Until recently, astronomers assumed that gravity was slowing the expansion of the universe that began with the big bang. At the end of the last century, however, they learned a shocking fact: The expansion was actually speeding up. The only way to explain this acceleration is that space is filled with… something else. Astronomers call this mystery matter ‘’dark energy.’’ They can’t see it, but they figure it has to exist everywhere, accounting for roughly 68 percent of the stuff in the universe. (Meanwhile, the atoms that make up planets, stars, your pet goldfish, and everything else account for less than 5 percent of the universe.)
Picture Credit : Google