We have waves, which (in theory) are generated by merging of massive black holes. These waves cannot reach us without of help of a medium, because, unlike photons, they are normal waves and definitely propagate trough medium.

Yes, distance extends and contracts, but it can be interpreted in different ways:

If we accept existence of Ether, then speed of light in Ether doesn't vary (in same conditions, as speed of sound in water doesn't change when water is waving), but "ether" contracts and expands instead.

If we will not accept existence of Ether, then "physical vacuum"/"quantum field"/"quantum atmosphere"/"* field"/etc contracts and expands or "space-time" bends. However, if we translate all that back to plain English, then we will get:

* Ether - hypothetical medium for light and EM waves made of subatomic particles in solid/superliquid/gaseous/plasma/etc form (we don't know yet), which is attracted to macro objects like atmosphere is attracted to bodies, but much lighter and much more extended;

* physical void - "void" means empty space (nothing), but "physical void" is not an empty space, but space filed with quantum fluctuations, where "quantum" literally means "integer" but refers to subatomic particles, and "fluctuations" means that these particles are moving or appearing and disappearing to fast for us to measure, so "physical vacuum" means "space filed with subatomic particles in superliquid/gaseous/plasma/etc form (we don't know yet)";

* "quantum field" literally means "3D array of integers" and refers to subatomic particles of unknown origin;

* "quantum atmosphere" literally means "3D array of integers attached to nearest atomic object" and refers to subatomic particles attracted by bodies.

* "space-time" literally means "mathematical technique when time is added to vector of coordintas: [x,y,z,t], and "bending" means applying of transformations to space-time vectors or fields.

And so on.

Literally, we can talk about this_thing using various names. (BTW: I prefer to use "QA" instead of "Ether", because "Ether" is strongly associated with pseudo-science.)

So problem is not in accepting of fact of existing of subatomics particles in vacuum, but in believing in "bottom", unbreakable "elementary" particle. Many scientists thinks that there is bottom, but I disagree, because Pi is irrational number, so 3D space cannot be filled with round objects without leaving of a bit of empty space, no matter how small or large objects are. Thus there always will be a bit of empty space between particles filled with even smaller particles.

So, if we will accept that we can zoom in indefinitely and we still see particles at each level of zoom, then Ether is natural outcome of that:

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