On Ether and the Michelson-Morley Experiment

     Ether was a hypothesized medium that allows light to travel through space. If such an ether exists, then the speed of light depends on the direction of Earth's motion. Of course, as the Earth moves around the Sun, its direction of motion changes. When Michelson and Morley detected no such seasonal variation in the speed of light, the ether hypothesis had to be abandoned. The Michelson-Morley experiment played an important role in Einstein's special theory of relativity. This theory's most fundamental principle is that the speed of light is constant independent of the speed of the source or the speed of the observer. This is completely counter-intuitive with everyday experiences, where the observed speed of an object depends on whether one is moving toward or away from it and depends on whether the "thrower" of the object is in motion. (See section on special relativity in the JSP report.) Light does not behave like an ordinary object. Nor does it behave like an ordinary wave, which requires a medium in which to undulate -- water waves need water, sound waves need air, etc.. Nowadays, scientists know that light is the oscillations of electric and magnetic fields (or forces) and propagates through empty space.

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