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B De Sitter equilibrium

  1. Nov 28, 2017 #1

    I was reading this paper where ideas presently originally by Dyson, Kleban, and Susskind about de Sitter equilibrium have been expounded by the authors. I have a few specific questions.

    1. Could de Sitter space exist, for instance, in the heat death of an expanding universe like our own?

    2. What is the justification for believing that this equilibrium state in maximum entropy could produce universes with quantum fluctuations?

    3. Is this model testable or falsifiable?
  2. jcsd
  3. Nov 28, 2017 #2


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    Definitely. If dark energy is a cosmological constant, then the eventual fate of our observable universe is to effectively become de Sitter space.

    There's some debate about that. It might not:

    The simple picture is that de Sitter space has Hawking radiation at its cosmological horizon, in a manner similar to black holes. This gives the system a finite (though very, very small) temperature which can feed fluctuations. As the above paper argues, however, that may not be accurate.

    Andy Albrecht later came out with a paper describing an experimental test of this idea:

    He argues that the model predicts a finite spatial curvature that depends only upon the ratio of matter density to the cosmological constant density, with a value of about 0.02 given the current ratio. As the 2015 Planck results show that the curvature parameter is less than 0.005, this model is likely ruled out by current observational evidence.

    This means that the de Sitter equilibrium idea is almost certainly not correct in its original formulation, but it's always possible that there are some modifications or additions to the idea that might make it fit observation, or there was an error in how it was formulated. So it's not necessarily useless or impossible. But certainly the specific, original idea doesn't seem to have panned out.
  4. Nov 28, 2017 #3
    @kimbyd thanks. I will read through those papers tomorrow.
  5. Nov 29, 2017 #4
    In regards to this first paper:

    1. Are you one of the authors? The first author's name is uncannily close to your moniker.

    2. Would it be correct to say that one of the conclusions of the paper is that quantum fluctuations from de Sitter space is extremely unlikely?

    3. Is the paper arguing that inflation is more than likely a one-time event as opposed to eternal?

    4. Is the paper implying a multiverse based on the many worlds interpretation of QM by the branching of the wave function?
    Last edited: Nov 29, 2017
  6. Nov 29, 2017 #5

    What would happen if Andy was right in the long term future of the universe? Would the universe recollapse on itself or something like that - how would the dSE hypothesis be avoided?
  7. Nov 30, 2017 #6


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    No, I am not :)

    That's what they're saying, yes.

    That's a much stronger conclusion that I don't think is supported. It's merely saying that this particular method to produce inflation spontaneously isn't very likely. It doesn't rule out the possibility of other mechanisms.

  8. Nov 30, 2017 #7


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    It wouldn't recollapse, no. The future history would be empty de Sitter space for all hypothetical observers.
  9. Dec 1, 2017 #8
    Aren't they saying that the fluctuations are an impossibility in de Sitter rather than very unlikely? Or did you meant something else by 'very unlikely'?

    Oh, okay. So the problematic equilibrium would be avoided, there wouldn't be any radiation or particles at all, just empty space?
  10. Dec 3, 2017 #9


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    They are saying that thermal fluctuations do not occur in de Sitter space. In terms of our actual universe, which isn't exactly de Sitter, they're merely extraordinarily unlikely.

    I don't know what you mean by "the problematic equilibrium". But yes, there would be no radiation or particles, just empty space.
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