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I have seen many science fiction movies that depict traveling in space through wormholes. The appearance though, and the time it takes to cross a wormhole, tends to vary:
• On one hand, we have the spherical, black hole-looking, wormholes that can be crossed instantaneously.
[](https://i.stack.imgur.com/CkX2L.jpg)
• On the other hand, we have these large spiral, tunnel-like wormholes.
[](https://i.stack.imgur.com/Znf7q.jpg)
Now, as far as I've seen, crossing these wormholes takes a few minutes or hours, but sometimes it takes years. However, it is said that while crossing the wormhole, even if it takes thousands of years for you to cross, in real time you get to your destination in no time.
Now, I'm designing a civilization of technorganic aliens that travel space using wormholes. Since I want my story to be as close as possible to real science, which one of these wormholes is closer to reality, and could they both be possible? If not, why? And if yes, how?
Edit: I'm editing the question to explain how theses wormholes of mine work. The idea is that a wormhole opening devise is placed on the front of a spaceship, that launches a small projectile (about the size of a baseball bat) in front of the ship at high speed (the speed of the projectile is faster than the ship so that it won't collide with the ship moving forward). When it activates, it creates a small wormhole which it makes bigger by adding exotic matter into it, stoping the wormhole from collapsing in on itself until the spaceship makes it to the other side. The wormhole will close after the projectile that created the wormhole runs out of exotic matter; the ship though has already crossed.
It should be noted here, that, if the second form of wormhole is the correct one, the wormhole will remain open to the "driver's" perspective, since to him the trip takes ages, yet in real time the trip took almost zero time and the wormhole closes shortly after the ship exits the wormhole.
[Answer]
Funny thing about wormholes... The time you take to travel through them is approximately fixed, and depends only on the model you choose.
Also, the traversal time is the same for the traveler and an external observer, adjusted by relativity - that is, if you enter it at a sufficient fraction of $c$ to have noticeable time dilation, you will experience a different rate of the passage of time from what an observer would measure; but cross it at low enough speeds and the traversal time should be the same.
The traversal times were calculated by Kip Thorne and Michael Morris in a 1988 paper: ["Wormholes in Spacetime and their use for interstellar travel: A tool for teaching general relativity"](https://web.archive.org/web/20160528122626/http://hostel.ufabc.edu.br/%7Ececilia.chirenti/pt/aulas/2015/RG/listas/Wormholes.pdf). They are (quoted from [an answer on Physics Stack Exchange](https://physics.stackexchange.com/a/20153/56299)):
>
> 1. **Infinite-Exotic-Region Wormhole** (exotic matter distributed throughout space) ~ **1 hour**
> 2. **Large-Exotic-Region Wormhole** (exotic matter confined to large finite radius) **‚â• 7 days**
> 3. **Medium-Exotic-Region Wormhole** (exotic matter loosely restricted to throat) ~ **200 days**
> 4. **Small-Exotic-Region Wormhole** (exotic matter closely restricted to throat and must have negative mass-energy density) **‚â• 0.7 seconds**
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(You can find more detail in the Thorne-Morris paper and in the book ["The Physics of Stargates: Parallel Universes, Time Travel, and the Enigma of Wormhole Physics"](https://books.google.co.uk/books?id=GJT4g1hNUGIC&q=%22infinite+exotic%22#v=snippet&q=%22infinite%20exotic%22&f=false))
So if you want some realism according to current knowledge, pick one of the above and apply it to your world.
Suggested theme song for wormhole traversal: [Shooting Stars, by the Bag Raiders.](https://www.youtube.com/watch?v=feA64wXhbjo)
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The time it would take to travel through a wormhole would depend on how 'loose' the throat of it is. To me it would make since that the more developed the technology gets the shorter the wormhole gets. It would be something like, the current wormhole tech makes the distance 60% shorter, while older tech would 10% shorter. I like to compare it to roads. In the past we had to build them around mountains, but we developed technology that allows us to dig tunnels through them.
Inside the wormhole would look like a tunnel. The portal of the wormhole would be 2D and can only be entered on one side.
It should be noted that wormholes can not be traveled instantly. Short distance wormholes may look instant, but would actually a micro-fraction of a second to travel.
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In a previous question - [How might kinetosynthesizing "plants" look?](https://worldbuilding.stackexchange.com/questions/122867/how-might-kinetosynthesizing-plants-look) - I introduced a worldbuilding thought experiment of mine centered around a habitable moon, heated by tidal forces, which orbits a rogue planet gas giant.
This planet harbors complex life, including animal-like fauna. Now, Earth animal use their coloration for many things - camouflage, mimicry, and display among them - but these things are only useful if there are other sighted beings around to see you.
On a rogue planet, there would be no need for a sense of sight, because there would be no sun and therefore virtually no light, except during fires, volcanic eruptions etc. My question is; **on a moon where no life forms can see, what need would animals have to be one colour or another?**
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"color" has a lot to do with reflection and absorption of energy. Depending on the intensity of and proximity to your tidal force heat, it might be the case that creatures evolved to absorb and reflect different amounts and spectra of these tidal energies.
While I am not sure that would lead to vastly different "colors" in what we think of as visible, it could/would result in conceptual "color" differences.
Diet might also play a role in creature "color". For example, did you know that flamingos are not naturally pink? [Why are flamingos pink](https://www.sciencefocus.com/nature/why-are-flamingos-pink/)
Exposure to other environmental factors might also play a role, such as a potential greening from exposure to copper.
[Answer]
**You specifically said *animals***
Plants would still need color to achieve the most efficient photosynthesis possible from what little light arrived from other sources. Even if you're rogue between galaxies, the sky is never completely black. So, plants have reason for color even if there's nothing around to see them.
Blind animals, on the other hand, would have none. Color would certainly exist, but only as a byproduct of the chemistry of their skin/hair/fur/etc. It wouldn't otherwise matter.
**But there deserves to be a frame challenge**
How many of your animals would actually be blind? The number of species on Earth that are totally blind [is quite small](https://en.wikipedia.org/wiki/Blindness_in_animals). Granted, they are all deep-sea or cave-dwelling species where what we call visible light is in short supply, but remember... your night sky is not totally black (unlike a cave or the depths of the sea).
But that's only light *visible to humans.*
I can easily believe that on a rogue planet experiencing eternal night the development of both [ultraviolet](https://www.theatlantic.com/technology/archive/2011/08/6-animals-that-can-see-or-glow-in-ultraviolet-light/243634/) and [infrared](https://sciencing.com/animals-can-see-infrared-light-6910261.html) spectral vision is completely believable. Add to this that [tri-color vision is pretty much unique to Earth's primate species... including humans](https://en.wikipedia.org/wiki/Blindness_in_animals#Colour_blindness) (the rest see in duo-color, functionally black-and-white) and it's totally believable that your animals would see just fine.
Another way to look at this is that animals don't necessarily see color (see below). They do see contrast (Human periphreal vision is this way). From this perspective, it's only important that a caterpillar be the same color green of a leaf for those species of birds that see green-and-white (greenscale, and I don't actually know if any bird sees in a "greenscale"), but perhaps it's more important that the caterpillar be the same *luminosity* of the leaf in question so that it blends in via the grayscale we assume most animals enjoy.
But, let's consider a bit more science...
>
> But, what color does the animal see? Vision, like all of our senses, is processed in the brain. Without being able to get into the head of an animal, it is only possible to know what colors can be detected and not how they "look" to the animal. ([source](https://askabiologist.asu.edu/colors-animals-see))
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In your case, critters avoiding infrared-seeing predators would evolve body heat similar to the thermal conditions of their preferred surroundings. Their skin would have absorption characteristics that allowed the edges of their bodies to blend into their background. We don't think of that as color because we don't see that color spectrum. But evolution would accomodate a predator whose brain can process infrared (or ultraviolet) frequencies systematically.
So, I believe you would have sighted creatures and they would enjoy the color of their world, which would IMO evolve in spectrums that we humans don't see and can't appreciate.
*One last note, according to [this article](https://cosmosmagazine.com/biology/incredible-bizarre-spectrum-animal-colour-vision), some terrestrial critters have 6 photoreceptors and one butterfly has 15! More types of photoreceptors means the ability to see finer shades of color. Given this data, your moon may evolve critters with very high numbers of different photoreceptors to take advantage of what little light exists. They wouldn't see color the way we do at all and they would likely be completely blind in the strength of our sunlight, but they'd see a world of brilliant — if dim — color.*
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I'm considering writing a fantasy novel which takes place on a world with a ring. This ring is a very important part of the story, and I therefore want to be as accurate as possible in describing what it would look like from the surface, and how the light would interact with it at different locations and times.
[This article](http://www.planetary.org/blogs/jason-davis/20130626-earths-skies-saturns-rings.html) is the best resource I have found, but it is limited. I cannot, for example, tell what it would look like during sunset/sunrise. Would the rings slowly become visible/invisible as the planet rotated? Would they be close enough to the surface to be visible even when in the planet's shadow? What about the shadow cast by the rings themselves (they're there on Saturn, so I assume they would exist on my planet as well). Are those limited to specific lattitudes? When do they appear? Just how dark would it be? Would the ring be outlined at all, like during a solar eclipse? These are questions a few pictures (though admittedly fantastic ones) cannot fully answer.
That is my question: **Is there a resource which will allow me to see how the rings/sky/sun/earth looks at any location/time on my planet?** Ideally would be a scientifically-correct 3D simulation which I can play around with all I want, but I have yet to find one.
**Notes:** For all details, assume the planet is earth (or identical to Earth) and that the rings are identical to Saturn's rings, save that they are scaled down to Earth's size (they maintain the same Planet/Ring ratio). Remove the C and D rings (the two innermost).
[Answer]
A few things to think about:
The rings would be in the plane of axial rotation, that is, right above the equator. So how it would look depends greatly on where you live on the planet. If you live on the equator for instance the rings will always look like a thin line in the sky. As you move away from the equator the rings would expand until you reach far enough north or south when you can't see the rings at all because they are below the horizon.
If the planet has a tilt, like earth, the position of the rings in relation to the sun over the course of the year would change. Each latitude would have a distinct "ring shadow calendar", of which duration (how many days out of the year), intensity (darkness of the shadow), and how that darkness changes during the day as the position on the planet enters and exits the shadow would change.
For instance, if you're in a mid-latitude, and you're in "ring shadow season" you may wake up to a sun rise, and then the sun "goes behind" a ring. A few hours later it comes out again and things get brighter, and then darker again as the sun passes behind another ring. At mid-day the cycle reverses itself.
<http://www.planetary.org/multimedia/space-images/saturn/saturn_seasons.html>
Show a good photo of what this may look like. Imagine you're on the surface, passing through the shadows during the day.
The rings would look like high, dark clouds, and the light/dark transitions would be pretty dramatic.
If you're in the summer season, you wouldn't experience ring shadow at all during the day.
But what would the rings look like themselves? When you're in the summer side of the rings, they would be brilliant, reflecting the sun. The rings would be bright throughout the night as well, but the planet's shadow would also be visible, looking as if it is moving across the rings throughout the night.
You can get a good idea of this shadow here:
<http://www.businessinsider.com/cassini-last-pictures-saturn-rings-nasa-2017-9?r=UK&IR=T>
and
<https://twitter.com/wescallisontnn/status/913555294277345280>
When you're in the winter side of the rings, you're on the shadow side or back side of the ring, and they would be dark, though you would still see them due to light reflecting off of ring dust.
<https://apod.nasa.gov/apod/ap121231.html>
Shows a the backside of the rings. Not nearly are bright, but you can see the bands. You can also imagine being on the surface, passing through the different bands of shadow during the day. At night you'll see dim rings and the planet's shadow going across the sky just as you would during the summer.
But what happens during sunrise and sunset? The rings would retain their brilliance, but wherever the light travels farther through the atmosphere, more blue light scatters out, leaving red light. This would be most noticeable after the sun sets, making the portions of the ring that appear near the horizon look orange - just like the moon looks when it rises. So at night (on summer side at least) you get bright rings that go from orange to white back to orange as they span across the sky.
One thought is that summer, especially at mid latitudes, would be a very bright time of year, given the amount of light reflecting off the rings throughout both day and night.
[Answer]
So you are concerned about the appearance.
The best thought I have have on that is 3D modeling software.
Blender is a free program that is easy to learn how to use.
You can setup your surface, a light source, and then a reflective plane and let it bake. If you give more details about location on your planet I could probably do a few renders for you at different times of day, but honestly it would probably be a fun project to figure out yourself.
Important details (material of ring, affects reflectivity and color). Type of star. Distance from star. Planet's axial tilt compared to the stellar plane. Thickness of atmosphere. The latitude of viewer, ect.
OK, so I did some initial rough (ROUGH) renders from an orbital perspective. These are not necessarily to scale, though I think I got the lighting write. I treated the rings as thin Torus, set to 95% opacity (B Type rings block most light). I treated it as a solid ring rather than a banded one. A banded one would result in mostly the same effect (just banded) that we are seeing in these images (though with atmospheric distortion).
The most important thing to take away from these initial renders is that the effect will depend on three important factors.
-What time of the year is it?
-Where on the planet are we?
-How large are the rings?
Of course, as I am posting these, I just realized that I wasn't using cycles rendering, so they aren't nearly as physically accurate as you would probably like, I can rerun them in the morning and then do renders from the surface of the planet. (Been too long since I have used blender, a bit rusty).
[](https://i.stack.imgur.com/PySAr.png)
[](https://i.stack.imgur.com/ltKVK.png)
[](https://i.stack.imgur.com/eJrpV.png)
[](https://i.stack.imgur.com/Dfn8P.png)
[](https://i.stack.imgur.com/9gCyP.png)
However, despite the fact that I goofed up, we can still see a few important points, that might not be entirely evident from the renders without the context.
During winter, the ring will cast a hemisphere on your portion of the world. This will block much of the sunlight putting you in a night time situation.
This will only be at particular latitudes.
The latitudes effect will shift as the season shifts. The area affected also becomes smaller.
As spring comes, the ring does not cast much of a shadow on the planet, anywhere.
I assume once I redo it with cycles, we will see it reflecting light onto the planet for the hemisphere that is experiencing summer.
I will edit once I have better orbital renders, and then again once I have the surface renders.
[Answer]
nBos AstroSynthesis. It is a full, scientifically accurate, star system simulator. Can do entire sectors of space. Allows you to generate planetary systems with full accurate orbits, and even animate their motion. It's going to be the closest thing to what you are looking for.
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I searched 'earth with rings' on Google, and I got the following picture:
You could put the rings in this picture into context on your planet, but you should be able to get a simple description from this.
Plus, it's all up to you to decide how your planet will look.
**Edit**
The picture is not 'scientifically accurate' at all. It's simply a picture to help represent my thoughts. (It is just a 'cool picture').
During sunset, the ring(s) would reflect light from the sunset, making them red, orange, yellow, pink, etc. The dark side of the rings would have a tint to them (depending on the sunrise/set colors), but it wouldn't be as noticeable or bold.
The shadow of the rings would be cast during the late morning, noon, and early afternoon depending on the hemisphere. The shadow would be similar to that of an eclipse, but it would be once per day.
The rings could rise and set. Realistically, the rings wouldn't *rotate* around the planet, as that would fling them out into empty space, but they do orbit around on their plane. I do think it would be more dramatic for the rings to rise/set, because then characters could refer to different times than noon, sunrise, or sunset. If the rings did not *rotate*, there would be a line from the arctic to the antarctic, on both sides of the planet, that would be in constant shadow of the rings. There would be a lot of tourism here, I would imagine, but I'm not writing the fantasy novel.
In higher latitudes, the rings would act similarly to the sun, where they would be visible all the time, day in, day out, for the entirety of the year.
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[Question]
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This is a water world with depths ranging from 2-3 kilometers deep up to vast shallows of only a few meters deep usually around volcanic islands, where there are coral islands not bigger than Hawaii's Big Island.
The planet has a 23 hour day, gravity is just slightly lower than the Earth, the large moon causes tides to be twice as strong as on Earth, it has an axial tilt of 14.6 degrees and has permanent ice at both poles, while the temperature at the equator is on average 30 degrees Celsius.
The main feature on this world are the multitude of floating islands of vegetation that are several hundred kilometers in diameter with a handful that are over a thousand kilometers in diameter.
These plant islands come in several varieties from massive Sargassum like seaweed creating soggy mats of weeds that break up and come together regularly, to colonies of plants that twine together on the surface hardening into a wood like island between 2-10 meters thick and several hundred kilometers in diameter while its roots form an entire ecosystem under the water.
The islands would be too low to affect the wind, but with tens of thousands of these islands floating around the ocean, would it help keep waves from becoming too large, and possibly help to dampen the numerous storms and hurricanes?
[Answer]
Seemingly unrelated, but very related at the core:
How do you spot oil slicks on the open ocean?
Answer: You look at the waves!
This is what happens when [SAR imagery](https://en.wikipedia.org/wiki/Synthetic-aperture_radar) from planes or satellites is used to spot illegal oil dumps. The trick is, that the radar reflectivity of the sea surface depends on the presence of surface waves of a specific wavelength. And the oil slicks look dark in SAR images, because they dampen the short waves that are abundant everywhere else on the ocean. This works even with the thin contaminations that result from ships cleaning their tanks.
So, if a thin film of oil can sufficiently dampen waves with a wavelength of several centimeters, it stands to reason that a thick floating island can easily dampen waves of many meters in length.
Of course, the shore line of your floating island will go up and down with the waves, but if you go some hundred meters away from the shore, all but the largest waves should be entirely dampened out. The total dampening of a floating island should actually be more than the dampening of a rock island, because the floating island won't reflect the waves. It will actually absorb them and turn them into heat.
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Tsunamis are no threat to floating islands, by the way: Tsunamis are waves with extremely long wavelengths. They only become dangerous when their wavelength is reduced by the low water depths near shores. As long as there is enough water beneath a floating island, it will just move a bit up and down when a tsunami passes underneath.
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Storms are a big problem for your floating islands, though. Hurricanes have immense power, and they will tear at the trees on the floating islands. And with the high equatorial temperatures, you have to expect many strong hurricanes. The hurricanes will threaten to tear your floating islands apart.
You might work around this problem by suggesting that the floating islands consist of plants with extra long horizontal roots, which actively entangle themselves with each other. They actually evolved to stabilize the floating islands. If you have a several meters thick layer of entangled roots, you should get some robustness against even hurricanes. This should work out, since the forces exerted on land by storms are similar for nearby points: The whole island will feel an enormous amount of force acting in a certain direction, but the forces trying to tear the island apart will be orders of magnitude smaller.
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The greatest danger to your floating islands, however, is that they will drift between different climate zones. The ecosystem of the floating islands needs to be able to survive drastic climatic changes. They need to be able to strive with hot, wet, equatorial weather, as well as with dry sunny weather, or frosty conditions, changing on a timescale of years.
How you adapt your flora and fauna to this, is up to you. I wouldn't think, its impossible to do, but it requires some thought to come up with a sketch of an ecosystem that can tolerate such drastic climate changes. Maybe some species will drastically change their appearance with the changing climate, while some others will become extinct outside of their home climate and only survive in the form of spores. This could lead to quite some interesting dynamics, imho.
[Answer]
# Waves
Depending on how close or far the islands are from each other, the surfaces waves would break on the islands further from the center, keeping the ones near the center from seeing large waves. Also, with the fact that the islands are coral, that means that the energy from the wave can break on the coral before they actually reach the shores of the island, reducing the size of the waves that the islands are seeing.
# Hurricanes and Storms
As for hurricanes, the sheer number of them prevent any storm from really getting too bad, because in order for hurricanes to gain any power, they need to have vast, open, areas for them to gain energy due to cold air interaction with the warm water. As for storms though, they can form anywhere so they won't really be influenced. Given the fact that the equator temperature is 30 degrees Celsius you would almost certainly be seeing regular tropical storms around it, that could travel with the wind to any of the islands, although tropical storms would be the worst your planet would see.
# Tsunamis
The biggest issue that the islands would have is flooding due to fluxes in weather or tsunamis caused by island rock falling into the body of water that it's floating on. The coral around the islands will help dampen these but they won't stop them completely. Now the free floating bodies of dried seaweed like plants would help mitigate the effects of them if they were stable enough to survive a heavy impact, because if it were to hit one of those large bodies then the tsunami would loose it's power because of the amount of energy transfer that happen at once.
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**Tidal waves**: these are formed involving the entire volume of water. Something affecting only the surface like your floating islands will do pretty much nothing on them. I expect their influence to be noticeable where the height of the highland is no less than half the depth of water.
**Surface waves**: here your islands, provided they are sufficiently clustered, will scatter the waves and mitigate their influence on the coasts.
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They might affect the wind more than the waves.
If the islands are flexible, they will move up and down with the water, and won't sap much energy from the wave.
With the sun hitting the island, making it warmer and changing the air pressure, it might cause the wind to change.
A lot of weather is created by the differences of land & water. Without land your planet's weather might be a lot more homogeneous, and might not get many hurricanes.
[Answer]
I know things like floating ice or lots of jellyfish do dampen the waves (at least near the shore)
Dampening waves should have no effect on wind speed or rain during storms and hurricanes.
Changing surface area of the ocean, and its ability to absorb or reduce heat will have effect on weather, but I do not know enough to see which way it will go
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*Inspired by this question: [Sexual reproduction without biological sex](https://worldbuilding.stackexchange.com/questions/44879/sexual-reproduction-without-biological-sex)*
*And, to a lesser extent, this question: [Would a society of simultaneous hermaphrodites have gender roles?](https://worldbuilding.stackexchange.com/questions/65500/would-a-society-of-simultaneous-hermaphrodites-have-gender-roles)*
*I'm not particularly well-versed in biology at all, let alone the wide variance of sexual characteristics that exists in the world, so I apologize if I've misunderstood/misused any terminology here. (Or if my questions are somehow just beyond stupid in a way that I failed to realize.)*
For my purposes, I'm imagining a (preferably as close to human as possible) species that has exactly one biological sex. Every individual of this biological sex has all the necessary anatomical requirements to be the father or mother in a reproductive exchange. In case it's somehow relevant, their anatomy is also arranged in such a way that one couple can be simultaneously participating in two exchanges. This means that both members of one couple could be simultaneously pregnant with a child fathered by the other member of the couple.
So the main question here: **If you have two children of the same two parents, but with swapped parental roles in their conception (the father of one is the mother of the other and vice versa), is there any inherently meaningful difference between the two siblings beyond two siblings who have the same parents as each other, both of whom are in the same parental roles?**
I realize that a society comprised entirely of such a species could easily create social constructs such as children taking the surname of their biological mother or labeling such cross-siblings as something indicative of a relationship closer than a half-sibling but further than "actual" siblings. I'm less concerned with purely social constructs that might arise than I am with actual, meaningful differences that would affect them in the future more than "actual siblings" would be expected to experience.
If a social construct were to arise from such differences (as I expect they would), then I'm definitely interested in those sorts of downstream effects. In fact, the main reason I'm asking the question is so that I can eventually come up with exactly those kinds of downstream effects. But I'd like to set the foundation of my social constructs on something more solid than just other social constructs.
For instance, as AlexP brought up in comments, the intra-uterine environment [can be very important](https://en.wikipedia.org/wiki/Transgenerational_epigenetic_inheritance) because of [genomic imprinting](https://en.wikipedia.org/wiki/Genomic_imprinting) and/or [metabolic imprinting](https://en.wikipedia.org/wiki/Metabolic_imprinting). Aside from potential disorders that might happen at the statistical fringe, what noticeably-common differences might we see between cross-siblings? Since both parents could nurse the child, would some differences be mitigated by having a child's father nurse them instead of the mother? Would differences in mitochondrial DNA cause significant differences? Are any noticeably-visible or significant characteristics only heritable from one parent? These are all sub-questions of which I'm unsure of their relevance to the larger discussion.
I wish I could be more specific in what I'm looking for, but I'm struggling to find the words to describe it at the moment. Hopefully, I can think of a better way to word all of this fairly soon and edit my question accordingly.
[Answer]
That depends.
Do they use isogametes, or sperm and ova?
If they use isogametes, do they lay eggs, or use internal gestation / live birth?
If they use isogametes and lay eggs, the potential differences will be utterly negligible--limited to things like the effects of diseases or nutritional deficiencies in the mother that might compromise egg production.
If they use isogametes but have internal gestation, then there will still be no genetic differences, but the developmental environment has more opportunity to produce differences. I would not, however, expect them to be large enough or common enough to be of any social consequence. (Doesn't mean a society of such creatures couldn't still *decide* that the facts of parentage were important, though, purely as a social construct, maybe for purposes of inheritance or whatever.)
If they use dimorphic sperm and eggs, do their cells include any organelles with independent genetic material, like mitochondria or chloroplasts?
If their DNA (or equivalent) is strictly nuclear (or equivalent), then can we also assume "normal" reproduction of individuals with diploid genetic structure via haploid gametes that each carry half of the parents genetic information, despite their physical dimorphism? If so, there will be no genetic differences, and this is the same as the isogamete case--only the effects of the developmental environment *may* be relevant.
If they do have organelles with independent genetic material, then there will be potentially significant differences between children with different mothers in the same pair of parents, because organelles will come only from the mother. In humans, this is why certain metabolic diseases are passed strictly through the maternal line.
Additionally, if the assumption of "normal" haploid-diploid recombination of nuclear genetic material with equal contributions from each parent is wrong, and they have some other more complex reproductive system which introduces different proportions of genetic material from each parent independent of the organelles, then you could easily get very pronounced and obvious differences between children of different mothers.
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Logan already gave a great answer to the biological differences of the reproduction itself. I want to address the evolutionary psychology and how it would in term affect cultural differences, as I believe there will be some significant ones.
**Cheaters sometimes Prosper**
*For the record whenever I say male or female please interpret that as meaning 'the herm who played the role of male (providing sperm) or female (birthed the child) in a given mating', it makes the answer much cleaner to not have to constantly add that qualifier*
One issue that has shaped human culture and laws since their onset unfortunately still plagues our poor herms, and that is the possibility of infidelity. The male can never know with 100% confidence that he was not cheated on by his partner. Thus one would generally trust the child that came out of their womb as being theirs more then they trust a child birthed by another herm who could have theoretically mated with a different male and have birthed that male's child instead of yours.
This effect would start as one of evolutionary psychology. A hem will instinctually prefer investing resource on the child that definitely shares their genetics over investing resources on a child that potentially may not share their genetics.
How significant this psychological inclination to prefer children you birthed is depends on how assured the male is that he is the father of a child. If the animals were polyandrous or polygynandrous (ie the herm playing the role of female regularly mates with multiple males) then a herm would dedicate most of their resources to the children they birthed since there is a very real possibility they didn't father the child of a herm they mated with. If a species instead split off in such a way that a mongomous couple was isolated from all other herms during mating time so that it would be difficult for a partner to find someone to cheat with then the male is far more likely to treat children equally since he is relatively confident of the paternity of the child.
Just because a species is 'monogamous' does not mean this doesn't matter, because every monogamous species every studied still had regular cases of extra-pair copulation (ie cheating), simply put cheating is too effective an evolutionary strategy for it to never occur in a species. For humans the frequency of non-paternity events (ie the guy who thinks he is the father isn't) seems to be somewhere around 2-4% in modern history. I would presume that number would be higher in prehistory, where there was less technological or cultural means of assuring paternity, but we don't really know. That matters because the frequency of non-paternity events in prehistory, when our instincts for handling the possibility of non-paternity would have evolved, would decide how much effort were willing to dedicate to raising our partner's children.
If we assume your herms had a human-like mating strategy then I'd say a 3-6% frequency of non-paternity would be common in prehistory, which means that on an instinctual level a herm is willing to dedicate 3-6% more effort into raising a child it birthed over a child it's partner birthed.
Arguably in the 'traditional' nuclear family, where two herms raise a pack of baby herms, the issue with infidelity is small enough to likely only play a small role in differences in how children are raised. However, there are situations where paternity is less certain where that lack of confidence would lead to more significant preference for children the herm birthed itself.
Studies show that non-paternity events are more common in couples that aren't married, couples with less education, couples of lower socioeconomic level, couples that regularly fight or have marital/relationship problems, and couples where travel or work keeps the two individuals apart for large lengths of time. In these couples the higher chance of a non-paternity event would translate to an instinctual preference for the child one birthed being much higher. As an extreme example if a herm has a documented history of cheating then it's quite likely that their partner is going to favor the child that they birthed because of the very real difficulty of being certain of the paternity of the other child. The point being that there will be certain situations where you may expect to see a marked preference for one child over another due to paternity concerns.
Socially I imagine this would lead to a likely cases of inheritance putting preference on children birthed by a herm over those fathered by the herm. Of course without separate sexes passing inheritance down the male line no longer makes sense, so in most cases, where a couple is married and have intermingled their assets, it wouldn't really come up since neither of the adult herms would have a higher claim to those commingled assets then the other herm does. Still in cases of royalty or other situations where one herm clearly has a greater claim to assets or some genetic lineage then the other herm likely children birthed by that herm would get priority for inheritance and similar policies.
**Milking pregnancy for all it's worth**
*(I really need to come up with a better pun)*
Assuming that your herms are roughly similar to mammals then that would mean they need to provide milk to their young. While it's quite possible that both herms would be able to produce milk and nurse a young it's possible that the one that birthed the young, and went through all the hormonal cues of pregnancy, would either be the sole provider of milk or the primary one. This actually factors in to the above point, since a herm is more willing to provide resources to a child they know shares their DNA the female would have more incentive to provide milk to the child then the male would, since she knows she is feeding her own child.
*If* the female either is the only provider of milk, or the primary provider, then this would also render her the primary caregiver, since until very recently it was impossible for the non-lactating male to feed a nursing child. If this happens the 1-2 years of nursing and child-rearing would likely impart an increased bond between mother and child over that of the father, and likely the mother would traditionally be the primary care giver even after the child stopped nursing, as she would have already grown to know the child's needs and personality better while nursing the child. The fact that the mother already is more invested in the care of the child she birthed, if only by a small amount, would further encourage the mother to continue as child-rearing everything else being equal.
In a modern society where there are plenty of means for a non-lactating individual to care for a nursing child these sort of restrictions need not apply, but cultural and social norms would already have been built up over generations during which only the lactating herm could care for the child. These norms would still be taught and passed down to children, even if they don't necessarily make sense in a modern society, and thus would likely still be impacting gender/parenting roles even in a more modern society.
Of course this is one area you get plenty of say in, it's easy enough to create herms where either both partner's lactate equally or children don't nurse, in which case this entire section becomes moot.
**It's allot harder to be a dead beat mom**
One could expect that issues with a male not sticking around to care for the child will still happen in a herm society just like it does in our current society. Thus single mothers raising children will happen far more then single fathers still, and thus the legal system will likely have protections in place for herms who birthed a child if her partner isn't assisting in providing for it. In fact if a herm is raising a child by itself it will likely be presumed to have birthed the child for this reason.
**Gender disparity will still exist, because you can be a dick even if you also have a vagina**
*I need to add a very important caveat to this entire section, that I'm speaking purely about evolutionary psychology. The below is a true and known aspect of evolution that can be demonstrated. That does not necessarily mean I believe that it should be used to dictate anything about how modern society should be structured or believe it makes a significant difference between sexes in modern society. In fact I'll go so far as to say someone trying to use this as claims of superiority of one sex over the other or to justify treating sexes differently in modern society is butchering evolution and science and is all around a terrible person*
It's a known fact that herms have a preference when it comes to mating, they would prefer to play the role of a male. Males dedicate far fewer resources into producing young then the female does, allowing the male to dedicate those extra resources in potentially mating with other herms and producing more offspring. This preference is more significant with a polygamous mating system then a monogamous one, as the male is free to mate with other herms immediately after impregnating a female in a polygamous mating system. However, even in a monogamous mating system this preference will still exist as there is always sexual conflict with the two sexes trying to offload as much work as possible on their partner's even in monogamous systems.
Thus the evolutionary psychology of the herms will be two fold, first a preference for being the male, and secondly a belief that whichever herm played the role of the male is likely 'stronger' or more evolutionarily fit then the one playing the role of the female, as he was able to somehow convince/force the female to accept the less preferable role.
This bit of evolutionary psychology is going to have a significant affect throughout all of your society and culture, which will generalize favor the ideal of herm-as-male. Your see it in everything from royalty and other rich/important figures always insisting on mating as the male to society treating unwed females as a bigger problem then unwed males to Axe body spray commercials promising that your get all the herms begging you to be their male because all the herms are culturally encouraged to be males over females on some subtle level so playing the role of male is just 'sexier'.
Unfortunately we have also seen consistently that those with power will do everything they can to consolidate power, in fact males in human history did quite a bit of power consolidating by exploiting a small physical size advantage into things such as laws and policies that gave females less legal rights as males to policies design to refuse women education or the ability to get a job (so they had to stay dependent on their male partners) or spreading of misinformation about women that denigrated them to make males seem more powerful by comparison (like claims that women are less intelligent or that they were too 'emotional' to hold a job or that they were more comfortable being subservient).
Please note this is not a situation limited to males. Females have been shown to be just as willing to consolidate power whenever they were in a position of power, it just so happened that differences of physical size and childbearing costs generally put males in a better position to do so in the past.
In a herm society I could see somewhat similar tendencies occurring. While any herm could mate in any position the ones in power, be it financially, politically, or physically, will both consolidate power, to put themselves in a better position in the future, and likely insist on mating in the male role. As a side effect they may also create systems that make it harder for a herm who has already mated in the female role to gain 'power', in any format, in order to cut back on competition and ensure that once they have mated as a male they will get to keep that position.
As an example I could see herms making claims that females who are pregnant or nursing shouldn't be allowed to attend school as they need to dedicate all their energy to their child and/or would be too distracted/distracting to get her education. While there would be all kind of arguments why this just 'made sense' one of the unspoken reasons would be that of consolidating power. If two herms mated at a young age the one that mated as a male would be able to continue going to college while his partner couldn't, thus he would have the education that allowed him to get a better job and thus be better suited as the 'bread-winner' then the female who was refused an education. When the time comes around for another child to be had he can thus argue he is too busy bringing in the money to be pregnant and thus insist the other herm again be the female. Basically taking one opportunity of being the male in the first mating as an excuse to justify his gaining the skills necessary to always get to maintain the role of male.
All the above is talking in very large sweeping terms across all of society. It's quite possible that many herms would regularly swap the male and female roles and that some herms would have a preference for female role for instance. Likewise it's quite possible many of the herms who created or propagated systems which helped males consolidate power may not fully understand how those systems were in fact assisting in the consolidation of power. In short, I can anticipate patterns likely to show up across the society as a whole, but that doesn't mean you should presume every individual in that society share's that belief or motivation.
Regardless the net result is that a sort of gender role where herms mating as males were preferentially favored, or herms that mated as females were somehow subjugated, is not at all impossible. If such a case existed that would then have a very significant effect on how a child would treat each of their parents. For instance such a system would likely encourage forcing female mated herms to be responsible for child rearing, which in term would affect the parental bond with the child as in my previous point. For that matter the child may grow up to treat each parent differently based off how society treated the two types of mating. For instances your likely to hear "my dad can beat up your dad" sort of arguments which cite the herm that mated as a male as the one to beat up because society expects male mated herm's to be 'stronger' then female mating herms.
Put more generally once society creates gender roles based off of method of mating those gender roles are going to affect all aspects of life, including how the children and parents interact with each other. A whole separate question could be dedicated to just how many difference such roles could create, so I'm not going to waste time explaining each one in depth.
**Down with gender roles**
If you don't want these sort of gender roles to be as prominent in your world there is, luckily, a simple evolutionary justification for decreasing these roles. If monogamous mating are the norm then it's possible that herms regularly alternated between the male and female mating role every other mating.
From an evolutionary stand point this would make sense because, as I stated before, it takes more energy for the female to birth a child then for the male to father it. If the goal is to pop out children quickly then waiting for the female to regain the lost calories/resources she expanded in birthing a child could slow the rate at which pregnancies could happen. By alternating who plays the role of male it would be possible to better spread out the resource cost of multiple mating's, thus potentially allowing more total mating for a monogamous pair.
If such a system had evolved before modern society and culture evolved then gender roles would be far less drastic, since it would be the evolutionary norm for partners to alternate matings and thus every herm would be expected to occasionally mate as a female. This wouldn't entirely remove the problem though, as evolution would still favor the male role of mating and that would still have some affect on their evolutionary psychology. In particulate there is a possibility that modern societies, where medicine and technology made child mortality lower and thus couples spent more time on raising existing children rather then birthing new ones to replace deceased kids, that a preference for the male role may grow in 'vogue' as it no longer became necessary to alternate roles in mating just to keep up with the demands of constant pregnancies. Still, this would at least significantly decrease the degree of preference for specific gender roles.
There is another catch with this possibility, the fact that it only makes sense when your goal is to constantly produce kids. Putting most of your effort into producing lots of kids, rather then in raising existing kids, is more of an R-type strategy by definition, and generally sapience is primarily a k-type mating strategy. In layman's terms the really smart animals likely would have a large gap between pregnancies while the took the time to raise and teach their newborn smart child how to use his smarts to survive, and if that happened then a herm has enough time to catch up on the calories lost during the birth in the years between pregnancies spent raising the existing child.
The solution to such a problem would be to put the herms in a harsh environment where infant mortality is extremely high. I'd cite penguins as the perfect example of this. The male and females trade off time spent caring for their unborn child (in this case an egg) by passing the egg back and forth because it's the only way the two of them can manage to raise an egg in such a harsh environment. While alternating pregnancies is a bit different then trading eggs there are quite a few analogs that one can draw. still I'm getting a bit off topic now so I'm going to stop here by saying if you wanted to ensure herms traded off mating roles it's probably worth asking a separate question so we can go into more detail about the reasons.
**Who's your daddy?**
Finally there could be quite a significant difference in parentage based off of mating role because it's entirely possible that 'realistic' herms would never know their father. Generally hermaphroditism only persists in a world where it's hard to find mates due to individuals of the species being highly isolated. I already went into quite a bit of detail as to why that was at the beginning of [this](https://worldbuilding.stackexchange.com/questions/113916/why-would-males-exist-in-species-with-hermaphrodites/114294#114294) answer, so rather then repeat myself I'll encourage you to check out that answer.
The point being it's quite possible that herms only met up long enough to mate and then went their separate ways, meaning a young herm would only be raised by it's mother and thus there would be a significant difference in how a herm was raised depending on which herm was their mother.
This point gets a little complicated if you actually want intelligent herms with their own culture, because the degree of isolation necessary for hermaphrodites to stay an evolutionary good idea isn't exactly supportive of evolving sapience or culture. In fact I have a [separate](https://worldbuilding.stackexchange.com/questions/58147/how-to-justify-evolution-of-a-sapient-hermaphrodite-species?noredirect=1&lq=1) question just for trying to justify the existence of sapient herms.
However, I can say that it's quite possible that herms at least started as a mostly isolated spaces and thus their instincts are less in favor of monogamy and/or put much higher emphasis on the maternal bond over the paternal since in their distant ancestry the paternal bond didn't really exist, how much that is true depends on how you justified your sapient herms existing in the first place.
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[Question]
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It’s the mid–late 20th century, and NATO and the Soviet bloc wipe each other out in a nuclear war while the southern hemisphere [eats its popcorn](https://s-media-cache-ak0.pinimg.com/236x/66/1d/c5/661dc54ac78e4b7e3342588cdcbb4db5.jpg). Dust fills the atmosphere and nuclear winter sets in; the ecosystem collapses. Which third world countries would be most likely to survive and why? If the answer is “zero”, how could the events of the nuclear war be changed so that at least one would survive?
A country is considered to have “survived” if:
* Its government either has continuity from before the war, or has successfully transferred authority to a single successor government
* Its people regard themselves as belonging to the same state as from before the war
It can:
* lose a substantial amount of its population
* lose its agricultural base as long as it has some means of feeding a sustainable subset of its population (greenhouses, hydroponics, etc)
* lose segments of its population unevenly (“only the rich survive” or “only the military survive”)
* alter its policies or nature of governance radically (a democracy can become a military dictatorship or vice versa)
* integrate survivors and territory from outside its original borders
* move its capital or have a radically different population distribution
It cannot:
* be itself integrated into another larger federation
* collapse and be refounded by survivors in the same “ethos” as the original country
* be a first or second-world country involved in the nuclear war
* be a state or province from a first or second-world country involved in the nuclear war (so no Republic of Wisconsin).
[Answer]
Fortunately in the event of a nuclear winter you only have to follow this [travel advice](http://www.news.com.au/travel/travel-advice/safest-places-in-the-world-to-survive-world-war-iii/news-story/57a99583927164147a8a6afbaa728dc5)
>
>
> >
> > STAY SOUTH
> >
> >
> >
>
>
> Since all of the world’s nuclear powers are in the northern
> hemisphere, stay south of the equator.
>
>
> Countries like Australia, New Zealand, South Africa and Argentina are
> temperate with plenty of space to grow food, and since they’re well
> out of the way you’re unlikely to be targeted.
>
>
> If you choose to stay at home, it’s probably best to avoid Alice
> Springs, due to America’s top secret facility at Pine Gap.
>
>
> According to the classic post-apocalyptic fiction *On The Beach* by
> Nevil Shute, Melbourne is an excellent bet. The plot suggests that if
> nuclear war breaks out in the northern hemisphere, the Victorian
> capital is likely to be one of the last places the radiation cloud
> reaches.
>
>
> If war spreads, you could always go further south to Antarctica. It
> will be chilly, but with adequate supplies and shelter you could
> survive several months.
>
>
>
This suggests that the more likely survivor countries will be Argentina, Australia, New Zealand and South Africa.
However, all is not lost for the survivors in the Northern Hemisphere. This scenario about a [global nuclear war](http://www.johnstonsarchive.net/nuclear/nuclearwar1.html) between the NATO and Warsaw Pact nations and occurring in 1988.
>
> It estimates ~3 billion survivors a year after the exchange, and ~45 million survivors in the US alone.
>
>
>
The geopolitical situation has moved on significantly since this scenario was devised. So the re-establishment of a GMD Nationalist government in China is a fantasy (it would take an interesting set of political conditions for this to happen). The glib statement about peat bogs burning for several years overlooks the fact that this will contribute substantially to global warming in the post-WW III world.
This scenario can be used for guidance. It suggests that the US government is most likely to survive. While, by 2040, or fifty-two years after a nuclear war in 1988:
>
> Some of the surviving nations have emerged by now as major powers, including Australia, New Zealand, China, Argentina, and Brazil.
>
>
>
Obvious the place to be in the aftermath of a nuclear war and in the event of a nuclear winter is to go South.
The question was about which Third World countries will survive in the event of a nuclear winter. Australia and New Zealand are certainly First World countries. Argentina and Brazil can almost qualify too. China historically has been a major super-power, and is modernizing fast but may fit the bill of being a Third World country. South Africa has a mixture of affluence and poverty. All in all, it is more probable that many nations will survive with their governments intact. Most likely they will be coalition governments or military dictatorships but generally similar to the governments during the Firs and Second World wars. Third World nations are probably going to be "eaten up" by stronger nations in their rush to survive and rebuild.
A recent review of the consequences of [nuclear war](http://www.globalresearch.ca/nuclear-winter-turning-a-blind-eye-towards-armageddon-scientists-warn-of-the-existential-danger-of-nuclear-war/5554221?print=1) specifically about the climatic impact. While the Physicians for Social Responsibility published a [report](http://www.psr.org/news-events/news-archive/how-a-limited-nuclear-war.html) suggesting even a limited nuclear war will result in global climate change and a famine affecting two billion people.
Research was unable to find anything about the impact of a nuclear winter on the South East Asia region. Nations like Malaysia and Indonesia surely will survive. While countries close to China will politically realign themselves in its sphere of influence to ensure their survival. Possibly India and Pakistan will wage nuclear war against each other, but if the northern hemisphere has been devastated this might stay their hand.
[Answer]
I don't see why the tropical "3rd world" countries, or at least those south of the Equator, for example Colombia, Ecuador, Guyana, Venezuela, Brazil, Uruguay, Paraguay, would have experienced so much more instability than what they usually do. Unless the nuclear winter was so cold that the entire Earth froze solid, agriculture would still be possible in the tropical belt. With America and Europe gone those countries would lose access to the global markets, but that would not kill them--those countries have enough qualified people to keep the lights on. It may be that some small countries, e.g. Ecuador or Guyana, would be annexed by larger ones, but other than that I see no insurmontable problems. African countries are different because at the time they were inherently unstable and in the absence of a world police force they would have probably gone through a phase of wars and rearrangements along ethnic lines.
An interesting line may be the develeopment of those countries freed from the supervision of the great powers, with the heart of civilization moving from Europe and North America to South America, Australia and New Zealand.
[Answer]
Independent Polynesian Nations like Samoa, Tonga, perhaps even Fiji etc,. would be good bets. So long as the sea still provided food. The land is fertile and crops are varied. The people are tough and versatile.
The political structure is only a thin veneer over underlying chiefdom/royalty lineages. Due to the strength of these connections the govt would not change although a lot of it's individual members would come to a sticky end. They would be replaced by others perhaps even from the same families. Taking away the First World would actually be better for the majority. They're isolated and self sufficient if they need to be.
They're homogenous populations with one main language, no religious conflict, and no real minorities except Fiji, which would probably get messy real quick, but would still probably keep it's govt unchanged.
[Answer]
We are looking for a country in the southern hemisphere with
(1) enough agricultural output,
(2) reliable source of energy, and
(3) ability to avoid being invaded by some other power.
Indonesia seems to fit the bill perfectly. It is the fourth largest agricultural producer in the world and an exporter of coal and crude oil. It is made of up of islands which makes it difficult to invade. It has a large population and a reasonable military to further deter aggression from China (which may or may not have been involved in the nuclear exchange in your scenario).
<https://en.wikipedia.org/wiki/Primary_sector_of_the_economy>
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[Question]
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In the award winning Studio Ghibli film, [Arrietty](https://en.wikipedia.org/wiki/Arrietty), there exists a creature known simply as the Borrower. Borrowers are a small version of human, no taller than a few inches, yet are otherwise the same in every way. We have asked before what the [maximum size of a human](https://worldbuilding.stackexchange.com/questions/51686/what-would-be-the-tallest-possible-height-for-humanlike-creatures-in-earthlike-c/52961#52961) is, but what is the minimum size? How could a creature like this realistically evolve? How close to the Depicted Borrower can I get using realistic anatomy?
A list of all of the Anatomically Correct questions can be found here
[Anatomically Correct Series](https://worldbuilding.meta.stackexchange.com/questions/2797/anatomically-correct-series/2798#2798)
[Answer]
Considering that humans evolved from "[...] a tree-climbing, furry-tailed insect eater that weighed between 6 and 245 grams" ([Nature News](http://www.nature.com/news/face-to-face-with-the-earliest-ancestor-of-all-placental-mammals-1.12398)), it is perhaps conceivable that small humans could evolve. After all we have mice, bats, flying squirrels and all sorts of other very tiny mammals.
The smallest of those are the [Etruscan shrew](https://en.wikipedia.org/wiki/Etruscan_shrew) at between 1.2 - 2.7 grams (1.8 grams on average) and the slightly more massive [Kitti's hog-nosed bat](https://en.wikipedia.org/wiki/Kitti%27s_hog-nosed_bat) at about 2 grams.
Interestingly these both evolved, from the above common ancestor ( which according to Nature has a probabilistic description, but no actual fossil record, and no suggested name in the article ), to be smaller than the smallest projected size of the common ancestor. Overall enough time has passed to see all of the variations that we see in class Mammalia in the world today, from shrews to humans to Blue whales.
But this does not answer the question of specific physical and mental characteristics that are ( as far as we all agree ) distinctly human. First let us go down the list of traits related to mental capacity since this is a large factor in determining the remaining resources to support metabolism beyond cognition. These cognitive traits are what traditionally makes us uniquely human, but have been shown to be explicitly *not unique* to humans.
### Cognitive Traits
1. Complex langauge? - [dolphins](http://www.ted.com/talks/denise_herzing_could_we_speak_the_language_of_dolphins?language=en)
2. ~~Tool use~~ - [too long to list](https://en.wikipedia.org/wiki/Tool_use_by_animals)
3. ~~Art~~ - [birds, primates, elephants](http://www.bbc.com/future/story/20140723-are-we-the-only-creative-species)
So it appears there is room for some creativity and tool use at the bottom of the mass spectrum, but it looks like language will be the hardest to explain at that level. However we are even beginning to question that based on [how it seems](http://www.scientificamerican.com/article/bird-brains-have-as-many-neurons-as-some-primates/) birds are able to imitate human vocalizations, and that is based on neuron density. In other words, by packing more neurons into a smaller volume, the ( choose your example ) of bird that imitates human sounds, including words and phrases, is approaching the brain to body mass ratio of primates. They have smaller skull cavities, but they are lighter and they pack more neurons into those spaces, which means their bodies are doing a similar kind of trade off to primates as far as cognition vs physical movement. Our brains consume about 30% of our daily calories and it would seem these birds are nearer to that range than previously thought, but I would caution that much more investigation in this area is necessary for any more definitive results.
### Physical Traits
The smallest known primate is the [Madame Berthe's mouse lemur](https://en.wikipedia.org/wiki/Madame_Berthe%27s_mouse_lemur) with a body length of 9.2cm (3.6 in) and a mass of 30g. This fits into the size range of a Borrower and is the same class of animal, however these creatures are very different anatomically than humans. The things we are perhaps most interested in are the hands, primarily opposable thumbs, since tool use, tool making and so forth are required for a creature like a Borrower, and perhaps the posture and gait of the animal, since we want them to stand up and walk around like people.
Other features like hair, curved nails, etcetera, I think we can assume, are merely cosmetic. Maybe such creatures would opt for hair removal but it would perhaps depend on their history, culture, and knowledge of medicine and disease. For example, only a couple of centuries ago many people shaved their heads and wore wigs to help prevent head lice.
One fact about hair is that smaller things, i.e. smaller volume to surface area ratio means higher heat loss. Many smaller animals may need their hair or may have completely different ways to cope with heat loss. The [naked mole-rat](https://en.wikipedia.org/wiki/Naked_mole-rat) is a mammal which is effectively cold blooded as it does not regulate its internal temperature and so remains close to ambient temperature. Most commonly, in addition to a thermal coat, such as hair, small creatures must have a higher metabolism, which generates more heat, in order to maintain a relatively constant internal temperature. However, we can assume that Borrowers would wear clothing like us, and would perhaps consequently have/need less hair, like us.
As for opposable thumbs, we are the only species that we know of which has this trait. However there are other very dexterous appendages that can accomplish some, but not all of what a hand can do, like tentacles. Interestingly, octopods also are [known to use tools](https://www.youtube.com/watch?v=AP_dpbTbess). Other posters may respond on the mechanical feasibility of opposable thumbs for a small, Borrower-sized species, but I do not see any physical reason why such a structure is not possible or would not evolve given all of the advantages related to tool making and manipulation that we are aware of in the human species.
Upright posture and walking gait is another question. We are familiar with the prairie dog, which stands upright, but does not have a natural upright gait, as do humans, but rather a posture and behavior that seems to be associated with an evolutionary advantage of being able to see farther, to spot predators, while closer to the ground. For smaller species it would seem that undergrowth and low ground cover flora in most environments would negate any such gains and preclude such an advantage.
Furthermore, there is the physics involved in a very short standing posture. Consider this from the point of view of trying to balance a broomstick on your hand, verses trying to balance a pencil. The broom stick is longer and requires less attentive movement to adjust and keep it balanced, while the pencil is short, has a lower center of gravity and will naturally topple over much faster than the broomstick. This means that an upright posture for a very short species would require quicker and finer adjustments for the creature to remain upright. However these effects can be offset by the size of the base of the posture, by making the feet larger or foot and toes more spread out.
Mice can stand upright and beg for food or sniff the air, but they are forming a tripod structure, with large haunches, a wide stance and they are leaning back against or balancing with their tails.
[Answer]
According to a recent scientific paper a creature like the borrowers could not evolve as they would be unable to survive.
<http://www.physics.le.ac.uk/jist/index.php/JIST/article/download/187/114>
Their eyes would be too small to take in enough light making them functionally blind. A borrowers metabolism would be unable to provide enough body warmth for them to survive, their hearing would be poor leaving them vulnerable to predators.
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[Question]
[
Since we're dealing with cat-folk already with the question about the [Khajiit](https://worldbuilding.stackexchange.com/questions/48778/anatomically-correct-khajiit), I figured we'd toss a different evolutionary lineage for furry humanoids around, that of the [hyena](https://en.wikipedia.org/wiki/Hyena).
Ever since the early days of D&D, the [gnoll](http://www.d20srd.org/srd/monsters/gnoll.htm) has been a most curious creature — a ravenous, bipedal, somewhat-social hyena-folk, as depicted below.
[](https://i.stack.imgur.com/z8ChT.jpg)
What would the evolutionary path be from the hyenas (presumably the spotted variety, as the rest are pretty strictly antisocial) we know (and occasionally love) to such a race be? Also, what behavioral features would develop, and what physical features would develop or be lost during the course of this evolution?
As always, [here](https://worldbuilding.meta.stackexchange.com/questions/2797/anatomically-correct-series/2798#2798) is the rest of the [Anatomically Correct Series](https://worldbuilding.meta.stackexchange.com/questions/2797/anatomically-correct-series/2798#2798).
[Answer]
**Evolution**
We start as you said with the spotted hyena, already a social scavenging animal, we only have to talk about its intelligence. Hyenas are actually [much smarter](http://www.livescience.com/34237-hyenas-last-laugh.html) than their stereotype suggests, in fact studies show that hyenas use wide diverse methods of opening man made boxes and also use trial and error in opening the box.
A few differences (that are very important) I have noticed between Gnolls and hyenas other than what you mentioned; the limbs. A hyena arm is much longer, more equal along its segments and has pads instead of hands. The evolution from hyena limb to Gnoll limb requires a method similar to primates;
1. **Hyena** - the hyena mainly scavenges off of other predators, in the case of a shortage of food in certain areas, these predators are much less likely to leave scraps. This means that mister hyena has to hunt on its own and is now a competitor of the bigger predators. The New, more hungry Lions are likely to chase out the hyena and that is where we get stage 2.
[](https://i.stack.imgur.com/gF1VJ.png)
* **Proto-Gnoll** - above is a map of where the Spotted Hyena can be found, the big patch of white is mainly jungle. This is where we are going to want our hyena to become a proto-Gnoll, still similar in many ways to the hyena, but the limbs are.... different. To make best use of their new jungle area (where predators are farther and fewer inbetween) their paws become more segmented to allow for tree grip, while their legs remain digitigrade in order to quickly run after prey or away from predators. Eventually they lose the whole final paw segment (which is the hyena equivalent of a foot), replacing it with a fully formed, human-like hand.
* **Gnoll** - Finally our Proto-gnoll looks like a Gnoll, but we still have to evolve sapience. Luckily based on our aforementioned Proto-Gnolls evolutionary history, we can treat them as carnivorous humans that can run fast. Which in turn means we can just say they evolved sapience just as humans did.
**Specific Anatomy and behavior**
* **Manes.** *Some Gnolls possess crestlike manes of hair going from their head
down their spine which rise up they become frightened or angry.* The mane can be explained easily through sexual selection, but having the main rise is harder. Lions fur doesn't rise when they get aggressive and they are one of the few animals with manes. So I cannot help here, but I would say the mane bristling is within reasonable doubt.
* **Loyalty.** *Gnolls are brutal hunters with a demonic ancestry who are
fiercely loyal to their pack.* Again Hyenas are not truly loyal pack hunters, they are pack scavengers. But the problem holds the answer, If we have or proto-gnoll evolve to be a pack hunter with a pack leader and we will have loyalty down. This behavior evolution coincides with their new jungle environment and its predators that don't leave corpses lying around.
* **Age.** *Gnolls reach adulthood by the age of 5 and live to around 30.* In zoo's Hyena's live for an average 12 years and a maximum of 25 years. So the age isn't out of the question.
* **Size.** *Most gnolls are over 7 feet tall.* Similar to how humans evolved height to look over talk grass, then when the gnolls leave the jungle, the height can only benefit their light frame.
* **Darkvision.** *You can see in dim light within 60 feet of you as if it
were bright light, and in darkness as if it were dim light.* Considering that the hyena is already nocturnal, this, like the age is already handled.
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[Question]
[
In the popular [merfolk](/questions/tagged/merfolk "show questions tagged 'merfolk'") topic, I always use the model of marine mammals, not water-breathing fish-like animals. They breathe *air*, that turbo-charged 20% oxygen fluid that enables the scale of metabolism that we enjoy as warm-blooded animals.
Recently, Dr. Mason [debunked the Triton Gill](https://m.youtube.com/watch?v=S5ep2vUMJt0) crowd-funding scam (note: I was a major sponsor of the debunking video). Only, he did such a good job of showing how such a thing could not possibly work on a fundamental level that it also destroys any hard-SF portrayal of such a device (or gill implant).
In particular, a liter of air contains 200 ml of oxygen, and a liter of water contains (if you could remove it all perfectly) 5 to 10 ml of oxygen.
One of the earliest SF stories I dabbled with featured a gill-pack with the appropriate size and weight of a SCUBA system, but was a gill: it seems plausible that near-future technology *could* have a membrane that allowed disolved oxygen to be extracted, and that membrane would be folded and branched to have a high surface area, coming in contact with all the water that passes through, and long enough to process all the water before it passes out the other side.
**The catch** is that you would have to pump about 100 liters of water per minute through the device. In a device, that would be an enormous jet!
For a human-sized/human-metabolism animal, how could you process this much water over your gills? Note that adding to their expanse, such as a long train, would be more tissue to feed, too.
On the other hand, fish like tuna and baracuda exist, that are fast and have red muscles. I suppose they must use their high energy level in bursts only and take a long time to recharge. Exploring that idea is one avenue: but note that the *brain* takes a lot of power all the time (but see [this question](https://worldbuilding.stackexchange.com/questions/28249/does-a-sapient-species-have-to-be-warm-blooded-and-if-so-can-it-still-be-a-rep). But also, cold water has more oxygen.)
In short, how can be have a water-breathing animal that's not sluggish/torpid and has a large brain?
[Answer]
One reason could be your water has just an higher oxygen level. (depending on how flexible your world is).
Also if I understand the video correct it assumes that you breath out much of your oxygen for calculating the 100 liters of water. You could get much lower if you calculate with the value that is used by the body. Following numbers I use came from the [German Wikipedia](https://de.wikipedia.org/wiki/Atmung).
A adult human takes between 11 and 15 breaths per minute and has a lung volume of 0.5 l.
21% of the air we breath in are oxygen, 17% we breathe out. So we use 4% of the air we breath as oxygen. That is 220 ml to 300 ml.
If I take the oxygen level of water from the video (0.01 l oxygen per l water down to 0.005) that means if I could get all the oxygen from the water I *only* need 22 (best case) to 60 (worst case) l of water per minute.
Best case is higher oxygen level with lower consumption, worst case the lower level with higher demand.
In another thread for mermaid it was proposed that the long hair could be used for extracting oxygen. Using such big and wide spread organ to absorb oxygen would increase the water that can be used.
The last thing I could imagine would be a lower metabolism while in water. If they can use their lungs there energy demand will get higher, their body temperature rises and maybe even getting more intelligent.
[Answer]
How about a species that has both gills and air breathing? It may be less plausible to have both, but if the species could alter metabolic rate/brain function, it could use a higher metabolism when at the surface but reduced metabolism while staying underwater. The higher brain functions would be shut down while gill breathing, resulting in a more instinctive rather than rational reaction to occurrences underwater.
[Answer]
Great White Sharks and Mako sharks are warm-blooded (well, heterotherms, anyway). Could you use some of their biology? Give your creatures a more efficient respiratory pigment in their blood than sharks have and they can grab more oxygen for every litre of water that passes over the gills.
[Shark heterothermy](http://www.sharkwatchsa.com/en/blog/category/482/post/987/shark-fact-29-02-2012/)
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[Question]
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---
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## Context:
I'm designing a "demi-universe," accessible from Earth (via appropriately supernatural means), that has the following internal topological property: given any point in 3D space, and any 3D vector, the ray from that point along that vector will eventually reencounter itself from the opposite orientation. In less formal terms, **if you go in any direction, *in all three dimensions*, you will eventually "loop" back to where you started**:
* If you go east, you will eventually arrive at your starting point from the west.
* If you go west, you will eventually arrive at your starting point from the east.
* If you go north, you will eventually arrive at your starting point from the south.
* If you go south, you will eventually arrive at your starting point from the north.
* If you go up, you will eventually arrive at your starting point from below.
* If you go down, you will eventually arrive at your starting point from above.
Moreover, in any of these directions, or any other you could care to name, the distance required to make exactly one complete "loop" is the same (and is large by human terms but still significantly smaller than Earth's diameter). These conditions force the world to be geometrically a hypersphere, or rather the "surface" of one.
In addition, the world has a form of gravity with a strength approximately that of Earth's, but always pointing in the same direction (which thus becomes "down" by virtue of there being no other way to distinguish directions).
Assume that this world contains air with approximately the right pressure and composition for humans to breathe comfortably, and further assume that there are mechanisms that will "refresh" the air's composition as humans convert the oxygen content to carbon dioxide. Also, assume that any food and material requirements that can't be produced on-location can always be imported from Earth without too much trouble, and that any unusable waste can be dealt with similarly. Finally, assume that the world is a completely closed system aside from any deliberate transport of matter and energy to and from Earth (and the above-mentioned air refreshment mechanisms).
## Question 1:
What kinds of weather patterns can one expect from a world like this?
## Question 2:
What sorts of societies would form from long-term human colonies within this world?
[Answer]
## Answer 1:
The weather will be quite boring. As you say
>
> "assume that the world is a completely closed system aside from any
> deliberate transport of matter and energy to and from Earth"
>
>
>
That means the system will be nearly at its maximum entropy. Everything is the same temperature. Hopefully that temperature is hospitable to life. The only gradients that exist are there because of this portal from Earth, and that is most likely a very small source/sink in a very large world.
## Answer 2:
While it might be novel to visit this place, it wouldn't be a very interesting place to live. There is nothing that I know of which would be easier to do in such a place (except not get lost if you can keep going in the same direction). All the energy that people need to grow food would need to be brought by the humans. The societies would be similar to those that might develop deep underground, but there couldn't be very much branching from Earth culture because constant deliveries of supplies and energy would need to be made from Earth. Isolation would mean death.
[Answer]
Let's start with the size of the hypersphere. You say
>
> the distance required to make exactly one complete "loop" is the same (and is large by human terms but still significantly smaller than Earth's diameter).
>
>
>
The Earth's diameter is about 13,000 km. I think a hypersphere circumference (length of the "loop") of 1200 km (about 9% of the earth's diameter) can be considered "significantly smaller", so I'll take that value. Thus, since the circumference is a great circle, we can calculate the radius of the hypersphere as $R = 1200\,\mathrm{km}/(2\pi) \approx 200\,\mathrm{km}$. This is certainly large enough that for human-sized objects, the curvature effects are negligible (that is, the space feels flat; being in the hypersphere doesn't feel fundamentally different than being in Earth's space). The total volume of the hypersphere is $2\pi^2 R^3 \approx 16\cdot 10^{7}\,\mathrm{km}^3$, According to [Wikipedia,](https://en.wikipedia.org/wiki/Orders_of_magnitude_%28volume%29) this is about the volume of Lake Baldegg, Switzerland.
Since you assume a gravitational field pointing towards the "south pole" of the hypersphere, all the landmass will be collected in a sphere around that point.
As of your comment, the landmass should fill 20% of the hypersphere. According to my calculation (see section "Calculations" below) this gives a landmass with surface area of about $11 R^2 \approx 440\,000\,\mathrm{km}^2$. This is according to [Wikipedia](https://en.wikipedia.org/wiki/Orders_of_magnitude_%28area%29) between the size of Japan and the size of Spain.
Now, what would you see when you stand on that surface? Well, let's start with what you see if you look parallel to the surface. I'm assuming that the land mass is the only thing blocking sight. Since the light follows a great circle, and the landmass fills less than half the space, the view in that direction is not obstructed, and you see the back of your own head. Now you'll immediately object: The back of your head is 1200 km away, so you won't really see it. But that doesn't consider the spherical geometry: All rays re-converge, as if there would be a huge magnifying glass between you and the back of your head. Indeed, the rays converge twice, once on the opposite side of the hypersphere, which is somewhere up in the air (so if something happened to be at that place, say a bird flying by, it would obscure your head), and due to that extra crossing, you'll see the back of your head upside down.
Next, let's look at the floor. Since the rays, following great circles of the hypersphere, apparently are bent away from the land surface, the surface looks more curved than it is, as if the sphere you're standing on were smaller than it is. Behind the horizon begins the back of your head, and when you follow upwards, you'll see the rest of your body from behind, until you reach the floor you're standing on. That will then reach up to the "sky", as if in a gigantic cave. Note that all that is still turned around by 180 degrees.
Apart from these optical effects, I don't expect anything particularly interesting in the hypersphere. As the others already wrote, there will be no weather to speak of. Any humans living there would not form a colony, but more the equivalent of a moon base, where everything important has to be brought from Earth.
---
# Calculations:
If $w$ is the 4D coordinate along the "axis" of the hyperball, the volume of the landmass (which is spherical in the hyperspherical geometry) is
$$\begin{align}V &= \int\_{-1}^{w\_0}4\pi\rho^2\,\mathrm dw\\
&= \int\_{-1}^{w\_0}4\pi(1-w^2)\,\mathrm dw\\
&= \left.4\pi\left(w-\frac13w^3\right)\right|\_{-1}^{w\_0}\\
&= 4\pi\left(w\_0-\frac13 w\_0^3 + \frac23\right) \stackrel!= \frac15\cdot2\pi^2
\end{align}$$
So we end up with the equation
$$w\_0 - \frac13 w\_0^3 + \frac23 - \frac\pi{10} = 0$$
Solving this numerically with Mathematica gives as only viable solution $w\_0 = -0.369295$.
[Answer]
Question 1: No weather
You have even heating everywhere so beyond occasional breezes there is nothing to generate atmospheric currents. You have no sources of atmospheric water so no evaporation to form clouds and no precipitation.
Question 2: None, they are all dead.
With no water cycle there can be no life here.
Assuming this was somehow fixed (for example water magically appearing in the sky) then it would have very little affect on society. The world you describe is large enough that for most people the details become irrelevant. The lack of compasses might make navigation harder. The lack of seasons would mean there wasn't much need to develop food storage techniques and shelters could be simple.
A good starting point would be looking at our own tropical societies, places that live with very little seasonal variation.
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[Question]
[
This is the first question in my *Arctic Airships* series of questions. The second one is [Arctic Airships, Part 2 - Navigation](https://worldbuilding.stackexchange.com/questions/8682/arctic-airships-part-2-navigation).
**The premise:**
An Earth-like planet plunged into an ice age roughly 2,000 years prior to the story. The ice sheets extend to a latitude of about 50 degrees above and below the equator, though I this story (so far) takes place in the planet's Northern Hemisphere. At a latitude of about 67 degrees north are a series of ten or so small villages, each with a population of 500 people.
The technology is roughly that of the late Victorian era - so no automobiles. In fact, there is no clear boundary between icy land and frozen-over water, and it would be extremely dangerous to travel overland in any way. Submarines have not been developed, nor have airplanes; a lack of fossil fuels means that internal combustion engines are nonexistent.
**The airships:**
The transportation system between villages is an informal fleet of semi-rigid airships. Each is privately owned, and may range in size from 100 feet to 500 feet (30-152 meters) - nothing spectacular. They are a motley bunch, ragged and as patchwork as can be; the one thing that ties them together is that they provide the villages' primary source of power. The one big stride forward has been in photovoltaic cells, and the airships are outfitted with them along much of their body. Wind and hydropower are impractical for various as-yet undetermined reasons; fossil fuels are nonexistent and nuclear power is way too advanced, so this is the only power source for the villages. The engines run on electricity; there are anywhere from four to ten engines on each airship, depending on its size.
The villages are space about 10 miles apart on average - not a lot. The airships provide a sort of taxi service, bringing passengers and freight. The majority of the time, though, they stay aloft, gathering the Sun's energy (ground-based stations are impractical because of the icy terrain, and for some reason airspace near the ground is unstable; cruising altitude is the only place to be).
---
Do the airships provide a feasible method of generating power? If so, about how many would be needed to provide the villages with enough electricity, (bearing in mind that the airships consume electricity and stay aloft for long periods of time, as well as that there may not be as much sunlight here as in other parts of the world)?
---
**Clarifications:**
The solar power generation rates and airship engine efficiency rates are comparable to the solar power and airships of today. The engines are comparable to high-class electric motors in both size and efficiency, such as [Solar Impulse](https://en.wikipedia.org/wiki/Solar_Impulse_Project).
Power is released at each village via charging cables when the airship docks. Electricity is stored onboard in the form of rechargeable batteries which have an essentially infinite lifespan. The energy is needed only for household use - there's no large-scale industry in this world, just small pockets of people. The houses are decently insulated and pretty energy-efficient insofar as they retain heat very well.
[Answer]
<http://nunavutenergy.ca/Renewable_Energy>
I'd use Nunavut (Canada) as a decent reference point as to solar generation.
"Locations along the Hudson Bay coast in the Kivalliq region receive the highest amount of solar energy in Nunavut. The amount of solar energy that reaches coastal areas of the Kivalliq region is comparable to the amount of solar energy that reaches southern Quebec, much of Ontario, and the Maritimes."
They actually get a decent amount of sun, assuming the Solar cells are put at the correct angle. If you add in these airships are over top of clouds, you should get an added effect of sunlight reflecting from the clouds and amplifying the amount of sunlight actually striking these panels.
As far as energy generation goes, these ships should be able to provide a decent amount of power...more than enough to power a small colony.
That said, there are several challenges:
Most electricity we use is generated 'on demand'...there is very little for storage, energy is needed and we burn fossil fuels to meet the demand.
In this scenario, during night times (and exaggerated during winter months) there are large periods of the day in which there would be no light and therefore no energy. If the colony is far enough north, you would even get periods of 0 sunlight for around 2 weeks.
This means to be truly feasible, you need to either have the population consume energy in time with the sunlight (this includes 0 light during evening hours) or have some advanced version of electrical storage.
Simple solution is they've developed capacitors capable of storing large amounts of energy, or perhaps some battery technology that's capable of transferring to chemical energy for later use.
As more of a social solution...you use the energy when you have it and don't use it when you don't have it. It would give a period in the summer where 24 hour sunlight provides around the clock energy, and a period of 24 hour darkness where there is no electrical use (society tends to hibernate during this time). And of course in-between hours...the difficulty here is most of the population has high points of energy needs, along with low points. Not many of us use electricity in the afternoon....we are off earning a living and other tasks. After dinner, we are consuming electricity at our highest rates...so there would need to be a method of distribution or (once again) some manner of storing the energy during low use periods to use during high use periods.
I'm a little torn on the idea of a gigantic power cable dangling off an airship though. Kinda seems like an anchor pulling you down that you'd have to fight to keep afloat.
added note on daylight:
75 degrees is a long ways north and you're probably not realizing how long the day and night actually are. The transition from 100% daylight to 0% daylight occurs unreasonably fast. cool little tool: <http://astro.unl.edu/classaction/animations/coordsmotion/daylighthoursexplorer.html>
At 75 degrees, you are looking at roughly Nov 3rd to Feb 7th of complete darkness (3 months, around 100 days). From Feb 7th to May 1, this transitions rapidly from 0 hours to 24 hours of daylight. May 1 to august 10th is 24 hour sunlight (3 months, around 100 days?). And then back to a quick transition to 24 hour darkness by Nov 3rd. Little odd that the transition periods are shorter than the 100% darkness or daylight days.
At 67 degrees, you get about 4 weeks of 24 hour darkness/daylight. I think this is more what you are considering. Apparently at 90 degree's, you get 24 hour daylight or 24 hour darkness with no in between. Sept 22nd - That would be a weird day to see the sun just disappear.
[Answer]
As someone who is working with the winter theme for several years now, I feel partially obligated to chime in.
Really, really cold weather is a complex stuff. It introduces several complications to things that otherwise would be really straigthforward. I could talk about several diferent factors that one should take into account while creating something like this, but for now I will focus on your energy issue, to keep the scope to the question.
---
***Why do we need power?***
Power, be it in the form of heat from a fire or generated by some electric means, is crucial to any kind of more civilized human population. You use it to warm up your kids when it's cold, to work metal, to prepare food, to light up your village when it's dark. We need power to run our machines, to power our vehicles. You need some form of energy to do almost anything more complex on a human settlement, and from where that power comes from really makes a difference.
***Conversion = Loss***
Anything you do with your avaliable power source will reduce the avaliable amount of power, be it converting it from one form to another, transfering it or just *storing* it. Even the most advanced batteries we have today can't really store energy forever, losing it slowly over time.
While the sun generates a ton of power [citation needed], you can't exactly tap on it without some big losses.
[Let's take this site into account](http://photovoltaic-software.com/PV-solar-energy-calculation.php), and do some quick math.
According to this site, the global formula to estimate the electricity generated in output of a photovoltaic system is something like this:
```
E = A * r * H * PR
```
Where:
* E = Energy (kWh)
* A = Total solar panel Area (m²)
* r = solar panel yield (%)
* H = Annual average solar radiation on tilted panels (shadings not included)
* PR = Performance ratio, coefficient for losses (range between 0.5 and 0.9, default value = 0.75)
So, let's start.
