Alleged acausality of the diffusion equations: A reply

Abstract
Two facts are pointed out: (1) Only when the diffusion equation is inadmissibly applied, outside its defined range of validity, does it lead to acausal predictions; (2) although there are many instances in which usually diffusive hydrodynamic variables propagate wave-like in condensed systems, none of them are connected with this appearance of acausality. DOI: http://dx.doi.org/10.1103/PhysRevD.64.088504 © 2001 The American Physical Society