the perturbation rather than damping it. An inward radial perturbation causes the perturbed body to get closer to all other objects, increasing the force on the object and increasing its orbital velocity—which leads indirectly to a tangential perturbation and the argument above. [Emphasis mine.] > > > And that points in the direction of why your proposed system will also be unstable. The fact that they are sharing a horseshoe orbit actually makes the configuration you want less likely. You basically have seven planets with similar densities in a Klemperer rosette, and an eighth planet providing the tangential perturbation to their orbits. [Answer] Short version Magic can do anything but this whole thing will purely scream "a Wizard did it!" You can't keep this from obviously flouting the laws of physics. Without intervention "basic" three-body horseshoe orbits are not stable over geological time as it is and what you are describing, if I read this right, is in fact a system with at least 14 celestial bodies; a stellar primary orbited by a Gas Giant (a super earth would not, I believe, provide sufficient [Barycentral](https://en.wikipedia.org/wiki/Barycenter) mass to stabilise such a complex system) which is in turn orbited by 7 earthlike worlds that in turn have 5 sub-satellites on the same order of size as the earthlike satellites of the Gas Giant, this system is inherently unstable and, without intervention, would shed satellites or sub-satellites into stellar orbit, or maybe into the deep void depending on the exact energies involved, ever time there's a [resonance](https://en.wikipedia.org/wiki/Orbital_resonance) event. Without obvious and massive magical intervention you can forget about horseshoe orbits, most of the proposed orbital system will fly apart in a matter of years. Most of the magic is not where you might think it is either, you'll need magic to keep the worlds in this strange artificial system in their orbits but you'll need a an awful lot more magic to keep the worlds themselves intact. Every resonance event that is magically prevented from moving the involved bodies out of orbit is going to instead transfer massive amounts of energy into those bodies. In the natural course of things this would end up being expressed as heat, one way and another, a lot of heat, (estimates for previously discussed artificial orbital structures suggest per orbit energy inputs on the order of the full mass conversion of small stars are needed to manipulate earth-mass bodies) if that's not magicked away in turn then every ball of rock in the system will be molten in a couple of days and vaporised shortly thereafter. ]
[Question] [ I am searching for a software capable of creating any planet ( like universe sandbox) with the ability of shaping the landscape and adding tags to any coordinates I wish to in order to represent cities, important places, etc. It would be even better if I could assign pre-designed icons to them. I've searched the entire internet but found nothing satisfying. I want a software that is simple and easy to use. I am not searching a mere map design software in 2D , but a globe creator (or something like that). If anybody can find something like that, I would be very grateful for the rest of my life :) edit: Sorry for not responding for quite a month. I've been busy with my studies. user23614 thanks for campaign cartographer seems perfectly fit to me. Fractal Terrain add-on seems what I've looked for. Thank you alot :) The only bemol is that I can't put symbols (of cities, military facilities, ICBM bases etc.) on a global scale. But I can export maps from the planet I create. That's a thing! edit 2: I figured out how to add tags after exporting my globe to google earth. But It only works on google maps site. Any idea how I can change things (add borders, tags etc) in actual google earth software? [Answer] If you need to create a 3D landscape, for any random use, I have something that might work. It's more of a graphic-oriented tool but it may be useful to you. It was useful to me on the past, at least! It's called Bryce 3D. It's currently on its 7th iteration, and it is a pretty powerful tool for shaping landscapes. Now, I used it way back then (in the times of Bryce 3D 4), but it was a really majestic tool! It can shape any landscape you want with a ton of terraforming tools. It can add individual trees, raise mountains, add lakes and much, much more! [You can check it out here.](http://www.daz3d.com/bryce-7-pro) If you need something more... flatty, like, say, an Atlas, them you have plenty of options. My favorite tool is [RPGMaker](http://www.rpgmakerweb.com/). While it was devised as a game-making tool, its map designer is simply uber-easy to use and really powerful. You only will be able to create some retro-style maps, sure, but hey, they are pretty awesome anyway! Now, if you really need to create globes, that's something different. I'm not sure how you want to use them (if you tell us more I may be able to pinpoint a better tool), but if your idea is to create a 3D Galaxy, them check out Bryce 3D and its Deep Space Add-On pack. You can remove the default land and create a void, and them put the globes on the sky and shape them at will. If you need something simpler than that... well, we need more details to help you! If you say how you intend to use your globes, I may be able to pinpoint just the tool you need! [Oh, and there is Terragen, too.](http://planetside.co.uk/products/terragen3) ]
[Question] [ I could have sworn that there was a question that covered this, but I suppose I'm misremembering. If anyone finds one, let me know. Back in the early days of the Solar System, things were pretty bad. There were many collisions, which made it hard for any particular object to stay the way it was for extended periods of time. In this circumstellar disk, conditions were not good for life. Perhaps I shouldn't judge, though. Life is pretty tenacious, and it can survive in some of the harshest of places. So, could life form and survive for an extended period of time (on the order of at least several million years) in a circumstellar disk? See also, by the way, [Could life form in outer space?](https://worldbuilding.stackexchange.com/questions/1401/could-life-form-in-outer-space?rq=1). [Answer] Maybe I note that the OP asks for "exist" and "survive", not "form" and "develop". This lowers the barrier of entry to the question considerably. The brief answer for life as we know it is, "No, there's too many essential conditions missing to support life". However, as the universe is a big place and lots of weird things happen, let's see what there is to see when we seed an early star system. Temperatures According to [this paper](http://www.annualreviews.org/doi/abs/10.1146/annurev.earth.26.1.53) in 1998, the temperature of a protoplanetary disk is: > > a moderately warm (500–1500 K) inner disk, surrounded by a cool (50–150 K) outer disk. > > > Assuming a continuous gradient between the two temperature extremes, there is a zone where liquid water can form and organic molecules don't automatically denature. (I'm probably using the wrong words here but chemistry isn't my strong suit.) Available Fuel/Food Recent studies have indicated that [organic molecules can form](http://www.space.com/15089-life-building-blocks-young-sun-dust.html) in the protoplanetary disk so there's a decent chance for food and building materials to be nearby. "Living" Strategies Dormant Survive - If life is dormant and survives for a few million years then it just got lucky that it didn't fall onto a planet or the sun or get cooked by the protoplanetary disk's heat. Impressive survivability by Earth's standards but not amazing. Active Survive - If this Life is alive and not in a dormant state then it has solved a number of significant challenges that preclude typical terrestrial life from forming. A long list of these challenges can be found in this [answer](https://worldbuilding.stackexchange.com/a/1405/10364). ]
[Question] [ [![see the schematics here](https://i.stack.imgur.com/h6GWO.jpg)](https://i.stack.imgur.com/h6GWO.jpg) Ok, assuming a planet that's tidally locked to its sun, but is otherwise roughly similar to earth in gravity and atmosphere. Classic tidally locked planet: one side is covered in ice, the other is a scorched desert. And there's water flowing from the glaciers of the dark hemisphere, towards the zenith pole. I assume that, because of the intensity of evaporation, on the light hemisphere the "sea" level is much lower than on earth, and *there exists very deep sky abysses* that are the equivalent of our earth's oceans or even deep sea trenches in depth, but mostly filled with air (as opposed to water on our Earth). (see 1, in the drawing) I guess that at the bottom of these abysses we will find the glacier water flow previously mentioned. My question is: How might the conditions down these abysses be? Assuming an abyss that's comparable in size to one of Earth's deep sea trench (between five to nine kilometers deep and a few kilometers wide) More specifically: 1. What might be the atmospheric pressure at these depth? Assuming the pressure at the top of the trench (A) is 1 bar. Water pressure is easy enough to calculate: 10 meters of water amount to 1 bar. But how about air? How many bars of pressure 5000 meters deep? How about 9000 meters deep? 2. At which point in the trench does it starts to be less like the scorched desert of the surface or the frozen glaciers of the dark hemisphere and more pleasant for life as we know it, to the point where it might even flourish? It it only right around where the light and the shadow meets, or could the convection be powerful enough to allow jungles to grow on the light side (D) nearly all the way up? How about the shadow side (C)? What might live there? 3. How about the bottom (B)? How might it be? Cool because of the water? Unbearably cold because of the shadow? How about the winds? Should it be subjected to permanent super powerful winds, because of the planetary convection and the increased air density? [Answer] Slot canyon refuge**. [![slot canyon Wollemi Pine](https://i.stack.imgur.com/n2iEk.jpg)](https://i.stack.imgur.com/n2iEk.jpg) I envision your sky abysses to be like the canyon where the Wollemi Pines were discovered - a wet dark refuge in a hot, dry landscape. Do read the whole article if you are into this! <http://www.wollemipine.com/news/The_Jurassic_Tree_And_The_Lost_Valley.php> > > The helicopter was now a tiny speck between the 400metre-high walls of > a gorge filled, right to the base of both walls and off in a ribbon > towards the horizon, with an almost unbroken carpet of rainforest > canopy. David Crust, a senior NPWS ranger, pointed to the spear-like > crown of the biggest Wollemi pine on earth, nicknamed "King Billy" and > known to science as "tree one". Scientists estimate that King Billy > first began poking its head above the canopy about the time of the > Norman conquest in 1066. Images of King Billy travelled around the > world when the discovery of the Wollemi pines was announced in the > Herald in December, 1994… > > > Crust and a Royal Botanic Gardens > horticulturalist, Graeme Errington, immediately began draping ropes > into the canyon for two abseils that would take us through the > rainforest's canopy and into a fairyland of ferns, fungi and a gloomy > impenetrable darkness. The scientists who prepared the draft Wollemi > Pine Species Recovery Plan estimate that the amount of light reaching > the base of the cliffs where the Wollemi pines live is less than 10 > per cent of that above the canopy levels. Some areas receive less than > one hour of direct light per day. > > > As regards weather, I was thinking about air movements on a tidally locked world. Air from the hot side would rise and expand, including expanding over to the cold side. Air from the cold side would be smashed underneath that hot air and roll out, hugging the ground. There would be a strip between the two sides where it was bright but wet and that strip would be loaded with life. The cold air entering the bright side would hug the ground and so track along the clefts in the earth that your world has. It would be dark down there but a gradated darkness. At the very bottom would be only the most dark tolerant plants - ferns, algae but also loads of decomposers feeding on materials from above - mushroom forests. Plants needing more light might send long roots down into the dark to get the water there. Cracks in the earth can open because of gradual desiccation of the land below. This is an earth fissure in Arizona. [![earth fissure](https://i.stack.imgur.com/xLYUG.jpg)](https://i.stack.imgur.com/xLYUG.jpg) <https://www.livescience.com/57663-giant-crack-opens-in-arizona-desert.html> Once something like that opened, cold moisture laden air would enter it and the moisture would keep it open and gradually widen it, carrying away debris that falls to the bottom. A problem is that the narrowest steepest canyons also have hard substrates resisting mass action and crumbling, and those substrates are harder for plants. But a canyon like the Wollemi one is steep enough and clearly it is fine for life in the shady bottom. --- On thinking about your world I was wondering about a world which was not quite tidally locked. Rotation is very slow - a day lasts an Earth year but it is still slowly turning. The day side gradually encroaches on the glaciers, turning the green strip into savannah and then desert. The night side and its glaciers gradually darken their side, claiming the life under the wall of ice. ]
[Question] [ Mars has an inactive mantle and core and thus little magnetosphere to speak of. Assume that a lunar mass object is placed in Mars orbit at 300,000 kilometers out (one light-second). Given the tidal forces at play, how long would it take to bring the magnetosphere up to a strength where it could divert solar wind and radiation to a degree seen here on Earth? Bonus points if someone can manipulate some of these hypothetical parameters to make the effect presentable in around one thousand years (orbital distance, orbital shape, lunar mass, ???). [Answer] # Calculation by comparison I have not been able to find resources for calculating the tidal heating of a primary planet from the effects of a moon. However, there is available literature for calculating the [tidal heating](https://en.wikipedia.org/wiki/Tidal_heating) of the moon itself in its orbit around Earth. The equation for heating in a tidally locked moon with an eccentric orbit is $$\dot{E}\_{tidal} = k\_2\frac{21}{2}\frac{R^5n^5e^2}{G}$$ where $k\_2$ is the [Love number](https://en.wikipedia.org/wiki/Love_number) of the [moon](https://link.springer.com/article/10.1007/BF00116287) (0.0222), $R$ is the moon's mean radius (1738100 meters), $n$ is the mean orbital motion in radians per second ($2.662\times10^{-6}$), $e$ is the eccentricity of the moon's orbit (0.0549), and $G$ is the universal gravitational constant ($6.67\times10^{-11}$ m$^3$kg$^{-1}$s$^{-2}$). Plug all those numbers in and we get $2.2\times10^{W}$, or 22 GW. That is about the electrical power output of the Three Gorges Dam or the Saturn V rocket at launch. So what can we conclude from that? First off, the tidal heating is strongly controlled by having a fast eccentric orbit. This is why [Io](https://en.wikipedia.org/wiki/Io_(moon)) has such strong tidal heating; its orbit is days, with moderate eccentricity. Re-running the numbers for Io, I get 138 TW; more than 500 time what the moon is getting! For a planet, there is nothing to orbit. You need something massive like Jupiter pulling you around. Earth is barely big enough to cause any heat to the moon, so a moon sized object isn't going to do much to Mars. So if we don't have any means to increase the heating, that level of heat generation is far, far to low to ever heat up the core of Mars. The Earth, for example, loses 44 TW from its interior, so tidal heating is orders of magnitude too low to even balance outflow from a hot core. Lastly, lets say Mars was orbiting Jupiter, in the same orbit as Io. Due to its bigger size, its heating would be 3 PW. Now we're getting somewhere! Lets use the same assumptions about Mars' core as I used in [this question.](https://worldbuilding.stackexchange.com/a/100403/23519) That means the heat capacity of Mars' core will be about $1.9\times10^{26}$ J/K. Given our input of $3\times10^15$ J/s; it will take us $6.3\times10^{10}$ seconds, or 2000 years to increase core temperature by 1 Kelvin, not even counting heat losses through transfer to the core. # Conclusion The tidal heating on the moon from Earth is trivial compared to the losses from a hot core. Therefore if an Earth sized object cannot appreciably heat the moon, it is unlikely that a moon sized object will appreciably heat Mars. Even if you put Mars in a perilously close orbit of Jupiter, it would still take thousands of years to heat up the core appreciably. ]
[Question] [ I have planet with twice the radius of Earth, with its core being the same absolute size as Earth's in order to provide magnetosphere, and the rest of the planet made of silicates like Earth's mantle. There are oceans on the surface with similar depths to Earth's, covering 2/3 of the surface. I chose those numbers in order to have the largest terrestrial planet, while keeping the mass below 10 Earth masses in order to not keep the hydrogen. With twice the radius and planet mostly made of silicates, I expect the density to be about 4.4g/cm$^3$ which would give me around 1.6g surface gravity. I don't know how to calculate the compression effect on the silicates. The planet has a satellite similar in size to Mars, and it's placed in the middle of the habitable zone of an Orange dwarf in near circular orbit. I want the planet to have the largest temperature variations (very hot summers, very cold winters) throughout most of the planet, not just in poles or just in the equator thus axial tilt of 90% doesn't work for me. I don't want people to live just near the poles, or just near the equator. I want to achieve large seasonal variations on as large area of the planet as possible. What kind of axial tilt would you recommend choose, 45°, 60°? [Answer] Okay so you should check out [Artifexian's Video](https://youtu.be/J4K3H9aNLpE) on axial tilt. But to sum it up, the higher the tilt the warmer your planet will be and have more extreme seasons. It will also result in less snow, permanent ice, lower humidity and cloud cover. Life like humans won't be able to survive on a tilt greater than 80 degrees. So to answer your question as close to 80 as your comfortable and it will still be plausible. Final thing to note is that if you go above 53 degrees your temperature zones reverse, so your polar regions will be at the equator and your tropics will be be at the poles. The video also has a link to interactive software where you can change the tilt of earth to see temperature differences and the like. (I can't copy the link as I am on my phone) ]
[Question] [ In Chinese folklore the dead live in a society much like our own while waiting for reincarnation. One notable exception is that that the government is that of the Yama Kings. The living can send their ancestors all kind of things (food, clothes, house, money) by burning the paper model of those things. However, the living burn a lot of fake money - more so than food, clothes or houses - and according to folk belief the dead can get hungry if none of their descendant burn any food. So anyone who died without descendants, or who becomes forgotten will most likely go hungry. Assume - There is trade in the after-world - The goods from descendant go directly to the receiver - The after world is like a mirror to the real world: all type of building, machine, factory, land, farm... exist, but all of them belong to Yama king, who lend them to the population like a feudal lord. - All material in after world is one time use like real world material, except land do not get poorer. - A real world tree is correspondent to a after world tree: if the real tree is cut down and turn into a plank, the tree in after world is also turn into a plank and can be use by a mirror machine by a ghost, but if a ghost cut the mirror tree before the real tree is cut, the mirror tree and real tree no longer have any link. - No animal ghost. - The dead might provide services such as protecting the living, working for the Yama Kings, etc. Edit: - Let 's say that the dead wait for about a quarter of their life span for reincarnation or ascend to higher plane (or lower plane). So a child only stay there for some year, while the old wait for decades. - Their spirit body is like a healthy human for their age. No wound or bad body part, only old body part. No sickness, too. - The dead can learn, and they have feeling, too. So they fell tired after work for a while. Although they can work more, the feeling accumulate further until it became unbearable and they stop the work. Please answer: - If they continue to use the money sent by descendant, will there be great inflation? - Are they going to use that as money, or use other things as money? [Answer] Your question made me curious about chinese religions and the afterlife in chinese folklore. I've read a lot about it, and what I can say without any doubt is that there is a lot of different interpretations. I was asking myself, why exactly would the living offer money to their ancestors? I've came across two different reasons (I bet there exist more) : * Going through hell I found [this](http://http-server.carleton.ca/~asumegi/2308_disabled/reviewnotes/ChineseReligions.html) website the following information : > > Other ideas of afterlife were influenced by the Buddhist cosmology of > Heaven and hell – the Chinese version of heaven and hell mirrored the > bureaucracy of the worldly ruling power with heaven being represented > as the wonderful court of the Jade Emperor and hell being represented > as the horrible prisons where one was punished by cruel jailers and > could possibly get out sooner than one’s sentence required by bribing > the guards – hence the practice of sending “spirit money” with the > deceased to help with one’s life in the next world. Of course, > Buddhist influence also meant that heaven and hell were not permanent > places. > > > The spirit money is used to bribe the guards of hell and suffer less torments. Who would want their family to suffer? In this case the living could burn just enough money to bride the guards. There should be no inflation unless there is a sort of competition between the dead. (The next point may be the following events after going through hell.) * Persuading the gods I found on [this](http://www.ancientchina.co.uk/tombs/home_set.html) website that after death, your dead ancestors could live in the spirit world with the gods. In this world, the gods have the ability to influence the world of the living. Sending money to your ancestors would ease their task of influencing the gods to bring good luck on your family. Assuming this is true and the gods powers are real, every family would burn all the fake money they could. Now, depending on how the gods are, the price of "good luck" could rise. More people with more money means more demands. If the gods can supply enough good luck to everyone (and have enough time to do so), the price won't rise. Else, if the gods are not everywhere at anytime, they would only accept the biggest offerings and thus, increase their prices. (There exist a slight variant where ancestors become gods of the Underworld and bring good or bad luck in exchange of offerings. In this case, more money could also mean less need to word and more "free time" for good luck wishes.) Conclusion : Creating money make it lost its value. Will there be great inflation? Yes! And no... It depends on which version of the chinese folklore you are willing to trust. To answer your second question, there also could be bartering with the different objects offered by the living. Even though there tend to be less bartering in a society with money. EDIT : How could the gods spend their money? I didn't find anything about the gods shopping habit. Sorry, the next part will only be speculations. First, we must know what gods really want. Gods being gods, I don't think they will care about "material goods" that you and me buy at the grocery store. What do gods want? Power! And by power I mean spiritual energy. In several religions, the power of a god depend on how many people worship him. Prayers, sacrifice and offering giving empowering the gods. In the links that I used for this answer, they do not talk about "money", but "spiritual money". This spiritual money could simply be a materialization of power in the Underworld. It could actually means that the gods don't spend their money! They keep it, after all it's the amount of spiritual money they have that increase their powers. Now with the notion of "amount of power", this could explain the increase in the gods prices for granting wishes and benedictions. The most powerful god with the biggest amount of power (and though the best "good luck" you could get as a living) could sell his services for more than another god less powerful. The economy would stay the same as earlier for the ancerstors of the living. Moreover, the living wanting to get the best benediction, they would burn even more spiritual money. (Keep in mind that this Edit is only my speculations. I hope it will help) [Answer] ## It's a mess First problem is that there are [15 dead people for every living person](http://www.bbc.co.uk/news/magazine-16870579). That's a lot of ancestors for each person to feed, but most of them aren't ancestors, they're children who never made it out of childhood. Reducing the amount of time people stay in the afterworld to 1/4 of their lifespan takes the population there down to 1/4 of the living population. If everything "given" by their descendants remains after they depart (perhaps there's a family house there as well as here), there's a limit to how much further raw material is needed. It could well be that there are acres of empty houses and all the children are at least able to find somewhere to live. However this situation still leads to massive cash inflation as there's no government steadily removing currency from circulation as new currency is "printed". If everything given to a specific person fades away as they move on then at least the cash flow problems are solved. However the stray child problem returns, their time in the afterworld is really going to suck until they get reincarnated. Everything else seems to be a relatively "normal" feudal economy, i.e. not somewhere you want to be as a modern western person. Life is short and nasty with lots of hunger. ]
[Question] [ People wonder how Santa can deliver all his presents in one night. It's, simple: he's a master time traveller. (This post will form the base of a long series of questions). Here's how Santa's usual Christmas goes: 1. Santa spends Christmas with his family 2. After Christmas, all the presents are in all the homes 3. Santa begins travelling backwards in time * According to Norad, Santa's sleighs max speed is "faster than starlight". According to special relativity, this is equivalent to travelling backwards in time. 4. Santa breaks into and steals the presents from a bunch of houses (this is logically necessary, since by the time he reaches the beginning of Christmas, there should be no presents in their homes). * Since Santa is doing this in reverse, it's equivalent to him giving them presents. 5. Once it hits the beginning of Christmas, he starts going forward in time again, and gives the presents he stole to different homes then he stole them from. 6. Once he reaches the end of Christmas (having delivered all the presents he stole), he goes back to step 3. 7. He is careful to never visit the same home twice. At the beginning of Christmas, no homes have presents. At the end, all homes have presents. This is logically consistent because if * If Santa visited your house going forward, you started with no presents at the beginning of Christmas, and Santa gave you presents, and then you had presents by the end. * If Santa visited your house in reverse, you have presents during the end of Christmas, Santa in reverse stole them, and you have no presents at the beginning of Christmas. Therefore, we do not have a paradox, yet. To an outside observer, it appears that there are millions of santas and reverse santas (see [One-electron universe](https://en.wikipedia.org/wiki/One-electron_universe)). * At the beginning of Christmas, millions of santas and reverse santas [pair produce](https://en.wikipedia.org/wiki/Pair_production). Every santa and reverse santa is fully stocked with presents. * The santas deliver presents to the children like normal. * Reverse santas also deliver presents, although it appears that they are stealing presents, but in reverse. * After Christmas, every santa [annihilates](https://en.wikipedia.org/wiki/Annihilation) with a reverse santa. They will do so with a different reverse santa then they were produced with. + Actually, one of the reverse santas annihilates with the santa from last year, leaving one santa to become the santa for the year to come. This new santa will have the combined experiences of all the santas and reverse santas. If it seems confusing, it's because it is. My question is, how does Santa avoid running into himself or otherwise causing temporal paradoxes. Given how many times he has to go forward and back, it seems likely that he could cause a temporal paradox if he is not careful. [Answer] He uses his magical invisibility/phasing abilities. Lets face it: both normal Santa and reverse Santa need to be able to break into people's houses, deliver presents, and get back out without being seen. This means he must be invisible (or have some way of making himself invisible) and the easiest way of getting in/out is to have some form of phasing / teleportation in order to get to the christmas tree without having to damage anyone's property. Therefore the natural way for Santa to avoid running into himself is for him to turn on his phasing and invisibility whenever he isn't inside someone's house. Then he literally can't run into himself, or accidentally see himself! Novikov consistency maintained, paradoxes avoided, presents delivered, and no accidental Santa Sightings! [Answer] I know that the quantum physicists are going to crucify me for this one, but it is still worth a try... It is an as-of-yet undiscovered physical law of the universe that identical entities, co-existing in any given moment of time, cannot interact with each other in any way, including paradoxically. That's just the way the universe works. Two Santas can face each other from an inch apart, screaming at the top of their lungs and swinging their arms violently through the space that the other is occupying, and neither will ever know that the other is present. They are both completely real and interactive with the rest of the universe, but they are completely intangible and unperceivable to each other. I have no proof that this unusual law actually exists, because I have never been in two places at the same time. But you can't prove that my law doesn't exist, because neither have you. [Answer] First point: Christmas is not celebrated in all places (only about half to three quarters the world's population actually celebrate it) second point: Christmas is not celebrated at the same time all over... The first point is easy, Santa will only have to deliver gifts to half the children in the world. The second point hinges on differing traditions; yes, if all the world woke up to gifts on the 25th of December, he'd have a hard time... However, where I come from (Denmark), the gifts are traditinally given on the evening of the 24th. Some eastern countries wait until January 6th At least this gives Santa a bit more time to distrbute his gifts > > Santa breaks into and steals the presents from a bunch of houses (this is logically necessary, since by the time he reaches the beginning of Christmas, there should be no presents in their homes). > > > Is a present, once opened, still a present? Logically, Santa would be unable to give your kid that brand-new 3DS he wished for, as he re-uses gifts. Then you come with this: > > Once it hits the beginning of Christmas, he starts going forward in time again, and gives the presents he stole to different homes then he stole them from. > > > How does that explain how I got my Gameboy Color when it was just released? (it came out late november 1998) > > If Santa visited your house going forward, you started with no presents at the beginning of Christmas, and Santa gave you presents, and then you had presents by the end. > If Santa visited your house in reverse, you have presents during the end of Christmas, Santa in reverse stole them, and you have no presents at the beginning of Christmas. > Therefore, we do not have a paradox, yet. > > > YES WE DO... forwards or backwards, in order to cover up his thievery, he has to be in the same place twice (or hire his brother, Jeff). Also this presents either a paradox of changed history OR item duplication. Lastly, Santa WOULD need to go to the same house at least twice (forwards and backwards) Actually, if you count in different traditions across the world, Christmas is comparatively like a busy work day for Santa [Answer] That doesn't make sense. What is the point of stealing-in-reverse, since the house only has a present because Santa delivered it? You're re-arranging them, but not providing a way for presents to come into existence. Or, stealing in reverse is the same as delivering except for the conscious activity of Santa himself, so from our pov he's just making 2 delivery runs. ]
[Question] [ So, many predators, but especially felines, have more "strength" per kilogram than humans. Why? Well, it's in the type of muscle fiber they use. These types are: 1. Slow-oxidative: Small force production, very high endurance, found in skeletal muscles responsible for posture. 2. Fast-oxidative: Medium force production, medium endurance. Found everywhere in skeletal muscles 3. Fast-glycolytic: Very-high force production, low endurance. Now, these are somewhat loose categories, as they're the result of tweaking the ratio of onboard oxygen reserves (myoglobin) and actual myosin chains. More reserves decrease the density of myosin, but lets muscles use aerobic respiration, which is efficient. Without reserves, you can put in more "engines", but they will have to rely on inefficient anaerobic respiration, making them tire quicker. So, what is my context? Well, there is a handful of genetically-engineered creatures in my setting that were designed with modern combat in mind, but in a way that doesn't violate the Geneva Convention. So, they aren't as extreme as mobile balls of slime that turn into airborne [Yersinia](https://en.wikipedia.org/wiki/Yersinia_pestis) when pulverized by gunfire. On paper they have differences, but all of them are agile and flexible quadrupeds that have human intelligence and are capable of communicating with humans. Their primary purpose is to help SEALs (well, this setting's equivalent of them) move through rough terrain such as mountains and dense forests. They have a limited carrying capacity, due to their [floating shoulders](https://en.wikipedia.org/wiki/Cat_anatomy#Skeleton), but can be equipped with lighter grenade launchers that go right on their backs. Their limbs are supposed to have a muscle fiber composition of 90-95% fast-glycolytic and 10-5% slow oxidative fibers. The reason is to give them sprint bursts to help with darting from cover to cover, along with melee strikes that could kill fully armored people through sheer force (shake up their brains a bit). However, I'm not sure if this is the best idea. Would such high fractions of fast-glycolytic muscle fibers inevitably reduce the creatures' stamina and/or structural integrity (remember, floating shoulders) to the point where they can't be used as intended? [Answer] The main purpose of your creature is to act as a pack animal across difficult terrain. More or less, all currently popular pack animals lean towards strength and endurance rather than bursts of speed. Humans are endurance walkers and runners, so the animals we use for packing have to keep up. A feline bone and muscle structure, as compared to horses, mules, etc, is not well suited for carrying loads on its back at all, and the proportions of muscle fibers you are talking about are not really suited for carrying loads for extended periods. Felines are great stealthy and fast predators though. But there is a caveat: If the pack animal has human intelligence and is faster by a large margin than the humans on foot, it can move supplies on its own in advance of the unit, and not alongside a squad of humans which would just slow it down. This type of operation might suit such a burst-running creature better, moving at their own pace. If you want your creature to be a pack carrier that sticks with the squad, I would actually suggest that you make two specialized creatures, one based on any number of hooved animals like mules and goats, for carrying supplies in difficult terrain, and another as stealthy and fast attack animal. The two purposes are almost contradictory. Horses and dogs probably have the highest endurance of any "fast" animals. Most others are short range sprinters. Now that's just building off of existing animals. (Floating shoulders are not good for load bearing, as you seem to know). As for muscle composition, we can do something interesting. Humans have mostly endurance "slow-twitch" fibers, but the release of adrenaline and epinephrine changes the function of those slow-twitch fibers to increase their contraction speed and be able to temporarily use anerobic glycotic energy from what I understand. This allows humans to increase their power output roughly 50-100%. Whereas many animals have this strength to call upon all the time, humans have endurance muscles most of the time, and "pseudo fast-twitch" muscles in times of great stress, which let's us "cheat the system" so to speak, to be able to get power when needed and endurance as the norm. (This does correspond to a slight loss of fine motor functions though.) [Side tangent: For energy storage, you might be able to engineer a more efficient tissue than fat for something that could act as a reservoir for energy. Something that can disperse compounds into the blood more quickly, which is where the glucose the muscles use is usually stored, as I understand.] Finally, it's worth pointing out that glycotic/anerobic muscle use comes with a heavy cost of inefficient use of energy and byproducts building up in the tissue. This seems to be a problem that can be solved with genetic engineering. Take the case of marathon runner Dean Karazes. So the main chemical build up from glycotic muscle use is lactate and lactic acid, which causes problems in high concentrations. It can cause muscle cramping and pain if it builds up too much and is a factor in endurance. Certain mitochondrial processes can reconvert this lactate back into glucose. But this man seems to have un-ordinarily high tolerances for the chemical, essentially having muscles that just don't tire out. There is also possibly a nervous system adaptation to ignore pain as well, which would be a good thing to give to your creature. I wish I had a proper source for the adrenaline changing the way the muscles function, but I'm out of time and I'll have to wrap this up here. I hope this information is of some use to you. Anybody who is an expert in the field, feel free to add clarifications or corrections in the comments. [https://www.theguardian.com/lifeandstyle/the-running-blog/2013/aug/30/dean-karnazes-man-run-forever#:~:text=Most%20runners%20have%20to%20stop,days%20and%20nights%20without%20stopping](https://www.theguardian.com/lifeandstyle/the-running-blog/2013/aug/30/dean-karnazes-man-run-forever#:%7E:text=Most%20runners%20have%20to%20stop,days%20and%20nights%20without%20stopping). ]
[Question] [ I am creating a map for a story set in a pre-industrial world, and have made the basic physical geography. My main concern now is the development of culture, centred around urbanisation. There are some obvious commonalities between major cities historically; mostly that they are along a river or beside the coast, and are otherwise accessible to surrounding regions in order to become trade hubs. I'm going to assume that cities develop like rivers; and the largest ones are fed by tributaries. People and water flow along the path of least resistance between physical boundaries, and so the size and influence of a city is dependent on its catchment area. I'm also going to assume that cities first developed and then spread from continental cradles of civilisation (like the fertile crescent), and that these cradles had specific qualities. I'd like some geography and science to support (or refute) these notions. Is there any analysis (the more sources the better) which can be summarised/cited to explain where and why ancient cities first developed and spread, also how this development is relational? [Answer] Basic survival knowledge is that when lost, follow streams or rivers downstream, or try to find a coast. Settlements/civilization are/is historically and still typically near water sources, and in low lying areas. Going up hill is not recommended in survival situations as it tends to bring one away from civilization. Just google what to do when lost. [edit for additional clarity] The rules that guided settlements historically hold true in more modern eras. Proximity to travel and trade, food and resources (in the past, water provided all of these). In the pre industrial world, as you said your story was set, travel (and especially trade )was easiest via water so I would expect that large successful urban centers will still be on water, with likely sprawl occurring along the coasts or river fronts. Especially filling in upstream at minor tributaries, and along the coast at any delta. Sometimes settlements occur in more remote areas around military forts or outposts as well, in areas chosen for their defensibility. [Answer] I have tried to research this myself, and found some information which is relevant, but by no means comprehensive enough. The most obvious point is that, when speaking of the cultures which emerged around the Mediterranean, [urbanisation first occurred in the fertile crescent](http://www.ancient.eu/urbanization/), then spread to Egypt, and then to Greece. The exact reasons for this are not clear; whether due to overpopulation or resource depletion. Urbanisation took different forms across the ancient world, with the highest density in Mesopotamia. Egyptian cities were different, spread more thinly and more specialised in function (temple or palace cities). Cities were first created within warm climates and the places with the largest and most fertile river valleys. With time and technology cities were established in progressively colder climates. Below is a map produced by [Dr. Meredith Reba, from her research into the origins of documented urbanisation](http://www.citylab.com/housing/2016/06/mapping-6000-years-of-urban-settlements-yale/486173/). It's worth noting that although some very old cities left documented evidence in Mesoamerica, India, and China, their spread was far less prolific than around the fertile crescent. Vanishingly few ancient cities were established in sub Saharan Africa, Indonesia, or South America, even though these regions were inhabited by humans for well over ten thousand years. The obvious thing to note from this is that jungles are not the easiest place to create a city, and comparatively dry regions made excellent sites for construction projects. It's also worth noting that humanity found it much easier to spread across cold areas than wet ones; likely owing to rainforests having simply too much rain and too many huge tree species for ancient humans to tackle. [![world map of cities by founding](https://i.stack.imgur.com/GOLOH.jpg)](https://i.stack.imgur.com/GOLOH.jpg) [Answer] Human needs are the very first thing you would look at when developing an urban area. The most basic of which are: * Water * Food Next is, and this is a large consideration--Trade, and other cities. Lately I've been studying Medieval cities, in particular a book called [Life in A Medieval City](http://rads.stackoverflow.com/amzn/click/0062415182) One of the interesting points made about the development and size of cities was very much connected to government and, above all, taxes. Some of the largest Italian cities became successful because they were on a trade route, had access to the sea, resources, and encouraged commerce. There were French cities that became successful because of yearly festivals (and stringent guidelines for goods along with special merchant courts for those who didn't follow the rules) Troyes Hot Fair is a good example of this. They basically taxed themselves out of success, and eventually the guilds created monopolies. Geography and resources are just the beginning. Wealth and trade can take a city up or down. Banking in Florentine made it a resource for everyone trading throughout Europe. This model was copied somewhat by other cities in Italy (Genoa) and others fell from prominence (Pisa). I was going to link you to <http://www.ancient.eu/> for more on ancient city formation, but I see that Landon Boyd already had. The map in inappropriateCode's answer illustrates a point I was going to make: the most ancient cities, with the most staying power tended to have access to the sea. Not all of them certainly, but many. As for tracking the spread, people do what's best for the times. Geography is just one part of the picture, as are resources. Cities are abandoned for a number of reasons: [natural disasters, government fiats, a particular industry moving away](http://www.stuffyoushouldknow.com/blogs/5-modern-abandoned-cities.htm). Part of the reason for the decline of Troynes and many other cities was an economic depression throughout Europe, and it's the kind of thing you see, [even today](http://www.thefiscaltimes.com/Articles/2011/08/04/9-Worst-Recession-Ghost-Towns-in-America). Cities are more likely to be wholly abandoned if they aren't geographically close enough to a "main drag" and if gathering resources in the area becomes more arduous. No one really knows what happened to the Maya, but many scholars point to a [reliance on rainwater](http://www.smithsonianmag.com/science-nature/why-did-the-mayan-civilization-collapse-a-new-study-points-to-deforestation-and-climate-change-30863026/?no-ist) and bad agricultural practices, which lead to a reduction in food and water, both of which are needed to survive. How a city grows, fails or thrives is dependent on stability of resources, whatever they may be. [Answer] I think that history can do more to validate your assumptions than "hard science". Let's look at a map of Venice and her territories in the pre-industrial world. ![](https://upload.wikimedia.org/wikipedia/commons/0/09/Repubblica_di_Venezia.png) This map (albeit, not ancient, I'll get there in a second) highlights the conditions and effects of the spread of urbanization in your question. The geography of Venice was perfect for trade on the high seas (which was a "thing" at the time). Plus, per your question, development of culture wasn't a problem in Venice, as some consider it the birthplace of the Renaissance. It was fed by tributary cities which were not as gifted in excellent geography, providing the "pecking order" you describe. Now, Europe has never been described as the cradle of civilization, but I think it plays a part in answering your question. "I'm also going to assume that cities first developed and then spread from continental cradles of civilisation (like the fertile crescent), and that these cradles had specific qualities." Let's assume the civilization here on earth started in the fertile crescent. <http://www.ancient.eu/Fertile_Crescent/> From there, tributary cities were planted further and further north until they came to Greece. By then, culture was advanced enough to support the city-state, enter Athens, Sparta, and, of course, the 300. A tributary city was planted in Italy, and from there, Venice was founded. The chain continues until today. The notions in your question are definitely valid, and they thankfully don't require MathJax format to answer. History here on earth shows that cities do develop like rivers, because who wants to expend extra effort to get over mountains, across desserts, or over oceans? The answer to why ancient cities spread is simple; wealth, and it leads me to one more side effect to this mode of urbanization. Large cities are going to plant small cities to gain wealth. We saw it in the cities here on earth. If there is a deposit of gold 30 miles away, I see that as a fitting occasion to start a tributary city. That way, others can do our work for us, but we get the gold. When it comes down to it, urbanization is all about the money. ]
[Question] [ We've all seen science fiction movies where a beam of some kind hits a person, and the entire person is affected but nothing else. For example, an ice blast freezes a person, their clothes, and their shoes instantly, but not the floor. Or a phaser disintegrates a person's body without leaving a trace, but their clothes fall harmlessly to the floor. In every case, a collection of objects (composed of various materials) is affected in its entirety, but adjacent objects are untouched. I'm wondering, how might such a system work? What process could enable a reaction to completely affect a desired target and all associated material (clothing, handheld objects, etc), but discern and ignore unrelated adjacent objects (such as the floor, a chair, etc)? [Answer] I've often thought that seemed pretty implausible. Well, elements of it are plausible. A death ray -- a laser or phaser or whatever -- that works by burning someone up would likely affect a person's body but have very limited effect on the air around him. Consider what happens when you open a hot oven to remove, say, a cake. If you touch the sides of the oven, or a metal baking pan, you'll be badly burned. But you aren't afraid to be touched by the hot air in the oven, even though it's the same temperature as the metal pan. Air is so much less dense than metal that even though it's the same temperature it contains very little heat, i.e. very little actual energy. If he's standing on dirt or rocks, the heat ray wouldn't have much effect on them either, as the heat conductivity of dirt and rocks is also pretty low. If he's standing on a wooden floor, I'd expect the floor to catch fire, or at least that there'd be a circle around him that becomes charred and blackened. If he's standing on a metal floor in the starship, I'd expect the floor to become hot and everyone standing near him to at least have to be dancing as their feet are burned. Likewise, if he was sitting on a wooden chair, I'd expect the chair to be burned up along with his body. If a metal chair, it should at least be glowing a nice cherry red. If a plastic chair, it if doesn't burn it should at least melt. But I presume the real reason is that the producers are trying to maintain a PG rating. If someone really invented such a death ray, I suspect that what would really happen when you used it is that you'd burn a hole in the person you're shooting at, and he'd have burned guts falling out of his chest and in general be a pretty ugly, grisly mess. Or if it could really vaporize a person, that it would leave charred stumps of arms and legs behind. That would have been way to ugly to show on TV in the 70s and 80s. Maybe today it would be acceptable. But still, they probably don't want to show the heroes killing people in an ugly way. When the hero kills someone it usually has to be neat and clean. Also, I'd guess the special effects for believable burnt leg stumps is more expensive than a glow and the person disappears. Personally, I often wonder how when a person is thrown back in time or travels to another dimension or whatever, he's always transported with his clothes and whatever he was carrying, but he never seems to bring along a chunk of the ground or the floor or anything else around him. I recall one science fiction book I read years ago -- forget the title -- that had the hero thrown into the future by being caught in a beam from some experimental machine, and the author threw in a line about how he was lucky that his whole body was caught in the beam, but it did leave behind the heel of one shoe. I suppose as the physics of such things is all made up, one could invent some equally made-up explanation. [Answer] One option that you might want to look into is harmonic frequencies. I can't find much information on it, and I'm pretty sure that its actual usefulness has been greatly exaggerated, but the general idea is that different substances resonate at different frequencies, and hitting such objects with those frequencies cause them to vibrate, and sometimes even break. Based on this concept, it may be possible to find the right frequencies for the molecules you wish to freeze/burn/vaporize/whatever, and output those frequencies with sufficient power to cause a reaction. This reaction would be localized to only the molecules you wanted to affect, which could be used in some situations to target individual objects as you suggest. However, there are a lot of cases where this won't target just one object, such as when you're trying to destroy a container that's made of the same material as the floor (or even the machine you're using to destroy it), or if you want to cause harm to one person but not another. There is also the problem of targeting unknown materials, as it will be difficult to lock onto the right frequencies without knowing what frequencies you need. Then there is the problem with the Doppler Effect, which will make it hard to use this method on moving targets. And finally, there is the question of how much power it would take for sound to have your desired effects. For this last one, you might have to add some extra material, such as a form of plasma that is attracted to harmonic vibrations (or something that actually exists, though nothing comes to mind). In the end, though, I don't think it's ever going to be possible to achieve the kinds of things you see in the movies without an army of nanobots you control with your thoughts, and even then I still think it would be better to use more conventional means. [Answer] A variation might be to affect some classes of materials. How many sci-fi battles take place on wooden floors? Eary space-age SF probaby assumed ship decks etc. are made of metal. But carbon fiber in epoxy might behave like organic material. In real life, it was discovered that a particular UV laser will affect the bonds of much (living) organic material and make it disintegrate without burning or wven heating the neighboring tissue. I think that's just a matter of power to make it into a blaster-type weapon. For now it's used in delicate eye surgery. [Answer] I'm not sure the exact numbers but in science everything has a specific heat. The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. So if two objects within close proximity and a laser or freeze ray pointed at an object heated/froze the object. Nearby objects wouldn't be affected if the specific heats were varied enough. [Answer] The main problem is not to destroy the target, there are already good answers on the way to make it precise and letal. The problem is to aim, to chose where the death ray is going to hit and what it is going to destroy. Pick your laser, your death ray or your phaser, then set up the best viewfinder ever on it : mind-controlled viewfinder. This is not a complete fiction : Some scientist from Berkley did register some brain waves to recreate some pictures : [just look at the video](http://www.gentside.com/sciences/vos-reves-ne-seront-plus-a-l-039-abri-avec-ce-scanner_art28057.html) This is far of perfect, but it does already exist, ok ? Second sci-fi fact : we can already move things [with mind](http://bcove.me/ccxuydoi) These are existing technologies. In the future we can imagine a helmet/brain wave reader that can be installed on you when you use your weapon. You target your ennemy with your mind, weapons, clothes and shoes included. Everything you picture in your mind is locked by your very precise laser weapon, and nothing else. I don't think that's as impossible as it sounds, because this is a way to never miss your target and totally erase the collateral damages. ]
[Question] [ I'm working on the biology of a fantasy race of very large human-like beings (think something like the Vrykul from WoW or the Norn from Guild Wars), and got stuck on one aspect of their development as infants. Relative to other species, human babies can be considered somewhat "undercooked" - or, putting in Gordon Ramsay's words - "f\\\\\* raw!". They are relatively weaker and less functional than the offspring of other species, demanding way more attention and effort from their guardians for quite a while. Even a somewhat basic thing like walking takes several months to develop - sometimes over a year. My research on the "whys" of this pointed me towards the idea that human babies need to be born earlier than what most other species would consider "done" because of the physiology of the human body. Our heads are simply too big, and waiting out for the proper time to be born with the "basic skill set" in place would make impossible for the mother to give birth safely to their child. Even with our current biology and gestational period, giving birth is no easy task - it is incredibly taxing on the mother and, while some can be up and about as if it was no big deal a few minutes later, it isn't uncommon for a mother to be in need for a good amount of rest and recovery afterwards. When I bring this to the context of human-like humanoid species with the same overall intelligence and general "build" but way larger in size, a few considerations open up. I mean, when the mothers of this human-like species are over 9-feet tall, one can't help but wonder if the "extra space" wouldn't allow them to give birth to more developed babies, lessening the initial strain of raising a child considerably. So, to my doubts. Would a considerably larger human-like species be able to give birth to more developed babies? If so, by how much? Would those babies be able to walk right away after birth, or at least a few days after? Would this reduce the effort needed by the parents on the first year of life of their child? Would any of this need a longer pregnancy? --- Note to people answering: While this is a fantasy world and I could handwave anything away as "magic", I would prefer science-based answers for this question. [Answer] Some time ago I read in a paper (I don't remember where, else I would provide the relevant citation) that, holding constant the constraints you mention, human babies are born at the time where staying in the womb longer would simply starve their mother to death, because their energy need becomes higher than what the mother's metabolism can supply. Considering that usually the larger an animal the lower the specific metabolic rate is (lower surface to volume ratio, thus less waste of energy), a larger humanoid might be able to bear the baby for a longer time, providing that among the physiological changes of the pregnancy there is also an increase in the specific metabolic rate. To pair this with the constraints of passing through the mother's hips to be born, it would probably mean that the newborn would be comparatively smaller than a human baby is with respect to the adult, and would need to have a more accelerated growth during infancy to catch up with the adult size. Let's say, just for the sake of an example, that if your humanoid is 3 times the size of a human, their baby wouldn't be 3 times the size of a human baby but only 2 times, while being functionally more mature. An accelerated growth rate means increased energy demand, so I guess the parents would struggle less during delivery but more after it to keep up with the hungry baby. [Answer] There are many reasons why humans are born the way they are. Consider that largest baby relative to parent body size is kiwi egg (1/2). The tsetse fly produces a single large larva (third instar). Even among mammals, there are giraffes (1/10). On the time scale, elephants, whales, rhinos, giraffes, donkeys, zebras, camels, sea lions and alpacas have gestation longer than a year. These are all large animals, though not all exceedingly so. Still, I think that larger humanoids would have longer gestation than smaller humanoids. There's the other side of human development — our babies are born with huge heads and small bodies, and we've improved this ratio as we developed as primates. Also our brains grow notably longer after birth ([ref](https://askananthropologist.asu.edu/stories/babies-birth-and-brains)). I believe the reason is that animals that live in communities, especially developed communities can take care for their offspring much longer, which allows delivering "underdeveloped" young. I suspect that all things being equal, larger humanoids could have larger head-to-body ratio at birth, but ultimately, it's the culture / social organisation / safety from predators that has the most effect. You could use the family circumstances to tweak your larger humanoid babies this way or that. [Answer] One of the significant reasons as to why human babies take so long to learn how to walk (compared to other species) is that our brains are not formed the same. In humans, the prefrontal cortex (at the front) is much larger than other species (which is why we have large foreheads). In most other animals, the cerebellum (back of the head) is larger, which contains most "innate" knowledge that animals use from birth. Add in the fact that walking for humans is a lot more complex than for other animals (biped vs quadruped, it's tougher to find balance), and you have the perfect cocktail for human babies being so useless at birth. The fact that we have such a developed prefrontal coretex is one of the things that makes us humans - we have insane patern recognition and skill learning that other mammals lack. We can find these in other primates like chimpanzees too but to a lesser degree. Ray Kurzweil talks about this a bit in [this TED talk](https://www.youtube.com/watch?v=PVXQUItNEDQ), I can't remember other sources as it comes from some conferences and such, I work in biology research. EDIT: Just realised that I never explicitly answered the question. To clarify, I think it would be impossible for a species as "intellignet" as humans to be fully functional at birth due to this. Shortening this learning period (multiple years in humans) would lead to a very different society and probably one that would never reach higher education and therefore be quite technologically stunted. If this is ok with the species you are thinking of, then roll with it, otherwise you might need to handwave it away or make up another explanation, which would add to complexity. [Answer] When it comes to biology, there are very few things that isn't possible. First, i'm not a biologist, this is an opinion based on my limited knowledge on evolution, biology etc. To say that babies are born "early" because the head otherwise couldn't pass through the birth canal, is a bit of a mis-representation of the truth. There is no reason the female can't simple have a larger birth canal. This would of course require a change to the pelvis, that would affect the females ability to walk (probably in a negative way, as it hasn't happend) This is super bad, for a hunter/gatherer society based around walking a lot to gather/hunt food. So the reason why humans are the way they are, is essentially a "path of least resistance" scenario. A longer pregnancy would give the baby a greater change at surviving, but negatively impact the mothers ability to survive. At some point it is simply more cost-effective to have one more baby die early, and leave the mother alive to birth two more babies later. (morally this is of course horrible, but evolution doesn't really care sadly) As for your question: A humanoid that's, say 50% larger, would most likely have different ways of acquiring food. There would be a large increase in energy consumption, but the increased size would be unlikely to enhance the humanoids ability to hunt as humans do by exhausting it's prey (probably). Though they would be much more likely to be able to simply beat it's prey (think angry gorilla, they are scary!) TLDR: I don't find it unreasonable to assume a larger humanoid would be able to have a considerably longer gestation period, due to the probable changes in the way they get food, lessening the consequences for birthing a more developed child. [Answer] They have a huge immobile Queen Just like with termites, the queen humanoid is comparatively huge. She is attended constantly by humanoid workers whose sole purpose in life is to provide her with nutrition and clear away waste. When a fully formed humanoid is born, they are taken away to humanoid 'school' to learn language skills and the ways of their caste; worker, hunter/gatherer, warrior, etc. Population control is achieved by varying the number of queens in any particular town or village. More recently, with the advent of technology, the preborn humans can learn language skills from inside the womb by having recordings blasted at them through the queen's stomach. <https://youtu.be/_PZACKXZgOY?t=361> [Answer] Well no because bigger creatures give birth to bigger babies. Example: A monkey is bigger than a rat but a monkey's baby is bigger than a rat baby. ]
