## ABSTRACT

This chapter argues that a similar universality holds, empirically, in the case of the weak interaction, giving a strong indication that this force too should be described by a renormalizable gauge theory. The largest ‘diameter’ will be associated with the smallest mass m, in this case the electron mass. Schwinger’s one-loop calculation provided a fundamental early confirmation of QED, and was the start of a long confrontation between theory, experiment which still continues. The interested reader is referred to the extensive review by Jegerlehner and Nyffeler, upon which we shall draw. The moral of the story so far, then, is that we can perform a one-loop renormalization of this theory, at the cost of taking additional parameters from experiments and introducing new terms in the Lagrangian. On the ‘low-energy effective field theory’ interpretation, we can enjoy the calculational advantages of renormalizable field theories, while acknowledging – with no contradiction – the likelihood that at some scale ‘new physics’ will enter.