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Singularities and Quantum Gravity

  1. Feb 27, 2007 #1

    marcus

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    This just out:

    http://arxiv.org/abs/gr-qc/0702144
    Singularities and Quantum Gravity
    Martin Bojowald
    41 pages, lecture course at the XIIth Brazilian School on Cosmology and Gravitation, September 2006
    IGPG-07/2-4, NSF-KITP-07-19

    "Although there is general agreement that a removal of classical gravitational singularities is not only a crucial conceptual test of any approach to quantum gravity but also a prerequisite for any fundamental theory, the precise criteria for non-singular behavior are often unclear or controversial. Often, only special types of singularities such as the curvature singularities found in isotropic cosmological models are discussed and it is far from clear what this implies for the very general singularities that arise according to the singularity theorems of general relativity. In these lectures we present an overview of the current status of singularities in classical and quantum gravity, starting with a review and interpretation of the classical singularity theorems. This suggests possible routes for quantum gravity to evade the devastating conclusion of the theorems by different means, including modified dynamics or modified geometrical structures underlying quantum gravity. The latter is most clearly present in canonical quantizations which are discussed in more detail. Finally, the results are used to propose a general scheme of singularity removal, quantum hyperbolicity, to show cases where it is realized and to derive intuitive semiclassical pictures of cosmological bounces."
     
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  3. Feb 27, 2007 #2

    marcus

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    Bojowald evidently now has appointments both at Ashtekar's institute at Penn State (the main place for non-string, or background-independent, QG in the United States) and also at David Gross' KITP at Santa Barbara (a center for string researchers).

    It looked as if things were shaping up this way judging from the atmosphere and talks at the 3-week KITP workshop in January, that Bojowald helped organize, called The Quantum Nature of Spacetime Singularities. Videos from that workshop are online and we've discussed some of them here at PF.
     
    Last edited: Feb 27, 2007
  4. Feb 28, 2007 #3

    jal

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    Hi!
    Another step forward.
    Martin Bojowald is encouraging people to develop different simple models in the hope of discovering some partial answers that could be applied to a final model.
    Sounds like he’s on the same wavelength as Baez.
    Martin Bojowald proposes a model … “quantum hyperbolicity”.

    NOTE: p. 31
    FIGURE 15. Effective curvature potential in a Bianchi IX model
    THERE ARE 12 “nodes”
    The problem, DYNAMICS, …. is to have those 12 “nodes” do their dancing in 3d and figure out which of those configurations mean something and how they relate to the triads (12).
    -------
    I'm going to post further thoughts in my blog
    jal
     
  5. Feb 28, 2007 #4

    wolram

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    In theories without singularities is origonal information retained, or is there
    some scope for morphology?
     
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