In 1998, two independent teams of astrophysicists discovered a baffling phenomenon: the Universe is expanding at an ever-faster rate. The current understanding of gravity can't explain this cosmic acceleration. Scientists think that either a mysterious force called dark energy is to blame—or a reworking of gravitational theory is in order. Travel to the University of California's Lick Observatory to learn how astrophysicists use distant stellar explosions to observe the expansion of space. Then watch a team at Fermilab assemble the Dark Energy Camera, a new device researchers hope will find compelling evidence of what's propelling the Universe to expand at an increasing pace.