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

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Etymology

Origin of quantum mechanics

First recorded in 1920–25

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Example Sentences

See Examples For:

quantum mechanics

One example is the Wheeler-DeWitt equation, which appears in attempts to combine quantum mechanics with gravity.

From Science Daily ● Oct. 30, 2026

In other words, the internally generated measure of time could still be used to make predictions about the quantum system's behavior, much as conventional time is used in standard quantum mechanics.

From Science Daily ● Oct. 30, 2026

Although the fundamental equations of quantum mechanics can describe the other two processes, calculating how energy is lost through atomic vibrations presents substantial computational obstacles.

From Science Daily ● Oct. 23, 2026

Examples include the mass and electric charge of an electron and the Planck constant, which plays a central role in quantum mechanics, the branch of physics that describes matter and energy at extremely small scales.

From Science Daily ● Oct. 11, 2026

As we saw in the last chapter, quantum mechanics tells us that all particles are in fact waves, and that the higher the energy of a particle, the smaller the wavelength of the corresponding wave.

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

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