Lets suppose that, somehow, your airship have $9000$ square feet $(30ft\times 300ft)$ of usable solar-colecting area. That's a really big airship, according your parameters. That gives us around $850m^2. $
My source says that Norway receives around $200\text{kWh}$ per square meter... *per year*. So, let's do a really crude math and split that evenly year-around:
* $200 / 365$ $\approx = 0.55\text{kWh}/m^2$ per day of solar exposure, assuming $100\%$ efficiency.
Most commom modern solar panels of the have something around $15\%$ of efficiency collecting solar power, using advanced manufactoring processes.
That means that a $1m^2$ worth of modern solar panels on a norway-like have a daily output of:
* $0.55 \times 0.15 = 0.0825$ $\text{kWh}$ per square meter per day.
Performance Ratio takes into account disturbances to the solar panels, like dust, snow, a few clouds, power losses generated by the internal structure of the solar panels, and things like that. The default value for modern solar powers is $0.75$. So, taking that into account:
* $0.0825 \times 0.75 \approx= 0.062 \text{kWh}$ per square meter per day. That's around 62 Wh *per day* per $m^2$.
You could use a light bulb for something like an hour!
So, let's equip our airship with a ton of solar panels.
* $0.062kWh/m^2 \times 850 m^2 = 52.7 \text{kWh}$ worth of power on a daily basis.
If you devise a super efficient electric heater that uses 1kWh per family (normal heaters use around 1.5kWh to heat a single room) , and keep it on for a full day, one of such ships can only suply the heat demands of *two* houses.
You would need several airships to power all the houses on your village confortably. Each 850m² airship could power:
* The daily heating needs for 2 houses, or
* 36 modern 60w Ligth Bulbs for a day, or
* 42 10-minutes baths using a 7500w shower, or
* Cook food per 30 minutes 20 times a day using an electric oven.
Most people around the world that really needs heat use some type of oil for heating and coal or gas for cooking. Electric power, while convenient, can become expensive really quick if you don't keep an eye on your usage. I think that, if you want those things to fly around AND power your houses, *each* family would need at least one 850m² airship.
Also, your airships would be really heavy. Since you don't have wood, you would need some type of ligth material to build then, and a huge amount of power to make them take off. Unless you use some kind of heated gas, like helium, to make them "ligther than air", they can't really fly solar-powered. And, if they do have some gas to make them lighter, they would be really, really propense to accidents, and you can't repair them anymore since you don't have the resources to build them!
---
I would like to contribute a bit more to your scenario with some extra considerations:
The Major issues:
* So far north, during an Ice Age, you have an ice sheet. Plant's can't grow on ice sheets, since the soil is far away from the surface.
* Your people don't have wood. You can't grow trees on an ice sheet!
* Your people don't have paper. Since you don't have trees, unless they write directly in leather or stone, they don't really have anything to write on.
* You don't have rubber or easy access to any insulating material, so... that would be a huge problem.
* All of your homes would be glacialy cold. Again, since you don't have wood, you would need to build houses out of stone. I don't have any idea about *how* they would build such houses.
* Your people can't really mine for any type of mineral. You can't work almost any metal with such tech without fossil fuels or some other type of non-electric power. Since you can't work metal, you can't create the tools needed for true mining.
* Even if at somepoint your people had something avaliable to create tools, tools need constant replacement. They break, become dull, rust, etc. Bone tools only take you so far, you need true metal tools for complex works.
* You don't have any type of cloth avaliable, only leather. Even if you had sheeps, you won't be able to shear them (missing tools) or weave the wool (can't build the machinery to weave it).
* You don't have inks. Since you can't mine and can't really travel, unless you have a ton of exotic, colorful herbs that grow on the extreme cold, your people can't relly color stuff.
* Food is an issue. You basically only have meat for food, and you can't hunt. Your people can't use guns, since they lack the minerals to create them, and they can't use bows, since you don't have wood or other suitable material. You can't use spears, to - no wood! Caribou are really fast animals, and even a baby-caribou can run extremelly fast. Unless your people hunt using stone knives and ambush tatics, your people have some problems. Actually, I don't even know what your caribou would eat, since you can't have any type of plant matter on the surface of an ice sheet.
* You don't have glass. Even if you indeed have sand, you can't create a furnace to melt the sand to create glass. That means, among other things, that you also don't have any kind of lightbulb around anymore.
* It is not possible to have a SolarImpulse-class engine with your avaliable tech. To manufature such engine, you need all the tech around it - which includes high precision, automated manufactoring and advanced eletronics.
My suggestion to you is, if you really want to focus on airship travel, to create a canyon-based world. That way you can use all the normal stuff - trees, fossil fuels, etc, while still barring overland and aquatic transport. People would live on the top of extremely high and extremly steep canions ([something like this](http://40.media.tumblr.com/3cbbb27ddf7eba87f94764a9ab7cb55d/tumblr_nfir79XvGT1r8l89mo1_1280.jpg), just way higher), so they really would need airships to move around if the canions are complex enough. Also, if you create them high enough, they could be way above the clouds, so you can't really see what's down there.
Just my 2¢!
[Answer]
Since we are working within a high latitude ice desert, we have the great example of Antarctica to work with. During the summer, you would be getting around $8\space\text{kilowatts per m}^{2}\space\text{per day,}$ which is impressive.
.
About $0.3\text{ kilowatts per m}^2 \space\text{per hr}$, on account of the three months of constant light at $75$ degrees. During the winter though, you would have nearly no available energy: maybe $0.5\text{ kilowatt hours per m}^2\text{ a day}.$
Since you specified the size ($100-500$ ft long), I'll take a historical sample in the within that range: the Zeppelin LZ 120 Bodensee, at $396$ ft long. It had 4 245 horsepower engines; this is about 183 Kilowatts. Combined, $732$ kilowatts.
Assuming perfect efficiency (which you wouldn't have, the best we have today is $44\%$ efficient), you would need about $2200\space m^2$ to power the ship ($732\text{ kW/0.33 kW per m}^2$.). This is larger than the area of the top of the airship, meaning that it wouldn't be able to power itself constantly. But the airship wouldn't always be moving, so it could charge during the most of the day it's not ferrying people. I imagine villages so small wouldn't need many ferries. A society like that of the early 1900s wouldn't require too much energy, so the airship could provide a few hundred kilowatts to the village (so like a kilowatt a person a day). Whatever the case may be, your people wouldn't have a whole lot to work with.
In the end, winter seems to be a nearly impossible obstacle to overcome. No sun would grind everything to a halt.
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This post is unrelated to feasibility, but I'd like to give a suggestion as to how to make this world a bit more feasible.
Most of the comments discussing feasibility follow tow lines: why are these people living in such an utterly inhospitable environment, and how are they manufacturing airship components and advanced fuel cells up there.
Over the course of 2000 years, I'd expect people to expand beyond a few small villages, given sufficient resources, and to adapt to the environment better than just about anyone on earth right now. It seems like, in order for people to live in a small population that far north, they need a very compelling reason to stay. In a world depleted of fossil fuels, however, there is one good reason to venture to Northern Alaska in an ice age: oil.
What if these people have been sent here from regions further to the south that need oil products for producing their advanced technology? The airship nomads could harvest oil without even needing to drill for it if they're experts at scavenging old technology buried under the ice. Without having any knowledge of the drilling processes, they could mine down through the glaciers to the old prospecting towns and drain oil, lubricants, and anything else valuable from the old oil drilling equipment, as well as salvaging machinery.
All of this could get flown south on their airships, which may not be as good as skis/kayaks for short, overland journeys, but would definitely be superior for transporting large quantities of goods given that the Northern ocean is completely iced in. In exchange for their oil products, which they themselves don't use, but which are more valuable than gold to the southern industrialists, the airship nomads receive solar panels, capacitors, and other technological goodies from their southern neighbors. They themselves don't have the technology to produce such things, being of a Victorian level of technological development without the infrastructure in place to really go much beyond that, but they can trade for some of them.
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Living so far north for such long time would be easier if your heroes adapted to rugged life of [Eskimo](http://en.wikipedia.org/wiki/Eskimo) (if over sea, fishing and hunting) or [Sami](http://en.wikipedia.org/wiki/Sami_people) (if overland, following caribou herds).
Eskimo way is more flexible (easier to get out to south - but for unknown reason they never did: when polar explorers met them, they thought Eskimo are the only people on Earth), so if you want your heroes to be stuck, put them beyond high mountain range and make sea narrows around it too turbulent to freeze. Unlikely will any plant grow there, it is all hunting, fishing and gathering.
Good energy source would be seal and whale blubber. You need to be aware of [rabbit starvation](http://en.wikipedia.org/wiki/Rabbit_starvation) - if diet consists from lean meat only - you need fat, and [adequate level of fat is important for brain development](http://www.ncbi.nlm.nih.gov/pubmed/20329590). Your people will starve on lean caribou meat diet. Fishing salmon is other good idea (if you do not want to go to ice to hunt seals).
Small isolated groups of people are at risk to lose technology, even if very primitive, read article about [Tasmanian tribesmen](http://discovermagazine.com/1993/mar/tenthousandyears189) link thanks to @Serban Tanasa - about how 5000 Tasmanians lost elementary skills like fishing and bone tools.
If you really want to fly out over the mountains, better bet would be hot air balloons heated by blubber. Not sure what would be good light material to make balloons. Maybe you can establish some fish with [big swim bladder](http://en.wikipedia.org/wiki/Swim_bladder), [fill it with methane](http://en.wikipedia.org/wiki/Arctic_methane_release), and use it to be lighter when going over mountains.
BTW those high mountains to the south your heroes need to cross also make huge shade, making your solar energy even less plausible. Just sayin'.
I promised a link about part of Canada NOT covered by glaciers during last glaciation period: [Cypress Hills](http://en.wikipedia.org/wiki/Cypress_Hills_%28Canada%29) - the northernmost point in North America that remained south of the continental ice sheets during the Wisconsin glaciation.
There is no reason why group of determined and well provisioned explorers, during decade with improved weather, could not find a pass over mountains. People cross Himalayas. Even crossing glaciers. In worst case they can go multi-camp campaign, most people hauling provisions for next year attempt. There should be some legends about better life farther south - you can use that drive to power your story, instead of solar airships.
[More interesting facts about Arctic methane](http://www.theguardian.com/environment/earth-insight/2013/aug/05/7-facts-need-to-know-arctic-methane-time-bomb)
You may have hard time to maintain metal-oriented technology with so little fuel available for smelting. Your people may revert to [copper-age technologies](http://en.wikipedia.org/wiki/Chalcolithic) if they can find a vein of 99% pure copper like [Old Copper Complex](http://en.wikipedia.org/wiki/Old_Copper_Complex) - your people don't have to melt it, so no fuel is needed, just hammer it to shape they need.
Funny how Amerindians abandoned best copper mine of all Bronze Age 3K years ago.
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Is it possible that a group of "elite" humans have highly advanced technology, but have kept it hidden?
For example, is it possible that some people already had powerful computers and automobiles (like modern one) several decades ago (say, in the 1950s), but hid it from "common people" ?
And maybe later they gradually introduced these technologies for the "common people". Or maybe they didn't introduce those technology and they still have more powerful equipment.
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Possible, yes. If you don't mind altering history a bit. However, beware introducing things that are used publicly. Computers, sure! You can have one in your basement/vault/secret hideout. Automobiles, no. You're going to drive it around and you need space for that. It's much harder to protect.
Back in 1950, communication on a global scale was still, well, bad. I can't source this claim, to a quantifiable degree, but there was no internet. There might be global communications for politics, industry and academics, but certainly not for the common people.
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To get superior technology, without fantasy elements, you need:
* Consumable resources
* Brainpower
* Static resources
Or more simply put, you need materials to experiment on, tools to experiment with, and scientists to do the actual research and develop the goods.
I imagine that any "elite" group of people is very, very, very rich.
So a lab and shell companies that buy a truckload of supplies more or less each month are easily set up.
But the brainpower, that's a tricky one. Academics is based on peer research. You (for the academics here, I hope I got it right) spend your life working in a field, trying to find out why something works why it does. A lot of time goes into this. You work based on the research of others - others that have researched the things you research before.
**Academics is a culture based on sharing.**
This contradicts the culture where an elite group **secretly** has superior tech.
Communication enables sharing. Thus, for this to be viable, you'll have to take away communication. This could work in 1950, but in modern times, I don't think it's viable anymore. Nearly everybody in developed countries carries a camera and a global communication device.
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Only for a short time.
The word here is "scale". Unless you have reached the point of singularity, it is highly unprobable that the few dozens or hundred of scientifics/technicians working secretly for you can keep any advantage against hundreds of thousands or millions of scientifics/technicians that work "publicly". Even if you have in your pockets "the best of the best", that would not be enough.
And, you will want not to have more than dozens or hundreds and not more because otherwise you could not keep such project secret. Also, your project is generating (almost) not revenue compared with those projects that end up being used to build cars, washing machines and instant pudding.
Add into the mix that technological advances are unpredictable. Maybe in the 40s you had the best experts in the design of electronical valves, and gloated about how you could build the best televisor sets in the world. But you could not foresee that some degenerate would invent the transistor, making your advantage moot.
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There is one well known example in the real world - computers.
A lot of computing technologies that is considered to have been invented in the US was actually already implemented and used at Bletchley Park (or its successor GCHQ) in the UK. But due to the Official Secrets Act was not allowed to be disclosed to the public.
One specific example is public key exchange. Today, we call the algorithm for public key exchange the Diffie-Helman key exchange due to the first published practical algorithm by Whitfield Diffie and Martin Helman. But the first implemented algorithm (which turns out to be essentially the same) came almost a decade earlier out of work done by James Ellis at GCHQ.
There is a slight difference between what happened here and the scenario you mentioned. Instead of gradually introducing computing technologies to the public the UK government **never** introduced them. Instead they were only declassified long after "the public" have re-invented all those technologies themselves.
The net effect is that while the UK government spent a lot of money developing computers and algorithms none of them could be commercialized, thus none were commercially successful. Instead, re-inventions of those technologies in the US became commercially successful and were re-imported into the UK for public use.
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For a fiction story, one could, of course, postulate a lone genius or a small group of geniuses, living in some isolated or segregated community, and keeping all their inventions secret.
Some technologies are not useful on a small scale. There'd be little point in building a railroad network, for example, if your secret cabal all live in one building. Where will the trains go? An assembly line to produce one car per week isn't really an assembly line. Etc.
Some technologies are hard to hide. If you invented the airplane 50 years before anyone else and you are flying it around, wouldn't someone see you sooner or later? Maybe you hide behind stories of UFOs or some such, but some things are hard to really use in hiding.
But the big catch in practice is that advanced technology often requires a large and complex infrastructure. Suppose someone in the mid-1800s -- let's call him "Charles" -- got a stroke of genius and figured out how to design a computer. How could he really build one? It's awfully tough to build a factory to make integrated circuits in your garage using a crowbar and a sledgehammer. He could try to build a mechanical computer using the tools and materials available, but even this would be very difficult. The supporting technology just isn't there, and it would be very hard to build it all from scratch.
A lot of modern technology requires bringing together materials and expertise from many people. The economist Milton Friedman once said that no one in the world can even make something as simple as a pencil. It takes many people. The wood may come from the Pacific Northwest. The lead may come from West Virginia. The metal may come from Minnesota. The rubber for the eraser probably comes from India. And then other people have to cut and plane the wood, smelt the melt, etc. People have to ship all these materials around. There are probably ultimately hundreds of people involved in making a simple pencil.
You could do it if you had some huge organization that can draw resources from a large number of places and people, and then operate in secret without having to account to all these people for what they're doing. Like a government.
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I am working on an earth-like empire (actually, an alternate-universe Earth with Belgium as the global powerhouse) which, instead of using fossil and nuclear fuels, uses light as their principal form of energy. The idea is that, apart from just the raw energy in light, they also use patterns of light and dark for everything, from powering their machines, houses and vehicles to waging war with it. They are about 500 years in the future compared to our time (but still human), and they have figured out a way for feasible interstellar travel using light (*they* have, *I'm* still working on it).
I'm currently trying to figure out the following issues:
1) What could push an entire planet to focus on light instead of fossil and nuclear fuel? One option would be a nuclear war that scared people away from using nuclear fuels, but that has been done in Blake and Mortimer and I don't want to use that.
2) What method could they use for interstellar travel? For regular travel, my idea was that they figured out a way to essentially travel through the power grid. However, that method can't work for long-distance travel. I could say that they managed to increase the speed of light and use light beams to travel there, but that's been done in Blake and Mortimer as well as Futurama.
3) How can I use the light-based technology to implement a darker edge to the culture? I don't want to create a purely utopic society. I want the empire to look nice for someone who just entered it, but anyone who spends more than a month starts to sink into a gray-and-gray moral zone.
A solution would likely involve different physics from those in our universe. I don't yet have a plan for these physics, so any suggestions on how they should be changed are welcomed.
## background information about the empire
The empire serves as a background for a science-fiction space opera set in a golden age of space exploration: mankind has settled colonies across the Sol system, and is preparing to expand into the stars. Interstellar explorers are sent out to track suitable habitats for humanity. Someone from our time (the protagonist) lands right in there and gets involved in major events.
The empire itself is a combination of history and fiction: The Belgae tribe was a match for the Roman Empire and became a satellite state and a powerful ally of the Romans. After the fall of the Empire, a number of historical figures born in the empire (or one of the states it conquered) started to systematically take over the rest of the world. around 500 years in their past, the entire world has been unified, but already with significant improvements in technology compared to our stage. It is at this point that they started developing light-based technology.
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Tackling your issues in order:
1. The main reason I would see the planet moving to a light based power source would be some quantum leap forward in the technology. That is, someone has to invent the technology first, and it must be widely regarding as awesome. It must be powerful enough to take on their current energy needs. Most importantly, it MUST be cheap. In order everyone to abandon fossil fuels, this option must be super cheap to implement. There will be very rich and powerful people trying to fight its adoption. To counter those people, the cost must be such that it can be put into place and there is an immediate savings. There are certainly a ton of benefits to this type of power, but the motivating factor would be cost.
2. For interstellar travel I would recommend looking at [Solar Sails](https://en.wikipedia.org/wiki/Solar_sail#Interstellar_flight). Solar pressure pushes on large mirrors to propel the spacecraft. The interplanetary version of this is already being used, so it just needs to be upgraded with some better technology. The hypothetical interstellar version could be powered by high intensity lasers. I highly recommend reading the Wikipedia article!
3. What is the down side to the light based power source? Is there a side effect? My first concern would if there were health consequences to the power source? Do the new power companies need to rip open the ozone layer to get better and more lucrative? Imagine that there are still plenty of ways for energy cartels to develop and exploit the system in an attempt to make more money. (Avarice is always a good motive.)
Is energy distributed fairly across the masses? I hate to just recommend the classic conflict of the haves vs the havenots, but I see this world as having larger and larger skyscrapers, reaching closer to the light source. At the same time, the people down on street level are literally stuck in their shadows, getting very little light.
--I hope this helps a bit, good luck!
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Let's tackle these issues, one at a time:
1. **Why go to light for fuel?** It doesn't cause that much cancer, no overtly deadly byproducts, and the sun makes a lot of it for free. Maybe these people have a very strong sense of environmental stewardship, or they want a system that lasts practically forever. Also, if they have space flight, they could rely on [space-based solar power](http://en.wikipedia.org/wiki/Space-based_solar_power)! As an interesting technical side note, [gamma radiation](http://en.wikipedia.org/wiki/Gamma_ray) *is* both very high energy light and a byproduct of nuclear reactions, so I wouldn't rule out nuclear power entirely! Finally, light can be used to make [solar-thermo-power plants](http://en.wikipedia.org/wiki/Solar_thermal_energy).
2. **Light-Based Interstellar Travel?** [Solar sails](http://en.wikipedia.org/wiki/Solar_sail), all the way! They can be used many times, require no fuel, and if you're tricky with your [orbital mechanics](http://en.wikipedia.org/wiki/Orbital_mechanics), you can go anywhere! (It may just take a while...)
3. **How to find the darker side of the Empire of Light?** Just because they use light for things doesn't mean that they don't have the personalities or problems that we do. Also, [not all light is visible](http://en.wikipedia.org/wiki/Visible_spectrum), so you can have a light-based power conduit that doesn't produce visible light. (Throwing someone in such a conduit may [result in cancer](http://en.wikipedia.org/wiki/Radiation-induced_cancer), or bursting into flames, etc.) There can be inadvertent environmental downsides as well, such as [mining](http://en.wikipedia.org/wiki/Mining#Environmental_effects) for the proper minerals to make the solar panels.
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1. For fossil fuels it would be most likely depletion of the resources. For nuclear fuel, it could be a ban of nuclear technology, either because it could be used to produce nuclear weapons, or due to fear of the dangers of nuclear technology.
2. The most obvious way to use light for interstellar travel would be if they have ultra-strong lasers and use the recoil of the emitted light for propulsion.
3. One possibility is a certain group of people (ruling class, specific corporations, illegal organizations) having (officially or unofficially) the power over the light technology. That power might be used from simple things like denying someone access who doesn't obey their will (possibly camouflaged as technical failure, but in a way that those it is directed at know why it happened, but cannot prove it), to using the light as weapon (again, camouflaged as accident), or even all the way to possibly directly manipulating people's brains through mechanisms we don't know yet (some interaction of light with neurons, or maybe "hacking" the brain through its reaction on subconscious light patterns caught by the eyes).
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Here are three scenarios that could answer the third question "*How can I use the light-based technology to implement a darker edge to the culture?*"
**3a). The dark side shines a light**: A common scenario for future energy is that we have giant solar panels in space, which convert sunlight to electricity and then beam the energy down in the form of microwaves, to a receiver on earth. You can simplify this by assuming they're converting sunlight to microwaves directly by shifting the frequency [1]. Or perhaps they simply have mirrors in space, which focus the sunlight onto receivers on earth. In any case, you have a civilization with potential death-rays in space.
**3b) A thought flickers by**: In animal experiments on the brain, using light to trigger activation in specific brain cells is a common technology, so you could build on this to describe a machine-brain interface. Unplug the cable in their neck and that fiber-optic cable takes in and transmits ambient light in the room. That light could be surreptitiously altered to mimick the signals usually going through the cable, or induce an epileptic seizure.
**3c) You can run, but you can't hide:** There's a whole lot of fiber-optic cables in this society. But we can transmit light at any frequency, including invisible ones, and change the frequency upon arrival to suit our needs. You can do away with a lot of cables if people would just build their houses in a material which is transparent to some frequencies. The light can then be modulated to another frequency inside the house. This cuts down a lot on cables for both power transmission and data transfer but has at least two downsides:
1) You risk frying people inside the house or someone's neighbour, if they get in the way of the beams, happen to stand at a focal point or a place where waves interfere constructively. This happens rarely, but is as accepted a risk as the risk of fires from household electronics and car accidents are in our society.
2) Everyone's houses are transparent in some frequency, so you can illuminate a house and, with the right camera, see everything that's going on inside. Everyone's data transmissions are also readily available to bystanders unless they use encryption.
[1] <http://www.newscientist.com/article/dn3750-alchemy-with-light-shocks-physicists.html#.VL5Ss0Z0xaQ>
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>
> 1) What could push an entire planet to focus on light instead of fossil and nuclear fuel? One option would be a nuclear war that scared people away from using nuclear fuels, but that has been done in Blake and Mortimer and I don't want to use that.
>
>
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Light energy as we know it today is hardly sufficient replacement for fossil and nuclear fuel, so it would either because they found a breakthrough (that we have yet to discover) or they fear the use of polluting the planet through nuclear war or otherwise. However, I find that "fear of polluting the planet" is a weak reason. If we were still waging war, it would be because there are still some people that are looking out for their own best interests and hence you wouldn't likely see everyone begin using a lesser form of energy for the "betterment" of mankind.
Therefore, the reason would have to be advantageous. My idea is that they discover a form of radiation that comes from light that can not only be transformed into energy, but through quantum mechanics, it can also be teleported. This means you can have devices that don't require charging or batteries and work anywhere, so long as the plant collecting light energy is active (the connection between the device and the plant could be through quantum entangling or it could be by proximity). The devices can also be incredibly thin, even transparent.
This would issue in a new age of technology shortly thereafter. You begin seeing weapons being created to harness this power, likely storing the energy and releasing in bursts. It would become far more practical to use in a war scenario since you no longer need ammo, you have no mechanical components so it is less likely to break, and it is still just as lethal as a pistol or even a sniper rifle. For the same reasons, you would see siege weapons begin to favor light energy over projectiles since you'd obviously prefer to burn a hole through a tank rather than explode a projectile next to it (which if it is heavily protected, it could resist). This might lead to other technologies, always through light energy, that would provide shielding against light-based weapons.
>
> 2) What method could they use for interstellar travel? For regular travel, my idea was that they figured out a way to essentially travel through the power grid. However, that method can't work for long-distance travel. I could say that they managed to increase the speed of light and use light beams to travel there, but that's been done in Blake and Mortimer as well as Futurama.
>
>
>
A theorized possibility for interstellar travel has been to use a large reflective parachute [known as a Solar sail](http://en.wikipedia.org/wiki/Solar_sail) facing away from the nearest star. The light coming from the star would continually reflect off the parachute and push the spacecraft faster away. This approach seems to have the best long-term results, approaching even near the speed of light given enough time. It seems logical that such a civilization would combine the shielding technology with the parachute, initially using the shielding to reflect off high-powered lasers to get an initial boost, then relying on the star's light to continue pushing away (shielding presumably consumes energy, so it isn't practical to think that it would stay on, however, depends if realism if what you're after or not).
>
> 3) How can I use the light-based technology to implement a darker edge to the culture? I don't want to create a purely utopic society. I want the empire to look nice for someone who just entered it, but anyone who spends more than a month starts to sink into a gray-and-gray moral zone.
>
>
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1. There are all sorts of ways you could do this. In the episode [Justice](http://en.wikipedia.org/wiki/Justice_%28Star_Trek:_The_Next_Generation%29) in Star Trek: The Next Generation, there is a utopian society which enforces laws by using only one form of punishment: capital punishment.
2. Suppose they find a way of preserving your brain's state on a computer as a way of achieving immortality. The government could abuse this system by forcing people to do what is asked of them by the government or else you would not be able to preserve yourself on a computer in this way. These people would be ostracised as a consequence, and so you would end up with a culture with very few people that resist the government, or do so in secret. Naturally people who have already been immortalized in this way must do the government's bidding or risk getting deleted.
3. Suppose they find a way of harnessing light energy to convert into matter, and food can be fabricated given enough energy. The government uses this to force people to do the government's bidding by threatening to reduce their energy rations, not because not enough energy exists but because they wish to have control. The government could hide this just the same by claiming the former.
These are just a few ideas, though I think there are many other ideas you could use. Really any dystopia would do in this case. The light energy technology could simply substitute any technological requirement before such a scenario could become possible.
I hope that helps!
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I want to be able to apply tools or methodologies to help ensure consistency in my world. For example:
### Burning world
Imagine a planet with a land mass around the equator on which a great fire rages East to West at a rate allowing for regrowth by the time it gets back to it's starting point, so that it never ends. It would interrupt suspension of disbelief to see buildings on such a planet that are susceptible to burning and are too big to be built quickly in the time between one passing of the fire and the next. Similarly I would not expect to see trees taller than can grow in the allowed time, unless they have some way of surviving the fire. I would expect to see either short, young trees, tall spindly fast growing but young trees, or old trees with very thick spongy fireproof bark and a shape reflecting a growth pattern of repeatedly having the smaller branches burned off and regrowing from the older, thicker branches.
### Slow quiet world
Imagine a world where travel is slow and there is no electronic telecommunication. A journey of more than 100 miles cannot be completed in a single day. In such a world foods available in a market should be either local or long lasting, in order for it to be realistic that they reached the market in sufficiently good condition to sell. Similarly news of events from the previous day should only cover a maximum radius of 100 miles, and for most news much less than that.
# Methodically checking for inconsistency
While I can think of these specific examples, this doesn't assure me that a world I build is free of inconsistencies that don't happen to occur to me. How can I test a world as I build it to highlight inconsistencies? Are there approaches used in other fields that can be applied to consistency in world building?
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*I first came across the idea of a planet with an unending circling fire in the following book, which I have hidden in a spoiler block since the planet is introduced near the end of the book, although I wouldn't expect that knowledge to detract from enjoyment of the book:*
>
> The Player of Games
> Iain M Banks
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[Answer]
The best way to catch problems is to have someone else check your work. Have them read descriptions, look at maps, and read definitions. Ask them if they see and slight inconsistencies. Even a small problem, or something that annoys/nags them could lead you to a true problem.
Then, do this with several people, to catch all the mistakes.
Finally, accept the fact that you will make some mistakes, and be prepared to fix them. Don't be discouraged by things you miss. It happens to everyone.
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okay here's what I would suggest, create a calendar for your first area
Day 1 of month 1 is the first day that the flames should be hitting the area
Last day of month 1 is the day that the storm has moves on
So the days in which the flames are coming back will be the end of the year.
Divide up the rest of the year into months of the same size as the first, or smaller units if you need.
For the sake of simplicity, I'll use a 30 day month, with 12 months.
So "January" would be the fire days. Then you can map out what should happen in that area each month. Trees start growing back in month 3, should be a foot tall in month 4, 6 feet in month 10 etc.
This can also be translated into distance and movement. At 3 months, the fire is 1/4 away around the world. For the purposes of travel, characters who travel 1/4 of the way around the world, would have their calendars turned back 3 months.
If you keep track of how much time passes, and where they are, you should always be able to determine where the fire is and what is happening where they are right now.
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For context: I'm writing a story where the main antagonist is an empire that builds Dyson swarms around every star they can get their hands on. The protagonist lives on a planet around one such star, and over the course of several years, he watches as the planet's climate changes from one resembling Earth today, to one resembling Earth during the last Ice Age. If the Dyson swarm is completed, his home planet will be rendered utterly uninhabitable, and the protagonist's desire to keep that from happening that is what motivates him throughout the story.
I've heard that blocking roughly 2% of the sun's light would be enough to lower Earth's temperature from where it is now to pre-industrial levels. So what percentage would you need to block to lower the temperature to uninhabitably cold levels?
Also, some related questions: could a Dyson *swarm* block out enough light to do this, or are Dyson *spheres* needed? At what point does the dimming of the sun become noticeable to naked eyes on the ground? How would the cooling be affected if only one side of the sun was being partially blocked?
[Answer]
Thermodynamics will give you an approximate answer here.
A planet without an atmosphere can be reasonably approximated as a black body radiator. The energy thus radiated goes at the 4th power of the temperature--cut the sunlight 16 fold and you halve the temperature--note that the units are Kelvin (or if you're die-hard imperialist, Rankine), not Celsius! Earth's average temperature is 287K. Cut the sunlight 10% and you lower the Earth's temperature by about 5 degrees.
It gets more complex when you add an atmosphere, the Earth gets about 32 degrees of warming from the greenhouse effect. I suspect this will remain basically constant until the cooling starts trashing the ecology.
There's also the matter of time. That 10% would certainly trigger an ice age but it wouldn't happen all at once--the ice would just accumulate faster than it melted and slowly grow, reflecting the sun back and cooling the planet even more.
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It depends a bit on what you mean by uninhabitable.
But having said that, your best bet would be to find some analogue to measure against. Probably the best in this case is to consider the decrease in energy in going north or south from the equator.
According to [this source](https://earthobservatory.nasa.gov/features/EnergyBalance/page2.php)
The Arctic and Antarctic circles only receive 40% of the energy of the equator. So as a very rough guide I would suggest a Dyson sphere blocking 60% of Earths light would eventually make Earth uninhabitable.
But it does depend on the exact habitation conditions and it also depends on the speed of onset and the time frame. A few days would be less of a problem, months and years would be deadly.
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Happy New Year, and welcome to WBSE. I expect someone will have a better answer than me, soon. But, for now:
Sunlight on a bright day has something like 120,000 lux. Many crops require something like 5 to 10,000 lux a day to grow at a decent rate. So, as you get down to 10% of the sun's light... that means even a bright day is barely enough to manage the crops, so cloud cover could be enough make them weak. Most plants need about 500 lux to survive in general.
So, maybe life could scrounge by with as little as half a percent of light, as far as plants go.
Of course... everything will like die of cold, before you get to that fraction of sunlight. You might want to check out the question and my answer about what would happen if the sun disappeared, for comparison: <https://worldbuilding.stackexchange.com/a/100223/35649>
Unfortunately, I can only guess at what rate reducing light reduces heat. Maybe halving the light would reduce the world to -10 Fahrenheit? That'd be really devastating, but not unlivable. If it is a linear scale, you'll need to take out a lot of heat before you can get rid of all life. If you just want to get rid of humans... well, my answer shows that it's possible for humans to survive even without the sun, at least for a couple of centuries (under optimal conditions).
] |
[Question]
[
So... I'm fiddling with Yet Another Bipedal Digitigrade Species. There is tons of material on the *legs*, but seemingly not so much on the *hands*.
### Short Version
So... I'm wondering; is it possible to design a "hand" that can function as both a digitigrade 'foot' *and* be useful to a civilized tool-user?
### Longer Version
As we know, digitigrade forepaws have extended metacarpals, and the range of motion between the metacarpals and proximal phalanges is from roughly in-line to about 90° *forward/out*. In humans and most other species with grasping fingers, the range is from roughly in-line to about 90° *backward/in*.
Another challenge is claws, especially the retractile variety, which effectively 'eat up' a useful joint. That said, I'm not sure how much it would really inconvenience most people if the last two digits of their fingers were fused.
An obvious solution is to provide the MC/PP joint with a greater range of motion. Is this plausible? If not, is it plausible that a species with such 'fingers' would be able to grasp objects anyway? (What might the thumb look like?) Or is there any other 'hand' design that could be used?
### Notes
* 'Hands' should be able to grasp objects well enough to plausibly be able to survive in any period of development (assume technological progression similar to human).
+ Should be able to grasp a pencil / thin rod. Bonus points if they can use chopsticks.
+ Should be able to grasp a tool handle / thicker rod.
+ Should be able to grasp a ball / apple / etc.
+ Okay if they need to use two hands more often than humans.
* Should be able to 'stand' on forelimbs with weight partially carried by the metacarpals. Should ideally be able to walk like this, but okay if they can't run (on all fours) very well.
* Phalanges are probably longer than otherwise; closer to human proportion.
* There is definitely a thumb, although I'm not entirely sure what it looks like or how it stays out of the way for walking-on-hands. Ideally it is opposable, at least to the tips of the other fingers when said fingers are curled. (Maybe not to each finger joint.)
* Should be able to have "retractable"¹ claws.
(¹ For you pedants out there, yes I know claws are really *pro*tractile.)
[Answer]
**You may have to be satisfied with less dexterity**
Right, so, the thing that makes digitigrade legs work is that their digits, their toes, the things that maintain the creature's balance both while stationary and in motion, are rather large and strong compared to the toes that we as humans have, though this is mainly to allow them to fulfill the same function as what our plantigrade feet do with the shape of their rather robust heels and metatarsals. Point is you need a point of contact that can not only deal with the frictional stresses of locomotion but the compressive stresses on the bones as well, along with strong enough muscles that aren't likely to tear just because you decided to run instead of walk.
Even simply pressing my hand into a theoretically digitigrade posture, allowing only the whole of the underside of my fingers and most of my thumb to touch the table and maybe a little bit of the palm where the fingers connect under the knuckles, hurts, so expect proper digitigrade forelimbs to be rather robust with longer, thicker palms, thicker fingers, and larger, more structurally-sound knuckles. This sadly leads to a sacrifice in dexterity and range of motion, but assuming finger length doesn't shrink relative to the increase in hand size they should still be able to clench the fingers into something like a fist and pick up most things we can, barring extremely tiny/thin things like needles. Obviously they're not going to be doing knife tricks, or stitch-work without an intermediary tool(something tapering and pincer-like that allows their larger digits to work with smaller objects), but they should be fine to do most things.
If you really want claws this limits their dexterity more severely, but with the increase in finger size you'll have larger and more robust fingernails which should be able to deal quite a bit of damage on their own judging from what people can already do to other people's faces with our admittedly frail nails. Clubbing things with their larger forelimbs would also deal considerably more blunt damage than our fists can do as well, so they might not even need weapons but of course with larger and stronger hands comes the ability to wield larger and heavier implements so it's something to consider in their military potential.
[Answer]
# Have them knuckle-walk like the great apes do.
Like John mentioned in a comment, having fingers that can flexibly bend in both directions is likely to result in fingers that are either bad at being used for walking, or bad at being used for gripping.
So, you can split the circle by only having them bend in one direction: inwards. They'd then walk around on their knuckles and the backs of their fingers, like a backward-pointing foot, and use the insides of their fingers for gripping things.
This is an inverted posture from the positions you see the "fingers" used in animals like dogs or cats, but which preserves the full functionality of the fingers in this context.
[Answer]
You are asking for opposable thumbs on a digitigrade, and that's a little difficult if you are going digitigrade on both the front and back.
But if you are looking for "paw-like" aesthetics and you aren't totally married to complete digitigrade, let's start with paws that have close to opposable thumb function. Not the complete package, just clawed (non-retractable, I am sorry) with pads.
There are kangaroos, raccoons, koalas, pandas, possums, and opossums. I am leaving out all of the apes because that's just too hand-like, and all of the birds, reptiles, and amphibians because that's too different in format.
Kangaroos, we can eliminate because they rarely get down on all fours, and the design is quite different (mainly because of the hopping). Might be worth a look but, I think it's not a win.
Hie thee to yon google machine and type in two things. First, take that list of animals with paw-like opposable thumb function and type in each animal individually "opossum runs" "raccoon runs" and so on, so you get to see how they move. You may find it fits enough of what you want even though they are not digitigrade. Also, look at the same animals with the search "on hind legs" or "runs on hind legs."
Basically, you can find these animals adopting the stance of digitigrade and plantigrade as it suits them. Structurally, some are plantigrade (bears). If you want real opposable thumbs, plantigrade, at least on this planet's evolutionary track is the way to go. It gives the most versatility.
A cat, which is a digitigrade can stand plantigrade on its back feet if they need to. However, the STRUCTURE is digitigrade, and while there are advantages, one of them isn't opposable thumbs.
You can also find videos of each of these animals listed gripping onto things with surprising dexterity, and if you pushed it a little further, you might have a lot of what you need.
You weren't finding any info on digitigrade hands because, well, digitigrade does not equal hands or anything like that.
On this planet, anyway. You can design what you like. But the examples above are all animals with the kind of versatility you want and at the very least a paw-like structure that isn't something like a bird, reptile, or primate.
] |
[Question]
[
I'm running a mysterious, shadowy, acronym-lettered agency which deploys agents all across the world (and beyond) to deal with supernatural and paranormal events. What they encounter is often completely random, and includes everything from cursed vending machines to shape-shifting man-eating dogs (think SCP).
Still, there are a couple commonalities or general patterns to the supernatural events my agents encounter. For example, all my agents are trained to preform regular "reality checks" and "regressive memory path reconstruction" which are both designed to make sure that they don't get caught in illusions or dreams and so that they notice if their mind is being tampered with somehow (A surprising amount of supernatural creatures make those who witness them be unable to remember them or have them loose memories).
Recently, there's been an uptick in time-travel related accidents and I'd like to write some guidelines for my field agents to minimize the risk to themselves, the world, and causality in general when investigating these strange phenomena. The major complication is that time travel rules are inconsistent between events. So far we've had agents:
* Stuck in groundhog-day style time loops (of various duration)
* Use a functional time machines (boxes where you punch in dates and go there)
* Get caught in areas of accelerated, reversed, or slowed time
* Kill their grandparents and fade slowly from existence
* Kill their grandparents and keep existing just fine
* Be unable to kill their grandparents for some reason
* And much more
So far, we've (and I'm ashamed to admit this) avoided most accidents and paradoxes seemingly by sheer luck but my science team tells me that one wrong move could doom reality as we know it. That's why I'd like to put some reasonable precautions in place for my field agents to follow to minimize paradoxes and time-travel related issues.
For example:
* Agents are not to leave items they brought with them behind whenever preforming a "jump"
+ Special care should be taken to avoid ranged weapons with unrecoverable projectiles such as firearms
* Agents are not permitted to interact with past or future selves
* etc...
The question:
**What are some guidelines/operational procedures will permit my agents to investigate temporal and time-travel related phenomena while minimizing risk of creating paradoxes for the greatest amount of time-travel systems.**
[Answer]
# Get a team of historians
OK, so you have two broad areas where you want to avoid tampering with time causality - travelling to the past, and travelling to the future. You need a dedicated team of people to let you prepare for each:
## Travelling to the past
*Memo: To all agents. In light of the recent patricide incident with agent Dereka (previously agent Derek), we remind you what to do in the event of retrotemporal displacement:*
1. Find out *when* you would be travelling.
2. Find out *where* you would be travelling.
3. Find out any other related information you can before travelling there: individuals involved, specific locations, the entity or type of being handled (if any), a phenomena or type of phenomena being handled (if any), etc.
4. Fill in form P45-T - be as accurate and as complete as possible. YOUR EXISTENCE MAY DEPEND ON IT!
5. Submit the form to the History Analysis and Paranormal Preparation Investigation and Event Response team.
6. You will get a *detailed* steps to take and not take based on an in-depth investigation of historical records.
7. Read it THOROUGHLY!
8. Be *absolutely sure* you've read it THOROUGHLY!
9. Follow the guidelines the team has put out for you.
10. DO NOT DEVIATE FROM THE GUIDELINES!
11. Do not "wing it".
12. Do not say "Wait, I think I remember how this goes".
13. Do not use any knowledge outside the guidelines in order to fulfil your task.
14. Do not try to save your pet from your childhood from premature death.
* Not your dog.
* Nor your cat.
* Nor your hamster.
* Nor your *gold fish*.
* Nor any other pet.
15. Do not try to save, neutralise, or interact anybody else, if it's not in your guidelines
* Don't kill Hitler.
* Don't save Martin Luther King.
* Don't save 2Pac.
* Don't go anywhere near your ancestors.
* Don't visit Elvis.
16. Dress and act according to the time period you would be travelling to, as to not draw suspicion.
* Reminder: we do have a retro dress and fashion department but the inventory is limited, so you would be *assigned* an available, appropriate costume.
* Reminder: every agent is required to train in at least one older dialect of their mother's tongue and another language.
* Reminder: you are *not* to introduce any "new" dances, moves, handshakes, slang, catchphrases, and anything similar.
17. *Only* pay, do business, or exchange any money, if the guidelines allow you to.
* In fact, don't even drop any money.
* Probably best if you never carry on the assignment.
* We mean it! The Agency is *very* strict on controlling the inflation and maintaining the wealth distribution consistent.
*Seriously, people - you are **professionals**. The guys in history analysis work* really hard *to give you the best chance of both resolving the temporal anomaly and returning to the same world you left.*
## Travelling to the future
*Departmental guidelines for responding to situations involving protemporal displacement:*
1. If at all possible, notify The Agency in the future after temporal displacement. To minimise disruption, to future agents, you should submit Visiting Investigation Personnel standard form outlining your type of assignment and operational parameters. In the protocol classification field, add "McFly" to the classification shortcode. This would ensure it's handled appropriately. You will receive guidance worded as best as possible.
* Reminder: you are still to follow the rules applicable for retrotemporal displacement and follow the guidelines *as closely as possible*
2. Minimise your exposure to the world. Communicate with as few people as possible and visit as few public places as possible to aid other future operations.
3. Make as many detailed notes as possible for when and where have you done what.
4. Upon completion of the assignment and returning to appropriate temporal coordinates, submit report form PH-U7UR3 to the Subdivision for Anachronisitc Diminishment with Data and Events Retroanalysis.
* Reminder: be *as detailed as possible*. Document every steps you've made.
* If possible, *literally*.
* Reminder: this information will be used to produce the guidelines you will receive in step 1. Your *future success depends on your ability to correctly explain it*.
*All agents are also to remember that their reports are taken into account when preparing you for missions that are not related to temporal displacements. The Agency will never intentionally send operatives where a different version of themselves is known to be acting. Nobody wants what happened with agent M. Your reports are examined with the aim of avoiding any other incidents of similar variety.*
[Answer]
**Step 1: Don't get involved**
The first day of training new agents, they are escorted into a room and told to sit down. Upon doing that, a man politely walks into the room and announces that under *NO* circumstances are field agents *ever* to get involved in a space-time anomaly. Doing so could jeopardize the time-space continuum and threaten the existence of all of mankind.
This process is repeated day after day, and probably also subliminally entered into the field agents as well. Time travel is NOT A TOY.
**Step 2: If you do get involved, accept that it's going to be the worst case scenario**
Time travel is messy. Let's face it, half the time it seems like nothing is going to go wrong and you get back to the present time only to discover that you left your favorite pocketwatch back in the 1830s, and now Nazis riding dinosaurs are in charge of everything. Other times you go back it time and kill certain well-known historical figures years before they can do anything, only to find out that nothing has changed whatsoever. These things just happen with time travel. Sometimes it works out how you want, but in general, convenient time travel is the kind of thing that happens to *other* people. You are a member of this SCP-analogue organization. You don't get that lucky.
**Step 3: Remove ALL the evidence**
Things happen to researchers and field agents. Terrible things. Abnormal rifts can tear people in half, eldritch creatures can horrify, and sometimes you're just dealing with an honest-to-goodness monster that's perfectly willing to kill you. Given that, instruct all agents that, upon discovering that they've come across a time anomaly, they are to perform any and all actions they deem necessary to ensure the possibility that affecting the time space continuum isn't affected.
Thus, to this end, time machines are to be destroyed when deemed safe, and quarantined via sending them to the end of the universe when destruction of said craft is deemed to be unsafe. They are *never* to be dismantled or examined. The last thing we need are erratic time machines parts flying through the space-time continuum.
Bubbles of oddly affected time are to be avoided. When discovered, all agents are to be extracted, and perimeters are to be set up until the area returns to normal. If the area does not ever seems willing to be returned to normal, the area must be quarantined and sealed off. Stables bubbles may be useful for various purposes, such as accelerating research projects or storing dangerous persons within.
Personal time experiences, that is a localized time effect which only effects a single agent in any way that would affect the linear timeline, i.e. sent forward/backwards/sideways in time (We must not rule out sideways!) can only be dealt with by making sure that said anomaly (the agent in question) is not permitted to effect anything. Regrettably, this will almost certainly necessitate the willful demise and complete eradication of the agent in question, but all field agents will understand the necessity of it. (It is recommended that field agents have the means to permanently eradicate themselves anyway, given the nature of many of these assignments.)
[Answer]
**It is not luck. It is hard, hard work.**
The failure of your clueless bumblers to create accidents and paradoxes is not due to their gifts or their great good luck. It is active management by entities in your own timeline. Agents from this group exert influence through time and reality to run interference and minimize damage caused by (your) bull-in-a-china-shop style time travel.
Unlike your hamhanded selves, these agents are quite sophisticated. They are extremely subtle and artful and their influence is nigh impossible to detect.
But not deduce, and you have deduced it. No one is that lucky. Something bad should have happened and it has not. There is a reason.
The next step is to study the events which have happened, and learn the techniques of these timeline managers. When an agent is stuck in a loop, what was that agent trying to do? The vanishing and nonvanishing grandpa-killers: how do they differ? Accepting that you probably cannot effectively communicate with the agents who are running interference for you, you can at least learn their patterns and methods and so avoid unpleasant outcomes for your time travelling agents.
And eventually, you can use these agents for your own ends. Your association can trick these agents of continuity into intervening and by doing so, themselves create the change in the timeline you are trying to achieve. You need to get this right on the first try: these entities will not be pleased when they realize they have been played. Fortunately your new timeline will have its own agents of continuity which will prevent things from changing back.
] |
[Question]
[
Assuming power can be provided, what would be the more practical primary armament for a tank using an electromagnetic cannon? I am looking for a good compromise between accuracy, cost and durability of the cannon. Assume that high temperature superconductors are common place in this universe.
[Answer]
# Coilguns (assuming current technology)
Ironically, rail guns have arguably received more attention for development in military applications. Unfortunately, however, there have been some major setbacks. The Navy is documented of having been developing rail guns as weapons as far back as 2005, yet as of 2018 [there have been some hugely limiting problems](https://www.globalsecurity.org/military/systems/ship/systems/emrg.htm):
>
> There are a number of things the Navy still doesn't know how to do. How is it possible to shoot more than about three or four rounds out of an EM rail gun before having to change the barrel? How is it possible to build the kind of pulse forming networks that are needed to be able to shoot not direct fire weapons, but 200 mile indirect fire weapons? There is a lot of potential that a capability like EM rail gun could bring. But there are many risk to EM rail gun.
>
>
> ...
>
>
> Railguns face two types of problems : engineering problems, and physics problems. Engineering problems, such as the size of pulse power units, are engineering problems that can be resolved with suitable applications of time and money. Physics problems, such as barrel life, are rather less amen able to such brute force solutions, and are the reason that not everything that can be described can be built, or built in a useful form.
>
>
>
Wikipedia [summarizes the challenges of rail guns](https://en.wikipedia.org/wiki/Railgun) (emphasis mine):
>
> The heat generated from the propulsion of the object is enough to erode the rails rapidly. Under high-use conditions, current railguns would require frequent replacement of the rails, or to use a heat-resistant material that would be conductive enough to produce the same effect. At this time it is generally acknowledged that it will take major breakthroughs in materials science and related disciplines to produce high-powered railguns capable of firing more than a few shots from a single set of rails. The barrel must withstand these conditions for up to several rounds per minute for thousands of shots without failure or significant degradation. **These parameters are well beyond the state of the art in materials science.**
>
>
>
This really only leaves coilguns - mostly for their capacity for fire regularly. Some important items of note:
* Although coilguns typically have lower velocities than rail guns, tanks don't need to fire at the same distance/velocity as the Navy needed in the first link above
* The biggest issue with coilguns is timing, but the issues with timing in coilguns [dates from WWII on to the 1980s](https://spectrum.ieee.org/consumer-electronics/gadgets/for-love-of-a-gun), which is now much easier to deal with via computers.
* NASA has many uses for coilguns, and [is actively pursuing it's usage](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190000731.pdf)
In conclusion, although the railgun has arguably received more attention, there are some strong material limitations with it's usage in war. Coilguns, on the other hand, are limited mostly by timing and design issues, which are much easier to deal with today, and therefore make coilguns more practical for tank cannons (assuming current technology).
[Answer]
**Railguns. Because you are writing awesome fiction, not working for DARPA.**
Coilguns have a limited upside for awesomeness. At the end of the day they are glorified doorbells. Yes they are more practical. So is commuting with your Prius as opposed to your jetpack. If you are trying to shoot things in real life, work on the coil guns and you may be on the wrong website.
Railguns can be made into sweet near future scifi with nonmagical real physics-based schemes. You know that because already are thinking along those lines with your high temp superconductors.
<https://www.halfbakery.com/idea/Superconducting_20railgun_20projectile#1137552946>
Using a superconductor for projectile or rails sidesteps much of the current issues with ohmic heating and rail ablation.
Another idea I had for railguns was more plasma.
<https://www.halfbakery.com/idea/Plasma_20Rail_20Railgun#1186761424>
Plasma armatures are used on some railgun projectiles - the armature is behind the projectile and gets turned to plasma when the electricity comes on. The plasma then conducts the electricity, closing the loop that provides propulsive force. Leaving the projectile out of this means more options for projectile composition. Why not do that with the rails too? Regenerate your plasma rails after each shot! In my scheme, graphite is used. I like graphite also because if the condensing graphite plasma were not vented appropriately, once they were in a real fight your tank crew would soon look like chimney sweeps.
] |
[Question]
[
**Question: Would a modern-day teen, trained in using the north star for directions when camping/hiking, notice a difference in how the "north star" (Polaris) works when transported suddenly to 1350 BCE?**
My novel has children (up to age 14) from the Southwestern United States in 1995 time travel to Ancient Egypt (and later the Sinai Peninsula) around the time period 1350 BCE. They are being looked after by local people and they join them on the Exodus (yes, that one) out of Egypt. The modern-day kids don't have to actually navigate, but some will try to figure it out anyway.
Basic constellations are common knowledge among American schoolchildren, especially ones like mine who do not live in an urban area. I expect most of them will know about the North Star (with at least a couple of them knowing how to find it). Some of my characters are boy/girl scouts and, speaking from my own childhood training, would have learned how to find *and use* the North Star for directionality and travel. Others may have learned from family campouts, summer camp, or just from other children/adults.
The North Star, however, has not always been the one we know, Polaris. [Axial precession](https://worldbuilding.stackexchange.com/questions/146349/how-to-calculate-rate-of-axial-precession) is a very slow process but one that will be relevant for the time period I'm looking at.
>
> A consequence of the precession is a changing pole star. Currently
> Polaris is extremely well suited to mark the position of the north
> celestial pole, as Polaris is a moderately bright star with a visual
> magnitude of 2.1 (variable), and it is located about one degree from
> the pole, with no stars of similar brightness too close.
>
>
> The
> previous pole star was Kochab (Beta Ursae Minoris, β UMi, β Ursae
> Minoris), the brightest star in the bowl of the "Little Dipper",
> located 16 degrees from Polaris. It held that role from 1500 BC to AD
> 500. It was not quite as accurate in its day as Polaris is
> today. Today, Kochab and its neighbor Pherkad are referred to as
> the "Guardians of the Pole" (meaning Polaris). ([ref](https://en.wikipedia.org/wiki/Axial_precession))
>
>
>
[This picture](https://en.wikipedia.org/wiki/Beta_Ursae_Minoris) shows the Little Dipper constellation with the current North Star, Polaris, just past the end of the Little Dipper handle, and the former North Star, Kochab, in the left bottom corner of the dipper (when rotated to "hold water"). [An enlargement of the graphic is here](https://en.wikipedia.org/wiki/Beta_Ursae_Minoris#/media/File:Ursa_Minor_IAU.svg).
[](https://i.stack.imgur.com/29XAK.png)
The night sky is a huge big deal in low-artificial-light areas, so everyone will notice it and talk about it. It will become an even bigger deal when they leave Egypt and enter the Sinai Peninsula and people are trying to figure out where they're going. So no way will my characters (ancient and modern) not talk about this.
[Answer]
The short answer is: Yes, they absolutely would notice a difference. As you noted, Kochab was the closest star to the North Celestial Pole during the time you mentioned, but even so, it wasn't near enough to be an actual pole star. In fact, Kochab never gets closer than 7 degrees to the NCP, which is about 14 full moon widths.
The simulated skies would appear as the left side of the image below:
[](https://i.stack.imgur.com/OngmB.png)
As you can see, there is no pole star at the time you mention, and even though Kochab is close, it's still much farther than Polaris is today (Polaris is actually the second-best pole star after Alpha Draconis over the Earth's 26,000 year cycle, we're all just lucky to be born today).
Anyone staying put and watching Polaris during the time would find that it moves in a circle *around* the NCP, but that the pole itself would be dark.
Naively attempting to use Polaris or Kochab as a navigational aid would cause them to travel in a Northwesterly arc, rather than due North, as the stars moved around the pole, but so long as the person knew that Polaris and Kochab were not directly on the NCP, they could still use them to navigate.
So yes, they would notice a difference if they were paying attention, but if they just found themselves there at night and didn't know they had been transported 3000 years in the past, or didn't think to account for stellar drift, they could get lost simply trying to use what they know about stellar navigation today.
Another problem they might find is that the sheer number of stars away from light pollution makes it a little difficult to find your bearings. This is something I noticed myself when I went from a highly light polluted sky to a sky completely devoid of light pollution. Despite being an astrophotographer, I had a lot of difficulty picking out the skymarks and constellations I normally would have no problem finding in the suburbs. Unless you've been under a completely dark sky a few times, it's very easy to get overwhelmed.
[Answer]
Yes, they will.
If you look at movement of the stars at night, it looks like all stars circle around Polaris. That's because it is very close to the axis of Earth's rotation.
[The same wiki from which you took the image in the question](https://en.wikipedia.org/wiki/Pole_star) also says:
>
> In 3000 BC, the faint star Thuban in the constellation Draco was the North Star, aligning within 0.1° distance from the celestial pole, the closest of any of the visible pole stars. (...)
>
>
> **During the 1st millennium BC, Beta Ursae Minoris ("Kochab") was the bright star closest to the celestial pole**, but it was never close enough to be taken as marking the pole, and **the Greek navigator Pytheas in ca. 320 BC described the celestial pole as devoid of stars**. In the Roman era, the celestial pole was about equally distant between Polaris and Kochab.
>
>
>
Then we go to [Beta Ursar Minoris's wiki](https://en.wikipedia.org/wiki/Beta_Ursae_Minoris), and it says:
>
> From around 2500 BCE, as Thuban became less and less aligned with the celestial north, Kochab became one pillar of the circumpolar stars first with Mizar, a star in the middle of the handle of the Big Dipper (Ursa Major), and later with Pherkad (in Ursa Minor). In fact, circa the year 2467 BCE, the true north was best observed by drawing a plumb line between Mizar and Kochab, a fact with which the ancient Egyptians were well acquainted as they aligned the great Pyramid of Giza with it. This cycle of the succession of pole stars occurs due to the precession of the equinoxes. Kochab and Mizar were referred to by Ancient Egyptian astronomers as "The Indestructibles" lighting the North. As precession continues, **by the year 1100 BCE Kochab is within roughly 7° [SIC] of the northern celestial pole**, with old references over emphasizing this near pass by mentioning Beta Ursae Minoris as "Polaris", relating it to the current pole star, Polaris, which is slightly brighter and will have a much closer alignment of less than 0.5° by 2100 AD.
>
>
> This change in the identity of the pole stars is a result of Earth's precessional motion. After 2000 BCE, Kochab and a new star, its neighbor Pherkad, were closer to the pole and together served as twin pole stars, circling the North Pole, from around 1700 BCE until just after 300 AD. Neither star was as proximitous to the celestial north pole as Polaris is now. Today, they are sometimes referred to as the "Guardians of the Pole."
>
>
>
So from these, we can infer that:
1. In the era your protagonists are transported to, stars would seem to circle around an area close to Beta Ursae Minoris, not Polaris;
2. If your teen protagonists are smart enough to know about Polaris, they will know that the true North is more related to a seemingly empty patch in the sky than Polaris.
3. If they know about precession, they will understand why this is so, and it won't bother them much.
It will still be easy to find the North through the stars. Here in the south the star closest to Earth's axis is very far from it, and yet we manage :)
] |
[Question]
[
In [haplodiploid sex-determination system](https://en.wikipedia.org/wiki/Haplodiploidy), female/diploid individuals are developed from fertilized eggs by means of sexual reproduction, while male/haploid individuals are developed from unfertilized eggs by means of parthenogenesis.
So assume there is a highly intelligent haplodiploid species. All female/diploid individuals of this species have the humanoid appearance (even though they do not necessarily look like human females), while all male/haploid individuals are mere egg-sized "balls" that possess neither human form nor sentience. The male/haploid individuals are produced periodically in the way similar to menstruation (or hens laying eggs) and have a very short lifespan respectively. As a result, female/diploid individuals of this species would exchange the male/haploid "eggs" (or "testes") that they produce with each other when they need to reproduce female/diploid offsprings of next generation. Since those male/haploid "eggs" (or "testes") exist outside of the bodies of female/diploid individuals and are disposable by nature, this species is technically not hermaphroditic.
So my question is whether such a radical sexual dimorphism between female/diploid and male/haploid individuals is plausible or not. It seems that in most haplodiploid species like Hymenoptera (ants, bees, and wasps) the physical morphology of male/haploid drone individuals is not radically different from female/diploid individuals despite the fact that they are technically also sperm pockets exchanged between female/diploid queen individuals of different colonies. One possible reason why this may be implausible is that sexual maturity always takes a long time (maybe one decade or even more so) to reach for a highly intelligent humanoid species even though all male/haploid individuals are just insentient "eggs". In other words, it is simply too costly for female/diploid individuals to produce disposable "testes" on a regular basis.
Or maybe the reproductive mechanism of this species can actually work?
Update 1: Another possible issue may be that the radical sexual dimorphism between female/diploid and male/haploid individuals diminishes the main evolutionary advantage of haplodiploidy. It has been proposed that haplodiploidy may evolve as a mechanism to get rid of defective genes that are much more visible in haploid individuals. But if those male/haploid individuals are mere balls, then it would be nearly impossible for female/diploid individuals to observe the existence of those harmful mutations. That is to say, if male/haploid individuals are mere balls, then the risk of accumulating recessive traits (or inbreeding) would be greater for them.
Update 2: Since @Willk points out that this species is functionally equivalent to simultaneous hermaphrodites, the post now can boil down to the question *whether or not it is evolutionarily plausible for a human-like species to evolve a way of fertilization without the involvement of penile objects*.
PS: I prefer using terms like "diploid" and "haploid" to terms like "female" and "male" to avoid some unfortunate implications.
[Answer]
**These are hermaphrodites, and what you are calling males are actually gametes**.
Your "males" are haploid (like gametes), and are nonsentient (like gametes). They are produced in excess (like gametes) and their sole function is to mediate sexual reproduction (like gametes).
Your "females" can make these male gametes and also receive them, presumably to combine with some internal different sort of gametes. Because the "females' can make both types of gamete, they are hermaphrodites.
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Answering the comment:
/the question becomes whether it is evolutionarily plausible for a humanoid, mammalian-alike species to evolve a non-penetrative way of reproduction other than parthenogenesis/
Sure. The gamete you describe (the "male") is an **egg**. You could call an egg an external womb though probably fairer to call a womb an internal egg, since eggs were first. The "male" gamete is big and presumably resource rich. It is fertilized by the other partner with a spray of gametes onto the egg (in fish, called milt). The embryo develops inside because that is how eggs work. There is no reason humanoids could not lay eggs.
[Answer]
There could definitely be such a difference, just look at other examples of sexual dimorphism. What you are thinking of is called sexual gigantism, and is predominant in spiders. While perhaps not originating in the exact way that you are describing, take a look at [an example of this](https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwicmeyq2ZPiAhWywVkKHUUiBHcQjRx6BAgBEAU&url=https%3A%2F%2Ftwitter.com%2Fvenomslab%2Fstatus%2F997751720993112064&psig=AOvVaw1yCsQCErRsVqK4ihbPGhMz&ust=1557671643045068), and you will see that the females can be much bigger and more complex than the males. This is rampant throughout many other spiders, simply because the females have to raise the young while the males die soon after fertilization. This is why they are smaller and less complex, because when they are basically disposable, you don't want them to have to be so big. The males also die soon after fertilization. Concerning Hymenoptera, while there is not such a drastic dimorphism, it is still there.
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[Question]
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A newly-built base on the moon has the first two compartments of a pressurized greenhouse farm. An airlock system automatically seals one compartment off the others when pressure sensors indicate a pressure drop is caused by failure, including that of meteor impact.
The airlocks allow the settlers to move the plants from the vacuumed greenhouse into the sealed one without losing air. All plants are Earth crop plants. Assume all measures have been taken to allow a fast removal of plants from the damaged greenhouse into the intact one.
How long can these plants survive in vacuum until they are saved?
[Answer]
The main issue is that, as one of the two greenhouses starts venting to the outside, the decompression of the air will cause a lowering of the temperature, which will eventually freeze the plants.
As soon as the water inside the cells freezes they will explode due to the volumetric expansion resulting from the ice formation. If the water doesn't freeze, it will evaporate, again bursting the cell. Once a cell is broken you can do nothing to repair it.
>
> How long can these plants survive in vacuum until they are saved?
>
>
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Considering that the heat capacity of leaves is pretty low, I realistically expect 100% mortality within the first minutes after the temperature drops freezing point or the water evaporates.
[Answer]
We can calculate that. Since the air is gone convection cooling [1] isn't relevant anymore. I'm going to ignore conduction cooling [2], assuming the greenhouse is isolated from the lunar surface. This leaves us with radiative cooling [3]. Conveniently radiative cooling can be calculated using these online calculators [4] [5].
The damage won't be equal across all the plants, so I'll run the numbers for a few examples. The greenhouse will be run at 301 K, a temperature that came up when I googled *optimal greenhouse temperature* [8]. I will assume the plant to be dead as soon as 273 K are reached, as water will freeze here.
**Cabbage and Head Lettuce**
Assumptions:
$radius = 15 cm$ average cabbge radius
$density = 362 kg/m^3$ bulk density of cabbage
$molar mass = 18,02 g$ molar mass of water (there's a lot of water, plant mass and air; thus should add up to water)
Cooling Time:
$ca. 900 s = 15 min$
**Apple, Tomato and Fruits**
Even when the plants are dead seeds could be salvaged to grow the next generation.
Assumptions:
$radius = 5,3 cm$ average apple radius
$density = 740 kg/m^3$ density of apples
$molar mass = 18,02 g$ molar mass of water (there's a lot of water, plant mass and air; thus should add up to water)
Cooling Time:
$ca. 660 s = 11 min$
**Seedlings and buds**
I'm assuming to deal with a roughly spherical seedling meaning a very young one.
Assumptions:
$radius = 0.1 cm$ average seedling radius
$density = 600 kg/m^3$ average density of leaves
$molar mass = 25 g$ molar mass of water plus ca. 7 g
Cooling Time:
$ca. 7,3 s$
**leaves**
Assumptions:
$thickness = 0.1 mm$ average leaf thickness
$density = 600 kg/m^3$ average density of leaves
$specific heat = 1,76 J/g\*K$ value for wood, but I could find nothing better (I'm not sure if the higher water content of the leaf will increase cooling time or if the difference in material will worsen it.)
Cooling Time:
$ca. 7 s$
## Other thermal factors
Not all plants will die at the same pace and my calculations just show when frost damage will start. Leaves, seedlings and buds will reach 257 K (-20 C) after around 15 s. My guess is that thats the point of no return concerning damage. Be aware that roots and trunks could survive way longer, the former because they are buried (assuming the greenhouse uses dirt instead of nutriant rich water, which would make things way worse for the roots (see evaporative cooling [6])) and the latter because they are thicker. Yet some plants could be lucky enought to be saved at 2 to 5 times the limit I guess. Additionally I assumed that the plants can radiate heast away freely. In reality the plants and the structure will radiate heat at each other and since the moon base will be insulated, truly losing the heat could take some time. This might increase the timescale by a few orders of magnitude. Keeping the heat lamps, lights and radiators on will counteract the heat loss as well, potentially making thermal damage improbable/impossible.
So unless the plants end up outside the greenhouse or the roof is ripped of freezing seems to be out of the equation.
## Conclusion
Be aware that temperature won't be the only source of damage. Decompression will take a toll, depending on its speed and exposure to vaccuum itself will hurt due to evaporation. This experiment [7] exposed plants (radish, lettuce and wheat) to 0.015 atm pressure for 30 min. They wilted a bit due to dehydration, but grew in fine afterwards.
So vaccuum doesn't seem to borther the plants much and your colonists are in no hurry to restore the greenhouse.
*This is disappointingly anticlimactic...*
[1] <https://en.m.wikipedia.org/wiki/Convection>
[2] <https://en.m.wikipedia.org/wiki/Thermal_conduction>
[3] <https://en.m.wikipedia.org/wiki/Radiative_cooling>
[4] <http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/cootime.html>
[5] <http://mc-computing.com/science_facts/RadiationBalance/CoolingCalc.html>
[6] <https://en.m.wikipedia.org/wiki/Evaporative_cooler>
[7] <https://www.google.com/amp/s/www.newscientist.com/article/mg20927953-500-vacuum-of-space-no-match-for-the-mighty-radish/amp/>
[8] <http://www.just4growers.com/stream/temperature-humidity-and-c02/understanding-the-optimum-temperature-for-plants.aspx>
[Answer]
The plants are in trouble, but the precise amount of time they have is dependent on many factors.
The primary problem your plants will face will be evaporation. This won’t just dehydrate them though, it will freeze them. Plants are porous. They are covered in little holes called stomata that allow them to breathe, but which also let out water. The boiling point of water is dependent on atmospheric pressure. In a vacuum, water boils even at 0 degrees Celsius, the temperature at which it freezes. Because when water evaporates it takes heat with it liquid water left in a vacuum will continuously boil off until the remaining water is below 0 C and freezes solid. Plants are basically just porous bags of water and so the exact same thing will happen to them, albeit slightly slower.
Interestingly we have pretty good estimates of how long this will take because vacuum cooling is actually frequently used for rapidly refrigerating produce. For leaves, it should take only a couple minutes of hard vacuum for them to freeze while for thicker parts of the plant it might take closer to 30 minutes.
So the primary determinant of how fast your plants are going to freeze is how severe the decompression is. If the plants are immediately plunged into vacuum they will only have a few minutes, but if it’s a slower leak then they could last for hours.
With respect to radiative heating and cooling, another factor we need to take into account is whether it is day or night on the moon. The surface of the moon during the day can reach over 100 C while at night it reaches below -150 C. This means a lunar greenhouse will need to be cooled during the day and heated during the night. If your decompression happens during the day it’s possible the sun’s warmth may help stave off freezing from evaporation. If it happens at night they will freeze somewhat faster.
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[Question]
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I'm currently playing with a geographical setting that's flat rather than round and thus doesn't follow a lot of the same rules as one modeled as a planet. I've found resources concerning climate in Earth-like or planetary environments, such as: [Creating a realistic world map - Currents, Precipitation and Climate](https://worldbuilding.stackexchange.com/questions/1353/creating-a-realistic-world-map-currents-precipitation-and-climate).
However, these mostly refer to features that don't exist in my world, like latitudinal bands or pressure systems resulting from the rotation of the planet (eg. Coriolis effect). I'm trying to come up with a reasonably grounded scientific approach to determine climate around some constant features. I'm also open to adding elements and systems that would add complexity or influence it in an interesting way.
Here is some additional information and a map for reference:
Height map of the northern region -
[](https://i.stack.imgur.com/9Zvvo.jpg)
Full world map, although most is WIP and doesn't have as much detail; may refer to it for a better sense of the general geography -
[](https://i.stack.imgur.com/5y3BG.jpg)
* The elevation of the land and waterways are as shown in the height map provided.
* Uniform gravitational field independent of distance to surface, strength roughly equivalent to Earth.
* Lower atmospheric composition similar to Earth. I imagine it would be different at upper levels where the Earth equivalent is subject to diminishing gravity.
* Sunlight comes from two sources at fixed points above the surface and radiate outwards as shown by the circles on the map. The radius of the larger (blue) and smaller (green) circle is roughly 10,000km and 2,000km, respectively. I drew them as a reference following the inverse-square law, with the outermost circle representing temperatures in the area around 0 deg Celsius, subject to local variations depending on the geography. I imagine it would be very dark from this point onward as well; temperatures would decline steeply beyond. I wanted the temperature at the center of both circles to be roughly 27-28 deg Celsius, after factoring in the overlap.
* I assumed that temperature would be somewhat proportional to the intensity of the emitted light and drew the inner circles with increments of 5 degrees, which would then be subject to other local conditions which I'm trying to determine now. Open to correction if I'm completely off on this point.
* The intensity of the light fluctuates to create day-night cycles similar to Earth, but not seasons. As such, the sunlight received in a given area stays relatively constant. I assume this also means temperature/climate (?) should remain relatively constant.
* Winds of undecided velocity blow radially from the same point as the light source. These may interact with other sources of wind; what those are, I'm not too sure.
* The 'ocean' has a drainage point to the west/left and flows in that direction. Its main source is further south (not shown on the map). I've been mulling the idea of conceiving it as a freshwater, ocean-sized river/lake but I'm not sure how plausible that is.
* Assume the flora in this universe has evolved to adapt to the season-less environment.
This is all the relevant information I can think of now but will add more if it occurs to me.
Given these conditions, what are considerations that could guide the creation of a scientifically-based climate/biome distribution in the region?
Edit: Posted my own answer with information from my own research and understanding to supplement the helpful posts by others.
Answers with more details as to practical application of the concepts to a map would be very welcome.
[Answer]
As with any climate system, start with the energy sources and sinks. On earth, that’s the equator and the poles, respectively, and on your planet, that’s near the lights and distant from the lights, respectively.
Areas near the lights will be warm, and thus air found nearby will be less dense and will rise to be displaced by cooler air flowing in. This will stabilize into a toroidal circulation cell centered around the lights. As you point out, from the surface this would feel like a radial flow towards the light source. The velocity would depend on a *lot* of factors, including temperature, uninterrupted distance, and turbidity measurements.
Assuming the atmosphere is also earthlike, as the air moves towards the lights and warms, it’ll also pick up water and becom moister. This water will then precipitate out into clouds and rain as it rises, making the areas near your lights cloudy, wet, and warm - a perfect rainforest setting. Moving away radially, you’d likely have wet temperate rainforest, drier forests, savannah/grasslands, tundra, and then icy desert in all the areas most distant from either light source. The light source in the south looks much larger than the one centered in this map- it’s possible you’d actually end up with a scorched area nearby if it’s of sufficient temperature, but I’d need to know more about the land/ocean nearby to give a decent estimate.
You may get some cool interactions between the two lamps- it’s likely a jet stream will form as the two toroids (toruses?) collide and have descending branches in approximately the same area.
More locally, you’d still have sea breezes and Mediterranean climates on the coasts because the sea breezes are powered by the day-night cycle and the differential heat capacity of the ocean relative to land.
