Symmetry operations

Abstract

The effect of symmetries in the case of quantum systems leads to a group theoretical classification of energy spectra and corresponding state spaces, and in addition to selection rules for processes. Hence, the symmetry concept offers an effective method for the treatment of quantum systems. It should be pointed out, however, that the use of group theory is by no means restricted to the case of perfect symmetry, i.e., even for broken symmetries a group theoretical classification is often meaningful. The latter possibility is important, as all real physical systems, e.g., crystals with impurities, have broken symmetries.