It is straightforward to falsify theories that make clear predictions, should they happen to be wrong. It is impossible to falsify ideas that involve invisible components.
Specific theories of dark matter (e.g., WIMPs) can be seen to be increasingly unlikely, but can they be falsified outright? If we decide that WIMPs have been practically falsified – to all intents and purposes – that doesn’t mean dark matter is wrong, just that we’ve spent the past four decades building dozens of giant experiments costing billions of dollars and frustrating thousands of careers barking up the wrong tree. The unseen forest that is the ‘dark sector’ is vast; there are limitless opportunities to bark up other wrong trees.
How could we know if the entire dark sector is a non-entity? On many occasions, I’ve had colleagues say to me that they would “only consider MOND as a last resort.” OK, so when do we know we’ve reached that point? After an eternity of searching for unseen, undetected non-entities seems a little late.
This is the bind we’re in. Most of us (scientists working in the field) are unwilling to consider something as radical-seeming as MOND until dark matter has been falsified. But dark matter cannot be falsified. So we patch up our hypotheses accordingly, rinse and repeat with every new crisis#. This has been going on for nearly my entire career, to the point that I now see junior scientists who seem to think this is how science is supposed to work. Why wouldn’t they? They’ve known nothing else.
I empathize. I started from the same place: there has to be dark matter, it has to be non-baryonic, it is almost certainly a new particle and that new particle is almost certainly a WIMP. It was the hardest thing to realize and accept that we could be wrong, wrong, wrong, and wrong on all counts. I worked incredibly hard to avoid that conclusion. I take solace only in the fact that at every epoch in human history we’ve had a cosmology that we were absolutely sure$ was right but that later turned out not to be. Maybe we’re a blessed generation who finally got it right. Or maybe we’re just the latest in a long line of brilliant savants who fooled themselves into thinking we understand more than we actually do.
I remain unwilling to say that dark matter has been falsified because I don’t think it is falsifiable. That, in itself, is usually considered to be a bad thing for a scientific theory. Perhaps at some future point it will be portrayed that way for dark matter, but in the present I’ve heard plenty of scientists pretend like it is somehow a good thing. Certainly it makes a fertile playground for theorists, so I guess good/bad is a matter of perspective. I suppose an infinite forest of trees in a conveniently unobservable dark sector is an irresistible opportunity for a dog! with an insatiable bladder.
I do, however, think that dark matter has been practically falsified. If I’m wrong about that, it is possible to demonstrate. To be clear, I don’t just mean WIMPs. I mean dark matter as an explanation for the mass discrepancies observed in extragalactic systems. No kind of dark matter* can suffice. I came to this conclusion before I really knew anything about MOND, which is why I was receptive to it. Others haven’t had that experience, so aren’t.
I don’t expect other scientists to accept that an entire paradigm is wrong because I say so. I do, however, expect them to acknowledge that the dark matter hypothesis should be falsifiable. It is incumbent on each scientist to establish for themselves criteria by which that conclusion could be reached, should it be appropriate.
For me, the problem is the contradiction present in the dynamical data for galaxies. We simultaneously require galaxy disks to be maximal and also for them not to be maximal. The only way to avoid this contradiction is to engage in fine-tuning: one must build a model in which everything works out just so. Since dark matter is not otherwise falsifiable, a requirement for fine-tuning& is pretty much the worst thing we can say about it.
The contradiction as framed by others
The contradiction that concerns me has certainly been noticed by others. Usually, they choose to come down on one side or the other. The problem is that they’re both right.
On the one hand, it is clear observationally that the luminous mass matters to the dynamics of galaxies. For example, Swaters et al. note that
the luminous mass dominates the gravitational potential in the central regions, even in low surface brightness dwarf galaxies
which is to say, disk galaxies are maximal. We’ll explore what that means below, but you can see the effect by eye:
On the other hand, there are no residuals from the Tully-Fisher relation.
The inference from this observation is that galaxy disks cannot be maximal. As Courteau & Rix put it,
The case of δlog(V)/δlog(R) = -0.5 expected% for a maximal disk is ruled out
which is to say, disk galaxies are not maximal – even the high surface brightness (HSB) disks that dominated their sample.
They say this because maximal disks – or even those that contribute noticeably to the mass budget at small radii – predict deviations from the Tully-Fisher relation. They did this by intentionally focusing on the point where the stars should contribute the most. I’ve shown similar things many times, so here let’s let LCDM advocate Frank van den Bosch demonstrate it:
So galaxies cannot be maximal. Only they have to be to have the observed correlation between the luminous mass distribution and the kinematics, as seen in the first figure above. Well, which is it? Are all galaxies maximal? Or none? Or can they both^ be right?
Maximal disks
Maximal disk is a technical term that is well known to people who work on the subject but not outside that relatively narrow&& field. So what do we mean by this term?
In essence, a maximal disk is one in which the stars provide practically all the mass at small radii. The depiction of NGC 6946 above illustrates maximum disk. Sure, the rotation curve flattens out at large radii and we need to invoke dark matter. But the observed stars explain the amplitude and shape of the inner rotation curve quite well. In this case there is a compact bulge at the center of the galaxy that causes a sharp rise in the rotation curve right from R = 0. (This is an example of Renzo’s Rule.) The disk (plus bulge) is maximal in the sense that we cannot attribute any more mass to them without exceeding the observed rotation curve.
The amplitude of the portion of the rotation curve due to the stars depends on their mass-to-light ratio. While this cannot exceed maximum disk, it could be lower. So conceivably, the good match to the shape of the observed rotation curve is a chimera, and really this galaxy is dark matter dominated. That is a possibility many seem to have embraced, but while it might work for the disk, it does not work for the bulge. As we suppress the contribution of the stars as Courteau & Rix argue we must, then the rotation curve looks more and more like that of the dark matter halo alone. That goes up and flattens out (and ultimately must turn over again somewhere beyond the edge of the data) but it has no features.
One thing the rotation curve due to the dark matter halo cannot do is go up then down then up again. Yet that is exactly what it needs to do to explain the inner peak inside 1 kpc if the bulge component is not maximal. I suppose we could have a smaller dark matter halo inside the main dark matter halo that does this, but its mass distribution would have to be practically identical to that of the bulge. That’s insane. Why would we invoke a second dark matter halo when the stars are right there?
In this case, the stars have the right mass for what we expect from stellar populations. There was a long debate historically about whether the optical band mass-to-light ratios for maximum disk were consistent with those expected from stellar population synthesis models. For a long time they looked close but a bit high. This difference has pretty much gone away now that we have access to near-infrared data: the two are consistent, and having a stellar mass-to-light ratio much below the maximum disk value for high surface brightness disks becomes problematic from a population perspective.
Indeed, the 3.6 micron M*/L = 0.37 M☉/L☉ in the case depicted for NGC 6946 with a maximum disk. That’s reasonable but on the low side for what is plausible for the stars in a mature spiral galaxy like this. Halving that strains credulity, so there is no room for a second inner halo, or even for the cusp predicted** for the primary cold dark matter halo. Stellar mass really does seem to dominate in the inner parts, just as Swaters et al. said.
