Abstract

The Zisman-Stueckelberg-Feynman interpretation describes antiparticles as negative-energy particles moving backward in ordinary time. Its consistent reconciliation with relativity leads to time-symmetric relativity and extends the symmetry to the full Lorentz group O(1,3), including four-inversion. On this basis the article formulates time-symmetric relativistic quantum mechanics, derives the general probability current and relativistic wave equations, and discusses causal propagators and gravitational self-regularization of loop diagrams at the Planck scale.