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Rainer Weiss is an American physicist who invented the Laser Interferometric Technique (LMT). This technique is used to detect gravitational waves, which are ripples in space-time that are caused by the acceleration of massive objects. Weiss's work on LMT led to the development of the Laser Interferometer Gravitational-Wave Observatory (LIGO), which was responsible for the first direct detection of gravitational waves in 2015.