Editing Bell test (section)

===Locality loophole===
One of the assumptions of Bell's theorem is the one of locality, namely that the choice of setting at a measurement site does not influence the result of the other. The motivation for this assumption is the [[special relativity|theory of relativity]], that prohibits communication faster than light. For this motivation to apply to an experiment, it needs to have space-like separation between its measurements events. That is, the time that passes between the choice of measurement setting and the production of an outcome must be shorter than the time it takes for a light signal to travel between the measurement sites.<ref name="Bell-1987b">{{cite journal|first=J. S. |last=Bell |year=1980 |title=Atomic-cascade photons and quantum-mechanical nonlocality|journal=Comments on Atomic and Molecular Physics |volume=9 |pages=121–126}} Reprinted as {{cite book|chapter=Chapter 13 |first=J. S. |last=Bell |title=Speakable and Unspeakable in Quantum Mechanics |publisher=Cambridge University Press |year=1987|page=109}}</ref>

The first experiment that strived to respect this condition was Aspect's 1982 experiment.<ref name="Aspect-1982b">{{cite journal |first1=Alain |last1=Aspect |first2=Jean |last2=Dalibard |first3=Gérard |last3=Roger |year=1982 |title=Experimental Test of Bell's Inequalities Using Time-Varying Analyzers |journal=[[Physical Review Letters]] |volume=49 |issue=25 |pages=1804–7 |doi=10.1103/PhysRevLett.49.1804|bibcode = 1982PhRvL..49.1804A|doi-access=free }}</ref> In it the settings were changed fast enough, but deterministically. The first experiment to change the settings randomly, with the choices made by a [[quantum random number generator]], was Weihs et al.'s 1998 experiment.<ref name="Weihs-1998">{{cite journal|first1=G. |last1=Weihs |first2=T. |last2=Jennewein |first3=C. |last3=Simon |first4=H. |last4=Weinfurter |first5=A. |last5=Zeilinger |year=1998 |title=Violation of Bell's inequality under strict Einstein locality conditions |journal=[[Physical Review Letters]] |volume=81 |issue=23 |pages=5039–5043 |arxiv=quant-ph/9810080 |doi=10.1103/PhysRevLett.81.5039 |bibcode=1998PhRvL..81.5039W|s2cid=29855302 }}</ref> Scheidl et al. improved on this further in 2010 by conducting an experiment between locations separated by a distance of {{cvt|144|km|mi}}.<ref name="Scheidl-2010">{{cite journal|first1=Thomas |last1=Scheidl |first2=Rupert |last2=Ursin |first3=Johannes |last3=Kofler |first4=Sven |last4=Ramelow |first5=Xiao-Song |last5=Ma |first6=Thomas |last6=Herbst |first7=Lothar |last7=Ratschbacher |first8=Alessandro |last8=Fedrizzi |first9=Nathan K. |last9=Langford |first10=Thomas |last10=Jennewein |first11=Anton |last11=Zeilinger |year=2010|title=Violation of local realism with freedom of choice |journal=[[Proceedings of the National Academy of Sciences of the United States of America|PNAS]] |volume=107 |issue=46 |pages=19708–19713 |doi=10.1073/pnas.1002780107|display-authors=etal|bibcode=2010PNAS..10719708S |arxiv=0811.3129 |pmid=21041665 |pmc=2993398 |doi-access=free}}</ref>