| a theory of the mechanics of atoms, molecules, and other physical systems that are subject to the uncertainty principle. Abbreviation: QM |
| quantum mechanics n. (used with a sing. or pl. verb) Quantum theory, especially the quantum theory of the structure and behavior of atoms and molecules. |
The branch of physics that deals with the behavior of matter at the level of the atom, the nucleus, and the elementary particle. At this level, energy, mass, momentum, and other quantities do not vary continuously, as they do in the large-scale world, but come in discrete units, or quanta. (See Bohr atom and photon.)
