Happy new year to those who observe the Gregorian calendar. I will write a post on the observations that test the predictions discussed last time. It has been over a quarter century since Bob Sanders correctly predicted that massive galaxies would form by z = 10, and three years since I reiterated that for what JWST would see on this blog. This is a testament to both the scientific method and the inefficiency of communication.
Here I provide links to some recent interviews on the subject. These are listed in chronological order, which happen to flow in order of increasing technical detail.
The first entry is from my colleague Federico Lelli. It is in Italian rather than English, but short and easy on the ears. If nothing else, appreciate that Dr. Lelli did this on the absence of sleep afforded a new father.
Next is an interview I did with EarthSky. I thought this went well, and should be reasonably accessible.
Next is Scientific Sense:
Most recently, there is the entry from the AAS Journal Author Series. These are based on papers published in the journals of the American Astronomical Society in which authors basically narrate their papers, so this goes through it at an appropriately high (ApJ) level.
We discuss the “little red dots” some, which touches on the issues of size evolution that were discussed in the comments previously. I won’t add to that here beyond noting again that the apparent size evolution is proportional to (1+z), in the sense that high redshift galaxies are apparently smaller than those of similar stellar mass locally. This (1+z) is the factor that relates the angular diameter distance of the Robsertson-Walker metric to that of Euclidean geometry. Consequently, we would not infer any size evolution if the geometry were Euclidean. It’s as if cosmology flunks the Tolman test. Weird.
There is a further element of mystery towards the end where the notion that “we don’t know why” comes up repeatedly. This is always true at some deep philosophical level, but it is also why we construct and test hypotheses. Why does MOND persistently make successful predictions that LCDM did not? Usually we say the reason why has to do with the successful hypothesis coming closer to the truth.
That’s it for now. There will be more to come as time permits.
If empirical evidence at galaxy level complexity already seems weird from the General Relativity (GR) point of view (without introducing an imaginary dark matter) it’s only natural to expect more weird observational facts when seeing them from a GR perspective at higher hierarchical levels and even more at “universe” scale complexity.
What’s really weird is to keep using GR beyond its apparent complexity level of applicability and not expect “weird” results.
Thanks.
In MOND, the gravitational potential in low-acceleration regions follows a logarithmic dependence but that obviously is not the case for GR.
In GR, cosmological redshift is attributed entirely to the metric expansion of space. In MOND, if the logarithmic potential influences large-scale dynamics, it could offer an alternative explanation for part of the observed redshift.
The long-range gravitational potential could create an additional contribution to the observed redshift, mimicking or modifying the effects of metric expansion.
MOND is a GR killer.
You mean gravitational redshift or blueshift? But isn’t the universe quite isotropic, except for the Hubble Void (leading to a little blueshift from outside the void)?
My bad, actually it’s redshift for going into the void. And it’s an interesting thought: the observed redshift at high redshift might also be caused by big gravity wells, rather than big outward velocity. Decreasing the inferred distance may be balanced with having less distance between observed galaxies, leading to big gravity wells and therefore also redshift. I do think though that below a0 this has very little effect.
But another funny fantasy thought: an object so far away that we can’t see it, perpendicular to the universe plane, but with so much gravity that it pulls on everything with force a0, might cause mond through the external field effect starting from an even smaller fundamental constant. Only in order to have a0 equal for everything: If light accelerates with a0 towards the centre of a sphere, that sphere has radius 7.5E23 km or 80 billion lightyears. That gives a positive curvature of 78 million lightyears deviation at 10 billion ly distance – but would that be observable with light also bending that way? Thanks Jeremy jr, your thought have taken me to an interesting speculation 🙂
Sorry, this speculation is nonsense I see now. I based it on a wrong interpretation of the EFE for g_ex > a0 > g_in, multiplying a0 with g_ex/a0 instead of G. Stupid mistake.
Hi Stacey, I enjoy all of your writings, and you’ve definitely improved my understanding on physics and astronomy. If I can me a most humble request, would you consider raising the volume on your mic for your interviews? Sorry if that’s a hassle, could also maybe request the recorder to adjust the gain so your volume is closer to theirs. It’s a small help to those of us who have to keep the volume down while listening.
