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Meissner corrects the Immirzi parameter

  1. Jul 14, 2004 #1

    marcus

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    http://arxiv.org/gr-qc/0407052

    Black hole entropy in Loop Quantum Gravity
    Krzysztof A. Meissner
    10 pages

    "We calculate the black hole entropy in Loop Quantum Gravity as a function of the horizon area and provide the exact formula for the leading and sub-leading terms. By comparison with the Bekenstein-Hawking formula we uniquely fix the value of the 'quantum of area' in the theory."
     
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  3. Jul 14, 2004 #2

    marcus

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    companion paper from Jerzy Lewandowski et al

    http://arxiv.org/gr-qc/0407051

    Black hole entropy from Quantum Geometry
    Marcin Domagala, Jerzy Lewandowski (Uniwersytet Warszawski)
    12 pages

    "Quantum Geometry provides microscopic degrees of freedom that account for the black-hole entropy. However, the procedure for state counting used in the literature contains an error and the number of the relevant horizon states is underestimated. In our paper a correct method of counting is presented. Our results lead to a revision of the literature of the subject. It turns out that the contribution of spins greater then 1/2 to the entropy is not negligible. Hence, the value of the Barbero-Immirzi parameter involved in the spectra of all the geometric and physical operators in this theory is different than previously derived."
     
  4. Jul 14, 2004 #3

    jeff

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    The above is all baloney as I've explained in another thread. For convenience I'll repost those comments here.


    In a nutshell, lqg (I discuss strings below) must take the position (see Black Hole Entropy from Loop Quantum Gravity. Note that I checked with rovelli that there has been no significant changes in the arguments as originally given in this paper) that the entropy S in hawking's famous formula S=(1/4)A refers only to black hole states that are causally connected to hole exteriors. But this stands in direct opposition to the near universal view – based on a preponderance of theoretical evidence - that S counts all hole states. (see On the nature of black hole entropy for a dissenting view, which however the author of this paper apparently no longer holds).

    In other words, lqg is inconsistent with holography, which is regarded as perhaps the most profound insight into quantum gravity that the past thirty years of research has produced. Holography is the idea that physical information ultimately scales as area and not as volume. In the case of black holes, all of the apparently volume-extensive properties of material falling into a black hole reappear area-extensively on the event horizon. This is a very strange idea which we of course don't yet completely understand, but it's nonetheless regarded as perhaps the best clue we've got about what a correct quantum theory of gravity should be like.

    Let me illustrate the above statements. As you probably know, LQG states are given in terms of lattices called spin-networks whose nodes represent quanta of volume and links represent quanta of area. It is thus obvious in LQG that only links can contribute to the black hole area-entropy relation, and equally obvious that the surface they puncture must be the event horizon. This trivially produces in the macroscopic limit the expected proportionality S ~ A between horizon area and entropy. There’s nothing deep about this result: It’s exactly what one would naively expect from this misleadingly intuitive point of view.

    However, as I discussed above, the correct interpretation of S=(1/4)A is actually quite strange. It would be remarkable if a theory could take this very odd viewpoint and as a result produce the correct factor of 1/4. But this is precisely what string theory achieves!!

    In string theory we can explicitly construct black holes out of D-branes of various masses and charges. Then we can use the rules in string theory that tell us how to count the states of D-branes to calculate the number of black hole microstates associated with a given macrostate: We are counting all of a black hole’s states, not just some subset of them. Completely independent of this calculation we can compute the black hole entropy in terms of the masses and charges of the D-branes out of which the black hole was constructed. It’s then verified that in the macroscopic limit these two unrelated calculations agree precisely and yield the correct factor of 1/4. It’s kind of hard to believe that this sort of magic is just an accident and thus hard to take LQG seriously in light of this, which, relatively speaking, hardly anyone does, as I’ve stated many times.

    From the above point of view the problem with LQG is that it’s not holographic: the nodes in spin-networks represent the kind of volume-extensive fundamental degrees of freedom that shouldn’t be involved in a correct fundamental theory of quantum gravity.

