Albert Einstein’s theory of general relativity, developed 100 years ago, predicts the existence of gravitational waves. In February 2016, the Laser Interferometer Gravitational-wave Observatory (LIGO) became the first experiment to observe gravitational waves, created by two black holes spiraling into each other. The discovery became known as the chirp heard around the world. Four month later, a few hours before this public lecture, LIGO announced the discovery of a second signal. This lecture, given by Dr. Barry Barish, LIGO director from 1997 to 2006, explains the physics of gravitational waves, the detection technique used by LIGO, the observations made and the implications these discoveries have on our understanding of the cosmos.