On September 14, 2015, at 9:50 a.m. and 45 seconds UTC, you were, for the briefest moment, just a little bit taller. The gravitational wave crest that washed through you had been traveling across the cosmos, warping space itself in its wake, for 1.3 billion years, ever since it was set off by the violent merging of two black holes each 30 times more massive than the Sun. You might not have noticed the boost—after all, you grew by less than one millionth the width of a proton—but physicists at the Laser Interferometry Gravitational-Wave Observatory (LIGO) did.
