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Heat death the ultimate endgame?

  1. Aug 16, 2011 #1
    I recently caught Brian Cox in BBC's Wonders of the Universe. I got caught on the heat death theory of the end of the universe.

    I understand the concept of entropy and that the universe is heading toward a state of maximum entropy.

    Cox used the example of desert sand to illustrate high entropy and a structured sand castle for low entropy. But he then went on to explain that there is nothing stopping individual grains of sand spontaneously forming the exact same castle - a low entropy structure, it's just extremely unlikely, due to the 2nd law of thermodynamics, that everything tends toward high entropy rather than low entropy.

    My question is, on a long enough timeline, following heat death and achieving maximum entropy, would it be possible, no matter how unlikely or how long the time frame, that the low potential radiation energy left as the only property of our universe could spontaneously form a low entropy state, kick starting a chain of events resulting in universe 2.0 (or x.0), as all the universe's energy still exists, just in a state of low potential energy which could be influenced by this low entropy state?

    Is heat death the ultimate endgame? Do we know?

  2. jcsd
  3. Aug 16, 2011 #2
    This would be overlooking the second law. Entropy never really decreases, it only appears to.

    For example:

    Not only is it very unlikely for your sand castle to form on its own in the shape your desire, but it requires a lot of wind to facilitate the process. Even if the sand castle forms, the wind itself is an increase of entropy that would overpower the sand castle in the system as a whole.

    An apple is an amazing feat in a decreased state of entropy, however in order to create such a master piece a lot of entropy increase has taken place in the sun and on the earth.

    However a more advanced concept known as Conformal Cyclic Cosmology does propose that the end is not the end, but the beginning of a universe x.0 just as you say.

  4. Aug 16, 2011 #3


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    Not really. There's no current science that suggests anything will happen after the heat death. However there are alternative theories for the http://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe" [Broken].
    Last edited by a moderator: May 5, 2017
  5. Aug 18, 2011 #4
    Thanks LostConjugate,

    I was hoping to clear a few more points in relation to heat death before moving on to Conformal Cyclic Cosmology:

    First, are these statements correct:

    1. Entropy is similar to energy in that all that will ever be already is, just in various states/structures/systems.

    2. Life as we know it is reliant on low entropy, dense structures binding high amounts of potential, workable energy, such as your apple, the sun, earth, etc. and cannot exist in too high an entropy system.

    3. The effect of time's arrow is to seek an even distribution of energy, for the universe to reach a state of maximum entropy, thermal equilibrium and total uniformity.

    4. In a state of maximum entropy, energy is in a state of such low density as to be considered non-gravitational and to possess almost zero potential / workability, effectively 'killing' the universe.

    Now, returning to Brian Cox example of the desert - high entropy, and the sand castle - low entropy, and his statement that there is nothing stopping the sand particles spontaneously forming the castle, it is simply overwhelmingly improbable.

    It seems to me that he was saying that this extreme improbability is due to the effects of time's arrow and the natural tendency/preference for everything to form high rather than low entropy systems. However, no matter how improbable, this is not always the case and low entropy systems do occur, as we wouldn't be here otherwise. Life is a cosmic anomaly and exists due to the above improbability occurring.

    I guess if that is correct, it leaves me with three questions regarding heat death:

    1. How is maximum entropy achieved in an ever expanding universe?

    2. In the timeline leading up to heat death and maximum entropy, is it possible, although almost totally improbable, that low entropy systems will form over a long enough timeline resulting in something of an endless cycle?

    3. In the timeline leading up to heat death and maximum entropy, is it possible, although almost totally improbable, that at a certain point, a system of entropy, gravity, energy and thermodynamic instability that could match the conditions prior to cosmic inflation, again forming, over a long enough timeline, something of an endless cycle?

    What I really want is to understand just what Cox was explaining re the possibility of the sandcastle spontaneously forming; that it could happen, that there is nothing stopping it occurring naturally, it is just extremely unlikely, improbable.

    I had assumed that his example was a metaphor explaining the existence of low entropy systems such as your apple, the planets, stars and life; that no matter how unlikely or improbable the chances, it did happen at least once and may happen again once we are gone, but again, it is extremely improbable.

    Thanks all.
  6. Aug 18, 2011 #5


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    I don't think that is true. Total entropy can (only) increase, whereas energy is conserved.

    I don't know about "dense", but the rest of it seems true, or at least plausible to me. I think that as entropy increases, the amount of energy in the form of waste heat increases at the expense of the amount that can do useful work, and this would eventually lead to life being impossible.

    I don't know about this. I'm not sure what you mean by, "an even distribution of energy." I also don't know much about the relationship between entropy and the so-called "arrow of time" (aside from the obvious that the Second Law says that certain processes are irreversible). So I'll leave it at that.

    I'm not sure why you're harping on this 'density' thing. Structures can be low or high density, and these are relative terms anyway. Perhaps the distinction you're looking for is inhomogeneous (structured) vs. homogenous?

    No. There are two ways of looking at things. The macroscopic view, which is that this quantity called "entropy" must always increase (overall), and therefore certain processes are irresversible (and systems do not return into a more ordered state from a disordered one). The microscopic way of looking at things is to count up the number of "microstates" of a system (states with different configurations on atomic scales, but all having the same macroscopic properties such as temperature, internal energy etc). When you do this, you note that the ordered states are just a few outcomes out of very very many, (vastly many in fact), possible outcomes. THAT is why they are improbable. So the improbability of these states is a way of explaining the way entropy works using a microscopic model of the system.

    Well, people have already pointed out to you that the apparent decrease in entropy within this system is accompanied by a large increase in entropy of the surroundings. Overall, the entropy of the universe must increase in any process.
    Last edited: Aug 18, 2011
  7. Aug 19, 2011 #6
    1. 'The idea of heat death stems from the second law of thermodynamics, which states that entropy tends to increase in an isolated system. If the universe lasts for a sufficient time, it will asymptotically approach a state where all energy is evenly distributed.'
    http://en.wikipedia.org/wiki/Heat_death_of_the_universe" [Broken]

    I am probably wrong, but from the above I had concluded that as the amount of energy in the universe is finite, one not being able to create or destroy it, so too must entropy be finite. Once all energy is evenly distributed, entropy could no longer increase. It must have a maximum limit it can reach before it can increase no more, if it is related to the even distribution of energy.

    2. Ah, I see your point regarding dense. So a low entropy structure/system does not then, by nature, necessarily have to be dense?

    3. See 1 re even distribution of energy.

    4. This may be another hole in my understanding, but I had though the more dense an object, the more energy/potential energy it holds. Also, the more dense an object, the more gravity it exerts. The more gravity, the higher chance of attraction. The higher the chance of attraction, the higher the chance of low entropy systems forming.

    5. With regard to 'systems do not return into a more ordered state from a disordered one', when stars form from within nebuli, on the macroscopic level aren't they creating a more ordered state than exists within the nebuli as a cloud. This still follows the fact that overall, entropy increases, but not until after creating a lower entropy, higher ordered system. A more ordered state created from a more disorganised one.

    I'm unsure of systems on a macroscopic level.

    6. Thanks, I understand that now. But if my understanding of 1 is correct, with the universe achieving heat death, a state where all energy is evenly distributed (as per 1), entropy must stop increasing, right.

    As a sidebar, can maximum entropy even be reached in an ever expanding universe?

    Thanks. Your inputs are making this a lot clearer for me. My partner is wishing she had never recorded Wonders of the Universe for me...
    Last edited by a moderator: May 5, 2017
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