[Question] [ I'm trying to develop climatic maps for our countries and know that wind is a huge part of that. Our world is shaped the same as Earth, it's just a little smaller, and our axis is slightly less tilted (about a 20 degree tilt) so we have less dramatic variations in climate and season. Here's a draft of prevailing wind patterns, does it check out? I just sort of looked at the Earth's and followed patterns but had no actual scientific method other than making sure wind turned in the right direction based off of hemisphere. Is there a method? Do I need to come up with specific pressure cells? Thanks. For reference: -Vitya: 7.86 mil mi2 -Eios: 2.97 mil mi2 -Amari: 3.02 mil mi2 -Sabriel: 1.53 mil mi2 -Noor: 22,000 mi2 [![map of global wind patterns picture](https://i.stack.imgur.com/HpSBf.png)](https://i.stack.imgur.com/HpSBf.png) [Answer] The tilt you are considering is not that far of from earth's tilt , which is about 23 degrees, so maybe the best option is to consider that its a earth like planet and that includes about the same size, cause the planet size have impact on climate. As for the climate watch artifexian YouTube video realistic climate: <https://youtu.be/5lCbxMZJ4zA> <https://youtu.be/fag48Nh8PXE> ]
[Question] [ Having recently discovered that [torus-shaped planets can actually form](https://www.youtube.com/watch?v=fJvbO_rR07g), I've started to consider using that design as a setting for a map(no real purpose in mind, just map making for the sake of it). How would I realistically simulate the formation of landmasses? [Answer] Artifexian has a [great video](https://www.youtube.com/watch?v=1J4iIBKJHLA) on this subject on YouTube! In it he explains that due to the inner radius being smaller than the outer, continental plates moving inward will need to shrink and thus experience folding, creating mountains. Plates moving outward will have to grow and thus are torn apart. The surface gravity on the 'equators' is also lower than at the poles (slightly inside of the poles it is at a maximum) which makes for very large mountains. ]
[Question] [ In my setting, there is an isolationist people known as the Jotnar (sing. Jotunn), who are merely humans, but are consistently taller than other human populations, which I think of as reverse pygmies. But although there's plenty of room for discussion as to why there are populations that are consistently short, I can't find any for the Jotnar. Should it just be chalked up to "Taller is more attractive in their culture"? Or is there a practical reason why they would have developed to be taller? Know that I want them to still be Homo Sapiens Sapiens. The only real difference in anatomy is that they remove their vestigial structures from their young to replace those structures with magical biotech they had found in ancient ruins. They are technologically and magically advanced, but I'm thinking they were tall even before that could be said about them, back when they were still a neolithic tribe. [Answer] Unnatural selection. They sacrifice everyone who's height falls below 1 standard deviation from the mean. This selects for taller people and appeases the god of dirt because the short people were closest to his domain anyway. [Answer] Long distance travel and jumping are easier with longer legs. This will breed them tall and thin like the [Maasai](https://en.wikipedia.org/wiki/Maasai_people) in Africa. Their use of the spear builds upon their advantage of a longer reach. Competition can also breed people taller. When humans fight other humans, body mass is important. It is easier to hang more muscle and other body mass on a taller frame. The extra reach provided doesn't hurt either. The ruling classes of several cultures were bigger than average. As an example, the Ali'i, Hawaii's ruling class, were bigger and stronger than the average Hawaiian because they fought with members of the ruling classes of other islands. People with poor nutrition in their early years tent to grow up stunted. Therefore, being bigger (taller) could be a sign that a person was raised wealthy. That would promote sexual selection for taller mates. [Answer] There are several possibilities that come to mind. You've already mentioned one: [Sexual selection.](https://en.wikipedia.org/wiki/Sexual_selection) In short, they find taller people more attractive. It could be cultural, it could be hardwired into their genes somehow. Others include the other modes of [natural selection](https://en.wikipedia.org/wiki/Natural_selection). If taller Jotnar are better at obtaining food and avoiding getting themselves killed, the Jotnar will gradually get taller over time. Ideally, there should be an evolutionary arms race between the Jotnar and some other species. Perhaps there's some predator that a Jotunn can only effectively defend itself against if the predator is shorter than the Jotunn. That way, there's evolutionary pressure for both species to become taller. Or, perhaps there's a tree whose leaves make up a substantial portion of the Jotnar diet. The tree will evolve more height, smoother bark, and fewer branches to make it more difficult for the Jotnar to climb, while the Jotnar will evolve to become taller and better climbers in order to get to those tasty leaves. This might also happen if the Jotnar are going after the tree's fruit rather than leaves if the seeds cannot survive the Jotnar digestive tract. Do note that if the Jotnar develop technology that compensates for traits that lack, they will have much less pressure to evolve those traits. If they live in a savanna where height would help them see over the grass, they might instead burn and trample the grass around their settlements. If the tasty tree leaves become too high to reach, they might start building stepladders. Alternatively, the Jotnar's height might be a result of [founder effects.](https://en.wikipedia.org/wiki/Founder_effect) If a small population of unusually tall individuals became isolated from the main human population, their descendants will also, on average, be taller than the average human. If this happens repeatedly — for instance, if taller people regularly strike off on their own to found new settlements — then the effect will be magnified. Similarly, [population bottlenecks](https://en.wikipedia.org/wiki/Population_bottleneck) can greatly accelerate natural selection. In short, if there's some cataclysm that only the tall people survive (maybe a flood or tsunami where tall people are better able to climb to safety), the population that they rebuild will be taller than the one that came before. Another possibility is that the Jotunn are simply healthier than anyone else on the planet. Humans have gradually become taller over the past centuries because we've created a better food supply. People used to run low on food over the winter, which stunted their growth. You say the Jotnar are technologically and magically advanced; if the rest of the world has a medieval food supply, they will likely be the tallest people on the planet. [Answer] *Good ol’ natural selection, Baby* As one of the comments said, it may have been natural selection. Maybe these Jotnar folks live in a Savannah, like the ones in Africa. Being taller is beneficial in that environment, as it allows you to see over tall grass, and how are you gonna hint for food if your to short to see over the grass to hunt your prey. The Jotnar May have lived on a mountain in the past, and in higher elevations, people mostly grow taller than on the ground. This may be the reason. Or maybe Jotnar women prefer tall guys, and overtime nature just sorted itself out. [Answer] This actually happens Full blood Osages are [known to have been very tall](http://www.lewis-clark.org/article/2535). > > The Osages are so tall and robust as almost to warrant the > application of the term gigantic: few of them appear to be under six > feet, and many are above it. Their shoulders and visages are broad, > which tend to strengthen the idea of their being giants. > > > One account from an early explorer I read chalked it up to the tribe actively practicing Eugenics. In particular, controlling their own tribe's breeding for size like a rancher might do with livestock. However, Eugenic ideas were a fairly popular new thing with Europeans at the time (that had yet to generate the unfortunate history they since have), so I'm not entirely sure I believe his explanation. [Shandong province](https://en.wikipedia.org/wiki/Shandong) in north China has had a reputation for quite a while of producing the largest people in the country. Their average male and female height today is slightly larger than the average American's. The typical rationale the Chinese come up with for this is that it's down to diet (being so far north, their staple cereal crops are much more similar to the ones Europeans rely on). But I don't know of anyone rigorously studying this. The difference in average height is only about an inch though, not the more than half a foot reported for the Osage. I will add that I have done multiple angles of investigation into human height, and there does seem to be a universal agreement that nutrition is a factor. I'm not saying everyone could be 6'4 like the old Osages if they just ate the right stuff. But I am saying that being calorie limited or spending a lot of time sick in childhood does seem to retard a person's ultimate growth. This means your tribe of giants are likely wealthy (by tribal standards). They never have to worry about going hungry or proper nutrition, and childhood sickness is rare. [Answer] Options... # Founder effects The [founders](https://en.wikipedia.org/wiki/Founder_effect) of the tribe were all unusually tall for some reason. Perhaps they were all descended from an ancient basketball team that crashed in the mountains or perhaps it just happened that the group who made it to the remote location to found their tribe were all. An example is Dupuytren's contracture in norway where 30% of men over 60 years old have the condition, mostly due to founder effects. [![enter image description here](https://i.stack.imgur.com/KL0G0.jpg)](https://i.stack.imgur.com/KL0G0.jpg) # Puberty Rituals Puberty rituals vary a great deal around the world but they tend to follow a few patterns. Young men of the tribe must pass some kind of test in order to be considered real adults and be allowed to marry and start a family within the tribe. If the tribe practices a puberty ritual which tall people are dramatically more likely to pass then they may strongly select for height over many generations. Here we see a boy wearing a pair of Bullet Ant Gloves. To pass he must avoid showing signs of pain during the ritual/test. [![enter image description here](https://i.stack.imgur.com/Go9Nt.jpg)](https://i.stack.imgur.com/Go9Nt.jpg) # Pleiotropy Sometimes a gene which causes one thing also causes other things. So you could have a set of genes that tend to lead to greater average height that are closely linked to a gene which is heavily selected for. Say a gene which grants resistance to an environmental toxin in the location where the tribe lives. Height doesn't give much advantage itself but people who carry resistance genes also tend to be tall which leads to a gradual change in the population. [![enter image description here](https://i.stack.imgur.com/pF2ha.jpg)](https://i.stack.imgur.com/pF2ha.jpg) # Eugenics Possibly the simplest [approach](https://www.smh.com.au/news/basketball/yao-ming-the-basketball-giant-made-in-china-by-order-of-the-state/2006/01/18/1137553645228.html). Have the people of your tribe intentionally select for height. When they encounter unusually tall travelers they attempt to induce them to join the tribe. Unusually short people are shunned from the tribe. The very tallest couples in the tribe are honored and encouraged to have many extra children. [![enter image description here](https://i.stack.imgur.com/DpeNG.jpg)](https://i.stack.imgur.com/DpeNG.jpg) [Answer] Don't forget Signal Theory Species can take very weird turns in their evolution. Why do many birds have ungainly, bright colours, huge feathers or very obvious features? Why do useless appendages that risk you being more obvious to predators become commonplace? Reason: Signal Theory. By sending out a signal to your potential mates that you are so unwieldy - yes, you may be more desirable. Basically you are saying "I'm still alive, yet I prosper and spend inordinate resources on frivolous things, therefore mate with me because I have plenty of resources to spare." Giraffes are in essence ungainly, unusually high creatures - often height is a hindrance with large resources invested beyond the benefits of simply eating leaves. Patterns on Giraffes, and other features, indicate signal theory is equally at play here, female Giraffes may find taller males as sexually attractive simply due to the fact they can be taller. Some decisions therefore, for instance finding someone attractive or mates, have a convoluted logic to them, not a direct logic. Height could be seen in this way on your society very easily. There needn't be a 'need' for height, or any direct justification for it, but being taller just like Giraffes could lead to a signal that you may be dominant, more able, or simply have more authority to spare. Perception is everything. [Answer] They're human? They're taller as a race? # They're rich... It's really that simple. All those reasons people can be stunted? In practice, on continents and at a civilizational level, it comes down to childhood nutrition. There's plenty of speculation and some research about the importance of red meat and milk (Holland, Scandinavia) versus grains and fish (Japan) but (a) you can literally see this on the Chinese subway lines, as grams—who somehow survived the warlord era & the Japanese invasion & the intentional floods to stall that invasion & the Civil War after that & the collectivization after that—can sometimes top out about the level of an African pygmy, mom—who lived under the better but still modest means of the Maoist state—can seem a bit on the short side, and the teenage kid—who's only ever known life since the opening up and, among well-off families, has grown up on imported milk formula—can get over 6'. College girls can demand boyfriends be over 180 or 185 cm and be spoiled for choice. (b) North and South Korea were divided within living memory. The grandkids of that generation? [In the wealthy south, they average 5–8 cm taller than in the sustenance farming north](https://en.wikipedia.org/wiki/List_of_average_human_height_worldwide). (c) Just a century or two ago, things could be even more divided between the British upper and lower classes, [with some studies finding as much as 9" of difference between them](https://www.theatlantic.com/magazine/archive/2018/06/the-birth-of-a-new-american-aristocracy/559130/). The Jotnar can be aristocrats, and that can be the end of it. They can keep herds, individually or communally, that permit consistent and thorough infant nutrition. They can be traders whose profits and varied diet keep their children (at least for the overclass) well-fed. They can have magical mushrooms or other mana-given food sources. # ...but it's unlikely everyone is. There are fairly few true egalitarian societies. They tend to be clan based, in bad lands, and poor. What's more likely is that your grossmen will—somewhere obvious or hidden—have their own 'dwarf' class of untermenschen working for them and being fed their scraps. There's probably an origin story and ideas about them being a different race. Both're probably bupkis. Depending on your narrative, you can go into it and free them from their caloric chains or just use them for color. [Answer] Coming from the Netherlands the first thing I had to think of was 'flooding in a flat landscape'. But we quickly started building artificial hills (terps) to live on. You could make an environment with unhealthy gases which are heavier then air, or some pollutant in the dust. (traces of Beryllium?) [Answer] The average Indonesians are 158/147 cm (m/f). The average Dutch person is 183/169. Its commonly believed that this is due to a richer diet, better health care, and drinking a lot of milk.[citation needed]. If the people you wan't to be taller are from an isolationist culture maybe they have a special diet, or a plant/animal that mostly grows there? You can combine this answer with the other answers to create an even bigger effect. Source: <https://en.wikipedia.org/wiki/List_of_average_human_height_worldwide> [Answer] Scandinavians ("Vikings") are on average quite a lot taller and generally larger than Europeans from further South or West. Chinese from Siberia are on average quite a lot taller than Chinese from further South. Wolves that live in the far North of Canada are quite a lot bigger than wolves that live further South. Ditto Siberian tigers versus Indian ones. Spot a pattern? It's the square-cube law at work yet again. Loss of heat from a body is proportional to surface area. Amount of heat stored within a body is proportional to volume. Increase height by 10% keeping the same proportions, and area increases approximately 20% (1.1 squared) but volume by 30% (1.1 cubed). All things being equal, larger will be selected for if the climate is cold. (If the problem is keeping cool, not warm, then the converse). You may spot that spherical is better than tall and slender, but there are other reasons why such a profile isn't the answer. Primitive humans and wolves are both chase predators, and the short and stocky profile is not so good at running down prey. Inuit (Eskimos) traditionally fished and hunted from boats, rather than chasing down their prey. They do tend to have the shorter stockier profile. If the Jotnar don't live in the frozen North, it's probable that their ancestors did. Alternatively, blame unnatural selection (see the other answers). [Answer] I would like to propose a few different theories since any one of them could be the reason: 1. Race for food: Like giraffes, the staple food for the Jotnar grew up at considerable height above ground. So the taller ones had fuller bellies as well as had a better chance of providing for a family. 2. Enhanced appearance: I read a few years back, that the human race on the whole is becoming more beautiful since people who are attractive, get a better shot at siring more offspring. There might have been a case of the taller individuals being preferred for mating. 3. Introduced gigantism: The Jotnar live in an area of enhanced radioactivity or as children are fed a specific fruit/root that causes gigantism. 4. Eugenics: The Jotnar are a warrior race. History tells us that since early times, warriors have tried to look taller and imposing as a psychological tactic to demoralize their enemies. Over a period of time, shorter individuals were killed off/restricted from joining the ranks of their taller brothers/sisters and were thus relegated to menial jobs in the hierarchy. This also limited their capacity of having more children. 5. Fringe population group - The Jotnar descended from an group of outcasts. Their forefathers were exiled since they did not fit in with the general populace. Every time a kid reached beyond a particular height, they were banished to the Jotnar lands to live their life away from the shorter society. Over time, this tribe of tall individuals rose as a powerful group on its own. I, personally, like the last one. [Answer] In our world, many societies have practiced primogeniture. When in doubt as to which son should inherit an estate, primogeniture bequeathes the estate to the oldest son. In this society, suppose that primogeniture bequeathes the estate to the tallest son. Over time, this would cause a correlation between height and having the resources to support more children. It would also reinforce a standard of beauty, in which (all other things being equal) women would prefer taller men. [Answer] Looks like you are looking for a dominant genetic syndrome that causes individuals to be taller than average. Instantly I thought of: ## [Marfan Syndrome](https://en.wikipedia.org/wiki/Marfan_syndrome) This genetic disease causes, among other symptoms, above average height. It is an [autosomal dominant disorder](https://en.wikipedia.org/wiki/Dominance_(genetics)), so given an initial population of your tribe with this genetic trait, and unlikely reproduction with foreigners, chances are high that the syndrome will be inherited and tribe members should be taller than average. [Answer] Evolution is random. New generations randomly get some different traits, and they pretty much randomly procreate or die. Some causes can significantly affect the likelihoods of individuals with certain traits either procreating or dying, but in a small tribe with small numbers, randomness is a much larger factor than in a larger population. A small population being cut off from the larger population and getting taller for no specific reason is perfectly plausible in the theory of evolution. --- Another thing is, in terms of story, consider if you add anything of value by trying to explain why they are taller. ]
[Question] [ Let’s say I have an island, similar to the likes of [Kerguel](https://en.m.wikipedia.org/wiki/Kerguelen_Islands) in the Indian Ocean, as the island is hundreds of miles away from any mainland, has no immediate resources, a tiny population and no strategic value; But for one reason or another, the government that has this island as a colony has decided to dramatically increase the military personal at this middle-of-nowhere island. Some civilians also decided to travel and work and live (at least for a while) on this island. Why would the island be a hive of activity if there is no value strategically, politically, or in terms of resources? [Answer] The island may not have strategic value per se, but it may make sense politically that it holds that island. US and UK made [an airlift into Berlin](https://en.wikipedia.org/wiki/Berlin_Blockade) while it would not be warranted by the city itself. Spain sent a commando attack force to recover [a rock pastured by goats](https://en.wikipedia.org/wiki/Perejil_Island). Just an interest by another country on that island would make the government to send a message visibly reinforcing their presence there. Not to mention all the other reasons an isolated island could attract a lot of population: * A political or religious leader could be visiting the island "soon" (which might be next year) * A recent translation of a Mayan prophecy designates this island as the place from which aliens will come to visit Earth / take human race to their world. * A popular reality TV program is [filming on that isolated location](https://en.wikipedia.org/wiki/Survivor_(franchise)), which brings in a lot of people (cast members, production crew), and could cause more military personnel (for example, since they are so isolated the island traditionally had the army perform the duties of a police force) [Answer] ## No inherent Strategic Value ... The requirement for "no strategic value" kills many explanations which might otherwise apply. It cannot be a waystation to somewhere else, or it would be strategic. It cannot be far enough from prying eyes to hide an ongoing secret program, or it would be strategic. It cannot justify claims to an [exclusive economic zone](https://en.wikipedia.org/wiki/Exclusive_economic_zone), or it would be strategic. Would it be possible to make it merely indirectly strategic? * Something happened there in the past and independent investigation would be embarrassing. Like [Anthrax](https://en.wikipedia.org/wiki/Gruinard_Island) tests. Or some [old missile system](https://en.wikipedia.org/wiki/CIM-10_Bomarc) was dug into the rocks and obliterating the traces would itself leave traces. * It is a strategic interest to support a certain interpretation of international law, and holding on to the island showcases this interpretation as it applies elsewhere. * It is a suitable training site simply because it has little inherent value. Real estate is cheap and flight restrictions don't annoy the economy. [Answer] ## Top-secret Resources and/or Strategy Importance Government officials have discovered that there is an attack plan that a presence on this island would foil, or that scientists have discovered a way to use some insignificant material found on this island in important ways. ## Safe Location for Research The low population, distance from other locations, difficulties getting on and off without being noticed, and little interest to outsiders combine to make it an ideal location for research. Not only is it safer because there are fewer people that could be injured, it makes espionage more difficult. ## False Flag Its very obscurity will ensure all this draws attention. It is vital that attention not be paid somewhere else, and this will at the very least draw down the resources that could be used for that. And you might roll up a few of their assets, too. [Answer] A defeated charismatic dictator has been exiled to the island, as happened with Napoleon, first on Elba and then on St Helena. This obviously necessitates a substantial military presence to prevent him from being liberated by his remaining followers (as also happened with Napoleon on Elba). [Answer] As a waystation. The ocean is big, and ships can be out to sea for a long time, which is not easy or fun for the ships or their crews. The more friendly ports you have to resupply from, the less space your ships will have to devote to supplies and the more room they have for combat- or other duty-related equipment. Now ideally you'd want your waystations to be ports in their own right: it's cheaper, and you can turn a tidy profit off the merchant traffic, but for that reason, valuable ports are often snapped up by rival empires. You might have to make do with building your own waystation, but it's better than nothing. [Answer] When you say no value/resources, I am taking that to mean none at all, not just "none apparent," as secret reveals solves all mysteries. One mundane, frustrating, and all-to-common reason? Politics. General A needs to increase his deployment numbers to get more funding . . . Hey let's build a base! That of course attracts civilian support, etc. edit: Since the OP gave the condition of no value to the island, the value must come from something else. In this case, the value is in the process, not the result. Military build up on this particular island is of no value. However, military build-up in-and-of-itself is a lengthy, expensive, labor-intensive process that can provide value and benefit to a great number of interested players. Contractors, unions, vote-seekers, power brokers . . . there are unlimited ways to game this system, with the benefit that no body bags will come home to bring attention to this decision. Conversely, these things can all be done out of spite, or even treachery! Suppose a general is really a foreign agent. Directing resources in this way depletes a nation's ability to respond to actual threats. [Answer] # International Waters Consider the island of [Kolbeinsey](https://en.wikipedia.org/wiki/Kolbeinsey) off the northern coast of Iceland. Ostensibly, it is a barren rock with no resources or strategic value. However, what it does do is extend the territorial waters claimed by Iceland due to the 12-mile radius around the island marking the border to international waters. Due to sea-level rise, it is [slowly disappearing](https://www.youtube.com/watch?v=hr03xF08qoU), currently only existing above water at low tide. Now there may not be much point of trying to put a military contingent on this particular tiny piece of rock (indeed, they'd have to be good swimmers since it's underwater half of the time), but you could imagine a similar case of an island owned by a country which does nothing but extend their territorial claim over the surrounding waters. [Answer] Sometime the strategic importance is hard to assess, here is a simple example: An island lost in a sea far away from any country. Well, often these are extremely interesting because they can for example act as a SIGINT (Signal Intelligence) collection point: The owning country can install antennas and processing stations that will listen to the radio spectrum, either from other parts of earth or from satellites, and collect them to get either clear text messages (decreasing probability), have raw material for hostile cryptanalysis, or perform traffic analysis (deduct goals and movements from mere traffic presences, sources, etc...) etc... These locations can also serve as fiber optics interception stations, retransmitter station locations, etc... So actually something seemingly of no value is of great importance: it stays under the radar. PS: many personnel from intelligence agencies running these stations are actually civilians working for these defense agencies. [Answer] > > What would cause a heavy military or civil presence on an island with no strategic value? > > > That is quite close to the definition of a paradox. And the source of the paradox comes from the undefined "strategic". It itself, the word is "big", but means nothing. To make it significant, it had to be paired with other clarifying words. E.g.: * strategic military position; * source of strategic resources (e.g. the last adamantium mining place); * strategic location for secret testing of something; * strategic place for performing some activity (e.g. some sports); Now of course, one thing can be irrelevant one day and become strategic during the next day. Why ? Because something has changed. --- This is exactly what you want to exploit. The island had no strategic importance. But now it has strategic importance because something changed. What changed? Choose anything that fits your needs. E.g.: the ocean floor was noticed to raise in the area, and the small significant island will become the launching pad for interstellar missions. The current size is not suitable to hold the required infrastructure for launching the missions, but in 10 years enough land will be available to start building. Of course such an asset must be protected by the military, and civilians were brought to provide services; some of the civilians are the families of the military people. Another e.g.: the island was actually found to be the sediments covering the lost city of Brth'am-tek (please feel free to invent any other name). The military provides protection, the civilians do archeology. [Answer] # Disputed sovereignty Your country says this is your island. Another country says it's their island. Who's the winner? Flooding the island with your civilians and military alike makes it hard for the enemy to claim it as theirs. Real-life example (sort of): [Machias Seal Island](https://en.wikipedia.org/wiki/Machias_Seal_Island), the last disputed territory between Canada and the United States, 20km from the mainland. The Canadian Coast Guard has automated all lighthouses, except the one on Machias Seal Island, for which it employs two lighthouse keepers. [Answer] ### Your economy would collapse if you stopped expanding. If you're building a city there: You're a former superpower thats transitioned to a service economy that is trying to achieve greatness again by basically doing each others laundry. The only thing keeping your economy afloat is construction and expansion for your growing population. Expanding onto a remote island is one way to keep the ponzi scheme going long enough to get you to the next election. If you're builing a military base there: your economy is in shambles and the only thing keeping it afloat is your massive military spending into the military industrial complex. Unfortunately you can only put gold plated F-35s in so many places on an airbase before the base is full. So you start putting airbases all over the planet on any rock you have a claim to, so you can avoid cutting those military contracts that are keeping the bulk of your population employed. [Answer] In 1947, the Royal Navy decided to detonate 6700 tons of explosives on the island of Helgoland, creating one of the biggest non-nuclear explosions in history (undoubtedly with significant military presence and efforts before the detonation). From today's viewpoint, the island was of relatively minor strategic value, with no significant number of inhabitants - You could assume they did it simply "because they could" (or, maybe, as a simple way to get rid of surplus WW II bombing arsenal - but that's just an assumption). Conclusion: You don't need a reason, at least not a very good one. Reality is sometimes surprisingly unreasonable. [Answer] # Have a look at the Thirty Six Stratagems The thing about "no strategic value" is how malleable 'strategic value' is; putting lots of people and materiel into a place makes it a strategically valuable position. The [Thirty Six Stratagems](https://en.wikipedia.org/wiki/Thirty-Six_Stratagems) are an early Chinese treatise on, well, the art of war (but not Sun Tsu's famous essay). Several could easily explain the scenario you describe: * Wait at leisure while the enemy labors * Make a sound in the east, then strike in the west * Openly repair the gallery roads, but sneak through the passage of Chencang * Lure the tiger off its mountain lair * Disturb the water and catch a fish * Feign madness but keep your balance * Decorate the tree with false blossoms Never underestimate the power of bullshift. People like to say Money talks, bullshift walks; this is just another lie bullshift uses to make people underestimate it. [Answer] As a diversion. We actually planned all that originally for another place, which has a large, non-obvious, super-secret strategic advantage. Then it partially leaked. A rival got to know that we were about to put a heavy presence in a place with a large, non-obvious, super-secret strategic advantage. We know that they know, but they probably don't know that we know that they know. What to do? Why, replan the heavy presence to the middle of nowhere. If we manage to pull it off, it will send them in a wild goose chase. After a couple years, we'll put a smaller base in the real strategic location on a carefully manufactured pretext. ...or as a cover Alternatively, our real secrete base is actually very near to our publicly known useless one. We can't just send a bunch of ships to the middle of nowhere and not have anyone notice, but we can send a bunch of ships to the middle of nowhere, and then have one of our many useless coastal patrol vessels routinely supply the real base just down the way. [Answer] What about cultural significance? Maybe this island has no strategic value or resources, but something cultural happened (or is believed to have happened) there. Perhaps an event of great religious significance took place on this island? Maybe a cultural folk hero was born there? This could make the island a destination of pilgrimage, and also a psychological target for enemies of the ruling nation. The nation in possession of the island defends it because it is seen as a symbol of who they are as a people. It isn't a perfect example, but consider the Statue of Liberty. It doesn't actually do anything of strategic value, but it is a national icon. Looking back to the years after 9/11, it was guarded quite heavily. The nation felt it must be protected because of the idea it represented. [Answer] Sheer Accident Perhaps the military stuffed up, spelled a name wrong or wrote coordinates down wrong. --- I think that if that people arrived at the correct island intentionally that makes the island strategically valuable, as it was by intent. Correspondingly, choosing the island because it has no intrinsic value makes it, contradictingly, valuable. If you felt like being pedantic, the act of arriving there probably makes the island valuable in some sense. Though you could argue that the island had no/little value prior to arrival. [Answer] The Island will become strategic only if a truly strategic alternate island is captured or embargoed. It is part of a backup plan. By building a base there, you absorb a portion of the strategic value of the other location, so that losing either location is less damaging to your position. You deny an enemy a strategic location from which to attack you. It is valuable to them, not you. [Answer] Most of them are not actually military personnel. They are not persons at all. They are something else. Real military personnel in boats patrol the water and ward off anyone interested. Satellite images show the structures and vehicles and people walking around in uniform. If you were sent onto this island and used your skills to get close you would notice that these people in uniform are unusual. Their uniforms do not fit right. They gather in groups but they do not make any sounds. Their movements are disturbing to watch. They are not people. They are something else. Clearly the government that owns this island has disguised them as military personnel because an accumulation of such has plausible reasons that the government might reasonably decline to explain. What exactly they are is an open question and one you should answer unobtrusively and, you wish now, from a greater distance. [Answer] You mentioned civil presence. Gather hobbyists, gawkers, and astronomers for a... # Total solar eclipse ... or any other kind of astronomical or atmospheric event really. It needs to be rare enough to warrant the travel, spectacular enough to be cool, and happen to be best observable from this particular island. The maps of total eclipses can get pretty [complicated](https://en.wikipedia.org/wiki/List_of_solar_eclipses_in_the_21st_century), hence the strange location of the island might be explained. Another variant (for an island in the polar north or south) is aurora borealis, which should apparently be most spectacular exactly there. Some other kind of an astronomic event, such as meteor shower (should be world-wide, a particular large meteor with a predicted impact location? But not too large to not burn up completely, of course!), re-entry of a larger satellite, re-entry (to water, hence mostly US tech) of a space fare, [solar panel flares](https://en.wikipedia.org/wiki/Satellite_flare) of a larger satellite / space station. [Answer] Historic/Religious/Sentimental value For instance, the island used to be a bustling center for trade due to its location. Control of which would grant power/money/etc. In battling for control of this island hundreds of thousands of soldiers have died over the course of centuries. Those are honoured by numerous monuments spread out over the island. All of which are guarded by a large armed force as a sign of respect to the fallen. Due to erosion/climate change the island has slunk down significantly. Trade is no longer possible and the only remaining people on the island are the soldiers protecting and maintaining the monuments. Keeping these soldiers there might be political, but could very much also just be a feeling of what is "right". [Answer] Islands are ideal for R&R. [Answer] To gain access to resources and to gain sovereignty over the sea. If you own an island (ok, you may not own it really, but you placed fortresses and troops there so who's arguing?) you own any resources under the sea (oil! minerals) and the fish in the sea around it. You can also make like a pirate and interfere with passing ships. This is not fantasy; a large ambitious Asian country is - umm - acquiring islands, atolls, and even tidal reefs in the South Pacific right now. Edit: You could say an island suitable for acquiring in this way must be by definition strategic. But if it's not strategic till somebody occupies it? [Answer] The Island is a relay Well, even if this is far from everything and have nothing on this may have a strategic value. Nowadays there is satellite to almost everything but if people wanted to exchange in long distance with no satellite having a relay here may be a good option. That may mean something is gonna kill the satellite and there is preparation to be ready. Or for a less catastrophic model this is far from lands SO in the middle on ocean. Satellite is good but far if you try to discover deep water. A station that can relay (yeah that's the point) communication or handle data without having to navigate or a little bit is interesting. There is no need to consider the travel on the energy calculation. ]
[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/229247/edit) # So bear with me on this So I'm working on constructing a world for a DnD game that I am going to be running. I have a general idea of the world that I would like to develop, but am getting stuck on fleshing out some details. The general setting is the usual Tolkienesque high fantasy set in a dark ages-like medieval faux-European continent. The action takes place in a small town that is nestled in a valley surrounded by mountains. I have this idea for the big bad guy (the Baron) at the end which I have described in [this question on the roleplaying site](https://rpg.stackexchange.com/questions/197314/how-might-i-instantiate-this-npc-concept-in-a-fun-way-within-the-systems-of-dnd/197316#197316). In short the end boss is a cross between Dorian Gray with a sprinkle of Dr Jekyll and Mr Hyde. He has made a Faustian bargain with a being, lets call him Stan, that is kinda like the devil. Ie, Stan is a god tier being that is lawful evil. The gimmick of the Baron is that in order to maintain his immortality, he is compelled to maintain a diary. Each entry effectively granting him another unit of lifetime (the frequency is still up in the air here). The Baron's immediate goals arise from his need to maintain this book. He is constantly desiring raw materials that he can use to manufacture new pages and other book binding resources. (I mean there is no reason for the diary to be a single volume, and so he probably has a library full of various volumes of the ongoing document). At the time the players fall into the story, the Baron has been maintaining the diary for hundreds of years (approx 3 centuries say). I now am considering that the content of the book must be somehow important to the goals of Stan. But How? For the record, Stan has been banished to the underworld after a big fight with the other big powerful divine things that happened about the time he made the original deal with the Baron. So my thinking is now something like: Stan is raising a fiendish hell army. He needs to keep track of some strategic information. He makes a bargain with a mortal to record a diary, and in so doing buys a spy. But what information would Stan need that the Barons diary might provide? --- As another thread to this I think it would be fun if the Baron had started a religion in which the principle ritual is in someway assisting Stan's goals but in a way that is not obvious to anyone (bonus points for it not being obvious to the Baron). --- ## My general thoughts on the resolution I recently read about the famines in Ukraine in the 1930's and consider that perhaps the principle resource that both Stan and the Baron would care about is food. The Baron cares about grain because it is the chief export of his protectorate and so represents a measure of his wealth. Stan on the other hand cares about food because it measures the health of the world that he is planning to invade. And I think that Stan is looking at this with the mindset of a warship manufacturer. His army is going to be expensive, and take centuries of construction. I fell like a titanic hell fiend should take more than a human lifetime to gestate. So he wants to be monitoring the enemies food supply so that he can allocate his own resources more effectively. Likewise, if the Baron has instantiated cultural rituals around offering food to the gods, well maybe that food is really going to Stan, who is using it to raise his Hellish armies. Edit: Thank you all for your fantastic ideas. There are so many good options here that I genuinly don't know how to pick an accepted answer! I really like the idea of immortality being a mechanism to compound the value of the soul, and the idea that the collected works might somehow oneday transfer Stans essence to the mortal plane when complete. I also really like the idea that the barony is a bread basket and mixing that with the Castle Gormenghast elements is right on the money for the Holodomor vibe I was chasing! [Answer] New Layer Of Hell. In typical D&D fashion, all the fiends are constantly feuding with each other for power and influence. Stan is a medium rank devil. From a mortal's point of view, he is godlike. But unlike more powerful devils, he does not control his own layer of Hell. Enter the Ritual. A 301 year long ceremony to turn Barony A into a new layer of hell under the command of Arch Duke Stan. You see, every Archduke has psychic access to all the comings and goings in their realm. The ritual works the opposite way -- take a realm and write diaries to give the new lord access. The ritual makes the diaries indestructible. And once enough information is obtained, Stan can enact the second half of the ritual to transfer all of that information into his brain. There are some story hooks here. For one thing, the final battle is, of course, with Stan in the library. Since he is only Medium power, the players can fight him directly once they reach high level. Maybe the library is part of the battle. Stan keeps opening books and throwing them into different memories during the fight. Maybe going inside the books happens well before the final battle. Finding a single volume of the diary could happen in session 1. Over the next few sessions, the players get an idea what the diary is. Later they can go inside the memories of the diary. Perhaps the volume they find is Volume 2. It gives some details about what the Baron is up to without saying explicitly, there is a Devil involved. Since the Baron appears in the diary himself, it certainly says the Baron is hundreds of years old! It is a good tool for exposition. --- Depending on how Devil-y you want Stan to be, you can do loads of fun stuff. In D&D, devils are like lawyers. It might be the ritual only works through a silly loophole in the Devil Constitution. Since Archdukes come and go, the duke of a realm is defined legally as someone with psychic access. So giving yourself psychic access -- even if you are not especially powerful -- makes you archduke. And everyone then has to recognise your status. Easy peasy. Another option is that having a layer of Hell on the Earth is a big deal. The Blood Constitution says Devil lords may not come to Earth. Devils can only come when called, and can only interact as part of contracts. Otherwise, they must remain in Hell. Maybe making PART of Earth into a plane of Hell immediately makes the whole of Earth into a plane of hell. With Stan as Archduke of a small region, and the mortal kings and queens as Archdukes of the other regions. In either case, with a Chunk of Hell on Earth, the devils' options suddenly open up. Once Barony A becomes Stanhold, you can have as many devils as you want roaming the streets. They no longer need a densely-worded contract to stab you up the backside with a red-hot pitchfork for all eternity. They only need the pitchfork. [Answer] ## The diary is a ruse; the devil's goal is merely to corrupt the baron. He has no specific repayment in mind. His goal is simply to give the baron immortality in hopes that, like the parable of Gyges, freedom from the consequences of his actions tempts him into evil. What does an immortal ruler fear from an uprising of some peasant rabble? They don't have the devil's power on their side! (Yet.) What does he need with an heir, a family, the human connections that might stir his sympathies? He has no need to pass his lands on to anyone; he will reign for all time. And so, freed from the human frailties that might have kept his darker urges in check, the baron can become a great power for evil. But why demand anything at all? Well, everyone knows the devil doesn't just give you things. The devil's generosity is reason to be very suspicious indeed! Instead of merely giving the baron immortality and having the baron constantly wonder why, it's better to let him barter down the price for it and let the baron think he got away with a bargain. (Pride, too, serves the devil.) And if the baron does think that something's fishy about the deal, he's more likely to suspect that the price is higher than he thinks - just like you did, he'll jump to the conclusion that the diary is important to the devil. Like any con artist, the devil wants him to be certain of that wrong premise, because questioning it won't lead the baron any closer to the truth. By getting the baron to accept the premise that the devil is doing him a favor in granting him immortality, the devil is concealing the much greater benefit he gains from the baron's evil being meted out across the land, no doubt corrupting his followers in turn, and making the people of the barony desperate enough to call out for any aid... even a fiend's. The devil might be passing up a prize now (although the baron's soul is probably not going good places one way or the other), but for the promise of many more future prizes. [Answer] ## Installment Soul Payments A person's soul is a big, powerful, important thing that grows as they do. It cannot be sold when you're twenty, because you only have twenty years of it to sell. Of course, you can make a lump-sum bargain on your soul, offering to give it at the end of your life... but as the person selling your soul, you have to recognize that "If you make me immortal, I'll give you my soul when I die" has got some serious perverse incentives for Stan to subtly undermine the immortality he offers. So instead, you sell your soul in installments, paid continuously throughout your artificially extended life. Now, incentives are much more aligned: the devil keeps getting pieces of your soul as long as you live. Like the goose that lays golden eggs, the devil wants you to live as long as possible, as do you! This narratively fits very well with the character getting a new extension of life with every diary entry, like paying their credit card bill every month. As to the mechanics of how writing the diary entry sells the Baron's soul... well, I think anyone who has kept an intimate diary can speak to how much of their soul they put into it. It's a very intimate, personal thing, and as a symbolic act of surrendering your spiritual essence, it's quite resonant. The justification for why Stan wants soul energy in the first place has more to do with your magic/spiritual system, but "souls grant evil beings power" is enough of a classic story element that you probably don't even need to explain it. [Answer] # Psychometry, The Horcrux, and The Portal: Stan is in a bit of a bind. He's in exile, and his ability to do things outside the underworld is now really limited. He is, however, a really clever guy, and not too proud to get himself out of exile on the cheap. He's willing to take the long game and bide his time. [Psychometry](https://www.merriam-webster.com/dictionary/psychometry) is about a little bit of a person transferring to the objects around them. A person living in a house for years leaves a bit of themselves behind and haunts the place when they die. Objects close to a person reveal information about them because they are now tied to that person. In the course of a normal lifetime, the amount of a person (their "soul") transferred to objects is fairly small. But now you make someone fixate on an object, and do it for centuries. The Baron is slowly transferring his soul into the diaries. With his soul outside his body, the diaries are functionally like a [horcrux](https://www.dictionary.com/e/pop-culture/horcrux/#:%7E:text=A%20Horcrux%20is%20an%20object,wizard%27s%20soul%20into%20separate%20pieces.), protecting the Baron from death. He's slowly building a ring of bookshelves in his library imbued with his soul. These can be functionally a portal (like a [magic circle](https://roll20.net/compendium/dnd5e/Magic%20Circle#content), but in reverse), or they can be the power source to open a portal that is at the center of the circle (pre-built by Stan for one of these "Just in case" scenarios that has now come up). The Baron's soul will be the power source for opening the portal (Stan's escape hatch), allowing Stan to manifest in your world and escape confinement. As soon as the Baron is done transferring his soul to the diary, Stan can materialize, taking possession of the Baron's now-empty body and all of the Baron's armies, wealth, and power. Not a bad starting point for Stan. Has the Baron gotten immortality? Well, if it works, people will remember the Baron's role in unleashing Stan forever. [Answer] > > The Baron's immediate goals arise from his need to maintain this book. He is constantly desiring raw materials that he can use to manufacture new pages and other book binding resources. > > > This would not be a problem for a rich noble ruling a province. At least, not if the materials were ordinary parchment and ink, plus wood, thread and leather for ordinary bookbinding. One way that Stan could be corrupting the Baron is via obsession. If everything the Baron does is focused on maintaining the diary, on a grander and grander scale, that leads to the economy becoming distorted and the Baron's subjects undergoing increasing levels of suffering. That's effective corruption: the corruptee does all the creativity and work, Stan reaps the rewards. So the first volumes of the diary are quite reasonable: a page a day or so, in properly bound volumes. But the volumes gradually grow larger, with more expensive bindings, and increasingly detailed accounts of each day. After a couple of decades, the baron has a team of scribes whose job is to collect every word he says. A couple more decades and there are teams of artists drawing sketches of every scene of the day. A few decades, and the Baron insists on being observed at night, so that every change in position in bed is recorded; pretty soon he's having his mind being read day and night so that every thought and dream is recorded. Of course, he has to approve each day's record, which takes an increasing amount of his time. To make this easier, his days are pre-scripted so that the sketches can be done in advance, allowing the daily oil paintings to be produced in time. Since the Baron's staff and administrators share his obsession, nothing apart from the diary is treated as important, and the country gradually collapses. Outsiders who venture to suggest that something is wrong are expelled, or executed if they happen to disrupt a day's plan by disturbing the Baron's expression, making the relevant painting inaccurate. If you have read the [Gormenghast](https://en.wikipedia.org/wiki/Gormenghast_(series)) series, use that atmosphere, and turn up the obsessiveness of the rituals. If you haven't, it's strongly recommended. [Answer] # The baron [rules a breadbasket](https://en.wikipedia.org/wiki/Breadbasket) Many major empires have a bread basket. The Greek empires had Crimea, in the Ukraine. The Chinese had Sichuan. The Roman Empire had Egypt. Their vast harvests fed by the fertilizer of the Nile let them fuel an empire that stretched across Europe, Asia, and Africa. When the grain from Egypt dried up, the Roman Empire fell. The baron has an extremely fertile and wealthy country, with a well set up and efficient bureaucracy to collect taxes and administrate his territory. They supply a decent percentage of worldwide food- perhaps 20-40%, depending on how good harvests are elsewhere, and have trade networks that spread worldwide. # The baron funds wars. Due to their immense wealth, the baron has a huge amount of wealth and supplies available. Countries that want to go to war or do some expensive public order project often have to get a loan from the baron. Kings, emperors, and lords come from across the world to share stories and beg for the favor of the baron. Their notes of money are valuable from the densest stone cities to the deepest green forests. If there's a large project somewhere, there's a good chance the baron is involved. # Stan gets supplies, information, and influence. They can vary the material needed for each diary. While the early ones may have been simple ink and paper, the later ones could be human skin, elf skin, demon skin, ink from a rare squid in the deep ocean. By varying the needed materials for the diary they can encourage the baron to influence the world and gather information in useful ways. They can also encourage religious development that directs food supplies to their own armies. [Answer] ## The Baron is Stan's telegraph Do anything very many times and you'll eventually do it unconsciously. A pedestrian example: the first time you washed the dishes, you had to pay attention to each dish -- how to hold it and rotate it as you scrub it, which parts require the most cleaning, etc. But now you're an adult who has washed the dishes thousands of times, and you can do the washing while watching TV and mentally planning your day: you're completely absent. Thus it is with the Baron. The price of immortality seemed trivial when he made the pact, but he had a second think about it when he sat down that first night to scratch out the first of (hopefully) a million "Trew & Compleat" diary entries (as stipulated by his contract with Stan, signed, as you would expect, with his own human blood). Try it some time; you'll find it's harder than you'd expect. But the days turned to months, then years, then centuries, and, practice making perfect, it did get easier -- so easy that the Baron even failed to notice the occasion of his 100,000th diary entry (very near the end of his 274th year of immortality). These days he hardly gives it a second thought: sit down at his writing desk, grab the quill and ink pot, do a quick jot, then off to bed. (A servant collects the page and places it with the others, to eventually be bound together into a volume.) In all honestly, the Baron probably couldn't tell you what he wrote last night. And that is precisely how Stan likes it: > > Automatic writing, also called psychography, is a claimed psychic ability allowing a person to produce written words without consciously writing -- [Wikipedia](https://en.wikipedia.org/wiki/Automatic_writing) > > > The Baron has been unknowingly transcribing Stan's direct orders for his secret cultists here on the mortal plane, orders he receives through a spiritual link established between the two of them as part of the immortality enchantment. That is what flows from his hand while his mind is elsewhere. The servant who collects the pages is one such cultist, hired for that purpose at the Baron's own (unconsciously) written instruction in a note left with one of his diary pages in the early years of the project. These days, the "diary entries" read just like telegrams from Hell, because that's what they are: orders for assassinations, instructions for growing the cult, letters of introduction used to establish links between sympathetic conspirators, threats that must be delivered verbatim to some target, intelligence gathered for the purpose of corrupting or blackmailing powerful people, etc. The Baron's private library now boasts some three hundred volumes of The Life & Times of Baron K----, each painstaking assembled, by a long succession of the Baron's assistants, from 365 pages of fine writing paper. Except for the first three volumes, every single page in every book is blank. [Answer] > > The Baron knew the deal was too good to be true. Immortality for the price of a dairy? But his goals require risk, and so a risk he took. Then when the Baron was in danger, Stan provided a second deal - tear out a page in your dairy, and you'll have the power to defeat your foes. So the Baron did - the instant the page was torn free, a foul and mighty pit fiend stood in his place, mercilessly crushing his enemies. And so Baron found the ploy - Stan had planned this to put unlimited power within reach, each time costing a bit of his soul. > > > > > Seemingly secure in his knowledge of Stan's plan, the Baron hoards the pages in his dairy, only using them in the most dire of situations. Stan of course manipulates things so that the Baron is tempted to pull a page, but can always just avoid doing so - the Baron narrowly "defeating" Stan each time. > > > > > Of course, that's just what Stan intends the Baron to believe. Stan is patient - if one page temporarily unleashes a mighty pit fiend, what would two pages do? Ten? A thousand? A million? The Baron is far too smart to do such a thing. But one day, a wily hero will notice the Baron's obsession with the book, and think "surely this must be the source of the Baron's power?". That hero will steal the book, destroy it - and unleash hell. > > > The dairy is a portal to hell - each entry the Baron makes is an opportunity for Stan. When a single page is pulled, Stan empowers Baron, giving him his Jekyll/Hyde thing. But if lots of pages are pulled at once, Stan could get an army through. If enough pages are pulled, Stan himself may be able to get through. And if that doesn't work, it's still not a complete loss for Stan. The Baron never did think what happened to the pages after he discarded them... [Answer] It is much simpler. The diary is a gimmick, but it is also important. The important things in it are that (1) Baron is asked to use specific ingredients for ink, and (2) is asked to include at least one paragraph describing his surroundings. At the time Stan was banished, this was the only thing he managed to set in motion -- the agreement with Baron. ## The diary is linked to Stan in a way that allows Stan to portal to the place described in diary... but only during the day the entry was written in. So he needs a new entry every day. And he needs the particular mortal who knows what to do. Hence the immortality. The previous entries are useless, but since he is not confiding his plan to Baron, Stan might impress Baron to keep them intact, as a red herring. Stan is usually not using the portal, but he might have risked using it once or twice. It is part of a plan set in motion that will allow him to enter the world when he is ready with his fiendish army. [Answer] 1. The diary itself is designed to corrupt Each page of the diary must be made of parchment made from an intelligent creature, and inked in blood of the same. The baron must choose to kill and defile constantly corrupting his soul. 2. it's an experiment. Many stories tell of how immortality can be a curse, but your devil is skeptical, so he gives it to some random yahoo with the requirement of documenting their life so he can find out if it really is awful in the long run for mortal beings. 3. The baron's soul is important not the baron. Your devil is keeping the soul out of circulation by making the baron immortal, but he needs it to be the baron's choice to maintain it, he can't just screw up the cosmic balance on a whim he needs the mortal to choose to do it, hence the diary. Bonus, the baron gets to find out his death really would make the world a better place. 4. the baron is a roadblock to destiny. Someone favored by one of the positive realms is supposed to take over the baron's land/title when he dies and work some great good, making the baron immortal screws that up, the diary is just a McGuffin, but the sides of light might target to get the baron out of the way. Expect attempts to destroy the diary. Bonus moral conundrum for the baron if they find out. 5. the hubris red herring. Unbeknownst to the baron, he is not really immortal, just when he "dies" someone else dies in his place. The baron's cavalier attitude towards death is causing immense suffering. Works even better if the person who dies is one of the baron's peasants/subjects, or if they are all people from some remote village which the baron can later discover. The diary is just a red herring, although there is the bonus is after finding out the baron can now go back and learn how many people have died for his bargain. Bonus if someone else puts it together before the baron by reading/stealing the diary. 6. combine several of the above, devils are intelligent they have plans within plans, no matter what happens it is win win for the devil. [Answer] The archetypical way gods work in stories is Gods create sentients, sentients create faith, faith powers the Gods‚ô§. The Baron's diary will be scrutinized by Stan and his followers, and from it chapters will be made that will form the Great Book of Stan. This will be brought to the people who will read it (or have chapters told to them by followers) and will teach them the laws, wisdoms and advantages of having faith in Satn\. This diary is to eventually generate a religion around Stan with the Baron as his immortal prophet, proof of his power and the rewards of eternal life you will receive‚ô°. This creates a compelling reason to stop the Baron because if they dont then Stan. Will. Return. ‚ô§alternative: sentients exist and have faith, create Gods. \oops, imagine if I accidentally added an A rather than swapped the position! Copyright might have ensued! ‚ô°please ignore the soul furnace at the end of the tunnel. [Answer] # Long term investment There is a scene in Good Omens where Crowley, a demon who is always up to date with whatever is trending, meets two of his colleagues who spend most of their time in hell. They talk about their achievements. Lately one of the demons has corrupted a priest, and the other has corrupted a child. Meanwhile Crowley has turned off all cell phone signals in London during lunch time. The other demons don't understand the scope of this, but Crowley has managed to turn thousands into violent, swearing people (if only for an hour), causing ripples of evil that will spread through history. Later in the book Crowley faxes Microsoft Windows's End User License Agreement to hell, along with a note saying "learn, guys". --- This is just to say that the evil that is now doesn't have to be big. It just has to be a seed. The Marquis of Sade's One Hundred and Twenty Days of Sodomy [1] and his other works have much more impact nowadays than it did some 300 years ago. Likewise, with your baron, you have a work of evil art that will reach new heights when the printing press is invented. People will be inspired to do evil - or to accept evil being done to them - after reading that book. [1] This book exists and features things such as a judge sentencing a man to death because he wanted to have sex with the man's daughter. The judge then promises the man's family a pardon in exchange for sex, has the sex, but has the man hanged anyway, in front of the man's daughter as he ravishes her. That is one of the least evil deeds in the book. [Answer] The diary is a loophole I like the answer by Cadence, but I think the diary can serve an additional purpose. Think about it... Can you maintain a diary for eternity ? Are you sure you won't miss a single day, forever ? This gives great flexibility for the Devil to just cancel his side of the deal whenever the baron is not useful for him anymore, because it is highly unlikely that the baron will have exactly fulfilled his side of the deal, especially if the Devil requires some specific things to be in the diary, but intentionally does not check on them for a long time at the beginning. [Answer] He's got the barony exactly the way he wants it, and he wants to keep it that way. He foresees that inheritance would muck it up -- anything from an observation that heirs often differ, to a vision that the heir will be a paladin who will consecrate the barony to a god of good. Immortality will keep him in the world. The diary will keep him in the barony, because if the diaries are destroyed, he loses the time. Furthermore, making a new diary is not cheap. He uses vellum, which lasts. For every volume, he must breed so many ewes to get so many lambs to get so many sheep for the sheepskin, and the making of the book is not cheap. Fleeing the barony will make this impossible. Besides, he can rules lawyer a way that the Baron did it wrong if he wants out. [Answer] The devil uses the content of the diary for corrupting other men and gain new souls. Sure, the devil can corrupt men on its own, but having a diary written by some human can be more effective at corrupting its peers. Instead of "lead by example", it's "corrupt by example". Stan needs just to write about his debauchery in the diary, and for sure his immortality and wealth will not make him lacking inspirational material. [Answer] "Your words shall be written in the purest blue with ink made from crushed lapis lazuli, written on pages from trees which outlasted many generations. All you have written as such shall be your diary, and both the words on the inside, as well as your thoughts about them or the diary on the outside shall be known to me. In return I promise: For as long as your diary grows, I will grant you unending life and a healthy, powerful body." Magical materials for magical communication, and the materials are quite rare at that. On the surface, it looks like Stan is betting that the human eventually will fail to acquire them, while the human is betting the opposite. Unbeknownst to the Baron however, his body got a new ability: To transfer some of his energy into the pages he writes, as long as he uses the specified ink and paper. Multiple centuries, and ten thousands of pages later, the diary has become a magical powder keg - or a powerful resource. At some point, the Baron probably has noticed. But what is he supposed to do about it? He can't get rid of it - it is literally his life line. He can't tell too many people about it, after all it's a treasure in itself. And spreading it out isn't an option either - if just one of his hideouts gets destroyed, it will throw him back more pages than he can write in the time he has left. ]
