Topic summary
Spin singlet
Extracted from the Wikipedia article Singlet state.
Singlets and entangled states
The possibility of spatially extended unbound singlet states has considerable historical and even philosophical importance, since considering such states contributed importantly to the theoretical and experimental exploration and verification of what is now called quantum entanglement. Along with Podolsky and Rosen, Einstein proposed the EPR paradox thought experiment to help define his concerns with what he viewed as the non-locality of spatially separated entangled particles, using it in an argument that quantum mechanics was incomplete. In 1951 David Bohm formulated a version of the "paradox" using spin singlet states.