Editing Michelson–Morley experiment (section)

{{Short description|1887 investigation of the speed of light}}
{{For|interference experiments on matter|Hughes–Drever experiment}}
[[File:Michelson morley experiment 1887.jpg|thumb|300px|Michelson and Morley's [[interferometer|interferometric]] setup, mounted on a stone slab that floats in an annular trough of [[mercury (element)|mercury]]]]
{{General physics}}

The '''Michelson–Morley experiment''' was an attempt to measure the motion of the [[Earth]] relative to the [[luminiferous aether]],<ref group=A name=blum /> a supposed medium permeating space that was thought to be the carrier of [[light waves]].  The experiment was performed between April and July 1887 by American physicists [[Albert A. Michelson]] and [[Edward W. Morley]] at what is now [[Case Western Reserve University]] in [[Cleveland]], Ohio, and published in November of the same year.<ref name=michel2/>

The experiment compared the [[speed of light]] in perpendicular directions in an attempt to detect the relative motion of matter, including their laboratory, through the luminiferous aether, or "aether wind" as it was sometimes called. The result was negative, in that Michelson and Morley found no significant difference between the speed of light in the direction of movement through the presumed aether, and the speed at right angles. This result is generally considered to be the first strong evidence against some [[aether theories]], as well as initiating a line of research that eventually led to [[special relativity]], which rules out motion against an aether.<ref group=A name=staley/> Of this experiment, [[Albert Einstein]] wrote, "If the Michelson–Morley experiment had not brought us into serious embarrassment, no one would have regarded the relativity theory as a (halfway) redemption."<ref group=A name=Folsing>{{cite book|author=Albrecht Fölsing|title=Albert Einstein: A Biography|isbn=0-14-023719-4|year=1998|publisher=[[Penguin Group]]|url-access=registration|url=https://archive.org/details/alberteinsteinbi0000fols}}</ref>{{rp|219}}

Michelson–Morley type experiments have been repeated many times with steadily increasing sensitivity. These include experiments from 1902 to 1905, and a series of experiments in the 1920s. More recently, in 2009, [[optical resonator]] experiments confirmed the absence of any aether wind at the 10<sup>−17</sup> level.<ref name=Eisele /><ref name=Herrmann2 /> Together with the [[Ives–Stilwell experiment|Ives–Stilwell]] and [[Kennedy–Thorndike experiment]]s, Michelson–Morley type experiments form one of the fundamental [[tests of special relativity]].<ref name=rob group=A />