Is it possible to violate the second law of thermodynamics?
In science, as in fiction, there are fantastic characters. Perhaps most of them were invented during the discussion of the second law of thermodynamics. The most popular of them was Maxwell's demon, which was invented by James Clerk Maxwell, the author of the famous system of Maxwell's equations, which completely describes electromagnetic fields. The second law (or law) of thermodynamics has many formulations, the physical meaning of which, however, is identical: an isolated system cannot spontaneously transition from a less ordered state to a more ordered one. Thus, a gas consisting of molecules moving at different speeds cannot spontaneously split into two parts, in one of which molecules moving, on average, faster than the average statistical speed, and in the other - slower.
Many physical processes fall into the category reversible. Water, for example, can be frozen, and the resulting ice can be melted again, and we will get water in the same volume and condition; iron can be magnetized and then demagnetized, etc. In this case, the entropy (degree of order) of the system at the starting and ending points of the process remains unchanged. There are also processes that are irreversible in the thermodynamic sense - combustion, chemical reactions, etc. That is, according to the second law of thermodynamics, any process ultimately leads to either maintaining or reducing the degree of order of the system. This disharmonious situation greatly puzzled physicists in the second half of the 19th century, and then Maxwell proposed a paradoxical solution that would seemingly allow one to circumvent the second law of thermodynamics and reverse the steady growth of chaos in a closed system. He proposed the following “thought experiment”: imagine a sealed container divided in two by a gas-tight partition, in which there is a single door the size of a gas atom. At the beginning of the experiment, the upper part of the container contains gas, and the lower part contains complete vacuum.
Now let’s imagine that a certain microscopic watchman is assigned to the door, vigilantly monitoring the molecules. He opens the door for fast molecules and lets them through the partition, into the lower half of the container, and leaves slow ones in the upper half. It is clear that if such a mini-watchman is on duty at the door long enough, the gas will split into two halves: in the upper part there will be a cold gas consisting of slow molecules, and in the lower part a hot gas of fast molecules will accumulate. Thus, the system will be ordered in comparison with the initial state, and the second law of thermodynamics will be violated. Moreover, the temperature difference can be used to obtain work ( cm. Cycle and Carnot's theorem). If such a watchman is left on duty forever (or a shift is organized), we will get a perpetual motion machine.
This funny watchman, who was nicknamed “Maxwell’s Demon” by the scientist’s witty colleagues, still lives in scientific folklore and excites the minds of scientists. Indeed, a perpetual motion machine would not harm humanity, but here’s the problem: apparently, for Maxwell’s demon to work, it itself will need energy supply in the form of an influx of photons necessary to illuminate approaching molecules and sift them. In addition, when sifting through molecules, the demon and the door cannot help but interact with them, as a result of which they themselves will steadily receive thermal energy from them and increase their entropy, as a result of which the total entropy of the system will still not decrease. That is, with this explanation, the theoretical threat to the second law of thermodynamics was averted, but not unconditionally.
The first truly convincing counterargument was formulated shortly after the birth of quantum mechanics. To sort the approaching molecules, the demon needs to measure their speed, but he cannot do this with sufficient accuracy due to the Heisenberg uncertainty principle. In addition, due to the same principle, he cannot accurately determine the location of the molecule in space, and some of the molecules in front of which he opens the microscopic door will miss the door. In other words, Maxwell's demon turns out to be a macroscopic bull in a microcosm china shop, which lives according to its own laws. Bring the demon into conformity with the laws of quantum mechanics, and it will be unable to sort gas molecules and will simply cease to pose any threat to the second law of thermodynamics.
Another compelling argument against the possibility of the existence of a demon watchman appeared already in the computer era. Let's assume that Maxwell's demon is a computer automated door-opening control system. The system performs bit-by-bit processing of incoming information about the speed and coordinates of approaching molecules. Having passed or rejected a molecule, the system must reset the previous ordered information - and this is equivalent to an increase in entropy by an amount equal to the decrease in entropy as a result of gas ordering when passing or rejecting a molecule, information about which has been erased from the computer demon's RAM. The computer itself, moreover, also heats up, so that in such a model in a closed system consisting of a gas chamber and an automated access system, entropy does not decrease, and the second law of thermodynamics is satisfied.
It's a pity for the demon - he was a nice character.
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An amazingly helpless explanation for the impossibility of Maxwell's Demon!
