Big Mysteries: Dark Energy

Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up!  That observation is just mind blowing, and yet it is true.  In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.

Related video:
http://www.youtube.com/watch?v=oPNrcKeqbBM