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Journal of Physics A Mathematical and General

A causal account of non-local Einstein-Podolsky-Rosen spin correlations

Christopher Dewdney, Peter Holland, Anastasios Kyprianidis

Published Oct 1, 1987• 91 citations
Publisher

Abstract

The authors give a causal interpretation of a double Stern-Gerlach experiment on the basis of spacetime solutions to the Pauli equation. For an initial singlet state, they determine the continuous particle trajectories and spin vector orientations. The graphical results exemplify how non-local actions of the quantum potential and quantum torque give rise to a correlated evolution of dynamical variables.

DOI
10.1088/0305-4470/20/14/016

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The authors give a causal interpretation of a double Stern-Gerlach experiment on the basis of spacetime solutions to the Pauli equation. For an initial singlet state, they determine the continuous particle trajectories and spin vector orientations. The graphical results exemplify how non-local actions of the quantum potential and quantum torque give rise to a correlated evolution of dynamical variables.
In this paper we study a two-step version of EPR-B experiment, the Bohm version of the Einstein-Podolsky-Rosen experiment. Its theoretical resolution in space and time enables us to refute the classic "impossibility" to decompose a pair of entangled atoms into two distinct states, one for each atom. We propose a new causal interpretation of the EPR-B experiment where each atom has a position and a spin while the singlet wave function verifies the two-body Pauli equation. In conclusion we suggest a physical explanation of non-local influences, compatible with Einstein's point of view on relativity.
The century-old Stern–Gerlach setup is paradigmatic for a quantum measurement. We visualize the electron trajectories following the Bohmian zig-zag dynamics. This dynamics was developed in order to deal with the fundamentally massless nature of particles (with mass emerging from the Brout–Englert–Higgs mechanism). The corresponding trajectories exhibit a stochastic zig-zagging, as the result of the coupling between left- and right-handed chiral Weyl states. This zig-zagging persists in the non-relativistic limit, which will be considered here, and which is described by the Pauli equation for a non-uniform external magnetic field. Our results clarify the different meanings of ‘spin’ as a property of the wave function and as a random variable in the Stern–Gerlach setup, and they illustrate the notion of effective collapse. We also examine the case of an EPR-pair. By letting one of the entangled particles pass through a Stern–Gerlach device, the non-local influence (action-at-a-distance) on the other particle is manifest in its trajectory, e.g. by initiating its zig-zagging.
Introduction The paradox of Einstein, Podolsky and Rosen was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional variables were to restore to the theory causality and locality. In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics. It is the requirement of locality, or more precisely that the result of a measurement on one system be unaffected by operations on a distant system with which it has interacted in the past, that creates the essential difficulty. There have been attempts to show that even without such a separability or locality requirement no ‘hidden variable’ interpretation of quantum mechanics is possible. These attempts have been examined elsewhere and found wanting. Moreover, a hidden variable interpretation of elementary quantum theory has been explicitly constructed. That particular interpretation has indeed a grossly non-local structure. This is characteristic, according to the result to be proved here, of any such theory which reproduces exactly the quantum mechanical predictions. Formulation With the example advocated by Bohm and Aharonov, the EPR argument is the following. Consider a pair of spin one-half particles formed somehow in the singlet spin state and moving freely in opposite directions. Measurements can be made, say by Stern–Gerlach magnets, on selected components of the spins σ 1 and σ 2 .
The Stern-Gerlach experiment is the fundamental experiment in order to exhibit the quantization of spin and understand the measurement problem in quantum mechanics. However, although the Stern-Gerlach experiment plays an essential role in the teaching of quantum mechanics, no complete analysis of this experiment using Pauli spinors is presented in the pedagogical literature. This paper presents such an analysis and develops implications for the theory of quantum measurement. We first propose an analytic expression of both the wave function and the probability density in the Stern-Gerlach experiment. Our explicit solution is obtained via a complete integration of the Pauli equation over time and space. The probability density evolution describes a slipping of the wave packet into two separate packets due to the measurement device, but it cannot account for impacts. We therefore calculate the de Broglie-Bohm trajectories, which not only explain impacts naturally, but also accounts for the spin quantization following the magnetic field gradient. It is then possible to propose a clear explanation of measurement effects in the Stern-Gerlach experiment.
Abstract The discussion of the recently derived quantum Hamilton equations for a spinning particle is extended to spin measurement in a Stern–Gerlach experiment. We show that this theory predicts a continuously changing orientation of the particles magnetic moment over the course of its motion across the Stern–Gerlach apparatus. The final measurement results agree with experiment and with predictions of the Pauli equation. Furthermore, the Einstein–Podolsky–Rosen–Bohm thought experiment is investigated, and the violation of Bells’s inequalities is reproduced within this stochastic mechanics approach. The origin of the violation of Bell’s inequalities is traced to the the non-local nature of the velocity fields for an entangled state in the stochastic formalism, which is a result of a non-separable probability distribution of the considered particles.
We introduce a local phase-field framework for describing spin entanglement in which measurement correlations arise from an internal scalar phase associated with each fermion. The phase is defined by two underlying real fields and evolves according to local relativistic dynamics. When particle pairs are produced at a common spacetime event, a phase-locking constraint is established at creation, after which the internal phases evolve independently without any nonlocal interaction.Spin measurements performed by Stern–Gerlach analyzers are modeled as local filtering operations that depend only on the internal phase and the analyzer orientation. Using this deterministic local response, we derive the exact quantum correlation function; when inserted into the CHSH expression, it attains the standard Tsirelson bound.The framework preserves locality, parameter independence, and no-signaling, while providing a concrete physical ontology for spin correlations based on internal phase structure. We compare the model with earlier phase-based approaches and outline experimental configurations—such as time-resolved and multi-stage Stern–Gerlach measurements—that could probe the dynamical evolution of the internal phase. The results demonstrate that exact quantum entanglement correlations can emerge from a strictly local phase-field description.Bell’s theorem constrains models in which measurement outcomes are functions of pre-assigned discrete values. The present framework instead employs a continuous internal phase field as the relevant physical variable. Measurement outcomes are deterministic functions of the local phase and analyzer orientation. The model preserves locality, parameter independence, and no-signaling, while allowing outcome dependence, which is permitted within Bell’s framework.