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Moved page from wikipedia:en:Maxwell's demon (history)
此词条暂由彩云小译翻译，翻译字数共2191，未经人工整理和审校，带来阅读不便，请见谅。
{{short description|Thought experiment of 1867}}
[[File:Maxwell's demon.svg|right|340px|thumb|Schematic figure of Maxwell's demon thought experiment.]]
Schematic figure of Maxwell's demon thought experiment.
麦克斯韦恶魔思维实验示意图。
'''Maxwell's demon''' is a [[thought experiment]] created by the physicist [[James Clerk Maxwell]] in 1867 in which he suggested how the [[second law of thermodynamics]] might hypothetically be violated.<ref>{{cite book |author=Cargill Gilston Knott |title=Life and Scientific Work of Peter Guthrie Tait |publisher=[[Cambridge University Press]] |year=1911 |pages=213–215 |chapter=Quote from undated letter from Maxwell to Tait | chapter-url=https://archive.org/stream/lifescientificwo00knotuoft#page/212/mode/2up}}</ref> In the thought experiment, a [[Demon (thought experiment)|demon]] controls a small door between two compartments of gas. As individual gas molecules approach the door, the demon quickly opens and shuts the door so that only fast molecules are passed into one of the chambers, while only slow molecules are passed into the other. Because faster molecules are hotter, the demon's behaviour causes one chamber to warm up and the other to cool down, thereby decreasing [[entropy]] and violating the second law of thermodynamics. This thought experiment has provoked debate and theoretical work on the relation between thermodynamics and [[information theory]] extending to the present day, with a number of scientists arguing that theoretical considerations rule out any practical device violating the second law in this way.
Maxwell's demon is a thought experiment created by the physicist James Clerk Maxwell in 1867 in which he suggested how the second law of thermodynamics might hypothetically be violated. In the thought experiment, a demon controls a small door between two compartments of gas. As individual gas molecules approach the door, the demon quickly opens and shuts the door so that only fast molecules are passed into one of the chambers, while only slow molecules are passed into the other. Because faster molecules are hotter, the demon's behaviour causes one chamber to warm up and the other to cool down, thereby decreasing entropy and violating the second law of thermodynamics. This thought experiment has provoked debate and theoretical work on the relation between thermodynamics and information theory extending to the present day, with a number of scientists arguing that theoretical considerations rule out any practical device violating the second law in this way.
麦克斯韦恶魔是物理学家詹姆斯·克拉克·麦克斯韦在1867年创造的一个思想实验，在这个实验中，他提出了如何假设性地违反热力学第二定律。在这个思想实验中，一个恶魔控制着两个气体舱之间的一扇小门。当单个气体分子接近这扇门时，这个恶魔迅速地打开和关闭这扇门，只有快速的分子进入其中一个腔，而只有慢速的分子进入另一个腔。因为速度更快的分子温度更高，恶魔的行为导致一个腔室升温，另一个腔室降温，从而减少熵，违反了热力学第二定律。这个思想实验引起了关于热力学和信息论之间关系的争论和理论工作，一些科学家认为理论上的考虑排除了任何以这种方式违反第二定律的实际装置。
== Origin and history of the idea ==
The [[thought experiment]] first appeared in a letter [[James Clerk Maxwell|Maxwell]] wrote to [[Peter Guthrie Tait]] on 11 December 1867. It appeared again in a letter to [[John William Strutt]] in 1871, before it was presented to the public in Maxwell's 1872 book on [[thermodynamics]] titled ''Theory of Heat''.<ref name=Leff>[[#Leff Rex 02|Leff & Rex (2002)]], p. 370.</ref>
The thought experiment first appeared in a letter Maxwell wrote to Peter Guthrie Tait on 11 December 1867. It appeared again in a letter to John William Strutt in 1871, before it was presented to the public in Maxwell's 1872 book on thermodynamics titled Theory of Heat.
1867年12月11日，Maxwell 在写给彼得·格思里·泰特的一封信中首次提出了这个思想实验。它在1871年写给约翰 · 威廉 · 斯特拉特的信中再次出现，后来在麦克斯韦1872年出版的热力学书籍《热力学理论》中公之于众。
In his letters and books, Maxwell described the agent opening the door between the chambers as a "finite being". [[William Thomson, 1st Baron Kelvin|William Thomson (Lord Kelvin)]] was the first to use the word "demon" for Maxwell's concept, in the journal ''[[Nature (journal)|Nature]]'' in 1874, and implied that he intended the mediating, rather than malevolent, connotation of the word.<ref>{{cite journal |author=William Thomson |year=1874 |title=Kinetic theory of the dissipation of energy |journal=[[Nature (journal)|Nature]] |volume=9 |issue=232 |pages=441–444 |doi=10.1038/009441c0 |bibcode=1874Natur...9..441T|author-link=William Thomson, 1st Baron Kelvin |doi-access=free }}</ref><ref>{{cite journal |year=1879 |title=The sorting demon Of Maxwell |journal=Nature |volume=20 |issue=501 |pages=126 |bibcode=1879Natur..20Q.126. |doi=10.1038/020126a0 |doi-access=free }}</ref><ref name=Weber>{{cite book |author=Alan S. Weber |year=2000 |title=Nineteenth Century Science: a Selection of Original Texts |publisher=[[Broadview Press]] |page=300}}</ref>
In his letters and books, Maxwell described the agent opening the door between the chambers as a "finite being". William Thomson (Lord Kelvin) was the first to use the word "demon" for Maxwell's concept, in the journal Nature in 1874, and implied that he intended the mediating, rather than malevolent, connotation of the word.
在他的信件和书中，麦克斯韦描述特工打开房间的门是一个“有限的存在”。威廉 · 汤姆森(开尔文勋爵)是第一个在1874年的《自然》杂志上使用“恶魔”这个词来描述麦克斯韦的概念的人，他暗示这个词的意思是调解，而不是恶意的。
== Original thought experiment ==
The second law of thermodynamics ensures (through statistical probability) that two bodies of different [[temperature]], when brought into contact with each other and isolated from the rest of the Universe, will evolve to a thermodynamic equilibrium in which both bodies have approximately the same temperature.<ref name="Bennett87">{{cite journal
The second law of thermodynamics ensures (through statistical probability) that two bodies of different temperature, when brought into contact with each other and isolated from the rest of the Universe, will evolve to a thermodynamic equilibrium in which both bodies have approximately the same temperature. The second law is also expressed as the assertion that in an isolated system, entropy never decreases.
热力学第二定律天文台通过统计概率确保了两个不同温度的天体，当它们相互接触并与宇宙其他部分隔离开来时，将会演化成一个温度相近的热力学平衡天文台。第二定律也表达为在孤立系统中，熵永远不会减少的断言。
| last = Bennett
| first = Charles H.
In other words, Maxwell imagines one container divided into two parts, A and B. Both parts are filled with the same gas at equal temperatures and placed next to each other. Observing the molecules on both sides, an imaginary demon guards a trapdoor between the two parts. 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. Likewise, when a slower-than-average molecule from B flies towards the trapdoor, the demon will let it pass from B to A. The average speed of the molecules in B will have increased while in A they will have slowed down on average. Since average molecular speed corresponds to temperature, the temperature decreases in A and increases in B, contrary to the second law of thermodynamics. A heat engine operating between the thermal reservoirs A and B could extract useful work from this temperature difference.
换句话说，麦克斯韦想象一个容器分成两部分，a 和 b。两个部分在相同的温度下充入相同的气体，并且挨着放置。通过观察两边的分子，一个想象中的恶魔守卫着两部分之间的活板门。当一个来自 a 的比平均速度快的分子飞向活板门时，魔鬼打开了它，分子就会从 a 飞到 b。同样地，当一个来自 b 的比平均速度慢的分子飞向活板门时，魔鬼会让它从 b 飞向 a。B 中分子的平均速度会增加，而 a 中分子的平均速度会减慢。由于平均分子速度与温度相对应，因此 a 中的温度降低，b 中的温度升高，这与热力学第二定律相反。在热源 a 和热源 b 之间运行的热机可以从这种温差中提取有用的功。
| title = Demons, Engines, and the Second Law
| journal = Scientific American
The demon must allow molecules to pass in both directions in order to produce only a temperature difference; one-way passage only of faster-than-average molecules from A to B will cause higher temperature and pressure to develop on the B side.
魔鬼必须允许分子在两个方向上通过，以便只产生温差; 只有比平均速度更快的分子从 a 到 b 的单向通道会导致 b 方向产生更高的温度和压力。
| volume = 257
| issue = 5
| pages = 108–116
Several physicists have presented calculations that show that the second law of thermodynamics will not actually be violated, if a more complete analysis is made of the whole system including the demon. The essence of the physical argument is to show, by calculation, that any demon must "generate" more entropy segregating the molecules than it could ever eliminate by the method described. That is, it would take more thermodynamic work to gauge the speed of the molecules and selectively allow them to pass through the opening between A and B than the amount of energy gained by the difference of temperature caused by doing so.
一些物理学家已经展示了计算结果，表明如果对包括恶魔在内的整个系统进行更全面的分析，那么热力学第二定律实际上不会受到破坏。物理论证的本质是通过计算表明，任何恶魔都必须“产生”更多的熵，分离分子，而不是用所描述的方法可以消除。也就是说，需要更多的热力学功来测量分子的速度，并有选择地允许它们通过 a 和 b 之间的开口，而不是由于这样做所产生的温差而获得的能量。
| date = November 1987
| url = https://ecee.colorado.edu/~ecen5555/SourceMaterial/DemonsEnginesAndSecondLaw87.pdf
One of the most famous responses to this question was suggested in 1929 by Leó Szilárd, and later by Léon Brillouin. He realized that some measuring processes need not increase thermodynamic entropy as long as they were thermodynamically reversible. He suggested these "reversible" measurements could be used to sort the molecules, violating the Second Law. However, due to the connection between thermodynamic entropy and information entropy, this also meant that the recorded measurement must not be erased. In other words, to determine whether to let a molecule through, the demon must acquire information about the state of the molecule and either discard it or store it. Discarding it leads to immediate increase in entropy but the demon cannot store it indefinitely. In 1982, Charles Bennett showed that, however well prepared, eventually the demon will run out of information storage space and must begin to erase the information it has previously gathered. Erasing information is a thermodynamically irreversible process that increases the entropy of a system. Although Bennett had reached the same conclusion as Szilard's 1929 paper, that a Maxwellian demon could not violate the second law because entropy would be created, he had reached it for different reasons. Regarding Landauer's principle, the minimum energy dissipated by deleting information was experimentally measured by Eric Lutz et al. in 2012. Furthermore, Lutz et al. confirmed that in order to approach the Landauer's limit, the system must asymptotically approach zero processing speed.
