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✪ Science show. Issue No. 63. Advances in The Big Bang Theory
Subtitles
According to the second law of thermodynamics, the entropy of the universe is constantly increasing. Accordingly, when any process is carried out in the Universe, the entropy will always be greater than or equal to 0. And in the previous video, we found out that this can have a lot of different consequences. Whether you understand entropy as a constant multiplied by the natural logarithm of the number of states your system can take on, or as the heat in the system divided by the temperature at which it is added, both of these descriptions, combined with the second the law of thermodynamics, they tell us: when a hot body is next to a cold one - let's say ... Let's draw. This is T1, and this is T2 - then heat will be transferred from a hot body to a cold one. We showed this in the last video with the help of mathematical calculations. Heat will be transferred in this direction. One of the people who commented on the last video wrote: "Could you tell me about Maxwell's demon?" I'll tell you! Because this is a very curious thought experiment, which seems to refute the principle in question and the second law of thermodynamics. Yes, and his name is very entertaining - "Maxwell's demon." However, it seems that it was not Maxwell who called him a "demon" at all, but Kelvin. Well, you know, these guys were interested in everything. So, Maxwell's demon. This is the same Maxwell after whom the famous equation is named, so he was really interested in a lot of things. Among other things, he was the first person who managed to create a color image. And in the middle of the XIX century. So, before us is a very insightful scientist. But what is Maxwell's demon? When we say that one body has a higher temperature than another, what do we mean? We mean that the average kinetic energy of the molecules of this body colliding over here... that the average kinetic energy of these molecules here... is higher than the average kinetic energy of the molecules here. Please note: I said - the average kinetic energy. And we talked about this more than once. Temperature is a macro state. We know that at the micro level all these molecules have different speeds. They collide with each other, transferring the inertia of motion to each other. This one here can move really fast in that direction. But this one can move quite slowly. This one can move really fast like this. But this one can move quite slowly. All this is rather confusing. But we can draw a distribution graph. If you know the microstates of everything, you can draw a small histogram. For T1 we can say... Let's say we use the Kelvin scale. Look, here is my average temperature, but I have a general plot of particle distribution. That is, this is the number of particles. And I will not build any scale here. You got the main idea. So I have a lot of particles that make up T1, but I also have certain particles that can be very close to absolute zero. Of course, there will be few of them, but still. That is, you have a set that is probably T1, and a set of particles that could have a kinetic energy higher than T1. Higher than average kinetic energy. Maybe we're talking about this one. Maybe this is the particle that has practically no kinetic energy. This means that we have a particle that is almost completely immobile, which stands in one place. Here we have a general graph of particle distribution. Similarly, in this T2 system, on average, the molecules have a lower kinetic energy. But there may well be one particle that has a very high kinetic energy. But most of them have a lower energy on average. So, if we draw a distribution plot for T2, then our average kinetic energy will be lower, but the plot will probably look something like this. No, not really. It will probably look like this. Or maybe like this. Let's try a little differently. Let's bring the line here. Perhaps our graph will look something like this. So, pay attention - in T1 there are some molecules that have a lower energy than the average kinetic energy of T2. Here they are, these molecules. These are the slow guys. And note that there are some molecules in T2 that have a higher energy than the average kinetic energy of T1. Here they are. So there are fast guys in T2, even though T2 is, let's say, "colder" and has a lower average kinetic energy. If we look at the microstate, we will see individual molecules that are moving quite fast, and individual molecules that are moving quite slowly. So Maxwell said, “Hey, what if I had—of course, he didn’t use the word demon, but we’ll use it because it looks very curious and mysterious, but it really isn’t.” , - what if I had someone - let's call him a demon - with a little loophole right here? Let me make a neater drawing. So, between these two systems... Let's say they are isolated. Let's say they are separated from each other. Here is T1 with many particles with different kinetic energies. And here is T2. I make them separate, and maybe they're only connected here. T2. These guys have slower kinetic energy. And Maxwell, doing his little thought experiment, said: "Imagine that I have someone in charge of one loophole - let's say this one - and he controls it." And whenever a really fast particle from T2, one of these, approaches the loophole - flies towards it - let's say, here it is ... And this particle moves very quickly. It has very high kinetic energy and is perfect for our loophole. And then the demon says: “Hey, I see this thing. She's heading for my loophole." The demon is about to open its hatch and allow this particle to enter T1. And when the demon opens its hatch, this particle will