In article <
628ddeb3....@news.aioe.org>,
er...@flesch.org (Eric
Flesch) writes:
> On 23 May 2022 08:48:49 +0100 (BST), Lou <
noeltu...@live.co.uk>
> wrote:
> > If galaxies are said to spread apart with expansion
> > then galaxy distribution observed now,...and reversed 13 billion
> > years should give us an image of galaxies that should be much
> >closer together in the Hubble deep field.
>
> Remembering that we see back 13 billion years in every direction, your
> point boils down to that we should see those early galaxies as larger
> on the sky.
Not sure what you are referring to hear. In general, angular size is
not inversely proportional to distance. In some cosmological models it
has a minimum (i.e. the angular-size distance has a maximum).
> But their surface brightness is very faint at the
> distance so we would be seeing their brightest cores only.
Right.
> I'm not
> defending the BB model, but I'm pretty sure it accomodates your point.
Indeed. "The size of a galaxy" is not very well defined, certainly not
in any way which can be valid at greatly different redshifts.
> However, way back in 1993, Nilsson et al (ApJ 413,453) showed in their
> Figure 5 that the apparent size of radio lobes decreases linearly with
> redshift, as though the universe is endless flat space. Nilsson
> commented about this: "The crucial assumption here is that the linear
> size-redshift correlation, if it exists, can be neglected". To my
> knowledge, this linear correlation has not been refuted
> observationally to the present day.
Kellerman claimed around the same time that he saw the minimum in the
angular size. Several papers showed that his analysis was flawed. With
regard to Nilsson et al., that conclusion---even if it holds
up---depends on the lack of evolution; in other words, one needs a
"standard rod".
In any case, several lines of evidence have converged on what is now
known as the concordance model of cosmology. We know the parameters
well enough that we can calculate the dependence of observable
quantities on redshift. If something deviates from that, we can be
pretty sure that evolution is involved, not that the concordance model
is wrong.