Originally Posted by ExpErdMann

Thanks, Tim. If we were to summarize, I suppose it would go like this. Maxwell weakened the light ether hypothesis, and the Einstein killed it with SR (plus negative Michelson-Morley result). Then Einstein brought back a different kind of medium, which we aren't supposed to call an ether anymore. We don't know exactly what the medium is, but we can equate it with Einsteinian spacetime. And if the medium expands then the waves superimposed on it will expand likewise. This makes sense when you put it this way, but I was under the impression that conventional physics would not describe light as waves in 'spacetime' so bluntly. Don't they prefer to dodge this question, as it just gets us back to the old, classical ether again?

Originally Posted by ExpErdMann

and the Einstein killed it with SR (plus negative Michelson-Morley result).