The sources of Schwinger's Green's functions.

Schweber, Silvan S · Proc Natl Acad Sci U S A · 2005

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Abstract

Julian Schwinger's development of his Green's functions methods in quantum field theory is placed in historical context. The relation of Schwinger's quantum action principle to Richard Feynman's path-integral formulation of quantum mechanics is reviewed. The nonperturbative character of Schwinger's approach is stressed as well as the ease with which it can be extended to finite temperature situations.