Hubble Telescope Makes New Discovery

The Hubble Space Telescope has shown that a mysterious form of energy first conceived by Albert Einstein, then rejected by the famous physicist as his "greatest blunder," appears to have been fueling the expansion of the universe for most of its history.

This so-called "dark energy" has been pushing the universe outward for at least 9 billion years, astronomers said Thursday.

The idea of dark energy was first proposed by Einstein as a means of explaining how the universe could resist collapsing under the pull of gravity. But then Edwin Hubble _ the astronomer for whom the NASA telescope is named _ demonstrated in 1929 that the universe is expanding, not a constant size. That led to the big-bang theory, and Einstein tossed his notion on science's scrap heap

There it languished until 1998, when astronomers who were using supernova explosions to gauge the expansion of the universe made a shocking observation. It appeared that older supernovae, whose light had traveled a greater distance across space to reach the Hubble telescope, were receding from Earth more slowly than simple big-bang theory would predict. Nearby supernovae were receding more quickly than expected. That could only be true if some mysterious force were causing the expansion of the universe to accelerate over time.

Cosmologists dubbed the force "dark energy," and ever since they've been trying to figure out what it is.