Dark matter -- Modified dynamics: Reaction vs. Prediction

Abstract

The dark energy-cold dark matter paradigm ($\Lambda$CDM) has gained widespread acceptance because it explains the pattern of anisotropies observed in the cosmic microwave background radiation, the observed distribution of large scale inhomogeneities in detectable matter, and the perceived overall expansion history of the Universe. It is further {\it assumed} that the cosmic dark matter component clusters on the scale of bound astronomical systems and thereby accounts for the observed difference between the directly detectable (baryonic) mass and the total Newtonian dynamical mass. In this respect the paradigm fails; it is falsified by the existence of a simple algorithm, modified Newtonian dynamics (MOND), which explains, not only general scaling relations for astronomical systems, but quite precisely predicts the effective gravitational acceleration in such objects from the observed distribution of detectable baryonic matter -- all of this with one additional universal parameter having units of acceleration. On this sub-Hubble scale, the dark matter hypothesis is essentially reactive, while MOND is successfully predictive.