Bailyn, Charles. ASTR 160: Frontiers and Controversies in Astrophysics, Spring 2007. Yale OpenCourseWare: Astronomy, Accessed 23/9/14 http://oyc.yale.edu/astronomy/astr-160/lecture-22 License: Creative Commons Attribution-Noncommercial-Share Alike 3.0 license Professor Bailyn offers a review of what is known so far about the expansion of the universe from observing galaxies, supernovae, and other celestial phenomena. The rate of the expansion of the universe is discussed along with the Big Rip theory and the balance of dark energy and dark matter in the universe over time. The point at which the universe shifts from accelerating to decelerating is examined. Worries related to the brightness of high redshift supernovae and the effects of gravitational lensing are explained.