I hadn’t intended to return so quickly to the issue of high-redshift galaxies, but SPT0418-47 jibes nicely with last week’s piece on 13.5 billion year old galaxies as studied by Penn State’s Joel Leja and colleagues. In that case, the issue was the apparent maturity of these objects at such an early age in the universe.
Today’s work, reported in a paper in The Astrophysical Journal Letters, comes from a team led by Bo Peng at Cornell University. It too uses JWST data, in this case targeting a previously unseen galaxy the instrument picked out of the foreground light of galaxy SPT0418-47. In both cases, we’re seeing data that challenge conventional understanding of conditions in this remote era. This is evidence, but of what? Are we wrong about the basics of galaxy formation? Do we need to recalibrate the models we use to understand astrophysics at high-redshift?
SPT0418-47 is the galaxy JWST was being used to study, an intriguing subject in its own right. This is an infant galaxy still forming stars in the early universe, observable through the bending of its light by a foreground galaxy to form an Einstein ring. In other words, we’re seeing gravitational lensing at work here, magnifying the young galaxy’s light, out of which information can be extracted about the primordial object. And within that light, astronomers have now found a second galaxy which manifested itself in two places in the ring.
Image: This is Figure 1 from the paper. Caption: Figure 1. Left: Hα pseudo-narrowband image of the SPT0418 system, averaged over the channels including the Hα emission in the original spectral cube. The strongly lensed ring and the two newly discovered sources (SE-1 and SE-2) are highlighted by a red annulus and gray and black ellipses, marked as “A,” “B,” and “C,” respectively. The lensing galaxy is shown as the central bright source. The 835 μm continuum is plotted as the thin black contours, with the levels 2, 4, 8, 16, 32 × σ where σ = 56.7 μJy beam −1. Right: the spectra of the three sources integrated over the regions highlighted in the left panel, using the same color scheme. The spectrum for the ring is scaled by a factor of 0.1 for clarity. The small black bar below the Hα line marks the wavelength coverage of the pseudo-narrowband image. The potentially detected lines are marked by vertical dotted lines. Credit: The Astrophysical Journal Letters (2023). DOI: 10.3847/2041-8213/acb59c.
ALMA (the Atacama Large Millimeter/submillimeter Array) data could do no more than hint at the background galaxy’s existence, but working with spectral data from JWST’s NIRSpec instrument, Peng discovered the new light source within the Einstein ring. The unexpected find was a galaxy being gravitationally lensed by the same foreground galaxy that had made SPT0418-47 available for study, though considerably fainter.
What stands out here is the analysis of the chemical composition of the new galaxy’s light, which shows strong emission lines from hydrogen, nitrogen and sulfur atoms whose redshift showed the object to be about 10 percent of the age of the universe. The new galaxy, dubbed SPT0418-SE, appears to be close enough to SPT0418-47 that the two galaxies will interact with each other, making the duo a case study for galactic mergers. All of which is helpful, but here again we run into a fascinating problem. The newly discovered galaxy shows levels of metallicity comparable to our Sun.
It’s a conundrum. The Sun drew on earlier stellar generations to build up elements heavier than helium and hydrogen, and the Sun is roughly 4.6 billion years old. Amit Vishwas (Cornell Center for Astrophysics and Planetary Sciences) is second author on the paper:
“We are seeing the leftovers of at least a couple of generations of stars having lived and died within the first billion years of the universe’s existence, which is not what we typically see. We speculate that the process of forming stars in these galaxies must have been very efficient and started very early in the universe, particularly to explain the measured abundance of nitrogen relative to oxygen, as this ratio is a reliable measure of how many generations of stars have lived and died.”
But let’s turn back a minute, for we’re looking at two early galaxies, and it’s intriguing that SPT0418-47, the first of these, shows its own anomalies. Data from ALMA allow astronomers to see that although 12 billion years old, this object has a more mature structure than would be expected. No spiral arms are apparent, but a rotating disk and bulge are found, with stars packed tightly around the galactic center. Simona Vegetti (Max Planck Institute for Astrophysics), co-author on the 2020 paper on SPT0418-47 (citation below), had this to say three years ago:
“What we found was quite puzzling; despite forming stars at a high rate, and therefore being the site of highly energetic processes, SPT0418-47 is the most well-ordered galaxy disc ever observed in the early Universe. This result is quite unexpected and has important implications for how we think galaxies evolve.”
