By Peter Weiss
Albert Einstein’s general theory of relativity predicts that the speed of gravity equals that of light, but no one’s ever been able to measure gravity’s speed.
Now, a research team says it has done just that and found evidence that Einstein was right. However, skeptics are questioning whether the experiment measured what it was supposed to.
More than 80 years ago, Einstein worked out the equations that describe how a stationary mass bends light with its gravitational field (SN: 12/21&28/02, p. 394: Getting Warped). Recently, Sergei M. Kopeikin of the University of Missouri in Columbia extended those equations to the changing gravitational fields around moving bodies, such as Jupiter.