Sept. 14, 2015, was one of the most important days in science history. It marked the first-ever detection of gravitational waves, tiny ripples in space-time (the four-dimensional union of space and time), a milestone notched by the Laser Interferometer Gravitational-Wave Observatory (LIGO).
Since that day, LIGO — composed of two highly sensitive laser interferometers located in Hanford, Washington and Livingston, Louisiana — has been joined by two smaller gravitational wave observatories: Virgo, which came online in Italy on Aug. 1, 2017, and the Kamioka Gravitational Wave Detector (KAGRA) located in Japan, in late 2019.
