|copy of the|
international prototype kilogram
The official kilogram, a cylinder of platinum and iridium maintained by the International Bureau of Weights and Measures, is more than 130 years old. It is stored under three glass domes in a safe in a basement in Sèvres, France, and can be accessed only with three independent keys.One would also assume that such a unit is accessible, which this cylinder is not; kept under glass. Though there are several replicas around the world which are periodically checked with the IPK.
Technically, the cylinder is not even the official kilogram until it has been cleaned in an authorized manner to remove contaminants. It is the only remaining international standard in the metric system that is still a man-made object. Some scientists now believe the official kilogram may be losing mass, which defeats its only purpose: constancy. This adds new urgency to a longstanding search for a new official kilogram, based, like the meter, on one of nature’s fundamental numbers, called constants.
So we may see a future definition based on fundamental constants rather than objects. Of course this inhibits us measuring whether or not these constants are in fact constant over space and time.