Talk:Modified Newtonian dynamics

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Former featured article candidate 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.
Article milestones
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[edit]

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)


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:[edit]

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 (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 (talk) 14:32, 17 August 2010 (UTC)

I removed the following part:[edit]

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[edit]

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)


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. 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. :) 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. -- 05:21, 31 March 2007 (UTC)

Principle of least astonishment???[edit]

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?[edit]

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? 23:33, 12 October 2005 (UTC)

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


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 (talk) 22:07, 4 August 2011 (UTC)

a0 times age of universe does not equal c ?[edit]

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:

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. 16:07, 3 June 2006 (UTC)

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


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"? •Jim62sch• 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)


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! •Jim62sch• 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.  ;) •Jim62sch• 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. •Jim62sch• 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[edit]

But how does 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?[edit]

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[edit]

(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)


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[edit]

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? 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 . In MOND, it could be , or it could be , or something "in between". I don't know whether this is an omission in the article or in MOND itself. (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)


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[edit]

Maybe someone should make a note about this on the article page? --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[edit]

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)

External links[edit]

Why does the last external link point to a fake Discover Card website? —Preceding unsigned comment added by (talk) 08:31, 8 May 2008 (UTC)

Presumably at some point in the twisted history of the web it pointed somewhere useful. I have removed the link. - Eldereft ~(s)talk~ 16:06, 8 May 2008 (UTC)

Too much editorialization[edit]

This article is a serious mess. Some editors seem to assume that MOND was intended to discredit the dark matter hypothesis, but in truth, it was only meant to explain specific phenomenon that require extremely improbable conditions (evenly distributed mass in unlikely geometric configurations). One of the implications of MOND is that there is less dark matter in the universe than CDM would indicate but the theory is *not* at odds with the concept of low-luminosity baryonic dark matter, which could still account for another 5% of the observed large-scale missing mass density.

Some editors also insist on labeling MOND as a "fringe science" and attempt to editorialize the article by stating that it enjoys the support of an "extreme minority." Please, read the literature before making statements like this. MOND was proposed in 1983 and was largely ignored until it proved to have enormous predictive power for LSB galaxies and star clusters, at which point it was thought that the theory would never be tenable until it could be made to cooperate with relativity. Now that Bekenstein and others have formulated TeVeS, it has been receiving more attention. This discourse has taken place in peer-reviewed academic journals like ApJ and at international conferences like JHEP. Please leave the arguments to the experts - there are a number of scientific reviews disputing MOND, as well as scientific reviews disputing CDM. There is no consensus yet, and the missing mass problem is too complex and pervasive to be solved by one model alone.

As it stands, this article should just explain the mechanics of MOND, describe its empirical successes, describe the difficulty of formulating an experiment, and briefly list its advantages and disadvantages with respect to CDM. Jettoki (talk) 13:41, 18 May 2008 (UTC)

"Phenomenon" is a single, not plural, word. It's plural is "phenomena". (Hope this helps!) Unfree (talk) 08:47, 10 August 2009 (UTC)

Removing leading spaces[edit]

Guys, don't you know that it is impolite to start a line with a leading space (that translates into no break) since there are users of wikipedia who have monitors nerrower than 200 inches and therefore those poor souls can't read texts wider than about 12 inches just scrolling them vertically (and it is pain in the ar... to scroll each line horizontally)? Or should it be addressed to the guy who invented the rule that a leading space translates into no break ? Jim (talk) 11:52, 3 July 2008 (UTC)

Why do we have such a silly theory as MOND in wikipedia[edit]

... if the only legitimate theory of gravitation explaining all the observed facts is Einstein's relativity? IMHO, new theories should be allowed only when there is a problem with the old ones, just not to let cranks (unfortunately like myself) pull legitimate scientists in endless discussions about what is the fact and what is not. If my observaion that Einstein's theory explains the Hubble redshift in stationary space (a.k.a. "Einstein's universe") together with its acceleration and therefore the (alleged) expansion of the universe is clearly an illusion can't be published in a scientific journal (which IMO might enlighten a lot of astrophysicists but in editors's opinion won't be interesting to them) why such a silly stuff like MOND can be published and seriously discussed? Jim (talk) 12:09, 3 July 2008 (UTC)

