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Smolin dispelling false impressions of the singularity

  1. Dec 6, 2014 #1

    Doug Huffman

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    Gold Member

    From Unger and Smolin's new The Singular Universe and the Reality of Time: A Proposal in Natural Philosophy, e-book page 403/576

    "It is important to dispel some false impressions about the cosmological singularity theorems which are widely spread due to misleading accounts in some popularizations.
    • The singularity does not occur at a point from which the universe expands. Cosmological singularities are entire spacelike surfaces. The curvature and energy density become infinite all over space simultaneously, a finite time to the past of typical observers. A universe can even be infinite in spatial volume an arbitrarily short amount of time after the singularity.
    • The singularity is not a moment of frozen time. The singular set is not in fact a part of the spacetime geometry where time is not flowing.
    • The singularity does not restrict the solution of the Einstein equations. The whole point is that generic solutions are singular, which is to say that there are an infinite number of solutions to the Einstein equations which look like large expanding universes at late times, have an initial cosmological singularity, but differ by the details of the geometry just after the singularity. There may, for example, be lots of gravitational waves, and black holes, present just after the singularity. So the singularity does not eliminate the need to specify an infinite number of initial conditions to determine which solution of the Einstein equations describes our universe.
    • There is no event, force or influence which starts the universe evolving. The cosmological singularities are simply boundaries to the extension of a spacetime history to the past. There is nothing there, before the singularity, which starts the universe going.
     
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  3. Dec 6, 2014 #2

    Chalnoth

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    Honestly, I really don't like talking about the singularity in the way he does here. The singularity itself is mathematical nonsense. Asking what the singularity was like is rather like asking about those classic nonsense questions like how many angels can dance on the head of a pin.

    What I like to say is that the singularity represents the fact that our current theories aren't a complete description of our universe: the description of the universe with a singularity in it has to be wrong before we extrapolate all the way back to the singularity.
     
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