The universe, which is believed to be driven by the mysterious force known as dark energy, is expanding at an accelerating rate. The rapid expansion has mystified scientists.

Following the Big Bang theory, it was believed that the universe was created out of a massive explosion. It was theorized that the pull of gravity would slow the universe's rate of expansion over time, but in 1998 determined that the expansion actually is speeding up, not slowing down.

, scientists generally believe that dark energy, while its particulars are uknown, appears to be causing the universe's increasing expansion.

"We're trying to understand why that is. It's a very odd thing," said Eisenstein. "Gravity pulls things together, so you'd expect gravity would be pulling the universe back together so that it would expand at a decelerating rate. But something is causing the universe to expand at an accelerating rate. Either we misunderstand how gravity works on the largest scales, or there's some extra thing in the universe that actually causes gravity to repel structure."

Here on Earth, the , which is the world's largest , is also looking for clues about the ingredients of dark energy and its effect on the expansion of the universe.