Diffusive mass transfer by nonequilibrium fluctuations: Fick's law revisited - art. no. 012105

Recent experimental and theoretical works have shown that giant Fluctuation s are present during diffusion in liquid systems. We use linearized fluctua ting hydrodynamics to calculate the net mass transfer due to these nonequil ibrium fluctuations. Remarkably, the mass flow turns out to coincide with t he usual Fick's one. The renormalization of the hydrodynamic equations allo ws us to quantify the gravitational modifications of the diffusion coeffici ent induced by the gravitational stabilization of long wavelength fluctuati ons.