Henry Spencer [[EMAIL PROTECTED]] wrote: > On Wed, 18 Dec 2002 [EMAIL PROTECTED] wrote: > > Article arguing that the speed of gravity may be infinite... > > It has long been understood that orbits would not be stable if gravity > showed any detectable aberration (change in apparent direction with motion > of the observer), implying that either gravity's velocity is inordinately > high or else it does not propagate at all. > > Orthodox general relativity says that gravity is a matter of the shape of > space -- it's not a form of radiation at all. There is no exchange of > radiation between Earth and Sun to keep Earth in its orbit; Earth is > moving through space curved by the influence of the Sun, and Earth > naturally follows a curved path as a result. (I oversimplify a bit.) > > Gravity waves, aka gravitational radiation, carry *changes* in the > curvature of space. Relativity predicts that they move at the speed of > light, a prediction which has not yet been verified (although there is > some indirect evidence, like measurement of the energy loss of binary > pulsars, which agrees quite closely with relativity's predictions here). > > If the name "metaresearch.org" hadn't made your bogometer twitch, by the > way, the name "Tom Van Flandern" at the top should. He's a frequent > advocate of, to put it politely, far-out theories. It's possible that > he will eventually be verifiably right about something, but that is not > the way to bet. Don't sell your relativity textbooks yet.
Kook or no, I think he's right.
I think essentially it boils down to Einstein's equation:
8 pi G = T
where G is the Einstein tensor (geometry) and T is the stress-energy
tensor (matter). General relativity follows from the equality, and is
well tested. Changes in the matter distribution are reflected
*instantaneously* in the geometry. So it should be no surprise that
this is, effectively, an action-at-a-distance theory.
Cheers,
Bob McElrath [Univ. of Wisconsin at Madison, Department of Physics]
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