continue its movement and end up in T1. The demon closes the hatch again: he wants the fast particles to move from T2 to T1. When he sees a slow particle approaching him, one of these, he reopens his loophole and allows the particle to enter. It goes like this. And if this continues, how will it end? Well, eventually there will be separation – and it may take some time. But the separation will affect all slow particles... Let me draw it. The border will be brown, because now it's not entirely clear where what is ... great ... We'll talk about this a little more. So here is the border. And here is a loophole in it. What will happen at the end? All the fast particles... some of them were already in T1, right? Some of the fast particles that were originally in T1 will still be on this side of the barrier. Let's draw it: the main thing is not to confuse anything. So, now all the fast particles from T2 will also get stuck here. Because eventually they will all get close to our loophole if we wait long enough. Thus, a lot of particles that were originally in T2 will also accumulate here. So, we'll have a lot of fast particles here. Likewise, all slow T2 particles will remain on the other side. Here they are, these slow particles. And the demon will let in all the slow T1 particles - I won't even call them T1 particles anymore. I'll call them particles 1. Now, the demon will let particle 1 in here. Slow Particles 1. So what happened here? This was a hot body, but this one is cold. According to the second law of thermodynamics, heat must move from here to here. In this case, the temperature should become approximately equal. That is, a hot body should become colder, and a cold body should become hotter. The temperature will become average. But what did our little demon do? He made a hot body even hotter, right? Now the average kinetic energy here is even higher. The demon moved all these particles with high kinetic energy over here, so now this graph will look like... Something like if you moved all these particles over here... The distribution graph will now look something like this... Let's try... For T1 it will look like this so. As for T2... the demon took all the hot stuff from here and the cold stuff from T1. Accordingly, these guys will disappear. They won't be here anymore. And he added them to T2. So, the distribution graph for T2 will look like this, we will erase this, of course. The demon took these guys from T2. Let's erase it all. This was the old distribution schedule for T1. So the distribution plot for T2 now looks something like this. And the new average for T2 will probably be something like this. This is my new T2 system. And my new T1 system will move a little to the right. The average will be higher. So, our demon, apparently, violated the second law of thermodynamics. Let's wrap it all up. My little charts are stacked on top of each other. This example shows that a hot body has become even hotter, and a cold body has become even colder. So, Maxwell seems to be telling us: "Yes, we have violated the second law of thermodynamics." And scientists have puzzled over this for years. Even in the twentieth century, some continued to wonder what was wrong here. And here is what is wrong here ... And I will prove it to you with the help of mathematical calculations ... This is almost the same as the example with a refrigerator. We have a certain demon that opens a small loophole when it suits. Here it is, it's a demon. When fast particles go from here, or slow particles from here... To do it right, he has to keep track of where all the particles will be. It will have to track all particles. And these are not some macroparticles. These are micromolecules or atoms. The demon will have to account for electrons, which can only be seen with a special microscope. And at the same time, he will have to track this countless number of particles. Just think about it! If he doesn't have superpowers, he must have the coolest computer. It must be a computer of incredible power. But any computer generates a lot of heat. So, taking into account different molecules to measure the speed of their movement will also generate heat. It will be very hard work. After all, you have to measure everything! Demon will have to work hard. So the answer is that... And it's not that easy to prove mathematically... What if you really wanted to create such a demon - and in today's world you would probably use some kind of computer with various sensors to do this , and some people have actually tried to do it at a certain level... Now, this computer and its whole system will create more entropy - here, this delta S. It will create more entropy than the entropy that is lost when the cold side is cooled and heated hot. So Maxwell's demon and I haven't done anything definite. I didn't prove it mathematically. But Maxwell's demon is a very interesting thought experiment because it gives you a little more insight into the difference between macro and micro states. And also about what happens at the molecular level in terms of temperature, and how you can make a cold body even colder, and a hot body even hotter. But our answer is not at all paradoxical. When you think about the entropy of an entire system, you must include the demon itself as well. And if you include the demon itself in the system, then it will increase entropy every time it opens its loophole - it takes a certain energy to open the door. But in doing so, the demon will create more entropy than the entropy that can be lost, say, when one of these slow particles crosses over to the other side of the barrier. Anyway, I just wanted to tell you about it, as it's a really interesting thought experiment. Until the next video!
