Observability and Predictability in Quantum and Post-Quantum Physics

Abstract

I introduce a framework to distinguish two domains of physics - the manifest (i.e. the directly observable empirical records in terms of manifest configurations) and the non-manifest domain of physics (i.e. the things that the manifest configurations signify according to a physical theory). I show that many quantum 'paradoxes' rest on ambiguous reasoning about the two domains. More concretely, I study so-called 'surrealistic' trajectories, the 'delayed choice quantum eraser', and 'weak measurements'. Finally, I show how the alleged puzzles resolve in the framework provided. I then formally define and address the question of whether quantum uncertainty could be fundamental or whether post-quantum theories could have predictive advantage whilst conforming to the Born rule on average. This notion of what I call 'empirical completeness' refers to actual prediction-making beyond the Born probabilities, and thus delineates the operational notion of predictability from a 'hidden variable' programme in quantum theory. I study how empirical completeness connects to signal-locality, and argue that a partial proof for the impossibility of predictive advantage can be established for bi-partite quantum systems. The relevant results demonstrate signal-locality as a sufficient principle that might explain the fundamental chanciness in present and future quantum theories and, in turn, reconciles us to many quantum features as aspects of limits on Nature's predictability.