Comment on ``Dynamical Heterogeneities in a Supercooled Lennard-Jones   Liquid''
  In two recent interesting letters evidence was presented for the existence of a growing dynamic correlation length when we approach the glass transition from the liquid phase (a similar divergence is present also in the off-equilibrium dynamics below $T_c$). Here we would like to point out that this phenomenon can be easily predicted using the replica approach. 
S. Franz and G. Parisi