Does Science need Intersubjectivity? The Problem of Confirmation in Orthodox Interpretations of Quantum Mechanics

Abstract

What must an interpretation of quantum mechanics do in order to be considered viable? We suggest that one vitally important criterion is the following: Any successful interpretation of quantum mechanics must explain how our empirical evidence allows us to come to know about quantum mechanics. That is, an interpretation of quantum mechanics must be able to tell a sensible story about how empirical confirmation works in the context of quantum-mechanical experiments, otherwise the whole project will be self-defeating: we cannot rationally believe an interpretation of a theory which tells us we have no good reason to believe that the theory itself is right, because our only reason for believing the interpretation is our belief that the theory is right!The 'probability problem' and the related problem of confirmation has been much-discussed in the context of the Everett interpretation [1-5], but it is evident that other interpretations which also postulate major changes to our usual ideas about the relationship between observers and reality will be vulnerable to similar objections. In this article, we will focus on the class of interpretations sometimes known as 'orthodox' interpretations [6] or alternatively 'Copenhagenish' interpretations [7]. These are interpretations which posit nothing but 'unitary dynamics to characterize the dynamical evolution of a state vector' and which 'deny that we should think of a system as having an observer-independent state.' [6] Orthodox interpretations differ from the Everett interpretation because they tell us that measurements have unique outcomes, but those outcomes are relativized to an observer. Examples of orthodox interpretations include Copenhagen interpretations [8-10], neo-Copenhagen interpretations [11-17], QBism [18], pragmatic interpretations [19] and some versions of relational quantum mechanics [20] 1 . Certain forms of the 'It from Bit' hypothesis may also fall into this category [22, 23] 2 .It has been observed that interpretations of this kind challenge the standard scientific doctrine of intersubjectivity about measurement outcomes and other macroscopic events [24-28], i.e. they imply that measurements and other macroscopic events will not typically have the same outcome for all macroscopic observers. Proponents of orthodox interpretations have historically taken a rather cavalier attitude toward this fact -for after all, every interpretation of quantum mechanics has some features which appear strange to our classical intuition, so it might seem that orthodox interpretations are no worse off than other approaches in this regard. However, what this discussion overlooks is the fact that intersubjectivity plays a vitally important role in the process of empirical confirmation, and thus the failure of intersubjectivity in orthodox interpretations means that these approaches have serious difficulties in fulfilling the crucial criterion of showing how our empirical evidence could allow us to know about quantum mechanics. This is not just a matter of learning to accept s...