Dark energy and the accelerating universe
An explanation of how the universe's expansion was at first slowed down by gravity and then began to accelerate
In 1998, astronomers began to believe that a mysterious dark force is pushing apart the contents of the universe faster today than just after the Big Bang. The suspicion followed studies of distant "standard candles" called type Ia supernovae. These exploding stars share the same intrinsic luminosity and fade away at known rates. Yet, a group of distant type Ia supernovae appeared dimmer than expected, meaning they were farther away than they should be if the universe is expanding at a constant...