It is notable in the history of science as a theory that explained certain observations but did not pan out. The modern versions are kinda out there, but Milgrom's original proposal was perfectly legitimate science. - Eldereft (cont.) 20:31, 3 July 2008 (UTC)
It did not pan out since it couldn't explain all observations as general relativity could. MOND tries to explain physics with outdated for about a century belief in attractive forces acting at the distance. For this reason it is not legitimate science any more but an about 300 years old item from the history of science. Of course we may still use a mathematical model with attractive forces understanding that it is only an approximate mathematical model not a natural phenomenon. But as long as we know that it is surely not legitimate science it shouldn't be treated by wikipedia as such.
IMO, it is treated like a legitimate science only because there is enough wikipedia editors who don't understand gravitation (90% according to recent poll, who don't know that in contemporary science there are no forces acting at the distance and can't imagine how gravitational force is generated only when one object is in contact with another and so they take it as a fundamental force acting regardless of contact between the objects) and wikipedia represents the prejudices of majority. IMO, wikipedia should pay more attention to suppressing prejudices and surely not to reinforce them. Please note that popularization of Einsteinian gravitation is banned from wikipedia by its editors and as a result over 90% of physicists (and astrophysicists, the guys who need this knowledge badly) don't know the reasons for gravitational forces. Unfortunately my opinion is that of minority and so by definition it doesn't have a chance here :) Jim (talk) 09:57, 9 July 2008 (UTC)
BTW, you might use the remark just above this one (titled "removing leading spaces") in your talk page to make it easier to read. Jim (talk) 15:26, 9 July 2008 (UTC)
Wikipedia talk pages are not for giving opinions on their subjects; they're for improving articles. Wikipedia has articles on lots of falsified (yet notable) theories; for example, alchemy. -- SCZenz (talk) 16:22, 9 July 2008 (UTC)

Apparently it's not so silly. A major scientific study has just added significant support to the MOND theory at certain scales and under certain conditions: (talk) 17:34, 25 February 2011 (UTC)

Purpose of MOND[edit]

When I first learned about MOND, it was a Scientific American article that made an interesting claim. It said that MOND was created as a rival theory to Dark Matter, mainly so there could be another theory against which the Dark Matter theory could be tested. MOND wasn't expected to pass whatever tests they threw at it. The reason it's still around is that it passed the tests better than anyone expected. I don't have a reference right now, or I would add this myself, but I feel this history should be in the article. —MiguelMunoz (talk) 19:32, 27 November 2008 (UTC)

Dependent on satellite's mass?[edit]

"...the effect of MOND results in an increased velocity beyond a given range (actually, below a given acceleration, but for circular orbits it is the same thing) that depends on the mass of both the planet and the satellite..."

You sure it's dependent on the mass of the satellite? —Preceding unsigned comment added by (talk) 19:33, 20 February 2009 (UTC)

I deleted the comma before "that". Unfree (talk) 08:58, 10 August 2009 (UTC)

New paper proposes MOND could be tested in solar system[edit]

Just read this on NewScientist: Phantom menace to dark matter theory, which is based on a new paper by Milgrom: MOND effects in the inner solar system.

