What is mond: Definition and 69 Discussions

Modified Newtonian dynamics (MOND) is a hypothesis that proposes a modification of Newton's law of universal gravitation to account for observed properties of galaxies. It is an alternative to the hypothesis of dark matter in terms of explaining why galaxies do not appear to obey the currently understood laws of physics.
Created in 1982 and first published in 1983 by Israeli physicist Mordehai Milgrom, the hypothesis' original motivation was to explain why the velocities of stars in galaxies were observed to be larger than expected based on Newtonian mechanics. Milgrom noted that this discrepancy could be resolved if the gravitational force experienced by a star in the outer regions of a galaxy was proportional to the square of its centripetal acceleration (as opposed to the centripetal acceleration itself, as in Newton's second law) or alternatively, if gravitational force came to vary inversely linearly with radius (as opposed to the inverse square of the radius, as in Newton's law of gravity). MOND departs from Newton's laws at extremely small accelerations that are characteristic of the outer regions of galaxies as well as the inter-galaxy forces within galaxy clusters, but which are far below anything encountered in the Solar System or on Earth.

MOND is an example of a class of theories known as modified gravity, and is an alternative to the hypothesis that the dynamics of galaxies are determined by massive, invisible dark matter halos. Since Milgrom's original proposal, proponents of MOND have claimed to successfully predict a variety of galactic phenomena that they state are difficult to understand as consequences of dark matter.Though MOND explains the anomalously great rotational velocities of galaxies at their perimeters, it does not fully explain the velocity dispersions of individual galaxies within galaxy clusters. MOND reduces the discrepancy between the velocity dispersions and clusters' observed missing baryonic mass from a factor of around 10 to a factor of about 2. However, the residual discrepancy cannot be accounted for by MOND, requiring that other explanations close the gap such as the presence of as-yet undetected missing baryonic matter.The accurate measurement of the speed of gravitational waves compared to the speed of light in 2017 ruled out a certain class of modified gravity theories but concluded that other MOND theories that dispense with the need for dark matter remained viable. Two years later, theories put forth by Constantinos Skordis and Tom Zlosnik were consistent with gravitational waves that always travel at the speed of light. Later still in 2021, Skordis & Zlosnik developed a subclass of their theory called "RMOND," for "relativistic MOND," which had "been shown to reproduce in great detail the main observations in cosmology, including the cosmic-microwave-background power spectrum, and the matter structure power spectrum."

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  1. L

    I Would discovery of a galaxy without dark matter disprove MOND?

    I’ve been reading about LCDM and MOND recently. And there have been reports of galaxies with little dark matter. I know the lack of dark matter in NGC1052-DF2 was shown not true afterwards. But if such a galaxy without dark matter is actually discovered, would this be sufficient to disprove MOND?
  2. F

    I Mond - gravity as two separate forces?

    Is it possible that MOND might be standard gravity plus an additional force that is inversely proportional to distance. One that is also a property of matter? I ask, because viewing this way begs the questions: If two, then why not more, and if more then perhaps a series with a hope of...
  3. Ranku

    I Distinguishing between the effects of dark matter and MOND

    How do we distinguish between the effect of dark matter and MOND with respect to flat rotation curves in galaxies? How would the shape of the rotation curve differ between the two?
  4. ohwilleke

    I New Preprint on Wide Binaries Supports MOND

    In a dark matter hypothesis, wide binary stars should exhibit no dark matter phenomena since dark matter halos are so much bigger than pairs of distant gravitationally bound pairs of stars. But, in a MOND hypothesis, wide binary stars should be more strongly bound to each other than Newtonian...
  5. strangerep

    A Is MOND Inadequate for Explaining Vertical Oscillations in Galaxy Motions?

    Stacy McGaugh's blog post of 7-Apr-2023: A Few Words About the Milky Way left me gobsmacked. A "few" words? Ha! Here follows my "short" version... Stars in a galaxy don't have just a flat orbit around the galaxy centre. During their orbit they also do small oscillatory motions up and down in...
  6. A

    A MOND: Two Small Masses at Great Distance - Orbit Speed

    In MOND should two small masses placed at a great distance orbit faster than in Newtonian dynamics? Would it be theoretically possible to do this experiment in the solar system, or would the presence of the sun and earth be a problem?
  7. A

    Where Can I Find Up-to-Date Resources for Studying MOND Theory?

    Can you recommend papers and books to study MOND? I know that a lot of MOND theories have been ruled out by recent observations, so I don't know where to start without wasting time studying from outdated references. I know GR from Carroll's book and cosmology from "Physical Foundations Of...
  8. haushofer

    I Does Superfluid Dark Matter provide a successful explanation for MOND?

