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Since it is predicted that Cosmos is no less than 250 times that of the observable Universe (13.8 Blyrs) in size:

MIT Technology Review

I wondering how you can calculate any age of matter creation (13.8 Byrs) in a small pocket of the total Universe thus cosmos?

Would the above not mean that in cosmological scale our observable Universe could be already there long before the 13.8 Byrs life span and there was no matter creation or any Big Bang but only inflation of the already existed matter in that region of space? This could be just an effect of Dark Energy expansion of space.

Of course that would also mean that matter in our observable Universe is much more older.

It is believed according to BB theory that the more to the far end of the observable Universe you go the number of galaxies will drop and galaxies will be much more elementary in their morphology.

But what if the new Webb space telescope finds out that this is not the case as predicted?

Would that mean that the Big Bang theory is wrong? Or needs to be revised?

What if the Webb's new more powerful than Hubble, Ultra-Deep Field image reveals that the number of galaxies is much more than predicted?

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The current "bottom-up" idea of structure formation suggests that galaxies are built up over cosmic time from the mergers of lots of smaller galaxies. There is now plenty of chemical and dynamical evidence that this happened for the Milky Way galaxy (see Helmi 2020 for a review of that evidence) and we can see the process of galaxy mergers taking place all around us (e.g. the Antenna galaxies). It is also well established that more distant galaxies tend to be smaller and to resemble less-and-less the grand-design spirals and giant ellipticals that are seen in the low redshift universe.

Therefore it is not altogether correct to say that as we go back in time, the number (per unit comoving volume) of galaxies should decrease. Conselice et al. (2016) show that it is true that the comoving number density of large galaxies (stellar mass $>10^{10}M_\odot$) decreases monotonically from now back to $z=8$. However, the density of smaller galaxies (stellar mass $<10^7 M_\odot$) continues to increase back to this epoch.

Nevertheless, it is true that as you go back even further, one should encounter the "dark ages", where the first galaxies and stars were yet to form, probably at $z \geq 15$. At present, the most distant galaxies observed are at $z \sim 10$ and are unlikely to be "typical" examples - they are likely luminous quasars or galaxies undergoing powerful bursts of star formation. It is to be hoped that JWST will provide a much more detailed picture of what is going on at these redshifts with much less observational selection bias.

If JWST revealed a higher number density of galaxies at high redshifts than predicted by structure formation models then the implications would depend on what kind of galaxies they were. Basically though it would mean that structure formation needs to happen earlier. One thing to bear in mind is that the relationship between redshift and time since the big bang is highly non-linear. The difference between redshifts of 10 and 11 is equivalent to only a small age difference between 470 and 420 million years after the big bang (i.e. 50 million years). The difference between redshifts of 14 and 15 is only 300 to 270 million years after the big bang.

But you are right - for example finding strong evidence for a quasars at $z>15$ would be a massive challenge to current models.

I don't follow your argument that our observable universe might be somehow older than the universe as a whole. The region outside our observable universe would have been created in the same big bang and would have the same age. There are multiverse models where entirely separated universes can be created in different pockets of inflation but I don't think that is what is being referred to by the statement that the universe much be $>250$ times the size of the observable universe. I suspect that is an extrapolation based on limits to the flatness of the observable universe. In any case, JWST can only measure the observable universe and it is the observable universe that is estimated to have an age of 13.8 Gyr.

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  • $\begingroup$ Thank you for your canonical answer provided. I actually was referring that creation of cosmos is older than creation of our observable Universe (Big Bang) and If I understand it correctly the 13.8 Byrs refers to the age of the observable Universe and not the cosmos as a whole. Therefore my argument is that there was possible no BB but only expansion of the cosmos due to Dark Energy and if there is evidence that this is not true. $\endgroup$
    – Markoul11
    May 15, 2022 at 13:16
  • $\begingroup$ But @Markoul11 the JWST can only measure what is going on in the observable universe - this is what appears to have an age of 13.8 billion years. We have no evidence about what is happening in the unobservable universe. If there are other parts of the cosmos that are older we will never observe them. $\endgroup$
    – ProfRob
    May 15, 2022 at 13:23
  • $\begingroup$ I totally understand the scientific method and you are absolutely right. But sometimes IMHO this is not enough. One cannot ignore that what is actually theoretically proven that the cosmos is larger than our observable Universe and therefore interlinked since our observable Universe is not a closed system. I think it would be better to admit that we cannot know and this problem is unsolvable due to our observational limitations. $\endgroup$
    – Markoul11
    May 15, 2022 at 13:47
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    $\begingroup$ @Markoul11 It is not interlinked. Anything that happens in the unobservable universe cannot influence what happens in the currently observable universe otherwise it becomes observable... $\endgroup$
    – ProfRob
    May 15, 2022 at 14:24

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