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Big Bounce generic, Date and Hossain

  1. Jul 21, 2004 #1

    marcus

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    the Big Bounce is generic in LQC, say G.Date and G.Hossain
    in a new paper http://arxiv.org/gr-qc/0407074

    In LQC, as long as there is a scalar matter field, the bounce is
    generic in the sense of being independent of
    quantizing ambiguities and details of scalar field dynamics.

    they also find that in a closed universe the Big Crunch singularity
    goes away as well (in LQC) and is replaced generically by a bounce.

    It looks to me like part of LQC coming of age---Bojowald got the
    original result which zapped the Big Bang singularity and now more people
    are joining in and corroborating and extending his result. these two
    authors, as it happens, have found, or helped to find, a useful approximation of Bojo's original cosmological difference equation by a differential equation (see their equation 1) which looks nicer and neater than the difference equation especially in their choice of notation. More exactly, they have an "effective Hamiltonian" to approximate bojo's
    original LQC Hamiltonian, and it looks as if they are milking that effective
    Hamiltonian cow for all its worth. Both guys are of the smart young bunch of researchers that have gotten into Loop during the past few years
    and right now they are in Chennai which looks like might become another center. So it is a "field maturation" paper, I think, as if people are finishing digging a tunnel thru the mountain and Bojo made a hole and saw some
    sky thru it and other people help make the hole larger and after a while break out into the open daylight at the other end.

    It is a short paper---the work looks good as far as I can tell. Here is an introductory paragraph exerpt

    -----quote----
    It has been long expected that the existence of singularity in the classical general relativity which has been shown to be quite generic thanks to the singularity theorems, will be removed when classical framework of gravity is extended to a quantum framework of gravity.

    Despite of tremendous efforts made, unfortunately we still do not have a fully satisfactory theory of quantum gravity. In the las tcouple of decades two strong contenders have emerged: the string theory approach[1] and the loop quantum gravity (LQG) approach[2].

    Theissueof fate of classical cosmological singularities has been addressed head-on within the LQG approach. More precisely, the adaptation of LQG methods to cosmological context, known as loop quantum cosmology (LQC) [3], has made impressive progress on the issue of singularities. It has been shown that the isotropic models (flat and closed)[4], and more generally the diagonal Bianchi class A models [5, 6], are free of singularity.

    It is time now to explore further consequences of LQC corrected cosmologies.
    ---end quote---
     
    Last edited: Jul 21, 2004
  2. jcsd
  3. Jul 21, 2004 #2

    marcus

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    Another exerpt from Ghanashyam Date and Golam Hossain new paper

    ---quote---
    Some of consequences of LQC corrected cosmologies have already been noted. First, there is a natural mechanism for inflation [7,8,9] within the context of isotropic models.

    Secondly, for the Bianchi IX model there is a suppression of chaotic approach to singularity [10].

    Thirdly, there is indication of a bounce at the big crunch singularity as well [11].

    All of these have been explored within the framework of an effective Hamiltonian which incorporates the most significant non-perturbative corrections. These modifications stem from the non-trivial definition of the inverse triad operator in LQC[6, 12] which ensure that the matter density, spin connection components remain bounded as universe approaches zero volume.

    ---endquote---
     
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