Aether was the hypothetical material that fills the region of space. It was assumed to be the medium that allows light and gravity to propagate in space. Throughout the late 1800s and early 1900s, some experiments were carried out to prove if the aether exists.
Flat-Earthers (and geocentrists alike) often use the results of these experiments to support their case that the Earth is stationary. But they are wrong. These experiments were conducted to prove if the Aether theory, or if one of its competing hypotheses —like the Special Relativity— better explains reality.
In 1871, George Airy attempted to measure the drag of light that would change the stellar aberration of light by using a water-filled telescope, instead of an air-filled one. His observation did not indicate the change exists and does not support the Aether drag hypothesis, hence the popular name “Airy’s failure.” It does not support a flat & stationary Earth as the underlying phenomenon —the annual stellar aberration— can only occur if the Earth is in motion around the Sun.
The Michelson-Morley experiment in 1887 proved that if the Earth is in motion, then Aether could not exist. This experiment alone cannot confirm if the Earth is or is not in motion, but that does not stop flat-Earthers. The fact that the Earth is in motion had to be concluded from other observations.
Georges Sagnac in 1913 conducted an experiment where he rotated his interferometer. He concluded the Aether exists, but only because he was unaware of what we call now the Sagnac effect. This effect is used today in optical gyroscopes, and cannot possibly be utilized had the Aether theory is correct.
The Michelson–Gale–Pearson experiment (1926) was a very large interferometer designed to detect Earth’s rotation by measuring the resulting Sagnac effect. The experiment was successful and confirmed the angular velocity due to Earth’s rotation.
References
- Aether (classical element) – Wikipedia
- Why do Why do flat earthers say that the Michelson Morley experiment, Airys failure, and sagnac prove flat stationary earth? – Quora
- Does Airy’s failure prove the earth really is flat? – Quora
- Sagnac effect – Wikipedia
- On a supposed alteration in the amount of Astronomical Aberration of Light, produced by the passage of Light through a considerable thickness of Refracting Medium – George Biddell Airy
- On the Relative Motion of the Earth and the Luminiferous Ether – Albert Abraham Michelson and Edward Morley
- Sur la preuve de la réalité de l’éther lumineux – Georges Sagnac