Or that Hubble actually discovered Einstein's Cosmological Constant, the effect balancing gravity? Which would equal flat space.
Consider the ball on a rubber sheet analogy of gravity; Now put the rubber sheet over water, so that where it is pushed down by the ball, is balanced by what pushes up inbetween. Such that the inward curvature is balanced by an outward curvature, between galaxies. Thus the impression the universe is expanding, rather than just the spectrum of the light crossing space between galaxies, that is cancelled out by gravity.
The first patch to Big Bang Theory, before Dark Matter, Inflation and Dark Energy, was when they realized that redshift increases proportional to distance in all directions. Creating the effect that we appear to be at the center of this expansion. So it was changed from an expansion in space, to an expansion of space, because Spacetime!
Which totally ignores the central premise of SR, that the speed of light is measured as a constant, in any frame. If intergalactic light is redshifted, it isn't constant to intergalactic space. More lightyears, not expanded lightyears.
The speed of light is still being treated as the metric against which this expansion occurs. It's like saying, well our theory still works, if we just assume 1+1=3, so 1+1 must =3.
Given we are the center of our point of view, an optical effect would be the logical explanation and multispectrum light "packets" do redshift over distance, as the higher frequencies dissipate faster, but that would mean we are sampling a wave front, not observing individual photons, which goes to the issue of just how fundamental quantization is. Or is it more a function of our ability to detect and measure only particular quantities.
The James Webb will be observing the background radiation, if it ever gets up and so the question is where it is the residue of some primordial event, or simply the light of ever more distant sources, shifted down into the radiological spectrum.
If this effect compounds on itself, that would explain the curve in the rate of redshift, so no Dark Energy necessary.
