so what i am saying is that aether is disproved because of the outside observer thing. and NOT because of the mirror thing. if you didn't see it i updated my post above: to add to that i think the mirror thing is just for you to understand that light is a relative constant, and not just any shitty constant that you get in math.
when scientist first started with this aether theory is because they think light is like sound, and that it must have a special medium that is not air, because some space does not contain very much air particles. so this suggested or fantasy like aether would be a great medium for light. just like the hobbits
edit: aether is false... people got noble prize for it by disproving it. so i don't know what the hell you going on about the density of aether.