Einstein famously used the phrase 'spooky action at a distance' to describe the continuing interaction between distant photons that possess the quantum mechanical property of entanglement. A paper in this week's Nature (http://www.nature.com/nature) gives the lower speed limit of any such 'spooky action' as 10,000 times the speed of light. Experimental tests known as Bell inequalities have all but ruled out a classical explanation for these correlations between entangled photons, but the possibility remains that a first event could influence a second one, if the influence occurs faster than the speed of light. The test performed by researchers based in Switzerland lasted more than 24 hours, and ran between two Swiss villages 18 kilometres apart with the source precisely in the middle. Taking advantage of the Earth's rotation, the experiment allowed the determination of a lower bound for the speed of any such influence. The team conclude that the minimal speed of hypothetical spooky action at a distance for this experiment is at least 10,000 times the speed of light. The existence in nature of a real spooky action at a distance is therefore deemed implausible. In a related commentary in Nature, Terence Rudolph says "any theory that tries to explain quantum entanglement... will need to be very spooky - spookier, perhaps, than quantum mechanics itself". Abstract (citations omitted): 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 performed, and loopholes related to locality and detection 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 18km 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 1023 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.