However, surely the mass of that cylinder is changing. What about the atoms that fall off every time it is picked up? Do we really want the definition of something as important as the SI unit for mass to be something that changes ever so slightly with time?
Therefore, I found this article to be interesting from the Physics Arxiv Blog:
Why not make the kilogram equal to the mass of a certain number of carbon-12 atoms, specifically 2250× 28148963^3 of them?
Then a kilogram would be a cube of carbon 8.11cm on each side (8.11cm is roughly the length of 368,855,762 carbon atoms laid side by side).
With that definition, almost anybody could make a kilogram in their own kitchen given some carbon and a knife.I think this would be a good idea. Then the definition of the kilogram would remain fixed forever and would be something anyone could compare to with relative ease. (That is, easier that comparing with a cylinder in France hardly anyone is ever allowed to touch.)