The essence of the paradox
In 2010, physicists from Chuo Universities (jap. 中央大学 ) and the University of Tokyo
In 2015, an autonomous artificial Maxwell demon was implemented as a single-electron transistor with superconducting aluminum leads. Such a device allows a large number of measurement operations to be carried out in a short period of time.
Explanation of Maxwell's paradox
Maxwell's paradox was first resolved by Leo Silard in 1929 based on the following analysis.
The demon must use some kind of measuring device to estimate the velocities of the molecules, such as an electric flashlight. Therefore, it is necessary to consider the entropy of a system consisting of a gas at a constant temperature T 0 , (\displaystyle T_(0),) a demon and a flashlight, including a charged battery and an electric light bulb. The battery must heat the filament of the flashlight lamp to a high temperature T 1 > T 0 , (\displaystyle T_(1)>T_(0),) in order to obtain light quanta with energy ℏ ω 1 > T 0 (\displaystyle \hbar \omega _(1)>T_(0)) in order for light quanta to be recognized against the background of thermal radiation with a temperature
In the absence of a demon, energy E (\displaystyle E) emitted by a light bulb at temperature T 1 (\displaystyle T_(1)) absorbed in a gas at a temperature T 0 (\displaystyle T_(0)) and in general the entropy increases: Δ S = E T 0 − E T 1 > 0 , (\displaystyle \Delta S=(\frac (E)(T_(0)))-(\frac (E)(T_(1)))>0,) because ℏ ω 1 T 0 > 1 , (\displaystyle (\frac (\hbar \omega _(1))(T_(0)))>1,) a p Ω 0 ≪ 1. (\displaystyle (\frac (p)(\Omega _(0)))\ll 1.)
In the presence of a demon, the change in entropy: Δ S = ℏ ω 1 T 0 − p Ω 0 > 0. (\displaystyle \Delta S=(\frac (\hbar \omega _(1))(T_(0)))-(\frac (p)( \Omega _(0)))>0.) Here, the first term means an increase in entropy when a quantum of light emitted by a flashlight hits the eye of a demon, and the second term means a decrease in entropy due to a decrease in the statistical weight of the system Ω 0 (\displaystyle \Omega _(0)) by the amount p , (\displaystyle p,) which leads to a decrease in entropy by an amount Δ S s = S 1 − S 0 = ln (Ω 0 − p − ln Ω 0 ≈ − p Ω 0 . (\displaystyle \Delta S_(s)=S_(1)-S_(0)=\ln (\Omega _(0)-p-\ln \Omega _(0)\approx -(\frac (p)(\Omega _(0))).)
Let's consider this process in more detail. Let the vessel with gas be divided into two parts A (\displaystyle A) and B (\displaystyle B) with temperatures T B > T A , T B − T A = Δ T , T B = T 0 + 1 2 Δ T , T A = T 0 − 1 2 Δ T . (\displaystyle T_(B)>T_(A),\quad T_(B)-T_(A)=\Delta T,\quad T_(B)=T_(0)+(\frac (1)(2) )\Delta T,\quad T_(A)=T_(0)-(\frac (1)(2))\Delta T.) Suppose the demon chooses a fast moving molecule with kinetic energy 3 2 T (1 + ϵ 1) (\displaystyle (\frac (3)(2))T(1+\epsilon _(1))) in an area with low temperature A (\displaystyle A) and directs it to the area b. (\displaystyle B.) After that, he selects a slowly moving molecule with kinetic energy 3 2 T (1 − ϵ 2) (\displaystyle (\frac (3)(2))T(1-\epsilon _(2))) in an area with high temperature B (\displaystyle B) and directs it to the area A. (\displaystyle A.)
In order to preselect these two molecules, the demon needs at least two light quanta, which will result in an increase in entropy when hit in his eye. Δ S d = 2 ℏ ω 1 T 0 > 2. (\displaystyle \Delta S_(d)=2(\frac (\hbar \omega _(1))(T_(0)))>2.)
