[Zondartul]

Rule #1 of talking about the aether is "don't call it aether". Nowadays it's "spacetime this" and "mass-energy tensor that" and "properties of vacuum something else".... and we still end up with empty space behaving like a funky fluid.

[ISL]

The aether originally suggested a preferred reference frame -- something thoroughly debunked by tests of special relativity.

The universe could still have various preferred/interesting frames (the CMB's rest-frame sure is interesting), but it won't have much, if anything, to do with the movement of particles or light.

[Akronymus]

> The aether originally suggested a preferred reference frame -- something thoroughly debunked by tests of special relativity.

AFAIK, lightspeed could differ based on which direction you go without breakung relativity. And we haven't measured the single direction lightspeed.

Not that I actually think it differs based on direction.

[BlarfMcFlarf]

Notably, though, unlike an aether, none of those things have a measurable rest frame.