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I Contraction prior to expansion?

  1. Oct 9, 2015 #1
    A number of contemporary models propose that the universe was contracting prior to expansion. However I have found this critique of such a proposal from Geroge Elliss:
    “initial conditions have to be set in an extremely special way at the start of the collapse phase … in an acausal way (in the infinite past).”

    If this model is true, it rests on a knife-edge of fine-tuning. However, all the careful setup must be done over an infinite distance in the infinite past. This is troublesome to say the least. Indeed, it is partly to avoid acausal fine-tuning that cosmic inflation was first proposed.

    Secondly, however, “the collapse phase is unstable, with perturbations increasing rapidly, so only a very fine-tuned collapse” would yield the universe we see today. As a result, the model rests on a knife-edge with no feasible way to find its balance. Although this model involves an infinite past, it is not very popular for these reasons."

    Any thoughts, is Ellis right if so why are so many cosmologists working on collapsing prior contracting models?
     
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  3. Oct 9, 2015 #2

    marcus

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    Curious, I never heard that argument---or that the collapse phase had to have a 'beginning' with "initial conditions", for that matter.

    Do you have a link to the place Ellis was making that argument? It may have special assumptions---not to be taken out of context.

    Could be several years old too, would be nice to have a date.
     
  4. Oct 9, 2015 #3

    marcus

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    I could of course be wrong, Palmer, but I suspect you will not find that "quote" from Ellis in any of his professional writings as a cosmologist.
    It sounds like something from the related RELIGIOUS discussion and I see it comes up in a Creationist book not by Ellis but by the theologian William Craig:
    Reasonable Faith: Christian Truth and Apologetics
    https://books.google.com/books?isbn=1433501155

    This updated edition by one of the world's leading apologists presents a systematic, positive case for Christianity that reflects the latest work in the contemporary hard sciences and humanities. Brilliant and accessible.

    The purported quote occurs in footnote 105 on page 145 and is a second hand---something that Craig says that James Sinclair SAYS that George Ellis said to him. And the exact wording looks as if it has been reworked by William Lane Craig. It runs on without a clear demarcation of where the quote ends and Craig's interpretation begins.
     
    Last edited: Oct 9, 2015
  5. Oct 10, 2015 #4
    Very interesting Marcus. I guess the fact that this claim is not in the peer reviewed literature means it has less weight and should have less attention.
    However I am still curious as to what the response would be from those that think bouncing cosmologies are plausible from this allegation?
     
  6. Feb 9, 2017 #5
    This is what George Ellis Said. This is from The Blackwell Companion to Natural Theology 2009 p. 143

    The problems are related: first, initial conditions have to be set in an extremely special way at
    the start of the collapse phase in order that it is a Robertson-Walker universe collapsing; and
    these conditions have to be set in an acausal way (in the infinite past). It is possible, but a great
    deal of inexplicable fine tuning is taking place: how does the matter in widely separated causally
    disconnected places at the start of the universe know how to correlate its motions (and
    densities) so that they will come together correctly in a spatially homogeneous way in the
    future??
    Secondly, if one gets that right, the collapse phase is unstable, with perturbations increasing
    rapidly, so only a very fine-tuned collapse phase remains close to Robertson-Walker even if it
    started off so, and will be able to turn around as a whole (in general many black holes will
    form locally and collapse to a singularity).

    So, yes, it is possible, but who focused the collapse so well that it turns around nicely? (pers.
    comm., January 25, 2006)

    This was something addressed by Carroll in a recent lecture he gave earlier this year at a meeting of the American Astronomical Society. so I guess acausal fine tuning is really a problem.

    Link: http://www.preposterousuniverse.com/blog/2017/01/25/what-happened-at-the-big-bang/
     
  7. Feb 10, 2017 #6
    Ellis wrote a paper in which the universe is cyclic with contracting and expanding phases, so I don't think he's entirely against the idea. https://arxiv.org/abs/1511.03076
     
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