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Multiverse and Eternal Inflation Disproved?

  1. Feb 5, 2015 #1
    Hi. I am a first-year physics undergraduate student, and really want to become a cosmologist eventually.

    I was looking into how eternal inflation can generate a multiverse and came across this paper on the arXiv: http://arxiv.org/abs/1408.2249

    It claims to have shown that eternal inflation cannot be stochastic and that the universe would "blow up" if such a process did indeed occur. Therefore, according to the paper an infinite multiverse would not result from inflation.

    Any thoughts on this? The mathematics is obviously quite beyond my level!

  2. jcsd
  3. Feb 5, 2015 #2

    Ken G

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    Gold Member

    It certainly doesn't sound like good news for advocates of "eternal" stochastic inflation, but I can't say if they have made any mistakes. I was a little puzzled by their conclusion that the problem is not well posed, which seems contradictory to their conclusion that eternal inflation doesn't work. It is almost like they are saying that eternal inflation cannot be a unique solution, but they're not really sure if it is a solution at all, or not. The whole business reminds me a bit of the arguments that surround black hole physics inside the event horizon-- when even GR experts cannot agree on how the solutions should behave when you include quantum fields, or quantum field experts cannot agree on what will happen when you include GR, I'm not sure we have much hope of really knowing who to believe. Personally, I'm reserving judgement on any of this, be it black holes or inflation, until there is a theory that extends to the Planck regime (and I don't say unification of GR and QM, because we don't know that a successful theory in the Planck regime will do that).
  4. Feb 6, 2015 #3
    Thomas, thanks for sharing that paper. I had not seen it before. Analysis of data from the Planck satellite is also not looking good for inflation. See


    Steinhardt, one of this paper’s authors, gave a talk on the subject available here. http://webcast.in2p3.fr/videos-6161

    I'm a little surprised because inflation seems to be such an important part of our current understanding.
  5. Feb 6, 2015 #4
    Actually, the paper demonstrates that "eternal inflation described by such a stochastic force term does not lead to future eternal behaviour." It does not rule out the possibility of stochastic inflation, nor does the paper make any claims about the universe blowing up. In essence, all this paper is really saying is that the Chaotic Inflation theory does not create eternal inflation, and therefore no multiverses are created.
  6. Feb 6, 2015 #5
    I understand why the Inflation theory was necessary. It was the only way we could explain how the universe has such a homogeneous temperature everywhere. However, there are two significant questions that have yet to be answered:
    • How did inflation begin? and
    • What was the mechanism that caused inflation to suddenly stop?
    If Inflation begins 10−36 seconds after the Big Bang, what caused it? Why did the universe suddenly begin expanding faster than the speed of light? Then just as suddenly Inflation stops between 10−33 and 10−32 seconds after the Big Bang. Why did Inflation end? How could Inflation end?

    Until those questions can be answered the Inflation theory will remain a convenient explanation for why the universe has such an evenly distributed temperature, but a very dubious explanation.
    Last edited: Feb 6, 2015
  7. Feb 6, 2015 #6
    Hi.. The paper does show according to my reading that solutions to the field equations blow up /diverge to infinity. Solutions to the Einstein field equations are "universes" are they not? FLRW, Schwarzschild, etc...
  8. Feb 6, 2015 #7
    "Note also that the way Mathematica apparently handles ∞ in its numerical integration algorithm is to provide unbelievably large numbers, in this case, on the order of 10222, which for all purposes is to be taken as ∞ in these computations."

    I have a real problem with something that is finite becoming suddenly infinite when mathematics is applied. It may be an "unbelievably" large number, but it is still finite. Neither FLRW, nor Schwarzchild, makes any reference to infinity.
  9. Feb 6, 2015 #8
    Well, no numerical algorithm actually produces "infinity" as an output, you see your numerical algorithms diverge to very large numbers, like Runge-Kutta, Euler-Maryama, etc... How would you even put infinity in your software package?
  10. Feb 6, 2015 #9
    I would not even suggest that anything was infinite, much less try to account for infinity through software. The singularity of a black hole may be incredibly dense, but it must still be finite since its mass and radius is finite. Saying that something is "infinitely" dense when its mass and radius is finite is just being mathematically lazy, in my opinion.
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