Information causality, the Tsirelson bound, and the ‘being-thus’ of things

Abstract

The principle of ‘information causality’ can be used to derive an upper bound—known as the ‘Tsirelson bound’—on the strength of quantum mechanical correlations, and has been conjectured to be a foundational principle of nature. To date, however, it has not been sufficiently motivated to play such a foundational role. The motivations that have so far been given are, as I argue, either unsatisfactorily vague or appeal to little if anything more than intuition. Thus in this paper I consider whether some way might be found to successfully motivate the principle. And I propose that a compelling way of so doing is to understand it as a generalisation of Einstein's principle of the mutually independent existence—the ‘being-thus’—of spatially distant things. In particular I first describe an argument, due to Demopoulos, to the effect that the so-called ‘no-signalling’ condition can be viewed as a generalisation of Einstein's principle that is appropriate for an irreducibly statistical theory such as quantum mechanics. I then argue that a compelling way to motivate information causality is to in turn consider it as a further generalisation of the Einsteinian principle that is appropriate for a theory of communication. I describe, however, some important conceptual obstacles that must yet be overcome if the project of establishing information causality as a foundational principle of nature is to succeed.