Scientists give weight to kilogram measure update

AFTER years of nursing a sometimes dusty cylinder of metal in a vault in Paris as the global reference for modern mass, scientists are updating the definition of the kilogram.

At the end of a week-long meeting in the Palace of Versailles, Paris, the world’s leading measurement aficionados at the International Bureau of Weights and Measures will vote on Friday to make an “electronic kilogram” the new baseline measure of mass.

The kilogram has been defined since 1889 by a shiny piece of platinum-iridium held in Paris. The problem is, the “international prototype kilogram” doesn’t always weigh the same. Even inside its three glass bell jars, it gets dusty and dirty, and is affected by the atmosphere.

The new definition involves an apparatus called the Kibble balance, which makes use of the Planck constant to measure the mass of an object using a precisely measured electromagnetic force.

“In the present system, you have to relate small masses to large masses by subdivision. That’s very difficult and the uncertainties build up very, very quickly,” said Ian Robinson, a specialist at Britain’s National Physical Laboratory.

“One of the things this (new) technique allows us to do is to actually measure mass directly at whatever scale we like.”

But while the extra accuracy will be a boon to scientists, Robinson said that, for the average consumer buying flour or bananas, “there will be absolutely no change whatsoever.”