Can the Michelson Morley experiment be considered as proof that there is no cosmic aether? The experiment gave a null result. But it seems that it had a disproportionately negative effect on the concept of an aether. It seems to me that quite pre-determined assumptions were made as to how an aether behaves around a planet - like a flowing gas in a compressive atmosphere.
How can we say that a cosmic aether would behave in a certain way and then declare it's non existence because certain expectations were not observed?
There is a lot of space within an atom, what if the aether passes through the planet? That's just one idea from a dummy like me!
What about viscosity and compressibility of the medium? (I'm only pontificating here).
If we can accept gamma rays, spacetime and gravity as we do - (without detectable winds but with penetrating capacity and present through spacetime) then how can we discount an aether so easily?
My understanding is that by the time of the experiment, the main idea for the hypothesised aether was that it was not expected to flow around, or be disturbed by, objects and that it would have to permeate matter freely. So it would behave precisely as you are suggesting.
However if there were such an aether, the earth would be travelling through it, at varying rates, because of its orbital motion around the sun. Also, at any moment, the rate of motion through this aether in one direction would be different from the rate of motion measured in a direction at right angles. This should mean that - if light were a disturbance in an aether medium, i.e. like waves in water - the speed of light would be different in the two directions. This is what the experiment famously showed was not the case.
That result could only be consistent with an aether that was always stationary with respect to the Earth, i.e was completely dragged along with it, so that there was no motion through it by the earth. But there were other experiments that were not consistent with this idea.
The only way to rationalise all these results was that the speed of light was independent of the relative velocity of source and receiver. This, by the way is also consistent with Maxwell's equations for electromagnetic radiation (which includes light), which does not specify an aether at all, but only finite, fixed, values for the magnetic and electrical properties of space.
One can - and Einstein originally did - regard the curious fact that empty space has fixed electromagnetic properties as a sort of effective aether, though of a completely immaterial kind.
Edited by exchemist, 18 June 2019 - 08:14 AM.