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[Question] [ I am trying to imagine a scenario in which there is a world that has been terraformed in so far as it has water and oxygen but there is only one area which has been established as a strong foothold for more advanced life. This is modeled on the known effects of lakes, rivers, mountains, forests and seas and seems fairly reasonable. Now obviously the soil quality is going to be fairly questionable in places and non existent in others. What are the hard limits the inhabitants are going to run up against when attempting to plant trees and (for my illustration) other more advanced plant life outside of the natural valley zone? I figure we are roughly into reclaiming wilderness/desert territory? [Answer] **Start at the bottom** It all starts with the little guys when you are talking about ecosystems. Bacteria, mold, etc etc etc. Single celled organisms. To spread your Eden you are going to have to do a few things. 1. However you managed to create your little green space you will spread from there. This will happen naturally if you protect the environment around your Eden and maintain the balance of the ecosystem. Maintaining the balance in an ecosystem is no small task...the smaller the system the less it can absorb system stress. 2. Prep the battle field (so to speak). Plants require certain minerals and organics to survive. Spread them around the radius. This will include minerals which could be mined from your terraformed planet as well as organic matter/bacteria etc which could be grown/cloned. Don't forget the insects. Once the organics and microscopic organisms are up and running add bugs. 3. These things (if you maintain the system) will gradually spread on their own, at a certain critical point you won't be able to effectively impact the ecosystem anymore as it will grow to be self sufficient. Thats how building the system would work. I must re-iterate that this is incredibly difficult, the intricacies of ecosystems are still way more complicated than we understand. Rarely do you see a situations where humans 'helping' and ecosystem actually helps (with the exception of clean-up operations). Mainly I am referring to killing off predators or culling herbivores etc etc etc. Anyway, rant aside... **Your questions/points:** You can't just have a bunch of oxygen floating around in the atmosphere. Its pretty dang flammable...like a lot. The atmospheric composition of earth is a mix of course and you would need the same mix, or at least close to the same to create what you are talking about. Its tough for me to ignore the idea that you just BAM have an atmosphere like earth but no life on the planet. Planting outside the zone. If you have the atmosphere, all you need are nutrients (compost) and water and the correct temperature range/light (lat/lon). Super easy...I mean relatively speaking. In reality to terraform you would probably have to start with domes for people to live, each dome (you'd need many many many of them) would have a gas farm...which skipping the obvious fart jokes would help modify the atmosphere to something tolerable for plants, bacteria, insects etc. Over time the farms aren't necessary as the plants will spread etc etc etc. ]
[Question] [ We see a lot of movies and books with humans(or near human creatures) that live for hundreds of years. I've seen numbers for long lasting human ranged from 150 all the way up to 7000( and I'm sure that number is higher). Lets say I want to make an average human live for 200 years. What changes need to be met to allow this to work. [Answer] According to Richard Dawkins, there's nothing inherent in the human body that causes senescence. It's just that there has never been any evolutionary pressure towards longer living humans. So the "fix" would be to forbid anyone from reproduce until they reached the age of 30 years or so. As the species began evolving from this artificial selection pressure, you'd gradually increase the minimum required breeding age. This would not be difficult to accomplish from a technological perspective. However, it would be devilishly difficult to implement from a sociological/political perspective. I couldn't find the direct reference but I did find [this very similar question and answer on the biology stack exchange](https://biology.stackexchange.com/questions/3758/is-it-possible-to-increase-lifespan-through-controlled-evolution) > > I think this would probably work. The grandmother effect, which is one > of the main theories for human longevity after fertility might > indicate that human lifespan would increase if the children come > later. > > > ... > > > The Belyaev experiments which produced domesticated foxes by strong > selective breeding took some 30ish generations to complete though they > saw a significant effect in just 10. It could take a similar numbers > of selection rounds in this cse. 4-500 years. Ethical issues aside, > this is why most geneticists study flies. > > > Just have to disclaim here: We will never do this. Many unthinkable > consequences would result. > > > [Answer] Well, mimic cancer. Scientists have found out that cancerous growths, despite multiplying like crazy, do not suffer aging, that's because your DNA has two protective ends that are reduced gradually as your cells divide, called telomeres, which serve as a way to determine how long it will live. In cancer cells, however, the enzymes that produce/"regenerate" this protection is off the charts, meaning it doesn't really age. Also I'd add that having more efficient ways to maintain the DNA would ensure the cells could go on for a loong time. However, should you want to reach thousands of years of age, the next main issue would be what makes them sapient: the brain. You see, unfortunately, the brain does not have infinite storage space, though apparently, unless my sources are incorrect, it does have space enough for 300 years of existence before you're basically incapable of coherent thought. How to bypass this? Forget about it, litteraly. The humans would need to have a brain that selects a lot more what to keep and what to throw away. In this case, you could have a race of humans with a love of notes and photographs serving as a means to stimulate certain memories they want to keep for longer periods. (sorry if some part of this is incorrect, I don't know as much regarding the brain and how it deals with memories) ]
[Question] [ Hey guys so I've posted on this site before and I've finally made an account so I'd like to ask again about mine and my friend's webcomic WIP. Biology wise, I've made three main groups of animals, a four-limbed, mammal-like group, a six-limbed group that is quite mammal-like but also very insect-like, with adaptable limbs, and of course the obligatory insect/arthropod group. The group I want to focus on is the first one however, as the main character's companion and also the sentient race fall under this group. To elaborate, they have smooth, sometimes scaled skin (scales grow in patches and lines in certain places according to the needs of the creature), no feathers or fur and they can get quite large. behaviorally, they are also quite like mammals, deer-like and cow-like herbivores are abundant and predators most commonly rely on stalking and capturing instead of lying in wait. Their environment, or at least the one touched upon in the comic, will be a fairly stable, fairly even temperature plains and forest. Of course its an entire planet so there are deserts and tropics but the planet does not really have oceans, more like large seas. The plains and forest are the focus though, the mammal-like group will mostly be on the grass plains. Of course that's all quite general, being an entire group of animals, but it's the most accurate mode i can make. I know it's a broad question but I need help deciding whether they are ectothermic or endothermic, maybe even in-between (so far I'm leaning towards the last two). [Answer] The choice of metabolism type (warm or cold blooded) depends on the activity type of your creatures. Endothermic (warm blooded) creatures tend to consume dozens of times more energy than ectothermic (cold blooded) creatures and are also far more active. # Carnivores If you want your carnivores (meat eaters, hunters) to be active predators and need to hunt a lot, then you have to make them warm blooded. A python or boa constrictor eats only *once* in 3 months or so and then goes on a long sleep. Other snakes, lizards and alligators (all cold blooded reptiles) eat far less than mammals which are warm blooded and far more active in their environments. This gets all the more important when your carnivores are large sized (10 feet or more). Such creatures would need a **lot** of warming up before they could get active on a cold winter morning. You don't see snakes out in the wild during winter as the temperature is too low for them to be active at all. In contrast, wolves, lions and other mammalian predators are active year round because of their warm blooded metabolism. The summary of all this is that if you want active, agile predators that are often hungry (need to hunt at least three times per week), then you should go with a warm blooded metabolism for them. # Herbivores Now comes the issue of herbivores. Here you have more choice. Some herbivores (take fore example, elephant sized ones) are so large they don't need to run to protect themselves from predators. Due to their low energy requirements (lazy lifestyle), these can afford to be cold blooded. Smaller herbivores (anything that needs to *run* to protect itself against predators) would definitely have to be a warm blooded creature. # Gigantothermy For big, huge, giant animals like [Sauropod Dinosaurs](https://en.wikipedia.org/wiki/Sauropoda), things get a bit complicated. They are so huge that the fat layer(s) on their muscles protects their inner organs from cooling down even when the temperature is too less. This shielding effect provides them with a sort of semi-warmblooded metabolism which is known as gigantothermy. Giant carnivorous dinosaurs such as T-Rex, Giganotosaurus, Spinosaurus, Carnotaurus etc are also thought to be semi-warmblooded if not completely endothermic. # Growth Concerns Another **important** factor determining warm or cold blooded metabolism is how fast you want your creatures to reach adulthood. For example, for creatures such [Bruhathkyosaurus](https://en.wikipedia.org/wiki/Bruhathkayosaurus), scientists estimate that if they were purely cold blooded, their hatchlings would require *more than 100 years* to reach adulthood. However, if their bodies incorporated any type of warmbloodedness or semi-warmbloodedness (e.g. gigantothermy), then the hatchlings could reach adulthood in ~35 years. Now that's some serious difference! # Feeding Concerns A purely warmblooded creature requires nearly 4 times the food that a cold blooded creature of the same type and weight requires. Elephants spend most of their time in feeding. Now think about a sauropod dinosaur and imagine how much it would need to eat, if it were a purely warmblooded creature? Also consider how much vegetation is available in the region. A group of warmblooded sauropods, the size of Seismosaurus, Diplodocus or Amphicoelias would literally strip an area (of 2-3 miles) clean of all vegetation in less than a week. Also consider how much dung they would spread in the region due to their fast digestive systems. I guess you don't want to have that in your environment. *Shit happens* # My Recommendation * If you have active carnivores, they ***have*** to be warmblooded, no matter what their size. * If your 4-legged mammal-like creatures need to run to protect themselves, they *should* be warmblooded. * All herbivores which are just too large to be in the scope of any predator, should be placed under gigantothermy (basically cold blooded, but so large that their internal body temperature remains nearly the same because of thick fat layers). * You **CAN** have creatures which switch between cold and warm blooded metabolisms as they grow from infancy/hatchling to adulthood. If you have elephant sized coldblooded/gigantotherm creatures, I suggest you keep them warm blooded in their juvenile years and then gradually switch them to coldblooded as they reach adulthood. This would simply mean that they *produce less heat* from their food. Although no examples exist in our world, it is *theoretically* possible. This is specially important if you don't want to put your creatures in juvenile times for dozens of years (like the sauropod dinosaurs). [Answer] The lack of feathers or fur would suggest warm blooded as those are adaptations used by warm blooded animals to regulate their body temperature. On the other hand in a stable warm environment that may not be needed. For example elephants have neither. You should look at the behaviour of your animals. If they are nocturnal or early morning they pretty much need to be cold blooded to explain that. If they bask in the morning to warm up then are active during the day then that also says cold blooded. Either would certainly be plausible, however if you want them to be sentient then I would suggest warm blooded. The variations in body temperature would effect their thinking. ]
[Question] [ I am working on an alien species with mammal-like features and characterized by radial symmetry, in opposition to bilateral. They have four lower limbs arranged in a square-like disposition, with the palms all facing outwards(they have ape-like hands), sustaining a central torso which grows out of the junction; the animal is meant to have a pretty heavy build. In order for it to really be able to functionally operate with a 360 degrees angle, I need the head and arms to be able to move independently of the central torso, given that full torso rotational capacity is out of the question, and it's not even that pretty. The head problem is solved by owl-like adaptation, only amped up. But I am not sure how to go about the upper limbs matter. I have thought of simply giving them four arms, and possibly of extending that to having two sets of forward facing eyes on the "front" and "back" of the head, which would allow the functionality provided by radial symmetry to be maintained with a "static" configuration, rather than one requiring active movement on the part of the animal. Yet, that is not really the concept I had started with, and I would like the animal to only have 6 limbs overall, since with eight I feel it's already losing too much of the mammalian "feel"; in the end it will come down to how much I want to adhere to "science", but I want to listen to this "side of the equation" and consequently I am very interested about your opinions : **would it be possible for the upper limb junctions of this animal to roate in such a way that full functionality is always maintained?** The only thing I can think of is that it may perhaps be able to fully rotate its arm at the shoulder junction, and given that the alien has its five fingers pentagonally arranged around its palm, the problem of the human thumbs changing place is not there. I am *not* asking about the likelihood of such a being evolving *given our current knowledge of the evolution of life on one single planet*, yet that's where we must start, of course. It is clear, however, that out-of-the-box thinking has to be used in these matters. And besides, would an arachnid-like leg structure (and consequent gait) be feasible for such an animal (7-15 tons range)? Any insights? Edit : I would also add, I mean the upper limbs to be articulated. I have thought of the possiblity of them having proboscis-like limbs, which would indeed solve the problem of rotation given that there would be no junction, but the fact of the matter is that, again, it doesn't fit with the "feel" I want the alien to stimulate. Besides, in the same story there are already creatures which use such a tentacular configuration, and I'd rather avoid redundancy. [Answer] Given the constraints, I might suggest looking at it a bit differently. The creature is large and heavy, so needs trunk like supporting limbs, If all six limbs are used to support the ancestral beast, then the individual limbs can be smaller, which allows for more flexible limbs and gives evolution a better starting point for articulation. So we start with a circular body plan with six limbs arranged radially around it, placed underneath to support the bulk of the animal. Since you already want it to be radially symmetrical and move in all directions, the limbs will need some unusual articulation and flexibility, which is good, since the "hip" joint will need to have a wide range of motion. The "feet" will need to have toes which can evolve to become fingers, which is going to be difficult since they have to support a great deal of weight. On earth large animals have either shrunk their toes or evolved hooves, but we can go by the example of the great apes and have the fingers/toes rolled up in motion so the creature walks on its knuckles. The complex articulation of the "hip" joints allows the creature to lift one or perhaps two limbs at a time above the center line so the hand can come into view and be used. Initially, this would be for behaviours like grooming and feeding (bringing food to the mouth), but as the creature evolves finer motor control and more adept articulation of the fingers can take place to allow for simple and then complex tool usage, hand signing and other complex behaviours. While it may be possible for this to happen on all six limbs, specialization reduces the amount of resources that the creature has to devote to this (we already need a lot of brainpower for intelligent behaviour, the amount of brainpower to control six fully articulated limbs/hands and be able to balance and move might be overwhelming, leaving the creature vulnerable to other ill effects ranging from mental illness to being so focused on limb use that it is vulnerable to predation to being less capable of hunting or foraging). So the body plan would be generally disc or hemispherical in shape, with six very complex hip joints equally spaced around, allowing the limbs to swing up from a pillar like standing stance to over the centerline and reach the top part of the animal for grooming and feeding. [Answer] Keep in mind several things: * [Square-cube law](https://en.wikipedia.org/wiki/Square-cube_law) - Spider-like limbs are going to be increasingly brittle and unable to hold weight the bigger the creature gets, which is likely why we don't see many creatures with such limbs beyond a certain size. If you look at elephants, they are incapable of jumping and they have padded feet to soften each step. * Features generally serve a purpose from an evolutionary standpoint. This isn't to say that there aren't things which serve no purpose (like our appendix for instance), however they also don't get in the way. A radial symmetry would likely *serve* some purpose. Perhaps such a creature can move faster this way. If this is the case, it would likely move like a wheel, and its limbs would end in claws to grip into the dirt to propel it forward. * Correllary to the point above, you don't see features which aren't useful for a creature specialized in a certain role. If this creature can move quickly, they aren't going to use a carpace (think of a cheetah). If it is an herbivore, then it moves fast to run *away* from predators, and inversely if it is a carnivore, then it moves fast to catch prey. In other words, don't give an herbivore pointy teeth. * Symmetry for creatures on earth is external, meaning that we don't always see two of every type of organ in our bodies. This implies that evolution doesn't care much about symmetry beyond balance and durability, so this creature doesn't have to be radially symmetric in *every* way. Given this, I don't think you would see a torso attached to a wheel-type lower body with limbs without a matching part on the other side to counter-balance. You would likely see eyes or sensor organs on both sides as well. You wouldn't see a torso attached to a wheel-type lower body with the torso on top, because there'd be no reason for radial symmetry. This would present a problem, because it isn't a "do nothing" feature. It would get in the way of movement. I hope that helps. [Answer] > > And besides, would an arachnid-like leg structure (and consequent gait) be feasible for such an animal (7-15 tons range)? > > > No. The legs need to be straight vertical under the body, [as with an elephant](https://en.wikipedia.org/wiki/Elephant#Legs.2C_locomotion.2C_and_posture). ]
[Question] [ I'm currently working on [an experiment using Worldbuilding Stack Exchange](https://worldbuilding.stackexchange.com/questions/22688/how-long-will-it-take-to-form-a-new-dialect-and-language-in-underground-steampun?lq=1), and so I'm working on a [constructed language](http://en.wikipedia.org/wiki/Constructed_language) to be used by some of the people in my world. I have some of the main points down, but I'm also interested in learning about the more general aspects of language-building. What is a good book that talks about the process of creating constructed languages? Specifically, I'd like one that focuses on [*a posteriori* languages](http://en.wikipedia.org/wiki/A_posteriori_(languages)), because my language is in part based on (British) English. [Answer] Try the Verduria website. Very detailed, and comes with its own Language Construction Kit. <http://www.zompist.com/virtuver.htm> <http://www.zompist.com/kit.html> A snippet for you: *"This set of webpages (what’s a set of webpages? a webchapter?) is intended for anyone who wants to create artificial languages— for a fantasy or an alien world, as a hobby, as an interlanguage. It presents linguistically sound methods for creating naturalistic languages— which can be reversed to create non-naturalistic languages. It suggests further reading for those who want to know more, and shortcuts for those who want to know less. "* ]
[Question] [ An earlier question here concerning a cube-shaped planet got me thinking. Suppose an artificial world-sized engineering project as described in [this answer](https://worldbuilding.stackexchange.com/questions/8830/how-would-a-civilization-that-has-been-living-on-a-cube-earth-differ-from-one/17616#17616) > > The K-II civilization that built it would stock it with interesting life, just as we would fill a garden pond or terrarium. If that civilization still exists, they would be watching. > > > What kind of mechanical arrangement could provide for different planetary analogs on each face? **I'd like to have regular sunlight (like ours) on 4 faces, with rising and setting. But, 2 faces have red dwarf suns that are fixed in the sky.** For example, the planet could be in orbit around a neutron star, with the main sun at a trojan point (L4) and a red dwarf in L1. The problem is that the planet's axis won't turn to stay pointed at L1. In general, the planet rotation needs to be roughly in the same direction as its orbit, to keep the 4 "belt" facets turning under the sun. There are things like [statites](https://en.m.wikipedia.org/wiki/Statite) to allow something to hover over the pole, and that could be a mirror to implement the red dwarf. *But*, I want something more durable. It should be stable over geologic time with minimal corrections. The stars themselves don't have to be normal. They can be (relatively) low-mass and nearby constructed suns, so there is some flexibility in the mechanics. I don't even mind having them turn on and off! A constructed sun would still be too large and heavy to simply orbit the planet: the planet would be lighter. Any ideas on how to arrange things? The big problem is how to keep something *un*moving when everything is moving to remain in orbit. If the planet were locked with its orbit than the near face would be non-moving. So how do we get sun movement over 4 other faces? I like the idea of a statite or some less durable implementation for the *second* red face, and this has indeed been lost before the present time in the story. I don't mean to allow the motions to be arbitrary, still powered by mysterious means. The system should work according to normal laws of gravity and mechanics, once it has been set up. So the example, "The problem is that the planet's axis won't turn to stay pointed at L1." Is problematic because "just making it turn" via unknown technology is *not* a hard-SF answer. I want a mechanical system that will move naturally according to known laws. [Answer] Cube orbiting a neutron star tidally locked no rotation. Red stars\* at the L1 and L2 points with a yellow star\* in a polar orbit of the cube. [![enter image description here](https://i.stack.imgur.com/AiBBe.png)](https://i.stack.imgur.com/AiBBe.png) \*Assuming you can make artificial star like objects much smaller than the planet. [Answer] Assuming that this cubic planet has a uniform mass distribution within its volume, it will not have a uniform gravitational field like that of a spherical body or a point mass, significantly complicating all orbits but geostationary ones. The variable gravitational field as the planet spins will also nudge objects out of the L1, L2, and L3 Lagrangian points, as these locations are dynamically unstable. The two red dwarfs could be of equal mass and sit in circular orbits around their mutual center of mass. The binary red dwarf pair orbits in a plane perpendicular to its orbital plane around the star. The planet would be located at the center of mass around which the stars orbit, but the stars would really be orbiting each other because the planet's mass is negligible. The stable point at which the planet sits is like the L1 Lagrangian point The stars could then turn on only when they were over the poles (or only over one pole). This would produce a day/night cycle at each pole. However, the red dwarves would produce frequent eclipses of the primary star during two periods each year (when the orbital plane of the red dwarf binary is aligned so it passes through the primary star). However, as there is no known mechanism allowing the stars to turn off, so one could instead have a large plate made of something like graphene orbit each star. Each plate would have an orbital period of half that of the binary star pair, phased so that it would block the star when its orbit went over the non-polar faces. As the plates would orbit symmetrically, the force on the planet from the plate orbiting one star would be cancelled by the force from the plate orbiting the other star. If red dwarf lighting is only desired at one pole, then the plates can have orbital periods equal to that of the red dwarf binary. However, the dwarves might be visible in the skies above the non-polar faces in this arrangement. I am also not certain of the ability of the graphite plates to resist tidal forces. If one wants continuous polar illumination, no eclipses, and doesn't like having the planet at a point where it is vulnerable to small external perturbations, a different solution is required: Place red dwarves at the planet's L4 and L5 points (although given the mass ratio, it is maybe better to describe the planet as being at the Lagrangian points of the stars). Then place a pair of large parabolic mirrors at the planet's L2 point. The mirrors should be connected to each other so that they move and rotate as a single object (they are too far away from the star and planet for tidal forces to matter much). The mirror pair will have a rotational period equal to the orbital period of the planet, so that they will always point at the red dwarves. Inside each parabolic mirror, a secondary mirror near the focal point would concentrate the light into a beam. The beam from each parabolic concentrator would be directed out a hole in the back of the primary mirror, and reflect off of a planar mirror to direct it out perpendicular to the ecliptic plane. A rod made of something like carbon nanotubes would be attached to the mirror pair along its rotational axis and also extend perpendicular to the ecliptic plane as far as is structurally feasible. Mirrors at the ends of this rod will direct the light beams from the two planar mirrors into the atmosphere over the planet's poles. The atmosphere could then diffuse the light and refract it downwards. Illumination on the polar faces would vary in both angle and magnitude depending on the time of day due to the cube world's rotation and non-spherical atmosphere. Polar lighting would always be at a low angle to the horizon and would be largely indirect. The mirror system has no moving parts and is a single object. However, a system of reaction wheels and ion thrusters is required to keep it in orbit in the long run because the L1 point is dynamically unstable. Perturbations would come from moons of the cube world or from any other planets. [Answer] I suggest a system somewhat different from Josh King's answer, but instead of one red star being closer to the center of mass of the system, have them both along the same vertical axis as your cube world, which also rotates about its vertical. This trio then orbits synchronously with a Sol-sized yellow star around an extremely massive black hole, neutron star, what have you, near the center of mass of the whole system. Here is a conceptual (not to-scale) rendering: [![Cubeworld with 2 Red-Sun Faces and 4 Day-Night Yellow Sun Faces](https://i.stack.imgur.com/TZVlo.png)](https://i.stack.imgur.com/TZVlo.png) Here the yellow star and the red ones would each be on the order of 1 AU from the cube world, which itself would be several (dozen? hundred? Whatever it takes...) away from the supermassive center of the system. So long as the yellow star and cube-red-stars system complete their orbits about the center in the same period, this should achieve the desired effect without any need of artificial stars. ]
[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/15654/edit). Closed 8 years ago. [Improve this question](/posts/15654/edit) # Scenario: The most feared evil scientist in the world, Sinister Norman Van Deathtoyou, is on a mission to destroy everything. Humans, Earth, The Universe, even *the very fabric of space and time*. But, being the cliche evil scientist that Sinister is, he must do this in a complex fashion that only he needs to understand. First, he invents time travel. Yes, this is a bit far fetched but Sinister is an extremely intelligent guy with unparalleled motivation (So please blindly accept this as fact). This time travel has rules, and these rules are important and **must** be followed exactly: * Sinister has discovered that the Universe does everything possible to disregard paradoxes. This means that the [predestination paradox](http://en.wikipedia.org/wiki/Predestination_paradox) that is often associated with time travel is completely irrelevant. * Also, none of that "uhhh but if he destroys reality in the past then he will never have been born to destroy reality" garbage. Sinister has found that the universe still runs linear even if he goes to a different point in time. *If he destroys reality at any point in time then he will still have succeeded in destroying reality*. * Time travel is extremely intrusive to a human's health and only one single trip can be survived. * I don't know all of the actual science behind what the destruction of the universe means in a technical sense and I don't really care all that much. Numbers are great but there are many more important things! # Goal: Describe a method in which Sinister can make one trip and do the absolute minimum (in terms of the actual action) in order to destroy the very fabric of time and space, effectively annihilating everything. *Bonus points to creativity, thoughtfulness, and uniqueness of responses.* [Answer] How to Destroy the Universe with a Time Machine... Change the initial conditions which are responsible for the [Baryon Asymmetry](https://en.wikipedia.org/wiki/Baryon_asymmetry). All matter and anti-matter should have cancelled out, but it didn't (citation: reality). All our scientist has to do is figure out why (note: this is one of the great unsolved problems in physics), then use the time machine to go back and alter initial conditions to make baryon annihilation symmetrical. Or, travel to the inflation period (10^-32 seconds after the Big Bang) and make an alteration which would cause the Universe to choose a lower energy state than we currently (apparently) occupy, known as [vacuum decay](http://www.worldsciencefestival.com/2014/09/will-higgs-boson-destroy-universe-cosmic-death-bubble/). Or simply travel to the inflation period. The current large scale structure of the Universe is a result of small, chaotic motions in the very early Universe. Introducing any sort of perturbation during this period, such as a suicidal human and their time machine, would likely radically alter the large scale structure of the present day Universe. You'd still have stars and planets, but different ones in different places, and no Earth. Look, I didn't say it would be easy. [Answer] By triggering [vacuum decay](http://en.wikipedia.org/wiki/False_vacuum#Vacuum_decay). > > If this were the case [the Universe is in a false vacuum], a bubble of > lower-energy vacuum could come to exist by chance or otherwise in our > universe, and catalyze the conversion of our universe to a lower > energy state in a volume expanding at nearly the speed of light, > destroying all of the observable universe without forewarning. > > > Plotwise it isn't as interesting because once it's triggered, it propagates at or near the speed of light - meaning no information about the event can outrace its effects AND there is absolutely nothing you can do about it after it has been triggered. If the event is triggered, it will ultimately devastate the entire Universe. Ironically, the event could have already been triggered and we will never know it. The event is so devastating, it is possible that not even subatomic particles will survive. [Answer] For time travel to work, there must be one of four possibilities- (1) fate as far the time traveller is concerned- nothing changes. You add energy and almost certainly mass to the past and future doesn't change. Its like a physical movie film, damaging or changing the start doesn't change the end. Basically suggested by quantum physicists that the quantum states lose randomness. (2) You cease to exist before you actually interact with the past (3) the whole universe ceases to exist. (4) the laws of physics change to fit with extra mass and energy in the universe. (3) & probably (4) mean you don't have do anything in the past to destroy everything. [Answer] (All my knowledge of the subject comes from the wiki, so I might just misunderstand it.) Doc needs to increase the [density of the universe](http://en.wikipedia.org/wiki/Friedmann_equations#Density_parameter), and it would collapse (<http://en.wikipedia.org/wiki/Fine-tuned_Universe#Examples>, <http://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe#Density_parameter>) Doing that with a time machines seems feasible, if you are able to send a noticeable part of the universe back in time. If you move matter back in time, it becomes 2x dense (old one + new one on top of it); iterate until you get the desired density. (I guess it would better be done at the beginning of the universe, while it's relatively small). [Answer] To destroy, Norman Van Deathtoyou must first create. That's right, you heard me, I said create. What must he create? A **LOT** of Dark Energy. I mean, much, much more. It counteracts gravity and if you somehow stuff enough of it into our universe everything in it will explode. Since our universe has a virtually infinite amount of matter, it will take at least a couple hundred times what already exists. This is really the only way to totally destroy everything, and even then the universe will exist. It will simply be sparsely filled with pure energy. [Answer] **Make The Universe Punch Itself In The Face** The exact answer depends on exactly how this happens: > > Sinister has discovered that the Universe does everything possible to immediately resolve paradoxes. > > > But what you want to do is create a paradox that the universe will resolve in such a way that it ends up destroying itself. This will take some experimentation with the anti-paradox mechanism, but once you understand how it works there should be some way to set things up so that resolving a paradox requires a universe-ending event - dividing by zero, ripping apart spacetime, etc. [Answer] Simple! If we accept either of the [two most supported potential ends of the Universe](http://www.wikipedia.org/wiki/Ultimate_fate_of_the_universe), destroying the Universe is just two simple steps. * Travel to last second before Big Rip / Big Freeze * **Wait one second.** Job done! ]
[Question] [ **Basic background** The cosmic entities that forged the world got a little more than they bargained for. Even the most powerful of them were but limited aspects of the underlying magic of the cosmos. The world they created, and the races they blew life into are not so limited. In particular, the sapient races of this planet carry within them a more prefect blend of these aspects than the gods have, though they have far less power. As a result, after years of bowing to the gods' ever more cumbersome and capricious rule, they rebelled, and wielding an aspect of destruction alien to the ruling deities, they killed them off. Humanity was left with the ruins. **And onto the question:** So we're now left in a world with massive edifices the gods built to house themselves. Lets assume they're made well enough to stay standing for at least a few centuries, aren't so big they just crush through the planet's crust, but are made of materials that humans can work. Humanity has a vested interest in building its ruling cities in these places, as the ambient magic proves useful for the ruling mages. Further, they don't want to destroy the ruins completely for fear of the same fading. So, what do these cities look like, how do they grow? Lets suppose that most god-dwelling contain a few spires, some sweeping walls, and sit atop a nice plateau. Most of the internal rooms will be far too big for a human to use as a single space unless they are using it as some sort of large open square/marketplace/field/park. How do you build inside a building? **Technology/Magic levels:** The main inhabitants of the upper cities are in a roughly Early Modern technology level. Largely pre-gunpowder and steam (though a part of this is societal taboo, so other areas may be better along). However the nations they rule are non-magical and are in more of an early industrial stage, so they may have some benefits of this (Again though, taboo segregates) Magic is plentiful, if somewhat dangerous. It is shipped in bulk as a magical mist/condensate from certain areas where large numbers of gods died in the rebellion of mankind. When properly channeled it could be used to achieve large projects such as levitating large objects/bulk material and stengthening or enchanting building supplies. [Answer] Many cities were built on the remains of older cities, and indeed the mark of ancient cities is often a hill or mound where the earth has finally blown over and covered the final layer of the city. Troy is perhaps the best known example, but these mounds exist throughout the near and middle east. I have the feeling the normal human fear of disturbing the dead/awakening unknown powers would have kept the population well away for the first few centuries, until the tradition faded from history to fable. The new cities would then be built on the top of a low mound, with the more impressive structures rising half buried from the earth. The new rulers would incorporate these pieces as part of whatever new palaces, temples or other structures they wanted to build, so an ancient tower would have new walls coming off at whatever angles supported the scheme the royal architect had in mind. Since you did not specify size, I am imagining rather outsized buildings, so the ruins would not be fully incorporated into the new city, perhaps two or three new structures might be built on the recycled remains of the older one. For the buildings that have fallen into ruin, their foundations would serve much the same purpose, and the fallen stonework would become the walls and towers of the new buildings. This leaves some interesting issues for the new inhabitants. Since the city is built on the partially buried remains of an older city, there might be tunnels and passageways under the new city which are not clearly mapped or defined. Skillful thieves, assassins and spies would be constantly working underground to try to determine the layout and how this could be used for their purposes. Ordinary people might also seek out surviving underground structures, for use as cheap housing or ways to evade the taxman or royal guard. And of course since this is a magical setting, items of power might still be concealed somewhere in the old remains (doubly so, since the hiding places are now in rooms hidden under the new city.) The people of the city might also be less than keen on people burrowing away underground, since that might awaken ancient magic, and the rulers would also be less than keen since they could be taken by surprise from underground. Periodically, the King sends the Royal Guard below ground to sweep the area, roust out people and block the more threatening passageways. A special corps of mining engineers might be in the ruler's employ for this purpose as well, or perhaps a select group of small guardsman adept at moving and fighting in confide spaces. So the new city will be built on a hill around a seemingly random collection of old towers and walls with new structures attached to them. The city will be a hive of activity, both the normal day to day activities above ground, and a much more furtive existence underground. [Answer] Considering that your god-corpses are effectively mana-batteries, and your gods are said to be all powerful, we can assume that they probably build things out of conjured unobtainium. Why? Well if the gods are very large creatures (as hinted in the large sweeping spaces paragraph) quarrying out enough regular stone to make cities their size is going to make alot of large holes in the ground and require an astonishing amount of labour. On the other hand, of course, this could be exactly the sort of tyranny your humans may have rebelled against? Who knows? The problem, therefore, is how easy is it to work with the materials of your ruins? If it so happens that this material is uber-strong and channels power; then you basically don't WANT to work with it. The most you may wish to do is tear some holes in the ceilings to give yourself some light, and then build inside the buildings. The old walls will make for excellent load bearing structural pieces that could form the core of your community, and then smaller wooden and stone structures would erupt around it in the form of regular housing. Their old roads would likely dictate the design of the vulture city built on the corpse. One thing very similar to this is the city of Tal Verarr in [Red Seas under Red Skies](http://en.wikipedia.org/wiki/Red_Seas_Under_Red_Skies) (the second book in the 'Gentleman Bastards' series by Scott Lynch). This place is built over Elderglass, left behind by the gods. Mostly because no-one can even work the stuff except maybe the Bondsmagi. On the other hand, if this material is, like its creators, very vulnerable the magic of man; you probably want to remove it and replace it with mundane materials if you expect your city to be attacked by jealous neighbours. Or at least ensure that its parts are not visible to attack. Thucydides has already covered some of the other main points, like people exploring the ruins. In terms of engineering challenges, I can't really say without knowing for sure about the materials. ]
[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/14198/edit). Closed 8 years ago. [Improve this question](/posts/14198/edit) If all humans had four fingers and no opposable thumbs, how would the world be different? When I say 'have no opposable thumbs', I mean if humans never evolved them. Specifically, I'm looking for differences in technology and western culture/society, but feel free to explore other possible effects. [Answer] Opposable thumbs are [great at manipulating things](http://www.nsta.org/publications/news/story.aspx?id=49036). So great, in fact, that one of the few species with opposable thumbs has risen to the top and wiped out countless other species. I imagine that technology would advance slightly slower. How much slower? Honestly I have no clue, but we might currently be using 1970's tech at best if we lacked them. I don't see much of an effect on culture/society. Since these people never had opposable thumbs to begin with, they probably wouldn't miss them. Cities wouldn't be thrown into anarchy or nations toppled simply because Joe Blow and Sandy Mandy over there don't have thumbs. [Answer] There would be major differences both technologically and culturally. Starting with technology, think back to all the basic tools that pretty much rely on the ability to grip - stone knives & spears, even into the future, ropes, pens, screwdrivers, swords, bows, even guns would be affected. I'm not saying they'd be impossible to use without opposable thumbs but certainly a lot more difficult and so probably wouldn't have developed as naturally as they did, if at all (difficult to use would mean thrown aside and forgotten). I would wonder if we would ever get past the iron age, and would certainly be a lot slower to reach it and to advance beyond. But why would that affect culture? Well presumably without such technology, the spread of mankind would surely have been much different. For a start, we would be less inclined to stand upright as user6760 said above. But even looking to more recent times, without the Long-bow would Britain have conquered as much as they did in the middle ages? Without such a mastery of ropes and knotting they would surely not have the dominant Navy they did, if indeed such a Navy could even exist. It's doubtful the Renaissance could have happened without the existence and skill in delicate instrumentation. To build your world, if you were to be honest in your story, you'd need to start at the beginning of civilisation at the Stone-Age and imagine how each invention would be different if it was made for someone with no thumbs, and then the following generations of inventions would have to evolve from those, rather than from real inventions. You should find that quite quickly you have branched quite far away from what happened in real life. ]
[Question] [ So, I read the question, the associated answers and comments located [here](https://worldbuilding.stackexchange.com/questions/4460/could-two-planets-be-tidally-locked-to-each-other-so-close-they-share-their-atmo), as well as some others that were more divergent than what I was hoping for. Basically, imagine two earth-like planets very close to each other and tidally locked. Say that there is something like 100 miles between them and some sort of magical\advanced technology structure is keeping the planets in this configuration: **What does this do to things like gravity, wind speeds, etc.?** I would see gravity being close to being cancelled out on the surface, possibly with the effect of small, floating islands of material being possible. How far would the effects be noticeable felt by those on the planets? What would weather patterns do in the area? [Answer] The two planets would each have a ring of land around their 'equator', with a large ocean on the side pointing away from the other planet and another ocean *connecting* the two planets. Ships could probably be driven up this water bridge to get from one planet to the other. This would happen due to the effective tides the two planets would apply to one another. The gravity of the other planet would pull one bulge up to what would probably be hundreds of miles in height, but since the planets are closer to this, the ocean would bridge the gap between them. On the opposite side of the planets, the inertia of the two planets spinning around each other would cause a similar bulge, resulting in a deep ocean. The connective column of water would also be surrounded by enormous storms at all times. Since the planets are tidally locked, and orbiting extremely rapidly (given the low orbit altitude), the coriolis forces would be huge, and drive similarly huge storms, which would expand under the low gravity as the approached the connection point and then crash into each other, since they'd approach the connection point from opposite directions. (Storms on both planets would move in the same angular direction, clockwise or counter-clockwise, since the tidal lock effectively 'spins' both planets the same way). Assuming the planets were both in the plane of the sun, the mega-ocean on the far side would spawn these storms, which would then tear across the land on the windward side of the ocean before hitting the connection point. The habitable portions of the planets would be towards the poles and on the leeward side of the far oceans. This is all under the assumption that the planets won't warp under each other's gravity. They're well within the Roche limit for each other so tidal effects would normally rip the planets apart. We'll chalk that up to alien magic as well. [Answer] The two worlds would form an "egg" shape and the entire planet would deform into this shape. At the surface you would not get zero gravity or things flying towards the other planet. Counter-intuitively you would feel exactly the same net force (gravity+centripetal) at every location on the surface of the planet, and the planet would change shape to match that with only localized variation such as hills or mountains. See also these other questions and answers: [Can an atmosphere englobe a planetary ring?](https://worldbuilding.stackexchange.com/questions/1274/can-an-atmosphere-englobe-a-planetary-ring/1280#1280) [Could two planets be tidally locked to each other so close they share their atmosphere?](https://worldbuilding.stackexchange.com/questions/4460/could-two-planets-be-tidally-locked-to-each-other-so-close-they-share-their-atmo) This discussion: <http://chat.stackexchange.com/transcript/message/18052695#18052695> Which continues here: <http://chat.stackexchange.com/transcript/17213/2014/10/8/13-21> And this sketchtoy: <http://sketchtoy.com/63271225> You can see the initial misconception (where zero-g would be) and then the correction. ]
[Question] [ Due to my [previous question](https://worldbuilding.stackexchange.com/questions/9862/tame-and-sovereign-dragons) being too broad, I have split the question up, however; most of the notes will be back at the previous question, so feel free to look up the notes there. The question is, what would the regular peasant think of the dragon-human kingdom, who is not part of said dragon-human kingdom? Consider how sovereign dragons raid castles and steal cattle, but the tame dragons are full members of society. [Answer] I would say that normal peasants would would be terrified of the dragons of a nearby kingdom. The Sovereign dragons would scare them enough, they can take what they want and the peasants can do nothing about it. However, the neighboring kingdom has dragons in it's army. Soldiers are scary enough, but you can recognize them and know that if your army is around they can protect you from them. But a huge flying beast could rampage through a small company of men with little trouble (whether or not they have ever done so or even if they would is irrelevant). They are huge carnivores that could be sent against them. Because of this I think most surrounding kingdoms would be very wary about them and might be plotting to bring them down. This could include the Sovereign's because it could be an unnatural situation and the partnership could make both groups (tame dragons and humans) to be much, much stronger with the ability to dominate the others. So either they will try and be close ally's or plot destruction (and maybe try to coerce some dragons to their kingdoms). ]
[Question] [ A region of the galaxy is controlled by three human factions. * The Empire of Excellence (faction colors are black and white) * The Alliance of Freedom (faction colors are blue and white) * The Union of Justice (faction colors are red and yellow) As it follows from their names, they value excellence, freedom and justice the more respectively. But this is often just propaganda (see below). The three evolved earlier from Domain of Excellence, Federation of Freedom and Republic of Justice, after each faction had their satellite states incorporated. The **Empire of Excellence** is not a monarchy. It is governed by the Supreme Council of the Excellent, the highest sort of the citizens. All the population is divided into three classes, and each class in divided into at least three sorts. The highest class, the Selected, have full citizen and voting rights, but only the first and the second sorts are allowed to occupy management positions. Only the first sort participates in the Supreme Council and makes laws. The second class are the Tolerated, have restricted rights and no voting privileges. The first sort of the second class has nearly full citizen rights except voting while the third sort has their rights severely limited. The third class is the Garbage. The state aims at best at as harsh exploitation of them as possible. The first sort is deemed to forced life-long labor at huge state plants, but they are moderately fed and cared about so to serve as long as possible. The second sort is deemed for as harsh labor as possible and upon sickness, eliminated. The life of the third sort is not valued at all, they are used for medical experimentation or for most dangerous and health-damaging works. The factories are mostly owned by big enterprises or state, but private slaves are forbidden. The division into classes is based on genetics, at least this is what the state propaganda says. POWs usually go into the Garbage class. The **Alliance of Freedom** thinks Empire of Excellence and the Union of Justice are tyrants, but trades with them a lot. As the most valuable thing in the Alliance is freedom, a lot of things are allowed. This includes all sorts of sexual perversions and deadly games, including sexual snuff, death fighting, Russian roulette lotteries, as well as (paradoxically) slavery. One thing is important: a slave is who signed a slave contract, and their children are not slaves themselves, unless they also sign a contract (which is allowed at very early age). Virtually any form of contract is allowed. The Alliance is composed of several entities which may have quite different laws, headed by the Coordination Assembly. One of the important sources of the slaves is from trading with the Empire of Excellence. The representatives of the Alliance visit the forced labor plants in the Empire and select slaves for them from the ranks of the Garbage. Formally the Garbage people have to sign a slave contract with the Alliance representatives, but little who refuses. The Alliance propaganda represents such method of obtaining slaves as a voluntary contract and as a mercy for those people, who as it claims, are dreaming of an opportunity to get out from the Empire's plants. Thus they say, they save people's lives by buying them into slavery. The **Union of Justice** is governed by the All-Union Congress who are selected on the mixed principles of meritocracy and election. Only those who have decorations and merits can participate in a multi-staged elections into the multiple-level bodies the highest of which is the All-Union Congress, having several thousands of members. The Union thinks their adversaries are unjust. Upon conquest of the territories belonging to other factions, their elites are often eliminated or put into correctional facilities for prolonged time so to restore the justice. The Union's propaganda says they are against any kind of slavery but they have a lot of correctional facilities used for forced labor, and anybody supporting practices deemed unjust or disliking the Union's ideology is risking to end up in these places. --- Given the above, I wonder what ethical, moral, economic, ideological, political, or legal issues may arise in such a world in the course of peaceful or hostile interaction between the factions. [Answer] I will answer basing my answer on my knowledge of political science and some conjecture that I have done on the political systems that you described. So, before starting, I make a small clarification. The ones that you want to treat are non-democratic political regimes. These regimes can be essentially of two types: authoritarian and totalitarian regimes. The differences are deep, and can affect the ideological, military, economic legal issues that arise around them. **Authoritarian regimes** * These regimes do not have a strong ideology, but continuously repeat keywords that characterize their political system. For example, in your particular case, the Empire of Excellence’s keyword is, precisely, excellence. Without a precise ideology, in fact citizens are free to act within the limits of keywords policy. * An authoritarian regime allows several institutions to continue to exist with the government, although it is in fact a dictatorship. * The authoritarian regime has an extreme need for a charismatic figure in power, since there's not an ideology deeply rooted in the population. Obviously as soon as the charismatic figure ceases to exist, the system collapses. * The authoritarian regime goal is the de facto to hold power. Nothing less, nothing more **Totalitaran regimes** * These systems instead, are based on a profound ideology, rooted in every aspect of daily life. Ideology does not only want power, but wants to shape reality at its will, to change the world according to his own vision, and therefore also the people. People are forced to act in accordance with the ideology, and every aspect of daily life is penetrated by ideology. * The leader is not so necessary. A charismatic figure can help, but the ideology will continue to exist even without it. In this, totalitarian regimes are much more difficult to break down. * As the political scientist [Hannah Arendt](http://en.wikipedia.org/wiki/Hannah_Arendt#The_Origins_of_Totalitarianism) says, the regime bases its strength on terror and the common enemy. The common enemy serves to pull together the people and make it a united mass easily foldable to the will of the regime. Terror is instead an adjunct of propaganda, but also the engine of the movement of people. The terror is infused in order to make people constantly insecure, and therefore bring them to rely on the system, that provides them security (and terror). After these clarifications, I would say that Excellence and Freedom are authoritarian regimes, while Justice is totalitarian. Now I will focus individually on the various factions. **Excellence** *Political/Economic issues* Being an authoritarian regime, there should be a power struggle between various organizations. In this case, the government and the big enterprise. The political system would be dualistic, with the political environment that presses to stay in power, and the economic environment that wants more power. The caste system that you created could further exacerbate the conflict (if such an inept governor belongs to the first category of Selected, and a capable CEO is the second category, the conflict for the power is unavoidable is inevitable.) *Ethical* Also, while I was reading the description you've done, I immediately thought of the movie [Gattaca](http://en.wikipedia.org/wiki/Gattaca). The problems that may arise between the various citizens would be of the same nature as those presented in the movie. **Freedom** *Ethical* The problem here is precisely the word "freedom." Surely the Alliance legal definition of freedom is completely different from that of the Empire and the Union. In this case, objectively speaking, The Alliance is simply licentious, not free. Some enlightened minds may raise ethical questions on this very difference. Citing as arguments (for example) that if a poor child without parents decides to become a slave, is not because he freely decides to do so, but because otherwise he would probably die. And also about the sex: from what you write I think pedophilia is also permitted. But sex, objectively speaking, should be put into practice to involve pleasure to both partners. Can a child really feel at ease with an adult? And so on. I also think that the society would probably become a nihilistic nightmare. If everyone (except slaves) can have it all without any consequences, the world would be too perfect, and therefore the world would be populated only by 1. Perverts, individualistic and selfish hedonistic people who have no other purpose in life rather than get pleasure at all costs, regardless of the suffering of others 2. Nihilists who seek emotions compulsively and therefore may also incur in violent acts of self-harm (included suicide) 3. Slaves Also, you might think that the generations of young people (16-26) living in this period, may also decide to rebel against the system to follow higher moral values. Unfortunately incurs a sociological problem. I'm talking about the paradigm of the structure and the paradigm of action. According to the paradigm of the structure social beehavior and individual system of values and morals is determined by the environment, society and culture surrounding the individual. (For example, a child growing up in an war zone will have moral values and behaviors very different from a child growing up in a protected environment, such as a child growing up in a dangerous environment etc.). According to the paradigm of the action instead we act according to a purpose, our action is directed towards others and we give to it a subjective sense. So our actions can not be attributed to abstract entities such as society, but only to the individual. The reasons for an individual to act in a certain way can be understood outside, even if they originate inside the individual. The individual is conditioned by the context, but it is not at the mercy of external forces, deciding how to act according to the way of the action. If you decide to follow the paradigme of structure you must know that society will never change except through external interventions. The people inside it will feel the culture of unrestrained hedonism , of slavery and risk seeking as something **normal**. Even a child,, although uneasy at the idea of having to become slave, will see it as normal. But if you privilege the paradigm of action, certainly it will not change society, but you can allow the creation of values systems of opposite to those recognized. For this, I suggest you watch or read [Blade Runner](http://en.wikipedia.org/wiki/Blade_Runner) by Philip K. Dick, or [Running Wild](http://en.wikipedia.org/wiki/Running_Wild_(novella)) by James Graham Ballard (or any other novel of Ballard) **Justice** *Ideological/Social* Soviet Union. Put all the negative aspects of Soviet totalitarianism in Justice. *Legal* In addition, a purely legal issue: the Soviet Union led to the distinction between jure imperii (acts put into practice by the State that are part of their duties) and jure gestionis (acts attributable to the State, however, are not part of its duties) given that the Union had de facto gained control of all aspects of private life. For more informations search about the operating limits of territorial sovereignty. ]
