# Knowledge of Quantum Hidden Variables Enables Backwards-In-Time Signaling
## 6 Conclusions  
All interpretations of quantum mechanics that rely on hidden variables, such as the de Broglie-Bohm theory [28], have some kind of censorship mechanism which prevents the revelation of the values of the hidden variables in practice, e.g., see [34]. Hence, one may claim that our protocol is of no practical relevance. Even without such censorship, previous investigations on whether Bohmian mechanics implies change of the past hidden variables in the context of quantum erasure concluded that \"there is no change of the past whatsoever\" [35]. Nevertheless, the protocol presented in our paper reaches the opposite conclusion for a wide class of hidden variables by making use of quantum contextuality. While we agree with previous findings that there is no change of the past in Bohmian mechanics, our results show that it is misleading to think of Bohmian mechanics as a \"hidden variables\" theory because defining hidden variables for all observables except positions is in Bohmian mechanics superfluous. From an instrumental point of view, Bohmian mechanics is best viewed as a theory of positions of macroscopic objects explained in terms of microscopic positions of their constituents, without any sharp borderline between \"non-hidden\" macroscopic positions and the \"hidden\" microscopic ones [34].  
In previous works [36; 37; 38] we have seen that quantum uncertainty is vital for reconciling quantum nonlocality in space and time with relativistic causality. Indeed, full access to the hidden variables in our protocol renders quantum uncertainty ineffective and thus it cannot circumvent the BITS.  
One can then take the implications of our argument as further evidence that the censorship mechanism that prevents the knowledge of the hidden variables must be strongly enforced if one wants to preserve chronology. In other words, knowing the hidden variables not only allows for superluminal communication, but it even allows for communication to the past. As explained above, this is a stronger statement than simply requiring that [PERSON] locality (i.e., no superluminal communication) is satisfied. Of course, if hidden variables are unknowable as a matter of principle, they can then be considered unphysical for all intents and might be relegated to the realm of metaphysics as \"unperformed experiments have no results\" [39; 40]. That is the core implication of this paper.  
In essence, our conclusion is that in contextual (fully deterministic) hidden variables models for quantum theory, where agents have underdetermined choice and can know the values of the hidden variables, communication to one's own causal past would be possible, negating the non-relativistic notion of causality. The same conclusion holds also under slightly broader hypotheses that do not require undetermined choices on the part of an agent, as discussed in Section 5.  
[PERSON] conceived the main idea which was later developed by all authors. All authors gave final approval for publication. All authors have read and agreed to the published version of the manuscript.  
A.C. and E.C. were supported by Grant No. FQXi-RFP-CPW-2006 from the Foundational Questions Institute and Fetzer Franklin Fund, a donor advised fund of Silicon Valley Community Foundation. E.C. was supported by the Israel Innovation Authority under Projects No. 70002 and No. 73795, the Quantum Science and Technology Program of the Israeli Council of Higher Education, and the Pazy Foundation. L.M. acknowledges funding from Unipv \"Blue sky\" project--grant n. BSRI718573 and the FQXi foundation grant FQXi-RFP-1513 \"the physics of what happens\". H.N. acknowledges funding by the Ministry of Science of the Republic of Croatia and by the European Union through the European Regional Development Fund--the Competitiveness and Cohesion Operational Programme (KK.01.1.1.06).  
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We would like to thank [PERSON] for helpful comments and insightful discussions.  
The authors declare no conflict of interest.