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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Quanta. History and essence of scientific discovery
Directory / The most important scientific discoveries Scientists have long tried to find a formula that accurately and in full agreement with the experiment would describe the radiation spectrum of a black body. Experimenters have long established that the spectrum of a black body resembles a pointed hill or a camel's hump. The top of the hump, where the radiation is maximum, is at a certain wavelength, the value of which depends on temperature, and to the left - in the direction of short wavelengths and to the right - in the long-wave direction, the radiation intensity decreases sharply. In 1892, the Russian physicist Golitsyn in his dissertation "Research in Mathematical Physics" considered the problem of radiant energy. In this work, Golitsyn arrives at a result that can be formulated as the following law: Absolute temperature is determined by the totality of all electrical displacements, and it is the fourth power of absolute temperature that is directly proportional to the sum of the squares of all electrical displacements. Thus, he came close to the ideas of the future quantum theory - the photon gas Einstein. And no wonder that his thoughts were not understood by his contemporaries. In the 1864s, Wilhelm Wien (1927-XNUMX) obtained a formula that was in good agreement with experience in the short-wave region, but was not suitable in the long-wave part of the spectrum. In 1900, John William Rayleigh (1842–1919) made an attempt to apply the law of uniform distribution of energy over degrees of freedom to radiation. Vin describes this attempt as follows: “Lord Rayleigh was the first to approach this question from a completely different angle: he tried to apply to the question of radiation a very general law of statistical mechanics, namely the law of the uniform distribution of energy between the degrees of freedom of a system in a state of statistical equilibrium ... Radiation in empty space can also be represented in such a way that it will have a certain number of degrees of freedom. The fact is that when the waves are reflected back and forth from the walls, systems of standing waves arise that are located in the gaps between the two walls ... The individual possible standing waves also represent here the corresponding elements of the occurring phenomena and correspond to the degrees of freedom. If each degree of freedom is given the amount of energy attributable to its share, then Rayleigh's radiation law will be obtained, according to which the emission of radiant energy of a certain wavelength is directly proportional to the absolute temperature and inversely proportional to the fourth power of the wavelength. This law agrees with the data of experience just where the law considered above ceases to be just, and therefore it was at first considered a law with limited justice. Thus, there were two formulas: one for the short-wavelength part of the spectrum (Wien's formula), the other for the long-wavelength part (Rayleigh's formula). The challenge was to match them. "Ultraviolet catastrophe" was called by the researchers the discrepancy between the theory of radiation and experiment. A discrepancy that could not be eliminated in any way. Logical and justified mathematical calculations invariably led to formulas, the conclusions from which were completely at odds with the experiment. From these formulas, it followed that a red-hot furnace should, over time, give off more and more heat to the surrounding space and the brightness of its glow should increase more and more! Contemporary "ultraviolet catastrophe", physicist Lorenz he remarked sadly: "The equations of classical physics turned out to be unable to explain why a dying furnace does not emit yellow rays along with radiation of large wavelengths ..." Max Planck succeeded in "sewing" these formulas of Wien and Rayleigh and deriving a formula that accurately describes the radiation spectrum of a black body. German physicist Max Karl Ernst Ludwig Planck (1858-1947) was born in the Prussian city of Kiel, in the family of a professor of civil law. In 1867 the family moved to Munich, and there Planck entered the Royal Maximilian Classical Gymnasium, where an excellent teacher of mathematics first aroused in him an interest in the natural and exact sciences. After graduating from the gymnasium in 1874, Planck studied mathematics and physics for three years at the Munich University and for a year at the Berlin University. During his time in Berlin, Planck acquired a broader view of physics through the publications of eminent physicists. Hermann von Helmholtz and Gustav Kirchhoff, as well as articles by Rudolf Clausius. Acquaintance with their works contributed to the fact that Planck's scientific interests for a long time focused on thermodynamics - a field of physics in which, on the basis of a small number of fundamental laws, the phenomena of heat, mechanical energy and energy transformation are studied. Planck received his doctorate degree in 1879, having defended his dissertation "On the second law of the mechanical theory of heat" at the University of Munich. In 1885 he became an adjunct professor at the University of Kiel. Planck's work on thermodynamics and its applications to physical chemistry and electrochemistry won him international recognition. In 1888 he became an adjunct professor at the University of Berlin and director of the Institute for Theoretical Physics. During the same time, Planck published a number of papers on the thermodynamics of physical and chemical processes. The theory of chemical equilibrium of diluted solutions, which he created, gained particular fame. In 1897, the first edition of his lectures on thermodynamics appeared. By that time, Planck was already an ordinary professor at the University of Berlin and a member of the Prussian Academy of Sciences. From 1896, Planck became interested in the measurements made at the State Institute of Physics and Technology in Berlin, as well as in the problems of thermal radiation from bodies. Carrying out his research, Planck drew attention to new physical laws. He established on the basis of experiment the law of thermal radiation of a heated body. At the same time, he encountered the fact that the radiation has a discontinuous character. Planck was able to substantiate his law only with the help of the remarkable assumption that