Comment on `Do electromagnetic waves always propagate along null geodesics?'

Abstract

We study the propagation of Maxwellian electromagnetic waves in curved spacetimes in terms of the appropriate geometrical optics limit, notions of signal speed, and minimal coupling prescription from Maxwellian theory in flat spacetime. In the course of this, we counter a recent major claim by Asenjo and Hojman (2017) to the effect that the geometrical optics limit is partly ill-defined in G\"odel spacetime; we thereby dissolve the present tension concerning established results on wave propagation and the optical limit.