Journal of Statistical Physics, Vol. 79, Nos. 1/2, 1995. p. 231-241.
We consider lattice gases where particles jump at random times constrained by hard-core exclusion (simple exclusion process with speed change). The conventional theory of critical slowing down predicts that close to a critical point the bulk diffusivity vanishes as the inverse compressibility. We confu'm this claim by proving a strictly positive lower bound for the conductivity.