Causality violations in realistic simulations of nuclear collisions

Causality is violated up to 75% in the early stages of state-of-the-art heavy-ion hydrodynamic simulations. Only after 2-3 fm/c of evolution, do we find that ~50% of the fluid cells are definitely causal.  Inclusion of pre-equilibrium evolution significantly reduces the number of acausal cells, but does not eliminate them. Our findings imply that relativistic causality imposes constraints on the available parameter space of heavy-ion collision simulations.