The exchange of molecules will lead to a decrease in the total entropy Δ S m = Δ Q (1 T B − 1 T A) ≈ − Δ Q Δ T T 2 = − 3 2 (ϵ 1 + ϵ 2) Δ T T . (\displaystyle \Delta S_(m)=\Delta Q\left((\frac (1)(T_(B)))-(\frac (1)(T_(A)))\right)\approx -\ Delta Q(\frac (\Delta T)(T^(2)))=-(\frac (3)(2))\left(\epsilon (1)+\epsilon _(2)\right)(\ frac (\Delta T)(T)).) Quantities ϵ 1 (\displaystyle \epsilon (1)) and ϵ 2 , (\displaystyle \epsilon (2),) most likely small ∆ T ≪ T (\displaystyle \Delta T\ll T) and therefore Δ S m = − 3 2 ν , ν ≪ 1. (\displaystyle \Delta S_(m)=-(\frac (3)(2))\nu ,\quad \nu \ll 1.)
So the total change in entropy will be Δ S = Δ S d + Δ S m = 2 ℏ ω 1 T 0 − 3 2 ν > 0. (\displaystyle \Delta S=\Delta S_(d)+\Delta S_(m)=2(\frac ( \hbar \omega _(1))(T_(0)))-(\frac (3)(2))\nu >0.)
The temperature of the demon can be much lower than the temperature of the gas T d ≪ T 0 . (\displaystyle T_(d)\ll T_(0).) At the same time, it can receive light quanta with energy ℏ ω (\displaystyle \hbar \omega ) emitted by gas molecules at a temperature T0. (\displaystyle T_(0).) Then the above reasoning can be repeated with the change of conditions T 1 > T 0 , ℏ ω 1 > T 0 (\displaystyle T_(1)>T_(0),\quad \hbar \omega _(1)>T_(0)) on conditions T2<
T
0
,
ℏ
ω
1
>T2. (\displaystyle T_(2)
In popular culture
In fiction
- In the story "Monday begins on Saturday" by the Strugatsky brothers, Maxwell's demons are adapted by the NIICHAVO administration to open and close the entrance doors of the institute.
- In Sergei Snegov's story "The Right to Search", one of the characters was called "Maxwell's Demon Lord" "...why do I wear the strange nickname Demon Lord? Of course, I corrected it: not Demon Lord at all, but Maxwell’s Demon Lord… I was able to actually implement Maxwell’s brilliant idea.”
- In the "Cyberiad" by Stanislav Lem, Maxwell's demon is referred to as a "demon of the first kind". The heroes of the book create a "demon of the second kind", capable of extracting meaningful information from the movement of air molecules.
The mental experiment is as follows: suppose a vessel with gas is divided by an impenetrable partition into two parts: right and left. There is a hole in the partition 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, "hot" (fast) molecules will be in the right vessel, and "cold" - "remain" in the left.
Thus, it turns out that Maxwell's demon allows heating the right side of the vessel and cooling the left side 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 Second Law of Thermodynamics)
The paradox is resolved if we consider a closed system that includes Maxwell's demon and a vessel. For the functioning of the Maxwell demon, it is necessary to transfer energy to it from an external source. Due to this energy, the separation of hot and cold molecules in the vessel is carried out, 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 dog) 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 daemon must remember the results of the speed measurements (deleting them from the daemon's memory makes the process irreversible). Since the memory is finite, at some point the demon is forced to erase the 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 in an experiment, Japanese physicists were able to achieve an increase in the internal energy of a system using only information about its state and without transferring additional energy to it.
Getting energy from information was first theoretically described by the British physicist James Maxwell in his thought experiment. In it, a certain creature, later called "Maxwell's demon", guarded the door between two rooms. The demon, knowing the energy of a molecule approaching the door, opens the passage only for "fast" molecules, closing the door in front of the "slow" ones. As a result, all "fast" molecules will end up in one room, and slow ones in another, and the resulting temperature difference can be used for practical purposes.
The implementation of such a "demonic" power plant requires much more energy 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 re-emerged 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 the "Maxwell demon".
