Talk:Modified Newtonian dynamics

I removed the following part:

Spiral galaxies offer compelling evidence that this is more than an observational artifact. M51, for example, has two main arms (see fig. 1), each of which has an exterior end approximately 180° behind the interior end connected to the bulge. It thus appears that the edge completes an orbit in almost the same time as the interior. However, if Newton's universal law of gravitation holds for galaxies (as it should), stars at the edge should move much slower, and the spiral arms should be stretched around the bulge a hundred times, which would make the two arms completely indistinguishable.

(Image Removed)

The existence of spiral galaxies alone does not provide compelling evidence for the flattening of the rotation curve, since the galaxy's arms do not consist of stars; they are pressure waves rotating around the galaxy's center independently of the matter comprising the galaxy. AxelBoldt 11:20 Aug 15, 2002 (PDT)

---

For comparison purpose, the same curve for the Solar system -- (properly scaled) -- is provided (curve C in fig. 2).

Am I missing something? I see the letter C but no associated curve. --Nate 21:14 Nov 27, 2002 (UTC)

I can't see curve C in Fig. 2 either. [Feb 5, 2004 Wes Hughes]

Galaxy rotation problem

Does it make sense to essentially copy all of Galaxy rotation problem into this article?

Aragorn2 15:07, 25 Sep 2003 (UTC)

I just ran into this article, the first paragraph is indeed copied (but it is allowed under Wiki GNU Free Documentation License. Anyway, the majority of the article is dedicated to the solution of the problem by Milgrom's MOND. A descripition of the problem is neccesary. MathKnight 22:21, 28 Aug 2004 (UTC)

Rotation curves are not evidence

"Since MOND was specifically designed to produce flat rotation curves, these do not constitute evidence for the theory."

I don't agree with this formulation. Any theory aims to match its predictions with already known observations. By the same principle the standard model of particle physics would be useless, because it "depends on 19 parameters, whose numerical values are established by experiment".

Only data that has been used to produce $a_{0}$ should be dismissed as evidence.

References

Misleading statements in Introduction

Ruslik0 MrOllie Your global edit here [1] and the revert[2] is particularly unhelpful. The problem with the page is that it is not NPOV and offers opinions that are not supported by citations. The whole introduction reads as if MOND is wrong rather than explaining what MOND is about. All the current cites notably are articles which rejects MOND over dark matter. While is important to argue for and against hypothesis, the article should first explain what MOND is, and then discuss issues with the theory. right

It is certainly not "...supported by a minority of astrophysicists..." over dark matter, because dark matter hasn't been observed. Also MOND has its problem that no accountability in physics exists as to why Newtonian dynamics has to be modified. In some recent studies, it has even been proposed both might be valid. The truth is at the moment most astrophysicists are still uncertain which one is correct, which is why they do so many observations and studies about galaxy clusters. Looking at [3] there are still average 20 papers on MOND and about 200 in dark matter in galaxy clusters. Most are about looking for observational evidence, rather than cosmological importance of dark matter itself (A different topic.)) Also just because it is not studied it is much, it does not mean it is rejected.

MOND successfully predicts the rotation curves of galaxies, while the quantities of dark matter are presently unknown, and because of this, cannot predict why the rotation curves the galaxies are as they are. It is not that either of model is supported by astrophysicists, it's just that there is no evidence to support that either are correct. (I think you're mixing up cosmological dark matter versus the dark matter galaxy rotation problem. MOND has never been globally directly applied to cosmological problems because it's not testable.)

I have removed this statement, but it was changed again. An actual citation will need to be provided to support this statement that it is "...supported by a minority of astrophysicists..."

To quote Scarpa 'Modified Newtonian Dynamics, an Introductory Review'[4] "Despite many attempts, MOND resisted stubbornly to be falsified as an alternative to dark matter and succeeds in explaining the properties of an impressively large number of objects without invoking the presence of non-baryonic dark matter."

The only support for this statement is in this article at the very end. "However, because MOND is not widely accepted by many scientists, the new study's findings are controversial. Sabine Hossenfelder, an astrophysicist at the Frankfurt Institute Advanced Studies, told Live Science in an email that she was pleased to see researchers working on gravitational simulations of MOND. But "as they admit the paper themselves, they are using an approximate calculation that needs to be confirmed… [and] they haven't quantified how large the disagreement with data is," she said. "So I think it remains to be seen how good this argument actually is."" [5]

My recently added citation is by Hodson (2017).[6]

I also again modified the 4th paragraph, which quotes almost word for word the cite, and added the new one which openly says "All these are beyond the scope of our work here, which is to show that there could be an empirical gravity relation that can, without actually invoking dark matter, account for the missing mass in galaxy clusters."

