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Quantum gravity theory will become falsifiable?

  1. Aug 14, 2004 #1
    When do you people think an actual quantum gravity theory will become falsifiable? I know that a big criticism of string theory right now is that it can't make any experimental predictions, but as far as I know, loop quantum gravity can't either. I was wondering what your guesses are for when there will be ways to test quantum gravity theories?
  2. jcsd
  3. Aug 14, 2004 #2


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    to get a sense of the time-table look at
    http://arxiv.org/hep-th/0408048 pages 27 and 28

    look at Smolin's scenario A and scenario B
    some quantum gravity approaches ( type A versions )
    have essentially been ruled out----see Smolin's points 4,5,and 6 on
    page 28

    Some close relatives of Loop have already been casualties of
    the testing process-----observations performed on synchrotron
    radiation from the Crab Nebula were especially important.
    An important paper in shooting down these variants of QG
    was is cited [130] by Smolin.


    So LQG, and closely allied approaches, have taken some hits and
    some possible QG has already been weeded out.

    More stringent tests particularly on the Type B side now are in progress
    or planned for near term. Smolin gives some idea what to expect over next 4 or 5 years based on what is going up. GLAST is planned for 2007
    and that will be extremely important for LQG----just pray the budget is not cut!

    It is just an urban myth that LQG does not make testable predictions and is not already guiding experiment------it's just that the experimental programs which it guides, and which are designed to shoot down one or more assumptions or constrain one or more parameters, are astronomical observation programs.

    If GLAST flies as planned, and if it does not see tiny differences in speed of light, depending on gammaray energies, showing up after the light has traveled a billion lightyears or so, this will be tough for LQG to cope with
    and will falsify somebody's favorite version which predicts such slight variantions.

    After they both travel a billion LY, the more energetic of two photons is just a teensy bit out ahead of the other. But the effect is too small to observe unless the photon energy is very high (gammaray bursts, collapse of neutron stars, collision of neutron stars, very violent events)

    Neutron stars are the flint that makes the spark that maybe lets you see a discrepancy. Well that's a way to test LQG and that's the plan.
    Better have a careful look at "Invitation to LQG", the above link
  4. Aug 14, 2004 #3


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    If gravity probe b returns a null result wont that be major
    constraint on most theories presently accepted?
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