In the Michelson–Morley experiment of 1887, what hypothetical medium were scientists trying to detect?

The Michelson–Morley experiment of 1887 sought evidence for luminiferous aether, the proposed medium for carrying light.

Physicists in the nineteenth century often treated light as a wave, and many assumed that waves needed a substance through which to travel. They called this invisible substance the luminiferous aether. If Earth moved through it, light should have traveled at slightly different speeds in different directions.

Albert A. Michelson and Edward W. Morley used an interferometer to compare light beams sent along perpendicular paths. Their result found no meaningful difference, producing a null result rather than the expected “aether wind.”

The result did not immediately create special relativity, but it weakened the aether hypothesis. In 1905, Albert Einstein explained electrodynamics without requiring such a medium, making the experiment historically important in the development of modern physics.