Physics has a long history of employing demons as thought experiments in order to probe the limits of human knowledge. Maxwell’s demon is such a thought experiment: a molecule-sorting demon invented in 1878 by James Clerk Maxwell in order to con/test the universal validity of the second law of thermodynamics. The second law of thermodynamics not only postulates a universal increase of entropy and an “arrow of time” but also has been based on human ignorance, the assumption that there is an objective world independent of us that we can know only incompletely. Maxwell’s demon figures the scientist’s ability to acquire knowledge about the microscopic molecular world but ostensibly without the expenditure of work. This essay offers a rereading of Leo Szilard’s influential account of Maxwell’s demon (1929), which explores the influence of human intelligence on scientific measurements in relation to an increase of entropy and the irreversibility of measurements. Opening up ambiguities in Szilard’s account of measurement and memory and comparing it to quantum mechanical experiments (the quantum erasure effect), the author reads both through Karen Barad’s onto-epistemological framework of “agential realism” and Jacques Derrida’s ghostly logic of time, proposing that all measurements are haunted and that scientific activities, reconfigured as intra-active work, constitute time, rather than accumulating knowledge in time. At stake in such a deconstruction of the scientific “arrow of time” from within physics is the possibility of making a difference that matters in science or, in other words, accounting for transformation and rearticulation work as physical work.
Physics has a long history of employing demons as thought experiments in order to probe the limits of human knowledge. Maxwell’s demon is such a thought experiment: a molecule-sorting demon invented in 1878 by James Clerk Maxwell in order to con/test the universal validity of the second law of thermodynamics. The second law of thermodynamics not only postulates a universal increase of entropy and an “arrow of time” but also has been based on human ignorance, the assumption that there is an objective world independent of us that we can know only incompletely. Maxwell’s demon figures the scientist’s ability to acquire knowledge about the microscopic molecular world but ostensibly without the expenditure of work. This essay offers a rereading of Leo Szilard’s influential account of Maxwell’s demon (1929), which explores the influence of human intelligence on scientific measurements in relation to an increase of entropy and the irreversibility of measurements. Opening up ambiguities in Szilard’s account of measurement and memory and comparing it to quantum mechanical experiments (the quantum erasure effect), the author reads both through Karen Barad’s onto-epistemological framework of “agential realism” and Jacques Derrida’s ghostly logic of time, proposing that all measurements are haunted and that scientific activities, reconfigured as intra-active work, constitute time, rather than accumulating knowledge in time. At stake in such a deconstruction of the scientific “arrow of time” from within physics is the possibility of making a difference that matters in science or, in other words, accounting for transformation and rearticulation work as physical work.
Maxwell's Demon is a thought experiment devised by J. C. Maxwell in 1867 in order to show that the Second Law of thermodynamics is not universal, since it has a counter-example. Since the Second Law is taken by many to provide an arrow of time, the threat to its universality threatens the account of temporal directionality as well. Various attempts to "exorcise" the Demon, by proving that it is impossible for one reason or another, have been made throughout the years, but none of them were successful. We have shown (in a number of publications) by a general state-space argument that Maxwell's Demon is compatible with classical mechanics, and that the most recent solutions, based on Landauer's thesis, are not general. In this paper we demonstrate that Maxwell's Demon is also compatible with quantum mechanics. We do so by analyzing a particular (but highly idealized) experimental setup and proving that it violates the Second Law. Our discussion is in the framework of standard quantum mechanics; we give two separate arguments in the framework of quantum mechanics with and without the projection postulate. We address in our analysis the connection between measurement and erasure interactions and we show how these notions are applicable in the microscopic quantum mechanical structure. We discuss what might be the quantum mechanical counterpart of the classical notion of "macrostates", thus explaining why our Quantum Demon setup works not only at the micro level but also at the macro level, properly understood. One implication of our analysis is that the Second Law cannot provide a universal lawlike basis for an account of the arrow of time; this account has to be sought elsewhere.
It is nearly 150 years since Maxwell challenged the validity of the second law of thermodynamics by imagining a tiny creature who could sort the molecules of a gas in such a way that would decrease entropy without exerting any work. The demon has been discussed largely using thought experiments, but it has recently become possible to exert control over nanoscale systems, just as Maxwell imagined, and the status of the second law has become a more practical matter, raising the issue of how measurements manage our ignorance in a way that can be exploited. The framework of stochastic thermodynamics extends macroscopic concepts such as heat, work, entropy and irreversibility to small systems and allows us explore the matter. Some arguments against a successful demon imply a second law that can be suspended indefinitely until we dissipate energy in order to remove the records of his operations. In contrast, under stochastic thermodynamics, the demon fails because on average, more work is performed upfront in making a measurement than can be extracted by exploiting the outcome. This requires us to exclude systems and a demon that evolve under what might be termed self-sorting dynamics, and we reflect on the constraints on control that this implies while still working within a thermodynamic framework.
Demon, the famous thought experiment of James Clerk Maxwell, has been devised in 1867 as a counter example for the Second Law of thermodynamics. During the 140 years since the Demon was first suggested, numerous attempts have been made to counter Maxwell's argument. The attempts have been to show that Maxwell was wrong, since his Demon cannot work for one reason or another (see Leff and Rex 2003 for details and references). In this paper we show (following an argument by Albert 2000, Ch. 5.) that Maxwell was basically right, in the sense that his thought experiment is compatible with the laws of mechanics as well as with central principles of statistical mechanics. We then derive some (weak) restrictions on the Demon's efficiency. Finally, we prove that the Demon's cycle of operation can be completed (in particular, the Demon's memory can be erased) without increasing the total entropy of the universe. We draw some conclusions about the way to understand the meaning and role of probability in classical statistical mechanics
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 and show that it 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.
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.