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Energy cannot be created nor destroyed. Humans require energy (food) to operate, but that energy must return back to the environment one way or another.

If given an unlimited supply of handwave material which does not absorb/emit any energy whatsoever, could we construct a box where humans could live indefinitely in a closed system?

Details

  • I would like to use the most primitive technology possible; current technology preferable
  • You can make any assumptions you want about the material of the box (i.e. massless, infinite strength, etc.)
  • You can put as many people in the box as you want (including just one person who lives forever), and have them follow any rules you want (population never exceeds X, etc.)
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    $\begingroup$ As Dan says in his answer, it's about energy, not the "box". As long as you can pump energy into the "box", and those that live inside of it, you are able to reverse entropy and live. Moreover there isn't just food, we also breath and require heat to maintain our internal temperature. You don't need a box, the solar system is perfectly able to maintain humanity in its current form, you would "only" need to replace the sun when its dying. That's the only threat to your closed system. $\endgroup$ – r41n Jan 17 '17 at 9:49
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    $\begingroup$ how big is the box? does it contain the sun? What technological assistance is allowed? $\endgroup$ – John Jan 17 '17 at 15:06
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    $\begingroup$ How do you know we're not already living in a closed box? $\endgroup$ – Brad Thomas Jan 17 '17 at 16:22
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    $\begingroup$ We're already living in a closed box, it's called the Universe. I think you should ask how small a box could humanity live in and for how long? $\endgroup$ – Schwern Jan 17 '17 at 19:53
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    $\begingroup$ The universe COULD be a closed system. It is not with certainty a closed system. $\endgroup$ – Durakken Jan 17 '17 at 23:09
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Not indefinitely. Entropy must increase over time in any closed system, so the energy required by even one human will eventually no longer be available in a form which can be usefully harnessed.

Our solar system is almost the box that you describe. It isn't closed but is so far away from anything else that energy input is minimal. It contains a power source with a very long lifespan which is used to provide energy to humans and could theoretically support them for billions of years. If humans build a Dyson sphere (which is far from possible with our current technology) then we could harness as much as possible of the energy emitted by this power source. However, the power source will eventually be depleted (and will become deadly to us long before that).

Your box would need to contain a power source which lasts forever -- longer than the Sun! Current technology is incapable of providing this. In fact, it's completely impossible in a closed system.

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    $\begingroup$ What do you mean that the energy won't be in a form that can be usefully harnessed? Do you mean that the energy will, for example, become distributed in the "atmosphere" in the box? How do we know that this energy can never be usefully harnessed? $\endgroup$ – Ovi Jan 17 '17 at 6:01
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    $\begingroup$ @Ovi In a closed system, there is "internal energy" (the total amount of energy in the system) and "free energy" (the internal energy which can be used to perform work.) While the internal energy remains constant, free energy decreases over time. You would eventually reach a system in perfect equilibrium, which unfortunately precludes life. $\endgroup$ – Dan Smith Jan 17 '17 at 7:15
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    $\begingroup$ "What do you mean that the energy won't be in a form that can be usefully harnessed?": Increasing entropy means that all differences between places go away. This is a possible eventual fate of the universe, called "heat death." Every location in the box will have the same temperature, and all mass will be uniformly distributed throughout the box. You cannot even see anything because there is an absolutely uniform, featureless glow. $\endgroup$ – Peter - Reinstate Monica Jan 17 '17 at 12:59
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    $\begingroup$ The reason we can survive in this "box" (Earth) is that we keep pumping energy into it from the Sun but excess entropy (i.e. heat) is radiated away into space. To do work you need an energy differential like that, similar to a voltage (electrical potential) to harness electrical energy or height (gravitational potential) to use that kind of energy. Once the energy evens out, the temperature difference stabilizes, the voltage goes to zero, and everything falls together as closely as possible, there's no potential energy left to do work. (Except maybe "dark" energy? haha) $\endgroup$ – Scott Whitlock Jan 17 '17 at 21:50
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    $\begingroup$ @cybernard: "Taking our water with us" on a large scale is ridiculous, at least as long as we cannot come up with a revolutionary new propulsion not even conceived today. Mars will be out of the "green zone" of our sun soon after it entered it, and will still be unable to retain an atmosphere (it can't really even today, and by then the solar wind will be much worse). Then comes the Helium flash ("ouch, too much energy!"), and after that things just become too unstable. If you want a "stellar exodus", you'll have to look for a new home outside the solar system, orbitting a younger star. $\endgroup$ – DevSolar Jan 18 '17 at 12:57
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Dan Smith's answer is most likely the correct answer: it cannot be done.