Image: Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, have revealed an extremely distant and therefore very young galaxy that looks surprisingly like our Milky Way. The galaxy is so far away its light has taken more than 12 billion years to reach us: we see it as it was when the Universe was just 1.4 billion years old. It is also surprisingly unchaotic, contradicting theories that all galaxies in the early Universe were turbulent and unstable. This unexpected discovery challenges our understanding of how galaxies form, giving new insights into the past of our Universe. Credit: Rizzo et al./European Southern Observatory.
So the new galaxy, SPT0418-SE, adds to earlier evidence that the early universe was considerably less chaotic than we once thought. The new paper summarizes the issue with reference to the unexpectedly strong emission lines found in the data:
This spectroscopic study of a z > 4 galaxy opens up many questions, including the spatial arrangement and stellar/gas/metallicity distribution of the companion; the merging hypothesis of SPT0418-47; the dark-matter halo of the system; the overdensity of this potentially crowded field; reconciling the relatively high chemical abundances with the short formation time and the moderate stellar mass for the whole system; and interpreting the small [N ii] 122 and 205 μm luminosities in the context of either a soft radiation field and/or a high N/O.
But again that note of high-redshift caution that I mentioned last week:
We attempt to reconcile the high metallicity in this system by invoking early onset of star formation with continuous high star-forming efficiency or by suggesting that optical strong line diagnostics need revision at high redshift. We suggest that SPT0418-47 resides in a massive dark-matter halo with yet-to-be-discovered neighbors.
Clearly scientists will be looking hard at how high-redshift targets are interpreted even as they continue to hypothesize about astrophysical mechanisms and star formation efficiency to explain seemingly mature objects at this early era. The game is afoot, as Sherlock Holmes used to say, and we’re a long way from reaching firm conclusions. The data are going to start coming fast and furious as we keep mining JWST and using ALMA to examine the universe in this early stage, as witness the image below, which I found just this morning. It shows us another remarkable object.
Image: The radio telescope array ALMA has pin-pointed the exact cosmic age of a distant JWST-identified galaxy, GHZ2/GLASS-z12, at 367 million years after the Big Bang. ALMA’s deep spectroscopic observations revealed a spectral emission line associated with ionized Oxygen near the galaxy, which has been shifted in its observed frequency due to the expansion of the Universe since the line was emitted. This observation confirms that the JWST is able to look out to record distances, and heralds a leap in our ability to understand the formation of the earliest galaxies in the Universe. Credit: NASA / ESA / CSA / T. Treu, UCLA / NAOJ / T. Bakx, Nagoya U.
The paper is Bo Peng et al., “Discovery of a Dusty, Chemically Mature Companion to a z ∼ 4 Starburst Galaxy in JWST ERS Data,” The Astrophysical Journal Letters 944 No. 2 L36 (17 February 2023). Full text. The paper on SPT0418-47 is Rizzo et al., “A dynamically cold disk galaxy in the early Universe,” Nature 584 (12 August 2020), pp. 201–204. Abstract. The GHZ2/GLASS-z12 paper is Bakx et al., “Deep ALMA redshift search of a z 12 GLASS-JWST galaxy candidate,” Monthly Notices of the Royal Astronomical Society Volume 519, Issue (4 March 2023), pp. 5076–5085 (abstract).
Is there any possibility at all that the light from these distant galaxies is being altered by the intergalactic medium, adding other elements in the spectrum and being further redshifted, increasing its apparent distance and age?
This is precisely the theory Eric Lerner (of focus fusion efforts: LPPfusion.com) has espoused for decades: that massive plasma filaments are interacting with light to produce this effect, as well as what we see as 3-degree background radiation, and are interacting with gas within galaxies to produce the velocity anomalies that we have attributed to dark matter.
The observed galaxies are only weird if we suppose that they formed in an early universe. If one supposes a much older, non-expanding universe, the galaxies look as we would expect: like ours
Webb—the last hope of steady staters
A. T. ,
The effect you speak of, I believe ( wrong thing to say?), is associated with the 21 centimeter line of hydrogen. It has been used to map inter galactic clouds between here and quasar sources deep in space. In the radio realm though, it would be a sequence of peaks less and less offset by cosmic red shift.
