Quantum fields are not fields; comment on “There are no particles, there are only fields,” by Art Hobson [Am. J. Phys. 81(3), 211–223 (2013)]

Abstract

In Ref. 1, Hobson defends the superiority of the field concept in quantum physics, in comparison to the particle concept. His view is that if we acknowledge that the fundamental constituents of physical reality are fields, and not particles, then much of the interpretational difficulties of quantum physics would disappear. However, as we shall briefly explain in the present comment, quantum fields are no more fields than quantum particles are particles, so that the replacement of a particle ontology (or particle and field ontology) by an all-field ontology, will not solve the typical quantum interpretational problems.Let us start by considering the main reason why a quantum entity cannot be considered a particle, then show that the same argument applies, mutatis mutandis, to the field concept. A particle (or corpuscle) is, by definition, a system localized in space. This means that if a physical entity is a particle then, in every moment, it must be characterizable by a specific position (for instance of its center of mass) in our three-dimensional Euclidean space. Let us call this fundamental attribute spatiality.Then, if microscopic entities are assumed to obey Heisenberg's uncertainty principle (HUP), as we know they do, one is forced to admit that the concept of "microscopic particle" is a self-contradictory one. This because if an entity obeys HUP, one cannot simultaneously determine its position and momentum and, as a consequence, one cannot determine, not even in principle, how the position of the entity will vary in time (by solving the classical equations of motion). Consequently, one cannot predict with certainty its future locations. Now, according to the reality criterion formulated by Einstein, Podolsky and Rosen [2], and further refined by Piron and Aerts [3][4][5], the notion of actual existence is intimately related to the notion of predictability, in the sense that a property can be said to be actual, for a given physical entity, if and only if should one decide to observe it (i.e., to test it), the success of the observation would be in principle predictable in advance, with certainty.According to this general reality (or existence) criterion, one must conclude that a microscopic entity obeying the HUP cannot actually possess the property of being always present somewhere in space, as there are no means to predict its spatial localizations with certainty, not even in principle. Therefore, whatever its nature is, it is a non-spatial entity, and if only for this reason it * Electronic address: autoricerca@gmail.com cannot be considered a particle [5]. But then, if quantum entities are not particles, as they are intrinsically non-spatial, what can we say about their nature? Can we affirm, as suggested by Hobson, that they are mere fields, i.e., that the wave function ψ t has to be simply interpreted as a real space-filling extended field?Our point is that this cannot be done. Indeed, although classical fields, contrary to classical particles, are spatially extended entities, spread out over space,...

Mecánica cuántica fundamental, una propuesta didáctica

“…El objetivo de la actividad es presentar la naturaleza cuántica de los qubits, a saber, el estado cuántico, a la luz de unos esquemas experimentales con los que se determinan sus propiedades. 17 Por ejemplo, en el análisis de resultados del esquema de la Fig. 2, llamado Complementariedad, se enuncia el principio de indeterminación, según el cual no es posible, por razones fundamentales, determinar simultáneamente los valores de propiedades cuánticas incompatibles.…”

“…La propuesta de[13] exhibe otro uso crítico de la historia, muy afín a la MCF, en la que también puede decirse que prima la jerarquía conceptual sobre el orden cronológico 5. Veáse por ejemplo la interesante propuesta de[15], y el debate que provocó en[16],[17] y[18].…”