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What about GLAST?

  1. Jul 16, 2007 #1


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    I just read in The Trouble with Physics that the Gamma Ray Large Area Telescope was scheduled to launch in the summer of 2007. It was supposed to determine if photons of different energies travel at different speed.

    So, has the telescope began operating as scheduled? What are the results so far?
    Last edited: Jul 16, 2007
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  3. Jul 16, 2007 #2
  4. Jul 16, 2007 #3
    Last edited: Jul 16, 2007
  5. Jul 16, 2007 #4


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    The notion of a frequency-dependent variation in the speed of light, is not in the primary science objectives for GLAST, as far as I know. This was proposed by Fotini Markopoulou-Kalamara, who is a colleague of Lee Smolin at the Perimeter Institute. The idea is that space has a fine-scale structure, and that EM must interact with space as it propagates through it. Intuitively, high-frequency EM (short wavelengths) will interact more frequently than low-frequency EM, and that might be detectable as a frequency-dependent offset in EM arrival times.
  6. Jul 16, 2007 #5


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    Smolin's book was written in 2005 and came out in 2006
    during those years it was established that in some form of 3D gravity with matter, a kind of dispersion relation should hold.

    a keyword search term was DSR (deformed special relativity)

    Many people thought this would extend to 4D and a lot of effort was put into extending the result so that it would apply to our usual universe. this research effort lasted at least till around January 2007.

    Then Jerzy Kowalski Glikman gave a seminar talk at Perimeter around that time explaining why it didn't go through and why the result was so hard to get.

    In several papers that came out up thru March 2007 I got the impression that people were giving up on trying to make LQG/SF formalism predict an energy dependent speed of light.

    There were reasons to hope it might work (such as what happens in 3D) but it didn't work.

    So AFAIK LQG does not predict energy dependent speed of light after all!

    However IT AIN'T OVER TIL IT'S OVER and there probably are people who are still trying to derive that prediction in 4D, and they might succeed, and GLAST has been delayed and now is not supposed to go up until 2008. So there is still time for someone to go on record with a prediction!

    At the Loops 07 conference in June 2007 there was no talk about DSR---suggesting that the idea has been put on hold.
    Last edited: Jul 16, 2007
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