In the late 19th century the luminiferous aether ("light-bearing aether") was invoked as the medium for the propagation of light, when it was discovered, from Maxwell's equations, that light is an electromagnetic wave. By analogy to mechanical waves, physicists assumed that electromagnetic waves required a medium for propagation, and hypothesized the aether. Aether was thought to be a fluid which was transparent, non-dispersive, incompressible, continuous, and without viscosity. This idea of an aether has since been rejected by the vast majority of scientists.
Other than the question of propagation, the aether was intended to solve the problem that Maxwell's equations require that electromagnetic waves propagate at a fixed speed, c. As this can only occur in one reference frame according to Newtonian physics (see Galilean-Newtonian relativity), the aether was hypothesized as the absolute and unique frame of reference in which Maxwell's equations hold. Later it was regarded as the seat of all electromagnetic energy and attempts were made to describe matter in terms of vortices in this fluid.
Many experiments were conducted to prove the existence of aether. It appeared to be verified by Fresnel's determination that the velocity of light relative to the aether on passing through a medium of refractive index n and velocity v (in the same direction) is
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2 Aether theory postulate experiments 3 Timeline 4 Classical References 5 External links |
The key difficulty with the Aether hypothesis arose from the juxtaposition of the two well-established theories of non-relativistic Newtonian dynamics and of Maxwell's electromagnetism. Under a Galilean transformation the equations of Newtonian dynamics are invariant, whereas those of electromagnetism are not. Thus at any point there should be one special coordinate system, at rest relative to the local aether, relative to which Maxwell's equations assume their usual form. Motion relative to this aether should therefore be detectable.
The most famous attempt to detect this relative motion was the Michelson-Morley experiment in 1887, which produced a null result. To explain this apparent contradiction the Lorentz-Fitzgerald contraction hypothesis was proposed but the aether theory was finally abandoned when the Galilean transformation and the dynamics of Newton were modified by Albert Einstein's theory of relativity and when many experiments subsequent to Michelson-Morley failed to find any evidence of aether. Most current physicists do not see a need to have a medium for which light to travel through.
An alternative experiment that tests for the existence of the aether is the Trouton Noble experiment.
Some classic field physicists (like Dayton Miller and Edward Morley) continued research on the aether for some time. There remain some modern proponents of aether theory. Its mystic appeal draws pseudoscientific proponents. Its intuitive appeal draws protoscientific proponents. Its conservative history draws classical field proponents.
It rather easy to create aether theories which conform to the null result of the Michelson-Morley experiment, but it becomes increasing difficult to create theories that are consistent with all of the related experiments which are consistent with no aether. Modern analysis of aether must be consistent with all of the experiments testing phenomena.
Disadvantages and Critics
Aether theory postulate experiments
Timeline
Classical References
External links