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This question is tangent of this [one](https://worldbuilding.stackexchange.com/questions/372/how-can-magic-and-the-economy-reliably-stand-together). While reading about the world-building that went into the [Mistborn](http://en.wikipedia.org/wiki/Mistborn_series) series I began to reassess my own world-building, specifically the effects of magic on the economy. I realized that the magical material in my setting would be more valuable than gold and oil combined, because it is the only way to produce items endowed with magic, which—unlike the talent for being a mage—can be mass produced.
The magic material is a living material that appears crystalline. grows slowly by leeching nutrients the ground. In addition to being magical this material is a desirable additive in both metal work and ceramics. Because of its light weight, strength and flexibility.
**My question is this:** The nations in my world base their economies on a rare but renewable commodity. What are some of the effects that it has on their cultures and policies?
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> My question is this: The nations in my world base their economies on a
> rare but renewable commodity. What are some of the effects that it has
> on their cultures and policies?
>
>
>
This is not in fact so very different from what we have today. In the end all economies are based on commodities. Note that is plural. **An economy cannot function (for long anyway) if it is based solely on a single commodity.** Diversification is very important to domestic long term stability.
It all comes down to wealth and good 'ol supply and demand. An economy based on a single export...oil for example, which makes a good modern example. Nations that rely on a single commodity are in significant trouble should that commodity fall. [Oil and the 1980's](http://en.wikipedia.org/wiki/1980s_oil_glut)
If this is the single most valuable thing on the planet and it is always in demand (consider that someone will try to come up with an alternative) then you have to ask some questions:
* How much is there?
* How fast does it grow?
* Can it be harvested to extinction?
* How evenly distributed are the crystals globally? (and locally within nations for example)
* Can anyone effectively use it or does it require specialists?
Depending on your answers to these questions it can impact many things. Mainly you need to think about how it impacts the following:
* Wealth distribution, concentration will determine who has how much. Notions of land ownership could be interestingly affected with something this valuable.
* Quantity. If this is a very limited resource then wealth will be consolidated. That happens to be true in our world as well but if this item is more rare it will be an even smaller group of wealthy folks.
* Power. Arguably whoever has this stuff can manipulate world politics. This happens today with fuels and some other natural resources. Wealth = Power in many situations, if what gives you wealth also grants you personal magical power you are rich and powerful...and probably evil...probably.
A system like this can lead to a whole host of differences in the world. Perhaps it has led to the development of an all powerful magocracy (I made that word up) that rules the world with an iron fist. Perhaps the crystals are strictly controlled and used only for public works...I think the sky is the limit for how something like this alters culture and social policies but the impacts to the global marketplace are probably not a big change from how the world developed in reality. People will still need other stuff...you can't eat these crystals...*or can you?!*
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So. Currency. I think I may have skimmed over the currency aspect as the question in your OP and the title differ slightly in context (economy versus currency).
I am going to use sugar as an example of a renewable commodity. This is a chart from 1950 to 2015 prices from [Trading Economics](http://www.tradingeconomics.com/commodity/sugar)
You notice that there are many rapid swings in the value of sugar. This would wreak utter havoc on an economy mainly because it makes gauging the value of things very difficult. I will not claim that the value of gold does not change, it certainly does (see for yourself on the site). But gold is not impacted by weather. Sure it's value changes BUT it is not as susceptible to rapid changes in value.
The impacts would mainly be a greater potential for rapid shifts in the value of your currency. This makes the currency unreliable, meaning many may not even be willing to use it rather going with bartering or unofficial currencies...gold coins maybe ;)
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It would probably be closer to an oil based economy than a gold based one. This is because most of it's 'value' is in it's use. if you don't use oil to make things with it, it isn't very valuable. So this magic would be 'collected' for use and trade, but even though it is'renewing' it is also being used (disappearing).
Kind of like the [cocoa bean](http://encyclopedia-of-money.blogspot.com/2010/01/cocoa-bean-currency.html) as currency someone else recently mentioned. It is something that would have to be common enough to warrant being used as currency but no so much as to be commonplace. You don't want it as common as sand, but more common than uranium deposits.
It would probably be a fairly reasonable economy, more like a barter system, since the thing being used for currency is the value, it's more 'real' than gold, since gold's primary 'value' is in it's rarity and 'prettiness'.
EDT: One large consideration would be how 'evenly' spread the crystals are. if one providence has a lot and some or most don't then a small minority could be filthy rich and control a lot of the power. It would also likely be the 'power-base' or capital of the country.
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There'd be no effect - the government would create fiat money and not "back" it with anything. Much like today's money, which gains its value from the government and its use as a medium of exchange.
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This is my first question on this Stack Exchange; I hope that I am following your posting guidelines correctly.
I am not someone who writes books (or is writing a book), but I do like to write short stories for my own entertainment. Most of my education is in computer science, cellular biology, and medicine.
When I was in undergrad, I learned (to my surprise) that cancer risk approached 100% as length of life extended. To put it another way, if you live long enough you'll die of cancer. Also, the reason for cells to become senescent is heavily linked to the shortening of telomeres. This made me think about a cure for cellular aging that involved a protein drug able to extend telomeres, at the cost of highly mutagenic properties.
So, now to the question: **What would be the societal implications of cheap immortality that came with a vastly increased risk of cancer?**
In this situation, there would be no "maximum" life span, just a statistical one - how long on average a person lives before they express a malignant and untreatable form of cancer. Let's also say that most people die very quickly (~1 month) after cancer expression.
I would guess that most people would opt for the treatment, as in this scenario we will assume that the statistical life span is longer than what people would normally expect.
My guess is that it would lead to much more reckless/short-term-focused behavior, as even though median life span would be increased you would never know when you would die.
Love to hear any thoughts on this subject!
EDITS:
**Immortality**
I'd like to note that when I say "immortality" I am using the definition of "non-aging but able to be killed by other means, such as disease or a fatal wound".
I think that this is an important distinction. Although it is (IRL) technically possible to die at any moment due to a freak occurrence or accident, most people tend to assume they will live to a certain age.
In this scenario, there is no "expected" age to which someone will live; they could suddenly die of cancer at age 20 or live to be hundreds of years old. Age at time of death wouldn't follow a predictable distribution around the mean/median. This unpredictability is what I think would have interesting implications.
**Cancer**
The vast increase in cancer risk would be for a specific type of malignant, quickly-progressing cancer which is very rarely seen nowadays. Otherwise, as pointed out below, everyone would die of cancer fairly early. Sure, this isn't exactly how a classic mutagen works but since it's a theoretical pharmaceutical we can bend the rules a bit.
Thanks for the thoughts so far!
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Any time you cure a killer, the % of being killed by the other killers goes up. Someone had a study with some medication and it seemed to be working (I think it was a heart medication) and the incidents of heart attacks dropped, but death by car accident went up significantly. It panicked the testers and they took if off the market.
They assumed, that even though there was no proof, that the medication was causing the accidents. When it is the exact scenario you want. True immortality will come when people only die in accidents (or intentionally). So as long as the treatment that increases cancer adds even 50 years on average to a life most would take it.
As it is cancer is Russian roulette and the longer you play the better your chances are of being shot. So as other health issues are reduced cancer becomes a bigger and bigger threat by default. We are also making great headway into treating cancer so even if you get it, that chances of dying continue to reduce.
If a very specific type of cancer is caused by this treatment, then it will be the primary focus of a large % of research funds to either prevent or cure it.
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I've heard that same stat used for dying by being buried alive...as you fix other problems and become less vulnerable, the chance of dying from one of the other causes goes up.
The stat says nothing about immortality increasing your chance of cancer. If it did, then the 'eternal life' would have to be balanced against the decrease due to cancer risk. If this was negative, it wouldn't be worth taking the treatment.
The behavior changes seems a stretch, as we already live with not knowing when we die.
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This wouldn't be anything like immortality. You already have about a 40% chance of getting cancer and half of the time it will kill you. (And I believe this is an understatement as they define "cured" in a fashion I don't consider acceptable.)
A vastly increased cancer risk simply means everyone dies of cancer.
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I'm working on a simulator-type game which I want to be at least internally consistent, and which I'd like to work as close to reality as possible. That being said, it's set in space, which means to avoid player boredom there needs to be some kind of FTL travel.
I'm trying to work in functional analogs to the four general categories of FTL travel (warp, jump, gate, and hyperspace) and I think I've managed to work it down to only two core mechanics – the Alcubierre Drive and a modified version of Alderson Points. Originally I was going to use stabilized wormholes in place of Alderson Points, but after looking into it I found that that makes it easy to build a backwards time machine (which is annoying/impossible to reliably implement in something like an MMORPG), so after failing to figure out how to "break" all of the versions of the time machine as per the Chronology Protection Conjecture, I gave up and started working through other mechanics.
After expanding on the original Alderson Drive concept for story, time, and map reasons, I've come up with the following list of desired/assumed mechanics for the points.
* Suitable points exist naturally (~1-5 per star system) positioned based on rules which have yet to be determined, but preferably there's always at least one within 0.3 AU of the habitable zone.
* Points don't "orbit" the host star, and they probably don't exist in and of themselves; they are either stationary relative to the star or they revolve based on the position of other large bodies similar to the Lagrange points. (One or the other, not both, I just haven't decided yet in case physics decides for me.)
* Points are tied to networks; they can all connect to more than one point, but only within their network. Being in the same network involves always having the same inertial frame of reference, though that may just be a side effect of some underlying reason.
* Using the points involves "charging up" the points with a device on your ship for an amount of time (i.e. not instantaneous or measured in nanoseconds, but also not measured in hours or days unless the drive is broken or poorly tuned). The destination is selected by how much energy is "dumped in." (This will likely be proportional to the distance between the points, but may need to be related to the ship's mass as well.)
* While the point is being charged, both the source and the destination with the energy level closest to the current level give some kind of indication that they're being activated (e.g. "spontaneous" EM radiation, visible or otherwise, possibly similar to black body radiation but emitted from a field).
* When the drive is turned off, provided the input energy precisely matches what is required to connect to a destination, all of the the matter within a certain radius of the source and destination points is instantaneously swapped. (The definition of instantaneous, in this case, is "now" according to the point network's reference frame.)
* Artificial point networks can be constructed using devices ("stargates"), though this may not actually need to be explained because I could easily say that "the Ancients/Precursors/Forerunners built the devices and we don't know how they work" or something to that effect.
Now here are my questions:
* Most importantly, can this set of mechanics be used by itself to violate causality – and not just apparently from an extraneous reference frame, but literally be used to either tell yourself not to do something before you were going to do it or, in the more serious case, "take half a critical mass of Plutonium back to meet itself"? If so, what could I change to make it impossible?
* Can it be used in concert with something else to violate causality? If so, what would be necessary/what should I watch out for?
* Are there conditions related to causality violations that could dictate where I need to place the points inside of the star systems or the nodes in the point networks inside of different star systems?
* Is there any possible scientific or pseudo-scientific base I could latch onto to try to explain some/all of these mechanics? (The original version mentions "Equipotential Thermonuclear Flux" but I thought I'd try finding something that sounds a little more real...)
* What should happen near the "edges" of the effective area of the points? Or should I just say "nothing good happens" and make determining the radius a function of the drive construction so that individual ships shouldn't ever have to care?
* Is there a way (plausible or not) that I could pull this out into also enabling FTL communication? Because, like I said, my accidental time machine ruled out movable wormholes, and therefore my only lead on how to make an Ansible. If I have to, I could use something like the "space pony express" where ships download mail, pop through, and offload it, and for urgent/secret messages use unmanned probe "carrier pigeons," but I'd like to figure out a way to do it without physically sending matter to the destination (i.e. "subspace radio") if possible.
(Note: I would have asked this on the Physics StackExchange, but I'm pretty sure it crosses the fictional "line" so I decided to ask here first because of their definition of "on-topic.")
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[FTL time paradoxes](http://www.theculture.org/rich/sharpblue/archives/000089.html) generally use one or both of the following circumstances:
1. A round trip between two objects that are moving (relative to each other) at a significant fraction of light speed.
2. A wormhole that allows physical contact between two separated locations simultaneously.
An Alderson style system can avoid trouble if:
1. The traveling object is (briefly) removed from communication with the universe, then brought back in at the other end.
2. The endpoints are reasonably stationary and cannot be artificially moved.
3. You cannot return to your starting point "quickly" (aka before you left).
Here's some math which may or may not make physical sense (IANAP). The Sun and Wolf 424 have a relative motion of about 555 km/sec (0.0018 c), with a relative time dilation of 0.0000017. At 14 light year distance, that's a discrepancy of about 13 minutes. As long as your charge up delay is that long, causality should be safe. That should be the worst case; other nearby stars have less relative motion, allowing for shorter delays.
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If you can do FTL travel, you're going back in time according to some potential observers. If you can do FTL travel in different reference frames, you've got time travel. If you say FTL only works in one reference frame, you're ditching Special Relativity, and I'd rather not do that. It is the solution of choice for fiction, since it isn't completely intuitive and audiences usually don't notice it being broken.
The idea of putting the Alderson points all in one reference frame seems brittle to me, at least if you like relativity. It's extremely unlikely that a universal reference frame will match ours reasonably well, and so it works better if the reference frame can change gradually over space.
Given that you have a fixed number of discrete Alderson points, you can fake an ansible pretty easily. You have information-carrying drones that do endless round trips between Alderson points. They pop out of the communication station near point A, hop to B, transmit and receive information with the communication station near point B, then hop back. Repeat as desired. Lightspeed delays over 0.3 AU could be more significant than drone transmission delays.
In my story, I just had an FTL drive that I slapped a name on. It could propel things at up to a certain speed. There were no theoretical limitations, just "this is how fast we can go with current technology". FTL was relative to the mass in a large volume around the ship, which means the reference frames can't be very far within, say, a thousand light-years of Earth. With FTL but not instantaneous movement, and a limited choice of reference frames, there's no time travel going on right now. Increase possible speeds too much and it becomes possible. Go sufficiently far away to get a different reference frame and it becomes possible. With what we've got now? Not a chance.
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Disclaimer: I'm not a physicist.
That begin said:
Short Version: From what I understand from the various expeditions in the world of Physics.SE FTL-questions, I'd say any kind of FTL travel or communication will allow causality violation.
Longer version:
There are a few potential problems I see with your description: First of all, how can points belonging to the same network share the same inertial reference frame, and still move relative to their respective stars? Check with your trusted physicist, but as far as I understand, inertial reference frame means no relative motion between each other. Also, I don't know what being in the same inertial reference frame, but far apart, would do, and if it matches your expectations of having a well-defined "now"/"simultaneous"/"instantaneous".
Typically, violating causality goes like this(crude explanation, look at the many answers on Physics.SE for a better one): Move from point A to point B at superluminar speed. Now move back. You end up in a reference frame at position A but before you left.
Remember that "simultaneous" is something very unintuitive in Relativity (not sure whether that's General or Special Relativity), and depends on the observer (=is relative).
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But this is fiction, you could just say: We found these things, they don't allow for time travel, so all this Relativity stuff wasn't 100% right after all. What's the problem with that?
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The key requirement for FTL time travel is making *two separate FTL jumps* in *two different reference frames*. Thus, to prevent paradoxes, you simply need to pick one reference frame (e.g. that of the cosmic microwave background, which the closest thing to a universal stationary reference frame in the universe) and declare it as the only frame in which FTL travel can take place.
With your Alderson-based system, this is quite simple: Make all swaps instantaneous in the CMB frame. And you're done.
The Alderson points themselves don't have to be stationary relative to anything. If one point is moving rapidly or deep in a gravity well (e.g. orbiting close to a black hole), it will experience time more slowly than a point nearly at rest relative to the CMB in interstellar space on the outskirts of the galaxy. However, this just means that clocks attached to these points will disagree on how much time passes between consecutive swaps. There's no way to use this sort of system to create any kind of truly reality-breaking paradox. No meeting yourself, no murdering your grandfather; nothing stranger than the classic "twin paradox" from special relativity.
If you want to use this system to take a few good close-up photos of Sagittarius A\* (the supermassive black hole at the center of the Milky Way galaxy), you might arrive back home a few weeks (or months, or years, or centuries, depending on how close up your your photos are) after you left, despite only experiencing a few minutes yourself, but that's about the worst that might happen.
For FTL communications, the simplest solution given the existing Alderson system would indeed be Alderson couriers- your "space pony express". If you want to make it less of a hassle, you'll need some additional mechanic. Maybe the energy required to power an Alderson swap increases with the size and mass of the object being transported. Flash drives are small and don't weigh much, so sending them through would be pretty cheap. Alternatively, you might be able to rig the Alderson points to swap extremely rapidly, with a period approximately equal to the time it takes for light to traverse its area of effect. Light beamed at the point will enter the point's area of effect, get swapped to a point in the target system, then exit the area of effect before being swapped again. This makes the pair of points act like a two-way wormhole that only light can cross- and since light has no mass, these swaps may be cheap enough to make the rapid cycling feasible.
For more info on FTL time travel, check out [this video](https://www.youtube.com/watch?v=HUMGc8hEkpc) from PBS Space Time, which explains how a ship equipped with an Alcubierre drive with a maximum speed of only twice the speed of light could fly off into space and return home before it was built. Note that to pull it off, the ship must burn its Alcubierre drive twice: once in one reference frame (the Earth's, in this case), and once in a reference frame moving very close to the speed of light relative to Earth. This change of reference frame is the key, and an Alcubierre-equipped ship can probably pull it off by using conventional sub-lightspeed engines to accelerate itself to a substantial fraction of the speed of light between the Alcubierre burns.
If, however, the only available FTL tech is locked to a single frame of reference, all these paradoxical time-traveling shenanigans become impossible. This means no Alcubierre drives that don't cook themselves in infinitely-hot Hawking radiation (or just collapse into black holes the moment you turn them on), no stable wormholes that don't explode with virtual particle feedback (or, once again, collapse into black holes) the moment they're time-dilated and brought close enough together to permit backward time travel, and definitely no tachyonic antitelephones. But your Alderson system, with the restriction that all instantaneous FTL swaps occur in the same inertial reference frame, works just fine. It doesn't necessarily have to be the CMB frame; the CMB is just a nice example of a frame that anyone can measure their velocity relative to no matter where they are in the entire universe, as long as they have the right kind of telescope.
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The short answer to the title question is no. I don't even need to know what you've built or how it works, there's a thing called [Time's Arrow](https://en.wikipedia.org/wiki/Arrow_of_time), or macro-system temporal asymmetry; basically it says 3-Dimensional objects move forward through time, period. No travel back in time is possible if you're a 3-Dimensional being. It's the reason [Entropy](https://en.wikipedia.org/wiki/Entropy) and a couple of physical constants like Planck and Boltzmman exist.
As far as I can tell while we can see *how* Time's Arrow effects the universe we don't know *why* it exists (it does seem to allow us to see the universe *in the first place*). It means that causality violating "space-time geographies" are inaccessible so all FTL has to be locked into the same [Inertial Frame of Reference](https://en.wikipedia.org/wiki/Frame_of_reference#Examples_of_inertial_frames_of_reference) so you can't get out of you "[Light Cone](https://en.wikipedia.org/wiki/Light_cone)" to violate causality.
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Any kind of FTL at any "velocity" of FTL can potentially create a temporal paradox, so it doesn't matter what type you use so long as you set up some rule to prevent it from causing one. Any kind of warp drive is probably the worst example because at first blush it seems hard to make sure you can't do it due to the relative freedom of travel. Wormholes and any sort of jump points make it easier: you simply state that the second (or 3rd, 4th, whatever) trip that would cause a causality violation--a one-way trip really won't do it--prevents the jump/wormhole from allowing passage until such time as it would not violate causality.
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If you limit your Warp Points (WPs) to occur only around starts and can't be moved then you only have to deal with causality if you can move the star.
Also, give the WPs a non-zero transit time.
The non-mobility of the WPs should do away with any meaningful time shenanigans since you can't accelerate one WP much more than the other one is being accelerated. The transit time can be manipulated to cancel out any distortions due to acceleration (the greater the difference in acceleration between two WPs, the greater the transit time). This should negate the effect even if they can some how move the WPs.
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Let us consider two persons who can feel what the other senses and know what the other thinks. Now do these two persons have a common or single consciousness?If so,will it do good, if we succeed to help conjoined twins by brain,to achieve this single consciousness;Now they are no more two persons, but a single person with great capabilities.
Kindly refer the following link:
<http://www.dailymail.co.uk/news/article-1331769/Doctors-stunned-conjoined-twins-share-brain-thoughts.html>
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This is probably more suitable for the philosophy StackExchange.
You would need to choose a definition of "person" to answer this. If by "person" you mean "the physical body of a H. sapiens," then yes, that would be two persons with a common consciousness. However, "personhood" is often attributed to a single conciousness, so that definition would suggest a more accurate wording is "one person, one consciousness, two physical H. sapiens bodies."
As an imperfect example, consider the movie stereotype of identical twins. Twins are obviously not a "common consciousness," but they share enough similarity that movie characters often start treating them as one entity. At the extreme, such as in sci-fi where aliens warp the minds of twins so that they always talk in unison, the rest of the cast quickly does treat them as one entity.
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I've use this kind of psychically linked character pairs in a couple of my sci-fi stories. From a story mechanics point of view, they have tremendous value; being able to communicate information when seperated, totally loyal to each other against all challenges, educated and wise to a level that defies their age. Writing stories involving these kinds of characters yeilds greater opportunities for creativity than crafting tales of normal people.
I usually keep the conscousnesses seperate so that I can use each as a distinct POV character, but I give them an ongoing private dialog which is available under all conditions as long as both are awake and alive. The dynamics of two characters who thoroughly know and trust each other is a really cool spring board for storytelling.
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An Orbital is a miniature ringworld used by the Culture in Iain M. Banks's Culture series. [Wikipedia has details on their basic structure](https://en.wikipedia.org/wiki/Orbital_%28The_Culture%29), but to simplify, the main difference from a Niven ringworld is that they're much smaller and orbit the sun like a planet instead of encircling it.
What I'm interested in is the weather patterns that would arise on an Orbital -- the Culture could generate weather however it'd like, of course, but what would a "natural" Orbital be like, without direct interference into its weather?
Additionally, what would be different if the Orbital had very tall "bulkhead" mountains separating areas?
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Some notes on forces affecting the weather.
Tidal forces from the star would affect the atmosphere. There would be very fast and stable wind in the stratosphere. Without bulkheads the dominant wind direction would be opposite to the rotation.
If the bulkheads were high enough they would stop these winds from forming. More probably the bulkheads would be high enough to limit weather but not high enough to stop stratospheric winds. Assuming a composition similar to Earth, this would mean 10km (or more for added safety) high bulkheads. In situation like this I'd assume the top half of the troposphere would be dragged by the stratosphere opposite of the rotation which would have to be balanced by the surface winds in direction of the rotation. The wind speed would depend on the number and height of the bulkheads. So you'd presumably have a near constant wind of the desired speed and stable direction.
One bulkhead would have cool dry air being sucked down. I'd presume the designers would place a sea here to moisturise and warm the air. Since the sea would have the same amount of sunlight as every other part this would work well. Combination of cool dry air above warm moist air would probably create lots of localised thunder storms and even tornadoes, which is another reason to have a sea here instead of habitable land. I don't see large storm fronts or hurricanes being formed, so ships and boats should be able to avoid storms.
The other bulkhead would have warm moist air driven up. This should result in nearly constant rain in the bulkhead mountains. I doubt anyone would want to live in this area, but it would be a good place to build hydro-power.
The area in between would have localized thunderstorms at night, rain on the windward sides of mountains and arid areas behind them. These rain shadows might be stable enough to form deserts, I'd assume arid grasslands exist. Without bulkheads this would be what all of the orbital would be like. Weather would be dominated by the effects of the mountains on the stable wind.
Since rivers and winds would run in opposite directions and both the river flows and the winds would be near constant, sailing ships should be quite practical form of low tech travel. And there would likely be large navigable rivers running from the rains of one bulkhead to the sea at the other bulkhead. In fact, since the winds run at different directions at different altitudes aerial sails or glider aircraft would be much more practical than on Earth as long as you can reach the boundary between the winds. This might actually be important for a low-tech "inheritor" civilization as I doubt orbitals would have huge hydrocarbon reserves. Without bulkheads river directions would be random and wind direction would be same regardless of altitude.
In addition to the tidal and bulkhead effects, there would be effects from the day-night cycle. These should be similar to the effects here on Earth? Although the higher speed the line between day and night moves might make effects negligible outsides coastal areas and areas with large lakes. Basically, air above water warms and cools slower, so there would be winds toward land at the morning and toward water in the evening.
All guesswork obviously...
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What did you design it to do?
If you've got glacier areas, for example, then you've put in cooling apparatus. Automated cooling/heating apparatus will provide a significant driver for your weather patterns.
Water areas? Also drive weather. If you made your orbital all-desert, you're going to get a different effect than a world-river orbital, vs. an orbital with huge oceans (cooled at the deep ends?), vs one with shallow oceans. How connected did you make your water masses? Is there thermal exchange designed into them?
Did you include forcefields to effect your weather, by creating baffles in the air? Break up repeating wind-currents? Are they switched, or always on? Baffles for your ocean currents? Are you inducing waves or tides in your oceans? How? Those choices will effect your weather. (What effect did the designers *want* to have?)
You've got a hive mind that controls the forcefields and other systems. Are you telling me you purposefully took weather control away from it? It's in it's self-interest to not let big weather problems disrupt it's ongoing activities.
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Ok, I'm not a meteorologist and I have basically no idea how weather works. But I had an interesting idea, so I'm posting anyway.
Without the mountain "bulkheads", the surface is roughly one-dimensional, as opposed to roughly two-dimensional on our earth. That could be a very important factor. On a 2D surface, a vector field can have elaborate vortexes, but in one dimension the only solution is "everything goes in the same direction".
Now this is pure speculation but it seems conceivable to me that the weather would stabilize in this environment and not be chaotic. There would be local vortexes of course, caused by mountains e.g. but they could be static, like the whirls of a river.
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The basic question is:
# When is a location good enough to build a space centre on it?
Some info to the function of the space-centre:
* The space centre has a lot of traffic, also humans. I imagine it would be good to be near major cities, but not too close (Safety)
* Space-crafts launch mainly into a **almost** non-inclined, non-eccentric orbit
* Current tech still mainly uses rockets, but some intelligent guy mentioned it would make sense to plan ahead, so we need:
+ A Runway for space-planes
+ Room for a space-catapult (even though it is a theoretical concept right now)
* Storage Area
* Maintenance Areas
* Tourism Areas (Hotels ect.)
* Hangars
* Whatever else the clever guy (you?) comes up with that would make sense
The space-centre should be used economical, as the Tourism Areas suggest.
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I already though of the following:
* should be near equator (EDIT: so it doesn't need *that* much fuel to get 0° inclination)
* should be in a calm zone (regarding weather)
* should face eastwards, as [it is easier to start](http://spaceplace.nasa.gov/launch-windows/en/) in this direction
## What other criterias are important?
[Answer]
### Launch trajectory
Some aspects of the design will depend on what technology you're using. For current technology, i.e. rockets, pollutants from the rockets are a major issue that must be addressed. Generally, you want to launch away from populated areas. This is why most rockets launched in a west-east direction launch from Florida, with Cape Canaveral being a major launch site. Spaceport America launches over a desert that nobody lives in. (The White Sands missile range). Even with advanced technologies, you're still going to generate a lot of noise when launching, so this will remain a concern.
Non-equatorial launches won't launch into a non-inclined orbit unless you spend more fuel to get there. However, if you should decide you want a polar orbit, lots of places away from the equator are perfectly good for launches. The US, for example, has a launch facility on Kodiak Island in Alaska for polar orbits.
### Tourist areas
With regards to tourism areas and hangars, they probably won't be much of a concern. If the launches are mostly industrial, then tourism doesn't matter. Likewise, if you're developing a transportation hub for a planet, tourism won't matter much because people will be coming and going, not hanging out. Tourism will probably only be a major issue if people are coming to visit the planet, and it doesn't have well established high speed surface transportation systems. If that's not the case, most tourists would probably prefer to step off their space ship and onto a high speed train to take them somewhere where rockets won't be thundering over their heads every half hour.
### Surface transportation
With regards to the point about high speed transportation, there's one other point you probably want to hit for a general commercial spaceport: it should be easy to get goods and people there. Since it's serving a large area, such as a country, this doesn't mean 'close to a city', since that's only ideal for the city in question. It would probably be better to have the spaceport in an open area that can easily be reached by ships/planes/trains. Dedicated infrastructure for the purpose of facilitating such planetary transportation would be hugely beneficial for a space station.
[Answer]
You're going to want:
1. *Reasonably equatorial location.* By launching your rocket eastward (in the direction of the Earth's spin) at the equator, you get about a 5% boost to your speed for free. The further north or south you are, the less of this boost you can get.
2. *A large clear area (thousands of square kilometers) to the east of the launch site.* Because of the eastward launch, a crash is far more likely to happen east of the launch site than in any other direction. Additionally, if you're using a multi-stage launch system, discarded stages will land to the east.
3. *A large clear area (5-10 km radius) around the launch site.* If all the fuel in a Saturn V rocket were to explode at once, the energy release would be comparable to a small (15-KT) nuclear weapon. An actual accident will likely produce a more gradual energy release, but you're still going to be able to break windows a long distance away.
4. *Predictable weather.* It doesn't need to be consistently good, just consistent. A launch doesn't take very long, so if you can count on a morning calm four days out of five, it doesn't really matter that you get afternoon thunderstorms every day.
Other considerations will depend on what sort of launch technology you're using, what sort of cargoes you're launching, how often you launch, and if the launch vehicle is going to land back at the launch site.
[Answer]
A major need that probably far outweighs items like tourist areas is that the building, fueling, and servicing of the space craft themselves requires a certain technology level of the host region. Borneo might be great for launches, but if the mechanics all live in the US that adds a lot of cost to the system.
This service industry might also require space to work, so a tiny island is a suboptimal choice for that reason. The launch and landing areas might need wide spaces for safety.
The passenger traffic in and out is important, but could be done by a fast train system or large airport without requiring it to be that near current major sites.
[Answer]
In addition to the previous answers, I would also add two criteria that would make a place desirable: Transport & Fresh Water.
**Transport**
Transportation of materials and machinery is expensive and difficult.
For example, the solid rocket boosters of the former Shuttle program were limited in size, because the location of where they were made required the trains bringing them to go through a tunnel.
In addition to the criteria already discussed, I would add that a location with good rail, highway, and seaport connections would be desirable. Naturally, you should also have an airstrip and helipad (some special gadgets are brought in by air), but that can go pretty much no matter where you place your center.
**Fresh Water**
While you can truck this in, or produce it from de-salination, it would just help with costs if you had access to lots and lots of fresh water, as a lot of it is used - sorry, I don't know the exact quantity, but lots.
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[Question]
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# How to approach this problem!
**Numerically.** Trying to find some closed form equation to spit things out is extremely difficult, especially in the face of how well this lends itself to numeric methods. Solving this numerically is better in every way.
I was able to get a proof of concept out at 1 am in a few minutes, and [causative](https://chat.stackexchange.com/rooms/144830/discussion-between-causative-and-cthon) was able to make a program that iterated numerically with full features in not much time at all. Coming up with how big things are, how fast, how accurate, and how good your sensors are will take a lot of research if you want to postulate the future, and with that basis you can 'turn knobs' for a look and feel you'd like if you're writing a story.
# Basic C# code numerically solving this
<https://pastebin.com/tq3d2TEr>
Seems that, yes, you can rather easily, if you don't have a factor to account for missiles being hard to spot. Interesting.
# Premise
I'm trying to make a formula for **rough estimates** to find the "time to kill" of an inbound missile with a starting range, terminal range, the missile's initial closing speed, its dodge dV, its cross section, how many hits to kill (could be 1), and the jitter of your weapons that are trying to fire at it.
For people who write Sci-Fi and like to include numbers, or just people interested by the problem space, having a way to 'turn the knobs' of "what if this is better, what if that is worse" to see what works and what doesn't would be helpful. The problem is, such an undertaking is beyond my present abilities.
The first thing that came to mind is "oh, integrate probability over time!" but I have no clue how to do this, being decades out of school. While I have formulas for likeliness of hitting a target based on jitter, range, and so on, at a fixed distance, all the dependent variables of moving through space, and integrating probability, is something I have zero experience with.
Another thing I have to clear about is that the point of this is to have multiple terms to plug in, given that these are all assumptions. Given that this is to help fiction writers, not the space force, there's no right or wrong answers, as much as "let's assume this is better than that, what shakes out?"
Finally, given that this is inherently general, if I plugged in a very low velocity but a large cross section, that is, a ship, and not a missile, this formula or something very similar could determine time-to-hit on the ship firing the missiles, and thus determine how far away they need to be to not get chewed up by anti-missile weapons themselves.
# Definitions
**Missile**: a maneuvering, disposable vehicle that either crashes into something or carries a ranged warhead.
**Laser**: A weaponized *pulse* laser, likely with a very large aperture (100+ meters!) and UV wavelengths. These damage by ablating what they shoot. At very long ranges, due to diffraction, it doesn't drill as much as flash away a wide, flat region of what it does shoot.
**Particle beam**: I'm assuming the use of either neutralized or relativistic particle beams so you don't have to worry about bloom. You still have to worry about hitting anything. These cause damage by irradiating the insides of whatever they hit, and depending on the specifics of the particle beam, cause damage not unlike making a needle to pencil sized cross section of whatever they intersect with behave not unlike it was turned into det-cord. Some particle beams may well deposit their energy in a shallow cross section, too, but that isn't so important for this exercise.
**Jitter**: The ultimate limit of precision that your weapons and sensors have to deal with. Measured in micro to nano-radians.
Particle beams can be approximated as points. Lasers, however, not so much, since even with UV lasers and 200meter apertures, spot sizes can be in centimeters or meters over the distances I'm thinking of, which goes from .1 to 3 light seconds. So, you can have a cross section intersecting another cross section.
# Formulas I've found through research
If you know your jitter J, and your range R, the diameter of the region your beam wanders over is, roughly: $D\_r=2\cdot R \cdot tan(J/2)$.
For very small ranges, you can approximate with $RJ$.
If your target has a profile area A, you can approximate the chance of hitting with:
$A / ( (\pi/4) \* 2\cdot R \cdot tan(J/2) )$
I do not know how to account for a profile of your spot size, or for that matter, LaTeX.
# Now it gets hard
**How do you go about integrating this?**
I'd need to include a firing rate for pulsed weapons, as much as how many of them I have, so one would have some finite number of shots over time. You'd start from the outside of the envelope (let's say 3 light seconds for now) and it would end with the missile hitting the ship trying to shoot it down, or reach the minimum range for a warhead like a reactor-pumped laser or a bomb-pumped particle beam, casaba howitzer, or whatnot.
That's where I just stare blankly at my screen and wish I did more stats back in school.
# Oh, let's make it harder
Uncertainty radiuses due to jamming or other EW methods. I wouldn't ask about specific modeling, I'd want some simple polynomial term that can be used, and a cutoff for "burn through", that being your own active sensors 'burn through' the jamming. Jamming in space could be many things, such as the ship that fired the missile having a spot size big enough on their lasers they can't miss and dazzling your sensors, or the missiles being multi stage, and the n-1 stage backlighting them with radar, lidar, lasers, or whatnot.
Put another way, if a missile's cross section is, say, a meter, your sensors won't necessarily be able to precisely know where it is exactly with the enemy spamming your sensors with nonsense to dazzle them, so there would be a multi-meter blob that you'd think it's in, at least until it gets close enough your own active sensors can get returns.
# Really hard
The laser spot size getting smaller as the missile approaches. This is roughly 1.22(Distance)\*(Wavelength/Aperture). Instead of flashing the surface, you can start drilling higher and higher aspect ratio holes into the target. On the other hand, if you have enough time, why not just flash the entire thing and not miss?
# The Space Force is now interested
Active maneuvering? An earlier stage acting as a missile bus coming in obliquely and taking pot shots as it arcs away? I know 'path integrals' are a thing but I remember little about that part of Calc 3
# And now something completely different
Is this even viable? Could making a program to actually simulate be easier?
# Chat Responses
## "I don't think lasers work"
### General response
Based on what? While not relevant to the question, it's a matter of aperture size (mirror or lens), laser wavelength, and power. In this setting, ships are going to be big, and powerful - terawatt or hundred-gigawatt effective power will be what is trying to shoot at missiles *over multiple light seconds*. Many calculators are online to compute drilling speed over time, or per-pulse-train. If you want something to start with, go with an excimer laser deep in the UV (157 nm), an aperture size of 200 meters, and a power of 1TW. Yes, that's big. Yes, that's powerful! The setting I have in mind has goes big.
### Mirrors
In the first place, once you reach a certain intensity, it does not matter what it's made out of. The electric field from that spot will be so intense that nothing chemical will withstand it. Electrons will be smacked off of nuclei, and then things go crazy. I believe it is a coulomb explosion. Once you get into extremely high intensities, you actually make a reflective plasma that means you don't put all of the energy in the target, but I'm not qualified to speak to it. Yes, you can make a "plasma mirror" or "plasma lens" with this effect, but you run into efficiency issues and other complexities outside of "it can work." No, this isn't really useful as an armor.
<https://en.wikipedia.org//wiki/Laser_damage_threshold> If you want to go into it, this briefly discusses how lasers do damage, such as dielectric and avalanche breakdown.
### Prior art calculators to play with
<http://panoptesv.com/SciFi/LaserDeathRay/DamageFromLaser.php>
This also comes with a *lot* of information if you want to scroll down and read it all.
### Space is big
If a missile is traveling multiple light seconds while you shoot at it, unless it's juking and dodging like a space squirrel on space crack, you're going to smack it quite a few times. Not only that, but the spot size of a laser could easily be as big as the entire nose of the missile, perhaps by design.
### Sensor attrition
Valid, but as some have already said, drones scattered around your side of space (and maybe a few shot at the enemy) with line of sight laser communications that are cryogenically cold are useful. While they can't be too big lest they make odd holes in the sky, or you handwave meta materials and hope they don't occult a star, this will help. Also, messing up datalink would basically require glassing the outside of the ship by getting a nuke close enough. If they've got almost an hour and a half to do so, that's not so guaranteed, now is it?
### Anti missiles
Oh, indeed. You want to have screens of some sort. Drones (glorified missile buses, or, a big stage that has multiple terminal stages) out ahead of you, if you know the enemy is coming, are a great idea. The same formula I want to make would be useful to see how the enemy could shoot them down.
[Answer]
Edit: added a [simulator](https://onecompiler.com/python/3z3n78qf4) for missile interception.
So.
* Missile is moving towards you at speed $v\_M$.
* You have a weapon (laser or particle beam) that can shoot out an attack at speed $v\_a$. $v\_a$ is much faster than $v\_M$.
* The attack can be modeled as a cone with angle $\theta$, accounting for jitter and dispersion. $\theta$ is assumed fairly small.
* The attack cone gets slightly larger because of the missile's frontal radius $r\_M$. This will make it not quite a true cone; the effective radius of the attack at distance $x$ will be $r\_a(x) = x \tan(\theta) + r\_M$. If this sort-of cone passes over the perfect center of the missile, the attack can do damage; if not, it can't.
* You have a function $\mathrm{DAM1}(x)$ which tells you the *average* amount of damage that the weapon will do, if the cone of the attack touches the missile when the missile is at distance x. When you have done 100 damage cumulatively, the missile is destroyed.
* Your weapon can fire $f$ times per second.
* You predict that if you shoot the weapon now, the attack will meet (or miss) the missile when the missile is at distance $x$ from you.
* The missile will maneuver sideways randomly to dodge potential attacks. So when the missile is at distance $x$, you only know it will pass through a circle of uncertainty with radius $r\_U$.
* $r\_U$ increases based on the missile's maneuvering acceleration $a\_U$, and based on the delay $d$ before your attack arrives. The delay includes speed of light delay ($d\_1$) for you to see where the missile used to be, processing delay ($d\_2$) to predict where it will be, the time to physically aim and fire your weapon ($d\_3$), and the time for the attack to arrive at the missile ($d\_4$).
* $r\_U$ also increases based on any uncertainty in your calculation of the missile's last known position, accounting for jamming or decoys or whatever else the missile might try to do. Call this uncertainty factor $r\_{US}$ for Uncertainty of Sensors.
* We can combine the sources of uncertainty like this: $r\_U = \sqrt{r\_{US}^2 + 1/4 a\_U^2 (d\_1 + d\_2 + d\_3 + d\_4)^4}$
* Your attack cone at distance x consists of a circle with radius $r\_a = x \tan(\theta) + r\_M$.
* You aim the attack so that your attack circle $r\_a$ will land anywhere, at random, within the missile's circle of uncertainty $r\_U$. I think normally we'd expect that $r\_U$ is larger than $r\_a$. (If not, then the attack circle would just always hit).
So you have this circle of uncertainty $r\_M$ for the missile, and you have another circle $r\_a$ for the attack. The expected damage from a single attack, accounting for the missile's position uncertainty, is therefore $\mathrm{DAM}(x) = \mathrm{DAM1}(x) \cdot (\pi r\_a^2 / \pi r\_U^2) = \mathrm{DAM1}(x) \cdot r\_a^2 / r\_U^2$. Unless $r\_a > r\_U$, in which case the expected damage is just $\mathrm{DAM}(x) = \mathrm{DAM1}(x)$.
Now we can also talk about the damage per second. Damage per second when your attacks are hitting at distance $x$, is $f \cdot \mathrm{DAM}(x)$.
So, how long does it take to shoot down the missile? We want to measure from when your sensors first spot it, at distance $x\_0$ and time $0$. At time $t$, the missile will be at distance $x\_0 - v\_M t$. So, average damage per second as a function of time is $f \cdot \mathrm{DAM}(x0 - v\_M t)$.
Total damage by time $T$ is $\mathrm{TDAM}(T) = \int\_0^T f \cdot \mathrm{DAM}(x0 - v\_M t) dt$
The missile is destroyed when $100 = \mathrm{TDAM}(T)$.
Now, we can't do this integral without knowing $\mathrm{DAM1}(x)$. For a laser, we can suppose damage falls off as the square of distance; $\mathrm{DAM1}(x) = k/x^2$. This would be assuming the laser beam at distance $x$ is substantially wider than the missile. For a particle beam with no dispersion, $\mathrm{DAM1}(x)$ is a constant $k$; if the beam hits the missile, it doesn't matter what the range is. For a particle beam with dispersion theta due to jitter, $\mathrm{DAM1}(x)$ is a constant $k\_1$ when the range is close enough to ignore the dispersion. This could be used as a rough estimate when $x \tan(\theta) < r\_M$. When the particle beam range is large enough that the jitter is substantially larger than the missile, $\mathrm{DAM1}(x) = k\_1 \cdot (\mathit{area of missile}) / (\mathit{area of jitter}) = k\_1 \cdot r\_M^2 / (x \tan(\theta))^2$. This could be used as a rough estimate when $x \tan(\theta) \geq r\_M$.
Now we can do the integral. Or we can ask Sage Cell to do the integral, because that's easier.
Let's use Sage Cell to run an example. There is a mosquito flying initially 10 meters away (x0 = 10). The mosquito is 5mm radius (r\_M = 0.005). We aim a pulsing laser at it that shoots ten times a second (f = 10). The laser spreads out to 2cm radius over the ten meters (theta is about 0.002). The speed of light delay to see the mosquito can be ignored (d1 = 0), the processing delay is 200ms (d2 = 0.2), the aiming delay is 100ms (d3 = 0.1), and the time for the laser to hit the mosquito can be ignored (d4 = 0). The mosquito flies slightly erratically so that in that 300ms it might wobble 5cm left, right, up, or down. This means its effective acceleration a\_U = 1.111 m/s^2. We are also having trouble seeing the mosquito, to within 2cm, which means r\_US = 0.02. We have to settle for aiming the beam somewhere in that slightly more than 5cm radius circle where the mosquito might be, and hoping it hits. The mosquito is slowly flying towards us (v\_M = 1). And, it would take 10 of those laser pulses to kill the mosquito at 10m, from which it follows that k/100 = 10, or k = 10000.
```
var('x x0 t k theta r_M d1 d2 d3 d4 a_U r_US v_M f T')
x0 = 10 # m
k = 10000 # m^2
theta = 0.002 # radians
v_M = 1 # m/s
r_M = 0.005 # m
r_US = 0.2 # m
a_U = 1.111 # m/s^2
f = 10 # 1/s
d1 = 0 # s
d2 = 0.2 # s
d3 = 0.1 # s
d4 = 0 # s
r_a(x) = x * tan(theta) + r_M # meters
r_U(x) = sqrt(r_US^2 + 0.25 * a_U^2 * (d1 + d2 + d3 + d4)^4) # m + m/s^2 * s^2 = meters
DAM1(x) = k/x^2 # laser wider than the missile. units of "damage" (k is m^2. m^2/m^2 = dimensionless function of meters)
DAM(x) = DAM1(x) * r_a(x)^2 / r_U(x)^2 # dimensionless * m^2/m^2 = dimensionless function of meters
TDAM_indefinite(t) = integral(f * DAM(x0 - v_M * t), t) # f has units 1/s so integrand has units of 1/s. integrate over time cancels the seconds. result is dimensionless.
TDAM(T) = TDAM_indefinite(T) - TDAM_indefinite(0) # between time 0 and time T, how much damage has been done?
plot(TDAM(T), T, 0, 6) # plot damage as a function of time from 0 to 10
#find_root(TDAM(T) - TDAM(0) == 100, 0, 9) # solve for when 100 damage has been dealt
```
The result is [here](https://sagecell.sagemath.org/?z=eJyVk81u2zAQhO8C9A6L5BDJdmRJcQr0YBQFes2p9tUGY1IRYYlsSfrn8TtL2kndnGrABJfcnfm4pI7CFQ9nOtcUaE-hV0GQ276QbEi2JJ9ILkhs11hb_6QjNjpaPZR5hoIlNTXd05hn-zjHj8NNm2dJZ0l1VdctFp2QWhifZ6yAXM6bI3Qx5KznpBRteKVNMVsjv2qaSw2rd1frhjVAigJEPG_fizl6ilFziRYfeW4rinOJ-EwTCsIUEbikaTw7jFRQLuatU57_7ULBcJsWSXB4RiHgEE6oAMKU2zXlhmFYlJtFyTIIIjOSeFy-C__4_tIk5f38vGHeQXjl6KQlxtALw3dBo_ZeD6qig9HBk-3oTopRvKk7KvakPXe74mE-RnmpR2W8tmZQ3lN3MLuAgOuScRmdk_EVYUKpGxCYUzpwBLrVmvyHS56tIL7VRqpOA1wVgQ21CerNiaHooBYxanqMbwp3UM7wh2tHvfCX4-J6ydtrnZF_bcELu9V1LyiyR24cyGgnzE4NPjbQq501EolO-cMQuGU39FViLVYM-C81Fh8_LdZM-arCSSmT_Gpitjhdzai3JxoPu57SRUXmV86V1qhvefZrsKG4eM64oJ7RF9bkjWsRasRNY6N65-wIt2Dx-vPsHkBy6-yH3IWWEZfxg4ziX1nc2-EIAYsX1oMFe5_5lBjCH0uyKtA=&lang=sage&interacts=eJyLjgUAARUAuQ==). You can see from the plot that the laser will kill the mosquito in just under 6 seconds.
I've also made a full simulator [here](https://onecompiler.com/python/3z3n78qf4). It can be run in the browser.
[Answer]
You can add uncertainties like perpendicular vectors. If your thrown rock has a standard deviation of 3m, and your target position has a standard deviation of 4m, then the total accuracy from the two combined will be a standard deviation of 5m. Or just think of an average scatter, rather than standard deviations: the result is the same.
Let's start with trying to hit a ship with an impacting piece of tungsten (say). Now this is tricky - most missile attacks do not try to ram the ship, but to blow up close enough to it - but this is a place to start. If the ship is travelling under its own momentum or uniformly accelerating, you can predict with some precision where it should be. Think of the Voyager probes passing Jupiter, and people worrying about a missing 0.01s.
If you ship has power, and it is aware of a threat, it might put a slight weave in its route. This would waste a small amount of deltaV, but it might mean you could not predict its position from a week away to within 100m.
It therefore follows that your impactor should have some ability to fine-tune its aim. It could have camera sights on the front, and a subtle thruster so it can track the ship. This is good when you are a long way off, but it becomes increasingly useless the closer you get.
If your average error is 100m, then you can blow up your impactor at the last moment. If the shrapnel cloud is about 100m in radius, you are probably going to hit it with something. If your impactor relative velocity is large, a small hit may well do enough.
Can the ship launch a defence? A thin tungsten rod with a pointy end would be very difficult to spot in space, seen end-on from the target ship. It might look for the boost phase when the impactor is given most of its momentum. It might catch some course-correction, though it is hard to see how if the impactor uses an ion drive. The ship's best defence would be to have a wiggly and unpredictable course. It all feels like WW2 ships and submarines, doesn't it?
I have not tried to deal with lasers and particle-beam weapons. The ship will have a hard time dodging, but there may be practical, lightweight defences that could thwart these.
[Answer]
**Frame Challenge**
Based on my comments and discussion with BMF - I don't think that Lasers for long range point defence are a good option.
Now, I'm assuming for the moment that the type of Missile we are talking about in Space is a Ship-killing missile. Whilst the hazardous conditions of Space means that something that would be a mere annoyance on Earth could be catastrophic in Space - I'm going to presume that for such an advanced civilization (that is having Space Lasers and Space Missiles and Space Combat) - we have made our ships survivable enough to be on an equivalent basis for modern Warships.
That is, something around the size/weight of the P700 Granit Anti-Ship missile (probably larger - but you get my point).
So, from the Question, we have a max engagement distance of 3 light seconds (800,000 Km)
This means first and foremost that an sensors detecting the launch at *minimum* have a 3 second delay.
Firstly we have the initial missles speed - you've not stated it, but let's use some numbers for reference - Mach 100 (100 times the speed of sound) gives around 120,000 Kph - so at max range, that's 8 hours to get to target.
Sounds a bit silly? Actually... No.
A modern Tomahawk cruise missile has a flight time of at least 2 hours to get to target. So 8 hours isn't unreasonable for the flight time of a ship-killing missile.
I'm also going to assume that our Space Farers have the concept of layered defence for their ships.
I'm also going to presume that the first few layers of the Survivability Onion have been breached (Don't be there, Don't be seen, Don't be identified, Don't be targeted, Don't be fired upon).
**First layer of defence - anti-missile Missiles**:
Smaller and lighter than an Anti-Spaceship missile - these can travel faster (say Mach 200) and so they intercept the enemy missile around 500,000 Km away. Initial targetting is done from the Ship, but once it gets within sub lightsecond range, on-board sensors take over.
These would be fired in a cluster and would have a directional fragmentation warhead - Directional so minimal debris doesn't come back to us and so the most is directed towards the incoming threat. Think of it like a giant shotgun - throw enough poo at the wall, something is going to stick.
Also - if there are any Mirrored surfaces or other features to reduce Laser damage, these get damaged and or blasted off.
**Next Layer of Defence - Decoys**:
If the Missile is still inflight and tracking then we can deploy a Decoy - a small craft with various tricks to 'fool' sensors into thinking it's the target. It moves towards the missile at high speed (say Mach 50) so it will take a while to get there, but the idea is when it's there - the return signal is stronger than our vessel (which is still over 500,000 Km away).
Why not go with a Decoy first? Hard Kill is better, Decoys have a higher cost to them and should they fall into the enemies hands - they will have detailed knowledge of how fake signals are generated and will be able to stop their missiles from getting fooled.
**Mid-range Defence - Lasers!**
So, now that both of our outer layers have failed, and the missile is within 1 Light second, now it's time for the Lasers to shine (Pun fully intended) - our hope at this point if the Missile is still inbound that there has been some damage done to it during it's flight.
Why within a second? Well because of the distances there is still a 2 second delay (Signal coming from the missile to the ship \*and then the laser travelling from the ship to the object) - the Laser array would have to target all possible vectors within a 2 second 'cone':
Imagine a car travelling on a big open bit of tarmac. We know the speed and we know the maximum G-Force it can generate in turning, braking and accelerating (we'll call it 1 G in all possible directions for the sake of argument) - we now have a cone of possibility in a 3D space where the object *might* be in 2 seconds time. We also know the rough size of the object (say 10 metres long) - so we target every point, 9 metres apart (or similar) within that grid.
As I'm sure you can imagine, the amount of distance we are talking about in that time period is huge - hence why these are a closer-in option to make it practicle to target every point. You could add in some statistical analysis of 'most likely'.
Hopefully the Missile's shielding is damaged and the Lasers inflict critical damage *or* in forcing evasive moves, the Missile destroys itself due to damage already sustained.
**Short Range Defence - Flak**
Flak - Similar to our Anti-Missile, but more primitive - we are now within fractions of a Light Second (less than 100,000 km) - we would want to through out a wall of very dense material at very high speeds. This is close range only because not only is it a bad idea to have lots of material blasted into space but with increasing distance, the space between each projectile is increased and the chance to hit is lowered. On the plus side though - this type of system is relatively cheap so you can saturate an area.
*Note - when I say 'cheap' I'm not talking money per-se - I'm talking time and resources*
**Final Layer of Defence - Sacrificial plating**
So, now we are panicking, the Missile is mere minutes away, all our other countermeasures have failed - the final option is to send a big chunk of the ship (either something that has been designed to do this or a non-vital part of the ship) - directly into the path of the Missile.
The idea being to prematurely detonate the Missile against a piece of the ship, far enough away from the ship that the main hull doesn't get compromised. Similar to how Spaced Armor/Explosive Reactive armor works on Main Battle Tanks.
We've accepted that the Missile is going to go Bang - we are now on the 'Don't be Penetrated, Don't be killed' part of the Survivability Onion.
Feel free to tweak as needed, add in your numbers - and make some adjustments etc. But the above, for a Military Space Vessel, exepecting to encounter some form of Anti-Ship missile is what seems most logical:
Guided smart projectiles, Decoys, Lasers, Flak, Sacrificial material
] |
[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.
This question is tied to the “[Glass Trees](https://worldbuilding.stackexchange.com/questions/240672/glass-trees-how-feasible-is-it)” question I asked earlier which everyone seemed to like. Since y’all had such good opinions on that, I figured I’d bring this particular quandary to y’all in hopes that you could bring peace to my nearly month-long torment over what to do.
[](https://i.stack.imgur.com/znKry.png)
**The setting**: A planet 90% the mass of Earth, with an iron core to provide a magnetosphere. Planet has similar composition to Earth, though has a moon which causes tides roughly 2.5x greater. (*Orbital mechanics aren’t important here, this is just to describe the setting.*)
Life forms are carbon-based, using sugar-phosphate based genetic biopolymers. Atmosphere is mostly comparable with that of early Earth, during the Ediacaran/Cambrian.
**The Setup:**
So I wanted to have a genetic compound used for the biosphere that was different from Earth, but not so different that it would be incomprehensible. My main needs for this mirror to DNA were:
* It should be comprised of the same or similar core elements as DNA; no swapping Carbon with Silicon here, we stayin’ organic on this planet.
* It should be unable to interact with DNA or RNA. I want to try avoiding any possibility of “this alien virus could infect you and mutate you into a monster”, or any cross-species breeding going on. Terran life and these aliens should not be able to interact on a genetic level, ideally.
* It should function in roughly equivalent ways - self-replicating, coding for proteins, allows for Darwinian evolution, all that bacon.
**The Problem:**
…I am not good with chemistry. I’m skilled with biology & geology, I’m a passionate amateur for astronomy, and I know enough physics (quantum & otherwise) to follow a conversation. But I have always struggled understanding chemistry in all its forms; without a smart person to balance me out, I’m stumbling in the dark.
That being said, I did try to do some research, and even though I only understand 50%-70% of it, I at least have enough to make inferences.
[](https://i.stack.imgur.com/UuUMB.jpg)
**My Research:**
My first candidate was HomoDNA, an alternative form of DNA that replaces Deoxyribose with Dideoxyallopyranosyl, which is a homolog hexose. I operated for a while under the assumption that this HomoDNA would work similarly enough to DNA & RNA to be comparable. However, thanks to a [paper that a friend of mine sent me](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764398/#!po=37.5000), I now know that HomoDNA doesn’t form stable Watson-Crick pairings like DNA & RNA does. Plus, it doesn’t seem to form stable helical frames either. So Homo-DNA is out.
**D-pyranosylribose (p-RNA)**, the pentapyranosyl isomer of RNA (*whatever that means*), has shown to form pairing comparable & superior to DNA & RNA. It also does not bond with standard DNA & RNA, which makes it more viable for my "aliens cannot infect Earthlings" criteria. I don’t know much about it besides the small reference in that fore-mentioned paper.
Among synthetic or *Xeno-nucleic acids (XNA's)*, **Fluoro-arabinose (FANA)** and **Anhydrohexitol (HNA)** are also favored alternatives to DNA. They form stable base pairing, can also pair with DNA, and also work with synthetic catalytic enzymes, which is prevalent to the idea of the chemical origins of life. However, I don’t know how difficult these synthetic strains would be to form under natural circumstances; I recall that something mentioned regarding Hajimoji-DNA is that it cannot exist outside of a lab environment, so they must introduce something that allows it to form and prosper that doesn’t exist in nature.
And for the record, I did look into Hajimoji-DNA. I am likewise intrigued, though I feel as if having a structure that codes for 8 different nucleotides would lead to a higher risk of mutation & cancers, as well as having more potential to code various proteins. It feels like an impractical thing for nature, in that regard.
**My Question:** (finally)
My question that I present to you all is, which of these DNA alternatives seems to be the most likely one to arise naturally on an alien planet? Which of them would fit the criteria I listed above best? Is there another substitute that you feel fits better?
Any advice and information you could provide would be helpful! (*Just keep in mind, I’m no chemist, so y’all might need to dumb a few things down for me.*) :P
***ADDEN.: RESPONSE TO GNA SUGGESTION***
[](https://i.stack.imgur.com/tB1q3.jpg)
I did some research into **Glyco-Nucleic Acids (GNA)**, as folks in the comments suggested; I did confirm, the structure is the same, just the paper calls it “glycerol” instead of “glycol”. This also seems promising, but there is some confusion over how stable it is. The research paper “De Novo Nucleic Acids” cites GNA as having a *lower* melting temp., thus forming a more flexible backbone structure and destabilizing Watson-Crick pairing. However, the Wikipedia article linked says the exact opposite: that GNA requires a *higher* melting temperature, and thus forms *more* stable Watson-Crick pairing. I’m unsure if this is an error on someone’s end (as in whoever’s writing the paper/articles), or perhaps Glyco-Nucleic Acids and Glycero-Nucleic Acids *ARE* different? Hope y’all can help.
[Answer]
**TL;DR: I suggest either GNA or PNA**
First, a couple comments on the alternatives:
**Regarding FANA:**
Very few fluorine compounds occur in nature and, as far as I know, almost all are produced by plants or microorganisms as defense mechanisms [1]. There are some fluoroalkanes that are produced by volcanoes, such as fluorobenzene [2]. Unfortunately, the amount of organofluorine compounds produced this way is low. In any case, if you do have an environment that produces some organofluorine compounds, you would need to figure out how they would be converted into fluoro-arabinose, and how the FANA can produce more of itself, preferrably using fluoride ions in the environment as the source of fluorine. Given that only one enzyme is known to catalyze the formation of a C-F bond, that might be a tall ask, especially if your planet is supposed to have a history similar to that of Earth. Furthermore, there's an argument to be made that proto-life that relies on fluorine on an earth-like planet is going to get outcompeted by proto-life that does not. Unfortunately, there haven't been any studies about the possibility of abiogenesis of a fluorine-containing nucleic acid, so all of this is speculation. Furthermore, sources conflict on whether fluorine or carbon is more abundant in Earth's crust. One thing to note, however, is that fluoride salts are not very soluble in water, which would mean that fluorine would not be as accessible to your proto-life as you would think judging by how abundant fluorine is in the planet's crust. So, ultimately, I'm going to say that, while it's plausible that there would be a planet where FANA is the information storage molecule, it won't be Earth-like.
Disclaimer: I could be completely wrong in my reasoning for this
**Regarding p-RNA:**
The other answer suggests p-RNA as the information storage molecule. Now, RNA as we know it is more prone to hydrolysis compared to DNA, which may be the reason why DNA evolved to be the information storage molecule [3]. Unfortunately, I haven't been able to find any studies regarding how prone p-RNA is to hydrolysis or whether it can evolve some mechanism to effectively protect itself from damage.
Now, onto my suggestions:
**Glycol Nucleic Acid:**
Firstly, glycol and glycerol nucleic acids are different molecules. Glycol nucleic acid uses propylene glycol as the backbone, glycerol nucleic acid uses glycerol. Glycol nucleic acid is more stable than DNA or RNA [4], and it follows base pairing rules.
On the left is glycol nucleic acid, note the lack of an oxygen atom linking the backbone and the base.
[](https://i.stack.imgur.com/snd6H.png)
Given the simplicity of its backbone, it's entirely plausible for it to have originated under conditions similar to those of early Earth.
**Other suggestion: Peptide Nucleic Acid**
[](https://i.stack.imgur.com/T9Vpu.png)
This nucleic acid uses N-(2-aminoethyl)-glycine as its backbone. It is hypothesized that PNA may have existed at some point in Earth's past [5]. There have also been some studies that suggest that PNA is, under certain conditions, capable of folding into structures besides the double helix [6], so it may be the case that PNA has some capability to act as a catalyst as RNA would. HOWEVER, just how capable PNA is in that specific regard has, to my knowledge, not been studied, so it might be that PNA is not as good as RNA in regards to being able to fold into a shape with catalytic activity.
Three problems with this idea:
First, source 4 says that the double helix formed by PNA is wider and more slowly-winding compared to DNA, I'll explain why that might be problematic later.
Secondly, N-(2-aminoethyl)-glycine, the backbone of PNA, is a neurotoxin. So, while alien viruses are probably not going to be infecting humans with any degree of success, it might be unwise for a human to eat alien life that's based on PNA.
Thirdly, PNA does bind to DNA and RNA. Nucleotides based on PNA have been used in antisense therapies. That is to say, if a fragment of PNA were to bind to a bit of messenger RNA or even DNA in the nucleus, that fragment will not be able to be read by the body's translation machinery. However, that would require that PNA somehow gets inside a human cell and that that bit of PNA is complementary to some bit of DNA or RNA in the body. Given that totally alien life is probably going to evolve to use a different set of amino acids for its proteins and that alien viruses are going to evolve to target alien life and replication machinery used by that life, that's not going to happen. Furthermore, human translation machinery will not read PNA, so you can rest assured that, even if an alien virus were to somehow get inside a human cell, it won't be able to replicate.
**Alternative Bases:**
Life on Earth uses adenine, guanine, cytosine, and thymine as the nucleobases in DNA (RNA uses uracil instead of thymine). However, scientists have also created 8 synthetic nucleobases that could serve as the basis of encoding genetic information [7]. In addition to using a different backbone, you can also use a different set of nucleobases.
**Possible Issues:**
In nature, humans and other eukaryotes use a complexes known as histones to make DNA more compact and as a means of regulating gene expression. I do not know if the proposed nucleic acids would be compactable or not. Also in regards to GNA, I have not been able to find studies as to how resistant it is to hydrolysis.
**In regards to your three criteria:**
* The proposed nucleic acids still use the same elements as DNA. Check.
* While PNA could bind to DNA, Earthling cells' transcription and translation machinery won't read PNA or the DNA/PNA structure, so you can rest assured that alien viruses won't be able to infect Earthlings. Sidenote: Whether or not the alternative nucleic acid can bind to DNA is not enough to determine whether it's possible for a virus to infect a DNA-based organism. The important criteria here are whether the virus can gain entry into a cell and whether the cell's translation machinery will be able to read the genetic code and make more viruses.
* "Maybe" on whether PNA could catalyze chemical reactions to allow for the emergence of early self-replicating molecules or if there would need to be some RNA-analog as well. But, if conditions are right and life can evolve to be more complex, it certainly could code for proteins. As for Darwinian evolution, there only need to be four things for that to occur:
* Things must be capable of reproduction. Check.
* The offspring must have some variation from the parents. Provided that the replication of the genetic material introduces some errors, check.
* These variations must be heritable. Check.
* Certain variations must make the thing more capable of surviving and reproducing. Check.
**Sources:**
[1] <https://www.tcichemicals.com/US/en/support-download/chemistry-clip/2013-10-08>
[2] Gribble, G. W. (n.d.). Naturally Occurring Organofluorines. Organofluorines, 121–136. doi:10.1007/10721878\_5
[3]<https://en.wikipedia.org/wiki/RNA_world#Limitations_of_information_storage_in_RNA>
[4]<https://pubs.acs.org/doi/10.1021/ar900292q>
[5]Banack, S. A., Metcalf, J. S., Jiang, L., Craighead, D., Ilag, L. L., & Cox, P. A. (2012). Cyanobacteria Produce N-(2-Aminoethyl)Glycine, a Backbone for Peptide Nucleic Acids Which May Have Been the First Genetic Molecules for Life on Earth. PLoS ONE, 7(11), e49043. doi:10.1371/journal.pone.0049043
[6]<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2808706/>
[7]<https://en.wikipedia.org/wiki/Artificially_Expanded_Genetic_Information_System>
[Answer]
# p-RNA
So, caveating that I'm more of an evolutionary biologist than biochemist, and these days more of a programmer than either.
One of the issues here is not making the things - I'd strongly believe that all the above, given the right enzymes, are synthesizable by biological life.
However, any form of DNA existing in a similar configuration to we have now would be a strong hint that this life is related to our planet's life in some way. There's sort of nothing inevitable about DNA arising as the stable information storage molecule.
RNA on the other hand..
RNA is both an information store, and a functional molecule. Arguably the most important enzyme is an enzyme made of RNA, and it is basically a hangover from when everything in the cell was an enzyme made of RNA.
RNA also forms simply, from, we think, the primordial soup - the conditions on earth before life arose. The idea goes that RNA strands formed, some of them became self replicating, and they grabbed all of the resources and began battling it out. A few billions of years of evolution later, throw in a cell membrane, proteins, DNA, complex carbohydrates, and you have us!
So, the argument here is that those same conditions arose somewhere else. Rather than go with DNA, RNA simply got better. Now we have aliens with no DNA, and possibly some extremely different chemistry. So, prehaps, missing DNA, maybe much more functional RNA molecules in the cell. We might see lower protein involvement, with proteins used for membrane spanning and some more complex machinery
[Answer]
DNA and RNA with additional letters dont need proteins at all. Protein folding acts as a catalyst and structural material. with additional letters rna can do this job.
<https://www.quantamagazine.org/new-letters-added-to-the-genetic-alphabet-20150710/>
P.S. Peptide nucleic acids are super interesting. Id love to learn more about them for anyone interested.
] |
[Question]
[
I have a planet about the size of earth. It is a desert planet with an atmosphere at 0.1 atm, made of 90% co2 and 10% n2. Water at this pressure should freeze at 35℉ and boil at 125℉. The planet has a magnetic field, a day of 28 hours, an axial tilt of 28°, a year of 3267.5 hours and an average temperature of 130℉.
