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Relativistic Causality and Bell’s Theorems

“Bell’s theorem” can refer to two different things. One is the theorem that John Bell proved in 1964; the other, the theorem he proved in 1976. His 1964 theorem is the incompatibility of quantum phenomena with the joint assumptions of LOCALITY and PRE-DETERMINATION. His 1976 theorem is their incompatibility with the single property of LOCAL CAUSALITY. Although the two Bell’s theorems are logically equivalent, their assumptions are not. Hence, the earlier and later theorems suggest quite different conclusions, embraced by operationalists and realists, respectively. The key issue is whether LOCALITY or LOCAL CAUSALITY is an appropriate expression of RELATIVISTIC CAUSALITY. The answer rests on one’s basic notion of causation. For operationalists the appropriate notion is what I will call the Principle of AGENT-CAUSATION, while for realists it is REICHENBACH’s Principle. However, by breaking down the latter into even more basic Postulates – COMMON CAUSE and DECORRELATION – it is possible to obtain a version of Bell’s theorem in which each camp could reject one assumption and be satisfied that those remaining reflect its Weltanschauung. Formulating Bell’s theorem in terms of causation is fruitful not just for attempting to reconcile the two camps, but also for better describing the ontology of different quantum interpretations and for more deeply understanding the implications of quantum mechanics. Time permitting, I will discuss what the implications might be for our notions of causality and/or the most satisfactory interpretations, as I see it.