Proton decay has not been observed, but even if it happens, it needn’t be an obstacle to life, as such. For humans in anything remotely like our present form you need protons, but not for life in general. Entropy, however, is a problem. All life depends on having an energy gradient of some form or other; in our case, basically the difference between the temperature of the Sun and that of interstellar space. Now, second thermo can be stated as “All energy gradients decrease over a sufficiently long time”; so eventually, for any given form of life, the gradient it works off is no longer sharp enough to support it. However, what you can do is to constantly redesign life so that it will be able to live off the gradients that will exist in the next epoch. You would be trying to run the amount and speed of life down on an asymptotic curve that was nevertheless just slightly faster than the curve towards total entropy. At every epoch you would be shedding life and complexity; your civilisation (or ecology) would be growing constantly smaller, which is of course a rather alien thing for twenty-first century Westerners to consider. However, the idea is that by growing constantly smaller you never hit the wall where the gradient just cannot support your current complexity anymore, and instantly collapse to zero. An asymptote that never hits zero is, presumably, better than a curve of any shape that hits the wall and crashes—at least this is true if your goal is longevity; of course, pure survival is not the only goal of humans, so there’s a value judgement to be made there. You might decide that it’s better not to throw anyone out of the lifeboat and all starve together, rather than keep going at the price of endless sacrifice and endless shrinking. And, of course, if we can extrapolate to such incredibly distant beings at all, there’s going to be quarrels over exactly who gets thrown out, and the resulting conflict might well make the asymptote shrink drastically, or collapse, as resources are used to fight instead of survive. To survive literally forever you need to be lucky every time; entropy only needs to be lucky once.
That said, even with total entropy you get the occasional quantum fluctuation that creates a small, local gradient again—in fact, arbitrarily large gradients if you wait arbitrarily long times; if somehow you were able to survive the period between such events, you could indeed live for ever. In fact, if you are able to wait long enough you will see a quantum fluctuation the size of the Big Bang. The problem is, of course, that a human, and probably life more generally as well, is extremely low-entropy compared to the sort of universe you get at 10^1000 years. In fact, interstellar space from our era would look rather low-entropy compared to that stuff. So the difficulty is to protect yourself against the, as it were, sucking vacuum that tries to rip the low entropy out of your body, without using up your reserves of energy on self-repair.
Overall, I’d say it doesn’t look utterly hopeless, although it is subject to a Fermi paradox: If survival over arbitrary timescales is possible, why don’t we see any survivors from previous BB-level events? If my account is correct, it seems unlikely that ours is the first such fluctuation.
You would be trying to run the amount and speed of life down on an asymptotic curve that was nevertheless just slightly faster than the curve towards total entropy.
Is the total subjective time finite or infinite?
That said, even with total entropy you get the occasional quantum fluctuation that creates a small, local gradient again—in fact, arbitrarily large gradients if you wait arbitrarily long times;
Does the expansion of space pose a problem? If you had a universe of a constant size, you’d expect fluctuations in entropy to create arbitrarily large gradients in energy if you wait long enough, but if it keeps spreading out, the probability of a gradient of a given size ever happening would be less than one, wouldn’t it?
Also, wouldn’t we all be Boltzmann brains if it worked like that?
The intention was to make it infinite, otherwise there’s no use to the process. You’ll notice that the laws of thermodynamics don’t say anything about the shape of the downward trend, so it is at least conceivable that it allows a non-convergent series.
If you had a universe of a constant size, you’d expect fluctuations in entropy to create arbitrarily large gradients in energy if you wait long enough, but if it keeps spreading out, the probability of a gradient of a given size ever happening would be less than one, wouldn’t it?
This doesn’t look obvious to me. You get more vacuum to play with; the probability per unit volume should remain constant.
Also, wouldn’t we all be Boltzmann brains if it worked like that?
This doesn’t look obvious to me. You get more vacuum to play with; the probability per unit volume should remain constant.
I was assuming that there has to be stuff in space for stuff to happen. I guess I was wrong.
Do you know we aren’t? :)
There’s a chance that our experiences are just random, which we can’t do much to reduce. All we can do is look at the probability of physics working a certain way given that we are not random. That cosmology would be ridiculously unlikely given that we are not random, because that would require that we not be Boltzmann brains, which is extraordinarily unlikely.
