October 02, 2006
Monday

ALBUQUERQUE, N.M. -- "Stuff" isn't a very scientific word, but its use grows common when scientists try to describe dark energy - an unseen force pushing all the bodies in the universe apart at ever-faster speeds.

Considering that dark energy could one day tear the entire universe apart, the scientific community would like to understand that "stuff" better, said Tom Vestrand, a scientist at Los Alamos National Laboratory.

Last month, NASA selected the lab to be part of a team competing to develop a mission that would study the enigmatic force.

"We can't see this mysterious stuff - that's why we call it 'dark energy,' " Vestrand said. "There's all kinds of thoughts about it, but nobody really understands what it is."

The team's proposal, called Destiny, will vie against two other groups. NASA is expected to select a winner in late 2008, with the earliest launch date in 2013, said Tod Lauer, an associate astronomer at the National Optical Astronomy Observatory in Tucson, Ariz.

Should Destiny win, NASA would supply its $600 million budget.

"The thing we need to do is get a history of how the universe expanded very, very precisely, and what dark energy had to do with that," said Lauer, who is leading the Destiny team. "Destiny will give precise measurements as to how that happened."

Scientists first realized something was wrong with their models of the universe in 1998, Vestrand said.

Computer models at that time predicted a slow, steady expansion of the universe spreading out from a central point, as part of the big-bang theory.

But observations of ancient supernovae - which were farther away than they were supposed to be - suggested the objects in the universe were actually moving apart at a much faster rate, Vestrand said.

"There was something wrong with the models," he said. "From the observations, there was something that caused the galaxies to move apart faster than it would without this negative pressure."

The explanation? Dark matter, which is different from dark energy, Vestrand explained.

Dark matter holds things together, while dark energy pushes them apart.

"We know dark matter is there because if you look at galaxies and calculate how much gravity you need to keep them together, you can only account for a fraction of that through visible things," Vestrand said.

Dark matter has been studied for decades.

But to understand dark energy, scientists need to look at more supernovae and see how fast they are all moving away from each other, he said.

Destiny will look at about 3,000 of them with a Hummer-sized telescope and camera, trying to gather more data on the enigmatic dark energy, Vestrand said.

So far, the dark "stuff" has altered models of the universe and drawn a very strange picture of its evolution.

In the first 6 billion or 7 billion years, galaxies expanded away from each other slowly because gravity pulled things together and tried to keep them in place, Vestrand said.

But about 5 billion years ago, galaxies got far enough apart that gravity couldn't hang on as well, he said.

And then the mysterious "stuff" took over and gave all the galaxies an extra shove away from each other, like a dad pushing his kid on his first bike.

Never-ending expansion doesn't bode well for the continued existence of life. While it won't happen for billions of years, the continued expansion could mean that everything will get extremely cold, as suns burn out and everything - eventually even planets - drifts away from everything else, Vestrand said.

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