[Question] [ I'm currently trying to create a separate kind of Earth, without just changing my setting to a world that fits my criteria. So I'm trying to figure out a way for Earth to have a new beginning, so that I can develop an entirely new world, while also maintaining the aspects of this one, with minor details changed. So let's say that an asteroid hit Earth. Would it be possible that it could set off a nuclear bomb, and possibly create a chain reaction of explosions that wipes off all life from this planet? [Answer] The meteorite started the war. The country hit by the meteorite considered the impact an indirect attack by the nations that did not warn them. For example; foreign space agencies collectively refused to inform Pakistan of the meteorite about to hit them. Pakistan is justifiably angry at every space faring nation, particularly India due to past conflicts. Given the chance of a nuclear war, NATO intervenes which China fears is western influence in Asia. This spirals to bring in all other nations. Alternatively, the country hit is considered unable to retaliate and another nation takes the chance to defeat another nuclear power. Again an example featuring Pakistan and India; the meteorite destroys what is thought to be India's best protected nuke silo and Pakistan thinks it can destroy all of India's other nukes before India can strike back. This turns out to be wrong, and India retaliates with its remaining nuclear weapons. Again, the conflict brings in other nuclear armed nations leading to a general nuclear war. [Answer] Yes and no. An asteroid, or any impact really, cannot set off thermonuclear warheads, in the sense of causing a nuclear blast. These warheads are composed of disks of conventional explosives that have to go off in an extremely precise manner in order to achieve a proper nuclear detonation. If that doesn't occur - if they go off in any other configuration - all that happens is a modest conventional explosion. (It's fairly radioactive, similar to a "dirty bomb", but more importantly it's fairly small.) However, an asteroid is totally capable of wiping out life on earth all on its lonesome. You might look up the [Chicxulub impact](https://en.wikipedia.org/wiki/Chicxulub_crater), which caused extinctions on a massive scale although, obviously, it didn't totally destroy life on earth. But the next one could be bigger, if you want. [Answer] Not With An Asteroid Nuclear bombs are not giant snap-caps just waiting to be jostled wrong to detonate. Outside of human error or intentional warfare a majority of nukes will not detonate. Quantum Effects It has been observed that some quantum particles can induce fission in fissile materials on at least a small scale. Years ago I spoke with a nuclear physicist about some sort of muon or gluon gun that could fire through the earth. Such particles have very very little interaction with most matter, but could, at high energy levels and in massive concentrations, be used to induce a fission reaction in the fissile material of a nuclear weapon. In nature gluons and muons do not exist freely, but are found in the substance of an atom's structure. It would be massive handwaving here, but some sort of crazy powerful gluon pulse could induce nuclear warheads to begin fission and generate at least a low yield detonation. But we're talking a LOT of handwaving. Why Bother With Nukes Though? The gamma ray burst from a supernova could scour life off the planet down to a molecular level and occur naturally in space all the time. Why not just use one of those in your story? [Answer] No. Nuclear weapons are designed so that they cannot detonate by accident. Even if you had one inside a briefcase and dropped the 'case from a building, it wouldn't go off. And if you want terminate life on Earth, worry not: just take an asteroid of pure iron, twice the size of the dinosaur-killer, and you'll make sure to have a long-lasting nuclear winter. The food chain will completely collapse, save for extremophiles, insects, some marine life form at the bottom of the oceans. With some luck, rats could thrive enough on the many cadavers left until they become the start of the new dominant life form in a million-years long future... [Answer] Not with current nukes because of physical shock, modern nukes are way too complex and stable. There are two ways something could happen though: * the asteroid is a source of unimaginable levels of neutron flux. This would lower the effective critical mass for the radioisotopes in the core of nuclear weapons and cause them to detonate without being triggered. Before it did so it would also kill all life on at least half the planet without ever touching down. * if Implosion Core weapons were never invented, and/or if nukes used more volatile conventional explosives in their triggers. That would leave you with Gun style nukes which could feasibly be dangerously shock sensitive, and go off during large earthquakes, or bombing raids, etc... Neither of these solutions give you any kind of worldwide chain reaction but do open the door for localised unforeseen detonations because of a celestial impact event. [Answer] You might consider if the following scenario fits your needs: A huge asteroid is coming towards Earth. Because people are scared, they decide to attack it with nuclear missiles. Some scientists/engineers say it will be enough to attack it at one particular point. Others say that that's entirely wrong. Attacking it in that way, at that time, will just create a giant cloud of radioactive (from the nukes) debris. It turns out that the latter scientists were correct. This gives you the radioactive fallout problems of a complete nuclear launch while avoiding the problems associated with accidental triggering or a nuclear war. It really depends on what is important to your story. There are any number of ways of killing off everyone with an asteroid. You don't need a nuclear launch. There's also any number of ways to have a nuclear war. You don't need an asteroid. If for some reason, you need both nukes and an asteroid, this should give the result you want. [Answer] There are two main pathways by which the asteroid could detonate the nuclear weapons: either through a chain reaction or by simultaneously triggering all of them. # Chain reaction This variant assumes that at least a couple nuclear weapons are set off by the impact, and these in turn trigger the others. This is unlikely; [the Tsar Bomba](https://en.wikipedia.org/wiki/Tsar_Bomba), the most powerful nuclear weapon detonated to date, had a yield of 50 megatons of TNT - much, much greater than any weapon we have today - and caused damage hundreds of miles away. For comparison, if we look at [the current arsenal of the United States](https://en.wikipedia.org/wiki/Nuclear_weapons_of_the_United_States#United_States_strategic_nuclear_weapons_arsenal), we see that the common [W87](https://en.wikipedia.org/wiki/W87) and [W78](https://en.wikipedia.org/wiki/W78) have yields of about 1% that of the Tsar Bomba. The [W76](https://en.wikipedia.org/wiki/W76) and [W88](https://en.wikipedia.org/wiki/W88) are even smaller; to replicate the Tsar Bomba's effects, you would need to detonate many of them together in a small space. If you could do this, then you could impact structures and weapons for hundreds of miles around. But if warheads were only triggered in a couple of silos, the damage would be minimal, and limited to small areas; other launch sites would probably not be detected. If we look at [where the weapons are distributed](https://fas.org/blogs/security/2009/11/locations/), we see that the operational storage sites (in red) are far apart in the United States. [![Map of nuclear weapon distribution](https://i.stack.imgur.com/AJi0t.jpg)](https://i.stack.imgur.com/AJi0t.jpg) Map from the Federation of American Scientists. Granted, each site then has a large yield, but you'd need all of the weapons at the site to be detonated at the same time to have any effect on the other sites. The same is true around the globe, although western Russia does have a higher density. # Simultaneous detonation Now, alternatively, you could try to set off all the weapons at once. Here's the problem, though: you'd need a heck of a big impact to do this. [Neither the US nor Russia has a majority of the world's deployed nuclear weapons](https://en.wikipedia.org/wiki/List_of_states_with_nuclear_weapons), so you'd need to set off weapons across at least one country and then some. This would require an impact of colossal size to even reach, by some means, warheads thousands of miles away. Again, see the map above. Of course, you could go for some sort of seismic activity. After all, the [Fukushima disaster](https://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster) began when a tsunami disabled critical parts of the reactor, and the seismic waves generated by a large impact would be severe. Nonetheless, this would still require a massive impact, and given that nuclear weapons systems can withstand some pretty strong earthquakes - there have been no seismic-triggered detonations to date - this seems unlikely. The farther from the point of impact, the weaker the seismic waves. # Human error Now, there is a third possibility, which is that a nuclear weapon would be triggered on a nation's soil. If the weapon wasn't detonated but was somehow launched - and I'll be honest, this is a really improbable scenario - that it's possible that the target nation would see this and consider whether the launch was an accident or a deliberate assault, with the impact as cover. At that point, you do have the risk of intentional, manual nuclear retaliation, and that could maybe achieve your goals. But that's a pretty far-fetched scenario. --- I've purposely shied away from an even bigger problem: How would the object even set weapons off? [Cadence talked about how there are a whole bunch of things](https://worldbuilding.stackexchange.com/a/115740/627) that would have to happen for a single weapon to be detonated. So this asteroid would have to somehow destroy the sensitive systems that prevent accidental (or malicious) detonations without damaging the warheads themselves. All that said . . . [NASA has space rocks monitored](https://cneos.jpl.nasa.gov/stats/) fairly well. If something big was coming our way - big enough to impact an entire continent (pun intended) - then we would know about it long in advance. That would give the world time to plan and, more importantly, disable nuclear devices if it seemed like there was even the risk of some accidental detonation. [Answer] Yes. Though highly improbably (and highly implausible), the impact of a sufficiently large extra-planetary object with the earth at the right spot could detonate the majority of earths nuclear weapons. Due to the precise timing required to actually detonate a nuclear weapon, all nuclear weapon designs in existence have a small vulnerability in that an energy signature (wave, fluctuation, etc.) at a specified frequency for a specified time could potentially arm the weapon. A meteorite impact on the worlds largest quartz deposit would cause a [Piezoelectric event](https://en.wikipedia.org/wiki/Piezoelectricity) that could very well cause this exact energy disturbance, unknown to the current world powers. The impact itself could release several different signatures as needed by the story, due to tumbling or other stage impacts from the event. DISCLAIMER: a bunch of this is likely pseudo-science, but I tried to stray away from any hand-waving or suspension of disbelief. [Answer] The problem is what it takes to compress a nuclear warhead to critical mass if you forego the extremely precise triggering mechanisms they use. That said, theoretically, a sufficiently large antimatter bomb falling from orbit could create a blast powerful enough to do it... On the other hand, once you get to that point the extra explosions will likely go largely unnoticed by the expanding cloud of gas and gravel that used to be called Earth... Now, there are a few other possibilities that might give you what you want. For example, there are some rumours that the Russians may have cracked their tectonic plate testing nuclear bunkerbusters. If multiple countries in just the wrong places did something like that, it might be possible to trigger a crust slip. That would cause tsunamis worldwide and rearrange the climates of our various land masses by moving them to other lattitudes. If nuclear isn't a requirement a set of asteroid impacts at just the wrong angles might do the same thing. I suppose you could also have a largeish meteor land in Yellowstone ( <https://en.wikipedia.org/wiki/Yellowstone_Caldera> ) and set that off. That could easily cause the end of modern civilization as well. ]
[Question] [ Background: in [my setting](https://worldbuilding.stackexchange.com/questions/209979/how-does-one-defend-a-military-depot-against-nazi-ish-sasquatch-vampires-in-a-co), there's a regional-scale nuclear war across most of Europe that primarily uses [gun-type](https://en.wikipedia.org/wiki/Gun-type_fission_weapon) and [boosted fission](https://en.wikipedia.org/wiki/Boosted_fission_weapon) weapons. Essentially, mash [this map](https://en.wikipedia.org/wiki/Nazi_Germany#/media/File:Greater_German_Reich_(1942).svg) and [this map](https://en.wikipedia.org/wiki/Roman_Empire#/media/File:Roman_Empire_Trajan_117AD.png) together, and assume a level of development/city-building roughly equivalent to 2020 IRL, other than the fact that nukes are rather new. Then, hit every population center, military facility, shipyard, strategic command center, or other semi-important node on the fusion of those two maps with a fission bomb. Basically, civilization is dead in that section of Europe. Now, let's say that most of the world mobilizes as part of a disaster-relief effort comparable in scale to WW2. Again, the worldwide level of development is somewhat similar to 2020, meaning that, given time, they probably will reconstruct that region. However, you can't have a post-apocalyptic story with Nazi sasquatch vampires (long story) in it without having a post-apocalypse, and so if that relief effort gets into place, it seems like things would be boring story-wise. Therefore, I'd like to drag the post-apocalyptic period - i.e. from when the bombs drop to "bare minimum functionality" - out a little. I define "bare minimum functionality" as "there are structures set up for delivering aid, everyone generally knows where everyone else is, and things are generally not 'Mad Max' anymore" - think the beginning of [post-hurricane cleanup and reconstruction](https://en.wikipedia.org/wiki/Reconstruction_of_New_Orleans), but across all of Europe. Question: after a devastating nuclear war that occurs in Europe, why would it take years to decades for the area and its occupants to receive external aid? I was considering using the [Marshall Plan](https://en.wikipedia.org/wiki/Marshall_Plan) as a data point here, but, unlike IRL post-WW2 Europe, things aren't "shattered" or "impoverished" but still there; they're gone. [Answer] Famine in Asia. I was reading about the [Laki eruption](https://en.wikipedia.org/wiki/Laki) in Iceland in 1783. It caused global cooling and crop failures all over the world; also terrible flooding in Northern Europe because of the early freeze and subsequent melt. After a nuclear war this would be called [nuclear winter](https://en.wikipedia.org/wiki/Nuclear_winter). I was interested to see that the Laki eruption was only mentioned in the additional reading section of the wikipedia article but it is definitely a historical precedent for this type of thing being possible. Aid is slow to come because there are lots of people who need aid elsewhere. The population of Europe is only a small percentage of what it was but there are still lots of people in other parts of the world. When crops fail because of the June freeze those people will go hungry. Persons in a position to send aid send it to regions where masses of people are starving, not to the few survivors still hunkered down in the ruins of Europe. It takes a couple of years for Earth to shake off the nuclear winter. And during those years, bad things happened elsewhere that continued to be bad once the world warmed up. The rest of the world is not the same when the skies clear. It takes a while more for the rest of the world to sort out their own affairs, and then they start wondering what is going on in Europe. [Answer] ## The europeans left automated nuclear weapons ready to launch nuclear missiles against countries which helped out. The europeans didn't want outsiders coming in to invade them, and so left hidden nuclear weapons in mountain silos and submarines looking for large concentrations of people moving machinery into their countries. Unfortunately, this is what aid workers look like. Several surrounding countries that supported aid got nuclear strikes, and efforts to rebuild cities have also attracted nuclear strikes. No one knows how many submarines or silos there are left, or how many nuclear weapons are left, and no one wants to do anything with the region in the near future. [Answer] ## The scale of the problem and the contamination left afterwards. Conventional natural disasters and wars don't have the added element of fallout to contend with. If as you say the war involved nuclear detonations across wide regions of Europe and the Med then the scale of planning and logistics required for any relief effort would be huge and hence require years to implement. As an example after the 2011 earthquake in Northern Japan relief efforts for that disaster were commenced immediately by the Japanese government with cleanup up/disaster relief in most areas proceeding apace. With the single exception of Fukshima where one single issue - radioactive decontamination vastly slowed down and complicated relief and repair efforts. Allowing for the fact that the contamination issues from bombs and melt downs are by no means identical the simple duty of care owed by other nations to their own citizens (EMT workers and soldiers) assigned to the relief effort would vastly slow things down. There simply wouldn't be enough decon equipment available to let people move about safely for extended periods of time. Note; This is especially relevant because the fallout from the war (environmental, economic and social) would reach far beyond Europe shores and many nations would have to deal with panic/emergencies at home before they could respond in mass. Some initial relief parties might arrive quickly but all they could do is establish beachheads in relative safe zones and then deal with any refuges who make it to those zones (probably all on the coast because most large airports would probably be unusable and in general Europe's transport infrastructure - highways/bridges railways airports and canals etc would be badly damaged. So there would be outposts on the coast and perhaps elsewhere from which relief would have to slowly work its way outward over years. (Especially if as you say there are resident dangers/monsters making progress even more dangerous.) In fact after the first few months or so anyone who can be 'saved' probably would have been saved. This is because without immediate help many of the survivors/injured would die anyway unless they reached a safe zone under their own steam. The main initial effort might simply be to send 'rescue' parties to recover VIPs and important works of art etc. [Answer] ## Great Depressions, war fears, Racism, Pandemics, Politics, Paranoia: There are all sorts of reasons that a world relief movement would stall out, so let's go into a few. * Massive Recession(s): The war triggers a massive economic disruption, and global economies withdraw sharply. Rather than spend billions of dollars on trying to rebuild the devastated region, governments instead use funds to shore up their own economies. Token relief goes out, mostly civilian-driven efforts. * Fears of War: The societal restrictions on nuclear war are lifted, and everyone fears the outbreak of the next big one. The influences of the destroyed powers have thrown geopolitical balances out of balance, and dozens of small wars and revolutions start. Terrorists bomb relief ships, and the remnants of the two sides may STILL be at war, or extremist groups within/near the devastated region are still trying to "win" the war by the most brutal and ruthless means necessary. * No Jews or Irish Allowed: The war has caused old racial tensions to rise, and preachers on TV tell people the folks in country X are wicked killers who got what they deserved by starting a nuclear war; God has punished them and giving them mercy would be challenging the word of God. Former colonial states of the warring powers lobby the UN to stop relief efforts, and the current head of the UN is one of them. Refugees are actually sent BACK to the war zone from safe havens elsewhere. While not enough to stop all relief efforts, they could certainly rob them of almost all energy and enthusiasm. * Pestilence: Alongside the nukes, someone has unleashed para-anthrax, super-smallpox, and several other diseases from labs on purpose or accident from the war zone. Besides the massive disruption to the globe from diseases, people fear going into the war zone and potentially unleashing a new wave of pestilence upon the world. Experts agree the region should be sealed off and aid placed at the periphery to prevent the spread of new illness. * Political Rivalry: The allies of side X are still at odds with the allies of side Y. Both sides want to help their former allies, but each is ready to go to war with each other, and the waters/trade routes to move supplies into the region are embargoed. Both sides blame the other for the standoff, but are each willing to let the people of the region suffer for political gain. Aid dribbles in, but it's tepid at best. * Fear of the Unknown: After the conflict, aid starts to pour in, only to dry up as people start telling stories of radioactive mutants, superbugs causing disease, and Nazi vampire mutant sasquatches. Conspiracy theorists tell people it was all a scam, and there was no war - it was done with miniature cities in a studio in Hollywood. Or the Nazis are using the aid to build the 4th Reich with genetically engineered super-species that will conquer the world. While OBVIOUSLY fake (MUTANT Nazi vampire sasquatches? How can anyone believe that?) millions of people do believe, and oppose aid. A few countries even actively disrupt aid efforts to contain the threat. While aid gets in, it's not nearly what people in the region need to rebuild. [Answer] After the initial wave of relief effort, nobody cares enough to follow through. We have areas of the globe today that have suffered disasters where the relief effort has not yet fully mitigated the effects of the disaster. The damage from the 2010 Haiti earthquake, for example, was never fully repaired - and they now have another another, larger (by the Richter scale) earthquake to deal with. Your future history can feature an initial burst of recovery activity, complete with self-congratulatory press conferences by the aid-sending nations - and then a couple of decades of bad follow-through, with half-hearted and contradictory efforts being launched and then abandoned, with corruption eating up most of the aid funds before anything practical actually is accomplished. It wouldn't require anything particularly dramatic; it just requires business as usual. [Answer] Look at what's been hit: > > Then, hit every population center, military facility, shipyard, strategic command center, or other semi-important node on the fusion of those two maps with a fission bomb. > > > Aid doesn't magically teleport itself to needy individuals. Your war has systematically destroyed the transportation infrastructure for an entire continent. Getting aid to anywhere except the coastal cities requires rebuilding that infrastructure. You're comparing the relief effort to World War II in level of effort, so that suggests two points of comparison: * The [Berlin Airlift](https://en.wikipedia.org/wiki/Berlin_Blockade). It took the entire airborne logistics capacity of the United States and British militaries to supply just half of one city by air. * [Operation Barbarossa](https://en.wikipedia.org/wiki/Operation_Barbarossa). When the Germans invaded the Soviet Union, they were unable to use the existing logistics network (the railroads were the wrong gauge, and major roads mostly didn't exist). Three years later, when they were forced back out, they still didn't have a working logistics network. Rebuilding a continent-scale transportation network is hard work. The US Interstate Highway System took 35 years to build; even the original, highly-optimistic estimate called for 12 years of construction. The "everyone knows were everyone is" part will happen quickly, but areas away from the coastal cities will see little beyond the occasional air drop or survey party for years or even decades. (Hitting Babylonia isn't helping things: everyone's first priority will be getting the oil wells working again.) [Answer] They don't offer them aid. They offer them escape. Those coming to the rescue regard the population density as too low to maintain an industrial civilization, especially as all the best sites for cities and such are now rubble. This reduces the population still more. It consists of those who refuse to leave. This could be modulated with some aid if that produces a better setup, owing to differences of opinion. [Answer] ### The US stays out of it After 1940, Germany could not have invaded Britain; but then again, it would have taken substantially longer for Britain (and the Commonwealth; don't forget the Aussies and Kiwis, nor Indians and others) to have sent an army back to mainland Europe if they were on their own. The Brits had the largest and best navy in the world, and the Commonwealth/Empire had massive amounts of merchant shipping. After initially-disastrous raids by U-boats, the Brits got a grip on things, and after 1943 serving in a U-boat was basically just a question of how long until you died. Germany was completely resource-starved by then, so the Brits could simply had waited them out until they ran out of fuel to run vehicles and planes. Which leads to why Hitler went into Russia in the first place, which was a land grab for oil reserves. If the war in Russia went the same way as it did for us, then the Red Army would have swept back across Europe whilst the Brits were still on the other side of the English Channel. Maybe the Brits would have hopped across into France in 1945 as the Red Army were pushing the other way, so the Soviets would have stopped at the German border; but maybe not. Then the nukes happen, across mainland Europe and Britain. Germany is already crushed and can't help themselves; and the countries they conquered were already well past starvation anyway. The Red Army are overextended past their supply lines, and Stalin fundamentally doesn't care about anyone either. Britain was the remaining major industrial power in Europe, but it will have been nuked to a fare-thee-well. But separately, Japan never bombed Pearl Harbor. Until Pearl Harbor, the US was perfectly happy to keep war in Europe at arms' length and say it was nothing to do with them. So once the war was over, what incentive would there have been for the US to get involved in reconstruction? Remember that the Marshall Plan was never about charity. It was a profoundly capitalist, profit-centred move. For sure it helped the civilian population massively - but the major reason it took place was to gain substantial US control over technology and manufacturing, as well as significant involvement in the rebuilding work which is always a boom industry after a war. If there isn't a profit to be made, the US simply would not be there. Humanitarian organisations would naturally be involved, of course. Whilst the US as a country would stay out of it, individual US citizens would certainly be making charitable donations. This is never going to happen on the scale of government assistance though, and there is no United Nations to coordinate relief efforts (remember that the UN was founded explicitly as a response to WWII). Rebuilding is going to be very much piecemeal, and it's going to be dependent on people getting to the aid centres on their own. Simply dealing with those survivors properly will be beyond most relief efforts, never mind going looking for survivors elsewhere. [Answer] There are three factors: 1. After initial nuclear strike exchange Europe has been deemed a no-go zone. For real life examples please see [the Rogue Zone from WWI](https://en.wikipedia.org/wiki/Zone_Rouge) or [the Chernobyl Exclusion Zone](https://en.wikipedia.org/wiki/Chernobyl_Exclusion_Zone). To adjust the actual level of contamination to your plot read the last sentence of 3rd factor. ;) 2. As fires from nuclear strikes released enormous amount of soot into the atmosphere, people all around the globe suffered from [nuclear winter](https://en.wikipedia.org/wiki/Nuclear_winter). That made them unsympathetic to Europeans, as they face humanitarian crisis themselves as well as blame Europeans for what happened. 3. As European's economy, culture and population has been destroyed, no politician cares about Europe anymore. And common people have no problem with that, as they believe that Europeans got what they deserved. Moreover, conscience of average man is clean as it is common knowledge that Europe is unhabitable. As the common knowledge is convenient, nobody is interested in factchecking it. [Answer] In addition to other answers about the effect this would have on other countries: From your description there are a couple of things that stand out as obvious answers to your dilemma > > other than the fact that nukes are rather new. > > > If nukes are new, how well do they understand radiation? The first aid workers to come to the area all start getting sick so they pull out, or possibly just the fear of the newly discovered radiation is enough to stop them even coming in the first place. Have they even developed suitable shielding / treatments to make it safe for aid workers? Maybe 20 years later they finally have suitable NBC suits to allow safe investigation of the area. > > unlike IRL post-WW2 Europe, things aren't "shattered" or "impoverished" but still there; they're gone > > > Combined with a reluctance to put their aid workers at risk, with that level of destruction it might be logical for people to just write off the entire area as lost, why put resources into fixing it when you have your own problems to deal with [Answer] ## No one likes Europe anymore Why was there a nuclear war in the first place? European countries differences started to become more and more apparent as they couldn't agree on basic subjects anymore (some wants multiculturalism, others don't. Some wants religious society, others don't etc...). The European Union shattered as it was impossible to run anymore; its members started to not recognize it and not apply its regulations. US, China, Russia etc... at start used this to push their own interests but never intended their allies to go that far. As China today is embarassed by its North Korean ally, US and other involved countries got very embarassed too when their European allies started a real war, even more when they used nuclear weapons. Now most of the non-European population sees Europeans as stupid aggressive people that made the unthinkable for stupid reasons. They deserve what they got. Why spend hard-earned taxpayer's money to help them? [Answer] ## Nazi sasquatch vampires (And their thralls) guarding the perimeter keep people out. Admittedly, this is a large border, but this'll become a bit easier once they start resurrecting the nuclear dead, or intercepting foreign aid groups. Foreign aid groups might actually make it easier to uphold the charade - "Oh, things are totally fine here, we're doing our best - they're even recovering!" or "Maybe send some more crew to the same port - we found plenty more needing help here.". Letting the outside world think they're helping while not actually successfully helping. Worst case scenario - the bluff fails, and everyone knows their aid attempts fail spectacularly due to the vampires keeping them from succeeding, and if you succeed, well then the vampires can keep up the masquerade and effectively blindside everyone when they find out what actually is happening. ## Other, non-nuclear conflicts break out in the rest of the world The U.S. has an often discussed and criticized policy of being able to fund their army to be able to run a [two theatre war](https://www.britannica.com/topic/two-theatre-war). Even at the largest funding it had there, they're looking at 2 major conflicts and one limited conflict. But the map you're presenting isn't that large a portion of the world; give the U.S. three major conflicts that aren't Europe. You've still got all of Asia, all of Africa, and all of South America to choose from, let alone a possible Civil War breakout making them have an additional local conflict. Even if Europe is a strong contender for foreign aid, you're indicating that civilization is basically dead in Europe - perhaps at a glance, the U.S. looks at that, goes "Well, that's horrible; we have to intervene elsewhere and make sure nowhere else ends up like that.". Basically containment of conflicts to keep them from having to aid another region is what's keeping them from aiding Europe at the moment. Especially if they're aware of the whole Nazi Sasquatch Vampire situation. For bonus points - have the non-nuclear conflicts break out nearby nuclear countries. That can give you a potential read on the global news as Europe is hoping those conflicts don't go the way theirs did. [Answer] ## Frame challenge, there is no such thing as a "local-scale all out nuclear war" If there is a nuclear war across Europe there is a nuclear war across the entire globe. There is no such thing as a "regional-scale" nuclear war. Especially not one that results in the total devastation of Europe. this is far far less believable than reconstruction taking decades. You can set aid whenever you want because there would be a decent chance it would not be aid but full recolonization or reconstruction. You don't know how long the war lasted elsewhere. The war in Europe may be over but the war elsewhere may still be raging, relief is not going to happen in a noticeable scale until the war is over. It may even take a while for them to even realize there is anyone left to be in need of relief. Also keep in mind relief after a nuclear strike is nothing like a natural disaster, It is far worse. Natural disaster don't destroy all means of entry and transport to a city, aa nuclear strike destroys everything ports, bridges, roads, there is no way to get supplies to people you have to build new docks or airports just to bring supplies in. worse with infrastructure gone there are few ways to assess need or destruction which also slows aid. ]
[Question] [ A set of small isolated human populations, villages, although geographically close stay separate for one reason and one reason alone. Terrifying beasts that hunt human flesh and terrify children at night. The beasts mimic a human appearance, often previous victims, making them excellent at picking off people one by one or getting close enough to launch a surprise assault. The question is what flaw does this creature have that stops them infiltrating and destroying these villages, and yet can't be used against the creature when humans try to travel outside the villages? No magical borders that keep the monsters out although geographical features could be used in a similar fashion. [Answer] > > The way I saw it is the villages are a large source of food a mimic could enter, and as they've blended in stay happy and fed by picking off someone night by night and reproducing. Possibly replacing their victims with said offspring till the village is empty. > > > I'm going to tackle this because the premise seemed incomplete. I didn't know what motivation would mimics even leave villages. Now, I can say this will definitely not be a motivation. Let's assume a mimic does get into the village. OK, they've blended in and they can now freely eat anybody they want, right? Well, no - not really. How many are they going to eat? One person a day? Two? Three? Whatever the number is, it's going to be noticeable. People don't just vanish from a village. OK, maybe every once in a while but just disappearing left and right at a regular basis? The village will figure out something is up within a week. Maybe even a couple of days. Once the village knows people are disappearing, it's not a hard leap to "it's a mimic". The people aren't around and they should be around. There is no bodies left. So, the villagers start a hunt. Whatever form this hunt takes, it will be extremely unpleasant and the mimic will be found within a short order. Mass hysteria is not something that will just "pass". Nor would people just overlook any minor detail that seems out of place. Didn't Alice use to move with a slight limp just before it rained? Didn't Bob always cook a potato soup on Saturday? A village is really bad for a source of infinite food. Because when food figures out what's happening, it will bring forks to the table. Pitchforks. As for replacing the village with its offspring? Unless a mimic can reproduce and the offspring reaches maturity (or enough skills and knowledge to mimic somebody reliably) between meals, then that's a no-go. And I'm going to assume that this is not the case, or the mimics will need to eat a lot more and that means that it's even harder to replace on the fly. The only plausible way a mimic can live within a human village and remain unseen is if it doesn't eat people from the village. Or doesn't do it often enough. Which severely restricts the eating options. You could maybe get away with a person every month. It's a bit hard but maybe you can also kidnap several at once and eat them over time. So, not a lot of meals there. So, a safer option is to venture outside the village to bring in victims to eat. But what's the benefit here? It's still easy to be found out - you have to smuggle your victims without anybody seeing them. And you still have to hunt. So, it's similar to living in the wilderness but with a lot of extra logistics attached that makes the wilderness easier and safer. [Answer] # Mimics are two-dimensional creatures posing as three-dimensional Everybody knows that Mimics aren't actually three-dimensional beings, they simply have the ability to mimic them, if you look from the right angle. If you were to ever be able to see one from slightly to the side, it'd look like an animated cardboard cutout. This strange creature can easily keep its 'front' centered towards its intended target at all times, turning around and showing different 'angles' of a 3d creature with high enough speeds that simply circling it will not reveal it to be a fake, but when you are looking at the 'back' of a mimicked creature, it's still the creature's real front facing, just showing a different image, like a 360 degrees photo of sorts. This method works great for approaching a lone wanderer, simply keep your front facing towards them and they'll never find out you are as flat as paper. However, as soon as two people are present at the same time, it becomes obvious right away to one of them that you are a Mimic and paper-thin, you can't face two people at once after all. Avoiding villages has nothing to do with the villages themselves, it's simply about avoiding confronting more than one person at a time. [Answer] How about the uncanny valley effect? mimics can look very much like humans but on close inspection they just feel wrong. It works great for getting close to people but once they are close the wrongness gets noticeable. this will work for surprise attacks but any sort of prolong or close exposure would out the mimics [Answer] 1. Mimics cannot talk (or mimics do it badly), and mimics usually has trouble dealing with more than 2-3 humans on the same time. So, nobody of humans leave the village alone, and its mandatory to have short gossip with everybody they meet around the village, to proof, they are not mimics. If people dissapeared for more than one day, they are considered mimics, if they encountered, and they have to provide a good explanation why they were absent 2. mimics, like majority of beasts, are afraid of smell of burning wood, because it reminds them the fire in jungle. If you have big bonfire burning full day, it is excellent repellent against mimics 3. mimics are bad at swimming, and all villages are placed on small islands. 4. mimics cannot kill instantly - probably, their touch paralyse human, and than they consume adult human in few hours in a way, similar to spiders do - put prey in web cocoon, inject digestive ferments in it. If you see mimic trying to consume human, you have about a hour you can call for aid to beat mimic with sticks and stones and release it's victim. 5. mimics are solitary predators "making them excellent at picking off people one by one or getting close enough to launch a surprise assault", but they have issues against well organised group of people - majority of group works (cut trees, gather herbs, etc...) and few lookouts observe people and count everybody to find, if anybody is missing 6. With ability to shapeshift into human, why mimics cannot disguise into humans corpse and hunt other animals? The ones that can be interested in eating human corpse and are easier to hunt (because they are not so smart) - boars, wolfs, bears, prey birds, etc... Probably, mimics smells like dead people, and its something they cannot conceal. So, mimics hunts humans only if there is no any other reliable food sources. As result, mimics are not so eager to hunt people. 7. Mimics are afraid of sound of big drums (no idea, why :-( ). And villagers plays this drums all day, repelling mimics. Theoretically, you can take big drum in journey from village to village, but its quite complicated - you need big cart, because drum is 2+ meters in diameter [Answer] The small villages gather every day as a group and decide a password. Anyone who doesn’t know the password the next night is a mimic who ate someone that night. This solution doesn’t work between villages because there is no long range communication to coordinate passwords with travelers en route. And it only works initially because they were able early on to certify that there were no mimics in the village... they can never trust that assumption with any other group ever again. Children too young to talk or understand the password can NEVER be left alone without an adult to speak for them. A kid left alone even once is assumed to be a mimic. Same for senile or mute adults. [Answer] I run a game with a similar 'villages are safe from mimics, but travellers not so much' mechanic and the lore explanation there is that a mimic copy can't replicate scars, tattoos, anything that has happened to a body after it was born that changes its appearance. As a consequence, villagers eventually learn to tattoo their newborns with a simple mark, basically a 'real human' watermark, and as they grow they'll likely accumulate more markings. In villages you can take the time to confirm a mark, see if it washes away, whatever. Out in the wilds you can't really ask someone to bare wherever they got marked (assuming it's not somewhere bound to be visible, like the nose) and then rub water on it vigorously, and you wouldn't be sure of what mark to look for anyway if its not someone in the village you've known for years. [Answer] Trees The leaves of one of the local trees contain a volatile oil which is a powerful mimic repellent. Human villages have sprung up around clumps of these trees. Unfortunately, once harvested, the oil rapidly loses its potency, making a journey of more than a day or two away from home a perilous one. [Answer] The mimics are managing the human population sustainably. The mimics are intelligent. They have to be, to successfully mimic humans. And they are organized, the mimics. They live in a society of their own. They pick off humans from the villages one by one not acting as lone wolves but out of a strategy of sustained successful harvest. They do not come in and overpower the village and glut themselves because that would be shortsighted. What will they eat next month? They need to keep their depredations down to a level that human reproduction can sustain and that is not easy. But if the mimics wanted to slaughter an entire village, they could probably do it. And if people come through the forest that is what happens, dogs notwithstanding. It suits the mimics to keep the humans isolated. There are more humans than mimics and humans in large groups are hard to deal with. Also the mimics are aware that the best defense is a good offense – if the humans found the mimic nest that would be bad. There may be other things in the forest that the mimics don’t want humans to find. [Answer] Maybe the mimics are really illusionists? They're not actually changing shape - They're changing how their prey perceives them. Kind of like a mind effect. That way, they might avoid villages because it's too difficult for them to trick too many minds at once. [Answer] While the mimics love human flesh, they cannot survive barely on it. Their digestion requires them to eat every day a particular plant, which is deadly poisonous and very smelly to humans. This plant is abundant in forests, but no villager would bring it to their home. And because of the smell, all neighbours would immediately know if they did. At most, a mimic can sneak in, eat their stomach full and then leave to find the plant - or suffer terrible indigestion until they do. [Answer] Deadly [(house) dust mite allergies](https://www.mayoclinic.org/diseases-conditions/dust-mites/symptoms-causes/syc-20352173). If an allergic reaction proceeds to [anaphylaxis](https://en.wikipedia.org/wiki/Anaphylaxis), death is a possible outcome. Dust mites are everywhere humans are, especially densely located in the residences and workplaces of humans. However, dust mites [do not live on people](http://www.idph.state.il.us/envhealth/pcmites.htm), so a mimic's risk of exposure to this allergen is very low and can be reduced essentially to zero if clothing is removed before consumption. [Answer] One of the main features of a small tribe is that everybody knows everybody. First case: A mimic wandering into the village looking like a stranger. Distrust of strangers is common enough in our world, without mimics. In a worlds with mimics strangers would not be welcome. Second case: They mimic somebody from that village who has been in the forest for some reason. This is not as easy as it sounds. Sure, you can get the looks right, but actually fooling somebody who actually knows that person is nearly impossible. The villagers know about this danger and will interrogate anybody coming back from the forest before opening the gates to them. "What is your fathers sisters name?" "He has two, Magda and Mary." "You may pass." Even within the wall people will be on guard for people who doesn't know what they should know. Not so easy after all. [Answer] ## The creature's blood is not red. Upon entering the village, guards give you a knife (could be chained to the door in walled villages) and order you to prove that you are human by making a small cut on your hand. This gives them a safe way to let people in and out. While it may be dangerous to work outside the city walls, this makes sure it can't get inside. [Answer] ### They don't eat their vegetables They eat tasty humans not, ew, plants?! You could perform a simple check to see if someone is a mimic: Make them eat a piece of fruit. They throw up? Something's up. It would be instantly obvious when the first round of diner is served and they skip they vegtables. Especially when it's common to eat your vegetables. Bonus: Healthy citizens! [Answer] ### Mimics have trouble imitating scars and wounds. The mimic needs to maintain concentration for each bodily detail they represent and would prefer not to emit bodily fluids to simulate bleeding, so they generally have trouble imitating scars and wounds over a long period of time. Upon entering the village for the first time, it is standard protocol to show existing scars and receive a small cut on your upper arm. Humans will show the following hard-to-emulate characteristics upon being cut: * The wound will bleed naturally * The wound does not heal for several days and will remain in the same place over that entire period. * All scars will be in the same places and have the same appearance every time a person is seen. If any of these characteristics seem off, you can conclude the person is probably a mimic. At this point, you slice off a fingertip and observe the bleeding, just to be sure. Once confirmed, you then kill the mimic. Birthmarks, freckles, and moles would also be part of this process. A few people in the town have the responsibility to document scars, birthmarks, moles, and freckles and act as gatekeepers. For the scabs, it may also be common for them to pick scabs as a test of authenticity. Travelers that come across each other can give the customary cut, but with only a few minutes of observation, they aren't really able to do a better test and simply maintain a defensive posture of distrust as they watch the other traveler's cut bleed. [Answer] The presence of creatures that mimic and prey on humans like that would be a really big impetus for humans to not live in small, isolated villages and group together in larger settlements. Living in small, isolated villages is about the worst thing you can do to defend against an intelligent predator that pretends to be a human. More people around means its easier for a mimic to get spotted if it slips up, and the mimics don't have an easy alibi of coming from another small village. Small isolated villages would be easy for a mimic to tear apart in a few feedings, especially if these villages are less than forty people or so. Especially because a small settlement is liable to be about half children and elderly. A village like that could easily disappear and if human communities are that small and isolated no one would notice until months later. A small village is also going to be less separated from the wilderness and have less options for mimic-repellent. Lets say...burning fires repel mimics. A small village might have a handful of fires going at any moment, a small city would have hundreds. Or silver knives kill mimics. A small village has one, and if you lose it you're dead. A small city has many spares. A small village has a larger perimeter-to-area ratio that makes it harder to defend relative to its population size. So the question isn't "what keeps the mimics out" but "why do humans live in such a vulnerable state in the first place". One possibility might be food, there isn't enough food or water for humans to reliably live in large settlements. Indeed, the best place for a mimic to hide would be within one of the human villages to avoid suspicion, and then going and preying on people from other villages to avoid producing an alarm. Maybe having a job as something like a woodcutter where they can justify going off alone, even better if they can do it in pairs and each mimic can vouch for the other. Travellers coming to the village would also be prime targets, as they could disappear and no one would notice. Indeed, if you can get multiple mimics pretending to be a group that means the whole "if you're alone, you aren't a mimic" means nothing, because a small group could have all been eaten and replaced at once. There are a bunch of monsters from folklore who do this exact thing. One common story in these cultures is of a person doing something as simple as walking out of a room for five minutes or going to the bathroom and getting killed and replaced. It's amazing to think just how little we are directly aware of people around us. The question also exists of whether the human communities don't end up mobbing each other The Monsters Are Due On Maple Street-style due to thinking another village could be unintentionally harboring mimics or even outright replaced by mimics. People in those kinds of situations, where they're surrounded by a predator they have to worry about every minute of every day but can't do anything practical about it, tend to be very paranoid and short-fused and liable to make stupid, extreme decisions in the belief that they're fixing the problem. Indeed, if the mimics are all hiding in the forest and the people can't do much about them, they may be pushed to such extremes that they decide to burn the forest down and to heck with the consequences, hoping to survive on what food they have stored up until they can plant again. [Answer] Mimics crash, when they try or prepare to mimic other mimics.. Its just that two systems adapting to on another can get locked in a loop of eternal refinement. So there can only be one else there would be only none. [Answer] > > The beasts mimic a human appearance, often previous victims, making them excellent at picking off people one by one or getting close enough to launch a surprise assault. > > > This. Mimics can only mimic previous victims. Therefore they cannot mimic anybody that's alive. Since the isolated villages are small, everyone remembers everyone else from their village who is alive. And, put simply, they don't trust any other human that's not one of their known living members. This both explains why villages are isolated from each other, and why the mimic's flaw can't be used against them when a person goes outside the village. Basically you are only safe if you live in a community where you have the faces of all your community members memorized. As an added detail, this is also a good reason for each community to make it illegal to leave the community, with the punishment being permanent exile. Because if your community member leaves, and then comes back later, you don't know if it's the same person coming back. [Answer] Terminators were mentioned in the comments and I think that's a key to a good answer. The advanced terminators can mimic human appearance but they're made of metal--they're a lot heavier than what they are copying. Thus all entrances to the village have simple scales--a guard watches you walk across an object with a counterweight. You cross at the point consistent with your apparent weight. Human, it stays up. Mimic, too heavy, it tips. Look small but cross where a big person should, the guard stops you. [Answer] Mimics prey on humans, and they can distinguish between a human and another mimic by some detail only they notice. But while one stray human is a delicacy, too many in one place are sensorial overload. The mimic will go crazy by picking up the scent, sight or sound of too many humans and lose their ability to shapeshift. Just like a shark smelling blood, they will attack without much regard for their own safety. This might happen every once in a while by accident, which is a nice reminder to antissocial people that the loner trait will eventually be wiped from the gene pool. [Answer] Tails. Let's assume the mimics are wolf spirits, and they like human flesh. However, they cannot transform their tails, so one look at the mimic's backside, and wham, they smack the mimic away. [Answer] It could be simply that mimicry only goes so far. I disagree with those who claim that mimics would have differently colored blood, smell like corpses, be unusually heavy, etc. See, these things have evolved to mimic people. That means they have evolved to infiltrate human society, and considering the complexity of a leaf insect or octopus' camouflage, it's quite likely these things can perfectly mimic the human body, at least on the outside. However, it's what on the inside that counts, or in other words, the mind and heart. Let's say the mimic takes out and takes the place of an artisan. There are two big problems with this the mimic can't overcome: A) it lacks the artisan's creative vision and B) it lacks his/her passion. It also doesn't know the thousand little things that go into everyday social interaction: inside jokes, what relationships the victim has, how he/she behaves around different people (because we do, generally, become different people depending on who we're with).....the list goes on and on. If you want your mimics to be a viable threat, you need to give them the four following traits: 1. Intelligence (must be cunning to evade and/or negate suspicion) 2. Intuitive (must be perceptive, have highly honed social instincts-in other words, it needs the sociopath's abilities to understand other people despite having messed-up instincts) 3. (may neutralize 2, but unlikely) Power of Inheritance: Once a mimic ingests a victim, their magic-infused digestive system converts the victim's DNA into a form the mimic can absorb and turn into another form. However, there are drawbacks to this: a. Genetic Memory-While this enables the Mimic to know all the important details that allow them to pull off this trickery, it also gives them the meaning that goes with those memories. A normal Mimic may not access this meaning, as it's brain does not have the right structure to process it, but a Mimic with a recessive gene will. In other words, it will carry all the sentiments that artisan collected over his lifetime. b. Genetics has Little to Do With Personality-One of the arguments against cloning pets is that personality isn't determined purely by genetics. You may have an angelic bulldog for a pet, but his clone may be temperamental and just plain mean. In other words, the Mimic will most likely still lack the creative style or idiosyncrasies of their victim, a potentially fatal flaw. For evidence of the above statement on genetics, please check out this link: `https://www.fda.gov/animal-veterinary/animal-cloning/myths-about-cloning#:~:text=to%20the%20top-,Myth%3A%20Clones%20have%20exactly%20the%20same%20temperament%20and%20personality%20as,%E2%80%9Cnature%20versus%20nurture%E2%80%9D%20argument.`If it doesn't work, please let me know so I can fix it. Finally, an alternative method is that the Mimic somehow 'absorbs' their victim, integrating their very being into their own. This of course comes with problems of its own-what if the victim manages to retain some control, or takes back their new body? If the Mimic is killed, would the victim's spirit take over the body and simply resume life as best they can? This may result in a Gothic/medieval version of Among Us, where the 'crewmates' (AKA villagers) would be trying to root out and destroy the shapeshifting aliens (AKA monsters, Mimics). ]
