Michelson, Albert Abraham (1852–1931)

German-born US physicist. With his colleague Edward Morley, he performed in 1887 the Michelson–Morley experiment to detect the motion of the Earth through the postulated ether (a medium believed to be necessary for the propagation of light). The failure of the experiment indicated the nonexistence of the ether, and led Albert Einstein to his theory of relativity. Michelson was awarded the Nobel Prize for Physics in 1907 for his measurement of the speed of light through the design and application of precise optical instruments such as the interferometer. He was the first American to be awarded a Nobel prize.

He invented the Michelson interferometer to detect any difference in the velocity of light in two directions at right angles. The negative result of the Michelson–Morley experiment demonstrated that the velocity of light is constant whatever the motion of the observer. Michelson also made a precise measurement of the speed of light.

Michelson was born in Strelno (now Strzelno, Poland); his family emigrated to the USA and Michelson attended the US Naval Academy at Annapolis. Later he studied in Europe at Berlin and Paris. He was professor at the Case School of Applied Science in Cleveland, Ohio, 1882–89, and at Chicago 1892–1929. Michelson first experimented with his interferometer in 1881. The presence of ether would have caused a change in the interference pattern, but he could detect none. In collaboration with Morley, he constructed a much more sensitive interferometer, but again found no change. Michelson developed his interferometer into a precision instrument for measuring the diameters of heavenly bodies and in 1920 announced the size of the giant star Betelgeuse, the first star to be measured.