  Glassy systems are ubiquitous in nature, and are characterized by slow
relaxations to equilibrium without a typical timescale, aging and memory
effects. Understanding these is a long-standing problem in physics. We study
the aging of the electron glass, a system showing remarkable slow relaxations
in the conductance. We find that the broad distribution of relaxation rates
leads to a universal relaxation of the form log(1+t_w/t) for the usual aging
protocol, where t_w is the length of time the perturbation driving the system
out-of-equilibrium was on, and t the time of measurement. These results agree
well with several experiments performed on different glasses, and examining
different physical observables, for times ranging from seconds to several
hours. The suggested theoretical framework appears to offer a paradigm for
aging in a broad class of glassy materials.
