History 181B - Class 39

History 181B: Modern Physics

Class 39 (4/28/03)
Rethinking quantum field theory

Navigation

Outline

Reprise: Quantum field theories through the 1930s
    Where QFTs come from
    The problem: Infinities
    High energies, short distances, and the physicists' response

A temporary expedient: Heisenberg's S matrix (1942-44)
S is for scattering: How to treat interactions
Black-boxing what you can't observe

Facing the infinities? Renormalized QED
    Experimental stimuli
    Is the old QED right or wrong?
    Renormalization hides the infinities
    Meaning and significance of a debatable practice
    War work and postwar theory
        Tomonaga-Schwinger
            QFT in full flower
            The Rad Lab and black boxing
        Feynman (begin): Diagrammatics

Names and terms

Primary	Secondary
quantum electrodynamics (QED) electron-positron pairs vacuum polarization fine structure constant alpha = e²/ h-bar c S matrix Lamb shift Willis Lamb (1913- ), NP 1955 bare charge vs. effective charge renormalization Sin-Itiro Tomonaga (1906-1979), NP 1965 Julian Schwinger (1918-1994), NP 1965 Richard Feynman (1918-1988), NP 1965	subtraction procedures coupling constant Polykarp Kusch (1911-1993), NP 1955 magnetic moment (of the electron) operationalism

Assignment

Victor F. Weisskopf, "The Development of Field Theory in the Last 50 Years," Physics Today 34:11 (1981): 69-85.

First assignment: Read pp. 69-77.
This is dense reading. It starts back in the early 20th century, so the first part (through Dirac) should be a review. If the equations don't mean anything to you, try reading in between them. The assignment is mostly aimed at people who already know a bit of quantum mechanics or quantum field theory, so if you don't, just do what you can.