LSB galaxies
The issue that confounded me was whether the low surface brightness (LSB) galaxies I was working on were maximal or not. My inital expectation was that LSB galaxies would be stretched out versions of HSB galaxies. I expected them to shift off of the Tully-Fisher relation and follow the line δlog(V)/δlog(R) = -0.5. They did not do that. If I didn’t have them be maximal, I found that I could explain pretty much any slope other than the one observed (δlog(V)/δlog(R) = 0). That required fine-tuning to perfectly balance the lesser contribution of stars in LSB galaxies which we had to back fill with dark matter just so. I spent ages running around in circles trying to make that work. Every time I thought I had succeeded, I realized I had assumed something that made it so: tautologies abound.
If we want to explain the shapes of rotation curves as seen up top, we need the stars to contribute to the gravitational potential. For that to work for LSB galaxies, we have to turn maximum disk up to eleven:
A crazy-high stellar mass-to-light ratio is what happens if we just ignore what we know about stars and just focus on the kinematics. But we do know a lot about stars. Population models indicate stellar masses that are very submaximal. Even boosting the mass-to-light ratio doesn’t get us very far. LSB galaxies aren’t really maximal in the same sense as HSB galaxies, and there is even less room for the expected cuspy halos that are already problematic when the stellar contribution is small.
Fine tuning is unavoidable
Even if we ignore what we know about stars, we still have a fine-tuning problem. The lack of a shift in the Tully-Fisher relation with either surface brightness or radial size implies that disks are all the same mass surface density. So we observe a wide range of surface brightness, but the surface mass density is always the same. That makes no sense, and is just another example of squeezing the toothpaste tube: we can make a model look OK from one perspective as long as we don’t look from another.
Worse, we still need to explain the role of the luminous mass in LSB galaxies. These are dark matter dominated at almost all radii, and yet the distribution of the observed stars and gas is predictive of the kinematics. This is a contradiction to Newtonian dynamics. The only theory that does this right – and predicted it a priori – is MOND. But that’s too horrible to contemplate, so we shield our eyes and ignore%% one or the other set of inconvenient facts. As a result, the field has become moribund, and will remain so until we free ourselves of our invisible demons.
#We’ve experienced so many crises that we seem no longer able to recognize new ones. JWST observations of high redshift galaxies follows a well-worn trajectory: an observation that contradicts the standard model is made, much huffing and puffing ensues, the theorists get to work constructing implausible models, these are accepted as patching up the hypothesis (whether satisfactory or not), and the field moves on as if nothing happened.
$To give one historical example, prior to Hubble’s discoveries in the 1920s, it was thought that the Milky Way was the entire universe. Certainly there were no other galaxies comparable to the Milky Way:
“No competent thinker, with the whole of the available evidence before him, can now, it is safe to say, maintain any single nebula to be a star system of coordinate rank with the Milky Way. A practical certainty has been attained that the entire contents, stellar and nebular, of the sphere belong to one mighty aggregation.” [i.e., the Milky Way]
-Agnes Mary Clerke in The System of the Stars (1890)
!It used to be that one would not claim a detection of dark matter until all astrophysical alternatives had been exhausted. Now it seems to be the fad to claim a detection first on the off-chance it works out later. I already peed on that tree! It’s mine!
*Excepting some sort of hybrid “dark matter” that is invented to do what ordinary dark matter cannot. By ordinary I mean CDM, WDM, SIDM, and every other variation on particle physics that simply invents new mass with no consideration of how the observed galaxy dynamics comes about. That would include primordial black holes and various macroscopic DM ideas (e.g., MACHOS, strange nuggets). Coming up with half-baked ideas for new particle dark matter is big business these days, but any idea not informed by observed astrophysics (which are most of them) is doomed to fail.
Examples of hybrid dark matter that are informed by observed astrophysics include dipolar dark matter and superfluid dark matter. Regardless of whether these specific cases are viable, the point is that the observed dynamics are a fundamental aspect if nature and require a commiserate explanation. Simply throwing in some extra mass with some fine-tuned feedback models can never provide a satisfactory explanation. Note that coming up with extra mass is mostly done by particle phenomenologists while feedback models are built by numerical astrophysicists. There is very little overlap between these communities; they pretty much just take it on faith that since dark matter has to exist, the part they don’t know about will magically work out.
&The classic example of fine-tuning in the sense that I mean is the Ptolemaic model of epicycles and deferents. If one adds enough of these and tunes them just so, anything can be fit. Note that epicycles are not explicitly falsifiable for this reason; we rejected them because they got ridiculously complicated and there turns out to be a more parsimonious explanation. The same thing holds now for dark matter and MOND.
%This slope is expected because Newton teaches us that V2 = GM/R. δlog(V)/δlog(R) = -0.5 follows from taking the logarithm of this at fixed mass. Galaxies are observed to span a large range of radius at a given mass, but not a corresponding range in circular velocity.
^Yes, they can both be right, but not with dark matter. Only MOND naturally explains both observations simultaneously.
Also, for the hyper vigilant, Courteu and Rix (1999) use a slightly different definition of velocity than I do in this Tully-Fisher residual plot. I went through all that in McGaugh & de Blok (1998) and in McGaugh (2005) and it makes no difference to the discussion here.
&&A vote we held at a conference on disk dynamics in Rome in 2000. The question of whether disks were maximal was posed; most people voted no based on the statistical lack of residuals from Tully-Fisher. After the vote, one of the dissenters noted that those who voted in favor of maximal disks were the people who actually worked in the subject. Those of us with other concerns were persuaded by the statistical evidence because we didn’t engage with the details of real, individual galaxies in the same way.
**The NFW halo famously gets the inner shape of the rotation curve wrong (the cusp-core problem), but it is also wrong at intermediate radii and at large radii. Other than that it’s great.
%%A common excuse I here for this behavior is that galaxies are “small” and nonlinear – complicated entities that we can never hope to understand, so whatever they do can be ignored as irrelevant. As a scientific argument, that’s pathetic. Galaxies should be complicated in LCDM, but in observational reality they’re kinematics are sufficiently simple that they obey a single effective force law. That’s one thing they should not do, just as a complicated set of epicycles and deferents shouldn’t always add up to the inverse square law.
Colin Rourke’s dark alternative is well worth studying.
In short, when we take account of the wobbles of space time itself, induced by central supermassive black holes, there is no need for dark matter.
https://arxiv.org/abs/1911.08920
Frame dragging is a real effect, but it is far too weak to explain the observed mass discrepancies, especially in LSB galaxies. Besides, if I recall right, it is frequency-dependent, not acceleration-dependent as the data require. Frequency dependent hypotheses, like those that are distance-dependent, can be excluded as the first order effect https://arxiv.org/abs/astro-ph/0403610
“$To give one historical example, prior to Hubble’s discoveries in the 1920s, it was thought that the Milky Way was the entire universe. Certainly there were no other galaxies comparable to the Milky Way:”
The Shapley-Curtis debate held on April 26, 1920, at the U.S. National Museum in Washington, D.C., between Harlow Shapley and Heber Curtis regarding the scale of the universe and the nature of spiral nebulae is the point at which the existence of other galaxies comparable with the Milky Way became a scientific theory. Both Shapley and Curtis were part right and part wrong. Shapley was right in that he placed the centre of the Milky Way at the centre of the system of globular clusters; Curtis was right in his assertion that the galaxies were like the Milky Way, not nebulae within it.
