Galactic Dynamics Without Dark Matter: A Phenomenological Comparison of MOND and Emergent Gravity

We present a comparative phenomenological analysis of Modified Newtonian Dynamics (MOND) and Verlinde’s emergent gravity as alternatives to particle dark matter at galactic scales. Focusing on key empirical regularities—flat galaxy rotation curves, the baryonic Tully– Fisher relation, and the radial acceleration relation (RAR)—we examine how each framework links observed dynamics to the distribution of baryonic matter in the low-acceleration regime. In MOND, these relations arise directly from a modified acceleration law characterized by a universal scale a0, yielding highly constrained predictions and naturally accounting for the observed universality and low intrinsic scatter of the RAR. In emergent gravity, MOND-like scaling can be reproduced at an effective level through an additional entropic contribution to the acceleration, but existing predictions rely on restrictive assumptions such as symmetry, isolation, and equilibrium, making their robustness across diverse galactic environments less clear. We argue that the small scatter and environmental stability of galactic scaling relations provide stringent discriminators, and that, at present, MOND offers a more tightly constrained phenomenological description of galactic dynamics, while emergent gravity remains an intriguing but less predictive framework.