  The relaxation dynamics of many disordered systems, such as structural
glasses, proteins, granular materials or spin glasses, is not completely frozen
even at very low temperatures. This residual motion leads to a change of the
properties of the material, a process commonly called aging. Despite recent
advances in the theoretical description of such aging processes, the
microscopic mechanisms leading to the aging dynamics are still a matter of
dispute. In this Letter we investigate the aging dynamics of a simple glass
former by means of molecular dynamics computer simulation. Using the concept of
the inherent structure we give evidence that aging dynamics can be understood
as a decrease of the effective configurational temperature T of the system.
  From our results we conclude that the equilibration process is faster when
the system is quenched to T_c, the critical T of mode-coupling theory, and that
thermodynamic concepts are useful to describe the out-of-equilibrium aging
process.
