What is quantum mechanics and why can the quantum world be calculated and even understood, but cannot be imagined? In an attempt to imagine a Universe built on these principles (or rather, even whole clusters, fans of universes), many quantum physicists delve into philosophical and even mystical spheres.
In 1874, 16-year-old high school graduate Max Planck faced a difficult choice: to devote his life to music or physics. Meanwhile, his father wanted Max to continue the legal dynasty. He arranged a meeting for his son with Professor Philip von Jolly, asking him to cool the heir's interest in physics. As Planck wrote in his memoirs, Jolly "portrayed physics as a highly developed, almost completely exhausted science, which is close to assuming its final form …". This opinion was held by many at the end of the 19th century. But Planck nevertheless chose physics and was at the origins of the greatest revolution in this science.
In April 1900, physicist Lord Kelvin, after whom the scale of absolute temperatures is now named, said at a lecture that the beauty and purity of the building of theoretical physics was overshadowed by only a couple of "dark clouds" on the horizon: unsuccessful attempts to detect the world ether and the problem of explaining the radiation spectrum of heated Tel. But before the year ended, and with it the 19th century, Planck solved the problem of the thermal spectrum by introducing the concept of a quantum - the minimum portion of radiant energy. The idea that energy can only be emitted in fixed portions, like bullets from a machine gun, and not water from a hose, went against the ideas of classical physics and became the starting point on the path to quantum mechanics.
Planck's work was the beginning of a chain of very strange discoveries that greatly changed the established physical picture of the world. The objects of the microworld - molecules, atoms and elementary particles - refused to obey the mathematical laws that had proven themselves in classical mechanics. Electrons did not want to revolve around nuclei in arbitrary orbits, but were confined only at certain discrete energy levels, unstable radioactive atoms decayed at an unpredictable moment without any specific reasons, moving micro-objects manifested themselves either as point particles or as wave processes covering a significant area of space …
Accustomed to the fact that mathematics is the language of nature since the 17th century scientific revolution, physicists staged a real brainstorming session and by the mid-1920s they had developed a mathematical model of the behavior of microparticles. The theory, called quantum mechanics, turned out to be the most accurate of all physical disciplines: so far not a single deviation from its predictions has been found (although some of these predictions come from mathematically meaningless expressions like the difference between two infinite quantities). But at the same time, the exact meaning of the mathematical constructions of quantum mechanics practically defies explanation in everyday language.
Take, for example, the uncertainty principle, one of the fundamental relationships of quantum physics. It follows from it that the more accurately the speed of an elementary particle is measured, the less can be said about where it is, and vice versa. If cars were quantum objects, drivers would not be afraid of photo-registration of violations. As soon as the speed of the car was measured by radar, its position would become uncertain, and it would certainly not be in the frame. And if, on the contrary, its image was fixed in the picture, then the measurement error on the radar would not allow determining the speed.
Crazy enough theory
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Instead of the usual coordinates and velocities, a quantum particle is described by the so-called wave function. It is included in all the equations of quantum mechanics, but its physical meaning has not received an intelligible interpretation. The fact is that its values are expressed not by ordinary, but by complex numbers, and in addition are not available for direct measurement. For example, for a moving particle, the wave function is defined at each point of infinite space and changes in time. The particle is not at any particular point and does not move from place to place like a small ball. It seems to be smeared over space and to one degree or another is present everywhere at once, somewhere concentrating, and somewhere disappearing.
The interaction of such "smeared" particles further complicates the picture, giving rise to the so-called entangled states. In this case, quantum objects form a single system with a common wave function. As the number of particles grows, the complexity of entangled states grows rapidly, and concepts of the position or velocity of an individual particle become meaningless. It is extremely difficult to contemplate on such strange objects. Human thinking is closely related to language and visual images, which are formed by the experience of dealing with classical objects. The description of the behavior of quantum particles in a language that is not suitable for this leads to paradoxical statements. “Your theory is insane,” Niels Bohr once said after Wolfgang Pauli's speech. "The only question is, is she crazy enough to be correct."But without a correct description of phenomena in the spoken language, it is difficult to conduct research. Physicists often comprehend mathematical constructions, likening them to the simplest objects from everyday life. If in classical mechanics for 2000 years they were looking for mathematical means suitable for expressing everyday experience, then in quantum theory the opposite situation developed: physicists were in dire need of an adequate verbal explanation of an excellently working mathematical apparatus. For quantum mechanics, an interpretation was required, that is, a convenient and generally correct explanation of the meaning of its basic concepts.then in quantum theory the opposite situation developed: physicists were in dire need of an adequate verbal explanation of an excellently working mathematical apparatus. For quantum mechanics, an interpretation was required, that is, a convenient and generally correct explanation of the meaning of its basic concepts.then in quantum theory the opposite situation developed: physicists were in dire need of an adequate verbal explanation of an excellently working mathematical apparatus. For quantum mechanics, an interpretation was required, that is, a convenient and generally correct explanation of the meaning of its basic concepts.
