Editing Hidden-variable theory (section)

=== Bell's theorem ===
{{Main|Bell's theorem}}

In 1964, [[John Stewart Bell]] showed through his famous theorem that if local hidden variables exist, certain experiments could be performed involving quantum entanglement where the result would satisfy a [[Bell's theorem|Bell inequality]]. If, on the other hand, statistical correlations resulting from quantum entanglement could not be explained by local hidden variables, the Bell inequality would be violated. Another [[no-go theorem]] concerning hidden-variable theories is the [[Kochen–Specker theorem]].

Physicists such as [[Alain Aspect]] and Paul Kwiat have performed [[Bell test experiments|experiments]] that have found violations of these inequalities up to 242 standard deviations.<ref>{{cite journal | author = Kwiat P. G.|display-authors=etal | year = 1999 | title = Ultrabright source of polarization-entangled photons | journal = Physical Review A | volume = 60 | issue = 2| pages = R773–R776 | doi=10.1103/physreva.60.r773 | bibcode=1999PhRvA..60..773K| arxiv = quant-ph/9810003 |s2cid=16417960 }}</ref> This rules out local hidden-variable theories, but does not rule out non-local ones. Theoretically, there could be [[Bell test loopholes|experimental problems]] that affect the validity of the experimental findings.

[[Gerard 't Hooft]] has disputed the validity of Bell's theorem on the basis of the [[superdeterminism]] loophole and proposed some ideas to construct local deterministic models.<ref>{{cite arXiv | eprint=quant-ph/0701097 | author1=Gerard 't Hooft | title=The Free-Will Postulate in Quantum Mechanics | date=2007 }}</ref><ref>{{cite arXiv | eprint=0908.3408 | author1=Gerard 't Hooft | title=Entangled quantum states in a local deterministic theory | date=2009 | class=quant-ph }}</ref>