http://arxiv.org/PS_cache/arxiv/pdf/0808/0808.3316v1.pdf
Testing spooky action at a distance D. Salart, A. Baas, C. Branciard, N. Gisin, and H. Zbinden Group of Applied Physics, University of Geneva, 20, Rue de l'Ecole de Médecine, CH-1211 Geneva 4, Switzerland August 25, 2008 In science, one observes correlations and invents theoretical models that describe them. In all sci- ences, besides quantum physics, all correlations are described by either of two mechanisms. Either a firrst event influences a second one by sending some information encoded in bosons or molecules or other physical carriers, depending on the partic- ular science. Or the correlated events have some common causes in their common past. Interest- ingly, quantum physics predicts an entirely differ- ent kind of cause for some correlations, named en- tanglement. This new kind of cause reveals itself, e.g., in correlations that violate Bell inequalities (hence cannot be described by common causes) between space-like separated events (hence cannot be described by classical communication). Einstein branded it as spooky action at a distance. A real spooky action at a distance would require a faster than light influence defined in some hy- pothetical universally privileged reference frame. Here we put stringent experimental bounds on the speed of all such hypothetical influences. We per- formed a Bell test during more than 24 hours be- tween two villages separated by 18 km and approx- imately east-west oriented, with the source located precisely in the middle. We continuously observed 2-photon interferences well above the Bell inequal- ity threshold. Taking advantage of the Earth's ro- tation, the configuration of our experiment allowed us to determine, for any hypothetically privileged frame, a lower bound for the speed of this spooky influence. For instance, if such a privileged refer- ence frame exists and is such that the Earth's speed in this frame is less than 10^-3 that of the speed of light, then the speed of this spooky influence would have to exceed that of light by at least 4 orders of magnitude. <more>
