I show how Sir William Rowan Hamilton’s philosophical commitments led him to a causal interpretation of classical mechanics. I argue that Hamilton’s metaphysics of causation was injected into his dynamics by way of a causal interpretation of force. I then detail how forces are indispensable to both Hamilton’s formulation of classical mechanics and what we now call Hamiltonian mechanics (i.e., the modern formulation). On this point, my efforts primarily consist of showing that the contemporary orthodox interpretation of potential energy is (...) the interpretation found in Hamilton’s work. Hamilton called the potential energy function the “force-function” because he believed that it represents forces at work in the world. Various non-historical arguments for this orthodox interpretation of potential energy are provided, and matters are concluded by showing that in classical Hamiltonian mechanics, facts about the potential energies of systems are grounded in facts about forces. Thus, if one can tolerate the view that forces are causes of motion, then Hamilton provides one with a road map for transporting causation into one of the most mathematically sophisticated formulations of classical mechanics, viz., Hamiltonian mechanics. (shrink)

I will argue, pace a great many of my contemporaries, that there's something right about Boltzmann's attempt to ground the second law of thermodynamics in a suitably amended deterministic time-reversal invariant classical dynamics, and that in order to appreciate what's right about (what was at least at one time) Boltzmann's explanatory project, one has to fully apprehend the nature of microphysical causal structure, time-reversal invariance, and the relationship between Boltzmann entropy and the work of Rudolf Clausius.

The basic kinds of physical causality that are foundational for other kinds of causality involve objects and the causal relations between them. These interactions do not involve events. If events were ontologically significant entities for causality in general, then they would play a role in simple mechanical interactions. But arguments about simple collisions looked at from different frames of reference show that events cannot play a role in simple mechanical interactions, and neither can the entirely hypothetical causal relations between events. (...) These arguments show that physics, which should be authoritative when it comes to the metaphysics of causality, gives no reasons to believe that events are causal agents. Force relations and some cases of energy-momentum transfer are examples of causal relations, with forces being paradigmatic in the macroscopic world, though it is conceivable that there are other kinds of causal relation. A relation between two objects is a causal relation if and only if when it is instantiated by the two objects there is a possibility that the objects that are the terms of the relation could change. The basic metaphysics of causality is about objects, causal relations, changes in objects, and a causal primitive. The paper also includes a discussion of the metaphysics of forces and a discussion of the metaphysics of energy and momentum exchanges. (shrink)