<p>Not by very much. You can use an <a href="https://www.astro.ucla.edu/%7Ewright/CosmoCalc.html" rel="nofollow noreferrer">online calculator</a> to convert redshift to distance. Assuming that a redshift of z=11.1 was the most redshifted object found before James Webb, this corresponds to a light travel time of 13.306 billion light years. If Webb wore to find an object at z=25, which is probably beyond what it is able to achieve, this would correspond to a light travel time distance of 13.59 billion light years.</p>
<p>You can then easily calculate (13.59/13.306)^3 and end up with an increase in observed volume of about about 6,5 percent.</p>
<p>Now if James Webb wore to find a galaxy with an infinite redshift, which it obviously will not, this would correspont to a light travel distance of 13.72 billion years. You can do the math (13.72/13.306)^3) and end up with an increase in volume of about 9.6 percent.</p>
<p><strong>Answer:</strong> Even if James Webb was to find an object with a redshift of z=25, which is more than double the pre James Webb value, the observable volume will just increase with about 6.5 percent. This is due to the fact that using the current model of converting redshift to distance at high redshifts the distance to the point of emission of the observed light will vary very slowly with increase in redshift.</p>

CC BY-SA 4.0
2022-09-28T20:40:55.543Z
Sorry, this answer is not correct. You're calculating a "volume of time", which would only make sense if the Universe didn't expand, in which case it would be equivalent to the real volume.
pela
CC BY-SA 4.0
2022-09-28T13:25:05.717Z
2022-09-28T13:25:05.717Z
Agerhell
<p><strong>tl;dr</strong> Conservatively 10%, realistically 25%, optimistically 60%.</p>
<hr />
<p>I assume that by the &quot;observable-by-us Universe&quot;, you mean not the <em>theoretically</em> observable Universe, which is given by the distance light has had the time to travel since the Big Bang, but the part of the Universe where we may practically see galaxies and other objects, not including the cosmic microwave background.</p>
<h3>Current redshift record</h3>
<p>The currently most distant, spectroscopically confirmed object is the galaxy <a href="https://en.wikipedia.org/wiki/GN-z11" rel="noreferrer">GN-z11</a> (<a href="https://ui.adsabs.harvard.edu/abs/2016ApJ...819..129O" rel="noreferrer">Oesch et al. 2016</a>), which has a redshift of <span class="math-container">$z=11.1$</span> and hence a distance of just over <span class="math-container">$d=32$</span> billion lightyears (Glyr). The volume inside the sphere with us in the center and GN-z11 on the surface is <span class="math-container">$V = 4\pi d^3/3 \simeq 140\,000\,\mathrm{Glyr}^3$</span>.</p>
<h3>How far will James Webb see?</h3>
<p>Predicting the redshift record for James Webb is not easy, since it depends on the unknown physical conditions of even younger galaxies. The important quantity is their (surface) brightness which depends not only on intrinsic properties such as their star formation rate, dustiness, and compactness, but also on the properties of the intergalactic medium, in particular to which degree it is (re-)ionized and hence able to transmit the light from the galaxies. Moreover, we also don't know how many there, so estimates rely on extrapolating their distributions of luminosities (luminosity functions) from lower redshifts.</p>
<p>Rather conservative predictions for Webb's redshift record are around <span class="math-container">$z\simeq13\text{–}16$</span>
(<a href="https://ui.adsabs.harvard.edu/abs/2016MNRAS.455.2101M" rel="noreferrer">Mashian et al. 2016</a>;
<a href="https://ui.adsabs.harvard.edu/abs/2018ApJS..236...33W" rel="noreferrer">Williams et al. 2018</a>;
<a href="https://ui.adsabs.harvard.edu/abs/2019ApJ...873...96M" rel="noreferrer">Mahler et al. 2019</a>;
<a href="https://ui.adsabs.harvard.edu/abs/2020MNRAS.499.5702B" rel="noreferrer">Behroozi et al. 2020</a>), corresponding to an age of the Universe of 250–300 million years after the Big Bang (whereas GN-z11 is seen ~400 Myr after the BB), and a distance of 33–34.5 Glyr.</p>
<p>These estimates hence correspond to volumes of <span class="math-container">$\simeq 150\,000\text{–}170\,000\,\mathrm{Glyr}^3$</span>, i.e. an increase of up to roughly 10–25%.</p>
<p>However, sometimes we're lucky and line up with a massive cluster of galaxies acting as a gravitational lens which magnifies the light from distant background sources by factors of tens, hundreds, or even thousands. This may potentially allow James Webb to see some of the very first galaxies, predicted to have formed at <span class="math-container">$z\sim20\text{–}30$</span>, 100–200 Myr after BB. I don't know of any peer-reviewed papers doing any serious estimates, but NASA routinely cites Webb's predicted record as &quot;<em>200 (or 250) Myr, possibly even 100 Myr</em>&quot; af the BB (e.g. <a href="https://webb.nasa.gov/content/science/firstLight.html" rel="noreferrer">here</a>). If we really discover a galaxy 100 Myr after the BB, that would correspond to <span class="math-container">$z=30$</span>, and a distance of 38 Glyr, i.e. a volume of <span class="math-container">$225\,000\,\mathrm{Glyr}^3$</span> which is 60% larger than our current &quot;observable-by-us Universe&quot;.</p>
<p>The extension of our probed volume may not seem like a lot. A better way to understand the significance of this is to think about the age of the Universe at that time: It is likely that we will make the unknown epoch of the Universe half, or maybe even a quarter, of today's value.</p>
<p>For comparison, the volume inside the region from which the cosmic microwave background was emitted at <span class="math-container">$z=1100$</span> is <span class="math-container">$390\,000\,\mathrm{Glyr}^3$</span>, while the volume of the (theoretically) observable Universe is <span class="math-container">$413\,000\,\mathrm{Glyr}^3$</span>.</p>
<p>The figure below is pretty much to scale:</p>
<p><a href="https://i.sstatic.net/D6z8c.jpg" rel="noreferrer"><img src="https://i.sstatic.net/D6z8c.jpg" alt="obs-uni" /></a></p>

