# Talk:Modified Newtonian dynamics

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Modified Newtonian dynamics is a former featured article candidate. Please view the links under Article milestones below to see why the nomination failed. For older candidates, please check the archive.
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Date Process Result
September 6, 2005 Featured article candidate Not promoted
March 23, 2007 Good article nominee Not listed
Current status: Former featured article candidate
WikiProject Physics / Relativity  (Rated C-class, Mid-importance)
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## old comments

To those working on this article: A great deal of information about MOND is available on the web, but only a fraction of it is relevant! Please try to use sources from the last few years, as many of the criticisms directed at MOND have lately been silenced by new research. Bekenstein's paper is a great place to start. Also, it would help to have some grasp of the history of dark matter theories -- currently, the most attractive aspect of dark matter is its reliability in predicting gravitational lensing, but it has never been as accurate or consistent as MOND in predicting rotational curves in galaxies and clusters. And the sheer number of candidates for dark matter that have been completely ruled out is truly astounding. Good luck researching! Eventually, this should make a nice featured article. Jettoki 04:12, 7 September 2005 (UTC)

## Observation

Experimental research in this field is increasing, its now only a matter of when not if. —Preceding unsigned comment added by Omeganumber (talkcontribs) 01:17, 1 March 2008 (UTC)

## Just a note:

Occams Razor does not suggest that the simplest explanation is usually correct. Rather, it states that plurality should not be posited without necessity. In other words, one should not propose hypotheses with unecessary assumptions. Occams razor can't tell us whether MOND or Dark matter is correct since neither make unneccesary assumptions. Rather, both make necessary (but unverified) assumptions to explain the available cosmological data. Its true that MOND makes more assumptions. Only more data can tell us whether or not those assumptions are necessary. —The preceding unsigned comment was added by 72.138.186.68 (talk) 21:19, 21 March 2007 (UTC).

MOND is an empirical formula that works very well on the galactic scale. Any proposal that is given a status of theory must explain why MOND works so well. Relativity + CDM fails this test, so its no longer an acceptable theory. Another failure is an explaination for Abell520. —Preceding unsigned comment added by 115.113.9.11 (talk) 14:32, 17 August 2010 (UTC)

## 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)

## Criticisms

I fail to see how MOND violates the principle of least astonishment. CDM theories are currently postulating six dimensions and heretofore unfathomed classes of matter. MOND is really just a revision of previous theories; it's not very glamorous. I would just remove this section, but I want more opinions. CDM and HDM have always seemed several degrees more radical than MOND to me. 24.88.16.137 17:22, 4 September 2005 (UTC)

Dark Matter theories come in many flavors and colors. Not all of them require extra dimensions. Some simply involve uniformly distributing normal Hadronic black matter through the interstellar space. These are certainly more mundane than a revision of Newtons Second Law of Motion. Anyway, the section is added on a light note and should not be taken too literally/seriously. Loom91 18:18, 4 September 2005 (UTC)
Yes, but if you track CDM and HDM theories over the past 40 years, you find that they become more and more far-fetched. The mundane incarnations have little or no evidential confirmation, and the radical incarnations are often ridiculous. The principle of least astonishment should work against claims that dark matter is "evenly distributed," since that would be terribly improbable, given the number of places we find gravitational anomalies. I figured this was a bit of a humorous addition, but it would be more fitting over at Dark Matter, I think. :) 24.88.16.137 17:12, 5 September 2005 (UTC)
From the POV of a non-astrophysicist (moi), dark matter/energy theories seem pretty convenient, & MOND w/in Occam's Razor (or PoLA, a term I rather like...). Agreed MOND is more radical in overthrowing Newton, but, didn't Einstein do that, too? (Not to equate...) If it's not observable terrestrially, how but change? Trekphiler 16:09, 2 December 2005 (UTC)

In this section I noticed a sentence to the effect: 'describes accelerated object'. Either it describes accelerated objects or it describes an accelerated object. I don't know which is clearer in this instance, so I didn't make a visible change. The edit is invisible. I request that a "maintainer" of this page take a look rather than just relying on my drive-by. --24.129.18.76 05:21, 31 March 2007 (UTC)