Also Vesto Slipher started measuring velocities of galaxies at the Lowell Observatory in 1912 and by 1917 had measured 25, of which 21 were receding. So the evidence for galaxies being outside the Milky Way was available a full decade before Hubble. Indeed as the Clarke refractor telescope used by Slipher had been built in 1896 this discovery could have been made a couple of decades earlier if it had not been for Percival Lowell’s obsession with Martian canals.-
Slipher’s velocities were utilized by Hubble, so maybe we’d call it Slipher’s Law had the order been reversed. The IAU recently voted to call it the Hubble-Lemaitre Law which I voted against because I thought Slipher-Hubble would have been more appropriate. They were the observers, after all. Lemaitre was the theorist who seemed to be the only one who understood what Einstein’s theory predicted for the universe, at points in the ’20s apparently including Einstein himself.
In addition to the Great Debate – a detour I chose not to take in this post – there is a nice quote from Shapley upon receiving a letter from Hubble describing his discovery of a Cepheid in Andromeda: “Here is the letter that destroyed my universe.”
I like the idea of humanity freeing itself from invisible demons to make scientific progress. That’s a rather familiar storyline.
I also like the idea of diving into exactly how we created these demons in the first place.
Did the demons arise from the chasm beneath some leap we made, or from the edge of a circle we made clear? Could the dark sector possibly be avoided by going back to the basics and taking things much more literally?
Take the study of quantum gravity for example. Maybe we need to pivot away from trying to solve the abstract regime we can’t measure, and instead develop more concretely the connection between the quantum measurement that we are performing and the gravitational description of what we are observing.
Maybe this is the only real quantum gravity problem we need to solve, and then maybe the underlying theory is just recognizing how we made the dark demons in the first place.
Jeremy Jr. suggests a set of “candidate cluster-native parameters” including Hot-gas mass fraction, etc., etc., as possible important physical parameters derivable for a cluster of galaxies independent of galaxy data.
I would add to that list the total angular momentum LT of the galaxy cluster, which I suggested on July 5, 2026, for the missing baryon problem in general.
Why? Because there is the reasonable possibility that the MOND acceleration depends upon both the total baryonic mass MT and the total baryonic angular momentum LT according to this expression for the MOND acceleration:
a0 = G^3 MT^7/LT^4
with the ^ arrow signifying “to the power”. For single galaxies the variations in the a0 value could be very small so that a fixed value works universally. However, one would need to know both parameters MT and LT for each galaxy in order to verify this universal application.
For galaxy clusters, again one requires MT and LT in the same expression. Let’s assume that the MT is known precisely. But the LT for clusters can be lower than expected for the known MT value because the cluster LT depends upon at least these three factors: (1) the IC gas rotation speed, which can be less than assumed, (2) the IC stars can each rotate slower than expected and even if their angular momentum vectors all align they would contribute less angular momentum, (3) the individual galaxy angular momentum vectors do not align but point in different directions. With these factors for lowering LT in the denominator, one can easily accommodate a shortage for the baryonic MT in the numerator, i.e., if there is “missing baryonic mass”. Therefore, the total cluster angular momentum LT should be considered to be an important “cluster-native parameter”.
Your previous response then was the true statement: “Angular momentum isn’t entirely independent of mass so I’m not sure there’s additional leverage here.”
May I suggest that you reconsider the importance of LT. The above expression for a0 would apply to clusters of galaxies at one extreme and would apply to single galaxies as well, essentially meeting an important requirement to “reduce to a0 for the single galaxy limit”.
The puzzle you’re looking at, which I call the wider RAR, can be seen as the main puzzle in the mass discrepancy. Quite a few intermediate values for a0 have been found recently between the galaxy a0, 1.2e-10, and g++ in clusters, 2e-9. The transition acceleration is different in different environments, within clusters, groups, and so on.
I didn’t know of more than those two values until I started looking into eMOND recently. Obviously a range of values for a0 is a major set of clues, about what makes MOND tick, and the mass discrepancy generally. eMOND suggests, with no explanation, a correlation between a0 values and environment (in their case with the depth of the gravitational potential), and some recent data in a range of environments means this is very much where we need to look, and hopefully find a correlation.
A very interesting numerical relationship was found across a sample of 52 non-cool-core clusters by Chan and Del Popolo (you might be able to try out your angular momentum formula with this). They say, where r[c] is the core radius:
“By plotting the RAR for different subsamples (at rc , 2rc , and 3rc) the corresponding a0 are 1.9 × 10−9 m s−2 (at rc), 1.2 × 10−9 m s−2 (at 2rc), and 3.9 × 10−10 m s−2 (at 3rc). We can see the trend of larger discrepancies from the galactic RAR as one gets closer to the centres of galaxy clusters.”
Looking into it, the PSG interpretation came together more – briefly it’s this. The emitted medium has to start dissipating faster for some reason at a0, because if that slope steepens it boosts accelerations for (helically refracted) matter. Rather than self-interaction of the waves starting up and causing that, it’s likely to be loss of coherence, which can indeed speed up dissipation in waves. And it happens naturally at a particular point, like the MOND transition does. Loss of coherence can be delayed if the waves are more directionally aligned in the first place. The change may always start at around g = 2e-9, but the delay due to alignment takes things to a lower acceleration scale, and the delay varies between environments.
So to test the idea, the need was for an approximate ‘alignment index’ for the emitted wave field, in different environments. If this works, it’d be high where a0 is low (such as in the outer parts of galaxies), and low where a0 is high (such as in clusters, where the waves come from all directions). Intermediate values should have intermediate alignment indexes, and a pattern should appear.
So far, there’s a clear but loose pattern, I made a graph and put it in a preprint paper, https://gwwsdk1.wixsite.com/link/newpreprint-pdf
(I’m told it’ll replace the earlier paper there this afternoon.)
The ordering of the data points works so far – disks, groups, cool-core clusters, rich clusters etc. And in the quote above with 3 radii within clusters it also works, you get higher a0 values nearer the core – emitted waves will be more aligned further out, as in galaxies. I hope this is of interest, and whether or not this version turns out to be right, I hope both sides of the argument look at the wider RAR, and that someone finds a truly close correlation with something, because then we could start making progress.
Just a word of caution – everything Chan and Del Popolo write on this subject is said in bad faith. They’re the internet trolls of this subject.
Thanks, it helps to know you think that. I did notice they were putting forward a different view from mine, and was surprised they didn’t present the finding as a good possibility for a way forward, as I see it. I hope you think their actual observations are correct. (btw, the paper is up at the link now.)
