On Quantum Non-Locality, Special Relativity, And Counterfactual Reasoning

Abstract

(1964), and others following him (Clauser et al. 1969; Wigner 1970; Belinfante 1973), have shown that some of the predictions of quantum mechanics conflict with “local hidden variables theories” (also called “local realistic theories”). Henry Stapp1 has worked over many years to strengthen these results by showing, without recourse to any assumption of “realism” or “hidden variables” or (following (1935)—henceforth referred to as “EPR”) “elements of reality,” that quantum mechanics contradicts the locality demanded by the special theory of relativity. In a recent article (Stapp 1997), which he regards as perhaps simpler, and technically better, than his earlier ones, he argues that there is inconsistency among the following: “(1) the validity of some simple predictions of quantum theory; (2) the explicitly stated locality conditions [that is: three principles—labeled “LOC1,” “LOC2,” and “LOC3”—described by Stapp as aspects or forms of “the crucial locality assertion suggested by the theory of relativity”]; (3) the general idea that physical theories can cover a variety of special instances that can be imagined to be created by free choices of experimenters; and (4) the general principles of modal logic.”2 Of the last category of premises—the general principles of modal logic—Stapp says that they “merely formalize what we mean by modal language;” and he argues that modal, and in particular counterfactual, statements can play a legitimate role in scientific reasoning. This last claim, put so generally, seems to us quite reasonable; but we wish to insert a caveat at the outset as to the statement that the principles of modal logic “merely formalize what we mean by modal language”: modal language and modal argumentation are tricky; and “merely what we mean” may conceal presuppositions legitimately made in the context of ordinary language, but challengeable in the light of fundamental scientific theories.