Abstract. The apparent random outcome of a quantum measurement is conjectured to be fundamentally determined by the microscopic state of the macroscopic measurement apparatus. The apparatus state thus plays the role of a hidden variable which, in contrast with variables characterizing the measured microscopic system, is shown to lead to a vi-olation of Bell’s inequalities and to agree with standard quantum mechanics. An explicit realization of this interpretation is explored (for details, see [1]) for a primitive model of cloud chamber inspired by Mott [2]. Being highly non local, this interpretation of quantum mechanics is argued to open the way to faster-than-light information transfer.
Abstract. The apparent random outcome of a quantum measurement is conjectured to be fundamentally determined by the microscopic state of the macroscopic measurement apparatus. The apparatus state thus plays the role of a hidden variable which, in contrast with variables characterizing the measured microscopic system, is shown to lead to a vi-olation of Bell’s inequalities and to agree with standard quantum mechanics. An explicit realization of this interpretation is explored (for details, see [1]) for a primitive model of cloud chamber inspired by Mott [2]. Being highly non local, this interpretation of quantum mechanics is argued to open the way to faster-than-light information transfer.
The apparent random outcome of a quantum measurement is conjectured to be fundamentally determined by the microscopic state of the macroscopic measurement apparatus. The apparatus state thus plays the role of a hidden variable which, in contrast with variables characterizing the measured microscopic system, is shown to lead to a violation of Bell’s inequalities and to agree with standard quantum mechanics. An explicit realization of this interpretation is explored (for details, see [1]) for a primitive model of cloud chamber inspired by Mott [2]. Being highly non local, this interpretation of quantum mechanics is argued to open the way to faster-than-light information transfer.
Abstract Quantum states in superposition cannot be observed, suggesting that they merely embody information on possible measurement results. Yet, we think of them as describing physical systems that evolve in time according to given mathematical equations. Furthermore, evolution takes place in physical space-time, and local causality is imposed on space-time by Special Relativity (a sequence of cause and effect that constitutes a fundamental principle by which we think about and do scientific work). It is therefore strange that there is non–locality and violation of causality embedded in Quantum Mechanics. We try to give here a first step to see whether a deterministic and local interpretation is possible. We will show that Bell’s inequality is not conclusive about the non–local nature of Quantum Mechanics, in that there exists an interpretation of reality (which we put forward) which is local and in which Bell’s inequality cannot be derived. Assuming determinism and locality a new Bell-like inequality is derived, which is always satisfied by Quantum Mechanics and which allows for local hidden variables [1].
We propose a novel interpretation of quantum mechanics in which microscopic particles possess definite positions, momenta, and spins at every moment, independent of measurement. These physical quantities are not determined by hidden variables but are randomly realized according to the wave function’s probability distribution. Measurement outcomes reflect the particle’s actual state rather than a wave-function collapse. By treating the measured and measuring systems as a single composite system, we introduce a conditional probability decomposition of the wave function that preserves interference without invoking instantaneous collapse. Potential experimental tests of the conditional probability decomposition are discussed. This framework provides a coherent understanding of quantum measurement, nonlocal correlations, and the EPR paradox, while remaining consistent with all standard quantum predictions including Bell inequality violations and GHZ state.
We give a counter example to show that determinism as such is in contradiction to quantum mechanics. More precisely, we consider a simple quantum system and its environment, including the measurement device, and make the assumption that the time evolution of the global system, the quantum system plus this environment, is deterministic, i. e., the time evolution is given by a dynamical trajectory from some initial conditions. From this, we prove a type of Bell inequalities which are violated by quantum mechanics, reaching the conclusion that our quantum system evolves in a non deterministic way. In order to seize the interest of this conclusion, one must realize that it cannot be reached from the present experimental violation of Bell inequalities predicted by quantum mechanics, since this violation is compatible with non-local realism.
This work proposes a threshold-based picture of decoherence in quantum measurement. Microscopic quantum dynamics remain fully continuous and unitary, but real detectors implement thresholded amplification and nonlinear gain boundaries that partition continuous microscopic inputs into discrete macroscopic outcomes. Within this framework, discreteness and irreversibility arise from scale asymmetry between a continuous microscopic energy distribution and a finite macroscopic threshold ΔE_threshold, without invoking fundamental collapse, branching, or uncontrolled environmental decoherence. The measurement apparatus effectively performs an analog-to-digital conversion: it maps a continuous input distribution ρ(E) to a binary output variable X_eff ∈ {0,1} according toP(event) = ∫_{ΔE_threshold}^{∞} ρ(E) dE,while the recording layer irreversibly erases phase information by structural codomain restriction. This threshold-based decoherence model preserves standard quantum mechanics, provides an operational bridge across major interpretations of quantum theory, and locates the origin of discrete outcomes in the architecture of measurement rather than in quantum ontology itself. In short, this paper views discrete measurement outcomes as emerging from threshold detector architecture rather than from any fundamental discreteness of the quantum substrate.
Quantum mechanics famously posits two distinct evolution rules for the state of a system: a deterministic, unitary time evolution under the Schr¨odinger equation, and a probabilistic “collapse” of the wavefunction upon measurement as dictated by the Born rule. The apparent inconsistency of these two dynamical laws – one continuous and one discontinuous – constitutes the quantum measurement problem. This foundational problem, which underlies the emergence of definite outcomes from quantum superpositions, has persisted since the theory’s inception. In this review, we present a comprehensive and rigorous examination of the measurement problem and survey the leading approaches that seek to resolve or circumvent it. We begin by formulating the measurement problem and its conceptual challenges. We then discuss in detail the major interpretations of quantum mechanics and theoretical frameworks addressing the problem: the Copenhagen interpretation, Everett’s many-worlds interpretation, de Broglie–Bohm pilot-wave theory, objective collapse models, the role of decoherence and environment-induced superselection, and epistemic approaches such as QBism. For each interpretation, we describe the core principles and mathematical formalism, assessing how (and whether) it attempts to solve the measurement problem. We also review modern developments and experiments relevant to quantum measurements, including tests of Bell inequalities, observations of decoherence and macroscopic superpositions, weak measurements and quantum eraser experiments, and thought experiments ‘a la Wigner’s friend. We highlight how these results inform the ongoing debate. Finally, we discuss open problems and challenges that remain in fully resolving the measurement problem.