rcain wrote:Giorgio wrote:rcain wrote:... whether wave-like or not, a related observation (and a question that has always intrigued me), the effects of gravitation do now appear to 'propagate' at the speed of light +/- 20%::

http://www.nrao.edu/pr/2003/gravity/

I do not agree, their test just proved that radio waves are bended by a gravitational field. At the most they proved that light moves at the "speed of light", but this experiment gives no clues in regards to the speed of gravity.

thats what i thought at first, but reconsidered, i conclude they must have made reference to the 'rate' of bending (dt) relative to movement/acceleration of jupiter. otherwise, i agree their conclusions would not make sense.

I found this extremely interesting webpage:

http://physics.wustl.edu/cmw/SpeedofGravity.html
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# In all calculations of the effects of finite propagation speed (electrodynamics, gravitational waves), for slowly moving sources, the first non-trivial effects appear at order (v/c)^2, NOT at first order (v/c), which is what Kopeikin claimed

# If you're working to only the first order in v/c, then all that counts is the uniform motion of the planet, Jupiter (its acceleration about the sun contributes a higher-order, unmeasurably small effect). But if that is the case, then the principle of relativity says you can view things from the rest frame of Jupiter. But in this frame, Jupiter's gravitational field is static, and the speed of propagation of gravity is irrelevant.

# A detailed calculation of the effect was done by Clifford Will (here), in a model of gravity in which the speed of gravity can be different from that of light, and showed explicitly that, at first order in (v/c), the effect depends on the speed of light, not the speed of gravity, in line with intuition.

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Lot of stuff to read during the weekend, but seems like they indeed measured speed of light and not gravity.