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Scientists Calculate Most Precise Age Yet for Universe

TIMES SCIENCE WRITER

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 Tuesday.

By the latest estimate, the universe is at least a billion years younger than some scientists had predicted. The results are based on eight years of painstaking calculations, observations with NASA’s Hubble Space Telescope and a range of celestial measurements.

The new findings were made public Tuesday in a news conference by Wendy Freedman of the Carnegie Observatories in Pasadena, who led an international team of 27 astronomers working with the Hubble telescope, and in separate research by Australian physicist Charles H. Lineweaver that is to be published later this week in the journal Science.

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The new insight into the timing of primordial creation has profound implications for what researchers believe is the size, behavior and eventual fate of the universe. The finding reconciles a cosmic age crisis in which astronomers feared that, by some measurements, the universe paradoxically appeared to be younger than the oldest 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, darker and more attenuated 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.

Caltech astronomer Charles Steidel, who studies the formation of galaxies 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 Mt. Wilson Observatory 70 years ago, astronomer Edwin Hubble discovered that the universe is expanding, and ever since, scientists have tried to calculate how fast it is flying apart.

The National Aeronautics and Space Adminisitration 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. Indeed, it has been a major mission of the sometimes troubled space telescope.

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, NASA astronomers measured Hubble’s constant at 70 kilometers per second per megaparsec, with an uncertainty of 10%. That means that a galaxy appears to be accelerating 160,000 miles per hour faster for every megaparsec (3.3 million light-years) it is away from Earth. Lineweaver arrived at a similar value by studying cosmic microwave radiation left over from the Big Bang and examining 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 about 13.5 billion years, Freedman said, if different assumptions about the amount of matter in the universe are used in the calculations.

Indeed, 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. “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 2; now we are just as passionate about [a margin of] 10%,” Kirshner said. “What was once a very big disagreement is now narrowing down.”

If, after 70 years of effort, scientists are approaching the value of Hubble’s constant with greater certainty, the understanding of other aspects of the universe is still in flux.

In related research also made public Tuesday, cosmologists at Princeton University and at the Lawrence Berkeley National Laboratory concluded that, based on the best astronomical evidence available, galaxies are indeed flying away from each other at a faster and faster clip.

At the same time, the universe’s visible matter is about one-third of what is needed to explain its structure, suggesting that other forces may be at work.

“What it all means for the future of the universe is that it suggests the universe will keep expanding forever, faster and faster” said Princeton cosmologist Neta A. Bahcall.

“Eventually,” she said, “all the galaxies will recede from each other and the universe will become much emptier and colder and darker.”


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