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Friday, October 7, 2011

Redefining standard units


An international team of researchers is in the process of redefining two international standard units to be more in line with the constants of nature.  If the rest of the scientific community accepts their results, we may have new standards for the measurement of mass and of electrical current.

The Système Internationale d'unités (SI) includes seven definitions of measurement that are used to calibrate everything else.  However, some of those definitions rely on factors are not as immutable as we might hope.  For example, mass is measured in kilograms, which are currently defined as the mass of a specific block of platinum-iridium alloy.  That means that everything in the universe weighs some number of these nuggets of alloy.  What if the ‘International Prototype Kilogram’ got damaged?  Much better to have that measurement defined by an unchanging constant. 

To that end, scientists led by T.J.B.M. Janssen of the National Physical Laboratory at Teddington are studying the quantum Hall effect in graphene.  This effect relates electrical resistance to the Planck constant and to the electron charge.  If the quantum Hall effect turns out to be universal, it will allow researchers to redefine the kilogram in terms of the Planck constant and amperes (measurements of current) in terms of electron charge.

You can watch Janssen’s description below.




By the way, the other SI units are the meter for distance, the second for time, the Kelvin for temperature, the candela for brightness and the mole for amount.