Scientists used a polymer object about 300 nanometers in size, resembling a bead. Its shape is chosen in such a way that it is energetically more profitable to rotate clockwise, as this is accompanied by the release of mechanical energy. Counterclockwise rotation, on the contrary, leads to the "twisting" of the bead and an increase in the mechanical energy stored in it.
The bead was placed in a special solution, and because of 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. Such an operation did not transfer additional energy to the system, but at the same time did not allow the bead to "unwind" back. Thus, using only information about where the bead turned, scientists were able to increase the supply of its mechanical energy only due to the energy of the Brownian movement of molecules.
The law of conservation of energy is not violated in this case. 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 power nanomachines or molecular machines, said Vlatko Vedral, a physicist at the University of Oxford who was not involved in Sano's experiment, according to Nature News.
"It would be very interesting to discover the use of this principle of energy transfer in living systems," the scientist added.
The leading researcher of the Laboratory of Quantum Information Theory of the Moscow Institute of Physics and Technology 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 passes 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 able to disrupt the natural order of things, and eliminate disorder, if you like. It will reflect high-energy atoms or molecules, change flows and thus start completely different processes within the system. A similar process can be carried out using our quantum device.
Schematic representation of Maxwell's demon. Photo: commons.wikimedia.org
We have shown that although quantum mechanics, in general, just provides this very classical law of thermodynamics and ensures the natural order of things, it is possible to artificially create such conditions under which this process can be violated. That is, now Maxwell's quantum Demon, in other words, an artificial atom (it is commonly called a qubit, i.e. a quantum bit) is able to make heat transfer 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 start natural heat flows in reverse. At the same time, our super-refrigerator 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 energy source is taken into account, the validity of the second law of thermodynamics is restored, and the world order as a whole will not be violated.
As for the field of application of Maxwell's quantum Demon, i.e. of our device, then, first of all, it is, of course, the field of quantum mechanics. Well, for example, an ordinary 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 can cool them or some individual microchips. Now we are learning to do this with close to 100% efficiency.
And, of course, such experiments will allow in the future to talk about the creation of a perpetual motion machine of the second type. No batteries are required, the engine will be able to extract energy from the nearest thermal reservoir and use it to move some kind of nanodevices.
A perpetual motion machine of the second kind is a machine that, when set in motion, would convert into work all the heat extracted from the surrounding bodies. According to the laws of thermodynamics, it is still considered an unrealizable idea.
Physicists from Finland, Russia and the United States pioneered Maxwell's autonomous electronic 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 the British physicist James Clerk Maxwell. We are talking about a certain device that functions in such a way that it leads to a violation of the (apparent) 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 by 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 balloon, 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 shown by the German physicist Rudolf Clausius, it makes impossible the spontaneous transfer (i.e., without doing work) of heat from a colder body to a hotter one, or, equivalently, 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 an efficiency of one hundred percent is 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 clear later). Physicists were looking for contradictions in it, and one of them (along with the heat 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 glory of the demon Maxwell was eclipsed by Schrödinger's cat (or cat). Meanwhile, like a pet from quantum mechanics, the imp of a British physicist served as the source of many important discoveries. In particular, thanks to him, the thermodynamic theory of information and the related concept of information entropy arose.
In the 1960s, a researcher from the American company IBM (International Business Machines) Rolf Landauer formulated the principle, which was given his name. He associated the loss of a bit of information in any physical system with the release of a corresponding amount of heat (or, equivalently, with an increase in thermodynamic entropy). Landauer's work was of fundamental importance to computer technology and continues to this day. The expression, named after Landauer, as well as the Americans Claude Shannon and John von Neumann, allows you to determine the limiting physical characteristics of the device (primarily its power and size), at which information is destroyed. Man-made processors have gone from a heat dissipation that is billions of times greater than that predicted by Landauer's principle to today's values that are only a thousand times greater.
Let there be a memory cell containing information encoded in bits (with values zero and one). If you destroy it (that is, transfer it to a state containing only zeros or ones), heat will be released. In the language of thermodynamics, this means the entropy of the system goes to zero, since the most ordered state (described only by zeros or ones) has been reached. Landauer liked to repeat that "information is a physical quantity", this was his motto.
