Last April, at a meeting of the American physical society in Washington, D.C., representatives of three independent laboratories announced new high-precision measurements of the strength of the force of gravity. To the astonishment of the audience, the three measurements disagreed with one another by considerable amounts, and worse, none of them matched the value that physicists have accepted as correct for more than a decade. No one could offer so much as a hint to explain the discrepancies.
To illustrate the magnitude of the predicament, imagine a felon hunted by the police. They know that he is hiding somewhere along a street of ten blocks, with ten houses on each block. On the basis of previous information, the police have concentrated their surveillance on a particular house in the middle of the second block, when suddenly three new and presumably trustworthy witnesses appear. One places the miscreant in the very first house of the first block, the second singles out a dwelling near the end of the first block, while the third witness points to a house way across town at the other end of the street, more than eight blocks from the stakeout.
Experiments to measure G are painfully sensitive to every stray gravitational influence, from sparrows flying over the roof to earthquakes in the antipodes.
