  The emergence of macroscopic variables can be effected through {\it coarse
graining}. Despite practical and fundamental benefits conveyed by this
partitioning of state space, the apparently subjective nature of the selection
of coarse grains has been considered problematic. We provide objective
selection methods, deriving from the existence of relatively slow dynamical
time scales. Using a framework for nonequilibrium statistical mechanics
developed by us, we show the emergence of both spatial variables and order
parameters. Although significant objective criteria are introduced in the
coarse graining, we do not provide a unique prescription. Most significantly,
the grains, and by implication entropy, are only defined modulo a
characteristic time scale of observation.