    I was glancing through https://arxiv.org/abs/1605.07458 I don't fully get why scale invariance kicks in below a certain acceleration. Is this because the centripetal force becomes constant? I do see that Newton's second law with the centripetal force included is scale invariant. This symmetry...
  9. K

    I MOND from MacDowell-Mansouri geometrical formulation

    One poster is a strong promoter of Deur and Deur theory of how to get MOND out of GR via self-interaction and analogy to QCD. There is intense skepticism of Deur's approach, which has 0 citations other than the author. I saw this paper, High Energy Physics - Theory...
  10. K

    I Noncommutative geometry and asymptotic safe gravity and MOND

    I saw 2 recent papers on MOND are they promising [Submitted on 21 Jul 2022] Noncommutative geometry and MOND Peter K.F. Kuhfittig Comments: 5 pages, no figures Subjects...
  11. K

    I MOND from galaxies that are fractal

    I found these papers, the first is that galaxies are fractal based on observation Fractal Analysis of the UltraVISTA Galaxy Survey Sharon Teles (1), Amanda R. Lopes (2), Marcelo B. Ribeiro (1,3) ((1) Valongo Observatory, Universidade Federal do Rio de Janeiro, Brazil, (2) Department of...
  12. Frabjous

    A Is this MOND advance a big deal?

    I read this article https://physics.aps.org/articles/v14/143 about this paper https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.161302 How potentially significant is this?
  13. M

    A MOND Theory Primer: Stacy McGaugh's Research Program Explored

    The astronomer Stacy McGaugh has become the most prominent public promoter of MOND (modified Newtonian dynamics) in recent years, on the grounds that it makes many successful predictions, yet according to the standard "LambdaCDM" (dark energy plus cold dark matter) paradigm, there's no reason it...
  14. K

    I Does the external field effect prove MOND over dark matter?

    this paper, Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies Kyu-Hyun Chae1 , Federico Lelli2, Harry Desmond3, Stacy S. McGaugh4, Pengfei Li4, and James M. Schombert5 Published 2020 November 20 claims a 4 sigma...
  15. A

    A How Would MOND Solve the Dark Matter Problem and Affect Quantum Gravity?

    Assuming that the dark matter problem is finally solved by some kind of MOND, how that would change the scene for quantum gravity?, how that would change the proposed/expected properties of the Graviton (massless spin 2 particle)?
  16. E

    B Gravitational Lensing & MOND: Does DM Explain Observations?

    Do gravitational lensing observations support the need for huge amounts of DM? If so, what do the MOND proponents say about that?
  17. fresh_42

    A New MOND Simulation: First Galaxy Formation Model in Milgromian Gravity

    There is a new paper on a MOND simulation, and the participating institutes provide some credence. https://arxiv.org/abs/2002.01941 As I understood it, they have tested mainly against disk galaxies. However, shouldn't it be tested against ring, ellipse galaxies and nebulas , too? And a more...
  18. Arman777

    I MOND -- Understanding Equations

    I am reading an article written by Sanders and McGaugh In the article, the first equation is written as $$F = f(r/r_0)GM/r^2~~~(1)$$ where ##x = r/r_0## Then it goes like if $$f(x) = \begin{cases} 1 & \text{if } x <<1 \\ x & \text{if } x >>1 \end{cases} $$ So the equation becomes $$F =...
  19. K

    I Can the MOND theory be experimentally tested?

    I have read about LISA Pathfinder. Can a satellite with gravitational test instruments, such as a torsional pendulum, test the MOND theory at L1 and L2? Maybe both MOND and dark matter are needed to explain velocities of some remote stars and the formation of large galactic structures.
  20. P

    B Is there reasoning behind MOND?

    I've been reading a lot about MOND, an alternate theory attempting to explain the rotation of galaxies without using dark matter. It claims that at large distances gravity is proportional to 1/r rather than 1/r^2. In the published article, there are countless experiments done providing evidence...
  21. wolram

    B Why does MOND fit rotation curves so exactly?

