quantum mechanics

American  

noun

Physics.

1. a theory of the mechanics of atoms, molecules, and other physical systems that are subject to the uncertainty principle. QM

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quantum mechanics British  

noun

1. (functioning as singular) the branch of mechanics, based on the quantum theory used for interpreting the behaviour of elementary particles and atoms, which do not obey Newtonian mechanics

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quantum mechanics Scientific  

1. A fundamental theory of matter and energy that explains facts that previous physical theories were unable to account for, in particular the fact that energy is absorbed and released in small, discrete quantities (quanta), and that all matter displays both wavelike and particlelike properties, especially when viewed at atomic and subatomic scales. Quantum mechanics suggests that the behavior of matter and energy is inherently probabilistic and that the effect of the observer on the physical system being observed must be understood as a part of that system.

2. Also called quantum physics quantum theory

3. Compare classical physics See also probability wave quantum uncertainty principle wave-particle duality

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quantum mechanics Cultural  

1. The branch of physics that deals with the behavior of matter at the level of the atom, the nucleus, and the elementary particle. At this level, energy, mass, momentum, and other quantities do not vary continuously, as they do in the large-scale world, but come in discrete units, or quanta. (See Bohr atom and photon.)

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Other Word Forms

• quantum-mechanical
  adjective

Etymology

Origin of quantum mechanics

First recorded in 1920–25

Example Sentences

See Examples For:

quantum mechanics

That idea clashes with the classical expectation that each particle should possess its own separate physical reality, a feature of quantum mechanics that famously troubled Albert Einstein.

From Science Daily ● Sep. 29, 2026

The connection is one of the most counterintuitive features of quantum mechanics and has challenged physicists' understanding of reality for decades.

From Science Daily ● Sep. 20, 2026

Their work suggests that certain alternatives to standard quantum mechanics, known as quantum collapse models, could have surprising consequences for the nature of time itself and for the ultimate precision of clocks.

From Science Daily ● Sep. 11, 2026

The work touches on one of the biggest unsolved problems in modern physics: how to reconcile quantum mechanics with gravity.

From Science Daily ● Sep. 11, 2026

Modern quantum mechanics combines both ideas, and it is customary today to think of light as behaving in some circumstances as a beam of particles and in others as a wave.

From "Cosmos" by Carl Sagan