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Progress to testable QG/M path integral

  1. Jan 4, 2006 #1


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    the intent of this thread is to gather links and other information that can
    help us gauge the progress being made towards a TESTABLE
    theory of QUANTUM GRAVITY WITH MATTER (QG/M) specifically in the "covariant" sum-over-histories or PATH INTEGRAL version.

    (I am classifying Freidel's group field theory variant of spinfoam QG as essentially a path integral approach because of its equivalence to spinfoam)

    if you have information to share about the status of research along these lines, please consider contributing some online references.
    it doesnt matter if you think progress in this direction is slow or fast, in this thread I am not looking for arguments to prove some particular case.
    I especially want to look at some recent papers of Laurent Freidel and people that co-author with him or work on similar research. Freidel has a path integral approach that includes matter and appears to work in 3D which he is hopeful can be extended to 4D.
    one interesting feature is that the same mechanism that provides for the quantum spacetime dynamics (the QG part) also provides feynman diagrams for the particles of matter---so it is really QG/M, if I understand correctly what he says.
    another interesting feature is that a form of DSR is derived from the 3D QG/M theory----so there is energy dependence of the speed of gammaray photons. It is important to emphasize that the DSR is not merely assumed or postulated or guessed but rather it is logically derived. For this Freidel QG/M theory to work there must be a slight energy dependence-----if I understand correctly----and would make the 4D version TESTABLE, if the same DSR thing carries over.
    So if Freidel and the others succeed with their program of extending the already proven results from 3D to 4D, then they will have a theory that predicts something that might or might not be observed. One will be able to look at a Gammaray burst (GRB) and see whether or not the more energetic photons are arriving a little bit earlier (after traveling for a billion years) so that the spike is skewed. And if one does not observe this, it is evidence against the theory.
    So what this example shows is that it is a reasonable goal to develop a testable QG/M path integral theory. And we can also look at Renate Loll's CDT which is path integral QG, and see how close she is to including MATTER and to being TESTABLE, which she must do to be in this race.
    And we might also look at recent work of Carlo Rovelli which is also path integral, and is in preliminary stages of including matter. Maybe there are some other developments towards a testable path integral approach to QG/M, which we should know about.
    I will start by getting some links and some quotes about Freidel's program. These will take some time to assemble---- I think they'll show that they aren't at the goal, but will give some basis for telling if they are getting to where they have a shot at it.
  2. jcsd
  3. Jan 4, 2006 #2


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    for starters, here's a link:
    this is post#96, scroll back to post#95 for a related paper coauthored by Shahn Majid.

    this is about a paper by some other people besides Laurent Freidel, e.g. Jerzy Kowalski-Glikman (post#434)

    this has some references to papers by Daniele Oriti (post#429)

    I guess one thing to register is that what we are talking about has some depth in people----other major people like Shahn Majid (noncommutative geometry, connected to DSR) and Jerzy K-G (also DSR) and Daniele Oriti.
    We are not just talking about Perimeter Institute, but things going on at Cambridge, London Queen Mary, Uni Wroclaw in Poland.
    Last edited: Jan 4, 2006
  4. Jan 6, 2006 #3


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    this paper of Smolin discusses the relevance of GLAST and Auger.

    Falsifiable predictions from semiclassical quantum gravity
    Lee Smolin
    9 pages
    "...A consequence of DSR realized with an energy dependent effective metric is a helicity independent energy dependence in the speed of light to first order in the Planck length. However, thresholds for Tev photons and GZK protons are unchanged from special relativistic predictions. These predictions of quantum gravity are falsifiable by the upcoming AUGER and GLAST experiments."

    The GLAST satellite is due to be launched next year, in 2007.
    The Auger groundbased array is for studying Ultra High Energy Cosmic Rays (UHECR) and it is already in operation. The first scientific results were just posted on Arxiv.


    The First Scientific Results from the Pierre Auger Observatory
    T. Yamamoto (for The Pierre Auger Observatory Collaboration)
    4 pages, 1 figure, Proceedings of the PANIC 2005 conference

    "The southern site of the Pierre Auger Observatory is under the construction near Malargue in Argentina and now more than 60% of the detectors are completed. The observatory has been collecting data for over 1 year and the cumulative exposure is already similar to that of the largest forerunner experiments. The hybrid technique provides model-independent energy measurements from the Fluorescence Detector to calibrate the Surface Detector. Based on this technique, the first estimation of the energy spectrum above 3 EeV has been presented and is discussed in this paper."
    Last edited: Jan 6, 2006
  5. Jan 7, 2006 #4


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    It's not popular yet, marcus. Pierre Auger Observatory results will take time to sink in. This is the frontier of science. Expect many citations in the months to come, if that is any consolation . . . . or if being sharp on picking up the importance of this kind of data is recognized. Perhaps we should review the history of PAO, and results it is capable of offering.
    Last edited: Jan 7, 2006
  6. Jan 10, 2006 #5


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    How does path integral QG remove BB and BH singularities?

    This is a significant conceptual gap, it seems to me.

    Most of the LQG community (except for those working in cosmology) are actually involved in path integral approaches----like spinfoam and CDT and Freidel's GFT which is somehow a variant of spinfoam.

    But the allied cosmology research is mostly LQC, as established by Bojowald with the close support of Abhay Ashtekar. This a CANONICAL approach intended as a symmetry-reduced simplification of LQG.
    It is in this LQC context that the BigBang singularity was eliminated and the same people involved with this have extended this to partial results about the BH singularity. The mathematical picture replacing the two classical singularities looks similar---in each case there is a quantum Bounce. So there is a plausible connection between Bang and Hole.

    What impresses me as lacking is any research in the PATH INTEGRAL approaches that does the same thing: replaces each classical singularity by a BOUNCE.
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