Macroscopic Local Realism: How Do We Define It and Is It Compatible with Quantum Mechanics?

We introduce the concept of different orders (microthrough to macro-) of local realism. ``Macroscopic local realism'' states that events occurring at a location B cannot induce (immediate) macroscopic changes to a system at a location A spatially separated from B. ``Local realism'' in its entirety excludes all sizes of change. ``Local realism'' in its entirety is used by Einstein, Podolsky, and Rosen to deduce that results of position measurements (for certain correlated systems) are predetermined. The value for the predetermined position is specified with an uncertainty which is microscopic. ``Macroscopic local realism'' allows one to deduce only the existence of ``elements of reality'' with a macroscopic uncertainty. While Bell's theorem invalidates local realism in its entirety, little is known of the validity of ``macroscopic local realism.'' We consider macroscopic experiments where the experimental error associated with measurements is macroscopic. We formulate the Einstein Podolsky Rosen argument for such a macroscopic situation. We propose that violations of Bell inequalities in such macroscopic experimental situations would imply the failure of ``macroscopic local realism.'' 1998