Electrodynamics and spacetime geometry I: Foundations

TL;DR

This paper investigates the fundamental link between spacetime geometry and electromagnetism, deriving Maxwell's equations in curved spacetime and exploring new electromagnetic phenomena induced by gravitational effects, with potential astrophysical and gravitational wave applications.

Contribution

It formulates Maxwell's equations on curved spacetime using tensor calculus and explores the physical consequences of spacetime curvature on electromagnetic phenomena, including potential generalizations of vacuum relations.

Findings

Maxwell's equations are explicitly expressed in (pseudo) Riemannian manifolds.

Spacetime curvature induces new electromagnetic couplings and phenomena.

Potential applications in astrophysics and gravitational wave detection.

Abstract

We explore the intimate connection between spacetime geometry and electrodynamics. This link is already implicit in the constitutive relations between the field strengths and excitations, which are an essential part of the axiomatic structure of electromagnetism, clearly formulated via integration theory and differential forms. We briefly review the foundations of electromagnetism based on charge and magnetic flux conservation, the Lorentz force and the constitutive relations which introduce the spacetime metric. We then proceed with the tensor formulation by assuming local, linear, homogeneous and isotropic constitutive relations, and explore the physical, observable consequences of Maxwell's equations in curved spacetime. The field equations, charge conservation and the Lorentz force are explicitly expressed in general (pseudo) Riemanian manifolds. The generalized Gauss and Maxwell-Amp\`{e}re laws, as well as the wave equations, reveal potentially interesting astrophysical applications. In all cases new electromagnetic couplings and related phenomena are induced by spacetime curvature. The implications and possible applications for gravity waves detection are briefly addressed. At the foundational level, we discuss the possibility of generalizing the vacuum constitutive relations, by relaxing the fixed conditions of homogeneity and isotropy, and by assuming that the symmetry properties of the electro-vacuum follow the spacetime isometries. The implications of this extension are briefly discussed in the context of the intimate connection between electromagnetism and the geometry (and causal structure) of spacetime.