The US National Science Foundation LIGO ( Laser Interferometer Gravitational-wave Observatory ) has been called the most precise ruler in the world for its ability to measure motions smaller than 1/10,000 the width of a proton. By making these extremely precise measurements, LIGO, which consists of two facilities—one in Washington and one in Louisiana—can detect undulations in space-time called gravitational waves that roll outward from colliding cosmic bodies such as black holes. LIGO ushered