Citation from this site: ?Newton thought that gravity?s force was instantaneous,? Kopeikin said. ?Einstein assumed that it moved at the speed of light, but until now, no one had measured it. Kopeikin worked with Ed Fomalont. On Sept. 8, the scientists measured the shift of a quasar, a celestial object that resembles a star. Jupiter?s gravitational force caused the radio waves from the quasar to shift as Jupiter passed by it closely. [Note: They measured the apparent shift in position of the quasar when its radiation passed near Jupiter.]
?We have determined that gravity?s propagation speed is equal to the speed of light within an accuracy of 20 percent,? Fomalont said. [Note: That is, at best, a 20% swing with no clear procedure for determining how much is due to gravity and how much is due to speed of gravity.]
The observation recorded a slight ?bending? of the radio waves coming from the quasar because of the gravitational effect of Jupiter. The bending resulted in a small change in the quasar?s apparent position in the sky in addition to the deflection of light calculated by Einstein in 1915. ?Because Jupiter is moving around the sun, the precise amount of the bending depends slightly on the speed at which gravity propagates from Jupiter,? Kopeikin said. ?Since the effect is very small, Einstein neglected it in his calculations.? [Note: I am unable to find any statement from Kopeikin to justify the statement that the amount of bending depends on the speed of gravity.]
Citation from above site: Astronomers usually assume that so-called "lensing events" convert a point-like source like the quasar into a ring, as the radio waves are bent round the edges of the lensing object - in this case Jupiter. But this assumes that the gravitational fields are static, while the light or radio waves move.
So in 2001 Kopeikin decided to develop a more realistic model. In this, as Jupiter moves, the changing gravitational field interacts with the radio waves coming from the quasar. The calculations show that if gravity has a finite speed, the ring-like image seen at Earth will be subtly warped compared to the shape expected if the gravitational changes propagate instantaneously.
[Note: Kopeikin was expecting a corona, which happens in some gravitational lensing cases, but didn't get it. ]
Researcher Ed Fomalont, an astronomer at the NRAO, says "If we find that the speed of gravity is faster than the speed of light then Einstein's theory of general relativity breaks down."
Tom Shanks, Professor of Physics at the University of Durham, UK, thinks the experiment is a modern version of Sir Arthur Eddington's historic eclipse expedition. "From Einstein's theory of gravity, we believe mass curves space and this can cause light to follow a curved path." The first test of general relativity was to observe the bending effect of the Sun's mass on distant stars during an eclipse - Sir Arthur Eddington in 1919 showed that the position of stars in the sky moved depending on whether the Sun was near their line of sight. The amount they moved was close to the general relativity prediction. The new experiment will do much the same thing using Jupiter instead of the Sun and quasars instead of stars. "This means that by watching what happens to the positions of the quasars on the sky as the gravitational field of Jupiter moves past their line-of-sight, the scientists can test other aspects of the general relativity theory," says Professor Shanks. One aspect is to check how soon the gravitational, space-curving, effect of Jupiter is "felt" by the space around it, through which the quasar light is passing. This will be done by seeing if the movement of the quasar positions caused by Jupiter's space curving effect follows the predictions of general relativity. "If they do, then this will be a proof that gravity's space-curving effect is transmitted at the speed of light," he adds. "If the quasar positions do not move according to the prediction of general relativity then it will suggest that gravity's space-curving effect transmits at some other speed and place a question mark against the whole of Einstein's theory of general relativity."
[Note: This says a discrepancy from the relativistic prediction will indicate when the gravitational effect is felt and disprove general relativity. No discrepancy proves that gravity moves at the speed of light. The September measurement was a repeat of previous measurements, using radio frequency radiation instead of light frequency radiation. Eddington's measurement was "close." The September measurement was within 20%. The actual observations simply indicate an apparent shift in position consistent with the supposition that the path of radiation is bent by gravity toward the source of the gravity. Theorists step in and try to explain why the bending occurs and, in this case, try to distribute the bending between gravity and the speed of gravity.
I believe this procedure has added nothing to knowledge of gravity. I believe it cannot be interpreted as addressing the speed of gravity. I believe gravity bends radiation because radiation is material. I believe the region of influence of a particle's gravity is eternally in place with respect to the particle. If a particle moves, every point in the region of influence moves simultaneously. I believe that the gravitational region of influence is not affected by the particle's spin and the electromagnetic region of influence is affected by spin.]