Causation does not explain contextuality

TL;DR

This paper demonstrates that quantum correlations cannot be explained by non-contextual models, even when considering arbitrary causal structures, challenging realist interpretations of quantum mechanics.

Contribution

It proves that quantum contextuality persists regardless of causal assumptions, extending the understanding of quantum correlations beyond traditional causal frameworks.

Findings

Quantum predictions require contextual explanations.

Non-contextual models fail under arbitrary causal structures.

Contextuality is fundamental, not just a consequence of causal assumptions.

Abstract

Realist interpretations of quantum mechanics presuppose the existence of elements of reality that are independent of the actions used to reveal them. Such a view is challenged by several no-go theorems that show quantum correlations cannot be explained by non-contextual ontological models, where physical properties are assumed to exist prior to and independently of the act of measurement. However, all such contextuality proofs assume a traditional notion of causal structure, where causal influence flows from past to future according to ordinary dynamical laws. This leaves open the question of whether the apparent contextuality of quantum mechanics is simply the signature of some exotic causal structure, where the future might affect the past or distant systems might get correlated due to non-local constraints. Here we show that quantum predictions require a deeper form of contextuality: even allowing for arbitrary causal structure, no model can explain quantum correlations from non-contextual ontological properties of the world, be they initial states, dynamical laws, or global constraints.