For all practical purposes, assuming an intial population of metal poor stars, there is possibility of very massive, quick burning first generation stars that enriched the medium quickly. Overabundant due to some quirk of an early galaxy distinct from a Milky Way. If that is not the case, then there might be something about early universe physical conditions conducive to metallicity. O stars and worse fueling fire cracker supernovas?
The big problem here is that nobody wants to acknowledge the obvious: The supposed “big bang” never happened. The discovery of an old galaxy comparable to our own Milky Way just 600 million years after the supposed “bang” settles the question.
This galaxy, 1.4Gy after the supposed “bang” has a chemical composition like our own, what is completely impossible if the universe “started” just 1.4Gy earlier.
The solidity of star formation theories is questioned, the galaxy formation theories are thrown overboard, but the big OBVIOUS thing is not done:
THERE WASN’T ANY BIG BANG!
The whole of the cosmology edifice is destroyed, but some people continue to try to deny the obvious. It is time to go on and
1) The red-shift is NOT the consequence of a Doppler effect, there was no big bang. What is the red-shift then? Alternative explanations are needed.
2) The CMB is not the consequence of any big bang. What is it? Or is just the background NOISE of all the galaxies so far away from us that their light is red-shifted beyond recognition?
The whole edifice of cosmology is broken. But do not cry.
Three thousand years ago, Indian researchers arrived at the conclusion that the universe was resting on four elephants, in the four cardinal points. That was cosmology THEN. It didn’t work well. The “big bang” will join those theories into the enormous trash can of failed cosmologies.
jacob
“Indian researchers arrived at the conclusion that the universe was resting on four elephants”
Of course not! I thought everyone knew that it’s resting on a giant tortoise.
And then another tortoise, and so on…
That’s a mighty tall stack of tortoises. In the interests of scientific inquiry we must remain open to the possibility of an elephant being present deep down, beyond the range of our instruments.
No,no,no, it turtles all the way down to a plank turtle !
In the familiar illustration (see Wikipedia, “World Elephant”) there are both elephants and turtles. The idea was really no more outlandish than Greeks writing of Titans, and we must be careful this isn’t taken to belittle India or come into unnecessary conflict with religion. Tracing back to a major original source (also in that Wikipedia article: https://www.valmiki.iitk.ac.in
/sloka?field_kanda_tid=1&language=dv&field_sarga_value=40 ) we see that the World Elephants are mentioned in the context of a story where the 60,000 sons of Sagara are annihilated to ashes by a sage saying “H’m”, so I suspect it wasn’t first published in a scientific journal.
Let’s not forget that there are many metal-poor small galaxies at high redshift as theory predicts. ( https://arxiv.org/abs/2212.04568 ) This is just one curious case of an old galaxy in a young universe. Given the malleable nature of spacetime this should be interesting but not terribly surprising. After all, it hasn’t been long since people were debating whether the universe was open or closed, where by closed people would say the entire universe would be like a giant black hole. Could part of the cosmos be at such a low gravitational potential energy relative to the rest that light from an old galaxy looks redshifted? Could this anomaly be something local, like the gravitational lens affecting this object was dragging spacetime away from us and the light from a nearer object had a very long journey? Or could it be something truly weird, like the Big Bang or cosmic inflation happening at different times in different places? JWST is looking almost to the edge of the observable universe – I think some of these galaxies may never have been able to see each other at all, so in a sense it is seeing more than one ‘universe’.
Read and I mean read all of Halton Arps books on quasars and galaxies being ejected from the cores of galaxies and you find that it all fits. Collaboration have imaged a jet in the heart of the nearby radio galaxy Centaurus A. https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQlk1yf2o-wWLD2FyXYMnGYxHzHkAkKcnN8xw&usqp=CAU
Centaurus A is the nearest quasars and has ejected thousands of galaxies from it’s core. New matter new redshift is what they are seeing.
I infer from the indignant tone of your contribution that you are are convinced that the entrenched cosmological establishment is desperate to maintain the current orthodoxy of an expanding universe evolving from some primordial Big Bang. Presumably, these ultra-conservative scientists are determined to preserve current, incorrect theories in order to promote their funding and their careers.
I believe just the opposite is the case. The one way to guarantee to establish your reputation in science is to help demolish an established but mistaken paradigm and replace it with another. The system is successful because there is always an incentive to question the old, and if possible, replace it with the new. Scientists LOVE contradictions and inconsistencies in new data, Its job security for them, and a potential spot in the history books. The system is not always successful, and sometimes leads to blind alleys, but for the most part it works.
