Tuesday, March 20, 2018

More about MOND v. Dark Matter

* MOND solves the Missing Baryon Problem.

* In MOND there isn't a Lithium 7 problem arising from Big Bang Nucleosynthesis, but there is a deuterium problem which is similar in character but smaller in magnitude.

Large scale structure forms sooner in MOND than in lambdaCDM, consistent with new observations of the very ancient universe (also here), although this is much harder to model precisely because it is a non-linear theory.

* MOND is insufficient to replace all dark matter in clusters, but sister theories like MOG and Deur's work do successfully deal with that issue. The Bullet Cluster is more of a problem for dark matter particle theories than it is for modified gravity theories, as a class.

* There are several successful relativistic modified gravity theories, although toy model MOND is not one of them and is not applicable to relativistic conditions. MOND was developed as an alternative to General Relativity in domains of applicability where General Relativity itself is approximated for practical purposes by Newtonian gravity.

* MOND models all galactic rotation curves with a single experimentally determined universal parameter in a fit that is indistinguishable from perfect given measurement errors. Dark matter theories should not have such low scatter and can only come close to this fit with 16 parameter models fine tuned to existing conditions.

* Dark matter can't explain the Crater II galaxy dynamics. MOND predicts an external field effect that is observed but has no place in conventional General Relativity with or without dark matter.

* Dark matter can't explain MOND-like effects observed in wide binary stars.

* MOND has made multiple predictions that have born out. Dark matter has repeatedly failed to make accurate predictions.

* Deur's work explains all or more dark energy phenomena, explains variations in apparent dark matter amounts in elliptical galaxies, and explains cluster phenomena, and ties MOND/dark matter/dark energy phenomena to quantum gravity foundations.

* There aren't great models of what MOND predicts in the CMB, largely because as a non-linear theory it is hard to model. But, MOG fairs pretty well.

* Direct detection experiments and collider experiments have failed to see any experimental evidence of  beyond the Standard Model particles that could be dark matter candidates over a broad swath of parameter space. For example, here.

* Purported dark matter annihilation signals have all turned out to be false alarms with other explanations. For example, here.

* The inferred dark matter distributions rule out a broad swath of parameter space including the parameter space axiomatically assumed in lambda CDM theories, which assume nearly collisionless dark matter despite the necessity that it have interactions with baryonic matter to have distributions so tightly correlated with baryonic matter.


neo said...

Deur 2 papers on the topic An explanation for dark matter and dark energy consistent with the Standard Model of particle physics and General Relativity has zero citations and Implications of Graviton-Graviton Interaction to Dark Matter has 4 citations, 3 self-citation. Lee Smolin's work MOND as a regime of quantum gravity has 8 citations, only 1 self citation.

Dark matter does predict CMB and gets it exactly correct. I suspect that within the MOND framework, dark matter consists of primordial black holes that exists between galaxies.

it seems most parsimonious with current data that there is MOND + standard model with dark matter black holes.

btw any updates from Moriond 2018 LHC results?

andrew said...

Deur's work isn't widely known or cited, but it is pretty solid in method and analysis. In my humble opinion, it is the best work to devise a theoretically well grounded modified gravity approach to date, but suffers mostly for the sociological reason that it is done by someone outside the field who is applying mathematical insights from QCD which aren't widely known outside that field. Citations are not a measure of truth.

Dark matter, in general, and black hole dark matter, in particular, can't explain the data and is inconsistent with the data.

I haven't seen Moriound 2018 LHC results. In prior years, conference paper abstracts and slides have been posted at a conference website, so you may want to look for that. Honestly, it probably hasn't made news because there isn't much new to report at the LHC. We are by all accounts in a new physics desert there.

neo said...

I'm skeptical of gravitons, also Smolin notes previous research that the MOND ao is on the same order as the cc.

Both Ethan Siegal and Sean Carroll explain those instances in which dark matter does explain data which I've mentioned before.


which convinces the vast majority of astrophysicists of dark matter, something even Stacy McGaugh acknowledges.

Ethan Siegal acknowledges that MOND does explain data at the galaxy better than dark matter on his articles on Forbes, but that MOND does not and cannot explain certain facts like CMB

i was thinking that to keep the standard model, black hole dark matter might be quantum mechanical black holes on order of 1 planck mass + MOND

yes there's no reporting of Moriound 2018 LHC results, not even new gluino or squark bounds. all i've seen is Jester's claim of no new physics which Tomisino retweeted but no discussion of LHC

andrew said...

The limitation on black holes less than 3 times the mass of the Sun (which is as small as can be created with any current process), called primordial black holes, as dark matter, is very strict indeed. They have to be formed in the first 0.00000!%ish of the universe and would evaporate due to Hawking radiation below a certain mass by now and microlensing and other tools rule them out for almost the entire DM parameter space. Also, DM to fit the standard model of cosmology, needs to collisionless, which primordial black hole dark matter is emphatically not.

andrew said...

Moriund 2018 conference papers are at https://indico.in2p3.fr/event/16579/timetable/#all.detailed

The first few days are electroweak, the next few days are cosmology, the final bit is QCD.

neo said...

