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

Physicists still lack a complete quantum theory of gravity that describes gravity at the smallest scales.

From Science Daily ● Jun. 19, 2026

The research, published in the journal Physical Review D, introduces a new mathematical framework for connecting quantum theory and gravity.

From Science Daily ● Mar. 9, 2026

Over time, Lorentz invariance became a foundational assumption in modern physics, especially within quantum theory.

From Science Daily ● Jan. 8, 2026

If her guess about these universes was right, and they were the multiple worlds predicted by quantum theory, then some of them would have split off from her own much earlier than others.

From "The Amber Spyglass" by Philip Pullman