If the world is not deterministic, then at the very least, some individual events just happen ’by chance’. But the frequency of such events and correlations between them could be subject to constraints, whether local or non-local. Hans Reichenbach introduced a principle weaker than determinism but non-trivial: that every positive correlation should be traceable to a common cause (defined in terms of temporal precedence plus certain probabilistic relations). This principle turns out to imply the Bell Inequalities, which quantum theory violates. This chapter discusses the logical relations between indeterminism, common cause models, the Bell Inequalities, non-contextual hidden variable models, and various concepts of locality and non-locality, as well as the experiments designed to reveal the predicted violations.
Keywords: Bell Inequalities, chance, common cause model, determinism, hidden variables, indeterminism, locality, non-locality, Hans Reichenbach