The first line in Para 2 is a mess e.g. "Created in 1982 and first published in 1983 by Israeli physicist Mordehai Milgrom, the hypothesis attempts to explain why the velocities of stars in galaxies were observed to be larger than expected based on Newtonian mechanics." It needs to be fixed. MOND is a theory that possibly explains why the velocity of stars at the outer boundaries of galaxies maybe larger then what Newtonian mechanics predicts. It would be best to say something like : "Israeli physicist Mordehai Milgrom published a possible theory in 1983 as to why the velocity of stars or the galaxy rotation curves at the outer boundaries of galaxies maybe larger then what Newtonian mechanics predicts."

Do you with this change agree?

Comment: Like all scientific articles, it is very important not to talk in absolutes, and not state things that may be in contention. This is why you should write in more passive language (in degrees of certainty) rather than direct statements. e.g. 'x is certainly/likely/possibly/unlikely' NOT 'x is true/false'. In this case, both MOND or dark matter maybe true, but as their sources or causes are not fully understood, there are the possibilities that they might both right , each right, or both wrong.

Itchycoocoo (talk) 02:56, 3 June 2024 (UTC)

Ruslik0 MrOllie I used this research tool Scispace asking "Is MOND discarded?" [7] This should be enough to satisfy that "...supported by a minority of astrophysicists..." is incorrect, and should be removed.

The summary says: "MOND (Modified Newtonian Dynamics) is not entirely discarded, but its validity and extensions have been under scrutiny. Recent analyses have shown that observations of dwarf spheroidal galaxies align well with MOND predictions, attributing previous discrepancies to uncertainties in data and assumptions [1] [2]. Additionally, the gravitational-wave event GW170817 has constrained relativistic extensions of MOND, ruling out theories like TeVeS but not falsifying MOND itself [3]. Furthermore, modified inertia (MI) formulations of MOND, which have received little attention, can differ significantly from modified gravity (MG) theories in predicting phenomena like the external-field effect, showcasing the complexity and ongoing exploration of MOND and its variations [4]. Overall, while challenges and constraints exist, MOND remains a subject of active research and debate in the realm of gravitational theories."

If it is argued on scientific falsification "Is MOND falsified?" [8] The summary says: "Based on the research provided, Modified Newtonian Dynamics (MOND) is not definitively falsified, but rather constrained in certain aspects. While MOND is empirically motivated and successfully reproduces astronomical observations without invoking dark matter [1] [2], the gravitational-wave event GW170817 and the corresponding gamma-ray burst have ruled out modified gravity theories that differ non-conformally from physical geometry, impacting relativistic extensions of MOND [3]. Additionally, MOND's success is linked to the idea of a critical acceleration scale, suggesting a fundamental connection to the distribution of matter in the universe on medium scales [4]. Therefore, while MOND faces constraints and challenges, it continues to provide valuable insights into gravitational dynamics and remains a topic of ongoing research and debate in astrophysics."

(My bold.) Itchycoocoo (talk) 06:45, 3 June 2024 (UTC)

The majority of astrophysicists reject MOND. This is stated in the cited source. The fact that you think this is "not NPOV" is astoundingly dumb, and along with your use of AI as some kind of reliable source shows that trying to engage with you is a complete waste of time. Hemiauchenia (talk) 07:12, 3 June 2024 (UTC)

WP:GF and WP:PA are applicable here. If you want a WP:DRN, this kind of response will get you no friends. Also the reference given does not say this, as said here.[9] Read it yourself. [10] Scarpa (Ref. 4. says this in my contention.) AI or not, the link articles in Scispace cites specific questions within peer review papers, that can be verified independently anyway. Thanks. Itchycoocoo (talk) 08:28, 3 June 2024 (UTC)

I am not sure what you disagree with? Do you think that the majority of astrophysicists subscribe to MOND, not minority? Ruslik_Zero 10:16, 3 June 2024 (UTC)

No. It just needs to be deleted. Problems with MOND is explained anyway later on the page. Itchycoocoo (talk) 21:18, 3 June 2024 (UTC)

Itchycoocoo, I don’t understand some of your arguments because they seem like non sequiturs to me.

