Universal behavior of nonequilibrium fluctuations in free diffusion processes

We show that giant nonequilibrium fluctuations are present during the fret: diffusive remixing occurring in ordinary liquid mixtures and in macromolec ular solutions. The static structure factor of the fluctuations is measured by using a quantitative shadowgraph technique. We show that structure fact ors at different times and from different samples can be rescaled onto a si ngle master curve without any adjustable parameter, thus giving strong evid ence that nonequilibrium fluctuations are a universal feature of free diffu sion processes.