2 v 2 2 7 A pr 1 99 8 Is Quantum Mechanics Non - Local ?

Stapp has recently argued from a version of the Hardy type experiments that quantum mechanics must be non-local, independent of any additional assumptions like realism or hidden variables. I argue that either his conclusions do not follow from his assumptions, or that his assumptions are not true of quantum mechanics and can be interpreted as assigning an unwarranted level of reality to the value of certain quantum attributes. In a recent paper [1] H. Stapp has argued that quantum mechanics is non-local. He bases this conclusion on a weak definition of locality for a physical theory and an examination of the predictions of quantum mechanics for a specific two particle Hardy-type [2] [3] experiment. It was already known since the 50's from the theorem of J.S. Bell [4] that quantum mechanics violated the correlations expected in any theory which is both local and is " hidden variable " theory, in which the statistics arises out of the lack of knowledge of the values of local hidden variables which determine the outcome of the experiment itself. However, Stapp's argument claims to strengthen that conclusion by arguing that no local theory cannot give the same predictions as quantum mechanics. Ie, he reaches the conclusion that quantum mechanics is non-local. In his paper, Stapp claims that his proof that Quantum mechanics is non-local applies only if one assumes that locality holds in all frames of a special relativistic system. However I will take this as a given, that locality is to be taken to apply to any two systems when causally separated from each other. The temporal order of experiments which are space-like separated is assumed to be irrelevant. To begin, let me first present the argument in my own way. Stapp phrased his argument in the form of a logical calculus, which I will examine later. He considers a very general situation in which measurements are made at two locations, L (for left) and R (for right). At each location two possible measurements are made which he designates by L1 and L2 for the left and R1 and R2 for the right. In this first section I will specify his generic situation by having the measurements be made on the spins of two particles, one particle labeled L on the left and the other ,R, on the right. These two particles are placed into a specific correlated state. For purposes of illustration, …