Einstein's general theory of relativity suggests, among other things, that masses in space distort the geometry of space-time. In addition, moving objects emit waves of gravitational radiation that carry energy away into space.
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Gravity is the weakest of the fundamental forces, and the effects of gravitational waves are also weak. The waves squeeze and stretch space as they pass, but the effect is sub-atomically small.
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The effects of gravitational waves had been observed indirectly by studying binary pulsars. These are pairs of dense neutron stars that orbit each other. As they orbit, they disturb the space-time around them. They give off energy in the form of gravitational waves. This loss of energy causes the neutron stars’ orbits to decay. The decrease in orbital speed can be detected from Earth.
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In 2014, the Harvard-Smithsonian Center for Astrophysics announced the first direct evidence for gravitational waves. By examining the map of Cosmic Microwave Background radiation, astronomers found a faint but distinctive curling pattern. This pattern is thought to have been generated by gravitational waves when the universe inflated a tiny fraction of a second after the Big Bang.
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