I think it's high time we asked a definitive question.  What if the cosmological redshift measurements were in fact NOT a measurement of recession velocity?  Yes, greater redshift does seem to be related to distance, but recession velocity is (ahem) stretching it a bit. 

Seriously.

If redshift were not velocity, the question is how we would have to alter all theories about, well, just about everything.  Here's a partial list:

    * Universe is not expanding
    * Big Bang would go out the window
    * Dark Matter out the window
    * Dark Energy out the window
    * Inflation era out the window

So, if we throw all that out the window, what's left?  Suddenly, alternative cosmological theories become ... no longer "alternative".  Mainstream cosmology is thrown on its backside.  What happens to all the theories?

For some reason, I believe that this is a real possibility. 

Any comments?

The cosmological redshifts are not considered to be measurements of recessional velocity this is a common misconception. They are considered to be measurements of the amount that space is expanding between us and the distant galaxies. The galaxies should not be considered as ejecta scattering into pre-existing space. Rather it is thought that space itself expanding from within and that gives us the redshifts but you have a valid point that redshifts may not be indicators of an expanding universe. Even Edwin Hubble was never convinced that his redshifts were necessarily indicators of expansion. We should expect the Standard Big Bang model to conform to observations but it has been necessary to add ad hoc patches to the theory to make it fit and you mentioned the main fixes: inflation, exotic dark matter, and dark energy. These are telling us there is something wrong with our picture.

Whether redshift is due to expanding space or receding galaxies (yes, it's "expanding space" - I stand corrected) the question remains.  What will become of our cosmological theories?

I don't expect the Standard Model to ever go quickly or quietly but if it did....? The same observational evidence that supports the SM also supports a good number of alternative theories. I suspect the demise of expansion theory would begin a search for a new “correct” theory but this may be a mistake. I suspect we have so many alternative cosmologies because there are many correct ways of considering the same body of evidence and having more than one point of view gives us perspective. Our alternative cosmologies can't compete with the Standard Model because there is no consensus as to which of many models is correct and that may be our reality. We may need to consider the universe from two or three perspectives to acquire a feel for its underlying reality that can't be found in any one model.

bangstrom said:

The same observational evidence that supports the SM also supports a good number of alternative theories.

That has ever been part of the problem. Hubble seems historically ignored past the seminal 1929 paper - his fight was for a static universe with arguments that the brightness did not correlate with an expanding universe - others seemed to argue that the brightness curve was due to evolution of the objects in question.

A frustratingly large number of phenomena can be explained either way. Either you posit a completely unknown redshift mechanism for a nonexpanding universe or quasars brighter than a thousand galaxies for an expanding universe.

Not having a reliable means to get independent distances means that expanding universe theories are used in part to prove themselves via redshift α distance rules. Supernovae were supposed to be the nail in the coffin, but we've seen that they're not.

If the Standard Model went, so would the pressures for a number of phenomena: "reignition", anthropic principle, the rather short 13.7 billion year timeline, the mystery behind metallicity of "early" galaxies, dark energy, dark matter (at least the exotic kinds), "big bounces" (I can't believe that's started to come around again from WMAP analyses), possibly even SMBHs, though I wouldn't rule those out.

I really, really, really want the Webb to survive. Short-sighted is both a terrible pun and the truth behind the defunding effort.