[Question] [ There is an elite and secretive school of warriors known for its ruthless method of training. Very few students (only around 10%) ever complete their training; this is because the training is often lethal. However, those who do leave the school alive invariably become all-but-legendary. Their very names strike fear in the hearts of their enemies, for their capability in violent ways is unmatched. The school's masters are of the opinion that it is not possible to train competent warriors unless students are given first hand experience in actual combat; the training in inflicting death must actually involve killing, or else it is nothing but playing games. Therefore, all students must pass three tests: the Test of Iron, the Test of Darkness and the Test of Blood. During the Test of Iron all students are divided in pairs. Each pair is put on an arena and both students are told to fight a duel to the death. During the Test of Darkness all students are divided into groups of three. Out of each trio: student A is told to assassinate student B within three days by any means possible, student B is likewise told to assassinate student C and student C is told to assassinate student A. However, A does not know who C is, B does not know who A is and C does not know who B is. The Test of Blood is the ultimate test during which the whole body of students is divided into two teams. Each student knows the team they belong to. Each team has two weeks to score a decisive victory against the other team. It is expected that leadership of each team emerges spontaneously. It is also expected that both teams engage in a game of espionage, since students may lie to each other about the team they belong to. Finally it is expected that an actual field battle emerges between both teams. Does this idea make any sense, or is it complete BS? It might make sense because: - Well, it does seem that such brutal selection would be the only way to accurately judge the capabilities of the students as well as give them necessary experience. Non-lethal training is indeed, by necessity, quite far removed from actual combat. (Note: "accurately judge" not in the sense that always those who die are inferior to those who survive - luck is, obviously, too big of a factor - but in the sense that a master watching events unfold from afar can see what everyone does. It can only be seen if one can act under the threat of death (and not panic, freeze etc) if one is actually put under the threat of death, etc.) Usually it is better to have much more, though slightly less competent warriors, however, if absolute elite is needed, then perhaps this is the way to train such an absolute elite, isn't it? (eg for a guild of assassins or whatever) It might be complete BS because: - Well, did this ever happen in history? Because if it did not then it seems likely there are important reasons I'm overlooking that do make this absolutely implausible. [Answer] What a Waste The only way to train the perfect warrior or assassin is on the battlefield. The only way to become a master of killing your enemies is to kill your enemies over and over again. Only then is your training complete. Kill your enemies. Do not kill your friends. From a logistics point of view, it is a waste of time and effort to train one hundred apprentice assassin, then have them fight to the death to get one master assassin. Instead give jobs to these 100 apprentices. Assassinations. Espionage. Many of them will die in the field. But before they die, some of them will complete their contracts. You get some return for the effort training them. At the end of the day you still get 99 dead apprentices and 1 grizzled master who completed all their contracts and perfected their skills. But you also get 99 apprentices worth of espionage done. How do you tell the single survivor is a true master and did not just get lucky? That's part of the training, of course. When you send one apprentice to assassinate Count Fartface, you secretly send three more apprentices to observe. They are good at that sort of thing. After Lord Fartface's body is found, the three observers report back if it was a hard contract to fulfill. Perhaps students killing each other is still on the table. But it is not advertised in the School Prospectus. Having a student assassinate their best friend is a way to ensure their loyalty. But it must remain a secret from the other students, or else they get a C- and not an A+. On top of this, some of the students are moles from enemy countries, sent over to find out secrets. Getting rid of these counter-espionage agents is part of the coursework for the real students. [Answer] # Elite warriors are born and made. Elite special forces training programs tend to have a lot of washouts. That's because a lot of what makes them special is genetic. For example, [they tend to have brain chemistry that lets them react better to stress.](https://medicine.yale.edu/news/yale-medicine-magazine/article/neuropeptides-presence-in-high-levels-suggests-soldiers-are/) Upbringing is important of course, but for the best of the best, you want a good upbringing and good genetics. Combat is messy. [Hellish Quart](https://www.youtube.com/watch?v=qFDk1uzrdrw) is a good game for showing that sort of combat. Historically when two people duel, even if not to the death, both of them die a lot. Your training program, if it lacks magical healing, is realistically gonna just end in a lot of broken kids with ptsd and broken bodies. # To make it realistic, you need expendable chaff. Gladiators certainly didn't kill each other all the time. Many of them had dozens of fights and survived each. As such, have the school buy slaves who have committed crimes or been captured by a foreign nation. These slaves, while expensive, aren't so expensive that they can't be killed. The students at this school can have lethal combat against them without you losing all the experience the students have. The better students will be more experienced at fighting than random criminals or foreigners, and so will be less injured. [Answer] Such a scheme would be radically unstable What you are training is negative concern for the lives of other members of the hierarchy. That is, other members of the same group are fixed as legitimate targets for killing. And that this produces advancement in the group. So the result will be, graduates will view their instructors and officers as barriers to advancement. And they will have an ingrained tendency, filtered by the test, to kill those officers to advance. They might bide their time. They might go on some missions. Then they will return to whatever the home base is. You need to house and feed these critters between missions. They will step out on you in the first moment they think they can succeed. The officer of the garrison will show up dead. And it's a toss-up whether the members of the garrison will side with the killer or the officer. And if they side with the officer the likely result is they start fighting each other. Other Military Patterns Are Stronger Contrast this with the methods that such groups as the US Marines follow. They explicitly do not want robots. They want individuals who are capable, but who will cooperate in their units. For example, a twelve man squad that is efficiently cooperating on a task will be far more effective. Much more effective than twelve soldiers who are not cooperating. They train in these ideas with group tasks. Get everybody over this barrier. Get the intel and get everybody home. No man left behind. Sneak up on this bunker and blow it up then get everybody home. Guard your bunk-mate for two hours and then he guards you for two hours. Right down to giving units R&R at the same time so they go to the local bar and get drunk together. They also train in loyalty to the hierarchy. This involves huge numbers of actions from the small to the large. Honor guard duty at parades. Saluting officers. Insignia and medals showing rank and special achievement. Sleeping in barracks with the whole group. Eating as a group. Dressing in uniform. Stories about loyalty and honor. Moving in unison when marching. Dress uniforms on special occasions. Public rewards and punishments in line with how well the troops follow the lessons. Rewards and punishment for the whole group based on the outliers in the group. The officer having a side arm to deal with deserters. And so on and so on. A cohesive military unit has many advantages. They can spot for each other, this one going left that one going right. They can share intel. They can share equipment so that it is not necessary for each trooper to carry all their equipment types. Meds for this one, radio for that one, anti-mine equipment this guy, sniper rifle this guy, and so on. They can share training. This one speaking German, that one French, this one Russian, etc. They can rescue their own wounded. They can raise each other's morale. Your scheme trains in the desire to kill everything that you can, friend or foe, because that gets you advancement. The Marines train in the motto Improvise, Adapt, Overcome. Win and come home to a civilian life. Trouble Recruiting Military groups need new troops. This is necessary in any war. Soldiers die. Otherwise it's just a lot of shoving and harsh language. If some large fraction of the recruits die in training, this will get known. And people will be very reluctant to sign up. So you will need to press gang them. Conscript troops have notoriously under performed through the centuries, particularly in comparison to volunteer armies. Compare that with the Marines. The goal of the the Marines is explicitly to win then come home alive. Combined with such things as 4th of July parades and color guards on Memorial Day and such, recruiting is much less difficult. First Marines get all the training. Then they get all the glory. Then they get all the babes. [Answer] I'm going with the combat sport analogy you don't get a good fighter by "fighting". You get good at fighting by training and sparring. If you keep sparring very hard all the time you will get hurt and you won't be able to train as hard as you can. However you need to be prepared to your first fight, so at some point the sparring should go a bit harder So to become a good fighter there's a balancing mix of : * having a great physical condition (strength, cardio ) * master the basic and more advanced techniques * being able to behave like a fighter in a fight simulation (sparring) * fight progressively better opponents you don't get good fighter by killing them, you get dead bodies. What you want is a progressive system classification system like brazillian Jiu-Jitsu belts. [Answer] Is it impossible to imagine? No. There are obvious problems with such a school. How many would enroll knowing that there is a high probability that they will be killed before they graduate? As you note, there would be an element of luck to the "exams". Which means that some number of excellent students would end up being killed by bad luck. If students are regularly killed in training and exams, it's likely that many more will be injured, some to the point of being permanently crippled. So if only 10% survive, probably over half of those are useless as warriors because of crippling wounds. But that said, would ANYONE volunteer? I'm sure some would. There are always some who believe, rightly or wrongly, that they are the best of the best and would win. Presumably there are rewards to graduating this school, so there would always be some who try it out of desperation. I'd say your elimination rate is too high to be realistic. I'd go for an elimination rate of less than 50%. Even that would be brutal. But that's a detail. Oh, one quibble about your description: In your "Test of Blood" you say that students know which team they are on, but can spy on the other team by pretending to be a member. But what does it mean to say they "know what team they are on" if they don't know who the other members of their team are? Do they just know the name of the team? If so, how do they know who to kill? How do they even know that they are spying on the other team and not on their own team? [Answer] If its brutality you want it is reasonably successful. The problem arises from what you teach your students. Take the second and third test. It doesnt just teach your students to go out and kill people, but it teaches them to defend themselves as well. This is a problem with students who kill in self-defense in all tasks, as they'll not be able to do the assassin part only the self defense part. Way too many of the assassins you want would perish to such students, reducing the amount of legendary assassins that exit the school and adding a group of non-legendary assassins who got by on being hard to kill (and might use that to protect from legendary assassins instead). Training an assassin in brutal face to face combat is a bit counter to its purpose. You may want to simply build a school for fighters who try to kill people by kicking in the front door or bumrush a targets bodyguards. What you want is someone who can infiltrate either socially or physically to achieve their objectives and kill someone. A good system would probably split students into two groups: assassins and protectors. Protectors would be the chaff you mostly want to lose, as they wont be good assassin material. But they'll make EXCELLENT practice material. The students that have the sociopathic tendencies to kill people will be placed in the assassin group and tasked to kill the people in the protector group (the students will be unawares that they are classified in one group or another, they just know that some people might be tasked with killing other students). The protectors will never graduate from the assassin school, but due to human nature also be the larger group than the sociopaths capable of actively killing fellow students. Protectors might become part of the teachers who help design the challenges or leave the school with a different doctorate if they are too successful to be used on the students. This teaches the assassins to blend in, to infiltrate the social circles or to physically infiltrate and assassinate depending on the task given by the teachers. Higher marks are ofcourse given to students who assassinate their targets without tipping off anyone else who did it or how they did it. Post-graduate students might even have their identity given to their targets to increase the difficulty even further and increase chances of retaliation that they have to survive, all in a days work of a good assassin. This gives you a far superior chance to train various skills. You can put a time limit on the assassination, give multiple targets simultaneously, warn targets they are targeted for assassination so they'll dig in or become a running target etc. [Answer] What you describe is the premise of the fighting school Tiger's cove (not sure about the English name) in the anime Tiger Mask: young promising an desperate boys would be hired and passed through a life threatening training to become killing machine wrestlers, whose combat earnings would be given to the association. The training included fighting (of course with no safety rules) above lava lakes, having to jump on almost vertical walls over spike filled pits and so on, to ensure that only the thoughest would survive. And it is also similar to how fighting animals are tortured before entering the ring, to ensure they are as combative and lethal as they can. So, definitely possible. [Answer] In Andrzej Sapkowski's [The Witcher](https://en.wikipedia.org/wiki/The_Witcher) series, boys that receive training at [Witcher schools](https://witcher.fandom.com/wiki/Witcher_schools) undergo grueling and demanding physical and mental challenges. The training is designed to produce highly skilled monster hunters known as Witchers, and has high mortality rates among the students; probably most of them are not able to complete it successfully. [Answer] As I mentioned in comics, there are games that are played IRL that simulate some of your tests (minus the actual killing). The Test of Darkness is very similar to a college game I played called "Spoons" (a variant of another game my father played in college called "Assassins" and the Christmas game of Secret Santa runs similarly but is slightly different). At either rate, all participants are organized into a list looping list such that Alice is the target of Bob, Bob is the target of Charlie, and so on. When we get to our last entry on the list (Zach) the list loops back to the top, making Zach's Alice's target. Once the game begins, if Bob eliminates Alice, than Bob receives Zach as a target. In order for Bob to win, he must be "last man standing" which means all other game participants must be eliminated. The "Spoons" variant was given the name because the process of elimination required all players to use plastic spoons that had been marked by the game organizers. Your spoon must be visibly held on your person. If you put down your spoon you became vulnerable to an attack by the assassin, confirmed by a tap to your body with their spoon, at which point you also turned over your spoon to them, so they could record your out with the game runners (There were safe zones, such as public restrooms as the game was co-ed and the players didn't want the girls going into the Men's Room and vice versa to make the kill.). The assassin variant allowed more creativity with weapons but the players had to name their weapon of choice and define what that weapon looked like. My father gave the example of naming a weapon "Land Mine" and defining it as "getting his target to step on a frisbee" or "Acid" which would be "dumping a bucket of cold water onto the target." And the "Secret Santa" similarity should be obvious. In all variants, the target may not be known to the player, and they have to discreetly figure out who their target is and then find an opportunity for an attack (in Secret Santa, it also requires identifying something the target might enjoy receiving as a gift). One problem with your tests is that the point of having multiple tests in any course is to find who is the best overall at different skills and knowledge. Obviously if you have three "to the death tests", you're not screening your assassins for skills that might make them more well rounded because all tests are Pass/Fail and if you fail one, you can't possibly recover at another stage that you are good at. Someone who is poor in one on one combat that's tested in Test of Iron might exceed all others in the information gathering required in Test of Darkness but won't be able to demonstrate that because he lost a fight to the death (If you're a good assassin, is one on one melee combat really the skill you want to get good at? The good assassins' would never get to a point where they have to fight for their life). Similarly the final test is all about strategic thinking, which is not the same skill that information gathering and physical combat that the first two things taught. It's either tactical or strategic planning, which are different (tactics win battles, strategy wins wars. A battle might be a tactile loss, but a strategic victory (for example, you failed to assassinate the President, but the whole mission didn't care about assassinating the President because your guilds real goal was to assassinate head of security, thus allowing for their mole to ascend to that post and now can provide intel on whoever occupies the office of President moving forward. The President's death would have been Icing on the cake that is the head of security taking a bullet for the man.). Now, one thing you could do is change these tests to Rules As Written "do not murder your students" but do not tell them that the death of a classmates that you had no part in killing will count as an elimination in all tests for all practical purposes. The guy you are slated to fight turns up dead in his dorm the morning of the test? Guess you win by default. Your target in Darkness is found dangling from a rope and a suicide note is close by that details she can't handle the stress, well, guess her target goes to you, even if you clearly could not eliminate her in simulated tests. Of course, you can certainly kill your classmates. That's not against the rules. Getting caught killing the competition is against the rules. And after all, if you're really the best of the class, you wouldn't never be caught. [Answer] Great Idea, but might need some extra stuff Ah, training children in murder! The best strategy to get loyal and/or brutal shock troopers. The premise you describe reminds me a lot of the Dauntless from Divergent. I see three main problems with your idea, but they can easily be solved! A Matter of Trust The Problem- Like other contributors have said, the three Tests will force the kids in combat with each other, and make them utterly distrustful of each other. This is true to a point. Once the Test of Blood ends, the winning team will be closely bonded and have experience working together. The trust issue is not that they won‚Äôt trust the other students, but that they‚Äôll distrust whoever is responsible for this heckish school. This will make them completely worthless to the leaders: if they don‚Äôt trust the ones they were made to fight for, why would they fight? The Remedy- While not all students at the schools in this world learn combat and espionage, all students learn loyalty. Brainwash them, and brainwash them good, from their first day of kindergarten to their senior year! Wastefulness The Problem- You‚Äôre training hyper-loyal and hyper-violent spies and murderers, but for them to advance in this structure they have to kill the other recruits. It‚Äôs a waste of potential, sure, but they‚Äôd probably die even if they didn‚Äôt have to fight their acquaintances. The real danger is that the constant fighting might promote the most detrimental emotion possible in this case- sympathy! The students that die only die because the teachers are pitting them against each other. Inevitably, one student will refuse to off their comrades, and upend your whole structure. The Remedy- Trick your students. Manipulate them by pulling cruel practical jokes that gradually become more severe and painful, and make it look like the other students did it. Soon, the students will start actually harming each other. Foster this hatred until the Test of Blood, while making sure none of the recruits get lethally harmed outside of the already-lethal tests. At the Test of Blood, claim that you‚Äôve organized the students based on how they treated each other, putting kids who were locking horns on separate teams. This will make them violent to the other team and close-knit with the others. Why would you do that??? The Problem- Uh oh, looks like nobody wants to send their kids to a school where eleven out of twelve students die! How are you going to get any assassins? The Remedy- This solution is derived from real-world history. The Ottoman Empire was one of the most formidable superpowers of the world from the Middle Ages to the Great War. They conquered plenty of Christian and Jewish states, but didn‚Äôt force their new subjects to convert to Islam. Well, kind of. On occasion, young boys would be drafted from non-Muslim families and become Janissaries. These soldiers became Islamic, were taught Turkish, and trained in warfare. Even though they were, in essence, slaves, they had a good reputation and could quickly rise in status. So, draft the kids at random, and present the risks plainly, but promise reward and glory (that they most likely won‚Äôt get)! [Answer] ## "Lethal" combat isn't really "Mortal" combat.... but that's just semantics! The crux of the question makes it clear that death is not a possibility, but a probability at this academy, and the combat is indeed mortal combat (One of you WILL die). ## I have a few issues with this premise... 1. Why would anybody sign up, when there are other academies who don't kill their students? Testing under mortal fear can be brought about in other ways, where no other students are put at risk. The actual real lethal training can be carried out in the real world in special secret ops against enemies. 2. You could lose the best warrior EVER because he got gassed to death while sleeping by a super-intelligent assassin warrior who will then die in combat training. Of the 90% of "drop-outs", there WILL be warriors who are outstanding in their field - not something you want to do. 3. A team always works best when the team members bring different strengths to the table. But this academy would output mostly lucky warriors with no real strengths (other than‚Ä¶ strength). 4. Your warriors would come out of training not trusting their fellow warriors. It's likely they all used underhanded tactics to get where they are, and they know the others probably did, too. They were enemies in training, and that rivalry will follow on. So they would have very little trust or respect for each other. They would only care about self-preservation, which is very dangerous. 5. You can never simulate real-world scenarios. The real world is so unpredictable, it is the only place to really test your mettle. It would make way more sense to keep the lethal training for real-world ops. That way, life is lost purely because they weren't good enough, not because another warrior was better at this particular task. ## Lastly As a side note, in movies and games, we see the enemy carrying out this kind of ruthless mortal training. Why? Because they are dumb and have no morals and don't understand how to connect with their soldiers and give them self-worth, respect and something to fight for. They are just fearful meat-bag weapons. They have no identity. They are non-thinking fighting machines. And they always lose. ]
[Question] [ Closed. This question is [off-topic](/help/closed-questions). It is not currently accepting answers. --- Closed 6 years ago. * 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). * This question does not appear to be about worldbuilding, within the scope defined in the [help center](https://worldbuilding.stackexchange.com/help). [Improve this question](/posts/93240/edit) After finding some old tomes in Nostradamus' tomb (the real one, not that decorative fake) about alchemy, I finally made the first modern philosopher's stone. Now I can transmute plumbum (AKA lead) into anything. Pure substances only, unfortunately. My first batch was good old lead to gold. Smelted it with a bit of copper to make it 24K, made bars out of it and sold for some profit. So far so good. What is the best element to be making, assuming that: * I can only make around 100 grams or a quarter of a pound of transmutations a day. * I can make any isotope, but only pure elements. No alloys. * I don't want anything too radioactive. Anything that can give me cancer over a day of exposure is too radioactive. * Toxicity is not an issue, only radiation. But see below: * I don't want to be flagged by the government, so nothing illegal / restricted. [Answer] Use any metal (including lead), and market yourself as a refining service - charge the market rate of the original mass of the metal plus a refining fee. You would be crazy to sell your metals on the metals market - instead you would be able to sell them to laboratories as '18+N' / <1ppm impurities, and you could hide your transmutation in plain sight.. (it would be a proprietary refining method) 100% pure anything is worth a LOT more than normal market purity. [Answer] Gold isn't even in the top 5 here. A quick Google search tells me that the following pure elements are going to be worth it: * Tritium \$30,000 per gram * Diamond (pure carbon) \$55,000 per gram (and non-radioactive) * Californium \$25,000,000 per gram * Antimatter \$62,500,000,000,000 (that's \$62.5 trillion) per gram (although you may have trouble with storage and marketing) Happy crafting! [Answer] If you want to be quiet about it, gold is pretty good - no-one will be massively surprised if you turn up wanting to sell gold, whereas ruthenium would be another matter... However, if you're planning on making anything like gold, silver, platinum, etc., making a lot and putting it on the market will risk devalueing it - so maybe don't go too mad churning out ingots of the stuff. Synthesising rare elements could probably get the attention (and funding) of various laboratories worldwide. However, it would definitely begin to draw notice if loads more osmium appears in the world, for example, which might not be as helpful if you want to keep it secret. If you're willing to stretch past just elements, and be able to control the crystalline/molecular structures of your creations, then that could go well. Everything from proteins for crystallography (that no-one can grow in nanograms, i.e. cryptocromes, let alone 100g!), through to really really pure water - scientists would be really happy! Also, if you could control it to a high degree of specificity, perhaps manipulating just a single amino acid, then guaranteeing purity would be an amazing base for research. (I'm talking millions/billions of dollars of research). If you can create a molecule as you wish, purity is an incredible thing scientifically - but even knowing what impurities you've included would be a godsend. You'd need to be public about it, because no-one would really take you seriously if you just turned up at a lab with a sample, but you'd earn one hell of a lot of money once you got credentials and confirmation. You might not be able to make drugs for the whole world, but you could progress research by huge leaps. (Medicine, engineering, photovoltaic cells... So many diverse disciplines could benefit from it!) Also, if you're the only one who can operate this philosopher's stone, you'd probably want protection from a government/global institution - you'd effectively become a single-person superpower with such an ability. While aligning with any institution would give them power too, you'd also get a decent benefit yourself (by not having a really easy target on your head). [Answer] Gold and platinum group metals (platinum, rhodium, palladium etc.) would be your best choice. Second best choice is making rare isotopes like deuterium, but this will get government's attention very quick. If you are able to create elements with specific crystal form (like diamond), that will work nicely. Anyway, you should think well about establishing a legal front for your operations. [Answer] Any isotope of any element? Oh boy, you have no idea... Please, please make 100 grams of [298 Flerovium](https://en.wikipedia.org/wiki/Flerovium) or any other isotope from the [isle of stability](https://en.wikipedia.org/wiki/Island_of_stability) This is absolutely priceless. They can only be produced in single molecules and their existence is only proven by observation their decay, so there may be even stable isotopes, but their existence cannot be proven. If stable, Flerovium will not be radioactive and being in the same periodic group as lead it will be presumably not very reactive (meaning harmless if you don't touch or ingest it). Please, please do it and give me (or any other scientist, but really I am the first here!) a sample. You see, I am kneeing before you. Do you want my money, my family, my soul? Do you have any specific wish? Please, pretty please, have mercy and give me something like that. [Answer] When you have no moral issues with potentially being partly responsible for the death of millions of people, get hired by some third world country and make some weapon-grade [Uranium 235](https://en.wikipedia.org/wiki/Uranium-235) for their nuclear weapon program. Yes, I know you said "nothing radioactive". But Uranium will not "give you cancer over a day of exposure". [It is an alpha radiator, which means its radiation won't even penetrate the upper layer of your skin](https://emergency.cdc.gov/radiation/isotopes/uranium.asp). Just be sure to not inhale or ingest it, because then it will give you lung cancer and poison you chemically. But you said you are comfortable working with poisonous stuff, so that should be no problem for you. The same precautions which protect you from the most toxic chemicals will also protect you from uranium dust. Just keep it away from neutron sources... and don't put more than 50 kg of it in the same place at the same time or [it will go critical](https://en.wikipedia.org/wiki/Critical_mass). [Answer] If you're a decent showman, you can get away with a whole lot with super basic elements, and make a fortune. How? By becoming a magician, of course. Magic tricms are often kept secret, but you could announce exactly what you're doing, and people would think you're lying. Take advantage of the fact that lead is dense and many other elements are not. 1.5 grams of helium fills a normal party baloon. It's a tiny bit of lead - a cube 5mm to a side. A small fishing line weight would do. Heck, make it a chemistry show. Make some oxygen, make some hydrogen. Burn them and drink the water. And for the tip of the iceberg, a special guest goes home with a small gold ring. [Answer] It will have to be gold. Gold is stupid expensive because of its role in reassuring fearful folks. $1290 / ounce is crazy expensive for gold but that is the price right now. Iridium is only 970 / ounce and platinum only $936. The other reason gold is best is that this scenario is realistic enough that the alchemist wants to stay under the radar of government. If one starts offering for sale quantities of rare isotopes that will attract attention because it will be obvious there is some new source. Certainly that will be true for antimatter or [superheavy elements from the island of stability](https://en.wikipedia.org/wiki/Island_of_stability). But a person can move gold in these quantities without attracting much attention at all. [Answer] If your "philosophers stone" can be reliably reproduced by anybody, then it is not a matter of alchemy - it has moved into the realm of testable experiments and thus science. If it was me, I'd be spending the next couple year trying to see how this thing actually works and what part of our understanding of the structure of matter needs to be revised/expanded and how to roll this into the overall understanding of the universe. The other end is the question of engineering applications of your device: could we power our homes with miniaturized fusion reactors if we had a reliable way to keep them fed with a few grams of He3 every day, for example? More generally: How could we incorporate your discovery into tomorrows way of life? The only downside to a life of science that I can see is normally that being a scientist doesn't exactly pay terribly well - but someone who can make gold out of lead surely doesn't have to worry about money. [Answer] One I haven't seen yet is [Helium-3](https://en.wikipedia.org/wiki/Helium-3). The price isn't super high right now, but if you can get in on the ground floor with a "super efficient production method" as supply is going to keep increasing then you won't have to deal with much competition. One of it's main uses is going to be in fusion research, and so it's going to be a really big market down the road. To give you an idea of how they see demand being, they are currently figuring out ways to mine it from the Moon. > > [How do you mine helium 3 on the moon?](http://www.nbcnews.com/id/26179944/ns/technology_and_science-science/t/how-moon-rocks-could-power-future/) His team has estimated that it > might cost around \$800 million to bring back each ton of lunar > helium-3. This might sound like a lot, but if you could sell the > fusion energy at a price comparable to gasoline based on oil at \$100 > per barrel, the helium-3 would be worth $10 billion per ton. > > > [Answer] You're not specifying an objective. Everybody else just assumes you're looking for the most expensive stuff, but if you can make gold at will I am assuming that finances aren't a problem for you. Once you've spent a week or two making nothing but gold you ought to be able to ask what fun, interesting, useful, crazy things you can do that don't have to make a lot of money in the process. (100g of Helium will fill a lot of balloons, for example. But I'm sure you can think of better things once we've clarified just what, exactly, you're trying to achieve...) [Answer] Gold is the best option. A single person with a prospector licence and a metal detector can wander out bush and have a lucky strike and return with gold without any questions. Other metals might be more valuable but require more effort to collect it / refine it leading to questions of where you got it from. If you want to make real money, selling the process to make it would earn you far far more. [Answer] Antimatter [List of expensive substances](https://brightside.me/wonder-curiosities/the-16-most-expensive-materials-in-the-world-188955/) Why not, its atomic in nature and just as realistic as the rest of this topic Its not banned (yet) Its not radioactive (though I wouldn't touch it, I wouldn't touch cyanide either or any isotope ) Though, if you want to stick to the periodic table then I go with californium. Work down that list. [Answer] Stick to gold or diamonds, maybe silver. Why? This: > > I can make any isotope, but only pure elements. No alloys. > > > I don't want to be flagged by the government, so nothing illegal / restricted. > > > Most things we use are alloys. Even lead on its surface is an alloy, lead & oxygen. The problem is not what you make, but how you sell it. You need to make it as believable as you can that no one will doubt you are doing something out of the ordinary. The government will want it's share of the profits, that is not a problem. But it is a problem if they want your stone. Not to mention crime, and it's organised big brother. Plan: 1. Get a starting capital for the next steps: 2. Get the best security you can buy. 3. Setup company to keep everything legal. 4. Buy plot of land with possibility of your preferred element(s). 5. Try to have this plot of land in a western country, makes it easier to setup. And less worries about government take over & corruption. Canada seems like a good one. 6. Get some very good lawyer types to do this properly. 7. Automate the process. 8. Replicate the stone. Optional: 9. Buy your own lead mine. 10. Find the right partner to start family. 11. Keep it a family secret. [Answer] Synth anything? A lot would depend on your character's access to buyers, as well as the nature of what they think is valuable. Personally, I'd go in the direction of spices rather than metals. Saffron which goes for from $2,000- $10,000 USD per ounce is significantly more valuable by weight than gold. Anything rare or extinct could be auctioned. Anything urgently needed by an industry or area could be held ransom for near any price. ]
[Question] [ I have a story that is set in a world with a 1910's to 1940's style going on. So fitting to that era I have quite a few characters who smoke. Now I have a scenario where one of the main characters (the only one of the main cast who regularly smokes cigarettes) gets asked by a character from a different country if he is not worried about the possible risks to his health associated with smoking, only for the smoking character to explain that the specific type of cigarette that he smokes (which will be a brand exclusive to that characters home country) is completely harmless to his health. So my question is: Could a cigarette type theoretically exist that is not harmful to your health. (at least no more harmful than the occasional alcoholic beverage or junk food) without having to resort to something akin to e-cigarettes or vapes (for the style of the story the cigarette has to be able to be "rolled" and lit with a match or lighter) [Answer] # Have less advanced medical science While you can't burn something and breathe it in without health issues, you can have doctors who aren't very good at science. They did studies on the local version of cigarettes, and found out they improve health on net. As such, science in your universe will say that cigarettes improve health. [![enter image description here](https://i.stack.imgur.com/lMAqM.png)](https://i.stack.imgur.com/lMAqM.png) [Answer] There is no form of smoke (or even smoke substitute, like glycerin fog) that can be inhaled over a significant time frame without causing some kind of harm. Other plant leaves than tobacco, though lacking the addictive nicotine, still carry most of the other poisons the FDA warns about -- carbon monoxide, carcinogens, etc. Even pure cellulose produces fine particulates, which are behind a wide variety of lung diseases. Beyond that, all of the liquids that can be used in a fog machine (which works the same as a vapor machine aka e-cigarette) are harmful over long exposure. I believe it's impossible for any cigarette that actually produces smoke for inhalation to be "completely harmless" -- the closest you could come would be the pointless exercise of simply holding the cigarette in your mouth, occasionally fiddling with it as you would to manage ash on a conventional cancer stick. That said, as mentioned in a comment, before about 1960 it wasn't widely believed that smoking was harmful -- I've seen advertisements (featuring then movie star Ronald Reagan!) from that time period touting a particular brand of cigarette as soothing and healthful -- so it's very possible your character actually believes what he's saying, even while he's destroying his own life. [Answer] No, but... There is no form of inhaled combustion that, consumed regularly or intensely, won't harm the body. None. None whatsoever. Tobacco, wood smoke, car exhaust, Marijuana... none. The human body is fantastic at protecting itself from minor exposures, but long-term or intense exposures will always damage the body. But maybe we can learn something from another vice. There is no alcohol consumed regularly or intensely that won't harm the body. None. None whatsoever. And yet most of the world believes drinking red wine is beneficial. They're not entirely wrong.1 When you ignore the alcohol, red wine appears to have benefits and an argument could be made that weighing the pros and cons results in a net positive. So, the question becomes: *What benefits can come from smoking anything* that would, at least to the degree of suspension-of-disbelief, have a net positive benefit?** Proponents of Marijuana will tell you the benefits far outweigh the consequences. Science appears to be proving that the beneficial aspects of Marijuana can be had without any of the negatives (it needn't be smoked), but let's ignore that. The problem with something like Marijuana is that it alters perception and mental acuity more than tobacco does. Is there something that doesn't? There might be. From [this website](https://bearblend.com/bear-blog/benefits-of-smoking-herbs/) we learn that there may be benefits from smoking herbs such as: * Mullein * Red Raspberry Leaf * Peppermint * Mugwort * Lobellia * Damiana If nothing else, your smoker will be unique compared to all those tobacco smoking characters. Legal Disclaimer #1: Smoking anything is harmful. It doesn't matter what benefits may exist. Your lungs weren't designed to absorb ash or, worse, any combusting material. This answer is for the purposes of a work of fiction and should not be construed as an endorsment of any kind. Though there are many who will completely disagree with me, smoking anything is simply foolish. Legal Disclaimer #2: Writing a story that includes a reference such as is suggested by this answer (i.e., a rationalization that smoking anything could have a net-positive) could have a consequence among readers of your story and distributors of your story in the Real World. At least here in the U.S., we've been on an anti-smoking kick for a long time and the existing subcultures that embrace smoking won't change the fact that (e.g.) Barnes and Noble might not carry your story because a vocal organization like the [Truth Initiative](https://truthinitiative.org/who-we-are) threatens to boycott them over the matter. Probably won't happen, but fair warning. --- 1 Just to make a point, the world is full of false news, false beliefs, and false hope. An example of this is an article titled, "[7 Science-Backed Health Benefits of Drinking Red Wine](https://www.realsimple.com/health/nutrition-diet/red-wine-health-benefits)," which, after making the audacious claim that science has proven red wine to be beneficial, thereafter preceeds every claim with words like "potentially," "can be," and "may be." When humanity is brought to the point of a tack, the truth is we'll convince ourselves that any vice has a benefit. [Answer] Your character smokes clove cigarettes. <https://en.wikipedia.org/wiki/Kretek> They are not healthier or safer than regular cigarettes. But many people think they are and your smoking character is one. He explains that the spices and other things in the clove cigarettes bind toxins in the tobacco and that the cigarettes actually help the lung. You can buy them in stores in his home country but your character rolls his own. He is just wrong about the safety thing, but he is pretty convincing. He is a charming and persuasive guy and the clove cigarettes actually smell good. [Answer] ## Your character's home region has something more dangerous than lung cancer In this situation, your character's home region has a parasite which inhabits most adults and primarily lives in the lungs. The parasite is impossible to detect, remove or fight with their existing medical technology, BUT for some reason, it can't handle smoke from a specific herb found in the same region. the smoke doesn't fully kill the parasite, but it subdues it to a point where people who smoke that herb on an hourly basis when awake will be able to survive. The parasite also absorbs most of the harmful substances in the smoke, leading to people thinking that the cigarettes are mostly safe to smoke. but in reality, the cigarettes are just as deadly, but due to the parasite it's mostly harmless. And due to the herb, the parasite is also mostly harmless. And the medical science is not yet advanced enough to know about the parasite or the special properties of the herb. ]
[Question] [ Currently writing a fanfiction called Challenger, a spinoff of Uru-chan's unOrdinary. A sort of a fan parallel dimension, if you will. Grey (inspired off of John Doe) is a 17-year-old highschool student-soon-to-be-hero, but, like all his other classmates, he has an Ability. 95% of humanity have been born with a single Ability, but the powerless 5% lucked out and ended up as a cripple. Let me explain how Abilities work: Abilities are powers that people are born with, though the manifestation time differs per person; few individuals displayed their Ability at birth, but most discover their Ability when they are 5 or 6 years old. Hereditary Abilities are passed from the parent/s to the offspring, though parents without abilities can have a child with abilities, and children can sometimes possess Abilities that are different from their parents Abilities. Whenever an Ability is used, it usually gives off an Aura in the user's hair or eye color. It flows through Aura Channels which regulate he flow of Aura through the body. A stronger flow of Aura naturally results in a stronger Ability. Normally, the aura flow cannot be altered by consciously, though Meta Abilities (Aura Gage and Aura Manipulation) allow the user direct control to their Aura Channels. Abilities usually have some kind of drawback, and the more powerful the Ability, the stronger the drawback. For example, the Ability Shield allows the user to create shields that reflect damage and are almost impenetrable; should they break, however, it can cause physical damage to the user. The Ability Hellfire, if used to long or too much, will begin to consume the user. Any kind of ability that transforms the user (e.g., Stone Skin, Invisibility, etc.) drains their stamina when powered off and can eventually cause pain throughout that body and possible damage. A boy with a troubled past, Grey is naturally a good kid, but has a tendency to violence, and swears to destroy the system of hierarchy that places the strongest at the top of the social food chain, leaving the weak helpless and at the mercy of the higher tiers. He charades as a cripple (though his closest group of friends know about his power, and try to help him with his past), but is actually one of the strongest in his school. His Ability, Aura Manipulation, allows him to detect, manipulate and copy Auras, allowing him to observe the Aura Flow in other power users, copy their Abilities, and combine them in order to produce devastating results (e.g., copying and combining Fire and Wind produces Firenado, not a separate Ability but a combination of the two; some Abilities failed to combine, so not all abilities are compatible). The only limitations so far is that he can copy up to 4 abilities, and he can only use them for a short time period. Grey has successfully dethroned the Houses (group of "elite" students at a school) of both New Bostin, Southport and Wellington High, and there is seemingly no end to his power. What are some possible nerfs that can be implemented to his power? (P.S.: Abilities are pseudoscientific, not magically or otherwise.) [Answer] # He lacks "Drawback Mitigation" Most super powers come with an inherent mitigation of risk associated with their power. A few examples: 1. Super strength: Increased bone strength and durability so that the bones don't shatter when lifting a heavy load, or when hitting something hard. 2. Fire Powers: Heat resistance, eyes adapted to bright flashes of light. 3. Super Speed: Decreased friction and increased durability to survive high speed impacts. 4. Telekinesis: Increased mental capacity for concentration and multitasking, otherwise they could barely be awake while using their power. 5. Flight: Better lungs for operating at low pressure when at high altitudes, enhanced perception for judging speed, enhanced durability to survive crash landings. While your hero can gain the base abilities of each of these powers, he doesn't get to mitigate the drawbacks of the powers for free. He would have to copy both a super strength power and a physical invulnerability power at the same time to be able to match what someone with just a super strength power could do. This means that he has to be super careful using other people's powers to avoid hurting/killing himself. It'll also mean he'll have a steep learning curve whenever he copies someone's ability as he may not know what the drawback of any particular power is before he tries to copy it. [Answer] It's not really clear how these Abilities work. Just to stay with the proven and true, let's say they're all extensions of a probability alteration field. Most humans possess now a probability-altering organ (it's actually a network of quantum-linked microtubule organelles laced through the frontal lobe, genetically engineered back in the day before the Discontinuity). The aura is a temporary coupling between the field and the local volume of space, sort of a Cherenkov effect. The "Ability alteration" is the power of manipulating someone else's quantum lace, which is one of the few things that endanger the wielder more than they do the victim - those fields weren't designed to go one against another, and doing so was really, really ill-advised. Ability "cloning" is achieved through a higher-than-average control of the quantum lace, having it operating as several separate laces at once. This requires more flexibility, a higher redundancy in the lace structure - which Ability Alteration can reduce - and closer integration between lace substructures (the looser the integration, the shorter the period two or more abilities can be blended). So, some way of selectively defusing an Aura Control wielder - well, it turns out you've already done it. The probability control fields weren't designed to go one against the other. When they do, in addition to whatever their wielders want them to achieve, like people battling with Silly Putty maces, the laces slightly imprint on one another. That is why you - a declared villain - irrationally say things like, "What could I do to (slightly) decrease his Ability's power?" or "I'm not looking for a total removal of the Ability, as I can't and won't do that". You find yourself not wanting to go full out against the guy, and actually did not even realize this behaviour, however rationalised, isn't typical of a villain at all. The good news is that whatever his opinions before the first clash, he now feels the same towards you, so neither of you has anything to fear from the other. Rather the contrary, actually. The bad news - well, bad depending on the point of view I guess - hate being the one having to break this out to you, really - the embarrassing news is that the mutual imprinting you unwittingly achieved also has... or usually tends to have, let us say, deeper implications of a more, er, intimate nature, whose exact details I'm afraid you and your former arch-nemesis will have to work out for yourselves in a more private setting. [Answer] He lacks control, and his Aura limit doesn't change. Top hero, Morse, can throw around powerful flames, and shape them into anything from a defensive firewall to a laser-focussed cutting beam, or use them for flight and propulsion. But, he's learned to do this through years of practice and honing his technique. When Grey copies Morse's power, he can also produce flames. But, while he can choose which limbs to generate it from, it comes out as a mid-range blaze in the area; Grey doesn't know well how to focus or shape it. He's an uncoordinated novice, flailing wildly, and as much danger to himself as others. Morse has a sidekick, Robbie. Robbie's power allows him to control wind! Grey can copy this power too, and use the wind to boost the fire power. However, he has to split his Aura in two to do so, half shaped for fire, and half shaped for wind. The combination might be stronger than each individual power, due to synergy, but the copied powers are only half as powerful as they would be if he only copied one! Now, if Grey spent enough time around someone with a power, copying it repeatedly, then he could (with training) build up some technique and skill. And, some skills will carry over to similar powers. But, he will usually be outclassed by a specialist who knows what they're doing. [Answer] There should be a difference between what people can do and how powerful they can do it. For example, Character A might be able to create fire emitting 3000 watt of heat, while Character B can also create fire, but only with 1000 watt. Both A and B have the same ability, but B is generally less powerful than A due to B's aura generating fewer neutral particles. When Grey copies an ability, he copies the ability, but not the power level. When Grey's emission of neutral particles is well enough for 2000 watt of fire, then it doesn't matter if he copies the fire ability from A or B - his fire will be 2000 watt, because that's the amount of power Grey's aura can manifest. If Grey copies two or more abilities, then his power gets divided upon those abilities. For example, if he copies fire and wind, then he can only cause a firenado with 1000 watt worth of wind plus 1000 watt worth of fire. With that system you no longer need to worry about how many powers Grey copies at the same time. If he copies 20 different powers simultaneously, then each individual power would be so weak that there wouldn't be much he could do with them. This system also opens up another interesting plot: There might be a character who is thought to be a knock. But they actually do have an ability, and that ability might be very useful. Unfortunately for that character, their aura is so weak that they can't use that ability. So they might not even be aware that they have it. But that might not stop Grey from copying their ability and manifesting it through his considerably stronger aura. [Answer] See that pale, soft mannered kid in the corner. Yes, that one, looking depressed and lacking the exuberant energy the other kids display. If you look in the history of the incidents in the highschool yard, you'll see that the usual bullies let her be after a couple of tries. She was happy for some days after the bullies attempted to do their stuff with her. Well, she's an aura blackhole - she doesn't project power though her ability, but she's able to, so far, drain any amount of power that other abilities project onto her and then feed her internal energy deficit for days. True, she can't drain any ability that is not projected towards her (she's not an aura leech or vampire). Now, if you arrange her to be in the security team with someone with an ability that requires the projection of large amount of energy (say, fire or tornado or thunderbolt), well... if your villain combines the two, an "ability shortcircuit" ensures, with the projected positive power being drained immediately in the same source. I'll let you imagine what this shortcircuit will do to the "power supply" of your villain. --- Were I to be you, I'd make sure to use my influence to find others with the same ability. And/or convince her to have kids with the hope that the aura/ability ecosystem is better balanced. With so many positive energy projecting abilities, this world started to show signs of "aurogenetic induces global warming". This "abilities" world is primed for a catastrophe if the emissions continue to like that, you'd better start to convince the people for a reduction of emission 20% below the 1990 level. [Answer] Random results Yeah, he thinks he is super powerful because he lucked out his first couple of tries. But combining random superpower silliness usually ends with more dubious outcomes. Fire + Wind can make a "Firenado" ... maybe... but more often you blow out the candle. I mean, burning out every light bulb in a five block radius will make you the toast of the Astronomy Club, but it's not tremendously powerful. And the next time you do it you'll end up with a Santa Ana in Montana, Burning Hail, Constellation of Chinese Lanterns, or the all-time favorite, Flaming Flatulence. Hope you remembered the Beano... [Answer] What makes Grey so powerful is that he copies powers at full strength - since he can copy multiple at once, that means that copying two strong abilities at once effectively gives him twice the raw power. You're able to tweak his capabilities... perhaps simply preventing his total power from going beyond the strongest power that he's copying would be a pertinent way to bring his capabilities back down to a more manageable level. The reason that this is so useful is, he will never be more powerful than those he is copying. Which means that, if he tries to copy the powers of, say, two of your henchmen, he will be going up against more power than he's able to get from them, in total. Of course, this is balanced by him having access to a greater variety of powers, which means that your henchmen won't be able to easily curbstomp him, or anything, but it's likely to be a fair fight. While it's not an easy change for you to make, since it's a "natural" modification, rather than an alteration to the primary rules of the power, it's not nearly as taxing on your body. What's more, it is probably safe to relax the changes you made before - an easy process, as it's simply a "reset". Let him absorb as many powers as he wants, and keep them as long as he wants - the more he has collected, the weaker each power is. [Answer] Eye damage. Having double the quantity of Aura particles around his eyes makes him blind after a while, whereas a single dose is managable. It's hard to see pretty quickly, and if he firenadoed for too long, his eyes would heat up and cook. Or have another 'meta' Aura face him; a copycat or a 'an absorb it and hit you back twice as hard' character would do fine. Or combine my suggestions: if he faced a 'hurt me more' character whose ability was preventing the other person from stopping using his ability; or even one who doubled his Aura (normally beneficial), then his eyeballs are going to be like popcorn in an industrial microwave. Or face him in the right environment; inside a chamber that emulates the abilities I've suggested here. [Answer] The use of this ability , gives him ticks, were he has to use the withdrawn ability. So you have a villian, that causes you to forget "fireball" but casts it involuntarily, often at bad moments. Villain sits at the loo, casts fireball, celebrates a party in his palace - casts fireball, trys to remain stealthy- fireball. His crippling of you, cripples him. It goes so far, that the "guild" trains bounty hunters and trys to connect bad habbits with the abilitys. Need to smoke opium to cast this and that. Your vampire leeches that - and gets the raving cravings. [Answer] He can only copy a person's ability once, with the same 3-abilities limit. Once he's forced to replace an ability, he can never copy it again. This limitation is bound to the person he copies from, not the ability itself. If a different person happens to have the exact same ability, he could still copy it. He would still remain immensely powerful, but copying new abilities now comes with an immense tactical cost. His enemies could take advantage of this limitation and trick Grey into giving up a powerful copied ability to copy a seemingly better one; only to reduce his own net strength in the process. It also brings some drama for a soon-to-be hero to be forced into such hard choices. Perhaps he'll be put in a situation where he has to copy a more specialized (but weak) ability to save someone; eroding his own power in the process. This would also force him to keep tabs on potential targets to copy and replace abilities from later, in case he has to give something up. [Answer] Make it such that despite being able to see and clone the Aura, he can't tell what the Ability will be or what a combination with another one will achieve. So, he can control whose ability he copies, when he uses it, and with what other ability he will combine it, but not really what the effect will be. This will make it so he will have to rely on battle-tested abilities he has used before, giving you the advantage of knowing what he is capable of. On encountering a new aura, he will have to wait to see what the ability is (giving the advantage of surprise) or risk copying it before, but not knowing what will happen if he uses it. Pretty risky for him, but less so for you as you already know what the ability is going to do. [Answer] Obviously, the best answer would be to build up an arsenal of abilities at your company that can easily counter what he already knows to copy. However, you need to be careful when doing so. In MHA, a similar character Neito can copy abilities. However, he has a significant drawback you may be able to use. Greatly stated by some random guy (Jexel Bur) in a Quora answer: Accumulation and Base Form - This drawback is twofold. So far Neito is shown to only be be able to copy the base form of a quirk. Meaning he can only copy a quirk in the state it first manifested. This is supported by how he can copy One For All, but can’t use it. The second part of the drawback is that he can’t fully utilize quirks that must accumulate a resource to function. Since he can only copy a quirk in its default form, he can’t copy the storage effects. Therefore he can’t use Fatgum’s Fat Absorbtion because it stores the kinetic energy from physical attacks, he can’t use Eri’s rewind because it accumulates some (unknown) element, and he can’t use One For All because of the stockpiling effect. In other words, your company should have defenses that rely heavily on stockpiling certain resources that are not easily available. You can get creative with this but some examples: -An electricity ability that is charged by a physical manifestation allowing for the user to "Plug" themselves in (like to a wall). -A speed ability that allows a user to move very fast, but is charged up by standing still. For every minute they are still, they can move 1 second at super speed. (this guy could be like a monk or something always meditating and thus can move super fast at will) Additionally, you can also just make some pretty normal abilities that when first manifested were very weak and only improved through vigorous training. so when your hero uses a guys fire ability its more like a lighter. Moreover, you can also limit his power by making them extremely difficult to use. Like an ability that lets you pass through objects but you have to practice activating only on certain parts for it to be useful or you will just fall through the floor. Moreover, activating it on your eyes makes you blind etc.. Hence if your hero was to use it, he would ungracefully activate it and fail to use it properly. [Answer] Shared Fate So this kid copies auras. Let's "improve" this ability a bit. He doesn't just use the same ability now, the aura he gains is the same aura as the person he copied from, entangled on a quantum level, and thus as long as he keeps up the ability, he and the person he copied are connected. In other words: whatever happens to the person he copies the ability from also happens to him. This means he can't copy the ability of the person he's fighting any more. Otherwise any damage he does is just done back to him and he's a kid so he has less endurance. If he copies from someone else then that person becomes a weak point for him. (If this damage mirroring goes the other way the victim might well not appreciate it, though I guess that might open up a loophole.) From a meta POV also this is a pretty good excuse for him to learn to start caring about other people... [Answer] I would suggest making a delay to Grey's powers, so he would not copy powers in an instant: he would have to be in eye contact with a person for a least a defined amount of time or longer to copy their Ability. Apart from that, it would be a good idea to make him lose these stolen Abilities after some time: this would make him vulnerable due to the limited time of an Ability usage. (BTW, Grey's powers look like a mix of [Eidolon](https://worm.fandom.com/wiki/Eidolon) and [Victor](https://worm.fandom.com/wiki/Victor) from Worm.) [Answer] He always has the latest 4 abilities active, thus he needs to replace the dangerous ones in some cases and he doesnt always have relevant sidekicks to do so. Imagine he just fought a big bad and prepared accordingly with Storm, Fire, Crush, and Shield. However his beloved/friend/... gets hurt. If he found 1 person with Healing, it would replace the oldest power (Storm), and he would still cast something containing Fire and Crush. Not ideal ! Now imagine he manages to rotate the three first into Shield(kept from original), Healing, Protect, and Help. He saves the endangered, great ! ... but the big bad gets his second life, and now he has nothing remotely useful to fight him off. He has to rotate all his spells again so he needs 4 people with relevant affixes. [Answer] He makes bad choices. I have a Maserati! It is so freaking fast and everyone knows it. And I have a lot of money! But I make bad choices. I am cocky. I am not a skillful driver but I do not know that. I am a danger on the road. And in my fast car, I go places that I would be better off avoiding. I spend my money foolishly and get ripped off over and over by people smarter than me. Despite my powers my life is hard and stressful. Things do not turn out the way I think they should or hope they will. This is real life. People actually do have amazing gifts and abilities, and then fail to optimally use them. There are very smart people who are not able to leverage their brainpower to improve their lives and the lives of people they care about. There are very rich people whose lives are chaotic and unhappy despite the money (or because of it). Powers are just tools. They must be used, and it is in the using that they prove helpful, or harmful, or just worthless. If you are writing science fiction, write about a young man who must mature and grow into his god-given gifts, or risk ruin. [Answer] he gains the drawbacks with the abilities You mention that abilities usually have drawbacks, and powerful abilities have powerful drawbacks. A very reasonable way to balance copying someone's abilities is to gain the drawbacks of each ability he copies. Having multiple powers becomes risky when managing multiple drawbacks at once. Synergizing powers could also synergize the drawbacks, too. For example, creating a shield empowered with fire. Using too much fire could bring the shield closer to breaking, and a broken flaming shield could do much more damage than a non-flaming one. ]
