quantum theory

American  

[kwon-tuhm thee-uh-ree, theer-ee] / ˈkwɒn təm ˌθi ə ri, ˌθɪər i /

noun

Physics.

1. any theory predating quantum mechanics that encompassed Planck's radiation law and a scheme for obtaining discrete energy states for atoms, such as the Bohr model.

2. any theory that treats certain phenomena by the methods of quantum mechanics.

   a quantum theory of gravitation.

---

quantum theory British  

noun

1. a theory concerning the behaviour of physical systems based on Planck's idea that they can only possess certain properties, such as energy and angular momentum, in discrete amounts (quanta). The theory later developed in several equivalent mathematical forms based on De Broglie's theory and on the Heisenberg uncertainty principle See wave mechanics

---

quantum theory Scientific  

1. See quantum mechanics

2. Any of various theories that makes use of the assumptions, principles, and laws of quantum mechanics.

---

Etymology

Origin of quantum theory

First recorded in 1910–15

Example Sentences

See Examples For:

quantum theory

While later discoveries refined that picture, Bohr's model helped pave the way for modern quantum theory.

From Science Daily ● Jul. 5, 2026

According to quantum theory, that should be possible.

From Science Daily ● May 18, 2026

Macroscopicity allows scientists to evaluate experiments involving systems such as nano-oscillators, atomic interferometers, and nanoacoustic resonators by measuring how effectively they rule out even tiny deviations from standard quantum theory.

From Science Daily ● May 11, 2026

Unlike classical physics, which predicts precise trajectories for everyday objects such as cricket balls or communications satellites, quantum theory can only predict the likelihood of where a particle might be observed.

From Science Daily ● Mar. 10, 2026

Overbye notes: "Bohr once commented that a person who wasn’t outraged on first hearing about quantum theory didn’t understand what had been said."

From "A Short History of Nearly Everything" by Bill Bryson