• Ruslik0 MrOllie I used this research tool Scispace asking "Is MOND discarded?" [7] This should be enough to satisfy that "...supported by a minority of astrophysicists..." is incorrect, and should be removed.

—That is not any kind of evidence for minority or majority opinion. A theory can have a minority following but still not be proved wrong, which is certainly the case here. MOND is a minority belief, as the references show.

• If it is argued on scientific falsification "Is MOND falsified? Same problem: irrelevant to establishing majority/minority opinion.

You seem to be arguing, with some of your statements, that physicists are simply agnostic. If that’s true, you will need citations. I don’t think it’s true. From the many, many physics articles I have read, and commentary about astrophysicists by astrophysicists, the majority belief is that dark matter is more likely to be the answer. Of course the confidence varies from person to person: Most probably are not fervent believers, but that’s not what this conversation is about. What it’s about is which hypothesis an astrophysicist is willing to stake their career on. Strebe (talk) 20:51, 3 June 2024 (UTC)

Thanks for your interesting points. I do agree that things need to be cited, however, I can't seem to find a cite that truly confirms that there is a minority or majority opinion. The given cited Scientific American article doesn't actually say this.

I think the statement "It is supported by a minority of astrophysicists as an alternative to the more widely accepted hypothesis of dark matter in terms of explaining why galaxies do not appear to obey the currently understood laws of physics." infers MOND is almost considered as pseudoscience, and not worthy of investigation. Perhaps it is better to write something like: "It is as an alternative hypothesis to the more widely accepted dark matter in terms of explaining why galaxies do not appear to obey the currently understood laws of physics.", because it still infers that dark matter is favoured.

A third alternative is just replace the word 'supported' with 'investigated', which the Scientific American cite[11] does say. I.e. "Right now a few dozens of scientists are studying modified gravity, whereas several thousand are looking for particle dark matter. Perhaps modified gravity is wrong, but perhaps the scientific community is not putting in a good faith effort to know for sure. The universe has had a habit of surprising us; we should be prepared to greet what future data reveal with open minds. The stars may still have secrets, but they are under close surveillance." Moreover, the reason why there are more people investigating dark matter is because there is some physical missing particle that can be discovered. With MOND, it is basically modifying Newton's Second Law, more restricted in proving it is causing the anomalies. Would this option be acceptable? Itchycoocoo (talk) 22:28, 3 June 2024 (UTC)

We're supposed to paraphrase the sources. The present wording is a good paraphrase of what the source says and correctly reflects it. MrOllie (talk) 22:49, 3 June 2024 (UTC)

I think the statement "It is supported by a minority of astrophysicists as an alternative to the more widely accepted hypothesis of dark matter in terms of explaining why galaxies do not appear to obey the currently understood laws of physics." infers MOND is almost considered as pseudoscience, and not worthy of investigation.

I disagree that it implies any such thing. It implies what it says, which is nothing like your interpretation.

Here are citations that state or imply that dark matter is the majority opinion:

• "In the search for a cosmological model that perfectly explains our universe, most astronomers invoke the notion of dark matter… In the 40 years since it was devised, MOND’s achievements continue to be overshadowed by cosmology’s love affair with dark matter."
• "It comes down to whether you are willing to entertain the possibility that there is a mysterious new force that does not involve any new sources, yet also does not respond directly to where the actual sources are. (And in the process reproduces exactly what we would see if there were CDM.) You may think that is plausible -- I, and most people in the field, do not. Therefore, we believe that there is non-baryonic DM, and the question is how it behaves."
• In cosmology or relativity departments, institutes, and research groups, the focus is obviously on cosmological observables and it seems that dark matter is by far the favoured approach.

