Gauge fixing

Summary

Gauge fixing is the choice of an extra condition on the potentials of a field theory. The condition removes, fully or in part, the freedom to change the potentials without changing the physical fields. In electromagnetism the four-potential is determined by the fields only up to the gradient of a function, and a gauge condition picks out preferred potentials. Different conditions, such as the Lorenz gauge and the Coulomb gauge, simplify the equations in different ways. Gauge fixing is also a necessary step in the quantization of gauge theories.