"The Michelson-Morley experiment (MMX) was intended to measure the velocity of the Earth relative to the “lumeniferous aether” which was at the time presumed to carry electromagnetic phenomena. The failure of it and the other early experiments to actually observe the Earth's motion through the aether became significant in promoting the acceptance of Einstein's theory of Special Relativity, as it was appreciated from early on that Einstein's approach (via symmetry) was more elegant and parsimonious of assumptions than were other approaches (e.g. those of Maxwell, Hertz, Stokes, Fresnel, Lorentz, Ritz, and Abraham)."So, given that I know nothing about physics, this is probably going to sound like a stupid question. But I've always wondered how it is possible that a person A moving at speed observes light emitted from their frame of reference at c, and then a person B sitting still (relative to person A of course) sees that same light travelling also at c. It seems like that just shouldn't happen.
So I think I'm right when I say it has something to do with space and time being perceived differently depending on how fast you are going.
The idea was that as earth is seen to move with the solarsystem as well as around the sun you would find a different speed of light relative what motion you measured that speed in. That as the aether was thought of as some absolute 'frame of reference' which all bodies moved relative. But the light was measured the same speed everywhere (approximately, as good as could be done by that time.). And that was a headache because even if you assumed no aether, you still had to explain why that light speed didn't change with Earths motion, against or with it.
To make sense of that, and later even more refined experiments, came two assumptions, that light was a 'constant' and that the reason why it constantly gave the same speed ignoring the motion of the object it rested on, like earth, must be that something happened with the measuring equipment, a Lorentz contraction. Learning about this Poincaré suggested that this local time, as indicated by clocks 'moving in the aether', could be synchronized under the assumption of a constant light speed.
It is said that Einstein based his assumptions not so much on this, but instead on Maxwell's equations, that also gave radiation a absolute speed. But he must have known of those results and ideas too. And as far I know all experiments done so far has validated his definitions. The thing with it is that you start from those experimental results, and then you keep on building. That was what Einstein did when he later presented GR, in where 'gravity' became equivalent to a uniform constant acceleration.
As all 'clocks' differ with their motion, as defined relative some observer, he now could bind how clocks differed in a motion to gravity. And all of this came from one postulate, as I see it. That lights speed in a vacuum was a constant 'c', no matter from where it was sent, if in motion relative the observer or not. It's a whole 'frame work', and I all to often put it all together :) but it all works out experimentally, and what it comes down to for me is 'c'.
To assume differently you need to give a definition to those experiments already done, where you prove how light can be a variable at the same time as it always give you a constant 'c' when measured locally as I see it. And that one should be tricky, especially as gravity and 'clocks' works out beautifully in Einsteins definitions, and also fits very well with Special relativity following his definitions.
experimental basis of Special Relativity.