Equivalence principles exotica

This is a short review of the different principles of equivalence stated and used in the context of the gravitational interaction. We emphasize the need for precision in stating and differentiating these different equivalence principles, especially in the context of prevalent confusion regarding the applicability of the weak equivalence principle in quantum mechanics. We discuss several empirical results pertaining to the validity of the equivalence principle in exotic physical sitautions not directly amenable to experimental tests. We conclude with a section on the physical basis of the universal validity of the equivalence principle, as manifest in the universality of free fall, and discuss its link to cosmic gravity.