I was raised to believe that it was rude to tell people I told you so. Yet that’s pretty much the essence of the scientific method: we test hypotheses by making predictions, then checking to see which told us the correct result in advance of the experiment. So: I told you so.
Our paper on massive galaxies at high redshift is out in the Astrophysical Journal today. This is a scientific analysis of the JWST data that has accumulated to date as it pertains to testing galaxy formation as hypothesized by LCDM and MOND. That massive galaxies are observed to form early (z > 10) corroborates the long standing prediction of MOND, going back to Sanders (1998):
Objects of galaxy mass are the first virialized objects to form (by z=10), and larger structure develops rapidly
The contemporaneous LCDM prediction from Mo, Mao, & White (1998) – a touchstone of galaxy formation theory with nearly 2,000 citations – was
present-day disc [galaxies] were assembled recently (at z<=1).
This is not what JWST sees, as morphologically mature spiral galaxies are present to at least z = 6 (Ferreira et al 2024). More generally, LCDM was predicted to take a long time to build up the stellar mass of large galaxies, with the median time to reach half the final stellar mass being about half a Hubble time (seven billion years, give or take). In contrast, JWST has now observed many galaxies that meet this benchmark in the first billion years. That was not expected to happen.
In short, one theory got its prediction right, and the other got it wrong. I say expected, because we can always attempt to modify a theory to accommodate new facts. The a priori predictions of LCDM were wrong, but can it be adjusted to explain the data? Perhaps – but if so, that’s because it is incredibly flexible. That’s normally considered to be a bad thing in a theory, not a strength, especially when a competing theory got it right in the first place.
This has happened over and over and over again. After the initial shock of having MOND’s predictions come true in my own data (how can this be so?), I’ve spent the decades since devising and executing new tests of both theories. When it comes to making a priori predictions, MOND has won over and over again. It has consistently had more predictive success.
If you are a scientist reading this and that statement doesn’t sound right to you, that’s because you haven’t been paying attention. I get it: MOND seems too unlikely to pay attention to. I certainly didn’t before it reared its head in my own data. So ask yourself: what do you actually know about MOND? IT’S WRONG! OK, after that. Seriously: how many papers have you read about MOND? Do you know what its predictions are? Do you know what its successes are, or only just its failings? Can you write down its formula? If the answers to these questions do not come easily to you, it’s because you haven’t taken it seriously. Which, again, I get. But it is also an indication that you may not be playing with a complete set of facts. Ignorance is not a strong position from which to make scientific judgements.
I will expand more on the content of the science paper in future posts. For now, it boils down to I told you so.
You can also read more in SciNews, Newsweek, and the most in-depth article so far, in Courthouse News.
It seems that dark matter is a child of naive reductionism, the idea that theories can have an unlimited complexity range of applicability.
But in reality Quantum mechanics and General Relativity only provide meaningful predictions in very simple systems.
General Relativity fails at galaxy complexity level unless unobservable dark matter is introduced while MOND doesn’t need it, but then dark matter has been used to fill GR holes almost everywhere, they need dark matter to keep the illusion that General Relativity can be applied universally.
And that illusion seems to be cherished with religious fervor.
It’s been interesting reading your posts as a layman and then encountering some of the intellectual maneuvers you criticize, out in the wild. Saw this in Quanta, from last month:
“Initially, astronomers speculated that such huge, bright things so early in the universe were at odds with the prevailing theoretical model of the cosmos. But people have softened on that claim. Our best model of the universe — a set of equations describing the evolution of matter and radiation along with dark energy and dark matter — is not dead yet.
“‘There was a lot of sensationalism’ in JWST’s early days, said Alice Shapley of the University of California, Los Angeles. ‘There is no need for that. The data are so beautiful; let’s just study the universe we have.'”
“Speculation”, “people have softened” (who?), “best model”, “not dead yet”, “sensationalism”, “there is no need for that”, “so beautiful”, “let’s just study the universe we have”. I was surprised to encounter, in such a short quotation, so many expressions of apparent defensiveness. It almost reads like a confession!