You’ve seemed open to eMOND as a possibility, and so perhaps potentially to some other correlation that links the different RARs. But I understand that your work, and Milgrom’s, has been under attack for a long time, and it must be hard to shift ground under those conditions, when you’ve been holding firm against unreasonable treatment. But if the RAR does turn out to be a wider thing, what you and Milgrom have done in discovering it is still absolutely central – without it we’d be back in the dark ages.
Reading their introduction again, they point out problems with both positions, but they’re still very entrenched in the either/or mindset, and trying to score points against MOND and the RAR. But there are other ways for modified gravity to prevail, and turn out to be universal, outside the limiting, premature assumptions they make. What they find can make the pattern more significant, not less so – it’s just early days, and we don’t know yet. Do you think there could be some correlation, eMOND or some equivalent, that brings it under one heading?
I do, however, think that dark matter has been practically falsified. If I’m wrong about that, it is possible to demonstrate. To be clear, I don’t just mean WIMPs. I mean dark matter as an explanation for the mass discrepancies observed in extragalactic systems. No kind of dark matter* can suffice. I came to this conclusion before I really knew anything about MOND, which is why I was receptive to it. Others haven’t had that experience, so aren’t.
what about finding sterile neutrions, axions, or even magnetic magnetic monopole?
how would finding any of these affect MOND hypothesis?
Sterile neutrinos have been hypothesized as a candidate for the unseen mass in clusters of galaxies, so those would help IF they had the right properties. Same for axions – QCD axions could exist and be irrelevant to the missing mass problem, or axions with the right properties could be the missing mass (though they wouldn’t address the concerns raised here.) Magnetic monopoles are neither here not there
so dark matter particles could exist, such as sterile neutrions and axions, and not solve the missing mass problem in galaxies?
do you accept other dark matter explanations that don’t involve galaxy rotation and missing mass problem in galaxies?
that dark matter may not explain the missing mass in galaxy rotation but they could explain other observations and exist
in a mass ration of 5 times that of baryonic matter, but are so light weight and spread so thinly they aren’t in galaxies,
perhaps in the voids of deep space between galaxy clusters?
for example, do you accept dark matter explanation for the third peak in the CMB, but those dark matter particles are spread too thinly
to explain missing mass galaxy rotation curves?
would say MOND for galaxies work, and dark matter
exist in the deep voids of space far away from baryonic matter?
Any number of particles that might be called “dark matter” – a rather vague term – could exist and not solve the mass discrepancy problem. We already have such an example in neutrinos: https://tritonstation.com/2017/03/08/neutrinos-got-mass/
I do not see how it could be possible to have dark matter with the required cosmic properties but somehow magically not be in galaxies. https://tritonstation.com/2023/08/17/required-dark-matter-properties/
All the other questions you pose have also been answered at some point in this blog.
Satire:
“Dark matter” does not sound scientific enough. We should call its constituents “skotions” (from the ancient Greek for “dark”).
Searching for skotions sounds much better than searching for WIMPs.
What hope do you have for the future of the astronomy/cosmology community? It seems like you say a lot of finetuning is the biggest falsification we can get, and we already have that, right? Do you still see hope for a future generation of scientists that do astronomy and cosmology the way Popper and Lakatos proposed?
Can we perhaps make progress by simulating cosmic history with MOND related to the little red dots?
I’ve kinda given up hope.
Thank you for your honesty. I might send you an email in the hope my own theory gives some new ideas.
Although I do have hope, it may not be for science in the current American-European system. I see too much decadence: that people follow rules, agreed ways of working and tools to keep the system up and running rather than really being passionate on their work and doing it properly.
The fine-tuning is really telling us something with the potential to unify the MOND and CDM camps:
1. If DM exists, the disk-halo conspiracy needs a causal explanation for why DM arranges itself “just so” to offset changes in visible mass distribution.
2. If the Newtonian force law has to be modified at low accelerations, MOND also is not off the hook – it needs to supply a causal WHY?
I wonder about the fact that the visible fraction of total matter steadily decreases from a maximum at cluster cores (~ 15-20%), to ~ 5-10% for HSBs to less than 1% in LSBs and dwarfs, yet the BTFR remains serene. What if DM is just very tightly coupled ordinary matter, that can itself be ionized (perhaps spectrally degenerate with other ions) under extreme conditions? This would explain the differential visibility as well as the gravitational coupling. It would violate BBN baryon-photon ratios. I suspect the deeper message could be that resolving the MOND/DM debate will stress the cosmological model itself, not just small scale dynamics
Re 2.) Mond doesn’t need to supply the why, that has to come from some other ‘real’ theory. Mond is not a theory, it’s more analogous to Kepler’s law of motion (this is just my opinion). And in that regard is a big hint as to a good theory… more smart people should be working on it. This way to ‘fit’ the data works! We don’t know why yet. My favorite idea is some quantum effect, I’m from a solid state background and to me quantum effects show up at low temperatures/ energies/ accelerations. Maybe gravitons start to condense, IDK I’m an experimentalist (or was.)
“When you believe in things, you don’t understand, then you suffer.”
– S. Wonder, 1972
The argument between different effective theories of gravity will never be resolved, because none of these theories includes a testable proposal for a physical mechanism by which gravity actually operates.
In order to make such a testable proposal, it is first necessary (as Penrose has often remarked) to observe some genuine influences of gravity on quantum physics. This is difficult, because particle physicists regard it as a matter of faith that gravity has no influence on quantum physics.
Nevertheless, the experimental results are quite interesting. Many investigations into weak interactions have observed such effects, although they are denied by the mainstream, and other “explanations” proposed instead. What is called CP violation of neutral kaon decays is one clear example of gravitational interference in a quantum experiment. The neutron lifetime anomaly is another. There are quite a few others, once you start to notice and look for them.
In other words, it is not that WIMPs are modifying gravity, it is that gravity is modifying WIMPs. And the defining feature of weak interactions is that they involve the emission or absorption of neutrinos and/or antineutrinos. So whatever the true physical mechanism for the force of gravity, we can be sure that neutrinos are involved somehow.
Curiously, this is a line of inquiry that I’ve been working on – a connection between the effective gravitational force at astronomical scales and the weak force. This isn’t, however, a new research area. There’s a 2007 paper titled: “Gravi-Weak Unification”, by Fabrizio Nesti and Roberto Percacci and others. In the model I’ve been developing aside from providing a possible explanatory framework for parity and CP violation, along with a way to estimate its magnitude in individual particle decays (other than the math heavy Standard Model way), it also imposes a strict limit of 3 generations of leptons and quarks. That limit was long ago established by different means – the resonance curve of thousands of Z decays, and the relative abundance of helium to hydrogen in the Universe.
Recently I came across reports of deviations from the Standard Model (SM); such as an APS (American Physical Society) article titled: “A Widening Anomaly Strains the Standard Model”, by Slavomira Stefkova, and posted on July 8, 2026. That raises hope that at long last a crack in the SM of particle physics is being revealed. Certain Flavor Changing Neutral Currents (FCNC’s) have been under intense scrutiny at CERN’s LHC and elsewhere for about a decade, with future exploration scheduled at the Belle 2 facility in Japan. These involve the transmutation of a B quark to an S quark; such as a neutral, strange B meson decaying into a phi particle and a pair of muons (opposite charges). The goal of some theorists, including amateurs like myself, is to deduce a mechanism whose origin is at the particle scale which can successfully explain MOND’s empirical law in galaxies and extend it to larger scale astronomical structures.