对这个问题最著名的回答之一是1929年由 Leó Szilárd 提出的，后来由莱昂 · 布里渊提出。他意识到，只要某些测量过程是热力学可逆的，就不需要增加熵。他认为这些“可逆”的测量可以用来分类分子，违反了第二定律。然而，由于熵和熵之间的连接，这也意味着记录的测量不能被擦除。换句话说，为了决定是否让一个分子通过，恶魔必须获得关于分子状态的信息，要么丢弃它，要么存储它。丢弃它会立即增加熵，但是恶魔不能无限期地储存它。1982年，查尔斯 · 班尼特指出，无论准备得多么充分，恶魔最终都会耗尽信息存储空间，并且必须开始删除它先前收集的信息。擦除信息是一个热力学不可逆性，它增加了系统的熵。虽然贝内特得出了与西拉德1929年的论文相同的结论，即马克斯韦尔式的恶魔不能违反第二定律，因为熵会被创造出来。根据兰道尔原理，埃里克 · 鲁兹等人通过实验测量了删除信息所消耗的最小能量。2012年。此外，Lutz 等人。证实，为了接近兰道尔的极限，系统必须渐近接近零处理速度。
| issn =
| doi = 10.1038/scientificamerican1187-108
John Earman and John D. Norton have argued that Szilárd and Landauer's explanations of Maxwell's demon begin by assuming that the second law of thermodynamics cannot be violated by the demon, and derive further properties of the demon from this assumption, including the necessity of consuming energy when erasing information, etc. It would therefore be circular to invoke these derived properties to defend the second law from the demonic argument. Bennett later acknowledged the validity of Earman and Norton's argument, while maintaining that Landauer's principle explains the mechanism by which real systems do not violate the second law of thermodynamics.
和 John d. Norton 认为 Szilárd 和 Landauer 对麦克斯韦恶魔的解释是从假设热力学第二定律不会被恶魔侵犯开始的，并且从这个假设中得出恶魔的进一步属性，包括在消除信息时消耗能量的必要性等等。因此，调用这些派生属性来保护第二定律不受恶魔论证的影响是循环的。后来承认 Earman 和 Norton 的论点是正确的，同时坚持 Landauer 原理解释了真实系统不违反热力学第二定律的机制。
| id =
| accessdate = November 13, 2014| bibcode = 1987SciAm.257e.108B}}</ref> The second law is also expressed as the assertion that in an [[isolated system]], [[entropy]] never decreases.<ref name="Bennett87" />
Although the argument by Landauer and Bennett only answers the consistency between the second law of thermodynamics and the whole cyclic process of the entire system of a Szilard engine (a composite system of the engine and the demon), a recent approach based on the non-equilibrium thermodynamics for small fluctuating systems has provided deeper insight on each information process with each subsystem. From this viewpoint, the measurement process is regarded as a process where the correlation (mutual information) between the engine and the demon increases, and the feedback process is regarded as a process where the correlation decreases. If the correlation changes, thermodynamic relations as the second law of thermodynamics and the fluctuation theorem for each subsystem should be modified, and for the case of external control a second-law like inequality and a generalized fluctuation theorem with mutual information are satisfied. These relations suggest that we need extra thermodynamic cost to increase correlation (measurement case), and in contrast we can apparently violate the second law up to the consumption of correlation (feedback case). For more general information processes including biological information processing, both inequality and equality with mutual information hold.
虽然 Landauer 和 Bennett 的论证只是回答了热力学第二定律和整个 Szilard 引擎系统的循环过程之间的一致性(引擎和魔鬼的组合系统) ，但是最近一个基于非平衡态热力学系统的方法为每个子系统的每个信息过程提供了更深入的洞察。从这个观点出发，将测量过程看作是发动机与恶魔之间相关性(互信息)增加的过程，而反馈过程看作是相关性减少的过程。如果相关性发生变化，则应修正热力学关系，例如每个子系统的热力学第二定律和涨落定理，对于外部控制，则满足第二定律，例如不等式和具有互信息的广义涨落定理。这些关系表明，我们需要额外的热力学成本来增加相关性(测量案例) ，相比之下，我们可以明显地违反第二定律，直到消耗相关性(反馈案例)。对于包括生物信息处理在内的更一般的信息处理过程，不等式和互信息平等都成立。
Maxwell conceived a thought experiment as a way of furthering the understanding of the second law. His description of the experiment is as follows:<ref name="Bennett87" /><ref>Maxwell (1871), reprinted in [[#Leff Rex 90|Leff & Rex (1990)]] on p. 4.</ref>
{{quote|... 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.}}In other words, Maxwell imagines one container divided into two parts, ''A'' and ''B''.<ref name="Bennett87" /><ref name="Sagawa">{{cite book
Real-life versions of Maxwellian demons occur, but all such "real demons" or molecular demons have their entropy-lowering effects duly balanced by increase of entropy elsewhere. Molecular-sized mechanisms are no longer found only in biology; they are also the subject of the emerging field of nanotechnology. Single-atom traps used by particle physicists allow an experimenter to control the state of individual quanta in a way similar to Maxwell's demon.
现实版本的马克斯韦尔式恶魔也会出现，但是所有这些“真正的恶魔”或者分子恶魔都有其降低熵值的作用，并且在其他地方熵值的增加中得到了适当的平衡。分子大小的机制不再只存在于生物学中; 它们也是纳米技术新兴领域的主题。粒子物理学家使用的单原子陷阱使得实验者可以像麦克斯韦魔鬼那样控制单个量子的状态。
| last1 = Sagawa
| first1 = Takahiro
If hypothetical mirror matter exists, Zurab Silagadze proposes that demons can be envisaged, "which can act like perpetuum mobiles of the second kind: extract heat energy from only one reservoir, use it to do work and be isolated from the rest of ordinary world. Yet the Second Law is not violated because the demons pay their entropy cost in the hidden (mirror) sector of the world by emitting mirror photons."
如果假想的镜像物质存在，Zurab Silagadze 提出恶魔可以被设想，“恶魔可以像第二类永久移动物一样: 只从一个蓄热池中提取热能，用它来工作，并与其他普通世界隔绝。然而，第二定律并没有被违反，因为恶魔通过发射镜像光子在世界的隐藏(镜像)区域支付了他们的熵代价。”
| title = Thermodynamics of Information Processing in Small Systems
| publisher = Springer Science and Business Media
| date = 2012
In the February 2007 issue of Nature, David Leigh, a professor at the University of Edinburgh, announced the creation of a nano-device based on the Brownian ratchet popularized by Richard Feynman. Leigh's device is able to drive a chemical system out of equilibrium, but it must be powered by an external source (light in this case) and therefore does not violate thermodynamics.
在2007年2月的《自然》杂志上，爱丁堡大学的 David Leigh 教授宣布了一种基于 Richard Feynman 普及的布朗棘轮的纳米装置。李的设备能够驱动化学系统脱离平衡，但它必须由外部源(在这种情况下是光)提供动力，因此不违反热力学。
| location =
| pages = 9–14
Previously, researchers including Nobel Prize winner Fraser Stoddart, created ring-shaped molecules called rotaxanes which could be placed on an axle connecting two sites, A and B. Particles from either site would bump into the ring and move it from end to end. If a large collection of these devices were placed in a system, half of the devices had the ring at site A and half at B, at any given moment in time.
之前，包括诺贝尔奖获得者弗雷泽 · 斯托达特在内的研究人员创造了一种环状分子，叫做轮烷，可以放置在连接两个位点 a 和 b 的轴上。来自任何一个位置的粒子都会撞上环，并将其从一端移动到另一端。如果在一个系统中放置大量的这些设备，在任何给定的时刻，一半的设备在 a 处有环，另一半在 b 处有环。
| language =
| url = https://books.google.com/books?id=oKWi-J6LOsEC&pg=PA13
Leigh made a minor change to the axle so that if a light is shone on the device, the center of the axle will thicken, restricting the motion of the ring. It only keeps the ring from moving, however, if it is at A. Over time, therefore, the rings will be bumped from B to A and get stuck there, creating an imbalance in the system. In his experiments, Leigh was able to take a pot of "billions of these devices" from 50:50 equilibrium to a 70:30 imbalance within a few minutes.
Leigh 对车轴做了一个小小的改动，如果灯光照在车轴上，车轴的中心会变厚，限制了环的运动。然而，如果它位于 a，它只能阻止环的移动。因此，随着时间的推移，光环会从 b 碰撞到 a，然后卡在那里，在系统中造成不平衡。在他的实验中，李能够在几分钟内将“数十亿个这样的装置”从50:50的平衡变成70:30的不平衡。
| doi =
| id =
In 2009 Mark G. Raizen developed a laser atomic cooling technique which realizes the process Maxwell envisioned of sorting individual atoms in a gas into different containers based on their energy. The new concept is a one-way wall for atoms or molecules that allows them to move in one direction, but not go back. The operation of the one-way wall relies on an irreversible atomic and molecular process of absorption of a photon at a specific wavelength, followed by spontaneous emission to a different internal state. The irreversible process is coupled to a conservative force created by magnetic fields and/or light. Raizen and collaborators proposed using the one-way wall in order to reduce the entropy of an ensemble of atoms. In parallel, Gonzalo Muga and Andreas Ruschhaupt independently developed a similar concept. Their "atom diode" was not proposed for cooling, but rather for regulating the flow of atoms. The Raizen Group demonstrated significant cooling of atoms with the one-way wall in a series of experiments in 2008. Subsequently, the operation of a one-way wall for atoms was demonstrated by Daniel Steck and collaborators later in 2008. Their experiment was based on the 2005 scheme for the one-way wall, and was not used for cooling. The cooling method realized by the Raizen Group was called "single-photon cooling", because only one photon on average is required in order to bring an atom to near-rest. This is in contrast to other laser cooling techniques which use the momentum of the photon and require a two-level cycling transition.
