How may entropy be reversed?

[RainDreamer]

"Will humankind one day without the net expenditure of energy be able to restore the sun to its full youthfulness even after it had died of old age?" or in essence, can we stop, or even reverse entropy?

Half a serious question, half a reference to a certain scifi story. (space cookies for those who gets it)

Do you think it is possible? To reverse the direction of entropy and stop it from reaching maximum? Is it possible to prevent the heat death of the universe?

Edited March 1, 2015 by RainDreamer

[K^2]

The fine grain entropy is a conserved quantity. The increasing coarse entropy is the direction of time. Either way, the answer is no.

[Bill Phil]

Is it possible? Well, first let me ask you what reference frame? Multiverse? Yes. Universe? No.

You see, entropy is always increasing for the whole mechanism, unless acted upon by another mechanism. If each mechanism is a universe, then you can move around entropy as you see fit (assuming you're a Type V civilization). But then you would have a multiversal entropy that's constantly rising. Everything is doomed to die. Kind of sad, really.

[Dodgey]

There is as yet insufficient information for a meaningful answer.

[RainDreamer]

Is this problem unsolvable in all conceivable circumstances then?

[rtxoff]

If the end of the universe is a single singularity which results in another big bang there is an natural mechanism of countering entropy. However as far as we know the universe won't end in the big crunch but we could be wrong.

[lajoswinkler]

If you mean the system, then yes, it can. Refrigerators, evaporating brine, organisms, they're all reversing system entropy inside their own borders, by increasing (a lot more) entropy of the surroundings.

Total universe entropy - never.

[vger]

IF my some really finite chance, humans lived long enough to worry about it... that would be quite an interesting time.

[Frozen_Heart]

As far as known physics goes. No.

[K^2]

Is this problem unsolvable in all conceivable circumstances then?

Only due to the statement. You are trying to achieve something that contradicts itself. Forward direction in time is due to increase in entropy. You can make entropy decrease in that direction, but then it will be reverse direction in time, and you still have entropy increasing in a forward direction. It's how our perception of time works.

On the dynamics level, time direction is irrelevant, but on dynamics level you don't care about coarse entropy, and fine grain entropy is conserved as I've pointed out.

[lajoswinkler]

As far as known physics goes. No.

I'd say it goes beyond physics.

[vger]

I'd say it goes beyond physics.

It's a moot question anyhow. We still don't sufficiently have the "big bang" figured out, which would make it rather difficult to even take a guess at any bizarre attempts to prevent the universe from collapsing again. Just thinking about that just puts other weird pointless questions into my head, but I don't want to derail.

[lajoswinkler]

Well ok, that would be resetting in a large crunch and destruction of matter itself, but if we don't take that into account, then entropy will grow forever.

[PB666]

For the sun to be restored you would have to remove carbon and helium and replace them with hydrogen and deuterium. To do that you would have to stop the sun and that has its own consequences. You could add hydrogen and that has its own consequences, so pretty much leave well enough alone.

Your thought process is however misguided because our sun will not be ours in 400 million years. Our species is conservatively on 1.8 million years in age, unconservatively 230,000 years. There is no way to control the fate of our species for 400 milion years, it will go either to a much more evolved and capable genera (or phyla), or join the do-do bird.

That means in about the time that the Sun goes Big Red, we will have either found a way off this rock, or be extinct, probably the latter. If we have not found a way to travel interstellar within the next say 1000 years, I think our fate is sealed anyway you look at it.

[Newt]

For the sun to be restored you would have to remove carbon and helium and replace them with hydrogen and deuterium. To do that you would have to stop the sun and that has its own consequences. You could add hydrogen and that has its own consequences, so pretty much leave well enough alone.

Yeah. Refueling the Sun would also probably take so much energy that it would not really stop entropy, just keep one small star going for a while longer.

Your thought process is however misguided because our sun will not be ours in 400 million years. Our species is conservatively on 1.8 million years in age, unconservatively 230,000 years. There is no way to control the fate of our species for 400 milion years, it will go either to a much more evolved and capable genera (or phyla), or join the do-do bird.

