The Measurement Problem, an Ontological Solution

Michael Esfeld

Philippe Grangier

This note presents a concise and non-polemical comparison of several major interpretations of quantum mechanics, with a particular emphasis on the distinction between FAPP-solutions ("For All Practical Purposes'') versus ontological solutions to the measurement problem. Building on this distinction, we argue that the Contexts-Systems-Modalities (CSM) framework, supplemented by the operator-algebraic description of macroscopic contexts, provides a conceptually complete, non-FAPP ontology that naturally incorporates irreversibility and the physical structure of measurement devices. This approach differs significantly from other ontological interpretations such as Bohmian mechanics, spontaneous collapse, or many-worlds, and highlights the major role of contextual quantization in shaping quantum theory.

Yukio-Pegio Gunji, Keisuke Ito, Yoshiyuki Kusunoki

Eugene Paul Wigner

Timothy Speed

The measurement problem of quantum mechanics is predominantly treated in contemporary foundations research as an unresolved problem of dynamics or ontology. Accordingly, dominant solution approaches aim either at additional collapse mechanisms (e.g., GRW-type models), at ontological branching (Many-Worlds interpretations), or at an information-theoretic reinterpretation of state and measurement.The present contribution advances a different thesis. It shows that, despite their methodological differences, these approaches share a common categorical presupposition: they treat the transition from possibility to facticity as an intra-worldly describable occurrence—whether as a dynamical process, an ontological splitting, or a state update. It is precisely this presupposition that is called into question here.Starting from an ontological distinction between possibility and facticity, it is argued that measurement cannot be understood as a temporal event within an already structured world. Rather, it marks a boundary at which temporal, processual, and informational descriptions lose their applicability. The transition to objectivity is therefore not an explainable event, but an irreversible restriction of the space of possibility, through which world becomes factically binding in the first place.Against this background, dynamical collapse models, Many-Worlds interpretations, and information-theoretic ontologies are comparatively analyzed. The aim is not a refutation of these approaches, but a precise boundary determination: it is shown in what way they each provide formally successful answers to partial aspects of the measurement problem, while at the same time presupposing the categorical status of facticization that they claim to explain.The contribution does not understand itself as an alternative interpretation of quantum mechanics, but as an ontological clarification of its domain of validity. It proposes that the measurement problem should no longer be treated as the search for a hidden mechanism, but as an indication of a structural boundary of physical description itself.

Shan Gao

Spontaneous collapse theories provide a promising solution to the measurement problem. But they also introduce a number of problems of their own concerning dimensionality, vagueness, and locality. In response to these problems, advocates of collapse theories have proposed various accounts of the primitive ontology of collapse theories—postulated underlying entities governed by the collapse theory and underwriting our observations. The most prominent of these are a mass density distribution over three-dimensional space, and a set of discrete “flash” events at space-time points. My argument here is that these primitive ontologies are redundant, in the sense that the structures exhibited by the primitive ontologies that allow them to solve the problems facing spontaneous collapse theories are also present in the wave function. But redundancy is not nonexistence; indeed, the fact that the relevant structures are already there in the wave function shows that the mass density ontology and the flash ontology exist whether they are explicitly postulated or not. By the same token, there is no need to decide between a wave function ontology, a mass density ontology and a flash ontology.