You need not invoke Copernicus or Darwin, recent science is full of examples. The number of human chromosomes wasn’t correctly determined until 1956, continental drift and plate tectonics was rejected by geologists until the 1960s, and when I was an astronomy student in 1964, I still favored the Steady State Theory, and that Martian vegetation followed summer melt water from the poles. Clearly, a universe with a singular birth, evolving to an eventual death, seemed too religiously convenient to be true. An unchanging and utterly homogeneous (in both space and time) universe was more acceptable to my prejudices at the time. But the detection of the CBR proved me wrong. I accepted it. So maybe I’m wrong again. So what? Show me the data and maybe I’ll accept that too. The universe is under no obligation to conform to our philosophical preferences.
Eventually, the weight of evidence sets us straight. Today, a new set of observations at the very limit of the reach of our telescopes questions the established orthodoxy. Fear not, it won’t be long before more data evaluated by the scientific establishment will settle the question once and for all. And if we’re lucky, even more irreconcilable mysteries will be revealed. And if we’re really lucky, some issues will never be settled once and for all.
I don’t know the answer to this latest Webb puzzle. My guess (and its only a guess) is that the apparent contradiction is either an experimental anomaly, or some misconceptions as to conditions in the early universe. Perhaps our major cosmological model is completely wrong (unlikely, but it can’t be ruled out). But we should not be throwing out a long-lasting and multiply confirmed theory on the strength of one observation at the very limit of our instrumental capability. We need more data, and more analysis.
There are no ultimate Truths, and no sinister conspiracies. Save that for politics and religion.
I am not an astrophysicist, but I do know that MOND theorists had predicted this result years ago. Under MOND, galaxies grow much more quickly than under the currently orthodox lambda-CDM theories, and would be expected to be approximately full size in the time range of the galaxies studied by JWST.
The answer to that Alex Tolley is No. The wavelength of light is very red shifted, so we know it must be from that galaxy. Oxygen in galaxies that early would certainly put a strain our estimation of the age of our universe. If we consider that our universe is older than predicted or thought, then there is no conundrum and no need to rethink how galaxies form.
Do not underestimate how much “let there be light” influences conclusions.
Nay, from this result it looks like the Galactic AC found a way to reverse entropy on its own without the need for further studies. :)
[ http://www.thelastquestion.net/ ]
When the manifest universe degrades into absence of manifestation, o the persisting Cosmic Consciousness and Chaos, Purusha & Prakriti generate another universe.
“ALMA’s deep spectroscopic observations revealed a spectral emission line associated with ionized Oxygen near the galaxy, which has been shifted in its observed frequency due to the expansion of the Universe since the line was emitted.”
Oxygen ?! A rather complicated element to be present in the early Universe, don’t u think ?
Stars below the 8 solar mass limit which could produce oxygen white dwarfs would have had enough time to evolve into them so long as they are higher up on the mass scale.
According to Sabine Hossenfelder, this was a prediction of Modified Newtonian Dynamics that JWST could find evidence for.
https://www.youtube.com/watch?v=h6DhWQzYuuk
Modified Newtonian Dynamics is pure Bull….
Perhaps Modified Einsteinian Dynamics…Even Einstein’s famous equations can’t resolve the gravity issue, only on large scales.
Modified Einsteinian Dynamics is pure Bull…. General and Special relativity are first principles and will never be modified. There is just too much physics and physical evidence to support it. The same is true of Newton’s law of universal gravitation and inverse square law.
Relativity and Quantum theory does not equate, therefore both must be modified to account for the physical world we live in, so not so bull… And we don’t know how much dark matter is influencing the local gravity either as we can’t observe it so we will all have to wait for new theory of everything.
“…. General and Special relativity are first principles and will never be modified.”
Uh, ever hear of quantum entanglement ? entangled states are suspected to communicate via collapse with infinite velocity
Its not too surprising that unexpected pockets of “metals” may be detected in the earliest galaxies. The current wisdom is that galactic evolution and stellar formation was substantially different in the early universe, that conditions were more turbulent, the chemistry was mostly hydrogen, etc.
