In relativistic quantum field theory, the interaction between electrically charged fermions and electromagnetic fields is described by coupling conserved four-currents ($j^\mu$) to photon potentials via gauge-invariant equations such as the Dirac equation for spin-1/2 particles. The electromagnetic potential $A_\mu$, determined by source currents through Maxwell's wave equations in a specific gauge, mediates interactions that propagate causally rather than acting instantaneously at a distance. This framework unifies relativistic kinematics with quantum mechanics to describe particle scattering and force mediation via virtual photon exchange.
In relativistic quantum field theory, the interaction between electrically charged fermions and electromagnetic fields is described by coupling conserved four-currents ($j^\mu$) to photon potentials …