In her November 2021 article (page 44), Katie Robertson presents an elegant synthesis of Maxwell’s, Loschmidt’s, and Laplace’s demons. Implicit in the text—and explicit in the conclusion—is the thesis that the second law of thermodynamics remains above reproach. Although that might have appeared to be the case at the close of the 19th and 20th centuries, it is not in the 21st. Since the mid 1990s, at least three dozen potent second-law challenges have advanced into the literature, some with strong experimental support, more than the total proposed during the previous century and a half.1 One example involves two opposing filaments, each formed from a different material, in a diatomic gas atmosphere at uniform temperature.2 Due to the different dissociation rates for the diatomic gas at the two surfaces, permanent gradients in pressure and temperature are formed, in apparent conflict with the second law.
The most successful of the newer demons do not suffer the ailments of their ancestors: They are macroscopic in size rather than microscopic, they operate on molecules wholesale rather than individually, and they don’t think too much. Typically, they involve thermodynamic spatial asymmetries by which macroscopic energy reservoirs, which are regenerable thermally2,3 or by other means,4 are created at one or more of the system boundaries, standard hallmarks of discontinuities in chemical potential. Evidence for such demons should not be overlooked here, especially considering that they undercut the primary thesis of the work.