

Glorious silicon globes could hold key to elusive PERFECT kilogram - gadders
http://www.theregister.co.uk/2012/11/20/quantum_kilogram/

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lutusp
I can't believe this encyclopedic article fails to mention the fact that one
of the reasons for wanting to abandon the physical standard mass is that its
mass has measurably changed over the years, and that the most likely reason
for the change is that cosmic rays impinge on the standard mass and collide
with particles within it, which turns a tiny amount of mass into a tiny amount
of radiated energy, which is radiated away.

The wish to abandon a physical artifact is well-founded regardless of the
proximate reason, but the most commonly stated reason deserves mention.

