In classic internet fashion I only did a quick skim/search of the article and preprint of the paper (linked in this article). However, neither make mention of the bullet cluster [0] or "particle dark matter" and seem to rely more on galaxy rotation curves.
While the bullet cluster may not be as definitive as we would like, it is at the very least very strongly suggestive of particle dark matter or something similar. As far as I remember modified gravitational theories without particle dark matter don't offer a good explanation of the bullet cluster (in short, evidence of a non- or weakly interacting but gravitational matter).
I won't argue with schemes like MOND or this proposal that can explain rotation curves, but the bullet cluster at the very least is a more interesting test these days. Without even a mention of some alternative explanation here (from my quick look), it is a non-starter for a dark matter-less theory. And a pretty glaring omission (again, maybe I missed it) for what is a well-known observation.
Still, alternatives for quantum gravity, and anything that might say something about dark energy, are exciting. Falsifiable ones especially. But if you didn't address the bullet cluster then...
After a little more of a skim: the paper seems mostly to be about reproducing an equation like that of MOND (modified Newtonian dynamics). Which, fine, some people are fans of MOND (not most, and for good reason from the theoretical which this might address, to the practical like previous comment), but there's a whole lot more than just the dynamics of rotating galaxies to consider. Without even going into that (bullet cluster, lensing, n-body simulations, galaxy formation, etc.) it doesn't (yet?) replace anything.
Most important is still the CMB. Back then everything was ionized and yet we have extremely good evidence of matter that only contributed gravitationally to density perturbations and not via the ordinary electromagnetic path. There is no way to explain this merely by modifying the law of gravity. So even if MOND or similar approaches turn out to be correct, they can never explain all aspects of dark matter. Only particles can.
Sure, but the origin of this preprint is in the stochastic-classical/uncertain-quantum "postquantum-classical" theory the Oppenheim group is working on. Their theory is premised on a weakening of the gravitational interaction at short distances (it's "asymptotically free" and thus renormalizable) compared to perturbative quantum gravity (which is non-renormalizable by power counting). However, they discovered that the gravitational interaction in their theory can be too strong. More technically, in their diffusion limit they extract a different scalar potential than from GR's weak field limit, with the former growing (statistically) stronger with increasing radius. This in practice means even with a highly similar source, their theory predicts significantly different geodesics compared to General Relativity.
Rather than abandon the theory or complicate it such that it becomes compatible with fully classical GR, they solved a Schwarzschild-de Sitter (static spherical symmetry and an expansion term which "washes out" the extra-strength gravitational potential before it gets too strong) spacetime with a galactic mass (described simply and with some restrictions) and found that the geodesics are within a standard deviation or so of stable circular MONDian orbits. That result would relieve some of the immediate concern that their theory is unphysical, and drive them towards further study of its large-length-scale behaviour.
(In fact their result is better than some earlier attempts to make a generally covariant MOND by adding auxiliary gravitational fields to GR (see the overview by Famaey & McGaugh 2012). Postquantum-classical gravity was on a relativistic footing from the start, although exactly how diffeomorphism invariance and manifest covariance of formulations works in postquantum-classical gravity is really interesting, see <https://arxiv.org/abs/2402.17844> if you want details)
It would be interesting to see how their theory does does -- it would have to be studied numerically -- with any sort of CDM halo. Various stellar binaries are also an obvious place to look, since for sufficiently wide ones, you can't "wash out" the extra strength of the scalar potential with an expansion term. (Wide binaries are really rough on MOND too, for comparable reasons).
"While this study demonstrates that galactic rotation curves can undergo modification due to stochastic fluctuations, a phenomenon attributed to dark matter, it is important to acknowledge the existence of separate, independent evidence supporting ΛCDM. In particular, in the CMB power spectrum, in gravitational lensing, in the necessity of dark matter for structure formation, and in a varied collection of other methods used to estimate the mass in galaxies"
I won't get into an argument about MOND. Don't take my word for it, take the vast majority (all but a few?) of anyone working in the field. And don't take Milgrom's word for it (or the one reference given) either, for that matter, as clearly he has a horse in the game. Sure you can continue to make MOND work to some degree, but is it really predictive if you keep adding things to make it work? What is the underlying theory? (The proposal in this linked article is interesting in that regard.)