I like the idea of a drainage point in the ocean. It’s a fun way to play with the non-planetary dynamics and it adds a lot of character to your world. Depending on the flow through this drainage point, the ocean might still be dominated by oceanic circulation and overturning based on temperature and salinity gradients. There might even be some mix of net flow and overturning circulation, which could create some cool helicoidal effects.
The idea of a freshwater ocean is an interesting one. The ocean is currently salty because it’s the result of millennia of weathering salt-containing rocks that are washed into the ocean and not removed. To make a freshwater ocean, you could either have minimal uplift and thus minimal erosion but would lose a lot of the topography, or you could have some sequestering agent. You’ve already got a drainage point in the ocean- that’s a great start. As long as the input into the system is also freshwater, you’ll probably be fine. Otherwise, I’d look into salt-based biological shells (like diatoms or coccolithophores, but that build their shells out of salt instead of silica/carbonate) as an easy way to sequester any salt present in the water and keep it fresh.
[Answer]
I think we can say a few things about it beyond what @Dubukay said in his good answer.
First, there *would* be "seasons", but they'd be arrayed in space rather than in time. The warmer areas would be summer *all the time,* and further away from the brightest area it would be cooler and then you'd get to an area where it frosted each night, then to where it froze at night and finally to perpetual winter.
Any area where it didn't frost at night would be tropical, which might well produce some interesting adaptations. Perhaps even more interesting would be the areas which freeze at night, but never undergo a true winter. I suspect you'd get an interesting new kind of plant with some sort of anti-freeze system!
One other, subtle, effect you'd see: The leaves on plants are governed by two things: The competition *between* plants for light, and the necessity that a leaf get some light at least some of the time. With a source that continually moves, leaves grow semi-randomly, even on a single plant. But on your world the position of the lights would be fixed and plants could now evolve to optimize the placement of their leaves. You'd doubtless see leaves all rowing in the same orientation facing one or the other light or facing some average of the two. (It's hard to tell in advance what would yield the best results.) You plants would look *really, really strange* to Earth-eyes!
[Answer]
Here's my answer based on the research I've done and my own rudimentary understanding of the subject.
To begin with, I'll refer to [Geoff's Climate Cookbook](http://web.archive.org/web/20130702032446/http://jc.tech-galaxy.com:80/bricka/climate_cookbook.html), which lists the following as the basic physical principles from which 'virtually everything important about climates can be deduced.'
1. All heating comes from the sun.
2. Water heats and cools much more slowly than land; water thus acts as a stabilising effect on temperature.
3. Hot air rises, cold air sinks; this is because air expands as it heats up and thus becomes less dense.
4. Cold air gives rise to areas of high pressure, and hot air gives rise to areas of low pressure.
5. Wind flows from areas of high pressure to areas of low pressure.
6. Due to the Coriolis effect - the effect of the rotation of the earth on the flow of air - winds are deflected to the right in the northern hemisphere, and to the left in the southern.
7. Rising air is conducive to the fall of precipitation, sinking air is not.
8. Warm air carries more moisture than cold air.
**Wind**
From this, we can surmise that given a uniform surface (eg. all water), the wind will blow from the cold outer regions (high pressure) inwards toward the light source (low pressure). If I'm not mistaken, the temperature gradient would be steeper the further away you get from the light source due to the inverse-square law, so the winds would be stronger. These would be the prevailing winds somewhat equivalent to the ITCZ/STHZ/PFs on a planetary body.
Land masses should affect the pressure distribution in the same way as on Earth according to principles 2, 3 and 4. Most guides usually refer to the pressure belts on Earth at this point, so what I have to say on this topic is my personal conjecture. Feel free to correct me if I'm mistaken.
In the winter, land on Earth creates high pressure areas on the land and low pressure areas over the surrounding ocean, with the opposite being true in summer. Since there are no seasons in this setting, the land should constantly create either low or high pressure zones, presumably depending on the climate in that region and therefore how far it is from the light source. Central regions would create pressure distributions equivalent to Summer on Earth, whilst outer regions would be more similar to Winter. The larger the land mass, the more intense the effect. I don't think the East/West distinction applies in the absence of Earth's pressure belts.
Sea breezes should still occur owing to the day-night cycle, but my understanding is that these would be stronger in the warmer inner regions where the temperature gradient would be higher. In the colder regions further from the light source, they would be less pronounced or non-existent if they oppose the prevailing winds that flow inwards to the centre. Might also be worth considering mountain/valley breezes, but most sources I've consulted never mention it so I'm not sure it's significant on a macro scale.
**Rain**
Warm winds blowing over the oceans will pick up moisture. It will then rain over land as a result of convection causing the air to rise, or orographic lifting if it encounters a mountain range. Mountains should still experience rain on the windward side and rain shadow on the leeward side.
It should rain more towards the warm centres, assuming the winds have had a chance to pick up moisture. If it's wind from a dry inland region, there should be little rain. The mountain ranges in the map provided should make the southern coast dry (a problem for me because I drew the map without thinking about it and plotted the rivers assuming it would be the opposite). The distance inland from the ocean should also be considered; the longer it has to travel over land, the more moisture it will lose on the way.
Cold winds blowing over the ocean in outer regions will pick up less moisture than warm regions.
**Temperature**
The circles on the map represent intensity of sunlight, with the outermost circle being 0 deg Celsius, local conditions notwithstanding. Winds blowing hot or cold air from other regions will affect this, as will large bodies of water that regulate temperature fluctuations from day/night. I imagine precipitation would have a cooling effect as well. Last factor I can think of would be altitude, with temperatures decreasing the higher above sea level the land gets.
**Biomes**
Geoff's Cookbook includes a table based on the The Köppen–Geiger climate classification that might be useful as a reference:
[](https://i.stack.imgur.com/h8cNT.png)
Biome should depend mostly on the temperature and precipitation; the latitude in this setting is irrelevant. As there is no seasonal variation, it's impossible to have exact matches for everything in the Köppen system, but the ones where Summer/Winter remain relatively similar should be most instructive.
Higher altitude usually leads to lower temperatures that will affect biomes. Areas of higher rainfall are more likely to have forests as opposed to grasslands/steppes.
**Additional References**
[Pixie's Tutorial Applying Geoff's Climate Cookbook](https://www.cartographersguild.com/showthread.php?t=27118)
[The Köppen–Geiger climate classification made simpler by Azélor](https://www.cartographersguild.com/showthread.php?t=27782)
[Wikipedia article on Diurnal temperature variation](https://en.wikipedia.org/wiki/Diurnal_temperature_variation)
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[Question]
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How would a four-legged bird's flight differ from a regular two-legged one?
Would it be slower in flight but have more power taking off?
The bird in question is modeled on a bird of prey.
(four legs of equal size and two wings)
[Answer]
Any flying bird is aerodynamic. We designed planes from looking at birds, so it makes sense to consider the following:
* Weight
* Aerodynamics
* Purpose
**Weight**
Adding an extra two legs to a bird is going to add weight. Which could impact is flight capabilities depending on leg thickness and size of bird. A griffon would have more chunky legs versus a pigeon, meaning more weight is being added.
A bird of prey should not have any real trouble with weight since their legs are very small anyway.
**Aerodynamics**
Here we can see a very elegant eagle, and a bird of prey.
[](https://i.stack.imgur.com/SyGZm.jpg)
Let's say we add two more legs, where do the legs go? If they go at the front you can clearly see that the bird would lose aerodynamic efficiency, adding them side by side with its current legs most likely wouldn't effect it at all, however I don't see this providing any benefit whatsoever should this be the case. This leads on to purpose.
**Purpose**
Eagles, owls and all predatory birds hunt using their legs or feet. Adding two more legs could help improve efficiency when hunting but at the same time it could hinder the bird.
For example, an eagle will use two feet, it only has one chance to grab its prey, add another two legs, it now has twice the chance to grab. For the better it becomes easier, but the bird would become lazier and wouldn't rely on precision as much as its two legged friend.
Whether this is a benefit for your scenario then great, but as a general answer to your question, I don't believe it will affect the bird much, although it would not really serve a real purpose.
Unless the bird in question was a mythical creature like a griffon or a [hippogriff](http://harrypotter.wikia.com/wiki/Buckbeak) where its size requires having more than two legs.
[Answer]
Most vertibrate life on earth follows a 4 limb body plan (in this instance, the wings are two limbs and the legs are the other two).
There are a number of mythical creatures with 6 limbs; Pegasus, griffons, dragons, etc.
One way to get 4 legs and wings is to have the wings double as legs.
Something like the [Quetzalcoatlus](https://en.wikipedia.org/wiki/Quetzalcoatlus), which probably used it's wings as extra feet for instance.
[](https://i.stack.imgur.com/uDYun.png)
But you probably wouldn't want to ride these for long distances on the ground.
Really the only reason to have a flying mount is to fly. A ground animal can carry more weight. It can haul a load. It can wear heavy armor.
If a creature can fly, having limited ground mobility isn't a bad trade. If you need to get somewhere quickly, take off. If you need to get somewhere and don't want to be seen in the air, take a horse.
[Answer]
I like the idea of a six limbed body plan. If your thing has four legs and two wings it can be more of a hawk, where it uses it's wings to travel but hunts by pouncing from the air and then is basically a lion on the ground. Long jumps for chasing sure. Even powerful enough to carry plenty of weight by the air back to the nest after its made its kill - sure. But don't expect it to be agile or graceful, this is a land predator that can fly.
Contrary-wise you can also have the falcon version of this animal that hunts other flying things (this is an and, not an either or) that has four wings and two stubby talons for ripping up whatever it can catch. This thing would be very fast and maneuverable in the air.
You are looking at creating a whole new taxonomy of griffin like creatures. There's a lot of room here to design what you like.
[Answer]
# It would depend on the legs, or not.
If an otherwise normally flighted bird has a tiny pair of Tyranosaurus arms, it isn't going to make much difference one way or the other.
If they have a full on second set of drumsticks, they are going to be heavier and not fly as well as if they weren't carrying the extra weight.
Finally... look at existing birds with two legs... some of them take off gracefully and strongly with their legs kicking off under them... others don't use their legs at all... others have to get a running start... still others bounce like beach balls when they attempt to land.
Nature being what it is... 2 more legs can be anything you want it to be if your narrative is thoughtful enough.
[Answer]
The only flying creatures with more than 2 legs are insects like bees or wasps.
Considering that the take off is an minuscule fraction of the time dedicated to flight, I don't see a clear advantage in having an additional pair of legs.
There might be a small advantage in having more grip on impervious area, but that would be probably overcome by the additional volume needed.
It may be different if the birds are non flying, like emus or ostriches. But in that case it would be better to evolve the unused wings to something like arms, for searching food in the ground or all those funny stuff primates do.
[Answer]
To answer the first part, only really at take-off and landing since coordinating six limbs is going to be a more complex task than four. Take-off and even more-so landing is going to be restricted to spaces where this bird can get all four feet on a fairly even keel, no landing on thin branches for this critter.
As to flight speed that's about what the bird is designed to do, to be competitive as a bird of prey it needs to be as fast as a modern bird with the same specialty, whether it's a vulture with huge flat gliding wings or a falcon that relies on speed and precision it will have those same characteristics. Whatever it does it is almost certainly going to need a proportionally larger wingspan at a given mass than a two legged bird though because four legs are going to produce more aerodynamic drag.
[Answer]
In my opinion, such a bird wouldn't be particularly maneuverable due to its center of mass being farther forward than ordinary avians. The difference in take off is negligible as well, sense it would just end up using its back legs to kick off the ground.
However, with two pairs of talons, this birdie could be amazing at climbing and landing on vertical surfaces. Not only that, but they would be able to grab and eat prey without risking a fall. Or maybe they could ambush landing birds, kicking off their perches while ensnaring their prey at the same time. If there spines are flexible enough, they could hunt nimble creatures that use trees as cover, like squirrels or monkeys.
However, regardless of their size, I don't think these hypothetical birds would make good mounts. In order to fly, they would have to have light-weight bones, which can't really support the weight of a human. Of course, a well done aerial combat scene or description of a flying caravan would make me too enraptured with awe to care about bird bones.
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[Question]
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I'm creating a fantasy-world generator. So far I've got it generating a reasonably good surface map, complete with terrain, cities, and borders. Here's a link for anybody who wants to try it: <https://drive.google.com/open?id=0Bxgb9V1OuYfpUFdmOWRxb2VrOGM>. This is a *super* early build, but still feedback is appreciated! The basic program workflow is:
1. Generate height map (mountain ranges, coastlines)
2. Generate Terrain from Height Map. For the surface, this involves placing forests, wilderness, fields, swamps, etc, in places that would make sense given the mountains/oceans.
3. Generate provinces, cities, and kingdoms based around the generated geography.
I have this working pretty well for the surface-world, but one thing I want to do is expand the map downwards to include an Underdark-like world below. The methodology I have for making the height-map is all good, but I'm at a bit of a loss over what types of terrain/biomes to use to fill in this underworld. In terms of geography, it will contain a maze of wide-open caverns, with large underground lakes. There will be points here and there where this connects with the surface-world and travel/trade is possible. To give you an impression of the scale I'm talking about, the underworld would line up exactly with the map generated in the example above, the underground lakes would be roughly the same size as the surface ones, and the caverns would be 3-8 “blocks” wide (1 block = 1 small coastal island). One thing we cannot do is have holes in the "roof" to let the sunlight in below. This is due to technical limitations of the program that I don't want to deal with.
Some of the caves will obviously just be bare rock, but if civilizations are to live/thrive down here they'll need more than just rock. This underworld will mostly be populated by dwarves and goblins (I may add an even lower level full of daemons, but they don't really apply here).
Presumably they need some sort of “fertile” terrain similar to the farms on the surface, from which their civilizations would emerge and expand. Maybe mushrooms fields/forests could work? I know mushrooms get energy from existing biomatter, but maybe I can say that these get their energy from geothermal heat. Maybe then they could grow alongside lava flows the same way fields/forests grow along rivers? Any other ideas? They'll definitely be fishing the underground lakes, so maybe some kind of fish-farming next to the waters? Any other ideas for food-sources that could create the surpluses needed to build a civilization, or other underground terrain types that would look cool from a top-down strategic view?
I'm not looking for total realism here, just some believably and internal consistency. Thanks!
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The first thing to do is figure out what sort of analogues we are looking for in an underground terrain. From there we can discuss how different environmental factors might interact to create that terrain
* Deserts: low precipitation, fairly barren environments (sounds like the default for underground caverns). Sand and dunes are frequently featured (bigger "ask"). Lots of mostly smaller animals operating "in cycle" with the environment to avoid environmental hazards.
* Forests: multistory plant life as larger plants loom over smaller ones. Fertile soil and highly active biome due to lots of plants. Lots of plant competition for sunlight/energy (interesting...). Lots of animals that interact vertically with the environment, taking advantage of height for defense as well as attack.
* Mountains: large changes in elevation creating notable geological features. Rugged terrain and rapid atmospheric change makes traversal difficult. Also notable is the concept of a tree line: large plants can only grow up to a certain altitude. Lots of highly mobile animals adapted to dealing with rough terrain and reduced food supply.
* Plains: broad, fairly flat terrain with a lot of short plant growth. Often a "transitional" type between two other terrain types. Lots of "fast" animals to run over flat land, slower animals generally operating in packs for defense.
There are others, but these four tend to be considered the basic "types." I chose my wording carefully for these to provide for our underground analogues. Notice that ***plants*** and how they interact with the environment are generally at the core of how we define our biomes. Let's focus next on the energy and resources that will form the core of our biomes.
* Light: not really much direct light underground, so the only sunlight would exist at surface caves. Bioluminescence is an option, so chemotrophic lichen and fungus would use the glow to attract mobile animals to help it spread (be releasing seeds/spores/pollen onto the animal). There may be *some* photosynthetic plants growing toward the lichen in response, but it's... unlikely. Absent a strong light source, lot of creatures would use alternate means of sensing their environments - either infra-red vision or echolocation.
* Water: while you won't really have the normal precipitation based rain cycle, there are still a number of sources for underground water.
1. A surface river could divert into a cave and give us an underground river - a very dynamic environment.
2. Cracks in the rock above lets water drip through the ceiling, forming stalactites in normal cave formations. Expect relatively still pools.
3. Related to 2, you could have large tree roots breaking into subsurface caves, bringing water along with it. These potentially would be very diverse areas, with the existing biomass of the tree roots forming the base of the environmental web as life "suckles" at the roots of the tree. Sentient creatures might even craft religious imagery centered around life giving tree roots.
4. Aquifers would exist as deep underwater lakes and, potentially, threaten settlements built near semi-permeable rocks with flooding if the stone wall cracks.
5. Steam - your geothermal processes at work provide both heat and humidity. Hypothetically, you could also have light in the picture if the steam is provided by a body of water trickling into an open, glowing lava flow.
* Heat: as mentioned above, this would be readily available once you get deep enough or close enough to a geothermal source. Interestingly enough, cool dark cave closer to the surface might be an analogue to a wasteland without access to water or an energy source...
Which brings us back to our four terrain types.
1. Deserts = Barrens: the cool and dry caves are resource poor, arid areas not well suited for life.
* Traversal of these barren caves and labyrinthine passages connecting them would be avoided until necessary.
* Lifeforms present would exist more at the fringes of the biome itself (where some plants thrive) and much of the internal food web would be based upon predation. Where water does intrude, you'd see the "oasis effect" clustering around the water source.
* Why cross the desert? Primarily because of trade - getting to the surface in many cases would require crossing the barrens, since travelling up the subsurface rivers would be nearly impossible. Going from one underground settlement to another might require passing through a barrens as a natural barrier to settlement expansion.
2. Forests = ... forests. Really.
* You wouldn't have "trees," but consider a deep geothermal cave with the "floor" of the forest as the actual ceiling
* plants will scramble and compete for heat and moisture, trying to get as close as possible to the source, but biologically limited
* roots can only be so strong, so there's a limit to how "tall" they can be before pumping moisture up to the roots becomes impossible (just like trees)
* Living things don't really like being burned and boiled, so there's a natural limit to how close to the magma or steam vent a plant can get.
* Like a jungle flipped upside down, animals would travel along the ceiling or jump from trunk to trunk, nesting in the root systems of the larger plants and nurtured by the water condensing on their "leaves." You could even have subterranean "monkeys" brachiating across vines and flying "birds" nesting in the canopy.
3. Mountains = sinkholes - deep, treacherous terrain with specially adapted life.
* Basically think of a cone-shaped mountain... and invert it, flipping it upside-down with the "tip" as the deepest point.
* Where the wall slopes are shallow, you'd have forests and habitations.
* The steeper the slope of the walls and deeper the sinkhole, the harder it is for creatures to live there. You'd have "goats" scaling cliff faces and agile "wildcats" hunting them.
* For the biggest/deepest caves you'd have magma pools at the antapex (fun new word!). The fumes and dry heat creates a comparable if inverted barren environment to surface mountains, requiring special gear and bottled air in order to travel that far.
4. Plains = mushroom/lichen marsh.
* The moist environment near subsurface rivers could have a build up of real soil/silt from upstream
* This rich substrate and extensive moisture throughout would potentially grow mats of mushrooms and plant life.
* Something like enoki mushrooms - filamental and tall - could substitute for grass that smaller creatures would hide in. Other forms of "brush" could also be involved.
* This would be a broad, flat cave that would regularly see flooding, much like the area surrounding the Nile river. This would also be a prime location for sentient creatures to farm in.
## Environmental Interplay
Now that we've established what our environments are, we can talk about how geographically they connect and transition.
1. Rivers - surrounding areas are fertile marshland. Perfect for any settlement, but probably inhabited by something culturally **hobbit-like.** Probably the main culture to engage in interaction with the surface through passages carved upriver.
2. Tree root complexes - the underside of an ancient forest. This is where you'd find tree-worshiping **subterranean elves** carefully cultivating the plant growth. Probably the likeliest home for bioluminescent algae/lichen as well. Elves would be averse to fire (destructive to their habitat) and would prize plant/woodcraft from the sacred roots over metalwork.
3. Sinkhole ranges - "mountainous" regions where the higher slopes could support plant and animal life might be an ideal place for **dwarven cultures** carving caves into the slopes. Focus on forging and foraging.
4. Barrens and labyrinth - a series of caves and passages connecting different rivers together. A potentially harsh environment that's home to hunters building their camps around oases. Might be an ideal region for **archtypical goblins** wielding rock based weapons and leather armor (from prey). Would "raid" connected fertile environments.
5. Steam caves - water interacting with geothermal sources, rivers flowing from marshland into deeper areas will lead to these "upside down jungles." You might see various civilizations intruding into these areas, but limited by the availability of usable ground to build on. Detrius falling from the upper layers of the cave to the floor would be moist, fertile soil if anyone were willing to risk collecting it.
6. Magma caves - expect a fairly hot and dry and therefore barren environment, though you could still have aboriginal style nomadic cultures.
7. Oil reservoirs - not really capable of supporting life, but potentially an interesting geologically barren feature - a "liquid desert" quite important to any civilization capable of tapping into this natural resource.
8. Stillwater lakes - Overall cold and resource poor areas for land dwellers, you'd have underwater food webs in a sufficiently large lake that would be exploited/fished by the other cultures for food.
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## Guano fields
Seriously.
There are cave systems on earth with entire ecosystems that are based on the energy extracted from bat droppings. Bats fly out of the cave at night, feast on the insects above ground, return to the cave and poop out the remains. The guano is very rich stuff, full of energy and nutrients. It's fed on by insects, which in turn are prey for amphibians, and on and on.
For your purposes, you could almost treat piles of bat guano like waterholes, with oases of life built up around them.
## Hydrothermal vents
This actually reminds me a lot of a question I asked about [feeding a city built around hot springs in a polar desert](https://worldbuilding.stackexchange.com/questions/59456/would-a-food-chain-based-on-bacteria-in-hot-springs-be-able-to-support-a-human-p). I think for your purposes, you could use the information about chemosynthetic bacteria in hot springs.
Add a geothermal area with hot, chemical-rich water welling up from underground. The water would be host to colonies of bacteria, which in turn would be eaten by filter feeders like molluscs and tube worms. You'd have a situation akin to a deep-water [hydrothermal vent](https://en.wikipedia.org/wiki/Hydrothermal_vent) or black smoker, with the same potential for life.
Ultimately, it seems that the most important factors for life on earth are liquid water, and a source of energy. These two are often the same factor. As long as you've got those, you can generally justify some kind of life.
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You need some kind of energy source for life to exist. I think geothermal energy would be the coolest: you have geothermal vents like those at the bottom of the ocean that are surrounded by thermophiles (<https://en.wikipedia.org/wiki/Hydrothermal_vent> for more info on this).
Alternatively to get around the "no holes in the roof", could there possibly be constructs from an extinct civilization that channel sunlight? Once those are in you can have plant life and from there various cave creatures.
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An underdark is always funny and challanging.
I can imagine several options for "underground farming" as you called it.
Some where already mentioned so i won't repeat them ( like hydrothermal vents ).
* Live is completely carnivore/insectoid. That is, insects eat dung from higher life forms, they grow more insects to consume. And they consume others that live in the deep. Not to mention guys from above that get lost underground (insect farming)
* There is some form of magical light source in a big cave. Think of a sun-like orb of radiation or an ancient hyper-tech "lightbulb" that spends enough energy to sustain plant growth. This may or may not need to be charged with actual sunlight from time to time. Or permanent portals that are opened in front of the sun so there is a permanent flow of light. I also like the idea of giant glass-tubes delivering sunlight from the surface to farmers and cities. You could have a complete jungle underground, although I would not see the necessarity since you could just have a jungle on the surface lol (normal farming)
* Life forms don't need to sustain like surface dwellers. "Somebody must have dug all these tunnels". Maybe somebody did. Maybe somebody ate it's way through the earth, like a giant stone dragon. And the folks living there are it's descendents. Like stone-kobolds. And they can digest some or all stones. ("stone-farming"? giant roots from trees?)
* Underground may be partially or completely underwater. This way fresh nutrients and fish can be washed inside the cave-system and creatures living there could find enough food to survive. (fish-farming, shells)
* Go all-out fantasy and have the whole planet be hollow with an artificial sun hovering in it's center. Archmage GibGob always had a fable for the sun and tried to capture it for many years until he made his own. Also possible with nuclear-fusion powerplants that produce electricity, depending whether you go magic-fantasy or tech-fantasy (normal farming)
* There is only as much life underground as surface dwellers bring down there. That means, under each major elf-forrest, dwarfen mountain or human city sewers, there is life, and these are "islands" of life in a cave system of stone and darkness. (no farming at all)
* There could have been a giant "world-tree" and after it's death it's deep ranging roots rotted away, giving space for the civilisation underground. Mushrooms and other plants could be grown from the remains of the roots
EDIT: sorry for my weird writings, I kind of got carried away but won't change it now that i posted it
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Well, the strongest barrier that might prevent life from appearing might be described by that analogy :
it’s like hoping to cook an apple pie by mixing the ingredients with random quantities and at a random orders. That is even with the right conditions and with the correct amino acids, no self replicant form of living would ever emerge *(due to the complexity of the required molecule mixture)*.
By habitable I mean being able to :
* Walk on it’s surface with normal earth clothing.
* Drink surface liquid water without treatment.
* Create soil by mixing local pounded rocks and earth bacteria.
* Breath dioxygen through bottles filled by electrolysis of water *(the electricity could be produced through solar panel)*. You just wear heavy bottles and pipe in noses which allow you to drink and eat normally.
Dioxygen being an oxidizer, it can’t exist at breathable quantities over long period.
* Being able to grow edible plants with artificial atmosphere *(this would be done by filling transparent box with the correct gas ratios)*. The vegetables would be brought in the form of seeds.
Those conditions basically correspond to what can be brought through the first space probe landing on such planet *(provided it also carry humans)*. The idea is once landed they could supply their own needs.
Of course, this implies the following conditions :
* Habitable atmospheric pressure.
* Must have ground which is not covered by water *(this exclude complete ocean planets)*.
* The star should be stable *(typically red dwarf tends to multiply by twice the radiated power from time to times)*.
* Have liquid water on it’s surface.
* The gravity shouldn’t be too high or too much low.
* The atmosphere should be non toxic *(no cyanogen please)*.
* There shouldn’t be massive radiation like X-ray or microwaves *(don’t know if uvc is a strong barrier if you wear sunglasses)*.
* The ground should have the following atomic elements in small quantities on it’s surface because they are required components of humans or edible earth plants :
nitrogen carbon chromium copper molybdenum cobalt selenium nickel manganese zinc iron magnesium phosphorus sodium chlorine boron lithium potassium vanadium silicon fluorine arsenic iodine calcium.
* Have enough light so edible earth plant can grow.
* Not be struck with large asteroids too much often.
By comparison Earth without life would have accumulated more methane gas *(because of volcanism)* than the atmospheric dioxygen can convert to carbon dioxide. The resulting greenhouse effect would had been strong enough to start boiling oceans away. Water vapour being a powerful greenhouse gas itself, this would lead to a [runaway greenhouse effect](https://en.wikipedia.org/wiki/runaway_greenhouse_effect) *(sounds something that could explain how Venus is now)*. The average temperature would be around 900℃.
So could a lifeless planet or moon or asteroid or comet be habitable for actual humans if we exclude natural breathing from habitability criterias ?
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So the main issue as you've stated is the runaway greenhouse effect.
The best I can come up with is to consider that the planet is covered almost entirely by ice. Think somewhere between ice-age Earth and Enceladus. The low albedo of the planet (near 0.9 for snow compared with 0.06 for water [1](https://nsidc.org/cryosphere/seaice/processes/albedo.html)) should compensate for the fact the high levels of methane keep temperatures warm enough for liquid water to exist (at the equator?). I haven't done the maths on this, but it seems feasible that the would be possible- it is, after all, the same process that makes ice-ages on Earth self-sustaining, at least for a time.
If it helps, a slower rate of rotation of the planet would create a larger temperature differential, ensuring more liquid water on the daylit side, which may then freeze on the dark side. This would also allow for evaporation, and hence snow, and snow is a much higher albedo than ice.
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If the planet is in the goldilocks zone of a stable star and had an atmosphere thick enough to stop most meteorites from making it to the ground, habitability without life would not be inconceivable. Oceans and lakes of (sterile) water is of course necessary. As well as sufficient light from the star.
The main determinant is the atmosphere. If you wish to breathe through a nasal prong, the atmosphere can't be outright poisonous (e.g. partially carbon monoxide), and it will have to contain a certain degree of oxygen from the start since a nasal prong only can deliver a portion of your total consumption.
One alternative would be a scuba-like regulator connected to a tracheostomy, which could allow you to draw breath from your oxygen tanks and exhale through your vocal cords. (if you wish to keep the mouth free)
Another obstacle to overcome, I think, is the hardness of the soil. Assuming this is, like earth, a volcanic planet which over time has developed an atmosphere, the landmass would consist mostly of rock. And since you can't plant seeds in rock, that would be a problem. That is why I think rain is the most crucial phenomenon on such a planet. Rain erodes the rock to sand, and downfall could also create ice-ages that would be crucial in creating the soil and form of the landscape.
You could of course also bring soil with you, provided you had enough room and fuel in the shuttle, but I assume you wish to expand your food production as well.
In order to grow plants, many microorganisms are needed because "large" plants such as grains, grasses, or trees can't produce some of the biological biochemicals needed (in other words fertilization). This is what bacteria, moss, and the like are good at. Therefore I would suggest that the settlers bring not only seeds but a bibliotek of different microorganism colonies as well.
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You have asked a very difficult question. I would wager that life itself is not a requirement for **all** the things humans would want with a planet, but having already-existent life on a planet makes things far better and flexible. Here is some explanation.
Life on Earth has formed cycles of elements and substances. For example, carbon cycle, water cycle and nitrogen cycle. This cycling of elements (a process where atoms of an element absorb or release energy and form different chemical compounds, so that they end up in being the same compound which they started with) enables the elements to be used and reused over and over again forever.
In the absence of life on a planet, the planet might be able to sustain human life for some time (ranging from thousands to millions of years, depending on the number of humans and the size of the planet), but this will gradually create dumps of compounds which would not cycle back into their original formulas. This will (in a long time) result in humans depleting all the natural resources of the planet.
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You underestimate the power of organics when it comes to growing crops. The elements you require are often present as a direct result of life. For these molecules to be bonded/present without life seems unlikely to happen (not completely impossible. Soil is extremely complex and teeming with life. And that life needs sh\*t and/or decaying matter. I'm talking literal waste product here. There's a whole ecosystem in our soil. Now, you might be able to do it temporarily with our own waste products, but it would be difficult for it to be self sustaining over a decade.
Think too, about the dustbowl created by NO VEGETATION covering the soil in the US during the depression. BY saying there's no life, at all, if there is particulate matter made from hard stone, and no roots or anything to keep this soil there. These are dustbowl conditions. So, in this case, you would have to contrive something in order for that not to be so. And if it isn't sand, it would be rock, and getting something to grow is rock is difficult. Difficult, but not impossible. Expect big dust storms.
Honestly, I think no life whatsoever with these conditions is difficult--and I am very very glad the breathability thing got crossed off, because that was going to be a big issue.
The conditions you are talking about are perfect for life, and so rarely happen. Some of the conditions actually aren't likely to happen without it (like the perfect combination of organic compounds in the soil without anything living around).
Now, I can see some of these conditions on a world in the Devonian Era type world, but that would require life.
Great question BTW! I know my answer might not be quite what you are looking for (it's a very detailed question that might better be broken up in some way?) but I hope it's a start!
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Yellowstone National Park is the site of a large supervolcano that is somewhat due for an eruption in the geological near term. I have seen slides and discussions to the effect that large portions of the American central highlands and Midwest would be inundated by several dozen millimeters of ash in the event of a large eruption at this supervolcano. Widespread forest fires in the near region and subduction events triggered as a result of the eruption on the west coast also seem at least plausible.
Seismologists no doubt closely monitor this site; an impending eruption might be forecast by several months. Yet given the scale of this event, it is difficult to imagine any preventative efforts the country could take to wholly mitigate the negative effects of this kind of disaster, even with foreknowledge.
In the event we had some forewarning of the event,
1. How would the USA fare?
2. How would the world at large fare?
3. As a side note, what would the disaster zone look like? Feel free to wax poetic.
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This would be really bad. The United States would experience short-medium term economic devastation and be hit by major economic aftershocks for many years thereafter.
Let’s make an assumption that there is broad scientific agreement that the eruption is definitely going to happen with a six month warning period (this is unlikely in practice, but a useful simplification for this exploration).
Given that this is pretty speculative and the geological record is likely to have substantial inaccuracies, we can’t be certain about the size or classifications of the affected areas. For a rough estimation, I’ll use this map:
[](https://i.stack.imgur.com/TPBOJ.jpg)
(It's worth noting that the depiction of ash fall ranges here are not particularly detailed and somewhat optimistic. There's a more comprehensive exploration of potential ash levels in [this paper](http://onlinelibrary.wiley.com/doi/10.1002/2014GC005469/full).)
The kill zone covers most of three states. Fortunately these states are relatively sparsely populated, but you’re still looking at almost three million people. This region is going to experience pyroclastic flows and will be almost entirely unsurvivable. This means *at least* three million people will need to be evacuated with no expectation of their home, business, or town surviving the event.
The broader ash zones are going to experience levels of ash fall that will kill crops and animals, cause widespread roof collapse in buildings, and damage cars to the point of being unusable.
The rest of the country will also be affected with most of it seeing some amount of ash, which even in small amounts can cause electrical damage, invade homes, and contaminate water supplies.
This would be an economic disaster without precedent in recorded history.
**Before the Eruption**
The forewarning, while likely to save lives, will only compound the economic damage. In the year leading up to the explosion there will be immense anxiety as increasing numbers of scientists agree with the predictions. This will cause some people to flee the entire region in advance. Businesses will cease to open in that area and many might hastily relocate. This could cause the economies in anywhere from three to ten of the closest states to collapse before the eruption even happens.
Then there’s the matter of evacuating three million people. Where do you put them? How do you feed them? The pressure from relocating so many people will increase the load on other state economies. Unemployment will soar. And that only assumes that the three million in the kill zone are evacuated, when many more millions are likely to be mandatorily or voluntarily evacuated from other nearby areas. You’ll also have some people who won’t heed the warning — either they won’t believe that it’s going to happen or are simply unwilling to abandon their property for the life of a homeless refugee in some other state.
At this point there would probably be a nation-wide challenge to feed and house so many displaced people.
**Post Eruption**
It’s worth noting that we don’t know how long a potential eruption might last. A four day event should be simpler to handle than a month-long eruption that’s constantly spewing ash, but both would be devastating.
All non-emergency aircraft in the U.S. and Canada would be grounded for the duration of the event and for some time afterwards. Power outages would be nationwide and systemic damage to power lines could result in months without power for many people, particularly in the core ash fall regions. The areas with the most ash would also see roads and ground transportation become unusable. Forewarning should at least ensure that most are prepared for this, but it will still massively impede emergency services. Another major danger across the highest ash fall regions is roof collapse. The weight of ash will cause widespread damage and loss of life.
Many of these effects will be felt all the way out to the coasts, including in states already hit hard by managing refugees from the interior. Food shortages are almost a guarantee, even with preparation, and now you have to deal with the most catastrophic problem: the eruption and ash fall have just hit America’s heartland. Agriculture will be utterly devastated, with widespread crop failure and livestock death. Water will be polluted with ash and in many states the remaining population will be in full-on survival mode. Starvation is likely in some places along with major unrest. These problems would take *years* to resolve and the damage to some of these state economies could last decades. A severe economic depression is all but a certainty.
**International Effects**
These are more speculative. It is safe to say that stock markets would plunge throughout the forewarning period. This is unlikely to be limited to the U.S. since the forecast would be for widespread devastation of one of the world’s top economic powerhouses. This could have severe consequences on economies worldwide.
Canada would certainly share in some of this misery. Yellowstone is close to southwestern Canada and could see severe damage on par with many of the central states. This is actually pretty noteworthy as it could seriously limit Canada's ability to assist the U.S. in the aftermath.
Worldwide travel would *probably* be mostly unaffected. There may be cancellations out of an abundance of caution outside of the Americas during the event, but the ash cloud should not pose the same long-term problems it will cause in North America. Much of this depends on the actual ash cloud itself and may be impacted by the time of year.
The most troublesome international effect is the possibility for climate change. Substantially smaller eruptions such as Tambora in 1815 caused major global effects (the “year without a summer”) and Yellowstone would be far worse. Substantial cooling and even global circulation of ash could cause a global agricultural crisis that might exist for years and kill many, many more millions worldwide.
If you’re interested in what the aftermath would look like, I’d suggest looking up images from the 1980 Mt. St. Helens eruption. In short: a flattened, devastated wasteland.
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many stuff: it could crash the stock market, could cause an economical catastrophe because of closed airports due to the gas, which carries tiny stones in.
It would destroy american farmland, and would also plunge the world into a volcanic winter.
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The United States are gone. I've read in a NatGeo about the volcano that ash fell all the way to Cuba in one of the Yellowstone explosions, covering almost completely the Mississipi basin. That means that the world just lost one of its granaries. It will take many years for american agriculture to restart. And that assuming that the eruption will be just a single big explosion without follow-up explosions spilling more ash.
Our current global food supply is alredy quite vulnerable and when food prices rise people start burning things, like in the Arab Spring, in Russia in 1917, and at this very moment in France. In the case of a Yellowstone eruption the food price WILL rise. A lot. Because the US is one of the greatest agricultural countries, exporting food to the whole world.
And with the global cooling, that may be big enough to end current interglacial period, other granaries will go offline - The european plains from France to the Caspian Sea, The Yellow River, The argentiean pampas and maybe the brazillian highlands.
So, what will happen? Long term social collapse as the heavily urbanized industrial civilization suffers from revolutions. Some of these revolutions will be successful, other will be crushed but none will solve the big issue: there is not enough food and it will be a long time before food production starts growing again. The only "good" things that the revolutions will accomplish is the killing of billions, reducing the pressure. I'm pretty sure that some first world countries will start nuking and gassing 3rd world countries to steal their farmlands in a few decades after the eruption.
About forewarning: Forewarning would allow the nations to stockpile food. If the geologist gave, say, six months before the explosion with the volcano giving clearly visible clues that it would really blow, some food would be stockpiled. In the case of the United States, machinery to clear and rebuild the roads and power lines as soon as possible, with fuel and spare parts. That would reduce how many people would die in the first months. The preparations would also involve calling home some troops, like the ones in Europe, and positioning them in strategic places of the country to impose order. At the same time, build up of an expeditionary force to take over by force of arms fertile lands (maybe the Congo basin?) The american people would be very motivated and there would be endless lines of voluntaries, looking for free meals in the army. About the rest of the world: Preparation is food stockpile, that would mean no exports. Without the granaries, like Brazil, USA, Argentina exporting, that would mean that by the time the volcano really explodes some countries will alredy have starving people. The chinese and the arabs in particular, will have problems.
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Based on [this](https://worldbuilding.stackexchange.com/questions/28659/killing-off-indiana-jones) question however, instead of killing off normal humans, I wish to kill off magical humans. I wish to prevent others from entering in my dungeon, so I have set up a multitude of magical traps. However, over time, the traps will become depleted and anyone can pass through after that. *My question is : What is the best way to create a maze of horrors? What is the best way to terrify the explorers?* A simple trap like shooting arrows works only once.
Note: In my world, people can use elemental type magic along with holy type magic (buffs) while I can use dark magic(necromancy). I have a lot of time to prepare my dungeon, along with the materials (poisoned arrows etc). However I need an effective way of killing off explorers, using magical creatures will not help as a pesky Hero might kill them off anyways.
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Use headology. That is, use the normal way of thinking to completely trick and kill adventurers. Like an easily spotted pit trap. And then another. And another, except where you'd stand to avoid it, like the other two is actually trapped on the third one. In between, have some sort of mundane arrow trap just to keep them from thinking about it too much.
The dark and the unknown are the things people are most afraid of. Do not underestimate the power of lanterns lighting on their own, and then, at just the right moment, snuffing out completely, with soft laughter in the dark. Even before anything real happens this will freak people out. Set up a detect life spell that turns on the lights, and another at the end of the hall that turns it off. Permanency should do it. At this point, have a door open. Tell them they can leave now. Do a count-down.
Also, find ways to deplete spells and use auto reset traps. Hire talented artists. They are worth the gold. By the time they get to the real encounter, they won't trust what they see, so they might not strike and some will die. Or you can make some, but not all the encounters real. Mix things up--make some things magical and others totally mechanical.
Never use the same thing twice. Or do, just to set up an expectation that will be completely wrong.
Make sure that avoiding one trap just leads you into another...Throw in some necromancy and it's just good, dark fun. Any trap with a zombie is a good one--so, one could be, you avoid a mech trap, but a zombie is set to grab one person out from a wall (or do an upgrade so the undead has a good grapple). Make it a ledge so the choices are: die in a trap or come to zombie. Anyone trying to help would not have much room to maneuver and help would be limited by whoever happens to be next to him. If it works well, it's a surprise attack, they are grabbed and pulled in, never to be seen again. If you can pipe in his screams, so much the better....
Edit: And since you are looking to trap magic users, have things triggered by the use of certain spells, like, oh say FLY. Basically, think like the adventurers. If you had their spells, what would you use to counter? Have a healing orison trigger a poison dart/ arrows that seeks the center of it. Make sure that whatever they end up using has a nasty consequence.
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You don't need any magic, nor anything out of the ordinary. A wall and some paint will do.
(Source: a rare safe for work moment from a webcomic called Oglaf)
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Does your world allow using dark (or any other existing kind of) magic for reading people's mind? As was pointed out numerous times in many stories, the scariest thing for any person is something he/she/whatever can't understand and can't even begin to understand.
I assume there is some kind of Core of Dungeon (treasury or any other final destination for all these pesky Heroes). To make it impenetrable you have to surround your core with multiple magical spheres (we don't want these pesky heroes to dig around our traps, right?). We can break these spheres in 3 groups.
Group 1: scanning spheres - they read everything there is in spongy brains of intruders.
Group 2: scaring spheres - they scare off intruders by making their best nightmares reality (with Illusion magic or your equivalent, use information gathered by Group 1). Add some regular low-maintenance traps (like pitfalls with spikes) to wear them off as much as possible.
Group 3: basically, everything else to kill/scare off the most obnoxious of intruders.
There can be only two weaknesses in this system - either omniscient Hero (and I have no idea how to ward off this one) or dumber-than-brick-wall but devilishly robust Hero (same).
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Suppose you were an astronaut on a space ship in the near future. Or an on an asteroid mission where little to no gravity is available. In such a situation it would be difficult to justify taking a large supply of blank paper. Perhaps you might have a few blank notebooks in your personal allowance but those will only let you so long.
So, how do you go about producing more paper for yourself? What are good feedstocks? Or how might you modify typical paper making techniques for micro gravity?
I am looking for science-based answers for a near future setting. Exactly how near future is not important.
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Maybe you'll have *durable* sheets that can be washed and reused, rather than disposable. That would be handy for printers too, which can erase the fed sheets as well as print. Note this idea of plastic sheets is used in Marvin Minsky's novel [The Turing Option](http://rads.stackoverflow.com/amzn/click/0446364967).
You might also combine e-ink sheets with traditional marking, or virtualize the marking like on a screen now. Even if a sheet needs to be placed over a command tablet to work with, people might find "real" paper lacking after being able to select, drag content, etc. like with a painting program but *totally* intuitive.
As for pulp-based paper making, I think it will adapt easily. If anything, pulp won't settle out so that makes it easy; you might even do without so much water and mix in air! Flattening the pulp against a screen will happen through acceleration of the screen and with moving air.
If they have renewable resources like growing plants, there may be facilities for handling materials and performing tasks that require gravity, like centrifugal chambers of various sizes, and other procedures already figured out for zero g. Maybe your hobbiest will adapt the equipment used for washing potatoes, or separating wheat from chaff, for example. Existing gardening stuff may involve materials handling in ways that can be adapted.
Instead of pulp, suitable sheets might be produced using polymers or other thin films that form on membranes. A *coating* process in the fab might be adapted to making sheets that aren't attached to another surface but peel off like old fashioned paint without proper primer (as I remember from a kitchen adventure when I was a kid).
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The biggest problem I see here is the water use required for making paper. In space, water is incredibly precious, to the point that all waste fluid is collected and purified to be reused. It seems like a better option would be to use something like a computer tablet that you can get an infinite number of "pages" without having to physically make new paper.
If you still decide you want traditional paper, another problem you are going to have is it containing the pulp before it solidifies in the paper. If you I don't have gravity, you're going to have to watch that the paper doesn't float away and jam up equipment. To deal with this issue, you should look at the plans for how they'll have [surgery in space](http://www.theatlantic.com/technology/archive/2012/10/blood-in-zero-gravity-nasa-tries-to-prepare-for-surgery-in-space/263171/).
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Actually it wouldn't be that bad. Modern production methods means you could have a machine you feed with bleach, water and used paper, and on the other end you get fresh dry sheets and dirty water for purification. Contained pulp making, roller press, roller drying, no problems with **making** paper.
The things you **would** have problems with:
* Purifying water you use to remove paint (pulp water can be in closed loop)
* Disposing washed away ink
* Supply of bleach / print paint remover
* Printer ink / pens / pencils
So when producing paper is certainly possible and pretty easy, it's also not practical for other reasons than production itself.
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My first thought was, "You can always *simulate* gravity with rotation, so why not use a centrifuge?" In zero gees, it's pretty easy to spin things.
As for "good feedstocks", the most obvious answer is hemp. As EVERYONE knows, it is easy to grow hydroponically, in confined spaces with artificial lighting. People have been talking for decades about replacing trees with hemp in the paper-making industry -- it's the association with marijuana (and the strength of the logging industry) that's prevented that from happening, not any particular technical detail.
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I think that paper will be a luxury item. Most people will see it as an inefficient information storage medium. It will have more mass and volume that digital storage and mass = money if you have to move it. Extra mass needs extra reaction mass (which, itself needs extra reaction mass, etc.).
The mechanical problem of making paper is easily solved since the only part that requires gravity is the separation of the pulp and the water. I see two ways to overcome this. Spin the screen (as has been mentioned elsewhere) or spray at high speed onto a nonstick surface (make a paper "paint" that you peel off.
The real kicker that I see is that you need fibers to produce the paper. For efficiency, I think most hydroponic plants will be selected for their consumable to waste ratio. As such, most plants in space will have no or minimal fibrous parts. So, you would have to plan ahead and select non-optimal plants.
Another source of fiber is animal hair. I think that wool is best but I don't know how efficient sheep will be to raise in space. I've heard that goats are the most likely for small habitats.
This may not be too much of an issue if the clothing is fiber based. In that case, there is already a fiber producing infrastructure and paper can be made out of worn out clothes.
If I remember my James Burke correctly, monks raising sheep led to cheap wool underwear. Plentiful worn out underwear, turned into rags, led to cheap paper which led to the spread of literacy.
The same mechanic could work in space. You just have to figure out the most efficient way of producing the fiber in the first place.
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Yesterday, some weird aliens decided to test their cloning device on earth. It blew up, and killed the aliens. However, it also created a one foot tall exact copy of everyone on earth. ( I shall call them: Mini me's. They pop into existence anywhere within a few feet of the Original, and they are exact copies in nearly every way.)
They have all of the original's memories. The only difference is that they are one sixth the size of the Original. They also have the same medical conditions and things like that. However, only biological matter is cloned. So they wouldn't have tattoos, earrings, or clothes. (AH! Cover it up!) One clone per person is made.
Everyone is cloned, as long as they are not brain dead. So a man who's heart just stopped is cloned, and that clone's heart is stopped. Terminally ill people have terminally ill clones. Sad, but it is true.
Also, these little people **are** able to reproduce and have tiny offspring.
The only bond you have between yourself and your little copy is your appearance and memories. You look exactly alike, your mini me remembers being your size and doing everything you did up until the cloning. It will be very disorienting for them.
How would the government of the modern United States respond to this event? What would be the important factors to consider? For the purposes of this question, please assume that the US government is actually effective, and please avoid discussing individual politicians. This is a question about the US government in general, not the US government right now.
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The government will, fairly quickly, have to adjudicate a few matters:
* **Citizenship:** Since technically these little people weren't *born* (the aliens *made* them), it's not clear what if any citizenship they hold. Since it would be impractical to have half the world's population be stateless, I think the government would consider them to inherit the citizenship of their "sources", same as they inherited other characteristics.
* **Identity:** While the little people start with all the memories, skills, and presumed credentials of their sources, the government will quickly decide that the sources are the original people -- who have jobs, leases, contracts, tax obligations, and more -- and the little people are "extras". Doing otherwise would be sheer chaos, and some in government will surely point out that, if needed, the big people could force the matter. In the end, the little people will inherit no jobs, credit-card debt, or obligations from their sources.
* **Rights to assets:** These mini-people need to be able to eat, obtain medical care, pay for services, and so on. They need money. Are they on their own, as if they'd appeared at the border with only the clothes on their backs? It would be politically untenable to require each source person to give half his assets to his mini clone (though some will make a comparison to child-support laws), and aside from the contents of their wallets no money or durable goods were introduced into the system as part of this cloning. I predict that in the *short term* the government would tap refugee-aid organizations and budgets to cover immediate needs and provide tax benefits to people who adopt their clones. In the longer term there would be a broader debate in the country that parallels the debates about social welfare and immigration.
* **Special services:** Quite aside from how they came to be and how they fund their day-to-day needs, little people have special needs that society has never had to address before. Will the Americans with Disabilities Act be brought into play, with public transportation, buildings, roads, and school systems being required to provide for the size-challenged? Or will owners and providers of services argue that refitting buses, stairwells, curb cuts, elevator buttons, and more goes well beyond "reasonable accommodations"? In the end, the matter will be brought to the courts and new legislation will be required. While there will be pressure for the little people to form their own colonies where *all* the roads, buildings, counter-tops, light switches, and so on can be scaled to them, others will argue against creating ghettos and for full integration.
* **Employment law:** In some professions the little people are out of luck; being a construction worker doesn't immediately transfer to the full-size person's job. But in other professions, there is now a glut on the workplace pool. Since (per "assets" above) there's going to be a desire for the little people to be self-supporting, the government might have to relax its wage laws and union protections. In order to get that many more people into the workforce, it's going to have to be permissible to lower compensation.
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They will decide to take over, given their smaller size they will think they can enjoy more resources of the planet. A studio apartment would become a luxurious loft and so on. They have our memories so they know all our passwords and pin numbers, the ones with less scruples will steal all they can from their regular-sized clones... prices of baby clothing will go through the roof.
The takeover wont be immediate or organized from the beginning, at first will be just a matter of human nature: they will get more and more power thanks to their ability to work on miniaturized technology and eventually they will be the only ones that can afford travelling as airlines wont waste any time in cramming six times the number of people in an airplane each paying a regular ticket price. For regular sized people the tickets will become incredibly expensive. The rest of the transport industry will follow, and from there restaurants, hotels and so on. Regular sized people will push favoring the miniclones because of monetary reasons without caring for the consequences. Their vacations will be better than ours, their life more affordable, they will be happier and spend more time babymaking... Once they will multiply and their number will be higher than the regular people they will vote for their own representatives in government and cut us off. Regular humans will end living in areas less accessible to the miniclones, eventually going extinct.
Hundreds of years later the minipopulation will end with having grown enormously, they will realize that they overdid it and went through the planet like a swarm of locusts in a field. Miniwars and unrest will be the norm but advancement in technology will allow a small group of miniscientists in a minibase in Antarctica to find a way to make interstellar travel a possibility so they still have hope... some *little* hope.
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Not sure for the long term, but in the short term, unless your cloning machine is spatially aware, you are going to have a lot of little people falling out of the sky/drowning/etc. You are also going to have a lot of people trapped in dirt or walls. Many of the clones of people in planes will appear outside of the plane. Anyone who is sky diving will have their clone appear and free fall. Same goes with people who are rock climbing. A lot of people on the water will have clones that are immediately underwater. Depending on the skills of the original (and the depth they are at), the clone may or may not survive. For people underground, the clone may end up submerged in the earth. Likewise, for people in/near buildings, the clones may end up stuck in the walls.
After the initial carnage, I imaging most of the clones would start to be incorporated into society. You will need to deal with food supplies and whether the clones have the same rights as the originals (can they vote?). I imagine that some would seperate into special towns built for clones, but some would prefer to stay within the normal society.
You will also have to deal with the psychological issues that come about due to everything that happened in the first paragraph.
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On day one we kill 20% - 80% with shovels.
Most of the little people that survived would hide in the storm sewers and wilderness where they would be eaten by rats and other critters.
The few that survived would be hidden either by their cell donors or by strange people.
We would all remember that day when those creepy homunculi tried to attack us.
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As far as the American government is concerned, and if recent history is to be our guide, both houses will be totally paralyzed by partisan non-issues and unable to pass any relevant legislation much less conduct an understandable discussion.
Barney Frank will campaign to franchise them as natural-born American citizens because he knows their diet of table scraps will make them natural-born socialists. Also, it will take 99.5% less weed per capita to keep them happy.
Donald Trump will threaten to build lots and lots of teeny little walls, but they'll all be great. The Donald will gain some initial traction because it will take approximately 650 mini-people to shout down the insanity of one Trump supporter.
Meanwhile the executive will wring its hands and desperately try to appease the groundswell of Tea Party yahoos who are noisily denying that the event ever even happened.
The bulk of the American mini-person population will emigrate to Australia to escape the widespread dysfunctional chaos. Upon reflection, the bulk of the normal-sized population will attempt to follow.
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This is definitely the most believable. Consider the news stories we've read lamenting the theft of *coronavirus vaccination secrets* (can you believe there's such a thing?) Alien clones that have pirate copies of everyone's memory aren't going to receive nearly so much consideration.
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How big can an underwater animal really get before physics get in the way? (I'm sure feeding would likely get in the way first, but ignore that!).
The [Blue Whale](https://en.wikipedia.org/wiki/Blue_whale) is currently the largest animal on planet earth the record holder 108 ft. long. The [Megalodon](https://en.wikipedia.org/wiki/Largest_prehistoric_animals#Mackerel_sharks_.28Lamniformes.29) topped out close to 70 ft. [The Lion's mane Jellyfish](https://en.wikipedia.org/wiki/Lion%27s_mane_jellyfish) has been measured to 120 ft. long though masses much smaller than either of the other 2.
So how big in ocean's as large as ours, could an animal conceivably be? And does the size of the planet make a difference? Would life inside Titan be able to be larger?
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## On Earth
**Depends entirely on the beast in question.**
Blue whales are the largest ***mammals***, and they develop quite severe spinal issues in their old age - even having water support their bulk, their skeletal system still takes a beating. Clearly a mammal can't get much bigger (not with a standard bone structure and composition), even in the oceans.
An animal that doesn't have bones, however, might grow to be quite a bit larger.
The problem becomes, as you've mentioned, how would that creature eat enough to sustain itself. The problem only grows as you envision a population of hundreds of such monsters.
Whales solve the problem by ingesting a large amount of water and then spitting it back out, filtering small creatures out in the teeth and then swallowing them.
Squids on the other hand, capture their prey and eat it the good ol' fashioned way. So a kraken (aka a giant squid) would probably go after proportionately large prey, such as a blue whale. There's not that many blue whales to go around though, nor really whales of any other kind.
Fish would be too tiny for the kraken to even bother with, at which point it's probably targeting seafaring vessels and snatching people off the decks - another time honored kraken tradition.
I think this is the reason why so often in fiction these gigantic animals are one of a kind - the results of experiments, or mutation triggered by some other-worldly event (radiation from a meteor, etc).
## Alien World
Imagine a planet with lower gravity than earth, or on which creatures have developed on different principles than on Earth (aka skeletal structure and composition, etc.).
It would make total sense for mega-sized species to develop if they don't face the "structural" issues that Earth bound creatures do. (In Avatar, for example, the size of the local species is explained by them having carbon nano-tube naturally occur in their bones - it's basically hand-waving the size issue aside).
At that point you're making up your own rules though.
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**Don't forget other lifeforms**
I think the most heavy living being on earth was a mushroom that does have a mass of over 100 tons...
Well, while this may not be a leviathan as described in your question, you should take in account that corals are animals too, If you consider a coral reef as a hive-like animal, they may exceed any other animal ever existed in size.
And it is an underwater-animal, so this somehow does apply to you question. Of course, coral reefs can sink ships, but usually they do not tend to be the most aggressive animals in existence (more like the most passive ones).
But if you are not afraid of handwaving, you can construct a coral reef of the size (and mass) of an aircraft carrier that is kind of intelligent and goes for new sources of food by itself. Add some tentacles and... wait, don't do this.
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This is for a novel I'm writing. The basic premise is that massive networks of mycelium running under the soil combine to form a decentralised intelligence that has been managing life and conditions on the planet for hundreds of millions of years. Think Gaia theory, but way weirder. Humans occasionally making contact with the mycelial intelligence explains much religious and supernatural experience in my world.
The big conflict/mystery of my novel is that the mycellium have decided humanity have outlived their usefulness and engineer a population cull. But what I need to explore further is: how if at all might what in essence amounts to entire ecosystems acting with self awareness impact humanity?
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Edited to add: Thank you for all the responses. Its given me a lot of food for thought.
My thinking is the mycelia is "magically" intelligent as a result of its current biology. We already know that mycelia will link up, share resources and communicate, so its not too much of a stretch.
MY thinking is that the mycelia doesn't have much ability beyond what actual mycelia has. They mostly manage the ecosystem by nurturing certain plants, or feeding them particular chemicals in order to achieve specific changes.
In terms of knowledge and psychology, i'd see them as having extensive ecological knowledge, but a very poor understanding of anything that happens at human timescale - not none, but little. We're talking immensely long-lived intelligence. They're quite happy to invest a few decades into a plan, since thats a trivial length of time for them.
As for methods, I see them going for something subtle and targetted. They don't need to wipe out humanity completely - a 90% population drop would be more than sufficient. And I imagine their preferred method would be to have us do it to ourselves somehow, preferably in a way that would keep collateral damage to other species or wider ecosystems to a minimum. My thinking is drugs that undermine critical thinking, and promote the kind of psychology that would breed violent ideologies or something like that.
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Self awareness or the [Hard Problem of Consciousness](https://en.wikipedia.org/wiki/Hard_problem_of_consciousness) has been extensively debated by scientists, psychologists and philosophers. So what I (or anyone else, for that matter) can provide here is not a definite answer, but only an opinion based on common knowledge and some assumptions.
Self awareness is a property somewhat different from intelligence. A mycelium may be self-aware right now, for all we know. Some religions believe that this indeed is the case and every creature possesses a soul that makes them self aware. From a scientific point of view, we do not know if other organisms are self-aware like we are, but it is often assumed since we evolved from them. Of course, for this to be said, we have to make the assumption the we ourselves are self aware.
Intelligence, on the other hand, is something that can be quantified. We have a pretty good idea as to which creature has how much intelligence based on their behaviour, as well as studying their nervous systems.
Returning to your question... If you have said that mycelia are capable of fighting against humanity, you've granted them intelligence and power. Self-awareness, probably similar to humans is also required, but that is only a small condition. Now that they are an intelligent species , we can raise the usual questions:
1. How intelligent are they? Equal to humans, way ahead of us, or slightly ahead?
2. Do they have the same physical form as actual mycelia or is it different?
(a) Do they have an intricately developed nervous system like a human? Is it microscopic? Or are you granting them intelligence by magic, without altering their physical form?
(b) How much physical strength do they have? For example, even if they knew how to create a nuclear weapon, they may not have the physical strength to actually build one.
3. What knowledge have they acquired so far? It is likely that a species with similar intelligence and different physical form from humans (not to mention a different environment and differently abled physical senses of the organisms themselves) will have evolved a different social system and culture, as well as different levels of knowledge in different scientific fields.
4. What inherent psychological rules are they genetically designed to follow? For example, humans tend to perform activities for personal luxury. They desire fame, power and love in varying amounts. They naturally detest pain. They have instincts that cause them to be nervous in specific scenarios and frightened in others. Is any of this true for the species?
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Have you seen that one movie with Mark Wahlberg, "The Happening", where plants mutate to produce "spores" which make people go crazy and commit suicide?
If a plant based intelligence - who's been running the world behind the scenes - suddenly decided to cull mankind they might be able to do something similar (but maybe more realistic).
Subtlety genetically modify our crops in a way that was lethal to us, but not necessarily to animals, for example (imagine mycelium slowly weaving itself into the plants in major cities, and releasing a toxin at a carefully timed/planned moment). Or making grass give off a hallucinogenic substance which causes people to become incredibly violent, and lose their ability to reason - think "28 days later".
At that point you have a lot of leeway as to how this intelligence would deal with mankind. Whether the mycelium intelligence would deal with humans "personally", or just set the stage for World War 3, and thus for humanity to wipe itself out.
The problem as I see it is that I don't know how humans would be able to defend themselves, or defeat this intelligence that they don't even know exists.
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To answer your question, you need to look at what the ecosystem is willing to do to get rid of humans. Just because a conscious entity believes something has outlived its usefulness does not mean it automatically engages in total warfare to get rid of it. I'm sure we don't think mosquito have any usefulness, but they still exist!
An ecosystem that is conscious will be well aware that everything it does hangs in a balance. It may be able to get rid of the humans, but it must live with whatever it does to get rid of us!
So how badly does the biome want us gone? Are they willing to sacrifice all land-dwelling life to get rid of us? How about just forest life? Are they willing to make it harder for deer everywhere to reproduce for the rest of time? These kinds of questions will answer what they actually do.
As for what they can do? By your description, they have been like a gardener maintaining a garden of prized rose bushes. Think about how much damage a gardener could do to their garden by simply not helping.
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Dexyan mentioned *Cordyceps*, an unusual type of fungus that hijacks its host's nervous system to spread and eventually makes its host position itself (just before it dies mind you) in just the right place to disperse its spores. For ants, Cordyceps has its dying host climb up a plant and bite down on the underside of a leaf, right over a well-used ant trail, so its spores will infect any ants passing by below.
You said the mycelia believe humans outlived their usefulness, yes? You didn't specify, so I am left to conclude one of the two choices:
1. humans have become a detriment (threat) to the mycelia instead of a benefit,
2. humans have become aware of the fungi's meddling and/or has become awfully willful, and the mycelia *will not* allow humans to leave its control. Think Britain during the American Revolution, or if you want an example more like what I'm thinking, the Othermind of the Breath-of-Evil plant in the *Wings of Fire* series. Seriously, it's a self-aware and *sapient*, possessive, and power-hungry plant. I'd highly recommend researching it, though you'll likely have to go on a fandom.wikia site to do so.
While the mycelia is relatively limited in its options (poisonous and/or infectious spores can only do so much against an intelligent, adaptive species such as ourselves, which will likely realize what's going on, don gas masks and hazmat suits, and try its darndest to exterminate the mycelia) it will likely see the potential in hijacking humanity and effectively taking their intelligence and resources for themselves.
Why? Because they have *extensive ecological knowledge*; humans have and are continuing to cause mass extinctions, and the mycelia has had an awful lot of time to realize our sheer destructive potential. Destroying a fungus is one thing; destroying an army of intelligent humans is quite another. Mycelia are connected despite the distance between continents, so they likely know of Hiroshima and will realize the need to take care of the nuclear threat.
Ergo, they will hijack small creatures that are relatively common (and stealthy) to spy on and find out whoever has the code to the nukes. Ants, roaches, pigeons, and rats would be essential. Then, after locating their targets, the mycelia will strategically sprout a fruiting body and spam spores on the unfortunate humans.
"But why not hijack the animals and have *them* deal with the humans?" Humans are the greatest exterminators on the planet, we're great survivors due to intelligence and adaptiveness, and some of us would likely pull off survival *despite* an all-out assault from the animal kingdom. Sure, it'd be difficult to make shelters against *everything*, but if we can create nukes and send a man to the moon, we can surely survive such an attack.
At this point, the mycelia, which communicates with each other, will realize the untapped potential of the human mind (and genetic engineering). It will realize humanity is still useful; to act as think tanks and manpower, as well as bring it to the best possible genetic state.
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Vegitarians and Animal rights activists would protest against antibiotics.
It could be a devicive issue like "abortion."
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mycelia allready are somewhat intelligent, as they give moreor less nutrients to plants depending on how they are and what are their needs, if you just make it so it is more powerfull individually, plus their hivemind capacity which can do many things said over in other answers, plus something like zombie fungi, which already exists and affects insects, makeing them do their bidding, then you have an all-out apocalypse as a lot of this planet is covered in mycelium networks, if you make your civilization live in a forest planet, then even more is, they also are quite difficult to eliminate, if you take a chunk of earth, there is more underneath, very deep there is still mycelia, which quickly regenerates, and if you try to poison it, it cuts of the poisond parts, and the chunk with mycelium still tries to grow, if it can, it will be able to spread spores, to infect more of the cities with mycelia, sorry for the disorder, any mistakes are because of my spanish keyboard bye, hope this was helpfull
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**Frame challenge**
They live under the soil, and even if they poke fruiting bodies into the air, these don't have eyes or ears.
They don't have the power of movement in the animal sense. Their thought processes are so slow that movement of even a snail is fast beyond their understanding.
In other words they cannot have any comprehension of the animal world at all, let alone the difference between a horse and a human. The best they can do is direct the roots of trees etc. in the direction they desire. Just possibly they could have some vague awareness of earthworms as incredibly fast creatures that move through the soil leaving tunnels.
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I know that someone has asked how chemistry would be in four dimensions but I was wondering what would chemistry be like in two dimensions? From what I understand, in two dimensions, particles, instead of being either fermions or bosons, would be [anyons](http://en.wikipedia.org/wiki/Anyon). Anyons can only exist in two spatial dimensions and, unlike fermions and bosons, do not have to have spin that is either half integer or integer. Would the existence of anyons in two spatial dimensions have an impact on chemistry and whether there would be chemicals in two spatial dimensions?
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### You can build complex organisms
Leptons (electrons, muons, etc.) are point-particles and I think quarks can safely be considered as points in space too. I think it's safe to consider that they can exist in 2D. Consequently, you still are able to achieve complicated chemistry since you can build flat atoms and with them you can build flat molecules, then flat proteins and give your proteins some complex behaviours like "hooking" one to the another. Removing a dimension does not make mechanics impossible.
### I don't think you should care about flat orbits
Particles do not obey our common sense of "location", the very notion of orbit is **irrelevant** in quantum mechanics. Basically they are somewhere and then somewhere else, they don't move from one place to the other, they just somehow change their location in space-time accordingly to the probability of being there or there. It gives us the very famous "tunnel effect" with allow electrons to "move through" impenetrable walls. The only thing which should still apply is the [Pauli exclusion principle](https://en.wikipedia.org/wiki/Pauli_exclusion_principle) and the Fundamental forces.
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Although answers have been provided, I think it is very important to note that not all chemistry would be possible, and the formation of proteins would be impossible.
Atoms bind based on electric forces, and the structure and stability of familiar molecules is greatly dependent on 3 dimensions. For example, hydrocarbons are chains that require 3 dimensions. The hydrogen atoms form rings around the carbon atoms that are chained to each other along a different dimension.
In 2 dimensional space, the mechanics for this structure do not exist. The bonds between the atoms would not support "moving" the carbons further apart to make room for more hydrogen (that would break the bond) or forcing the hydrogen atoms together into a single plane, which would make it unstable (they would repel each other since the valence of carbon maintains the bond with the electron, the exposed protons repel). You cannot just "flatten" the structure and expect it to remain stable, especially for more complex molecules like proteins.
So while basic molecules may exist, and even complex ones, they would not likely be similar to anything we experience in 3 dimensional space. However, that does allow some creativity in your writing, since you can justify when the rules of 3 dimensional space "do" or "do not" apply, if you like.
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Per [this physics stackexchange answer](https://physics.stackexchange.com/a/492021/31335), QCD works pretty much the same in 2D, so hooray! You get stable atomic nuclei!
The lower dimensionality, however, means that there is less space (both actual physical "volume" and state space) for nucleons to pack into energy shells, so you have fewer stable nuclei--the periodic table is truncated at the bottom. Additionally, the reduction in space for electrons means that you fill up orbitals faster, and the periodic table is squished horizontally.
Fortunately, however, life doesn't use most of our periodic table very much, so there's probably plenty of structural complexity left for your 2D life to use.
Introducing anyonic electrons weirds things. No longer can you depend on Fermi statistics to define the energy shell structure. You would probably get significantly more variation in the chemical properties of your limited set of stable elements... but they would be much harder to predict, and the periodic table would no longer be particularly periodic.
You also have the issue that 2D electric fields only decay proportional to $\frac{1}{r}$, which means that isolated charges have no escape velocity, and it is impossible to fully ionize an isolated atom. It's a good thing opposite charges neutralize! This has some fun consequences in that 2D atoms can absorb arbitrarily high-energy photons; while there may be energy band gaps that allow transparency to some lower energies, all matter should end up opaque to high-energy light. That makes UV shielding by a planetary atmosphere conveniently easy, if you want this chemistry to support lifeforms.
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I don't know much chemistry but assuming that atoms can exist in two dimensions, i.e. electrons orbit flat, then surely you can make molecules. The problem of course is that any non-2d connections in molecular structures are impossible, which is a lot of limitation.
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A necromancer decided to raise an army of zombies to attack the neighbouring kingdom. It's a relatively small and decentralized kingdom, about the size of Denmark. In this world, zombies cannot infect zombism to living beings. But getting bitten can still inflict other diseases like rage. The only way to create new zombies is with necromancy, a dark form of magic known to only a few.
Assuming the necromancer has access to about 10 000 fresh corpses to start the invasion. Once the invasion is started, he will not be able to create new zombies for a while because it's exhausting and he is busy waging a war. After a while it will become possible the crate new zombies to replace the decayed ones by using the fresh corpses of the countryside.
Zombies are slow and dumb but do not fear danger. Zombies do not suffer and move even if you cut their head off. Limbs that are severed or damaged enough will stop moving. If the body parts become too decayed, they will stop responding to magic. Zombies will continue to move unless all the limbs are dead or if you hack the torso in pieces. I believe the decomposition rate might be faster than on a corpse lying still because the zombies are moving. The magic makes the zombies move but it does not slow the decaying rate.
**Considering the decaying rate of the human body, is this kind of invasion even possible? How long will it take before the initial army falls into pieces by itself?**
**Are there any natural techniques or type of environments that would slow down the decaying process?**
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**Mummification**
If the body can walk headless and he have a decaying body, we can assume that it is not 'live', but walking only with magic. With this scenario, it is possible to use good old mummification. This will boost your time to use the corpses, but will need someone or something do do the mummification process. If you can use magic on that, would be wonderful. The corpses will still decay, but on a pretty low rate.
**Cold**
A good environment to start the invasion is a very cold one. Your necromancer should wait untill the winter comes, so he can use the bodies on a even slower decayment rate combined with mummification. The downside will be, probably, slower Zombies.
**Conclusion**
You don't even need the cold environment if you have a good mummification process. With that, your Zombies could live hundreds of years! If your magic need to account for the weight of the body, with less weight they will be faster.
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> When buried six feet down, without a coffin, in ordinary soil, an unembalmed adult normally takes eight to twelve years to decompose to a skeleton
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The reason this happens is that you've cut off access to certain types of insects, namely flies (blowflies and flesh flies)
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> When a decomposing body starts to purge, it becomes fully exposed to its surroundings. At this stage, microbial and insect activity reaches its peak, and the cadaveric ecosystem really comes into its own...
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> ...fire ants made little sponges out of dirt and used them to fill in the cut and stop up the fluid.” The ants monopolised the wound for more than a week, and then it rained. “This washed the dirt sponges out. The body began to bloat then it blew up, and at that point the flies could colonise it.”
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Depending on the times, circumstances, and other variables - such an invasion is possible. It depends how effective your zombies are in putting down human defenders, and how quickly you can put down the defenders before they start to figure out (evolve) solutions to fighting your zombies.
How long your zombies will take to fall apart ranges from over 58 hours to years, depending on whether you salt them, pickle them, mummify them, put anti-fly poison in them, etc. 58 hours after death, is the earliest time that microbes have been found in all organs of the body. The biggest problem is once the microbes have caused skin slippage and bloating to occur, then the flies really get going (see above).
Denmark's largest distance is 250mi. Average walking rate is 3.1mph. Which means your zombies can walk the longest distance in 80 hours. Ignoring, of course, the numerous islands that are part of Denmark, mountains, etc. Depending on how fast you put down the defenders, your zombies could liquidate (heh) the nation prior to liquefying themselves. :)
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Taking your second question first.
Arid and/or cold territory would greatly extend the useable timeframe. So would having access to salt flats where you could send your zombies to cover themselves in salt for a bit of seasoning prior to your campaign.
For your first question.
28 Weeks Later talked about the interval since 28 Days Later, where the majority of infected had died off. Of course their version was super rabies rather than being undead.
There would be rot and decay, but there would also be a massive attack by carrion eaters. Vultures and Crows would be constantly circling. Ants and other insects would take a huge toll on the army. If there is something like Army Ants in the region, swarms would quickly decimate slow moving Zombies.
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At first I was thinking soak them in rum to kill the bacteria, and while that would work it would also make them an easy torch, a quick match would reduce them to ashes. (though it might explain their wandering gate and unintelligible mumbling!)
So my next one would be to dry them out. Remove all moisture from the bodies, turn them into people jerky. It will slow the decay to almost nothing (look at [mummies](https://en.wikipedia.org/wiki/Mummy)!) It will also make the body more resistant to cutting attacks! Jerky/leather is much harder to cut than flesh with normal moisture content.