2009年，Mark g. Raizen 开发了一种激光原子冷却技术，该技术实现了麦克斯韦设想的基于能量将气体中的单个原子分类放入不同容器的过程。新概念是原子或分子的单向墙，允许它们朝一个方向运动，但不能回头。单向壁的操作依赖于一个不可逆的原子和分子过程，即在一个特定波长处吸收一个光子，然后吸收一个自发发射到另一个内部状态。不可逆性与磁场和/或光产生的保守力相耦合。Raizen 和他的合作者提出使用单向壁来减少原子团体的熵。与此同时，Gonzalo Muga 和 Andreas Ruschhaupt 独立地提出了一个类似的概念。他们的“原子二极管”不是用来冷却的，而是用来调节原子的流动。在2008年的一系列实验中，Raizen 团队证明了单向壁对原子的冷却作用。随后，丹尼尔 · 斯特克和合作者在2008年晚些时候演示了单向原子墙的操作。他们的实验是基于2005年的单向墙计划，并没有用于冷却。Raizen 群实现的冷却方法被称为“单光子冷却” ，因为平均只需要一个光子就可以使原子接近静止。这与其他利用光子动量需要两能级循环跃迁的激光冷却技术形成了鲜明的对比。
| isbn = 978-4431541677
}}</ref> Both parts are filled with the same [[gas]] at equal temperatures and placed next to each other. Observing the [[molecule]]s on both sides, an imaginary [[Demon (thought experiment)|demon]] guards a trapdoor between the two parts. 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''. Likewise, when a slower-than-average molecule from ''B'' flies towards the trapdoor, the demon will let it pass from ''B'' to ''A''. The average [[speed]] of the molecules in ''B'' will have increased while in ''A'' they will have slowed down on average. Since average molecular speed corresponds to temperature, the temperature decreases in ''A'' and increases in ''B'', contrary to the second law of thermodynamics. A [[heat engine]] operating between the thermal reservoirs ''A'' and ''B'' could extract useful [[work (physics)|work]] from this temperature difference.
In 2006, Raizen, Muga, and Ruschhaupt showed in a theoretical paper that as each atom crosses the one-way wall, it scatters one photon, and information is provided about the turning point and hence the energy of that particle. The entropy increase of the radiation field scattered from a directional laser into a random direction is exactly balanced by the entropy reduction of the atoms as they are trapped by the one-way wall.
2006年，Raizen，Muga，和 Ruschhaupt 在一篇理论论文中指出，当每个原子穿过单向墙时，它散射一个光子，并提供了关于转折点的信息，从而得出该粒子的能量。定向激光向随机方向散射的辐射场的熵增与被单向壁俘获的原子的熵减成正比。
The demon must allow molecules to pass in both directions in order to produce only a temperature difference; one-way passage only of faster-than-average molecules from ''A'' to ''B'' will cause higher temperature and pressure to develop on the ''B'' side.
This technique is widely described as a "Maxwell's demon" because it realizes Maxwell's process of creating a temperature difference by sorting high and low energy atoms into different containers. However, scientists have pointed out that it is not a true Maxwell's demon in the sense that it does not violate the second law of thermodynamics; it does not result in a net decrease in entropy Only a year later and based on an earlier theoretical proposal, the same group presented the first experimental realization of an autonomous Maxwell's demon, which extracts microscopic information from a system and reduces its entropy by applying feedback. The demon is based on two capacitively coupled single-electron devices, both integrated on the same electronic circuit. The operation of the demon is directly observed as a temperature drop in the system, with a simultaneous temperature rise in the demon arising from the thermodynamic cost of generating the mutual information. In 2016, Pekola et al. demonstrated a proof-of-principle of an autonomous demon in coupled single-electron circuits, showing a way to cool critical elements in a circuit with information as a fuel. Pekola et al. have also proposed that a simple qubit circuit, e.g., made of a superconducting circuit, could provide a basis to study a quantum Szilard's engine.
这种技术被广泛地描述为“麦克斯韦魔鬼” ，因为它实现了麦克斯韦通过将高能和低能原子分类到不同的容器中产生温差的过程。然而，科学家已经指出，它不是一个真正的麦克斯韦恶魔，因为它没有违反热力学第二定律; 它不会导致熵的净减少。Demon 是基于集成在同一电路上的两个电容耦合的单电子器件。恶魔的运行被直接观察为系统中的温度下降，同时由于产生互信息的热力学成本而引起的恶魔中的温度上升。2016年，Pekola 等人。证明了在耦合的单电子电路中存在一个自主魔鬼的原理，展示了一种以信息为燃料冷却电路中关键元件的方法。等人。也提出了一个简单的量子比特电路，例如，由超导电路制成，可以为研究西拉德的量子引擎提供基础。
== Criticism and development ==
Several physicists have presented calculations that show that the [[second law of thermodynamics]] will not actually be violated, if a more complete analysis is made of the whole system including the demon.<ref name="Bennett87" /><ref name="Sagawa" /><ref name="BennettSchumacher">{{cite journal
Daemons in computing, generally processes that run on servers to respond to users, are named for Maxwell's demon.
计算机中的守护进程，通常是运行在服务器上响应用户的进程，以麦克斯韦恶魔的名字命名。
| last1 = Bennett
| first1 = Charles H.
Historian Henry Brooks Adams in his manuscript The Rule of Phase Applied to History attempted to use Maxwell's demon as a historical metaphor, though he misunderstood and misapplied the original principle. Adams interpreted history as a process moving towards "equilibrium", but he saw militaristic nations (he felt Germany pre-eminent in this class) as tending to reverse this process, a Maxwell's demon of history. Adams made many attempts to respond to the criticism of his formulation from his scientific colleagues, but the work remained incomplete at Adams' death in 1918. It was only published posthumously.
亨利·亚当斯在他的手稿《历史的阶段法则》中试图用麦克斯韦的恶魔作为历史隐喻，尽管他误解和误用了最初的原则。亚当斯将历史解释为一个走向“均衡”的过程，但他认为军国主义国家(他认为德国在这个阶层中处于领先地位)倾向于逆转这一过程，这是麦克斯韦的历史魔鬼。亚当斯曾多次尝试回应他的科学同事对他的公式的批评，但在1918年亚当斯去世时，这项工作仍未完成。这本书是死后才出版的。
| last2 = Schumacher
| first2 = Benjamin
| title = Maxwell's demons appear in the lab
| journal = Nikkei Science
| volume =
| issue =
| pages = 3–6
| date = August 2011
| url = http://www.nikkei-science.com/wp-content/uploads/2011/08/201108_032.pdf
| issn =
| doi =
| id =
| accessdate = November 13, 2014}}</ref> The essence of the physical argument is to show, by calculation, that any demon must "generate" more entropy segregating the molecules than it could ever eliminate by the method described. That is, it would take more thermodynamic work to gauge the speed of the molecules and selectively allow them to pass through the opening between ''A'' and ''B'' than the amount of [[energy]] gained by the difference of temperature caused by doing so.
One of the most famous responses to this question was suggested in 1929 by [[Leó Szilárd]],<ref name="Szilard">{{cite journal
| last = Szilard
| first = Leo
| title = Über die Entropieverminderung in einem thermodynamischen System bei Eingriffen intelligenter Wesen (On the reduction of entropy in a thermodynamic system by the intervention of intelligent beings)
| journal = Zeitschrift für Physik
| volume = 53
| issue = 11–12
| pages = 840–856
| date = 1929
| url =
| issn =
| doi = 10.1007/bf01341281
| id =
| accessdate = |bibcode = 1929ZPhy...53..840S | s2cid = 122038206
}} cited in Bennett 1987. English translation available as [http://aurellem.org/jaynes/sources/Szilard.pdf NASA document TT F-16723] published 1976</ref> and later by [[Léon Brillouin]].<ref name="Bennett87" /><ref name="Sagawa" /> 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. Since the demon and the gas are interacting, we must consider the total entropy of the gas and the demon combined. The expenditure of energy by the demon will cause an increase in the entropy of the demon, which will be larger than the lowering of the entropy of the gas.
In 1960, [[Rolf Landauer]] raised an exception to this argument.<ref name="Bennett87" /><ref name="Sagawa" /><ref name="Landauer">{{cite journal
| last = Landauer
| first = R.
