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Given LQC would a massive black hole undergo inflation?

  1. Jul 24, 2010 #1
    I just read the thread on inflation is very unlikely. Then I read the paper by
    Abhay Ashtekar, David Sloan
    Loop quantum cosmology and slow roll inflation

    Although, I did not comprehend all of the implications what seemed to be implied was
    Given enough mass at some critical density inflation must occur.

    Did I just miss the point or is this a reasonable conclusion that comes directly out of the math?
  2. jcsd
  3. Jul 24, 2010 #2


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    Several issues. It has beens shown to pretty much everybody's satisfaction that in the LQC framework looking at the BB you find time evolution extends back and shows a bounce. A collapsing phase of the universe--reaches a density where quantum corrections make gravity repellent, initiating inflation.
    Many different cases have been studied including some where the assumptions of isotropy and homogeneity are weakened---so you don't have to assume that the collapse is perfectly symmetric or uniform for the bounce to occur.

    But that kind of collapse is different from a BH collapse. For some reason the collapse of a whole universe is simpler and easier to model than a BH collapse.

    So the question emerged, some 5 years ago (perhaps more) in the literature: does BH collapse lead to a bounce? Or at least do especially "nice" BH collapses lead to a bounce?
    Does the expanding region that issues out from the bottom of the whole have full spatial 3D dimensionality or can it turn out defective, missing a dimension. They do a combination of computer simulation and analytical studies on this kind of thing.

    I don't remember all the LQG researchers who have published papers on this question. My impression is that mostly they find that a bounce occurs, but sometimes unsatisfactory, and they always need to make simplifying assumptions about the collapse---some at least partial symmetry---just to do the calculation or make the simulation do-able.

    Some of the people who have studied LQG BH collapse are Leonardo Modesto, Kevin Vandersloot, Dah-Wei Chiou. I would need to do a search to dig up other names.

    My impression is that this question of LQG BH bounce-or-not-bounce is still unsettled.
    No one of the senior people (Ashtekar, Rovelli, Freidel, Thiemann, Barrett...) has made a clear pronouncement. It always seems to be work by post-docs---risk-takers essentially.

    The above is all I can properly say as an outside observer, but I will add my own personal observation. The weird thing about BH that makes it different is, what happens when the BH evaporates? If collapse causes a new region of spacetime to billow out of the bottom, how do you keep track of the information? (unitarity) And does any form of energy-conservation apply? And would the new region just split off on its own when the original BH dried up? There are too many headaches involved here.

    Conclusive work has not been done. Maybe it is one of those things that it's better not to think about for now. But you are right in one sense---there is enough similarity that LQC tools are used to study BH collapse, and the LQG mechanism for a BH bounce is there at least subject to simplifying assumptions. An intriguing unsettled area of inquiry.

    If you are curious and want links to papers by, for instance, Modesto, Vandersloot, Chiou, just ask. I might be able to dig up ones by others too.
    But be prepared for the partially unsatisfactory inconclusive character of BH work so far.

    BTW I think the Ashtekar Sloan paper is great---Ashtekar's work is solid and the conclusion about inflation being inevitable in the LQC cosmic bounce context is exciting. It just doesn't apply directly to black holes.
    Last edited: Jul 24, 2010
  4. Jul 24, 2010 #3
    Thankks Marcus
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