Okay, so maybe I did continue the argument a little :) I love for people working on alternative less mainstream ideas. But MOND was never very alive to begin with, let alone decades later. Let's move on.
Absolutely. I'm out of the field these days, but e.g supersymmetric WIMP dark matter was the most popular but got more and more clugely with low energy supersymmetry seeming less likely (or not as useful in solving the problems it meant to solve). Everyone would come up with some tuned ad hoc model for whatever dark matter "signal" was in fashion (before being ruled out); none of those were compelling. Fun to play with maybe, but didn't really tell us anything.
Who cares? This has literally never been a requirement of science and I don't know why people bring it up for MOND. What was Isaac's Newton's underlying theory when he proposed his law of gravitation? No explanation for why two masses attract, therefore we should reject an effective description? That's nonsense.
A theory is scientific if it describes what we observe, period. If you have a deeper explanation right off the bat, that's a bonus, otherwise that's the goal of further research.
The other poster adequately addressed the implicit hypocrisy applied to MOND vs. LCDM, so I'll just leave this reference for a proper analysis of who has been making predictions vs. tweaking their theory to fit observations:
From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity, https://arxiv.org/abs/2110.06936
Fine, rather than "underlying theory" use some other words, basically does any new proposal give us predictions, solve some unexplained phenomenon, do something simpler and more compelling (sure, a matter of taste, but so is all of this to some degree), in short, does it tell us something new. Newton certainly did as he gave a law to describe and predict successfully the motions of the planets, for instance. I don't think we are saying anything different really. There wasn't a predicitve framework before (as far as I know), but then there was, so that is certainly progress. But the bar gets ever higher as we know more for what a theory should do. Just writing down an equation that can fit some data and can make predictions is great but is not the end of the story. We could just have some arbitrary functions that fit the data we have and call it a day.
Yes. Sone researchers went looking for the absence of EFE to disprove MOND and wound up finding it instead. MOND has predictive power. Moreover, we keep finding that lenticular and dense elliptical galaxies have "no dark matter", which is a prediction of MOND.
One of the reasons why things "keep getting added" to MOND is that it's known to be incomplete. The equations to reconcile MOND with relativity are not known and are tougher (but not necessarily impossible) than the Newtonian equations.
So it's expected that things will have to be added. That the equations are tricky for us mere mortal humans should not be held against it; the universe has no requirement that equations must be easy to solve.
Iirc, One of the articles has a diagram with four dark matter less galaxies in a sweeping curve. But if you look at the diagram, there's no less than two other dark matter less galaxies off the curve so one must wonder if it's just a coincidence
The article in question here is a followup to that, as a preprint and linked in this submission: "In a recent paper [0], which has not been peer-reviewed"
Indeed, This is a peer-reviewed paper. However I do not know why it took more than two years from submission to publication. However that does not say much as I don't want someone to misinterpret this as a judgment on quality of the paper.
A peer review and a popular article exploring the proposal, though written by someone pretty qualified, are not the same thing. At the very least the audience and evidence presented are not nearly the same.
No. Peer review is an established process in which the editor chooses usually two to four expert peers who review the paper. It is double blinded to reduce bias.
It is also not the point of peer review to judge the correctness of the theory. Reviewers check relevance, novelty, plausibility, consistency, overall correctness of methodology. "I think this is wrong" is not something an editor would accept as an argument not to publish. That's something you can write in a new paper. And I don't think Hossenfelder would like to see it not published just because she thinks it's wrong.
I think this theory is wrong about the sources of randomness.
But it's super cool that they show that a bit of randomness could explain dark matter and energy.
Personally I believe that the randomness might come from chaotic "background" gravitational waves from sources outside of universe and from times before Big Bang.
I don't know if I'd call her "contrarian" but I think it's safe to say she's not exactly filled with starry-eyed optimism. Maybe a lot scientists generally become increasingly jaded and skeptical after years of seeing a lot of big claims and hopes much of which end up amounting to very little, but physicists seem to have had an especially rough time.
She's been that way on physics forever, and she was at least interesting there, but she's moved on to subjects outside of her field, and that hasn't worked as well at all.
