Testing the speed of ‘spooky action at a distance’

Salart, Daniel, Baas, Augustin, Branciard, Cyril, Gisin, Nicolas and Zbinden, Hugo (2008) Testing the speed of ‘spooky action at a distance’. Nature, 454 7206: 861-864. doi:10.1038/nature07121

Author Salart, Daniel
Baas, Augustin
Branciard, Cyril
Gisin, Nicolas
Zbinden, Hugo
Title Testing the speed of ‘spooky action at a distance’
Journal name Nature   Check publisher's open access policy
ISSN 0028-0836
Publication date 2008-08-14
Sub-type Article (original research)
DOI 10.1038/nature07121
Volume 454
Issue 7206
Start page 861
End page 864
Total pages 4
Place of publication London, U.K.
Publisher Nature Publishing Group
Language eng
Formatted abstract
Correlations are generally described by one of two mechanisms: either a first event influences a second one by sending information encoded in bosons or other physical carriers, or the correlated events have some common causes in their shared history. Quantum physics predicts an entirely different kind of cause for some correlations, named entanglement. This reveals itself in correlations that violate Bell inequalities (implying that they cannot be described by common causes) between space-like separated events (implying that they cannot be described by classical communication). Many Bell tests have been performed1, and loopholes related to locality2, 3, 4 and detection5, 6 have been closed in several independent experiments. It is still possible that a first event could influence a second, but the speed of this hypothetical influence (Einstein's 'spooky action at a distance') would need to be defined in some universal privileged reference frame and be greater than the speed of light. Here we put stringent experimental bounds on the speed of all such hypothetical influences. We performed a Bell test over more than 24 hours between two villages separated by 18 km and approximately east–west oriented, with the source located precisely in the middle. We continuously observed two-photon interferences well above the Bell inequality threshold. Taking advantage of the Earth's rotation, the configuration of our experiment allowed us to determine, for any hypothetically privileged frame, a lower bound for the speed of the influence. For example, if such a privileged reference frame exists and is such that the Earth's speed in this frame is less than 10-3 times that of the speed of light, then the speed of the influence would have to exceed that of light by at least four orders of magnitude.
Keyword Bell inequalities
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ
Additional Notes Published under Letter.

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Mathematics and Physics
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Created: Thu, 24 Mar 2011, 08:25:19 EST by Mr Cyril Branciard on behalf of Physics