Steven Weinberg on Theory

“Quantum mechanics is not itself a dynamical theory. It is an empty stage. You have to add the actors: You have to specify the space of configurations, an infinite-dimensional complex space, and the dynamical rules for how the state vector rotates in this space as time passes.”

“I learned about renormalization theory as a graduate student, mostly by reading Dyson’s papers. ... From the beginning it seemed to me to be a wonderful thing that very few quantum field theories are renormalizable. Limitations of this sort are, after all, what we most want, not mathematical methods which can make sense of an infinite variety of physically irrelevant theories, but methods which carry constraints, because these constraints may point the way toward the one true theory.”