Not an answer, but there is a beautiful short sci-fi story by Isaac Asimov that touches on this theme called “The last question”. I don’t know if it is okay to provide a link but it isn’t hard to find online.
Might life in our universe continue forever? Does proton decay and the laws of thermodynamics, if nothing else, doom us?
Proton decay has not been observed, but even if it happens, it needn’t be an obstacle to life, as such. For humans in anything remotely like our present form you need protons, but not for life in general. Entropy, however, is a problem. All life depends on having an energy gradient of some form or other; in our case, basically the difference between the temperature of the Sun and that of interstellar space. Now, second thermo can be stated as “All energy gradients decrease over a sufficiently long time”; so eventually, for any given form of life, the gradient it works off is no longer sharp enough to support it. However, what you can do is to constantly redesign life so that it will be able to live off the gradients that will exist in the next epoch. You would be trying to run the amount and speed of life down on an asymptotic curve that was nevertheless just slightly faster than the curve towards total entropy. At every epoch you would be shedding life and complexity; your civilisation (or ecology) would be growing constantly smaller, which is of course a rather alien thing for twenty-first century Westerners to consider. However, the idea is that by growing constantly smaller you never hit the wall where the gradient just cannot support your current complexity anymore, and instantly collapse to zero. An asymptote that never hits zero is, presumably, better than a curve of any shape that hits the wall and crashes—at least this is true if your goal is longevity; of course, pure survival is not the only goal of humans, so there’s a value judgement to be made there. You might decide that it’s better not to throw anyone out of the lifeboat and all starve together, rather than keep going at the price of endless sacrifice and endless shrinking. And, of course, if we can extrapolate to such incredibly distant beings at all, there’s going to be quarrels over exactly who gets thrown out, and the resulting conflict might well make the asymptote shrink drastically, or collapse, as resources are used to fight instead of survive. To survive literally forever you need to be lucky every time; entropy only needs to be lucky once.
That said, even with total entropy you get the occasional quantum fluctuation that creates a small, local gradient again—in fact, arbitrarily large gradients if you wait arbitrarily long times; if somehow you were able to survive the period between such events, you could indeed live for ever. In fact, if you are able to wait long enough you will see a quantum fluctuation the size of the Big Bang. The problem is, of course, that a human, and probably life more generally as well, is extremely low-entropy compared to the sort of universe you get at 10^1000 years. In fact, interstellar space from our era would look rather low-entropy compared to that stuff. So the difficulty is to protect yourself against the, as it were, sucking vacuum that tries to rip the low entropy out of your body, without using up your reserves of energy on self-repair.
Overall, I’d say it doesn’t look utterly hopeless, although it is subject to a Fermi paradox: If survival over arbitrary timescales is possible, why don’t we see any survivors from previous BB-level events? If my account is correct, it seems unlikely that ours is the first such fluctuation.
Is the total subjective time finite or infinite?
Does the expansion of space pose a problem? If you had a universe of a constant size, you’d expect fluctuations in entropy to create arbitrarily large gradients in energy if you wait long enough, but if it keeps spreading out, the probability of a gradient of a given size ever happening would be less than one, wouldn’t it?
Also, wouldn’t we all be Boltzmann brains if it worked like that?
The intention was to make it infinite, otherwise there’s no use to the process. You’ll notice that the laws of thermodynamics don’t say anything about the shape of the downward trend, so it is at least conceivable that it allows a non-convergent series.
This doesn’t look obvious to me. You get more vacuum to play with; the probability per unit volume should remain constant.
Could be. Do you know we aren’t? :)
I was assuming that there has to be stuff in space for stuff to happen. I guess I was wrong.
There’s a chance that our experiences are just random, which we can’t do much to reduce. All we can do is look at the probability of physics working a certain way given that we are not random. That cosmology would be ridiculously unlikely given that we are not random, because that would require that we not be Boltzmann brains, which is extraordinarily unlikely.
Not an answer, but there is a beautiful short sci-fi story by Isaac Asimov that touches on this theme called “The last question”. I don’t know if it is okay to provide a link but it isn’t hard to find online.