 For a given physical system, define its ‘configuration space’ to be the space of possible instantaneous states of that system. (For example, the space of possible distributions of N particles in Euclidean space, according to a Cartesian coordinate system laid down on that space.) As the system evolves, the point in configuration space representing the system’s instantaneous state traces out a continuous curve. On this picture, metaphysically possible worlds are represented by (rising) curves in the product space formed from configuration space and a one-dimensional space representing time. Nomologically possible worlds are represented by those curves that are allowed by the dynamics. For example, in the Lagrangian formalism, the nomologically possible worlds are represented by those curves which extremize the action: a particular functional of such curves.