6 Quantum electrodynamics

Finally, we get to the last part of the course, where we try to quantize electro-

magnetism. Again, this will not be so straightforward. This time, we will have

to face the fact that the electromagnetic potential

A

is not uniquely defined,

but can have many gauge transformations. The right way to encode this infor-

mation when we quantize the theory is not immediate, and will require some

experimentation.