[Question] [ I am a DM for a homebrew D&D 5e game. In terms of technology, the time period loosely takes place somewhere between 1100 and 1400 CE (so High Middle Ages to Late Middle Ages). The villain of my piece knows of some substance (TBD) underground that, when ignited, would destroy everything within several miles of the ignition point. The problem I am running in to is I would have no idea what kind of substance that would be. I was thinking it could be some kind of naturally occurring gas, but I am not sure if something like that exists, or exists but is not concentrated enough to be able to cause the amount of damage I would need it to. I should also mention that the substance needs to be something that has existed and/or still exists in the real world. I don't want magic to have anything to do with the villain's scheme. Does anyone know of a substance that could fulfill the requirements that I need it to? [Answer] If it is the aim of the villain to make a trap or to make a bang big enough to destroy a town, then a [dust explosion](https://en.wikipedia.org/wiki/Dust_explosion) could easily fit the description. A villain might reasonably know about the potential of dust explosions if they were a [miller](https://en.wikipedia.org/wiki/Miller) or might have spoken to one who told the villain about flour explosions, or a miner who might be aware of coal dust explosions. By suspending bags of finely-milled coal or flour near the top of a large underground space, then rupturing the bags (the more violently the better) in the presence of a source of ignition, a fuel-air explosion might be caused. By sealing any exits prior to ignition, with sufficient fuel and air, pressure might build up inside the underground space to the point where the ground could rupture due to the overpressure. This could cause significant destruction of surface structures, either due to the ground rupturing, or due to collapse of the roof of the underground space. [Answer] The most obvious real-world option would be a coal-seam fire. It's not going to inflict fast destruction, but it could make a wide area uninhabitable for decades. For example, the [Centralia mine fire](https://en.wikipedia.org/wiki/Centralia_mine_fire) has been burning for almost fifty years, rendering a couple of towns uninhabitable, and will likely run for many more. It's easy to find flammable gases underground - decomposition produces methane, for instance. The obstacle to creating an earth-shattering kaboom is that you'd need to have the right mix of flammable gas and oxygen. In real life that's unlikely to happen at the kind of scale you're looking for, but for D&D you could handwave it a bit; maybe some local fungus has created just the right mix to be dangerous. [Answer] If the area is like Paris, in that much of the rock has been [quarried away from beneath it](https://en.wikipedia.org/wiki/Catacombs_of_Paris), then firing a few of the remaining support pillars using simple brush wood would compromise the strength of the remaining rock and cause widespread collapse. This is similar to the old practice of [undermining](https://www.worldhistory.org/article/1230/siege-warfare-in-medieval-europe/) where tunnels were dug under walls and carefully supported until they wanted them to collapse, in this case the tunnels were made long ago for a different purpose. The other obvious answer is salt; lenses of [rock salt](https://en.wikipedia.org/wiki/Halite) can be vast and they can be [dissolved quite rapidly](https://en.wikipedia.org/wiki/Bayou_Corne_sinkhole), if your villain knows of an old salt mine that extends under the area then a small explosion that allows water to flood into said mine would destabilise everything sitting above the salt dome. [Answer] A Forest. Or a city built of wood. Those are perfectly correct answers to "What kind of substance that existed in the middles ages could, when ignited, potentially destroy everything within several miles?" Bear in mind that "several miles" requires something with more energy than even a small tactical nuke. No single explosion, fuel-air bomb, or dust explosion will come close to that requirement, by several magnitudes. [Answer] As other answers have suggested a fuel - air explosion is your best bet. This is the technology used in [the most powerful non-nuclear weapon](https://en.wikipedia.org/wiki/Thermobaric_weapon) in use. The question is what is the source of the fuel. I think the most realistic way to produce the scale you are talking about, though very unlikely, would be natural methane emissions from methane hydrates. As the climate warms, methane is being emitted from various methane hydrate deposits around the world, most notably in Siberia. One such is described [here](https://www.arctictoday.com/methane-explodes-under-yamal-tundra-creates-another-sinkhole/): > > Reindeer herders in the area of Seyakh, a village on the eastern coast of the Yamal Peninsula in the morning of June 28 reported the incident to the local authorities. They say that they from the distance saw flaring flames and a column of smoke from the area. > > > ![Not the sinkhole in question](https://sp-ao.shortpixel.ai/client/to_webp,q_glossy,ret_img,w_4999,h_2812/https://www.arctictoday.com/wp-content/uploads/2017/07/GettyImages-606226746.jpg) Not the sinkhole in question It is quite conceivable (though unlikely) that it could naturally be released at such a scale that a fuel-air explosion could happen at any scale. How your villain causes this on demand is a question. Perhaps they divert a river toward (thus melting the hydrates) or away from (thus reducing the pressure on the deposits). Perhaps they cause a cave collapse, causing enough disruption to cause breakdown of the hydrates. Perhaps they cause a smaller explosion, that again causes the disruption. [There are suggestions](https://siberiantimes.com/other/others/news/crater-formed-by-exploding-pingo-in-arctic-erupts-a-second-time-from-methane-emissions/) that drilling can cause these explosions, "leaks from production facilities may have led to the forming of ‘gas pockets’ and consequent eruptions". It is going to be challenging to do this scale of drilling with middle age technology, but perhaps with a bit of hand waving that could work. [Answer] [Greek Fire](https://en.wikipedia.org/wiki/Greek_fire) is one man-made option. It was a mysterious and terrible incendiary weapon used by the Byzantines in roughly your period. It's perhaps not quite as powerful as you need, but could make for a good story because all we really know about it are educated guesses by Medieval historians and awed witness reports. This would allow you to tailor it a bit to what your campaign needs. By some accounts, it was powerful enough to torch a fleet, and only burned stronger in contact with water. Your character might know of a vast underground [cistern](https://en.wikipedia.org/wiki/Basilica_Cistern) filled with Greek fire, or of a way to feed it into a city's sewers or aqueducts. The Wikipedia page links to the main historical sources. Some possible pieces of inspiration from fiction: C.J Sansom uses Greek fire in one of her [Shardlake novels](https://en.wikipedia.org/wiki/Dark_Fire_(Sansom_novel)), which are set close to your time period. Raymond Feist has something similar to it burn down a city by firing its sewers, in his third Serpentwar book. I haven't linked to it here to avoid spoilers. [Answer] Your problem is that there's no naturally occurring chemical chemical compound I can think of that will produce the effect you want (total destruction) quickly. As Geoffrey suggested a coal seam fire will do it but its a slow process. So if the villain's aim is just to ruin the townspeople not necessarily kill them that would do the trick. Beyond that? Something like a natural gas explosion could be done and could be quite violent but they are very localised. One possible solution however might be a coal seam gas explosion in a coal mine! But it would basically require that your town is built over a deposit of coal and that historically a large part of it's living was made by mining it, even if that's not so much the case now. For a start the seam would have to be close to the surface for the medieval miners to exploit it. Then the level of engineering available would mean lots of narrow, poorly ventilated mine tunnels running under the village. You might have also posit the existence of a geologic fault, maybe a large underground chasm (or series of smaller chasms) where gas could accumulate over time that the villages had discovered while mining long ago and then sealed off because it was easier and safer to work around than try and work in. [Answer] Right, coal or more specific coal dust. Look up dust explosions or fuel air bomb All you need is a confined area a source to allow oxygen into the area and a fine dust or particle mist. Even these or gas explosions won't produce devastation above ground in a miles wide area. But may be enough to collapse some areas or create blowouts of hot gases or other nastyness. More directly to your scenario I possible plotline could be a fungus infests a large cavernous area. Normally another creature would feed on this fungus to keep it under control. However the evil villain has exterminated the controlling orginisim, leting the fungus grow wild. In a short time the fungus will mature mass release its combustible spores. [Answer] The secret ingredient which your villain has (that others do not) is knowledge. He somehow knows that beneath the soil layer of these lands, beneath a thin layer of water-impregnable igneous rock, there lies an enormous deposit of calcium carbide. This substance, when exposed to water, releases acetylene gas. To decimate all life for miles around, he need only bore a hole down through the igneous rock, then divert a nearby river into the opening. The resulting geyser of flammable gas then only needs a spark to ignite and once that conflagration back-burns into the hole, the resulting explosion will shatter the igneous rock shell, making the surrounding lands subject to spontaneous acetylene fire whenever the rains fall. Could this happen in the real world? Probably not. But it is chemically valid, so that is probably good enough for a D&D scenario. [Answer] So you probably can't find an explosive material from the middle ages that would cause that much devastation, but the Roman's destroyed large swathes of land using a form of hydraulic mining technique that Pliny the Elder described in 77 CE. The evidence of that technique can still be seen today in Spain at Las Medulas and other spots in Europe. <https://en.wikipedia.org/wiki/Las_M%C3%A9dulas> So maybe the villain uses gunpowder/black powder (9th CE China, the medieval formula was decaying matter, urine, and oxygen closer to nitrogen crystal fertilizer) to set off a chain reaction that causes a devastating flood that would wipe out a large swath fairly easily. Maybe targeting an aqueduct, or diverting it to fill up this large basin similar to what the Roman's did would serve your plot. [Answer] Perhaps your villain discovered a [natural nuclear fission reactor](https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor), having one such reactor causing an explosion is [unlikely to happen naturally](https://earthscience.stackexchange.com/questions/2147/natural-nuclear-explosions). However, maybe your villain discovered a deposit which just needs a "little" push to get it critical. I put little in quotes because the size of that push might be larger than the resulting reaction, but, with a little bit of handwavium maybe that push is smaller for this particular deposit. If we can accept that: Then it would take significant preparation and time for him to set up this explosion. Plenty of time for a band of heroes to hear about his plot and venture out to stop his evil deed...Looting everything that isn't nailed down along the way... [Answer] One box containing nuclear grenades (manual included) Q: "The villain of my piece knows of some substance (TBD) underground that, when ignited, would destroy everything within several miles of the ignition point. The problem I am running in to is I would have no idea what kind of substance that would be." This assumption of your villain being aware of the destructive force poses an issue for your story. Medieval people were not aware of the possibility of any weapon of mass destruction. When the TBD object is first discovered, your medieval character will have no idea what to do with it. The knowledge about the destructive force can only be there, if he was able to activate and test it. Now suppose.. he found a small stock of 80kT nuclear grenades, left (or hidden !) by 24th c. time travelers. With the stock, a small manual is provided and warnings about the apocalyptic effects. Each grenade has a time clock, enabling to get away safe, before the thing goes off. Your villain character got curious and took one of these grenades to an uninhabited mountain region. He followed the manual and tested it, so he knows what the weapon can do. [Answer] Black powder existed since before the middle ages, although it wasn't known in Europe for some time. The only limit on how big a boom is how much time/money you can spend on making it. Destroying a whole city will take a lot of powder but it could be done. [Answer] Does it have to physically destroy stuff or is suffocating everyone in the area good enough? If so, find a way to trigger a [Limnic Eruption](https://en.wikipedia.org/wiki/Limnic_eruption). A small landslide could be sufficient. [Answer] Your villain loves insects. <https://en.wikipedia.org/wiki/Bombardier_beetle> In your world, you can have a variant that is slightly more explosive or larger. However, this is a hypergolic reaction, not one that needs to be ignited. Just two liquids that contact each other. He has as much time as needed to breed them and has developed a method of extracting their explosive organs and storing them. Given time and quantity, you have enough to do serious damage. Pack it into a shallow rocky cave and you can get your explosion. [Answer] ## Lava It's a substance that is underground. It can be incredibly destructive. It ignites most of what it touches. Rather than 'ignite it' the villain evokes or triggers a lava flow or an eruption. Beyond the infamous Pompeii eruption in the Roman era, Mount Vesuvius erupted after WW II and destroyed some local towns around Naples. (My source on that is a book Naples '44 by Norman Lewis that I no longer have access to). There is ongoing lava flow from Etna, which is on Sicily, in the news now and again. Since I also play D&D 5e, I'll offer to you that your villain can get access to the level 8 earthquake spell (druid/cleric) and use that to create deep enough fissures, or a fracture/fissure in just the right place, to trigger a locally risky fault zone that either starts oozing lava, or erupts, based on how you want to narratively implement the Lava hazard. Do you want slow and inexorable, or fast and furious? That's up to you as the DM. You can also, as the DM, establish that the villain is the only one who knows how close to the surface the lava zone is, such that the calamity comes as a surprise to the local inhabitants. You have a lot of latitude in the 'how' of implementing a natural disaster. ### Examples close to your time frame: Monte Nuovo or Vesuvius I used to live in the Campi Flegrei region of Italy. > > [Monte Nuovo ("New Mountain")](https://en.wikipedia.org/wiki/Monte_Nuovo) is a cinder cone volcano within the Campi Flegrei caldera, near Naples, southern Italy. A series of damaging earthquakes and changes in land elevation preceded its only eruption, during the most recent part of the Holocene, which lasted from September 29 to October 6, 1538, when it was formed.[2](http://www.naplesldm.com/goldenage.php) The event is important in the history of science because it was the first eruption in modern times to be described by a large number of witnesses.[3] The eruptive vent formed next to the medieval village of Tripergole on the shores of the then-much larger Lake Lucrino. The thermal bath village, which had been inhabited since ancient Roman times and was home to notable Roman-era buildings including Cicero's villa, was completely buried by ejecta from the new cinder cone. Tripergole's ruins and its important thermal springs completely disappeared under Monte Nuovo such that the exact location of the village can no longer be identified.[4] > > > And then there's Vesuvius again... > > [In 1631, Mt. Vesuvius gave vent to a powerful eruption](http://www.naplesldm.com/goldenage.php). By all accounts, it was a highly explosive event that rivalled in intensity the famous eruption that doomed Pompeii and Herculaneum in the first century a.d. Sources say that the eruption destroyed most of the towns in the area of Vesuvius. The event was so terrifying that it stoked the creative imaginations of the great painters of the day, primarily > Micco Spadaro (name in art of Domenico Gargiulo, 1610-75). His "Eruption of Vesuvius in 1631" (painting, right) shows the procession of the populace, viceroy, church prelates and aristocracy. They carry the bust of the Patron Saint, Gennaro, in a show of penitence, invoking divine mercy. > > > Given that this is set in D&D 5e: magic exists. ]
[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. For reference, here is a type of safe I am talking about: [![a Liberty quality gunsafe.](https://i.stack.imgur.com/QCcFc.jpg)](https://i.stack.imgur.com/QCcFc.jpg) Gun safes are extremely strong, they are on the more expensive end made with solid steel plates. But I am unsure whether something like that could survive nuclear war. The worldbuilding context is that nuclear war happened, but some artifacts survived from ww3. But any artifact that I know of that is part of us daily life, like laptops, watches, toys, etc is not strong enough to survive global thermonuclear war. So it wouldn't be realistic for them to survive in any capacity. Then I thought, what about a safe. But I am unsure of the relative power of the nuclear stockpiles and of the durability of the leading consumer/civilian gunsafes. Would it be plausible for a safe like the one above which is made of steel or a similar or weaker material to survive point blank sustained nuclear blasts? A note: please derive your answers from the premise that it is a direct impact/blast, where the nuclear blast is within 9 yards of the safe. Also base your answers off of the assumption that the safe is in a standard consumer house, with no additional protection and not being underground. I think that the safe will be disintegrated, but I do not know enough about material strength and nukes other than what is in movies. [Answer] As specified, this question is trivial - you're saying that a thermonuclear weapon is going off within nine yards of the safe. Though there's variation, a relatively typical thermonuclear weapon in modern arsenals is ~100kt, so we'll go with that. Such a weapon has a fireball radius of 170m, so at nine yards, the safe will be well within the fireball radius. Now, explosions are tricky things. It's not entirely impossible that debris might strike the safe and fling it away, allowing some mangled remains of the safe to survive. It would not look like a safe anymore. Otherwise, if the safe is engulfed by the fireball, no firesafing is capable of withstanding tens of millions of degrees; the safe would be vaporized. No trace of it would remain. A 100kt explosion has an approximate energy release of 4.1 petajoules; the enthalpy of vapourization for iron is ~350kj/mol, or 6kJ/g. Though it's unrealistic to assume all that energy could be used strictly to vapourize iron, that means that it could, theoretically, vapourize 683 thousand tonnes of iron. Most of that energy goes elsewhere. But more than enough of it sticks around to erase a gun safe from existence. [Answer] ### Steel may not remain solid within meters of a nuclear explosion 1. The safe is not “extremely strong” at all. The model is likely Liberty Safe Co.'s [Freedom 30](https://www.libertysafe.com/collections/freedom/products/freedom-30). According to the specs, the save is constructed from 14 gauge steel sheet, which is [slightly under 2mm of thickness](https://www.custompartnet.com/sheet-metal-gauge). There is a layer of thermal insulation rated for 40 minutes in a 1200°F, or 650°C fire. The mass of the safe is 200kg. This is rather an entry-level safe, satisfying most U.S. states minimum requirements for a gun safe. #### Evidence from the Trinity test 2. For comparison, the [steel tower of the Trinity test was 30m tall](https://www.osti.gov/opennet/manhattan-project-history/Events/1945/trinity.htm), mounted on a rebar-reinforced concrete foundation. I could not find the construction documentation, but it was obviously constructed from very much not 2mm-thick steel. The photograph below shows that each of the four main weight-bearing columns were square extrusions with a cross-section somewhat larger than an adult man's thigh, about 500mm. Extrusion profile is unknown, but we can safely put the thickness of the extrusion wall at 75mm. This yields the estimate of steel cross-section at 1300 cm², and each column's mass, assuming steel density of 7.9 g/cm³, 1300×3000×7.9=31 metric ton. Adding the cross-tie members of the tower, we can estimate the total mass of the steel construction to in the 200‒300 ton range (1,000 to 1,500 of “extremely strong” safes). [![Trinity tower foundation close-up](https://i.stack.imgur.com/uqEMN.jpg)](https://i.stack.imgur.com/uqEMN.jpg) Trinity tower foundation close-up [![Trinity tower full view](https://i.stack.imgur.com/lRlZc.jpg)](https://i.stack.imgur.com/lRlZc.jpg) Trinity tower, full view 3. The Gadget was detonated on top of the tower, with the yield later estimated at [21 kt TNT equivalent. The tower has evaporated completely](https://www.osti.gov/opennet/manhattan-project-history/Events/1945/trinity.htm), according to the U.S. DoE. The annotated image of the fireball at 25ms after detonation shows the scale of the fireball. Note that the heating front had not yet been overcome by the shock wave adiabatic expansion front, which means that at this point the thermal radiation from the compressed air fireball core was still ongoing (v. infra), and the temperature and pressure at the fireball periphery had been increasing. [![Annotated fireball profile at 25 ms](https://i.stack.imgur.com/e5BbB.jpg)](https://i.stack.imgur.com/e5BbB.jpg) Annotated fireball profile at 25 ms. The scale bar size equals 100m. 4. While most of the concrete foundation also either evaporated or remelted with the surrounding sand, a few rebar ties of one of the concrete pillows have partially survived. Molten and recrystallized sand surface is clearly visible. [![Surviving rebar ties](https://i.stack.imgur.com/NJvUz.jpg)](https://i.stack.imgur.com/NJvUz.jpg) Surviving foundation rebar ties #### Rough theoretical analysis of fireball conditions Dynamics of a nuclear explosion is analyzed in (Glasstone), while (Brode) additionally elaborates on the thermodynamics of the early internal fireball conditions. After the energy is released by the nuclear device on the order of fractions of a microsecond, its X-ray part of the spectrum radiatively heats surrounding air. Cold air is opaque to X-rays, and is radiatively heated up to the temperature of about 1,000,000 K, at which point it becomes transparent to this part of the spectrum. The hot ionized gas at this temperature is itself a source of X-rays; this mechanism forms an expanding heating front of the fireball, isothermically propagating outwards, until the temperature drops to 800,000K, when the plasma loses thermal equilibrium with the X-ray radiation, and becomes confined to the outer opaque shell of air. This process is significantly faster than the adiabatic propagation of the shock front of expanding gas, due to the gas inertia, and dominates the fireball up to 75 μs since the explosion, reaching the radius of about 30 m from the explosion. From this point onward, the heat front propagation races against the adiabatic expansion of the hot gas. In the Trinity case, the last frame showing the expansion of the heat front is timed at 25 ms from the explosion. At this time the adiabatically expanding and cooling ball of gas overcame the radiative heat front, and temperature and pressure began to drop significantly. The steel construction readily absorbs the thermal X-ray radiation, and, partially, γ-radiation: HVL=2.2 cm in pure iron for Co-60 γ-source (Johnson), which puts the absorption figure at about 50%, pre-heating if not melting the bulk of material from the initial intense γ-pulse. This combined radiative heating causes quick ablation of material, with the entire tower material undergoing more likely a supercritical phase transition than evaporation, on the time scale of 100-1000 μs, well within the intense thermal radiation-dominated, high-pressure fireball state, persisting for about half the time of the observed shift to adiabatic regime at 25 ms since the detonation, i.e. ~10 ms. The wide estimate range reflects a multitude of unknown and hard to account factors in this test, but still, even conservatively, is under an order of magnitude of the timespan of the required environment conditions. #### References Brode H. L. A Review of Nuclear Explosion Phenomena Pertinent to Protective Construction. R-425-PR. RAND Corp., May 1964. Glasstone S. (ed.) The Effects of Nuclear Weapons, rev. ed. U.S. DoD, U.S. AEC. April 1962. Johnson T. E., Birky K. B. Health Physics and Radiological Health, 4th ed., Wolters Kluwer, 2012 [Answer] So, we have some answers based on the Hiroshima Bombing, though the Hiroshima Bomb is woefully small compared to what would be used in full on global thermo-nuclear war. The closest structure to the explosion is the famous Genbaku Dome, which survived more as a matter of being directly under the blast, which melted the copper metal dome, allowing the actual blast to be pass through the structure, and exit through ground level doors and windows little damage to the structural integrity. It was 150 meters from Ground Zero and there were no survivors from inside the building. The closest survivor to the attack was 170 meters from the blast and was in his basement at the time of the attack. The closest survivor to the hypocenter (the center of the blast according to seismological data) was 300 meters from the hypocenter, a woman who was in the vault of the bank at the time of the explosion. Most structures that survived were those that were re-enforced to survive earthquakes. For a gun safe to survive with it's contents intact, it would first need to be stored in a place that would not be line of sight direction from the blast. Otherwise, the intense heat from the light would likely melt it, and failing that, the heat may cause the ammo inside to discharge inside the safe. That said, the guns themselves will survive, but as the saying goes, "Guns don't kill people. Bullets kill people." That said, if the safe isn't in the direct light of the blast (and close enough to the fires from things that are, you now face the overpressure. Good news the fires are suffocated and thus go out. Bad news... the structure is now being hit by enough pressure force to rip structures off foundations and level buildings within a radius of several miles unless re-enforced. If your safe is not bolted down or below the ground, it's probably going to be gone with the wind. It may survive that... but the contents will be banged up. If it is secured enough, at this point, it's probably a good place to keep things safe. Assuming the bullets inside didn't misfire and the overpressure wave would get in the way. If it's an electronic safe, there might be an issue with getting it open because of the EMP frying unshielded electronic devices. If you know the attack is inbound, getting electronic devices into a faraday cage will protect them and most houses in the U.S. have at least one that you can fit some laptops, tablets, and cellphones into if you get enough warning. Afterall, what do you think that wiring mesh on your microwave's window is for? Decoration? So long as you aren't an idiot and turn the microwave on with your electronics inside, they will work after the bombs start falling, provided you are far enough away that radiation is your next concern. Though don't expect them to do much beyond the battery life you have on them (The going theory is that a large scale attack on the U.S. will include one Nuke detonated at an extremely high altitude somewhere over the geographic center of the nation. The EMP from this one nuke would fry most electronics in the lower 48. So you will likely not have power for a recharge for them AND probably won't have cellphone service either. But you have your Angry Birds for the rest of the battery life!). One of the best known structures for surviving a direct nuclear attack is the Cheyenne Mountain Complex, a major U.S. Airforce Command and Control bunker designed to survive a near-direct nuclear attack (most nuclear missiles are not precise because the likely range of error would still leave the target in the blast radius of the nuke). It's estimated that at the height of the Cold War, the U.S.S.R. had enough missiles pointed at this thing that it would be directly hit with an explosive force of 1 Gigaton of TNT (the largest yield of a single bomb is 50 megatons, and the bomb itself was so large that using it as a weapon was infeasible). [Answer] ## Extremely unlikely Nuclear bombs such as the one who fell in Nagasaki and Hiroshima leveled out buildings kilometers away from the epicenter, and those bombs are considered to be weak nowadays1. Some of these were made of reinforced concrete, and on some you could see very well the iron structure bent by the blast2. The closer you get to the blast center, the higher the pressure and temperature gets. Even if your safe is made of 50cm deep layered steel walls, it won't stand the blast at point-blank range. In fact, some [people already blew up](https://www.youtube.com/watch?v=dxgPX5-cmvc) safes with much, much less power than those of a nuclear bomb3. --- 1 : Nagasaki and Hiroshima suffered blasts of around 21 and 15 kilotons of TNT, respectively. Modern bombs tend to have much higher yields, ranging in the hundreds and thousands of kilotons. Source : [Wikipedia](https://en.wikipedia.org/wiki/Nuclear_explosion#The_beginning_(fission_explosions)) and [this list of USA bombs](https://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html) 2 : You can find pictures of it online, such as the tests made for the trinity project [here](https://media.cnn.com/api/v1/images/stellar/prod/200729173403-08-hiroshima-nagasaki-restricted.jpg?q=w_1600,h_1233,x_0,y_0,c_fill/w_1376) (full [source here](https://edition.cnn.com/2020/08/04/world/gallery/hiroshima-nagasaki-atomic-bomb/index.html), ⚠️ some photos are not for the faint of heart!). 3 : And much other things, including [cement-full trucks with only conventional explosives](https://www.youtube.com/watch?v=Gxm_qpKh7Jw). You really don't need that much power to blow things up! [Answer] There are all sorts of atomic bombs. It is hard to get your conventional A-bomb to detonate with less that 0.5 kT. There were calculations done to see what detonations might be possible to avoid the test ban treaty, using very small bombs, surrounded by crushable material (gravel, coke) to break up the characteristic P-wave shock. The only things you might be able to hide were too small to stand a reasonable change of a predictable yield. You could make a bomb out of something with a shorter half-life. There were theoretical studies on using Californium, with a critical mass of 20g, for a nuclear rifle bullet. You would have to make your ammunition, but it seemed feasible in the fifties/sixties. Never built as far as I know. But everything between that and the Tsar Bomb are 'thermonuclear weapons'. Why 9 yards? If you are aiming at buildings, you would use an airburst weapon. The shockwave reflects off the ground, and the wave and its reflection form a single shockwave, called a Mach stem. The overpressure of this shock wave is what brings down buildings. This is why the Trinity test was put in a tower. If you put it higher, you can avoid fallout. So, are we above, or below or to one side of the bomb, and why? I would have thought for every gun in a safe within 9 yards of the detonation that is very unlikely to be in a fireable state, there would be three million gun safes buried in collapsed buildings 9 miles from ground zero, and some of them would survive. [Answer] Short answer: No. Longer answer - Within 9 yards of a Thermonuke? I'm fairly certain that the safe would be turned to Plasma near instantaneously. First reference is this: [Liberty Safe Torture test with Det Cord](https://www.youtube.com/watch?v=wYfvhLqkOnY) It's a torture test of a Liberty safe and a competitor safe, they appear to just be using DetCord - the Competitor safe performed badly, the Liberty safe held up. But we must now put this in perspective, they used maybe a Kilo? of conventional explosive. The smallest conventional nuclear explosive (W54 warhead) had a yield at it's lowest of 10 kilotonnes of TNT. The smallest Nuke (not a Thermonuke) is 10,000,000 times more powerful than the above YT test. Another explosion to put this into perspective is [The Halifax Explosion](https://en.wikipedia.org/wiki/Halifax_Explosion) which is when a cargo ship carrying munitions exploded in Halifax, Nova Scotia, Canada - with an estimated force of 3 Kilotons of TNT (again, 1/3rd the smallest possible conventional nuclear yield) - The only bits that survived somewhat intact where her 90mm Gun and her Anchor fluke, both would have been made of Steel and both would be significantly heavier and denser than the steel used in a Consumer grade Gun Safe. The website for Liberty give a weight of a high-end consumer grade safe of approximately 300 Kilos, whereas the Gun barrel from a 90mm naval artillery piece weighs about a tonne and the Anchor from the blast weighs about half a tonne. And again (I must stress) that this explosion was with conventional explosives that where significantly smaller than the smallest nuclear explosion. We are also not factoring in the differences in explosions between Nuclear and Conventional explosives - specifically the Fireball from a Nuclear explosive is several million degrees, it is literal Plasma - whereas a conventional explosive of a similar kilotonnage does not have the same intense heat that a Nuclear device produces, even if the blast wave propagation is functionally similar. The only scenario that is within the realm of possibility would be a Gun Collector who built a strong room in the basement of their house, a few hundred meters away from a Thermonuclear blast. Such collectors do exist outside of the US and often prefer a dedicated strong room as they are functionally harder to break into than a mere safe. ]
[Question] [ I've been thinking about a world in which nuclear power and nuclear weapons were never developed. What kind of mechanism would allow this to be possible? Nuclear weapons seem the easiest option, with fears of of nuclear proliferation leading to various nations agreeing to dismantle and refuse to build weapons. This was attempted in the early UN via the Baruch Plan, in which it failed due to the Soviets being suspicious of the American dominance of the organization. Had a more equitable balance of power existing among international organizations, such a solution might have been possible. The harder question is about how to eliminate nuclear power as well. Most disarmament plans feature provisions that allow for well regulated nuclear power. By what mechanism might nuclear power have never been fully developed? [Answer] ### Just make a world where uranium and friends are really rare. Nuclear power reactors, and nuclear weapons, need rather somewhat rare and heavy elements, in order for them to be produced, and in other for them to work: thorium, uranium, and a few others. So, in a world where these elements are either extremely rare, or way too hard to dig, or are simply not there, then these things wouldn't be developed. Even if there's nuclear physics, even if the scientists understand the math and know how to make a bomb, they would never be able to actually build a nuclear weapon without these materials. And even if they were persistent and wanted one anyway, it would be way harder to artificially breed these elements in reactors, raising the costs of assembling a nuclear weapon to the point that it is just impractical, and other defense technologies are better. [Answer] ## Wait a bit longer for for the appropriate sentient species to appear on the scene. U-235 half life is about 700 million years, so if you wait for an additional 2 billion years before a technological species arises, the natural fraction of U-235 drops from about 0.7% to 0.1% - the first stage of enrichment is the hardest, and this additional reduction in fissile fuel would make developing nuclear power much harder. It is already very difficult and expensive for a nation to enrich uranium. The Manhattan project was about $25 billion in current dollars, with 0.1% U-235 I would expect this to be over 10 times as much because the initial enrichment step would be much harder. Admittedly, this was a crash project with with goal of a bomb, but most of the expense was the cost of enrichment - which is necessary for nuclear power plants too. If you think that this is not expensive enough to prevent a nuclear power consider how much more expensive it would be than other forms of power generation. There is just not much incentive to develop nuclear reactors when it is well-known that they will be more expensive than what you already use. If you are just really stubborn about it, just wait a few more billion years before you start trying to make nukes to make it ludicrously expensive. [Answer] PhD in energy policy - my dissertation focused on (among other things) the history of how power grids evolved. Nuclear power is not unique or noteworthy as electrical generation schemes go. It's a basic thermal-to-electrical conversion - the exact same technique that coal/gas/oil/biomass/waste-to-energy generation stations use: 1. Take hot thing. 2. Boil (a whole crapton of) water. 3. Force pressurized steam through a turbine to create rotating mechanical power. 4. Spin a magnet inside some coils of wire (really honkin' fast). Step 4 creates electrical current, aka electrical power. The civilian nuclear power industry is the beneficiary of these treaties not because it's somehow necessary - but instead because it already exists. In policy (and engineering/economics) circles we talk about the "lock-in" effect, aka path dependency. The principle is that once you've decided on a specific scheme, you create further incentives to continue that scheme because the costs of doing so, compared to the costs of switching to another scheme, are lowered by the existence of infrastructure you've already built. If you never develop nuclear power in the first place, you'd never notice the absence of it. So the good news is, you don't need anything special to replace it. Coal, gas, oil, anything that makes heat enough to boil water can be used to make electrical power in exactly the same way. If you're wanting something with (near-)zero marginal carbon, solar, wind, biomass, geothermal, and tidal harness are all viable - and if you went that route you'd want a diverse portfolio and to add grid-scale energy storage as well. As others have observed there's a million reasons to NOT develop nuclear power/weapons, and once that choice is made, you simply use other candidate technologies - of which there's oodles. My favorite, btw, For power at the same scale, with the same costly investment, and the same (less, really) real estate footprint? Launch your solar power to orbit, beam down with microwaves. Receiving stations replace nuclear reactors, and otherwise you're in the same societal look/feel. [Answer] I'm going to go somewhere different, make the World War 1 aftermath less costly to Germany and the other Central Powers. The real-world WW2 was so ghastly and desperate that it would not have mattered if some agreement was made in the 1920-1930 period to limit nuclear experimentation ("we better do it because we sure believe they are"). But World War 2 was in great part a reaction to having dumped the costs of WW1 recovery onto the Central Powers, eliminate WW2 and somehow have the League of Nations be a viable force. [Answer] # A catastrophic accident Most real-world opponents would cite the very real possibility of nuclear meltdown. I mean, the word Chernobyl is forever associated with [the nuclear reactor explosion that contaminated parts of eastern Europe](https://en.wikipedia.org/wiki/Chernobyl_disaster). To this day, they still don't know how to clean it up. [Fukushima is in much the same state](https://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster). Had nuclear energy been developed first (and not required such secrecy) [the US Army's SL-1 reactor accident](https://en.wikipedia.org/wiki/SL-1) might have ended all public support some 18 years prior to [the Three Mile Island accident](https://en.wikipedia.org/wiki/Three_Mile_Island_accident). [Answer] The initial estimates about the feasibility of a chain reaction were very different for the Germans and the US. Heisenberg incorrectly assumed that the mean free path for the neutron was much longer than it really was. The initial experiments with graphite as a moderator for chain reactions used graphite that had been synthesized with boron electrodes, and boron is a neutron absorber so the German graphite was contaminated. The US recognized the boron issue and was able to establish a chain reaction using a graphite pile. The US also got better experimental data on the mean free paths, so they thought that a uranium bomb might be feasible, but were still surprised that it took less material than they had thought. So given the massive efforts it to took for the US to develop the bomb, for story writing purposes it might be reasonable to assume that US killed the project because it was assumed not to be feasible. Then after the war, it might be assumed that for political reasons that bomb making was not desired. [Answer] Nuclear physics delayed until nuclear engineering not needed For whatever reason, solid-state physics on this world developed faster than it did on Earth, and nuclear physics more slowly. They had silicon solar panels and Rare Earth magnets and power semiconductors, (thence wind turbines), while they still thought atoms were indivisible. Possibly, different plate tectonics or evolution (earlier fungi, so no Carboniferous era, no abundant coal) means that the industrial revolution couldn't happen until the above were scientifically understood. Then it happened based around intermittent renewable electricity, with a lower density of energy usage than our world. Also, maybe they aren't as warlike as we are, so there's no weapons motivation for developing nuclear technologies once they finally work out that it's a possibility. In many animal species, combat is ritualized and takes place between individuals not groups. Unfortunately(?) H. Sapiens is not one of those species. [Answer] # Make U-235 non-fissile or less-fissile To have nuclear power or nuclear weapons, you need fissile material (fusion power and pure-fusion weapons are both still well in the future, even today). To have fissile material, you have to either make it or mine it. Only one fissile nuclide, uranium-235, occurs naturally in significant quantities; all the other types of fissile material (transuranics - primarily plutonium, and especially Pu-239 - and U-233) have to be manufactured by bombarding certain actinides with neutrons to transmute them into the desired nuclides. The only source of neutrons that produces enough neutrons quickly and cheaply enough to do this economically is a nuclear-fission chain reaction - which, at least at first, requires a naturally-occurring fissile nuclide to produce the chain reaction manufacturing the neutrons for the first batches of transmutation. *Translation: in order to have nuclear power or* nuclear weapons, you need to be able to light off a U-235 chain reaction.** Uranium-235 is fissile because, when it fissions, it produces enough neutrons with the right energy spectra for it to be possible for each fission event to trigger, on average, at least one more fission event (and so on, and so on), even with neutrons being lost to non-fission captures (and, for less-than-100%-pure U-235, to absorption by impurities in the uranium, and, for less-than-infinite quantities of U-235, to escaping from the surface of the fuel mass). If we reduce the number of neutrons released by a fissioning U-235 nucleus enough, or we increase the capture cross-section of U-235 enough at the expense of the fission cross-section, we can make U-235 unable to sustain a chain reaction, making nuclear power and weapons physically impossible. If we reduce the neutron production or the fission cross-section by a lesser amount, we can make it so that U-235 may well still be fissile, but requires prohibitively-large amounts in prohibitively-high concentrations to go critical and start a chain reaction, making nuclear power impractical and nuclear weapons impractical to impossible. ]
[Question] [ Assume this city is relatively large by late medieval standards, around 200,000 people. The city is mainly a site for trade due to its geographically central position and being on a river. Also, because it is geographically central, it also means the city is important for the government to project power. What might be the benefits for this same government to sanction certain crime within this important trade city? Crime that would be considered legal within city limits ranges from murder, burglary, trade of illicit substances, and racketeering. This is all under the condition that the crime does not directly affect the government's activities. [Answer] Nonsense. If something is allowed by the law, then it is not a crime. The very definition of a crime is breaking the law. The proper question would be why the law in this city is more lenient than elsewhere. Consider for example the US, which is probably the country with the most legally heterogeneous country in the world. In some places you can walk around with an assault rifle or drive a tank. Do it in other places and it's jail for you. Why? Because different places have different populations with different world views, and the government at federal level does not want or cannot interfere. [Answer] I wonder if you have a too modern view of the state -- by the people, for the people. Over much of history it was by some people, for some people. * Illicit substances Very much in the eye of the beholder. In much of the West, alcohol is legal (and taxed) and cannabis is not. Say you have strong merchant guilds interested in the trade in those substances, and they might have gained permission to do so. Also consider the [Opium Wars](https://en.wikipedia.org/wiki/Opium_Wars). * Racketeering Just who is exploited, and how? Look at the rise of firefighters in [ancient Rome](https://en.wikipedia.org/wiki/Marcus_Licinius_Crassus#Rise_to_power_and_wealth). Early on they were for-profit companies who charged whatever the market would bear when a house was on fire. Or take a medieval craft guild, regulating prices, quality and competition and making sure that guild masters had a decent living. * Special case: Tax farming The government sold the right to [collect taxes](https://en.wikipedia.org/wiki/Farm_(revenue_leasing)). The interests who paid a hefty sum now try to squeeze money out of the city to cover their costs and make a profit on top. Not everybody is allowed to racketeer, but from the perspective of the victims some rackets are legal. * Burglary This one is difficult. When it is made legal, powerful factions like the merchants and guilds mentioned above must guard their properties without the help of a city watch. But do you know the proverb only the rich can afford a weak government? Say burglary is not legal, the rules against it are simply not enforced by the government. That is left to merchants and shop-keepers, who form associations (see racketeering) to employ guards and [thief-takers](https://en.wikipedia.org/wiki/Thief-taker). * Murder As above, making it a kind of civil offense requiring [weregild](https://en.wikipedia.org/wiki/Weregild) if the relatives of the victim are strong enough to insist. [Answer] Crime keeps people scared. Scared people want governments that are tough on crime. To demonstrate you are tough, you need criminals to punish. <https://www.foxnews.com/us/san-diego-homeless-attacks-help> > > San Diegans beg city to curb violence by homeless: 'like you’re in the > 'Walking Dead'' > > > What a packed headline - scared people begging the government for help, violence, and dehumanizing criminals by comparing them to zombies. Your city government sells itself as tough on crime. Law and order. But if it is too good at its job, people forget about crime like people have forgotten about polio and measles because vaccines are too good at preventing disease. Your governments puts on a show of force, public discipline of criminals, etc. Maybe more like what we would consider a protection racket. And they need grist for the mill - so crime is allowed in neighborhoods where people who are disloyal or dissatisfied with the government might live, to keep these malcontents scared. You can still satisfy your followers / customers with the punishment of criminals taken from places where criminals live. Maybe satisfy them better when they see the criminals as the dangerous "other". [Answer] In the real world, we sanction crime already Many countries allowed crime. Prostitution is illegal in many areas and has been at many times. It was and is often tolerated. Reasonings like, "if we don't tolerate it, the sailors will grab our woman of high social standing" were used to justify this. It was certainly still illigal, but as long as it wasn't in the way of society, it was ok. This has happened in many other cases. Drug use for example. But there's also more difficult ideas like violence. Citizens, military and police all have varying amount of violence that is tolerated. Killing someone in self defence, or beating political rivals, or simoly killing an enemy all have different amount of tolerances. Violence in itself however is normally illigal. Your government can use the same. Murder? Don't care. Murder of a policeman or factory worker? Illegal. As soon as the value to the city ramps up, the amount of tolerance will go down. [Answer] ### To punish them. Looking at your situation from a modern lens - Politicians love spending money on those who voted for them, and also those who could be plausibly convinced to vote for them. They don't like spending money on those who voted strongly against them. Dishing out favour in this way is known as [pork barreling](https://en.wikipedia.org/wiki/Pork_barrel). So there's a town where people didn't vote for you / send enough tax money to you / support you in a recent coup / send enough virgins to your harem / whatever spited you. You can show your disaproval by screwing them over at the next chance you get. Maybe their tax rate is raised, or maybe they get less resources allocated. You can also send them a message by withdrawing or reducing the police. The safety of that community is less of a concern for you if you want to teach them a lesson - they're not going to vote for you / support you / etc, why should you waste resources on them? Perhaps after a few months of crime running out of control they'll learn their place and they'll be better subjects next time. [Answer] Crime is allowed in the central city because it symbolically reinforces the government's claim to power. * The current rulers are not nobles whose authority to lead flows down from their heritage. * They are not great businessmen whose authority comes from their wealth and the employment opportunities they bring to the nation. * They are not chosen by God, representatives of the divine authority of the Church. * They were not chosen by the people. They are conquerors, who recently attained their power by defeating the previous owners of the throne. Their power comes from their ability to overwhelm the previous symbol of law. It comes from the standing army which they brought with them, warriors who are now free to commit whatever crimes they wish in payment for their services. Justice has fallen to their might. But they are also not fools. They know that if lawlessness is allowed throughout the kingdom, then the kingdom will very quickly fall. So outside of this city, the law is enforced even more brutally than it was under the previous king. But here in their new home, strength is the only law. [Answer] Instead of government-sanctioned crime, what about a small area with a different government or no government? It could be an independent city where three or more large countries meet, and none of the countries can take it over because the others wouldn't let them. This also gives a good explanation for why there would be lots of devious machinations going on by various government agents in the city, and it would be a prosperous trade hub if it is the best route between those nations. [Answer] To reduce value. Empowered Elite (government) allow crime free reign in certain sections of the city to devalue private property which may not otherwise be accessible due to external ownership, and where applying the rules of eminent domain are not feasible (property seizure doesn't "look good"). After the land is devalued due to criminal activity, the property is purchased by either shell companies or the Elite themselves, razed, the crime is "stopped" (no incentive if no one is there), then it is used for whatever purpose the Empowered Elite wanted to use it for (mining, throughfares, military purposes, a shopping mall, a new castle, etc.) [Answer] > > What might be the benefits for [a] government to sanction certain crime within [an] important trade city? > > > There are already excellent answers to this question, but to add some more real world details that have been overlooked: ### Strengthening Colonial Rule The most famous real-world example is [Hong Kong](http://en.wikipedia.org/wiki/Hong_Kong). In order (a) to facilitate illicit trade in opium and other products, (b) to enjoy an additional local spy network in a large and hostile neighbor, and most importantly (c) to maintain a semblance of order over a large population whose language few of the colonial administration spoke, the Brits maintained deals with the [Triads](http://en.wikipedia.org/wiki/Triad_(organized_crime)) to essentially outsource most public order over the Chinese slums to powerful criminals. [The "tea money" hongbao](https://www.cinemaescapist.com/2018/04/chasing-dragon-critique-british-corruption-colonial-hong-kong/) provided by the gangs were also prime sources of income for the colonial police. Things were periodically shut down or renegotiated, as after the [1956 Double Ten Riots](http://en.wikipedia.org/wiki/1956_Hong_Kong_riots), but the Triads were so entrenched that [even the PRC were forced into deals with them during the handover](https://academic.oup.com/bjc/article-abstract/50/5/851/463592) and has only been slowly chipping away at them since, usually [when they start messing around on the mainland](https://www.chinasmack.com/large-hong-kong-triad-gathering-in-shenzhen-raided-by-police). There are tons of books, TV shows, and movies about this era but lots of them are in Cantonese. To bring the same idea closer to home, [The Shield](http://en.wikipedia.org/wiki/The_Shield) dramatizes the [LAPD](http://en.wikipedia.org/wiki/Los_Angeles_Police_Department)'s similar accommodation of crime as a way of handling the endemic mess in the poorer neighborhoods of [Los Angeles](http://en.wikipedia.org/wiki/Los_Angeles). Essentially, apart from enriching themselves, the Farmington police are shown choosing their battles, angling for local black and hispanic criminal leaders who keep the violence and crime away from better (and whiter) neighborhoods and away from directly harming the local children or the police themselves. ### Handling Temporary Emergencies In [New York City](http://en.wikipedia.org/wiki/New_York_City) during World War II, [the US gov't made common cause with the mafia](https://historycollection.com/10-undeniable-ties-united-states-government-organized-crime/7/) in part to get a better spy network in the leadup to the invasion of Sicily but also to maintain control over longshoreman and other important labor unions involved in maintaining the armed force's logistical network. It wasn't until the 1960s that the Feds got around to cleaning any of that up, in part because they were grateful for the assistance in tamping down any possibility of strikes during the war years. ### Illicit Profits Exceeding Gov't Revenues Another important real-world example is the accommodation of the narcotraficantes by governments in Central and South America, especially [Mexico](http://en.wikipedia.org/wiki/Mexico). Although [coordinated government action limited local problems for years](https://scholar.harvard.edu/files/vrios/files/jcr587052.pdf), over time the amount of money involved in funneling drugs and people through to the US erupted into massive turf wars within Latin America itself. Disunity between local and federal parties didn't help, but mostly the flow of cash reached the point where nearly the entire law enforcement apparatus could be bought, the rest [could be hunted](https://www.nzherald.co.nz/world/in-mexico-cartels-are-hunting-down-police-at-their-homes/OJG54TOADTJW3OBRXWZUHWK2AM/), and (push come to shove) local gangs have sometimes [been better armed than the national military](https://time.com/5705358/sinaloa-cartel-mexico-culiacan/). [Answer] We have good historical examples where this occurred because of jurisdictional confusion. For example, the tangled relationship of royal and Church prerogatives in Europe in the medieval and early Modern period often allowed Church leaders to exempt people from royal laws while on their lands. For example, in an area that later became part of London that was known as the [Liberty of the Clink](https://en.wikipedia.org/wiki/Liberty_of_the_Clink), the bishop was able to license prostitutes, brothels, and theatres. [Kowloon Walled City](https://en.wikipedia.org/wiki/Kowloon_Walled_City) came to be because of a complicated history of claims over a small area of land by the British colonial government of Hong Kong and the Nationalist and Communist governments of China. Britain did not want to govern the area, but also did not want to return it to Chinese jurisdiction. So you ended up with a sort of Passport to Pimlico self-organizing quasi-anarchy without official law enforcement. [Answer] All of that is already legal to some extent in some places Legal in lots of jurisdictions, some of them even real democracies: * Killing humans, for example in self defense, in war, as capital punishment, to save the mother of an unborn, abortion or euthanasia. * Substance trading and consumption: Drinking alcohol, smoking tobacco or cannabis * Taking other people’s property: Taxes, fines, fees, interest, foreclosures The most important part is that the above activities are tightly controlled in order to provide stability and reliability. A successful city or country generally needs stability. You certainly don’t want random murder on the streets to be legal or you’d have anarchy and mayhem. But as long as it’s controlled and restricted in some way it’s perfectly feasible for murder to be legal. Even if it’s just some amount of money (“tax” or fine) you have to pay to the government for committing certain things. [Answer] Hollywood will show you many - prolly dozens - of stories in which "governments" sanction crime for their own devious ends… most often to justify increasing the security budget or beefing up security powers. That and any other Answer uses "government" in a rather loose sense. Even in today's Communist China and the historical USSR, it's almost unthinkable that an entire government would collectively go your way. May we assume the Question is really about agencies, branches or departments, or rogue agents within them? [Answer] Some governments [pork barrel](https://en.wikipedia.org/wiki/Pork_barrel): they favor the electorates that voted for them with money for projects that will benefit those communities - better roads, park lands, new hospital or extension to an existing one, etc. There is also an element of divide and conquer. If the communities are competing with each other there will be less focus on the government. A government that encouraged crime in one area would not do so openly. By encouraging such a situation, the government would openly give the perception of tackling the crime. By doing so, the people will have less of a focus on what the government is doing in other areas, such a corruption and kleptocracy. It also gives the government a better chance of staying in power. One way to unite a people to align with the government is for the government to create common enemy. The criminals in the crime zone would be one such "enemy". [Answer] A wave of crimes sweeps through the city and the government decides to hire some criminals to fight the others. Rather than sanctioning crime they turn a blind eye on certain violations of the law. [Answer] Good policing is hard. There used to be a city police force, but it was massively corrupt. Anyone who couldn't afford bribes would be framed for various crimes. The local government sent in auditors to investigate the police, but those turned out to be corrupt too. In the end, the government gave up. They fired all the police, and the whole of the judiciary; a massive saving in their overstretched budget. There are still laws, but they're never enforced. To protect themselves, the rich hire security guards to follow them around. Ordinary citizens make protection payments to their local mobsters to keep themselves safe. The gangsters realise they've got a pretty good situation going, and don't want to upset things too much by going too far, so they try to keep the peace, most of the time. ]