I also took interest in the title of the article, “The ‘Beautiful Confusion’ of the First Billion Years Comes Into View”. I think there’s a common temptation to wax eloquent about the beauty and mysteriousness of nature as a way of excusing the weak explanatory power of one theory or another (though of course it’s a tricky balance … most theories prove weak at some point … the universe IS mysterious, and beautiful, etc. etc.).
Ah well, I interpret the explicit doubling down as a sign that things are coming to a head, however slowly. It’ll be interesting to watch.
https://www.quantamagazine.org/the-beautiful-confusion-of-the-first-billion-years-comes-into-view-20241009/
Yes, these are coping phrases we use when in the throes of cognitive dissonance.
Indeed, I should add that this is a psychology I’ve seen repeated many times. First, a surprising result. Then much hand-wringing and concern; is it The End for our favorite theory? Then there is a gradual push back from many voices saying “it’s not so bad” in various ways. This is repeated, first quietly, then more stridently, until it seems that indeed, it isn’t problematic, it was never problematic, it was silly to think it was problematic; hell, we expected this all along. It’s a process, a psychological process, not a scientific one.
That’s why most of our paper in ApJ is devoted to testing what LCDM actually predicted in advance. Yes, it is a genuine problem. Will it be solved? It will definitely be asserted that it has been solved. The question is whether that solution is satisfactory or not. Many of the problems that have arisen in the past are considered to now be solved; sometimes those solutions are satisfactory but in this field mostly they are not.
“Despite the predictive successes of MOND, we do not yet know how to construct a cosmology based on it.”
This is probably the work that needs to get done before people are willing to abandon Lambda CDM for MOND. People want a story of the universe’s origin and evolution, and while Lambda CDM provides such a narrative, MOND currently does not.
Yes, I think that is a correct diagnosis of the psychology. But we’re not going to get there unless we make the effort, and we’re not going to do that as long as we’re comforted with stories of invisible mass making everything right.
One often hears statements like “MOND is not a complete theory” or “I will begin to take MOND seriously only after it can be used to construct a complete cosmology”.
Some comments:
—There is no such thing as a “complete” theory. The standard model of particle physics — the paradigmatic example of a successful theory — depends on 19 numerical constants whose values are unrelated and arbitrary. Einstein’s theory of GR does not predict what color socks I will wear tomorrow, or how the yearly rainfall in Toledo correlates with the average temperature there. Even GR’s predictions about gravitational waves typically depend on auxiliary hypotheses, or on input from other theories — solid state, electrodynamics, stellar astrophysics.
— When an accepted theory is challenged by a newcomer, the latter typically targets a regime where the old theory failed, and is only slowly extended to other areas. Quantum mechanics was in this stage for about 70 years; some would say it still is. Imagine where we would be now if 20th-century scientists had said “I will wait to read about quantum mechanics until it is a complete theory”.
— Which would you prefer: a “complete” theory that (as Stacy emphasizes) can not possibly be correct, or an “incomplete” theory that has demonstrated it is on the right track?
Anyway, I cringe whenever someone excuses their inattention to MOND on the grounds that it is an “incomplete theory”.
Remember Arthur Kosowsky’s initial (1997) response to this?
YOU HAVE NO COSMOLOGY!
Given how many times we’ve been wrong about cosmology, I almost consider not having one to be a strength rather than a weakness.
Exactly. Better to leave holes in the jigsaw, than fill them before we’re ready to. It slows progress like nothing else, partly because of the point you made on another post about how reluctant people are to go backwards, and decide that part of their framework was wrong. But one wrong idea in there can be like a spanner in the works, and can hold up progress for decades. There’s a quote that probably came from Josh Billings, but has gone to many places: ‘what gets us into trouble is not what we don’t know, it’s what we know for sure that just ain’t so.’ The other version is ‘The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge’. So people may want a story of the universe’s origin and evolution, but it’s the wrong attitude if we’re not ready to get one.
I’ve been using that quote from Billings for ages; it leads all of my public talks and one of my 1998 papers. At that time I thought the attribution was to Yogi Berra!
The other quote is also quite apt. The illusion of knowledge is a severe affliction here: dark matter can explain everything everywhere all at once, providing the comforting illusion of comprehension in the face of perpetually repeated surprises.