| title = Irreversibility and heat generation in the computing process
| journal = IBM Journal of Research and Development
| volume = 5
| issue = 3
| pages = 183–191
| date = 1961
| url = http://www.pitt.edu/~jdnorton/lectures/Rotman_Summer_School_2013/thermo_computing_docs/Landauer_1961.pdf
| issn =
| doi = 10.1147/rd.53.0183
| id =
| accessdate = November 13, 2014}} reprinted in [http://domino.research.ibm.com/tchjr/journalindex.nsf/c469af92ea9eceac85256bd50048567c/8a9d4b4e96887b8385256bfa0067fba2?OpenDocument Vol. 44, No. 1, January 2000, p. 261]</ref> He realized that some measuring processes need not increase thermodynamic entropy as long as they were [[Reversible process (thermodynamics)|thermodynamically reversible]]. He suggested these "reversible" measurements could be used to sort the molecules, violating the Second Law. However, due to [[Entropy in thermodynamics and information theory|the connection between]] thermodynamic entropy and [[information entropy]], this also meant that the recorded measurement must not be erased. In other words, to determine whether to let a molecule through, the demon must acquire information about the state of the molecule and either discard it or store it. Discarding it leads to immediate increase in entropy but the demon cannot store it indefinitely. In 1982, [[Charles H. Bennett (computer scientist)|Charles Bennett]] showed that, however well prepared, eventually the demon will run out of information storage space and must begin to erase the information it has previously gathered.<ref name="Sagawa" /><ref name="Bennett82">{{Cite journal | last1 = Bennett | first1 = C. H. | title = The thermodynamics of computation—a review | doi = 10.1007/BF02084158 | journal = International Journal of Theoretical Physics | volume = 21 | issue = 12 | pages = 905–940 | year = 1982 | pmid = | pmc = | bibcode = 1982IJTP...21..905B | url = http://hexagon.physics.wisc.edu/teaching/2014f+ph805+quantum+information/papers/bennett+thermodynamics+of+computation+ijtp+1982.pdf | type = Submitted manuscript | citeseerx = 10.1.1.655.5610 | s2cid = 17471991 | access-date = 2017-12-10 | archive-url = https://web.archive.org/web/20141014151011/http://hexagon.physics.wisc.edu/teaching/2014f%20ph805%20quantum%20information/papers/bennett%20thermodynamics%20of%20computation%20ijtp%201982.pdf | archive-date = 2014-10-14 | url-status = dead }}</ref> Erasing information is a thermodynamically irreversible process that increases the entropy of a system. Although Bennett had reached the same conclusion as Szilard's 1929 paper, that a Maxwellian demon could not violate the second law because entropy would be created, he had reached it for different reasons. Regarding [[Landauer's principle]], the minimum energy dissipated by deleting information was experimentally measured by Eric Lutz ''et al.'' in 2012. Furthermore, Lutz ''et al.'' confirmed that in order to approach the Landauer's limit, the system must asymptotically approach zero processing speed.<ref>{{cite journal |doi=10.1038/nature.2012.10186 |title=The unavoidable cost of computation revealed |journal=Nature |year=2012 |last1=Ball |first1=Philip |s2cid=2092541 }}</ref>
[[John Earman]] and John D. Norton have argued that Szilárd and Landauer's explanations of Maxwell's demon begin by assuming that the [[second law of thermodynamics]] cannot be violated by the demon, and derive further properties of the demon from this assumption, including the necessity of consuming energy when erasing information, etc.<ref>{{cite journal |author1=John Earman |author2=John D. Norton |name-list-style=amp |year=1998 |title=Exorcist XIV: The Wrath of Maxwell's Demon. Part I. From Maxwell to Szilard|url=http://www.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist1.pdf|journal=Studies in History and Philosophy of Modern Physics|pages=435|volume=29 |issue=4 |doi=10.1016/s1355-2198(98)00023-9|bibcode=1998SHPMP..29..435E}}</ref><ref>{{cite journal |author1=John Earman |author2=John D. Norton |name-list-style=amp |year=1999 |title=Exorcist XIV: The Wrath of Maxwell's Demon. Part II. From Szilard to Landauer and Beyond |url=http://www.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist2.pdf|journal=Studies in History and Philosophy of Modern Physics|pages=1|volume=30 |issue=1 |doi=10.1016/s1355-2198(98)00026-4|bibcode=1999SHPMP..30....1E}}</ref> It would therefore be circular to invoke these derived properties to defend the second law from the demonic argument. Bennett later acknowledged the validity of Earman and Norton's argument, while maintaining that [[Landauer's principle]] explains the mechanism by which real systems do not violate the second law of thermodynamics.<ref>{{cite journal |author=Charles H. Bennett |year=2002–2003 |title=Notes on Landauer's principle, reversible computation, and Maxwell's demon |journal=Studies in History and Philosophy of Modern Physics |volume=34 |issue=3 |pages=501–510 |arxiv=physics/0210005 |bibcode = 2003SHPMP..34..501B |doi=10.1016/S1355-2198(03)00039-X |s2cid=9648186 }}</ref>
== Recent progress ==
Although the argument by Landauer and Bennett only answers the consistency between the second law of thermodynamics and the whole cyclic process of the entire system of a [[Szilard engine]] (a composite system of the engine and the demon), a recent approach based on the [[non-equilibrium thermodynamics]] for small fluctuating systems has provided deeper insight on each information process with each subsystem. From this viewpoint, the measurement process is regarded as a process where the correlation ([[mutual information]]) between the engine and the demon increases, and the feedback process is regarded as a process where the correlation decreases. If the correlation changes, thermodynamic relations as the second law of thermodynamics and the [[fluctuation theorem]] for each subsystem should be modified, and for the case of external control a second-law like inequality<ref>{{cite journal |author1=Hugo Touchette |author2=Seth Lloyd |name-list-style=amp |year=2000 |title=Information-Theoretic Limits of Control |journal=Physical Review Letters |volume=84 |issue=6 |pages=1156–1159 |doi=10.1103/PhysRevLett.84.1156|bibcode = 2000PhRvL..84.1156T |pmid=11017467|arxiv=chao-dyn/9905039 }}</ref> and a generalized fluctuation theorem<ref>{{cite journal |author1=Takahiro Sagawa |author2=Masahito Ueda |name-list-style=amp |year=2010 |title=Generalized Jarzynski Equality under Nonequilibrium Feedback Control |journal=Physical Review Letters |volume=104 |issue=9 |pages=090602 |doi=10.1103/PhysRevLett.104.090602|pmid=20366975 |arxiv = 0907.4914 |bibcode = 2010PhRvL.104i0602S |s2cid=1549122 }}</ref> with mutual information are satisfied. These relations suggest that we need extra thermodynamic cost to increase correlation (measurement case), and in contrast we can apparently violate the second law up to the consumption of correlation (feedback case). For more general information processes including biological information processing, both inequality<ref>{{cite journal |author=Armen E Allahverdyan, Dominik Janzing and Guenter Mahler |year=2009 |title=Thermodynamic efficiency of information and heat flow |journal=Journal of Statistical Mechanics |volume=2009 |issue=9 |pages=P09011 |doi=10.1088/1742-5468/2009/09/P09011|arxiv = 0907.3320 |bibcode = 2009JSMTE..09..011A |s2cid=118440998 }}</ref> and equality<ref>{{cite journal |author1=Naoto Shiraishi |author2=Takahiro Sagawa |name-list-style=amp |year=2015 |title=Fluctuation theorem for partially masked nonequilibrium dynamics |journal=Physical Review E |volume=91 |issue=1 |pages=012130 |doi=10.1103/PhysRevE.91.012130|pmid=25679593 |arxiv = 1403.4018 |bibcode = 2015PhRvE..91a2130S |s2cid=1805888 }}</ref> with mutual information hold.
== Applications ==
Real-life versions of Maxwellian demons occur, but all such "real demons" or [[molecular demon]]s have their entropy-lowering effects duly balanced by increase of entropy elsewhere.<ref>{{Cite book|title=Physics in mind : a quantum view of the brain|last=R.|first=Loewenstein, Werner|isbn=9780465029846|location=New York|oclc=778420640|date = 2013-01-29}}</ref> Molecular-sized mechanisms are no longer found only in biology; they are also the subject of the emerging field of [[nanotechnology]]. Single-atom traps used by particle physicists allow an experimenter to control the state of individual quanta in a way similar to Maxwell's demon.
If hypothetical [[mirror matter]] exists, Zurab Silagadze proposes that demons can be envisaged, "which can act like perpetuum mobiles of the second kind: extract heat energy from only one reservoir, use it to do work and be isolated from the rest of ordinary world. Yet the Second Law is not violated because the demons pay their entropy cost in the hidden (mirror) sector of the world by emitting mirror photons."<ref>{{Cite journal|arxiv=physics/0608114 |title=Maxwell's demon through the looking glass |journal=Acta Physica Polonica B |volume=38 |issue=1 |pages=101–126 |year=2007 |last1=Silagadze |first1=Z. K |bibcode=2007AcPPB..38..101S }}</ref>
Category:Philosophy of thermal and statistical physics
类别: 热力学和统计物理学哲学
== Experimental work ==
Category:Concepts in physics
分类: 物理概念
In the February 2007 issue of ''[[Nature (journal)|Nature]]'', [[David Leigh (scientist)|David Leigh]], a professor at the [[University of Edinburgh]], announced the creation of a nano-device based on the [[Brownian ratchet]] popularized by [[Richard Feynman]]. Leigh's device is able to drive a chemical system out of [[Chemical equilibrium|equilibrium]], but it must be powered by an external source ([[light]] in this case) and therefore does not violate thermodynamics.<ref>{{cite journal | doi = 10.1038/nature05452 | volume=445 | issue=7127 | title=A molecular information ratchet | journal=Nature | pages=523–527 | pmid=17268466 | date=February 2007 | last1 = Serreli | first1 = V | last2 = Lee | first2 = CF | last3 = Kay | first3 = ER | last4 = Leigh | first4 = DA| bibcode=2007Natur.445..523S | s2cid=4314051 }}</ref>
Category:Nanotechnology
类别: 纳米技术
Category:James Clerk Maxwell
类别: 詹姆斯·克拉克·麦克斯韦
Previously, researchers including Nobel Prize winner [[Fraser Stoddart]], created ring-shaped molecules called [[rotaxane]]s which could be placed on an axle connecting two sites, ''A'' and ''B''. Particles from either site would bump into the ring and move it from end to end. If a large collection of these devices were placed in a system, half of the devices had the ring at site ''A'' and half at ''B'', at any given moment in time.<ref>{{cite journal|last1=Bissell|first1=Richard A|last2=Córdova|first2=Emilio|last3=Kaifer|first3=Angel E.|last4=Stoddart|first4=J. Fraser|title=A chemically and electrochemically switchable molecular shuttle|journal=Nature|date=12 May 1994|volume=369|issue=6476|pages=133–137|doi=10.1038/369133a0|bibcode=1994Natur.369..133B|s2cid=44926804}}</ref>
Category:Fictional demons and devils
类别: 虚构的魔鬼和魔鬼
Category:Thought experiments in physics
类别: 物理学思维实验
Leigh made a minor change to the axle so that if a light is shone on the device, the center of the axle will thicken, restricting the motion of the ring. It only keeps the ring from moving, however, if it is at ''A''. Over time, therefore, the rings will be bumped from ''B'' to ''A'' and get stuck there, creating an imbalance in the system. In his experiments, Leigh was able to take a pot of "billions of these devices" from 50:50 equilibrium to a 70:30 imbalance within a few minutes.<ref>{{cite journal |author=Katharine Sanderson |date=31 January 2007 |title=A demon of a device |journal=[[Nature (journal)|Nature]] |doi=10.1038/news070129-10 |s2cid=121130699 }}</ref>
Category:Perpetual motion
类别: 永动机
Category:1867 introductions
类别: 1867年引言
<noinclude>
<small>This page was moved from [[wikipedia:en:Maxwell's demon]]. Its edit history can be viewed at [[麦克斯韦妖/edithistory]]</small></noinclude>
[[Category:待整理页面]]
{{short description|Thought experiment of 1867}}
[[File:Maxwell's demon.svg|right|340px|thumb|Schematic figure of Maxwell's demon thought experiment.]]
