Path Integrals in Quantum Field Theory – A Friendly Introduction

I’d like to start the story on relatively stable ground: the land of classical physics. More specifically, I’ll introduce the idea of a classical Lagrangian field theory. The idea is that many physical systems take a similar form; there is a space of possible configurations of the system (which we usually refer to as fields), but those that arise in reality are those which minimise a certain action – a functional on the space of fields. In lieu of giving a (probably unenlightening) abstract definition, I’ll give a few examples.