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- Why is the observable universe so big? 7 answers
I understand, I think, the argument that the position is based on. Said in a sentence, the 15Bly's is in the temporal dimension only therefore space drops out because the redshifting absorbs the interim expansion of space which maintains a constant $c$ throughout. When the measurement is not in terms of time but in terms of distance the redshifted component of light must be translated back to distance and added to the initial displacement.
I get the reasoning to the extent my explanation says I do (it might be wrong and if so please treat it as the first part of my question). I accept that the reasoning itself is self-consistent and that the conclusion reflects a legitimate way to look at things.
But despite trying quite hard, I haven't yet been able to see that this view merits its advancement from supplementary/alternative view to the primary view, displacing the observable physicality in the process. Let me briefly provide a little illustration.
Currently the number given to what is explicitly described as the observable or visible universe is ~50 Bly. As it is stated surely it is a false statement, for the physicality of what we see in the telescope, across the board is the universe as if no interim expansion ever happened.
This issue is not whether a larger universe can be anticipated, but whether the interim expansion merits being moved over from the unobservable-but-anticipated universe into the actual visible universe.
Surely that is a mistake, since the interim expansion is no more visible than any other region in the unobservable universe. It's not in our light cone.
So can anyone explain what is going on for me? It doesn't appear legitimate to cite redshift as the physical justification, because for one thing it has been known since Maxwell that redshift and time are mutually small 'r' relativistic. When we look at a high redshift galaxy, time is slower in the observed galaxy relative to the observer time from the perspective of the observer. That's surely the primary physicality, and not the view that adds the interim expansion. Not because the expanding universe is not the best explanation but because the interim expansion is outside our light cone.