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B LIGO paradox

  1. Nov 16, 2017 #1
    I'm puzzled that the stretching of space by a gravitational wave stretches the LIGO arm but not the light within it. Because we are told that the red shift of a distant galaxy is caused by light being stretched by the expansion of space (the universe).
     
  2. jcsd
  3. Nov 16, 2017 #2
    It might be worth investigating the magnitude difference between light and matter... I'm going to now. :-p
    Such a small amount over a very long time...
     
  4. Nov 16, 2017 #3

    phyzguy

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    Many people have asked this question, in fact it is even on the LIGO FAQ list:

    http://ligo.org/science/faq.php
     
  5. Nov 16, 2017 #4
    Last edited: Nov 16, 2017
  6. Nov 17, 2017 #5

    phyzguy

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  7. Nov 17, 2017 #6
    If I remember correctly, LIGO does not detect changes in the wavelength of its beams directly but by inferring it from how far out of phase two different lasers become.

    When they leave, the beams are perfectly in sync, when they come back, any deviation from that is from the fluidity of spacetime.

    This is because it spent less time in one arm than the other because it got slightly longer or shorter as the wave passed. That’s why it can be detected from within the wave itself.
     
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