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On April 2 2022 I asked for estimates of expected results. How much larger will the "observable by us" universe be when JWST becomes operational?.

As of Jan 27 2024 with JWST operational for about 18 months how much larger (percent) is the observable sphere? I would not consider CMB to be the prior limit.

Would gravitational lensing be suitable for inclusion in this?

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  • $\begingroup$ Can you perhaps use the values and estimates in the question, with the data "before z="10.6" after z="13.2" and so at the "conservative" end of the scale, and a volume increase of about 10% $\endgroup$
    – James K
    Commented Jan 27 at 17:16
  • $\begingroup$ @JamesK Thanks, but I do not feel I have solid enough grasp of this subject to provide limits. I thought I'd leave it to the SMEs here (Subject Matter Experts) to provide currently accepted values for "before" and "after" and argue for or against positions. $\endgroup$
    – BradV
    Commented Jan 28 at 15:20
  • $\begingroup$ @BradV I realize my answer below pretty much is the same as the comment I gave below my previous answer. Nevertheless, that's the current state of affairs. But I'm quite positive that the distance record will be broken once again :) $\endgroup$
    – pela
    Commented Jan 29 at 11:09
  • $\begingroup$ @BradV I added a figure that show you how the volume increases with observed redshift. $\endgroup$
    – pela
    Commented Jan 30 at 22:45

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The current redshift record is set by the JADES galaxies. The highest-redshift one at $z = 13.20$ isn't too convincing tbh, but there's one at 12.6 that looks better, and the one at $z = 11.6$ should be good enough. But if we go with z ~ 13, then according to the answer you link to, the volume of the "observed" Universe is $\simeq150\,000\,\mathrm{Glyr}^3$.

In that answer, I equated that to 10% more than in the pre-JWST era. However, this was based on the prior redshift record of GN-z11, which had been measured to $z\simeq11.1$ (Oesch et al. 2016). But that redshift was, as is the case with the JADES galaxies, measured in a somewhat imprecise way, namely by the spectral break at the Lyman α line. That is, there wasn't any spectral lines, but just the break that comes from the intergalactic medium absorbing any radiation bluer than Lyman α, and the exact wavelength of this break depends on many obscure factors.

With JWST, it is now possible to observe such lines from GN-z11, and its redshift has been established at $z=10.60$ (Bunker et al. 2023). This actually means that the observed Universe was a little smaller before than we thought. It seems a little like cheating, but this in turn means than the fractional increase is a little larger, so 13% instead of 10%.

Gravitational lensing does indeed help observing more distant galaxies, and for this reason JWST has targeted several massive galaxy clusters, to look for distant background galaxies. These galaxies were unlensed though.

The plot below shows the probed volume as a function of the redshift of the most distant known galaxy. Since the very first galaxies are thought to form at $z\simeq20\text{–}30$, an increase of more than $\sim50\%$ is unlikely. But stay tuned; I'll update this plot along the way :)

enter image description here

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  • $\begingroup$ Is redshift value directly propotional to distance from earth? $\endgroup$
    – Vaelus
    Commented Jan 28 at 16:00
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    $\begingroup$ @Vaelus I guess this is a separate question, but no, unfortunately not. The redshift reflects the relative increase of the size of the Universe. Because the fractional increase is larger when the Universe increases from, say, 5% to 10% than when it increases from 95% to 100%, photons redshifted more in the past. Moreover, the expansion hasn't been constant throughout the history of the Universe: in the beginning it decelerated, but later it started accelerating. So the exact relation requires a model of the expansion history, i.e. (numerical integration of) the Friedmann equation. $\endgroup$
    – pela
    Commented Jan 28 at 20:30
  • $\begingroup$ I guess this is all clear to physicists, but... is z scaled such that "z=11.6" corresponds "11.6 billion (light)years"? If not, what is the radius of the observable universe atm? $\endgroup$
    – AnoE
    Commented Jan 29 at 11:27
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    $\begingroup$ Thanks @pela! I think nobody will judge you for self-promotion if it helps the answer. The chart in the top left corner of pg3 of that paper would fit into your answer very well, assuming you have the copyright for it and want to add it. ;) $\endgroup$
    – AnoE
    Commented Jan 29 at 13:51
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    $\begingroup$ @AnoE Thanks! To be honest, I don't really know if I have the rights to the diagram. Although I produced it myself, I may have handed over the rights to Springer (the publishing company), along with my left kidney and my firstborn. But I suppose I'm allowed to make a new one, so I'll do that :) $\endgroup$
    – pela
    Commented Jan 30 at 14:32

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