It has been attributed to Mark Twain, Will Rogers, Artemus Ward, and Satchel Paige was the other baseball player. The second version has been falsely attributed to Stephen Hawking, but it all came from historian Daniel Boorstin, who made the point in several of his books, and built some of his approach to the history of science around it.
These people exactly like children like bedtime stories.
Reality can’t care less about humans wishful thinking.
I think that is a very wise statement. Scientists in every field have been on the hunt for a “complete” theory in their areas of study since the dawn of science. Yet here we are, always at the edge of what we don’t fully understand. You never said MOND was a complete theory, only that LCDM fails to be one.
The paper is very good, and it’s refreshing to come across a categorical statement that the hierarchical galaxy formation paradigm is broken, not merely ‘challenged’. In going back to the very first observable light sources MOND is here entering the realm of Big Bang cosmology itself. By way of caveat I would offer three points.
1. The paper acknowledges: ‘It is conceivable that we have the cosmology wrong’, referencing e.g. Li et al. 2023. The latter authors point out that in an expanding universe angular diameter distance is smaller than luminosity distance by an extra factor of 1 + z. They test this using two independent samples of ultracompact radio sources. Under the assumption of constant luminosity densities, they find that the data are in perfect agreement with a non-expanding universe – essentially another iteration of the Tolman test. The result accords with several other tests that favour a static universe (LaViolette 2021). Thus those who believe that the cosmic expansion paradigm should be abandoned because it is broken find themselves in the same position as those pressing for MOND to be taken seriously. McGaugh et al. admit that conceivably this other fundamental aspect of LCDM is wrong but leave it at that. Their case depends on its not being wrong, because the quantification of stellar mass (as in fig. 6 of the paper) is calibrated to an expanding universe, and if the universe is not expanding, stellar mass is progressively underestimated going back in time. They end by remarking, ‘Despite the predictive successes of MOND, we do not yet know how to construct a cosmology based on it.’ While it is not clear to me just what is meant by this, I think it is correct. In which case, “I told you so” may not be quite the right note to strike?
2. MOND makes DM redundant, and under it galaxies assemble by hierarchical merging much more quickly than under LCDM, though still off-stage. We begin to see galaxies at the point where growth is dominantly in situ. On the other hand, Oehm & Kroupa 2004 say: ‘If there were to be no DM halos around galaxies, then galaxy–galaxy encounters would be significantly less dissipative, galaxies would encounter each other multiple times, and mergers would be rare.’ I am puzzled by this apparently different assessment. How is one to know which view is correct?
3. The paper leaves unaddressed the other major problem with the earliest galaxies: their extraordinary compactness. As one press release put it, “Stars are approximately as numerous as in our own Milky Way galaxy … but contained within a volume 1,000 times smaller.” If MOND assembles stars into galaxies much more quickly than LCDM does because gravity is greater beyond a certain distance of separation, should it not also keep them closer together once they have assembled?
1. Yes, I told them galaxies would form early. I’ve also predicted reionization would happen earlier than expected in LCDM. There are limits one can place in the absence of a complete theory, and everything in MOND pushes structure formation to earlier times.
2. I’m talking about the chaos of formation of fragments within ultimately bound systems at very early times: the collapse doesn’t have to be smooth and monolithic. Oehm & Kroupa are talking about mergers between distinct galaxies at late times. We’re not talking about the same thing.
3. A compact mass of stars is indeed tightly bound, and excavating that is a huge problem: once buried in a deep potential well, it is very hard to get them back out. This happens in any theory, it’s a terrible problem in the Newtonian regime; we don’t understand this in any paradigm so I decided it was beyond the scope of this work (which is long enough, I think). But indeed, high-z galaxies are very compact, with effective radii that are smaller than local galaxies of the same mass by a factor of 1+z . That’s the same factor Li 2023 notes. So maybe the assumption of a Robertson-Walker geometry is breaking down? This is where we really need a complete theory.
OK this is a stupid reply, as I’m mostly ignorant of all the details. But I like figure 2 from your paper. (Which is from R.H. Sanders,1998) And though it’s by no means a complete theory, if there were some hot dark matter in the form of neutrinos (or something) that might be closer to the truth. So can you (we, someone) add hot DM to the mix and ask when we’ll start to see x-rays* (or some other signal) from clusters of galaxies.
