Physics Colloquium - Descartes, Du Châtelet, d’Alembert: How Collisions Transformed Physics

Here is a familiar story: up until the early 17th century, physics was a part of philosophy, and then the Scientific Revolution happened culminating in Newton's Principia of 1687. After that, physics was a separate discipline. This story has been told many times, and challenged in many ways, but a common thread persists in which we think of 18th century physics as having already separated from philosophy and as offering a stable period of "normal science" within the "Newtonian paradigm." In fact, the split took another century of struggle and development by philosophers and mathematicians. I will make this vivid by tracing the central role of collision theory. I will argue that collisions lie at the heart of the origins of modern physics, from the break with Aristotelian physics to the eventual separation of physics from philosophy in the late 18th century. With the rise and fall of collisions as central to physics, the goals, methods, and subject-matter of physics were all transformed, along with its relationship to philosophy. Key figures in my story include Descartes, Du Châtelet, Euler, and d'Alembert.