Out in the cosmos, there is really no such thing as "empty space." Much of space is actually "dark energy" -- a force that has overcome gravity and is pulling galaxies apart, expanding the universe. Alex Filippenko, one of the world's leading astronomers, will delve into this great cosmological mystery in "Dark Energy and the Runaway Universe," on Saturday, Nov. 7, starting at 7 p.m., at the University of Delaware's Clayton Hall Conference Centre.