# I Heat Death of the Universe, Total or Not?

1. Feb 3, 2016

### greswd

Let's assume that the universe will evolve over time to resemble the one predicted by heat death theorists.
We're also assuming that the Big Bounce, Crunch, Rip etc. don't occur.

Is it possible that while it resembles a heat death scenario, the heat death will never be total?

That means: is it possible for life to exist (in some form or another) forever?

(I'm defining life from a physicalist point of view, which Schrodinger defined as an embodied metabolism.)

2. Feb 3, 2016

### Ronie Bayron

This is a nice concept for simulation. As for the moment we do not know what is inside the negative part of the equation, given there'll be no crunch to happen, may be some stable materials remain as is.

3. Feb 3, 2016

### anorlunda

The second law requires an external energy source for life. What source would that be?

4. Feb 3, 2016

### greswd

I think that depends on the type of lifeform. I'm just wondering if what Schrodinger described as an 'embodied metabolism' is always possible.

Last edited: Feb 3, 2016
5. Feb 3, 2016

### anorlunda

No, the second law of thermodynamics does not depend on the type of life form. Put it in other words, perpetual motion machines are impossible, and a life form is a machine.

6. Feb 3, 2016

### greswd

But your question was about what the source of energy would be?

Life cannot exist if the universe reaches a state of total heat death, I was asking if the universe will reach that state in a finite amount of time. If it takes forever, than maybe some form of life, an embodied metabolism, could exist, and there would be the possibility of there being life existing in the universe forever, til the end of time.

7. Feb 3, 2016

### anorlunda

Yes, but you missed the point of the question. Life (in any form) can not exist without an external source of energy.

8. Feb 3, 2016

### greswd

Sorry, I'm too thick, you'll need to ask me clearer questions lol.

"Life cannot exist if the universe reaches a state of total heat death, I was asking if the universe will reach that state in a finite amount of time. If it takes forever, than maybe some form of life, an embodied metabolism, could exist, and there would be the possibility of there being life existing in the universe forever, til the end of time."

What is your opinion on this?

9. Feb 3, 2016

### maline

My guess would be that for any level of energy concentration, there is a finite time beyond which such a level will be scarce in the universe. So any particular life form, requiring some minimal energy, would come to an end.
Also, don't forget about the absurdly low temperature due to the expansion...

10. Feb 3, 2016

### greswd

That may be so, but could a type of lifeform (or metabolic processes) exist for every level of energy decrease?

11. Feb 3, 2016

### greswd

My motivation is regarding the future of mankind. Our descendants might run out of resources and end the human race.

Total energy in the universe should be finite, but it is conserved, so maybe our descendants might find a way to keep converting energy to a useful form, allowing them to last forever.

12. Feb 3, 2016

### phinds

This is just silly. Nothing lasts forever. The heat death will be total for all practical purposes as far as the human race is concerned, even in some wildly morphed form.

13. Feb 3, 2016

### bcrowell

Staff Emeritus
We have a FAQ on a closely related topic: https://www.physicsforums.com/insights/will-all-matter-be-converted-to-photons/ . The references therein should be sufficient to answer your question about heat death.

For your question about the end of life, a more formal way to pose the question is whether the cosmological facts make it possible, in principle, to perform an infinite computation. There is a well developed physical and thermodynamic theory of computation, and computation is a necessary and probably (in theory) sufficient condition for life. The answer to this is not obvious and depend on the value of the cosmological constant:

Dyson, Time without end: Physics and biology in an open universe, Reviews of Modern Physics 51 (1979), pp. 447–460, doi:10.1103/RevModPhys.51.447

Krauss and Starkman, 1999, Life, The Universe, and Nothing: Life and Death in an Ever-Expanding Universe, http://arxiv.org/abs/astro-ph/9902189

The Dyson paper shows that an infinite computation is possible for a certain cosmological model, but the later Krauss paper shows that given what we now know about the cosmological facts, it's not possible.