Strebe (talk) 23:17, 3 June 2024 (UTC)

Strebe (talk) 23:17, 3 June 2024 (UTC)

These sort of responses doesn't surprise me. It comes down to the notion that the observed rotational curves of galaxies are being caused by invisible particles or by unknown behaviour of gravitational forces. No one really knows. Yes MOND is a drastically different approach to the problem of the observed mass discrepancies in astronomical objects. Such a point of view is hardly radical at all but would seem to be a reasonable scientific approach. Yet, mention MOND evokes strong benign reactions among astrophysicists and cosmologists (and seemingly Wikipedians!.) Oh well. Itchycoocoo (talk) 01:27, 4 June 2024 (UTC)

Can you please go over what has been said here? Because your conclusion seems, again, to be non sequitur. The only thing under dispute here is whether a majority of astrophysicists subscribe to dark matter theory or not. It’s nothing about whether or not the theory is correct. At all. In fact, I have strong doubts about dark matter theory, but that doesn’t give me license to portray MOND more favorably, or to omit the clear facts. Strebe (talk) 01:51, 4 June 2024 (UTC)

There is no "subscribe to dark matter theory or not". There is "does dark matter fit the observations better than MOND" or not. At present the vast majority of astrophysicists believe it does. This doesn't preclude some discovery making MOND more attractive as a research topic, and it certainly does not mean MOND is "refuted" (the parameter space is large enough that MOND is not refuted). Neither does it mean that the people who work on MOND believe it's correct; they just believe that there is some possibility that MOND can explain X observation.

One should also stop harping about observed rotational curves. Galaxy dynamics is the one part of the evidence for dark matter that MOND can (arguably, right now) explain as well as or better than CDM. But the evidence for dark matter comes from multiple angles, and MOND currently has no real explanation for cosmological observations. (I know there is Skordis & Złośnik's paper, but even if you accept that theory, it's only one facet of multiple cosmological observations.) There's also stuff like this: [12]

The current lede is not good, it does not make clear that MOND is currently relatively fringe. It's not fringe in the sense that it's crackpot, but it's fringe in the sense that the vast majority of astrophysicists believe it is inferior to Lambda-CDM, to the point where many don't bother working on it. Banedon (talk) 02:17, 4 June 2024 (UTC)

My objection has nothing to do with either 'theory' being superior to another. MOND is just an alternative explanation/ hypothesis to explain the behaviour in the rotation of galaxies as by the Tully-Fisher relationship. It is a prediction that supports the observations. Dark matter is also an alternative explanation, but it is yet to be verified. Dark matter has serious implications for cosmology, because if it is open pervasive throughout the universe, it has serious changes to the models cosmology adopts. This is why more people are investigating it. Until dark matter is found, there is no need to even say who favours what, as neither versions are proven. DM continues to be investigated because there are multiple ways in trying to detect it. With MOND it is mostly theoretical science. That's all I'm saying.

All that really needs to be said in this sentence is: DM is more widely accepted. That should be enough. Itchycoocoo (talk) 02:25, 4 June 2024 (UTC)

MOND is but one of a bajillion modified gravity theories out there. Don't give me the "it explains ___" argument - all of these modified gravity theories explain some observations (they all reduce to GR in some limit, remember). Current lede needs to make that clear; it also has much too few sentences to illustrate the problems with MOND. Banedon (talk) 02:28, 4 June 2024 (UTC)

I've rewritten the lede in full. Banedon (talk) 03:19, 4 June 2024 (UTC)

I accidentally edited your edit b/c it was still violating NPOV.

Academia does not work by majority vote. Just look how toxic String Theorists got in the defense of their hopeless endeavor. Please don't let it get that far and let varying views be seen.

As being bold is correct, I won't apologize for my edit, though I should have read the talk page first. But this gatekeeping bullshit by 'the majority' is just bullying and needs to stop. I'd be ready to put that to arbitration if need be.

--89.14.60.19 (talk) 02:04, 16 October 2024 (UTC)

It seems to me that your edit is the one that eliminates “varying views” by censoring the fact that the majority of cosmologists do not subscribe to MOND. It is hard for me to understand what you are raging about. Strebe (talk) 19:01, 16 October 2024 (UTC)

Thanks. That revision is pretty good. "...it also has much too few sentences to illustrate the problems with MOND." I think that was my point. My response was more to do with Strebe's question not you. Sorry. Itchycoocoo (talk) 04:21, 4 June 2024 (UTC)

References

On James Webb Space Telescope & MOND

Here are two lay articles, perhaps somewhat sensationalized, & the scholarly article that they cite.

