Towards an emergentist approach to the measurement problem of quantum mechanics
Organização:  IUHPST/DLMPST 
School of Economics, University of Buenos Aires
24 / 07 / 2023

The measurement problem is a long-standing problem regarding Quantum Mechanics (QM) or, at least, its interpretation. Roughly speaking, the measurement problem arises from the opposition between the deterministic and linear evolution described by the first axioms of QM and the indeterministic and nonlinear modification portrayed by QM’s last axiom – the so-called “collapse postulate” or “projecting postulate”. We can find several ways of formulating the measurement problem in the literature. For instance, according to Ladyman and Ross (2007: 180-181), following Maudlin (1995: 7), the measurement problem can be presented as a trilemma: 1. All measurements have unique outcomes 2. The quantum mechanical description of reality is complete 3. The only time evolution for quantum systems is in accordance with the Schrödinger equation The problem is that QM often attributes to quantum objects superpositions with respect to the properties that we can measure. We do not seem to observe the superposition of macroscopic objects like measurement devices contradicting (1), and so we have a problem if we continue to assume that the particle and the apparatus really don’t have definitive states in accordance with (2), and that the time evolution is always in accordance with (3). (2007, p. 180-181) Another way of putting the measurement problem is: “If quantum theory is meant to be (in principle) a universal theory, it should be applicable, in principle, to all physical systems, including systems as large and complicated as our experimental apparatus”. (Myrvold, 2018) However, this leads to the following: “a state in which the reading variable and the system variable are entangled with each other. The eigenstate-eigenvalue link, applied to a state like this, does not yield a definite result for the instrument reading.” (Myrvold, 2018) So, if we consider that QM is a universal theory; if we consider that a property of being “quantum” is in a superposition state; and if we consider that a property of being “classic” is in a well-defined state, then the measurement problem, in general, can be stated as follows: how, as a result of a measurement, does a system in “quantum superposition” transforms into a system in a well-defined state? However, while the measurement problem has been a central problem in the philosophy of physics for decades, the relation between the measurement problem and the concept of emergence has received very little attention. That is, despite the multiplicity of solutions and formulations of the measurement problem, all seem to assume that QM is a universal theory; all seem to assume that classical entities or properties are metaphysically reducible (or identical, in some cases) to quantum entities or properties. Nevertheless, do we need to accept this micro-reductionist assumption? Maybe we can question it, and maybe it is this assumption that makes the measurement problem problematic. This paper aims to i) analyze this micro-reductionist assumption (the universality of QM) and its consequences to the formulation of the measurement problem of QM; ii) explore the possibility of an emergentist account of classical-quantum relationship, its feasibility and advantage.

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