Schwinger's Quantum Action Principle. I. From Dirac's Formulation through Feynman's Path Integrals to the Schwinger-Keldysh Method

2014/02/16 by K. A. Milton, Milton, K. A.
Physics and Astronomy · #FOS: Physical sciences #History and Philosophy of Physics (physics.hist-ph) #Quantum Physics (quant-ph) #physics.hist-ph #quant-ph

paper · pdf · doi:10.48550/arxiv.1402.3762

49 pages, 8 figures, submitted to EPJ H

arxiv created 2014/02/16 · arxiv updated 2014/02/18

Abstract

Starting from the earlier notions of stationary action principles, we show how Schwinger's Quantum Action Principle descended from Dirac's formulation, which independently led Feynman to his path-integral formulation of quantum mechanics. The connection between the two is brought out, and applications are discussed. The Keldysh-Schwinger time-cycle method of extracting matrix elements is described. Part II will discuss the variational formulation of quantum electrodynamics and the development of source theory.

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