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

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

Scientists later confirmed this effect with neutrons, helium atoms, and even larger molecules, establishing matter-wave diffraction as a key principle of quantum mechanics.

From Science Daily • Apr. 28, 2026

Because of this, defining memory in quantum mechanics has remained a challenge.

From Science Daily • Apr. 14, 2026

Quantum batteries operate using core principles of quantum mechanics, including superposition and entanglement, rather than the chemical processes used in today's batteries.

From Science Daily • Apr. 4, 2026

Once quantum mechanics was accepted, so, too, would the mysterious powers of zero.

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