The universe is growing mass!!!

 …or is our unit of measure shrinking?

…holding her hand on the top of her head to feel which way it was growing
— Alice's Adventures in Wonderland by Lewis Carroll

There are real problems in living in the same universe you are trying to measure. The French Academy of Sciences in 1791 sought to put an end to the myriad standards of measurement in every other French town and set one standard "for all people, for all time." Over time these standards have been untied from a physical artifact, which the French never really wanted in the first place, to what, we hope, are constants.

For example a meter was intended to be one ten-milllionth of the distance from the North Pole to the equator. But in 1983, the relationship between the meter and the speed of light was officially inverted, with the meter being redefined as “the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second.” (The second, in turn, being defined by certain fundamental properties of the cesium 133 atom.)

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 American prototype is one of some four dozen such national standards around the world, and each of those, in turn, is accountable to an even higher authority: a regal artifact called the international prototype kilogram. Familiarly known as Le Grand K and held in a vault just outside of Paris under three bell jars, it dates back to the 1880s, when it was forged by the British metallurgist George Matthey from an alloy of nine-tenths platinum and one-tenth iridium. As a metric unit, the kilogram is “equal to the mass of the international prototype,” according to the official definition. In other words, as metrologists like to point out, it has the remarkable property of never gaining or losing mass. By definition, any physical change to it alters the mass of everything in the cosmos. 

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.

Here is a fascinating history of the search for a universal, immutable standard for the kilogram.

[This is referenced on Kottke, but I wanted to spread the fascination.]