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Clear slides online for 10/14 obs. QG talk (do we see BH->WH bounces?)

  1. Oct 13, 2014 #1

    marcus

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    Last edited: Oct 14, 2014
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  3. Oct 13, 2014 #2

    marcus

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    Observational QG is a growing theme in research. The title of this talk is
    Searching for quantum gravitational observations
    It challenges an earlier mindset about the observabiliity of QG effects, and questions some earlier statements quoted from Steven Weinberg and Robert Wald. I think it's an excellent, clear, coherent set of slides. It will be interesting to listen to the talk and see what questions are raised by the seminar audience (at various locations: Perimeter, Penn State, LSU, Marseille, Erlangen, Nijmegen, Warsaw etc.) Sometimes at an ILQGS talk they speak up from several different locations and it is difficult to know who is asking a question or commenting. At other times only people at a few locations such as Penn State, LSU, and Perimeter participate in the discussion. We'll see.
    http://relativity.phys.lsu.edu/ilqgs/

    The talk draws on white hole and Planck Star papers by Rovelli in collaboration with Vidotto, Barrau, and Haggard.

    The Loop gravity bounce has the effect of converting a BH into a WH in situ. And extreme time dilation associated with the high density at bounce means there must be a long wait before the outside world sees the bounce. For small primordial black holes the waiting time is on the order of the present age of cosmic expansion.

    A recent paper on observational effects of QG by two phenomenologists Aurelien Barrau and Julien Grain is relevant here. They devote a substantial section of the paper to analyzing the prospects for detecting various types of radiation (from high energy gamma down to centimeter-wavelength radio emission) from primordial BH end-of-life bursts. The Barrau-Grain paper is the most recent thing we have on this so I'll give the link.

    http://arxiv.org/abs/1410.1714
    Loop quantum gravity and observations
    A. Barrau, J. Grain
    (Submitted on 7 Oct 2014)
    Quantum gravity has long been thought to be completely decoupled from experiments or observations. Although it is true that smoking guns are still missing, there are now serious hopes that quantum gravity phenomena might be tested. We review here some possible ways to observe loop quantum gravity effects either in the framework of cosmology or in astroparticle physics.
    25 pages, 8 figures. Draft chapter for a volume edited by A. Ashtekar and J. Pullin, to be published in the World Scientific series "100 Years of General Relativity"
     
    Last edited: Oct 14, 2014
  4. Oct 17, 2014 #3
    Hi MArcus,

    Thanks for sharing. Great talk BTW. All familiar voices Smolin, Ashtekar etc.(I hope i didn't get confused on the general idea).. What does Rovelli means by Trapping. Does it include the whole content of the information--(conserved physical property), reconfigured and later on bounces back in a time reversal invariant fashion?
     
  5. Oct 17, 2014 #4

    marcus

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    I think "trapping horizon" and "trapping surface" mean the same things and are used interchangeably.
    A trapping surface around an intense concentration of mass is a surface where all the future light cones TILT INWARDS so that nothing not even light can escape.

    An 'event horizon' is trapping for all eternity. It is permanently trapping. A mere trapping surface may LOOK just like an event horizon, to an outsider, for now. It can even cause Hawking radiation in the thin sheath of vacuum outside it, just like an event horizon does.

    The difference is that trapping can be temporary. Maybe due to quantum effects at high density the core concentration of mass is going to blow up!
    Then it will no longer be so concentrated, and its gravity will not be so strong!
    then the light cones will TILT BACK OUTWARDS A BIT.
    And the exploding core will burst out through where the trapping surface used to be.

    Rovelli and Vidotto have some diagrams sketching the tilting of the light cones. They get skinny as they tip inwards and fat again as they tip back outwards. To get the R&V paper you just google "planck stars".

    I can't answer your whole question. I think at this point the experts can only GUESS as to whether BH collapse rebounds in an end-of-life explosion and what spectrum of particles and radiation one should expect. If it can be described by gluing on a time-reversed WH picture that would be great. There is a paper by Haggard and Rovelli which suggests that is possible. In any case however the explosion is described/modeled, it would solve some aggravating paradoxes if all the information content is spewed back out at the end.
     
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