*I’m assuming all the hot gas in galaxy clusters is somehow related to DM, but this may not be true.
1. Yes, I told them galaxies would form early. I’ve also predicted reionization would happen earlier than expected in LCDM. There are limits one can place in the absence of a complete theory, and everything in MOND pushes structure formation to earlier times.
2. I’m talking about the chaos of formation of fragments within ultimately bound systems at very early times: the collapse doesn’t have to be smooth and monolithic. Oehm & Kroupa are talking about mergers between distinct galaxies at late times. We’re not talking about the same thing.
3. A compact mass of stars is indeed tightly bound, and excavating that is a huge problem: once buried in a deep potential well, it is very hard to get them back out. This happens in any theory, it’s a terrible problem in the Newtonian regime; we don’t understand this in any paradigm so I decided it was beyond the scope of this work (which is long enough, I think). But indeed, high-z galaxies are very compact, with effective radii that are smaller than local galaxies of the same mass by a factor of 1+z . That’s the same factor Li 2023 notes. So maybe the assumption of a Robertson-Walker geometry is breaking down? This is where we really need a complete theory.
Further to the above, Oehm & Kroupa are not taking MOND into account when making that statement, so point 2 falls by the wayside.
DM and MOND compete to describe, among other things, the “acceleration discrepency”. I’ve seen people say MOND is not compatible with GR, but I don’t understand why. Discrepencies can arise in the way we measure frequency, or the rates of clocks, so how can we distinguish whether MOND describes an intrinsic property of mass or a measurement effect?
GR is not compatible with QM. GR obviously needs something else anyway
I don’t see how General Relativity applies in the solar system and in the cosmos, but not at some intermediate scenarios where MOND applies.
Since cosmology is an elaboration of the FRW model based on General Relativity, if we throw out GR, we should also throw out what it tells us about cosmology and start afresh. Derive the expanding universe from MOND. Further a local inertial frame in GR is not so if MOND applies. Perhaps this too requires us to reevaluate what redshift means.
I am not suggesting we throw out GR. I am suggesting that there may be a deeper underlying theory that encompasses both GR and MOND: https://tritonstation.com/2023/02/20/imagine-if-you-can/ That presumably would involve changes to cosmology, in which case FLRW may be a first approximation but not necessarily completely adequate.
That makes sense. We really should be considering spacetime metrics with a cosmic or extremal black hole AND a cosmic horizon, such as Conformal Schwarzschild-deSitter or a similar variation. What if you just couldn’t tell the difference between looking at the cosmic horizon of an expanding young universe and looking at the event horizon of a cosmic black hole?
I’m pretty fond of quantization of spacetime consequently for black holes – a theory that explains gravity the quantum way should be background independent like LQG. And afterwards somehow another theory should resolve the tension between MOND and (emergent from LQG) General Relativity.
Carlo Rovelli and Fransesca Vidotto theorized that this leads to a repulsive planck-scale force for matter that is collapsing into a black hole. That explains black holes as planck stars, solving the information paradox by not allowing the singularity.
GR without dark matter fails at galaxy level complexity, that is a fact. Scientists used to believe in scientific theories being falsifiable but somehow they seem to want GR at any cost, even at the cost of disregarding objectivity.
GR is very accurate for simple gravitational systems, like quantum mechanics is very accurate for simple quantum systems. But you don’t use quantum mechanics to describe very complex systems of quantum objects like living beings.
Any theory X”replacing” GR will produce the same results as GR for simple systems and the same results as MOND for galaxies dynamics, and something else for galaxy clusters, … Obviously each step here correspond to a hierarchical level, somehow each level can’t be described accurately by a single theory.
But exactly the same can be seen all around us. No single theory can describe multiple hierarchical levels, not even in principle as particle physicists like to claim.
“I don’t see how General Relativity applies in the solar system”
The solar system has its own dark matter issue – see the Planet Nine hypothesis to explain discrepancies in the behaviour of extreme trans-Neptunian objects in the solar system. Without the Planet Nine hypothesis, general relativity is already falsified in the outer reaches of the solar system.
