just to be sure, i meant to say that the result of this one experiment is that the speed of propagation of gravity is within ±20% of c or, between (0.8)c and (1.2)c. not (0.2)c.But it's so easy to say that c is the speed of light, since it is :)
About your statement of gravity lies in the speed of 20% of c...
i dunno that they define gravity in this experiment. they were measuring some tangible effect, no matter how they define it. i think when GRists think about gravity, they think of it as a curving of spacetime that is caused by masses and that changes in that curvature also propagate at c. if gravity happened instantaneously, then that would mean that instantaneous communication could conceivably be done over vast distances by somehow creating a gravitational disturbance (like blowing up a star) that would be detected before a change in light from that star was detected.What do they define gravity as? Curved Spacetime or particles? I would like to see the explanation of this statement. Because i find it hard to believe that geometrical curving can be that slow. ( I was surprised of that gravity didn't happen instantly (if for example the sun disappeared) )