Sorry if the volume was inadequate. I specifically asked each host if the sound was OK, and each said it was. I guess OK for them isn’t OK for everyone, but so far as I knew, we had it set right.
Is it only me who finds the gesticulation and the Ahas, Mhms and Indeeds by the host very distracting and unhelpful? Stacy’s presentation, on the other hand, is perfect.
I think you’ve put the argument for the scientific method about as well as it’s been put – at 5.05 in the AAAS journal video, you say: ‘what really matters is what we predict in advance of the observation – we are very skilled as theorists at explaining things after we know what it is we need to explain.’
That says a lot, it has underneath it the point that there are a lot of what I call ‘conceptual variables’ in cosmology. Not only do they allow people to explain things after the fact – I left cosmology for many years, after an initial look at it, as I felt there were too many alternative possibilities. I look for the underlying picture first, then try to get to the mathematics – I think we’ve reached a stage where two steps are needed. People are trying to find shortcuts to the step after next, searching through the mathematics, which I’d say we often can’t do any more. I’ve come back to it for several reasons, having finished the other areas of the theory – QM, time, gravity – including your good influence, and the recent importance of MOND and surrounding questions.
But it’s very worthwhile to point out how good we are at spinning explanations when we know the target. It underlines the major difference between MOND and DM, the importance of which isn’t always obvious.
I also emphasize this point because it sometimes seems to me that practicing scientists have forgotten that this is how science is supposed to work. We’ve been surprised so many times so often and had to tweak things after the fact that we come to think of that as normal rather than as a symptom of some deeper problem. Dan Baeckström notes this effect in the comments to the theory post – https://tritonstation.com/2024/12/20/on-the-timescale-for-galaxy-formation/
> Weird.
🤯 😃
Like you, Lerner is big on theories being successful if they make predictions that are successful.
There are also mature spiral galaxies at redshift z=5 comparable to the Milky Way:
https://arxiv.org/pdf/2412.13264
And so far, they fall on Tully-Fisher.
Hi Stacy. Good that you raised this evidence against expansion. There are more recent papers published in peer-reviewed journals that show there is no expansion.
Observations contradict galaxy size and Surface brightness predictions that are based on the expanding universe hypothesis
https://academic.oup.com/mnras/article/477/3/3185/4951333
UV surface brightness of galaxies from the local universe to z ~ 5
https://www.worldscientific.com/doi/abs/10.1142/S0218271814500588
With the galaxies that seem to fail on the Tully-Fisher relation, is the flat rotation speed faster than it should be. Are they at z = 5, or also at higher redshifts? Perhaps you can you say a bit more on that, or give a reference, thank you.
I hope to get to it in a future post. There is a section on it in the paper with references if you’re eager. In a nutshell, there is no clear evidence for deviation from or evolution of the Tully-Fisher relation up to z = 2.5. Beyond that, there are only a handful of anecdotal cases, so I wouldn’t make any claims about TF. But the known cases rotate fast, over 250 km/s; that’s a massive galaxy to exist early on.
I have a question about the difference betwen MOND and LCDM with respect to overall star metallicity at high z and the impact of that on the JWST data analysis (if there is one).
I see two scenarios – in the first one, also stars form earlier in MOND, not only large scale structure. This means that with MOND, we will have stars with higher metallicity compared to LCDM at, say, z=6.
In tje second scenario, stars form at about the same time in MOND and LCDM, but since large scale structure forms earlier in MOND, it will be much easier to “contaminate” the interstellar medium with metals as more stars are close together compared to LCDM. That means, again, a higher star metallicity at the same redshift in MOND vs. LCDM.
Of course, there is also the posibility to have a combination of the scenarios…
I’m asking this as the metallicity of the stars influences luminosity, so I’d expect a lower surface brightness at high z in MOND, compared to LCDM for a “standard” galaxy.
The metallicity does influence luminosity, but it is a modest effect. It is one of the considerations that get wrapped up in stellar population modeling. My colleague Jim Schombert has made a point of building models that self-consistently track the build up of stellar metallicity as galaxies evolve, and this matters to some things (like the color dependence of M*/L) but isn’t a huge factor for this topic.