Edt: Oh, instead of rum you could pickle them! That is another preservative that kills off decomposing bacteria! They will all have a very distinctive smell too...
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Ok so there are a few factors to consider here
**Climate:** bodies decompose faster in warm wet weather. If the conditions are right the body can decompose to an unuseable grade in less than a week. Moisture is key. Dry deserts have been known to preserve bodies for decades same with frozen terrain.
**Preservation:** There are plenty of preservatives that could be applied to a body to desicate and or preserve it. Having your wizard command your zombies to take a bath in an arsenic solution after being risen would be a good way to preserve them longer as well as make them toxic to the enemy. There are plenty of embalming techniques to consider along these lines. A wax arsenic compound has been applied to preserve tissue so far indefinitely to almost lifelike appearance.
**Answer:** attacking during winter would be ideal (GOT har-har) as that would be a more conducive environment. Your mage could instruct his zombies to preserve themselves which would increase their lifespan. If a natural solution to preservation is absolutely necessary then try a fungus that absorbs the moisture and produces a desiccating and preserving enzyme.
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If you didn't preserve them in any way ie. feeding them yoghurt, they would rot in a few days. And they probably wouldn't be that dangerous anyway, because their motor system would rot with the rest of them.
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My world contains a race of creature that does not speak to communicate, they sing.
They are humanoids, living in similar conditions as humans. They are intelligent, they have a complex langage, they can cast magic with their voice.
The song have to be a very particular sound that can be sweet or pretty loud. Not only a voice, but several sounds making a beautiful melody that can not be confused with anything else. For comparison I have a church organ in mind for the "song", but I don't know whether it's possible coming from a single humanoid. I have to make one of them mute in the story, what leads to the question :
**What kind of organ (tongue, lungs, vocal cords, something totally new...?) does a creature needs to perform such a song ?**
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The animals in nature with the best singing vices are birds; they achieve their facility by virtue of their [syrinx](https://en.wikipedia.org/wiki/Syrinx_(bird_anatomy)), an organ located at the fork of the trachea.
A humanoid with a syrinx would be able to produce two separate notes simultaneously. It is also shown that some species of bird are able to vary the notes they produce extremely rapidly, potentially altering the note produced with each vibratory cycle of the syrinx membranes, potentially introducing harmonics that the being could use to emulate any sound in their syrinx's pitch range, and could emulate an instrument with more than two notes.
This could quite easily be used to produce sounds that could be considered to sound similar to a pipe organ.
An interesting side effect of this is that said humanoids would simply open their mouths and complex sounds would come out - there would be little need for manipulation of the lips, tongue and pharynx.
The primary disadvantage would be that said humanoids would have difficulty producing sibilant sounds - their tendency would probably be to produce a whistle rather than a hiss - due to the many rapid random variations in syrinx tension that would be required. They should be able to produce sibilants as we do (turbulent airflow past the tongue), but the idea may be quite alien to them initially.
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Pipe organs are a very early form of [additive synthesis](https://en.wikipedia.org/wiki/Additive_synthesis).
Monty Wild's answer alludes to the requirement to produce multiple sounds at once. The solution of using modulation is great for adding harmonics to a single note, but pipe organ music tends to also use chords to produce the characteristic sound.
One way to reduce the number of notes and harmonics needed would be to fix the key of their communication. For instance on a 'western' human keyboard there are 12 semitones that can be combined into a scale. The most musical but sparsest scale I am aware of is a pentatonic scale featuring 5 frequencies in each octave and the numeric doubling and halving of those notes.
As for anatomy to achieve that I'm reaching here. However, you could replace the vocal chords (which have monophonic but continuously variable pitch) with a series of pipes that have fixed tuning, each with the ability to resonate at different [harmonics](https://en.wikipedia.org/wiki/Harmonic) (see the picture at the top of that article to imagine what the sound waves would be doing in those pipes.
From that you would be able to produce a pipe organ like sound with the number of separate tones they can produce being equal to the number of pipes. The higher the fundamental note, the smaller each pipe could be, so you'd probably find that a large portion of their speech may be ultrasonic for human ears.
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I was trying to create a world that has extensive massive rain-forests unlike anything on earth where the trees interlock with thick branches to allow them to rise much higher into the air (several hundred meters) and provide stable support. This is heavily inspired by a hypothetical alien planet I saw on a National Geographic documentary when I was younger, which you can see here:
<https://www.youtube.com/watch?v=Pw2tggyZeAQ>
Now they argue here that they got assistance from biologists and ecologists to see if such an ecosystem would be possible, but I wanted to run by here to see if that's something that can really be justified.
The thinking goes that on earth, we have trees going up to around 95 meters, their size is restricted by the simple problems involved in creating something tall enough that can go higher and still stand on its own without collapsing, but also the ability of the tree to transport water up to that height from the ground, which eventually becomes unfeasible with the xylem system.
In the show, the solution is that the trees take advantage of endless, heavy rains and fogs, catching water directly at the very top and funneling it down rather than fighting gravity, while they grow struts and supports that interlock and support them against each other over a huge area, allowing them to rise much higher into the air.
I poked around a bit and it seems that both of these solutions appear a bit on earth, giant sequoias collect some of their water from the top, making use of extensive fog:
<http://articles.latimes.com/2002/sep/01/news/adme-redwoods1>
Additionally Banyan trees(<http://en.wikipedia.org/wiki/Banyan>) seem to lock into place against each other with support roots over a wide area, though they don't go nearly as high as I'm proposing.
The Documentary also supposes that this planet has a much denser (3atm at sea level) atmosphere than earth, would this assist in carry water vapor and such?
If somebody better educated in biology and physics could help me out with this, explain where this idea may break down and why it would be much appreciated, thanks!
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There are a few limitations to the height of trees.
The first is the strength of the building materials they are made of. Wood is actually a very strong material so in theory trees can grow very tall.
The second is stability - the taller you go the harder it is to not fall over. In the youtube video the trees solve that problem by interlinking with each other at the top. This would certainly work.
The third is getting water up from the roots to the top of the tree. This is the main limitation preventing trees on earth growing any taller. If enough regular rain was coming then a catchment system as proposed in the video would solve that problem.
So in other words yes, the trees as described in the program are plausible.
The denser atmosphere will help slightly by providing a small amount of lift to the trees - although it will also make wind more powerful. This would make the interlocking even more important.
The main limitation is going to be at the edges of the forest, where you have trees not supported on one side. Additionally you have the problem of where new trees come from - as they would not be able to grow up from the darkness below to reach the light.
Trees near the edge may well be shorter, then the height increases as you go deeper and deeper into the forest.
Trees deep in the forest would most likely reproduce using a sucker type arrangement where a new tree growing is provided materials by the ones around it rather than using seed dispersion. This would be needed because the seeds would be in complete darkness so have no chance to grow.
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This is a question about the same magic explained in [this one](https://worldbuilding.stackexchange.com/questions/12859/magic-that-alters-living-cells-how-to-efficiently-battle-with-it). I also explain the magic below.
**Explanation:**
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> In my fantasy novel, magic is a natural part of the world. It is not some mystical force shrouded in mystery, but rather backed by science (though only I, the author, know it's true workings).
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> In my world, magic is a force that by its nature changes living cells. It is similar to radiation, but different in the respect that it changes what the cell does, usually in a beneficial way. For example, if the cells of an eye were exposed to magic, the magic might make the eye also see infrared light.
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> There are those in my world who can control the change worked by the magic. (They can force the magic to make the eye see infrared light. They can also use magic to make that same eye go blind.)
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**Question:**
Using this magic, could a tree be grown into a specific shape, or made to form specific things solely with its wood? My goal here is to have individuals (think elves) be able to grow a living tree into a house, building, tower, shelter, etc. If possible, I would also like them to be able to grow armor out of the tree - have the tree shape the armor and then pinch it off, like it would a dead leaf.
Let me be clear here. Control cannot be established over the cells. They can simply be altered, so that they produce different chemicals or react differently. You cannot, for instance, just take control of a vine and have it weave itself into a basket. It would have to be grown that way.
Would growing on this scale be biologically possible, and if so, how would it be done (what in the cell would need to be changed)?
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Your key in this will be the plant hormone auxin. Auxin causes most growth in plants. Auxin makes the cells it is in elongate, making the plant grow in a specific direction. You can see this when plants grow toward light. Auxin gathers on the side of the plant facing away from the light. This causes the dark cells to elongate and the plant grows towards the light.
You should have your elves be able to cause plants to create auxin. They will also need to be able to effect the growth speed of plants. The elves could make the plants point one direction with auxin, then have them grow a certain length. More auxin adjusts the growth direction. Using this ability and the power to make stems thicken and you could grow a house from a tree.
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You mean something like **this?** ([**WP:Tree shaping**](https://en.wikipedia.org/wiki/Tree_shaping))
[](https://i.stack.imgur.com/GRbi3.jpg)
*from Wikipedia courtesy of Peter Cook, depicted*
[](https://i.stack.imgur.com/D5kNW.jpg)
*Living root bridges in Nongriat village, Meghalaya, India by Arshiya Urveeja Bose* (CC) *via Wikipedia*
If it's possible to do by training vines and plants, then it's certainly theoretically possible to do so by biological adaptation (whether magical or using genetic means or otherwise).
I am new so don't have rep to post the relevant wiki links, but the above wikipedia article on "Tree shaping" has much, much more where that came from that your elves might be interested in. See also WP: *Vine training* and *Living sculpture*.
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Let's say in an alternate world, Homo Sapiens died out but another Homo species evolved. Homo Carnivorous is very similar to Homo Sapiens with one big difference. Homo Carnivorous can only digest meat and cannot digest plant matter. Because they are evolved to be carnivores, Homo Carnivorous can get far more nutrients from uncooked meat than regular humans can. Homo Carnivorous can also eat any non-poisonous or non-venomous animal. Homo Carnivorous is otherwise identical to humans in most other ways.
If Homo Carnivorous evolved alone on Earth, would they ever make the jump from stone-age hunter-gathering to a bronze age and sedentary civilization? Agriculture seems far less valuable for carnivores. They would eventually have to create it in order to feed their domesticated animals, but fattening up animals to eat them is far less efficient than simply eating the plants. I imagine that Homo Carnivorous takes up herding and pastoralism at first, but that is inherently nomadic and doesn't give birth to a true civilization. Starting a civilization would also be harder due to the reduced population of carnivores.
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# Historical Precedence?
The transition from hunter-gatherers to agriculture is still an area of active study. It is possible, however, to have a city without agriculture. [Poverty Point](https://youtu.be/5kwXmjEbav8) was an ancient city that bucked the trend of "early cities were based on agriculture."
# An Alternate Path
May I introduce you to [aquaculture](https://oceanservice.noaa.gov/facts/aquaculture.html#:%7E:text=Aquaculture%20is%20breeding%2C%20raising%2C%20and,of%20threatened%20or%20endangered%20species.), the practice of raising fish (and other water critters) for consumption. This could, depending on nutritional needs, produce the basis of a carnivorous city mirroring an "agriculture" path. This would, of course, depend on aquatic habitats much in the same way that traditional ancient cities were on farmland!
The other path is simply to have the environment be abundant with game. This could mean various prey animals migrating in/out of a territory so these early people need not move around or risk ecological collapse.
# A Note On City Size
City size is going to be a bit limited, though. This is just because of [trophic](https://en.m.wikipedia.org/wiki/Trophic_level) levels, which is a bit outside the scope of this question. I would expect smaller populations compared to an omnivorous settlement, or simply smaller people.
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**The only condition we've been able to divine is that they absolutely need to be [eusocial](https://en.wikipedia.org/wiki/Eusociality) to achieve it.**
By this I mean:
* The group cooperates to raise and provision the young.
* There are different age groups mixing together:
* Division of tasks/responsibilities such as reproduction, food gathering, group protection between different groups. This is commonly observes in mammals, some crustaceans and Hymenoptera such as wasps.
This would make it unlikely for a solitary predator species, or one that lays its eggs then wanders away taking no care of them to ever develop civilisation.
There are creatures such as amphibia that tend and care for their young to an astonishing degree, but lack the other sophistications necessary for civilisation to develop, but should those characteristics evolve within any species then they basically have a chance in the long-run of achieving it.
**In conclusion, yes.**
Your smart carnivores can either adopt the behaviour by instinct, or because their cognition has evolves sufficiently for them to overcome any instincts to behave in a way that's counter-civilisation. What it would take to convince them to want to cooperate when it's not their tendency naturally to do so (if that's the case), I leave for another question.
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I understand this is not part of the question, but one suggestion which has been explored fancifully has to do with communication, namely telepathy.
Ok, so before you get out the torches and pitchforks, hear me out. :D
Following from my comments on the question, the answer is *it depends*.
I think one of the fundamental requirements for advanced civilization, and thus the technical and engineering capacity to resolve and ultimately propel the problem of obtaining enough meat to support a *presumed* critical mass of intelligence over all, is a function of network density in that the sharing of information is necessary to advance the sciences.
A number of suggestions have been made already, including societal structures and forms of production including aquaculture. But the core of the problem is invariably information and knowledge based.
We don't have evidence for telepathy, obviously, but we can suggest from what we know about information science, neuroscience, biology and even into quantum mechanics that it's perhaps not outside the realm of possibility. Consider sharks sensing electric fields and eels producing them and you're on the right track there.
We know that neurons are plug and play. These little cells care not what kind of information you give them, they simply grow toward and figure out how to differentiate signals. Macaques have been shown to cooperate to move a robot arm in a suprabrain activity in order to fetch and receive treats with the arm.
Furthermore, we also know that the brain is a complicated gizmo and it does some pretty amazing things, often things we're not aware of or kinds of thoughts, feelings or senses that fall just below our threshold of attention.
Again, not going fully creepy mode, but just genuinely questioning the nature of what is and the potential with regard to what we do know.
Obviously, and again without turning on the creepy tap. We're already voluntarily placing hardware into the brains of individuals with motor impairments and learning the language of neurons so we can explicitly reconnect it to synthetic body part replacements. The distance between that kind of technology and direct, conscious communication is perhaps smaller than it looks. We just shy away from it because it sets off all of our warning signals and fears about self and identity and privacy and so on.
So if you need a way to "get over the hump" of challenges which lead to advanced civilization under such constraints, this may be a good option to consider.
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The most common answer is "tidal forces" "wind" since all of these are by-products of the planet's [Coriolis force](https://en.wikipedia.org/wiki/Coriolis_force).
Or there are rnd into generating energy from the earth's magnetic field, but that falls flat since allegedly nonuniform magnetic fields aren't good for generating energy.
I'm looking for a more direct way.
If we strip down the problem:
"Ok, we have this very massive spinny spinny rock." Let's attach a generator to the spinny spinny rock.
Let's say we don't care about the why, and the fact that the sun might be a way better power source, and building a Dyson swarm might be easier.
Just purely let's think about how would we do that.
(We don't care about the planet losing its angular momentum here.)
Question 2:
Is there a way to do this, but keep it on the planet's ground?
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There are several methods of extracting energy from angular momentum of a planet. They're in use right now, on Earth, and all of them can be done on the ground.
Start with [tide power](https://en.wikipedia.org/wiki/Tidal_power) -- this generates electricity with turbines spun by flowing water due to (mainly) Lunar induced tides. Tides also are behind the one-face visibility of the Moon, the internal heating of Jupiter's an Saturn's inner moons -- in other words, tides convert angular momentum into vertical stretching of material which then can be extracted as useful energy.
Next, [wind power](https://en.wikipedia.org/wiki/Wind_power) -- the wind patterns we know (dependable winds from a limited range of directions most of the year) are due to Coriolis effect bending the circulation cells that would otherwise run direct from poles to equator at ground level. Further, Coriolis increases the energy of those winds by converting Earth's angular momentum into angular momentum in the wind, which allows extracting energy from the linear velocity.
Finally, those wind patterns carry evaporated water to high ground; we extract energy from that water via [hydroelectric generation](https://www.britannica.com/science/hydroelectric-power). That energy is directly due to gravitational potential, but the water got up in the hills or mountains or high plains due to the Coriolis-drive winds, and the falling water also carries a little angular momentum, as mass moves closer to the axis of rotation.
I've seen proposed methods to extract energy without contact from extreme objects like micro black holes; many of those depend on the way a spinning hole drags spacetime around itself, but those aren't in current use and may never be practical (I certainly don't want a black hole based power plant on *my* planet).
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**Gyroscope**
The idea of using a gyroscope to extract energy from the Earth's rotation has been around for decades.
A gyroscope (that is not aligned with the Earth's axis) in a frictionless environment will slowly wobble once over 24 hours. In theory, energy could be extracted from that wobble.
The problem is that gyroscopes lose energy to friction. You would need to design a gyroscope such that more energy could be extracted from the wobble than lost to friction.
If a super-low (or zero) friction system were feasible (e.g. superconductor levitation), then you could make an enormous gyroscope (perhaps several kilometres in diameter) to extract a modest amount of energy as it wobbles.
You would also need a system that could accelerate the gyroscope to full speed and then decelerate back to zero with near perfect efficiency. Thus you could reset the gyroscope after you have extracted the energy from the wobble each day.
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Note: when you extract tidal energy, it will reduce angular momentum of the moon, not the planet. Actually, a tidal energy plant will force the moon into a slightly lower orbit.
**Spacecraft launch**
When question #2 is allowed to be "no", a common use of angular momentum is launching spacecraft: there's a reason spacecraft carrying sats are launched from French Guyana. This place is on the equator, which results in maximum angular momentum. Less fuel is needed, because a lot of energy can be harvested.
**Space elevator**
Lifting mass out of Earth’s gravity well without using rockets. An extremely strong cable extends from Earth’s surface to the height of geostationary orbit. Competing forces of gravity at the lower end and outward centripetal acceleration at the farther end would keep the cable under tension and stationary over a single position on Earth. Mass will escape the surface much easier.
**Walk west**
Whenever you put a force to the ground in east-west direction, you will slow down the rotation of the planet.
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In The Long Utopia (Pratchett & Baxter) there's a whole arc about an alien race speeding up the rotation of Earth (well, a *version* of Earth). The method used is a Planetary Spin Motor, as described by Freeman Dyson. It's a bit involved but ultimately it's transferring kinetic energy from a bunch of conductive masses thrown into the planet's magnetic field and applying it to the planet as rotation. Changing the direction of transfer - by altering the trajectory of the masses. This would extract rotational energy as velocity in your masses, which can then be converted to electrical energy by passing them through a series of coils that bleed away the kinetic energy.
Something similar could be achieved by tidal coupling rather than electromagnetic couple. The Moon is tidally coupled to the Earth and as a result the Earth's rotational energy is transferred to the Moon. The result is the Earth's rotation is slowing down and the Moon's momentum is being increased, raising its' orbit slowly. Very, very slowly.
Back to magnetic coupling, David Brin published a story called Tank Farm Dynamo which involved an orbiting double platform joined by tethers. As the station orbits the Earth it passes through the magnetic field, which induces current flow in the tethers between the two platforms. Here's an except from the story:
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> For an instant I saw the Earth not as a broad vague mass overhead, but as a spinning globe of rock, rushing air, and water, of molten core and invisible fields, reaching out to grapple with the tides that filled space. It was eerie. I could almost feel the Tank Farm, like a double-ended kite, coursing through those invisible fields, its tethers cutting the lines of force -- like the slowly turning bushings of a dynamo.
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> That was what young Emily Testa had compared it to. A dynamo. We could draw power from our motion if we ever had to -- buying electricity and paying for it in orbital momentum. It was a solution in search of a problem, for we already had all the power we needed.
>
>
>
As the POV character points out though, they had plenty of power. Turns out that what they really needed was to find a way to *increase* their orbit, not decrease it. You can always hook up solar sails or simply use thrusters to increase your momentum, then use the magnetic coupling to the Earth to turn that momentum back to electrical power. Each watt you draw comes directly from the rotational energy of the planet.
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[Question]
[
So on real-life Earth, tetrapods have either plantigrade or digitigrade legs. In both cases, the knee bends forward, but in digitgrades the ankle joint can give the illusion of a "backwards knee". I am curious about how leg with a true backwards knee would compare performance-wise to digitigrade (and plantigrade) legs. I've included a labelled illustration to indicate how the body parts line up between the leg structures I'm proposing.
[](https://i.stack.imgur.com/KUpC9.png)
The reading about plantigrade vs. digitigrade legs indicates that plantigrade legs are more stable and better for long-distance walking, where digitigrade legs are better for speed. Would the backwards knee/reverse plantigrade setup be closer to plantigrade or digitigrade? How would it affect things if these creatures didn't have a kneecap equivalent at all (like our elbows)?
(As a footnote, the beings I'm thinking about giving these backwards knees to are horizontal bipeds like ostriches, not humanoids.)
[Answer]
It will be closer to plantingrade. You see, the digitigrade leg isn't just about the ankle working as a second backwards knee, it's an adaptation that diminishes the surface area of the foot that touches the ground and usually extends the limb, making the creature more silent and more efficient at running. In addition, a digitigrade leg is good for running usually due to its disposition of muscles and tendons, with the fastest animals usually concentrating the muscles on the upper leg and relying mostly on tendons for the lower leg articulations (this allows for more elastic movement, meaning smaller loss of energy and momentum while running, as well as making it easier to move the limb, as this disposition of muscles and tendons tends to reduce mass at the extremities, thus making the limb easier to move).
Your reverse plantigrade leg is basically a backwards leg with an inverted (for us at least). The creatures which do have such a limb orientation are bats, which all move on the ground in a quadrupedal way and aren't exactly gracious at it. The one animal I know that has this limb structure and is also known to run is the common vampire bat (Desmodus rotundus). These bats, due to their specialized lifestyle, have become well adapted to be able to move on the ground despite their extensive adaptations for flight. Let's look at how they run, yes?
[](https://i.stack.imgur.com/WDaTl.gif)
From this we can see how these bats
1-run in a quadrupedal fashion.
2- rely mostly on their arms to run.
The main issue with the platigrade structure in your scenario is that it's structured to bend in a way opposite to the one in which the weight is being angled towards. If you ever tried to arch yourself backwards, you've likely noticed how hard it is to balance yourself. Such a arrangement of the legs by itself isn't necessarily bad (most bats have it, as far as I know, so it's clearly advantageous from them in some way), but for a bipedal ostrich-like creature this will be a problem. Not only they won't be nearly as fast or stable as an ostrich, they'll also not be as energy efficient, as once they "unlock" their knees they'll have to dedicate a lot of energy to balance themselves while running or walking.
Regarding the kneecap, its function is to help extend the joint as well as protecting it from impact, so I see another potential disadvantage at lacking it (ostriches, which are extremely adapted for running, have 2 kneecaps per leg).
[Answer]
Consider a human walking.
[](https://i.stack.imgur.com/rD5XD.gif)
Pay attention to the side view and what happens with the foot, ankle, and knee. As the planted foot goes underneath the body it starts extending, lifting the heel off the ground and then the toes giving a final thrust. After that thrust happens, the knee is bending allowing the toes to clear the ground, then the upper leg swings forward with the lower following and swinging forward to bring it in a direct line with the upper leg so the foot is forward of the body, in position to plant the heel for the next step.
The lower leg is acting like a pendulum. If there were no muscles there at all the walking motion would still work, as you can see with someone who has a prosthetic limb after an above-the-knee amputation where the entire step is accomplished purely by the motion of the upper leg. Because the lower limb is acting like a free-swinging pendulum, there's very little energy required on the part of the lower leg muscles after the foot is lifted in order to get ready for the next step. Essentially, as the upper leg swings forward the lower leg is swung forward for free. Then, as it's planted, the body travels over the top because of the motion of the upper leg.
The only major exertion on the part of the lower leg is that final toe-thrust. And note that the upper leg and lower leg are straight when it happens, allowing the force to be transmitted as efficiently as possible to the whole body. If the knee bent as that thrust was happening, there'd be an inefficient energy transfer.
That's why things like crouch-running or walking can't be sustained: the always-bent knee means less efficient energy transfer. A person in reasonable shape can walk continuously for hours. Someone forced to walk with their knees even slightly bent the entire time might be able to go a few hundred meters and probably be in agony by the end.
Now look at your backwards knee. The lower leg can't exploit the pendulum effect because it will be required to be pulled upward in order to swing forward. While the human lower leg swings forward and is stopped without muscular effort from going further by the knee joint, in the backwards knee you need muscles to straighten the leg on the step and keep it straight because the natural inclination would be for the joint to fold forward. The muscles are forced to be working all the time.
Now think about what happens on the last part of the step, as the toes generate the thrust as the hell is lifted. Well, *how* is the heel lifted? Again looking at the normal knee: just as the toe thrust is finished, the upper leg swings forward, causing the knee to bend. This shortens the overall effective length of the leg, allowing the foot to just clear the ground as it swings forward.
On the backwards knee, that can't happen. There's no smooth, energy-efficient way to lift the lower leg in order to clear the ground as it moves forward. The only way I can see it happening is that reverse-kneed biped would have to continually hop, pushing off hard enough so there's enough room to clear the ground so the ankle and knee can be bent to pull them up to clear the ground. This will inevitably result in a lot more energy directed at moving the body up and down instead of forward, thus a lot less energy efficient overall.
There might be one way around the bouncing torso problem, and that's if the reverse-kneed biped never actually straightened the knee, keeping it flexed continuously to basically act as a shock absorber to minimize the amount of upward thrust directed into the torso. But then that again runs into the energy efficiency problem: a significant portion of the force created by the feet and toes isn't being used for forward motion and is lost.
Going back to the point I made about a prosthetic lower leg and how in a normal human knee it doesn't require anything other than the motion of the upper leg in order to function, a prosthetic lower leg on the part backwards-knee biped would require some kind of powered mechanism in order to function. That demonstrates the difference in energy efficiency between the two: one can function without power, one could not.
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[Question]
[
I had an idea to have a character that could control cobras, mainly for the visual idea of a character wearing cobras, with them slithering around parts of the body, hidden under clothes or showing.
The images of Hindu gods with 5 or 7 cobras behind them with their hoods out in a fan shape similar to large gothic collars inspired me, although with the Hindu images I believe they were a 7 headed snake/ one body instead of 7 separate snakes.
My story takes place in a world/ universe of super powered beings similar to Marvel/ DC.
So my question is how can someone who can just control a pack of cobras be worthy of being in a group of high powered characters?
I thought the snakes could strategically be sent out to creep up and bite the enemy, they could also be useful for stealth missions, getting into small places to retrieve items etc but the thought of strong characters dying from snake bites would seem un likely and boring.
Any ideas to make this character more than just someone capable of killing low level characters would be very helpful. Even if it means adding complementary powers to the character or the snakes as long as their not too OP and defeat the point of a snake using strategy.
[Answer]
A cobra controlling character carrying around 5 snakes (roughly 30kg) at all times would need to be strong. 30kg might sound little, but if you carry this every day, including while chasing or running from enemies, you have to be fit.
Other associated attributes to someone being friends with snakes could be charming, unpredictable, slender, flexible and calculative. Smart. Or wise. Maybe this character is very, very old, but keeps "fresh" with a regular venom intake, that only the character can survive and knows about. That could be the deep dark secret that he/she wishes nobody to discover, like, without my snakes I would die within short time. This character has knowledge the group depends on, they have to have him/her around in order to succeed. Maybe the character is not completely sold on their mission, but there is something in it for him/her.
Don't trust a snake, I would assume. Maybe the character is a traitor. Or twist that idea around and have everyone EXPECT him/her to be a traitor, by totally being misunderstood.
The snakes could be special snakes, with more than one venom. It could either be the highly effective and deadly venom, or their bites could merely stun enemies, making them unable to move. Or it could make people talk, like a truth serum. And of course they use which ever the character commands them to.
[Answer]
Most super heroes from DC and Marvel are probably **not** immune to poisons. Usually when a character is immune to poisons this is due to them being:
* Purely mechanical or some other kind of construct (i.e.: Vision, maybe?)
* Imbued with a super immune system (Wolverine, Deadpool; Superman when not exposed to Kryptonite)
I recall the Scorpion poisoned Spiderman at least a couple times in the cartoons and comics. Captain America can definitely be poisoned, since he can get drunk. The Hulk can be affected by tranquilizers, so he can be poisoned. And so on.
If your character can have a cobra that is intelligent enough to stalk someone and bite, and if that cobra has some super poison that deactivates super powers or causes death or serious injury, your character would fit into Tony Stark's [Superhuman Registration Act](https://en.wikipedia.org/wiki/Registration_Acts_(comics)#Marvel_Comics):
>
> As depicted in the Civil War crossover and series, the public outcry that follows this event leads the government (with the support of Iron Man and fellow Illuminati member Reed Richards) to quickly enact the Superhuman Registration Act (SHRA), 6 U.S.C. § 558, which required those with naturally occurring superhuman abilities, super abilities acquired through science or magic (including extraterrestrials and gods), and even non-super powered humans using exotic technology, such as Iron Man, to register as "living weapons of mass destruction."
>
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Also notice that if you can control cobras, you also probably can control snakes too. Some anacondas don't want none unless you've got buns, hun eat alligators and even cows. They have quite the force. I could not find a paper on their grip strength, but the largest anacondas are said to squeeze at around 90 pounds per square inch. That's like having an elephant or a school bus on your chest. You could have your pet kill Cap or Batman with such a hug.
[Answer]
Certainly such a character can be useful to help other heroes advance in the story, and their poison can be effective, I don't think it'd be too far fetched to have this character "unlock" some secret hidden power from the cobras (or have powers of their own).
For example, the Greek mythology has [Medusa](https://en.wikipedia.org/wiki/Medusa), whose head of poisonous snakes would turn anyone into stone just by looking at her. Perhaps your character doesn't have super strength or speed, but it's a gigantic pain to have an enemy you're not allowed to look at!
This idea of asymmetrical powers is incredibly useful in hero stories. Precisely because everyone has a unique skill set, everyone (in a well-constructed story) is needed to help advance the narrative. This also makes battles more complicated, giving a rock-paper-scissors like effect between the heroes (Thor can't fight your cobra-wielding character without being turned into stone, but Hulk is so "blinded" by rage he doesn't turn to stone, etc).
Some other ideas of how to use snakes as a super-powered advantage:
* The poison is lethal to all humans *except* your character, who is actually *healed* by the venom. Having snakes around him means whenever he gets shot or cut, a snake bites him there and it heals up. In close combat the snakes bite other characters, killing them.
* The snakes can combine together to turn into something else (I'm stealing from the Exodus story where Moses and Aaron's staffs turn into snakes and back into staffs). Perhaps the snakes can turn into a ladder, sword, water raft, or something else useful.
* When ordered in the right way the cobras can form a portal, channel some other dimension's energy, or otherwise access non-natural energy.
* The character can speak with cobras, meaning they become useful as spies. Or heck, maybe cobras are super smart and can solve complex puzzles.
[Answer]
**Controlling a pack of cobras is cool.**
This character's power is not cobras. It is that he can control living things. He happens to really dig cobras and likes how they feel moving around on his body because he is that kind of guy. He can actually wear his cobras as clothes because he can control the cobras, even when he is asleep. Sometimes he wears other animals instead of or in addition to the cobras. For the other supers he is kind of a hard guy to be around.
He might have his cobras fight, but he is worried about losing them. Usually the cobras stay with him and he just rounds up whatever is local, or gets some living things in advance and brings them to the fight. He might be able to control people too, somewhat, depending on the person and his or her state. He is a cobra wearing Jedi mind trick dude.
[Answer]
The first time a cobra is controlled it's just an ordinary cobra. Venom, snake movements, the usual thing. Each time it's controlled, presuming it does something useful for its master, it gets a little bigger, a little stronger, a little more likely to breathe fire, and a little tougher to damage. After the 100th time it grows wings and can fly. After the 500th time it gets the ability to talk. After 1000 times it gets the ability to morph into a human-like shape. And so on.
This increase in power of the cobra is actually due to the increase in power of the controlling entity. Snake-charmer guy is learning the ins-and-outs of his ability, where the power comes from, how to control it, etc.
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[Question]
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I am creating a carbon planet with seas of methanol on its surface, but I am not sure that this is possible.
It is predicted that carbon planets are depleted of water, since the available oxygen would be depleted by reacting with carbon to mainly form simple compounds such as carbon monoxide, carbon dioxide or carbonate ion. But would something similar happen with low molecular weight alcohols, such as methanol?
According to this [work](https://arxiv.org/abs/1906.04695), methanol is formed in molecular clouds mainly in dust grains through the successive hydrogenation of carbon monoxide. And it is destroyed by reacting with the hydronium ion, one of the most abundant ions, produced from water.
I think that, due to the greater amount of carbon available and, therefore, of carbon monoxide, methanol would be more abundant in the medium and due to less amount of water, it would be less prone to dissociation. Considering this, it would be logical to think that a carbon planet with seas of methanol on its surface be possible.
But I am not an expert on this and I have not found papers on it, so I would like to hear suggestions. Is it possible a world like this or could methanol also end up like water?
[Answer]
**Interstellar methanol clouds!**
I read up on [methanol](https://en.wikipedia.org/wiki/Methanol#cite_note-22), I was surprised to learn that methanol is one of the most common molecules in interstellar space!
<https://web.archive.org/web/20110720152236/http://www.jodrellbank.manchester.ac.uk/news/2006/cloud/>
Upgraded MERLIN spies cloud of alcohol spanning 288 billion miles
>
> Astronomers based at Jodrell Bank Observatory have discovered a giant
> bridge of methyl alcohol, spanning approximately 288 billion miles,
> wrapped around a stellar nursery. The gas cloud could help our
> understanding of how the most massive stars in our galaxy are formed.
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Where is it coming from? Apparently methanol formation in space is different from what happens in gaseous environments, and comes from hydrogen reduction of carbon monoxide.
<https://www.researchgate.net/publication/248627944_Observational_constraints_on_the_formation_of_interstellar_methanol>
>
> The absence of13C depletion as compared to CO2ices pointsto a methanol
> formation from cold CO, possibly via hydrogenation of CO on grains...
> In addition, while the hot core componentshows a CH3OH/H2O gas-phase
> ratio similar to that in ice, this ratio is 60 times higherin the
> compact ridge component. This increase is accompanied by a decrease in
> thewater abundance, suggesting that water here is consumed in the
> formation of methanol in accordance with formation from mixed
> H2O/CH4ice.
>
>
>
Space is different! Back to the question: I can imagine that a rocky planet or a carbon planet in the vicinity of a colossal cloud of methanol might accumulate an environment largely made of this methanol, which then might condense into lakes according to pressure and temperature conditions. In fact, condensation of a methanol cloud like this might be your mechanism for building the carbon planet in the first place.
[Answer]
I noticed you had a question about whether a carbon planet was possible earlier also. I don't remember the answer given, but what you're looking for is effectively a hydrocarbon cycle. For more real-world research on this matter, look up the moon Titan in our solar system - it's the only moon we know of with an atmosphere, and it has rivers and seas of hydrocarbons!
More specific to your question, keep in mind what conditions are needed not only for methanol to rain from the sky, but for it to exist in liquid form at all. In short, you need high pressure and low temperatures. On earth, pressure at sea level does increase when it rains, but not by THAT much - you probably don't feel like weak in the knees to the point of collapse when a slight drizzle breaks out. On this planet though, you might. It also often gets colder when it rains (see: Indian monsoons). Here, it either already was freezing (I'm assuming so at least in the regions where there are seas) or it becomes even colder than its already low temperatures when it rains. So how cold is this? Under our atmospheric conditions, methanol turns solid at -97.6 C and starts boiling at 67.2 C. To do some of your Titanic research for you: the average temperature on Titan is -179 C. Periodically though, it does seem to drizzle a little bit of methane, and there do seem to be seas on Titan made of liquid hydrocarbons.
So what weather effects cause such dramatic changes in temperature and pressure? Feel free to **copy off of Titan**. Otherwise, consider something I just made up: **upper-atmosphere tornadoes**. These tornadoes would not necessarily touch the ground, but contribute to the necessary pressure difference and temperature drop needed to support periodic rain. Long-lasting, sustained batches of these tornadoes could sustain seas underneath. I hope this is useful!
[Answer]
It depends on what molecules are most stable/lowest energy in given environment. I am not a chemist, so can't say for sure, but methanol probably isn't, [see Wikipedia](https://en.wikipedia.org/wiki/Methanol):
>
> It does not persist in either aerobic (oxygen-present) or anaerobic
> (oxygen-absent) environments. The half-life for methanol in
> groundwater is just one to seven days, while many common gasoline
> components have half-lives in the hundreds of days (such as benzene at
> 10–730 days).
>
>
>
Granted this is due to biological activity, but it indicates methanol is easy to react with overall.
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[Question]
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I am in the early stages of developing an alien species and one of their defining traits is that they are empathic upon physical touch. They can only sense feelings/emotions/intent, not read minds, and do not have this ability unless they are in physical contact with the other person (the sole exception to this is "married" couples, who have a permanent emphatic bond regardless of physical contact as long as they are in "range" of one another).
This empathic talent is passive, not actively controllable, so they cannot "attack" or deliberately influence anyone via this sense or anything like that. Physical contact, even slight, is therefore understandably viewed as more intimate in their cultures than it is in many human cultures.
What kind of government would be well suited to a species with this kind of trait, or might they prefer? To simplify things for those answering, assume that the empathy is the only distinction between them and humans.
[Answer]
I don't see how anything would change. Humans already have the ability to detect another persons emotions by the expressions on their face and their posture.
There might be new weaponized scare tactics where a politician imagines a horrifying scenario, then passes it down through the people until everyone agrees with them. But even this isn't really all that different then what the media does now. (In some countries this is quite literally true).
If anything I would suggest there would be a slight trend towards a family oriented system. Villages all being one family and governing themselves because they can all empathically trust each other. A centralized government would be a rule by strangers. Empathic people might be more concerned about the trustworthiness of strangers.
[Answer]
I think the crucial aspect here is physical touch.
In many animal societies touch is used as a mechanism to elaborate the bonds of a society. Both in the positive aspect of knitting together and supporting individuals into a society and in the destructive element of oppressing or excising individuals within/from a society.
Given that touch has an elevated nature in this society its effects will be greater. It might even be considered a requirement in certain social conventions, such as a handshake to seal a deal. Perhaps there would be a handshake to open negotiations? ie. Prove to me that you are here honestly, and desire to reach a resolution that isn't too terrible for me.
Conversely I can see this being used in an exploitative fashion. Torturers would be able to use it to glean more optimal ways of inflicting pain and misery. They need only a more accurate read of the individuals emotional and motivational state. The person wishes to escape? Plan a room/situation that allows them to feel like they are escaping, only to have them literally through themselves into a worse situation. Nothing like being in pain, and knowing that it was your own fault.
I see this as a more extreme society. It is probably going to tend toward tyranny more often than not.
* Perhaps its the tyranny of repression, where by individuals are strictly forbade from physical contact so as to prevent the negative consequences, but at the cost of the good. In such a society individuals will be deeply afraid of contact, even so much that individuals initially experience the worst when they do marry, perhaps they never experience the good.
* Or it will tend toward a tyranny of love where you cannot have a bad day, were to even eat means that you must disclose your emotions and motivations to the other individual. In such a society if you have depression, it will be judged as a personal defect, perhaps to the point were society judges that it is better for the depressed individual to not exist than to be interacted with.
It is possible for such a society to keep the middle road, but this would take a lot of societal organisation. Much more than our human societies at least, simply because touch is so much more compelling and powerful than it is in our own societies.
Otherwise I see no particular reason for why such a society could not manifest in any of the societal models humans have already discovered: Anarchy, Monarchy, Communism, Republic, Democracy, etc... There just needs to be a little thought about how the power of touch transforms the small interactions between individuals, like how they greet, trade, court, learn, etc...
One interesting consequence might be that these individuals lack the skill to visually infer emotional and motivational state like humans can. We do it by monitoring body posture, facial ques, eye direction, etc... perhaps because they can infer this from touch, these skills are not manifested fully. Perhaps there is an individual without the touch ability who is remarked as having godly powers because they can tell the emotions/motivations of another from a distance without touch.
] |
[Question]
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I'm currently contemplating ways to make dragons have a sustainable energy source in a medieval world, while still acting like the traditional soaring, adventurer grabbing, gold hoarding dragons (not necessarily with fire breath). One of those ways I thought of was Gold.
Is there a biological way to use gold as some form of energy for a otherwise purely biological creature, and how effective would it be? This would mean that there is a way to use gold somewhere along a reaction chain to fuel the creation ATP or maybe some other less traditional biological energy source.
You can assume that other essential nutrients will still be taken in by the dragon.
A bit of reference for these dragons:
They are based off of Dwarf Fortress' dragons
They grow to be about 25,000,000 cm3, and a body model capable of flight, they do not breath fire, however.
If gold is sadly not usable as a fuel, instead explain how it could be used as a biological catalyst, it's a perfectly acceptable answer as well. (Thanks for pointing this out, John)
[Answer]
I'm not even going to try to summarise this stuff in much detail - just a *very* brief overview and some block quotes and links, okay?
Gold functions extremely well as a catalyst when ground into nano-scale particles, and is in active use and R&D both in biochemistry research and standard chemistry research - in specific it's very useful for converting CO into CO2, and also for synthesis of vinyl chloride through acetylene hydrochlorination - there are also several other articles and abstracts out there dealing with the specificity of the size requirements of the nanoparticles for gold to be highly effective as a bio-catalyst; bottom line: you could posit that your dragons have specific gold-binding transfer proteins (see last link at bottom for THAT article) that enable secondary and tertiary metabolic pathways which supercharge their high-demand flight muscles - or conceivably (you'd have to research the chemistry) you could tie the vinyl chloride production and the attendant acetylene byproduct in such that a dragon, absent gold, can walk/crawl but would have trouble flying, whereas a gold-imbibing dragon is fast as hell, can fly, and ***can*** in fact breathe fire on demand.
I quote at length (sorry) from abstract at link below:
>
> Gold has fascinated people for millennia; its bright lustrous yellow color has been molded in great works of art, and it has been prized because it is the most noble of the metals and is considered immutable. Gold colloids have also been used to color glass for centuries, and the most vivid example is perhaps the Lycurgus Cup which dates to the fourth century AD and is a very early example of dichroic glass which changes from green to a translucent glowing red when light is shone through due to the presence of colloidal gold nanoparticles.(1) It was Faraday who presented the first scientific paper on the properties and preparation of gold colloids and demonstrated these vividly colored nanoscale structures at the Royal Institution in 1847.(2) Indeed, these gold sols are still stable and remain in the Royal Institution in London to this day.(3) Perhaps it was the perception of the immutability of gold that hampered the development of the chemistry of gold. Until about 40 years ago gold was thought of as one of the least interesting elements in the periodic table with very few pages devoted to it in textbooks of the day. However, now gold is known to have an exceptionally rich and exciting chemistry, and gold nanoparticles have been finding efficacy in many applications especially in the medical arena for cancer treatment.(4) The topic of catalysis by gold is now a very well-studied topic as both homogeneous(5,6) and heterogeneous catalysts.(7) The new advent in the interest in the chemistry of gold has its origins in two discoveries in the 1980s when gold was found to be the best heterogeneous catalyst for both the oxidation of carbon monoxide at ambient temperature(8) and the synthesis of vinyl chloride by acetylene hydrochlorination,(9) and the gold catalyst has recently been commercialized for this process in China.(10) The use of gold complexes as homogeneous catalysts is now well-advanced after the initial discovery;(11) however, although heterogeneous gold catalysts are now finding commercial application the nature of the active gold species in these catalysts has until recently been an intensely debated topic. In this Outlook the recent advances in understanding the nature of the active site for the two reactions for which gold is, without doubt, an exceptional catalyst, namely, carbon monoxide oxidation and acetylene hydrochlorination, are discussed.
>
>
>
<https://pubs.acs.org/doi/full/10.1021/acscentsci.8b00306>
And herein another lengthy quote - this article focussing on studies of the mechanical and physical aspects of *how* gold nanoparticles used for catalysis react:
>
> Gold has always been perceived as a precious material: you win a gold medal when you prove to be the best in a competition; you only get a Gold credit card when you are a preferential customer, and the jewelry made of this material is amongst the most valuable. However, gold has also unexpected properties: It can act as a catalyst and transform carbon monoxide (CO) to carbon dioxide (CO2) when it comes in the form of tiny pieces, called nano-particles.
>
>
> Gold suddenly enhances desired chemical reactions as a catalyst for example in the removal of odours and toxins or to clean automotive exhaust gases. Researchers from Switzerland, UK, the USA and the ESRF (Grenoble) have monitored the catalytic process and proposed an explanation for the high catalytic activity of gold. They publish today their results in the journal Angewandte Chemie online.
>
>
> The team used nano-particles of gold instead of bulk gold. The catalyst structure looks as if someone had pulverized a piece of gold and spread the tiny nano-sized pieces over an aluminum oxide support. The properties of the nano-particles are very different from those of bulk gold. Only when the gold atoms are confined to the size of just a few millionth of a millimetre they start showing the desired catalytic behaviour.
>
>
> Scientists already knew that gold nano-particles react with this kind of setup and catalyses CO with oxygen (O2) into CO2. What they did not know was how the oxygen is activated on the catalyst. In order to find that out, they set up a cell where they could carry out the reaction, and in situ perform an X-ray experiment with the ESRF beam.
>
>
> The researchers first applied a flow of oxygen over the gold nano-particles and observed how the oxygen becomes chemically active when bound on the gold nano-particles using high-energy resolution X-ray absorption spectroscopy. While constantly monitoring the samples, they switched to a flow of toxic carbon monoxide and found that the oxygen bound to the gold reacted with the carbon monoxide to form carbon dioxide. Without the gold nano-particles, this reaction does not take place. “We knew beforehand that the small gold particles were active, but not how they did the reaction. The nice thing is that we have been able to observe, for the first time, the steps and path of the reaction. The results followed almost perfectly our original hypotheses. Isn’t it beautiful that the most inert bulk metal is so reactive when finely dispersed?” comments Jeroen A. van Bokhoven, the corresponding author of the paper.
>
>
> The possible applications of this research could involve pollution control such as air cleaning, or purification of hydrogen streams used for fuel cells. “Regarding the technique we used, the exceptionally high structural detail that can be obtained with it could be used to study other catalytic systems, with the aim of making them more stable and perform better”, says van Bokhoven.
>
>
> One of the great advantages of this experiment is the nature of catalysis. The fact that once the material has reacted, it goes back to its initial state, has made the experiments easier. Nevertheless, in technological terms, it has been very demanding: “We combined the unique properties of our beamline with an interesting and strongly debated question in catalysis. Some extra time was needed to adapt the beamline, to the special requirements of this experiment,” explains Pieter Glatzel, scientist in charge of ID26 beamline, where the experiments were carried out. At the end, it only took the team a bit over half a year to prepare and carry out the experiments and publish the paper. “This is a very nice recognition of our work,” says Glatzel.
>
>
> The article appears in this week’s international edition of Angewandte Chemie with a very high impact among the chemistry audience. In addition to this, the paper has been attributed the status of Very Important Paper, which is given to only 5% of all the publications in this journal.
>
>
>
<https://phys.org/news/2006-06-gold-catalyst.html>
<https://www.news-medical.net/life-sciences/Gold-Nanoparticles-as-Catalysts-in-Biology.aspx>
[Answer]
Here's a way gold can be use to get more energy, although it's not really using biological means.
Remember, dragons are just big, really big, lizards with wings. And lizards are reptiles, which are poikilothermic. Hence, lizards bask in the sun to bring their body temperature up. But heating up a body of 25 m^3 is going to require lots of energy. Which is why your dragons want mirrors, to reflect more sunlight onto them.
So, your dragons require gold so it create a tiny layer of gold on the inside of its wing which it can use to reflect more sun light to its body. And since it's on the inside of its wings, it will slowly lose some gold due to wear and tear. Hence, it requires a regular intake of some gold to replace the reflective layer.
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You do it like Smaug does.
[](https://i.stack.imgur.com/6rPUy.jpg)
You have a massive pile of the stuff and you eat everyone who turns up to steal it....
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Gold is insanely non-reactive. In order to dissolve it you need aqua regia(Nitric Acid, Sulphuric Acid, Cyanide) So any chemical process is pretty much out of the question.
Since Gold is further down the periodic table than iron attempting to get energy from nuclear fusion is out since that would absorb rather than release energy.
With only one natural isotope which is stable, fission and nuclear decay is out.
Being highly reflective, photovoltaic uses are out.
The best bet is to use it as a counterweight and drop it down a deep shaft and use the potential energy change to power whatever. As for how to restore the potential energy? That's what dwarves are for, and they make a toothsome snack.
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Explanations for fire setting are easier to come by than explanations for fire resistance. Being able to set fires with nothing more than their hands, my 'fire-setters' need protection from the flames. So far, traits such as bony/keratinous plates or lots of protective skin would change the physique to something that appears less human. Perhaps symbiotic bacteria would work if there was a way to make the fire-setters not look furry with it. I'm mostly caught in a search for something at least *slightly* grounded in science.
How could my fire-setters have their skin and hair remain mostly undamaged in extreme heat?
Any kind of scientific explanation flies. Crazy diet, alien biochemistry, pretty much everything that works is fine with some explanation. As long as my fire-setters externally appear mostly human in shape, their skin and hair is reminiscent of humans', and they can maintain their fire resistance biologically. I don't mind at all if their abilities are limited, so long as they can at least withstand temperatures around 1,000 degrees Celsius (1,832°F) for at least an hour.
Don't worry about evolution, as these creatures are man-made. If this is too absurd and I should just hand wave, I understand.
**Edit:** Other requirements are that they think like humans and can fulfill basic requirements of living things such as having metabolisms, regulating themselves, and reproducing. I would prefer for them to have DNA and RNA unless this is impossible.
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# Aerogel
[](https://i.stack.imgur.com/Iq7Ib.jpg)
While your beings appear entirely normal from a distance, or while not playing with fire, a closer examination when they /are/ will find their skin and hair encrusted with almost entirely translucent, pale-blue structures, like so:
[](https://i.stack.imgur.com/qNz1h.jpg)
What will this take, diet wise? Well, aerogel is made of silicon alkoxides, so they'll need to consume a lot of silica, which should be easy enough... and they'll also need a lot of ethanol! Beer is a good source of both silica and ethanol, so they'll probably drink shitloads of beer.
Their bodies can do hydrolysis reactions organically as the fire-setters begin to sweat out the chemical precursors to our aerogel, extruding it through their pores as they biologically form the M-OH-M bridges that are necessary for the structure.
Nowadays, the way we go from this superstructure to aerogel is with a solvent exchange, since exposing the stuff to high temperatures necessary for supercritical drying is tricky, but your species can already create fire, so problem solved! Transition the rest of the liquid medium inside the sweated-out pre-aerogel to a supercritical fluid, and bang, you have an amazing heat-insulator.
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Possibly look at the [diatom](https://en.wikipedia.org/wiki/Diatom) - an organism that is able to process silica to build its cell wall. This is abnormal in the animal kingdom, but you could potentially create a scenario where scientists developed living beings with thick skin that is able to store silicates and react to heat by quickly synthesizing a silicate-based asbestos-like layer with a reflective glass-like surface. In other words, something similar to a [fire proximity suit](https://en.wikipedia.org/wiki/Fire_proximity_suit).
This may raise questions of metabolism, method, and how quickly you can actually do that (diatoms are tiny, as are cell walls), but you may have to chalk it up to the miracles of future science. Might also want to make silica in some way part of their diet.
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super absorbent polymer gel as a thin coated oil instead of normal sweat. holds tiny bubbles of water in layers. the fire has to burn through each individual layer evaporating the water. under the oil is normal skin.
<https://en.wikipedia.org/wiki/Fire_retardant_gel>
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So, I was reading this [article](https://www.space.com/40375-super-earth-exoplanets-hard-aliens-launch.html?utm_source=notification) about how difficult it would be for any alien race to escape an exoplanet with about 10 times the mass of Earth.
It states they probably would even lack satellites.
Taking into account a planet like the one in the example, where "escaping" the planet or even putting up satellites would be impossible, how feasible would be the existance of a humanoid race, like humans, and how close to our appearance could they get?
Usually one would think they might look like DnD's dwarves due to the gravity being higher, is that a must or is there a way for their bodies to be more similar to our human stature and bulk?
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10 times the mass of Earth? I don't think there'd be much in the way of terrestrial life there at all, aside from ground cover. That's a lot of weight to lift up, and biologically speaking it's just not feasible. The most you'd get is probably some short, squat plants, or things like plants.
However, I'm going to make one assumption: this planet has oceans. Liquid water oceans to boot - maybe that's Earthling chauvinism, but I'm doing it anyway. And in that case, there would be a lot of life. Consider the kind of pressure exerted by the deep sea on our planet - we get a lot of weird things seen in deep oceans. This planet would have ALL its life like that, except without the lack of visible light. Very few bony animals, lots of things like squid or sponges or tube worms. Actually, those squid things are the most promising candidate for intelligent life - considering how smart our octopuses and cuttlefish are, it's not too far a stretch to assume that if intelligent life were to form on our hypothetical heavy water world, it'd resemble them. And if we assume our squid could have two long tentacles and two medium tentacles plus a lot of short tentacles, and if you squint really hard, they could look humanoid. So I guess there's your answer - "humanoid" life on that planet would be squids.
...I had to work really, really hard not to make a Splatoon joke here.
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High-G environments arent condusive to tall creatures. In the Marines we had to specifically re-learn how to fall down because in full gear your full weight can be pushing 375 to 400 pounds and its really easy to seriously injure yourself by just falling over. On a planet with 10 times the gravity I would weigh in at almost 2000 pounds. My diaphragm wouldnt be able to inflate my lungs, my blood would pool in my feet instead of circulating, falling down would be like getting hit by a truck but that is irrelevant because my body would basically collapse under its own weight into a mushy puddle before I could fall down anyways.
Humanoid body structure is not suited to high G at all. To give you an idea of how crazy high G can get you must realise that on a planet with 10 times the gravity of earth an object dropped from 1 meter would be moving at 219 miles per hour by the time it hit the ground.
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With that mass planet would have to be less dense to support humanoids... but its possible. I believe you can go to about 2g safely maybe even less (mind you there might be issues with magnetosphere due to less iron in core but its hard to calculate). This humanoids would be much more stocky and culture would be different since you tire a lot more there. Biggest change would be to big animals on the surface. Legs like elephants or dinos and such. Plants will be shorter. Carnivores would probably depend more on traps than chasing and so on and on. There would also be more water on such planet.
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I'm trying to layout a scientifically correct evolution path for the octopus to develop intelligence on the post-human Earth. I'd like to know if it's possible for an octopus mom to choose, or use other environmental factors (temperature, oxygen level, etc) to impact its egg or hatchling's gender ratio? I hope that's possible as some sources say octopus do not have sex chromosome.
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In the last couple centuries, many cultures around the world would kill a newborn in the case twins were born, or if the child is born ill or with malformations. This happened in Japan up to the 20th century (*mabiki*), in Australia, in Africa, and in some indigneous tribes in South America [it is still practiced today](https://www.telegraph.co.uk/news/worldnews/1555339/Girl-survived-tribes-custom-of-live-baby-burial.html).
### What the expletive does this have to do with mollusks?
Humans usually bear one child at a time, sometimes two. More than two children in one pregnancy is rare, and more than eight fetuses in a human womb is unheard of.
Cephalopods, on the other hand, are spawners. They may have thousands of children from one single fertilization, and only a few are expected to live to become adults. Were them to develop intelligence comparable to ours, it is not a stretch to expect their views towards abortion and infanticide, at least regarding their own species, to be much different from humans'. These might be generally more acceptable to them.
To make myself clear: just as there is no general consensus on the ethics of abortion between humans, there might be no consensus in a cephalopod society. But I believe the cephalopod society would be, in general, more accepting of it. As for infanticide, it has been a thing among humans, I think it would be a thing among them too.
So if a cephalopod family wishes to have more male or female offspring, they could resort to different methods.
* **Before technology allows them to probe a child's sex during egg and larvae stages:** They can wait until a larvae is advanced enough to show primary sexual characteristics, and dispose of the larvae in some way. That would be **infanticide**.
* **After technology allows them to probe a child's sex during egg and larvae stages:** They can simply discard the eggs they don't want. That would be **abortion**.
There is indication that [sexual determination in mollusks is oligogenetic](http://www.bioone.org/doi/abs/10.4003/0740-2783-23.1.89) (see AlexP's comment in the question). If so, they might one day acquire the technology to do fertilization *in vitro*, using gene markers to find out which gametes have the genes for the desired sex. That way gender rations could be adjusted without neither infanticide nor abortion.
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> I'm trying to layout a scientifically correct evolution path for the octopus to develop intelligence on the post-human Earth.
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We don't really know how evolution works in the sense of being able to make a scientifically *correct* path. And there can presumably be many paths leading to the same end result (intelligence).
I'd suggest that for a human-like intelligence the key stage is the development of some form of sophisticated communication to act as a language. Evidence in people born deaf suggests that if they are taught any form of communication (typically sign language) they can develop an *inner voice* which allows for the development of an active intelligence and without this they do not. It seems to be a key step in our development. I'm not really familiar with communication between octopi but I gather that they have some relatively developed features in this sense.
So you probably just need them to continue to develop better communication and tool handling skills from the ones they already have. Mucking around with sex (as usual) will just complicate things. :-)
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> I'd like to know if it's possible for an octopus mom to choose, or use other environmental factors (temperature, oxygen level, etc) to impact its egg or hatchling's gender ratio ?
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I'm not aware of Earth octopi having this capability now, but if you're writing about them in some future they could always develop such an instinct.
However a likely flaw here is that there's no evidence to suggest male or females are going to be more or less intelligent on average. At the very least this kind of story based decision would be politically incorrect and draw a lot of the wrong type of criticism. I'd suggest caution with this idea.
The problem with exploiting any such mechanism is that initially your octopi will not have self awareness sufficient to make a conscious decision. You're really better off developing a mechanism that relies on either random chance (and works out at the required ratio) or having them develop a systematic biology that does the job (e.g. first they produce predetermined male eggs, then female eggs in turn). Some mechanism that does not rely on "making a decision" in creatures that we would assume don't have such high level of conscious thought.
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> I hope that's possible as some sources say octopus do not have sex chromosome.
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As a side note I'd suggest you link to your sources in your questions for those sort of statements. Doing that will likely get more interest from people in your questions.
This doesn't really make much difference to your intention. Even if they did have a chromosome that determined sex, or a group of them, this might be manipulated by e.g. diet - choosing a diet that's richer or poorer in certain chemicals than normal for a period prior to mating. It may even be an easier mechanism to create (in a book that can gloss over details a bit) than something else.
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Sex ratio is more or less irrelevant.
your biggest issue with octopi is getting them to stop dying after mating, It is hard to evolve child rearing when you are not alive at the same time as your offspring. Only getting to mate once also locks you into having many many offspring at once (r strategy). Since we don't know why they die after mating you can get away with hand waving such an alteration.
Once this happens something like mimic octopus could get a lot of benefit from teaching their offspring different mimic techniques which will go a long way to intelligence, as it gives high returns for evolving language, empathy and the like, and could even encourage pack hunting to evolve.
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In the book [The Quantum Universe](https://en.wikipedia.org/wiki/The_Quantum_Universe), the author suggests that:
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> If the human race evolved in an underground cave system, never to see the sky, it is possible that they could have imagined a ball of gas and calculated its maximum mass.
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This is in reference to the [Chandrasekhar Limit](https://en.wikipedia.org/wiki/Chandrasekhar_limit).
Anyway, if the human race had evolved inside an underground cave, how would science have evolved? Would our current level of technological development be possible (assuming you could mine for resources)?
For example, would Cave Newton have developed his Law of Gravitation without having observed the motions of the planets?
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Let's have look, at what you can do living underground:
1. They can determine that the earth rotates. (pendulum)
2. If they do some measurements they'll find out that the earth is a ball, if their caves are a global system.
3. They could define Kelvin, find out what is the lowest possible temperature.
4. They would at some point measure the flow of the temperature within the earth. How much heat is produced in the core and how much heat radiates away at the surface if it has a certain temperature.
5. By 2.-4. they can calculate the radius of the ball. (Depending on whether a star heats it up they might get it completely wrong)
6. Measuring earthquakes precisely should determine the radius more precise. It will lead them to the question what the additional heat source is. (That is assuming there is a star close by.)
7. Making measurements like in point 6 leads to the discovery of tides. (If they aren't already known.) Using 1. they'll calculate, that the sun circles the earth once every year, while the moon does so once every month. They'll probably assume that the moon is bigger and the heat source is something else, like the temperature of space.
8. Things get harder now. Determine that tides are actually some form of gravitation is for them probably as hard as for us the discovery of relativity theory. That leads quickly to somebody measuring the gravitation constant $G$. With that in mind they can sort out the solar system: The earth is bound to the sun, while the moon is bound to the earth.
9. At this point the society is generally on a technologically level as today. At latest when using particle accelerators they will find out that fusion exists. They understand that the sun might do fusion. That solves the temperature problem from 6.
10. With more precise measurements of tides they might discover more planets. The tide from Venus is at it's hight about 0.007% of that of our moon. They might measure that.
So yeah, they might discover that there are other planets. Of course things might go in completely different direction.
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**You can observe the same laws of physics anywhere in the universe**. It doesn't matter where you live, you can and should come to the same conclusions.
But what *degree of science* would they have? How far would they have developed?
Well, we cannot answer that. Look at us normal above-the-ground humans. My grandfather once told me a story of how his village was visited by a witch once when he was a child, at least his mother believed she was because of her nose. The cows certainly did not like her. He is still alive and lives in what most people would call a developed European country. This is just an example of how perception can change within a single generation. Written human history (let's say = attempts at science) dates back to 4k B.C.. We still tell the time like those people did, based on a system on the number 60. Those people were truly amazing, but the people living on the British isles of about that time took a thousand years [to pile a bunch of stones on top of each other](https://en.wikipedia.org/wiki/Stonehenge). One of the more overrated achievements of the human race if you ask me.
If human perception/ability/technology can drastically change within a generation as well as geographically, you should see that it is just impossible to answer "if x were the case, what would people think/have developed?". Too many variables are at work here. You cannot even make such a statement for us above humans without asking specifically about one point in time and space or even a single individual human.
This might be a bit more general than your question, but I do not think you specifically asking about one thing changes anything. How we view our world scientifically has changed drastically within the last 50 or so years. And then came our super fast computers and changed everything again. Also there are so many branches of science ... We always get back to the fact that one cannot answer that question.
For the sake of a story/world, you can do it **any way you want**.
It might have taken them longer, but technological progress is, as the word itself suggests, no constant in time and it isn't even a constant in space. Maybe they would've been faster, who knows. Maybe there was a **nerd cave** that developed fast while the cave next door didn't at all. And then there was a plague and the other cave caught up. There are so many variables. Btw, I doubt very much that the law of gravitation which is often associated with Newton had as big of an impact as Coulomb's law for example. What do planets matter if you want to produce microchips? I'm sorry my dear Astronomers, but if I had to build a civilization and given the choice, I would take the electrical engineers instead.
The only thing I want you to consider is of course that you shouldn't flood a cave with toxic industrial waste, but that is a given I think. We shouldn't even have done that above the ground. If you want you can even have them dig tunnels to the surface to "blow of steam" there.
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Working with [this question](https://worldbuilding.stackexchange.com/questions/39064/how-and-when-could-a-dyson-sphere-civilization-figure-out-the-shape-and-size-of) but with more of a fantasy bent, I was wondering how long it would take a civilization to learn/realize that they lived on the inside of a Dyson sphere (or hollow earth or something similar) under the following circumstances:
* Light is provided by a central source that emits directional light somewhat akin a lighthouse.
Like this:
[](https://i.stack.imgur.com/cxwF0.png)
* Gravity Some force that may or may not be gravity but approximates gravity regardless pulls in a uniform manner towards the shell without the shell rotating.
* A 3 AU sphere as described in the original question.
Barring magical methods (divination magic, praying and asking deities, etc.), could a civilization living on the inside of such a Dyson sphere determine that they A) didn't live on a flat plane and/or B) lived inside of a sphere and when (at what real-world technological level) could they accomplish it?
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I think they will figure it out pretty early on, at a fairly low tech level.
The reason is the directional light source.
At 3 AU the ground will slope up toward the horizon, but it will be so gradual that it will be hard to notice before the haze of distance obscures the view.
But at night this stops being as much of an issue. As the light rotates away from you it will get get dimmer at your location, but brighter further up. This gives at least two ways to know that you're in a sphere, and to see how big it is.
Assuming a 24 hour day (full rotation of the light source), after 6 hours the light will be a quarter of the way around the sphere. That means you'll be able to look up and see the lit up area, and even at ~1 AU you should at least be able to make out certain large details such as oceans with minimal telescopic equipment. Even with the naked eye you'll see the path of the light as it travels around the inside of the sphere. Jupiter is 5.2 Au's away and can be plenty bright. The reflected sphere light might be bright enough to read by.
To get the size of the sphere is some fairly simple math. Place two markers several miles apart. Time how long it takes for the terminator to travel from one marker to the other. Now you know the time it takes to travel that distance, so it's easy to calculate a full 24 hours worth.
Due to atmospheric scattering the terminator line may be hard to distinguish at ground level, but not impossible. You may have to find the distance between two large landmarks part way along the sphere, and then watch the terminator move between them from a great distance away.
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The light(s) of "day" would be visible at "night". Changes in size and brightness being related to the position of the light in the "sky", dimmer an smaller when closer to the far side brighter and bigger close to the right angle, and brightest and smaller close to the horizon. Clever people might be about to find the shape from that little evidence.
If the light follows a predictable path you can relate the speed of the terminator to the angular speed of the spot at night to find the radius. Measure the terminator either by looking at or from a mountain or using synchronous clocks across a wide distance, but be warned you can make the terminator move faster than the speed of light with this setup, which makes measuring it a non-trivial task. But you should be able to put a lower limit on the size for any lower limit you can put on the speed.
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Fly something towards the center, and continue in a straight line. The gravity would not pull in a way that normal gravity does, it would not keep you from just traveling straight and flying straight into the ground. This is because you wouldn't fall to it if you were going straight.
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Or vice versa. Let's assume humanity or some equally advanced intelligent species discovers life, or even a plethora of life, out amongst the stars, and decides that they want to make contact to see how intelligent they are. But instead of sending them sensible things like mathematical proofs and other various equations, we decide we're going to have a little fun messing around with these aliens and format our intelligence test like a game or series of games. Because apparently we enjoy the sounds millions of frustrated aliens make as they get stuck playing unforgiving 90s point and click adventure games and old escape the room Flash puzzles.
But how would we convey the idea of a game or challenge to them, much less the rules? Given the broad variety of alien psychologies and physiologies potentially on display here, what would our best bets be if we want to put together a collection of games to launch to the aliens in the hopes that they'll recognize a few of them? Squid-people can't exactly play soccer or tennis, and many human games that don't involve physical activity (the kind that might be incompatible with certain body plans) rely on what might be considered uniquely human logic (see the adventure games mentioned above, as well as almost every videogame ever besides Pong).
So what kind of games could we send to these unknown aliens in the hopes that we'll have at least a few of them in common? (Off the bat, my first couple guesses were pattern-matching games, games that subtly incorporate different kinds of math, and perhaps maybe simple strategy games like go, shogi or chess that require a dynamic and flexible approach to problem solving. However, even these have issues)
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Bear with me, please... I'm going to start on what seems like a somewhat tangential topic, then come back around to your question because I think the first informs the latter.
The first game will likely be "who can disclose the least information while we get to know each other and decide if we can trust each other." The book "The Three-Body Problem" won the Hugo in 2015 for laying out a strong argument that the first sentient species to detect another sentient species should probably launch an all out genocidal attack on the other species without ever disclosing that the attack is coming -- that tends to put a damper on other types of games. The reason for this being the correct strategy is pretty simple: resource consumption. Deeper analysis of this argument is outside the scope of this question, but I find the argument rather compelling. There are many other reasons, explored on this forum, that suggest that we won't be playing games with alien species. EXCEPT...
That particular argument and most of the similar arguments for us being in conflict cease to apply if the two species have 100% no interest in each other's worlds and resources. So a species that colonizes the upper atmosphere of gas giants and needs to stay far away from a sun to be at a comfortable temperature wouldn't be interested in Earth, and vice versa. We might have some conflicts over mining resources in the asteroid belts, but those aren't genocidal arguments.
Which brings us to games.
If two species are sufficiently dissimilar that they aren't interested in each other's homeworlds, then they may get to know each other well enough for games. But if you accept the argument that two such species must be from wildly different worlds, then we aren't looking at anything *personally* physical. No soccer, baseball, etc. Those would all be ruled out not just by different physiology but from the physical inability to exist in each other's physical locations.
*Mechanically* physical seems feasible -- think NASCAR in space. Three loops around the sun, first to graze Phobos wins. Similar events where the challenge is some sort of engineering challenge would be viable games.
The intellectual games would come with time, and presumably would be whatever humans are playing at the time. If we have sentient species, we would be building up communication for trade and general knowledge sharing, and eventually communicating tic-tac-toe and checkers and chess and Go -- but they PROBABLY already know Go.
[Tangent: Go is a game played on a grid with black/white stones. [It has only 9 rules](https://en.wikipedia.org/wiki/Rules_of_go#Basic_rules), and variants of the game have, according to unverifiable legend, arisen independently in various parts of the world in human history. This has given rise to the theory that since this grid-of-stones seems like such an intuitive game, and its strategy is surprisingly deep, that all sentient species would at some point stumble into it. Therefore, aliens already know Go. Go study the rules of Go and decide whether it is something you think could just naturally develop in any species that spends time studying geometry.]
Anyway, after we tire of Go, we could communicate with them any game we want.
Now... on that note... why would we tire of Go? Because it is a total-knowledge game. All total-knowledge games will eventually be solved by computers, and it will simply be who has the deeper read of the game tree. Tic-tac-toe is fully solved... so is checkers... others will come with more computation. Ian Banks, in his novel [The Player of Games](https://www.goodreads.com/book/show/18630.The_Player_of_Games), posited that only games with some element of chance in the early stages would continue to be interesting, and it was best if that chance element would lead to a game that had never been played before. In his novel, multiple species compete in various games with different handicaps between players of different skill, but always with some random element thrown in. Think like Chess, but where the board is the topology of a randomly chosen continent. Or poker, but with a randomly chosen number of cards (no one would ever see the full deck, so you could never be sure how many cards are in any given suit when bidding). That sort of thing. I recommend reading the novel -- over the course of a few hundred pages, Banks delves deep into various kinds of games and why they work or don't work across cultures, far more than I can summarize here.
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So I was deciding on ways to end my world in a futuristic scenario, and I had an idea. As we all know, Earth has two poles, and these poles are moving constantly (Magnetic Poles are different from actual Poles). The recent average movement is about 10KM a year. In the past the poles have completely reversed, as in, the North Pole became the South Pole.
This is all because of how the molten core of our planet fluctuates and moves. The outer liquid iron core is constantly moving around a solid inner iron core creating a magnetic field that spans thousands of kilometres into space. This magnetic field (Magnetosphere) protects our upper atmosphere and Ozone from being blown away by charged particles that emanate from the sun.
[](https://i.stack.imgur.com/SlJS2.jpg)
Astronomers hypothesised that the weakening of Mars' magnetosphere is the reason its atmosphere almost entirely blew away.
Whilst our core is cooling (over billions of years) I wondered if it might create multiple poles, which would lower the extent our magnetosphere reaches and create more holes where the magnetosphere springs from, severely crippling our protection against solar winds perhaps to the point where it blows away our atmosphere.
Anyways, what I'm asking is, could there be more than just two poles?
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## Absolutely.
It is believed that in the past the earth had multiple chaotically spread poles and that this only changed recently around 650 million years ago when the core became less turbulent.
Our planet's dynamo is incredibly complex, so it is entirely possible that it might revert to that less orderly state, where many poles will onces again start appearing and disappearing for millions (or billions) of years.
Even more plausibly however, our poles also (north and south) periodically switch places in an event known as geomagnetic reversal, during which many poles temporarily emerge, this is even quite likely to happen within our lifetime as the last one was 780,000 years ago, yet 450,000 years is the average duration between each switch.
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Yes, during a [geomagnetic reversal](https://en.wikipedia.org/wiki/Geomagnetic_reversal) (which lasts from about 1000 to 10000 years, but sometimes it's much shorter) Earth magnetic field weakens and many local poles can appear.
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## Yes, for a number of reasons, and it's somewhat realistic
@AngelPray and @RandovanGarabik are absolutely correct, geomagnetic reversals may weaken the magnetic field and cause multiple poles. While the shortest reversals usually take 1,000 years, you could handwave a mechanism or catastrophe to speed up the process - or have it jumpstart, etc.
In addition, other planets we have observed have very complex magnetospheres; it's reasonable to conceive of something as simple as a pole reversal here at home.
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For my fantasy world, I have what I think is a really cool idea. The world is flat, and elliptical in shape. If you touch the silvery edge, well, let's just say bad things will happen. (Not relevant...) This edge is an impenetrable, indestructible wall.
This world is like a coin, with two sides. Each side is the same (for the purposes of the question), and the giant island slopes downward until it meets itself. This leaves most of the ocean without a solid floor.
Assume that gravity is magically inclined to drag everything down to the equator of the "coin". with 1g of force, and this gravity is the same all around.
The world has a high "ceiling" of sorts, above each surface, uniformly heating and lighting each side of the coin. ~72°F
That is the full extent of the world, no sun, moon, or stars for you to be concerned about.
