The quantum measurement problem may have a resolution in de Broglie-Bohm theory in which measurements lead to dynamical wavefunction collapse. We study the collapse in a simple setup and find that there may be slight differences between probabilities derived from standard quantum mechanics versus those from de Broglie-Bohm theory in certain situations, possibly paving the way for an experimental test.
The quantum measurement problem may have a resolution in de Broglie-Bohm theory in which measurements lead to dynamical wavefunction collapse. We study the collapse in a simple setup and find that there may be slight differences between probabilities derived from standard quantum mechanics versus those from de Broglie-Bohm theory in certain situations, possibly paving the way for an experimental test.
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.
In a recent paper, Brida et al (2002 J. Phys. B: At. Mol. Opt. Phys. 35 4751) reported the first experimental realization for testing of de Broglie–Bohm (dBB) theory against standard quantum mechanics (SQM), based on a suggested scheme presented in Golshani and Akhavan (2001 J. Phys. A: Math. Gen. 34 5259). However, some details of their experiment are not compatible with our suggestion. Therefore, their conclusion, in which the experimental data are in complete agreement with SQM but show some deviations from dBB predictions, cannot be considered as a final verdict.
Abstract If we are not persuaded of the approach to recovering causality in quantum physics through the de Broglie-Bohm theory (perhaps because, like Einstein, we think this route ‘too cheap’) or Popper’s reinterpretation of the meaning of probability, we must seek alternative solutions to the problems of quantum probability and the collapse of the wave function. Even if we choose to accept what quantum probability tells us concerning the fundamental indeterminism and acausality of the quantum world, we are still left to trouble over quantum measurement.
We try to give a physical meaning to the wave function or quantum state of a system, apart from being a very efficient tool for predicting results of measurements on that system. In other words, we ask what does it mean for a system outside the laboratories to have a wave function? We first explain why two possible, and probably common, answers to that question do not really answer it. Then, we explain how the de Broglie – Bohm theory does give a satisfactory meaning to the quantum state outside the laboratories, while avoiding the problems faced by the other answers.
The collapse postulate in quantum mechanics is problematic. In standard presentations of the theory, the state of a system prior to a measurement is a sum of terms, with one term representing each possible outcome of the measurement. Many dynamical collapse theories imply that the quantum wavefunction is fundamental, and that particles are just a temporary “bunching up” of the fundamental wave-like entity. Quantum mechanics is often taken to be an indeterministic theory. Quantum mechanics represents the state of a system in various ways, but the representation that is most perspicuous for understanding collapse theories uses a wavefunction. Consistency with special relativity is, therefore, a problem for dynamical collapse theories, but perhaps not an insuperable one. Some have argued that the wavefunction needs to be supplemented to counteract the effects of the novel quantum vagueness introduced by dynamical collapse theories. The ontological consequences of dynamical collapse theories remain an area of active debate.
Abstract We will first define what is meant by “hidden variables”. Then, we will review theorems proving the impossibility of theories introducing such variables in a naive way. Next, we will outline the de Broglie-Bohm theory and show that it is not refuted by those theorems. To do that, we will explain how “measurements” work in that theory, using the examples of spin measurements and of momentum measurements. Those measurements do not reveal pre-existing properties of the quantum particle but are the result of interactions between that particle and the measuring apparatus. And this is why the de Broglie-Bohm theory is not refuted by the theorems on the impossibility of hidden variables. We will also explain the relationship between the no “hidden variables” theorems and nonlocality, with and without introducing Bell’s inequalities.