One alternative to the Planet Nine hypothesis in explaining the observations in the outer solar system is… MOND:
https://iopscience.iop.org/article/10.3847/1538-3881/acef1e
There’s something GR can’t explain, and I’ve been meaning to ask you what MOND does with it. Talking of quotes, another idea that has a few quotes around it is that the things we understand least hold the best clues. Not just the one attributed to Asimov (the phrase that heralds new discoveries is not Eureka, but that’s funny) – John Wheeler said ‘In any field, find the strangest thing and then explore it’. He didn’t say the best clues are there, but he wasn’t being like someone watching ‘the Twilight zone’ – he knew that’s where you find things out.
So what about the planes of satellite galaxies problem – in three nearby systems including our own, satellites tend to orbit in a flat plane, with the suggestion of co-rotation. They shouldn’t – most theories can’t explain it, including GR and LCDM. In my picture from Planck scale gravity, the satellites are emitting the medium to make their gravity fields, so a disk of it builds up, bringing more satellites into that plane. Do you have a view of it (no need to, given the sayings above!), and does MOND have anything that relates to it?
Btw, a few years ago I wrongly attributed to Mandelbrot your Louis Agassiz quote about the sequence of 3 responses to new and startling facts. A good quote gets echoed everywhere.
Planar satellite distributions seem more probable in MOND. See, e.g., https://arxiv.org/abs/1712.04938
More generally, being a long range force-law with less dynamical friction than standard DM, MOND is good at making long, narrow features like tidal tails. One of the few upper limits on how much DM one can have is given by the need for tidal tails not to be dragged back down as soon as they launch, e.g., https://arxiv.org/abs/astro-ph/9902217. This is a good example of a constraint that was controversial, people tried to argue it away, those arguments didn’t really solve the problem, so they chose to forget about it.
With cycling season over, it’s back to some amateur, armchair theorizing. An ambitious goal, among several, is to find an underlying mechanism for MONDian behavior. MOND works so beautifully at the galactic scale that it simply can’t be ignored, and is surely telling something deep about the Universe, as has been emphasized many times, here on this blog and elsewhere. As a retired engineering technician in the oceanographic field doing hands-on work, be it in a machine shop, fabricating systems for the engineers, etc., I have no illusions of cracking this puzzle anytime soon, or indeed ever. But it’s a fun challenge, even if nothing ever comes of it.
The Robertson-Walker metric was derived before anyone understood the Large Scale Structure of the Universe. So it may only be valid for a ‘God’s-eye’ view of the Universe in its totality. And is it really surprising to see flatness across the Universe if your line of sight is through one (or many) deSitter-like Voids?
I’ve often wondered if galaxies don’t actually behave as if their radial size were being constrained in some way. And by extension structures weren’t also under that same constraint. Following this line of reasoning I wonder if pressure from the expansion of the Universe, localized to the Voids, might be ‘squeezing’ structures into smaller volumes than they might naturally occupy; as if that pressure were inducing, in terms of GTR, a curvature surrounding all gravitationally bound objects. That might explain an apparent coincidence between a0 and the accelerated expansion of the Universe that few people seem to be addressing.
Here I concur with other cosmologists: I really really don’t want to give up the RW metric, and it is striking that the angular diameter distance to the surface of last scattering is so precisely consistent with a flat RW geometry. But I’ve noticed that the universe has a certain disregard for our hopes and desires.
If we really want to say the universe has a definite age, then I am guessing we simply can’t be definite about the spatial extent or precise location of the mass-energy of the universe. In this case RW is fine, and the result is an invisible dark sector. If we want to locate the otherwise dark mass-energy in some other metric, maybe we have to give up on knowing the age of the universe?
The expansion rate sets the basic timescale for the age of the universe to something close to the Hubble time, 1/H0 = 13 or 14 Gyr. Separately, the ages of the oldest stars, the coolest white dwarfs, radioactive cosmochronometers, and even the isotopic abundances in interstellar dust grains all point to a similar age. So there is pretty good agreement of the nominal age of the universe with the age of its oldest contents. So I think a model needs to respect that to be successful, even if it isn’t exactly LCDM.