The Nesti et al paper was written in the context of supersymmetry, and left-right symmetry, before the LHC was switched on. It does not appear to make any actual predictions, or to actually explain anything. It therefore sits somewhere on the spectrum between already falsified and unfalsifiable, right next to dark matter…
That Nesti, et. Al. paper I referenced just to show that a connection between gravity and the weak force has been considered in the past. It’s very technical and I could barely understand it (I’m a retired electronic technician, learning high energy particle physics slowly, bit by bit). I didn’t realize that it was developed in the context of supersymmetry. Since the lightest supersymmetry particles have not shown up at the LHC, or elsewhere, SUSY has been pretty much ruled out, and their paper as you point out, for other reasons as well, is between falsified and unfalsifiable. There was another paper I looked at too: “From weak interaction to gravity”, by M. Novello and A. E. S. Hartmann, inspired by a 1970 idea by professor Stueckelberg at Geneva University. That was published on 21 April, 2021, so well after the LHC had come up empty on the lowest energy SUSY particles predicted. Professor Stueckelberg’s idea I found very appealing.
Lately, I’ve been participating in a thread at physicsforums “LHC To Announce Its Lepton Universality Violation Results On Tuesday (20-Dec-22)”. I became hopeful that this B meson decay anomaly would provide support for my rather amateurish theory. But, alas, a very knowledgeable forum member provided reasons why he is skeptical that the anomaly has a beyond the Standard Model explanation. In a Physics Today article: “Analysis of B meson decay hints at new physics”, posted June 01,2026, it’s speculated that a Z prime (Z’) boson, or leptoquark, could account for the anomalous angular distribution of the decay products of the B meson, which the article states deviates by about 4 sigma from the Standard Model prediction. If a heavier version of the Z (the Z’) was being emitted with the other, usual decay products I assume that could explain the anomalous angular distribution of the other decay products, and aligns with my model. But I’m not sure if they mean that a virtual Z’ could also do that, not to mention that there might not be enough phase space to allow an extra particle to be emitted (as best as I understand it). Also, a real Z’ would have to decay to a pair of particles, everything obeying all conservation rules.
IMHO, B meson anomalies are likely to arise from the same cause as K meson (i.e. kaon) anomalies. I haven’t looked at the problem in detail, because I believe there is lower-hanging fruit. Every particle physics anomaly I have looked at in detail has always turned out to have a plausible explanation in terms of some (conjectured) influence of gravity. Hence I take them all as clues for the building of an as yet unknown quantum gravity theory. If such a theory can deal with the hard problem of explaining particle anomalies, then it can surely deal with the easy problem of reducing to GR in the appropriate limit.
If we are trying to understand this discrepancy through one-dimensional projections maybe that in and of itself is part of the difficulty.
We may very well be projecting away information already present in the baryonic distribution.
Better resolved 2D studies might help explain the empirical facts we so clearly see in 1D.
We make full use of the available information in 3D data cubes; 1D rotation curves are just a convenient depiction.
For your opening question, basically ‘how could we know if DM is wrong?’, the realistic answer is ‘when we replace it with something better’. That’s what actually happens in history – with epicycles, and anything else. I looked at the present view of time, and found it had elements that simply don’t add up, but which are taken on trust. George Ellis, Lee Smolin and others think the same, or something similar. Because these elements are untestable, the only way to get past them is to replace them with something else – until then, they’ll be blocking the hole in the jigsaw into which they don’t fit, making it less likely that we find a real solution.
Why does that happen, rather than the scientific method holding sway, as it should? Saying ‘we don’t know yet’ is healthy – leaving holes in the jigsaw helps progress, but it makes people feel insecure. They’d rather cram something in there. We got used to getting security out of scientific knowledge from 20th century attitudes, which told us we knew it all, or a lot of it. That came from rapid progress at the time. Since then we’re stuck, but people don’t want to step back, and say well actually, these new puzzles mean we know a lot less than we thought.
There are plenty of ways in which LCDM has come near to being falsified, but some skate over them – sometimes there’s a need to take one issue and keep pointing it out, as they do with the bullet cluster (even though it’s inconsistent with both MOND and LCDM). I think perhaps that issue should be flat rotation curves being found to extend several times further than the theoretical limit of the DM halo. That doesn’t falsify DM, but it does falsify LCDM – or is it just the NFW halo? It also seems to falsify attempts to explain away the RAR as an artifact that arises in LCDM. It seems the million light year FRCs might remove the need to compare halos with MOND in detail – if we know they don’t exist anyway.
There are a lot of hints that the solution will include an element of explanation, rather than just a new particle, or a new bit of mathematics. The wall we’re up against is that we’ve reached a point where we need a conceptual underpinning to move forward. And the contradictions you point out suggest some unexpected twist: weird clues like that mean that even a basic hybrid theory with MOND and DM won’t quite do it. You can ‘feel’ it intuitively when you look at the clues – it’s going to need something a bit more unexpected.
Re 2.) Mond doesn’t need to supply the why, that has to come from some other ‘real’ theory. Mond is not a theory, it’s more analogous to Kepler’s law of motion (this is just my opinion). And in that regard is a big hint as to a good theory… more smart people should be working on it. This way to ‘fit’ the data works! We don’t know why yet. My favorite idea is some quantum effect, I’m from a solid state background and to me quantum effects show up at low temperatures/ energies/ accelerations. Maybe gravitons start to condense, IDK I’m an experimentalist (or was.)
“… there has to be dark matter, it has to be non-baryonic, it is almost certainly a new particle …”
I attempted (quite unsuccessfully) to convince Professor Mordehai Milgrom & Professor Eduardo Guendelman to hold a joint press conference announcing the empirical success of FUNDAMOND string theory based upon Guendelman’s new version of string theory.
Many astronomers & astrophysicists assume that, after quantum averaging, Einstein’s field equations are completely correct. If there are 3 different types of inertia, namely, Newton-Einstein inertia, Milgrom inertia, & Guendelman-Guth inertia, then it is likely that Einstein’s field equations are slightly wrong (as suggested by MOND’s successful predictions). Instead of dark matter particles, there might be 2 new types of spontaneous symmetry breaking (explaining the dark matter phenomenon & the dark energy phenomenon.
It seems to me that the quantum gravity experts generally fail to understand the importance of the FUNDAMOND problem.
Alves Batista, Rafael, et al. “White paper and roadmap for quantum gravity phenomenology in the multi-messenger era.” Classical and quantum gravity 42, no. 3 (2025): 032001.
https://iopscience.iop.org/article/10.1088/1361-6382/ad605a/meta
Is Guendelman in the same ballpark as Newton & Einstein?
