Cosmic Age Crisis Lessens

May 26, 1999|By ROBERT LEE HOTZ Los Angeles Times

Astronomers, peering at the edge of forever, have determined that the universe is between 12 billion and 13.4 billion years old, resolving one of cosmology's most fundamental and perplexing questions with unprecedented precision, independent research teams announced on Tuesday.

By the latest estimate, the universe is at least a billion years younger than some scientists had predicted, but not as young as many had feared. The results are based on eight years of painstaking calculations, observations with the National Aeronautics and Space Administration's Hubble Space Telescope and celestial measurements.

The findings were released in Pasadena, Calif., by Wendy Freedman of the Carnegie Observatories, who led an international team of 27 astronomers working with NASA's Hubble Space Telescope, and in separate research by Australian physicist Charles H. Lineweaver that is to be published this week in Science.

The new insight into the timing of primordial creation has profound implications for what researchers think is the size, behavior and eventual fate of the universe. The finding reconciles a cosmic age crisis in which, by some measurements, the universe paradoxically appeared to be younger than the galaxies it contained.

Combined with other recent observations, it also suggests that the universe may never actually end. It may simply expand forever, becoming an ever colder and darker void as the eons unfold.

"That is really a very impressive achievement," astrophysicist Michael J. Turner at the University of Chicago said of the new age estimate.

California Institute of Technology astronomer Charles Steidel, who studies how galaxies formed and the structure of the early universe, said, "It is a great piece of work, really rock solid."

By any measure, it is the most precise answer yet to a question first posed on a mountaintop overlooking Los Angeles. At the Mount Wilson Observatory 70 years ago, astronomer Edwin Hubble discovered that the universe was expanding, and ever since, scientists have tried to calculate how fast it is flying apart.

In all, NASA has spent several billion dollars in the effort to refine the speed of that expansion, considered as fundamental a fact about the universe as the speed of light.

The newest conclusions about the birth of the cosmos arise from a growing understanding of a mathematical yardstick, called the Hubble constant, used to gauge the speed at which galaxies are accelerating away from each other. The constant is one essential ingredient in the equation used to determine the age and size of the universe.

By studying 800 pulsating stars in 18 distant galaxies, the NASA astronomers measured Hubble's constant at 70 kilometers per second per megaparsec, with an uncertainty of 10 percent. A megaparsec is 3.26 million light years, and each light year -- the distance light travels in one year -- is 5.9 trillion miles.

That means that a galaxy appears to be accelerating 160,000 miles per hour faster for every 3.26 million light years it is away from Earth. In his research, Lineweaver arrived at a similar value by studying cosmic microwave radiation left over from the Big Bang and a half-dozen other cosmological measurements.

Combining the Hubble constant measurement with estimates for the density of the universe, Freedman's team determined that the universe is approximately 12 billion years old -- similar to the oldest stars.

The age estimate could change to as much as 13.5 billion years, Freedman said, if different assumptions about the amount of matter in the universe are used in the calculations.

Lineweaver in Australia used slightly different assumptions about the density of matter in the universe and the forces acting on it. He came up with an estimate of 13.4 billion years.

His margin of error, however, brings it well in line with Freedman's estimate.

"Our results are in agreement," said Lineweaver at the University of New South Wales in Sydney, Australia. "The most awe-inspiring conclusion is that the universe has not been around forever; it had a beginning."

Not every scientist in the field greeted Tuesday's announcement enthusiastically.

Astronomer Allan Sandage at the Carnegie Observatories, who studies supernova explosions as a way to gauge the Hubble constant, said his research group sharply disagreed with the new findings.

"We believe [the Freedman group] has systematic errors," Sandage said. "They have announced a final number and they are not correct."

Harvard University astronomer Robert Kirshner, head of a third team studying the Hubble constant, downplayed the differences.

"We used to disagree by a factor of two; now we are just as passionate about [a margin of] 10 percent," Kirsshner said. "What was once a very big disagreement is now narrowing down."

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