the energy of atomic vibrations is not arbitrary, but can only take on a number of well-defined values. Planck found that light with an oscillation frequency should be emitted and absorbed in portions, and the energy of each such portion is equal to the oscillation frequency multiplied by a special constant, called Planck's constant. Here is how Planck himself writes about it: “It was at that time that all outstanding physicists turned, both from the experimental and theoretical side, to the problem of the distribution of energy in the normal spectrum. However, they were looking for it in the direction of representing the radiation intensity as a function of temperature, while I suspected a deeper connection in the dependence of entropy on energy.Since the significance of entropy had not yet found its due recognition, I did not in the least worry about the method I used and could freely and thoroughly carry out my calculations without fear of interference or advance on anyone's part. Since the second derivative of its entropy with respect to its energy is of particular importance for the irreversibility of the exchange of energy between an oscillator and the radiation excited by it, I calculated the value of this quantity for the case that was then at the center of all the interests of the Wien energy distribution, and found a remarkable result that for this case the reciprocal of such a value, which I have here designated K, is proportional to the energy. This connection is so stunningly simple that for a long time I recognized it as completely general and worked on its theoretical foundation. However, the precariousness of such an understanding was soon revealed before the results of new measurements. Namely, while for small values of energy, or for short waves, Wien's law was also perfectly confirmed later, for large values of energy, or for large waves, Lummer and Pringsheim first established a noticeable deviation, and the perfect deviations carried out by Rubens and F. Kurlbaum measurements with fluorspar and potassium salt revealed a completely different, but again simple relationship, that the value of K is proportional not to energy, but to the square of energy when going to large values of energy and wavelengths. Thus, two simple boundaries were established for the function by direct experiments: for small energies, the proportionality (of the first degree) of the energy, for large energies, to the square of the energy. It is clear that, just as any principle of energy distribution gives a certain value of K, so any expression leads to a certain law of energy distribution, and now the point is to find such an expression I that would give the energy distribution established by measurements. But now nothing was more natural than to compose for the general case a quantity in the form of a sum of two terms: one of the first degree, and the other of the second degree of energy, so that for small energies the first term will be decisive, for large energies - the second; at the same time, a new radiation formula was found, which I proposed at a meeting of the Berlin Physical Society on October 19, 1900, and recommended for research. ... The radiation formula was also confirmed by subsequent measurements, namely, the more accurately, the more subtle methods of measurement were used. However, the measurement formula, if we assume its absolutely exact truth, was in itself only a happily guessed law, having only a formal meaning. On December 14, 1900, Planck reported to the Berlin Physical Society about his hypothesis and the new radiation formula. The hypothesis introduced by Planck marked the birth of quantum theory, which made a real revolution in physics. Classical physics, in contrast to modern physics, is now called "physics before Planck." Planck's monograph Lectures on the Theory of Thermal Radiation was published in 1906. It has been reprinted several times. His new theory included, in addition to Planck's constant, other fundamental quantities such as the speed of light and a number known as the Boltzmann constant. In 1901, based on experimental data on black body radiation, Planck calculated the value of the Boltzmann constant and, using other known information, obtained the Avogadro number (the number of atoms in one mole of an element). Based on the Avogadro number, Planck was able to find the electric charge of the electron with the highest accuracy. From Planck's formula, in the form of special cases, both Wien's law and the Stefan-Boltzmann relation could be obtained, showing that the total radiation energy of a body is proportional to its absolute temperature to the fourth power. Physicists breathed a sigh of relief: the "ultraviolet catastrophe" ended quite well. Planck was by no means a revolutionary, and neither he nor other physicists were aware of the deep meaning of the concept of "quantum". For Planck, the quantum was merely a means of deriving a formula that gave satisfactory agreement with the blackbody radiation curve. He repeatedly tried to reach agreement within the classical tradition, but without success. This is how Planck described the doubts that tormented him: "... either the quantum of action was a fictitious quantity - then the entire derivation of the law of radiation was fundamentally illusory and was simply a game of formulas devoid of content, or the derivation of this law was based on the correct physical thought - then the quantum of action had to play a fundamental role in physics, then its appearance heralded something completely new, hitherto unheard of, which seemed to require a transformation of the very foundations of our physical thinking ... " At the same time, he noted with pleasure the first successes of quantum theory, which followed almost immediately. The position of quantum theory was strengthened in 1905, when Albert Einstein used the concept of a photon - a quantum of electromagnetic radiation. Einstein suggested that light has a dual nature: it can behave both as a wave and as a particle. In 1907, Einstein further strengthened the position of quantum theory by using the concept of a quantum to explain the puzzling discrepancies between theoretical predictions and experimental measurements of the specific heat of bodies. Another confirmation of the potential power of the innovation introduced by Planck came in 1913 from Niels Bohr, who applied quantum theory to the structure of the atom. Author: Samin D.K.
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