ABSTRACT
Let us try again. Why do people work on string theory? ‘Quantum field theory’ is three small words: but three small words that
have spawned a bookcase full of textbooks. We have seen in earlier chapters that the Standard Model of particle physics is an example of a quantum field theory. Quantum field theories are in a sense just – just! – the quantum mechanics of theories such as electromagnetism. That is, they do not exist as something additional to ordinary quantum mechanics, but are rather particular examples of quantum mechanical theories. They are the quantum mechanical theories of fields (for example, the electromagnetic field). They operate under the same rules and obey the same equations as any other quantum mechanical theory. However, to categorise quantum field theories simply as examples of quantum mechanical theories is as accurate as categorising Hamlet simply as an example of a book. The statement is as wrong as it is possible to be while still being right. Quantum field theories are both highly important and filled with subtleties. As outlined in the introductory chapters, there are indeed sufficient subtleties that these theories spent their first twenty years being viewed as fundamentally flawed, and their second twenty years being regarded as calculational black magic, before a deeper conceptual understanding finally arose.