• Randall, Ian (2024-11-12). "NASA Webb revelations challenge traditional theory of gravity". Newsweek. Retrieved 2024-11-17.
• Plain, Christopher; Whalen, Ryan (2024-11-15). "James Webb Space Telescope Finds Stunning Evidence for Alternate Theory of Gravity". The Debrief. Retrieved 2024-11-17.
• McGaugh, Stacy S.; Schombert, James M.; Lelli, Federico; Franck, Jay (2024-11-01). "Accelerated Structure Formation: The Early Emergence of Massive Galaxies and Clusters of Galaxies". The Astrophysical Journal. 976 (1): 13. doi:10.3847/1538-4357/ad834d. ISSN 0004-637X.

Peaceray (talk) 23:21, 17 November 2024 (UTC)

The fact that MOND supporters keep publishing papers supporting MOND is totally unsuprising. It also doesn't mean that there has been a paradigm shift where MOND has now suddently become the scientific consensus or on equal footing to LambdaCDM. Lots of papers are published in cosmological physics, and unless this paper is widely considered significant in future publications I think its undue to include. Hemiauchenia (talk) 23:32, 17 November 2024 (UTC)

I've added this paper to the article. One can certainly argue it's undue, but then one would have to cleanse the relevant section. Banedon (talk) 07:33, 18 November 2024 (UTC)

MOND FAQ

After attending the MOND 40 conference in St. Andrews in 2023 I realized there are a lot of misunderstandings about MOND floating around. To clear these up I've been writing a FAQ on my webpage with the help of several authors in the field. There is a lot of material there, far more than could possibly be included in this article without creating several spin off articles. But I'm posting the link here anyone wants to read up on MOND and include material in the wiki article.

The MOND FAQ

I have also added this link to the External links section because I think the engaged reader may benefit from the additional material. Once the FAQ is finished I'll see about merging the content onto the wiki. ScienceDawns (talk) 20:38, 4 February 2025 (UTC)

I would like to see some astrophysics expertise, particularly in modified gravity, for this kind of link. Banedon (talk) 01:43, 5 February 2025 (UTC)

Concur with Banedon. We don't need FAQs from people with no expertise in the topic. I would highly suggest not merging the content from the FAQ onto Wikipedia. Wikipedia exists to summarise existing literature, which considers MOND to be a minority theory. It does not exist to provide defenses for MONDs validity against academic criticisms. Hemiauchenia (talk) 02:39, 5 February 2025 (UTC)

Sure I get that. Authority is all you have to go on to trust my FAQ summary. I can't expect you to read the entire FAQ, read the literature to then add the citations and rewrite it in encyclopedic style before it is fit for inclusion, just to make sure what I've said there is correct. I do find it curious you think it defends MOND against academic criticisms? There are plenty of fatal failures to the theory (dwarf galaxies, no relativity so no lensing, the whole thing about clusters, the ad hoc interpolation function which is not properly known at high accelerations and of course literally all of cosmology because again no relativity). To the extent the FAQ has been completed it explicitly points out such failures. Perhaps the somewhat clickbaity titles bother you, which is reasonable. And yes, it does debunk a number of misconceptions about MOND in the popular media (ok that have on rare occasions also popped up in careless literature). But I don't think that counts as "defending MOND against academic criticism". That's just science communication. You won't hear ridiculous and baseless claims out of me like that "LCDM has been ruled out with infinity sigma" (actual quote from Pavel Kroupa). I care about facts. MOND is a good theory for explaining galaxy dynamics and several related phenomena that tells us how dark matter particles or whatever makes up Ωm should behave in galactic environments. And it deserves to be properly understood because of that.

Why this article needs improvement

As for this wiki article, there are numerous errors present (edit: this is a to-do list now):

