Gravitational wave detectors

Instruments that detect gravitational waves by measuring their tiny effects on distance or motion. They include laser interferometers, resonant-mass devices, and pulsar timing arrays.

Michelson interferometer: An optical instrument that compares light traveling along two perpendicular paths. Laser interferometers use this layout to measure changing differences in arm lengths.
Gravitational wave: A propagating disturbance in spacetime produced by accelerating masses. These detectors measure the minute strains carried by the waves.
GW150914: The first directly detected gravitational-wave signal, recorded by LIGO in 2015 from a black-hole merger. Its observation established that interferometers could detect signals from distant cosmic events.
Joseph Weber: An American physicist who pioneered resonant-bar experiments to detect gravitational waves. His experiments helped establish gravitational-wave detection as an experimental pursuit.
Einstein Telescope: A proposed European underground gravitational-wave observatory with a triangular network of long interferometer arms. Its planned sensitivity would extend observations to earlier and more distant cosmic events.
Laser Interferometer Gravitational-Wave Observatory: A U.S. network of laser interferometers designed to detect gravitational waves. Its long, highly isolated arms show how interferometric detection is implemented.
Gravitational-wave strain: The fractional change in distance produced by a gravitational wave. Strain is the quantity interferometers and other detectors are designed to measure.
Binary black hole: A pair of black holes orbiting a common center of mass. Their inspiral and merger produce many of the strongest signals detected so far.
Resonant bar detector: A massive metal bar designed to vibrate in response to passing gravitational waves. Weber's bars were an early detector design, later surpassed in sensitivity by interferometers.
Cosmic Explorer: A proposed U.S. observatory using surface-based interferometers with arms tens of kilometers long. Its greater scale is intended to improve reach beyond current ground-based detectors.

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