True, though, "constant to the frame" is the issue.
The expansion is effectively being denominated in units based on the speed of light. If the lightspeed were to remain constant to an expanding frame, it would have to speed up equivalently. Stretched lightyears, as space expands, not more lightyears.
But then, no redshift.
Here is an interesting paper I came across, some years ago;
h ttps://fqxi.org/data/forum-attachments/2008CChristov_WaveMotion_45_154_EvolutionWavePackets.pdf
(gap after h, to keep it all from downloading)
Making the point that multispectrum light "packets" do redshift over distance, as the higher frequencies dissipate faster. Yet that would mean we are sampling a wave front, not individual point particles of light, that have traveled billions of lightyears. Which would mean photons are the smallest measureable quantity of light, not irreducible particles.
Another paper making that particular argument;
h ttp://fqxi.org/data/essay-contest-files/Reiter_challenge2.pdf
Some other speculations;
About missing mass; What if gravity is not so much a property of mass, as mass is an effect of this process of energy condensing into form, of which gravity is just the lower ened of the spectrum. Then it would start all the way out there, where light first starts to quantify and the excess "gravitional" effect is this initial curving the light inward into what becomes mass.
Consider that galaxies are light radiating out, as mass falls in and that overall, space does appear flat, meaning the inward curvature of gravity is matched by this outward expansion. So why does overall space have to expand? Wouldn't some sort of cosmic convection cycle make more sense?
Then Hubble would have actually discovered evidence of the cosmological constant, what Einstein proposed to balance gravity.
I raised this point once, back on the old Mysteries of the Universe section of the NYTimes comment threads, in the 90's. To which another commentator pointed out that it doesn't really require curvature of space, as what is measured with the inward curvature is mass, while what is measured by the outward curvature is radiation and so they just have to balance out. He also said he'd studied cosmology at the University of Chicago and presented the idea to his adviser, as his thesis paper. To which his adviser advised that it is all well and good, but if he wanted to pursue it, he should propably find another profession to make a living.
As for Dark Energy, when it was first proposed, about 99, what they had been expecting to find was the rate of redshift declining at a steady rate, from the edge of the observable universe in, but what they found was it dropped off rapidly, then flattened out. To use a ballistics analogy, it was like the universe had been shot out of a cannon and after slowing, a jet motor kicked in. Presumably the dark energy.
Yet if you consider what is actually being seen, from our point of view outward, rather than what is presumed, the edge of the universe inwards, the redshift starts off slowly, gradually building, then eventually goes parabolic. Which is what an optical effect, compounding on itself, would look like.
So the cosmic background radiation, coming from the edge of the universe, wouldn't be evidence of a primordial event, but the light of infinite sources, shifted off the visible spectrum. Making it a perfect black body radiation. The solution to Olber's paradox, where is the light of infinite sources.
That my interpretation of the evidence. No multiverse required.
