Roundest objects in the world created

When asked by the Pope to demonstrate his artistic skill, 14^th century Italian painter Giotto di Bondone supposedly drew a perfect circle freehand and said: "That's more than enough." Now, an international group of engineers and craftsmen has gone him one better and built a pair of nearly perfect spheres that are thought to be the roundest objects in the world.

The unusual balls, discussed last week at the SPIE Astronomical Telescopes and Instrumentation conference in France, were created as an answer to the "kilogram problem".

The kilogram is the only remaining standard of measurement tied to a single physical object: a 120-year-old lump of platinum and iridium that sits in a vault outside of Paris, France. But the mass of this chunk of metal is slowly changing relative to the 40-odd copies kept by other countries, and no one knows why or by how much.

So researchers charged with policing units and measures, called metrologists, have come up with several suggestions to redefine the kilogram. In 2011, the International Committee for Weights and Measures will try to decide the issue.

One proposal, pushed by an international team called the Avogadro Project, aims to define the kilogram in terms of a specific number of silicon atoms. Just how many? That's where the newly created silicon spheres come in. - continued on new scientist