Abstract

The rotating discs argument against perdurantism has been mostly discussed by metaphysicians, though the argument of course appeals to ideas from classical mechanics, especially about rotation. In contrast, I assess the RDA from the perspective of the philosophy of physics. I argue for three main conclusions. The first conclusion is that the RDA can be formulated more strongly than is usually recognized: it is not necessary to ‘imagine away’ the dynamical effects of rotation. The second is that in general relativity, the RDA fails because of frame-dragging. The third conclusion is that even setting aside general relativity, the strong formulation of the RDA can after all be defeated, namely, by the perdurantist taking objects in classical mechanics to have only temporally extended temporal parts, which immediately blocks the RDA. Admittedly, this version of perdurantism defines persistence in a weaker sense of ‘definition’ than pointilliste versions that aim to define persistence assuming only instantaneous temporal parts. But I argue that temporally extended temporal parts can do the jobs within the endurantism– perdurantism debate that the perdurantist wants temporal parts to do and are supported by both classical and quantum mechanics. Introduction The story so far 2.1 The RDA 2.2 Intrinsic properties and the idea of velocity 2.2.1 The intrinsic–extrinsic distinction 2.2.2 Velocity to the rescue? 2.3 ‘Naturalism’ 2.4 The accompaniments of rotation 2.5 Two kinds of reply: against the consensus Describing rotation 3.1 Rotation is kinematic 3.2 Beware of rigidity 3.3 An improved RDA: allowing the actual accompaniments 3.4 The RDA fails in general relativity Perdurantism without tears: the classical case 4.1 Rejecting instantaneous temporal parts 4.2 Replying to the RDA 4.2.1 ‘Kinematics’ 4.2.2 ‘Dynamics’ 4.2.3 An ‘anti-pointilliste’ objection and reply 4.3 Intrinsic properties of non-instantaneous temporal parts 4.3.1 Can the perdurantist appeal to them? 4.3.2 Temporal intrinsicality at an instant is rare 4.3.3 A better reason for temporal intrinsicality 4.4 Non-instantaneous parts can do the jobs 4.4.1 Humean supervenience revisited 4.4.2 The problem of change 4.4.3 Puzzles of coincidence 4.5 Instantaneous velocity is hardly extrinsic Support from decoherence in quantum theory 5.1 Classical and quantum: relativizing the intrinsic–extrinsic distinction 5.1.1 Unitarity: momentum as temporally intrinsic 5.2 Position and existence as nomically extrinsic