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

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

Cat qubits are named in honour of Erwin Schrödinger, whose cat-in-a-box question in 1935 helped illuminate some of the thinking behind quantum theory.

From BBC • Feb. 27, 2025

JJ: There’s so much contradiction within the music on “Quantum Baby” that mimics quantum theory.

From Los Angeles Times • Dec. 4, 2024

Minic instead argued that the quantum theory behind Einstein's gravity and standard model for matter is gravitized quantum theory.

From Salon • Nov. 13, 2024

A black hole is a zero in the equations of general relativity; the energy of the vacuum is a zero in the mathematics of quantum theory.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife