Metric system could get an overhaul
Units such as the kilogram and meter are supposed to be constant. But they are not always. Many of the metric system's basic measurements are based on natural phenomena -- and some may be more variable than people once thought.
“The problem with the kilogram is that it is not possible to determine if the prototype [by which it is defined] changes over time,” said Peter Mohr, a physicist at the National Institute of Standards and Technology. “It seems to.”
NIST symposium to highlight the metric system
Because of these uncertainties, the international body that oversees the International System of Units, or SI — the old metric system — is considering a proposal to update some of the key definitions in the system to more firmly ground them in the fundamental constants of nature. The proposal would update the definitions of the kilogram, the unit of measure for mass; the ampere, the unit for electric current; the kelvin, the unit for temperature; and the mole, the unit for amount of a substance.
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FRIDAY FEATURE: A history of measurements