Universal Expansion

[five_distinct]

I remember a thread from a few months back, and in all my searching I can't find it, where someone was trying to figure out if there would be a galaxy somewhere travelling so fast that a space-ship leaving earth at around c would be at rest to it (if it somehow managed to catch up to it or whatever, I don't remember the exact scenario).

Anyway, what's important to me in this question is this: Is the space added in the expansion being added in the voids, or added everywhere uniformly? I seem to remember explanations saying it was added in the voids... But I don't recall exactly.

[Squashed]

...it was added in the voids...

Well, that would depend upon your definition of "voids".

According to what I have read the expansion is between galaxies which could be defined as a "void".

But I have also read that expansion elongates in-transit electromagnetic waves (light) which red-shifts the wavelength and so the "void" must also include "between the ends" of the electromagnetic waves.

Furthermore, since matter is composed of energy and since the energy may be electromagnetic in nature then possibly "void" would encompass the very structure of matter - but this would only apply if matter was composed of a sort of "trapped" energy.

Trapped Energy:
In particle accelerators when a collision is orchestrated anti-matter particles are created and when these anti-particles collide with regular matter then electromagnetic waves are emitted which contain the momentum of the original particles and so I envision, maybe incorrectly, that matter is the result of collided electromagnetic waves that result in a "zero sum" of electromagnetic momentum.