CC BY-SA 4.0
2022-04-03T11:30:52.523Z
"The figure below is pretty much to scale:" - apart from the size and density of galaxies which is vastly out of scale ;-)
asdfex
CC BY-SA 4.0
2022-04-03T19:56:19.937Z
@asdfex AND... does not show home of LGM
BradV
CC BY-SA 4.0
2022-04-03T22:09:36.540Z
@asdfex Okay, the galaxies aren't, but the _telescopes_ are indeed 4 billion lightyears long ;-)
pela
CC BY-SA 4.0
2022-04-04T13:46:05.250Z
[Dr Becky just explained](https://www.youtube.com/shorts/wVbf4dyieYc) the gravitational lens technique you mentioned, which [Hubble used to spot the most distant star ever seen](https://hubblesite.org/contents/news-releases/2022/news-2022-003).
Wyck
CC BY-SA 4.0
2022-04-27T09:54:06.703Z
Could you expand your answer to estimate approximately how the improvement in angular resolution and ability to pick up weak signals will affect how distant galaxies the telescope will be able to pick up? Supposedly there is no longer a linear relationship between redshift and distance/time so no matter how redshifted objects you pick up there needs to be no change in the estimate of time passed by since the big bang etc?
Agerhell
CC BY-SA 4.0
2022-04-27T09:58:08.597Z
There are claims of an object already found (believed to be a galaxy galaxy) found at a redshift of z=13.27 https://en.wikipedia.org/wiki/HD1_(galaxy)
Agerhell
CC BY-SA 4.0
2022-04-27T20:05:44.893Z
@Agerhell These are good questions, but a good answer will be quite involved, and unfortunately I won't have the time to go into this at the moment. The details can be found in the papers I cite, but perhaps you should ask a new question, so someone else can answer.
pela
CC BY-SA 4.0
2022-04-27T20:06:33.850Z
@Agerhell Regarding the z = 13 galaxy, it's a photometric redshift, i.e. not spectroscopically confirmed, so it doesn't count (yet) :)
pela
CC BY-SA 4.0
2023-04-11T17:15:36.187Z
JADES-GS-z13-0 seems confirmed with redshift 13.2 putting it at 325 million years from BB, d=33 Glyr.  This gives 'observable' increase of roughly 7.6% so far. And still no little green men.
BradV
CC BY-SA 4.0
2023-04-12T11:33:02.857Z
@BradV Mnyeah… The spectroscopic confirmation of JADES-GS-z13-0 isn't too convincing. But the Curtis-Lake / Robertson papers announced three others, of which JADES-GS-z11-0 at z ~ 11.6 looks convincing. But note that they're confirmed not from emission lines, but from the less precise Lyα break (and in the case of JADES-GS-z13-0 could well be a lower-z Balmer break). GN-z11 discussed above was confirmed in the same way, but recently had a "real" spectroscopic confirmation of z = 10.603 from multiple emission lines ([Bunker+ 23](https://arxiv.org/abs/2302.07256)).
pela
CC BY-SA 4.0
2024-05-31T10:10:30.420Z
@BradV [We're slowly approaching](https://cosmicdawn.dk/news/james-webb-discover-record-distant-galaxy-again/).
pela
CC BY-SA 4.0
2024-06-01T01:12:52.123Z
@pela thanks so much!
BradV
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2024-06-01T12:33:12.940Z
@BradV Stay tuned for more updates in the future ;-)
pela
CC BY-SA 4.0
2022-04-02T22:41:45.623Z
2022-04-02T22:46:47.223Z
2022-04-02T22:46:47.223Z
pela
<p>Right now, using all our various current means of observing, we can &quot;see&quot; a sphere of X diameter around us. Webb will increase that to Y diameter. So our observable volume will increase by some percent (Volume Y - Volume X) / Volume X.</p>
<p>I'm not sure I can rely on any values I find for X and Y using google searches.   As of April 2022 what is the diameter of what we can presently observe and what is the expectation for JWST?</p>
<p>ADDITION: my apologies for not having enough subject matter expertise to frame my question as well as it might have been. I was thinking along the lines of pela's response. With JWST having a better set of instruments etc our practical ability would have farther reach. I've known there were physics limits to what could ever be observed that could not be changed. the CMB is not the type of observation I had in mind when asking the question.</p>