Guendelman, E. I. “Dynamical string tension theories with target space scale invariance SSB and restoration.” The European Physical Journal C 85, no. 3 (2025): 276.
https://link.springer.com/article/10.1140/epjc/s10052-025-13966-9
In the standard form of Einstein’s field equations, replace the –1/2 by
–1/2 + FUNDAMOND-data-function & replace the Λ by
Λ + dark-energy-data-function.
If I understood what I have read correctly, galaxy dynamical simulations are calculated using Newton’s Laws in differential form, but then I don’t understand how this can work, given the massive size of galaxies, with some stars a hundred or more light-years apart. It seems to me that different parts of the galaxy will have different effective centers of mass attracting them, based on the different travel times of gravity from near and distant masses. In fact, if the galaxy is moving through space, in some cases the effective COM’s may be outside the galaxy. So I am wondering if numerical simulations include this effect, or whether is is somehow negligible.
You are correct that causality is an issue over the vast sizes of galaxies. For spiral galaxies like our Milky Way, the orbital timescale at the radius of the sun from the Galactic center is 200 to 250 million years. The Galaxy has been around for at least ten billion years, so old stars have made 40 or 50 orbits. That’s enough time for things to settle down and a clear center to be established. Numerical simulations with time resolution adequate to track that can do so.
Is it true to say that we don’t have a Newtonian or classical connection to the gravitational environment of the galaxies we observe and simulate?
The numerically simulated evolutions have to match the evolutions of the probability density functions and correlations of the quantum particles in our detectors, which of course are not classical or Newtonian. How do we know that MOND isn’t created in our own statistical quantum interactions?
wut?
It just seems like MOND may be related to how we actually describe the object using statistical mechanics of ensembles and distributions in dynamic equilibrium that must emerge from the statistical quantum mechanics of measurement.
The emergence of the extended properties spacetime and gravity might just exist within our descriptions, not out in the real world.
That’s why I wonder if the real quantum gravity problem isn’t first discovering how the dark sector emerges from one or more of the informational transformations from quantum to classical to relativistic.
The dark sector resists any locally real measure, but no locally real measure was used to infer it’s existence in the first place. That’s just my 2 cents on the topic. Probably useless babble at this point.
Am I right in thinking that the calculation of a galaxy cluster’s stellar mass assumes that the system is in gravitational equilibrium?
The *stellar* mass follows from the total luminosity: count photons and figure out how many stars it takes to make them all. It’s not that easy of course, but there is no assumption about gravitational equilibrium, just bookkeeping for the amount of light. The dynamical mass, on the other hand, does assume gravitational equilibrium, and I’m told by people who work on clusters that there is no such thing as a cluster in equilibrium.
Yes, my language was very loose, pardon – I had in mind baryonic/dynamic mass, as calculated (I understand) from velocity dispersion on the assumption of gravitational equilibrium, and giving rise to the mass deficit attributed to DM. In my unorthodox view, cluster galaxies originated from primeval super-conglomerations of matter, giant stars that at very high z are interpreted as impossibly/implausibly compact galaxies. (In a non-expanding universe, which I also favour, they would also be orders of magnitude more massive.) Not dissimilar is the concept of a ‘black hole star’ (Kokorev et al 2026). My main evidence for this scenario would be the overmassive Brightest Cluster Galaxies that lie at the centre of clusters, usually, in the case of the bigger clusters, in pairs, as if they had first split in two in the course of multiplying. In that case, clusters would not be in dynamical equilibrium, the motion of galaxies would be primarily outward (unless and until gravity began to reverse the motion). What we interpret as galaxies merging – such a common phenomenon at high z – would be galaxies splitting. So I wonder whether this might not be the reason why clusters appear to give rise to a mass deficit.
If, as you confirm, clusters are not in gravitational equilibrium and this is the norm, how can a mass deficit be inferred on the basis that are in equilibrium?
Gravitational lensing is sensitive to mass enclosed by a lensed image but doesn’t care about dynamical equilibrium. It also indicates a discrepancy.
Fair point. I suppose the question then (which must have been addressed) is whether the mass deficit inferred from the velocity dispersion is roughly equal to the mass deficit inferred from gravitational lensing.
Roughly but not always. Dynamical estimates sometimes run higher, but it is hard to know how much of that is disequilibrium and how much is that we’re measuring different things/making different assumptions.
Hi Stacy,
As you know, there are electric charges in our world, but no magnetic charges.
Furthermore, there are left-handed neutrinos and right-handed antineutrinos, but not the opposites of either.
I have a rough idea of how both asymmetries can develop naturally.
Similarly, I have an idea regarding Dirac’s large numbers, specifically (R(Universe)/R(Proton))² = number(protons)
Both of these are very helpful to me.
At the moment, the above asymmetries and dependencies seem to arise by themselves.
MOND
You are one of the few who advocate for MOND.
And your situation is frustrating.
The opposite would be:
Thousands of astronomers are working on MOND, and you would be just one among many.
Enjoy your situation.
Best regards and have a successful day
Stefan
PS: Laughlin: “The Different Universe” p. 28f. (You should have this book on your bookshelf.)
One of the greatest disservices we do to our students is to teach them that physical law is something
that obviously ought to be true and thus may be legitimately learned by note …
… that meaningful things have to be fought for and often require great suffering to achive.
It is a privilege that way, and I’ve made many predictions and discovery without the pressure to be first among many. But I also feel like we’re not making any real progress, and that can only happen with a community that reaches critical mass. So many talented people instead spend their careers chasing ghosts.
Dear Stacy,
Yes, discussing things with adults is frustrating.
Sometimes I point out to someone
that you can start with something incorrect
and, through correct transformations (and how Ptolemy used engineering ingenuity),
arrive at something true and very precise.
Everyone immediately cuts off any further discussion.
(There are very few exceptions: you, Michael Kobel, Robert Betts Laughlin)
So a few weeks ago, I gave a talk twice to a class at my former high school.
Maybe “one of the students will catch the ball” I’ve thrown their way.
Who and where is Copernicus 2.0
– Logic: False leads to True
– Copernicus, Kepler, Newton
– Prerequisites for differential calculus
– Point masses and the continuum
– We can observe both in the case of planets
We cannot confirm either of these prerequisites in microphysics.
Electrons are not points.
(If they were points, we wouldn’t have the trouble with the double-slit experiment.)
Accordingly, the use of differential calculus is inappropriate.
In 1951, Solomon Asch conducted his famous conformity experiment.
Modern physics looks similar in fundamental areas.
Best regards, and have a nice weekend
Stefan
Chandru Krishnamurthy makes a good point: “If the Newtonian force law has to be modified at low accelerations, MOND also is not off the hook — it needs to supply a causal WHY?” In terms of Guendelman’s new version of string theory, let us reconsider Professor McGaugh’s question: “How could we know if the entire dark sector is a non-entity?” Maybe there really are dark matter particles of a surprisingly simple nature. Let us assume that gravitational energy is conserved & there are 3 different types of inertia: Newton-Einstein inertia, Milgrom inertia, & Guendelman-Guth inertia. Maybe gravitons can have 3 different types of quantum spin: Weinberg spin, Milgrom spin, & Guendelman-Guth spin.