Unfortunately, I don't understand enough of physics to update the article in light of this new paper. Maybe somebody else could reference this new paper somehow? --JVersteeg (talk) 13:05, 9 July 2009 (UTC)

High significance[edit]

What does "at high significance" (at the end of the article's text) mean? Unfree (talk) 08:43, 10 August 2009 (UTC)

Added source[edit]

Did not add any content, as it is well over my head. FX (talk) 14:01, 27 August 2009 (UTC)


Here's a quote from the article right now:

"Actually, Milgrom provided several interpretations of his proposal, one being a modification of Newton's second law of motion. However, this proposed interpretation is inconsistent with conservation of momentum, requiring some extraordinary gymnastics to regain plausibility"

I think the term "extraordinary gymnastics" is unencyclopedic and not suitable for a scientific article. How about "unconventional physical assumptions" or something more in-depth (quoting from that reference):

So in the proposed interpretation, the MOND formula does not conserve momentum. By the same token it does not conserve angular momentum, nor energy. Milgrom sidesteps the problem by stipulating that the MOND formula is only valid for test particles moving on a given background, e.g., stars moving in the collective gravitational field of a galaxy. We may inquire more generally, does the MOND formula, or some closely related one, represent a modification of inertia in test particle motion? To comply with the conservation laws we likely want the formula to arise from a Lagrangian. The kinetic part of the Lagrangian should give us the μ(|a|/a0) a part with whatever “corrections” are required. However, it is a theorem that no MOND-like dynamics exists that simultaneously has a Newtonian limit for a0 → 0 (all accelerations are large), is Galilei invariant, and is derivable from a local action [32]. (“Local” means that the relevant Lagrangian can be written as a single integral over volume.) This prohibition is even more stringent from a relativistic standpoint [33]. Accordingly Milgrom introduced a nonlocal action, i.e. one which is a functional of complete orbits, but cannot be reduced to an integral over a Lagrangian [32]. This approach does not quite reproduce formula (1) generically, but that formula is recovered for the special case of circular orbits.

Inasilentway (talk) 05:16, 24 September 2009 (UTC)

Problems with Explanation, Needs Expert Attention[edit]

There are two major flaws with this article, which I will detail below.

The article starts out by saying that one formulation, the changing of Newton's second law of motion, requires some complexities to overcome the violation of the conservation of momentum. After saying that a better formulation is to modify gravity, it goes on with an explaination via Newton's second law. "In the everyday world ... F=ma as usual."

It appears to involve Newton's second law, for the force caused by gravity, with the implication that it's only changed for forces due to gravity.

This does suffer from obvious violations of conservation laws, as explained. So, I think this explanation needs attention from an expert, to explain correctly or at least consistently.

Second, the part concerning "the process's environment" doesn't make sense. It gives an example of a satellite around a planet, being in the environment of the star so having to include the star's gravity, thus raising above a0.

But, that would mean, trivially, that binary stars experience a large 'a' from each other, making the total above a0, and thus display classic rotation velocity, in contrast to single stars and unbound gas. But... the matter in a star is experiencing its own self gravity, holding it together and causing pressure (and causing any fountains to fall back in, etc.). So all the atoms in the star are experiencing a's above a0 anyway. The example shown is actually an argument against its validity!

So, everything above "The mathematics" section fails to explain the phenomonon and in fact contradicts it. It needs attention from an expert (someone who understands the math section, at least) to write a lay explaination that actually explains the subject.

Długosz (talk) 22:17, 27 October 2009 (UTC)

