  Diffusion may obliterate fluctuation signals of the QCD phase transition in
nuclear collisions at SPS and RHIC energies. We propose a hyperbolic diffusion
equation to study the dissipation of net charge fluctuations. This equation is
needed in a relativistic context, because the classic parabolic diffusion
equation violates causality. We find that causality substantially limits the
extent to which diffusion can dissipate these fluctuations.