• The argument of the interpolation functions given are inverted on the right hand sides (should be a/a0 not a0/a). The arguments are given correctly on the LHS.
• The article says: "[gravity's] rate of change—including the curvature of spacetime—increases with the square root of mass (rather than linearly as per Newtonian law) and decreases linearly with distance (rather than distance squared)". This is incorrect because curvature is the second derivative of the potential. Only the first derivative of the potential (the gravitational field/acceleration) decays with these factors.
• It also says: "For example, it has been claimed that MOND offers a poor fit to the velocity dispersion profile of globular clusters and the temperature profile of galaxy clusters,[74][75]" Source 74 is an old popular science publication that's not publically available but I've managed to track it down. It says nothing about globular clusters. Neither does Shayae (the other source). GCs actually do have velocity dispersions that flatten out. See Hernandez et al. (2012).
• The article states that the discrepancy was first identified for clusters by Swiss astronomer Fritz Zwicky in 1933. While technically true as stated, the dark matter problem had been discovered already well before that (see the history section on the dark matter article).
• The article states that "MOND-compliant gravity, which explains galactic-scale observations, was not previously detected closer to Earth". This is not correct. MOND contains Newtonian gravity as a limit. All measurements on Earth that conform to Newtonian dynamics such as the laboratory tests by (Gundlach et al., 2007) satisfy MOND. All relativistic experiments falsify MOND however.
• This bit: "It is important to note that the Newtonian component of MOND's dynamics remains active at accelerations well below the a0 value of 1.2 × 10−10 m/s2; the equations of MOND assert no minimum acceleration for the Newtonian component. However, because the residual Newtonian-like dynamics of MOND continue to decline as the inverse square of distance below a0—just as they do above—they comparatively vanish as they become overwhelmed by the stronger “deep-MOND” linear dynamics of the theory." is incorrect. You can't just add the Deep-MOND and Newtonian limits together and get MOND. You need to use the interpolation function as this same wiki article explains. If you just add the limits you double the expected kinematic acceleration at a0 which is not what MOND predicts and is strongly ruled out by data from rotation curves and elliptical galaxies (see Lelli et al, 2017) and strong lensing (Tian & Ko, 2017).
• The following is just wrong: "Within the Solar System, the v 4 = GMa0 equation makes the effect of the a0 term virtually nonexistent; it is overwhelmed by the enormous—and highly Newtonian—gravitational influence of the Sun as well as the variability of Earth's surface gravity." The baryonic Tully-Fisher does not apply in the solar system. The interpolation function applies. Same mistake as the previous point.
• Milgrom did not determine a0 to be 1.2*10^-10m/s^2. Begeman et al. (1991) did that. Milgrom's own estimate was about 70% too high at 2*10^-10m/s^2. Subsequent measurements have supported the value by Begeman et al.
• The article talks about a 1-to-1 correspondence in the high acceleration regime and then states MOND and Newton diverge rapidly. That's imprecise. In the Deep-MOND regime there is still a bijective relation between the baryonic and kinematic accelerations. For every one baryonic acceleration there is only one kinematic acceleration, it's just that the two aren't equal anymore.
• The article says "The external field effect implies a fundamental break of the strong equivalance principle (but not necessarily the weak equivalence principle)". This is inaccurate. Both the AQUAL and QUMOND lagrangian *require* the WEP to be satisfied. The way it says it here implies that the WEP could be broken.

The overview section also lacks citations and contains a number of paragraphs that read like original research. The description of MOND as modified inertia or modified gravity is messy. The lede describes MOND as modified inertia even though the vast majority of the literature uses MOND as modified gravity (either QUMOND or AQUAL). In fact the article itself does tell you this much later on. Throughout the article switches several times between modified inertia, modified gravity or what Milgrom calls "pristine" MOND which is essentially agnostic on the issue. It would be better to introduce MOND in the lede as Milgrom's forumula as it applies to modified gravity, mention that a modified inertia version exists and relegate all discussion of that to its own section. That would give it the weight it is due without giving the reader the wrong impression of what MOND is about in practice.

The article also lacks up to date information. Topics that are lacking are for example:

• That Cassini rules out MOND from solar system dynamics (Hees et al., 2014)
• That long period comets rule out MOND (Vokrouhlický et al., 2024)
• That LLR rules out the simple interpolation function (Exirifard, 2013)
• The radial acceleration relation (RAR) & its interpolation function (Lelli et al., 2017)
• The weak lensing RAR (Brouwer et al., 2021 & Mistele et al. 2024)
• The strong lensing RAR (Tian & Ko, 2017)
• The work on bar rotation speeds (Roshan et al., 2021)
• The work on satelite galaxy planes (Pawlowski et al. 2013 & Müller et al. 2018)
• The QUMOND lagrangian is missing, though QUMOND is mentioned (Milgrom, 2010)
• The laboratory tests of small accelerations (Gundlach et al., 2007)

There are several more minor wording issues I'd want to tweak but I think I've made my point.

