Gravitational waves are not theoretical; they are real and have been directly detected. The existence of gravitational waves was first predicted by Albert Einstein in his general theory of relativity in 1916. According to this theory, gravitational waves are ripples in the fabric of spacetime that propagate outward from accelerating massive objects, such as binary black hole or neutron star systems.
The direct detection of gravitational waves was accomplished by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015. LIGO consists of two observatories, one located in Hanford, Washington, and the other in Livingston, Louisiana. The LIGO detectors use laser interferometry to measure tiny changes in the lengths of two perpendicular arms caused by passing gravitational waves. The detection of gravitational waves was a monumental achievement that confirmed a major prediction of Einstein's theory.
Since then, LIGO and other gravitational wave observatories, such as the Virgo detector in Italy, have made several detections of gravitational waves. These detections have provided crucial insights into the astrophysics of black holes, neutron stars, and other extreme cosmic events. Gravitational waves have been observed from merging black holes, merging neutron stars, and even from the collision between a black hole and a neutron star.
The evidence for gravitational waves comes from the precise measurements made by these detectors, which match the theoretical predictions of general relativity. Additionally, the observed gravitational waves exhibit characteristic waveforms and carry energy away from the source, consistent with the properties predicted by the theory.
In summary, gravitational waves are not just theoretical; they are real and have been directly detected by gravitational wave observatories. These detections provide strong evidence for the existence of gravitational waves and confirm a fundamental prediction of Einstein's general theory of relativity.