Keith & Russ talk with Stephan Meyer of the University of Chicago's Department of Physics, Department of Astronomy & Astrophysics, and Enrico Fermi Institute. Meyer takes us back to the Big Bang and explains why the universe appears to be expanding faster than previously theorized. He also tells us the difference between dark matter and dark energy, and why they have everything to do with the acceleration of the universe's expansion. Aired Feb. 17, 2013.