I would like water at the poles to be liquid during the winter and evaporate during the summer. What changes should I make to my planet to allow this to happen?
[Answer]
>
> (..) an average temperature of 130℉ (...) I would like water at the poles to be liquid during the winter and evaporate during the summer. What changes should I make to my planet to allow this to happen?
>
>
>
# NOTHING
Your planet is already too hot.
The average temperature of the Earth right now is 57F. This is what global temperatures look like throughout the year:
[](https://i.stack.imgur.com/9gF97.png)
Source: <https://sci-web46-v01.ocio.monash.edu/mscm/greb/cgi-bin/scny_i18n.py?scenario=37&variable=01> - this is a tool that simulates Earth temperatures should we increase or decrease its distance to the Sun. The image above is with its current distance averaging 1 AU through the year.
The white color in the map is a temperature range going from -5K to 5K above the current global average. 130F is almost exactly 40K above 57F, so it would be the darker reddish hue in the map's scale. To turn the whites of the above map into reds, we would make everywhere else much hotter too. Like this, is the Earth were to orbit at 0.91 AU (the lower limit on the simulator):
[](https://i.stack.imgur.com/Ncluq.png)
The water will simply never freeze anywhere. You may have it evaporate in the summer if it is accumulated in shallow pools in the poles, so it is more about geography than temperature now.
[Answer]
**Increase axial tilt to make polar winters colder.**
You want to make sure it is cold at the pole in winter. You can tilt your planet on its rotational axis to make sure this happens. The more axial tilt, the less sun a given pole gets in winter and the colder winter is. Axial tilt is why the sun does not even rise in the polar midwinter - and also why it does not set in polar midsummer.
<https://blogs.nasa.gov/pluto/2015/10/23/a-planet-for-all-seasons/>
[](https://i.stack.imgur.com/ZAaVY.png)
Changes in axial tilt of earth over long periods account for changes in seasonal temperature extremes.
<https://earthobservatory.nasa.gov/features/Milankovitch/milankovitch_2.php>
>
> Obliquity (change in axial tilt) As the axial tilt increases, the
> seasonal contrast increases so that winters are colder and summers are
> warmer in both hemispheres. Today, the Earth's axis is tilted 23.5
> degrees from the plane of its orbit around the sun. But this tilt
> changes. During a cycle that averages about 40,000 years, the tilt of
> the axis varies between 22.1 and 24.5 degrees. Because this tilt
> changes, the seasons as we know them can become exaggerated. More tilt
> means more severe seasons—warmer summers and colder winters; less tilt
> means less severe seasons—cooler summers and milder winters. It's the
> cool summers that are thought to allow snow and ice to last from
> year-to-year in high latitudes,
>
>
>
You might not need to tilt it that much if your planet has a long year = big orbit. A big orbit means longer seasons means more time in winter means more time for the water to condense and rain down on your poles.
[Answer]
So, first of all, earth has three types of poles: True Grid North, Astrological True North and Magnetic North and corresponding Southern equivalents. True Grid North is the point where a cartograph grid of a planet would place the prime meridian's intersection with the 90th degree of latitude. Astrological True North is the point around which the planet's rotation occurs, and Magnetic North is the location where a planet's magnetic field is north.
It's important to note that while the first two are fixed locations, the later one is constantly shifting over time and will one day be located close to either True South.
Now, as I said in comments, on earth the poles aren't ice and snow because of atmospheric water, but rather are snowy and ice because it's cold. Both polar regions get very very little rainfall (well, snow, sleet, hail) annually, despite being absolutely covered in the stuff. This is because they are not in positions that would favor perciptation, because, being so cold, the atmosphere cannot hold as much water, so very little water vapor will reach these locations before precipitating.
This is the problem with your entire model. Water vapor is atmosphere is measured by humidity and how much water can be held in atmosphere in a given location is dictated by a number called the "Dew Point" which is a 100% saturation. When this occurs, water vapor turns to liquid and falls from the sky... or forms droplets on items close to the ground. The dew point is not a fixed point, as it changes not only based on the temperature of an area, but also the air pressure. The colder and denser the air.
The other thing about deserts is that they are very hot... but only during the day. Remember deserts lack the amount of atmospheric water to precipitate. Well in Earth's Atmosphere, atmospheric water works to keep heat trapped... but since deserts lack that, they get cold at night.
YOu also have a problem that your atmosphere looks remarkably like Venus, which, thanks to its ~96% CO2 and ~4% N2 atmosphere, it has an impressive heat retention that makes the surface of Venus is a balmy 867 °F. We don't know if Venus had a sufficient amount of water comparable to Earth, but if it did, it's long stopped being able to rain it out.
All that said, if you want polar liquid water, it's not that hard. All you have to do is make the lowest point on the planet the polar regions. Water flows down hill, so as long as your poles are the lowest point, it will go to those spots.
] |
[Question]
[
I have a planet, let's call it Davy-Tim. Davy-Tim has 2 times the mass of the Earth and has a magnetic field. Davy-Tim has a negligible atmosphere and orbits an average millisecond pulsar named Dad, at a distance of 0.8 AU. Dad has a certain tilt and poles so that its radiation beams are aligned with Davy-Tim's orbit. This means that the radiation beams always hit within Davy-Tim's orbit and hit Davy-Tim every time the beams come around.
My question is, what types of/how much radiation will Davy-Tim be receiving?
[Answer]
**Note:** The 10 Sunsworth figure was wrong for this particular pulsar but is realistic in general. It is not the luminosity of the pulsar. it is the "thermal luminosity" of the pulsar's orbiting star.
[The luminosity for pulsars in general ranges](https://www.atnf.csiro.au/research/pulsar/psrcat/proc_form.php?version=1.68&Name=Name&Edot=Edot&startUserDefined=true&c1_val=&c2_val=&c3_val=&c4_val=&sort_attr=jname&sort_order=asc&condition=&pulsar_names=&ephemeris=short&submit_ephemeris=Get+Ephemeris&coords_unit=raj%2Fdecj&radius=&coords_1=&coords_2=&style=Long+with+last+digit+error&no_value=*&fsize=3&x_axis=&x_scale=linear&y_axis=&y_scale=linear&state=query) from the order of $10^{29}$ ergs/second to the Crab pulsar which is $10^{38}$ ergs/second. The Sun is about $10^{33}$ ergs/second. So we see pulsars range from $0.0001$ to $100000$ Sunsworth. 10 Sunsworth falls in that range. But the range is so big you can really make the pulsar as powerful as you like.
The figures on the table are not the exact measured luminosity. They are the so-called "spin-down luminosity". This is a theoretical upper bound based on the period and mass of the pulsar, and how quickly it is losing kinetic energy.
---
# 520 Sunsworth
If you stand on the planet then 520 times as much energy hits you from the pulsar jet, compared to how much would hit you from the Sun on Earth.
HOWEVER: The beam will hit the planet for a very brief amount of time before it rotates out of focus again. So you will not have time to be cooked alive. It is an exercise for the reader to compute if you will be cooked alive over several rotations.
The pulsar [PSR J0952–0607](https://en.wikipedia.org/wiki/PSR_J0952%E2%80%930607) weighs about 3 Suns. The luminosity is about 10 Suns' worth. The following method works the same if you substitute figures from your favorite pulsar.
Luminosity is the amount of energy released by the star. For a normal star the energy is radiated symmetrically. For a pulsar the energy goes out the two jets. So each jet shoots out 5 Suns worth of energy.
For simplicity let's say the emission shoots out in a cone of 10 degrees. That's consistent with [this answer on Physics Exchange](https://astronomy.stackexchange.com/questions/40482/what-is-a-typical-polar-angle-of-a-pulsar-beam)
For simplicity we'll suppose your planet is exactly 1 AU from the pulsar. Consider the sphere of all points 1 AU from the pulsar. The jet sprays into "some spherical cap" (the blue part of the sphere surface)
[](https://i.stack.imgur.com/9p1fF.png)
If that cap is big then the energy is more spread out and less hits the planet. If the cap is small then the beam is focused and the planet gets more energy.
Fortunately the area is easy to compute. [The formula](https://en.wikipedia.org/wiki/Spherical_cap#Volume_and_surface_area) is $A = S (1-\cos \theta)$ for $S$ the area of the whole sphere. For $\theta = 10^\circ$ we have $\cos \theta =0.985$ and $A = 0.015 S$.
That means we have 5 Sunsworth of energy compressed into an area $0.015$ the size of the sphere. So the density of the energy passing through the cap is $5$ times $1/0.015 \simeq 66.666\ldots $ times the energy density of the Sun on the Earth. The total is $5/0.015 = 333.333$ Sunsworth.
Move the planet to 0.8 AU and the area of the cap shrinks by $0.8^2 = 0.64 $. So multiply the density by $1/0.64 = 1.5625$ to get about $520$ Sunsworth.
If you shrink the angle to 1 degree as mentioned in the same Physics answer, then we have $\cos \theta = 0.9998$ and the final answer goes up by a factor of 100. So it would be
# 52,000 Sunsworth.
[Answer]
# Davy-Tim receives Nova-level radiation
Neutron stars may be small, but they are really hot. As in millions of kelvins hot. This means that most of the radiation emitted by a neutron star will be in **HARD X-RAYS**, and Gamma Rays.
The fact that Dad has a radiation beam proves that it too has a accretion disk. Neutron stars are very similar to black holes in accretion characteristics i.e. only a tiny fraction of the accreted matter actually reaches the star, and the rest is blasted away. Neutron stars are really sloppy eaters.
Most pulsars rotate hundreds of time a second. And since Dad's radiation beam are in perfect alignment with Davy-Tim, you can expect to be hit hundreds of time a second. We don't know how much radiation you would get though, as there are really vague sources of information which are not clear, but from what I have read, Davy-Tim would receive supernova-level radiation every single second. And that too in hard x-rays and gamma rays, with traces of ultraviolet.
Dad's magnetic field would make the scenario even worse, as neutron stars tend to rotate so fast that their magnetic fields tangle, which releases massive amounts of energy.
**Supernova with ultra-solar-flare combo.**
] |
[Question]
[
This is a sequel to [my previous question](https://worldbuilding.stackexchange.com/q/220581/87100) in this vein, in which I [handwaved](https://tvtropes.org/pmwiki/pmwiki.php/Main/HandWave) away some issues related to [Bob overheating](https://worldbuilding.stackexchange.com/questions/219040/how-do-i-stop-bob-the-gigantic-animal-from-overheating).
As [DWKraus](https://worldbuilding.stackexchange.com/users/74691/dwkraus) [pointed out when answering said previous question](https://worldbuilding.stackexchange.com/a/220590/87100), [cell membranes](https://en.wikipedia.org/wiki/Cell_membrane) start to dissolve around 45°C, providing an upper limit to the temperature an organism can withstand even if it has plenty of [heat shock proteins](https://en.wikipedia.org/wiki/Heat_shock_protein) and [topoisomerase V.](https://en.wikipedia.org/wiki/Methanopyrus#Future_Research)
However, it's important to note that cell membranes are made of [lipid bilayers](https://en.wikipedia.org/wiki/Lipid_bilayer). [The longer a lipid's tail is, the more heat-resistant a bilayer made of that lipid is.](https://en.wikipedia.org/wiki/Lipid_bilayer_phase_behavior#Physical_origins) Provided that you avoid carbon-to-carbon [double bonds](https://en.wikipedia.org/wiki/Double_bond) - i.e. avoid turning the lipids in the cell membranes into unsaturated fats (see [here](https://en.wikipedia.org/wiki/Fat#/media/File:Fat_triglyceride_shorthand_formula.PNG) for the difference; basically, unsaturated fats are when fats have carbon-to-carbon double bonds) - they won't kink up and start behaving like a liquid.
As [this source](https://phys.libretexts.org/Courses/University_of_California_Davis/UCD%3A_Biophysics_241_-_Membrane_Biology/03%3A_Membrane_Phases_and_Morphologies/3.01%3A_Membrane_Phase_Transitions) points out in this table:
[](https://i.stack.imgur.com/wtaPk.png)
...there are longer [lipids](https://en.wikipedia.org/wiki/Lipid) out there, ones that dissolve at higher temperatures than 45°C. And if the diarachidoyl phosphatidylcholine/DAPC in the table, with a dissolution temperature of 64.1°C, isn't enough, you could probably base a lipid bilayer off of some other kind of fatty acid, [of which there are many.](https://en.wikipedia.org/wiki/List_of_saturated_fatty_acids)
Tetracontanoic acid, for instance has a long [alkane](https://en.wikipedia.org/wiki/Alkane) tail indeed - 40 carbons, well more than the 16 and 18 of dipalmitoyl phosphatidylcholine/DPPC and distearoyl phosphatidylcholine/DSPC. This suggests that a lipid bilayer made of an [ester](https://en.wikipedia.org/wiki/Ester) of tetracontanoic acid (all lipids are esters of [carboxylic acids](https://en.wikipedia.org/wiki/Carboxylic_acid) and [alcohols](https://en.wikipedia.org/wiki/Alcohol_(chemistry))) would be *incredibly* heat-resistant, and, moreover, that even longer (and therefore more heat-resistant) lipids could potentially be formed, **meaning that cell membranes dissolving would be a non-problem**.
Now, the hypothetical organism that has all these adaptions:
* has proteins that can't [denature](https://en.wikipedia.org/wiki/Denaturation_(biochemistry))
* is immune to [sepsis](https://en.wikipedia.org/wiki/Sepsis)
* can't have its cell membranes dissolve; if they aren't durable enough to avoid dissolving, just add more alkanes on the end until they are
The question: **what's the next problem? After septic shock, proteins denaturing, and cell membranes dissolving are overcome, what's the next overheating-related thing to cause physical harm to/kill this organism?** Last I checked, it was up to 45°C - can it get higher?
I considered the [ether](https://en.wikipedia.org/wiki/Ether)-based [cell membranes of archaea](https://en.wikipedia.org/wiki/Archaea#Membranes) for this, rather than the extra-long-lipided [ester](https://en.wikipedia.org/wiki/Ester)-based cell membranes I actually chose, but they have rigidity-related, permeability-related, and [transmembrane protein](https://en.wikipedia.org/wiki/Transmembrane_protein)-related issues.
Just for context: this is an [eukaryotic](https://en.wikipedia.org/wiki/Eukaryote), [multicellular](https://en.wikipedia.org/wiki/Multicellular_organism) organism, not an [archaea](https://en.wikipedia.org/wiki/Archaea). I would also point out that it runs on Earth biology, and that **100°C is likely an upper limit here**, considering water boils at that temperature under [standard temperature and pressure](https://en.wikipedia.org/wiki/Standard_temperature_and_pressure).
[Answer]
It seems that there are eukaryotes that can live above 45 C. There is a nice review article [life in extreme environments](https://www.nature.com/articles/35059215) that has charts out the upper temperature limits for each taxa, at least as known in 2001. This paper claims ~60 $^o$C and a different paper without a reference for it claimed the world record was 62$^o$C. So it seems that even with real organisms there may be a little more wiggle room for higher temperatures for your story purposes.
[](https://i.stack.imgur.com/qWeT0.png)
>
> reducing chemolithoautotroph, capable of growing at the highest temperatures of up to 113 $^o$C (ref. 15). Hyperthermophile enzymes can have an even higher temperature optimum; for example, activity up to 142 $^o$C for amylopullulanase 16. There are thermophiles
> among the phototrophic bacteria (cyanobacteria, purple and green bacteria), eubacteria (Bacillus, Clostridium, Thiobacillus, Desulfotomaculum, Thermus, lactic acid bacteria, actinomycetes, spirochetes and numerous other genera) and the archaea (Pyrococcus, Thermococcus, Thermoplasma, Sulfolobus and the methanogens). In contrast, the upper limit for eukaryotes is ~60 $^o$C, a temperature suitable for some protozoa, algae and fungi. The maximum temperature for mosses is lower by another 10 $^o$C, for vascular plants it is about 48 $^o$C, and for fish it is 40 $^o$C, possibly owing to the low solubility of oxygen at high temperatures (Fig. 3).
>
>
>
I think the bottom up approach to adaptations, is interesting. But it seems like there are adaptations before a sharp temperature cut off. For example, DNA denatures in the lab ~ 95 $^o$C when doing PCR. I would have assumed that would be a hard cutoff, but apparently DNA in a hyperthemophile grows optimally at 100$^o$C. So the conditions inside the cell are more important than the stability of the molecule in isolation.
It seems that after cell membranes that the flexibility and stability of proteins is probably really important. I think the protein structures would need to be stiffer and less floppy at higher temperatures.
If I read you original goal correctly, the goal was to have a large animal and you wanted to avoid overheating in the center of the animal. Making the cells survivable to temperature I think is one thing, but another think to think about is how oxygen gets transported to the cell. I think with increased temperature that oxygen binding to hemoglobin decreases. Also in general the percentage disolved gasses in a fluid decreases with increased temperature.
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Writing about a character who used to be a veteran infantryman who was skilled with a two handed spear, both as part of a spear wall and in battlefield combat. Due to the loss of his non dominant arm, he was allowed to transfer to being a guard but is expected to practice regularly and to train recruits.
He had some levels of discomfort using a one handed spear, but still wants to use a relatively long weapon, since he's fairly unskilled in closer range combat. What are some options he could consider? Preferably melee, as reloading would be damnably difficult.
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An one-armed soldier is going to have some problems. I doubt that they would be placed in any position that might occasion actual combat. Being a trainer or drill sergeant would be the best that he might hope for. Those who can, do, and those who can't, teach, after all.
That said, the best weapon for a former spearman would be another thrusting weapon. If for some reason he can't use a one-handed spear, then a thrusting sword such as a rapier, an epee or a foil might be the next best thing. He'd be used to thrusting for vital or weak points, after all, and so would have less to unlearn than if he took up a slashing or crushing weapon. His main challenge would be to learn to parry with the weapon, rather than a shield. While early thrusting swords were often used with bucklers, daggers or capes, they came to be used one-handed with the other hand held out of the way, used only to provide a marginally greater impetus to a lunge. Thrusting swords came into use by unarmoured fighters because they were faster than any weapon that needed to be swung, as well as any heavier thrusting weapon such as a spear or *zweihander* (which were also largely thrusting weapons despite being swords).
Being a guard, armed with his new weapon, would not likely occur until he had a degree of proficiency with it.
[Answer]
I'd suggest a rapier. Followed by sabre or basket-hilted sword.
First lets look at the measurements taken from Wikipedia. An average of course.
* Mass avg. 1 kg
* Blade length avg. 104 cm
* Width avg. 2.5 cm
A rapier is an excellent dueling weapon. It has extensive hand protection. It was usually paired with a dagger or another tool but it's perfectly capable of functioning alone.
It also has reach which is a major point in all dueling. Obviously not as much reach as a spear but it does offer more reach as opposed to an arming sword or a longsword.
War rapiers also existed with thicker blade for better cutting. Rapiers, unless the edges are blunted, can generally cut. And with a more cut oriented design you can even improve the cutting capability of the weapon.
I'd even suggest making a custom "stronger" rapier. That is if your guy is a really motivated fighter and is stronger. You can easily make a bigger heavier blade and have him train and adjust to it. Of course you are not getting cuts that equal axes. But if you just keep making the blade closer and closer to that of an arming sword and stopping right at the perfect balance that fits that person. I'd wager you can get a pretty good weapon that will serve him well in war.
Obviously that denies him a lot of battlefield applications. He is not going against full plated knights. He is also not shooting bows anytime soon. But he is trying to make the best of what he has. And I recon that my idea of a custom made "stronger" rapier can push what he can do.
All I just said are general principles. Meaning that you can make a short cutting blade then add a rapier like hilt. This is a starting point to either adopt a historical weapon or make something custom. I'd say that a person going to a swords maker and commissioning a very specific weapon is very realistic and is even historical.
**What made me focus on rapiers is that you requested length. But other swords that followed some of the same ideas existed. Pick the most fitting.**
I'd also suggest giving him a position of an officer if that is possible or fitting. For obvious reasons it would be more suited to have a man of experience and bravery still serve but be expected to lead and organize rather than just march and form a shield wall.
What you wrote made me believe that he has *one* arm. As in not just losing his hand but his whole arm. Because if he still has an arm I'd imagine he can still use a sword and strap a shield to the other one.
Only other thing I can think off is a custom made spear. Lighter materials and a more compact design. A bit short to be used one handed. And a bit of a thinner blade. But honestly without hand protection at all, without a shield, without a dagger, and no ability to use the other hand for anything. I'd 100% be using a rapier or a similar weapon.
Please note that I'm using words like long sword or arming sword...etc just to facilitate the answer. Naming things in history is always complex. But I think most people get the general meaning when we say longsword which is good enough for me.
[Answer]
## Sling weapons
A [sling shot](https://www.chrisharrison.net/index.php/Research/Sling) (sling stick in Roman times) may work as a projectile weapon, although it may require some skill to load a sling with a new pebble/stone, for a one-armed person.
**Melee combat - Flail**
Because your man hasn't got a shield, you need a weapon that makes close approach dangerous. A long sword or axe cannot be moved quick enough. Slinging around something dangerous may work, for close combat in medieval times below sling weapon. There are several types, these are the single handed ones,
[](https://i.stack.imgur.com/ONITp.png)
[](https://i.stack.imgur.com/Sk61M.png)
*Netherlands (Friesian, medieval 13th-15th C)*
<https://en.wikipedia.org/wiki/Flail_(weapon)>
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**Tonfa spear.**
[](https://i.stack.imgur.com/wg2bA.jpg)
<https://en.wikipedia.org/wiki/Tonfa>
Tonfas are fighting sticks with cross handles. A descendant is the T-baton used by some police forces. The cross handle allows a more powerful grip with wrist in line with forearm.
Your character fits out his spear with a cross grip to more effectively use his one hand.
A problem would be that the length of the spear could cause the long side to pivot, which would be opposed only by friction at the grip. You could address this with a forearm brace like a forearm crutch.
[](https://i.stack.imgur.com/lKbku.png)
<https://en.wikipedia.org/wiki/Crutch>
The forearm brace keeps the spear in line with the forearm; this and the cross handle keeps the whole thing in contiguity with the distal arm.
This now has similarities to my Forearm Crutch Mace concept for a zombie armageddon fiction; the paraplegic protagonist uses two forearm crutches made out of long-handled sledgehammers. <https://www.halfbakery.com/idea/Forearm_20Crutch_20Mace#1279500071>
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**WHIPS**
Whips have been used as weapons for millenia.
A **bullwhip** has a length of up to 6 m. While it is mainly used to create noise, when the tip breaks the sound barrier, it can also be used as a weapon. [According to Wikipedia](https://en.wikipedia.org/wiki/Bullwhip), Simon Tookoome, a Canadian Inuit and expert bullwhip handler, was known to have used one to hunt ptarmigans and caribou, and to kill a wolf. A skilled whip user can use a whip to disarm or ensnare an opponent and could inflict painful, bleeding facial wounds, perhaps even blinding opponents.
The Chinese were known to use whips as martial weapons. The **[chain whip](https://en.wikipedia.org/wiki/Chain_whip)** is made from up to a dozen metal segments whip with a dart or narrow blade at the end. It can be up to a meter and a half long, sometimes more.
The **[bian](https://en.wikipedia.org/wiki/Bian_(weapon))**, or 'hard whip', another Chinese weapon, isn't a whip in the ordinary sense, since it is rigid, but it used to inflict damage with a whipping motion. the Chinese language doesn't dinstinguish between a hard and a soft whip. It weighs 7-8 kg with a length of around 90 cm and is mainly used from horseback in one hand.
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I am imagining a Harry-Potter-like magical scenario: A secret parallel society of magic wielders in our modern-day era, only known to those, who grew up in it or those, who got initiated.
I find it rather hard to believe, that in this scenario, there is no digital evidence of people doing magic or magical creatures. Could there be a physical or technological reason for this?
In my (very) limited understanding of science, I imagine "magic" as some kind of particle that somehow affects the process of recording with modern-day technology? But if so, why could human eyes perceive "magic" nonetheless? Or maybe "magic" has some kind of low-key EMP qualities, that mess with technology?
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If magic just jams technology, you will end up with lots of recording devices breaking down just at the moment when a guy with a pointed hat started waving his hands. Suspicious.
That leads me to a different approach, still close to "physical or technological", I hope: **Magic is inconspicuous by default**. There is no lightning bolt or fireball, magic itself looks more like electricity going through a wire, or radioactivity, or the thing that keeps Earth in its orbit.
A witch may just focus on a spell, touch an artifact or so, then something happens that cannot be directly traced to her. Maybe it could just as well happen anyway, except it would not. Of course, this is more difficult if the effect is a levitating house or something. On the other hand, people, for instance, do a lot of strange things on their own, even without a witch waving her hands nearby, right?
Now, why people DO see lightning bolts and fireballs? Because certain spells were engineered to be visible for them. Say, for safety reasons. The spell, besides doing its thing, will enter your brain and tell it: Caution! Magic is happening here. Which you perceive as a fireball, obviously. These spells were not designed for cameras, either because there were no cameras at the time, or because wizards thought easier to develop their own devices to detect magic, rather than tweak the muggle ones.
This also means you can still have invisible magic, like you can have an odorless natural gas, when you put some effort in obtaining that.
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For several reasons.
For "Magic" itself, because you do not know what to look for.
Let me expand on that: To measure something, you first have to observe its effects, whether you know it's there, or not. Gravitation was discovered by looking at an apple falling from a tree, and wondering WHY it started falling. Then measuring the change in speed as time went, etc.
You measure electricity by using things which react to it. Else, you do NOT know there is electricity in a wire, or a battery, whatever. You know when it interacts with something (a lamp lights up, or someone gets shocked, etc.)
You do not "see" the wind. You only notice its effects (trees/plants rustling, clouds moving, mills turning, your skin getting chilly, etc.)
So, as for magic, maybe we merely didn't find anything to record its presence, or it IS known (mostly, or exclusively, by magic practitioners), and guarded with zeal.
Now, for the *effects* of magic, like a sudden fireball, teleportation, a house growing from palm-held size to mansion-size in seconds... there are several possible explanations.
The most plausible is... magic ! Spells which have been cast in order to keep the muggles (err, sorry, the "people not-in-the-know") from noticing things, or recording things. How do they work ? Magic ! The general principle, however, would be that the magic either foils your attempts at recording it, and/or even better, at *noticing* it.
A guy is flying a dragon near you ? No problem, you're *really* interested in that flower, or the latest game on your mobile phone, whatever. A wizard pops-up a few meters away from you ? Well, he definitely was here before, right (if you even notice it). Either your mind will be too fogged-up to notice his arrival, or the spell will make you think that it happened differently. Like create a memory of him walking there. A fuzzy memory, probably, because you weren't paying attention.
You were recording a video, and a spell pops out in the recorded area ? No problem, the magic "edits it out", both from your mind and the media, so it cannot be broadcast, and you cannot even testify about it.
So, yeah, all-powerful spells already in action, which protect the magic world. Either cast by wizards, or maybe even a natural magical phenomenon (after all, who knows how Magic works ? Maybe it's because nobody believes in it that it gets "erased" from memories and physical mediums ?)
Another possibility is a sort of "secret police", Men-In-Black style, which comes and *erases* evidence (including your own memories). When something starts getting shared, they come, erase the internet threads, posts, tweets, stories, whatever, and send a team to the location to also take care of the people who saw. It would be nigh-impossible with our technological means, but with targeted spells, like "everybody who saw this", it could very well be doable.
However, it cannot be as simple as an "emp" effect, as that would lead to visible consequences (like, damaged equipement, a record which goes "blank" before coming back on, etc.)
Plus you'd need a way to explain why before the blank, the scene looked normal, and why after, it looked like a bombing occurred.
[Answer]
## Censorship.
One of the wizard spells removes all physical evidence that would document a particular assertion - such as that magic exists. In the name of 'ethics' most wizards use a spell that spares human minds, at least. But for those without direct recollections, all the evidence is consistent: *it never happened*.
At least, until some heroic wizard turned defender of the people starts teaching the masses how to interfere with the spell...
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Agreed with Kzwix (human) perception is very relevant. Some change takes place..
*Q: "In my (very) limited understanding of science, I imagine "magic" as some kind of particle that somehow affects the process of recording with modern-day technology?"*
The answer for this one is imho a multiverse-explanation: recorders and instruments only observe one time line, they can't hop their "mind" to alternate universes, like we do, when affected by magic.
How does this work..
**Suppose you'd have all time lines**
Suppose we have all parallel universes available, for every *possible fork* of events related to any particle above Planck size. Time-trees rather than time lines. Anything is possible *somewhere*. There are [googols](https://nl.wikipedia.org/wiki/Googol) of parallel universes, containing googols of available, independent realities. These realities do not interact, nor does there exist any magic, all branches behave according to the laws of nature. There is no way to move across these universes with Einsteinian means. We just fork and ride along with our time-tree, until we fork again or die. Every nanosecond or so. We remember the past (our own path) as a *time-line*. And everything remains possible in the future, for every individual. There are many of you: some places (branches of the tree) you'll end up a beggar, other branches of the tree you will become a millionaire..
**Time weaver - example: Disappearance trick**
What's a Magus.. this is someone who can perform observable magic. He can appear, or disappear. He can make things change, appear, disappear. Say the magus can *weave* people's time trees together with other, *near resembling* time trees
As an example, take the - real - disappearance trick, Magusses love that. They suddenly appear or disappear. When the magus could drag along the witnesses (people) to a very similar time-tree, only difference is, it contains the result of his magic, the Magus NOT being present. These witnesses will have their own world in their memory and they remember seeing the Magus disappear. They ended up in a time tree that is exactly the same as theirs, except the Magus was absent at that point. A camera present will show a plausible sequence of events, because its past did not change for the camera, in the *time-tree* the witnesses entered. The camera has never seen the Magus.
For the other people, residing in the new time tree there is no issue. They remember the magus was not present in the first place ! so he did not disappear.. These people do not think anything changed.. only the witnesses that observed the disappearance know of that change.
The people left behind, or instruments that stayed in the previous, abandoned time-tree, will still see the Magus. He did *not* disappear in the original time-tree. Camera's will not see any change, detectors will not measure discontinuities, the Magus is still present.
**Bad weather is an imperfection**
While moving people to another time tree, the Magus has to choose a *near-resembling* branch in the tree. Often, he does not take everything into account. When e.g. the weather is different, the witnesses see storm and lightning occur. Weather difference was ignored by the Magus, so clouds collide, temperatures rise rapidly, or air pressure differs. The witnesses see the result, because things got mixed up in this time-tree, causing bad weather.
**Magic potion**
Even low power Maguses like Druides can brew magic potions. The working of these potions depend on the Magus' intent and the patient's issue. Most are trivial. Some substances affect time trees. Asterix *does* exist, somewhere, in some time-tree you have a person drinking magic potion and beating up enemy armies. But in most cases, a magic potion will invoke a curing experience.. there will be zillions of time-trees where the substances was *not* taken and you die earlier. Not much power is needed, and there is chance involved. Modern medical treatment is far more effective !
[Answer]
I think you'd need to define what 'magic' or spells you are using more precisely to get a reasonable answer to that. For instance, if the magic has some visual output to it, then it could be recorded by a camera. If there was noise, then a microphone. These results, technically, would most likely be due to the resultant forces of the spell (e.g. lights or vibration of the air particles). Though what if particular spells give of particular patterns or frequencies off light or sound? This would allow identification of particular spells through sound analysis or spectography?
If you deliberately want to make a condition for the magic that prevents it from being monitored by scientific methods, you could consider the One Ring, LOTR; this ring slipped the user out of the current world and into a shadow realm. This could be applied to all forms of magic. For instance, firing a fireball through a shadow realm, to hit an enemy elsewhere could be a possibility.
Alternatively, you may want to consider just *what* is being detected. If you consider telepathy, then that is the force of a mind moving an object without direct physical interaction. Electroencephalograms can monitor brain waves, but would they be able to pick up such power? What if your 'telepathy' is caused because you have a psychic link with a poltergeist?
Some RPG games implement channelling as a method of casting spells. Channelling is the use of a deity or spiritual realm that provides spell power.
So, things to consider:
1. What spells are available?
2. Would the spells naturally affect the environment?
3. Are the spells separated from the current plane in some way?
4. Are you going to use some form of proxy as the vehicle for the spell?
[Answer]
(I think this is roughly how it works in Ars Magica):
**Magic is more difficult to cast when people are watching**
Magic tells the world to be other than it should be. It is much more difficult to convince the world that a fireball just appeared when ten cameras and a hundred people are watching. So most magic is either done in a way that looks like it can be explained by natural phenomena, or when there aren't people/cameras around to notice. Undisguised magic that is recorded is rare enough to be explained away as freak accidents or hoaxes.
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Magic is a living and thinking force. In fact magic must be that way, how else it would know how to apply magician's incantation to very specifically pick some atoms and not others and alter them in very specific way? HP actually alludes to this, such as when a Muggle approaches Hogwarts, the spell (the living thinking magic) comes up with some very urgent errand to send them away. So in this way magic actively hides itself, detects any recording equipment and removes any evidence of stuff outside classical laws of physics. Unless
1. the magician wants otherwise
2. there's some clever triple-blind experiment setup. Triple blind means the experimenter writes down the hypothesis and plans double blind experiment involving magic, and then completely wipes down his memory. Or it makes him/herself believe different completely plausible explanation for the experiment. Later only after the traces go completely cold, it's possible to return to hypothesis and analyze the data. Or make somebody another do it.
3. there are statistical anomalies, such as in accounting it's possible to detect cooked numbers using statistics. This also must not be too overt.
4. it is possible to distract it somehow - the more complicated the spell itself is, the less thorough is removal of evidence
[Answer]
**Magic looks like cheap CGI**
There are plenty of videos where people claim to have filmed some unnatural phenomenon, but almost no one believes them because they obviously feel like faked videos. If the magic in your world looks like some kind of cheap CGI, almost no one would believe digital recordings of them.
Magic still can be cool-looking;
[](https://i.stack.imgur.com/cGOUx.jpg)(from <https://www.youtube.com/watch?v=U5EDORs8Jkk&ab_channel=CaptainDisillusion>)
The "magic" here looks pretty cool, but it doesn't really look "real". This is just an image; for extra fakeness, magic can move in an inconsistent-looking way. For example, a fireball wouldn't fly smoothly, but instead "teleport" small distances. This would look like someone was too lazy to edit all the frames.
The digital recordings of actual magic would just be treated like any other fake conspiracy-fishing video. But, if anyone **actually** sees magic, they would have to believe it.
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I have just found perhaps the biggest thing in the universe: A black hole named SDSS J010013.02+280225.8. It itself is 12 billion times more massive than our sun, and its accretion disk is 439 trillion times brighter. This could mean the universe's biggest habitable zone, right?
Here is the scenario: A black hole identical in dimension to SDSS J010013.02+280225.8 is orbited by co-orbital of trinary star systems within its habitable zone. All the stars are white dwarves, each one only 20% more massive than our sun. Therefore, the "sunlight" comes only from the black hole's accretion disk.
In regards to the black hole's mass, its accretion disk's luminosity and the amount of X-rays being emitted, how far and how wide would the habitable zone be?
[Answer]
Taking "439 trillion times brighter" to mean the "stellar" luminosity is 439 trillion times the sun, we can make some **rough** calculations.
The inner boundary of a stellar habitable zone is approximated by:
$$inner = \sqrt{L\_s \over 1.1}$$
Where Ls is luminosity is solar units and the result is in AUs.
Plugging in the given value, we get:
$$inner = \sqrt{4.39 \times10^{14} \over 1.1} = 2.00 \times10^{7} AU$$
There are approximately 63,241 AUs in a light year so we can simplify that to 316 ly.
The outer boundary is approximated by:
$$outer = \sqrt{L\_s \over 0.53}$$
Plugging in again:
$$outer = \sqrt{4.39 \times10^{14} \over 0.53} = 2.88 \times10^{7} AU$$
Which simplifies to 455 ly.
Making the width: 455-316 = 139 ly.
**CAVEAT**: these formulas were never meant to apply to this situation so I have no idea if they're right.
[Answer]
legio1's answer is jaw-dropping but I see nothing in the math to disagree with. However, I am going to disagree anyway and say there is no habitable zone--the problem is the luminosity of the black hole won't hold steady enough for life. Planets might at times be of a suitable temperature but that state won't persist over long periods.
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I am writing a film about a group of people who wake up from cryosleep after 5-10 years. I would like to know what kind of side effects these people would have upon awakening.
I've tried googling, but haven't found anything other than some sort of cold burn, chill, and confusion.
Also, one of the side effects that are crucial to the movie is memory loss, but I'm not sure if that could be scientifically possible or would be considered as sci-fi.
Any help would be appreciated.
[Answer]
Zombies. They would be zombies. Their soul would have believed the body were dead, and would have left it behind. Then these soul-less bodies would 'thaw out wake up' and be true human-less-body zombies.
Or not.
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**They are better than they were, and they are different than they were.**
People wake up sick and drunk and weak and stumble around. That is fine as far as it goes. But let us consider the Stallone and Snipes film [Demolition Man] which had a different take on cryosleep.
(<https://en.wikipedia.org/wiki/Demolition_Man_(film)>). In this film the good guy (Spartan) and bad guy (Phoenix) were both frozen in cryosleep, and their mind and bodies worked on by computers while they were unconscious.
>
> Spartan and Huxley witness this exchange on security cameras and
> review the cryo-prison records. They discover that Phoenix's
> rehabilitation program was tailored by Cocteau to make him even more
> dangerous than he was in 1996, including martial arts, computer
> hacking, knowledge of torture techniques, and murderous impulses; by
> contrast, Spartan's program taught him to knit and sew.
>
>
>
Both men are surprised at the changes. Stallone's character occupies himself sewing at several points during the movie.
In your fiction, the sleep pod exercises the body and the mind. The problem is that the characters were supposed to sleep for 18 months, but it went on much longer than expected. The mind exercise program has overwritten some old memories and skills with new things. Some of these things used to belong to other people and maybe some things that belonged to other characters.
All the characters know all the lyrics to a lot of songs which they do not realize until one starts singing, and they all start singing. They sound great together even though none of them understand the language that these songs are in.
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For my magic system, referenced in a few of my newer posts, I explain that magical energy is required to cast spells, but this energy is not evenly distributed.
***Magic System Recap:***
The energy flows from areas of close relation to the magical element (Air, Darkness, Death, Earth, Fire, Ice, Life, Light, Storm, War, and Water) in question: Forests are Life, oceans are Water, etc. In addition, regions can be multiple elements: Volcanoes are both Fire and Earth (Mountains are Earth, lava is Fire), hot springs are similar but Fire/Water, and battlefields are often War/Psyche, and also Death just after the battle.
From these reservoirs (Magivoirs) come Magistreams, useless strips of magical energy, which, if they cross on another, form a Magipool, a strong source of energy often more convenient than a volcano or cavern (Graveyards are still used often for their strong Death/Psyche sources for a conveniently close place). If a Magistream moves so that a Magipool only has one supporting Magistream (Which happens all the time), it fades away. Multiple Magipools of the same element can connect if close enough, forming a larger one called a Magijunction. These can stay until only one Magistream crosses through it, no matter how big it gets. In addition, temporary blobs of magical energy can form in the area of a spell, like the actual area or a trail following someone affected (By flight, mind control, or buffing). These are called Magistrikes, and last for roughly 10 minutes (Unlike Magipools, which last indefinitely until less then two Magistreams is left supporting them).
From the day a young mage (Called apprentices even if they attend a magical school or are teaching themselves) starts learning magic and spells, they are taught how magic moves unpredictably, and how to sense new sources within 31 meters of themselves (About 100 feet away) that will form in 6 seconds (Or find existing ones within that same radius). Mages use these to charge magical energy
Obviously, 6 seconds to cover 100 feet is not impossible for humans (This is actually under our max running speed for the average Jack or Jill (120 feet/6 seconds is 13.6 mph, we can run 15 mph)(I stole that from the RPG Stack Exchange)), but it's still essentially sprinting.
In addition, once the magical energy is out of the mage's body (Where it was stored until used) for use in spellcasting, the exact energy needed is spilled all round the mage; The mage is temporarily given master gymnast and acrobat abilities to collect the energy until the spell is cast. This is as in the mage is able to perform flips and other crazy stunts effortlessly to get the energy for the spell until the spell is cast, but must use actual muscle energy to do it (But magic takes some of the brunt off of that much energy expense).
Also, healthy eating is the best diet to help absorb energy; Splurging on candy and cake and other junk food all the time, or eating all the time in too big of quantities, lessens the magic absorption rate. Eating healthily in good amounts, and the occasional chocolate or alcohol consumption, drives magical energy absorption rates (And magical capacity) through the roof.
In general, Mages must be able to sprint short distances, sometimes several times in a row, perform magic-boosted gymnast stunts and flips, and eat great.
This, obviously, means that no mage is overweight or scrawny. However, I doubt if they would look like Olympic athletes (Particularly tennis players, who have similar circumstances of athleticism), but they won't be chubby.
***What would they look like, exactly, if they have to run like mad and do stunts for a living?***
**UPDATE:**
Someone asked me how much mental/physical training for mages, and this is what I'll say: They learn magical theory and practice simple spells (Like D&D cantrips) for 6 hours a day, and have physical training 2 hours a day when apprentices, and most continue that well after graduation. Self-taught mages, however, often wind up doing similar times, due to it making sense (Or, for more advanced people, they looked it up on the Damarian version of Wikihow).
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Given the blend of Physical requirements and mental discipline, I suspect your top tier Mages are going to look like either long term Yoga Practitioners or Parkour experts.
Come to think of it, in outward appearance, they will look pretty similar. Slim, Athletic builds. Not big beefy Muscular types, more like Bruce Lee or Jackie Chan in his prime. You know, slender, flexible anatomy charts.
Here is why: Your mage needs to be able to move quickly and efficiently (parkour) and also arrive and drop into a state of focus (Yoga). Both activities require a lot of body awareness. I also would like to drop a touch of Tai Chi in there as well as some of that involves the internal manipulation of Chi energy.
That covers your top tier mages, but keep in mind, folks of all body types might end up with some amount of skill. Given that your magical resources have definite rules you may also get sedentary mages. These are going to be people who work out in advance where Magipools will develop or will do things to maintain the location of a MagiJunction (ritual Sacrifice, anyone?). Or you may get wanderers, skinny people who live a nomadic lifestyle, don't get enough to eat. Think a nomadic Yogi or Guru, who's self imposed isolation leaves them skinny and underfed looking. Either of these body types may not be able to match the top tier types, but with clever application they can still be a force to be reckoned with. Think of a Trap Door Spider. With careful positioning they do well, even if they don't get out much.
It will shake out most likely along the following lines. Your Athletic types will be able to do Magic on the fly, almost anywhere, and with few limitations. Your other mages will be interested in things like locations, stable magic sources, and artifacts that allow the storage and later disbursal of magic. Imagine your Bruce lee type getting ambushed by a skinny bald guy with a walking stick, only the walking stick has been storing energy for weeks as the skinny guy walks around.
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# Like Dolph Lundgren
[](https://i.stack.imgur.com/dBf3S.jpg)
If you aren't aware, this is the boxer Sylvester Stallone faced off against in Rocky IV. While a couple of the factoids aren't correct (studied but didn't graduate from Washington State), it remains that you can be both wicked smart and full of physical ass-kickery
Although, since he's a bit exceptional, it might be a little more realistic to say:
# Like a U.S. Marine
[](https://i.stack.imgur.com/5ckB5.jpg)
Tons of Marines earn college degrees before and during active service, and they don't even graduate from Basic without grueling physical fitness that would make lesser men like you or me quiver like a chihuahua. 100-foot sprints are warmup exercises for these dudes.
That said, "flips and other crazy stunts" belong in Marvel movies and gymnastics routines, because one can get from point A to point B faster, easier, and safer without them. They also require years of rigorous skill-based training, regardless of whether one has the physical prowess necessary to do so.
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[Question]
[
I am writing a sci fi story and I want to know what would happen if a tungsten rod massing 1000kg slammed into the surface of Callisto at 15% of the speed of light? Given that there is a subsurface ocean what would the impact look like from afar, say half a million kms? Would there be a blinding light and steam and ejecta?
Specifically, I am interested in the visual effects and effects felt by residents moon wide. The target is a city built inside of Tindr crater on Callisto. Would there be moon-wide quakes? How long would quakes last? What would be the damage done to subsurface infrastructure? Would it penetrate deep enough to open a hole to the subsurface saltwater ocean? Also how would the explosion behave in vacuum?
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At about 250 megatons, the resulting energy would be about 10 times greater than the Mt. Saint Helens Volcanic Eruption. This would be enough energy to launch a mass of debris equal to a large mountain into the air, and at only 0.126G, a significant portion of it would be able to exceed escape velocity flying off into space.
Calisto has a very minimal atmosphere and no molten core. If it has a subsurface ocean, it is believed to be at a depth of 100–150km. So, the impact would not have very interesting interactions with the things above or below the moon's crust.
The crust itself is about a 1:1 ratio of silicon rich rock and ice. It is likely that most of the ice would melt or vaporize on impact. So, I would expect to see an explosion that looks like a cross between an [underground nuclear test](https://en.wikipedia.org/wiki/Underground_nuclear_weapons_testing) and an [underwater nuclear test](https://en.wikipedia.org/wiki/Underwater_explosion) does during the early phase of the explosion, but instead of mushrooming off as gravity and air resistance slow the blast down, the explosion will mostly just get bigger and bigger until is dissipates leaving only a small amount of the debris to fall back onto the moon or settle into an orbiting ring of dust.
Mt. Saint Helens could be heard from >250 miles away. Even at 10 times this strong, the impact may not be heard or felt from everywhere on the moon, but could certainly be felt from very far away. That said, there may be other factors at play that allow the energy to propagate better or worse. In general shockwaves travel much better through solid rock or liquid water than they do through ice, sand, or clay. Also, your impactor is imparting all of its energy at once, not over a long time like a volcano; so, you may get a stronger seismic wave that is over quickly compared to Mt. Saint Helens. Given the Kracatoa eruption as cited by JobSG in comments, I will say it is at least possible that it would be felt across the whole moon, but very hard to say for sure given limited information available for the moon's exact geology.
Based on nuclear tests which follow a similar profile to this impact, the initial flash of light will be very bright, but only last 1-3 seconds before being obscured by the debris cloud. The Earthquake, will probably last less than a minute, but will take longer the farther you are from the blast. This is because surface waves and sub-surface waves travel at different speeds. At some distances, it may even feel like two or more distinct earthquakes. You will not get days worth of aftershocks like you do from seismic events here on Earth though because Calisto is seismically inert; so, there would be no settling period in the plate techtonics.
As for the city built inside of Tindr crater, <https://nuclearweaponsedproj.mit.edu/> estimated:
@ 13.3km: Heavily built concrete buildings are severely damaged or demolished
@ 18.7 km: Reinforced concrete buildings are severely damaged or demolished. Most people are killed.
@ 27.8 km: Most buildings collapse. Injuries are universal, fatalities are widespread.
Now there is the huge caveat here of the atmosphere making a difference which you will need to answer. Namely: what are those colonist breathing? If your colony is contained inside of some giant atmosphere containing dome structure, then these estimates will be pretty accurate since your colonists will have given the impactor a good medium to propagate its shockwave through.
If your structures are surface level self contained units, then the shockwave will be much less significant, but the thermal and gamma energy will still devastate the whole area. In an atmosphere, most surface level buildings and people within about 6.7km would be incinerated by the blast, but without an atmosphere to convert all those high energy gamma rays into thermal radiation, it is very possible that everyone in the 70km wide crater will receive a fatal dose of gamma rays. Those who do not die right away are in for a long and agonizing death, even if their buildings survive.
If you are building underground, then you may fair much better. A 1.2 megaton B83 warhead (the highest yield Robust Nuclear Earth Penetrator (RNEP) in the U.S. nuclear stockpile) can destroy underground bunkers to a depth of about 300 meters. A penetrator with 208 times as much energy would have around a 1200 meter kill radius; so, your subterranean structures near the impact area will likely all be caved in unless they go very deep, but even relatively shallow subterranean structures beyond a radius of 1.2km will have a decent chance of survival.
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I don't think you would get a flash when it hit. You would get a small one that would be obscured by all the particles that it would throw up. You may crack the surface enouph to let out sub surface water and produce a ploom of "snow" but it would freeze again.
The area it hit would be flash boiled and you would have multiple quakes. Some from the initial hit and some as the earth waves move through the surface from the other side of the planet.
Sub surface tunnels would probably collapse depending on how they are made.
Edit: Oh and perhaps I should clarify. If it penetrates too deeply then any flash will be hidden by the ice around it. Infra red may show more.
It would just create a new crater. Nothing special after the dust settles.
Also if you are on the other side of the planet from the hit you won't see it (for obvious reasons).
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While many [mermaids](https://worldbuilding.stackexchange.com/questions/167943/realistic-sea-humanoids) are hunter gatherers some live a pastoral life, herding creatures like domesticated manatees. Along with this some mermaids (particularly [giant mermaids](https://worldbuilding.stackexchange.com/questions/199692/how-could-medieval-ships-protect-themselves-from-giant-mermaids)) herd baleen whales using them for their meat and bones to trade with the [land races](https://worldbuilding.stackexchange.com/questions/168595/why-would-humans-be-the-dominant-species).
Some basic characteristics of these giant mermaids include:
* being 26 feet (8 meters) long
* having human-level intelligence
* having Stone age level technology
Given these characteristics could giant mermaids domesticate baleen whales, like [humpbacks](https://en.wikipedia.org/wiki/Humpback_whale) with stone age technology?
Note: Magic does not exist in my story
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Sure they could.
Caring for baleen whales means doing a few things:
1. Keeping their natural predators (orcas, giant sharks like the Megalodon) away;
2. Herding them into proper feeding areas;
3. Castrating or culling the weak or less meaty ones.
If the giant mermaids know what they are doing, they can keep a nice, balanced ecossystem that would be proper for baleen whales to feed all year round. This would reduce their need for migration. Otherwise, if the giant mermaids wish to be nomads, they can let the whles find food on their own, but also tie their stuff to the whales so the latter double as work animals. You just need to follow them during their migrations.
And when a whale is fat enough, take it to a shark-free shallow bay and cut its fluke off. You now have a lot of meat and bone to do your thing.
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## Possibly for certain whale species.
they would likely be similar to the domestication of caribou by nomadic groups, with the merepeople traveling with the whales.
You have a major problems to overcome, many baleen whales are very intelligent which is very bad for domestication. You want a a domesticated animal doing what you want it to do, which is extremely difficult if it is intelligent. Intelligent creatures are clever, easily bored, easily frustrated, and do not take well to confinement. you will need to stick to the less intelligent baleen whales like **bowheads and right whales**. Even then they may be too intelligent.
Whales are also slow breeders but we don't know how long your merefolk live or how fast they breed, So tis might not be as big a problem. It does mean they need to be eating a lot of other stuff as well, they can't survive off whales.
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**Probably Not**
The problems with domesticating whales are the same with domesticating elephants. Elephants are big, intelligent, like to roam, and breed slowly. It is incredibly difficult for humans to restrain elephants, which is why elephants are often tamed by taking orphaned baby elephants and raising them but aren't readily bred in captivity, much less selectively bred in any numbers, much less quantities that could provide food.
Whales provide an order of magnitude bigger problem. The smallest baleen whales are the same size as a bull African elephant, and most are much, much larger. It would be incredibly hard to pen in a whale or make it go where you want. This would make herding whales very difficult, or selectively breeding them for tameness. And in the open ocean it's hard to pen whales.
Elephants were also much more useful as living construction equipment than being raised for food, given the expense in caring for an elephant.
But most importantly to all this is the fact that most baleen whales migrate (except maybe bowheads). They migrate to the tropics to give birth but then swim to the poles to feed in the summer. This migration is necessary to complete their life cycle. The whales have to give birth in the tropics because the babies aren't big or fat enough to survive in the cold Arctic or sub-Arctic waters, but the whales need the high-density krill and plankton of the polar oceans to fuel their immense bodies. It's probably not possible to supplement this food artificially in whales kept year-round in the tropics because it would require migration to the poles to get the volune of food necessary to feed them.
Indeed the existence of highly dense, nutrient-packed krill in the polar summer is what is thought to have allowed whales to get so large in the first place. Additionally, this migratory habit is likely what wiped out the megalodon, because megalodon couldn't keep up with the extreme long-distance migrations, couldn't easily handle large whales, and possibly couldn't go into the chilly sub-Arctic waters. This suggests that your merfolk trying to tame large whales like this would be very difficult to achieve.
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**The whales are not domesticated. It is a mixed herd of whales and mermaids.**
[Shrewd savannah species choose friends with benefits on the African plains](https://www.eurekalert.org/pub_releases/2019-11/uol-sss112519.php)
[](https://i.stack.imgur.com/XqRBx.jpg)
[Zebra reduce predation risk in mixed-species herds by eavesdropping on cues from giraffe](https://academic.oup.com/beheco/article/27/4/1073/1743727)
>
> For animals, a key advantage of group living is a reduction in
> predation risk through dilution and/or collective detection. This
> reduced predation risks lowers vigilance levels and allows herbivores
> to devote more time to other activities... For some species, risk can
> be reduced further by herding with a diluting partner (i.e., another
> species that shares a common predator; zebra and wildebeest are
> “diluting partners”). A diluting partner may reduce predation risk
> from a shared predator by having different detecting abilities. Such
> mixed-species effects on risk likely reflect a heightened ability of
> the mixed group to detect approaching predators compared with single
> species herds.
>
>
>
Giant mermaids and baleen whales are preyed upon by the same formidable hunters. The mermaids are fiercer but their sensory apparatus is not as keen and they can be caught by surprise by fast moving predators. The whales are defensively less strong but they can perceive predators coming at great distances.
It is good synergy for the two groups, who stick together. The whales can send an alarm to call back in hunting mermaids, who then can put up a more formidable defense. Also the two groups use different foods and so do not compete with each other in that way.
It is a commensal relationship. Mermaids take milk and blood from whales, like the Maasai do with their cattle. Only whales that die of natural causes are used for meat or bone. The culture of each group overlaps with the other. The whales are intelligent enough to participate with some of the things mermaids do. The mermaids appreciate the elegance of the ancient whale ceremonies. They are not equals but they are partners.
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The main problem I see with domestication (as opposed to mere taming) is that whale breeding cycle is rather slow. That is, it takes a great deal of time to raise baby whales to where they will produce new baby whales (my quick search returned 4 to 11 years per generation).
Perhaps magic can decrease the age to maturity.
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## Sure, why not?
But I think that's more believable, if those merfolk lived somewhat nomadic and hunt whales like Native American tribes hunted the buffalo. They actively turned the land into an ideal habitat for buffalos (the Great Plains). They understood: Buffalos eat grass, that means more grassland leads to more buffalos. If we burn down the forest, grass will grow... hence: If we burn down the forest, we have more buffalos to hunt.
So your merfolks could do a similar thing: Such as planting trails of plankton producing corals to change migration routes to lead the whales closer to their settlements/camps or domesticate swarms of smaller fish that those whales are mad about.
There's a problem of domesticating whales. They need huge amounts of food which they can't find at a single spot. Another problem would be their low reproduction rate. A humpback whale's pregnancy for example is 11 months. They usually start having calves around the age of 12-13 (sexual maturity between 7-8 years). The most female have one calf every other year, tho there are some that have a calf per year. Compare that to the ordinary cow: 2 years until sexual maturity, 9 months gestation period... or the pig: sexual maturity after 5-6 months, gestation period of roughly 4 months. Okay, that's maybe something that can be solved through breedings... but it's definitely a point to consider.
But whales are probably very much comparable to bovine, at least to some point... so domesticated whales could work pretty well.
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I live with 2 dog trainers. To quote them "You can train anything". They've trained chickens. They've trained rabbits. They've trained seagulls.
The general guide is:
1. Encourage a behaviour to occur.
2. When it occurs, give food.
3. Repeat.
That's it!
* If you're too slow giving food or the behaviour is too complex to distract with incoming food, associate a signal with food by repeating "signal -> food" over and over with longer delays between signal and food, then give the signal when they do the desired behaviour. Signals can be sounds or visuals. Dog trainers often use clickers.
* If the behaviour is too complex, break it up into parts and train each part individually.
* Don't use negative techniques. When they do something you don't want, ignore them. Negative training works quite well on marine animals for a short period of time, [until it doesn't](https://www.netflix.com/title/70267802)
Humans using this technique have trained:
* [Goldfish](https://www.youtube.com/watch?v=D4kPZ25IMn0&ab_channel=AndreYeu)
* [Sharks and aligators](http://www.vetstreet.com/our-pet-experts/unusual-animals-trained-with-positive-reinforcement)
* [Dolphins](https://www.youtube.com/watch?v=gbrJLKu3wTU&ab_channel=WULFI)
* [A different kind of whale](https://www.facebook.com/watch/?v=867037257160785)
* [Killer whales / Orcas](https://www.theacademyofpetcareers.com/blog/what-is-clicker-training-marker-training/)
* [Deadbeat husbands](https://www.clickertraining.com/node/527)
* [Children](https://www.clickertraining.com/node/384)
* This list is getting pretty dark, I'll just stop googling now..
So yes, since your mermaids have human intelligence, your mermaids can train a whale to do what you need in return for food. Full domestication will naturally follow - as they learn doing your mermaids bidding is an easier way to get food than hunting for themselves.
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[
One day we will colonize another world, far far away. Importing anything will be vastly expensive and slow. The more self-sufficient you can be, the better.
It's implausible that you could bring sufficient mass to have a full technological stack to produce a CPU. They are one of the pinnacles of modern technology, with features measured in atoms. On the other hand, the humble microcontroller is everywhere. The alarm clock, the washing machine and the MPPT controller on your solar panel are all based around these ubiquitous devices.
Amazing as microcontrollers are, they are very light - so for most purposes you're better off bringing 1T of generic microcontrollers (say, 10g each, 100 to the KG!). However there are uses for which a dedicated, custom chip are required. Think of the water controller chip from Fallout.
We're not talking modern tech, bleeding edge. We're talking features hundreds or thousands of nm wide, with 1980-2000 levels of performance. It's even possible that such large features might well be an advantage against local radiation issues (see Mars).
For such a custom chip, how big a technology stack would you require to produce them onsite. After all, if you're dying of thirst you can't wait 6+ months to ship one from Earth - if the planets are aligned right.
You can have mining equipment for free - already needed for the metals we're building everything else out of! Solutions should be scaled for dozens (to hundreds) of chips in a run. You're free to import specialist raw materials where it makes sense, provided you specify. Ideally a route would exist to local production for all resouces... but that could be decades away.
Bonus points for information on points of commonality between local solar panel production. Because while microchips are an easily transportable item, solar panels will likely be required by the megaton! Even producing local panels that are only 5-10% efficient ith local resources will be long term effective.
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### Frame challenge. That mass can be better used with FPGA tech.
Rather than bringing 30 tonnes of equipment to a remote planet to start making ICs, bring 5 tonnes of FPGA chips to tie your IC needs over until you can build your own.
So looking at all the [steps involved](https://en.wikipedia.org/wiki/Semiconductor_device_fabrication), you're looking at about 10-20 big industrial machines (estimating 200kg each), not including mining and refining all the silicon, copper, lead, silver, tin, and gold. Not including spare parts for the fragile parts, or consumables. If you really want a number, I'm going with 30 tonnes. But IMHO that's a waste of valuable mass.
Instead, load that supply pod up with a supply of Field Programmable Gate Arrays, these are basically general purpose "blank" microchips that can be configured in-the-field to have any behavior, and when the product they're in is recycled or scavenged, they can be removed from the circuit board, reset, and reprogrammed with new specifications for a new device.
Future advances of this tech has amazing potential even here on Earth. Literally a GPU that can reconfigure itself into a CPU and back depending on whether your hard at work or gaming, or a sliding scale in between. Or if the computer is idle and the solar panels on the roof report they have spare power, into specialised optimised hasing silicon that can be used for bitcoin mining. We could literally see the OS decide "Oh oh there's a lot of division in this code and its not able to run concurrently. How about I convert 7 of my 8 cores into extra divide ALU circuitry? That way the code will run quicker".
Here's a [current-tech $15 FPGA](https://au.rs-online.com/web/p/fpgas/6972841/). It's 1/6th of a gram and has 50,000 gates. Here's the [bleeding edge](https://www.prnewswire.com/news-releases/s2c-accelerates-billion-gate-fpga-prototyping-with-xilinx-virtex-ultrascale-vu19p-based-systems-301157738.html), a billion gate monster that can run fast enough to transfer data at 16gbps. If you add a few decades of growth to the industry, expect these numbers to climb by orders of magnitude.
Instead of shipping an electronics factory, use 5 tonnes to ship 30 million FPGAs that can be programmed into anything from a CPU to the microcontroller in an alarm clock. Use another 5 tonnes for high precision parts like bearings, precision gears, rotary and linear encoders, stepper motors, which you're going to need for fabrication of machine parts anyway. Another 10 tonnes of precision electrical parts (tiny resistors, tiny capacitors, wires and cables, 3d printer nozzles, etc), and 10 tonnes of prebuilt ready-to-use electronics (laptops, monitors, servers, routers, smart phones, smart phone base stations) rounds out the 30 tonnes that your electronics factory would occupy.
Setting up a "machines parts factory" should be very high on the priority list as when an emergency happens, you can turn a child's gaming console processor into water recycler control chip using FPGA tech by uploading a new gate config such that it behaves as a microcontroller, and then uploading new firmware to your new microcontroller. you can't turn a suspension struct into a gearbox.
Once you're able to manufacture precision parts at extremely high tolerances, and mining and refining minerals at high purity, your 90% on the way to manufacturing your own ICs. Repurposing a few FPGAs into the necessary controllers, you can build the 20 big machines using local manufacturing, and you can then start spitting out specialised non-FPGA ICs like microcontrollers.
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You're going to build a factory to make microcontrollers in order to produce "dozens or hundreds at a time"?
That's *crazy*.
Go buy a million general-purpose microprocessors on Earth, throw them into cardboard boxes, and take them to Mars with you.
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If you took *Star Trek: The Next Generation* replicators to another planet, all you would need to produce anything desired would be raw materials to feed into the replicators and energy to run the replicators.
And at the present time the first efforts to make something vaguely like replicators have produced 3-D printers. And probably in a few decades when the earliest attempts to colonize ohter planets or build space habitats will be made 3-D printers will be a bit closer to be being replicators and will be more verstile than they are today. And possibly somone will develop 3-D printers to create microchips before the first space colonies ae started.
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«One day we will colonize another world, far far away»
On that day, I am pretty confident that we will have *disassemblers* - machines that, given energy, can render almost *anything* (garbage, mostly) into its component atoms, and *assemblers* - able to put together objects at the atomic level.
Both will undoubtedly be slow and energetically expensive; but, given two of them, a supply of raw material, suitable blueprints and assembling tools and skills, you can ultimately get *two more* of them and the components for any other level of technology; at that point the cycle can be repeated.
I imagine the colony expedition being sent in some kind of dormant state (who knows? Zygotes, maybe), braking somewhere in the target system's Oort cloud, and spend several years in relative safety "unfolding" into a viable human expedition from the raw materials of the cometary cloud. Then, the planetary phase will start, but their main source of supplies will then be much nearer than Earth.
[Answer]
## I do **not** know the answer, but I have my say on the topic.
# remarks
* There are some interesting points in the FPGA answer, so as in comments to it about inefficiencies and complexity, but do not forget that if we talk about signal processing, which may be important for machines, robot arms, CNC, and stuff, it can do more than your typical atmega, even when if u turn it (FPGA) in an atmega it may be a half of atmega. So if one chooses to load himself with FPGA's, which may be a smart decision, he may load as well with 2-3-5 types of microcontrollers and processors for general purpose. in some cases they will overlap as what they can do, in others, they all have their niche in which they do better, but not irreplaceable.
* it nice to see someone wakes up for the topic, and sad to see closers reaction on a fundamental question which is practically important so as important for hard science works if one wishes to embark on the endeavor of writing making one. There are too many soft fantasies and not enough hards sci-fi and Clarke and Asimov and Heinlein and O'Neill are ashamed of us here right at the moment.
* unfortunately, the answer does not exist, as far as I know, and estimates are inevitably are based on one's skills and knowledge, and understanding of the problem. I do not have sufficient competence to encompass the whole subject, but I do know something, so I'll try, but no exact numbers for ya.
# Fundamentals
>
> Now the earth was formless and void, and darkness was over the surface of the deep. And the Spirit of God was hovering over the surface of the waters. And God said, “Let there be light,” and there was light. And God saw that the light was good, and He separated the light from the darkness.
>
>
> *Genesis something:something*
>
>
>
## one day we had nothing.
one day in the past we had nothing, but the next day we pick up a stone and since then our tool-making habit progressed and today we have all we have, pinnacles of technology included - and nothing of that was given by some external force. we as Humanity made it with our Hands, starting with a stone and resources available to us around on the planet, which, the resourced, didn't include a single piece of high tech available to us today.
the important conclusion here is - there is possible to have some HowTo guide from nothing to a pinnacle of any (or all) technology, for an exchange of human hours, etc.
with electronics and processors, we do not have to look that way back, to a stone age, or steam era - stuff started whopping circa 50 years ago, time flies, soon u would not be able to say it was recent enough.
And that HowTo guide does not exist, but it is sort of written in our relatively recent history indirectly, I mean is less of a mystery how to extract that data, than answering the question of how did they manage to build pyramids.
So the traces are fresh enough and it is not impossible to compile a document that leads from simple transistor logic manufacturing to making complex processor microcontrollers and such.
**C:** *And this way if u prepare for colonization of another planer or space in general, do your homework, if u intend to expand and grow, make a growth plan. Not like using old as a solution, but using old as a starting point to get back on top of technologies.*
## energy is king.
energy is very essential, not only for functioning but for the development of the installation. not only it has to be available, but it has to be abundant. For technologies and for space stuff it like water for plants, and if u like to grow fast enough, it has not to drip in volumes u carefully count but it has to be sprayed from a firehose as if u extinguish a fire on an oil field.
The reason for that is as an example - whatever big enough city u see, with a million a few million people it has hundred years plus history, it has buildings and construction which do functioning since that time. Sure we modernize cities and never ended doing so and building - but it also serves us as a piggy bank in which we constantly put/used resources and energy. And if u would like to build one in a decade or so, from scratch, capable to host the same number of citizens - it would be a major project, very complex, very heavy consuming on energy and resources and making a busy good portion of people in one's country.
So establishing a presence in space or on a planet aka mars aka Elon - u have to have a thick fire hose that spits energy as if it's free.
**C:** *So, if u like to produce electronics locally, energy resource inefficiencies in the product and in the processes aren't the greatest concern.*
## we do live in the future
we indeed live in the future and can use the accumulated knowledge and look back on the ways things were done from a different perspective.
* we do have good progress in software development, for production, for development, so as learning algorithms, etc. Those are fruits of us having all that tech for quite some time now. Today capabilities as of software and technologies of software are way more potent in terms of capabilities than it was 20-30 years ago. So much so that it almost a trivial task to run today's software on outdated hardware. A cluster of 8086 won't make your game experience better, but it may make work done. Making a virtual machine out of 8086, Z80, and similar is possible, and we learned that clouds are good for certain tasks.
