In the preceding chapters, we dealt with examples of fields generated by static charges; these fields are functions of space. In later chapters, we will deal with fields generated by moving charges; these fields are functions of both space and time. Thus, spacetime is the arena within which the fields perform their dance, and before we study the dynamical laws governing this dance, we had better examine the geometry of space-time.

In Newtonian physics, length is absolute and time is absolute. This view of the geometry of spacetime is firmly engrained in our intuition, rooted in our everyday experience. It is a view that stood unchallenged for hundreds of years but then was suddenly demolished in 1905 by Albert Einstein with his theory of special relativity. In relativistic physics, neither length nor time is absolute. Instead, there is only one single absolute quantity that characterizes the spacetime geometry: the spacetime interval. This spacetime interval consists of space intervals and time intervals intimately joined together. This was first recognized by H. Minkowski, who in his incisive analysis of the relativistic geometry of spacetime wrote, "Henceforth space by itself, and time by itself are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality." ^[1]

Before we enter into the discussion of Einstein's theory, we will briefly review the properties of spacetime and the meaning of relativity in Newtonian physics.