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.
 M. D. Mazurek, M. F. Pusey, R. Kunjwal, K. J. Resch, and R. W. Spekkens, ``An experimental test of noncontextuality without unphysical idealizations,'' Nat. commun. 7, 11780 (2016).
 R. W. Spekkens, D. H. Buzacott, A. J. Keehn, B. Toner, and G. J. Pryde, ``Preparation contextuality powers parity-oblivious multiplexing,'' Phys. Rev. Lett. 102, 010401 (2009).
 H. Price, ``Does time-symmetry imply retrocausality? How the quantum world says “Maybe”?,'' Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 43, 75-83 (2012).
 M. S. Leifer and M. F. Pusey, ``Is a time symmetric interpretation of quantum theory possible without retrocausality?,'' Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 473, (2017).
 A. Carati and L. Galgani, ``Nonlocality of classical electrodynamics of point particles, and violation of Bell's inequalities,'' Nuovo Cimento B 114, 489-500 (1999).
 C. J. Wood and R. W. Spekkens, ``The lesson of causal discovery algorithms for quantum correlations: Causal explanations of Bell-inequality violations require fine-tuning,'' New J. Phys. 17, 033002 (2015).
 A. Bisio, G. Chiribella, G. D'Ariano, and P. Perinotti, ``Quantum networks: General theory and applications,'' . Acta Physica Slovaca. Reviews and Tutorials 61, 273-390 (2011).
 A. Bisio, G. M. D'Ariano, P. Perinotti, and M. Sedlák, ``Optimal processing of reversible quantum channels,'' Physics Letters A 378, 1797 - 1808 (2014).
 M. S. Leifer and R. W. Spekkens, ``Towards a formulation of quantum theory as a causally neutral theory of Bayesian inference,'' Phys. Rev. A 88, 052130 (2013).
 M. Ringbauer, C. J. Wood, K. Modi, A. Gilchrist, A. G. White, and A. Fedrizzi, ``Characterizing Quantum Dynamics with Initial System-Environment Correlations,'' Phys. Rev. Lett. 114, 090402 (2015).
 F. A. Pollock, C. Rodríguez-Rosario, T. Frauenheim, M. Paternostro, and K. Modi, ``Non-Markovian quantum processes: Complete framework and efficient characterization,'' Phys. Rev. A 97, 012127 (2018).
 J.-M. A. Allen, J. Barrett, D. C. Horsman, C. M. Lee, and R. W. Spekkens, ``Quantum Common Causes and Quantum Causal Models,'' Phys. Rev. X 7, 031021 (2017).
 J. Pearl, Causality. Cambridge University Press, 2009.
 S. Durand, ``An amusing analogy: modelling quantum-type behaviours with wormhole-based time travel,'' Journal of Optics B: Quantum and Semiclassical Optics 4, S351 (2002).
 Ä. Baumeler, A. Feix, and S. Wolf, ``Maximal incompatibility of locally classical behavior and global causal order in multi-party scenarios,'' Phys. Rev. A 90, 042106 (2014).
 C. Branciard, M. Araújo, A. Feix, F. Costa, and Č. Brukner, ``The simplest causal inequalities and their violation,'' New J. Phys. 18, 013008 (2016).
 J. Friedman, M. S. Morris, I. D. Novikov, F. Echeverria, G. Klinkhammer, K. S. Thorne, and U. Yurtsever, ``Cauchy problem in spacetimes with closed timelike curves,'' Phys. Rev. D 42, 1915-1930 (1990).
 F. Echeverria, G. Klinkhammer, and K. S. Thorne, ``Billiard balls in wormhole spacetimes with closed timelike curves: classical theory,'' Phys. Rev. D 44, 1077-1099 (1991).
 M. Nielsen and I. Chuang, Quantum Computation and Quantum Information. Cambridge University Press, 2000.
 M. Scully and M. Zubairy, Quantum Optics. Cambridge University Press, 1997.
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