The future of the kilo is a matter weighing heavily on the minds of scientists around the world.
The kilo is a much revered and polished lump of metal resting under two bell jars in the International Bureau of Weights and Measures headquarters outside Paris, France.
Sitting undisturbed except for an occasional dusting, the kilo is a polished cylinder of platinum and iridium alloy that is the keystone against which every other kilo is measured.
Even though the replicas held around the world are no more than a milligram out, they are not accurate enough.
And the world’s scientists are contemplating the catastrophe a fire or other event could cause if the original kilo was destroyed.
So they have voted for a virtual kilo.
The virtual kilo
The virtual kilo will allow measurements to within a billionth of a gram and finally put to rest the fear of the demise of the keystone kilo.
The original kilo derived from the mass of a given volume of water at zero centigrade and spawned the metric system.
The new is the Kibble balance, an electromechanical weight measure that assesses the weight of an object by the strength of an electric current and a voltage passing through.
“One key reason for doing this work is to provide international security,” said Ian Robinson, a fellow at the National Physical Laboratory, London.
“If the Pavilion de Breteuil burned down tomorrow and the kilogram in its vaults melted, we would have no reference left for the world’s metric weights system. There would be chaos. The current definition of the kilogram is the weight of that cylinder in Paris, after all.
“We are going to change all that. We are going to create a method for weighing the kilogram completely accurately until the end of time. We will have released ourselves from a single point of failure.”
The kilo is not the first metric measure to fall to modern technology:
- Time – Once a second was 1/86400 of an average day. Now, it’s the time a caesium atom takes to vibrate 9,192,631,770 times
- Length – the metre was 1/10 millionth of the distance from the equator to the north pole represented by a platinum bar. Now, the metre is the distance travelled by light in a vacuum in 1/299,792.458thof a second
Temperature, electric current and luminous intensity have all had make overs as well.