I think any vestiges of a singular, expanding universe model will eventually go the way of epicycles.
Consider that the very first patch applied to it was when they realized these distant galaxies are all redshifted proportional to distance, making us appear to be at the center of the universe. So it was changed from an expansion in space, to an expansion of space, because "spacetime."
Which would seem to totally ignore the central premise of Special Relativity, that the speed of light is constant in all frames, given that if it's being redshifted, intergalactic light is not constant to intergalactic space. More lightyears, not expanded lightyears.
The premise seems to be that light is a wavy line and when it gets stretched out, the line is less wavy. Thus somehow the space being defined by the speed the light crosses it, aka, lightyears, is a different space than that determined by the spectrum of the same light.
Somebody has been sniffing too much chalk dust on this one.
Wave action is generated by the energy passing through the medium, like energy traveling through water creates ripples, not as just a wavy line. Though this raises the question of what is the medium, aka, aether, but the reality is that we only detect that wave property when it passes through whatever is being used to measure it. The information extracted is not necessarily synonymous with the underlaying energy.
It should also be noted the only metric used to measure inter-galactic space is still in terms of lightspeed. Which means it is still the denominator in this relationship. If it were the numerator, it would be a "tired light" theory.
We are at the center of our point of view, so an optical effect would be logical and it has been noted that multispectrum light "packets" do redshift over distance, as the higher frequencies dissipate faster, but that would mean we are sampling a wave front, not detecting individual photons. Which opens a much larger can of worms, as to whether quantization is fundamantal, or a function of detection and observation. Information versus energy.
Though if this effect compounds on itself, that would explain the parabolic change in the rate, so no dark energy required.
As for space, three dimensions are a mapping device, like longitude, latitude and altitude.
If all physical properties are removed, the non-physical qualities remaining are infinity and equilibrium. Which would be implicit in Special Relativity, as the frame with the fastest clock and longest ruler would be closest to the equilibrium of the vacuum, the unmoving void of absolute zero.
As you point out in the reply to my comment, zero is fundamental. Though like the number line, infinity is the other parameter.
So what fills space is energy and the patterns/information it generates. The energy radiates out, toward infinity, while the patterns coalesce in, toward equilibrium. Like a wave, the energy expands out, as the ripples settle back to equilibrium.
The energy goes to the future, like consciousness, while the patterns recede into the past, like thoughts.
Cosmic feedback loops, like galaxies. energy out, form in.
The dark matter issue of excess gravitational effect is due to mass being part of the spectrum of this inward curvature of information, that starts with waves and quantization, not gravity as a property of mass.