If an object sunk into the sea, it would sink until it reached the bottom of the oceans, a mile from each surface. A fish happily swimming on one side would appear upside down from the other.
My question is, how would aforementioned changes affect the ocean?
[Answer]
## This will change both the continent and the sea in unusual ways.
### 1) The ocean floor will create itself anyways.
Bear with me on this one.
If your world has light (solar radiation), it will have a **water cycle**, because water molecules will be warmed to the point of vaporization. The water cycle drives **weathering and erosion**, which wears down the land over time.
As sediment slides off the continent on either side of the "coin", it will sink to the lowest point - where both faces of the world meet at the bottom of the sea. Congruent particles will meet each other and remain at the boundary; because the worlds are exact, mirrored copies, matter will run into its counterpart when it reaches the bottom.
Most sediment that reaches the bottom will remain there, because there are no **tectonic forces** at the boundary that would lift sections of the seafloor back up. Sedimentary rock will form over millions of years, then become metamorphic due to pressure; a muddy floor with rock underneath will inevitably exist.
### 2) This means the continent will be flatten and shrink over time.
Tectonic and volcanic forces are primarily driven by the convection of rock deep within a planet. Since this world is only a mile thick, it will not have tectonic plate movement, nor will it be able to support any large volcanoes. Therefore, no new landmasses can form - and the continent will continue to erode from the outside-in until the entire world is a shallow sea.
### 3) The center of the continent will be an inhospitable desert.
Similarly to how super-continents in the past (on Earth) harbored central deserts, your continent will likely be the same. Water is too distant, and most precipitation falls closer to the coast. It's worth noting that this desert will neither be hot nor cold - it should be at about the same temperature as the rest of the world, since there aren't seasons in a world with no axial tilt - but it will be very, very dry.
### 4) Many sea creatures will be fine.
Plankton and other microorganisms will still be able to thrive, because the light and nutrients they rely on will still be present in this world. Krill and other creatures that feed on these will in turn not be affected, and so on - so you can still maintain a healthy food chain in this world if it's based on those in the shallows on Earth.
### 5) Say goodbye to deep-sea ecosystems.
This seems most obvious. Creatures will not evolve to be suited for an extreme lack of light, nor will they evolve to feed on the heat and nutrients found in deep-sea vents. As a result, many large Earth creatures that dive deeper may not be able to survive on this world.
### 6) Two-world creatures may evolve.
Before the seafloor is sufficiently thick, some creatures may take advantage of protection on one side - the world boundary - and develop so that they're attached to their other-side counterparts! While matter cannot be exchanged, and both halves will require energy, decreasing the efficiency of such a system, they may be able to conserve heat energy.
### 7) There probably won't be any tides.
On Earth, the pull of our moon is responsible for moving large amounts of water, producing tides. It seems like this world will not have a moon, so you may expect to see somewhat smooth sailing.
### 8) Wind may be wonky.
One of the important wind-driving pressures we have on Earth is the **Coriolis Effect**. It's caused by the **rotation of the Earth**, and results in somewhat spiral-like wind patterns.
] |
[Question]
[
Suppose humanity found a rocky planet outside the solar system. It is in the habitable zone of its star, has breathable air, clean water etc. A true paradise.
Only problem is, its surface gravity double that of Earth.
Let's forget for a while that this is going to be extremely taxing on whatever colonists decide to settle there. They are going to anyway, simply because they can.
I am thinking, though, that many everyday things we use on Earth could become awkward or even dangerous to use. For example, dropping a glass of water from a table would be much more dramatic. Showering could be painful. Riding a bike down a slope would become a new radical sport.
How would the settlers adapt their equipment, appliances, toys etc. to cope with a higher gravity?
[Answer]
A number of complications come from 2x gravity.
First any fall would be considerably more deadly. My (at the time) 60-year-old mother broke her wrist fairly badly by simply falling down in a Home Depot parking lot. She has no medical conditions that impair the strength of her bones; that's just life. 2x the gravity would likely increase this threat. I assume some sort of soft exoskeleton would be normal for day-to-day, and a more robust hard suit when anything physical was involved.
Simply standing up and walking would be challenging, if not impossible. A 200 pound athletic man would suddenly be lugging around 400 pounds, and would not be able to run (likely at all) or even travel very far distances. For this reason the exoskeleton likely needs to be upgraded with robotics to take pressure off the muscles.
Blood pressure is also an issue. To quote a source:
>
> Under normal conditions, your body must maintain 22 millimeters of
> mercury blood pressure to get blood from your heart to your brain.
> Each additional +Gz (blood flows from the head to the feet) that a
> person experiences multiplies that requirement: The body has to muster
> double that at 2g, triple that at 3g, and so on until they hit around
> 4 or 5 G's, at which point most folks will pass out due to oxygen
> starvation because all the blood stays in their feet.
>
>
> This condition is known as G-LOC (G-induced loss of consciousness).
> Fighter pilots, with the aid of flight suits packed with air bladders
> that force blood out of the lower extremities as well as specialized
> breathing and tension techniques, can be trained to withstand up to 9
> +Gz.
>
>
>
So the exoskeleton also should provide external pressure like a flight suit to allow blood pressure to be maintained.
Further still the increase in atmospheric pressure (from the increase in gravity) would make it harder to breathe in and out, while simultaneously forcing extra gasses in your bloodstream including oxygen and less-than-ideal other gasses included. We could negate both of these issues by suiting entirely up with oxygen tanks and a sealed mask, or we'll have to accept the drudgery of simply breathing and carefully terraform the atmosphere to an ideal composition.
Likely buildings will be built around asinine safety with railing common, stairs rare, and most floors designed to provide traction.
Transportation costs will be significantly more, and flight will be expensive enough that most long-range transportation will depend on railcars designed to avoid frictional costs.
Chairs will likely be reclined to be more comfortable, since the human body is designed to handle Earth's gravity, not sitting up in 2x, and even with the exosuits it will likely still be more comfortable to simply not avoid fighting gravity as much as possible.
The people will likely be unusually muscular even in ways that you normally would not expect (for example, muscle builders don't exercise blinking, but in this world every blink rips down muscles considerably more and the body will respond to try to build them back up stronger).
Toys will likely be far less physical-activity focused with again a concern for safety.
Cooking will be changed since the boiling point of water will be considerably higher, and any chemical reaction to add air to food (such as yeast causing bread to rise) will fantastically fail, most likely, producing dense food.
Most plants from Earth simply won't survive; as plants depend on osmosis to draw water up, they depend on osmosis being stronger than the force of Earth's gravity. In a 2x gravity world this likely will no longer be the case. Thus if this new world doesn't come with plants, the colonists will likely have to depend on plantstuff for food to be shipped to them from off world.
Credit to @DaaaahWoosh for some of the ideas.
[Answer]
Remember, after the first few generations, the colonists and whatever species they bring will have acclimatized to the new gravity. You'd expect the first generation born there to develop denser bones than their parents, have stronger hearts and so forth. The first set of colonists might simply stay on floating platforms half the planet's radius away from the surface, with only the fittest young adults allowed onto the surface. They'd need to spend time terraforming the surface anyway to make it habitable, before they can actually set up shop, so why not use this time to ensure the next generation can survive without technological support. This could also be sped up with genetically engineering humans, plants and animals to be physically more robust. Or shorter.
] |
[Question]
[
**Because who needs a space craft?**
*Picture this:*
While performing a routine spacewalk, outside your small, 1-man space pod, a fault in the propulsion system controls causes the pod to explode, launching you into a *low orbit* of the Earth.
Now with a limited air supply, and only your own space suit & MMU (Manned Manuvering Unit) at your disposal, **you are tasked with re-entering Earth's atmosphere, in a survivable manner**. (Please note, that chance of survival does not need to be 100%).
*The Question:*
Is it scientifically possible to survive re-entry in this manner, and if so how? **If not**, and if it would be possible, if the scenario were to be modified, please describe how it could be modified, in order to make it possible.
**Note:**
Your MMU does *not* need to be of the modern NASA variety. The story is set in the near future, so the design can be slightly more advanced (but still within reason for an MMU).
***Edit:**
Originally, I had planned for the MMU to provide a wireless transceiver (allowing the astronaut to calculate his re-entry angle based on GPS signals?), a set of manuvering thrusters which set his re-entry vector & slow him down to prevent a crash - if possible, and possibly the material needed to construct a rudimentary heat-shield (if such material would feasibly be used in construction of an MMU).*
[Answer]
There are many problems to overcome:
According to [NASA](http://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html), most meteors of a radius of `80 feet` burn up in the atmosphere so that they cause little to no damage. So, we need to somehow cool off our poor guy so that he isn't a pile of ashes by the time he hits (or floats, if he was ashes) to the ground. Add a very potent **coolant system** or **heat shield**.
Now that we've solved burning up, we still have to consider landing. Terminal velocity at sea-level for an upright human is about 200 mph. Most meteors burn up around 30 miles, so our friend would have to decelerate in a "mere" 30 miles, either requiring a reverse propulsion system to boost him upward, or a parachute. The former would also require some kind of stabilization system, such as gyroscopes, to avoid flipping over. The problem with a upward thrust is that gravity will push down when you are not at terminal velocity, so you would have to supply a continuous thrust of around `9.9 m/s^2` for about `10` minutes to slow him down to land safely (which is impractical), so you would need a **parachute**. To be safe, we also include a upward-accelerating **jetpack** to ensure a safe *landing*.
---
All in all, your chances for survival are fairly slim, but it could be possible to survive such a fall.
[Answer]
If this sort of scenario was considered likely, the MMU might incorporate a "ballute".
This is a low mass substitute for a reentry heat shield, and has the added bonus of being an air bag for your final landing. Real life use includes being used to retard bombs (so the bomber can escape the blast) and this has been proposed for real life space missions. The movie 2010 has the Russian spacecraft using a ballet to aerobrake in the orbit of Jupiter, so the technique is versatile.
[](https://i.stack.imgur.com/6z89h.jpg)
[](https://i.stack.imgur.com/IaRhP.jpg)
Now this might not be a common thing to add to an MMU, since while lighter than a heat shield, the mass of the fabric and gas bottles to inflate the Ballute will still be considerable, and make manoeuvring in space slow and unwieldy (you will also require far more fuel for your MMU to work). It would be like suggesting you always carry a parachute and a backpack full of survival gear for both desert and arctic conditions, on the off chance you fall out of an airplane or window.
For your scenario, if the construction shack can't send a rescue pod out quickly enough to pick up the unfortunate astronaut, they might be able to launch a "reentry pack" with prepackaged ballute, inflation gear, extra oxygen, survival kit and a powerful solid fuel rocket motor. It intercepts the astronaut, who rapidly straps it on (or the robotic arms on the device grab him and pull him aboard), then it orients itself, the solid fuel motor fires to begin reentry and the ballet inflates. For simplicity, the device might actually be designed to land on water so the ballute becomes an improvised life raft as well (using it as an airy bag on land might bounce you face first into the desert floor....).
Happy landings
[Answer]
Even if it is possible, it won't happen; since the astronaut was in a space pod, his or her suit probably wasn't designed for re-entry. A space suit strong enough to withstand re-entry would be so bulky and reinforced, it might as well be a small spaceship.
Of course, the odds that this astronaut survived the pod explosion to begin with are, shall we say, astronomical.
[Answer]
See [MOOSE project of General Electric](https://en.wikipedia.org/wiki/MOOSE) designed in the early 1960s - only 90 kg. I bet that with modern materials we could make it even lighter.
[](https://i.stack.imgur.com/ZN411.png)
The key to make re-entry easier is to increase surface to mass ratio. If you have good ratio then even [paper plane made from silicone treated paper](https://en.wikipedia.org/wiki/Paper_planes_launched_from_space) would survive.
[Answer]
The real concern with this situation isn't related to falling to Earth (gravitational potential energy), but to the problem of kinetic energy.
Anything in low-Earth orbit travels at a high speed:
>
> The mean orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s (28,000 km/h; 17,000 mph)
> — [Low Earth orbit - Wikipedia](https://en.wikipedia.org/wiki/Low_Earth_orbit)
>
>
>
Using round numbers, an astronaut and environmental equipment might weigh 100kg.
100kg, traveling at high speed has a lot of energy:
```
E = mv²
m = 100 kg
v = 7.8 km/s
E = 100 kg × (7.8 km/s)²
= 100 × 60 km² / s²
= 6 000 000 000 m²s⁻²
= 6 GJ
```
So, before you can even think about what happens when falling down, you have to do something with all that kinetic energy *before* you are even *able* to fall down.
According to [Kyle's Converter](http://www.kylesconverter.com/energy,-work,-and-heat/gigajoules-to-tons-of-tnt), 6 gigajoules is as much energy as in 1.4 tons of TNT.
1.4 tons of TNT produces a serious amount of heat, and you will be at the center of that process.
Forget about re-entry.
Imagine you're on solid ground here on Earth, sitting on 1.4 tons of TNT.
What are your chances of surviving when that energy is released, even if its release were slowed down enough to not be an explosion?
To say you would be toast would be an incredible understatement.
[Answer]
Let's see what happens:
First, you have to enter on a very narrow angle. Too deep, you black out, tumble and die. Too shallow, you bounce and you probably run out of life support before you come back down. That's an accuracy you're not going to accomplish by eyeball.
Second, as you enter you need to maintain just the right shape to cause the shockwave to flow around you rather than touch your suit anywhere. You lose orientation, the plasma gets to your suit and you burn.
Third, even if the plasma doesn't touch you it's very, very hot. Most of that energy becomes hot air behind you but you're going to pick up some of it. You're going to need unobtainium insulation on your suit if you want something thin enough that you can actually move about in your suit. Oh, but if your suit is that well insulated how did you keep from cooking yourself while you were in space??
Fourth, the deorbit maneuver requires actual rockets, something that is unlikely to be on a suit for safety reasons. Cold gas thrusters aren't good enough.
There's only one way to survive the trip: Change your species to Kerbal. :) (And even then you need to burn the 600 m/s in your jetpack to shed some of the 2,300 m/s orbital velocity you have.)
[Answer]
Given you had enough supplies, you could force an intercept to a space station. If you had 60 m/s, and some solar panels to power life support, you might not be screwed. But the force in reentry would almost surely kill you. Even taking the heatshield from your pod, pushing it to a deorbit trajectory, and duct-taping yourself to it after covering the heatsheild with the pods cover to ensure wake stability is better.
] |
[Question]
[
Imagine a creature that's a little bit like a human, but with much shorter legs and stronger arms long enough to reach down to the bottom of the torso/ top of the legs. It can easily stand upright and walk around on two legs, but when moving around prefers to do so in a "leaning forward" position, in order to utilize its arms for greater speed and agility. It is generally quite large, and carries most of its weight around the lower torso area.
In hand-to-hand combat it would generally outmatch any human due to its immense reach, its immovability (thanks to the heavy weight and and low center of gravity) and its strength, which is at least on par with the strongest of humans, if not greater.
It can also move very quickly for short bursts, using its arms to propel itself forward and allowing it to charge into others with a massive momentum, but cannot sustain a charge for longer than a few seconds.
However, given a level of medieval technology, how would this type of creature fight with weapons? Which weapons would be best for it, and what kind of fighting styles would it use?
Obviously there can be more than a single type of weapon, humans use many different types, I'm more looking for which weapons would offer the most benefit for the fighting styles you choose. These can be weapons that were invented for humans, or a new invention that is created to fit the physicality of this new creature.
In addition, what compositions of armor would offer the most benefit for this creature to fight with your chosen fighting style? What would offer the most protection, whilst still maintaining the least restrictiveness?
It does not have the dexterity to use its feet to hold weapons, and the hands do not have to be the same design as human hands (though at least would need an opposable thumb), but they must be strong hands. This means that when holding any weapons to fight with, its mobility would be greatly reduced as it can no longer effectively use its arms for movement.
They would be fighting both humans and others of their own kind. So what would be the most advantageous technique to fight by harnessing its strengths and minimizing its weaknesses?
---
For clarification, **I'm not looking for one single fighting style**. I know that humans can use a range of different techniques to fight, because they have been adapted to suit our bodies.
I'm asking **which of these fighting styles** that we have, or a new one that you have created, would work better for a bottom-heavy, long armed, short legged humanoid. This means that you can choose more than one; in fact, I would encourage it.
In addition, I'm looking specifically for fighting solo, or in small groups, rather than within the ranks of an army. This can be in any conditions, but would generally be in pretty wide open spaces on reasonably flat ground.
[Answer]
New Answer to question after edit:
For this answer, I'll be basing the creature off of this image (drawn to the description of OP) of the creature in a 100% upright, back straight position.
[](https://i.stack.imgur.com/b4wbf.jpg)
A side view should look somewhat hunched like a gorilla, in order to facilitate the type of movement OP has described. Note that you can't actually have the lower body carry the majority of the weight if you want a super strong upper body, since the upper body has to have extensive muscling.
Since OP has said that the majority of the fighting will be:
>
> fighting 1v1 and small group fighting they're most likely to be coming
> up against an array of blade types and short hand-held weapons (short
> swords/ maces/ rapiers), as well as larger two handed weapons
> (warhammers, greataxes, bastardswords)"
>
>
>
the ideal armor would have to be chain mail armor, but only on the body section, and not for the arms (we leave the chain armor off the arms because if it's a one piece it may restrict shoulder movement more than his muscles already do). Chain mail provides good mobility and flexibility while giving decent protection against slashing from blades. The fighter will still be weak to thrusts from rapiers and the like, so he'll have to parry those in order to prevent damage. Chain mail also doesn't protect against the war hammers or great axes, but it won't be a problem if we give him the weaponry I'm about to suggest.
First, take a look at the following two diagrams.
[](https://i.stack.imgur.com/9XUe6.jpg)
[](https://i.stack.imgur.com/xq007.jpg)
If you look at the first diagram, you can see that point A and C represent the relaxed and maximum raised positions of the arm. If you look at point D on the spec, you'll see that I've tried to represent the extensive muscling in order to provide massive arm strength. This extra muscle will get in the way in terms of raising his arms, preventing many overhead blows from being possible. Compare it to the human diagram, where there isn't that much muscle on the shoulder area. Since we can already see that he wouldn't be able to move swiftly on his feet based on what OP has said, the weapon must be able to be used while mostly stationary, while making up for the weaknesses in his armor. Since the weaknesses in his armor can be overcome by parrying the incoming attacks, as long as the weapon allows for good parrying abilities, everything is good.
To this, I suggest an unconventional weapon. Use shields with plated arm protection. Take a look at the arm section I've drawn here:
[](https://i.stack.imgur.com/mLkCH.jpg)
This drawing here depicts what I mean by plated arm protection. By only plating the outer section of the arm, we maintain maximum mobility while still allowing the use of his arms to defend himself.
I say to give him (viking style) shields because the shields allow the species can still maintain his mobility while having good defense and offense through shield bashing. With shields, he is able to push away many thrusting attacks, or use his arms to deflect attacks. While even heavy plate armor has trouble dealing with maces or war hammers, a shield can designed to handle the punishment. Shield bashing with his immense strength can cause more damage than a punch as well.
But how would he do this? With what "style"?
Well, there's really no "style" that would work here, but here's what he can try to do.
Taking advantage of the somewhat wide open flat areas that they'll be fighting on, and his immense reach, I suggest using a karate style blocking and punching system for his upper body. (Disregard his lower body since his legs are too short for good karate kicks) This is because his immense reach means that he can intercept attacks using his forearms earlier than most other fighters. The plated arm protection allows him to parry Rapier thrusts, or longer thrusting weapons (spears, pikes etc). I also suggest that he can use those shields deflect attacks instead of just using his forearms. By punching towards the larger weapons (great axes, war hammers), a well aimed punch can completely throw the opponent off balance by reversing the movement of the heavy weapon. Furthermore, because shield bashing does not require overhead blows, we can avoid the limitation of his muscles blocking his arms from being raised.
To take advantage of his "speed bursting dash with arms" ability, he can hold his shields and use them while dashing, and place his shields flush to the ground while dashing (use them as hand-shoes). By propelling forwards, then thrusting his arms out, he can put his entire body weight behind his shield bashes, allowing for even more power. And since these dashes are only short distances, this allows for "chained" short dashes between multiple enemies.
I imagine the dash would look something like this (Arrows represent the directions of force):
[](https://i.stack.imgur.com/PI25E.jpg)
As you can see, the first step would be to place the shields against the ground. The second step would be to throw himself forwards using those shields and launch himself into the air towards the target. Upon landing closer to the target (the completion of the single step dash), he can thrust a shield (or two) to cause damage. This easy 3 step process can be repeated back and forth between different opponents if required.
In terms of offensive attacks using his legs, he can attempt a gymnastics move type attack. By using his arms as pillars on the ground, he can throw his legs forwards as a kick - kind of like this:
[](https://i.stack.imgur.com/0ITti.jpg)
---
Pre-edit answer:
Normally, I would ask you to clarify your question. Do you want to know which weapons would be best for this creature, or are you looking for a specific style? You're asking over 5 questions in the body of your actual question, and usually, this would already make me put in a vote for closure.
However, since I can answer all these questions in the same succinct answer, I won't make that request.
First of all, you haven't described a creature that's "a little bit like a gorilla human" - You've basically described an upright chimp, minus the feet dexterity.
For this answer, I'll be using the image of a chimp-like human in my mind.
Now, the questions: **However, given a level of medieval technology, how would this type of creature fight with weapons? Which weapon would be best for it, and what kind of fighting style would it use? In addition, what composition of armor would offer the most benefit for this creature to fight? What would offer the most protection for the fighting style, whilst still maintaining the least restrictiveness? What would be the most advantageous technique to fight by harnessing its strengths and minimizing its weaknesses?**
Given a medieval technology, assuming that this creature has attained at least human level intelligence, it would not have a specific weapon type to use at all. The humanoid build and intelligence would drive the creatures to use whatever weapons fit the situation. While you could train a specific member of the species to be god-like at a particular weapon, it's more likely that the entire species will operate more like the human army - swordsmen, archers, pikemen, the lot.
Even humans don't have a "best fighting style". Every style has its own weaknesses, and at the end of the day it's the fighter that beats the other fighter, not the fighters style. Get this through now; **There is no perfect style**. Different members of this species will probably end up training in different styles, simply because at a human level of intelligence, choice is something crucial to the species - that means it'll be impossible for them to ALL train in the same style, since at some point one or two of them will branch out and more will follow. This also means there is no "Best technique" since every technique has a weakness. A person who has a single basic kick practiced 1000 times is more dangerous than one with 1000 different kicks practiced one time each - an old proverb (I don't remember where it came from) that can be interpreted as "even the most basic of techniques, if practiced enough, can be deadly."
Based on the above two answers (and further details you've provided), we can say that there is no best armor for this creature to fight. You've gone and asked a question with no answer. The armor composition depends on what kind of weapons the creature is facing. Plate armor against blades is standard, mail/leather for archers, etc etc. Again, there is no best fit.
**TL;DR: You've asked the wrong questions, mate. Whatever you're doing in your story, if you're working with humanoid like creatures, can branch off our history. They can essentially use or make use of a large majority of our fighting styles, armor, and weaponry. There is no answerable "best fit" for any of your questions in which a weakness cannot be found. You're better off using some creativity and mixing styles (if you want something that isn't completely the same as human styles). Note that styles often come with weapons training specific to that style, so you may want to use those for your warriors.**
[Answer]
The best weapons are the ones that compensate for the fighter's limitations and make the most out of his unique abilities. To sum up:
* His weight and low center of gravity allows him to win most strength-based contests. Furthermore, if he can connect and grab an opponent, he'll be able to put him off-balance in most cases.
* His strength is a big advantage if his opponent is within his grasp. He can then easily subdue or hurt him.
* His mobility and agility are an issue, as a fast opponent could evade him or attack him from behind.
His weapon and armor should then increase his grasping ability and allow him to make the best out of it, while protecting his blind spot.
I suggest **a gruesome long flail made of chains and hooks**. The fighter flails it around and can hit and grab any enemy in a large radius. Once caught, the enemy is violently pulled toward the fighter who then have him within his arms' reach.
The fighter can wear a heavy armor, which makes sense since he''ll probably be a good target for archers. For added efficiency, **the armor could be covered in spikes**, so that caught enemies are propelled to their death upon it.
He would learn techniques for quickly disposing of his victims - untangling his flail, unpinning them - or for turning them into weapons or projectiles, as if his flail was a sling.
[Answer]
To take advantage of a solid centre of gravity and long reach, the creatures might find it best to fight with large polearms or axes, and have a close combat style similar to sumo wrestling in order to grapple with opponents.
As noted, there are thousands of fighting styles, and most are dependent on the skill of the practitioner rather than the style itself. A Bruce Lee or Chuck Norris is going to take you apart regardless of what style you know, unless *you* are a grand master of your particular fighting art. Similarly, some of your creatures are going to trip over their shoelaces and be easy to defeat, most will have a reasonable skill in whatever martial art they have studied and a small percentage will be highly skilled and difficult to defeat (unless you "cheat" by using ranged weapons, siccing a dragon on them or doing something outside the normal pattern of fighting and combat behaviour. I would suggest poison myself....).
One other thing which hasn't been mentioned up to this point is the natural habitat of these creatures. I am going to guess that they evolved in a rainforest environment , much like real gorillas in our world. In a rugged, heavily forested environment, swinging swords and axes might not work too well, so they would have preferentially used ambush tactics and perhaps short stabbing spears that would not hinder movement in the forest that much. Once you get out of the woods, these tactics would not work as well, so in the "mainstream" environment, they would adapt the sorts of weapons and fighting arts that already work in open fields.
] |
[Question]
[
I was trying to put together an idea for a Gas Giant like planet that could possibly support some kind of fairly complex life, and I hit upon a few ideas:
-Located in a habitable zone roughly similar to Earth
-Composition and Structure roughly similar to Neptune or Uranus
The basic idea here is that Jupiter and Saturn are almost entirely comprised of Hydrogen and Helium, have a really high internal temperature and massive pressure, not conductive to much!
Now I don't know if Uranus or Neptune are really different enough for this to be plausible but it seems worth a shot to consider, so here is the idea I'm forming that anyone is free to shoot down.
Since this hypothetical planet is roughly the same as Neptune and Uranus in chemical composition then it means large amounts of water Ice, Methane and Ammonia form the bulk of the planet, perhaps creating a massive Ocean like I've seen proposed for some such planets in their star's habitable zone. This sounds like a nice base to build off of in forming life and its relatively close proximity to the sun could keep its outer layers nice and balmy.
But I don't know if life can really develop without a clear surface, or if the temperatures and pressures would still be too much of a problem (I understand that Uranus has a cooler core than the rest so I though I could do something with that but its still seems to be thousands of degrees Celsius so maybe not). I guess different forms of life could develop adapted to the different strata and the temperature, makeup and pressure until it gets too close to the core, but I don't know if all the organic matter would just eventually get mashed into the superhot core where it could be no longer used (would some kind of internal convection get around this?).
Next I was wondering if Photosynthesis is really possible here, assuming that nature can't produce a creature that would float in the upper Hydrogen/Helium portions of the Atmosphere that would limit life to places down where denser, heavier clouds begin, would enough sunlight penetrate that deep to be useful? If not, could I simply make it so there's less light gases so the distance between life and the sun isn't so bad? (maybe much of the light gases are blown off by its relative proximity to the sun?) Or could life subsist off of internal heat, chemical energy and electrical storms?
Finally, in terms of actual life would huge balloon animals really be possible like Carl Sagan proposed or would that stretching things too far?
Thanks to anyone who reads this and answers!
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It's possible, but would be nothing like life on Earth.
**Factors that make Neptune a better place to live than some other gas giants**
As you mentioned, unlike Jupiter and Saturn, Neptune has an internal mantle of hot, highly pressurized water, methane, and ammonia. Life living in this mantle wouldn't have to fly continuously, like atmospheric life would. The bottom of the mantle may also contain [diamond-bergs floating on an ocean of liquid carbon.](http://www.astronomynow.com/news/n1001/21diamond/) This gives life a solid place to live that's more habitable than the core of somewhere like Jupiter. Life evolving here would also have access to both carbon and water.
There's also energy available on Neptune. While the sun doesn't heat it all that much, there's an as of yet not fully explained source of internal energy specific to Neptune that radiates out more than twice as much energy as it receives from the sun. Energy from this source could provide an alternative to sunlight to drive an alternative to photosynthesis for Neptunian plants.
**Why life is still unlikely**
In the upper mantle, it may be that there is too much current moving liquids about to allow life to remain somewhere with consistent temperature and pressure for long enough to evolve. Molecules that were conducive to life might form at one altitude, but then be plunged deep into the mantle by convection currents and denatured.
Deeper down, life forming on the diamond bergs wouldn't have to worry about the convection currents, but would need to contend with pressures hundreds of thousands of times greater than those found on Earth, along with much higher temperatures, probably in the range of thousands of degrees Kelvin. This would all but prevent the formation of the sorts of molecules that make up life on Earth.
That's not to say that some other sorts of molecules couldn't form the basis of life at that depth. There could be other sorts of molecules that are *only* stable at these sorts of temperatures and pressures. We haven't done enough research to know for sure, since the sorts of temperatures and pressures needed to compress carbon into diamond *and then cause it to melt* are difficult to produce.
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Many sci-fi questions here are derailed by complaints that the proposed version of FTL breaks causality. However, [relativity-safe FTL concepts do exist](https://physics.stackexchange.com/search?tab=votes&q=alcubierre). What range of conditions allow FTL (movement, teleportation, or communication) but not time travel?
Time paradoxes I've seen are based on FTL interchange between [relativistic reference frames](http://www.theculture.org/rich/sharpblue/archives/000089.html). *(edit: see update below)* Problems occur when the differential between time frames is larger than the travel time. Is that correct? If so, we can avoid paradox by requiring lower velocities (FTL and/or reference).
Also, those paradoxes use reference frames moving away from each other. If the reference frames are moving towards each other, does paradox still occur?
My goal is to establish parameters for physics-tolerant FTL, so that future answers don't need to nitpick about closed timelike curves.
Here is one example that I think should work:
* vessels can shift to & from "hyperspace", but travel still requires local time (at minimum, hours per light year plus some overhead even if you don't move).
* vessels can't enter or exit hyperspace at high real velocity (>1% c) relative to some local center of mass (e.g. galactic core). Technobabble about nonlinear fluidic space available if needed.
* separate vessels enter separate instances of hyperspace, cannot intercommunicate.
UPDATE:
In the "[Sharp Blue](http://www.theculture.org/rich/sharpblue/archives/000089.html)" article, the diagrams display Lorentz transformation as a slanting of the space-time axes, and FTL is assumed to be instantaneous. But non-instant FTL would also have a slope, and it seems like paradox could be avoided if the FTL is steeper than the dilation angle.
Mathematically: dilation slope as a function of (relative) frame velocity goes from f(0)=0 to f(c)=1, while the FTL slope as a function of travel velocity goes from f(c)=1 to f(infinity)=0. I'd need to refresh my analytic geometry to make the terms cancel, but such values are determinable. Why is this approach not valid?
CONCLUSION:
[Dan Smolinske's answer](https://worldbuilding.stackexchange.com/questions/10461/hypothetical-criteria-for-non-paradox-ftl#answer-10499) explains why my thinking is incorrect: even if the endpoints of the FTL don't experience paradox directly, a relativistic observer traveling near an endpoint does.
[celtschk's answer](https://worldbuilding.stackexchange.com/questions/10461/hypothetical-criteria-for-non-paradox-ftl#answer-10466) provides a solution: require a primary reference frame, such as the ether in [Lorentz Ether Theory](https://en.wikipedia.org/wiki/Lorentz_ether_theory). Lorentz's math is more complex than Einstein's (Occam's Razor FTW) but their results are indistinguishable *for velocities below c*. They only differ during FTL; the ether can prevent paradox.
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Time travel due to FTL follows directly from the relativity of simultaneity: In different frames, the temporal order of events is different. This is true for *all* events which are spacelike to each other, which just means that you need FTL to get from one event to the other. So if you want to solve it with delays, then the delays have to be so that you end up not doing FTL travel at all. Note BTW that also the Alcubierre drive is *not* free from possible time travel paradoxes.
FTL without time travel paradoxes can be achieved in two ways:
* Restrict FTL to a preferred frame so that going to the past *in that frame* is not possible (which prevents closed timelike loops and thus paradoxes)
* Allow time travel, but invent a mechanism which prevents paradoxes (the main mechanisms are a self-consistent universe and multiple timelines).
As preferred frame, an obvious choice would be the rest frame of the cosmic microwave background (which BTW is also the frame relative to which the age of the universe is measured). Possible explanations for such a preferred frame include
* Relativity might not be fundamental. While for the physics we know it holds, there might be a deeper level where it does *not* hold, and FTL travel might need that deeper level (e.g Star Trek's subspace might be considered such a deeper level).
* Relativity *is* fundamental, but the FTL technology depends on pre-existing phenomena (for example, some space-filling fields) which have a preferred frame. That is, while *in principle* your FTL technology would allow time travel, *in practice* it doesn't because you depend on existing resources which fix a certain reference frame.
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> In the "Sharp Blue" article, the diagrams display Lorentz transformation as a slanting of the space-time axes, and FTL is assumed to be instantaneous. But non-instant FTL would also have a slope, and it seems like paradox could be avoided if the FTL is steeper than the dilation angle.
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Consider a situation with three entities. A and B are at rest relative to each other and are extremely far apart (say across a galaxy, thousands of light years). D is moving at a significant fraction of *c* relative to both, but is much closer to B (within 1 light year).
If your suggestion worked, you can now violate causality by using B as a relay between A and D. A <-> B communication can be instant since they're at rest. Even if B <-> D communication is light bound, the overall result of A <-> B <-> D communication will be faster than your "safe" FTL bound, resulting in paradox.
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Any faster than light travel will create paradoxes.
The article you linked to on [relativistic reference frames](http://www.theculture.org/rich/sharpblue/archives/000089.html) explicitly states that:
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This is for any degree of faster than light travel, it's just that the faster you go the more obvious the problems are.
I don't think that you can avoid this, but for the sake of your story you might have to ignore it, but as long as you ignore it in a consistent way and make sure that you establish your "rules" of FTL before you rely on them as a plot point, you should be OK.
I remember one episode of Star Trek: The Next Generation where they used a micro warp jump to create the illusion that a ship was in two places at the same time - the light from the original location still arriving at the enemy ship for a few seconds after the jump. Because it fitted with the already established parameters of the Star Trek warp drive (or at least didn't wildly contradict it) you felt that it was a logical outcome and one that would really happen, rather than actually highlighting the paradox at the heart of the problem.
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My favorite FTL setting has a way around this by literally having the paradox-avoidance built in. Your FTL engine or your FTL message simply won't work, or simply won't send, if moving in that direction or messaging that person can create a time paradox. The paradox-avoidance goes down to the quantum level, so it's not a human or human-device thing.
So you'd be able to jump a trillion light-years away with no problem, as long as you're causally disconnected from the starting point. So waaay out might be ok, while the closer you get (say within the galaxy) the dicier it gets, until it becomes literally impossible.
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Create a society for your characters to interact with that has dedicated itself to constructing a lifestyle and environment that facilitates time travel. The society spends its time, energy, and resources living in a manner thats easily interchangable throughout time and in an essence terraforms the physical space they occupy for time travel.
Off the top of head one would need an extraordinary amount of clones doing the exact same thing every day as part of a hive. Their consistent hive lives are constantly engineering their physical enviornment over an unconceivably long period of time specifically to eliminate paradoxal contaminates. Essentually using the lives of trillions or more hived clone slaves throughout millenias to pave paradox proof worm hole highways through space/time.
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There is no causality problem with the Alcubierre drive. Like all metrics, all matter stays inside the lightcone, and there are no closed timelike curves involved with it. A modification of that metric does involve closed timelike curves, but it is a different spacetime. A variety of theorems and conjectures probably makes it impossible to go from an Alcubierre spacetime to a version that would violate causality (mostly having to do with blueshifting of incoming fields, divergence of the vacuum energy and non-uniqueness of the spacetime evolution). Those same theorems also apply to wormholes, by the way.
The point is that this kind of FTL isn't actually faster than light. The object inside does not move faster than light. In the case of the Alcubierre drive, it does not move at all. The spaceship just sits at the same spacetime point while the spactime around it does all the work. This is related to the fact that in cosmological expansion for instance, objects can recede from us faster than the speed of light (it was this observation that led to the idea of it).
Not that the Alcubierre drive doesn't have problems, but causality isn't among them.
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So as a geographic feature and major historic event I have a meteor (and the resulting crater) idea in my head.
The idea is that the meteor sort of resets civilization. Obviously I don't want it to kill off all life on the planet as no people = boring story.
So the basic question is, could a meteor destroy civilization (defined in this case as large nations/empires/trade/organized learning) around the planet and not kill off all life?
How would that look, what would happen to civilization and why?
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Yes. A large enough metor could raise a [massive dust cloud](http://en.wikipedia.org/wiki/Impact_winter) over the earth and cause a large shift in geography. The dust cloud could prevent crops from growing well killing civilization by reseting the population that the earth's agriculture could support. The temperature would also plumet, killing more people unprepared for the cold. Earthquakes and other geological shifts could kill more people and turn cities and buildings into toppled ruins. Eventually, once the dust cloud cleared civilization could begin to produce more food again and temperatures would reset, allowing life to go on.
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A little research on the eruption of Krakatoa might give you some ideas, as would digging into the whole nuclear winter question. In essence, I'd approach this by figuring that your planet would get very cold for a while.
One possibility is that the planet was previously rather warm, and so most of the larger settlements and whatnot tended to be up toward the poles. After The Big Strike, the world gets cold, so everyone starts clustering around the equator. The problem, of course, being that they therefore cannot mine the old settlements for stuff and ideas, such that they necessarily end up with a more rudimentary technology. That, combined with dramatically lowered population, might have the "reset" effect you're looking for.
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An option that's more surgical in its devastation, but that doesn't give you the crater you want, is to drop the meteor into the sea. Civilizations tend to form around bodies of water (such as the Mediterranean). Throw a meteor into an inland sea like that, and the resulting tidal wave will wipe out the coastal civilization, while leaving the nomadic tribes of the interior alone.
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After sufficiently large tsunami (multiple large meteors in multiple oceans) surviving civilizations would be:
* Mormons in Utah (which is located in Great Basin and guarded from oceans by high mountain ranges)
* civilizations deep in central Asia: Tibet and various \*Stans (Kazachstan, Kirgizstan, Afganistan) - they can live without modern technologies
* people high in mountains in Andes
I think Mormons would be well positioned to recover, if they survive initial impact. They generally have 1 year of supply of basic food, and they still can grow more.
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In prehistoric times, there used to be a [dwarf elephant species](https://en.wikipedia.org/wiki/Dwarf_elephant) in many Mediterranean islands.
They were about 1.5-2 meters high, but probably became extinct before the arrival of the first human beings
If these elephants were still alive at the arrival of the first human beings (and managed not to be made extinct by them), and they had been domesticated, I was wondering if and how it would have any meaningful impact in the development of mediterranean civilizations (Greeks, Carthaginians, Romans...).
So, my question is: for a mediterranean civilization of the Classical age, what could be the use for a dwarf elephant (if any)? Or their breeding would still be too costly compared to their utility?
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**Dwarf elephants are still elephants.** They're hella strong. They'd probably be used for the same things regular elephants were used for:
* **Construction**
* **Warfare** - not sure who's going to fight you if you have an elephant on your side, and a relatively portable one at that. Interestingly, because these elephants are relatively small, island nations in the Mediterranean could learn to dominate their regions by deploying elephant cavalry with incredible speed, because these guys might even fit on a boat! Rome's mighty legions would be replaced with Rome's mighty small elephant navy!
* **Ivory farms** - unfortunate possibility
* **Tourism** - we don't need to be too imaginative
* **General transportation** - who needs horses
* **Pets**
* **Exotic food**
Hope this helps!
[Answer]
**Rich people's pet.**
[](https://i.stack.imgur.com/FjLmF.jpg)
Rich folks like exotic animals as pets. They have ligers and binturongs now but the ancients definitely had cheetahs and monkeys. Docile little elephants would make great additions to courts of the ancient world.
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# Cockfights
Except these would be more like elephant fights. Bring your elephant to the ring, see how it matches to other people's elephants. The smaller form factor means they would be easier to control than the big ones we got today - it would be like the bull and camel fights that are held in countries like Oman and Saudi Arabia. And if my experience with dogs has taught me anything it's that the smaller the breed is, the more crazy and aggressive it is. Don't know if it applies to elephants but it would make for critters with a hella lotta fight in them.
Disclaimer: I am totally against this kind of thing and I would never put an animal to fight another. If it puts your conscience at ease, imagine the scenario above involves pokéballs.
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Riding food and labor. this could all be ways depending on what your civilization has around if there something a better alternative then the might not use the elephants but if there is not they would use the elephants for those three. War could also be used they would make a greek shock cavalry.
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A moon-sized asteroid approaches Earth in the near future, where space tourism has become normal. The Earth has a few satellite structures above Mars conducting research, as well as successful terraformed farmland on the surface. Going into a suborbital space to experience zero gravity for a few minutes costs about as much as a plane trip across country today. In this scenario we have developed the technology to support megastructures in space, and need for farm land has pushed artificial farming to where we only need 1/4 the amount of land to grow the same amount of food.
The world comes together and decides that they should make an attempt to save at least one million people by migrating them into an orbital space station. The space station should be able to travel from orbit to Mars where it could link up with the Martian Base, in a worse case scenario where the asteroid causes variance to the gravity of the planet.
Accounting for fuel, engines, rockets, farmland, water, living spaces, hospitals, waste management, etc. how large would this space station have to be? I am looking for an estimate, I realize an actual square footage is next to impossible.
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For the sake of convenience let’s start with the assumption that your population will desire a North American urban population density and a globally averaged diet.
The city of Austin TX has approximately 1,000,000 residents and a surface area of approx. 800 km^2, for a density of about 1,250/km^2.
The City of New York (5 boroughs) NY also has a surface area of approx. 800 km^2 but a population of approx. 8.5 million, for density of about 10,500/km^2.
However the density of the Manhattan borough is close to 28,000/km^2. That is the highest density population center in North America with a population of at least 1 million and possibly near the limit of Western cultural tolerance (or we could reasonably expect it would be even higher by now). For our purposes let's say a few more people can be squeezed in to conveniently round the figure to 30,000/km^2.
So the station would need at least 1,000,000/30,000 km^2 of surface area (assuming living structures are approx. as multidimensional and compacted as Manhattan), or 33.3 km^2. Since much of the surface of Manhattan is pavement for cars, and we'll assume that citizens of space will have learned to do without that kind of freedom, let's then shave 10% off of the requirement for a nice rounded living space of: 30 km^2.
For food production usage, let's take the conservative approach of using globally averaged statistics since they're easy to find. According to one source (<https://ourworldindata.org/yields-and-land-use-in-agriculture>) approx. 50% of habitable land on earth, or 104M km^2, is used for agriculture. Of that 77% is used for livestock and 23% for crops. Let's now take the somewhat controversial liberty of assuming that 0% of your station's residents will derive calories/protein from livestock simply because farming livestock is so incredibly inefficient and, generally, sufficient non-livestock alternatives exist. 23% (crops only) of earth's agriculture equates to 11M km^2.
Now let's assume that the earth's population is a rounded 8,000,000,000 (in the near future). Let's also assume (quite ridiculously - this is a fictional model) that all of earth's population has equal access to earth's total yield of crops and there is 0% wastage. That means it takes 11M km^2 of crop surface area to feed 8,000,000,000 people, or approx. 725 people per km^2.
So a population of 1,000,000 would need close to 1,400 km^2 of crop surface area, using modern terrestrial practices of course.
As you can see the ratio of this area to living space of 30 km^2 makes the latter insignificant.
However I believe it's reasonable to assume that necessity would be the mother of invention when it comes to occupying space and crop yields / km^2 could be greatly increased over terrestrial norms. Let's be incredibly inventive and say efficiency could be increased by a full order of magnitude. Then you're down to 140 km^2. Much more plausible.
So at this point we have:
140 km^2 for crop production and 30 km^2 for living space, for a total of 170 km^2.
That means if your station's structure was a cylinder 2 km wide it would have a height of 26 km. To put this in perspective Manhattan is about 22 km long.
Now consider this. What if the station wasn't divided into urban/rural areas like on earth but was instead all rural with the residents living "off the land". In that scenario the station could be significantly smaller and perhaps even a more pleasant habitat.
[Corrected cylinder calculation.]
[Answer]
There are two general requirements - power and space.
**Power**
1,000,000 humans need about 2,000 calories per day each plus energy for day-to-day functions. Total up the calories and convert it to something workable, and we have a total of 96.85 MW. That is a lot, but that pales in comparison to energy. The [average US household](https://www.google.com/search?q=size+of+average+us+household&oq=size+of+average+US+hous&aqs=chrome.1.69i57j0l4.5690j0j7&sourceid=chrome&ie=UTF-8) uses [900 kWH per month](https://us.sunpower.com/how-many-solar-panels-do-you-need-panel-size-and-output-factors), giving us a princely total of 480.8 MW. Add them up and we need 577 MW.
Now you said 'indefinitely' so instead of using something like a nuclear powered core, I've elected to use solar panels, because the Sun lasts longer than the core. Judging from the answers [here](https://www.quora.com/How-much-more-efficient-are-space-solar-panels-than-terrestrial-panels) at 40% efficiency you'll only needs about 1,068,518 square meters of solar panels. Incidentally, a small nuclear power reactor can [achieve the same output](https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-power-reactors/small-nuclear-power-reactors.aspx). So, uh, your choice, more or less.
**Space**
Now for space. Food storage and preparation wouldn't use traditional Earth means of growing food - that's time consuming and takes up too much space, even with your method of cutting it down by a quarter. Instead, the garbage would be sorted and all organic waste would be broken down by bacteria strains and then cultured or synthesized into nutrients. Disgusting - yes. Efficient - also yes.
It sounds like this is going to be boosted into place, so I'm assuming that the main boosters are more of less external, and the only boosters within the design are for corrections.
Since I'm just approximation everything, I'm not going to go through careful lists. Instead, I'll just instead assume that everyone would get a 5 by 10 by 5 box for living space, personal effects, and utilities. That seems to be to be the bare minimum required. May be a tight fit on taller people, but they can just ask for their box to be upright.
In addition, every 100 people could probably use the space to organize together in some assembly room, as well as having it function for several recreation purposes so add another 20 x 20 x 5 area. For larger assemblies, just have people assemble in their personal ones and use wall screens to link them together.
That's a total of 270 million cubic feet. There will be more things required because you always need more space/time/money etc., so I'm just going to round that number up to 300 million cubic feet. In terms of design, I'd argue for as large of a superstructure as possible, so things can be safely ejected in case of an emergency or contamination. In fact, I'd actually recommend that you don't even make this one giant station, instead make this a fleet of colony style ships with a few thousand on each one. That will, of course, require a bit more space, but I stand by my estimates - 300,000,000 cubic feet, and 1,000,000 square meters.
(Sorry for using both square meters and cubic feet. You can use 8.5 million cubic meters instead.)
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The [Lusca](https://en.wikipedia.org/wiki/Lusca) (its name meaning 'Octopus Shark') is a cryptid from the Bahamas, supposedly a 6-9 meter (or even 23 meter) long man-eating Octopus that lives within the blue holes, dragging victims down into the winding underwater cave system that connects all Blue Holes.
Given that [Blue holes](https://learningenglish.voanews.com/a/blue-holes-some-of-the-least-explored-areas-on-earth-134628763/116987.html) are anoxic and are not super conducive to Octopi and their eggs due to the lack of currents/oxygen, is there any way to realistically modify a lusca-like organism to thrive in the hostile environment of a Blue Hole?
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> A link showing that there is life within Blue Holes, albeit small organisms rather than man-eating sized monsters <https://news.nationalgeographic.com/news/2012/02/120202-blue-holes-new-life-alien-oceans-europa-space-science/>
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[Answer]
Let's start with a template animal for the enormous Lusca. [The giant pacific octopus is a good candidate.](https://en.wikipedia.org/wiki/Giant_Pacific_octopus) We're talking about this guy:
Scientists disagree on the size record for that species, but Guinness quotes it as a 136kg (~300 lb.) one who had an armspan of 9.8m (~32 ft.) (see the wiki in the link above). Way smaller than the giant and colossal squids, but hey, you asked for an octopus.
Now let's see about anoxic waters. They are defined as [waters with an O2 contentration of 0.5mg/L or less.](https://en.wikipedia.org/wiki/Anoxic_waters) The abyss is similar - [dive deep enough, and the O2 concentration falls from 4-6mg/L to less than 2mg/L.](https://en.wikipedia.org/wiki/Oxygen_minimum_zone) And you know who lives in the abyss? The squids I mentioned before!
Since squids and octopi are related, let's say the Lusca has characteristics of both. [It may use the same trick as the Humboldt squid to survive in low oxygen areas:](http://blogs.discovermagazine.com/inkfish/2014/05/27/no-oxygen-no-problem-says-squid-that-can-shut-down-its-metabolism/#.XT0sjZDQ-yU)
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> In a new study, Seibel and his colleagues pulled Humboldt squid out of the ocean and held them in tanks of normal or low-oxygen water for up to three and a quarter hours. Then they carved up the squid and scrutinized their tissues to see what was happening on a molecular level.
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So your beast gets in energy-saving mode at the bottom of the blue hole, and switches to full run-and-disembowel-the-player mode when near the surface (this is actually how the Humboldt squids do, except they go to the *Oxygen Minimum Zone* instead). The lusca's *modus operandi* is to pull victims into the blue-hole for the same reason that alligators and crocodiles drag their larger prey into the water - due to the hunter's adaptations, the prey will quickly drown/asphyxiate and thus stop struggling, while the hunter will be able to last longer there. For a regular water-breathing animal, being dragged into a blue-hole is like being an air-breathing animal dragged into the water.
Finally, as for how it can keep its brood safe in low oxugen waters - it doesn't. The lusca is an octopus, which means it is a master of misdirection. It lays eggs around the blue-hole, not in it. The caves where it lays eggs are hidden behind plants and/or coral, and they are protected by mother lusca. She is such an adept at camouflage that if you find the eggs and try to eat them, you will be dead before you know what hit you.
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The Lusca could have evolved from a large octopus. This octopus may evolve to move faster, and become fully bipedal. Due to being faster, they might try to become predators. This would lead to the beak growing into a large jaw, with a living layer surrounding it in order to allow regeneration. The jaw might become so large that the arms are no longer needed to feed, and so they would likely turn and point backwards. They might gain some sort of movement-sensor like a lateral-line on their jaws, which may transform into something resembling eyes. They may evolve to retract their jaws and extend their radula as a lure. The lure might become more like a tentacle, and become able to grab the prey and draw it into the jaw. Some individuals might learn to make their lure appear like a human, to draw in human prey. This evolutionary path would lead to the Lusca
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I'm working on a world where water acts as a high-temperature superfluid. Specifically, H2O's [lambda point](https://en.wikipedia.org/wiki/Lambda_point) is above its boiling point. Thus, all liquid water on the planet behaves as a superfluid. It still boils and freezes normally, at 100$^{\circ}$C and 0$^{\circ}$C, respectively. I haven't worked out the exact physics that permits this, so take this as given for the following question if possible.
I'm having trouble understanding how this superfluid would function on a global scale. Assuming an Earth-like planet, there's plenty of water to go around. If I understand superfluid physics correctly, the following phenomena will be observed:
* A thin film of water covers the entire planet, per the [Rollin film](https://en.wikipedia.org/wiki/Rollin_film)
* All areas beneath sea level are submerged. Caves and tunnels are filled by the Onnes effect as soon as they form and are exposed to water. Similarly, all lakes and streams above sea level are empty
* Superfluid water is highly thermally conductive, indicating that all water on the planet is the same temperature, regardless of depth or latitude
+ Following from this, the poles will not have sea ice - frozen water on the planet must be kept separate from any liquid water or the ice will be melted as the heat is redistributed
* Waves are present in the ocean and the water film, existing as first, second, and third sound
* Currents in the ocean are far more powerful, as superfluid water has no viscosity to slow it down. The currents therefore move at the speed of the air flowing above them, but they are also much shallower because the deeper water isn't dragged along
* [Gyres](https://www.nationalgeographic.org/encyclopedia/ocean-gyre/) in the ocean do not exist as we know them, but instead are large-scale collections of [quantized vortices](http://ltl.tkk.fi/research/theory/vortex.html). There are multiple possibilities for the fine-scale structure of these vortices, as a [function of temperature and pressure](https://www.pnas.org/content/96/14/7760).
* The superfluid ocean still obeys density-dependent dynamics, but lacks an overturning circulation due to homogenous temperature.
+ The definition of density in superfluids is apparently [debated?](https://journals.aps.org/prb/abstract/10.1103/PhysRevB.61.11282)
I've been unable to find any information about the effect of impurities in superfluids, so I have no idea whether this ocean would be salty. Depending on the response to this question and the answers I get, I may post a followup question asking for more help with the water cycle and mechanisms of erosion that would make this superfluid ocean salty, but for now assume it's pure water.
**Is the logic above sound and in line with real-world physics, as best we understand it? Are there additional differences between an ocean on Earth and an ocean in an alternate universe where water acts as a room temperature superfluid?**
[Answer]
You've got a few errors:
>
> Similarly, all lakes and streams above sea level are empty
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You'll still have lakes and streams, they just won't stay wet for very long. "Zero viscosity" doesn't mean "infinitely fast flow", so any time you get rainfall, you'll get temporary ponds and lakes. The Rollin film ensures that even endorheic basins eventually drain into the ocean, but conventional streams are still the preferred way for water to flow.
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> Following from this, the poles will not have sea ice - frozen water on the planet must be kept separate from any liquid water or the ice will be melted as the heat is redistributed
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It takes time to melt ice. The sea may have high thermal conductivity, but glaciers don't. You're not going to have ice shelves on the scale of Greenland or Antarctica, but you'll still have glaciers protruding into the water, and if the glaciers are thick enough, icebergs (though they won't last nearly as long as they do on Earth).
>
> Waves are present in the ocean and the water film, existing as first, second, and third sound
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The Rollin film doesn't have "first sound" waves (it's not thick enough).
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> Currents in the ocean are far more powerful, as superfluid water has no viscosity to slow it down. The currents therefore move at the speed of the air flowing above them, but they are also much shallower because the deeper water isn't dragged along
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Fast, shallow currents aren't very powerful. The lack of dragging means there isn't much water moving -- the "currents" are basically just a surface film.
---
On the subject of impurities, superfluid helium can dissolve substances, with interesting results: see [quantum solvent](https://en.wikipedia.org/wiki/Quantum_solvent).
] |
[Question]
[
Would it be possible to make ammunition for railguns and gauss rifles that would degrade over time either through a natural process or by the means of star radiation, so the missed shots don't endanger future space traffic? Hopefully turning into something less harmful after leaving the star system.
I was thinking about some kind of a carbon composite with enough iron mixed into it to keep the ammunition magnetic and with enough mass to keep the ammo effective. I know that carbon is tough and can be shaped, not to mention the wide variety of materials that are made from it, plastics, cellulose, diamond etc.
The projectile would degrade over time, eventually crumbling to smaller, less harmful, pieces and eventually to dust. Similar to plastics, but it would have to be much faster.
Another option that came to my mind is to compress some kind of a dust mixture and use that. it could contain some kind of a charge or maybe just some volatile or unstable materials that would do the trick after a some distance.
**What sort of materials do we have now that we could use so that the future railguns don't fire back at us after turning around some massive space object?**
Although it would be probably rare. a galaxy wide civilizations could encounter this problem eventually. We usually try to make things last, so this would be opposite to what materials are in demand for now. But I am still curious what are our options.
[Answer]
**Make projectiles of supercold materials that thaw and sublimate away in space.**
[Superconducting railgun projectile](https://www.halfbakery.com/idea/Superconducting_20railgun_20projectile#1137552946).
Your projectiles are made of solid oxygen or perhaps a noble gas cooled to freezing. Superconductivity is an excellent quality for an electromagnetic weapon projectile as ohmic heating is a big problem otherwise. With no resistance to the flow of current the superconducting projectiles will not heat up as they are fired.
Until later, and that is what the OP wants. Supercold projectiles with low freezing points will sublimate readily. The lower the melting point of any object the more readily it will sublimate away as a gas. Even a steel projectile has some amount of sublimation, but projectiles which are extremely cold and with a low freezing point (e.g. a frozen noble gas, or oxygen) will more readily sublimate away as the gas due to ambient radiant heating as they fly through space.
This also will produce narrative possibilities - for example, cooling the punch with a railgun round fresh from the freezer.
] |
[Question]
[
I fear the math involved is beyond my capabilities on this one. I have what I consider to be more than a Layman's understanding of the physics involved, and I believe I can follow the math well enough to spot glaring errors, but practical application, combined with the actual crunching of the numbers is more than I can do, in this case.
Here are the known quantities to start with:
The Planet:
1. Gas Giant (in any layman's definition of that term, even if scientific terms might call it something else like ice giants or brown dwarf or gas dwarf, etc)
2. Maximum mass must be small enough that no layman might mistake it for a star. Other than that, its mass can be adjusted as needed, so long as it can plausibly remain a Gas Giant, with the given mass, for 70 million years (not so small it's gas gets blown away by solar wind faster than that).
3. Radius/diameter must be great enough that the planet would appear, at a minimum, at least as big as Earth's moon when viewed from the surface of its moon (1/2 degree angular size), but has no maximum angular size.
4. Density/composition can be anything scientifically plausible as long as the above mass and radius/diameter limits are met, and it could still be called a gas giant.
The moon:
1. Is rocky/metallic (solid surface, not primarily ice, not gas-giant-like, not water or liquid surface. if it matters)
2. The diameter of the moon cannot exceed 6000 KM (radius of 3000 KM), and would preferably be closer to 5000 KM if other parameters can be met without increasing it further.
3. Surface gravity on the moon must be within a range of 75% - 125% of Earth's gravity.
4. Composition/density can be hand-waved, to some extent, to accomplish the gravity requirement within such a small size (I think [correct me if I'm wrong] this is going to be something in the range of a mostly osmium/platinum core, which I know isn't going to be particularly plausible. But on this one point, only, I don't really care as long as it could be made of something 'stable-ish' on our known periodic table, e.g. no neutronium)
5. Distance from the planet is whatever distance yields the greatest orbital time while keeping the planet close enough to appear as big as earth's moon
I'm guessing the answer is going to involve a brown dwarf (for max mass, and therefore max size for the visibility requirement and max gravity allowing a stronger pull from so far away) with a maximum density moon also of maximum size (again to grant a strong enough pull from so far away) as far as possible from each other to remain within the visibility requirement.
However, I can also see how I might be mistaken, as a more massive planet might crush itself smaller under its own weight, making it harder to stay visible from far enough away to extend the orbit time.
How long can I make this orbit take, within those parameters? And how do I accomplish that?
---
**EDIT**: Either my original question wasn't clear, or I seriously underestimated the importance of another factor, to the point that I omitted it completely. So here I'll address both:
First, I suspect some may think I was asking about the time it takes for the planet+moon pair to orbit their star. I'm not. I'm asking, instead, about the time it takes for the moon to orbit it's planet. I assumed that the influence of the star would be negligible for this, so I did not provide details.
Next, if I'm wrong, and the star is that important, then here are **the star's requirements**:
1. color: Sol-like (a human tourist to this moon might notice the color difference when arriving on the moon, but would adjust and stop noticing after a day or three)
2. Goldilocks zone: distance from the star should be such that stellar radiation should be a significant factor, but not necessarily the only factor (Tidal forces by the planet, a higher radioactive composition, excessive heat from moon formation, etc., can also be factors but should be kept to a minimum wherever possible) in keeping the moon at a survivable temperature for humans if other life support features (atmosphere, gravity, etc) are also present.
3. Stability: Any scientifically plausible type of star that does not vary drastically enough, during a period of 500 million years, to adversely affect any life already on an otherwise habitable planet or moon in its goldilocks zone.
4. Mass, radius, density, composition, distance from the planet, etc.: can all be adjusted as needed, as long as the color and goldilocks requirements are met. But bonus points if its angular size, viewed from the moon, appears the same size or larger than the planet does.
**Summary, in layman's terms:** I want the moon to take as long as possible to orbit the planet, but the planet and star should appear at least as big, in the sky, as earth's moon and sun. How long can I make that orbit take?
[Answer]
[Hill sphere](https://en.wikipedia.org/wiki/Hill_sphere) will define the limit of how distant a moon can be from a planet. Its formula is:
$$r\_H \approx a\_p(1-e)\sqrt[3]{\frac m{3M}}$$
Where $a\_p$ is planet's semimajor axis, **e** is planet's orbit eccentricity, **m** is planet's mass and **M** is star's mass.
For a [moon's orbital period](https://en.wikipedia.org/wiki/Orbital_period#Small_body_orbiting_a_central_body), formula is:
$$T = 2\pi\sqrt{\frac {a\_m^3}\mu}$$
Where T is orbital period, $a\_m$ is moon's orbit semimajor axis and $\mu$ is Gm - the [standard gravitational parameter](https://en.wikipedia.org/wiki/Standard_gravitational_parameter)
For round orbits (zero eccentricity), Hill's formula becomes
$$r\_H \approx a\_p\sqrt[3]{\frac m{3M}}$$
Combining two formulas ($r\_H$ is $a\_m$), we get:
$$T = 2\pi\sqrt{\frac {a\_p^3}{3GM}}$$
Let's substitute with Sun and Jupiter values:
$a\_p = 7.78 \times 10^{11} m$
$G = 6.674 \times 10^{-11}\frac {m^3}{kg \times s^2}$
$M = 1.989 \times 10^{30} kg$
$$T\_{max} = 2.16 \times 10^8 s$$
or about **6.85 years** (maximum)
This is the maximum possible orbital period for a Jupiter's moon. Note that Jupiter (or other gas giant's) mass is irrelevant to the final result. Practically stable orbits are found to be within 1/2 to 1/3 radius of Hill's sphere. Assuming $a\_m = r\_H / 2$:
$$T = 2\pi\sqrt{\frac {a\_p^3}{24GM}}$$
so, realistically
$$ T = 7.63 \times 10^7 s$$
or about **2.42 years**
---
Now let's see about host planet's visible size.
The formula for angular diameter is:
$$\delta = 2 arcsin(\frac d{2D})$$
where d is planetary diameter and D is the distance. Substituting:
$d = 1.4 \times 10^8 m$ (Jupiter's diameter)
$D = 2.65 \times 10^{10} m$ ($a\_m$, realistic moon's orbit's size)
we get
$$\delta = 0.302$$
Earth's Moon visible size is about 0.5 degrees. Our moon is just a little bit too far! So, **angular size becomes a limiting factor**. As @Ash mentioned, gas giants are unlikely to get larger than Jupiter without becoming stars.
Let's reverse the formula:
$$ D = \frac{d}{2 sin(\frac{\delta}2)}$$
For $\delta = 0.5$ degrees, this yields
$D = 1.6 \times 10^{10}$, or **16 million km** (double @Ash's estimate)
plugging this number to the orbital period formula, we get:
$$T = 3.57 \times 10^7 s$$
or **413 days** or **1.13 years**
---
Next, let's see if our planet/moon fits into a [Goldilocks zone](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone)
For Sun, reasonable high end estimate (without designing any exotic planetary atmosphere) is about 2.4 AU. Jupiter's orbit is 5.2 AU, which is definitely too far. Our angular requirement had put the moon on 16 million km orbit - compared to the Hill sphere diameter of 53.1 million km. Let's see how close our Jupiter can be to Sun so that moon's orbit would not exceed 1/2 of the radius of Hill sphere, while host planet's visible size stays at 0.5 degrees.
$$a\_p = 2 \times a\_m \sqrt[3]{\frac {3M}m}$$
Which gives us
$a\_{goldilocks} = 4.69 \times 10^{11} m$, or **3.13 AU**. **Another limiting factor!**
Calculating moon's orbital period for host planet orbiting Sun at 2.4 AU gives us
$$T = 2.395 \times 10^7 s$$
or **277 days**, or **0.76 years**
[Answer]
Short answer:
It seems quite possible for hypothetical habitable exomoons to have days as long as two Earth weeks. Day lengths of several Earth months or years seem to be less plausible.
Long answer:
Alexander's answer is pretty good as far as it goes.
But according to my rough calculations, a planet orbiting at 2.4 AU from the Sun would have a year about 3.7180 Earth years, or 1,358.0228 Earth days, long, and its hypothetical moon could have a month/day no longer than about 150.8914 Earth days long, not the 277 days that Alexander calculates. There is another complicating factor which Alexander did not allow for in his calculations.
There have been a lot of other questions about habitable moons of gas giant planets in the habitable zones of stars, and it is a good idea to refer to those questions and answers to see if they have any useful information, as I state in my answer to this question:
[How long will it take to discover they live on a moon and not on a planet?](https://worldbuilding.stackexchange.com/questions/125617/how-long-will-it-take-to-discover-they-live-on-a-moon-and-not-on-a-planet/125653#125653) [1](https://worldbuilding.stackexchange.com/questions/125617/how-long-will-it-take-to-discover-they-live-on-a-moon-and-not-on-a-planet/125653#125653)
And I gave links to two earlier questions about habitable exomoons.
The article "Exomoon Habitability Constrained by Illumination and Tidal heating" by Rene Heller and Roy Barnes *Astrobiology*, January 2013, discusses factors affecting the habitability of exomoons.
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/>[2](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/)
And it suggests that the longest possible day for a hypothetical habitable exomoon would be less than, for example, a single Earth year long.
It is assumed that the vast majority of habitable exomoons would be tidally locked to their primaries, rotating at the same rate as they orbited those planets, and thus keeping one side facing the planet at all times and other side facing away at all times. Thus the moon's month, or orbital period around the planet, should be same length as it's day, the time the moon takes to rotate through 360 degrees.
Thus I tend to call it the month/day of the moon, since as the moon orbits and the planet and also rotates it will rotate in relation to the star or sun in the solar system and thus the sun will rise and set and a spot on the surface of the moon will experience a period of daylight and a period of night during the moon's orbital period around the planet.
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> On moons, however, tides from the star are mostly negligible compared to the tidal drag from the planet. Thus, in most cases exomoons will be tidally locked to their host planet rather than to the star (Dole, 1964; Gonzalez, 2005; Henning et al., 2009; Kaltenegger, 2010; Kipping et al., 2010) so that (i.) a satellite's rotation period will equal its orbital period about the planet, (ii.) a moon will orbit the planet in its equatorial plane (due to the Kozai mechanism and tidal evolution, Porter and Grundy, 2011), and (iii.) a moon's rotation axis will be perpendicular to its orbit about the planet. A combination of (ii.) and (iii.) will cause the satellite to have the same obliquity with respect to the circumstellar orbit as the planet.
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<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/>[2](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/)
The longer the month/day is, the hotter the day side will get, and the colder the night side will get. The longest possible day or night for a planet would be if that planet was tidally locked to its sun, and thus had eternal day on the near side and eternal night on the far side of the planet.
There is a fear that a planet tidally locked to its sun would lose its atmosphere and water because the hot air and water vapor from the day side would flow to the night side and condense and freeze until everything was frozen on the night side.
If that was the case, a planet that had a sufficiently long day period would have almost all of its water and atmosphere frozen on the night side during the long night. Only the water and atmosphere that was melted and sublimated at dawn would exist as a thin atmosphere that sublimated at the same rate as it froze out.
On the other hand, it is possible that the circulation of air and water between the light and the dark sides will transfer enough heat to the dark side to keep the air and water unfrozen.
>
> This pessimism has been tempered by research. Studies by Robert Haberle and Manoj Joshi of NASA's Ames Research Center in California have shown that a planet's atmosphere (assuming it included greenhouse gases CO2 and H2O) need only be 100 mbs, or 10% of Earth's atmosphere, for the star's heat to be effectively carried to the night side.[74] This is well within the levels required for photosynthesis, though water would still remain frozen on the dark side in some of their models. Martin Heath of Greenwich Community College, has shown that seawater, too, could be effectively circulated without freezing solid if the ocean basins were deep enough to allow free flow beneath the night side's ice cap. Further research—including a consideration of the amount of photosynthetically active radiation—suggested that tidally locked planets in red dwarf systems might at least be habitable for higher plants.[75]
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<https://en.wikipedia.org/wiki/Planetary_habitability#Other_factors_limiting_habitability>[3](https://en.wikipedia.org/wiki/Planetary_habitability#Other_factors_limiting_habitability)
So at the present time it seems possible that even a tidally locked planet could be habitable, and thus there doesn't seem to be any known limit based on freezing out the atmosphere to how long the day and night of a habitable exomoon could last, which is good for your desire to have it as long as possible.
According to "Exomoon Habitability Constrained by Illumination and Tidal heating"
>
> The synchronized rotation periods of putative Earth-mass exomoons around giant planets could be in the same range as the orbital periods of the Galilean moons around Jupiter (1.7–16.7 d) and as Titan's orbital period around Saturn (≈16 d) (NASA/JPL planetary satellite ephemerides)4. 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)
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<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/>[2](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549631/)
So they estimate that a habitable exomoon might have a month/day as long as maybe 17.0 Earth days. But what is really important is:
>
> 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)
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The source, Kipping 2009a, seems to be:
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> Kipping D.M. Transit timing effects due to an exomoon. Mon Not R Astron Soc. 2009a;392:181–189.
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<https://arxiv.org/abs/0810.2243>[4](https://arxiv.org/abs/0810.2243)
According to Alexander's answer, if the exomoon was orbiting a planet orbiting a star as massive as Sol (the sun) at a distance of 2.4 AU, assumed to be the other limit of the habitable zone, the habitable moon could have a month/day of 277 Earth days or 0.76 Earth years.
If the year of the planet has to be at least nine month/days of the moon long in order for the moon to have a stable orbit, the year of the planet would have to be at least 2,493 Earth days, or 6.825462 Earth years.
There are many different scientific estimates of the habitable zone of the Sun, or of a star that is exactly like the Sun. Some estimates give the some a very narrow habitable zone and other estimates give it a very broad habitable zone.
Since you are interested in the longest possible month/day of your moon, and thus the longest possible year for the planet orbiting it's star, lets calculate it for various outer edges of the Sun's habitable zone.
If the hypothetical moon's planet orbits a star exactly like the Sun at a distance of exactly one AU, the planet will have a year exactly one Earth year long, and the longest possible length of a month/day of a habitable moon of that planet would be one ninth of an Earth year, or about 40.5833 Earth days.
According to this paper:
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> Hart, M. H. (1979). "Habitable zones about main sequence stars". Icarus. 37: 351–357. Bibcode:1979Icar...37..351H. doi:10.1016/0019-1035(79)90141-6.
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The outer edge of the Sun's habitable zone is only 1.01 AU from the Sun. According to my rough calculations, a planet orbiting at that distance would have a year about 1.01503 Earth years, or 370.7424 Earth days long, and its hypothetical moon could have a month/day no longer than about 41.1196 Earth days long.
According to this article:
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> Vladilo, Giovanni; Murante, Giuseppe; Silva, Laura; Provenzale, Antonello; Ferri, Gaia; Ragazzini, Gregorio (March 2013). "The habitable zone of Earth-like planets with different levels of atmospheric pressure". The Astrophysical Journal. 767 (1): 65–?. arXiv:1302.4566. Bibcode:2013ApJ...767...65V. doi:10.1088/0004-637X/767/1/65.
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The outer edge of the Sun's habitable zone is only 1.18 AU from the Sun. According to my rough calculations, a planet orbiting at that distance would have a year about 1.2818 Earth years, or 468.1803 Earth days long, and its hypothetical moon could have a month/day no longer than about 52.0200 Earth days long.
According to this article:
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> Kasting, James F.; Whitmire, Daniel P.; Reynolds, Ray T. (January 1993). "Habitable Zones around Main Sequence Stars". Icarus. 101 (1): 108–118.
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The outer edge of the Sun's habitable zone is 1.37 AU from the Sun. According to my rough calculations, a planet orbiting at that distance would have a year about 1.6035 Earth years, or 585.6943 Earth days long, and its hypothetical moon could have a month/day no longer than about 65.0771 Earth days long.
According to this article:
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> Kopparapu, Ravi Kumar (2013). "A revised estimate of the occurrence rate of terrestrial planets in the habitable zones around kepler m-dwarfs". The Astrophysical Journal Letters. 767 (1): L8. arXiv:1303.2649. Bibcode:2013ApJ...767L...8K. doi:10.1088/2041-8205/767/1/L8.
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The outer edge of the Sun's habitable zone is 1.68 AU from the Sun. According to my rough calculations, a planet orbiting at that distance would have a year about 2.1775 Earth years, or 795.3423 Earth days, long, and its hypothetical moon could have a month/day no longer than about 88.3713 Earth days long.
According to this article:
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> Spiegel, D. S.; Raymond, S. N.; Dressing, C. D.; Scharf, C. A.; Mitchell, J. L. (2010). "Generalized Milankovitch Cycles and Long-Term Climatic Habitability". The Astrophysical Journal. 721 (2): 1308–1318. arXiv:1002.4877. Bibcode:2010ApJ...721.1308S. doi:10.1088/0004-637X/721/2/1308.
