You may not be aware of the fact, but physicists express your waistline in volumes of platinum with iridium. Does that make you feel uncomfortable? They agree!
A team of American, Swedish, French and British scientists want to relate the kilogramme for mass (m) and the ampere for electric current (I) to the fundamental constants of nature, respectively the Planck constant h and the electron charge e.
But can we? Different kilograms of mass we can balance and compare and amperes we can measure as a force between two conducting wires. Nature’s constants h and e are however theoretical. They do their work in calculations, but you cannot see or otherwise sense them.
Scientists have found a relation though between m & I and h & e, in what they describe as the quantum Hall effect, a voltage difference within a conductor – on the quantum mechanical level.
Closing in with graphene
It has been tested using conventional conductors, which leave a margin of uncertainty. In the first SI experiment to use that new superconductor graphene the international research group thinks it has come very close: supporting the kilogram and ampere redefinition up to an uncertainty of just 86 parts per trillion, as they write in Wednesday’s edition of Nature. The researchers have also just published their findings investigating the quantum Hall effect with graphene to redefine SI Units in the New Journal of Physics.
If the new definition is accepted it will be the biggest change since the SI Units were universally introduced 51 years ago.
© Rolf Schuttenhelm | www.bitsofscience.org