The Spin-Echo Experiment and Statistical Mechanics

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In this paper the spin-echo experiment is examined in the light of three different approaches to statistical mechanics: the coarse-graining Gibbsian approach, the interventionist Gibbsian approach, and the Boltzmannian approach. The conclusions of this examination are almost exactly opposite to the conclusions of Ridderbos and Redhead [1]: Firstly, it is argued that the spin-echo experiment does not tell against a coarse-graining approach to statistical mechanics. Secondly, it is argued that the interventionist approach to statistical mechanics is itself somewhat problematic as its statistical mechanical counterpart of thermodynamic entropy has a number of properties that actual thermodynamic entropy seemingly does not. In the final section of this paper a feature of coarse-grained entropies (their relativity) is noted that may enable coarse-graining approaches to reconcile conflicting intuitions about the behaviour of entropy in the spin-echo experiment, which may be considered a further advantage of such approaches.