Currently, a physical reference weight is held in a special vault in Paris. “Le Grand K” is a precise cylinder of platinum-iridium metal inside a glass bell jar that weighs exactly one kilogram.
Since 1879, it has actually defined what one kilogram of mass is, and all international weights held in Canberra, Washington, DC and Beijing refer to that single physical standard: Le Grand K. On Friday, international scientists are meeting in Geneva on a proposal that would eliminate the physical specimen as the reference weight. Instead, physicists and engineers would redefine the kilogram to refer to physical constants like the speed of light and Planck’s constant.
The vote, which is expected to be unanimous, would move the reference of mass from a physical specimen to a somewhat intangible, but very precise and immutable, series of numbers and equations. It’s the equivalent of moving from gold coin currency to paper or plastic and then onward to a Bitcoin.
Farewell Le Grand K.
This story is featured in the 15 November 2018 edition of The Warren Centre’s Prototype newsletter. Sign up for the Prototype here.