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licensors for your use of the machine generated PDF functionality and any output derived therefrom Gravitational waves Author K Lee Lerner Date 2021 From Gale Science Online Collection Publisher Gale a Cengage Company Document Type Topic overview Length 975 words Content Level Level 5 Lexile Measure 1520L Full Text Gravitational waves are normally described as ripples in the fabric of space time Although discussed abstractly as early as 1893 by British electrical engineer Oliver Heaviside 1850 1925 and in 1905 by French mathematician and theoretical physicist Henri Poincar 1854 n1912 as ondes gravifiques German born American Physicist Albert Einstein 1879 1955 formally predicted the existence of gravitational waves in 1916 as part of his General Theory of Relativity In part the imagery of ripples across fabric or waves across the surface of a calm lake are devices needed to describe phenomena that take place in space time the fusion of three dimensional space with a fourth dimension of time Space time also championed by Einstein is often visualized as a fabric stretched taught upon which masses such as stars and plants sit Their masses individually sink into a slight depression depending on the mass and so distort the fabric around them Gravity is represented by the attraction created by depressions or wells surrounding each mass in which objects are accelerating toward the mass When masses are accelerated a change in velocity created by a change in either magnitude of speed and or direction or travel they disrupt the fabric of space time much as a boat generates waves when accelerating on a calm sea Gravitational waves then travel at the speed of light through space time distorting space as they go somewhat like waves distort the surface of calm water Gravitational waves are produced by violent and energetic processes Just as one might not be able to see a stone plunging into water gravitational waves traveling from events distant from us in space and time provide evidence that something did disturb the space time surface or fabric The nature of the waves especially their energy level then tell us about what type of process created the initial disturbance The most intense and therefor most easily detected waves result from the colliding black holes the collapse and explosion of stars condensing neutron stars etc Einstein even predicted residual gravitational waves from creation of the Cosmos in accord with Big Bang theory General relativity predicts a number of phenomena such as the bending of light by massive objects like stars and the precession of the planet Mercury both which have been well verified by direct observations While Einstein predicted gravitational waves existed but he did not think it would be possible to measure the subatomic distortions produced by waves reaching Earth from distant astronomical events The first proof of the existence of detectable gravitational waves came in 1974 when Princeton University astronomers Joseph Taylor and Russell Hulse both working at the Arecibo Radio Observatory in Puerto Rico decommissioned in 2020 after damage to cables supporting the main dish discovered and observed a binary pulsar created by two extremely massive neutron stars in orbit about each other One of the neutron stars was a pulsar sending out measurable radio waves Careful observations of the rotation showed deviations exactly as predicted by Einstein s general relativity theory and subsequent observations since that time are in exact accord with the emanation of gravitational waves produced by predicted changes accelerations in the respective orbits Observations of slight distortions in the timing of pulsar radio emissions since recorded further strengthened evidence for gravitational waves The first direct evidence of gravitational waves came in September 2015 via the Laser Interferometer Gravitational Observatory LIGO a consortium of observing stations including a pair of vary large and sensitive large laser interferometers based in the United States LIGO was capable of physically sensed the sub protonic distortions in space time caused by gravitational waves generated from the collision of two black holes nearly 1 3 billion light years away and hence 1 3 billion years ago Each LIGO apparatus consists of an L shaped tunnel with two arms At the end of each arm is a mirror and where the two arms meet there is a laser beam splitter Each arm has the same length When a laser beam is shot into the tunnel it goes through the beam splitter so both beams have the same phase initially The beams are reflected from the mirrors and recombine at the original entry point where the intensity of the beam is measured by a photodetector As long as both arms have the same length the beams interfere constructively and the maximum intensity will be measured If a gravitational wave passes through the apparatus the length of the tunnel arms will change one arm will become slightly shorter and the other will become slightly longer The laser beams will then be out of phase when they recombine because they traveled different distances and there will be some measurable destructive interference The challenge in making these measurements is to minimize vibrations caused by seismic activity or human activity that could disrupt the experiment and lead to false signals To minimize these effects sophisticated automatic mirror control systems were developed to keep the mirrors from moving due to vibrations In