Weinberg spin might correspond to the gravitons associated with Newton-Einstein inertia, while Milgrom spin corresponds to the FUNDAMOND inertia & Guendelman-Guth spin corresponds to Guendelman-Guth inertia. The mathematics of Guendelman’s version of string theory might be able to justify such a simple scheme of dark matter particles.
Hi Dr. McGaugh, I admire your tenacity and focus on the data. I have a very limited physics background, as the following might attest. But to me, it appears that gravity is not so much modified at a=10^-10ms-2, but boosted – that it interacts with another force that seems to appear out of nowhere.
Curiously, we have an analog on Earth, where static and then dynamic friction have no impact on the movement of objects until the friction point is passed.
I would imagine that if there was a force acting away from the centre of mass of a galaxy, it would presumably interact with gravity, and the resulting normal force friction could boost the apparent gravitational force.
If two galaxies were close enough, this force could cancel each other out, which might explain galaxies with no dark matter. Two big ifs though.
Anyway, just my two cents. Thanks
Yes, the effective gravity is boosted. The how and the why remain profound questions.
“… dark matter as an explanation for the mass discrepancy observed in extragalactic systems …”
I say Milgrom is the Kepler of contemporary cosmology & Guendelman is more-or-less on a par with Newton & Einstein. Is what I say wrong? Consider 2 propositions:
(1) Dark matter particles exist because the dark matter phenomenon should be explained in terms of particle physics. (2) Dark energy particles exist because the dark energy phenomenon should be explained in terms of particle physics. Can Guendelman’s new version of string theory reconcile FUNDAMOND with the 2 preceding propositions? If we reject the conventional theory of gravitons confined to spin-2, and hypothesize a new theory of gravitons having triple spin, namely, Weinberg spin-2, Milgrom spin (justifying the dark matter phenomenon), & Guendelman-Guth spin, then, using Guendelman’s concepts & mathematics, someone might be able to find a mathematically elegant theory that looks good in terms of both FUNDAMOND & particle physics.
According to Niels Linnemann, Chris Smeenk, & Mark Robert Baker, “GR as a classical spin-2 theory” (March 2024, arxiv.org):
“Starting in the 1950s, several physicists explored the possibility that general relativity (GR) follows—in one way or another—as the unique extension of a linear field theory for gravity. With such approaches, gravitational degrees of freedom are described as massless spin-2 particles, or “gravitons”, propagating against a background spacetime. Within physics, this appealing line of work has contributed to making the case for the inevitability of GR, and to assimilating GR with other field theories. This assimilation has helped launch attempts to formulate quantum gravity in the covariant approach: a perturbative treatment of GR, as a non-linear extension of a free field theory in Minkowski spacetime, opened up the possibility of applying techniques like those used for other quantum field theories. Later work established that GR is perturbatively non-renormalizable, but this derivation is still cited as support for the claim that string theory incorporates gravity because it contains a graviton in its particle spectrum. … With regard to inevitability, Weinberg and others have emphasized that via this line of work strikingly modest assumptions yield the full complexities of GR.”
https://arxiv.org/abs/2403.08637
Did Noble Laureate Weinberg fail to understand the importance of the FUNDAMOND problem & the possibility of FUNDAMOND inertia (connected to Milgrom spin)?
Is possible that nature’s gravitons are both the dark matter particles & the dark energy particles?
Possibly, but one problem that comes to mind is that intriguing possibilities may end up becoming non-falsifiable theories. That may be the situation we are already in with dark particle theories.
Why not try applying information-theoretic analogs of string theory to what we already measure, to construct more falsifiable theories? Our cosmological description emerges from measurable bits, so if the is a scale-invariant version of string theory, how could it be applied to what we already measure?
(1) Dark matter particles exist because…
Hi David,
For myself, I’m looking for a better understanding of our space.
And producing the known elementary particles seems difficult enough to me…
Stefan
“Yes, the effective gravity is boosted. The how and why remain profound questions.” https://en.wikipedia.org/wiki/Weakly_interacting_massive_particle
The MOND gravitational acceleration surprisingly adds to the Newtonian gravitational acceleration. If the FUNDAMOND modification to Einstein’s field equations surprisingly slows down time in addition to the Einsteinian slowing of time, then there might be either surprising new sources of MONDian mass-energy or there might be Guendelmanian gravitons that are different from Weinbergian gravitons. Instead of MONDian WIMPs, there might be Weakly Interacting Guendelmanian Gravitons (WIGGs). The WIGGs would be associated with a new form of spontaneous symmetry breaking that might be derived from Guendelman’s new version of string theory.
@ Stefan G. Freundt “… a better understanding of our space …” — in The Wolfram Physics Project ( https://www.wolframphysics.org ) , the theoretical physicists are working with ideas connected with Wolfram’s idea that there are “atoms of space” near the Planck scale. As Weinbergian gravitons travel through space, they might create some type of “Wolframian” disturbance among the atoms of space — this hypothetical disturbance might be the key to understanding FUNDAMOND (the hypothetical, relativistic generalization of MOND).
‘It is impossible to falsify ideas that involve invisible components.’ In my opinion DM is falsifiable. The theory makes predictions and those predictions prove not to be true. That’s surely as good as it ever gets in cosmology. For example, quasars formed, theoretically, where DM was densest, and shouldn’t be isolated objects because lesser halos of DM should have attracted smaller concentrations of ordinary matter in their vicinity. However, when Eilers et al. (2024) studied five quasars at z = 6–7, they found that the number of neighbouring galaxies varied arbitrarily from 47 to zero. The matter concentrated in the quasars themselves varied widely, from 1.2 to 11.5 billion solar masses. “Some of them seem to be sitting in the middle of nowhere,” said the lead author in a press release. “It’s difficult to explain how the quasars could have grown so big if they had nothing to feed from.”
So far as I can see, DM has proved unfalsifiable only because astronomers have lost sight of how science works. A theory which is not falsifiable is not a scientific theory. A scientist who refuses to accept that a theory has been falsified is not, in that respect, a scientist. Pavel Kroupa rightly insists on this. The fact that DM is invisible is neither here nor there. The ether was invisible, but it still ended up in the waste bin.
I consider the *concept* of dark matter to be unfalsifiable. Specific flavors of hypothesized DM might be falsifiable, but that only matters if – as you say – we accept that it is so. It is neither quick nor easy for a scientific community to come to such a clear conclusion. Aether is a good example. Nowadays we teach it as if it were a binary: a credible possibility before the Michelson-Morley experiment and falsified thereafter. But “thereafter” took decades and aether persisted, like DM, as a “must-have” for many, and for some even after Einstein. In retrospect we can cite Michelson-Morley as its death knell, but that wasn’t obvious at the time (including to Michelson and Morley). Perhaps in the future the demise of DM will be clear and dated to some event that has already passed, but right now we’re still living the controversy.
