Calls for Kilogram to be Redefined (Physicists Have Had Enough of the Wait)

Calls for a redefinition of the kilo are coming from the National Institute of Standards and Technology (NIST) since, unlike all other international standards, it is defined by a physical object - a platinum-iridium alloy kept in Paris.

The metre, for example, used to be calculated as ten-millionth of the distance from the north pole to the equator but has been updated to be the distance light travels in one 299,792,458th of a second.

A lump of alloy, on the other hand, is subject to slight deviations and does not remain constant. Also, it means that other nations have to rely on regular trips to the French capital to calibrate their standard masses.

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