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.

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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

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quantum theory Scientific  

1. See quantum mechanics

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

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Etymology

Origin of quantum theory

First recorded in 1910–15

Example Sentences

These understandings include attempts to reconcile general relativity with quantum theory — a challenge explored both in philosophy and popular science discussions.

From Science Daily • Jun. 8, 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

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

The alternative histories hypothesis sounds rather like Richard Feynman’s way of expressing quantum theory as a sum over histories, which was described in Chapters 4 and 8.

From "A Brief History of Time: And Other Essays" by Stephen Hawking