The argument about the quantum uncertainty of the world is used as an argument! Consequently, the author has no arguments against the impossibility of the existence of a demon in a model thermodynamic world consisting only of mechanical particles. After all, if the world consists of mechanical particles, it makes no sense to say that the demon will “heat up”, that he needs to “illuminate” the particles in order to determine whether to open the partition, etc.
The simple idea that a mechanical demon does not need to illuminate or otherwise interact with particles did not occur to the professor. The demon can, knowing the initial momenta and coordinates of all particles in the vessel, simply calculate the moments when a fast particle flies up to the partition and open it. Moreover, during elastic collisions no heating occurs; accordingly, the entropy of the demon does not increase.
In general, the root of the professor’s difficulties and all of modern physics is unclear ideas about entropy. Physicists insist that this is an objective category, while its definition includes the subjective concept of “disorder,” “measure of disorder.” There is no objective measure of disorder.
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> An explanation astounding in its helplessness... the argument about the quantum uncertainty of the world is invoked!
You may think the explanation is helpless, but that doesn’t change the fact that it is correct. The impossibility of Maxwell's demon is directly related to quantum uncertainty.
> The demon can, knowing the initial impulses and coordinates of all particles in the vessel, simply calculate the moments when a fast particle flies up to the partition and open it.
The demon cannot know anything like that. AND main reason Here it is precisely quantum uncertainty. But even without it, in a purely mechanical world, accurate prediction of the trajectories of molecular motion turns out to be impossible due to the effect of exponential divergence of trajectories, which is studied in the theory of mathematical billiards. An arbitrarily small error in knowledge of the initial positions exceeds any given value in a short time.
There is another reason. In order for a demon to track all the positions of molecules, it must have sufficient memory and be able to change its contents based on the results of its influence on the molecules. Memory is a physical device and has entropy. Calculations show that the entropy accumulated by this memory just compensates (or exceeds) its decrease in the gas. (All the calculations were given in one of the articles in the journal “In the World of Science” back in the 1980s, but I can’t give a link now.)
> In general, the root of the professor’s difficulties and all modern physics is unclear ideas about entropy.
Entropy is indeed a complex concept, but in this particular issue everything is clear with it.
> Physicists insist that this is an objective category, whereas its definition includes the subjective concept of “disorder”, “measure of disorder”.
You are wrong. The _definition_ of entropy does not include the concept of "disorder". It is used only for a popular, and therefore figurative and inaccurate explanation of this concept. Formal definitions of entropy (by the way, there are many of them) do not contain anything like this. Here, for example, are the two most popular definitions from physics:
Entropy is a quantity proportional to the logarithm of the number of microstates that realize one macrostate in which the system under study is located (S = k*ln(W)).
The entropy gain is the energy received by the system divided by the temperature of the system (dS = dQ/T).
You can read more about this, for example, here: http://www.cultinfo.ru/fulltext/1/001/008/126/734.htm. In this rather large encyclopedic article, the “measure of disorder” is mentioned only once, and that was as an explanation for the equation S = k*ln(W).
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>> The impossibility of Maxwell's demon is directly related to quantum uncertainty.... The demon cannot know anything like that. And the main reason here is precisely quantum uncertainty... In order for a demon to track all the positions of molecules, he must have sufficient memory and be able to change its contents based on the results of his influence on the molecules. Memory is a physical device and has entropy.
HaHa. HaHaHa. And the demon also needs arms and legs to open and close this door. And you have to eat... Is it really possible that this riddle is still being solved with such vulgar excuses using clever words like entropy, quantum uncertainty... the memory of a demon (!!!) It’s funny to God.
There is no demon. Let's imagine a room filled with bouncing balls - ideally elastic and not subject to friction (an acceptable mechanical analogy of gas molecules). On one side of the room there is an opening blocked by a barrier of some height. Balls bouncing above this barrier will eventually fly out of the room into the next room, and in the first room only sluggishly bouncing balls will remain. Does the barrier need memory or energy, photons, muons, bosons or synchrophasotrons? Does he need to calculate some kind of entropy or attract astral forces? In order to immediately stop attempts at the topic “fast balls will come back from the next room,” we will make a funnel in the second room through which the balls fly into the third room, and it is difficult for them to fly back.
In electronics, the barrier effect (electrons with energy above a certain value without losses (!) pass the barrier, those without - do not pass, but do not lose energy either) has long been known and is widely used. Look on Google - for general development.
