Mar 18, 2009: Even rounder thing

[Coign]

Not to overshadow Bruce but while trying to figure out how you make a perfect sphere I found a site where they do that.

And to spoil the surprise...

you grow it.





http://www.csiro.au/news/PerfectKilo...iaRelease.html

While a physical object will still be necessary for calibrating scales and balances, the silicon atoms in the sphere will always remain the same. It is for this reason that the scientists working on what’s known as the Avogadro Project are collaborating to determine what is effectively the number of atoms in a sphere. Once the number of atoms is known, the definition of the kilogram can be based on it from then on.

The best sphere the ACPO team has made had a total out-of-roundness of 35 nanometres. That is, the diameter varies by an average of only 35 millionths of a millimetre, making it probably the roundest object in the world.

It has taken three years to produce the 20 cm long cylinder of silicon. The special silicon, known as monoisotopic silicon, was made in Russia and grown into a near perfect crystal in Germany. It will take something like twelve weeks to make one sphere 93 mm in diameter (the team will make two).

And some more current info.

http://www.csiro.au/science/ps35k.html

OUTCOMES
On Friday 4 April 2008, these two spheres were presented to representatives of the Avogadro project.
Now it's up to these countries, and others in this major international effort such as Italy, Belgium, Japan and the US, to determine what is effectively the number of atoms in a sphere. Once the number of atoms is known, the definition of the kilogram can be based on it from then on.

Click this link for some more pictures including a rough look at the sphere.

http://www.acpo.csiro.au/avogadro.htm

And some very detailed information on where the scientific community is at on defining/redefining the mass of a kilogram. For right now it seems that the silicon sphere is not the standard and that they still use the old platinum/iridium weight as the International Standard.

http://www.bipm.org/en/scientific/mass/faqs2_mass.html