Thanks to Albert Einstein’s general theory of relativity, we have known that gravitational waves exist for more than a century. It wasn’t until 2015, however, that LIGO physically detected the existence of gravitational waves caused by two colliding black holes 1.3 billion light-years away.

What are Gravitational Waves?

Gravitational waves are essentially ripples in the fabric of space-time. In the same way that disturbed water creates waves, and moving electrons create electromagnetic waves, gravitational waves are created by any accelerating mass. These waves are invisible and travel outwards from the source at the speed of light, stretching and bending anything they cross as they ripple through space.

The largest gravitational waves come from some of the most cataclysmic, high-energy events in the universe, such as merging neutron stars, supernovae and colliding black holes. In fact, the black hole collision from the first gravitational waves ever detected released 50 times more energy during the last tenth of a second, than the energy released by everything else in the observable universe combined! If you had been close enough, the immense force from the gravitational waves would have torn you to shreds.

Luckily, Earth is far from any destructive collisions, and by the time the waves reach us, they will have shrunk thousands of billions of times , which also makes them very difficult to detect. This is why in 2015, humanity achieved the impossible with the first ever detection of gravitational waves thanks to one of the largest research facilities in the world, LIGO.

What is LIGO?

LIGO stands for Laser Interferometer Gravitational-wave Observatory. Although considered an observatory, LIGO does not make observations through a telescope. Instead, it uses an optical arrangement of lasers and mirrors called an interferometer, which works by superimposing two beams of light to create an interference pattern. The interference pattern is then projected onto a photodetector so precise, that it can detect signals a thousand times smaller than the nucleus of an atom! This is the smallest measurement ever attempted by science.

LIGO consists of two university research centers at Caltech and MIT, and two detector sites in Hanford and Livingston, more than 3000km apart. Each interferometer is built in an ‘L’ shape with two arms, each 4km long. These arms were so long that when engineers were designing the detectors, they had to take the curvature of the Earth into account!