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September 6, 1999

Speed Of Gravity

An Alternate View


In an earlier posting on Relativity Dissidents, I included a reference to Tom Van Flandern's book Dark Matter, Missing Planets and New Comets: Paradoxes Resolved, Origins Illuminated in which he presents a case for gravity propagating at many times the speed of light. To maintain an even balance on this, I have since received a response referring to the work of Jim Woodward at Cal Tech, Fullerton, that includes the following:.

Nordtvedt showed pretty conclusively that the orbiting planets generate what he called a "gravitomagnetic" field, due to the motion of their mass through space. It's analogous to the magnetic field created by the motion of charges (and the analogies between electromagnetism just go on and on, don't they?). It's this relatively small force that, when added to the vector pointing from, say the Earth to where the Sun was 9 minutes ago, gives a resultant vector pointing to where the Sun is right now. This makes it (incorrectly) seem as if gravity propagates instantly. On Jim's web page, there is a piece where he talks about Nordtvedt's work.

The URL for Jim Woodward's web page is: http://chaos.fullerton.edu/~jimw/general/

So, is the super-luminal speed of gravity not real after all, or does the above represent, essentially, mathematical device to keep things within the bounds of currently accepted theory? I must admit that I haven't gone into it sufficiently to be able to offer a definitive answer.

When I invited Tom Van Flandern to comment, he replied that the Nordtvedt effect has no real connection to the speed of gravity issue, and that in any case, the description above is not correct. Even if it were, two of the six experiments quoted in his book survive such an objection and show that gravity nonetheless propagates strongly ftl.

My conclusion is that we live in interesting times. I don't think I'd subscribe to the idea of an imminent "Theory of Everything" or the notion that "The End of Science," is in sight any more than was the case with the fads attending the end of any previous century.

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