There were a number of fundamental questions to be answered. What is the real structure of quantum objects? Is the uncertainty of their behavior fundamental, or does it only reflect the lack of our knowledge? What happens to the wave function when the instrument detects a particle at a specific location? Finally, what is the role of the observer in the quantum measurement process?
Dice god
The notion of the unpredictability of the behavior of microparticles ran counter to all the experience and aesthetic preferences of physicists. Determinism was considered the ideal - the reduction of any phenomenon to the unambiguous laws of mechanical motion. Many expected that in the depths of the microworld there would be a more fundamental level of reality, and quantum mechanics was compared with a statistical approach to the description of gas, which is used only because it is difficult to track the movements of all molecules, and not because they themselves "do not know" where are. This "hypothesis of hidden parameters" was most actively defended by Albert Einstein. His position went down in history under the catchy slogan: "God does not play dice."
Bohr and Einstein remained friends despite the fierce scientific controversy over the foundations of quantum mechanics. Until the end of his life, Einstein did not recognize the Copenhagen interpretation, which was accepted by most physicists. Photo: SPL / EAST NEWS
His opponent, Niels Bohr, argued that the wave function contains comprehensive information about the state of quantum objects. The equations make it possible to unambiguously calculate its changes in time, and in mathematical terms, it is not worse than material points and solids familiar to physicists. The only difference is that it does not describe the particles themselves, but the probability of their detection at one point or another in space. We can say that this is not the particle itself, but its possibility. But where exactly it will be found during observation is fundamentally impossible to predict. “Inside” particles there are no hidden parameters inaccessible to measurement that determine when exactly they decay or at what point in space appear during observation. In this sense, uncertainty is a fundamental property of quantum objects. On the side of this interpretation,which began to be called Copenhagen (after the city where Bor lived and worked), was the power of "Occam's razor": it did not assume any additional entities that were not in quantum mechanical equations and observations. This important advantage persuaded most physicists to accept Bohr's position long before the experiment convincingly showed that Einstein was wrong.
Yet the Copenhagen interpretation is flawed. The main direction of her criticism was the description of the process of quantum measurement. When a particle with a wave function diffused over a large volume of space is registered by the experimenter at a certain place, the probability of its stay away from this point becomes zero. This means that the wave function must instantly concentrate in a very small area. This "catastrophe" is called the collapse of the wave function. And it is a disaster not only for the observed particle, but also for the Copenhagen interpretation, since the collapse proceeds contrary to the equations of quantum mechanics itself. Physicists refer to this as a violation of linearity in a quantum measurement.
It turns out that the mathematical apparatus of quantum mechanics works only in a piecewise continuous mode: from one dimension to another. And “at the junctions” the wave function changes abruptly and continues to develop from a fundamentally unpredictable state. For a theory seeking to describe physical reality at a fundamental level, this was a very serious flaw. "The device extracts from the state that existed before the measurement, one of the possibilities it contains," wrote one of the founders of quantum mechanics Louis de Broglie about this phenomenon. This interpretation inevitably led to the question of the role of the observer in quantum physics.
Orpheus and Eurydice
Take, for example, a single radioactive atom. According to the laws of quantum mechanics, it spontaneously decays at an unpredictable moment in time. Therefore, its wave function represents the sum of two components: one describes the whole atom, and the other - decayed. The probability corresponding to the first decreases, and the second increases. Physicists in such a situation speak of a superposition of two incompatible states. If you check the state of an atom, its wave function will collapse and the atom with a certain probability will be either whole or decayed. But at what point does this collapse occur - when the measuring device interacts with the atom, or when the human observer learns about the results?
