Space and Time in $S$-Matrix Theory

Basic elements of a theory of measurements of space-time correlations are developed within the framework of a strictly mass-shell $S$-matrix theory. The "$i\epsilon$ rule" for the resolution of pole singularities is derived from a macroscopic mass-shell causality condition. The experimental and theoretical significance of form factors is discussed from the point of view of analytic $S$-matrix theory. They are defined as constructs of mass-shell functions, and the conditions under which they can be ascribed approximate experimental significance are examined. The possibility that asymptotic field theory is contained within analytic $S$-matrix theory is briefly discussed.