Editing Hidden-variable theory (section)

== Recent developments ==
In August 2011, [[Roger Colbeck]] and [[Renato Renner]] published a proof that any extension of quantum mechanical theory, whether using hidden variables or otherwise, cannot provide a more accurate prediction of outcomes, assuming that observers can freely choose the measurement settings.<ref name="Colbeck-Renner2011">{{cite journal|author1=Roger Colbeck|author2=Renato Renner|title=No extension of quantum theory can have improved predictive power|year=2011|volume=2|issue=8|journal=Nature Communications |doi=10.1038/ncomms1416|bibcode = 2011NatCo...2..411C |arxiv = 1005.5173|pages=411|pmid=21811240|pmc=3265370}}</ref> Colbeck and Renner write: "In the present work, we have ... excluded the possibility that any extension of quantum theory (not necessarily in the form of local hidden variables) can help predict the outcomes of any measurement on any quantum state. In this sense, we show the following: under the assumption that measurement settings can be chosen freely, quantum theory really is complete".

In January 2013, [[Giancarlo Ghirardi]] and [[Raffaele Romano]] described a model which, "under a different free choice assumption [...] violates [the statement by Colbeck and Renner] for almost all states of a bipartite two-level system, in a possibly experimentally testable way".<ref name="GhirardiRomano2013">{{cite journal|author1=Giancarlo Ghirardi|author2=Raffaele Romano|title=Onthological models predictively inequivalent to quantum theory|year=2013|arxiv = 1301.2695 |bibcode = 2013PhRvL.110q0404G |doi = 10.1103/PhysRevLett.110.170404|volume=110|issue=17|journal=Physical Review Letters|pmid=23679689|page=170404|s2cid=197479}}</ref>