  We propose a physical interpretation of the perturbative breakdown of
unitarity in time-like noncommutative field theories in terms of production of
tachyonic particles. These particles may be viewed as a remnant of a continuous
spectrum of undecoupled closed-string modes. In this way, we give a unified
view of the string-theoretical and the field-theoretical no-go arguments
against time-like noncommutative theories. We also perform a quantitative study
of various locality and causality properties of noncommutative field theories
at the quantum level.
