It turns out that nobody can say for sure, at least not in a way that won ‘t change ever so slightly over time. The official kilogram – a cylinder cast 118 years ago from platinum and iridium and known as the International Prototype Kilogram or “Le Gran K ” – has been losing mass, about 50 micrograms at last check. The change is occurring despite careful storage at a facility near Paris.That ‘s not so good for a standard the world depends on to define mass. Now, two U.S. professors a physicist and mathematician – say it ‘s time to define the kilogram in a new and more elegant way that will be the same today, tomorrow and 118 years from now. They have launched a campaign aimed at redefining the kilogram as the mass of a very large but precisely-specified – number of carbon-12 atoms.
Their proposal is that the gram 1/1000th of a kilogram would henceforth be defined as the mass of exactly 18 x 140744813 carbon-12 atoms.