[Question] [ Suppose I have a "free energy" device of the following characteristics: **Cheap, Materials Easily Accessible** *Basic wire (coils) and electronics components in an unintuitive configuration* **Solid State** *There are no moving parts and minimal electronics in the device.* **Energy Conversion Is Perpetual** *As long as the device can keep generating a rotating magnetic field.* **Energy Level Adjustable** *According to the magnetic field strength around the device. Output levels exceed the energy required to cause the effect by ~300 times* **Horizon Independent** *Operation of the device is not dependent on it's orientation or distance from the Earth* **Positive Feedback** *Feeding the output back into the input causes the device to destroy itself (and everything in the immediate area...think 100 Megawatts dissipated in a microsecond in a device the size of your hand)* Given these characteristics, would a government or other organization try to inhibit the use of such a device assuming an otherwise realistic setting? Would the danger of misuse and economic turbulence outweigh the potential benefits? Keep in mind that everyone could easily build one if the device's construction become common knowledge. [Answer] I'm going to attempt to draw together a few ideas. **1. The Internet** You state that the construction of this device is 'unintuitive'. However, think of how quickly we can communicate today, and how quickly things get leaked. Without serious government restriction, the plans for this thing will be easily Googleable within weeks, if not less. Even if your government does restrict this device, the plans will most likely still be available on the dark web. **2. Global Warming** Free energy could have an effect on global warming. As mentioned in the comments, all the energy created will eventually dissipate as heat, which could eventually burn Earth to a crisp. Now, say it takes 30MJ (megajoules) to start up: $$ 30\text{ MJ} \times 300 = 9000 \text{ MJ} $$ $$ = 9\text{ GJ} $$ We get left with a 9 gigajoule output. If we take that and the [heat capacity](http://en.wikipedia.org/wiki/Heat_capacity) of air (which is [1.005 kJ/kg K](http://www.engineeringtoolbox.com/air-properties-d_156.html) at room temperature), we can work out the heating effect. The heat capacity tells us how much energy it takes to heat up 1 kilogram of air by 1o Kelvin. $$ 9\text{ GJ} = 9,000,000\text{ kJ} $$ $$ 9,000,000 \div 1.005 = 8955223.8805 $$ So, we can heat up approximately 8.95 million kilograms of air by 1oK. The approximate mass of the atmosphere is $5.1480 \times 10^{18}\text{ kg}$, so if the 9GJ output is output per second, then we need $(5.1480 \times 10^{18}) \div 8,950,000 = 5.75 \times 10^{11}$ seconds or around 18,239 years to heat up the entire atmosphere by 1oK (call it 18,000 to make up for my rounding). So, if you've only got a few of these devices then the effect won't be too bad (and certainly less than global warming is now), but you can see that it could become a problem. **3. Terrorism** Sort of linked to the first point. If the plans for this are available on the internet, then it's a terrorist's dream come true. They can build it reasonably easily, it can be concealed fairly well (although admittedly it would get picked up at airports), and it does a fair amount of damage. If you want to put this device into a story I'd suggest rethinking the positive feedback idea. Perhaps you make it compulsory for these devices to have an earth or ground cable to siphon off the massive overload, or maybe you give each of them internal batteries to hold some charge. Yes, it could still be weaponised, but a weaponised version might stand out a bit. --- It's a good idea, in theory. I think it needs a bit of refining, then it's ready to go in your world. [Answer] Heinlein had a product called a Shipstone in the book [Friday](http://en.wikipedia.org/wiki/Friday_%28novel%29). I believe that they were solar-charged batteries. The questions you're asking here remind me of the issues with which he was dealing. In his book, Shipstones had kicked off a small nuclear war. Heinlein also believed that corporations would engage in assassination of their enemies though. If Sony has the North Korea guy whacked, then you'll know Heinlein was on the right track. Anyway, if there was a truly revolutionary, non-polluting energy source, most countries would end up embracing it. Certain countries might try to restrict them, but the problem is that it's the producers who want to restrict it. The consumers would prefer it. Consider how much pressure there is to switch from fossil fuels, which are the cheapest form of energy now, to renewables. If we had a sudden new source of cheap, non-polluting energy, there's no way that countries like Japan and Germany wouldn't embrace it. The US is more difficult, as it is both a producer and a consumer of fossil fuels. In the long run though, I'd expect cheaper to win. If the device is easy to build in a garage, then I don't see how countries could really stop it even if they wanted. What are they going to do, arrest people for canceling their electric bill? The easiest way to keep these devices out of the hands of everyday people is to supply cheap energy so as to make it unnecessary for people to build their own devices. So my prediction is that these devices would be embraced in safer ways. People would be discouraged from owning their own, but utilities would use them to replace existing power plants. Over time, more and more places would have them. If they could find a safe way to make devices slag themselves without exploding, they could make devices more generally available. For example, electric cars could be powered by their own device. If someone tried to use the positive feedback trick, the device would short out and then make itself nonoperational. If someone tried to unseal the device, the same thing. [Answer] It's like considering the possibilies of quantum compute by mostly thinking about its use in encryption, as if nothing much else will change when exponential time problems can be solved at polynomial time. Technologies like power generation, compute, time dilation and self replication are inter-related, each bumps up possibilities in the others. Being orginised by orginisations like governments making sence at all is itself a factor of our evolutionary and technological position. For example, imagine if as a result, food and products are suddenly free, but that bairly even registers enough to make whatever is the equivalent of the news, if there is one, because other changes are even more startling. [Answer] Global warming, take II: ArtOfCode did a fine job of showing the device could cause environmental problems. I'm going to address why it would cause problems. Think of any cold-climate city in the world. The occupants of course use heat to remain comfortable. With this device power is incredibly cheap. Nobody's going to bother with insulation anymore, that costs a lot more than simply providing more heating. Now, lets look at the business district. Want to make your street more attractive to customers? Blow warm air onto the street. When your neighbors join in your street becomes a more attractive shopping location. Pretty soon the whole business district is warmed up. Soon the city will get in on it--heating elements in the roads will be cheaper than snow plows & salt. [Answer] Now, for some positive effects of this device: 1) All new powered land and water transport are electric. Not counting the battery, electric cars are simpler, cheaper and more reliable than gasoline engines. Now you only need to provide a starting jolt, your car then runs as long as you want. The advantages are even greater for trains (which actually are electric anyway even if that electricity is coming from a diesel engine) and ships. 2) The electric propeller airplane has no fuel costs. They still won't be cheap but they'll be a lot cheaper than current planes. I'm not sure if you could make an electric jet. 3) NASA uses it for deep space. The NERVA design gave an ISP of 850. Since this has a much lower weight the ISP will be higher. It can also run closer to the safety limit, thus giving a still higher ISP. I would guess something near 1000 would be possible. As this is roughly 3x the best space-storable propellants we have now (yes, this is cryogenic, but you have enough power that refrigerating it is no big deal) that is a truly huge breakthrough for them. (The rocket equation is exponential. 3x the ISP is **far** beyond just 3x as good.) ]
[Question] [ I want to make a hot planet habitable for mankind. It could be a planet in the habitable zone like Venus or outside of the zone like Mercury. These are just examples. Someone said here: [Terraforming a very cold planet?](https://worldbuilding.stackexchange.com/questions/2479/terraforming-a-very-cold-planet) that terraforming a cold planet is easier that a hot one. Still, is it possible to make a planet colder? > > Example 1: A planet in the habitable zone is too hot for human > habitation due to atmospheric reasons. Can it be cooled down? > > > Example 2: A planet is too hot due to solar proximity. Can it be cooled > down? Can it be moved away from the star? > > > What are the different techniques or technologies that could be used to lower the surface temperature of a planet? \*including possible not too far future technologies. [Answer] Fundamentally you have two choices (assuming we don't have some sort of super future tech like planetary force fields, portals, moving the planet into a larger orbit, cooling the sun, etc). * Increase outgoing heat * Reduce incoming heat The first one could be tried a little using giant heat sinks or similar but is not really practical so that leaves the second option of reducing incoming heat. Now you have three choices: * Make the planet's surface more reflective For example ice caps reflect away a lot of incoming heat. Similar could be done with artificial substances. * Make the planet's atmosphere retain less heat/more reflective Dust in the upper atmosphere similar to an Impact/Volcanic/Nuclear winter could reflect away heat. Stripping out greenhouse gasses would cause it to retain less heat. * Block the heat before it reaches the planet A giant mirror, sail or similar placed in space between the sun and the planet could reduce the incoming sunlight. ]
[Question] [ **Closed**. This question needs [details or clarity](/help/closed-questions). It is not currently accepting answers. --- **Want to improve this question?** Add details and clarify the problem by [editing this post](/posts/1168/edit). Closed 9 years ago. [Improve this question](/posts/1168/edit) I have a world that I largely have figured out in a big picture sort of way. It's sort of a Buddhist realms style "multiverse" with multiple realms encompassing the true universe. In this multiverse people can travel between worlds in the multiverse, and while largely keeping their same biology, they may be forced to adapt a more humanoid form. My problem is that I am having trouble with is how to represent a humanoid from a more extreme realm. Take for example a human-like creature from Dante's 9th circle of hell. My thought is that some variety of alternate evolution could have taken place, where rather than evolving a more insulated body, they instead evolved into a creature with a lower body temperature so they could reduce the amount of energy required to maintain their core body temperature. Perhaps they even developed hair in shades of white, grey, and blue to reflect more energetic wavelengths of light to prevent their body from getting too warm. Now my question is: for this variety of creature what other traits could one expect a common example of such a creature to exhibit on Earth? For example, since hair and skin color are caused by the same chemicals, would one expect a different common skin color? Would their height and "energy" requirements be greater or less than those of a common human? I hope this is clearer than my original question. It is kind of difficult for me to put into words. [Answer] There are actually a few problems with the concept as you have described them. First, energy wouldn't necessarily depend on average body temperature, because one could be better insulated. (If you're ok with merely humanoid looks, not true human, an extra layer of fat would be no problem). But if they have the same internal build as humans, then yes, they would need to use more energy to keep their average body temperature. I don't think height has a large effect on average body temperature. Second, skin and hair color are independent. You can see this in human bodies because when someone stays out in the sun for a long time, their hair gets blonder (it bleaches), but their skin grows darker. Human skin won't naturally have colors other than those produced by [melanin](https://en.wikipedia.org/wiki/Human_skin_color) (brown, skin is white without the melanin pigment). [Hair color](https://en.wikipedia.org/wiki/Human_hair_color) is the same way, but different varieties of melanin enable more types of colors. You could introduce new pigments to the alien's body, or use [structural coloration](http://en.wikipedia.org/wiki/Structural_coloration) to make strange skin colors. ]
[Question] [ Wanted to create Flora (and maybe organisms overall) that evolved near stark white coloration due to the high output of radiation from it’s, at the time, high energy F-Type star. It’s a star and of it’s specific class at that so i’m aware it’ll always be around a relatively similar energy output, but could a star eventually after it’s original formation cool or become more stable (less solar flares for example) enough that plants could evolve color changing and bioluminescent cells to handle the varying degrees of radiation. I’d been concerned around the concept of “Would these cells still be necessary if the star is less intense”? But then thought, if a period of enough variation during the stars more high energy state while transitioning to a more stable one would these cells then become prolific and only still be present now due to evolutionary selection during a majority of the planets history and the general time scales in question. There terrestrial bound multi-cellular organisms that receive energy partially through an distinct form of photosynthesis and physical charges due to the high amount of (volcanic soil laden with silicate iron and obsidian) on the planet. I wanted the concept of electromagnetism to be common, to the extent where there’s form of dynamism within the cells that evolved partially non-organic matter, like a living neodymium magnet. (The Systems star being around 1.7 billion years old and planet 1 billion, with its planet orbiting around 2.0 AU and the atmosphere primarily comprised of and nearly equal parts mix of hydrogen, helium and oxygen with a density similar to that of earth) [Answer] With the amount of energy that the plants would get from the star being so high even after it cooled off an appreciative amount they wouldn’t be able to use normal photosynthesis that uses a chlorophyll adjacent chemical and would instead probably have to make an inorganic photo cell the feasibility of which has been shown to exist in engineered bacteria and nano particles of cadmium sulfide, the researchers have shown that bacteria can self assemble the nano particles into complex structures in a bio mineralization process for controlled optical properties, it is not to far of a stretch that the plants on your planet would be able to adapt and use a similar process to create energy from the sulk gut they receive, the photosynthesis process for them would require more steps but it would be no less efficient or viable than normal processes the extra steps would be required due to the extreme environmental conditions that the plants are subjected to, the electricity that the photocells produce would be used in an electro synthesis process to produce the required chemicals needed for growth and energy storage unless the planet’s ecosystem stored the electricity produced rather than using chemical energy storage. The plants would then have to be able to produce conductive materials but that has already been shown in certain species of common soil bacteria growing bio filaments that are nearly as conductive as copper with active research into improving the conductivity and potential of mass production. In conclusion the idea of the plants turning a part of themselves into inorganic photocells is both feasible and entirely likely that in such an environment they would develop such at the first opportunity as it allows for massive benefits when compared to conventional photosynthesis in such a high energy environment. The idea is great and would allow for a very unique and possibly symbiotic ecosystem run on electricity. Sources: <https://www.pnas.org/doi/full/10.1073/pnas.1523633113> <https://www.science.org/doi/abs/10.1126/science.aad3317> <https://www.frontiersin.org/articles/10.3389/fmicb.2019.02078/full> These sources are what I could find on the specific things mentioned and I’m not sure if this is the only material on the subject as I don’t really understand research jargon, it is interesting nonetheless [Answer] It is hard to predict what possible forms life can take based on the one planet we know has life on it. It is hard to see how life could exist without carbon, as this element has a unique ability to bond to itself and to other elements to create complex compounds. Silicon, and silicon-oxygen compounds can form a few multi-atom compounds, but silicon-based life is thought [unlikely](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7345352/) if water is present, as silicon compounds will easily turn to stable silica, and are unlikely to change back. Sulphur can bond to itself, but it con only support two bonds so it can't do anything much. If our life-forms are carbon-based (not proven, but seems likely) then an F-type star will give off more ultraviolet light. This has enough energy to break a single carbon-carbon bond. This is why we use suncream, but it is not necessarily harmful to life. Most of earth's current life-forms are descended from creatures that lived around volcanic vents, far from sunlight. There are bacteria living in the gaps in rocks miles below the earth's surface. One has evolved to live off the energy from [the radioactive decay of uranium](https://www.sciencedaily.com/releases/2006/10/061019192814.htm). Even if the life started on the planet surface, it may be under a thick, smoggy atmosphere, and the short wavelengths cannot penetrate. The difference between an F-type star and our Sun may not be significant. Is there a reason for life to use photovoltaics? According to [this article](https://engineering.mit.edu/engage/ask-an-engineer/can-we-calculate-the-efficiency-of-a-natural-photosynthesis-process), single-crystal photovoltaic cells are about 10% efficient while photosynthesis is about 6%. However, photosynthesis absorbs a bigger fraction of the light. If life evolved photovoltaic cells, it would probably come up with some way of enlarging the surface area and trapping the reflections. But our single-crystal voltaic are not very compatible with carbon-based life forms. It seems likely that opsins, the chemicals we use in our eyes to see, may have been a precursor to photosynthesis. They are able to absorb light, and turn it into internal molecular energy. We do not know of anything that uses opsin for gathering energy today, but the blue-sensitive opsin that we have in our S-cone cells is shared with some species where our common ancestor is so far back, it may predate multicellular life. What were single cells using opsins for if not for gathering energy? So, it seems creatures have evolved at least two carbon-based chemical schemes for converting light to energy, and there may be others. If the life forms on your planet are not wholly strange, life may have begun in the darkness, or in deep water, or under clouds where the UV did not penetrate. It might evolve to use the energy from the sun. Sort wavelength light has more energy per photon, so any organic conversion of light to internal energy might use blue light, but avoid the UV which could be harmful. Harvesting energy from red light and IR is harder, but may be possible. There are other strategies: deciduous trees choose to have more efficient leaves with thin surfaces, but up with the extra damage, and scrap them and grow a fresh set each year. Carbon can conduct electricity. Buckytubes may be able to superconduct. It is possible to store magnetic energy as a circulating current in aromatic ring molecules. The European Robin is believed to use [quantum entanglement](https://https:/https://www.wired.com/2011/01/quantum-birds/) to detect tiny variations in magnetic field. It is not impossible to imagine some life-form producing a long photovoltaic fibre like a spider spinning thread. Life will probably adapt to use some energy source when there is nothing better. We have torpedo fish and electric eels that can handle high voltages and currents. But we do not know of anything using photovoltaics. My guess is opsins or chlorophyll or other such molecular photon capture processes are an easier option than photovoltaics. [Answer] Here are some of my reasons and solutions to your problem. Remember, I am an artist, not a safety inspector or physicist, so I like when things catch on fire and/or explode. 1. **Stark White Coloration:** * Flora might have initially evolved to be stark white as a natural defense mechanism against the intense radiation from the high-energy F-type star. White pigments or reflective structures could help dissipate excess energy and prevent damage to plant cells. 2. **Radiation Tolerance and Bioluminescence:** * Plants may have developed bioluminescent cells as a way to cope with the high radiation levels. Bioluminescence could serve to dissipate excess energy and act as a secondary form of energy storage, providing a buffer against extreme radiation fluctuations. ### Transition to a More Stable Star Phase: 1. **Color Adaptation and Evolution:** * As the star transitions to a more stable phase with less intense radiation and solar flares, evolutionary pressures could favor flora that can adapt their coloration. Plants might evolve the ability to change color to optimize absorption of the reduced but still abundant light, maximizing photosynthesis efficiency. 2. **Preservation of Bioluminescence:** * Even in the more stable phase, the ability for bioluminescence may persist due to its dual function as a radiation buffer and a potential means of communication or attracting pollinators during darker periods. ### Electromagnetic Interaction and Non-organic Incorporation: 1. **Integration of Non-organic Matter:** * Given the abundance of electromagnetic interaction due to the silicate iron and obsidian in the volcanic soil, evolutionary processes may lead to the integration of non-organic materials into the flora. Living neodymium-like magnets could be incorporated into the cellular structure, enhancing the electromagnetic properties of the organisms. 2. **Utilizing Electromagnetic Energy:** * Flora and organisms could evolve to harness electromagnetic energy from the soil and other environmental sources, enhancing their overall energy acquisition and utilization. ### Evolutionary Timelines and Selection: * Evolutionary selection during the planet's history and transitional phases of the star could indeed lead to the proliferation and retention of specific traits, like bioluminescence and color adaptation, even after the star stabilizes. Traits that were advantageous during high-energy phases may still confer benefits or versatility in the altered but stable conditions. ]
[Question] [ I've already asked a few questions about Lamia on this site $-$ female hybrids of half snake and human (sort of like mermaids) represented in Alendyias, a world of chaos $-$ only to find myself realizing Lamia are prone to mutations. This isn't usually a problem. One type of mutated Lamia, the Maralith, has six arms, sure, but they make it work. Another type, the Gorgons, have scales all over, claws and fangs and legs, that's different but advantageous. But then we get to Dracenae. Normal Lamia have a serpentine trunk instead of legs, starting below the waist. Dracenae, on the other hand, due to mutation or changes in gene expression, have a pelvis and legs more like normal human's, each ending above the knee and seguing into a serpentine trunk. In other words, they are like the snake-people in the *Percy Jackson* series, but biological and with someone unwilling to just handwave. (Yes I know, that last part is a weakness and I try to be mindful of it.) **My question is, with the single snake trunk split into two smaller limbs, can they move effectively? Or would this mutation effectively cripple them?** To make things clearer, [How would a person who is a snake from the waist down move around?](https://worldbuilding.stackexchange.com/questions/35282/how-would-a-person-who-is-a-snake-from-the-waist-down-move-around) may look similar, but it is not, for the simple reason that a Dracenae has to move with very different appendages below the waist (short legs with snake trunks below the knee, instead of one solid snake trunk). The general idea is the same though, please assume here that the human organs are in the humanoid half as in there. **To clarify further,** these are mutated Lamia, which have single tails of the right length and proportion necessary for balance and movement, and like Lamia they can technically slide on their belly but would rather move more like a cobra, with the upper half reared up. **The only difference** is that these Lamia have rudimentary legs with their snake tail split between the legs, and while I am no expert, I suspect slithering side by side may not work (though if I am wrong, *please* correct me) and walking like a person, in a standing position, will be just impossible. Please let me know if more information is needed, or if the question can be improved, I'm always open to feedback! [Answer] **Underwater** Such 'legs', with some weight assistance from being somewhat buoyant in water, would function well underwater. While I admit that such appendages would be much better suited to simply swimming, they would at least allow a good enough though somewhat slow approximation of upright bipedal locomotion when submerged. **Alternatively, upside-down, in the trees** Depending on the prehensility and overall curl/grip strength of these appendages, they could work exceedingly well in the dracenae's favour as a means of swinging from branch to branch in a forest, and may result in a rather frighteningly fast arboreal creature if they have the appropriate adaptations to handle being upside-down and swinging around almost all the time. Should they find themselves on flat ground they'll be in trouble of course, but so long as they have a network of grippable things to hang and swing from they should be more than fine. **Alright, bear with me, for I have another alternative** All dracanae are double side-winders, with snake trunks whose ventral scales face each other at the knees and whose tails extend out to the sides. Here is an actual side-winder's locomotion: [![enter image description here](https://i.stack.imgur.com/7zdDP.gif)](https://i.stack.imgur.com/7zdDP.gif) Picture the snake's head being where the dracanae's knee is. Now copy/paste it to their other side for the other leg and boom, you've got a creature that moves forward by side-winding both their sideways-stickin'-out snake trunks at the same time. They could also move backwards, or side-to-side like a crab by having one trunk slither forward normally and the other backward(orientation of the ventral scales is key here), or turn by winding one slower than the other, or turn on the spot by only winding one of their legs and anchoring the other. Just about the only issue I foresee with this kind of locomotion is sudden stops, which will topple their top-heavy bodies onto their bellies if they don't stop slow enough or catch themselves with their hands or perhaps a long stick of some sort. [Answer] ## 1) Slithering on both snake-legs simultaneously Both snake-legs are on the ground and each slithers ahead. For an observer it might look similar to a human kneeling on a moving cart: the up and down bobbing from taking steps is missing and the upper body will hardly move (in particular the arms will not be swinging back and forth). ## 2) Slithering on one snake-leg, combined with steps One snake-leg is one the ground and moves ahead by slithering. The other leg is lifted up, pushed forward and put down. Now this snake-leg starts to slither while the first leg takes a step. It might look somewhat like a human (slowly) sliding on ice while feigning taking little steps. ## 3) Walking on "knees" Both legs are moved in turn, the snake-legs themselves are mostly rigid when on the ground. It might somewhat resemble how a human would move when walking on their knees. ## 4) Walking on "hind-snake-legs" Mostly the same as variant 3. But to increase the length of each step (and increase the movement speed) the snake-legs "stand on their tail-end". Not literally on their tail though, that would very likely be not sturdy and strong enough. This might be comparable to a human walking on their toes - possibly a bit wobbly. If the length from ground to hip matches that of a human, this might look very similar to how a human moves. --- I'd speculate that variant 1 is probably the least strenuous, while variant 4 might be reserved for emergencies. Mode 2 is probably the most illustrating - only this species can move in that fashion, neither humans nor lamias can emulate it. ]
[Question] [ One thing I don't see discussed often in regards to naga is how much constriction pressure their tails would have. Given their size, I'd imagine it'd be much more pressure than a green anaconda, which has the highest recorded constriction pressure at 90 pounds per square inch (and coincidentally is also the largest extant snake on the planet). Some back of the napkin math comparing muscle density comes out to about 200 psi for a naga, but that feels awfully little, given their size. Is this estimate accurate, or can it stand to be refined? [Answer] The naga's constriction pressure is not only due to its size, muscles, etc. Naga (at least in the conventional definition) are magical, and semi divine beings. As such, they are supernatural, not simply in the sense of being superhuman. As this stands, there is no way to give a biology or science based answer to this. A 10 foot Naga that is 20 feet wise could have a psi of 400, if it is empowered by magic/divinity. The hybrid nature could go both ways, in terms of strength. In some mythologies, pure bred monsters are stronger, but in others, being bred with a human makes the offspring stronger. Since it is magic, you get to decide whether you want it to be consistent or not. In other words, is magic A always magic A? Or does magic A sometimes follow the rules of Magic B? So in short, since a Naga is a mythical, semidivine, magical being that does not follow any scientific biology, it is up to you to define how much psi the Naga can apply. The magical component makes it so that you have the freedom to establish your own rules. ]
[Question] [ Helioforming is the ignition of gas giants of various sizes, or black dwarves, to create protostellar or even stellar celestial bodies. This can be achieved in two ways: compression or mass increase, both of which elevate the celestial body's density over the critical point for fusion to happen. I have been thinking about a way to achieve this feasibly in a (somewhat) high/hard sci-fi setting and I think I found a solution: dark matter, specifically WIMP dark matter. WIMP stands for Weakly Interacting Massive Particle, a potential candidate for dark matter, which means particles that interact weakly with baryonic matter but possess a considerable mass and thus can create impressive gravity wells while being effectively invisible and intangible. My solution would consist of utilizing technology to manipulate dark matter and deposit a considerable amount of it in a gas giant's core, increasing its mass while not increasing the volume, and thus maximizing density increase, until the ignition point is met. On top of that, since dark matter is much more abundant than baryonic matter, it would be much easier to obtain and use on a truly massive scale. The idea came from the following video [by Isaac Arthur on dark matter technologies](https://www.youtube.com/watch?v=GHXG3xrIDLY) Would such a feat be feasible for a civilization between level 1 and 2 on the Kardashev scale in a setting with physics resembling the real world? [Answer] You could use this method to make a gas giant fuse hydrogen and become a "star", however unless you had some cheap method of keeping the dark matter inside it, the effect would be temporary. Unless WIMPs are heavier than atoms, they wouldn't stay inside a star on their own. A star is not a fire that keeps "burning" on its own; once the planet's mass dropped back to normal it would revert to being ordinary gas. For a long-term star, you'd have better luck adding hydrogen. ]
[Question] [ I have been creating aliens species for a while now, and the idea of a sapient, tool-wielding, spacefaring civilization that doesn’t have arms as we know them excites me. I would like my aliens to have a scientifically plausible design. For simplicity, relevance, and lack of acceptable concept art’s sake, imagine this species as being a cheetah with scales and hooves. I have been trying to design a way for them to have several “tails” that can each be used almost as well as a human arm. I designed a sort of arm-like appendage that had its own shoulder-blade-pelvis structure in the rump, and the “fingers” of that arm were long enough to reach the front of the creature. This is obviously doomed to fail, and I need a better solution. Edit: I had also tried to split the spine into several independent prehensile tails which was even more doomed to fail than the arm-fingers idea. Also, the arm-fingers idea is too similar to actual arms and fingers for my liking. I have seen tentacles be suggested in other questions over prehensile tails, and I am inclined to agree, but how to place several of them on the body escapes me. These creatures are speed based apex predators and as such must be relatively lightweight and aerodynamic. They will use their limbs for hard manual labor, fighting, and tweaking minute computer parts. How many of these limbs are needed is up for debate, but ideally more than one (In concept art I am fond of there being 4 or 6) so more complex tasks can be performed with the limbs working together. I have also become VERY attached of the idea that they can create a whip-crack noise with their tails, but I fear that may not be possible. Important note: they can turn their heads like owls and are remarkably flexible, so the manipulation limbs being located further back is not as much of an issue [Answer] Have you thought of a group tentacles / trunks in place of what would be a lions main? they could fold and weave around it's neck for protection. Perhaps even adding osteoderms to the outside of the trunks for better protection. The trunks could feed into the creatures neck chest and lungs for better air flow when it is in pursuit phase. Then wrap around its prey to help hold onto to, manver, and attain a better grip with its teeth, finding and clamping down on it's preys air pipe during the kill phase. Big fan of Niven,the fithip (sp?) the elephantine aliens with the 2 trunks, mentioned in comments, are one of my favorites. Another are the Moties. hey are engineer type aliens that are asymmetric. 2 small manipulator arms on one side, 1 large gripping arm on the other. like a walking workbench. Perhaps combining the two, with 1 large gripping trunk below the neck, and 2 smaller more delicate on the top and sides of the neck? With all of these appendages, you may want to think of how they are controlled. Ex: > > An octopus' central brain – located between its eyes – doesn't control > its every move. Instead, two thirds of the animal's neurons are in its > arms. “It's more efficient to put the nervous cells in the arm,” said > neurobiologist Binyamin Hochner, of the Hebrew University of > Jerusalem. “The arm is a brain of its own.” > > > [Answer] Your aliens don't have arms, but they could have hydraulically controlled protuberances similar to a [chameleon's tongue](https://reptilis.net/lacertilia/chamaeleonidae/tongue.html) that eject out when needed and stay out for as long as they are needed. Such protuberances would normally be within the body of the alien. At the end of each protuberance finer hydraulic control systems would allow the formation of a hand like structure capable of gripping with between two and four hydraulically formed finger like appendages and a hydraulically formed thumb or thumbs. The other option is telekinesis. [Answer] # Any of your previous ideas, minus the hard labour Personally I think you're overlooking the intelligence of the creatures in their manipulation efforts. They don't need to *do* heavy labour. They need to be smart enough to *handle* it. The difference is that you use your environment to assist you. How many humans are required to unload a container ship? An insane amount if done manually, a fraction if aided by machines. There is no reason a space faring civilization needs to do heavy manual labour. Possibly even when they were still evolving they quickly invented things to assist them. That means your creatures can have minute and adaptive manipulation appendages of your chosing. The rest of the environment is molded by them for their needs. Items up to a certain size and weight are mostly created to be picked up and handled by their appendages. After that they are created in a way they can be picked up by other mechanisms. Like box can be picked up by a forklift. This makes the distinction between humans and your aliens also better. Instead of having a human reference point of what your aliens should handle or carry, you have their viewpoint. They can still be incredibly skillful and well adapted to do all tasks via mechanical support, but personally they won't be hauling heavy stuff. This also makes sense evolution wise. You can't have one creature do it all. You need to balance it's capabilities with efficiency. [Answer] # tHINk aLieN: You are limiting yourself to imagining Terrestrial biology. Think outside the box! Just because it doesn't exist here doesn't mean it can't in a completely different biology. For example, what if their "bones" are more like pipes carrying hydraulic fluid? Limbs wouldn't have muscle, but instead they would have a pressure chamber in their torso that forced fluid through whichever pipe lead to the limb that needed to move. Fingers, for that matter, could be light inflatable tubes whos shape is controlled by which valves are open or closed. For that matter, what if the joints were rotational rather than hinged, and operated like tiny rotors driven by pressure? And/or the limbs could be grown but not alive like hair, if you wanted. The limbs could consist of pairs of rotating forks, and additional forks at the end of forks spread out like fans for delicate work. Your cheetah-lizard-goats could even have wheels. What a leg up (pardon pun) when they hit an industrial revolution. This is just one idea, but mostly I would urge you to remember that you are talking ALIEN, and they don't need to be limited by our ideas of what biology should or shouldn't be. ]
[Question] [ Considering the impressive complexity of the vast mycelium networks that permeate the world, I was wondering if it would be possible for a civilization to use mycelium as a "coding" mechanism to create organic technology. Perhaps, they develop an "internet" of sorts using mycelium networks as a basis. Their use of metal would largely be limited to war technology, but they would largely be an organic civilization. Is this possible? [Answer] **Drugs. Maybe Houses Too.** The only example that comes to mind is how Penicillin is produced by a fungus. It is believable that other funguses could be genetically modified to produce other useful drugs. Of course this is a far-cry from a fungus-only tecnholosphere. It is much harder to believe the things they used to design the drugs or genetically modify the fungus are themselves made of fungus. Perhaps if your aliens are able to intuitively interface with other life forms (See Lillith's Brood) on a cellular level then this becomes more believable. Anything other than chemical manufacture sounds unbelievable. It does sound like a lot of fun though. I want a world where people drive around in big mushrooms and live inside even bigger mushrooms. [![enter image description here](https://i.stack.imgur.com/Clyzb.jpg)](https://i.stack.imgur.com/Clyzb.jpg) Zoom zoom losers here I come. Get on it. --- **Extra:** As Demigan points out, it is believable that specially bred fungus is used as a building material. For example you build a mesh frame over a hillock and then impregnate it with spores. The fungus draws nutrients from the soil and eventually makes a hard dome around the hill, complete with foundations that extend into the soil. Then you dig out the hill and live inside. It is difficult however to imagine why people would build their houses like this in the first place. It requires generations of breeding fungus. It also requires to build the frame out of *SOMETHING*. Why not just build the whole house out of that something? Perhaps there is simply not much wood or stone in the environment. [![enter image description here](https://i.stack.imgur.com/CxcAQ.png)](https://i.stack.imgur.com/CxcAQ.png) [Answer] Have you ever heard of the Yuuzhan Vong from Star Wars? They had an entirely organic tech tree, so maybe take some of their ideas (amphistaffs for weapons and door membranes?). Additionally, it’s your magic world, fungus can do whatever the heck you want it to do. ]
[Question] [ i'm in the early stages of designing a scifi game and want to use as little handwavium as possible (without ruining the fun). The first part of the game takes place in the asteroid belt and includes handwavium in the form of being able to break down just about anything into individual atoms and using a 3d printers make everything from an ingot to a fighter craft. The intended reaction mass is blocks made of ~11.75% Invar (FeNi 64/36% 8,100kg/m³ specific heat capacity peaks at 545j/kg K at 200C Curie temp of 230C) ~88.25% silica harvested from asteroids. Depending on the ship the blocks may be as small as 0.01m³ ~30kg or as large as 1m³ ~3,000kg. I had the thought of hitting the pellets with high powered lasers and feeding the resulting plasma through a [VASIMR thruster](https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket). Or lunching the pellets with a coilgun and hitting them with lasers in something akin to a rocket nozzle to direct the expanding gas while avoiding the whole chunks of very high speed material flying around the solar system. Would the expanding gas cause more thrust than just the momentum from the magnetic acceleration? The smallest drone has a single 5m long coil, followed by quad 20m, quad 40m, and eight 60m for the largest thrusters. Backstory Edit: Your ship was sent in advance to build the infrastructure for our first colony at Proxima b. The follow on ship with the colonists was scheduled to arrive 1 year after you but after 2 years the captain decided to head back and find out what was going on. FTL comms don't exist and the experimental FTL drives that we were testing maxes out at 2c and only works in interstellar space so the crew was all in cryo sleep for the trip. When you wake up you find the ship is badly damaged and floating in the asteroid belt. Edit 2: FeNi 64/36% means the alloy is 64% iron 36% nickel. 8,100kg/m³ means a cube that is 1 meter on each side has a mass of 8,100 kg. Specific heat capacity is how much energy you can pump into the material to heat it 1C (or K). The higher it is the more you can heat it can absorb without losing necessary properties like... Curie temp is the temperature that a magnetic metal rapidly loses it's magnetism. [Answer] **Induction furnace / coilgun hybrid.** I wince at lasers and fast moving pellets. Much waste, much danger. The horror of moving parts! I propose instead that you melt your reaction mass using an [induction furnace](https://en.wikipedia.org/wiki/Induction_furnace). > > An induction furnace consists of a nonconductive crucible holding the > charge of metal to be melted, surrounded by a coil of copper wire. A > powerful alternating current flows through the wire. The coil creates > a rapidly reversing magnetic field that penetrates the metal. The > magnetic field induces eddy currents, circular electric currents, > inside the metal, by electromagnetic induction.[9] The eddy currents, > flowing through the electrical resistance of the bulk metal, heat it > by Joule heating. > > > [![induction forge](https://i.stack.imgur.com/7JJgg.jpg)](https://i.stack.imgur.com/7JJgg.jpg) <https://interestingengineering.com/video/this-steel-bar-gets-heated-up-in-only-12-seconds-using-an-induction-forge> No waste. Nothing moves. Electricity makes molten metal. I thought maybe the induction furnace and coilgun could share the same coil which would be elegant. But the furnace is AC and AC is no go for a coilgun, or if go, go back and forth very fast. So they would have to be closely approximated coils. And that is fine because the electrical needs are different. Here is a nifty thing. As the heated mass turns to liquid, glowing drops are pulled off the main mass and into the coilgun, then fired out the back of the ship. <https://en.wikipedia.org/wiki/Coilgun#Non-ferromagnetic_projectiles> > > By having the projectile pulled towards or levitated within the > center of the coils as it is accelerated, no physical friction with > the walls of the bore occurs. If the bore is a total vacuum (such as a > tube with a plasma window), there is no friction at all, which helps > prolong the period of reusability > > > Hopefully the stuff stays mixed so the conductive metal components can pull along entrained silicates and their mass. This setup lends itself to a cutscene showing the ingot in the coil as it begins to glow, then shed glowing globules into the coilgun and out the back. [Answer] Vasimir might be the better option in the sense that on paper at least easily tunable when it comes to your rocket thrust/efficiency ratio. My (lay) opinion would be that assuming the two competing drives are more or less equal in all important metrics the issue with pellet drive would be varying the trust efficiently. Varying the size of the pellets is impractical which leaves varying the power output of the laser, pellet ejection rate and/or perhaps the strength of the magnetic field in the nozzle. Which is not to say it any or all of the above couldn't be done. Just that engineering that aspect of the drive might be 'simpler' with Vasimir ]
[Question] [ In my story, mages are only able to cast spells through a technological device (I imagine it as something similar to a watch). The source of their magic is a region in the brain capable of producing non-physical neural particles that, when filled with "intent", are capable of manipulating energy and matter. All human beings produce these particles to a greater or lesser extent, which disperse randomly in the environment. For this reason, even if, for example, a mage focused on an object and tried to move it, its scattered particles would not be sufficient in strength and quantity to do so. Therefore, it is necessary to use a technological device that channels a sufficient amount of particles to reach the target. This device works on the basis of an ore that will have great economic and geopolitical importance in my story, but I'm not sure how to explain its relation with neural particles. I thought about the possibility that it for some reason attracts them through its radiation or the technology inside the device is simply made of this material, something like the use of rare earth ores in the production of high technology, being essential for the transformation of the particles and their intent into a sort of code with coordinates with the target's location and the spell's ultimate goal. At first these are just ideas and I don't know if they even make any sense. I want to find an explanation that is as realistic and scientific as possible, but because I understand little of the subject, I end up finding some difficulty. How could this device work and what could be the relation between the ore that composes it and the neural particles? [Answer] **Your device is an analogue to a [polarizing filter](https://en.wikipedia.org/wiki/Polarizing_filter_(photography)).** A polarizing filter is a passive device that allows some light to pass through it and blocks other light, depending on its polarization (the orientation of its waveform, loosely speaking). It is useful for when we want to selectively reduce a uniformly polarized component of incoming light (like the glare of reflected sunlight, for example) while allowing disorganized, ambient light to pass through in greater proportion. **Since you compare your "neural particles" to photons, perhaps you can handwave similar properties for them - analogues to wavelength, energy, and polarization** - and have these properties contain the information that corresponds to the intention (or lack thereof) of the mind that generates them. **Let's further handwave that the intent to do "magic" is encoded in the neural particles' "polarization"-analogue property.** Consider the following model: 1. A normal mind, or a mage's mind when not focusing on doing magic, produces neural particles (NPs) that are not polarized in any particular direction. Their polarization is distributed in relatively uniform randomness, and they all cancel each other out - no magic, deliberate or otherwise, is done. 2. A mage's mind, when focusing on an object with the intent to work magic upon it, bombards the object with a concentrated stream of NPs, all polarized in a particular direction which corresponds to the mage's intent. Unfortunately, due to an unhappy coincidence of physics (perhaps some sort of conservation law), NPs are always created in pairs with opposite polarization. So even though the mage is sending a beam of NPs that would accomplish the magic they desire, they are also unintentionally sending a beam that has the exact opposite effect. So the two beams cancel out and no magic is done. 3. The same as case 2, but now the mage has positioned your device, made of the rare ore, in between their brain and the target object of their magic, in a specific orientation or using a specific configuration. The NPs polarized according to the mage's intentions pass through the device, reach the target and take effect, but the oppositely-polarized NPs are blocked by the device. Magic is accomplished! Possible points to consider: * **Why the rare ore? How does the device work?** Your rare ore, when processed with the proper metallurgy, forms a crystal lattice with the unusual property that it selectively blocks some NPs and passes others. However, it need not be passive filtering like a real-life polarization filter for light, where the only thing that matters is physical orientation. You're hand-waving the physics of the NPs, so you can choose to have the device need to have electricity or magnetic fields (or whatever else) applied to make it operative. * **If the unblocked beam's magic does work on an object, where does the blocked beam's energy go?** If you want some elegance in your handwaved physics, perhaps your filter heats up as it blocks NPs, proportionally to how much work is done by the unblocked beam. Maybe your device would have a heat sink or cooling system attached to prevent it overheating and breaking or becoming ineffective. * **If this device blocks your own anti-magic, maybe it can block your opponent's magic.** If magi are fighting each other, their devices may be useful not only to enable their own magic, but perhaps could also be used to protect themselves or other targets from an opponent's magic. ]
[Question] [ Suppose we grant a 1 time scientific miracle for exotic matter to power Alcubierra wrap drive, then could two such drives communicate with each other? The drive discharges exotic matter particles around the spaceship and caused a massive distortion of spacetime, could the spaceship still communicate with outside world where the distortion gets attenuated and is barely noticeable. Communication can be in the form of electromagnetic waves or gravitational wave, I have a chasing scene and a kamikaze scene. The chasing scene shows a superior drive catching up to the other drive and the kamikaze scene is where both drives meet in a awe inspiring dramatic head on collision. If the answer is a radio silence then I will not need the scenes anymore. [Answer] ## No need to use radio or any medium Suppose your ship has an Alcubierre drive. Its propulsion is based on a space time warp. The ship will deform space time in its vicinity, to be able to travel faster than light, it manages to deform surrounding space time so the ship will cross more of it per time unit. It takes shortcuts, it gets detached from space time, translated.. [![enter image description here](https://i.stack.imgur.com/jf7g6.png)](https://i.stack.imgur.com/jf7g6.png) **Range of influence** The scale of above picture is far off reality.The range of space time deformation can't be anywhere near to the ship, its gravitational field (gradient, or the exotic matter, as you like) would destroy it. The range of space time bending must be considerable, multiple AE's around the ship, when fully unfolded (interstellar) An Alcumbierre drive cannot start full power anywhere near an inhabited planet, its gravitational waves would deform it. **Kamikaze or chase** In a kamikaze (approach) the travel speed of both ships will increase ! On distances of multiple AE's, the drives would find extra space time deviation and accellerate, because the forward deviations in space time caused by the ships enhance eachother! Same sign! I wonder if a real "Kamikaze" would even be possible, or the move can be controlled on the kamikazing ship. The probability of an actual collision at FTL speed is quite small and may invoke time paradoxes (?) When a chase happens, there could be another issue. The two ships cannot be anywhere near each other, the gradient on the back will be opposite.. the Alcumbierre drive will partially compensate that bump, with energy loss.. and both ships would decellerate. Sign is opposite! **The other ship is very aware of your presence, instantly** Now suppose.. in more peacefull circumstances.. you have another ship, also with Alcubierre drive.. the deformation of space time caused by your ship is instant, and it must be added to the existing shape of space time. That counts for both ships. Therefore, the other ship will know exactly where you are, and what your vector of travel is. It will need that information, to accurately adjust its own space time deformation. Other ships know your travel plan in detail.. and they can adjust their field to your presence, you need to adjust your field to theirs. These adjustments need to happen high speed, instantly, and full automatic. **For communication, an Alcubierre drive has a separate frequency modulation option** Deformations will occur instantly, everywhere in space time. All the Alcubierre drive needs to do for "communication", is to provide some high frequency modulation component.. and use its field generator to transfer information, as an additional deformation in space time. As it happens instantly, that is how Alcubierre ships can communicate instantly. The modulation (information) itself cannot be fast, but a sound channel, say 16kHz sampling, or 38 kBaud digital information transfer may be feasible. Say 2-5 telephone connections, or 200 sensor channels.. [Answer] An Alcubierre drive distorts the fabric of space-time in order to move a pocket of space-time and its contents. However, neither the ship nor its bubble of space-time moves, so while the ship and its warp bubble moves relative to other objects, at any instant, it is also stationary. Additionally, while the drive fields cause a positive distortion in front of the ship and a negative distortion behind the ship, these distortions are no different to a gravity field save that the front field is positive, and the rear field is negative. The fields need not be so strong that they become an artificial black hole and white hole. Given these facts, it can then be seen that electromagnetic radiation would be able to both enter and leave the warp bubble. The ship would be visible within its bubble, if only briefly to a stationary observer, As radio waves are a variety of electromagnetic radiation, if an Alcubierre warp ship is emitting radio transmissions, they will escape the warp bubble, and could be detected from another Alcubierre warp ship. The positive and negative gravity fields of the warp ship may cause gravitic lensing, but they won't prevent detection, and neither will the drive cause red- or blue- shift. If a receiver is aboard another warp-ship, as long as the receiving ship is behind the transmitting ship, detection would be possible. ]
