The Roundest Object In The World
12 October 2008, 17:50
Categories: tools
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The kilogram, as a unit, has been defined by the mass of a 120-year-old lump of platinum and iridium that sits in a vault outside Paris. But the mass of this chunk of metal is slowly changing relative to the copies kept by other countries, and no one knows why or by how much. So some researchers are proposing defining the kilogram in terms of the mass of a specific number of silicon atoms.
Now, a group of international researchers has created a purified silicon sphere that could be used for this purpose. After months of grinding, the team produced two spheres with diameters of 93.75 millimeters, each with a mass that matches the Australian copy of the kilogram. The spheres are as close to being perfectly smooth as is possible; the small-scale roughness of the balls varies by only 0.3 nanometres, and their curvature by 60 to 70 nanometers. “If you were to blow up our spheres to the size of the Earth, you would see a small ripple in the smoothness of about 12 to 15 mm, and a variation of only 3 to 5 meters in the roundness,” said optical engineer Achim Leistner.
Posted by: The Editors
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