The value of things like the watt, the meter and the kilogram would seem to be pretty well established. But these are the things that keep some scientists awake at night.
The kilogram is based on a chunk of platinum and iridium kept in a bell jar at the International Bureau of Weights and Measures near Paris. But it is shrinking since it was produced in 1889. Scientists say that the piece of metal has lost the weight of at least a fingerprint, which does not seem to be much. However, more accuracy is required in the modern world.
Research at the National Physical Laboratory in Britain has tied the kilogram to a mathematical constant based on the frequency of light instead of a physical mass.
“This research will underpin the world’s measurement system and ensure the long term stability of the very top level of mass measurement,” said Ian Robinson, the project leader. “Although the man on the street won’t see much difference — you’ll still get the same 1-kilogram bag of potatoes – these standards will ultimately be used to calibrate the world’s weighing systems, from accurate scientific instruments, right down the chain to domestic scales.”
Scientists said the system might go into effect by 2014.