But if the formation of supermassive stars was more frequent soon after the big bang, its not too surprising that as these stars quickly evolved, the creation of the heavier elements and their subsequent distribution
into the interstellar medium my have been much more accelerated than it is today. In other words, even though the early universe was still mostly hydrogen and helium, quickly forming and exploding massive supergiants may have been dumping large quantities of metals
into surrounding pockets of local space. Maybe this is what we are detecting, small amounts of very hot fusion products glowing across the cosmos, their light over-represented in our observations here, today.
A thorough survey of many very old galaxies will have to be conducted to sort this out, always keeping in mind that spectroscopy is a qualitative, not quantitative science. And it will involve the teasing of data from very faint, highly red-shifted light.
Isn’t the other issue that the galaxies are large rather than small at this early age that is not predicted by models of galaxy formation?
If the redshift could be explained by the velocity that is not due to expansion, that may be a more parsimonious explanation.
I expect this will be resolved by more observations. Of not, models of the early universe will have to be modidied.
The current wisdom is that conditions in the early universe favored smaller galaxies and bigger stars, wither due to the higher mass density of space, or the lower metallicity of the ISM, is not clear. And, of course, the role of dark matter, if any, must be considered as well.
But if the faster evolution of more massive stars returns more metals, faster, to the ISM, through supernovae and planetary nebulae outgassing, then our models may have to be adjusted. Are we seeing a trend here, or just a minor anomaly exaggerated by selection effects acting on sparse observations?
Unexpected results from a powerful new telescope are to be expected. That’s why we build them! But I hesitate questioning the current models outright on the basis of such spotty evidence. The possibility that all our theoretical foundations of cosmology are dead wrong cannot be ruled out; heaven knows it has happened before! But there is some value to the conservative approach here. The current world view is established and accepted, and has survived multiple attempts to dislodge it. It deserves our loyalty, at least until the heavy weight of evidence can be properly marshalled against it.
If one could look far enough afield/back in time, one should approach the singularity of the Big Bang. An unimaginable density and mass, and perhaps also gravitational force (and consequent redshift?). How much of such features might be seen at the present limits of the most powerful telescopes?
And what would there be of the point singularity smeared into an infinite shell just beyond any approach to it?
Sounds like the boundary replacing Hawking’s ‘no boundary.’
“Hawking’s earlier ‘no boundary theory’ predicted that if you go back in time to the beginning of the universe, the universe shrinks and closes off like a sphere, but this new theory represents a step away from the earlier work. “Now we’re saying that there is a boundary in our past,” said Hertog.”
https://scitechdaily.com/constraining-the-multiverse-stephen-hawkings-final-theory-about-the-big-bang/
Well, at the very least, the observation is an inconsistency that raises eyebrows as soon as it is read. But there is a big “on the other hand” too. This is an exception to a larger rule of “observation” based on red shifts.
With a sampling of one, the Andromeda Galaxy flies toward us ( relatively) against the predictions of Hubble’s Law. Hubble’s Law appears to apply rather well overall though.
The first hypothesis that comes to mind I don’t think will work very well either – and that is that the light was bent somehow from a more local source. Light can be shifted to the red from passage close to a massive object. That would be the result of conditions between here and there.
On the other hand, the nature of “inertia” is a stumbling block in General Relativity. If it is a component of dynamics that is based on the distribution of mass, then I have to wonder whether physical behaviors would remain constant over time. The believers in such iinertia, I would often ask, what would you expect to see if you look into distant space and see a more compact universe? Well, perhaps we just did.
Perusing the comments made on this article, I decided to try and clarify certain points. None of this is speculation, just an attempt to put it into a broader context.
No structure can form in a perfectly homogeneous universe. No nebulae, no galaxies, no stars. There must be inhomogeneity to avoid a universe that is little more than a low density cloud of cold H and He atoms and molecules.
The surface of last scattering constrains the degree of homogeneity when the universe was about 300,000 years old. That’s what the CMBR observations tell us, with a pretty good degree of certainty. What came before is speculative and can only be modeled, so far. What came after is largely observable. Whether the inhomogeneity that we see was there from the beginning or was due to physical processes before or after that time is difficult to determine.
These earliest stars and galaxies are closely associated with homogeneity measurements of the CMBR because they arise not long after (astronomically speaking!). The conclusions of this paper are not dependent on whether the universe at that epoch is the same as the universe near our time and place within it. This raises the possibility that the CMBR is not as good a measure of homogeneity as we’d like or the distribution of matter (of all species) and interactions is not as is expected.
