  Nonlocality as a fundamental aspect of quantum mechanics is witnessed by
violation of Bell inequality or its variants, for which all relevant studies
assume some correlations exhibited by local realistic theories. The strategy of
Bell's theorem is to establish some criteria to distinguish local realistic
theories from quantum mechanics with respect to the nonlocal nature of
entangled systems. Here we propose a model independent study of nonlocality
that needs not to assume any local theory since observation of the expected
nonlocal effect is straightforward quantum mechanically. Our proposal involves
a bipartite polarization-entangled system in which one photon immediately
reduces into a circular-polarization (CP) state when its partner at a
space-like distance is detected in another CP state. The state reduction of the
photon can be mechanically monitored because a CP photon carries angular
momentum and exerts a torque on a half-wave plate whose mechanical motion is
measurable, which is well described by quantum mechanics and independent of any
local realistic assumption.
