Scientists from around 60 nations voted unanimously Friday to redefine the kilogram.
For more than 100 years Paris has been home to Le Grand K — or the International Prototype Kilogram as it is officially known — a block of metal that previously defined the weight of a kilogram.Until now, everything from kitchen scales to gym weights around the world was manufactured to the standard set by the cylinder of platinum iridium, which has been kept in a high-security vault in the French capital since 1889.Different countries have their own “prototype kilograms” that serve as national standards, which were calibrated to the Paris artifact.
The decision at the General Conference on Weights and Measures in Versailles, France was greeted with great excitement as officials approved the new definition, which is based on the Planck constant — a physical constant observed in the natural world — rather than the precise weight of a piece of metal kept under lock and key.
The reason for the change to the International System of Measurement (SI) units was that over time the prototype lost atoms and therefore mass because it is “susceptible to damage and environmental factors,” according to the National Physical Laboratory (NPL), which houses Kilo 18, Britain’s copy of Le Grand K.
The redefinition will come into effect on World Metrology Day on May 20. The conference is hosted by the International Bureau of Weights and Measures.