Science is a large field. Being an expert in physics won't make you an expert in other scientific fields, yet somehow people love to know the opinion of their favourite heroes of any topic.
Remind me of Jurgen Klopp rebuking some journos that wanted his opinion, as successful football coach, on COVID.
Just the field of physics is so large that most would probably not dare to state criticism in other sub fields. Like a Nobel prize winner in solid state physics would never judge the work of a high energy particle physicist and vice versa.
Hossenfelder is definitely qualified to talk about the OP, but her videos about transgender people shouldn't be given more credit than videos from almost any other person.
There is definitely value in people popularizing scientific consensus even when they aren't experts in the field, Bill Nye talking about climate change is useful even though he's not an expert. But when you aren't an expert and aren't trying to convey the consensus of people who are experts, you're Just Some Person With An Opinion.
It's when a popularizer starts having opinions that aren't widely shared in a field that they aren't themselves expert in that things can start to go wrong.
Being publicly contrarian about stuff you're an expert in can be interesting, being publicly contrarian about stuff you just don't know much about is at best not very useful and at worst harmful.
The thing is, progress in physics has become hard because physics has been extraordinarily successful. Between them, general relativity and the standard model (of quantum mechanics) explain all of the phenomena that humans see or create on earth and all the star-level things we can observe. Things only get hard once you reach enormous scales of the distribution of matter in the universe. So the situation can only seem "bad" to someone who isn't seeing the larger picture imo.
Clickbait implies she doesn't cover the topics in her thumbnails, or that they are misleading or inaccurate in some way. That hasn't been my experience watching her videos.
Honestly, I'm watching a bunch of people punch down at imaginary people, I'm not sure there's really anything here than whining about a good article and bizarre irrational stack ranking
I'm not sure I know what you're talking about, but there's nothing imaginary about how bad some "science journalists" are, and the notion of a bunch of HN commenters "punching down" at either journalists or physicists with much bigger platforms than we have is dubious.
I knew you were saying one of a couple rather weird things. I still don't know which, but I thought the substance of my comment addressed all of them and you haven't bothered to respond to that, so I guess my point stands? We were both nitpicking, so you don't get to claim the high ground.
I'm not arguing with you at all, it wouldn't make any sense to, you're not making any claim other than imagining I claimed articles where the journalist doesn't know anything about the topic are always good.
Recap:
I observed the thread was absurd because:
- it opened complaining about the science journalist writer who didn't know the topic.
- after it was resolved the author wasn't a science journalist or someone who didn't know anything, people were arguing about the stack-ranking of the imaginary science journalist
Now you're here, continuing to argue against a strawman for no discernable reason. We all get it, you and some other people are making sure we understand we're wrong, it can be bad when people write things they don't know about.
> you're not making any claim other than imagining I claimed articles where the journalist doesn't know anything about the topic are always good.
I definitely never argued or even believed any such thing. I started off in this (granted, rather silly) thread with a lukewarm defense of Hossenfelder, then you took a weird tangent on it and I disagreed with your framing (or what I could grok of it). Maybe you have me confused with someone else?
Yes, but in the article under discussion, she's writing like a science journalist. A theoretical physicist's criticism of the paper belongs in a published paper of her own, not a pop science article.
I think it's important to point out that reading the abstract and then throwing it into gpt4 would result in a more informative article than the current one.
The article spends about a third of its time waxing loquacious about MOND - hossenfelder's own theory - before dismissing the current paper for having equations that are just "too simple" .
Now I'm not a physicist. I'm an applied category theorist working in business process modeling of all things. But when I was reading hossenfelder's article I was hoping it would describe how oppenheim models the spectral dispersion of stochastic gravity. This is the linchpin of how oppenheim predicts physically observable phenomenon from the model.
That was missing. There have been other articles, which at least mentioned it in passing. I was hoping hossenfelder, being a physicist, could help clarify that for a wider audience. They made a choice not to.
> waxing loquacious about MOND - hossenfelder's own theory
"Modified Newtonian dynamics (MOND) [...] Created in 1982 and first published in 1983 by Israeli physicist Mordehai Milgrom" [1]
"Born 1946" [2]
"Sabine Karin Doris Hossenfelder (born 18 September 1976) is a German" [3]
I suppose a SciFi story where it eventually turns out that they are the same person (presumably as an unintended consequence of an experiment designed to test their theory) could be fun.
