Non-relativistic objective collapse theories have been remarkably successful in addressing the conceptual problems of standard quantum mechanics. Despite substantial efforts, the project of extending them to the relativistic domain remains burdened by significant conceptual objections and technical challenges, often taken to cast doubt on the viability of the program as a whole. On the conceptual side, relativistic collapse theories have been claimed to face challenges involving tension between instantaneous collapse and relativity, frame-dependence of property values and probabilities, the possibility of superluminal signaling and the failure of narratability. On the technical side, persistent infinities, difficulties in constructing fully covariant frameworks and the apparent need for non-standard fields have hindered the development of workable models. In this paper, we offer a systematic rebuttal of the conceptual objections and provide a structured account of the remaining technical challenges. We conclude that relativistic collapse theories do provide a promising route toward a fully relativistic quantum framework that overcomes the conceptual limitations of standard quantum theory.
Non-relativistic objective collapse theories have been remarkably successful in addressing the conceptual problems of standard quantum mechanics. Despite substantial efforts, the project of extending them to the relativistic domain remains burdened by significant conceptual objections and technical challenges, often taken to cast doubt on the viability of the program as a whole. On the conceptual side, relativistic collapse theories have been claimed to face challenges involving tension between instantaneous collapse and relativity, frame-dependence of property values and probabilities, the possibility of superluminal signaling and the failure of narratability. On the technical side, persistent infinities, difficulties in constructing fully covariant frameworks and the apparent need for non-standard fields have hindered the development of workable models. In this paper, we offer a systematic rebuttal of the conceptual objections and provide a structured account of the remaining technical challenges. We conclude that relativistic collapse theories do provide a promising route toward a fully relativistic quantum framework that overcomes the conceptual limitations of standard quantum theory.
Spontaneous collapse models provide a possible, testable solution to the quantum measurement problem, but constructing a relativistic version applicable to quantum field theory remains an important open challenge. Challenges in constructing relativistic collapse models include avoiding superluminal signaling and foliation dependence, controlling energy production, and ensuring vacuum stability. Here, we present a relativistic collapse framework that addresses these problems at the cost of introducing a new space of physical states, whose complete characterization is left open. A modified, history-dependent Aharonov--Albert prescription describes instantaneous nonlocal state updates on arbitrary spacelike foliations while preserving foliation independence. To ensure vacuum stability, we modify the standard unitary evolution through a prescription that we name dynamical vacuum subtraction. The resulting dynamical map is linear and trace-preserving but not positive on the full set of standard density operators. We establish no-signaling by proving microscopic parameter independence, and identify conditions under which standard nonrelativistic collapse dynamics are recovered. Finally, we apply our framework to a free massive scalar field, obtaining finite particle-number and energy-increase rates at leading order in the long-time regime, together with further promising evidence for the consistency of the framework.
One of the most puzzling facts about quantum mechanics is that although quantum theory offers a very accurate framework encompassing phenomena going from chemistry to high energy physics, it does not provide us with clear indications favoring some world view in the relativistic domain. Consequently, many physicists have held an instrumentalist point of view. Even though in non-relativistic physics already exists a realistic interpretation of quantum mechanics due to Heisenberg, who considers quantum states as states of disposition (the real tendency interpretation), the efforts for extending this interpretation to the relativistic domain were found wanting. The basic problem is the dependence of the states on the frame within which collapse takes place. We show here that a suitable use of the causal structure of the devices involved in the measurement process allows us to introduce a covariant notion for the collapse of quantum states and to preserve the tendency interpretation in relativistic quantum mechanics. However, we shall see that this extended interpretation requires the introduction of a relational concept of reality.
Abstract Quantum mechanics and relativity are two of the most successful theoretical frameworks in modern physics, yet their conceptual foundations remain difficult to reconcile at the deepest level. Quantum theory describes physical systems through states, observables, probabilities, measurement contexts, superposition, entanglement, and nonclassical correlations. Relativity describes physical processes through space-time structure, causal order, invariant physical law, observer-dependent decomposition of time and space, and constraints on signal propagation. This article examines the conceptual relationship between quantum measurement, relativistic causality, and space-time description. The purpose is not to present a mathematical unification but to analyze how the two frameworks organize physical explanation differently and where their interpretive tensions arise. Special attention is given to the measurement problem, the status of quantum states, the role of observers and reference frames, the meaning of locality, the distinction between correlation and causal influence, and the challenge of describing quantum processes without privileging a single global time. The article argues that many apparent conflicts between quantum theory and relativity result from importing classical intuitions into domains where they no longer apply. Quantum entanglement does not permit controllable faster-than-light communication, yet it challenges classical separability. Relativity forbids superluminal signaling, yet it does not require that all physically meaningful correlations be reducible to local classical properties. Measurement introduces another difficulty because standard quantum theory often describes state update in a way that appears instantaneous, while relativistic space-time does not provide a universal present. The discussion develops a conceptual framework in which quantum measurement is treated as a physical interaction, relativistic causality as a constraint on operational influence, and space-time description as an organizing structure for events rather than a simple background stage. This analysis is relevant for quantum field theory, quantum information, relativistic quantum foundations, and future approaches to quantum gravity.
Abstract The conceptual unification of quantum mechanics and relativity remains one of the central challenges of modern theoretical physics. While quantum theory successfully describes microscopic phenomena through probabilistic wave dynamics and field quantization, relativity establishes the geometric structure of space-time and the causal organization of physical events. Despite extensive progress in quantum field theory and relativistic quantum frameworks, foundational tensions persist regarding locality, causality, and coherence. This study presents a conceptual and structural analysis of quantum field coherence within relativistic space-time. Rather than focusing on specific unification proposals, we examine the compatibility conditions between quantum coherence, relativistic causality, and space-time structure. Particular attention is given to field-based interpretations of quantum states, entanglement propagation limits, and covariance requirements. The analysis synthesizes perspectives from relativistic quantum field theory, conceptual foundations of quantum measurement, and geometric interpretations of space-time. We argue that coherence phenomena can be understood as structurally constrained by relativistic causal order, without requiring violation of space-time locality. The aim of this article is to clarify foundational relationships between quantum coherence and relativistic structure through a conceptual framework that integrates field-theoretic and geometric viewpoints.
More than sixty years after the general acceptance of Quantum Mechanics, and notwithstanding its enormous practical success, the nature of the fundamental objects appearing in its framework is unclear, and the debate concerning its conceptual foundations still goes on. This paper tries to examine what may be claimed to be one of the most ‘properly quantic’ ( Lévy-Leblond 1977 ) approaches to this problem, namely ‘no-collapse’ versions of the non-relativistic quantum mechanics of closed systems: Everett’s theory and the ‘pilot wave’.
Quantum mechanics has seemed to defy all attempts to construe it realistically, but antirealism, like the many‐worlds hypothesis, is even more difficult to accept. In order to give a realist construal of quantum mechanics, we need first to distinguish the objective and rational aspect of reality from the paradigmatic thing‐like aspects of having determinate physical properties: quantum‐mechanical entities may be real in the former sense though not in the latter. Anti‐realist arguments are based on the difficulty of giving an account of quantum‐mechanical collapse and the apparent superluminal velocities involved. Objections to superluminal velocities on the score of the special theory of relativity are found not to be conclusive, and the price—there being some preferred frame of reference—to be acceptable. A sketch of a probabilistic account of quantum‐mechanical collapse is offered, which makes the difference between the macro‐ and the micro‐world a matter of degree rather than kind. If that, or some other, account proved acceptable, we could be quantum‐mechanical realists, though quantum‐mechanical reality would be very different from that of material objects in hardware shops.