Quasiparticles and Emergent Individuals

Guay, Alexandre [UCL] Sartenaer, Olivier [UCL]

Physicists often qualify quasiparticles (anyon, skyrmion…) as emergent phenomena or entities (Negele & Orland 1998). Moreover the use of the word “particle” seems to position these entities as potential physical individuals or quasi-physical individuals. In this paper, both elements and their relation will be explored. First, we will discuss in what sense quasiparticles could or could not be considered as emergent phenomena or entities, depending on which criterion is adopted. Our analysis will concentrate on two bundles of properties often invoked in the context of emergence. Note that these requirements can be understood as incompatible. 1) In what way quasiparticles are constituted or not by their basis? To answer this question, a basis will have to be identified. Essentially, are quasiparticles collective behavior of particles or topological properties of quantum fields? In many ways, for the physicists, they are both but from an ontological point of view, these options generate different philosophical consequences. If particles are the basis, the constitution of quasi-particles will rely on a mereological relation. On the other hand if the basis is quantum fields, they are ontologically close to particles. However, different quantization processes, one for particles, the other for quasi-particles, could still make an ontological difference. 2) In what way do quasiparticles imply the existence of downward causation? In well-known physical phenomena, for example the quantum Hall effect, quasiparticles behavior seems to put constraints on the basis understood as particles. But can we claim a stronger relation between the ontological levels, like causality (manipulation or transmission)? In order to answer this question, a clearer notion of constraint will have to be provided. From these analyses we will sustain that in many cases quasi-particles can be considered as genuine emergent phenomena, even if not in a strong sense.