This is definitely a problem with the article... As a theoretical physicist I can say that the complete resolution to the problem of conservation laws and not reducing to Newtonian mechanics unfortunately is: "MOND is clearly incorrect."
Indeed, there was a recent talk by one of the big GR experts titled something like "why you should try to understand GR, not modify it" in response to these kinds of theories. No theoretical physicist has ever really taken MOND seriously. It was written down as a toy effective theory, and was taken way too seriously by other people.
One of the above comments above is asking why we have such "silly" articles, but unfortunately as wikipedia is inherently written by non-experts they will always be here and there's not much that can be done about this. (talk) 01:40, 18 April 2010 (UTC)
As a theoretical physicist, you could say that (in a section for "acceptance" perhaps) with proper citations. Długosz (talk) 19:23, 19 April 2010 (UTC)
You're missing the point. The point is that the entire article needs to be replaced with text that only says: "this is a crackpot theory of interest to no one." Because no serious theoretical physicists study this theory. There is simply not much to say about MOND other than that it was a bad idea, never well-motivated, and turned out to be wrong, to no one's surprise. There also are almost no references against MOND because its flaws are so basic that no one could/would publish papers saying it's wrong. This is actually a big issue with a lot of the "fringe" science on wiki articles; there are more papers published on why the crackpot idea is right than why it's wrong because everyone already knows all the reasons it's wrong! (talk) 00:12, 22 April 2010 (UTC)
Galactic rotation curves are still not predicted by a particle-only theory of dark matter, whereas MOND models them extremely well. As said by a physicist researching MOND at his colloquium, this makes the theory "interesting enough to be worth looking into". IP above is wrong - this is not fringe science - nobody I've seen interested in the topic believes it is the answer (especially because it is junk for predicting anything else in the dark matter repertoire - galactic clusters, globular clusters, etc), just a model that fits a currently-unmodeled phenomenon, therefore "interesting enough to be worth looking into".
That is one difficulty with reporting on science second-hand - many fall into the trap of thinking that every researcher pursuing a theory "believes" that theory. When a "toy" fits a phenomenon almost dead-on, that's when it becomes important, even if ultimately unrealistic. SamuelRiv (talk) 13:47, 1 June 2010 (UTC)
Galactic rotation curves ARE and have, for more than a decade, been predicted and very accurately modeled by dark matter. Search the archive if you don't believe me. In fact, MOND does not do this: the parameters of MOND need to be modified for each galaxy independently; this is something a fundamental theory cannot do! (I can't say "well for these things F=ma, for these things F=2ma, for these things F=1.5ma+1...") The only sense in which MOND is interesting is the sense in which I described in my comments above. And I am not "reporting on science second hand" I am, in fact, an actual theoretical physicist who studies, among other things, gravity. Almost no one in the gravity community or theoretical physics community takes MOND seriously, c.f., the talk I mentioned above about the gravity conference. (talk) 04:39, 12 June 2010 (UTC)

Have there been any new developments in MoND in the three years since these comments were written that might rehabilitate it wrt Dark Matter? Does the article need to be marked as Fringe Science? David Spector (talk) 20:10, 2 January 2014 (UTC)

No, it is not fringe science. A URL for a youtube video of a Sean Carroll lecture titled "Dark Matter vs. Modified Gravity" is here Now I ask, is he a theoretical physicist who takes MOND seriously?Michael9422 (talk) 19:34, 29 July 2015 (UTC)

Empirical Formulas and Science[edit]

MOND is an empirical law that explains the Galactic rotation curves extremely well. It is not a theory and such expectations should not be made out of it. It is like the Kepler's Laws. They did not explain anything else other than planetary rotation. They were emperical laws that were explained by Newton's Gravitational theory.

MOND is a similar law, and it must be explained by any acceptable theory of gravitation. Currently existing theories do not explain it. I am no fan of TeVeS as it is just a relativistic extension of MOND. It is not a theory that is built from the scratch, as Relativity was built. I think that the article should make it clear in the beginning that MOND is not a theory, and is just an empirical law, that must be explained by any acceptable theory of gravity.

I think that the trouble with the theory of Relativity is that it does not account for the Planck length, which is another fundamental constant like the speed of light. I think MOND arises because of the inaccuracies that arise in Relativity due to absense of the Planck length. Until we have unification of Relativity and Quantum Theory, we won't be able to explain the MOND Law. Unfortunately it does mean that current theories do not work in low gravitational regimes, and consequently, anything we do with them on those scales, are bound to result in wierd unexplained phenomena like Dark Matter, Dark Energy. It could be possible that other problems like the Flatness problem, are also a consequence. —Preceding unsigned comment added by (talk) 06:14, 18 August 2010 (UTC)

