Can Somebody Please Say What Gibbsian Statistical Mechanics Says?

Roman Frigg (London School of Economics), Roman Frigg

Roman Frigg, London School of Economics

Can Somebody Please Say What Gibbsian Statistical Mechanics Says?

Among working physicists, Gibbsian statistical mechanics (GSM) is the most widely used version of statistical mechanics. Yet a closer look at GSM reveals that it is unclear what exactly the theory says and how it bears on experimental practice. The root cause of the difficulties is the status of the Averaging Principle, the proposition that what we observe in an experiment is the ensemble average of a phase function. We review different stances toward this principle, ranging from unconditional acceptance to blatant rejection. We find all of them wanting and suggest that the problem finds an elegant solution if one adds a Boltzmannian definition of equilibrium to GSM, which results in what we call the `Gibbsmannian approach'.