Hubble finds mysterious force pushing apart universe

Feb 20, 2004

Hubble Measurements Support Einstein Prediction of Mysterious Force Pushing Apart Universe
The Associated Press

LOS ANGELES (AP) - The mysterious "dark energy" that is pushing apart the universe appears to be the constant force that Albert Einstein once predicted, according to measurements made by the Hubble Space Telescope.
NASA scientists announced their findings Friday, and details are to appear in an upcoming issue of Astrophysical Journal.

The force is an unknown form of energy that behaves in an opposite manner from the pull of gravity. Dark energy causes the galaxies within the universe to move apart from one another at ever-increasing speeds.

Einstein called the force the "cosmological constant." He theorized its existence to balance the universe against normal gravity and keep it from collapsing on itself.

Einstein ultimately dismissed the theory as his greatest blunder, but subsequent observations of supernovas, or distant stars that exploded long ago, gave it credence. Scientists now know dark energy causes the universe to expand and accelerate. It makes up an estimated 70 percent of the universe.

What was unclear is whether dark energy is stable.

If it grows stronger with time, the universe could end with galaxies, stars, planets and, ultimately, atoms coming unglued in a violent expansion that theorists call the "big rip."

In the alternative, dark energy could fade away to the point where it flipped in force, pulling the universe back together in what's called the "big crunch."

The latest Hubble observations announced Friday suggest dark energy is unwavering, just as Einstein predicted.

"Right now, we're about twice as confident than before that Einstein's cosmological constant is real, or at least dark energy does not appear to be changing fast enough - if at all - to cause an end to the universe anytime soon," said Adam Riess, of the Space Telescope Science Institute in Baltimore, which looks at data sent from the Hubble.

Even if Einstein was wrong, dark energy won't spell an end to the universe for at least another 30 billion years, scientists said.

The latest results come from the measurements of multiple supernovas that exploded when the universe was half its present age of nearly 14 billion years.

The apparent brightness of a certain type of supernova allows scientists to gauge the expansion rate of the universe at different times in the past. That in turn allows them to measure any change in the strength of the force exerted by dark energy.

Further research is needed to prove dark energy is indeed a constant force, scientists said.

However, NASA's decision to no longer repair Hubble means the work will be interrupted until a replacement can be built and launched. ^---

On the Net: http://www.hubblesite.org/

AP-ES-02-20-04 2301EST

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