IMHO this is among the more intelligent of the above comments. Whether you call it a law or theory, the relevant question is does it make predictions and how well do those predictions pan out. And of course, a theory with more free parameters than predictions doesn't count for much. MOND seems to have done well with only one free parameter. DM seems to need a lot of ad-hoc input. If MOND also raises questions about conservation of energy and/or momentum in circumstances were we have not done experiments yet, well that's fair game. It seems to me that MOND might be shocking but we are a far distance from dismissing it. —Preceding unsigned comment added by (talk) 23:14, 7 March 2011 (UTC)

Root or Origin, from where the new constant a0 called 'critical-acceleration of MOND' emerges, is proposed in a recently published paper, titled "Genesis of the 'critical-acceleration of MOND' by Hasmukh K. Tank (Progress in Physics, Vol.-4 2012). Abstract of the paper is: "As an attempt to explain the “flattening of galaxies rotation-curves”, Milgrom proposed a Modification of Newtonian Dynamics MOND, in which he needed a new constant of nature a0 , termed as “critical-acceleration-of-MOND”, in his best-fit empirical formula. But so far it has been an ad-hoc introduction of a new constant. Whereas this article proposes: (i) a genesis of this constant; (ii) explains its recurrences in various physical situations; and (iii) its role in determining the size and radii of various structures, like: the electron, the proton, the nucleus-of-atom, the globular-clusters, the spiral-galaxies, the galactic-clusters and the whole universe. In this process we get a new interpretation of “the cosmological-red-shift”, that the linear part of the cosmological-red-shift may not be due to “metric-expansion-of-space”; and even the currently-believed “accelerated-expansion” may be slowing down with time." With this paper MOND seems to gain a status of a 'Scientific-Theory'. What is your opinion? — Preceding unsigned comment added by (talk) 11:48, 21 September 2012 (UTC)

Article (Especially Middle and Last Areas) Badly Needs Non-technical Language to Translate the Topic for the Average Non-Scientist Reader[edit]

Wikipedia is not a cloistered journal for scientists only. Wherever possible scientific language should be in parallel to common-English explanations so that non-scientist readers may also follow the topic. There is no need to omit the scientific language, but Wikipedia policy requires a parallel track in the writing that explains as much as possible to non-scientist readers.

This dual writing track (technical translation) is not only a Wikipedia policy, it is courteous and considerate behavior. "Technical" tag added to article until improvements are made. (talk) 17:25, 25 February 2011 (UTC)

My compliments to the writers of the article. As a non-scientist, I found this article extremely clear in its non-technical explanations (though of course I can't expect to understand the mathematical parts). I think the article does a very good job balancing the technical and non-technical writing, even though only two of its sentences have been modified, and one paragraph added, since the technical tag appeared. So I disagree with the technical tag. Duoduoduo (talk) 20:50, 5 May 2011 (UTC)

Dark Matter: Just Fine, Thanks[edit] William M. Connolley (talk) 14:23, 2 March 2011 (UTC)

I think it qualifies under Discussion and criticisms. Seems to refer to criticism I've heard elsewhere. However, I'm not enough proficient in physics to add this. Rursus dixit. (mbork3!) 18:36, 9 October 2012 (UTC)
Or just lazy... Rursus dixit. (mbork3!) 18:37, 9 October 2012 (UTC)

Criticisms and Pioneer anomaly[edit]

The criticisms and discussion section actually promotes MOND by saying it predicts the Pioneer anomaly - whereas the anomaly is accurately predicted by a pressure of reflected thermal radiation. So in fact the Pioneer anomaly is evidence against MOND rather than for it since if the version of MOND used to predict the anomaly was true the anomaly would be added to the thermal one. I think there is a big problem with that section as it is currently. Dmcq (talk) 11:20, 27 February 2013 (UTC).