However, entropy does not always need to increase. Entropy is permitted to remain the same. Such systems are called reversible systems.

Current quantum theory suggests that everything is done through reversible operations. However, to reverse the operation, you do need all of the outputs from it. Unfortunately, electromagnetic radiation is one of the potential outputs from such a system and it tends to propagate outward at the speed of light. In the real world, this is typically assumed to be an irreversible process, but with your handwavium, we could reflect this energy back. We could actually start to talk about reversing macroscopic effects!

The first step to this process would be to define what "human" is. This is a known challenge in philosophy with no agreed upon answer, so I don't expect to find one soon. However, if you did find a definition that was acceptable and could be expressed as some equation of space and time, you could take the Fourier transform of that expression to get the frequency distribution of "human." With this, you could construct your box with its perfect reflective walls into a structure which is resonant at those frequencies. Any human energy which is put into this system would become a standing wave within it, capable of existing forever.

Of course, any one of those steps would be considered an insurmountable hurdle, but the current scientific theory doesn't forbid it. The book Manifold Time by Stephen Baxter plays around with it at one point.

And no, I do not have any idea what the frequencies of "human" are. Find the meaning of life, and you'll probably be able to derive the frequencies from that!

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  • $\begingroup$ Of course, life itself -- at a minimum "human life" as defined by the question is an entropy increasing process. So closed box with living humans can't be eternal. You are certainly stretching the definition of human by quite a bit. As a harder science approach to same is the book, The Physics of Immortality by Frank Tipler -- it is a pretty awful book in many ways, but it does develop the concept mathematically in some detail. $\endgroup$ – Gary Walker Jan 17 '17 at 9:40
  • $\begingroup$ Hmmmm... what's the definition of a "reversible" quantum operation? I think not that it can be actually reversed! That's impossible for a multitude of reasons (the results leave our time cone, for example; and there is no way to reconstruct the original state for principal quantum reasons). The meaning is only that CPT invariance holds; i.e. a reversal of charge, parity and time vector would (!) not violate any physical laws. Note the CP part... even quantum physics are not T invariant. $\endgroup$ – Peter - Reinstate Monica Jan 17 '17 at 13:25
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    $\begingroup$ @GaryWalker The definition of "human" was stretched long before I got there =) You are right that if you explicitly define "human" to include being an entropy increasing process, then there's no way to do it without increasing entropy. However, when people have talked about "what makes us human" for millennia, they haven't talked about entropy. They talk about passion and kindness and virtue. They talk of a soul, though nobody has a physical definition for one. Perhaps "what makes us human" is not an entropy increasing process, but rather shrouded in such a process. $\endgroup$ – Cort Ammon - Reinstate Monica Jan 17 '17 at 14:27
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    $\begingroup$ @PeterA.Schneider That's why the handwavium material is needed to reflect the results back into the system so that nothing can ever leave our time cone permanently. $\endgroup$ – Cort Ammon - Reinstate Monica Jan 17 '17 at 14:34
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As far as we know the universe we live in is a (damn giant) closed box, and we live in it for quite some time. Enthropy death will apply to any isolated box, no matter how large: therefore indefinite life is a no go.

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    $\begingroup$ The universe will also end eventually, as it is indeed also a closed box and thus subject to the rule of entropy. $\endgroup$ – Erik Jan 17 '17 at 7:17
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This question disregards the very nature of life, the universe and the rest. Heraklitus early discovered the very principle underlying nature: Everything is a process. Panta rhei. A human being is a process. It depends on a sustained energy and matter flow. We are not static entities — we are dynamic patterns, standing waves in a steady flow.

Without a source and a sink of energy there is no flow. A perpetuum mobile is not possible.

