The basic Maxwell's demon opens the gate between regions A and B when it sees a molecule moving from A to B but none moving in the opposite direction. The major standard objection to this violation of the second law of thermodynamics is that the demon would not be able to distinguish the molecules from the equilibrium background black body radiation unless it illuminated them with a beacon emitting radiation corresponding to a different temperature, thus bringing about an increase of entropy.
The basic Maxwell's demon opens the gate between regions A and B when it sees a molecule moving from A to B but none moving in the opposite direction. The major standard objection to this violation of the second law of thermodynamics is that the demon would not be able to distinguish the molecules from the equilibrium background black body radiation unless it illuminated them with a beacon emitting radiation corresponding to a different temperature, thus bringing about an increase of entropy.
According to (1) and (2), no work is done by Maxwell’s demon who knows the speed of molecules in a gas and opens a door in the wall to allow fast molecules into a second empty chamber. Thus, one has cold molecules in one chamber and hot, in the other, “seemingly without applying any work” (1). In other words, the second law of thermodynamics is violated because entropy decreases without work being done. The 2018 paper (2), also states that no work is done in such a situation. We argue that a number of different types of work or energy expenditure are required by the demon. First of all, position and time measurements of a molecule must be made before a speed calculation can be taken. In principle, this information must be acquired and stored, either in an electronic form, some kind of writing or in a brain and this requires energy/work. Next, a calculation of speed must be made and this again requires work. Then energy is required to make the decision whether the speed meets a certain threshold and energy is required to remove the data from memory. In addition, work must be done in opening the door for each fast molecule. The door does not open without work being performed because it must move and so requires a force by Newton’s laws. The force acts over a distance and then the force must be applied in the opposite direction so work again is done. Even if there is very little friction in the system and the force is tiny as well as the distance, some work must be done. Furthermore, there are time issues as the door must be opened very quickly and then closed quickly, so vf-0 = acceleration * t and distance = .5*acceleration*tt applies. A certain speed vf must be reached and if t is tiny, acceleration cannot tend to 0 and acceleration is then multiplied by mass. As a result, it seems curious that statements about no work are made in the literature (1), (2). As an example of a system which bypasses the demon, but accomplishes the same goal as Maxwell’s demon, one may see that work is required. It is possible to create two tunnels one after the other to play the role of the demon. There is a potential hindering motion in the first tunnel. Only partilces with kinetic energy greater than some limit V1 reach the end of the first tunnel. The rest come to a stop and then are accelerated back to their original speed, but move in the opposite direction. The ones that reach the end of the first tunnel are then pulled by a force in the second tunnel which restores kinetic energy of V1 and so they exit the second tunnel with their original speed and enter a second tunnel. One may see that in this example which replaces Maxwell’s demon that work is done and even calculate the exact amount.
Maxwell’s demon emanates from a thought experiment proposed by James Clerk Maxwell in 1867 to illustrate the statistical nature of the second law of thermodynamics. Subsequently researchers wondered whether such a demon could in fact violate the second law. Leon Brillouin argued that the entropy produced during the demon’s measurement precluded such a violation. Years later Oliver Penrose and Charles Bennett observed (independently) that a Maxwell’s demon gathers information and stores it in a memory. Penrose showed that erasure of such a memory sends sufficient entropy to the environment to preclude violation of the second law. Notably this is so even when measurement produces arbitrarily little entropy. Bennett obtained the same result using Rolf Landauer’s seminal research on the thermodynamics of computation. The stunning shift in focus from measurement to erasure provided the impetus to better understand the role of information in quantum mechanics and thermodynamics. Indeed the linkage of information with physics is the principal legacy of Maxwell’s demon. Szilard’s one‐particle classical “gas” model and its quantum mechanical extension, together with postulated connections between entropy and algorithmic information, have provided useful insights. We review the long history of Maxwell’s demon and assess the current status of the second law in the context of the demon’s operations.
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.
"Maxwell's 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
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