The kilogram has put on weight, but not too much. Just a few micrograms.
British researchers at Newcastle University revealed on Monday that the original kilogram is likely to be tens of micrograms heavier than it was when the first standard was set in 1875. They used a state-of-the-art Theta-probe XPS machine, the only one of its kind in the world, to measure the weight gained by the standard kilogram.
“Statute decrees the IPK (international prototype of the kilogram) is the kilogram,” lead researcher Peter Cumpson, professor of MicroElectroMechanical Systems at Newcastle University, said. “It doesn’t really matter what it weighs as long as we are all working to the same exact standard — the problem is there are slight differences. Around the world, the IPK and its 40 replicas are all growing at different rates, diverging from the original.”
The first standard kilogram was set in 1885 and the international prototype of the kilogram was sanctioned in 1889. “Its form is a cylinder with diameter and height of about 39 mm. It is made of an alloy of 90 per cent platinum and 10 per cent iridium. The international prototype has been conserved at the BIPM near Paris since 1889.”
The researchers, however, said that people should not expect to become a bit lighter just because the kilogram had become a bit heavier.
He explained that the change would have a huge impact on trade. “But mass is such a fundamental unit that even this very small change is significant and the impact of a slight variation on a global scale is absolutely huge.”