Pre-Quantum Electrodynamics

Lagrangian for quantum electrodynamics

\begin{equation} {\cal L} = \bar{\psi} \left[ i \gamma^\mu \left( \partial_\mu + i e A_\mu \right) - m \right] \psi - \frac{1}{4} F_{\mu \nu} F^{\mu \nu} \tag{qedL}\label{qedL} \end{equation}