Persistence and Relativistic Shapes

A Joint Colloquium with the ISU Departments of Physics and Philosophy

Dr. Yuri Balashov
University of Georgia

Material objects (atoms and molecules, cats and dogs, human persons and stars) persist over time and survive change in their properties.  How do they manage to do it?  This is a hot topic in contemporary analytic metaphysics.  According to one view, objects persist by enduring – by being present, in their entirety, at multiple moments of time.  According to the rival view, objects persist by perduring – by having distinct "temporal parts" at different moments of time and, therefore, by being only partly present at such moments.  On this view, objects are, quite literally, four-dimensional; they are extended in both space and time and occupy compact regions of spacetime.  Until very recently the debate between these metaphysical views (and their variants) largely proceeded by abstracting from physics.  This situation has now changed; various physical considerations have been brought to bear on the persistence debate.  But the outcome is unclear.

In an earlier work ("Relativistic Objects," Noûs 33 (1999): 644–662) I developed an argument favoring one view of persistence (viz., perdurance) over its rivals, based on considerations of the relativity of three-dimensional spatial shapes of physical objects in Minkowski spacetime.  These shapes exhibit a remarkable unity: they can be lined up neatly in spacetime to fill a nice four-dimensional volume, without "corrugations" and "dents."  I argued that, while the perdurantist can easily explain this fact by noting that all the three-dimensional shapes are "slices" of a single four-dimensional object, the endurantist cannot match this explanatory achievement, because she denies the existence of four-dimensional objects.  The argument is, in essence, an inference to the best explanation.

The argument has since come under criticism (in the works of Ted Sider, Kristi Miller, Ian Gibson, Oliver Pooley and others).  I attempt to respond to these criticisms.  I shall begin by introducing the debate about persistence, more or less "from scratch."  But those who want to get some prior exposure to the relevant issues might look up the entries on "Time", "Identity over Time" and "Temporal Parts" in the Stanford Encyclopedia of Philosophy: