Editing Semiclassical physics (section)

{{Short description|Use of both classical and quantum physics to analyze a system}}
{{Use American English|date=January 2019}}{{No footnotes|date=November 2018}}

In [[physics]], '''semiclassical''' refers to a theory in which one part of a [[Physical system|system]] is described [[quantum mechanics|quantum mechanically]], whereas the other is treated [[classical mechanics|classically]]. For example, external [[field (physics)|field]]s will be constant, or when changing will be classically described. In general, it incorporates a development in [[exponent|power]]s of the [[Planck constant]], resulting in the classical physics of power 0, and the first nontrivial approximation to the power of (−1). In this case, there is a clear link between the quantum-mechanical system and the associated semi-classical and classical approximations, as it is similar in appearance to the transition from [[physical optics]] to [[geometric optics]].