Explaining Geodesic Motion: A Problem-of-Motion Perspective
General Relativity (GR) is commonly taken to explain the geodesic motion of “free” test bodies; unlike in Newtonian mechanics, the Geodesic Principle (GP) is viewed as a theorem of the field equations rather than an independent postulate. Although this view is widespread in physics, it has received philosophical criticism. While these critiques are valuable on their own terms, it is a desideratum to have a hermeneutic lens that reconciles philosophical analysis with common physical intuition and practice.
I propose a framework grounded in the history of what can be called the “Problem-of-Motion (PoM) tradition.” I argue that when embedded in this tradition, the GP is best understood as adverting to the base case of an idealization strategy. By shifting the focus in this way, one can more precisely characterize the relevant explanandum as well as the explanans (i.e., the specific dynamical resources of GR doing the explanatory work). I conclude by suggesting a pluralistic sense in which GR explains geodesic motion.
(This talk is based on joint work with Nicholas Teh.)
