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You are usually pretty good at explaining things to those of us outside the hard sciences, but the speed of gravity? Speed of light OK, but what is the speed of gravity?

Robert L. Schrag
North Carolina State University
Raleigh, N.C.

An object with mass creates a gravitational field around itself. Imagine that the object moves; then, the strength of its field everywhere in space changes. The speed at which that change ripples through space is the speed of gravity .–P. Weiss It would seem to me that the shift in the apparent position of the quasar was due to the bending of light by Jupiter’s gravity. I would conclude that it is proof of Einstein’s proposal that gravity is due to the bending of space around a massive object, but I fail to see how this can be construed as an indication of the speed of gravity.

Stephen Moody
Richmond, Va.