Maxwell's demon is a character in an 1867 thought experiment by the Scottish physicist James Clerk Maxwell, meant to raise questions about the second law of thermodynamics. This law forbids (among other things) two bodies of equal temperature, brought in contact with each other and isolated from the rest of the Universe, from evolving to a state in which one of the two has a significantly higher temperature than the other. The second law is also expressed as the assertion that entropy never decreases.
Maxwell described his thought experiment in this way:
- "... if we conceive of a being whose faculties are so sharpened that he can follow every molecule in its course, such a being, whose attributes are as essentially finite as our own, would be able to do what is impossible to us. For we have seen that molecules in a vessel full of air at uniform temperature are moving with velocities by no means uniform, though the mean velocity of any great number of them, arbitrarily selected, is almost exactly uniform. Now let us suppose that such a vessel is divided into two portions, A and B, by a division in which there is a small hole, and that a being, who can see the individual molecules, opens and closes this hole, so as to allow only the swifter molecules to pass from A to B, and only the slower molecules to pass from B to A. He will thus, without expenditure of work, raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics." [1]
In other words, Maxwell imagines two containers, A and B, filled with the same gas at equal temperatures, placed next to each other. A little 'demon' guards a trapdoor between the two containers, observing the molecules on both sides. When a faster-than-average molecule from A flies towards the trapdoor, the demon opens it, and the molecule will fly from A to B. Thus, the average speed of the molecules in B will have increased, while the molecules in A will have slowed down on average. However, since average molecular speed corresponds to temperature, the temperature in A will have decreased and in B will have increased; this is contrary to the second law of thermodynamics.
Is Maxwell correct? Could such a demon, as he describes it, actually violate the second law? One of the most famous responses to this question was suggested in 1929 by Leó Szilárd. Szilárd pointed out that a real-life Maxwell's Demon would need to have some means of measuring molecular speed, and that the act of acquiring information would require an expenditure of energy. Szilárd's insight was expanded upon in 1982 by Charles maxwells demon H. Bennett, who argued that to determine what side of the gate a molecule must be on, the demon must store information about the state of the molecule. Eventually, the demon will run out of information storage space and must begin to erase the information that has been previously gathered. Erasing information is a thermodynamically irreversible process that increases the entropy of a system. Therefore, according to Bennett, Maxwell's demon reveals a deep connection between thermodynamics and information theory [2].
Real-life versions of Maxwellian demons (with their entropy-lowering effects, of course, duly balanced by increase of entropy elsewhere) occur in living systems, such as the ion channels and pumps that make our nervous systems work, including the human brain. Single atom traps allow an experimenter to control the state of individual quanta in the same way as Maxwell's demon. Molecular-sized mechanisms are no longer found only in biology; they are also the subject of the emerging field of nanotechnology. A mechanical implementation exists as a commercially-available device, called a Ranque-Hilsch vortex tube. Due to conservation of angular momentum, hotter molecules are spun to the ouside of a tube while cooler molecules spin in a tighter whirl within the tube, allowing venting of each from opposite ends of the tube.
Maxwell's demon in culture
- Maxwell's demon plays a significant role in the book The Crying of Lot 49 by Thomas Pynchon.
- Maxwell's Demon makes appearences in the popular manga Oh My Goddess!, by Kosuke Fujishima.
- It also makes appearances in Her Majesty's Wizard by Christopher Stasheff.
- Maxwell Demon is a fictional character from the movie Velvet Goldmine.
- The term Maxwell's Demon is mentioned in the Square Super Famicom title, Radical Dreamers, when the player attempts to access the third ending.
- Maxwell's Demon is mentioned as well in the Novel Homo Faber by Swiss author Max Frisch, as well as in the Novel The Cyberiad of science fiction author Stanisław Lem.
- Maxwell's Demons are used as doorkeepers in a magic research institute in the Novel Monday Begins on Saturday by Boris and Arkady Strugatsky.
- The novel The Hercules Text by Jack McDevitt features Maxwell's demon as a plot device to demonstrate that our knowledge is very limited in the face of alien scientific understanding.
- Isaac Asimov and Larry Niven both have also written a short story in homage to Maxwell.
- The webcomic Mac Hall has a strip referencing Maxwell's demon.
- Maxwell's Demon is a character in "The Adventures of Captain Baseball Bat Boy", a fictional TV show within the video game Max Payne 2: The Fall of Max Payne.
- The character Duo Maxwell, from the anime Mobile Suit Gundam Wing, could also be seen as a tribute to Maxwell's demon.
- In the video games Tales of Symphonia and Tales of Phantasia, there is a summoning spirit known as Maxwell, another possible tribute to Maxwell's demon due to the summon's special characterisitics.
- Maxwell Demon is the leading character in a children's story by [3]Jacqui Rowe: "Maxwell Demon and the Butterfly's Wing" in Shazkaz and other Stories (The English and Media Centre 2004)
- Maxwell's Demon is mentioned in the song A Metaphysical Drama by Vintersorg
- Maxwell's Demon is mentioned in the book Maxie's Demon by Michael Scott Rohan
External links and references
- Harvey S. Leff, Andrew F. Rex (editors), Maxwell's Demon 2: Entropy, Classical and Quantum Information, Computing, Institute of Physics, 2003 — an anthology and comprehensive bibliography of academic papers pertaining to Maxwell's demon and related topics. Chapter 1 provides a historical overview of the demon's origin and solutions to the paradox. The 1st edition from 1990 (out of print) contained several additional relevant papers.
- Charles H. Bennet, "Demons, Engines and the Second Law", Scientific American, pp.108-116 (November, 1987).
Electronics Topics
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
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