Aside from a yearly ceremonial peek inside its vault, which can be unlocked only with three keys held by three different officials, the prototype goes unmolested for decades. Yet every 40 years or so, protocol requires that it be washed with alcohol, dried with a chamois cloth, given a steam bath, allowed to air dry, and then weighed against the freshly scrubbed national standards, all transported to France. It is also compared to six témoins (witnesses), nominally identical cylinders that are stored in the vault alongside the prototype. The instruments used to make these comparisons are phenomenally precise, capable of measuring differences of 0.0000001 percent, or one part in 1 billion. But comparisons since the 1940s have revealed a troublesome drift. Relative to the témoins and to the national standards, Le Grand K has been losing weight — or, by the definition of mass under the metric system, the rest of the universe has been getting fatter. The most recent comparison, in 1988, found a discrepancy as large as five-hundredths of a milligram, a bit less than the weight of a dust speck, between Le Grand K and its official underlings.
This state of affairs is intolerable to the guardians of weights and measures. “Something must be done,” says Terry Quinn, director emeritus of the International Bureau of Weights and Measures, the governing body of the metric system. Since the early 1990s, Quinn has campaigned to redefine the kilogram based not on a physical prototype but on a constant of nature, something hardwired into the circuitry of the universe. In fact, of the seven fundamental metric units — the kilogram, meter, second, ampere, kelvin, mole, and candela — only the kilogram is still dependent on a physical artifact. (The meter, for example, was redefined 30 years ago as the distance traveled by light in a given fraction of a second.)
For Economicus, these are the Holy Relics!
ROFLMAO!
Actually, I suppose there are ramifications beyond economics, & it's pretty interesting.
No one can say for sure why the prototype and its brethren are drifting apart. One rather obvious possibility, suggested by Taylor, is that the national prototypes and even the témoins have been used more often than Le Grand K, which has been handled only three times since 1889. The handling could subtly contaminate the surface. A more exotic theory posits that slight variations in Matthey’s alloy lead to different rates of outgassing, the technical term for the gradual escape of gases trapped in the metal. Whatever the explanation, the divergence is problematic, and not only for theoretical reasons. In fields ranging from particle physics to global commerce, the erratic behavior of the master kilogram shows that a system of measurement based on a physical artifact can’t be trusted. “This is simply not a satisfactory situation,” Quinn says. “You have an object made with the technology of the 19th century upon which a very large proportion of modern measurements are based — not just mass, but electrical measurements and measurements of force and heat and light.” The metric energy unit known as the joule, for example, is defined in terms of the work needed to move a 1-kilogram mass a given distance over a given time period. And the luminosity of light, or candela, is measured in terms of power, designated in watts, or joules per second. In other words, if the kilogram is unreliable, the joule and the candela become unreliable as well. Nobody at the grocery store is fretting over whether a kilo of bananas is a speck of dust lighter or heavier than in their great-grandparents’ era, but the change could eventually matter enormously to engineers optimizing computers and fiber-optic networks.