Prediction and indirect proof
In 1916 Albert Einstein found in the equations of general relativity that accelerating masses should send ripples through spacetime at the speed of light. The effect was so tiny that Einstein doubted it could ever be measured, and at one point he even questioned whether the waves were real. In 1974 Russell Hulse and Joseph Taylor discovered a binary pulsar, two neutron stars orbiting each other, whose orbit was shrinking exactly as expected from energy lost to gravitational waves. That indirect evidence earned them the 1993 Nobel Prize in Physics.
LIGO's first detection
From the 1970s Rainer Weiss, Kip Thorne, Ronald Drever and others pushed the idea of catching the waves directly with laser interferometers, leading to LIGO's two observatories, with 4-kilometer arms, in Hanford, Washington, and Livingston, Louisiana. On September 14, 2015 both picked up a signal, GW150914, from two black holes of about 36 and 29 solar masses merging some 1.3 billion light-years away; it was announced in February 2016. The arms changed length by about one ten-thousandth the width of a proton. Weiss, Barry Barish and Thorne won the 2017 Nobel Prize in Physics.
A new astronomy
On August 17, 2017, LIGO and Virgo caught waves from two colliding neutron stars, GW170817, and telescopes worldwide then saw gamma rays and light from the same spot, evidence that heavy elements like gold and platinum are forged in such kilonovae. It marked the dawn of multi-messenger astronomy. Today LIGO, Europe's Virgo and Japan's KAGRA observe together and have logged hundreds of events, and the space-based LISA mission is planned for the 2030s. Gravitational waves may open a window on the early universe, which light can't reach, and on dark matter.
FAQ
- Can you feel a gravitational wave passing through Earth?
- No. By the time they arrive the distortion is so small that only ultra-precise laser interferometers can measure it.
- How are gravitational waves different from gravity?
- Gravity is mass curving spacetime; gravitational waves are ripples that spread out when that curvature changes.
Sources reviewed: 2026-10-26
References
- Einstein, A. (1916). Näherungsweise Integration der Feldgleichungen der Gravitation. Sitzungsberichte der Königlich Preußischen Akademie der Wissenschaften, 688–696.
- Abbott, B. P., et al. (LIGO Scientific Collaboration and Virgo Collaboration). (2016). Observation of gravitational waves from a binary black hole merger. Physical Review Letters, 116, 061102.
- Abbott, B. P., et al. (2017). GW170817: Observation of gravitational waves from a binary neutron star inspiral. Physical Review Letters, 119, 161101.