So in a seed ship or a survival box of any other kind you will need an energy source, and you will need to get rid of heat, eventually. You can slow the flow as much as possible, but not stop it. The same is true for mass. The seed ship / box will over time lose mass, and you'll eventually need to replace it.

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Even with enough energy and resources to supply the system, you may have other considerations to take into account. For instance, from a biological perspective, note that the population size will strongly affect the number of generations that can survive in a closed environment. Low size populations are known to result in the accumulation of DNA errors/mutations/deletions, and ultimately lead to the extinction of the species (so called Bottleneck effect).

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Since we don't actually know if the laws of thermodynamics are correct (and we have reason to suspect they're not) it is possible that humans could survive in a closed box indefinitely like you describe...

The reason is basically because your box is a perfect reflector. Assuming Earth is in the center, all energy radiated away would reflect back to Earth, move around, and do whatever before radiating away again. There is no reason to suspect, given known actual laws of physics and not the non-laws of thermodynamics there is no reason to suspect that the Earth would suddenly blow up or something spreading that energy/matter into a more even form and there is no reason to ssuspect that if there was something like that on the horizon that humans could see that they wouldn't figure out a way to fix the problem, especially when you realize that all the matter and energy would still be there, within reach of humans rather than speeding away from Earth making it ever more spread out and less dense.

There would be big challenges though, for example, keeping the planet spinning indefinitely since it would still be losing energy. Or defending against radiation incoming as it would be increasing over time, but those are sub questions which would make a very very long post to consider if we could actually figure those things out, which I think we could.


For those of you who see my dismissal of Entropy and Thermodynamics as non-laws and want to argue; The fact is a Scientific law is an observation about reality, a fact that has been "observed". Thermodynamics is a theoretical model presuming things about things we have never seen and such aren't Laws. So while they have merit in that they work roughly for Open systems we have seen, they are ultimately talking about a system we either have not seen, making them not a law, or a system we have seen and it doesn't work like the model says it should thus they're wrong. Either way, both justify taking them with a grain of salt for these Closed box systems.

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    $\begingroup$ "Since we don't actually know if the laws of thermodynamics are correct (and we have reason to suspect they're not)" We do? What are they? $\endgroup$ – Schwern Jan 17 '17 at 20:33
  • $\begingroup$ @Schwern things like virtual paricles, vacuum energy, the universe in itself's existence, quantum physics where the actual rule is something like you can come to different answers at different times for a particular system, but in the end it all balances to input is equal to output even though some input is vanishing at times and output is magically appearing at others... heck even this question when you think about it breaks the thermodynamics... you have to argue that a planet eventually magically blows up to get entropy or thermodynamics is wrong in it's presumption about closed systems $\endgroup$ – Durakken Jan 17 '17 at 23:06
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    $\begingroup$ None of those call into question the macroscopic Laws of Thermodynamics anymore than quantum tunneling means I can teleport. Virtual particles conform, no energy is created nor destroyed. Vacuum energy is very poorly understood. "Quantum physics" is so broad as to be meaningless and your definition of it doesn't make sense. I have no idea what you're referring to about a planet blowing up. You're incorrect that Thermodynamics is not law. A law describes repeated observations without a mechanism (that's theory). The Laws of Thermodynamics propose no mechanism of action and match observation. $\endgroup$ – Schwern Jan 17 '17 at 23:26
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    $\begingroup$ Saying thermodynamics isn't "proven" because we can't exactly produce a perfectly closed system is a very tired argument. We can create approximations of closed systems, account for the approximations, and test them, yes. The scientific method exists because we must extrapolate laws and theory from imperfect data, and verify them by making and testing predictions. I don't know what you mean about the Universe not functioning according to the Laws of Thermodynamics. $\endgroup$ – Schwern Jan 17 '17 at 23:49
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    $\begingroup$ This is about as useful as saying I can't "prove" the Sun will come up tomorrow. Scientific laws are statements based on repeated observations which describe the universe, they are not limited to the observations themselves else they'd have no predictive power. You're taking a hard line on observing thermodynamics of a perfectly closed system, but seem fine with virtual particles and vacuum energy; got some of them lying around you can look at? $\endgroup$ – Schwern Jan 18 '17 at 0:02

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