``The language of Dirac's theory of radiation'': the inception and initial reception of a tool for the quantum field theorist (Q2084276)

The paper gives a cogent reconstruction of how Paul Dirac came to interpret the various terms in a quantum-mechanical perturbation expansion as describing ``virtual'' processes, a view that the author calls ``picture of subsequent transitions''. This is relevant for current philosophical debates on whether such virtual transitions (and, in quantum field theory, virtual particles) have ontological significance.