Gravitational Waves Detected
LIGO detected gravitational waves for the first time, confirming Einstein's prediction
February 11, 2016
A Ripple From 1.3 Billion Years Ago
On September 14, 2015, detectors at the LIGO observatories in Washington and Louisiana simultaneously registered a signal lasting just 0.2 seconds. Scientists spent months verifying it before announcing on February 11, 2016 that they had detected gravitational waves — ripples in the fabric of space-time caused by two black holes, each about 30 times the mass of our Sun, colliding 1.3 billion light-years away. Einstein had predicted gravitational waves in 1916. It took 100 years to confirm them.
How They Detected It
The signal stretched and squeezed the LIGO detector by less than one-thousandth the diameter of a proton — a change so tiny it seems impossible to measure. LIGO achieved this using laser interferometry: splitting a laser beam down two 4-kilometer arms, bouncing it off mirrors, and detecting whether one arm had changed length relative to the other. The detector is sensitive enough that it would register the vibration of a truck driving past — every such source of noise had to be identified and accounted for.
A New Way to Listen to the Universe
The detection opened a new field: gravitational wave astronomy. Scientists can now "hear" cosmic events — black hole mergers, neutron star collisions — that produce no visible light. In 2017 they detected two neutron stars colliding, simultaneously observed by light telescopes worldwide, confirming theories about how heavy elements like gold and platinum are created. The three LIGO founders won the Nobel Prize in Physics in 2017. The universe, it turns out, has been vibrating all along.