The “paradox” of these balls and, accordingly, Maxwellian vessels is solved very simply - the very fact of sorting the balls is not work. Work is the use (taking) of energy from fastballs. And having once used (taken away) the energy from the ball, we turn it into a slow one - which will no longer jump over the barrier. To continue the cycle, fresh balls are needed from outside.
>>With that said, I recommend that when discussing scientific issues... trust your fantasies a little less.
And I would recommend you not to refer to stupid superstitions just because they contain smart and fashionable words...Answer
In fact, completely closed systems do not exist in nature; this is an abstraction for deriving thermodynamic formulas. And in our reasoning, we don’t even notice how we unintentionally move towards open systems. And in open systems, entropy must be treated as follows from the works of Ilya Prigogine. But that's not the point now.
Maxwell's demon breaks the closedness of the system, even if it sits inside the vessel.
Firstly, it needs an influx of energy to do its work (the batteries need to be charged), and secondly, the information that is embedded in this robot (demon) is also given OUTSIDE, that is, there is an exchange of energy and information with the external environment.
And under these conditions, the work of the demon may well provide a solution to the problem according to Maxwell: the molecules will be distributed according to their velocities. BUT! Thanks to the controlling influence of an external intelligent principle.
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You can come up with a mechanical Maxwell demon that will let through not molecules, but faster small particles in Brownian motion. Then quantum mechanics and thermodynamics do not work, only mechanics, and everything depends on the energy consumption of the demon to fix the particle, close the door, and the speed of the particles themselves, which depends on the temperature of the environment.
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The law of thermodynamics in this mental experiment of Maxwell is really violated (SELF-TRANSITION TO A MORE ORDERED STATE!), but there is no need to fool your head because of the costs of opening and closing and heating the “valve” (let’s say there is this membrane-diode - this is a problem of technology, and not theoretical physics).
So, having sorted the molecules in the manner described above, we get: the temperature of fast molecules is higher than the initial one, BUT THE TEMPERATURE of SLOW molecules is PROPORTIONALLY LOWER. Consequently, the overall orderliness of the system will not change here yet (not counting the costs of the “sorter”). Let's say they are negligible.
Further, by using the energy of fast molecules, for example, to do work, we will thereby lower their temperature, and therefore the overall temperature of the entire system. Having performed these manipulations with the gas a certain number of times, we will eventually approach absolute zero and then the process of extracting energy in this way will become impossible. (So it’s not clear to me what kind of perpetual motion machine we’re talking about in the article). So, we extracted energy, lowered the temperature and greatly increased order? molecules in this system. (They also increased the volume of gas - what’s wrong with the orderliness?).
This means that a closed system can self-cool to 0 (in exchange for releasing an equivalent amount of energy minus the efficiency of the “sorter”), i.e. moving into a more orderly one? (and volume?) state, and SELF-TRANSITION TO A MORE ORDERED STATE is not allowed by the 2nd law of thermodynamics.
It seems to me that the amount of energy that was needed to create the initial conditions was equally released as a result of cooling. But the orderliness (in foreign words, entropy) has not changed - it just seems to be in different units and volumes.
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>>To be fair, it should be said that first it was necessary to spend money (energy) on creating clearly separated vacuum and gas, i.e. the system initially had potential energy and order: (a clear region with gas and vacuum), and as a result, there is gas everywhere, but cold and of a larger volume. And how to measure this orderliness?
Everything is much simpler. Where there is gas, the pressure is above zero. Where there is a vacuum, there is pressure = 0. The pressure difference is potential energy. Temperature difference is also potential energy. We extract them. And don’t worry about the disorder - we do some work at the expense of cooled molecules - this work will create enough entropy to reassure its fans.
>>It seems to me that the amount of energy that was needed to create the initial conditions was equally released as a result of cooling.
Yes, but the nice thing is that it wasn’t us who spent this energy :) If, say, we simply take atmospheric air containing a mass of fairly energetic molecules, divide it with a barrier membrane, use the temperature difference and release cold air back - it will be free (free does not mean “eternal”!) engine. And at the same time, climate cooling is a hit for the countries of Central Africa.Answer
Yes, I don’t argue. Molecules can be divided according to some principle. But this does not mean that their ensemble (fast or slow) under equilibrium conditions (when we can talk about the temperature of the system) will not redistribute velocities among the particles according to the distribution function. And again there will be fast ones and there will be slow ones. Otherwise, we need to talk about a different model of the state of matter.
