Editing Copenhagen interpretation (section)

===The Heisenberg cut===
Much criticism of Copenhagen-type interpretations has focused on the need for a classical domain where observers or measuring devices can reside, and the imprecision of how the boundary between quantum and classical might be defined. This boundary came to be termed the [[Heisenberg cut]] (while [[John Stewart Bell|John Bell]] derisively called it the "shifty split"<ref name="Bell-Against-Measurement" />). As typically portrayed, Copenhagen-type interpretations involve two different kinds of time evolution for wave functions, the deterministic flow according to the [[Schrödinger equation]] and the probabilistic jump during measurement, without a clear criterion for when each kind applies. Why should these two different processes exist, when physicists and laboratory equipment are made of the same matter as the rest of the universe?<ref>{{cite journal|title=Einstein's Mistakes |first=Steven |last=Weinberg |author-link=Steven Weinberg |journal=[[Physics Today]] |date=November 2005 |volume=58 |issue=11 |page=31 |doi=10.1063/1.2155755|bibcode=2005PhT....58k..31W |s2cid=120594692 |doi-access=free }}</ref> And if there is somehow a split, where should it be placed? [[Steven Weinberg]] writes that the traditional presentation gives "no way to locate the boundary between the realms in which [...] quantum mechanics does or does not apply."<ref>{{cite news | first=Steven |last=Weinberg|author-link=Steven Weinberg |title=The Trouble with Quantum Mechanics | url=https://www.nybooks.com/articles/2017/01/19/trouble-with-quantum-mechanics/ | work=New York Review of Books | date=19 January 2017 | access-date=8 January 2017}}</ref>

The problem of thinking in terms of classical measurements of a quantum system becomes particularly acute in the field of [[quantum cosmology]], where the quantum system is the universe.<ref>'Since the Universe naturally contains all of its observers, the problem arises to come up with an interpretation of quantum theory that contains no classical realms on the fundamental level.', {{cite magazine|arxiv=quant-ph/0210152|author1=Claus Kiefer|title=On the interpretation of quantum theory – from Copenhagen to the present day|url=https://archive.org/details/arxiv-quant-ph0210152|magazine=Time|pages=291|year=2002|bibcode=2003tqi..conf..291K}}</ref><ref name=":4">{{cite journal|last=Haag|first=Rudolf|author-link=Rudolf Haag|year=2010|title=Some people and some problems met in half a century of commitment to mathematical physics|journal=[[The European Physical Journal H]]|volume=35|pages=263–307|bibcode=2010EPJH...35..263H|doi=10.1140/epjh/e2010-10032-4|number=3|s2cid=59320730}}</ref> How does an observer stand outside the universe in order to measure it, and who was there to observe the universe in its earliest stages? Advocates of Copenhagen-type interpretations have disputed the seriousness of these objections. [[Rudolf Peierls]] noted that "the observer does not have to be contemporaneous with the event"; for example, we study the early universe through the [[cosmic microwave background]], and we can apply quantum mechanics to that just as well as to any electromagnetic field.<ref name="Peierls" /> Likewise, [[Asher Peres]] argued that physicists ''are'', conceptually, outside those degrees of freedom that cosmology studies, and applying quantum mechanics to the radius of the universe while neglecting the physicists in it is no different from quantizing the electric current in a [[superconductor]] while neglecting the atomic-level details.<ref name="peres1998">{{Cite journal|last=Peres|first=Asher|author-link=Asher Peres|date=1998-12-01|title=Interpreting the Quantum World|url=|journal=[[Studies in History and Philosophy of Modern Physics]]|language=en|volume=29|issue=4|pages=611–620|arxiv=quant-ph/9711003|bibcode=1997quant.ph.11003P|doi=10.1016/S1355-2198(98)00017-3|issn=1355-2198}}</ref>

{{Blockquote|text=You may object that there is only one universe, but likewise there is only one [[SQUID]] in my laboratory.<ref name="peres1998"/>}}