Kepler`s laws of planetary motion[edit]

original research removed per talk page guidelines

See,"Kepler`s laws of planetary motion, mathematical derivation", for circular orbits, if a galaxy`s disc could be apportioned into n, smaller notional swept disc, maybe the observed curve (B), in Figure 1, showing velocity plotted against radial distance, has a correlation with a square root spiral`s radial difference equation, y = (1+n)^0.5 -(n)^0.5, provided n, is a whole number. Since GM has units of angular velocity squared by meters cubed, a radial distance, r=[G*M/(w^2)]^1/3, with orbital velocity v=[G*M*w]^1/3. Acceleration may also equal [G*M*w^4]^1/3. Cuberoottheo (talk) 13:27, 20 May 2014 (UTC)

You haven't said why you wrote this. Dmcq (talk) 12:22, 27 May 2014 (UTC)

Modified Newtonian dynamics, needs an explanation as to why Newton`s law seems to be modified.Cuberoottheo (talk) 13:23, 28 May 2014 (UTC)

The first sentence of the article explains why the theory has been proposed. You seem to be talking about your own idea. That is considered WP:Original research on Wikipedia. We can only put into the articles what has been discussed in reliable sources. Dmcq (talk) 14:32, 2 July 2014 (UTC)

If the profile of a galaxy`s disc, (z & Z,being twice the height of the disc), varies by A FUNCTION with distance from the hub, and mass density is uniform, then (w^2)/G=m/(z*pie*r^2)=M/(Z*pie*R^2), hence, m=[(w^2)/G]*[z/Z]*R*r^2. Galaxy discs have bumps and wiggles, see arxiv:0804.1314, maybe its a root spiral radial difference function, that varies the height of the disc? .Cuberoottheo (talk) 09:10, 4 July 2014 (UTC)

Proposed merge with Gauge Vector-Tensor gravity[edit]

Topic is not notable enough on its own but could make a nice addition as a section in the main MOND article. Gaba (talk) 13:15, 24 September 2013 (UTC)

It might be very specific for physics, but that doesn't necessarily mean that it's not notable enough. I don't know so much about physics, but I would wait a bit before merging the two, because it looks somewhat interesting. Maybe this thing is able to solve some of the problems of the former MoND theories. --Mathmensch (talk) 00:57, 29 November 2013 (UTC)
It is mentioned enough and notably in its own right for an article and it isn't the same topic as a possible theory. As the previous reply says we would have to be pretty sure the proposed theory really was the accepted explanation of the observations and currently it just is not at that stage. Dmcq (talk) 12:23, 29 November 2013 (UTC)

Confused about introduction[edit]

"When the uniform velocity of rotation of galaxies was first observed, it was unexpected because Newtonian theory of gravity predicts 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."

Unfamiliar with the physics of this, so here is my reading: 1) Suppose a star S and two planets A and B, which orbit S from a nearer and further distance. Newtonian physics predict that B will orbit more slowly than A, whereas in reality B orbits at a rate such that it circles the sun nearly as often as A (over any given time interval, say "years.") 2) If I read those assumed facts correctly, than I'm confused by this: "For example, planets in the Solar System orbit with velocities that decrease as their distance from the Sun increases." What? The first sentence says Newtonian physics predicts that planets further out would move more slowly, and notes that the reality is unexpected (in other words, outer planets in fact orbit more rapidly), but then this second sentence states that outer planets "orbit with velocities that decrease as their distance from the Sun increases." (In other words, outer planets in fact orbit less rapidly.) What? Is this an outright error, or is some clarification needed? --RichardAlexanderHall (talk) 02:17, 18 June 2014 (UTC)

Did you read the first sentence and its reference to the galaxy rotation problem? I think a short statement of that problem here would probably help but I haven't the foggiest how you got your interpretations of the sentences even if you don't know what the problem being addressed is. Dmcq (talk) 09:08, 18 June 2014 (UTC)
I've put in a short statement from that other article about the problem being addressed. Dmcq (talk) 11:09, 18 June 2014 (UTC)

Two Sections, Same Purpose?[edit]

