The Gravity of Things

A delicate problem arose with the publication of Newton's Philosophiae Naturalis Principia Mathematica in 1687. On the one hand, Newton's concept of gravity gave us the first rigorously predictive theory of motion. For the first time in history, we were able to carefully predict the motion of planets, when comets would return, and where our cannonballs would land. With an equation composed of three simple letters, Newton was able to discover a set of constants underlying all motion ranging from the motion of the planets and stars to a leaf falling from a tree. The problem was that gravity's ability to exercise this influence on entities at a distance was entirely mysterious. How could the Moon, for example, influence ocean tides on Earth when there is no direct interaction between them? In Principia Mathematica, Newton had discovered much about how gravity functions, yet the mechanism of gravity remained unknown. Indeed, within the Newtonian framework we weren't to ask questions about how gravity functions at all. It was enough that Newtonian theory could make accurate predictions about the movement of planets, comets, moons, and so on. It was enough that it allowed us to get our cannon balls where we wanted them. How gravity was able to affect objects in this way was set aside as a question in the euphoria of the new predictability occasioned by these simple equations, these few letters and symbols, which now allowed us to predict the movement of objects.

The problem was simple. Naturalistic and materialist thought has always argued that in order for a causal interaction to occur between two entities, there must be a direct interaction. One entity must touch the other to affect in it.