  We propose a new experiment employing two independent sources of spin
correlated photon pairs. Two photons from different unpolarized sources each
pass through a polarizer to a detector. Although their trajectories never mix
or cross they exhibit 4th-order-interference-like correlations when the other
two photons interfere on a beam splitter even when the latter two do not pass
any polarizers at all. A wave packet calculation shows that the experiment
permits a very discriminatory test of hidden variable theories.
