Photo: Mysterious Dark Energy Has Existed For Most of Time, Scientists Say



Scientists studying distant star explosions (top) have confirmed that the mysterious force known as dark energy has existed for at least 9 billion years—two-thirds of the universe's history.

Dark energy (illustrated bottom) is a force that opposes the gravity given off by dark and normal matter, causing the universe to expand. Scientists are still not quite sure what dark energy is or how long it has been around, but they believe it makes up about 70 percent of the universe's substance.

Image courtesy NASA, ESA, and A. Riess (Space Telescope Science Insitute)/illustration courtesy NASA


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