Schematic figure of Maxwell's demon thought experiment.
麦克斯韦恶魔思维实验示意图。
'''Maxwell's demon''' is a [[thought experiment]] created by the physicist [[James Clerk Maxwell]] in 1867 in which he suggested how the [[second law of thermodynamics]] might hypothetically be violated.<ref>{{cite book |author=Cargill Gilston Knott |title=Life and Scientific Work of Peter Guthrie Tait |publisher=[[Cambridge University Press]] |year=1911 |pages=213–215 |chapter=Quote from undated letter from Maxwell to Tait | chapter-url=https://archive.org/stream/lifescientificwo00knotuoft#page/212/mode/2up}}</ref> In the thought experiment, a [[Demon (thought experiment)|demon]] controls a small door between two compartments of gas. As individual gas molecules approach the door, the demon quickly opens and shuts the door so that only fast molecules are passed into one of the chambers, while only slow molecules are passed into the other. Because faster molecules are hotter, the demon's behaviour causes one chamber to warm up and the other to cool down, thereby decreasing [[entropy]] and violating the second law of thermodynamics. This thought experiment has provoked debate and theoretical work on the relation between thermodynamics and [[information theory]] extending to the present day, with a number of scientists arguing that theoretical considerations rule out any practical device violating the second law in this way.
Maxwell's demon is a thought experiment created by the physicist James Clerk Maxwell in 1867 in which he suggested how the second law of thermodynamics might hypothetically be violated. In the thought experiment, a demon controls a small door between two compartments of gas. As individual gas molecules approach the door, the demon quickly opens and shuts the door so that only fast molecules are passed into one of the chambers, while only slow molecules are passed into the other. Because faster molecules are hotter, the demon's behaviour causes one chamber to warm up and the other to cool down, thereby decreasing entropy and violating the second law of thermodynamics. This thought experiment has provoked debate and theoretical work on the relation between thermodynamics and information theory extending to the present day, with a number of scientists arguing that theoretical considerations rule out any practical device violating the second law in this way.
麦克斯韦恶魔是物理学家詹姆斯·克拉克·麦克斯韦在1867年创造的一个思想实验，在这个实验中，他提出了如何假设性地违反热力学第二定律。在这个思想实验中，一个恶魔控制着两个气体舱之间的一扇小门。当单个气体分子接近这扇门时，这个恶魔迅速地打开和关闭这扇门，只有快速的分子进入其中一个腔，而只有慢速的分子进入另一个腔。因为速度更快的分子温度更高，恶魔的行为导致一个腔室升温，另一个腔室降温，从而减少熵，违反了热力学第二定律。这个思想实验引起了关于热力学和信息论之间关系的争论和理论工作，一些科学家认为理论上的考虑排除了任何以这种方式违反第二定律的实际装置。
== Origin and history of the idea ==
The [[thought experiment]] first appeared in a letter [[James Clerk Maxwell|Maxwell]] wrote to [[Peter Guthrie Tait]] on 11 December 1867. It appeared again in a letter to [[John William Strutt]] in 1871, before it was presented to the public in Maxwell's 1872 book on [[thermodynamics]] titled ''Theory of Heat''.<ref name=Leff>[[#Leff Rex 02|Leff & Rex (2002)]], p. 370.</ref>
The thought experiment first appeared in a letter Maxwell wrote to Peter Guthrie Tait on 11 December 1867. It appeared again in a letter to John William Strutt in 1871, before it was presented to the public in Maxwell's 1872 book on thermodynamics titled Theory of Heat.
1867年12月11日，Maxwell 在写给彼得·格思里·泰特的一封信中首次提出了这个思想实验。它在1871年写给约翰 · 威廉 · 斯特拉特的信中再次出现，后来在麦克斯韦1872年出版的热力学书籍《热力学理论》中公之于众。
In his letters and books, Maxwell described the agent opening the door between the chambers as a "finite being". [[William Thomson, 1st Baron Kelvin|William Thomson (Lord Kelvin)]] was the first to use the word "demon" for Maxwell's concept, in the journal ''[[Nature (journal)|Nature]]'' in 1874, and implied that he intended the mediating, rather than malevolent, connotation of the word.<ref>{{cite journal |author=William Thomson |year=1874 |title=Kinetic theory of the dissipation of energy |journal=[[Nature (journal)|Nature]] |volume=9 |issue=232 |pages=441–444 |doi=10.1038/009441c0 |bibcode=1874Natur...9..441T|author-link=William Thomson, 1st Baron Kelvin |doi-access=free }}</ref><ref>{{cite journal |year=1879 |title=The sorting demon Of Maxwell |journal=Nature |volume=20 |issue=501 |pages=126 |bibcode=1879Natur..20Q.126. |doi=10.1038/020126a0 |doi-access=free }}</ref><ref name=Weber>{{cite book |author=Alan S. Weber |year=2000 |title=Nineteenth Century Science: a Selection of Original Texts |publisher=[[Broadview Press]] |page=300}}</ref>
In his letters and books, Maxwell described the agent opening the door between the chambers as a "finite being". William Thomson (Lord Kelvin) was the first to use the word "demon" for Maxwell's concept, in the journal Nature in 1874, and implied that he intended the mediating, rather than malevolent, connotation of the word.
在他的信件和书中，麦克斯韦描述特工打开房间的门是一个“有限的存在”。威廉 · 汤姆森(开尔文勋爵)是第一个在1874年的《自然》杂志上使用“恶魔”这个词来描述麦克斯韦的概念的人，他暗示这个词的意思是调解，而不是恶意的。
== Original thought experiment ==
The second law of thermodynamics ensures (through statistical probability) that two bodies of different [[temperature]], when brought into contact with each other and isolated from the rest of the Universe, will evolve to a thermodynamic equilibrium in which both bodies have approximately the same temperature.<ref name="Bennett87">{{cite journal
The second law of thermodynamics ensures (through statistical probability) that two bodies of different temperature, when brought into contact with each other and isolated from the rest of the Universe, will evolve to a thermodynamic equilibrium in which both bodies have approximately the same temperature. The second law is also expressed as the assertion that in an isolated system, entropy never decreases.
热力学第二定律天文台通过统计概率确保了两个不同温度的天体，当它们相互接触并与宇宙其他部分隔离开来时，将会演化成一个温度相近的热力学平衡天文台。第二定律也表达为在孤立系统中，熵永远不会减少的断言。
| last = Bennett
| first = Charles H.
In other words, Maxwell imagines one container divided into two parts, A and B. Both parts are filled with the same gas at equal temperatures and placed next to each other. Observing the molecules on both sides, an imaginary demon guards a trapdoor between the two parts. 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. Likewise, when a slower-than-average molecule from B flies towards the trapdoor, the demon will let it pass from B to A. The average speed of the molecules in B will have increased while in A they will have slowed down on average. Since average molecular speed corresponds to temperature, the temperature decreases in A and increases in B, contrary to the second law of thermodynamics. A heat engine operating between the thermal reservoirs A and B could extract useful work from this temperature difference.
换句话说，麦克斯韦想象一个容器分成两部分，a 和 b。两个部分在相同的温度下充入相同的气体，并且挨着放置。通过观察两边的分子，一个想象中的恶魔守卫着两部分之间的活板门。当一个来自 a 的比平均速度快的分子飞向活板门时，魔鬼打开了它，分子就会从 a 飞到 b。同样地，当一个来自 b 的比平均速度慢的分子飞向活板门时，魔鬼会让它从 b 飞向 a。B 中分子的平均速度会增加，而 a 中分子的平均速度会减慢。由于平均分子速度与温度相对应，因此 a 中的温度降低，b 中的温度升高，这与热力学第二定律相反。在热源 a 和热源 b 之间运行的热机可以从这种温差中提取有用的功。
| title = Demons, Engines, and the Second Law
| journal = Scientific American
The demon must allow molecules to pass in both directions in order to produce only a temperature difference; one-way passage only of faster-than-average molecules from A to B will cause higher temperature and pressure to develop on the B side.
魔鬼必须允许分子在两个方向上通过，以便只产生温差; 只有比平均速度更快的分子从 a 到 b 的单向通道会导致 b 方向产生更高的温度和压力。
| volume = 257
| issue = 5
| pages = 108–116
Several physicists have presented calculations that show that the second law of thermodynamics will not actually be violated, if a more complete analysis is made of the whole system including the demon. The essence of the physical argument is to show, by calculation, that any demon must "generate" more entropy segregating the molecules than it could ever eliminate by the method described. That is, it would take more thermodynamic work to gauge the speed of the molecules and selectively allow them to pass through the opening between A and B than the amount of energy gained by the difference of temperature caused by doing so.
一些物理学家已经展示了计算结果，表明如果对包括恶魔在内的整个系统进行更全面的分析，那么热力学第二定律实际上不会受到破坏。物理论证的本质是通过计算表明，任何恶魔都必须“产生”更多的熵，分离分子，而不是用所描述的方法可以消除。也就是说，需要更多的热力学功来测量分子的速度，并有选择地允许它们通过 a 和 b 之间的开口，而不是由于这样做所产生的温差而获得的能量。
| date = November 1987
| url = https://ecee.colorado.edu/~ecen5555/SourceMaterial/DemonsEnginesAndSecondLaw87.pdf
One of the most famous responses to this question was suggested in 1929 by Leó Szilárd, and later by Léon Brillouin. He realized that some measuring processes need not increase thermodynamic entropy as long as they were thermodynamically reversible. He suggested these "reversible" measurements could be used to sort the molecules, violating the Second Law. However, due to the connection between thermodynamic entropy and information entropy, this also meant that the recorded measurement must not be erased. In other words, to determine whether to let a molecule through, the demon must acquire information about the state of the molecule and either discard it or store it. Discarding it leads to immediate increase in entropy but the demon cannot store it indefinitely. In 1982, Charles Bennett showed that, however well prepared, eventually the demon will run out of information storage space and must begin to erase the information it has previously gathered. Erasing information is a thermodynamically irreversible process that increases the entropy of a system. Although Bennett had reached the same conclusion as Szilard's 1929 paper, that a Maxwellian demon could not violate the second law because entropy would be created, he had reached it for different reasons. Regarding Landauer's principle, the minimum energy dissipated by deleting information was experimentally measured by Eric Lutz et al. in 2012. Furthermore, Lutz et al. confirmed that in order to approach the Landauer's limit, the system must asymptotically approach zero processing speed.
