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Quantum mechanics is a fundamental theory that describes the behavior of nature at and below the scale of atoms. [2]: 1.1 It is the foundation of all quantum physics, which includes quantum chemistry, quantum field theory, quantum technology, and quantum information science. Quantum mechanics can describe many systems that classical physics cannot.
This is an accepted version of this page This is the latest accepted revision, reviewed on 15 November 2024. Description of large objects' physics For other uses, see Classical Mechanics (disambiguation). This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find ...
Classical mechanics is a model of the physics of forces acting upon bodies; includes sub-fields to describe the behaviors of solids, gases, and fluids. It is often referred to as "Newtonian mechanics" after Isaac Newton and his laws of motion. It also includes the classical approach as given by Hamiltonian and Lagrange methods. It deals with ...
In the words of quantum physicist Richard Feynman, quantum mechanics deals with "nature as She is—absurd". [4] Features of quantum mechanics often defy simple explanations in everyday language. One example of this is the uncertainty principle: precise measurements of position cannot be combined with precise measurements of velocity.
Action principles are "integral" approaches rather than the "differential" approach of Newtonian mechanics.[2]: 162 The core ideas are based on energy, paths, an energy function called the Lagrangian along paths, and selection of a path according to the "action", a continuous sum or integral of the Lagrangian along the path.
Leonard I. Schiff (1968) Quantum Mechanics McGraw-Hill Education; Davydov A.S. (1965) Quantum Mechanics Pergamon ISBN 9781483172026; Shankar, Ramamurti (2011). Principles of Quantum Mechanics (2nd ed.). Plenum Press. ISBN 978-0306447907. von Neumann, John (2018). Nicholas A. Wheeler (ed.). Mathematical Foundations of Quantum Mechanics ...
This makes the action an input to the powerful stationary-action principle for classical and for quantum mechanics. Newton's equations of motion for the ball can be derived from the action using the stationary-action principle, but the advantages of action-based mechanics only begin to appear in cases where Newton's laws are difficult to apply.
Introductory quantum mechanics textbooks suggest that quantum mechanics goes over to classical theory in the limit of high quantum numbers [15]: 27 or in a limit where the Planck constant in the quantum formula is reduced to zero, . [10]: 214 However such correspondence is not always possible. For example, classical systems can exhibit chaotic ...