[Question] [ I am writing a science fantasy book that takes place on the planet Luyt (inspired by Luyten B/Gliese 273b). Because the orbital period of the planet is about 18.6 days and I have chosen to make the Luyt-Luyten's Star Spin-Orbit Resonance 4:1, there isn't a great natural way to mark days for the humanoids that have been transplanted here. I want to have a series of satellites that mark time for the inhabitants of Luyt. The year on Luyt is 336 days, 4 x 84 seasons. Each season is comprised of three 24 day months followed be a 12 day festival. To mark this time there are four groups of satellites (inner, darred, rudden, and outer). There are 3 to 4 satellites in each group. Each group revolves around Luyt at a different distance and a different velocity. | Lunar Group | Orbital Period in Luyten days | Range of the Orbital radius (km) | | --- | --- | --- | | Inner | 4 | 0 - 1 x 10^7 | | Darred | 12 | 1 x 10^7 - 2 x 10^7 | | Rudden | 24 | 2 x 10^7 - 3 x 10^7 | | Outer | 84 | 3 x 10^7 - 4 x 10^7 | Model: <https://www.geogebra.org/m/ptwk37u9> Essentially, I am trying to make a calendar clock with 14 hands out of a planet and satellites. If this calendar is not perfectly accurate, that would actually add to the story (as festivals could be variable length by minutes, hours, or even a day or two to adjust to the placement of the satellites). i.e.: Sommer-fest ends on the syzgy of the moons Merieke and Onadar. My background is in Mathematics and Computer Science, not Physics or Astronomy. My blundering research leads me to believe that the placement of satellites around a planet is much more complicated than can be accounted for by far future "hand-wavy" science. Questions: 1. Can a planet as close to it's sun as Luyten B is to Luyten's star have any satellites? 2. Can a series of 14 satellites have anything even close to this relationship (i.e.: make a calendar clock)? [Answer] Short Answer: Your desired orbits for your moons present some problems, but I suggest some possible solutions. Long Asnwer in Five Parts: You may want to consider where you want your story to be on the scale of science fiction hardness. <https://tvtropes.org/pmwiki/pmwiki.php/SlidingScale/MohsScaleOfScienceFictionHardness> Part One: Orbital problems. The rings of satellites would have to orbit within the Hill sphere of your planet, the zone where satellites can have stable orbits. According to Wikipedia: > > The Hill sphere for Earth thus extends out to about 1.5 million km (0.01 AU). The Moon's orbit, at a distance of 0.384 million km from Earth, is comfortably within the gravitational sphere of influence of Earth and it is therefore not at risk of being pulled into an independent orbit around the Sun. All stable satellites of the Earth (those within the Earth's Hill sphere) must have an orbital period shorter than seven months. > > > <https://en.wikipedia.org/wiki/Hill_sphere#Formula_and_examples> The large size of Earth's Hill sphere is somewhat favorable for your satellite set up. However, the more massive a star is, the more luminousit is and the father away its habitable zone is, and the less massive a star is, the less luminous it is and the closer its habitable zone is. And the relationship between the mass of a star and its luminosity (and thus the distance at which a planet can orbit in the habitable zone), is not linear. A small difference in the mass of stars creates a larger difference in their luminosities. So planets which orbit stars of different luminosity at the distances where they receive the same amounts of radiation from their stars will not experience equal gravitational and tidal foreces from their stars. Planets orbiting dim red dwarf stars in their habitable zone will be orbiting where the gravity of the itheir stars is much stronger than the Sun's gravitational pull on Earth. That is why it is usally believed that most or all planets that close to red dwarf stars will have become tidally locked to their stars, though your planet seems to have a rotational period/orbital period resonance instead. As the Wikipedia article explains, the size of a planet's Hill sphere depends on the mass, of the star, the mass of the planet, and the semi-major axis of the planet's orbit. According to the simplified equation used for low eccentrity orbits, the radius of a planet's hill sphere will be approximately equal to the semimajor axis of the planet's orbit multipled by a number which is the cube root of the ratio of the planet's mass to three times the star's mass. Luyten b has s masss of 2.89 plus or minus 0.26) that of Earth - 2.63 to 3.15 the mass of Earth. Having a higher mass than Earth's is good for having a large Hill Sphere. Luyten's Star has a mass of 0.26 times the mass of the Sun. The star having a lower mass than the Sun is good for the planet having a large Hill sphere. The orbit of Luyten b has a semi-major axis of 0.09110 AU. Having such a small semi-major axis is bad for the planet having a large Hill sphere. According to my rough calculations, the Hill sphere of Luyten b should equal approximately 0.0211 to 0.0223 of the semi-major axis of its orbit around Luyten's Star. Thus the Hill spere of Luyten b should have a radius of approximately 0.0019222 to 0.0020215 AU, or approximately 287,557.0271 to 302,412.0956 kilometers. I found an online Hill sphere calculator: <https://www.vcalc.com/wiki/KurtHeckman/Hill+Sphere+Radius> It gives the Hill sphere radius of Luyten b as approximately 265,362.19277423 to 281,810.59421183 kilometers depending on the mass entered for Luyten b, a bit smaller than my calcuations. If the mass of Luyten b is exactly 2.89 that of Earth, the radius of the Hill sphere would be 273,833.39572197 kilometers. > > The Hill sphere is only an approximation, and other forces (such as radiation pressure or the Yarkovsky effect) can eventually perturb an object out of the sphere. This third object should also be of small enough mass that it introduces no additional complications through its own gravity. Detailed numerical calculations show that orbits at or just within the Hill sphere are not stable in the long term; it appears that stable satellite orbits exist only inside 1/2 to 1/3 of the Hill radius. The region of stability for retrograde orbits at a large distance from the primary is larger than the region for prograde orbits at a large distance from the primary. This was thought to explain the preponderance of retrograde moons around Jupiter; however, Saturn has a more even mix of retrograde/prograde moons so the reasons are more complicated.[3](https://www.vcalc.com/wiki/KurtHeckman/Hill+Sphere+Radius) > > > <https://en.wikipedia.org/wiki/Hill_sphere#True_region_of_stability> So if Luyten b has a mass of 2.63 Earth mass the outer edge of its region of true stability would be between 88,454.063 and 132,681.09 kilometers. So if Luyten b has a mass of 2.89 Earth mass the outer edge of its region of true stability would be between 91,277.796 and 136,916.69 kilometers. So if Luyten b has a mass of 3.15 Earth mass the outer edge of its region of true stability would be between 93,936.863 and 140,905.29 kilometers. Using this orbital period calculator, and using the mass range of Luyten b, and setting the mass of a satellite as 0.1 that of the moon: <https://www.calctool.org/CALC/phys/astronomy/planet_orbit> If Luyten b has a mass of 2.63 Earth, a satellite at the edge of its region of true stability would have an orbital period of 1.86785 to 3.43147 Earth days. If Luyten b has a mass of 2.89 Earth, a satellite at the edge of its region of true stability would have an orbital period of 1.86789 to 3.43154 Earth days. If Luyten b has a mass of 3.15 Earth, a satellite at the edge of its region of true stability would have an orbital period of 1.86793 to 3.43160 Earth days. So the outermost satellites of Luyten b in long term stable orbits would have orbital periods of 1.86785 earth days or 44.8284 Earth hours to 3.43160 Earth days or 93.653282.3584 Earth hours. There is another calculation to make. Heller and Barnes, in "Exomoon habitability constrained by illumination and tidal heating", 2013: <https://faculty.washington.edu/rkb9/publications/hb13.pdf> On page 20, say: > > The longest possible length of a satellite’s day compatible with Hill stability has been shown to be about P)p/9, P)p being the planet’s orbital period about the star (Kipping, 2009a). > > > Since you want the orbital period your planet to be about 18.6 Earth days, and since Luyten b has an orbital period of about 18.650 Earth days, the longest orbital period of a moon in a stable orbit around it would be about 18.650 divided by 9, or 2.072222 Earth days. Their source is: Kipping, D.M. (2009a) Transit timing effects due to an exomoon. Mon Not R Astron Soc 392:181–189. And here is a link if you want to follow what Kipping says: <https://arxiv.org/abs/0810.2243> I believe that you want there to be 4 days of your planet in one orbital period. If th orbitalperiod is 18.650 Earth days, the planetary days will be about 4.6625 Earth days long, which is about 2.25 times as long as the maximum stable orbital period of about 2.072222 Earth days days. And you want the rings of satellites around your planet to have orbital periods of 4, 12,24, and 84 Luyten days, which would equal 18.65, 55.95, 111.9, 391.656 Earth days. All of which are several times, or tens of times, or hundreds of times as long as the maximum periods of long term stable satellites around Luyten b or any world with a similar mass in a similar orbit around a similar star. Part Two: Trojan Moons. There is one bright side: You desire 14 satellites in 4 groups, which makes 2 groups with 3 satellites and 2 groups with 4 satellites. And a group of three satellites sharing the same orbit is perfectly possible. There could be a large moon orbiting your planet, with two smaller moons in two of its Lagrange points, the L4 and L5 points, 60 degrees ahead of and 60 degrees behind the large moon in its orbit. That is called a trojan orbit. So each of those three moons would be seen in the same relative position at regular intervals equal to 1/6 th of the orbital period at that distance, followed by no moons for the other 4/6 th of the orbital period. And there actually is an example of a planet in our solar system which has two different moons that each have two smaller moons in trojan positions. Tethys has 2 trojan moons ahead and behind it, and Dione has two trojan moons in its orbit. But there is a problem. Caculating the stabiity of trojan orbits is said to be complex, but there is a rule of thumb about the relative masses of the objects for stable orbits. > > As a rule of thumb, the system is likely to be long-lived if m1 > 100m2 > 10,000m3 (in which m1, m2, and m3 are the masses of the star, planet, and trojan). > > > <https://en.wikipedia.org/wiki/Trojan_(celestial_body)#Stability> In this case m1 is your planet with 2.63 to 3.15 the mass of Earth, m2 is the large moon in orbit with less than 0.0263 to 0.0315 the mass of Earth, and m3 would be one of its trojans with mass less than 0.000000263 to 0.00000315 the mass of Earth. If one of the small trojan moons had less than one millionth the mass of your planet, and if it had the same density, it would have one millionth the volume of your planet and thus one hundreth of its diameter. Luyten b is likely to have less than 1.5 the radius of Earth, and so hypothetical trojan moons of Luyten b would be likely to have a diameter of 0.015 the dddiameter of Earth or less - a diameter of 191.13 kilometers or less. So they would appear as bright dots of light or as small extended objects in its sky. Another big problem with having 2 of your sets of moons being larger moons with 2 trojans each is that trojan objects do not stay exactly in the L4 and L5 positions. Instead they tend to wander away from them and back again. Thus you could not count on the trojan moons always being exactly 60 degrees ahead of or behind the larger moons. That would not be very good for calendars! Part Three: Rings of Moons. sean Raymond's PLanetplanet blog has section The ULitmate Solar system, where he tries designing scientifically plausible solar systems with as many habitable worlds as possible. <https://planetplanet.net/the-ultimate-solar-system/> In the ultimate engineered solar system he says that a paper by Smith and Lissauer shows that equally spaced and equally mass planets can share an orbit around a star. They calculated stable orbits for 7 to 42 planets sharing an orbit. <https://planetplanet.net/2017/05/03/the-ultimate-engineered-solar-system/> <https://ui.adsabs.harvard.edu/abs/2010CeMDA.107..487S/abstract> So you could put a ring of 7 to 42 equally massed and equally spaced moons around your planet, separated by 8.5741 to 51.4285 degrees. Assuming that the total mass of the ring should be less than about 10 percent of the mass of your planet, each moon could have no more than about 0.00238 to 0.01428 the mass of your planet, and thus no more than about 0.0062594 to 0.0449 the mass of Earth. Assuming that each moon had the same average density as Earth, their volume would be proportional to their mass relative to Earth. They could have diameters no more than 0.18429 to 0.3555 that of Earth, or no more than 2,348 to 4,529 kilometers. So their maximum possible diameters could be similar to that of the Moon, and they would probably be only a fraction as distant as the Moon is from Earth, so they might be as impressive or even more so than the Moon seen from Earth. So if you can figure out a way to use a ring of 7 to 42 moons sharing the same orbit equally spaced along it in your calendar, this may be useful to you. And of course it would be extremely improbable for a planet to naturally acquire or form a ring of equally spaced and equally massed moons. Theodds agains that happening naturally would be astronomical. So it would be very probably that any such ring of moons around a planet wwould have been created artifically by an advanced civilization for some purpose. Part Four: Synodic Periods. Did you know that astronomical objects, like the planet Earth, have different types of days, and different types of months, and different types of years, and that the differences betweent the lengths of those periods is important for constructing a calendar? A sideral day is the natural rotation period of a world, the time it takes to rotate 360 degrees of arc with respect to the distant background stars. The sidereal day of Earth is about 23 hours, 56 minutes and 4 seconds long, or about 86,164 seconds long. There are about 366.25 sidereal days in an Earth year. So during each sidereal day the Earth moves about 0.98 degree in its orbit around the Sun. So when a sidereal day is completed, and a point on the surface which pointed directly at the Sun at noon is now pointed at the exact same direction relative to the stars, the direction to the Sun has moved by almost one degree, and Earth has to turn for about 4 minutes and 56 seconds more until that point on the surface is pointed directly at the Sun again. So the solar day, the amount of time it takes for the Sun to more 360 degrees as seen from a point on the surface, equals 24 hours, and there are about 365.25 solar days in an Earth year. <https://en.wikipedia.org/wiki/Sidereal_time> Apparently there are five types of months of different lengths in astronomy: > > The following types of months are mainly of significance in astronomy, most of them (but not the distinction between sidereal and tropical months) first recognized in Babylonian lunar astronomy. > > > The sidereal month is defined as the Moon's orbital period in a non-rotating frame of reference (which on average is equal to its rotation period in the same frame). It is about 27.32166 days (27 days, 7 hours, 43 minutes, 11.6 seconds). It is closely equal to the time it takes the Moon to pass twice a "fixed" star (different stars give different results because all have a very small proper motion and are not really fixed in position). > > > A synodic month is the most familiar lunar cycle, defined as the time interval between two consecutive occurrences of a particular phase (such as new moon or full moon) as seen by an observer on Earth. The mean length of the synodic month is 29.53059 days (29 days, 12 hours, 44 minutes, 2.8 seconds). Due to the eccentricity of the lunar orbit around Earth (and to a lesser degree, the Earth's elliptical orbit around the Sun), the length of a synodic month can vary by up to seven hours. > > > The tropical month is the average time for the Moon to pass twice through the same equinox point of the sky. It is 27.32158 days, very slightly shorter than the sidereal month (27.32166) days, because of precession of the equinoxes. > > > An anomalistic month is the average time the Moon takes to go from perigee to perigee—the point in the Moon's orbit when it is closest to Earth. An anomalistic month is about 27.55455 days on average. > > > The draconic month, draconitic month, or nodal month is the period in which the Moon returns to the same node of its orbit; the nodes are the two points where the Moon's orbit crosses the plane of the Earth's orbit. Its duration is about 27.21222 days on average > > > <https://en.wikipedia.org/wiki/Month> there are more than 13 sidereal months in an Earth year but about 12.3 synodic months in that period. Wikipedia lists 10 different types of astronomical years: <https://en.wikipedia.org/wiki/Year#Astronomical_years> And these can be usefull in constructing a calendar which uses a "year" that is much longer than the actual orbital period of your planet. The period it takes a moon to orbit a planet once depends on the mass of the planet and the distance of the moon from the planet. The rotation rates of planets vary greatly, but every planet has a distance at which a moon orbiting above the equator would be in a geostationary orbit and would always seem to have the same position in the sky, though the stars would move behind it. A moon orbiting closer than that geosynchronous orbit would have a sidereal period shorter than a day, and a moon orbiting above the geosychronous orbit would have a sideral period longer than a sidereal day. The farther inside or outside the geosychronous orbit the moon orbited, the greater would be the difference bwweenits orbit and a day - and thus the shorter would be the difference between its synodic period and a day. For example, if the moon took 100 days to compete one orbit, it would take the world only a little more than one day to get ahead of the moon and then catch up with it again. But if the moon took only 0.99 days to complete one orbit, each day the moon wouldd would get 3.6 degrees ahead of the turn world, and after about 100 days the moon would catch up to the turning world and would be in the same position in the sky again. And if one moon takes 2 days to orbit the planet, and another moon takes 2.1 days to orbit the planet, the inner moon will orbit 180 degrees in 1 day and the outer moon will orbit 171.42857 degrees in 1 day. Each day the inner moon will get 8.57143 days ahead of the inner moon, until after about 41.9999 days, or 42 days if people round up, the inner moon will over take the outer moon and they will be in their same relative positons as when they started. So if you want to create a calendar period or "year" which is many planetary orbital periods long and equals 336 Earth, or 336 Luyten b days, you can calculate some relationships between the planetary rotation and an orbital period of a moon, or the orbital periods of two or more moons, which has that length. Part Five: Artificial Satellites. In *Star Trek: The Original Series* The *Enterprise* ws often said to be "orbiting" a planet. But when the ship lost pwoer, the orbit immediately started to decay, unlike a realistic orbit. So possibly those alleged "orbits" involved the starship using its engine power to constantly hold itself up while circling at a speed much less than the orbital speed at its distance. So possibly the satellites that the settlers on the planet use for their calendar are spacecraft of some kind, which trave in circles around the planet at speeds different from the orbital speeds at their respective distances from the planet. Those spcef craft could travel around the planet low and be very large, and so be visible from the surface. Or they could "orbit" very high, and shine very bright lights down at the planet, so those lights can be seen from the surface. And possibly those spacecraft were built by the colonists to serve as factors in their calendar. Or possibly they were left behind by an advanced civilization that the colonists know nothing about. Conclusion: There are a number of problems with your moons, but I have suggested some possible ways to get around them. [Answer] You can answer this question fairly easily yourself, if you have a mathematics background. First, you need to determine the size of your planet's [Hill Sphere](https://en.wikipedia.org/wiki/Hill_sphere), using the formulas in that article. You need to decide on your planet's mass to do that, because we have only a vague idea of that from astronomy. That gives you the maximum distance from your planet that satellites can reach without coming loose from the planet and going into orbit around the star. You can then calculate the [orbital period](https://en.wikipedia.org/wiki/Orbital_period) for a circular orbit of that radius using the formula in that article. I suspect you'll find that your planet can have satellites, but they can't have orbital periods nearly as long as you want. However, there's a different problem with this piece of worldbuilding. Having so many satellites with periods that are an exact number of local days screams "this is artificial." It will be *obvious* to the reader that these satellites were carefully placed by someone or something with considerable power. If that isn't the case in your story, the reader will have a major red herring to cope with; if it is, you're betraying the existence of those powers as soon as the reader finds out about the orbital periods. ]
[Question] [ This is related to my previous question: [How many survivors would grow on earth years after a worldwide nuclear holocaust?](https://worldbuilding.stackexchange.com/questions/220975/how-many-survivors-would-grow-on-earth-years-after-a-worldwide-nuclear-holocaust) In an earth with roughly a billion modern day survivors, and 20 million former USA citizens are trying to survive and organize themselves after nuclear holocaust, which areas (specifically the area in the former USA) would have the greatest success during the 10 year nuclear winter (soon turning into cities)? For example, those living in the center of a large area of good farmland, for instance, will always have an advantage over those who are alive in the middle of the Appalachian or Rocky Mountains, simply because they've got a food advantage. As such, to be considered successful, the areas need to have a relatively staple production (or import) of food in order to maintain and grow the population. Also, areas more likely to recover and/or to turn into cities (and therefore with higher population) will be considered more successful. In case it is not possible, consider the areas with the lowest decrease in population and highest sustenancy instead (even if it is insufficient). This is under the assumption that large population centers like Chicago, New York, military installations, etc, were specifically targeted by nukes. By large, I mean greater than 500k population. For reference, the nuclear strikes started at January 1 2020, and targeted specific countries such as USA, Canada, Russia, China, UK, France, India, Pakistan, Italy, Iran, Korea, Israel, Saudi Arabia. [Answer] The numbers in the question (10 year-long nuclear winter and 500k+ population cities being destroyed) suggest that the OP is thinking about the global all-out nuclear war. These [two](http://climate.envsci.rutgers.edu/pdf/RobockNW2006JD008235.pdf) [papers](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JD030509) are based on a similar scenario. The main difference is that Day 0 is the 15 May while in the OP's scenario Day 0 is the 1 January. I strongly recommend reading these papers. [This article](https://www.ncbi.nlm.nih.gov/books/NBK219156/) suggests that if the nuclear war starts in January, soot will be removed from the atmosphere faster compared to July. The figures shown in the article are based on the 1986 model which is not as accurate as models used today. I also did not find any new studies modelling winter-time nuclear war. Therefore, it is hard to estimate how much milder the consequences of the January-start all-out nuclear war will be compared to the May-start all-out war. Contemporary models suggest that even a [limited regional nuclear conflict](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013EF000205) would result in climate change, massive ozone loss, and global famine. --- *In the worst-case scenario* (similar to projections in the first two papers linked above), *only **Hawaii** has a chance to start rebuilding*. The continental US will be unable to grow any crops at least for the first 3-4 years after the end of the war. It is important to mention that Hawaii is not self-sufficient when it comes to food. According to the [2012 government report](https://files.hawaii.gov/dbedt/op/spb/INCREASED_FOOD_SECURITY_AND_FOOD_SELF_SUFFICIENCY_STRATEGY.pdf), 85-90% of food was imported. It's been 10 years, but judging from the newspaper headlines the situation has not improved much and Hawaii is still incapable of sustaining itself. In the nuclear winter scenario in addition to disrupted imports, Hawaii will face shortened growing seasons and a higher probability of natural disasters due to climate changes. This will make recovery very difficult. How the continental US will fare in milder scenarios is hard to predict. However, coastal areas in the south of the country (not Southern states, geographical south) should have an easier time than northern and central regions. If people manage to survive, the population is most likely to be drastically reduced due to global nuclear famine. Most survivors will have to migrate south. The level of technology will drop significantly. Please note that in the worst-case scenario human extinction is not impossible. The initial casualties might be relatively low. But the changes triggered by the soot in the atmosphere have the potential to make survival for humans as species extremely challenging. [Answer] **Fresno!** [![fresno](https://i.stack.imgur.com/aF2zI.jpg)](https://i.stack.imgur.com/aF2zI.jpg) <https://en.wikipedia.org/wiki/Fresno,_California> Fresno has a population of 500,000. It will probably not itself be nuked. If LA is nuked, survivors from Bakersfield and the surrounding areas will come north to Fresno and survivors from San Francisco will come south and so Fresno might actually gain population. Fresno is surrounded by some of the best agricultural land in the world. The climate is warm and even with nuclear winter they will be able to feed themselves. Plus the creative and industrious spirit of Fresno will serve them well after the apocalypse! Fresno will certainly be the capital of the West Coast. ]
[Question] [ I am trying to come up with a plausible speculative physics explanation for a story I am writing where the conceit is that phsyicists discover the universe is a simulation. The idea is that the simulation is reset to a particular time in the past (assuming there is some way the base universe computer knows what it was then), except that a specific volume of space surrounding the time traveler in isn't. This has the effect of destroying the present universe (and everyone in it) and restarting it. Question: What do you think of my current below explanation? Can it be improved? My answer: Scientists discover that our universe is indeed the result of a simulator in a more complex (base) universe simulating a simpler universe (akin to us living in 3d simulating a 2d or 1d world) and quantum mechanics is some optimisation technique to make it easier for the base universe to compute our reality. We in the simulated universe then discover how to hack it. The way we do this is that a branch of quantum computing develops to explore weird artifacts / patterns in the superpositions that has something to do with the Mandlebrot set (the weird artifacts). Realising that this might be the artefact of our simulation being rendered by another more complex universe, the scientists try to discover more about how the software of the universe works by probing these artefacts. They do this by asking specific questions in the quantum computer (or other quantumy things) and use deep learning networks to encode the data. By doing this for long enough and giving the neural net the ability to run its own quantum experiments, the neural net figures out the architecture of the base reality enough to be able to transfer its knowledge of the codebase of our universe to being able to hack it somehow. I assume that sims can affect hardware in the real world. For instance, if in some far future on Earth we create self-aware sims and they figure out that they are running on a computer, they could try to crash the computer by, for instance, doing lots of processor intensive tasks that might cause the computer to overheat and crash the computer. I’m also assuming that the true nature of base reality physics is far beyond human comprehension so only massive amounts of experiments and self-learning by a massive neural net is possible to understand whatever is really there). Does any of this idea seem believable given the concepts involved, or am I wholly misunderstanding some things? How could you tweak it? What speculative physics would you suggest is best for this story concept? It's key that the time travel element occur by means of restarting the simulation. A key story element is that some characters really don't want the time travel device to work as it will end up killing them and everyone they know. Also, the discovery the world is a simulation has interesting implications for religion. Finally, I am wondering what else one could do if this was all possible? e.g. could the universe be made of voxels and hackers could switch them on and off etc. Ideally I want hacking to be possible with tech that could conceivably be done within the next 50 years. If anyone has better ideas of how to accomplish this task, or it's been thought of before, very grateful! [Answer] **Reproduce the simulation on your computer and run it faster. Predict the future.** Hacking your own running simulation is like tinkering with the plane you are flying in. You would want to have a very good reason because there are a lot of outcomes which lead you you not flying any more. Similarly hacking your own reality. If you change it you may be unable to go back because there will be no you. But once you understand the sim you can reproduce it and model it. If I am a Sim and I can set up my version of The Sims to reproduce my current state of things, I can then run the model 100x faster, tweak the model to introduce a difference then see what the future brings. I can run multiple simulations and not mess with my own reality until I know exactly what will work. Then I can mess with it in the regular ways; nothing quantum and spooky. For example you could test various interventions for global warming and see which one worked best, which ones don't work and which lead to disaster, then set out doing the one that works best. It might be possible to understand the past by running your sim at negative speed to see the state of things at some prior time that led to your current state. --- Knowing the future and knowing the past for the benefit of human kind will be the big picture that the bosses are working on. I normally bring those people coffee and sometimes pizza but I have some smarts too. I will come in after hours to use the model and determine how I can become a rock and roll star. It involves having pants that are tight which is the easiest part for me. [Answer] **Memory Overflow** aka *" Uh-oh Morty, this crowd looks too small for one of our famous rap concerts! I don't think we can perform our new song 'The Recipe for Concentrated Dark Matter' for a crowd this tiny!"* [![enter image description here](https://i.stack.imgur.com/Mtgpl.jpg)](https://i.stack.imgur.com/Mtgpl.jpg) Everyone knows the quantum hack is too complex for humans to get their head around. We have enough trouble understanding quantum mechanics in the first place. Fortunately quantum computers don't need to understand quantum mechanics. They just need to be programmed with the rules of interaction in mind. Fortunately (again) we don't even need to program our computers. We use a neural net for that. A quantum program on a computer with 1000 Qbits is just 1000 nodes with edges connecting them. Each program is a different assignment of weights to the edges. The weights control how information flows between nodes. The neural net is used to decide the weights. As you said, quantum mechanics is just an artifact of the simulation, that allows it to save memory by not resolving events (leaving them in superposition form) until absolutely necessary. The hack works in principle by forcing a lot of resolutions over a small space/time frame. This causes a memory overload. The part of the Big Simulating Computer (BSC) memory that describes the Small Quantum Computer (SQC) then overflows into the adjacent parts of BSC memory. That means the parts of the simulation described by the second block of BSC memory change. For example if the first segment of memory describes the SQC and the adjacent segment describes an Oak tree on the far side of the planet, then running the program might change the Oak tree into an Ash tree. More likely however the Oak tree will suffer a EXISTENCE FAILURE CLASS 1. [![enter image description here](https://i.stack.imgur.com/ETy6d.png)](https://i.stack.imgur.com/ETy6d.png) Different programs will have different effects on the tree. Any program a human comes up with will just make the tree collapse into a puddle of quantum data. The Neural net uses trial and error and a lot of classical computing power to learn useful changes to the tree. The same principle applies to making changes to the entire universe. You just have to find the bit of BSC memory that says what time it is, and use the SQC to replace that bit with whatever time you want it to be, without ruining the rest of the simulation. ]
[Question] [ The plants are organisms with soft cells that don't have walls. Their flesh is soft, with a gelatinous-seeming texture (rather than the fibre-based texture common to vegetables and herbs). Most terrestrial plants have a coat of hard chitinous scales that do not overlap, and an endoskeleton made up of a stiffened cartilaginous tissue, with the softer nutritious tissues in between. There are no soft-bodied plants on land, as the soft flesh can't stand on its own. The scales often have sharp hairs or other such defences between the scales when herbivores are common. Aquatic plants generally lack the endoskeleton, and have sturdier, less flexible flesh to make up for it. The plants' anatomy is composed of straight stems and flat leaves, both of which have all three of the tissues mentioned. They also vary in size from the scale of a small flower (around 10cm high) up to tree-like sizes (around 40m high), with the stiffness and thickness of the cartilage increasing with size. The scales similarly vary in strength from shell-like to almost not present, depending usually on the soil nutrients and amount of predators. The scales also come in a variety of sizes, grain-like to resembling an exoskeleton, based on similar criteria to the strength. The herbivores would vary in size roughly in the range of modern mammals, and have a set of limbs and mouthparts What are some adaptations that would be common amongst the herbivores (specifically the foliovores) for gathering, consuming, and digesting these plants? [Answer] ## A possible answer *NOTE: What follows is a possible solution, not the only solution. Evolution is frighteningly creative but is limited to what it has to work with.* **Setting the stage** For simplicity, we’ll go medium sized. Our herbivore is a quadruped mammal about 80cm at the shoulder (if it helps, I’m picturing a large-ish goat). Its targeted food is one of these plants standing about 1.1 m tall (again, if helpful, I’m picturing something classically “tree shaped” just smaller). **On to eating** The first obstacle is the “sharp hairs”. It’s hard to know what these are exactly but I’m going to assume they function as thin thorns like those found on the [prickly pear cactus](https://en.wikipedia.org/wiki/Opuntia). Many animals eat prickly pear, but most do so by carefully getting between the relatively widely spaced thorns. Based on the description, I get the impression that these hairs are much closer together so that strategy won’t work. Fortunately for us, there are also animals that just munch prickly pear without much care about the thorns. They do this with a few key evolutionary innovations. So, here’s our first set of changes: * Toughened lips and other soft mouth tissues to resist the hairs * Rotary mastication to push the hairs into falling over * Decent set of molars to grind up the hairs so they don’t pose a threat to the guts * Pain tolerance because the above will only get you so far * OPTIONAL - Prehensile lips and/or tongue to move things around Next obstacle: hard chitinous scales. These range from very weak and small to “shell-like” and “resembling an exoskeleton”. On the small/weak end this is no problem, some good grinding molars and you’re set. But let’s go for the tougher end. Shell-like suggests a need to physically break or pry apart these scales. Here a comparison to clams and oysters is probably the best approach. In very broad strokes, eating clams and oysters requires tool use (e.g., bashing them on rocks), suction power (pulling them open) or brute jaw strength. Since herbivores aren’t usually bright enough for tool use and our “goat” doesn’t have anything to pull these scales off with, let’s go with jaws. Here I’m thinking we borrow from a decidedly not herbivore: [bone-crushing dogs](https://en.wikipedia.org/wiki/Borophaginae). Next change: * Serious bone-crushingly powerful jaws Our herbivore now has a mouth full of juicy goodness. Now we have a choice: swallow this stuff in all its gooey, crunchy goodness, continue grinding, or find a way to spit out the scales. Given that our herbivore’s mouth may very well contain sizable pieces of broken “shell-like” scales, swallowing now has a lot of risk, so let’s not. (Note that if eating something with softer scales, swallowing is certainly an option.) Either grinding or spitting would work in our case and it’s likely that evolution will produce species that do both. *Option 1: grind it to dust:* We already have the hardware for grinding (bone-crushing jaws and some good molars) so this seems the obvious solution. But grinding thorn-like hairs and grinding shell-like scales are very different things. I’m thinking shell grinding takes too much energy and causes too much wear and tear to be a good path. *Option 2: spit it out:* This seems the safer option, but it requires some specialized hardware. Our herbivore needs to separate the problematic scales from the juicy goodness. If you’ve ever watched video of a hyena cracking open a bone to get at the marrow (or, if you’ve every tried it yourself), you’ve seen part of the solution. Our next set of adaptations: Dexterous tongue to maneuver the good stuff in and the bad stuff out Mostly closable mouth so suction can be used to gather up more goodness **On to the guts!** But first, a brief aside about the cartilaginous endoskeleton. The tools above will likely make quick work of this endoskeleton if its stiff enough to easily cut. If it’s not stiff enough to grind up, it can probably be swallowed and left to the guts. Once swallowed, our meal will probably be a little easier to deal with than regular earth plants. The lack of cell walls means a lot less cellulose to deal which will make digestion a bit easier. Any herbivore lucky enough to be munching on one of the softer species of “plant” will also have some extra chiton to deal with and everyone will be dealing with the materials from the endoskeleton. Overall, these changes will be the least impressive. If these plants also include silica phytoliths (like real grasses) or lignin-heavy wood, the same processes used today will apply. *Ok, that was my stab at this. I would advise caution on one point: I’ve almost certainly forgotten or oversimplified something. It also goes without saying that I’m not an expert on herbivory.* [Answer] **Either the Aggressive Anteater-like eating equipment...** The interior is gooey. There is hard and yucky stuff that you don't want to deal with both on the surface and on the inside of the plant. So, just ignore all of that and go straight to the juicy bits. The herbivores in question would probably have a needle-like beak that can pierce the outer shell, with a very long "mouth" that can shove a tentacle-like tongue inside the plant. The gooey bits would then be slurped out, leaving just the empty husk - which would probably be filled soon by the plant, if it manages to survive and heal it out. **Or the Vegan Vampire solution.** For teeth-enabled herbivores or omnivores, you would probably have a few vampire-like fangs that could pierce and suck out the juicy bits, without having to deal with the rest of the plant nor chewing the uncomfortable bits. For creatures of this type, they would probably use their front claws/paws to remove a bit of the bristly hair before going in for a bite. [Answer] # Completely different ones The "hard walls" most plants have was an evolutionary pressure that herbivores had to adapt to (flat teeth for grinding, ruminant gut bacteria, etc.). What you are proposing is that we remove that evolutionary pressure. In that case, another evolutionary pressures would have dictated the ability to reproduce. There's no way for us to know which pressures would be most important in this case, because the lack of a problem isn't an evolutionary pressure. [Answer] Terran herbivores' adaptations to terran cellulose and lignin which surrounds each cell in plants was to evolve a wide variety of mechanical and chemical means of breaking down that cellulose and lignin that makes them very different to carnivores, which must merely ingest the food they obtain, which may or may not involve chopping the food into bite-sized chunks. In the OP's ecology, the line between sessile autotrophic 'plants' and motile heterotrophic 'animals' is far less clearly defined than is the case on Earth. This means that the line between 'herbivores' and 'carnivores' will be similarly blurred. The difference could well be that of speed, the carnivores more adapted to chasing down and catching motile prey while the herbivores will be more adapted to fleeing and/or self-defense. However, when it comes to eating these soft, fleshy 'plants' with their armour, hard scales, cartilage and thorns, there are a number of obvious adaptations: The 'herbivores' dentition will likely be very similar to that of a carnivore, in that they would be adapted to slicing up meaty flesh, cutting through tough skin, and scraping flesh from tough, less easily digestable surfaces. This would tend to make a herbivore much more likely to become an opportunistic carnivore. Where plants make themselves abrasive so as to wear down the teeth of the herbivores that eat them, the herbivores may counter with continually growing open-rooted teeth like a horse's molars, or infinitely replaceable teeth like a shark's. Where the foliage that the herbivores may eat is covered in fine thorns or penetrating hairs, this may be dealt with in the same manner as giraffes which eat thorny acacia foliage deal with the same problem: an armoured mouth and gullet which can tolerate chewing and swallowing sharp, spiky food. In order to get past thorns and penetrate armoured skins, there are a number of adaptations that could assist: 'Herbivores' heads and any other limbs which may be used to deal with thorny protective measures could develop tough - potentially armoured - skin of their own. If thorns are a problem, tough, horny, smooth surfaces will allow the herbivore to simply push past them. Eyes will be set well back from the mouth to keep them away from the thorns, or they may be armoured themselves. Thorns may also be dealt with by breaking them off with a protected limb before using other, more sensitive organs and appendages to crack the 'plant' open. Where a 'plant' has a particularly tough skin, herbivores may develop very powerful jaws in order to simply bite through into the soft interior, or they may develop hammer-like or military-pick-like limbs to respectively smash or puncture the plants' tough rigid or flexible carapaces prior to inserting their relatively slender feeding apparatus into the soft interior. Limbs may be strong so that when a hole is punctured through the outer armour, the herbivore may use its strength to tear the plant's body open to provide access to the edible interior. An example of this may be the [*Palorchestids*](https://en.wikipedia.org/wiki/Palorchestes). Not mentioned by the OP is the possibility that the plants may make their own flesh toxic. This would discourage opportunistic attacks by carnivores and unspecialised herbivores which may be poisoned, but some herbivores would evolve to be able to neutralize any toxins that the plants they feed upon may create. However, this may increase the metabolic cost of feeding upon these toxic plants, a problem that tends to lead to a large size and a leisurely lifestyle in order to reduce energy consumption per unit mass, large animals having a lower basal metabolic rate to smaller animals. Many of these adaptations to herbivory in this environment would also lend themselves to carnivory, so true exclusive 'herbivores' and 'carnivores' may not actually exist, but instead each species may lie somewhere along the scale of omnivory between the two extremes. Also not mentioned by the OP is the possibility of symbiotic relationships between 'plants' and certain 'animals' where the animals protect the plant in exchange for some incentive such as food and/or shelter. Eating such a plant would require dealing with both the plant's innate defences and its symbiotic defenders, though an animal evolved to do that may well simply eat both plant and its o(symbiotic defenders. ]
[Question] [ I've just been working on this post-apocalyptic setting and was wondering what level of weapons technology it would be able to support. Essentially a combination of land degradation, global warming (due to stuff like changed rainfall patterns and the spread of pests) and the depletion of resources like oil and rock phosphate (not to the point where they have been completed used up, but to the point where the easy to access deposits are mostly gone and what remains is much more expensive) led to a gradual but significant decrease in global food production. Exacerbated by increasing droughts, natural disasters and the emergence of new diseases (as habitat loss brings humans into contact with animals), our globalised, industrialised society collapses as billions die in a series of wars, famines and plagues. Now it has been almost a century since society as we know it ended, and about 90% of humanity once again makes a living from hunter-gathering or subsistence agriculture (largely in the form of pastoralism or shifting agriculture due to poor soil quality and climate variability). The rest of humanity lives in small market towns or some larger cities that have popped up along major trade routes or near areas with some rare and useful resource/asset (like an old hydrolectric dam). While many of these cities have some degree of industrial manufacturing and some more modern technologies like electricity and wood gasification, the lack of resources and loss of more technical knowledge mean that they are pretty primitive by modern standards. Mining would be fairly limited as most easily accessed mineral deposits have been mined out and few groups would have the technology or resources to access the deeper deposits, so most metals would have been scavenged from the ruins and/or recycled over generations by survivor communities. While day-to-day survival is the main concern of most people, various conflicts still occur ranging from tribal cattle raids to major wars between city-states. And I was wondering what sort of weaponry would likely be used. Of course this would vary based on what groups we are talking about (the army of a large city state would obviously have more advanced weapons that some isolated hunter-gatherers), but I imagine that even the most advanced groups would be limited on what they would use due to a lack of resources. The question is less what they *could* produce (as many cities probably have have the technical knowledge to make weapons of at least a WW1 level) and more what they would produce (as these cities would lack the population and industrial capacity to supply a WW1 level army, with the various market towns and nomadic tribes being even more limited). I personally imagine that the advanced cities would maintain a limited stock of bolt/lever action rifles (that use black powder cartridges and mercury fulminate firing caps) with some Girardoni style air rifles (the setting would remove many of the disadvantages associated with them historically as modern materials that have been scavenged/reproduced in limited quantities would make reservoirs less likely to crack, while electric pumps powered by water/air/biofuel would make filling them easier than with hand pump). Most other peoples would use black powder flintlocks, that the more advanced peoples manufacture and the less advance trade for, while some more isolated peoples rely on bows and spears. Of course, I'm really interested to hear what other people have to say. Would the weaponry be more or less advanced than what I've described? Are there any technologies that I've forgotten? Thanks for any feedback [Answer] ## The Info Age Collapse will not Happen Everywhere 10% of the current world population is still a lot of people. Basically, you've sent the world population back to the 1700s which was enough people to support the early industrial revolution. This means you still have enough people for factories, major shipping companies, etc. as long as someone is able to maintain order in any significant portion of the world. More over, you have not necessarily destroyed modern knowledge and technology. Currently, ~26% of the world's power is met by renewable energy; so, depending on what method people used for wiping each other out, it is very much possible that enough renewable power infrastructure was left over (or built in the aftermath) allowing new civilizations to fully power themselves entirely on renewable power sources. Also, every war has a winner... or at least a least loser... So, while 90% of your world was wiped out, it is likely that a few nations mostly survived. They would have achieved thier goals of wiping out thier enemies and procuring the resources they need to not completely collapse. So while your super powers may have all nuked each other to into oblivion on day 1, you might have places just remote and civilized enough like New Zealand or South Africa to have survived the main conflict mostly untouched. Or it may have gone the other way where a major power like the United States or China developed good enough of a national missile defense system that they single handed wiped out all of thier rivals in a massive nuclear offensive while being able to mostly stop most attempts at fulfilling Mutually Assured Destruction. Either way, you will probably have a few pockets of civilization still producing fighter jets, tanks, and computers, but most of the world will become more like many parts of Africa and South America are now: a weird hodgepodge of primitive technology ruled over by local warlords who have managed to buy, borrow, or steal a few modern marvels that give them incontestable control over thier territories. So to answer your question, it is very much possible that some factions will remain that are 100+ years more advanced than we are today. These factions may very well have populations in the 10s or even 100s of millions and possess technologies that do not even exist yet (plasma riffles, nanite swarm weapons, holographic or neurological computer interfaces, etc.). Basically, think about how the United States economy pulled ahead of the rest of the world following WWII because they avoided the massive devastation that happened to the rest of the world, only the devastated nations in this case are much more devastated. The collapse of supply lines will certainly cause a major economic depression at first, even in those countries that do avoid the bulk of the conflict, but as long as these countries still have thier existing computers and machine shops (or at least a few guys with better than normal garages full of tools that can be quickly worked back up to proper machine shops), they should be able to fill in the missing production gaps over the next 5-20 years before all of thier old stuff breaks down and stops working... and once they do they will enjoy at least a few decades of hegemon status that will allow thier technology to flourish and advance very quickly as they exploit the rest of the world for its resources. ## Addressing Resource Scarcity Most of the issues our world is facing on its current track have far more to do with environmental damage and a hand full of very rare resources. Both of these issues are self-solving in a future with a smaller human population. Fossil Fuel depletion is not nearly as much of an issue as it was assumed a few decades ago. Every year we are discovering that many of our fossil fuel reserves are much larger than we first though and new ones are being found deeper and deeper. At this point in time, human kind has identified more than enough fossil fuel reserves to trigger a run-away greenhouse effect at current levels of consumption. This means that humanity will never be forced to give up fossil fuels because they have run out, instead we will have to choose to abandon them before we kill ourselves with them. However, it has been estimated that the Earth's environment can sustain ~500 million civilized humans indefinitely. So, once you reduce the human population to about 770 million people (assuming at least 1/3rd of them are forced into the uncivilized wastelands and that there is not a significant recovery of our population), consumption will be reduced enough that man kind could safely continue burning fossil fuels for hundreds of years using only the reserves we know about today. Most common, industrially used materials like iron and aluminum are also far too abundant to ever run out. Over the course of the next few hundred years, we may be forced to use slightly less rich aluminum and iron sources which will be a little bit more expensive to refine. But economically viable versions of the ores we use most are literally everywhere on Earth. The elements we are at much bigger risk of running out of today are the rare Earth elements used in many electronic devices (Yttrium, Scandium, Holmium, etc.). That said, many manufacturers are already working on phasing out the use of rare Earth elements from of thier designs; so, by the time we get to the point where we run out, we should not need them anymore. And if your post apocalyptic people need these elements, they just need to go find a bunch of old computer parts. Once you eliminate 90% of humanity, the amount of resources you can scrounge out of what is left over will be far greater than what you actually need. The other somewhat scarce elements we need to worry about are conductor metals like copper and gold. While scarcity is also starting to become an issue in these areas today, it is mostly because we are using so much of the stuff at any given time with our current populations. Just like with the rare-Earth elements, unless the old cities have been vaporized, then you will have 10 times as much copper of this as need just sitting around, already refined in the form of powerlines and household wiring. Depopulation will also mean we could no longer utilize all available landmass; so, natural landscapes will begin to re-emerge in many parts of the world making the lumber industry and crop-rotation viable again. [Answer] While it's a crude rule of thumb, it's a fairly good one: 90% of technology is material science. The second rule is one about firearms--the gun is only one quarter of a mechanical system composed of the firearm, the propellant, the projectile, and the operator. So what materials are available to your cities? If it's WWI-level weapons, well, that's almost at modern firearms levels. WWI-era firearms are high grade steel and precision mass metalworking. From what you describe earlier, I doubt that's the case. To set up mass manufacturing, not only do you need the tooling which produces the product, you need the tools to produce the tooling. In most cases, that's very heavy equipment relying on a lot of infrastructure. It'll be hard to answer your question with more specific definition of specific metalworking techniques available. Also consider: scavenged modern equipment isn't going to last very long esp. with frequent use. Gaskets wear out, manifolds erode, and without replacements it's probably only 50 years at the absolute most that the last few operable pieces of modern machinery are still working, ship-of-Thesaus-style using scavenged parts from all the other dead examples of the same machinery. In short: can you clarify more specifically which materials production techniques are available, so we can figure out what you can actually do with them? ]
[Question] [ I have a species in my sci-fi setting, that are basically land-dwelling sapient nautilus. They differ from most concepts of "land-dwelling cephalopod" in that they're supposed to be the tallest creatures in the setting, towering over everybody else, up to three meters in height: [![From a "leaving the cradle" webcomic](https://i.stack.imgur.com/gKma5.png)](https://i.stack.imgur.com/gKma5.png) What anatomical quirks can allow them to have posture like in the provided picture, without taking away the dexterity and bendability of their tentacles? I was thinking about some cartilage-like cores in the tentacles that are resistant to compressive forces but can bend to relatively tight circles, so the muscles of the tentacles mainly work to prevent the cores from bending the wrong way. Probably even with a gradual increase of bendability, so that they're stiffer near the beginning than near the "hands". Could that work? [Answer] Shear tentacle strength is all that is needed for a cephalopod to go vertical and once the evolutionary advantage of a higher point of view expressed itself, those individuals with stronger tentacles would have a survival advantage over others. If a mutation introduced cartilage structures onto which the tentacle muscles could exert force, all the better. Given enough time and survival pressure, a creature such as you describe could easily evolve. The only objection I have is to the shell shown in your illustration. There is no reason for it to be located so high in the air, consuming a maximum amount of effort to hold it there while adding nothing to the survivability of the beast. I would hang the defensive shell under the center body mass, between the tentacle legs, leaving the sensory organs and maybe a beak at the top. Articulate the body so that it can still roll up into the shell when needed, but practically drag it on the ground and/or sit on top of it in less threatening times. [Answer] Does it need to stand, or can it simply float, like the alien creature named [Huragok](https://www.halopedia.org/Huragok) in the Halo series? This is a Huragok, a floating octopus-squid-like alien, that is the most intelligent species in the known Halo universe. Their size alone is enough to tower any human, apart from the fact that they can float quite high. They are also strong enough to lift weights heavier than them. For more details please refer [this page.](https://www.halopedia.org/Huragok) [![enter image description here](https://i.stack.imgur.com/BkN36.png)](https://i.stack.imgur.com/BkN36.png) [Answer] You want to look into [soft robots](https://biodesign.seas.harvard.edu/soft-robotics) and, to a lesser extent, [compliant mechanisms](https://www.youtube.com/watch?v=97t7Xj_iBv0). [Soft robots](https://www.softroboticsinc.com/) use a bendable membrane and fluid pressure to achieve the same results as robots made of metals and hard plastics. [Compliant mechanisms](https://www.compliantmechanisms.byu.edu/about-compliant-mechanisms) are a little different, relying on the deformation of materials traditionally thought of as rigid, such as [titanium](https://www.youtube.com/watch?v=crkDtLzZG0g). Not only are these methods feasible, they are directly [inspired](https://youtu.be/qevIIQHrJZg?t=108) by [biology](https://youtu.be/058hRtaCWC0?t=454). From one education [video](https://youtu.be/058hRtaCWC0?t=454): > > "Is this a little like an octopus? Is that how you can think of it?" > > "There is some connection there." > > > A more scholarly [source](https://www.automate.org/blogs/5-innovative-applications-of-soft-robotics) describe how prosthetic limbs are a possible use of soft robots, and the [M1 Mobile Manipulator](https://www.dndkm.org/Technology/TechnologyFactSheet.aspx?TechnologyID=1183) is a compliant robot designed to replicate a human torso, head, and arms. ]
[Question] [ Long ago, I asked [a question](https://worldbuilding.stackexchange.com/questions/120454/an-inverse-great-dying) on what would create an inverse Great Dying. Allow me to clarify on what I meant: 252 million years ago, the worst event in the history of life on Earth occurred. 70% of all terrestrial species and 96% of all marine species became extinct through, according to geological records, a combination of events--flood basalt eruptions in Siberia, runaway greenhouse effect caused by the melting of methane ice, even the formation of the supercontinent Pangaea itself. So an "inverse" Great Dying refers to an event in which 96% of all terrestrial species and only 70% of all marine species became extinct. The best answer I got was a gamma ray burst from a nearby supernova (some tens of light years away.) So imagine the planet Earth 252 million years ago. All the continents were clumped together as one singular landmass, Pangaea. Climate gradients from equator to poles were modest. And then, instead of a series of lava eruptions in Russia, life was hit hard by a gamma ray burst from the supernova of a nearby star. The ozone layer had been cut down to less than one percent of its original thickness. Exposed to solar radiation, 96% of all terrestrial species died out. Based on what we know of Late Permian terrestrial flora and fauna, who would account for the surviving four percent? [Answer] **Burrowing detritivores.** [Fossil Worm Burrows Reveal Very Early Terrestrial Animal Activity and Shed Light on Trophic Resources after the End-Cretaceous Mass Extinction](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737216/) After the Cretaceous mass extinction, worm burrows were some of the first fossil traces to appear. > > Survivors of the end Cretaceous extinction event were able to > withstand both short- and longer-term repercussions of the bolide > impact and ongoing Deccan vulcanism. Global thermal radiation caused > by re-entry of asteroid impact ejecta apparently presented an > immediate and potentially deadly, short-term consequence of the impact > [8]. Robertson et al. [46] suggest that this intense pulse of infrared > radiation would have killed exposed organisms, and infer that > survivors were protected within burrows, natural cavities, or bodies > of water. Earthworms not only live in the soil, but are also capable > of employing several mechanisms that allow them to withstand > unfavorable environmental conditions: their protective egg-bearing > cocoons can remain unhatched until conditions improve, and the worms > can enter a state of quiescence or diapause, or can burrow deeply to > avoid adverse conditions near the sediment surface [43]... Sheehan et > al. [48] suggested that detritivores would have thrived on existing > stores of dead and decomposing carbon resources despite decreases in > primary production. > > > Worms are protected from radiation, and a postapocalyptic world is full of worm food. Organisms sharing earthworm habitat could also survive - land crustaceans (isopods), other worm types like nematodes, and the ancient springtails. Microscopic soil animal also inhabit this soil sanctuary - mites, tardigrades and rotifers. --- From comments: /what about plants?/ I did not realize that the extinction event counted plants among species going extinct. I think that for extinction events in our timeline plants did a lot better than animals - example: [No mass extinction for land plants at the Permian–Triassic transition](https://www.nature.com/articles/s41467-018-07945-w#:%7E:text=In%20the%20current%20state%2C%20there,the%20end%20of%20the%20Permian.&text=The%20fossil%20record%20of%20land,diversification%20or%20relatively%20stable%20diversity.) Killing all the plants is harder. A gamma ray burst that let anything live would spare some seeds and plants would bounce back to a world without herbivores and they would thrive. Let us assume the plan extinction is from higher incident UV. Plants that need full sun would die with the full UV. Survivors would be those that are ok in low light because shady niches would be shaded from UV as well. Given that some of the most ancient plant lineages are low light specialists today in our timeline ([mosses, ferns](https://worldbuilding.stackexchange.com/questions/153351/nocturnal-photosynthesis/153358#153358)) I would guess that the low light adapted ancestors in these lineages would be the survivors in a bright UV world. So those ancients get their world back. Exposed areas will be claimed by lichens which I suspect (but do not know) must have some sort of super UV durability given their unique ability to tolerate exposed areas at high altitudes. The high UV circumstances would need to outlast any durable cones or seeds in the soil or once things ease up the gymnosperms will come back swinging. There could be plant refugia like the [Wollemia](https://en.wikipedia.org/wiki/Wollemia) refuge in our timeline - a larger niche which by virtue of topology was protected from UV and where UV sensitive plant species that had been wiped out elsewhere might persist thru the UV apocalypse. ]
[Question] [ Assuming ancient levels of technology, perhaps 2500-1500 BC, how would one be able to make a underground city like that of [Kaymaklı](https://en.wikipedia.org/wiki/Kaymakli_Underground_City), while having it be able to be breathed in and, is possible, have a basic water system? I am aware that at least the breathing is possible, but not fully aware how it is so. Also, how are these kept from collapsing when mining larger chambers? Larger Chambers as in around 4.6m x 5.5m to a little above. This spreads into various different groups of rooms branching off one another, and various tunnels as well. This would be separated into general storeys, perhaps around 15-20, going upwards and downwards in the mountains, total that is, not 15-20 in both directions. In a real-world analogue, one could compare it to just being built into mountains. Mostly the lower ends of them, and not near the peaks. Sort of like the Andes in terms of the vast rainforests on one side, and very dry deserts on the other, very typical for mountains, I know, but this is just the kind of mountains I thought of when conceptualizing the city. Would be preferable if sources of how this was done are cited, and if possible, linked to. Thank you. [Answer] ## Favorable Geology: You need some kind of intrinsically favorable geology to form a large cave city. In the case of Turkey, There was a large sheet of hard, durable stone over the top of a very soft malleable stone. This meant the structures had a very hard roof of stone that held together well as a unit, while simultaneously having an extremely soft layer of rock in which to dig. But even softer rock carved in a solid piece is very cohesive and unlikely to collapse in the way a typical roof composed of blocks might. As for technology, they pretty much used trial and error. If the air was bad in an area, they dug a shaft from the side or above (if needed) to give ventilation. If you wanted a really big chamber, the upper hard stone could work like a large single slab. Vent/smoke holes could be quite small, certainly not passible by an attacker. Much of these cities was not actually all that far from a surface of some kind, so distances to dig ventilation were not that bad. Where it got deep, long air shafts that would be difficult for attackers to ascends and descend were constructed straight up and down. Other kinds of natural structures are possible where large caverns have formed underground (such as magma chambers) that would likely provide a large internal space in which to build a city. Many volcanic rocks are extremely hard and can provide a lot of strength to support large roofs. If you look at the lava caves in Iceland, for example, there are some extremely large chambers and cave systems that would provide space for numerous inhabitants. A large [vacated magma chamber](https://guidetoiceland.is/book-holiday-trips/inside-the-volcano) could provide enough room for a sizeable city to be built within. Ventilation in this case might be provided by a hole in the ceiling or a large cave entrance. Lava caves allow at least the possibility of geothermal heating and water, a possible reason people would want to build a city inside what would amount to an extinct volcano. I'm sure other folk here could come up with additional geological sites with favorable conditions to allow different kinds of underground cities. [![enter image description here](https://i.stack.imgur.com/xoiHK.png)](https://i.stack.imgur.com/xoiHK.png) [Answer] **Another option might be a large natural cavern or series of smaller interconnected caverns.** Depending on the size of the space available man made structures could be built in the larger sized spaces and if tunnels and rooms are dug out at angles from a cavern to increase the amount of space available waste stone from the tunneling process could be used to construct buttresses to help support the ceiling at key points. ]
[Question] [ So I read [an article](https://www.space.com/36472-saturn-moon-titan-electric-sand.html) on the sand on [Titan](https://en.wikipedia.org/wiki/Titan_(moon)) and its static properties. To sum up the article the gravity and atmosphere there make it so the triboelectric effect isn't overwhelming like it is on Earth, and thus the sand has a much stringer static cling. This article goes on to speculate jokingly that sandcastles could last up to weeks due to the static cling. Thus my question is what structure would the sand need to be shaped, and what kind of technology would be needed to make functional, life-sized architecture out of this sand and not just have it last a few weeks, but upwards for hundreds of years? [Answer] ### Some decent hydraulics should do the trick: > > what kind of technology would be needed to make functional, life-sized architecture out of this sand > > > A hydraulic press capable of reaching 7000 bar should do the trick: [![enter image description here](https://i.stack.imgur.com/oCBmN.png)](https://i.stack.imgur.com/oCBmN.png) [![enter image description here](https://i.stack.imgur.com/NYnRz.png)](https://i.stack.imgur.com/NYnRz.png) [video source](https://www.youtube.com/watch?v=W5BFn8d1sIQ&ab_channel=HydraulicPressChannel) This will turn sand like that into SandStone, which can make large sand castles which last for long periods. (I doubt it'd stand up to liquid methane rain so it might need a layer of plaster and coat of paint) I know this isn't the answer you're looking for. Sorry :-( Titans static electricity can make sand dunes 100m high that face into the wind, but that's not enough power to keep roof and ceilings in place in a multi story castle, especially under dynamic loads of castle life. Trying to calculate the required static charge needed to hold a castle together like this I'm coming up with ludicrous levels of voltage that would just arc and discharge - and the discharge arc would melt the sand into glass. ]