对这个问题最著名的回答之一是1929年由 Leó Szilárd 提出的，后来由莱昂 · 布里渊提出。他意识到，只要某些测量过程是热力学可逆的，就不需要增加熵。他认为这些“可逆”的测量可以用来分类分子，违反了第二定律。然而，由于熵和熵之间的连接，这也意味着记录的测量不能被擦除。换句话说，为了决定是否让一个分子通过，恶魔必须获得关于分子状态的信息，要么丢弃它，要么存储它。丢弃它会立即增加熵，但是恶魔不能无限期地储存它。1982年，查尔斯 · 班尼特指出，无论准备得多么充分，恶魔最终都会耗尽信息存储空间，并且必须开始删除它先前收集的信息。擦除信息是一个热力学不可逆性，它增加了系统的熵。虽然贝内特得出了与西拉德1929年的论文相同的结论，即马克斯韦尔式的恶魔不能违反第二定律，因为熵会被创造出来。根据兰道尔原理，埃里克 · 鲁兹等人通过实验测量了删除信息所消耗的最小能量。2012年。此外，Lutz 等人。证实，为了接近兰道尔的极限，系统必须渐近接近零处理速度。
| issn =
| doi = 10.1038/scientificamerican1187-108
John Earman and John D. Norton have argued that Szilárd and Landauer's explanations of Maxwell's demon begin by assuming that the second law of thermodynamics cannot be violated by the demon, and derive further properties of the demon from this assumption, including the necessity of consuming energy when erasing information, etc. It would therefore be circular to invoke these derived properties to defend the second law from the demonic argument. Bennett later acknowledged the validity of Earman and Norton's argument, while maintaining that Landauer's principle explains the mechanism by which real systems do not violate the second law of thermodynamics.
和 John d. Norton 认为 Szilárd 和 Landauer 对麦克斯韦恶魔的解释是从假设热力学第二定律不会被恶魔侵犯开始的，并且从这个假设中得出恶魔的进一步属性，包括在消除信息时消耗能量的必要性等等。因此，调用这些派生属性来保护第二定律不受恶魔论证的影响是循环的。后来承认 Earman 和 Norton 的论点是正确的，同时坚持 Landauer 原理解释了真实系统不违反热力学第二定律的机制。
| id =
| accessdate = November 13, 2014| bibcode = 1987SciAm.257e.108B}}</ref> The second law is also expressed as the assertion that in an [[isolated system]], [[entropy]] never decreases.<ref name="Bennett87" />
Although the argument by Landauer and Bennett only answers the consistency between the second law of thermodynamics and the whole cyclic process of the entire system of a Szilard engine (a composite system of the engine and the demon), a recent approach based on the non-equilibrium thermodynamics for small fluctuating systems has provided deeper insight on each information process with each subsystem. From this viewpoint, the measurement process is regarded as a process where the correlation (mutual information) between the engine and the demon increases, and the feedback process is regarded as a process where the correlation decreases. If the correlation changes, thermodynamic relations as the second law of thermodynamics and the fluctuation theorem for each subsystem should be modified, and for the case of external control a second-law like inequality and a generalized fluctuation theorem with mutual information are satisfied. These relations suggest that we need extra thermodynamic cost to increase correlation (measurement case), and in contrast we can apparently violate the second law up to the consumption of correlation (feedback case). For more general information processes including biological information processing, both inequality and equality with mutual information hold.
虽然 Landauer 和 Bennett 的论证只是回答了热力学第二定律和整个 Szilard 引擎系统的循环过程之间的一致性(引擎和魔鬼的组合系统) ，但是最近一个基于非平衡态热力学系统的方法为每个子系统的每个信息过程提供了更深入的洞察。从这个观点出发，将测量过程看作是发动机与恶魔之间相关性(互信息)增加的过程，而反馈过程看作是相关性减少的过程。如果相关性发生变化，则应修正热力学关系，例如每个子系统的热力学第二定律和涨落定理，对于外部控制，则满足第二定律，例如不等式和具有互信息的广义涨落定理。这些关系表明，我们需要额外的热力学成本来增加相关性(测量案例) ，相比之下，我们可以明显地违反第二定律，直到消耗相关性(反馈案例)。对于包括生物信息处理在内的更一般的信息处理过程，不等式和互信息平等都成立。
Maxwell conceived a thought experiment as a way of furthering the understanding of the second law. His description of the experiment is as follows:<ref name="Bennett87" /><ref>Maxwell (1871), reprinted in [[#Leff Rex 90|Leff & Rex (1990)]] on p. 4.</ref>
{{quote|... 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.}}In other words, Maxwell imagines one container divided into two parts, ''A'' and ''B''.<ref name="Bennett87" /><ref name="Sagawa">{{cite book
Real-life versions of Maxwellian demons occur, but all such "real demons" or molecular demons have their entropy-lowering effects duly balanced by increase of entropy elsewhere. Molecular-sized mechanisms are no longer found only in biology; they are also the subject of the emerging field of nanotechnology. Single-atom traps used by particle physicists allow an experimenter to control the state of individual quanta in a way similar to Maxwell's demon.
现实版本的马克斯韦尔式恶魔也会出现，但是所有这些“真正的恶魔”或者分子恶魔都有其降低熵值的作用，并且在其他地方熵值的增加中得到了适当的平衡。分子大小的机制不再只存在于生物学中; 它们也是纳米技术新兴领域的主题。粒子物理学家使用的单原子陷阱使得实验者可以像麦克斯韦魔鬼那样控制单个量子的状态。
| last1 = Sagawa
| first1 = Takahiro
If hypothetical mirror matter exists, Zurab Silagadze proposes that demons can be envisaged, "which can act like perpetuum mobiles of the second kind: extract heat energy from only one reservoir, use it to do work and be isolated from the rest of ordinary world. Yet the Second Law is not violated because the demons pay their entropy cost in the hidden (mirror) sector of the world by emitting mirror photons."
如果假想的镜像物质存在，Zurab Silagadze 提出恶魔可以被设想，“恶魔可以像第二类永久移动物一样: 只从一个蓄热池中提取热能，用它来工作，并与其他普通世界隔绝。然而，第二定律并没有被违反，因为恶魔通过发射镜像光子在世界的隐藏(镜像)区域支付了他们的熵代价。”
| title = Thermodynamics of Information Processing in Small Systems
| publisher = Springer Science and Business Media
| date = 2012
In the February 2007 issue of Nature, David Leigh, a professor at the University of Edinburgh, announced the creation of a nano-device based on the Brownian ratchet popularized by Richard Feynman. Leigh's device is able to drive a chemical system out of equilibrium, but it must be powered by an external source (light in this case) and therefore does not violate thermodynamics.
在2007年2月的《自然》杂志上，爱丁堡大学的 David Leigh 教授宣布了一种基于 Richard Feynman 普及的布朗棘轮的纳米装置。李的设备能够驱动化学系统脱离平衡，但它必须由外部源(在这种情况下是光)提供动力，因此不违反热力学。
| location =
| pages = 9–14
Previously, researchers including Nobel Prize winner Fraser Stoddart, created ring-shaped molecules called rotaxanes which could be placed on an axle connecting two sites, A and B. Particles from either site would bump into the ring and move it from end to end. If a large collection of these devices were placed in a system, half of the devices had the ring at site A and half at B, at any given moment in time.
之前，包括诺贝尔奖获得者弗雷泽 · 斯托达特在内的研究人员创造了一种环状分子，叫做轮烷，可以放置在连接两个位点 a 和 b 的轴上。来自任何一个位置的粒子都会撞上环，并将其从一端移动到另一端。如果在一个系统中放置大量的这些设备，在任何给定的时刻，一半的设备在 a 处有环，另一半在 b 处有环。
| language =
| url = https://books.google.com/books?id=oKWi-J6LOsEC&pg=PA13
Leigh made a minor change to the axle so that if a light is shone on the device, the center of the axle will thicken, restricting the motion of the ring. It only keeps the ring from moving, however, if it is at A. Over time, therefore, the rings will be bumped from B to A and get stuck there, creating an imbalance in the system. In his experiments, Leigh was able to take a pot of "billions of these devices" from 50:50 equilibrium to a 70:30 imbalance within a few minutes.
Leigh 对车轴做了一个小小的改动，如果灯光照在车轴上，车轴的中心会变厚，限制了环的运动。然而，如果它位于 a，它只能阻止环的移动。因此，随着时间的推移，光环会从 b 碰撞到 a，然后卡在那里，在系统中造成不平衡。在他的实验中，李能够在几分钟内将“数十亿个这样的装置”从50:50的平衡变成70:30的不平衡。
| doi =
| id =
In 2009 Mark G. Raizen developed a laser atomic cooling technique which realizes the process Maxwell envisioned of sorting individual atoms in a gas into different containers based on their energy. The new concept is a one-way wall for atoms or molecules that allows them to move in one direction, but not go back. The operation of the one-way wall relies on an irreversible atomic and molecular process of absorption of a photon at a specific wavelength, followed by spontaneous emission to a different internal state. The irreversible process is coupled to a conservative force created by magnetic fields and/or light. Raizen and collaborators proposed using the one-way wall in order to reduce the entropy of an ensemble of atoms. In parallel, Gonzalo Muga and Andreas Ruschhaupt independently developed a similar concept. Their "atom diode" was not proposed for cooling, but rather for regulating the flow of atoms. The Raizen Group demonstrated significant cooling of atoms with the one-way wall in a series of experiments in 2008. Subsequently, the operation of a one-way wall for atoms was demonstrated by Daniel Steck and collaborators later in 2008. Their experiment was based on the 2005 scheme for the one-way wall, and was not used for cooling. The cooling method realized by the Raizen Group was called "single-photon cooling", because only one photon on average is required in order to bring an atom to near-rest. This is in contrast to other laser cooling techniques which use the momentum of the photon and require a two-level cycling transition.
