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Revisiting the Measurement Problem

Olímpia Lombardi

Published Feb 19, 2026• 0 citations
Publisher

Abstract

Abstract Chapter 6 was devoted to argue that the MHI offers a solution to the measurement problem for both ideal and non-ideal measurements, and to show how it provides a distinction between reliable and non-reliable measurements in the non-ideal case. However, in the last decades more complex measurement scenarios have been considered, some as old as the so-called Wigner’s friend experiment, and others recently designed to test the theoretical predictions of quantum mechanics. For this reason, in the present chapter, the measurement problem is revisited from the perspective of the challenges that those scenarios pose to interpretation.

DOI
10.1093/9780198951407.003.0012

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Abstract Chapter 6 was devoted to argue that the MHI offers a solution to the measurement problem for both ideal and non-ideal measurements, and to show how it provides a distinction between reliable and non-reliable measurements in the non-ideal case. However, in the last decades more complex measurement scenarios have been considered, some as old as the so-called Wigner’s friend experiment, and others recently designed to test the theoretical predictions of quantum mechanics. For this reason, in the present chapter, the measurement problem is revisited from the perspective of the challenges that those scenarios pose to interpretation.
Abstract In rough terms, the quantum measurement problem is the problem of explaining how, when a system in a superposition state is measured, the pointer observable of the measuring apparatus is always found in a definite value. Although quantum mechanics involves several interpretative challenges, the measurement problem has been the main focus of the interest of physicists and philosophers working on the foundations of the theory: most interpretations were designed specifically to solve it. In this chapter, it is shown that the MHI offers a solution to the measurement problem for both ideal and non-ideal measurements, and that, in the non-ideal case, the interpretation distinguishes between reliable and non-reliable measurements. I have also explained how the MHI accounts for consecutive measurements. Finally, it is emphasized that the MHI approach provides a new, more physical understanding of the concept of quantum measurement.
During many years since the birth of quantum mechanics, instrumentalist interpretations prevailed: the meaning of the theory was expressed in terms of measurements results. However, in the last decades, several attempts to interpret it from a realist viewpoint have been proposed. Among them, modal interpretations supply a realist non-collapse account, according to which the system always has definite properties and the quantum state represents possibilities, not actualities. But the traditional modal interpretations faced some conceptual problems when addressing imperfect measurements. The modal-Hamiltonian interpretation, on the contrary, proved to be able to supply an adequate account of the measurement problem, both in its ideal and its non-ideal versions. Moreover, in the non-ideal case, it gives a precise criterion to distinguish between reliable and non-reliable measurements. Nevertheless, that criterion depends on the particular state of the measured system, and this might be considered as a shortcoming of the proposal. In fact, one could ask for a criterion of reliability that does not depend on the features of what is measured but only on the properties of the measurement device. The aim of this article is precisely to supply such a criterion: we will adopt an informational perspective for this purpose.During many years since the birth of quantum mechanics, instrumentalistinterpretations prevailed: the meaning of the theory was expressed in terms of measurementsresults. However, in the last decades, several attempts to interpret it from a realist viewpointhave been proposed. Among them, modal interpretations supply a realist non-collapseaccount, according to which the system always has definite properties and the quantum staterepresents possibilities, not actualities. But the traditional modal interpretations faced someconceptual problems when addressing imperfect measurements. The modal-Hamiltonianinterpretation, on the contrary, proved to be able to supply an adequate account of themeasurement problem, both in its ideal and its non-ideal versions. Moreover, in the non-idealcase, it gives a precise criterion to distinguish between reliable and non-reliable measurements.Nevertheless, that criterion depends on the particular state of the measured system, and thismight be considered as a shortcoming of the proposal. In fact, one could ask for a criterionof reliability that does not depend on the features of what is measured but only on theproperties of the measurement device. The aim of this article is precisely to supply such acriterion: we will adopt an informational perspective for this purpose.
The measurement problem is seen as an ambiguity of quantum mechanics, or, beyond that, as a contradiction within the theory: Quantum mechanics offers two conflicting descriptions of the Wigner's-friend experiment. As we argue in this note there are, however, obstacles from within quantum mechanics and regarding our perspective onto doing physics towards fully describing a measurement. We conclude that the ability to exhaustively describe a measurement is an assumption necessary for the common framing of the measurement problem and ensuing suggested solutions.
Can normal science-in the Kuhnian sense-add something substantial to the discussion about the measurement problem? Does an extended Wigner's-friend Gedankenexperiment illustrate new issues? Or a new quality of known issues? Are we led to new interpretations, new perspectives, or do we iterate the previously known? The recent debate does, as we argue, neither constitute a turning point in the discussion about the measurement problem nor fundamentally challenge the legitimacy of quantum mechanics. Instead, the measurement problem asks for a reflection on fundamental paradigms of doing physics.
Abstract Although much has been written about the measurement problem, there is still significant disagreement about what the problem really is and what a solution should look like. In this chapter I present a brief introduction to quantum mechanics and the measurement problem, and then I argue that the measurement problem should be understood in part a problem of epistemology: solving the problem requires telling a consistent story about how the reality underlying quantum mechanics could allow us to reliably come to know about that reality via the medium of our empirical evidence for quantum mechanics, and an interpretation of quantum mechanics which fails to achieve this is self-undermining.