[Question] [ In base to my question about [How could a dragon develop blue fire breath?](https://worldbuilding.stackexchange.com/questions/196909/how-could-a-dragon-develop-blue-fire-breath), one of the most interesting solutions is that the dragon could be able to produce aerogel for resist its own fire, so why not?, aerogel have a lot of more interesting characteristics, in addition to the high temperature resistance is extremly light and resistant compared with its weight and density. And compared with other strange biological features this looks easy to develop, with the different types of aerogel. Inorganic based on metalic oxides, organic based on carbon polymers and the two which I thought are more helpful for this question, the silica and graphite aerogels. [![](https://i.stack.imgur.com/SZBQF.png)](https://i.stack.imgur.com/SZBQF.png) Currently the stingging nettle can synthetize silica spines and marine sponges use silica en their skeletons. And carbon, practically the life is based in carbon and carbon dioxide is extremely abundant. Although it has a limit of resistance to heat, which is very high of 500-2000 ° C, if a dragon could produce this material in its body, it could regenerate it when it wears out. Thing that is useful too for other kind or fire manipulators, [How would a "flaming collar" work in an animal and how could it be useful?](https://worldbuilding.stackexchange.com/questions/191304/how-would-a-flaming-collar-work-in-an-animal-and-how-could-it-be-useful) And apparently the raw materials are the easy part, but I don't know how aerogel is produced and how a living creature could produce it in its body, neither I know if this could be product of natural evolution or obligatory genetic engineering product. By the way, if aerographite (aerographene) is other problem already exist a question about [Could a living creature produce graphene?](https://worldbuilding.stackexchange.com/questions/141427/could-a-living-creature-produce-graphene) and I thought by myself I can solve that probkem [Answer] Aerogels are usually made by removing the water from a gel, leaving a porous matrix which was once present in the gel. The closest resemblance to an aerogel in living creature I can think of is cork. Cork is the bark of some trees, which have developed this type of bark to, guess what, get protection from fire. The main obstacle you will face is that, both for cork and sponges, the size of the "holes" you can leave in the matrix is dictated by the size of the cell/organism producing it. To go smaller than that you would need some trick. One of this trick would be to have the cell assemble an internal proteic structure, not water soluble, and then die. The structure, remaining after the cell, would sum up with those of the neighbors and produce the very fine structure of an aerogel. [Answer] First off what is an aerogel. A [gel](https://en.wikipedia.org/wiki/Gel) is mostly liquid with some dilute linked solids holding it together. Biology produces lots of gels (mucus, the vitreous humor of the eye, cartilage, tendons and blood clots) so no problem there. [Aerogel](https://en.wikipedia.org/wiki/Aerogel) is what happens when the liquid in a gel is removed in such a way that the diffuse cross linked solid is left behind. This is the hard part. Normal drying won't work as evaporation happens at the edges of a gel producing a flow of the liquid that destroys the delicate linking of solids and causes them to shrink and crumble. To get aerogel you need the liquid to leave the gel as a gas throughout the gel simultaneously so as not to damage the remaining solid matrix. This usually involves precisely changing the pressure and temperature of the materials to reach the supercritical point, where there is no distinction between a liquid and a gas, and thus no evaporation liquid gas boundary. Then replace the liquid/gas binder with another gas and lower the pressure. These reaction tend to happen at fairly high pressures, most current aerogel production uses liquid CO2 at around 73x atmospheric pressure, other liquids use even higher pressure than that, and making a gel with liquid CO2 is a complex process. But wait, you said a DRAGON! Normal biology probably won't produce the pressures necessary, but fire can! If your dragon's fire ignition method is internal it could likely produce a high pressure region in that fire gland/orifice/bladder/whatever. And it would likely be coated with a mucus gel. It could then theoretically (given some specific mucus chemistry) produce a thin layering of aerogel from the mucus using the temperature and pressure of the flame. If this layering of aerogel was retained and built up over time it might be comparable to a very solid fire resistant type of scar tissue building up from repeated breathing of fire. This type of buildup of aerogel would mean that young dragons would be less able to breath fire without injury, but older dragons would have developed a nice aerogel liner allowing them to burninate with impunity. [Answer] I'm going to go with **direct extrusion**. Basically, you want to 3D print the entire aerogel using specialized protein channels in the cell membrane as the extruders. The gel is prevented from collapsing due to its electrical charge, which repels the outer strands of the gel from the equivalently charged outer layer of the cell membrane. The inner layer is oppositely charged, but the cell pays the energy cost, at the channel, to push these charges apart. The cells that secrete aerogel adjoin on a very dry space, but they have well maintained lipid membranes. In those membranes are channels, through which fibers can be moved. The fibers are assembled in the cytosol and are as durable as is feasible. Ordinarily, the aerogel simply is moved outward by myosin-like motors at the same rate as it is produced. However, the aerogel needs to be cross-linked, so every now and then the cell starts extruding a batch of new fibers through previously untapped channels. These channels each start off joined to an existing channel, and the fibers are solidly cross-linked at a three-way junction to start. But then the channels separate, remaining within the membrane, and the halves are moved around by the cytoskeleton. After a short time, they meet up with another channel and splice their fibers together, after which one channel becomes again temporarily inactive. ]
[Question] [ I've done lots of studying into gigantism. Whether it's from acromegaly or simply a quirk of genetics, humans often suffer once they reach past a certain height. There's plenty of variables of course: People with acromegalic gigantism are afflicted with numerous medical problems, and no two cases are the exact same. Even for those naturally born to grow giant, the square-cubed law is a merciless bastard that makes the current design for the human body ill-suited for being anything taller than 7 feet tall, let alone 8... ...but what about an older design? More specifically, the design of the stockier, more robust neanderthal species? They seem to tick a LOT of boxes for being better suited for gigantism than humans: They have a squatter, more robust build (better suited for heavy bodies), they have straighter spines (which may provide better support in standing) and their bones were naturally heavier and stronger than us modern humans (bone structure is among the biggest issues with giant humans). I'm writing a character whose design is derived directly from a neanderthal build. However, the character I made is 8'3 and calculated to be nearly 700 pounds. Would a neanderthal body structure alone be able to compensate for this kind of size and weight? Or would it be necessary to make the bones more dense, like an LRP4 gene mutation? The character in question is a product of genetic engineering, and thus does NOT need to be refined for any kind of survival in the wild. It's just another story of unethical humans playing god. Question is, would a story with this premise be realistic? Can a giant with a neanderthal's skeletal structure handle it's estimated size and weight? [Answer] The explanation of why the square-cube law is effective at limiting the upscaling/downscaling of organisms is that the weight of organisms grows with the mass, which is proportional to the volume, thus the cube of linear dimensions, while the resistance capability of the bones grows with their cross-section, thus with the square of the linear dimensions. If I look at the description of the [anatomical difference between Neanderthal and Sapiens](https://en.wikipedia.org/wiki/Neanderthal_anatomy), I read that the more robust appearance is due to shorter bones, not to larger cross sections, especially in the limbs. I conclude then that the problem with the cross section and the weight it can support stays unchanged. ]
[Question] [ My goal is make a world where you cannot fall. So in my world (or at least city) you slow down as you fall so you wouldn’t be going fast enough to get hurt when you land. Im thinking the air is like scales, smooth one way, rough the other, so you can smoothly travel up but there is more resistance when you are going down so you don’t fall too fast. So your terminal velocity would be way lower than normal. People travel by flinging themselves across the city and then they just float down:D I haven’t decided if you’ll still slow down if you just trip, or if objects falling from small heights still slow down, I feel like they would. If we had greater air resistance would that mean that if you tripped would you fall slower than usual or would the resistance be negligible? Another possibility would to have a layer of “elastic air” that would slow you down when you reached it and it would stretch until you reached the ground and exited, then it would spring back up. This is my first question so let me know if I need to adjust it! I just edited it with more details of what I’m trying to do. [Answer] Could be the entire city is inside a utility fog. <https://en.m.wikipedia.org/wiki/Utility_fog> Despite the name, a utility fog is not a fog at all, but rather a solid lattice of 10 micrometer scale robots having 50 micrometer scale arms. Each grain in the network holds the hands of other robots, giving anywhere between 0 and 100 micrometers from one another. With this big a gap, you can breathe and see through it. It’s only slightly thicker than a cloud of pollen. The robotic mesh can re-arrange on command. It can conducts people inside the fog by simply getting out of the way, or enhance mobility by lifting them up. It is powered by ground and data nodes. A few questions on this stack exchange have envisioned broadly deployed utility fogs for technological “magic” or Pokémon-like monsters in a tiny ball. Utility fogs fit a lot of the bill for a real sci-force field, but the “field” is this metal framework that can rapidly thicken, self-heal, lift someone up, crush them, display imagery, emit sound, and so on. Your city’s utility fog might allow people to pass through horizontally with ease, but arrest the fall of anyone dropping vertically. In fact, as a safety system alternative to seat belts is utility fog’s initially documented use case. [Answer] Why not just have a thick atmosphere? To get to a comfortable temperature on a planet like Uranus, you have to go to 50 atmospheres or more of pressure. At such high pressures, air resistance increases, so terminal velocity decreases. Technically, [per the formula](https://en.wikipedia.org/wiki/Terminal_velocity), it looks like it decreases according to the inverse square of the density, so 49 atmospheres means 7 times lower terminal velocity, I think. (Correct me if I'm wrong ... I know this gets to be a very technical area of science!) Given a planet in a fairly distant orbit with a very thick atmosphere - not as thick as Uranus if we want them walking on land, but thick - we should be able to make it so they don't fall very hard. Note, by the way, that if we reduce a 120 mph Earthly terminal velocity to, say, 12 mph by making the air pressure 100 atm, well, ordinary walking will still take much less force to maintain than is needed to push against gravity. [Answer] If you lower the gravity enough, and thicken the atmosphere enough, you can lower terminal velocity until you cannot die by falling off a cliff. ]
[Question] [ Pretty much title says it all. It just needs to not be afraid of explosions and pull a trigger or other activation mechanism on command, if it understands by itself when to shoot, then even better. Doesn't have to aim or move around the weapon, it is fixed.. It just needs to pull the trigger. [Answer] just my opinion (i dont know much about gun) assuming they use common gun trigger. [![enter image description here](https://i.stack.imgur.com/9lQqq.jpg)](https://i.stack.imgur.com/9lQqq.jpg) joke aside, snake can be trained or guide to at least, and i believe their constriction can help push the trigger, though i am not sure can they get used to the loud sound or vibration of the explosion or not. otherwise i think monkey is a good choice, they can be trained even with audio command, and can hold or push the gun trigger at least, regarding not afraid of explosion i believe that they can be train to get used to the loud sound. from:<https://lifetimestock.com/media/18744> [![enter image description here](https://i.stack.imgur.com/fssFA.png)](https://i.stack.imgur.com/fssFA.png) from:<https://www.shutterstock.com/search/monkey+with+guns> [![enter image description here](https://i.stack.imgur.com/qN2p0.jpg)](https://i.stack.imgur.com/qN2p0.jpg) from: <https://www.stripes.com/blogs-archive/the-rumor-doctor/the-rumor-doctor-1.104348/is-photo-of-baboon-with-a-machine-gun-fake-1.111041#.X_SNq7hHNTc> [![enter image description here](https://i.stack.imgur.com/vSIDd.jpg)](https://i.stack.imgur.com/vSIDd.jpg) [Answer] [Insects are trainable](https://www.quora.com/Is-it-possible-to-train-an-insect), and since you're allowing "other activation mechanisms", I'd suggest that you could stimulus-response train an ant or tiny beetle to walk onto stimulus = YES triggering mechanism. The size of the gun so activated is up to you! Just put the triggering mechanism [under the little yellow ball](https://www.youtube.com/watch?v=bZhu5-3ZmoE) and you can redefine the term "killer bee"! Insects will serve your purpose well because their relatively simple nervous systems don't allow for higher emotions like "fear" and just from ordinary observation, insects don't seem to be particularly fazed by human made bangs like fireworks or gunshots. ]
[Question] [ So, dragons, gryphons, what have you. They're usually (before Skyrim and Game of Thrones in the dragons' case) depicted as six-limbed, quadrupedal creatures. Now, the thing is, staying aloft is much easier than getting into the air. **If I could cheese the takeoff, I could basically cheese flying.** According to a 2013 paper from Michael Habib, evolution often constrains the maximum size of flying creatures based on how they take off. Birds, for example, have a mass-inefficient launch scheme, as they use their legs to get the ground clearance for their wings. Those legs become dead weight during flight. <https://www.academia.edu/12192191/Constraining_the_air_giants_limits_on_size_in_flying_animals_as_an_example_of_constraint_based_biomechanical_theories_of_form> Bats and giant pterosaurs, however, can take off using their flight muscles and wings to pole-vault into the air. This works for about wingspans of 11 meters, the predicted wingspan of giant pterosaurs. For heavier dragons, we could alter the wing's shape to have a higher surface area at the expense of aspect-ratio, which might not be a big problem. The aspect ratio determines aerodynamic efficiency, as a high-aspect-ratio (read: very long and narrow) wing can generate more lift at lower speeds by separating a longer tube of air around it. However, due to how long it is, this wing-type requires lots of muscle to move because of leverage, and ridiculous ground clearance, forcing the bird to taxi, and get to sufficient speeds that way. We are looking for a middle ground here, which comes on the wings of eagles, pelicans, and stonks. Slotted, lower-aspect-ratio wings with a big area are preferred. While they require some speed, they don't suck at gliding, require less ground clearance, and the slots can ~~enslave~~ harness the wingtip vortices. But, here's the thing, assume we made the wings, they span about 11 meters and have a realistic wing loading (25> kg/m^2). Got all that? Well, we still have the issue that launch strategies are morphology-specific, and my dragons and gryphons have a lower profile than the quetzalcoatlus (i.e: they aren't as tall as a giraffe), plus an extra pair of lighter limbs, optimized for burst-speed. So, now I'm here, thinking if there's a way to come up with a sensible launch strategy that can work with a creature that's less vertical than a giant pterosaur, and has six limbs. **It's supposed to either exploit the creature's body plan, work in spite of, or regardless of it.** **What should that launch strategy be?** [Answer] Hm... I am not a expert on aerodynamics of the biology of flight, but such a creature might fly using a couple methods. It may: * Have a sort of sac on itself that stores pressurized air, and that gives the organism the punch it needs to launch into the air, and it would continually fire bursts of air to keep itself afloat-the sacs could be located on the 6 arms, then the creature would be able to control it's flight much better. Sort of similar to how an octopus 'flies' in water. * You could have a creature that has 6 legs that are also wings, although then the body plan of the creature would be a mess and idk whether it would be able to fly or move at all. Overall the sac method is the best, as it's been used by organisms here on earth already. Honestly the biggest issues here are aerodynamics and weight. [Answer] Why would the pterosaur and bat approach not work just because you added two more limbs? If you have any decent-sized dragon actually rear up on its hind limbs, it's going to look very tall: that isn't any reflection on its typical posture when you're talking of a six-limbed dragon. If the wings are sturdy enough, they can be used to push off the ground together with the four legs (or two legs and two arms, however those are defined for this creature). If there's enough muscle in the wings for true flight (not just gliding), there's enough muscle in them to provide a lot of lifting force when taking off, presumably enough to gain the necessary clearance to flap the wings; otherwise, this creature probably wasn't able to fly properly in the first place. Your solution is actually very simple: **the wings don't need clearance for taking off when pushing them against the ground is what gets you that clearance**. Of course, there's still the problem of cramming in sufficient musculature for six limbs in a dragon-sized flying creature (not to mention the vital internal organs and arteries and so on) without making it too heavy to take off, but that isn't in the scope of your actual question. [Answer] ### Running jump I would have posted this sooner, but I was mesmerized by my [source material](https://i.stack.imgur.com/seLeV.jpg). In the linked gif, notice the Malinois' form: after a running start it plants its front paws, plants its back paws immediately behind its front paws, then leaps again off its back paws. Though I wouldn't want it to jump off my back, the same principal could work for a dragon, depending on size. If you want your dragon to be able to run at speed, consider limb structure on four-legged animals. With a few exceptions, most of use "[rear-wheel drive](https://phys.org/news/2010-03-elephants-4x4s-scientists.html)", which requires stronger back legs than front and lends itself well to jumping under speed [Answer] make it go to its hind legs, here, you start flapping a bit, then you get a bit of a jump, synchronized with the flapping, and if you get enough thrust, you could get of the ground, but what you really want is this, a launch that uses all 4 legs foreward, and the wings to get a bit of upthrust here, otherwise, running, to flight is not very good, but it is what some birds, and in most stories, gryphons, even if this is technically worse than birds, and better, as it tells you they can run fast, but it is more flight drag, after that i can not really see it work, apart from insect takeoff and one that is a mix of some i said, as well as others ]
[Question] [ Looking at 3D Modeling a Deuterium Fusion laser-based reactor that outputs to a direct-energy conversion (tube or something?) based off Halo lore. (WIP fan project of mine, modeling a UNSC ship from inside out.) What I need to understand is the sort of equipment that the reactor should have - cooling, how the direct energy conversion works (ie what the layout could theoretically look like) and any other pertinent details that the reactor would require, so that I can model a plausibly realistic engine room layout. So basically, I'm fishing for recommendations for what the engine room is going to need in it, scientifically speaking. The reactor would be powering thrusters that are basically around 50-60 feet tall/wide and likely 200-300 feet long. Basic lore I'm working off is from the Installation 00 video on the Pillar of Autumn's Fusion Reactors: <https://www.youtube.com/watch?v=etUcTLautgc&start=1890> Timestamp provided for the exact point they discuss what the 'direct energy conversion' involves. [Answer] Tubes and pipes and copper windings and cables. It's not as if your reactor exists. So just make it stylish as you like. If you like kraken or snakes, make the cables snaking in and out. If you like steampunk, make brass tubes. If you like stinky diesel engines and spidery moving limb parts, make a V8. If you go all singularity sci fi, make it look like a small box in the cupboard. You won't see the actual working components under layers of isolation against heat and radiation. What you can see are the tubes and pipes going in and out through the isolation wall, and there are many of them because an actual working design would have an energy density which would be crazy. Compared to a V8, which you can see because the temperatures involved are not high, just think that you need to isolate and guide hard radiation into your converter and that plasma temperatures are like 10 million degrees, so you need active casing. And that's what you will see, and those you can design as you like. <https://de.m.wikipedia.org/wiki/Wendelstein_7-X> The general reactor chamber is either a ring (tokamak, stellerator), or a ball (laser fusion, condensed tokamak). Out from there you have x-ray collectors which work like solar cells on high energy, in many layers. For the ions and electrons you have a tunnel going out from the core, which is tasked to capture first the motion energy then the ion itself for energy production. That laser fusion thing may also have a magnetic piston, not with mechanical moving parts but with the same working principle. To capture neutrons, you have a layer of material inside the reactor which then degrades into new fuel. So. Looks like a 50 meter hairdryer with thousands of (your design choice) either cables or pipes or both going in and out. [Answer] **Straight 8.** [![enter image description here](https://i.stack.imgur.com/vcuhO.jpg)](https://i.stack.imgur.com/vcuhO.jpg) <http://www.gallowayengines.com.au/gallery-images/classic-restoration> Your engine will be based on a straight 8 piston internal combustion engine. Instead of pistons each cylinder is a reaction chamber. Having multiple chambers allows time to load and position the fusion fuel and the cylindrical shape allows circumferential lasers to trigger fusion. The open end of the cylinders double as exhaust jets. The other reason to use an internal combustion engine as a model is that many exist, and they look sweet - 100 years of looking like an engine should look. They are bulky chunky beasts amenable to handsome 3d modelling. And if someone calls it out as looking like the pride of 1951 Detroit" you can answer "Indeed. Its engineers were big fans of the Buick." ]
[Question] [ One of the conceits of my world is that the brain takes advantage of some physical processes we don't fully understand resulting in an incorporeal brain-like organ called the Yau-body. Fairly early vertebrates evolved the capability to connect to an parallel incorporeal realm and grow structures there that supplement the brain. Early on, this was fairly simple and just enabled better proprioception by simulating a simple model of the physical body. In higher mammals and especially primates, this process is much more robust, involves more parts of the brain, and results in almost an entire duplicate of the most of the brain's state stored in the incorporeal Yau-body. In humans, comparing the state of the physical brain and it's incorporeal duplicate is the primary way in which consciousness emerges. Naturally, this process also results in some more sci fi stuff, but for this question let's focus on consciousness and neuroanatomy. Assuming all that, what parts of neuro-anatomy are most involved here? Here are the requirements as I see them. * Something phylogenetically old needs to be involved. There should be something deep down in the lizard brain that we share with early vertebrates that is the core of this system. * The advanced thinking/reasoning/language parts should not be the primary drivers here, but part of this system should be in regular contact with those parts. Perhaps acting as a sort of information hub for them. * Activity in the related regions should be correlated with attention, arousal, or the sense of self when studied. What brain parts and processes should be involved here? To be clear, I don't plan on getting deep into the weeds of neuroscience in the primary text, these extremely narrow details will be used only in some optional in-universe diagrams meant add verisimilitude. [Answer] Psychological science major here (thesis in neuroscience). You're pairing function with structures, but the brain is more complex than that. If cognition is a commodity, then it is the product of a global economy recruiting simpler resources from all over. Just like how an iphone might be misunderstood as being built in the store you purchased it at, it's easy to think that the neurological operation is reducible to a single place of manufacture in the brain. With this in mind, if I were you I'd scrap or modify trying to have an explicit function attached to the organ(s). They are just another link in the supply chain. Assuming a material view, the brain is already fully functional as is, so does not need any more modules to achieve functions (attention, arousal, and sense of self)it already performs unless you enhance them in some way (this may already be your intention). Rather, they would perform a particular operation that modifies cognitive operations somehow. I would take a step back and instead of starting from cortical structures, I would start from the connective pathways that facilitate communication between both existent and fantastical structures. Something like the corpus callosum and other mylinated white matter pathways but instead of communicating between hemispheres, it communicates semi directly between distal areas of the brain by avoiding corporeal constraints (such as sending visual information straight from the retina to the occipital lobe, or straight from occipital to motor and central executive processes). This would give immediate fitness improvements by improving reaction time. Once there's a pathway set up with a function, that pathway is also subject to natural selection, including the possibility of incorporeal structures evolving that have different properties (and therefore different potential outputs) than corporeal anatomy. Another possible perk of incorporeal brain anatomy is that it could circumvent gyrification and other processes that happen in utero. The brain has to grow from a blue print which comes with structural limitations (think the difference between a prefabricated shelter and a normally constructed building). If you want the evolution of brains to stay similar to modern brains, you probably want an additional cost to this sort of thing, probably increased energy use, so that the course of evolution doesn't radically alter the brain foundations. Civilization would look a lot different if we could all tereport everywhere and didn't need roads or doorways. [Answer] **In my Father's house are many mansions: if it were not so, I would have told you. I go to prepare a place for you. John 14:2** The world is full of unseen dimensions and energy planes. Our physical beings inhabit one both others are accessible to us. Just as our brains are divided into a right and left hemisphere which concern themselves with intuition and reason, humans in your world have a third mind which concerns itself with these unseen worlds and the powers and presences that manifest therein. This ability would have clear evolutionary benefit if forces chiefly operating on these planes could affect the physical plane which our bodies inhabit. Disruption of earth energy could be a harbinger of impending disaster, and forwarded creatures seek shelter. Psychic energies stemming from the mass mind of many individuals can be better apprehended and understood. The limits to this are the imagination of the author and the potentially limitless hidden worlds accessible to our third mind. The nice thing for a fiction is that from the perspective of the third mind you can riff on well trod themes involving the right and left brains and their division of labor and specialties without falling into cliches or established camps of thinking as regards our divided consciousness. That is what science fiction does best. You can also tap into new age type thinking about these various dimensions for your point of view - my quote at the top is Jesus, but he was quoted in the context of a chapter on the many energy dimensions around us in the book [Ascension Magick](https://rads.stackoverflow.com/amzn/click/com/0738710474). The author deals with these unseen realms and how we can access and understand them. Possibly with a third mind? I have not read the whole thing. [Answer] A second brain already exists...probably. Ever have a "gut feeling" about something? > > The enteric nervous system (ENS) is known as the "second brain" or the brain in the gut because it can operate independently of the brain and spinal cord, the central nervous system (CNS). It has also been called the "first brain" based on evidence suggesting that the ENS evolved before the CNS. > > > While the ENS and "gut brain" already exist it is not very well understood, you could make it more established/understood/dominant in your world. It's already thought to affect mood and general well-being. I could see it being the link to your altbrain and because it's not really understood you could get away without having to name folds in the headbrain that would be a bit harder to suspend belief for. In your brainbuilding you could have it have a more pronounced effect or leave as is and simply have the gutbrain be the connection to your altbrain. Because ENS is theorised to have developed before the CNS, you could also include other species in your brainbuilding. [Answer] > > Plausible enough to suspend disbelief? Should I remove any of these parts or get some other parts involved? > > > I'm going to do a brief frame challenge here. You're asking a *very* narrow question, which is 'which parts of the brain being named will help suspend disbelief about my magic/sci-magic system'. In general belief is going to be suspended based on complex factors largely related to your presentation in a number of ways. Perhaps your presentation will be generally superior if you feel that the neuroscience of your brain/magic connection is particularly on-point. But putting that aside for a moment, I would suggest that a *better question* might be to ask how you can increase the verisimilitude of this situation in multiple ways. Things like 'intentionally making the neuroscience side of this magic system messy in a real-world evolutionary sort of way' may serve your purposes better than naming one specific part of the brain over the other. Having things loop in and out of this other dimension and be used for all kinds of weird things some of which are defunct or not really applicable to the modern creature will help sell that part of it. In other words I suggest branching out somewhat from 'which part of the brain' and rather looking at making it a *complex system of interaction with the brain*. This helps in several additional ways, not least of which that it's far less confusing for a reader to hear an explanation of a system described as complex than a bunch of words and terms a layman does not understand. ]
[Question] [ It has been said that humans are capable of reaching up to a billion light years away before expansion has taken those galaxies permanently out of reach without FTL methods. I aim to have a civilization use stellar engines from their home galaxy to reach these far out galaxies, build stellar engines on those stars and return them back to their home galaxy, red dwarfs will have the longevity of trillions of years for the long and slow journey back from the furthest reaches. The largest known galaxy ic1101 has 100 trillion stars, which is massive compared to the trillion stars in Andromeda and around 400 or less billion stars in the Milky Way. In 4 billion years we will have the Andromeda and Triangulum galaxy merger with the Milky Way and by 100 billion years the local group will have merged into a super galaxy of under 2 trillion stars, at this time without out intervention there will be no new matter that can enter this super galaxy as all other galaxy groups and cluster would be out of reach and sight. One of the major issues with bringing stars home with stellar engines is that the dark matter which is the bulk of the binding mass of the galaxy does not come with the star, neither does the black hole or inter stellar gas unless other methods are used to move or collect them. At an estimate there are 500,000 trillion stars within one billion light years from Earth and if that many stars were tried to be contained within one galaxy it would be thousands to hundreds of thousands times larger than the largest known galaxies, And with a tiny fraction of the necessary dark matter to hold the super galaxy together it might not be possible to have so many stars as part of one system We do have some ultra diffuse galaxies which are low or free from dark matter, they are the remnant of a galactic merger and clusters of stars that were thrown further out gravitate together without dark matter but these clusters or dwarf galaxies are small in comparison housing around 10 billion stars, similar to the size of the Triangulum galaxy There are a few possibilities i had thought of to achieve this from lifting material to vastly increase the galactic centres black hole or even some sort of megastructure on immense proportions, possibly a simple arrangement like a globular cluster would work, there are proposed systems of matrioshka brains on clusters of red dwarfs but could that exist without lots of collisions on the massive scale i am after? What methods that are within the laws of physics could an advanced species with stellar engine/megastructure and star lifting capabilities use to support a galaxy of 500,000 trillion stars (mostly red dwarfs) that has only a tiny fraction of the necessary amount of dark matter to bind it? Could it possibly exist as super giant globular cluster through a specific arrangement? [Answer] **Your stars show up under their own power. They stay under their own power.** From OP: > > I aim to have a civilization..., build stellar engines on those stars > and return them back to their home galaxy.. > > > Then > > What methods that are within the laws of physics could an advanced > species with stellar engine/megastructure and star lifting > capabilities use to support a galaxy of 500,000 trillion stars (mostly > red dwarfs) that has only a tiny fraction of the necessary amount of > dark matter to bind it? > > > Imagine an area of ocean far out at sea. We all have motorboats, we worldbuilders. I actually have a hot tub on mine. We all get together in an area of open ocean because we want to watch the Northern Lights. We motor there from our various places of origin. Once we are there we want to stay together, for camaraderie and so on your boat you can hear the sweet band I have playing on mine. We continue to use the motors to keep us in a tight group, not drifting off randomly from waves and wind. So too your collection of stars. They have star lifting apparatus already on them which is how you collected them in the first place. Continue to use that to keep them collected as you see fit. [Answer] Barring some technology that allows for violation of thermodynamics (mass creation ex nihilo), your species will also need to collect dark matter. This is tricky, because we don't know yet the exact nature of dark matter. You can't just drag it along with you via gravitation... it comprises the bulk of the mass of most galaxies, which directly implies that the stars you are moving are less than that bulk, they simply don't have enough gravity to bring it with you. Perhaps one of the best candidates for dark matter today is the axion. It's a primordial fundamental particle with low mass (this might be the biggest difference between it and WIMPs). Among other things, axions explain CP symmetry in our universe. Axions comprise a new "field" that makes CP symmetry happen, and if that field could be manipulated then it might also be possible to manipulate axions on a scale large enough to drag some back with you. I propose powering your axion field manipulators with the galactic mass that you're discarding, the "not long lived" stars that will burn out before your plan is complete. Perhaps even the singularities and galactic core black holes and so forth. The field manipulation will only be able to bring back some smaller fraction of the sum of axions, you won't get 100% of them or even 50%. To be honest though, if your species can do these things, I'm not sure they'll care so much about moving stars. This is beyond Kardashev 3 tech, veering strongly into 4+ realms. ]
[Question] [ My civilization is planning to being starlifting, mining a star by heating up portions of its surface and using a powerful magnetic field to channel the matter away from the star and into storage units. This is obviously not an easy task, and so these beings are looking for any advantage they can get. This means they're willing to pick and choose stars that will make the endeavor as easy as possible, and because they're only interested in hydrogen and helium, they have their pick of the galaxy. They want stars that are intrinsically favorable to star lifting because of their properties - temperature, mass, etc. Unfortunately, I don't know much about star lifting, and therefore I don't know what properties my civilization would want in a star. I have some basic ideas: * A low surface gravity, so it's easier for material to escape the surface * Perhaps a low magnetic field, so there's little interference with the artificial magnetic field * A cool surface temperature, to make it less dangerous to handle the hot plasma I don't know just how important these factors are, however. What characteristics should a star have to make starlifting easy? By "star", I mean a body fusing hydrogen or heavier elements. It doesn't have to be on the main sequence, of course, but it also shouldn't be a brown dwarf or a compact stellar remnant like a white dwarf or a neutron star. [Answer] **Previous Concepts** I did a quick literature review for this on google scholar, and unfortunately it seems like there isn't much research on the topic. I did however find [this](https://www.bis-space.com/membership/jbis/2017/JBIS-v70-no12-December-2017_fh83da.pdf#page=36) short article, which has a useful, if extremely simplified model (*n.b.* for whatever reason, it seems like the values they got in this article for specific energy required to remove mass from the photosphere are off by exactly two orders of magnitude, so keep that in mind if you want to do your own calculations with this). Basically, it just assumes that you have some kind of laser array rotating around the star dumping energy into a patch of the photosphere (whose depth is determined by photon mean free path), and that the energy imparted is enough to get every atom within the patch to escape velocity. This model is, of course, very simplified-- it doesn't take into account the fact that there is going to be energy transport from the heated patch to the rest of the star that reduces escaped particle flux, or that as the star's mass changes, the mean free path and escape velocity will change, amongst other things. I'm not going to probe to deeply into that article's model, but I'll leave it there for reference about some improvements we can make to it's model. One worthwhile thing we can note about the model is that the closer the typical thermal speed of atoms in the photosphere are to escape velocity, the less energy we have to apply to them. Unfortunately, I don't know enough about stellar equations of state to determine how this relates to other properties of the star like mass, but it might be a good direction to look in if you're well versed in that area. Now, the other thing to note is that this model is a pretty extreme way of going about the task of star lifting-- depending on the timescales you want to go about this on, the required power of your array is somewhere on the scale from a sizable percentage of to many times the output of the sun. A more feasible method would be to instead take advantage of the processes in the sun that are already responsible for ejecting material into space. **An Alternate Approach** Specifically, taking advantage of magnetic reconnection would likely significantly reduce the required energy. You see, in plasmas with zero resistivity, the plasma completely follows the magnetic field-- this is called the [frozen in flux condition](https://en.wikipedia.org/wiki/Alfv%C3%A9n%27s_theorem) and a consequence is that the mangetic field topology can never change. So, in this limit (known as *ideal MHD*), when two different ropes of magnetic fields collide, they can get tangled and bounce off each other but they stay two separate ropes. However, when there is a non-zero resistivity, the magnetic field *can* change topology and so the two colliding ropes can snap into a lower energy configuration of two loops where the magnetic tension carried in the initial fields is converted to kinetic energy of the bulk plasma fluid. If the two initial ropes are part of magnetic field loops wandering around the surface of the sun, then this can result one of the high kinetic energy loops being ejected out into space-- this is precisely what a [coronal mass ejection](https://en.wikipedia.org/wiki/Coronal_mass_ejection) is. My thoughts are that a sufficiently advanced civilization might be able to drive the surface of the sun in such a manner that accelerates and seeds this process of re-connection. If you then have a strong guide field set up, you can direct this ejection into some area where you can store it. There are a few advantages to using this process. The main one is that you are using the sun's energy itself in the form of its magnetic field to push your plasma into space, which should decrease the energy requirements significantly. The second is that the plasma that makes it into space has a far lower temperature than in the other scheme, which makes it easier to contain. This isn't actually as trivial as it sounds-- a naive calculation of diffusion in fully ionized plasma actually suggests that higher temperature plasma is easier to contain magnetically. To get the full picture you have to take into account turbulent processes and collective affects, after which it is generally found that diffusion across magnetic field lines is indeed more pronounced in higher temperature plasmas. As for downsides, the main one is that you are beholden to the internal magnetic field of the star to do the bulk of the work for you, so you might not be able to move as quickly or capture as large a percentage of the sun's mass. Now, reconnection is a notoriously finicky process and tomes have been written describing it in various regimes. One of the simplest models is the sweet parker model, which I won't really delve into here, but despite it's many inaccuracies it has some useful results. One of them is that the outflow velocity of the plasma bubble is approximately the alfven velocity: $$v\_A = \frac{B}{\sqrt{\mu\_0 \rho}}$$ Where $\rho$ is the density of the plasma in the magnetic flux ropes and $B$ is the magnetic field strength of these ropes. In general, if your civilization were to use this method they would want to find a star where $\rho$ and $B$ were such that the Alfven velocity was comparable to the star's escape velocity. They would also want to find a star with a very active magnetic field and lots of surface flux ropes to facilitate harvesting energy from it. Another thing they might look for is one where the re-connection rate $R = v\_{in}/v\_A$ is high, since that means they can pull plasma off more quickly. In the Sweet-Parker model, $$R = S^{-1/2} = \sqrt{\frac{\eta}{L v\_A}}$$ Where $\eta$ is plasma resistivity, $L$ is the length of the reconnecting strip, and $S$ is a dimensionless parameter called the Lundquist number. However, the Sweet-Parker model differs from observations by several orders of magnitude thanks to a whole host of instabilities and turbulent effects. In reality we tend to see reconnection ocurring at a fairly quick rate that depends very weakly on $S$, so it probably wouldn't be a high priority parameter for your civilzation. I just figured I'd include it for posterity. **TL;DR:** If the star-lifting model you want to use is hitting the star with enough radiation that the hot spot particles are above escape velocity, then it's pretty hard to avoid ridiculous energy requirements and your best bet is to try to find a star whose photo sphere particles are as close as possible to escape velocity already. If instead your approach is to try to seed coronal mass ejections, finding a star with a very magnetically active surface and alfven velocity close to escape velocity would be good zeroth order metrics for star suitability. If you want more in depth answers then I recommend looking towards the literature on magnetic re-connection and turbulent plasma dynamics for some more precise criteria. [Answer] blue supergiant stars would be ideal, but hypergiant stars is what you'd want. these die quite young because their awesome size means they fuse elements such as iron. and such stars would have a lot of them in quantity equal to dozens of times more mass than the entire solar system. it is speculated that machine life would favor these stars more than main sequence stars like ours. and would be a one stop shop for all of their needs. Provided you could milk it fast enough. [Answer] It would seem that the easiest approach might be to look for a binary or tertiary system where the masses and attraction between the stars creates a "matter-swapping" phenomenon, allowing your civilization to harvest the H/He at further distances from the star surface. An example would be: <https://www.eso.org/public/news/eso2002/> regarding the HD 101584 system. (a lighter read explanation of that specific example: <https://www.syfy.com/syfywire/hd-101584-a-binary-star-casts-out-a-bizarre-hourglass-of-gas> ) for fiction purposes if you don't have to stick to very specific real-life examples, maybe go for a combination of Red Giant / Blue SuperGiant and a White Dwarf? Could be a basis for some cool problems trying to implement a stable system for lifting the matter from the specific point/area in space where the gas streams converge or something alike :) [Answer] It took some Googling to find this answer so here you go: TL;DR at the bottom # Brown Dwarfs. I found a few quotes on Quora about these > > CFBDSIR 1458 10b, the star is what's called a brown dwarf. These oddball objects are often called failed stars because they have starlike heat and chemical properties but don't have enough mass for the crush of gravity to ignite nuclear fusion at their cores. > > > With surface temperatures hovering around 206 degrees F (97 degrees C), the newfound star is the coldest brown dwarf seen to date. > > > and > > WISE 0855−0714 is the coolest star discovered[2](https://i.stack.imgur.com/7TqHh.jpg)—it is a sub-brown dwarf star 7.2 light-years away from Earth, and its temperature ranges from 225–260 Kelvin. > > > The first quote provides a very comprehensive definition of brown dwarfs, basically these stars have the hydrogen necessary for fusion, but they don't have the mass, and therefore the heat and gravity for fusion to take place. Certain gas giants like Jupiter also have an abundance of hydrogen gas. The advantage here is that, the surface temperature is just very close to the boiling temperature of water, which means that heat shouldn't be an issue. However, you will not be able to obtain helium from these stars. Just one quick sidenote, hydrogen gas doesn't necessarily need to be obtained from stars or gas giants, it is available in abundance in space, it would be far easier to collect it from there. ## Star Color-Temperature Chart # [Star Color - Temp Chart](https://i.stack.imgur.com/7TqHh.jpg) As you can see the redder the cooler. It's not visible there, but the neutron star, due to its high density, has a surface temperature of a whopping 599726.85ºC. So avoid them. Therefore, you're better off going with orange stars if you want both hydrogen and helium. ### One Thing Though. Honestly, star-mining is a wasteful and unnecessary endeavor (obviously I don't your book's plot so I don't know if its a key lot element) but still, here's a tip. If the society just sent collector probes out in every direction, or if they mined from the brown dwarfs and/or gas giants I mentioned earlier, they would obtain an abundance of hydrogen, which they could then put in a fusion reactor to get helium, along with some free energy in the process. TL;DR: Redder stars are cooler; Collect hydrogen from brown dwarfs, then instead of mining stars, make your own in a fusion reactor. ]
[Question] [ The fantasy world is set in medieval times (1100 A.D - 1400 A.D). The mission is to travel from the mainland to an ice continent using a ship, a distance of say from England to the North Pole. The sea being traveled across is tame, though there are some icebergs the closer you get to the arctic continent. The purpose is to mine precious stones in the ice. The only outstanding source of technology or magic is stones that generate wind. These stones are used by sailors to give their sails a bit of an advantage over the seas. What sort of ship could sustain travel like this (a cog, a galley, etc)? How long would it take? And how many crew members would be needed (and what would their roles be)? [Answer] I think this could be done by one man in a kayak, provided there are things to hunt along the way, and the individual is adapted and skilled at arctic living. At least, I recall my middle school classes indicating the Eskimos did long solo hunting trips. The distance is large, but not impossible, particularly with your wind-stones. If you are not hunting along the way, the problem is carrying enough food and keeping warm. You might need a fleet of cargo ships delivering supplies. ]
[Question] [ Tengu are humanoid creatures with many avian features, including **wings and beaks**. Now, this is a problem when it comes to disguises. Disguises in this setting work by covering one's body in utility fog, which can accurately mimic just about any common material, as far as shape, texture and feel goes. The problem with utility fogs is that they're additive, and so, you can't subtract from a collision mesh (the object), only add to it (disguises are also called container meshes for this reason). This is especially painful for a tengu who tries to make a human disguise, since if they're found out, well, humans don't tend to be kind towards tengu kind. **So, how could a tengu's human disguise hide away the beaks and wings without exposing any of the collision mesh while also minimizing the risk of failing when closely observed?** The setting is feudal japan, tengu are flesh and blood, not yokai, there's no other magic or anachronistic tech besides these utility fog "container meshes". [Answer] **Mutilation** Disguising features as clothes could work, until humans find out and every person with heavy clothing and masks/really big noses became immediatly suspicious. The only way to overcome this is mutilating the beak and wings. Of course not many tengu would do this, only those dedicated to espionage. [Answer] # Disguise the beak and wings as clothing. Simply put, if these disguises are only additive, then just use them to layer clothing over the top of your inhuman features. Your beak becomes a mask with a really long nose. Your wings become a cloak or really baggy sleeves. ]
[Question] [ ### Background My world has a form of magic that is similar to telekinesis; that is, it makes things move. I also have technology that is essentially the same as today's real world. Thinking about it, this seems like it could be really useful for powering certain sorts of devices. There is, in fact, a certain type of electrical generator that is powered by magic. It consists of a fixed-magnet rotor surrounded by one or more pairs of coils. The rotor has no axle or bearings; it is spun and held in place solely by magic. As a result, the generator can be fully enclosed with no exposed moving parts; is is very nearly "solid state". Of course, this means it necessarily produces alternating current (DC would require brushes), possibly in several phases, but solid state circuitry can easily rectify this into fairly constant DC. (Alternatively, the generator has a mobile ring of permanent magnets which spins around a set of fixed coil-wrapped arms. I suspect this might actually work better, especially since the moving portion doesn't need an axle or bearings. The objective is to avoid brushes so as to minimize wear.) ### Question How *small* can I make such a generator? Can I make it, say, the size of a 2032 watch battery? (At least, small enough to fit in a Smart Watch?) It should be able to generate at least 2 watts. Do any such devices (obviously, unlike my magic-powered generators, they would need an axle that can be externally driven) exist in real life? Alternatively, is there some other way I can generate the required energy in the available size, using only the ability to make things move? ### Extensive Details This isn't necessarily relevant, but... I've previously asked about this magic system [here](/questions/160428) and [here](/questions/160846); those might provide some interesting details. In particular, magic is powered by the metabolism of living beings. For our purposes, what this means is that the generator has a constant supply of magic-energy *as long as it is on or near a person* (or, in some cases, an animal or other living source of magic). The generator isn't a "spin up once and coast" system; it is constantly being supplied with "fresh" kinetic energy via magic (when active; they can be made to have an "off" switch, and for safety and durability reasons, will halt themselves if separated from the person "feeding" the magic or if something happens that the rotor becomes stuck). Also, and this happens to be extremely convenient, by nature of how generators work (and by how I imagine my magic working), a magneto-type generator will always provide exactly the electricity needed with fairly low waste. Specifically, magic causes the rotor to turn at a fixed speed, which translates into the amount of magic energy used to keep the generator spinning being directly correlated to the amount of electricity being consumed by whatever is connected to it. I can just spend the (very small) amount of extra magic to keep it spinning *even if the connected device is off* with minimal to negligible consequences. (Conceivably, there would be a delay as the flow of magic adjusts to changing power requirements, but this is what power regulation circuitry is for, and I need that anyway, at least in the form of an AC/DC rectifier.) [Answer] One easy generator to make is a faraday disk or homopolar generator. And it should easily fit in your specified 2032 battery dimensions. [![enter image description here](https://i.stack.imgur.com/uwrNj.png)](https://i.stack.imgur.com/uwrNj.png) In the image the power is developed between the center axis of rotation and the outer edge, as the disk spins. These power sources generate a great deal of current at a low voltage and have been used to power welding machines. The drawback of this design is the rotating contacts. For your application, since you have **magic**, you can fix the conductive disk, and rotate the magnets generating the field B shown in the image. Any permanent magnets will work for your application. To generate more power, spin the magnets disk faster. The faster you go, the more power you get. To get 2W out of the generate, you'll need to put in at least 2W of kinetic energy spinning the magnets plus any losses resistive losses in the disk. The thickness of the disk is determined by airflow for cooling and the current flow delivered to the load. 1 mm of gold can carry over 40 Amperes of current safely, which is much higher than you are going to need. Your buck-boost or resonant power converters can convert the output voltage to whatever value and waveform you need. ]
[Question] [ Monotremes are the oddballs of the mammal family, the echidnas and especially the platypus are absolutely absurd creatures with their bizarre anatomical features and mishmash of reptilian and mammalian traits. [Of particular note is that they lay eggs and run a much lower core body temperature than other mammals.](https://en.m.wikipedia.org/wiki/Monotreme) These traits at first appeared to be nothing more than a a curiosity and sign of their primitiveness, but I pondered the advantages such a “toolkit” might bring. I came to the conclusion that monotremes actually have features that would be extremely beneficial for growing to massive sizes that placental mammals cannot reach. Although the idea seems absurd on its face, we can examine what constrains the size of placental mammals and examine traits of what we know to be the largest land animals to ever exist; the sauropod dinosaurs. Placental mammal size is quite limited compared to the [dinosaurs for three primary reasons; metabolism, reproduction, and biomechanics.](https://www.nationalgeographic.com/science/phenomena/2013/02/25/dinosaur-reproduction-not-ancient-gravity-made-sauropods-super-sized/) Placental mammals have to eat a lot of food to keep their fast metabolisms going, while reptiles and monotremes need to eat a lot less. Pregnancy in placental mammals is arduous on the mother and simply put the larger the baby the longer and more costly the pregnancy. Egg laying gets around this as it takes far less energy and maternal commitment. Dinosaurs also had a different bone structure and air sacs that allowed them to grow larger, so both placentals and monotremes lose out on those. I’m not expecting the monotremes to reach sauropod size, but given that they have the metabolism and reproductive method suited for large sizes of expect them to at least have be reaching larger sizes than the placentals. But my conjecture isn’t borne out by evolutionary history, as the [largest monotreme was about sheep sized](https://en.m.wikipedia.org/wiki/Zaglossus_hacketti). So what prevents the monotremes from getting big besides getting pushed to the very fringe by the other two mammal families? What would it take for gigantic monotremes to evolve? Would being isolated on a continent free of other mammals suffice? Or is there something else? [Answer] **Nothing is really preventing them from getting big** Something to point out first, nobody really knows what the monotreme family tree looks like. Their fossil record is restricted to two continents (South America and Australia) and Australia is infamous for having a bad fossil record. There are maybe twelve species of monotremes known in the fossil record, along with some loosely related forms in a broader group called Ausktribosphenida, and most of them are some type of semi-aquatic platypus-like form. In fact, echidnas are believed to have become secondarily terrestrial from an aquatic platypus-like ancestor. We have pretty much no idea what was happening on land with mammals during the Cretaceous in Australia and Antarctica. For all we know there is some species of giant carnivorous monotreme akin to *Repenomamus* from China in Cretaceous polar Australia and we just haven't found it yet. Even in places where you had monotremes like South America there were often other groups like dryolestoids experimenting with terrestrial niches. What seems to have happened is marsupials and placentals moved into South America and Australia and prevented monotremes from really diversifying. The best way to get monotremes to diversify would be to either stop northern mammals from dispersing to South America around the K-T boundary, or stop them from dispersing to Australia, which would give monotremes a whole continent to play with (if they can outcompete the dryolestoids and gondwanatheres). On the whole, there are no features to suggest that monotremes are constrained to be the size they are, but there is nothing to suggest they can be gigantic either. We simply have no idea as to this group's evolutionary limits. What is keeping mammals from reaching sauropod size is probably the presence of teeth. The largest mammals (*Paraceratherium*) are about the same size as the largest non-sauropod dinosaurs (big hadrosaurs and ceratopsians, large theropods). It's been suggested that because mammals and many ornithischian dinosaurs all have complex chewing batteries this puts a constraint on their size, because their head increases disproportionally relative to size in order to chew efficiently enough to process food. Sauropods (and to a lesser degree stegosaurs) just swallow food whole, so they can get away with having tiny heads relative to their body size. ]
[Question] [ Humanity has discovered entire worlds filled with creatures that would question their understanding of biology, but one creature, if it can be called, has brought up many many questions. **Appearance and behavior** The amoeba sea is a massive colony of amoeba Like organisms that stretch across nearly 75% of its planets surface, which is why it’s called a amoeba sea. The surface is solid enough to walk on, but isn’t solid enough for heavy objects, or prolonged standing. the amoeba sea is purple in color and underneath it, one could see either slow moving or completely immobile dimly lit lights which are thought to be some form of bioluminescence. The sea seems to slowly pulsate, which scientists think is a result of the air, but there isn’t any proof to back it up. When being walked on, the researchers noted that the surface starts to become a lot more more liquid like, and in one instance, a scientist had “fallen” through the surface, and was presumed to be dead. This suggests that the amoeba sea will weaken is surface, causing any living organism to fall through and presumably be digested. When a drone had been sent to go under the amoeba sea, it found thousands upon thousand of preserved yet dead bodies and small cave systems filled with the amoeba like organism, which suggests that either the organism is actively yet slowly corroding rock in search for food, or has grown and replaced an entire sea. **extra facts** Recently, it has been seen that the local wildlife are safely capable of eating it, which means that the colony of amoeba like organisms might not feel pain, or just don’t react and is filled with enough water and nutrients to keep an animal fed for a few hours or days. **what environmental pressures would lead to a amoeba sea, and what parts of it are and aren’t feasible?** [Answer] ## You're looking for photosynthetic slime molds on a primordial world. **The colonies need to be smaller.** The most glaring issue with this colony is its sheer *size*. Even alien amoebas need to eat - but if they take up 75% of the planet's surface, chances are they won't leave much room for prey, or nutrients, or much of anything. Even though many colony-forming eukaryotes and tons of bacteria live in our oceans, they haven't physically filled it because there is far, far too little food in the ecosystem. I can't give you a quote for how much of the ocean can be covered in this organism, but I highly doubt it exceeds 10%. If you're looking for a good place to put colonies, consider placing them near the coasts, where most sea life is on Earth. **The ocean probably can't be physically solid.** Solid structures atop a constantly moving sea won't last long. They also don't make much sense for undifferentiated, unspecialized colonies of microorganisms that need to eat. In a thick amoeba mat, how do the ones in the center get any food? I could see some structures forming in a manner similar to [slime molds](https://en.wikipedia.org/wiki/Slime_mold) (which are related to Earth amoebas!). You could create some vein-like tissues and organs to distribute nutrients, or to communicate about threats. However, nothing too thick would be able to hold itself together. This also rules out digestion. **Purple coloration can be explained by photosynthesis.** A colony (or group of colonies) this large definitely can't eat other organisms to get nutrients; what else could possibly be numerous enough to supply food? Instead, your colonies will make their own food from sunlight. [Early photosynthesizers](https://www.livescience.com/1398-early-earth-purple-study-suggests.html) on Earth used retinal, a purple pigment less efficient than the green chlorophyll we know and love. This is ideal for your world. **Your world is probably very young.** One hypothesis states that since chlorophyll is more efficient, the once-dominant retinal became far less prominent over time. Retinal may be one of the many pigments for photosynthesis that early life forms try out across the universe before reaching peak efficiency for their (sun-like) host stars. Inefficient purple pigment makes the most sense on a young world. A young world is also consistent with the absolute dominance of your amoebas over the environment. They are likely among the first producers to evolve, so they have little competition and virtually zero macroscopic predators. The one caveat here is that you can't really have land animals, and bioluminescence is unlikely. Finally, a young world may also be consistent with the pristinely preserved bodies within the ocean. Decomposers may not yet be common - so dead scientists don't break down easily. ]