Funnel - no doubt interesting. But, in my opinion, we should talk, first of all, about the energy funnel - the heat funnel. A mechanical funnel is unlikely to “draw in” particles, except perhaps the substance itself. Those. We must not forget that we are talking about some “representatives” of the ensemble, and not about its deterministic distribution, as, for example, at the interfaces between media. For an individual particle to have speed is not a characteristic, because you need to immediately answer - relative to what this speed is measured.
Once again I want to express my delight at the beauty of the task. And why is it not being resolved? I think that my solution is quite suitable, although not necessarily true.
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But the question is formulated somewhat differently. The "molecular" engine is powered by temperature.
1. Where is the engine of a molecule?
2. Why should there be fast and slow molecules if the temperature is the same?
Because of collisions. Impact - the speed dropped. Warming up - the speed increased.
Well, the Demon collected fast molecules. So the remaining slow ones will accelerate to the speed of the fast ones and the gradient will disappear!
2. Can a person orient molecular “motors” to move in one direction?
Yes, by ionizing the gas and applying a field to it.
3. Is there any other possibility other than electromagnetic field"orient" molecular motors?
Probably the movement of molecules when irradiated with infrared light is caused by the expansion of electron clouds. And the molecules in the gas mass begin to be “pushed” by electron clouds. These “shocks” are probably the reason for the movement of molecules.
If there are few molecules or there is only one molecule, then during infrared irradiation its electron clouds begin to be repelled from the walls of the vessel.
Are there any other considerations?
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There is a problem in physics that can roughly be called the “reversibility-irreversibility” problem, and the thought experiment with Maxwell’s demon is only one of its most striking illustrations. All physical laws, with one exception, are time reversible, and the possibility of realizing Maxwell's demon does not contradict them! An exception is the second law of thermodynamics, which has many different formulations. The simplest of them is that heat cannot spontaneously transfer from a body with more high temperature to a body with a lower temperature. The possibility of the existence of Maxwell's demon contradicts exclusively this law. Thus, any attempt to prove the impossibility of Maxwell's demon that does not explicitly or implicitly use the second law is doomed to failure. It should be noted that all physical laws, including the second law, are a generalization of experimental data.
All these problems can be discussed seriously only with a professional understanding of thermodynamics, statistical physics, quantum statistics, and physical kinetics; future theoretical physicists study this mostly in their undergraduate years for about six semesters. Non-professionals should not take on the solution to this problem - no one is trying to independently calculate the orbits of asteroids or calculate the electronic structure of semiconductors, and this is much simpler.
Some notes for professionals. 1) Entropy can be introduced in a consistent manner only for an equilibrium system, while the second law fundamentally speaks of non-equilibrium processes. 2) Statistical (through statistical weight) and thermodynamic (through heat and temperature) definitions of entropy always coincide. 3) From the quantum mechanical (through the density matrix) definition of entropy it strictly follows that the entropy of a closed system remains unchanged. In general, there are many questions here.
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The author is wrong. History suggests that truly worthwhile discoveries and inventions were made by “non-professionals.” Your so-called professionals are a bunch of idiots and sycophants. Maxwell's demon has existed for a long time. This device, invented in 1931, is called a Ranke-Hilsch tube. It allows you to separate gas or liquid into hot and cold flows using a vortex. Moreover, much more heat is obtained than the energy expended to create the vortex.
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>>heat cannot spontaneously transfer from a body at a higher temperature to a body at a lower temperature. The possibility of the existence of Maxwell's demon contradicts exclusively this law.... Non-professionals should not take on the solution to this problem - no one is trying to independently calculate the orbits of asteroids or calculate the electronic structure of semiconductors, and this is much simpler.
Non-professionals should not take on anything at all - if it requires a professional solution, it is paid for and has an impact on something. But what's wrong with _just chatting on a free forum_ about something not related to your professional competence? It’s unlikely that anyone here seriously thinks that he is “solving” something (except, perhaps, the author of the article;-) And I think someone is also calculating the orbits of asteroids - just in a different thread :)))
Regarding the second law, there is this point: how generally is it correct to identify “the transfer of heat from one body to another” with “the division of one body into components (or two bodies)”?Answer
I completely agree with you. By the way, it will be correct - heat cannot spontaneously transfer from a body with a low temperature to a body with a higher temperature. The exact formulation of the second law belongs to W. Thomson and M. Planck: “In nature, a process is impossible whose full effect would consist only in cooling the heat reservoir and in an equivalent lifting of the load.” But: in nature, Maxwell's demon exists if it is possible to create a diode of molecular dimensions, a molecular diode. Such a diode is capable of converting the thermal movement of electrons into an ordered one, that is, into an electric current. There is also a patent for a gradient tunnel diode with operating frequencies up to the ultraviolet range, which, according to the authors, is capable of converting even thermal fluctuations of electrons into electric current. This is our demon.
