Observers' measurements in premetric electrodynamics I: Time and radar length

TL;DR

This paper develops a framework for understanding observer measurements of time and length in premetric electrodynamics, revealing how modifications to electrodynamics affect light propagation and proper time, impacting classical relativity tests.

Contribution

It introduces a metric-independent description of measurements in premetric electrodynamics, extending the understanding of observer measurements beyond standard metric-based theories.

Findings

Electrodynamics modifications alter light propagation and proper time normalization.

Measurements of time and length are influenced by premetric perturbations.

Both effects must be considered in interpreting classical relativity experiments.

Abstract

The description of an observer's measurement in general relativity and the standard model of particle physics is closely related to the spacetime metric. In order to understand and interpret measurements, which test the metric structure of the spacetime, like the classical Michelson-Morley, Ives-Stilwell, Kennedy-Thorndike experiments or frequency comparison experiments in general, it is necessary to describe them in theories, which go beyond the Lorentzian metric structure. However, this requires a description of an observer's measurement without relying on a metric. We provide such a description of an observer's measurement of the fundamental quantities time and length derived from a premetric perturbation of Maxwell's electrodynamics and a discussion on how these measurements influence classical relativistic observables like time dilation and length contraction. Most importantly, we find that the modification of electrodynamics influences the measurements at two instances: the propagation of light is altered as well as the observer's proper time normalization. When interpreting the results of a specific experiment, both effects cannot be disentangled, in general, and have to be taken into account.