[spunkets]

"It has long been known that the propagation speed of gravitational (and also electrodynamic) forces is faster than light in forward time."

No, this is not known at all. Both fields propagate at the speed of light.

[JamesP81]

No, this is not known at all. Both fields propagate at the speed of light.

Really? I had read somewhere something about gravity propagating at greater than light speed, perhaps even instantaneously. I'm not a physicist, so I wouldn't really know...

Let me ask this question then: if gravity does propagate at lightspeed then if the Sun were to disappear completely would it's gravitational pull on the other planetary bodies in the system persist for a short time (it'd be about 8 minutes for Earth, IIRC).

[The_Reader_David]

Any force mediated by a massless vector boson will propogate at the speed of light.

It's not so clear that gravity is such a force: do we believe string theory's attempts to construct a theory with a graviton, despite string theory predicting a contra-factual massless scalar field, and still not being well-forumlated (is the background 10 dimensional? 11 dimensional?. . .), or do we take the fairly well-validated approach of general relativity in which gravity is the curvature of space-time, and not a field that propogates at all?