The ontology of Local Quantum Physics, Rudolf Haag's framework for relativistic quantum theory, is reviewed and discussed. It is one of spatiotemporally localized events and unlocalized causal intermediaries, including the elementary particles, which come progressively into existence in accordance with a fundamental arrow of time. Haag's conception of quantum theory is distinguished from others in which events are also central, especially those of Niels Bohr and John Wheeler, with which it has been compared.
The ontology of Local Quantum Physics, Rudolf Haag's framework for relativistic quantum theory, is reviewed and discussed. It is one of spatiotemporally localized events and unlocalized causal intermediaries, including the elementary particles, which come progressively into existence in accordance with a fundamental arrow of time. Haag's conception of quantum theory is distinguished from others in which events are also central, especially those of Niels Bohr and John Wheeler, with which it has been compared.
Rudolf Haag's Local Quantum Physics (LQP) is an alternative framework to conventional relativistic quantum field theory for combining special relativity and quantum theory based on first principles, making it of great interest for the purposes of conceptual analysis despite currently being relatively limited as a tool for making experimental predictions. In LQP, the elementary particles are defined as species of causal link between interaction events, together with which they comprise its most fundamental entities. This notion of particle has yet to be independently assessed as such. Here, it is captured via a set of propositions specifying particle characteristics and then compared to previous particle notions. Haag's particle differs decisively with respect to mechanical intuitions about particles by lacking, among other things, even an approximate independent space-time location. This notion is thus found to differ greatly even from those of relativistic quantum mechanics and quantum field theory, which have been applied to the known elementary particles.
Quantum theory is commonly narrated by beginning with objects already called photons, electrons, atoms, or molecules and then asking why those objects display wave-like behavior. Whole Pattern, Local Event (WPLE) reverses that explanatory order. Its ontological principle assigns priority to the Whole: the most fundamental quantum reality is not taken to be an assembly of independently localized corpuscles. The term wave names the Whole's intrinsic wave-like, non-corpuscular quantum character - expressed in quantum theory through phase-sensitive amplitudes, coherence, superposition, and nonseparability - without identifying the Whole with an ordinary oscillation in three-dimensional space or with any single wavefunction. In WPLE, particle-like localization manifests in local physical events such as detector transitions, ionizations, clicks, and other localized registrations. The localized morphology of such an event is not projected backward into a continuously localized corpuscular history unless independent physics warrants that description. Particle species, quantum numbers, and effective particle persistence remain intact. Standard quantum mechanics is compatible with this ordering but does not deductively establish it. The positive case for Whole-priority is abductive: nonseparability makes whole-state structure irreducible in important cases; the standard formalism does not require primitive corpuscular trajectories; localized events are nevertheless ubiquitous; and Whole-first ordering treats interference, entanglement, and localized registration without assigning rival wave and particle substances to one pre-given microscopic object. The paper distinguishes this proposal from Bohr, Everett, Bohm and Hiley, priority monism, relational quantum mechanics, Haag and Pashby, GRW flash ontology, decoherence, wave-function realism, and recent work by Goyal. WPLE does not introduce a new outcome-selection dynamics. Its central principle is compact: Whole (wave-like coherent/nonseparable quantum structure) + local interaction -> localized event (particle-like manifestation).
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.
The recent work of P. Teller and S. Auyang in the philosophy of Quantum Field Theory (QFT) has stimulated the search for the fundamental entities of that theory. In QFT, the classical notion of a particle collapses. The theory does not only forbid classical, i.e. spatiotemporally identifiable particles, but it makes particles of the same type conceptually indistinguishable. Teller and Auyang have suggested competing ersatz-ontologies which could account for the ‘loss of the particles’: Field quanta vs. Field events. However, both ontologies suffer from serious defects. While quanta lack numerical identity, spatiotemporal localizability, and independence from basis-representations, events – if understood as concrete measurement events – are related to the theory only statistically. I propose an alternative solution: The entities of QFT are events of the type ‘Quantum system S is in quantum state Ψ’. The latter are not point events, but Davidsonian events, i.e. they can be identified by their location inside the causal net of the world.
The axiomatic formulation of an Algebraic Relativistic Quantum Field Theory leads naturally -via the Haag-Kastler axioms- to the fact that operators representing observables generate a von Neumann algebra localized in a space-time region in which said observations are made. I present and explain the axioms, as well as the mathematical preliminaries needed to understand them and apply them to the so-called causal diamond and Fermi's Two-Atom System. The latter shows the importance of formulating axioms concerning causality that try to make compatible the requirement from Special Relativity according to which no causal influence can travel faster than the speed of light and the quantum mechanical theory of measurement and preparability of states. For a relativistic field-theoretic setting, these concepts must be re-formulated, and this reasoning suggests that the operator algebra must be a type III von Neumann factor. I also introduce some philosophical problems concerning our usual notion of causality from Hume to contemporary theories of counterfactual causation and show how the algebraic structure of the theory is deeply related to the causal one and how this theory can be extended if we change the way we think about causality, measurements, and local preparability of states.