For the first time, the heat released during the destruction of a bit of information was measured by scientists from France and Germany. The memory cell was a quartz bead with a diameter of two micrometers, placed in water. Using optical tweezers, physicists created a couple of potential holes in which the bead could be. 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 a decrease in the depth of the pits. With the help of rapid physicists observed the transition of the system from one state to another. The process was accompanied by heat release, the water temperature rose, and this was recorded. The data obtained turned out to be close to those predicted by the Landauer 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 speeds of particles. At some point, the memory becomes full, and the daemon needs to erase it in order to continue working. This requires doing work exactly equal to the work that theoretically could 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. Wouldn't it be some kind of super demon influencing a lesser demon? The answer to this question was first proposed in 1929 by one of the participants in the Manhattan Project, the American physicist Leo Szilard. The device named after him provides Maxwell's demon with autonomous operation.
It was first realized by Japanese scientists in 2010. Their electromechanical model is a polystyrene bead with a diameter of about 300 nanometers, placed in an electrolyte. The electromagnetic field did not allow the bead to move down, 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, which require energy to function. The latter circumstance again does not allow violating 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 (an autonomous Maxwell demon).
The system is based on a single-electron transistor that forms a small copper island connected to two superconducting aluminum leads. Maxwell's demon controls the movement of electrons of different energies in a transistor. When a particle is on an island, the demon attracts it with a positive charge. If the electron leaves the island, the demon repels it with a negative charge, which causes the transistor temperature to drop and the demon to rise.
The demon performs all manipulations offline (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 the low temperatures in the system make it possible to register extremely small changes in it. This system also does not violate the second law of thermodynamics and is consistent with the intuitive notion 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 make it possible to study microscopic phenomena in thermodynamics. On the other hand, they show how important it is to produce entropy from the information received by the demon. It is this that, as the authors of the study believe, may be useful for designing 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.
"Maxwell's Demon" is a thought experiment invented by James Maxwell in 1867 to illustrate the seeming paradox of the Second Law of Thermodynamics. The main character of this experiment is a hypothetical intelligent microscopic creature, which later received the name "Maxwell's demon".
Let us assume that a vessel with gas is divided by an impenetrable partition into right and left parts. There is a hole in the partition 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 some sufficiently long period of time, all the hot molecules will be on the right, and the cold ones on the left. Thus, it turns out that Maxwell's demon, without additional energy supply, can heat one part of the vessel and cool the other.
As a result, it turns out that the entropy of a system consisting of two halves is greater in the initial state than in the final state, and this contradicts the thermodynamic principle of non-decreasing entropy in closed systems, i.e. the second law of thermodynamics.
After all, it follows from the second law of thermodynamics that it is impossible to transfer heat from a body with a lower temperature to a body with a higher temperature without doing work.
The paradox is resolved if we consider a closed system that includes Maxwell's demon and a vessel. For the functioning of the Maxwell demon itself, it is necessary to transfer energy to it from a third-party source. Due to this energy, the separation of hot and cold molecules would be carried out.
Here is such a memorable bas-relief appeared in honor of James Maxwell and his elusive demon on the wall of one of the US universities.
And if such a demon could exist in reality, then it would be possible to create a heat engine that would work without consuming energy.
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 daemon must remember the results of the speed measurements (deleting them from the daemon's memory makes the process irreversible).
Since the memory is finite, at some point the demon is forced to erase the old results, which ultimately leads to an increase in the entropy of the entire system as a whole.
In 2010, physicists from the University of Tokyo managed to turn the thought experiment into reality. The scientists noted that Maxwell's famous demon inspired them to create this experiment. Japanese physicists for the first time managed to turn information into energy.
They have created a working nanoscale system that can convert information into energy at an efficiency of about 28 percent (by comparison, the efficiency of the most modern internal combustion engines is slightly more than 40 percent). Scientists do not exclude that in the future the principle they have developed will make it possible to create systems in which the dimensions of both the controlled object and the “demon” will not exceed hundreds of nanometers.
And in 2015, physicists from Finland, Russia and the United States created an autonomous artificial Maxwell demon, which was implemented as a single-electron transistor with superconducting aluminum leads. Maxwell's demon controls the movement of electrons through a transistor.
The setup will help to study microscopic phenomena in thermodynamics and can be used in qubits for quantum computers.
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