MOND - dark matter - modified newtonain dynamics

Welcome to the MOND pages

The Modified Newtonian Dynamics (MOND) s a scientific theory proposed by Moti Milgrom as a solution to the missing mass problem in extragalactic astronomy. Rather than invoking some invisible form of dark matter, it hypothesizes a subtle change to the effective force law at extremely low accelerations (< 10-10 m/s/s).

The basic issue, in brief, and what's at stake.

The Dark Matter Tree - a fanciful representation of the mass discrepancy problem.

Why consider MOND?

A single galaxy might seem a little thing to those who consider only the immeasurable vastness of the universe, and not the minute precision to which all things therein are shaped.
Paraphrased from the Ainulindalë by J.R.R. Tolkein.

Scientific Literature
Extensive list of the literature concerning MOND, complete with links to the actual papers when available, and the occassional commentary.
MOND Review by Milgrom on scholarpedia (first edition 3/2014).

Frequently Asked Questions
A comparison of how ΛCDM and MOND fare in various observational tests.
The External Field Effect in MOND and its explanation.

Some remarks on intellectual honesty and cognitive dissonance | The Blind Men and the Garden.
Insightful article on the difficulty of objectivity, even in science.

Funding: please visit Science Bucks.


MOND in the News
See also this more extensive link

The Missing Universe 4/14 (Astronomy magazine cover story) | also here
From Quarks to Quasars 11/29/13
MOND Predicts Dwarf Galaxy Feature Prior to Observations 8/28/13
National Geographic [Also here] | Yahoo News | newKerala | DNA India | Z News (India) |webindia | Athiest nexus | Science 2.0 | Science Newsline | Science News

Ciel & Espace interview with Milgrom (8/13).
Letter from Milgrom to Bahcall in 1982 (7/13).
It amazes me that all the basic issues are already present.


Material concerning Dark Matter
Experimental Searches for dark matter - a perpetual quest?

Flowcharts: the dark matter flowchart (c. 1986) | the data interpretation flowchart (2012)

The great Dark Matter Debate (11/18/2010 Bethe Colloquium, Bonn University, Germany).
Also available at this local link.


Material written at the Popular Level
Philosophical aspects of the debate over Dark Matter and MOND
Sure to provide fodder for sociologists and historians of science for decades to come.
A popular perspective [HTML] | [PDF]
written for Astronomy Now (January 2002)
There have been a number of good, popular level reviews lately -
see the appropriate section of the literature page.
Milgrom's article for Scientific American (August 2002)


Slides from a few talks related to MOND
MOND overview for the Carnegie Cognitive Astrophysics workshop, March 2014
Skype talk for the dark matter seminar at the University of Arizona, March 2012
Review talk for Modifed Gravity Approaches to the Dark Sector, June 2010
Colloquium given at DTM, April 2008
Colloquium given at TRIUMF, February 2008
Physics department colloquium given at George Mason University, April 2007.
Review talk given at the Alternative Gravities and Dark Matter Workshop, April 2006.
Physics department colloquium given at the University of Rochester, April 2006.
Review talk given at the interdisciplinary conference Dark Matter in the Universe, October 2005.


Material related to the Dynamical Evidence
Comparison of MOND and Dark Matter | New table (11/2011)
Includes a table itemizing various observational tests and how each fares.
Example of a MOND fit to a rotation curve.
Comparison of MOND and CDM fits to the rotation curve of NGC 1560.
Lots and lots of fits (2003).
These are plotted log(V)-log(R) for data with velocity errors < 5%.
Points with error bars are the data; red lines are the fits; light blue lines are the Newtoinian stars+gas.
Residuals of MOND fits (3/2012)
Predictions made by Milgrom in 1983 which were subsequently confirmed (in 1998 and again in 2011)
A MOND fit to the rotation curve of a low surface brightness galaxy.
Mass-to-Light Ratios and Stellar Populations
Remarkably reasonable.
Roster of galaxies which have been used to test MOND:
84-0-11
MOND performs well in the Milky Way, providing detailed information about the surface density profile.


N-body computations
Modelers beware: implementing MOND is not a one line change to standard particle-pushing codes. Chris Mihos explains why. (The inertial modification is inherently nonlocal.) [See also a more sober write-up.]
Other numerical approaches are necessary. For example, Brada's thesis; Ciotti, Londrillo, & Nipoti; Tiret & Combes.


Big Bang Nucleosynthesis and the Baryon Density
BBN: Comparison of the density of baryons in ΛCDM & MOND.
The Missing Baryon Problem goes away in MOND.


Large Scale Structure
An outline of the formation of large scale structure in MOND.


Material related to the Cosmic Microwave Background
The CMB is widely perceived to be a problem for MOND, but this is (at best) an overstatement. The amplitude ratio of the first-to-second peak of the acoustic power spectrum was predicted in advance by McGaugh (1999) with a MOND-motivated model. This prediction remains bang-on in the WMAP data, so I would be more sympathetic to assertions about the CMB had that community been more honest in acknowledging this successful prediction. (They would have burst at the seems with excitement if a similarly accurate prediction had been made conventionally. I also made such a conventional prediction in 1999, but that wasn't the one that worked). Instead, my prediction was widely ignored until the third peak was measured. That does not agree with the prediction of the model I presented in 1999, a fact that cosmologists are much more eager to acknowledge. The amplitude of the third peak observed by WMAP merely falsifies the simple ansatz I used to make the prediction, not MOND itself. Indeed, I pointed out in the original papers that the ansatz must fail at some level, so I am hardly surprised that it does. All this means is that there are degrees of freedom (like a scalar field) that can oscillate separately from baryons in whatever the relavistic parent theory of MOND might turn out to be.
The real test was for ΛCDM: the third peak had to be higher than predicted by pure baryonic damping. ΛCDM survives this test. It "wins ugly" in that, in order to obtain a fit, we have had to nearly double the baryon density over what it was so confidently known to be before it wasn't. That, and the no-CDM prediction for the second peak is still bang on. Amazing coincidence, that.

