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Foucault's Pendulum, a Classical Analog for the Electron Spin State

R. A. Linck

Published Jan 1, 2013• 0 citations
Publisher

Abstract

Spin has long been regarded as a fundamentally quantum phenomena that is incapable of being described classically. To bridge the gap and show that aspects of spin's quantum nature can be described classically, this work uses a classical Lagrangian based on the coupled oscillations of Foucault's pendulum as an analog for the electron spin state in an external magnetic field. With this analog it is possible to demonstrate that Foucault's pendulum not only serves as a basis for explaining geometric phase, but is also a basis for reproducing a broad range of behavior from Zeeman-like frequency splitting to precession of the spin state. By demonstrating that unmeasured electron spin states can be fully described in classical terms, this research opens the door to using the tools of classical physics to examine an inherently quantum phenomenon.

DOI
10.31979/etd.q6rz-n7jr

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Spin has long been regarded as a fundamentally quantum phenomena that is incapable of being described classically. To bridge the gap and show that aspects of spin's quantum nature can be described classically, this work uses a classical Lagrangian based on the coupled oscillations of Foucault's pendulum as an analog for the electron spin state in an external magnetic field. With this analog it is possible to demonstrate that Foucault's pendulum not only serves as a basis for explaining geometric phase, but is also a basis for reproducing a broad range of behavior from Zeeman-like frequency splitting to precession of the spin state. By demonstrating that unmeasured electron spin states can be fully described in classical terms, this research opens the door to using the tools of classical physics to examine an inherently quantum phenomenon.
Despite conventional wisdom that spin-1/2 systems have no classical analog, we introduce a set of classical coupled oscillators with solutions that exactly map onto the dynamics of an unmeasured electron spin state in an arbitrary, time-varying, magnetic field. While not addressing the quantum measurement problem (discrete outcomes and their associated probabilities), this new classical analog yields a classical, physical interpretation of Zeeman splitting, geometric phase, the electron's doubled gyromagnetic ratio, and other quantum phenomena. This Lagrangian-based model can be used to clarify the division between classical and quantum systems, and might also serve as a guidepost for certain approaches to quantum foundations.
We proposed a Quaternionic mechanical system motivated by the Foucault pendulum as a classical model for the dynamics of the spin 1/2 system. We showed that this mechanical system contains the dynamics of the spin state of the electron under a uniform magnetic field as it is given by the Schrodinger-Pauli-Equation (SPE). We closed with a characterization of the dynamics of this generalized classical system by showing that it is equivalent with the dynamics of the Schrodinger Pauli Equation as long as the solutions to the generalized classical system are roots of the Lagrangian, that is the condition L = 0 holds.
Stokes parameter formalism is applied to show the analogies between the motion of an asymmetric Foucault pendulum and several phenomena known from optics and atomic physics. Nonlinearity-induced precession of elliptical orbits of the pendulum is shown to correspond to twisting transformations used for spin squeezing of atomic systems. Transitions between regimes of predominant nonlinearity and regimes where the Coriolis force or the asymmetry of the pendulum are dominant correspond to quantum phase transitions in the Lipkin-Meshkov-Glick model. A Foucault pendulum with highly anisotropic damping can emulate an optical Zeno effect where a sequence of polarizing filters inhibits polarization rotation of light in an optically active medium.
The driven quantum harmonic oscillator is fundamental to a number of important physical systems. Here, we consider the quantum harmonic oscillator under non-Hermitian, PT-symmetric driving, showing that the resulting set of Wigner-space trajectories of an initial coherent state is identical to the set of real-space trajectories of the classical Foucault pendulum. Remarkably, in the case mapped from the trivial 1D pendulum, the corresponding quantum dynamics are those of an oscillator with periodically evolving momentum but fixed position, a novel type of dynamics which are forbidden in classical systems.
Although intrinsic spin is usually viewed as a purely quantum property with no classical analog, we present evidence here that fermion spin has a classical origin rooted in the geometry of three-dimensional physical space. Our approach to the quantum/classical interface is based on a formulation of relativistic classical mechanics that uses spinors. Spinors and projectors arise naturally in the Clifford's geometric algebra of physical space and not only provide powerful tools for solving problems in classical electrodynamics, but also reproduce a number of quantum results. In particular, many properites of elementary fermions, as spin-1/2 particles, are obtained classically and relate spin, the associated g-factor, its coupling to an external magnetic field, and its magnetic moment to Zitterbewegung and de Broglie waves. The relationship is further strengthened by the fact that physical space and its geometric algebra can be derived from fermion annihilation and creation operators. The approach resolves Pauli's argument against treating time as an operator by recognizing phase factors as projected rotation operators.
This work proposes a wave-entity perspective of the electron spin qubit, treating the electron as a continuous physical wave rather than a point-like particle. In this theoretical framework, each spin qubit corresponds to a distinct current density configuration, offering a resolution to the paradox of a particle appearing to spin both up and down simultaneously. We further predict the existence of a persistent, azimuthally asymmetric magnetic field associated with the wave-spin qubit, an effect not anticipated by the conventional particle-spin model. Notably, the qubit’s relative phase governs the orientation of both the current and the magnetic field, suggesting a mechanism for direct, local interactions between qubits. This phase-dependent coupling could form the basis for inherently parallel quantum computing architectures, in contrast to the sequential operations of gate-based logic. While this framework is grounded in theoretical analysis, it yields testable predictions—particularly regarding the magnetic field structure—that invite experimental verification. By treating the electron wave as the fundamental physical entity, rather than a probabilistic abstraction, we explore the possibility of a quantum model that is deterministic, local, causal, and fully consistent with special relativity.