Matthias Egg

PhD student and research assistant
Epistemology and Philosophy of Science
University of Lausanne
Department of Philosophy
CH-1015 Lausanne

e-mail: Matthias.Egg@unil.ch

• Scientific realism
• Causation
• Philosophy of Quantum Qhysics
• Philosophy of Scientific Experimentation

I defend a version of entity realism that rests on a distinction between causal and theoretical explanation, and I claim it to be an adequate stance in the philosophy of particle physics. Traditionally, the debate on scientific realism has centred around the question of whether presently accepted scientific theories are (at least approximately) true in the sense of some correspondence between theory and reality. This indicates that the debate has largely been about theories, and has often neglected the pragmatic and experimental aspects of science. Entity realism (also known as experimental realism) can be viewed as an attempt to balance out this disequilibrium and thereby to establish a position in the debate that can accommodate the best arguments from both the realist and the antirealist side.

After a discussion of some general points of criticism levelled against entity realism, I study two cases from 20th century particle physics to evaluate in these contexts the applicability of the causal concepts on which entity realism relies:

1) The neutrino hypothesis and neutrino detection. The case of the neutrino can shed light on some important aspects of entity realism. One is the question of how hypothetical entities come to be accepted as real. The neutrino first appeared as an explanatory posit, was then embedded in a theory and much later experimentally detected. The study of this development informs us about how the causal role assigned to an entity relates on the one hand to the theoretical framework in which it is embedded and on the other hand to the relevant experimental evidence.

2) Virtual particles. Calculations of many important quantities in quantum field theory can only be performed within the framework of perturbation theory. The internal lines of the corresponding Feynman diagrams are said to stand for virtual particles, which makes it tempting to interpret these particles as the unobservable causes of the calculated (and observed) effects. However, only a careful investigation into the notion of “cause” employed here can reveal if entity realism commits us to a belief in the reality of virtual particles.

Drawing on these case studies, I will discern the different ways in which causal notions are used in practice and examine how they can be compatible with the laws of quantum physics that govern the subatomic domain. This will further clarify the notion of a causal explanation, on which my version of entity realism rests. The goal is to state robust criteria for the distinction between causal explanations, which necessarily have ontological import, and theoretical explanations, which do not.