Bailyn, Charles. ASTR 160: Frontiers and Controversies in Astrophysics, Spring 2007. Yale OpenCourseWare: Astronomy, Accessed 22/9/14 http://oyc.yale.edu/astronomy/astr-160/lecture-12 License: Creative Commons Attribution-Noncommercial-Share Alike 3.0 license One last key concept in Special Relativity is introduced before discussion turns again to black celestial bodies (black holes in particular) that manifest the relativistic effects students have learned about in the previous lectures. The new concept deals with describing events in a coordinate system of space and time. A mathematical explanation is given for how space and time reverse inside the Schwarzschild radius through sign changes in the metric.