An absolutely black body is called suchthat it absorbs all radiation falling on it (or rather, into it) radiation both in the visible spectrum and beyond. But if the body does not heat up, the energy is re-radiated back. This radiation emitted by an absolutely black body is of particular interest. The first attempts to study its properties were made before the appearance of the model itself.
In the early 19th century, John Leslie conducted experimentswith various substances. As it turned out, black soot not only absorbs all the visible light falling on it. It emitted in the infrared range is much stronger than other, lighter, substances. It was thermal radiation, which differs from all other species by several properties. Radiation of an absolutely black body is balanced, uniform, occurs without energy transfer and depends only on body temperature.
Such a unique object that radiatesonly a certain kind of energy, could not help but attract attention. Since we are talking about thermal radiation, the first formulas and theories as to how the spectrum should look, were proposed in terms of thermodynamics. Classical thermodynamics was able to determine at what wavelength the radiation maximum should be at a given temperature, in which direction and how much it will shift when heated and cooled. However, it was not possible to predict what is the distribution of energy in the spectrum of an absolutely black body at all wavelengths and, in particular, in the ultraviolet range.
According to the ideas of classical thermodynamics,energy can be radiated by any portions, including as small as desired. But in order for an absolutely black body to radiate at short wavelengths, the energy of some of its particles must be very large, and in the region of ultrashort waves it would go to infinity. In reality, this is impossible, infinity appeared in the equations and was called the ultraviolet catastrophe. Only Planck’s theory that energy can be radiated in discrete portions — quanta — helped solve the difficulty. Today's equations of thermodynamics are special cases of the equations of quantum physics.
Originally completely black body representedlike a cavity with a narrow hole. Radiation from the outside enters such a cavity and is absorbed by the walls. The radiation spectrum that an absolutely black body should have, in this case, is similar to the radiation spectrum from the cave entrance, the hole in the well, the windows into the dark room on a sunny day, etc. But most of all with him coincide the spectra of the cosmic background radiation of the Universe and the stars, including the Sun.
It is safe to say that the morea particular object of particles with different energies, the stronger its radiation will resemble blackbody. The energy distribution curve in the spectrum of an absolutely black body reflects statistical patterns in the system of these particles, with the only amendment that the energy transmitted during the interactions is discrete.