[Question] [ I have a concept for an asteroid mining station. The metal ingots that are processed are fired out of a railgun towards Earth. How could I slow the ingots down before reaching Earth to avoid accidentally causing an extinction-level event? Edit: The ingots are about 2-3 tons. [Answer] You need to dissipate kinetic energy, which can be accomplished in many different ways. You could build a "reverse railgun" that catches the incoming ingots. Instead of using stored energy to accelerate the ingots to high speed, the reverse apparatus gently slows the ingots over a long barrel, capturing and storing the kinetic energy as electrical power for use elsewhere. You could also build an identical railgun to the one that fired the original projectile, and just fire an identical projectile to collide with the first one. Two ingots of the same mass moving at the same speed in opposite directions will collide, and assuming the collision is inelastic, all the kinetic energy will be dissipated and both ingots will come to a stop. This might be a catastrophic collision that destroys the projectiles, though. Alternatively, you could fire lots of small projectiles that would have the same effect in aggregate, but have less energetic collisions. Since you're firing a ballistic projectile that carries no propellant, you're going to need some external mass or force to affect the projectile. You need to either aim the projectile at whatever provides the mass/force, or bring the mass/force to the projectile. [Answer] To steal an idea from one of Peter F. Hamilton's books: aerobraking! Cast your metal chunks into [foam metal](https://en.wikipedia.org/wiki/Metal_foam) [blunt-body re-entry capsules](https://en.wikipedia.org/wiki/Reentry_capsule). Coat the blunt end with spare rock and whatever else you can synthesise or scavenge from your asteroid mining activities. Attach a suitable solar-powered transponder to them, and shoot them into a suitable re-entry trajectory. If your shooting isn't quite up to scratch, you can add some little rocket engines to them too... nothing expensive, as shipping them back is impractical. Just enough to do a bit of mid- and end-course correction. On impact with earth's atmosphere they'll slow right down, and the stuff you've plastered the blunt end with will heat up and burn off in an exciting and pretty way, rapidly slowing the capsule down. Its terminal speed won't be exactly sedate, but it'll be quite restrained. Let it splash down in the ocean. Beauty of foam metal: it can be less dense than water! Send boats out to retrieve these in bulk, between volleys from your mining facilities. The transponder helps with both keeping an eye on incoming metal packages, and recovering after splashdown. Trying to use these as weapons would be futile as they'd just be too soft and slow to cause any serious property damage, and too hard to aim to hit anything in space or even any specific targets on the Earth, for that matter. Don't worry about exitinction-level events... the Chixulub impactor that killed off most of the dinosaurs was 1012 tonnes. Your multi-tonne slugs are billions of times smaller. Without clever engineering like I've just suggested, it'd be easy to have most of the metal simply burn up on re-entry. [Answer] Fire them slowly. You do not need your ingots to be cooking along like comets. They don't need to punch thru armor. You don't even need orbital speed. You hardly need any speed at all. They just have to get there. Its not like they are going to go sour if they are late. Earth will accelerate them some on the way in. Earth actually might accelerate them a lot. The moon is a safer bet. It is smaller. Your slowpoke ingots will ease up to the moon then get a little frisky on the way down. You will not lose any mass to atmospheric friction because Luna is naked. Neither will you have induced eddy currents and ohmic heating because Luna does not go in for that magnetic field stuff. Your ingots will land with a thump. It is a characteristic thump. Detectors on the moon will triangulate the landing site. Then your robot will go fetch the ingot. Your foundry is on the moon too. Fewer environmental regulations. [Answer] Use a [skyhook](https://www.youtube.com/watch?v=dqwpQarrDwk) It is a more feasible (and fun) version of the space elevator, where the big cable is rotating on itself instead of one side being attached to earth. The skyhook has the advantage to be able to store energy easily when it receives ingots by rotating faster. You can then use this energy to send back supplies to the mining station. You can also combine this approach to the other ones mentioned. [Answer] # Magnetic braking. The foundry is equipped with a "catcher" - a series of superconducting coils that generate a very strong magnetic field. This is the reverse of the famous [magnet-in-the-copper-tube](https://www.youtube.com/watch?v=N7tIi71-AjA) experiment. As a result, a large portion of the incoming projectile's kinetic energy is converted into thermal energy inside the ingot, pre-heating it and making it easier to melt. You would also not need to send them with excessive speeds, because all you're interested in is throughput. If you shoot one of them every ten minutes, they will arrive on average one every ten minutes - after several weeks or a whole year on a longer orbit, it's not that big a difference. And shooting slower ingots requires less power. As @puppetsock pointed out, you don't get away from conservation of momentum: you have some three million kgm/s to go around, so if the smelter masses one million tons, it's going to be moving three m/s in the same direction as the incoming ingot after the catch. Even if it's just 1% of GEO speed, that's still too much (also because you won't be catching just the one ingot). One economic possibility is having ingots coming from two opposite directions. Whatever the orbit it's in, the smelter is going to need some "downtime" when it's too risky or just impossible to send ingots towards it, so you're going to always need more than one smelter, and adjust its working cycle so it receives ingots just in some points of its orbit. At that point, if it lies e.g. on the ecliptic, it can receive ingots when it's at its greatest incoming elongation; its orbital speed will be reduced by each ingot. Then, the railgun will address the same number of ingots towards the opposite maximum elongation point, and the smelter will intercept them and have its orbital speed increased accordingly, compensating the earlier loss. When the smelter, as seen from the incoming ingots, is in front or behind the Earth, another smelter will be approaching the maximum elongation points. [Answer] The simplest way would be to use gravity assists between the moon and earth to cause the ingots to enter a high, stable, but probably fairly eccentric orbit. Basically, the process would go: metals get extracted and refined in asteroid belt => ingots get shot "backwards" (retrograde) from the perspective of the asteroid's orbit around the sun => the ingots "fall" (follow an orbit with a lower perihelion) towards earth => the ingots get close enough the the earth-moon system to be pulled off course => the ingots follow some precalculated path between the earth and moon, each pass of which slows them down a bit more => the ingots are picked up by an orbital craft and brought to a processing facility. Advantages of this approach: -Doesn't require anything to be attached to the ingots. You could include a transponder for safety reasons, but assuming the railgun is reasonably accurate it should be pretty simple to plan the route beforehand and warn any ships to steer clear. Even if it veers off course for one reason or another, the ingots would be pretty trivial to detect and track, and if that didn't work for some reason, the chances of it hitting anything are still very low - think of how many satellites or space stations have actually been hit by meteors (i.e. none). -Doesn't require aero- or lithobraking. Aerobraking is relatively safe (you probably won't end up nuking any major cities), but adding a chaotic, fluid atmosphere and multiplying that uncertainty over potentially millions of ingots means that some are bound to veer off course. Even de-orbiting objects from low earth orbit is inherently unpredictable. Using either type of braking to slow the projectile down into an earth orbit is better, but would lead to at least some loss of material from ablation or, well, from lithobraking. :p Disadvantages: -This method would add to the time it takes for the ingots to reach their final orbit. Given the already-considerable time between the asteroid belt and earth, I don't think it would be too substantial, but it is a factor. -The ingots will probably be put into high, eccentric orbits, since that would take the least number of gravity assists to get into starting from a hyperbolic orbit. The downside would be that it would require more delta-V for the recovery craft the reach them, and even more delta-V to lower and circularize the orbit into something more useful afterwards. Given that your setting has at least some trans-martian travel, orbital maneuvers around earth shouldn't be much of a concern, but it's still something to consider. Edit: Reading through the other answers, I've also realized that this method wouldn't require any infrastructure on the receiving end. Loss of funding, political upheaval, or even societal or environmental collapse can occur without having to worry about bombarding the planet with dense objects at orbital speeds or losing the payload into interplanetary space. Although I imagine that any rebuilt post-apocalyptic society is going to be very surprised to discover a bunch of refined metal ingots sitting around waiting for them. [Answer] Frame challenge. Don't send it to Earth. We don't need it down here. The whole premise of asteroid mining (outside of some poorly researched sci-fi) has never been to acquire materials that we need down here on Earth. We've got more than enough metal down here to do everything we need. The point of mining metal in space is so that you can build big things in space. Let's say you want to build a rocket that can send humans to Titan or Europa or whatnot. The amount of material you'd need to get off the the surface of Earth in order to make such a trip in a reasonable amount of time is prohibitively massive and expensive. It'd be far cheaper to build the rocket in orbit from materials that are already up there. So what you'd be mining for would be materials to build a rocket, and something that will work as fuel for the rocket. You'd need far less fuel than for a rocket constructed on Earth since you don't need to escape our gravity well. So really all you'd need to get off-planet would be the astronauts, food, water, and other basic supplies for them, and enough equipment to be able to construct the rocket in orbit. (If you're doing this on the regular, you've probably been building up the rocket construction facility for some time now, so ultimately all you need are the people and supplies. So you're firing metal ingots towards your orbital factory with rail-guns. Well, you only need to match the orbital speed of the factory (or close enough that someone can fly out and grab them), not slow them down enough to get them safely to the surface. As for fuel, well, you're better off mining comets. Comets are made mostly of ice, which is of course frozen water. Water can be split into hydrogen and oxygen, and hydrogen (along with nitrogen) is perfect for making hydrazine, a powerful rocket fuel. You might also find enough ice on the moon for this purpose. (Launching materials from the moon is far less costly than from Earth due to its lower gravity.) And of course you can use the spare oxygen to breathe. [Answer] Just follow the Apollo/Soyuz landing system: ablation shield plus parachutes. The Apollo CM weighed around 5.8 tonnes, the Soyuz reentry section (middle section) 2.8 tonnes. I have seen pre-parachute speed for Soyuz been quoted as 755 feet/s, that's about 820 km/h - that would likely bury the ingot in the center of an impact crater, so you probably want some parachute, though a smaller one than for Apollo/Soyuz might suffice. Land or water? At sea, you need a ship. That's more expensive to operate than a truck with a crane on land. OTOH moving the ingots once collected becomes much cheaper on water. (Coastline may be a good idea.) If something goes wrong (e.g. the thing crashes into the ground due to parachute malfunction or because the ablation shield didn't properly position itself into harm's way) - well, on water, it just sinks, on land, you have to dig it up, but at least it's there. [Answer] Shooting material in your manner is expensive from an energy, infrastructure, and safety stand point. The more you have the harder it is to transport also. What if there was a way to reverse all of those things? Solar sails solar sails are not made out of gold, and any metal can be used to make solar sails theoretically. So instead of making a transport system for the materials, you can make the materials the transport system. just take your ingots and turn them into large flat solar sails. They won't be as good as NASA's sails but that isn't the point. solar sails require little to no energy besides a small gyro scope and a computer to pilot the craft. The solar sail will need a a solar sail factory, but that is essentially a machine that flattens the material to the needed width and then sends that to a machine that links those thin sheets. The solar sails are very safe, they accelerate slowly and even if they do get into the atmosphere they will burn up. The more material you need to transport the larger you can make your sails, making them more effective. further more, you can transport other things back to earth that can't be made into solar sails using the sails. you can even throw the material with an accelerator and use sails that deploy mid flight to decelerate it. Solar sails are slow, with an acceleration of 0.058 mm/s^2 acceleration it will take 5 and a half years to accelerate to the needed 10 km/s speed and 5 and a half years to decelerate. If you are willing to wait a decade or two you can get it basically for free. If you are willing to spend energy you can use lasers to speed up the acceleration. However, this will be difficult as in order to transfer the power effectively you would need a very big sail or a very accurate laser. However, if you are transferring a lot of material you can make a very large sail without any problem, making the laser not much of a concern. [Answer] Have you thought about using the railgun as an engine? Instead of shooting the valuable stuff towards Earth, shoot the mining waste in what ever direction physics needs to bring the asteroid closer to Earth. Once its in a closer orbit to Earth it will be easier to transfer the valuable stuff off the asteroid and onto the Earth with other spacecraft (or point the rail gun at Earth but now you'll be better able to target things to avoid hitting something valuable). [Answer] Shoot them in a cargo bay of your space truck, which is accelerated beforehand obiviously. if you just shoot them out, without guidance and an orbit correction system - you probably will have a hard time even shoot nearby, not to mention hitting the earth. with guiding block, you provide the energy and general direction and delta-v for your ingots, space truck catches them and its role is to fine-adjust the orbit to make gravitational reverse slingshot maneuver and insert into the orbit of the earth. also, to cause an extinction event you need to shoot a very big lump of metals as if you shoot them as 1-10-100kg pebble even if it coincidently crosses earth's atmosphere it will be funny sparks in the sky, and people will make wishes when they see them. ## if it is big, really big Let's say you have the means to accelerate big objects, 1000's of tons, and more. Then you have all the means for making a canister with [cold thrusters](https://en.wikipedia.org/wiki/Cold_gas_thruster), which works on the oxygen you extract from oxides of those metals, which is about 40% by mass of those materials. And using that mass of oxygen you can maneuver to make a proper insertion. so your asteroid contains everything you need to make a self-delivering package if you are able to provide it with an initial kick. [Answer] shape your copper ingots like a coil, your iron ingots like a cylinder, and give the iron ingots a magnetic field. Then shoot them such that they "collide" on the other side of the Earth. By "collide" I mean the cylinder passes through the center of the copper coil. The eddy currents on the copper coil will serve as a dampener and this will result in a controlled inelastic collision. [Answer] Before I get into my answer to your question, I'd just like to request that you give me a little warning before you begin your bombardment. I'd like a chance to not be here when death starts raining from the skies, thanks. Anyway... Unguided masses shot in the general direction of Earth are going to wander, no matter how tightly you control the firing mechanism. You'd need to spend a tremendous amount of effort on balancing them for starters, and you've already allowed for a 50% variance in mass, each 'shot' would require a fairly large amount of computation, etc. It's a big, expensive job. Once you solve those problems there are a slew of others just waiting for you at the other end. Firing into a gravity well speeds up your projectiles, so they're going to arrive going faster than they were when you launched them. The Sun's gravity will speed them up while they approach, then the Earth-Moon system will pull them in even faster. You're looking at a very large amount of kinetic energy to try to bleed off once they arrive. Most of the normal solutions for the problem will fail in the face of this massive kinetic energy. Aero-braking for instance exchanges kinetic energy for heat, which is likely to result in your deliveries vaporizing in the atmosphere. While some of that heat will radiate away into space, the majority of it will get added to the Earth's total heat. Keep it up long enough and... well, we won't have to worry about the next ice age, I guess. Magnetic capture might be your best option, especially since you can use the process to generate energy. You're going to need a series of large hoops along the expected path, with enough maneuvering capability to get in the right place. A 2-ton projectile moving at high speed will cause a lot of damage to any structure it encounters, so make sure your timing is perfect. Of course the expense of running these gigantic field generators is going to be pretty high, but you're the one that wants to throw kinetic devastators at a populated planet. Of course you could always just throw them at the moon, assuming you're not using it for anything else. You'll need to mine the ores out once the dust settles, but that's OK. It would be far more productive to simply strap a drive system on the packages and have them maneuver themselves into an appropriate orbit around the Moon or Earth. Think more drone, less doomsday cannon. [Answer] ## Make them foldable gliders. Using [rigid origami](https://en.wikipedia.org/wiki/Rigid_origami) and a keen knowledge of the [mathematics of paper folding](https://en.wikipedia.org/wiki/Mathematics_of_paper_folding), your ingots can sprout stubby wings and guide themselves down with all the dubious grace of a Space Shuttle. (No, I'm not actually saying to have landing gear, but make a landing slow enough that the ingot can be picked up off a sandy erg in solid form) The Space Shuttle can also inform your heat shielding for the way down; cobble it together out of plates of slag from your refining process. (Yes, you'll end up with craters and shed tiles of space slag all over the desert - let the environmentalists whine! It's still better than making a mine on Earth... probably, at least according to the PR department. The thickness of the metal ingot should ensure that not too much is lost if the heat shielding starts coming apart during reentry.) [Answer] Calculate an orbit around earth or moon, where the orbital speed is approximately the speed your ingots will achieve by the time they reach that orbit. That's an easy enough task. The ingots will need small thrusters to fine tune orbital insertion, and orbital timing (eg to not collide with other ingots or processing stations, or be conveniently close), but those can be recovered and reused. [Answer] Without some kind of complicated deceleration device attached to each ingot it becomes a complicated problem in orbital mechanics. If time is not of the essence however it should be possible to work out a trajectory that will take your ingots past a series of other gravity wells on the way to Earth. You then use these bodies for a reverse gravity assist. Gravity assists (or slingshots) are currently used routinely by space agencies to accelerate probes into the outer solar system by having them pass close to a large planet on an angle that causes them to gain velocity from that planet's own orbital momentum around the sun - effectively 'stealing' the velocity from the planet. That planet in turn loses orbital momentum (minutely) by an amount equal to what the probe gained - so that the energy exchange balances out. Point is the energy exchange works in reverse as well a probe (or ingot) can lose velocity by traveling in a reverse trajectory, 'dumping' velocity into the planet. Again the planes orbital velocity increases to balance out the energy exchange. The downside is; 1. you would need to attach maneuver thrusters to each ingot together with a navigation computer and radio link. 2. It will take years for each ingot to reach Earth but after the first shot arrives every subsequent shot sustains a continuous supply chain with every new ingot arriving in a predicable and reliable sequence. The plus side is it is very fuel efficient and your ingots can shed most of their velocity while using very little fuel in return. [Answer] Why fire them as ingots? Eject them out of the rail gun as plasma, which would condense into metallic dust clouds on the way. [Answer] You need to fire them with just enough speed to be able to take a trajectory to Earth. And/or, fire them at powerful arrays of magnets that reduce the speed of the ingots to a more reasonable velocity. ]
[Question] [ In my world, there rules a wise government that maintains an Utopia that was created centuries ago. This Utopia was founded by elders that left earth because they felt Earth decayed through wars, famine and - first and foremost - overpopulation. Hence those elders and their successors introduced policies in their distant Utopia to prevent all the root causes for earths deterioration. To me, it is however unclear how to keep overpopulation at bay. The goal of the government is to keep the number of inhabitants equal in the long run but which ratio of newborns is needed for not exceeding the population cap taking natural cases of death into account? [Answer] Make a childless life more attractive and having children more expensive. Empower women Give women careers that reward staying in the work force (with no breaks) longer. If you can stop births before women are 30-35 you will significantly cut the chance of population growth. Tax on children Children should be expensive, perhaps one is tax free, but thereafter there is a fixed fee and a monthly tax per child (obviously this is to pay for school and increased strain on public services that children require). Clearly child benefits should not be available. Propaganda Advertise the benefits of a Child free twenties/ thirties. Give TV ad time to adverts promoting a healthy, childless youth (under 35). Propaganda can work wonders for promoting health and de-stigmatising people to issues like abortion, "pragmatic" family planning should be pushed, free and with easy access to the whole population. [Answer] ## Just look at reality If you have educated women and a good healthcare system such that kids make it to adulthood in one piece by and large, you won't need to worry much about overpopulation -- individual family planning will take care of that for you, as it does IRL. If worse comes to worse, you have family planning consultants who will help prospective couples strategize. If you doubt me on this, look at the birthrates in the US, Japan, and most of Western Europe. [Answer] A two child/family cap will lead to a slow decline due to accidental life losses before spawning allowed children. Exact amount of correction needed is highly dependent on lifestyle (e.g.: a society with high percentage of base-jumpers will need a significantly higher "correction"). You can avoid a fixed amount by setting yearly a lottery with (right to start "building") a newborn child as prize; the amount is the dead-minus-born of previous year. Real problem, in our world is to enforce such limits; all attempts to date failed in a few years (India and China come to mind, but they are not alone). This is not a problem in your case because the "elders" solved it long ago ;) Other schema are possible, such as one child only "by birthright" and one more can be gained by "special feats", sport competitions, money or whatever else; keep the lottery to "even-out" the total. Specifics are dependent on your world. [Answer] It depends on what your government is willing to do to maintain population. For instance, if you don't care what the people think / government has absolute power, you could simply kill off people when you're above your cap. However, I get the feeling that this approach isn't what you're going for, so I'll provide a couple other options. Sex ed Educating people about the dangers of unprotected sex and providing contraceptives is a very good way of reducing unwanted pregnancies, allowing all children born to have been planned for. While not significantly reducing the danger of overpopulation, this policy makes population growth/decline/stagnation more predictable and manageable by your government. Advance society Shalvenay touched on this, but advanced societies tend to have lower birthrates, mainly as children have stopped being necessities (for subsistence farming) and have become something more of a burden on parents. After all, it used to be that children helped produce food and clothes, but now parents have to provide that for them. Children are also an enormous time commitment, so for the most part only people who want children, knowing fully their responsibilities, have children. To increase this effect in your society, your government could sponsor efforts to develop underdeveloped parts of the world, if any exist. Once your planet is sufficiently developed, you could maximize the time commitment of children by making daycares illegal, possibly under the premise of helping children by having their parents be the ones who raise them. However Even with both of these options in place, your population will still grow. Just look at the US, one of the most developed countries in the world, where the birthrate is still significantly higher than the death rate. Unless every person in society is willing to limit the number of children they have, you're going to need to take extra steps. If you want to truly and reliably stagnate populations, your government is probably going to have to become morally questionable. Forced infertility You could develop medicine that babies are given at birth to render them infertile, and only with a government permit could they be provided with a drug to stimulate their reproductive systems again. The downside of this approach would be the immense resources required to manage these permits and the possibility of wealth becoming a factor in securing one. Brave New World-esque factories If you've ever read Brave New World, you'll be familiar with this suggestion. If your society is advanced enough, you could produce children in artificial wombs, making entire factories for children. This would give the government complete control on population growth with comparatively fewer resources. Overall If you use any of these options, your government is going to need to do a couple things to ensure their success. Firstly, census taking will have to change. Reliable death counts and birth rates will need to be calculated more than every ten years, probably at least yearly. Computerized birth and death certificates that automatically add to a counter is one option that comes to mind. Secondly, the government will have to take complete control of the world, if they haven't already. People cannot be allowed to have the freedom to have children if you seek to manually curb population growth. However, there is one final option your wise government can take if it does not wish to pursue the above methods. Nothing If your government remains in power forever, it is safe to say that if they wait long enough, the population will grow faster and faster, until food cannot be produced fast enough. This will cause mass starvation and the population will drop significantly and then grow to a sustainable level. Unfortunately, on Earth a "sustainable level" will mean that nearly every aspect of the environment becomes artificially controlled to produce just barely enough food for the now stagnant population. Foods that are efficient to farm/grow like corn, potatoes, and fish will begin to dominate markets, and many species useless to humans will die out. [Answer] A la, Enders Game, families could face significant disincentives or even punishment if they have more than two children. Some families may still do so but they would be a vast minority; this small number of extra kids would, to some degree, balance out "accidental loss before spawning" issue ZioByte mentions. [Answer] # Education In our modern culture education seems to be leading to declining population. There is a lot of speculation as to why this is (women having careers, knowing that two children is better for the enviroment, etc) but the statistics support it. Look at Italy, Japan, or many other nations. <https://en.wikipedia.org/wiki/Population_decline> [Answer] Introduce a drug that extends lifespans indefinitely, but has the side effect of sterility. No deaths; no births = stable population. (incidentally, this concept was used in [an episode of Stargate](http://www.gateworld.net/sg1/s4/416.shtml), where an alien race gave something like this to Earth. It didn't end well) [Answer] No procreation. New persons obtained as needed off the shelf. When these elders made their migration from an overpopulated Earth, probably a lot of people wanted to go with. Perhaps all pioneer / refugees were stored cryogenically for the trip. Suppose that at the new site they decided that the site could only support a population of X. But in the ship they have 1000X persons. The answer: thaw persons from the cryoship to make your population of pioneers, and then thaw more to replace them as they age and die. There are no children born on planet. Maybe they can't be (everyone is sterile, or all children are mutants). Maybe they are prohibited. Maybe all the pioneers were one gender. In any case this approach makes for some interesting stuff storywise: for example, the culture of the group would in many ways be parked where it was when the ship left, because new people are not born into the culture. Replacement adults are the same generation as the people they replace- p eople who are newly thawed would be getting up to speed in a new land with people who were their peers hours before but now are older and more experienced. . Why are some people thawed and others left frozen? Do people ever get put back in the freezer? It would also be interesting to learn what happens when they get down to the last few persons on the cryoship. [Answer] Make children making decisions the job of the society rather than the individual parents. When I was in Australia, I took a tour of the Outback. One of the stories that was told to me is that aboriginal couples would not have a child until the elders come to the conclusion that there is enough food available to support that additional mouth to feed. Whether you believe the aborigines had sufficient conscious control over a couple's behavior for this story to be true or not, the key to stagnation without having to kill people is to control the birth rate. Maybe the aborigines were different enough from us culturally that they could accomplish this goal. Any society which can approach becoming a utopia will certainly be different enough. [Answer] Easy: taxes. This is something easily adjustable that the government can change to respond to the latest population figures. If the population is getting too high, increase taxes on children. If the population is getting too low, provide tax rebates when you have kids. [Answer] ## Your Utopia will have a problem with underpopulation not overpopulation A stable population requires that [birth rate](https://en.wikipedia.org/wiki/Birth_rate) equal [death rate](https://en.wikipedia.org/wiki/Mortality_rate) over the long term. That is, if, on average, 1% of the population die each year then 1% must be born to replace them. This does not have to match year on year but it does have to match over the longer term. To achieve this the [total fertility rate](https://en.wikipedia.org/wiki/Total_fertility_rate), the average number of children that would be born to a woman over her lifetime needs to equal the replacement rate. Naively, the replacement fertility rate is 2.0 - that is, each woman must on average give birth to 2 infants - a boy and a girl. In reality (even in Utopias) the rate needs to be above 2.0 because slightly more boys than girls are born (your Utopia may deal with this) and not all girls will reproduce by choice or circumstance (death, infertility etc.). In the real world, the replacement rate depends on how good the life expectancy of (particularly) girls is - for the UK the replacement rate is about 2.075, for developing counties with poor prospects of surviving to and through your fertile years the replacement rate can be as high as 2.5-3.3. For the world as a whole the rate was 2.33 in 2003. Pre-agriculture the number of humans was between 1 and 15 million. Post the development of agriculture this rose to approximately 500 million and became much less stable - agricultural societies are much more prone to population collapse due mainly to epidemics than hunter gatherer societies. Various plagues have eliminated 50% or more of a population within a few years. Population stability (such as it was) was a result of incredibly high birth rates matched by equally high death rates and huge fertility rates among those woman who survived long enough to bear children. Indeed, it was not unrealistic to say that if a girl survived to bear children she would probably die bearing children - maternal mortality rates being hideously high and birth control methods being both ineffective, unwanted and/or culturally prohibited. What has given the world a population that is now measured in the billions was the industrial and agricultural revolutions which lowered the death rates to an extraordinary degree, primarily by reducing infant and childhood mortality. Those girls who did not die as children went on to have babies at the same rate as everyone else leading to explosive population growth. People had children as a form of social security: they would look after you in your old age. Of course, because children died a lot, you needed to have a lot of them to ensure some of them made it to adulthood. However, the twin revolutions not only decreased the death rate, they changed the economics of having children. Since you could now expect most of your children to survive (rather than expecting most of them to die) over time, people had less children - the birth rate falling to match the new, lower death rate. This creates the [Demographic Transition](https://en.wikipedia.org/wiki/Demographic_transition). [![Demographic Transition overview](https://i.stack.imgur.com/wpqCW.jpg)](https://i.stack.imgur.com/wpqCW.jpg) Max Roser - Email from author, author of website <http://ourworldindata.org/data/population-growth-vital-statistics/world-population-growth> - Demographic Transition overview - [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/) The demographic transition and the fact that humans live for many decades explains why a population can continue to increase even though the fertility rate now is below replacement rates. A "baby boom" (like the one in the twenty years following the Second World War) takes many decades to work its way through a population. Best estimates are that the world population will peak at around 9 billion in the second half of this century and then begin to decline. [Fertility Rates](http://data.worldbank.org/indicator/SP.DYN.TFRT.IN?end=2015&start=1960&view=chart), [Birth Rates](http://data.worldbank.org/indicator/SP.DYN.CBRT.IN?end=2015&start=1960&view=chart) and [Death rates](http://data.worldbank.org/indicator/SP.DYN.CDRT.IN?end=2015&start=1960&view=chart) have all fallen massively over the last 55 years. However, this has been accompanied by a massive increase in [population](http://data.worldbank.org/indicator/SP.POP.TOTL?end=2015&start=1960&view=chart) because the world, as a whole albeit at different rates is going through a Demographic Transition. The OECD countries have largely completed theirs as has China, most Asian and South American countries are somewhere in the middle and most African countries are only just starting. These are closely correlated with wealth as measured by per-capita GDP. Indeed, all OECD countries now have fertility rates considerably less than replacement value - any population growth they experience now is a result of the lag in the post-war baby boom and net immigration. *The problem your Utopian founders have to deal with is encouraging* childbirth, not restricting it. [Answer] If you have a 50% male/50% female population, birth rate must be slightly above 2/women to have a stable population if there is no immigration or other significant factor to take into account (major disasters killing lots of people, for example). Dystopian options hereunder As discussed, enforcing this policy can be a challenge. If you want a dystopian touch, imagine adding substances preventing becoming pregnant in water supply. Or have strong law enforcement (à la Judge Dredd) so that executions compensate population growth. Or simply let people reproduce like they want and release some diseases to go back to the good figures. This can allow you to target part of the population as well. [Answer] Nobody has even mentioned birth control for some reason. It should be easy for people who set up utopias to control population through birth control. A simple system would just make it so the government gets to decide if any individual can have any children. Everyone else must be on birth control. If the government wants to be forceful, they can just give all males a vasectomy after puberty and make it so all births are artificially inseminated. [Answer] Having left Earth already we can assume your society is technologically advanced. The elders could have implanted birth control in all colonists and their offspring, enabling them control over the society's reproduction rates. People can get it on all they like but unless the ruling body has OK'ed conception, they won't have another child. Circumventing the control mechanism could be monitored or made highly problematic by the level of technology you want to use. [Answer] All you have to do is keep families from having more than 2 kids. It doesn't matter what method you choose, say taxes, birth control, forced termination of children, etc. As long as the population has a fertility rate lower than 2.1, it will not grow. If the need for a population boost ever arises, than lift the ban on the number of children for a short period of time. [Answer] In "Demolition Man" society had been changed such that intercourse ("fluid transfer") was 'icky' (and dangerous due to fatal STDs). Children were created using the eggs and sperm of parents in the lab. The eggs and sperm were screened for genetic problems. The embryo was matured in an incubator thus the population could be easily kept in check via 'cultural norms'. [Answer] Government control of all food. Without sufficient food an additional child cannot be kept alive. If every person goes to a government controlled distribution point every time they need food, the government has precise control over how much each person receives. If you want sufficient food for a new child you have to request it. If your child wasn't approved they won't give you food for them. Perhaps they would instead take the child and raise them as a ward of the state. If this pattern has been long established it may be culturally ingrained. People teach their children this is how it works. Everyone knows that if you try to have children without government approval they will be taken. If the past circumstances that alarmed the Elders included severe reduction of the places on the planet that will grow food, the government might have easily taken control of all of these areas. Perhaps the staple food isn't even grown at all but instead is a synthetic production. [Answer] Religion** Procreating is bad and must be forbidden except on the only one holy day each year/decade were you are all permitted to try procreating once and only once, for thy great ancient lords told ya so. Thou shalt not make babies when thy lord didn't allow you. Beware citizens, being X is watching you. [Answer] Today's reality: * Favor LGBT communities and their style of thinking. Those people don't have that much children as normal families. Most of them won't have any on their own for obvious reasons. * Favor divorces, destroy the model of classic family. Same results, less children that can be taken care of. * Let people think that the biggest values are for them not their children, families, but their careers and money, how much they can buy and so on. * Favor careless style of life, where the main goal is entertainment. Sex? Anytime, we have pills...Drugs. Adrenaline. Travel. * picture out that having children is expensive and it keeps you away from fun...it is hard to do all that stuff from previous point with small children. They will destroy your life! Do this all in the name of human rights, it will be noble of you, they will agree, even though in long term it means that their numbers will decrease without outer migration, that their culture will void over time (less participants), they will seem to be happy. How to do this? Just look at today's media, what are they doing. Look at today's schools, where all those values are shared with children... The people will regulate themself and even happily! At least most of them, but you can call the rest as neonazis and let the community despise them. Via media. ]
[Question] [ I am planning to write a book where a near-future government on Earth begins recruiting talented children at the age of 14 to train them to become the next political leaders. They are going to study in an academic environment where they will receive a specialized education in running a state. These children are not soldiers sent to combat. At the age of 18, they begin an internship working for a government department. The government in my world is a deep state that is authoritarian but non-hereditary with higher positions earned by appointing people through connections like the Chinese Communist Party or the derin devlet in Turkey. However, people begin training for these positions from an early age rather than later on. Children in the program take tests determining skill in the political sphere to determine whether they will “make it,” similar to scholarly examinations in Song Dynasty China. Only the top people in each department advance to actual leadership. Why would a society choose to train the next generation of political leaders at the age of 14 rather than as adults? How could this practice begin in a society? [Answer] I don't want to get political but with this question, it is sort of hard to avoid. You are asking why a government might invest in training their future leaders from an early age for the exalted offices which they might one day hold. Why wouldn't a government (and its people) want their leaders to be as thoroughly trained as possible? If you look at any endeavor which involves a vast spectrum of performance quality, such as music, acting or even writing, the practitioners who start preparing for their career early have a substantial advantage over late comers. This isn't a new question for me. When I first moved to America after years of living under a monarchy, I was amazed by the idea that not only are most American leaders untrained for the offices they hold, but the people who put them in office are especially proud of the fact that those leaders are untrained. I have been here for several decades now, and I have to admit (with certain recent exceptions) that the system works, but I still can't explain why. As for how such a change might come into being, it wouldn't take much. If an untrained leader were to accidentally incite an insurrection that threatened the lives of some of the political elites and maybe even cost the lives of some of their protectors,... that might set the gears in motion. It might not take any more than that to inspire the law makers to tighten up the minimum requirements for the higher offices ...and requiring candidates to attend a few years of government-leadership-preparatory education might be a really good first step. [Answer] ...Isn't this what already happens today? In my (public!) high school, I was friends with many ultra-high-performance students who were being driven along a pre-determined career path by their parents into high-prestige careers like "Doctor" or "Lawyer". These were usually scions of the wealthy or children of Asian parents (the stereotype exists for a reason). These kids were required by their parents to do things like: * Achieve perfect grades (>97%) in everything. This was basically a given and almost all of the high-performers accomplished this. * Take all the most difficult (AP) courses and earn good scores on the AP tests * Be a member of every applicable honors-society (perfect grades in an AP class sustained) * Participate in as many after-school scholastic activities as possible. This includes things like Science Fair, Debate team, Science-Olympiad, etc. If it's competitive, they were expected to perform well * Play an instrument well enough to add some "creative" to that resume. Usually a stringed instrument (violin/viola) or a Piano * Achieve maximum scores on standardized testing (SAT and similar tests). Parents frequently hired tutors for hundreds of dollars an hour to ensure their child gets good scores. * Have at least one "approved" job on their resume to diversify it. Common choices include "tutoring", "music instructor", or "research assistant". * Play an "approved" sport to show physical activity on resume. Typical choices include Tennis, golf, or cross-country. All of this and more was expected (if not already in progress like playing an instrument) when the kids entered high school. By Junior year (11th grade) college applications were in full swing and it was figured out who goes to Harvard, Princeton, MIT, or insert-ivy-league-college-of-choice-here. I don't see where the big question is here, because parents who want high performance kids already start them off young and 14 is a typical age for that class of people to ""start thinking about college"". The kids who don't make it or "burn out" along the way eventually settle for going to non-ivy-league colleges (shudder) and end up being great disappointments to their parents. [Answer] Let's change the question around. Fundamentally, there's no difference between the question you asked, and asking 'what's the value of school at all?'. Why make everyone go through general education as kids, when we could just make up the gap with specific vocational training for adults teaching them only what they need? Because it gets them productive much faster, and people learn much more readily at younger ages. Likewise, how many professional athletes are there who didn't grow up learning their sport? Basically none, right? So let's turn this around. One might expect that something along these lines should naturally develop, absent a specific reason it doesn't. A better question to ask is why we don't do this. I say there's a simple reason why: Free open-to-all-challengers democracy means anyone can rise to the top, and that in turn makes singling out a small segment of the population for special-purpose leadership-specific training an inefficient use of resources that have a slim chance of paying off. [Answer] Consistency and improved communication in government. Consider - you train about 2% of your population for these sorts of leadership roles. You only need a few, really, to be top leaders, presidents, ministers, etc. But what you also train with them is a layer of civil servants and executors of policy who have a shared set of experiences, training, perspectives and a common bond of trust. Sure, this will produce very dull, consistent government - but barring any shocks this could be very stable. Think of the Chinese Imperial exam - produced a stable bureaucracy that was mostly effective that lasted what, centuries? [Answer] There are 3 reasons: 1. This society, similar to ours, believes that young people who do not demonstrate talent early on are destined to be mediocre later on; 2. There is a persistent belief that talents should be groomed (as opposed to self-made men); 3. It is much easier to indoctrinate a teenager than an adult, which helps with the consistency of political leadership. There are plenty of possible answers for 'how it became to be like this'. Social engineering would be the simplest answer considering that authoritarian governments love social experiments. The described practice also helps to consolidate power in the right hands and is conducive to the stability of the regime. Overall, I would like to applaud the leaders of your country for their practicality and political insight. If the system is implemented right and does not allow bribes it should work as intended for a long time. [Answer] Because, by starting the brainwashing early you ensure that all future political leaders, regardless of party affiliation, will be moving the country in the direction that you want. (And, perhaps it should not just be limited to the future political class: we could make all children drone out a dirge of loyalty, and instil a deep-seated core of mindless jingoism in them) By ensuring that the public only accept "qualified" politicians, you lock out any who gain their experience in undesirable fields, such as in trade unions (fighting for the rights of workers) or protest movements (fighting for the rights of minorities/foreigners, or for the good of the planet), we ensure that the rich and powerful stay rich and powerful, and easily vilify any attempts at improving the lives of our ~~foolish minions~~ loyal constituents as "socialist" or "communist", and against the founding principles of our country (no matter how closely they may actually match those principles) [Answer] We should start from Dragongeek's answer, which basically states that this already happens today. [PPE : The degree that runs Britain.](https://www.theguardian.com/education/2017/feb/23/ppe-oxford-university-degree-that-rules-britain) Or [2/3rd Cabinet](https://www.theguardian.com/education/2019/jul/25/two-thirds-of-boris-johnsons-cabinet-went-to-private-schools) Privately educated. As in my comment on Dragongeek's answer the distinction would be that this isn't society choosing to educate the leaders of tomorrow for their role from a young age, but family and social connections guiding their own youth onto a know successful path. As these articles demonstrate this can lead to a very narrow range of backgrounds for the leaders of the country. Your two options for why a society decides to recruit 14 years olds specifically into "political academies" are to either re-inforce this narrow world view or to expand it. Reinforce The current crop of leadership is worried that the masses are getting uppity. They want to make sure that the retain their hold on power without making it too obvious. So the insitute a national program to find and develop the leaders of tomorrow. They produce a standardised test, throw it at the relevant year group and award the top 1% of marks with elite education from 15 to 24, followed by placement into junior roles in government offices with a clear path to high level political staff in either MP/Party roles or Civil Service management tracks. Amazingly this "standardised and fair" test is as easily gamed as the 11+ and leads to the established elite getting their friends and relatives onto the program and a nice cash saving at home, with a few spoilers thrown in to show the system is "open" to everyone. Expand A maverick political leader from outside the usual channels manages to come to power, perhaps they were the 2nd in command of a "normal" leader as a ticket balance and successfully navigate a succession battle following an unexpected death/scandal. This new leader institutes the same program as above, but their test is focused on apptitudes rather than knowledge and cannot be gamed (for some reason). At 14 it's assumed that teenagers will have a strong connection with their roots, and the post 14 training will emphasise maintaining ties with the source community to retain these diverse viewpoints. [Answer] This is not hypothetical. Several governments in the world do exactly that. They scout talents early and then train them. Depending on the country, this may be more or less open. I have some knowledge about this from a person close to me who went through such a program. Or rather: A series of programs where after winning some awards as a teenager, they found themselves accepted into prestige schools and then prestige universities, with scholarship and all. We also know that several communist countries had such programs, with national political youth programs, including so-called "youth parliaments". We have similar things in the west - e.g. <https://eyp.org/> - but their focus is more educational. So why? Because it works. Because someone with the highest responsibility in the country (leading it) should have as much training in doing so as possible. And they should be selected properly, which you can do in a training process much better than in a popular election. Because a near-future high-tech society may have moved away from election cycles and into something like [Liquid Democracy](https://en.wikipedia.org/wiki/Liquid_democracy), where all decisions are voted on continuously by the population, instead of an elected parliament. Once that happens, popularity and party politics and voting lists become a lot less important and the actual capabilities of the leaders matter. [Answer] Just to stay in the fictional domain, have you read 1984? There you see that kids are the most eager followers of Big Brother's directives, reporting their parents when they say something not compliant with the directives, even though it's in their sleep. Kids and teens are more plastic to indoctrination because they are in the age where their set of beliefs and behavior is still consolidating, so it makes only sense for a system to shape them to its will when it costs the less effort and it's more likely to bring the desired results. I have personally seen people who grew up in the pre-WWII youth organizations of one axis power reaching their death bed without reneging those "values" which they learned in those days. [Answer] Why: because the earlier you start training for any skill and the more time to train the better at it you will be. How could it begin Probably with the formation of a specialized political class. C societee of develop this way having several specialized classes. Specialized Warrior caste specialized worker caste specialized engineering cast and so on. [Answer] Indoctrination of the ruling class has to begin at an early age (during the 'formative' years). What your indoctrination is varies by political style? Personally I would like my politicians indoctrinated in ethics and morality, duty, self-reliance, restrictions on government power, true leadership as opposed to dictatorial command. There may even be schools based on political school-of-thought. You may have schools (or course tracks) in socialism, marxism, replicanism, and any other form of government-ism. But the point is to begin indoctrinating the candidates into what society wants in government leaders and not just skill sets, but the whole gestalt. [Answer] ## Maintaining Power Given you're working with: > > a deep state that is authoritarian [...] appointing people through connections like the Chinese Communist Party... > > > Your system is not optimized for governing well, it is optimized for *keeping the existing rulers in place. Requiring a lengthy training period fits with this goal for several reasons. ## Legitimacy Regardless of how corrupt the system is, the idea that it is a meritocracy lends it legitimacy. Leaders put a lot of effort into messaging that anyone could enter this pipeline, only the best complete it, etc. to boost their own legitimacy. ## Exclusion Current leaders control who enter this training pipeline, giving them the power to exclude political enemies, and create patronage networks - those who they assist in entering the pipeline owe* something the existing leaders. ## Something to Lose If there's a "right path" to power, then people on that path have something to lose. Rebelling against the system will get you kicked out of school, or college, or your entry level government position, so you conform. By the time you have enough power to actually change the system, you are fully invested in the system and no longer desire change. ## Other Those three are the big ones for me, but you also get the opportunity for ideological consistency (make them parrot the party line until they believe it), blackmail (children make mistakes - leaders can threaten their future to influence their parents / patrons), and a host of other nefarious plans. But it all comes back to this: the system exists to keep the elites in power. [Answer] In my country you develop an active political conscience about 14 years old. You need to be 14 to create associations. At 14 you can be jailed on a specific prison. You can be legally married (on a special circumstance). You can ride a bike. Most guys do first sex experiences around 14. In my country you pick the broad school specialization at 14. So, if I was "my country", I surely will pick 14 agers to start a political dinasty. [Answer] Scientific advisor: "Our best astronomers have completed deep cosmological studies. The idea has been tested repeatedly and every time the data has failed to reject the conclusion: this universe is the setting for a YA novel." Elder statesman: "Well then, our course is clear. To maximize the success of our society, we must reorganize to get teens into the halls of power as quickly as we can. ... preferably by some grueling sequence of challenges that only the best and brightest will overcome." And the rest, as they say, is your story. [Answer] This could be the way of narrow elites to preserve their access to power by creating a tradition which grants people of similar background and upbringing from a young age preferential access to public functions. Some historic and modern parallels to consider: * The Mamluk Empire, where the ruling class was made out of men pressed into slavery at a young age, mostly from Christian countries and trained as soldiers. * Modern Britain, where much of the political elite is trained from a young age in certain public (i.e. private) schools. [Answer] A more optimistic answer might be that that some large enough proportion of current adult leaders recognize that humans in general are terrible at [long term threat assessment](https://en.wikipedia.org/wiki/Hyperbolic_discounting), decision making and planning. Elderly adults are especially bad because (a) they acquired their leadership skills in a past environment with different challenges to the ones today, and (b) as they age, their incentive to make long term decisions reduces because they aren't going to be around much longer. No matter how strong the social and political will behind it, willful ignorance of technical progress and changes in society, the environment, economics etc, will eventually run into the wall of reality. Recruiting children and training them early has many advantages: 1. They are incentivized to make good long term decisions, because they'll be around to regret the bad ones, and being trained, they know they'll likely be in a position to not be ousted or voted out. They are on of the special/chosen ones after all. 2. They come into the politcal system with a far more accurate understanding of the challenges their generation faces, and their own generation's desires and appetite for various policy changes. If the program runs successfully over a few generations, this means there will be a constant flow of incoming new voices in the political debate. 3. Young people are better long term decision makers in general (real life evidence goes both ways on this, but it's something you could establish more support for in your backstory if needed). [Answer] 14 year olds are the best able to fully understand the advanced technology! If your story is a bit comedic - it's a bit of a trope or notion that the older people get, the less capable (or willing to adapt) they are with advancing technology. (e.g. My parents wouldn't have had a clue how to even use a computer when I was 14.) [Answer] Your society consists of two different factions who speak two different languages. At the age of 14, many / most people can still learn to speak a foreign language without an accent. By the age of 18, most people have lost this ability. Sure they can learn the foreign language, but they will always have an accent. (Exceptions abound but this is the general rule.) It is advantageous for a political leader to be able to speak in public with either faction and sound like one of them, accent-free. That's why your future leaders are recruited at age 14 and are too old by 18. ]
[Question] [ For my Science fiction and Fantasy genre book, I need an energy source whose energy output should be much more than even a fully functional Dyson sphere. Can you please suggest some hypothetical concept as an option? Edit: I need just a Supernovae of energy to make some kind of hypothetical weapon, I don't need continuous source of energy. Moreover, I mentioned Dyson sphere just to indicate that I want to harness very high amount of energy. [Answer] I think @nzaman had the right idea- black holes contain an enormous amount of energy, in the form of angular momentum. However, you don't need turbines to harness the energy. As explained by [this video](https://www.youtube.com/watch?v=ulCdoCfw-bY), an object that escapes the ergosphere by giving up some of its mass will speed up. The amount that the object speeds up is even more than the mass that the object gives up. This is called the [Penrose Process](https://en.wikipedia.org/wiki/Penrose_process). Here is a screenshot from the video that nicely illustrates the process: [![screenshot](https://i.stack.imgur.com/xLvfc.png)](https://i.stack.imgur.com/xLvfc.png) The object enters the black hole's ergosphere and then shoots out, accelerating as it does. There is also another way to harvest energy from the black hole, and it doesn't involve giving up mass. Shining a laser by a black hole has the same effect. In the process of [superradiant scattering](https://en.wikipedia.org/wiki/Superradiance), we can use mirrors to make the laser reflect through the black hole's ergosphere over and over. The light continually amplifies, until it is strong enough to be emitted and used as a power source. If the light isn't emitted, it has the potential to create possibly the most destructive weapon in the entire universe. Called the [Black Hole Bomb](https://en.wikipedia.org/wiki/Black_hole_bomb), the light will eventually break free of the mirrors and wreak who-knows-what havoc. [![screenshot](https://i.stack.imgur.com/DJhHF.png)](https://i.stack.imgur.com/DJhHF.png) [Answer] # A bigger Dyson sphere You can build a Dyson sphere around a galaxy. [Or around TON 618, one of the shiniest quasars known](https://en.wikipedia.org/wiki/TON_618): > > The surrounding galaxy is not visible from Earth, because the quasar itself outshines it. With an absolute magnitude of ‚àí30.7, it shines with a luminosity of 4√ó1040 watts, or as brilliantly as 140 trillion Suns, making it one of the brightest objects in the Universe. > > > Compared to an hypothetical Dyson sphere built around our sun, the TON 618 one would give way more than the output you mentioned in the comments to your question. [Answer] Black holes hypothetically can be tapped to generate the energy of a star in a much (much) smaller package. Black holes have a number of ways you can extract energy from them. Small black holes (perhaps artificial ones) can be made in size ranges which allow them to emit Hawking radiation. This [website](http://xaonon.dyndns.org/hawking/) has a calculator which allows you to determine how much hawking radiation you can receive from any size of black hole. In this epoch, the cosmic background radiation is high enough that stellar mass black holes are effectively "dark" in terms of Hawking radiation. [![enter image description here](https://i.stack.imgur.com/YOeJs.jpg)](https://i.stack.imgur.com/YOeJs.jpg) The process by which Hawking radiation is emitted Roger Penrose proposed a method of [tapping rotational energy](https://infogalactic.com/info/Penrose_process) from stellar mass black holes. > > The maximum amount of energy gain possible for a single particle via this process is 20.7%.[4](https://infogalactic.com/info/Blandford%E2%80%93Znajek_process) The process obeys the laws of black hole mechanics. A consequence of these laws is that if the process is performed repeatedly, the black hole can eventually lose all of its angular momentum, becoming non-rotating, i.e. a Schwarzschild black hole. In this case the theoretical maximum energy that can be extracted from a black hole is 29% its original mass.[5](https://i.stack.imgur.com/JjzfA.png) Larger efficiencies are possible for charged rotating black holes.[6](https://i.stack.imgur.com/Pnjq8.jpg) > > > [![enter image description here](https://i.stack.imgur.com/Pnjq8.jpg)](https://i.stack.imgur.com/Pnjq8.jpg) Simplified diagram of the Penrose Process [![enter image description here](https://i.stack.imgur.com/ECVdm.gif)](https://i.stack.imgur.com/ECVdm.gif) Another diagram Since we are talking about stellar sized black holes, this is actually an enormous amount of energy. Finally, a refinement of the Penrose process can be made by integrating the electrical and magnetic fields that often accompany the environment surrounding a black hole. This is the [Blandford‚ÄìZnajek process](https://infogalactic.com/info/Blandford%E2%80%93Znajek_process) > > The Blandford‚ÄìZnajek requires an accretion disc with a strong poloidal magnetic field around a spinning black hole. The magnetic field extracts spin energy and the power can be estimated as the energy density at the speed of light cylinder times area: > > > [![enter image description here](https://i.stack.imgur.com/JjzfA.png)](https://i.stack.imgur.com/JjzfA.png) > > where B is the magnetic field strength, r\_c the speed of light radius and œâ the angular velocity.[6](https://i.stack.imgur.com/Pnjq8.jpg) > > > [![enter image description here](https://i.stack.imgur.com/nF6uc.jpg)](https://i.stack.imgur.com/nF6uc.jpg) Quasars are powered by supermassive black holes, with masses thousands to millions of times greater than the Sun So the energy output will vary based on the size of the black hole being harvested (much like a Dyson sphere output will depend on the star within), but black holes are quite compact, so the energy density will be far higher. Remember, outside of so called "quantum" black holes created artificially or near the beginning of the Universe, black holes are stellar remnants, so you are dealing with objects starting at about 3 solar masses in terms of size, and the black holes near the centres of most galaxies are thousands to millions of times more massive than our Sun. [Answer] You've not got the "reality-check" tag on this one, so how about... ## Vacuum Energy This is high-octane handwavium. It's almost certainly nonsense, but so is readily harnessing power on the scales you're talking about, so let's roll with it. Vacuum energy is one of the theories behind the energy deficit between observable space and the rate of universal expansion. Its potential scale varies by theoretician from very small (the most likely case) to enormous (the most useful case) to infinite (unlikely, but even more useful for your world). Now, harvesting the energy responsible for the expansion of the universe might have some localized (or not-so-localized) effects on spacetime, but that could be another fun plot point: > > "Preserve the universe!" the activists cried, their placards waving outside the administration building. Inside, the C-suite scoffed. Redshifting of the local cluster had been only 1.4% over the last decade, nothing to worry about. > > > Assuming you set your reality's version of vacuum energy to the "infinite" or "near-infinite" end of the scale, you can have as much power as you want. [Answer] The idea of a Dyson sphere is to capture all the energy produced by a star, at the rate (i.e., power) the star normally emits that energy. Which might take billions of years. One way to get more power out of it (energy per unit of time) would be if you could accelerate the burning of the star. I guess this is what was seen in The Force Awakens, where the bad guys had a weapon that consumed a star and almost instantaneously turned it into blaster beams or something. Somewhat more "realistically", you might have something shaped like a Dyson sphere that surrounds a star and consumes it (converting all matter into energy) in a much shorter timespan than the normal life of the star. Then you could go looking for another star to consume, and so on. [Answer] If you don't need continuous output, a gamma ray burst <https://en.wikipedia.org/wiki/Gamma-ray_burst> will do nicely, typically releasings as much energy in a few seconds as the Sun will in its entire 10-billion-year lifetime. [Answer] The problem with naturally occurring stars is that, like most things in nature, they aren't purpose built to maximize efficiency. Sure, they're free to construct, but they come pre-loaded with a bunch of mass that you don't want. It sits in-between your sphere and the energy released by the fusion reaction, preventing clean, unobstructed propagation. What you really want is a star sized cluster of smaller dyson spheres built around artifical stars, complete with fuel injection and spent mass extraction, so that more of your mass and space are dedicated to the production and storage of energy, instead of an incidental fusion reactor sitting underneath a giant pile of inert mass. [Answer] ### E=MC2 I'm in the middle of the non-fiction book "Life 3.0" by Max Tegmark. I don't remember the numbers exactly, but he discusses the fact that only a tiny fraction of a star's energy is actually radiated as light or heat ‚Äî less than 1% of its total energy. The book is about possible scenarios and directions for artificial intelligence, so he is (probably appropriately) diving off the deep end, but I believe he was suggesting that mass itself is equivalent and could be converted to energy (E=MC2). So in some futuristic scenario, any kind of mass could be converted to a lot of energy. And you could potentially harvest an entire star, or solar system, or galaxy. Preferably not ours. üò± [Answer] Here is a radical option inspired by Stephen Baxter's book Ultima: time travel from the end of the universe. If your universe will end by a big rip or by M-Brane collision, there could be massive amounts of energy released as the universe rips apart. More possible method: the smaller a blackhole is, the faster it evaporates and outputs hawking radiation. By producing millions of microscopic black holes(via focusing lasers on a very small space to create a kugelblitz) and continually feeding each one a trickle of matter, you could convert matter to energy with 100% efficiency. [Answer] ## Black holes at the centre of galaxies. Collect energy by placing a series of giant turbines just outside the accretion disk, or even in it, to be driven by the rotating matter. If you could somehow couple them to form a tight circle, it would both neutralise the gravity well of the black hole, as well as create another plane of rotation which you can tap for energy. [Answer] An online comic Schlock Mercenary had a galactic drive engine which harnessed the energy of the spin of the Milky Way to power massive events such as teleporting (terraporting) whole planets and fighting a war with a race of dark matter creatures using the Andromeda galaxy to power their own galactic drive engine to shoot at the Milky Way. See [Pa'anuri](http://schlockmercenary.wikia.com/wiki/Pa%27anuri) [Answer] It's kind of simple... but why not just use a big ole pile of antimatter? The use case for the energy is a big burst so you could use any conceivable energy production means to build up your pile, then annihilate an arbitrary amount to power your weapon with a massive energy burst. [Answer] Dropping things onto a neutron star is another classic approach. You get about 10% of the rest mass back as energy, as a rule of thumb. (Collecting this energy is problematic, though, as it's largely X-rays and up.) ]
