Gravitational Waves

Gravitational waves are disturbances in spacetime’s curvature, generated by accelerated masses, that propagate as waves from their source at light speed. Predicted by Einstein in 1916, they differ from electromagnetic waves, which are oscillations of fields *through* spacetime; gravitational waves are oscillations *of* spacetime itself. As a wave passes, it stretches and compresses space, and any objects within it, perpendicular to its direction of travel. This effect is incredibly small. For even the most violent cosmic events, the change in distance over a kilometer is less than a proton’s width, making detection extraordinarily difficult.

For decades, their existence was only inferred indirectly from the Hulse-Taylor binary pulsar, whose orbital decay matched predictions of energy loss via gravitational radiation. The first direct detection occurred on September 14, 2015, by the Laser Interferometer Gravitational-Wave Observatory (LIGO). The signal, GW150914, originated from two merging stellar-mass black holes over a billion light-years away. This landmark discovery, earning the 2017 Nobel Prize in Physics, opened a new window onto the universe. Gravitational-wave astronomy allows scientists to observe phenomena invisible to traditional telescopes, like black hole mergers, and to test general relativity in extreme gravity regimes.