Ars Technica: Quantum entanglement has been shown to exist and, so far, has not been affected by the distance between the entangled particles. How entanglement works without violating relativity’s limit on the speed of information transfer is still not understood. One explanation is the idea of nonlocality, which suggests that entangled particles are still considered part of the same quantum system regardless of the distance between them. But the concept of nonlocality is uncomfortable to some theorists. An alternative theory suggests that there are hidden, nonmeasurable, variables in quantum systems, but a new analysis has shown that hidden variables would still allow faster-than-light communication. In a paper in Nature Physics, researchers describe how they examined a theoretical entangled system in which hidden variables were allowed to communicate faster than light. They determined that because of the symmetry inherent in quantum systems, the measurable variables would also transfer information faster than light. But faster-than-light communication violates the theory of relativity. Although that fact doesn’t necessarily disprove hidden-variable explanations for quantum entanglement, it might mean that relativity would need to be adjusted.