It is tricky to use metallicity as a time stamp, even though we do it all the time. The build up of metallicity in a closed box depends on the gas fraction; if you use up the gas fast you get to high metallicity fast, so time seems sped up. Open the box to allow outflows or pristine inflows and all bets are off.
For elliptical galaxies, the stars are old, so even in LCDM you have to make them early, just presumptively in little clumps that have yet to merge. (This was called “downsizing” for a while. I haven’t heard the term lately, but it seems to have been subsumed into the common lore.) Which is all a long way of saying that what you say makes sense, but probably can’t be used to distinguish the theories.
There’s a lot of evidence coming from many directions that space is flat, but that the universe is expanding. As we try to interpret very new data, you can’t just pick one bit of evidence out of a great many, and say therefore ‘expansion does not occur’. We’re still in the process of weighing up a lot of evidence.
But it’s true there are some things that on the face of it look like a non-expanding universe – I haven’t looked far into them. It’s hard to imagine anything that would lead to a cancellation, or a partial one. But the early universe scenario I’ve been looking into for 5 years, and published last year, could have bearing on it – I’ve been meaning to ask Stacy whether it might fit the data generally.
Some current theories describe extremely rapid early events, like VSL theories and inflation. But they can’t explain the fast early galaxy formation that followed – slower, but still too fast for standard theory. It’s as if a cosmological time rate starts fast, then slows to the present rate. We know time can vary in other situations, and leave permanent age differences between objects – even dust grains that move differently for a few seconds do this, it happens constantly across the universe. (Time dilation is not understood: we have the mathematics, that’s different.)
I have a theory that goes into several areas. It has a mechanism for the local time rate that leads to a varying cosmological time rate, and has a picture in which the overall time rate and the universe’s total mass-energy start high, then descend in proportion over time. (Something similar is found in a gravity field for the same underlying reason – in GR the local time rate and matter’s energy descend in proportion as one approaches the mass). In a theory called Planck scale time theory (PST), Kerr ’24, there’s a specific mechanism for it, which works well, it led to rederivations for relativistic energy and time dilation.
I’ve been trying to find the equation that relates redshift to time rate, for T[z]. I have an approximation that works nearby, and fits small anomalies, which are similar in SNe and GRB data – studies of each showed, on top of a 1 + z stretching of events, a slight shortening of events. They’re stretched on average by (1 + z)^0.95 and (1 + z)^0.94. These are within the error bars, and could be nothing, but it could be a slightly faster time rate in an expanding universe, with the curve flattening out near the bottom of the graph, as the time rate approaches T[0].
I’ve been meaning to ask if a relationship between time rate and total mass might come out of the general data, leading to the equation I’ve been looking for. One of many problems this potentially solves you mentioned the other day – the powerful gravitational wells in the early universe should never ‘let go’, but we don’t see them nowadays. Also the accelerating expansion, which would simply be a result of decreasing mass, so less gravity pulling things together. And the ‘downsizing’ sequence in galaxy formation, first mentioned in 1996, in which stars in more massive galaxies formed earlier and quicker. It seems to me these points might help pin down the relationship between redshift and time rate (with total mass-energy).
The mechanism underneath the theory is summarised on a pdf, if it’s relevant, it’s the third link here https://aibi4qm.wixsite.com/link/timetheory . Hope this is of interest – it seems to me that in the present confusion, lateral ideas might help. But without the near-proof from another area of the same theory that I’ve posted on the ‘million-light-years’ page, this would be a lot more far-fetched, and less worth mentioning – to me early on that was a bit of solidity with uncertainty around it. So could this kind of scenario possibly fit the data – and could you perhaps see a way to get to that equation? Thank you.
If by T[z] you mean the cosmic time-redshift relation, there is no closed analytic formula in LCDM; one has to compute it numerically. There are approximations; there is a good one in Peacock’s cosmology textbook as I recall, but it is an approximation.
Sorry, no, in VTC, varying time cosmology, which is a spinoff from PST, T[0] is the present time rate, T[z] is the faster overall time rate in a given era at redshift z.
It may be possible to get there from the way the total mass changes (with the time rate), via the accelerating expansion.
Incidentally, if it’s of interest, the mathematics of the gravity theory is all in one place now, https://gwwsdk1.wixsite.com/link/summary-pdf , with just the equations, including the near-proof, and predictions for experiments.