That means in about the time that the Sun goes Big Red, we will have either found a way off this rock, or be extinct, probably the latter. If we have not found a way to travel interstellar within the next say 1000 years, I think our fate is sealed anyway you look at it.

I would say that giving mankind a millennium is a tad alarmist. We have survived in this star system for a considerable period, and we probably are not going to have some cataclysm that destroys all mankind in the next thousand -- that is absurd. Smash earth with a couple large asteroids like the one that flew past a bit ago, even smash cities directly, and humanity will be virtually the same. Give us another five-hundred year dark age, and chances are will will recover and get back going again, reduce humanity to the bronze age, and chances are we will be able to recover before something truly bad happens. You have to remember that recorded history is barely the blink of an eye in the vast scale of time the Earth has lived through, a huge setback for civilization is really not that long in the grand scheme of things, and we can probably get back to where we were before, albeit differently. I hope we have interstellar travel (not necessarily FTL) before 3000, we probably could do it with modern technology, but I do not think that failing to do that will have any major consequences orrisks for humanity in itself.

I agree about the fate of humanity, by the time the earth is uninhabitable for humans, if any of us are still around they will be in museums of truly ancient history, and research labs (dead the lot of them). Our posterity will not fit the bill for homo sapiens by a long shot. But they may still be our civilization, and its preservation is more what we should care about.

[K^2]

We still don't sufficiently have the "big bang" figured out, which would make it rather difficult to even take a guess at any bizarre attempts to prevent the universe from collapsing again.

It is in no danger of collapsing. The expansion of the universe is accelerating. There is no guarantee that this will keep up, but it's pretty much certain that universe cannot shrink bellow current size. Whether it expands ad infinitum or reaches an equilibrium size is somewhat debatable. The later case would make the entropy question more relevant. But that's exactly where fine grain vs coarse entropy distinction becomes critical. Time will simply have to become a local phenomenon.

If the universe keeps expanding, it's a moot question. As energy density drops to zero, heat death is inevitable regardless of what you do about entropy.

[MartGonzo]

Asimov's, The Last Question

and no, no theory I ever came across as to how it could be done.

singularity and Will according to Asimov.

[WestAir]

The existence of a white hole? Time traveling worm hole?

[K^2]

The existence of a white hole? Time traveling worm hole?

Adding a closed time-loop wouldn't offset global entropy. Just local. And as pointed out earlier in this thread, a refrigerator can already reverse change in local entropy.

If time was cyclic globally, that would be a much more interesting scenario. I don't think it's possible to cause that, since that requires a topology change, and there is absolutely no evidence that topology of space-time can be modified. (E.g., General Relativity tells us how to manipulate existing wormholes, but nothing about creating a brand new one.) In either way, thermodynamics of a cyclic-time universe should be similar to that of a static universe.

[Rune]

There is as yet insufficient information for a meaningful answer.

Best answer.

[Scoundrel]

The question was from Asimov's The Last Question. It was actually my introduction to him when I was a little kid, as it was a show at the planetarium, and it introduced me to the idea of critical thinking. Also a bittersweet bit of trivia: it was narrated by the late Leonard Nimoy. Doubt you can find it now as that was the 80s, and there's nothing on youtube.

Edited March 2, 2015 by Scoundrel
fixed image

[Majorjim!]

Most physicists would say that entropy is the only law of physics that cannot be broken/reversed/bent.

[Stargate525]

Most physicists would say that entropy is the only law of physics that cannot be broken/reversed/bent.

What's that old adage? You can't win, you can't break even, and you can't not play?

[-Velocity-]

Isn't there a fantastically small chance that entropy could actually run in reverse for some indefinite time? After all, isn't entropy at least mostly, or entirely, simply that "disordered" states are more common than "ordered" states, and once you have a huge number of particles, the chances of them progressing from order to disorder becomes, statistically, effectively certain? So the question is, if you waited an extremely long time, through random chance, could entropy reverse itself in a closed system? Like maybe you have to wait 10^100^100^100 years, but eventually, you could observe the entropy in a macroscopic system reverse itself- maybe you might see heat flow backwards (from cold to hot) for a few seconds?

[Technical Ben]

Easier to replace the sun... no? Turn it into a binary system, then... oh, that might make it worse!