Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

MMx for GR

  1. Jun 12, 2005 #1
    I would assume there are experimental attempts to use an MMx type interferometer to check out some of the questions that are debated about photons in a G field. For example, if we have a single leg interferometer (no back and forth reflections to gain a greater effective length) and set it up calibrated horizontally (so the light path is parallel to the earth's surface) then, instead of rotating the instrument in the plane of earths surface we rotate it so that the light path is vertical. - so if the photon velocity is the same going up as it is going down after reflection, we would expect to see a fringe shift due to hf energy difference (a Pound Repka verification) but with different technology. Anyone have a reference to any such experiment.
    Thanks, Yogi
     
  2. jcsd
  3. Jun 12, 2005 #2

    Garth

    User Avatar
    Science Advisor
    Gold Member

    I'm not sure of your proposed set up, but if one half-beam was horizontal and the other went up to be reflected back to the origin, surely the "going-up" and "going-down" Pound Rebka gravitational red shifts would cancel out?
    If the beams were horizontal with one half-beam reflected after a long light path length and the other only a short one, then you could extend tests on the equivalence principle by testing whether "photons fall at the same rate as particles". The Sun provides a gravitational field in which the Earth is free-falling and any anomaly would show up as a cyclical shift with a period of 24 hrs.

    Garth
     
    Last edited: Jun 12, 2005
  4. Jun 13, 2005 #3
    Thanks Garth - what i had in mind was to eliminate the sometimes argued notion that the photon is actually slowed by a G field rather than frequency shifted - in other words obviating the explanation sometimes given that the observed frequency change is due to a Doppler-like affect based upon the slowing of the photon beam in a G field. If both legs are calibrated in the horizontal position and the apparatus rotated so that one leg is now vertical, - then since the photon fringe pattern is observed at the same height as before the rotation, there should be no energy difference a la Pound-Rebka. In the unlikely event of an observed fringe shift, the premise that the photon velocity going up is the same as going down would need to be revisited.
     
  5. Jun 13, 2005 #4

    Ich

    User Avatar
    Science Advisor

    I guess this would rather be a test of Young´s modulus.
     
  6. Jun 13, 2005 #5

    pervect

    User Avatar
    Staff Emeritus
    Science Advisor

    Me too, though I haven't worked out any numbers. Basically the arm would tend to compress when you raised it vertically due to it's own weight and it's physical "springiness" (Young's modulus).

    I would also think that any effect of speed not modelled by relativity would have severly impacted the Shapiro time delay tests that have already been done.

    There's no shortage of experimental confirmations of relativity.
     
  7. Jun 13, 2005 #6

    Garth

    User Avatar
    Science Advisor
    Gold Member

    But nobody's tested to see whether "photons fall at the same rate as particles".

    Garth
     
    Last edited: Jun 13, 2005
  8. Jun 13, 2005 #7

    pervect

    User Avatar
    Staff Emeritus
    Science Advisor

    As I mentioned, we have looked at the general issue of gravitational time delays (the Shapiro effect), and found them to be consistent with GR.

    I assume you are looking for some specific effect predicted by SCC, but I'm not quite sure what you are looking for at this point.

    For instance, I'd expect that almost any theory would predict the speed of an electron beam in a vacuum would approach 'c' in all directions as the energy per electron was raised to infinity.
     
  9. Jun 13, 2005 #8
    pervect - but the Shapero effect is often cited by anti-relativists as evidence of light anisotrophy due to gravitational fields.
     
  10. Jun 13, 2005 #9
    Ich - interesting observation - you could probably detect the contribution due to length compression by making side-by-side systems each made from a different material with a known modulus - so the effect of the weight could be calibrated-out based upon a knowledge of the materials after taking readings from both systems
     
  11. Jun 13, 2005 #10

    ohwilleke

    User Avatar
    Gold Member

    Many of the current gravity wave experiments are glorified inferometers. I'd type the acryonmns, but I'd probably get them wrong at this time of night. Google gravity wave experiment.
     
  12. Jun 14, 2005 #11
    ohwilleke - to the extent there are large separations between the sensors, I suppose you could consider them interferometers - but the separation distance is primarily for eliminating local effects that would lead to spurious false positives.

    The 64 dollar question is still as Garth put it: "do photons fall like particles?"
     
  13. Jun 14, 2005 #12

    Garth

    User Avatar
    Science Advisor
    Gold Member

    pervect In Eotvos type experiments the principle of equivalence has tested the question, "Do all particles, gold, aluminium etc., fall at the same rate?" My question is a natural extension, which nobody has tested to my knowledge.

    SCC does actually predict that photons fall at 3/2 the gravitational acceleration of particles - and predicts that after an 8km path length in the LIGO gravity wave interferonometer the path should be attracted towards the Sun by 2 x 10-12 m. relative to the solid Earth. Has anybody looked for this effect?

    Garth
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: MMx for GR
  1. MMX in water (Replies: 22)

  2. MMX explanation question (Replies: 27)

Loading...