Today we will talk about the essence of such a concept as “ultraviolet catastrophe”: why this paradox appeared and are there any ways to resolve it.
Classical physics
Before the advent of quantum, classical physics reigned in the world of natural science. Of course, mathematics was always considered the main one. However, algebra and geometry are most often used as applied sciences. Classical physics explores how bodies behave during heating, expansion, and shock. She describes the conversion of energy from kinetic to internal, talks about concepts such as work and power. It is in this area that the answer lies to the question of how the ultraviolet catastrophe occurred in physics.
At some point, all these phenomena were so well studied that it seemed there was nothing more to discover! It got to the point that talented young people were advised to go to mathematics or biologists, since breakthroughs are possible only in these areas of science. But ultraviolet catastrophe and the harmonization of practice with theory proved the fallacy of such ideas.
Thermal radiation
Classical physics and paradoxes were not without. For example, thermal radiation is the electromagnetic field quanta that occur in heated bodies. Internal energy turns into light. According to classical physics, the radiation of a heated body is a continuous spectrum, and its maximum depends on temperature: the lower the reading of the thermometer, the “redder” the most intense light. Now we will directly get to what is called the ultraviolet disaster.
Terminator and heat radiation
An example of thermal radiation is heated and molten metals. In Terminator films, industrial objects often appear. In the most touching second part of the epic, the iron machine is immersed in a bath of gurgling cast iron. And this lake is red. So, this shade corresponds to the maximum radiation of cast iron with a certain temperature. This means that this value is not the highest of all possible, because the red photon has the smallest wavelength. It is worth remembering: liquid metal radiates energy both in the infrared, and in the visible, and in the ultraviolet region. Only there are very few photons other than red.
Black body
To obtain the spectral power density of radiation of a heated substance, use the approximation of a completely black body. The term sounds scary, but in fact it is very useful in physics and is not so rare in reality. So, a completely black body is an object that does not “release” photons that hit it. Moreover, its color (spectrum) depends on temperature. A rough approximation of a completely black body is a cube, on one side of which there is a hole measuring less than ten percent of the area of the whole figure. Example: windows in apartments of ordinary high-rise buildings. Therefore, they appear black.
Rayleigh-Jeans Law
This formula describes the radiation of a completely black body, relying only on the data available to classical physics:
- u (ω, T) = kTω 2 / π 2 c 3 , where
u is just the spectral density of the energy luminosity,
ω is the radiation frequency,
kT is the vibrational energy.
If the wavelengths are large, then the values are plausible and are in good agreement with experiment. But as soon as we cross the line of visible radiation and enter the ultraviolet zone of the electromagnetic spectrum, the energies reach incredible values. In addition, when integrating the formula in frequency from zero to infinity, an infinite value is obtained! This fact reveals the essence of the ultraviolet catastrophe: if a body is heated well enough, its energy will be enough to destroy the universe.
Planck and his quantum
Many scientists have tried to circumvent this paradox. A breakthrough, an almost intuitive step into the unknown, has led science out of a dead end. The Planck hypothesis helped to overcome the paradox of ultraviolet disaster . Planck's formula for the distribution of frequencies of radiation of a completely black body contained the concept of "quantum". The scientist himself defined it as a very small single action of the system on the surrounding world. Now a quantum is the smallest indivisible portion of some physical quantities.
Quantums come in many forms:
- electromagnetic field (photon, including in the rainbow);
- vector field (gluon determines the existence of strong interaction);
- gravitational field (graviton is still a purely hypothetical particle, which is in the calculations, but it has not yet been found experimentally);
- Higgs fields (the Higgs boson was recently discovered experimentally in the Large Hadron Collider, and even very distant from science people were happy to discover it);
- synchronous motion of lattice atoms of a solid (phonon).
Schrödinger cat and the demon of Maxwell
The discovery of quantum led to very significant consequences: a fundamentally new section of physics was created. Quantum mechanics, optics, field theory caused an explosion of scientific discoveries. Prominent scientists have discovered or rewritten laws. The fact of quantization of systems of elementary particles helped explain why the Maxwell demon could not exist (in fact, three explanations were proposed). However, Max Planck himself did not accept the fundamental nature of his discovery for a very long time. He believed that a quantum is a convenient mathematical way to express a certain thought, but no more. Moreover, the scientist laughed at the school of new physicists. Therefore, M. Planck came up with an insoluble, as it seemed to him, paradox about the Schrödinger cat. The poor beast was both alive and dead at the same time, which is impossible to imagine. But such a task has a very clear explanation in the framework of quantum physics, and the relatively young science itself is already striding around the planet.