Science: Fickle Universe

Younger by half? Maybe

How old is the universe? The question has perplexed scientists, to say nothing of theologians, at least since the 17th century, when an Irish divine, James Ussher, used the Bible to calculate the world's birth date as 4004 B.C. Since then, astronomers contemplating far-off stars and galaxies through powerful telescopes have steadily increased Ussher's figure. Today many scientists agree the universe goes back as far as 20 billion years, when it was created by an explosion irreverently referred to as the Big Bang.

Last week a team of astronomers, led by Marc Aaronson of the University of Arizona's Steward...

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