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<http://iopscience.iop.org/article/10.1088/0004-637X/721/2/1308/meta>[5](http://iopscience.iop.org/article/10.1088/0004-637X/721/2/1308/meta)
The outer edge of the Sun's habitable zone is 2.00 AU from the Sun. According to my rough calculations, a planet orbiting at that distance would have a year about 2.8284 Earth years, or 1,033.0829 Earth days, long, and its hypothetical moon could have a month/day no longer than about 114.7869 Earth days long.
According to this article:
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> Ramirez, Ramses; Kaltenegger, Lisa (2017). "A Volcanic Hydrogen Habitable Zone". The Astrophysical Journal Letters. 837: L4. arXiv:1702.08618 [astro-ph.EP]. Bibcode:2017ApJ...837L...4R. doi:10.3847/2041-
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<http://adsabs.harvard.edu/abs/2017ApJ...837L...4R>[6](http://adsabs.harvard.edu/abs/2017ApJ...837L...4R)
The outer edge of the Sun's habitable zone is 2.4 AU from the Sun. According to my rough calculations, a planet orbiting at that distance would have a year about 3.7180 Earth years, or 1,358.0228 Earth days, long, and its hypothetical moon could have a month/day no longer than about 150.8914 Earth days long. That is the same distance from the Sun that Alexander used to calculate a month/day of 277 Earth days.
However, this seems to involve atmospheric hydrogen concentrations of 1 % to 50 %, which do not seem compatible with an oxygen rich atmospheres suitable for humans.
According to this article:
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> Fogg, M. J. (1992). "An Estimate of the Prevalence of Biocompatible and Habitable Planets". Journal of the British Interplanetary Society. 45 (1): 3–12. Bibcode:1992JBIS...45....3F. PMID 11539465.
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The outer edge of the Sun's habitable zone is 3.00 AU from the Sun. According to my rough calculations, a planet orbiting at that distance would have a year about 5.1961 Earth years, or 1,897.8946 Earth days, long, and its hypothetical moon could have a month/day no longer than about 210.8771 Earth days long.
According to this article:
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> Pierrehumbert, Raymond; Gaidos, Eric (2011). "Hydrogen Greenhouse Planets Beyond the Habitable Zone". The Astrophysical Journal Letters. 734: L13. arXiv:1105.0021 [astro-ph.EP]. Bibcode:2011ApJ...734L..13P. doi:10.1088/2041-8205/734/1/L13. Cite uses deprecated parameter |class= (help)
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<http://adsabs.harvard.edu/abs/2011ApJ...734L..13P>[7](http://adsabs.harvard.edu/abs/2011ApJ...734L..13P)
The outer edge of the Sun's habitable zone is 10 AU from the Sun. According to my rough calculations, a planet orbiting at that distance would have a year about 31.6227 Earth years, or 11,550.218 Earth days, long, and its hypothetical moon could have a month/day no longer than about 1,283.3575 Earth days long.
But this last calculation involves planets with significant amounts of hydrogen in their atmospheres, equal to or greater than Earth's total atmospheric pressure, which would not be consistent with a breathable oxygen rich atmosphere for humans.
<https://en.wikipedia.org/wiki/Circumstellar_habitable_zone>[8](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone)
Another way to change the possible length of the year of the planet and thus of the month/day of the moon, is to change the mass and thus the luminosity of the star in the system.
A relatively small change in the mass of the star can produce a much larger change in the luminosity, and thus in the distance of the habitable zone, and thus in the length of the years of planets in the habitable zone, and thus in the maximum possible length of the month/days of moons orbiting those planets.
And a relatively small change in the mass of the star can produce a much larger change in the rate at which it uses up is nuclear fuel and thus the time it depends on the main sequence stage of its life before becoming a red giant star and then a white dwarf star.
And if you want your hypothetical moon to have multi celled lifeforms, or an oxygen rich atmosphere breathable for humans, or intelligent natives, or most of the other things which are usually needed to make a world interesting in science fiction, you will want it to be billions of years old and thus you will need the moon's star to be of a spectral type capable of remaining on the main sequence for several billion years.
[Answer]
All the worlds actually plotted (that I've seen the stats for anyway and I looked pretty hard at this a couple of months ago) that are more massive than Jupiter, including small Brown Dwarf Stars, have been found to have a higher average density and thus a smaller radius. So Jupiter would appear to be as large as Gas Giants actually get in nature, purely in terms of radius.
Taking that as a base the orbital distance, for a 1/2 degree angular size, is pretty much 8 million Kilometres, well within Jupiter's Hill Sphere (for an approximately Sol mass star) of 53 million Kilometres. The Earth, or something substantially similar, would orbit it in 145 days and 19 hours.
Here are the tools I used to get the answers:
[Jovian Statistics](https://en.wikipedia.org/wiki/Jupiter)
[Angular Size Calculator](http://www.1728.org/angsize.htm)
[Orbit Calculator](http://www.calctool.org/CALC/phys/astronomy/planet_orbit)
All stars have a goldilocks zone so all you need is a yellow star, something with a G [spectral classification](https://en.wikipedia.org/wiki/Stellar_classification).
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[Question]
[
### Background
In case you haven't heard: there are places in the Amazonian Jungle called [*Devil's Gardens*](https://en.wikipedia.org/wiki/Devil%27s_garden). The gardens are large swaths of land composed of almost entirely one single tree the Duroia hirsuta. This tree's roots have the ability to secrete growth inhibitors along side it's symbiotic relationship between this tree and the lemon ant, this tree is able to negate competition by killing them. There are other trees that create clonal colonies in which the colony grows new trunks from a root system underground.
### Question
So I am wondering: is it feasible that a tree could evolve to use its roots to search our other trees and grow a new clone through the trunk of its competitor? Which should split the competing tree in half and kill it all at the same time reproducing.
[Answer]
In regards to the splitting aspect of your question, I believe that a mistletoe hybrid would be best.
Mistletoe seeds, deposited by birds and other animals, burrow into the trunks of nearby trees, and split the bark as they grow, sapping nutrients from the original tree as they go.
[](https://i.stack.imgur.com/plleP.jpg)
As it stands, even naturally occurring mistletoe has the potential to kill many native trees, though generally it is not in the mistletoe's best interest, as it gets a majority of its nutrients from its living host tree. If the hybrid were to be able to establish a more effective root system that spread down to the ground or perhaps take over the host's own root system, then it could completely displace any plant that it takes over.
With birds being the main way in which it spreads, the mistletoe hybrid could spread very quickly through an area, since most mistletoe-eating birds nest in non-mistletoe plants, effectively planting the seeds in exactly the places where they are needed the most.
[Answer]
Something similar to what you depict is done by the [Ficus watkinsiana](https://en.wikipedia.org/wiki/Ficus_watkinsiana), better know as strangler fig.
Its well deserved name comes from its growth cycle: when a bird eats one of its figs, it can drop one of the seeds, through its excrement, on a tree. When this happen the seed grows around the tree trunk, reaching the ground and enveloping the host tree until it [dies for lack of light and air](http://www.geocities.ws/fiordan54/pagine/botanica_strangolatrici.html).
The fig strategy allows for a better position of the young plant with respect to light gathering (sprouting higher than the ground) and also ensure a suitable support while the plant grows.
In your case the young plants should start from the ground level (thus with less light), and should compete with an adult plant. Moreover, being a clone, could not randomly pick advantageous genetic traits.
I am not saying it is impossible, there are trees propagating via roots, I just think this might be possible but less effective.
[](https://i.stack.imgur.com/FRwLz.jpg)
Of course, using the strangler fig mechanism, preventing other trees from growing is a bad idea, as then one will lack growth substrates.
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[Question]
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So, let's just say that the US Military has a tactic that involves setting forests alight and deploying troops there for combat. I don't know if this is plausible, or why they would do this, but I ask that you take these conditions as real when answering (Though, if you do think this would be an efficient tactic, then please do let me know in the comments/in your answer.)
What would a specialized soldier for fighting in forest fires look like? The main things I want to know are:
1) What protective gear would they need?
2) Would they wear special camouflage for the burning environment?
3) Are there any weapons that would be especially effective in this environment?
4) Would they use special vehicles, or would the normal, real ones suffice?
To group it all into one question, what would constitute a specialized modern soldier that fought in forest fires?
[Answer]
Sealed gear with an independent air supply is a must. Depending on the role of these soldiers will change their level of armament. If you wanted they could all be equipped with modern exoskeleton technology. As they are unlikely to be deployed for long periods of time this makes the technology quite viable in this case. Additionally it would allow greater armour capacity,oxygen capacity and allow them to move more freely without tiring from the weight.
A basic level of fireproofing is a must as is heat proofing. This can be achieved through the use of non-flammable coatings and materials,cooled gel layers in the armour supplanted if really necessary by an integral AC unit. Similar to that used in modern Bomb Disposal Suits,Land Warrior and Future Soldier equipment load-outs.
If they are intended to set fires and fight in them I'd recommend starting with napalm airstrikes or white phosphorous artillery bombardment. In a forest or jungle you would spontaneously have a firestorm. Ideal camouflage is a mixture of native forest pattern with accents of black and red. Black for the smoke and ash,red for the raging blaze around them. Add some pieces like used on ghillie suits to break up their outline and make them look like phantoms amidst the smoke and flames.
Weapons wise I'd say that assault rifles,battle rifles,shotguns loaded with slug and HE shells, as well as white phosphorous grenades and grenade launchers would be very effective. The assault rifles and battle rifles providing good firepower,versatility and would be in their effective range within said blaze almost constantly due to the smoke and reduced visibility. The shotguns would be ideal for close quarters engagements and the HE shells serve to further disorient the enemy;additionally they can be used to blast apart barricades and target light vehicles (humvees,technicals,doors,etc). The grenade launchers would provide an easy means of blasting areas with troops sheltering from the blaze (hiding in trenches,bunkers,pill boxes,basements,etc) and the use of fire as a psychological weapon would be extremely effective. Light machine guns would also be ideal for their standard uses within squads for suppression of enemy troops.
For vehicles I'd recommend most MBT's (main battle tanks) with slight modifications where necessary for comfort of troops inside to grant heat protection and prevent smoke from entering inside. You can give the tanks a coaxial flamethrower (as is sometimes done) to make them literally spray fire everywhere as they advance alongside their main gun and turret. APC's for rapid deployment girded up a bit would be nice. But more realistically AFV's (armoured fighting vehicles) would be more useful in a slash and burn operation. Standard air cover can be provided if with reduced visibility,you can fly a drone or two overhead to keep an eye on enemy troop movements to coordinate with ground forces. Making artillery support via mortars brought close to the front easier to manage alongside the firepower of the AFV's and MBT's.
Using weapons that produce fire (white phosphorus,napalm,flamethrowers,incendiary rockets,etc) would add to the horror and confusion. While the solders equipped, (the "Flame Troopers", "Pyroneers", "Grey Devils",whatever name you like);for the inferno would seem monstrous. This can be added too with armour design,decals,the camouflage and also their equipment. If you wanted to be extra cruel they can have specialized recon units that carry camouflaged fire blankets and cover themselves with them in the burning areas. They then would seem to rise from the ashes when attacking enemy troops. Like demons or burning men. Which given the blanket may be on fire,they would very much look like it.
All in all,I found this to be a very interesting idea. Plenty of practical and psychological warfare potential.
[Answer]
Well, let's take the obvious idea.
# Fire fighters with guns
Take a fire fighter with the typical high-protective forest fire gear. Remove the water hose. Give them an M4 instead. Voila.
But wait.
# Caveats
High-protective fire fighter gear features an oxygen mask and oxygen/fresh air tank. I'd imagine it's quite highly pressured, similar to aqualung. You cannot afford a bullet to a high-pressure tank in a combat situation. But there are options.
* More shielding;
* Tank protection, similar to fuel tanks in combat planes;
* No high-pressure tank, but CO2 restoration chemicals: make O2 again from CO2.
# ABC gear
All modern armies have something similar already. Namely the gear, designed to protect the soldiers from elements on atomic, biological, or chemical warfare. It's very roughly a full body condom.
It already protects from all bad components of a fire, except, well, heat and maybe physical damage such as crashing down burning branches. It might make sense to combine ABC gear with firemen's outfit, if going to war into burning forests is a thing.
# Why should they?
I think that any modern army just won't go into a burning forest. Because, they don't have to.
* Someone is hiding there? Encircle a forest and wait for anyone who tries to leave it.
* There is something hidden? Wait until the forest burns down completely and then fetch the item.
* You need something else inside? As the old and a bit grim [joke](https://www.reddit.com/r/Jokes/comments/1fmwo2/the_lapd_the_fbi_and_the_cia/) tells us, even a bear would confess to being a rabbit with a bad enough treatment.
[Answer]
No amount of high-tech gear will protect soldiers from forest fires. Think of this: every now and then there are impressive forest fires, and firefighters die while fighting those anyway. Firefighters specialized in surviving in fires, so if they also have to spend time and effort learning how to shoot and fight a war, they will be less prepared to survive in a fire.
If you are going to set forest alight, you don't need soldiers. You need ninjas:
[](https://i.stack.imgur.com/xo1AJ.gif)
### 1) What protective gear would they need?
Ninja outfits.
### 2) Would they wear special camouflage for the burning environment?
They would use their ninjutsu to survive the fire. As for camouflage, they are already the stealthiest thing you can have.
### 3) Are there any weapons that would be especially effective in this environment?
Bamboo darts and wooden shuriken. In the fire they will be lit, so an enemy that manages to avoid most flames may still be lit.
### 4) Would they use special vehicles, or would the normal, real ones suffice?
Ninjas don't need land vehicles.
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[Question]
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## Primary question
If this world averages a *visible* light level of [civil twilight](https://en.wikipedia.org/wiki/Twilight#Civil_twilight) (about 1000x dimmer than full daylight, or 500x brighter than full moonlight) during the day, what kind of plants can I get away with?
## Information
The planet as determined by my previous question [here](https://worldbuilding.stackexchange.com/q/102441/45157) and my personal solidifying of elements has these characteristics so far. Flexible characteristics are things I am currently going with but are not vital to any story or world-building elements yet.
**Flexible Characteristics:**
* No moon
* very little tectonic movement, so (relatively speaking) quite flat (this would probably mean shallower water and few mountains).
* Gentle seasons (Similar to near equator on Earth).
**Important Characteristics:**
* Majority of, or all year, is above freezing
* Almost constant fog.
* Frequent rainfall (usually light drizzles)
* Light exposure much lower than full sunlight on Earth
## Additional Details
* The planet was not always dark like this. It has been dark for a very long (undetermined) period of time but was not always so dim. It is as dim as it is because of astrological events and its incessant fog.
* Because of the planet's flatness, fog, and frequent drizzling, I am assuming lots of shallow, stagnant, or slow moving, bodies of water (marshes) and plains.
* I can assume that fungi and mushrooms will be fine with the low light levels and I may end up using them as my "woody" plants, but I am not confident in determining what other types would be reasonable. [Mangrove trees](https://en.wikipedia.org/wiki/Mangrove) maybe?
* I am hoping for leafy plants or even trees even if they grow very slowly.
Answers just need to be plausible. Some magic is totally acceptable. I am looking for a spectrum of plants with a few more specific examples.
[Answer]
# Your plants must metabolize higher energy light waves
Higher energy light penetrates more deeply through particulate matter. In the case of both various astronomical phenomena from the other question and incessant fog, infrared light will be totally blocked, visible light will be heavily attenuated, and ultraviolet light will be attenuated very little.
[](https://i.stack.imgur.com/iwpgs.gif)
You can see there that visible light is in an absorption 'gap' in water. That means visible penetrates through water much more than IR radiation or UV light smaller than about 200 nm. This is why both plants and our eyes use visible light. But notice that the absorption is even lower in the near-UV spectrum.
Photosynthesis using chlorophyll is optimized for the light conditions on Earth. However, there are extant alternative pathways for metabolizing UV radiation. [Carotenoids](https://en.wikipedia.org/wiki/Carotenoid) are [accessory pigments](https://en.wikipedia.org/wiki/Accessory_pigment) that work alongside chlorophyll, extending its range as low as 400 nm, just into the UV range. Another accessory pigment, [Oenin](https://en.wikipedia.org/wiki/Oenin), can absorb [as low as](https://en.wikipedia.org/wiki/Chlorophyll#/media/File:Spectra_Chlorophyll_ab_oenin_(1).PNG) 200 nm. There may be other undiscovered or extinct light absorbing pigments as well. You can have plants pick up accessory pigments, such as Oenin and Carotenoids, to up their energy intake in the low light conditions.
However, there is one more catch. Here is plot of received EM radiation on Earth by wavelength:
[](https://i.stack.imgur.com/uAUcK.gif)
Look to the far left in the 200-400nm range (the near UV area). Just as water's absorption goes down on the specturm, the sun's radiation also goes down. That is due to the sun's ~6000 K surface temperature. If you really want to make UV light a thing, you are going to have to find a way to increase the Sun's radiation levels at smaller wavelengths. The only way to do this (in a science based manner) is for the sun to get hotter.
[](https://i.stack.imgur.com/jJCJ3.jpg)
Bump up your sun's surface temperature to about 8000 K as an F-type Main Sequence star, like [Procyon](https://en.wikipedia.org/wiki/Procyon). Now, your new UV driven plants can flourish!
[Answer]
You could take cues from the flora of the rainforest floor.
[](https://i.stack.imgur.com/rkcRt.jpg)
[source](https://www.pinterest.com/pin/560064903636476489)
I have read that as little as 2% of sunlight penetrates to the forest floor.
Vegetation is sparse; a lot of ferns and mosses (I wonder why these more primitive plants do better in low light areas?). Here is a schematic for flora of the different levels of the Australian rainforest.
[](https://i.stack.imgur.com/BFciF.jpg)
[Answer]
What if your inhabitants are recent arrivals, and have vision that is not matched to what gets through the atmosphere. E.g. if they have eyes that see only medium and far UV, an earth type planet will be very very dim on the surface, because most of that is blocked by the atmosphere.
Similarly if they saw by near infrared.
Or give them vision across a large range of infrared -- they see many more colours than we do, but vision is blurrier due to the longer wave lengths.
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[Question]
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Hybrid dirigible airplane with an extremely large surface area on the top and bottom. Talking at least 100 km2. It would likely be several modular pieces put together, given its size. It would need to stay aloft for months on end. Stay aloft above most of the weather, ie 40,000 to 50,000 feet, for more access to solar power. Some ability to maneuver with propellers or other means, though I do not expect much considering it's massive size. Maybe 10 mph or so laterally or in addition to the winds direction. Ability to station keep, or at least slow significantly down. See issues with scenario below for specific questions about feasibility, reasonably close to hard science please.
**Purposes for this behemoth:**
* To block out the sun in the east-central pacific to disrupt El Nino. Including sea water drawn up for increased cloud formation.
* To block out the sun near wildfires, droughts, lethal record temperature areas. In order reduce the temperature and potential create rain.
* To collect solar power for propulsion, ship functions and for inhabited areas below for use.
+ Via tether or microwave.
+ Not intended for large habitation, space for the crew, research and a hotel for the great views of Earth and the night sky.
+ Possible transportation of goods and people but not main purpose.
+ Launch platform for rockets to orbit.
+ Test bed for tether system for future potential space elevator/tether.
**Issues with scenario:**
* Is there enough lifting gas, Hydrogen, Helium, even pure Nitrogen? the hybrid design should help with lift significantly.
* How much temperature drop can be expected with a couple days of shading with this size structure?
* Is it maneuverable? Can it station keep (or slow down) at all? Can it stay aloft for months? Can it be powered by solar power alone?
* Is a tether feasible from this altitude with current technology?
[Answer]
This question has several facets to it, I'm going to try to answer as many as I can, edits to follow.
## Lifting Gas Availability
Helium is a limited resource, although a lot of it is currently produced as a side effect of natural gas extraction. [2008 production](https://en.wikipedia.org/wiki/Helium#Occurrence_and_production) was ~169 million standard cubic meters (SCM) of helium. This would not even be close to enough for your mega-structure. 100km x 100km x 100m = 1x10^12 cubic meters or 6000 times the yearly production. (I assumed 100m thickness it could easily be bigger depending on the density of your craft)
Hydrogen however is not very limiting at all, as it is abundantly available in water, requiring only [electricity](https://en.wikipedia.org/wiki/Electrolysis) to extract it. So despite the [flammability issues](https://en.wikipedia.org/wiki/Hindenburg_disaster) and diffusion problem, you are going to have to use hydrogen. On the plus side it is the most effective [lifting gas](https://en.wikipedia.org/wiki/Lifting_gas) available.
You could also use hot air, which simply requires heat.
## Temperature Drop
So I'm going to do a bunch of big approximations to get a back of the envelope calculation for this using a quick and dirty energy balance model.
So the [Sun](https://en.wikipedia.org/wiki/Solar_irradiance) provides ~1000 W per square meter, but only when it's shining and there is a lot of variance over day, night, seasonally, and with latitude. Average all of that variability out over a year and most places on Earth's surface will see an average of around 250 W/m^2. (Using this lower number will underestimate cooling rate during the day)
Some relevant [properties of Air](http://www.engineeringtoolbox.com/air-properties-d_156.html):
Specific Heat: ~1.0 kJ/kg K
Density:~1.0 kg/m^3
(varies a lot with [altitude](http://www.engineeringtoolbox.com/air-altitude-density-volume-d_195.html) and temperature but a rough average for a quick calculation)
So if we remove 250 W/m^2 from a column of air 15 km tall we can figure a rough temperature drop.
Mass of the column of air = 15km \* 10km \* 10km \* 1kg/m^3 = 1.5 x 10^12 kg of air
Rate of energy removal = 250 W/m^2 \* 10km \* 10km = 2.5 x 10^10 W
E = m*c*T to power P = m*c*T/s
solve for T/s = P/(m\*c) = .0000167°K/s or .001°C/minute or 1.44°C/day
To get the final coldest temperature you would need to factor in convective heat transfer involving the mixing with warm from air outside of the shade zone (this cooling would cause winds to develop. Anti-cyclone!) as well as radiative heat transfer and heat from geothermal sources, and water motion for oceans or large bodies of water, in general it would be a really complex set of calculations and very specific to the location and timing of the shade placement.
But to simplify it you are essentially creating a stable stationary [cold front](https://en.wikipedia.org/wiki/Cold_front), which can have temperature drops of up to 30 °C (54 °F) so this would be a likely upper bound for temperature drop from ambient levels in the region under the shade.
## Balloon Tethers
Balloon tethers are definitely possible and in common usage at lower altitudes.
[Barrage Balloons](https://en.wikipedia.org/wiki/Barrage_balloon) were used to raise nets of metal cables into the air to impede enemy aircraft. They were raised to ~4,500 m (15,000 ft.), modern [tethered balloons](https://en.wikipedia.org/wiki/Tethered_balloon) are used primarily for military surveillance and reconnaissance, as well as communications. Some [current military systems](https://en.wikipedia.org/wiki/Tethered_Aerostat_Radar_System#Technical_and_operational_data) operate at altitudes of 15,000 ft. with 25,000 ft. long tethers.
Longer tethers and higher altitudes are likely possible with existing materials and even better for possible near future materials. For tether material strength over those distances the important factor is known as [Specific strength](https://en.wikipedia.org/wiki/Specific_strength) or breaking length, how long a tether can be to support its own weight. Modern existing materials can be quite long Kevlar and Carbon fiber have a breaking length of ~250 km (for reference 50,000 ft is ~15 km).
The bigger issue for tether strength would be if it was used to resist the force of the wind on the balloon structure, but if it is a powered structure capable of some maneuverability, or the tether is not secured to the ground these forces could be mostly negated.
## Flight Characteristics
Most of these issues would be an engineering design problem, but not impossible, blimps and zeppelins have been shown to function so it definitely can be done, it just needs to be scaled up a lot.
It won't be fast, will need to be aerodynamically streamlined to resist winds, and will likely not be very maneuverable. Your best bet on travel would be to find favorable winds, by changing altitude, and going with the wind.
As for solar power, the [Hindenburg](https://en.wikipedia.org/wiki/LZ_129_Hindenburg#Specifications) used 4x Daimler-Benz DB 602 (LOF-6) diesel engines each 890 kW (1,200 hp), so total power of 3500 kW.
The Hindenburg had a diameter of 41m x 245m long; so using only the top half of the surface for solar cells (π \* D \* L)/2 provides roughly 16000 m of surface. Using [solar cells](https://en.wikipedia.org/wiki/Solar_cell_efficiency) (20% efficient) to provide 200 W/m then provides 3200kW.
So comparable instantaneous power, but it would likely be underpowered if requiring continuous thrust for any length of time. And it would be worse when considering storage losses required for night running. As for energy storage hydrogen fuel cells would seem like the obvious choice over batteries, given the likely use of a hydrogen lift gas.
[Answer]
**Feasible enough that if I ever become a multi-billionaire I will build one.**
Your station will need:
* Airbags that don't catch fire
* Rain
* Lots of solar panels
Your station alternates between above the weather for most of the time, and ducking in to rainstorms to collect water to electrolyze into hydrogen (for lift). The oxygen is vented as far away from the station as possible. You don't want liquid oxygen anywhere near your hydrogen gasbags.
I slightly doubt the ability for solar to provide enough production rate to replace hydrogen lost through the gasbags, so you may need a nuclear reactor of some kind.
Over vigorus hairbrushing is a crime. DC brushed motors are illegal, and many other minor rules have to be enforced to prevent fire.
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Because it isn't hanging beneath one big gasbag (I envisage lots of small ones), each individual part of your station is effectively zero weight. This is why blimps can be bigger than aircraft. An aircrafts wings have to support it's fuselage, but most of an airships structure is self supporting. As a result, you could probably come up with some sort of farm/ecosystem on board, to make a truly self sustaining system.
However, I doubt that a space elevator would be any more practical if anchored(?) to a flying platform. Space (near vacuum) is only 100km up. Geostationary is 40,000km, so you still need thousands of kilometres of cable (and cable length is the important factor in space elvators).
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To block out the sun, the platform needs to appear sun-sized. My thumb (1cm) can block out the sun at arms length (100cm). Thus the rule of thumb is that an object that is sun-sized will be 100 times further away than it is large. (For proof, the sun is 1.4 million km diameter at 150 million km). As a result at your operational altitude of 10km, your platform will need to be a 100m disc. That's not unfeasible as the Hindenburg was 245 meters long. If you bolted three hindenburgs together (they are only 40m wide), you could block out the sun from 10km altitude.
How much effect will that have on the temperature? Unfortunately, no-one seems to have studies on 100m shadecloths at high altidude. However, [this study](http://hortsci.ashspublications.org/content/45/1/83.full) found that the shade of a tree tree dropped the air temperature by 0.6 - 2.5 degrees Celsius at mid-day, and the ground temperature by a massive 3.3 - 8.1 degrees. This implies that a 100m area of shade may well have a larger affect than I anticipated in earlier versions of this answer. However, to keep the spot of shade in the same place, your platform will have to move very rapidly to counter Earth's rotation.
Your question states you want 100kmx100km. How big will that appear if it is at 40,000ft? It's only 10km up, so it's going to appear *freaking massive.* The sun appears with a 0.5 degree angular width. Your platform will have a ... 160 degree angular width. In other words, if you are directly under it, there will be a 10 degree ring of sun on the horizon. I could well accept that that will have significant affects on climate, considering that it's larger than most mountains.....
Or if you mean 100 square kilometers (ie 10kmx10km) then your station is 'only' 60 degrees wide. Still pretty significant.
Using it as a launch launch platform for rockets to orbit is not unfeasible either. There is a company doing [airship to orbit](http://www.jpaerospace.com/atohandout.pdf), and they plan to have a station at 140,000 ft altitude. I wouldn't want rockets anywhere near my hydrogen gasbags, but I can't see why you couldn't have reasonably large areas without gasbags to permit this sort of thing.
---
Your station will not have a very high speed. It will probably travel similar to balloons: find an altitude where the wind is blowing the direction you want to go.
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Side note: The upcoming [Mortal Engines movie](http://www.imdb.com/title/tt1571234/) is likely to feature airhaven - a flying city using airship-type technology.
[Answer]
I think a blimp of that size could be done, but I do not see any way to have it stand against upper atmosphere winds.
This behemoth should be relatively flat and, if round, it would have a diameter exceeding 11km; giving it a (*very* conservative) height of mere 100m you end up with a cross-section exceeding 1km2. To remain static against winds would require enormous power.
OTOH, given the enormous dimensions and fact you don't really need a rigid structure I think it could be done without special gasses, an old-fashioned hot-air balloon could suffice, probably with just solar power; During the night it would loose a bit, but not enough to really drop and next morning sunshine should be in position to restore lost heat (this in the hypothesis we are able to take advantage of the square/cube law and thus have a huge mass of hot air which can lose heat through a (relatively) small surface (i.e.: do not make your balloon too flat) which is also what weighs down (i.e.: the structure is relatively lighter than equivalent smaller installations, so you need air "less hot").
I also am not real sure about effectiveness of such a beast as sun-shield because I think it is too small (by orders of magnitude) to have a real effect on climate, but I might be wrong.
[Answer]
Monster LTA designs have been postulated, most famously by [Buckminster Fuller](https://infogalactic.com/info/Buckminster_Fuller) and his "[Cloud 9](http://www.geniusstuff.com/blogs/flying-cities-buckminster-fuller.htm)" flying city. This is actually a rigid airship built from a giant geodesic dome, and utilizing the squad/cube law.
>
> A half mile (0.8 kilometer) diameter geodesic sphere would weigh only one-thousandth of the weight of the air inside of it. If the internal air were heated by either solar energy or even just the average human activity inside, it would only take a 1 degree shift in Fahrenheit over the external temperature to make the sphere float. Since the internal air would get denser when it cooled, Bucky imagined using polyethylene curtains to slow the rate that air entered the sphere.
>
>
>
[](https://i.stack.imgur.com/SlMcc.jpg)
*Cloud 9 in flight*
While a sphere is the most efficient shape for a Cloud 9, there is no reason that an oval, disc or other shaped object would not work, so long as the weight of the fabric and structure are always increasing at a much lower rate than the mass of entrapped air as the structure grows in size.
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[Question]
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All this discussion of discussion of life after death and rather the faithful should fear death : [Why doesn't the verified existence of heaven change characters' attitude toward death?](https://worldbuilding.stackexchange.com/questions/67790/why-doesnt-the-verified-existence-of-heaven-change-characters-attitude-toward/67801#67801) reminded me of an old story Idea of mine.
The basic premise is a serial killer who found religion, but can't overcome his need to kill; instead coming up with a rather twisted view of religion to fit into that need to kill (he doesn't think the killing is moral, but he is trying to do it as close to 'right' since he can't control himself anyways).
He reasons that Heaven is better than life, and so killing someone who is certain to go to Heaven is a mercy. However, killing the most pious individuals is not good because these people are helping to convert and thus save other individuals, a cause worthy of their 'suffering' in life a little longer to do His work. Instead the most important people to kill are those that are at risk of going to either location, if they can do something to just barely earn Heaven it's important to kill them immediately so they don't have time to backslide morally and end up in Hell.
Thus he finds, stalks, and studies morally ambiguous Christians, on the edge of earning Heaven or Hell in his mind, and eventually sets them up with a test. He creates a trap where his potential victim is given a choice to do something great, most likely save the life of someone they think is going to die, but only if they risk their own life.
If, and only if, the victim does the noble deed to save someone they should die, as in doing so they have committed an act good enough to earn Heaven and should be sent there immediately. If they don't risk themselves they must live, so they don't go to Hell yet and have chance to possibly find redemption and earn Heaven before their death.
What I need is a way for the killer to create convincing traps like this that will not lead anyone to believe there is a serial killer on the loose. That means the ones that fail his test and run away should have no reason to think they were being tested or the circumstances were arranged. Likewise those killed should have their deaths ruled as natural causes, accident, or anything other than murder. Since most of the victims come from the same church and are known to many within the church the manner of their death must have either enough variance or ambiguity that no one who has heard of the multiple deaths will notice enough of a pattern for church members to be suspicious.
Ideally there would be *just* enough of a pattern for the one cynical officer who suspects a subtle serial killer to identify individuals as possible victims without it being obvious enough to convince others *or* his identifying that they are all being tested before their killed yet.
How can the killer set up his tests without drawing undue suspicion on himself?
[Answer]
Nothing is new under the sun.
You're probably looking for an extreme version of the Cathari movement (heresy), which provides all the justification which a serial killer could want.
Roughly speaking (and almost certainly a cartoonish oversimplification), Cathars believed the God of the old testament was evil, and had created a corrupt world. Everything material was created by him, so everything material is evil. Later, Christ came along, and he is a separate, good god. Also, souls are angels held captive by our (corrupt) bodies.
In practice, this seems to have led to a mostly-generic puritan lifestyle with a few quirks. Mostly, you had clean-living communities who worked hard and took care of each other. Some of those quirks were offensive to the church (refusing all sacraments, because they were worldly and so corrupt), some were neutral (no meat, dairy, swearing oaths, or killing), some were laudable at the time (frequent fasting), and one is exactly what you're looking for: the consolamentum.
Cathari society can be divided into the Believers and the Perfects. Believers are just regular guys. They try to live right and all, but they don't have any extreme requirements on them. Perfects are people who are dedicated to purifying themselves. They live a strict ascetic lifestyle; surrender all possessions to the community; preach, pray, and do charity work all day; etc. *And when they die, their souls go free to become angels and hang out with Christ.* The actual process of becoming a Perfect was a fairly mundane ritual named "the consolamentum," which I read as roughly comparable to a modern baptism: a certain aount of ritual, but nothing really exciting. After that, you just had to maintain the ascetic lifestyle until you died to get the good ending.
Any optimizer reading this would immediately see the loophole: behave however you want all your life, get this ritual on your deathbed, starve for however long it took you to finish dying, be an angel forever. It's not clear that it actually went this way very often, but it IS clear that the contemporary propaganda against the Cathars described them that way. There are also some specific charges that Cathars who timed this poorly (received a deathbed consolamentum, then recovered) *were smothered by their friends to prevent them from screwing up*. Libel or truth, that's your serial killer tie in.
So, you have this large, established body of doctrine to draw from. You have a creepy not-quite-business-as-usual religious vibe (including dormant angels inside people!). You have the standard serial-killeresque belief that everything worldly is corrupted (though with an established, existing religious belief behind it). And you have a very plausible excuse for killing people.
Also, it was based in France, so you might have to take a field-trip there for research ;)
[Answer]
Not that I've given this much thought. No.....not at all....
**Death by prayer**
Setup a spot for your flock to pray with a cushion made of dodgy material and of poor craftsmanship. Having them sit or kneel is preferable, and making the surface small enough to force them into a single spot is needed. Have a highly radioactive material in a lead/water lined box with a hydraulic lid.
Have your murderer set up extensive surveillance on the next subject. Buy burner phones for your murderer, and have them call the victim with a message implying that if they don't pray for a loved one's safety, the loved one will suffer the "wrath of [deity]". Destroy the phone, and dispose of the remains. If they don't pray multiple times for them (and they checked!), the loved one will continually suffer unfortunate "accidents".
When they've prayed for the loved one enough, begin introducing radiation in doses to them as they prey using the hydraulic lid when they pray, and closing it when they aren't there.
This method will be slow enough to give enough time between cases that other churchgoers probably won't notice, especially with the variations radiation can cause. Bonus points for being in a location with a nuclear plant.
I may have more options later...
[Answer]
>
> What I need is a way for the killer to create convincing traps like
> this that will not lead anyone to believe there is a serial killer on
> the loose. That means the ones that fail his test and run away should
> have no reason to think they were being tested or the circumstances
> were arranged. Likewise those killed should have their deaths ruled as
> natural causes, accident, or anything other than murder
>
>
>
The trap *per se* need not be anything special. Any situation in which someone is in danger is a potential "trap", so our killers starts by:
1. Devising ways of putting someone in *apparent* danger of death, from which they can be saved by someone else risking his life.
Things like trapping people in burning buildings or in cars sinking in iced-over lakes or hanging for dear life over chasms or having a foot trapped between the docks of a rail line.
Since the danger should only be apparent, the killer must either be ready to save himself those people in a non-suspicious way (e.g. pretending himself to be the selfless saviour), or he can himself impersonate the person in trouble (but this is tricky in case of subsequent investigations).
This allows to set up a trap, either with the same danger, or a different one.
For example the killer fakes being trapped in a car on a iced-over lake. The unsuspecting would-be saviour dares the ice himself; little does he know that the killer has a thermal diving suit on under his clothes, and that the ice has been mined so that it *is* solid, but will crack at the click of a button. The body of the helper will be found; that of the luckless helpee will not.
This will not be suspicious *the first time*. If the killer travels a lot, not even the second or the third.
The fourth time he'll have to come up with something different.
Choosing all victims from the same church is probably a dead giveaway; he can perhaps off two or three of them, but no more.
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A lot of people are probably familiar with this sort of handwavium in fiction when it's asked where a shapeshifter's extra mass comes from. Most choose to ignore that question. In works that pretend to be slightly more credible, they simply state that no extra mass is being created at all and that the shapeshifter is in fact merely grossly obese. Or at least they would be, were they not using their power to simply make themselves look like a 200lb man who actually weighs 500lbs. Presumably this is done by eliminating a lot of the empty space either in the human body or between the molecules themselves.
But this begs the question. How much mass can you actually handwave away like this before it becomes really obvious that this 150lb woman is actually a 700lb shapeshifter in disguise? Density is still a thing, and at some point the surface area to density ratio of all this compacted flesh and biomass is going to make the shapeshifter's legs sink into the very ground they walk on, no matter how careful they are to conceal their true weight.
When would this happen? What's the realistic limit to how much mass a shapeshifter could conceal in a humanoid frame before the extra weight becomes obvious? I'm assuming it would have to be greater than 500lbs but I'm not sure.
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Due to my own weight, I was really interested in shoes. And this can be a good way to see this.
High heels break way too easily if the user weighs more than 100kg / 220lbs. Actually, most soles are designed around this maximum weight, but on flat soles, like sneakers, it would be much harder to actually notice damage. So, your shapeshifter would wear flat shoes, and change them much more often, or would wear shoes from the shops for heavy people (like fat people shops, shops for sportsmen etc).
Other things are ladders and old stairs. Your typical ladder has a maximum load of 150kg / 330 lbs. You will probably not see your 700lbs shapeshifter using ladders, and wooden stairs will creak under it.
And then, of course, you can take it swimming. If he is walking on the bottom instead of swimming, here you have your shapeshifter.
[Answer]
The easiest way to switch mass to volume is fat vs. muscles.
You've seen those pictures where 5lbs of fat was the size of a forearm where 5 lb of muscle where size of a fist. So the obvious way would be to hide that extra mass in super hard biceps and abs. And by hard I mean deadlift plates hard.
In the greatest battles between pinky and nightstand shapeshifter would kick that nightstand into daylight. That's how you would spot it, the energy needed to move that weight would end up on objects coming in contact with the shapeshifter. Broken handles, buttons pushed into the coffee machine.
You ever tried to pull doors that need pushing? Shapeshifter would pull them out from hinges. Him putting his hand on a table would be equal to you smashing your hand on that table.
If he was aware of this you would notice that he avoids elevators with people in them as his weight could trigger an alarm. They wouldn't sit casually on things like tables, sofas or wooden chairs. They may even not sit at all not being sure if the chair would support that weight. They would not tap their fingers on surfaces because that could leave dents.
They would act as a 700lb human. I'm not sure about the puffing and sweating (we're talking alien here). They would use other people to do things for them (like opening doors, windows, moving objects) and avoid interactions of any kind. So no people touching them, no sports.
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The setting is a generally nondescript mid-medieval vaguely European society. No magic is present, except what is explicitly discussed in this question.
Twenty kingdoms, connected by trade routes but distant enough to have mostly segregated politics, are functioning as normal one day. The next, a giant tower explodes through the ground in the dead center each of their largest cities, killing civilians and destroying buildings.
The towers are met with (obvious) concern, but eventually several kingdoms discover that each tower has a doorway (wide and tall enough that two trade wagons abreast can comfortably, and easily pass through), and in fact each tower has exactly one doorway, with no other openings whatsoever. Some brave (or foolish) explorers determined that, by magic, through a series of large empty rooms these doorways connect with the other kingdoms' towers.
The towers appear to be perfectly indestructible. If the doors are barred from the outside they are impossible to open from the inside (although just like normal doors or gates, they cannot be instantly closed). There is nothing to be found in the towers' rooms, just empty slate floors, marble walls and ceilings, and great openings interconnecting them.
Traveling from one doorway to another is a matter of hours, instead of the weeks or months of travel required to travel between the kingdoms previously.
They've just discovered a means to drastically, drastically reduce the time to move trade, people, and potentially armies.
Assume most of the kingdoms aren't stopped by superstition.
Specifically dealing with trade and defense against invasion, what would an intelligent, sensible policy for a kingdom to adopt in this situation? What is the best policy to balance the advantage of trade with defense of the kingdom with this new opening (effectively forcing twenty of the largest cities under different kings to share borders)?
[Answer]
For defense, the area around the new tower will be cleared of all existing buildings. A double spiral path winds outward for several loops around the building. For normal usage, one spiral will be used for outbound traffic and the other will be for inbound. These roads are wide enough for wagons to be pulled through the curves, possibly wide enough for wagons to pass one another should one break an axle or something.
These roads are separated by thick stone walls. The walls are tall enough prevent climbing. The walls are wide enough to allow defensive works to overhang the pathways with murder-holes and bridges allow quick movement to any point on top of the spirals. Towers on the outside of the spirals contain the only stairways to the top.
Some of the bridges also house the winches for a portcullis below them, allowing the spiral pathways to be closed off against any invaders.
The area within the tower may be an absolute nightmare of logistics managing traffic to and from 20 separate endpoints. Unless each tower has a unique, non-overlapping, 2-lane path to each other tower, traffic will constantly be running into each other.
The kingdoms may actually come to an agreement where traffic from one kingdom is limited to only a few destinations and then only on a set schedule. The destinations would be set up so that you could still reach any other city, you may have to pass through 1 or 2 other cities first though.
[Answer]
Start the United Nations!
Assuming these towers are basically wrappers to some extradimensional space-time where people can meet in passing and otherwise interact with each other, each nation should send a small contingent of representatives to camp out inside the tower. These contingents can negotiate to control the flow of goods through the newfound portals and, in times of need, quickly pass word to seal the doors to their respective nations. In general, however, the Towerspace is agreed to be neutral territory and the presence of an excessive military force is deemed a violation of the Tower Treaty requiring corrective action from the remaining nations.
The empty rooms are quickly populated first by diplomats and soldiers, then by merchants, and finally by the commoners/travelers. In the end, you end up with the World City, a glorious mashup of every nation with access to the Towerspace.
Of course, creating articles to allow another nation to join would be hard...
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I came up with anthropoidal creature that has several subspecies, let's call them red, green & blue, that can interbreed with each other. My problem in this setting is that:
1. I don't want any ugly hybrids,
2. I don't want any of the subspecies to disappear due to interbreeding
So this is what my proposal how should their reproductive system work:
Each individual contains chromosomes that are shared for all the colors e.g. 80, plus certain amount of chromosomes unique to each color e.g. 20.
Males produce sperm which contains half of the genetic material, just as humans do in this case the sperm would contain 50 chromosomes of which 40 are shared & 10 are unique for each color.
When couple of same color (red & red, green & green, blue & blue) have a child it works the same way as in humans. The child could either be male or female, will have the same color as its parents, and has 50% DNA from its mother and 50% DNA from its father.
However when a couple of different colors (red & green, red & blue, green & blue) has a child, the mother reproductive system only uses the shared chromosomes of the specie from the father's sperm, while the chromosomes with different color are discarded and mother's own chromosomes are used instead. So in that case the child will be always be a female, will have same color as its mother, and will have 60% DNA from its mother and 40% DNA from its father.
[Answer]
The simplest way to achieve the desired result is through the Mitochondrial DNA. Humans and most other eukaryotes contain a smaller, secondary genome outside of their nuclei in another organelle called the Mitochondrion. This mitochondrial genome is very useful for our purposes because it is only inherited from the mother through the egg.
If you imagine three significantly different mitochondrial genomes: red, green, and blue you will arrive at precisely your desired scenario. There is only one set of mitochondrial DNA per organism so there can be no hybrids. In any cross-population procreation only the mitochondria of the mother is passed on meaning all of a female's offspring will have identical mitochondrial genomes regardless of the genotype of the father.
Edit: To address the plausibility of the mitochondrial genome influencing phenotypic traits.
It is certainly plausible that mitochondrial DNA could encode phenotypic traits like skin color, but perhaps unlikely. The mitochondrial genome in humans is ~30,000 nucleotides in length and contains 37 genes. This means compared to the nuclear genome it is ~1/100000 the size and contains ~1/5000 of the genes. The chance of any given trait being encoded by the mitochondrial genome is thus somewhat small, but those 37 genes (most of which aren't actually proteins, but rather encode RNAs) do have functions. There are many [disorders](https://en.wikipedia.org/wiki/Mitochondrial_DNA#Mutations) caused by mutations in the mitochondrial DNA.
I don't know of any phenotypic traits encoded by the mitochondrial DNA but currently we are much better at finding disease alleles than we are at finding the loci that govern more complex traits like skin, or hair, or eye color. This means there may be phenotypic traits encoded in the mitochondrial DNA that we don't know of, or there may not be, but I would argue that either way it's certainly plausible that the genes transcribed in the mitochondrial DNA could influence such features.
[Answer]
## Hybridogenesis
There is no system like this on Earth. The closest is hybridogenesis, where one parent is a sexual parasite on the other to produce hybrid offspring which only pass down the parasite chromosomes. Species that engage in hybridogenesis are dependent on it to reproduce and consist of only one sex.
## Mendelian alleles
If your goal is to have subspecies with traits which cannot be watered down through interbreeding, then an alternative is that subspecies is determined by a single gene.
Let's call the resulting alleles Cᴿ, Cᴳ and Cᴮ. These genes are recessive or dominant, so there are only three possible phenotypes of red, green or blue. Let's assume the dominance pattern is a circular B>R>G>B. The possible genotypes (and phenotypes) are CᴿCᴿ (red), CᴳCᴳ (green), CᴮCᴮ (blue), CᴿCᴳ (red), CᴿCᴮ (blue), and CᴳCᴮ (green).
If the allele is located on the X- or Z-chromosome or its equivalent, then heterozygous (XY, ZW) offspring (who have only one allele) will be the same color as the parent who contributed the X- or Z-chromosome. (Males are XY or ZZ, females are XX or ZW.)
[Answer]
Apologies if this has been said...
The premise is that a mixed marriage has only daughters in which color comes solely from the mother. Therefore
1. Doesn't matter where it comes from in a non-mixed.
2. There can never be mixed color females
3. If mixed matings happen at all, females will outnumber males
4. If mixed marriages are common, females will greatly outnumber males and the overall population will slowly decrease. (But it will stabilize probably at some lower limit.)
5. If one "color" is more desirable for some social reason, that color will increase in population and the others decrease because those females will have more mates.
6. If gestation is of significant length, polygamy will likely be the norm due to the females being so numerous.
7. There will be no mixed males, since they all come from non-mixed unions.
Whether or not there are mitochondria doesn't matter; there will be some biological explanation for the premise (first paragraph) but the story can probably be told without revealing how the genetics actually work.
Seems to me it would be rather easy to program a simulation, but I can't afford the time to do it. I shouldn't even be typing this, but it's an interesting problem and I'm quite tempted. :-)
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Garm the Berserker wanders into the lonely homestead of Greenroot Farm. The mayor of the nearby Stonybrook Village directed Garm here, implying that Old Borgi would have some work for him. "Really, no wood to chop?" Garm rests his axe on the ground, the blade nearly half as tall as the old farmer. "Not today, but if you can bring me 20 redfruit, I'll pay you with 10 coppers." Garm slung his greataxe over his shoulder, "I accept this task. I will return victorious!" An wizened smile crossed the old farmer's face as the adventurer departed. "There's always someone willing to do the dirty work," he chuckled to himself.
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So imagine a classic RPG world where the above scenario is typical. Farming communities have a small population, with a great number of adventurers passing through on a daily basis. Often the farmers have a few assistants/children to help them, but the majority of the work is done by the adventurers seeking quick coin and the mysterious "XP". In this world, an adventurer can expect to find some amount of work to do in each village. That is, there is no uncertainty of employment when travelling to a new place. I want to make this as realistic as possible. Rather than the residents just happening to need certain favors whenever someone passes through, I want them to expect to have hapless adventurers to order around on a daily basis and base their income on this labor.
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Questions:
Could an agricultural workforce be made up almost entirely of day laborers?
What would the impact be on permanent residents of agricultural communities (both landowners and other workers)?
Would food be less or more expensive with this type of labor readily available?
[Answer]
There are major costs in this system some are listed below but first, we must ask:
**Why is everyone moving around?????**
Answer?
**Really big monsters.**
There are really large, powerful monsters that slowly move around and change the size of their hunting zones.
People continually flee hunting zones and move into newly vacated ones as monsters move on or are defeated. Many adventures are refugees moving and looking for a place to settle or hunting the next monster. NPCs are former travelers or adventures who have found somewhere to settle or earned their land by killing the monster that plagued it.
**Costs of most workers being migrants.**
*Coordination is a problem.*
Some adventures are low level like Tim 'the Puny' a 1st level bard. Tim and those like him are happy to pick cabbages for a few coppers/xp. But Throg 'the Load', a 23rd level barbarian with the strength of 100 men, wants 10,000 gp because that is how much he could make killing dragons with his bare hands, which he loves doing.
So we need to have situations that require massive skill and have massive rewards along with low difficulty ones with low reward. This makes coordination harder because the adventurer has to know both that there will be jobs in the next town and that they will be suited for him. Even if there are openings in the area for a dragon wrestler, Tim won't be able to work.
Some jobs require specific skills. If you want someone to craft a magic staff, neither Tim nor Throg can help. You need a wizard or enchanter like Hera 'the Enchanting'.
*Training is a problem.*
Migrant workers are most useful in fields (pardon the pun), where little training is needed. The farmer spends 5 minutes teaching Tim how to pick a cabbage and then Tim works for 5 days and leaves. Where this doesn't work is fields that require training. Even though Throg is strong enough to be a blacksmith, it will take 3 years to train him, and by then Throg has moved on. Even if Throg tries to find and train with a blacksmith in every town it will still take much longer for Throg to train than if he had stayed put. This would create a strong incentive for a traditional apprenticeship- stay in one place to learn the basics, then move abroad once you have the skill.
*Equipment is a problem.*
Some jobs require specialized equipment.
Midas 'the Golden' is a 48th level alchemist with the ability to transform lead into gold, but he needs a complex and large laboratory to do it. If he has to travel around then he either needs dozens of wagons or he can't make gold anymore.
[Answer]
>
> Could an agricultural workforce be made up almost entirely of day laborers?
>
>
>
Yes. As an analog, look at the US agricultural system. While not "almost entirely", it makes heavy use of migrant labor, people moving from region to region following various harvests and plantings which need a lot of labor for a brief time.
[](https://i.stack.imgur.com/rrlEN.png)
[Source: USDA Economic Research Service](http://www.ers.usda.gov/topics/farm-economy/farm-labor/background.aspx#migrationpatterns)
This is an average for US agriculture as a whole, and only for hired workers (vs the owners and full-time employees). Certain very labor intensive crops will require more hired workers than the average. And a fantasy setting won't have the mechanization that the modern world does and thus will need more labor.
Good enough to show it's feasible.
>
> What would the impact be on permanent residents of agricultural communities (both landowners and other workers)?
>
>
>
It's great for the landowners! They get a lot of cheap labor, right when they need it at harvest or planting time, and then once the work is done they can be paid off and disposed of. They don't have to care for those laborers for the rest of the season.
The local (stationary) agricultural workers will be harmed. The influx of a supply of migrant labor will drive wages down. Not only during harvest and planting, but it will have a knock-on effect. The landowners will say "why hire you at $X/hour when I can get four adventurers for that?" So long as there are always a few adventurers hanging around town, short on coin, the threat of hiring them is enough to drive wages down. It doesn't matter whether there's actually enough labor to make good on the threat.
Cheap labor also devalues skilled labor and mechanization. Why train and hire and expensive skilled worker when you can get four unskilled adventurers? They each do half the work, but you can hire four times as many for the same money! Why invest in machinery to do the work when you can hire cheap adventurers?
This would also be used to break up any unions... I guess in a fantasy setting guilds. Don't want to deal with the guild rules or prices? Hire a bunch of adventurers. If guild workers can't get work, and if the guild doesn't have leverage over the employers to make them use guild workers, guild workers will defect and start working for lower pay and worse conditions.
Then there's the issue of having all these migrant workers with little connection to the local community. Once the work is done and they're paid off they're suddenly flush with cash and out of work. This is both a boon for the locals, since they can sell them things, and a bane, since a bunch of bored, young adventurers from out of town might get drunk and rowdy.
>
> Would food be less or more expensive with this type of labor readily available?
>
>
>
Cheap labor drives down production cost. How much so depends on how labor intensive the particular food is.
In an environment with many farms competing with each other, this would drive down the price of food. In a non-competitive environment with a few farms colluding they'd keep prices high and pocket the extra money as profit. The latter is very likely in a medieval setting with no government oversight and no global food transportation. Nobody is going to break up a monopoly and there's no cheap fruit from Argentina to compete.
But at the same time, there would be less money in the local community to buy the food. Instead of local farms paying local workers and keeping that money in the community, the local farms pay migrant workers and their pay leaves the community. So the locals have less money.
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One premise of my current planet-in-progress is that certain locations in the universe are inherently tied to my PIP. For example, all the people and things that have vanished in the Bermuda Triangle were transported to my PIP (how/why is irrelevant to this question).
However, acceleration due to gravity on the surface of my PIP is significantly higher than *g* on Earth. NASA is currently [conducting a study](http://www.nasa.gov/twins-study/about) on how microgravity impacts humans, but my question is the reverse.
How long can humans from Earth survive being unexpectedly (but safely) transported to a different, Earth-like planet with higher gravity?
An equation to calculate the survival duration vs. *g* increase is most welcome.
[Answer]
## Between 1.5 g and 2 g
This previous answer: [Low Tech Inertial Dampers](https://worldbuilding.stackexchange.com/questions/17139/low-tech-inertial-dampener-options/17147#17147) may contain the reference materials you need (this answer has a chart for human g-tolerances over short durations).
This answer on the [Space Exploration: Maximum Long Term G Force](https://space.stackexchange.com/questions/6154/maximum-survivable-long-term-g-forces) concurs. It states that a 1.5 g force for 7 days experiment was performed with no known negative side effects.
As far as the references attached to that question go, it looks like humans can survive *positive* g loads of between 1.5 g and 2 g indefinitely.
However, the higher g loading probably leads to shorter life times. No one has performed that test to completion yet :)
[Answer]
Anyone who has gone into space(not that I have) knows that you experience 2-3 gs exiting the atmosphere. That means humans can endure up to at least 3 gs for a *short* period of time.
However, for longer periods of time Earth-born creatures will become shorter, stouter, and generally weaker because of the way Earth has 'spoiled' them with relatively low gravity.
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What would the most efficient way for a language to spread over a large area over a short period of time (about 600 years)? Imagine this is a medieval type world, and the goal is to spread the language from say, New York down to Florida (basically just the east coast).
History has shown three major ways of spreading culture (and therefore, our language):
1. **Conquest:** Through warfare, the tribe that speaks language A can conquer language B and C speaking tribes. By forcing them to work as slaves in the field and only giving them basic rights if they learn language A, over many generations, the captured peoples would learn how to speak language A. This can occur on a small scale (within tribes), or on a much larger scale (British India spread English all throughout the subcontinent).
Pros: Quick and easy. Guaranteed language spreading.
Cons: Lots of people dying. A fairly large price to pay if you're a small tribe trying to spread your language.
2. **Survival of the Fittest:** This is a far more passive approach. Through farming and sustainable agriculture, the tribe that speaks language A can spread its language by simply surviving. When other tribes around this group are dying of starvation and disease, this small yet well-developed society has enough food and medicine to go around for everyone. After most people in surrounding tribes are dead, this tribe can claim this land as farmland, and as such, any survivors of the dying tribes will be forced to learn language A.
Pros: Far fewer deaths.
Cons: Not guaranteed language spreading; what if other tribes flourish as well? what if this tribe is conquered by another or dies out? Also, farmers tend to be isolated so language spreading can be quiet difficult at times.
3. **Trade/Missionaries:** Through trade, the tribe that speaks language A can spread its language. Basically, merchants go by foot/horse/ship to any remote trading post to trade their goods. In the process, the people they are trading with will need to create new words for items not in their language (Example: squash and skunk are two words that were added into English after trading with Native Americans. Squashes and skunks did not exist in England, so they didn't have a word for either of them). In addition, some of these merchants may permanently choose to live near the trading post. By doing this, the merchants are peacefully inducting their language into a foreign society. Over time, as this minority becomes the majority, language A dominates. Also, by spreading their religion, missionaries indirectly force new adherents to learn a new language if that religion is dominated by a certain language (language A).
Pros: No one is dying.
Cons: Definitely not guaranteed diffusion; what if the minority never becomes a majority?
My question is,
Which one of these methods is the most effective/efficient way to spread a language over a large area over a time of about 600 years? Take into account human lives lost, any costs involved, and how much time it would take for this language to be in widespread use in a foreign land. Cheers!
[Answer]
I hate to answer this way, but **it depends.**
If you're surrounded by kingdoms that are more powerful than you, conquest isn't going to get you very far. If the other cultures are well entrenched, survival of the fittest wont get very far. If there is already a lingua franca for trade, trade won't get you very far.
The best direction for a language to spread is to look at the world around it, and act according to it, rather than trying to follow some codified set of behaviors for spreading languages.
[Answer]
Cultural domination.
You can't conquer the whole world, but you can make your kingdom the center of it. It requires spending a lot of money though.
* Invest in art. The next time a talented painter, sculptor, musician or a poet is treated harshly by his or her own king, they will consider moving to your kingdom and use their talents to make your cities more beautiful. It will attract attention and that, in turn, will attract even more artists. So, let them come. Let them build and create: beautiful temples, palaces, halls full of paintings. And that means more pilgrims and aristocrats wanting to see all that beauty. They will talk about it and spread the knowledge of how awesome your kingdom is and they will use terms from your language to do that. And poems? Come on. Of course you have to recite the poems in their original language. Just hear how beautiful this language is.
* Invest in diplomacy. Be the king who can reason with everyone and negotiate treaties as the objective third party. Forge alliances and trade agreements. Soon everyone will come to you for advice and start to write more often in your language because it will be the most efficient way to communicate with their other partners.
* Invest in science. Build universities. Publish almanacs of old knowledge and new ideas. Just as with artists, make it easy for scientists to move to your country and work. Get ahead a bit so universities in other countries will be motivated to use your books and therefore your language to talk about new inventions.
With these things in place after some time the whole civilization will start to perceive your language as the medium of communication about all things worthy of talking about. They will start to teach it in schools - first, because you'll give them this idea, but later they will continue on their own. French in Europe in the early modern period and English nowadays are good examples.
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[Inspired by this question](https://worldbuilding.stackexchange.com/questions/6747/a-small-group-recreating-modern-technology)
Let's say a small group of people, 10-15 or so, were going to travel back in time to the mid-1970s, the time of the first personal computers. They can have experienced software developers and hardware engineers in the group, and can each bring one laptop or tablet computer with them, which (given today's limitations) can hold an arbitrary amount of technical data.
Knowledge is not a problem, but the technological installed base is. The technology to create modern computers does not exist back then, and as the development of such technology is an inherently iterative process, the technology to create the technology to create modern computers also does not exist.
Assuming our group has specifications, and a limited amount of hardware to reverse-engineer, but very little in the way of money, how long would it take them to be able to mass-produce modern (2010s-level) computers?
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I can't give you a total timeframe I'm afraid. I'm a software guy and this is more of a hardware question. Here are some things to think of though:
1) You'll want to team up with people that have money and are already developing. It shouldn't be hard to do so. Show them your laptops and they love you, if not you still have apparently brilliant ideas.
2) *IF* you're willing to show your laptops to the world this will drastically accelerate development by itself. Everyone knows the infamous quote "there is a world market for maybe five computers." You're starting a little further along in time then that quote, but truth is people still weren't convinced that computers as PC were going to go anywhere, which limited it's development. You need a certain 'critical mass' of people using a technology before it really takes off. Demonstrating the power of a computer will significantly increase funding put into developing them. This assumes you're willing to be known and show off your laptop.
3) There are many things you can bring to software development, though most of these ideas would have to wait until computers were just a little more developed then the time frame you mentioned. These ideas include:
* The Internet! In truth the basic idea of the internet is very simple, and could have been pulled off much sooner then it was. No one could see what it would develop into and thus no one funded effort into making it happen, but it could be done. In addition, the first internet was WAY too trusting. It's quite amusing to watch the development steps of the internet. We started out with a system that had to be managed and required you to 100% trust everyone, we ended up with a system that was effectively self-repairing non-monitored, and works even if you don't trust anyone else on the internet actually is who they say they are, including the middle-man in your communication. I could rave about how amazing and cool the final internet is from a technical perspective for hours, but my point is that most of these intent mistakes are not about technical limitations. If you know ahead of time where you want the internet to go you can avoid most of these missteps.
* Converting to higher order languages like Object Oriented sooner. Never EVER let anyone use a goto statement...EVER (sorry, geek programming joke). Demonstrate that human developers are going to be more costly than hardware. Encourage more people to go into software development earlier so we don't hit the point of desperation we're at now (many programers are incompetent, but still employed because it's them or no one. To be frank we have far more of a need for computer skills than we have people with them)
* Avoid Y2K from ever happening...maybe. Honestly the original idea made sense at the time, but you could get people to start moving away from it long before Y2K became a risk. However, to be honest the 'risk' of Y2K was always rather exaggerated by doomsday predictors who simply used Y2K to explain why the year 2000 was somehow destined to lead to doom. Still, there are some real costs that could be saved by starting the switch to an epoch/timestamp based date system sooner.
* Help people to avoid all the notorious mistakes of past design and implementations. This is a much bigger boon then you may think, because *were still stuck with them*. As a side effect of the need for backward comparability we can't do away with things, even if everyone agrees they were mistakes, because too much of our infrastructure is now designed to work with that mistaken design. We have annoyances in our languages and operating systems today that date back to bad decisions made decades ago due to this. Avoiding those original bad decisions would save time for decades to come.
* Avoid the dot com bust and our economy going to pieces by pointing out that internet will be great, but only once we have enough people using it and people on the internet have a real service to provide.
* Make people stick to a POSIX standard (i.e. Unix/Linux style computers) from the get-go. More UNIX-Like OS instead of windows or mac. Yeah this is probably more of a cultural artifact then a technological one, but it would be nice today if we had a standard OS architecture and language instead of effectively 3 (Windows, \*nix, Apple).
* Going along with the earlier bullet point: set up standard APIs! There is so much time and effort lost due to everyone having different approach to doing the same thing. I need to write my code to run on three different operating systems, with a GUI that works on Internet Explorer and Firefox/chrome (though IE is getting better about compliance finally), and may different protocols for communication. To a certain point varying protocols are going to be inevitable. However, if your people are in a position to influence growth you could do more to try to get common APIs from the get go. Who knows, maybe if regular common APIs were setup and ISO standards more rigorously followed in the early years it would lead to present day developers being better about trying to figure out standards to share instead of everyone building their own.
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I noticed that the overall arc of the answers centers around the idea of a small group of tech 'heroes' going back in time and taking over the future by using their secret knowledge. It's an old idea, but there is a problem with it.
No small group of people could ever duplicate the full efforts and output of the entire population of engineers who worked in the 1970s and 1980s. The size of the economy is just too large, and there are just too many variables - competitors, other researchers, etc.
Knowing the secret future tech is a start, but at some point you won't go much faster unless you let the details out of the bag.
I suggest that the winning strategy is not to build the tech, but to work on owning the companies that are building the tech. This is where a future-enabled understanding of what is possible would really pay off. You can select the most likely winners based on your knowledge, instead of trying to be the genius/hero inventors.
The advantage of this is that it would scale much better than hardware hacking.
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I would expect at the early point, that it wouldn't be a whole lot faster than the original development cycle. The problem of course is that those already doing development have the money and resources. So this group without seeking out Intel, AMD or one of the other chip manufacturers It will take a long time just to get going. Actually there is a good chance that without joining forces they would actually be behind for quite a while.
On top of that, the laptop they bring back would need to have all of its data backed up in hard copy, because it would be the only hardware and software that could read the data and your average laptop seems to last about 5 years, granted without the viruses prevalent today, it might make it 10 years before dying, as long as it's taken care of.
But once they get going they will be able to run through the different iterations needed to produce today's tech. It would speed up faster and with knowledge of what works reducing the error in trial and error. I would guess 10-12 years faster.
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About the same time would be my guess, because of Moore's law ;)
Even assuming you have detailed and proprietary information of every system ever built - what does that give you?
Sure, you do have some low risk IP... but if you use it you might very well end up restricting the growth and diversity of computing. MS wouldn't exist because IBM would know the value of OS's and not give them the contract. The military might confine everything under TOP SECRET. And let's not get into patents (either having them, or not)!
Ignoring that for a second you'd still have to build up the practical knowledge, techniques and materials necessary to do everything from build a semiconductor to build an app. You still need to train 10's of millions of highly skilled technical people and build up 100's of millions of man years of collective expertise. This'll take time, probably about the time you've got.
This is all due to moore's law - the most valuable thing about technology isn't how fast your cpu is. It's how fast it's going to be tomorrow! Unfortunately no matter how much knowledge or computation power your group has... progress is a living process of the human collective, not stale notes on a hard disk.
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*First let’s assume that somehow we get over the program with changing history and therefore the people in the group not being born, educated, or the laptops they are carrying not have been made, due to the changes they make to history.*
Firstly they will need lots of money, but as they know history, they can make lots of money by investing in the stock market know how prices will move the next day.
Once they have got this money…..
They could sponsor research into the areas they know are going to be important, so speed up the research process.
One of them could become a researcher and help speed up the development of TCP/IP
Introduce the concept of signing messages to USENET, so stopping a lot of the spam problems that hit USENET in its later years.
Give scholarships to students going to universities that covered microprocessor design in detail, so spreading the information quicker.
Likewise for universities that teach all maths students about abstract data type.
Outside of IT, sponsor universities that make students do a project using VisiCalc regardless of the subject the student is reading.
Sponsor research into switching power supplies.
Start sending large amounts of SPAM, so that the problem is thought about before all the email standards are wrote.
By the end of the 70s, they could invent RAID disk systems.
Put types into C a lot sooner.
Sponsor universities on the condition that they used Pascal (and then Modula-2) rather then C in most teaching of programming.
Create and give away for free a OS (along the line of UNIX) written in Pascal and sponsor all universities that uses it to research and teach OS design.
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Say an alien species with the capabilities of space travel were to visit a planet like Earth. (or vice-versa)
Given that the "invasion" is so big that any government or army would be able to cover it up, what cultural effects would this visit have on our society, and how would we adapt to the advanced technology?
Assume the alien would visit in the mindset of cooperation, but supporting scientific and economic gains as a primary goal.
Something to consider: The Native Americans were visited by the Europeans, which caused the NA culture and population to diminish greatly. The difference I am proposing is not dissimilar to this event.
I understand there is a [question](https://worldbuilding.stackexchange.com/questions/1390/what-would-be-the-consequences-of-an-exploratory-group-discovering-a-more-advanc) already asked (though in reverse) along these lines, but was closed due to being too broad. I tried making it less broad
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If you look at the history of human civilizations encountering each other for the first time, generally, when one is significantly more advanced than the other, the end result is *catastrophic* for the civilization with the lower level of technology. Jared Diamond's Pulitzer-winning *Guns, Germs and Steel* is largely about this idea.
If you wanted to do a story where things went pretty smoothly for humans in an alien invasion scenario, what you'd need to rely on is the idea of the psychology of the very-advanced invaders being radically different from anything we see in analogous human conflicts. This is obviously pretty wide open territory to explore. You could make that difference about the aliens' culture, their biology, or just the fact that they've survived long enough to build spaceships capable of traveling so far and thus moved beyond the attitudes of humans.
On the other hand, if you wanted to directly model an invasion story of the history of cultural conquests on Earth (which, by the way, I'd find pretty cool) major factors you'd want to think about are disease, human superstition, opportunistic human behavior, and the tendency of low-tech cultures to profoundly underestimate high tech weapons/technology.
You'd also want to carefully think about what specifically the aliens want on Earth, and how they plan to go about getting it. If you're talking about a small group of alien scientists wanting to take core samples in Antarctica, wise cooperation from Earth governments might minimize the impact of the entire event. If you're talking about a situation that puts aliens in close, prolonged contact with the human population (making use of human labor or evacuating populated areas, for example) then you'd have human resentment and fear combined with poor understanding of alien weaponry, possibly resulting in violent skirmishes with devastatingly one-sided results. Less obviously, think about how complex our economy is and how reliant we are on having existing networks of transport and trade intact. Our alien invaders might not be interested in exterminating us outright, but there's a lot to carelessly mess up in our human ecosystem.
As for the long term, realistically, the Native American analogy you put forward seems like it could make for a plausible story, but do keep in mind that exposure to European diseases was a massive factor in that case; it's far easier for cultures to collapse when they've already had their numbers massively reduced by a sweeping, extremely contagious and deadly virus. Then again, deadly virulent disease being spread on first contact between cultures is the norm, not the exception on Earth, so we might encounter something similar with aliens, depending on their biological similarity to us (or perhaps they're just teeming with deadly infectious nano-bots).
Without an element of disease or warfare dramatically reducing the size of our populations, we'd probably hang onto more of our cultural identities for longer, but in the end, we'd all pretty much break down into predictable groups: those who tried to fight the aliens (dead), those who sought opportunity to use the chaos of the invasion to get ahead (rich), those who sided early and worshipfully with the invaders (depends, but rarely ends well in human history), and those who kept their heads down and quietly adapted (alive but maybe unrecognizable in a few centuries, especially if this is an alien species we're reproductively compatible with).
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Your question is pretty broad as it is now so I will focus on one aspect you mentioned: the economy. I make the assumption that no disease will be transmitted between the species because somehow, the visitors took their precaution.
They came here partly to make business. We represent 7 billions consumers. This is probably not negligible unless they control a bunch of other planets. It represent some good opportunities for both races but they will probably end up with the advantage because they have more money, more resources and are more advanced technology.
As they are here for cooperation, they are unlikely to enslave us but might try to use us as cheap labour. But this might actually be a good thing. Who knows, if the difference of wealth is large enough between the two races, maybe they consider Norway as a poor country! Their entrepreneurs will seek to move jobs from their planet(s) here because it's cheaper. And this could solve all European economic problems.
Their companies will also bring new knowledge and new technologies that will benefit Earth in the long run. Maybe we will eventually surpass them and buy their planet.
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You should read the book <http://en.wikipedia.org/wiki/Roadside_Picnic> - deals with exactly this situation: civilization few millions years ahead of us visits earth, spends some 6 months, and leaves. We are left to deal with remnants like insects deal with remnants of a human picnic: fire, empty cans with good food, some poison after oil change, etc. And we have no idea what is going on, because found artifacts do not comply to our underastnding of physics. Those aliens are few millions years ahead of us, you know :-)
Aliens may not even recognize us as worth trying to communicate with. Imagine if we visited our cavemen predecessors 50K years back. How would they make sense of TV? And we have same biology that them. Aliens might have different biology, means of communication etc.
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Each answer here seems to mainly cover one aspect of this question, so I may as well do the same. So, I shall look at the technology.
You may also want to have a look at [this question,](https://worldbuilding.stackexchange.com/q/5140/2685) if you haven't already, as it looks at the development of technology with access to advanced resources.
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As many of the answers on that question say, **technology wouldn't develop instantly.** However, the major difference is that as long as these aliens establish a friendly contact, they may be willing to come back periodically. This would have the advantage of enabling us to get help in building technology from people who already have it and know how it should be done. If the aliens find our atmosphere conducive, they may even be willing to send an engineering contingent to live with us for a while. In simple terms, when we have **active help** in making new technology instead of static notes from the future, technology would advance faster, especially if the aliens allow us to use their tools.
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That's a lot of ifs. Why would the aliens do this for us? Well, as you say, they have come in a mindset for their own gain. Mutual gain is conducive to this: if they give us things, we should be more willing to give them things.
For example, we may have technologies here that they don't. Obviously we can't best them on space travel - after all, they got here not us there - but perhaps our medical science is better or we have a better understanding of the history of the universe. If this is true then we may be able to help them prevent diseases and viruses that are killing their population.
Perhaps a more appealing concept, though, is the possibility of mutual work to solve larger mysteries. Do the aliens have an FTL drive? Time travel? If they do, then we could give them our science on the universe's history, then they could go back in time to verify what we have. Might cause some uproar here on Earth due to conflicts of belief, etc, but there are plenty of discoveries that could be made like this which wouldn't cause such controversy.
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I would suggest reading the short story "Flashes", by Robert J. Sawyer. It's about modern humans coming into contact with incredibly advanced aliens communicating via radio.
In it, the protagonist is put out of work because of information sent from the aliens which void his line of research. Many others are put out of work/research as well. Because some researchers have had their entire lifes study disproven overnight, there is a string of suicides in the academic world.
Also in the academic world, students no longer attend school because entire fields of study are being re-written on a nearly daily basis.
The governments try to control the spread of the information, but because the information is sent via radio waves, anyone can listen in.
