Free Propagation and Successive Scattering
From the time of his thesis and during his struggle to understand the Dirac equation, Feynman is preoccupied with finding the quantity that will determine the evolution of the wave function. While working on his thesis, he finds that the time evolution of the wave function is determined by the classical action, which is integrated along the possible paths that connect the start and end points of the particle. There is no classical action in the Dirac equation’s description of quantum electrodynamics (QED), since the equation introduced a new degree of freedom: spin. In RMP48, Feynman constructs an action that yields the Dirac equation using his quantization method. However, because he cannot justify the action independently, Feynman considers this treatment to be “purely formal” and unsatisfactory (see Section 3.5).
KeywordsWave Function Pair Production Dirac Equation Quantum Electrodynamic Free Particle
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