3 Fundamental Properties of the Electromagnetic Field
3.1 CAUSALITY; DOMAIN OF DEPENDENCE
Solutions of the time-dependent Maxwell equations are observed (macroscopically) to obey the principle of causality. This means that if ρext and Jext are zero for t < 0, and if E and H are identically zero for t < t0, where t0 is some value of time less than zero, then E and H are in fact zero for all t < 0. In other words, there is no effect (field) before the cause (source). When solving initial/boundary-value problems for fields, causality must often be used to select the correct, unique solution of Maxwell’s equations out of several possible ones. In this section, we study the implications of causality and their connection with the so-called ...
