Kastner, Ruth (2025) Maxwell's Demon Is Foiled by the Entropy Cost of Measurement, Not Erasure. [Preprint]

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Abstract

I dispute the conventional claim that the second law of thermodynamics is saved from a "Maxwell's Demon" by the entropy cost of information erasure, and show that instead it is measurement that incurs the entropy cost. Thus Brillouin, who identified measurement as savior of the second law, was essentially correct, and putative refutations of his view, such as Bennett's claim to measure without entropy cost, are seen to fail when the applicable physics is taken into account. I argue that the tradition of attributing the defeat of Maxwell's Demon to erasure rather than to measurement arose from unphysical classical idealizations that do not hold for real gas molecules, as well as a physically ungrounded recasting of physical thermodynamical processes into computational and information-theoretic conceptualizations. I argue that the fundamental principle that saves the second law is the quantum uncertainty principle applying to the need to localize physical states to precise values of observables in order to effect the desired disequilibria aimed at violating the second law. I obtain the specific entropy cost for localizing a molecule in the Szilard engine, which coincides with the quantity attributed to Landauer's principle. I also note that an experiment characterized as upholding an entropy cost of erasure in a "quantum Maxwell's Demon" actually demonstrates an entropy cost of measurement.

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Item Type:	Preprint
Creators:	Creators Email ORCID Kastner, Ruth rkastner@umd.edu
Keywords:	Maaxwell's Demon, Entropy, Landauer's Principle, Szilard engine
Subjects:	Specific Sciences > Physics > Quantum Mechanics Specific Sciences > Physics > Statistical Mechanics/Thermodynamics
Depositing User:	Ruth E. Kastner
Date Deposited:	24 Mar 2025 13:35
Last Modified:	24 Mar 2025 13:35
Item ID:	24936
Subjects:	Specific Sciences > Physics > Quantum Mechanics Specific Sciences > Physics > Statistical Mechanics/Thermodynamics
Date:	23 March 2025
URI:	https://philsci-archive.pitt.edu/id/eprint/24936

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