PhysicsLAB Resource Lesson
Famous Experiments: Michelson-Morley

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These two scientists, Albert Michelson and Edward Morley, conducted one of the most important null result experiments in history at Case Western University in 1887. Using an interferometer floating on a pool of mercury, they tried to determine the existence of an ether wind by observing interference patterns between two light beams. One beam traveling with the "ether wind" as the earth orbited the sun, and the other at 90º to the ether wind. If light was a mechanical wave, then the speed of light should vary with the earth's motion through the ether - for example, like a boat traveling up and down stream; sometimes the current increases the boat's relative speed, other time it hinders, or slows, the boat's speed relative to the shore.
The interference fringes produced by the two reflected beams were observed in the telescope. It was found that these fringes did not shift when the table was rotated. That is, the time required to travel one leg of the interferometer never varied with the time required to travel its normal counterpart. They NEVER got a changing interference pattern.
The experiment refuted the hypothesis that the earth is in motion relative to a "luminiferous ether" through which light propagates. The null results of the experiment indicated that the speed of light is a constant, independent of its direction of propagation. Another consequence of their experiment was the building skepticism in the existence of the ether - scientists no longer believed that light was a mechanical wave.
In 1907, Albert Michelson was awarded the Nobel Prize in Physics for his work in spectroscopy and precision optical instruments.

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