CC BY-SA 4.0
2022-04-02T22:23:19.327Z
On what grounds do you presume that the observable universe should get bigger? Travel time and speed for light is the same, irrespective of wave length.
planetmaker
CC BY-SA 4.0
2022-04-02T22:44:28.200Z
I think the OP is referring to not the the _theoretically_ observable Universe, but the "_practically_ observable Universe of objects (i.e. not including the CMB)".
pela
CC BY-SA 4.0
2022-04-04T11:37:16.610Z
Considering OP explains that he is a layperson, I find it pretty easy to interpret this question as "how much larger will the sphere/volume of practically observable space in the wave length visible to JWST be" and to explain this interpretation in the answers... I find the question perfectly valid and understandable from the POV of someone who does not have much knowledge about these things. @JamesK
AnoE
<observable-universe><james-webb-space-telescope>
How much larger will the "observable by us" universe be when JWST becomes operational?
BradV
# How much larger will the "observable by us" universe be when JWST becomes operational?

(Asked by: username_0 on 2022-04-02)

Right now, using all our various current means of observing, we can "see" a sphere of X diameter around us. Webb will increase that to Y diameter. So our observable volume will increase by some percent (Volume Y - Volume X) / Volume X.

I'm not sure I can rely on any values I find for X and Y using google searches. As of April 2022 what is the diameter of what we can presently observe and what is the expectation for JWST?

ADDITION: my apologies for not having enough subject matter expertise to frame my question as well as it might have been. I was thinking along the lines of username_2's response. With JWST having a better set of instruments etc our practical ability would have farther reach. I've known there were physics limits to what could ever be observed that could not be changed. the CMB is not the type of observation I had in mind when asking the question.