    In fact, things are even worse for LQG. If LQG truly is a fundamental theory of gravity as claimed, deriving the black hole area-entropy relation shouldn’t require recourse to outside arguments. However, implicit in the above is that one has to justify the LQG point of view by using thermodynamical and statistical mechanical arguments, and not just to derive the proportionality, but the factor of a 1/4 as well, the latter presently appearing impossible to do: Spin-networks are absolutely fundamental in LQG and so simply don’t contain anymore information which would allow us to get the right answer.

    Needless to say that none of this is a problem for strings.

    So in summary LQG fails to pass the only reliable check of the correctness of a QG theory that we have while strings are completely successful.

    Let me make one final remark about the string result. The statements that LQG people make to the effect that the kinds of black holes involved in the string calculation are unrealistic are wrong-headed. The string calculation has been performed successfully on both non—supersymmetric holes and four dimensional holes. There is thus every reason to expect - and we pretty much do - that it’s only a matter of time before the correct result will be produced in all cases. The same can never be expected of lqg period.
     
  5. Jul 14, 2004 #4

    marcus

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    gamma = 0.237533

    the new value of the Barbero-Immirzi parameter
    calculated by Meissner is
    0.2375329579...
    which rounds off to 0.237533

    wonder how this will play with the various black hole
    quasinormal vibration modes
     
  6. Jul 14, 2004 #5

    jeff

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    As has been explained to you multiple times by myself and others, the whole quasinormal vibration thing was a case of jumping the gun. Take your head out of the sand and get over it, as smolin, rovelli and everyone else have.
     
  7. Jul 14, 2004 #6
    nice finds Marcus-keep up! so much is going on right now- it's like the mysteries of the universe are unfolding in real-time :eek:

    ___________________________

    /:set\AI transmedia laboratories

    http://setai-transmedia.com
     
  8. Jul 14, 2004 #7
    Can Marcus even read??? Or is he just ignorant!
     
  9. Jul 14, 2004 #8

    marcus

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    thanks for the encouragement setAI, you stay tuned in too!

    BTW there is a new popular article just out

    by the German science writer Rudy Vaas

    (he is the one who did "The Duel: Loop versus String")

    the new one is about the removal of the big bang singularity
    by Martin Bojowald using loop quantum cosmology

    The Inverted Big-Bang

    http://arxiv.org/physics/0407071
     
  10. Jul 14, 2004 #9

    jeff

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    Look up histrionic personality disorder in the DSM IV.
     
  11. Jul 15, 2004 #10

    selfAdjoint

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    There you go again. I haven't read your refutation in detail either, but if you think it's that good why don't you publish it where LQG experts can take a shot at it? My own view is that you haven't shot down these new papers until you've done that, and the community has responded. So I think Marcus is perfectly justified in ignoring your war dance.
     
  12. Jul 15, 2004 #11

    marcus

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    I dont know what refutation Jeff can possibly mean. Real work has been done on BH vibration modes. We now have a new candidate for the Immirzi parameter. It seems natural to look at the situation again and see how one plays against the other----which i suggested.

    what a priori reason would there be not to do that?

    certainly no harangue about past lines of investigation
    whether well-reasoned or not, anyway here's what i said

    and here is Jeff's reply
    which sounds irritated but doesnt make sense to me at all

    For all I know the critics of LQG may have given up on trying to use "the quasinormal vibration thing" as a way to refute LQG.
    that would make sense. There was a time when Lubos Motl and friends would argue that LQG must be wrong because of some small numerical difference in Immirzi gotten by calculating this way and that. But I think they gave up on that----maybe it was "jumping the gun" on their part. But I dont think Rovelli has stopped being interested in accurate determinations of the Immirzi, or in BH vibration frequencies! He talks about these things in his book that is coming out. Anyone with a real interest in Quantum Gravity has plenty of reason to be interested.

    so, given the new determination of the Immirzi-----roughly 3/4pi----
    it make sense to ask, and I do, how it plays with BH vibrations

    the BH is one of the laboratories for Quantum Gravity, anything you can ask about a BH that relates to LQG is good to ask

    quantum gravitists sometimes refer to the BH as their "hydrogen atom"
    (like whatever the hydrogen atom was for Bohr----the thing he learned on by trying to understand its energies and vibrations----that's how they see the BH)

    I think it is great that Jerzy Lewandowski and friends have recalculated the BH entropy

    Black Hole Entropy from Quantum Geometry
    http://arxiv.org/gr-qc/0407051

    I wonder if they will present the paper at GR17 in dublin next week.
     
