Jul 4, 2008

Weight, the final frontier*

Comics are educational. Today's User Friendly comic got me curious, and I ended up learning something new about the kilogram - or rather, how one keeps a standard of weight so we know whether or not we have a kilo (as we "locals" say).

I got curious about the reference to the roundest objects in the world, so I went a-googling and found that there is a reason besides "because we can" for creating the spheres:

"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. […] 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.

We don't have a reliable alternative to the physical prototype sitting in Paris, which itself is no longer reliable. With the new ultra-round silicon sphere, we may have an object that can serve as a new prototype, and we may be closer to our goal of redefining what defines the kilogram. We'll find out just how close when the International Committee for Weights and Measures meets again in 2011.

*) "Space… the final frontier."

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