I'm a bit confused as to why there are two different sections (Consistency with Observations and Discussion and Criticism) that each seem to be to be serving the same purpose. The only difference is that Discussion and Criticism seems to be Bullet Clutster-specific. I don't know why discussion of the Bullet Cluster observations should be pulled out from the discussion of other observations, though. (talk) 00:22, 10 July 2014 (UTC)

Planned re-write[edit]

I am planning to re-write this article, and thought I'd get any thoughts people might have before I start making changes. In my opinion, it needs to: 1) Be easier for the lay reader to get the basic drift of the theory from the outset; 2) Have a more coherent structure so that the thread of the discussion is clearer; 3) Include more detail on what the theory does well and badly, what the different formulations of it are etc, and what its status is within the physics community; and 4) Have the See Also / Further Reading / External Links sections cleaned up and better connected to the text. Hopefully doing this will let us get rid of the cleanup tags.

On a slightly unrelated note, I'm unclear on where I'm allowed to take figures from. Can I take plots from arXiv papers under Fair Use or something like that?

-- HFD90 (talk) 20:51, 9 October 2014 (UTC)

Article re-written[edit]

OK I've revamped the article. I hope you'll agree that the structure is more coherent now and that the description is both clear enough for the lay-reader to get the basic gist and detailed enough for the physicist to see how the theory works. Comments welcome, and of course please correct anything that you think needs correcting. --HFD90 (talk) 19:20, 12 October 2014 (UTC)

Please clarify something in the section on the interpolating functions. 'a' is defined as the normal Newtonian acceleration, but the 'a' inside the mu(a/a0) is in a different font. The question is, does it also stand for the normal Newtonian acceleration? I have looked at the papers listed in the reference, and I find them confusing as well on this point. I am writing a program to plot MoND velocities, and I find that treating that 'a' as normal Newtonian acceleration does not work. Can someone clear this up? — Preceding unsigned comment added by (talk) 01:53, 27 October 2014 (UTC)

Sorry for taking ages to answer this. Yes, the 'a' in the formulae is just ordinary acceleration, e.g. v^2/r for circular motion. Acceleration is a kinematic quantity, so no modified theory of dynamics can change what it means -- it just describes how a particle moves through space. Think about MOND as providing an alternative to Newton's laws for calculating acceleration (and hence a spacetime trajectory) given a mass distribution. Does this help? HFD90 (talk) 03:40, 7 February 2015 (UTC)

One more idea about the reason why discrepancy in velocity[edit]

If the space would have a density. We talk all the time about expanding universe, but never considering that space as such could actually have properties on its own and that in some places space could be more dense than in the other. Somehow there is always assumption that space is infinite, only the mass is that what has exploded. But it could be that the space only exists in the bubble, which is expanding.

Now, if the space would have density, then close to the center of galaxy the density of space would be more than towards the outer edge because of gravity. Every star however also has a field of gravity and close to each start or any mass or source of gravity the space would also be more dense.

In order for an object to travel through the space at high speed, one idea would be to use gravity to condense the space just in front of the object and then expand the space behind the object.

It could be that the stars orbiting the galaxy travel at higher speeds, because of the effect of their own gravity. By having large mass and large gravity they can travel through space at higher speed than objects with lower mass. (dragging all the planets and everything with them). When close to the center of the galaxy the space is already condensed due to the gravity of the central black hole and relative effect of the mass of the stars is not so strong as on the outer edge.

It would also mean that black holes could travel with speeds in excess of the speed of light, because the space could be condensed and expanded by a possibly very large factor.

It would also mean that the speed of traveling through the space is somehow proportional to objects "speed" and mass or gravity of the object. Some object would have more mass and less speed and other less mass and more speed, but their observed velocity would be the same. — Preceding unsigned comment added by 2A00:EE2:2500:900:5557:C857:4AEF:3D52 (talk) 18:29, 28 August 2016 (UTC)