“It will give us ears to the universe where before we’ve only had eyes.” LIGO is the most precise detection device ever built.

PROFESSOR KARSTEN DANZMANN, Director of the Max Planck Institute for Gravitational Physics and LIGO collaboration member

Nothing can escape its gravitational force, not even light. Whenever such masses accelerate, as did our two black holes that had been circling each other before they collided, the masses warp both space and time. And the waves they send out across the cosmos do the same—but on a far smaller scale: The gravitational waves produce relative changes with the length of only one- sextillionth. It was clear that a device for measuring such a minute change would have to be more precise than anything humankind had ever previously invented. And that’s where the pair of lasers came in: specifically, the laser interferometers that detected those gravitational waves on September 14, 2015. The Laser Interferometer Gravitational- Wave Observatory ( LIGO) consists of two huge laser interferometers located 2,000 miles apart to eliminate error. Each of the detector’s structures consists of an L- shaped building with two steel vacuum tubes 2.5 miles long. A laser beam is split, travels down each of the tubes, and is then reflected by two sets of mirrors—the smoothest ever made. If there’s even the slightest variance in the length of the two beams, the detector sounds an alarm. And “slightest” can mean a distance 10,000 times smaller than a proton, in itself a subatomic particle. It took over a century for Einstein’s theory of gravitational waves to be tested because the technology was simply not available yet. In the future, researchers hope to be able to detect more gravitational waves and thus to confirm physics theories and expand our knowledge of them: What occurs in rapidly rotating neutron stars? Why do exploding stars emit giant bursts of gamma rays? Will black holes come to divulge some of the secrets they’ve been keeping for billions of years?