Age o' the Universe

     HUMANS KEEP CAREFUL TRACK OF THEIR BIRTHDAYS SO WE ALWAYS KNOW
HOW OLD WE ARE.  BUT IT'S A WHOLE DIFFERENT STORY WHEN YOU TRY TO FIGURE
OUT THE AGE OF THE EARTH OR THE SUN OR THE UNIVERSE. SINCE NO ONE'S BEEN
AROUND RECORDING BIRTHDAYS FOR STARS AND PLANETS, SCIENTISTS HAVE TO RELY
ON INDIRECT METHODS TO DETERMINE HOW OLD THEY ARE. THE PROBLEM IS,
DIFFERENT METHODS GIVE DIFFERENT ANSWERS, AND NO ONE IS SURE YET JUST WHAT
THE RIGHT AGE IS.  
     ONE METHOD, FOR EXAMPLE, MEASURES THE AGE OF STARS. IF YOU KNOW HOW
BIG A STAR IS AND HOW FAST IT'S BURNING, YOU CAN FIGURE OUT HOW LONG IT WILL
LAST AND HOW LONG IT'S BEEN BURNING UP THAT FUEL. SAYS ASTRONOMER ALEX
PHILAPENKO:

     Philapenko: "If we know how massive a star is we know how much fuel it has to burn. . .  So .. .
we can determine an age until it runs out of fuel. It's much like determining how long your car will go on
the freeway on a tank of gas at 60 miles per hour."  
     USING THIS METHOD TO MEASURE SOME OF THE OLDEST STARS, GIVES US SOME
IDEA OF HOW OLD THE UNIVERSE IS.  ASTRONOMERS THINK THAT SOME OF THE OLDEST
STARS ARE 20 BILLION YEARS OLD, SO THE UNIVERSE MUST BE AT LEAST THAT OLD. 
BUT THIS CONFLICTS WITH ANOTHER IMPORTANT MEASURING METHOD.  THE SECOND
METHOD DETERMINES HOW FAST A STAR IS MOVING AND HOW FAR AWAY FROM US IT
IS.  IF WE ASSUME THAT THE STAR STARTED OUT AT THE SAME POINT PLANET EARTH
DID AT THE BIG BANG, THEN THIS INFORMATION CAN TELL YOU HOW LONG THE STAR'S 
BEEN TRAVELING SINCE THE BIG BANG--IN OTHER WORDS, HOW OLD THE UNIVERSE IS.  
AND THIS METHOD GIVES AN AGE THAT'S CLOSER TO 10 BILLION YEARS OLD--JUST
HALF AS OLD AS SOME STARS!  RIGHT NOW, THERE'S ENOUGH UNCERTAINTY IN EACH
OF THE METHODS THAT SOME SCIENTISTS THINK THEY MIGHT SOME DAY BE
RECONCILED.  BUT IF NOT, SAYS PHILAPENKO:

     Philapenko: "then we really will have a dillemma and it will mean that there's something wrong
with one of the theories either the theory of the expanding universe, or maybe the theory of how long stars
live, and that's exciting.  that's what science is all about."