cosmology - As the universe expands, why do some things stretch but not others?

I got into watching a video on Olbers' Paradox a few days ago, and from there read about the origins of the universe, its expansion, and so on... it's always fascinated me, but now something about it bothers me. I've heard many analogies about it (the dot-balloon, the raisin bread loaf, and others), but none really seem to explain this question. (This comes close, but dances around the answer more than explain it.)

At the beginning of the universe as we know it, the universe itself was very small, so all the stars giving off light would have made it very bright (16:29 in this video). Since that time, the wavelength of that light has been stretched (17:01, same video). I found a few explanations saying that space itself stretched (here; described as "ether" in the article), which would stretch out the wavelengths.

But here's what bothers me: If space is stretching out, redshifting all the light soaring around our universe, why are we not stretching? Theoretically, the universe is expanding an incredible amount faster than the speed of light, and the edge of the universe is an unimaginably large number of megaparsecs away from us. But should we not notice some of the stretch here, too?

That is to say, if the light in space (the "ether", though I'm not fond of that term) is stretching out, why is everything on Earth still the same size as it was a hundred years ago? Is it stretching uniformly, but we are just unable to notice such a small stretch? Or does mass have some property that space and light do not, that prevents it from stretching out? I've also heard about time stretching, too; does this have an impact on it?

Answer

This is not my field but the way I understand it is that the expansion involves unbound states. It does not affect bound states. For example protons, bound by the strong interaction, once generated, during the expansion, and decoupled, i.e. the quark gluon plasma has stopped existing, remain protons with the dimensions we know them. Incorporating your comment question:

Is there an answer as to whether the cosmological or atomic force was larger initially?

I assume that by "cosmological force" you mean the effect of the cosmological expansion, cosmological constraints.. In the current model of the universe energy is contained within it in a progressively larger volume, where particles appear in an interacting soup and thermodynamically the available energy per particle is very large, forming a quark-gluon plasma.

As expansion progresses locally the cosmological constraint becomes smaller than the strong force ( in the case of protons appearing) and therefore there is no longer a dissolution and recreation of protons from the energy soup of the Big Bang, in this case the quark gluon plasma which should exist before protons can appear. Atoms and molecules are equally strongly bound by the electromagnetic force.

The same is true for galaxies, which are a gravitationally bound state and separate between each other due to the expansion but remain bound internally.

The effect of the extra effective dispersive potential of the expansion on the binding of matter is very very small.

However the only locally visible effect of the accelerating expansion is the disappearance (by runaway redshift) of distant galaxies; gravitationally bound objects like the Milky Way do not expand.

Photons (and neutrinos) are not bound states, and therefore follow the expansion of space changing their wavelength due to it. Always keep in mind that this expansion happens locally at every spacetime point of what we define as space time for usual physics studies.

This is a field which is researched still, but this model seems to fit observations up to now.