# Causation does not explain contextuality

Centre for Engineered Quantum Systems, School of Mathematics and Physics, The University of Queensland, St Lucia, QLD 4072, Australia

### 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.

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[8] Simon Milz, Fattah Sakuldee, Felix A. Pollock, and Kavan Modi, "Kolmogorov extension theorem for (quantum) causal modelling and general probabilistic theories", Quantum 4, 255 (2020).

[9] K. B. Wharton and N. Argaman, "Colloquium : Bell’s theorem and locally mediated reformulations of quantum mechanics", Reviews of Modern Physics 92 2, 021002 (2020).

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