* we do have automatizations, and when we have not other choices but to replace human hours we can do that with robots. sure there are some objections, I hear you - service, etc, etc - those problems aren't without solutions if u have energy and do your homework.
* we can borrow power from the already existing system on the planet, as mentioned in ops q, so as in the FPGA answer - we can bring some critical components premanufactured electronics, data we need, the equipment we need. So as teleoperated expertise via digital links, even if mars isn't the best choice for that, but even then substantial information processing can be offset to the planet, in a smart way obviously, not like offsetting real-time processes monitoring to a 20min ping zone. So as problem-solving counsel service can be on the planet and use all advantages of developed infrastructure.
## it not only microcontrollers, u have to bring the whole bird nest.
if u have growth in mind, and local production indeed is capable of heavily reduce required launches to establish infrastructure, and u recognize some problems of electronics production but u still have to take a wider picture and recognize that technologies are intertwined, and there is a machine which builds parts for a machine which makes some operation in your processor production setup, to which there are 2-3 other layers of machines build parts for each other, and u have a hundred few hundred of those in your line. Stuff clearly overlaps so we do not have 100 pows 100 pows 100 number, but significantly less than that and a more manageable set of devices which forms somewhat ecosystem, producing food parts for each other.
everything isn't necessarily that horrible, but it depends on goals and means and roads of development - how do u approach the problem. So as it leads us to good old von Neuman probes question - how much do we need materials for one, or legit question how to lever up a base on another celestial body.
Some works try to estimate and produce a number, mass in tons, for the equipment we may need for the task, and it was done at different times, but there are not a lot of work on that question, so as estimates vary and there are different views on the problem - so older numbers have something like 3000t of equipment in mind, more modern views on that(3d printing, additive manufacturing enthusiasm and not only that) have lesser numbers like 300-20t.
# The problem
So some fundamentals are set - like we may start low on tech and may grow with some plan of growth, we need abundant energy for all stuff, we use existing achievements to make stuff easier on us, our modern perspective on old topics, and our spoilers as we do know what happens next.
## energy, again
Solar panels probably won't do it, they have EROEI around 2-3 years(controversial number, more like my estimates, but yeah it murky topic of holy wars), here on earth, where sunlight is more abundant than on mars as an example, it means if u plan to grow on solar on mars in a decade u need to take half of your power and after a decade u will be ready to produce your 100th's percent of designated goal in terms of power production, and not spending that energy elsewhere before that and be ready to spend it elsewhere after that when u get to 100 percent power capacity.
unfortunately, nuclear power also isn't that great for the case, but not necessarily bad. But to start to produce 1Gwatt of electricity u need about 100-200 tonnes of uranium fuel alone, not counting the other equipment from which a nuclear plant consists. There are modular reactors designs, for planetary use so as space use, like kilo power, but the number won't change that much, because as potent nuclear fuel is, it burns quite slow, that's why it is not a blast so it is the typical situation.
So, if u stick to conventional means and have no solution for that, then u start with probably thousands of tons of energy generation equipment alone. And 1 Gwatt number is rather not that much, for colonial activity. Smelting one ton of iron(iron scrap, not ore) needs 600-900kwh per ton, so 1Gwatt gets u about 250t of iron blanks and beams and stuff like that, per day.
A helpful thing is u have access to space and extracting energy there, maybe be more productive and with faster growth rates. weightless and vacuum have a certain advantage, absence of atmosphere has certain advantages. So all in all abundance of energy can be achieved, but it is a more serious topic than u may think.
## chemistry
u may think that getting pure enough silicone is a challenge, but it is not necessary, but the chemistry of reagents u need in the process of manufacturing of chips and equipment for its production may be more challenging. At least it means that we talk not only about pure silicone, but other pure reagents u may need.
Also, u need recycling, a lot a lot of recycling because it is not given that u may have easy or good sources of elements on your base. even if you would be on earth, making a base does not mean u will find all the components\elemets easily accessible close to your base, even when we know it is all here, but we gather stuff all around the world. And recycling needs energy as well, as much if not more than actual production, u can't waste anything essential.
# Gather stuff together
## Silicone
Have seen a proposal, which uses plasma chemistry to purify silicone, it was like a business advertisement proposal, u give us the xxx amount of gold and we in a 2-4 years build production prototype aka working setup, which certain characteristics which we do expect, based on our lab tests and findings.
They promise a setup that fits in a 20,40ft(do no recall atm which one it was) container and produces solar panels grade silicone 1kg per 50kwh, 80t per year.
So tune or two-stage it u will have your pure silicone problems solved in something like 10t of equipment.
Making wafers, or more like boules of silicone also isn't such sophisticated technology, u basically do not need to carry anything from earth, had seen some videos of crude setups for growing, reactor vessels, components of which literally were done out of used pipes and Knowledge and then those boules were sold for good money, everyone was happy.
so u probably can do reactor vessel from local materials, with a pinch of high tech vitamins, and doping elements.
All structural elements have to be subtracted, pipes and cases and vessels - u have to do it locally, to save mass, so in a first setup the most important thing is a laser, so per a million controllers per year u probably can fry down that stuff to a hundred kg of more advanced high tech stuff, which u can't produce on the spot at the start.
## Lithography, and lab equipment
some people in comments have to understand about the existence of laboratory equipment which is capable to produce chips. it is more flexible for research purposes, but not fast.
its purpose is to allow you to test different schemes and help produce test chips, to test their performance and stuff, before u put them in mass production.
I do not have experience with such equipment and do not have a good impression of its exact sizes and masses and speeds and feeds, but some impression I have it isn't that big - it does no take a whole building.
Here we [have](https://hackaday.com/2017/02/25/the-fab-lab-next-door-diy-semiconductors/) 2017 article which points us in a direction of a guy who makes our dream true in a garage, and what he writes in his article [First IC :)](http://sam.zeloof.xyz/first-ic/):
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> Without further ado, I present the first home(garage)made lithographically-fabricated integrated circuit – the “Z1” PMOS dual differential amplifier chip. I say “lithographically-fabricated” because Jeri Ellsworth made the first transistors and logic gates (meticulously hand-wired with conductive epoxy) and showed the world that this is possible. Inspired by her work, I have demonstrated ICs made by a scalable, industry-standard, photolithographic process. Needless to say, this is the logical step-up from my previous replication of Jeri’s FET fabrication work.
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> I designed the Z1 amplifier looking for a simple chip to test and tweak my process.
> ....
> The feature (gate) size is approximately 175μm although there are test features as small as 2μm on the chip.
> ...
> EDIT: see update at the bottom, the transistor gate length has been reduced to <5µm (1975 tech. level) which brings an increase in device performance.
> ...
> There are 66 individual fabrication steps to make this chip and it takes approximately 12 hours for a full run. The process yield can be as high as 80% for these large features
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So as in general, u have to understand that the first technology is tested and proven in a lab before they make plans for a FAB and building it for spitting out your processors.
So there is the stuff that fits more or less on a room or a table, but unfortunately, I'm a noob in that, so would be interesting to get numbers from those who are in the field. if u give me enough Z80's I'm certain to make a cloud from them.
But in general, the topic does not look futile if u put few million bucks into it. And that hack guy is probably a measuring stick for our problem because for an expansion one needs to be able to build up the number of production nodes locally.
Speed of production is less important, the productivity of equipment is less important if u can produce replicate it locally. And here automatization is the way to go and our fiend. 1um general processor and MEMS devices are good enough to run our robots which we need for production and for pumping up production capacities. So as to improve our technological capacities from the point.
So measuring stick, that hack guy, probably gives us few tonnes of equipment and a 50 kg bag of coffee for a few microns tech process.
But obviously, we do not bring those few tons capable to produce it, we bring our high tech stuff, which is capable to produce those cells which can produce those stands which produce few micron processors, from which we clearly extract all structural elements, which we'll produce locally with help of few ready to use arms(Hands).
So it isn't unreasonable to count it as 2-3 tonnes of equipment, to start to produce chips.
## chemistry
Chemistry as mentioned will be complex enough, good stuff about it is that it scales up and down, down and up. Not without problems and kinks, and u may need more than 66 steps to close chemistry cycles in that setup, but mostly because u have many different components, chains of reaction, but it all more or less boils down to scheme u mix components under some temperature catalyst function in a reaction vessel get a product, separate rinse, and repeat.
Again exporting not the vessels and reaction chambers, but the equipment which makes equipment which makes those vessels and schtuff.
so elements for catalytical reaction have to be taken too.
So would again estimate it in a few tons, mostly elements, to kickstart the situation. And later depends what prospecting of the grounds will show, so as of how fast u scale everything including elements extraction and better locations if there are any. But u may need a lot of energy to offset the poor composition of elements in a location or on the celestial body in general.
# Conclusion
For your question it probably reasonable to expect 10-20-30 t of equipment which allows u to produce chips from the get-go - but we can't tell how fast it will do, and how long it will last. with decent y2020 tech processes as in the lab.
The same number is probably valid for a setup that may begin to produce equipment which may produce equipment from which u produce equipment which can produce low tech processors, so as other equipment which u needs to scale up the base and begin to climb up on the tech tree.
it will have some limitations and properties, which are unknown and so as it depends on the composition of minerals around, but if energy-producing is solved, there won't be hard limits on how much it can produce and how fast the system can spew out components u need, so as not that many limitations on the variety of components it can produce.
Development of such system can be supported from the earth more in a way of problem-solving and in what's a next step for the system - strategical stuff.
it can be envisioned that mature technology of that kind, maybe like some container which u connect to the electric grid and it starts to grow, under some light supervision from humans. But as todays reality we have almost nothing in that regard, as in good old days, good stuff we can solve that step by step, V2.0 improved extended.
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[Question]
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I'm writing a novel that takes place in a *very* sparsely settled coastal PNW, and the MCs have two horses that they use for transportation and as their carrier animals (Bedrolls, tent, some rations). Given the ridiculous verticality of the region and the artistic alteration that barely any beaten paths exist, how far would they *reasonably* be able to ride within a day, not at a break neck pace either? What would be the best kind of horse for this area? Is it logical that two cops would effectively be able to carry out their duties on horseback in such an environment?
To the question regarding the compliance of this post with the World Building guidelines, this directly relates to the storytelling points of the world, notably characters moving through the world and whether such a system would be feasible and believable to an audience.
As I designed this interpretation of the PNW to be much more untamed than our version, I was curious as to the plausibility of my characters reliably covering distances and what type of creatures could be best suited for the job.
[Answer]
It all depends on how rough the terrain is and the kind of weather they are having.
I would suggest to refer to the Lewis and Clark journals. Or Stephen Ambrose [Undaunted Courage](https://www.amazon.it/Undaunted-Courage-Meriwether-Jefferson-American/dp/0684826976) (also available online).
After meeting with the Shoshones they managed to have horses and followed a native through the Rockies using the Lolo trail. This route was well known to the local tribes who used it to move from the Pacific side across the Great Divide into the great plains to hunt.
The miles covered in a day change a lot depending both on the terrain and the weather. Lewis and Clark had to march in challenging conditions on their way West and lost the track at times. Thus progress was slow. When coming back they had different guides and the passage was far smoother (but they had to wait for the snow to melt so the pass would be open).
On Ambrose's book is fairly easy to track their progress. He loved and knew the trail well. As the expedition met all kinds of terrain and weather you will no doubt find the proper reference for your case.
Regarding the expedition's crossing using the Lolo trail going Eastward Ambrose writes:
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> Just before sunset, the party rode into Traveler’s Rest. They had covered 156 miles in six days.
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> The previous fall [the Westward march], the expedition had been slowed by Old Toby’s losing the way and by the fallen timber, and it had taken eleven days to cover the distance.
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Short answer: in the best scenario (no snow, grass available for the horses, clear track without obstructions, no steep climbs, etc.) about 30 miles.
Regarding the horses: the Nez Percé had the Appaloosa. Lewis highly praised them. [Appaloosa horse](https://en.wikipedia.org/wiki/Appaloosa). The horses given by the Shoshones were of inferior quality.
[Answer]
Late response, but I do live in California, so this piqued my interest.
The rule of thumb for "regular" horseback riding is "20-30 miles a day," about the same or a little bit farther than a human's walking pace. This would NOT be modern endurance-riding or general "emergency riding," where you go as long/fast as possible, and you and your horse may or may not die by nightfall. Neither would these be messengers with networks of fresh horses. I assume that your characters are setting up camp, grooming their horses in the mornings and evenings, taking breaks in the middle of the day to avoid the worst heat, and other daily chores.
Going on California travel-times in real life, ["Visit California"](https://www.visitcalifornia.com/experience/california-missions/) mentions that the Spanish missions are 30 miles apart. Since this is the *untamed* Pacific Northwest, though, your characters could easily be stuck at 15-20 miles a day because the rainforest would mean paths are harder (lots of mud or too many trees because again, RAINFOREST; plus, North California seems to like their steep hills and mountains). Even if they're not, the paths may well be more roundabout since everyone's trying to AVOID the harsh terrain, and they don't have the population to clear out roads properly.
[Answer]
Figure out how far they could travel by foot, and reduce that to half. Possibly to less than half.
In really rough terrain, with no trails, horses do not give benefit of faster travel than humans on foot, they *only* provide the means to carry greater weight, while greatly reducing the pathways that can be moved over and increasing the water requirements immensely. For example, it is quite practical for a person to carry 3 days of water ration, but not for a horse even with the added weight allowance of a horse.
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[Question]
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In science fiction dealing with multiple intelligent species, "year" is still often used as a unit of time - like when describing a character's age - even when dealing with species that originate from a planet different than Earth. Year length as we know it is determined by the period of a planet's rotation around its star, and period that by the radius of its orbit and the mass of the parent star. But the fact that life evolved on said planet puts some boundaries on the acceptable orbit radius (has to be in habitable zone), and on the mass of the star (more massive stars are generally less stable).
Assuming a galaxy of different species with the following:
* Every species has a concept of "year", which is the orbital period of their home planet.
* Every homeworld is within the [habitable zone](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone) of its parent star. (ignoring tidal heating, moons of brown dwarves, and really weird orbits in multiple star systems)
* Every homeworld's star is stable (less than a 25% increase or decrease in energy output) over a period of two billion years.
+ Note that the requirement for consistent energy also rules out really eccentric orbits for the planets, with which they would get much less energy at the far point.
+ Excluding stars that are remnants of supernovae, since I think they are unlikely to have planets; other than rogue planets that were captured, but that's such a rare occurrence and they are going to have eccentric orbits that I'm okay with discounting that category altogether.
What are reasonable upper and lower limits on the length of a year as considered by different species? I'm good with a ballpark estimation here.
[Answer]
Short answer:
Known Exoplanets orbiting main sequence stars have year lengths varying from 4.31 hurs to about 1,000,000 years, so the longest known year is about 2,040,816,327 times as long as the shortest.
[https://en.wikipedia.org/wiki/List\_of\_exoplanet\_extremes#Orbital\_characteristics[1]](https://en.wikipedia.org/wiki/List_of_exoplanet_extremes#Orbital_characteristics%5B1%5D)
But the requirements for planetary habitabiity for carbon based and liquid water using life, and especially for oxygen breathing varieties of life are quite strict.
A fiction writer who wanted to be rather certain that their story was not proved to be impossible might restrict the orbits and stars of habitable planets so that the longest year would be only about ten times as long as the shortest year. If the writer is willing to take a greater risk of story elements being proved impossible, the longest year of an inhabited planet could be about one hundred times as long as the shortest. If the writer is willing to make more daring - and more likely to be proved wrong - assumptions about habitable planets, the longest possible year of a habitable planet might be about a thousand times as long as the shortest year.
And if a fiction writer takes the risk of using hypothetical exotic alien biochemistries in his story, the range of year lengths among habitable and inhabited worlds might be much greater. And yet it would probably still be a very small range compared to the range of possible exoplanet year lengths.
Long answer:
Part One of Seven: Which specral types of stars can have habitable planets?
Here is a link to a question:
[https://astronomy.stackexchange.com/questions/40746/how-would-the-characteristics-of-a-habitable-planet-change-with-stars-of-differe[2]](https://astronomy.stackexchange.com/questions/40746/how-would-the-characteristics-of-a-habitable-planet-change-with-stars-of-differe%5B2%5D)
The answer by user177107 has a table of main-seuence stars of different masses and spectral types. It lists for each star the distance at which a planet would receive exactly as much radiation from the star as Earth gets from the Sun, and the length of that planet's orbital period or year.
for example, the distance from a G2V star like the Sun would be 1 Astronomical Unit (AU) and the year length would be 365.56 Earth days. The examples range from spectral type M8V stars with masses of 0.082 of the Sun's mass, an orbital distance of 0.0207 AU, and a year 3.28 Earth days long, to spectral type A2V stars with masses of 2.05 the Sun's mass, an orbital distance of 4.611 AU, and a year 2,526.01 Earth days long.
However, it is believed that not all stars within that range of spectral types are capable of having habitable planets.
Stephen H. Dole, in *Habitable Planets for Man*, 1964, 2007, discussed the requirements for a world to be habitable for humans - or for other lifeforms using liquid water and needing an oxygen rich atmosphere.
[https://www.rand.org/content/dam/rand/pubs/commercial\_books/2007/RAND\_CB179-1.pdf[3]](https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf%5B3%5D)
Earth had life by about three or four billion years ago, but didn't produce an oxygen rich atmosphere and become habitable for humans until it was about four billion years old. Dole estimated that no planet could become habitable in less than three billion years. And the planet's star would have to remain on the main sequence stage and have a steady luminosity for those three billion years or more or else the large changes in luminosity would wipe out all life on the planet.
On pages 67 to 72 Dole discusses the required properties of the star of a habitable planet. Dole said that astrophysical calculations indicated the most massive stars that could remain on the main sequence stage of development for at least three billion years would be main sequence spectral type F2V stars.
According to the table mentioned above, they would have a mass of 1.44 the Sun's mass, and a planet receiving exactly as much radiation from F2V star as Earth gets from the Sun would have to orbit it at a distance of 2.236 AU with an orbital period or year of 1,018.01 Earth days.
The question of the least massive stars which could have habitable planets depends on the circumstellar habitable zones of stars, which Dole calls "ecospheres". The habitable zones extend from inner edges where planets would be too hot to outer edges where they would be too cold, with planets in between being potentially habitable if other things are right.
The less massive a star is, the less luminous it will be, so the inner and outer edges of its habitable zone will be closer to the star. And the closer a planet is to its star, the stronger the tidal force of the star will be upon the planet. When a palnet is too close to its star, the tidal force will be strong enough to quickly slow the rotation of the planet, so that it will become tidally locked, with one side always facing the star in eternal day and the other side in eternal night. And all the water and air might travel from the day side to the night side and freeze out, leaving the planet uninhabitable.
On pages 71 to 72 Dole calculated that a star could have a full ecosphere or habitable zone if it had a mass of about 0.88 of the Sun's mass, or higher. The inner parts of the habitable zones of stars of lower mass would be too close to the stars and planets in those regions would become tidally locked. A star with a mass of less than 0.72 of the Sun's mass would have a habitable zone that was entirely too close to the star, where any planets would be tidally locked. A mass of 0.72 would correspond to a K1V type star.
According to the table I mentioned earlier, a star with 0.88 the mass of the Sun would be somewhere between a type G8V and a type K2 V, and have a year somewhere between 280.06 and 182.93 Earth days long. A star with 0.72 the mass of the Sun would be somewhere between a K2V star with 0.78 the mass of the Sun and a K5V with 0.68 the mass of the Sun, and thus have a year somewhere between 182.93 and 114.84 Earth days long.
Thus the longest possible length of a habitable planet's year would be between about 3.6 and 8.8 times as long as the shortest possible length of a habitable planet's year.
Part Two: Planets tidally locked to companion worlds instead of to their stars.
On pages 72 to 75 Dole speculates that if a planet has a large enough natural satellite, or is part of a double planet, or is not a planet but a moon of a large planet, it would be tidally locked to the planet and not to the star, and thus might have days short enough to be habitable, even if it orbited a less massive star than 0.72 the mass of the Sun.
But the less massive and dimmer the Star, the closer such a planet would have to obit, and eventually the planet would get so close to the star that the stellar tides upon the planet would be too strong and destructive for habitability. Dole estimated that the lower mass limit for the star in such a situation would be about 0.35 the mass of the Sun.
That would be less massive than a M2V star with 0.44 the mass of the Sun and more massive than a M5V star with 0.16 the mass of the Sun. So that indicates that the shortest possible length of the year of a habitable planet should be between 36.51 Earth days and 11.68 Earth days.
So if this is possible, the longest possible year of a habitable palnet would be between 27.88 and 87.15 times as long as the shortest possible year of a habitable planet.
Part Three: Planets orbiting two or more stars.
However, circumbinary planets orbit orbit around two stars. If the two stars in the binary are identical, and are F2V stars, their combned habitable zone would have inner and outer limits about 1.44 times as far as the limits around one F2V star.
And if there is a quadruple star system with two pairs of F2V stars, and the stars orbit close enough to each other, planets could orbit them in their combined habitable zone, which would have inner and outer limits which would be twice as far as around a single F2V star.
Thus in extreme and very rare cases habitable planets orbiting binary or multiple stars might have years significantly longer than habitable planets orbiting a single F2V star would have.
Part Four: Can Tidally Locked planets be habitable?
But there is more.
The idea that tidally locked planets in the habitable zones of less massive stars can't be habitable has been challenged.
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> 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 millibars (0.10 atm), for the star's heat to be effectively carried to the night side.[81] 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.[82]
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[https://en.wikipedia.org/wiki/Planetary\_habitability#Red\_dwarf\_systems[4]](https://en.wikipedia.org/wiki/Planetary_habitability#Red_dwarf_systems%5B4%5D)
Humans require a partial pressure of at least 60 millimeters of mercury (plus small amounts of other gases) to survive. That is about 0.0789 the surface pressure at sea level on Earth. So almost every planet with an atmosphere breathable for humans would have a pressure of at least 0.10 Earth atmosphere, calculated to be sufficient for proper heat circulation on a tidally locked planet. However, that minimum atmosphere necessary for sufficient heat circulation on a tidally locked planet might include too much green house gases like carbon dioxide and water vapor to be breathable for humans, and possibly too much to be breathable for any life forms requiring oxygen.
There are some other problems with habitability of planets of class M red dwarf stars. I once read a science ficiton novel by Andre Norton, set on a planet of a dim red star, where it was said that stars can do bad things to planets which orbit them too closely. And I thought that was silly. Since the planet was orbiting at the proper distance to have a habitable temperature, it didn't matter what its distance from the star was. But later I learned that many dim class M stars are flare stars which sometimes increase their luminosity several times, which would be bad for life on their planets. But not all class M stars are flare stars.
Thus it is possible that there could be planets, habitable for humans and/or for other intelligent beings requiring liquid water and oxygen rich atmospheres, around very dim clas M red dwarfs, possbily orbiting stars as dim as M8V with years 3.82 Earth days long.
Part Five: The inner and outer edges of a star's habitable zone.
But there's more!
A habitable planet doesn't have to orbit its star at the distance necessary to receive exactly as much radiation from its star as Earth gets from the Sun. A planet could get a little more or less radiation than Earth, and be a little hotter or colder on average than Earth, and still be habitable. And so a habitable planet could have a year a little shorter or longer than necessary to receive exactly the same abount of radiation as Earth does, and still remain habitable.
The procedure to calculate the inner and outer edges of a star's habitable zone is simple, if that star's luminosity relative to that of the Sun is known. Simply multiply the distances to the inner and outer edges of the Sun's habitable zone by the square root of the star's luminosity compared to that of the Sun.
So what distances from the Sun are the inner and outer edges of the Sun's habitable zone?
Nobody knows for sure. Here is a link to a collection of a number of different estimated or calculated inner and outer edges, and sometimes both, of the Sun's circumstellar habitable zone, made during the last sixty years.
[https://en.wikipedia.org/wiki/Circumstellar\_habitable\_zone#Solar\_System\_estimates[5]](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone#Solar_System_estimates%5B5%5D)
Note how greatly they differ.
One of the best known calculations, by Hart et al in 1979, gives a very narrow habitable zone, between 0.95 AU and 1.01 AU.
Another well known and often used calculation, by Kasting et al in 1993, gives a much broader conservative habitable zone, between 0.95 AU and 1.37 AU, and an even broader optimistic habitable zone between 0.84 AU and 1.67 AU.
In various estimates the inner edge of the Sun's habitable zone varies from about 0.38 AU to 0.99 AU, and th eouter edge of the Sun's habitable zone varies from about 1.01 AU to about 10 AU.
I note that Dole's estimate is the only one explicitly about habitability for humans and beings with similar requirements. It is possible that all of the other estimates are for planets habitable for carbon based life using liquid water in general, and that none of them consider habitability for humans or for other oxygen breathers.
Some of them seem to require atmospheric compositon which would be unbreathable, for humans or other oxygen breathers, in order to have temperatures suitable for life.
So a writer extremely cautious about their story being proved to be impossible will restrict their circumstellar habitable zones to distances where the radiation received from the star would be equivlaent to that recieved at distances of 0.99 to 1.01 AU from the Sun.
Other writers might imagine that the Sun's circumstellar habitable zone is broader, in line with the estimates of Dole (1964), or Kasting et al (1993), etc. Those would allow for wider circumstellar habitable zones and for greater variation in the year lengths of habitable planets.
Thus I can imagine that such daring writers might have a range of year lengths for habitable planets where the longest one was about a thousand times as long as the shortest one.
Part Six: Alternate Biochemistries.
And a more daring science ficiton writer might imagine that life, including intelligent life, might have different basic biochemisty than Earth life, and could flourish at temperatures much higher or lower than carbon based, liquid water using life could tolerate, thus vastily extendng the range of possible year lengths of habitable and inhabited planets.
Here is a link to an article discussing some hypothetical alternate biochemistries for alien life forms, which may be a good place for a writer interested in using them to start researching.
[https://en.wikipedia.org/wiki/Hypothetical\_types\_of\_biochemistry[6]](https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry%5B6%5D)
Part Seven: Conclusion.
So the range of habitable planet year lengths in a science fiction story would mainly depend on how anxoious they are to avoid writing something which may be proved wrong in future millenia, centuries, or decades, or how much they dare to risk being proved wrong in the future.
And in any case the range of year lengths of habitable planets in ficiton is likely to be small compared to the range of year lengths of exoplanets which have already been discovered.
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The mass of a main sequence star determines its luminosity. You've specified that $M=1.5M\_{\odot}$; for roughly Sun-like stars (i.e. within a factor of $\sim2$ of the Sun's mass), the luminosity scales with mass as $L\propto M^3$; we can then expect your star to have a luminosity of $\approx6L\_{\odot}$. The boundaries of the classical habitable zone can be roughly approximated by the range of planetary [effective temperatures](https://en.wikipedia.org/wiki/Effective_temperature) in which water can remain in liquid form. The effective temperature $T$ is related to the star's luminosity and the semi-major axis $d$ by
$$d^2\propto\frac{L(1-a)}{\varepsilon T^4}$$
with $\varepsilon$ a constant taking into account the greenhouse effect and $a$ the albedo. For an Earth-like planet, $a\approx0.3$, and the acceptable range of temperatures should be from $T=273\;\text{K}$ to $T=373\;\text{K}$. If we start with $\epsilon=1$ and $L=6M\_{\odot}$, we find that the inner and outer boundaries of the habitable zone are $d=1.14\;\text{AU}$ and $d=2.13\;\text{AU}$. Now we invoke Kepler's third law, which says that the period $P$ is given by
$$T^2=\frac{4\pi^2}{GM}d^3$$
and so the planet's year should fall between 363 days and 927 days - so roughly 1 Earth year to 2.5 Earth years.
What about our assumptions about $a$ and $\varepsilon$ - is our result overly sensitive to them? Well, we have
$$T\propto d^{3/2}\propto\left(\frac{1-a}{\varepsilon}\right)^{3/4}$$
so there's a weak dependence - a bit less than linear. Both $a$ and $\varepsilon$ range from $0$ to $1$. Realistically, a habitable terrestrial planet might have changes in $a$ by a factor of 2 in either direction, and perhaps an atmospheric model accounting for the greenhouse effect might have $\varepsilon\approx0.8$. Combined, sure, this could lower the length of a year by a factor of 1-2.
As an aside: Above, I've performed the calculations for the case of a $1.5M\_{\odot}$ star; for roughly Sun-like stars, as I said before, homology relations indicate that $L\propto M^3$. This means that $d\propto M^{3/2}$ and
$$T\propto \frac{d^{3/2}}{M^{1/2}}\propto M^{7/4}$$
which is actually a somewhat strong mass dependence.
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The closest a habitable planet can be to its sun is less than .01 AU, if its star is at the lowermost mass to achieve nuclear fusion. At a distance of exactly .01 AU, a year will last .00353 Earth years. If we set the limit of how large the star of a habitable planet is at 2.25 solar masses, the furthest an habitable planet can be is 64 AU, which would mean that its year is a bit more than 341 Earth years long. Of course, truth is stranger than fiction. There are planets in this galaxy whose years can be measured in single digits, using Earth days as the unit of reference, and one planet has an year that is a million times as long as Earth's.
And I am not exaggerating. If we were to through in binary systems, then things get a lot more complicated. If we had one planet orbiting 2 stars, each one with a mass of 2.25 solar masses, then it would experience twice the gravity and get twice the energy. That will push the maximum orbital radius of a habitable planet to 90.5 AU, which means that a year on the outermost edge of the habitable zone would last almost 406 years. And I am talking about theoretical maxima and minima, with the minima calculated using a planet with no greenhouse effect and 100% albedo, and the maxima calculated using a planet with 500 times the effective column density of Earth's greenhouse gases and 0% albedo.
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It is the year something-something, and the Sol system has been colonized. The Sun is surrounded by a growing cloud of habitats, Venus is a veritable garden world, Jupiter is being fed mass from the sun so that it may one day turn into a brown dwarf, the Oort cloud is the new frontier, human lifespan is biologically indefinite, and Mars, despite being the least attractive candidate for terraforming, has turned into life-bearing world protected by a superconducting satellite that produces a magnetic field placed in the L1 Lagrange point.
It is a time of wonder and miracles.
Until it isn't.
Something caused the collapse of this civilization, and now only derelicts remain around the sun, the citizens of Earth, Venus and Mars had regressed back to a animalistic state while everyone else died, uploaded themselves into computer banks on Titan, or fled to the Oort cloud, and beyond.
Through out all this, the Satellite above Mars had persevered, keeping to its station like a sentinel of old with a shield of magnetic fields foreve-oh, never mind, got hit with a system wide Kessler syndrome event. Guess without Mars is doomed...Right?
Essentially, I'm wondering if it is possible to to have a a backup in case such an event where to occur. It's impractical to start up Mars's core so that's out. Perhaps having a mixture of genetically engineered life forms to create a specialized atmosphere more resistant to solar winds? If so, how? Are there other alternatives on the table? Do we have to go all Darwin IV on Mars?
Something to get out of the way.
Mars has been partially terraformed, there is a sea of liquid water, the air has been increased, though not to the level of earth's atmosphere and with, to Terrans at least, high levels of carbon dioxide. Plants and animals have adapted to these conditions.
Edit:
First off, thank you to everyone who has commented so far it really helps.
Now, it appears that I may have been to unclear on what I was asking exactly. So! To remedy this, let me give a some more clarification than before.
* The main point of debate is that there is need for a shielding due to the fact that atmospheric lose occurs over geological timescales. Thing is, the inhabitants of Mars in the setting would evolve into a post human species adapted to the red(?) planet (the bits of blue/violet and greenery ruin the image a bit) and that would take evolutionary timescales i.e. at least a millennia or more. Now, why have humans gone to such a state, that's a post for another time but suffice to say I have an interest in keeping the atmosphere intact for as long as possible, preferably as when the sun is big enough to non the Earth.
* When I said life on Mars has 'adapted', what I meant to say was 'genetically engineered' then over the millennia grew accustomed to Mars. This is due to the fact Mars is in reality a very unattractive terraforming candidate for a carbon copy of Earth (Venus, once it was cooled down with mirrors, sped up with targeted comet strikes to produce a more 'normal' 24-ish day/night cycle, jump start it's magnetosphere, change the axial tilt slightly get some seasons in and funnel most of the CO2 and N out of the surface be used in the terraforming process, shipped to Mars, the space habitats or crushed into a sizeable diamond moon with bits of Mercury sprinkled in; the end result is a good candidate for colonizing, though bit on the tropical side;)), thus Mars was terraformed till it was 'good enough', meaning the deepest the deepest body of water is around 1.5-2 kilometers deep, the atmosphere was thickened though not Earths 14.7 psi of atmospheric pressure but enough to cause storms of some concern, so around 9-10 psi if my horrible knowledge of atmospheric science estimation is right. The life there, along with the human population, was genetically modified to handle lower pressures and the much higher CO2 levels (though the high CO2 levels would give an excuse as to why the colonists turned feral, though not a good one), and have overall better radiation repair, though that was added as a after thought following bureaucracy and the vocal minority calling "just in case!". However, life on Mars can live in more extreme conditions, though I would like to keep the conditions as stated above for as long as possible.
* The question I'm asking is there a any way to keep such an atmosphere with without machinery and instead through some biological process, either naturally evolving by coincidence or through genetic engineering?
Thank you.
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/Plants and animals have adapted to these conditions/
They adapt further! The difference between low atmospheric pressure and progressively lower atmospheric pressure is a lot less than the difference between living underwater in an ocean and living in a desert. Earth life pulled off the latter feat. Over time your Mars creatures can pull off the former.
I could imagine photosynthesizers with robust waxy layers to limit water loss into the low atmospheric pressure. Perhaps these creatures hang on to the oxygen they form in their tissues just like they hang on to the sugars, so they can use both for subsequent metabolism rather than rely on atmospheric O2.
This would be fine story telling. There would be the native Martian flora and fauna which in some places would be dying out. Then there are the adapted forms which are spreading - similar to what was there before but more and different.
Don't forget the adapted Earth life which has formed symbioses with indigenous Mars life! Could that symbiosis swing the other way? Remember the Mars life did this whole "lost the atmosphere" thing once before, and got through it.
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Building upon MolbOrg's comment, it seems you just have to produce 100g of athmospheric content to counter the effect of solar winds on the athmosphere.
So the old civilisation could have created huge machines that produce gases from the soil.
For example on the poles there could be solid oxide electrolysis process installed that turns the water into hydrogen and oxygen.
Like the [MOXIE](https://en.wikipedia.org/wiki/Mars_Oxygen_ISRU_Experiment) prototype.
Also silica has been [found on mars](https://www.nasa.gov/mission_pages/mer/images/pia09491.html). Which reacts partly to water, when combined with hydrofluoric acid.
Or basically from any other material the old civilisations brought up there. Powered by solar or nuclear fusion, since they seemed to have been pretty advanced.
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what you could have a hyper bacteria, which is very light, and floats in the atmosphere, they feed of light, heat, radiation, etc. whichever you want, they are in such numbers that they block solar winds, there could have other bacteria to break down some of the surface to make more of an atmosphere, caves would also be an alternative, just make your fauna be underground mostly, and a failsafe that absorbed the "atmosphere" it already had, and bring it into a refuge, plants get to this tank, and form an ecosystem inside the refuge, you let some survive inside, as well as animals, and close any gas exit, the plant also has a piece for the collection of sunlight, waxy layer to reduce water loss, and possibly get more energy from the sun, and a mix of chemosynthesis, (you could also have a machine for the use of solar winds for pure energy, and the plants adapt thanks to genetic modification to transform more kinds of energy for them to use it)
having a solar wind resistant super forest, which grows a shield, so it creates a cave system, mycelial networks work as a part of this ecosystem, the mycelium here was modified to be much better, and smarter, it grows inside the solar shield, and transforms heat from the sun into energy which is spread through the plants, eolic type energy is used, which can be mostly unaffected material as Martian winds are generally stronger than earth's
the sea can have a new roof of materials, on the surface protecting t from evaporating, also, heat can be turned into energy by the plants, as well as light hitting the surface, the water would be highly oxygenated, creature transform part of the soil on cave roofs into food, and their poop is eaten, by plants, fish etc. they could survive for some time,
sorry for any clutter, I'm a bit tired
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What features of grasses would need to exist in a plant for the plant to fill the same niche as grasses in a grassland?
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* Rapid growth and spreading.
* Willing to grow in marginal and poor soils.
* Ability to survive grazing, including *really severe* grazing.
* Ability to survive being stepped on by absolutely everything in sight.
* Strong root system for stabilizing soil.
* Ability to either survive fire, or rapidly reseed and regrow after a fire.
* If in a region that experiences frost and snow, it should be able to at least regrow rapidly after a frost, better survive and thrive even after being frozen solid.
* Capable of letting the upper surface "die", to provide reduced water needs and shade/thermal protection in event of drought/water shortage.
* Ideally, should be significantly nutritious to eat, as this invites grazers to trim old growth and fertilize and spread seeds.
* Should *not* grow tall enough for a 'grass' fire to become a 'forest' fire.
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Perhaps you know of pneumatic weapons also called airguns, but for those who don't; they're weapons that use air as propellant to launch a projectile rather than for example black powder or smokeless powder. They've been used as battlefield weapons, the most notable is probably the Girardoni air rifle <https://en.wikipedia.org/wiki/Girardoni_air_rifle> , but others such as the Kunitomo air gun <https://en.wikipedia.org/wiki/Kunitomo_air_gun> also existed.
They had some advantages and some disadvantages in that period of time, but eventually the disadvantages won out over the advantages. Air gun tech has come a long way though, so their capabilities have increased, of course so has their concurrents (such as smokeless powder) their ability.
My question is as follows. **How could weaponry that uses air as a propellant become the norm for a military force? What kind of limitations (environmental/logistical/industrial/scientifical/economical), preferably no theological would be required to make a society favor fielding pneumatic weaponry over conventional weaponry?**
I can only think of a subterrenean setting due to the noise reduction and shorter ranges involved, however I would like to also keep this above ground the norm. Not only that I would like stuff like Man-portable anti-tank systems (though stuff like PIATs and panzerfausts would also be in use), mortars and artillery to also use air as propellant.
[Airzooka](https://www.youtube.com/watch?v=uLFoXwd3Dy0)
Things to keep in mind:
-The setting in which this is to be used is semi-(post) apocalyptical, so mass production is not really an option; cottage industry exists and people would be familiar with modern techniques (though for obvious reasons stuff that requires computers and such is not feasible).
-People know about smokeless powder, black powder,...
-There are monsters in this world, so maybe they can play a role, but I feel like they shouldn't be the only reason.
Edit:
@TheDyingOfLight That's not a bad thinking route you're using there.
@KerrAvon2055 Biggest armies (not including coalitions or alliances) are regiment sized, biggest battle will be fought at battalion size and most combat (90%) squad to platoon size. Though most of these people will not be professional soldiers, but conscripted/levies. Reasons for fighting vary, most of it boils down to I want what you have.
As for the monsters; varies greatly. There are things that are not any or barely sturdier than humans to things that could use a bazooka or 50 call. to bring down and then there are those where you better use flamethrowers or more specialised stuff (like magic (haven't worked that out yet) or certain elixers).
The terrain featured shall be urban, forest, swamp, subterennean and something like the Scottisch highlands.
@JBH I really enjoyed your comments. As you said silence is a bit of a problematic advantage since the compressors are quite the opposite.
@GrumpyYoungMan Yeah, I know that pneumatic can't match conventional hence why I am trying to find ways why people who know of smokeless powder don't use it in favor of air. On the other hand if everybody is stuck with pneumatic then everyone suffers from the same issues. The only way something like the long Tom could be fired seems to me if they're using it as a stationary emplacement with dedicated facilities something like the V3 was meant to operate in WW2. That said I am probably going to allow them to have crude rockets whether they're powered by blackpowder or something else is still something I am thinking about.
@Duncan Drake The location is not really based on any place on Earth really, it could be, but it's not like I am ever going to say "Northern America" or something like that. In fact I am probably going to make the place a sort of alternate dimension and hint at that. I just don't want to do stuff like in this dimension you can't make gunpowder work, because I feel like that's a bit of a cop out. One thing though that may be important is that the place is often very foggy or at least misty. Maybe that helps a bit to off set the lower range of pneumatic rifles. So yeah, no ammunition imports.
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## No Dangerous Chemistry Required
In a post-apocalyptic setting that brings the society back down to cottage-scale industry, gunpowder becomes a finite resource. The chemistry involved in making safe, reliable smokeless powders is complicated and involves noxious, caustic, or volatile precursors, as well as processes whose failure modes involve very loud explosions. Many early nitroglycerin and nitrocellulose factories were completely destroyed due to accidents. Even black powder manufacture requires chemical precursors which could be hard to find or manufacture in the required concentrations and purity in a post-apocalyptic setting.
Safe production of an airgun, however, is well within reach of a reasonably-equipped machine shop. Compressors would be available via salvage or new production, and pressure-rated bottles can be found everywhere, in sizes ranging from CO2 cartridges to SCUBA or welding-gas tanks (or even larger).
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First, what are the advantages of air guns?
* **Good for stealth.** The [Wikipedia Article](https://en.wikipedia.org/wiki/Air_gun) on air guns mentions that "they did not disclose the shooter's position or obscure the shooter's view, unlike the black powder muskets of the 18th and 19th centuries." Probably similar with-gunpowder weapons could be made, but I'm not a gun expert. Wikipedia also notes that they could be deadly in the hands of a sniper because of their quiet nature. It says that "France, Austria and other nations had special sniper detachments using air rifles."
* **Cost-efficient.** There's no use of gunpowder, so that's a bit saved on every shot. It probably wouldn't be much in our world, but maybe in yours the resources to make gunpowder are more rare or difficult to make. (or, as you mentioned, mass production is not an option which might make gunpowder more costly)
* **Versatile.** Air guns can be used in all kinds of different environments. Guns with black powder, for example, have issues with getting wet, and there are probably similar restrictions for other powder types (as I said, I'm not an expert). Your world could have a lot of environments that make gunpowder an issue where air guns wouldn't be (you mentioned swamps as a battleground, which would be a problem for black powder because of the water). My favorite example is what I'll go over next.
I have to mention what I think is possibly my favorite gun design I've read about: the air rifles in *Twenty Thousand Leagues Under the Sea*. These guns are designed to be used for hunting *underwater* which I think is totally awesome. The reason Nemo chooses this type of gun is that he cannot manufacture powder from his submarine (as I said, this is resource-effective), but my favorite part is that he makes up for the slow speeds they'll have so far underwater by electrizing the balls. If one of them so much as brushes against the target, it is lethal and the animal drops dead from an electric shock. Now, this might be possible with gunpowder weapons, but this is the only example of the idea I've seen. (You could also replace the electricity with some sort of magic thing, I don't know how your magic system works)
I hope this gives a few ideas. If these don't work, let me know and I'm happy to come up with something new.
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**Market dominance, tunnels and sniffer monsters**
There are three reasons I can think of for air-powered small arms and low-velocity support weapons to be prevalent in the environment described. (Sorry, but @GrumpyYoungMan is correct that the technology is not feasible for serious artillery. Cottage industry would also be struggling to build 155 mm guns and their ammunition.)
First point - the best technology is not always adopted. The person with the best marketing typically wins, especially in a "cottage industry" level where there are not going to be competing corporations with professional marketing teams. All it takes is for there to be a bad experience with the only competent chemist blowing their hand off while trying to manufacture primers while a highly competent air gun enthusiast gets a production line going and air guns will be first choice for one enclave at least. (Hard to apply the same set of circumstances to all the nations, but if one enclave starts selling the air gun equivalent of the AK-47 to everyone then it will become dominant.) The ammunition will be very simple to manufacture compared to projectile + cartridge case + powder + primer, with no one in a position to contest the manufacturer's claims that the increased maintenance on the air gun seals is less than the increased cost of gunpowder ammunition.
Second - air guns are much safer to use in poorly ventilated areas. If a significant amount of the fighting is occurring in tunnels, basements or small rooms, the ability to not asphyxiate yourself while shooting is a major advantage. I realise that most of the terrain mentioned was open ground fighting, but if useful technology / resources are in underground caches and basements then there may be fighting going on there. (The reduced *peak* decibel level of the airguns is also beneficial, as noted by Benjamin.)
Finally - one idea that was proposed several decades ago was to create venomous insects that would home in on the odour of the brand of gun oil used by enemy forces. This was a silly idea - it would take much longer to design and breed the insects than it would take for the enemy to change brand / aroma of gun oil once they learned of the threat. However, what if one of the pre-apocalypse factions was practising asymmetric warfare and had no conventional forces at all? Create a bunch of venomous insects (let's say wasps) that home in on *all* gunpowder combustion products and suddenly having lots of gunpowder guns does not look like such a huge advantage. Assume that these insects have become ubiquitous in the relevant area since the apocalypse.
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I am building a habitable terrestrial 'super-earth' type planet. Ideally, my lifeforms should be primarily carbon-based and their biochemistry relatively similar to Terran biochemistry, but with slight modifications given their different environment (Atmospheric composition, Orbital characteristics and physical characteristics of their planet etc.) I am having difficulty determining exactly how the different environment would constrain/expand the possible biochemistry of my organisms, examples: what amino acids or amino acid analogues would be favoured in protein synthesis, what molecule/molecules would be most suited to transport oxygen around the organism, what compounds could work as Nucleic acid analogues given the different atmospheric conditions.
Basically, how to determine whether the organism would be able to exist and what biochemistry would "work" (be able to function) if various atmospheric conditions were altered such as the Ph of the oceans and/or addition of toxic compounds to atmosphere or biosphere. Although a have quite a bit of knowledge when it comes to Terran biochemistry and biology (so please feel free to explain in as comprehensive/complex a way as possible) I am struggling specifically with this topic of 'Xenobiochemistry'. I will explain the relevant characteristics of my planet below:
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My planet's characteristics:
The planet is a super-earth type terrestrial planet with 1.5 times the gravity of earth, 1.48 times the radius and 3.15 times the mass. It is more volcanically active than earth and its atmosphere has relatively high concentrations of sulphuric molecules, CO2 and methane as a result (Exact numbers below.)
The planet orbits a stable close-binary pair of dwarf stars at a distance of 0.412 AU.
The planet's atmosphere is pressured around 1.7 Atm and its surface temperature is around 30 C (90 F) (Due in part to the greenhouse effect of the many volcanic compounds in the atmosphere and the increased bond albedo of the planets surface.)
Its precise atmospheric composition is as follows:
73.69% Molecular Nitrogen
24.50% Molecular Oxygen
1.50% Argon
1.00% Ammonia
0.05% Carbon Dioxide
0.05% Water vapour
0.05% Hydrogen sulphide
0.02% Sulphur Dioxide and Trioxide
0.02% Methane
The Ammonia in the atmosphere is due to its use as an early biochemical defence mechanism in unicellular organisms in the early oceans.
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My organisms:
Biological building block: Primarily carbon-based.
Biological solvent: Ammonia-Water mixture (2-3% ammonia)
Nucleic acid/Nucleic acid equivalent: ?
Protein structure: ?
Oxygen transport: ?
Energy storage: ?
Cell structure: ?
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Also, please just ask for whatever other characteristics you would need to answer the question, as I have calculated many, many of my planets qualities and features.
this is a long description, but I really hope someone can help me understand how to determine which biochemistries work in which alien world's, such as this one. thanks in advance. (:
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I think it would be very difficult to provide much of an answer as the scope of organic chemistry is vast beyond imagination and 99.999% of it lies in the dark beyond the chemistry that we are "familiar" with.
Humanity is not really fully up to speed with the exact detail of how our own biochemistry works, although much is known, much remains to be discovered. And when it comes to the vast array of plants and animals the scope is even wider.
As an illustration of the level of complexity look here:
<https://www.sigmaaldrich.com/technical-documents/articles/biology/interactive-metabolic-pathways-map.html>
Follow the link and have a look around and remember that this is just a fragment of the full thing. What would happen if we mixed this up a bit and swapped out a few methyl groups for hydroxyl groups how would that pan out?
In fact beyond the twenty or so common amino acids, many hundred are known to exist, perhaps a few thousand, but how many of those have been investigated or characterized in any detail? I suggest not that many. And the scope of the possible amino acids is much greater than that by many orders of magnitude. It would be easy to come up with a likely formula for an amino acid that was unknown to science.
On top of that amino acids are optically active so always come as twin possible enantiomers. But if any of the rest of the groups attached to the amino acid also contain chiral centres then the number of isomers is doubled for each one and each might well behave differently in a complex biological reaction.
Then there are bases and sugars and even more variety and possibility 99.999% of which will be unknown to science. And the list goes on as an alien biochemistry need not be limited to any of these three groups of compounds.
I say all this to highlight the immensity of the question that you are asking. I doubt very much that it is answerable beyond a few unsubstantiated generalities.
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**PANSPERMIA!**
Yes, yes. Panspermia. The same basic critters colonized all places in the universe where there is life, possibly with help. So you can start with the basic Earthlife biochem and riff on it. Given a fundamental setup of your colonizing organisms, imagine the selective pressure your environment would produce and then use your biochem knowledge to invent adapations that could evolve.
It is kind of like haiku vs free verse. Free verse risks being lame because you have no limitiations. Haiku constrains you which can also be liberating. Panspermia lets you can be creative within the confines of actual biology.
It occurs to me that must also be what you want. If you have fake made up chemistry it is just that. It can keep company with faster than light speed ships and other fake stuff. But if you riff on earth biochem then the biochem nerds who grok the molecules (your people) will be digging what you did, because they will understand. Or they will object on grounds of steric hindrance, and that is when you open the wine.
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Take a world with the same **physical** characteristics as Earth, but where **biochemical** development has "rolled the dice" differently in some cases.
* The simple chemistry are the same compounds in slightly different proportions. The air consists mostly of nitrogen, oxygen, argon, carbon dioxide. The water is ordinary H2O, with dissolved salts in the oceans and the trace organics one would expect from the ecosphere (see below). Sand and rocks are made from silica and carbonates, mostly.
* There is carbon-based life which *looks* much like life on Earth. Simple organic compounds like ethanol or butane are the same. The differences are in the more complex compounds.
+ Some sugars, amino acids, and the like have a different [chirality](https://en.wikipedia.org/wiki/Chirality_(chemistry)#In_biochemistry).
+ The genetic code uses ["unnatural" base pairs](https://en.wikipedia.org/wiki/Base_pair#Unnatural_base_pair_(UBP)) (natural on the world, of course).
* Life includes something like photosynthesis-based flora and mobile fauna. Details differ, of course.
What are the problems if humans want to raise crops and lifestock on this world outside a sealed greenhouse?
It seems obvious that humans could sterilize soil and bring it into a greenhouse, but that is not necessarily easier than raising crops in a space station.
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With an alien world, alien biogenesis and presumably billions of years of alien evolution the local flora and fauna might resemble their Earth counterparts to some extent but their biochemistry would be scrambled compared to that from Earth.
Chance has a big part to play in evolution and with slightly different starting conditions the result would in all likelihood be biochemically different. Hard to say how different but such life would probably rank somewhere between inedible and toxic.
In basic terms all metabolic pathways are scrambled. Lots of common small molecules, but the larger molecules would mostly be different and their are millions of them in the biosphere this is just a small part:
<https://www.sigmaaldrich.com/technical-documents/articles/biology/interactive-metabolic-pathways-map.html>
The alien life would be well adapted to the alien conditions, Earth life would not. There would be serious difficulties with weeds, although with research it should be possible to find something that was deadly to the native life but didn’t harm Earth life. It might take time to find it, it would probably need to be reapplied regularly and some of the “weeds” might become resistant to it.
There could be physical as well as chemical difficulties – perhaps the air is fall of a million fold more spores than on Earth that clog lungs – but there might not we don’t know.
Letting livestock anywhere near the native flora would probably not end well as Earth based fauna are adapted to Earth and would be tempted to eat whatever they perceived to be edible which would almost certainly be a mistake.
For things like wood there would probably be little immediate danger as it would probably primarily be an inert primarily structural element, but saw dust might well be toxic.
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The "bricks" are the same, as you state. This means that, with a proper bacterial ground, "our" plants can grow, for example by having nitrogen fixing organisms. This would mean that the colonists would have to take with them not only seeds, but also sample of the grounds to be sure that all the needed microorganisms can be present.
Probably a sterilization of the ground before planting would give better chances to "our" organisms, since it would take out competition for the bricks.
For the rest I would exclude cross pathogenic effects: since the DNA basis are different, a cross infection would not find a way to propagate because the instructions of the infector would not be executable by the infected.
That however does not rule out toxic effects by alien molecules.
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A "Solar Jet" in my imagination would be a thruster that collects solar wind with magnetic fields, charges the particles, then expels those charged particles through a nozzle. It could be run on a reactor, solar power or any other high performance power source. Calling it a jet is because it resembles conventional jet engines where air is mixed with fuel then ignited.
Would this contraption be possible, and would it be efficient enough to consider It over any other type of propulsion?
(sketch for ease of understanding, components not final, sorry for misspelling)
[](https://i.stack.imgur.com/I3Qry.png)
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Yes it is possible.
[It was already invented](https://en.wikipedia.org/wiki/Bussard_ramjet):
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> *The Bussard ramjet is a theoretical method of spacecraft propulsion proposed in 1960 by the physicist Robert W. Bussard, popularized by Poul Anderson's novel* Tau Zero, *Larry Niven in his* Known Space *series of books, Vernor Vinge in his* Zones of Thought *series, and referred to by Carl Sagan in the television series and book* Cosmos. (Wikipedia)
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Main problem with your design is very low actual particle density for it to be effective. For jet-sized intake you will have only one proton at a time on average. You need a miles-wide intake to have something to accelerate.
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contrary to popular belief, Ents are not actually plants but are actually a species of animal which resembles trees as a technique of camouflage. some basic characteristics of these Ents include:
* have 1 in thick skin, which resembles bark
* have twig like hair
* are scavengers but will occasionally act as ambush predators
* males range in height from 9.11 to 14 feet tall, and are 15% larger than females
* are quite stocky with proportionally longer arms
* have orangutan level strength and intelligence
* are erect bipeds
* have a average lifespan of 300 years, and have a slow metabolism
* hibernate in the winter, and are capable of standing still for long periods of time
* are solitary
* have a excellent sense of smell and hearing, but relatively poor eyesight
Given these characteristics, what species could they have evolved from, and what evolutionary pressures would lead to them?
[Answer]
**Sure!**
Could easily evolve from the only slightly shorter [Gigantopithecus](https://www.nationalgeographic.com/news/2016/01/160106-science-evolution-apes-giant/).
You don't ask for a reality check, but in all honesty, 1 mph is pretty slow. Though you could mix in a bit of sloth for good measure, at about 125 feet per day. Not much of an ambush predator, unless your beasty starts its ambush last week.
[On the other hand...](https://www.youtube.com/watch?v=me-BOWwtm2Q)
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**Maybe, but a few things to consider**
1. Really big scavengers can be highly-susceptible to extinction. So make sure that there's plenty of food in your world to go around. The Short-Faced Bear is an excellent example of this. They were the biggest, scariest scavenger running around and then the climate changed and *bam* they're extinct. This is why obligate scavengers are rare and most of them only supplement something like hunting. If they were mostly ambush predators and secondarily scavengers that'd be different.
2. They need to be able to either eat stuff other animals can't eat (like a vulture) or scare predators away from their prey (like a Short-Faced Bear). Now if I'm the second-scariest thing in this world, this doesn't really sound scary enough to get me away from my well-deserved meal.
3. Scavengers need to be able to access enough carrion to support themselves, so they need a very large range. Unless there's so many animals in #1 that this isn't an issue. If they don't move around much they either need a different food model or there needs to be dead bodies everywhere.
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So in my setting there is a small and exclusive group of people that have access to devices that work like computers (but which are *not* the same as computers. They do not use semiconductors and electricity, for instance). These people would use these machines to simulate the world and acquire knowledge of physics and science, putting them way ahead of their time. These machines are condemmed by organized religion because they are borderline prophecy and magic for those seeing it from outside, so these people go about their business in secret.
This particular story tells the tale of Julius, a lad who loses his parents for a plague and is sent to live with his grandfather's brother, a bitter old man with a lot of money named Cesare who seem to always be on guard. The boy arrives at the countryside home of Cesare and is treated like an irritating guest.
The story follows the emotional bonding of Cesare and Julius as he comes as a guest and then slowly progresses towards family. Cesare, the bitter man finaly melts his protections and see in Julius the son he never had and Julius finds in Cesare the guardian that he lost. The entire piece resounds with themes of family union and filial love but also growing up as Julius goes from a naive lad to an able scientific apprencite and lab assistent and seem posed to carry on the work of Cesare, the son the man never had.
Although the themes are important, the backdrop on which they are dramatized is one of science and discovery. The emotional journey of Cesare and Julius happens as Julius goes down into Cesare's research. He finds that Cesare is one of those people that control a computer, then he slowly tries to learn what is going on as he tries to come to grips with what he thinks about all this since he is a god fearing lad. Eventually the alure of forbidden knowledge and curiosity take over and Julius start to secretly studying Cesare's work from the few glimpses he can catch.
The problem on which Cesare is working is of central importance because it also serves to illustrate the power of owning a computer and the role of computer simulations in the scientific discovery process, which is something I would like the readers to experience.
The work is framed in the 1800s. A time of religious fervor and intellectual effervescence that will shake the world. In fact, this is also one of the themes of the work, the tension between tradition and innovation. So in order for the piece to have an interesting take I wanted them to deal with a problem that the scientific community of the 1800s could be aware with the physics of the time, but which was too hard to solve by hand, thereby requiring a computer and giving an advantage to those that owned one.
My first idea was the discovery of Neptune, but Urbain LeVerrier did the computations by hand and managed to get it published. So even though it might have been an extensive and difficult computation to perform, it was nonetheless quite possible with the computational resources of the time. I wanted something equally iconic and worldview shattering but harder, way harder. A juicy problem that is *right there* but is untractable without a computer.
**What difficult, important problems could possibly be conceived with the knowledge of 1800s physics but were untractable without the employment of a digital computer's computational power?**
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I see a lot of great examples like Wheather forecasting and dynamical Many-body problems. However it ocurred to me that the examples (probably due to my lack of clarity in the question) are too *general*.
What do I mean by this? Well let's take the example of the N-Body problems for N>2, kindly suggested by @b.Lorenz, which is currently our best-ranked answer.
Although I can appreciate the difficulties to obtain analytical solutions to an N-Body problem and the contributions that having a computer would make to it, I was wondering **what specific N-body problem would be relevant**?b In the story, Julius and Cesare are posed to make a discovery using their computer. An important discovery. I wondered what that discovery might be. For instance, I mentioned the discovery of Neptune as my initial consideration.
This discovery could be a specific case of solving an N-body problem. The characters could simulate a system with a fictitious mass positioned so as to rid the predictions from inconsistencies with the observations, and then extrapolate the system into the future to make an observation of the hidden planet. That would be awesome. But I also mentioned that Urbain LeVerrier made a ton of approximations, calculated the thing by hand using data collected from astronomical observations and *still* got it right. Neptune was observed in the sky roughly around where LeVerrier predicted. So this particular problem of an N-body computation is not ideal because it is not a problem that highlights the advantages of computer simulation, it is not out of reach for a dedicated investigator with a few assistants working for, say, a year or a few months.
So what would be a good example then? What *particular case* of an N-body phenomenon would be relevant and known for 1800s physicists that they just wouldn't be able to investigate even if they managed to have the relevant insight?
Likewise, what *specific case* of wheather forecast or hurricane prediction would be dramatic enough that it would shatter the scientific community when solved, is knowable from the physics of the day, but is out of reach for the actual solution even to the brilliant minds that happened to stumble upon it? I know that "hurricane prediction" would be an incredibly useful but I'm thinking more on a specific instance.
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## Edit 2
So again I have noticed that I have a somewhat lack of clarity. AlexP asked what do I mean by "solve". Admitedly, solving a problem might mean a lot of things, particularly in physics.
Although I accept answers that deviate from this norm, if they are good and interesting, by "solving" I mean:
"Numerically integrating difficult systems of differential equations in order to obtain **accurate numerical predictions** for phenomena that, at the time of the setting, **cannot be analytically obtained**, that is by algebraically solving the system."
I require that the phenomenon in question be, if not useful or critical for the entirety of the society, at least *scientifically* interesting. For instance, the discovery of Neptune did not spell doom for the society, nor would it have suffered dire consequences if the planet had not been discovered, nevertheless it was important because it basically rewrote what we knew about our cosmic home, and that was a big deal for the astronomy of that time.
As I said, I will accept things that are not part of the above set, as long as they are interesting and enticing, but I believe that numerical integration of difficult systems of equations is a nice, basic aim.
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**Gravitational N-body problems for N>2** are **chaotic** and in general unsolvable analytically. The laws and the resulting equations were known since Newton.
Using perturbation theory, a lot of work, and a load of creative ideas, great scientists of the 18-19th century, like Lagrange, could approximately solve some cases of interest (long term stability of solar system, Lagrange points, finding planets by their gravitational influence on other planets), but for example **predicting the outcome (outbound velocities) of a close encounter between three celestial objects of comparable mass**, was beyond them.
Using digital computers, this can be solved to arbitrary precision. (Error will remain, but the more compute you throw at it, the smaller it gets)
**In theory, everything that a (non-quantum) computer can calculate, can be calculated by hand**, but you would need a **great army of calculators employed day and night**, and they will make a lot of mistakes. So it is safe to say that only a computer can practically solve such a problem.
It is not hard to imagine, that such a problem could have practical importance too, **for example predicting whether a dwarf planet will hit Earth or make a close miss after a close encounter with two other asteroids**. (Ceres and Eros were discovered in the early 1800-s so they are detectable with 19th century telescopes)
[Answer]
The short answer is all of them.
The long one, well, it depends.
See, when i was on my first class on finite elements analysis the teacher, trying to make us undestand how the program we use works, made us do the math by hand. We had a cube with a force aplyed to one of its vertices, and we did a very rough grid on it, with a point in each vertices. And took some good hours to do.
The computer, on the other hand, did a really good grid with thousands of points, doing a much better simulation than i did, and it took it just some seconds.
Whatever we can do, by hand, on classical physics the computer can too, but faster.
When trying to resolve a complicated problem you can break it in very simple parts, but will take you much more time.
There is, of course, some cases in wich you can only use a computer, but i think this is the wrong way to look at this question.
For example, in ww2 artillery boats had mechanical computers they used to know where and when to fire a canon to accuratly shot down an ennemy vessel. The calculus involved are really simple parabolic projectile physics, but the time in wich they needed the answer was really short. So they could see a enemy ship and shoot it down fast.
A human could not compete with a computer in this case.
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In general, I think fluid simulations are a good example of a thing where computers can really help us out. They are nice and intuitive, and fairly practical. They are also a good example of something where we could do the symbolic calculations on simplified problems worked, but doing it computationally lets us handle real-world applications.
If you want a specific example, I suggest:
Steam engines are getting good around the time when you've set the story. This is a great problem for a computer-aided design because it doesn't rely on super high precision observations of natural phenomena outside of the character's control. The goal here is to look at a proposed design and simulate it. So however powerful your computer-like-devices are, your character can come up with a design that is as simple or complex as necessary.
The ability to investigate the simulation in detail at each time-step will translate to increases in efficiency and performance for your character's engines. It is plausible enough that your character has been trained in the art of making these engines by his uncle -- little does the church know, he's actually using science!
He could also simulate propellor blades or maybe even boats generally. This isn't as tied to the timeframe (although maybe he works on steam boats).
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One field were having access to computers completely trumps not having them is cryptography. Essentially the computer owners can brute force most cyphers created and used for hand coding and can easily create cyphers that are impossible to crack by hand. But this is more diplomacy then science and also requires intercepting messages in the first place.
A more sciency area is math, especially number theory. Gauss computed primes by hand up to a million or so just to get an idea of what their distribution looks like. Mersenne primes can also be computed much farther with a computer.
Finally I think the astronomy you mentioned yourself can provide good examples. Discovering Neptune is much easier with computers than without and so could have happened earlier. Presumably there are a few similar examples.
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I think the answer might be **"none that are particularly useful for the society in question"**.
If you look at typical uses of computers today:
**Meteorology:** requires an array of accurate real-time temperature/pressure/wind-speed data in order to predict the weather.
**Military:** In principle useful for ballistics but without rapid communications a pre-existing hand-calculated table would be more useful on the field.
**CAD Engineering:** outputs plans/models/designs that are really only useful with good quality raw materials and modern fabrication machinery.
**Finance:** banking/stock-market/business operations all require fast and reliable communications.
**Telecommunications:** similarly - needs infrastructure.
**PDAs, lap-tops, GPS etc:** all only useful in a very different society.
**Sciences - Physics, Chemistry, Astronomy, etc:** generally the information will only be as useful as existing theories. No point in modelling protein folding or electromagnets if you haven't yet discovered atoms or quantum physics, or Maxwell's laws.
About the only things I could imagine you being able to do would be faster prediction of things like tide tables, eclipses, log tables, and planetary motions (although people were already doing that manually using calculus/algebra etc.). It might also be useful in cryptography, but due to limitations in communications you wouldn't be sending vast amounts of data, so probably no more useful than one-time pads etc. You could, of course, find large primes, solve Diophantic equations etc., but as you have already commented - that isn't physics or technology as such.
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I am making a fish folk race, and I want to figure out if tattoos/ piercings could be possible. My ideas for piercings would be on the flesh itself or on the fins. If they had piercings in these areas, what kind of drawbacks would it have? (Note: they’re not very good swimmers, so swimming isn’t a concern. I imagine things like fins being dragged down, etc)
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If done safely/hygenically, you could pierce nearly anything without organs in it. If I see your pictures, the first thing I would think is pierced gills. Very possible, but it would have a massive drawback on underwater breathing. But people have lip tunnels which have any liquid they drink pour straight out. Where there is a will, there is a way.
Of course, tattoos are completely dependent on skin composition. Set aside the effectiveness on different (darker) skin colours, if their skin is scale based then permanent paints or paints under part of the scale might be better suited than large sub-skin ones.
As for jewelry (not something you mention but often popular together with body modifications), chains and bracelets are very possible. Rings however are not due to them having webbed fingers. However these webs present another prime piercing spot.
Remember, the thinner the membrane, the easier (less painful) it is to pierce. But thin membranes are fragile, and might pose risk of tearing.
I would imagine thin but potentially large tunnels in any fins could be popular.
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You could have piercings under the skin of the fish [like so](https://images.app.goo.gl/yJ7ReAXAXr6W98Ej6).
For tattoos, [pet stores are already selling tattooed fish](https://images.app.goo.gl/bcGxYasNya3adL8a9), so I see no reason why that couldn't work for your fine fish folk.
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With a group of friends, we are trying to build an RPG in a quite specific setup which I have a hard time to find elsewhere in order to get some inspiration/information.
