Researchers at the University of Geneva (Geneva, Switzerland) have determined a minimum speed for Albert Einstein’s hypothetical “spooky action at a distance” (see Salart et al., Nature, p. 861, Aug. 14, 2008). Two pre—existing underground fiber—optic paths, extending east and west from Geneva over 18 km, were equalized in length by adding a fiber coil to one of the paths. Identical unbalanced fiber—optic Michelson interferometers were added to each end. Entangled photon pairs generated in Geneva in a nonlinear crystal were sent each way to the interferometers.
Using two optically identical setups (but scanning the phase of one interferometer only), the researchers measured the correlation between the two photon detections over many Earth rotations. They were able to exclude any “common cause” explanation for the correlations, and, assuming that the Earth’s speed relative to a privileged frame is less than a thousandth of the speed of light, determined that a spooky action at a distance had to travel at 10,000 times the speed of light or more. Another explanation is that spooky action at a distance doesn’t exist and quantum physics is correct. Contact Daniel Salart at [email protected].