Let's set up a thought experiment (like Grandpa Maxwell). We will not divide one body into components, but take an insulated container divided by an impenetrable partition into two reservoirs. In a colder reservoir we place an array of nanorectennas (a rectenna is an antenna with a rectifier), tuned to resonate with the radiation of fast, hot molecules of this reservoir, connect the array with a bridge circuit of demons and - go ahead! We accumulate the resulting constant electric current and send it to a load (resistance) in a hotter tank and heat it to victory (or lift some kind of load). The second law is at rest. A perpetual motion machine of the second kind, of course, cannot be made in this way, since it is impossible to cool the first reservoir indefinitely, but an obvious violation of the second law is visible, isn’t it?Answer
This is not exactly Maxwell’s demon, of course, although the principle “take from the poor and give to the rich” (let’s call it the “inverse Robin Hood principle”) is ideologically close to our demon :)
And here I didn’t quite understand something: these “nanorectennas” - do they allow molecules or electrons to pass through? If molecules, then what kind of electric current are we talking about? And if it’s electrons (or ions in general), then what’s the point of filtering them by speed? a slow electron is also an electron and will produce the same amount of electric current as a fast one. True, this already turns out to be something like a regular electrolyte battery, only instead of electrolyte there is gas (why?). The meaning of the second (hot) tank is not clear to me at all.Further (we proceed from the fact that we are filtering molecules after all and trying to transfer heat and not electrical charge). “we connect the lattice [nanorecten] with the bridge circuit of demons” - so who is rectifying here? Rectennas or demons? if rectennas, then why are demons needed - and vice versa. If the rectennas are straightened, then the demon must sit IN EACH of them, and no additional bridges that straighten the flow from the entire lattice are needed; accordingly, there is no need to consolidate the flows from individual rectennas - that is, we return to the membrane (in which there is simply a “barrier” and "funnel" are combined with the word "rectenna"). If rectennas only filter molecules by speed (in both directions) - then these are no longer “rectennas”, but simply barriers, and all the most complex things (“funnel”) are done centrally. That is, this is simply a constructive difference, and not a fundamental one.
Filtering molecules by speed is not a very difficult task. For example, we take an ionized (say+) gas and a monomolecular similarly charged membrane (for structural rigidity, it can be attached to an easily permeable neutral frame). Only those gas molecules whose kinetic energy will be sufficient to overcome the Coulomb reaction will be able to slip through this membrane. It is important that the breakthrough (or rebound) of the molecule will be absolutely elastic - the extent to which the molecule slows down on approaching the membrane, the same extent it will accelerate upon rebound (from the same or the other side). The threshold of the required kine energy can be adjusted by selecting the size of the membrane cell and the charge on it.
The most difficult thing that can be required of a demon is to send molecules only in one direction. I don’t know how to teach a demon this, but you can make a knight’s move and save him from this work. In principle, it is enough that on one side of the membrane we are guaranteed to have only fast molecules from the original body. Some of them will fly back, but some will remain. Already good. How to use it?
— a thought experiment attempting to test the second law of thermodynamics was successfully implemented by physicists from Chuo University and the University of Tokyo.
The Japanese have created two bonded polystyrene balls, each 0.3 micrometers in diameter. One was on the surface of the glass, the second could rotate around the first. The installation was filled with liquid. Its molecules randomly pushed the balls (Brownian motion), naturally, with equal probability both clockwise and counterclockwise.
Feedback systems, Japanese physicists say, could represent a new type of machine that converts information into energy. Theoretically, in the future, such devices could be powered by Brownian motion of micromachines.
The picture shows conditional diagram experiment. The position of the rotating rotor is replaced here by a ball jumping up the steps randomly. When the ball bounces up, Maxwell's clever demon puts up a barrier to prevent the ball from rolling back down. In this case, the “demon” itself does not push the ball (illustration by Mabuchi Design Office/Yuki Akimoto).
Next, the authors added a weak electric field, which created a torque. It was analogous to a ladder, along which the ball could “climb”, increasing potential energy. Sometimes the molecules pushed the rotor against the action of the field (ascent), sometimes towards the field (jumping down the steps). But in general, the rotor rotated where the external field pushed it.