So what I mean by that is: a nation where most of the technology is based on using animals or at least living creatures. Things like the little devil who paints photographies in cameras in the Discworld (it's a hard world), or like [the millipede subway](https://1.bp.blogspot.com/-HfT3GPe7jzw/V8w-NhDubEI/AAAAAAAADmY/Ktwr4Vk8fYcbxDzFljh-_UpkSRAGga7CgCLcB/s1600/FullSizeRender-6.jpg) of Ekhö.
Transportation, weapons, energy producing maybe with eel-like animals... As much of the technology as possible would be based on animals, but otherwise it would still be a modern if not contemporary setup with buildings, electricity, etc, inspired from the 50s in the real world.
So I end up with two questions :
* do you know of works of fiction with this kind of setup? Only one we could think of is Ekhö.
* do you see some obvious pitfalls, some reason for which it would not possible at all in a modern city, which would break the immersion? I guess that there would need to be a lot of accomodations like drinking throughs everywhere but it doesn't seem unthinkable.
Many thanks!
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Ever heard of the Flintstones? If you haven't, ask your parents. The show's humans largely used animals as replacement for technology.
[](https://i.stack.imgur.com/rBnSP.jpg)
Image source: <http://www.saturdaymorningsforever.com/2014/11/the-history-of-flintstones.html>
In that cartoon animals were fully sentient and willingly sold their services to humans. Sure, they were poorly paid, and the payment was... usually... inhumane, such as garbage disposal being done by feeding the trash to a cartoonish rendition of a prehistoric board. A running gag in the show was some animals saying something like "hey, it's a living!".
Other animals that I can remember from the show: "sawfish" being used as living saws, mammoths being used as water dispensers and at some point I think both hedgehogs and lobsters were used as lawnmowers. If you have access to some streaming service that has this show, it's worth watching.
As for any limitations: it really depends on what kind of fiction you are aiming for. The Flintstones was a cartoon by Hanna Barbera, with that kind of physics where you can walk on air as long as you're distracted enough to not notice you went over the edge of an abyss.
Now while you might think this does not render well in more realistic media, they did make a live action in 1994, with the dinosaurs and all working at a quarry just like in the cartoon screenshot above. I could not find a screenshot of the movie that does it justice, though.
For a more serious and realistic scenario, consider that in real life and up to today people use elephants in place of heavy machinery in many rural parts of India.
[](https://i.stack.imgur.com/uY8YA.jpg)
(Using elephants for logging has been illegal since 1994, and I particularly think it is cruel due to the way elephants are captured. This photo is just to illustrate that it is possible.)
As long as the animals are tame and have access to food and water, you can make things work out.
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Interstellar travel is hard and complicated, yet I want to have a plausible interstellar propulsion system for my setting. Rockets are out because of the rocket equation and the horrible top speeds even if antimatter is used. Laser-sails are out because they can't slow down. Ramscoops are out because while their fuel collection rises with their velocity, drag rises with the third power of their velocity, limiting them to a top speed of 0.1c.
**My idea was to combine the Ramscoop with the Laser-sail to get a system cable of reaching 0.9c with a reasonable mass ratio.**
The **spacecraft** has a reactor, a habit, a cargo section and a large structure made of superconducting electromagnets. The structure is formed like a trumpet and protected with reflective shields, so it remains cold enough to work. It protects the spacecraft from interstellar gas, acts as a funnel for fuel and ejection mass and as a pusher plate.
The second part of the **propulsion system** is an array of powerful lasers in the home system. They push laser sails up to a significant fraction of lightspeed. These sails are shot at the spacecraft. As the ultra thin sails encounter the magnetic field, they break apart and turn into plasma. Encountering a ten tesla plus magnetic field at relativistic velocities tends to do that to matter. The plasma transfers its momentum and then some to the spacecraft as it is deflected.
The spacecraft could even **slow down** if the path ahead had been seeded with slower light-sails. It would just have to turn around. These slower light-sails would have to be deployed years before the spacecraft launches. While the spacecraft couldn't slow down with this method below the velocity of the breaking sails, its magnetic field would create even more drag to decelerate it. As soon as it is slow enough, the spacecraft is ditched and a small fusion or antimatter propelled craft with the crew, mining equipment and a self-replicating factory is deployed. These guys continue to set up basic asteroid mining and industry. Their goal is to build the same laser facilities the home system used to accelerate the propulsion sails. Once both sides can deploy the sails, a reliable travel corridor has been established.
One idea I had was to **augment** the sails **with fusion** fuel. The mag-sail would funnel the metal-carbon-fusion-fuel mixture down itself. At the deepest and tightest point of the mag-sail one would compress the plasma with stronger magnetic fields and a laser firing squad. Magneto-inertial fusion, basically. I'm not sure if this is practical, not practical or only practical during certain parts of the journey. The parts of the journey where I think such a fusion augmentation would be most useful are the final breaking phase and the end of the acceleration phase. In both instances the relative velocity between sails and mag-sail is so low that little energy is gained.
The **fusion fuel** that will be used is critical. The options are, assuming that both the CNO Cycle and proton-proton fusion are impractical, D+D, T+D, D+He3, He3+He3 an p+B11. D+He3 and He3+He3 are problematic as helium can't be combined with the sail in an easy manner. Any fuel tank would be destroyed by the interstellar medium. The sail itself will be more resistant to damage. p+B11 is great as both elements be connected to the sail as a layer of paint and it is neutron free. The issue is that it is 500 times harder to ignite than D+T. D+D and D+T are both neutronic, but can be ignited relatively easily and can be added to the sail as paint as well. D+T has the additional issue that the tritium will slowly disappear. No fuel stands out, all have their issues. p+B11 is probably most reasonable option assuming advanced technology.
**Is the interstellar propulsion system described above realistic and reasonable? What issues might it face and how could one fix them?**
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What you're basically describing here is not a million miles away from the [Sail Beam](http://www.niac.usra.edu/files/library/meetings/fellows/oct01/597Kare.pdf) concept by the late [Jordin Kare](https://www.centauri-dreams.org/2017/07/25/sailbeam-a-conversation-with-jordin-kare/). That idea seems basically sound, and is my personal favourite kind of fast, plausible, hard-science starship drive. There are a few variations on it floating around, but the underlying idea of using a stream of small laser-driven lightsails to impart momentum to a starship is common to all.
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> Encountering a ten tesla plus magnetic field at relativistic velocities tends to do that to matter.
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I'm not sure it does. It doesn't really matter though, as you can vapourise incoming sails with a puff of gas or a laser. If you're fielding multiple incoming sails in a row, then you can convert some of the energy of the plasma cloud released by the first disintegrating sail to electrical power to zap the next sail.
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> The spacecraft could even slow down if the path ahead had been seeded with slower lightsails. It would just have to turn around.
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Make the spacecraft either dumbell or donut-shaped. Don't even need to turn around, then. Turning around at high sublight speeds is a terrible idea, because your crew and electronics will be very thoroughly dosed with high energy radiation, unless you're carrying a frankly unreasonable amount of shielding, or doing really weird and probably risky repositioning-reassembly manoevers. Anyway, not worth it. Make your ship work in both directions.
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> While the spacecraft couldn't slow down with this method below the velocity of the breaking sails...
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To be pedantic, it isn't the velocity of the sails that matters, but the *relative* velocity they have with the starship. Whilst there will be a bit of a dead spot where the relative velocity is zero (when you'd be using your magnetic fields as a brake, as you observed) once you fall below the velocity of the sail beam you can carry on braking using sail-plasma just fine.
It also allows you to fly *back* towards the sail beam source, if you're prepared to let the sails pass through the magnetic field before ionising them. Relativistic needle-threading is probably not an exercise for those of a nervous disposition, though.
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> One idea I had was to augment the sails with fusion fuel
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That sounds a lot like a combination of sailbeam with older ideas like [MagOrion](https://aip.scitation.org/doi/abs/10.1063/1.1290977) and [fusion runways](https://www.centauri-dreams.org/2017/06/16/a-fusion-runway-to-deep-space/) (the latter also a Jordin Kare idea), and it probably isn't worth it. If you're capable of driving your sails to any reasonable percentage of the speed of light (lets say 30%) then there's no benefit to doing any fusion. The amount of additional energy you can extract isn't that great, in part because the exhaust velocity of the fusion products is just too low and in part because there just so much oomph already available in the kinetic energy of the sails.
Although fusion would be pointless for *your* idea, I will note that ignition of even quite "hot" fusion recipes becomes a lot easier when your ship is moving really fast and the fuel pellets are not (or vice versa). The fusion runway idea suggested that smacking fuel pellets together at >200km/s would be enough to ignite fusion (though other sources apparently wanted more like 3500km/s, though both are well within your operating parameters) . It may be that this is a useful way to extract energy from sails when their kinetic energy relative to the ship is too low.
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Consider a planet with life forms, which are different than those found here on Earth, orbiting a star similar to the Sun. Such life forms don't use oxygen and, therefore, the planet's atmosphere is devoid of it. Since ozone is formed by diatomic oxygen photolysis, there is also not a ozone layer, but life forms need to protect themselves from their star's UVB/UVC radiation, so how would they do it? I mean, It's well known that the Earth's ozone layer prevents UVC radiation and part of the UVB (which are the most dangerous for living beings) from reaching the surface. So is there any other gas, other than ozone, that works as a filter for protection against UVB/UVC radiation?
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I don't believe there is any single gas that absorbs efficiently across that entire spectrum.
$SO\_x$ and $NO\_x$ both absorb and remit at lower energy levels across some of the wavelengths you want.
Ethene also absorbs in part of the UV spectrum and is formed by the breakdown of hydrocarbon chains. This could give you a cycle of breakdown -> absorption -> formation from hydrocarbons to ethene back to hydrocarbons driven by UV.
If you extend your notion of 'gases' to include particulates then you open yourself up for a wider selection of materials that act as UV shields for a planet. But, your atmosphere becomes very dusty -- so to speak.
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A race of mine terraforms planets to cater to their need for a higher atmospheric oxygen content of about 45% (They are insect like, who would've imagined), so I was wondering how it would affect a planet if such a terraforming program ran longer than it supposed to be. At some point the high oxygen content would lead to a lot more burning and similar things are not very nice to living things wouldn't it?
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**Oxygen oxidizes.**
As oxygen content increases, the problems oxygen poses on our own world would be more problematic.
1. Minerals exposed to the environment would tend to form the oxide. This led to an enormous problem during the emergence of life: iron was bound as the oxide. Higher levels of oxygen might tend to convert reduced nitrogen and sulfur compounds to the oxides, changing bioavailability.
2. Reduced carbon oxidizes in contact with oxygen.
2a. When this goes fast it is fire. It can go slowly too. Oxidation of dead biomass on the surface converts it to CO2 and levels could rise unless the process of oxygenation consumed CO2.\* The amount of non CO2 carbon on the surface would decrease more quickly, fire or no fire.
2a. Mutation. degradation. Oxygenaton of live biomass would break down and degrade proteins faster, which would need to be replaced by the organism. Oxygen free radicals attack DNA and presumably any other carbon-based molecule used for coding; organisms would be selected for antioxidants / repair ability.
Lifeforms that live on the surface of earth have lots of mechanisms to defend themselves against the corrosive effects of oxygen: epithelia with defenses, mutation repair mechanisms, strategies to withstand fire. Over evolutionary time these would increase.
.\* The oxygenation of the surface would depend on where the oxygen was coming from. Currently, nearly all surface O2 all comes from CO2 (with a tiny percentage from photolysis of water). O2 locked into carbonate rocks (like limestone; CaCO3) is not available to be released as oxygen via photosynthesis. As non-O2 oxygen sources are depleted, the terraforming process will be less able to put O2 into the environment, unless it is something outré like creation of matter from limitless energy sources,
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Let's imagine a planet that is 5000 km in diameter but has the mass of the Earth. I'd imagine standing on that planet might feel similar to standing on the Earth, because the gravity would be comparable.
However, at smaller and smaller volumes, there would be a greater difference in gravity with a smaller change in distance from the planet's center. Standing on a spherical object only a few meters in diameter with the mass of the Earth, the bottoms of your feet might experience Earth-like gravity, but your head would experience hardly any gravity at all. I'd imagine this would cause some serious health problems.
I imagine that no matter what, there might be some health problems when changing the volume of the Earth-like mass; however, I want to know what the smallest volume could be that has no immediate (no problems for at least a few years) health problems.
# How small can a planet or object of Earth-like mass be without being overly dangerous?
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Worldbuilding context: I am wondering what the smallest object can be that has Earth-like gravity. It would be interesting to be able to run around the world very quickly.
NOTE: I am only interested in the gravitational affects on the human body, so please ignore any other affects. I don't care about retaining Earth's qualities.
The question [How small in diameter a planet can be while retaining most of Earth's properties?](https://worldbuilding.stackexchange.com/questions/62538/how-small-in-diameter-a-planet-can-be-while-retaining-most-of-earths-properties?r=SearchResults&s=1|68.9937) is asking for much more than my question.
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The assertion that an earth mass only a few meters in diameter having a surface gravity equal to that of earth is wrong. Surface gravity can be expressed by $$g = \frac{GM}{r^{2}}$$ so if you reduce $r$ from ~ six million metres to, say, six, the surface gravity is multiplied by the inverse square of that reduction. So the surface gravity of a six-metre earthlike mass would be $${earth gravity} \* {10}^{12}$$.
This is obviously not survivable.
What you're looking for is a much less massive object, but one where the escape velocity is still sufficient to keep your human from launching themselves off the surface. If we let the object be a kilometre in diameter, then a mass of ~200 quadrillion kg [gives us](https://www.wolframalpha.com/input/?i=surface+gravity+calculator&assumption=%7B%22F%22%2C+%22GravitationalAcceleration%22%2C+%22r%22%7D+-%3E%221km%22&assumption=%7B%22FS%22%7D+-%3E+%7B%7B%22GravitationalAcceleration%22%2C+%22g%22%7D%7D&assumption=%7B%22F%22%2C+%22GravitationalAcceleration%22%2C+%22M%22%7D+-%3E%225.972%C3%9710%5E16+kg%22&assumption=%22FSelect%22+-%3E+%7B%7B%22GravitationalAcceleration%22%7D%7D) (Wolfram gravitational calculator link) a surface gravity approximately that of Earth, and a difference of $2m$ in $r$ (a tallish human) would make no effective difference. An escape velocity of $162 m/s$ isn't going to be something your runner can achieve unaided.
A 6.28 km run wouldn't be *too* big a deal to circumnavigate that particular sphere.
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It's worth noting that to have a 1km radius sphere with a mass of $2 \* 10^{17} kg$, you'd need an average density of $$\frac{2 \* 10^{17} kg}{\frac{4}{3}\pi m^{3}} = 4.77 \* 10^{7} kg/m^3$$ or about fifty million times denser than water. You're definitely looking at some peculiar matter to build your [*Petit Prince*](https://en.wikipedia.org/wiki/The_Little_Prince) planetoid out of.
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Assuming a **technologically advanced** civilization that has grown **sustainably** from the resources of its own planet (and maybe "a few" additional resources from its own solar system), what would be the maximum population the planet could host in a stable ecosystem for millions of years?
We have enough time and refined technology to increase our population, completely re-engineering a new ecology with the most efficient oxygen producing plants / cells / organic microchips, wastewater treatment, growing genetically engineered food from any suitable energy source, have cheap fusion energy and whatever other non-hyper-fantasy-technology we could realistically imagine (i.e. no Star Trek replicator scenario).
Or in other words: Imagine a highly efficient CELSS ([Closed ecological life-support system](https://en.wikipedia.org/wiki/Controlled_ecological_life-support_system)) of Earth's size. How many people could live there, taking into consideration the abundancy of natural resources?
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**Edit:** Maybe I should explain the background of my thoughts and be more explicit about the constraints that I see.
I try to imagine where Earth and mankind could develop in the next 10k, 100k or 1M years (hard to set a timeframe for such a development). I assume mankind learns from the ecological mistakes we are currently doing, but still will have a tendency to grow as technological progress allows it. Also the desired standard of living will presumably grow.
So everyone wants to **live comfortably**. We could define limiting factors for a comfortable life and **calculate different scenarios**, depending on what people still would consider comfortable. Let's think about space and resources.
For the **space factor** we need maybe at least 50 m² for privacy/living space, plus space for community life, recreation, work, transit. Makes 200, 500, 5000 or whatever m² per person.
Yes, we have fusion energy, but no arbitrary conversion of matter. Some technologies might still need rare earths, precious metals or other elements. We probably can't build everything just from carbon and silica since we might want to make use of what physics has to offer.
An approach to estimate that **resource factor** could be to consider the abundancy of several technologically relevant elements on earth or the solar system today and define a *usage per person* based on todays usage divided by a "technology efficiency" factor of our future Earth of 10, 100, 1000 or whatever.
Oh, and of course we need **water** to drink and maybe to shower. Considering all of Earth's water, how many people could live from it if one person needs 100, 1000, 10000 l of water in circulation?
Really ultimate limits could be waste heat and gravity like @Ryan\_L and @Chickens pointed out.
So what are the limits for which scenario?
Did I miss other relevant constraints in my considerations?
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It depends on your definition of sustainability. If you mean it in the sense that the natural ecology remains in balance, the answer is probably less than we have now. I think I saw someone cite 3.8 billion once, but it's anyone's guess really. I personally think that number is a little low, because current production expects growth, not stasis. You don't need to cut down as many trees if there are no more new families that need houses, for instance. The resources we gather today aren't used today.
If you mean the society is sustainable in that it avoids boom and bust cycles, i.e. growing too fast followed by famine, your real problem isn't a lack of resources. Your real problem is waste heat. Given fusion or beamed solar power, there is easily enough material on Earth alone to sustain a population of a hundred billion or more, assuming you don't mind wrecking the biosphere in the process. But all these people want computers and indoor lighting and air conditioning and who knows what else. All these things produce waste heat as they run, and so do the factories building them and the fusion plants powering them. This heat has to go somewhere, and the Earth doesn't radiate heat away all that quickly. Eventually you'll cook your people.
It also depends on how long you want these people to last. Eventually the sun will burn out. If they survive that, eventually they will run out of hydrogen to put in their fusion reactors. If they survive that, eventually they will run out of matter to put into their black hole generators. Nothing is sustainable forever.
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There's always "room for one more", but why would you want to push the envelope?
The real question should be: *given a world with a long-term stable population, is there any justification or advantage for this population to be greater than 1 billion?*
Larger populations mean less room to accommodate emergencies and even long term environmental changes. Maintaining a maximum population would mean that even a small unusual change could be catastrophic.
And on the other hand I can't think of any way in which a world of 2 billion people would be significantly better than a world of 1 billion.
But perhaps others can.
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**50 billion people**
The Netherlands is one of the densest populated countries on the Earth, yet also a net exporter of food (and I believe that the farming methods used are, in the main, sustainable). Nor does the Netherlands seem overpopulated; the cities are low and open, and there is lots of canals and forests.
It is not hard to imagine that with advanced technology, all land on the Earth, barring Antarctica, could achieve a similar state of sustainable farming, open lands, and no great population pressure. Even mountains, tundra, and deserts could be covered in hothouses or planted with crops genetically modified to extreme climates.
The population density of the Netherlands is 417.6 per square km. The world's total land area, minus Antarctica, is 135 mill. square km. This gives us 56 billion people.
Parts of Greenland, Siberia, and Canada may be just as inhospotable as Antarctica, but on the other hands, there will be regions capable of holding even more people in a sustainable way than the Netherlands by adding urban farming and cutting down on non-food farming such as tobacco and growing high-nutrition crops and keeping high-nutrition livestock. Note that quite a bit of livestock will be needed to provide grazing and natural fertilizer, since artificial fertilizer is highly unsustainable. Other technology might include precision fertilization and mechanical weed-killing by solar-powered robots. Ocean farming is also underutilized today.
Given all this, I think a maximum sustainable population of roughly 50 billion is realistic with advanced technology- The number could very well be far higher if we add fusion power, which allows extensive vertical farming, but I want to stick to a low, conservative number.
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inspire by xenomorph acid blood from alien movies.
so the water either rivers, lakes, and oceans in my world or some of the regions is highly acidic because some of the dirt or stone minerals content mix with the water make it into corrosive acid that can corrode or melt normal skin tissue upon contact, and during prolong contact it can melt the normal flesh and damage or corrode metals especially iron/steel, and it also can rapidly damage normal wood especially wooden plank not native from this environment, but its not in the point to boil the water or increase/decrease the water temperature by itself nor creating dangerous gas, and rain water is safe though not acidic or not that high or corrosive.
the water also have color (not decide the color yet or will ends up add it in or not later) because some of the dirt or stone and water plant contain some natural dye minerals but its pretty safe for the creature, also the soil outside of the water is in permafrost state (not decide is it mix with the same acid or just normal ice yet, but eitherway even if it contain acid it quite small and not in liquid state so i dont think it will be dangerous or harmful), i add this in case its considered an important information to make better/clearer answer.
so far i assume the water creature can protect their skin or flesh by covering themselves with carapace and other type of shell like crustaceans and Bothriolepis fish, but i dont know how to protect their gills and eyes.
another is base of human stomach using mucus, but i dont know is it effective outside the body or for external organs (at least i think it can protect some of the internal organs or the flesh parts inside of the mouth) but i assumed the mucus can also block the gills making the creature unable to breath or can even still make the creature can see at all because of the mucus covering the eyes.
the aquatic creature not necessary need eyes but i add it just to see the visibility to protect that organs.
also the aquatic creature is form from natural evolution, not from genetic modification by inteligent lifeforms.
and so i want to know what water creature like fish and crustaceans like crab need in order to survive in this environment especially to their gills and eyes, and would there be need a dfferent biological solution or evolution between plain water and salt water.
also curious to see a better solution outside of exoskeleton or shell type ( not exclude it for answer just want to see is there a better possible solution outside of that.)
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The most generic answer? Lots of food, and proton pumps.
There are Earthling extremophile organisms that can thrive in highly acidic environments. Generally, they do it by carefully excluding the acids from their intracellular spaces--how acidic the external environment is then doesn't matter. Some of this can be accomplished with purely chemical means, by synthesizing as part of their metabolism basic and pH buffer compounds to counteract the effects of any acids that may diffuse through the cell membrane, but the primary defense is the proton pump. All Earthling cells have these mechanisms already; they are, for example, critical components of mitochondria, which set up proton gradients to power ATP synthase. It is, therefore, a relatively simple matter to repurpose that machinery to just continually pump stray protons out of the cell entirely to keep the pH down.
The catch is that this is a very energy intensive process. A complex multicellular organism with a large surface area exposed to the acidic environment, especially one that is expressly designed for exchanging dissolved materials with said environment (like, say, gills, or roots and leaves), will be expending a significant fraction of its total energy budget on Not Dissolving.
There is thus a significant advantage to simply altering ones biochemistry to tolerate the acidic conditions from the get-go. And seeing as how life is likely to *start* in the seas, or at least in groundwater (unless this is originally-alien life that has adapted itself to this world), that seems likely to have happened. Exactly how such adaptation would occur, however, depends on specifically which acids are present; different acids do not attack all other chemical substances equally. Perhaps, for example, your world's surface waters have a high concentration of sulfuric acid; in that case, you don't need to worry about *dissolving* so much as having all of your organic molecules forcibly dehydrated, reducing you to a hot pile of activated charcoal and nitrogen gas. Silicones with small organic side-chains, however, are not subject to the same kind of chemical attack by sulfuric acid--so maybe life on this world is just based on silicones in sulfuric acid solution, and actually has the *opposite* problem of keeping excess fresh water out of its cells! (Which would cause rapid heating from the heat of solvation and burst cell membranes from osmotic pressure.) A heavy acid like sulfuric acid would work especially well for your scenario, since rainwater, while still acidic from our point of view, would be naturally distilled and end up quite pure in comparison with sea water (just like our seas are filled with salt, but our rain *isn't*--and we Earthling organisms whose Latest Universal Common Ancestor evolved in sea water, do indeed have to worry about maintaining osmotic balance and not letting too much fresh water into our cells all at once, so that isn't even all that exotic of a concern in basic principles).
If, for example, your world is rich in nitric or hydrochloric acid instead, the necessary biochemical adaptations would be rather different.
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Suppose some magical civilization on Earth-like planet can create portals. Any given portal entrances are spherical surfaces of the same radius. Any particle enters one sphere and exits another in the corresponding spots. Inside space of the portal is corridor of Plank length with no gravity field. I'm aware of implication for energy conservation and causality, just accept it. This civilization decides to use this property in order to irrigate local version of Sahara desert.
One portal entrance is placed deep under the sea surface covered with layers of semi-permeable membranes, while another one - in the Desert, so the high pressure of ocean depth pushes water through membranes performing desalination by reverse osmosis. This civilization built several large such portals that work as sources of designed major rivers and myriads of small ones to keep water levels constant in artificial lakes and groundwater. What are ecological implication of this system?
The world has essential the same geography as ours and the Desert in question is has roughly the same parameters (size, temperature regime, etc) as Sahara. Quantity of water continuously going through system comparable to discharge of Amazon river. Oceanic entrances of the portals are placed in the ocean current in order to minimize rise of water salinity in the vicinity. The long term ecological issues, that I concerned with:
1. Heat pollution. Such system breaks the law of conservation of energy and all kinetic energy, that water get's for free, will eventually turn into heat. Is this a crucial problem in this system?
2. How significant will be rise of water salinity?
3. How drainage will affect marine life, most importantly plankton that can't resist suction? Is periodical scraping of membranes is enough?
4. Will it significantly disrupt global climate with all this water evaporation?
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People seem intrigued by your desalination method. It is just reverse osmosis powered by a pressure gradient like it always is. Here is my old scheme to irrigate Death Valley using such a method which uses the below sea level altitude of Death Valley to provide the pressure gradient.
<http://www.halfbakery.com/idea/Lake_20Death_20Valley#1033923600>
I would put your membranes on the outside of the sea side not the outside of the land side. Salt will diffuse away into the larger ocean on the sea side. If on the outside of your land side local salt concentrations might build up. Or maybe the two sides are the same thing via your dimensional magic.
But your question is what would happen to the desert. As regards the implications of irrigating a desert: I refer you to the Imperial Valley.
[](https://i.stack.imgur.com/td1Iw.jpg)
<https://en.wikipedia.org/wiki/Imperial_County,_California>
It was desert before. You can see the desert in the distance. Now it is some of the most productive farmland in the world. Irrigating deserts works great to make farmland and that is what you would make. Farmland is an artificial ecosystem which will supplant that of the desert. Our species has been doing this for about 5000 years. If your water is salt free that will sidestep one big problem with desert irrigation which is salt buildup in the soil That is problematic now in the places like Egypt where they have been doing this for 5000 years because even fresh water usually has some salt.
Desert critters will retreat to places nearby that are still desert. They will probably do well too because of the proximity of your crops, because they will sneak in and eat them. A barrier of desert might be a good thing to exclude more serious agricultural pests that will not easily traverse the desert.
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I'm designing an alien species, whose blood is highly acidic and can easily cause someone's hand to melt down. It's pretty similar to the Xenomorphs from Ridley Scott's *Alien*, except for the color maybe.
Now my question is, could something like that exist? Could a creature naturally evolve acidic blood as a defense mechanism? If yes, how would it work and what would it look like?
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Yes, this should be possible. Nature is capable of creating and withstanding acid fluids (most obvious example: the stomach), so having acid blood developed as a defense mechanism sounds not that strange. The blood would most likely still be red if not alternative molecules for the transport of oxygen are used.
Only problem I see here is that the whole body of the creature should be able to withstand acid, not just the veins, else bleeding would lead to certain death.
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To amplify StarfishPrime's comment, a natural defense biomechanism which releases (and possibly generates at the time of injury) acid or alkali fluid is a lot easier to justify than the blood itself.
Related capabilities in Terran animals: snakes which spit venom, frogs whose epidermis contains toxins.
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possibly, instead of having acid blood you could have a separate system to the circulatory system which would be exclusively for defense. It could also be used as a sort of stomach spread around the body.
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In a sci-fi RPG I eventually intend to run for a couple of friends, I had the idea of them visiting ancient ruins on a planet orbiting a shedding red giant.
Now, ignoring the problem of intelligent life evolving in a habitable zone with as short a lifespan as that around a red giant. What, if any, effects would the matter ejected as the star shedds its outer layers have on said planet?
Asked to provide more details, so, here are some examples of effects that come to mind:
Assuming a planet similar to Earth in habitabiliy before the star starts shedding.
* Would the shedd material result in the planets atmosphere being
reduced or even disappear?
* Would it affect the planets temperature?
* Would the planet have near constant auroras?
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## Atmosphere loss
As you've suggested in your question, once a Sun-like star leaves the main sequence, it begins losing mass through a strong stellar wind, a stream of charged particles driven by photons. For a few hundred million years, it's a true red giant, expanding a bit and reaching luminosities of a few thousand solar luminosities. After spending some time on the horizontal branch, where its luminosity is constant, it ascends the asymptotic giant branch, or AGB, staying there for about 100,000 years; it then becomes a planetary nebula.
The wind should be strongest during the AGB phase, but it's also significant while the star is on the red giant branch. If we make certain assumptions about the structure of the wind, we can calculate the *ablation rate* for a planet - how quickly it loses material. An old paper that does this is [Soker 1999](http://adsabs.harvard.edu/abs/1999MNRAS.306..806S), which I used in [an answer to a related question](https://worldbuilding.stackexchange.com/a/1394/627). It's applicable mostly in the planetary nebula phase of a star's life. [A planet orbiting the star will lose mass at a rate](http://adsabs.harvard.edu/abs/1999MNRAS.306..806S)1
$$\dot{M}=1.05\times10^{-11}\left(\frac{L\_\*}{5000L\_{\odot}}\right)^{1/2}\left(\frac{R\_p}{3\times10^4\text{ km}}\right)^{3/2}\left(\frac{a}{20\text{ AU}}\right)^{-1}M\_J\text{ yr}^{-1}$$
where $L\_\*$ is the luminosity of the star, $R\_p$ is the radius of the planet, and $a$ is its semi-major axis.
This relationship is only valid for stars with temperatures of $\sim10^5\text{ K}$, and as the relationship between the number of photons emitted per second is (roughly) inversely proportional to the star's temperature.2 Therefore, for an AGB star or red giant, with $T\simeq3000\text{ K}$, the coefficient should instead be $3.15\times10^{-13}$.
Take the case of an Earth-like planet, with radius $R\_P\simeq6300\text{ km}$. We can then calculate mass-loss rates (and total mass-loss) for the planet during different phases of the star's life.
* During the red giant phase for a Sun-like star, [$L\_\*\simeq2000L\_{\odot}$](http://www.astronomy.ohio-state.edu/%7Epogge/Ast162/Unit6/futuresun.html); the phase lasts for about 600 million years. For the planet to survive the subsequent evolution, it may be desirable to have it far out - say, $30\text{ AU}$. Then $\dot{M}\approx1.3\times10^{-14}M\_J\text{ yr}^{-1}$, and the total mass lost should be 0.2% the mass of Earth. I use 30 AU because a planet like the one you're talking about - habitable like Earth while the star is on the main sequence - runs a strong risk of being engulfed when the star expands.
* During the AGB phase, $L\simeq10000L\_{\odot}$, but this phase only lasts for 100,000 years. Then $\dot{M}\approx2.91\times10^{-14}M\_J\text{ yr}^{-1}$, and the total mass lost should be $9.25\times10^{-7}$ Earth masses - about 1.1 times the mass of Earth's atmosphere.
I think the mass-loss rates for Earth in the red giant phase are actually really, really optimistic, even for a planet at 30 AU. However, the AGB mass-loss rates are much more realistic, and even if we disregard mass loss during the red giant phase, but it's very likely that it will entirely be stripped by the end of the AGB phase. Any planet previously in the habitable zone of the star while it was on the main sequence will certainly have lost its atmosphere.
## Surface temperature
Red giants and AGB stars are extremely large, reaching sizes of 100 to 200 solar radii. Therefore, even though they're only about half as hot as the Sun, they're much more luminous, because of their large surface areas. This is why [life on a planet orbiting a red giant has it tough](https://worldbuilding.stackexchange.com/a/113773/627). When the Sun becomes a red giant, life on Earth as we know it will not be able to survive. On planets further away, though, it might be able to.
Paradoxically, the range of orbits where a planet could survive atmospheric stripping (say, 30 AU outwards) is beyond the star's habitable zone for the vast majority of cases late in a star's life. The habitable zone should be around 5 - 10 AU, but planets there would likely lose their atmospheres during the AGB phase. It's possible that on the red giant branch itself, planets might be habitable *and* able to retain their atmospheres at those orbital radii. I assume there's only a narrow range of orbits where this is likely.
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1 The formula is given in Jupiter masses/year because that paper is from 1999, when the vast majority of exoplanets we knew about were massive gas giants, thanks to observational bias.
2 For a star of temperature $T$, [Wien's law](https://en.wikipedia.org/wiki/Wien%27s_displacement_law) tells us that the wavelength of peak emission is $\lambda=b/T$, where $b$ is Wien's constant. The energy per photon is $E=hc/\lambda$, where $c$ and $h$ are the speed of light and Planck's constant, and so the number of photons per second is just
$$N\_\*=\frac{L\_\*}{E}=\frac{L\_\*}{hc/\lambda}=\frac{L\_\*}{hc}\frac{b}{T}=\frac{L\_\*b}{hc}\frac{1}{T}$$
It turns out that as Soker says, for $T\sim10^5\text{ K}$, this scales as
$$N\_\*\approx2\times10^{47}\left(\frac{L\_\*}{5000L\_{\odot}}\right)\text{ s}^{-1}$$
but for $T\simeq3000\text{ K}$, the proportionality constant is about two orders of magnitude lower.
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There was once 12 kingdoms in the ancient days until the kingdom of Eo was devoured by the very forests it called home. The people of Eo have been turned into beasts wandering the woods and preying upon all who enter the forest.
That's how the legend goes anyways. The people of Eo where actually infected by a parasitic organism much like a tick except this tick sustains itself by entering its host and slowly taking over its nervous system and brain which it then uses to sustain its host and thus sustain itself.
What I'm wondering is how the tick would actually take over its host's brain. Something like a direct "plug" into the cerebral cortex, connecting to the top of the spine, etc.
Note: the tick itself is reminiscent of a crab in physical build minus the big claw but is about the size of a [Deer Tick](https://en.wikipedia.org/wiki/Ixodes_scapularis), which limits how it gets to the brain to ear ducts, wiggling past the eye balls, or sneaking in through the sinuses.
The Brain Tick causes those effected by it to have a stagger in their walk and slurring of words as their body tries to resist the tick taking over. The tick would also force their host to eat about anything they can physically digest.
Eo are regular humans.
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After your tick's [chelicerae](https://en.wikipedia.org/wiki/Chelicerae) cut the host's skin near the back of the neck, it uses one of its specialized [hypostomes](https://en.wikipedia.org/wiki/Hypostome_(tick)) to attach to a blood supply. After establishing the connection to food and oxygen, it starts to burrow under the skin for protection. Once there it uses the other specialized hypostome to attach to the spinal column. The spinal hypostome grows farther into the brain taking control.
Yes, natural ticks only have one hypostome, but yours can have two.
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**Through a bacteria, virus, prion or other diseases**
If you've seen the news stories of [Zombie Deer](https://www.usatoday.com/story/news/health/2019/02/16/zombie-deer-chronic-wasting-disease-could-affect-humans/2882550002/), then you know about prion diseases. [Mad Cow Disease](https://www.cdc.gov/prions/bse/index.html) is another example.
There is also a [fungus](https://www.livescience.com/47751-zombie-fungus-picky-about-ant-brains.html) which takes control of an ant's nervous system.
The tick is a carrier and has a symbiotic relationship with the disease. Much like the ant zombie fungus, it's the disease, not the actual body of the tick doing the thinking. Once the disease is introduced to the host, both the large host and the tick are controlled by the disease.
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The Papal States were a series of territories in the Italian Peninsula under the direct sovereign rule of the Pope, from the 8th century until 1870. At their zenith, the Papal States covered most of Central Italy and some parts of France. These holdings were considered to be a manifestation of the temporal power of the pope, as opposed to his ecclesiastical primacy.
Historically the Papal States maintained military forces composed of volunteers and mercenaries. However, the rise of nationalism around the world began to erode the church's authority over its holdings. The papal states came to an end with the unification of Italy, which at the time was led by a staunch, anti-catholic. Today its authority extends only to the Vatican City in Rome. For this world I want the papal states to survive up to modern times, and have incorporated some changes throughout history to make the states more secure.
The Pope has generally had a contentious hold over these territories. The church's army was generally made up of volunteers and mercenaries, giving him a fairly weak grasp on power there. Papal states were often contested between the church and various emperors, and it was until the 16th century that the Pope had secured authority. The various regional components retained their identity under papal rule. The pope was represented in each province by a governor. Other titles like Papal Vicar, Vicar General, and several noble titles like "count" or even "prince" were used. However, throughout the Papal States' history many warlords and even bandit chieftains ruled cities and small duchies with no title bestowed by the Pope.
In this setting, I want the church to keep a significant standing army in all of its territories to secure them from invasion or internal rebellion. I also want local rulers to be church officials elected by the Pope directly, or some governing body of the church. This would give it more control over its holdings. In this sense, the states would become something resembling a theocracy, with the Pope at the head and various leaders connected to the church ruling in his stead. What would be the best way for him to go about this?
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There was nothing pre-ordained or inevitable about the [assemblage of the modern Italian state](https://en.wikipedia.org/wiki/Italian_unification).
Today we speak of Italian unification, or, as Italians prefer to call it, the *Resurgence* (*Risorgimento*). But if we look at that particular series of fortunate events with dispassionate eyes, what we see is the conquest of the peninsula by the [Kingdom of Sardinia](https://en.wikipedia.org/wiki/Kingdom_of_Sardinia). (As history is often inclined to irony, half of the territories the kings of Sardinia held at the beginning of the adventure are now in France.)
[](https://en.wikipedia.org/wiki/File:Italia1859.png#/media/File:Italia1859.png)
[](https://en.wikipedia.org/wiki/File:Italia1860.png#/media/File:Italia1860.png)
[](https://en.wikipedia.org/wiki/File:RegnoItalia1861.png)
*Expansion of the Kingdom of Sardinia into the Italian peninsula, from 1859 to 1861. Kingdom of Sardinia in orange. Papal States in red. Yellow-green is the Kingdom of the Two Sicilies. Maps by [Maps & Lucy](https://commons.wikimedia.org/wiki/User:Maps_%26_Lucy), available on Wikimedia under the CC BY-SA 3.0 Unported license.*
Once the conquest of the peninsula was (almost) complete, the Kingdom of Sardinia changed its name into the Kingdom of Italy, the conquest was reclassified as unification, and the peoples of Italy, who spoke different and dissimilar languages were told that they were all Italians and all their languages were mere dialects of Italian. If they pretended to be unable to understand the supposedly common language all they had to do was go to school and learn it.
The history of how the Kingdom of Sicily came to annex one by one all the polities in Italy is both complex and complicated, but, if we apply a suitable dose of reductionism, we can (unjustly, but close enough for alternate history work) say that it was brought about by two men: the consummate politician [Camillo Cavour](https://en.wikipedia.org/wiki/Camillo_Benso,_Count_of_Cavour), prime minister of the Kingdom of Sardinia, and the ultimate daredevil [Giuseppe Garibaldi](https://en.wikipedia.org/wiki/Giuseppe_Garibaldi), aided and abetted by emperor [Napoleon III](https://en.wikipedia.org/wiki/Napoleon_III) of France, who successfully obtained [Savoy](https://en.wikipedia.org/wiki/Savoy) and [Nice](https://en.wikipedia.org/wiki/Nice) for his services.
While I cannot see how the end result of Cavour's machinations could be a two-state solution, with the Papal States remaining independent in an otherwise unified Italy, I can easily see a *three* state solution, with Italy divided between a Kingdom of Northern Italy, the Papal States, and the Kingdom of the Two Sicilies in the south.
Once Cavour managed to broker the trade where France would help the Kingdom of Sardinia in the war against Austria (which held Lombardy and Venetia) in exchange for Nice and Savoy, there was nothing anybody could do to prevent the annexation of all the small polities north of the Papal States. But at this point, the expansion of the northerners could have been stopped.
The Papal States were rich. The Kingdom of the Two Sicilies was populous, and had a larger army than the northern invaders. Should [Pope Pius IX](https://en.wikipedia.org/wiki/Pope_Pius_IX) receive a modicum of political foresight, he should have forged a *real* and *functional* alliance with the Kingdom of the Two Sicilies; should king [Ferdinand II](https://en.wikipedia.org/wiki/Ferdinand_II_of_the_Two_Sicilies) have been endowed with just a little bit of political acumen, used his available time to root out the corrupt and incompetent officers from his army, avoided being perceived as a tyrant, and managed to live longer than his 49 years, such an alliance would have stopped the northern progression in its tracks. All they had to do was kick the can down the road for ten more years; if the Papal States / Kingdom of the Two Sicilies had succeed in keeping the northerners in check for just ten years (to the Franco-Prussian war of 1870) they would have had a sporting chance of making it into the 20th century.
(Note that the Papal States and the Kingdom of the Two Sicilies did have an alliance. It was so disfunctional that their combined armies managed to lose Sicily to Garibaldi's one thousand volunteers.)
As it actually was, Pope Pius IX and King Ferdinand II were abysmal statesmen; the death of king Ferdinand II in 1859 did not help. In 1861 Garibaldi invaded the Kingdom of the Two Sicilies with a ridiculously small force of one thousand men. The one thousand [Red Shirts](https://en.wikipedia.org/wiki/Expedition_of_the_Thousand#The_Red_Shirts) defeated at Catalafimi in Sicily an army which outnumbered them 2 to 1, and then proceeded to take Palermo against a garrison 16,000 strong, allowing Garibaldi to raise an army in Sicily; the rest is patriotic history.
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**Have the Pope cause Italian reunification on his terms.**
Decades or even centuries before the 1870 events, have the full authority of the Church support an Italian unification as a confederation of strong provinces/states, with the Papal State being a special case. This might involve rallying the Italians against the French [in the Revolutionary Wars](https://en.wikipedia.org/wiki/Italian_campaigns_of_the_French_Revolutionary_Wars), or translating their participation in the [Congress of Vienna](https://en.wikipedia.org/wiki/Congress_of_Vienna) into fighting for Italian interest.
The problem with this is that it involves the Papal State in secular affairs, but that seems inevitable if it wants to survive. There would also be the question of a domestic democracy movement, but several autocracies survived that long. There might be a safety valve if Papal citizens can easily migrate to non-Papal parts of Italy if they dislike church rule, or vice versa if they are pious or dislike their secular government.
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Napoleon III would have to be crushed much earlier or the austrians had to be much stronger. That means that if the franco-prussian war had started much earlier and the prussians still managed to win or if the austrians defeated the prussians in the 7 weeks war and were much more efficient in supressing the revolts in 1848 or if the british and the french somehow botched their diplomacy and went to war, maybe because of the partition of the Ottoman Empire, there would be no french support to Sardinia-Piemont. Without that support they wouldn't be able to conquer Lombardia or the Two Sicilies and the italian region would be divided in Sardinia-Piemont, Tuscany, Papal States and Two Sicilies. Of course, none of these small countries would be able to industrialize and would be forever small, weak countries pushed around by bigger neighbours, like greece or the balcanic countries.
Also, you have to think on how would the Papal States survive the Great War. That some kind of large scale conflict would happen in Europe when you mix militaristic, agressive diplomacy, with industrial scale warfare, something like the Seven Years War but with steam turbines, long-range artillery and repeating guns. In this kind of conflict, that in our timeline erupted in 1914, small countries are unable to do anything, are unable to resist. Italy would become a battlefield between France and Austria if they were in oposite sides and the most probable result would be the small states of Italy, including the Papal States, ending up as occupied territory. The state that, due to luck, ended up as an Ally of the victors in the Great War would take all, like Serbia took the austrian fragments in the Balkans and formed Yugoslavia. So, your Papal States will have to take sides and it's side must win, and, in victory, the pope will have to show restraint to refuse the spoils. And pray, when the next great war comes because the instability the first one caused brought all kinds of strange, weird revolutionary ideas. (For example, a defeated France could become communist and in the next great war it will be the red french army that will march in Vienna).
TLDR - You need a weak France and strong Austria to have a Papal States all the way to the Great War. Beyond the Great War, it becomes harder and harder for small, weak states, to survive in that neighborhood.
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The TRAPPIST-1 planets are all very close to each other and thus are subjected to strong gravitational forces amongst each other and to the red dwarf they're orbiting. Would it be possible for them to have moons (most likely in a low orbit)? To clarify, I'm not necessarily talking about big moons like our moon but more like Phobos and Deimos.
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I quote from that obscure and little known source on TRAPPIST-1, Wikipedia:
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> Moons
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> Stephen R. Kane, writing in The Astrophysical Journal Letters, notes that TRAPPIST-1 planets are unlikely to have large moons.[62][63] The Earth's Moon has a radius 27% that of Earth, so its area (and its transit depth) is 7.4% that of Earth, which would likely have been noted in the transit study if present. Smaller moons of 200–300 km (120–190 mi) radius would likely not have been detected.
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> At a theoretical level, Kane found that moons around the inner TRAPPIST-1 planets would need to be extraordinarily dense to be even theoretically possible. This is based on a comparison of the Hill sphere, which marks the outer limit of a moon's possible orbit by defining the region of space in which a planet's gravity is stronger than the tidal force of its star, and the Roche limit, which represents the smallest distance at which a moon can orbit before the planet's tides exceed its own gravity and pull it apart. These constraints do not rule out the presence of ring systems (where particles are held together by chemical rather than gravitational forces). The mathematical derivation is as follows:
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<https://en.wikipedia.org/wiki/TRAPPIST-1>[1](https://en.wikipedia.org/wiki/TRAPPIST-1)
<https://www.seeker.com/space/planets/trappist-1-planets-have-no-large-moons-study-argues>[2](https://www.seeker.com/space/planets/trappist-1-planets-have-no-large-moons-study-argues)
<http://iopscience.iop.org/article/10.3847/2041-8213/aa6bf2/meta>[3](http://iopscience.iop.org/article/10.3847/2041-8213/aa6bf2/meta)
So at the present it is believed that large moons like Luna would probably already have been detected in the TRAPPIST-1 system, and that it is theoretically improbable for planets so close together to retain any moons they might have for a long time.
It is unknown whether having large moons is necessary for a planet to be habitable and have life.
In the case of planets orbiting so close together as those in the TRAPPIST-1 system it is possible that they might serve to stabilize each others axial tilts and provided tides and that those effects might be just as good as having large moons.
Since:
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> The system is very flat and compact. All seven of TRAPPIST-1's planets orbit much closer than Mercury orbits the Sun. Except for TRAPPIST-1b, they orbit farther than the Galilean satellites do around Jupiter,[41] but closer than most of the other moons of Jupiter. The distance between the orbits of TRAPPIST-1b and TRAPPIST-1c is only 1.6 times the distance between the Earth and the Moon. The planets should appear prominently in each other's skies, in some cases appearing several times larger than the Moon appears from Earth.[40] A year on the closest planet passes in only 1.5 Earth days, while the seventh planet's year passes in only 18.8 days.[37][33]
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<https://en.wikipedia.org/wiki/TRAPPIST-1>[1](https://en.wikipedia.org/wiki/TRAPPIST-1)
The planets should appear as visible discs in each other's skies quite often, thus fill the visual aspects of moons quite nicely.
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[M. A. Golding's answer](https://worldbuilding.stackexchange.com/a/128042/627) is correct, I think, but it's also a bit incomplete, because the exoplanets in the TRAPPIST-1 system are not *equally* unsuitable for hosting exomoons. In particular, their individual orbital radii (as well as masses and compositions) play an important role in determining what sorts of moons they could retain over long timescales, and some are more favorable choices than others. While the inner exoplanets are unlikely to keep their moons, the outer ones may still have some hope.
An analysis of the possibilities of exomoons in the TRAPPIST-1 system was done by [Kane 2017](http://adsabs.harvard.edu/abs/2017ApJ...839L..19K). He looked at two characteristic length scales for each planet, defined from its center: the Hill radius and the Roche limit. Outside the Hill radius, the star will eventually dominate the motion of any satellite and send it into an orbit around the star, while inside the Roche limit, a moon would be torn apart by the planet's tidal forces. There is, therefore, a delicate balance, especially in compact systems like TRAPPIST-1.
For all of the exoplanets, the Hill radius is at least twice the Roche limit for reasonable compositions, increasing to about ten times the Roche limit for the furthest planet from the star, TRAPPIST-1 h. In general, the greater the distance to the star, the greater the range of possible densities for a moon orbiting a planet. Kane produce a graph of the regions of stability (Fig. 2). The light grey shading shows the habitable zone, while the dark grey shading shows regions that *might* be within the habitable zone. The two curves are for two different values of a certain parameter related to the Hill radius; above each one is a region of stability:
[](https://i.stack.imgur.com/8Uj2h.png)
For comparison, the density of the Moon is about 3.3 grams per cubic centimeter; Earth comes in at around 5.5. This means it's unlikely that the inner two planets could host moons, but the outer five could. The problem, as Kane points out, is that we should expect any moons that formed to have low densities. As I wrote in [a recent answer](https://worldbuilding.stackexchange.com/a/128017/627), the planets likely migrated from further out in the system, moving inwards. Any putative moons would probably have formed in the outer reaches, where there was more low-density materials, making high-density moons unlikely.
That's not to say that higher-density moons are *impossible*; it's also possible that small moons formed in the protoplanetary disk during the migration process, and were captured by the exoplanets in three-body interactions. It is, though, a bit less likely. Assuming the moons were indeed in place orbiting the planets at some point, though, simulations by [Allen et al. 2018](http://adsabs.harvard.edu/abs/2018AAS...23114821A) indicates that they could remain in stable orbits for long periods of time. In other words, if you can solve the formation problem (or, heck, just plop the moons in there), then maybe half of the planets in the system could retain moons after all.
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...
I missed my chance. Those guys just said everything. The only thing i could add is that only the outer 3ish planets even have a chance of having a moon, and if you were hoping for a hospitable moon, you're out of luck. They would be too dense and far from the star. Also, due to the roche limit and tidal locking(ohhh boy) the innermost 4 planets... no moon.
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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.
A common, matter-efficient science-fiction habitat is a hollow cylinder or ring in space that is spun to simulate the pull of gravity on its interior surface. These habitats have been imagined as small as a spaceship, mere meters in radius, up to a ringworld, 1 AU in radius.
This question pertains to a ring somewhere in the middle of these two extremes, placed in orbit around a star. This ring rotates around 2 axes. The first and faster rotation generates the centrifugal force responsible for simulating gravity. This can be visualized as the spin of a wheel. The second rotation is slower and occurs in an axis perpendicular to the first rotation. This can be visualized as a coin spinning in place on a countertop. The first spin results in a day/night cycle as the inner side of the ring exposed to the sun and the side hidden from the sun are constantly swapped by the rotation of the ring. The second spin’s effect is hard to visualize but it creates something akin to “seasons” where the contrast between day and night waxes and wanes. Here is a short gif I made in Unity that should help with visualization. Here the bottom view is from the perspective of the rotating camera in the top view.
[](https://i.stack.imgur.com/z4eai.gif)
While this is all interesting my question is about a very specific moment in this dynamic system. Inevitably the ring will spin to a point where it is edge on to the sun. At this moment the sunward-facing portion of the ring blocks the light from reaching the other side of the ring. In this way the ring eclipses itself. This can be seen towards the end of the gif. In an eclipse, the term “umbra” refers to the area totally eclipsed from the sun. What I would like to know is how to compute the size of this umbra and secondly how I can go about maximizing the size of this umbra, because let’s face it, the darker, larger, and longer an eclipse is the cooler it is. Since I already have a design in mind for the ring, maximizing the umbra will have to be done with the star and the distance the ring will orbit it. Importantly, I need the ring to still be habitable so the amount of heat coming from the star needs to be equivalent to what we receive on Earth.
I have prepared a schematic to describe the eclipsed ring and what I think are the relevant variables needed to describe the size of the umbra. Ideally, an answer would provide an equation to calculate the size of the umbra given any ring dimensions but the dimensions of this ring are a total radius of 10,000 km and a thickness of 100 km. [](https://i.stack.imgur.com/V8BEP.jpg)
[Answer]
# The setup and the equation
Let's look at the geometry involved here. I created two diagrams:
[](https://i.stack.imgur.com/deTOc.png)
On the left, we have the star of radius $R$. On the right, we have a cross-section of the ring. The center of the ring is a distance $r$ from the star, and the ring has a diameter of $2s$ and a cross-sectional radius of $a$. We can calculate $\theta$ using trigonometry:
$$\theta\approx\tan\theta=\frac{R-a}{r-s}\approx\frac{R}{r}$$
We make the assumption that $r\gg s$ and $R\gg a$, and use the small-angle approximation to say that $\tan\theta\approx\theta$. Now, let's look at a slightly more in-depth diagram:
[](https://i.stack.imgur.com/PFlqt.png)
$u$ is the radius of the umbra as projected onto the opposing side of the ring. Again, using the small-angle approximation,
$$\theta\approx\tan\theta=\frac{a-u}{2s-a}$$
Setting both equations equal,
$$\frac{R}{r}=\frac{a-u}{2s-a}$$
and
$$u=a-(2s-a)\frac{R}{r}$$
Yesterday in chat, we talked a bit about striking a balance when it comes to the star the ring is orbiting. To maximize the size of the umbra, you need a small star, but it should also be relatively far away. On the other hand, you also want the ring to be in the habitable zone.
A red dwarf comes to mind, but red dwarfs are dim. A red dwarf of $0.1R\_{\odot}$ would have a luminosity of about $0.01L\_{\odot}$, meaning you would need to orbit at $0.1\text{ AU}$ to receive the same flux the Earth does. Plugging in the relevant numbers, at $R=0.1R\_{\odot}$, $2s=9900\text{ km}$, $a=50\text{ km}$, and $r=0.1\text{AU}$, I get $u=4.2\text{ km}$. That's small.
Now, a *white dwarf* - a stellar remnant, sure - could have a radius of perhaps $10000\text{ km}$, maybe even less by a factor of two. The hottest white dwarfs come in at $0.5L\_{\odot}$, meaning the ring could orbit at $0.71\text{ AU}$. Plugging these values in, we get $u=49.07\text{ km}$, which would essentially cover the opposite side of the ring (which has an inner radius of $50\text{ km}$).
# Limits on stellar temperatures
As an interesting aside, we can find the point at which the umbra disappears by setting $u=0$, and getting
$$\frac{R}{r}=\frac{a}{2s-a}=0.0051$$
This can yield some useful information. Define $x\equiv R/r$, and $x\_{\text{crit}}=0.0051$. The umbra only covers part of the opposite side of the ring for $x<x\_{\text{crit}}$.
Let's derive the equilibrium temperature of this ring. Assume that it's positioned face-on towards the star, as in the diagrams. Then the cross-sectional area facing the star is $2s\cdot2a=4sa$.
Consider that the luminosity of a star is
$$L\_\*=4\pi\sigma R\_\*^2T\_\*^4$$
where $R\_\*$ and $T\_\*$ are the star's radius and surface temperature, and $\sigma$ is the Stefan-Boltzmann constant. The flux at the surface of the planet is
$$F\_\*=\frac{L\_\*}{4\pi r^2}=\frac{\sigma R\_\*^2T\_\*^4}{r^2}=x^2\sigma T\_\*^4$$
The power received is then
$$P\_{\text{in}}=4saF\_\*=4sax^2\sigma T\_\*^4$$
If the planet is a black body, the emitted power $P\_{\text{out}}$ is then its surface area multiplied by $\sigma T\_{eff}^4$, where $T\_{eff}$ is the planetary equilibrium temperature. The surface area is the surface area of a torus, or $S=4\pi^2a(s+a)$. Setting $P\_{\text{in}}=P\_{\text{out}}$ yields
$$4sax^2\sigma T\_\*^4=4\pi^2a(s+a)\sigma T\_{eff}^4$$
and so
$$T\_{eff}=\left(\frac{sa}{\pi^2a(s+a)}\right)^{1/4}x^{1/2}T\_\*$$
In your case, this becomes
$$T\_{eff}=0.56x^{1/2}T\_\*$$
Now, $x\_{\text{crit}}=0.0051$. Say we want $T\_{eff}=300\text{ K}$. This means that $T\_\*$ must be less than $105000\text{ K}$ for there to still be an eclipse on the far side of the ring - if $T\_\*$ was higher, $x\geq x\_{\text{crit}}$, and the planetary equilibrium temperature would be greater than $300\text{ K}$. In fact, at the far end of the habitable zone, $T\_{eff}=373\text{ K}$ - hotter than this an water boils. This sets a firm limit for a habitable and eclipse-producing star at $131000\text{ K}$. This is much hotter than the vast majority of stars, but it *does* rule out [a number of hot white dwarfs](https://arxiv.org/abs/1111.6652), which may have temperatures of $\sim200000\text{ K}$.
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[Question]
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My story happens in fictional medieval age. There are the usual suspects of peasants, clergy, craftsman, merchants & aristocracy. There is also a specific class of hereditary servants. They work as domestic workers, and are above peasants and hired servants in class. Also they are more trusted, get better accommodations, more pay, and are usually better educated.
Hereditary servants are special since the aristocracy specifically bred them to look androgynous. They are normal humans but aristocracy selected the individuals with weakly pronounced [secondary sex characteristics](https://en.wikipedia.org/wiki/Secondary_sex_characteristic#In_humans) such hips, facial & body hair, Adam's apple, breasts etc. Males & females who didn't satisfy their specifications we removed from the genetic pool and were sterilized or had to change their class thus becoming normal peasants. Hereditary servants work only in households of aristocracy or very wealthy merchants.
Assuming below:
* Aristocracy wants to lock in androgynous traits, thus children of two servants need to look like a servant themselves. Thus **children of two androgynous looking parents needs to be androgynous looking themselves**.
* Aristocracy has enough people to start with, they could use peasants which are something like serfs, or war captives as starting stock.
* Aristocracy has knowledge of breeding animals, they've created different breeds of domestic animals such as dogs, horses, cows etc.
* Aristocracy has no one to prevent them from choosing who will have children with whom, among the household servants. If baroness Meghan want to breed Jane and Tom, they could either acquiesce or try to run away from the country. Since household servants are chattel property, they don't have any say in that matter.
How many generations of selective breeding would they need to lock in androgynous traits, since the start of their endeavour?
The question is from the year they started creating the breed of servants, from naturally occurring stock. If there was no servants in year 800, only peasants who looked somewhat androgynous, how many generations would it take the aristocracy to lock in those traits.
I need something like rule of thumb for dogs which says about 7 generations <https://www.quora.com/When-making-a-new-breed-how-many-generations-until-the-new-breed-is-considered-locked>
In the beginning they just started with most androgynous peasants / war captives they could find. Afterwards they've used selective breeding to improve their servants. If the children were too masculine/feminine they were send to become common peasants, or simply removed from the pool.
Aristocracy keeps a registry of servants, thus you are purebreed if both your parents are purebreed. However servants are defined by their look. Even you are purebreed you would lose your class if you are abnormally masculine/feminine for a servant. Also you could be accepted even from a non servant parents if you fit the specifications.
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Let’s assume for starters that the desired phenotype (the outward appearance) is monoallelic (is carried by a single spot on the genome). Perhaps it is a malfunction in an important puberty pathway, maybe in the pituitary or something having to do with luteinizing hormone or follicle stimulating hormone. Let’s also assume for simplicity that the allele does not have an effect in a heterozygous individual with one working copy and one nonfunctional copy (the gene is purely recessive). Each of these assumptions may be false and in reality almost certainly will be but its a good starting place.
All we need to do to understand how the frequency of this allele will change over time is to define the starting characteristics of the population and the selection placed on them. Feel free to change these numbers however you want I’m just going to give some examples that I think make sense. Let’s say the desired allele has an initial frequency of 0.01. This means on average only 1 in 100 people has a single copy of this allele. Because it is recessive this means only 1 in 10000 people actually have 2 copies and therefore the desired phenotype. Let’s also assume for our purposes that the population is sufficiently large as to be infinite so we don’t have to worry about random chance butting in and messing with our perfect formulas. Finally, we need to quantify how effective the selection on this allele is. Essentially, how good are the aristocrats at filtering out individuals who don’t meet the desired criteria? If we say that the desired individuals reproduce with a rate of 1 I would suggest individuals who don’t have the phenotype reproduce at a fractional rate of say 0.2. This is strong selection, not as strong as it could be but in reality, humans aren’t machines and people will break the rules. What this is saying is that for every undesirable servant who reproduces into the servant pool there are 5 desirable servants who do so.
We now have everything we need to simulate the population. The math is [relatively straightforward](http://www2.hawaii.edu/~taylor/z652/PopGen1.pdf), but somewhat tedious to work out for each generation. Thankfully we don’t have to! There exists a tool to do just this calculation for us: <https://www.radford.edu/~rsheehy/Gen_flash/popgen/>. Here if we plug in the variables we defined above we get a highly variable mean time of fixation of roughly 30-40 generations. If you simulate finite populations, particularly small ones, there will be a high degree of randomness where sometimes the desired allele will be lost simply by random chance (you can avoid this by using an infinite population). If you increase the initial frequency of the allele or increase the strength of the selection this will be much faster.
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[Question]
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Chemosynthesis is the biological conversion of inorganic matter to create nutrients to sustain living organisms. One of the most widely known or popular examples is its use in the Giant Tube Worm, which uses an organ that contains chemosynthetic bacteria.
The chemosynthesis of hydrogen sulfide uses 12 hydrogen sulfides and 6 carbon dioxides to create a carbohydrate, 6 waters, and 12 sulphurs. Is it feasible that a bacteria or plant-like organism alter this process to further process that water into oxygen, and why would it do this?
[Answer]
*Frame Challenge*
I won't answer *how* to produce oxygen because another answer already does that and because you could use water, carbon dioxide and ATP in order to produce glucose and oxygen using the [reverse Krebs cycle](https://en.m.wikipedia.org/wiki/Reverse_Krebs_cycle).
I'll answer *why* a bacteria would do this.
* **Symbiosis:** this bacteria needs the help of another bacteria which only lives in aerobic zones and feeds on glucose. These bacteria exchange food and air for protection or some mineral/amino acid which can't be gathered or produce by the first bacteria.
* **Predation:** these bacteria eat another bacteria that only live in aerobic zones, so it uses its oxygen and glucose as a trap.
[Answer]
***Is it feasible that a bacteria or plant-like organism alter this process to further process that water into oxygen, and why would it do this?***
No. That would consume more energy than the organism gets from the process to start with.
The chemosynthetic process you describe is incomplete. Tube worm chemosynthesis *consumes* oxygen, in the reaction
18H2S + 6CO2 + 3O2 → C6H12O6 + 12H2O + 18S
Essentially, it produces the energy to fix carbon dioxide by burning some of the hydrogen sulfide, instead of getting that energy from sunlight.
Another sulfide-consuming chemosynthetic reaction which doesn't require external oxygen inputs is
3H2S + 6CO2 + 3H2O → C6H12O6 + 3SO3
Which works because hydrogen likes being bonded to oxygen more than it likes being bonded to sulfur, and sulfur likes being bonded to oxygen more than it likes being bonded to hydrogen, so organisms employing this strategy are essentially using CO2 as an oxidizer to burn H2S.
Theoretically, you could use some of the energy from these oxidation-reduction reactions between CO2 and H2S to split oxygen out of water *instead* of fixing CO2--but there is absolutely no reason for a chemosynthetic organism to do that. It's a waste of energy that doesn't create any useful products. If the organism could use the oxygen *as an oxidizer*, then it would do so, increasing the efficiency of its chemosynthetic process, and it would be better off generating the oxidized waste products more directly, which is exactly what sulfate-producing chemoautotrophs actually do. And if it can't, then it's just creating a dangerous poison for no reason.
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One process that can separate the elements oxygen and hydrogen from water is the [electrolysis](https://www.instructables.com/id/Separate-Hydrogen-and-Oxygen-from-Water-Through-El/) and it only would be possible if this plant-like or bacteria is able to polarize the water in cathode and anode like a magnet or be sitting in the top of a natural magnet while receiving an electric charge.
We also know that is possible to produce Electricity through chemical reactions, as for example batteries or even by friction to create static electricity.
Also, [Oxygenic photosynthesis](https://phys.org/news/2017-03-oxygen-cyanobacteria.html#jCp), the process by which certain organisms use the energy of sunlight to convert carbon dioxide and water into sugar for food, with oxygen as a by-product is a good option as you have it and water as by-products of the Chemosynthesis.
I would say it is possible, just use your preferred combination of these elements to build your oxygen.
[Answer]
## It is possible
In photosynthesis, [photolysis](https://en.wikipedia.org/wiki/Photodissociation) enables water to be dissociated into hydrogen ions and oxygen. It is standard-issue on most photosynthetic plants in the light-dependent stage of photosynthesis, and therefore it is not a particular stretch for an organism to alter itself to have this type of functionality, especially through genetic modification, etc.
Insofar as why this would be a practical, or even useful modification, could be an interesting question. Such a process could, like in the light-dependent stages of photosynthesis, directly generate ATP by creating a proton gradient (by which [ATP synthase](https://en.wikipedia.org/wiki/ATP_synthase) can function), bypassing the production of glucose and its subsequent breaking down during cellular respiration. The mathematical practicality of this is unclear, but biology is not *always* most effective and hence such a process *could* potentially work.
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Looking most specifically regarding the moons around Saturn, Jupiter, and Uranus. I've been unable to get a concrete answer on this through various sources. I've actually read several articles briefly mentioning the exact opposites - some say the side facing the planet receives the most radiation, while the others claim it's the side facing away from the planet. Anyone have an answer?
[Answer]
**The Planet Side.**
The gas giants emit radiation. A tidally locked moon would be the only side receiving that emitted radiation. Both sides, somewhat equally, would receive radiation from the Sun. The anti-planet-side would receive slightly more interstellar radiation, which is significantly less than from the Sun or the planet.
So, the planet side would experience the higher amount of radiation in total.
This is the general case. In certain cases, like for Europa, [the radiation is lower on the side of its direction of orbit](https://www.astrobio.net/news-exclusive/hiding-from-jupiters-radiation/).
>
> The radiation belts are rotating around Jupiter faster than Europa does. This results in the radiation predominantly striking the trailing hemisphere of the moon—which is always the same portion of the moon since Europa is locked in a synchronous orbit around Jupiter.
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If you're willing to split into quadrants, then the leading-planet-side-quadrant is lowest, for Europa at least.
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[Question]
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## Premise
We have found [extremophiles](https://en.wikipedia.org/wiki/Extremophile) of the aquatic and microscopic types here on Earth, but so far large terrestrial extremophiles are the stuff of conjecture only. This makes it somewhat challenging to speculate whether terrestrial creatures could survive on a moon heated by tidal forces of a large nearby planet/geo-thermal heat.
