Metaphysical Explanation in Physics

Shamik Dasgupta (University of California, Berkeley) - What are we doing when we use abstract entities like numbers or vectors to represent physical quantities like mass or acceleration? There has been considerable work on the *mathematics* of measurement, the task of stating representation and uniqueness theorems that describe conditions under which a quantity can be represented and the ways in which the representation can be transformed. But there has been less work on the *metaphysics* of measurement, the question of what underwrites our talk when we say that x is 5 kgs, for example, or that y is accelerating at 10 m/s^2 in a certain direction. Here I motivate and defend a non-factualist account of this talk. The function of this talk is not to *describe* x or y as being a certain way—in particular, its function is not to describe how they’re related to familiar “standard objects” (*contra* Wittgenstein), nor to attribute them a property that's picked out via these standard objects (*contra* Kripke). Rather, its function is to *cohere* with other statements in one’s linguistic community. Thus, “x is 5 kgs” fulfills its function, and is hence the right thing to say, to the extent that x is half as massive as things that others have called "10 kgs." a quarter as massive as things that others have called "20 kgs," and so on. I then explore the implications of this view regarding the grounds, or metaphysical explanation, of this talk. One implication is that there is no metaphysical explanation of why x is 5 kgs, yet there is a metaphysical explanation of why “x is 5 kg” is the right thing to say: it’s because it coheres with what others in in one’s linguistic community have said. Finally, I show that these implications about metaphysical explanation have significant ramifications for how we interpret initial value problems and the concept of determinism. Roughly, theories that might be thought to be indeterministic turn out to behave in entirely deterministic ways.

Elizabeth Miller (Yale University) - In their theorizing about the world, two groups of philosophers give starring roles to basic local concreta—objects arrayed in space-time or, if we prefer, points or (bounded) regions of space-time itself bearing intrinsic states (of “occupation” or other material decoration). In a debate about the metaphysics of laws of nature, Humeans maintain that all nomological (and other) facts about the world supervene on the spatiotemporal distribution of some metaphysically basic local qualities. In a debate about the demands of empirical coherence on physical theories, primitive ontologists insist that an adequate physical theory must directly describe some fundamental local beables, constituents of the familiar macroscopic landscape that figures centrally in our empirical data about the world. Members of both groups agree that we need some basis of local concreta to metaphysically explain some “derivative” facts about or features of the world, but why don’t they agree about more? A comparatively boring hypothesis emphasizes that the two groups start out with different work for their basic local concreta to do: primitive ontologists want their base of local beables to account for some fairly limited data, facts about the actual configuration of macroscopic objects, while Humeans want their mosaic of local qualities to metaphysically suffice for all facts about the world, including facts about what actually is not but—in some physical sense—could have been the case. Perhaps, then, they agree entirely about the role of local concreta in accounting for some limited data but go on to disagree, more or less independently, about what reality, especially modal reality, beyond such data is like. I explore a more interesting hypothesis, which suggests a deeper tension between Humeanism and primitivism: at the core of primitivism is a general constraint on metaphysical explanation at odds with the Humean worldview. Specifically, Humeanism incorporates distinctive violation of a local screening off (LSO) condition: the basic local concreta within a part of space-time metaphysically explain, and so screen off, its local physical state from happenings elsewhere in space-time.