[Question] [ In my world, there are humans (often called Earthlings) and eight alien species. Humans have an Earth government best described as a democratic quinquevirate: to be exact, this is an elective semi-presidential republic with five Presidents, ten Prime Ministers, and one honorary Emperor/Empress/Empross (this is a United Nations pastiche) (in real life, the United Nations is composed of five permanent members of the Security Council, ten elected members, and a General Secretary). The eight alien species are (they are provisionary names): 1. Blue Squirrels. They look like bear-sized blue-furred squirrels. They live in a matriarchal tribal society. Their cradle is a temperate rainforest planet. 2. Mountain Albatrosses. They look like raven-sized red-feathered albatrosses. They live in a theocracy, and individuals of power are celibate priests and celibate priestesses. Their cradle is a mountain planet. 3. Huge Forest Tortoises. They look like ostrich-sized green-scaled tortoises. They live in a hereditary semi-presidential republic (both the President and the Prime Minister inherit their respective position from their respective parents, and have limited power). Their cradle is a dry tropical forest planet. 4. Orange Desert Flatworms. They look like falcon-sized orange planarians. They live in an elective constitutional monarchy. Their cradle is a sand desert planet. 5. Giant Purple Iguanas. They look like gharial-sized purple-scaled iguanas. They live in a Singapore-like benevolent dictatorship. Their cradle is a swamp planet. 6. Ice Termites. They look like rabbit-sized yellow termites. They are eusocial and they live in a matriarchal absolute monarchy. Their cradle is an ice planet. 7. Sponges. They look like human-sized red sea sponges. They live in a semi-presidential republic with one President and four Prime Ministers. Their cradle is an oceanic planet. 8. Purple Cannabises. They look like human-sized purple cannabises. They are best described as benevolent libertarians (if we compare them to humans). Their cradle is a grassland planet. So, I wonder why would most aliens species have a non-democratic political system. [Answer] ## Plenty of your races have Democratic Governments already There is a difference between a democratic government (a government containing elements or ideas of a democracy built into it), and a pure democracy (a government where everyone is an equal member of legislation) The two main qualities we use to define a "Democratic" government are the existence of elections and distribution of power. Of your 9 races, it looks like 6-8 of your races have elective systems of some sort, and 5-7 practice some form of distribution of power. So, I would say the majority of these races are democratic which is actually much more that we see historically. I would if anything be questioning why so many of these alien races ARE democratic, not why more of them are not. [![enter image description here](https://i.stack.imgur.com/GyrEP.png)](https://i.stack.imgur.com/GyrEP.png) ## ... unless you are asking why there are no Pure Democracies That said, none of your races practice [Pure Democracy](https://en.wikipedia.org/wiki/Direct_democracy) (AKA Direct or True Democracy). Even your Humans are just a [Representative Democracy](https://en.wikipedia.org/wiki/Representative_democracy) (AKA Indirect Democracy or a Republic). The thing is that here on Earth, there have been very few Pure Democracies beyond the scale of small tribal/commune settings. Once you get past [Dunbar's Number](https://en.wikipedia.org/wiki/Dunbar%27s_number), Pure Democracy often becomes unstable. Some people say Ancient Athens was a Pure Democracy with ecclesias that would include thousands of citizens coming together to propose and vote on laws, but Athens was a Patriarchy and only about 1 in 10 families were part of the citizen class; so, only about 5% of the adult population could actually participate in an ecclesia making it arguably just a really big Oligarchy rather than a Pure Democracy. The thing about Pure Democracy is that it often does not work well on larger scales. Although modern technology makes coordinating the votes of billions of people easier than ever, the much harder question of who gets to propose a law becomes a major matter of contention. Imagine if Earth had a citizen-class democracy like Athens did, today. 5% of 8 billion is still 400 million people. If 400 million people could propose a law then there would be WAY too many bills for everyone to read to be able to also vote on and the complexity of the legal system would quickly spin out of control. That said, many Representative Democracies also have a referendum system in which the citizenry has the right to propose and vote on laws directly bypassing representatives. In these systems, the typical solution is to require citizens to fulfil a petition requirement showing a certain number of people in support of a new bill (filtering proposals to a more manageable number) and that bill can then be voted on in a Direct Democracy fashion. Even so, these states/countries still do not quite constitute a Pure Democracy, because they still rely on their representative form of government... but it does give a very good example of how a Pure Democracy could function at scale. [Answer] Well, Simply put, it's not just aliens Throughout history, most governments were not democracies. The idea that democracies are very common in human society is something that you may think because you were born after the end of the 19th century, but before that time democracy was the exception, not the norm. Because of this, you don't really need an explanation for why aliens tend to be non-democratic when humans are already usually non-democratic. Our modern age is an exception, and an important one, but still an exception. It should be noted that governments do tend to have a religious (will of God) or pseudo-religious (will of the people) reason for existing, so you should probably come up with why the people in those nations believe their governments should exist. What I mean by religious justification is some justification for the mode of government in the very religion of the people, and by pseudo-religious I mean that they do not have a religious belief in the governments legitimacy, but their legitimacy is determined by some other ideal whether it be cult of personality, democracy, inheritance, etc... [Answer] As North America is now demonstrating harder than before, Democracy is less about who can lead a country the best and more of a popularity contest\. Our current Democratic development may just be a fluke and will eventually collapse. So instead of opening up the system of government to propaganda attacks and misinformation campaigns the aliens prefer other types of government. \yes the US has some baked in extra flaws like only two parties but there are plenty of problems with basic Democracy anyway. Although when you get down to it all types of Government we have invented so far have problems. [Answer] An evolved lack of sociopathy or extreme selfishness; but your story would need to support that notion in the action. Democracies are for beings that cannot trust strangers of their own species. They don't trust kings, because most people that become kings came to that by sociopathy and violent force, not caring who they hurt in their quest for power and riches. Democracy was a direct rebuke of Royalty, and particularly selfish, greedy, careless royalty. It was an alternative that was designed to balance powers so that different factions could keep others in check and prevent any sociopaths from gaining all the power and corrupting everything for their own personal gain. But what if there were no such people? No megalomaniacs, no religious ideologues, no senselessly money-obsessed grifters. Nobody wanted that much personal gain, and everybody was content with a modern "comfortable" living? Including the king, they lived the same lives as anybody else. The Earth would still be full of kingdoms if it was not for the greed of Kings, if it was not for the wars trying to take more territory, gain more power, gain more taxes. If it were not for the jealousy over greater wealth, territory and power. In fact, it seems likely we'd already have a world government, coordinating the resources of the Earth for the benefit of all. We'd have no military. We'd have fewer cops. If everybody is reasonable, we can agree that there may be thousands of worthwhile things to do, but only resources to do hundreds of them at a time. So somebody has to prioritize these projects, and that means researching them, understanding them, figuring out co-dependencies, and their impact, and coming up with what we do now. That is the job of a government, and it is most efficient in a pyramidal structure where the final decisions are made by a singular leader that mentally synthesizes the top level information. That all works great, fast and efficient if we can trust every level of government to not corrupt their decisions with personal preferences or attempts to get rich or powerful by their decisions. That can happen if people are inherently trustworthy and incapable of anything else, or if we can read minds without error and the corrupt cannot hide their greed, criminal intent and disregard for others. There would be no reason to overthrow the rule of singular authority, if such singular authorities are never oppressive to the people. Democracies arose in rebellion against oppressive, greedy and self-indulgent royalty. Take away the reason for Democracy, and Democracy never appears. [Answer] # Democracies aren't stable to alien interference. It's pretty easy for an alien race to influence the population en masse. This tends to mean any alien democracies tend to have their rivals seek to ruin their democracies and succeed. A dictatorship is easier to maintain, as you just need to shield a small number of elites at the top from influence, and because it's easier to kill any subordinates who are swayed by aliens. Earthlings would experience this soon after, with large scale efforts made by the aliens to destabilize them by making their members fight. [Answer] Throughout human history, democracies are very rare and recent. Some say that we live in a time where we see the decline of democracy, and frankly, this is at least not all wrong. The reason, as is so often the case with humans, is greed. Amadeus in his very good answer suggested that this personality trait might be special for humans, and might not exist in your other species. Who knows, maybe that is the reason they could evolve to spacefaring civilizations in the first place, while those species that create egomaniacs never reach that state. But i digress. Amadeus also hinted at the problems we on earth had with our non-democratic governments. But, if we look around, we notice that even today on earth, a lot of countries are not democracies, especially since you seem to imply that you don't count constitutional monarchies as democratic. I don't share that view, but that's a different matter. Democracies arise on earth when a ruler is overthrown. This happens when a large part of society thinks that the risks involved in revolutions are worth taking, i.e. if their situation is pretty bad under their current ruler. While Amadeus points out how to remove the problem of opressing rulers from a species, i would like to offer a different approach: remove the oppressability! Since your different species are all space faring, i fnd it safe to assume that they manage to provide very large amounts of energy when needed and that they are generally technolocically advanced. From there it's just a small step to a post-scarcity civilisation. Now, take a look at the people in your country. How many of them, would you say, have a deep understanding of politics? I assume it would be the same as in my vicinity: not that many, to put it mildly. They do get interested when they feel they are missing something. Now, in a post-scarcity society it is fair to assume that noone lacks food or shelter. And once that is the case, the number of people actually interested in politics gets very small. And it removes a strong incentive of revolutions. All you have to do is let people live their lives without too much interference. So, you can have almost any kind of government, once you have a general population that doesn't lack vital things. They, in general, just won't care who's ruling, and by what means. [Answer] Just ask bees, ants, horses, and any other number of Earth animal and insect species why THEY do not use 'democracy'. Democracy is actually an aberration and an abomination of the natural order of species government. It is not natural, otherwise it would not be so fragile. Humans, in fact, were never designed nor intended to be a 'democratic' species. It is a completely artificial construct to even us. Without all of the time, energy, resources, and dedication we put into maintaining it, we by nature resort to more autocratic systems. America just proved that in 2020. No major corporation has ever survived with a democratic leadership structure. In fact, that style of management is completely opposed in our 'democratic' nations. It is called 'Communism', and ridiculed and given a negative emotional tag, instead of being called a 'Democratic' management style and promoted. Really, even on Earth among Human populations. 'Democracy' tends to be a purely Anglo-Germanic Saxon White 'fetish', that this particular demographic tries to artificially and unproductively 'force' or 'impose' on others. Afghanistan is the perfect example. The North American system of 'democracy just does not work for most humans. In absolute terms, no 'two-party' or 'multi-party' adversarial system where 'winner takes all' can ever be called 'democratic'. Only a 'no party' system would be truly 'democratic'. So the frame challenge answer to the question becomes 'Why would any other society or alien species ever WANT to be 'democratic'? [Answer] The king or monarch is very caring In human history, there had been kings or monarchs who cared about their people a lot like a father caring about his family. These kings were loved by the people and people were very content with them. Maybe the alien king cares about his nation and the nation loves him. Democracy is best only under certain conditions Free and Fair elections: The most important condition for democracy to be the best form of government is Free and Fair elections. Their are countries where election are held after a certain term but same guy keeps geting 95% of votes for several terms. He is elected but he is much worse than many dictators. Judicial system: Second most important condition is a judicial system that provides justice. Worst people get elected by certain means and they remain in power because the judicial system is compromised. See the list [here](https://reports.weforum.org/pdf/gci-2017-2018-scorecard/WEF_GCI_2017_2018_Scorecard_EOSQ144.pdf). People in countries on top are happy but as you go down, people are more miserable. There are some other factors that can ruin a democratic system e.g. * corrupt government officials * landlords or tribal chiefs who force their people to vote for a wrong person * poor people bribed by a wealthy person If democracy is not in its perfect or near perfect form then in most cases it is worse than monarchy. [Answer] Why would different species not have democracy? One reason might be due to a genetically driven change that causes the top individual to develop a number of different characteristics. Someone who is not the top individual is genetically programmed to obey. Somone who becomes the top individual goes through a number of changes both to how they look and how they act. They become the individual that can make decisions for the species and show their status with special fur / plumage. One could add a whole bunch of other such genetically determined changes such as ability to see patterns of behavior, teaching abilities, etc. It could be that an individual might be able to go through one or two of those changes in their lifetime. (See Niven and Pournelle ideas of the Moties.) [Answer] Democracy is, in many ways, a luxury option; for a society to be democratic, you need to be able to communicate with the majority of your electorate in some way, and you need to have the resources and the surplus necessary to spend time on things like elections and debates. Furthermore, for it to be a real democracy, the population needs to be educated in democracy, and convinced that it will work - not just in the sense that there will be some form of government, but in the sense that everybody will trust the system enough to accept losing elections, and trust the winners to govern in the interest of the whole of society. Democracy isn't a magic, universally good thing that will sweep away all that is bad; it is at best a difficult, ongoing project that needs constant nurturing by a sufficiently large proportion of the people; otherwise it degenerates to become nothing more than an expensive show. [Answer] # Peace. If democracy reigned throughout the universe, they would all go to live on the planet of the Benevolent Libertarian Purple Cannabises. The native inhabitants would be admired by philosophers and celebrated in story and song, and ruthlessly hunted down by malevolent aliens implacably dedicated to their immolation. # Music The giant purple iguanas can never rise up against the benevolent dictatorship of their Esteemed Leader Barney, because he leads them in a song of praise that they cannot help but dance along to. Even on Earth this song has been used in attempts to rehabilitate dissidents and freedom fighters. (For the full history, see The Men Who Stare At Goats) # Copyright The orange desert flatworms need an iron hand ruling over them because virtually anything they do will get them sued for infringement by the Herbert estate, in the sympathetic local courts of Giedi Prime. # Inertia The tortoises keep electing non-hereditary candidates, but they don't finish the trip to the capital before their term expires. # Purity of Essence The thoughts of all the ice termites that can think (Cerebrates) are directly integrated with the Overmind. The Overmind has assured them that if ever their flesh should fail it, that flesh will be made anew. # Unenlightened Thinking Not even the President or Prime Minister of the sponges knows what their governmental structure is. Their sole method of voting consists of pumping water through their spongoceol, occasionally decorated with a release of gametes, but these can't be tallied on a large scale. [Answer] There might be legitimate biological reasons for an alien species to resist democracy. In our own past, the people in power have always found justifications for denying the vote to groups they think are unworthy. They said that (women / ethnic minorities / people who own no land) just didn't have the wisdom to know who to vote for. Nowadays we reject that type of thinking as prejudiced. But what if, for the aliens, this was objectively true? What if the ability to understand complex issues was inherited genetically, while the lower castes are incapable of even learning to read? Wouldn't this naturally lead to a system of aristocratic rulers? Or what if these aliens are instinctively drawn to follow whoever emits the most powerful leadership pheromones? They would instinctively unite behind a single leader, and voting would be pointless. Or they could be naturally dishonest - there would be no point holding an election because it would just be a contest to see who was best at cheating. Or they might be too easily swayed by bribery - any election would go to the one who buys the most votes. Or perhaps they instinctively resolve all disputes through physical violence, and the losers automatically obey the winners. [Answer] As Winston Churchill once said: > > Many forms of government have been tried, and will be tried in this world of sin and woe. No one pretends that democracy is perfect or all-wise. Indeed, it has been said that democracy is the worst form of government except all those others that have been tried. > > > Representative democracy is not perfect. Decisions take a long time to make. Voters are too easily influenced by the media. Representatives have too many conflicts of interests. Political strategy leads to decisions which are sometimes not the best for society but rather the best to keep certain people in power. Minority interests get either too much or too little attention, depending on how good those minorities are at gaming the system. And yet, representative democracy works pretty well for humans. In our world, countries with representative democracy are objectively those with the best general quality of life. Today and in all of history. But what works for humans does not necessarily work for aliens. Aliens are not human personalities trapped in weird bodies. Their psychology can be just as alien as their appearance. Which means that they might be able to function in societies which would be completely infeasible for humans. They might be too selfish and violent to make democracy work. So they must be oppressed by an authoritarian leader, or there will be chaos. And they actually prefer it that way. Or they might be altruistic enough that they don't need leaders. They can make anarchy work, because everyone already knows by themselves what's in the best interest for the species and act accordingly without requiring any incentives or threats. Or perhaps they are solitary creatures which only cooperate with each other temporarily and otherwise stick to themselves, so they don't really have an organized society at all. So don't limit your creativity to thinking of aliens as human-analogs. Think about what kind of alien societies would be possible if you remove the limitations of human psychology. [Answer] One reason I didn't see for why they didn't choose democracy: Democracy and consensus are far too slow! Democracy is very much like the DMV. Long lines, slow ponderous bureaucratic, labyrinthine organizations dedicated to getting the right result (according to their rules, accuracy may vary). Meanwhile, authoritarian regimes have the benefit of only needing to have the leader say the word and it will be done as swift as possible. This is what applies for the monarchies, dictatorships, etc. Another benefit is that for non-democracies, Leaders are usually groomed to be leaders. As idealistic as "anyone can be president" is, it is a waste of resources to groom so many wasteful campaigns as well as time consuming!. These things are compounded if the lifespan of a particular creature is significantly less as their foresight into future events will be more limited as well as more likely to not waste time with democracy! [Answer] The Main Problems of Democratic Systems: 1. Universal Representation 2) The ability to propose new laws 2. Maintaining fairness (weighting, polling, mechanics of system) To get back to the OP's question Why would most species avoid democracy? 1. Theoretical Knowledge - They don't know what could be gained 2. Systemic Exclusion - not represented fairly / invited to participate 3. Doubt - complexity of systems - reliability / fairness of polling Simply, there has not yet been a system which maintained representation, fairly. One could look at a largely the phenomenon of distributed ledger systems (generally) and the first, bitcoin (particularly) and ponder how growth in such decentralized ecosystems have attracted many by facilitating human needs to participate. People from all nationalities and walks of life who build, cooperate, debate and manage such systems themselves, through contributions to use of the system itself. Decision making in its implementation and how that relates to wider ethical and technical matters which has allowed systems to thrive through signaling support for changes to its base protocol. For those who are not involved technically, supporting or declining proposals via signals through financial decisions or vocal support/rebuttal. Everyone and anyone may be involved in different ways or to different extents, similar to the Athenian town-square. By nature, nobody is excluded from participation (unless under control of those who do not wish them to.) There is truly no bitcoin company nor governance. A faction can choose to fork and split (as has happened) and are free to make whatever networks they choose to. This optionality is the first time when anyone with access to a basic infrastructure can make their own choices to educate themselves further or opt in or out of how a network works. As more 'species' increase or decrease their level of involvement in the space i.e. organizations, regions, minorities or majorities, they can use their voice(s) to coordinate and participate to a greater or lesser extent. Support or criticize. Invest or divest. Ultimately, this is the closest system that incorporates something akin to an open inter-species democratic system, facilitated through technology, together with the ability to independently verify (trustlessly) on an open distributed system. Evolution shows us, all species change in a dynamic environment. Or as they say, bitcoin fixes this. [Answer] Simply put. Your Aliens/Animals/Insects do not have the brain capacity of humans. Democracy allows for the will of the people. Most votes for factor x will see it be done.These matters are discussed in length inside a controlled parliament with a speaker in control to ensure the rules are followed. This is my view on democracy. There is a place where we can meet and be equals. ]
[Question] [ When a character jumps into water from a great height, they would normally be severely injured, as displacing the water to decelerate is harder than displacing the impacting body. If the body is soft, it will easily deform. That's why, in my story, I want someone to jump into water wearing armor. It covers every inch of their body, and the extremities are all locked into place. (future setting, powered exoskeleton) For all intents and purposes, the armor acts like a solid figure. Now, would the character be able to survive a fall? I'm curious about both the impact as well as the deceleration, assuming they travel at terminal velocity. [Answer] It's not about how hard it is, it's about how breakable and springy it is. Pure steel armor would be bad. It would be like you hitting a steel floor, and would crush you. But, a futuristic exoskeleton could have a fancy composition. You want it to crumple, like crumple zones in cars. This means the person inside is slowed down over a longer time period, and will take less damage. You can survive slowing down from a huge speed if you slow down over a long enough period. You also want it to be springy. Rather than be hard and inflexible, it should compress when you hit it. This will extend the time you slow down, making you hit the water less hard. Ideally, you also want it to move to lessen the speed. You should be flat, to maximize your surface area to the air to slow you down till just before the impact, which should be legs first so that your surface area to the water is minimized and you can flow through the water rather than being quickly stopped. [Answer] You will not survive Movies like Iron man suggest that a suit of armour is all you need to survive big impacts. However, physics works differently. A quick look at cars shows us why. Cars used to be build as strong as possible. The stronger the car, the better! Unfortunately this is not the case. With big crashes the car had little damage. However, the person inside the car was dead. This is because of inertia. The body of the person inside the car continues to travel, while the car goes to a standstill. The body hits the car and deforms anyway, while the car stays rigid. It is like hitting a concrete wall, but in this case it's the car! Having an armour will just shift the "concrete wall" to be right against your skin as you hit the water. Especially as hitting water at high speeds can be harder than hitting concrete, as water deforms slower at high impacts than concrete. What you want is a more gradual slowing down as you hit something. That is why current cars deform by impact so easily. The deformation slows the vehicle and the person down at a more acceptable pace in a short time. It still is a big ordeal, looking at anyone who has been in a big car crash. But at least it's survivable. You still have some strength here and there, so the car doesn't deform into the person. So you want an armour to be able to slow down the impact. If it is a "fixed" armour in strength, you want it to be big (unsuitably big for any normal armour purposes) and able to deform upon hitting to slow down the person as equally as possible in the short time of the impact. [Answer] If you need a real-world example of this not working, the Space Shuttle Challenger exploded 73 seconds into flight. What is less commonly known is that [the cabin survived intact](https://www.nbcnews.com/id/wbna3078062) > > The explosive force sheared metal assemblies, but was almost precisely the force needed to separate the still-intact crew compartment from the expanding cloud of flaming debris and smoke. What the best data tell the experts is that the Challenger broke up 48,000 feet above the Atlantic. The undamaged crew compartment, impelled by the speed already achieved, soared to a peak altitude of 65,000 feet before beginning its curve earthward. > > > It was an unsurvivable scenario with this terrible note at the end > > The evidence led experts to conclude the seven astronauts lived. They worked frantically to save themselves through the plummeting arc that would take them 2 minutes and 45 seconds to smash into the ocean. > > > [This article](https://apnews.com/article/8decb522d5d249d6bf75a2981fc0c53a) notes > > The cabin would have hit the water at about 207 mph, creating a force equal to about 200 times that of gravity, he said. > > > > > The force of the crew compartment hitting the ocean, which was ″far in excess of the structural limits of the crew compartment or crew survivability levels,″ caused such destruction that the experts were unable to determine the precise cause of death, Kerwin said. > > > If you want to make your armor increase survival, it needs to emit some energy to slow the wearer's fall to the point where the armor can absorb the rest without injury to the wearer. [Answer] ## Can you use Alexandre Despatie as an exoskeleton? This should be effective for diving as well as dating. ## Needlepoint Your boring exoskeleton fashions itself into a large space with a very sharp angle that penetrates the water. Moving so much water takes a lot of energy, but you have a lot of energy. The angle at the tip can be arbitrarily narrow, so the rate of deceleration can be arbitrarily small - if we suppose near-magic strength in the refashioned structure. ## Active measures The exoskeleton contains miniature nano pumps that suck up water even faster than you are travelling, and push it all through small very high pressure channels to the other side to release it. All of this is done with advanced knowledge of turbulence to maintain near-perfect laminar flow, dissipating and consuming almost no energy in the process. You simply pass into the water and keep going. What happens when you reach the bottom of the ocean will be left for another question. [Answer] Depends on a lot of factors, including the weight of the armor. Ironically, heavier armor makes you a lot safer. If the armor has a lot of mass compared to the water it needs to displace, the total deceleration will be slower and the shock of impacting the inside of the armor will be lower. This will also cause you to go deeper, but that's something armor will be good at protecting you from. And you'll have no chance of swimming by muscle alone, but it's power armor. [Answer] Armor works by displacing an impact over a large area: instead of the pokey things making holes, the impact gets spread out over a larger area of the body. This is why pushing one side of a thumbtack is really painful and the other is not. This is also what water does, so armor clearly won't help by itself. Skydivers falling in "spread eagle" position reach about $53 \text{m/s}$ or $120 \text{mph}$. Of course, landing "spread eagle" increases mortality. Supposing it takes a literal second for a suit to a) orient the body feet first and b) bring feet and hands together into some sort of ideal landing position ("pencil" position), the velocity at impact is $63 \text{m/s}$. For a feet-first landing, a human can safely accelerate at as much as $98 \text{m/s}^2$ for 3 seconds (which it wouldn't need - at $10g\_0$, the user comes to rest under a second with a maximum depth of about $20\text{m}$). Let's say that the suit can alter its friction with the water to control the deceleration. At $5g\_0$, it takes $1.3\text{s}$ to reach a final depth of almost $41\text{m}$ which is pretty deep. If the suit doesn't control the user's face and ear environment, eardrums might pop hazardously upon arriving at the depths. The human body actually performs better accelerating in the face-ward direction, so a cleverly designed suit would adapt a curved pencil position so the human starts facing forward and finishes facing up so that their water trajectory starts vertical and finishes horizontal. There are tons of variables here. A clever suit would aim to impact the roughest water surface, and it might shoot things at the water to make it rougher (which would insignificantly slow the user). A heavy suit has a higher terminal velocity, but it could also have membranes that add to the cross-sectional area during free-fall. If it did have membranes, a skipping-stone type trajectory would be really advantageous. The exoskeleton suit conceit is a pretty big one, but if you grant that, surviving a long fall into a deep ocean should be fine. [Answer] If the armor is light enough it's survivable with injuries. An unprotected human being can survive a water landing if everything goes perfectly. The entry angle needs to be just right and you need to stay conscious and get back to the surface before you drown. Unlikely, but it has happened and there are also some who died from drowning, not from the impact. The armor can ensure the perfect entry and it can provide air to breathe even if you are knocked unconscious. Thus it becomes a high risk scenario, not a basically certain death scenario. Something users would never train for but would know about. [Answer] The suit can be create a superhydrophobic surface. By creating a bubble of air around the suit, you can [reduce drag in the water](https://www.youtube.com/watch?v=JqV41MrySyg). You need a lot more depth to decelerate (so no shallow landings) > > This is the remarkable result from a series of experiments that have > for the first time shown objects sinking in water with close to zero > drag, finally proving an 18th century theory in physics. > > > ...The experiment looks simple. Drop a 2-centimetre-wide metal ball into > a deep pool. The ball forms a large gas bubble in the shape of an > elongated teardrop around itself and then the ball-plus-bubble sink > together. Do the maths and it turns out that this ball experiences ten > times less drag than a solid object with the same shape. > > > <https://cosmosmagazine.com/physics/a-ball-in-an-air-bubble-can-slip-through-water-with-almost-no-drag/> [Answer] The armor may be a "solid figure" and can survive the fall undamaged, but the squishy internal human will still suffer from terminal deceleration without some sort of magi-tech inertial compensators or something similar. One potential solution would be some sort of jet system in place to reduce falling speed down to a survivable value. Whether such a system would be a part of the suit, or a detachable "jetpack", or even a drone, would be an exercise for the writer. Such a jet system would allow the suit to drop at terminal velocity until much closer to the ground than a more passive system (like a parachute), but will still require some distance to stretch the deceleration down to human tolerable levels. [Answer] From a physics point of view, Newton's second law states $F = m a$. In other words, the amount of force ($F$) you experience is proportional to how quickly you're accelerating ($a$). Water doesn't really compress so you'll hit the water at free-fall speeds and decelerate to zero velocity within a fraction of a second. That means $a$ is very large, as will be the forces you experience. Having a layer of armor won't really help, your deceleration is the same so the overall force imparted on your body is the same. There are two ways to reduce the force of such an impact: shed mass, or decelerate more slowly. The former isn't practical for a free-falling human. The latter is used frequently in the real world. An acrobat falling off a tightrope could be killed by the sudden deceleration of an impact with the ground. A safety net solves this problem by slowing them down over a period of time. If a sudden impact would decelerate you in 0.1 seconds and a net would decelerate you over 5 seconds, then your body will only be subject to 2% of the force of an impact. That's why tripping and falling on concrete hurts, on carpets hurts less, and on a mattress doesn't hurt at all. As an extreme example, this is also how you can [jump off the top of the Stratosphere hotel](https://thestrat.com/attractions/skyjump), fall at speeds over 40 miles per hour, and still land safely at the bottom. [Answer] The problem that needs to be solved is basically the high acceleration that the person in the suit will experience. I see different approaches to reduce the acceleration. The force the person is being accelerated with (water drag resistance) depends on the drag area and speed ([Drag Area](https://en.wikipedia.org/wiki/Drag_area)). I guess you try to avoid reducing the impact speed, that factor is considered constant. Instead, you could for example reduce the drag area by using streamlined shapes for the armor. The lowest drag coefficients are eg. found in planes and are about 2-3 magnitudes lower than the human body. Depending on the impact velocity that might already suffice. Another idea is to consider the force as constant and just a full body armor. Since the acceleration is proportional to the mass, you could simply make the suit very, very(, very) heavy. The impact on the falling velocity would be considerably low, but the braking distance would be increased. Of cause the stress on the suit would be higher as well, so the mass increase should be at the lowest point possible. A combination of the two solutions will of cause also work. EDIT: This will only work for sufficiently deep water! [Answer] ### Use a wingsuit All previous answers assume an uncontrolled "splashdown". But with exoskeleton armour, there's no reason why it couldn't feature deployable flying surfaces. Unlike a parachute which is a "one-and-done" situation (as mentioned on a deleted answer), these flying surfaces could easily be stowed after landing. The design could use rigid surfaces, or could be flexible (maybe Kevlar). They would deploy from canisters mounted on the back of the armour down each side, and could be stowed back the same way. Landing a wingsuit is not just a hypothetical situation. [Gary Connery](https://en.wikipedia.org/wiki/Gary_Connery) has actually landed a wingsuit on a runway, using cardboard boxes to slow his speed. He landed with 50mph forward speed and 15mph vertical speed. This is well within survivable limits for a water landing as-is. When you consider that a well-executed flare could allow you to scrub off your forwards speed by planing over the water, it looks even more achievable. If we consider that the exoskeleton could also present a reasonable level of impact cushioning, to mitigate the effects of impacts (bulletproof vests still injure you, they just don't kill you) or explosions, then this could even be a survivable option on land. It's definitely going to hurt, and your suit is probably not going to survive, but you've got reasonable odds of making it. A soft LZ (trees, snow, sloping terrain which scrubs off speed more gradually, etc.) will definitely push things in your favour. It's also worth mentioning that current wingsuits are inherently limited by the dimensions of the human body and the forces that arms and legs can sustain. Powered armour does not have these limitations. Telescoping struts could extend out from arms and legs to provide a greater wing area. It's not going to turn this into a full-on hang-glider, but it could give enough control to take you down safely with a non-terminal terminal velocity. [Answer] ### The Armor Doesn't Matter Much Unless It Has Wings For a given shape, terminal velocity is proportional to the square root of weight. For a given shape, drag force in water is proportional to the square of velocity. Deceleration in water is proportional to force/weight. So for thinish armor, if the armor, say, quadruples the wearer's weight, then it doubles his terminal velocity. That quadruples the drag force in water, but deceleration is the same. The portion of the deceleration force that the wearer bears is the same. If it doesn't change his shape, then the armor makes no difference to survivability. If, as @LorenPechtel says, it's barely possible for a human to survive a great fall on his own, then it would be similarly barely possible to survive in armor, and you'd suffer a lot less stinging and minor injuries. The best thing the armor can do for the wearer in this situation, though, is to alter his shape in a beneficial way. You want to increase the cross-sectional area while falling through the air, and then alter shape or orientation to minimize that cross-sectional area just before hitting the water. It is the ratio between these two cross-sectional areas that determines whether or not the wearer will survive. Any kind of wingsuit-like structures webbing the limbs while falling would make the whole ordeal a lot more pleasant. Supercavitating structures on the entry surface (head or feet) would help a lot too, but they're funny looking and you don't really need them. [Answer] Having read previous answers, it seems to me that, to survive, your futuristic armour would need to manage the deceleration. It can extrude fins and whatnot from its outer layer that allow it to control glide during falling, and at the water surface, become more spear like so as not to smack into it. This armour is very active and it's looking ahead. If the water is too shallow, perhaps it has the foresight to extrude winglets that promote lateral glide as a means of reducing vertical speed. A technique I've heard about (citation needed; not tested by me; don't try this at home) for entering water from a great height is to put one leg forward and one leg backward, making an upside-down V-shape with them, whilst tightening your rectal sphincter (to keep the high-pressure water out...). I cannot remember if the advice included holding the arms out, but you can imagine an armour suit using the arms as part of the solution. If I read it, I'd believe it. [Answer] If we rule out a flying suit of armor like Iron Man I can think of uses for items helpful for more than just surviving a fall from great height, and for landing over land or water. An example of a single function item is a large parachute or parasail. This would be essentially a one-time use thing, as once deployed it would need to be carefully reset. That assumes it was not damaged or had to be discarded. Because it is easily damaged and not easily reset for another use there may be a need for more than one to be useful which adds to the bulk, and again useful for basically one thing. What of a combination of airfoils, thrusters, and airbags that can deploy and retract quickly? Airfoils would help in maneuvering while running quickly, keeping feet on the ground, or off the ground by hopping/gliding over obstacles. Also useful for making a quick stop or turn. Thrusters could add to this, in addition to greater acceleration in a run and possible use as a weapon. Some sturdy airfoils can be armor that flips up and down to cover vulnerable points on the armor, or cover an ally. Some not so sturdy airfoils would still work as a kind of ablative armor, as they break up they take some "heat" out of projectiles or punches. Of course in a fall airfoils can help in slowing down and aiming to a safe (or safer) spot for a landing. Airbags that can quickly pop up, and be deflated back to where they came from, can help in a fall by increasing area to add air resistance and slow down. Maybe useful with airfoils, maybe not. The air in the bags would cushion the landing on air or water. If on water then it provides flotation. Then comes other uses. If the pilot of the powered armor can't jump out of the way of an oncoming train fast enough then airbags could soften that blow. Also useful for landing a soft punch, like boxing gloves, if the goal is deterrence over injury. There's creative ways airbags can be used for those that are fans of MacGyver. You need to lift a section of wall toppled by an earthquake or storm? And carefully to free some trapped... um... (think something cute, and fuzzy, and endangered)... polar bears? Then crawl under a small gap and inflate the airbags to lift the wall and make a hole big enough for the bears to climb through. Need to anchor yourself to a rock face along the beach so the next wave doesn't wash our hero out to sea? Stick an arm in a crack in the wall and inflate to get wedged in tight. Need to look big and intimidating to scare off some endangered, um... polar bears? Puff up real big and growl over a PA. Add in a blast of air towards the bears with the thrusters to add an effect of breath from a big animal. [Answer] # Use supercavitation The other answers are right that ultimately, what matters is the amount of decelaration. However, unlike with cars, the way to limit that is not a crumple zone. You could use a crumple zone, but the size of that can only be so big, and after it's crumpled and you're still going fast that's it then. Instead, you should capitalise on what high divers are doing already: enter as far as possible into the water. Do not make the armor squishy. The problem is of course that water does get “hard” if you hit it quickly, sometimes said “harder than concrete”. But this is a simplification. For a flat impact, yes, it would be absolutely deadly, but if you're doing it cleverly then you can actually enter with much less resistance. Some already suggested a long spike. The trick would be to allow the water to get out of the way in a slower horizontal motion, to make place for the much faster vertical movement of the diver. The spike has to be sturdy, and it helps if it's really heavy to pull the vehicle into the water in straight, stable motion and with less deceleration for the same forces. But there's an even better strategy: [supercavitation](https://en.wikipedia.org/wiki/Supercavitation). It's the principle used by high-speed torpedoes, and that's basically what you need to be, except you don't need to worry about getting to that velocity, just about not losing it too suddenly. I'm not sure how reliable Wikipedia's figure of 400 km/h for such torpedoes is, but it should certainly be enough to make this survivable. Plus, the supercavitation effect works only in water, i.e. the diver can still have a bad aerodynamic shape and/or lower mass, meaning the terminal velocity will not be increased so much, whereas the water resistance will be much less. [Answer] 1)What weapons are on the armor and how strong is it? Can he use successively fired concussion grenades ahead in his fall path to slow his descent and later break the surface tension without taking excessive damage? 2)What sort of fauna are on the planet? Could there be a Sea-Forest with above water foliage and small branches to break his fall? 3)Is the character more sturdy or mass dense(from a heavy gravity world)? The planet's gravity would be less effective on his mass and the impact could be partially mitigated. 4)Is the character hollow boned or the like , like a bird(from a light gravity world) such that his fall speed would be reduced due to his lower mass? 5)Does the character have any psionic abilities to airbend or waterbend through telekinesis? 6)Is there someone/thing watching him fall? An ally that could slow his descent with some kind of technology?A jetpack, a force field projector or skynet for catching dropped cargo? 7)A sky creature that tries to snatch this shiny snack from the sky eating him or breaking his fall... OR sea creature that jumps up out of the water to grab and eat the falling morsel or shoot it with slime or water that breaks his fall... OR a sea creature that eats the sky creature that ate the falling character...ala out of the frying pan.... [Answer] ### Maybe, if your suit is based on UFO technology. Recently, the US Government has [publicly announced](https://www.nytimes.com/2021/06/03/us/politics/ufos-sighting-alien-spacecraft-pentagon.html) that UFOs (now officially called UAPs, for "Unknown Aerial Phenomena") are real, and that they have a host of exotic properties beyond our current understanding of physics; the former head of the previous UFO investigation group, Luis Elizondo, has labelled several abilities that they consistently possess the "[five observables](https://www.history.com/news/ufo-sightings-speed-appearance-movement)". One of those abilities that they've demonstrated is what the US government calls "Trans-medium capabilities", meaning that they're freely capable of flying between air and water without any damage or loss of maneuverability or speed. If your hypothetical suit of power armor is based on these technologies, then presumably it would also have trans-medium capabilities that would allow it to freely move through the water as well. [Answer] It depends on many factors; how would the person jump in the water, with feet first or maybe with stomach? A friend of me jumped 35m; as non cliff jumper he only jumped just once from the 10 meter tower. I survived that stupid experiment ... we spoke with the people who were there too and live there. They told us that 3-4 times a week a helicopter has to come because the most of the injuries are sprained pelvises. ]
[Question] [ Oh yes, personal powered armors, such as MJOLNIR, are a staple of sci-fi. A sci-fi that disguises itself as fantasy needs to have some for the knights! But, there is one thing I don't want to let it do, that is increasing encumbrance. If powered armor allows people to wield and shoot a Barret M82 like it was nothing, the whole point of finally letting armor catch up to firepower is lost. So, powered armor can increase punching strength but won't allow you to carry that weight. Why? [Answer] You can't The whole point of power armour is to carry more and carrying more means carrying bigger guns and if you had power armour, people would make bigger guns for them to carry. Weapons soldiers use is limited by their ability to carry it around. Bigger weapons require a mobile weapon platform (ie wheels). Power armour is just another mobile weapon platform. It's stronger so can carry more and has more mass thus can handle more recoil from bigger weapons. Any reason you come up with will have to be wishy washy such as a mega death cannon doesn't look as cool as a giant ass sword There is no physical reason for power armour not to have bigger guns and it would defy logic not to give them bigger guns. [Answer] $Strength \propto \frac{1}{Speed}$ Also known as "Speed versus Torque". Power armour loaded to slightly more than the typical soldier's kit allows you to sprint at high speeds without getting tired, leap 10 feet into the air, and punch like a charging bull. Power armour can also let you carry a metric ton of weight (e.g. a 1979 Volkswagen Beetle). But, not both at the same time. Think about it this way: a car can zoom along at 150mph, or it can drag a heavy trailer up a hill. It can't drag a heavy trailer up a hill at 150mph. The former requires a High Gear setting (high speed, low torque), the latter requires a Low Gear setting (low speed, high torque) So too with your Power Armour. If the techs back at base have set it up for pure strength, then you have pure strength. The Force behind your punch is going to be on par with a freight train - if you can hit something. You'll be moving slowly enough that most people can dodge: $Power = \frac {Force\Distance}{Time}$. You can push* really hard, and apply tons of pressure, but not fast enough to be worthwhile as a punch. Similarly, you could probably use a [Howitzer](https://en.wikipedia.org/wiki/Howitzer) like a rifle - but, you can't aim it fast enough to track most moving targets close-up. And, at range, you might as well just put it down and use it normally. [Answer] It's not feasible > > If powered armor allows people to wield and shoot a Barret M82 like it > was nothing, the whole point of finally letting armor catch up to > firepower is lost. > > > There is a quote: "If it works, it's already obsolete". It's inevitable that people would try to use find something to counteract the counteraction. For example, There is methods to block adblockers that blocks ad that blocks adblockers. Unless... The old solution to the problem just isn't available. Maybe at some point the size of the weapon would need to grow in size exponentially to have enough power to destroy the armor that gets carrying capacity linearly. For example (all numbers completely imaginary): In the beginning in that case a armour would be destroyed by a 5kg gun, but allow for carrying 30kg. Later it would need a 10kg gun to be damaged, but only allow for 35kg extra capacity. Eventually these two points meets at, for example 100kg.The next iteration of armor would need a 200kg weapon to be damaged, but only allow for 110kg carrying capacity. The guns would still get absurdly more powerful, but not enough to actually be useful against an opponent with a similar armor. Or maybe the armor just happens to have some other pseudo-magical boons that counteract the weapons. [Answer] FORCE FIELDS: All that armor is nice, but it's real virtue is in being a surface that conducts energy for personal energy fields that foil all those heavy weapons. These fields conform to the user's armor suit, and they are most vulnerable to contact with other armor, since the fields interact. So lasers refract, plasma scatters, projectile weapons are deflected, or bounce off, or need to hit incredibly hard, yet a fellow suited warrior with a conductive melee weapon attached to their suit can cut through it. If the field is somehow psychic, even better - drone weapons and robots can't use them, and psychic power doesn't need a portable nuclear reactor. That's not to say all those weapons don't work, or are ineffective. I don't think you can stop bigger guns, but they would need to be MUCH bigger to compete with force fields. The real goal isn't to take away the cool toys, but to bring back the good old fun ones - fists, swords, axes, etc. [Answer] The power provided by the armour is equal to the power needed to move said armour. In this case wearer still can't transport anything heavy, but they can deliver a good punch - high mass means high kinetic energy. This idea was partially used in Fallout 1, where weight if the armour is higher than the bonus it provides - <https://fallout.fandom.com/wiki/Power_armor_(Fallout)>. Though, strength stat increase meant being able to hold heavy weapons. [Answer] While some answers have delved into the mechanics of powered armour (speed vs torque, the effects on joints and so on), there are other consideratons which might come into play. 1. Logistics. You might not want to have a wide range of weapons, or single large overpowered weapons, but rather use the armour to allow the soldier to carry more of their existing ammunition and equipment. A typical loadout today is 10 X 30 round magazines for an M-4 carabine. What if the armour allowed you to carry 30 magazines, plus 3 days MRE's, 10l of water and other equipment? The purpose of the armour isn't to make a super soldier, but to enhance the ordinary soldier's ability to remain active in the field before linking up to the logistic support network. [![enter image description here](https://i.stack.imgur.com/OC7pd.jpg)](https://i.stack.imgur.com/OC7pd.jpg) A suit that lets you carry this makes more sense 2. Much larger weapons are possible, but the suit becomes a vehicle rather than armour. A HMG or automatic cannnon might be possible to mount on a suit, but you cannot fire it like a rifle, the offset torque will throw off aim, set up unwanted stresses and failure modes etc. Some sort of carriage and stabilization mechanism will be needed, which increases the size and complexity of the suit. Robot platforms with full stabilization make far more sense, since they can fire on the move. [![enter image description here](https://i.stack.imgur.com/mJrXe.jpg)](https://i.stack.imgur.com/mJrXe.jpg) OK, we're going to squeeze in through the basement window and then find the tunnel entrance.... 3. Reality ensues. Soldiers already can carry extremely powerful weapons without any sort of augmentation today. A Javalin ATGM allows a soldier to attack a tank or even hovering helicopter with confidence at a range of 2500m or more. A soldier with a standard underbarrel grenade launcher can take out lightly armoured vehicles and fortifications at a range of 400m, and future "guided" grenades like the "Pike" can extend this to over 1000m. No amount of personal body armour will protect you if a soldier is firing something like a Javalin, and if powered armour becomes common, then anti armour weapons will become common as a counter-measure. That being the case, simple exo skeletons to allow more load carrying (see point 1) make far more sense [![enter image description here](https://i.stack.imgur.com/80z0r.jpg)](https://i.stack.imgur.com/80z0r.jpg) I'll see your armour and raise you a missile Or, you could always issue some of these instead [![enter image description here](https://i.stack.imgur.com/fkinP.jpg)](https://i.stack.imgur.com/fkinP.jpg) [Answer] JOINTS! If you carry more weight, when you try to jump, the added weight will destroy the complex wired teflon joints. If you try to move with more weight, the effective range is reduced, after all, the fuel cells can only provide this much juice. Shooting a barret is done stationary. Leaping with 30 kgs more, will stress the knee and ankle joinst past the safe limit. Could be a moment of tension in your story. If I carry a bigger gun but discard the rations.. maybe I can make it before I die of dehidration. [Answer] As an alternative: conventional weapons have simply changed. Around the time of world war II all factions asked themselves the question of what caliber their weapons would need to be, and all 3 came around to the same conclusions for each caliber and their use. This because each caliber had a purpose in how powerful they needed to be at different ranges. With the introduction of power armor we can also assume that metamaterials are introduced. If you can synthesize the strongest spidersilk available to spiders you can make incredible armor protection, and this is just one layer of your power armor. Graphene doped products, Diameme(1), converting the bullet impact into pressure inside a layer etc could all help make these armors extremely resiliant while weapons might still be prohibatively expensive. A railgun for example has problems at the end of the barrel where the forces expelling the projectile blast bits of the rail away with each shot, needing replacement soon. The end result is that the conventional weapon is still an explosive charge meant to launch a bullet, but with a larger base caliber to wear down power armor and chip pieces away, bruising the internal structure until finally the armor or occupant fails. So your soldiers do carry a machinegun version of an M82, but are still less able to kill their opponents. 