Generalized Einstein Relation in an aging colloidal glass

We present an experimental and theoretical test of the Generalized Einstein Relation, a particular form of a fluctuation–dissipation relation, in an out-of-equilibrium visco-elastic fluid. Diffusion and mobility measurements of micrometer beads immersed in a colloidal glass and used as thermometers, are performed during aging. The observed deviations from the Generalized Einstein Relation are interpreted as directly related to the change in the glass relaxation times with aging time. In our scenario, deviations are only observed in the regime where the observation time scale is of the order of a characteristic relaxation time of the glass.