But physicists added a “demon” - a high-speed camera observing the ball and a computer that controls the field. Every time the rotor took a step against the field in Brownian motion, the computer moved the latter so that the ball could turn, but when the rotor tried to rotate back, the field blocked it.
This is how an analogue of the door opened and closed by Maxwell’s demon was created: the rotor increased its energy due to the thermal movement of molecules.
However, the installation does not violate the laws of nature, since the operation of the “demon” (camera, voltage correction system) requires energy. But the Japanese emphasize: this experiment for the first time in practice proved the reality of a heat pump - Maxwell's demon, theoretically substantiated by Leo Szilard in 1929. Such a machine extracts energy from isothermal environment and transforms it into work.
General principle heat pump – Maxwell's demon (“Szilard engine”). A macroscopic system (computer) controls events in a microscopic system (in reality - a rotor and a field, but conditionally - a room with molecules and a partition) by receiving information about it. Energy in a microscopic system increases (and can produce useful work), but not completely free, since the “demon” consumes energy to obtain information and control actions (illustration by Shoichi Toyabe, Eiro Muneyuki, Masaki Sano/Nature Physics).
Answered by leading researcher at the Laboratory of Quantum Information Theory of MIPT and the Institute of Theoretical Physics named after L.D. Landau RAS Gordey Lesovik:
— According to one of the formulations of the second law of thermodynamics, heat moves from a hot body to a cold one. This is a common and understandable phenomenon. But if you launch Maxwell’s Demon into a closed system (it is believed that it increases the degree of order in the system), then it is capable of disrupting the natural order of things, and eliminating disorder, if you like. It will reflect high-energy atoms or molecules, change flows and thereby launch completely different processes within the system. A similar process can be accomplished using our quantum device.
Schematic representation of Maxwell's demon. Photo: Commons.wikimedia.org
We have shown that although quantum mechanics, in general, precisely ensures this very classical law of thermodynamics and ensures the natural order of things, it is possible to artificially create conditions under which this process can be disrupted. That is, now Maxwell’s Quantum Demon - in other words, an artificial atom (it is usually called a qubit, i.e. a quantum bit) is capable of making sure that heat is transferred from a cold object to a hot object, and not vice versa. This is the main news in our work.
In the near future, we plan to create a quantum refrigerator in which we will experimentally reverse natural heat flows. At the same time, our superfridge will not be able to expend energy on transformations itself, but (in a sense) extract it from a source that can be located a few meters away from it. From this point of view, our quantum refrigerator will be (locally) absolutely energy efficient. To avoid misunderstandings, it is important to emphasize that when a remote source of energy is taken into account, the validity of the second law of thermodynamics is restored, and the world order as a whole will not be disrupted.
Regarding the scope of application of Maxwell's Quantum Demon, i.e. our device, then first of all this is, of course, the field of quantum mechanics. Well, for example, a regular computer often heats up during operation, the same thing happens with quantum devices, only there these processes are even more critical for normal operation. We will be able to cool them or some individual microchips. Now we are learning to do this with close to 100% efficiency.
And, of course, such experiments will make it possible in the future to talk about the creation of a perpetual motion machine of the second type. No batteries will be required, the engine will be able to extract energy from the nearest thermal reservoir and use it to move some nanodevices.
A perpetual motion machine of the second kind is a machine that, when put into motion, would convert into work all the heat extracted from the surrounding bodies. According to the laws of thermodynamics, it is still considered an unfeasible idea.
Physicists from Finland, Russia and the USA have pioneered Maxwell's autonomous electron demon. The authors published the results of their research in the journal Physical Review Letters. What are Maxwell's demons and how they can interfere with the operation of computers, says Lenta.ru.
The intrigue around Maxwell's demons has persisted in science for 150 years. The concept of a supernatural being was proposed in 1867 by British physicist James Clerk Maxwell. We are talking about a certain device that functions in such a way that it leads to a violation (apparently) of the second law of thermodynamics - one of the most fundamental laws of nature.
In his thought experiment, Maxwell took a closed gas cylinder and divided it into two parts with an inner wall with a small hatch. By opening and closing the hatch, Maxwell's demon separates fast (hot) and slow (cold) particles. As a result, a temperature difference arises in the cylinder, and heat is transferred from a colder gas to a hotter one, which would seem to contradict the second law of thermodynamics.
