Michelson-Morley experiment

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TheMichelson-Morley experiment, performed byAlbert Michelson andEdward Morley between between April and July of 1887, aimed to detect theaether wind, by measuringspeed of light several times against all possible angles of aether wind, over a period of several months.

The experiment was an attempt to establish the truth of ascientific paradigm, but which instead completely demolished it, paving the way for therevolutionary changes inphysics at the start of the twentieth century. It is now seen as a triumph of thescientific method, as it is a shining example of the principle that if thetheory doesn't fit thefacts, then change the theory.

Despite this, the experiment has been labelled as having been covered up, and it has been misquoted byflat earthers and proponents ofmodern geocentrism, as a proof of the Earth being stationary.

Background[edit]

Until this experiment, it was believed that light was propagated through a medium known asluminiferous aether, for which there was no direct evidence but which had been around as an idea sinceAristotle. The experiment consisted of measuring the speed of a light beam as it travelled, firstly in line with theEarth's movement around theSun, then, a second time, across the line. Differences between the two speeds would establish "etheric drift", proving the existence of aether and revealing some of its properties. However, the experiment revealed that the speed of light was the same regardless of its orientation.

The experiment[edit]

A schematic of the Michelson-Morley experiment

The original Michelson-Morley experiment setup from 1887.

The system used what was called theMichelson Interferometer. It used a light source that emitted white light to a half-silvered mirror placed at 45° angle. The mirror passed half of the light through it, and half was reflected 45°. The split light then bounced back from two mirrors, and back at the half-mirror, light was reflected to an eye-piece. The two beams of light traveled in different directions, but an identical distance, so the eyepiece would showinterference pattern if the light was slowed or deflected by the aether wind.

One key idea was, that the aether wind could not remain undetectable in all direction the Earth was moving, at all times. The experiment's setup rested over a stone slab that had a ring shaped groove filled withmercury, that acted as a bearing, and that allowed turning the setup 360° to account for all directions of aether wind.

However, as the original paper states, these speed changes were never observed:^[1]

“”

It appears, from all that precedes, reasonably certain that if there be any relative motion between the earth and the luminiferous ether, it must be small; quite small enough entirely to refute Fresnel's explanation^{[note 1]} of aberration.

—Michelson, Morley (1887)

Thenull result (i.e. that disproved thehypothesis) perplexed scientists, but it has since beenreproduced by scientists over 30 times, and no one has been able to get a different result.

The bitching and whining from flat-earthers[edit]

In hisvideo Eric Dubay claims "The Michelson-Morley and Sagnac experiments attempted to measure the change in speed of light due to Earth’s assumed motion through space. After measuring in every possible different direction in various locations they failed to detect any significant change whatsoever, again proving the stationary geocentric model."

Dubay againlies by omission. The experiment was about measuring speed of light as the Earth moves through the hypotheticalaether wind, not space. As stellar aberration had already shown Earth was moving, the aether drift experiments were about detecting aether wind to confirm the medium through which light travels. The result stated "If the Earth moves, then aether does not exist". Because stellar aberration had already shown Earth moves, therefore aether does not exist.

Dubay has alsoclaimed the results have been swept under the rug, sohere isNeil deGrasse Tyson calling the experiment something "that's on the top of the list of most important scientific experiments", and "one of the mere handful of experiments that completely transformed physics". The experiment is also present onLive Science's list of 32 most important physics experiments, onWikipedia's list of historically important scientific experiments, and onDiscover Magazine's list of top-10 science experiments of all time. There's even aseparate paper titled "On the importance of Michelson-Morley experiment", discussing the importance.