Physicists announced they have observed disturbances in the fabric of spacetime called gravitational waves for the first time in history. Albert Einstein first predicted the existence of gravitational waves in 1915, as part of his general theory of relativity, but they weren’t observed until 100 years later, on September 14, 2015. They were witnessed at two special observatories built specifically to look for this elusive phenomenon, which will help scientists better understand the origins of the universe.
Physicists have concluded that the gravitational waves detected were produced 1.3 billion years ago when two black holes collided to form one gigantic black hole. This phenomenon has been predicted (see Scientific Breakthrough Provides Insight into Black Holes), but now scientists have proof.
With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universe—objects and phenomena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples. — Kip Thorne, Caltech physicist
This discovery was observed by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Louisiana, and Washington state. The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. The detectors were built in 2002 and operated for several years without detecting any gravitational waves. Then in 2015, the observatories were given a major upgrade that made the instruments more sensitive, and gravitational waves were finally detected.
At each observatory, a two-and-a-half-mile long interferometer acts like an antenna to detect gravitational waves. Unlike optical or radio telescopes LIGO can’t “see” electromagnetic radiation, such as visible light, radio waves, or microwaves. Instead, each interferometer “listens” for gravitational waves by using laser light split into two beams that travel back and forth down tubes. The beams monitor the distance between mirrors because according to Einstein’s theory, the distance between the mirrors will change by an infinitesimal amount when a gravitational wave passes by the detector. In this way, LIGO “feels” for invisible gravitational waves, which are not part of the electromagnetic spectrum.
These tools are called interferometers because they work by merging multiple sources of light to create an interference pattern that contains information about the gravitational waves. They are often used by engineers and scientists to make extremely small measurements. LIGO’s interferometers can measure a distance 1/10,000th the width of a proton.
The Advanced LIGO detectors are a tour de force of science and technology, made possible by a truly exceptional international team of technicians, engineers, and scientists. — David Shoemaker, project leader for MIT Advanced LIGO