A group of people reportedly sent them a message asking them to stop, but because there is a 23(or so, I don't quite remember) light year distance, they could only possibly stop 46 years from then. The group asked them to stop because they were sending all forms of knowledge; from music to space travel to weapons. At the end of the short story, the Canadian CN tower is bombed by a group of terrorists from an anti-matter bomb, whose schematics came in the previous evening.
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Those advanced aliens are already here, friend. Though friendly aliens do exist, it is hostile aliens which are in control here. The friendly aliens, due to agreements between their civilizations and those of the hostile aliens, are unable to interfere or offer us any substantial type of assistance.
There is not going to be an alien invasion, an alien invasion has already occurred. They are not going to take control of this planet from us, they have already taken it.
If you look at a dollar bill, where the eagle with outstretched wings is located, there is actually the profile of a Grey alien--the classic ET--cleverly hidden there. It's mouth and chin are covered by a hanging flag. The circle of stars above the eagle is in the center of its forehead, where the "third eye" or pineal gland is located, indicating that these beings are pure telepaths. There is a banner above each wing of the eagle. The bottom edge of the banners define the top edge of the Grey's eyes. This portrait is obviously not easy to see, it has been cleverly concealed. But when you remove the overlying symbols it is impossible to miss.
Ask yourself: Is it likely that a liberal black Democrat would either order or allow chemtrails to be sprayed? Chemtrails contain nano-viruses, other disease vectors, insect DNA which has literally been weaponized to allow it to combine with human DNA when the chemtrail material is breathed in or contacts the skin, and many other harmful or deadly things. People have literally had wood lice hatch underneath their skin and erupt through it. This is not difficult to confirm, if one searches for it on the internet. Does Obama seem like the type who is likely to approve of or order this kind of assault on our own people? Is a liberal black Democrat your first suspect for someone who would sign Presidential orders which allow the military to take complete control of the country and declare martial law whenever they are ordered to? Or to continue deliberately killing the dollar and guaranteeing a catastrophic crash of the economy followed by a depression, rather than balancing the budget? Or to do everything in his power to goad Russia and China into a war with us? Only someone who hates America would do any of those things. Only someone who hates...humanity. If you happen to live near Washington, D.C., pick up an infrared-capable camera and take some photographs of the area just above the White House and see what shows up on the photographs.
We do not run the show here on Earth and we haven't for a very long time. Martial law is on its way in, and so is a drastic population reduction--genocide. Who would want such a thing? Only those who fully intend to be the planet's new owners...and they are not human.
Ask yourself how a group of black people could migrate north out of Africa 80,000 years ago and, by the process of natural, unrelated genetic mutation alone, "evolve" into Chinese, Swedes, Eskimos, Polynesians and every other racial group we see today. According to evolutionary doctrine, such a change would require a far longer time than that. Yet we are told that is exactly what happened. It's not. We are a long-term science project, carried out by aliens. Why do you think so many of the reported alien races look so very similar to humans? They don't--we look similar to THEM, because their DNA was used to genetically engineer us long ago.
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I was looking at these two questions:
[Expanding Occupied Underground Habitations Safely](https://worldbuilding.stackexchange.com/questions/609/expanding-occupied-underground-habitations-safely)
[Does Living without access to Sunlight have known Physical/Psychological effects?](https://worldbuilding.stackexchange.com/questions/394/does-living-without-access-to-sunlight-for-extended-periods-have-known-physical)
And in a story I'm writing, the characters are hurled into an impact winter progressing over a period of weeks. And so, in an attempt to survive where help isn't coming, they search for other survivors and so on. And so I'm wondering, **when these survivors get together**, assuming an asteroid has hit elsewhere and screwed up the ozone/blocked the sun (partially? All of it? Not sure how that works.) - **would an ideal place to re-start civilization be underground? What challenges would be faced and what would the benefits be?**
Also, bonus points if you think parts of the NYC subway system that haven't been flooded/destroyed yet could be used as a starting point for underground "cities".
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Underground shelters could help improve survivability in the first days/weeks after an impact, as it provides shelter from raining debris and can also allow survivors to breath cleaner air that has fewer particulates. For the most part, though, this only affects those relatively close to the impact itself (but, of course, far enough away to survive the impact).
After the initial impact and the immediate effects have passed, however, I wouldn't call it ideal. While there are certainly [advantages to living underground](http://en.wikipedia.org/wiki/Earth_sheltering#Benefits), arguably the biggest challenge of rebuilding civilization there lies in expansion; on the surface, you can expand to your heart's content (barring natural barriers that, for the most part, can be worked around, or just expand in a different direction instead), but underground you have to devote considerable manpower, energy, and resources just to give yourself the space to then build within. Granted, digging techniques could be adapted such that much of the "build within" is merged into the "dig the space" -- e.g. dig a tunnel, then a doorway in the side and a home on the other side -- but you're still devoting considerably more resources to the effort of expansion (it's a lot easier to build a house than to excavate one!) that you cannot then devote to other considerations of growth, such as maintaining utilities, working farmland (I'm assuming you've got appropriate methods for underground living here), developing infrastructure, re-discovering important technologies, etc.
One thing to keep in mind in an Impact Winter scenario is that it's nowhere near as apocalyptic as Hollywood has portrayed it, and despite the colder temperatures (which will warm back up as time goes on) the surface is nowhere near hostile enough to require survivors to bury themselves in underground cities.
On the other hand, you could easily have a group of survivors that have seen one too many Hollywood apocalypse movies who *do* assume their best odds of survival are underground -- if life has taught us anything, it's that just because they're wrong doesn't mean that people won't still do something!
Other points:
**Advantages:**
* Easier to heat/cool to comfortable temperatures
* Increased security (fewer access points)
* Shelter from debris and particulates (quickly moot within days/weeks of the initial impact)
**Disadvantages:**
* Food: You'll be unable to rely on natural growth and will have to devote energy into artificial means such as hydroponics with electric grow lights
* Growth: You'll be very limited in how much space you have, and very restricted in how quickly you can expand said space
* Ventilation: Without artificial (read: electric) methods of improving ventilation, air can quickly grow toxic, and any underground gas pockets that are accidentally breached can be quickly fatal to the entire community
* Confinement: Should something happen and you have to evacuate (e.g. gas pocket), you've got fewer egress points and will quickly find panicking people trampling one another far more than in a surface community
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Their main problem would probably be to find food. Plants don't grow underground/without sunlight. Of course, if they have sufficient supply of canned food to survive until the surface is habitable again, that would solve the problem.
However without fresh food, there may still be deficiency diseases, especially Scurvy. However again, this problem may be solved with supplies of food supplements or specific long-lasting foods like pickled cabbage. Also maybe it's possible to temporarily come to the surface (potentially with appropriate protection measures) to collect fresh plants even if living on the surface is otherwise not possible.
The problems of missing sunlight have already been explored in the other question you linked to.
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How big was the asteroid? Why are there only a few survivors left?
If it was because the impact itself killed most people off, the asteroid was very large and has created significant problems well beyond what would be faced if it was a small asteroid which triggered human-caused mass death (religious extremism bringing worldwide violence, fear causing nations to desperately grab for resources causing WW3, etc).
The larger the asteroid, the more extreme the effects. Hot debris could cause global firestorms, resulting in a low-oxygen high-CO2 atmosphere - a couple of years of darkness and serious acid rain killing whatever survived the firestorm and killing off aquatic life too, followed by a hot earth as tiny life regrows. Big enough to wipe the ozone is big enough humans won't survive.
It will be difficult to thread the needle on big enough to kill most people directly, but small enough for scattered survivors to make it (presuming there is even any area in-between - I suspect big enough to cause eventual extinction comes before big enough to kill most people on impact).
If a smaller asteroid, the impact is more of a narrow regional problem with the exception of reduced sunlight. This isn't going to result in glaciers retaking to world, just relatively normal wintry temperatures holding year round (spring comes in a year or two instead of a couple months). Massive food shortages (no natural growing season for a year or 3) will cause global disruption and worldwide starvation, but some will be grown in greenhouses with supplementary grow-lights, probably in addition to aquaponic systems if you can get them set up (I foresee diets of bugs and farmed algae).
If you want scattered survivors after an impact, your best option is probably to go with a small asteroid, whose global effects are really just limited to not being able to grow food for a year or two, followed by human-caused disaster. Religious revivals (it was the angry fist of god) leading to mass warfare as the fanatics purge the unbelievers, plus skittish governments starting panicked wars of desperation to control resources, and general social panic being the source of collapse leaves civilization collapsed but humans not extinct. Nuclear exchange in the aftermath of impact would give you fallout as a reason to stay underground, as well as defensible shelter from roving bands of the various religious inquisitions.
People need sunlight and that is going to be difficult enough from the ash clouds - every moment of daylight should be spent outside, and even then they should be keeping a power plant going for greenhouse grow lights and supplementary lighting for vitamin D generation (especially to keep children from getting rickets). There better be a very good reason to stay indoors, and no asteroid is going to give you that without also spelling extinction.
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In your scenario 5 movies come to mind (A kid and his dog (people living underground after a N-war) Logans Run (Life during a Ice Age), and another three where a Asteroid hit. 1st one is a Big Ice Age after and the other is it hits Minneapolis - sort of a religious movie, last one is about a scientist who preps with the people who believe him - all else croak.
Back in the 70's it wouldn't be possible - or at least back to primitive living. Now in 2017 in MN we have a Hydroponic factory that supplies us with Tomatoes year round (they can not compete during the peak in summer) and several aqua culture places that raise fish (tilapia) and plants (lettuce and such). With the Solar Minimum coming we should be able to survive if the snow doesn't get too deep and the Power Plants keep on. In Turkey there's a place that has a underground city from several hundred years ago. So it was possible back then to survive.
One thing about now also is there is a lot of people who are "Preppers" and worried about things happening. So your book would be good if you write it for the Prepper people. There's been movies already (probably based on a book or so) that I outline above.
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As the title suggests, what happens to a planet geologically and geographically over time?
This question came to mind from the many sessions of Civilization I have played where when you set up a custom game, "World Age", measured in I want to say millions of years, is an option.
But this got me thinking what are the impacts of age on a planet? For this exercise lets assume we are talking about an earth-like world that was created and stable (supporting human life) from year 0.
The world I am working on is roughly 5000 years old (that is how much timeline I have developed) and in my head it appears much the same that the earth does today.
Does my world that has 5000 years of developed timeline need to change to fit the realities of a younger world? What would that look like?
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The concepts that the Civilization games use when modifying the world for "World Age" are based on the mechanical wear and tear that a world undergoes due to weather, seasonal change, and simple erosion. Hence why the Civ games measure age in the range of millions (erosion takes a really long time).
Civ World Age is taken into consideration before humans even show up, i.e. generating a world for humans to appear on at the basic level of civilization.
In Civ this is represented as an older world having smoother/flatter terrain and straighter rivers; a younger world hasn't been 'worn down by time' and has more jagged peaks and mountains, twisting rivers that haven't carved an 'easy path' yet, and more contrast between environments since there hasn't been an averaging out of terrian or geography yet.
However in the 5000 year range most of the change you'll see to a world would be from things done by the inhabitants and if you said earth like I'll assume a civilization that is also earth like: 5000 years won't see much change from weather or continental drift but humans can have a pretty drastic impact in that time.
Clearing forests, expanding cities, digging canals, man made lakes, and Civ "wonders" like the pyramids which would fit within your entire 5000 year time line from starting construction all the way to really old rock pile.
Edit: If the TOTAL age of your world is 5000 and people have been there since day 1, the other thing to consider would be that it may have a more Pangea (supercontinent) like appearance.
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Hopefully an actual geologist can weigh in here, but I'd say no, Civilization's assumption that elevations and steepness of topology trend downward over geologic time is not correct.
Of course erosion does wear down individual mountain ranges - compare the Appalachians and Rocky Mountains. However, continental crust is constantly being pushed about by tectonic drift. Every few million years a new mountain range starts building. Is there anything we can use to suggest that today's topology is flatter now than billions of years ago?
The tallest mountains currently in existence on earth are near the physical maximum for earth's crustal material and gravity (<https://skeptics.stackexchange.com/a/5866/3150>). If there was a long-term trend toward flatter terrain on a global basis, surely the highest mountains today, after several billion years of following this hypothetical trend, would be well below the maximum.
Of course, the calculations behind the highest possible earth mountain could be wrong. And as a world builder you could decree that the rock on your world is lighter, or stronger.
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Three things happen to a planet over time (a very long time actually):
* Erosion: wind, rain and even terrain vibrations will "flatten" the terrain over time. A very old planet would be very smooth and flat.
* Core temperature drops: over time the planet cools down, which means less volcanoes, lower average temperature. If the core actually begins to harden completely, certain geological things would change as well, such as slower landmass movement, different compass directions and a change of rotation of the entire planet.
* The planetary rotation slows down: which results in obviously longer days, a change of climate, and also gravity would increase, as the opposite force is dropping.
But please note that we are talking about millions of years for these changes. In 5000 years you would barely notice any of these.
] |
[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 am trying to design the fastest pelagic fish that is mechanically possible. The fastest real life fish can swim up to 80 mph. What body design would allow a fish to swim significantly faster than 80 mph? How large will it be? What kind of fish? What would the fins look like?
I would like the fish to be able to swim as fast as mechanically possible, preferably at least 150 mph.
IT CAN NOT BE A SUPERCAVITATING MISSILE WITH A FISH PAINTED ON IT.
All evolutionary and metabolic constraints will be taken care of.
[Answer]
**Supercavitating Missile with Fish Painted on the Side.**
[](https://i.stack.imgur.com/lRTYw.jpg)
Body design: Sleek metal cylinder with solid fuel rocket engine at the back and gas pump at the front. The pump ejects a bubble of gas through which the fish travels. This prevents cavitation damage.
Fins: Two stabilising fins at the back.
Top Speed: 230 mph
All evolutionary and metabolic constraints: Taken care of
---
Sarcasm aside, it's not obvious what type of answer you are looking for. There are several comments that point out how objects moving quickly though water suffer cavitation damage:
[](https://i.stack.imgur.com/2kWhW.jpg)
Cavitation is when the fluid gets churned up so small low-pressure bubbles are formed. The bubbles then collapse and damage whatever is nearby. [There is a well known predator](https://www.youtube.com/watch?v=QXK2G2AzMTU) that hunts this way. See also the [sexy version](https://www.youtube.com/watch?v=1wBYPjkGRdo).
If cavitation can make holes in a sleek metal propeller imagine what it can do to a living animal!
The question is tagged "hard science" so these comments are entirely appropriate. Ignoring problems like this makes the question no longer "hard science" and it's unclear where you draw the line for ignoring problems. In my answer I have ignored the problem "is actually a missile and not a fish".
] |
[Question]
[
The Old Ones build continent-sized bunker complexes to protect themselves from the enemy, which followed through the cosmic ocean. The Hunter succeeded easily despite their efforts and their corpses were entombed in the deepest vaults by their corrupted servants, so their masters may continue to dream in death. The vaults were later settled and expanded by the Dwarfs, yet their empires were destroyed as well. Now only the stupid, greedy and desperate enter the Underdark.
The bunkers are all roughly funnel-shaped cave systems, with radii between 500 and 1000 kilometers. Their ceilings have been waterproofed, yet they have become leaky over the last seven million years. While the magical superstructure is quite strong, continental drift and earthquakes have taken their toll. The water which flows together at the bottom of every bunker, where it is dispersed back to the surface via teleportation. The Underdark only begins at a depth of one to three kilometers. It is separated from the upper-world. Only few, mostly dwarven access shafts lead down. Underdark dwellers are adapted to the atmosphere down there. Upperworlders can handle it as well, but need acclimatization and can't handle it in the long run.
The Underdark has **forests of gigantic, phosphorescent mushrooms**, whose light is so weak that surface dwellers must spend at least a day in total darkness to see it. Dwellers of the depths can use it almost as well as daylight. **Normal mushrooms are quite diverse** down there. The Dwarfs use many species to get food, fibers, leather, and wood. Many species in the Underdark are phosphorescent, providing at least some light in habitable regions. Where the old Dwarfs installed sunstones, **woods of ferns** dominate. The significantly higher concentration of carbon dioxide in the local air helps them a great deal. The seas and lakes have **matts of chemosynthetic, endemic species**. They use methane, hydrogen sulfite and ammonia, which are significantly more common in the Underdark. Nutrients are provided by the water, which flows into the underground. All these plants provide food for the **horrific beasts** of the world below and the **Tiefling, Mindflayer and Dwarf-civilisations** down there.
While such undergrounds aren't uncommon in fantasy, I want to ground this thing in reality. I think that the [Movile Cave](https://en.m.wikipedia.org/wiki/Movile_Cave) makes a good blueprint for such an ecosystem.
>
> The air in the cave is very different from the outer atmosphere. The level of oxygen is only a third to half of the concentration found in open air (7–10% O2 in the cave atmosphere, compared to 21% O2 in air), and about one hundred times more carbon dioxide (2–3.5% CO2 in the cave atmosphere, versus 0.03% CO2 in air). It also contains 1–2% methane (CH4) and both the air and waters of the cave contain high concentrations of hydrogen sulfide (H2S) and ammonia (NH3).
> The cave is known to contain 48 species, among them leeches, spiders and a water scorpion. Of these, 33 are endemic. The food chain is based on chemosynthesis in the form of methane- and sulfur-oxidizing bacteria, which in turn release nutrients for fungi and other bacteria. This forms microbial mats on the cave walls and the surface of lakes and ponds which are grazed on by some of the animals. The grazers are then preyed on by predatory species. Nepa anophthalma is the only known cave-adapted water scorpion in the world. While animals have lived in the cave for 5.5 million years, not all of them arrived simultaneously. The most recent animal recorded is the cave's only species of snail, which has inhabited the cave for slightly more than 2 million years.
>
>
>
**Is the Underdarks ecosystem plausible, given the existence of the Movile Caves one?** The Underdark would probably have a bit less CO2 and more oxygen, due to the existence of the fern forests and slightly better ventilation. Would decomposition be enough to explain the ammonia, methane and hydrogen sulfite or are other sources required? Why is phosphorescence so widespread, dspite it being a waste of energy at first glance?
[Answer]
## Energy
All living things need energy to survive, though they get it different ways. On the surface this is easy - just absorb sunlight. The Movile cave has chemosynthesising bacteria, which is a bit more limited in energy output and by the fact that is gradually eats through the rock. You can see this limited energy availability in that the most complex animals are insects and scorpions. To make bigger, humanoid animals with their higher energy requirements available you need more energy, which you can get two different ways.
One, bigger caves - you already have this covered to some extent. If the production of food is less efficient, you'll need more food-producing area per person - the caves will have fewer people living in them that in a similarly sized area on the surface.
Two, going vegan. A carnivore eats animals and a herbivore eats plants, but each step in that process loses a lot of energy (about 90%) meaning that the plants need a hundred times more energy input than the carnivores do. Every step in the food chain you can cut out is therefore a great gain energywise. This means to be able to grow their society to full potential, our cave dwellers would probably be harvesting and eating the microbial mats directly. Yum!
You mention nutrients coming down with the water. If you get energy from this as well, like algae in the water, that would be an extra energy source and in this environment every bit helps.
## Energy hogs
Forests of mushrooms and ferns can use up a bunch of available energy and area, limiting what is available to animal species. You can see this on the surface too - a forest usually has less energy available for animals than grasslands given similar conditions. A way i see around his is that these plants only grow on land, and a lot of area is water covered by microbial mats, providing both grazing areas for herbivores and water farms of staple food for intelligent species.
The hardest pill to swallow is the presence of all these **horrific beasts**. Predators use more energy, large animals use more energy. Many species of large predators would require huge amounts of energy compared to other parts of the ecosystem. There is one thing that saves you here - your caves are gigantic. For comparison, a wolf has a hunting area measured in thousands of square kilometers. Your bigger caves can be measured in billions of square kilometers. Even everything being several orders of magnitude less efficient you can probably sustain a minimal population of one or two predator species per cave.
Again, eating plants helps. A grizzly bear is much larger than a wolf, but because it's an omnivore its territory is not much bigger. Since everything is more spread out, your predators would probably all have to be pretty mobile to be able to cover their range properly.
## Airlocks
The last big thing is how you maintain such a different atmosphere. If cave air is in some way connected to surface air, gases will diffuse and equalise over time. You would need to either be completely cut off, or have very slight exchange with constant production of your own gases. You say dwarves control the shafts of entrances, and the whole complex is built as a bunker? There are airlocks in all shafts, and the dwarfs maintain them.
[Answer]
### The Dwarves are short...much shorter than most people think.
Chemosythetic ecosystems are going to be energy-poor ones, and there isn't much you can do to change that. The Movile Cave has a diverse and complex ecosystem, but that ecosystem is limited to small species. Bigger animals require exponentially larger amounts of energy due to the square-cube law.
So scale down your ecosystem. The "humanoid" dwarves are actually ant-sized. The "horrifying beasts" are the largest of predatory crickets and centipedes. You're going to have to change their physiology somewhat (humans couldn't function scaled down that far), but there are plenty of questions here that can help you with that.
Direct interactions between the surface and the underground are so rare that very, very few surface-dwellers know the truth.
[Answer]
Yes the use of magic is probably wise to hold the ceiling up if the caves are 500-1000km across. Teleportation drainage for the leaky roof is also a good idea as I doubt there is any other way to keep the water out.
The basic set up other than that sounds plausible but one problem would be a source of light for the ferns. Phosphorescent mushrooms would not provide enough by several orders of magnitude.
] |
[Question]
[
Based on my reading on some science papers, large, wet terrestrial planets likely exist that are swathed in a thin atmosphere of nitrogen/hydrogen ($H\_2$ & $N\_2$). If life evolved on such worlds, they may very well develop a biological version of the "Haber Process" that is used to industrially manufacture ammonia ($NH\_3$). Since the biological version of the process would need to run at *much* cooler temperatures than the kiln-hot industrial Haber Process, the biological version can be called a "Cold Haber" process.
It would look like this:
$${3H\_2 + N\_2 \rightarrow 2NH\_3}$$
At least that's the contention of some papers I've read (see references below).
**Question in Full:**
**On an ${N\_2}$/${H\_2}$ atmosphere world would a Cold Haber process utilized by organisms run until it completely sequestered the non-dominant major gas (either ${N\_2}$ or ${H\_2}$) as ammonia? Or would something intervene to set some type of equilibrium long before the atmosphere was appreciably depleted of either ${N\_2}$ or ${H\_2}$?**
Basically...what might be the equilibrium atmosphere and why?
You may postulate the evolution of a biological process to utilize the ammonia, but need not. If you think the evolution of organisms using a complementary process is likely or feasible and want to include that by all means include it. That certainly would effect the answer to the question!
The answer is the difference between an atmosphere of ≈99% Hydrogen/Nitrogen with traces of ammonia in both air and water, and oceans saturated with ammonia with an atmosphere chock full of it.
**If needed here are parameters to run with:**
PRE-COLD-HABER ATMOSPHERE
* ${H\_2}$ & ${N\_2}$ (90%+ of atmosphere in any ratio of 10:1 hydrogen:nitrogen all the way to 4:1 nitrogen to hydrogen)
* ${H\_2O}$ Vapor (≈1%)
* ${CH\_4}$ (0.01 - 5%)
* Other trace to minimally-present compounds may include ${CO\_2}$, ${Ar}$, etc.
PLANET
* Oceans, continents, and some volcanic activity, much like earth
* Less UV received than Earth (1/3 at most, probably *much* less)
* Significant magnetic field
* Temperature: (I'd like the answer to account for more than a single planet's likely temperature range, but if needed let's go with a mean temperature between ${-40°C}$ and ${20°C}$ (your choice).
* Atmosphere between ${1bar}$ and ${20bar}$ (your choice)
OTHER BIOLOGICAL PROCESSES
* Such a world may evolve methanogenesis, converting plentiful hydrogen and outgassed $CO\_2$ to Methane and Water (${4H\_2 + CO\_2 \rightarrow CH\_4 + 2H\_2O + 193 kJ}$ per mol at ${25°C}$), deriving easy energy. This would likely mean the atmosphere's supply of carbon dioxide would almost entirely convert to methane.
* Such a world may evolve photosynthesis utilizing the following chemical reaction: ${CH\_4 + H\_2O + y \rightarrow CH\_2O + 2H\_2}$, converting methane and hydrogen in the atmosphere to biomass and water.
**In your answer please explain in detail your thought process. It should contain a discussion of the relevant chemical processes as well as what you suspect the new equilibrium atmosphere may be. If you can supply equations or calculations to back your answer, all the better!**
---
References:
Photosynthesis in Hydrogen-Dominated Atmospheres – <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284464/>
BIOSIGNATURE GASES IN H2-DOMINATED ATMOSPHERES ON ROCKY EXOPLANETS – <https://iopscience.iop.org/article/10.1088/0004-637X/777/2/95/meta>
A BIOMASS-BASED MODEL TO ESTIMATE THE PLAUSIBILITY OF EXOPLANET BIOSIGNATURE GASES – <https://iopscience.iop.org/article/10.1088/0004-637X/775/2/104#apj480437s4>
[Answer]
Your "cold Haber process" already exists--it's what nitrogen-fixing bacteria do on Earth! The ammonia generated by that process is then further transformed into nitrites and nitrates, with all three forms of bound nitrogen being used in various ways in terrestrial biology to build more complex molecules. This is an energy-intensive process for Earthlings, because we have to split water to fix nitrogen (just like we have to split water to perform photosynthesis), but that bottleneck doesn't exist on your reducing-atmosphere world.
On Earth, we avoid depleting our atmosphere of nitrogen because denitrifying bacteria eventually release it again, by using nitrates and/or nitrates (rather than straight oxygen) as electron receptors for respiration, producing water and nitrogen gas as byproducts. On a chemically-reducing world, however, per [your reference on hydrogenic photosynthesis](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284464/), we should expect the average biomolecule to be less oxidized than the average terrestrial biomolecule. Thus, we should expect to see far fewer nitrite and nitrate groups in reducing biology, and a lot more amides and amines.
The reducing-world equivalent of denitrifying bacteria, then, would be organisms that use ammonia, rather than free hydrogen, as an electron donor to reduce biomass and generate energy--exactly the opposite of Earthling heterotrophs which oxidize biomass to generate energy, which in both cases undoes the work done by photosynthesis in each environment to bind that energy.
So, the question boils down to this: do such denitrifying organisms actually make sense? Where would they be needed?
Denitrifying organisms make sense on Earth because oxygen doesn't get everywhere. Denitrifying bacteria can engage in high-energy oxidizing respiration in anoxic environments by simply decomposing mixed biomass on its own. Is that true of hydrogen on a reducing world?
Surprisingly, the answer may be "yes". In one sense, hydrogen should be more readily available on a reducing world than oxygen is on an oxidizing world, because free hydrogen will be primordial, seeping out of crustal rocks, and also because it can diffuse more easily through smaller spaces and more quickly into areas that would otherwise be depleted by rapid "respiration". However, hydrogen has a much lower solubility in water than oxygen does--while ammonia is *highly* soluble.
Thus, once biological nitrogen fixation starts up (which it ought to do rather quickly), sea life on this world might be expected to fairly quickly learn to breathe ammonia, instead of or in addition to hydrogen, thus releasing nitrogen gas back into the environment.
So, you will have the following cycles:
**CH4 + H2O -> CH2O + 2H2** via photosynthesis, restoring hydrogen to the atmosphere.
**2N2 + 3H2 -> 2NH3** via exothermic nitrogen fixation, removing both nitrogen and hydrogen from the atmosphere but introducing ammonia to the atmosphere and ocean (and lakes and rivers and so on). Because this is an exothermic process, unlike Earthling nitrogen fixation, you can expect microorganisms to do it continuously, releasing ammonia as a byproduct, rather than having the rate limited to what is needed for the construction of biomolecules. Incidentally, ammonia will also spontaneously react with carbon dioxide, so, although that paper says CO2 ratios are fairly arbitrary and dependent on geological production, in fact you should expect the overproduction of ammonia to result in nearly all of whatever CO2 is available being sequestered in the oceans as ammonium carbamate. After the CO2 is gone, then ammonia will start to build up.
**CH2O + 2H2 -> CH4 + H2O**
This is the basic form of reducing respiration, consuming hydrogen and releasing methane back into the atmosphere, as an analogue to CO2 in our atmosphere.
**CH2O + 2NH3 -> CH4 + H2O + H2 + N2**
**3CH2O + 4NH3 -> 3CH4 + 3H2O + 2N2**
These are ammonia-consuming reducing respiration reactions, which replenish nitrogen in the atmosphere and may or may not release some excess hydrogen.
So, you have one process that removes both nitrogen and hydrogen from the atmosphere; one process that replenishes atmospheric hydrogen (photosynthesis) and one process that replenishes atmospheric nitrogen (ammonia-based respiration).
I have no clue how to determine what the final equilibrium concentrations would be, but it would appear that it is perfectly plausible for both H2 and N2 to remain as major components of the atmosphere indefinitely. Meanwhile, you will have sea creatures that can respire using free hydrogen or ammonia, expecting that their individual consumption of ammonia will not significantly impact the pH balance of the ocean and will be balanced by the activity of nitrogen-fixing microbes, and land creatures which would avoid ammonia-based respiration and instead exploit the more freely-available atmospheric hydrogen, both for better energetics and because they can't afford to screw with the pH of their isolated body fluids.
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[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.
How do I calculate the thickness of the upper ice layer on cold ocean worlds like Europa, Enceladus, and Ganymede? I'm asking this for a programm I'm currently writing.
The given/known quantities are:
* Mass
* Radius
* Average density of metal (assume Fe) core, rock (assume MgSiO3) layer, and ice (assume H2O) layer
* Internal heat from tidal heating, radioactive decay and residual formation heat
* External heating from solar radiation (assume equal constant heating distributed over the entire surface or ignore it if it is irrelevant/minuscule)
* Pressure of the atmosphere above (assume pure N2 with variable pressure or no atmosphere)
I want to compute the thickness of the frozen (crust) and molten layer.
Bonus stuff: If easy adaptation of the formula for the calculation of the rocky layers crust thickness is possible I would appreciate it. Should it be possible, an adaptation to find the rocky crust thickness and the ice crust thickness on wolds where both are needed would be helpful.
[Answer]
For determining the ice layer thickness you can use a simplified 1D model, as follows:
* You want the ice to be present above a layer of water. This sets the temperature $T\_b$ at the ice-water interface. This would be 0 Celsius for pure water a 1 bar.
* You know the thermal flow coming from the core, $Q$
* you want the condition to be stationary, this means that the flow is entirely dissipated to the outer environment.
[](https://i.stack.imgur.com/ZBX6Y.png)
Therefore you have that $Q=$$\lambda \cdot A \cdot (T\_b - T\_a)\over d$, where $d$ is the thickness of ice layer, $\lambda$ is the thermal conductivity of ice, $A$ the surface and $T\_a$ the surface temperature.
If you have the possibility of setting the other interface temperatures as well, you can use the same equation to determine the thicknesses of all the layers.
Mind that this model can be used for a spherical shell as long as the thickness is small with respect to the radius of the shell. Else a spherical model would be more appropriate.
In that case it would be, assuming only radial flux, $Q=4 \pi \lambda R\_a \cdot R\_b$$T\_a - T\_b \over R\_b - R\_a$
[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.
While I'm sure there's hard-set rules, and someone with a degree in astrophysics may answer this question more thoroughly, I think you'll find that theres an incredible amount of factors to something like this.
Take Europa for example.
We estimate anywhere between [19 to 25 kilometers of ice](https://www.lpi.usra.edu/resources/europa/thickice/), but mind you. this is an estimate based on a bunch of data we have compiled over time, and even then, the estimate is only down to 6km, which, all-in-all is a big distance (not on an astrophysical scale, but you get what I mean).
We assume there's quite a bit of Liquid water under Europa's surface because of observed ejection of liquid and also how impact craters look/are formed. We also know that if there is liquid water, it is kept liquid simply due to Jupiter's gravitation [citation needed]. We can measure its size and can infer to how much water there is around it, regardless of state. But even in the real world, we come up short answering hard-set questions. We don't know how much not-water the inside of the moon is.
We also have evidence that the ice sheet around Europa might have been different thicknesses throughout its life.
And then we still haven't talked about tectonics or other geological events.
My advice? Let the user of your app, be it you, or anyone else, define themselves, how much ice they want, it's probably better that way, and if someone's worlds have different rules, then your app can accommodate to that by not setting any hard-set rules.
Interested to see what the app looks like/what it will be able to do though!
[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.
The layer under ice is the layer of possibly dirty water. Really, if you have tidal and residual warmth and temperature on the surface, "all" you need is "merely" the thermal conductivity of the ice and that of the water layer. The problem is, that the thermal conductivity of water is defined by convection cells structure and is unknown. And it cannot be known without inner observations. You cannot guess it theoretically. *The contemporary science cannot predict the behaviour of the turbulent flows.* Not only counting by formulae is impossible yet, but even the computer modelling. It is simply one of the unsolved tasks.
Edit. The situation is even worse. Here (<https://en.wikipedia.org/wiki/Turbulence_modeling>) you can see the maximum where the recent science reached. Only statistical evaluation of the evolution of flows. So, maximally you can guess how the structure of flows could evolve. And that structure is ***dynamic***, and because of that the thickness of the ice layer will dynamically change, and again it will influence that turbulence structure. So, you cannot say what the thickness is, because it simply changes.
Using the equations from the reference, you could guess the dynamical range of the changes. But, I am afraid, that is a great work for a doctor of Sc. degree.
[Answer]
There are [a whole bunch of different ways](https://www.kiss.caltech.edu/workshops/oceanworlds/presentations/Prockter.pdf) to determine the thickness of a planet's ice sheets; over the decade, dozens have been tried on Europa and other icy bodies. Broadly speaking, as we're working from a purely theoretical perspective, our method will have to be thermodynamic in nature - we can't look at cratering patterns or rifts in the ice. I'm going to briefly mention a couple of these treatments, all of which (at least in the case of Europa) appear to return similar results within an order of magnitude of each other.
## [Quick & Marsh 2015](https://ui.adsabs.harvard.edu/abs/2015Icar..253...16Q/abstract)
It turns out that [L.Dutch's simple approach](https://worldbuilding.stackexchange.com/a/142521/627) returns reasonable results. Let $Q\_D$ be the heat transferred to Europa by tidal dissipation. We know that $Q\_D$ is proportional to the temperature gradient within the ice, and that the gradient can be approximated as
$$\frac{dT}{dz}\approx\frac{T\_S-T\_M}{d}$$
where $T\_S$ is the surface temperature, $T\_M$ is the melting point of water, and $d$ is the thickness of the ice sheet. We then find that
$$d=\frac{k(T\_S-T\_M)4\pi R^2}{Q\_D}$$
where $R$ is the radius of the planet and $k$ is the thermal conductivity. Now, $Q\_D$ itself can be calculated from the physical and orbital properties of the planet:
$$Q\_D=\frac{21}{2}\frac{k\_2(\omega R)^5e^3}{Q\_oG}$$
where $\omega$ and $e$ are the tidal forcing frequency and orbital eccentricity, and the other parameters are constant. We then see that
$$d\propto \frac{T\_S-T\_M}{\omega^5 R^3e^3}$$
## [Ojakangas & Stevenson 1989](https://ui.adsabs.harvard.edu/abs/1989Icar...81..220O/abstract)
You can do a more detailed treatment of thermal equilibrium from a materials science perspective, focusing on how ice behaves at different temperatures. From a [rheological](https://en.wikipedia.org/wiki/Rheology) approach, Ojakangas and Stevenson derived a solution of the form
$$d=\frac{\ln(T\_M/T\_S)}{\left[\left(\frac{2}{a\_1}\right)\int\_0^{T\_M}\frac{q(T)dT}{T}+\left(\frac{H}{a\_1}\right)^2\right]^{1/2}}$$
where $q(T)$ is the volumetric dissipation rate and $a\_1$ and $H$ are constants. Calculating $q(T)$ may be non-trivial depending on the rheological model you assume.
---
In general, actually, the linear temperature gradient approach works fairly well. I would strongly recommend using it for your purposes. Here are some general notes, for whatever method you choose:
* You'll need to know the body's physical and orbital properties to compute the heat generated by tidal dissipation.
* The surface temperature $T\_S$ can be determined by standard calculations of [effective temperature](https://en.wikipedia.org/wiki/Effective_temperature#Surface_temperature_of_a_planet).
* You can use similar treatments to determine the structure of subsurface layers (see [Hussmann et al. 2002](https://ui.adsabs.harvard.edu/abs/2002Icar..156..143H/abstract)).
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[Question]
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# Introduction
*For more backstory, see [here](https://worldbuilding.stackexchange.com/questions/100613/can-you-design-your-own-plants-without-a-computer) and [here](https://worldbuilding.stackexchange.com/questions/101519/how-high-def-can-my-tv-be-without-computers)*
The 438th Harmonious Congress of the People of Mars was perhaps the most anticipated since the early years of the settlement. In a rare action, the Supreme Council of Harmony agreed to broadcast some of the proceedings of the Congress on tele-projector for all the tens of millions of Martians to witness. The occasion was, of course, significant. The Chief Designer was presenting to the Council, and indeed to all the people, a new 100 Year Plan for the Revivification of Mars.
There was a great buzz and anticipation in the air. Rumors flew that some great milestone had been met in the construction of an atmosphere. Already, if you received permission to surface walk outside the airlocks, you could see the fruits of the Bureau of Revivification. In the lowest latitudes, slender pine trees thrust skyward from the red dirt. In more seasonal climes, grass bloomed in great billows of green during spring. Running water could be seen for part of the year anywhere within 30 degrees of the Equator.
People had not been outside for generations stretching back to Old Earth. The first colonists had dug into dormant volcanoes and the cliff faces of vast chasms. Over the centuries, millions of miles of passages and corridors were extended under the surface. No one walked on the surface for centuries, save a few scientists perhaps. But in the past few decades, the air pressure had gotten so high-pressure suits were barely thicker than regular clothes. A rupture was no longer catastrophic.
All Mars waited with anticipation the speech from the Chief Designer. What would she propose? What was the next step for Mars? Was it possible that a Green and Blue Mars, a truly habitable Mars, would soon be a reality?
# Question
The Martian air pressure is above 10 kPa. The massive amounts of carbon dioxide available on the surface of the planet have all been vaporized. Nuclear driven oxygen synthesis has greatly sped the conversion of this carbon dioxide to oxygen, and widespread plant life is contributing its part. It will not be long until oxygen levels are 50% that of Earth; equivalent to 5 km altitude on Earth. High enough to be considered habitable and breathable to humans.
The Chief Designer and her team have decided that it is time to raise the atmospheric pressure on Mars. In order to do this, they will need to generate about 40 kPa of air pressure from some inert gas.
**Given the energy cost of transporting an inert gas from somewhere else in the solar system, and the energy cost of any chemical reactions needed to put it in the atmosphere, what is the least energy expensive way to add 40 kPa of air pressure to Mars?\***
For example, if the best gas is diatomic nitrogen, then the cost of transportation from a source in the outer solar system as well as the cost of turning whatever nitrogen compounds can be found into the diatomic gas must be considered.
### Considerations
* The Earth was hit by a large bolide 500 years ago. It is still glowing. Earth's former atmosphere and oceans are not available to be moved to Mars.
* Any other resources in the solar system are available.
* The O$\_2$ and CO$\_2$ information in the question are presented as facts; they are not relevant to the discussion.
* Technology level is near-future but mostly irrelevant. The correct answer will give an energy cost in Joules (or Calories, I suppose, if you like to be contrarian).
* Energy cost only has to consider the cost of moving the materials; a function of mass and whatever combinations of delta-v's will get it from its current location to Mars. The cost of rockets and fuels and such can be transparent.
[Answer]
I found you a moon: **Mimas**
Since I couldn't sleep I thought I would do some of the math so here it goes:
```
Radius_Mars = 3390 * 10^3 %in meter
Thickness_Atm = 66 *10^3 %Earth atomosphere is about 100km, took 2/3 for
mars in meters
Volume_Atm = 4/3*pi*(Radius_Mars+Thickness_Atm)^3 - 4/3*pi*Radius_Mars^3;
Volume_Atm = 9.7E18 m^3
Air_Density = 1.2 %kg/m^3
Needed_Mass = 0.3*Air_Density*Volume_Atm; %3.4E18 kg
Needed_Mass = 3.4E18 kg
```
So you need a mass of 3.4E18 kg to shoot from some moon (according to [wiki](https://en.wikipedia.org/wiki/Asteroid_belt)the astroids in the belt are mainly of C, S and M type so unsuitable), so find an ice moon with the lowest gravity. It would seem that Mimas orbiting Saturnus is mostly ice and has a surface as small as Spain. The mass of Mimas is 3.7E19 kg so only one order of magnitude higher. So instead of having to deal with escape velocity simply move to complete moon to Mars, the it will only become a question of how fast do you want it.
So if you have patience for a 10 years you have to move the intervening distance between Saturn and Mars, being roughly 1.2E9 km. So your average speed, taking into account that you need to decelerate for just as long would need to be
```
average velocity = 1.2E12/31E7 = 3834 m/s
```
So to calculate the energy just use the formula for kinetic energy
```
energy = 1/2*m*v^2
```
So the needed energy becomes:
```
energy = 1/2*3.7E19*3834^2 = 2.719E26 J
```
To put it into prespective if you harness all the solar radiation falling on earth you would need to harvest it at a 100% efficiency for 12.4 years to get the required energy. So I guess we won't be moving planets any time soon :D.
Since it is late it might be good to check the numbers.
[Answer]
An important preface: **without a stated time period to accomplish this task the energy cost cannot be calculated**.
I will make assumptions about time.
Current real Mars data.
<https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html>
>
> Atmosphere
>
>
> Surface pressure: 6.36 mb at mean radius (variable from 4.0 to 8.7 mb
> depending on season)
>
> [6.9 mb to 9 mb (Viking 1 Lander site)] Total mass of atmosphere: ~2.5 x 1016 kg
>
>
>
* 1 mb = 0.1 kPa. 6.36 mb = 0.636 Kpa.
* The proposed Mars from OP has air pressure of 10 kPa. 10 / 0.636 = 15.7.
The total mass of atmosphere has increased by 15.7 times.
* The current total mass of atmosphere is (2.5 x 1016) x 15.7 = 3.92 x 1017 kg.
* You ask to raise atmospheric pressure 40 kPa more (to a total of 50 kPa). Noted: adding gas mass might not cleanly convert to raising pressure but we will assume.
You want to add 4 times the current atmospheric mass to the current atmospheric mass.
* You want 4 x (3.92 x 1017 kg) = 15.7 x 1017 kg or 1.57 x 1018 kg of gas.
For reference, let us consider what it would take to import this much mass from Earth. I know that the conditions of the OP rule out Earth but this will give a sense of scale for these huge numbers.
<https://www.space.com/24701-how-long-does-it-take-to-get-to-mars.html>
We will assume the distance between Earth and Mars is 225 million km.
We will allow a leisurely 1 year to traverse this distance.
225,000,000 km/year is 7134 meters/second. It is so cool Google will do calulations like that for you!
Again to get things to scale: this is 25684 km/hour. That is a good clip but the New Horizons probe (from above link) went twice that fast, so OK.
Kinetic energy = 1/2 \* mass \* velocity ^2, where Kinetic energy is in joules, mass is in kilograms, and velocity is in meters per second
The joules: speed in m/s ^2 = 7134 ^2. = 50893956
Mass moved (from above) = 1.57 x 1018 kg
1.57 x 1018 kg x 50893956 = 7.9903511e+25.
Divided by 2 = 3.9951755e+25 joules to move required mass from Earth to Mars over 1 year.
Of course one must decelerate this mass when it arrives on Mars, unless you have some scheme to decelerate it for free by ramming the mass into the surface. Which could have ramifications, so to speak. The energy you put in to get it up to speed you must then put back in to slow it down: x 2, which fortunately is already done: 7.9903511e+25 joules.
It would be energetically more expensive to do it faster (because one must accelerate to a higher velocity) and less expensive to do it slower. If moving mass from farther away (e.g. Titan) the same holds: it would cost the same energy as moving it from Earth but take more time, or cost more energy to traverse the greater distance at the same speed. **Without a stated time period to accomplish this task the energy cost of the task cannot be calculated**.
---
Considering an alternative: this society must have a metric buttload of energy available to consider such an endeavor. From my point of view, this society has unlimited energy. Maybe they tap Casimir forces or are masters of fusion. Moving mass would be a trick with potential for disaster at many steps along the way. The logistics of gathering this much mass at its source, keeping it together en route, and decelerating it into Mars are daunting.
Instead, how about using that free energy to make the mass on site?
How much energy is in that much mass? Sweet online calculators!
<http://www.wolframalpha.com/widgets/view.jsp?id=b3aa19fe9dc706a3b4cdaa8ddb37d852>
1.57 x 1018 kg converts to 1.411 x 1035 joules.
Double checking with this calculator
<http://www.1728.org/einstein.htm>
I get 1.348e+35 in that much mass.
For scale, the sun puts out 3.725e+26 joules / second. To make the required mass using the entire energy output of the sun would take 361879194 seconds or 11.4 years. Depending on how your energy source worked, you could set up mass generation plants on Mars and let them chug away.
Of course if you want to get super fussy, these numbers assume that the new Martian atmosphere is the same gas composition and so same kg weight as the existing real Martian atmosphere which is mostly CO2. It is not specified in the OP what the new Martian atmosphere is made of: at 10 kPa and 50% O2 there is 50% something else which must be CO2. (You would be breathing really hard in that atmosphere and it would feel like you burped Coke into your nose).
* All gases have the same volume.
* All CO2 atmosphere (current real Mars) would be 44g/mol gas.
* N2 atmosphere imorted or created would be 28 g/mol gas. That is 0.63 the mass I used above. Those who are very interested can multiply accordingly for new numbers.
* You could make (but probably not find and import) an atmosphere of neon with 71% of the mass of your diatomic nitrogen atmosphere. That would be 0.45 the mass I used above for calculations. So just 4.5 years to produce with your energy to mass factories!
[Answer]
I would seriously consider the main belt asteroids. Delta V from Mars transfer to Ceres transfer orbit is 1.3 km/s. You shouldn't need to go to an asteroid the size of Ceres and you'll be throwing small chunks that will burn up in the atmosphere so you don't need to slow anything down.
Let's say you shoot 1kg chunks from 0 to 1300 m/s in 1 second.
This takes 650 meters (d = 1/2\*a\*t^2).
Energy is kg\* m^2 / s^2 or kg \* meters \* a
so this is 845000 Joules per kg (you can change the time or acceleration just so you still get that delta v and the energy won't change.
Let's call that 1 x 10^6 because our asteroid has some gravity.
Someone smarter than me said you're looking for ~2 x 10 ^18 kg. The total asteroid belt mass is 3 x 10^21 kg so that makes sense to me.
You need 2 x 10^24 Joules or
2 x 10^21 KJ.
"Palo Verde nuclear power plant in Arizona is the largest nuclear power plant in the United states with three reactors and a total electricity generating capacity of about 3,937 MW."
and 1MWh = 3.6 x 10^6 KJ
So 555.5 x 10^12 MWh is 1000 Palo Verdes running at max for 141 million hours (16000 years).
That's a little disappointing but maybe your launcher could use Ceres for a gravity assist. If you could get the delta v to more like 300 m/s that drops it to 7 million hours (800 years).
[Answer]
So, the other answers have established that it's not easy to move huge amounts of mass around the solar system. Why not try to solve the problem like NASA does?
## Making thin air out of rocks
In a reversal of the typical "making stuff appear out of thin air", an ingenious chemical process allows the production of thin air out of rocks. Specifically, a modified version of the [Fray-Farthing-Chen (FFC) Process](https://en.wikipedia.org/wiki/FFC_Cambridge_process) takes in metal oxides such as titanium dioxide, magnesium oxide, or sodium oxide and separates the two elements. This was first proposed in 2000, and immediately [earned a Nature paper](https://www.nature.com/articles/35030069). Although originally designed for the production of high-purity metals, this process picked up a lot of attention in the late 00's when NASA and others realized that it could be used to [produce oxygen out of lunar regolith](https://isru.nasa.gov/OxygenfromRegolith.html). This is known as "In Situ Resource Utilization" (ISRU), and NASA has [put some pretty serious money](https://phys.org/news/2005-06-lunar-oxygen.html) towards determining feasibility.
Specifically, [the Ilmenox process](http://energyprofessionalsymposium.com/?p=25168) uses a specially-designed reactor that strips the oxygen from the other elements in lunar or Martian regolith and [liberates it into the atmosphere](https://www.popsci.com/military-aviation-amp-space/article/2009-08/new-reactor-make-breathable-air-out-moon-rocks).
To quote from the [phys.org article](https://phys.org/news/2009-08-scientists-oxygen-moon.html) summarizing this development,
>
> Based on experiments with a simulated lunar rock developed by NASA, the researchers calculate that three one-meter-tall reactors could generate one tonne of oxygen per year on the Moon. Each tonne of oxygen would require three tonnes of rock to produce. Fray noted that three reactors would require about 4.5 kilowatts of power, which could be supplied by solar panels or possibly a small nuclear reactor on the Moon. The researchers are also working with the European Space Agency on developing an even larger reactor that could be operated remotely.
>
>
>
So, to summarize: we can use 4.5 kilowatt reactors to produce oxygen (or carbon dioxide) from moon rocks. The return on this is something like 1,000kg of oxygen per year. So our energy conversion is
$$\frac{4,500\ J}{1\ sec}\*\frac{31,536,000\ sec}{1\ year}\*\frac{1\ year}{1,000\ kg\ O\_2} = \frac{142\ MJ}{kg\ O\_2}$$
To borrow from WillK's excellent answer, we need something like 1.57 x 1018 kg of gas. To synthesize all of that *de novo*, we'll need **2.23 x 1026 joules of energy**. Curiously, that's in the same ballpark as the other answers - cool! However, I'll argue that my method is still superior for several reasons.
### Reason #1: Controlled progress
As many of the other answers point out, half of their energy cost comes from slowing down whatever they're throwing at it. With this method, the process is controlled from beginning to end - ramp up production or slow it down as necessary. To put that number in context, let's check out [everyone's favorite Wikipedia page](https://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)):
* If this was done with traditional fossil fuels, we can expect to take in 10,000 years if we used all the fossil fuels on Earth every year: fossil fuel reserve as of 2010 = 3.9×1022 J
* If done with nuclear tech, as your question proposes, we can expect to take more like 1,000 years, if we used all the uranium on Earth every year: global uranium-238 resources = 2.2×1023 J
* If we covered Mars in solar panels, we can expect to be done in about 100 years: total power received by Mars from the Sun $\approx$ 6.6x1016 W
* If we [cover the Sun in solar panels](https://en.wikipedia.org/wiki/Dyson_sphere), we're done in one second: solar output = 3.8×1026 W
[](https://i.stack.imgur.com/Rff4h.jpg)
### Reason #2: We're actually producing a gas
Most of the other answers have thrown something like a small moon or a whole bunch of rocks at Mars and called it a day. That's... not an atmosphere? Nor is it especially friendly to the inhabitants? Instead, with this method, we're producing atmospheric gases in any mix of carbon dioxide and oxygen that we'd like, allowing us to find a good balance between phototrophs and heterotrophs as we continue to terraform the place. Unless the other answers manage to find an extraterrestrial object made largely of nitrogen or neon, against all the traditional extraterrestrial body compositions we've thus far found, all that they'll do is add more rocks to the place - mostly silicates and metal oxides.
### Reason #3: Abundant high-purity metals as side-effect
"But wait," you say, "what about all the side products of the FFC process?" Well, I'm really glad you asked. As noted earlier, this process is traditionally used to produce high-purity metals by stripping the oxygen off of metal oxides. Now that we've reversed the roles, these metals are essentially "waste material" - guess we'll have to make [really cool buildings](https://www.google.com/search?q=martian+city+art&oq=martian+city+art) out of them instead.
[Answer]
Unfortunately, the only gases you can safely put in a terraformed body's atmosphere are oxygen and nitrogen.
Earth is out, so the only other feasible source for nitrogen is Titan (unless you have an economic way of instating a partial [CNO cycle](https://en.wikipedia.org/wiki/CNO_cycle) *and* have sufficient carbon or carbon dioxide source, and energy, in place).
Nitrogen on Titan - or any significant gravity well outside Mars's - possesses quite a lot more potential energy than it's feasible to unleash unto the red planet. The simplest way of delivering the nitrogen, i.e. supercooling it in frozen missiles and shooting them at Mars using linear accelerators, will result in even more energy. The frozen missiles will burn and disintegrate in the Martian atmosphere, *but* they will also heat it (and, not too much later, the ground) way too much.
Delivering the goods using reaction drives is unfeasible for the same reason. Each kilogram at Mars ground level would cost too much in either waste heat and/or environmental pollution.
Inertialess grav-drives would of course solve this problem, but they're not current technology; not even in sight.
What follows is *also* almost certainly not feasible, but due to logistic and economic constraints, not technological limitations.
# Stage One: build a base on Titan, install a launcher (actually, many launchers).
The Titan base will send projectiles onto a [Hohmann](https://en.wikipedia.org/wiki/Hohmann_transfer_orbit) transfer orbit, supplying the first part of the required delta-V. That'll set you back around 11 MJ/kg plus other 3.48 MJ/kg of escape velocity.
The launcher might be installed on a skyhook on Titan to reduce the second part of those costs.
A projectile is just an insulating shell over one ton of supercooled solid nitrogen, plus a solar-powered beacon, and will arrive at Mars after 5 to 18 years depending on planets positions. It has no manoeuvering capabilities.
# Stage Two: build the "catcher" (or a forest of them) in orbit around Mars.
The catcher will have to neutralize the incoming projectile's kinetic energy using electromagnetic braking. You will need a minimum of around 28.5 MJ/kg for that. This will also determine an alteration in the catcher's orbit. To balance that, some kind of thruster, maybe a ion engine, will need to be installed. We could perhaps use Phobos as a waystation - but that would limit us to *one* waystation, restricting both the number of catch windows and volley size.
Another possibility could be to harpoon the incoming projectile - it will be moving at around 7500 m/s - and decelerate it using a dynamo reel. That would allow recovering most of those 28.5 MJ/kg, even if even braking at 10 G will still require more than one minute, and paying out some 290 km of wire. A one-ton projectile falling in from Saturn will then develop a power of around 370 megawatt (28500 MJ in 76 s).
# Stage Three: drop the pellets on Mars.
Falling 6000 km from as low as Phobos, even with zero initial speed in respect to the planet (the Phobos launcher will simply neutralize the moon's orbital velocity), the frozen nitrogen pellets would still possess a potential energy of around 7.1 MJ/kg; even if they're close to absolute zero, they would only absorb about 0.3 MJ/kg to achieve the gaseous phase. We'd be left with an excess of more than 28 million calories per kilogram, which is unacceptable.
The only other alternative is a skyhook. The skyhook station would orbit in the same plane as the incoming projectiles, and alternately catch them from either side of the planet, thereby dumping the excess energy straight into Mars. We will require a sizeable series of skyhooks all around the planet - essentially, an artificial ring around Mars.
The gas would then be dropped straight down, neutralizing (and recovering a part of) those 7 MJ/kg of energy through magnetic braking.
The big question is now **how long would this take**.
Assuming each projectile weighs one round ton, we'd need around three thousand million *million* projectiles. Most of the required energy is supplied by gravity, but still we need launchers and catchers. With one thousand of each, we require three million million volleys, and at one volley per second (remember we're moving one ton of mass per launch, and incidentally we have to dissipate a *lot* of energy), that's **one hundred thousand years**.
] |
[Question]
[
On Earth, land vertebrates generally have four limbs. Other creatures such as insects can have more limbs, but those creatures tend to be small. I'm thinking of creating an alien ecosystem with relatively large, vertebrate-like creatures (larger than insects and with some kind of endoskeleton). Is it realistic for those creatures to have more than four limbs (six is good enough) and if so, what conditions would make it more likely for such a thing to evolve? To be clear, I am not interested in four-limbed creatures evolving extra limbs (from what I've read, that would be quite difficult, perhaps impossible), but creatures that have six or more limbs from their common ancestor.
I have seen some information on this topic, such as:
[Why would an animal need six legs?](https://worldbuilding.stackexchange.com/questions/48966/why-would-an-animal-need-six-legs/49048)
[tvtropes.org/pmwiki/pmwiki.php/Main/VertebrateWithExtraLimbs](http://tvtropes.org/pmwiki/pmwiki.php/Main/VertebrateWithExtraLimbs)
[planetfuraha.blogspot.com/2010/02/avatars-walking-with-hexapods-dont-walk.html](http://planetfuraha.blogspot.com/2010/02/avatars-walking-with-hexapods-dont-walk.html)
[www.xenology.info/Xeno/11.3.2.htm](http://www.xenology.info/Xeno/11.3.2.htm)
What seems to be missing much of the time, however, is numerical calculations. I would like to have, as much as possible, hard data on aspects such as stability (especially under different gravity conditions), a nervous system's ability to control multiple limbs, and the energy cost of extra limbs. Another issue that seems to be dealt with even less often is the number of fins that is useful for a fish or fish-like creature. As land-dwelling vertebrates on Earth evolved from a four-finned creature, and some similar process may happen elsewhere, especially on Earth-like planets, data about the usefulness of more fins to a fish-like creature should be useful as well.
[Answer]
Hexapod mobility is something that's currently being studied in robotics. [Ding et al. published a paper](http://cdn.intechopen.com/pdfs/10075/InTech-Locomotion_analysis_of_hexapod_robot.pdf) on the topic in 2010, where they discussed a variety of advantages that they saw in hexapod locomotion, such as:
* Increased static stability
* Increased efficiency while walking
* Ability to remain stable while using some legs as manipulators
* Ability to remain mobile after losing a leg by changing their walking pattern
A hexapod vertebrate would have similar advantages over a tetrapod vertebrate. For slow moving creatures, hexapod gaits would likely require less neural mass, since they're very statically stable. Faster moving creatures with more developed brains would likely rely on quadrupedal locomotion for speed, using the remaining two limbs as manipulators.
Beyond the question of feasibility in a terrestrial creature, the other pertinent question is whether six-limbed fish (or fish-like ancestors) would evolve. The most similar creatures to an ancestral fish, in terms of size, body plan, and ecological role, are likely the [eurypterids](https://www.researchgate.net/profile/Paul_Selden/publication/237424930_Autecology_of_Silurian_eurypterids/links/552d9c930cf2e089a3ad79d6/Autecology-of-Silurian-eurypterids.pdf), or sea scorpions. Like early vertebrates, eurypterids were mostly bilaterally symmetric free swimming creatures that used their limbs as paddles. Free swimming eurypterids generally had a single pair of primary swimming paddles, plus several pairs of crawling legs for moving along the bottom. Some eurypterids had an additional pair of grasping claws for manipulating their environments.
Interestingly, a similar gait has evolved in a modern fish: [trigloporus lastoviza](https://www.cambridge.org/core/journals/journal-of-the-marine-biological-association-of-the-united-kingdom/article/div-classtitlesix-legged-walking-by-a-bottom-dwelling-fishdiv/324E7A46C56F6F1A78C475AC157BB89A), though they've evolved a set of rays for locomoting across the ocean floor, rather than using their primary limbs. Ancestral hexapods would likely evolve on similar lines, but using primary limbs for sea floor locomotion instead of rays: four limbs for locomotion across the bottom of the ocean, an additional pair for swimming, and possibly an extra pair of limbs for manipulating their environments. Such an arrangement might even make it easier for them to transition to living on land, needing to transition only from crawling on the sea floor to crawling across the surface, rather than from swimming to crawling. The swimming limbs would likely either evolve to be used for locomotion or manipulation, or else be lost, leaving their descendants with four locomotion legs and two manipulators.
[Answer]
## It is plausible with more copies of the *Hox* genes
The [*Hox* genes](https://en.wikipedia.org/wiki/Hox_gene) control development along the head-to-tail axis of segmented animals such as vertebrates. They control a series of other genes that determine where limb buds begin to grow.
[](https://i.stack.imgur.com/KH0f6.jpg)
[source](https://www.fossilhunters.xyz/molecular-methods/signals-emanate-from-organizing-centers-in-developing-limbs.html)
The *Hox* genes are highly conserved; that is, mutations among these genes are often fatal and therefore rarely seen. Most vertebrates have four clusters of *Hox* genes. However, a chromosome mutation such as [translocation](https://en.wikipedia.org/wiki/Chromosomal_translocation) could theoretically duplicate some of the genes, producing extra copies which could produce another limb bud. This occurred in the [telost fishes](https://en.wikipedia.org/wiki/Teleost_fish), which have 7 or 8 clusters of *Hox* genes, and which has produced a pre-mandible which these fishes use to protrude their jaws outward from their mouths.
There have been a variety of experiments transplanting limb buds onto embryos, using insects, amphibians, avians, and mice. See this [1907 paper](https://embryo.asu.edu/pages/experiments-transplanting-limbs-and-their-bearing-upon-problems-development-nerves-1907-ross). These limb buds develop into full limbs:
>
> The intrinsic ability of the tissue itself to dictate the size of the growing organ was also highlighted in a transplantation experiment with two different sized salamanders where their limb buds were swapped. The limb buds of the larger species produced large limbs on the smaller hosts, and the limb buds of the smaller species produced small limbs on the large hosts (Twitty and Schwind, 1931). This result is consistent with the idea that limb buds are autonomous units programmed with the information necessary to produce the appropriately-sized appendage for the animal that will ultimately grow into an adult.
>
>
> [source](https://www.researchgate.net/publication/229654643_The_growth_of_eyes_and_limbs_transplanted_heteroplastically_between_two_species_of_Amblystoma)
>
>
>
It is therefore plausible -- although rare -- that such a mutation could produce more than 4 limbs.
[Answer]
First a definition of limb from merriam-webster.com
>
> a : one of the projecting paired appendages (such as wings) of an animal body used especially for movement and grasping but sometimes modified into sensory or sexual organs
>
>
>
The penis is definitely projecting, more or less. Does it qualify as a limb? According to the above definition, yes. Except it is not paired. You are skeptical. Then what if this sexual limb contained a rigid bone, like the arm? Bigger than an arm. A big bone. Like this walrus baculum, or "penis bone".
[](https://i.stack.imgur.com/jNmNN.jpg)
That is a sweet shirt, Dr Rowe.
A projecting fleshy part with a rigid bone inside of it is a limb by any measure, I think. Many (male) vertebrates have bacula and so qualify as 5 limbed, though most do not use this 5th limb for locomotion except in cases of extreme need.※ Could evolution further modify such a structure so that it might be useful for functions other than mating and possibly emergency locomotion? Might such a limb become prehensile, allowing the organism so endowed to, say, tip its hat in greeting? If it can happen to a tail or a finger, why not? The possibilities of the prehensile penis are ripe for exploration.
If I may add: calculations, schmalculations. Impossible in this circumstance. What are the numerical calculations relevant to evolving a tail? It is not just how big it is, but what you do with it, and what you choose to do depends on circumstance, ability, need and other variables. This changes not only generation to generation but minute to minute. It is not a process reducible to a single calculation.
---
※ I was hoping elephants, by virtue of the trunk, would qualify as 6 limbed. But like humans, elephants lack a baculum.
] |
[Question]
[
I'm working on a sci-fi/fantasy story that involves a future earth that has become tidal locked with the sun. Part of the story has an advanced civilization that has built a ring (halo) that circles the planet and provided an artificial night cycle for the sun facing part of the planet. As far-fetched as it is, how habitable would the planet be if a night cycle were reintroduced artificially? I know strong storms would form based on the flow of extreme cold air/hot air, but would it be fairly similar to our current climate?
Thanks!
[Answer]
# Absolutely!
Forgive me if I make a few assumptions, but it seems that this ring is rather large, considering that its able to completely block sunlight from hitting the earth. I'm also gonna assume that there are gaps or open areas in the ring as its way of switching between night and day on the light side of the planet.
Luckily for the people on that alternate Earth, people have already worked out if something like this is possible, with a few difference. As a matter of fact, its been something thought about doing to a planet in this solar system. It's the sweet young lady next door named Venus!
While instead of using a ring, its been theorized that a giant sunshade would be placed between Venus and the sun, blocking the light and cooling it down. The sunshade could then orbit Venus, allowing the light side face to experience day and night. This ring world of yours could do the exact same thing, although the cost to build it would be a bit larger.
However, why stop on just the side facing the sun? Those poor chaps living on the back side of this Earth want a little sunlight too! So how about we toss some big reflectors extending from the top and bottom of the inner part of the ring so that when the light can be bounced to dark side of the planet, which can be used to give both sides of the planet a day and night cycle.
Or if that doesn't work, then while a ringworld without any gaps in it blocks out the sunlight, a large reflector could be placed in a polar orbit and could provide the Earth with sunlight. Although, neat enough, this would cause the planet's light source to rise and set in the north and south instead of east and west.
If it's all done right, it should be possible to limit any major effects on the weather. I would assume, at least.
Here is a link to the paper detailing plans to terraform Venus, which includes the idea of sunshades, reflectors, and more.
<http://www.orionsarm.com/fm_store/TerraformingVenusQuickly.pdf>
Hope I helped!
[Answer]
As I understand it the [timescale for the Earth](https://en.wikipedia.org/wiki/Tidal_locking#Planets) to tidally lock to the Sun is of the order of some 40 billion years (probably longer).
And to put that in perspective, in something like [a mere 5 billion years the Sun will expand into a red giant](http://www.space.com/22471-red-giant-stars.html).
Worrying about day and night is going to be the least significant issue someone on Earth faces at that point. And on technology timescales like that, it is hard to conceive of the even a small minority of the then human population living on Earth.
] |
[Question]
[
Part of a series I'm starting since the recent *[What could make a star green?](https://worldbuilding.stackexchange.com/questions/64344/what-could-make-a-star-green)* did quite well and others could use the information here in their worlds.
---
## There aren't any "violet" stars.
[](https://i.stack.imgur.com/Rmam5.jpg)
When a star emits a significant amount of violet light, it also emits blue light, which humans are better at detecting. If any stars out there are actually violet, we see them as dark blue.
**[Of course, that hasn't stopped us in the past.](https://worldbuilding.stackexchange.com/questions/64344/what-could-make-a-star-green)**
How can such a star come about if they do not exist that way in nature (as far as we know) that appears violet to the unaided human eye? What natural circumstances would change the appearance or composition of a star in this way (so that it emits violet light)?
**The criteria for this are the same as they were with the previous question:**
**You can**
* Have elements or molecules outside the star (exotic if you wish) as long as they are stable wherever you put them and can as long as they can form naturally in real life.
* Change the composition of the star itself with (exotic if you wish) matter as long as it is stable and produces the desired effects
* Provide a solution that will eventually change color when the star expands
* Provide a somewhat speculative explanation but it should be based in real science
* Have the star "capture" whatever makes it violet after formation or have it form with this quality in the first place
**You cannot**
* Simply change the atmosphere of a nearby planet so it looks violet; it should appear violet(ish) from space
* Change the eyes of creatures viewing it; assume human eyes
* Have intelligent intervention; all circumstances should be possible in nature (rare is fine)
* Change the laws of physics or the characteristics of light
* Create the illusion of violet color from either an actual binary or an optical binary; this star should be standalone
---
While the ideas provided in the answers here may overlap those in the sister question to some degree, there are significant differences: the likes of oxygen and chlorophyl, for example, will not produce violet.
[Answer]
## Give it a circumstellar cloud of Argon
Some planetary nebulae, such as the Crab Nebulae appear purple because of ionized Argon.
[](https://i.stack.imgur.com/PrHCM.jpg)
Image copyrighted to Nasa
**Please Note:**
Human eyes have evolved to view yellow and green radiation, presumably because our sun emits radiation primarily in those wavelengths.
A green star is radiating right in the center of the visible light spectrum, which means it is emitting some light in all the possible colors. The star would therefore appear white — a combination of all colors. Earth's sun emits a lot of green light, but humans see it as white.
Purple stars are something the human eye won't easily see because our eyes are more sensitive to blue light. Since a star emitting purple light also sends out blue light — the two colors are next to one another on the visible light spectrum — the human eye primarily picks up the blue light. [Reference here](http://www.livescience.com/34469-purple-stars-green-stars-star-colors.html)
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**How about a star that is violet, when seen from some viewpoints, via the doppler shift?**
If a blue-dominant star (say peak emission nominally 470 nm) were coming toward an observer fast enough, the light -- including that dominant blue peak -- would decrease in wavelength. Enough speed, and the peak would sit in the violet band of the spectrum. A back of the envelope calc. suggests that the star needs about 10% of the speed of light to so shift it to violet (420 nm nominal.) A cooler (longer wavelength) star would need a greater approach speed. Seen from behind, the star would appear red shifted.
To appear violet, the star doesn't have to be coming straight at the observer. But, what if it is headed right at you?
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A couple of points, if I may.
That gorgeous lavender you see in pictures of massive stars and the nebulae around them is hydrogen. The Balmer alpha line (656.3 nm) is red. Hydrogen alpha photos of the sun, for instance, are true-color pictures. But the Balmer delta line (410.2 nm) is purple, as is Balmer-epsilon (although that one may be outside the range of many peoples' vision). The physics to understand what I just said is in Wikipedia, so I won't bother to explain. On a world in a starburst galaxy, you could be close enough to something like the Tarantula Nebula or 30 Doradus to see that glowing hydrogen with the naked eye.
A number of kinds of star are actually colored ultraviolet. Only a small part of the light they emit is reddish enough for us to see. Central stars of planetary nebulae, for example, are usually hotter than 50000 K, which we see as blue-white. If you could shift such a star's spectrum until its peak emission was near 400 nm, like hydrogen's Balmer epsilon, you would see those stars as distinctly blue, probably with some purple thrown in. (Assuming human eyes. Our own world has creatures which see well into the ultraviolet.)
Thanks.
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A solar system where an abundance of Arcanite asteroids near the center of of the system would allow the introduction of potassium sulfide into the outer shell of the sun and be expelled as a burst of violet plasma.
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**This sounds really stupid**, but I'm trying to think of a way to make [World Turtle](https://en.wikipedia.org/wiki/World_Turtle) work. And what I got after 5 minutes of careful deliberation, would be that the our earth would have to be 'flat' on the back of a giant turtle. And since I don't want mythical space turtles, I'm gonna presume that they live on a planet themselves.
Now disregarding the impracticality of there actually being a turtle who can carry the crust, the environmental changes that will happen from making the earth 'flat' and the general idiocy of this question.
If we took the crust of the Earth, made it like a giant pancake on the turtle's back, how big would the turtle[or is it tortoise?] have to be? And then how big would their planet be?
How it might look like on a smaller scale, since turtles can obviously navigate space.
[](https://i.stack.imgur.com/Srw8U.jpg)
What kind of tags can I even put on this?
[Answer]
Your world is a Niven-style Ringworld.
This gives you plenty of space for a "world-tortoise" to wander around in while still allowing you to arbitrarily set your gravity to pretty much whatever you want by setting the spin rate.
To paraphrase Niven, you could lay out the Earth flat, set it down in the landscape, turn away, and never find it again. The Ringworld has a *lot* of space available.
I would assume the rotation rate is actually fairly slow to give the tortoise only enough "gravity" to keep it walking along the surface, but not crushing it. The "gravity" experienced on the tortoise's back would be actual gravity, since it is so massive.
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The world is still a sphere and it's on a 4 dimensional turtle. It’s analogous to a disk laying on a 3D turtle. Just as the flatlqnders can’t look up or down and so are only aware of their disk, if we could look in the 4th direction we would see that every part of the inside of the sphere is resting on the 3D surface of a 4D shell.
The turtle is normal sized. Our little 3D world is “small” in their world.
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First of all, we must agree on the species. Do you consider that the turtle is a little red-eared slider (40cm), an African spurred (80cm) or a big sea turltle (more than 1m) ?
If we choose a non-scientific average of 50cm and considering the mean diameter of the Earth (12 742 kilometers) we can find that our planet is
25 484 000 times bigger. If we swap the position, our super-turtle shall measure 324 717 128 000 km, 230 000 bigger than the sun ...
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So I am proposing a ring-world of approximately 1600 km diameter. The ring spins for earth like gravity. The ring itself would be several kilometers thick with Earth like variations in elevation (i.e. mountains less than ~8 km above sea level, with ocean trenches of similar depth) The atmosphere would also be the same composition as Earth's. The ring would have Earthlike lighting levels.
The question: How far could you see in any direction?
I would think there would be a limit to how far you could see before the atmosphere would haze and limit your sight distance when looking towards the horizon (although there wouldn't be a horizon; maybe along the ring is a better term), but looking upward further past a certain point the haze should fade and you would be able to see the farther sections of the ring. Is this correct?
[](https://i.stack.imgur.com/oQ0ns.png)
Could someone help me out with specifics; distances, angles, etc? How would this change with elevation? Does less dense air equal farther sight distances?
Thanks!
[Answer]
I did some googling, and the best answer to how far the atmosphere of Earth would let you see if it went on forever was in [this post in Reddit](https://www.reddit.com/r/AskScienceDiscussion/comments/2t7gut/how_far_could_you_see_on_an_infinite_flat_earth/):
>
> The dominant effect should be the diffraction limit of your eye. You can resolve two objects separated by an angle theta equal to wavelength of light / diameter of telescope. For your eye, theta ~ 500 nm / 0.5 cm = 10-4 radians. If you had a building H meters tall at a distance of D, then you could see tan(theta) ~ theta ~ H/D (the first part comes from the small angle approximation), or H = 10-4 \* D. So, at 10 km (104 m), you could resolve a 1 meter object. At 10,000 km, you could resolve a 1 km structure. By "resolve", in this case, it would be your ability to see the object against the surface of the ground.
