How a new era of astronomy will ride on gravitational waves
Some 1.3 billion years ago, in a galaxy far, far away, two massive black holes collided violently, setting off ripples in the fabric of spacetime. These ripples, called gravitational waves, passed through Earth on Sept. 14, 2015. And for the first time ever, humans knew they arrived.
Albert Einstein's general theory of relativity had predicted gravitational waves a century earlier, but it wasn't until the Laser Interferometer Gravitational-wave Observatory (LIGO) was built at
