A quantum theory of relativistic scalar particles is developed in which the proper time $\tau$ is central. The unitarity and conservation laws which the theory exhibits with respect to $\tau$ are given acceptable physical interpretations. The problem of potential scattering of wave packets yields a result in agreement with Pauli-Weisskopf theory, except for the absence of vacuum processes. There is evidence that a finite theory of interacting particles is possible in the proper-time framework.

• Received 27 September 1967

DOI:https://doi.org/10.1103/PhysRev.166.1293