paper

Perspective on MOND emergence from Verlinde's "emergent gravity" and its recent test by weak lensing

arXiv:1612.09582

Abstract

We highlight phenomenological aspects of Verlinde's recent proposal to account for the mass anomalies in galactic systems without dark matter -- in particular in their relation to MOND. Welcome addition to the MOND lore as it is, this approach have reproduced, so far, only a small fraction of MOND phenomenology, and is still rather tentative, both in its theoretical foundations and in its phenomenology. What Verlinde has extracted from this approach, so far, is a formula -- of rather limited applicability, and with no road to generalization in sight -- for the effective gravitational field of a spherical, isolated, static baryonic system. This formula cannot be used to calculate the gravitational field of disk galaxies, with their rich MOND phenomenology. Notably, it cannot predict their rotation curves, except asymptotically. It does not apply to the few-, or many-body problem; so, it cannot give, e.g., the two-body force between two galaxies, or be used to conduct N-body calculations of galaxy formation, evolution, and interactions. The formula cannot be applied to the internal dynamics of a system embedded in an external field, where MOND predicts important consequences. etc. MOND is backed by full-fledged, Lagrangian theories that can be, and are, routinely applied to all the above phenomena, and more. Verlinde's formula, as it now stands, strongly conflicts with solar-system and possibly earth-surface constraints, and cannot fully account for the mass anomalies in the cores of galaxy clusters (a standing conundrum in MOND). The recent weak-lensing test of the formula is, in fact, testing a cornerstone prediction of MOND, one that the formula does reproduce, and which has been tested before in the very same way.

arXiv comment6 pages; added discussion of earth-surface effects

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