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Roger Penrose - Before the Big Bang

  1. Jul 24, 2009 #1

    This is an interesting video lecture by Roger Penrose talking about his Weyl Curvature Hypothesis. I found most of it fairly easy to understand. Maybe if someone can explain to me one thing: He talks about how entropy at the beginning of the universe was low or zero. But he also says (I think) that the background radiation shows thermal equilibrium, and that the early universe was almost perfectly homogeneous. Doesn't this mean that entropy was high?
    Last edited by a moderator: Apr 24, 2017
  2. jcsd
  3. Jul 24, 2009 #2
    I think the idea is that becuase one constrains the weyl cuvature to some value(zero?) this means that despite the universe being in a thermal state it still is in a very special state so the entropy is low. But it does seem confusing.
    Last edited by a moderator: Apr 24, 2017
  4. Jul 24, 2009 #3

    George Jones

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    Penrose thinks that gravitational entropy is low for uniformly distributed matter and high for clumped matter. See

  5. Jul 24, 2009 #4


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    Maybe i'm confused.. Who disagrees with that? That clumping increases entropy has been standard lore and textbook for a long time now. In the cases we can actually calculate in, thats always been the case.
  6. Jul 24, 2009 #5
    Penrose goes further than just that. He identifies the relevant degrees of freedom for gravitational entropy as the Weyl curvature tensor. As pointed out in the thread linked above by George, with a cyclic model for the Universe, he needs the entropy to be constant basically. So if I understand anything to his claim, the entropy flows to the gravitational field, and it takes an enormous change in thermodynamical entropy to make up a small change in the Weyl curvature so you get a very long process to transfer in this direction, while according to him when the Universe becomes conformal and undergoes a transition to the "next big bang", it takes literally no time since there is no reference for any kind of clock.
  7. Aug 10, 2009 #6
    met a man from cambridge today, live in kansas city.
  8. Oct 27, 2009 #7
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