John Bell, relativistic causality, and the arrow of time

► Bertlmann replies: In analyzing Bell’s theorem, Nathan Argaman emphasizes the tacitly assumed time asymmetry, which becomes the “culprit” in the context of a microscopic theory. John Bell certainly was aware of retrocausal formulations, where the causal arrow of time was abandoned, but he did not consider them as alternatives to local hidden-variable theories. The reason was simply that Bell, like Albert Einstein, did not accept the possibility that an effect might happen before the cause.

Sticking to his “no signals faster than light” idea, Bell demonstrated that ordinary quantum mechanics is not locally causal. We have to accept that nonlocal structure of quantum mechanics, which is experienced in nature.

In Argaman’s retrocausal model, the propagation of information from the apparatus backward in time to the source is allowed, and thus no instantaneous action at a distance is needed. Therefore, Argaman may conclude that Einstein’s spooky action occurs in the past rather than at a distance.

Since the variables, carrying information that has propagated into the past, must not be accessible on a macroscopic level, doesn’t Argaman’s retrocausal model just shift the problem from “nonlocality” to the arrow of time? Nevertheless, it is an interesting interpretation of an experiment like Einstein-Podolsky-Rosen and Bell.