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

Derived Forms

• quantum-mechanical
  adjective

Etymology

Origin of quantum mechanics

First recorded in 1920–25

Example Sentences

But as components approach atomic scales, engineers are increasingly running into the physical limits of silicon and the effects of quantum mechanics.

From Science Daily • May 30, 2026

The science which explains the way in which physical particles behave is called quantum mechanics and it's the basis on which quantum computers work - making them much better placed to solve these problems.

From BBC • May 28, 2026

Quantum computers, offshoots of quantum mechanics, can explore multiple solutions at once, and promise the kind of processing power that could revolutionize medicine, materials science, and other fields.

From Barron's • May 15, 2026

Physicists have demonstrated that even tiny chunks of metal can behave according to the strange rules of quantum mechanics, existing in states that spread across multiple locations at once.

From Science Daily • May 11, 2026

In quantum mechanics, the forces or interactions between matter particles are all supposed to be carried by particles of integer spin—0, 1, or 2.

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