Regular Article – Theoretical Physics
Quasi-geodesics in relativistic gravity
Department of Physics and Astronomy, Bishop’s University, 2600 College Street, J1M 1Z7, Sherbrooke, Québec, Canada
Accepted: 24 December 2020
Published online: 13 January 2021
A four-force parallel to the trajectory of a massive particle can always be eliminated by going to an affine parametrization, but the affine parameter is different from the proper time. The main application is to cosmology, in which elements of the cosmic fluid are subject to a pressure gradient parallel to their four-velocities. Natural implementations of parallel four-forces occur when the particle mass changes, in scalar–tensor cosmology, and in cosmic antifriction due to particle production.
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