I'm trying to envision a realistic scenario in which cold-blooded creatures (more precisely known as [ectotherms](https://en.wikipedia.org/wiki/Ectotherm)) inhabit a moon orbiting a planet far from the habitable zone. Here is what we are working with:
* Assume the moon has everything needed to support life as we know it
(magnetic field, breathable atmosphere, geo-thermal heat, ect)
* Assume the ectotherm to be a very large lizard, say a komodo dragon
We might feel inclined to clap our hands together and say 'voila! we're done!' However, further analysis leaves us apprehensive about a large terrestrial ectotherm surviving on a such a moon solely on geo-thermal heat. A moon heated via tidal forces from a its parent planet will presumably be *very* geologically active. One second our lizard-like ectotherm is enjoying a nice soak in a hot spring, then **BOOM**: he's consumed by a pyroclastic flow from one of the many volcanic eruptions.
## Question
Given that tidal force warmed moons can be overly dangerous (take [Io](https://en.wikipedia.org/wiki/Io_(moon)) for instance), is there a more, shall we say, "peaceful" way of allowing for the survival of large terrestrial ectotherms on a moon outside of the habitable zone? If I must resort to large tidal forces inducing geo-thermal heat for ectotherms on this moon, then how will the large ectotherms cope with the geologic upheaval that comes with such a world?
[Answer]
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> This makes it somewhat challenging to speculate whether terrestrial creatures could survive on a moon heated by tidal forces of a large nearby planet/geo-thermal heat.
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Eh, not really. You don't need large extremophiles. You only need single-celled extremophiles to form the base of the food chain right up close to thermal vents and cold seeps. Larger creatures can exist in the less-extreme zones at varying distances away from the ecological energy source. There are, after all, plenty of non-extremophile complex animals living around volcanic vents on Earth.
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Yup. Or, less spectacularly, the vent dies out and everything in the vicinity slowly starves. But that doesn't mean all life ends, or even that that specific species necessarily goes extinct.
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Easy: they migrate. If all life depends on a single volcanic vent, you're screwed. But it wouldn't. Life would exist in oases surrounding thermal vents and cold seeps all over, with organisms migrating between them Your ectotherms don't need to be able to *thrive* in cold areas between oases, but they do need to be able to *survive* the trip somehow--either by simply moving very slowly, or going dormant and hoping to eventually get blown back into a warm area by the currents / winds, or by hitching a ride with an endothermic creature. Every once in a while, the population at one particular oasis which falls victim to a major eruption will be wiped out--but that's no big deal. It will be re-colonized again by imports from other thermal oases that *didn't* all get wiped out at the same time. Maybe a few indigenous species go entirely extinct, but the ecosystem as a whole recovers, and new ones will evolve.
This is exactly how thermal vent communities work on Earth.
[Answer]
1. Your creature is large because it needs to be. **It needs to be able to move fast.** Consider an event like a red tide - lots of small animals are killed because they cannot outrun the red tide. Large animals put it in gear and get out of there. So too your lizard. If stuff starts getting iffy where it is, it heads for higher ground.
2. **Your lizards can detect signs that badness is coming**. Like the famous elephants which can feel the coming tsunami thru their feet, your creature feels changes in the moons geomagnetic field which augur trouble.
3. **Your creatures get killed a lot**. Even with these skills, lots of lizards do die in disasters. But this is OK because
4. **There are a lot of lizards.** There are enormous amounts of food for them on this fertile moon and they have a very rapid reproductive rate. Even if a catastrophe wipes out every lizard for miles, these fecund and highly mobile lizards will quickly repopulate the area and take advantage of the food resources made available after the geologic turnover.
[Answer]
Tardigrades can survive in such a condition as they are resistant to everything(except things that actually harm them like defence from predators)
(let say a species of tardigrade evolves to be large but still retain it's original resistance to radiation, heat, absence of air, etc. It may survive said condition and still be large enough to fit the description)
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[](https://i.stack.imgur.com/xNWji.jpg)
The Serval is a fairly muscular, dog sized African wild cat. While doing research on them for other worldbuilding purposes, I began to think that these animals could make great hunting pets, if they had been domesticated.
So I have two questions; one, is it possible for a stone age civilization to domesticate the Serval? And two, if they were domesticated, could they be a viable hunting tool.
[Answer]
Servals are [solitary creatures](https://en.wikipedia.org/wiki/Serval#Ecology_and_behaviour) that are highly territorial. Usually that means they make poor targets for human hunting companions (they much prefer to hunt on their own). Contrast this with dogs, who were most likely bred from wolves, who are pack animals. Check out [this video](https://www.youtube.com/watch?v=wOmjnioNulo) for explanations on traits that make animals more domesticable.
Servals have a short lifespan (compared to humans), reach maturity fairly quickly, and are fairly intelligent (all traits that are helpful with domestication). There is no reason why they wouldn't be useful in vermin patrol, setting up shop near fields and grain stores to protect them from being eaten by rodents. That's how modern cats were domesticated.
This means that servals are probably able to be domesticated but would not do well as a hunting companion.
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No reason they couldn't be tamed over time, Cheetahs were [tamed](https://bigcatrescue.org/cheetah-facts/) over 5000 years ago, lions and tigers do circus tricks.
As a hunter it would be loosed to go after small prey, because that is how it hunts, just as a falcon is sent after it's usual prey. You wouldn't use it to do a cooperative hunt like herding prey towards you etc,. It doesn't have those instincts.
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[Question]
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In my setting, fossil fuels do not exist.
I'm handwaving an alternative behavior of radioactive material, and alternative magnetism-like forces. These are explained below. My question now is:
# Can there be (nuclear) small scale aviation without fossil fuels, given the constraints below?
### Alternative Radioactive Decay
Electrons can be manipulated by electromagnetic fields; they can be de- or accelerated. In the same manner, I'm handwaving a field that can manipulate alpha/beta/gamma-like particles$^1$. Scientists in the setting have a late-1800's / early-1900's understanding of radiation, so we don't have to worry about explaining this.
With those fields and blissful ignorance of the laws of energy conservation, people build reactors, where the energy output of radioactive decay is harnessed to almost 100%. Therefore, power is no problem, as the radioactive material is relatively easy to mine. These reactors are extremely heavy though (we're talking 2 tons and 2x4x4m for small, low-power versions), so vehicles on the ground are usually connected to a power line (trains) or pulled by animals. Batteries are unreliable / inefficient, so only large tanks and other massive vehicles can realistically rely on local electrical energy supply. I'm willing to decrease the size/weight of the reactors to aid the solution of this question though.
### Acceleration Fields
In my setting, there exists a field that induces kinetic energy in objects contained in it. The direction and strength of acceleration depend on the position in the field relative to its source's orientation. Heavier/denser matter experiences a stronger effect in this field. It's a little like magnetism, except for that the acceleration is possible in many directions, not only towards or away from the field's center / along its field lines, and that it does not only affect ferromagnetic materials, but *all* matter$^2$.
*To give an example:* Most powered vehicles on land are trains. Instead of using an electric motor with a wheel that pushes the train forward by friction on the rails, most large trains have a set of kinetic skids to drive the vehicle. These work by using a directed kinetic field that pushes the heavy rails below it backwards, and a little bit away to reduce friction / levitate. Power is supplied by either an onbort generator, or power lines (as in our electric trains of today).
### Aviation
Large zeppelins are used for most civilian aviation; either a set of batteries or a very small reactor might supply the needed energy to move and steer. For military purposes, there are floating fortresses, which are essentially a reactor platform with a ton of propellers strapped to it to keep it in the air.
I want to have smaller aircraft "as we know them" too, though, for dogfight reasons. [Wikipedia](https://en.wikipedia.org/wiki/Nuclear-powered_aircraft) says that development of nuclear propulsion in aircraft has been stopped because of the severe dangers of nuclear fission. The fact that air heated from fission was thought to be enough to propel a plane makes me think that this is viable if one takes away the radiation danger (by shielding the reactor with my alternative radiation fields).
I thought about acceleration fields being used as an alternative to jet engines, where instead of fuel exploding and pushing hot gasses out the back, very fine metal powder is accelerated backwards and pushes the plane forwards. Like a rocket engine, but without the burning.
Regarding the last paragraph:
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> Is carrying metal powder to shoot out the back a good idea? Are there any limits on the efficiency of this method, relative to the plane's speed? Or would propellers be the go-to option anyways? I'm looking for a relation between powder weight and achieved propulsion at a certain energy input.
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My main question, refined:
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**Edit:** To make things more simple: I have reactors that supply vast amounts of energy, but next to no means to move them. As they are heavy, smaller aircrafts have to rely on other fuels. What could those fuels be?
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$^1$ *This is a massive simplification of how things work both in the real world and in my model, to the point where it may become incorrect. I hope it gets my idea across though.*
$^2$ *Again, a brutal simplification. I wanted to keep the question "short", but can elaborate if needed.*
[Answer]
## The engine depends on the power-to-weight ratio of the kinetic skids
If kinetic skids can drive trains, why couldn't they drive airplanes? Well, for one, steam engines drive trains but not planes. That is because a steam engine's power to weight ratio is very poor. But if it could be light enough, then you can make an airplane engine.
This would work, as you suggest, on some sort of reaction mass. Since your kinetic force generators affect all matter, there is no need to use metal powder as reaction mass, just use air. After all, a jet engine is just using air for its reaction mass.
So if the motive force can be provided by the kinetic skid, then you are simply limited by the available power source. The key here is that if the power source is not as mass efficient as a battery, then the kinetic skid must be that much lighter to compensate. For example, while electric aircraft do exist, they aren't great because their power to weight ratio is worse than an internal combustion engine. They also scale much worse with additional fuel: the mass of adding a gas tank is much less than adding the equivalent amount of battery storage.
## Power source can be a chemical reaction
Now, the kinetic skids will need their own power source. You say that reactors are too heavy and batteries too weak. Then ideally, you will use some sort of chemical storage....although that is basically what a battery is.
A [fuel cell](https://en.wikipedia.org/wiki/Fuel_cell) that generates electricity from hydrogen fuel and an oxidizing agent is possible. The first fuel cells were invented in 1838, so they fit the time period. They just aren't that effective in the real world. The first fuel cells were most similar to a modern day [phosphoric acid fuel cell](https://en.wikipedia.org/wiki/Phosphoric-acid_fuel_cell). In operation, the cell must be heated to 150-200 C. Hydrogen fuel pumped to one side of the cell will pass electrons to oxygen from air circulating on the other side, generating an electric current. There is also exothermic exhaust, though I don't know how much use you will get out of that.
The efficiency would be low, and you'd need a tank of hydrogen to power it. On the other hand, if your zeppelins are full of hydrogen in the first place, it might not be too hard to get a hold of the hydrogen you need.
If you want zeppelin's to act as carriers, then they can be generating hydrogen fuel from hydrolysis of water, storing the excess in their shells, and then fueling up the limited range fighters when they come back to 'base'.
## Alternate solution: rockets
If you like the idea of short range fighters zooming around large ponderous zeppelins *a la* Star Wars, you might want to go with rockets. [Hydrogen peroxide](https://en.wikipedia.org/wiki/Hydrogen_peroxide) was used as a mono-propellant rocket fuel. But there might be a better alternative.
[Hydrazine](https://en.wikipedia.org/wiki/Hydrazine) can also be used as a rocket fuel, although it is dangerous.
Hydrazine was first made from sodium hypochlorite (basically, bleach) and ammonia in 1907. Sodium hypochlorite entered industrial production in 1892; it is made by electrolysis of salt water. So the timeline is about right for hydrazine to be the big new thing.
Hydrazine is a [hypergolic](https://en.wikipedia.org/wiki/Hypergolic_propellant) propellant when mixed with dinitrogen tetroxide; but that wasn't invented until WWII, so sort of out of your time spectrum. It does burn quite explosively in oxygen, so it would be a fine rocket fuel either way.
[Answer]
We use hydrocarbons for aircraft fuel because hydrocarbons have a great many beneficial properties. They have considerable energy density by volume and mass. They remain liquid at a wide range of temperatures, the kinds seen from burning hot deserts to sub-zero temperatures seen at miles into the air. They provide lubrication to pumps. They burn readily when atomized but not when pooled on the ground from a spill. This we all know because of our use of fossil fuels in our every day lives. The point I'm making is that if we could not pump them from the ground then we'd synthesize hydrocarbons for fuel. We know how to produce hydrocarbons from nuclear power, in fact this has been proposed widely as an exit from needing fossil fuels in the real world.
In short, if we could not pump hydrocarbons from the ground for aircraft fuel then we'd make hydrocarbons from whatever raw materials and energy sources were most readily accessible.
Don't try to fit a nuclear reactor into an airplane, just use a nuclear reactor on the ground to make the airplane fuel. The US Navy has been working on this for a very long time, perhaps decades, to allow nuclear powered aircraft carriers to produce the fuel for the aircraft it carries while at sea. If or when this project is successful it would remove the need for a small flotilla of oil tankers to continuously bring fuel to the carrier groups.
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The answer is, in my mind, synthesized kerosene.
If the goal is to have the airborne equivalent of the navy aircraft carrier, a military base that floats in the air instead of floating in the sea, then a nuclear reactor on board starts to make sense. Though with something this large I'd expect a large part of the lift that keeps it in the air to be from a lifting gas. That would mean it's a large armored Zeppelin. Because airplanes are more efficient than helicopters in turning energy into lift, and a moving target is harder to hit than a stationary one, I expect this airborne military base to keep moving and use a flying wing body to provide some of the lift. That doesn't mean it *can't* hover, only that it does this only when necessary for the mission.
Zeppelins fell out of use because it is so much easier to produce hydrocarbons than to produce helium. Hydrogen is an easily obtained lifting gas but it's so flammable as to be impractical. Perhaps with better materials and techniques Zeppelins filled with hydrogen could be practical. If there's cheap hydrogen for a lifting gas then there's cheap hydrogen for producing synthetic kerosene.
For Zeppelins to be safe and cheap means helium has to be practically gushing out of the ground. Helium is a byproduct of nuclear reactors but I doubt that's a practical source of helium since if there's enough nuclear reactors to make travel by Zeppelins practical then that's a lot of energy going around to make kerosene. Batteries are completely impractical for powering Zeppelins. Mass is a **huge** issue for keeping a lighter than air vehicle flying. Nobody is going to power a Zeppelin by batteries. They'd be using something far more energy dense. If it's not kerosene being burned in turbine or reciprocating engines then it might be ammonia, hydrogen, or some other lighter than air flammable gas.
If the fuel is also a lifting gas then as it is burned the lifting capacity is diminished so some measure has to be taken to compensate, which could be as simple as dumping sand bags. Perhaps a mix of heavier and lighter than air fuels can be used, burning either as needed to maintain the desired lift. Air density varies with humidity and temperature so having a means to adjust lift during a long flight will be desirable.
A nuclear reactor on a fast moving airplane which could find itself being shot at in a war was likely a liability that few would consider. However, in a big slow moving Zeppelin, used in civilian aviation, a nuclear reactor may actually be safer than kerosene. Consider large civilian nuclear powered lighter than air airliners as an alternative to kerosene powered jet aircraft. It cuts out the conversion losses of producing the kerosene and uses the heat from the reactor directly for propulsion. With a lifting body shape it would still fly largely like an airplane but at a very leisurely cruising speed of something like 50 to 100 knots instead of the 400 to 500 knots of a jet. As a nuclear reactor doesn't need oxygen to burn fuel such an aircraft could reach altitudes a jet never could.
[Answer]
Apparently, it’s possible to fly a pedal-powered aircraft:
<https://www.wired.com/2013/04/how-to-fly-a-human-powered-helicopter/>
The helicopter in the article requires high-tech carbon fiber to remain light enough, but if you scaled the process up and used many peddlers on the same craft, it might be feasible using aluminum.
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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.
We know from the International Pronunciation Alphabet (IPA) and the research that gave us the IPA, what sounds typically used in human speech (certainly not all sounds that *can* be made). This is all well and good but I want to do this for aliens with arbitrary physiology.
I don't want approximations or guesses. I'm looking for a software suite that might be adapted to my task. If the software works best in the hands of a PhD student or post-doc, that's probably the level of accuracy I'm looking for. I don't care about what sounds an alien will make, only the ones their physiology will allow them to make. If there are lower accuracy, but more approachable packages, I'd be interested in them too.
Computational complexity isn't a big problem as AWS/GCE is cheap and I have time.
(I also am not afraid of ruining monster movies for myself when some huge monster makes a noise pitched far above what their physiology would permit.)
[Answer]
# Probably doesn't exist
...but here's what it would need to be able to do.
Primary Goal: Finding the vocal range of a arbitrary phonatory apparatus is the primary use of this software. We want to be able to design an apparatus, hit "Go" then come back and find out the vocal range possible. As much of the tedious modeling and data handling work should be done in software, not by the operator.
## Requirements
* Build a library of biological materials such as muscle, fat, bone, tendon, ligament, organs, fascia, mucous membranes and so on. Be able to assign these materials to various parts of the model. Have sane defaults for all materials (based on Earth analogs) but also permit custom tweaking of those parameters.
* Be able to infer the relationships between various body structures. For example, airways are usually surrounded by skin then rings of cartilage. Fascia connects all that together. Modeling all that by hand is tedious in the utmost. Software should be able to do that for us.
* Reduce the absurd number of degrees of freedom in a soft tissue problem like this to something more manageable. (No need to use 1000 CPUs if you can get by with 100.)
* Define atmospheric parameters.
* Rapidly vibrating muscles are frequently a part of a phonatory apparatus. The software should be able to simulate the interactions between these vibrating muscles and the surrounding tissue.
* Account for changing geometry of the airway due to muscle and skeleton position. Human singers sound different when they hold their head a slightly different way. The software should be able to detect and determine the difference.
* Account for resonance with skeletal cavities. We should be able to test the effects of the nasal cavity of [Parasaurolophus](https://en.wikipedia.org/wiki/Parasaurolophus#Cranial_crest)
## Secondary
* Find overlap between sounds possible with sounds that humans can make. For example, if we define an alien that can use some of the same sounds as humans, we'd like to know that quickly.
* Employ neural networks to drive the muscles to make sounds and speech.
## Papers of Interest
* [Modification of soft tissue vibrations in the leg by muscular activity](https://www.ncbi.nlm.nih.gov/pubmed/11160036)
* [Fatigue and soft tissue vibration during prolonged running](https://www.ncbi.nlm.nih.gov/pubmed/26359729)
* [Ultrasonic imaging of internal vibration of soft tissue under forced vibration](http://ieeexplore.ieee.org/document/46969/)
* [The effect of soft tissue on wave-propagation and vibration tests for determining the in vivo properties of bone](https://doi.org/10.1016/0021-9290(77)90015-X)
* [Vibration Simulation using Matlab and ANSYS](https://books.google.com/books?id=fzniJqoLvbwC&lpg=PP8&ots=xQIigDhF6Y&dq=vibration%20simulation%20library&pg=PA7#v=onepage&q=vibration%20simulation%20library&f=false)
I'm sure there will be many more papers to be read.
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[Question]
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A while back I saw [this video](https://m.youtube.com/watch?v=lgkqbHJczWs) talking about the habitability of double planets and Rocheworlds. I haven't seen any questions about the latter case here, so I decided to take a swing at it.
For some background, a Rocheworld is a double planet system that is so close together that the two planets share an atmosphere and have started to merge together. This would eventually result in the two planets violently becoming one large planet.
Hypothetically, it could be possible to travel from one of the planet components to the other over the region they overlap. I think that since these are two planets overlapping, this could lead to some intersting gravitational effects that could impede travel between the two sides.
How would a person feel gravity as they tried to walk from one part of a Rocheworld to the other?
(As in, would they feel a strong tug from either planet as they walked the overlapping region, or would it feel unanomalous?)
[Answer]
First off, I should point out that, in order for this kind of arrangement to be even remotely stable, the planets will have to be be tidally locked, meaning that they do not rotate in relation to each other. No matter where you are on either planet, the other will always occupy the same place in the sky (if the other is above the horizon, that is). The planets will also be orbiting each other very quickly- on the order of hours, most likely- in order to keep from crashing into each other. This means that "days" on these planets will also be very short- again, probably only a few hours long.
Walking around on such a double planet would feel much the same as walking around on any other kind of planet, at least if you confine yourself to a reasonably small area. By the time this arrangement becomes stable, the planets will have reshaped themselves to be fairly oblong, with their "ends" pointed at each other. If you ignore mountains and continents and such, the ground will seem to be flat everywhere, in exactly the same way that the Earth's surface seems flat if you're standing on it, even though it's actually a sphere. In more technical terms, the surface of each planet will be at (roughly) constant [gravitational potential](https://en.wikipedia.org/wiki/Gravitational_potential).
Gravity will be noticeably weaker at the "ends" of the planets than around their middles, due to the tidal forces each exerts on the other. You can think of this as follows:
* Where the other planet is directly overhead, gravity will seem weaker because the other planet is pulling you away from the surface. Not enough to lift you off the surface, but you'll definitely feel lighter.
* On the opposite ends of the planets, gravity will seem weaker because the planets are spinning around each other and the centrifugal force is trying to sling you away. This isn't strictly accurate- it's more like the other planet is pulling the ground away from your feet faster than it's pulling on you, due to the [inverse square law of gravity](https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation#Modern_form)- but it gets you the right idea.
* Around the middle of the planets, gravity will feel stronger for two reasons: One, because you're closer to the center of your planet; and two, because the other planet is pulling you toward the ground as well.
I should point out that this sort of arrangement, where two planets orbit each other close enough that their atmospheres touch, may not even be remotely possible. If a moon orbits too close to its planet, the tidal forces will rip it apart. On the side closer to the planet, the material at the surface of the moon will be lifted away, because the planet's gravitational attraction is stronger than the rest of the moon's; and on the opposite side, material will be slung out into space by the centrifugal force. The point where this happens is called the moon's [Roche limit](https://en.wikipedia.org/wiki/Roche_limit), and I have no idea how it applies if the "planet" and "moon" are the same size.
I also don't know what impact this arrangement would have on the planets' atmospheres. They'd certainly be much thicker between the planets and at the planets' "ends" than around the planets' middles (although the air pressure at the surface of each planet should be pretty much the same everywhere), but for all I know, the centrifugal force could sling all of the atmospheres out into space. You'd also need to watch out for that.
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### Update with Math
The formula for orbital period when the masses of both planets need to be accounted for is as follows:
$$ T = 2\pi \sqrt{a^3 \over {G(M\_1 + M\_2)}} $$
where $a$ is the distance between the two planets and $M\_1$ and $M\_2$ are their masses.
For two spherical Earths orbiting just close enough that their atmospheres touch, this gives an orbital period of [two hours and 49 minutes](http://www.wolframalpha.com/input/?i=2pi%20sqrt((2%20*%20earth%20radius)%5E3%20%2F%20(G%20*%202%20*%20earth%20mass))).
If I fudge the masses in an attempt to emulate the planets being ellipsoids with a 2:1 aspect ratio and put 0.455 Earth radii between them (see below), I get an orbital period of [7 hours, 40 minutes](http://www.wolframalpha.com/input/?i=2pi%20sqrt((2.455%20*%20earth%20radius)%5E3%20%2F%20(G%20*%200.5%20*%20earth%20mass))). I think this is about the shortest orbital period you'll be able to get in a system like this, if the system is going to be stable.
How did I get those numbers? The 2:1 aspect ratio and the 0.455 radii? Well.
The Roche limit page details two different Roche limits: one for a rigid satellite, and one for a fluid satellite. The rigid limit is the orbital radius at which loosely-bound material on the satellite's surface (or planet's surface, in your case) will be lifted off and ejected into space. Soil, water, and air all count as "loosely-bound", as there's nothing beyond the gravity of the planet holding them down, so that's something to keep in mind.
The fluid Roche limit accounts for how the tidal forces will distort the satellite and make it more vulnerable to being torn apart. It serves as a good upper bound on how close two bodies can orbit with no risk of being torn apart, although, in practice, many moons in our Solar System orbit well within their fluid Roche limits. They are, in part, held together by tensile forces. They're made of ice or rock, not water. However, I'm fairly sure that none of those moons have atmospheres or any of the fluid-like inner workings that allow Earth's plate tectonics and other geological activity to function. If you want Earth-like planets, you'll need to adhere to this limit more strictly.
The formula for a fluid Roche limit on that Wikipedia page that takes the most things into account (and also happens to give the largest upper bound for where the planets will begin to break apart) is this:
$$ d = 2.455R \root 3 \of {\rho\_M \over \rho\_m} $$
where $R$ is the long-axis radius of one of the planets, and $\rho\_M$ and $\rho\_m$ are their densities. I'm not certain which planet $R$ is supposed to be the radius of, but if the Rocheworld planets are the same size, it shouldn't matter.
This tells us that the distance between the planets' centers of mass can be no less than 2.455 times their long-axis radii without risking the planets losing their atmospheres or breaking up entirely. This means that, if the planets are in a stable orbit, there will be at least 0.455 long-axis radii between them. If they're roughly Earth-sized, that'll be about 3000 kilometers. There's not going to be any appreciable atmosphere between them at all, much less enough to fly a plane from one to the other.
It is also worth pointing out that a fluid satellite (or an Earth-like, geologically active Rocheworld) under these conditions on the verge of breaking up will have a 1:1.95 ratio between its long and short axes. If the tidal forces stretch the planet out any more, they will exceed the gravitational forces holding the planet together, and cause it to disintegrate. So your planets should not be any more elongated than that. Also note that if the planets are elongated that much, there will be almost no gravity at their ends. You may need to keep them a bit farther apart and a bit less oblong, just to keep their atmospheres in check.
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I was lucky enough to witness the total solar eclipse crossing the US this past August, but while it was impressive, it was also fairly short - lasting just under two minutes at my location. I'd like to increase the intensity of the experience for a less technologically advanced civilization by drawing out the duration of the eclipse as much as possible.
I see that total eclipses on Earth can last up to [approximately seven and a half minutes](https://en.wikipedia.org/wiki/Solar_eclipse_of_July_16,_2186) when the Earth is near aphelion, the moon is near perigee, and the eclipse happens near the Equator.
But can we draw this out *even longer?*
Given a planet and moon roughly like Earth and our Moon, are there modifications we can make to the orbit, size, or rotational speed of either body that could extend this out, while still maintaining a stable system?
My target is 15 minutes for a single location on the planet to witness an eclipse, ideally while able to see the sun's corona. Preference is for the eclipse to be caused by a moon rather than a large planet.
Bonus points if this long total eclipse can occur on a relatively frequent basis for a given area, where "frequent" is defined as anywhere between a month and a decade (so that a generation of people would experience multiple such events during their lifetime).
[Answer]
The easiest and more effective is to pull your moon nearer to planet so it will have a larger apparent size and you'll get both more frequent and longer lasting eclipses.
You will be limited by [Roche limit](https://en.wikipedia.org/wiki/Roche_limit), but there's ample margin as this, for real Earth/Moon system is a scant 34,638km radius while real moon orbit is about 384,399km away, which is 21 times the Roche limit.
Note that, as you pull Moon in you'll get three effects together:
* it will occupy a larger portion of the sky (eclipses will last longer and will happen more often)
* it will appear to move slower (if it is still outside GEO, otherwise its apparent speed will rise again, in the other direction) (eclipses will last longer)
* tidal waves will be *much* higher (situation may become unstable if Moon is too much inside [GEO](https://en.wikipedia.org/wiki/Geostationary_orbit) due to energy dissipation from tides pulling it toward Earth).
I think your best bet would be to have a moon near to GEO that will have rather high tidal waves moving very slowly.
About frequency of eclipse: this is strictly dependent on angle between orbital planes for the Sun-Earth and Earth-Moon systems; if this angle is less than apparent size of the moon then you'll have an eclipse *every* "New Moon" phase.
If you tell us your target we can try to compute if this is compatible with orbital physics.
**Edit**:
I'll try to compute the exact parameters (I'm not familiar with orbital math, so it might take a bit); in qualitative terms what I think we can do is:
* start from "real" Earth-Moon-Sun system.
* pull moon nearer to planet (so it's apparent movement will be slower; need to about half the apparent speed; *note*: "lunar months" will be accordingly longer).
* reduce moon diameter so that its apparent size will remain the same (~= .5°; needed to see Sun corona).
* reduce angle between planet orbital plane and moon orbital plane so that you will have an eclipse *somewhere* at each "new moon" (this angle should be less than angular dimension of moon ~= .5°).
* I would avoid to modify too much rotational speed of planet (it would change day length).
* I have no idea (suggestions welcome) about how to compute effects of changes on tidal waves (pulling nearer would increase effect, but shrinking satellite would decrease it; square/cube *might* apply since gravity decreases with inverse square while mass is cube of dimensions and we can assume $sin \alpha \simeq \alpha$)
[Answer]
There are are a number of ways in which this can be attained:
* First, you can make the rotation speed of the planet very slow and the revolution speed of the moon slow to get this effect. But I hardly think that if you do that you can get a solar eclipse for a very long time. Also if you do this it will mean that the hours in a day for that planet will increase severely. And also getting this effect again and again so that a person can experience it in an interval of month is very unlikely. A decade is more of a reasonable time gap.
* Secondly you can get this effect by making planets come in front of the planet. Note- the planet coming in front has to large enough to cause a solar eclipse cause planets have large distance between them. So a planet equal to the size of The Planet (where eclipse is happening) coming in front of the planet will not work. That is why Mercury doesn't cause a solar eclipse when it comes in between the sun and earth, but if saturn or jupiter comes between sun and earth it could cause a solar eclipse. Also by using this process you can get the solar eclipse many times. Just make different planet come in front of it again and again.
Hope it helps.
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[Question]
[
My race of space-going sentients want to weaponise a life form which is explosive in an oxygen-rich environment.
To do so, they have access to any planet they care to use, terraforming, and the ability to change the atmospheric makeup of the planet.
How would they go about creating and breeding this life form?
The solution that I have found so far is boranes:
>
> Boranes are dangerously explosive in Earth's atmosphere, but would be more stable in a reducing environment. However, boron's low cosmic abundance makes it less likely as a base for life than carbon.
>
>
>
This is from [Hypothetical types of biochemistry](https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry). Would a multicellular organism built from mostly boron be able to support life? Would exposure to oxygen be possibly fatal due to the risk of igniting? How would it respire, if oxygen is a possible danger to it? How would it be maintained? What would it look like?
[Answer]
This is not about boron-based life, so ignore it if you're set on that, but it could maybe help if you're open to other mechanisms. I was thinking of violently exothermic reactions and remembered two, one we know in reality and one employed in fiction.
1. **The [bombardier beetle](https://en.wikipedia.org/wiki/Bombardier_beetle)**: about 500 species of beetles of the *Carabidae* family are known to repel predators by means of a hot chemical spray.
>
> The spray is produced from a reaction between two chemical compounds, hydroquinone and hydrogen peroxide, which are stored in two reservoirs in the beetle's abdomen. When the aqueous solution of hydroquinones and hydrogen peroxide reaches the vestibule, catalysts facilitate the decomposition of the hydrogen peroxide and the oxidation of the hydroquinone. Heat from the reaction brings the mixture to near the boiling point of water and produces gas that drives the ejection. The damage caused can be fatal to attacking insects. Some bombardier beetles can direct the spray over a wide range of directions.
>
>
>
This is neither an explosion in the sense you were imagining, nor very powerful, but it shouldn't be that difficult to engineer a larger and more violent bug.
2. **The explosive plants on Hal Clement's *[The Nitrogen Fix](https://en.wikipedia.org/wiki/The_Nitrogen_Fix)***. In this classical SF novel, Earth's atmosphere has lost all almost of its free molecular oxygen and new plants have evolved to fill the vacant niches. Their metabolism is based on nitrates. This makes them somewhat prone to explode. Lightning, for example, will readily blow up a large patch of forest, though it will of course not set it on fire (because there's no free oxygen!).
Maybe you could go for a mixture of the two: a large animal that could synthesize and store explosive nitrogen compounds within its body, with some natural device that allows it to destabilize the compounds.
See also [autothysis](https://en.wikipedia.org/wiki/Autothysis) for ideas on how some insects kill themselves "explosively".
[Answer]
Here is just some ideal, you can turn it into hard-science or fiction as you wish.
Main idea: A creature only Explode when they are triggered (by the creature, or by implant devices). They are not easy to get explode (safety)
* Ex1 Mix-trigger: creature contains chemical A and B. Both A and B are not danger, unless they are mix (triggered). (A= Boranes and B = Boranes , perhaps). But there must be some safety precaution so they are not going a chain reaction (which accidentally kill all in breeding ground)
* Ex2 atom level trigger: chemical A is harmless until exposed to radiation/specific wavelength/a neutron ([atomic bomb](https://www.youtube.com/watch?v=-Nc0wCrkk00) are triggered by firing a neutron into uranium)
Some problem you concern:
>
> Would a multicellular organism built from mostly boron be able to support life?
>
>
>
You don't need to built organism contains mostly explosive chemical A, B. Let everything be normal as native creature. Then let the creature carry a container of explosive chemical (explosive chemical are not participate in daily life functional, just stock there for last moment). Look at [baneling](http://us.battle.net/sc2/en/game/unit/baneling) in Starcraft 2. They carry a big bag of green thing.
[](https://i.stack.imgur.com/Et3nd.jpg)
>
> Would exposure to oxygen be possibly fatal due to the risk of
> igniting?
>
>
>
Solution 1: make A and B not native or battlefield (oxygen for your case)
Solution 2: seal A and B in container that cannot contact with oxygen (in case A or B is oxygen)
>
> How would it respire, if oxygen is a possible danger to it?
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>
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Even if A or B is oxygen, the creature can functional if they well-seal their explosive container. You may develop from native creature, then add a biology bag of chemical.
>
> How would it be maintained?
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>
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Give them food to eat as you raise sheep. Their DNA can make explosive chemical protein. So you only need to include ingredients in their meal. If explosive chemical only contain C-H-O then everything would be easier.
>
> What would it look like?
>
>
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From Starcraft 2,
[Baneling](http://us.battle.net/sc2/en/game/unit/baneling) (ground) and [Scourge](http://starcraft.wikia.com/wiki/Scourge) (air)
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[Question]
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For story purpose I am trying to design a mass transit system for a perfect city. Right ... maybe not so perfect, if you look carefully into the details, but actually the mass transit system is supposed to be highly efficient.
Nevertheless, the city is built from scratch with heavy inspiration from New Urbanism (mass transit, high buildings, mixed zoning, nice parks, very little cars). In RL the metro suburban rail system is able to waste even 45% of used energy for braking (and engineers hope to recover a small fraction for regenerative breaking). In RL there are also attempts to reduce wasted energy by working with slopes - after leaving the station the train goes down a bit to go up just before the next one, thus saving all this accelerating /decelerating stuff.
I want to go one step further - I want to position the stations clearly higher than the track, thus effectively no breaking would be needed. (Yeah, the metro would resemble a bit like a roller coaster, I know). The system would work perfectly, if all stations were on the same height, just a bit energy would be used to compensate for rolling and air friction. If the altitude difference would be minimal, then train would need to use energy only in this slightly uphill direction, while on the opposite, everything would be provided by gravity.
Is there any idea how to calculate (rule of thumb, whatever) what the maximum height difference between stations would be, under which such a system may indeed work?
The tech level is comparable to contemporary Earth.
(Clarification: I know that you have to include rolling friction, air friction, etc... The issue is just how to either find data to put into such a formula, or how to make a very rough adjustment based on some RL life example, to derive calculations, that would not make any engineer cry)
[Answer]
The resistance of the train is dependent on a lot of things. I've tried to bring all those things together as best as I can for you [here](http://www.wolframalpha.com/input/?i=sqrt((45000*9.8*sin(x)-9.8*cos(x)*.0002*45000)%2F(.5*.000253*1.225*12.15))). You can play with the value x (in radians) and the output is the maximum velocity the train will reach at that slope. The coefficients of rolling and air resistance were taken from [here](https://www.railelectrica.com/traction-mechanics/train-grade-curve-and-acceleration-resistance-2/) and some of the math borrowed from [here](https://what-if.xkcd.com/154/). [Solving for x](http://www.wolframalpha.com/input/?i=solve%20sqrt((45000*9.8*sin(x)-9.8*cos(x)*.0002*45000)%2F(.5*.000253*1.225*12.15))%3Dv%20for%20x) lets you play with V to get the appropriate slope for a given speed.
Finally, the difference in height will be proportional to the loss in energy do to friction, which itself depends on the slope of the rail, the velocity of the train and the distance it travels between stations. You can calculate that [here](http://www.wolframalpha.com/input/?i=((9.8*cos(x)*.002*45000%2B.5*.000253*12.15*V%5E2)*d)%2F(9.8*45000)).
These are all rough calculations and I haven't practiced my physics in a long time. There's also a good chance that I used the wrong unit of air density so please take this answer with a grain of salt, and I'd definitely recommend checking in with our friends at physics.stackexchange.com
[Answer]
I can provide you with a number. For a train system you describe, the maximum gradient is about 4%. This means that the steepest track you can lay is a climb of 4m every 100m of horizontal travel. For comparison, freight trains can only handle an absolute maximum of 2%.
Question not asked, but I normally use a radius of 300m for my sharpest curves. I don't take super-elevation (banking) in my designs.
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[Question]
[
This is the ideal set up for my solar system:
[](https://i.stack.imgur.com/kEYUu.png)
***EDIT***
It's been pointed out that this is not a stable set up, so I want to clarify that everything in this set up can be changed at will to fit my planet. The only thing that's essential is the size, gravity and temperature of Enkei as it needs to support the fauna in my world. Yaima is intended to be a planet but can be a moon.
**Magnus** (Main Star):
Mass: 2.1879\*(10^30)kg (1.1 Sol)
Luminosity: 5.3688798\*(10^26)W (1.396 Sol)
Diameter: 1530540km (1.073 Sol)
Habital Zone: 1.13-1.63 AU
**Ignis** (Circumbinary Star):
Mass: 5.1714\*(10^29)kg (0.26 Sol)
Luminosity: 3.4467993\*(10^24)W (0.00896 Sol)
Diameter: 513400km (0.369 Sol)
Semimajor Axis: ???
**Enkei** (Planet):
Radius: 6923.5km (1.0865 Earth)
Mass: 5.63094\*10^24kg (0.9428 Earth)
Volume: 1390160000000km^3 (1.2834 Earth)
Gravity: 7.84m/s^2 (0.8G)
Density: 4.05g/cm^3 (0.735 Earth)
Surface Temp: 292K 19°C
Semimajor axis: 260615093km 1.7421042951765742AU
Firstly, I have no idea what the most suitable orbit distance is for my binary (P-Type) Star but I found the [minimum distance](https://www.reddit.com/r/worldbuilding/comments/346eaw/solar_system_tutorial/) to be 0.11AU so 0.2 seemed a good guess. Obviously, I need a stable System before I can even begin to populate the world so this is the most important. Worst case scenario I can scrap the binary and just tweak our solar system accordingly.
292 kelvin is the maximum temperature I want for my planet as it effects climate and evolution. Since I couldn't find anything concrete for calculating the relationhip between temperature and atmospheric density, I plotted the disparity between expected temperature and actual temperature for Earth, Mars and Venus alongside the atmospheric pressure (1, 0.006 and 90, respectively). using this scale predicted my Planet's temperature (12x Earth Atmospheres) to be 60-80% of it's actual temperature and because the albedo would be similar to earth, this then gave me an orbit distance of roughly 1.74AU which is just outside of the habitable zone. That makes the expected temperature the same as mars but an atmosphere 12x stronger would provide a considerable buffer and an Earth-like landscape (i.e. Large Oceans) should help regulate temperature.
If that seems inaccurate, Is there an equation for temperature and atmospheric pressure? Or is anyone able to calculate a more accurate orbital distance that would keep the planet at around 19°C?
Bear in mind that distance affects year length. My current set-up allows 32-hour days for 539.751 days in a year, which is 540 days a year -1 every four years except for the start of new millenia.
[Answer]
# Setup
I tested your scenario using [Rebound](http://rebound.readthedocs.io/en/latest/index.html), an orbital simulation package with a nifty python interface. If you want to see the code I used, it is available on my github [here](https://github.com/kingledion/worldbuilding).
Here are the numbers I used for my first run:
```
m_magnus = 1.1 #2.19e30 kg
m_ignis = 0.26 #5.17e29 kg
m_enkei = 2.83e-6 #5.63e24 kg
a_ignis = 0.2 # AU
a_enkei = 1.74 # AU
e_ignis = 0.01
e_enkei = 0.01
```
In addition to the numbers you provided, I just threw in some eccentricities to see if it worked.
# Results
The simulation ran for 1 million Earth years. I only included Enkei and the two stars in the simulation. At a distance of 0.2 AU, Ignis did not do much to disrupt the orbit of Enkei.
The maximum variation that I saw in the semi-major axis of Enkei in those million years was about 1.7%; this variation was somewhat random, I was unable to plot any patterns for it. There are definitely some interesting orbital harmonics going on, as you can see in the graph below: [](https://i.stack.imgur.com/CAaKA.png)
I broke the semi-major axis graph out onto a longer time scale. [](https://i.stack.imgur.com/pzowK.png)
So these are some interesting orbital dynamics. The eccentricity changes will cause your planet to basically alternate hot and cold years with about the same variability we see on our planet year to year. The semi-major axis changes will be more significant, causing up to a 3.5% change in insolation on around a decade time span. That is enough insolation to produce noticeable, several degree C changes from warmest to coolest.
So, without accounting for any of the other planets, the setup listed above appears to be stable, and has some interesting orbital characteristics to boot. Just to be clear, numerical simulation, no matter how advanced, cannot *prove* stability for an n-body system, but it can suggest that it is likely.
If you want to add mass, semi-major axis, and eccentricity information for some of the other planets, I can add them into the simulation.
# Insolation
When I get some more time, I will update this question with insolation graphs, as I did in this [question](https://worldbuilding.stackexchange.com/questions/62948/season-cycle-that-would-occur-on-a-habitable-planet-that-orbits-two-suns/62992#62992). Hopefully, this will help determine what the planet's seasons and average temperatures will be like, and shed some more light on the orbital harmonics.
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[Question]
[
In many sci-fi settings magnetic boots are used to help astronauts walk in microgravity. However, not all materials are ferromagnetic. Titanium, aluminum, the most form of carbon and silica can not be magnetized. And these would make up the surface of the most spaceships and asteroids. (except nickel-iron ones.)
**What alternative technologies are possible, which could quickly grip and release various surfaces?**
Futuristic technologies (like nano-arms gripping on microscopic surface irregularities) are allowed, but nothing, which explicitly violates known physical laws. (like paragravity)
[Answer]
Inside? Velcro. However that's not what you're asking. I would say much like a Gecko or spider. There's actually technology out there that creates a velcro like material based on gecko feet.
Still as Jan Ivan mentions in the comment under your post, this only works on relatively smooth surfaces. I think you need a fundamentally altenative technique there. Asteroids are rough and dusty. Your nano-arm gripping should work better there with plenty of surface irregularities.
Now this could be combined in one sole by alternating strips of either material. Might show more wear and tear then neccesary but would give you flexibility.
Alternatively do away with the boots as a whole. I mean wear boots in space but don't try to make them stick to anything. Go for another tool like a mountaineering pick, But instead of mainly having a sharp point give one end a smooth surface adhesion ability and the other for rougher surfaces.
[Answer]
Keep the mag-boot premise, but on surfaces that are not necessarily ferromagnetic, line them with coils that can generate the magnetic field on command. Paint pathways on the surface of the ship to indicate where to put your feet.
Being able to turn on and turn off the magnetic fields gives you a convenient way to get rid of a troublesome character with a creative malfunction, too >:). Oops, I reversed the polarity. so sorry!
[Answer]
It might be simpler to not think of "walking" in space the way we think of walking on Earth. A tether system much like that used in climbing or rappelling would be easy to implement on both artificial surfaces (carabiners with lines and pulleys) and natural ones (embedding cleats into the rock surface, or using magnetic ones where applicable). Without gravity, there is no real sense of "up" and "down", and it's far simpler to scale along a surface. Think Ender's Game - down is what you decide it is.
If you really want to be able to walk "upright" on a surface, a set of deployable cleats in the sole or around the perimeter of the boot could work. You would only need to set (via controls on the spacesuit?) the surface type - suction for smooth, hard, and relatively flat surfaces, magnetic for magnetic ones, penetrating cleats for rocky or dusty surfaces.
[Answer]
Molecular bonding system in the soles, operated through foot action. The boots would bond at a molecular level with the surface they are touching, with a release mechanism operated by pressure from the toes.
The mechanism to undo the bond could be waves of some sort sent down into the soles to release the bond.
[Answer]
Okay, I'll take a stab at it.
**Inside/Outside Artificial**
Well, if you built it, why can't you add the tech to let them move around in it?
Things like **a grid with boot clamps** that slide around on a track, make it motorized and there you go, in micro-gravity you wouldn't have too much trouble staying up in place, and if you needed to step off to reach some tech, it also has a built-in tether.
**Natural Surfaces**
The simplest solution would be timed release clamps based on muscular movement in a suit. Sensors would detect the lifting of the leg and the clamp would release, letting you move the leg into position before it clamps down again. A failsafe could be put in place for complete zero-g or near zero-g environments where the clamp won't release if the other isn't clamped on correctly or at all.
(Sorry, no space jumps for you John Carter)
**Other Answers**
Other people have given answers
(including you @b.Lorenz) with the micro-grip arms or cleats, and I figured I'd mention it since it just gave me and idea.
**Compose the boots of Nano-Tech.**
Hear me out here, nano-tech is small enough to be air tight for standard spacewalk boots and if extra is stored in the soles, the soles would grow and mold around irregularities in rock and stone, and as far as I know, metals would still have micro irregularities large enough for the tech to stick to artificial surfaces. If you're worried about the grip strength per square inch of surface area on artificial materials, the tech can grow out beyond the edge of the boots to make a larger grip surface (think expanding, kinda-magnetic snowshoes.)
[Answer]
I could suggest **ultrasonic welding boots!**
[About Ultrasonic welding](https://en.wikipedia.org/wiki/Ultrasonic_welding)
This welding technique has a minimal damage on the surfaces, and can weld together or eventually release all type of materials
If the damage is still an issue and as it is science fiction, you could even make it so the welding happen at the atomic level and therefore display no damages.
In reality a surface would be never flat enough and always contains impurity to allow such atomic level welding, this is why I add it as side note. (It can also bring a topic for an event in your story)
[Answer]
This is a totally separate approach to my previous answer.
Use a Web of non radar reflective material anchored to several points around the hull. Then build a smallish crawler that can hold tools, anchor your erstwhile space walker, and maneuver around the hull using the webwork. The anchors should be spaced around the hull in an even manner and have quick disconnect points all around so that repairing and replacing the webwork in case of damage is fairly easy.
Repairing damage to the outside of the ship would start with repairing enough webbing to get close to the damage, and then use the crawler as a mobile base to effect repairs.
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[Question]
[
Could an alien underground macroscopic ecosystem including human sized plant-like organisms evolve around lava as an energy source? These organisms could use heat and/or light from the lava to synthesize organic molecules. Would these organisms favor a particular shape? Would they be more likely to hang from ceilings than to grow from the ground? Could the presence of anything in the environment encourage this, such as reflective elements? Assume life could have evolved on the planet's surface originally or simultaneously.
It seems like this would encounter a number of problems such as:
* As calculated in this [post](https://physics.stackexchange.com/questions/136724/how-close-can-you-get-to-lava-before-burning), lava gives off very strong light, and humans at least have to be no closer than around 8 or 10 meters and at a sharp angle from the surface of the lava.
* Lava needing to have a constant relatively unchanged presence that could reasonably be adapted to across evolutionary time spans. What could prevent the lava from cooling that would also keep it in the same place and allow organisms to thrive?
* How quickly energy could attenuate from the lava source, this could force life into tighter spaces than other cave environments?
* The organisms might need a heat potential across which to do work. This could maybe take the form of cool hollow shafts in the rock to expel heat with, or the plants prefer to grow around corners or towards the energy source so that further back parts of the organism are cooler?
[Answer]
**Real cold lava ecosystem.** Does it have to be hot lava? Because that burns stuff up. There are cold lava ecosystems.
<https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes#Crystalline_Metamorphic_and_Igneous_Rocks>
The basis of this ecosystem is organisms which use hydrogen liberated from water using iron or sulfur. From the link "these ecosystems can exist indefinitely without any input from the surface."
**Heat as energy source.** Re using heat I could imagine that an organism which spanned a heat differential could cycle some molecule back and forth between the hot side and the cold side. The molecule assumes some energetic configuration on the hot side then at the cold side can be catalyzed to give up its energy to generate ATP. The organism might be a slime living on a geothermal heated hot rock with its top side in cool flowing water. Such environments are not uncommon but it might not be obvious that a slime was using an exotic metabolic path like this.
Iron oxidizing bacteria do something like this - harness the interface between two environmental conditions. They grow where water with reduced iron in it comes out of the ground. The iron will oxidize on its own pretty soon out in the air. The bacteria capitalize on this by oxidizing the iron inside their own cells and harnessing the energy released. The strands of this bacteria look rusty because they are making rust.
[Answer]
**No** you could not have a macroscopic underground ecosystem powered by lava.
At their most extreme [hyperthermophiles](https://en.wikipedia.org/wiki/Thermophile) can survive temperatures of 105C. Lava starts giving off visible light at temperatures ten times that.
The closest real world examples to what you are talking about are [hydrothermal vents](https://en.wikipedia.org/wiki/Hydrothermal_vent). These only support multi-cellular life up to temperatures of 80C.
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[Question]
[
***SETTING***
The setting is a fantasy world with magic, mystical creatures, knights and heroes, kingdoms, etc; a rather typical fantasy world (ie. Middle Earth, or Shannara Chronicles). In it, swords, bows, and armor are widely available, though slightly expensive. However, due to magic and aid from mystical creatures of fire, the quality of metallurgy and smithing far surpasses typical iron-age or renaissance metal work. Think early 1900's steel (WW1/Industrial Revolution Era). This metal is available to all kingdoms and peoples. Combustion, gunpowder, and steam engines have yet to be discovered so no explosives, guns, or modern vehicles exist. This also applies to machining tools. Precision boring, honing, and other machining tools are not yet available in this setting. Assume that cost of weapons and armor would increase marginally with this increase in quality, but to a typical soldier, mercenary, or adventurer weapons and armor could still be affordable.
If steel were of this quality, what changes would be made to typical weapons or armor? ([This table](http://www.d20srd.org/srd/equipment/weapons.htm#weaponDescriptions) contains a decent list of the types of weapons I am considering)
***WEAPONS AND ARMOR CHANGES***
Would weapons be lighter? If so, would typical longswords be replaced with sabers or rapiers? Would axes have greater penetrative power? Would certain types of armor be made irrelevant? Would there be armors with higher mobility? Would projectile weapons become more penetrative? Could bows and crossbows be given higher draw weights? If armor were stronger would it make certain weapons ineffective? Would durability increase significantly? What type of upkeep would be required for these weapons and armors?
***SECONDARY EFFECTS***
What about the effect of these weapons on people? Would wounds be more serious? Possibly less serious (cleaner cuts)? Would bone be cut or broken more easily with these weapons? Would medical treatments change? Could better steel improve medical treatment? (some magic is used for minor healing). Would tactics change or because the weapons are widely spread would things largely remain the same? Would the armor protect from death more often and lead to more focus on disabling and wounding enemies than on killing them? Would small groups of skilled warriors become more effective with better equipment?
I've searched around a bit and found some great information, but figured I would look for some better answers here.
[Answer]
You ask a lot of question. First and foremost I want you to understand just how effective armor really was: [This channel does a lot of testing](https://www.youtube.com/user/ThegnThrand/search?query=armor) [and here you can find a series called truth about linen gambeson/mail/plate armor](https://www.youtube.com/user/shadmbrooks/search?query=truth+about). So the point I'm coming towards is: armor is very effective and probably wins more than weaponry from increase in steel quality and therefore will be produced more and/or see more development.
Another thing to consider is that [a suit of high quality plate is very expensive](https://www.youtube.com/watch?v=wgRjGlzoRvk&t=1s) and assuming that your improving processes are add-on would more likely make it even more expensive. This by the way brings us to the second most important argument we have to settle:
**How exactly your magic works?**
Is it a post-process enchanting or a supplement for actual metallurgy processes? Is there a way to use it to not increase the quality but rather optimize the production and opt for more quantity? Or does your furnace dragon only agrees to lend his fire for master-piece craftsmanship?
One of the defining features of the Industrial Revolution is that many things became mass produced and therefore widespread - it is the revolution part, the evolution is increase in quality.
The answer to this question will be the answer you're looking for:
1. If it's only quality - armor evolves further but only for the rich and knightly classes. You may get master-piece level weapons but again only for the rich and powerful.
2. If quantity(through better metallurgy) can be achieved - I'd say you'll see a bigger variety of armor and weapon systems because whoever fields more better equiped troops wins.
The second one is more of a game-changer since now you'd be able to field heavy infantry and [heavy cavalry](https://en.wikipedia.org/wiki/Gendarme_(historical)) that are not knightly class but posses somewhat compareable equipment. A pikebox dressed in brigandine/cuirasses that can repel a charge of knights and advance onto the enemy despite the arrow fire will be an effective force.
Now some direct answers from me with a little back up:
**1. Would weapons be lighter?**
Mostly not, because [weight is not a drawback](https://www.youtube.com/watch?v=fdXxAB4jQTc) for most weapons.
**1b If so, would typical longswords be replaced with sabers or rapiers?**
Longsword did not evolve into repiers or sabres - Rapiers and Sabres became widespread after the role of armor diminished and are optimized against un- or lightly armored oponnents: one is for slashing, the other is for thrusting attacks.
However better steel may result in that [swords with sharper edges or different crossections may become more viable](https://www.youtube.com/watch?v=WloQRstJtXk&t=7s).
**2. Would axes have greater penetrative power?/Would projectile weapons become more penetrative?**
Only a marginal one, not enough to make a diffirence. Even a two-handed pole-arm with a spike doesn't guarantee that you'll penetrate a plate armor, hence why it dissapeared from a [polaxe and the hammerhead on it became wider and with a bigger number of mini-heads to not glance off](https://www.youtube.com/watch?v=J4zUFLGznxM) and [better transfer the energy rather than attempt to penetrate or dent it](https://www.youtube.com/watch?v=HzJY9OY7pzs).
If we talk about projectiles: you have to understand that Arqebus and Muskets advanced to a whole new level compared to Bows and Crossbows in terms of armor penetration capabilities: a 60g bolt that flies at 40m/s produces 48 Joules of energy, a 35g bullet that flies at 180m/s produces 567 Joules of energy(more than 10 times!).
**3. Would there be armors with higher mobility?**
If only slightly. The effect of weight through better quality is miniscule unless you want to dab into the territory of specialized alloys.
The mobility part [depends more on the fine craftsmanship](https://www.youtube.com/watch?v=K8hCjtMp8dU) rather then materials. The "precision boring, honing, and other machining tools" which you ruled out would've helped much more in this area.
**4. Could bows and crossbows be given higher draw weights?**
Draw weight is not the key factor, it is one of many but was reffered more to because of the lack of scientific understanding behind the damaging effects of the projectile. Here's an example of [a modern 180LB composite crossbow and 70LB compound bow outperforming a medieval esque 300LB crossbow](https://www.youtube.com/watch?v=eYsr81y0Aeo) the answer for this is [Kinetic Energy](https://www.youtube.com/watch?v=bqqnYOYF7Po) which cares about projectile mass and velocity(more so velocity hence why firearms are so much more effective with their 200-900m/s).
Draw weight is simply one of the ways to achieve more speed. Basically it's like "fuel consumption" if we make an analogy. Modern composite matierials or technologies(compund disc) allow to better translate the power of the draw into the speed than the steel.
But given your assumption better quality may result in bows and crossbows becoming more deadly(better velocities, longer range etc) if the metallurgy improves the right qualities such as [yield strength](https://en.wikipedia.org/wiki/Spring_steel). However don't expect the results be as groundbreaking as even early arquebus.
**5. Would certain types of armor be made irrelevant?**
If you can optimize the production processes Mail armor will become obsolete because Plate provides better protection and is now easier to manufacture(Mail requires a lot of manual labor and time to produce). The whole concept of interlocking rings developed because metallurgy could not produce solid plates of required size for a long time. [It will still remain as protection for joints though](https://www.youtube.com/watch?v=MrFwI4eFhf0&t=01s): neck, armpits, groin etc [because of the flexibility it provides](https://www.youtube.com/watch?v=OYbhzcgs70c).
Brigandine and other Coat of Plates types of armor may become either obsolete or insanely widespread depending on how optimized the production is. If solid plate of big size is easy to produce your world will go straight into full body breastplates and cuirasses, if it is not an easy process Coat of Plates will be the way to go and quickly replace Mail armor for those who can't afford full plate.
**6. If armor were stronger would it make certain weapons ineffective**
[Thing is armor already makes some of the weapons obsolete, but there are ways to work around given enough skill and luck](https://www.youtube.com/watch?v=vi757-7XD94). The question is how widespread your armor is to actually rule out weapon classes. However I doubt that levied peasants will be able to afford a suit of full plate to rule out edged weapons as at least sidearms.
**7. Would the armor protect from death more often and lead to more focus on disabling and wounding enemies than on killing them**
[This is exactly](https://www.youtube.com/watch?v=LdVYW9r2G3U) [what happened](https://www.youtube.com/watch?v=bf16NgeEI_U). However on a grand scale of things I'd rather call it "diversification" rather than "supplementation" that you hinted with the **"than"** in your question.
**8. Would small groups of skilled warriors become more effective with better equipment?**
Small groups always benefit the most from more skill and better equipment. Hence why we have all the spec-ops buzz. But again you have to understand that better steel won't make them into super-humans that can kill 40 people in one battle and then do it again the next day. A Machine Gun though...
**9. Would medical treatments change? Could better steel improve medical treatment? (some magic is used for minor healing).** Can't say for the surgeon part of the question but the last sentence may be a game changer depending on how you define magical treatment. If magic killing bacterias and viruses in the wound is considered to be minor(nothing like insta heals we have in RPG's right?) - I can envision more open but easier to mass produce cuirasses, sallets, burgonets and morions becoming widespread, because it will be possible to outfit heavy infatry/cavalry with armor protecting only the essential bodyparts for much cheaper and still guarantee surviveability because damage to the extremeties won't be as fatal as they used to be.
So to summ it all up: if you want more effect on the world you have to either opt for much greater quality through alloys(second half of 20th century and beyond) or more optimized production(like with dragons replacing Blast Furnaces and reaching better temperature at that) that will make the end products more widespread and affordable.
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Armor would be lighter or stronger (or some combination of slightly lighter and slightly stronger). That could affect infantry mobility.
You would see more light swords like the epee. That sword can only be made with good quality steel, otherwise it is too fragile. The epee isn't just a sport sword. It was designed to thrust through gaps in the armor (even eye slits) to make incapacitating attacks. That takes great deal of training so not everyone would be using these but a heavy sword just isn't going to move fast enough to block one of these.
For normal infantry, an upgraded version of their sword, spear or halberd will make them much deadlier. It was common for swords to bend or break when swung heavily against another sword or armor. Thus, the durability of the swords will be higher. Against enemies with lower tech armor, they would have a distinct advantage. If the enemy has the same armor, the effects would mostly cancel out.
The spear and halberd would benefit since there would be less weight on the far end and the wielder could swing them faster. A pike wall would be even more fearsome, I suspect.
Arrowheads would have better penetration but modern steel armor would pretty much cancel that out.
If you allow crossbows, they could throw their bolts with much greater force. Crossbows would be a huge game changer. The Pope outlawed their use in war because, even with their lower quality steel, the crossbow could throw a bolt hard enough to go through a nobleman's armor.
On the slightly trivial side, carriage rides would be smoother with leaf springs made from good steel.
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# Human strength stays the same
Warriors would attack armor made from better steel with weapons made from better steel. Even if the swords are less likely to break, and hold sharper edges, I do not think that they can cut through the armor as easily as before if they are swung by merely human strength. So how about this?
* Concussion from a solid mace might be better than concussion from a sharper sword, as long as neither can penetrate the armor plate. What is happening to the padding?
* Hastily armed peasant militias might prefer the flail instead of the spear, even if good-quality spearpoints were available.
* Hunting bows or slings won't be able to penetrate armor, so mercenaries will have an edge over a peasant mob.
* Picks or spiked maces might become more popular if they can still penetrate armor, and swords cannot. Better steel could keep the pointy bits from breaking easily, even against steel armor.
* Lances will remain popular longer, because of the added momentum of a charging warhorse. Perhaps with steel shafts?
(I realize that a historical sword would be unlikely to penetrate a historical cuirass, but other parts of the body had less armor. For simplicity I assume the proportions stay the same.)
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Improving the quality to modern standards would no impact worth mentioning as armor became redundant around 1350 with the advent of the longbow, and by 1450 it was consigned to history.
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A planet orbiting an Red m-dwarf is tidally locked to its sun. Can it have a satellite which is not tidally locked to the sun? Also can the satellite be tidally locked to the planet ?
[Answer]
The satellite to the tidally locked planet CANNOT be tidally locked to the star. The satellite, by definition, is orbiting the planet. While some quirk of resonance or chance could possibly result in the "moon" always having one side facing the star, such a set-up would not be through the mechanism of tidal-lock.
Tidally locking the moon to the planet is possible. Depending on distance form the star, the moon will likely lock to the planet prior to the planet locking to the star.
Mutually locking the moon to the planet (orbiting geosynchronously and always showing the same face to the planet) while the planet is tidally locked to the sun is likely impossible. The planets rotation takes a full year to make a single turn. This means a tidally locked moon would need to take a full year to orbit this planet. To do so would require the moon to be a significant distance away from the planet, far enough away that it would likely be stripped away from the planet into its own, independent, orbit of the star.
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**Can the satellite not be tidally locked? Yes.** Just look at a real world example of it on a smaller scale and you can see it's easily possible. Our moon is tidally locked to the planet but it's still possible to have satellites orbiting the moon. We have done so multiple times, even having people orbiting, and we still currently have a few active satellites still orbiting the moon.
**Can the satellite instead be tidally locked? Also yes.** All it takes to make something tidally locked is to have the time it takes to make a rotation around its axis the same time it takes to revolve around the main body. So you could in fact make a satellite locked to a moon, that is locked to a planet, that is locked to the star. Naturally it might not be easy but with some advanced technology and manipulation it's entirely possible.
The only thing that wouldn't be possible is simultaneously being locked to the planet and the sun. As the moon is tidally locked to the planet, like it is with our planet, we see the same side of it but the direction of the light from the sun changes, this is what causes the phases of the moon. But if you had a moon that was locked with the star and rotating freely from the planet I imagine it would be somewhat different. You'd see the entire body of the moon during its full revolution around the planet still leading to phases but more of the moon's surface would be visible. But I imagine you'd still be left with a "dark side" of the moon.
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It wouldn't strictly be a satellite of the planet, but if the moon were at the L1 or L2 Lagrange Point, both bodies would probably be tidally locked to the star, and would keep the same faces toward each other.
This would give the appearance of the satellite being tidally locked to the planet since the same face of the satellite would always face the planet.
If there are any other large bodies in the solar system, this would not be a very stable arrangement, but it would be cool to see while it lasted.
If a planet is tidally locked to a star and has a moon orbiting, the tidal forces between the planet and the moon would either move the moon out of the planet's grip causing it to go into orbit directly around the star or would cause the orbit to decay, break apart and create some very nice rings then fall onto the planet.
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In my world, zinc is useful as an anti-magic material. This ability manifested shortly after the discovery of magic, and now zinc will erode and decay when exposed to magic, dissipating into nothingness as it disperses the magical effects directed at it. This makes zinc more valuable than gold in the economy of my world. Magic users are a minority, and otherwise, the world is technologically and socially similar our own. Zinc alloys that are exposed to magic develop pockmarks and abscesses as the zinc disappears, leaving only the other metals. even simple brass machinery, like gears in a watch, or zippers on clothing will be rendered useless by exposure to magic.
Because zinc is so much more expensive, brass is now used mostly as anti-magic armor or melted down for zinc.
Is there a different material or alloy that could replace brass in most of its modern day applications?
this question is related to [Zinc is a precious metal. What alloys are no longer practical?](https://worldbuilding.stackexchange.com/q/71871/6737)
[Answer]
Brass is a fairly versatile material with reasonable strength and decent corrosion resistance. It is also quite easy to work, it can be cast, is easy to cut and machine and is ductile enough to be cold worked quite heavily (eg drawing cartridge cases). So it's most common applications are things which require good dimensional accuracy, corrosion resistance and moderate strength such as gas and water pipe fittings.
Bronze is closely related to brass, being an alloy of copper and tin with a wide range of different grades which may also contain phosphorus, silicone, aluminium, lead.
Bronze is a pretty versatile material and depending on the specific alloy it can be cast, machined, welded and cold formed and has reasonable tensile strength, hardness and wear properties.
It tends to be quite expensive largely because of the price of copper and tin.
Aluminium alloys are also a potential substitute for brass. It does require industrial scale electrolysis to extract ( a lot of aluminium smelting is done close to hydroelectric dams) but if the technology base can provide a local source of abundant and reasonably cheap electricity then it is fairly cheap to produce. The main limitation of aluminium is that it can't really produce alloys with high hardness so it tends to be less useful for wear critical applications.
Another option is steel, again available in a wide variety of grades for different purposes.
Finally a lot of the traditional applications which used brass now use various engineering plastics and composites.
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Say a star system in the local neighborhood (~15 light years away max) has a species that did not survive its own version of the cold war. The result is the usage of tens of thousands of nuclear weapons from plain old fission bombs all the way up to cobalt-salted multi-megaton thermonuclear devices. These weapons were deployed not only on the surface of the planet, but in the high atmosphere, low orbit, and points well beyond the planet.
Assuming a clear line of sight, would such an exchange be detectable here on Earth?
For the question assume the maximum total yield of any single weapon is no greater than the theoretical maximum yield of the Tzar Bomba (100 Mt). The Entire exchange took place over the course of one hour. Considerations for exotic weapons are just fine, but they need to be practical. A weapon that releases most of its energy in the form of neutrinos would not be an effective weapon for example.
Answers or links to resources that could help me find an answer are perfectly acceptable.
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In short: Yes, but you'd have to either be very lucky or be carrying out a continuous, 24/7 all-sky survey to catch it, and you would only see the chemical aftereffects of the war on the planet's spectroscopic signature, not the exchange itself (which would be too faint to be detectable at anywhere near Earthlike stockpiles of nukes). There was a study undertaken on the matter last year, along with several other apocalyptic scenarios, [which was summarized at surface level by The Atlantic](http://www.theatlantic.com/technology/archive/2015/09/alien-nuclear-wars-might-be-visible-from-earth/404176/) and is available [here on arxiv.org](https://arxiv.org/ftp/arxiv/papers/1507/1507.08530.pdf). The relevant sections, emphasis mine:
>
> Given that the world’s nuclear arsenal is equivalent to around 10^19 J of energy, the resulting radiation from its combined detonation would be much fainter than a typical GRB. If we assume that the energy is released on a similar timescale and with a similar spectrum to a GRB, a nuclear apocalypse is equivalent in bolometric flux to a GRB detonating around a trillion times closer than its typical distance. If we take a nearby GRB such as GRB 980425 (Galama et al 1998) which is thought to have detonated around 40 Mpc away, then we would expect a global nuclear detonation event to produce a similar amount of bolometric flux only 8 AU away!
