October, 29, 2021, h. 16-18 CET

The main aim of this talk is to clarify what we mean when we say "particle", and then use such a notion to interpret some physical phenomena. Quantum field theory (QFT) is the theoretical background of particle physics. However, as a Received View, a particle interpretation of QFT seems to be undermined by a series of no-go theorems. This would mean that the fundamental ontology of QFT is not an ontology of particles. Yet, particle physics uses the notion of particle to describe and interpret its formal structure and its experimental results (as, for example, in the Standard Model of Elementary Particles). As such, even if particles might not be ontologically fundamental, we would need a clear definition of what a particle is. In this talk, I will then present and discuss some possible definitions of the notion of particle. There are in fact several different definitions of this notion in the literature, and some of them seem to be mutually exclusive. In particular, on the one hand, I will present and discuss some intuitive and general definitions of the notion of particle. I will also show why such definitions are not eventually compelling. On the other hand, I will discuss some other definitions, which have been proposed in the specific context of quantum physics and QFT in order to - at least partially - avoid the above mentioned no-go theorems. These definitions seem to support the idea that it is possible to define a notion of a quantum particle by "relaxing" the intuitive and general (classical) notion of particle. Finally, I will present two other interesting (though very abstract) definitions of the notion of particle that have been proposed in the formalism of algebraic QFT.

Audio - Slides