    I have been reading this article https://tritonstation.wordpress.com/2018/10/05/it-must-be-so-but-which-must/ so why does Mond fit so well over dark matter models?
  22. M

    A Shaposhnikov and Hossenfelder, Higgs and MOND

    We had two papers yesterday making big claims in the realm of minimal BSM theory. http://arxiv.org/abs/1803.08907 Conformal symmetry: towards the link between the Fermi and the Planck scales Mikhail Shaposhnikov, Andrey Shkerin (Submitted on 23 Mar 2018) If the mass of the Higgs boson is put...
  23. Adrian59

    A Galaxy dynamics explained without DM or MOND

    I have been working on a discovery that could explain galaxy rotation curve without dark matter or modification of Newtonian dynamics. However, I was unable to make any comment within this forum since this was unpublished work. However, the same discovery has been made independently by Kenneth F...
  24. nomadreid

    I Does this variant of MOND exist?

    MOND theories are not very popular, but they don't seem to be going away. As I understand the original one, acceleration is a function of the amount of acceleration which would be predicted by Newton's Law. I saw a proposal recently (not yet published, hence I cannot give a reference) which...
  25. K

    I Scale of a in MOND and cosmological constant

    in 2 recent papers by Lee Smolin and Erik Verlinde it is claimed that the scale of acceleration as required by various MOND theories is on the same order as the cosmological constant both researchers suggest that instead of cold dark matter, or even modified Newtonian dynamics, MOND-like...
  26. K

    I MOND as a purely quantum gravity effect

    Four principles for quantum gravity Lee Smolin (Submitted on 6 Oct 2016) Four principles are proposed to underlie the quantum theory of gravity. We show that these suffice to recover the Einstein equations. We also suggest that MOND results from a modification of the classical equivalence...
  27. E

    I MOND: Explaining the “Missing Mass” Problem in Galaxies

    I’ve been reading various things on the internet about how Modified Newtonian Dynamics attempts to solve (or just model?) the “missing mass” problem in galaxies. It sounds more reasonable to me than hypothesizing conveniently undetectable dark matter. But I am wondering why they are using what...
  28. wolram

    MOND and the missing baryons problem

    http://arxiv.org/pdf/1508.04001v2.pdf Although i am not a proponent of MOND this paper gives an alternative to the missing baryons problem The colliding ‘Bullet Cluster’ is often adduced as strong evidence for DM, with the understood – 3 – implication that it is evidence for the...
  29. Earnest Guest

    Does the Bullet Cluster Disprove MOND and Challenge ΛCDM?

    I've read a lot of opinions and a lot of published pieces about the Bullet Cluster. Please correct me if I'm wrong, but the Bullet Cluster doesn’t prove ΛCDM (it has far too much collision velocity for such a model) so much as as it disproves MOND. The argument seems to be: MOND can describe...
  30. D

    MOND : Help with fitting procedure

    I am looking for pedagogical guides to fitting rotation curves with MOdified Newtonian Gravity. I want to study how to fit the luminosity data as well as the kinematic data. I have studied some published papers on MOND fits(Sanders, Mcgaugh, blok etc). But, they are not sufficiently elaborate...
  31. M

    Deur's modified gravity: a type of MOND inspired by QCD

    I found a few curious arxiv papers by Alexandre Deur (via Twitter). Deur works in QCD. He explains QCD strings (flux line between quark and antiquark) as due to attraction between gluon field lines, ultimately due to gluon-gluon interactions. Phenomenologically this adds a linear term to the...
  32. Chronos

    Is MOND still a viable theory for dark matter?

    This paper appears to further the case for DM vs MOND http://arxiv.org/abs/1401.3162, A simple model linking galaxy and dark matter evolution.
  33. us40

    Why is the scientific community divided on the existence of dark matter?

    Hello, I found same number of arguments and observation regarding dwarf galaxies which supports mond (modification of Newtonian dynamics) and generally same number of arguments and observational support for dark matter so why large number of physicist community is in favor of dark...
  34. Alain De Vos

    Mond & formula for acceleration

    Mond uses the function μ ... Instead why not propose a scalar name it "dim" , a function of the location. Basic physics says:.........a=GM/r^2 but on the outer edge of our galaxy :...a=sqrt(GMa0)/r^1 So in general a=Cte/r^(dim-1), with dim=3 (for us, on a local scale on Earth mass is...
  35. T

    What is the current status on MOND

    I wondered if MOND is still considered a possible alternative to cold dark matter? See section titled "Alternatives to dark matter" http://en.wikipedia.org/wiki/Galaxy_rotation_curveOne other question: when I play the galaxy rotation video it appears to me almost as if the arms are...
  36. Chronos

    Another nail in the MOND coffin?

