Hans Halvorson Physics, Logic, Philosophy

Relativity and the Metaphysics of Material Objects

Graduate Seminar — Spring 2025 (half term, beginning the week after spring break)

Overview

Einstein’s theory of relativity revolutionized our understanding of space and time. But did it also transform the metaphysics of material objects?

This seminar explores how relativistic physics bears on fundamental questions about what physical objects are, how they persist, and how they are represented in spacetime. We will examine whether relativity favors a field ontology over a particle ontology, whether it supports a four-dimensional (“worm”) view of persistence over three-dimensional endurance, and what role (if any) is played by classical notions such as rigidity, shape, and localized structure.

A recurring touchstone will be John Bell’s famous essay “How to Teach Special Relativity”, and in particular his analysis of the spaceship paradox. Bell uses this case to argue that relativity forces us to rethink the physical coherence of extended bodies, rigid motion, and dynamical explanation—issues that sit squarely at the intersection of physics and metaphysics. The paradox provides a concrete way to ask: what does it really mean for something to be a single object in a relativistic world?

The seminar will combine close reading of contemporary philosophical work with careful attention to the physics itself.

Seminar leaders

  • Hans Halvorson (Princeton University)
  • Claudio Calosi (University of Venice)
  • Damiano Costa (University of Lugano)

With visits from Heather Demarest, Cody Gilmore, and Thomas Sattig

Central questions

  • If relativity is true, how should we understand the nature of physical objects?
  • Does relativistic physics favor fields over particles as fundamental?
  • Does it support a four-dimensional ontology of objects over a three-dimensional one?
  • What becomes of classical notions such as rigidity, shape, and localization?
  • How should we understand persistence, identity over time, and objecthood in a relativistic spacetime?
  • What do thought experiments such as Bell’s spaceships reveal about the limits of classical metaphysical categories?

Topics

Possible topics include:

  • Relativistic constraints on object persistence
  • Four-dimensionalism and spacetime ontology
  • Relativistic invariance and metaphysical structure
  • The status of particles in quantum field theory
  • Rigidity, extended bodies, and Born rigidity
  • Bell’s spaceship paradox and the metaphysics of extended objects
  • Symmetry principles and ontological commitment
  • Structural realism and object realism in relativistic physics
  • Kripke’s rotating disk argument

Sample readings

Selections may include:

  • John S. Bell, “How to Teach Special Relativity”
  • Yuri Balashov, Relativistic Objects
  • Yuri Balashov, “Persistence and Spacetime”
  • Claudio Calosi, “The relativistic invariance of 4d shapes”
  • Heather Demarest, “Persisting despite the relativistic odds”
  • Jack Himelright and Sebastián Murgueitio Ramírez, “Getting back in shape: Persistence, shape, and relativity”
  • Hans Halvorson, “Invariance and ontology in relativistic physics”
  • Harvey Brown, Physical Relativity (selections)
  • David Malament, “Classical General Relativity” (selections)

Additional contemporary papers will be assigned.

Format

The seminar will be discussion-based, with short presentations by participants and intensive engagement with both philosophical arguments and the relevant physics. Students with backgrounds in philosophy of physics, metaphysics, or theoretical physics are especially encouraged to participate.

For questions or enrollment information, please contact the seminar leaders.