The appearance of single-particle wave functions as field operators or arguments of a field functional in quantum field theory is often regarded as a second quantization, since these wave functions were themselves obtained by quantizing mass points (“particles”). I argue here that this language, though reflecting the historical development, is misleading. Spatial fields must be regarded as the true and only physical variables (in quantum theory becoming the arguments of a fundamental wave functional). This includes spinor and other fields which never become classical. Apparent particles are no more than the result of decoherence in the measuring device or by means of other environmental scattering processes, without playing any fundamental conceptual rôle in the theory or its interpretation. A remark on gauge fields is added.
The appearance of single-particle wave functions as field operators or arguments of a field functional in quantum field theory is often regarded as a second quantization, since these wave functions were themselves obtained by quantizing mass points (“particles”). I argue here that this language, though reflecting the historical development, is misleading. Spatial fields must be regarded as the true and only physical variables (in quantum theory becoming the arguments of a fundamental wave functional). This includes spinor and other fields which never become classical. Apparent particles are no more than the result of decoherence in the measuring device or by means of other environmental scattering processes, without playing any fundamental conceptual rôle in the theory or its interpretation. A remark on gauge fields is added.
Nothing can be made out of nothing. William Shakespeare , King Lear Historically, quantization of the motion of particles was developed first. The state was described by a wave function and observables by operators. When dealing with interactions between particles and fields, such as the electromagnetic field, the fields were treated classically. Classical field equations look like the quantum mechanical equations for the wave function of the field quanta. For example, the Klein–Gordon classical field equation is similar to the quantum mechanical wave equation for a relativistic spinless particle. Quantizing the fields, leading to quantum field theory, appears to be quantizing a theory that has already been quantized; hence the name “second quantization.” In reality, there is only one quantization and one quantum theory. The method of second quantization is important in the study of many-particle systems. It enables us to express many-body operators in terms of creation and annihilation operators, thus rendering calculations less cumbersome. Moreover, the method makes it possible to treat systems with a variable number of particles; that is why the method initially emerged in the context of quantum field theory. In Chapter 1 we indicated that any one-particle wave function may be expanded in a complete set of states. In this chapter, we show that products of single-particle states, when properly symmetrized, form an orthonormal basis for the expansion of the wave function of an N -particle system.
Quantum field theory (QFT) can be analyzed in terms of its mathematical structure, its conceptual system for physical descriptions, or its basic ontology. The analysis can be done logically or historically. In this chapter, only the genesis of the conceptual foundations of QFT relevant to its basic ontology will be treated; no discussion of its mathematical structures or its epistemological underpinnings will be given. Some conceptual problems, such as those related to probability and measurement, will be discussed, but only because of their relevance to the basic ontology of QFT, rather than their intrinsic philosophical interest. Here, by basic ontology I mean the irreducible entities that QFT is invented to describe. The often mentioned candidates for the basic ontology of QFT, in fact of the physical world, are the discrete particle and the continuous field. Another possible candidate (the spacetime point) has also been suggested recently (Redhead, 1983). Since the aim of this chapter is to analyze the historical process in which the conceptual foundations of QFT were laid down, rather than the logical structure of QFT which philosophers of the present day treat, no discussion of the last possibility will be given. The content of this chapter involves the formation and interpretation, in a roughly chronological order, of the concepts of the wave function, quantization, quantization of the field, the vacuum, interactions between fields, and renormalization. The first two topics will be discussed in relation to the quantization of the field, with their role being taken as the starting point of the conceptual development of QFT.
Abstract This is an attempt of a non-technical but conceptually consistent presentation of quantum theory in a historical context. While the first part is written for a general readership, Section 5 may appear a bit provocative to some quantum physicists. I argue that the single-particle wave functions of quantum mechanics have to be correctly interpreted asfield modesthat are “occupied once” (i.e. first excited states of the corresponding quantum oscillators in the case of boson fields). Multiple excitations lead to apparent many-particle wave functions, while the quantum states proper are defined by wave function(al)s on the “configuration” space of fundamental fields, or on another, as yet elusive, fundamental local basis.
This preprint presents a field-first interpretation of wave-particle duality grounded in the ontology of Quantum Field Theory (QFT). The framework treats quantum fields as the fundamental ontology of physical reality, while particles are understood as excitation states of their respective fields. Wave-like phenomena, including interference, diffraction, tunneling, and coherence effects, are interpreted as arising from the propagation and interaction dynamics of these excitations rather than from an independent wave ontology. The central thesis is that wave-particle duality does not represent two distinct physical realities, but rather different observational regimes of a single field-based process. Localized interactions appear particle-like, while propagation and interference phenomena appear wave-like. This interpretation is fully consistent with the existing mathematical formalism of Quantum Field Theory and does not introduce new physical laws or modifications to established quantum mechanics. The purpose of this work is interpretive and conceptual. It aims to provide a clearer ontological framework for understanding the relationship between quantum fields, particles, and wave-like behavior while reducing the conceptual ambiguity traditionally associated with wave-particle duality. This document represents the initial preprint release of the field-first interpretation framework.
Up to a point, the quantum theory developed in chapter 5 was quite general. However, the systems we had in mind were non-relativistic ones consisting of a fixed number of particles. In this chapter, we extend the theory to deal with systems in which the number of particles can change. There are several reasons for wanting to do this. The most obvious is that we need a method of describing high-energy scattering and decay processes in which particles can be created and destroyed. A second is that, when we try to make quantum theory consistent with special relativity, we encounter difficulties (discussed in chapter 7) that can be resolved only in this more general setting. The final reason is that, even for systems of non-relativistic particles, the mathematics rapidly becomes intractable as the number of particles increases. A useful device for dealing with large systems is, roughly speaking, to imagine adding an extra particle, which serves as a theoretical probe of the state of the system. To put the matter another way, the method of second quantization developed in this chapter provides a means of dealing with the entire system by considering only a few particles at a time.
Up to a point, the quantum theory developed in Chapter 5 was quite general. However, the systems we had in mind were non-relativistic ones consisting of a xed number of particles. In this chapter, we extend the theory to deal with systems in which the number of particles can change. There are several reasons for wanting to do this. The most obvious is that we need a method of describing high-energy scattering and decay processes in which particles can be created and destroyed. A second is that, when we try to make quantum theory consistent with special relativity, we encounter diculties (discussed in Chapter 7) that can be resolved only in this more general setting. The nal reason is that, even for systems of non-relativistic particles, the mathematics rapidly becomes intractable as the number of particles increases. A useful device for dealing with large systems is, roughly speaking, to imagine adding an extra particle, which serves as a theoretical probe of the state of the system. To put the matter another way, the method of second quantization developed in this chapter provides a means of dealing with the entire system by considering only a few particles at a time.