Causality in Quantum Electrodynamics

Abstract

Quantum mechanics, even in its early and simple phases, has often been regarded as a non-causal discipline. The argument supporting this view cites the uncertainty principle as prohibiting the ascertainment of complete knowledge concerning physical states upon which causal prediction could be based. Recent developments in atomic physics have added new and puzzling features to the problem of causality insofar as they operate, not only with intrinsically unmeasurable states, but also with time reversals which have been interpreted to mean that the effect can be prior to the cause. Feynman’s theory of quantum electrodynamics is particularly rich in unorthodox suggestions which tantalise philosophers. The purpose of the present paper is to exhibit them, appraise their methodological function and see in what manner they violate the rules of causal description. This purpose, it seems, is best achieved by a sequential discussion of three questions: What does causality mean in physics? What is the new method of quantum electrodynamics? Is this new method compatible with the causal doctrine in some satisfactory form?