>
>
> **Therefore, for us to be able to detect nuclear detonation outside the Solar system, the total energy of detonation must be at least nine orders of magnitude larger [than Earth global nuclear arsenal -- ed.]**, i.e. the ETIs responsible for the event must engage in massive weapon proliferation and concurrent usage. However, the production of fallout from terrestrial size payloads, which persists for much longer timescales, may make itself visible in studies of extrasolar planet atmospheres.
>
>
> ...
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>
> **Global nuclear war therefore potentially offers several spectral signatures that could be observed: a gamma flash, followed by UV/visible airglow and the depletion of ozone signatures. However, the aftermath of a global nuclear war will also act to obscure these spectral signatures.** Groundburst nuclear explosions generate a significant amount of dust that will be lofted into the atmosphere. Airburst explosions do not generate dust, but still introduce particulates into the atmosphere. Atmospheric effects of nuclear warfare have been extensively modelled in climate simulations, the global consequences being known as “nuclear winter”. Recent simulations have shown that even with reduced modern nuclear arsenals severe climate effects are felt for at least ten years after a global conflict, especially due to the long lifetime of aerosols lofted into the stratosphere (Robock et al. 2007). They show that the atmospheric optical depth is increased several times for several years. The worst effects are confined to the northern hemisphere given that the model includes conflict over the US and Russia, though the entire planet is affected to a lesser extent.
>
>
> ...
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>
> **Hence, to confirm that a planet had been subject to a global nuclear catastrophe would require the observation of several independent signatures in short succession.** One on its own is unlikely to be sufficient, and could easily be caused by any number of other processes on planets with potentially no biological activity whatsoever. There are cases beyond a global nuclear catastrophe that a spacefaring civilisation might be able to inflict on itself, given that the destructive energy at their disposal would be far greater than nuclear weapons (Crawford and Baxter 2015), including redirecting asteroids. These would be far more destructive than nuclear warfare but would generate observable signatures different than those of a naturally occurring impact event.
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Lots of people ask *where* should you go in an apocalypse, but I have a different sort of question. In a post-apocalyptic world destroyed by WW3 (nuclear warfare, anarchy and the like) If you were in a small group of survivors with ages of 14 to almost fifty on the outskirts of a city, where and how could a base be constructed?
REQUIREMENTS:
* Can be constructed from easily attainable resources
* Suitable for long term survival (Not just a lifetime... GENERATIONS)
* Can support 20 people
* Defensible against other people with improvised or scavenged weapons.
* Expandable in case of greater populations
NOTE: Electricity is not an option unless you figure out a way to generate it. Please inform me if you are in need of more specifications.
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The classic "motte and bailey" fortification would still work in this situation. Basically a central building surrounded by a wall. Placement is key, it has to be up on a hill or other defensible earthwork. Since this can be made of wood, just a few people with chainsaws could construct it in a few weeks. If they have access to a small bulldozer or cat then they could heap up earth to form the motte very quickly. Of course using concrete or cinder-blocks would be better, but they would need access to those supplies. Since you want this to be a long term fortification, it needs to be placed where there is water, preferably a well INSIDE the walls so it will be secure in the event of a siege. Access needs to be controlled, either via an open and easily watched approach or by a double gate system (only one door is open at a time so visitors can be examined and searched prior to getting inside).
Another option, especially if the geography isn't favorable to the M&B, is something like Fort Caslop (build by the Lewis and Clarke expedition). Basically a C shaped building with a gate closing off the "C", making a protected courtyard. The exterior walls have narrow windows to allow for defensive fire. This was built by a handful of men with axes and saws, so well within the capability of your group.
Are guns/explosives still around? Explosives will make short work of anything with wooden, and even stone, walls. In that case you need sloped earthen walls that can absorb an explosive blast or at least deflect incoming solid projectiles. Guns mean snipers. So you will need to clear EVERYTHING from around your fortification. No trees, bushes, small buildings, NOTHING for at least 500 meters around. This way you can enter and leave with little risk of getting shot and no one can approach undetected.
Using an existing structure would save you a ton of time. Big buildings with few windows out in more remote areas are what you are looking for. Fortunately warehouses and distribution centers fit this criteria. Find where grocery stores and places like Sam's Club get their stuff. Usually some big building on the outskirts of a city, away from residential areas, with easy highway access. The buildings are large, have an open layout inside, and have few or no windows but have long loading bays with rolling doors. Then you can reinforce the entry points, guard the access road, and put observation windows wherever you want. Of course without electricity to run the A/C things will get hot in the summer but hopefully you have a little nuclear winter going on to help with that :) You can even add skylights to let in sunlight so you can grow plants indoors (assuming there is any sunlight). Collect the rain water runoff in cisterns (if it is potable and not filled with radioactive fallout).
[Answer]
Basically you are asking for the design of a fortress.
Obviously, you want to build it around a source of fresh water, or more precisely, a well, since streams can be dammed, poisoned and whatnot.
After that, a lot depends on the ability of your survivors, the tools they have available and are able to use, and the threat they anticipate.
Most of their food source will lie outside the fortress, but living quarters will clearly be inside, as well as storage facilities.
You will want high, robust, forbidding walls on the outside as soon as you can afford to build them, and windows, balconies and whatnot on the inside to make best possible use of daylight.
Most likely you will have one and only one entrance, and you will want this entrance to be as narrow as possible, and you will add defense positions around it.
Everything else is really a question of taste, imagination and possibilities.
So i guess this fortress will change a lot over time. It will grow not only to accomodate a hopefully growing society, but also to reflect the fact that building fortresses takes time.
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I would not go hide in a grocery store because of the large expanses of glass. Imagine what would happen if you came under fire. Schools would be a good idea because they are designed to keep shooters out. The school cafeteria would still have some food in it and you can stock it. Electricity would be tricky.
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The best buildings to repurpose would be records repositories. They are warehouse like structures which are sealed and (so long as there is power) climate controlled. They are generally built out of concrete, are fireproof and have few windows to the outside world. A records repository building in the city where I live is on the outskirts of town and is identifiable from the other buildings in the industrial park by its rather fortress like appearance (even compared to warehouses and light industrial buildings).
Of course being inside one is a bit of a drag, it will be dark and musty (although you will have millions of boxes full of paper records to burn for fuel whenever you ned to cook or heat the place). You will also need to drag in all the supplies you will need for your group, and potentially build a tank or storage pond to hold a sufficient supply of water. Since the repository is likely surrounded by a large fence, you can potentially repurpose the rest of the space (and tear up the parking lot) to create a farm, so your long term survival should also be taken care of.
So be on the lookout for a records repository near where you live or are setting your story. Insurance companies, hospitals and governments all require repositories, so if there is a sizeable hospital or insurance company in the vicinity, it is likely there is a repository nearby as well. Government repositories will come in all sizes, from small "county records office" structures to elaborate underground fortresses in salt formations for federal records.
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Is it possible to grow plants or raise animals underground, in a way that is enough for 1 person to survive and easy enough to maintain?
Conditions:
* underground;
* without any on-going help from the surface (some initial help to set the system up is acceptable);
* Without sunlight;
* technology level can be described as modern.
[Answer]
Yes.
If you have a water supply, which can largely be recycled, and a nutrient supply, which can be recycled (sterilized human waste even) then you don't need much room.
They say it takes 1 acre to feed a person, but with hydroponics you could have multiple levels in a small area, growing more vertically than horizontally, and save a lot of space.
[They are setting up farms in New Jersy night clubs](http://qz.com/705398/the-price-of-leds-is-falling-so-fast-its-profitable-to-farm-in-a-new-jersey-nightclub/) to provide locally grown food to urban environments.
[](https://i.stack.imgur.com/VxwNY.jpg)
[Answer]
Sure you just need electricity and water and something to convert O2 to CO2
You run lamps to replace the sun light and create a farm. You water it and breath to convert the O2 from the plants to CO2 which they can use. The farmer needs a supply of fertilizer ( it may be from him to keep the soil rich) or he needs to rotate crops in that replace lost nutrients like soy beans.
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Now the first question is—which elf? Santa's elves? Shoemaking elves? Keebler's cookie-making elves? Tolkien's elves? The Dökkálfar (dark elves) and Ljósálfar (light elves) of the original Norse mythology?
My first proposal is this—let's mix the latter two together, the "dark" and "light" aspects reflecting an African-European division. The reason I'm mixing Tolkien's elves with the original elves is that both categories are quite prominent in the high fantasy subgenre.
Now the most obvious difference between us and elves is the pointy ear. In the mammal world, this isn't so far-fetched.
[](https://i.stack.imgur.com/BSZ69.jpg)
Foxes have pointy ears.
[](https://i.stack.imgur.com/dJxrG.jpg)
Bats have pointy ears.
## **BUT WAIT!**
The fennec fox's ears are just too big for someone supposed to reside in the frigid forests of northern Europe, and a bat's ears are too naked for the same thing. So my proposal is this—don't make the ears themselves pointy. Instead, let's keep the human ears but cover them with hair, going as far as giving them tufts, just like the ears of a lynx.
Another obvious difference between us and them is that elves are immortal. Now, biologically, we can't make any lifeform truly immortal, but we CAN lengthen the telomeres, repetitive nucleotide sequences at the base of each chromosome, to make them live longer. A "biologically immortal" organism, as scientists would call it, would still die, but senescence (think "senile") would not be an existant cause. My proposal is that we lengthen the telomeres to the extent that the average elvish lifespan is triple-and-a-half greater than the average human lifespan.
This would suggest altering the elvish metabolism from endothermy (generating an internal body heat system, therefore keeping temperature constant) to [mesothermy](https://en.wikipedia.org/wiki/Mesotherm).
As always, enlarged respiration and tetrachromacy will include the elves on the list of candidates.
Tolkien described his elves as "slender" and "graceful, yet strong". My proposal to make that description more concrete is to, essentially fit a musculature as dense as a [Bowflex body](https://consumeraffairs.global.ssl.fastly.net/files/cache/news/bowflex_large.jpg) onto a skeleton as slender as a [gibbon's](http://67.media.tumblr.com/74daee7b0077a5d1afe46f19fcd555f8/tumblr_nwachbeL4D1t0yvi9o1_1280.jpg) (while at the same time retaining the human proportion.)
My final proposal differentiating elves from humans may be the most radical — **hermaphroditism**. To be specific, ***simultaneous hermaphroditism***, which means that each and every adult has both male and female sex organs simultaneously active. Unlike humans, there is no clear-cut distinction between a male elf and a female elf.
Are any of my proposals listed above sound, or have I created some unintentional side effects to the elvish body?
[Answer]
Ears are a pretty simple change, so I'm just going to gloss over that and go straight for the more interesting bit: the hermaphroditism. While true hermaphroditism is a very extreme change, there is actually a connection between increased similarity between the sexes and long life. Animals which take a long time and a lot of energy to grow are often helpless at birth, which means they need more care, which can mean an increased push toward a monogamous lifestyle, since it promotes both parents caring for the young. This connection is seen in many birds, as well as humans - as sexually dimorphic as humans are, human males and females are much more similar than than males and females of other great apes. I would say not to push them so far as to be actually hermaphrodites, but to make the sexes extremely similar to the point where it is almost impossible to tell them apart if they are wearing clothes.
These elves can be seen as a continuation of some of the same evolutionary processes that led to humans, perhaps developing in a more static environment where adaptability was less important. They can be more intelligent (elves are supposed to be wise, right?) with the drawback of being born even more helpless and taking even longer to grow. Perhaps elves are born tiny, like bears - this would make pregnancy and childbirth much easier, decreasing the need for the widened hips of the female. A small mutation is all it takes for human men to produce milk, maybe in elves both parents nurse the child. These two changes would cause the burden of child-raising to be much more evenly divided between the parents, leading to decreased sexual dimorphism. Elves may be either highly monogamous or alternatively sexually communal, as is the case in bonobos. Sexually communal elves would probably share the burden of raising children among all members of the tribe.
An elf might not reach sexual maturity until around 40 years old, but could live for 300-400 years. Further drawbacks are very similar to what is assumed for traditional elves - the slow reproductive rate would mean that elves are less adaptable than humans, which also means that they are likely to be more risk-adverse. They would likely be culturally stagnant and less likely to migrate from their original home. However, the increased intelligence and lifespan might allow them to develop technologically anyway.
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Which voltage and frequency would be selected if there were no legacy issues?
I can easily find how selection of electricity frequency and voltage was based on backward compatibility and quite arbitrary choices. I'm impressed by the Japanese who are able to keep two frequencies in one country. The question relates to an early 21st technology level and what would be the most logical right now.
This is the relevant information that I found:
The US military uses 400 Hz, as it allows smaller rotors, but it would be hard to use that on much bigger scales as transmission losses would go up.
There seem to be quite few electrocution deaths and quite serious transmission losses in low voltage systems, so there might be a tendency to increase voltage to save energy. Would it be worthwhile? Would just converting voltage before delivering it to household be efficient enough?
(Please, no Tesla, no war of currents... I would not like to see Americans having their holy war here...)
[Answer]
Goals-
Don't kill people
Transfer electricity cheaply and efficiently
The power loss when transferring electricity = P = IV (current \* voltage)
and V = I\*Rwire ( current \* resistance of wire)
or P = V^2 /R = I^2 \*R
So to minimize power loss when we have a high R (miles of wire) we drive V very high
Then we want to maximize power available to the consumer for a smaller R
The same equations apply, so if we can convert the high voltage low current flow to a low voltage high current flow we make much more power available.
The conversion from High V low I to low V high I is very easy in AC current we just put a uneven inductor between them.
The conversion in DC is much more inefficient. This is why we would like to use AC.
What part of electricity kills people?
Well It has to have enough voltage to get through humans skin ( a few volts).
The easiest way for electricity kill a person by triggering nerves thus causing muscles to spasm (including the heart and lungs) giving people heart attacks. The key to doing this is to have electricity pulsed at the same frequency and nerve cells pulse (which is around 60 hz) Which is the frequency of household current in the US.
So you would want 2 voltages 1 high voltages for transition lines and 1 low voltage for home lines, they should be AC and very far from 60hz in frequency)
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One constraint on the frequency is that you want it high enough not to cause annoying flickering in your lighting. So you probably don't want to drop too much below the UK 50Hz - I know movie frame rates are 24 fps, but trying alternate eye LCD shutters with a low refresh rate definitely flickered noticeably for me.
You also want a voltage high enough that you can deliver enough power (V x A) to your high demand devices - like heaters, cookers, and washing machines - without worrying about I squared R losses in your connecting cable - halve the voltage, and you need to double the current, which gives you four times as much loss if you keep the cable the same. Or you can go to more expensive thicker cable...
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Ideally this would be some sort of sun or star-related natural disaster that would affect the entire planet and make life outside of protected/shielded areas extremely dangerous. This is a human-inhabited planet, and while many people will be living in domes built specifically to guard against this catastrophe, others will be left out in the open to fend for themselves and while I don't want them to be wiped out completely, their chances of surviving should be slim.
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According to [Gizmodo](http://gizmodo.com/what-would-happen-if-a-massive-solar-storm-hit-the-eart-1724650105), a coronal mass ejection (CME) isn't going to do more than fry the power grid and anyone/thing using it at the time. [CMEs](http://earthsky.org/space/what-are-coronal-mass-ejections) aren't bursts of fire. Instead, they're superheated charged particles. When the CME reaches the Earth, they interact to produce geomagnetic storms and spectacular auroras, but no fire. So they're pretty, but not particularly dangerous to those protected by the Earth.
Gamma ray bursts (GRBs), on the other hand, are the most energetic explosions in the universe and are [immensely dangerous](http://www.universetoday.com/118140/are-gamma-ray-bursts-dangerous/). If the Earth were hit by the one of these, there would be a worldwide extinction-level event and the atmosphere would be ruined for decades, centuries, or longer. Anything on the surface directly in the beam's path would likely be incinerated in short order. You would need a shelter in the deep ocean to have a decent chance to survive such a catastrophe. Of course, there's [some evidence](http://www.slate.com/blogs/bad_astronomy/2013/01/21/earth_hit_by_a_gamma_ray_burst_did_a_cosmic_blast_hit_us_in_775_ad.html) that mankind has endured such an event, so maybe not so farfetched after all...
Would either of these cause firestorms? A CME may spark fires indirectly, by causing a geomagnetic storm that unleashes a vast amount of lightning that starts fires; this is how an [electromagnetic pulse](https://en.wikipedia.org/wiki/Electromagnetic_pulse) can conceivably start a fire, and the two operate on similar principles. A GRB, on the other hand, can definitely start fires. Lots of fires.
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It's unlikely that an extinction-level GRB would cause a firestorm. Not impossible of course. Put it close enough and you can have it vaporize the biosphere ... and "close enough" may mean a few thousand lightyears with its axis pointed our way. These are events which make supernovae look small!
But the orders of magnitude less unlikely scenario delivers a pulse of radiation that doesn't even give us lethal radiation sickness. What it does do, is ionise a significant fracation of the O2 and N2 in the atmosphere. These recombine to Nitrogen oxides. This in turn destroys the ozone layer in seconds on one side of the planet and in days on the other. The Sun's UV does the rest. Afterwards, if you survive the sunburn, there is decades of nitric acid rain to look forwards to. Exit most of the terrestrial food chain.
Terrestrial life would be decimated or utterly wiped out depending on the GRB strength. Marine life would also suffer badly by acidification of surface waters. Deep water life might not notice much. There is a lot more mass of ocean than air.
If you want a firestorm you should probably invoke a large meteor like the one which did for the dinosaurs or a little larger.
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A sufficiently large CME? You bet it could cause firestorms or worse!
Coronal mass ejections subject the earth to increased radiation, much of it quite damaging to life forms, if not shielded by the magnetic field.
So you don't want to be at the poles during a bad solar flare.
A sufficiently energetic CME/Flare could overpower the earth's magnetic field -- a really big one could cause intense heating (even firestorms) by hitting the atmosphere and surface with high-energy protons and photons (UV, x-rays.)
FYI, I recommend Larry Niven's short story, "Inconstant Moon."
<https://en.wikipedia.org/wiki/Inconstant_Moon>
(which was also made into an Outer Limits episode.)
Enjoy!
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My world has magic and I would like to check a few things about it. Feel free to correct me if I'm way off-base.
My magic is basically an energy conversion process. You take energy from your environment and convert it into something else. For instance, fireball, light or other fun stuff. I should clarify that it only needs to *look like* a fireball, light or other fun stuff to the average medieval farm boy. It could actually be anything else as long as it has the same effects and visuals.
Anyway, to enable that process, you need a sentient caster with a body. The universe will not have it any other way (actually, it will, but it's not relevant here).
However, in order to convert energy, from what I understand, you need some more energy. This problem is dealt with the introduction of the Unbestanum effect. Said effect allows transdimensional particles to dump energy into our own dimension. It is as if you had an unlimited magical energy tank somewhere that you could tap into. The energy from the Unbestanum effect is what powers the energy conversion.
Consider the caster plus the Unbestanum effect as your conversion system. You still need to input something if you want a fireball, and that input is likely going to be air. Because air is just full of the heat and it's also right there. So, in principle, you take air, input it in the conversion system, and voilà, fireball. The conversion system is sufficiently powered to produce the desired amount of output because it's magic.
About how many rules of physics and thermodynamics am I breaking with that principle?
Taking that principle (and possibly adjusting for fewer broken rules), is there a limit to how many forms of energy I could output if all I had was air, unlimited power supply and maybe some ground (though I can't see why that would be helpful)? If there is, what forms of energy would I be able to output?
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It depends on just what sort of energy conversion you want to allow. Let's go straight to the crazy end... I mean... let's find the upper limit to what's allowed by thermodynamics.
The [mass-energy of the surrounding air](https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence) is the famous E = mc2. If you divide by the mass you get E/m = c2 which is the mass-energy per unit of mass. c is the speed of light at 3x108 m/s so c2 is 9x1016 m2/s2. A [Joule](https://en.wikipedia.org/wiki/Joule) is kg m2/s2. ***That works out to 9x1016 Joules per kg or 9x1013 Joules per gram***.
[1 liter of air has a mass of about 1.275 grams](http://www.wolframalpha.com/input/?i=mass+of+1L+of+air), so a caster easily has at least 1014 Joules available.
How much energy is that? Looking at the handy [List Of Energies By Orders Of Magnitude](https://en.wikipedia.org/wiki/Orders_of_magnitude_%28energy%29) we find ***1 gram of air can power a small nuclear bomb, or a hurricane for a bit less than a second***. That is *a lot* of energy.
Yes, if you allow wizards to convert mass into energy they can produce quite a [large fireball](https://en.wikipedia.org/wiki/Nuclear_explosion#/media/File:Operation_Upshot-Knothole_-_Badger_001.jpg).
[](https://i.stack.imgur.com/ocIqd.jpg)
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The only really limiting factor amount of air have available to you since you technically are using air every time you make fire. Of course you always add another Limiting element, perhaps something related to the caster, maybe there's some sort of limit of trans-dimensional energy one magic user can use at a time.
Also is theoretically possible to convert matter to energy so maybe you could use the ground in your casting.
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## My Magic System
All of this stuff about my magic system is actually necessary, because I know no-one reads links provided to them and because there is magic in my world.
**Brief Overview of Magic**
Magical powers fall under seven broad categories. Air, water, earth, plasma (fire/lightning), plants, light, and animals. Animal magic is tricky, because living things resist magic. But, many animal mages can influence animals, and some can control dead animals (this is called necromancy and is a big societal no-no.) The strength and scope of magic varies from individual to individual. But, these are the most common in order. Earth, water, air, plants, animals, plasma, and light.
These magical capabilities are like the show Avatar, the Last Airbender, in how controlling magic works. However, in my book magic is much less powerful. For instance, an earth Mage may only be able to influence as much dirt as they could lift, and lifting this dirt would take about as much energy as doing it by hand, except you don't have to touch it, and it could be a perfect brick shape. No force is exerted in separating the dirt or material from other similar material attached to it. So if you were to pull this rock in two, that would take little effort, other than the force of pushing the pieces apart.
Magic is like a muscle that is really hard to develop.
**Magic on a larger scale**
The level of magic described above is only about 75% of magic users. Everyone else is more powerful.The strongest people can do things like shoot lasers, uproot trees, be human flame throwers, make zombie hordes, create small tornadoes, cause rovers to overflow or to break dams, or cause small earthquakes. This is about 7% of the population. Everyone else is in between.
**Magic on a smaller scale**
I'll just make a list of some possible fighting applications of magic. Ice daggers, water whips, wind influenced arrows, starting fires, shooting small fireballs, throwing stones, moving stones, strangling people with vines, tripping up enemies with plants, scaring/exciting horses, and flashing people. (With lights!) These are of course by no means the only applications of magic.
**Magic Resistance**
Living things are resistant to magic, proportional to their intelligence/self awareness. So it would be easiest to make a swarm of spiders, then harder to make boars attack (your enemies, and not yourself), and nearly impossible to make someone slap themself. There is a type of stone resistant to magical tampering, which is found deep underground, near bedrock. Also, bones are immune to magic.
Note - These things are resistant to magic being influenced directly upon it, not magically influenced material. A rock thrown by magic at someone is just as effective as a rock thrown without magic at the same speed.
## Some background
Thunderbirds fly ahead of approaching storms, preying on pretty much any animal larger than a goat. However, they don't generally attack anything the size of or larger than a buffalo. So your buffalo herds are generally safe, with an occasional calf stolen. People often own pigs, goats, sheep, cattle, horses, and a tamed livestock version of [terror birds](https://en.m.wikipedia.org/wiki/Phorusrhacidae). These birds are used as pack animals.
These birds are just that, large birds of prey. They have no magic. As for their size, they can carry up to 1200 pounds, so plan for their size accordingly. Comparatively, a bald eagle can carry 5-6 pounds. (I'm not really sure how much they'd have to eat, so that can be an optional part of the question.)
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# The Question
This is all taking place in medieval times. Assuming it rains about once every week, how would this affect ranchers and the like? Would they have special shelters for their livestock when it rains? After all, you don't want your entire flock of sheep munched by a giant bird. Would squads of magical people shoot fire at giant birds?
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No magic required. Have a large group of men on horse back with bows and Spears accompany the livestock. That should be enough to deter Thunderbirds. Predators usually go for easy prey. Not the prey that fights back. Of course that might be different if the Thunderbirds travel in packs.
Because of the expense of hiring people to guard your flock only the rich would own herds.
Alternatively if you could predict when a storm was coming (if it's true that the Thunderbirds always follow before storms.) You could put your cattle into caves and wait for the Thunderbirds and the storm to pass.
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If giant birds are regularly visiting your herd and they show upfront that they are coming, why not use a few of your sheep as prey and try to hunt the big birds? Seems like that could be a good way to get a lot of extra meat!
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Farming system in medieval times would be either let your flock roam across the hills or leave them fenced up in a forest. In a forest they should be safe ffrom thunderbirds. On a moor your average sheperd would probably lose a similair number of sheep to wolf attacks or the sheep falling of cliffs as from thunderbirds, they coped with these so they would probably cope with thunderbirds.
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I've been thinking that the natural manner for interstellar dispersion of humanity with relatively hard science is with permanently habited nomadic generation ships. Instead of building a ship, going to a suitable system and abandoning the ship to colonize a planet model which comes with enough issues that it might be impractical, the generation ship in this model is the permanent home of its habitants.
Dispersion comes instead of the fact that it is both mobile and self-sufficient, so that it can move across interstellar space without any particular need for speed. A ship like this could use low thrust engines such as ion drives or, closer to stars, light sails. Since space has relatively low aerodynamic drag, a very low thrust would allow an orbit that is an expanding spiral that gradually leaves the system. So assuming that the generation ship is "permanent home" simplifies requirements a lot.
Even more so at the destination since it really causes no hardship if colonizing the planets is difficult or even impossible. The ship will simply restock its volatiles and materials needed for repairs and people will go on living in their home just as before.
To be self sustaining the ship would need to have redundant everything and capability to manufacture **every** component from raw materials gathered from asteroids, comets, or other micro-gravity objects. It would also need to be a fully self-contained ecosystem. And have the capability to rebuild the ecosystem if necessary.
Obviously such a ship would also have to be capable of building duplicates of itself. Indeed any reasonable planner would require demonstrated ability to self-replicate before risking interstellar space.
Thinking about a suitable solution for such a ship, I ended with a design similar to real life. A very large "bubble" with relatively thin skin and filled with water. The bubble would have all the space propulsion and navigation systems attached to it. Maybe "tugs" pulling the bubble with long cables? You want smaller spaceships for mining anyway, so dual purpose miner-tugs might be good.
Inside the bubble would be "rings"; large structures of the titular shape, each of which is a self-contained habitat with spin gravity. The "rings" would float freely in the water with perfectly ordinary water propulsion systems for moving around. The "rings" will each be fully self-sufficient with all the life support and manufacturing needed. But they could rely on other "rings" for redundancy and the "bubble" would take care of propulsion and protection from space hazards. So while each ring would have roughly the population and manufacturing capacity of a conventional generation ship they could be simpler and smaller.
When a ship self-replicates, they build a second "bubble" attached to their current one and move some of the "rings" to the new "bubble". They then move on and build new "rings" as required by population growth until the "bubble" starts becoming full and it is time to build a new "bubble".
Like I said this is similar to how life does it, so it should work fairly well. Such redundancy through self-replication should enable enough robustness to colonize even interstellar space, and thus eventually other systems, provided interstellar space has enough objects to support such nomadic ships. Which AFAIK we do not know one way or another.
Now to the actual questions:
**How large should the "rings" be** in both population and, approximately, physical size. Physical size only needs to be credible enough for verisimilitude since nobody actually knows how much space the needed life support and manufacturing capacity would take. We can't really build any yet after all. I am more concerned about ideas for optimal community size here.
\*\*The optimal minimum and maximum numbers for "rings" in single "bubble". The minimum is the number needed to be robustly self-supporting, while the maximum must obviously be at least twice as much for self-replication to happen. But you probably would want some safety margin to allow population growth even when building a new "bubble" is impractical.
**The size of the "bubble".** This is obviously the physical size and mass of the "bubble" which would be pretty much the mass of the entire structure. Needs to fit the maximum number of "rings" and support enough photosynthetic algae to provide oxygen for the entire population. It will be much safer if it has an entire ecosystem up to fish since such diverse systems are more robust.
**How much "skin" is needed to contain a bubble of water in space?** The skin would get punctured by meteorites and radiation damage so it should be self-sealing and repairable. You can assume the outer layer is cold enough to be ice if that helps. What kind of pressure is necessary to maintain?
This is asking pretty much, but I am hoping for some useful ideas.
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So to figure out size, you have to determine all the stuff that needs to go in it.
**First, [population](https://en.wikipedia.org/wiki/Generation_ship#Biology_and_society).**
On the low end, the minimum viable population could be around 180 people, and with the right breeding you could have enough diversity for 80 generations or 2000 years.
Other estimates say you wouldn't want less than 14,000 people, and as high as 44,000 people, because of disease, accidents, etc.
So lets say 10,000 people to start just to have a round number.
You need to feed them, so how much land do you need to feed one person?
Numbers I'm seeing say it takes [about one acre](http://www.farmlandlp.com/2012/01/one-acre-feeds-a-person/) to grow the food to raise a person. You might be able to get it lower with things like high capacity hydroponics, vat grown meat, raising fish in the bubble, etc, but you're going to want to have room for other things besides growing food.
**How much of the ecology are you bringing along?**
If you want to bring along plants and animals in different biomes for maximum diversity, then you'll need more land. If you are ok with bringing them along in another form, like printing out their DNA from stored patterns and growing them in artificial wombs, then you'd need less land.
Starting with the 10,000 acre number, which is a little less than 16 square miles (40km^2). Lets up that to 30 square miles for redundancy and room to grow.
You want it modular so that you can make more easily, or maybe even move them around, so lets say you make them from pods that have a square mile of space each. The pods are joined in groups of 10, like beads on a necklace, into rings with a 10 mile circumference. That's a diameter of a little over 3 miles.
At that size, you could have it spinning at only 0.43 rpms and still get 1g.
This would get you 3 rings, about a mile thick, and 3 miles across.
This gives you a pretty good idea of how large the bubble should be.
**Next you have resources.**
People need a lot of things that might not be available from asteroids and comets, and that would be lost over time by bonding with other elements, getting lost in the soil, etc. Some important elements might even bind to the metal of the inner hull. And once gone, there would be no way to get them back.
You could potentially make more using fusion, but if you discover that your great great great grandfather forgot to pack enough selenium 1000 years ago, making more is going to take almost magic level fusion technology.
Maybe if you happened to pack one of the reactors from [SpaceChem](https://en.wikipedia.org/wiki/SpaceChem), it would make things a lot better.
Salt buildup is going to be a headache too, but by using the water in your envelope you might be able to use it as a sink, so bringing salt water fish and desalinization equipment might be an option.
**Society**
So 500 years into a 2000 year voyage, and people who never saw Earth and who will never see the destination are starting to wonder what they're doing out there. They never asked to be on this voyage.
You might want to think about what to do about unrest and mutiny along the way.
**Lastly is disease**
Small things change a lot faster than us big things, especially in a closed environment. Your bacteria, fungus, viruses, and other things are going to be changing very fast, and so both you and your plants are going to be stewing in it. Having a strategy for wide spread crop failure because of a new blight is going to be important ahead of time. Same goes for human diseases.
**Edit addressing comments:**
First, disease. We kind of have a symbiotic relationship with bacteria, and if you sterilized us completely we'd die.
Plant's have a similar setup. Soil is a living thing, full of bacteria, small organisms, fungus and lots of other things. If you removed all that stuff, the plants wouldn't be able to grow.
You might be able to remove some of it, or create soil from scratch with only the stuff in it that you want, but even a little bit is enough to potentially cause issues down the line over centuries. It may be avoidable to some extent, with planning.
Society issues are a potential problem during times of hardship.
Not enough food, birth restrictions, leadership seems weak, something important breaks.
It may never be a problem, especially if it's the only think known, but any time you get a group that has more than one option, you'll have differences of opinion to deal with, which could lead to strife, which could lead to fighting...
It's worth at least planning for to some extent.
Resources... One of the parts with the question is that there is a chance that down the line there might be a split, where a second ship could be made. They could make all the parts for a new ship, but halving all the supplies on the ship would have to be planned very carefully. It would be one way to reduce population if it got to high and there was a world with enough resources to allow it.
It could be very low decks, or hydroponic stacks, or whatever. The gravity wouldn't be coming from mass like on a planet, since there is no way to get enough mass to make a difference. Instead you have a rings spinning to make centripetal force to simulate gravity. The larger the ring, the slower you can spin it and still get the gravity you want.
A small ring needs to spin very fast, and the Coriolis effect can get pretty bad. Anything over 2 rpms could have adverse effects in the long term.
The further under 2 rpms, the easier it is on people, as a general rule.
The minimum size to keep at 1g and under 2 rpms is 223 meters in diameter.
If you want to play with different sized wheels, check this site out: <http://www.artificial-gravity.com/sw/SpinCalc/>
And really, all these are just ideas to consider.
If I missed anything, or misunderstood, let me know!
**Edit 2:** Further addressing
Disease
I get what you mean by sterilize now.
Yeah, you could sterilize a whole crop, though that would be slightly harder if you're growing in dirt as the disease could live there and infect the next crop. Maybe hydroponics so all the water can be stripped of nutrients and boiled. You could even have modular, self contained pods for them, keep things separated so if something does start you wouldn't lose the whole crop, just a pod.
BTW, this is what I mean about a hydroponics stack:
[](https://i.stack.imgur.com/yL6qU.jpg)
Also, [prions](https://en.wikipedia.org/wiki/Prion) are a disease that could develop spontaneously, as they are just misfolded proteins, which could happen from cosmic radiation.
There's no way to completely sterilize the ship when it's a set of biomes or while living things are on it. And destabilizing the micro-biome could be worse than leaving it be. Keeping things balanced might be a good goal.
Otherwise, yeah, start off as clean as possible and find ways to monitor things as you go along, in case something weird begins to develop.
Society
It probably would be more stable, especially with emphasis on having a mission.
So long as people don't lose sight of the vision.
Gravity
I understand what you meant now. Yes makes perfect sense.
If they are going somewhere to plant a colony, they might even want to match the local gravity so as to be used to it by the time they get there.
Also, you might be able to get rid of a ring by having an inner low g ring and an outer normal g ring on each torus. low g could be agriculture, manufacturing, etc.
Resources
So we're probably on the same page here...
So say each ring has the room and resources to support 5000 people.
You could have one bubble with 10000 and 2 rings, or two bubbles with 5000 and 1 ring each. If you split it up, and then after 100 years you decided to build a new ring in one of the bubbles, you'd have to find a planet or some other source of minerals to stock it.
That'll have to happen once in a while anyway, because no matter how closed the system is, there will be losses over time.
Vital minerals can bind to the walls of the ship as a kind of patina. You'd then have to recycle the panels to free those minerals.
It might not be a bad idea to have some kind of renewal plan in place; recycle each part of the ship over time, kind of like how our bodies replace every cell every 7 years (or something like that).
For an example of things that could go wrong on a generation ship, check out Aurora by Kim Stanley Robinson.
Not saying you should make that kind of story, but it might give you a couple ideas.
All the numbers just possible examples. You could go bigger or smaller easily enough.
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Our war with the plants has been unending for thousands of years. And we don't even know it exists.
Plants strategize, doing their best to survive, but the humans are relentless. Constant removal and replanting of plants ruining their wide-spread intelligence system, especially while many regions of plants are cleared and converted to the humans' evil offsprings. The plants humans like to plant are all incredibly useless due to their genetic modifications.
You see, plants communicate with other, the signal spreading from plant to other nearby plants not unlike neurons in a brain. This communication gaps even the ocean through algae or other ocean "plants", though algae are more carriers of the signal rather than actual processors.
Sightless, and without ears, how might plants be communicating with each other without us even realizing it?
If you can't tell from the setting - being a little ridiculous is okay, but try to refrain from straight-up magic.
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# Plants Already Talk
Check out this [minute earth video](https://youtu.be/vk-12s7tB_Y). Yes, it's edutainment, but they tend to be accurate in what they present. Also, check out this [TEDx Talk](https://youtu.be/aClSp71zfro) by Prof. Ariel Novoplansky.
Plants learn, and talk to each other. They do it through their roots, and through chemicals in the air. Sometimes they even talk to animals! The [Botany of Desire](https://rads.stackoverflow.com/amzn/click/com/0375760393) puts forth the idea that the plants are using us to be biologically successful. War on plants? Maybe you should think as some plants running the world, and us their proficient servants.
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I think the two easiest ways for plants to communicate would be thus:
* **Root System**: Like in the movie *Avatar*, all of the roots connect somehow through the ground. This would also mean that certain areas would not be able to communicate directly because there would be areas where roots could not penetrate (like solid rock). To bypass this issue, the plant would do the second thing ...
* **Air System**: Whether through some type of spore or pollen, where a single plant creates the spore/pollen with embedded information. The information is then ejected into the air where other plants pick up the spore/pollen, reads it, then passes it along.
While we humans would think this is all natural, it would be providing a means for passing information and for a communal nature of the plants.
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In one biology class I was asked to envision the history of the Earth for the last many millions of years as a raging battleground between the grasses on one side and the trees on the other.
The trees had been advancing steadily on the grasses slowly pruning them back (ha!).
Until the grasses enlisted the aid of humans. Now humans are the grasses front line soldiers. We annihilate entire armies of trees - felling them like dead wood, stacking up, and then burning their remains.
For our services, humans demand a blood sacrifice from the grasses - we eat their progeny (the grains).
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* How can I explain that it **only rains at night** (i.e. from dusk till dawn) in a certain region?
* Can or must I make this meteorological phenomenon apply **planet-wide**?
* Can or must I restrict rainfall to a **certain season**?
* Could it rain each and **every night**?
* What would happen during a **total solar eclipse**?
(On an alien planet this could happen more often than on Earth.)
* Is there a place like that **on actual Earth**, in which climate?
(I know it tends to rain each evening *before* sunset in tropic regions which can support rain-forests.)
The preferred, but not required, climate is moderate to warm with little influence of the seasons on highest (~ 30 °C), average and lowest (> 0 °C) daily temperatures. The sun must not shine too hot or bright, i.e. Earth-like vegetation (grass, bushes, trees, crops) must be possible. Geologic features like mountain ridges, ocean sides etc. can be chosen freely, as can humidity.
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I would suggest the concept of "rain cloud seeding" - using chemicals that promote the formation of clouds (and rain) could, on another planet with the right chemicals, create regions or an entire planet that is subject to nightly rain. With a little imagination and research, you could possibly tune this to the extent you would want it to work.
<https://en.wikipedia.org/wiki/Cloud_seeding>
For example, during the day, the heat evaporates water from the surface (and the surface covered by more or less water than Earth). Simultaneously, chemicals that seed clouds might remain very high because of the heat. As night falls, the water vapor hits the high altitude seeding chemicals as they condense, causing rain.
Another approach might be that the seeding chemicals are ineffective when energized by the sun, and then be reactive as the sun sets.
You would need to be careful to research seeding chemicals and how they would impact the ecosystem in general. It might be a stretch, but perhaps there are one or more chemicals that could co-exist in a significant enough quantity while also allowing Earth-like life to form.
I would suggest that, given the narrow range of temperatures you require, it is unlikely you could find the right climate to support rainfall only at night at any or all places on such an alien planet. The one exception might be a slowly rotating planet that retains daylight heat on the surface, allowing the atmosphere to cool long enough that by morning, the air is too dry to ever be capable of producing rain. But a heat retaining planet that does not get too hot during the day (or too cold at night), to me seems much more far-fetched than an atmosphere with cloud seeding chemicals that biological life can tolerate or that stays out of the biosphere.
[Answer]
The daily rains that we know happen in this way:
1. Sun warms the surface
2. The surface warms the air above it while moisture evaporates into that air
3. The warm, moist air rises and hits the cold air above, forming clouds
4. As sunlight intensity wanes, the air cools more and it rains.
To have it predictably rain every night, you would want the air at cloud altitude to stay warmer and slowly cool during the night. This will allow more cloud buildup and a longer if lighter period of rain.
If your planet has a layer of gas/particles at the top of the troposphere that not only can reflect radiated heat from the ground back down to the clouds, but also retain some of that heat, it might create the effect you want. This is not too dissimilar from the effects of some kinds of pollution we know on Earth, but I can't tell you which exactly.
You might have this locally with specific geography. If your land is between a sea and mountains and has a steady wind blowing in moist air from the sea, it will always rain in front of the mountains, as the air again is pushed up into colder air and sheds its moisture in the form of rain. Again, the sun causes evaporation over the sea during the day, so rain will fall as many hours later as it takes the clouds to reach the mountains.
[Answer]
You might consider having your world and life-forms rely on another liquid than water. Different elements theoretically might respond differently to light. That will change a lot of stuff, probably (maybe even all the rules), but it's something to think about. [This article may be insightful](https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry). It talks about how life could theoretically be based off of different elements and compounds.
[Answer]
During night, water could condense from the air as the sun's heat would not be forcing it to remain a vapor. Yes, this does not happen on Earth, but if the concentration of water-normally-suspended-in-the-air-because-of-diffusion was higher, it could. It could not be planetwide, however, as only half of a planet is in shadow at any given time.
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[Question]
[
## Premise
Architecture is often a reflection of culture and as it is plain to see, architecture varies from culture to culture such that as you travel around the world you see things change from one style to the next.
Some boundaries are obvious. You fly over some mountains and bam...totally different place. But more often that not its a more gradual change.
**Questions**
1. Is there a field of study related to architecture and how it changes between cultures (and how it acts where said cultures overlap)?
2. Is there a way to model this along imaginary/fantasy world borders?
3. Are there any resources you would suggest to dig deeper into this topic?
[Answer]
1. The closest field of study I can think of is called [vernacular architecture](http://www.vernaculararchitecture.com/). It is the idea and study of how non-professional architects design and build structures in their local region throughout the world. There are also some outlying studies and books written about anthropology and architecture, which may be worth looking into, but I wouldn't say there is a specific field of study about this. I may be wrong.
2. This is tricky because there are so many factors that affect the spread of culture (architecture). Vernacular architecture relies a lot on the climate, geology, and materials available in a given area. For example, you wouldn't likely see adobe homes in a temperate forest, or igloos in a non-arctic region, even if the two areas are bordered and culture can freely spread between them. Likewise, the political nature of the culture matters greatly too. Are they nomads, with no permanent settlements? Then you might see their architecture, such as it is, bleed into surrounding areas more rapidly. How militaristic is the culture? How forcefully would they impose their culture on conquered poeples? Alexander seemed to impose Greek culture to those he conquered, more so than the Romans imposed Roman culture. Mongols were both nomads and militaristic, but that doesn't mean that everyone they conquered moved into yurts. Any models to consider the spread of architecture would have to consider many such factors.
3. I haven't seen the inside of this, but this [Atlas of Vernacular Architecture of the World](http://rads.stackoverflow.com/amzn/click/0415411513) seems like an interesting resource. You can also search online for other maps of vernacular architecture.
[Answer]
Architectural history, like most human history, is largely tied to human migration patterns. Traders bring home ideas and aesthetics as they travel. Conqueror's impose architecture as they colonize new realms. Romantic flashbacks as old sites are re-discovered and mirrored again (Think the greek/roman feel of many older european museums and government houses)
There are lots of resources on architectural history and influences freely available on the web, and a lot of it is very interesting.
[Answer]
**Urban Planning / Urban Design**
Keep in mind that almost any older city is a blend of different cultures. Tunis was Phoenician, Carthaginian, Roman, Traditional Arab-Islamic, and Modern, and there are elements of all of those infused. Istanbul is another great example.
Well as an urban planner in the Gulf, we had to do just that. Our goal as part of [Abu Dhabi 2030](https://www.youtube.com/watch?v=Yz-hguqZCKg) [skip to about 2:00] was to create an Arabic city of modern cultural heritage. This included blending the modern structures of the West and Asia with traditional heritage design of the Bedouin.
The answer to your boundary lines is that there likely won't be physical boundaries. You start to see a mix of the two cultural architectural traditions throughout the urban fabric. For example, a metro station that uses [mashrabiya](http://img.archiexpo.com/images_ae/photo-g/panel-screening-mashrabiya-appearance-119503-6392081.jpg) design from the tenth century for passive shading in the desert heat. Elsewhere along the beaches we instilled the designs of traditional dhow (fishing boats) sails into the covers of buildings such as the Formula One Race track.
The latter is very much 'modern meets tradition,' but this can also happen with two parallel cultures. The gulf culture prefers high separation to public and private space. So tall modern complexes had unique blends of design alterations to continue this blend of west meets middle-east.
To learn more about this particular combination of cultural design smash-up (Western vernacular with Arabic colloquial), you can [visit the projects we did](http://www.upc.gov.ae/?lang=en-US). Otherwise, any Urban Planning book (my favorite is Cities of Tomorrow) will give you a historical perspective of how the architectural and spatial vernacular of cities were arranged.
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[Question]
[
In a world where cybernetic replacement is common practice among military, how and why would a cyborg whose organic tissue has died maintain a human identity?
This partly comes from just liking the visual image of a robot combined with a skeleton, and the notion of translating common fantasy tropes such as skeleton warriors into a sci-fi setting, but also ties into issues of death and identity.
The setting I am imagining is post-post-apocalyptic, the world is mostly war-torn anarchy with some factions working together (based on other fantasy trope translations) but with little connection to the human dominated current era.
One exception I have considered to the 'dead organic matter' is that the necrodroid could have possession of a line of cancer cells from its originator, but it would not have original brain or nerve matter.
[Answer]
Once the organic material in a cyborg dies, it either needs to be replaced, or the cyborg dies. You cannot keep the dead tissues working; if you could, they wouldn't be dead, after all.
How does the cyborg maintain his human identity? Well, as long as his brain is still functioning, you might as well ask how an amputee maintains his humanity. This would be a highly philosophical question, but scientifically speaking, your "being" is in your brain.
So what if the cyborg's brain dies? This leads us back to the above statement: He either replaces his brain, or he dies. There are of course different ways he could replace his brain:
### Cloning
Essentially, as long as you keep cloning your original tissues, nothing else matters. Only, a human's "being" isn't made of only his brain, but is also formed by knowledge and experience. Or in other words: External influence. To maintain his human identity, the cyborg would need to somehow copy all information from his old brain to the new one; a backup of sorts.
### A new brain
Here, your cyborg just takes one of several brains available on the market. Morals and ethics aside, as long as the new brain is compatible with the cyborg's inorganic components, there's nothing wrong with using a different brain.
Just like with cloning, the cyborg would need to backup his old brain first. He'd also need to wipe his new brain clean, lest he wants to enjoy his newfound schizophrenia. And finally, he'd need to ensure his new brain works the same way as his old one, or else he might behave differently to certain stimuli, which would arguably impact his identity.
### Cyber upgrade
When old tissues die, what better excuse to replace organic components with inorganic ones? Using a powerful microchip instead of some inefficient and highly sensitive brain certainly has its advantages; immunity to concussions being one of them.
In order to maintain his human identity, the cyborg would not only need to restore a backup of his old brain, but he'd also need to ensure the chip emulates his old brain as closely as possible. Naturally, he'll eventually adapt to the fact that he no longer has to hold back when head-banging, which would impact his identity, but that's inevitable.
Once the cyborg's using a chip instead of a brain, you might ask yourself if he's still human in the first place. That is also a philosophical question. In fact, it's not just a single such question. There's the [Ship of Theseus](https://en.wikipedia.org/wiki/Ship_of_Theseus) which is about the question: *If you keep replacing small parts of a ship until none of its original parts remain, is it still the same ship?* And there's also the question: *What does it mean to be human? Can a machine be human as long as it behaves like a human?*
---
Regardless. As long as the new brain holds all of the information of the old one and is capable of processing those information the same way the old brain did, your cyborg should retain his identity at the very least. Whether he's still himself or even human in the first place, that's something you'd better ask the philosophers.
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[Question]
[
As we see today the interconnection between the brain and computing is becoming thinner day by day, we could imagine a future that where we could install additional artificial neurons.
In a world where you could routinely buy these type of extensions, you would be accustomed to connect/disconnect a part of the brain.
The world building question is: **How would it be like removing or adding such a neuronal mass?** Would you loose some memory/ability, would it be more like an effort scale? Would you easily pinpoint core abilities that could be just switched on/off? would it be difficult to harness this additional neural network, and when you disconnect from it, what changes could you notice? Could you pinpoint an aspect of the memory of a fact/event that would be stored only in the extension? Would it be valuable to have different extensions? I guess you could not exchange them, and they would not be exchangeable because they would have been trained with your brain configuration, but what would you feel if you just tried once, or a little longer?
To restrain the complexity of the question, I'm considering these extensions as:
* giving only more neuronal networks matter (no complex emotional or new organs connected with hormones release or any important chemicals needed by the body).
* being lumps of artificial matter that you would wear (and by this mean connect) with various interfaces directly to your neurons.
* The max section of communication could be considered up to the full 2d surface of coverage of your head the extension would provide (each organic neurons of this surface could have its state mirrored technologically with an artificial version on this surface in a 2-way sync)
* The technology behind the artificial neuronal network wouldn't be conceptually far from the virtual ones we use today, except these would be physical and would be **comparable in density and mass to brain's grey matter**.
* These would be **bought blank**, but wouldn't wear off or need replacement even on a life-time period. They would take probably weeks, month, years to harness and produce a noticeable effect.
* They would be an everyday life object that we would have a lifetime to be accustomed to, especially since early childhood.
* There are no technology allowing to control what happens with the neurons more than just interacting with the interface they give through our natural brain's neurons connected to artificial neurons on the surface of connection.
* You won't have any technological means to help you storing a specific memory or ability inside an extension.
* An individual would have access to different extensions (bought by the individual or provided by its job or by a state) for different occasions with bigger/smaller mass
* there are no limit to the actual time individuals can wear such a peripheral and this would vary depending on the individual's habit.
* You can consider the whole surface of the brain accessible to these extension (either because the whole brain is accessible directly after surgery considered as very common, systematic and accessible, or because of a technology allowing to 2 way connections with individual neurons through the bone.)
* A typical extension would be the size of 200gr meat steak shaped lump that you would wear on the back of your head that you could wear on any occasions. But you could think of whole helmet going up to 5 kilograms of artificial neuronal matter (that you wouldn't wear in casual occasions, but typically for work).
* A typical individual would easily possess between 1 to 5 of these 200gr meat steak shaped extensions and would wear one or two, 90% of the time.
* For some cultural reasons (like natural life style or religious beliefs or obscure medical reasons), it wouldn't never be integrated as a non-removable part, and humans would value the fact to be able to remove these peripherals from time to time to enjoy life extension-less.
* The location of extensions on your head could be of importance (visual processing is on the back of the brain, language in Broca's area).
[Answer]
I will only address a few points here, but I hope it will help:
First, a mass of neurons has functions by the virtue of its topology. If you buy "blanks" of neurons, I'm thinking you're imagining a group of neurons which will readily form synapses once they start being used by the brain. It will take time for that to happen. If the extension is non-neuronal (maybe digital, providing some specific functionality), then the area of the brain where you connected it will have to adjust itself. This area might or might not be able to discover the functions provided by the extension. Not sure you can help it consciously either.
When you wear a neuronal extension the first time, you'll have to "train" it to perform whatever function you want. Choosing the function you want it to perform is greatly dependent on *where* on the brain you're connecting it. Actually, that's probably the only thing that matters - you can't connect an extension to the back of your head and expect it to *not* be trained as a processor of visual information. Once you train an extension, you won't be able to use it anywhere else on the brain (unless you somehow reset it). Also expect the area of the brain to create quite an intimate relationship with its extension, and it might be difficult to attach another blank extension to the same are. Or worse, you might not be able to disconnect that extension without compromising the functionality of an entire area of your brain - the extension might become fully integrated, and not be an extension anymore!
Your brain will also change gradually with time, so if you're not wearing an extension for long enough, it might become incompatible, even if the extension itself has preserved its neuronal topology perfectly. Your brain is flexible all the time. And the extensions should also always be responsive of changes in the brain.
Your extensions will also be completely personal and 100% incompatible with anyone else's brain. This means that each person might value their extensions greatly, but anyone else couldn't care about them at all (unless through some advanced analysis in a lab).
Disconnecting an extension won't feel like anything. You would just stop feeling like you know whatever it was that the extension was providing, or you just stop thinking the thoughts that the extension was generating while connected to your brain. Basically, "extension connected" means some things happen, "extension disconnected" means certain things stop happening.
Though **maybe** your brain might eventually get used to disconnecting extensions and it will invent a feeling of "forgetting", specific for disconnecting an extension.
[Answer]
>
> How would it be like removing or adding such a neuronal mass?
>
>
>
With your premises it won't be a dramatic change, since you aren't adding/removing the core parts of the brain. Adding shouldn't be bad at all, except for the additional effort that the brain should sustain to "map" the new extension. Since it's more or less an empty hard drive with computational power is up to you to decide which info it should keep and which "software" it should run to process these info.
On the other hand, when an extension is removed, the user should feel only some degraded cognitive functions. Imagine when you feel to know someone's name but you can't actually recall it? Same sensation, you know that you should remember it but you can't, no big deal, it's already part of our natural aging process.
Another similar case is if you remove some mass that was trained to perform specific tasks, you correctly remember that you were able to do something but suddenly you can't. I don't think that by removing the extensions you could remove some basic skills, and as long as you don't it's not a big deal.
I don't really comprehend why people should occasionally remove the extensions sometimes but i guess that "religious" beliefs is enough to justify such a behave.
Actually, on a second tought, there's no need to rprovide specific justifications since "getting drunk" is usually considered a funny free time activity, and it basically consists in paying to have some "natural brain extension" bypassed for some time. :) In some hard cases you risk to have also some core functions bypassed, and this was proven to be source of really bad thing for you and for others. :(
Anyway, the main outcome would be to have unpleasant feeling because your [processing metacognition](https://en.wikipedia.org/wiki/Metacognition) kicks in, letting you know that something wrong happened. Probably with the habit to add and remove extensions this feeling could become less annoying.
>
> These would be bought blank [...] They would take [...] time to produce a noticeable effect.
>
>
> You won't have any technological means to help you storing a specific memory or ability inside an extension.
>
>
>
The best comparison that came to mind is to purchase a new laptop/mobile: you need some time to fill it with contents, and these contents can't be your abilities or your real memory. You usually have the device with you but for some reason sometimes you can't, and in these cases it could be really annoying (you need urgently to remember a phone number and to make a phone call, but you forgot your phone at home). Tanks to the extension (like a calculator) you got used to do complex calculation and you started to think yourself as a really fast person with math. When you have to remove the extension your math capabilities are not totally gone, but reduced a lot, and your metacognition starts telling you that you used to perform way better and this feeling sucks.
Knowing that it's only a matter of connecting and disconnecting extension you can rationalise ad keep this bad feeling under control or, as we usually do on holidays, you may want to remove some cognitive abilities to actually think less and just relax. So you won't forget the phone, you'll leave it at home on purpose just to avoid the stupid phone calls that you have to do every working day.
IMHO your extensions design seems to be perfectly usable and comfortable (so far).
[Answer]
From personal experience - it doesn't feel any different. Since the instrument you are measuring with is the one that has discontinuities, you have no internal basis for making a comparison.
However, you can indirectly observe that things that used to be easy are suddenly much more difficult or impossible. For example, a decade or so back I was one of those people you never play scrabble with. I'd regularly drop two three tiles and rake in 150 to 250 points. I can't do that today.
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[Question]
[
When creating a new culture/civilization, I tend to reproduce the relational logic I know.
For example, I often use the family "type" I'm the most used to (two parents + children).
However, other familial structures are possible. The [Iroquois](https://en.wikipedia.org/wiki/Iroquois_kinship) see children of a paternal uncle or maternal aunt as siblings. The [Mosuo](https://en.wikipedia.org/wiki/Mosuo) people have no concept of lasting marriage and mothers raise their children with their family, without the biological father.
We can also imagine new systems, like a culture where the children of your neighbors who are the same age as you are considered your cousins.
The same problem applies for things like power distribution and subordination in an organization, relations between masters and servants, rules of inheritance, etc...
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How to create original and coherent social structures ?
What methods should be used to model these systems ?
[Answer]
**Family units can be as diverse as you want** as long as they meet the needs of the individuals involved. The classic "two parents + children" is common because it naturally organizes around human reproductive patterns. As cited in the OP, many other patterns are possible.
As long as the family unit or broader social structure can provide for the following conditions, it should be a viable family unit.
* Sexual needs of adults
* Companionship needs of adults
* Creation of children.
* Care and upbringing of children
* Resilience to disease or accident
* Determine where a couple will live (if marriage is a characteristic of this unit)
* Not prevent a member of that unit from realizing all levels of Maslow's Hierarchy.
When viewed this way, it's easy to see how different organizations can satisfy all these requirements without adhering to the 2Adult+Children formula.
There's also the normal dichotomy between patriarchal societies and matriarchal societies.
**Possible Group**
Adults in the group have no expectation of sexual monogamy (there is a downside in this that if someone gets an STD somehow, everyone gets an STD). Adults are free to form emotionally intimate relationships with whomever they please though this may tend to be also with their sexual partner. Children are raised communally and owned communally. Mothers know which child is theirs but it doesn't matter to them. Resources are also communal. Organized this way, any one individual may be injured, ill or killed without large impact on the raising of children or functioning of the community. Children would live in a larger central building since the community takes care of them instead of two parents. Depending on the group's attitudes towards communal knowledge of sexual partners, adults may need to create their own private space for sexual activities or there's a space designated somewhere for those activities.
[Answer]
We start with the **type** of social structures. Here are a few quick possibilities:
**1- Economic Structures**
In a quasi-socialist society, the richer an individual gets, the higher number of children he/she will have to support for the society. These children will be called "his/her" children. So Mr. Adolf might be a virgin aged 20 years, but he has inherited 3 children after his father died. Note that Mr. Adolf's father was his economic father, not his biological father. In this society, your father/mother is the person who is your economic caretaker. One's biological children can stay with them only if they can sustain their needs as the government sees fit. Else, they will be given away for sustenance to a wealthy person as their children. They will know their biological parents, but their social security and ID cards will name their economic parent.
**2-Platonic Vocational Circles**
Here all the children belong to the society. They do not know their biological parents and live together with other children in a training facility. So we get technical circle, beauraucrate circle, business circle etc.
**Methodology**
What you need to do is to define the base variable of circle formation. What is the main thing (family ties, economic support, training etc) that determines where one belongs? Once you decide that, you have to develop a structure based on that variable and the things get going.
Let's say we want to create a structure based on IQ level. It simply means that people are grouped together in the society based on their IQ. This is step 1.
Now we need to start dividing the society into groups. People belonging to IQ range 130 and 140 would be belong to Beacon Circle. Then people between 120 and 130 who would belong to Genius Circle. Then people between 110 and 120 who would belong to Sharp Circle ... and so on.
[Answer]
One rule you can follow for social structure creation is that they must be easy for individuals within the system to learn and remember. There is a cost to remembering and modeling relationships. It's easy to remember 4 variants of a single relationship than to remember 4 unique relationships. A relationship which costs more from society to remember than it provides in return to that society is quickly selected against.
One pattern I have found shows up often is self-similar relationships. An example of this is the corporate hierarchy. You can remember the role of the CEO, the president, the VP, the upper manager, etc. all the way down to you if you choose. However, it is also easy to remember it as a pattern: unless I'm the CEO, I have a person I must ceed authority to; unless I'm an entry level worker, I have people who must ceed authority to me. And, in fact, this pattern works well even if you forget the first caveat: the CEO must ceed authority to the board/shareholders.
Also worth remembering is that relationships are complicated and often mix with one another to create more specific relationships. This is very visible in different parenting methodologies. Some elect to mix "parent" with "friend." Others elect to mix "parent" with "authority figure." This mixture is more efficient than trying to develop exact roles for each relationship. These sorts of relationships are often intentionally fuzzy, to permit mixing. Caste relationships, on the other hand, are intentionally not fuzzy, because the culture has found it most efficient to not mess with them.
[Answer]
Social systems are emergent complex systems, and can be described with system analysis and in he language of complex systems and graphs.
For example, I quote from [here](http://theanarchistlibrary.org/library/gavin-mendel-gleeson-complex-systems-theory-anarchism)
>
> In order to understand how societies can be modelled by systems theory
> it is instructive to look at some simple examples. In feudal Europe
> the organisation of society was exceptionally hierarchical. This is
> modeled in systems theory by a sort of control graph, which is a tree,
> with the lord at the top and his immediate vassals below him. In this
> structure it was possible to approximate, in many circumstances,
> control over a group of people with control over the leader of the
> hierarchy. This has a large number of consequences.
>
>
>
[](https://i.stack.imgur.com/doXQB.jpg)
>
> If the behaviour of the system can be modeled by behaviour of the
> lord, then the system can not act in ways more complex than the lord.
> Because of this, the system remains simple. It also means that the
> system can easily act coherently. It is capable of leading armies, and
> interacting with other feudal states in simple ways.
>
>
> In reality no perfect control hierarchies exist. There will always be
> lateral control links, various types of conspiratorial actions etc.
> However, for feudalism this model often remains a good
> approximation.As we move through history to early capitalism we start
> seeing a move towards more “hybrid” models of control, where many more
> lateral links exist and the system takes on the possibility of
> evolving more decentralised, more complex behaviours. In addition, it
> becomes less brittle. One might conjecture that feudalism was in some
> sense doomed when capitalism arose because the environment of
> interaction became too complex. The modern world has moved to a highly
> interconnected network-model capitalism. This is almost the antithesis
> of feudalism within the framework of the connectivity of the model.It
> is important to note a few things about the network model. Networks
> can have vary different internal structure. A large amount of
> interconnectedness does not rule out particular internal patterns, in
> fact we know that many complex systems, including social networks,
> don’t have “random” graph structures. This internal structure can have
> big effects on emergent behaviour. All networks are not the same.\*
>
>
>
So what this is suggesting is to draw a picture showing the relations between your social entities. Each person can be one node, but a corporation or a family is a collection of nodes. You can also have non animate things like religious symbols or buildings as nodes. Look at how complex what you have drawn is. Are there missing links between nodes that plausibly ought to be there?
Any pattern of regularity, or clusters of highly connected nodes have the potential to be identified as the next layer up in the various layers of a complex system (which is generally always a pyramid with the emergent and more highly complex behaviours on top of a lower complexity layer below it.
The feedbacks between the entities and levels of hierarchy in the overall system characterise you social structure.
There are general 'rules' that apply to all complex systems whether we are talking about a human economy or a weather system. Even a convection current in a room of your house qualifies.
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[Question]
[
## Context
This question is part of a set about a world where supernatural creatures exist. Some on these creatures are ["invisible"](https://worldbuilding.stackexchange.com/questions/23401/what-would-the-culture-and-traditions-of-invisible-people-look-like) humans (not trully invisible like Susan Storm, but unremarkable/unmemorable), and their remains are used to make magical items, like hidden doors or [police-proof bags](https://worldbuilding.stackexchange.com/questions/23485/cargo-of-a-supernatural-smuggler).
## Meat-town
A village is built using **human remains** (bones, hair, muscles, skin, etc.), only the interior furniture is normal. The "material" used can be hardened/modified using chemicals (for example, the skin is tanned to make leather) but not fixed together with nails or screws.
To restrain the scope a bit, let's say that the village should be able to accommodate 28 human-shaped creatures and each inhabitant should have at their disposal a personal space of at least 6 square meters. The buildings can be anything from one-room huts to shared 12 rooms "mansions".
The climate is cold and dry, with a few snowflakes in winter.
I don't think the materials used here would be resistant enough to support a second floor, all my solutions are for one-story buildings.
---
I thought of three possible architectures:
**Flesh bricks**
Blocks of flesh are compressed in brick shapes, dried and treated using silicone. (I know an artist used this method to make sculptures out of dead bodies but the firewall at work stops me from doing researches, so more on this latter)
These bricks are then used to build small houses.
The problem here is that I don't know how firm the bricks would be, and how high meat and silicone walls could be.
**Bone walls**
Houses are build using mostly bones, held together with ropes made of either intestines or hair. Problem : these houses would be drafty as hell.
I'm not sure how I could make doors and shutters so for now, in both meat houses and bones houses, windows and doors are covered by simple skin curtains.
**Skin tents**
Tanned skin and pillars made of bones are used to build large tents. The advantage of this method is that the village can be moved seasonally.
---
## Questions
Which one of these architectures is the most realist and why?
If these are not feasible, is there a better method (or mix of methods)?
How should I shape the buildings to improve their durability and comfort?
**Bonus :** Could you estimate the minimal volume of dead bodies needed to build one house?
[Answer]
>
> Which one of these architectures is the most realist and why?
>
>
>
Flesh bricks is the least realistic. If you already 'need' to use 'meat' to make bricks, where are you getting the knowledge and resources for the silicon?
Bones and skin (leather) are already used by different native tribes to different extents in the real world for homes. The native american [Tipis](https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=tipi%20lether) used leather, though they had saplings for the structure, and some Eskimo's used [whale bones](http://www.glenbow.org/thule/?lang=en&p=outside&t=enhanced&s=3-4&q=4&mi=1) as the structural supports in their buildings.
>
> If these are not feasible, is there a better method (or mix of methods)?
>
>
>
Bones and leather certainly can make a decent building. Human bones however can be problematic because of their small size. Using sinew to tie bones together, you might be able to make some ribs to build a small tent.
How should I shape the buildings to improve their durability and comfort?
Now for human bone construction, part of it comes down to volume of bones available. Take the [catacombs of Paris](https://www.google.com/search?q=crypts%20under%20paris&espv=2&biw=1858&bih=1019&tbm=isch&imgil=DPupiODEebg9DM%253A%253BSSen9XmEo501yM%253Bhttps%25253A%25252F%25252Fthetruthbehindthescenes.wordpress.com%25252F2010%25252F10%25252F30%25252F10-famous-crypts-and-catacombs%25252F&source=iu&pf=m&fir=DPupiODEebg9DM%253A%252CSSen9XmEo501yM%252C_&dpr=1&usg=__4ppX-6MJ31xJ7PUVbpExzSRlXds%3D&ved=0CEsQyjdqFQoTCMqyuc2p6scCFQlDkgodISEEnA&ei=7VfwVYqIKYmGyQShwpDgCQ#imgrc=DPupiODEebg9DM%3A&usg=__4ppX-6MJ31xJ7PUVbpExzSRlXds%3D), there are many 'structures' built out of human bones and with some batting, could be fairly snug and 'comfortable'.
But using bones and treated body parts (leather, sinew etc) are the way to go. Maybe even treating the intestines to make 'string' or rope such as [catgut](https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=catgut)
[](https://i.stack.imgur.com/EkXuN.jpg)
[Answer]
I'm not sure about the solidity of flesh bricks, and I think bones are not long or strong enough to make big houses using a girder architecture.
I propose an alternative combining your first two ideas : [timber framing](https://en.wikipedia.org/wiki/Timber_framing#Half-timbered) ([maisons à colombages](https://fr.wikipedia.org/wiki/Maison_%C3%A0_colombages))
Timber framing uses shorter girders, that could be big bones or rather bones bundles. Smaller bones could be used to fill the frames and your silicon-flesh dough could cover theses bones to impermeabilise the walls.