Comments on specific events in chronological order

1999: No-CDM model provides best-guess prediction for CMB in a MOND universe.
Strictly speaking, only the shape of the power spectrum is predicted in the absence of CDM. This represents MOND only under the ansatz that a MOND version of GR is identical to standard GR in the early universe. More properly, this is a test for the existence of non-baryonic dark matter, and says nothing directly about MOND.
2000: No-CDM prediction realized in BOOMERanG microwave background data.
Associated press release, Sept. 27, 2000.
2001: How the No-CDM prediction fares with DASI and updated (in May, 2001) BOOMERanG CMB data.
2003: No-CDM & WMAP (Feb. 2003).
WMAP 1st:2nd peak amplitude ratio bang on the No-CDM prediction.
WMAP polarization detection confirms the prediction of early reionization.
The critical third peak remains ill-constrained.
2004: The WMAP second-year data are late.
2005: BOOMERanG reports new data from its 2003 Antarctic flight (Aug. 2005).
The WMAP second-year data are a year and half late and counting...
2006: WMAP finally reports new data (March 2006).
The systematic uncertainties concerning the third peak are really daunting. We need to know the point spread function incredibly well. It is not obvious that there can be no instrumental non-linearities that might make the PSF for faint sources differ from that of the bright calibration source (Jupiter).
2006: The Third Peak in TeVeS (April 2006).

2013: Planck reports on the power spectrum.
As expected, Planck provides a much improved version of the CMB acoustic power spectrum. All peaks are now clearly visible. The 1:2 peak ratio remains exactly as predicted by McGaugh (1999) while the third peak is clearly higher than it would be in a purely baryonic damping spectrum.
The net upshot: nothing new.
ΛCDM provides an excellent fit to the improved CMB data just as MOND provides an excellent fit to improved rotation curve data. As before, one's interpretation depends entriely upon which you find more impressive.


Material related to the Bullet Cluster
The bullet cluster has become the most cited piece of evidence against MOND.
The problem is that, even after consideration of MOND, there remains an unexplained mass discrepancy. This is generally the case in rich clusters, the bullet cluster merely shows the general effect in spectacular fashion. However, there is no evidence that requires the unseen mass to be the non-baryonic cold dark matter required by cosmology. While it is certainly unpleasant to invoke dark baryons, it appears to be unavoidable in both ΛCDM and MOND.
It is always unwise to over-interpret a single object, especially when aspects of that object are also problematic for ΛCDM: the collision speed makes a lot more sense in the context of MOND. That doesn't mean we can't understand it in ΛCDM, but then the same holds for MOND.

In general, even if we consider the bullet cluster to falisfy MOND, it does not relieve us of understanding the observed phenomenology in galaxies.

Comments on the Bullet Cluster claim to require dark matter.
The full text of my reply to press inquiries (from which published quotes were extracted).
Paper by Angus et al. fitting the new data.
Preprint examining the collision velocity of the clusters. This is more naturally understood in terms of MOND than CDM. [Published in MNRAS (2008) 383, 417]
The bullet cluster is also a problem for ΛCDM.
Milgrom's comments on the Bullet Cluster
An unsolicited, independent perspective
Related talks by Angus: PPT | text
The collision velocity of the bullet cluster in CDM and MOND.
A counter-example to the bullet cluster - Abell 520.
The dark matter ring in cluster 0024+17.

Material related to Tidal Dwarfs

Can tidal dwarfs falsify dark matter?


Criticisms
MOND is an idea people love to hate. They already know dark matter is right, so MOND must be crazy talk: no need to consider the evidence! Often they seek to blame the messenger, because this is a cosmic heresy of the tie-'em-to-a-stake and light-'em-up variety.

Courage is not the absence of fear, but rather the judgement that something else is more important than fear.
- Ambrose Redmoon (James Neil Hollingworth)

Cosmic fallcies | Attitude

Some remarks on intellectual honesty and cognitive dissonance.
Not everyone holds a high standard of intellectual honesty. Here is a simple test to distinguish true scientists from wannabes.


Rebuttal of criticisms made by Foreman & Scott and N. Gnedin.
Note: I have no intention of submitting my rebuttal to a journal. The nonsense by Forman & Scott has no business being published in a refereed journal, and stuff that happens on arxiv should stay on arxiv.

The sociology of modern cosmology has a disturbing amount in common with the Inquisition in the time of Galileo. To paraphrase the Pope's censor,
It is OK to consider [heliocentrism/MOND] as an abstract hypothesis that is convenient for making certain astronomical computations. But don't dare to suggest it might have something to do with reality.

Comments on the sociology surrounding the recent (early 2013) controversy about the temporary closing of the Dark Matter Crisis.
Bad scientist! Bad!


Link to further material, including other MOND related sites. MOND - dark matter - modified newtonain dynamics
MOND - dark matter - modified newtonain dynamics
MOND - dark matter - modified newtonain dynamics
MOND - dark matter - modified newtonain dynamics
MOND - dark matter - modified newtonain dynamics
MOND - dark matter - modified newtonain dynamics
MOND - dark matter - Modified Newtonain Dynamics
MOND - dark matter - modified newtonain dynamics

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