In quantum foundations, there is growing interest in the program of reconstructing the quantum formalism from clear physical principles. These reconstructions are formulated in an operational framework, deriving the formalism from information-theoretic principles. It has been recognized that this project is in tension with standard _ψ-ontic_ interpretations. This paper presupposes that the quantum reconstruction program (QRP) (i) is a worthwhile project and (ii) puts pressure on _ψ-ontic_ interpretations. Where does this leave us? Prima facie, it seems that _ψ-epistemic_ interpretations perfectly (...) fit the spirit of information-based reconstructions. However, _ψ-epistemic_ interpretations, understood as saying that the wave functions represents one’s _knowledge_ about a physical system, recently have been challenged on technical and conceptual grounds. More importantly, for some researchers working on reconstructions, the lesson of successful reconstructions is that the wave function does _not_ represent objective facts about the world. Since knowledge is a factive concept, this speaks against epistemic interpretations. In this paper, I discuss whether _ψ-doxastic_ interpretations constitute a reasonable alternative. My thesis is that if we want to engage QRP with _ψ-doxastic_ interpretations, then we should aim at a reconstruction that is spelled out in non-factive experiential terms. (shrink)

Few researchers of the past made sense of the collapse of representations in the quantum domain, and looked for a new process of sense-making below the level of representations: the level of the phenomenology of perception and action; the level of the elaboration of knowledge out of experience. But some recent philosophical readings of quantum physics all point in this direction. They all recognize the fact that the quantum revolution is a revolution in our conception of knowledge. In these recent (...) readings of quantum physics, quantum states are primarily generators of probabilistic valuations. Accordingly, they should not be seen as statements about what is the case, but as statements about what each agent can reasonably expect to be the case. Three features of such non-interpretational, non-committal approaches to quantum physics strongly evoke the phenomenological epistemology. These are: their deliberately first-person stance; their suspension of judgment about a presumably external domain of objects, and subsequent redirection of attention towards the activity of constituting these objects; their perception-like conception of quantum knowledge. But beyond phenomenological epistemology, these new approaches of quantum physics also make implicit use of a phenomenological ontology. Chris Fuch’s participatory realism thus formulates a non-external variety of realism for one who is deeply immersed in reality. But participatory realism strongly resembles Merleau-Ponty’s endo-ontology, which is a phenomenological ontology for one who deeply participates in Being. This remarkable analogy is supported by Merleau-Ponty himself. Indeed, 50 years before QBism, Merleau-Ponty acknowledged the strong kinship between the status of quantum mechanics and his phenomenology of embodiment. He did so in two texts that remained unpublished until after his death: Visible and invisible, and the Lectures on Nature. The final part of this article is then devoted to a study of Merleau-Ponty’s conception of quantum physics. (shrink)

We present a derivation of the third postulate of relational quantum mechanics from the properties of conditional probabilities. The first two RQM postulates are based on the information that can be extracted from interaction of different systems, and the third postulate defines the properties of the probability function. Here we demonstrate that from a rigorous definition of the conditional probability for the possible outcomes of different measurements, the third postulate is unnecessary and the Born’s rule naturally emerges from the first (...) two postulates by applying the Gleason’s theorem. We demonstrate in addition that the probability function is uniquely defined for classical and quantum phenomena. The presence or not of interference terms is demonstrated to be related to the precise formulation of the conditional probability where distributive property on its arguments cannot be taken for granted. In the particular case of Young’s slits experiment, the two possible argument formulations correspond to the possibility or not to determine the particle passage through a particular path. (shrink)

I consider the fact that there are a number of interesting ways to ‘reconstruct’ quantum theory, and suggest that, very broadly speaking, a form of ‘instrumentalism’ makes good sense of the situation. This view runs against some common wisdom, which dismisses instrumentalism as ‘cheap’. In contrast, I consider how an instrumentalist might think about the reconstruction theorems, and, having made a distinction between ‘reconstructing’ quantum theory and ‘reinventing’ quantum theory, I suggest that there is an adequate instrumentalist approach to the (...) theory that invokes both. (shrink)

The program of reconstructing quantum theory based on information-theoretic principles enjoys much popularity in the foundations of physics. Surprisingly, this endeavor has only received very little attention in philosophy. Here I argue that this should change. This is because, on the one hand, reconstructions can help us to better understand quantum mechanics, and, on the other hand, reconstructions are themselves in need of interpretation. My overall objective, thus, is to motivate the reconstruction program and to show why philosophers should care. (...) My specific aims are threefold. (i) Clarify the relationship between reconstructing and interpreting quantum mechanics, (ii) show how the informational reconstruction of quantum theory puts pressure on standard realist interpretations, (iii) defend the quantum reconstruction program against possible objections. (shrink)