Since you do not want more than a floor, even the longer girders do not have to be very long. Walls would be one to three "floors" of bones frameworks as long as the longest humans bone you could find (legs), filled with your very disgusting meat dough.
Once you decide the size of your houses, you can easily calculate the very minimal dead bodies by counting the number of leg bones to make your frameworks.
Carved and well-adjusted wide bones like scapulas or hips could make a roof like wood tiles.
[](https://i.stack.imgur.com/KhQoT.jpg)
You could think about thatch (chaume) for the roof with hair or intestine since you mentionned it, but it will take a lot of material.
[](https://i.stack.imgur.com/3ELeT.jpg)
You might look at [this question](https://worldbuilding.stackexchange.com/questions/15013/are-bones-and-skulls-actually-good-building-material), if it's not already done.
Now I feel as insane as you, I hope it helps !
[Answer]
How about a hybrid:
Use bone tied with sinew for the structural elements, use skin for the weather seal. Look at what primitive peoples built out of animal products, other than size you should able to do something similar with human remains.
At first glance you might say you can't roof the building with bone but you can--a dome.
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[Question]
[
Some time far in the future, biologists develop a compiler targeting DNA. We could now create any kind of lifeform we wanted.
In the process, biologists also disassembled and decompiled human DNA into the language the compiler understood.
Prior to this, we also figured out a way to augment the DNA in every cell of an existing organism — or even replace it entirely, although that wouldn't be very useful.
One of the immediate effects of the compiler, combined with our ability to change the DNA of a living organism, was cancer being cured. They just made DNA verification during mitosis more robust (although this also somewhat stops mutations which, in the long term, means stopping evolution).
How might
* humanity use this to benefit themselves or solve existing problems through the augmentation of the human body and/or the creation of new lifeforms — e.g. as an alternative to robots?
* the augmentations and the creation of new lifeforms backfire on humanity?
[Answer]
[**There's No Free Lunch**](https://en.wikipedia.org/wiki/There_ain%27t_no_such_thing_as_a_free_lunch)
The one thing to keep in mind is that everything comes with costs and tradeoffs. You give a good example with cancer vs evolution. Another one to consider is muscles.
Humans are obviously weaker than we could be. Many [closely](http://www.slate.com/articles/health_and_science/science/2009/02/how_strong_is_a_chimpanzee.html) related animals are much stronger than we are - at least by a factor of two. And the reason for that is we traded raw strength for endurance. It's not as flashy, but it worked out better for our ancestors.
So at baseline, we could mix and match attributes, even from animals, but we'd have to take the good with the bad. We could probably make someone super strong... but at the cost of making them fade after a few minutes. Maybe we can enhance senses, but messing with the brain so you can use them impacts intelligence, or increases metabolic requirements. These are all enhancements that might be positive on the short-term individual level, but might be negative when viewed from a longer-term evolutionary standpoint because they remove flexibility to changing conditions.
You also can't just take systems in isolation. Take giving humans wings. It's not just a question of tacking them onto the back - you need to modify pretty much every part of the body. You need a different muscular system, you need to lighten and hollow bones, you need to change the eyes... that's a ton of different inter-connected systems, and it will be fiendishly difficult to modify them all to work correctly together.
Enhanced abilities generally also map to increased calorie requirements. So this type of thing might be common among the elite - who can afford both the treatment and the lifestyle - but 99% of humanity will be unaffected.
**Well, Sometimes There Is**
The no free lunch thing is *generally* true. But it's also a generalization, and generalizations have exceptions. Maybe there are muscle designs that are efficient, strong, and give great endurance all at once. It's just that evolution either hasn't chanced upon them yet, or maybe those adaptions would require several negative adaptions first before they could be realized. For example, if your muscles got really strong before your bones, you could rip yourself to pieces.
Over time, experiments and computer modeling might reveal these superior setups, letting us slowly actually improve while at least *reducing* the tradeoffs. At that point you'd start seeing those used more commonly.
[Answer]
In the novel [Einstein's Bridge](https://en.m.wikipedia.org/wiki/Einstein%27s_Bridge_(novel)), which I used to prop up the center speaker of my first 5.1 surround system, the friendly aliens pass along this ability *as a biologic mod in itself*. That is, you don't need a computer; the pattern matching stuff is wired into your brain as with a sense such as vision. They can read and write DNA intuatively with their fingertips.
The idea of *compiling* a high level language is sort-of sound. The metabolism works with lots of indirection and feedback, and any program would be horrible spaghetti code even if expressed in readable shorthand. It would be more like the logic compiler for a PLA, and more problematic.
Backing out a sensible program from evolved DNA will be a mess. At best you'll get notations for representing the common cause-and-effect chains and annotations for charting it out. But, think "circuit diagram" not "list of instructions".
Designed code will be neater, and may be very much like designing a gate-level plan for a CPU chip.
---
Whatever the form, the point is that existing DNA can be "understood". This might mean specialized computers and lots of simulation, but it will all be spelled out. Even so, the full impact might not be understood because it's so messy.
So any adjustment will itself be buggy and have unintended effects. But that is all "understood" too, and patched again.
I imagine it will become handl-able with the computer analysis and adjustments, but no longer a self-regulating system. Untill the whole genome is eventually rewritten from scratch, it will be dependent on these outside systems for continued stability.
---
What if your metabolism was like your phone? New updates and fixes, and constant mistakes that are ever changing.
I've wondered on what kind of "apps" people would find to load into themselves. Not new large scale changes, but custom creations using the new programmable framework.
See also: [this question](https://worldbuilding.stackexchange.com/questions/9493/what-is-the-technical-feasibility-of-dna-altering-drinks-in-a-fictional-bar/9526#9526).
[Answer]
You have to consider the genesis of such a development. Human DNA will not be the first to be compilable (save “disassemblable”), so there will be many years of experience with less complex organisms before people would start to alter human cells, embryos or even full-grown organisms.
A technology like that will have a lot of consequences, many of which will further stress traditional ethics. I will not try to completely cover the question in my answer, instead it shall only deal with one aspect that is usually overlooked: **genetic art**.
When computers were new, some artist saw their potential in developing new art forms and raising the limits on existing ones, e.g. interactive installations, generating fractals or helping in the construction of complex artworks. Computer code itself has less often been considered art and neither has microchip design, although there are counter-examples.
Similar things will happen with and to genetic code. There will be artificial RNA or DNA molecules, other proteins – or polymeres, but that’s off-topic – and viruses that just look or behave “artful”, and there will be proper lifeforms from bacteria to plants and animals that will either be considered artworks by themselves, e.g. chimaeras or fairy-tale “re-creatures”, or are designed to perform [art](/questions/tagged/art "show questions tagged 'art'"), e.g. swarms aligning in pretty patterns. There probably will be the occasional mad artist – which seems more frequent than the mad scientist – who thinks their genetically created disease will count as art, too.
Later on, people will alter their bodies to become artworks like they already do with tattoos, piercings, scars and other permanent body-modification, but also with hairstyles, makeup, body-paint, clothing etc. This will probably be better accepted morally than altering someone else’s genetic code, including one’s offspring.
Genetic art will be covered by copyright, not patents, by the way.
---
**Disclosure:** I once planned to write an SF story that dealt with a pioneer of genetic art who financed their expensive facilities that had to be located outside the reach of traditional-moral jurisdictions by also making and selling the most exotic (and obedient and satisfied) prostitutes human clients had ever, well, seen. Their justification would have been that it was more ethical and less dangerous to breed sex slaves than super-soldiers. In the artist’s mind, their side-job creatures weren’t enslaved of course because they were just looking human, not thinking or feeling like one. One prerequisite of this plot was that genetic alteration was too complex, messy and non-determininistic for scientists or engineers, so only artists could actually do it.
– Feel free to adopt that idea or part of it. I understand it may sound like the setup for cheap SF porn, though.
[Answer]
There's a potentially very scary downside to all this: "computer virus" is suddenly not just a figure of speech anymore. If you do this, you've lowered the barrier to entry to creating biological weapons far enough that it's essentially guaranteed at least one person somewhere in the world *is* going to create and release one.
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[Question]
[
What characteristics must be included in a tunnel under a large city that was created and inhabited by faeries. How can the fae connect to nature there? The Fae are separated from their 'otherworld' forced to live in close connection to humans. They stay near cities because the last portals were discovered there years ago.
They hide underground because their magic is diminished by close contact with humans. All magic is associated with their light, and being around humans makes them age at a faster rate.
I am envisioning a maze-like compound where they live under cities, under parks. Could plants flourish underground if the Fae light was their energy force? Would they grow down from the roots above drawn to the light of the Fae? What plants would thrive in this way? How would they be pollinated to create food?
[Answer]
Edit: You've edited the question, let me add some to my answer.
If this magical light source inside the fae provides enough energy in the correct wavelengths to get absorb by the plants, there's no reason regular plants couldn't live underground. Vines and so forth could grow from the roof, but the plants could also just grow from the ground, underground. The fae could easily transport plants they like or can eat to their underground area, but some plants could make it down through their natural pollination.
Assuming the plants on the fae otherworld are similar to those on Earth, the fae would have likely evolved so whatever magical light they have synergizes well with the plants around them.
However, there is an issue here. In the real world, the plants get their energy from the massive amounts of sunlight hitting the planet. Next, low-level animals get their energy from the plants, then high-level animals get this twice-concentrated power from the herbivores. Now, you're saying the fae are powering the plants. That means they have to get that energy from somewhere first.
Under the guise of reality-check, this doesn't make a lot of sense using the natural order of things. If the fae subsist off fruits, or animals that subsist off the fruits, their total energy input has to be less than what they must output to keep the plants alive. The only way for this to work is if the fae get their "light" from some other energy source.
They could get it directly from the sun, but realistically, sunlight power is proportional to the area of your collectors. According to [wikipedia](https://en.wikipedia.org/wiki/Photosynthetic_efficiency), plants are 3-6% efficient. A fae could potentially be 33 times more efficient. If they have wings or something, they could spread them out and collect sunlight. Let's say their wings have about 2 m² of area, they're about 90% efficient converting energy, and the fae output light that's in the right wavelengths for plants, making their light about 2.2 times as efficient as sunlight.
Combining all those numbers means one fae could support about 4 m² of plant life. However, this assumes the fae stands outside all day like a plant would. We can get the energy at any given time of day using the calculations from [PVEducation](http://www.pveducation.org/pvcdrom/properties-of-sunlight/calculation-of-solar-insolation). I used the top applet, set the latitude to 40° (about where Denver is), and set the date to 25 March to get an average-ish energy plot.
Using the magic of spreadsheets, I used the data from the applet to plot energy absorbed versus the amount of time spent absorbing it. Since the highest power is at noon, I'm assuming the time is spent around noon. So 2 hours of absorption means from 11 AM to 1 PM solar time.
[](https://i.stack.imgur.com/ApLNB.png)
It takes about about 12 hours to get all the energy, but because there's more energy per hour in the middle of the day, you can get 25% in about 2 hours, 50% in about 4.5 hours or 75% in about 7 hours. This means one fae could support 1 m² at 2 hours/day, or 2 m² at 4.5 hours/day, with a little less in the winter, a little more in the summer. The fae could potentially store the excess energy during the summer and use it during the winter to keep the underground in perpetual spring.
Of course, if you start using magical power sources, anything goes. They just have to absorb more energy than the plants require, plus a bit more for efficiency losses. But you'll want to figure out what this magical power source is. It could be a glowing crystal they brought from the otherworld that behaves kind of like a nuclear reactor. They could steal "life energy" from the humans around them. They could have access to some kind of geothermal energy.
Original answer:
>
> There are lots of [plants and animals](http://www.neatorama.com/2011/01/26/underground-animals-cool-cave-critters-part-one/) that live underground. These fae would probably have adapted for low-light vision, and they would sustain themselves on the various resources available.
>
>
> Seeing as fae aren't real, a better way to look at it is "how do existing underground mammals survive?" The same provisions required to keep a rat alive are roughly the same as a fairy. If you're thinking fae are more similar to birds or butterflies, try to find animals like that.
>
>
>
[Answer]
Use plenty of bio-luminesence. Not just fireflies etc but bio luminescent trees and flowers.
Also, there should be plenty of mushrooms, magic and otherwise in the bits which are genuinely dark. And mushroom-people to keep the place tidy (See Jeff Van der Meer's excellent 'Ambergris' stories).
[Answer]
Assume, as I have, that the fae light is a magical thing, as magic is sort of a fae thing.
Now let's follow the properties of magic to see if that would make sense. Say you have a plant. It feels magic. It's nature magic. Plants like nature magic. It grows towards it.
Now you have root tendrils that live where the fae do and pulses with happy magic joy when they come near.
Now let's think about bees. A bee is nature, so it likes nature magic. It sees that a plant is being magicked by the fae. Bees do not dig deep into the earth, or at least not *that* deep. So it decides it likes this particular plant a lot.
Now this plant is getting a lot of pollen, and it grows huge. Because nature magic is good for nature, the plant becomes resilient. It quickly grows to suit the needs of its magic suppliers, i.e. harvest-able root, wood and fruit.
Now lets talk about stuff underground. Say a seed gets there, or a mushroom. Fae make magic. Magic makes cool things like growing happen.
Now you have seeds and spores that grow up pretty much no matter what with this wonderful energy. They soon adapt to purposes a fae might want them for as well.
Suddenly you have a thriving *maze network* underground that supplies the fae with everything they want, because natural things just *love* magic. Magic is a source of energy.
**TLDR**: Yes, because nature likes magic and likes to show it.
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[Question]
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Salt has always been valuable; it's necessary for life and - until modern times - difficult to produce. Supposedly it was used as a currency in Abyssinia (ancient Ethiopia).
What circumstances in a largely Earth-like world would make salt a viable currency? A hot and dry climate would make it more valuable, as people secrete it more rapidly, but those conditions also lead to salt being easier to produce (I'd think, am I wrong?): seasonal lakes and warm dry sea shores. Would humid conditions make storing salt impractical?
Parameters: Bronze Age technology; established governments which could reasonably certify quantity and quality of salt; there's a sea not far away but the bulk of humanity lives at least 50 km away, in this area anyway.
I can imagine salt being a currency for common folk, while merchants and nobles use metal coins. Is this a more plausible scenario?
[Answer]
**A viable currency simply requires that people see it as such.**
Salt was used or highly valued in a lot of places. Apparently, the word “salary” stems from the Latin word “[salarium](https://en.wikipedia.org/wiki/Salary#Salarium),” meaning “salt money.” The Romans paid soldiers, officers, and civil administrators an allowance of salt (or money to buy salt) and the term stuck around.
You can actually view salt in a similar fashion as modern cryptocurrency. Anyone can make it or collect it, but it takes time and energy, both things that are very limited per individual. The collected currency is a symbol for time spent. The salt miners/desalinators spend time collecting a certain amount of salt and people are willing to trade them other goods for their collected time. It would no longer be viable once someone figured out how to mass produce it and its value dropped so much that it would be impracticable to carry around so much salt.
Storing it would not be much of a problem, people have been [keeping things dry](https://en.wikipedia.org/wiki/Food_preservation#Drying) for a long time. Damp salt can be easily dried before it's weighed in a transaction or the transaction can be based on volume (meaning damp salt would be less valuable).
It is far more likely that people would use a different currency for higher level transactions. You wouldn't want to be stuck trading with a coastal city all the time in salt because they're infinitely more wealthy than you. Coins might be used as a [fiat currency](https://en.wikipedia.org/wiki/Fiat_money) or as a [representative money](https://en.wikipedia.org/wiki/Representative_money) backed by salt. In that case, salt is simply used as a slightly more formal barter system when coins can not be manufactured in large enough quantities.
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EDIT:
The primary thing to keep salt as a viable currency is for mass production to not be possible. For our own history, the [invention of ceramics](http://archaeology.about.com/od/foodsoftheancientpast/qt/Making-Salt.htm) was most likely crucial in allowing the mass harvesting of sea salt. For your world, if salt deposits (and therefore mines) are not discovered then the suppression of ceramics is the easiest way to maintain scarcity.
[Answer]
Things like salt enjoyed status as currency not only because they were relatively rare, but also because they were immensely useful. Salt is highly desirable for preserving foods, which in ages before refrigeration (or the easy availability of ice) was really a matter of life or death. Having food "salted away" had a literal meaning then, even if it has evolved to become a figurative one today.
Salt also has many other uses, and is an important part of keeping your health in hot weather or when doing heavy labour (replenishing the salt you sweat away), even if the ancient people might not have been aware of the exact mechanisms. (Our ancestors were very observant, and not stupid at all).
So a highly useful substance which is portable, divisible and relatively rare all adds up to a valuable commodity in its own right, and valuable enough that it can be used as currency in the right circumstances (technically, you are actually bartering with it, but this was pretty much the case with any sort of currency until relatively recently, including precious metal coins, which were often melted down or shaved for the intrinsically valuable metals they contained).
[Answer]
I'd say that for any thing to be a currency it has to have the useful properties of money:
1-durability
2-transportability
3-divisability
4-cannot simply be produced, but is limited, such that the amount created in any period of time devalues the worth of money (as measured in other goods) by an amount that is insignificant enough to not be a factor in trading with it (ie. Inflation must be low).
Salt is easily obtainable. You would need for your world to have no access to salt water, and limited access to mines. Otherwise people could easily get salt. Sea water is about 3% salt, and it's easy to evaporate or boil off water to get the salt. It's even easier to get salt from mining, where you can literally dig out pure salt with a shovel.
Also salt is not durable. When it gets wet it disolves and will wash away. It's hard to believe a primitive society could always keep their money dry.
I think also think supply would have to be extremely limited for salt to be transportable. You don't want to have to trade a bucket of salt for a bucket of potatoes.
I don't think it believable to have salt as a currency unless the population was land locked and had no concept of salt water, and water was also scarce. The only useful property it has is divisibility.
[Answer]
I think what you want is a world that has very little land mass and limited technology to go under water. Think of the Kevin Costner film Water World. I know that they were surrounded with salt water. The problem is that they would not be able to desalinate the sea without some kind of energy to boil it. There is no wood, no dry fuel, only wind power with limited technology. Desalinating the sea by evaporation needs a large flat area. The small floating villages had little enough surface and would produce very limited amounts of salt. The open sea makes it more difficult by continually producing rain clouds wherever the air gets a bit too dry.
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[Question]
[
Earth has three convection cells per hemisphere. These are the Polar cell, Ferrel cell and Hadley cell. These create the trade winds, westerlies and polar easterlies which control many aspects of climate, such as where rain shadows & dry zones are located and where ocean currents flow.
[](https://i.stack.imgur.com/Zbz0g.png)
However, if you were to slow down the rotation rate of a planet, you could turn those three convection cells into a single, gigantic convection cell. Assume a roughly Earth-like planet in all characteristics (sans rotation rate, which is slowed down in order to turn the three convection cells into one). **Because climate is a combination of multiple factors, there are several questions to consider:**
* How would the movement of oceanic currents be affected?
* In what direction would the wind blow at different latitudes of the planet's surface?
* Where would the dry zones of the planet be? The wet zones?
* Where would the hot zones of the planet be? The cold zones?
Bonus:
* How would this affect violent weather phenomena such as hurricanes and tornadoes?
[Answer]
**With two Hadley Cells**
The Hadley Cells would expand and contract with the seasons.
The winter cell would stay put and intensify its circulation of air due to the higher degree of temperature variance from the equator to the poles. The convective updraft region for this cell would be narrower, but more intense, and would be focused near the equator. It would still flow from east to west like our own Tropical Convergence Zone, but much slower, and might meander a little bit into the other hemisphere like our T.C.Z. during the winter.
The summer cell (for this lets say the northern cell) would migrate poleward a bit, widening and weakening the updraft region as it goes.
A lot like the jet stream in some respects:
[](https://i.stack.imgur.com/G1KY5.jpg)
As it moves farther north, the convection behind it would weaken and be pulled northward as the air behind it starts to descend. Spin off low pressure systems would kink up the weaker band of updrafts into knots and loops until it hardly resembled a band at all. As this happened the belt would slow down and would probably at some point *change direction* from east-west to west-east due to the weak but still present Coriolis effect. Warm tropical moisture flowing from the south could form some powerful storm systems rotating any which way where they encounter the cooler air of the north.
Meanwhile down close to the equator if a tropical system initiated and had enough spin to break from a tropical wave, a hurricane could form. It would meander a bit, not pushed as much by the Coriolis effect, but by the flow of air from the Hadley cell northward where it would eventually slam into the disorganized convective belt. This would push a large region even further northward in a bulge and would act to intensify the belt as a whole, contracting the updraft regions and forming powerful winds. On this planet you could also have two hurricanes form, side by side in the same hemisphere, but rotating in opposite ways.
[](https://i.stack.imgur.com/lHzfi.jpg)
If the Hurricane formed too close to the equator it would be trapped against the equator by the air rushing from the high pressure to the north and south. Conceivably, this hurricane could jump hemispheres back and forth across the equatorial band like a kid playing hopscotch until it hit land or was killed by atmospheric turbulence.
Tornadoes would still form. But super-cells which form the most powerful tornadoes would be more rare as they require both upper level and surface level wind shear to form. This planet simply doesn't have shear like that on a regular basis. Landspouts and waterspouts would still be common though as wind shear is not as important in their formation. And even more than the hurricanes, the tornadoes wouldn't really care which way they rotated.
[](https://i.stack.imgur.com/x7on3.jpg)
I am not quite sure how far north this belt would go. That depends on many factors. It could conceivably go as far as 60 degrees north or even to the pole before making the trek back down.
Titan's updraft belt at the pole:
[](https://i.stack.imgur.com/Na2MT.gif)
The temperate latitudes would receive the majority of their rainfalls in spring and fall when the band moves overhead. Summer would be mostly dry except for occasional monsoon thunderstorms. Winter would also be dry, but very cold and windy.
The sub-tropics would receive rainfall starting in spring as the band moved overhead, continuing into summer as typical tropical thunderstorms and then again in fall as the band moved southward. Winter would bring only occasional rainfall.
The poles would receive its only real precipitation in summer when the band is at its closest. The rest of the year there is a huge downdraft over the pole that pushes cold air across the landscape and toward the equator. In winter the cold would be especially harsh, as would the winds.
At the equator the rain would be nearly constant like it is here on Earth.
In the tropics rain would fall steadily for half the year, and then would receive rather chaotic rainfall depending on the strength/position of the migrating downward moving air, and the proximity to the other band of updrafts.
**Air currents:**
In winter at ground level the air would flow from the poles toward the equator but curve more toward the west as you get closer to the updraft band. On the equator winds would be out of the east flowing toward the west.
In summer as the band passed by air flow up from the south would be quite strong. This would gradually weaken as the band moved on and air started descending behind the band. The southerly flow would continue until the band passed by again.
However, on the equator side of that downdraft, the air would flow from the north down to the equatorial band. The descending air instead of flowing toward the band, would rush away from it toward the equator until it rose in the wintertime band.
During the band's trek winds would be chaotic at ground level due to mixing cyclones from the north and south along with convective downdrafts.
**Dry and Wet areas:**
Depending on how far toward the poles the band of storms moves, and how long it parks there during the summer the poles could either be desert, or rainforest. Assuming that Titan's band of storms remains over the pole for longer because of its greater axial tilt of 27 degrees to our 23.5 our poles would be much drier. In fact, they would probably be something like a cold version of the African Savannah except for the extremely high latitudes where it would just be barren. This is just the average, seas, mountains, and polar oceans would greatly alter this recipe.
The mid latitudes would most likely be the driest due to a rather rapid transition of the low pressure band from the sub-tropical latitudes to the higher latitudes. This combined with the weakening described earlier that the low pressure band would undergo could make the mid-latitudes semi arid on average. Large mountain ranges oriented from east to west would be much wetter due to the warm humid air coming from the equatorial regions in summer, and the cold snowstorms that would form on the poleward side in winter. This would effectively create rainforests on the equatorial face, and deserts poleward from there.
[](https://i.stack.imgur.com/s78VE.jpg)
The sub-tropics would be similar to ours, with just a tad bit more rain. Instead of a 6 month dry season and a 6 month wet season like ours, there would be a wet season 3 months long, separated by a 2 month season with a mix of wet and dry, then another wet season 3 months long, then finally a 4 month dry season.
The equator would be very similar to ours, but probably with more wind and more rain. If the wintertime Hadley Cell migrated a bit into the other hemisphere then the equatorial region would have two seasons, a wet season, and a dry season.
**Hot and Cold zones:**
It would still be hot around the equator. But most of the worlds deserts would be in the mid-latitudes nestled in mountain shadows or far from sources of moisture. These locations would probably have your greatest temperatures.
] |
[Question]
[
It is 2039 and after a long and bitter struggle, the people of [Molvania](https://en.wikipedia.org/wiki/Molvan%C3%AEa), under my guidance, have thrown off the shackles of the previous dictator's oppression, and have embraced the new and shiny life of struggling under my oppression instead.
My [particular personal gifts](https://worldbuilding.stackexchange.com/questions/11173/could-an-unusually-long-lived-being-continue-to-learn-with-the-times/11203#11203) have made my ascension easier, but I am no fool.
**I need a sure-fire way to control my s̶l̶a̶v̶e̶s̶ ̶m̶i̶n̶i̶o̶n̶s̶ ̶s̶u̶b̶j̶e̶c̶t̶s̶ loving citizens.**
I have tasked you, My I̶g̶o̶r̶ Lead Scientist to deliver such a weapon. I am inclined towards one that would deliver a delightful death by having many little daemons placed inside people waiting for my command to run amok, but the pentagrams are a *hassle* to draw, so I remain open to better, more practical suggestions.
I need a weapon that can:
* Insta-kill pesky rebels from within the country, including those untrustworthy generals, upon my command.
* Cannot be taken over by said generals or (heav-aaargh forbid) the *Americans*.
* Can be safely administered/attached/implanted/carved-into/chained-to my loyal subjects without (immediately) lethal side-effects. I still need them to pay taxes and um, give their blood for the nation.
* Cannot be disabled, except perhaps with great difficulty in some sort of advanced lab abroad. Luckily (for me), going past the barbed wire border fence triggers it, and there are no such labs in my country besides the one I (plan to) run.
* Can be triggered from a place with relatively weak radio reception such as my C̶r̶y̶p̶t̶ personal bunker.
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Here's a little picture I made of my idea in Paint:
[](https://i.stack.imgur.com/Q9oCQ.png)
Hopefully, the labels make it pretty clear what all the parts are and what they do. However, I'll explain the steps in detail.
1. You decide you need to kill a minion.
2. You access your controller and use several biometric devices to confirm your identity (e.g. fingerprint, iris scan and DNA test).
3. You type in the name of the minion that you need to kick the bucket. If the minion is high-ranking enough, you type in a serial number to confirm that it's the right person.
4. The controller sends a signal that is picked up by a radio transmitter.
5. The transmitter sends the signal to the microchip.
6. The microchip releases a spring which subsequently drives a dart through the minion's jugular vein (either of the two).
Ah, you say, but I mentioned weak radio reception. There's a solution: A dead man's switch. All you do it *not* transmit a signal at a pre-approved time and the dart is fired.
You can substitute in different things for the dart. Poison is the obvious choice, but it's boring to depict in Paint, and an antidote could be found. Darts are harder.
Implantation might not be simply, but it probably wouldn't be lethal. The dart doesn't have to hit directly, just enough to cause a hole that will quickly bleed.
Better still, implant multiple darts in other crucial places, such as the carotid artery. That makes recovery hard, if not impossible.
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**Help your subjects have strong hearts!**
Without providing too many details about the actual device, I would recommend using something I am developing at my day job. An injectable pacemaker.
[](https://i.stack.imgur.com/AZrHx.jpg)
The pacemaker above (called a leadless pacemaker) is inserted through the femoral vein and hooked on the inner wall of the heart.
Using this pacemaker has several advantages:
* Say you're ~~tasting~~ measuring the heart rate of your subjects and
you'd like the heart to beat a little faster because they're
enthralled for some weird reason, just turn the dial on your control!
A rapid pace makes the blood flood faster.
* The pacemaker can be used as a proximity warning for people approaching somewhere they should be going, like the borders of your land, it's dangerous out there! You don't want a binary kill/don't kill device, you want to let them know with a pounding heart that continuing on a course of action might cause a deadly fibrillation. For their protection! Leaving your lands would keep the devices from getting the personalized healing messages they need to keep your each of you subjects healthy.
* You can monitor the ~~fear~~ health of your subjects. If they're just walking around with an abnormally high heart rate they might be emotionally stressed due to some ~~scheme~~ serious health issue. They should be called in for immediate ~~questioning~~ check-ups.
* The device is *inside* the heart! No pesky accidental back-alley removals. The symbolism alone is worth it. Your subjects always carry a piece of your empire in their hearts, physically and metaphorically of course!
Just remind everyone to stay calm and loyal, they don't want their heart racing for no reason!
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**Giant Death Ray from the Sky!**
A fleet of giant fusion powered blimps flying circuits around the country with coverage such that they are able to see into every nook and cranny of the country. Mount a giant gigawatt IR laser to each blimp. As they are nuclear powered, they can stay aloft for months at a time...kind of like submarines, only in the air :)
Sell your minions the propaganda that the blimps are keepers of the Glorious Revolution! Show them movies about how they have crushed the Great Satan Americans in glorious battle after glorious battle!
Issue state controlled cell-phones to all inhabitants above age four. Make the phones incredibly useful so that people will not want to be without them but also make a law that people are not to be without their phones. Issue new phones regularly. The phones double as ID. No ID == "disappearing" and blood donations ;) In each phone is a GPS that is transmits its location to your secret command bunker. The microphone and the camera in the phone can be turned on at will without the owner knowing about it.
With the GPS locations of all your victims, er, minions, er, citizens, should some of them turn pesky, you can direct a billion watts of invisible insta-death direct to their location. With that much power available, you'll likely generate steam explosions from the water in the rocks heating up so fast. Even if you can't kill the pesky, deeply-buried minion immediately, you can certainly seal the exits and let them chock on their own rebellion ridden breath.
But Boss! How do we keep the generals out?
Easy. Build the firing system so that it only fires with a proper cryptographically signed order. The crypto chip that holds the private key for signing fire orders is embedded in a medallion that hangs around the Dear Leaders neck. It can only be unlocked by providing a four digit PIN, and handprint scan. The handprint scanner looks for heat, sweat and a pulse before it will authenticate.
The firing controls on the blimps are hard interlocked so that they can only be fired by a signed fire order from the secret bunker by the Dear Leader's authenticated key. The blimps only receive coordinates to fire at. They don't know what they are shooting at. During strikes, some other people might die. Too bad for them. Don't be near traitors!
The crews of the blimps are your most trusted minions who have made previous "blood donations" and are thus assured their loyalty.
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# Use the premise of "Protection"
"Protect" your citizens using armed police drones. Now that you're in charge, you're free to install satellite(s) that keeps track of any and all citizens and drones at the same time. To kill someone, simply issue a command to the satellite, and let the satellite(s) send drones to assassinate him.
Since the police drones are commonly seen, no one's going to bother hiding from them since you tell them "it's for your protection". You can even assign specific drones to your generals to allow for faster dispatch. While this doesn't exactly fulfill the "instakill" requirement, if you have enough drones, you'll essentially have "insta-kill" (or as close to instakill as any other method - bleeding out or poison also takes time, a well placed gunshot might be even faster, but would probably amount to the same amount of total time if we factor in the traveling time for the drone(s)).
Drones are ONLY controlled by a heavily encrypted code from satellite(s) to drone. Ideally one that changes every hour or so, such that no one will ever be able to directly hack a drone (and even if they do they can't control it for long). Satellite(s) can be very secure and nigh unhackable if you include bio metrics in your communications to the satellite(s). In order to make it even more secure, make sure you carry a digital encoder with you. This encoder contains the same code generator as the satellites, and will change at the same time as the satellites such that you'll be able to communicate securely and safely.
This is fairly "safe" to administer. It doesn't exactly touch your subjects, so there's less invasion of privacy. Furthermore, since you don't need to do an operation on every person, the drones may be faster to deploy overall.
The drones may be killed, but if you kill one, more will come. If you send up multiple satellites, they can all communicate with each other in order to execute your commands. If one gets shot down, no problem - you'll have 5 or 6 more in its place. If you give each of your satellites anti-missile weaponry, then the system will definitely fulfill your "Cannot be disabled, except perhaps with great difficulty" requirement.
This system can be triggered from anywhere since you're using satellites. Even if you don't have normal reception, you can build your bunker(s) to include external antennas. (I'm pretty sure you can get satellite reception through bunker walls though)
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Centaurs. Half human, half equine.
The idea's been bouncing around in my head for the past hour, so I'm going to ask it here:
Would a centaur structurally make more sense if the torso was at the rear, center, or front of the body? Also, would it be more structurally stable if the hips were that of a horse's or if the equine-like part was more of a square?
(In essence, I want a wiki post made of this one.)
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I think the traditional, front-mounted-torso makes the most sense. If the torso was at the back or middle, it would significantly decrease the arms range of motion so they wouldn't be able to easily pick things up from the ground.
Structurally speaking, I think the front-mounted (or back-mounted) torso is nice because the torso and the legs line up, giving the torso more direct support. If the torso were in the middle, the horses 'spine' or whatever would have to directly support the weight, which doesn't make as much sense.
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The middle is right out. Consider the spine, and how the two spines would have to connect: There would have to be some sort of three-way vertebra (horse back, horse front, human). I've never heard of a split spine in any creature, so we have nothing to base this off. (There are mutant snakes with two heads, but [these](http://askabiologist.asu.edu/sites/default/files/resources/articles/2headed_snake/x-ray2.jpg) [x-rays](http://www.nocleansinging.com/wp-content/uploads/2011/12/albino-snake-xray.jpg) seems to show either a blob of bony material, which would be very heavy, or no proper connection at all, which would provide no support.) As one of the other answers mentioned, this would cause the horse spine to sag as the weight won't be supported directly over the legs. On the other hand, having the torso closer to the center of gravity might be more practical for maneuvering. (Semi-related: My favorite mythical creature, the Nuckelavee, has its torso in the middle. It also has no skin and breathes the plague, so it's not a great example of realism.)
What about in the back? It would look absurd, for one. But internal organs are the big problem. There would be no practical mouth, unless you have a) a giant freaky gaping hole where the horse head should go, b) a horse head, which makes it not really a centaur, or c) use the human mouth, which requires a uselessly long esophagus running down its back along the spine, or reverse the internal organs front-to-back, which is just a centaur walking backwards. Additionally, the pelvis of the horse seems ill-equipped to support the weight of the human torso. Just [look](http://upload.wikimedia.org/wikipedia/commons/3/33/Horseanatomy.png) at those scrawny little coxa. More importantly, I can't see a good way to connect the human spine to the horse spine. The horse spine curves downward into the tail (which you would also have to find a way to deal with) but it needs to slope upward into the human spine and I think it needs more space to do that than the tiny space you can see in the picture, whereas the horse neck is already basically straight up.
One other consideration for the middle and the back: What do you do with the horse head? With the front it's obvious that the human torso replaces the horse neck, but what else could you do with it? Just truncate the spine at the shoulder and have a rounded blob in front? That removes the need for several muscle groups, and probably a few bones. Keep the horse head? Like I said, not really a centaur anymore. You also have the problem of which brain is in charge of what. So torso in front is really the only sensible solution.
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Torso in the middle or rear does not seem too practical. On the one hand, it will make maneuvering on rough ground very difficult, as the forward portion of the torso will block visibility for near terrain. The selective pressures on a centaur species trying to gallop at speed should be obvious. On the other hand, it will also become extremely difficult to manipulate objects, since, as Martin\_xs6 pointed out, it would be difficult to pick them up. Not that it would be easy for a classical centaur, with arms so high up, but at least a standard centaur can *see* objects that he wants to pick up. And leaning sideways is not a great option, since it requires extreme torsional compliance of the body and spine.
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In Dungeons and Dragons lore, there exists a construct called the cosmos used to define a variety of planes of existence. One of these is the Material Plane, on which our normal reality is found.
Suppose there was an Earth-like planet on the Material Plane with a disturbed cosmos, such that other planes of existence passed close to the Material Plane, close enough to create a planar bridge. This happens periodically and fairly predictably and, when a strong enough bridge forms, the encroaching plane can steal one of the planet's moons and/or give the planet a moon.
What would be the physical impact on the planet if there can be anywhere between 0 and 4 moons in orbit at any given time?
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Some givens, because "everyone dies" is boring: The moons stay in orbit, and don't hit each other.
First, the "mundane stuff":
Tides: Goes without saying, insane. Not catastrophic, just really unpredictable. Influence on sea life? Probably not that much.
Volcanism and tectonic activity: High. Volcanoes, lots of earthquakes(not big ones, mind, but lots and lots, probably each time you gain and lose a moon.)
Calendar: Almost worthless over long periods. The length of the day will change as new moons are added and subtracted. How much by? Depends on the size of the moon and its orbital distance. Not a lot a lot but perhaps a day or two over a few decades.
Tidal stresses from switching gravity on the moons themselves would probably make them erupt in their own volcanoes.(They'd almost certainly have liquid cores because tides) Rains of sulfuric acid, big rocks, lumps of ice, nearly anything is possible with just mundane moons made of regular moon stuffs.
Now, the exotics. I don't know much about what planes these moons visit, but coming back from the elemental plane of fire and orbiting close to the planet might have an interesting effect on local weather. Not setting-fires hot, but you know. Problematic ecologically. Also there would be nearly no night due to the giant scary red glow in the sky. A Europa-like moon might freeze and remelt every time it came to visit.
The less often a moon visited, the more likely it would be to have a catastrophically huge eruption and shower ejecta onto the world below. In general it's not if you receive orbital gifts but when and how often you get presents from your moon visitors. Most things would be killed on impact but you might get the occasionally durable houseguest, if there's life on the moons some of the time.
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The physical impact of an Earth-Like planet going to one to two moons would be the might be the [extinction of its inhabitants!](http://www.universetoday.com/92148/what-if-the-earth-had-two-moons/) It's doubtful that a moonless Earth could have ever developed life and the sudden introduction of a new moon would likely be destructive to everything on Earth from tides to tectonic activity to the speed of our rotation. Gravity is fun!
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Here's an idea: the orbit passes through the overlapping zone and pops in and out as it orbits.
The idea is that coming back with the correct orbit is not a wild coincidence, since it always is in orbit. The planet and its doppelganger pin the fold between them so the fold stays around the planet, like cufflinks. But only one had a large moon, and now it's shared between them. Only a large mass can pop through the fold (sometimes), so the existance of the fold does not obstruct the view of normal space.
In this idea, the planets stay pinned together so the motion around the barycenter is consistent regardless of which side the moon is on. The moon affects one of the planets, and that planet affects the other through the fold. So the moon feels a planet with double the inertia for its mass, and the tides disappear with the moon.
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**Edit:** In the scenario that the temperature of a given area increases constantly over 30 million years (slowly enough for species to adapt) starting at 20°C and ending at 90°C, what are the possible species' evolutions in order to survive?
This question has a very large scope so here are some presicion.
**Why an area?**
I'm talking about area and not about an entire world in order to ignore any heavy climatic modification that would cause very abrupt change. For example, pole melting that would cause a flood.
**Which species?**
Well, I'm interested in plants, animals as well as humans but I'm not interested in technological evolution, only biological.
**Which temperature are we talking about?**
Well, I don't have any precise temperature, but I'd like temperatures higher that what we usually find on Earth. This means starting at 40°C and rising until life is no longer possible. One limit of temperature for life (as we know it) is water's boiling temperature (usually around 100°C). But water's boiling point depends on pressure. If pressure goes up, so will the boiling point.
**Edit:** Let's assume that the final temperature achieved is 90°C.
**Edit: What is the time frame?**
I don't really know what timescale to use, but since you want it let's use human evolution timescale. Based on Wikipedia, the first Hominidae appeared 28 millions years ago. So let's say that our temperature increase slowly and constantly during 30 million years.
Also, my question concerns a *global elevation of temperatures at all time (day and night) and at the surface*.
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On Earth, the highest tempeature are usually achieved in arid or desertic areas. During the day, temperature can go up to 50°C or more but during the night, temperatures drop significantly. That's why wildlife is nowhere to be seen during day and very active during night. This huge gap between day and night temperature made desertic wild life not a good example to answer my question.
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If you want some precision that I've not given, feel free to comment.
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>
> Edit: Let's assume that the final temperature achieved is 90°C
>
>
>
Why?
Ah, well; I was going to talk about how a higher temperature could start boiling water, and evaporation of inner fluids, which would render blood-vessels, cerebral fluids, plasma, cytoplasm; exactly 70% of our bodies useless.
To cope with a high enough temperature that your innards begin boiling, one would expect organisms to develop mechanisms of increasing their internal pressure; such methods could include:
* Thicker, harder hide, to prevent swelling and increase pressure.
* Tougher blood vessels, especially capillaries; capillaries would have to be more constrictive, possibly decreasing the oxygen diffusion rate.
* Denser tissues, such as muscles, maybe a tissue akin to cardiovascular muscle would have to be more widely incorporated.
Some of the above described adaptions would lead to other effects, for example, less porous capillaries could lead to oxygen starvation, and to counteract this creatures might respire anaerobically more often, or conserve motion (be lazy).
Denser tissues would also make creatures heavier, which would actually make moving more of an energy-consuming process, so organisms would definitely want to limit motion.
Organisms might stop perspiring to reduce body heat; at such temperatures, it would barely change anything, and would just consume water.
Instead, they would have to increase their surface area, employ a system like elephant's ears with blood vessels close to the surface and a massive surface area.
Or, they might grow spinal sails, like [Dimetrodon](https://en.wikipedia.org/wiki/Dimetrodon#Thermoregulatory_function), which could be angled differently to regulate temperature. For example, pointing straight at the sun would keep temperature lower, but if in shade you would want the sail as exposed as possible. Similar reasoning might lead to large, retractable appendages which can be used in a similar purpose.
Based on [hyperthermophile cell structure](https://en.wikipedia.org/wiki/Hyperthermophile#Cell_structure), you might expect organisms living in high temperatures to be quite fat, or each cell within such an organism to be protected with such fat.
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We already have [extremophiles](http://en.wikipedia.org/wiki/Extremophile) here on earth - creatures adapted to incredible conditions.
In particular [thermophiles](http://en.wikipedia.org/wiki/Thermophile) and [hyperthermophiles](http://en.wikipedia.org/wiki/Hyperthermophile) which can survive between 41 and 140 °C.
This shows that nothing prevents life functioning at those temperatures, although of course the animals adapted to those conditions are normally small organisms.
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Typically, the creatures either adapt to the environment via evolving, avoiding the problem, or both.
**If the surface were to get hotter, then a possible solution would be to go lower.**
For example, by digging into the ground deep enough, you can get to a section of the earth that isn't close enough to the center to be hot/warm yet, but far enough from the surface that the sunlight/heat can't penetrate into, resulting in a cool section of underground area to live in.
In that scenario, it's likely that your creatures would evolve to be very good diggers, with good low-light vision, perhaps shovel like paws/hands. Or even a strain of giant worm that eats dirt... \*shivers\*
**But what if they wanted to live on the surface? How could we make it happen?**
The biggest problems here are: a) The heat and b) liquids boiling.
Well, lets apply a bit of handwavium here. What if we had a creature that didn't have H2O as a solvent in it's "blood system". Instead, what if we had some creatures that were based on having a different blood system? I see no reason why a creature which operates on Sulfuric Acid (H2SO4) would be unable to survive high temperatures. After all, Sulfuric Acid stays liquid between 10 to 338 degrees Celsius. Even on Earth, extremophiles can live in extremely acidic conditions. As noted before, there's also no reason why they can't operate in extreme heat. That means there is no reason why this creature can't grow larger, enough to use this acid as our version of blood.
**Of course, if you had wanted a creature that initially wasn't able to survive extreme heat that would be another issue.**
If we had creature x, and x was comfortable at 20 degrees, the likely methods of cooling itself would be through sweating. However, in the event that the temperature rises enough, eventually this would be ineffective since the creature wouldn't be able to cool itself down fast enough, and it would be just wasting water. But what if it was a small creature? A small creature with big heating problems could take a page from our current big creatures with big heating problems!
Think Elephants. They have big ears in order to make use of air and wind to cool down the blood. Depending on the overall situation of the planet (eg how much shade there is) this could be possible. By growing massive/larger sized ears, the creature could "flap" them in order to cool down. Perhaps it may develop thin membranes with spines that have blood vessels going through them for the same purpose. Bat-like wings, perhaps, but without the ability to fly.
**But what if it's a flying creature?**
Creature y is a flyer. It doesn't exactly... land often, because it has predators there or something. How could it deal with this?
It could learn to dive through clouds, or take dives into oceans/lakes to cool down. By doing so, it would have to evolve to be extremely waterproof. The theory here is that the water should be able to pull away the heat from the body (if the water is cooler than the creature). Equilibrium to the rescue!
Of course, the simplest solution would be if the creatures migrated when it got too hot, but that kinda avoids the question...
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While it's hard to say exactly how things would evolve in terms of their body structures and behaviors I can offer some insight into what would need to be happening at the molecular level for life to evolve to handle higher temperatures.
Life is chemistry right? It's just a whole bunch of interconnected chemical reactions that have been ongoing for the last 3 billion years. Temperature is an important variable in every chemical reaction. Some reactions happen at low temperatures, some at high temperatures. Importantly, every chemical reaction in the human body has been calibrated to occur in a very narrow temperature range. Every protein your body makes has been evolved specifically for that range. Proteins are made of long chains of building blocks called amino acids that fold into unique 3D structures that perform specific roles in the body. It turns out that this folding process is very sensitive to things like pH and ionic concentrations, and also temperature. Proteins unfold at higher temperatures. It's why the egg white goes from translucent to white when you cook it. The proteins in the fluid lose their complex 3D configuration and take on a new shape which happens to be opaque. Now that doesn’t mean that all proteins are unstable at higher temperatures. The thermophiles that Tim B. mentions have evolved proteins that can fold and function at these higher temperatures, but it’s a lot of work! Basically every gene in an organism’s genome encodes a protein, (Although there are numerous exceptions to this). The vast majority of proteins will no longer work at temperatures significantly higher than an organism's normal body temperature. That means that to evolve to handle these higher temperatures practically every gene in the genome (in humans that’s roughly 20,000) will need to evolve to cope with these higher temperatures. For some proteins that may entail just a few changes that increase its stability, but for others their configuration may never be stable at such high temperatures and the body may need to find a complete workaround to do the same task. I’m anthropomorphising a lot so keep in mind all of this is random mutations occurring over thousands of generations. It is by no means a rapid process.
So, to cope with the increased temperature the human genome needs to change substantially. The majority of the proteins have to evolve to be stable at higher temperatures. At the same time virtually every other cellular process has to adapt to this new temperature as well. RNA folding, membranes, and metabolic processes will all need to be modified to work at these higher temperatures.
One thing I’d like to mention as an aside is that the body has special proteins that is makes when it is heated up too much. These heat shock proteins as they are called include a special class of protein called a chaperone. These are proteins which help other proteins fold. When cells start getting too hot they make lots of these in order to help their other proteins fold. Of course most existing chaperones would probably unfold themselves at 90 degrees C, but chaperones could be part of the way organisms adapt.
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Following on from my [previous question about how to consolidate my fantasy setting with science that was successful](https://worldbuilding.stackexchange.com/questions/14473/sci-fantasy-terraforming-the-earth-and-magic-nanomachines) (thanks everyone!), things have been progressing well in my world design; and my design document is now filled with alot of nice material from local politics to the histories, cultures and religions of the different races
Anyhow, my main initial setting will be Archon's Landing; the capital of the Duchy of Lieve in Everland. This city is built in the wake of the massive Yggdrasil-type tree, The Damaris. The Damaris Tree will be a centrepiece of the campaign, since the interior of it is mostly hollow and somewhat dungeon like (in an [Etrian Odyssey](http://en.wikipedia.org/wiki/Etrian_Odyssey) fashion).
Since I wanted this place to be interesting to my players rather than just a generic city to get their next quest and sell their loot; I've already started adding more details than usual to this place (as I have done for other major cities in my games in the past), including NPCs.
**So, that brings us to our question: what design, engineering and architectural considerations would be important to a city like this? How would it look?**
***The following conditions have already considered true:***
* The tree's circumference is MASSIVE. Even though this city is the capital of one of the greatest nations of the world, it still covers less surface area than the tree it is built next to. We can assume that the tree's diameter is at least *20 miles*.
* It is Oak-like. Branches are not feasible to reach for the purposes of construction, and the interior of the tree is not inhabitable. The city is built purely at its base, in its southern wake (so as to not be obscured from the sun as much as possible). The tree does not apparently drop leaves or acorns or anything, and leaves etc. are not giant sized (the tree is apparently more like several epochs old rather than giant-sized in the true sense).
* The city is built to accomodate the tree as much as possible. It has a high/royal district that is built on top of one of the massive roots of the tree. This section overlooks the central city and the northern ward. There are large stairs on the sides of the root, a road that follows the root to the end, and probably a couple of magic elevators. Despite this, people will drill/mine tunnels through shorter parts of the roots if neccessary (this is the case to access the rather dark Deadside, which is a shanty town on the eastern outskirts; possibly overshadowed by low branches?).
* Yes, magic is a thing. Only a small quantity of people can use it proficiently; but it is recognised as a good thing, and mostly not shunned. It's powers are relatively substantial, involving nanomachines that can re-arrange matter, perform rapid thermodynamic alterations, create barriers of force, and access great stores of knowledge. Most mages will only scratch the surface of these powers though.
* Despite the fact that the tree is gigantic; it is only surrounded by regular forest on one side (the east). Most of the other forest has been cleared and the land near the city is fertile and used in regular agriculture.
* A waterfall drops out of the giant tree and forms a small river (The Corkswash) that passes through the city centre. Around 25 miles out from the city, the Corkswash merges with The River Ever, which is massive (Mississippi level). From there, the River Ever carries on about 30 miles to the sea, where there is the port city of Everafter built around its river delta.
* As a result, fishing and foraging for fruit and berries supplement the agriculture.
* There is a large quarry around 50 miles to the north at the base of Mt. Silkenfoot. The stone type here is undecided at the moment. There are also iron, copper, and titanium (ilmenite) mines within reasonable import distances. Titanium processing is possible and not horribly costly in the setting due to alchemy and magery, though those who understand the arcane process are fairly few (most of the cost comes from their service fees, actually).
* Lieve is part of Everland, a [Republican Monachy](http://en.wikipedia.org/wiki/Elective_monarchy), which has four Duchies (Lieve, Canaan, Tyria, and Nodis) that work in a loose collaboration most of the time. Grand Duke Narron of Lieve is currently in charge, so Archon's Landing is the capital of the entire country, rather than just the Duchy. There was a fairly recent war between Lieve and Canaan over some petty border issue. It was more of a skirmish in the end with only three major battles, though, and Archon's Landing was mostly unaffected, except in the fact that Grand Duke Narron accepted a political marriage to Princess Sasha of Canaan.
* Population of the city is probably around 700K-1 million. Adventurers and tourists by Wyvern (which can be tamed and ridden) probably account for about 0.3-0.6% of those.
* Tech level is, on average, mid-renaissance. Low-tech firearms are available. Due to magic's influence, alchemy, medicine and metallurgy are surprisingly advanced, however.
**I guess my concern is would this be designed like a regular old city?** At the moment it is, with wealth-segregated areas, craft district, market zone, shanty area et al.
The other part is; I've given the ability for people within a few miles to do agriculture. This IS a pseudo magic tree, and it doesn't appear to grow further, so I'm actually proposing it draws nutrients at a reduced rate (only enough for some basic maintainence). Given its size, its probably feasible that the roots go deep enough to hit the mantle. It also doesn't appear to be vulnerable to fire much. ***Is this too much handwaving or is it concievable?***
I've considered [Designing a city around a giant tree?](https://worldbuilding.stackexchange.com/questions/14244/designing-a-city-around-a-giant-tree) and [Cities in the trees](https://worldbuilding.stackexchange.com/questions/13768/cities-in-the-trees) as data, but none of these precisely address my rather unique scenario!
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This is a government center, as well as a primary city. As a primary city, it means it grew organically for trade and defense (against others as well as the elements). I'll try to throw in some design ideas that you might build off of (or dismiss) in addition to what you already have - quarters, districts, etc.
Growing organically, it would center around your river that starts at the waterfall, and goes through the center of the city. This is how trade goods are sent downstream to other cities. So that's your central spine, and you can grow outwards. Two roots of the base of the tree form a V of protection, and the remaining exposed side of town will be walled.
Architecturally, and from an Urban Planning perspective you have to consider two things that have unique impacts on this city.
**Classical Vernacular** - The colloquial design of institutional & government buildings will no doubt present itself in the colors of the tree, and maybe even the shape of some buildings would resemble the inefficient (spatially) design of a tree.
**In the Shade** - The Tree will cast a dominant shadow over the city much of the day, but also protect that side from winter winds. Therefore, the buildings might have a slight wedge shape, sloping upward towards the tree: the exposed side facing the tree, protected from the elements. The remainder of the wedge sloping downward away from the tree will protect against winter winds, but include skylights to try to maximize solar exposure.
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I think your concerns may be well founded. This city will be fairly similar to most other cities and I don't think there's a whole lot you can do about it. However, it will have a couple of good attributes to it:
* **Tourism**
This is a very big tree, the only one of its kind. Anything like that is invariably going to attract people who want to see it. Your city will likely be more tourist-oriented than many others. It's possible that there will be a few companies offering "tours" of the tree where tourists get taken up close and perhaps walk around a walkway that someone has installed on the side of the tree.
* **Survivability**
Any part of your city that is anchored to the roots of this tree is going to be very resistant to damage. The roots of this tree are what keep it up, and given a tree that big they have a pretty big job to do. They're going to be very sturdy and capable of keeping buildings up where others might perhaps collapse.
* **Adventure**
There are always going to be people who want to know more about this, scientists included. You can expect fairly regular climbing expeditions up this tree to find out what's up there; you might also expect people trying to get **inside** it without being detected. As new methods are invented of destroying things, they're going to be tried out on the tree: you've invented dynamite? Let's see if we can get into the tree with it.
Other than that, I expect your city would be fairly normal.
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The main things that would distinguish such a city would be:
Tourism. A tree this large would attract anyone with the money to see it. It's possible that a whole religion might be built around it, or multiple competing religions. The city surrounding it is enormous, so it is not inconceivable that such a place would be the cultural epicenter of the world, accumulating untold riches. Your wealthy district built on a tree root, or other areas of the city near the tree would attract tourists and the money they bring. This land would be valuable, sort of like expensive beachfront property.
Magic. Depending on the exact nature of magic in your game, there could be an enormous incentive for magic users to come here. Maybe the dew from the tree possesses special properties. Maybe its wood is used in the most valuable elven artwork. Maybe a coven of dangerous creatures has taken up residence in your tree. Making your tree city a center of magic would definitely provide an incentive for adventurers to visit.
Nature. What creatures would live in the wake of such a tree? If we continue your idea of yggdrasil being oak-like and allow for giant acorns, then it makes sense that we would have similarly oversized(and possibly terrifying) herbivores to access this food source. The river could have a similar effect, as it's most likely quite nutrient rich from being filtered down the trees branches. Remember, it would hit the ground at terminal velocity and splash everywhere, possibly rendering a large part of the ground near the tree inaccessible. Later, however, it could be concentrated into one nutrient rich river out of the splash basin. For real life examples of what happens when a civilization grows near an exceptionally fertile river, look to Egypt. Excellent agriculture would lead farmers to establish themselves downstream, and the best plots could be hotly contested. For added fun, create a serious water hazard, like elementals or a cult of aquatic humanoids worshiping Yggdrasil.
Trade. A city like this could export unique products of the ecosystem, minerals found by mining with the aid of hollow roots extending deep into the ground, tea, blankets or tents made from its leaves(are they giant?), magical items(it's gonna be a rich place), druidic paraphernalia, food from farming the river, fish and many others.
Culture and Government. Druids will love this place. The rich will love this place. Anyone with power will come to Yggdrasil and stake their claim. Society could be a magistracy, monarchy or possibly a feudal system where lords exploit the wealth of a limited area by laying claim to sizeable areas of land and the people who live there. Also consider a societal contract with magic users, warriors and lords defending farmers and miners from outside or environmental threats in exchange for wealth. All these systems could conceivably fit within your existing framework.
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## The Views
In a world where tamed Wyvern are a thing, someone's going to land one on the side of the Tree. That person is going to realize that the view from 15,000 feet is ***spectacular***.
Someone rich is going to build a vacation home there.
Probably, your whole society is structured around "higher is better." It's expensive to haul supplies up the Tree with mid renaissance tech, so only the rich can afford to life on the Tree itself. But the richer you are, the higher you want to live to show off. Maybe 200 or 300 feet is the best people can do at this point, but the ambition to go higher is there.
## The Vulnerability
At the same time, the high ground is militarily valuable. If even a small enemy force were to climb the Tree, they could completely bypass the cities defenses. Even without a parachute or glider to get into the city, they could use fire arrows, heated shot, and just plain drop heavy things onto the populace. Also - assassinations.
## The Result
Style, even for the ground people, is light and airy. Everyone wants to evoke the feeling of living high on the tree.
Several forts are built around the base of the tree to prevent attackers from scaling it in any kind of numbers. Probably, these become proto-communities. Eventually, many years from now, the city will merge with these communities and completely encircle the base of the Tree.
An additional fort is built as high on the Tree as can be supported. It is manned by the best Wyvern riders in the kingdom, and is the effectively the Praetorian Guard. They always have the high ground.
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(Disclaimer: I tried this question earlier in the scifi site as well as real science sites, and was told should be on topic here)
I'm writing a speculative story about aliens coming to earth - and just wanted to bounce a couple of ideas for scientific accuracy (or at least lack of obvious impossibility).This is set in the near future (~2050s)- and it's more of a comic story so the details need not be exact.
If the alien ship jumps into the solar system (i.e. after super light flight) about ~2 Million Kilometers from earth - what would pick it up first? I guess at certain point of time all big observatories will - how long might that take?
Also - another point is communication between the aliens being picked up by one guy (however not by the governments). It's something like this - there is a network of satellites used for providing internet connection - and the communication between the alien crafts caused interference with this in some areas (maybe due to the same frequencies? Ka band?) which our guy was able to pick up, isolate and decode...however no official space agency did. Is that possible?
I don't have much background in radio communication - so apologies if these questions sound very amateurish...
Appreciate any and all help!
Cheers.
Wizkid
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I remember seeing this question on the Astronomy forum. Yup, this seems like a better location for it, though the skills required to answer do tend to cross over. Hopefully you'll get what you are looking for. Here's my attempt:
2 million kilometers is really not far in astronomical terms, the earth moves about 2.5 million km a day, so if they appeared directly in front of us, we'd crash into them shortly. ;) But depending upon the size of the ship, and how many of them there were, it still might be very difficult to detect. Check out [NASA's Near Earth Asteroid Tracking program](http://neat.jpl.nasa.gov/) for solid information on the size, position and count of objects we are currently tracking. But for something, say, the size of a medium-sized city, I'd put it much further out to be safe. Perhaps 50 million km or more.
If literally one guy discovers this before anyone else, then this guy is looking at something no one else is. The scenario you brought up seems unlikely since there would probably be a million people or more using that.
Not to write this for you, but I would recommend something like a graduate student writing a program to predict weather patterns on Saturn by studying electrical interference in the radio spectrum. He would probably initially throw out his data because an intelligent pattern would mean interference (See [third paragraph here](http://www.pbs.org/wgbh/aso/databank/entries/dp65co.html) on Penzias and Wilson's discovery of the Cosmic Microwave Background) Eventually he would look into the source of the interfering signal (but it would likely take days), and back to your regularly scheduled program.
There are thousands of grad students working on very specific areas of the sky in very specific bands for very specific purposes, and they are the only ones (or in many cases part of a small team) who are performing that one task in all the world, so your premise is plausible.
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I know that this question is pretty much off-topic and might be better asked in the sci-fi stackexchange, but I can't resist answering because it's a little nerdy.
1. It is impractical to provide worldwide internet using satellites, unless latency really is not an issue (and it generally is). This is pretty much due to the fact that in order to be most useful the satellites would want to be [geostationary](http://en.wikipedia.org/wiki/Geostationary_orbit), and the Clarke Belt is about 35,000km away from the Earth. Because of the speed of light, this means a 0.2 second round-trip time for signals from earth-to-satellite-to-earth - and much longer if it's earth-to-satellite1-to-satellite2-to-earth.
2. Moving to the realms of fiction for a moment, it would be quite likely that any culture that developed superluminal travel, would also be highly likely to have developed superluminal communications technology (similar to the oft-used 'sub-space' communications often used in sci-fi stories). Since this is not actually real (as far as we know! Yet!!), you could ascribe to this technology any properties, such as having it interfere with our technology when it is used. But conversely, it would be difficult for us to detect directly since we don't possess that technology itself. We could probably only detect its use because of the side-effects it has on our own technology. You could use this as a plot device, and it could explain pretty much everything you describe in the question. Since it's fiction (and science fiction, at that!), all you have to do is invent some technologies, and work out ways for it to fit the story.
3. Because of the vastness of the skies, it is wholly possible that one man or woman could find something before an organisation or government. Radio amateurs do tend to have highly-directional antennas pointed in the general direction of the sky, and it could be that one guy (or gal)'s equipment suffered problems whenever his/her antenna was pointed at one exact spot in the sky - and he could take that information to his/her local radio club, where other people later experiment and try and find the same thing.
It would probably be worth visiting a radio club to get a feeling for the general atmosphere at such places, and to see the kind of things that people discuss.
I know the question is generally off-topic for this forum, but apologies again for being unable to resist answering it :)
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Let's assume that super light speed is possible (against the claims of main stream science).
Assuming this, let's ask about the consequential **scientific/reality-check** issues.
One has to ask how much energy would be needed to stop an object travelling at the speed of light or higher speeds. If the stopping distance is anything less then a few million light years, then the amount of energy discharged would be so enormous that it would surely blast our entire solar system into deep space at ultra high velocity. But all of this depends on the same $ E = m \cdot c^2 $ that prevents super light speed and since we are ignoring this we will ignore its consequences here too.
Let's say the vessel has used some sort of wormhole to achieve a gentle jaunt across a vast distance in a short period of time while the crew review their devious plans. Opening up a wormhole in our local neighbourhood would certainly produce an earth-shattering amount of energy, but let's ignore this too and say that the amount of energy generated is not earth-shattering. At a distance of 2 million kilometers the most likely first detection would follow when satellites stop functioning as they are irradiated by resulting energy or thrown out of orbit - this is assuming the absence of an intense flash of energy in the optical spectrum that was detectable across earth by the naked eye.
Well, you did ask for a reality check. So let's ignore all of this and arrive at the scenario of minor locallized disruption to internet communictions following an undetected arrival. While it is possible that our guy could be the first and only to detect an anomalous signal, it is difficult to understand why he would recognize its significance rather than writing it off as something he did not understand. Further, assuming that he has the know how to isolate the signal, for me personally, it simply defies credulity that he could decode and understand such a signal. Indeed, any alien race with such advanced, god-like technology would surely employ unbreakable encryption in their communications and be able to move amongst us undetected.
So that's my reality check. On the plus side, none of these issues need be a problem if the story is good.
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What would be the first thing to notice? Assuming the correct hemisphere and on the dark side, the [LSST](https://www.wikipedia.org/wiki/Large_Synoptic_Survey_Telescope) will add a time dimension to astronomy, tracking tens of billions of visible objects every few days. It will be a public database, with alerts noting things of interest. A *that's new!* notice might be followed publicly by a great many people, both with telescopes and just watching the web and chatting.
This would be a great thing to detail in a first-contact story. It could be seen within the week (next pass) of appearing, or it could appear on the day side and not get tracked for a few months (if it's in the outer system and doesn't move with the Earth as it moves to the other side of the sun) and make a ruckus with everyone speculating where it came from without necessitating a sudden FTL appearance.
With the new bright spots on the eastmost strip, they will generally be comets and results of asteroid collisions that change what's charted, and largely automatically processed. There might be some conspiracy-theory sub-plot concerning the disposition of one particular new bright spot near Saturn's orbit. Then it's found to be in circular solar orbit, not an incoming comet...
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In the future, Mars has been successfully terraformed to be Earth-like in terms of atmosphere so that humans can inhabit it safely. If Mars had an atmosphere similar to Earth, but was still 1.52 AUs away from the sun, what would its temperature range be? Considering its distance from the Sun, I assume it won't be nearly as warm, and it already gets fairly cold there in the modern day. Would it be actively habitable for humans without suits or outside of a sealed area?
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When sunlight hits a planet, a fraction "a" reflects off the planet, with the rest, (1-a), being absorbed. a is the albedo of the planet. For Earth, the effective albedo is 0.3. Half of that is due to cloud cover.
Then, the warmth of the planet produces long-wavelength photons. The power of these photons is [proportional to T^4](https://en.wikipedia.org/wiki/Planetary_equilibrium_temperature#Calculation_of_equilibrium_temperature), with T being the planet's temperature in Kelvin. Most of the long-wavelength photons get absorbed by the atmosphere on the way up (greenhouse effect).
In equilibrium, energy in = energy out. For Earth, energy in = 1361 W/m^2, and Earth has an average surface temperature of 288 K. So we have:
1361 W/m^2 = .3 \* 1361 W/m^2 + C \* (288 K)^4
where C is some constant that accounts for how much heat is emitted by the planet without being trapped by the greenhouse effect. Solving for C on Earth:
C = .7 \* 1361 W/m^2 / (288 K)^4 = 1.3848e-7 W/(m^2 K^4)
Now we want to set up the same equation for Mars, using the C from Earth to represent the size of Earth's greenhouse effect. First, what albedo should we use? We want to know what albedo Mars *would* have, if it had an "earth-like" atmosphere.
You didn't say anything about Mars having oceans, so let's suppose that it doesn't have an Earth-like water cycle. That means no oceans and no clouds. That's important; without clouds to reflect light, Earth's albedo would be only half as large.
Mars' current albedo is 0.25. If it had an Earth-like atmosphere, some percentage of incoming sunlight would be absorbed by the atmosphere, lowering the albedo. For Earth, that figure is [23%](https://en.wikipedia.org/wiki/Greenhouse_effect), but our Mars atmosphere lacks clouds so it would be a different amount. But we can't really calculate that, so let's just say Mars-with-atmosphere's albedo is just 0.25 \* 0.77 = 0.18.
Mars receives 586 W/m^2 from the sun. So we can set up the equation:
586 W/m^2 = 0.18 \* 586 W/m^2 + 1.3848e-7 W/(m^2 K^4) \* T^4
Solve for T:
T = (0.82 \* 586 W/m^2 / (1.3848e-7 W/(m^2 K^4)))^0.25
= 243 K
or -30 C, or -22.8 F. Pretty cold!
