Einstein-Podolsky-Rosen effects from independent particle sources

In conventional Einstein-Podolsky-Rosen (EPR) experiments an unstable system decays into an entangled state of two or more particles. When appropriate measurements are made on this entangled state, phenomena are exhibited that run counter to our classical notions of local realism. Using a variant of a gedanken experiment proposed by Greenberger, Horn, and Zeilinger, it is shown that EPR effects can arise even when the particles come from independent widely separated sources.