From Big Medical Encyclopedia

QUANTUM THEORY (quantum, or wave, mechanics) — one of the main theories of physics describing properties and structure of atoms and molecules, patterns of the movement, interaction and transformation of microparticles.

The beginning To. t. it was necessary M. Planck's hypothesis about preryvny (discrete, separate portions of energy in quanta) the nature of emission and absorption of electromagnetic energy (1901). Further, substantially works of A. Einstein who developed To. t. light, N. Bor who created To. t. atom (1912), JI. de Broil who put forward the idea about wave properties of microparticles (1924) the basis of the uniform quantum-mechanical theory (quantum, or wave, mechanics) — bases of the modern doctrine about a structure of substance was created.

Modern To. t. proceeds from the dual, corpuscular and wave nature of the phenomena of a microcosm. E.g., the electromagnetic radiation, in particular light having the wave properties causing the phenomena interferences (see), diffractions, polarization (see), represent at the same time a particle flux — the photons (quanta of electromagnetic radiation) having the zero mass of rest, the number of the movement and moving with a speed equal to velocity of light in vacuum. The cathode rays, neutrons, atoms, etc. the particles having the weight, a charge, the number of the movement is at the same time characterized by such wave property as diffraction found at dispersion of particles on a surface of crystals (see. X-ray crystallographic analysis ).

For lack of external influence the quantum system (e.g., atom) is in a stationary state with the smallest energy. At impact on system (e.g., at absorption by atom of a light quantum) it moves to a new stationary level with higher energy. From this more high energy level the system can return to a reference state, having highlighted, e.g., quantum of energy (see. Luminescence ) or having spent it in the form of heat. The similar phenomenon leads to change of a condition of system and carries the name of quantum transition. As a rule, there are several opportunities of quantum transition determined by a resolution and probability of transition (see. Probabilities theory ).

Creation of the quantum-mechanical theory based on probabilistic, statistical interpretation of various cases of the movement, interaction, disintegration, mutually destruction (see. Annihilation ) microparticles, gave an impetus to use of achievements To. t. in chemistry, biology and medicine. In particular, promoted development of modern representations in mechanisms of sight, photosynthesis (see), photomutagenesis. Development To. t. structures of substance promoted development of a number of methods of the analysis of substance, including and biological (see. Spectral analysis , X-ray crystallographic analysis , Electronic paramagnetic resonance , Nuclear magnetic resonance ). There was a possibility of quantitative calculation of distribution of electrons and a prediction on this basis of possible physical and chemical properties of molecules and their activity that creates conditions for assessment of properties and the directed synthesis of pharmaceuticals, the mechanism of effect of carcinogens etc.

Bibliography: Blokhintsev R. I. Fundamentals of quantum mechanics, M., 1976; Bourne M. Atomic physics, the lane with English, M., 1970, bibliogr.; Ioffe A. F. The main of representations! modern physics, L. — M, 1949; Shpolsky E. V. Atomic physics, t. 1, M., 1974.

Yu. M. Shtukkenberg.