## Principle of least astonishment???

I've never heard physicists refer to this principle--the article itself states it's a computer science term. Why not Occam's Razor, which is pretty close to equivalent, and more widely used? Or is this, in fact, actually the term used in the literature on the subject? -- SCZenz 04:37, 6 September 2005 (UTC)

See above. Ockham's Razor is certainly more fitting of a scientific theory, but in the current state of the rotation problem, I would argue that MOND should be the last to be criticized as imaginative or overly complex. Furthermore, I have found no literature which criticizes it for this reason. The problem most scientists have with MOND is that it involves modifying a well-established law -- somehow that's more radical than postulating the existence of perfectly evenly distributed, invisible, inert and non-interacting matter of a class which no current particle theory can explain. If you want to change the PoLA to Ockham, go ahead, but the article should definitely mention Milgrom's contention that MOND is the simplest explanation. Jettoki 15:48, 6 September 2005 (UTC)
I was not at all commenting on whether MOND is the simplest explanation or not. I was commenting on the use of a silly piece of terminology. (It really sounds like somebody made up a new principle that meant the same as Occam's Razor!) I'll wait a bit longer to see if there's any other comment. -- SCZenz 21:40, 6 September 2005 (UTC)
If you ask for more comment, you can have it: I agree with SCZenz. -- Jitse Niesen (talk) 22:10, 6 September 2005 (UTC)
You asked what term the "literature" used, and I responded -- the literature doesn't actually use either, to my knowledge. I say either remove the section or replace PoLA with Ockham's Razor. This is definitely a POV issue, however, and the opinion of Milgromites should be considered. Jettoki 02:14, 7 September 2005 (UTC)

## What is the estimated value of a0?

The page currently says a0=1.2 10-10Km ms-2 but I don't know what units "Km ms-2" is supposed to be. Shouldn't it just be ms^-2? 206.222.212.218 23:33, 12 October 2005 (UTC)

I edited this back to ms^-2. 198.183.6.117 22:17, 18 October 2005 (UTC)

## Edit?

On the main page, this looks a bit cluttered to me:

velocity and the constant a0. The equation v=(GMa0)¼ allows one to calculate a0 from the observed v and M. Milgrom found a0=1.2 10-10ms-2. Milgrom has noted that this value is also "... the acceleration you get by

Is it possible to add spacing to avoid it? Trekphiler 15:41, 2 December 2005 (UTC)

What if our concept of time needs adjustment to accomodate deep MOND regime. Is it coincidence that the speed of light is a0 times the age of the universe, or is the speed of light itself a measure of the age of the universe? — Preceding unsigned comment added by 80.101.133.90 (talk) 22:07, 4 August 2011 (UTC)

## a0 times age of universe does not equal c ?

From the article:

Milgrom found a0=1.2×10^−10 ms^−2. Milgrom has noted that this value is also "... the acceleration you get by dividing the speed of light by the lifetime of the universe. If you start from zero velocity, with this acceleration you will reach the speed of light roughly in the lifetime of the universe."

The current estimate for the age of the universe is 13.7e9 years +/- 1% error, so one should get the speed of light by taking age times a0:

${\displaystyle 1.2\cdot {}10^{-10}m/s^{2}\cdot {}13.7\cdot {}10^{9}\cdot {}365.256\cdot {}24\cdot {}3600s=5.188\cdot {}10^{7}}$

which is a lot smaller than the speed of light (2.99e8 m/s). So, what's wrong here? --cslarsen 20:28, 16 May 2006 (UTC)

I think it's a mistranslation of the math Milgrom was using; that or it was an older estimate for the age of the universe. Will have to check. 24.88.16.137 16:07, 3 June 2006 (UTC)

Older estimate? c/a0 = 79 billion year old universe! It is necessary to clarify or remove the sentence.

