Gravitational wave is a type of radiation that carries gravitational force. The movement of matter through space creates gravitational waves.
The existence of gravitational waves was predicted in 1915 by the German-born American physicist Albert Einstein’s general theory of relativity. According to the theory, time and space are not absolutely separate. The theory refers to them instead as a single entity, space-time.
Gravitational waves can be thought of as moving ripples in space-time. The ripples stretch and shrink space-time, changing the distance between objects without causing them to move. Imagine two small rubber balls floating freely in space. If a gravitational wave passed by them, the distance between them would change, but neither would experience any force pushing them toward or away from the other. The farther apart the balls are, the more the distance between them will change.
Scientists think that violent cosmic events create powerful gravitational waves. The waves, however, are difficult to detect because they grow weaker as they travel outward from their source. Researchers expect the waves that reach Earth to be very weak. The strongest waves might change the separation between two balls 0.6 mile (1 kilometer) apart by less than a thousandth of the diameter of the nucleus of an atom.
In the 1960’s, the American physicist Joseph Weber developed the first gravitational wave detector. He attempted to detect vibrations that the waves produced in a large metal bar. In 1974, the American physicists Russell A. Hulse and Joseph H. Taylor discovered two dense objects called neutron stars in close orbit about each other. Observations showed that the stars’ orbits changed in a way that would be predicted if they were emitting gravitational waves. Scientists continued to improve detectors of the kind built by Weber. They also developed detectors based on devices called interferometers that use light to make precise measurements. These devices were not yet sensitive enough to detect gravitational waves, but researchers continued to build more sensitive instruments. In 2016, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that they had detected gravitational waves coming from two colliding black holes.
See also Gravitation (Gravitational waves) ; Interferometer ; Observatory (Gravitational observatories) ; Relativity (Gravitational waves) .