[Question] [ Recently, I’ve taken a small break to establish a story bound universe, so that these questions can actually prove useful in the future Recently, humanity has discovered a vast earth-like planet, with various ecosystems. However, in the desert, they find a creature that resembles one of Earth's many invertebrates, a scorpion. The scorpion seems to act like ants, having workers, soldiers, and a queen. **Queen** The stinger on the queen's tail seems to resemble that of a flat leaf, with a bulbous lump in the middle. This is thought to be an evolutionary advantage for self protection. This is also because their desert-like environment is seen to have a little more foliage than Earth's deserts. When in danger the queen will not only sting its attacker, but will spray formic acid, mixed with a potent venom, which quickly kills said attacker. The body of the queen has the texture of sharp rocks. This is thought to be a form of camouflage, but also a form of defense, in case she needs to move the colony to a safer location. In rare cases, she has been seen to have small plants growing on the back of her rocky-like body. The head of the queen seems to possess two to four horn-like nubs. Four indicating health, and old age. The eyes are green and are described as slanted like compound eyes. The pincers of the queen are fairly normal looking. They don’t have much of or any particular purpose other than to clamp down, hold, and tear prey. **Soldiers** The body of the soldiers look a lot more ridged and sharper than their queen or worker counterparts. Their pincers are a bit bigger than their body, and have hook-like nubs forming on the sides of said pincer. The stingers are a little bigger, and are capable of spraying formic acid further and in a wider arc than the queen can. **Workers** The body of the workers have a sleeker and smoother texture than the soldiers, but is still strong nonetheless. The pincers are smaller yet longer, and have a slight curve to them, indicating that they dig wide and long lasting tunnels. The head of the workers are flat in a way so as to block or wall-off the entrances of the colony from invading creatures. The stinger of the workers is small and doesn’t really spray all that much formic acid. **What evolutionary pressures would lead to such creatures, and are such creatures even feasible?** **extra facts** The scorpions are seen to frequently migrate. In a recently seen event it was found that sometimes many colonies will migrate together, but split off along the way to find suitable nesting locations. This also indicates that the scorpions are mildly passive to other colonies. [Answer] **Various prey and predators or fighting eachother** I see no reason this creature couldn't exist as there are hundreds of examples of real creatures that have developed similar traits, even if not necessarily all of them. Therefore there is no reason they wouldn't have other related personality traits. Preying mantis will sit perfectly still among leaves, waiting for other insects to wonder by and then strike quickly. Likewise, It is entirely common for various insects to have rocky or leaf-like body shapes to hide from large predators such us birds and rodents. Since the description of the queen seems to imply that they are very large creatures, I'm going to assume that they are more like lizards in size rather than insects. Also, since no other creatures were mentioned, I might assume they actually fight among themselves. There is precedence for this as it isn't unheard of for ants of separate colonies to almost literally go to war with eachother. This gives you the freedom to expand into multiple varieties, again much like ants (i.e. fire ants, red ants, bullet ants, etc...). Larger creatures that form clear, but simple, societies have every reason to develop in a way to defend against themselves essentially. Maybe some have a harder, stone-like exoskeleton; which in turn allows them to be protected from stingers, but is heavier and slower. Another variety is more leaf-like and camouflaged, which also allows them to be faster in exchange for being vulnerable to the stingers. Colonies fighting eachother also goes along with the idea that the workers have flat heads to block off enemies. You could just keep going with this and it really should work out just fine unless you get really crazy with it. [Answer] **Aereal predators** The scorpions you describe seem to have adequate defenses againsts ground menaces, but lack for aereal ones, so their best bet would be to remain still and not be seen. However, i'm not sure the role of the queen, why has it so formidable defenses? Isn't it buried in the soil and kept feed? Is the colony ever migrating? ]
[Question] [ (This is the third in a series of questions, starting with [Moved into further orbits to protect them, how much damage do Earth and Moon take when the Sun expands?](https://worldbuilding.stackexchange.com/questions/166627/moved-into-further-orbits-to-protect-them-how-much-damage-do-earth-and-moon-tak) and [How soon does the Earth's surface re-solidify after the red-giant Sun is replaced with a different star?](https://worldbuilding.stackexchange.com/questions/166804/how-soon-does-the-earths-surface-resolidify-when-the-red-giant-sun-is-replaced)) **The story so far:** To recap from my previous questions (and @StarfishPrime's answer to the first): Far future humans have attempted to save the Earth from destruction at the hands of an expanding Sun, by moving it and the Moon into a further orbit. They didn't, however, get them to a sufficient radius to save them completely. Giving up, they abandoned the solar system. A group of aliens, wanting to preserve something of the Earth and Moon for scientists to land on and study, arrive shortly after this and take action. They have brought a large gas giant (at least the size of Jupiter) with a solid rocky/metallic core, and by steering it into a very close orbit, ensure that it is engulfed by the Sun when it starts to expand. This eventually causes the Sun's red giant stage to end prematurely, as it sheds its hydrogen envelope. Thus, it becomes a [type B blue-white subdwarf](https://en.wikipedia.org/wiki/Subdwarf_B_star), similar to [Kepler-70](https://en.wikipedia.org/wiki/Kepler-70). Nevertheless, the Earth and Moon have taken a lot of damage. Tens of millions of years later, another group of aliens arrive to witness the results. The heat and escaping gases have burned/evaporated away the Moon's crust and most of its mantle, reducing its diameter from $\approx 3500 km$ to $\approx 700 km$. The Earth has fared better, its diameter being reduced by $\leq 130 km$. Depending on how soon the second group of aliens arrive, the Sun may still be the blue-white subdwarf, or may have become a bluer [Type O subdwarf](https://en.wikipedia.org/wiki/Subdwarf_O_star), or may even have gone past that stage to become a white dwarf. **And now... the question!** *What do the Earth and Moon look like now?* In particular, what colours do their surfaces appear to have, and has the Moon developed new "seas" on the side closer to Earth? **What my research suggests:** Let's start with a diagram of the Moon's geological layers - I think it will help clarify the reasoning that follows: [![Diagram taken from https://commons.wikimedia.org/wiki/File:Moon_Schematic_Cross_Section.svg. The creator, Bryan Derksen, released it unconditionally into the public domain, so there are no licensing issues.](https://i.stack.imgur.com/TMx7N.png)](https://i.stack.imgur.com/TMx7N.png) In the case of the Moon, if the stratified layers of its geology were not mixed up and rendered homogenous by the increased heat, the less dense materials in its crust and most of its mantle would have been lost. The heavier materials of the iron-rich core would have sunk back to the centre, leaving exposed the pyroxene and olivine of the lowest mantle region (the "zone of partial melt".) As this resolidifies, it may resemble the darker basalt of the Moon's seas/maria. However, coming from lower regions of the mantle, it might also be mixed with some iron (silvery - dark grey) and a little sulphur and/or iron sulphide. It could also be that the pyroxene and olivine are less mixed, resoldifying as green crystalline areas. If, by contrast, it was rendered relatively homogenous as the layers mixed, we might still expect the lighter elements (currently nearer the surface) to evaporate first. The Moon's outer layers are relatively light in colour, so I think the new, smaller Moon might look a little darker. That's before one considers the different wavelength of the starlight now reflecting from it, though. I understand that the reason for the maria being only on the near-side of the Moon is not currently known, or at least that there's no consensus on any one theory. In the case of the Earth, I think I'll need to plead even more ignorance. The atmosphere might resemble that which it had before photosynthetic life began to increase oxygen levels (CO\_2, nitrogen, some other gases) or might be maybe hydrogen, including the layers shed by the Sun. The resolidified new crust underneath this might look somewhat similar to the present-day crust, possibly varying a lot from place to place. Without there being another Large Heavy Bombardment, I don't think there would have been much new water introduced to the planet, and with the loss of oxygen there would be less for the hydrogen to react with. So I think there would no longer be any large oceans, and plant life would not have re-evolved in any form in so short a time either. Perhaps it would resemble present-day Venus? But with more hydrogen, due to the magnetic field continuing to function. And without sulphuric acid in the atmosphere, it wouldn't have the yellowish sky and opaque atmosphere of Venus. (*Disclaimer. As you have all probably guessed by now, I'm not a geologist! Or a chemist, for that matter. So you should take my reasoning with a pinch of salt.*) ## Sources: [Weber, R. C., Lin, P. Y., Garnero, E. J., Williams, Q., & Lognonne, P. (2011). Seismic detection of the lunar core. science, 331(6015), 309-312](http://gcc.asu.edu/patty/DOC/SeismicDetectionOfTheLunarCore_Science2011.pdf) [Heber, U. (2009). Hot subdwarf stars. Annual review of Astronomy and Astrophysics, 47, 211-251.](https://web.archive.org/web/20110721003323/http://www.sternwarte.uni-erlangen.de/~heber/araa/araa_revised.pdf) Plus [slides](http://astro.physics.ualberta.ca/rockies14/sites/default/files/conference_presentations/u71_present.pdf). [Wieczorek, M. A., Jolliff, B. L., Khan, A., Pritchard, M. E., Weiss, B. P., Williams, J. G., ... & McCallum, I. S. (2006). The constitution and structure of the lunar interior. Reviews in Mineralogy and Geochemistry, 60(1), 221-364.](https://web.archive.org/web/20141221063318if_/http://scripts.mit.edu/~paleomag/articles/60_03_Wieczorek_etal.pdf) And quite a few Wikipedia pages. [Answer] This answer contains two answers, rolled into one. First the Moon, then the Earth. ## The Moon: **The Moon - in short:** Lots of green and black crystals, but because of the sun they look a bit bluer than they would on Earth. **The Moon - in full:** First of all, although I said that the surface *"may resemble the darker basalt of the Moon's seas/maria"*, it won't actually *be* basalt, since the Moon's mantle doesn't contain the necessary plagioclase. It's primarily composed of olivine and pyroxene. Some volcanic and meteoric rocks composed of mixtures of these two minerals have been found on Earth. I'm going to base the Moon's appearance on those, since they seem consistent with what would be expected for these materials in the Moon itself. However, since the new Sun is bluer than the old yellow Sun, I'm going to assume that the green looks more blue-tinted than it would under our Sun. Here's an image of one such rock. Albeit with some basalt (grey) also mixed in: [![Image taken from https://en.wikipedia.org/wiki/File:Peridot_in_basalt.jpg. As per licensing conditions, credit goes to Wikimedia user Vsmith (https://commons.wikimedia.org/wiki/User:Vsmith)](https://i.stack.imgur.com/bApGT.jpg)](https://i.stack.imgur.com/bApGT.jpg) *As per the licensing conditions (CC3.0, see [here](https://en.wikipedia.org/wiki/File:Peridot_in_basalt.jpg)), credit for the above image goes to Wikimedia user Vsmith.* And here's another: [![Image taken from https://en.wikipedia.org/wiki/File:Peridot_olivine_on_basalt.JPG. As per licensing conditions, credit goes to Wikimedia user Pyrope (https://commons.wikimedia.org/wiki/User:Pyrope)](https://i.stack.imgur.com/vKutV.jpg)](https://i.stack.imgur.com/vKutV.jpg) *As per the licensing conditions (CC4.0, see [here](https://en.wikipedia.org/wiki/File:Peridot_olivine_on_basalt.JPG)), credit for the above image goes to Wikimedia user Pyrope.* Here's [yet another one](https://cabezaprieta.org/geology/scarborough/fig_0043.php) that I don't think I can embed (licensing reasons). Very similar to the above image, it shows a rock with green olivine crystals, black pyroxene crystals, and some basalt sections visible. Ignore the basalt, and you have something quite similar to what the Moon will look like. [The Encyclopaedia Britannica](https://www.britannica.com/science/pyroxene/Crystal-structure) provides some information on the colour of pyroxene. Importantly, this includes the following: > > Iron-rich ferrosilite orthopyroxenes range from brown to black. > > > Another type of pyroxene is described as being darker when its iron content is higher, so I'm going with black. The appearance of clinopyroxenes seems to be more variable. It's hard to say for sure, but I think I'm safe with green-to-black colouration. Though that's slighly circular reasoning based on the images of rocks I've looked at. As I mentioned, I'm going to base this on actual rocks found on Earth, so there will be visible separate green crystalline olivine crystals and black pyroxene crystals. [Wikipedia states](https://en.wikipedia.org/wiki/Olivine) that olivine weathers quickly on the Earth's surface, but with no water and only a very thin atmosphere on the Moon I don't think this will be an issue. Olivine is typically green, and gem-quality olivine is referred to as peridot. [It is stated](https://www.minerals.net/gemstone/peridot_gemstone.aspx) that the more iron this contains, the deeper the shade of green it will be. We're looking at an iron-rich geological layer, so the olivine will be a very deep green. I don't know how much of the Moon's lower mantle is composed of pyroxene and how much is olivine, so I'm going to have the black and green crystals feature in roughly equal quantities. I've noted that the exposed region is the lower mantle, and suggested in my question that there might be some pure iron and/or iron sulphide visible. I've decided that if this is the case, there are only fairly small regions of both. I can't rule out the possibility that the extra iron would simply have resulted in the pyroxene being one of the more iron-rich varieties. ## The Earth: *(Before reading this, please read the section devoted to the Moon. This section builds on it.)* In the case of the Earth, the exposed rock is from the mantle. Whether it's the lithosphere or the asthenosphere doesn't matter - they have different mechanical properties but the same geological composition, since they're both part of the upper mantle. [Wikipedia](https://en.wikipedia.org/wiki/Upper_mantle_(Earth)) states: > > Upper mantle material which has come up onto the surface is made up of about 55% olivine, 35% pyroxene and 5 to 10% of calcium oxide and aluminum oxide minerals such as plagioclase, spinel or garnet, depending upon depth. > > > That fits with the images in my Moon answer - mostly green crystal with some black and a small minority of other subsances. [This page on America's geology](https://cabezaprieta.org/geology/scarborough/earth_cross-section.php) states that rocks such as the ones in the image do indeed come from the mantle; and you can google "mantle xenoliths" for further confirmation. What about weathering of the olivine? Well, without heavy asteroid bombardment similar to the LHB, the Earth won't have regained water. But how the exposed rock might react with the atmosphere I don't know. I *think* the atmosphere at this point would probably consist mainly of carbon dioxide ($CO\_2$) and dinitrogen ($N\_2$) (sources: [Wikipedia](https://en.wikipedia.org/wiki/Atmosphere_of_Earth#Evolution_of_Earth's_atmosphere) and a paper called ["Earth's Earliest Atmospheres"](http://cshperspectives.cshlp.org/content/2/10/a004895.full.pdf) in which I've just ignored references to water vapour.) Now, dinitrogen is odourless, colourless, and [forms about 78% of the present-day Earth's atmosphere](https://en.wikipedia.org/wiki/Nitrogen). Carbon dioxide is also colourless, so I think we can see the Earth's new surface from space. Dinitrogen would I think be mostly inert, but $CO\_2$ can react with olivine. Though it won't react as fast as it would if water were present. (source: ["Mineral carbonation in peridotite rock for CO2 sequestration and a method of leakage reduction of CO2 in the rock."](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.915.4248&rep=rep1&type=pdf)). Ditto pyroxene. Olivine *that doesn't contain iron* and carbon dioxide can react to form magnesium carbonate and silicon dioxide (which I suppose would mean "quartz".) I'm not a chemist, so I don't know if I can infer anything about iron-rich olivine from this. But much less of the Earth mantle's olivine is iron-rich than that of the Moon, so this is useful for four fifhs of the olivine. Magnesium carbonate is a white salt, Pyroxene *that doesn't contain iron* and carbon dioxide can react to form dolomite and quartz. The amount of pyroxene without iron is, again, much higher on the Earth than on the Moon. Dolomite crystals are opaque white. Quartz occurs in several different colours, and I don't know which one(s) to expect. Still, I don't think the conditions for the impurities that cause these colours seem likely, so white/transparent would I think predominate. So I'd say we've got a small minority of black crystal from the iron-rich pyroxene, and a larger minority of green crystal from the olivine, UNLESS $CO\_2$ reacts with either of those. The rest of the planet, depending on how fast the reactions have occurred and over how much time, might be mostly white crystal and salt, or a much more whitened green with some faded-formerly-black, or white areas mixed in with green areas... And if the sun is not a white dwarf yet, there should be a nice bluish tint to it all. Very pretty! (if my reasoning is correct.) Well done you aliens! ## Sources: [Workman, R. K., & Hart, S. R. (2005). Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters, 231(1-2), 53-72.](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.466.4451&rep=rep1&type=pdf) [Wieczorek, M. A., Jolliff, B. L., Khan, A., Pritchard, M. E., Weiss, B. P., Williams, J. G., ... & McCallum, I. S. (2006). The constitution and structure of the lunar interior. Reviews in Mineralogy and Geochemistry, 60(1), 221-364.](https://web.archive.org/web/20141221063318if_/http://scripts.mit.edu/~paleomag/articles/60_03_Wieczorek_etal.pdf) [Zahnle, K., Schaefer, L., & Fegley, B. (2010). Earth's earliest atmospheres. Cold Spring Harbor perspectives in biology, 2(10), a004895.](http://cshperspectives.cshlp.org/content/2/10/a004895.full.pdf) [Dabirian, R., Beiranvand, M., & Aghahoseini, S. (2012). Mineral carbonation in peridotite rock for CO2 sequestration and a method of leakage reduction of CO2 in the rock. Nafta, 63(1-2), 44-48.](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.915.4248&rep=rep1&type=pdf) ]
[Question] [ Perissodactyla is an order of mammals consisting currently of the seventeen species of horses, rhinoceroses and tapirs. Usually, any clade is connected by a coupling of genetics and physical morphology. The ancestor of all perissodactyls, even the extinct brontos and indriks, looked a bit more like this: [![enter image description here](https://i.stack.imgur.com/HLI3c.jpg)](https://i.stack.imgur.com/HLI3c.jpg) This is *Hyopsodus* of the ancient family called the hyopsodontids. It was likely swift and nimble, living in burrows and perhaps hunting with echolocation like some species of moles still do today. The hyopsodontid family did not last long--living from the early Paleocene to the Eocene. But what if they held on a little bit longer, long enough to assume a larger, more otter-like form and taking on an evolutionary path similar to the archaeocetes, the earliest of the true whales? Back home, whales are confirmed to be artiodactyls, with their closest living relations being hippopotamuses. But in this alternate Earth, a clade parallel to whales--let's call them "illhveli", for clarity's sake--are perissodactyls. Using modern perissodactyls as reference, what sorts of anatomical, skeletal or other kinds of morphological differences should I watch out for in an odd-toed cetacean ("illhveli") in comparison to our even-toed cetacean ("whale", "dolphin", "porpoise")? [Answer] There is no predicted difference, so any difference is up to you. *Hyopsodus* is [very close](https://www.semanticscholar.org/paper/A-new-apheliscine-%22condylarth%22-mammal-from-the-late-Zack-Penkrot/d628f900a3e135b769f30638657c0b7f7ff7861e) to split in condylarths that leads to artidacyles and perrisodacyles, there is little anatomical difference present that is not lost in cetacea. Hyopsodus is smaller but not that much smaller. the ankle structure is different but whales lose that difference. Whales are so derived for aquatic living that they have lost the noticeable anatomical differences. to put it a different way the differences within existing cetacea is far greater than any difference inherited from that far back, if you want to make it different you can but there is nothing inherited from *Hyopsodus* that will cause it. If you want them to look like otters, or hippo, or walrus you can, you get to decide all the evolutionary path they take. [Answer] We will assume (we have to assume something!) that the basal perissodactyl offered in the OP has in it to potential to evolve into these later forms, because it did. How to transition to an aquatic form? Let us consider what perissodactyls do well, judging from modern forms. They do well as vegetarians, using hindgut fermentation and eating large quantities of low quality fodder. Larger body size can accommodate this lifestyle better. Extant perissodactyls are horses, zebras and rhinoceri. One large bodied semiaquatic mammalian herbivore is the hippopotamus. Could the aquatic perissodactyl be something like a hippo – a large bodied four legged swimmer, grazing aquatic grasses and seaweeds? Yes. **Behold Desmostylus, the aquatic perissodactyl!**. [![Desmostylus images](https://i.stack.imgur.com/jEPMr.jpg)](https://i.stack.imgur.com/jEPMr.jpg) From [Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia, Afrotheria)](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0059146#pone.0059146-Repenning2) > > Figure 1. Various restorations of desmostylians based on morphological > data illustrating the diverse lifestyles proposed. A, semi-aquatic > (like the polar bear) (from [17]). B, bottom wader (from Inuzuka's > restoration; the figure is printed with the permission of the > Geological Museum, Geological Survey of Japan). C, bottom > walker, Hippopotamus-like (from [73]); D, bottom swimmer, > sirenian-like (from [22]). E–F, active swimmer, pinniped-like > (from [23]–[24]). > > >   Their aquatic adaptations made it difficult to place desmostylians in a family group. The most recent cladistics analysis puts them in perissodactyla, and so a cousin to horses (Hippomorphs) and tapirs (Tapiromorphs). [Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4189980/) [![clade](https://i.stack.imgur.com/rPInk.jpg)](https://i.stack.imgur.com/rPInk.jpg) Different forms of locomotion were proposed for the desmostylians, as shown in the above artists depictions. As regards how aquatic they were, a recent bone analysis put the desmostylians closer to sirenians and pinnipeds than hippopotami and polar bears. These researchers (same source as art image) concluded “the bone microanatomical specializations of desmostylians (i.e. bone mass increase and a spongy inner organization) indicate that all desmostylians were probably predominantly, if not exclusively, aquatic.” --- But the OP did not want an oceangoing hippo. He wanted a WHALE! A whale must be provided, or risk a downvote! How to move from the 4-legged swimmer desmos to something closer to a cetacean? Let’s take a look at a desmo skeleton, and consider its lifestyle, and then see if nature has any examples we can use as a model for a cetacean-morph perissodactyl. [![desmo skeleton](https://i.stack.imgur.com/RsErl.jpg)](https://i.stack.imgur.com/RsErl.jpg) Depicted: skeleton of the desmostylian Neoparadoxica repenningi. From [The phylogeny of desmostylians revisited: proposal of new clades based on robust phylogenetic hypotheses](https://peerj.com/articles/7430/#fig-3) Those hind legs are already close together. As the creature gets larger and rare expeditions to the land become more a dragging than a walking those will probably fuse into a propulsive apparatus like a seal or a manatee. And manatees, or more properly sirenians, is where we will get the model for the whale-like perissodactyl: **Steller's sea cow**. [![stellers sea cow](https://i.stack.imgur.com/HBlMt.png)](https://i.stack.imgur.com/HBlMt.png) <http://lostzoo.com/animals/001_stellersseacow1_eng.html> Steller's sea cow was an immense relative of the manatee, growing to 10 meters long. They lived in the Pacific and ate kelp. They are famous for being huge, tasty and also going extinct almost immediately after they were discovered. It is proposed that the desmostylians went extinct because they were outcompeted by sirenians like the sea cow. Their lifestyles seem very similar and they were structurally similar too with skulls adapted to suctioning up sea plants. [![skull morphology coomparison](https://i.stack.imgur.com/rSpzS.jpg)](https://i.stack.imgur.com/rSpzS.jpg) <https://ocean.si.edu/ocean-life/marine-mammals/flippers-or-feet-extinct-mammal-may-have-been-replaced-todays-sea-cows> Steller's sea cow was whale sized at 10 meters. Scaling up a desmostylian to that size would mean losing / fusing hind limbs but keeping the feeding style and digestion of the smaller forms that really existed. Finally: how to distinguish this perissodactyl "cetacean" from extant cetacean The big difference would be diet. There are no vegetarian cetaceans. Distinguishing the illhveli from sirenians would be more difficult. Maybe tusks? Desmostylus had tusklike teeth and tapirs have tusks. Maybe illhveli would retain a tusk? [![enter image description here](https://i.stack.imgur.com/bWbta.jpg)](https://i.stack.imgur.com/bWbta.jpg) <https://www.reddit.com/r/Inktober/comments/9no0v6/medieval_whales_for_inktober/> ]
[Question] [ Would anyone be able to check some math/ let me know if I'm thinking of this the correct way? I had an idea of the moon appearing basically stationary in the sky, but in fact it orbits just faster than the rotation speed of the earth. From earth, it'd appear that it takes an entire year for the moon to make a complete orbit (which is obviously incorrect, as the earth is rotating). So if the moon is directly above you at midnight, it stays directly above you all day and to the next midnight, only moving forward an imperceptible amount. So in half a year, you'd see the moon make its journey across the sky. it'd appear at first on the eastern horizon for a couple weeks, then slowly make its way to it's noon (don't know if there's a better word for that) within three months, and then the next three months it'd slowly lower down to the other horizon, and then be gone for six months before you saw it in the east again. So theoretically (assuming a 365 day year), am i correct the moon would orbit earth 366 times a year? And thus it's orbital period would be 1/366 of a year? And then what other strange differences from Earth might be observed? I know you'd have a ton of solar eclipses and and crazy long tides and whatnot, I'm trying to think of what other effects this would have. Edit: I used Earth as an example, but I intend said planet to be roughly Neptune's size as a super-Earth, if that changes anything. [Answer] Yes it is entirely possible for this situation to occur for a time. However such a situation would probably not be stable long term. Geostationary orbit is well outside of the [roche limit for the Earth-Moon system](https://astronomy.stackexchange.com/questions/19926/how-wide-is-earths-roche-limit) so the Moon should not be disrupted by tidal effects, however the effects on the Earth's tides would be interesting to say the least. Probably ok for a number of other sized planets as well but calculations would be needed depending on the exact configuration. ]
[Question] [ Saturn has [rings](https://en.wikipedia.org/wiki/Rings_of_Saturn) of debris which orbit it, and it is possible to get a satellite into an orbit that will at least last a few years, so my question is as follows; How many satellites (or just the pure volume of material if it is easier) would we have to launch into a temporary orbit (unless a permanent orbit is possible) to create at least one artificial ring around Earth that is visible to the naked eye. [Answer] Quite a lot. From a quick internet search I have found [this](https://en.wikipedia.org/wiki/Project_West_Ford) > > a ring of 480,000,000 copper dipole antennas (needles which were 1.78 centimetres long and 25.4 micrometres [1961] or 17.8 micrometres [1963] in diameter) was placed in orbit to facilitate global radio communication. > > > [More in detail](https://www.universetoday.com/14484/does-earth-have-rings/) > > The US Military launched 480 million copper needles into orbit around Earth in a project called Project West Ford. Scientists could bounce radio signals off the needles and communicate between two locations on Earth. This worked for a few months after launch, until the needles were too far dispersed to allow for communication. In theory, if needles were continuously launched, it would be a functioning communications system > > > You can get a ballpark figure from the quoted text above. In medium Earth orbit you would need hundreds of millions of small objects to create a temporary ring. The further away you go from Earth, the more objects you would need to saturate the orbit. To keep the same linear density you would need to scale up the number by the same factor you scale up the orbit radius (2x as far the orbit will be 2x as long requiring 2x as many objects). ]
[Question] [ From some research, I have learned that atmospheric circulation - winds currents and ocean currents - depend on pressure and the Coriolis effect. But if the oxygen level is increased and the pressure is higher (as said in the question), how much would this effect be modified ? [Answer] **Winds will be slower, but there are a lot of second-order factors** The oxygen content is irrelevant but the pressure has a significant effect. Let's start by analyzing wind. In general, there are four forces: 1. The pressure gradient force, which is defined as $\frac{1}{\rho} \frac{\Delta P}{\Delta x}$. Note here the density term: a higher density reduces this force. This makes intuitive sense: if the density is higher, there's more stuff to move. This is a large reason why winds are faster the higher up you go (ignoring a lot of other complexities). 2. Coriolis force, which is defined as $2 \Omega v \sin \phi$. This is an apparent force thanks to the earth's rotation. While proportional to the speed of the wind, it isn't dependent on density. 3. Friction. This slows down the wind, thereby reducing the coriolis force and changing the direction. Density isn't a big factor. 4. Apparent centrifugal force. Again, density isn't a factor. So, all else being equal, the higher atmospheric density will reduce wind speed to about 58% of what it was. Another input, the pressure gradient ($\Delta P$) is also reduced. A major cause of pressure differentials is a temperature differential. For example, let's say we have an island. During the day, the land of the island will heat up more than the surrounding ocean, the air will rise, and thus there will be a surface low (and divergence aloft). At a high level, if a given air molecule (pedants, you know what I mean) has a higher temperature than the surrounding molecules, it will rise and get out of the way. What the ideal gas laws tell us is that the absolute number of molecules isn't relevant; it's the percentage of the molecules. From this angle, increased density means that you have to move a large number of air molecules to get the same change in pressure. This means the pressure gradient force is smaller than it would be on Earth. This is obviously just one example, without formal math behind it, but my suspicion would be that wind speeds are slower as a consequence here as well. Note also that wind speed isn't quite the same as wind strength; it may be slower, but there's more air moving, so it will feel stronger for a given speed. Nonetheless, winds being slower will in general cause ocean currents to slow as well, as the wind pulls the water along at the surface. This opens up a countervailing effect: with the winds and ocean currents slowing, temperature gradients will likely sharpen in some places, which will increase the pressure gradients and thus the winds. Ultimately, the weather system will settle into a new equilibrium which can't be analyzed without running a weather model under your conditions. There may also be some interesting effects based on the heat absorbed by the added air mass that I haven't thought through. One final note about extreme weather events: 1. Thunderstorms won't be much affected, though some probability that they'll be less severe on average. Thunderstorms are caused by the rising of humid air. Severe thunderstorms are aided by wind shear (on the vertical axis), so they may be a little less likely to form if winds are slower. 2. Tropical storms (ie hurricanes) will have slower winds for all the same reasons mentioned above, but will likely still do as much damage. More air moving at a slower speed will still have the same amount of momentum. Their energy source is warm sea surface temperatures, which is unaffected by the density. 3. Tornados have about the same analysis as hurricanes, though they're driven by north-south temperature gradients. In general, you could probably make up whatever you want about their frequencies being set by the new equilibrium the climate settles into and I would believe it. [Answer] The Coriolis effect is generated by the rotation of the planet, thus content of oxygen doesn't affect it. Also, different content of oxygen has negligible effects on the thermal properties of the atmosphere, since it is a mixture of gases anyway. The increased pressure would make winds stronger, as there would be more mass of air withing the same flowing volume. ]
[Question] [ So, I have been watching a lot of flat-earth debunking videos on YouTube, which has tickled my world-building bone. So, I'm imagining a world with a sphere of sunlight-level luminosity hanging relatively low above a flat disc, square or plane with a number of large opaque objects orbiting it to create a rather complicated day-night cycle. What I'm wondering is, just how much atmospheric scattering would there be around these sun-shades, and how much variance could be achieved in the penumbra coloration by varying the size, shape and/or orbital radius of the sun-shades? Here's a mock-up of the situation I'm talking about, superimposed on the emblem of the United Nations: [![enter image description here](https://i.stack.imgur.com/Cn2Rl.png)](https://i.stack.imgur.com/Cn2Rl.png) In this image, the yellow star represents the sun, the red rectangle represents a sun-shade, and black represents the full shadow cast by the shade (i.e. that's where it's night). The area in orange is the approximate area of the penumbra, i.e. where the light scattering around the edges of the shade falls. What I'm wondering is, what colors can the combination of atmospheric scattering, diffraction and/or reflections from other (not pictured) sun shades produce? [Answer] Blocking sunlight does not cause scattering or change the observed colors in the way that a sunset does; it only makes the sky darker or lighter, depending on how much sunlight was blocked. With all of the sunlight blocked (the [umbra](https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra)), we have night or near-night. With none of the sunlight blocked (the [antumbra](https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra)), we have sky blue (not including sunsets). And with a partial amount of sunlight blocked (the [penumbra](https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra)), we would just have something that's between sky blue and dark blue or black, like shown in the following image: [![enter image description here](https://i.stack.imgur.com/cMoVa.jpg)](https://i.stack.imgur.com/cMoVa.jpg) Changing the shape would not have any spectacular effect on the coloration of the shadows as you've described, but it would have a very interesting effect on shadows cast by the partially eclipsed sun. Below, you can see the effects on shadows during a real-life solar eclipse: [![enter image description here](https://i.stack.imgur.com/XZmMg.jpg)](https://i.stack.imgur.com/XZmMg.jpg) [![enter image description here](https://i.stack.imgur.com/p1Pxz.jpg)](https://i.stack.imgur.com/p1Pxz.jpg) As you can see, the shadows have the same crescent shape as the eclipse itself. In your world, these shapes would vary as much as you would like them to, depending upon whatever shapes and sizes you choose for your sun shades. You have stated in your question that the sun shades were opaque. However, if you wanted to have the shades *partially* opaque, that would allow you to change the amount of blocked sunlight without needing to change the size and shape of each sun shade. If you *really* want there to be different colors, you could have some semi-opaque, colored shades that actually change the observed colors in whatever way you want them to. --- Or you could combine the varying levels of brightness due to the sun shades with the different colors available during a sunset: [![enter image description here](https://i.stack.imgur.com/a61LT.jpg)](https://i.stack.imgur.com/a61LT.jpg) [![enter image description here](https://i.stack.imgur.com/sazbd.jpg)](https://i.stack.imgur.com/sazbd.jpg)[![enter image description here](https://i.stack.imgur.com/o0W0H.jpg)](https://i.stack.imgur.com/o0W0H.jpg) ]
[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 4 years ago. [Improve this question](/posts/154027/edit) Bow and arrow are a basic part of many medieval and fantasy settings. Be it for assassins (silent), for (elven) tribes that live in harmony with nature (not industrialized), or to emphasize the skill of the shooter... All the more it's important to know how those weapons can be applied and what they are capable of to adjust the weapon use and the equipment the characters of your world have to carry. --- Accidentaly I came across a fact I would have never considered: ## The flight path of an arrow can be manipulated to a curve to shoot around obstacles (without magic). --- [This video](https://www.youtube.com/watch?v=4noxD3qSVNw) shows practically, shooting an arrow **not from the middle of the *bowstring***, but from **above or below** (while the **arrow still lies against the middle of the *bow***) will result in the arrow **leaving its linear flight path to perform a curved bulge** (around an object if there is any placed at that point) and **afterwards return to the straight flight path**. However **the distance/range for that seems to be limited**. [This video](https://www.youtube.com/watch?v=taEi9-XbGy0) goes more into detail, explaining and incorporating historic archery instruction. [For example that tricks like an 180° turn, shown [here at 0:39](https://youtu.be/qc_z4a00cCQ?t=39), require special blunt arrows without spearhead, with special holes in the shaft and prepared with lead at some points are needed as well as facing the wind in a particular direction which renders that stunt useless for battle.] (Thanks to [Li Jun](https://worldbuilding.stackexchange.com/users/62918/li-jun)) --- I hope this proves helpful to all the medieval assassins and elven warriors who now can show off how superior their archery skills are compared to the steampunk pistols of man or dwarves. [Answer] Certainly it is possible to shoot around an obstacle using a bow and arrow... but it requires the right conditions. The OP has already noted the effects of gravity, which causes the path of the arrow to curve toward the ground, but we should also consider that neither archer, arrow, target nor obstacle are likely to be used in a vacuum. Given that the arrow is most likely to be fired within a planetary atmosphere, the effects of wind could be significant, especially over a longer trajectory. In conditions of high, steady wind, an arrow could be shot across the wind, and somewhat upwind of the target so that the wind would carry the arrow around an obstacle in order to hit a target that is visually or functionally concealed by that obstacle. That is not to say that it would be an easy shot - a long range shot made cross-wind toward a target concealed by an obstacle, but with sufficient training, an archer could learn to achieve such shots as a matter of routine. Modern snipers and hunters using both arrows and bullets learn to compensate for wind drift, this is just a special case where the wind is used to make an otherwise impossible shot. No magic required. ]
[Question] [ Over several hundred years, a tide-locked, but otherwise Earth-like, planet orbiting a red dwarf is terraformed. The terminator is a very habitable zone, in terms of temperature, atmosphere, etc. Chemical composition is (now) almost identical with Earth's. Given the star always appearing near the horizon, would plants grow diagonally? They'd almost all orient toward the sunny side of the planet, no? So walking through a forest would look very different than here, even if everything else was the same? Though of course it wouldn't be the same. What Earth flora might survive there, in the absence of the day/night cycle? I'm going to handwave 'modified' plants, so this doesn't need to be utterly feasible, but what would you expect to do least-poorly in such an environment? [Answer] I don't think there is a complete list, but [tomatoes do not generally like continuous light](https://www.researchgate.net/post/What_happens_to_a_plant_that_is_kept_under_constant_light2). Otherwise most plants seem to be okay with it, but continuous light might be [detrimental to the health](https://www.sciencealert.com/scientists-have-found-a-worrying-effect-that-artificial-light-might-have-on-our-bodies) of animals (and humans) that have a diurnal cycle. Plants that photosynthesize will certainly grow towards the light. This phenomenon is called [phototropism](https://en.wikipedia.org/wiki/Phototropism). But gravity has an effect on plant growth as well (this is called [gravitropism](https://en.wikipedia.org/wiki/Gravitropism)), so stem-building plants will at first not grow horizontally but lean towards the light. We might assume that as the plants adapt to the directional light, the effect of gravity on growth direction might decrease, causing the plants to grow horizontally towards the low standing sun. But if all plants grow along the ground, most of them will continuously "stand" (or lie) in the shadow of other plants closer to the sun, so growing away from the ground might in fact be an advantage. I therefore think that most plants will continue to grow against gravity, especially as some of the sunlight will be refracted by the atmosphere and come from other directions as well. There are also many plants that prefer shade to direct sunlight and those will not grow towards the sun at all. Animals and humans will develop what is called a "free running activity cycle" under continuous light and loose their 24 hour diurnal cycle. I once lived above the polar circle in Russia, and many people there worked during what the clock said was night. [Animals show similar behavior](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3712422/). I've already linked to an article about detrimental health effects of constant light. Its authors assume that constant light will reduce the life span, so people and animals on your planet might not live as long as on Earth due to accelerated aging processes. Social changes coming with continuous light are already apparent on Earth. Before the advent of candles, the night was dark and people slept. Since we have cheap electric light, people can be awake and active at all hours, and many are. There are joggers with headlamps in the park, adolescents playing computer games until the early morning, young adults partying all weekend without pause, workers working in night shifts, and so on. The day-night-cycle still influences the lives of most of us, but under continuous sunlight we might assume that at any given time of the "day" there will always be one third of the population asleep and two thirds awake, with people tuning their cycles to their jobs or their friends and family. There might be a more active part of the "day", because it might be more efficient to synchronize certain activities. For example, a school might want to have all kids there at the same time. Other activities might be desynchronized intentionally, with shops and leisure activities opening when people don't have to work. ]
[Question] [ I'm trying to find someone (s) with enough geology knowledge to help me figure out some of the specifics of the world I'm building. (Earth-like in age, distance from star, size, tilt) I'm doing my best to reproduce what I can see on earth in roughly equal proportions. But I'm wondering if there's more accurate ways to do this. I'd love anyone who has the right knowledge to tear into this and tell me what could never happen, or what I haven't done enough, etc.) so I can make changes. Thanks! :) Blue lines are divergent, Red are subduction, Yellow are transform. The arrows do not denote plate speed yet, they are just there to help me keep direction consistent on a sphere. For the record, I've been following Artifexian's videos on this, but there's nothing about vetting the actual shapes in there. [![enter image description here](https://i.stack.imgur.com/Jvxgq.jpg)](https://i.stack.imgur.com/Jvxgq.jpg) [![enter image description here](https://i.stack.imgur.com/uxWwh.jpg)](https://i.stack.imgur.com/uxWwh.jpg) [![enter image description here](https://i.stack.imgur.com/pqSP2.jpg)](https://i.stack.imgur.com/pqSP2.jpg) [Answer] Two oddities jump to my eye: * the central plaque E is expanding on 270 degrees and subsiding on 90 degrees. Somehow this seems odd, considering the surface area. * left from that, you have on the same direction first a diverging margin (B-H, G-H), then a converging one (C-I). This is really odd, as it would mean an abrupt discontinuity in the mantle flow. ]
[Question] [ I wanted two characters unaffected by the heat and gravity to be close to a super massive black hole within the accretion disk, at times moving in orbit and at times completely still. Stars and planets will be engulfed by the black hole. Would it just be blindlingly white light or will the two viewers see something different? (I could change the frequency of light they are able to see if it creates a more impressive image.) [Answer] I understand this is intimidating and long but I felt everything I said here is necessary, for if any of it went unsaid somebody might ask about it later so I figure instead of making people ask for clarification I will make myself 110% clear. I promise you will not be disappointed if you take the time to read this answer. So to my understanding we want to know what you would see from the accretion disk of a black hole. I'm going to answer this in bits and pieces starting from the center to make sense of the chaos that occurs where a black hole is. The first and most important thing to consider is how sight works. Our eyes require light in order to see and perceive anything. Gravity from a black hole is so powerful that nothing beyond the event horizon escapes, not even light. This means that there would be a black blob in the center where no visible light escapes. While this sounds uninteresting it would really be quite mesmerizing as it is probable that nobody has seen such darkness in there lives, the effects on your eyes and mind are unknown. It would be an unspeakable experience. Beyond the center you wouldn't just see a blob with normal space behind it. We've already established the gravity affects light. so light coming from sources behind the "blob" (if nobody minds me calling it that) would all be visible in a ring around it. This would occur because any light that passes next to the event horizon would start to move toward the center of the black hole but would not be completely captured and would wizz away in a different direction than before. One might think you'd have to be at the right angle to see it as it is being forced in a random direction, but this is not the case. Light is coming from all around anyway and therefore no matter what angle you're at you will have light 'refracted' by the gravity and sent your way. So you would see a blob of uncomprehendable nothingness with a ring of blinding light around it. the ring would somewhat gradually fade outwards but would have a distinct edge on the inside as this is where the blob is destroying everything visible. Now we're outside the event horizon, beyond the ring of stuff thats not actually there, we move to the accretion disk, which is where our friends are. This is where matter, from around objects that either fell into the blob or passed close by, that has been trapped in orbit but not necessarily sucked into the void. some of it might eventually but that has no effect on our current issue. This matter could be any range of things, it could be mostly gasses, there might be some little asteroids, or maybe even some planets that our blob stole from passing stars, this all depends on the situation and size of the black hole. You mentioned a desire for a more impressive image so I'm going to do what I can to create that for you without defying physics (well physics as science currently understands). So the most awesome accretion disk we could hope for would have an accumulation of spherical asteroids/dwarf planets, like Pluto, and if we're lucky and they are far enough out that the heat isn't affecting them, they would be a little icy and would glimmer slightly in what little light is there, a comet or two, and in my opinion as little gas as possible. The reason I wouldn't want gas is because it would obstruct the view of the incredible nothingness that we call the blob. With that said what we have now is the 'blob', a ring of bright light immediately around it that fades rather quickly, and planets, comets and meteors with gasses floating around. Somebody could now argue that you wouldn't be able to see this very well due to a lack of light but heat does create some light and we already seem to have established that there would be a lot of heat here. Still, though, that's not enough light to make this impressive. At this point you can use creative license to say that in this vast void where everything is light-years apart and things take millions or billions of years to happen our friends are lucky enough that this black hole is currently luring in a star and has gotten it close enough that everything is lit up for the moment. What else is there to see, well we already discussed light coming from behind the blob but what about all around. Stars around would still be shining at you so the image we received before isn't totally accurate, there would not be total darkness outside what you see (or don't see) of the black hole. You would still have stars, however everything that passes through the accretion disk, even light, will be affected by the gravity, probably not completely displaced or refracted but still warped somewhat, and because it's all being drawn to the center of the blob all the light around you would seem to be turned that way and this would make the blob appear to be the center of the universe. Now we have stars all around seeming to be drawn to the blob, a nearby star illuminating the scene, icy planets and asteroids floating around through clouds of gasses all of it moving at different speeds depending on how fast it came into orbit a blob of breathtaking, mind-numbing nothingness with a ring of glorious light around it. But there is one last thing, not particularly anything *more* to see, but different from what you would normally imagine. We've discussed red shift but I'm not sure we fully understand it. One would assume that red shift means everything is slightly more red (i.e. green is now reddish green). This is absolutely untrue. Red shift is term referring to the way light waves are lengthened due to certain things such as massive gravity around a black hole. This means that light waves that have a wave length of 500 nanometers(nm) (this would be green/blue) would have a wave length of, say, 550 nm (more of a yellow) so to sum this up ultraviolet light you otherwise wouldn't see would now be purple light which you can see. otherwise purple light would be indigo, otherwise indigo: blue, blue: light blue, light blue: green, green: yellow, yellow: yellower, yellower: orange, orange: red, red: redder, redder: invisible infrared. and if the black hole is as massive as it would have to be for this amount of 'impressiveness' you'd probably have a red-shift far greater than 50 nm. but what people misunderstand most about red shift is that visible light is not the only light affected, ultraviolet rays will also stretch into visible wave lengths and replace any non-red colors that would otherwise be lost to redness. granted, ultraviolet is not coming from everywhere but where it is coming from would now be blues and greens and yellows. you would have a stunning and colorful cosmic view. To conclude, our friends are looking at a fantastically colored universe that seems to be converging into a total and unexplainable void, rimmed by radiant beautiful light and when they take a look around they realize there are many asteroids and planets moving around the void with them, and an occasional lost comet, all illuminated by the brilliant light of a bright blue star nearby. It is an incredible experience that they can never hope for anybody else to understand. P.S.- i looked into the previously mentioned view from 'interstellar' and It might be safer to assume that instead of a ring around the blob you might see that shape, but do not fear you will still see stars and trapped planets and asteroids if you are far enough out. so change it to a blob, with 'that shape' around it in bright light and a star lighting up planets and comets and whatnot. thank you :) I hope my answer is helpful and accurate. please comment if you disagree on anything. sources: <https://eyelighting.com/wp-content/uploads/2018/02/quality-of-a-light-source.jpg> <https://phys.org/news/2018-10-black-hole.html> <https://www.brandeis.edu/now/2018/october/eht-blackhole-wardle.html> <https://physics.stackexchange.com/questions/34352/how-is-light-affected-by-gravity> <https://www.physlink.com/education/askexperts/ae661.cfm> <https://www.space.com/25732-redshift-blueshift.html> <https://space-facts.com/wp-content/uploads/black-hole.jpg> <https://upload.wikimedia.org/wikipedia/commons/a/ab/Black_hole_jet_diagram.jpg> and as for extra-galactic jets, that light is most likely not visible anyway and if it was is moving strictly away from you so you would not see it. Thanks again. Hope you like :) [Answer] Firstly, your characters also need to be immune to the exotic array of radiation that an active Accretion disc outputs. Secondly, no they do not see a uniform disc. An accretion disc that is hot enough to be interesting also has a significant redshift on the part of the disc moving away from you (material is moving at a fair fraction of the speed of light) Thirdly, there are a range of echo images created by a rotating black hole on the 'approaching' side of the disc due to gravitational lensing. These show distorted blue-shifted images of the opposite side of the disc, highly-stretched parallel to the rotation axis of the disc. EDIT as per Thucydides suggestion: Here is a visualisation of a black hole from the film Interstellar using Kip Thorne's Kerr metric formalisation. The first is that actually used in the film. It is somewhat inaccurate for the sake of looking visually pleasing/simple. The next two images are increasingly realistic for moderate rotation speeds; they show redshift and a more realistic messy accretion disc. Lots of debate to be had about the exact details of these images for storytelling guidance (your view of a black hole changes a LOT as you move relative to it), but they are a good starting point [![enter image description here](https://i.stack.imgur.com/1RGaY.png)](https://i.stack.imgur.com/1RGaY.png) [Answer] This site right [here](http://jila.colorado.edu/~ajsh/insidebh/schw.html) is a hella fun site because it provides a description of what you would experience as you approach the singularity of a Supermassive black hole. You can watch the video and then it shows each major change and describes what is happening in when you look at it. The images labeled "Innermost Stable Orbit" are probably the very edge of the accretion disk. Note that the red lines on the black hole are not actually visible... the author attributes them to your "spaceship" painting them on your visual display as a big massive warning to avoid that thing. ]
[Question] [ It's a general question but my specific concern is whether different planets would crash into each other if a portal is made between them. We're assuming bare, naked, "hole in space" portals. This can be visualized like this: if you have two planets, and in between them is a wall that cancels and is not affected by gravity, and there's only a small hole in that wall, will the attraction between those two objects be less than if there's no wall. If the answer is yes, what's the largest portal that could be opened in the immediate vicinity of two Earth-size planets without causing problems? [Answer] First off, let me start out with the disclaimer that the concept of a wall through which gravity cannot pass doesn't really mesh with any scientific description of gravity, so any answer you get is going to come with a large dose of interpretation. That being said, the way I'm choosing to interpret this is analogous to the problem of what the electric field looks like if you put a metal plate with a hole in it in front of some electrostatic charge. You see, metal plates "block" electric charge-- more precisely, the electric field within one is always zero (alternatively, the voltage is always the same). The reason I'm talking about the electric field is that for charges that aren't moving, it works very similarly to how a gravitational field works. In both cases you have some potential-- $V$ in the case of the electric field and $\phi$ in the case of the gravitational field-- whose rate of change tells you the strength and direction of the field. The only difference is that charge is the source of $V$, while mass is the source of $\phi$. Now, if we have a planet on one side of the barrier and nothing on the other side, on the side with nothing, the gravitational potential will follow Laplace's equation: $$\nabla^2 \phi = 0$$ Don't worry if you don't know what those symbols mean-- the important thing is that Laplace's equation has **unique** solutions. A fairly straightforward consequence of this is that if you have a solution to Laplace's equation for one set of boundary conditions, it **can't** be the same as the solution for different boundary conditions. But clearly, the setup with the gravity cancelling wall has different boundary conditions than those without it, since in the former every part of the gravity proof barrier has $\phi = 0$. From this, we can definitively say that using the model you propose, the portal **would** affect gravity. As for the question of precisely how much, well, that depends on the shape of the portal and the mass distribution behind it. Even when specifying this, there likely isn't a closed form expression for any but the most simplistic limiting cases. To achieve any degree of accuracy, you would have to put in all this information to find boundary conditions at the barrier, and then use numerical methods to approximate a solution to Laplace's equation on the other side. **TL;DR** There is a mathematical solution to what you propose, but it requires more information to calculate and a significant amount of effort. [Answer] I would say the gravitational influence exerted by the portal would be determined by the mass behind the portal. So assuming the gates are perpendicular to the surface of the planet (and there are no mountains between the gate and space the only gravitic force that would be exerted on each side is the mass of a cylinder of air with the diameter of the portal reaching out to the edge of atmosphere, not doing much more than creating a slight weather disturbance. [Answer] Disclaimer 1: As another answer points out, much 'interpretation' of the question is needed to provide any kind of answer, so here's my interpretation: The "wall" is actually nothing more than distance, and "visualizing" this distance as a wall is simply for convenience of understanding of the question itself, not an actual physical barrier to the gravity. Disclaimer 2: I have no more than a [wikipedia level](https://en.wikipedia.org/wiki/Graviton) of understanding of string theory, gravitons, and gravity. As I understand it, and for the purposes of this question, Gravitons are effectively long straight lines (strings, as in "string" theory) radiating out in every direction from the mass object (in the case of the planet, they radiate out from each individual atom in the planet), and they affect anything they come in contact with, but the effect is lessened with distance. At the distances of the planets involved in this question, the effects can be considered negligible, all but non-existent, and effectively a 'wall' between them that reduces the gravitaional affect to (effectively) 0 ... Until you punch a "hole" in the "wall" with the portal. Now, the size of the aperture would have a VERY significant influence on the gravitational effect, similar to a pinhole camera's effect on light. Yes, light from the entire facing surface of the sun can get through the pinhole, and create an image on the back wall of the camera. But that image is a VERY pale spectre compared to the massive amount of light from the original object, because only a very tiny fraction of the light coming off of any particular area of the surface of the sun will be headed in the right direction to get through the hole. Similarly, for a (relatively) small portal between planets, it will be a very tiny fraction of the total number of gravitons from the atoms of the planets that are actually pointed in the right direction to make it through the portal and affect the planet on the other side. So the gravitational effect felt through the portal would be a pale spectre of the full gravitational force of the original objects. I lack the math skill and quantum physics knowledge to try and provide any sort of numbers or even estimates, but I think that (as far as this interpretation of the question is concerned) it's pretty clear that the size of the aperture is of HUGE importance to the size of the gravitational effect felt through it. [Answer] Lisa Randall asked the question how does a tiny refrigerator magnet overcome the entire gravitational force of the earth to lift a paper clip? In other words why is gravity so darned weak? Until she answered the question everyone thought gravity was leaking out of the universe. She showed that its the opposite and gravity is actually leaking into the universe. So without speaking to your overall question, yes physicists seem to believe the size of the aperture would affect flow just like a window or a dike affects water or air because gravity like air and water is composed of small (elementary) particles (gravitons) that form waves. Otherwise we would be crushed by all the gravity leaking in at once. ]
