Kilo prototype mysteriously loses weight

[NeoDevin]

And how would you go about counting these atoms?

Have your grad student do it...

 

[billiards]

I think we can rule that out because any comparison of masses (or weights) would require both objects to be at the same place (eg: in Paris).

Oh right, I was not aware that they had carried out the calibration at the same location, although now I think about it I don't see how else they could have really done it. In this case I will go with the "mass changed due to handling" argument, because in order for the masses to be in the same place at once, it is necessary for them to be handled.

And how would you go about counting these atoms?

Counting them? No. I wasn't thinking aong those lines, I was thinking more along the "how would you tell an alien species what a kg was?" pattern of thought. You could specify a finite number of carbon 12 atoms and then they could interpolate the exact weight you meant by integrating knowledge of the weight of a carbon 12 atom (which should be universal) in terms of their own practical weighting system.

 

[Moridin]

Scientists have been trying to find a natural reference for the kilogram for quite some time - as it is the only one left (of the SI base units) that is defined by a man-made object. The atomic mass unit has been proposed but there are a few problems, as hinted above. We can compare objects of a human size with the standard kilogram quite well, and compare the mass of atoms and so on compared to the carbon-12 atom, but the tricky part is between the two.

 

[mgb_phys]

Have your grad student do it...

There is a project to do this with a silicon sphere and use x-ray crystalography to precisely measure the atomic spacing then use the size of the sphere to calculate the number of atoms present. ( details in my post above)

At the moment this looks like a better bet than the Planck balance.