Dualities and intertheoretic relations

The idea of duality is at the core of the most relevant developments in recent fundamental physics. During the last forty years theoretical physics has used the notion of duality in different ways and frameworks: in the so-called dual resonance model of the late sixties, which gave birth to early string theory; in the context of quantum field theory, where a groundbreaking generalization of electromagnetic duality was conjectured by Claus Montonen and David Olive in 1977; in supersymmetric string theory, where various sorts of dualities are playing a key role in the theoretical elaboration. This paper is concerned with the significance of physical dualities from the viewpoint of philosophy of science. The idea is that, for its peculiarity, this ‘new’ ingredient in theory construction can open unexpected perspectives for the current philosophical reflection on contemporary physics. In particular, dualities represent an unusual type of intertheory relation, the meaning of which deserves to be investigated. It is the aim of the paper to show how discussing this point brings into play, at the same time, what is intended by a ‘theory’ and in which sense dualities are to be considered ‘symmetries’ (if they are).