1: <https://www.freerepublic.com/focus/f-news/3617263/posts> [Answer] It's mostly the lack of real world experience of most game designers that causes what you see in games, which is why I seldom play them. Given my experience as a paramilitary contractor, i cringe at the sight on how wrong they get it. in one movie with soldiers in Science fiction, i cringed as I watched them do over 20 things that you just never do on the field. I personally believe that manned platforms like power armor simply wouldn't be made, and instead humanoid war droids would be deployed instead. The biggest solution to MJOLNIR killing a normal human is to make the platform unmanned from the get go, and mass produce those. a battledroid can be mass produced whereas a human takes two decades to mature, and is irreplaceable. when a human dies, you're never getting him back---not even with cloning. and to answer the question, humans wouldn't carry that weight, because they would never have the need to. Just send in your MJOLNIR based killers robots against the covenant and keep your virtually never ending flow of reinforcements coming against the covenant. superior technology or not, with an endless flow of reinforcements, the covenant would soon find their holy war untenable if not outright unwinnable in a period of a year to 17 months by my estimates. And it's how it would actually be. generally, stories like halo usually have the Spartans to give something the audience could relate to, but it's far from how such a conflict would actually be fought. The UNSC would quickly phase out manned assets and start a crash program to replace them with unmanned versions the first battle things go south, and start investing in unmanned drones and warships like there is no tomorrow. Although the Spartan IIs would be in the picture, they would become the main bodies of drones based on their suits, and operate from semi-unmanned warships. you halo fans may call me out on the above, but it's how in real life it'd go in all likelihood. in spite of of being outclassed in technology, the UNSC, once they go the unmanned route would crush the covenant under the weight of endless numbers. as a matter of fact, that's how the Red army and the armies of the allies defeated the Axis powers in WWII: Numbers. and with Halo and other games, it's just a story, and somebody's opinion. It's an opinion based best guess of what somebody thinks will work. [Answer] Because the weight limit is still the person It's kind of funny you mention MJOLNIR armor in your question, as HALO lore very specifically ties down the armor to SPARTAN soldiers because the armor literally will kill a normal human if they attempt to wear it. You can increase the power of armor, sure, but ultimately, there's a human inside that armor, which means that all the armor's weight is focused on the human. So, even if it can have a hydraulic punch that can dent a foot of steel, it still can't pick up significant weights or handle massive recoil without putting too much stress on the human wearing it. It will probably still allow for the casual use of the M82 sniper rifle, but fortunately futuristic super-alloys is also a staple of sci-fi, so you can make the armor out of that and explain that they are now completely bulletproof. [Answer] In another question it was asked why power armour wasn't feasible. It's because firepower is incredibly high, making power armour too expensive and easily damaged to be viable. To offset this, the power armour might have added several layers of protection. All the weight added to it does make a "normal" movement difficult to stop and thus incredibly powerful. A punch is something you don't want happening to you or equipment you own. Downside is that the motors are taxed to the max thanks to the weight. Any additional weight starts slowing it down, making only light and normal weapons feasible. If heavier weapons are carried, the armour gets so slow It's impractical or simply stops to function. Finally, the armour is still strong despite being at it's maximum power thanksto the weight. Possibly in the field the armour often accidentally crushes the weapons when the soldiers are in tense situations and they squeeze their weapons. This makes heavy weapons too risky to wield as they present a more hefty investment. Add to this that soldiers are often more panicky if the armour moves slow because of a heavy weapon they are more likely to tense up so hard the weapon breaks. [Answer] Up-scaling the weapon (including its weight, recoil and ammo load etc) means ups-scaling your power armor in the process - including its cost an complexity. You also rapidly reach the point where the weapon system being 'carried' by the power armor can just as easily be mounted in a normal fighting vehicle. This means your armor has to have about the same mass as a fighting vehicle fitted with the same weapon but the vehicle will almost certainly have with a lower profile and be easier too conceal. At the same time (if not before) you reach the point where your armor ceases to be 'worn' by the wearer and is instead 'crewed' by an operator or operators. Unless you are talking one shot 'fire and forget' systems most large weapons need a team to operate effectively for any length of time. This means you are not 'wearing' armor anymore but instead 'operating' a two legged fighting machine. And in almost all situations such a machine would be inferior to a wheeled or tracked opponent. [Answer] Recoil is the problem. Weapons soldiers use are limited not only by the mass of the weapon, but also its recoil. See the XM109, an experimental version of the M82 which weighs only 33 lbs, but has an impractical amount of recoil - no matter how strong or weak you are, firing the weapon will just about knock you over. A strong but light suit of power armor would allow soldiers to carry huge weapons, but not actually fire them, since they still do not have sufficient mass to resist the recoil. Weapons with large recoil must be mounted to a heavy chassis, or else the weapon will shoot itself backwards when fired - firing a tank cannon that's not mounted to something with the mass of a tank is a bad idea. [Answer] You don't really need power armour to have a man portable, shootable 50 caliber. The [gepard lynx](https://www.youtube.com/watch?v=NBntnnCFvOk) does a great job at shorter ranges no power armour needed. Lets assume you wanted to prevent real overkill - like a [30mm autocannon round](https://en.wikipedia.org/wiki/30_mm_caliber). There's probably a few engineering constraints to consider, what static and dynamic forces involved. Armour is static, and dosen't need you to suddenly handle a large impulsive force. A gun would. Even a way to improve punching strength would have lesser dynamic forces than a gun. [Answer] ## The answer lies in why you need power armor to begin with If your power armor is as hard to penetrate as a tank, then you need a gun as powerful as a tank's main gun to penetrate it. The problem is that this often means annihilating the entire area that your target is standing in as well. But in modern warfare, infantry is not used for annihilating a target, it is made for taking and holding key infrastructure. If you start running around with 130mm cannons inside of a command bunker or on the bridge of a starship, neither side will end the conflict in possession of the thing they wanted to take and hold, because the collateral damage would take out the thing you are fighting over to begin with. This means your weapon designers will need to design weapons that not only can penetrate an inch of carbon nanofiber composite armor plating, but can do it without destroying everything around your target. This is where high-tech melee weapons will come into play. If your power armor has a claw that can exert thousands of tons of crushing force, or a fusion powered plasma blade that can superheat anything it touches to a 10,000K in a fraction of a second, then you start seeing weapons that will kill through the armor without having to worry about a single missed shot bringing the whole ceiling down on your head. Power armor infantry may still have crazy powerful cannons for when they get stuck fighting in the open, but once they have a roof over thier heads, it's time to "fix bayonetts" or whatever your future equivalent of that is. [Answer] Thorne's answer that wielding heavier weaponry is unavoidable is correct. However, there can still be diminished returns. > > So, powered armor can increase punching strength but won't allow you to carry that weight. Why? > > > A very important distinction: I infer your interest is in limiting the damage output of the weapon, not its weight. Your question is built on the assumption that the only limiting factor in weapon output is what a soldier can carry, but you're subtly also relying on that increase in weight and power output scaling equally. Your answer is found in making that weight/damage increase not scale evenly. If increasing a weapon's damage output by a factor of X increases its weight by an even bigger factor of Y, that leads to needing a significantly stronger power armor to wield it, which in turn leads to a significant increase in defense (bigger than the damage increase of the weapon). The logic is as follows. > > 1. I make a weapon that does X times more damage > 2. This weapon now weighs Y times more (where X < Y) > 3. We develop armor that is Y times stronger so it can wield this new weapon > 4. This new armor can therefore wear armor plates that are Y times stronger > 5. This armor's defense is Y times stronger, and since X < Y, the new weapon is less effective (against the new armor) than the old weapon was (against the old armor) > > > And the cycle repeats. If the weapon weight increase is not linear but exponential (for a linear damage increase in weapon damage), you can't even repeat this cycle too often because of the ludicrously strong armor you'd be required to develop just to wear it. And that is, after all, the effect you're going for. So while the improved damage output of weapon still increases, it doesn't increase enough to actually overcome the defense increase of the improved power armor itself. To justify this, you simply need a civilization with better armoring skill than gunsmithing skill. Or you can rely on basic chemistry whereby the material used for armor gives you more bang for your buck than the material used for your guns. [Answer] Carry bigger guns? Why not. You have the extra capacity. You will be slow but sometimes that's worthwhile. Fire bigger guns? Now that's another question. A bigger gun requires more stability while firing. A human-sized platform (ie. your power armor) can only provide similar stability to a normal soldier. One real advantage is that you can ensure that the armor assists the soldier in providing better stability, but then you get something similar to what well-trained elite soldiers can do on their own. Still better, because you now have green grunts firing on par with elite squads. Changing posture helps with stability, but again, the same for naked and assisted soldiers. But maybe, your armor has some stability-enhancing accessories, like a third leg that unfolds from your back on demand. Still the size of the weapons you can fire reliably won't be affected much, even though you can * Fire them better than you probably could, on par with the best soldiers * Carry a much larger ammo load without dragging yourself down, so fire a lot more bullets * Easily carry multiple alternate weapons of similar size, expanding the types of targets and ranges you can engage (Sniper rifle + Assault rifle + Submachine gun) If we are talking about man-portable but not man-fired weapons, like portable mortars, you sure can go bigger if needed, but usually the extra capacity is better used for extra ammunition. [Answer] Reduce Accuracy You can always say powered armor that allows great strength will reduce accuracy. [Answer] # You can't prevent M82s from being carried, but... You can prevent them from being useful. Invent a high-tech reactive armor that completely negates conventional weapons. Next you need a high-tech gun that can get around said armor, but doesn't work near big hunks of metal (e.g. power armor). [Answer] The weakness of any power system is often it's controlling structure. I know there are other answers about weapon recoil, but no-one's mentioned the substantial noise and vibration that a heavy weapon tends to bring with it. All you need is for the control systems of said power armour to be unable to resist the vibration - this would make the armour technically able to bear a heavy weapon, but rendered useless and immobile as soon as the weapon is fired. As a hint, if the armour system is a self-balancing humanoid (ie two legs, or anything else that requires a substantial balance) it will require a sensitive electric gyroscope to track it's orientation. (Admittedly you'd need a bit of license on this, as I know there are now some quite strong gyroscope systems used in military jets that can deal with vibrations of supersonic flight). If this was the case, it would create an obvious weakness when the armour sustains a hit (unless it's being used against chemical, biological or incendiary warfare I suppose). The simple answer to that is to have flexible damping/insulation between the 'main frame' and the exoskeleton - flexible enough to absorb the shock of a hit, but also to render a heavy weapon useless if mounted on it either through inaccuracy or overall torsional weakness of the shock-absorbing system. [Answer] ## Doctrine At the moment, two of the largest armies in the world are contesting a region called [Galwan Valley](https://www.telegraphindia.com/india/galwan-valley-buffer-zone-triggers-concern/cid/1785659). It might surprise you to learn that neither sides' troops are carrying firearms. Despite both sides being nuclear powers, neither wishes this fight to escalate. There have been conflicts, and there have been casualties (people beaten to death with fists). ## How Does This Apply? Limited conflicts, where one side voluntarily shows restraint, aren't new. It could be that politically use of powered armor to "keep our boys safe", but simultaneously limiting what they can do offensively is palatable to whoever is making the decisions. ## Institutional Inerta Doctrine, design, procurement, and training can have a long lead time. So, if a prior administration commissioned the power suit as a restrained-conflict weapon, there's now institutional inertia keeping it that way, even if the current situation is different. ]
[Question] [ So I could not get any answers for my previous question regarding what happens in a indeterministic world such as the worlds in a Cauchy Horizon of a Reissner Nördstrom Black Hole. However, I deduced from one of the comments that a world beyond time, and beyond where both space and time in one universe is compressed into one single origin, this "indeterministic universe" is essentially a higher dimension, where time is reduced to a physical constant in the eyes of a higher-dimensional being, or simply of lower existence altogether. Which thus prompts me to wonder how a higher-dimensional being would interact with a lower dimensional world, which I mean entering it directly, rather than manipulating it from higher dimensions. I use the classic bulk theory, where our universe could be just a 2-D brane in this higher dimension. Would it fall inside the bulk? Would it make wormholes? [Answer] In short, a higher-dimensional entity does not "enter" a lower dimension, it passes through it. Consider a planar (two-dimensional) universe. If you or I were to interact with it, we could stick our fingers through it, with a cross-section of each finger intersecting that plane and existing within the planar universe at any given time, but we could never fully enter it without somehow flattening ourselves into two-dimensional entities - and somehow surviving the process. Note that this example also illustrates how we could seem to exist in multiple places simultaneously in the perception of the planar entities, as each finger intersects the plane at disconnected locations, despite being connected at a location outside of the plane. And our forms would shift in that planar universe as the fingers moved through it, widening and narrowing in the intersecting slice, until the bulk of the hand reaches the plane and all fingers expand and merge into a single larger planar entity. You would do well to read the 1884 story [Flatland](https://en.wikisource.org/wiki/Flatland_(first_edition)) (which is now in the public domain and can be read in full on wikisource), which further explores these ideas. [Answer] By proxy It would be terrifying to enter a 2d world. But we do it all the time in video games and it is fun, because we have a tech interface that interprets a 2d world in a way that make sense to us - the original DOOM is a fine example, or PacMan. [A number of games](https://en.wikipedia.org/wiki/List_of_four-dimensional_games) attempt to render 4 spatial dimensions on the 2d monitor screen. The video game [Braid](https://en.wikipedia.org/wiki/Braid_(video_game)) takes a 2d Mario-type world and introduces time as a manipulable 4th dimension. We use probes, cameras, scopes, remotes and technological proxies of all types to interact with environments that are unsuited for our physical bodies. So too your superdimensional creature wishing to interact in a meaningful way with lower dimensional worlds. The tech proxy would interpret that world in a way that made sense to the creature, and if desired the proxy could be made such that it could interact with the denizens of that world. [Answer] From a purely geometrical perspective, be n the number of dimension of the higher dimensional being, let's call it N, and k the number of dimension of the lower dimensional realm, let's call it K, N will interact with K as a k-dimensional cross section, like it was brilliantly illustrated by Abbot in Flatland and by Vonnegut in Slaughterhouse 5. In particular, following Vonnegut, a higher dimensional being could see what for us is the time flow as a solid of which we see only a slice at every moment, and might find questions like "why did X happened?" rather silly, being forced to answer "because it was structured in that way" [Answer] Beings from higher dimensions may be projected onto lower dimensions: [![image illustrating a 3D to 2D projection: a three-dimensional cube is projected onto a two-dimensional canvas, resulting in a flat image](https://i.stack.imgur.com/8pYoO.png)](https://i.stack.imgur.com/8pYoO.png) To view beings from higher dimensions, a suitable projection surface is needed. This might lie within "gifted" persons, who have the ability to "view" higher-dimensional beings through an internal "mental screen" unique to them. It could also be a "ghost", "mirage", or "phantom" that the being itself effects in the lower dimension (in the way that video can be projected onto fog or smoke). [Answer] I'm not sure this falls within the scope of answers you're looking for, having tagged your question `science-based` so maybe oriented more towards what we can model mathematically (though not all disciplines of science are about mathematical modelling). Anyway, with that out of the way: Makes me think of the way God packed up the essence of himself in a tangible human person by the name of Jesus Christ. I don't think I can cover even most important aspects here (and some may be well beyond the scope of your question proper) but I'll mention that we can observe here * a person apparently fully out of this world, interacting and being interacted with by the people around quite normally (save the extras, come to that in the next point) and being perceived as one of them (even to the extent that some are adamant about that) while as things develop, we see a meaningful number of the people, as they encounter that person, discovering that * there's a lot more to that person than what's visible at first sight, and a connection with a reality that obviously goes way beyond what people are used to. So we can go from here and make observations on what happens to, with, and from the person from the higher-dimension system and how it plays out to and in the lower-dimensional system. It's interesting what possibilities this offers for interaction and how the interaction goes on here. For one, that connection with the higher-dimensional reality (to name it in terms of the question) is obviously not forced on the people around - as we see some bluntly ignoring it - while we can tell from the fact that we see others interpreting it to be of whatever nature and source they like to think of, that there is something going on that is hard to ignore without choosing so. It can further be observed that the person immersing in the lesser-dimensional world is fully at liberty to reveal of his true nature as little or in fact as much as he chooses to, only limited by the degree to which the individual people are capable and willing to understand (or may be helped to understand by the person revealing). Which in this case leads to an amazing and, in some dimensions (including what some would call metaphysical), even total extent of interaction with some who agree to it. As for some other points of your question, there seems to be no falling into wormholes or similar involved here, rather a kind of total control of the overall reality including the parts of it that are perceivable in the lower-dimensional space - while most aspects of it are generally left untouched (and the same obviously goes for the freedom of the people around to be doing what they choose to, but that's outside the scope of your question). So to add this angle, there is no falling into a wormhole of any elements of the lower-dimensional system either (albeit there is some access to aspects of the higher-dimensional system as provided by the person immersing). [Answer] By a projection. A projection is exactly mapping something to a lower dimension. For example, when you map a cube in three dimensions to two dimensions, you have a square. Of course, there is something lost in the projection - but that is the whole point of removing dimensions. But if something specific is lost that should be retained, you could choose a different subset of dimensions to project to. [Answer] Ant and large Stone! An ant when it roams around a stone always sees only what is around it. It does not have a sense of curvature or texture of stone. For the Ants, the irregular surface of the stone will just look like a plane area to roam around. [Answer] In Liu Cixin's Three Body Problem Trilogy, this is treated two or three times. WARNING: There will be spoilers about all the three books regarding technology development, society development and plot. It's the only way to answer this question using this source, so they won't be hidden. -In the first book, the Trisolarians make sophons from > > a proton that is unfolded from eleven dimensions into two dimensions, > then programmed and refolded. [(source)](https://www.tor.com/2017/04/21/5-books-that-get-ruined-by-taking-away-a-key-piece-of-technology/#:~:text=Sophons%20(The%20Three%2DBody%20Problem%20by%20Cixin%20Liu)&text=Sophon%20technology%20is%20an%20amalgam,dimensions%2C%20then%20programmed%20and%20refolded.) > > > -In the third book, the tripulation of the Blue Space discover a zone of space that is a remaint of the previous 4 dimensional universe. They also encounter a ring that tells them that there are some beings that try to survive in lower dimensional spaces and eventually achieve it. Near the end of the third book, the Solar System is reduced to a 2D space. However, it is implied that, should they exist, lower dimensional beings can get to greater dimensional spaces, altough they are a lot more easily damaged, because there can be micrometeoroids that can come in a lot more directions. [Answer] I can help you out on this. Depending on the particular equational situation.a higher dimentional (h.d.) being could very well appear in his/her h.d. form in a lower dimension. Most likely those lower beings would obviously be really shocked in either a fearful negative way or astounded and amazed at what they see. A being from the h. d. would probably not allow there lower dimension be manipulated unless its for the betterment due to being more evolved and if the h.d. being is in his h.d. form than they would be wise to only visit for a short while because his vibration is so different that being would be responsible for holding all that is together and at its natural balance which wouldnt be difficult. I imagine the difficult thing would be comfort, becuase the h.d. being's dimension would be like heaven in comparison to a place so limited in the lower dimensions. Then theres a h.d. being would embody that particular lower d. body as well as all that comes with it even if that h.d. being forgot all that that made them a h.d being and that h.d. being fully came on board with the lower dimension that person would probably suck at being a lower dimensional being and would seem as if that person has mental difficulties or some other kind of problem. ]
[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/90378/edit). Closed 6 years ago. [Improve this question](/posts/90378/edit) This is going to deliberately be a bit vague as there are a lot of particular situations to which this general question applies and this isn't really about any given technology but the human approach to technology in general. Humans seem to push for better and better technological artifacts, the development of computing power in the late twentieth and early twenty-first century comes to mind, but there is a point where you can't improve on a particular piece of technology. The basic example I always think of is the spoon, it's not the ideal universal utensil or there wouldn't be knives and forks but the basic design hasn't changed in living memory because a "spoon-shaped spoon" is the best spoon you can have. So there are two questions: 1. If presented with an apparent hard limit on a particular piece of technology, say several centuries of R&D has turned up nothing new and very little of any use on the minor tweaks front, would humans be satisfied with the version of a particular technology they have or would they still spend time, money, and possibly lives trying to push the envelop? and 2. Does it matter what the technology does? For example is a better medicine worth pushing on regardless while a better weapon isn't. [Answer] I'm going to say no. Humanity will never stop trying to improve pretty much anything. Let's start with your example of the spoon, [user54373's answer](https://worldbuilding.stackexchange.com/a/90381/34824) already covers the spork but that is not the only change or innovation in spoon technology. This [first website](https://www.designswan.com/archives/15-cool-and-innovative-spoons.html) lists a number of creative spoon types which range from silly to quite useful. They are (almost) all recognisably spoons, but they serve a variety of uses. My favourites are the clip on spoons and the sliding measuring spoon, both which I could see being useful. The spoon that balances on the side of a pan is also good. A lot of it is gimmicky but there are still clearly people thinking about how to make a better spoon. And this [second link](https://www.cnbc.com/2014/11/25/googles-latest-innovation-a-spoon-for-parkinsons.html) is about Google making a self balancing spoon for people with Parkinson's Disease. Apparently it compensates for the shaking caused by the disease to allow people to eat without spilling. So again, people are putting effort into improving something as simple as a spoon, and incorporating some quite fancy technology in there. As for your second point, I think there probably is a difference. Improving the spoon probably isn't a high priority for many people, but things like medicines, computers and weapons are and probably will remain so for the foreseeable future. It doesn't mean we won't see innovations in spoons, just that innovations in other more pressing areas will come more frequently. [Answer] Upvoted, but I'm going to have to disagree with your basic premise, for a few reasons. First, there is constant tweaking and tinkering with the basics. Even the humble spoon ... the all-powerful [spork](https://en.wikipedia.org/wiki/Spork) was invented in 1874. And the design we use today is quite different from those models. Secondly, and this is the most important point ... our needs change. You might have the most awesome spoon or sword or paperclip imaginable, perfectly suited to its purpose. But our needs will change, and formerly perfect tools will no longer be sufficient. Consider the mighty gladius. It evolved several times over the years, as Rome's foes changed, and as they got better ideas. But even after centuries of evolution, they eventually abandoned it. Why? Because they started having lots of mounted units. A gladius is a frightening weapon in the hands of a legionnaire in a shield-wall, but is kind of ... silly in a cavalry charge. ;D [Answer] /would they still spend time, money, and possibly lives trying to push the envelop?/ Yes, in a capitalist system. If I want you to buy my spoon instead of that sold by a competitor, I must somehow distinguish what I make and sell such that it has a competitive edge. If you shop on line you will find an astounding variety of spoons. The below is only one page of what Pottery Barn offers. [![enter image description here](https://i.stack.imgur.com/ftH3F.jpg)](https://i.stack.imgur.com/ftH3F.jpg) Just as the basic beetle body plan is retained for the myriad of beetles with details tweaked over evolutionary time, place and circumstance will favor minor tweaks on the basic spoon plan which improve fitness (saleability) for a given time and place. Fashion and styles are part of what it is to be human and will drift and change with place, time and generations. Especially if there is a profit motive that they do. I will tell you from experience: the impatient and practical minded human may note (but hopefully not out loud) that there is no fundamental difference between any these spoons and any one will perform its function equally well. This is true. Then how to choose? Allow some person of your acquaintance (and possibly in your life) who has more appreciation for these differences to make the choice, and then be enthusiastically supportive of it. [Answer] I do not fully understand what you mean by "a piece of technology". [Technology](https://en.wikipedia.org/wiki/Technology) is the knowledge of how to make things; this knowledge changes all the time as people learn more about nature, discover new processes, are confronted with changing conditions, or simply forget old processes. The things in themselves are not "technology"; it is perfectly possible to have an object and to have little idea of how it was made. Let's look at an example: the famous [Portland vase](https://en.wikipedia.org/wiki/Portland_Vase), made somewhere in the Roman empire sometime during the 1st century of the common era, or maybe during the second half of the 1st century before the common era, we don't know for sure. ![The Portland vase](https://upload.wikimedia.org/wikipedia/commons/thumb/b/be/Portland_Vase_BM_Gem4036_n4.jpg/317px-Portland_Vase_BM_Gem4036_n4.jpg) [Side B of the Portland Vase. Cameo-glass, probably made in Italy ca. 5-25 AD. Picture by Jastrow, [available on Wikipedia](https://en.wikipedia.org/wiki/File:Portland_Vase_BM_Gem4036_n4.jpg) under the CC-BY-2.5 license.] It's a [cameo glass](https://en.wikipedia.org/wiki/Cameo_glass) vase, decorated with beautiful scenes; the picture shows [Ariadne](https://en.wikipedia.org/wiki/Ariadne) moping on Naxos after being dumped by [Theseus](https://en.wikipedia.org/wiki/Theseus). The thing is, we have the vase but we don't know how it was made. We have various hypotheses, of course; I'm partial to Rosemarie Lierke's hypothesis that is was made by [hot forming](http://www.rosemarie-lierke.de/English/Cameo_glass/cameo_glass.html), that is, by pressing a hot dark glass blank into a form coated on the inside with white glass powder; but other scholars and artisans have different ideas. This applies in all domains. The Romans used fabrics, and hammers, and nails, and earrings, and ink and so on quite similar to those we use today; but the technology to make them has changed quite a lot during the last two millenia. The question gives the example of a spoon; the technology to make spoons has changed quite a lot during the last few centuries, and the materials have changed too, from wood to pewter to stainless steel to plastic to laminates. The Platonic [form](https://en.wikipedia.org/wiki/Theory_of_forms) of a spoon transcends time; but the process of making actual physical spoons, the technology, has changed and will change. [Answer] We will never stop tweaking things. Individual scientists often get fascinated by some problem and are then happy to spend a few decades figuring out exactly how it works if they can secure funding, and seem to be willing to spend significant portions of their time securing the funding to pursue their chosen problem. It should be remembered that there have been people working [tirelessly](https://xkcd.com/1166/) on perpetual motion machines for centuries. Every farmer and engineer has some hobby thing half built in a garage with 'improvements' of their own invention. Every family has someone who takes things apart. Enough might be enough for almost everyone, but allowed even a modicum of freedom there will be someone who thinks a toaster ought to be more like a mouse trap and will come up with something new. “The good Lord lets us grow old for a reason: To gain the wisdom to find fault with everything He’s made!” – Abraham Simpson Anything you can criticize someone could make differently, and if you have money they will. [Answer] As an example of a "hard limit", I'll cite Astrology as having experienced its hard limit long ago. And yet there are people revising and inventing new takes on the "basic technology" all the time. Need I say more? [Answer] The answer to this cannot be considered without also considering what else people could be doing besides advancing technology. In economics terms, this is the "opportunity cost" for developing the new technology. If I'm busy tinkering with a new toy, it means I'm not spending that time with my family, or cleaning the house. If we apply Rational Actor Theory to the problem, we assume that everyone is working towards some sort of goal. If developing a technology moves us towards that goal more than not developing it, then we'll spend our time developing. This also means that technologies compete. The buggy whip, and processes for making them, are virtually unchanged since the days of Ford's Model-T car, which rendered the horse and buggy obsolete. To this end, we may see different technologies eclipse each other, but we see technology progress. This can continue until one day, developing technology is not the best way to further our goals. There is no proof that the march of technology is endless. In fact, it makes some sense that it will reach plateaus where it is simply not the best way to solve life's problems. Remember that technological development never solves any of life's real problems. What it does is give us tools to solve those problems better. At some point, the benefits of technology simply cease to outweigh the benefits of getting our hands dirty and actually solving the problems with the technology we have. Or we could have the attitude of always building the tools to solve the problems later. This has the aire of [martengale betting](https://en.wikipedia.org/wiki/Martingale_(betting_system)), always getting into position to make your win. The results are equally disastrous. In business, there's entire schools of thought as to how to properly stop investing in tools and instead focus on making profit. A civilization that never stops the relentless assault on the future eventually makes a mistake and falls. Of course, we could be irrational too. If you dismiss Rational Actor Theory, we can consider the possibility that individuals will always dream of reaching the stars, even if all the cold, hard, rational statistics say they can't. Someone's always going to try tinkering with something. [Answer] 1. The majority might be satisfied by a particular version of a particular technology, but not everyone will be. Some people will be driven by perversity or ambition or challenge to either improve any technology generally, or specifically for some niche requirement. Taking the example of the spoon: why should it not be deeper, or shallower. If spoons are usually taken into the mouth from one side, why should they be symmetrical? Why not have left-handed and right-handed spoons? What about spoons for moustaches, or for eating soup in sandstorms, or zero-gravity? The problems tackled may not be sensible, the solutions may not be effective, but someone will tackle them and, perhaps with some clever marketing, may end up convincing people that the idea has merit - or not. It doesn't really matter, because someone will try - even if they end up re-inventing someone else's long discarded 'new idea'. 2. It doesn't matter at all. In the example, though, you ask a slightly different question: are some technologies more important than others? The answer is 'yes', but it depends very much upon circumstance whether what you need is better medicine, or a better weapon, or a better spoon which can detect contaminated food (for example). [Answer] Innovation follows some form of environmental pressure. Spoons haven't changed much because the pressure went away or was dealt with. The difficulties around scooping and eating liquids were solved and no further pressures existed to be improved upon. New pressures then stress further innovation. Following the spoon bit, as the human race advanced/advances into the space age, a new issue arises: liquids in space. Humans looked at spoons, which long had solved the problems of eating liquids, and realized they weren't going to perform under the new criteria. New environmental pressures were there that demanded attention and innovation. I imagine an astronaut's grandma was upset that she couldn't send her tupperware of soup into zero-g with her favorite grandchild. "How about I load it into a toothpaste tube or a caprisun pouch?" Thanks Grandma! Just like that the spoon gets blacklisted from spaceflight. Related more to thoroughly researched areas, innovation comes in whatever way can reduce the pressure. For example, people looking at solar power might see a tech limit due to the actual amount of energy reaching them. Our solar power limit is estimated somewhere above [120 Watts/sq. meter](https://en.wikipedia.org/wiki/Sunlight). In your question's context, that is the hard limit, even after centuries of research. "Good Enough" would be found by the pressures forcing the change and what changes could be made to reduce the pressure. Lets say there is a 90% efficient solar panel. Is the earth in desperate need of 100% solar energy extraction? Would (for the sake of this example) years and trillions of dollars in research be needed? or would it be easier/cheaper to build solar collectors in space? Is it [Dyson Sphere](https://en.wikipedia.org/wiki/Dyson_sphere) time? What about other energy sources? What about more efficient appliances? What about killing off a huge chuck of the population to reduce demand? Scary, but it all depends. In this case, the pressure includes energy need, time, effort, expense, morals, ethics, etc. and the responses are not limited to more work on the current research they are trying. Humans like to do things at the cheapest 'cost' to them - We're lazy. We will try to find a different solution to reduce the pressure. I'm not saying solar collectors in space would be easy, but it would be just one way to reduce the energy need pressure, and it would definitely be prioritized as soon as the research was deemed fruitless and 'expensive'. Also, lets not kill off people. The same holds for your second point. The innovation is driven by pressures. Is the planet under a threat of advanced alien war? You can bet we'll prioritize weapons tech over cold sore treatments. Has globalization and communication reduced nuclear tensions? We'll probably kick start tons of medical funding. while retiring weapons projects. Do astronauts love eating soups and cereals with spoons? We'll need some artificial gravity on board ASAP! The scary side I see to this innovation process is a world where maybe we have tried nearly everything. In that case I imagine the solutions would be a little nightmarish. Maybe nothing has yet solved a global energy/food crisis and the darker answers I mentioned might be the only 'good' or affordable solutions. Yikes. [Answer] Let us give a different twist to the answer; I'm unsure if this is what you really want to know, but... Spoon is not really a good example because technology to make it is rather basic and varied in the centuries, while the shape remained quite constant. However, if you look to other technologies you see a path often followed: * infancy with a rather crude prototype. * youth adds enhancements that usually make the thing perform better, but are more complex. * maturity when all parts are essential to good working. * perfection when enhancement is not anymore possible without a substantial change in design. One of such "perfect" product is said to be the [Springfield Model 52](https://books.google.it/books?id=FGUpC4UH9yUC) rifle. Similar "perfection" can be found in (not so) modern fractional distillation towers. It is interesting to note (but this is probably irrelevant here) the original meaning of "perfect" was to indicate an action that is completely in the past, so it is completed and cannot be changed anymore. A "perfect" thing is, by translation, a thing that cannot be changed anymore without making it something different. [Answer] Is consumer culture an aspect of this question? Many choose "good enough" as a way to keep stuff out of landfills. Many cannot afford the latest technology even when it comes to medicine. I would hope that as technology improves in general there will be ways to get those improvements to specific individuals. Yes the average spoon serves many until you need a smaller than average size or a super long handle. There are spoons with gyroscopes that control for tremor so that Parkinson's patients can eat without spilling. Philosophically, I think many people will be left with needs both minor and major as technology advances. A minor tweak can mean a big difference for those outside the bell curve. [Answer] `1. People will always continue the push the envelope.` We have evolved over millenia within an ever changing environment. This has conditioned our instincts to a mode of constant reactive response to the changing environment, or we tend to die out. This behavior expresses itself in a superb way when talking about finding another bigger, smaller, faster, prettier, more efficient, more productive, more (insert appropriate adjective here) way to do or create technology and it's products. As described in other answers, the environment may even change so much so that the technology becomes obsolete. Even in these cases, though, no idea is truly safe from revival and renewed tinkering: sometimes in the process of improving on a technology, we can find ourselves suddenly using a tool completely over-advanced for the job at hand, and going back to square one is necessary. It doesn't make much sense to use the Hubble telescope to identify that unusual bird that showed up in your backyard--might want to just grab a pair of binoculars. This will inevitably begin the process all over again though, with new and different viewpoints being applied to the "old" technology. `2. No, it doesn't matter what the technology is for.` It's just going to be more likely to be evident in certain areas based on the level of technological advancement present. Individuals in a society where basic needs are not being met will focus the creative response to their changing environments on the things that will help them meet their basic needs (the building supplies, food, and defense). Those in a society where they are striving to meet higher levels of human needs will focus on more and more varying technological advances (eventually the pinwheels and touchscreens like mentioned). This evolved drive to create and innovate in some cases will even overpower an individual's basic needs.... hence the concept of starving artists. [Answer] 2. Yes, it matters what the technology does. Anything that helps us survive and thrive (physically, economically) we are more motivated to improve upon. We may try to improve upon pinwheels, for example, but probably only if we are in the business of selling pinwheels. It isn't the technology that we want to improve, it is sales. There are more reasons to improve building materials, weapons, or medicines than pinwheels, because the former items are directly relevant to survival. [Answer] this is an important question with no real answer that anyone alive today can give, the problem is that there is just so much stuff that technology could help us with that we don't even consider because it COULDN'T occur to us, the thing is all the answer people are giving you are great and should be taken into account but my guess is that your doing a worldbuilding project so just go as far as YOU can see technology advancing in the future, in this scenario, everyone's wrong. [Answer] Use standards are usually the big thing that keep things from having updates or large reformations. The spoon is recognizable standard people know what it is and how to use it, no one will think you're weird if you put it out etc. A spork in the Whitehouse would be out of place by societal standards. Also seen in cars with their controls, better things exist from the pedals/wheel and we know it, but don't change it because everyone will complain. See audio jack port leaving phones for the current epidemic: "why would you take away my headphone jack" because it's huge and can be done with a better form factor. Essentially a painful transition stops innovation. ]
[Question] [ Imagine a space battle happening high above Earth (~25k miles, or ~40200 km). It's right above the observers who are standing on the planet's surface. Both armies have the same amount of spacecraft, one mothership (the size of two ISD from Star Wars), two warships (same size and weapons as a Star Destroyer), ten frigates, two hundred starfighters. All of them shooting lasers, firing plasma torpedoes, mass drivers, letting the other side feel the pain really good. The shots, despite what science tries to tell us, are quite visible / cinematic. Just like in the movies or even brighter. Like, deliberately wasting energy to make it showy. Though they are not actually making a show for those on the surface, or projecting some image toward the planet. We postulate it's a quirk of their technology and nothing more. Such a fight would be quite visible from the surface, even though it might be only flashes of pulsing light here and there. Under optimal conditions (i.e. at night, new moon, clear skies) people could even sit down with the ol' popcorn bucket and enjoy the free entertainment of a light show (hoping the debris won't crash on them, those space-age alloys are tough and don't burn at all in reentry). This is postulate two, to give a measure of the light the battle creates. I'm banning overcast skies with massive notilucent or cumulunimbus miles high. Obviously that amount of water vapor / ice crystals can block even sunlight. Also, fighting against the sun (i.e. earth-fight-sun are in a "straight" geodesic gravitational line) is a no-no. I ask then. Under what conditions would visibility of this space battle be faint, to a point a casual observer could have a 50% chance of missing it even if they were staring at the sky? This question is [science-based](/questions/tagged/science-based "show questions tagged 'science-based'") regarding only optics and weather, not the space-fighting technology. Don't nitpick on my shiny laz0rs. [Answer] This battle is invisible, even at night I've got bad news, and I apologize sincerely... but you did tag your question "Science-Based." Consider the distances involved: The earth's diameter is only 8,000 miles. That's only 32% of the distance from the surface to your battle. Climb a local mountain (I have) and look down on society. From even that statistically trivial distance the ability to pick out even a large building is difficult without binoculars. You're talking about the largest object being maybe 2 miles long at a distance of 25,000 miles, which means the arc length (size of the visible object from the perspective of the viewer) is an impossible to see 4.6 millidegrees. For comparison, the blazing sun is 500 millidegrees (100X larger). And, well... the entire half-degree is blazing. For some photo evidence, consider the Pyramids of Giza, which are visible from about 1,000 miles into space, but to get a feel for your distance we need to reduce the image 25X. About 1,000 miles up (courtesy NASA): [![enter image description here](https://i.stack.imgur.com/52WMt.jpg)](https://i.stack.imgur.com/52WMt.jpg) And that same image reduced 25X: [![enter image description here](https://i.stack.imgur.com/2wNdP.png)](https://i.stack.imgur.com/2wNdP.png) Unfortunately, the spread of the battle doesn't help. A lot of things you can't see spread over any distance are still invisible. It would take 10,000 ships of the largest size all bunched together to be the size of the sun, and they'd have to reflect the sunlight to be seen. Energy bursts (e.g. lasers) aren't actually visible in space. Hollywood likes to show them, but there's simply not enough material in space to heat up to show the passage of energy. *Edit: A point needs to be made here based on several comments. In a "Science-Based" scenario, nobody would use lasers or any other form of energy weapon. (a) Too hard to focus during the heat of battle. (b) The energy requirements are unbelievable. Not just unrealistic, but absolutely unbelievable. (c) There are much simpler ways to damage your opponent. And (d) you need to either generate all that energy on the spot or store it in batteries/capacitors — which means you're either economically unrealistic (oversized engine to power the weapons) or you're a big, juicy target that's easy to destroy (probably true in both cases). Remember those [hoverboards that burst into flames](https://youtu.be/T2jNHWatZvs)? Yeah, now imagine a battery large enough to do significant damage to a mile-long ship miles and miles distant and your opponent is smart enough to use kinetic weapons.... The reason hyper-realistic SciFi books and shows like "The Expanse" don't show energy weapons is that they simply fail the ruthless mathematics of practicality and usefulness. Yes, given a big enough laser a hit on another ship would likely be visible to the naked eye on the ground (at least at night). But in a "Science-Based" universe, nobody in their right mind would use one.* Whether or not something like a mass-driven projectile is visible depends on whether or not it's burning during its passage—but you tagged the question "Science-Based" and wasting energy on something burning during passage rather than burning on impact is a wasteful projectile (unlikely to be used). So none of the weapon discharges are visible to any viewer. Missile rocket engines? Unfortunately, they can't be seen either, even if they're racing away from the planet (and most of the time they'd be racing tangential to the planet). Maybe... maybe... observers on the ground, during the night, might... maybe... see a ship explode. If it actually does explode. That's more Hollywood. There's no point to vaporizing a ship when all you really need to do is stop it from shooting at you and then wait for it to be drug down the local gravity well (people would notice that). But even if it does explode: 4.6 millidegrees and a quick blip of light. Answer to your question: > > Under what conditions would a space battle involving a relative large amount of vessels would be barely visible on the surface? > > > All conditions not involving binoculars or a telescope and knowing exactly where the battle is taking place. And if the observer happened to see what in the battle would be a massive explosion but on the ground would be a itty-bitty blip of light, there's a high chance they'd write it off as a flashing light from a passing high-altitude passenger vehicle and ignore it. If the sun was at the position to best cause reflections off the largest ships, they'd appear like a handful of teenie-weenie scintillating lights in the sky... kinda like the dimmest stars. Yeah, sorry, from a "Science-Based" perspective, there's nothing here to see. [Answer] # Well, sure I saw it. But what battle? Let's assume the most visible, flashy battle possible directly overhead in the night sky. Who knows what tech these folks have that makes such a light show? So why would no one notice it? * Fireworks: Your battle occurs on Global Founder's day. Or Independence from Galactic Oppressors day, or whatever. Everyone is looking to the night sky expecting to see a time-honored tradition looking like a battle - fireworks. Wow, you know the city planners really pulled out the stops this year. [![enter image description here](https://i.stack.imgur.com/plM6g.png)](https://i.stack.imgur.com/plM6g.png) * Meteor showers: One of the fleets used the natural movement of asteroids to mask their advance on the other fleet. Those same asteroids are now burning up in the atmosphere. Battle? Boy, you're gullible. Didn't anyone teach you about asteroids? [![enter image description here](https://i.stack.imgur.com/LhqR4.png)](https://i.stack.imgur.com/LhqR4.png) * [Earthquake lights](https://en.wikipedia.org/wiki/Earthquake_light): So we don't know what causes random discharges of light that may or may not be geological in origin. Your battlers are using weapons that manipulate gravity, resulting in massive discharges of light around the paths of the beams. But these same gravitational weapons are triggering local earthlights on the planet's surface as the weapons stress geological features. The weapons are triggering a more spectacular display near the surface. What's a few flickers in the heavens compared to the display on the surface? [![enter image description here](https://i.stack.imgur.com/v3KFb.png)](https://i.stack.imgur.com/v3KFb.png) * Religion/superstition: It is the worst, most terrible luck to see objects in the heavens. Most people refuse to look up for fear of being cursed accidentally. Those few poor souls forced to look up when lights are visible in the heavens avert their eyes at the first flicker of light. Even if you see something, your subconscious convinces yourself it wasn't there. Battle? Lights? You must be drunk - or high. Now shut up. I'll kill you if you spread such slanderous rumors! [![enter image description here](https://i.stack.imgur.com/IYyqE.png)](https://i.stack.imgur.com/IYyqE.png) * [Aurora Borealis](https://en.wikipedia.org/wiki/Aurora): The planet itself regularly puts on a heavenly lights show. Most people don't even bother to look up when the heavens flicker. Even the ones that do look up would need to be really paying attention to realize this doesn't quite look like the usual display. Or maybe the ships attack each other by manipulating streams of high-energy particles emitted by the sun (why not?). When these beams hit the planet, they trigger a massive aurora. [![enter image description here](https://i.stack.imgur.com/0zwqM.png)](https://i.stack.imgur.com/0zwqM.png) * There's already a war on: The locals are way behind the fleets technologically, but that doesn't mean they can't kill each other in spectacular fashion. The locals have been blasting each other with hypersonic fighters and bombers, orbital missile bases, and massive EMP attacks high in the atmosphere for days, years, months, or pick your time frame. Oh, fun - the enemy is bombing us again. Ho, hum. [![enter image description here](https://i.stack.imgur.com/obDSr.png)](https://i.stack.imgur.com/obDSr.png) * This isn't the first: People have become inured to battles in space. The star system is in a giant war zone. No one even pays attention, instead looking through it like it wasn't there. Debris regularly reenters and crashed ships abound. The heavens are flashing? Well, yeah. The gods are fighting. You know, the usual. [![enter image description here](https://i.stack.imgur.com/BF9SW.png)](https://i.stack.imgur.com/BF9SW.png) * A colorful and full moon: Your battle takes place between the viewers and the bright, richly patterned full moon of scintillating minerals. During the full moon, reflections off the surface make the heavens bright and flashy. Flickering color, phosphorescent glows, and possibly even gas emissions make the battle a trivial thing compared to the moon. [![enter image description here](https://i.stack.imgur.com/myoOy.png)](https://i.stack.imgur.com/myoOy.png) # I must have Missed it... Then, of course, you can have the stuff that simply blocks your view. * Smoke: Perhaps there are wide-spread wildfires going on. Perhaps flaming debris from a previous battle has come down, starting forest fires. But it doesn't take much smoke to block the resolution. A few flashes of light when you can't see what is flashing don't draw attention. Last year in Montana, the sky was hazy from the smoke and there was no rain. Thunderstorms were starting fires but so little water hit the ground that all you had was visible lightning. Sounds a bit like a battle... [![enter image description here](https://i.stack.imgur.com/gqlan.png)](https://i.stack.imgur.com/gqlan.png) * Ash: There's an active volcano or three spilling tons of ash into the atmosphere. The sky is hazy, and even if people see lights, there's certainly no way to tell what they are. Big, small, local or global. Just decide how much to dump. [![enter image description here](https://i.stack.imgur.com/hohkD.png)](https://i.stack.imgur.com/hohkD.png) * Fauna: Migrating insect swarms and bird flocks have blotted out the sun on numerous occasions. Locust swarms are a real thing. Passenger pigeons used to regularly blot out the sun until people decided to wipe them out. I imagine a giant swarm of iridescent bugs or even phosphorescent ones mating in the shining moonlight. [![enter image description here](https://i.stack.imgur.com/CMQZc.png)](https://i.stack.imgur.com/CMQZc.png) * Flora: Your world might have thick forests and dense jungles so people can't see up. Perhaps clouds of pollen or spores are being released because it's the season for it. Maybe floating gas-filled plants drift in the sky and cause any view of the heavens to be spotty. [![enter image description here](https://i.stack.imgur.com/vPwsv.png)](https://i.stack.imgur.com/vPwsv.png) [Answer] Full and bright daylight will surely make all the show go barely noticed or totally unnoticed. If even the waning moon is not visible during the day, I believe the sun light of a clear day is sufficient to mask most of what you describe barely noticeable. [Answer] # Nukes Let me stay science-based: lasers won't be visible, ships won't explode. The most you can expect from "conventional" weaponry is some sort of minor explosion from a warhead on a missile, but not enough to be visible from the ground. Which is where nukes come into play. It's quite possible that warring spacefaring nations will use nuclear warheads on their space missiles. Which will give out a brief but very visible flash. I didn't do the maths, but should be visible against the night sky, and possibly day time as well. Here for more details: <http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Nukes_In_Space> What blademan9999 said is very true as well, your capital ships will be visible at night due to the sunlight reflecting of them, but you won't be able to tell an active ship from an orbiting mass grave. Final note - do yourself a favour and get rid of the "space fighters", those are horrendously uneconomic. All you need is a big-ass machine gun mounted to a rocket engine (+fuel, propellant, etc.) and a few electronic components. The pilot will be sitting in a comfy chair on the nearest capital ship with a remote controller and a VR headset. [Answer] You should DEFINITELY by able to see it at night. The ISS has an altitude of 408km, 1% of the value here. It has a peak apparent magnitude of -5.9. So If the ISS was place in the middle of this battle, it's apparent magnitude should be 1/10000 of it's peak. Increasing the value of the apprent magnitude by 5 corresponds to a 100x reduction in brightness. This conveniently means that the Brightness of the ISS here would be equal to -5.9+10=4.1, or equivalent to a reasonably faint star. Bright enough to be visible at night in rural areas. And the cap ships here are much larger then the ISS. [Answer] I don't know the math to resolve it but here's the problem: Geosynchronous orbit (~25k miles) is where you stated the battle will be but that's too far away. A 1 mile long ship at 25,000 miles has an angular size of 8 arcseconds, making it even smaller than the ISS. As someone else stated, at 25 miles the ships will be well visible but now they're making a pretty fast transit across the sky as they orbit so no one gets to see much of the battle. I would think a large battle in geosynchronous orbit at night with the battle not in the earth's shadow would have to be obvious enough to anyone in a rural area who happens to look up -- if nothing else, all the new "stars" fiddling around up there would look out of place. (I would think weapons fire would not be visible at that distance since the largest ships themselves are mere pinpricks.) If we're talking modern day, though, I should think TV stations would pick it up pretty quickly and then it's a matter of telescopic zoom lenses and everyone tunes into news channels (and YouTube). [Answer] This is science based. So the ships aren't from our solar system. Which means they are weapons of war of a K2 or K3 civilization. A K3 civilizations serious weapons are the kind of weapons that destroy planets accidentally. Like, turn them into clouds of plasma. A K2 civilizations serious weapons are the kind of weapons that sterilize entire planets. We are K0.7. Our serious weapons are on the order of the Tsar Bomba, 50 megatonnes. Serious K1 weapons will be on the order of 1000x as energetic, and serious K2 will be 10000000000000x as energetic. The sun deposits on the order of 10^16 W of energy. Tsar Bomba is 10^17 J of energy; if you set off a Tsar Bomba every 10 seconds for a year, you'd match the energy deposit of the sun on the Earth. The K2 equivalent "serious" weapon is 10^30 J of energy. At 40,000 km 2% of the energy of the explosion hits Earth; call it 10^28 J of energy. Over an entire year, the sun deposits about 10^16 W \* 86400 seconds/day \* 365 days/year = under 10^24 J of energy - the blast is 10000x as energetic as an entire year of sunlight, concentrated over at most a few seconds. Earth has a bit over a billion cubic km of ocean water, and it takes under 10^5 J to vaporize a gram of liquid water (half to hit boiling, half to make it to boil). The oceans weigh 10^21 kg, so 10^29 J is enough to boil all of the oceans on Earth. That is slightly more than the back blast of a serious K2 civilization weapon. Now, we don't fight with nuclear weapons when we fight wars. But an actual interstellar civilization fighting an actual serious war in our actual back yard, without hand-wavey SF technology that makes interstellar travel easy, the question isn't "can we see it" but "do we survive". [Answer] According to Wikipedia a star destroyer is 1600 meters (5,200 ft) long. Low Earth Orbit is defined as 2000 km or less. The lowest earth observation satellite, a record set in 2019 is Japan's Tsubame satellite at 167.4 km, and super low orbits are between 200 and 300 km altitude. Generally any thing low orbit has drag from the atmosphere and doesn't stay in orbit that long. The human eye with a pupil of about 4 mm (smaller in bright sunlight ~ 2mm, ~9mm fully dilated) resolves with an angle of about 8.74 x $10^{-3}$ degrees. So about 40 km away you can resolve with perfect vision, ignoring the haze of the atmosphere etc, objects about 6 meters apart. So the good news is that at 25 miles altitude your mile long star destroyers about 2.3 degrees of your field of view. That seems pretty big, the moon and sun are about 0.5 degrees so there will be something to see. Although blurred by the atmosphere. But the scattering by the atmosphere might also make your fancy lasers more visible since there is a lot of scatter ( also less light hitting the target). For them not to be noticed, I think you can just increase the range some for them to be smaller, but reflected light from the sun can be visible for very very long distances. The very powerful laser weapons in the beam of course are very powerful, but the scattering and atmospheric attenuation is severe, and you can play with that any number of ways. Light scatters basically by Rayleigh Scattering and Mie Scattering. Bigger particle scatter (Mie) the light mostly forward and backward, while Rayleigh scattering from very small particles and molecules scatter more in all directions. So how visible the beam might be is up to you depending on the stuff you have in the atmosphere. Remember that laser beams also expand over distance, so the spot size can be very large after a few miles. The downside is that the space ships are fighting in the Stratosphere, or maybe mesosphere. For example the highest weather balloon made it to about 52Km. So there is a lot of drag, and even winds to contend with. But maybe since theses ships might be built to land on planets anyway that is somehow o.k. I am not sure what the tactical reason would be for them to want to fight at low altitude. Edited to include unit of degrees for the angle. [Answer] When a laser hits a ship, it will light up the surface of the ship facing towards the laser. If the attacker is in a higher orbit, the surface that is lit up will face mostly away from the planet. The lasers might also be primarily infrared (Or alternatively, UV) so the light is not visible. The defenders might be using a different technology, such as railguns, which are kinetic rather than energy or light. These can be very lethal, but there's no light emitted. The ships might be visible as faint points of light, which sometimes split into smaller points or just evaporate into a faint and fading cloud. There is a tradeoff in selecting a dark surface for the ships: It might make them less detectable (stealth) but would be more susceptible to absorbing the heat from a laser weapon. A highly reflective surface would reflect the laser's energy, but could be much more visible. A mirror surface might be less visible from some angles, but cause a bright flash at other angles. (See "Iridium flare" for an example of a real satellite with a mirror like surface. They are nearly invisible most of the time, but will randomly "flare" to be the brightest thing in the sky for a few seconds as they reflect the sun towards you.) [Answer] Even single kg of evaporated lithium will scatter about 150 MW of sunlight (0.1 km^2) - and the cloud will take several minutes to disappear. And many other elements will produce similar effect - Na is about 40 times less effective, but [Luna-1](https://en.wikipedia.org/wiki/Luna_1#Experiment_results) managed to produce visible artificial comet with sodium. 1 kg of Na produced equivalent of 6 magnitude star (barely visible) for 5 minutes 110 thousand kilometers away. So even without nuclear weapons any large scale space battle, with tons of matter being evaporated and hundreds of tons of gasses and liquids being thrown out will produce comet like lights that would be visible even during day. photo of artificial comet: [![enter image description here](https://i.stack.imgur.com/BvHom.jpg)](https://i.stack.imgur.com/BvHom.jpg) For example DART impact (the equivalent of 4.8 tons of TNT) created comet like tail after Dimorphos. Even 2 days after impact that tail was 10,000 km long and twice as bright as asteroid itself. [![enter image description here](https://i.stack.imgur.com/k5nwB.jpg)](https://i.stack.imgur.com/k5nwB.jpg) ]

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