## Formula

The formula given in the article differs from the formula I'm familar with (this doesn't mean the article is incorrect, I'm just raising a question) -- F=ma2/a0. So which is "correct"? &#0149;Jim62sch&#0149; 23:43, 26 July 2006 (UTC)

Your representation is a limit value for the function mu(a/a0) when the effect is significant - useful approximation but the representation in the article is correct. —Preceding unsigned comment added by Mpurdy (talkcontribs) 08:26, 12 September 2007 (UTC)

## Rewrite

I'd like to rewrite the first paragraph. If my changes are viewed positively I'd like to continue working through this article, making it much easier to read. Do I just jump in and start doing this? I assume that people can delete my changes quickly if they don't like them. I have not done this before in Wikipedia, so I want to be sure that I am properly in the game. --Randal Leavitt 00:42, 28 July 2006 (UTC)

As we say: Be Bold! In other words, go for it. Certainly anything that makes this article more accessible to those without an advanced degree would be helpful. While you're at it, if you could recheck the formula, it's be appreciated. If you need an assistance, drop me a note on my talk page. Good luck and happy editing! &#0149;Jim62sch&#0149; 15:36, 28 July 2006 (UTC)
OK - I have replaced the first paragraph. I am away for a few days. I'll check in next week. If people think this is going in the right direction I move on to the second paragraph. --Randal Leavitt 18:08, 28 July 2006 (UTC)
Looks good so far...I made a few minor tweaks -- feel free to change them if you wish. Nice to see I'm not the only "geek" interested in this theory.  ;) &#0149;Jim62sch&#0149; 22:27, 28 July 2006 (UTC)
OK - I'll keep working along, paragraph by paragraph. Thanks for the improvements in the first paragraph. This will be slow. It takes me several days to revise a paragraph, and I will only be able to spend a little bit of time at this during the next couple of months. But I will persist. I think this is an excellent article, and I am very interested in the topic. --Randal Leavitt 23:53, 30 July 2006 (UTC)
Sounds good to me. &#0149;Jim62sch&#0149; 00:07, 31 July 2006 (UTC)

I would also like to improve the first paragraph. It seems a bit odd to open the article about MOND by talking instead about the rival theory of Dark matter. It is clear that we must mention both theories, and mention also that Dark matter is currently the preferred one, but without losing sight that this article is about MOND. Therefore, I propose the following wording:

In physics, Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newton's Second Law of Dynamics, to explain the galaxy rotation problem. When the uniform velocity of rotation of galaxies was first observed, it was unexpected because the Newtonian theory of gravity predicted that objects that are farther out will have lower velocities. For example, planets in the Solar System orbit with velocities that decrease as their distance from the Sun increases. The MOND theory explains the observed rotation curves, by suggesting that the acceleration of a particle is not linearly proportional to the force, at low values of acceleration. This theory does not have wide support among the scientific community, who currently prefer the alternative Dark Matter theory. This assumes that a halo of dark matter surrounds each galaxy, causing all the stars in the galaxy disc to orbit with the same velocity.

Please, comments. Dukeofalba

Sounds very clear to me, but not sure if the edit should be made. David Spector (talk) 01:15, 2 January 2014 (UTC)

## Forgive my ignorance

But how does http://arxiv.org/abs/astro-ph/0507619 factor into this?

It is a different thing entirely. That paper claims that no new dark matter or new physics (like MOND) is required to fix the galactic rotation curves; rather, its claim is that General Relativity fixes the rotation curves all by itself. For GR to disagree with Newtonian Mechanics by any detectable amount at large distances was considered sufficiently implausible by physicists that the paper was never really discussed or rebutted seriously as far as I know. -- SCZenz 23:57, 23 August 2006 (UTC)
At least one response was published and widely discussed. It rebutted the claims by arguing that the authors of the original paper had essentially made a subtle assumption which was equivalent to their own form of dark matter without realizing that they had done so. I don't have the site at hand, but it was discussed in many of the physics blogs that cover such issues at the time. Ohwilleke 05:21, 27 August 2006 (UTC)

Yes, and the value of dark matter is so much more than just flat rotation curves. In the standard cosmological model it is needed to enable structure in the universe to form as it should. I am only aware of Bekenstein's TeVeS as having been worked through and found to have some success in this other role of dark matter. HaludzaHaludza 15:04, 25 November 2006 (UTC)

## Inappropriate Tone - Que Faire?

As a newcomer in this game I am not sure what has to be done to remove the "inappropriate tone" tag. I am reading the guidelines as suggested. For one thing I would like to improve all the trailing subsections such as "References" to make them more complete and informative. So I am thinking about that "innappropriate tone" tag, but it will take a while. Randal Leavitt 04:51, 1 September 2006 (UTC)

