Textbook Quantum Mechanics and the Problem of Ontological Commitment

One important difference between quantum mechanics (QM) and most other scientific theories is that we cannot just look at QM textbooks in order to find out what the theory is about (beyond mere predictions of possible measurement outcomes). If questions about what is represented by the quantum formalism are addressed at all, the answers given by textbooks do not amount to a coherent ontology of QM. Proposals for such ontologies exist, but each of them has its own peculiar way of going beyond textbook QM, by either adding variables (e. g., the de Broglie-Bohm theory), modifying the dynamics (e. g., the GRW model) or reinterpreting our experience of unique measurement outcomes (e. g. Everettian QM). The fact that we are (currently, and to some extent in principle) unable to experimentally discriminate between these proposals creates a dilemma for anyone who expects QM to inform us about the structure of reality. One can either opt for one particular version of QM (as, e. g., Wallace (2012) does for the Everettian approach or Esfeld and Deckert (2017) for the Bohmian), but then one faces a problem of underdetermination that is usually considered problematic for a realist’s commitment; or one can limit one’s ontological commitment to some core content of QM unaffected by the underdetermination between its different versions, but this seems to sacrifice realism with respect to large parts of QM (as exemplified most explicitly in Hoefer forthcoming). In my talk, I will sketch a way out of this dilemma, by showing that the core of QM, as it is formulated in standard textbooks, allows for a much more substantive ontological commitment than is usually acknowledged. For this purpose, I will first defend the ontological respectability of textbook QM against a recent attack by Callender (forthcoming) and then substantiate my claim by looking at an example that has been claimed to be particularly troubling for an ontologically committed realism about QM, namely the case of spin (see Saatsi forthcoming). The features of the kind of realism I propose will highlight the way in which QM forces us to change our thinking about the ontological content of scientific theories. References: Callender, C. (forthcoming): „Can we quarantine the quantum blight?“ In French and Saatsi (forthcoming). Esfeld, M. and D.-A. Deckert (2017): A Minimalist Ontology of the Natural World. Routledge. French, S. and Saatsi, J. (Eds.) (fortchcoming): Scientific Realism and the Quantum. Oxford University Press. Hoefer, C. (forthcoming): „Scientific realism without the quantum“. In French and Saatsi (forthcoming). Saatsi, J. (forthcoming): „Truth vs. progress realism about spin“. In French and Saatsi (forthcoming). Walace, D. (2012): The Emergent Multiverse: Quantum Theory according to the Everett Interpretation. Oxford University Press