The second law of thermodynamics determines the direction of physical processes. In particular, as the German physicist Rudolf Clausius showed, it makes impossible the spontaneous transfer (that is, without doing work) of heat from a colder body to a hotter one or, what is the same thing, a decrease in the entropy (a measure of disorder) of an isolated system. In the formulation of the Frenchman Sadi Carnot, this law sounds like this: a heat engine with a coefficient useful action one hundred percent impossible.
The second law of thermodynamics was finally formulated in the 19th century. Then it was a law for a number of special cases (its fundamental nature became clearer later). Physicists looked for contradictions in it, and one of them (along with the thermal death of the Universe) was presented by Maxwell in a letter to his colleague Peter Tate.
The paradox immediately attracted the attention of scientists and science lovers. In the 20th century, the fame of Maxwell's demon was eclipsed by Schrödinger's cat (or cat). Meanwhile, like a pet from quantum mechanics, the British physicist's demon served as the source of many important discoveries. In particular, thanks to him, the thermodynamic theory of information and the related idea of information entropy arose.
In the 1960s, Rolf Landauer, a researcher at the American company IBM (International Business Machines), formulated the principle that bears his name. He connected the loss of a bit of information in any physical system with the release of a corresponding amount of heat (or, what is the same, an increase in thermodynamic entropy). Landauer's work had fundamental significance for computing that continues to this day. The expression, named after Landauer, as well as the Americans Claude Shannon and John von Neumann, allows one to determine the limit physical characteristics devices (primarily its power and size) in which information is destroyed. Man-made processors have gone from dissipating billions of times more heat than predicted by Landauer's principle to today's only thousands of times more.
Let there be a memory cell containing information encoded in bits (with values zero and one). If you destroy it (that is, transform it into a state containing only zeros or ones), heat will be released. In the language of thermodynamics, this means that the entropy of the system turns to zero, since the maximum ordered state (described only by zeros or ones) has been achieved. Landauer liked to repeat that “information is a physical quantity,” this was his motto.
For the first time, scientists from France and Germany measured the heat released when a bit of information is destroyed. The memory cell was a quartz bead with a diameter of two micrometers placed in water. Using optical tweezers, physicists created a pair of potential holes in which the bead could end up. These system states corresponded to the logical values zero and one. When the system was transferred to one state, the information was erased. The machine took into account many nuances, in particular fluctuations, whose role grew along with the decrease in the depth of the pits. Using Rapid, physicists observed the transition of a system from one state to another. The process was accompanied by heat release, the water temperature increased, and this was recorded. The data obtained turned out to be close to those predicted by Landauer's principle.
But what does Maxwell's demon have to do with it? The fact is that when sorting hot and cold molecules in Maxwell's thought experiment, the demon accumulates information about the velocities of the particles. At some point, the memory becomes full, and the daemon needs to erase it to continue working. This requires doing work exactly equal to the work that could theoretically be extracted from a system of hot and cold particles. That is, the second law of thermodynamics is not violated. However, a metaphysical question arises about the entity erasing the demon's memory. Could she be some kind of super demon influencing a minor demon? The answer to this question was first proposed in 1929 by one of the participants in the Manhattan Project, American physicist Leo Szilard. The device named after him provides Maxwell's demon with autonomous operation.
Japanese scientists managed to implement it for the first time in 2010. Their electromechanical model is a polystyrene bead with a diameter of about 300 nanometers placed in an electrolyte. The electromagnetic field prevented the bead from moving downwards, as a result of which it gained mechanical (potential) energy proportional to the work of the field. Maxwell's demon in such a system was the observer and his scientific instruments, the functioning of which requires energy. The latter circumstance again does not allow one to violate the second law of thermodynamics. Unlike Japanese scientists, their colleagues from Finland, Russia (Ivan Khaimovich from the Institute of Physics of Microstructures of the Russian Academy of Sciences) and the USA for the first time created not an electromechanical, but a completely electronic Szilard machine (Maxwell's autonomous demon).
The system is based on a single-electron transistor, which forms a small copper island connected to two superconducting aluminum terminals. Maxwell's demon controls the movement of electrons of different energies in a transistor. When the particle is on the island, the demon attracts it with a positive charge. If an electron leaves the island, the demon repels it with a negative charge, which causes the transistor's temperature to drop and the demon's temperature to rise.
