Sagnac Effect on Equatorial Plane: MG-P Exp & GR Twist

davek
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If one were to send two light beams around the equator east and west, would the Sagnac effect occur? I know Michelson-Gale-Pearson measured it, but in their experiment the two beams would each travel both directions in separate rectangles, so I wonder if the effect would be weaker/stronger. How would it be affected by the earth-rotation-induced space-time twist predicted by GR?
 
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It does occur, and is easiest to understand if you think in terms of an Earth-centred non-rotating frame. Simply, the Earth rotates through some angle while the light is in transit so the observer will see the light sent to the west return to him before that sent to the east.

Frame dragging would slightly reduce the effect but the amount would be negligible.
 
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By the time light moved around the equator, the lab setup moved 62 meters relative to an inertial system. Sure, you get an effect from it. It is so large you could simply use atomic clocks to measure the time signals need. And it is orders of magnitude larger than any GR effects.
 
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