Astronomers have used light to study the universe with optical telescopes for hundreds of years. We have expanded that view hugely since the middle of the 20th century, by building detectors and instruments sensitive to all the forms of what physicists mean by light: the electromagnetic spectrum, from gamma rays to radio. Yet the discovery of gravitational waves represents our first steps into studying the universe through the gravitational-wave spectrum, which exists independently from light, probing directly the effects of gravity as it spreads across the cosmos. It is the first page in a whole new chapter for astronomy, and science.
One hundred years ago Albert Einstein in his general theory of relativity predicted the existence of a dark side to the cosmos. He thought there were invisible “gravitational waves”, ripples in space-time produced by some of the most violent events in the cosmos – exploding stars, colliding black holes, perhaps even the Big Bang itself. For decades, astronomers have gathered strong corroborative evidence of the existence of these waves, but they have never been detected directly – until now. They were the last part of the general theory still to be verified.