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AGPhil: Arbeitsgruppe Philosophie der Physik

AGPhil 9: Philosophy of Physics 1

AGPhil 9.1: Talk

Wednesday, March 20, 2024, 11:30–12:00, PTB SR AvHB

What is fundamental in fundamental physics? — •Alexander Niederklapfer — London School of Economics and Political Science, London, UK

Metaphysicians as well as philosophers of science often turn to particle physics for a description of the most fundamental level of the material world. The common assumption is that it describes one clear account of what the basic building blocks of our universe are, and how they compose with one another to form more complex objects. I argue that this picture contains a major difficulty, because particle physics allows for more than one metaphysically meaningful procedure to decompose a system into (fundamental) parts. I identify and interpret two widely used decomposition relations appearing in quantum theories: the first relies on Wigner’s “definition‘” of particles and decomposes a quantum system based on the theory of group representations into a direct sum of parts, which is popular amongst recent structuralist interpretations of quantum theories. The second is the decomposition into a tensor product of statistically independent components, common in the literature on entanglement and quantum information. I then show that these two decompositions lead to different results for what the parts of a given system might be. I argue that these considerations show that there are conventional choices involved in finding the fundamental parts of an object which have not yet been widely recognised by either metaphysicians or philosophers of science. I also take this to provide a sense in which, as a result, a physical theory on its own is not enough to determine the fundamental ontology of the world.

Keywords: Quantum Field Theory; Metaphysics; Particles; Fundamentality; Mereology