Perfect silicon spheres were developed to redefine the kilogram because the platinum kilogram was changing in weight even in extremely strictly controlled physical conditions. If dust can ruin the platinum kilogram, why are people allowed to touch the silicon version?

Question

How is it that the sphere doesn’t become ‘contaminated’ with extra atoms from skin, clothes or even breath? Or is it just that these contaminants are very easy to clean off afterwards?

In: Physics

Answer 1

As I understand it, because the silicon version has done it’s job. The kilogram was the last SI unit that relied on a physical object as a reference point.

The platinum kilogram was just that. It was a kilogram.

The silicon spheres were a tool to help define Avogadro’s number (a constant that links the mass number of a chemical to it’s weight in grams) to the required accuracy.

By doing this, the Kg could then be redefined as a mathematical formula based on universal constants, rather than “that block of platinum in the vacuum chamber in France”.