References:

Begeman, K. G., Broeils, A. H., & Sanders, R. H. (1991). Extended rotation curves of spiral galaxies: dark haloes and modified dynamics. Monthly Notices of the Royal Astronomical Society, 249, 523–537. https://doi.org/10.1093/mnras/249.3.523

Brouwer, M. M., Oman, K. A., Valentijn, E. A., Bilicki, M., Heymans, C., Hoekstra, H., Napolitano, N. R., Roy, N., Tortora, C., Wright, A. H., Asgari, M., van den Busch, J. L., Dvornik, A., Erben, T., Giblin, B., Graham, A. W., Hildebrandt, H., Hopkins, A. M., Kannawadi, A., … Visser, M. (2021). The weak lensing radial acceleration relation: Constraining modified gravity and cold dark matter theories with KiDS-1000. Astronomy and Astrophysics, 650. https://doi.org/10.1051/0004-6361/202040108

Exirifard, Q. (2013). Lunar system constraints on the modified theories of gravity. International Journal of Modern Physics D, 22(9). https://doi.org/10.1142/S0218271813500648

Gundlach, J. H., Schlamminger, S., Spitzer, C. D., Choi, K. Y., Woodahl, B. A., Coy, J. J., & Fischbach, E. (2007). Laboratory test of Newton’s second law for small accelerations. Physical Review Letters, 98(15). https://doi.org/10.1103/PhysRevLett.98.150801

Hees, A., Folkner, W. M., Jacobson, R. A., & Park, R. S. (2014). Constraints on modified Newtonian dynamics theories from radio tracking data of the Cassini spacecraft. Physical Review D - Particles, Fields, Gravitation and Cosmology, 89(10). https://doi.org/10.1103/PhysRevD.89.102002

Hernandez, X., Jiménez, M. A., & Allen, C. (2013). Flattened velocity dispersion profiles in globular clusters: Newtonian tides or modified gravity? Monthly Notices of the Royal Astronomical Society, 428(4), 3196–3205. https://doi.org/10.1093/mnras/sts263

Lelli, F., McGaugh, S. S., Schombert, J. M., & Pawlowski, M. S. (2017). One Law to Rule Them All: The Radial Acceleration Relation of Galaxies. The Astrophysical Journal, 836(2), 152. https://doi.org/10.3847/1538-4357/836/2/152

Milgrom, M. (2010). Quasi-linear formulation of MOND. Monthly Notices of the Royal Astronomical Society, 403(2), 886–895. https://doi.org/10.1111/j.1365-2966.2009.16184.x

Mistele, T., McGaugh, S., Lelli, F., Schombert, J., & Li, P. (2024). Radial acceleration relation of galaxies with joint kinematic and weak-lensing data. Journal of Cosmology and Astroparticle Physics, 2024(4). https://doi.org/10.1088/1475-7516/2024/04/020

Müller, O., Pawlowski, M. S., Jerjen, H., & Lelli, F. (2018). A whirling plane of satellite galaxies around Centaurus A challenges cold dark matter cosmology. Science, 359(6375), 534–537. https://doi.org/10.1126/science.aao1858

Pawlowski, M. S., Kroupa, P., & Jerjen, H. (2013). Dwarf galaxy planes: The discovery of symmetric structures in the local group. Monthly Notices of the Royal Astronomical Society, 435(3), 1928–1957. https://doi.org/10.1093/mnras/stt1384

Roshan, M., Ghafourian, N., Kashfi, T., Banik, I., Haslbauer, M., Cuomo, V., Famaey, B., & Kroupa, P. (2021). Fast galaxy bars continue to challenge standard cosmology. Monthly Notices of the Royal Astronomical Society, 508(1), 926–939. https://doi.org/10.1093/mnras/stab2553

Tian, Y., & Ko, C. M. (2017). Mass discrepancy-acceleration relation in Einstein rings. Monthly Notices of the Royal Astronomical Society, 472(1), 765–771. https://doi.org/10.1093/MNRAS/STX2056

Vokrouhlický, D., Nesvorný, D., & Tremaine, S. (2024). Testing MOND on Small Bodies in the Remote Solar System. The Astrophysical Journal, 968(1), 47. https://doi.org/10.3847/1538-4357/ad40a3

ScienceDawns (talk) 10:08, 22 February 2025 (UTC)

I think you should directly make the changes to the article, instead of linking a FAQ. Banedon (talk) 11:19, 22 February 2025 (UTC)

Will do :) ScienceDawns (talk) 02:17, 24 February 2025 (UTC)

Section with original research

The article currently contains these paragraphs that lack citations and seem to be original research. Calling the original contributor User:Greg L who wrote most of this, do you have sources for this?

