Number 223 (Story #2), April 24, 1995 by Phillip F. Schewe and Ben Stein|
NEW MEASUREMENTS OF THE NEWTONIAN GRAVITATIONAL CONSTANT G , the number that determines the strength of gravity, depart significantly from the accepted value established in the 1980s. G is the least well known of all the fundamental constants; the accepted value of 6.6726 x 10**-11 m**3/kg-s**2 is known with a relatively high uncertainty of 0.01%. G is arguably the most difficult constant to measure because, among other reasons, gravity is the weakest of all forces and it is impossible to shield delicate measurements from the gravity influences of buildings and other nearby objects. Underscoring this difficulty, three scientists from international labs (the German Bureau of Standards, the Measurement Standards Laboratory of New Zealand, and the University of Wuppertal in Germany) reported at the APS Meeting new measurements of G which disagreed widely with one another and with the standard value. The Wuppertal value was 0.7% below the accepted value (corresponding to 7 standard deviations), the New Zealand measurements were 0.07-0.08% below (7-8 standard deviations) and the German Bureau of Standards value was a whopping 0.6% above (60 standard deviations). Although the techniques differed, the groups all essentially determined G by measuring the gravitational effects of cylindrical masses acting on objects suspended above the ground. Researchers at Los Alamos, the lab which helped set the 1980s standard, are undertaking a new measurement of G which may be five times as precise as current measurements, and may shed light on these puzzling results. A firmly established value of G will be important for future grand unified theories that attempt to relate G to fundamental constants associated with the other three physical forces.