Redefining the Kilogram

Scientists have crafted two new definitions for the common unit of mass. The fight to pick the best one is getting nasty.

Written byBob Grant

| 2 min read

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WIKIMEDIA COMMONS, POUSSIN JEAN

There's a secret war going on, and the future of science is at stake. The battle rages over the definition of "kilogram." Like many standards of measurement, the definition of a kilogram harkens back to scientific days of yore, when researchers were just beginning to empirically grasp the composition of matter. Since 1889, the kilogram has been defined as the mass of a certain platinum-iridium cylinder, called Le Grande K, that is housed at a sealed and guarded vault in Paris. In order for the cylinder to weigh exactly a kilogram, it must be taken out and cleaned according to strict rules. Invariably, such a process adds and subtracts millions of atoms—from cleaning products and simply handling the object—affecting the precise mass of Le Grande ...

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Meet the Author

Bob Grant
From 2017 to 2022, Bob Grant was Editor in Chief of The Scientist, where he started in 2007 as a Staff Writer. Before joining the team, he worked as a reporter at Audubon and earned a master’s degree in science journalism from New York University. In his previous life, he pursued a career in science, getting a bachelor’s degree in wildlife biology from Montana State University and a master’s degree in marine biology from the College of Charleston in South Carolina. Bob edited Reading Frames and other sections of the magazine.
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