Katherine Brading: Unity, Change and What There Is

The script opens with a welcome address for an academic speaker series, introducing Katherine Bren, a professor of philosophy at Notre Dame. Bren's expertise spans various areas of philosophy, including symmetries in physics, general philosophy of science, and 17th-century natural philosophy. The speaker also announces an upcoming talk by Alison Wy on the plurality of pluralism. The main topic of Bren's lecture is the tension between presentism and the block universe theory in the context of special relativity and the philosophy of physics.

This paragraph delves into the philosophical conflict arising from the combination of presentism — the belief that only the present exists — and the principles of special relativity. It discusses how the two concepts seem incompatible, leading to a debate within the scientific and philosophical communities. The block universe model, which posits that all points in time are equally real, is presented as an alternative to presentism, aligning more closely with the implications of special relativity.

The speaker explores the concept of ontological unity, challenging the traditional view that spacetime serves as the foundation for what exists. By revisiting Newton's physics, the speaker suggests that there may be alternative principles of unity that do not rely on spacetime. This paragraph sets the stage for a discussion on the role of dynamics in establishing the unity of the world and the potential implications for the debate between presentism and the block universe theory.

This section examines Newton's laws and their implications for the unity of physical bodies. It discusses how Newton's laws, particularly the law of motion, contribute to the understanding of bodies as unified entities. The speaker suggests that Newton's approach to the unity of the world through the laws of motion provides a different perspective on the debate between presentism and the block universe, one that does not rely on spacetime as the sole principle of unity.

The speaker further elaborates on the role of dynamics in establishing ontological unity, moving away from the traditional reliance on spacetime. By considering the conservation of motion and the behavior of composite systems, the speaker proposes that the laws of physics themselves contribute to the constitution of physical bodies and their unity. This perspective challenges the conventional understanding of spacetime as the ontological ground for the unity of what exists.

This paragraph discusses how the law constitutive approach offers an alternative account of how objects can persist through change while maintaining their numerical identity. It argues that the laws of physics provide the relations that allow a unity to undergo change without losing its identity, favoring endurantism over perdurantism in the philosophy of persistence. The speaker suggests that this approach is more aligned with presentism than with the block universe model.

The speaker reevaluates the roles of spacetime and dynamics in the context of ontological unity and the philosophy of persistence. They propose that spacetime may serve an epistemic role rather than an ontological one, organizing our knowledge of the world rather than grounding the existence of physical entities. Dynamics, on the other hand, are suggested as the true ontological basis for the unity and existence of entities, potentially offering a new perspective on presentism.

In this section, the speaker argues that presentism is not just a philosophical stance but an empirical thesis that can be supported or refuted by scientific inquiry. They suggest that the validity of presentism depends on the existence of genuine subsystems within the universe and that this is a question to be answered by the progress of science. The speaker concludes that their version of presentism, informed by Newtonian physics, is consistent with endorsing special relativity and is an open empirical question.

The final paragraph presents a series of questions and reflections on the speaker's argument, highlighting the complexity and nuance of the topic. It touches on the potential implications of the speaker's approach for the broader philosophical discourse, including the status of spacetime, the nature of dynamics, and the relationship between empirical evidence and ontological claims. The speaker acknowledges the need for further exploration and dialogue between philosophy and physics to fully understand these concepts.