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I How do cosmologists view loop quantum cosmology?

  1. Nov 24, 2016 #1
    recently this paper

    Quantum Gravity in the Sky: Interplay between fundamental theory and observations
    Abhay Ashtekar, Brajesh Gupt
    (Submitted on 15 Aug 2016 (v1), last revised 12 Nov 2016 (this version, v2))
    Observational missions have provided us with a reliable model of the evolution of the universe starting from the last scattering surface all the way to future infinity. Furthermore given a specific model of inflation, using quantum field theory on curved space-times this history can be pushed \emph{back in time} to the epoch when space-time curvature was some 1062 times that at the horizon of a solar mass black hole! However, to extend the history further back to the Planck regime requires input from quantum gravity. An important aspect of this input is the choice of the background quantum geometry and of the Heisenberg state of cosmological perturbations thereon, motivated by Planck scale physics. This paper introduces first steps in that direction. Specifically we propose two principles that link quantum geometry and Heisenberg uncertainties in the Planck epoch with late time physics and explore in detail the observational consequences of the initial conditions they select. We find that the predicted temperature-temperature (T-T) correlations for scalar modes are indistinguishable from standard inflation at small angular scales even though the initial conditions are now set in the deep Planck regime. However, \emph{there is a specific power suppression at large angular scales}. As a result, the predicted spectrum provides a better fit to the PLANCK mission data than standard inflation, where the initial conditions are set in the general relativity regime. Thus, our proposal brings out a deep interplay between the ultraviolet and the infrared. Finally, the proposal also leads to specific predictions for power suppression at large angular scales also for the (T-E and E-E) correlations involving electric polarization. The PLANCK team is expected to release this data in the coming year.
    Comments: Invited article, to appear in CQG. This paper is addressed both to the quantum gravity and cosmology audiences. Cosmologists can focus just on sections I, IV.C, IV.D and V without loss of continuity. 43 pages, 13 figures. Version 2 contains a few clarifications and new references, especially to compare and contrast related results in the literature
    Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
    Cite as: arXiv:1608.04228 [gr-qc]

    within the field of cosmology, how seriously do cosmologists consider LQG/LQC theory as a way to understand planck scale physics of the big bang as outlined in the above paper and similar?
  2. jcsd
  3. Nov 24, 2016 #2


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    I think it's generally considered to be a serious avenue of investigation, but not one that is likely to be experimentally verifiable anytime soon.

    I generally don't take claims seriously like the ones in this paper which claim to provide better fits to the data, as the amount of increased improvement is pretty minimal, and tends to be within the margin of error of the experiment. In order to convince a large number of cosmologists that this model is an accurate description of our universe, they would really need to have a number of independent lines of evidence which all converge on the same picture.
  4. Nov 24, 2016 #3
    how does the claims compare with string cosmology?

    how would having a viable theory of QG improve cosmology?
  5. Nov 25, 2016 #4


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    It's fairly similar in terms of its empirical status at the current time. I think string theory is still a little bit more popular, but that's not necessarily a good measure of which is more likely to be true.

    It would likely only have an impact on our understanding of the very earliest moments of our universe. It might provide insight into how our universe began and the precise behavior of that first tiny fraction of a second. But it won't change much beyond that.
  6. Nov 25, 2016 #5
    what are some examples of "a number of independent lines of evidence which all converge on the same picture" as for example loop cosmology?
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