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International Journal of Theoretical Physics

Theory of measurement in quantum mechanics and macroscopic description

Giovanni Maria Prosperi

Published Jan 1, 1994• 8 citations
Publisher
DOI
10.1007/bf00671617

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The theory of measurement in quantum mechanics

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The quantum description of the microscopic world is incompatible with the classical description of the macroscopic world, both mathematically and conceptually. Nevertheless, it is generally accepted that classical mechanics emerges from quantum mechanics in the macroscopic limit. In this paper, we challenge this perspective and demonstrate that the behaviour of a macroscopic system can retain all aspects of the quantum formalism, in a way that is robust against decoherence, particle losses and coarse-grained (imprecise) measurements. This departure from the expected classical description of macroscopic systems is not merely mathematical but also conceptual, as we show by the explicit violation of a Bell inequality and a Leggett–Garg inequality.
Abstract Quantum mechanics is the foundation of modern physics that is thought to be applicable to all physical phenomena, at least in principle. However, when applied to macroscopic bodies, the theory seems to be inconsistent. Wigner's friend and related thought experiments demonstrate that accounts by different observers described by the rules of quantum mechanics may be contradictory. Although still highly debated, such experiments seem to demonstrate an incompatibility of quantum mechanics with the usual rules of logic. Alternatively, one of the hidden assumptions in the thought experiments must be wrong. For instance, the argument is invalidated if macroscopic observers cannot be considered as physical systems described by the rules of quantum theory. Here we prove that there is a way to apply the rules of quantum mechanics to macroscopic observers while avoiding contradictory accounts of measurement by the observers. The key to this is the random noise that is ever present in nature and that represents the uncontrollable part of interaction between measured system and the surroundings in classical and quantum physics. By exploring the effect of the noise on microscopic and macroscopic bodies, we demonstrate that accounts of Wigner, the friend and other agents all become consistent. Our result suggests that the existing attempts to modify the Schrodinger equation to account for measurement results may be misguided. More broadly, the proposed mechanism for modeling measurements underlies the phenomenon of decoherence and is shown to be sufficient to explain the transition to Newtonian physics in quantum theory.
Causal–Continuity Stabilization Theory (CCST): Thermodynamic Stability and Branch-Internal Descriptive Continuity in Everettian Dynamics. DOI: https://doi.org/10.17605/OSF.IO/D6JN7. Causal–Continuity Stabilization Theory (CCST) is an interpretive framework that addresses the persistence of macroscopic descriptive continuity within fully unitary Everettian quantum mechanics. Rather than invoking ontological selection, probabilistic collapse, or inter-branch transition, CCST reframes continuity as a stability property of a finite physical substrate subject to irreversible thermodynamic and dynamical constraints. The theory introduces Thermodynamic Strain as a path-dependent measure of cumulative irreversible burden required to maintain coherent macroscopic descriptive structure across decoherence and branching. CCST remains fully compatible with standard quantum mechanics and preserves the physical reality of all branches, while providing an explicit stability-based criterion for when continuous macroscopic description remains physically well posed.