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The Quantum Nature of Spacetime Singularities-18-day pow-wow

  1. Jan 2, 2007 #1

    marcus

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    The Quantum Nature of Spacetime Singularities--18-day pow-wow

    http://online.itp.ucsb.edu/seminars/singular_m07-all.html

    starts this week at KITP SantaBar----8 January thru 26 January

    Look at the list of names. i will bold those whose research has been in background-free QG (mainly LQG and LQC)
    Name Arrive Depart
    Ashtekar, Abhay 6-Jan-07 26-Jan-07
    Berger, Beverly 8-Jan-07 26-Jan-07
    Berkooz, Micha 8-Jan-07 26-Jan-07
    Bojowald, Martin 8-Jan-07 26-Jan-07
    Borde, Arvind 15-Jan-07 26-Jan-07
    Brandenberger, Robert 8-Jan-07 26-Jan-07
    Damour, Thibault 8-Jan-07 26-Jan-07
    Gambini, Rodolfo 8-Jan-07 26-Jan-07
    Garfinkle, David 8-Jan-07 26-Jan-07
    Giesel, Kristina 8-Jan-07 26-Jan-07
    Hertog, Thomas 8-Jan-07 26-Jan-07
    Horowitz, Gary 8-Jan-07 26-Jan-07
    Hubeny, Veronika 8-Jan-07 26-Jan-07
    Jacobson, Ted, 8-Jan-07 26-Jan-07
    Lewandowski, Jurek 8-Jan-07 26-Jan-07
    Liu, Hong 8-Jan-07 26-Jan-07
    Lowe, David 8-Jan-07 26-Jan-07
    Myers, Rob 8-Jan-07 26-Jan-07
    Naculich, Stephen 8-Jan-07 19-Jan-07
    Nicolai, Hermann 15-Jan-07 26-Jan-07
    Pullin, Jorge 8-Jan-07 26-Jan-07
    Rabinovici, Eliezer 14-Jan-07 26-Jan-07
    Rangamani, Mukund 8-Jan-07 26-Jan-07
    Rozali, Moshe 8-Jan-07 26-Jan-07
    Shenker, Steve 9-Jan-07 11-Jan-07
    16-Jan-07 18-Jan-07
    23-Jan-07 25-Jan-07
    Silverstein, Eva 8-Jan-07 26-Jan-07
    Szulc, Bodzio 8-Jan-07 26-Jan-07
    Thiemann, Thomas 8-Jan-07 26-Jan-07
    Verlinde, Erik 8-Jan-07 26-Jan-07
    Wall, Aron 8-Jan-07 19-Jan-07

    Bojowald, who in 2001 showed that the cosmological singularity does not occur in Loop Quantum Cosmology and is replaced by a bounce, is among those in charge of the workshop, judging from this announcement
    http://www.kitp.ucsb.edu/activities/auto2/?id=332

    The Quantum Nature of Spacetime Singularities(Miniprogram)
    Martin Bojowald, Robert H. Brandenberger, Gary T. Horowitz, Hong Liu
    Jan 8, 2007 - Jan 26, 2007

    "One of the main goals of quantum gravity is to provide a better understanding of physics near the big bang and inside black holes where general relativity breaks down. Recently, there has been considerable progress toward this goal in both of the main approaches to quantum gravity. In string theory, this includes string gas cosmology, tachyon condensation, and holographic descriptions using the AdS/CFT correspondence. In loop quantum gravity, space is fundamentally discrete, and evolution in symmetric cosmological models is nonsingular. This three week miniprogram will combine experts in both areas and on the classical approach to singularities to make further progress on this fundamental problem."
     
    Last edited: Jan 3, 2007
  2. jcsd
  3. Jan 3, 2007 #2
    Thanks for the update Marcus! Wow, I see heavy-hitters from both camps. I eagerly await the talk slides and streams.
     
  4. Jan 3, 2007 #3

    marcus

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    I share your interest in what comes out of this. If you find media from the workshop (slides etc) before i do, please post it.

    One participant to keep a look out for, I think, is Ted Jacobson. He is both an observationalist and someone versed in theory, who has functioned as a QG "devil advocate". He has attended several QG conferences and offered serious scrutiny and rigorous skepticism.
    What I mean by observational is that Jacobson (and co-authors Liberati et al) analyze astronomical data in an attempt to falsify various versions of DSR and the like that have come up in various QG contexts.
    I don't know that Jacobson will have anything to say at this workshop, but if he does, and you notice it, I would like to check it out.
     