Both options look unattractive. The first leads to an unacceptable conclusion that the atoms of the measuring device are somehow different from the rest, since under their influence the wave function collapses instead of the formation of an entangled state, as it should be in the interaction of quantum particles. The second variant introduces into the theory the subjectivism so unloved by physicists. We have to agree that the consciousness of the observer (his body from the point of view of quantum mechanics is still the same device) directly affects the wave function, that is, the state of the quantum object.
This problem was sharpened by Erwin Schrödinger in the form of a famous thought experiment. Let's put a cat in the box and a device with poison, which is triggered when a radioactive atom decays. Let's close the box and wait until the decay probability reaches, say, 50%. Since no information comes to us from the box, the atom in it is described as a superposition of the whole and decayed. But now the state of the atom is inextricably linked with the fate of the cat, which, as long as the box remains locked, is in a strange state of superposition of the living and the dead. But one has only to open the box, we will see either a hungry animal or a lifeless corpse, and, most likely, it turns out that the cat has been in this state for some time. It turns out that while the box was closed, at least two versions of the story developed in parallel,but one meaningful glance inside the box is enough for only one of them to remain real.
How not to recall the myth of Orpheus and Eurydice:
“Whenever he could // He turn around (if turning around, // He did not destroy his deed, // Barely accomplished) - see // He could follow them quietly” (“Orpheus. Eurydice. Hermes” R M. Rilke). According to the Copenhagen interpretation, the quantum dimension, like the careless gaze of Orpheus, instantly destroys a whole bunch of possible worlds, leaving only one rod along which history moves.
One world wave
Questions related to the problem of quantum measurements have constantly fueled the interest of physicists in the search for new interpretations of quantum mechanics. One of the most interesting ideas in this direction was put forward in 1957 by an American physicist from Princeton University, Hugh Everett III. In his dissertation, he prioritized the principle of linearity, and hence the continuity of the linear laws of quantum mechanics. This led Everett to the conclusion that the observer cannot be viewed in isolation from the observed object, as some kind of external entity.
At the moment of measurement, the observer interacts with the quantum object, and after that neither the observer's state nor the object's state can be described by separate wave functions: their states get entangled, and the wave function can be written only for a single whole - the "observer + observable" system. To complete the measurement, the observer must compare his new state with the previous one fixed in his memory. For this, the entangled system that arose at the moment of interaction must be again divided into an observer and an object. But this can be done in different ways. The result is different measured values, but more interestingly, different observers. It turns out that in each act of quantum measurement, the observer is split into several (possibly infinitely many) versions. Each of these versions sees its own measurement result and, acting in accordance with it, forms its own history and its own version of the Universe. With this in mind, Everett's interpretation is often called the many-worlds, and the multivariate Universe itself is called the Multiverse (so as not to confuse it with the cosmological Multiverse - a set of independent worlds formed in some models of the Universe - some physicists suggest calling it the Alterverse).
Everett's idea is complex and often misunderstood. Most often, you can hear that with each collision of particles, the entire universe branches out, generating many copies according to the number of possible outcomes of the collision. In fact, the quantum world, according to Everett, is exactly one. Since all of its particles directly or indirectly interacted with each other and are therefore in an entangled state, its fundamental description is a single world wave function, which smoothly evolves according to the linear laws of quantum mechanics. This world is as deterministic as the Laplace world of classical mechanics, in which, knowing the positions and velocities of all particles at a certain moment in time, one can calculate the entire past and future. In Everett's world, countless particles have been replaced by a highly complex wave function. This does not lead to uncertainties,since no one can observe the universe from the outside. However, inside there are countless ways to divide it into the observer and the surrounding world.
The following analogy helps to understand the meaning of Everett's interpretation. Imagine a country with a population of millions. Each of its residents evaluates the events in their own way. In some, he directly or indirectly takes part, which changes both the country and his views. Millions of different pictures of the world are being formed, which are perceived by their carriers as the most real reality. But at the same time there is also the country itself, which exists independently of someone's ideas, providing an opportunity for their existence. Likewise, Everett's unified quantum universe provides room for a huge number of independently existing classical worldviews that arise from different observers. And all these pictures, according to Everett, are completely real, although each exists only for its observer.
