The Michelson-Morley experiment and The Aether
(just thinking aloud here)

 
The Michelson-Morley experiment was designed to confirm the existence of the supposed "Aether", which was presumed to be the medium in which light and other forms of electromagnetic radiation were propagated. 

 
The Aether
When it became obvious that light exhibited the properties of a wave, the question arose of what medium carried these waves. Since sound travelled through air, and waves on a pond were carried by the water, it was proposed that light must also be transmitted though some medium, and this medium was named "the Aether". The Aether was presumed to fill all of space, enabling light to travel through a vacuum, yet be "thin" or "ethereal" enough for the Earth and all other matter to travel through it easily. 

 
The Michelson-Morley experiment
The Michelson-Morley experiment supposed that the earth, not being stationary in the Universe, must be moving through the Aether. It also presumed that light being carried on the Aether, must appear to travel at varying speeds when measured by observers moving relative to the Aether, just as a ball thrown from a car moving in the same direction as yours hits you at a different speed than one thrown from a car travelling in the opposite direction towards you.

The experiment measured the difference in speed between two beams of light travelling at right angles to each other, so that each would be moving through the "Aether wind" at different speeds. No difference was found. The experiment has been repeated more precisely many times since, and still no difference in speed has ever been found. It is claimed that the only conclusion to be drawn from this "null result" is that the Aether does not exist.. 
What did it prove?
The expected result (of a speed difference) is based on several assumptions  (and there might be more than these):-
  1. The Aether exists.
  2. It is the medium through with light is propagated.
  3. That it is moving relative to the Earth.
  4. That the Aether passes through matter, so that the experiment can be performed indoors as reliably as in outer space.
  5. That space and time behave consistently within moving frames of reference. 
  6. That light will move faster when travelling with the Aether than when travelling against it. 
The null result is incorrectly claimed to prove that item 1 above must be false. But obviously, it could mean that any one or more of the assumptions above is false. But which one(s)?
  1. Obviously, but not necessarily.
  2. There's little point in discussing an Aether if this is not true.
  3. This is almost certainly correct. The Earth is not the centre of the Universe.
  4. Seems reasonable also. Light seems to behave on earth as in space.
  5. Special relativity enters here. Lorentz contraction was suggested as an explanation, but has since been discounted.
  6. Could it be this one? It assumes that light behaves as matter does, but light is so obviously different.

 
 

Copyright 2002 by Rob Storey

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