Wave function collapse: Difference between revisions

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Quantum theory offers no dynamical description of the "collapse" of the wave function. Viewed as a statistical theory, no description is expected. As Fuchs and Peres put it, "collapse is something that happens in our description of the system, not to the system itself".<ref name=FuchsPeresNo>{{Cite journal |last=Fuchs |first=Christopher A. |last2=Peres |first2=Asher |date=2000-03-01 |title=Quantum Theory Needs No ‘Interpretation’ |url=https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=7596444653d614458ee7aea0422dabfc95ace3e6 |journal=Physics Today |language=en |volume=53 |issue=3 |pages=70–71 |doi=10.1063/1.883004 |issn=0031-9228}}</ref>

Various [[interpretations of quantum mechanics]] attempt to provide a physical model for collapse.<ref name=Stamatescu>{{Cite book |last=Stamatescu |first=Ion-Olimpiu |url=https://link.springer.com/10.1007/978-3-540-70626-7_230 |title=Wave Function Collapse |date=2009 |publisher=Springer Berlin Heidelberg |isbn=978-3-540-70622-9 |editor-last=Greenberger |editor-first=Daniel |___location=Berlin, Heidelberg |pages=813–822 |language=en |doi=10.1007/978-3-540-70626-7_230 |editor-last2=Hentschel |editor-first2=Klaus |editor-last3=Weinert |editor-first3=Friedel}}</ref>{{rp|816}} Three treatments of collapse can be found among the common interpretations. The first group includes hidden variable theories like [[de Broglie–Bohm theory]]; here random outcomes only result from unknown values of hidden variables. Results from [[Bell test| tests]] of [[Bell's theorem]] shows that these variables would need to be non-local. The second group models measurement as quantum entanglement between the quantum state and the measurement apparatus. This results in a simulation of classical statistics called [[quantum decoherence]]. This group includes the [[many -worlds interpretation]] and [[consistent histories]] models. The third group postulates additional, but as yet undetected, physical basis for the randomness; this group includes for example the [[objective collapse interpretation]]s. While models in all groups have contributed to better understanding of quantum theory, no alternative explanation for individual events has emerged as more useful than collapse followed by statistical prediction with the Born rule.<ref name=Stamatescu/>{{rp|819}}

The significance ascribed to the wave function varies from interpretation to interpretation, and varies even within an interpretation (such as the Copenhagen Interpretation). If the wave function merely encodes an observer's knowledge of the universe then the wave function collapse corresponds to the receipt of new information. This is somewhat analogous to the situation in classical physics, except that the classical "wave function" does not necessarily obey a wave equation. If the wave function is physically real, in some sense and to some extent, then the collapse of the wave function is also seen as a real process, to the same extent.{{cn| reason=the ontological wave function literature should be represented, the paragraph based on Stamatescu is too compact now.|date=March 2024}}