The demon performs all manipulations autonomously (its behavior is determined by the transistor), and temperature changes indicate a correlation between it and the system, so it looks as if Maxwell's demon knows about the state of the system and is able to control it. The electronic demon makes it possible to carry out a large number of measurements in a short period of time, and low temperatures in the system make it possible to record extremely small changes in it. This system also does not violate the second law of thermodynamics and is consistent with the intuitive idea that information can be used to do work.
Why do scientists need such research? On the one hand, they are of clear academic interest, since they allow the study of microscopic phenomena in thermodynamics. On the other hand, they show how important the production of entropy is from the information received by the demon. This is precisely what the authors of the study believe can be useful for the design of qubits (quantum analogues of classical bits) of quantum computers, even despite the emerging progress in reversible computing, a story about which is beyond the scope of this article.
The thought experiment is as follows: suppose a vessel with a gas is divided by an impenetrable partition into two parts: right and left. In the partition there is a hole with a device (the so-called Maxwell's demon), which allows fast (hot) gas molecules to fly only from the left side of the vessel to the right, and slow (cold) molecules only from the right side of the vessel to the left. Then, after a long period of time, the “hot” (fast) molecules will end up in the right vessel, and the “cold” ones will “remain” in the left one.
Thus, it turns out that Maxwell’s demon allows you to heat the right side of the vessel and cool the left without additional energy supply to the system. The entropy for a system consisting of the right and left parts of the vessel is greater in the initial state than in the final state, which contradicts the thermodynamic principle of non-decreasing entropy in closed systems (see the Second Law of Thermodynamics)
The paradox is resolved if we consider a closed system that includes Maxwell's demon and the vessel. For Maxwell's demon to function, energy must be transferred to it from a third-party source. Due to this energy, the separation of hot and cold molecules in the vessel occurs, that is, the transition to a state with lower entropy. A detailed analysis of the paradox for the mechanical implementation of the demon (ratchet and pawl) is given in the Feynman Lectures on Physics, vol. 4, as well as in Feynman's popular lectures "The Nature of Physical Laws."
With the development of information theory, it was found that the measurement process may not lead to an increase in entropy, provided that it is thermodynamically reversible. However, in this case, the demon must remember the results of measuring speeds (erasing them from the demon’s memory makes the process irreversible). Since memory is finite, at a certain point the demon is forced to erase old results, which ultimately leads to an increase in the entropy of the entire system as a whole.
The success of Japanese physicists
For the first time, Japanese physicists were able to experimentally achieve an increase in the internal energy of a system, using only information about its state and without transferring additional energy to it.
The generation of energy from information was first theoretically described by British physicist James Maxwell in his thought experiment. In it, a creature, later called "Maxwell's demon", guarded the door between two rooms. The demon, knowing the energy of the molecule approaching the door, opens the passage only for “fast” molecules, closing the door in front of “slow” ones. As a result, all the “fast” molecules will be in one room, and all the slow ones in the other, and the resulting temperature difference can be used for practical purposes.
The implementation of such a “demonic” power plant requires much greater energy costs than can be extracted from the resulting temperature difference, so real engines operating on this principle have never been seriously considered by scientists. However, interest in such systems has resurfaced recently with the development of nanotechnology.
The authors of the study, Japanese physicists led by Masaki Sano from the University of Tokyo, put into practice a thought experiment involving “Maxwell’s demon.”
The scientists used a polymer object about 300 nanometers in size, resembling a bead. Its shape is chosen so that rotating clockwise is energetically more beneficial for it, since this is accompanied by the release of mechanical energy. Counterclockwise rotation, on the contrary, leads to “twisting” of the bead and an increase in the mechanical energy stored in it.
The bead was placed in a special solution, and due to its small size, it began to take part in Brownian motion and rotate - both clockwise and counterclockwise.
The researchers used special equipment to track each turn of the bead, and as it rotated counterclockwise, they applied an electrical voltage to the container in which it was located. This operation did not transfer additional energy to the system, but at the same time it did not allow the bead to “unwind” back. Thus, using only information about where the bead turned, scientists were able to increase its supply of mechanical energy only due to the energy of Brownian motion of molecules.
The law of conservation of energy is not violated. According to Sano's calculations, the efficiency of converting information into energy in their experiment was 28%, which is consistent with theoretical calculations.
Such a mechanism could be used to operate nanomachines or molecular mechanisms, says Vlatko Vedral, a physicist at the University of Oxford who did not take part in Sano's experiment, whose opinion is cited by the online publication Nature News.
“It would be very interesting to discover the use of this principle of energy transfer in living systems,” the scientist added.