Classical causal models cannot faithfully explain Bell nonlocality or Kochen-Specker contextuality in arbitrary scenarios

In a recent work, it was shown by one of us (EGC) that Bell-Kochen-Specker inequality viola- tions in phenomena satisfying the no-disturbance condition (a generalisation of the no-signalling condition) cannot in general be explained with a faithful classical causal model—that is, a classical causal model that satisfies the assumption of no fine-tuning. The proof of that claim however was restricted to Bell scenarios involving 2 parties or Kochen-Specker-contextuality scenarios involving 2 measurements per context.

Here we show that the result holds in the general case of arbitrary numbers of parties or measurements per context; the connection between fine-tuning and Bell-KS inequality violations is generic and not an artefact of the simplest scenarios. This result unifies, in full generality, Bell nonlocality and Kochen-Specker contextuality as violations of a fundamental principle of classical causality.

The article was published in: arXiv preprint arXiv:1909.05434.

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This work was supported (in part) by the Fetzer Franklin Fund of the John E. Fetzer Memorial Trust.