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Johnjbarton (talk | contribs) move the paragraph on Zurek's work to the section on decoherence. |
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While standard quantum mechanics postulates wave function collapse to connect quantum to classical models, some extension theories propose physical processes that cause collapse. The in depth study of [[quantum decoherence]] has proposed that collapse is related to the interaction of a quantum system with its environment.
Calculations of [[quantum decoherence]] show that when a quantum system interacts with the environment, the superpositions ''apparently'' reduce to mixtures of classical alternatives. Significantly, the combined wave function of the system and environment continue to obey the Schrödinger equation throughout this ''apparent'' collapse.<ref name=Zurek>{{cite journal |last=Zurek |first=Wojciech Hubert |title=Quantum Darwinism |journal=Nature Physics |year=2009 |volume=5 |issue=3 |pages=181–188 |doi=10.1038/nphys1202 |arxiv = 0903.5082 |bibcode = 2009NatPh...5..181Z |s2cid=119205282}}</ref> More importantly, this is not enough to explain ''actual'' wave function collapse, as decoherence does not reduce it to a single eigenstate.<ref name=Schlosshauer>{{cite journal |last=Schlosshauer |first=Maximilian |title=Decoherence, the measurement problem, and interpretations of quantum mechanics |journal=Rev. Mod. Phys. |year=2005 |volume=76 |issue=4 |pages=1267–1305 |doi=10.1103/RevModPhys.76.1267 |arxiv = quant-ph/0312059 |bibcode = 2004RvMP...76.1267S |s2cid=7295619}}</ref><ref name="Stanford1">{{cite encyclopedia▼
| last = Fine▼
| first = Arthur▼
| title = The Role of Decoherence in Quantum Mechanics▼
| encyclopedia = Stanford Encyclopedia of Philosophy▼
| publisher = Center for the Study of Language and Information, Stanford University website▼
| date = 2020▼
| url = https://plato.stanford.edu/entries/qm-decoherence/▼
| format =▼
| doi =▼
| access-date = 11 April 2021}}</ref>▼
Historically, [[Werner Heisenberg]] was the first to use the idea of wave function reduction to explain quantum measurement.<ref>[[Werner Heisenberg|Heisenberg, W.]] (1927). Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik, ''Z. Phys.'' '''43''': 172–198. Translation as [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19840008978.pdf "The actual content of quantum theoretical kinematics and mechanics"].</ref>{{Citation needed|date=March 2024|reason=need a secondary ref to support this claim}}
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Quantum decoherence explains why a system interacting with an environment transitions from being a [[Quantum state#Pure states as rays in a complex Hilbert space|pure state]], exhibiting superpositions, to a [[Quantum state#Mixed states|mixed state]], an incoherent combination of classical alternatives.<ref name="Stanford1" /> This transition is fundamentally reversible, as the combined state of system and environment is still pure, but for all practical purposes irreversible in the same sense as in the [[second law of thermodynamics]]: the environment is a very large and complex quantum system, and it is not feasible to reverse their interaction. Decoherence is thus very important for explaining the [[classical limit]] of quantum mechanics, but cannot explain wave function collapse, as all classical alternatives are still present in the mixed state, and wave function collapse selects only one of them.<ref name=Schlosshauer/><ref>{{cite journal |author1=Wojciech H. Zurek |title=Decoherence, einselection, and the quantum origins of the classical |journal=Reviews of Modern Physics |date=2003 |volume=75 |issue=3 |page=715 |doi=10.1103/RevModPhys.75.715 |arxiv=quant-ph/0105127 |bibcode=2003RvMP...75..715Z |s2cid=14759237 }}</ref><ref name="Stanford1" />
▲Calculations of [[quantum decoherence]] show that when a quantum system interacts with the environment, the superpositions ''apparently'' reduce to mixtures of classical alternatives. Significantly, the combined wave function of the system and environment continue to obey the Schrödinger equation throughout this ''apparent'' collapse.<ref name=Zurek>{{cite journal |last=Zurek |first=Wojciech Hubert |title=Quantum Darwinism |journal=Nature Physics |year=2009 |volume=5 |issue=3 |pages=181–188 |doi=10.1038/nphys1202 |arxiv = 0903.5082 |bibcode = 2009NatPh...5..181Z |s2cid=119205282}}</ref> More importantly, this is not enough to explain ''actual'' wave function collapse, as decoherence does not reduce it to a single eigenstate.<ref name=Schlosshauer>{{cite journal |last=Schlosshauer |first=Maximilian |title=Decoherence, the measurement problem, and interpretations of quantum mechanics |journal=Rev. Mod. Phys. |year=2005 |volume=76 |issue=4 |pages=1267–1305 |doi=10.1103/RevModPhys.76.1267 |arxiv = quant-ph/0312059 |bibcode = 2004RvMP...76.1267S |s2cid=7295619}}</ref><ref name="Stanford1">{{cite encyclopedia
▲ | last = Fine
▲ | first = Arthur
▲ | title = The Role of Decoherence in Quantum Mechanics
▲ | encyclopedia = Stanford Encyclopedia of Philosophy
▲ | publisher = Center for the Study of Language and Information, Stanford University website
▲ | date = 2020
▲ | url = https://plato.stanford.edu/entries/qm-decoherence/
▲ | format =
▲ | doi =
▲ | access-date = 11 April 2021}}</ref>
==History==
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