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LQG BH core diameter calculated

  1. Dec 2, 2007 #1


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    Kevin Vandersloot is an Ashtekar PhD now at Portsmouth UK with a EU Curie fellowship. He and another EU postdoc, C. Boehmer, have been studying the interior of the LQG black hole.

    As we know, the big bang can be modeled using LQG and it gives no singularity (no place where the model blows up and fails to compute). Well, also the black hole interior (inside the event horizon) can be modeled with LQG, and it gives no singularity. But it gives different results from the big bang model.!

    Vandersloot gets that an idealized test particle falling into the center of a LQG black hole undergoes damped oscillation and stabilizes at a distance of 0.4 - 0.5 plancklength from the origin.

    In other words, if we use this idealization of how matter would behave, what we see is something at the center which is about 0.8 - 1.0 plancklength in diameter. And this is INDEPENDENT OF THE MASS OF THE BLACK HOLE.

    Sounds crazy right? Well Kevin gave an ILQGS seminar talk last Tuesday with Ashtekar and Rovelli and others asking questions. The audio, and his slides are online. It sounded pretty clear and cogent to me.

    There are various ways to model BH interior using LQG and you have to remember we are just talking models so far---no help from experiment as yet. But like the case with the big bang one can at least CALCULATE stuff, and the model Kevin and C. Boehmer were using is well motivated compared to several earlier studies i've seen of quantum BH interior.

    Vandersloot and Boehmer have a recent paper about this posted on arxiv. But I would recommend the audio and PDF you find at the ILQGS website. It is the seminar talk dated 27 November. I experienced the seminar talk, with the questions and answers, as extra informative compared with the paper.
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  3. Dec 2, 2007 #2
    That is interesting, do you know if some of this might be in principle testable? (For example is it possible the model could be used to calculate some property of a black hole, which could then potentially be measured?)
  4. Dec 2, 2007 #3


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    By the looks of it, Ashtekar has apparently been urging students and co-workers in that direction---or else there was a spontaneous self-motivation. For example, one of the people who works closely with Ashtekar at Penn State, Param Singh, has given several seminar talks about this. I think it is still very up in the air because the theoretical BH models have been in flux as they have been improved over the past 2 years.

    Parampreet Singh's idea---I remember a 2005 talk---was about predicting the timevarying structure of a gammaray burst (GRB) from the LQG collapse model that he was then using, and he had some general predictions involving two stages and a detectable event that might be looked for. But I wouldnt think that work counts now.

    The past two years have seen a lot of change. Kevin Vandersloot uses a new BH model. And, as he says, the LQG model of the collapse process has to be studied, in light of theoretical developments

    The answer to your question I think is NO, there isnt anything yet. The QG people have been TRYING to derive things to look for like signature of the cosmological bounce model in the CMB-----or signature of black hole collapse models in the GRB.

    they know to go there, and have been trying, but they aren't there yet.

    Here is the URL for the International Loop Quantum Gravity Seminar (ILQGS) website

    It has Kevin's 27 November talk, and the talk Garrett Lisi gave, and a recent talk by Lee Smolin about including matter as braids in spinnetworks, and a talk by a Rovelli co-worker about the new spinfoam model, and so on. All the stuff is online audio and PDF, you just scroll down the listing. It is a good site. Jorge Pullin keeps it.

    I am sure that as soon as there is any important progress in phenomenology of LQG black holes we will see a seminar talk at ILQGS. So the fact that we dont see almost by itself says no, there is nothing in that department yet :smile:
    Last edited: Dec 2, 2007
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