The kilogram

In a world where everything strives to be the best and the biggest, scientists behind The Avogadro Project in Australia have sought a surprising superlative: the world's roundest object.

And they aren't just doing it for bragging rights. Instead, 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 Measures in Paris.