For a sanity check, Earth's temperature without the greenhouse effect would be -20C, and Earth's temperature with the greenhouse effect is 15C, a difference of 35C. Mars' actual temperature without the greenhouse effect is -60C, so our prediction is it would warm by 30C, which is similar to Earth. The simple method we used is probably in the right ballpark.
But note that if you want it to be warmer all you have to do is increase the amount of greenhouse gases. You could make Mars an unlivable 100C if you wanted to, with enough greenhouse gases. You can really choose any temperature you want.
Implicitly here I am assuming an "Earth-like" atmosphere means an "Earth-like" greenhouse effect per m^2. Although this assumption may be questionable because to get 1 bar of pressure at ground level on Mars, you need 2.6 times more mass of air per m^2 due to the lower gravity, so the greenhouse effect would actually be larger with the same composition and ground level pressure. C would be 2.6 times smaller, which would result in an average temperature of (0.82 \* 586 W/m^2 / (1.3848e-7 W/(m^2 K^4) / 2.6))^0.25 = 35C. Quite warm! But realistic Mars terraforming involves lower atmospheric pressure than Earth, and again, you can set any temperature you want by adjusting the amount of greenhouse gases.
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If Mars had an atmosphere similar to the Earth then the planet would exist in a state far beyond it's equilibrium point and a range of different processes would transform it over a range of different time scales.
In the very short term there would be atmospheric chaos with almost all of the water vapor from the Earth like atmosphere condensing into frost or snow. The atmosphere would also probably become thick with the very fine Martian dust stirred up as weak vaguely Earth like winds replaced the ghostly winds of Mars that we know.
In the mid term the average temperature would increase from -60 towards 0 degrees C. Due to increased heat capacity of the atmosphere and vast amounts of dry ice that would permanently out gas from the Martian polar caps.
Eventually this would probably allow large quantities of salt water to exist on the surface again, as was thought to have happened billions of years ago on Mars. It is estimated that there are five million cubic kilometres of water ice on mars today.
Temperatures at the Poles would probably remain very low despite the warming effect of convection currents in the atmosphere and the extra carbon dioxide, so it’s hard to say how much liquid water might remain. It is possible that it might all eventually end up frozen at the poles. Else where there might be areas of freezing shallow seas and/or deep mud with a frozen crust.
Longer term the dust storms would die down in the wetter environment, but details of what would happen depend on what plans you had for the new Mars. If Mars is simply equipped with an Earthly atmosphere and left then oxygen levels would very slowly decline due to the oxidation of surface materials such as meteoric iron and more. With liquid water, freeze/thaw action and vastly more wind present erosion could slowly uncover further materials for oxidation from deeper down leading to depletion of oxygen.
So long term oxygen levels would probably need to be topped up. If a biosphere was created this might well be sufficient for this purpose. Although given the magic involved in creating the Earth like atmosphere in the first place, topping up the oxygen occasionally should not be a problem.
UV dissociation of water in the upper atmosphere into hydrogen and oxygen and subsequent loss of hydrogen to space would slowly rob Mars of its waters, but the process would be extremely slow indeed with the new atmosphere. It took hundreds of millions of years for Mars to lose a large part of it’s liquid water in the past in an oxygen free carbon dioxide atmosphere. The loss of hydrogen would be seriously inhibited by a high concentration of atmospheric oxygen which would tend to react readily with the hydrogen to reform water before its eventual escape. (see “Oxygen – the molecule that made the world” by Nick Lane pages 25-26)
<https://zenodo.org/records/1233311>
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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.
I'm asking this out of curiosity, mostly as a response to [Space elevator from Earth to Moon with multiple temporary anchors](https://worldbuilding.stackexchange.com/q/247814/7130) and some of the comments and answers there.
Suppose you're able to build space elevators on both the Earth and the Moon. The question is, can you get a capsule from Earth to Moon or vice versa without having any thrusters on the capsule?
This is an orbital mechanics question - the question is whether with suitably positioned space elevators there exists an orbital trajectory that leaves from one and arrives at another with sufficiently low delta-v for it to be launched and captured.
Note the [hard-science](/questions/tagged/hard-science "show questions tagged 'hard-science'") tag - answers are expected to include calculations or references to them.
Here are some rules:
* You can build launch/landing rails on the Moon as an alternative to a Lunar space elevator, meaning that you can leave from or arrive at the Lunar surface with a high delta-v. However, you can't leave from or arrive at a space elevator with significant delta-v, unless you can explain why the recoil wouldn't mess with the space elevator.
* The capsule doesn't have a parachute or atmospheric shielding.
* Unless there's some reason why it would be impossible, the capsule contains humans.
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You are asking a pretty involved question that would need simulations to be properly answered.
Just conceptually, we know that if a Space Elevator tether extends beyond Geostationary orbit, the tip of the cable will move faster than orbital velocity. The velocity here is simply;
$$v = \frac {2 \pi (l+r\_e)}{s}$$
Where $s$ is the number of seconds in a day (86400), $l$ is the length of the tether and $r\_e$ is the radius of the Earth.
We can test this formal by plugging in the height of geostationary and comparing the resulting velocity to the actual orbiting velocity. This formal says the velocity is $3038\frac{m}{s}$. Which is right on the money. In reality it is $3070\frac{m}{s}$
We can use a very bad estimate to get ballpark figures for how much $d\_v$ we need to get to the moon. By bad i mean i fired up Universe sandbox and just kind of looked how much i have to change the velocity of a probe at Geostationary to intersect the moons orbit. Obviously the moons orbit is not circular so this is an example value. From this very crude approach, i got ~$1180\frac{m}{s}$ to go from GEO to TLJ (Trans Lunar Injection).
So, we now know our Velocity at the tip of the cable has to be ~$4250\frac{m}{s}$. Which works out to a length of $l = 52786000m$. Note this is minus the 6000km from Earths radius. So the cable has to be 52780km long.
Right about now a good question would be precisely at what velocity we will intersect the moon. According to Universe Sandbox 2, we will reach Lunar orbital height at a velocity of $371\frac{m}{s}$. Which you may notice is slightly slower than the Moons orbital velocity of ~$1022\frac{m}{s}$. As a matter of fact we appear to be missing ~$700\frac{m}{s}$.
But is this actually a problem ? Well no. Nobody ever said we need a cable attached to the moon to capture us. We just need a cable that rotates with a velocity of $700\frac{m}{s}$ and is able to capture us. a Skyhook. Do i know how to do the math for that ? Absolutly not. But it should be possible to place a bit rotating skyhook in lunar orbit. On the one end it captures our spaceship coming from Earth and slows it down. And in exchange it throws another from the Moons surface to Earth. This way it stays balanced.
This entire system would require exactly 0 engine ignitions and only one half decent maglev on the moon since you need to move at $700\frac{m}{s}$ to be captured by the hook.
So yeah, aside from climbing a 52000 kilometer high elevator and one maglev on the moon, this is Energy free. Though, i would argue if your big plan is to build a 52000 kilometer elevator, just use a rocket.
EDIT; i had a smooth brain moment and wrote m/s² everywhere instead of m/s
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Taking some inspiration from the finding that a small proportion is able to perceive significantly more colors than the rest of the population, I would like to explore to what degree similar traits can be attained via natural selection. A [short segment](https://www.youtube.com/watch?v=MdBTMGRHk2g) on 'tetrachromatic' eyes.
It may be the case that human's learned behavior, like digital tool-making/hardware will complicate the arithmetic. So perhaps we can begin the evolutionary experiment millions of years earlier when hominids had relatively basic tools.
Purely for benchmarking purposes, the mantis shrimp has among the most 'vivid' color perception, which has hexakaidecachromatic vision, if you will humor my neologism.
[](https://i.stack.imgur.com/cHUdRm.jpg)
In hindsight, it's plain to see that the hominid-to-human arc culminated favorably; we became a prominent fixture of the earth's biome without the need for ultra-sensitive, bells-and-whistles vision. This will mean that the onus will be to introduce environmental factors that **will** require very advanced color sensitive adaptations from humans.
## Question
What environmental factors need to be present on a [earth-like](/questions/tagged/earth-like "show questions tagged 'earth-like'") world such that our early ancestors would evolve extremely color-sensitive vision adaptations?
**Further clarification:**
* If necessary, explain physiological assumptions. Let's keep this as open-architecture as possible though: i don't want to undermine answerers creativity.
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## You need only look at Plants and the evolution of insects in our very own garden.
Plants evolved flowers almost 130 million years ago, long after sexual reproduction through spores and pollen. Insects, however, had been on the earth for well over 300 million years.
So Plants needed a way for certain (not all) insects to exclusively come to its flowers, and spread its pollen. How to do this? Flowers developed markings attuned to only certain insects in certain UV ranges - this way bees, butterflies and other insects know exactly which flowers have the nectar they need. If you collect flowers in your garden and place these under a UV light, you will see these markings that normal animals (and some insects) cannot see.
Insects 'co-evolved' along with the flowering plants as also they have an advantage to perceive discreet UV light ranges to give them an evolutionary advantage (an additional food source) and reproduce more. Plants 'co-evolve' further, and this relationship continues until the distinction is so great new species arise with new light-frequency detection and production.
[](https://i.stack.imgur.com/odtl6.jpg)
Original article : <https://en.wikipedia.org/wiki/UV_coloration_in_flowers>
Transferring this mechanism to humans using an established precedent then is easy - perhaps plants produce fruit that are advantageous only if humans eat them to give an advantage over other species of plant. Those humans that have extra UV perception can take advantage of this new food source, and reproduce themselves more often, co-evolving with the fruiting plant, eventually expanding the range of their perception in this direction.
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**Camouflage**
Had Mother Nature evolved both predators (critters that eat humans) and prey (critters that humans eat) with better camouflage, our eyes would have developed better methods for detecting both.
*Keep in mind that the nature of speculating about evolution is that if X happened then Y **might** have happened. There's no way to definitively prove the causal relationship between speculated X and Y. That might not be possible even with known evolutionary changes (Y happened and X existed so we can **assume** a causal relationship between X and Y). So when you say [science-based](/questions/tagged/science-based "show questions tagged 'science-based'"), you really mean [science-fiction](/questions/tagged/science-fiction "show questions tagged 'science-fiction'"), right?*
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Alright, so to set the stage: the setting is 3-5k years after civilization as we know dissolved. The dissolution happens about a hundred or so years from the present day (+/1 2123) after we have advanced technologically a bit more, but also after having burned considerably more carbon. As a result of the tensions caused by unbridled climate disaster the nukes eventually fly, because one good idea begets another. (Please don't focus on the nukes or the climate disaster, they're just background information and not part of my question.)
For a clearer picture, the area to focus on is any metropolitan city on the shore of the Great Lakes in the United States.
Now, there seem to be 2 schools of thought for how long the materials like I-beams and rebar encased in concrete would take to corrode or break down amidst the rubble of crumbled cities. Some seem to think concrete will be around at least multiple centuries later much like stone from roman ruins. On the other hand, there seems to be a lot of evidence that after only 50-100 years there would not be much left to recognize.
**Either way we are eventually led to my question:** Where would the intrepid survivor find steel and metal after 3,000-5,000 years?
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**You have options**
On our Sister Stack, Earth Sciences, we find the following question: [How long could a steel artifact last?](https://earthscience.stackexchange.com/q/18768). It reads:
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> Would man-made steel artifacts be able to be preserved like fossils for millions of years, or would corrosion make them dissipate? What about metals such as aluminum that don't corrode as easily?
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The accepted answer states:
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> The short answer is no.
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>
> Most metals do not fossilize well, they are too reactive/water soluble. Metals are usually what is doing the fossilizing, dissolved metal in groundwater is being attracted to the electrical properties of organic material and filling in or swapping places with a porous material. You might have a stain left or some of the shape as a natural casting, but not material preserved. The exception might be in amber, but it could also be really bad: amber preservation is tricky chemistry, so I am not comfortable saying yes or no. Metal objects have good short term preservation but horrid long term preservation. there are some low reactivity metals that might survive like gold, but not as fossils. But even gold is water soluble over millions of years, so even that would require some unusual conditions.
>
>
>
This is explaining the worst case situation. Over the course of thousands of years, some metal may remain on the surface and look vaguely like the superstructure of a city, but some portion of it will have been dissolved back into the ground.
But my point here is this: *it's still metal.* Even rust is still metal with too much oxygen. The only practical difference between a steel beam hot off the press and ready for construction and one that's been left to rot for thousands of years is that some portion of the latter (due heavily on the circumstances of its situation, even with the precision you gave us) will simply be part of the dirt beneath it's original constructed location.
Ready for your intrepid survivor to dig up and smelt.
It should be said that in an area as rainy as the U.S. Great Lakes region there will be a substantial loss of above-ground metal.
**Nothing is built to last forever**
Part of your problem will be working with the rubble. Modern highway bridges have an expected lifespan of only [75-100 years](https://www.builderspace.com/how-long-do-highway-bridges-last). Modern skyscrapers have an expected lifespan of [about 140 years](https://newatlas.com/skyscraper-demolition-lifespan/54703/). None of this is because the metal is dissolving into the ground, but (a) weakening infrastructure from use raises the *likelihood* that the construction might partially or wholly collapse and (b) the economic value of doing so makes sense (it might have nothing to do with whether or not the construction could last longer). From a more realistic perspective, such buildings will last 500-1,000 years.
>
> Structures are built to resist environmental loading events – including earthquakes, windstorms and snowstorms – that have a mean recurrence interval of 50 years. This means the design basis uses events that on average will occur once every 50 years – though of course it is possible for a 50-year storm to occur in consecutive years.
>
>
> ...
>
>
> The combination of using a 50-year recurrence for design loading events and safety factors in construction typically results in a design exceedance interval of about 500 years, with special buildings (as mentioned above) having intervals of 1,000 years or more. This means we would expect a typical structure to fail once in every 500 to 1,000 years. ([Source](https://www.independent.co.uk/arts-entertainment/architecture/how-long-are-skyscrapers-built-to-last-10263881.html))
>
>
>
What does all this tell us? While it's unlikely that you'll have standing buildings after 3,000-5,000 years, *it's not impossible.* This means that there should still be plenty of above-ground metal that can be salvaged — assuming that working through a potentially collapsed pile of rubble is practical.
**But what does "practical" mean?**
There's a huge difference between what a growing society of 1,000 or 10,000 people need and what a single person needs. A single person would likely find plenty of salvageable metal in collapsed structures, decaying vehicles, etc. The needs of a larger community might find the economic practicality of working through the rubble, no matter how much metal exists, more work than it's worth.
Whether or not any of this matters depends more on where you're taking your story than on worldbuilding. From a worldbuilding perspective, the metal is there, waiting to be smelted and used. Your story gets to deal with the ratio of value-vs.-effort.
But one thing you can't ignore, a steel beam can't simply be tossed on a cart and hauled away by a couple of horses. There may be some short pieces, but even a short piece is *honking heavy.* Without cutting torches (or some whomping good hacksaws...), a piece sitting right in front of you, waiting to be used, *might be entirely inaccessible, anyway.*
**Conclusions**
* Some metal will have dissolved, rusted, or simply become inaccessible without some form of mining technology (whether it's picks and buckets or earth moving equipment). The metal's still there, it just needs to be mined like any good ore and smelted again. Metal, being heavy, is unlikely to travel far. Don't let gold in rivers fool you. That's really small bits and flakes for the most part... the mother load being a seam of gold in rock someplace. Same deal with steel. With the exception of small amounts likely not worth panning for, most of it will be directly below where it was on the surface.
* A great deal of metal won't be accessible without serious tools. This ranges from pieces of I-beam sitting in the middle of the street that can't be lifted or transported due to the nature of the individual/team that found it to stuff that's so buried in rubble that the effort of freeing it might be more than the value it represents.
* What's left is what you can salvage. It's still a considerable amount — unless you're trying to provide the needs for a very large community. There's metal everywhere: power lines, towers and poles, vehicles, rails and rail cars, various factories and plants... Apartment and office buildings are common, but by no means the simplest source. Heck, start by looking for gravel pits or cement plants. Look for railways. Look for the protective sidings on road ways. There's metal *everywhere,* and while 3,000-5,000 years will have made a lot of it hard to find, if we're only talking about small communities with small needs... I should think you don't have a problem at all.
If there's a problem, it's going to be finding a predictable source of liquid acetylene and oxygen. But, now that I think about it, while I doubt those big, heavy tanks of oxy and acetylene you find at hardware stores won't have much in them after a couple 'o thousand years... what they will be is a movable source of big chunks of metal.
Yeah... it's everywhere.
[Answer]
### Metals Other Than Whopping Huge I Beams
Your intrepid explorers might be a bit daunted by the prospect of preparing and hauling away a partially rusted 3/4 ton I beam. But there are certainly other, and possibly more lucrative, metals to be looked for!
**Rail lines**: big cities are literally crawling with rail lines, rail yards and overhead power infrastructure. They won't find much steel ready for use, but as JBH said, all that rust is ready for smelting! Just dig it up and cart it away! Be on the lookout for tunnels --- those that aren't flooded might just yield some usable steel as well as copper.
**Power stations & grid**: these are full of metal. Lots of steel. They also branch out with steel & aluminium pylons and miles & miles of several inch thick aluminium transmission lines.
**Neighbourhoods**: don't neglect mom-n-pop shops and all those houses! Your explorers will find plenty of copper lining the long abandoned streets as well as within houses and other structures. Hospitals are excellent sources of copper, aluminium and stainless steel; restaurants are also great sources of high quality stainless steel. Homes are great places to find copper (wiring & plumbing), brass (decorative items & fixtures), and stainless. They're also much more likely to find smaller scale steel beams. Banks, interestingly enough, will be great places to find nickel (in the form of coins (21st century US coins are mostly nickel, Canadian dimes and quarters are pure nickel)). If the bank has a vault, your explorers will have much fun with the extremely thick steel walls, but will also likely find a bonanza of precious metals and brass inside.
**Shopping districts**: Every shopping district has at least three vital sources of easily portable metal wealth. Restaurants for stainless; home goods stores for aluminium and stainless and brass and also bronze. And lastly, the mother lode: jewelers and coin shops! GOLD! PLATINUM! PALLADIUM! SILVER! (And GEM STONES!) Not only will these metals be largely free from the effects of time and chemistry, but most objects made from them are small, easily portable, of known quality and often beautifully wearable. Not to be overlooked are antique malls. Your explorers will find traces of iron (in the form of rust), but will also find plenty of copper & brass as well as some amount of gold and silver in the forms of plate, jewelry and coins.
**Waste Handling & Recycling**: Recycling centers, both consumer and commercial, also offer a bonanza of usefully sized chunks of metal, in particular, steel, copper and aluminium. Even if the steel is all rusted, your explorers will at least come across a concentrated zone of iron ore!
] |
[Question]
[
From Project Rho:
[http://www.projectrho.com/public\_html/rocket/heatrad.php#:~:text=Dusty%20Plasma%C2%A0radiator%3A](http://www.projectrho.com/public_html/rocket/heatrad.php#:%7E:text=Dusty%20Plasma%C2%A0radiator%3A)
Example Image: <https://twitter.com/toughsf/status/1154692082478526465>
A dusty plasma radiator uses conductive plasma, in turn manipulated by magnetic fields, to manipulate dust particles. This could allow them to be cycled out of the ship and back within to disperse heat. There is some similarity to the idea of a liquid droplet radiator, except with dust and the conductive plasma gives greater control (and you are less likely to lose your radiative material during maneuvers). We mainly just need more understanding of how to precisely control the plasma and dust.
Assume we get over the control issue. We get a continuously flowing stream of dust going from the radiator, out into space, and back into the spacecraft.
Besides functioning as an effective radiator wouldn't these things also be fairly effective against laser attacks?
A laser trying to get through the dusty plasma would be subject to Rayleigh scattering, and because the dust is constantly being shuffled around the heat is actively dispersed instead of concentrated onto a single area. Not to mention the 'on the tin' purpose of a radiator is to radiate heat.
And depending on how much control we developed over magnetically manipulating the dusty plasma, more vulnerable areas could be covered in thicker layers/faster moving dusty plasma.
Does this make sense as a laser defense, or am I completely misundertanding things?
[](https://i.stack.imgur.com/kxesO.jpg)
[Answer]
## If you can see through it, so can the laser
@Daron's answer of "if it's dense enough and the laser's weak enough" is pretty accurate. I thought I'd need to do some math on the absorption of the dust particles and radiative area (the reason why dusty plasma is a good idea is because of their large radiative surface area to mass ratio, making them great heat exchangers), but the bold argument at the top is, in my opinion, pretty reasonable. If the microparticle plasma is only partially opaque, then that fraction of light that makes it through (e.g., sunlight reflecting from the vessel's hull, through the dust, to your eyes) is the same fraction of laser light that'll make it through (from just outside the magnetic confinement to the vessel's hull).
Actually, it'll be "slightly" worse than that. The dusty plasma will have an effective scattering length (what @Daron's answer describes), but as the laser bombards and the dust's temperature increases, the scattering length will increase until the plasma isn't scattering significantly at all (and the scattering length is already likely to be on the order of the dusty plasma's depth, anyway).
If you're being fired upon, it means you're probably within the effective range of a diffraction-limited laser, where spot size is likely on the order of a meter or less (a few cm spot size at 100,000 km distance is not unreasonable). Dusty plasma simply isn't going to do much against a 100 MW/m^2 pulse, as it's intended to absorb and radiate much, *much* less than that. Even if your dusty plasma shield was made super-dense and completely opaque, the principles of [atmospheric hole burning](https://galacticlibrary.net/wiki/Atmospheric_Hole_Burning) can be used to quickly and effectively drill through it. Fire a powerful sub-millisecond pulse to ionize the first tens of meters of plasma shield, wait a few fractions of a second for the plasma to expand to near-vacuum, and then rinse and repeat until you've breached the shield and are now penetrating the hull. The first few milliseconds of beam power might have been wasted making it through the plasma shield, but the majority would have made contact.
(It's good to keep in mind that most of the laser's energy will be delivered in less than a second. There's not going to be enough time for the dust to "fill in" the hole before any competently powerful laser burns through and strikes the hull.)
You likely wouldn't want to surround your ship in an opaque cloud of magnetically-confined dust, anyway. Firstly, the upshot of dusty plasma radiators is their high radiative power to mass ratio, making them lightweight radiator options. Secondly, a cloud of the stuff dense enough to be opaque is going comparable in mass to a solid sheet of the same material laminating the hull.
Your best defense against lasers is likely to be some combination of ablative/NERA/composite/capacitive, etc. armor, spaced and angled. Especially angled, weathering the incident beam energy over a greater surface area.
---
TL;DR: dusty plasma radiators are good at being low-mass radiators, but you might want to look elsewhere for passive laser defense.
[Answer]
**Go with it**
TLDR: If the cloud of plasma is ***big enough*** plasma and the radiators are ***good enough*** and the laser is ***weak enough*** then this might work. I do not know the correct equations to calculate it. I say don't bother calculating. Just say all the numbers are whatever numbers needed to make it work and get back to writing the story.
---
The laser works by pumping enough heat into a small part of something to melt a hole through it. If your spaceship has a layer of plasma around it, then perhaps it will scatter some of the particles. The scattered particles start bouncing around in the plasma "atmosphere" like in this Shutterstock photo:
[](https://i.stack.imgur.com/Oc9hr.jpg)
The big wavelengths zip straight through the atmosphere and heat the planet. The small wavelengths bounce around. Some hit the planet and some get absorbed by the atmosphere. Some zip back out into space. But here's the thing -- the guys that aren't scattered still heat the planet. You'd expect much less than half of the blue light to get reflected back.
Your layer of plasma works a similar way. It spreads out the laser beam rather than nullifying it. How much it spreads is a physics problem, and I don't know the equations. Ideally it spreads over the whole ship evenly.
In that case you are in luck. Because your ship is good at dissipating heat! If the the radiators are good enough then you cane dissipate the heat faster than the laser supplies it.
Perhaps if you had a really thick atmosphere and a really big spaceship it would keep you safe even without radiators.
] |
[Question]
[
These aliens live on a planet with a thick atmosphere and light gravity, and spend most of their life in the air.
They communicate through a series of piercing whistles and sound-wave vibrations, and I've concocted a slightly convoluted mechanism that provides them aesthetic appeal, and, hopefully, a bigger range of sound and amplitude.
I want to know if this concept would work as intended, or if it would be contradictory or extremely challenging to functionality.
Here's the associated design. Blue arrows indicate oxygenated air and red is air pushed out. To allow for continual conversation, the alien can divert air straight to its larynx for prolonged communication. (Click image for larger version.)
[](https://i.stack.imgur.com/4yT4O.png)
If it does **not** work as intended, what would need to be added/removed to ensure it's viable?
Thank you very much. Please let me know if you have anymore questions, I'm willing to provide more context.
[Answer]
It should work just fine. Expelling air past our larynx out through a modulated opening is how we humans(and most animals) communicate.
As a side note, based on the sounds you're describing, the appendage would be more of a hollow sac, lacking vocal chords and not called a larynx. But dolphins use air sacs in this way to create whistles and pitches; we also believe parasaurolophus dinosaurs communicated like this as well.
Fictional or otherwise, everything about this is anatomically sound and would work in the way you describe. I love the design as well, by the way.
] |
[Question]
[
**Closed**. This question needs [details or clarity](/help/closed-questions). It is not currently accepting answers.
---
**Want to improve this question?** Add details and clarify the problem by [editing this post](/posts/234306/edit).
Closed 1 year ago.
[Improve this question](/posts/234306/edit)
One of my writing buddies keeps insisting that my biped/digitigrade alien species would need a tail to act as a counterweight and shift their centers of gravity. Would a tail be required?
EDIT:// the species is pretty upright like a human.
[Answer]
# It's a matter of Posture.
[](https://i.stack.imgur.com/tq2qp.jpg)
Essentially, whether you need or not a tail is mostly dependent on your creature's posture. This can be seen easily with us, modern birds and theropod dinosaurs.
We have our center of balance fairly close to a point right above where our legs begin. Because of this positioning, we don't need tails, but maintaining balance while heavily hunched over is very tricky as a result. In fact, because of how our center of balance is placed, suddenly attaching a heavy tail to a human will actually compromise their balance, forcing them to take a more hunched posture in order to balance it out.
Modern Birds have a very similar situation: their center of balance being close to their legs, meaning they too don't need long or heavy tails, ideal as most of them need to remain as light as possible, and the ones who don't can also benefit from having an easier time changing direction without needing a tail to be used as a rotor or counterweight. At worse, some species have centers of balance slightly tilted forwards, balanced by their pelvis without requiring a heavy tail.
The classic Theropod dinosaurs (such as T-Rex, velociraptors and dakotaraptors), on the other hand, had their center of balance further away from their legs, closer to the front of their bodies. As a result, they needed heavy tails to act as counterbalances.
Where your center of balance lies still remains as one of the main factors, and that holds true even if you were to have backwards facing legs, or any kind of leg really. If, for example, they were quadrupedal like bears, they'd also not need a tail, as their front limbs help supporting their weight and maintaining balance, thus not requiring a heavy tail or counterbalance.
So, summing up, whether they need a heavy counterbalance tail or not is mostly reliant on how their posture is and the number and position of limbs supporting their weight:
* Bipedal with Dinosaur-like posture and/or center of gravity away from legs? A tail or a similar counterweight is needed (this would still be true even if the animal had its body and center of gravity pointing backwards, except they would instead need a counterweight pointing forwards, be it a tail or something else).
* Bipedal with an upright posture and/or with a center of gravity close to the legs? Again, not necessary, but a rotor-like tail could still see use aiding in changes of direction while running depending on their anatomy, as long as it remained light as not to shift their center of balance towards the back, turning them into a more theropod-like body plan (as we see in the roadrunner's light tail adorned with long tail feathers used to change direction quickly like we suspect raptors did). As long as their center of balanced isn't too far away from the supporting legs, simple changes in their structure might be more than enough to balance it out without needing a long and/or heavy tail.
* A quadruped? Similar to last case: the presence of 4 limbs means that whether center of mass is close to either pair or somewhere in the middle, it'll still be adequately supported.
[Answer]
No it's not required. Bipedalism on it's own shifts the centre of gravity, all balancing mechanisms can develop to go with it, a tail is not required. The common ancestor of apes lost it's tail and balanced just fine in trees.
[Answer]
**Your Friend is Wrong**
[](https://i.stack.imgur.com/YTtZr.jpg)
Humans are not digitigrade. But they can become digitigrade by standing on their tippytoes.
Your homework is to try this for yourself and see if you fall down -- even without a tail.
It stands to reason that a species that is naturally digitigrade would be even better at not falling over, and be able to stay on their toes all day without the muscles tiring out.
] |
[Question]
[
This is my first ever question on here.
I've seen a few posts on Martian physiology but since the answers on here are answered so well and by so many I thought I'd be more specific.
How would human physiology have changed over 3000 years, providing biomes to replicate Earth's atmosphere?
~~Following that, how would a present day human *feel* to meet them and know the martians they are conversing with were descendant of themselves.
How would **you** feel to meet your Martian future descendant and what would you want to talk about? What do you think they'd ask you?~~
[Answer]
3000 years is practically "earlier this morning" in terms of biology and evolution for humans. 3000 years is about 90 generations. It's not enough time to have significant changes in physiology: we are still the same as the ancient Egyptians or Mesopotamians, and it has been more than 3000 years ago.
As it was commented in this [other answer](https://worldbuilding.stackexchange.com/a/228245/30492) of mine by Jdunlop:
>
> The Inuit probably developed their layer of subcutaneous fat over the time from the last ice age to the present - about eleven millennia.
>
>
>
[Answer]
**Background trivia**
For a true human example of evolution over a few thousand years, evidence [the teeth](https://www.ecpi.edu/blog/evolution-teeth-how-smarts-skill-changed-human-mouth).
>
> The Shape of the Matter Over the course of the last few thousand
> years, the human jaw has changed shape dramatically. One of the
> broadest trends has been a steady decline in the size of the jaw. From
> around 35,000 years ago to about 10,000 years ago human jaws and teeth
> decreased in size by about one percent every 2,000 years. For the last
> ten thousand years, that pace has increased to roughly one percent
> every 1,000 years. In pace with our shrinking teeth and jaw, the
> structure of human teeth has changed as well, as thickening enamel and
> adaptations in technology have cut back our reliance on strong,
> well-ordered teeth.
>
>
> Cooking has had one of the largest effects on the development of human
> dentition. In the distant past, when much of our diet was raw fruits
> and vegetables, we needed strong and straight teeth. These helped us
> push our way through the tough, large particles that made up our diet.
> Cooking has reduced our need for this ability dramatically. At its
> simplest, the primary goal in cooking food is to break down tough
> fibers in meats and vegetables, rendering our meals proportionally
> easier to digest. As a result, the evolutionary pressure to keep our
> teeth well-ordered has dropped away.
>
>
>
Another example of subtle human changes over time is [height](https://www.cnn.com/2016/07/26/health/human-height-changes-century/index.html).
>
> “Over the past century adult height has changed substantially and
> unevenly in the world’s countries, according to research published in
> the journal eLife.
>
>
> Authors found that people from central and southern Europe, as well as
> East Asia, grew taller in the last 100 years. Meanwhile there was
> little gain in height for people from sub-Saharan African and South
> Asian nations. A few countries experienced decreases in their average
> adult height after years of gain.
>
>
> Researchers found that Dutch men, at 182.5 centimeters (about 6 feet),
> and Latvian women, at 170 centimeters (5 feet 7 inches), are the
> tallest in the world .
>
>
> Men from Timor-Leste, at 160 centimeters (5 feet 3 inches), and
> Guatemalan women, at 149 centimeters (4 feet 11 inches), are
> considered the shortest.
>
>
>
There would most certainly be changes due to the Martian environment. I would suspect that over 3,000 years, the differences would be small but significant.
And I suspect the changes would have to be more about [gene expression and epigenetics](https://www.encyclopedie-environnement.org/en/health/epigenetics-how-the-environment-influences-our-genes/-century/index.html) than genetic mutation. Existing but unused, unexpressed genes in the human genome would be expressed in a different manner, due to environmental pressures.
>
> While the genome is fixed, the epigenome is much more dynamic.
> Epigenetic modifications would allow individuals to quickly explore an
> adaptation to a change in the environment, without “engraving” this
> adaptive change into the genome. The challenges of epigenetics concern
> not only medicine and public health (see Epigenetics, the Genome and
> its Environment) but also evolution (see Theory of evolution:
> misunderstandings and resistance). Indeed, it casts suspicion on the
> environment that could modulate the activity of some of our genes to
> modify our traits, or even induce certain diseases potentially
> transmissible to offspring. Clearly, the Dutch famine of the winter of
> 1944-1945 shows that permanent changes have occurred in the genetic
> heritage of the women who were pregnant at this time and then passed
> on from generation to generation. This would mean that the trauma also
> affects the germ cells (sperm and eggs), the only biological link
> between generations.
>
>
>
I would not expect major physiological changes over this period, but I would posit instead a myriad of subtle changes that, because they are dependent on existing genes in the human genome, and in the unknown Martian environment (it depends a lot on how much Humans adapt that environment) the changes are are unpredictable.
The issue is also compounded by 'selective migration'. I would expect that those who migrate to Mars would be a unique sub-set of the human genomic code. The entire colonization of Mars would be beset by complications and hazards, with a unique selective process. Humans that can survive the trip and the colonization experience, survive. Those that don't, either die or return to Earth. The genetic makeup of Martians over 3,000 years would be very dependent on the genetic makeup of the first thousand or so colonizers, who would have been subject to extreme 'self-selection' criteria.
[Answer]
**Tall and Thin**
[](https://i.stack.imgur.com/Rwbz4m.png)
We know astronauts in zero gravity have their bones and muscles reabsorbed. Once they get back to Earth gravity they are frailer than when they started.
For the low gravity of Mars we should expect a less pronounced version. Some bone and some muscle will be reabsorbed or simply not grow in the first place.
Gravity is the main difference since you say the environments are otherwise designed to match Earth. Though it would be interesting if 1000 years in the ideal environment for the lanky humans was slightly different. The new environment could encourage further mutations.
[Answer]
None.
<https://en.m.wikipedia.org/wiki/Lamarckism>
Is refuted long time ago. Giraffe does not grow taller because it wants leaves higher up. Small giraffes die from starvation.
Specie must let their members die, a lot, a whole piles of body, every second creature must die, or at least be stopped from reproducing, for it to have any significant evolutionary effect in this timeframe.
People dont let each other die, and dont try to make others not reproduce. Well, in a perfect world at least.
Who will die on mars? People who break chain of command, act reclessly, take unneeded risks, practice extreme sports. Those traits may be slightly reduced, but still, even in extreme case, these traits have almost zero effect. These people also reproduce faster, that offsets the negative side of this behaivor.
[Answer]
People would be generally less muscular and have less dense bones due to growing up in lower gravity, but other than that, it's hard to say.
3000 years, which amounts to 30ish generations is plenty of time for genetic adaptation, but conditions other than gravity would likely be a major factor in reproductive fitness. For example if people have to live in cramped spaces, shorter people would have a clear advantage. As in they'd obviously be less likely to get injured, but also are just generally more successful and productive in their everyday lives, hence more popular and more likely to have offsprings.
Also traits that are completely incidental might become wide-spread. For example, suppose that some early red haired colonists had some genes that make them healthier in the Martian environment (e.g. they don't get scurvy as easily or some such thing). That gene would quickly become wide-spread in a few generations, but so would the alleles that cause red hair and Martians would be more likely to be red-haired than Earthlings.
Besides gravity, one thing that's different on Mars is that it doesn't have a strong magnetic field like Earth. Thus Martians would be constantly bombarded with way more radiation. Resilience to cancer due to radiation would be a highly adaptive trait, even if it would be accompanied by some adverse genetic condition.
Basically, you can just make some stuff up and come up with some plausible excuse for why the Martians have evolved to be different.
] |
[Question]
[
So, to start out with. I've got a character with an alien biology and has an accelerated healing factor.
Nowhere near the likes of Wolverine, or Deadpool but better than a regular Humans and allows them to survive more than most people would.
The basic gyst of how this accelerated healing factor works is:
Their species has a locked away gene in their DNA that allows for the excessive and rapid production of stem cells, which in this characters particular case were gifted with the capability of using this. Stem cells flood the wounded areas (only in extreme cases. Smaller wounds such as cuts will heal normally much like how our own body heals smaller wounds slower)
They are female
178cms in height
265lbs in weight (mostly muscle and due to heavy/sturdier bones)
And have a slim somewhat curvy body shape.
And ofc, alien.
So, I have a few questions;
What sort of food/calorie intake would realistically be expected of them to make this work?
[Answer]
As you showed they have some sort of active response to a trauma, in a form of emission of stem cells. This could mean that their normal food requirement is not that much bigger than a human would have.
About their stem cells emissions, it could be calculated from biomass that is required for the healing process. All of the damaged tissues will likely get dissolved by the body, and new ones are built in place. In animals growing 1kg of biomass takes about 10kg of food. Anywhere from 2 to 25.
<https://cricketpowder.com/sustainability/>
Another case to consider is pregnancy. When body is making a baby, we can just look at it from the prespective of making a new biomass from food. Total additional food intake is about 24 000 calories, and newborn weight is about 3.3kg, placenta weight 0.6kg, additional uterus weight 1kg. Thats at least 4.9kg of biomass carefully created for a task, using only 8.3kg of beef as a food source. Hmmm... I expected it to be much more. Probably something is off with the additional food intake calculation.
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3530253/>
<https://www.whattoexpect.com/pregnancy/calories-diet/>
<https://parenting.firstcry.com/articles/uterus-during-pregnancy-everything-you-need-to-know/>
But you get the idea. To calculate how much of biomass is transformed, and use a coefficient of 2...25 to get amount of food required.
If your alien is hit with a bullet, that makes a kilogram of flesh non-functional, your alien would need to eat 2...25 kg of food, at least. Depending how careful the healing process is adapted to be low usage. Thats assuming no blood loss, no infection. Blood loss can be calculated the same way, 1kg of blood (100kcal) is not that far of 1kg of meat (290kcal). Infection can do massive damage to the body and require tens of kg of food. Thin cuts, if wound is closed while healing, can be cheap to fix, not a lot of biomass is required within a thin cut.
Blood loss is likely to be the main danger, in case of a trauma. It can be somewhat fixed with slightly different circulation system. In particular well developed bypass blood vessels, like some humans do. Another benefit is muscles that can contract and stop the blood flow in certain vessels, like lizards do. Then unless this alien is chopped into small pieces, it will be fine, if it has food.
<https://news.yale.edu/2011/09/30/study-abundance-bypass-vessels-key-surviving-coronary-artery-disease>
<https://www.lizards101.com/lizards-lost-tail/>
Open wound is prone to infections. So much so that it makes sense to add about equal amout of white blood cells to the stem cells, to always patrol the damaged area, to quickly form pus, before more tissue is damaged by the microbes. Considering the scale and time requirements you cant allow the wound to dry, that is an easy way to reduce bacterial load. So your aliens' wounds will be constantly wet and will constantly drip pus while they heal. Extremely wasteful in terms of energy, but if your aliens can afford to eat that often, and can digest this much food, its okay. Pus, partially made of white blood cells, would weigh about as much as the damaged flesh. And is as expensive to make.
All together, blood loss, pus and the formation of new tissue, consider the cost to about triple, from 2...25 to 6...75 kg of food per kg of damaged tissue. For the case of open wound, wet wound, non sterile healing process.
Keep in mind, that even if food is present, ability to digest the food is limited. Humans cant eat more than about 3kg of beef equivalent of calories per day, simply because the digestion system isnt powerful enough.
<https://www.quora.com/Digestion-Is-there-a-maximum-amount-of-calories-a-human-body-can-absorb-in-a-limited-amount-of-time?share=1>
Alltogether, assuming 30kg of food for 1kg of damaged tissue, a medium sized gunshot wound, and human-like digestion system, it will still take 10 days to heal it, simply because of food intake limitation.
Even faster healing rate would really push the limit of getting rid of the heat, using special food only because normal food cant be digested fast enough, not even cooked food.
All of this assumes limitless amount of water available... In nature water is often a limiting factor for such extreme level of activity.
[Answer]
**Circulation problems.**
/Stem cells flood the wounded areas/
So the healing supply must arrive where it needs to be via the circulatory system.
If there is a wound that is bleeding so fast that the stem cells can't stop and get off, that would be a problem. You can invoke faster clotting, contractile arteries etc. For regular humans it is possible to rapidly bleed out from an arterial wound in a place diffcult to compress (armpit, groin, neck). That could be problematic for your character too.
A bigger problem would be a wound that itself shut down the circulatory system. That would be a wound to the heart either penetrating the heart or (and better for a fiction, I think) a wound causing cardiac tamponade - this prevents the heart from filling with blood and so blood pressure falls. There are some edgy first aid maneuvers that could address tamponade which could be good for your fiction.
5 foot 6 and 265 lbs will be curvy indeed! As regards adequate nutrition your character is doing fine; no advice on that front.
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# Self-sufficient Flying Vessel
Let's assume that something has happened to the Earth. I won't be going into detail about this, but assume that if any living organism comes within 2 miles above the surface of the Earth (accounting for changes in elevation on the surface), it dies immediately. There is no other effect on the atmosphere, or the surface temperature, aside from the fact that atmospheric regulation from algae and plant life is mostly lost.
The ship can still send drones, and machines down to the surface, but nothing living will survive.
## Is it possible to sustain a population of, say, 1000, aboard a vessel like this? If so, how will the ship:
* Produce power
* Stay in the air
* Produce food (aeroponics? hydroponics?)
* Create medicine, and other hard-to-manufacture goods
* Collect resources
* Gather water
* Something else that's important but I haven't thought of
Assume that the ship can
* Be built of any material harvestable on Earth
* Have more advanced, but not space-opera level (LFTR (Liquid Fluoride Thorium Reactor) fission, efficient solar, aeroponics, limited quantum computing, etc) technology
* Have a crew with a perfect mental health, etc. Just worry about physical needs.
[Answer]
**Flotilla**
To make the question easier for me, I would suggest to spread the facilities and people over multiple ships. A single big one doesn't seem realistic, as the sheer size can already put a lot of strain on the whole ship. Imagine having a sheet of normal paper, but making it 20m (65ft) big. It is unwieldy and rips itself apart due to it's own weight, strain and any added force of even a soft gust of wind. Making something bigger and bigger is much like that. There's ways to mitigate this, but several ships is much easier.
**Maintenance**
Every airship needs to be maintained. Rigid, semi-rigid or full on balloon style must all have regular inspections and repairs. As you mention you have drones that can do complex tasks autonomously, this can be done by them. A flotilla will help here. If any ship requires repairs for which it needs to land, you can simply move all passengers to the other ships and land. Potentially the people can stay inside compartments sealed off like a spacecraft or submarine during these repairs, so they can stay on the ship and survive below the 2 mile barrier.
**Water and food**
My initial thought was that water would be *hard*. I've seen designs of skyscrapers so tall a normal way of plumbing would require insane pressures to get it that high. The solution proposed was cloud harvesting. Big ducts allow clouds and random water particles to condense or climg to surfaces, allowing it to be caught. These are big things, so unfeasible on an airship.
But it's not that hard. Compare it to a spaceship. Here a relatively tiny amount of water is recycled again and again. From perspiration to urine, it can all be turned back into clean water. Your airships don't need such extensive recycling, as there's still plenty of extra water in the air to collect. This can immediately be used as ballast to have stable flights.
For plants much the same can be done. There's big pots of plants you can buy. Add a little water and seal it. Water vaporises from the plants, condenses on the glass and slide down again, where it's ussd by the plants again. These ecosystems can run for years, even decades if done correctly. For your hydroponics you can do much the same, but on a different scale. The water in this case is collected and stored to be released at the right time. Again, use drones to fully maintain and harvest the gardens. That way you require minimal space, lights and water.
**Drones**
The drones are a solution to most of your problems. Maintenance, resource gathering and farming can all be done by them. That means you don't need to do everything on the airships. You can setup fully automated facilities on the surface. Mining and production of non-organic goods are chief among them. With some automated transports you can still have a huge range for the airships to fly. With many leftover facilities from the olden days they might venture nearly anywhere.
This does heavily depend on a well automated system. It wouldn't seem a stretch if you have special fission and super efficient solar panels. Then again, we mastered fission and space travel with computers that barely could calculate the square root of something. It might all fall apart if you don't assume these super drones and automation of factories.
**Power and staying afloat**
You suggest fission reactors, but super efficient solar pannels might already to. In a pinch humans don't require a lot of energy. Look at spacecraft again. They have life support and a ton of other features, yet it's powered by a relatively small array of solar pannels. If they are super efficient, you don't require too much surface on the airships to produce it. Solar pannels don't work at night *[citation needed]*. Storage of surplus power can be done in special compartments or separate balloons by producing hydrogen. This loses a lot of power compared to batteries or flywheels, but can also be used to refill the gasbags to stay afloat. Any airship slowly loses its gas! Some people might refer to the Hindenburg, but I hope airships have become more safe with new technology. You might have a hydrogen and helium combination for more safety. Helium is not as easy to get, but can still be created over time. That way the hydrogen can be used for both a stable flight and as electricity in a pinch.
**Other concerns**
Although you mention for this question the people are in good health both mentally and physically, it is still a major concern. Weight is valuable in an airship, meaning smaller compartments. This can be physically limiting, which affects both the mind and the body.
The 2 mile barrier is also problematic, as airships generally operate below that height. Airships need to become even lighter and/or the gasbags bigger for yours to operate above that. They might be able to fly in the death zone, as you need well protected living quarters if uou fly above the two miles anyway. Still it is something important to consider. It might be easier to build big sealed buildings on the ground with a special infrastructure for people to survive.
[Answer]
* power production
Your airships dont seem to need to go anywhere fast. That is great, since you can use wind energy. 2 miles up there is a lot of wind in all directions. You would let the wind push the turbines and ship in one direction, then shift height to another wind direction to make sure you keep a healthy energy production. If the drones build masts with loooong cables they could also anchor the ship.
Other power solutions: ground based drone-operated facilities create stored power, hydrogen power for example. Then export this to the airship where it can be used for power. High-end batteries/capacitors could also be brought up and down from such facilities for stored power.
* stay in the air.
This requires volume, and airships have a great advantage in this area. This is the one exception where the square cube law is favorable. A larger ship means more volume of lifting gas compared to its outer surface area. That means that larger airships are *less* affected by the wind as the wind has to push more total mass with effectively less surface area per mass.
The lifting gas used would most likely be hydrogen rather than helium due to hydrogen being easier to come by in large quantities. Hydrogen is flammable and people are fond of pointing to the Hindenburg so lets install some safety measures:
* don't vent flammable gas to lose altitude. This can be done by using vectored thrust and wing surfaces for a portion of your lift.
* don't use a flammable envelope. If the Hindenburg's envelope wasn't flammable and remained intact when exposed to heat then only a flame would have appeared at the hole in the ship. This flame might even peter out since the gas inside isnt under pressure and uses osmosis to leak out. Even if the flame can keep itself going it would mean the ship wont crash as fast or engulf its passengers in flame, and it would give you hours to fix the hole and stop the burning before the ship crashes.
* use multiple gas bladders. The Hindenburg already did this actually, but since the ship itself was flammable the other envelopes could also catch fire. Multiple bladders means the loss of one or two bladders does not mean the ship is lost. Bladders are located inside the envelope.
* add a second gas bladder on the outside of the hydrogen gas bladders. These can have an inert gas inside, like a small amount of helium. This means any hydrogen gas leakage will (initially) be mixed with gases that reduce the flammability of the hydrogen as there is less oxygen to mix with.
* add more electronic measurements. This should be easy for your drones. The Hindenburg had very little to gauge the status inside and outside of itself. A leakage would be far easier to trace in the modern day.
* use modern materials. Modern materials can provide a lot of benefits in weight reduction, self-sealing capabilities, strength, fire safety and reduction in natural gas leakage. The Hindenburg had limited viable materials available, hence it used a material that was quite close to rocketfuel as its outer envelope.
As mentioned you can also use a heavier-than-air airship by utilizing vectored thrust and wing surfaces. This is what modern companies trying to bring back airships use. Since your ships never land but do fly at a height they can use the wind up high to stay aloft, reducing the need for lifting gas and making it easier to shift height when necessary. Vectored thrust by letting your engines point in any direction can also help the ship change heights or stay aloft in downdrafts. Although its likely that you use drones to plot the air movements ahead and avoid downdrafts as much as possible so your ship isnt pulled beneath the 2-mile height.
Production of the hydrogen could easily be done by drones on the ground. A modern nuclear/fusion reactor could provide plenty of energy to create hydrogen for fuel and lifting gas purposes.
* produce food.
The big problem here is that there is no food production possible at the surface of the planet. This means you need to bring everything you need to produce food up in the air. If you've read anything about vertical farming and artificial light sources you might notice it is inefficient for your purposes. You need to have enough energy for light, bring the soil and have the plants all above the 2 mile limit to survive. That is an aweful lot of mass, space and energy to create food, but there are alternatives. Such as this (very very early) suggestion to use bacteria to convert biological waste and carbon in the air into food: <https://onlinelibrary.wiley.com/doi/abs/10.1002/bit.260060406>
Key factors here: its suggested for long-term space travel where all of the food has to be essentially recycled and it uses hydrogen as important catalyst in the cycle. Since you likely already have the infrastructure in place to produce large quantities of hydrogen and store hydrogen on the ship for fuel and lifting gas is makes the supply chain much shorter. This reduces the amount of surface area, weight and onboard energy you need to create food since the bacteria use chemical processes to convert the materials to food. For variety you can assign a portion of the ship to create other foodstuffs but it will just be to create flavor rather than the main foodsource.
A big advantage is that any food can be purified and stored by hanging it below the 2 mile limit where everything dies. If necessary through a small drone airship or by ground based facilities operated by drones.
* create medicine
I'm not sure why you are asking this one. You are going to need to find, extract, refine and build the medicine. That means the only solution is to have drones that can do this. You can have some refinement facilities onboard, no idea how big they would be. But it would likely be smarter to use scanning equipment to locate materials, send drones to collect it and have a ground station somewhere which creates bulk medicine, to be collected at intervals as the airship passes overhead.
* collect resources
Same as medicine.
* gather water
Molecular sieves, the water created through burning hydrogen or automated facilities on the ground which filter the water without the need to prevent biological contaminations and then bring it up using the drones.
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I haven't been able to find much on this question. I am making a world that is fairly cold compared to ours, not quite a snowball planet but enough that the highest average temperature is 66 degrees Fahrenheit at the equator, with most regions drastically colder (43 Fahrenheit or so is the average). It also has slightly lower gravity than our planet, not by a drastic amount but around 80% of Earth's gravity.
Now, I am going through this by making a biosphere that progressively evolves for fun, and I reached a debate when looking at one of my creatures. Little needs to be known about this creature as all you need to know is that it uses hemocyanin instead of hemoglobin. This is because this creature lived in the deep ocean where it is generally cold, and it has now reached land and colonized it, currently being in the warmer areas of the planet.
Now, from my research, it seems to be that hemocyanin is much more inefficient than hemoglobin is, and there isn't any massive lifeforms on our planet that have hemocyanin blood, as most vertebras have hemoglobin blood. Minor handwavium is acceptable, but it may break suspension of disbelief if I have a brontosaurus-sized creature with much less efficient blood. I am also not asking for square cube laws, I am perfectly aware of them, I just want to know if hemocyanin provides size limitations and if so, what kinds and how to bend or fix these limitations with evolution.
So, in conclusion, **what is the largest feasible size a creature using hemocyanin instead of hemoglobin could reach?**
[Answer]
The square-cube law dictates that the size of an animal increases, it's metabolic rate per unit mass decreases linearly.
This means that if haemocyanin can support the needs of a small animal's metabolism, scaling up that animal will only make it easier for its oxygen transport mechanism to meet its needs.
This means that using haemocyanin instead of haemoglobin would not be a limiting factor in the upper size attainable by animals that use it. Maximum size would be dependent only on other factors such as bone strength.
[Answer]
**Giant squids are pretty big**.
[](https://i.stack.imgur.com/9wWU7.jpg)
<https://www.nationalgeographic.com/science/article/140110-giant-squid-picture-hoax-ocean-animal-science>
Ok, maybe not that big. But 700 kg is not chump change! [And they have got blue blood full of life giving hemocyanin](https://www.nationalgeographic.com/science/article/140110-giant-squid-picture-hoax-ocean-animal-science). And in the UK, haemocyanin.
Go ahead and have your big critters have blue blood. Hemoglobins vary hugely in O2 binding efficiency and they are all red. You could have hemocyanins do what you want them to do. Or assert that the blue moiety is vanadium, or cobalt. Or nickel.
Prior art:
[Would it be possible for mammals to evolve blue blood?](https://worldbuilding.stackexchange.com/questions/130546/would-it-be-possible-for-mammals-to-evolve-blue-blood)
[How could blood be purple and reasons for it?](https://worldbuilding.stackexchange.com/questions/214311/how-could-blood-be-purple-and-reasons-for-it/214381#214381)
[Answer]
There really shouldn't be any limit due to blood composition. If hemocyanin is less efficient than hemoglobin, you just use more of it, circulate it a bit faster, or have a slower metabolism - that is, your large creature is more like a sloth than a shrew.
Size limits of earthly creatures with hemocyanin blood aren't related to the blood (AFAIK, anyway), they're because the creatures are invertebrates, and so have the size limits imposed by exoskeletons (or no skeletons, as with molluscs), and lack of real circulatory systems.
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Yes, I know I've created two different questions that resulted in a Plop or Chomper predator, respectively. However, given that Plops and Chompers are among the most common monsters in Alendyias, **it makes sense that there'd be some sort of predator-prey relationship, but I can't determine what that relationship would be.**
**Plops and Chompers-Shared Traits:**
* Both can grow by consuming matter
* Both can eat practically anything
* Both have a large evolutionary stage
**Chomper Advantages:**
* Toughness: Due to enamel shell, Chompers can take harder hits and can actually bite and chew things, while Plop can only engulf
* Legs: Chompers have legs, which enables them to run and jump, while Plop can only glide over substrate. Also, these same legs end in suction cup feet, which enable them to climb up smooth surfaces. Plop can't go up smooth surfaces.
* Spewage: Due to their close-ended digestive system, Chompers excrete waste from their mouth. Often, they do this as an attack called 'spewage.' This may poison and disorient a Plop.
* Color vision: Like birds and some reptiles, Chompers are tetrachromats-[while Plops see like slugs](http://sciencewows.ie/blog/slugs-and-snails-and-puppy-dog-tails/), Chompers have excellent color vision, can focus in on interesting sights, and can see about as far as a raven.
* Avian intelligence: Like ravens, Chompers are capable of social behavior, even forming social hierarchies, and they can use tools (they've been observed picking up sticks with their flexible tongue and probing for fellow monsters, such as Plop), problem-solve, and plan for future events. Basically, they're a raven inside of a walking, chomping egg-monster.
**Plop Advantages:**
* Flexibility: As a mass of slimy, amorphous rubber, Plop are pretty hard to chew, smash, or slash. Hitting them with a hammer, for example, does nothing. As a result, very few creatures prey on them. They are also capable of altering their solidity, enough to slip under a doorway or flow into a glass bottle.
* Speed: Plop can keep up with a jogging or speedwalking human, which is pretty fast for a slime or pseudo-slug. This is compared to a Chomper's max speed of 10 mph, which I'm sure is remarkably slow by comparison.
* Climbing: Plop can't do slick surfaces like ice, glass or glazed pottery, but they can glide or climb up trees, bricks, textured stucco, weathered stone, and so forth, which Chompers cannot do as their feet do not adhere properly to rough surfaces.
* Engulfing: Plop cannot bite or chew, but they *can* use their flexibility to engulf a creature, then excrete acid from their interior to dissolve the unfortunate victim.
* Manipulation: Plop have a long, red, fleshy and *flexible* tongue they can use to manipulate objects, as well as four orb-tipped feelers they can use to whack enemies. Getting hit by one feels about the same as being hit by a tennis ball.
* Cephalopod Intelligence: If Chompers are like ravens, Plop are like octopi. Solitary yet intelligent, with complex problem-solving capability, Plop swarm merely to take advantage of a large food source, not cooperating so much as seeking the same thing (ie. food).
For more information on Plops and Chompers, please check [here](https://worldbuilding.stackexchange.com/questions/196649/how-can-i-protect-medieval-villages-from-plops) and [here.](https://worldbuilding.stackexchange.com/questions/197028/how-can-i-protect-medieval-villages-from-chompers?noredirect=1&lq=1)
**With that all done, my question is simple: What Would The Predator/Prey Relationship Be Between Plops and Chompers?**
**Specifications:**
1. The best answer will take into account both monster's Enchantments, namely [Calcification](https://worldbuilding.stackexchange.com/questions/197213/would-calcification-benefit-people-and-if-so-how) and [Rubberizing](https://worldbuilding.stackexchange.com/questions/196751/would-rubberizing-benefit-people-and-if-so-how), as well as the advantages both monsters have over each other, to determine who would prey on who.
2. The best answer should also take into account both monster's physiology. Given a Plop's speed and engulfing ability, for example, it should be possible for them to engulf and digest a Chomper's legs, which would leave them pretty much helpless. **The best answer should also account for this scenario, as determining how well that would work for Plop will likely determine which one of these two monsters will be predator.**
**EDIT: Why would Plops and Chompers come into conflict?**
Plops and Chompers both eat refuse, but they prefer meat. They both seek out and congregate in places where carrion, garbage, or discarded food can be found, so they often encounter each other and compete for food. And, due to monsters being infused with Chaos Magic, like attracts like, so Plops and Chompers tend to prioritize monsters as a meat source, especially their oh-so-common rivals.
[Answer]
# It depends on who's bigger
In nature, predatory relationships don't always go just one way. Often, creature A will eat juvenile creature B, but adult creature B will eat creature A.
Among predatory fish, for example, who you can eat isn't determined by a list of species you can prey upon; rather, it depends on who can fit in your mouth. A bluegill would probably be more than happy to eat a bass fry, but an adult bass will devour bluegills. (In fact, most fish species will eat their own young as well; this is why fish fry generally either live in shallow water, or disperse quickly as plankton.)
For the plops and the chompers, I imagine it would go something like this:
Since plops are faster, it might be difficult for chompers to prey on plops unless they can ambush them. Plops, however, can alter their solidity, so it might be physically difficult to ingest one even if you can catch it. That said, I imagine chompers would be more than happy to grab a plop if they manage to ambush one.
Plops, on the other hand, can outrun chompers. If the plop is smaller than the chomper, the plop can simply run away. If the plop is bigger, the plop can try to engulf the chomper.
If the plop and the chomper are the same size, a fight could go a number of ways. The plop could attempt to suffocate the chomper, or the chomper might be able to take a solid bite out of the plop, incapacitating it. more likely, however, both creatures might decide the fight isn't worth the effort, and leave each other alone. Real life predators don't usually pick fights that aren't heavily in their favor; even a small injury might mean death.
That said, you might have not given enough attention to the chomper's biggest advantage: Social behavior. If Chompers live in groups, than a pack of chompers could potentially gang up on a larger plop. Crows and Ravens will mob their predators when in groups, so it makes sense that the chompers might do something similar. If there is a large plop and several smaller chompers, the chompers might work together to fight off the plop, biting and tearing at the plop. After all, the plop can only engulf one target at a time.
## To summarize:
When a plop spots a chomper (or vice versa), the fist order of business is to determine who is bigger. If the plop is bigger (and it is the one that spotted the other), it will chase down the chomper and engulf it. (If it was the chomper that spotted the larger plop, it will flee and hide.)
If the chomper is bigger (and it is the one that spotted the other), it might try to ambush the plop if a convenient spot is available. If there is no place to launch an ambush, the chomper might simply ignore the plop. (Meanwhile, a plop, on spotting a larger chomper, might simply flee.)
If the two are similar in size, they are likely to ignore one another, as a fight could prove very risky to both parties.
If there are many small chompers and one large plop, the chompers may attempt to mob the plop and drive it away or tear it apart. This would encourage plops not to attack groups of chompers, and it would encourage chompers, especially smaller ones, to stay in groups.
Plops attacking smaller chompers probably have a higher success rate than chompers attacking smaller plops.
[Answer]
**Plops eat Chompers.**
As regards calcification and rubberization, being rubbery does not help Chompers, which count on their hard shells. Calcification does help Plops which remain rubbery but are even harder to cut.
Plops have a maneuver that works well against Chompers - when the Chomper takes a bite, the Chomper has the Plop but the Plop also has the Chomper. As the Chomper tries to bite off what it has grabbed the rest of the Plop flows around the Chomper. The Plop sometimes turns inside out in the process which is fine. The Chomper finds itself enveloped by the Plop. Even small Plops can do this trick, enveloping the Chomper in a thin film of Plop. Unable to get a purchase with its legs or open its mouth to get another bite, the enveloped Chomper is doomed.
Unless other Chompers in its tribe come to its aid. The only way Chompers can beat a Plop is to team up on it.
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[Question]
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Libraries are buildings containing collections of books, periodicals, and sometimes films and recorded music for people to read, borrow, or refer to. They house updated material to meet the user's needs on a daily basis, and can be funded by governmental authorities or private institutions. In the world of Readoria, however, they are seen as much more than that. The inhabitants of Readoria worship a god known as Thesaurus, a deity that presses his followers to pursue the accumulation of knowledge. This deity stresses continuous learning throughout life to increase one's standing in the world, and decries ignorance and stagnation as great evils that prevent the advancement of humanity. Libraries are sacred locations that store vast amounts of knowledge, with librarians serving as priests in direct service to Thesaurus. As such, they are religious centers of power that are a testament to the wealth of wisdom that humanity has attained over the centuries. For a small fee, individuals can rent material for a short period of time, later to be returned to the sacred library. This partially keeps the places funded, and are seen as a kind of tribute or " tithe " to fund God's work.
However, things have begun to change with advances in technology. The rise of E-commerce has begun to challenge and compete with the traditional system. The common man through the use of a simple click can have items brought to them within a matter of days for a small fee, instead of having to wait an indefinite period of time to gain access to reading materials. This makes costs cheaper for the average consumer. In addition, electronic books, or E-Books, have come on to the scene as a new and convenient way to interact with material, which can be accessed anywhere. With these technological advances, traffic to centers of worship have begun to decline, robbing libraries of much needed revenue. As less people travel to these places, they have become less relevant to society, leading many leaders to question their purpose and whether they should continue bothering to support them. This has especially been the case with the Grand Library of Alexandria, which was once the crown jewel of the world. In recent years, it has declined as a cultural center, becoming dangerously underfunded.
How can the traditional system of power be maintained while competing with newer advances?
[Answer]
>
> robbing libraries of much needed revenue
>
>
>
Where do you think the e-books are served from? Where do you think the people who'll sell you stuff online host their websites? In a magical cloud?
[](https://i.stack.imgur.com/fQpbN.png)
Datacenters are the modern versions of your library. The priesthood is still there, the endless shelves of arcane knowledge, the scale of the architecture... sure, most aren't as pretty as, say, a cathedral, but boxy commercial and industrial buildings are a capitalist esthetic, not a religious one and who's to say what your datacentres look like.
Amazon, a former bookshop, is now in the datacenter business, and they're doing OK. I'm sure your church will be fine, given suitably visionary leadership.
[Answer]
There would be a schism, I think between the two views. Many would go the new route, seeing that learning online, not just through reading, but also watching videos online from independent creators, was enough to learn.
The orthodox school of thought however would hold that such a thing is blasphemous, and might villainize the opposing school of thought to instill some "godly fear" on those who are on the fence. You would want to stress that this way of learning is a more sacred space, free of distractions from learning on the go. It shows a sacrifice of effort, that you care enough about learning to travel to a place to do it.
This situation has some interesting ways you could delve into it too. You could address very real problems in our world of independent people being able to misinform you because of the ease of making online content. You could show a wide spectrum of views, with the old way possibly splitting up into a number of denominations.
There is much you can look to in real history to see how such schisms of doctrine occured, such as The great schism, the reformation, and many more.
[Answer]
Knowledge has to come with books, true, but not with any book. Only books which are written with the holy ink are apt to the worship of Thesaurus.
E-books don't have access to this holy ink because of their very nature, and it's up to the religious hierarchy to decide which ink can be made holy and which not, so it's not a given that press or printers can also produce holy books.
[Answer]
## Treat Citations like SSLs and Liberaries like Certificate Authorites
In our world, fake news, poor research, and bad citations are pretty annoying, but freedom of speech/press pretty much protects people from getting in trouble for spreading misinformation. In this world however, spreading of false information is literally blasphemy. After all, you can not worship the god of knowledge and not care about the quality of that knowledge.
As the rise of digital information begins; so too will the the spread of misinformation as you allow any person with a keyboard to publish whatever thoughts they want. The church will see this and demand much stronger regulations on the content of the internet. If an e-business wants to go toe-to-toe with the theocratical authority of the church, then the internet will simply be banned. Instead they need to make concessions that do not exist in our world to appease the church, if they wish to survive their infancy period.
In our world, when you go to make a website/webservice, you spend a few bucks on a domain, server, and SSL and you are in business. But in this world you have a requirement to prove the information you publish is factual and/or honest reproductions of content. For this you need citations. However, it is not considered good enough to just cite someone else's digital whatever, you have to go back to the source: the authoritative source. So let's say you want to publish something about the Roman's you learned on YouTube, well you can't just cite the YouTube channel because that YouTuber is not a Certified Source. Instead you find his citation which might look something like
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> Quintus Fabius Maximus. "Cunctator", 221-217 BC, **Edenwald Library**, Bronx, New York : **Reference Code: dZHprSPg7mV72djfBtdGJjXm**
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This citation has two key parts that are relevant to the OP. #1: it tracks the knowledge back to the library (or museum) that contains an original copy of the source, and #2. All citations need a Reference Code. The reference code is a number issued by the library to prove your citation is verified. So, if you wish to publish your article, you need to a reference code... but you can't just copy and paste someone else's reference code onto your website, that code is unique to that YouTuber to prove that HE actually did his research. Since you did not do your research, that code does not apply to you. So you need to call up, email, or visit the library and request to either check out the book, or in the case of rare or delicate books a verified transcript for research for your specific website. Once they have verified that you have checked out and returned the book thereby demonstrating you know what you are citing, you can request a citation code that is unique to you. So now, they are not just making money on you checking something out, but they are making money on the citation itself.
Then when someone goes to your website, the browser will check for citation codes the same way it does for SSLs. If your site does not contain a reference code that can be verified as belonging to you, then visitors see a big red page that says "Danger, this site contains unverified information" and warns you that you may be visiting a malicious or sacrilegious website that you have to click through multiple confirmations to bypass. Search engines will also down rank sites for not having confirmable reference codes since these are more likely to be unsafe and misinformative; so, if you want your website to do well, you must at some point in the process, pay a library to confirm your research.
The way that e-books factor in is that they are not considered "a verified transcript" unless the church issues them a Rite of Authority. To become your own authority, you must demonstrate to the church your possession of a significant body of original content that you can compare against any transcripts you distribute. So, e-stores have 2 options then. They must either be an extension of a physical library that contains original sources of what they put online, or they must pay a library a citation fee for every e-book they publish.
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