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

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)

Questionable Revert

MrOllie Please explain this global revert.[13] The text in the 4th paragraph was just simplified and removed the word-for-word copying of text from the cite. You also removed an additional relevant more recent reference that confirms both versions of text in this article.

There is nothing contentious with edit [14]:

"Although MOND explains the anomalously high rotational velocities of galaxies at their edges by the Tully-Fisher relationship, it does not fully explain the velocity dispersion of individual galaxies within galaxy clusters. Some discrepancies may not be accountable by MOND, such as the presence of yet undetected missing baryonic matter or neutrinos."

The reverted version talks about "...factor of around 10 to a factor of about 2.", but this doesn't appear anywhere in the main body of the article at all. The Introduction is supposed to be a summary of the main article, not just word for word extract from a cite. Saying 'further back' is meaningless. It just looks like gatekeeping. Why? Itchycoocoo (talk) 02:03, 4 June 2024 (UTC)