Many people think of gravity as something they can believe in. But a few years ago, physicist Ephraim Fischbach of Purdue University turned the world of Newtonian physics on its ear by suggesting that a weird new type of gravity had been detected, which physicists began calling "the fifth force."
Before Fischbach, most physicists seemed satisfied that there were four forces: gravity, electromagnetism, the strong force (which holds atoms together) and the weak force (which causes radioactive decay).
Fischbach based his fifth force theory on strange readings done in Australian mine shafts and on earlier Hungarian experiments that appeared to indicate that at distances from a few inches to a few miles, the force of gravity was weaker than Newton had predicted. Dozens of experiments, requiring highly sensitive measuring devices, have been done since Fischbach's 1986 pronouncement. Sometimes there appeared to be a fifth force. More often, there did not.
But now, an international team of researchers carrying out the most detailed and sensitive experiment to date says there is no fifth force.
Using an ultra-sensitive LaCoste-Romberg relative gravimeter, the team took measurements from many points on a 1,000-foot meteorological tower in Colorado. They found the gravitational force measured by the gravimeter and that predicted by Newtonian physics were the same.
Eureka. Newton was right.