What the discovery of gravitational waves means

More than a billion years ago, two black holes in a distant galaxy locked into a spiral, falling inexorably toward each other, and collided. "All that energy was pumped into the fabric of time and space itself," says theoretical physicist Allan Adams, "making the universe explode in roiling waves of gravity." About 25 years ago, a group of scientists built a giant laser detector called LIGO to search for these kinds of waves, which had been predicted but never observed. In this mind-bending talk, Adams breaks down what happened when, in September 2015, LIGO detected an unthinkably small anomaly, leading to one of the most exciting discoveries in the history of physics.