The Einstein-Podolsky-Rosen paradox
The decisive argument in the Einstein-Bohr dispute was a paradox, which in 70 years has gone from a thought experiment to a working technology. His idea in 1935 was proposed by Albert Einstein himself, together with physicists Boris Podolsky and Nathan Rosen. Their goal was to demonstrate the incompleteness of the Copenhagen interpretation, deriving from it an absurd conclusion about the possibility of instantaneous mutual influence of two particles separated by a large distance. Fifteen years later, David Bohm, an American specialist in Copenhagen interpretation, who worked closely with Einstein at Princeton, came up with a fundamentally feasible version of the experiment using photons. Another 15 years have passed, and John Stuart Bell formulates a clear criterion in the form of an inequality that allows one to experimentally test the presence of hidden parameters in quantum objects. In the 1970s, several groups of physicists set up experiments to test whether Bell's inequalities were met, with conflicting results. Only in 1982-1985 Alan Aspect in Paris, having significantly increased the accuracy, finally proves that Einstein was wrong. And 20 years later, several commercial firms at once created technologies of top-secret communication channels based on the paradoxical properties of quantum particles, which Einstein considered a refutation of the Copenhagen interpretation of quantum mechanics.based on the paradoxical properties of quantum particles, which Einstein considered a refutation of the Copenhagen interpretation of quantum mechanics.based on the paradoxical properties of quantum particles, which Einstein considered a refutation of the Copenhagen interpretation of quantum mechanics.
From shadow to light
Few paid attention to Everett's dissertation. Even before his defense, Everett himself accepted an invitation from the military department, where he headed one of the units involved in the numerical modeling of the consequences of nuclear conflicts, and made a brilliant career there. At first, his scientific advisor John Wheeler did not share the views of his pupil, but they found a compromise version of the theory, and Everett submitted it for publication in the scientific journal Reviews of Modern Physics. Editor Bryce DeWitt reacted very negatively to her and intended to reject the article, but then suddenly became an ardent supporter of the theory, and the article appeared in the June 1957 issue of the magazine. However, with Wheeler's afterword: I, they say, do not think that all this is correct, but it is at least curious and not pointless. Wheeler insisted that the theory should be discussed with Niels Bohr,but he actually refused to consider it when in 1959 Everett spent a month and a half in Copenhagen. One day in 1959, while in Copenhagen, Everett met with Bohr, but he was not impressed by the new theory.
In a sense, Everett was unlucky. His work was lost in the stream of first-class publications produced at the same time, and it was also too "philosophical". Everett's son, Mark, once said: “Father never, never spoke to me about his theories. He was a stranger to me, existing in some kind of parallel world. I think he was deeply disappointed that he knew about himself that he was a genius, but no one else in the world knew about it. " In 1982, Everett died of a heart attack.
Now it is even difficult to say, thanks to whom it was taken out of oblivion. Most likely, this happened when all the same Bryce DeWitt and John Wheeler tried to build one of the first "theories of everything" - a field theory in which quantization would coexist with the general principle of relativity. Then science fiction writers laid eyes on an unusual theory. But only after the death of Everett began the real triumph of his idea (albeit already in the formulation of DeWitt, which Wheeler categorically disowned a decade later). It began to seem that the many-worlds interpretation has a colossal explanatory potential, allowing one to give a coherent interpretation not only of the concept of the wave function, but also of the observer with his mysterious "consciousness". In 1995, American sociologist David Rob conducted a survey among leading American physicists, and the result was stunning:58% called Everett's theory “correct”.
Who's that girl?
The theme of parallelism of worlds and weak (in one sense or another) interactions between them has long been present in fantastic fiction. Let us recall at least the grandiose epic of Robert Zelazny, The Chronicles of Amber. However, in the past two decades, it has become fashionable to build a solid scientific foundation for such plot moves. And in the novel "The Possibility of an Island" by Michel Houellebecq, the quantum Multiverse appears already with a direct reference to the authors of the corresponding concept. But the parallel worlds themselves are only half the battle. It is much more difficult to translate into artistic language the second most important idea of the theory - the quantum interference of particles with their counterparts. There is no doubt that it was these fantastic transformations that sparked David Lynch's fantasy when he worked on Mulholland Drive. The first scene of the film - the heroine is driving at night along a country road in a limousine with two men, suddenly the limousine stops and the heroine enters into a conversation with her companions - is repeated twice in the film. Only the girl seems to be different, and the episode ends differently. In addition, in the interval, something happens that, it seems, does not allow us to consider the two episodes identical. At the same time, their closeness cannot be accidental. The transformation of the heroines into each other tells the viewer that in front of him is the same character, only he can be in different (quantum) states. Therefore, time ceases to play the role of an additional coordinate and can no longer flow regardless of what is happening: it is revealed in spontaneous jumps from one layer of the Multiverse to another. The Israeli physicist David Deutsch, one of the main popularizers of Everett's ideas, interpreted the time as the "first quantum phenomenon". A deep physical idea, therefore, gives the artist reason to despise any boundaries that restrain his desire to diversify the options for the development of the plot and build "mixed states" of these various options.
In search of consciousness
An observer can be any system, for example, a computer, remembering its previous states and comparing them with new ones. “As people working with complex automata are well aware, virtually all of the accepted language of subjective experience is fully applicable to such machines,” Everett writes in his dissertation. Thus, he avoids the question of the nature of consciousness. But his followers were no longer inclined to be so cautious. The observer was increasingly seen as a thinking and volitional consciousness, and not just as a sensor with memory. This opens up scope for equally interesting as well as controversial attempts to combine in one concept traditional objectivist physics and various esoteric ideas about the nature of human consciousness.
For example, Doctor of Physical and Mathematical Sciences Mikhail Mensky from the Physics Institute. P. N. Lebedev RAS is actively developing its extended concept of Everett, in which it identifies consciousness with the very process of separating alternatives. Physical reality is of a purely quantum nature and is represented by a single world wave function. However, a rationally thinking consciousness, according to Mensky, is incapable of directly perceiving it and needs a “simplified” classical picture of the world, a part of which it perceives itself and which it creates itself (this is its nature). With a certain preparation, exercising free will, consciousness is able to more or less arbitrarily choose which of the infinite number of classical projections of the quantum universe it will “live”. From the outside, such a choice can be perceived as a "probabilistic miracle"in which the "magician" is able to find himself in exactly that classical reality that he desires, even if its realization is unlikely. In this Mensky sees the connection between his ideas and esoteric teachings. He also introduces the concept of "superconsciousness", which in those periods when consciousness turns off (for example, in a dream, in a trance or meditation), is able to penetrate into alternative Everett worlds and draw information there that is fundamentally inaccessible to rational consciousness.is able to penetrate into alternative Everett worlds and draw from there information that is fundamentally inaccessible to rational consciousness.is able to penetrate into alternative Everett worlds and draw from there information that is fundamentally inaccessible to rational consciousness.
A different approach has been developed for more than a decade by a professor at the Heidelberg University Heinz-Dieter Ze. He proposed a multi-intelligent interpretation of quantum mechanics, in which, along with matter described by the wave function, there are entities of a different nature - "minds". An endless family of such "minds" is associated with each observer. For each Everett splitting of the observer, this family is also divided into parts, following along each branch. The proportion in which they are divided reflects the probability of each of the branches. It is the "minds", according to Tse, that ensure the self-identity of a person's consciousness, for example, waking up in the morning, you recognize yourself as the same person as you went to bed yesterday.
Tse's ideas have not yet found wide acceptance among physicists. One of the critics, Peter Lewis, noted that this concept leads to rather strange conclusions regarding participation in life-threatening adventures. For example, if you were offered to sit in the same box with Schrödinger's cat, you would most likely refuse. However, it follows from the multi-intelligent model that you are not risking anything: in those versions of reality where the radioactive atom disintegrated and you and the cat were poisoned, the accompanying "intelligences" will not get to you. All of them will safely follow the branch where you are destined to survive. This means that there is no risk for you.
This reasoning, by the way, is closely related to the idea of the so-called quantum immortality. When you die, this naturally only happens in some of Everett's worlds. You can always find a classic projection in which you stay alive this time. Continuing this reasoning endlessly, we can come to the conclusion that such a moment when all your "clones" in all the worlds of the Multiverse will die will never come, which means, at least somewhere, but you will live forever. The reasoning is logical, but the result is inconceivable, isn't it?
Alexander Sergeev