Yes, that’s a great point. Does that just mean that a newer model should respect that LCDM supports a consistent age of the universe for scales where the universe appears flat? But if the universe doesn’t appear flat at all scales, or if the appearance of flatness requires the addition of fictitious components, then that suggests LCDM is incomplete. This raises the question, is the appearance of a flat universe the common denominator for measurements that produce an age of 13.X Gyr?
Great question. In GR, the geometry and expansion history are strongly coupled. That need not be true in some more general theory.
Even in GR, flatness is not required to produce an age of ~13 Gyr. A coasting universe that has strongly negative curvature, is completely empty, and expands at a constant rate gives an age of exactly 1/H0 = 13.4 Gyr for the directly measured H0 = 73 km/s/Mpc.
Indeed, it is a bit of a fluke that LCDM has an age so close to 1/H0. The expansion in LCDM decelerates strongly early on, then has an inflection and switches to acceleration. So the expansion jukes one way then the other to come out very nearly equal to the coasting case at the present epoch and only around the present epoch. That wouldn’t have been true in the past and it won’t be true in the future, so it is a remarkable coincidence that we live at a time when it is just so. This coincidence problem is considerably worse than the one early universe Inflation was originally adopted to cure, as the switch from matter domination (deceleration) to Lambda domination (acceleration) is rather abrupt (on a cosmic scale).
A reasonable first guess for cosmology in MOND, going back to Felten 1984, is a very low density (baryon-only) universe, which is close to the coasting case in GR. This is a tolerable match to some data, like the age and Type Ia SN. The one thing it does not explain at all is the angular diameter distance to the CMB. This statement assumes RW geometry, which may just be a first approximation to the geometry of the underlying theory in the same sense that Euclidean geometry is a local approximation to RW.
Even sticking with GR, one can fit the CMB geometry by invoking the same fudge factor we use in LCDM: Lambda. But now we need even more Lambda, with the resulting universe being rather old (about 20 Gyr). That’s hard to exclude, but I find it unlikely that the universe would just sit there doing nothing for 6 or 7 Gyr then suddenly kick into high gear.
This would imply squeezing strength growing with the size of the voids, not a 1/r asymptotic gravity strength rule. There would be no explanation then for gravity being correlated so well with baryonic matter distributions, since the voids would create the ‘MOND’-like effects. It would not explain Chae’s wide binary conclusions or anything with the EFE.
Oops…late time integrated Sachs-Wolfe
About the strong evidence for flat geometry – I’d say it means either a flat space theory is needed, or epicycles. The universe being at the critical density is one, inflation is the other, but neither looks good without fudging – Penrose has shown that inflation leading to a universe like ours is very unlikely.
I’ve been looking at the paper on satellite planes, looks like a close pass 7-11 Gyr ago, plus MOND, could explain the MW and M31 formations. But the third one is also comparatively nearby, and they were among the first few we looked at. And I didn’t know, but there are also much larger planes in the local group. ‘Pawlowski et al. (2013) looked for planes in the whole local group and found that 14 of the 15 non-satellite dwarfs lie on two very large and thin planes […] both parallel with the line connecting MW and M31. […] The local group thus has a high unexplained symmetry.’
My explanation might, potentially, cover that. But I can’t say it’s a detailed explanation. Some areas of PSG are quantitative, there are about 12 equations, and a clearly described picture in some areas. But for the satellite planes it just comes out of the conceptual picture – although I know, for instance, how the medium dissipates, and other things that can lead to numbers.
Do you think this could potentially work, or is it hard to say. It seems to me that if matter is emitting a material not unlike DM, that has gravity of its own, it might be easier to get planes at different scales, and various patterns going on.
I don’t know if that could work and I don’t know how many planes we have to explain. Planes are statistically more ubiquitous than expected in LCDM simulations; that much is well established. What it takes to do that is less clear.
For example, one way planes of satellites might form is through group infall: they are correlated in phase space because they arrived together. Full disclosure: I was one of the first people to suggest this, over a decade ago. I did so as a way to try to save LCDM, because that’s always the first recourse. One would have to adjust the balance of in situ satellites with those accreted in groups, which in that language would be subhalos containing dwarfs in a larger (but still small) halo… one necessarily has to imagine that the efficiency of galaxy formation depends on the mass of the parent halo, but we’re already to that point anyway and in this case it actually makes it easier to explain the missing satellite problem (the local subhalos were all suppressed; all dwarfs are accreted). That this can explain all planes always seemed like a stretch to me, so I haven’t pushed it, but it could play a role (e.g., https://arxiv.org/abs/2404.16110).
