Astronomers at the world’s largest radio telescopes are gearing up to measure the speed of gravity.



It is the first attempt to verify a key prediction of Einstein’s theory of general relativity, which says that nothing, not even the influence of gravity itself, can travel faster than light.



No one has ever tested this prediction, even though the assumption that gravity travels in waves or gravitons with a finite speed underpins much of theoretical physics. The difficulty is that if light and gravity travel at the same speed, how can you hope to see evidence of gravity’s speed?



The answer, says Sergei Kopeikin of the University of Missouri, Columbia, is by watching a distant quasar as the planet Jupiter moves in front of it and its gravity bends radio waves from the quasar.