Refraction, Reflexion and General Covariance
October 1, 2018
In this paper I show how we can recover the standard law of refraction and reflexion of geodesics as a consequence of Souriau’s general covariance principle, extended to a singular situation for the metric. Switching from a variational principle to a principle of invariance, or more precisely covariance, under a group of diffeomorphisms, which is in some sense more satisfactory.

To appear in The Journal of Geometry and Physics. And: here the author limited reprints.