On the Relation between Quantum Mechanical and Neo-Mechanistic Ontologies and Explanatory Strategies

Advocates of the New Mechanicism in philosophy of science argue that scientific explanation often consists in describing mechanisms responsible for natural phenomena. Despite its successes, one might think that this approach does not square with the ontological strictures of quantum mechanics. New Mechanists suppose that mechanisms are composed of objects with definite properties, which are interconnected via local causal interactions. Quantum mechanics calls these suppositions into question. Since mechanisms are hierarchical it appears that even macroscopic mechanisms must supervene on a set of “objects” that behave nonclassically. In this paper we argue, in part by appeal to the theory of quantum decoherence, that the universal validity of quantum mechanics does not undermine neo-mechanistic ontological and explanatory claims as they occur within in classical domains. Additionally, we argue that by relaxation of certain classical assumptions, mechanistic explanatory strategies can sometimes be carried over into the quantum domain. In the last fifteen years there has been a good deal of attention focused on the idea of mechanism as a central organizing principle for understanding both ontological and explanatory questions in the sciences. A group of philosophers of science often called the New Mechanists have argued that most of the phenomena that scientists seek to explain are the product of the operation of mechanisms, where mechanisms are understood as collections of objects (the parts of the mechanism) that are organized in such a way as to be productive of the phenomena in question. Our goal in this paper is to explore how well this neo-mechanistic worldview coheres with the picture of nature that we derive from quantum mechanics. There is prima facie reason to be concerned that the two pictures do not fit well together. The neo-mechanists suppose that mechanisms are composed of objects with definite properties, where these objects are connected to each other via local causal interactions. Quantum mechanics (QM) calls into question whether there are really such things as objects with definite properties and whether causal relations can be understood in terms of local interactions between such objects. Moreover, mechanisms are hierarchical in the sense that the parts of mechanisms may themselves be complex objects composed of subparts which are components of lower level mechanisms. It seems then that even complex macroscopic mechanisms must supervene on a set of “objects” that behave