I've heard this, too, and not being a physicist, I do have one comment. How can the propagation of gravity be measured? I mean, since the beginning of the universe, all matter would be exerting some kind of gravitational force on all other matter. As the universe expanded, and matter became heterogeneously dispersed, the same gravitational forces would still be present, but their magnitudes would be different. Since, according to relativity, matter cannot move faster than c, then could there be a way to test if it propagates faster than c? Could you have a mass osscilating in space and measure the effect of its gravity at some distance? Then modulate that oscillation and then measure a) the time to notice the oscillation at the point of measurement and/or measure the phase shift of the oscillation at the point of measurement? Just thinking oout loud.
We've had threads on this: First speed of gravity measurement revealed .