- what is the end product of hawking radiation of low mass primordial black holes? there's not an accepted theory of QG to tell us what happens to quantum mechanical "black holes"

MOND + some form of "dark matter" isn't "standard" cosmology although its certainly something Milgrom McGaugh are willing to entertain.

Ethan Siegal argument against MOND is that MOND still requires "dark matter"



Only Dark Matter (And Not Modified Gravity) Can Explain The Universe
Forbes-Mar 6, 2018
When you look at the full suite of data, rather than just some small details of what goes on in the messy, complex, nonlinear regime, there's no way to obtain the Universe we have today without adding in dark matter. People who use Occam's Razor (incorrectly) to argue in favor of MOND, or MOdified ...

Ethan Siegal and Sean Carroll are summarizing what the majority of astrophysicists and particle physicists have concluded.

I don't agree with Siegal that bc you need to add dark matter to MOND, that therefore there is no MOND.

btw thanks for that link that's a lot of papers,
i'm hoping just a one sentence summary - any new non-SM physics?

andrew said...

A good share of the Moriund 2018 papers are looking at charged lepton universality violations in B meson decays that have been observed. But, the anomalies are already starting to get weaker and are highly constrained by data that are good fits to charged lepton universality, so it is very hard to come up with plausible models that fit the data if the anomalies persist, which they probably won't. Honestly, this year is pretty subdued. I didn't see anything game changing in a quick skim of the papers.

I'm not impressed by appeals to authority, particularly as Ethan Siegal isn't a very prominent figure in the field and Sean Carroll isn't the most mainstream himself. And, quite frankly, the article reads more like a polemic and less like an honest and even handed assessment of the data. He continues to focus on very old rotation curve in galaxy data thinking that this is all there is. But, new data predicted in advance by MOND but not by DM theories, like the 21cm radio datapoint from EDGES, the Crater II galaxy, wide binary star measurements, and solutions to the Lithium 7 baryogenesis problem, the cosmic coincidence problem and the missing baryon problem, are all deeply damning to DM theories in ways totally independent of the galaxy rotation curve data.

The 21cm datapoint is particularly powerful, because together with a couple of other new measurements of metal content in very early stars and supermassive black hole and galaxy sizes very early on, serious doubt has been cast on the accuracy of the standard model of cosmology in the early era for which its CMB measurements are the crowning achievement and sole prediction of DM. (And, even toy model MOND gets two of the three peaks dead on.) Large scale structure and galaxy assembly took place much earlier, and cooling took place much more quickly, the lambda CDM predicts in a very robust way. And that is a very difficult problem with the lambda CDM model to fix. Further, the properties are DM candidates that could provide a mechanism for the lambda CDM model are increasingly overconstrained.

The notion that it is impossible to tweak some modified gravity theory, a class of theories that is equal or superior to DM theories in almost every other context, to hit the CMB third peak spot on is motivated, pessimistic reasoning. The two classes of theories are competing with each other in the first place because their phenomenologies are almost degenerate with each other. It is really so hard to imagine that a theory that produces identical rotation curves in galaxies might also have a very similar phenomenology in the early universe.

But, every time that a test like wide binary stars or the 21cm datapoint or Crater II comes along that can distinguish between between the two classes of theories, the modified gravity position comes away looking strong and the DM position comes away deeply flawed.

DM can't even reproduce the Tully-Fisher relationship without rigging simulations with sixteen adjustable parameters that don't have a basis in direct measurements of astronomy phenomena based upon current matter distributions, and even then, they struggle. DM is not a theory that can even explain much of the existing data very well. It is a leap of faith, and it becomes more Baroque with each new effort to try to make it fit new data points.

neo said...

Hey andrew you saw my post on Jester's blog, even Jester is a believer in dark matter

its not just an appeal to authority, Ethan Siegal and Sean Carroll are summarizing mainstream astrophysicists , something even Jester accepts. Jester rejected Stacy McGaugh paper as just 1 data point.

"And for all of these observations, there is no single modification of gravity that can reproduce these successes. There are a few vocal individuals in the public sphere who advocate for MOND (or other modified gravity incarnations) as a legitimate alternative to dark matter, but it simply isn't one at this point. The cosmology community isn't dogmatic at all about the need for dark matter; we "believe in" it because all of these observations demand it. "

Ethan Siegal and Sean Carroll summarizing the field also point out that using weak gravitatational lensing on galaxy clusters, you can infer how much mass there is. then by measuring all the visible matter, baryonic, you can deduce how much of that weak gravitatational lensing can be explained, leaving a deficit of mass roughly 5x visible matter.

"4.) The gravitational bending of starlight from large cluster masses in the Universe. "

MOND and its variations cannot also explain weak gravitatational lensing and the results gleaned from weak gravitatational lensing also matches the third peak in CMB.

the third peak is the dark matter peak.

assuming newton and einstein laws intact, each way to measure how much dark matter there is comes up with the same order of magnitude of 5x visible matter

If you read Ethan Siegal's article he does say

" MOND does have a big victory over dark matter: it explains the rotation curves of galaxies better than dark matter ever has, including all the way up to the present day."

in this respect Stacy McGaugh Milgrom et al are partially vindicated

Ethan siegal Sean Carroll jester are simply summarizing the evidence that convince the super majority of astrophysicists cosmologists particle physicists of dark matter, not merely fringe views and an appeal to authority