More on the demons of thermodynamics

Katie Robertson’s article gives a delightful overview of the vanquishing of demons haunting thermodynamics (Physics Today, November 2021, page 44 ). We want to add that Maxwell’s demon plays a special role in physics apart from concerns about vanquishing. Maxwell’s demon reveals a subtle link between information acquisition and thermodynamics.

Over the past two or so decades, that link has provided inspiration for the development of a robust field, stochastic thermodynamics, which enables analysis of the energetics of nonmacroscopic systems with information feedback. Stochastic thermodynamics formalizes what the demon has taught us informally—namely, that information is a resource that can enhance the ability of a system to do work, and erasure of each bit of information in the demon’s memory increases entropy by k_B ln 2 (with k_B being Boltzmann’s constant), assuring the sanctity of the second law. Without Maxwell’s demon, it is questionable whether stochastic thermodynamics and a host of interesting nonmacroscopic experimental results would exist today.