Field Concepts in Quantum Theory

Paul Teller

W. F. G. Swann

Mário Bacelar Valente

In this article the Dirac equation is used as a guideline to see the historical emergence of the concept of quanta, associated with the quantum field. In P. Jordan’s approach, electrons as quanta result from the quantization of a classical field described by the Dirac equation. With this quantization procedure – also used for the electromagnetic field – the concept of quanta becomes a central piece in the applications of quantum electrodynamics. This does not seem to avoid the apparent impossibility of using the concept of quanta – and with it the common interpretation of quantum fields – when interacting fields are considered together as one complete system. In this article it is defended that the type of analysis that leads to so drastic conclusions is avoidable if a clear distinction is made between the mathematical framework of the theory and the particular physical models (used in the empirical corroboration of the theory) that are constructed using the theory. When dealing with models there really is no system of complete interacting fields, and what we have is a description of the interactions between distinct fields. In this situation the concept of quanta is central in the description of interacting fields, the Fock space being the natural mathematical structure that permits maintaining the quanta concept when considering the interaction between fields.

Rob Clifton, Hans Halvorson

Philosophical reflection on quantum field theory has tended to focus on how it revises our conception of what a particle is. However, there has been relatively little discussion of the threat to the "reality" of particles posed by the possibility of inequivalent quantizations of a classical field theory, i.e., inequivalent representations of the algebra of observables of the field in terms of operators on a Hilbert space. The threat is that each representation embodies its own distinctive conception of what a particle is, and how a "particle" will respond to a suitably operated detector. Our main goal is to clarify the subtle relationship between inequivalent representations of a field theory and their associated particle concepts. We also have a particular interest in the Minkowski versus Rindler quantizations of a free Boson field, because they respectively entail two radically different descriptions of the particle content of the field in the very same region of spacetime. We shall defend the idea that these representations provide complementary descriptions of the same state of the field against the claim that they embody completely incommensurable theories of the field.

F. A. Kaempffer

Inge Svein Helland