In your reference [1] we see that hossenfelder has worked on their own version of MOND:
"Testing MOND using the redshift-dependence of radial acceleration – Sabine Hossenfelder and Tobias Mistele propose a parameter-free MOND model they call Covariant Emergent Gravity and suggest that as measurements of radial acceleration improve, various MOND models and particle dark matter might be distinguishable because MOND predicts a much smaller redshift-dependence.[81]"
That is the theory I'm talking about.
It also seems like I exaggerated how much of the article was dedicated to MOND, which was my bad.
The article is still poor coverage of the actual research
Yes, and for non-specialists it's enough to know that the paper isn't even peer reviewed yet, and not waste time on bla-bla-heavy clickbaity pop article..
This theory is trying to justify MOND, and MOND by itself has many problems. It has problems with explaining the bullet cluster, CMB spectrum, and rotation curves of some galaxies. This paper was not even peer reviewed. This is almost certainly nothing burger
The reason you think that this theory is trying to justify MOND is likely because hossenfelder spends about a third of the article discussing it instead of discussing the current theory.
MOND is hossenfelder's pet theory - they've done work on a version of it called Covariant Emergent Gravity
It's fine to say that any given new physical theory is almost certainly a nothingburger.. I agree with that. But please reread the article and confirm for yourself that what I say is true.
> This presents a testable deviation from classical general relativity, potentially observable when the other terms are small, such as at low acceleration. The absence of such terms is likely to falsify this model. On the other hand since diffusion of the metric can result in stronger gravitational fields when we might otherwise expect none to be present, it raises the possibility that diffusion may explain galaxy rotation curves and galaxy formation without the need for dark matter
It certainly doesn't seem like an extreme reading to call this a MOND theory.
The issue is not calling it a MOND theory, it's with saying this theory is trying to justify MOND, as if that was it's primary purpose. The primary purpose was actually to unify GR with quantum mechanics and this MOND part just fell out.
I'll grant that I was exaggerating. That's my bad. It's only 1/6th of the essay.
Re: making two comments:
I made the first point to criticize the low quality of the article. It is a low quality and dismissive article that misses an opportunity to talk about the technical meat of the theory, even through analogy. That's still true.
In the second comment I mentioned the mond thing it because it was directly related to a reader's misunderstanding, and because I felt introducing mond into the article was a red herring that had contributed to this misunderstanding. They reader thought this was specifically a MOND theory, and was therefore dismissing it out of hand. I don't think we should dismiss this theory so easily as that.
Re: Alt account
This is my only account. I lost the credentials to my old account, and it wasn't linked to my email.
Re: criticism
I drop stink bombs on things that I think are likely to misinform, and if I am wrong, I'm happy to correct myself.
Re: correction
I thank you for your comment and your correction. I know it was probably not very pleasant to write, and I know my self correction is not to the extent that you wanted, but your paragraph count helped me see I was exaggerating the MOND claim. Overcoming my own tendency to exaggerate things is very important for me, since it gets me in trouble, or gets my otherwise good arguments dismissed. I sincerely thank you for helping me with that.
Re: changing my opinion about the article
I still regard this article as an opaque and low effort treatment of the work at hand. Perhaps you could express how a particularly clear point in the article helped you understand more from the paper when you were reading it? That kind of testimony could help me understand how to see this as a good article, and to see where the value is. Thanks!
While the bullet cluster may not be as definitive as we would like, it is at the very least very strongly suggestive of particle dark matter or something similar. As far as I remember modified gravitational theories without particle dark matter don't offer a good explanation of the bullet cluster (in short, evidence of a non- or weakly interacting but gravitational matter).
I won't argue with schemes like MOND or this proposal that can explain rotation curves, but the bullet cluster at the very least is a more interesting test these days. Without even a mention of some alternative explanation here (from my quick look), it is a non-starter for a dark matter-less theory. And a pretty glaring omission (again, maybe I missed it) for what is a well-known observation.
Still, alternatives for quantum gravity, and anything that might say something about dark energy, are exciting. Falsifiable ones especially. But if you didn't address the bullet cluster then...
[0] https://en.wikipedia.org/wiki/Bullet_Cluster