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Volume 12: Pages 340-345, 1999

The Speed of Gravity

G. D. Ransford

P.O. Box 91, Cornwall, Ontario, Canada, K6H 5R9

Newtonian dynamics, as applied with great success to the solar system, assumes the instantaneous transmission of gravity, although science would now generally assume travel at the speed of light, c (and finds supraluminal speeds in space unpalatable). Laplace, based on the Moon's motion, first set about estimating the speed of gravity and proposed as his best estimate of the lower bound of this speed some 100 000 000c (c being underestimated, though, at the time). Eddington and a present‐day writer have returned to the subject, but no unflawed estimates based on modern observations, preferably of the Earth's orbit rather than of the Moon's (the latter being difficult to handle and indeed a stumbling block for Laplace), have been forthcoming. The present paper, based on an estimate of the drift of the sidereal year, subject, it is true, to a residual uncertainty but bolstered by other recent data, supports what, for Laplace, was an inspired guess: Making due allowance for relativity and solar mass loss, it proposes as a lower bound a speed of some 200 000 000c for gravity propagation in space.

Keywords: gravity, speed of gravity, Laplace, gravity treated by Laplace, aberration of gravity

Received: February 11, 1999; Published online: December 15, 2008