ABSTRACT
The critical comments of the last section set the stage for the introduction of a new theory of particles. It is a phenomenological theory, designed to describe the observed particles, be they stable or unstable. No speculations about the inner structure of particles are introduced, but the road to a conceivable more fundamental theory is left open. No abstract definition of particle is devised; rather, the theory uses symbolic idealizations of the realistic procedures that give physical meaning to the particle concept. The theory is thereby firmly grounded in space-time, the arena within which the experimenter manipulates his tools, but the question of an ultimate limitation to microscopic space-time description is left open, with the decision reserved to experiment. Correspondingly, no operator fields are used. The complementary momentum-space description plays an important role, but the possibility of ultimate limitations on this space is not excluded, and there is no appeal to analyticity in momentum space. The constructive principles of the new theory are intuitive ones— causality and uniformity in space-time. What emerges is a theory intermediate in position between operator field theory and S-matrix theory, which rejects the dogmas of each, and gains thereby a calculational ease and intuitiveness that make it a worthy contender to displace the earlier formulations.
