[paul cotter]

This is getting tiresome. There is no evidence for the existence of "aether". We can't prove or disprove it's existence, therefore it has NO place in real science. Science is based on observations and subsequent theories based on these observations. Wild speculation on what might be, without a scintilla of evidence, belongs in pseudoscience.

[alancalverd]

Aether was a fairly logical guess when radio transmission was discovered.  We knew that information can be transmitted by waves in solids, liquids and gases, and now we had the means of measuring wavelength, frequency and velocity of something rather more tractable than light, so the first guess would be that it was carried by some other medium.

Early radio textbooks used "compression of the aether" to explain radio propagation to soldiers, sailors and aviators who needed a quick and practical understanding of phenomena such as frequency, wavelength, diffraction, reflection, dispersion, interference and attenuation that could be visualised with ripples on water and which profoundly affected their life-critical use of the medium.

Maxwell actually derived his propagation equations as theoretical models of "fluctuations in a medium" with properties of permittivity ε and permeability μ. The power of this approach is in allowing us to model and predict propagation in any medium, but the observation that EM radiation propagates through a vacuum at a finite speed independent of direction requires us to assign values to ε₀ and μ₀ analogous to those of a real medium.

The problem with "fluctuations of the aether" is  the calculated elastic modulus and density of the material - the properties that determine the speed of waves. It has to be orders of magnitude stiffer than any known material and orders of magnitude less dense. We have no concept of a less dense material than hydrogen, or a stiffer material than, say, carbon steel. This is the point at which the search for aether becomes somewhat problematic as it also must have zero viscosity  (or the planets would spiral into the sun) and its mechanical properties must be independent of the amplitude and frequency of the wave over at least a range of 10¹⁸ - a degree of linearity unmatched by any other medium.

Therefore the minimum assumption is that Maxwell's model holds true in the absence of any medium, as long as we can assign independent experimental values to ε₀ and μ₀. It turns out that the values we measure from electrostatic and magnetostatic experiments (no need for any compressible medium as nothing is moving) give us the observed value for c.

Thus no requirement for an aether.

[hamdani yusuf]

AFAIK, every model of aether that has been proposed so far makes predictions contrary to at least one experimental result. Thus, this word comes with too much baggage for anyone who wants to propose a new theory of light. Perhaps it would be better for them to invent a new word for their idea.