  For hadron production in high energy collisions, causality requirements lead
to the counterpart of the cosmological horizon problem: the production occurs
in a number of causally disconnected regions of finite space-time size. As a
result, globally conserved quantum numbers (charge, strangeness, baryon number)
must be conserved locally in spatially restricted correlation clusters. This
provides a theoretical basis for the observed suppression of strangeness
production in elementary interactions (pp, e^+e^-). In contrast, the space-time
superposition of many collisions in heavy ion interactions largely removes
these causality constraints, resulting in an ideal hadronic resonance gas in
full equilibrium.
