  Nonequilibrium thermodynamics has shown its applicability in a wide variety
of different situations pertaining to fields such as physics, chemistry,
biology, and engineering. As successful as it is, however, its current
formulation considers only systems close to equilibrium --those satisfying the
so-called local equilibrium hypothesis. Here we show that diffusion processes
that occur far away from equilibrium can be viewed as at local equilibrium in a
space that includes all the relevant variables in addition to the spatial
coordinate. In this way, nonequilibrium thermodynamics can be used and the
difficulties and ambiguities associated with the lack of a thermodynamic
description disappear. We analyze explicitly the inertial effects in diffusion
and outline how the main ideas can be applied to other situations.