If you think the tone is fine as it is, feel free to remove the tag yourself. It's possible that it was added long ago and not removed even after the article matured. Your suggestions sound like good ideas, i hope you go ahead with those changes. Thanks! Foobaz·o< 13:30, 1 September 2006 (UTC)

## Proposal for MOND article

(with the objective of making it a featured artilce).
(Please help me improve this work plan before I get started.)

a. Gradual Change

I propose to work on the MOND artilce with the goal of achieving the changes listed here. I plan to do this work gradually, so for a while the article will not be consistent in terms of style and content. For instance, for a while the "References" section will contain both cited article information and external references as it does now. Eventually, all the parts will fit together properly. I like this approach because it allows one to back out easily from a single change that everyone objects to.

b. Citation Templates

Use the citation templates to cite all articles used to support the discussion and include the complete information for each citation in the "References" section. As a result the "References" section will contain only citation details. It will only include peer reviewed articles.

c. Sections at end of article

Arrange the sections at the end of the article so that we will have:

See also - A bulleted list of interwiki links and a short explanation of each.
Notes - For footnotes used in the article.
References - For all peer reviewed sources cited in the article.
Further reading - For references that are not specifically cited in the article.
External links - For listing relevant external web sites.

d. Lead section

will summarize the main points of the article
will NOT include links
will NOT have a title
will point out why we should care about MOND

e. Links

Wikipedia links only used once, the first time a term appears. So a topic such as "dark matter" will only have one link in the body of the article.

f. Style

"Summary style" recommendations followed to keep the top level article short. This may lead to the creation of sub-pages for more detailed discussions such as the Poisson equations.

g. Headings

The headings in the revised article will be

Header Overview
Header Original MOND proposal
Subheader Who and When
Subheader Modified formula for force
Subheader Resulting formula for orbital velocity
Subheader The Tulley-Fisher relationship
Subheader The Poisson equations
Header Tests of the concept
Subheader Consistency with observed data
Subheader Predictions
Subheader Observations that are not explained
Header Discussion
Subheader Intertia or gravity
Subheader Significance of a0
Subheader General Relativity
Subheader Ether
Subheader Scientific progress
Subheader Open Problems

h. Facts

A number of facts need to be corrected or clarified. I will make these changes gradually, one at a time, so others can respond without having to deal with a flurry of new things at once. The article is generally very good, but a few things could be tightened up. For example, MOND was introduced with a series of three papers, not two as stated now.

i. Figures

Both figures are subtley wrong, giving an incorrect impression. They also look rather unsophisticated. Figures are not my specialty. Could we find some better figures?

j. Verification

I am trying to verify the equations using gnumeric and data from actual galaxies. Gnumeric can reprocude Figure 1 showing the flattened velocity curve and the Newtonian curve nicely. However, I am having a hard time geting the numbers to work out. The main problem seems to be the mass of a galaxy. If anyone wants to look at my gnumeric file just let me know and I will email it. I would like to have it reviewed before using its results for the article.

Randal Leavitt 17:00, 4 September 2006 (UTC)

## Question

Does KATRIN have the ability to completely rule out MOND by proving neutrinios are not massive? --Deglr6328 09:46, 18 October 2006 (UTC) - I'm not sure that Neutrino mass enters into it. Additionally, neutrinos have mass difference, it stands to reason they have mass. WilyD 19:45, 7 November 2006 (UTC)

- I wouldn't say so as MOND isn't a theory. TeVeS, which can reduce to a 'MOND limit' to an extent may need them and TeVeS may well be ruled out by future direct measurements of neutrino mass. However, what TeVeS can and can't do isn't necessarily a done deal. A recent paper by Dodelson and Liguori showed that the spatial part of TeVeS's vector field needs to grow to enable growth of large scale structure- however, despite this crucial role it was not considered in the TeVeS bullet cluster paper by Angus et al. I think this is an ongoing issue. HaludzaHaludza 15:09, 25 November 2006 (UTC)

## Binary Stars

According to the article, we can't detect MOND on Earth because the Sun produces an acceleration greater than a0. Would this mean that binary stars are not affected by MOND, and should not have flat rotation curves? 81.86.156.9 14:01, 31 December 2006 (UTC)

