All About Space
Do gravitational waves travel at the speed of light?
Gravitational waves should travel at the speed of light, but in science we can never truly say that two things are exactly the same. We can only compare our measurements and say how much room they have to possibly be different. In the case of light and gravitational waves, you want to have an event that gives off both at the same instant, and then measure when both signals arrive. If a light wave and a gravitational wave were to race to us from Proxima Centauri, the nearest star after the Sun – a distance of a little more than four light years away – they would arrive at the finish line within a few nanoseconds of each other. Perhaps even closer, but that’s as good as our measurements have gotten up to now.
We think that gravitational waves should travel at the speed of light because that is what Einstein’s theory of general relativity predicts. But Einstein may not be the final word on gravity – just as Newton’s ideas on gravity had to be modified by Einstein. That’s why we make measurements, to find out all the cool stuff our theories can’t yet explain!