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)

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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

Central problem with MOND is not observations, it is a lack of cosmological scale.

In a recent series of edits @Hemiauchenia wrote:

• However, it has not gained widespread acceptance, with the majority of astrophysicists supporting the Lambda-CDM model as better explaining available data, with many critics arguing that MOND lacks a viable cosmological model.

citing two sources:

• Ethan Siegel (19 October 2022). "Why modifying gravity doesn't add up". Big Think.
• Keith Cooper (6 February 2024). "Cosmic combat: delving into the battle between dark matter and modified gravity". physicsworld.

These edits also removed a crucial source, Milgrom's own 2015 paper:

• Milgrom, Mordehai (February 2015). "MOND theory". Canadian Journal of Physics. 93 (2): 107–118. arXiv:1404.7661. Bibcode:2015CaJPh..93..107M. doi:10.1139/cjp-2014-0211. ISSN 0008-4204.

The sentence has several problems:

1. The "majority" claim is not supported by these sources (other sources do exist, say Turner's "The Road to Precision Cosmology").
2. The majority support for LCDM overstates the case for MOND. Astrophysicist don't consider MOND a serious alternative to LCDM because MOND only applies at the galaxy scale. At the galaxy scale MOND beats LCMD so it is not about observations but rather it is about being incomplete.
3. Two reporters on popular web site (Siegal,Cooper) are not "many critics". I found nothing in these articles to support the idea the the reporters did an extensive poll.
4. MOND's lack of viable cosmological model is the central and critical aspect of the problem with MOND and it is directly addressed by Milgrom in his review of MOND, eg

• However, none were shown to address fully the mass discrepancies in cosmology and structure formation that are otherwise explained by cosmological dark matter.

I think we can do better. Johnjbarton (talk) 18:11, 31 August 2025 (UTC)

I don't really care about the precise wording vis a vis Lambda CDM, but "lack of viable cosmological model" is a bit mystifying for the layman, and should be more clearly explained, and the the article's opening paragraph should make unambiguously clear that MOND is a minority theory only supported/researched by a relatively small number of astrophysicsts compared to dark matter theories.

I think the physicsworld source supports this claim: Baker echoes these concerns. “While it was a good step forward for MOND to be able to do that,” he says, “I don’t think it was enough to bring MOND back into the mainstream. The reason being [Skordis and Złośnik] have added a lot of extra fields to it, a lot of bells and whistles, and it really loses elegance. It works with the CMB, but it seems very unnatural.” and There’s still a long way to go for the scientific community to consider [MOND] a heavyweight rival to ΛCDM, and it’s certainly hampered by having relatively few people working on it, meaning that progress is slow.. Both these quotes give the unambiguous impression that MOND is a minority theory. This 2018 Scientific American article also states Right now a few dozens of scientists are studying modified gravity, whereas several thousand are looking for particle dark matter. Hemiauchenia (talk) 19:09, 31 August 2025 (UTC)

My primary concern is to not compare MOND to LCDM on the basis of cosmological observations because the real issue is that MOND makes no useful predictions. How about

• However, MOND is not a direct rival to the consensus cosmology called Lambda-Cold Dark Matter and relatively few astrophysicist work on it.(Ref physicsworld). MOND models galaxy-scale observations but it has no complete cosmological model and it does not explain effects at that scale which are attributed to dark matter in the consensus model.(ref Siegel)(ref Milgrom).

Johnjbarton (talk) 21:55, 31 August 2025 (UTC)

Pinging @Banedon, @Strebe:, @Ruslik0:, @MrOllie: from previous discussions Hemiauchenia (talk) 19:10, 31 August 2025 (UTC)

I agree Hemiauchenia has a point about the sentence being awkward, and modified it. Banedon (talk) 00:25, 1 September 2025 (UTC)

MOND also has a Solar System problem. See also this. Ruslik_Zero 19:52, 31 August 2025 (UTC)

This is already covered in the solar system section. It explains the problem, the caveats about testing MOND without a full MOND-ephemeris and evidence for and against MOND effects in the solar system. I don't think this is important enough to include in the lead. ScienceDawns (talk) 12:12, 1 September 2025 (UTC)

I agree with your point that MOND does not have a complete cosmological model and generally does not make cosmological predictions that can be compared to LCDM. Saying it only applies to galaxies is a bit too strong though. Globular clusters, open clusters, molecular clouds and possibly wide binary stars also show evidence of MOND. If you say "galaxy-scale and smaller" I'd be happy with your suggested sentence. ScienceDawns (talk) 12:10, 1 September 2025 (UTC)

A Commons file used on this page or its Wikidata item has been nominated for speedy deletion

The following Wikimedia Commons file used on this page or its Wikidata item has been nominated for speedy deletion:

• M33 rotation curve HI.gif

You can see the reason for deletion at the file description page linked above. —Community Tech bot (talk) 22:07, 7 September 2025 (UTC)

File is CC-BY in

• Nesti, F., Salucci, P., & Turini, N. (2023). The Quest for the Nature of the Dark Matter: The Need of a New Paradigm. Astronomy, 2(2), 90-104. https://doi.org/10.3390/astronomy2020007

Johnjbarton (talk) 22:43, 7 September 2025 (UTC)

That was long after the file was uploaded to Commons though. Hemiauchenia (talk) 22:47, 7 September 2025 (UTC)

Yes, and I suppose Nesti could have copied it from Wikipedia, IDK. And I doubt the virgina site created the content to be honest.

This file is the one on virginia. A very similar one is Rotation curve of spiral galaxy Messier 33 (Triangulum).png Johnjbarton (talk) 22:56, 7 September 2025 (UTC)

A Commons file used on this page or its Wikidata item has been nominated for deletion

The following Wikimedia Commons file used on this page or its Wikidata item has been nominated for deletion:

• M33 rotation curve HI.gif

Participate in the deletion discussion at the nomination page. —Community Tech bot (talk) 20:07, 8 September 2025 (UTC)