Fun fact: prototype mysteriously losing weight The 118-year-old cylinder that is the international prototype for the metric kilogram, kept tightly under lock and key outside Paris, is mysteriously losing weight -- if ever so slightly. Physicist Richard Davis of the International Bureau of Weights and Measures in Sevres, southwest of Paris, says it appears to have lost 50 micrograms compared with the average of dozens of copies. For scientists, the inconstant metric constant is a nuisance, threatening calculation of things such as electricity generation. But for most people, it won't mean anything. "The kilogram will stay the kilogram, and the weights you have in a weight set will all still be correct," Davis said.

"The mystery is that they were all made of the same material, and many were made at the same time and kept under the same conditions, and yet the masses among them are slowly drifting apart," he said. "We don't really have a good hypothesis for it."

The kilogram's fluctuation shows how technological progress is leaving science's most basic measurements in its dust. The cylinder was high-tech for its day in 1889 when cast from a platinum and iridium alloy.

At a November meeting of scientists in Paris, an advisory panel on measurements will present possible steps toward basing the kilogram and other measures on more precise calculations. Ultimately, policymakers worldwide would have to agree to any change.

source : www.startribune.com