In article ,
David Woolley wrote:
...The line of action of gravitation appears to be instantaneous
between orbitting bodies, so that distance is a non-issue to the effect.

That gravitational effects propagate at the speed of light (within
experimental error (which is at least 10 times smaller than c)) was
re-verified in the last year.

Not, alas, verified very convincingly -- last I heard, there is
considerable controversy about what that particular experiment tested and
how well it tested it.

While there is very good reason to think that gravitational effects
propagate at the speed of light, I don't know of any compelling
experimental result *directly* verifying this. There are some strong
indirect verifications -- both the precession of Mercury's perihelion and
the evolution of binary pulsar PSR 1913+16 are, *by current theory*, tied
to the speed of gravitational effects, and results from both show it as
the speed of light -- but those are at least potentially subject to
reinterpretation if new theory emerges.

Finally, a subtle point which some may have missed he what propagates
at the speed of light is *changes* to gravitational fields. The fields
themselves are (loosely speaking) the local curvature of space, and they
don't have to propagate to have effects, any more than a hillside needs to
propagate for a ball to roll down it. There is nothing that constantly
travels back and forth between the Earth and the Sun to keep Earth in its
orbit, so asking how quickly the whatever-it-is travels is meaningless.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |