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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Quantum mechanics. History and essence of scientific discovery
Directory / The most important scientific discoveries When the excitement of the first successes has passed Bohr's theory, everyone suddenly realized a simple truth: Bohr's scheme is contradictory. There was nowhere to hide from such a fact, and it explains the then pessimism Einstein, as well as Pauli's desperation. Physicists have been convinced again and again that an electron, when moving in an atom, does not obey the laws of electrodynamics: it does not fall on the nucleus and does not even radiate if the atom is not excited. All this was so unusual that it did not fit in the head: the electron, which "originated" from electrodynamics, suddenly got out of control of its laws. In any attempt to find a logical way out of such a vicious circle, scientists have always come to the conclusion: the Bohr atom cannot exist. It turned out that the motion of an electron in an atom obeys some other laws - the laws of quantum mechanics. Quantum mechanics is the science of the movement of electrons in an atom. It was originally called that: atomic mechanics. Heisenberg - the first of those who had the good fortune to create this science. Werner Karl Heisenberg (1901–1976) was born in the German city of Würzburg. In September 1911, Werner was sent to a prestigious gymnasium. In 1920, Heisenberg entered the University of Munich. After graduating, Werner was appointed assistant professor Max Born at the University of Göttingen. Born was sure that the atomic microcosm is so different from the macrocosm described by classical physics that scientists should not even think of using the usual concepts of motion and time, speed, space and a certain position of particles when studying the structure of the atom. The basis of the microworld is quanta, which should not have been attempted to be understood or explained from the visual positions of outdated classics. This radical philosophy found a warm response in the soul of his new assistant. Indeed, the state of atomic physics at that time resembled some kind of heap of hypotheses. Now, if someone could prove by experience that the electron is really a wave, or rather, both a particle and a wave. But there have been no such experiences so far. And if so, then it was incorrect to proceed from the assumptions alone of what an electron is, according to the pedantic Heisenberg. Is it possible to create a theory in which there will be only known experimental data on the atom, obtained by studying the light emitted by it? What can you say about this light for sure? That it has such and such frequency and such and such intensity, no more... In June 1925, the ill Heisenberg went to rest on the island of Heligoland in the Baltic Sea. He did not manage to rest - there he suddenly realized an unexpected truth: one cannot imagine the movement of an electron in an atom as the movement of a small ball along a trajectory. It is impossible, because the electron is not a ball, but something more complex, and it is impossible to trace the movement of this "something" as simply as the movement of a billiard ball. L. Ponomarev writes in his book: "Heisenberg argued: the equations with which we want to describe the motion in an atom should not contain any quantities other than those that can be measured experimentally. And from the experiments it followed that the atom is stable, consists of nucleus and electrons and can emit rays if it is disturbed from equilibrium.These rays have a strictly defined wavelength and, according to Bohr, arise when an electron jumps from one stationary orbit to another.At the same time, Bohr's scheme did not say anything about the fact that happens to the electron at the moment of the jump, so to speak "in flight" between two stationary states. And everyone, including Heisenberg, out of habit sought an answer to this very question. But at some point it became clear to him: the electron does not exist " between "stationary states, it simply does not have such a property! What is there? There is something for which he did not even know the name yet, but he was convinced that it should depend only on where the electron went and from where. Until that time, physicists had been trying to find a hypothetical trajectory for an electron in an atom, which depends continuously on time and which can be given by a series of numbers marking the position of the electron at certain points in time. Heisenberg argued that there is no such trajectory in the atom, and instead of a continuous curve there is a set of discrete numbers, the values of which depend on the numbers of the initial and final states of the electron. He presented the state of the atom in the form of an endless chessboard, in each square of which numbers are written. Naturally, the values of these numbers depend on the position of the square on the "atomic board", that is, on the row number (initial state) and column number (final state), at the intersection of which the number stands. If the X numbers of a kind of record of the "atomic game" are known, then everything necessary is known about the atom to predict its observable properties: the spectrum of the atom, the intensity of its spectral lines, the number and speed of electrons knocked out of the atom by ultraviolet rays, and much more. The numbers X cannot be called the coordinates of an electron in an atom. They replace them, or, as it was later said, they represent them. But what these words mean - at first, Heisenberg himself did not understand. However, immediately with the help of Max Born (1882-1970) and Pascual Jordan, it was possible to understand that the table of numbers is not just a table, but a matrix. “Matrices,” notes L.I. Ponomarev, “are tables of quantities for which there are strictly defined operations of addition and multiplication. In particular, the result of multiplying two matrices depends on the order in which they are multiplied. This rule may seem strange and suspicious , but does not contain any arbitrariness in itself. In essence, it is this rule that distinguishes matrices from other quantities. We have no right to change it at our whim - mathematics also has its own unshakable laws. These laws, independent of physics and all other sciences, fix in the language of symbols, all conceivable logical connections in nature, and it is not known in advance whether all these connections are realized in reality. Of course, mathematicians knew about matrices long before Heisenberg and knew how to work with them. However, it was a complete surprise to everyone that these strange objects with unusual properties correspond to something real in the world of atomic phenomena. The merit of Heisenberg and Born lies in the fact that they overcame the psychological barrier, found a correspondence between the properties of matrices and the features of the motion of electrons in an atom, and thereby founded a new, atomic, quantum, matrix mechanics. Atomic - because it describes the movement of electrons in an atom. Quantum - because the main role in this description is played by the concept of quantum of action. Matrix - because the mathematical apparatus necessary for this is matrices. In the new mechanics, each characteristic of an electron: coordinate, momentum, energy - corresponded to the corresponding matrices. Then the equations of motion, known from classical mechanics, were written down for them. Heisenberg established even something more: he found out that the quantum mechanical matrices of coordinate and momentum are not matrices in general, but only those that obey the commutation (or permutation) relation. In the new mechanics, this permutation relation played exactly the same role as the Bohr quantization condition in the old mechanics. And just as the Bohr conditions singled out stationary orbits from the set of all possible ones, the Heisenberg commutation relation selects only quantum mechanical ones from the set of all matrices. It is no coincidence that in both cases - both in the Bohr quantization conditions and in the Heisenberg equations - Planck's constant must be present. Planck's constant necessarily enters into all the equations of quantum mechanics, and by this feature they can be unmistakably distinguished from all other equations. The new equations that Heisenberg found were neither the equations of mechanics nor those of electrodynamics. From the point of view of these equations, the state of an atom is completely given if the coordinate or momentum matrices are known. Moreover, the structure of these matrices is such that the atom does not radiate in the unexcited state. According to Heisenberg, motion is not the movement of an electron-ball along any trajectory around the nucleus. Motion is a change in the state of the system in time, which describes the matrices of coordinate and momentum. Along with questions about the nature of the motion of an electron in an atom, the question of the stability of the atom also disappeared. From the new point of view, in an unexcited atom, the electron is at rest, and therefore should not radiate. Heisenberg's theory was internally consistent, which was so lacking in Bohr's scheme. At the same time, it led to the same results as the Bohr quantization rules. In addition, with its help, it was finally possible to show that Planck's hypothesis about radiation quanta is a simple and natural consequence of new mechanics. It must be said that matrix mechanics appeared very opportunely. Heisenberg's ideas were taken up by other physicists and soon, according to Bohr, it acquired "a form that, in its logical completeness and generality, could compete with classical mechanics." However, there was one depressing circumstance in Heisenberg's work. According to him, he could not succeed in deriving a simple spectrum of hydrogen from the new theory. And what was his surprise when, some time after the publication of his work, as he wrote, “Pauli gave me a surprise: the complete quantum mechanics of the hydrogen atom. theory of the hydrogen atom and how great is my surprise that you were able to develop it so quickly"". Physicists greeted the appearance of Heisenberg's matrix mechanics with great relief: "Heisenberg's mechanics again gave me back the joy of life and hope. Although it does not solve the riddle, I believe that now it is possible to move forward again," wrote Pauli on October 9, 1925. He soon justified his faith himself. By applying the new mechanics to the hydrogen atom, he obtained the same formulas as Niels Bohr based on their postulates. Of course, new difficulties arose, but these were the difficulties of growth, and not the hopelessness of a dead end. Author: Samin D.K.
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