Metaphysicians as well as philosophers of science often turn to particle physics for a description of the most fundamental entities in our universe. The common assumption is that physics readily provides a clear account of both what those fundamental building blocks are and how they come together to form more complicated objects, and, conversely, how compound objects can be seen as being composed of those fundamental entities. I argue that this picture contains a major difficulty because quantum…
Read moreMetaphysicians as well as philosophers of science often turn to particle physics for a description of the most fundamental entities in our universe. The common assumption is that physics readily provides a clear account of both what those fundamental building blocks are and how they come together to form more complicated objects, and, conversely, how compound objects can be seen as being composed of those fundamental entities. I argue that this picture contains a major difficulty because quantum theories allow for more than one metaphysically meaningful procedure to decompose a system into parts, fundamental or otherwise. I will identify and interpret two such procedures, mathematically given by the direct sum and the tensor product, and show that they lead to different results for what the parts of a quantum system are. This shows 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 take my findings to provide a sense in which, as a result, particle physics on its own is not enough to determine the fundamental ontology of the world.