  13. Jul 15, 2004 #12

    jeff

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    I'm not the only one who here who realizes that verbal insults are not the only way to screw around with people here.
     
  14. Jul 15, 2004 #13

    marcus

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    BTW this just out from Ashtekar

    http://arxiv.org/gr-qc/0407042




    Isolated and dynamical horizons and their applications
    Abhay Ashtekar, Badri Krishnan
    77 pages, 12 figures


    "Over the past three decades, black holes have played an important role in quantum gravity, mathematical physics, numerical relativity and gravitational wave phenomenology. However, conceptual settings and mathematical models used to discuss them have varied considerably from one area to another. Over the last five years a new, quasi-local framework was introduced to analyze diverse facets of black holes in an unified manner. In this framework, evolving black holes are modeled by dynamical horizons and black holes in equilibrium by isolated horizons. We review basic properties of these horizons and summarize applications to mathematical physics, numerical relativity and quantum gravity. This paradigm has led to significant generalizations of several results in black hole physics. Specifically, it has introduced a more physical setting for black hole thermodynamics and for black hole entropy calculations in quantum gravity; suggested a phenomenological model for hairy black holes; provided novel techniques to extract physics from numerical simulations; and led to new laws governing the dynamics of black holes in exact general relativity.
     
  15. Jul 15, 2004 #14

    jeff

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    Since the hawking-bekenstein relation should hold for any black hole, there can only be one correct value for the immirzi-barbero parameter. Unfortunately it was found that the part of the spectra of the types of quasinormal modes conjectured to fix the immirzi-barbero parameter depends on the kind of hole we're talking about.


    I didn't say or imply this. Stop twisting what I say.
     
    Last edited: Jul 15, 2004
  16. Jul 15, 2004 #15

    marcus

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    You seem not to understand. Please read my posts.
    By Meissner's work the Immirzi is fixed already at 0.237533...

    (whatever you are talking about using quasinormal modes to determine its value is past history, from this standpoint)

    Assuming Meissner's value is right, it is a new situation and I mentioned the obvious question, which I think will interest people, namely "how does this new value of the immirzi play with BH vibration frequencies?"

    I expect some clarifying LQG work on BH vibration and the Immirzi parameter will most likely play a central role as it does in everything
     
  17. Jul 15, 2004 #16

    jeff

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    I was only responding to your remarks about the quasinormal thing, explaining why it can never work. But if the argument leading to this new result is valid (I haven't reviewed it yet), the failure of the quasinormal idea doesn't matter.

    My fundamental problem with the lqg view is that it's not holographic, as I explain in my thread on the subject.

    Edit: Now that I have reviewed meissner's paper, I see it doesn't change anything. See my later post entitled Nothings changed.
     
    Last edited: Jul 16, 2004
  18. Jul 15, 2004 #17
    Good to see some sensible, rational discussion in here, instead of childish name calling. Much better :)
     
  19. Jul 16, 2004 #18

    jeff

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    Nothing's changed

    I read the paper and it doesn't really change anything qualitatively.
     
    Last edited: Jul 20, 2004
  20. Jul 27, 2004 #19

    selfAdjoint

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    Jeff, now that I have read Meissner's paper, I am curious. In what sense do you mean that nothing's changed? I can see one possible sense, that Meissner still computes [tex]\gamma[/tex] from his [tex]\gamma_M[/tex] - which he has calculated from first principles in QG - by appealing to the Bekenstein formula. So LQG still does not have a prediction of this formula.

    But in another sense it is a big change, because a big misunderstanding about the Barbero-Immirzi parameter has now been resolved. Now they can go back to their BH modes and redo them, possibly to get better results this time.
     
  21. Aug 1, 2004 #20

    jeff

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    Dreyer’s idea of uniquely fixing immirzi by using a conjecture due to hod in relation to results of an investigation of schwarzshild quasinormal modes fell through when it was found that quasinormal modes associated with other black hole types give different values of immirzi.
     
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