[jocaal]

When solving for the wave equation, the substitution made for J is sigma * E. So defined in terms of the E field and some conductivity constant. When solving the wave equation, there is no mention of charge density, everything is fields. This predicted the existence of electromagnetic waves. In reality, we know there is only electrons and photons. So thus the wave equation is the source of truth and what we call fields are just a consequence of the complex interactions between electrons and photons and this is studied in quantum electrodynamics.