  5. Jan 7, 2007 #4
    I agree that Ted Jacobson will be someone to watch for. He's made a lot of interesting contributions to black hole thermodynamics. Last time he was at PI, he made a rather cryptic comment about baby universes being created in the center of a black hole. I'm not sure if he was just playing devil's advocate, but I would be interested to hear more.

    Is there any indication that there will be slides or recordings made available?
     
  6. Jan 7, 2007 #5

    marcus

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    I don't know of any indication! KITP does have quite a bit available recorded on line, but I don't know their site very well. I am not sure where to look. If anybody finds some media from this workshop, please share link!

    thx.
     
  7. Jan 31, 2007 #6
  8. Jan 31, 2007 #7
    String Theory and LQG strenths and weakness from KITP UCSB final discussion

    These are the conclusions summarized from the final discussion at the KITP UCSB mini-program on resolution of singularities in String Theory and LQG. I repost this here since it seems to belong in this thread. R.

    String Theory strengths:

    1.Beautiful and complete AdS/CFT correspondence, a non-perturbative quantum description of quantum gravity in terms of an ordinary field theory, providing some tools for probing the question of what happens to black holes and cosmological singularities in AdS/CFT, albeit not in the most interesting sector of the theory.

    2.Perturbative string theory can shed light on some singularities, as in Eva Silverstein’s talk on Tachyon condensation.

    String Theory weaknesses:

    1.AdS/CFT correspondence is very indirect, involving answers to Gravity questions coded in a complicated way in ordinary gauge theory variables. The dictionary is very complicated, and we only understand a small part of it.

    2. String theory is lacking, even in principle, a non-perturbative way of addressing cosmological singularities in a closed universe, or anything else that can not be pushed into an asymptotic AdS/CFT framework. String theory does not currently offer any non-perturbative framework for describing closed cosmologies. Even perturbative string theory is not well understood in time dependent backgrounds.

    Loop Quantum Gravity strengths:
    1. Clear model of universe bounce in isotropic gravity coupled to free scalar field.

    2. Even with anisotropy, still allows evolution past classical singularity.

    3. Expectation value of curvature stayed finite in some kinematical states approaching singularity

    Loop Quantum Gravity Weakness: The whole theory still murky or ill-defined.
    1. How unique is this quantization approach?

    2. There are issues in local Lorentz invariance. Is it preserved in evolution?

    3. There are worries about fundamental discreteness in loop approach. How can LQG recover Lorentz invariance if it is built on a lattice-like structure?
     
    Last edited: Feb 1, 2007
  9. Feb 1, 2007 #8
    I suppose dismissing the fundamentally problematic nature of lqg as mere "weakness" is perhaps one way to be diplomatic without totally disgracing oneself as a scientist.
     
  10. Feb 1, 2007 #9
    Yes, I had some trouble condensing this thought. I think what Dr. Horowitz was getting at is that although parts of the theory have clarity and seem to be promising, on the whole the theory is less clear. For example, while it is promising that LQG can model baby universes inside the horizon, it is less clear what use this can be, since any consequences would seem to occur entirely beyond our ability to make observations. If there is a bounce, is there a unique solution or end state for any given starting conditions? Or do the results diverge? If some kinematic states do not lose structural elements near the singularity, how can the space-time invarient gauge be preserved?

    One should probably add that Horowitz was nearly as brutal against string theory. Anti de Sitter spaces obveously have intrinsic structures. Sure, you can model any desired behavior by running it across some shaped surface. But there is no way to determine, even in principle, what happens to these structures near the singularity. And it leaves unanswered the critical question, what is that shape made of?

    As Horowitz concludes, there are fundamental problems with both of these approaches, and each of them requires a fresh, new view of space-time to provide any way to progress in this area. Singularities provide an ideal laboratory to test the theories as curvatures and couplings become large. But my feeling is that these theorists are all hoping for some new idea to come along and save them....that would be, replace them.

    I was thinking time and space may be mutally self-propagating, with each space cycle producing a time cycle, and each time cycle producing a space cycle, in a way analogous to EM. The singularity only squashes half the wave, and the other half can still get through, after which it immediately can regenerate its partner. Then the singularity is split...when the space-like part of a Lorentz invarient is singular, the time-like part is still extant, and vice versa.

    But of course I am a tourist here and really have nothing to say. It will be interesting to watch for new ideas from the establishment.

    R
     
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