Bells-inequality experiments using independent-particle sources

In the usual Bells-inequality experiments two particles carrying spin or polarization are prepared in an entangled state generated from the decay of an unstable quantum-mechanical system. These particles are then delivered to spin or polarization analyzers. The statistics of the measurements reported by the analyzers are incompatible with our notions of local realism. Here we show that Bells-inequality violations occur even when the initial state is a direct product state. In fact, the two particles can come from two independent widely separated sources.