The coarse-graining approach to statistical mechanics: how blissful is our ignorance?

In this paper I first argue that the objection which is most commonly levelled against the coarse-graining approach -viz. that it introduces an element of subjectivity into what ought to be a purely objective formalism- is ultimately unfounded. I then proceed to argue that two different objections to the coarse-graining approach indicate that it is an inadequate approach to statistical mechanics. The first objection is based on the fact that the appeal to appearances by the coarse-graining approach fails to justify the coarse-graining strategy of ignoring the physical differences between so-called quasi-equilibrium distributions and equilibrium distributions. The second objection is centred on the notion of a coarse-grained entropy. I will argue that the required increase in the coarse-grained entropy is obtained by disregarding the dynamical constraints on the system. This undermines the very task statistical mechanics has set out to accomplish, viz. to provide a microdynamical underpinning of thermodynamics. (C) 2002 Elsevier Science Ltd. All rights reserved.