User:Banedon could I bother you for a yay or nay about removing/drastically trimming this? In my opinion the article would be better suited by a diagram showing that the accelerations in the solar system are much higher than a0. That's available in the literature so citations wouldn't be an issue. Thoughts in general about the changes I've made so far would also be appreciated!

Applications

Deep-MOND gravitational effects, which explain galactic-scale observations, have not been detected on Earth or in the solar system because the local gravitational field is many orders of magnitude larger than a₀. Even at the edge of the Solar System, where the Sun's gravity drops below a₀ the total gravitational field is still above a₀ due to the gravitational fields of the rest of the galaxy. On Earth's surface—and in national laboratories when performing ultra-precise gravimetry—the a₀ value is equal to 0.012 microgal (μGal), which is only twelve-trillionths the strength of Earth's gravity. A change in the laws of gravity below this acceleration is far too small to be resolved with even the most sensitive free-fall-style absolute gravimeters available to national labs, like the FG5-X, which is accurate to just ±2 μGal. When considering why MOND's effects aren't detectable with precision gravimetry on Earth, it is important to remember that a₀ doesn't represent a spurious force; it is the gravitational strength at which MOND is theorized to significantly begin departing from the Newtonian dynamic. Moreover, the a₀ strength is equivalent to the change in Earth's gravity brought about by an elevation difference of 0.04 mm—the width of a fine human hair. Such subtle gravitational details, besides being unresolvable with current gravimeters, are overwhelmed by twice-daily distortions in Earth's shape due to lunar gravitational tides, which can cause local elevation changes nearly 10,000 times greater than 0.04 mm. Such disturbances in local gravity due to tidal distortions are even detectable as variations in the rate of a Shortt double-pendulum clock, which was a national timekeeping standard in the late 1920s.

To give a sense of scale to a₀, a free-floating mass in space that was exposed for one hour to 1.2 × 10⁻¹⁰ m/s² would "fall" by just 0.8 millimeter—roughly the thickness of a credit card. An interplanetary spacecraft on a free-flying inertial path well above the Solar System's ecliptic plane (where it is isolated from the gravitational influence of individual planets) would, when at the same distance from the Sun as Neptune, experience a classic Newtonian gravitational strength that is 55,000 times stronger than a₀. For small Solar System asteroids, gravitational effects in the realm of a₀ are comparable in magnitude to the Yarkovsky effect, which subtly perturbs their orbits over long periods due to momentum transfer from the non-symmetric emission of thermal photons. The Sun's contribution to interstellar galactic gravity doesn't decline to the a₀ threshold at which MOND's effects predominate until objects are 41 light-days from the Sun; this is 53 times further away from the Sun than Voyager 2 was in November 2022, which has been in the interstellar medium since 2012.

Despite its vanishingly small and undetectable effects on bodies that are on Earth, within the Solar System, and even in proximity to the Solar System and other planetary systems, MOND successfully explains observed stellar and gas rotation velocities without invoking the existence of as-yet undetected dark matter particles lying outside of the highly successful Standard Model of particle physics.

ScienceDawns (talk) 13:24, 28 February 2025 (UTC)

@GregL: Fixing the ping. I don't have time to look at this right now, possibly later. Banedon (talk) 14:22, 28 February 2025 (UTC)

@Greg L: Sorry, really fixing the ping now. Banedon (talk) 14:25, 28 February 2025 (UTC)

Ok, I think the section is includable in different form - under a section heading "MOND on solar system scales" or something like that. It would need sources though, since it makes claims that are not obvious. Without sources, I would say delete the setion. Banedon (talk) 01:15, 2 March 2025 (UTC)

I've added a well referenced subsection on solar system tests in the "outstanding problems" section that should serve to replace this material. After a fair bit of searching I can't find any sources to back up the claims in the section I've quoted above. So I've gone and deleted the material from the article. We can leave it here in case sources do become available and we can restore some of it then. ScienceDawns (talk) 05:31, 2 March 2025 (UTC)