New Scientist has a report about two researchers who apparently have become the first to directly measure the speed of gravity. The measurement confirms Einstein’s contention that gravity traveled at the speed of light.
The scientists used an interesting method to measure the speed of gravity,
[Fomalont] Kopeikin found another way. He reworked the equations of general relativity to express the gravitational field of a moving body in terms of its mass, velocity and the speed of gravity. If you could measure the gravitational field of Jupiter, while knowing its mass and velocity, you could work out the speed of gravity.
The opportunity to do this arose in September 2002, when Jupiter passed in front of a quasar that emits bright radio waves. Fomalont and Kopeikin combined observations from a series of radio telescopes across the Earth to measure the apparent change in the quasar’s position as the gravitational field of Jupiter bent the passing radio waves.
As New Scientist notes, one of the main effects of the discovery is that it will undercut theories that postulate additional dimensions in the universe beyond the usual three.
Source:
First speed of gravity measurement revealed. New Scientist, January 7, 2003.