Hip Glossary: Quantum

In physics, a quantum (plural: quanta) refers to an indivisible entity of energy. For instance, a "light quantum", being a unit of light (that is, a photon). In combinations like "quantum mechanics", "quantum optics", etc., it distinguishes a more specialized field of study.

The word comes from the Latin "quantus", for "how much".

Behind this, one finds the fundamental notion that a physical property may be "quantized", referred to as "quantization". This means that the magnitude can take on only certain numerical values, rather than any value, at least within a range. For example, the energy of an electron bound to an atom (at rest) is quantized. This accounts for the stability of atoms, and matter in general.

An entirely new conceptual framework was developed around this idea, during the first half of the 1900s. Usually referred to as quantum "mechanics", it is regarded by virtually every professional physicist as the most fundamental framework we have for understanding and describing nature, for the very practical reason that it works. It is "in the nature of things", not a more or less arbitrary human preference.