Time-reversal invariance and time asymmetry in classical electrodynamics

摘要

We clarify several issues involving the concepts of time-reversal invariance and time asymmetry in classical electrodynamics. Specifically, we consider three questions: (I) If electrodynamics is time-reversal invariant, why are the radiative processes that occur in nature time asymmetric? (II) Why doesn't the time-reversal invariance of electrodynamics contradict the fact that a charged particle in motion feels a radiation damping force? (III) Why don't the advanced solutions to Maxwell's equations occur in nature-is there some principle that forbids them? We argue that these questions are not specific to electrodynamics, but also arise in many other systems in which waves are radiated, and answer them in the context of a simple model describing a coupled particle-field system in (1+1) dimensions.