Final Report Summary - SYMOB (Symmetries and the constitution of objectivity in quantum physics: A study on the non-representationalist theories of knowledge) The SYMOB project addressed some fundamental epistemological questions relating to the nature of objectivity and the possibility of a priori knowledge. Such questions were examined in connection with the conceptual problems raised by the interpretation of quantum mechanics. Unlike more traditional approaches, the proposed investigation focused on semantics (rather than on ontology). The general goal was to point out the shortcomings and intrinsic limitations of any interpretation of quantum mechanics that presupposes what can be called the 'representationalist paradigm' of language and knowledge, and to investigate the possibility of establishing the objectivity of physics without relying on the notion of a correspondence between symbols and objects. Such an investigation was expected to provide new insight into the way symbolic language in general, and physical theories in particular, work. By working out a suitable non-representationalist semantic framework (and by thus making viable both an instrumentalist conception of theories and a constructivist conception of knowledge), the project aimed to enable the dissolution of the main conceptual puzzles raised by quantum mechanics along the lines of Niels Bohr's late reflections on complementarity and holism. More generally, the instrumentalist-constructivist approach was expected to help clarify the nature of the (symmetry) principles that preside over the construction of physical theories, thereby providing an original contribution to the current debate on structural realism. The philosophical part of the project had strong links with the Kantian tradition. The proposed analysis of the notion of objectivity was inspired by both transcendental philosophy and the pragmatist trends in the philosophy of language. In particular, such an analysis attempted to throw light on the relation between the conditions of possibility of experience on the one hand, and the mathematical (predictive) structure of quantum models on the other. As the investigation progressed, however, the focus gradually shifted toward issues relating to meaning. The representationalist assumptions that are responsible for the difficulties encountered by the most common interpretations of quantum mechanics (realist and anti-realist alike) were recognised to reflect a particular semantic stance, inspired by logical atomism. The constructive part of the project undertook to get rid of those presuppositions by developing a relational semantic framework (which incidentally also provides an alternative to traditional structuralist approaches in the philosophy of physics). Robert Brandom's inferentialism proved here an important source of inspiration. The two main technical objectives of the project were addressed by taking this new insight into account. In so far as the measurement problem is concerned, the 'solutions' inspired by Hugh Everett's 'relative state' formulation were contrasted to Bohr's pragmatic 'dissolution'. The current standard 'solutions' which rely on decoherence were shown to be wanting due to their lack of clarity on their own semantic presuppositions. In so far as the a priori derivation of the quantum structures is concerned, the transcendental program was reformulated in a semantic perspective, by emphasising the link between a priori principles and syntax. This led to the critique of the existing axiomatic reconstructions of the quantum models, and to their reformulation based on the analysis of the concept of probability within the inferentialist framework. While completing such an 'analytic' derivation of the Hilbert space structure proved a very challenging task, some significant preliminary results were obtained. These partial results were important for two reasons. First, they provided decisive support for the overall philosophical program, contributing to making the proposed dissolution of the measurement problem more precise and rigorous. Second, they gave rise to a fruitful interdisciplinary program, which is being actively pursued in collaboration with other researchers. The results were collected in the first draft of a book and presented at an international workshop organised at Stanford University as part of the collaboration among American and French researchers fostered by the project.
