Scientists likely to redefine how much a kilogram weighs

Scientists are redefining the definition of the kilogram we use every day. The 129-year-old standard for the kilogram will change very soon. On November 16, scientists from around the world are meeting at the General Conference on Weights and Measures in Versailles, France, to vote on a new the definition of a kilogram that ties it to a universal constant in nature.

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When the definition changes, the General Conference on Weights and Measures will complete the original dream of the metric system, which was embraced amid the French Revolution. The metric system — which evolved into the International System of Units, or SI — was designed to be “for all times, for all people,” says Stephan Schlamminger, a NIST scientist involved with the redefinition.

“Objects always change,” says Stephan. With the new definition, he says, “we go from an object” on Earth “to the stuff that’s in the heavens,” he said.

Ian Robinson, materials and engineering specialist at Britain's National Physical Laboratory, told Reuters that the block doesn't always weight the same. Though its ensconced in three glass bell jars, it can still get dusty, and is affected by the atmosphere. "We live in a modern world. There are pollutants in the atmosphere that can stick to the mass."

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"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," Robinson said. "One of the things this (new) technique allows us to do is to actually measure mass directly at whatever scale we like, and that's a big step forward," he said.