Entanglement, Nonlocality, and SR

We define nonlocality and outline its history culminating in the confirmation of nonlocality in 2015. We now know that all entangled quantum states exhibit nonlocality, that violation of Bell's inequalities indicates the presence of nonlocal action, and that the universe is nonlocal irrespective of the validity of QP. We review the Rarity-Tapster-Ou experiment, the only demonstration to date of momentum-entangled quanta. In addition to demonstrating nonlocality by its violation of a Bell inequality, the experiment obviously and intuitively demonstrates non-locality, providing direct insight into the astonishing “nonlocal interference” that results from entanglement. A section on the apparent paradoxes of nonlocality discusses Einstein's concerns and how entangled systems can exhibit nonlocality without contradicting SR: Nonlocal interference prevents superluminal signaling by “camouflaging” non-locality so that local observers detect only local action. Alice can use entangled states to instantly “steer” Bob's photon into a set of basis vectors without Bob detecting this. Nonlocality predicts the simultaneous occurrence of spatially separated nonlocal sets of events, as observed in the laboratory. This appears to conflict with relativistic causality because in some co-moving reference frames the “effect” occurs before the “cause.” We resolve this dilemma. We discuss nonlocal phenomena that can be demonstrated by a single quantum.