The Cosmological Constant
http://relativity.livingreviews.org/Articles/lrr-2001-1/Review article by Sean Carroll (Caltech) on one of the most important open cosmological questions: the physics behind the acceleration of cosmic expansion. Requires undergraduate physics knowledge. Published in the electronic review journal, Living Reviews in Relativity
Submitted in section: Astronomy: Cosmology: Cosmological Constant and Dark Energy: The Cosmological Constant