The same thing could also happen in MOND: groups of dwarfs falling in together, just without the halos. This happens a lot: the things that are problems for MOND are usually also problems for [L]CDM, and the solutions we cook up can often apply to both. For example, dwarfs that are apparently free of DM now suffered some non-equilibrium event in the past to make them look that way.
Some time ago I was very surprised that the KBC void, that our local group of galaxies is located in, is only 20 percent less dense than the rest of the Universe. From watching videos about it I assumed it was perhaps 100 or more times less dense, as depicted in the graphic imagery. So, I guess, that helps explain why the RW metric is still favored by most astronomers.
If only we were being that rational about it. We teach our students that the Cosmological Principle of homogeneity and isotropy holds, and is observed to do so in the very early universe. From that starting point, it is practically impossible – in theory (GR) – for it not to continue to hold at the present time. Whether it does in fact hold at the present time is rather more dodgy, and the amplitude variation you describe as small is in fact more than should occur.
Beyond the specific example of KBC, a persistent, nagging problem is that voids are more empty than they should be in LCDM. Peebles worried about how to cure this with physics beyond the simple CDM he invented, e.g., https://arxiv.org/abs/astro-ph/0412586
Also a paper relevant to early structure formation: https://arxiv.org/abs/1001.1484.
https://scholar.google.com/scholar?hl=en&as_sdt=0%2C23&q=humitaki+sato+and+k+maeda+&btnG=
They used a Hubble value of 100 so there’s that. However, all these papers were published before Dark Energy was discovered. So my point is that because it is accepted that some relationship exists between a0 and the accelerated expansion of the Universe, these papers are early work seeking to tie baryon kinematics and subsequent matter structures to Void growth; not Void growth to gravitational collapse and subsequent clearing.
As for myself, these papers are interesting because I find it hard to attribute structure kinematics to something that can’t be found until all other potential questions have been resolved. And Voids are a very large question mark. For what it’s worth, Einstein (ca.1950) once said that not enough attention was being paid to spaces and the Universe had millions of spaces, all of them interacting with each other.
I wonder if the kinematic SZ and late time Sachs-Wolfe in some collaboration would offer some insights.
They don’t. I checked their Paper in Progress of Theoretical Physics (1984). What they do use is the parameter h, which is in units of 100 km/s/Mpc. It was an approach used before H0 was well known (de Vaucouleurs used to argue for H0=100 km/s/Mpc and Sandage for 50 km/s/Mpc in the days before measurements of the CMB structure gave rise to precision cosmology).
Yes, it was common practice to multiply distance-dependent quantities by h = H0/100 to account for the uncertainty in the Hubble constant. This is still sometimes done, especially in theory papers & simulation results.
“Dark Energy was discovered”
Translation:
A discrepancy between GR predictive /explanatory power and empirical evidence forced the ad hoc introduction of dark energy, exactly as with dark matter.
Congratulations on your preduction, Dr McGaugh.
thanks!
Could you speculate why MOND predicted galaxy development in the distant universe but CDM didn’t, even though both are, broadly speaking, “stronger-than-classical gravity”?
Also, I request you try MOND without “expanding space” and “a big bang”. Each of the tired light “rebuttals” can be debunked (lack of blurriness, SN light curves, and CMB). For starters, there exists the phenomenon of dispersion (dispersion measure, dispersion slope), where photons arrive delayed depending on the intergalactic medium (column of electrons, ions, and magnetic field), and evidently, galaxies are not blurred. It is known that photons can pass through a column of electrons without blurring.
I don’t need to speculate, but I do need another (upcoming) post to explain.
Good luck with your interview from EarthSky today! Just found the news item there. I’ll certainly read it afterward.
It is always fun to talk about science.
For those interested: the interview is at 1:15pm US Eastern time by Earthsky.org where there is also an article up: https://earthsky.org/space/mond-does-the-universse-need-a-rethink/
That link now contains a link to the youtube of the conversation.