Time is part of the geometry of the universe. It is sometimes said that in the Theory of Relativity, time becomes another dimension, on a par with the familiar three spatial dimensions. It would be difficult to make any clear sense out of such a claim: the structure of Minkowski space-time is quite distinct from that of a four-dimensional Euclidean (or Riemannian) space. So to understand the claim that time is part of the geometry of the universe, we must become clearer about just what “the geometry of the universe” means. That begins with consideration of the atomic elements that are structured by the geometry.