2009年，Mark g. Raizen 开发了一种激光原子冷却技术，该技术实现了麦克斯韦设想的基于能量将气体中的单个原子分类放入不同容器的过程。新概念是原子或分子的单向墙，允许它们朝一个方向运动，但不能回头。单向壁的操作依赖于一个不可逆的原子和分子过程，即在一个特定波长处吸收一个光子，然后吸收一个自发发射到另一个内部状态。不可逆性与磁场和/或光产生的保守力相耦合。Raizen 和他的合作者提出使用单向壁来减少原子团体的熵。与此同时，Gonzalo Muga 和 Andreas Ruschhaupt 独立地提出了一个类似的概念。他们的“原子二极管”不是用来冷却的，而是用来调节原子的流动。在2008年的一系列实验中，Raizen 团队证明了单向壁对原子的冷却作用。随后，丹尼尔 · 斯特克和合作者在2008年晚些时候演示了单向原子墙的操作。他们的实验是基于2005年的单向墙计划，并没有用于冷却。Raizen 群实现的冷却方法被称为“单光子冷却” ，因为平均只需要一个光子就可以使原子接近静止。这与其他利用光子动量需要两能级循环跃迁的激光冷却技术形成了鲜明的对比。
| isbn = 978-4431541677
}}</ref> Both parts are filled with the same [[gas]] at equal temperatures and placed next to each other. Observing the [[molecule]]s on both sides, an imaginary [[Demon (thought experiment)|demon]] guards a trapdoor between the two parts. 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''. Likewise, when a slower-than-average molecule from ''B'' flies towards the trapdoor, the demon will let it pass from ''B'' to ''A''. The average [[speed]] of the molecules in ''B'' will have increased while in ''A'' they will have slowed down on average. Since average molecular speed corresponds to temperature, the temperature decreases in ''A'' and increases in ''B'', contrary to the second law of thermodynamics. A [[heat engine]] operating between the thermal reservoirs ''A'' and ''B'' could extract useful [[work (physics)|work]] from this temperature difference.
In 2006, Raizen, Muga, and Ruschhaupt showed in a theoretical paper that as each atom crosses the one-way wall, it scatters one photon, and information is provided about the turning point and hence the energy of that particle. The entropy increase of the radiation field scattered from a directional laser into a random direction is exactly balanced by the entropy reduction of the atoms as they are trapped by the one-way wall.
2006年，Raizen，Muga，和 Ruschhaupt 在一篇理论论文中指出，当每个原子穿过单向墙时，它散射一个光子，并提供了关于转折点的信息，从而得出该粒子的能量。定向激光向随机方向散射的辐射场的熵增与被单向壁俘获的原子的熵减成正比。
The demon must allow molecules to pass in both directions in order to produce only a temperature difference; one-way passage only of faster-than-average molecules from ''A'' to ''B'' will cause higher temperature and pressure to develop on the ''B'' side.
This technique is widely described as a "Maxwell's demon" because it realizes Maxwell's process of creating a temperature difference by sorting high and low energy atoms into different containers. However, scientists have pointed out that it is not a true Maxwell's demon in the sense that it does not violate the second law of thermodynamics; it does not result in a net decrease in entropy Only a year later and based on an earlier theoretical proposal, the same group presented the first experimental realization of an autonomous Maxwell's demon, which extracts microscopic information from a system and reduces its entropy by applying feedback. The demon is based on two capacitively coupled single-electron devices, both integrated on the same electronic circuit. The operation of the demon is directly observed as a temperature drop in the system, with a simultaneous temperature rise in the demon arising from the thermodynamic cost of generating the mutual information. In 2016, Pekola et al. demonstrated a proof-of-principle of an autonomous demon in coupled single-electron circuits, showing a way to cool critical elements in a circuit with information as a fuel. Pekola et al. have also proposed that a simple qubit circuit, e.g., made of a superconducting circuit, could provide a basis to study a quantum Szilard's engine.
这种技术被广泛地描述为“麦克斯韦魔鬼” ，因为它实现了麦克斯韦通过将高能和低能原子分类到不同的容器中产生温差的过程。然而，科学家已经指出，它不是一个真正的麦克斯韦恶魔，因为它没有违反热力学第二定律; 它不会导致熵的净减少。Demon 是基于集成在同一电路上的两个电容耦合的单电子器件。恶魔的运行被直接观察为系统中的温度下降，同时由于产生互信息的热力学成本而引起的恶魔中的温度上升。2016年，Pekola 等人。证明了在耦合的单电子电路中存在一个自主魔鬼的原理，展示了一种以信息为燃料冷却电路中关键元件的方法。等人。也提出了一个简单的量子比特电路，例如，由超导电路制成，可以为研究西拉德的量子引擎提供基础。
== Criticism and development ==
Several physicists have presented calculations that show that the [[second law of thermodynamics]] will not actually be violated, if a more complete analysis is made of the whole system including the demon.<ref name="Bennett87" /><ref name="Sagawa" /><ref name="BennettSchumacher">{{cite journal
Daemons in computing, generally processes that run on servers to respond to users, are named for Maxwell's demon.
计算机中的守护进程，通常是运行在服务器上响应用户的进程，以麦克斯韦恶魔的名字命名。
| last1 = Bennett
| first1 = Charles H.
Historian Henry Brooks Adams in his manuscript The Rule of Phase Applied to History attempted to use Maxwell's demon as a historical metaphor, though he misunderstood and misapplied the original principle. Adams interpreted history as a process moving towards "equilibrium", but he saw militaristic nations (he felt Germany pre-eminent in this class) as tending to reverse this process, a Maxwell's demon of history. Adams made many attempts to respond to the criticism of his formulation from his scientific colleagues, but the work remained incomplete at Adams' death in 1918. It was only published posthumously.
亨利·亚当斯在他的手稿《历史的阶段法则》中试图用麦克斯韦的恶魔作为历史隐喻，尽管他误解和误用了最初的原则。亚当斯将历史解释为一个走向“均衡”的过程，但他认为军国主义国家(他认为德国在这个阶层中处于领先地位)倾向于逆转这一过程，这是麦克斯韦的历史魔鬼。亚当斯曾多次尝试回应他的科学同事对他的公式的批评，但在1918年亚当斯去世时，这项工作仍未完成。这本书是死后才出版的。
| last2 = Schumacher
| first2 = Benjamin
| title = Maxwell's demons appear in the lab
| journal = Nikkei Science
| volume =
| issue =
| pages = 3–6
| date = August 2011
| url = http://www.nikkei-science.com/wp-content/uploads/2011/08/201108_032.pdf
| issn =
| doi =
| id =
| accessdate = November 13, 2014}}</ref> The essence of the physical argument is to show, by calculation, that any demon must "generate" more entropy segregating the molecules than it could ever eliminate by the method described. That is, it would take more thermodynamic work to gauge the speed of the molecules and selectively allow them to pass through the opening between ''A'' and ''B'' than the amount of [[energy]] gained by the difference of temperature caused by doing so.
One of the most famous responses to this question was suggested in 1929 by [[Leó Szilárd]],<ref name="Szilard">{{cite journal
| last = Szilard
| first = Leo
| title = Über die Entropieverminderung in einem thermodynamischen System bei Eingriffen intelligenter Wesen (On the reduction of entropy in a thermodynamic system by the intervention of intelligent beings)
| journal = Zeitschrift für Physik
| volume = 53
| issue = 11–12
| pages = 840–856
| date = 1929
| url =
| issn =
| doi = 10.1007/bf01341281
| id =
| accessdate = |bibcode = 1929ZPhy...53..840S | s2cid = 122038206
}} cited in Bennett 1987. English translation available as [http://aurellem.org/jaynes/sources/Szilard.pdf NASA document TT F-16723] published 1976</ref> and later by [[Léon Brillouin]].<ref name="Bennett87" /><ref name="Sagawa" /> 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. Since the demon and the gas are interacting, we must consider the total entropy of the gas and the demon combined. The expenditure of energy by the demon will cause an increase in the entropy of the demon, which will be larger than the lowering of the entropy of the gas.
In 1960, [[Rolf Landauer]] raised an exception to this argument.<ref name="Bennett87" /><ref name="Sagawa" /><ref name="Landauer">{{cite journal
| last = Landauer
| first = R.
