Re: No Planck limit for time!???

From: Hal Finney (hal@finney.org)
Date: Fri Feb 21 2003 - 12:52:50 MST

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    BillK mentions the paper which Serafino found here:

    http://arxiv.org/abs/astro-ph/0301184

    > "If time moves along like business as usual even at Planck scales,
    > however, you have to reconcile the Big Bang model with an event that
    > isn't just off the scale, it's infinite!"

    The real issue here is that this is supposed to be a test of quantum
    gravity. According to that theory, uncertainty in space and time is
    present at the smallest scales, giving the universe a somewhat granular
    nature. This can be reflected in principle in the propagation of light
    over galactic distances. Lieu and Hillman claim that this should destroy
    interference patterns on such photons, in contrast to observations.

    However I found a Usenet post which pointed to two papers which deny
    this conclusion,

    http://xxx.lanl.gov/abs/astro-ph/0302333
    http://xxx.lanl.gov/abs/astro-ph/0302372

    Both claim that the authors made a mistake. (I just read the abstracts.)
    The first argues that the "kind" of interference is relevant, that
    what you see through the telescope is wavefront-based and will not
    be destroyed by quantum gravity, rather you need an amplitude-based
    interference detector like a Michelson interferometer. The second paper
    makes a similar point, arguing that the authors "vastly overestimated"
    the destruction of phase coherence in this system.

    I suspect that the critics are right. I recently read Lee Smolin's
    book, Three Roads to Quantum Gravity, and he mentioned some possible
    tests of the theory based on long-travelled photons. They are subtle
    effects, though. If the bare existence of interference fringes was that
    sensitive a test of quantum gravity, people would have figured it out
    a long time ago.

    Hal



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