According to P Graneau, the results of the experiment were not unequivocal, so maybe there was reason for the concept to persist. In any case, the vacuum is not empty but filled with a vast amount of energy.
Also, as far as I know, we can’t explain the frame of reference whereby an object (e.g. a planet, a supermassive black hole) spins in ’empty space’ (cf. Mach’s Principle). That too is pretty fundamental.
Could you explain to me what is usefully left of the concept of dark matter when it is no longer considered to interact with itself? I thought its only property was to exert a gravitational force, but if it doesn’t interact with itself, it doesn’t clump, and if it doesn’t clump, it can surely play no role in explaining how, near the beginning of time, ordinary matter began to clump into stars and galaxies. Sorry to be asking such a basic question.
Dark matter interacts with everything via gravity, including itself. Indeed, it has to clump, and in the standard model has to clump in order for stars and galaxies to form, as it provides the backbone to which the visible web of the universe clings.
There are many confusingly-named variations of dark matter. One is self-interacting dark matter. But that has some property in addition to gravity by which it interacts only with itself (so it does both: gravity plus entirely new force that only works for SIDM). Most hypothesized forms of DM only interact with visible matter via gravity.
Thank you. I will be going to the full paper shortly, but in the meantime this is the latest on the Bullet Cluster: https://www.skyatnightmagazine.com/news/bullet-cluster-dark-matter.
“Observations confirm it doesn’t interact much, if at all, with itself. Or, as the study puts it: “dark matter shows no signs of significant self-interaction’.” The Bullet Cluster is supposed to be the proof of DM par excellence, but it has never made much sense to me (especially if the reality is that the subclusters, each with their BCG, had a common origin where the superhot gas now is and that’s why they are going in opposite directions).
Right. By that they specifically mean SIDM. So lack of evidence in favor of SIDM implies that “normal” CDM is favored.
… meaning DM that does not interact with itself gravitationally but does interact with baryonic matter gravitationally? If so, the mind boggles.
No. Meaning there is no additional self-interaction between DM particles on top of their gravitational interaction.
All DM interacts gravitationally with baryons and with itself. SIDM hypothesizes an additional force between DM particles that is mediated by a new force that is only active in the dark sector. The carriers of this dark force do not interact with baryons, and are often referred to as dark photons (worst. name. ever.) These dark photons might themselves have rest mass, but are distinct from the SIDM particles that make up the bulk of the dark mass.
This is part of the problem with invisible entities. It is an invitation to theorists to run wild and bugger the principle of parsimony.
“… thousands of careers barking up the wrong tree. The unseen forest that is the ‘dark sector’ is vast; there are limitless opportunities to bark up other wrong trees. … I remain unwilling to say that dark matter has been falsified because I don’t think it is falsifiable.” What are the 20 most important questions about MOND and/or FUNDAMOND — are there any publications with such a list of questions? The MOND challenge might be somewhat similar to attempting to answer the question, “What biological organisms exist in the Andromeda Galaxy?” If there is empirical validity to Wolfram’s idea about “atoms of space”, then to each atom of space there might be associated a somewhat complicated spin matrix that yields essential information related to FUNDAMOND data and dark energy data. What does Wolfram now think about MOND and FUNDAMOND?
… “only consider MOND as a last resort” … The psychological reactions of many astronomers & astrophysicists against MOND might be an indication of how profoundly original & significant MOND is. What ideas, strategies, tactics, & techniques might promote MOND & FUNDAMOND? It might be a good idea to create a “FUNDAMOND Recruiting Society” (FRS) with the goal of recruiting young astronomers & physics to work on the problem of FUNDAMOND.
Does FUNDAMOND inertia actually exist? Angular momentum might be 11-dimensional, having 4 dimensions in terms of Minkowski space, 3 dimensions of Milgrom spin, 3 dimensions of Guendelman-Guth spin, and 1 dimension of quantum field theory (QFT) spin (ordinary quantum spin). The 11-dimensional angular momentum might be part of understanding Newton-Einstein inertia, Milgrom inertia, & Guendelman-Guth inertia. The expanded angular momentum might be carried by Guendelmanian gravitons, Wolframian atoms of space, or some other weird speculative mechanism.
Why do I think that the world’s 2 greatest living scientists are Milgrom & Guendelman? It seems to me that Green-Schwarz-Witten (GSW) string theory has many good features.
“One day we may understand what string theory really is. But even if we do, and the theory is on the right track, will we be able to learn how it works in nature?” — Edward Witten, “Nature”, Vol 438|22/29 December 2005
TITLE: “Unravelling string theory. String theory may provide the best clues yet about how to obtain a unified theory that describes all the laws of nature, but do we even understand what string theory is?”
https://www.ias.edu/sites/default/files/sns/files/Unravelling(1).pdf
However, the GSW string theory seems to me to be a form of non-FUNDAMOND string theory — I guess that FUNDAMOND string theory is necessary (i.e. MOND empirical successes need to be explained by some form of string theory).
Guendelman’s new version of string theory might be able to explain both the dark matter phenomenons & the dark energy phenomenon is terms of spontaneous symmetry breaking of string vibrations.
What might be occurring? Milgrom spin might interact with quantum spin to generate FUNDAMOND inertia. Guendelman-Guth spin might interact with quantum spin to generate dark energy inertia. These weird inertial influences might lead to modifying Einstein’s general relativity theory (which is limited by restriction to Newton-Einstein inertia). Is the preceding speculation wrong?
In any case, my guess is that the empirically correct version of FUNDAMOND requires some form of string theory & several new physical concepts.
I am convinced that Professor Milgrom of the Weizmann Institute is more than 20 years overdue for a Nobel Prize in Physics. My guess is that the 3 best MOND experts are Milgrom, McGaugh, & Kroupa. However, it seems that those 3 have very little understanding of string theory. On the other hand, the string theorists haven’t bothered to study MOND’s empirical successes & have failed to understand the importance of the FUNDAMOND problem. Is FUNDAMOND essential for understanding the foundations of physics? Is string theory essential for understanding the foundations of physics?
According to Joseph Polchinski, “What Is String Theory”, arxiv.org, 1994, pages 44–45:
“The main clue that leads us to string theory is the short-distance problem of quantum gravity … The more common expectation … is that the nonrenormalizability indicates a breakdown of the theory, and that at short distances we will find a new theory in which the interaction is spread out in spacetime in some way that cuts off the divergence. At this point the condensed matter half of the audience is thinking, “OK, so put the thing on a lattice.” But it is not that easy. … In fact, we know of only way to spread out the gravitational interaction and cut off the divergence without spoiling the consistency of the theory. That way is string theory, in which the graviton and all other elementary particles are one-dimensional objects, strings, rather than points as in quantum field theory.
https://arxiv.org/abs/hep-th/9411028
Have the string theorists made very little progress over the past 30 years? I think that I now somewhat understand FUNDAMOND string theory — although with an unfortunately shallow understanding. I believe that I understand enough to convince, in a few months, at least 20 of the younger string theorists that I am correct about Milgrom & Guendelman — this should enable those 2 to share a Nobel Prize in Physics by the end of next year. Am I deluded?