Has the kilogram gone on a diet? Maybe. For some reason, the official kilo — a lump of metal stored in a vault at the International Bureau of Weights and Measures outside Paris — has slimmed down by as much as 50 micrograms in the past century. Why this is happening, is a mystery.
The solution? Build a better kilogram. Researchers at the Australian Commonwealth Scientific and Industrial Research Organization are cutting, grinding, and polishing a boule — a big crystal — of ultrapure silicon 28 into two baseball-sized spheres (one is for double-checking). Once finished, it will weigh a perfect kilogram.