Correspondence principle

In physics, the correspondence principle is a principle, first invoked by Niels Bohr in 1923, which states that the behavior of quantum mechanical systems reduce to classical physics in the limit of large quantum numbers.

Related Topics:
Physics - Niels Bohr - 1923 - Quantum mechanical - Classical physics

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The rules of quantum mechanics are highly successful in describing microscopic objects, such as atoms and elementary particles. On the other hand, we know from experiment that a variety of macroscopic systems (springs, capacitors, llamas, and so forth) can be accurately described by classical theories such as classical mechanics and classical electrodynamics. However, it is not unreasonable to believe that the ultimate laws of physics must be independent of the size of the physical objects being described. This is the motivation for Bohr's correspondence principle, which states that classical physics must emerge as an approximation to quantum physics as systems become "larger".

Related Topics:
Atom - Elementary particles - Experiment - Spring - Capacitor - Llama - Classical mechanics - Classical electrodynamics

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The conditions under which quantum and classical physics agree are referred to as the correspondence limit, or the classical limit. Bohr provided a rough prescription for the correspondence limit: it occurs when the quantum numbers describing the system are large, meaning either some quantum numbers of the system are excited to a very large value, or the system is described by a large set of quantum numbers, or both.

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The correspondence principle is one of the tools available to physicists for selecting quantum theories corresponding to reality. The principles of quantum mechanics are fairly broad - for example, they state that the states of a physical system occupy a Hilbert space, but do not state what type of Hilbert space. The correspondence principle limits the choices to those that reproduce classical mechanics in the correspondence limit. For this reason, Bohm has argued that classical physics does not emerge from quantum physics in the same way that classical mechanics emerges as an approximation of special relativity at small velocities; rather, classical physics exists independently of quantum theory and cannot be derived from it.

Related Topics:
Reality - Principles of quantum mechanics - Hilbert space - Bohm - Special relativity - Velocities

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