Modified Newtonian Dynamics

Modified Newtonian Dynamics
Name	Modified Newtonian Dynamics
Field	Astrophysics, Cosmology, Gravitation
Introduced	1983
Proponents	Mordehai Milgrom, Jacob Bekenstein
Related	General relativity, Dark matter, MOND alternatives

Modified Newtonian Dynamics Modified Newtonian Dynamics is a proposed empirical modification of Isaac Newtonian dynamics intended to account for anomalies in galactic rotation without invoking Dark matter. Originating in 1983 by Mordehai Milgrom, the idea has motivated work across astrophysics, cosmology, and theoretical gravitation research and has influenced observational programs at facilities such as the Very Large Array, Sloan Digital Sky Survey, and Hubble Space Telescope.

Background and Motivation

Milgrom introduced the proposal to address discrepancies highlighted in studies by Vera Rubin, Kent Ford, and analyses of the Tully–Fisher relation and mass discrepancies in systems observed with the Poincaré Observatory and data later compiled in surveys like the Two Micron All Sky Survey and HIPASS. Observational tensions with expectations from Isaac Newtonian gravity and the Virial theorem motivated alternatives to the dominant Cold dark matter paradigm advocated in the Lambda-CDM model. Early proponents contrasted MOND predictions with rotation curves studied by teams associated with Royal Observatory, Edinburgh and the Carnegie Institution for Science.

Theory and Formulation

The core hypothesis modifies the relation between acceleration and force below a characteristic scale a0, inspired by phenomenology rather than a Lagrangian initially, connecting to principles of Galilean invariance and empirical fittings to rotation curves measured by groups using the Arecibo Observatory and Green Bank Telescope. Formalizations introduced nonlinear Poisson-like equations and interpolating functions; subsequent work by Jacob Bekenstein provided a variational underpinning. Theories attempt to recover Newtonian results in the high-acceleration regime tested in experiments at institutions such as CERN and California Institute of Technology, while reproducing galaxy-scale phenomena catalogued by the European Southern Observatory and analyzed in collaborations including Max Planck Society researchers.

Relativistic Extensions and Alternatives

To reconcile with relativistic tests exemplified by the Perihelion precession of Mercury, Gravitational lensing observations from Einstein rings and timing of Binary pulsars, several relativistic extensions were proposed. Notable is TeVeS by Jacob Bekenstein, which introduces additional fields and aims to satisfy constraints from Cosmic microwave background measurements by missions such as WMAP and Planck. Other approaches draw on frameworks from Brans–Dicke theory, Scalar–Tensor theories, and proposals inspired by ideas from Erik Verlinde and emergent gravity programs at institutions like Institute for Advanced Study. Competing alternatives include f(R) gravity and Emergent gravity, researched at universities including University of Cambridge and Princeton University.

Observational Tests and Evidence

Supporters highlight successes fitting rotation curves across samples compiled by Vera Rubin Observatory predecessor surveys, reproducing the Tully–Fisher relation and the baryonic-mass relations reported by teams from University of Groningen and University of St Andrews. Constraints arise from gravitational lensing analyses around clusters such as the Bullet Cluster examined by collaborations including Chandra X-ray Observatory and Subaru Telescope, and from dynamics in dwarf satellites of Andromeda and the Milky Way surveyed by programs like Gaia and Sloan Digital Sky Survey. Precision tests in the Solar System, using missions like Cassini and the MESSENGER mission, impose limits on allowable deviations from General relativity at high accelerations.

Cosmological Implications

Embedding the proposal into a cosmological framework challenges explanations of structure formation traced by the Large-scale structure of the Universe and observations from surveys such as BOSS and DESI. Relativistic formulations aim to reproduce features of the Cosmic microwave background power spectrum measured by Planck and WMAP, but often require additional components or novel mechanisms akin to sterile components discussed in contexts like Hot dark matter or modified initial conditions considered in studies at Lawrence Berkeley National Laboratory. Impacts on early-universe physics influence interpretations of results from Big Bang nucleosynthesis and the growth of perturbations evaluated by numerical codes developed at centers like Los Alamos National Laboratory.

Criticisms and Challenges

Critics emphasize tensions with cluster-scale dynamics illustrated by the Bullet Cluster and with the abundance and distribution of satellite galaxies reported in the Missing satellites problem and the Cusp–core problem debated within the Lambda-CDM model community. Challenges include achieving consistency with precision tests of General relativity such as those from LIGO detections of gravitational waves, reconciling relativistic lensing without substantial unseen mass, and producing a fully compelling cosmological model competitive with the Lambda-CDM model developed by collaborations across Harvard University, Princeton University, and Stanford University. Proponents continue to develop hybrid scenarios and to confront data from ongoing observational programs at facilities like the Atacama Large Millimeter Array and the James Webb Space Telescope.

Category:Astrophysics Category:Cosmology Category:Gravitation