Of course this is only valid if the conclusions of this study are valid, and it’s too early to say. However, this is not the only evidence of fairly large departures from homogeneity in the universe. I was reminded of that when I accidentally bumped into this article today:
https://www.bbc.com/future/article/20230302-the-giant-arcs-that-may-dwarf-everything-in-the-cosmos
This paper (and the discussion about it) is interesting, but hardly universe shattering. It is raising important questions about our observations and models that will hopefully lead to a deeper understanding. Or it’ll lead to nothing at all. Should its conclusions stand, nothing momentous will happen. Apples will continue not to fall upward. Gathering reliable data from far, far away and long, long ago isn’t easy.
I’ll have to admit you guys just love the big bang, to the extent of making up fantasy ideas to keep it alive, but as with any Dogma new data and new ideas must overtake it…
The giant arcs that may dwarf everything in the cosmos.
https://www.bbc.com/future/article/20230302-the-giant-arcs-that-may-dwarf-everything-in-the-cosmos
“According to Lopez’s article, it is extremely unlikely (a probability of just 0.0003 per cent) that such a large structure could have arisen by chance. It suggests that it may have formed due to something in the natural physics of the Universe that we currently don’t account for. Her findings directly challenge a central facet of the standard cosmological model – the best explanation we have for how the Universe started and evolved.
This facet, known as the cosmological principle, states that on a large scale, the Universe should look roughly the same everywhere, no matter your position or the direction in which you are looking.”
Halton Arp’s little bangs explains all these problems. The Cosmologist have to make dark fantasies about the universe to cover their ineptitude and closed minded bias.
Can we imagine the very early universe containing all matter that we now see, but constrained in a much smaller volume? In this matter – dense, swirling cauldron, mean distance separation matter (and dark matter) would be quite small, agglomeration highly encouraged; so much mass and energy present that gravity fields would strongly create galaxies?
In this environment, solar life times would be reduced, stars nearly adjacent, supernovas common; and have some have suggested, black holes created directly through the assistance of strong magnetic fields?
Is that possible? At the inception of the “big bang” wouldn’t that mean that all matter would be in a state of a singularity, i.e. the universe by definition would be a black hole but with an “event horizon” inside the radius of the speed of light? Isn’t it more likely that matter is created in the expansion until the density falls to a low enough value that independent aggregations can occur, creating the structures one sees in the CMB and the large-scale distributions of galaxies (and dark matter)?
No singularity and no event horizon. A singularity and a horizon imply that the universe is larger than what we can observe. That is, that there are other spacetimes than our own. Our cosmology is not dependent on whether they exist, or whether they are observable if they exist. It is an active area of research that has so far yielded very little.
I have always wondered if our current universe is just a collision between very, very large blackholes. As the event horizons cross over the smaller one explodes into the much larger one, in effect a big bang. The material expands and increasingly accelerates towards the larger blackholes centre. Who knows…
Isn’t the universe larger than we can observe? Given current expansion, galaxies will fall outside our observable region as the expansion will result in galaxies apparently moving away from us at over the speed of light. Isn’t the CMB the observable portion of the universe that we can see, which may not be the whole universe, especially if we are possibly just one bubble of many?
Cosmologist Brian Cox describes the origin of the universe (to a lay audience) as a speck in an energy ocean of spacetime that expanded into a small volume of energy during the inflation phase. If so, then the universe is larger than the original speck, even if it is unobservable.
Perhaps observable, at least at the beginning.
“He [Hawing] and Hertog laid out the mathematics needed to build a space probe that would be capable of detecting powerful gravitational waves created by multiple big bangs.”
https://www.cbc.ca/radio/asithappens/as-it-happens-monday-full-episode-1.4582515/stephen-hawking-s-final-theory-could-prove-the-existence-of-the-multiverse-1.4582520
By keeping my reply brief, I unintentionally overloaded the meaning which I imbued into the word “can”. There is a difference between what we observe and what we can observe. This is due to the rate of expansion and the surface (really a hyper-surface in 4d spacetime) of last scattering.
The mean free path of a photon was exceeding short before the universe cooled enough for electrons and protons to stick together to form neutral atoms. We see no photons from earlier than 300,000 years (age of universe). Because the universe is so exceeding flat and homogeneous, this event happens at almost the exact same time everywhere. The CMBR is from which the first photons traveled freely from that hyper-surface.
