Julian Schwinger, Renormalization, and Ineffective Field Theory
Abstract: In the late 1940s and early 1950s, Julian Schwinger developed renormalization methods for extracting finite results from quantum electrodynamics and laid the initial foundation for postwar quantum field theory (QFT) itself. He continued to work within the framework of QFT through the mid-1960s, long after most particle theorists had shifted their hopes for modeling the strong interactions to S-matrix Theory or the methods of current algebra. During this period Schwinger developed a unique, and remarkably prescient, understanding of the physical significance of renormalization. He also adhered to methodological scruples remarkably similar to those that, in the 1970s, led particle theorists to develop the now-dominant understanding of QFTs as effective field theories. In Schwinger's case, however, these methodological scruples led him to abandon QFT entirely in 1966 to devote himself to the development and elaboration of an alternative, largely fruitless theoretical framework for particle physics called Source Theory. In this talk, I argue that the reasons why Schwinger's methodological scruples and understanding of renormalization led him to Source Theory, rather than effective field theory, offer important insight into Schwinger's approach to physics, the state of particle theory in the 1960s, and the philosophical foundations of effective field theory itself.