Editing Measurement problem (section)

==Role of decoherence==

[[Erich Joos]] and [[Heinz-Dieter Zeh]] claim that the phenomenon of [[quantum decoherence]], which was put on firm ground in the 1980s, resolves the problem.<ref>{{cite journal |last1=Joos |first1=E. |last2=Zeh |first2=H. D. |title=The emergence of classical properties through interaction with the environment |journal=[[Zeitschrift für Physik B]] |date=June 1985 |volume=59 |issue=2 |pages=223–243 |doi=10.1007/BF01725541 |bibcode=1985ZPhyB..59..223J |s2cid=123425824 }}</ref> The idea is that the environment causes the classical appearance of macroscopic objects. Zeh further claims that decoherence makes it possible to identify the fuzzy boundary between the quantum microworld and the world where the classical intuition is applicable.<ref name="Zeh">{{cite book |author=Zeh |first=H. D. |url=https://books.google.com/books?id=6eTHcxeNxdUC |title=Decoherence and the Appearance of a Classical World in Quantum Theory |publisher=Springer-Verlag |year=2003 |isbn=3-540-00390-8 |editor=Joos |editor-first=E. |edition=2nd |page=7 |chapter=Chapter 2: Basic Concepts and Their Interpretation |bibcode=2003dacw.conf....7Z |arxiv=quant-ph/9506020}}</ref><ref>{{cite journal |last1=Jaeger |first1=Gregg |title=What in the (quantum) world is macroscopic? |journal=[[American Journal of Physics]] |date=September 2014 |volume=82 |issue=9 |pages=896–905 |doi=10.1119/1.4878358 |bibcode= 2014AmJPh..82..896J }}</ref> Quantum decoherence becomes an important part of some modern updates of the [[Copenhagen interpretation]] based on [[consistent histories]].<ref name="Belavkin94">{{cite journal |author=Belavkin |first=V. P. |year=1994 |title=Nondemolition principle of quantum measurement theory |journal=[[Foundations of Physics]] |volume=24 |pages=685–714 |arxiv=quant-ph/0512188 |bibcode=1994FoPh...24..685B |doi=10.1007/BF02054669 |s2cid=2278990 |number=5}}</ref><ref name="Belavkin2001">{{cite journal |author=Belavkin |first=V. P. |year=2001 |title=Quantum noise, bits and jumps: uncertainties, decoherence, measurements and filtering |journal=Progress in Quantum Electronics |volume=25 |pages=1–53 |arxiv=quant-ph/0512208 |bibcode=2001PQE....25....1B |doi=10.1016/S0079-6727(00)00011-2 |number=1}}</ref> Quantum decoherence does not describe the actual collapse of the wave function, but it explains the conversion of the quantum probabilities (that exhibit [[Interference (wave propagation)|interference]] effects) to the ordinary classical probabilities. See, for example, Zurek,<ref name=Zurek/> Zeh<ref name=Zeh/> and Schlosshauer.<ref name=Schlosshauer>{{cite journal
 | author = Maximilian Schlosshauer
 | title=Decoherence, the measurement problem, and interpretations of quantum mechanics
 | journal = Reviews of Modern Physics
 | volume = 76
 | year = 2005
 | pages = 1267–1305
 | doi = 10.1103/RevModPhys.76.1267|arxiv = quant-ph/0312059 |bibcode = 2004RvMP...76.1267S
 | issue = 4 | s2cid=7295619
 }}</ref>

The present situation is slowly clarifying, described in a 2006 article by Schlosshauer as follows:<ref name="Schlosshauer2">{{cite journal |author=Schlosshauer |first=Maximilian |date=January 2006 |title=Experimental motivation and empirical consistency in minimal no-collapse quantum mechanics |journal=[[Annals of Physics]] |volume=321 |issue=1 |pages=112–149 |arxiv=quant-ph/0506199 |bibcode=2006AnPhy.321..112S |doi=10.1016/j.aop.2005.10.004 |s2cid=55561902}}</ref>

{{blockquote|
Several decoherence-unrelated proposals have been put forward in the past to elucidate the meaning of probabilities and arrive at the [[Born rule]] ... It is fair to say that no decisive conclusion appears to have been reached as to the success of these derivations. ...

As it is well known, [many papers by Bohr insist upon] the fundamental role of classical concepts. The experimental evidence for superpositions of macroscopically distinct states on increasingly large length scales counters such a dictum. Superpositions appear to be novel and individually existing states, often without any classical counterparts. Only the physical interactions between systems then determine a particular decomposition into classical states from the view of each particular system. Thus classical concepts are to be understood as locally emergent in a relative-state sense and should no longer claim a fundamental role in the physical theory.
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