MichelsonMorley

The Michelson–Morley experiment was an influential 1887 physics test designed to detect the luminiferous aether by measuring Earth's motion through space with a Michelson interferometer. At the time, many physicists postulated that light travels through a stationary medium, the aether, and that Earth’s motion through this medium would produce a detectable aether wind affecting light’s speed.

The experiment used a light source, a half-silvered plate to split a beam, and two perpendicular arms with mirrors at the ends. The two light paths were reflected back and recombined to produce an interference pattern. By rotating the apparatus, the researchers expected to observe fringe shifts if the light’s travel time differed along the two directions due to Earth’s motion through the aether.

In practice, the observed interference fringes showed no significant shift beyond the experiment’s sensitivity. The result was essentially null; no aether wind effect could be detected. This challenged the then-accepted idea of a stationary aether and suggested that the speed of light is isotropic, independent of the observer’s motion or the light’s source.

Impact and legacy: The null result contributed to the abandonment of the aether hypothesis and influenced subsequent theoretical developments, including the Lorentz–FitzGerald contraction hypothesis and, more profoundly, Einstein’s theory of special relativity. Michelson received the Nobel Prize in Physics in 1907 for his precision optical instruments and discoveries, while Morley did not share in the prize. The experiment established a landmark in experimental physics and the refinement of interferometric methods, and it continues to underpin discussions of Lorentz invariance and precision measurements in modern physics.