[Question] [ My main antagonist is an infant Great One that's been imprisoned below the Moon's surface and I want its influence and physical form to have a weakness to direct sunlight which, I think, gives me a reason to make eclipses more than just a pretty event. Here's my logic: A long-dead organization cast a 'magic' spell that created a planet-wide barrier that severely inhibits the Great One's psionic/arcane/cosmic/spiritual/whatever influence through it. The catch, is that this barrier has a city-sized, funnel-shaped 'eye' or pinhole, anchored to the ritual site from whence it was cast (Central United States), through which the Great One can periodically poke its figurative tentacle. However, direct sunlight has a harmful effect on the little abomination so it remains inside its prison which, itself, has an extremely narrow view-hole through which the {eye of the barrier} can be seen. Like a pencil-thin shaft a football field long or something. Only when this tiny opening in the prison and the 'eye' of the barrier align well enough, can it exert its will on the surface of the planet in full force. Incidentally, I think this can only happen during lunar eclipses and total solar eclipses and even then, only when they coincide with the region of the barrier's ritual. {Partial illumination of the moon, like that seen during a lunar eclipse will not deter the Great One's influence and its view-hole (or even multiple view-holes) can be anywhere it/they need(s) to be on the moons's surface to make this idea work. As long as direct sunlight crosses the path between the view-hole(s) and the barrier's eye, the influence will be disrupted.} {I can change the angle or topography of the funnel shape or even give it a relatively small amount of motion around the anchor site, if necessary.} A couple things I've thought of that support this idea's validity: 1.) Yes, the Moon is tidally locked to the Earth, but I don't think this means the Moon would be at a good enough angle to align the barrier's eye and the Great One's peephole {every time it's visible in the sky}. If I understand my research, a blood moon or total solar eclipse would be the time the Earth and Moon are closest to zenith in the sky above their respective surface {which I imagine would be the only range of positions in the sky that align the view-hole(s) and the barrier's eye}. 2.) What about the full Moon? Too much direct sunlight. 3.) New moon? Depends on the angle. EDIT: I've clarified and added details, marked with {}, to the above text in response to an answer by Dalila. [Answer] The key to this whole thing is, in fact, the geometry of the funnel, the 'viewing' angle that it provides. Of particular importance is how much of the Earth can be 'seen' through it at any one time. The second most important factor is just how much sunlight is too much. Neither solar nor lunar eclipses achieve 'complete' darkness on Earth's surface or the Moon's, so unless there is leeway given for partial darkness, then there is no alignment or arrangement that will allow influence to escape. For simplicity, I'll narrow down the geometric range options to just 'wide angle', meaning the full surface of the Earth is 'visible' through the funnel, and 'narrow angle', meaning that only a portion of the Earth's surface can be 'seen'. Just how narrow is 'narrow' can be adjusted as needed for the story. The possible lighting limitations are solar eclipse, lunar eclipse, and new moon. Combining the angle options with the lighting options gives six possible alignment situations: 1. wide angle + solar eclipse 2. wide angle + lunar eclipse 3. wide angle + new moon 4. narrow angle + solar eclipse 5. narrow angle + lunar eclipse 6. narrow angle + new moon So, lets address each one: 1. For this option, the Moon's surface (the important part) will certainly be dark enough. This option also assumes that the area of totality is also dark enough. And the area of totality will certainly be visible, since the whole surface is visible. So the limiting factor will be how often the path of totality passes over the hole in the barrier. Any eclipse with a path of totality that passes over the hole will provide an opportunity for influence. 2. For this option, the whole of the Earth's surface will certainly be dark enough. This option also assumes that the whole of the lunar surface (the important part) is also dark enough. The limiting factor will be when the hole in the barrier is on the dark side of the Earth during the eclipse (about half of all of this type of eclipse, since the hole will be on the light side half of the time, and the dark side half of the time). So about half of all lunar eclipses will provide opportunity for influence. Though it will almost certainly NOT be alternating opportunities, but rather relatively long sequences of opportunities followed by relatively long sequences of eclipses with no opportunity. 3. For this option, the important part of the moon's surface will always be dark enough. A 'complete' new moon is practically never visible from a completely dark area of Earth's surface, but a very near new moon is visible from almost every area of the dark side of the Earth at some point during the night. If no leeway is given for partial illumination, even when the important areas are in near complete darkness, Then this rules out new moon completely as a possibility for influence. But it would also eliminate both types of eclipses, and lock the influence completely and permanently. To avoid that, it must be assumed that partial illumination of the surfaces is allowed, and that assumption opens the floodgate to allow influence any time even just the opening of the funnel is in darkness while the hole in the barrier is also in darkness and facing the moon. That would be many times per month, for significant durations for many of the instances. This seems significantly (prohibitively?) more than the 'once per special eclipse at special times' implied by your original question, so, to me, that seems to rule out all possibility of the "wide angle" options, in any form. 4. For this option, the moons surface is certainly dark enough. Assuming partial darkness is enough, the path of totality is also dark enough. Since the whole surface of the Earth is not 'visible', the visible area of the Earth is a limiting factor. The path of totality passing over the hole in the barrier is another limiting factor. So influence would ONLY be possible when the path of totality crosses the hole in the barrier AND the hole in the barrier is visible from the funnel AT THE SAME TIME. 5. For this option, the surface of the Earth is certainly dark enough. Assuming partial darkness is enough, the surface of the moon will also be dark enough. The hole in the barrier would need to be on the dark side of the Earth, but that will be relatively common compared to how often it's in the path of totality of a solar eclipse, so while it's a limiting factor, it's a minor one. The main limiting factor (assuming the hole in the barrier is in darkness) will be if the hole can be 'seen' from the funnel during the eclipse. 6. As with option 3, complete darkness on both important sides of the surfaces will practically never happen in these cases, so near complete will have to be allowed. Again, as with option 3, partial darkness will happen quite often, during lunar cycles, and earth day cycles. But as the completeness of the darkness increases, the probability of aligning the funnel and hole in the barrier decreases, which is exactly the opposite effect from eclipses. This alignment requirement would be so drastic that they would VERY rarely, if ever, align (I suspect they would never align) to allow influence, unless the alignment was intentionally (by the story teller, not the 'spell casters') set up to allow for influence at new moons, instead of eclipses. (TLDR) In summary: A wide viewing angle should be avoided, unless you want influence on a monthly bases, for days at a time. If you want eclipses to be the main thing, then New Moon's won't be. If eclipses are the thing, Lunar Eclipses are the more likely to cause influence because of how much of the important side of Earth's surface is dark during them. ]
[Question] [ I have an Earth-like planet that has no frozen poles. It is very similar to a Cretaceous Earth. Is there any sort of odd, yet reoccurring weather event, that could cause freezing air from the upper atmosphere to descend quickly to lower the temperature of several islands in a non-polar latitude down to freezing? Edit: By freezing an Island, I mean allowing water to get cold enough to form ice on the island, resulting in a colder climate than surrounding areas. Edit: My world has large oceans uninterrupted by any continents, with the world's only two terrestrial continents being at the poles and dominated by forests. This island is volcanic in nature, so having a higher elevation isn't unreasonable. [Answer] Like the comments already state several times, your whole idea is a long-shot. But given that, perhaps your planet can have some set of conditions that provide the Mother of All El Niño - La Niña cycles. Here on this Earth, [said cycle](https://en.wikipedia.org/wiki/El_Ni%C3%B1o%E2%80%93Southern_Oscillation) takes the form of periodic variations in the winds, currents, and temperature of the surface of the southern Pacific Ocean, which in turn influences weather patterns throughout most of the planet. This cycle is about seven years long, and the temperature variations are only about half a °C water temp, but still cause noticeable changes in precipitation and air temp across entire continents. Our scientists are just beginning to hypothesize about the exact cause and mechanisms, leaving you possibly even more freedom in a fictional work to handwave. For some reason, the axial tilt, the positions of land-masses, the contour of the ocean bottom, the orbits of its natural satellites, and presence of maedupium in the atmosphere, all conspire upon Thalassan-World to make a hundred-year long cycle with sudden shifts of +/-30°C. Just as an example. [Answer] This could happen regularly if the planet rotates around a [variable star](https://en.wikipedia.org/wiki/Variable_star): * a pulsating star or * a star with a strong [stellar cycle](https://en.wikipedia.org/wiki/Solar_cycle), i.e. it could last for 11 years (like the Sun) but at the minimum the star could dim significantly. You should be careful what star you choose as some are so unstable they would have huge stellar flares or even blow up in a supernova. $:)$ ]
[Question] [ So I've always assumed Mars never had enough available CO2 on-site for terraforming, something that [new research seems to have confirmed](https://www.nature.com/articles/s41550-018-0529-6?utm_source=dlvr.it&utm_medium=facebook). But my ideas have always relied on getting CO2 from alternate sources, e.g controlled impacts or in this case borrowing gas from Venus. The atmosphere of Venus is about 90 bars of pressure, and we'd only need around one (or more?) to bring Mars to a livable pressure. Transporting that gas however is a bit of a pickle. One idea I've had is using a fleet of Venus-Earth-Mars cyclers to transport pressurized Venusian gas (perhaps mostly unfiltered as Mars can make use of the nitrogen and trace elements too) to Mars. As an added bonus, the canisters can be created from on-site carbon and burn up on Martian entry. I'll opt for the cargo capacity of the average oceanic cargo ship of 25,000 tons, or a little under 23 million kilograms. In terms of mass, I'm not sure how much gas is required to bring Mars to 1 bar of atmospheric pressure. I assume it would be slightly more than Earth however due to the lower gravity. Earth's atmosphere has a mass of about 5.15 \* 10^18 kg. To make things simpler, I'll go with that. It would take one of our cyclers 2.239 × 10^11 trips to complete its objective, but a fleet of 100,000 would bring that to a more modest number...at 2.239 million trips. This is where my already poor math starts to fail: I can't calculate gravity assists and I don't know how long it would take a Venus-Earth-Mars cycler to complete a round trip. So I'll REALLY fudge it from here and just put in the time of an Aldrin Earth-Mars cycler, 779.27 days, and add an additional 200 days for the ~100 days it takes for the average spacecraft to reach Venus. ~2.683 years \* 2.239 million trips means Mars would have 1 bar of atmosphere in...6,007,200 years. Even with an accurate round-trip time for the cycler, that's still a 'yikes' from me. By the way, it would take only 300 years for 2 billion 25,000 ton ships to transfer the gas...I'm sure there is a much better use of interplanetary resources, probably. Another idea I've recently had is a mass driver (or a 'space hose'?) that would constantly fire Venusian gas towards Mars. It would be an orbital (either conventional or as an orbital-ring space elevator) or very high altitude platform (possible with helium aerostats and solar powered turbofans) that would fire gas either in the form of the pressurized containers mentioned earlier (good for in-atmosphere installations) or *straight up unprotected gas straight from the nozzle*, a high-velocity narrow jet being fired straight into space. From there I have no idea where to start...I don't even have my ideas for the 'space hose' solidified just yet. Still, I wonder **how long it would take an array of mass drivers to terraform Mars, and importantly would the naked gas in Venus-Mars transit have issues with drifting away from solar influence?** If anyone would like to offer math of their own, or their own ideas on how to transport the gas, feel free! [Answer] There is no such question "How long" in the situation, as you noticed that for yourself, starting with estimating values for one ship and moving to 100'000 and then considering an option for 2 billion of those. The answer depends on - what do you have to complete the task? And it also makes sense to get an understanding of the scale of the problem. You estimated the mass of a gas moved quite right, to create 1 bar of pressure it means it needs about 10t of gas per 1m^2 of the surface in earth case and mars case it needs about 3 times more(as gravity is about 1/3), and the total surface of mars is about 1/4 of earth. So as you noticed that doing that with a teaspoon is quite a long process. so it rather how long it should take to make sense and from that, you deduce what you may need for that. Launch window, and massdrivers won't free you from the necessity of following that, is about once a year(plus minus), for maybe abut few weeks of a month. So if we think about transporting let's say 6e18 kg per 100 years, we have 100 cycles to do that and need to launch 6e16kg per each cycle in a period of a few weeks. Hohmann Transfer maneuvers from venus orbit to mars orbit are 6.5km/s+5.3km/s so energy spend on launching material in one cycle is (proportional to first manuver 6.5km/s) : 6e16 \* 21.125e6 to do that in a week it needs about a square of solar panels or whatever about 39'000km x 39'000km. Generally, it is possible to accumulate that energy over a year, you have gravity based accumulator (the planet) and with 100% efficiency in all the process discussed, you may need a square with edge 5500km. Another one (and a little bit bigger one) you need to gain the energy you need to lift the 6e16kg from the gravity well of the veny, which is as deep as the earth's one. So a number of ships and resources spent on their construction, is not only expenses to worry, and 2 billion ships maybe isn't that much, as let's say they are 10% of the mass they carry which can be easy, as it 0g environment most of the time for them, rockets which start from earth have better ratios. And it can be about the right number of them in the case, and it is something like 6e15kg of construction. World steel production per year is about 1.7e12kg, but we do not have a goal of lifting a mass equivalent of our entire atmosphere, to lift that in space. moving atmosphere is a big task and you can't make it smaller by closing eyes on how big it is. You need to create an infrastructure of proper size on venus, around venus, and between mars and venus. For to provide the necessary energy for the task - lifting, processing, packing, launching etc. The energy source you may need is a scale of K1, and on its own is about 1e15 in case you accumulate energy, and more if you do not. Using carbon as for the construction of vessels which will contain the CO2 is a good idea, then you have a material you need to transport and the same material can be a source for construction material in the case, and it is possible to use carbon for the purpose. Also then you can worry less about returning of ships, so as about second delta-v maneuver in Hohmann Transfer, which is quite big actually and makes sense to save it. By making CO2 ice and make some reflective foil-like shell it possible to but the stuff in a collision with mars, what you need some msall correction engins attached to the thing. Generally, the task is big, and it needs big enough means to make it so. Transporting ice is viable and it saves a lot of efforts in thems of construction. Just streams are no go because of the launch window. You need a lot of energy and a lot of infrastructures hear venus. Making the stuff in 100 years is realistic if a right approach is chosen. Carbon as structural material so as carbon ice as structural material is a good thing in the situation. Massdrivers is probably the only viable option in the case. [Hohmann Transfer, Sun orbits](https://instacalc.com/50896) ]
[Question] [ I've asked a whole array of questions, so far, centered around an ongoing project of mine that features a world, in an alternate evolutionary timeline, where a variety of well-known mythological creatures live alongside humans. One of the species I'm now considering to include in this project are werewolves - not shape-shifting ones, but just wolf-like creatures with a human-like, or [orthostatic](https://en.wikipedia.org/wiki/Standing), posture. I've seen a few similar projects (As in "plausible fantasy creatures" projects) with werewolves, and all have made them orthostatic descendants of wolves, often without providing any explanation why a group of cursorial quadrupedal hypercarnivores even evolved to stand upright. Instead of humanoid wolves, I'd like to go for something a little more plausible; **giant, bipedal baboons**. Given that they are primates, it seems more likely that they might develop orthostasis (Since we did), and they have a very dog-like head, which could be developed into an even more wolf-like one. I know that humans evolved orthostasis by being descended from arboreal primates which were driven into a savanna habitat, where they were forced to become cursorial, but could not become quadrupedal since their ancestors had hands, and could not take up bipedalism with a theropod-like gait because they were tailless. However, **are there any other reasons, set of events, or evolutionary transitions, that would make a population of baboons or baboon-like primates evolve to be bipedal with an upright back, besides that of humans?** The main reason for this is just that I'd like to "shake things up" a bit, rather than copying the evolution of hominids. I guess that somehow making the ancestral baboons be tailless would be a good idea, to avoid ending up with these: [![https://vignette.wikia.nocookie.net/speculativeevolution/images/7/7b/Raboon_species.gif/revision/latest?cb=20120813103739](https://i.stack.imgur.com/N0JnG.gif)](https://i.stack.imgur.com/N0JnG.gif) Source: <https://speculativeevolution.wikia.com/wiki/Raboon> Another key thing is that baboons already live in the savanna, or at least Olive baboons and Chacma baboons(the ones with the most dog-like heads) do, so any transition to bipedalism will be different to humans'. An important part of the end result is that they still have fur - humans lost most of their hair after becoming cursorial. [Answer] It's thought that hominid bipedalism was ultimately a result of resource scarcity; we had to travel a long way between calories on the savannah and our bipedal gate was more efficient than our quadrupedal one so we had to walk upright to cover the distance. This led to better upright walking being a survival trait that was reinforced generation on generation. To have this same effect in baboons you need them to be fussier eaters; as it is their generalist diet means they don't need much travel to find food even in quite harsh environments. And you need them to be less efficient quadrupeds because as is they're extremely effective as quadrupeds. This might be accomplished by striping the savannah of ground level foods, either by flora species reductions or dietary adjustments. If baboons had to reach and climb for their food more often than not then longer arms and a more versatile hip and shoulder joints would become advantageous reducing their specialisation based effectiveness as quadrupeds. [Answer] Sometimes all you need is a stomach flu (and possibly some brain damage). In 2004 macaque in an israeli zoo got sick and had, in her care team's words, a near death experience (go figure). After recovering she would walk exclusively upright. The original links from newspapers from back then are sparse and most don't have pictures, but the story is preserved in [this wiki](https://en.m.wikipedia.org/wiki/Natasha_(monkey)). In a way it makes sense. Maybe it was our diet, or something in our gut, and not anything else that got us walking upright. Whenever I hear proponents of the paleo diet talking: > > *"Don’t worry about getting enough carbohydrates (...) you don’t NEED any at all. Contrary to popular belief, there is no lower limit to the amount of sugar your body needs.”* > > > -Dr. Ron Rosedale > > > ... I can't help but picturing those people knuckle-walking and screaming like chimps. So add some potatoes to your hominid species diet and watch the magic. They'll be walking upright before they develop larger brains. [Answer] Do your baboons have to become truly upright to fill the bill? A werewolf is a creature of *terror*, and humans are not always reliable narrators after a terrifying experience. A larger baboon, hostile to humans and with evolved nocturnal habits (perhaps due to its poor relationship to humans) might do the trick. If a peasant encountered a 5 foot tall baboon at night, and the baboon rose on to two feet to attack, the resulting tall tale might end up sounding pretty much like the description of a werewolf attack. Especially if the nocturnal baboon adapted to live in caves during the day, and lost much of its body hair and became albino as a result. An angry 5 foot tall albino baboon with the mange would certainly scare the living heck out of ME. ]
[Question] [ I've been curious about writing about a very durable exoskeleton humanoid species, but I have wondered about how the extra weight of a thick exoskeleton would affect their height. I do not see them as 'prawn like' insect-like creatures (like from District 9). Instead, the prehistoric armored fish would be a closer relative for the general make up of their thickly armored exoskeleton while retaining bipedal mobility. The main idea is their exoskeleton is some sort of ultra-dense variation of our bone material, thickness tbd, maybe 5-10mm, and effective armor against any bladed weapon and many pistol and submachine gun rounds. Side Question: The skeleton a human male weighing 200 lbs is supposed to be about 15% of that body weight, or 30 lbs...your skin is supposed to weigh another 15% or so, so another 30 lbs, that would leave 140lbs of guts for a 200 lb endoskeleton male. Anyone have any good guesses of what an 8mm thick complete human exoskeleton would weigh on top of the 140 lbs of guts? Thanks! [Answer] I would say use a mineralized protein fiber matrix in a Bouligand pattern similar to that of crustaceans with particularly hard claws. It wouldn't necessarily have to look like crab shell to benefit from it's structure and engineering. It likely wouldn't deflect bullets though, so much as be ablative. It wouldn't let the first one or two shots through any one plate and would fracture and chip to dissipate the kinetic energy. This would still generate enormous amounts of pain and could still potentially damage internal organs but wold not likely lead to fatalities unless the same plate was hit consecutively. Then you could have the person molt periodically to replace cracked plates for new ones. That said, the Mineralization of the shell would weigh heavily on the frame of the person. This structure is extremely hard but it would also make it dense and therefore heavy. The outer surface would be much denser than the inner surface as the inner surface should be more concerned with kinetic and thermal dissipation. It would have a greater density of pores and may even have capillaries to help dissipate heat. You could make more of the shell with the mineralized proteins but the more you do the denser the shell and the heavier the person will be and heat and kinetic dissipation become an issue. [Answer] You can have the exoskeleton in form of a honeycomb structure. In this, the Keratin will be joined together in a hexagonal maze, with lots of air space between them. This will reduce the overall weight of the armor to a great deal and still would be able to deflect the bullets to some extent. Naturally, the space in this honeycomb will be empty, so the creatures can have a good average height. On the other hand, they can be really smart and when an adult decides to become a warrior he will bath in some kind of fluid(natural/chemical) that will fill up these cavities with gel-like material to increase the bullet resistance. [Answer] Easy, if you are saying they somehow have a "super dense" bone structure on the outside just give them super dense muscular tissue ]
[Question] [ **How difficult would it be for a human to survive on a planet with an atmosphere 2-5 times as thick as Earth's but with gravity like Venus?** Would such an atmosphere be survivable? If yes, then how hard it would be to breathe, move and see/hear on the surface? [Answer] Are you talking about a human walking around with or without an Protective Gear? also is the make of the atmosphere the same as earth? 78% Nitrogen, 21% Oxygen and 1% other? I'm going to presume "thick" is basically density The density of Air at sea level is 1.225 kg per cubic metre, humans regularly breath at 5x atmospheric pressure (6kg/m3) when they go scuba diving, the density of water is roughly 997 kg/m³ and as a diver goes down 33 feet (10.06 metres) they add an atmosphere of pressure to themselves, the scuba gear they were in, specifically the regulators are designed to allow the correct amount of air from the tank for the pressure they are at. This is why divers must return to the surface very slowly, as they have been breath air at much higher density then their bodies can handle if not at the same atmospheric pressure. Do remember that the equipment is not designed to help them breath at these pressure as much as it is designed to allow them to breath underwater… at these pressures So at your upper estimate: 5x the density, humans are able to breath perfectly fine, they would be limited slightly in terms of movement, only because there is more air resistance to push against. **However** The issues come from the science behind a planet being like this, for a planet to be the same size as Venus, but 5x the atmosphere, would mean either 5x the gravity, or the composition of the atmosphere being something other than what we have here on earth. **5x the gravity** This would mean the bulk of the core of the Earth which is Iron, would have to be Californium or Einsteinium or some other similar heavy, very radioactive and usually very rare elements, which at these pressures and quantities would probably be close to if not exceeding critical mass in some cases. A core made up mostly of gold or lead would make the planet roughly 4x as dense. With this greatly increased density would come the side effects, the planet would not spin as fast, if it did then it would completely shed its out layers or worse than that, it would have either a much weaker or completely non-existent magnetic field, exposing the inhabitants to solar radiation constantly. **Atmosphere** If the composition was different, then it would mean that certain PPE was required only because something like Krypton roughly is 5x the density of nitrogen, therefore make the atmosphere 5x as dense (Yes… I am generalising again) however if humans where to breath this then they would not be able to effective remove it from their lungs, so would not be able to take a full breath to receive enough oxygen. Among other issues, however there would be some good points krypton, is often used in lighting and lasers… so an electrical arc would be exceptional bright. Imagine a lightning storm on that planet!!! So if it was atmosphere composition then PPE would definitely be a must If the reason for this happening is “it just is stop asking questions this is science fiction” then the only effect would be increased air resistance, that’s about it [Answer] If you're talking about an atmosphere the same composition as our existing one that's at 2-5 times the pressure of Earth's then no humans are will never survive that, oxygen at partial pressures over 0.3bar is toxic the minimum you're talking about is 0.42bar which will kill most people in a matter of days; the top end you're over 1 bar of partial pressure of oxygen and it'll kill you in hours. But you'd have to muck about with the laws of physics to maintain the same gas mix at those pressures. A real atmosphere will have Hydrogen as a free gas which is toxic to most life as we know it at very low levels. You're also going to have increased levels of certain sulfurous and nitrous compounds since they're more stable at higher pressures breathing those is also going to cause short and long term damage, low altitude Ozone will be an issue that way too. In fact between the oxides of nitrogen, sulfur and oxygen the lower atmosphere will probably be pretty corrosive. I've said this before in relation to questions about atmospheric composition but it bears repeating: there is no known relationship between the size of a planet or it's composition and the atmosphere it holds onto. [Answer] **Survivable/Breathing** Yes, humans can handle things like being deep underwater relatively well. Breathing pressurised air should not really be a problem as long as it has the same properties as air on earth (enough oxygen etc.). I cant think of a reason why breathing should be much harder. **Moving** For most human movement air resistance is not really an issue, running will be harder but most things should be fine. **Seeing** That's a tricky one, the short answer is that pressure doesn't affect the basic functioning of the eye and thus you could see just fine. BUT there are a lot of other effects with regards to pressure and environmental effects that might influence sight (think about the effect pressure has on moisture contents in the air). **Hearing** Your hearing is not really bothered by pressure since the pressure in the inner ear is the same as the air outside it. BUT sound would spread quicker in the thicker atmosphere (just like it would in water). AND you will have a squeaky helium voice (due to physics of the standing wave in your throat). Again there are many other factors which are related to pressure which can influence hearing, but these are the most obvious ones for pressure. ]
[Question] [ Is it possible to have a structurally self-supporting hollow Earth where the weight of the shell is balanced against the atmospheric pressure inside? * It must be human habitable (gravity is nice but optional) * It must be able to keep its occupants safe from radiation *from space...*. * It must be able to survive a long *long* time floating around the solar system without becoming *un*inhabitable. * The designers couldn't afford to use hand-wavium so they had to make do with more traditional construction materials (which, thankfully were *not* in short supply) Is such a structure actually possible, and if so, how big can it get before it isn't? [Answer] **Can we build it?** Sure. We can always depend on Clarkean Magic: > > Any sufficiently advanced technology is indistinguishable from magic. ([Arthur C. Clarke](https://en.wikipedia.org/wiki/Clarke%27s_three_laws)) > > > From the point of view of simple physics, we can make inflatable balls out of rubber and buoys out of metal. Therefore, such a shell is only a head scratcher from the point of view of where all the materials came from (but you said that wasn't a problem). **Can we inhabit it?** Again, sure. Fill with air, add atmospheric recyclers, build habitats, fill void with floating islands of fresh produce because... **No gravity** The [Shell Theorem](https://en.wikipedia.org/wiki/Shell_theorem) demonstrates why there is no gravity inside a sphere. Basically, it's because the gravity pulling toward any point on the inside of the sphere is perfectly balanced by all the gravity pulling toward all other points on the sphere. No gravity. *Well... you could have "gravity" along the equatorial region if you set the sphere to spinning, but only there. You'll need big honking thrusters to keep the planet both spinning and where it belongs... You should read Niven's "Ringworld" books, you'd like them.* **Radiation free** Possibly. If you have the muscle and the dough to build a basket ball this big, you can afford to coat it in a couple of yards of lead. Earth survives due to both its atmospher and its [magnetosphere](https://en.wikipedia.org/wiki/Magnetosphere). You're missing a boatload of mass, a liquid core, and that core probably needs to be rotating. So Clarkean defensive shields would be helpful. If you can't have shields, that layer of lead becomes really important. Don't get too close to a star and don't let any meteors hit you. That's the real problem. Planets generally take care of this automatically. You'll need to have some defensive system in place that deals with things more tangible than radiation. But, you can build the sphere, so you can build those, too. **Survival is paramount** This depends solely on how you build the interior. You have plenty of volume to work with and the capacity to get some gravity if that matters. You need broad spectrum light, water, atmosphere, something akin to soil (Orchids use bark...), and a way to hold it all together. Maybe nets. If you can build the sphere, you obviously can build all the equipment to keep the interior habitable. The light's the biggest problem because unless you have a bazillion glo-globes floating around you'll need to dedicate some of your limited surface space to light panels (a lot of it). *Of course, as you work through these details, it'll beg the question why you're simply not living on a planet orbiting a sun that does all this for you.* **And I want it WHOMPING big!** I'll be honest with you, you can make it as big as you want. But there comes a point where people need to ask why you're bothering? Think of it this way: Let's say you want one so large that it takes the utilization of all planetary mass within your solar system to do it. You now have a big honking sphere, let's say 10X the volume of Jupiter (I've not done the math, but just for fun, 10X), you've filled it with air, water, pizza, and cream soda. And you have a lifetime subscription to Netflix and more than enough interior surface to project the latest episode of *The Walking Dead* for societal enjoyment. Now what? Even if you could build such a creature (oh, let's call it a *[Dyson Sphere](https://en.wikipedia.org/wiki/Dyson_sphere)*) what would be the point? Economically, it's simpler to just inhabit other planets. Heck, it would be cheaper to *terraform* other planets. With the tech level needed to do this, it would be cheaper to convert your population to androids that no longer need food, water, or atmosphere.1 So, yes. As I said before, with enough Clarkean Magic you can do it. > > Can you launch an ICBM horizontally? > > > Sure! Why would you want to? (*The Hunt for Red October*) > > > --- 1 *Which really makes me wonder what those astronomers who think they've found evidence of mega-structures actually found. They really don't make any sense. But, people bought into the idea that NASA found a face on Mars. Until someone got a better look at it.* [Answer] > > Is it possible to have a structurally self-supporting hollow Earth where the weight of the shell is balanced against the atmospheric pressure inside ? > > > As a sphere this is a terrible idea and the most likely way you'd build a habitation in space would be as a cylinder ( e.g. an [O'Neill cylinder](https://en.wikipedia.org/wiki/O'Neill_cylinder) ) which has huge advantages, not the least of which is pseudo gravity. A single large structure is also a very bad idea. Let's say we build a single world like this and we have say four billion people on it. A single large asteroid can wipe it out because structurally it would be a disaster for a major impact to occur. It would, at a minimum, be ripped apart by an explosive decompression of the internal atmosphere. But build lots of smaller cylinders and one impact just damages one of them. A tragic loss, but not a catastrophic one. So the all-your-eggs-in-one-basket strategy is a dreadful idea. If you insist on spheres, you may as well build lots of them. > > It must be human habitable (gravity is nice but optional) > > > Humans need gravity for safe long-term biomechanical function. Gravity (or something equivalent) is *not* optional for long term human habitation. And for humans it needs to be be as close to one gee as possible. We are "designed" for one gee. We can live and work in zero gee for extended periods (months), but don't confuse that with living our lives out in microgravity. Here's [a brief article from Scientific American](https://www.scientificamerican.com/article/how-does-spending-prolong/) on the subject, although there are plenty more out there. As your hollow shell will have microgravity at best, this simply kills the idea dead for humans living there in the sense of a permanent home. It's still viable for short term (months) stays (followed by a lot of hard work to recover fully from the experience). A rotating sphere can provide some pseudo gravity of course, but it will vary with position and this means you're effectively making large areas effectively useless for habitation. The cylinder remains the ideal shape. > > It must be able to keep its occupants safe from radiation from space.... > > > This is fairly easy and can probably be considered trivial. > > It must be able to survive a long long time floating around the solar system without becoming uninhabitable. > > > Define "a long time". Years ? Decades ? Centuries ? Thousands of years or millions ? Let's say centuries. You need airlocks for leaving the sphere (if you want to). In principle you could prevent most outgassing on those timescales. Note that if an asteroid impacts it could create a leak. It's going to depend on the thickness of your shell, but at best you'd need ongoing maintenance. This leads to another issue with a single large (Earth-sized) sphere. If you have lots of O'Neill cylinders and you think there's an asteroid on the way, it's likely you can move far enough out of the way to avoid the problem at all. Such a cylinder has a huge mass, but it's movable and you can design in enough structure to make it safe for small impulse engines to do this. Your sphere has a huge mass *and* it's a bigger target. You have to move it further and you need much more energy to move it (and of course return it to it's original orbit). This makes it more vulnerable to asteroids, IMO. To afford extra protection you need a thicker shell. But that means you're making an even more inefficient use of resources than a fleet of O'Neill cylinders would. So it's a poor choice. > > The designers couldn't afford to use hand-wavium so they had to make do with more traditional construction materials (which, thankfully were not in short supply) > > > But we can make a more flexible "O'Neill fleet" from the same (if not fewer) resources. We gain safety and flexibility and a nice healthy pseudo-gravity and we loose nothing by building the fleet. The sphere just wastes resources. > > Is such a structure actually possible, and if so, how big can it get before it isn't? > > > Probably you can build as large as you like if you have the resources. It's inefficient and it doesn't provide a safe one-gee environment for your inhabitants. You might be able to prevent the atmosphere from becoming a dangerously gravitationally compressed core that destabilizes the system by carefully heating the core (e.g. solar energy gathered from the shell - itself a complication with lots of downsides) to keep it hot enough to prevent gravitational concentration. You could in principle combine this with a system to provide light on the interior in a day night cycle, but you would need *vast* transparent areas or equally vast light banks focused on the core. All very complex and with lots of potential problems. [Answer] Actually, yes. Not sure if passive support is a hard requirement, but with active support it's not to big a challenge. The idea is similar to that of an orbital ring. Build a ring of desirable size and make it spin with orbital velocity which will reduce strain of self-support to pretty much zero. Build another, hollow, ring around the first one which doesn't spin using the spinning one as support. The outer ring will experience gravity as it constantly "falls" towards the center of mass of both rings. Since you can build this orbital rings at any size you can "stack" them, displacing them radially around a joint center of mass. Since the outer rings don't rotate you can build a support structure between them and even "level" that structure. (Giving you a flat surface to build upon). Now this might sound a bit ridiculous, but you could use something heavy that produces energy, e.g. a "small", spinning neutron star to build something like a dynamo and provide the active support with energy and further provide earth like gravity, if you place it into the joint center of gravity. There are some caveats like the rotating magnetic field of the star, maintenance or the fact that lateral rotation of the orbital ring (assuming you want rotation of the planet) might require some tricks, but I'll let you solve those details. --- Also flat earthers behold, you could construct two such orbital rings and have a relatively small lateral displacement between them in a cylindrical shape and build a support structure between. In one direction you can walk around it, in the other you can literally fall of the edge of "earth" :D ]
[Question] [ My story is based on a Glacial Climate setting or an Ice Age. However the transition is gradual and humanity was given some time to adapt. The transition began in our real-world technological equivalent of Renaissance Period around the 15th century. Going by the same timeline, the story is set in 2100`s, thus it has already been in progress for 600 years. Given that Industrial Warming has not started until the late 17th century to the early 18th century and that the process gains momentum over time, are underground cities more suitable than surface cities for progressive glacial conditions? If not, what forms of habitation are plausible? [Answer] **The case for above ground dwelling:** It is simply far easier to build a house above ground then to dig below and then worry about groundwater, ventilation, and the fact that at some time you might live beneath a glacier. OTOH, the climate will (according to an Eric fagan book an the last ice age whose title I forgot) be drier, maybe even sunnier (not in your case with the particles etc.). I'd expect realy slow movement away from the glaciated mountains and onto the, due to lower sea levels newly existing, coastal plains. Some might even adopt a semi nomadic lifestyle - cheaply produced houses from compressed earth bricks that are left after a generation or so, only as much property as can be actually moved. The basic ice age nomad package may well consist of a press for compressed earth bricks and a ventilation/heat exchange system for their temporary (sort-of) passivhaus! Existing harbour cities will likely remain intact (coasts are glaciated last, if at all, unless you live in Norway) and gain interesting nwe real estate due to lowering sea levels. Given that the soviet union managed to move whole factories ahead of the Wehrmacht and behind the Urals, I suggest that a sheer production facility can always "outrun" a glacier. **The case for below ground dwelling:** This allows you to stay in one place, which in itself is not worth much when the place is covered by ice. However, you can't move mines anywhere, so I'd find it reasonable when major production facilities stay near the resources they consume. This could mean to move factories into old excavated mines. Minig is hard for reasons stated above, so I really think this will only happen where coal or ores are mined anyway or where the ground is exceptionally soft rock, like carst areas. Our below ground areas will likely use a combo of geothermal heat, solar power and fossiles/nuclear to supply their energy and to keep a patch above icefree. I'd expect them to have many greenhouses with cold adapted plants sitting on the ice surounding the city. ]
[Question] [ I'm currently trying to develop the world of a sci-fi story I'm working on, and a concept I've thought of adopting with the environment and characters is a common breeding system where identical twins (or sometimes not, asymmetric twins from the same egg have also been under consideration) are a commonplace byproduct of the world's evolution. I'd like to know the plausibility of this. My idea is for two twins to be born with natural, pheromonal connections between one another. The sexual organs of the twins would be the same, thus preventing immediate inbreeding. I'd also envisioned [most] twins consistently having lifelong reliance on one another. i.e. I also want to know how reasonable it would be to expect them to coordinate efforts in the acquisition of food and evade potential predators. As for mating, I thought if they shared the exact same DNA there would be less ingrained concern over which gets to spread its genes. Would this be accurate? Thanks in advance for anyone that tries to answer me. I'm doing what I can to keep things in the realm of reality, so it'd be much appreciated to know whether or not the universe I'm creating has a strong enough footing in the real world. As a brief recap and outline, here's how I'd imagine this type of reproductive cycle working: 1) Two genders needed to reproduce. 2) Upon fertilization, the egg immediately moves to naturally develop monozygotic twins. 3) Both offspring share the same gender. 4) The twins try and operate as a pair from birth. 5) When any mate(s) is/are found, twins shouldn't need to compete between one another too much because of their identical DNA and the beneficial nature of their cooperation. [Answer] ### 1) Two genders needed to reproduce. ### 2) Upon fertilization, the egg immediately moves to naturally develop monozygotic twins. ### 3) Both offspring share the same gender. [Armadillos do that in our world](https://en.wikipedia.org/wiki/Armadillo): > > (...) the nine-banded armadillo also exhibits delayed implantation, so the young are not typically born for eight months after mating. Most members of the genus Dasypus give birth to four monozygotic young (that is, identical quadruplets), but other species may have typical litter sizes that range from one to eight. > > > So this part is covered. ### 4) The twins try and operate as a pair from birth. ### 5) When any mate(s) is/are found, twins shouldn't need to compete between one another too much because of their identical DNA and the beneficial nature of their cooperation. Items 4 and 5 may be accomplished if some species of armadillo evolved to be social. As it is now, they solitary animals. --- Since we can find in our own real world features such as the ones you need, you don't need any suspension of disbelief nor handwaving to make it work for a fictional species. ]
[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/104219/edit). Closed 5 years ago. [Improve this question](/posts/104219/edit) When SETI tries to look for aliens, they always try to catch the echos of radio waves sent out from alien civilizations. But would an advanced civilization even bother to use radio waves? Are there hypothetical communication systems that are superior to radio waves? Or are radio waves truly the best way to go? [Answer] [Kudos to Justin for mentioning entanglement](https://worldbuilding.stackexchange.com/a/104224/21222). His idea about using quantum physics and more advanced, hitherto unseen technologies is right on spot. I'll just add another option that I think is in the same spirit: [tachyons](https://en.wikipedia.org/wiki/Tachyon). They are theoretical particles with a rather interesting set of properties: * They travel faster than light. They can never slow down to light speed; * Moreover, the less energy they have, the faster they go. When their kinectic energy approaches zero, their speed tends to infinity; * Due to their FTL nature, they may also allow communication backwards in time. Infinite speed makes for faster communication than sending regular particles through wormholes. Sending messages to the past makes it even faster than entanglement, though in sort of a cheating way. [Answer] If they were really advanced, the answer would probably be 'no they would not bother with electromagnetic communication'. Any electromagnetic communication would be spurious noise, some form of an anachronism. It really is, for interplanetary communications, quite limited and inefficient. In perhaps another century, humans could very well be remarking at our dependency on it, the same way we remark on our former dependency on the 'pony express' and snail mail. It is to be expected that their physics text book is much, much thicker than ours. With the advances that are being made in quantum physics, there is every indication they would use such principles as entanglement (principles that we are only guessing at), for instance. The notion that some will posit - that such communication is impossible - only slows down our discovery of it. **Edit** See for instance [Scientists Achieve Direct Counterfactual Quantum Communication For The First Time](https://www.sciencealert.com/scientists-have-achieved-direct-counterfactual-quantum-communication-for-the-first-time) **Edit** And another article [Nil Communication: How to Send a Message without Sending Anything at All](https://www.scientificamerican.com/article/nil-communication-how-to-send-a-message-without-sending-anything-at-all/) I have absolutely no doubt that there are quantum fields that we can not even speculate on. We just discovered the Higgs field, for instance, a previously unimagined and unimaginable field previously. There is no justifiable reason to believe that it will be the last one discovered. Even the Higgs field itself, if it could somehow be manipulated, could lead to some new form of communication. As Einstein himself called it. 'spooky action at a distance'. Just because Einstein had no use for it, and could not comprehend such a thing, does not make it impossible. [Answer] An advanced alien civilisation would likely have a more advanced means of communication than radio waves. In order to become an advanced civilisation however, they've likely passed through a period where (like us) they've relied on radio waves for their own communication. We as a species engage in archaeology to understand the past; we can hope that they might look at the radio spectrum as we do, looking for younger races. This of course assumes that their technical development has occurred in parallel to ours. It's possible that they've not discovered radio waves during their development, in which case they wouldn't think to look for them any more than we look for signals in gravitational waves, for example. ]
[Question] [ ## BACKGROUND So I was working on a map, when I suddenly realized that despite the [many](https://worldbuilding.stackexchange.com/questions/581/creating-a-realistic-world-map-landmass-formation) [helpful](https://worldbuilding.stackexchange.com/questions/23941/creating-a-realistic-world-map-vegetation-biomes) [tutorials](https://worldbuilding.stackexchange.com/questions/1353/creating-a-realistic-world-map-currents-precipitation-and-climate) [on](https://worldbuilding.stackexchange.com/questions/62363/what-geographic-features-occur-at-each-type-of-tectonic-plate-boundary) [this](https://worldbuilding.stackexchange.com/questions/102798/how-do-i-figure-out-my-planets-biomes-and-weather) [site](https://worldbuilding.stackexchange.com/questions/1020/creating-a-realistic-world-map-erosion) I have very little idea what I'm doing. I thought it might be a good idea to put on the breaks and ask for a reality check before I build myself into a corner. Hopefully this will provide me with some guidelines for going further. (And hopefully it's not already a total mess.) --- Here is the map as it stands. I've projected it over an equirectangular map of Earth to give a better idea of coordinates and scale. I've left the western antipodes, north, and any other landmasses basically uncreated for now, to give myself a free hand for later. My priority is to get as close as I can to the projected biome placement. (I know, better to start at the bottom and work up. But here I am.) Please keep in mind this is my first attempt at creating a realistic map - I want to get it right, but many concepts are still new to me. --- ## **Map 1 - Elevation and Projected Biomes** What I would *like* the map to look like. Priority biomes are marked with an asterisk\*, like so. Other biomes could be moved around more easily if needed. Mountains ranges are shaded. The biomes and elevation are pretty broad and simplistic right now, to be complicated later on - if anything is unclear please ask in the comments. ![map one](https://i.stack.imgur.com/wqCc8.jpg) **Notes:** *Savanna* - Preferably resembling northwestern sub-Saharan Africa. The saltwater swamp needs to be near it, but could be moved from its current location. *Highlands* - Preferably resembling Ethiopia and the great rift valley. *Volcanic Desert* - A bit of a misnomer, an important small desert surrounded by plains. --- ## **Map 2 - Tectonic Plates** ![map two](https://i.stack.imgur.com/Q1jBa.jpg) --- ## **Map 3 - Ocean Currents** ![map three](https://i.imgur.com/Has64S9.jpg) --- ## QUESTION **Do the above maps hold together, and is the projected biome placement shaping up to be realistic? If not, what can I do to improve it? If yes, does the current geography also imply other necessary or probable features?** [Answer] ## I like it! ...but it could still use a little work First of all, it's awesome to see someone so dedicated to a realistic world map. However, following *all* the rules *all* the time makes a novel non-fiction, not worldbuilding- so feel free to take any of these with a grain of salt or throw them out altogether. ### Map 1 Comments As you point out, this layout looks a little oversimplified and has very large biomes, so you may want to fill in some of the details after you've worked out the wind patterns. Biome assessment from the north to the south: * **Unknown landmass:** Probably going to be desertlike at the top (think Middle-East) and hot/rainy at the bottom. * **Stormy region:** I completely agree. This area seems to be under the [ITCZ](https://en.wikipedia.org/wiki/Intertropical_Convergence_Zone) and will also have some monsoon effects from the small waterway to the north. * **Wet tropical rainforest:** Looks good! You've placed it near the equator, so it's guaranteed to get lots of rainfall and be warm. The nearby mountains create a small problem- [rain shadowing](https://en.wikipedia.org/wiki/Rain_shadow). One side of the mountains will likely be much drier than the other, and this will depend on the wind direction. * **Volcanic desert:** Again, depending on wind direction, this area might get a lot more rain than you'd expect due to the nearby sea. Other than that, it looks fine- you can put Mordor essentially wherever you'd like and blame it on [mantle plumes](https://en.wikipedia.org/wiki/Large_igneous_province). * **Dry highlands:** The dry part is fine, it's the highlands that might be problematic. See below. * **Savannah:** This whole area wouldn't be savanna, it's almost surrounded by ocean and will thus be relatively humid, especially if it's low to the ground. The center part is probably savanna, due to middling rainfall and absence of mountains, but the borders will be more exotic. * **Swamp:** This one looks good! If possible, try to have rivers draining off into this area to create estuaries and deltas. Be aware that swamps tend to be fairly limited in size, however. * **Mountains & Taiga:** Also looks good! * **Cold Plains:** I'm not sure how consistently cold this would be. It looks like it's about the same latitude as Australia and that place can be brutally hot. See the ocean currents section below for some other ideas * **Steppe:** Again, winds are important but this one looks good. Expect some other biomes near the ocean edges, and it'll probably be more tundra than steppe. * **Partly Sunken Landbridge:** Not really sure what to do with this one, it doesn't seem to be a biome so I can't comment on it here. * **South Pole Continent:** Yes, yes it is. Please name it something better than "[not-north-pole-land](https://www.etymonline.com/word/antarctic?ref=etymonline_crossreference)" ### Map 2 comments Tectonic plates are tricky, but as a whole it looks like you've got the hang of it. Again, vaguely from north to south: * **Blue mass to the north:** Not much to say here. It may be tricky to justify the passage between the unknown landmass and the mainland without tectonic activity though. They look to me like separate continents, not different areas of the same continent. If it were me, I'd place a mid-ocean ridge in the middle there and say they're moving apart. * **Reddish-brown**: It's interesting to see a continent that's nearly 50-50 continental and oceanic plate, but there's no problems with that that I can think of. If possible, make the area under the "Stormy Region" continental shelf- if it's proper oceanic plate, you'll have subduction which would push your mountains away from the edge. * **Teal-green:** This is well placed! It explains the deep inland sea nicely. If I had to change anything, I'd have it move directly to the right instead- see below. * **Yellow:** The placement is fine, but I strongly recommend changing it's direction of motion towards the bottom left instead. That'll justify the absence of mountains along the teal-green/yellow border, which would have to be Himalaya-level huge (continent on continent collision). * **Light blue:** Mostly fine, except for the dry highlands. Those are going to be *very* hard to justify with this setup, as rift valleys are rarely flat, elevated areas. The inland sea looks good, but I'd expect it to be matched on the other side of the continent where the plates are doing the same thing. * **Bottom right, arrow without color:** I'm not sure what the plate looks like here but it should be a different one from the plate that has the easternmost portion of the continent. It's hard to have both continental and oceanic on the same plate. * **Large ocean** If possible, this area should have more mountains around it in general. It looks like the Pacific Ring of Fire, which is actively tectonic. However, the reddish-brown plate looks like it's actually opening up, which means that it should have large, thick continental shelves. ### Map 3 comments: The ocean currents are kinda... yikes. Ocean currents actually follow rather well-defined rules, mainly determined by surface winds- which actually depends on the direction of your planet's rotation. In either case, the Large Ocean will likely have a single encircling current, with a thin & powerful warm current moving from the equator to the pole on one side and a wide, slow current moving from the poles to the equator on the other. Those currents would follow the topography fairly well, then would spiral away from the coast at about 60 degrees south as the Algulhas, Gulf Stream, and Canary currents to on our world. The current between the unknown landmass and the mainland won't actually share the channel nicely- consider making this a [seasonal reversion](https://en.wikipedia.org/wiki/Indonesian_Throughflow) or a deep water/shallow water division Your inclusion of inland seas was wise- doing that will allow the formation of [cold and salty water](https://en.wikipedia.org/wiki/North_Atlantic_Deep_Water) that will power an overturning circulation for your planet as a whole and keep its temperature well regulated. [Answer] # Map Out Your Wind Currents Wind currents will determine which parts of your world get regular rain and which become deserts. I can't tell you how wind currents work, but it's important to map them out to determine the average humidity in an area. ]
[Question] [ One of the worlds I’m building has three moons in 1:2:4 resonance, with the full moons syncing up once a cycle, meaning all three are full at different times but at the same time when the moon with the longest orbit completes a single orbit. What I’ve been thinking about lately though is where they would appear in the sky based on their orbit and phase, especially after finding the following image: [![enter image description here](https://i.stack.imgur.com/uWwucm.png)](https://i.stack.imgur.com/uWwucm.png) Now, as far as I’m aware, the moon appears in roughly the same place to an observer because both the moon and earth are in constant motion. However, with multiple lunar bodies, I get the feeling this movement will have a more pronounced effect on observation. Essentially what I’m trying to figure out is where these moons would appear in relation to one another in the night sky and how much, if at all, they would appear to shift to an observer. [Answer] The 3 moons will roughly be on the same orbital plane, and once they are in the opposition to give a full moon, they will appear aligned. They will occupy the positions marked in red in the figure. [![enter image description here](https://i.stack.imgur.com/EtcTH.png)](https://i.stack.imgur.com/EtcTH.png) If their angular size in the sky is larger than the angular distance between them, the observer will see a fancy eclipse. If not, the sky will show a peculiar show of 3 full moons set on a straight vertical line. The inclination of their orbital plane with respect to the orbital plane of the planet will determine the elevation in the sky. ]
