CHAPTER 1 - THE BASIC CONCEPTS OF QUANTUM MECHANICS

Abstract

An attempt to apply classical mechanics and electrodynamics to explain atomic phenomena leads to results that are in obvious conflict with experiment. This marked contradiction between theory and experiment indicates that the construction of a theory applicable to atomic phenomena, that is, phenomena occurring in particles of very small mass at very small distances demands a fundamental modification of the basic physical concepts and laws. As a starting-point for an investigation of these modifications, it is convenient to take the experimentally observed phenomenon known as electron diffraction. This chapter discusses the basic concepts of quantum mechanics. The mechanics which governs atomic phenomena—quantum mechanics or wave mechanics—is based on ideas of motion, which are fundamentally different from those of classical mechanics. In quantum mechanics, there is no such concept as the path of a particle. This forms the content of what is called the uncertainty principle, one of the fundamental principles of quantum mechanics. This principle in itself does not suffice as a basis to construct a new mechanics of particles. Quantum mechanics occupies a very unusual place among physical theories: it contains classical mechanics as a limiting case, yet at the same time, it requires this limiting case for its own formulation. A typical problem of quantum mechanics consists in predicting the result of a subsequent measurement from the known results of previous measurements. In comparison with classical mechanics, quantum mechanics restricts the range of values that can be taken by various physical quantities, for example, energy.