A tutorial on the conservation of momentum in photonic time-varying media

TL;DR

This tutorial review explores how momentum conservation, specifically Minkowski momentum, applies in electromagnetic media with time-varying properties, linking fundamental physics principles with practical implications for the Abraham-Minkowski debate.

Contribution

It provides three independent approaches demonstrating Minkowski momentum conservation in time-varying media, enhancing understanding of electromagnetic momentum.

Findings

Minkowski momentum is conserved in time-varying media.

Three approaches confirm momentum conservation: boundary conditions, constants of motion, and Lagrangian symmetry.

Clarifies the role of momentum in the Abraham-Minkowski debate.

Abstract

Time-varying media break temporal symmetries while preserving spatial symmetries intact. Thus, it represents an excellent conceptual framework to investigate the fundamental implications of Noether's theorem for the electromagnetic field. At the same time, addressing momentum conservation in time-varying media sheds light on the Abraham-Minkowski debate, where two opposing forms of the electromagnetic field momentum are defended. Here, we present a tutorial review on the conservation of momentum in time-varying media. We demonstrate that the Minkowski momentum is a conserved quantity with three independent approaches of increasing complexity: (i) via the application of the boundary conditions for Maxwell equations at a temporal boundary, (ii) testing for constants of motion and deriving conservation laws, and (iii) applying temporal and spatial translations within the framework of the Lagrangian theory of the electromagnetic field. Each approach provides a different and complementary insight into the problem.