Some recent philosophical debate about persistence has focussed on an
argument against perdurantism that discusses rotating perfectly homogeneous
discs (the `rotating discs argument'; RDA). The argument has been mostly
discussed by metaphysicians, though it appeals to ideas from classical
mechanics, especially about rotation. In contrast, I assess the RDA from the
perspective of the philosophy of physics.
After introducing the argument and emphasizing the relevance of physics
(Sections 1 to 3), I review some metaphysicians' replies to the argument
(Section 4). Thereafter, I argue for three main conclusions. They all arise
from the fact, emphasized in Section 2, that classical mechanics
(non-relativistic as well as relativistic) is both more subtle, and more
problematic, than philosophers generally realize.
The main conclusion is that the RDA can be defeated (Section 6 onwards).
Namely, by the perdurantist taking objects in classical mechanics (whether
point-particles or continuous bodies) to have only temporally extended, i.e.
non-instantaneous, temporal parts: which immediately blocks the RDA.
Admittedly, this version of perdurantism defines persistence in a weaker sense
of `definition' than {\em pointilliste} versions that aim to define persistence
assuming only instantaneous temporal parts. But I argue that temporally
extended temporal parts are supported by both classical and quantum mechanics.Comment: 100 pages, no figures; an extract of this paper is at:
physics/040602