>
>
>
Ten thousand kilometers is larger than your ring world by around an order of magnitude, so while haze would affect visibility just as it does on Earth, you would be able to see quite well in all directions.
Now, one thing to consider about your atmosphere. If it has the same composition and density as ours, and in a ringworld with the same average temperature and gravity as those from Earth, the stratosphere should be approximately 18-19 km deep. Let's round it to twenty. [This calculator](http://planetcalc.com/1421/) (in the **"Area of circle segment by radius and height"** part of the page) gives us a chord length of aroud 504.38 kilometers. That's the longest distance light can travel in your world without leaving the atmosphere. That's two orders of magnitude greater than [the distance to the horizon on sea level on Earth](https://en.wikipedia.org/wiki/Horizon#Distance_to_the_horizon). Your world, though smaller than Earth, would provide its inhabitants with quite a sight.
**Edit:** Just to make things clear (no pun intended), haze and refraction would have their maximum effect on objects around 500 kilometers away from the observer. Farther than that, haze and refraction are actually reduced. But you'll see the whole ring in all directions without much distortion.
[Answer]
There are a number of factors that would influence how things actually *look* from the inside surface of a ringworld:
1. The diameter of the ring affects how noticeable the curvature is at short distances, well before the following factors come into play. The diameter and width also affect the apparent magnitude of the opposite side of the ring, which determines whether it can be seen, e.g., during the day.
2. As suggested, atmospheric scattering results in a sky-blue haze when looking through long stretches of air, just as it does on Earth. In addition, clouds and/or dust can further obstruct one's view of the ring.
3. The atmosphere's decreasing pressure (and therefor decreasing index of refraction) at increasing altitudes also results in [atmospheric refraction](https://en.wikipedia.org/wiki/Atmospheric_refraction), again similarly to Earth. This causes light to bend back toward the ground; as a result, objects at intermediate distances appear more elevated with respect to the horizontal than they actually are.
4. Variations in air temperature and pressure also have an impact on the atmosphere's index of refraction. Extreme cases on Earth produce mirages such as [Fata Morgana](https://en.wikipedia.org/wiki/Mirage#Fata_Morgana). Due to the upward curvature of the ring, these effects may be more pronounced at certain distances and light-lines passing through them may be more prone to yield reflected images of the ground (as opposed to the sky).
It is difficult to determine which of the above effects will dominate for a given viewing angle, but we can consider some specific cases. A thorough discussion of simulating atmospheric haze can be found on the [FlightGear wiki](https://wiki.flightgear.org/Atmospheric_light_scattering#Atmospheric_haze), in which the authors suggest 500 km of visibility is *possible* on exceptionally clear days, though visibility can be greatly reduced due to atmospheric conditions. For a 1600 km diameter ring with 19 km of atmosphere, the longest (straight) chord remaining entirely within the atmosphere is about 350 km and pertains to a viewing angle of roughly 12.5° above the horizontal. Atmospheric refraction should bend that angle's corresponding light-line slightly toward the ring, in effect shortening the amount of air it actually passes through. Accordingly, and especially because much of the atmosphere said light-line traverses has greatly reduced density, we can judge that observers should be able to see the ring structure with at most partial haze between 0 and 12.5° in ideal weather conditions. On the other hand, if visibility is a mere 100 km, then the ring would become fully obscured by haze from about 3.6° until somewhere around 12.5°.
As for larger angles, light-lines pass through less total atmosphere, thereby resulting in less atmospheric scattering, but the apparent magnitude of the viewed portion of the ring structure is also reduced because it is further away. That being said, if we assume the 1600 km diameter ring to have approximately the same albedo as the moon and to have a width of around 15 km, then the far side of the ring would have the same angular width as the moon as viewed from Earth and, thus, would also have the same apparent magnitude. Similar to the light and dark portions of a crescent moon, illuminated sections of the ring would be plainly visible even in full daylight while dark sections would not be seen.
Increasing the viewer's altitude affects the above in that (a) it reduces the maximum viewing angle and length of light-lines staying entirely within the atmosphere and (b) such light-lines pass through air of overall lesser density. As a result, viewers at higher altitudes see less haze and the haze they do see occurs at angles either nearer to or below the horizontal.
As a last discussion topic, unlike atmospheric refraction, inferior mirages (e.g., due to layers of hot air very near the ground) cause light-lines to bend away from the ring. Because of the ring's upward curvature, this has the interesting potential to continue bending for far greater distances than is possible on Earth, meaning that unexpectedly distant objects may appear reflected (and quite likely stretched or squashed) in the mirage. Such mirages, however, usually require an extremely small viewing angle of [less than 0.36°](https://iopscience.iop.org/article/10.1088/1361-6552/ab3c28) with respect to the horizontal, which is only possible for distances up to 10 km along the surface of a 1600 km diameter ring. On the other hand, superior mirages (e.g., due to temperature inversion) cause light-lines to bend even more toward the ring and may be especially prone to reflect objects of intermediate distance (say, 100 to 300 km for a similarly sized ring) such that they appear to float in the "sky" above more distant terrain. How frequently either of these phenomena occur depends on the kind of weather and terrain present on the ringworld; in particular, inferior mirages are most frequent in deserts while superior mirages are most frequent over oceans and frozen ground.
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[Question]
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Orbital construction facilities have a great many advantages over ground based ones: You can use materials from space without having to drag them up the gravity well, you can make vessels that don't have any atmospheric capability, and you can [cold weld](https://en.wikipedia.org/wiki/Cold_welding) certain metals. However: They also have downsides.
1: Everything is in microgravity: This makes it hard to keep hold of your work and simply removes the possibility of performing some industrial processes.
2: Everything is in vacuum: At least in a 'traditional' orbital construction rig, the thing being built isn't inside the thing doing the building, and even if it were making a solid shell to build ships in is hard.
3: Everything is either too cold or too hot: Space is cold, but heat doesn't move away from hot things very well, so your materials are too cold while your tools are overheating.
4: Large crews...: ...Are hard to feed and maintain while they work.
5: Any number of other things that I haven't even thought of yet.
**How can we resolve these issues, or minimise the amount by which they impede our glorious progress towards Spaaaaaaace! ??**
[Answer]
Many of the issues in building in microgravity are based on lack of experience and a large enough database for quality control. As well, there are time and distance issues (for example, if you have a defective part on Earth, FedEX can deliver a replacement the next day, while waiting for SpaceX to get a launch ready will take several days at best, but more likely weeks or even months).
For the near and possibly mid future, the best way to overcome these issues is to build modules in a factory on Earth, and then assemble completed modular units in orbit, much like the ISS was assembled. There are other historical analogies, the Type XXI U boats built near the end of WWII were built from modular assemblies sent by rail to the shipyard for final assembly, for example.
Even in the Plausible Mid Future, assembly of modules might be done in pressurized bays on the Moon and then sent into space via mass driver, or an asteroid could be hollowed out and spun for gravity and a pressurized bay for building and checkout will be used. A pressurized bay in microgravity may be used, if you are willing to put up with microgravity issues. Robots might (and indeed probably will) do the bulk of the work, but a pressurized bay allows a human quality control inspector easy access and the ability to get in without the restrictions of a spacesuit.
Based on this, future spacecraft and stations might resemble cylinders of various size attached to a central truss work. With construction bays in hollowed out asteroids, the modules could be of pretty impressive size.
As an alternative, for very large construction, a "balloon" could be inflated and pressurized, and construction done inside. The balloon will become the outer hull of whatever you are building, and all the other stuff you need built inside in the comfort of a pressurized environment. A variation of this idea is on the Neofuel site, which uses a rotating balloon filled with ice to form the structure, and the various structural elements built inside: <http://www.neofuel.com/iceship/index.html>
So in general, the progression will be to build modules on Earth for on orbit construction, then migrate to the Moon to mine materials and then build modular sections, moving to asteroids to make modules until *we* finally build large enclosures to define the outline of the spacecraft/structure and build the structures inside.
Grab some tools and get busy.
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Assuming present day technology, you could eliminate the vacuum and large crews problem by having a bunch of remotely controlled robots doing the construction. They would be controlled via a ground station below. You also get the added benefit of eliminating health problems that come with extended microgravity exposure for humans.
If we up the tech level a bit and assume we've perfected nanotechnology, then using nanobots (again, remotely controlled) to do the bulk of the contruction would be great.
Basically if you remove the human component, a lot of issues with building things in orbit go away. Remote controlled robots and industrial processes are the way to go.
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1: Microgravity
Some processes might actually be better in microgravity. Examples currently being researched include crystal growth or mixed density allows.
For everything else rotation is your friend. This need not be large wheels for the whole production facility, individual production line machines could have built in centrifuges for any level of gravitational equivalent force. You could have any level of "gravity" that you wanted tailored to your production requirements.
2: Vacuum
A lot of manufacturing processes require vacuum or inert gas atmospheres to displace the oxygen in our air. This would also potentially get you clean room level cleanliness without an atmosphere to transport dust/debris.
Again where you need an atmosphere you could provide one and it could be tailored to whatever need you require, avoiding oxygen, hydrogen, or other contaminants in metal forming works would make for much higher purities than easily achievable on Earth. Individual machines could have localized atmosphere areas varying from something similar to a TIG welder all the way up to fully enclosed pressure vessels.
3: Temperature issues.
Space can easily provide huge variations in temperature, from an ambient temp of ~2.7 K up to focused solar heating of 1000 of degrees. The main difficulty is moving heat effectively. Most large scale industrial manufacturing facilities already deal with this problem using active cooling systems (HVAC) it would not be much different in space. You would have to provide active cooling to parts with no atmosphere to transfer heat, but again in space this could be engineered to whatever heat level you want.
4: Large crews.
Build with robots. On Earth the direction has been for less and less workers with more automation of manufacturing, in space you have the added incentive that providing for the crew is expensive. Tele-presence general purpose robots could be used to monitor, and identify problems that creep up and should be able to fix most problems.
Overall as factories on Earth become more automated and sophisticated, the drawbacks to placing them in orbit decline, while certain manufacturing conditions can only be achieved in space.
The big drawback not addressed is transport costs. Your factories raw materials and supplies would need to all be supplied from orbit or other low gravity locations as launching anything from Earth to the factory is incredibly expensive ($1000's of dollar per pound) and would quickly eliminate any profit. Items could be deorbited to deliver goods to Earth fairly cheaply.
This would require a large amount of infrastructure to be in place before space manufacturing becomes the norm. Asteroid or lunar mining would need to exists along with all of the supporting refining and manufacturing processes to feed your factory. The possibility exists for the first round of factories to produce very high profit items (super computer chips, metal alloys, or medications).
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I have a group that's building a moon colony. The final end goal is a self-sufficient colony of at least 1 million humans.
They have access to one million metric tons of lift per week at nominal cost. If it matters, this is being done by superheros (flyers, energy producers, etc). Most materials are lifted, boosted toward the moon, then intercepted and landed. Overall this takes four days. Time-sensitive materials can reach the moon in as little as three hours under constant acceleration, but it's roughly ten times less efficient to do it that way.
**What resources does the colony need from Earth, and what is the most efficient way to transport those resources?** For example, sure we need air - how should we transport it, how do we divide each transport up, etc?
Edit: To clarify on the "way to transport", what I mean is in terms of storage. Assume they've got the mechanics down of getting stuff from point A to point B. But say you're transporting water - should you do it as liquid or ice? Or possibly both? Is it worth super cooling air to a liquid to make things easier, or should you compress it but keep it a gas? If you need to transport animals or plants, what's the best way?
Specifically I'd like to know about the following two scenarios:
* First year (what do we need initially)
* After 1-2 years (what do we need while we build toward self-sufficiency)
Average technology is 1990s, but the superheros have access to 2015-equivalent technology because of Spark-type supergeniuses. This is an AU Earth, and they're building it on AU Luna.
If they can get the resources elsewhere in the solar system more efficiently, they will do that instead. Keep in mind that almost everything else is farther away, which effectively reduces the efficiency since it takes longer to get there.
[Answer]
Partly what your colony needs will be determined based upon the specifics of what you mean by self-sufficient.
Do you mean "economically" or do you mean "catastrophe strikes the Earth and the colony needs to survive on its own?"
### Basic Requirements
Regardless of your definitions the initial requirements will be similar for either type (and those are very well defined by other answers). Basically figure out high mass needs, especially those that do not require special processing, and fill those needs first.
As mentioned in other answers, these will start as things like:
* Propellant
* Power
* Breathable air
* Potable water
* Food
* Productive Soil
* Radiation shielding
* Construction materials
The hurdle of providing these things to your new colony is a lot lower if you do a good job of picking a location in which many of these things are readily available without a great deal of processing - and it is why finding water at the Moon's poles is so exciting.
### Initial payback
Assuming you want economic self-sufficiency, as the colony becomes self-sufficient in these high-mass colony needs, the colony needs to determine what valuable low-mass things and services it can produce to compete with those provided by Earth.
Initially, these might be:
1. Servicing satellites
2. Refueling of satellites
3. Clearing space junk out of Earth orbit.
### Economic Self-sufficiency
As the colony continues to grow and establishes production infrastructure the colony will begin exploring goods and services it can create that are unique or superior to those available on Earth.
These might be:
1. Astronomical facilities and research facilities (no atmosphere, longer observation baseline)
2. Other scientific facilities and research (novel environments)
3. Biomedical research (novel environments)
4. Drug research (zero gravity is good for growing large protein
crystals)
5. Specialty Electronics (zero gravity and high vacuum -> extra pure materials)
6. Specialized high value mechanical items (e.g. zero-gravity ->
perfect ball bearings)
7. Novelty items (Moon rocks, etc. for collectors)
8. Specialized materials (zero-gravity & high vacuum makes especially
large and perfect crystal growth possible - or perhaps we'll be able
to make true high-temperature superconductors or super-long
nanotubes - km instead of mm in length)
### 3-D Printing
Ultimately, economic self-sufficiency won't be enough for a colony. It'll need to be able to survive without resupply (if necessary).
IMO, this is where 3D printing (and other "additive manufacturing" techniques) are a really exciting development. If you can supply the raw materials many different types items can be created with them as long as you have the design program.
Need a locking mechanism for your airlock? Program the part into your 3D printer, fill the feed bin with the proper materials, and a few hours later, voila: a new airlock mechanism.
Such devices will never replace high volume (& therefore cheap & high speed) manufacturing methods but would be perfect for the needs of a space colony.
So the real requirement would be to have the ability to build those 3D printer devices.
### What Else?
I view a population like a pyramid. You need a certain number of people at each level to support developments at higher levels. A space colony (with our current levels of knowledge and technology) will require lots of specialized knowledge and skills to keep going.
In a terrestrial country, it requires a certain population base to maintain a high technology levels. Some city-states side-step the issue by being embedded in a larger country that provides that support base.
But what that means is that the colony will either need to support a huge population, or a lot of work and technological advances will need to be achieved to "dumb down" the knowledge and skill requirements of the colony. So instead of an active closed-loop environmental system that requires human maintenance, we'd have research and develop a passive environmental system that maintains itself (think spaceship Earth).
### Transportation
Except for perishable items, transportation will use the [Interplanetary Transportation Network](https://en.wikipedia.org/wiki/Interplanetary_Transport_Network). Such trajectories use much less energy ($\Delta V$) than low-energy Hohmann Orbit transfers but can take decades to complete.
Humans or some other perishable items will at least require Hohmann Orbit Transfers.
[Answer]
In the short term, you are going to need:
* food
* water
* lots of oxygen cylinders
* heavy air conditioning and central heating systems
In this stage you are going to set up a colony and live in underground tunnel system where you would be safe from sun's scorching heat and the chilling nights.
In the long term, you would require:
* breathable atmosphere
* permanent food source
* water bodies (oceans, that is. an atmosphere without a large water body would bring horrific tornadoes and vortexes due to temperature difference between night and day)
* surface residence facilities (homes, to say it simply)
* a strong magnetic field (to deflect solar electromagnetic pulses)
* green plants (to start the carbon and oxygen cycles)
* lots of carbon in the crust (to provide building material for plants)
* I almost forgot ... an ozone layer too, if you please
The most efficient way of delivery of supplies (but not personnel!) is to first get them to ISS through rockets and then "shoot" then towards moon with a low velocity (3 km/s) cannon in a special, shock proof capsule. Once they enter lunar atmosphere, the capsules open up two layers of parachute to slow down the descent. The empty caps can later be transported back to ISS (and then earth) in batches.
Thanks to Frostfyre for reminding me that I missed that part in my answer.
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**In the first year, start with the basic life needs then move up from there.** After the obvious ones, air, water, food production, shelter, and fuel, then move on to heavy equipment. Gas products transport best as liquids. Keeping them cool during transport shouldn't be difficult since the vacuum of space is a fantastic insulator.
The largest long term materials requirement for the moon will be steel.
[From Space.com](http://www.space.com/55-earths-moon-formation-composition-and-orbit.html):
>
> The average composition of the lunar surface by weight is roughly 43 percent oxygen, 20 percent silicon, 19 percent magnesium, 10 percent iron, 3 percent calcium, 3 percent aluminum, 0.42 percent chromium, 0.18 percent titanium and 0.12 percent manganese.
>
>
>
My bet is that it is more efficient to produce the steel here on earth then ship it to the Moon for shaping and forming there. Not having to worry about shipping extra oxygen despite the massive transport capabilities would ease the supply chain load.
**Supply Requirements after the first year**
A self-sustaining Moon colony will need industry and space to house that industry. General industry requires a few things: Materials for tools and end products, expertise to make the tools, expertise to make the end products and the machinery to get all this done.
Ultimately, there's just going to be some stuff that the Moon just can't produce for itself or is just too difficult to produce in a lunar environment. These items will need to be imported from Earth or from orbital facilities around Earth.
*Short List of tool categories required for industry:*
* Atmosphere production and maintenance equipment.
* Mining tools in the form of explosives, ore extractors, and boring machines
* Cranes in various sizes, strengths and configurations.
* Thousands to tens of thousands of Lathes of various sizes
* Presses of various sizes and pressure capabilities
* "Basic" clean room environments for the creation of electronics.
*Atmosphere Production*
Many of the the industries we take for granted on Earth require huge quantities of free oxygen on Earth, which free oxygen doesn't exist on Mars except where we make it. Industry will need to be very careful about how much oxygen they produce and consume. It's likely that habitats and industrial areas will have separate oxygen production facilities.
Perhaps the regolith of the lunar crust may be processed into oxygen and feed stock for various industrial processes.
*Mining for Minerals and situating Industry*
Once mining equipment is dropped to the Moon (gently dropped), it's more efficient to using mining to build habitats and industrial areas than it is to build bubbles on the surface. Subsurface habitats benefit from the radiation attenuation power of rock and a natural leak reducer (compared to a bubble membrane).
[Answer]
[This](http://www.biospherics.org/biosphere2/) shows an attempt by humans to create a sustainable "biosphere" which would allow for humans to live inside it even if it is in an otherwise barren environment.
The project encountered many unexpected difficulties such as air reacting with one of the building blocks of the biosphere.
[Answer]
**Short Term**
* Water
* Oxygen
* Food
* Building Material
* Computers
* Spacesuits
**Long Term**
* Seeds
* Constant source of oxygen
* Constant source of water(Example: Lakes)
* Paper
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[Question]
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I found this on [Wikipedia](http://en.wikipedia.org/wiki/Impact_winter).
I'm aiming for **[the fastest climate change](https://worldbuilding.stackexchange.com/questions/1169/is-there-a-man-made-or-natural-event-that-can-cause-an-abrupt-climate-change-wit) possible** without that much advanced notice, e.g. perhaps a regional sized asteroid scientists miss or are too distracted to catch on time?
**Assuming the eastern part of the US would launch into deadly weather (cold not hot) conditions (but would allow survivors), where would this asteroid have to hit, what size would it be, and from the moment of impact, what would the breakdown be in layman's terms before the effects hit the eastern part of the US (aiming for NE)?**
Bonus points for assuming the eastern part of the US is frozen, where survivors would aim to migrate for warmer/safer weather conditions.
[Answer]
Pretty much everything you need is right there on that page. Here's a breakdown that largely re-digests your link, though I'll toss in a few extra tidbits to round it out a bit more.
* **Surprise**
This is actually the easiest bit. Space is big. *Very* big. Even our "little corner" of the universe is mind-meltingly gigantic. It would be pretty trivial for a major asteroid to sneak up on us and nobody notice.
If you want to make it even *more* likely to escape notice, it can come at us from the direction of the sun, where the sun itself would all but literally blind us to the oncoming threat. This would most likely have to be a retrograde orbit, which while uncommon/rare is not unheard of; naturally, ~6 months prior to the impact we'd be on the asteroid's side of the sun and could thus see it at night, but it'd be much further out and thus still more likely to be missed.
Another option is to put it on an unusually inclined orbit. Almost every object in our solar system orbits on or very close to a common plane. As a result, anyone looking for things in our solar system pretty much trains their telescopes to this plane. Anything coming at us from above or below is very likely to never be spotted at all.
One final option (well, I'm sure there's more out there, but this is the last I'm offering) would be an asteroid that looks like it won't be able to make it through the atmosphere, but have a surprising property that lets it punch all the way through. A comet hiding a dense iron core, for example. Under this scenario you could have it spotted, but all the experts telling everyone not to worry. Then *BAM!*
* **Size**
Depends on what it's made of. A dense iron core can be as little as 3km across and still cause "winter". A "softer" rocky meteor has to be bigger to survive punching through the atmosphere.
Really, for the purposes of fiction, pick any size between 3km and 10km (the size of the meteor that wiped out the dinosaurs) and call it a "rocky meteor", and you're good to go. There's so much variation even with similar compositions that you've got almost unlimited free reign here.
* **Impact Location**
Short version: Anywhere, depending on how massive and how dense it is.
For best results, land or shallow water will give you the most ejection of fine particulates, which is what will block the sun and give you your "winter". Obviously anything too close to the impact location will be vaporized, and for a good ways after that "merely" pulverized. These distances depend entirely upon what the meteor's made of and how big it is.
For a minimum of direct casualties, a larger object hitting in the middle of the ocean will still give you enough ejecta to block the sun and plunge the world into winter. Obviously coastal areas will be hit hard by tidal waves, but those are infinitely more survivable than the direct blast of a meteor impact.
For the Eastern US to survive the initial impact, put your meteor nearly anywhere else. An entirely separate continent would insulate the area against tidal waves and firestorms from the impact. Even as close as the Western US and the Eastern would likely still be around to enjoy the ensuing winter. You're best bet though is to have it hit in Asia or Australia; Europe or Africa would work too, but you might get tidal waves from these. Ditto the northern bits of South America. Antarctica would be an excellent choice because the ice there would be vaporized instantly on impact, adding water vapor to the atmosphere to further block out the sun; on the other hand, you'd also get so much ice calving that you could easily see tidal waves again, but I wouldn't expect these to be as devastating by the time they reached the Eastern US.
* **Breakdown of Impact**
As the meteor crashes through the atmosphere, it's going to start burning. This will be visible across huge swathes of the world; if at night, it will dramatically light up the sky. Pieces will break off as the atmosphere tries desperately to stop it, and you'll get smaller impacts all around and along its path through the air (as well as numerous fire trails that just end as the smaller bits burn up or explode).
When it hits the ground, there will be an explosion beyond anything you can comprehend, or really even hope to adequately describe. Hiroshima would look like a firecracker by comparison. There'd be an immense fireball, followed by a mushroom cloud climbing far up into the atmosphere; it would literally spread to cover the entire globe. Trees and other combustible material for many, many, *many* kilometers around will burst into flame as firestorms explode outward; this smoke will further contribute to the dark cloud blotting out the sun. Ground Zero will be a massive crater, and everything for another real good ways will be flattened if not completely pulverized. It will be felt all over the planet.
Larger debris ejected into the air will come crashing back down for secondary impacts all over the hemisphere; a large enough impact will send some of these on suborbital trajectories and hit the opposite side of the globe as well. None of these will come even close to the scope of the main impact though.
The effects would be quite rapid. The cloud of dust and debris and smoke will race rapidly across the entire globe, and plunge the whole planet into a reddish darkness. Temperatures will immediately start to plummet, and average ground temps will drop by around 13C (23F, if I did the math right). Not overnight, mind you, but pretty quickly; it will start off fast and slow down as the new "normal" stabilizes. Enough firestorms can increase this drop by another few degrees, but you're not realistically going to see (formerly-)sunny Miami freeze solid overnight. Still, it's enough that plenty of people will be tempted to migrate -- not that the conditions will be a whole lot better (other than warmer) further south.
Over time food supplies will dwindle, as crops die and agriculture comes to an almost instant crash. The social impacts -- riots of panicking people leading to completely collapse of order in many areas -- will be almost immediate.
Direct loss of food as most life across the planet faces extinction will cause up to 25% of the human population to starve to death (apparently we're quite smart or something). The ensuing social unrest and collapse of civilization in many areas will lead to even more deaths.
* **Duration of effects**
Within about a year enough of the particulates will have cleared from the air for global temperatures to have rebounded by almost half of what they fell by. You'll have similar "half-life" gains over subsequent years. Agriculture will start to be viable again around this time, but at nowhere near as productive of levels as it is currently. This, too, will improve over subsequent years.
* **Additional links**
+ <http://www.purdue.edu/impactearth/>
+ <http://impact.ese.ic.ac.uk/ImpactEffects/>
+ <http://janus.astro.umd.edu/astro/impact/>
] |
[Question]
[
It can be really hard to distinguish between sounds and find the source of a sound underwater. How could an octopus musician play music with defined notes that are not blurred (significantly) or changed by disturbances in the water nearby? Which instruments (if any) could the octopus even play?
Thanks!
[Answer]
**Underwater musical instruments**
The Danish band [Aquasonic](https://www.lifegate.com/aquasonic-music-underwater) plays underwater. They play intruments like
* electromagnetic harp.
* percussion instruments such as 24 Tibetan bells.
* a carbon fibre violin.
* a rhythmic instrument similar to a water wheel and a sort of organ
called hydraulophone.
**Underwater singing**
They also sing as in this [video](https://www.youtube.com/watch?v=GZ-OkKOJVkI).
Your band of octopi can sing and play instruments of similar type.
[Answer]
## Percussion only
**You'll need nine brains to design an instrument for it**
There is one answer now featuring an example of humans playing music underwater.. this comment will be too long for the small box, so I put it here.. and I certainly hope the octopus' nine brains can come up with some solutions. Really looking forward to hear the squid beat, but I'm afraid it will be percussion only.
I see an issue with melodic instruments. Underwater, there are no wind instruments that can work. Metal or moving parts will fall apart in salty water. And Earth octopuses of any size won't be able to handle strings on a guitar, a violin or a harp. Musical instruments were designed for ape fingers, not soft tentacles. It may be able to handle drums..
[](https://i.stack.imgur.com/YkLOz.png)
**This animal can't sing**
Also I wonder how an octopus would *sing*.. it has no vocal chords.. it is unclear how it produces sound, and it rarely does..
<https://tonmo.com/threads/humboldt-vocalizations.256/>
**The octopus may hear its drumbeats, but does it listen ?**
>
> The statocyst is a small hard chamber that contains sensory hairs,
> that can detect vibrations similar to those in the human ear.
> Although the octopus is capable of hearing, its capacity to hear is
> limited since they don’t have a chamber or organ to amplify sounds,
> which is present in other sea animals such as fish.
>
>
>
<https://outlifeexpert.com/do-octopuses-have-ears/>
.. so there is a debate among biologists, whether the octopus actually hears sounds and reacts to sounds. The octopus CAN hear frequencies below 1000 Hz, with some center (optimal) frequency at 600 Hz, with an organ intended for balance keeping. Only issue is.. these frequencies are theoretical range, based on the shape of the organ.
The organ used for sense balance and orientation is suitable for hearing low frequencies. But it is unknown whether the octopus has a *hearing function*. That is the debate. If you want to participate click here,
<https://www.youtube.com/watch?v=7jVHSO3-2eA&t=159s>
[Answer]
**Not a Problem**
Water does not blur or distort sound any more than air does. Cetaceans make and hear a wide range of sounds going from subsonic Blue Whales to the high pitched clicks of dolphins and toothed whales.
In fact sound travels faster in water than through air so there is less time for distortion.
The issue is more would a land instrument work the same way underwater. Would a drum or harp make the sound in the first place? Your homework for today is to find out for yourself at your local pool or ocean!
As for how the octopusses play their instruments they can do the same as people. Use their tentacles for string or percussion, or use their siphon for wind instruments.
The real interesting question is **how do octopusses hear**. Do they have designated earholes or do they hear on their whole body? The latter would influence how they enjoy their music and how they compose it.
] |
[Question]
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**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.
Very straightforward question, how big can a gecko get before the van der Waal force becomes insufficient to carry their body? In life, each of a gecko's four feet has a clinging strength of up to 20 times the animal's body weight. A possible response to the lizards growing mass might be thicker sturdier limbs and wider feet but for the sake of the question let’s assume they keep the same proportions.
[](https://i.stack.imgur.com/aZCeJ.jpg)
Here’s a cute gecko for your troubles.
[Answer]
This is another case where the square-cube law comes into play: the mass of the hanging gecko scales up with the cube of the length, while the contact area which ensures the gecko is sticking to the surface only grows with the square of that length.
$M \approx l^3$
$S \approx l^2$
If we take for good your figure
>
> each of a gecko's four feet has a clinging strength of up to 20 times the animal's body weight.
>
>
>
and considering that the ratio between mass and feet surface goes linearly with the length, a gecko 20 times the length of an actual gecko would be the maximum size that the gecko feet clinging mechanism could hold.
That would mean that the gecko could have a mass of about 8000 times a current gecko, with feet surface 400 times larger.
For reference with a real world animal, considering that a gecko can be about 20 cm long, this fictional gecko would be about 400 cm, or 4 m long. Good luck seeing something the size of an alligator hanging on the ceiling above your head.
] |
[Question]
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It's a common trope in the visual design of dragons, giant bats and other fictional flying beings to have wings that appear to be severely torn, cut, pierced, and otherwise worn down. It's also quite likely that the wing of a flying creature would be a prime target for its enemies in combat, so it might take on that appearance unwillingly.
My concern is that this would obviously affect the flying beast's ability to fly, but I'm not keen on the specifics of that. I can make a wild guess that this:[](https://i.stack.imgur.com/5ALIc.png) would be solid enough to support flight, and that this:[](https://i.stack.imgur.com/VV2HS.jpg) would let entirely too much air though to have sufficient lift remaining.
What I want to know is, at what point do holes in the wing become too much of a hindrance for the animal to achieve and sustain flight?
My interest is especially focused on combat with dragons. Would a single lucky sword-stroke, bite, or bullet be enough to ground the beast or would it take dozens of hits until half the surface area of the membrane is gone?
[Answer]
Aerodynamics is hard stuff. This is more of a physics problem that heavily depends on the specifics of the creatures. Things like the mass and volume of the Dragon, the strength of the wing muscles and bones, the strength of the actual skin/membrane, properties of the air they are flying in will all determine the answer to this.
Dragons have a problem with reality, in that their wings almost never are large enough to provide adequate lift / thrust to counteract their immense weight. So figuring out how much damage they can take depends first upon figuring out how the hell they are flying in the first place.
If they rely on utterly massive wings to keep their hefty bodies aloft, then small holes won't bring them down. Adding more holes will gradually reduce their thrust until they fall.
Additionally, if their skin has a "realistic" material composition, enough holes will eventually cause larger portions to fail under stress and tear/flap away.
Arrow holes in the middle of the membrane sections would cause less damage than the tears shown next to the support "fingers" in your image. The attachment points to the "fingers" would be under a ton of stress when flying, so having it frayed like that would probably cause larger tears and failure of the wing.
The real answer for how much damage a dragon wing can take is: How ever much you need them to. Anyone accepting that Dragons exist in your world, and that they can fly, can also accept that after "enough" damage, they'll fall from the sky.
] |
[Question]
[
As you know, mythical animals like the gryphon, dragon, wyvern, roc, etc can carry things as they fly.
For a big creature to fly, it either needs to massively increase the spread of their wings or have hollow bones which makes them fragile and unable/unsuitable to support a human to ride them on the back while flying. (This is as far as I know, correct me if I am wrong.)
So, I wonder about carrying or transporting a human using their feet, talons, or hands, like how eagles carry a goat/lamb. Will this allow them to fly while not hurting them? How big do they need to be so they can carry a human with their feet? Will this require a significant increase in their wing or leg size?
From: <https://news.sky.com/story/sea-eagle-seizes-lamb-and-carries-it-off-in-scotland-11716231>
[](https://i.stack.imgur.com/dmiu6.jpg)
From: [Rescued from an Eagle's Nest](https://en.wikipedia.org/wiki/Rescued_from_an_Eagle%27s_Nest) co-directed by Edwin S Porter and J. Searle Dawley for the Edison film studios.
[](https://i.stack.imgur.com/IpGXK.jpg)
I imagine the saddle would be like a [swing](https://thenorthernboy.com/wp-content/uploads/2018/06/IMG_6761-1024x1024.jpg), either the links or chains made of leather or metal. (Metal probably use for military to discourage or prevent a flying enemy cutting the link/chains. And, at least I assume if an enemy tried charging on the swing saddle it would probably tangle them both, so both would go down.)
The base would be made of leather. To make them more for [civilian use](https://cdn.specialneedstoys.com/products/images/l/8TSFS.jpeg), I also consider a cage or type of basket. It could also be made of wood or metal to allow them to [stand](http://www.moreinspiration.com/image/original?file=779cf670-48a3-4cba-8192-0857ae05cb15.png) better so they can be more versatile to dodge an attack. The only problem would be if the flying creature flies to fast or strong enough to make the swing level a full horizontal angle during flight.
I also assume the rider could control the flying creature using paragliding type of reins to maneuver around or use body movement, weight, or pressure to steer the animal in this case (but not sure can it work or not).
After the flying creature manages to fly using airport runway, it would catch the saddle positioned at the end of the take off and lock into a shackle on their feet, hands, ankle, or wrist, either just the two legs or all legs if it have four or more. Upon landing there would be a [pole](https://images-na.ssl-images-amazon.com/images/I/71Jshezs9gL._SL1500_.jpg) or [second floor](https://sites.create-cdn.net/siteimages/27/2/2/272228/6515337.jpg), so the flying creature could perch on to rest while below the rider gets off and/or saddle is removed from crew on the upper floor.
I assume the rider use throwing weapon or hand-reloaded crossbow for their range weapon, which have lower poundage because using warbow or stronger poundage crossbow requires both hands to shoot and firm footing. That seems risky not include how to reload the high poundage crossbow, but maybe it can be achieved while sitting like horse archer. I don't know how horse archers work, so correct me if i am wrong.
**If carrying them as I described is impossible, what would biological back designs or modifications look like so a human can ride this big flying creature without hindering or injure them?**
I know there is a question: [Can somebody live being carried a long distance by a flying, predatory creature?](https://worldbuilding.stackexchange.com/questions/97604/can-somebody-live-being-carried-a-long-distance-by-a-flying-predatory-creature) This is what I have checked so far. But, it is mostly about the survivability of being carried/grabbing purely on the body, not even the possibility of flight. My question is about being carried using a swing or pouch not directly on the person body, like stork carrying baby, but held by the feet rather than mouth. Then, that makes me wonder about the possibility of a giant pelican mouth, but i guess it is probably best to ask that in another question.
the question [How to make a viable flying mount?](https://worldbuilding.stackexchange.com/questions/69163/how-to-make-a-viable-flying-mount) that revered as duplicate seems more asking how to carry human without any clear specification, and also seems more regarding carry or ride on the back and method of flying as far as i brief check the answer and the question, none or just a brief mention in one of the answerer talking about bird carry small mamals and thats it no further explanation, while mine is specifically about carrying by grabbing using their leg and have special saddle and iam not asking a method to fly no jet propulsion or baloon etc just simple bird type flapping or gliding to fly.
[Answer]
Science based reality check – no it would not be possible for any sort of bird to carry an adult human because the human would be too heavy. A small child might just be carried.
<https://www.quora.com/What-is-the-maximum-weight-a-bird-can-carry-while-flying>
If you want humans to ride birds I suggest a planet with lower gravity and a greater proportion of oxygen in the atmosphere would help greatly
[Answer]
I wasn't aware there were any horse-sized flying creatures. I suspect it's that pesky cube square law again.
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[Question]
[
**Story Premise**
I am writing a short story in which the protagonist believes his android assistant is demonstrating signs of consciousness. The android's mind is based on deep-learning artificial general intelligence and has progressed well beyond human comprehension. My protagonist does not know how consciousness could have emerged and is frightened by the ramifications. He feels the only person he can discuss this with is an old friend and work associate who's opinion he respects.
The largest portion of the story is a dinner conversation in which they discuss the nature and origin of consciousness and the possibility of a soul, in order to decide what must be done with the android. They each bring a variety of perspectives to the conversation. My protagonist is a former Chief Data Scientist now involved in AI for robotics; his dinner partner is also a Data Scientist and entrepreneur. My protagonist considers himself nonreligious with a lingering Christian mindset. His dinner partner is a faithful Muslim.
**My Problem**
I would like to keep the dinner partner Islamic if I can. However, I'm having a difficult time determining the Islamic view on emerging consciousness in AI, and whether consciousness amounts to a soul. There are plenty of papers and discussion threads on the Islamic perspective of whether a machine can have a consciousness or a soul (even here). But all are based on the premise that the android was *intentionally built* with consciousness. My premise is that consciousness *emerged*. For the nonreligious, it is, therefore, an emergent attribute of the universe. For the religious, God-given.
**My Question**
Is it possible for a contemporary Muslim (within the constraints of his faith) to believe that God would give an android consciousness? We'll leave the question of whether it has a soul out of it since I intend to leave that for the reader to ponder.
Feel free to give me homework.
(P.S., If you think another faith would be more fitting, I'm open to hearing your thoughts).
[Answer]
First of all, the Quran seems to state that [animals are conscious](https://en.wikipedia.org/wiki/Animals_in_Islam) and that therefore they to praise God (Allah), which is why they have to be slaughtered a particular way in order for their meat to be eaten; it is meant as a sign of respect to the animal and as a form of 'sacrifice' on the animal's part to humans.
That does not however answer the question of a soul; it would appear that most Muslims believe that the soul of an animal does not survive the death of the animal, and that the soul surviving death and being received in Heaven is the exclusive domain of humans.
From that perspective, I'm of the view that the most likely interpretation of this occurence would be that the Muslim would indeed believe that the consciousness carries with it the ability to praise God, but that it does not possess a soul, or at the very least, it does not possess a soul that can survive the death of the AI's consciousness. In that sense, it would have all the hallmarks of a very intelligent animal in the eyes of Islam, except for two very important considerations;
**1) Origin of the consciousness**
There is the possibility that a Muslim (or a Christian for that matter) may view a conscious AI as a creation purely of Man, not of God. As such, it could be seen as an abomination as it is attempting to play in a space that has up to this point been the exclusive domain of God.
One interpretation of this could be that Man creates the body and mind, but God gives it the spark of life that makes it conscious. That would be the easiest interpretation in a religious context to work with, but it's just as possible that it could be rejected entirely as a man-made construct attempting to play God, which could be received with hostility. This of course brings us to the most important exception;
**2) Consciousness is not Liveness**
As a researcher in this field, my comments on the nature of AI in terms of consciousness, awareness, and liveness are well and truly on the record in this site and others. Without rehearsing that research once again in its entirety, the practical upshot of it is that you can have a machine that is intelligent, displays awareness and is potentially 'conscious' according to a narrow interpretation of the word, but none of that makes it alive. We tend to conflate ALL these terms because it's only now that we're reaching the point in AI research where it is important to know the difference between them.
Even if a computer is conscious and aware of its own existence, that doesn't make it alive and it doesn't have the same underlying drives we have, like hunger or a survival instinct, to contend with. It will be able to simulate emotions but not feel them. In other words, we do not have to imbue it with the same 'rights' we imbue other living things, especially other people. As such, we can categorically state that it cannot and will never have a soul.
As such, it fails the first test of consideration in terms of religion; it's not alive. It gets all the same level of consideration as a rock or a tool. In point of fact, that's all it is; a very intelligent tool.
While it may be able to fool us otherwise because of the human propensity for anthropomorphism, a Muslim with training in data science and machine learning will know this machine for what it truly is; a machine. As such, I'm not convinced that religion would even come into it. If it did however, I believe that this creation would have a status similar to an animal, provided of course Islam is free to interpret the spark of consciousness as being the sole element God has provided to the project.
I will state for the record however that this is just one possible interpretation of belief from someone who does not practice Islam and is based on my own personal reading of the Quran and other research to further my own understanding.
[Answer]
This is a weird question, because you're asking if a religious Muslim would believe that an android would have a consciousness, but not a soul. I suppose that would be a sensible question from an atheist perspective because scientists view the ultimate facility of humanity being its sentience - man's thought processes and logical components. Hence the 'Turing' test - a test that determines whether a machine can perfectly mimic a human's behavior.
The thing is, if you start from a *religious* perspective, (and, to clarify, I'm discussing the Abrahamic religions here) consciousness isn't even a conversation starter. The soul is. And most of the rest of my answer is going to echo Tim B II's second answer - a quote 'freethinking' computer is just an illusion created by a complex program. No program truly has free will or sentience. It's just a tool. Even if the tool is kind of creepy as to how useful it is, it's still just a tool.
[Answer]
**TL-DR the verses quoted in [the question](https://islam.stackexchange.com/questions/2320/is-it-haram-to-make-humanoid-robots) render my question irrelevant. Having an Islamic dinner partner is a non-starter for the purposes of my story.**
Thanks, everyone, for all the input.
The first comment that I received (Thank you, John Dvorak) directed my attention to an Islamic board on Stack Exchange. I did some research there before asking, of course, and came up with this thread, [Is it haram to make humanoid robots?](https://islam.stackexchange.com/questions/2320/is-it-haram-to-make-humanoid-robots)
I originally chose Islam to honor a past co-worker who's opinion I always respected. I was modeling the dinner partner after him and felt this was a good way to introduce a perspective that differed greatly from my protagonist's. I full well intended to find a Muslim beta-reader, but now I see I can't even make it that far.
Back to the drawing board!
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[Question]
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If you search this site for "railgun", you'll find a lot of questions and answers. But none seem to talk about what the ammo wouls be made off.
Considerations:
* The small-arms have the energy storage and release to do what is necessary.
* Metals going in excess of 3000m/s (or getting hit by something of that speed) behave like fluids upon impact. <https://en.m.wikipedia.org/wiki/Hypervelocity>.
* For my question the small-arms accelerate the projectile to a maximum of 8000m/s on a length of 1m. Longer barrels don't accelerate further but can reduce the recoil.
Considering the above I would like to know:
Which materials would the projectiles best be made out of.
What shape should it be.
What kind of damage would it do against various targets (unarmored, armored infantry, armored tanks).
Would it be useful to add kinetic energy by spinning up the projectile in the barrel before firing.
[Answer]
energy = 1/2 mv2 where m is mass and v is velocity. A railgun round is a kinetic impactor and you want to maximize energy delivered by your kinetic impactor.
Considering first a railgun projectile in the atmosphere:
**Maximize mass.** In the atmosphere, the air hits the projectile as fast as the projectile hits the air, and as v increases losses of kinetic energy to air resistance also increase. If there is an atmosphere and any distance over which it will exert friction, it makes sense to maximize m which will not be affected by friction.
**Shape**. An artillery shell or a bomb delivers an explosive payload. The best shape to deliver maximal volume is a sphere. So a shell deviates from a sphere shape only insomuch as is necessary to stabilize it aerodynamically.
The shape of a kinetic impactor in atmosphere should maximize mass at the same time minimizing the forward profile = minimizing air resistance. This favors a long thin pointed projectile - which is how kinetic weapons look - both real kinetic impactors, railgun projectiles and fictional orbital kinetic "rod from God" type impactors. The smaller the forward profile, the less air resistance there is. Depicted - a real kinetic antitank weapon.
<https://en.wikipedia.org/wiki/Kinetic_energy_penetrator>
[](https://i.stack.imgur.com/JWOs2.jpg)
**Stabilization: fin vs spin.**. Fins use push by passing atmosphere to stabilize. Spin uses gyroscopic action to stabilize. Fins work fine for an arrow, or for a bomb falling from a plane. The problem with fins on a bullet (a small kinetic impactor) is that a bullet is pushed by expanding gasses and pressure in the barrel of the gun. The bullet (or shell) should optimally occlude the barrel to optimize push by gases. Fins get in the way of this occlusion so spin is a better answer for a bullet. Also nice is that the barrel itself can impart spin at the same time it confines gas pressure: the barrel does double duty.
I have wondered before why kinetic impactors and railgun projectiles had fins (which necessitates a sabot or external breakaway casing, which you can see in the image). I assumed the sabot was because a shape optimal for being propelled from railgun or cannon was not optimal for the projectile and so there had to be a shape change - this is probably part of it. I think you need a sabot to accommodate the fins. But why not spin the kinetic projectile like a rifle bullet? The fins make a little bit of spin but not like a rifle bullet.
<https://en.wikipedia.org/wiki/External_ballistics#Long_range_factors>
There are issues with spin which can cause "spin drift". The farther your projectile goes the more problematic this becomes. Also, because spin drift has to do with interaction between the side of the projectile and the air, the more side a projectile has the more interaction of this sort occurs - so for a long thin projectile spin drift would be worse. Probably even for spin stabilized projectiles like shells or rifle bullets there is a point where added stability from added spin is counteracted by increased spin drift - so there is a maximum of spin you should have before your payoff decreases.
So: a very massive kinetic projectile for long range use should be long, pointed and have fins. I suspect long range sniper bullets and antitank bullets might be better off with this configuration but I have never seen one (readers - if you have please insert image!). Maybe a sabot is just too fussy for small arms and if you are shooting over super long ranges you should have a mounted gun.
---
Yet here were are, in a fictional world where cyborgs with onboard aiming software are firing small railguns with long barrels like buffalo rifles. Can we have a projectile without cumbersome fins and sabots? **I propose that this small railgun projectile be spun internally**. Within the conductive housing (which would be silver, the best conductor) is a massive osmium cylinder. The cylinder is spun up to immense speeds while in the gun using something like a drill. The soldier will need to do the aiming first because once the projectile is up to spin it will be very hard to shift the gun laterally. The internal cylinder does not interact with the atmosphere to cause spin drift and the massive osmium retains its rotational inertia very well. This thing will fly straight, no sabot, no fins. The sharp tip is a diamond.
---
What will happen with this or any hypervelocity kinetic impactor: if it hits a yielding target it will continue through to the other side and along its path. A shockwave will propagate through air, fluid and solid spaces within the target, disrupting other things within the target. An unyielding target will heat up or break, and pieces of the target will fly in an expanding cone through more distal parts of the target (spalling), disrupting what they encounter; the shockwave described above will also form. A near miss will cause damage via the shockwave through the air; this is true and was described even for cannonballs.
Werewolf infantry will be very surprised. Hopefully they are advancing in a straight line right towards you.
---
Space: In space there are different considerations, because air resistance is not an issue. As noted here [Railguns designs for hand held rifles and spacecraft](https://worldbuilding.stackexchange.com/questions/101941/railguns-designs-for-hand-held-rifles-and-spacecraft). You will not lose energy to friction by the air and so there is no need for spin or fins. The shape should be that which is best accelerated by the rails. It is possible you might disregard mass in favor of projectiles which can be accelerated to very great velocities since energy increases with the square of the velocity.
I envision the space railgun, barrel a kilometer long, solar panels charging the capacitors. It then spits out a little superconducting beryllium bead full of pressurized hydrogen, moving at 0.9c.
[Answer]
Since the options are; conductive vs magnetic.
Exhibit A **Aluminum!**
Since the 2 poles extend across rails, the *inert, safe & cheap* projectile can be from aluminum. More speed since it is lighter. Means you can carry more ammo.
Exhibit B **Ferrous- steel**
Coils don't touch the projectile. Hence hardness isn't an issue over the barrel. Propel a fletchette of crude iron for deforming on impact. *orrrrrrrr* Kinetick penetrators of Steel. So you are firing Armor Piercing rounds.
Plus!
You can fire delicate rounds with tech or explosives, since there is no heat buildup.
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[Question]
[
Thanks in advance for any input you can provide!
I have a moon called Vieneo <http://www.risetvp.com/Vieneo> which has some geological modelling of faults and epicenters over some range of time:
[](https://i.stack.imgur.com/9k57x.png)
What we are trying to determine is what affects the theoretical maximum energy release these epicenters represent. For example, the Richter-scale goes to 10.0 but largest value we have seen on Earth is 9.5. Based on size, density, composition, hydrology, etc... what would would you expect the maximum Vieneo quake to be on the Richter-scale?
* Mean radius: 2939.6 km (0.46x Earth)
* Mass: 1.46x1024 kg (0.243x Earth)
* Density: 13.78 g/cm3 (2.5x Earth)
* Hydrosphere: 13% (darkest areas are low elevations)
[Answer]
The maximum size of a quake is determined by the strength of the rocks making up the tectonic plates. The closest figure you have relating to that is perhaps the density. However, you need to know the density of the planet crust, not the average density of the planet. For instance, you could have lower density (correlating to lower strength) crust than Earth, but a larger iron core and end up with a higher average density.
According to Steven Johnson, a professor of geology, quoted in [this article](http://sci-why.blogspot.com/2011/06/how-big-can-earthquake-be.html):
>
> "Earthquakes occur when rocks break in response to a buildup of stress," he said. "Imagine taking a long, skinny icicle and you start trying to bend it until it breaks. You will not have to expend too much energy before the icicle breaks, because the ice is fairly brittle and 'weak.' But if you took a similarly shaped wooden stick, it would take you considerably more effort to break the stick. In other words, the earthquake you produced by breaking the stick is greater than the one produced by breaking the icicle."
>
>
>
In the end, we don't even know how to reliably predict the maximum size of an Earthquake from the fault lines we study on Earth, let alone a fictional planet. For the same level of tectonic activity, the maximum Vieneoquake could be 11 or 12 on the Richter scale (10 to 100 times bigger, 30-1000 times more energy release), but they'd happen less often. Or it could be much lower and happen more frequently. It all depends on the rock strength for maximum size and tectonic activity for frequency. That is, rock strength determines maximum energy storage and tectonic activity determines the energy input rate.
[Answer]
In order to get a big earthquake, you must move a large fault plane. On Earth, the biggest earthquakes happen in [Subduction Zones](http://www.ldeo.columbia.edu/~djs/aleut/info_for_public.html) where you get shallow-angle thrust faults; these can have moving surfaces measuring hundreds of kilometers to a side. The energy release is proportional to the area moving and the distance moved - but as a bigger fault area can take more strain before moving, the distance moved is proportional to the fault area. Overall, then the earthquake energy rises as the [cube of the fault length](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.460.3240&rep=rep1&type=pdf). (See eqn 15)
SO, what does this mean for your planet? Assuming similar composition to Earth, the factor is actually going to be the presence of subduction zones, and/or the [geothermal gradient](https://en.wikipedia.org/wiki/Geothermal_gradient). The reason being that on Earth, subduction zones give anomalously large earthquakes, dwarfing any others by at least an order of magnitude. If your planet has subduction, then that's where the biggest ones will be.
Outside of that, the key is the geothermal gradient. Earthquakes can only happen in brittle rocks; and at a certain temperature, rocks become sufficiently ductile that faults move by a aseismic slip. On earth, this limits the size of earthquakes by limiting their vertical rupture length - so the San Andreas fault cannot generate earthquakes greater than magnitude 8, for instance.
Your fictional planet is smaller than Earth, and therefore it might have lower internal heat generation and a lower thermal gradient. This in turn would allow for larger fault depths and therefore bigger, but less frequent Earthquakes. Perhaps up to magnitude 9 on a strike-slip fault like San Andreas, or magnitude 7 or so in an area of extension like the [basin and range province](https://en.wikipedia.org/wiki/Basin_and_Range_Province). The increased density (how?) would probably drive tectonics faster.
So, overall, assuming earth like composition (in the surface few hundred km at least), les frequent Earthquakes of a greater magnitude than Earth. Add 1-2 richter numbers to the ones you'd get in a similar tectonic setting.
] |
[Question]
[
The planet orbits a supermassive gas giant, almost double the size of Jupiter. But the planet orbiting it is also supposed to have rather large rings in my story.
**Question:** Is it possible for a moon of a gas giant to have stable rings?
I expect the answer to be no, because of the gravity from the gas giant. Am I right in this assumption? And if I am right is there any way to make it possible for the planet to have rings? In a plausible / semi-plausible way.
[Answer]
**The answer to your question is yes but.**
It is certainly possible for a moon of a giant planet to have a ring, but the key word in your question is “stable”. What do you mean by stable? A year, a century, a millennia, 50 millennia, a million years? Any of these might be considered “stable” at some level.
The problem is that asking how long such a ring would last for is a very complex question. It would depend on the orbit of the moon, the mass of the moon relative to the planet, the presence of other moons, their sizes and orbits and many other factors.
But as a thought experiment to suggest that it should be possible, consider a series of cases starting with a Jupiter sized planet and a moon, could the moon have a large ring – debatable… now imagine increasing the mass of the planet in stages eventually the planet is so massive it becomes a brown dwarf and then a star, by the time it’s a star the moon is better considered to be a planet.
Could a planet have a ring in a binary system, I suggest yes it could.
As the mass of the planet increase so does the stability of the moons ring, but how much mass is required to produce how much stability is very difficult to say.
[Answer]
The possible rings of Rhea have already been mentioned in the comments, but [Iapetus](https://en.wikipedia.org/wiki/Equatorial_ridge_on_Iapetus) is theorized to have once had rings. The moon has a huge equatorial ridge along its equator that could be the result of material from a ring system accumulating on the surface of the planet.
I think you could give your moon rings, but they would likely be thin, hard to see, and possibly unstable in the long run. However, since habitable gas giant moons are pretty theoretical, I think it's okay if you push the boundaries of realism.
[Answer]
General information here: <https://en.wikipedia.org/wiki/Ring_system>
It looks now like Saturn's rings are fairly long term stable.
A similar question came up on Astronomy SE: <https://astronomy.stackexchange.com/questions/20514/what-stabilizes-rings-or-accretion-disks>
And over in physics: <https://physics.stackexchange.com/questions/26643/why-arent-saturns-rings-clumping-into-moons>
The problem would be tides. Saturn has rings. It orbits the sun. The larger moons create and maintain the gaps in the rings that correspond to resonances with the moons.
Tidal forces go as the inverse cube of the distance. Put your moon far away.
Also give them shepherd moons to help keep them corralled.
Net conclusion: I think you are on solid enough ground to proceed with your story.
[Answer]
Stable is indeed the magic word here. The moon in your question has its own gravitational field, so if the ring particles are close enough to the planet, they could have a "stable" orbit. Loosely speaking, the moon's gravitational pull is able to overcome the planetary gravitational field for sufficiently small orbital distances between the moon and the ring particle.
The "sufficiently small orbital distance" here is called the "Hill radius". A ring particle orbiting *well within* this distance will have a *reasonably* stable orbit. Lots of weasel words there, but orbital stability is a sack full of weasels.
An approximation of the Hill radius for a moon in orbit around a larger planet is pretty straightforward to calculate, but I'll leave that to you.
] |
[Question]
[
This is a follow up to [What would physics be like in a wrap-around universe?](https://worldbuilding.stackexchange.com/questions/31184/what-would-physics-be-like-in-a-wrap-around-universe)
PyRulez commented, “Will gravity still make sense? (Namely, will it converge or not)?”
This was bantered about in the comments and one idea was mentioned briefly in one of the answers. But I’d like a more in-depth explanation.
There are several “obvious” answers that disagree. One can draw contour lines representing the potential on a spherical or toroidal map and note that it doesn’t explode or anything; this defines a navigable space useful in a game perhaps. But I think that ad-hoc field **doesn’t** follow the normal rules of falling off with the square of the distance. If you modeled it as normal space with infinite repeating grid of masses, would the field strength converge, blow up, or become chaotic, or what? Given this, what modification makes sense to produce a sensible wrap-around universe that is still mathematically sensible?
---
**Edit**: it appears that much of the “different answers” is due to the chosen topography. In particular, the video-game-screen wrapping which is easier for mental musing is not isotrophic.
I'm less interested in imposing something ahead of time than in learning what *does* work; conversly, what “interesting” universe parameters might be available for stories/games having more exotic situations.
[Answer]
I can give you a Newtonian analysis of the situation, which may or may not be correct. If you want a Newtonian universe, then great. If you want a general relativistic one, you'll need something more complicated.
# Example 1: Square domain
As a simple introductory example, let's say your universe is a rectangle with sides of length $l$. In other words, if you travel $l$ units in the $x$- or $y$- directions, you return to where you started.
Consider an object with mass $m\_1$ at $p\_1=(x\_1,y\_1)$ and a second object with mass $m\_2$ at $p\_2=(x\_2,y\_2)$. For simplicity, I'll set $y\_1=y\_2$, so the objects are a distance $x=|x\_2-x\_1|$ units apart. To find the force on $m\_1$, we have to create an infinite sum of all the forces on that object from the object on $p\_2$. Let's first look at the forces from the $+x$ direction. We have
$$\sum F\_{+x}=\sum\_{i=0}^{\infty}\frac{Gm\_1m\_2}{(x+il)^2}\tag{1a}$$
Likewise, we can do the same for the forces on $m\_1$ in the $-x$ direction:
$$\sum F\_{-x}=\sum\_{i=0}^{\infty}-\frac{Gm\_1m\_2}{((l-x)+il)^2}\tag{1b}$$
According to [Wolfram Alpha](http://www.wolframalpha.com/input/?i=sum+from+0+to+infinity+of+1%2F(x%2Bi*l)%5E2&rawformassumption=%22i%22+-%3E+%22Variable%22), the sum
$$\sum\_{i=0}^{\infty}\frac{1}{(x+il)^2}$$
converges1, and since $\text{(1a)}$ is simply this multiplied by $Gm\_1m\_2$, that must converge. The same logic holds for $\text{(1b)}$, as we've just inserted $(l-x)$ for $x$ and multiplied it by $-1$. If we add two convergent series, the resulting series must also converge. Therefore, on a square domain where the masses are separated by a distance parallel to a side, the force is finite:
$$\sum F=\sum F\_{+x}+\sum F\_{-x}$$
# Example 2: $n-1$-dimensional sphere (isotropic universe)
This easily generalizes to a special case. Let's say that we view our universe as the surface of an $n-1$-[sphere](https://en.wikipedia.org/wiki/N-sphere)2. In other words, in [set-builder notation](https://en.wikipedia.org/wiki/Set-builder_notation),
$$\text{Universe}=\{p(x\_1,x\_2,\cdots,x\_{n}):\sqrt{x\_1^2+x\_2^2+\cdots+x\_{n}^2}=R,\quad x\_1,x\_2,\cdots,x\_{n}\in \mathbb{R}\}$$
where $R$ is the radius of the universe. This is an $n-1$ dimensional universe embedded in $n$-dimensional space. In this $n-1$-dimensional space, there is no preferred direction, i.e. it is [isotropic](https://en.wikipedia.org/wiki/Isotropy). Therefore, for any two points $p\_1$ and $p\_2$ in the universe, we can connect them via a one-dimensional [geodesic](https://en.wikipedia.org/wiki/Geodesic), the shortest distance between them, on the sphere. There are actually going to be two paths, going in opposite directions, just as we had ones with length $x$ and $(l-x)$. One will be the geodesic, and the other will be in the opposite direction. For finite $R$, these paths should have finite length, and so the sums of $\text{(1a)}$ and $\text{(1b)}$ should hold.
Let's be careful, though. In $q$ dimensions, gravity falls of as
$$F\propto\frac{1}{r^{q-1}}$$
and so in this universe, we have
$$F\propto\frac{1}{r^{n-2}}$$
Setting $p=q-1$, Wolfam Alpha seems to indicate (by repeated trials up to $p=5$) that this type of sum (and thus the total force) converges for all $p\geq1$, with $p$ an integer. Therefore, for all $n-1$-spheres in two dimensions or more, the force of gravity should converge (it diverges in one dimension, where $p=0$).
# A proof for all simply-connected universes
Thanks to some comments by kingledion, we can come up with a rigorous proof for convergence on a number of [simply-connected](https://en.wikipedia.org/wiki/Simply_connected_space) Euclidean spaces. We deal this time with a wraparound $n$-dimensional universe of finite size3:
$$\text{Universe}=\{p(x\_1,x\_2,\cdots,x\_n):p(x\_a,x\_b,\cdots,x\_i,\cdots,x\_n)=p(x\_a,x\_b,\cdots,x\_i+l\_i,\cdots,x\_n),\quad x\_1,x\_2,\cdots,x\_n\in\mathbb{R}\}$$
equipped with the standard Euclidean distance metric
$$s=\sqrt{x\_1^2+x\_2^2+\cdots+x\_n^2}$$
The $l\_i$s may have the same for all $i\in\{1,2,\cdots,n\}$, as was the case with the $n-1$-spheres, or they may be different, as would be the case if we did Example 1 on a rectangular domain. You can travel along any Cartesian coordinate a certain distance - and you can redefine the coordinate system (i.e. by rotating it), meaning you could travel "diagonally" in Example 1. You'd just need to write out a new coordinate system with new $l\_i$s.
We write our net force equation as before:
$$\sum F=\sum F\_{+x\_j}+\sum F\_{-x\_j}$$
and, as with $\text{(1a)}$, we have
$$\sum F\_{+x\_j}=\sum\_{i=0}^{\infty}\frac{Gm\_1m\_2}{(x\_j+il\_j)^p}=Gm\_1m\_2\sum\_{i=0}^{\infty}\frac{1}{(x+il\_j)^p}=\frac{Gm\_1m\_2}{x^p}+\sum\_{i=1}^{\infty}\frac{1}{(x+il\_j)^p}$$
where I've set $p=n-1$. Let $l\_j=1$, and let $x>0$4. Take a step back and look at the [Riemann zeta function](https://en.wikipedia.org/wiki/Riemann_zeta_function), given by
$$\zeta(p)=\sum\_{i=1}^{\infty}\frac{1}{i^p}$$
Now, for each positive integer $i$,
$$x+il\_j>i$$
by our criteria, because $il\_j\geq i$ and $x>0$. Therefore,
$$\frac{1}{x+il\_j}<\frac{1}{i}\implies\frac{1}{(x+il\_j)^p}<\frac{1}{i^p}$$
It holds, then, that
$$\sum\_{i=1}^{\infty}\frac{1}{(x+il\_j)^p}<\zeta(p)$$
$\zeta(p)$ is finite for all positive integer $p$, and so it holds that the left sum is finite, and thus convergent. The $i=0$ term, which we removed, is also finite for $x>0$, and so the overall sum $\sum\_{i=0}^{\infty}F\_{+x\_j}$ converges, as does $\sum\_{i=0}^{\infty}F\_{-x\_j}$. Therefore, the total force is finite.
There's one important caveat here. Take a point $p\_\*\in\text{Universe}$. Move in some direction $x\_i$. The idea of a wraparound universe assumes that when you next reach $p\_\*$, you've traveling in the same direction as you were when you left. In other words, your velocity vector at the moment you reach $p\_\*$ again is parallel to the velocity vector when you left.
What if this wasn't the case? Well, we could imagine a topology where you leave $p\_\*$ going in the $x$-direction, and return to it from the $y$ direction. This introduces a totally new direction for the force to act on. While the proof of convergence still holds - because you'd have to travel a distance $l\_x$ to finish the full cycle - you also have to consider this weird force in a different direction. So gravity would still be finite, but . . . odd. I'd rather not consider those cases.
# More universes
I can't generalize this to all wraparound spaces, although I suspect that gravity may converge for many, if not all, Euclidean surfaces. I can't say much more for many [manifolds](https://en.wikipedia.org/wiki/Manifold) in general, as the [distance metric](https://en.wikipedia.org/wiki/Metric_tensor) (for those manifolds equipped with one) will likely not resemble the familiar Euclidean metric I used in the proof.
Indeed, general relativity would be needed for a truly accurate answer here. However, for the simplest sort of universes, using Newtonian gravity, I believe the force of gravity will indeed converge.
# Musings
* In [their answer](https://worldbuilding.stackexchange.com/a/73649/627), Schwern stated that the speed of light could have an effect, and assuming the Newtonian model (i.e. that gravity travels infinitely fast) would have a different result than modifying it so that gravity travels with some finite speed $c$. I talked this over [in chat](http://chat.stackexchange.com/transcript/message/35955923#35955923) with kingledion, and I believe this isn't a problem.
Take two objects at points $p\_1$ and $p\_2$ with masses $m\_1$ and $m\_2$, where $p\_1,p\_2\in\text{Universe}$. This universe can have any classic wraparound topology you want. At time $t=0$, these object are a distance $x\_0$ away from each other. However, the first object moves at some non-zero angle from the geodesic connecting the two. Therefore, at any time $t'$ the objects will interact as they were some time *prior* to $t'$. The argument was that this would add a weird force vector component not present in the infinitely fast gravitational model. This is because it would take the force of gravity different amounts of time to travel in each geodesic, specifically, a time $t\_p=s\_p/c$, where $s\_p$ is the length of a geodesic.
Here's why this doesn't work. In normal Newtonian physics problems in our wacky universe, we assume that gravity acts directly between two objects. It instantaneously "knows" the shortest path between them at any time. That's not really the case. Let's say that gravity takes an infinite number of paths between both objects. Each path $C$ has a distance $s\_C$, and it thus takes a time $t\_C=s\_C/c$ for the force to travel that far. However, for that path, we can also create another path $C'$ with the same distance, just in the opposite direction, like flipping something along an axis. That axis here is the geodesic between the two points. The only paths that don't cancel are that geodesic and the path opposite it.
This means, of course, that we don't have to assume that gravity "knows" where to go. That would be absurd. A point object with a mass creates a gravitational potential that is isotropic, and so a mass at any point could feel it. You can define a vector field $\vec{a}$ at any point giving the acceleration due to gravity. Therefore, in our example, we know that the object is going to be influenced by the gravity of the other no matter whether or not it's moving. We simply have to realize that this time, the paths that don't cancel aren't the original geodesic and its partner, but a new geodesic and its partner, connecting the new position and the position of the other particle.
* In these universe, [Bertrand's theorem](https://en.wikipedia.org/wiki/Bertrand's_theorem) might not hold. Simply put, it states
>
> are only two types of central force potentials with the property that all bound orbits are also closed orbits: (1) an inverse-square central force . . . and (2) the radial harmonic oscillator potential.
>
>
>
Assume our universe is a sphere. Place two particles on opposite sides, such that all of the forces between them cancel out. They're in an unstable equilibrium. Now, give them non-zero velocities such that the velocity vectors are exactly parallel. They'll move around the sphere and come back to where they started. The potential between them wasn't an inverse-square force potential; it was proportional to $r^{-1}$. However, the orbit was still closed! Actually, take a solitary particle on the sphere. Now give it some non-zero velocity. Even though the surrounding potential is zero, the orbit is closed.
Perhaps this doesn't violate Bertrand's theorem. It's not clear whether these particles are "bound"; there's no force between them, and so gravity isn't really affecting them. However, we could place *three* particles around the sphere, spaced apart evenly on a circle. Between any two, there is a non-zero force, but they're all at equilibrium because a third particle balances out the interactions. There *is* a non-zero force between any two particles. Again, this may not a "bound" orbit, as the force isn't influencing the motion at all. So it's not clear whether or not this is a workaround.
I suspect the above example fails for some reason, at least in a two-spherical topology. However, maybe there are other universes in which there are indeed exceptions to Bertrand's theorem. Exploring the relevant orbital mechanics would be interesting. Anyone up for simulating orbits on an $(n-1)$-sphere?
---
### Notes
1 Specifically, it converges by the [root test](https://en.wikipedia.org/wiki/Root_test), which you could do be hand, if you so desired, and gives us the result
$$\sum\_{i=0}^{\infty}\frac{1}{(x+il)^2}=\frac{\psi^{(1)}\left(\frac{x}{l}\right)}{l^2},\quad l\neq0$$
Here, $\psi^{(n)}(x)$ is the $n$th derivative of the [digamma function](https://en.wikipedia.org/wiki/Digamma_function).
2 In this notation (standard in mathematics), the surface of a circle is a one-sphere $S^1$, the surface of a round ball is a two-sphere $S^2$, etc.
3 This set doesn't define the space as being simply connected; it says nothing about its overall topology. However, those assumptions are implicit, and harder to write in set-builder notation. If I can come up with a rigorous proof for all Euclidean universes, I'll add it, but it could be hard - at least, it doesn't seem apparent at the moment. An interesting universe excluded here is the torus, which I could probably figure out if I had the time; it is multiply connected.
4 Here, $x$ is really given by
$$x=|\mathbf{x\_1}-\mathbf{x\_2}|$$
where $\mathbf{x\_1}$ and $\mathbf{x\_2}$ are the position vectors of the two masses.
[Answer]
Using the Gauss formulation of the law of gravitation. The integral of the inward force over a surface is equal to the mass within it. If you have a simply connected spacetime you can expand your volume untill it fills all of space ( even with a non simple spacetime you can fill all of space except a few surfaces and assuming continuous gravitation, no singularities) Then the surface integral becomes 0.
The universe must contain the same amount of positive and negative mass.
If we consider a wraparound square universe containing only a small mass then the gravitational pulls in each direction are infinite, but these cancel to yield a finite gravitational pull. However if the mass is non spherical and rotating, tidal forces fall off inverse cube, mass in a shell increases with the square of distance.Consider two shells of identical thickness but radius differing by a factor of 10. While the mass 10x further gives only 1/1000th of the force per mass, there is 100X more mass and so 1/10 the force. The total force from all the shells is some constant\*(1/1+1/2+1/3+1/4...1/n) which diverges to infinity.
These arguments prohibit any wraparound or infinite isotropic universe with locally normal gravity from having existed an infinite time with no damping effects on the propagation of gravity.
[Answer]
I'm going to assume your universe isn't infinitely old and follows the same basic rules ours does.
>
> *If you modeled it as normal space with infinite repeating grid of masses...*
>
>
>
There's problems with that approach. First is ***gravity propagates at the speed of light***. If your universe is large enough, or expanding rapidly enough, gravity won't have had time to "wrap around". If it has, it can only have done so a finite number of times. So no, you wouldn't model it as an infinite grid of masses.
Even if it had, gravity's strength falls off as the square of the distance. Each time it wraps around the universe it's getting exponentially weaker. The effect of subsequent trips around the universe is greatly diminished and will sum to a finite number (I think that's [what HDE is proving](https://worldbuilding.stackexchange.com/a/73627/760)).
---
But let's say gravity propagates instantly. There is no additional net force because the force of all those repeats cancels out. Here's why.
Let's assume a 1D universe 10 units wide. Let's say we have two objects, one very massive and one with very little mass. The massive object is at 0, the small one is at 5. So it's feeling the gravity of the massive object from 5 units away.
```
* .
0 5 10
```
This universe wraps around, -10 and 10 are the same.
```
* .
-10 -5 0 5 10
```
That means, effectively, there's another massive object out there 15 to the right.
```
* . *
-10 -5 0 5 10 -5 0
```
But wait, there's also one to the left at 25 units.
```
* . * . *
0 5 -10 -5 0 5 10 -5 0
```
But wait, there's also another one to the right at 35 units.
```
* . * . * . * .
0 5 -10 -5 0 5 10 -5 0 5 10 -5 0 5
```
But wait, there's also another one to the left at 45 units.
But wait, there's also another one to the right at 55 units.
But wait, there's also another one to the left at 65 units.
But wait...
What you wind up producing is a repeating line. There's an infinite number of masses to the right, and an infinite number of masses to the left. The net distance between our object and all the infinite masses is 0. Here's the proof using a generalization of [Cesàro summation](https://en.wikipedia.org/wiki/Ces%C3%A0ro_summation).
If you sum up the distances between the objects, we get a series.
```
5 - 15 + 25 - 35 + 45 - 55 + 65 - 75 ...
```
At first glance that diverges, and it does, but we can get a summation out of it. Does it oscillate around a number? Look at their partial sums.
```
5, -10, 15, -20, 25, -30, 35, ...
```
And take their mean values.
```
5, -5, 5, -5, 5, -5, 5, -5
```
All the positive values converge at 5. All the negative values converge at -5. So that series is summable to 0. This is the same technique used to show that [1 - 2 + 3 - 4 ... is 1/4](https://en.wikipedia.org/wiki/1_%e2%88%92_2_%2b_3_%e2%88%92_4_%2b_%e2%8b%af).
The net distance is 0, but does that mean net gravity is 0? I don't know how gravity works in 1 dimension, but let's assume it's still Gm/r^2. Set G and m to 1 and we get another series.
```
d = 5 - 15 + 25 - 35 + 45 - ...
g = 1/25 - 1/225 + 1/625 - 1/1225 + 1/2025 - ...
```
This is converging around 0.0367. Without a wrap around universe there'd be a pull of 1/25 or 0.04. So that means there's a slight negative pull of about 1/300.
The point of all this is to show that a wrap around universe with infinitely propagating gravity can be resolved. Scaling it up to multiple dimensions is outside my math and physics skills.
] |
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