The universe was supposed to slow down
For a long time, astronomers expected gravity to act like a brake on the universe's expansion. Then in 1998, two teams found the opposite: the universe is speeding up.Accelerating Expansion of the Universe
The clue came from exploding stars
Type Ia supernovae are useful because they shine with almost the same intrinsic brightness. If one looks dimmer than expected, it must be farther away than a slowing universe would predict.Accelerating Expansion of the Universe
