Concerning the Notion of "Time Interval" inS-Matrix Theory

The notion of time duration is considered within the framework of $S$-matrix theory. It is shown that Wigner's definition of the time delay, $-i\hslash \left[\right(\frac{d\ln S}{\mathrm{dE}}\left)\right]$, for a scattering process permits one to define time duration in a "coarse-grained" sense.