'Dark Energy' Thought to Fuel Universe Expansion

Astronomers have new evidence from the Hubble Space Telescope that a strange force was present in the universe billions of years ago. The force is called "dark energy." It's forcing the universe to expand at an ever quickening pace.

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Astronomers have new evidence from the Hubble space telescope that a strange force that pervades our universe was around billions of years ago. This force is called dark energy. It's forcing our universe to expand in an ever- quickening pace, and it's one of the deepest mysteries in physics.

NPR's Richard Harris explains.

RICHARD HARRIS: This phenomenon is so mind-boggling, sometimes it's easier to describe by analogy. That's what Adam Riess at the Space Telescope Science Institute does.

ADAM RIESS: Imagine you were having a tug of war. You are pulling on a rope and the other end of the rope disappears behind a curtain, and somebody or something is pulling on the other end. And we'll call that dark energy out there.

HARRIS: In 1998, Riess was among the astronomers who discovered the tug of dark energy. Nobody really knows what it is, but Riess and his colleagues can now say, at least, that it was present nine billion years ago when the observable universe was only half its present size.

RIESS: It was beginning to pull at that time. It was resisting you. You would be able to tell the difference between nothing on the other end of the rope, or some tugging.

HARRIS: That's one more fact, but it still doesn't tell us what we'd really like to know, which is, what is this mysterious ingredient that makes up 70 percent of our universe?

Richard Harris, NPR News.

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