Quantum Definition in Physics and Chemistry

What Quantum Really Means in Science

Quantum entanglement occurs when particles become linked across space and time, interacting even though separated by a distance.
Quantum entanglement occurs when particles become linked across space and time, interacting even though separated by a distance. MARK GARLICK/SCIENCE PHOTO LIBRARY / Getty Images

In physics and chemistry, a quantum is a discrete packet of energy or matter. The term quantum also means the minimum value of a physical property involved in an interaction. The plural of quantum is quanta.

For example: the quantum of charge is the charge of an electron. Electric charge can only increase or decrease by discrete energy levels. So, there is no half-charge. A photon is a single quantum of light. Light and other electromagnetic energy is absorbed or emitted in quanta or packets.

The word quantum comes from the Latin word quantus, which means "how great." The word came into use before the year 1900, in reference to quantum satis in medicine, which means "the amount which is sufficient".

Misuse of Term

The word quantum is often mis-used as an adjective to mean the opposite of its definition or in an inappropriate context. For example, the term "quantum mysticism" implies a correlation between quantum mechanics and parapsychology that has not been supported by empirical data. The phase "quantum leap" is used to suggest a large change, while the definition of quantum is that the change is the minimum amount possible.