    The relativistic pulsar-white dwarf binary PSR J1738+0333 II. The most stringent test of scalar-tensor gravity http://arxiv.org/abs/1205.1450
  37. mesa

    Question about MOND and gravity

    I'm trying to figure out the formula adjustment to Newtonian mechanics using MOND but I'm getting stuck. Wikipedia states: "Assuming that, at this large distance r, a is smaller than a0 so: μ × (a/a0) = a/a0" Why does 'a' being smaller than 'a0' get rid of μ?
  38. J

    Cosmological constant supports MOND

    Does the cosmological constant support MOND? The equation for critical density is as follows (in terms of mass rather than density): Critical density (90.4 x e54 gm) = matter (4.1 x e54 gm) + dark matter (20.6 x e54 gm) + dark energy/cosmological constant (65.7 x e54 gm). Most estimates...
  39. maverick_starstrider

    Is MOND Related to Renormalization? A Review on the Connection

    Hey, I'm just curious, MOND (Modified Newtonian Dynamics) seems to have a character of field renormalization where G is a running constant. Is there something to this relationship? Does anyone know of a review article that discusses this (or at least an article that someone in...
  40. J

    Some repetitive mistakes and misconceptions about DM, MOND, TeVeS, and cosmology

    First MOND was the first to predict the cosmic background radiation, as repeated in this recent article (2011) http://prl.aps.org/abstract/PRL/v106/i12/e121303 in its page 121303-3: Whereas the LCDM-1999 prediction was falsified (A1:2 = 1.8). Only after the WMAP data was known (A1:2 = 2.34 ±...
  41. H

    MOND paper says Bullet Cluster poses problems for Lambda-CDM

    I was reading a recent paper on arXiv.org on a novel simulation of MOND, and surprisingly they addressed the Bullet Cluster, which I guess is one of the more serious problems for MOND. What was even more surprising was that they said this posed a problem for Lamda-CDM models as well. Here is the...
  42. Z

    Flat Velocity Curve: Newton vs MOND Theory

    Consider a star of mass m at a distance r form the center of a circular disk galaxy. Newton's law: F = GM(r)m/(r^2) where M(r) is the amount of mass inside the radius r. If we consider a uniform galaxy then density (p) is p = M/L where L is the length = 2*pi*r. So M(r) = p*2*pi*r. Setting the...
  43. inflector

    New Paper on MOND by Bekenstein

    Has anyone read and digested "Alternatives to dark matter: Modified gravity as an alternative to dark matter" by Jacob D. Bekenstein? http://arxiv.org/abs/1001.3876
  44. A

    MOND/MOG vs DM: Deuterium Abundance Constraints

    I've read through a lot of the other MOND vs DM debate threads, but I was wondering whether or not this has been addressed: If observed abundances of deuterium place very tight constraints on \Omega_m being roughly .03 or so, wouldn't we have to posit DM as the other .27? To me, I think that...
  45. M

    Understanding the MOND Principle for Gravity and the Galaxy Rotation Anomaly

    I’ve been studying MOND and some of the ideas behind theories put forward to explain MOND. Based on this I’m now going to describe the simplest, but most critical concept that’s used to begin understand why Newton’s inverse square law breaks down. Dynamics won’t be considered since they are...
  46. astrorob

    Newton: Is MOND the Answer to Dark Matter?

    My question is this: Why are we (as a community) so eager to disregard modifying Newtonian Dynamics (MOND)? Of course it's incredibly accurate on macroscopic scales, but isn't science meant to be progressive? Since Zwicky's observation of galactic cluster rotation in 1922 and the...
  47. S

    August 2006 article promoting MOND

    An August 2006 article promoting MOND: http://discovermagazine.com/2006/aug/cover Is that theory any good?
  48. quasar987

    MOND GR: Bridging the Gap Between Newtonian and General Relativity?

    I heard a general theory of relativity was constructed based on MOND rather than on Newton's law of gravitation. How well do the predictions of the MOND GR compare with the classical tests of GR (such as light bending)? Basically, is it in better or worse agreement with experiment than...
  49. Jonathan Scott

    Can MOND be ruled out at laboratory scale?

    The empirical MOND explanation of galactic rotation curves involves switching over in the low acceleration regime from the Newtonian acceleration Gm/r^2 to the MOND acceleration term sqrt(Gm a_0)/r. This is normally achieved using an "interpolation function" which effectively switches off one...
  50. E

    Could gravity's strength also require denisty as an alternative to MOND

    MOND has been one alternative to DM. It is based on modifying acceleration of F=MA. As another alternative, could the strength of the force of gravity be much weaker than expected or predicted by GR when density is low, and as strong as expected by GR when density is above a threshold?