I find this theory intriguing but having read the question above, I think there is a more general case that needs answering.
Consider a small rocky planet orbiting a star that is many times more massive. The star is accelerated towards the planet, and vice versa, but due to being far more massive the star accelerates much less than the planet. Does MOND affect the star but not the planet? Is it possible that the force exerted by the star on the planet is not equal and opposite to the force exerted on the star by the planet? SheffieldSteel 23:08, 1 March 2007 (UTC)
The root of the problem is that the article doesn't state how to find the resultant of a set of accelerations. In Newtonian mechanics, it's unambiguous - the resultant is ${\displaystyle A=a_{1}+a_{2}+\ldots }$. In MOND, it could be ${\displaystyle A=\mu (a_{1}+a_{2}+\ldots )}$, or it could be ${\displaystyle A=\mu (a_{1})+\mu (a_{2})+\ldots }$, or something "in between". I don't know whether this is an omission in the article or in MOND itself. 81.86.156.9 (talk) 13:08, 24 June 2010 (UTC)
That is a very good question, and, I think, an important one. Any experts here? David Spector (talk) 01:30, 2 January 2014 (UTC)

## GA

I am failing this due to criteria 1 and 2.

• Observations of the rotation rates of spiral galaxies began in 1978. By the early 1980's it was clear that galaxies were not rotating in the same manner as the Solar System. A spiral galaxy consists of a bulge of stars at the centre with a vast disc of stars orbiting around the central group. Three choppy sentences with no flow at all
• it was clear that galaxies were not rotating in the same manner as the Solar System, how was it clear? who found this out? how did they find this information?
• This is the pattern seen in the Solar System, as shown in Table 1. You do not refer to images or tables while in the text.
• In the observed galaxies this pattern was not apparent. Stars near the outer edge were orbiting at the same speed as stars closer to the middle. If Newtonian theory applied then plotting the velocity of a star as a function of distance from the galactic centre should yield curve A in Figure 1 below. Three choppy sentences again.
• The images are too large and cause formatting problems remove the |355px from them to accommodate user preference.
• Several one sentence paragraphs that need to be merged, expanded or removed.
• Don't wikilink solo years - such as 2004
• This article lacks inline references, the current inline references are not formatted properly, please check {{cite web}} template on how to format references..
• References come after punctuation [1]. -> .[1]
• Too many external links
• Per WP:MOS See Also section comes before references.

Article needs better flow throughout and could definitional use some in-line reference to help verify facts. M3tal H3ad 07:18, 23 March 2007 (UTC)

## Article with experiment that might give a dent (or blow) to MOND

Maybe someone should make a note about this on the article page? http://sciencenow.sciencemag.org/cgi/content/full/2007/413/2?rss=1 --cslarsen 19:54, 16 April 2007 (UTC)

In reply[according to whom?]:

Good spot! Though, it's testament to how MOND has resisted development that even today, to my knowledge, one could not distinguish MOND's successes in galaxies as a modification to gravity or a modification to inertia. Something like TeVeS is a modification of gravity and so you could not see anything on the earth's surface as the gravitational field is much greater than the characteristic MOND scale.

Modified inertia, which would be called to account by the experiment you link, has not attracted much effort outside of Milgrom. To my knowledge he has so far been able to create a non-relativistic model of this which reduces to MOND only in the case of circular, presumably quasistatic, orbits and something more complicated generally. I'm not sure one could even anticipate the result of a table-top experiment.

Dear Anonymous, could you please clarify how distinguishing gravity and inertia is even possible? Is there some newly-proposed modification of the equivalency principle? David Spector (talk) 01:35, 2 January 2014 (UTC)

## a0 = speed of light/age of universe

But acceleration=change in velocity/change in time... Imagine Reason (talk) 05:16, 11 March 2008 (UTC) Could the reason be that the speed of light actually represents the age of the universe, and that our concept of time distorts our interpretation? Is it thinkable that the deep Mond regime actually is a distortion of time, rather than acceleration or mass? I am not that good in math, but could we eliminate time from the MOND equations and see what form it would take?

Sorry, your comment makes no sense to me. Can you clarify these vague notions? I believe the MoND regime is just the minimum radius where velocity is observed to be constant. David Spector (talk) 01:39, 2 January 2014 (UTC)