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Mathematics

Probabilistic Basis of Parametrized Relativistic Quantum Theory in Curved Spacetime

John R. Fanchi

Published May 18, 2025• 3 citations
Publisher

Abstract

A probabilistic basis for Parametrized Relativistic Quantum Theory (PRQT) has been developed for multicomponent eigenvectors and many-body applications in flat spacetime. This paper presents an extension of the multicomponent, many-body PRQT formalism to curved spacetime.
DOI
10.3390/math13101657

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Abstract In this work, we establish a novel approach to the foundations of relativistic quantum theory, which is based on generalizing the quantum-mechanical Born rule for determining particle position probabilities to curved spacetime. A principal motivator for this research has been to overcome internal mathematical problems of relativistic quantum field theory (QFT) such as the ‘problem of infinities’ (renormalization), which axiomatic approaches to QFT have shown to be not only of mathematical but also of conceptual nature. The approach presented here is probabilistic by construction, can accommodate a wide array of dynamical models, does not rely on the symmetries of Minkowski spacetime, and respects the general principle of relativity. In the analytical part of this work, we consider the 1-body case under the assumption of smoothness of the mathematical quantities involved. This is identified as a special case of the theory of the general-relativistic continuity equation. While related approaches to the relativistic generalization of the Born rule assume the hypersurfaces of interest to be spacelike and the spacetime to be globally hyperbolic, we employ prior contributions by C. Eckart and J. Ehlers to show that the former condition is naturally replaced by a transversality condition and that the latter one is obsolete. We discuss two distinct formulations of the 1-body case, which, borrowing terminology from the non-relativistic analog, we term the Lagrangian and Eulerian pictures. We provide a comprehensive treatment of both. The main contribution of this work to the mathematical physics literature is the development of the Lagrangian picture. The Langrangian picture shows how one can address the ‘problem of time’ in this approach and, therefore, serves as a blueprint for the generalization to many bodies and the case that the number of bodies is not conserved. We also provide an example to illustrate how this approach can in principle be employed to model particle creation and annihilation.
Parametrized Relativistic Quantum Theory (PRQT) extends conventional relativistic quantum mechanics by introducing an invariant evolution parameter (s) and a broader symmetry group. This paper presents the axiomatic and probabilistic foundations of PRQT. The resulting Stueckelberg equation is applied to the study of barrier penetration, with explicit calculations for scanning tunneling microscopy (STM). The STM application demonstrates high sensitivity to barrier width and quantitative agreement between exact and thick-barrier approximations.
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Relativistic quantum metrology provides an optimal strategy for the estimation of parameters encoded in quantum fields in flat and curved spacetime. These parameters usually correspond to physical quantities of interest such as proper times, accelerations, gravitational field strengths, among other spacetime parameters. The precise estimation of these parameters can lead to novel applications in gravimeters, spacetime probes and gravitational wave detectors. Previous work in this direction only considered pure probe states. In realistic situations, however, probe states are mixed. In this paper, we provide a framework for the computation of optimal precision bounds for mixed single- and two-mode Gaussian states within quantum field theory. This enables the estimation of spacetime parameters in case the field states are initially at finite temperature.
Using tangent bundle geometry we construct an equivalent reformulation of classical field theory on flat spacetimes which simultaneously encodes the perspectives of multiple observers. Its generalization to curved spacetimes realizes a new type of nonminimal coupling of the fields and is shown to admit a canonical quantization procedure. For the resulting quantum theory we demonstrate the emergence of a particle interpretation, fully consistent with general relativistic geometry. The path dependency of parallel transport forces each observer to carry their own quantum state; we find that the communication of the corresponding quantum information may generate extra particles on curved spacetimes. A speculative link between quantum information and spacetime curvature is discussed which might lead to novel explanations for quantum decoherence and vanishing interference in double-slit or interaction-free measurement scenarios, in the mere presence of additional observers.
We offer a new look on multiparticle theory which was initiated in a recent philosophical paper [1] of the author. To accomplish such feature, we start by a revision and extension of the single particle theory as well relativistically as nonrelativistically. Standard statistics gets an interpre- tation in terms of symmetry properties of the two point function and any reference towards all existing quantization schemes is dropped. As I have repeatedly stated and was also beautifully explained by Weinberg, there is no a priori rationale why quantum field theory should take the form it does in a curved spacetime; there is no reason why the straightforward generalizations of the Klein Gordon and Dirac theory should have some- thing to do with the real world. Perhaps, if we were to look differently at the flat theory, a completely satisfactory class of relativistic quantum theories would emerge. These may not have anything to do with quantum fields at all except in some limit.