The Real Problem with MOND
  Gravitational potentials in the cosmos are deeper than expected from observed
visible objects, a phenomenon usually attributed to dark matter, presumably in
the form of a new fundamental particle. Until such a particle is observed, the
jury remains out on dark matter, and modified gravity models must be
considered. The class of models reducing to MOdified Newtonian Dynamics (MOND)
in the weak field limit does an excellent job fitting the rotation curves of
galaxies, predicting the relation between baryonic mass and velocity in
gas-dominated galaxies, and explaining the properties of the local group.
Several of the initial challenges facing MOND have been overcome, while others
remain. Here I point out the most severe challenge facing MOND.
