Michelson- Morley experiment

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Michelson proceeded to invent a new instrument with accuracy far exceeding that which had been attained to that date, and that instrument is now universally called the Michelson interferometer. In trying to measure the speed of the Earth through the supposed "ether", you could depend upon one component of that velocity being known - the velocity of the Earth around the sun, about 30 km/s. Using a wavelength of about 600 nm, there should be a shift of about 0.04 fringes as the spectrometer was rotated 360°. Though small, this was well within Michelson's capability.

Working

The dominant theory of how light worked was that it was a wave of electromagnetic energy, because of experiments such as Young's double slit experiment.The problem is that a wave had to move through some sort of medium ... something has to be there to do the waving. Light was known to travel through outer space (which scientists believed was a vacuum) and you could even create a vacuum chamber and shine a light through it, so all of the evidence made it clear that light could move through a region without any air or other matter. the dominant theory of how light worked was that it was a wave of electromagnetic energy, because of experiments such as Young's double slit experiment.

The problem is that a wave had to move through some sort of medium ... something has to be there to do the waving. Light was known to travel through outer space (which scientists believed was a vacuum) and you could even create a vacuum chamber and shine a light through it, so all of the evidence made it clear that light could move through a region without any air or other matter.

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