Friday, 22 February, 2019

Kilogram, Amp and Kelvin Redefined in Largest Units Overhaul Since 1875

Kilogram gets a new definition Kilogram, Amp and Kelvin Redefined in Largest Units Overhaul Since 1875
Melinda Barton | 18 November, 2018, 08:18

FILE - A replica of the International Meter Prototype is pictured at the International Bureau of Weights and Measures, in Sevres, near Paris, Oct. 17, 2018.

The metric system - or, as it is known today, the International System of Units (SI) - is an awesome achievement of mankind.

Countries until now were also occasionally forced to send their own kilogrammes to France to be checked against the Le Grand K to see whether their mass was still accurate. Since energy and mass are deeply interconnected according to Einstein, researchers are able to use Planck's constant in order to precisely calculate mass, with the added benefit that it will not change over time. Their bathroom scales won't get kinder and kilos and grams won't change in supermarkets.

In future the kilogram is likely to be defined using the Planck constant, a quantum value that sets the fixed ways atoms can vibrate.

Unlike a physical object, the new formula for the kilo, now also known as "the electric kilo", can not pick up particles of dust, decay with time, or be dropped and damaged. This will result in a more democratic system and that is something we can definitely get behind! "We're in chaos", said Barry Inglis, a scientist from Australia. Everything else-the kilogram included-must adjust to this definition. Measuring masses much smaller than a kilogram will be easier now. In humankind's efforts to quantify and understand the world, stretching back centuries to when ancient Babylonians measured mass with stones, the vote marked a major milestone, scientists agreed.

Others, like these researchers from the National Institute of Standards and Technology in the USA, had a more permanent approach to their celebrations, by tattooing the re-defined unit onto their arm. "That was just leaving me in a puddle of tears".

Other SI units with new definitions include the mole, kelvin, ampere, and candela.

The new definitions impact four of the seven base units of the SI: the kilogram, ampere, kelvin and mole; and all units derived from them, such as the volt, ohm, and joule.

They made the change as the "Grand K" was losing mass: equivalent to the weight of a eyelash. L-to-R: Eric Lin, director, Material Measurement Lab, NIST; Claire Saundry, director of International and Academic Affairs Office, NIST; Willie May, U.S. member of the International Committee on Weights and Measures and former NIST director; NIST Director and Undersecretary of Commerce Walter Copan; Barbara Cordero, finance analyst, Office of Management Policy and Resources, IO, Department of State and James Olthoff, Acting Associate Director of Laboratory Programs, NIST.

Even in retirement, the "Grand K" and its six official copies - collectively known as "the heir and the spares" - will still be kept in the high-security vault on the outskirts of Paris where they are stored.