This is where our human perception runs into difficulty since we don’t easily grasp 4 dimensions and large-scale spacetime curvature. Hopefully this won’t cause too much confusion. My explanation may be a little clumsy even as I try to be clear. Blame me and not what I’m trying to explain!
The hyper-surface is not fixed, nor is it a fossil. Over time it is further away as photons from further positions of the hyper-surface catch up to us. That is to say, what we can observe is increasing. Also, due to the expansion, the CMBR is observed to cool as the amount of curved spacetime the photons have to “climb” increases. Energy conservation does not apply on cosmological scales, and, yes, that is consistent with general relativity.
What applies to the hyper-surface also applies to everything between it and us. Therefore more galaxies will be observed in the future. Of course, they will be young galaxies. The young galaxies we can observe now will have grown older, from our viewpoint.
Far into the future (I forget the estimated number), the curvature will become so high that we will no longer be able to observe further galaxies. That will be when the observed recession velocity is faster than the photons. The spacetime metric determines the value of ‘c’ but is itself not constrained (‘c’ is property of spacetime, not of photons).
So…what we observe is less than what we can observe. Stick around long enough and the observable universe will get larger, and eventually reach a limit assuming the expansion continues (but that’s another story).
That horizon of what we “can” observe is not an event horizon. The horizon is not unique since it is different at every point in the universe. The universe is not a black hole and there is/was no singularity. It is a limit to what we can observe due to cosmological spacetime curvature, because spacetime is expanding. The process may reverse but it probably won’t. The jury is still out on that.
What you quote from Brian Cox is one of many possibilities. Inflation remains a difficult hypothesis to test, and without that we don’t know if it’s true, even though it nicely explains why our universe (or our patch of it) is very flat (in 4D spacetime) and very homogeneous.
Clear as mud?
It’s a consequence of the fact that as we look outward we are necessarily looking back in time. So looking as far as possible means looking back to the first observable. As human beings living in a perceived here and now, we wonder what is ‘beyond’ the expanding boundary of our universe ‘now,’ not beyond its beginning. Assuming a negative curvature of infinite expansion we can imagine there is an asymptotic boundary beyond which a far flung fragment of our universe breaks away from any potential future observe-ability. It seems easier somehow imaging how a spacetime with positive curvature might channel the emanations from the early universe across the entire sky (e.g. visualising the expanding surface of an inflating balloon, with the CMB at the antipodal point to our observation). Trying to image how the expanding surface of a hyperbolic saddle might also scatter the CMB acros the entire sky defeats my attempts to visualise, unfortunately!
If the CMB ‘shell’ at last scattering was 1/1100 the size of the current universe then the background we observe today across the whole sky is a kind of optical illusion created by a curvature in spacetime not caused in the ‘here and now’ by gravity but rather by the expansion since the last scattering – which for must of that period was a positive spherical curvature overall. Seeing mature galaxies with red shifts suggestive that they formed so soon after that epoch… considering the higher density of the early universe, could gravitation be adding additional red-shifting to these galaxies, making them seem older than they are?
Certainly it’s possible simply because calculating z from instrument data is confounded by many factors. For example, is the spectroscopic data to calibrate emission lines all from the object of interest or “polluted” with emission from other sources in the same line of sight. For these weak and distant sources the challenge is greater. Without knowing their methods (and in any case I don’t have the relevant expertise) I can only trust that they, the referees and others in the process did their jobs. Now that the paper is out in the wild we may hear of quantitative alternative analyses (more than merely opinions!) in the coming weeks and months. It should prove interesting.
The universe may be sphere but all the matter and energy in the universe causes a local deformation flattening it, much like a penny sitting on a beach ball so it looks flat. Perhaps the red shifting is similar to a prism effect where light traveling through spacetime cause the light to spread out much like in a prism.
https://www.dkfindout.com/us/science/light/splitting-light/
Or an hyperbolic universe? If positive curvature can make a galaxy appear closer can negative curvature at the largest scale make one seem further away?
http://www.itspoa.com/itsadmin/Ll/LL.DE.asp?action=Paper_Information&id=1398&at=The%20Hyperbolic%20Universe%20Does%20Not%20Need%20Dark%20Energy&jn=Energy%20Research