I am trying to learn relativity theory and going through an introductory text on

Question

I am trying to learn relativity theory and going through an introductory text on special relativity. I stumbled on the Michelson-Morley experiment. The book claims (accounts) that the result of this experiments banished away the concept of Aether. In order to understand how exactly the results of this historical experiment refuted the long standing idea I think I need to know what exactly was the idea of aether. Can anyone describe the concept of aether, what were the evidences that propelled this idea?

Explanation / Answer

Wikipedia is always a good place to start: Luminiferous aether.

Short answer: the aether was postulated as the medium through which light propagates. In the years prior to quantum mechanics and Relativity, Maxwell's equations very successfully characterized electromagnetic radiation as a wave, and solidified the wave nature of light among physicists. All other "waves" with which we're familiar require a medium to travel through, (e.g. sound waves require air). So it was a ridiculous idea to have a wave that requires no medium to travel through.

So, the Michelson-Morley experiment sought to "detect" the presence of this aether by assuming that the Earth is in motion through the aether, and measuring the speed of light at different times of the year, looking for differences in the measured speed due to the solar system's constant drift through the aether.

There wasn't really any "evidence" for the existence of the aether. It was simply assumed to exist as a necessary medium for light waves to travel through, and became entrenched in the physics of the time, until we started getting contradictory data from ever-more-precise measurement instrumentation.

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