Gravity Waves

     IT'S EASY ENOUGH TO SEE GRAVITY AT WORK--DROP A BOOK AND EARTH'S
GRAVITY QUICKLY PULLS IT TO THE FLOOR. (SFX: book falling, bang!) BUT HOW DOES
THAT FORCE ACTUALLY WORK?  PHYCISIST BARRY BARISH AT THE CALIFORNIA
INSTITUTE OF TECHNOLOGY SAYS NO ONE COMPLETELY UNDERSTANDS GRAVITY:

     Barish: "We experience it daily compared to the other forces. (but) It's actually . . . the weakest of
all the forces and  . . .the one that scientists know the least about."

     TO LEARN MORE ABOUT GRAVITY, BARISH HEADS A PROJECT OF SOME ONE
HUNDRED SCIENTISTS BUILDING A GRAVITATIONAL WAVE OBSERVATORY. THESE
WAVES ARISE WHEN MASSIVE OBJECTS LIKE STARS COLLIDE. THE HUGE IMPACT SETS
UP SHOCK WAVES IN SPACE, MUCH THE WAY A THROWN STONE CAUSES RIPPLES
ACROSS A POND.  IF A WATERBUG WERE SITTING ON THE POND, IT MIGHT NOT EVEN
NOTICE THE WAVES, BUT IT STILL CHANGES THE BUG'S POSITION AND ORIENTATION. IN
THE SAME WAY, PASSING GRAVITATIONAL WAVES ARE SO WEAK THAT WE NEVER FEEL
THEM, BUT THEY DO HAVE AN EFFECT: THEY ACTUALLY MAKE DISTANCES LONGER
AND SHORTER.  

     Barish: "There's a burst of gravitational wave that comes to the earth just like a flash of light. ..
and. . . it elongates. . . things and it pushes them apart.  It makes them longer in one direction and in the
perpendicular. . . direction the distance gets smaller." (410:Xs)
     THE GRAVITATIONAL WAVE OBSERVATORY WILL BE MADE OF TWO
PERPENDICULAR TUNNELS, EACH TWO AND A HALF MILES LONG.  AT THE END OF EACH
TUNNEL WILL BE A MASS OF METAL AND A SYSTEM TO MEASURE WHETHER THOSE
MASSES SEPARATE OR GET CLOSER SIGNALLING THAT A WAVE HAS ROLLED BY.  IF THE
MASSES FEEL A GRAVITATIONAL WAVE, THE DISTANCE BETWEEN THEM WILL CHANGE
BY LESS THAN ONE MILLIONTH OF A SINGLE ATOM.  NEEDLESS TO SAY, THIS TAKES
INCREDIBLY ACCURATE MEASUREMENT TECHNIQUES, WHICH UP 'TIL NOW HAS BEEN
THE STUMBLING BLOCK FOR DETECTING THESE WEAK WAVES. BARISH AND HIS
COLLEAGUES HOPE THE DETECTOR WILL BE UP AND RUNNING BY THE YEAR 2000.