Bailyn, Charles. ASTR 160: Frontiers and Controversies in Astrophysics, Spring 2007. Yale OpenCourseWare: Astronomy, Accessed 21/9/14 http://oyc.yale.edu/astronomy/astr-160/lecture-9 License: Creative Commons Attribution-Noncommercial-Share Alike 3.0 license The discussion of black holes continues with an introduction of the concept of event horizon. A number of problems are worked out to familiarize students with mathematics related to black hole event horizons. In a longer question and answer session, Professor Bailyn discusses the more mystifying aspects of the nature of black holes and the possibility of time travel. Finally, the issues of reconciling Newton's laws of motion with Special Relativity, and Newton's law of gravity with General Relativity, are addressed.