A one-kilogram sphere of single-crystal silicon, one of the roundest man-made objects in the world. The object helped redefine a kilogram in terms of the number of atoms it contains
Latest News – Since 1889, Le Grand K, a sleek cylinder of platinum-iridium metal, has ruled from its underground vault in Paris. An absolute monarch, it was the very definition of one kilogram of mass. Scientists from around the world made pilgrimages to it, bringing along their national kilogram standards to weigh in comparison.
“The mother ship is never wrong,” said Robert Vocke Jr., a chemist at the National Institute of Standards and Technology (N.I.S.T.) in Gaithersburg, MD.
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No longer. Friday, in a small conference center located just steps from the Palace of Versailles, several dozen nations voted to overthrow Le Grand K and to redefine the kilogram and three other standard units of measure: the ampere, for electrical current; the kelvin, for temperature; and the mole, which describes the amount of a chemical substance. The vote fulfils an 18th-century dream. Henceforth, all seven units in the International System of Units, otherwise known as the S.I., will no longer be defined by material objects and instead will be defined only by abstract constants of nature.
“This arc of history started before the French Revolution and now, I think we’ve finished the journey,” said Stephan Schlamminger, a N.I.S.T. physicist. The “democratization of the units,” he said, is now complete.|kilogram
The S.I. originated at the end of the eighteenth century with just the meter and the kilogram. The idea was to standardize the basic units of trade and scientific measurement. After all, for one kilogram of gold coins to hold universal value, everyone has to agree on the exact definition of one kilogram…Read More
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