Australian scientists are trying to create the world's roundest objects: perfect silicon spheres to define a kilogram:
Scientists will use the spheres to determine how many silicon atoms make up a kilogram, and this will be used as the new definition — bringing the kilogram into line with other base units such as the metre and the second, which are all defined by physical constants.
"It's really an atom-counting exercise … and we'll come up with a new definition of the kilogram based on atoms, rather than based on the thing in Paris," explained Walter Giardini, of Australia's National Measurement Institute.
That thing in Paris is a solid platinum-iridium cylinder kept at the Bureau International des Poids et Mesures (BIPM), which mass is, by definition, exactly 1 kilogram.
International Prototype (Image Credit: BIPM)