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Michelson Morley revisited

  1. Sep 22, 2009 #1

    I think General Relativity would argue that the light travelling vertically, shown in the diagram by the blue track, would be faster than the beam travelling an equal distance horizontally in the predominantly stronger gravitational field. We are assuming no atmosphere. Is this correct or could there be other factors? I have a feeling the orange horizontal beam will win.

  2. jcsd
  3. Sep 22, 2009 #2


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    M&M doesn't tell who is faster, just if the difference changes with different orientation. You don't know the lengths of the arms with the accuracy to see who's faster.

    But let's say you have 2 tracks of exactly the same length: one going out of the G-field, and one staying low. Then yes, GR would predict the vertical to return first, due to gravitational time dilation.
  4. Sep 22, 2009 #3
    Yes that always puzzled me. I can see that would be a problem.

    Just as an addendum, there is a very fine video on YouTube by Martin Grusenick which seems to demostrate what I'm talking about.

    Last edited by a moderator: Apr 24, 2017
  5. Sep 22, 2009 #4


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    Despite his wonderful German accent, I think the commenters on both this video and his German version have a point, the effect is probably due to movement of the apparatus due to stresses from gravity. The wavelength here is 532 nm, a very small amount of movement in the apparatus can give rise to the shifts in the fringes that he observed.
  6. Sep 22, 2009 #5
    Do you think the gravitational differential between the horizontal and vertical positions would be too small to register any Shapiro type effect?
  7. Sep 22, 2009 #6
    Just learning basic GR SO could you elaborate on how time dilation relates to the trip time of the vertical transmission. I understand that clocks at the higher potential would be running faster but don't see how this leads to an earlier return relative to the low transmission.
    As an incidental question, would you know if the GPS system is calculated with equal transit time going up as coming down??
  8. Sep 22, 2009 #7


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    I have not done any calulations, but you can think of the two way signal as a light clock. And the horizonatal one is lower.
    Why not? GR doesn't predict different times for going up & down.
    Last edited: Sep 22, 2009
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