DFG-NSF: Observational Tests of Covariant Emergent Gravity

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General Relativity provides a well-tested, accurate description of gravitational phenomena over a large range of distances, but it remains a non-quantum theory incompatible with the Standard Model of particle physics. The development of a quantum theory of gravity is thus a central goal of fundamental physics. Observational clues arise from puzzles such as the "dark matter" and "dark energy" problems. These indicate an excess of attraction beyond what can be explained by the gravity of visible mass in galaxies (hence dark matter), and a net repulsion (dark energy) that drives the expansion rate of the universe to accelerate. It is conceivable that these diverse phenomena are related and may emerge from the quantum foundations of gravity. This work will develop and explore the observable consequences of Covariant Emergent Gravity, a theory that may provide a joint explanation for these as-yet ill-understood observations.This project aims to develop and test a new explanation for dark matter and dark energy. Verlinde has proposed the idea of gravity as an emergent phenomenon, but many of the consequences of this idea remain unexplored. A theoretical shortcoming is that it is not generally covariant. Recently, Hossenfelder addressed this problem by developing Covariant Emergent Gravity (CEG). CEG necessarily introduces terms beyond those already present in Emergent Gravity. The team proposes to develop this theory and to investigate whether CEG can be consistent with observations of galactic rotation curves. In particular, it will derive the formulas that govern the appropriate limit of the theory and numerically solve them to apply to real galaxies. This work must be carried out in the non-trivial, non-spherical case of the finite thickness cylindrical geometry appropriate to spiral galaxies. If the CEG hypothesis is incorrect, this work should readily falsify it. If there is some merit to it, it could point the way towards a fresh interpretation and potential resolution of the long-standing dark matter and dark energy problems, and provide insight into the nature of quantum gravity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.