ABSTRACT
We saw in Chapter 8 that a special class of interacting eld theories, the gauge theories, arise almost inevitably when we investigate the relationship between the `internal spaces' in which elds or wavefunctions exist at dierent points of spacetime. We found that the simplest of these theories can be interpreted in terms of observed electromagnetic forces and, indeed, that quantum electrodynamics agrees with experimental measurements with extremely high precision. In this chapter, I shall describe how the weak and strong nuclear interactions can also be interpreted in terms of gauge theories. It would be most satisfying if the three interactions could be explained in terms not of three dierent gauge theories but of a single unied theory. Such theories have, as we shall see, been proposed. Just what is entailed in this unication will become clear as we proceed, but it is not entirely clear at the time of writing whether a completely unied theory can be achieved, or whether such a theory could be subjected to any very stringent experimental test.
