This book continues our exploration of the most profound theory of science, Einstein's General Theory of Relativity.

We examine more carefully the properties of spacetime, the unity of space and time.

We explore the major features of curvature, how to measure it, and how to reduce its complexity to finding distances between nearby points.

We find a simple expression, 2M/r, which proves remarkably helpful as we explore the Schwarzchild metric, black holes, time dilation, and the expansion of the universe.