VOLKER STEGER / SCIENCE PHOTO LIBRARY VOLKER STEGER / SCIENCE PHOTO LIBRARY
Joos's interferometer. This device, engineered by Zeiss and Scott, was designed and operated by the German physicist Georg Joos (1894-1959). Joos used it to carry out a Michelson-Morley experiment in 1930, obtaining more accurate results than the original 1881 experiment. Both results showed that light does not travel faster or slower relative to a moving Earth. This led to Einstein's postulate that the speed of light is the same for all moving objects, which was the basis of his 1905 theory of Special Relativity. The experiment bounces beams of light back and forth along the interferometer arms. When aligned with the Earth's motion around the Sun, the expected differences in path length of the beams failed to appear.
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