[Question] [ There are few examples of radiotrophic ecosystems on Earth. Of those discovered, the radiotrophs are limited to single-celled organisms and unique mutant fungi. The reason seems to be due to a lack of concentrated radiation. The Chernobyl reactor is an energy source similar to a star or steam vent, able to support more complicated organisms. What would be a natural equivalent that would drive high energy ecosystems seen on the surface and deep sea? [Answer] I think you could do this with [**Radon**](https://en.wikipedia.org/wiki/Radon). Radon is radioactive and gives off alpha particles, which should be easier for a putative radiotrophic organism to handle than gamma rays. Radon is generated in the earths crust continuously. Being a gas which is generated in solid areas, it will tend to collect in pockets where it can - sort of like water collecting in favorable areas on the surface. These pockets can be shallow and so have access to nitrogen or nitrogenous compounds and other needed minerals percolating down from the surface. You do not want your radioactive energy source to swing from nonexisting to sterilizingly strong (the latter being a problem with the spontaneous nuclear reactors). Those swings are bad for the critters. The good thing about radon in this context is that the creation of radon is fairly steady and continuous, and the half life and so breakdown (into nongas elements) is short. So these subsurface pockets of radon should have stable levels of radioactivity. [Answer] [Natural nuclear reactors](https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor) are a thing. If might be possible that there are large deposit of radioactive material deep in the Earth that gives sustained power output. It is however thought that there isn't enough radioactive material in the upper crust of the Earth any more to sustain any natural reactors today. ]
[Question] [ Map is 1000 miles long and wide. In general, do these placements make sense? I'm also wondering: * where volcanoes would be? * why the coast is full of life and the west dead and barren? * where the equator would be? and if I can make the northern coast more rocky and full of islands -- plateaus and whatnot. This is a zone of safety for people, a haven protecting them from West & South. Perhaps 1-2 million people living here split between a few ruling faculties. [![enter image description here](https://i.stack.imgur.com/O1zOG.png)](https://i.stack.imgur.com/O1zOG.png) [![enter image description here](https://i.stack.imgur.com/I4DN4.png)](https://i.stack.imgur.com/I4DN4.png) (Tan/brown): Desert, dry land, hot. (Light-green): Arable. (Green): Dense forests. (Dark-green/dark-brown): Magic, cursed land, unnatural jungle, might be spreading. [Answer] > > where volcanoes would be? > > > Volcanoes are usually placed at the borders of tectonic plates. You can have rift volcanoes where two plates diverges (the African Rift Valley is an example), or subsidence region, where on plate sinks below another, creating mountains and volcanoes (this is i.e. the case for the Andes and for Japan). > > why the coast is full of life and the west dead and barren? > > > Dominant winds blow from the sea on the coast, discharging their water load on the mountains. The water flowing back to the sea makes life flourish in those region, while after the mountains the dry air cannot convey that much rain, thus it is a desert. > > where the equator would be? > > > I cannot add more than AlexP's comment. [Answer] If the dark green is supposed to be forested area, it seem unusual to me to have a desert border it so tightly in the lower left quadrant. In my experience, desert transitions to mountain or rock, or to a gradual progression of scrub, to grass, to trees. This is typically due to the influence of some water source like a river, above ground lake or underground lake (aquifer) that feeds the plant growth from underground, but that influence becomes more attenuated with distance from the water. So forests need a lot of water; then when there isn't enough to keep them alive grasses and small woody bushes can still survive, at a further distance those become fewer (this is scrub land), then the parts that get no reliable water at all (meaning a plant may go several weeks without a drop) become desert. (Cacti and other plants that can store water in their leaves or roots may survive.) [Answer] In addition to the above, you also have geological hot spots (Hawaii and I believe Yellow Stone) which are the results of pockets of geological activity below the plate... the place where they breech is constant, but it's the plate that moves that causes the change (the Big Island is currently seated over the spot where the rest of the Hawaii islands once were and is the only active volcano in the entire chain). Yours looks like it could be related to oceanic crust sub-ducting under continental crust (take a flipped negative of California with respect to the pacific ocean). This could give you the problem of more Earthquakes and Tsunamis in your coastal regions as a more immediate danger... and with Volcanoes you'll probably go long periods of dormancy followed by one big bang that will really mess up the local area (see Mount St. Helens) and you're not going to get a them with pools of bubbling lava and smoking cones (Hawaii does have the former, but it's a shield). ]
[Question] [ BACKGROUND: I have been working on a game called Rise: The Vieneo Province. Vieneo is a terrestrial moon (all details can be found [here](http://rise.unistellar.com/Vieneo)) but we have an atmospheric composition we arrived on from [another question](https://worldbuilding.stackexchange.com/questions/85033/hypothetical-terrestrial-moon-atmospheric-composition-validation): N, SO2, O, and trace CH4, NH3, H2O, Ne, N2, CO... Nitrogen 98.4% 2589 mb Sulfur Dioxide 1.0% 26 mb and Oxygen 0.6% 16 mb We have a perpetually overcast sky and a lot of rain in the game (like tropical environments on Earth) ... I am being told that we need more water vapor in the air because of the small hydrosphere of 13%. But with an average global temperature of 7.7 Celsius we are too cold. The middle of the cloud layer averages about 9.25 km above sea level and are about 2.5 km thick on average. QUESTION: What is the minimum increase in water vapor percentage and global temperature that will make the the described cloud layer and tropical precipitation work? I would like to remove the SO2 altogether in favor of the water vapor explaining the persistent cloud layer. Thanks in advance! [Answer] I'm not sure that you can have both a lower average temperature than Earth and a more active hydro-logical cycle. Perhaps you could have low lying volcanic regions that locally emit lots of water vapor (and dust for your condensation nuclei - does not have to be SO2). These clouds would then spread out and give you plenty of rain, so you would be all of cold, overcast and raining lots. How you get these features is another matter, some sort of volcanic calderas might be a solution - these could be your 'oceans'. So.. your moon has several water bodies, all sat in volcanic calderas and heated up by the magma therein - no genuine earth-like oceans. Water vapor evaporating from these caldera give you a permanent cloud layer at it hits the cold atmosphere. (Sorry if this is all a bit hand-wavy) ]
[Question] [ **This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information. I've been reading here for a little while, but this is my first question. I am trying to come up with either a concrete set of numbers for a single answer for a binary planet system, or a simple formula that allows me to play within a range of acceptable numbers that answer my question. Math and I don't really get along anymore, so the less complex your solution, the better. Even a solution via simple 3D modeling / illustration on spheres or geometric drawings is welcome if it also provides numbers that fulfill the solution. ALSO I'd like to keep this within the realm of **plausibility**, so sources for creating my system are listed after the question. I don't mind if the science pushes the boundaries of what we know. Unusual, rare, unlikely, and unique solutions are welcome; impossible ones are not. Here are the shadows I'm trying to achieve: Figure 1: The two possible shadows cast by each planet when all three bodies are in alignment [![The possible shadows cast by each planet when all three are in alignment](https://i.stack.imgur.com/N1pdbl.jpg)](https://i.stack.imgur.com/N1pdb.jpg) I'm going to leave my inaccurate drawings above for now because they better illustrate the landmasses and ocean areas on both planets. I'll replace them when I'm able. More accurate yet simpler sketches below along with (hopefully) improved wording. Requirements: 1. Binary planets (tidally locked to each other) orbit an M0 parent star at the outermost edge of its habitable zone. (See note1) Neither planet, nor the binary system as a whole, supports a moon. 2. Both of these planets must be **theoretically** capable (liquid surface water / atmosphere / pressure / mass / density-wise) of supporting a range of humanoid and other life forms (akin to Tolkien's world, minus mankind as an example), and share biomes. They must not be closer to each other than 3 times the radius of Planet B. (See note2) 3. Planet B must be larger than Planet C and not be wider than 12000 km in diameter (slightly smaller than Earth size); however, I strongly prefer Planet B to be as small as possible within the given constraints. 4. Planet C must not be smaller than 6000 km in diameter. (See note3) 5. During A-B-C alignment (Fig 1) [![Fig 1](https://i.stack.imgur.com/uyWdd.jpg)](https://i.stack.imgur.com/uyWdd.jpg) - A being floating in the center of the night side (it's in the middle of the ocean) of Planet B (point b) will see only a circle of darkness blocking the stars (behind Planet C) when looking toward Planet C. (Fig 1a) Planet C should fall well within the umbra cast by Planet B. - A being standing at point c will see a total eclipse of Star A by Planet B when looking starward. Only the corona should be visible (Fig 1b) [![Fig 1a and 1b](https://i.stack.imgur.com/eNScc.jpg)](https://i.stack.imgur.com/eNScc.jpg) 6. During A-C-B alignment, (Fig2) [![Fig 2](https://i.stack.imgur.com/CTCZf.jpg)](https://i.stack.imgur.com/CTCZf.jpg) - A being standing in the center of the night side of Planet C (point c) will see Planet B as a thin blue ring – with an apparent width not wider than 1/6 the radius of Planet B – with northern polar ice visible. More temperate landmass may be visible closer to the northern side of the equator.(Fig 2a) - A being standing at point b will see an annular eclipse of Star A by Planet C because Planet C is not large enough to eclipse it totally (Fig 2b)[![Fig 2a and 2b](https://i.stack.imgur.com/pLV8f.jpg)](https://i.stack.imgur.com/pLV8f.jpg) 7. Rotation period for the two planet system should not be less than 16 hours nor more than 64. Is this plausibly realistic? I simultaneously hope this question is not too long and that I've provided enough info. If not, please me know what I can to do improve. --- (note1) ~0.5 solar masses.  See *Habitable Planets for Man* by Stephen Dole ([second edition](https://www.rand.org/pubs/commercial_books/CB183-1.html)) American Elsevier Pub. Co. - 1970 pg. 81.  “For a special rare class of planets with extremely large or close satellites, there is an extension of the lower permissible primary mass [of the parent star] down to 0.35 solar masses.” [![photo image of referenced page](https://i.stack.imgur.com/1NbgO.jpg)](https://i.stack.imgur.com/1NbgO.jpg) My star falls well with this range, and the binary planet system fulfills the large/close satellite requirement. (note2) [Can binary terrestrial planets exist?](https://phys.org/news/2014-12-binary-terrestrial-planets.html) at Phys.org (note3) [Jim2B’s wonderfully detailed answer](https://worldbuilding.stackexchange.com/q/47415/20215#47437) to Worldbuilding question [Smallest possible habitable planet? (also taking density into account)](https://worldbuilding.stackexchange.com/q/47415/20215) [Answer] # Is It Possible? Yes, this arrangement is possible. The rest of the answer is how to figure this stuff out: # Let's talk about [angular diameter](https://en.wikipedia.org/wiki/Angular_diameter). Angular Diameter is how big something looks: small things, but up close to the observer, can look just as large as something very large but very large away. This "apparent size" is called angular diameter. (Also yes, you can call it "apparent size," and "angular diameter," and other names...) If the angular diameter is the same as something behind it, they will perfectly block each other. The relationship is: $$\delta = \arctan(\frac{d}{2D})$$ Where d is the diameter of the object in question, and D is the distance from some chosen observation point and the midpoint of the object in question. # Determining Your System I've made a little diagram showing you your situation:[![Back-of-Napkin calculations never looked so good.](https://i.stack.imgur.com/QTSCL.png)](https://i.stack.imgur.com/QTSCL.png) Remember, the little d's represent the diameter of the bodies in question, and big D's represent the distance between a middle point and the midpoint of the things in question. $d\_3$ is the diameter of the shadow. You should also note that sum $D\_1+D\_3$ is not (always) the distance between the planets, but the distance between the planet making the shadow and the edge of the shadow on the other planet. Also, this point which everything is measured from is not the point about which the two planets revolve. (That point depends on the mass of both bodies.) Also, it should be noted that $D3$ is really an absolute value- the shadow (d3) could be going the other way, inside the cone. For case 1, where the big planet overshadows the other one, the smaller planet's radius must be less than $d\_3$ and $D\_1+D\_2$ is (at least) the distance between the two planets. For case 2, where the small planet puts a shadow on the large one, the distance $D\_1+D\_2$ is the distance between the small plant's center and the center of the ring formed by edge of the planet's shadow. To make a ring, the larger planet's radius must be larger than $d\_3$ Using this information, you can figure out what the diameters and distances of your planets should be. ]
[Question] [ **Is it possible for under water Atlanteans to make explosives?** These Atlanteans have no magic but do have gills. They look like normal people other than the gills and webbed hands and feet. They live in peace but could benefit from explosives for hunting/fishing. Is it possible for this species to manufacture explosives? [Answer] **Yes** My first response was no but thanks for Bellerophon for the link about heat, **there is one way**. aquatic plants produce oxygen bubble, these can be trapped. Pure oxygen plus a container plus the right fuel can make an explosive. Ignition is tricky but not impossible, low output batteries could be produced as could chemical ignition. This oxygen could also be used for to produce heat for other things, like metallurgy and certain ceramics. However keep in mind, mixing chemical in an entirely aquaus setting would be very dangerous, chemistry research in general would be more difficult underwater where isolation is nearly impossible and you are basically forced to breath anything you are working with. This will severely limit chemical research. [Answer] Let's assume these folk may function quite well both in and out of water and have mastered some necessary prerequisite technical abilities (fire, ceramics, glass making, chemistry). Let's also assume that there is a flock or herd of some animals to provide a reasonable supply of excrement for nitrates. Dung from horses, sheep, pigs, chickens and bats have all been used as nitrates for making both fertilizer and explosives. It would be quite reasonable that Atlanteans would discover the value of dung-enriched soil for farming and proceed to develop concentrated fertilizer. It is also possible that they may even accidentally discover explosives as result. If non functional on land; then another alternative is available. Use hollowed out bones from large marine carcasses to make reflux condensors. Placed near the ocean surface to collect solar energy, this would provide a large supply of distilled water. Now our Atlanteans have the basis for electricity from desalination batteries. And can use fish intestinal material for making balloon bladders. Using electricity to perform electrolysis of water will separate it into hydrogen and oxygen. A fish bladder full of hydrogen and oxgen gas ignited by a spark will yield a potent explosion. H-OH torches burn quite a bit hotter than an acetylene torch so our underwater folk have the basis for both explosives and fire. If they can function to depths of about 4000 meters, then they would be able to collect gold silver platinum tin copper and vanadium as well after finding a black smoker volcanic vent. So it would take then longer to develop land dweller technology originating from use of fire, but there is no reason that it cannot be done. ]
[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. [Here](http://labs.minutelabs.io/Chaotic-Planets/#planetarySystem=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) is a link to an online animation of stars' movements in a trinary system. Basically, the three stars are orbiting around a barycenter; one (yellow in the animation, mass = 1) closer to it and the other two (red and blue; mass = 0.25) orbiting around each other as well. **How far apart would the planets and stars have to be for there to be a stable orbit in a habitable zone around either the yellow star or in a circumbinary orbit around the red and blue stars?** The mass of the yellow star can vary as needed, as long as it is roughly 4 times the mass of red and blue as in the animation. [Answer] **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. This kind of system could definitely host a planet given certain constraints. A useful rule of thumb for long-term stability in a gravitational orbit is that all orbits must be separated at least by a factor of 7 in radius (see, e. g. Publications of the Astronomical Society of the Pacific, 115:825–836, 2003 July). For example, a planet could orbit at 1 AU from a star, and both can orbit a barycenter with another star which is at 7 AU a safety margin, use a factor of 10. Having the planet orbit the single big star is easy. You can put it at 1 AU, and place the binary at least 10 AU away from the big star. If you want to have the planet orbit a single star in the binary, you need a bigger system. You could have the planet at 0.25 AU from one star, have the binary stars orbit eachother at 2.5 AU, and have the third star and the binary orbit eachother at 25 AU. Having the planet orbit the both stars in the binary is unfortunately very difficult. The problem is that the habitable zone of a 0.5 solar mass star is only 0.25 AU from the star (L~M^4). This means that to maintain the appropriate separation you would need the stars to orbit eachother at only 0.025 AU or around 5 solar radii. I think the stars can escape collision, but a system forming this way seems unlikely due to the tight constraints. If you scaled all of the masses up to avoid this problem the big star would die relatively quickly (within a few billion years), which might have a disastrous effect on life developing on the planet. If you want a circumbinary planet, you should probably have all the stars have the same mass as the Sun - then the binary could orbit at a more comfortable 0.1 AU and the planet could be placed at around 1 AU, with the third star much farther away. Edit: Added a reference ]
[Question] [ One of my fictional planets is a lot like Venus. Tons of volcanoes, extreme air pressure, similar density. The volcanoes are active. There is 1 creature here that depends on minerals and acids. Without acids, these creatures would be toast. Okay here is what I am proposing for a creature who absolutely need minerals and acids: The creatures have a cold field around them to protect them from volcanic temperatures. They are very heat resistant on the inside and as soon as lava gets into the mouth, it is supercooled. This supercooled lava is then digested by an extremely strong acid. Then the minerals are surrounded by weak polyprotic acids. This protects them from the HCl that is in their blood. HCl is like water for these creatures in that it is absolutely crucial to living. If HCl levels get low on the planet, a lot of these creatures will die from lack of acid. Is it plausible that these strong acids are like water in that they are necessary for these creatures to live? [Answer] First, Venus has not too much HCl, it has a much more sulfuric acid H₂SO₄. But from the viewpoint of the answer, it is the same. These acids have 2 major effects for us: 1. they change the biochemical reactions of our proteins. Many biochemical processes work differently in acidic environment. Essencially, they are poisons. For us. 2. they chemically destruct the proteins. Thus, they are destructive and also poisonous. None of them is unavoidable, it is only because the ancient oceans in them our biosphere started, simply wasn't any of them. But note: the main structure of the proteins are chemically strong things, around like the plastic materials. It is not an inherent disadvantage, a life could evolve in a such acidic environment without any major problem. Although their biochemical reactions would then require the acidic environment, thus the life in our clean water would be similarly unavoidable for them, as living in NaOH for us. You don't need some internal protection for them from their acidic blood, their whole body can be simply acidic. With sulfuric acid, and not with HCl. What is a major problem: They still need water. Without water, there are no complex biochemical reactions. Or, you need some fluid. And the Venus is so dry like the Sahara. Furthermore, Venus is too hot, with 400°C surface temperature makes the long molecular chains simply impossible. --- Note: HCl is a gas, it will be fluid only far below 0° C. What we call hydrochloric acid, is its solution in water. [Answer] One thing about World Building is that it works according to your whims and fantasies. Maybe on another planet, a silicon-based intelligent alien kid would be asking her grandfather "Pa, is it possible that on a planet far far away, there could be life forms based on carbon compounds instead of silicon?" The point is that you go on and make your creatures the way you want them. You cannot make your creatures 100% practical and flawless. No, even if a team of 100 top scientists sits together and works on such an alien creature for a year, they would definitely come up with a generally working model, but the minute details would still have to be filled in and a lot of little errors and loopholes here and there to be fixed. So go on and design your creatures the way you want them. In my this answer I could go the negative way and try to find critical flaws in your creature design, but who am I (or anyone else) to criticize? It is your world, you make it as you like it. Now, coming to life *as we know it*, I don't think it would be easy to define a creature so different from Earthly life. There are a **lot** of things which need to be in place, in order to make it work even in the most rudimentary form. For one, a creature depending so heavily on HCl that it would die in its absence sounds like it has evolved in a predominantly alkaline environment. Venus (or any super-volcanic planet) is far, faar from being alkaline at all. ]
[Question] [ In my world, an Omniscient creature exists. We don't know how it got here, or if it was created, but it's real, and it's been "willing" to help humans for a long time now. However, every thing we might ask to this being comes with a price : **One answer costs one human life**, given after the answer. It's omniscient, but it's got its limits : * It knows everything people know, and remembers everything since it was here, but **not more** (the first mathematicians and physicists were quite disappointed) * It cannot compute anything. Meaning that it analyses very well, but cannot create information out of those analysis (like solve unsolved mathematics problems, give perfect answers to philosophical questions, etc.) While **Omni** (as it's called) was used by governments as an executioner at the same time as an informant (hey, might as well use all its functionnalities for a purpose), those governments eventually got all the answers they needed (or maybe they didn't have enough people to execute), so Omni got moved to replace judges in courts. Of course, not all the trials needed Omni (and it's quite costly), but for some trials where both parties claimed they were right and the other was wrong, it could be used. In that case, people knew the price : If a party was found guilty by Omni then one responsible of the felony would be the price to pay (and the others would face their government's justice). There are exceptions of course, if both parties are truly honest and are both equally right (or wrong) then no answer is given, and no payment is needed. Omni is harsh, but not always. To end a trial, Omni can be used as a last resort, but it needs to be accepted by both parties. If a party refuses, then it is considered guilty. It's the way it goes. So in fact, the fear of Omni reveals the truth, most of the time. Thanks to this, since a few decades, trials no longer took ages to end, and the result was always justified. --- The human civilization on my earth is as advanced as us, no difference is to be noted. Omni cannot be bought or influenced, it will always tell the truth. I would like to know, **why would people, in their right minds, consciously use Omni in trials ?** Knowing that if they are guilty, they are condemned to death... I was thinking of using Omni as a bluff to frighten other parties (if you are guilty), but if the bluff is called, the price is going to be payed. If nobody were to use it, then only its existence (or the belief of its existence) would be enough for people to be 'honest'. Hence the second question : **What if Omni was gone a long time ago, and the government used its image to speed up trials, and criminality all in all. How long would it take for people to notice ?** [Answer] > > Why would people, in their right minds, consciously use Omni in trials? > > > Knowing that if they are guilty, they are condemned to death... > I was thinking of using Omni as a bluff to frighten other parties (if you are guilty), but if the bluff is called, the price is going to be payed. > > > **Accidents & Negligence** Example A: A was walking through a road even though it was a green light when the driver B was driving towards it. C, who noticed it, pushed A away from the trajectory of the car B. In the process, B hits C. Who is responsible for the fault? One can argue that it is A's fault because it a was a green light. You should wait for a red light. One also can argue that it is B's fault. This accident won't occur if B honk his car. In layman's view, this may be a straight A's fault for making the first violation. However, if we follow this logic even further, does this means that B has no responsibility of saving A's life if this incident happens? Does this mean that it is perfectly correct for B to just zoom through the green light no matter what happens with A? If B honks and breaks, he has make full duty on his part and he is innocent. However, in this case, he doesn't honks. Example B: An oil company is drilling on the sea. Earthquake attacks the area and oil spill is everywhere. Who is in fault? At one point, oil company, who makes a serious business, is at fault. Why the oil company does not make preemptive action? At another point, earthquake is a major action. However, if we just blame the "earthquake", this may seems unfair in comparison to doctor. When a patient died in doctor's hand, the doctor is put at blame for failing to save him. You may argue that the doctor got unlucky and it was the age factor that kills the patient, but isn't the reason doctor took years of study is to learn how to mitigate it? *TL:DR; Crime action that has no intention and simply based on negligence is tricky. It is very possible, in their right mind, for every party to plead innocent.* > > What if Omni was gone a long time ago, and the government used its image to speed up trials, and criminality all in all. How long would it take for people to notice ? > > > Very early. The moment that a person, who does not has to be in the right mind, calls it, the bluff is called. > > To end a trial, Omni can be used as a last resort, but it needs to be accepted by both parties. If a party refuses, then it is considered guilty. It's the way it goes. So in fact, the fear of Omni reveals the truth, most of the time. > > > Ah. If you have asked Omni, Omni would tell you that the party refuses is not always the guilty. There are a lot of cases where a long interrogation leads innocent to plead guilty. The reason? Stress caused by the interaction of the police, the intimidating setting of the room, etc. Innocent people may stressed out and refuse. You may say that "But everybody knew that Omni is always right!", but every human being has a (sometimes good) feature called skepticism and paranoia. You cannot just expect everybody to accept it. That is psychologically impossible, even with people in their "right minds". Take example of the oil company of the Example B. Even if the oil company knows it was an *uncontrolled* accident, the oil company may fear that they are wrong, afraid with the punishment of losing a live, and just plead guilty when there is a chance that he is innocent. [Answer] I don't think it could replace judges because they don't just tell the right part from the wrong (at least in civil law countries, I don't know how it works with common law) but they also determine how the law should be aplied, making it so that the same crime could give a man slightly different sentences depending on wich judge was presiding the court. Instead I think omni would be very useful as a one man jury or even as a witness, with the judge asking him who is guilty and then proceeding to determine the sentence. The thing is, if the defendant's sentence should not be to die, it would be necessary to find someone else to be sacrificed (maybe someone who is already on the death row, or depending on how evil/conscienceless the rulers are they could sacrifice beggars, low-lifes or war prisioners). [Answer] According to game theory, Omni should never be used. If you know you are guilty Omni will find it out anyways so no need to use it and risk your life, you would rather spend some time in jail. If you are not sure you are guilty, some Omni specialist will listen to your case and tell you if you are guilty from Omni's point of view. However some humans are irrational or might secretely hope that Omni won't know the truth. These might still use Omni even if they are guilty. [Answer] It's hard to say depends how long it takes for them to call their Bluff. As long as the government uses it only to intimidate the guilty then it can last a long time. But a minute they use it on someone who's innocent and knows it and he says yes to it, then the deceit will be exposed. There's no way the government could pretend that they still have the Omni at least without making themselves murders, because the Omni not only with the told the innocent party but also the guilty. And the penalty for the guilty is dead if the government were to continue the facade then it would killing people that it doesn't know for sure are guilty. ]
[Question] [ In 1846, following reports of the annexation of Texas to the United States, settlers in inland Northern California formed an army and declared independence there as the California Republic. At the same time, the United States and Mexico had gone to war, and forces of the United States Army and Navy entered into Alta California and overpowered the Mexican garrison and Alta Californian militia units. The forces of the California Republic abandoned their independence and assisted the United States forces after their arrival. The California Republic was never recognized by any nation, and existed for less than one month, but theoretically speaking it could be independent. It has access to the ocean and plenty of land; [![enter image description here](https://i.stack.imgur.com/4wGEM.png)](https://i.stack.imgur.com/4wGEM.png) Is it possible for the people of Alta California to remain independent? What is the smallest change I can make to history to allow for California to remain independent? [Answer] The primary reason that California (and Texas) both became parts of the United States is that a good many of the settlers there went specifically with teh intent of colonizing this land under the flag of the Republic as part of Manifest Destiny. While there were some adventurers that wanted to be in a free nation, there were many more American unionists. In the case of Texas, many of the most famous founders of Texas were pro-union (like Sam Houston, and Stephen Austin), Texas voters chose union by a large majority, and the Congress of Texas, which was generally pro-independence, was brought around because of Texas' mounting debt. The US government paid off 10 million of Texas' debt when Texas was annexed. The California republic was even more tenuous. A civil government was never really formed, and the militia that rose up in revolt against Mexico joined up with a US Army officer (John Fremont) within a month. So the revolt-havers specifically tied themselves to the US from the get get. So this points to the reasons that independent California is unlikely: American settlers were generally pro-America and pro-Union and governing a large area with low population and tax base will get you in debt fast. So the only reasonable explanation would be that California was peopled and funded by a foreign power BEFORE the influx of American settlers. In 1845 California had about 1500 Spanish and Mexican men, with 6500 women and children, and about 1300 American and 500 other European immigrants. Five years later, after the gold rush, about 100,000 more people had arrived. So a foreign power has to import at least 100,000 people before the gold rush to ensure that the state does not become inevitably American. Here is a strategy to do this: Russian colonization. In 1812, Fort Ross was established at Bodega Bay near San Francisco. In 1828, the Danubian Cossack host of 10-15000 men, under service to teh Sultan of Turkey, split, with one part going over to the Russians, and the other being massacred by the Turks. Instead, lets say the entire host went over to the Czar, who then banished/rewarded them with California. Many Cossacks died on a 3 year death march by land and sea across Siberia and the North Pacific, but in the end almost 20,000 men, women and children were established in the upper San Joaquin valley (Sacramento) where they expelled the Mexicans and repelled American settlers by force of the Cossack's legendary reputation for ferocity. Eventually, gold is found, and a rush of Europeans of all sorts fills the land. As the Cossacks were progressively suppressed between that time and the Russian Revolution, more and more Cossacks made the arduous journey to California where their farming villages and fearsome riders covered the San Joaquin valley and extended to Napa and Solano, and eventually north to the Willamette, Snake and Columbia basins. European settlers fill port cities like San Francisco, Oakland, and Monterrey. Still nominally part of Russia, formal independance doesn't come until after the Revolution in 1916. As losers flee the civil war, California (now known as Shelikhova) picks up a million more Russian imimgrants, establishing the new land as culturally Russian in perpetuity. [Answer] I see several possible answers - **A)** The United States does not enter Alta California because they are **too spread out** to manage the land they currently have effectively; any further across the continent and they will lose control in another area. Alta grows stronger because it is unopposed. **B)** The United States does not enter Alta California because they are preoccupied with **Mexico**, which in this version of history **is stronger**; Alta grows stronger because it is unopposed. **C)** Mexico wins the war and spreads itself across its new territory; similarly to **A)**, it is spread too thin to pose a threat, and Alta grows stronger because it is unopposed. ]
[Question] [ What colour will planetary rings made up of dust and rock (not ice) appear to be? Would there be a difference looking from space and from the surface? More importantly, how will the rings affect the colour of the sky? Eg during sunrise, sunset, sun behind or reflecting off the rings. I'm asking for an * earth sized planet, with a similar oxygen rich atmosphere. Ie in goldilocks zone * Rings would be made up of dust and rock particles, not ice. Ie Not a gas giant with rings made up of ice and dust. * Yellow to orange sun. I believe the sky will normally be in the shades of blue/indigo/purple due to scattering light. But I'm wondering what shades the sky will go when the rings interact with the light. If this all 'depends', is there any method of working it out for each situation? [Answer] You are correct that the answer is "it depends", what I can tell you though is what it depends on. The first thing to consider is your atmosphere. What light frequencies (colours) does it reflect? Which ones get through to the surface? Our atmosphere lets visible light through, which is one reason our eyes are tuned to those frequencies, but the scattering of blue light is why the sky appears blue. Note though that over time your vision would adjust to any ambient shading of the light though and adjust for it until it seemed normal. The second thing to consider is the materials making up the ring and how they are arranged. If the ring is mostly iron oxide then it might be red, sulfurous compounds yellow. Ice might be white, or blue, or any other colour. But those are wide generalizations, just find out what colour the material reflects and you have it. The final thing is the colour of the star. A red giant will naturally colour everything red, while a brighter blue star will shift things the other way. So now combine those two effects, and you have the colour of your rings: * In space you will see the reflected colour of the material as modified by the light the sun is putting out. * From the planet additionally you will have the absorption and scattering effect of the atmosphere. At night the rings would act a little like the moon, in that you would see the rings glowing to both the east and the west (although once in the shadow of the planet the glow would stop). During sunrise and sunset the illuminated part of the rings would be on the opposite side of the sky from the sun. Looking towards the sun it would potentially only be visible as a darker band if it moves in front of the sun. The rings would be very useful for navigation, telling position and direction would be much simpler than on earth. ]
[Question] [ The [Collared Peccary](https://en.wikipedia.org/wiki/Collared_peccary) is not the name of the greatest man stripper under the sun, but is a species of mammal in the family Tayassuidae found in North, Central, and South America. They are commonly referred to as Javelina, although these terms are also used to describe other species in the family. The species is also known as the musk hog. Although somewhat related to the pigs and frequently referred to as one, this species and the other peccaries are no longer classified in the pig family, Suidae. [![enter image description here](https://i.stack.imgur.com/5qhVD.png)](https://i.stack.imgur.com/5qhVD.png) Now, theoretically, if the Aztecs had domesticated these animals, the history of the Spanish conquest may have ended differently and as [CGP Grey explained in one of his videos](https://www.youtube.com/watch?v=wOmjnioNulo), just because a species *looks* like another, the internal behavior affect whether or not ancient people could domesticate them. > > Horse vs Zebra is his example, but does pig vs Peccary fall into this as well? > > > Could the Aztecs have domesticated this pig-like animal? If they could, when is the earliest they could have? [Answer] Domestication can happen very quickly, given the correct environment. We can take a look at the domestication of pigs (which are related but not in the same family), dogs, and foxes. In the Russian Fox experiment it only took a scant 25 years to domesticate them as pets. But first, there had to be individuals within the population which exhibited the "tame" traits that were needed. Zebras and horses aren't an apt analogy simply because it takes longer for a horse or zebra to mature and they don't have litters. With dogs, pigs, and foxes sexual maturity comes relatively early, and they have litters. This means a larger population to select from, much, much more quickly than something like a horse or zebra. Horses were an easier target than zebras, so they were domesticated. Take a look at this article on [pig domestication](http://www.sciencemag.org/news/2015/08/taming-pig-took-some-wild-turns), which outlines some of the selection and the fact that they bred with wild populations quite often. The same thing happened with dogs, which is one of the reasons why they can reproduce and have viable offspring with wolves. My answer is simple: any darn time you please, but it will be more difficult because they only have litters of 1-3, which is not very much compared to wild hogs (average of 4-6, up to 12). Of course, wild hogs may have the characteristic of higher litter yields because they interbred so frequently with tame pigs, which were more fecund (as they were selected for the trait by breeding) and later, natural selection also favored this trait. It's difficult to know what the litter yields were prior to our domestication of them. Domestication will change their characteristics. Not just in behavior, but also size, distribution of fat and overall appearance. You've got to keep in mind WHY they are being domesticated to decide what the changes will be. As far as I know, no one has tried to domesticate the collared peccary, so I don't know if it's possible, however, it is not beyond the pale, and could likely be done in just 40-50 years, which is an evolutionary eye-blink. As long as there are places and a society that can support it, this would not be as difficult as you may think. ]
[Question] [ For most of us, meteors are by far the ultimate planet killers. All it takes is one direct hit to suddenly wipe all life from the face of a world. But, rather than taking life away from a planet, what if a meteor impact is the reason that the world is habitable in the first place? In the story I'm writing, humanity discovers a habitable exo-world known as Elysium. It's an Earth-sized rocky moon orbiting elliptically around a Saturn like gas giant (known as Aphrodite) that is just over 4 times the mass of Jupiter. Elysium is well outside of the habitable zone of it's binary parent stars. But the moon's surface is kept nice and warm thanks to a giant impact crater that dominates it's face (known as the Cinder Fields). Although the crater should have cooled and sealed up thousands of years ago, the tidal force of Aphrodite on the moon's surface has kept it open and hot, warming up the planet's atmosphere and surface through the Cinder Fields. Could a world like this actually work in real life? [Answer] Yes! And even without the tidal heating. [O'Brien et al. (2005)](http://www.psi.edu/sites/default/files/imported/about/staff/obrien/Publications/ESF-Impact_abstract.pdf) modeled impact craters on Titan using finite-difference methods for various impact scenarios, including a wide range of sizes and temperature profiles. Here are some of their findings: > > A 15 km diameter crater in water ice with a depth/diameter (d/D) ratio of 0.1 and a volume fraction 0.05 of liquid can sustain the liquid for about 1,000 years. For the same crater in ammonia dihydrate, the liquid can persist for about 2,000 years. A 150 km crater in water ice with d/D of 0.05 and a volume fraction 0.1 of liquid can sustain the liquid for about 50,000 yr, and for the same crater in ammonia dihydrate, liquid can persist for about 100,000 yr. > > > Even 1,000 years seems pretty good. Yes, this isn't going to be nearly enough time for life to evolve, and neither will 100,000 years. But it's really good to sustain intelligent life that's already evolved - in this case, humans. I should note, though, that any body large enough to cause a crater taking up that much of the planet is liable to have terrible consequences, destroying much on the surface - if not the entire planet. This means that it isn't feasible for the crater to cover a substantial portion of the planet. ]
[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/39579/edit). Closed 7 years ago. [Improve this question](/posts/39579/edit) [![the world](https://i.stack.imgur.com/wc4vv.jpg)](https://i.stack.imgur.com/wc4vv.jpg) The setting is a **sci-fi/fantasy future Earth** ( ~5 million of years in the future) so mountain chains and general elevation is more or less the same of our own Earth, just out of position due to a slightly different poles location. Major difference is the desiccated Mediterranean basin, now a +3500 mt deep (11500 ft) empty salt waste. To help you visualize the current continents in the context of this tilt here’s a map with unaltered coastlines: [![earth coastlines](https://i.stack.imgur.com/njKHI.png)](https://i.stack.imgur.com/njKHI.png) **The plausibility of the landmasses and features as I arranged them is not important: what I need is a general idea of the biomes and environments.** Although I would like to have a general understanding of the global climate, if you can I would really appreciate a slightly more in-depth analysis of **the continent highlighted in the map below** (Western Europe + North-western Africa): [![continent](https://i.stack.imgur.com/2LWuf.jpg)](https://i.stack.imgur.com/2LWuf.jpg) **OPTIONAL REQUESTS:** I would like to keep things as scientifically believable as possible, but (for story reasons) **it would be great to have**: * Climate on the afore-mentioned continent approximating the **corresponding climate of North/South America** (the yellow dot in the center of the picture above is about same latitude as NY) e.g. North-western African coastline resembling more Florida in climate than Morocco * Specifically, I would like to have a **continental dry/continental humid climate** (or within “European” range) on the “Italian” land bridge across the deadly salty waste that is the empty Mediterranean basin. My explanation for this according to my own researches is that the lands across the empty basin would essentially behave as a high plateau with their own climate different from that of the geographical oddity that is a 3500 mt deep dry chasm. This chasm, according to [this paper](https://www.researchgate.net/publication/222698056_A_numerical_study_of_the_climate_response_to_lowered_Mediterranean_Sea_level_during_the_Messinian_Salinity_Crisis) about climate during the Messinian age (last time the Mediterranean basin was empty), would against expectations actually increase precipitations on nearby mountain ranges especially on the northeastern edge of the basin (ref. line 599 in the paper); rivers would eventually fall into the hollow abyss and gather as hyper-saline lakes at the bottom then evaporate, restarting this closed cycle. * Global climate possibly resembling to some degree the [Holocene climatic optimum](https://en.wikipedia.org/wiki/Holocene_climatic_optimum) e.g. “Green Sahara”. Every reasonable explanation that integrates this requests is more than welcomed (but if plainly impossible I’ll just surrender to evidence). There is a lot of useful stuff in [this paper](https://www.researchgate.net/publication/222698056_A_numerical_study_of_the_climate_response_to_lowered_Mediterranean_Sea_level_during_the_Messinian_Salinity_Crisis) about the Messinian Salinity Crisis (MSC) climate, though I honestly can’t understand most of the technical aspects but feel free to read it if you want to (jump to chapter 4. Discussion if you don’t want to read all the details). **TL;DR Can you help me setting the general climate for my world? bonus: is it possible to have a global climate resembling that of the Holocene climatic Optimum? (Or alternatively a climate on the continent depicted above equivalent to latitude to that of North/South America)** THANK YOU! Your help is immensely appreciated :) [Answer] Hmm, I'm not sure I agree that the elevation generally remains the same. Given that vast tracts of land now look submerged on the western side of the world, either the sea-level has increased (all that water from the mediterranean has to go somewhere unless it's locked by ice) or the land-level has subsided. The eastern side looks like the land has risen at places (south-east asia/australasia) and sunk at few (southern china). Tectonic plate shift with or without sea-level changes would mean that the mountain chains/general terrain elevation will have changed. There are two other things that will determine what the climate of this world is like: 1. What are the median temperatures like? If it's a warm world, there will be little landlocked ice, increasing the amount of liquid water in the weather cycle, indicating a warm, vegetation-filled world with marked storms, extreme weather events and generous precipitation. If it's close to current temperatures, you could expect polar ice caps in the north and south, wet weather along continental peripheries and narrow land isthmuses and dry and arid interiors similar to what we have today. If it's cooler, the polar caps would be larger, locking up fresh water and limiting the rise of sea-level caused due to med sea. This would mean a drier environment overall with vast belts of grasslands and desert interiors. 2. Are there any human/other-sentient-being-made developments changing the terrain (5my!) such as large scale land reclamation etc? Just how much of the biodiversity have they/we changed by now and how has that pushed the climate? Now if you like Holocene optimum temperatures, you'd have to decide whether it is due to orbital tilt changes (increasing the temperatures in one hemisphere but working differently in the other) or general global warming (increasing temperatures world wide). Both would mean higher sea-levels that would submerge low-lying places. Possible marshlands, thick tropical forests along the coasts. The wild card here is the North Atlantic Ocean; it no longer has the same size and is beginning to get landlocked, possibly disturbing the thermo-haline circulation that currently mixes deep-sea and surface sea water and creates a rich nutrient cycle. A large amount of salt would get trapped in the dry Med basin, reducing the salinity of the oceans overall. The current rain patterns may not hold in the adjacent land masses. The Messinian basin would probably be a very arid and deep salt flat with brine lakes at places fed by inflowing rivers, all of it surrounded by mountain ranges north and south. While it is difficult to compare this with any existing place, there may be clues from the past as you pointed. Adiabatic heating would mean the salt flat would be very hot (the compression hasn't yet lifted the med basin upwards) Winds roaring across the flats, blowing salt dust around during dry weather. Apart from a few salt-tolerant species, no life would be found on the open flats. But there might be little corridors for migration following river beds on the plain, along the green ridges set above the salt plain. While the eastern half might get precipitation, the western half might go into a rainshadow. As for the yellow dot place: The size of the salt brine lake may not be big enough to set up a closed cycle - eventually the lake would dry up due to the tectonic compression uplifting depending on when exactly you set your world. On the other hand, the possibly ice-capped mountains of the Alps would make a barrier for moisture winds blowing in from the Atlantic and getting funnelled into the Med valley. This would seem to indicate there would be some precipitation on the northern part of the green ridge. What is not sure is the moisture content of these westerlies. while this definitely can't be compared to the current levels of moisture obtained from the Med sea, it wouldn't be completely dry. The landbridge may not exactly be green and verdant unless the precipitation is at certain levels and then you need to take care that the rain (if any) doesn't leach essential nutrients from the soil and salt winds don't spoil the soil quality. Well, that's my take on it any way, happy to be corrected. ]
[Question] [ I've been designing a world and wanted to base it on a rather interesting cosmology proposed by the ancient Greek philosopher Philolaus. He was a very early opponent of geocentrism, believing that both the Earth *and* the Sun orbited around a third body he called the Central Fire. He claimed that the Sun's orbit around the Fire took a year and the Earth's took a day, and that the day/night cycle took place because the Earth was tidally locked to the Fire and we all lived on the other side. For a visual description, take a look at [this](https://upload.wikimedia.org/wikipedia/commons/8/8d/Antichthon.svg). The other body you see there is Counter-Earth (or Antichthon in Greek), but that can just be ignored for now and I'll ask about its revelance in another question if I want to include it. It should also be assumed that the "Central Fire" is in fact just another sun, though I'm interested in replacing it with a black hole which I'll ask about in a seperate question. So anyway, as my physics and astronomical knowledge is rather intermittent (and completely devoid of anything mathematical), this seems like an important place to start with questions. I want to make the "Earth" of this system have living conditions as Earth-like as possible (at least in the view of the Sun-side inhabitants). The most obvious concerns are: 1. Given that the orbiting sun would need to appear as Earth's, with presumably the same mass and at such a distance that it appears to be the same size, what does this mean for the central sun? More specifically, is there any possible configuration of mass or distance that allows it to hold the orbit of the other sun without making it impossible for the planet to be Earth-like (though obviously the face directed to the central sun will be scorched from 24 hour exposure). It's rather important for the model that one sun orbit the other, rather than them orbiting eachother, but I don't even know if this is actually even possible. 2. What would the result of the above look like to an observer on the planet, both on the side facing the orbital sun and on that facing the central sun? Are there any important planet-based observations arising from the model, or more specifically the way it arranges the orbits of the planet and the outer sun. In terms of how much I understand, I'm pretty competent with elementary ideas (I recently found out that all lightlike paths beyond a black hole's event horizon warp towards the singularity such that moving towards it is inevitable, and I know enough about relativity for this to make sense to me), but I'm not really capable of determining how they all interact together. Thanks in advance to anyone who can shed some light on this for me, it would be greatly appreciated (and hopefully interesting for you to consider). [Answer] The problem is that the arrangement indicated in this diagram... <https://upload.wikimedia.org/wikipedia/commons/8/8d/Antichthon.svg> ...simply cannot be reconciled with what we see in the sky every day. In that scenario, the sun would not only rise and set; it would approach and retreat every day. The sun would appear relatively small at sunrise, grow to an apparent much larger size at noon, then shrink again to sunset. The tides associate with a daily approach and retreat from the sun would also be significantly different than what we see on our Earth. The difference might not be that great, but solar tides are about 1/3 as high as Lunar tides, so it would have some effect even if not very great. Here's an alternative scenario: The Sun and the Earth are both in the same orbit around the "central fire", which is a black dwarf star. That is, it's an old, cold white dwarf which emits no visible light (altho it's probably still emitting some infrared... so you might want to stipulate this world's sun is a bit cooler or further away, to account for the difference. The Earth is in a "Trojan" position relative to the Sun's orbit; a Trojan position is a stable orbit. That is, it's 60 degrees ahead of or behind the Sun in the same orbit. The "central fire", the Sun and the Earth would be at the vertices of an equilateral triangle at all times. Assuming this alternate Earth has the same axial tilt, the same seasons and the same year length would be preserved. You might stipulate the seasonal variation is slightly less... the planet is slightly more temperate with slightly less seasonal variation... if the "central fire" emits much infrared radiation. Note that in this scenario, both sides of the Earth are equally inhabitable. You could still have a Counter-Earth, but it would not be hidden from view; it would be visible in the night sky near dawn and dusk, just like Venus is in our world. Occupying the opposite Trojan position, either leading or trailing the Sun in its orbit, it would always appear in the same position relative to the sun. Unlike Venus, it would not be a "wandering star". Here is a diagram: <http://hyperphysics.phy-astr.gsu.edu/hbase/solar/imgsol/LagrangeJup.gif> In the scenario I describe, the Sun would replace Jupiter, and the "central fire" would replace the Sun. The Earth would be in either the L4 or L5 position, with Counter-Earth in the other position. (The L3 position, which would be preferable for a more traditional "planet hidden behind the sun" scenario, is unfortunately not a stable orbit.) From everything I've read, the "Counter-Earth" scenario, with Earth's twin hidden behind the sun, simply isn't possible with what we understand about gravity and astrophysics. There's no stable orbit that would put two planets on exactly opposite sides of the Sun, and keep them there. The scenario you pointed to is an interesting variant, with Counter-Earth hidden on the opposite side of a one-face Earth, but again I don't see how to make that fit with being an alternative way of explaining what we see in the sky every day. Of course, if that's absolutely necessary for your scenario, you can hand-wave away the impossibility by using a near-magic technology (such as gigantic reactionless drives hidden deep inside Earth and/or Counter-Earth, forcing them to stay in a tidally unstable orbit). An assumption I'm making here is that the Earth and Counter-Earth were moved into their current positions, probably within the last 100 million years or so, by a technology sufficiently advanced to appear as magic (Thank you, Arthur C. Clarke!). First of all, the Sun coalescing in that orbit would "clear the orbit" of the gas and dust needed to form a planet, so no other large bodies (such as the Earth or Counter-Earth) would be formed during the planet-forming stage of the evolution of that solar system. Furthermore, chaos factors over a very long time period would cause both Earth and Counter-Earth to be lost from their stable position re the Sun. That is, this is a stable orbital configuration over the course of perhaps millions of years, but according to current astronomical theory, some or most of the planets have moved in and out in their orbits over the lifetime of the solar system, so this arrangement probably wouldn't be stable on the time scale of billions of years. Note this doesn't mean I'm stipulating the Earth and Counter-Earth can't be more than ~100 million years old. They could have been in orbit around other stars, with the planets cooling and life evolving for billions of years, and then moved into their current positions perhaps ~100 million years ago... or perhaps much more recently, if you'd prefer. I leave the problems associated with moving a major planet that far without disturbing the planet's crust, and without freezing it and killing off everything above the level of a microbe, as trivial engineering challenges for a society (or group, or entity) with near-magical technology. You haven't mentioned the existence of Earth's (or Counter-Earth's) moons. I think with the orbit I've suggested, a similarly large moon in a similar orbit would be possible for either or both planets, altho again those orbits might be less stable than they are in our universe, over extremely long time periods. [Answer] Kanderas, I'm going to add a second answer here, because I didn't directly address your question; rather, I pointed out why that scenario couldn't be reconciled with what we see in our sky. But what if we ignore that? How would things be different in your scenario, and what can we do to minimize those differences? The main problem I see, if the scale on your diagram is correct, is that the day/night temperature difference will be much greater, with the sun advancing and retreating by a large degree every day. Such a large temperature difference isn't compatible with the stable, mild conditions necessary for complex life to evolve, nor in fact with retaining an Earth-like atmosphere. If the uninhabited side is baked by unending daylight, it will soon be heated beyond the boiling point of water, and so lifeless as the moon. Worse, on the very hottest parts, it might get so hot that even water vapor would be disassociated into hydrogen and oxygen. If this happens, the hydrogen would escape into space, and slowly over the eons the planet would become lifeless as Mars. Contrariwise, if the "central fire" is just a massive object but not a sun radiating warmth, the dark side would freeze so hard that the atmosphere would freeze there, and it wouldn't be long until the entire planet's atmosphere (and hydrosphere -- the water, lakes, rivers, and oceans) would vanish away. In either case, either a terrifically hot or extremely cold "dark side" would create eternal hurricane winds flowing into the cold side, or away from the hot side, all along the terminator and probably thousands of miles into the inhabited side. If you're getting the idea that in this case, "inhabited" means "not very inhabitable"... you're right. This isn't a scenario for a habitable planet. But there are other assumptions we can make with much more temperate outcomes, so let's make them. Let's assume the "central fire" is a red dwarf star, emitting enough light (and infrared radiation) to keep the hidden side of our planet pleasantly warm, at a stable temperature that just happens to be the same as the average temperature of the inhabited side. Let us furthermore assume the Earth is in close orbit around this red dwarf, fitting your tidally locked scenario. Now, what we need to do is greatly expand the distance between the Earth's orbit around that "central fire" and the Sun. This has many benefits, not the least of which it greatly minimizes the objection I made in my first response. If the Sun's orbit is quite distant, relative to the Earth's orbit around the red dwarf, then the growing and shrinking as the Earth approaches and retreats from the sun will be unnoticeable, or at worst barely noticeable. Since in our universe, the Sun is some 93 million miles away, we have lots of room to do this and keep it realistic. In this scenario, we do lose our moon. A tight orbit around a red dwarf would be much too close for a stable large moon at a large distance, like Luna. A smaller one would be lost fairly quickly (on the geologic time scales) because of tidal dragging by the red dwarf. Of course, we can expand the Earth's orbit around the red dwarf and keep Luna... and also make more room to squeeze in Counter-Earth in an even closer orbit. But then an observer on Earth would start noticing that the sun grows and then shrinks as the day passes. If there is enough difference in the apparent size of the Sun to be noticeable, then there will be enough difference to cause a greater day/night variation. Even if the "dark side" of Earth doesn't freeze or roast, there still will be enough variation in day/night temperature to significantly affect evolution. Of course you can arbitrarily choose any evolutionary history you wish, since it's your world. But realistically, we'd tend to see much less variety in land animals. I'd suggest no land animals more complex than insects, and less variety in plants, too. Keep in mind that trees and grass are products of fairly recent evolution, so aren't likely to exist. Unless you plan to make the "people" in your story sea-dwellers, there's not going to be a lot of story-telling potential in this scenario. The trick here will be trying to choose a "Goldilocks" distance for the Earth to orbit the red dwarf; far enough away to allow a stable Luna orbit, but close enough to minimize the variation in the Sun's apparent size. This would be far easier if you stipulate that Luna's orbit is artificial... that it's the product of some long-vanished alien race which buried a reactionless drive deep in the moon to keep it in that orbit. --- Now, about using a black hole as the "central fire": That's a very bad idea, from the standpoint of scientific realism. Black holes have accretion disks pulling matter into them, and they emit very high energy radiation. (Even the thin interplanetary hydrogen and dust will be sufficient to create a weak but permanent accretion disk around the black hole.) They also have searchlight-like jets of high radiation and plasma emitted from their poles. Thankfully that wouldn't directly impact Earth, because Earth's orbit should be roughly perpendicular to those jets. But even the secondary radiation from the black hole and its jets would do really nasty things to the Earth's atmosphere, and remember that winds will flow from the inhabited side to the "dark side". Water will flow around the world, too. So, my advice is to not try to use a black hole as the "central fire". It's just too nasty. --- I hope you realize that in any variation, Counter-Earth is significantly closer to the "Central Fire", and thus has a significantly hotter surface. So any assumptions we use to make Earth relatively close to Earth-as-we-know-it will automatically rule out an Earth-like Counter Earth. Seems a pity to have a Counter-Earth and have it be as lifeless as Venus or Mercury. Frankly, if it was me, I'd make this a fantasy world rather than a scientifically realistic one. Then you could have Luna without worrying about its unstable orbit, and Counter-Earth might be the home of ifrits and fire demons! Obviously the inhabitants of that Earth would find a different name for the other planet; it's hardly a "Counter-Earth"! ]
