The most famous failed experiment in physics (1887)
Its whole result was that nothing happened — and that was the discovery.
Science · Physics
The Michelson–Morley experiment
1887
Physics — optics and relativity
The Michelson–Morley experiment, performed in Cleveland, Ohio in 1887, was an attempt to measure the motion of the Earth through the luminiferous aether, the invisible medium in which light was thought to travel. Albert A. Michelson and Edward W. Morley split a beam of light with a half-silvered mirror, sent the two halves down perpendicular arms and recombined them, looking for a shift in the interference fringes as the apparatus was rotated. The whole interferometer sat on a sandstone slab floating in a trough of mercury so it could be turned smoothly. They found essentially nothing — a shift far smaller than the one the aether theory demanded. It is the most celebrated null result in physics, and cleared the ground for Einstein's special relativity of 1905.
How to spot them
- ▸Its apparatus floated on a pool of mercury so it could be rotated without jolting
- ▸Often called the most famous failed experiment in the history of science
- ▸Performed in Cleveland, Ohio in 1887 by a naval-academy physicist and a chemist
- ▸It looked for a substance that turned out not to exist
- ▸Its lead author became the first American to win a Nobel Prize in the sciences
Key facts
A sandstone slab floated on a trough of mercury, rotated while the fringes were watched (1887)
Mercury gave frictionless rotation; the observer walked round the slab reading the eyepiece.
The 1887 search for the 'aether wind' caused by the Earth's motion through space
The expected fringe shift was about 0.4; nothing above about 0.01 was seen.
Its null result prompted the length-contraction hypothesis of FitzGerald and Lorentz (1889)
Objects were supposed to shrink in the direction of motion by exactly the amount needed to hide the effect.
Performed in Cleveland, Ohio by a physicist and a chemist whose names are now joined by a dash (1887)
Case School of Applied Science and Western Reserve University, now Case Western Reserve.
The experiment that cleared the way for the 1905 paper 'On the Electrodynamics of Moving Bodies'
How far it actually influenced Einstein is still argued over by historians.
Key ideas
- If light travelled through a fixed aether, the Earth's orbital motion of about 30 km/s should make light take measurably different times along arms pointing along and across the motion — like a swimmer crossing a river versus swimming up and back.
- Because the effect goes as the square of (v/c), about one part in 100 million, only an interferometer comparing light with itself was sensitive enough to see it.
- Special relativity dissolves the problem: the speed of light is the same for every observer, so there is nothing for the experiment to detect.
Quick-fire facts
- •Performed in 1887 by Albert Abraham Michelson and Edward Williams Morley; Morley was a chemist
- •Michelson had run a first, less sensitive version alone in Potsdam in 1881
- •Michelson won the 1907 Nobel Prize in Physics, the first American to win a Nobel Prize in any science
- •The device is a Michelson interferometer — the same design later scaled to 4 km arms in the LIGO gravitational-wave detectors
- •The observed shift was less than a fortieth of the value predicted by aether theory
- •It inspired the FitzGerald–Lorentz contraction and the Lorentz transformations that underpin special relativity
- •Michelson also made the best 19th-century measurements of the speed of light and measured the diameter of the star Betelgeuse
- •Modern versions using optical resonators have confirmed the null result to better than one part in 10¹⁷
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Sources
- American Physical Society — This Month in Physics History — November 1887: Michelson and Morley report their failure to detect the luminiferous ether
- The Nobel Foundation — The Nobel Prize in Physics 1907