**Tags:** observable-universe, james-webb-space-telescope

> **Comments:**
> **username_1**: On what grounds do you presume that the observable universe should get bigger? Travel time and speed for light is the same, irrespective of wave length.  
> **username_2**: I think the OP is referring to not the the _theoretically_ observable Universe, but the "_practically_ observable Universe of objects (i.e. not including the CMB)".  
> **username_3**: Considering OP explains that he is a layperson, I find it pretty easy to interpret this question as "how much larger will the sphere/volume of practically observable space in the wave length visible to JWST be" and to explain this interpretation in the answers... I find the question perfectly valid and understandable from the POV of someone who does not have much knowledge about these things. @JamesK  

---

## 2 answers

### Answer by username_2 on 2022-04-02. Score: 36 | Accepted answer

**tl;dr** Conservatively 10%, realistically 25%, optimistically 60%.

---

I assume that by the "observable-by-us Universe", you mean not the *theoretically* observable Universe, which is given by the distance light has had the time to travel since the Big Bang, but the part of the Universe where we may practically see galaxies and other objects, not including the cosmic microwave background.

### Current redshift record

The currently most distant, spectroscopically confirmed object is the galaxy [GN-z11](https://en.wikipedia.org/wiki/GN-z11) ([Oesch et al. 2016](https://ui.adsabs.harvard.edu/abs/2016ApJ...819..129O)), which has a redshift of $z=11.1$ and hence a distance of just over $d=32$ billion lightyears (Glyr). The volume inside the sphere with us in the center and GN-z11 on the surface is $V = 4\pi d^3/3 \simeq 140\,000\,\mathrm{Glyr}^3$.

### How far will James Webb see?

Predicting the redshift record for James Webb is not easy, since it depends on the unknown physical conditions of even younger galaxies. The important quantity is their (surface) brightness which depends not only on intrinsic properties such as their star formation rate, dustiness, and compactness, but also on the properties of the intergalactic medium, in particular to which degree it is (re-)ionized and hence able to transmit the light from the galaxies. Moreover, we also don't know how many there, so estimates rely on extrapolating their distributions of luminosities (luminosity functions) from lower redshifts.

Rather conservative predictions for Webb's redshift record are around $z\simeq13\text{–}16$
([Mashian et al. 2016](https://ui.adsabs.harvard.edu/abs/2016MNRAS.455.2101M);
[Williams et al. 2018](https://ui.adsabs.harvard.edu/abs/2018ApJS..236...33W);
[Mahler et al. 2019](https://ui.adsabs.harvard.edu/abs/2019ApJ...873...96M);
[Behroozi et al. 2020](https://ui.adsabs.harvard.edu/abs/2020MNRAS.499.5702B)), corresponding to an age of the Universe of 250–300 million years after the Big Bang (whereas GN-z11 is seen ~400 Myr after the BB), and a distance of 33–34.5 Glyr.

These estimates hence correspond to volumes of $\simeq 150\,000\text{–}170\,000\,\mathrm{Glyr}^3$, i.e. an increase of up to roughly 10–25%.

However, sometimes we're lucky and line up with a massive cluster of galaxies acting as a gravitational lens which magnifies the light from distant background sources by factors of tens, hundreds, or even thousands. This may potentially allow James Webb to see some of the very first galaxies, predicted to have formed at $z\sim20\text{–}30$, 100–200 Myr after BB. I don't know of any peer-reviewed papers doing any serious estimates, but NASA routinely cites Webb's predicted record as "*200 (or 250) Myr, possibly even 100 Myr*" af the BB (e.g. [here](https://webb.nasa.gov/content/science/firstLight.html)). If we really discover a galaxy 100 Myr after the BB, that would correspond to $z=30$, and a distance of 38 Glyr, i.e. a volume of $225\,000\,\mathrm{Glyr}^3$ which is 60% larger than our current "observable-by-us Universe".

The extension of our probed volume may not seem like a lot. A better way to understand the significance of this is to think about the age of the Universe at that time: It is likely that we will make the unknown epoch of the Universe half, or maybe even a quarter, of today's value.

For comparison, the volume inside the region from which the cosmic microwave background was emitted at $z=1100$ is $390\,000\,\mathrm{Glyr}^3$, while the volume of the (theoretically) observable Universe is $413\,000\,\mathrm{Glyr}^3$.

