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A Static and Eternal Universe vs The Second Law of Thermodynamics

  1. Aug 31, 2011 #1
    I've heard that the prevailing theory of cosmology before the Big Bang was that the universe is static and eternal. If this is true then how did they reconcile that theory with the second law of thermodynamics?

    Thank you...
     
  2. jcsd
  3. Aug 31, 2011 #2

    Chronos

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    A static and eternal universe was merely a belief system, and unsupported. GR changed that.
     
  4. Aug 31, 2011 #3
    Aside from not seeing any obvious long-term changes in the universe, I can believe that this notion was unsupported. However, I'm suggesting that it wasn't just unsupported, it was contradicted by contemporary physical knowledge like the second law. Either these two ideas can be reconciled, and I'd like to know how, or they somehow held this belief despite the contradiction, in which case I'd still like to know how...

    Thank you...
     
  5. Aug 31, 2011 #4
    This is historically wrong, the first model Einstein derived from his GR in 1916 was precisely static and eternal. So in fact at first GR not only didn't change that but proposed it, so it wasn't merely a belief system.
     
  6. Aug 31, 2011 #5
    It's easy, the current model is in contradiction with the first law instead of the second and nobody gives a damn.
    It's just a matter of wich of the the two laws you'd rather give up, and apparently the first law is now seen as less fundamental than the second by the majority, while 95 years ago (already with GR and until the thirties) they considered more fundamental the first so they favored static models. Who knows, maybe it goes the other way again eventually, or like you say they find out how to reconcile the 2 ideas but so far nobody seems to know how.
     
  7. Sep 1, 2011 #6

    Chalnoth

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    This is a wrong understanding. Einstein originally believed that our universe was static and eternal, and tried to adjust General Relativity to fit that belief. That attempt ultimately failed, as there is no stable static universe in General Relativity.
     
  8. Sep 1, 2011 #7

    Chalnoth

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    The difference is pretty tremendous. They had statistical mechanics at that time (it was formulated first by Boltzmann in 1870), so they knew, or at least should have known, that the second law was more fundamental than the first.

    As far as I am aware, however, they never reconciled thermodynamics with their belief in a static universe.
     
  9. Sep 1, 2011 #8
    Historical facts are historical facts, your quoted explanation doesn't contradict my post at all so there's no wrong understanding in what I posted. Kindly provide a quote of what exactly you understood wrong in my statements and how and I'll clarify it for you.
     
  10. Sep 1, 2011 #9

    Chalnoth

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    You said that GR proposed a static universe. This is false. You can't make an eternal static universe in General Relativity. Einstein made a static universe in General Relativity, but it was proven to be unstable, and that instability makes a static, eternal universe impossible.
     
  11. Sep 1, 2011 #10
    I said Einstein proposed a cosmological model in 1916 based in GR. Are you seriously arguing this is not so?
    If you want to argue like a 7-year-old that GR is a theory and therefore it can't propose anything so I expressed it in an unfortunate anthropomorphic way is fine, but grown ups I believe understood the correct meaning, that it was Einstein that proposed the model and not the theory itself. :biggrin:
    The fact that it is unstable has nothing to do with it being based on GR, there are many solutions to the GR equations that are not physical.
     
  12. Sep 1, 2011 #11
    By the way, actually it's not accurate to mix static with eternal.
    In fact static models are not eternal. Hoyle, Bondi and Gold "steady-state" model for instance was eternal and not static.
     
  13. Sep 1, 2011 #12

    Chalnoth

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    I'm saying that this cosmological model (a proposed static, eternal universe) was unstable, and thus could not ever have been eternal. That is, the model was not consistent.

    The fact that it is unstable contradicts the idea of it being eternal, which was part of the proposal. It was not a valid model.
     
  14. Sep 1, 2011 #13

    Chalnoth

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    Well, that's a different beast. That model was also wrong anyway.
     
  15. Sep 7, 2011 #14
    The natural way to reconcile the two ideas is through http://en.wikipedia.org/wiki/Poincar%C3%A9_recurrence_theorem" [Broken]. Every possible configuration will recur eternally. Such a universe would spend most of its time in a maximum entropy state, because most of its states would have this property, but eventually there would be a fluctuation that would drive it into a lower-entropy state.

    Nietzsche believed in eternal recurrence for this reason (as an implication of physics). Boltzmann apparently thought that the universe was created in this way. The issue has returned in http://arxiv.org/abs/hep-th/0208013" [Broken]. But these thoughts of Nietzsche and even those of Boltzmann were not part of the mainstream physics of their day, so as a matter of historical fact I can't tell you how the tension was resolved, or even whether it was much of an issue. Thermodynamics was only invented in the 19th century, it was a new mode of thought. The 19th century was also the century of Darwin and you had people like the biologist Haeckel proposing evolutionary cosmologies. Belief in progress, not belief in entropy, was the dominant idea of the time. There was no steady-state model of cosmology in the 20th century sense of a mathematical model. There must have been a point in time at which some mainstream cosmologist finally thought about the cosmic implications of the second law... I should try to find out when that was.

    edit: Wikipedia on http://en.wikipedia.org/wiki/Heat_death_of_the_universe" [Broken] fluctuating locally into a lower-entropy state, which then evolves back towards maximum entropy.
     
    Last edited by a moderator: May 5, 2017
  16. Sep 7, 2011 #15

    Chalnoth

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    I should mention that this view, in its simplest incarnation, utterly fails to explain our universe, because smaller decreases in entropy are exponentially-favored. This means that given this situation, it is more likely for the current universe, as it exists today, to fluctuate out of the equilibrium system than for an early universe to do the same (the early universe had much lower entropy). It is still more likely for this to happen for a single galaxy instead of the whole universe. It is still more likely for this to happen for a single solar system. It is still more likely for a disembodied brain to pop into existence, think a single thought, and disappear than it is for even our own solar system to come into existence all on its own.

    Such a model, then, predicts most observers are false observers: most are just Boltzmann brains that appear, think a single thought, then go back to equilibrium.

    So in order to have an actual universe, you need to have a model where the extremely low-entropy state at the start of our universe is actually strongly-favored over individual brains popping into and out of existence. Various models have been proposed that get around this issue, most often taking advantage of a physical process which favors fluctuations out of equilibrium that are small (as our early universe was quite small...much smaller than a proton).
     
    Last edited by a moderator: May 5, 2017
  17. Sep 7, 2011 #16
    Most scientists of the time believed in God. God by definition is not bound by the laws of physics and so can lower the entropy of the universe, or any part of it, at will.
     
  18. Sep 7, 2011 #17

    Chalnoth

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    I doubt many believed in an interventionist god. That sort of god belief has been rare among scientists for quite some time.
     
  19. Sep 7, 2011 #18

    Chronos

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    For historical correctness, see "The history of the cosmological constant problem" http://arxiv.org/abs/gr-qc/0208027
     
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