I think the fact that the Dyson and Krauss papers arrive at different conclusions shows that this is not as silly as you might have intuitively believed. It's rather subtle.

14. Feb 4, 2016

### maline

This would directly contradict the Second Law. Your OP made more sense: perhaps an infinite series of life forms that require lower and lower energies can survive on the dregs of useful energy that goes to zero only asymptotically. That's more or less equivalent to the "infinite computation" question, if we assume that life (and consciousness?) requires only computation.

15. Feb 4, 2016

### .Scott

There is a secondary issue which begs the question (ie, the OP). Even given that it may be possible for life in the form of "computation" to slow as resources slow, would the total amount of thought generated tend towards the infinite? Given that "human life" is more sophisticated than a clock, examining the limits of a clock can provide insights into the limits on human thought. The first issue is whether the clock can continue keeping time - reporting a unique number or other symbol - as the universe drifts into its warm death.

To accomplish this, the clock will work in one of two ways: either it is allowed to reach infinity in the limiting case or not. If it is allowed, then it will require an infinite number of bits of information to record the new time values. At this point, that does not seem possible. The current universe available to any clock is limited in mass and size. In the "heat death" version of doom, this would not change.

So only the second case works. This implies that the clock transitions from one state to the next slower and slower - to avoid running out of states. But that leads to this gnarly question: how much time elapses between the 2nd to last tic and the last tic? The problem is that to span an infinite amount of time, there cannot be a last tic - and so the number of tics cannot be infinite.

So there is a limit on human experience. Even if humans could transform themselves into something that would persist forever, it could not result in an infinite expanse of human experience.

16. Feb 4, 2016

### rootone

In the the heat death scenario we are talking of timescales in the order of trillions of trillions of years.
Humans or immediate ancestors appeared on Earth around 1 million years ago.
The earliest single celled organisms on Earth seem to have originated about 4bn years ago, fairly soon after the Earth was any way habitable.
95% roughly of all organisms that ever existed on Earth are now extinct.
The observable Universe is nowhere near even 1 trillion years old.
Considering these vastly different scales and the record so far, I think the idea of our species being extant in trillions of trillions of years is extremely unlikely

17. Feb 4, 2016

### Chronos

The heat death of the universe is based on the second law of thermodynamics that essentially states the total energy available to do work in a closed system will inevitably be exhausted. There are some surprisingly deep implications inherent to this apparently simple axiom. Allow us to just focus on the idea of a 'closed system'. If the universe is indeed infinite [as believed by many scientists], how is it possible to assert it is a 'closed system' in any logical sense.

18. Feb 4, 2016

### phinds

I would not think that you could declare it a closed system but surely for all practical purposes if there is very, very nearly zero energy in a space say the size of the current observable universe it is VERY hard to imagine how that energy could be made use of to support life. I do realize that "hard to imagine" is not at all "proven to be impossible", but still ...

19. Feb 4, 2016

### maline

That doesn't mean it will have to stop, just that it will have to repeat old readings. Meaning it will lose track of how many quintillions of eons have gone by. Also, if the mode of information storage is changed an infinite number of times, that could possibly differentiate between the repeats.
More than that- as long as the total number of tics is not infinite, the last tic must occur at a finite time- meaning death.

BTW, have you read Asimov's "The Last Question"?

20. Feb 5, 2016

### bcrowell

Staff Emeritus
The first sentence is not a correct statement of the second law. Nothing in the second law guarantees that thermal equilibrium will be achieved. That's important in this context because in realistic cosmological models, which incorporate dark energy, the exponential expansion prevents distant parts of the universe from coming into equilibrium with each other.

In general, people seem to be wasting a lot of time in this thread trying to reinvent the wheel. A lot of the posts read like attempts to use nonmathematical, nonrigorous reasoning to redo what was done mathematically and rigorously in the Dyson and Krauss papers. I realize that the Dyson paper is paywalled, but the Krauss paper isn't, and the Krauss paper is the one that uses what we now know to be an accurate cosmological model.