The figure below is pretty much to scale:

[![obs-uni](https://i.sstatic.net/D6z8c.jpg)](https://i.sstatic.net/D6z8c.jpg)

> **Comments:**
> **username_5**: "The figure below is pretty much to scale:" - apart from the size and density of galaxies which is vastly out of scale ;-)  
> **username_0**: @username_5 AND... does not show home of LGM  
> **username_2**: @username_5 Okay, the galaxies aren't, but the _telescopes_ are indeed 4 billion lightyears long ;-)  
> **username_6**: [Dr Becky just explained](https://www.youtube.com/shorts/wVbf4dyieYc) the gravitational lens technique you mentioned, which [Hubble used to spot the most distant star ever seen](https://hubblesite.org/contents/news-releases/2022/news-2022-003).  
> **username_4**: Could you expand your answer to estimate approximately how the improvement in angular resolution and ability to pick up weak signals will affect how distant galaxies the telescope will be able to pick up? Supposedly there is no longer a linear relationship between redshift and distance/time so no matter how redshifted objects you pick up there needs to be no change in the estimate of time passed by since the big bang etc?  
> **username_4**: There are claims of an object already found (believed to be a galaxy galaxy) found at a redshift of z=13.27 https://en.wikipedia.org/wiki/HD1_(galaxy)  
> **username_2**: @username_4 These are good questions, but a good answer will be quite involved, and unfortunately I won't have the time to go into this at the moment. The details can be found in the papers I cite, but perhaps you should ask a new question, so someone else can answer.  
> **username_2**: @username_4 Regarding the z = 13 galaxy, it's a photometric redshift, i.e. not spectroscopically confirmed, so it doesn't count (yet) :)  
> **username_0**: JADES-GS-z13-0 seems confirmed with redshift 13.2 putting it at 325 million years from BB, d=33 Glyr.  This gives 'observable' increase of roughly 7.6% so far. And still no little green men.  
> **username_2**: @username_0 Mnyeah… The spectroscopic confirmation of JADES-GS-z13-0 isn't too convincing. But the Curtis-Lake / Robertson papers announced three others, of which JADES-GS-z11-0 at z ~ 11.6 looks convincing. But note that they're confirmed not from emission lines, but from the less precise Lyα break (and in the case of JADES-GS-z13-0 could well be a lower-z Balmer break). GN-z11 discussed above was confirmed in the same way, but recently had a "real" spectroscopic confirmation of z = 10.603 from multiple emission lines ([Bunker+ 23](https://arxiv.org/abs/2302.07256)).  
> **username_2**: @username_0 [We're slowly approaching](https://cosmicdawn.dk/news/james-webb-discover-record-distant-galaxy-again/).  
> **username_0**: @username_2 thanks so much!  
> **username_2**: @username_0 Stay tuned for more updates in the future ;-)  

---

### Answer by username_4 on 2022-09-28. Score: 0

Not by very much. You can use an [online calculator](https://www.astro.ucla.edu/%7Ewright/CosmoCalc.html) to convert redshift to distance. Assuming that a redshift of z=11.1 was the most redshifted object found before James Webb, this corresponds to a light travel time of 13.306 billion light years. If Webb wore to find an object at z=25, which is probably beyond what it is able to achieve, this would correspond to a light travel time distance of 13.59 billion light years.

You can then easily calculate (13.59/13.306)^3 and end up with an increase in observed volume of about about 6,5 percent.

Now if James Webb wore to find a galaxy with an infinite redshift, which it obviously will not, this would correspont to a light travel distance of 13.72 billion years. You can do the math (13.72/13.306)^3) and end up with an increase in volume of about 9.6 percent.

**Answer:** Even if James Webb was to find an object with a redshift of z=25, which is more than double the pre James Webb value, the observable volume will just increase with about 6.5 percent. This is due to the fact that using the current model of converting redshift to distance at high redshifts the distance to the point of emission of the observed light will vary very slowly with increase in redshift.

> **Comments:**
> **username_2**: Sorry, this answer is not correct. You're calculating a "volume of time", which would only make sense if the Universe didn't expand, in which case it would be equivalent to the real volume.  

---

