What is the name of the paradox proposed by Einstein, Podolsky, and Rosen?

The paradox proposed by Einstein, Podolsky, and Rosen is the EPR paradox.

Published in 1935, the argument challenged whether quantum mechanics gave a complete description of physical reality. It considered two particles that had interacted and then moved apart. Measuring one particle could allow scientists to predict a property of the other, such as position or momentum, with certainty.

Einstein, Boris Podolsky, and Nathan Rosen argued that the distant particle must already possess definite properties, even before measurement. They believed this conclusion conflicted with quantum mechanics, which does not assign simultaneous precise values to certain pairs of properties. Their paper therefore suggested that hidden variables might complete the theory.

The EPR paradox is not the same as Heisenberg’s uncertainty principle, Schrödinger’s cat, or Bell’s theorem. Niels Bohr defended quantum mechanics against the EPR criticism, while John Bell later showed that local hidden-variable theories make experimentally testable predictions. Modern experiments violate Bell inequalities, supporting quantum predictions, though they do not permit faster-than-light messaging.