[Question] [ So, I'm writing a fanfiction; I don't know if this is a shunned topic here, but I'm asking anyway. In this fanfiction, a human finds himself in the Redwall universe, equipped only with a duffel bag containing an undefined set of "survival supplies and small valuables", salvaged from his car after it was submerged. He meets a tribe of semi-nomadic shrews, oppressed by more developed societies, and enacts a movement to take back their native land, using some of his tech know-how from our world in his effort. My grand plan involves him, over the course of his remaining lifetime, bringing about such an enormous burst of technological development that the continent where he introduces these changes is cordoned off by pseudo-divine powers-that-be blah blah blah. You didn't come here to read that; you came for the question. I've read a few answers [here](https://worldbuilding.stackexchange.com/questions/18390/trying-to-make-a-gun-making-scene-realistic?rq=1) and articles [elsewhere](http://rebuildingcivilization.com/content/lets-say-youve-gone-back-time-fixed) that provide some moderately helpful answers, but all of them rely on the world being ours. The problem with Redwall's universe is in the inherent differences between a single, united human species and a whole host of competing species of varying intelligence. Without the presence of work animals such as horses and bulls, agriculture would not develop anywhere near how it developed in our world; without any sort of consistency between soldiers, the military situation would look like a medieval version of the Jenkinsverse. Originally, I wondered whether it would be possible for someone from modern-day Earth, equipped only with a duffel bag of necessities, to fast-track a civilization from nomadic foragers into an industrial age; now, my only question is, **could he get anywhere at all?** **EDIT:** According to the comments, I haven't done enough to define the setting. The world is populated by a variety of different creatures, mostly rodents and mustelids. For the most part, carnivorous species are painted as villainous and herbivores and insectivores as good; this is broken in the cases of badgers and otters who are universally good creatures in the setting. Very few, if any, of the creatures shown are actually carnivorous; they may be cannibalistic, but this is treated with the same stigma as in the real world, and doesn't actually seem to be necessary. The technology level of the setting varies between hunter-gatherer and Iron Age; a few castles and fortresses exist in various locations, but they are easily outnumbered by various nomadic groups. An abandoned lumber mill is shown in one episode of the TV show, one character makes a passing mention of a 'machine' in a metaphorical sense, and another character is inexplicably able to build ballistae. Other than these instances, the setting is generally in a perpetual [medieval stasis](http://tvtropes.org/pmwiki/pmwiki.php/Main/MedievalStasis) (are TVTropes links allowed?). The only technological "development" shown is a ship in the most recent book that is outfitted with cart wheels, so that it is allowed to sail on land. Little consideration is given as to the ramifications of this, especially since the wheels don't appear to have any sort of suspension. You might be able to get more out of the [wiki](http://redwall.wikia.com/wiki/Category:Places), but not much. I'm only linking the Places page because I get the impression that architecture may give the best picture of the technology level, out of the pages available. [Answer] *Unfortunately I know nothing of Redwall apart from what I've just read on Wikipedia so I'm going to have to run with generic medieaval.* If your arbitrary person just happened to be an experienced blacksmith, steam engine hobbyist and part time shipwright, taking his tools to a world that already had a reasonable knowledge of mining for ore and coal, then yes, he could encourage some progress at a local level. Possibly even to the point of triggering an industrial revolution if he's really good. Okay he's an extreme case but it's just a hint of what would be required to have an effect. If your arbitrary person is just an ordinary Joe, then you're hiding to nothing. He's going to struggle just to survive. **The vast majority of modern people have a completely useless set of skills for such a world, and not enough knowledge of basic machinery or metallurgy to reproduce anything.** To go into a world like that you start by needing one of the major mobile skills of the period, Stonemason or Blacksmith, or something completely unexpected such as plumbing. *Can you imagine a plumber in a medieaval world? Fitting running water and central heating to a castle could change the world, even if you had to power the pumps with peasants.* These are the skills that will allow you to get a foothold to work from within the world. Everyone needs tools, (everyone needs weapons?) everyone needs horseshoes (normally), everyone needs kitchen knives, pots and pans. The blacksmith is the heart of a village. Kings and lords need houses and castles, but the work has to be done in the place the castle is wanted, the allows stonemasons (the original Freemasons) to move around much more freely than normal peasants (especially serfs). **A blacksmith with the knowledge to build a steam engine is the one man who can change a medieaval world most effectively.** It's going to be pretty hard for anyone else. [Answer] The presence of different races does not actually make a large change to things. It's not really any different to human societies where some people are stronger, some people better educated, some people have access to wealth and privilege, etc. It's the same differences but exaggerated, and they will have the same effects on people but exaggerated. If you can come up with a viable way for a human to do what you are suggesting in a human medieval society then you can take the same techniques to this world and the only thing that will change is the flavour. [Answer] Joe might well get started by selling the contents of his pack, but he is in trouble after that if he doesn't start adapting. He may want to change the world, but a few things need to be there before he can. Your average Joe, needs a decent grounding in history, and a huge backlog of trivial knowledge to make a significant impact. Anyone in a first world country is likely to have gone through enough schooling to meet the basics and will be better educated than the vast majority of the people (they are sentient animals, so they are people) he is likely to meet. He is also going to need powers of persuasion in addition to any other skills he may be granted due to the power of narrative convenience. How does this help? If Average Joe was a little bit of a history buff, he might use some of his knowledge of history to see where the tech level is and then lay plans for the next step. Are the peasants grinding stuff by hand? Maybe help them develop a simple water wheel powered mill. or even a wind mill. Harsh winters? get with the smith to start making some Franklin pot bellied stoves. Keeping your community warm and fed gains trust and then you can get into...Plumbing, and other concepts. Three field crop rotation, if it isn't already there. Fertilizers and such. You will note that I am not even touching on weapons. There is a reason for this. Who are you going to trust the judgement of, the guy who claims to make a better sword, or the guy who can help you keep your house warm in a harsh winter? This is why persuasive skills are necessary, you need to get your fellow townspeople to try your crazy ideas. Make your guy enough of an off-the-grid-living kind of guy he can even get into things like rocket stove design and high thermal mass heaters. If your Average Joe can start alleviating some of the survival pressures on his community, he will leave the smith with time to make better metals, for other types to be able to get creative in their own areas of expertise. It's a long term solution that will take longer than joe will survive. The second part, as Joe gets older, he may want to start teaching the young of the community. Paper may be hard to come by, but a slate and some chalk can go a long way. Teach the kids some math, some history, and teach them the value of the scientific method. ]
[Question] [ I recently learned the rudiments of *celestial navigation*, and have been pondering its three basic requirements: a clock, a book of star positions, and a sextant (or device for measuring star inclination). It got me wondering if someone, classically "trapped on a desert island", could sufficiently observe the stars and write a message-in-a-bottle that would, if picked up, lead rescuers to them if they didn't have any of the necessary items when they landed there (never mind the likelihood of any of these things occurring). The sextant can be crafted from local items (a couple sticks, a rock, some string, and a fair bit of math), so that's available. Without the book of star positions, the castaway could record his observations and let the message-finders use their book to figure out his location. But that leaves the clock; time is a key element of the data needed to use celestial navigation, at least the way it's classically done. So, the question is two-pronged: how can you tell time at night with some measure of accuracy? and what methods of star observation are useful for determining position without knowing the time? [Answer] If you're in the northern hemisphere, latitude is easy: Using your homemade sticks-and-rocks-and-string sextant, record the angle to Polaris (aka the North Star). Within whatever the margin of error of your homemade sextant is, that is your latitude. Unfortunately, it's impossible for you to calculate your longitude without a clock and (current year's) almanac. You can, however, record the apparent altitudes of other stars at moments like moonrise/moonset, as well as the apparent altitude of the moon at sunrise/sunset. Take as many of these readings as you can, record them as precisely as you can, and, assuming you can get the message to anyone, they can likely calculate your position within a small enough margin of error to have a reasonable chance of actually finding you. [Answer] You have four basic events to time your observations at, sunrise, sunset, moonrise and moonset. Measure the position of one star at at one of those events, and another at a later event. Be sure to describe what the constellations look like. (If you are not able to make a sextant, see what is currently straight up, or at the horizon) That is not going to help you to find your position, but it is enough for the receiver to figure out your longitude. He can then also calculate your day length, giving a reasonable estimate for latitude You are on an island? Use the tides to measure the time! If you have a steady slope at the shore, you can give your time of observation by a measure of the how high the water reaches. Write down the tide height for all your star positions. Be sure to give a lot of data points, [Answer] Draw a star map for the entire night sky, dusk till dawn, with indicators of when dawn happened and when dusk happened, along with what your best guess of the date is, and include your sextant readings on the chart. So as soon as the sun sets draw any stars/constellations that you see, and mark where directly over head is. As new stars appear over the horizon, add them to your chart, and as new stars are directly over head, mark their position. Continue until the sun rises. The people that find the bottle are already going to have an idea of what area you might be in from the prevailing currents. By figuring out when sunset and sunrise are in that area during that time of the year they can make guesses about what time of night those stars were directly over head. This should get them close enough to where searching only a few islands wouldn't be to hard. **Option B:** Make a couple 1 minute sand dials from what's available around the island. Maybe a coconut with a small hole, filled with sand up to a line, and then wait for it to all fall down. It's not hard to get pretty close to a time span of 1 minute just by counting. Then using those sand dials, build a couple 15 minute sand dials. As soon as the sun sets start the sand dial, and start the next one as soon as soon as the first runs out. Repeat until you've made your observations. ]
[Question] [ I know, it sounds like a geek swearing at Windows 8 on his work-owned computer. But actually I was just reading Peter Clines ([*Fold*](http://peterclines.com/books/the-fold-hc) and then had to order [*14*](http://peterclines.com/books/_14_) for instant delivery), and when I got to the monsters in the alternate universe I was distracted by them— by the biomechanics actually. (A general point there too: if you want to scare out a real geek you can't let any *puzzle* trump the horrifying aspects.) Imagine something that looks like a humpback whale with tenticles where the face goes and huge wings coming off the body. So really it sounds more like a cuttlefish. The wingspan is over a thousand feet. The wings were described as being membranes stretched over long fingers, like with a bat. So how does it get enough strength to beat such wings? Not just the torque delivered by the muscles, but how could thin sheets stay rigid enough to push through the air? I'm interested in the idea of "classic" flying giant monsters, as opposed to the idea that they are big in order to fly e.g. lighter-than-air airships, or non-physics magic. The much larger [*Saturn Rukh*](https://en.m.wikipedia.org/wiki/Saturn_Rukh) has beefy wings and they soar in updrafts and glide back down, following the dinural cycle. They don't *flap* and there is no land to stop on. How might a biological creature on this size scale be able to *fly* with heavier-than-air powered flight? It needs to be able to take off from the ground. It doesn't need to exactly hover like a hummingbird, but be able to keep station well enough to make up for the overall motion by reaching with its tenticles as it grazes over an area. How might wings be configured? What other options are there: jet power for VTOL, or something more like a jellyfish bell design? [Answer] The largest so-far known flying animal on this here earth was the [quetzalcoatlus](https://en.wikipedia.org/wiki/Quetzalcoatlus). At 10 meters, its wingspan falls far short of 1000 feet you mention. [![enter image description here](https://i.stack.imgur.com/AMEuW.png)](https://i.stack.imgur.com/AMEuW.png) (image from [wikimedia](https://en.wikipedia.org/wiki/Quetzalcoatlus#/media/File:Quetzscale1.png)) However, the mechanics were the same. Here was an animal larger than a Cessna which did have thin membranes spread over long, narrow, and hallow bones- and it flew. I suspect there is an upper limit to how far this process can go, At some point the physics of aerodynamics, tensile strength of bone, strength to weight ratio of muscle fiber, and so on will make it impossible to go any bigger. I would guess that said limit is far short of 1000 feet. However, "quetzy" shows us that the underlying concept is sound. EDIT: As noted in a comment, the "physics of aerodynamics" I mention also depends on the surrounding atmosphere, which has undergone changes here on this earth. Move the story to a fantasy world with a different gas composition and different pressure, it changes the equations. I still doubt the 1000 feet wingspan. ]
[Question] [ In the story I'm working on, a rift in space time opened up between our world and a layer of oxygen in a gas giant at some point in the past. Eons earlier, a species of fish symbiotically linked with algae (which lived in the fishes' back, providing nutrients in exchange for protection) mutated in a way that allowed the fish to fill its swim bladder with methane, enough so that the fish could float in the air like a balloon if it voided itself of everything in its digestive tract. However, because this mutation enabled the fish to escape predators and avoid competition, it became more and more prominent in the species, and, due to the [square-cube law](http://tvtropes.org/pmwiki/pmwiki.php/Main/SquareCubeLaw), the creatures themselves became larger and larger in order to have a higher lift gas/weight ratio, until entirely non-aquatic, self sustaining, [living gasbags](http://tvtropes.org/pmwiki/pmwiki.php/Main/LivingGasbag) ruled the skies. A few of these creatures ended up floating into the rift, where they propagated in the oxygen laden atmosphere. They were followed by birds, insects, and whatever else could sustain itself off the gasbags, including a few humans. These early settlers, first hunting of the backs of the creatures, were eventually able to create leather and bone, methane lifted crafts of their own, congregating in small aerial villages around supplies of communal lift gas. So, could something like this realistically happen? Besides the rift between worlds, I'd like the story to be bound by hard science as much as possible. The main problems I can see are... * The Planet: The planet is almost entirely gaseous, with different layers of atmosphere and a small, rocky core. Could this planet have any sort of magnetosphere? Having wind and a precipitation cycle would be good story wise, but the only way I can see that happening is through the lower layers of the atmosphere being heated and creating convection currents, but what could cause that? Could all of this happen while maintaining a gravity less than/equal to Earth's? * The Biosphere: Would this kind of environment be livable? Even if it were, what would happen to all the biomass? Would it slowly just leech of into the void as creatures died and shed skin cells? What about all those different minerals that are necessary for life, like iron? Meteorites might work, but I believe they would be too rare to support anything. * The Humans: With the resources and technology humans would have available, could they create their own airworthy craft? How long would their supplies of lift gas last? Would trade between villages by means of smaller vehicles be possible, or would everyone be bound to the villages? Perhaps there's a layer of lighter gas above the oxygen that they could harvest, but could they stay completely separate? Would the ecosystem even be able to sustain humans in the first place? Please feel free to point out any problems you see with scenario. [Answer] It sounds great for a story, but the gas giant planet alone has issues for science. Gravity and pressure are two huge things you need to deal with on a gas giant. [Hydrogen and Helium](http://www.space.com/18472-what-is-saturn-made-of.html) are the primary elements of most gas giants. These are the two lightest elements available. Saturn is not very dense but the pressure as you go in increases, first you get to liquid hydrogen and then eventually you reach metallic hydrogen. Jupiter is similar but much larger. Gravity will be pulling down and the atmosphere would be pushing in. Replacing any large quantity of the hydrogen with oxygen will first significantly increase the mass of the planet, increasing both the gravity and the pressure. On top of that Oxygen and Hydrogen like a little ménage à trois. Actually they are extremely reactive. So a lot of Oxygen will likely create a large water planet, not a gas giant. In either case you need a lifting gas lighter than the atmosphere to 'fly', and in a Hydrogen/Helium atmosphere you likely need H or He to float and warm it up greater than the surrounding air. So your fish will likely need to be [homeothermic](https://www.google.com/webhp?sourceid=chrome-instant&rlz=1C1CHFX_enUS603US603&ion=1&espv=2&ie=UTF-8#q=homeothermic). to keep their sac warmer than the air. A rip in space to say Earth from somewhere inside a gas Giant would have a huge pressure differential and I suspect jet like air streams would be coming out of the giant spewing anything near the rip at high speeds toward the earth. Take a bit for things to try and move the other way. [Answer] The gas giant planet is going to have lots of issues with the hard science part. @bowlturner has already discussed some of them, but you should also consider that the giant planets in our own Solar System are extremely energetic. The cores are still radiating heat left over from their creation to such an extent that Jupiter, for example, actually emits more energy than it receives from the Sun. So the atmospheres will have monster temperature gradients from the bottom up, which will lead to interesting weather effects (most of which we don't know yet). The Gas giant planets also have huge and active magnetospheres, but also intense radiation environments. Life forms sucked into the rift may well be fried by energetic radiation in very short order (to give you some idea, human astronauts will need to stay at Callisto in order to be outside of the radiation belts, or invest in massive amounts of shielding). Indeed, the Rift itself may be an unhealthy environment, and certainly easily avoided due to the bright glow at night as radiation leaks in and ionizes atmospheric gasses here. From a writing perspective, you seem to have a very interesting concept already, so I might suggest that unless the action on the other side of the rift is truly critical for the storyline you are working on, you either keep the action on the skies of the home planet, or if the rift is important, perhaps the rift leads to a similar planet with different conditions (your heroes drift through the rift into a desert planet like Arrakis, and must find a way to get water so they and their carrier fish can survive. Going the other way, a rift has been opened and predatory creatures are invading the Earthly biosphere). Have fun with this, and let us know if you publish anything. ]
[Question] [ I have a group of settlers that live on top of an animal, and I want his skin to be their mode of communication. In the morning, information is transmitted through chromataphores in the skin changing color (don't ask how the info is interpreted, I'm still working on it), and at night use channels and nodes of bio-luminescent light from luciferin-superoxide reactions. My question is, **is there a single chemical or system that can achieve both?** [Answer] I suspect that such a creature would at least be *plausible* although most readers probably won't give it a second look even if you used handwavium to explain it. First, the range of bioluminesence in the real world is [rather varied](http://www.webexhibits.org/causesofcolor/4ADA.html). Secondly, it appears that [fireflies can control the exact wavelength](http://phys.org/news/2010-01-scientists-fireflies-emit.html) of their glow (this is news to me and came up unexpectedly in my search). So you'd just have to mention that the creature has different cells for each color (I assume, as each color uses a different protein), in a close-packed matrix, and modulates which color is active at what strength via a complex system of modulation involving the water content. ]
[Question] [ Is it possible to have a multi-cellular complex organism capable of emitting ionizing radiation and I am not talking about banana I meant intelligent lifeforms that can develop tools also on top of that these species must consume radioactive substances in large quantity without suffering from any side effects and I am not talking about gorilla... and what kind of traits should my species have so that they cannot be harmed by their craving for exotic foods? [Answer] Radioactive isotopes generally have the same chemistry as the non-radioactive ones, so all the usual biological processes should be able to work in a world where only radioactive isotopes are available, at least briefly. To be able to survive with all that internal radiation, start with deinococcus radiodurans — it's only a bacterium, but it has the ability to repair its DNA. That same mechanism could probably work in the cells of a larger creature. You'd also want a fairly fast metabolism to deal with things like replacing all the iron in the blood faster than it turns into cobalt. So far, this is just a creature that can survive a high radiation environment, but it could easily evolve to depend on the radiation - for example it might require a highly efficient cooling system to handle the heat of radioactive decay, but the same system would cause hypothermia if that heat source was no longer available. ]
[Question] [ # Context In the near future, humans will have manufactured machine [sentience](https://en.wiktionary.org/wiki/sentient). Such a consciousness, the first of a new species, must operate on Earth. # Constraints A memristor-based human brain analogue, which seems the most likely candidate for sentience, requires about 700W peak power to operate and requires the area of a medium-sized pizza. This implies having sufficient batteries to supply the brain with continuous electricity. To date, double carbon batteries seem to be a marked improvement over any type of lithium-based battery. I haven't performed the calculations, but it seems reasonable to assume that such a species would not use flight to locomote, due to the weight of its power supply. (Solar powered flying machines exist, but they are huge, so they wouldn't fit inside a house, making it difficult to socialise with humans. Detachable [or foldable] wings and re-purposed electric motors for ground travel is possible, but that cascades into other problems that probably make it an impractical design.) # First Draft Obvious basic requirements seem to be: * Cameras (360 degree perspective, infrared, ultraviolet) * Speaker (broad frequency range) * Microphones (highly sensitive) * Arms (multiple) * Hands (because our objects are built for human-like hands) * Track-legs (locomotion, staircases, and height change) * Internal sensors (temperature, barometer, gyros, compass) # Questions What appendages or abilities would such a species need, if any, to: maneuver in our world, manipulate physical objects, build children (hence evolve), and interact with humans? In other words, if you could design an optimal inorganic sentient species without being held back by Earth's evolutionary baggage, what would it need? --- Here is a render of the first draft requirements (hands aren't drawn yet and a few other items are missing, but it serves to communicate the idea): [![Sentient Species v1](https://i.stack.imgur.com/eBPoQ.jpg)](https://i.stack.imgur.com/eBPoQ.jpg) # Additional Resources * [Fabrication of TiO2 thin film memristor device using electrohydrodynamic inkjet printing](http://www.sciencedirect.com/science/article/pii/S0040609012002441) * [Memristor -- The missing circuit element](http://www.cpmt.org/scv/meetings/chua.pdf) [Answer] **Use a remote body.** It's not "*being held back by Earth's evolutionary baggage*" like, for instance, needing to carry its brain along with its body. The obvious answer for a creature with a massive brain requiring a significant amount of power to survive is to keep that brain near a reliable power source. This is especially obvious if that creature has natural access to wireless technology. This is beneficial in several ways: * The creature is not killed when its body is destroyed * The brain can be housed near a reliable high-power source, like a hydroelectric dam or nuclear power plant. * The creature can have multiple modes of motility for different situations (legs, wheels, wings, and impellers) * It can effectively travel instantly from one place to another when moving from one body to another. All sensor data is already coming into the brain digitally, making that link wireless is not a difficult step. If I had my brain transformed into a computer, I would not be counting on battery technology to keep me alive, and given the option I don't think these creatures would either. ]
[Question] [ One of the planets I am building has a very large crescent shaped continent that I want to say came about when a super continent split and the areas below sea level flooded. Could this have happend? [Answer] Not only could this have happened, but it has happened many times here on earth. There is speculation about just how intense it was but the flooding of the Mediterranean basin here on earth could have been a cataclysmic event: <https://en.wikipedia.org/wiki/Zanclean_flood> It's a specific instance of an [Outburst Flood](https://en.wikipedia.org/wiki/Outburst_flood). You just need to have appropriately placed fault lines in the continent that pull it apart in the shape you want to then flood and the eventual flooding can be as fast or slow as you want depending on whether you lower the middle and then let water in or do it the other way around. ]
[Question] [ Suppose there is an Earth-like world with magic. Someone (maybe wanting a mining city or an isolated power base), thousands of years ago, wanted to build a city on a certain desert mountain, five hundred miles inland and 2 miles above sea level, (This city is on a slope facing in the direction of the ocean. The mountain has sand or dirt--enough, at least, so that the surface is not too hard/rocky to be a barrier to plants growing.) So they had a wizard create a river - that is, a river that flows up vertically, (without the salt and other chemicals), then goes in a right angle, flowing through the air in a straight like till it runs into the mountain. At that point it flows downhill like a normal river. What effects will the river have on the environment? [Answer] Erosion maybe should be extremely high where the river meets the mountain. Wizard should at least grow many plants before so there is no risk of flood. In the Cascada del angel (Angel waterfall) in Venezuela sometimes the water doesn't fall to earth because the sun evaporates it before it hit the ground and the Cascada has less than a mile of height. With evaporation there is going to be a lot of clouds and the river is going to generate a cold front so it's going to be a lot of raining. [Answer] (Originally posted when the question was a river at 10 miles high) The height of the mountain is an issue first. At that height you're in the clouds. Almost out of the troposphere. The river may or may not freeze. If it isn't frozen it's speed, if great, could cause rather turbulent winds and move the clouds toward the desert. If the river runs OVER the desert than the clouds might rain as they get near the mountain which would cause increased pressure. So you're desert wouldn't stay a desert very long. If the river doesn't flow over the desert the clouds would rain on the opposite side like they already do which is what caused the desert to exist in the first place. If the river is frozen or doesn't really flow much, Then you'd not see too many changes to the rest of the environment due to it's height. The river would act like a thermal sink and cool the atmosphere, but that high up the effect would negligible. The effects of the river at the bottom of the mountain might be a bigger issue. It might create a new lake and finally a river that returns to the ocean eventually. That would affect the area greatly I think. ]
[Question] [ Two days ago, I asked a [question how to stop a waterfall](https://worldbuilding.stackexchange.com/questions/25634/how-to-stop-a-waterfall). I got great replies, and had to reconsider some of my numbers. Now I came up with this calculations, and I would like to check 'm with all the geniuses here. Thanks in advance. I have to figure out where all the water for my huge waterfall comes from, and rain seems to be the best (only) option. I limited the width of my waterfall from 1km to about 300m, kinda like the American Falls of the Niagara Falls, who have an estimated water flow of 75,000 gallons/second. This way, all the water would fit through a tunnel with a diameter of 5m, where it was 18m before (thx @hde-226868). This thing should be possible to block. A smaller waterfall also needs fewer water, so I could go with 6,000 km² in stead of the 50,000 km² @RobWatts measured my 1km width waterfall would need. That's a surface of 75 and 80 km, but I would guess less when we have a cone like a mountain is. 6,000 km² on a mountain. What would be a realistic height here for the mountain, with an average grade of 7-10, to make it big enough to collect all the water needed for my waterfall? And how big would the ground surface be? Small follow-up on my previous question: would it be possible for this amount of water to disappear in a cave construction beneath the water, after rerouting it like @mikey said, if there's an underground passage to the sea? [Answer] Your mountain will have to be a bit bigger than you realize, I think. Assuming you need 6,000 $km^2$ of catchment to produce your flow, all of this needs to be sloped toward the river rather than toward the surrounding territory. So what you need is sort of like a [crater lake](http://www.nps.gov/crla/index.htm), although not necessarily quite as pretty. If this is the case, you can model the catchment area as a circle about 88 km in diameter, with a fairly small lake near one side which feeds the exiting river which has the water fall. The reason the lake needs to be fairly small is to keep the river flow rate close to constant. If the lake is the same size as the catchment area, the lake will drain and flow will cease until more rain feeds it. A small lake allows the surrounding soil and vegetation to act as a buffer on incoming rainfall. The lake itself does not need to be very deep, since it does not noticeably buffer the water flow. This means that the mountain can be almost any combination of sizes you want, consistent with the slope and the need to allow rainfall to reach the lake. If you make the height 30,000 feet, for instance, there is no way for rain clouds to make it over the rim to dump water in the lake. This also means that the mountain will not be impressively snow-capped, since a wide snow belt will mean most moisture has fallen as snow before the clouds pass over the rim to the catchment area. Let's assume a frustrum of a cone, with top 3 km above the surrounding terrain, with a 10% average grade. Then the slope to the rim will be 30 km. This will result in a base diameter of 88 km (for the catchment area) and 60 km for the slopes, for a total base diameter of 148 km.. Actually, a better idea is probably an asymmetric cone which has a catchment rim at relatively low altitude on the side facing the prevailing winds, and much higher elevations on the downwind side. This will allow rainclouds to be driven into the catchment area at low levels, then dump their moisture on the other side as they are forced upwards. This will allow the mountain to be arbitrarily high and impressive around much of its body, while still allowing rainfall to produce the waterfall. But it can't be high except for a relatively small pass, or air will be trapped over the catchment area and backpressure will keep most rainclouds from entering the desired area. How the tunnel was formed, how it was sealed, and how it was reopened are a sequence which you as a writer will have to deal with. Generally, such tunnels are caused by water eroding rock like limestone, which means that the channel was formed by water from the catchment area. Something must have happened to stopper it, and then something must have happened to remove the plug. [Answer] TL;DR: A Bigger Multnomah Falls **Yes, I think all of this is possible.** I'm trying to visualize your construct. Consider something like [Multnomah Falls](https://en.wikipedia.org/wiki/Multnomah_Falls#/media/File:Multfalls.jpg). At a rate of 4m3/second you can have make a *tiered* waterfall (see image). Unlike Multnomah Falls, your ascent should not be so easily undertaken - the cliffs should be higher and sheer. Where there is a bridge here is where your tunnel is. Where it says 4m3/sec you want significantly more. The source of these falls is mostly a freshwater artesian spring, augmented by some snow melt; but it maintains a seasonal flow. You very well could have the same setup. When the settlements upstream (above the top of the falls) accidentally re-route the river, it simply goes down the other side of their high plateau. This makes it *much* easier, since they simply have to reroute from the source of the springs, which may be closer to the other side of their 'mountain'. The steepness and size of your mountain is no longer restricted *to the waterfall's design and source* but you must now consider how your mountain functions where people cannot come up or go down it. Perhaps your mountain is really a plateau like [Mount Roraima](https://en.wikipedia.org/wiki/Mount_Roraima)? But with a natural river and springs. EDIT: A waterfall occurs (usually) when the river has worn out the softer stone around harder, igneous stone. The harder stone remains meaning the water goes over it instead of wearing it away as well. On your plateau mountain, the tunnel could have been caused by having a patch of softer stone in the center of harder stone (like granite). It is not unusual for magma to create weird stone formations of hard stone through soft stone like limestone. [In this image](https://upload.wikimedia.org/wikipedia/commons/a/a3/Geological_Dike_Cross-Island_Trail_Alaska.jpg), the volcanic igneous rock will remain one day long after the limestone washes or 'blows' away to processes. In your mountain, you have a volcanic tube and flow that created a wall with a hole in it, with sandstone or limestone in it millions of years ago. Over the millenia the river disolved the soft stone allowing for a ring or tunnel through which your waterfall now travels. ]
[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. So this was done in *Starship Troopers* and I am curious if it is realistic for interplanetary warfare. The idea is that aliens launch meteors at major metropolitan areas...and it ends poorly for those cities...like, they're gone. In this specific scenario aliens are using asteroids from our asteroid belt and launching them at earth to target specific cities. Never mind how they target (unless it is relevant to your answer) so accurately. Given a city that meets these criteria: * 450 sq miles of land area * Generally flat land area, no more than 500 feet min/max elevation change **How large would a meteor have to be to wipe out a city that size and could it be done without having major regional impacts?** Essentially I want a city destroyed but I don't want regional/global firestorms or cooling. Yes or no, please show your work. The best answer will demonstrate the process and appropriate calculations for the scenario. [Answer] Using the handy [Earth Impact Effects Program Calculator](http://impact.ese.ic.ac.uk/ImpactEffects/) for dense rock asteroids I arrive at a diameter of about 150m. Or a comet of about 100m. [Calculation result](http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=12&distanceUnits=2&diam=150&diameterUnits=1&pdens=&pdens_select=3000&vel=17&velocityUnits=1&theta=45&wdepth=&wdepthUnits=1&tdens=2500) The actual numbers I use: * Distance from impact: 12miles (corresponding to the radius of a circle with 450 sq miles area) * Projectile density: 3000kg/m^3 - Dense rock asteroid. * Impact velocity 17km/s - Typical for asteroids. * Impact angle 45 degrees. Effects; * crater diameter: 1.64 miles * No fireball * 2.47 cm of ejecta. * The major damage will be from air pressure. + Wood frame buildings will almost completely collapse. + Glass windows will shatter. + Up to 90 percent of trees blown down; remainder stripped of branches and leaves. [Calculations for the comet](http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=19.32&diam=100&pdens=1000&pdens_select=0&vel=51&theta=45&tdens=2500&tdens_select=0) Similar air burst damage as for the asteroid, but no crater since the comet will burn up in the athmosphere. [Answer] The energy released from the meteor impact is going to come from the meteor's kinetic energy. As the meteor comes to a sudden stop as it hits the city, most of that energy is going to be released into the environment (while some will be "wasted" in annihilating the meteor). The kinetic energy of a body is $ E=\frac{mv^{2}}{2} $. So we have two variables, mass and velocity. From the equation we can see that doubling the mass of the object, doubles the energy, while doubling the velocity, quadruples the energy. (If we get into relativistic velocities then mass dilation becomes a factor too but let's ignore that for now). So the question of how big the meteor needs to be is very dependent on the velocity of the meteor and how much energy we want out of it (with the proviso that the meteor is sufficiently large that it wouldn't completely burn up in the atmosphere before hitting the target city). For illustration, lets assume we want a destructive force similar to the bomb dropped on Hiroshima. That had a yield of approximately 16 kilotons. In joules, that's about $6.7 \cdot 10^{13}\;\text{J}$. So that's the kinetic energy we're looking for from our example meteor. To keep the math simple, lets assume that our meteor is moving at $50,000 \frac{\text{m}}{\text{s}}$ (which is within the velocity range of 'normal' meteors). Substituting the known values, we get $6.7 \cdot 10^{13}\;\text{J} = \frac{1}{2}m \cdot (5 \cdot 10^{4}\;\frac{\text{m}}{\text{s}})^{2}$. Solving for $m = 2\cdot \frac{6.7 \cdot 10^{13}\;\text{J}}{(5 \cdot 10^{4}\;\frac{\text{m}}{\text{s}})^{2}} = \frac{1.34 \cdot 10^{14}}{2.5 \cdot 10^{9}}\;\frac{\text{J}}{\frac{\text{m}^{2}}{\text{s}^{2}}} = 53,600\;\text{kg}$ or $53.6$ metric tonnes. The actual volume of the meteor will depend on its density. For example, Iron has a density of $7850\;\frac{\text{kg}}{\text{m}^{3}}$, so a $53.6$ tonne iron meteor would have a volume of just $6.8\;\text{m}^{3}$. Thats equivalent to a sphere just $2.35\;\text{m}$ in diameter, which is tiny in cosmic terms. If you want a larger amount of damage to cover your theoretical target city, you simply increase the size of the object or its velocity or both. Or you simply hit the city with a number of smaller meteors. [Answer] Using asteroids (or better yet, comets) would seem to be ideal at first because of the vast amounts of kinetic energy they can deliver. Comets are much better than asteroids because they are generally moving much faster in the inner solar system, in fact, a comet could theoretically be moving at something like 70Km/sec before it is no longer bound by the Sun's gravity. Even a small chunk of ice will deliver a pretty whopping blow at that speed. The problem is that asteroids and comets are quite a long way away, and you would need a lot of energy to change their orbits. Since the calculations will be all over the place depending on which particular object you are choosing and when you start the project (if the object is in opposition to the Earth [i.e. on the other side of the sun] when you begin your thrust manoeuvre, then you have the option of using a minimum energy orbit), we can just hand wave at this point and say "a lot" of deltaV would be required. As a military project, you want the strike to be as soon as possible after the order is given, but the reality is that using current and projected technology, the travel time could range from months to years. A minimum energy trajectory from Earth to Mars takes about 6 months to complete, and asteroids are even further away... Of course, making your energy budget even larger is the fact you are not accelerating a small object, but an object ranging in size from a hundred metres to many kilometres in diameter. You would need a ridiculously large rocket engine, or some sort of substitute like mile long mass drivers or improbably large solar sails. The energy rerelease or signature of such a power plant would be highly visible from Earth, so everyone on the planet would quickly figure out that something was up and start making plans to counter your asteroid strike. They would also have many months to years to prepare, so your asteroid would be met by a hail of kinetic energy impactors or nuclear weapons, leaving Dr Evil contemplating a rapidly expanding cloud of gas and rubble where the asteroid used to be. Frankly, it would be mush faster, simpler and even cheaper to send a fleet of nuclear tipped missiles towards the Earth rather than try pushing an asteroid or comet into an intersecting orbit. At least you know nukes work. Nuke them from orbit. It's the only way to be sure.... ]
[Question] [ In this scenario, corals, sponges and bryozoans have been extinct for 65 million years. In their place as reefbuilders are echinoderms, bivalves, barnacles and worms of the infraclass *canalipalpata*. As reefbuilders, what advantage or edge would any of them have over coral? [Answer] Reefs would have a hugely different look. Coral is kind of a 'growing stone' in that the bones of the coral stay behind and continue to support the growth of more coral and other life forms on top of it, in some ways like a tree, growing new wood on the outside. Barnacles, bivalves and other mollusks tend to build beaches and limestone bed rock. Barnacles would be a pretty slow way to build a reef, since for another layer to grow the previous layer will have to die. Coral is a much simpler life form than even barnacles. Coral while having spaces in its structure are very small compared to mollusks what have a 'living space' inside the hard shell. So a reef would be more likely to collapse in on itself periodically because they just aren't designed for that kind of weight. So mollusks would be a very poor reef creator. [Answer] In 65 million years, it is possible that one or more of the species named could have evolved to take the place of corals, but there would have to be some sort of evolutionary advantage to do so, and obviously the base creature would need to change their lifestyle to replicate corals. Barnacles would seem to be the best bet to evolve into a coral analogue. The key change will be to move from building 2D structures on surfaces to building 3D structures. This might be forced on them as competition for available surfaces becomes more intense. Barnacles of different species might begin in a competitive relationship, attempting to carpet over each other to secure the surface. Gradually, since carpeting a surface already covered with barnacles will be incomplete and leave a multitude of gaps, species will become more cooperative rather than competitive in order to create the sorts of 3D structures which maximise food gathering surfaces, spaces for symbionts to live and so on. Sixty Five million years is a long time in evolutionary time, so if a niche becomes open, eventually it will be filled. [Answer] I don't think that any of them would have an advantage over corals when it comes to building reefs. Perhaps they could manage to build some, but it would be hard. [**Echinoderms**](http://en.wikipedia.org/wiki/Echinoderm) Coral create coral reefs by secreting calcium carbonate[[1]](http://en.wikipedia.org/wiki/Coral#Reefs). Echinoderms have partial skeletons composed of calcite[[2]](http://en.wikipedia.org/wiki/Echinoderm#Skin_and_skeleton), which is, for our purposes, the same thing. Echinoderms can lose limbs ad regenerate them so it is possible that you could create structures with some of the skeletal material from disused limbs. A stretch? Yes. But not impossible. The thing is, echinoderms like to live on the seabed. This is not conducive to reef-building. The raw materials are there, but the ability to assemble them may not be. [**Bivalves**](http://en.wikipedia.org/wiki/Bivalvia) Bivalves are also composed in part of calcium carbonate[[3]](http://en.wikipedia.org/wiki/Bivalvia),1, like echinoderms and corals. They are, however - to quote Wikipedia - "sedentary", preferring to stay where they are on the seafloor. Once again, it appears like it would be difficult to create complex three-dimensional reef-like structures out of them. [**Barnacles**](http://en.wikipedia.org/wiki/Barnacle) Barnacles, too, do not move[[4]](http://en.wikipedia.org/wiki/Barnacle), meaning that their placement for reef-building must be crucial. That said, they grow *en masse* in large groups, making it especially easy for them to take over large areas. They can quickly cover an area in themselves. They are made of - yes, you guessed it - calcite, the same building material as corals. They seem to be the best bet so far to replace corals. [**Worms**](http://en.wikipedia.org/wiki/Worm) Worms have soft bodies, and are invertebrates. They would not be good reef-builders. --- 1 I'm sensing a pattern here. I assume you already knew about composition. ]
[Question] [ I am writing a soft science fiction set hundreds of years into the future, with Terrans ruling the known universe, establishing a number of vast interstellar empires, science and technology advancing in a steady pace any science fiction fan could imagine, and conflicts between political entities sporadic but recurring. However, **only Earth's technology advancement is regulated at early-to-mid 21st century level** by a union of governing bodies. This could have been done for a number of reasons. For instance, Earth could have been declared a demilitarized zone via treaties between nations, which is not to be violated even during wartime, as a sign of good faith. Earth would have a heavily guarded spaceport that connect it to the interstellar network, but other part of it must be kept behind in technology level. For all practical purposes, any devices or objects that are technologically futuristic to a early-to-mid 21st century level, or can be used in such a way that they will be the determining factor in technology advancement are outlawed. For example, possession of assault laser rifles are prohibited on Earth because they are too advanced in technology, as are building assault laser rifle manufacturing lines, even if the process can be replicated using contemporary 21st century technologies. This can be thought as in parallel to how meth labs are illegal but beakers and the ingredients are not in real life. Some immediate consequences one can imagine is that travelling to and from Earth might not be heavily restricted - for it might as well be a popular destination of sightseeing tours - but personal belongings of the tourists are inspected for violations. Exports to Earth are consequently heavily monitored at the customs, though not so much for commodity imports from it (except for luxuries), because any factory on Earth can't possibly match the state of the art material productivity or efficiency. My questions are: 1. **Economic concerns**. What form will Earth's economy takes shape? Will a free market approach work? Should it at least have some kind of trade protection in addition to the custom inspections, as even technologically adequate products might have been manufactured with much more efficient future technologies. Can someone exploit the price difference between Earth and other part of the universe without violating the technology regulation law? Does Earth use the same interstellar currency? Are fund transferring between Earth and the rest of the known universe allowed? 2. **Enforcement concerns**. How does the local Earth government combat "technology smuggling" effectively? Should the police force or other peace-keeping forces on Earth be exempt from the technology regulation? If so, wouldn't corruption within the authority exacerbate the situation? 3. **Intellectual technology advances**. Intangible technology advances, like new computer algorithms, can be smuggled to Earth without detection. Even with possible "brain scanner"s at the custom checkpoints, a malicious party can easily beam information from outer space to Earth via directed electromagnetic radiation. Besides, can you really draw a line and say what algorithms are banned and what are not? If someone uses a more efficient scheduling algorithm developed in the 22nd century in their business on Earth, would that really be the end of world? Should "algorithm" and "implementation of algorithm" be distinguished? What about intelligent AI systems? Hell, if someone proves `P=NP`, then a majority of 20th and 21st century encryption algorithms could potentially become obsolete. 4. What are some of the other ramifications of regulating technology advancement locally you can think of, and how may it be explained in-setting? 5. Last but most importantly, is this setting realistic and probable? Are there any unintended consequences that have slipped my mind that might become a plot hole in my story later? [Answer] Well, in part that would depend on the population and GDP ratio between Earth and the Rest-of-Universe. This would be plausible if the Earth were a Venice- or Salem-like touristic backwater ('this is how the originators lived') populated by the 25th century version of medieval fare re-enactors. Similarly, if it is inhabited by a very conservative population of Hassidic-Amish technology rejectors. ## Socio-economics Now, if the technology exists for fast interstellar voyages, unless there is some conveniently-located-alien-artifacts trick going on, the amount of energy available to the Outer Space civs must be billions of times higher than our current civilization's. This would make most current economic concerns meaningless (we could end hunger and homelessness in about 2 minutes). Unless the Outer powers are, dunno, genuinely evil, forcing billions of humans to risk death by cancer, get their bodies polluted in all sorts of horrible ways, and act by the ethics systems of 5 centuries prior would be unconscionable. Imagine the Chinese invading the US and forcing them to live by 15th century tech and morality. Those barbarians living by 21st century tech might [even boil animals alive](http://www.lobsterfrommaine.com/steamed-lobster-cooking-tips.aspx)... ## Enforcement Obviously, this won't be handled by the locals. Again, that's like asking 15th century sentries with torches, arrows and wooden ships to watch out for drone-drops, speedboats and submarines. A joint 'peace-keeping' force by the Outers would handle all this stuff in orbit or even at the Solar System Restriction-Zone borders. ## IT and IP As long as a proper star-system-wide quarantine is in place, even electromagnetic pulses can be cancelled out, and each tourist could be tagged by a nullifier that prevents unauthorized communications between tourists and Outworlders. Again, this reeks of North Korea to me, unless you stipulate that the conservative locals simply have no need of these newfangled technologies and perverted morals. ## Other stuff Well, there's the usual handwavium around FTL travel. You could avoid that if you make your Outer empires restricted to the (still huge) Solar system, with potentially millions living in habitats in the Asteroid belt. Also, without space elevators, building up a population of billions off-home-world would be a challenge in a time-frame of mere centuries. Perhaps vat-grown humans? ]
[Question] [ Lets take a 60km radius island where the people have access to early XXI century technology. The whole island was planned and artificially built, so it has no mountains or otherwise bad/sterile terrain. Since it was artificially built, there are enough rivers, lakes, and the hills /valleys were pre-planned so the freshwater from the rain makes it cycle smoothly. Also, there is no mineral production. Assume all mineral / metal needs come from asteroid mining/magic/etc. There is little to no surplus, but no scarcity, not even rare earth minerals. Aside from that, all the food, livestock, clothing and industrialized products and energy must be produced inside the island. They can use any technology available to an early XXI century Earth (some 20 years - 2035 - ahead at most). The industry and the society is [zero-waste](http://en.wikipedia.org/wiki/Zero_waste). And the island has no useable ocean around. So they cannot use seawater, fish or deploy boats or aquatic vehicles. Travel to other nations is rare, and is made by air. How large a population could this secluded island nation support? [Answer] Using the numbers from <https://worldbuilding.stackexchange.com/a/9589/7718>, each person needs approximately 1000m2 for food production. That number is already adjusted for various inefficiencies and is much larger than needed for other purposes such as living space, so is a reasonable approximation of total space needed per person. Your island is 11 billion m2, so you can fit in 11 million people without doing anything special. If you really want to maximize the population, go vertical. Covering the entire area with a hundred story building is well within the capabilities of 21st century engineering, and would let you squeeze in over a billion people. You would obviously need quite a bit of energy generation since the lower levels won't be getting any sunlight. At 1300W/m2 you need 14TW. That is equivalent to approximately 2000 large nuclear power plants. Cooling might be a problem, since we need to lose the equivalent of a 10kT nuclear bomb every three seconds. Using seawater would be easiest, but we could probably do it by bringing in air from outside the city if we really had to. The area around this island is going to be rather windy. ]
[Question] [ The earth is migrating, somehow (it doesn't matter how, but it's not directly destructive) into a higher orbit over the course of a century. Details: * The earth-sun distance will increase by 150,000 km (0.001 AU) per year until it is 1.1 AU in 2115. * This corresponds to a temperature drop of approximately 15C before accounting for feedback like increased ice cover reflecting more light. * Technological and scientific progress has stalled, so we're limited to what we have today or what we could build without significant R&D, but substantial resources. (How) Can we counter this temperature drop, e.g. by enhancing the greenhouse effect? [Answer] We do not really understand the climate well enough to tell **how** well we could compensate. However I checked the Wikipedia on Ice Ages and it seems there are quite a lot of things **vaguely** associated with starting and ending of Ice Ages. This would give us quite a lot of things to try and while it would require a detailed simulation to give a "maybe" level answer of if it would be enough, every little bit would help. And the disasters associated with the abrupt change in climate would probably have reduced the amount of people to support anyway... ## Greenhouse effect The obvious. Changes in carbon dioxide levels have been strongly associated with the starts and ends of Ice Ages and we already have and use the necessary technology on massive scale. And we have **lots** of carbon reserves even with current economics, with everybody motivated to not go extinct we could extract sea bottom methane clathrates and methane currently impractical to even properly study. And burning as much hydrocarbons as we can would give as lots of cheap energy for mega projects. Although we could simply release methane into the atmosphere, if we have no need for the energy. ## Oceanic currents These have an effect on sea ice in the Arctic and the Greenland glacier. Basically we'd want to increase the amount of warm water flowing in from the Atlantic. I have no idea how this circulation actually works, but it has been suggested the Bering Strait has an influence on this. We could either close it with a dam or make it deeper with small nuclear devices. Usually either would be insane, but desperate times... Similarly the Panama and the Suez could be blasted open to adjust ocean currents, if simulations suggested that might help. Although even in desperate times these canals would probably be too valuable to mess with on the scale needed to make a difference. Maybe if models suggested the fall in sea level would make them unusable otherwise? ## Glaciers If you make the glaciers, mainly Greenland and Antarctica, darker by seeding them with large amounts of smallish black objects, they will absorb more heat. And manufacturing and spreading the "grit" gives a good excuse to burn lots of hydrocarbons. Benefit this has is that the polar regions are generally the most effective place to increase heat as the starting temperatures are lower. ## Deserts Sahara, Arabia, Kalahari, and Atacama get plenty of sunlight. And then they uselessly radiate it into space. In the real world this makes people wonder about large scale solar power. With global Ice Age threatening people would be thinking about collecting the heat and using it to warm the planet. It is possible, although ridiculously expensive, to build huge networks of heat pipes connecting these deserts with nearby seas. Then you just fill the deserts with radiators that connect to the heat pipes when the temperature is high enough. Although the scale, and hence the cost, is astronomical, this has two advantages. It is simple, potentially zero moving parts and relatively cheap materials, so the maintenance costs once it has been built might be tolerable. More importantly it can be adjusted as needed in real time, which is a good feature to have, if you are meddling with the global climate on a massive scale. Which in this scenario we would be doing, anyway. ## Orbital changes While we can't really do anything about these, it is good to remember orbital effects other than the distance have a significant, if little understood, effect on global temperatures. Since we are, in theory, currently in the middle of an ice age and the change of orbits would almost certainly also mess up these cycles, it is possible there would be some warming effects from the change. [Answer] Even limited to today's technology, platoons of mirrors could be lofted into orbit to add energy to the Earth's climactic system. Elon Musk's "SpaceX" is already building rocket motors on an assembly line (each Falcon 9 needs 9 Merlins on the first stage and one more on the second stage and the Falcon 9 Heavy will use two strap on Falcon 9 first stages, for a grand total of 27 rocket engines), and since the rocket engine is by far the hardest part of building a rocket, we are already cooking with gas. Orbiting mirrors can be gauze like structures of aluminum foil in high or even geo synchronous orbit, so there is little difficulty there either. The real problem is since we really don't understand how climate works, and climate is a non linear system governed by chaos theory, adding energy via solar mirrors will produce all kinds of unexpected effects (the old story of a butterfly flapping its wings in Peru causing a tornado in Texas). Local "hot spots" created by the mirrors will be surrounded by chaotic weather systems, and most of these will probably end up overwhelming the hot spots, negating the desired effects. This means the other solutions would have to be humans burrowing underground, building greenhouses for agriculture, carrying out large scale genetic engineering so plants and animals can survive the colder climates and some percentage adapting to a neolithic hunter gatherer lifestyle like the Inuit. Each of these solutions has issues of its own, and there will be many sub groups carrying out different solutions, so hundreds or a thousand years after your event, hunter gatherers might be raiding greenhouses and hunting feral mutant goats and cows which had escaped from the initial genetically engineered flocks far in the past, while human civilization living in underground cities at a constant temperature worked to stop the depredations. ]