The M\"obius game and other Bell tests for relativity

TL;DR

This paper introduces multiparty Bell-like games that test the dynamical nature of causal relations in spacetime, providing device-independent methods to distinguish classical from gravitationally influenced causal structures.

Contribution

It develops novel multiparty games representable by directed graphs, linking causal dynamism to violations of classical bounds, and connects these to combinatorial optimization polytope facets.

Findings

Games can detect dynamical causal relations beyond classical bounds.

In Minkowski spacetime, winning probabilities are bounded, but gravitational effects can violate these bounds.

The approach links causal structure tests to combinatorial optimization techniques.

Abstract

We derive multiparty games that, if the winning chance exceeds a certain limit, prove the incompatibility of the parties' causal relations with any partial order. This, in turn, means that the parties exert a back-action on the causal relations; the causal relations are dynamical. The games turn out to be representable by directed graphs, for instance by an orientation of the M\"obius ladder. We discuss these games as device-independent tests of spacetime's dynamical nature in general relativity. To do so, we design relativistic settings where, in the Minkowski spacetime, the winning chance is bound to the limits. In contrast, we find otherwise tame processes with classical control of causal order that win the games deterministically. These suggest a violation of the bounds in gravitational implementations. We obtain these games by uncovering a "pairwise central symmetry" of the correlations in question. This symmetry allows us to recycle the facets of the acyclic subgraph polytope studied by Gr\"otschel, J\"unger, and Reinelt in the mid-80s for combinatorial optimization. In addition, we derive multiparty games in a scenario where the polytope dimension grows only linearly in the number of parties. Here, exceeding the limits not only proves the dynamical nature of the causal relations, but also that the correlations are incompatible with any global causal order.