| title = Irreversibility and heat generation in the computing process
| journal = IBM Journal of Research and Development
| volume = 5
| issue = 3
| pages = 183–191
| date = 1961
| url = http://www.pitt.edu/~jdnorton/lectures/Rotman_Summer_School_2013/thermo_computing_docs/Landauer_1961.pdf
| issn =
| doi = 10.1147/rd.53.0183
| id =
| accessdate = November 13, 2014}} reprinted in [http://domino.research.ibm.com/tchjr/journalindex.nsf/c469af92ea9eceac85256bd50048567c/8a9d4b4e96887b8385256bfa0067fba2?OpenDocument Vol. 44, No. 1, January 2000, p. 261]</ref> He realized that some measuring processes need not increase thermodynamic entropy as long as they were [[Reversible process (thermodynamics)|thermodynamically reversible]]. He suggested these "reversible" measurements could be used to sort the molecules, violating the Second Law. However, due to [[Entropy in thermodynamics and information theory|the connection between]] thermodynamic entropy and [[information entropy]], this also meant that the recorded measurement must not be erased. In other words, to determine whether to let a molecule through, the demon must acquire information about the state of the molecule and either discard it or store it. Discarding it leads to immediate increase in entropy but the demon cannot store it indefinitely. In 1982, [[Charles H. Bennett (computer scientist)|Charles Bennett]] showed that, however well prepared, eventually the demon will run out of information storage space and must begin to erase the information it has previously gathered.<ref name="Sagawa" /><ref name="Bennett82">{{Cite journal | last1 = Bennett | first1 = C. H. | title = The thermodynamics of computation—a review | doi = 10.1007/BF02084158 | journal = International Journal of Theoretical Physics | volume = 21 | issue = 12 | pages = 905–940 | year = 1982 | pmid = | pmc = | bibcode = 1982IJTP...21..905B | url = http://hexagon.physics.wisc.edu/teaching/2014f+ph805+quantum+information/papers/bennett+thermodynamics+of+computation+ijtp+1982.pdf | type = Submitted manuscript | citeseerx = 10.1.1.655.5610 | s2cid = 17471991 | access-date = 2017-12-10 | archive-url = https://web.archive.org/web/20141014151011/http://hexagon.physics.wisc.edu/teaching/2014f%20ph805%20quantum%20information/papers/bennett%20thermodynamics%20of%20computation%20ijtp%201982.pdf | archive-date = 2014-10-14 | url-status = dead }}</ref> Erasing information is a thermodynamically irreversible process that increases the entropy of a system. Although Bennett had reached the same conclusion as Szilard's 1929 paper, that a Maxwellian demon could not violate the second law because entropy would be created, he had reached it for different reasons. Regarding [[Landauer's principle]], the minimum energy dissipated by deleting information was experimentally measured by Eric Lutz ''et al.'' in 2012. Furthermore, Lutz ''et al.'' confirmed that in order to approach the Landauer's limit, the system must asymptotically approach zero processing speed.<ref>{{cite journal |doi=10.1038/nature.2012.10186 |title=The unavoidable cost of computation revealed |journal=Nature |year=2012 |last1=Ball |first1=Philip |s2cid=2092541 }}</ref>
[[John Earman]] and John D. Norton have argued that Szilárd and Landauer's explanations of Maxwell's demon begin by assuming that the [[second law of thermodynamics]] cannot be violated by the demon, and derive further properties of the demon from this assumption, including the necessity of consuming energy when erasing information, etc.<ref>{{cite journal |author1=John Earman |author2=John D. Norton |name-list-style=amp |year=1998 |title=Exorcist XIV: The Wrath of Maxwell's Demon. Part I. From Maxwell to Szilard|url=http://www.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist1.pdf|journal=Studies in History and Philosophy of Modern Physics|pages=435|volume=29 |issue=4 |doi=10.1016/s1355-2198(98)00023-9|bibcode=1998SHPMP..29..435E}}</ref><ref>{{cite journal |author1=John Earman |author2=John D. Norton |name-list-style=amp |year=1999 |title=Exorcist XIV: The Wrath of Maxwell's Demon. Part II. From Szilard to Landauer and Beyond |url=http://www.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist2.pdf|journal=Studies in History and Philosophy of Modern Physics|pages=1|volume=30 |issue=1 |doi=10.1016/s1355-2198(98)00026-4|bibcode=1999SHPMP..30....1E}}</ref> It would therefore be circular to invoke these derived properties to defend the second law from the demonic argument. Bennett later acknowledged the validity of Earman and Norton's argument, while maintaining that [[Landauer's principle]] explains the mechanism by which real systems do not violate the second law of thermodynamics.<ref>{{cite journal |author=Charles H. Bennett |year=2002–2003 |title=Notes on Landauer's principle, reversible computation, and Maxwell's demon |journal=Studies in History and Philosophy of Modern Physics |volume=34 |issue=3 |pages=501–510 |arxiv=physics/0210005 |bibcode = 2003SHPMP..34..501B |doi=10.1016/S1355-2198(03)00039-X |s2cid=9648186 }}</ref>
== Recent progress ==
Although the argument by Landauer and Bennett only answers the consistency between the second law of thermodynamics and the whole cyclic process of the entire system of a [[Szilard engine]] (a composite system of the engine and the demon), a recent approach based on the [[non-equilibrium thermodynamics]] for small fluctuating systems has provided deeper insight on each information process with each subsystem. From this viewpoint, the measurement process is regarded as a process where the correlation ([[mutual information]]) between the engine and the demon increases, and the feedback process is regarded as a process where the correlation decreases. If the correlation changes, thermodynamic relations as the second law of thermodynamics and the [[fluctuation theorem]] for each subsystem should be modified, and for the case of external control a second-law like inequality<ref>{{cite journal |author1=Hugo Touchette |author2=Seth Lloyd |name-list-style=amp |year=2000 |title=Information-Theoretic Limits of Control |journal=Physical Review Letters |volume=84 |issue=6 |pages=1156–1159 |doi=10.1103/PhysRevLett.84.1156|bibcode = 2000PhRvL..84.1156T |pmid=11017467|arxiv=chao-dyn/9905039 }}</ref> and a generalized fluctuation theorem<ref>{{cite journal |author1=Takahiro Sagawa |author2=Masahito Ueda |name-list-style=amp |year=2010 |title=Generalized Jarzynski Equality under Nonequilibrium Feedback Control |journal=Physical Review Letters |volume=104 |issue=9 |pages=090602 |doi=10.1103/PhysRevLett.104.090602|pmid=20366975 |arxiv = 0907.4914 |bibcode = 2010PhRvL.104i0602S |s2cid=1549122 }}</ref> with mutual information are satisfied. These relations suggest that we need extra thermodynamic cost to increase correlation (measurement case), and in contrast we can apparently violate the second law up to the consumption of correlation (feedback case). For more general information processes including biological information processing, both inequality<ref>{{cite journal |author=Armen E Allahverdyan, Dominik Janzing and Guenter Mahler |year=2009 |title=Thermodynamic efficiency of information and heat flow |journal=Journal of Statistical Mechanics |volume=2009 |issue=9 |pages=P09011 |doi=10.1088/1742-5468/2009/09/P09011|arxiv = 0907.3320 |bibcode = 2009JSMTE..09..011A |s2cid=118440998 }}</ref> and equality<ref>{{cite journal |author1=Naoto Shiraishi |author2=Takahiro Sagawa |name-list-style=amp |year=2015 |title=Fluctuation theorem for partially masked nonequilibrium dynamics |journal=Physical Review E |volume=91 |issue=1 |pages=012130 |doi=10.1103/PhysRevE.91.012130|pmid=25679593 |arxiv = 1403.4018 |bibcode = 2015PhRvE..91a2130S |s2cid=1805888 }}</ref> with mutual information hold.
== Applications ==
Real-life versions of Maxwellian demons occur, but all such "real demons" or [[molecular demon]]s have their entropy-lowering effects duly balanced by increase of entropy elsewhere.<ref>{{Cite book|title=Physics in mind : a quantum view of the brain|last=R.|first=Loewenstein, Werner|isbn=9780465029846|location=New York|oclc=778420640|date = 2013-01-29}}</ref> Molecular-sized mechanisms are no longer found only in biology; they are also the subject of the emerging field of [[nanotechnology]]. Single-atom traps used by particle physicists allow an experimenter to control the state of individual quanta in a way similar to Maxwell's demon.
If hypothetical [[mirror matter]] exists, Zurab Silagadze proposes that demons can be envisaged, "which can act like perpetuum mobiles of the second kind: extract heat energy from only one reservoir, use it to do work and be isolated from the rest of ordinary world. Yet the Second Law is not violated because the demons pay their entropy cost in the hidden (mirror) sector of the world by emitting mirror photons."<ref>{{Cite journal|arxiv=physics/0608114 |title=Maxwell's demon through the looking glass |journal=Acta Physica Polonica B |volume=38 |issue=1 |pages=101–126 |year=2007 |last1=Silagadze |first1=Z. K |bibcode=2007AcPPB..38..101S }}</ref>
Category:Philosophy of thermal and statistical physics
类别: 热力学和统计物理学哲学
== Experimental work ==
Category:Concepts in physics
分类: 物理概念
In the February 2007 issue of ''[[Nature (journal)|Nature]]'', [[David Leigh (scientist)|David Leigh]], a professor at the [[University of Edinburgh]], announced the creation of a nano-device based on the [[Brownian ratchet]] popularized by [[Richard Feynman]]. Leigh's device is able to drive a chemical system out of [[Chemical equilibrium|equilibrium]], but it must be powered by an external source ([[light]] in this case) and therefore does not violate thermodynamics.<ref>{{cite journal | doi = 10.1038/nature05452 | volume=445 | issue=7127 | title=A molecular information ratchet | journal=Nature | pages=523–527 | pmid=17268466 | date=February 2007 | last1 = Serreli | first1 = V | last2 = Lee | first2 = CF | last3 = Kay | first3 = ER | last4 = Leigh | first4 = DA| bibcode=2007Natur.445..523S | s2cid=4314051 }}</ref>
Category:Nanotechnology
类别: 纳米技术
Category:James Clerk Maxwell
类别: 詹姆斯·克拉克·麦克斯韦
Previously, researchers including Nobel Prize winner [[Fraser Stoddart]], created ring-shaped molecules called [[rotaxane]]s which could be placed on an axle connecting two sites, ''A'' and ''B''. Particles from either site would bump into the ring and move it from end to end. If a large collection of these devices were placed in a system, half of the devices had the ring at site ''A'' and half at ''B'', at any given moment in time.<ref>{{cite journal|last1=Bissell|first1=Richard A|last2=Córdova|first2=Emilio|last3=Kaifer|first3=Angel E.|last4=Stoddart|first4=J. Fraser|title=A chemically and electrochemically switchable molecular shuttle|journal=Nature|date=12 May 1994|volume=369|issue=6476|pages=133–137|doi=10.1038/369133a0|bibcode=1994Natur.369..133B|s2cid=44926804}}</ref>
Category:Fictional demons and devils
类别: 虚构的魔鬼和魔鬼
Category:Thought experiments in physics
类别: 物理学思维实验
Leigh made a minor change to the axle so that if a light is shone on the device, the center of the axle will thicken, restricting the motion of the ring. It only keeps the ring from moving, however, if it is at ''A''. Over time, therefore, the rings will be bumped from ''B'' to ''A'' and get stuck there, creating an imbalance in the system. In his experiments, Leigh was able to take a pot of "billions of these devices" from 50:50 equilibrium to a 70:30 imbalance within a few minutes.<ref>{{cite journal |author=Katharine Sanderson |date=31 January 2007 |title=A demon of a device |journal=[[Nature (journal)|Nature]] |doi=10.1038/news070129-10 |s2cid=121130699 }}</ref>
Category:Perpetual motion
类别: 永动机
Category:1867 introductions
类别: 1867年引言
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<small>This page was moved from [[wikipedia:en:Maxwell's demon]]. Its edit history can be viewed at [[麦克斯韦妖/edithistory]]</small></noinclude>
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