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A rchive Date
[ 07-06-2000 ]
Category
[ Science ]
sub-Categoy
[ Physics ]
      [A mysterious force of antigravity
      Study indicates that universe's expansion is speeding up
      ASSOCIATED PRESS

      WASHIGTON, Feb. 26 - Scientists studying exploding stars more than 7 billion light-years away have found evidence of a mysterious antigravity force that is causing the universe to expand at an accelerating rate. The finding supports a concept first proposed by Albert Einstein, who later discarded the idea and called it his biggest blunder.

      "IT IS SUCH a strange result we are still wondering if there is some other sneaky little effect climbing in there," Adam Riess, an astronomer at the University of California at Berkeley, said Thursday. He said he and the others in the 15-member international team that made the discovery "have looked hard for errors," but found none.

      The findings were discussed last month at a meeting of scientists in Los Angeles and reported in the journal Science.

      Using the Hubble Space Telescope and ground-based telescopes in Hawaii, Australia and Chile, the astronomers analyzed the light arriving from 14 supernovae, or exploding stars, that are 7 billion to 10 billion light-years from Earth. A light-year is the distance that light travels in one year - about 6 trillion miles.

      Riess said these stars are seen the way they were when the universe was only about half its present age.

      By repeatedly observing the objects and analyzing how their motion stretched the light, the astronomers were able to measure the speed at which the stars are moving away.

      This rate was then compared with the motion of supernovae much closer to the Earth.

      What they expected to find was that the expansion of the universe was slowing slightly from the effect of gravity, said team member Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics.

      "What people thought is that the universe was just coasting" from the force of the Big Bang, he said. "Instead, we found it is actually speeding up."

      Kirshner said this acceleration will continue and within billions of years many of the stars now seen will be gone from view.
      "The universe will be a very different place to look at," he said. "It will be very lonely."

      Rocky Kolb, a University of Chicago astronomer, said in Science that the finding is so startling "I think everyone should reserve judgment."

      Kirshner said that the conclusion will go through an intensive review by many astronomers before the results are accepted, although he noted that preliminary results from a parallel study by another astronomy group are in agreement.

      If the universe is accelerating, it could solve one problem for astronomers. Some measurements have put the age of the universe at about 10 billion years. This is younger than the measured ages of some stars, a dilemma that has confounded astronomers.
      With the acceleration of the universe factored in, said Riess, the universe would have to be about 14 billion years old, some 2 billion years older than the oldest star.

      "That would no longer make the daughter older than the mother," said Riess.

      Riess illustrated the acceleration force by comparing it to how a jet airplane is launched from an aircraft carrier. A catapult slings the aircraft from the deck, but once it is airborne, the jet's engines take over and the craft speeds up.

      The Big Bang, the theoretical beginning of the universe, started the motion of the universe, just as the catapult starts the jet moving. But after that, the expulsive force causes the universe to speed up, just as the jet's engine causes the airplane to go faster.
      "We're seeing the universe take off," said Riess.

      Riess said the "cosmological constant" first proposed by Einstein is "the only explanation we have" for the acceleration.
      He described the constant as "a repulsive force that is a property of vacuum in space and time."

      "Our everyday experience tells us that a vacuum is empty, that there is nothing in it, but that might not be true," he said. "There may be an energy, a force, associated with a vacuum."

      Over short distances, said Riess, this repulsive force can't be detected, but over distances of 7 billion to 10 billion light-years, "this force becomes something to reckon with, and is strong enough to overcome gravity and cause the universe to accelerate."

      © 1999 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.]


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