Scientists behind the Avogadro Project in Australia have sought to create the world’s roundest object. The remarkable sphere may provide a solution to what’s known as the “kilogram problem,”
Unlike other scientific units, which can theoretically be measured anywhere in the world based on natural properties, the kilogram is still based on a physical object: a cylinder of platinum and iridium that dates back to 1889.
So while the “meter” is defined as the distance light travels in a tiny fraction of a second, and the “second” can be counted by the precise decay of an atom, the kilogram is no more (and no less) than a physical mass that sits in a secured vault at the Bureau International des Poids et Mesures in Paris.
For reasons no one understands-and despite precautionary measures-the cylinder’s mass keeps changing.
In other words, the kilogram, as defined by the cylinder (and compared to 40 exact replicas of the cylinder kept in other countries), doesn’t weigh the same as it used to.
To solve that problem, researchers at the Australian Centre for Precision Optics, which is home to The Avogadro Project, are crafting nearly perfect spheres made of a highly pure and very stable form of silicon.
By calculating the sphere’s volume and weight, scientists should be able to determine the exact number of silicon atoms in the object itself, thereby providing an unchanging definition for the mass of a kilogram.
Per Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO), scientists settled on a sphere as the standard shape because it “has no edges that might get damaged,” and “only one dimension [its diameter] has to be measured in order to calculate its volume.”