![]() We shall see that when this condition is translated into the language of Hamiltonian mechanics, it tells us that the time evolution induced by the demon is one that compresses the set of states in the phase space. It is the assumption that the demon, when placed in a generic thermal environment, will always, or even just very likely, succeed in moving the thermal system far from its equilibrium state. It is a huge space of very many dimenions each of whose points represents one state the of the thermal system and demon together.Ī simple but quite powerful exorcism derives from an apparently innocuous part of a straightforward description of what a Maxwell’s demon must do. Associated with Hamiltonian mechanics is the idea of phase space. ![]() Specifically it is governed by Hamiltonian mechanics, which is about as general and generic as a physical system can be. ![]() The exorcism characterizes the demon as a little machine that obeys ordinary physical laws. As a result, we have overlooked a much simpler exorcism that makes no use of the notion of information. Critics-myself included-have sought to show that the information-based approach fails. Enthusiasts for it have sought to make the analysis work. A New Exorcismįor over eighty years, we have focused on the information-based approach to exorcism. Rather the information-based analysis is an enduring collection of mistakes and confusions. Elsewhere I have argued that these essential details have never been provided adequately. This information based tradition is initially intriguing and appealing, until one asks after the details of the analysis. Landauer and Bennett attributed the costs to dissipation that they believe is associated with erasing a computer memory. Szilard attributed the cost to processes that ascertain the state of a system of interest. That cost would be enough to undo the reduction in entropy brought about by the demon and thus to save the second law. Starting with Leo Szilard's work of 1929, that tradition sought to base the exorcism on an entropy cost associated with the processing of information. He argued through many examples that thermal fluctuations within the demonic machinery would so disrupt it that it must fail in its intended operation.Ī later tradition ignored Smoluchowski's recognition of the importance of fluctuations. Marian Smoluchowski gave the best completion of the analysis in 1912. Now we must seek something in its constitution that would ensure its failure. That means that it must be just another, ordinary physical system, even if it is a miracle of micro-engineering. As far as I know, everyone now agrees on the first step: the demon is naturalized. The problem became how best to argue for its failure that is, how best to exorcise the demon. Maxwell's demon must fail to reverse the second law, they felt. For Maxwell's text from the 1972 edition of Theory of Heat, click here.Īt the time that Smoluchowki wrote, there was some speculation that intelligent intervention may involve processes outside normal physics. It merely reveals that the second law fails if it is possible to manipulate molecules individually. Maxwell himself maintained that this thought experiment presented no special challenge to our science. This violates the second law of thermodynamics. When the process is finished, side B is hotter and side A colder while no work has been done. The net effect is that we start with a vessel filled uniformly with warm air. The slide operated by the demon is assumed to be very light, so that negligible work is done during the operation. The demon simply opened and closed an opening between two portions of a vessel filled with air so that the faster molecules collected one on side "B" and the slower ones on the other side "A". In letters from 18 and then in his 1871 Theory of Heat, James Clerk Maxwell described a tiny demon who could reverse the second law of thermodynamics. See " The Simplest Exorcism of Maxwell's Demon: The Quantum Version." It is easy to generate a quantum version by some simple substitions of quantum analogs for classical parts of the analysis. This exorcism is set within classical physics. Norton, " All Shook Up: Fluctuations, Maxwell's Demon and the Thermodynamics of Computation," Entropy, 15 (2013), pp. "A New Phase-Volume Based Exorcism of Maxwell's Demon" in John D. ![]() This page at at The text here is an expanded and edited version of Section 4. Exorcism of Maxwell's Demon The Simplest Exorcism of Maxwell's Demonĭepartment of History and Philosophy of Science
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