![]() Moreover, as the measurement events can be space-like separated 6, 7, 8, any influence-type explanation must involve superluminal influences 9, in contradiction with the intuitive notion of relativistic causality 10. However, theory predicts and experiments confirm that these inequalities are violated 2, thus excluding any past common cause type of explanation. Bell showed that if these correlated values were due to past common causes, then they would necessarily satisfy a series of inequalities 1. When measurements are performed on two entangled quantum particles separated far apart from each other, such as in an Einstein–Podolsky–Rosen 5 type experiment, the measurement results of one particle are found to be correlated to that of the other particle. The correlations observed in certain quantum experiments call into question this viewpoint. Given the theory of relativity, we expect moreover the speed of causal influences to be bounded by the speed of light. Importantly, we expect the chain of causal relations to satisfy a principle of continuity, that is, the idea that the physical carriers of causal influences propagate continuously through space at a finite speed. Our intuitive understanding of correlations between events relies on the concept of causal influences, either relating directly the events, such as the position of the moon causing the tides, or involving a past common cause, such as seeing a flash and hearing the thunder when a lightning strikes. Our result uncovers a new aspect of the complex relationship between multipartite quantum non-locality and the impossibility of signalling.Ĭorrelations cry out for explanation 1. ![]() Hence, assuming the impossibility of using non-local correlations for superluminal communication, we exclude any possible explanation of quantum correlations in terms of influences propagating at any finite speed. This superluminal communication does not require access to any hidden physical quantities, but only the manipulation of measurement devices at the level of our present-day description of quantum experiments. Here, we show that for any finite speed v with, such models predict correlations that can be exploited for faster-than-light communication. Yet, any such experimental violation could always be explained in principle through models based on hidden influences propagating at a finite speed v> c, provided v is large enough 3, 4. The experimental violation of Bell inequalities using space-like separated measurements precludes the explanation of quantum correlations through causal influences propagating at subluminal speed 1, 2.
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