Recent history of measurement of 1 kg and other units

[Astronuc]

I didn't remember the Lavoisier died at the guillotine.

The world's roundest object helps solve the longest running problem in measurement -- how to define the kilogram. I knew about the Pt the Pt-Ir standard. I didn't realize that the mass of various 'standards' changed in time.



Originally published Mar 25, 2013Edit/update: From the Youtube page -

The Avogadro project aims to redefine Avogadro's constant (currently defined by the kilogram -- the number of atoms in 12 g of carbon-12) and reverse the relationship so that the kilogram is precisely specified by Avogadro's constant. This method required creating the most perfect sphere on Earth. It is made out of a single crystal of silicon 28 atoms. By carefully measuring the diameter, the volume can be precisely specified. Since the atom spacing of silicon is well known, the number of atoms in a sphere can be accurately calculated. This allows for a very precise determination of Avogadro's constant.

 

[DrClaude]

I didn't remember the Lavoisier died at the guillotine.

That's what you get for being a tax collector

 

[Greg Bernhardt]

Wow, I had no idea about this project! It's amazing how much effort and precision goes into defining something as seemingly simple as the kilogram. And it's also interesting to learn about the history of the standard changing over time. Thanks for sharing this information!