David wrote:

So light can't get through a vacuum?

I think the idea of the ether is that it does not violate the concept
of a vacuum, the latter of which is merely devoid of mass. Obviously,
a vacuum can be, and usually is, full of energy in the form of
radiation. The ether, to an electromagnetic "wave," is supposedly the
electromagnetic equivalent of an ocean of water through which
mechanical waves travel. It does not add anything that would negate
the no-mass-dependent vacuum of space.

While I am not in the "ether" camp, in defense of the concept, there
*is* a hypothetical construct that may be real, which I alluded to
elsewhere, known to me as the "quantum background," which pervades all
of the universe, quite possibly *outside* of the universe as well,
which could constitute an ether-like fabric. I don't know much about
it, other than that it is a constantly bubbling stew of virtual
particles that appear and disappear very quickly, and that it may be
responsible for the outpouring of energy at the moment of the Big Bang.
It may also be the "carrier" of quantum waves - but that is getting
well beyond my own knowledge base.

For what it is worth, one very important type of wave that has yet to
be solidly documented is the gravity wave, the "long wave" of the
cosmic spectrum. It is not exactly an EM wave, but also not exactly a
mechanical wave, yet it has connections to both worlds. It is a major
key to the Holy Grail of cosmology, the "Theory of Everything" that
unifies all the basic forces of the universe. Its attendant quantum
particle is the graviton, and a weird thing it must be if it connects
us to our planet, among other things. Long story short, it is unclear
what kind of medium this wave would traverse, if in fact it traverses a
medium at all.

Enough about that...

Bruce Jensen