The Measure of All Things

On Friday a white sedan with “County of Morris Weights and Measures” painted on the doors was parked outside the supermarket where I most commonly shop. An inspector was likely inside the store checking the scales. There is also a statewide agency and a national one. Inspectors from various levels of government in all parts of the world have been performing much the same job for thousands of years. I’ve seen the car in the parking lot before, but it caught my attention more than usual this time because of an item in the news about weight – or, more accurately, mass. This past week the world got a new kilogram. Regrettably, it isn’t different in value from the old one, so if you have a metric bathroom scale (which I recommend just because the number in kilograms is so much lower than the number in pounds) you don’t get to recalibrate it. The value remains the same but it is calculated differently.

Standard weights and measures existed in Sumerian times. They were a necessity for trade then as they are now. There had to be some way of expressing how much of this one would trade for how much of that, and of course taxes (originally in goods – usually grain) had to be calculated somehow. Sumerian inspectors, like those of Morris County today, existed to counter the perennial temptation of traders to tinker with scales. Even after the invention of coinage in the sixth century BCE, the coins commonly were weighed when delivered because of the illegal but common practice of shaving gold and silver coins in hopes of passing them off at full face value while keeping the shavings. Larceny has never been far from the human heart. Inevitably there were discrepancies from port to port when measuring weights, lengths, and even time, since all standards were local. These problems continued into the 18^th century when the need for better standards grew more important not only for trade and industry but for scientific inquiry. Perhaps the most lasting benefit to have come from the French Revolution is the metric system adopted in 1795. The U.S. made the metric system official (yes, it really did) in the Metric Act of 1866; the English system is not official and never has been even though Americans cling stubbornly to it in everyday use, but for regulatory purposes its units are defined by metric conversion factors.

The metric system from the start was intended to be based on natural properties: the gram, for example, originally was the weight of 1 cubic centimeter of water and the meter was 1/10,000,000^th of the distance from the equator to the North Pole. Physical conditions can affect these measurements, however, so they were swapped out for physical objects by the end of the 19^th century. The meter became a platinum-iridium bar and the kilogram until this past Monday was a cylinder of 90% platinum and 10% iridium sitting in a case in Sèvres. These, too, presented problems. The length and mass of these objects are not constant but change slightly due to contamination and oxidation, so in the latter half of the 20^th century an effort was made to define metric units in terms of constants. In 1960 the meter was redefined as the distance light in a vacuum travels in 1/299,792,458 second. But what is a second? It is not enough to say it is 1/86,400^th of a day, because the length of a day varies as earth’s rotation rate varies with changing sea levels. In 1967 a second was redefined as the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium 133 atom, even though this means International Atomic Time drifts slowly from Universal Time (the common clock based on the earth’s rotation). The kilogram for a long time resisted efforts at redefinition since various proposed redefinitions proved to be ultimately circular. On Monday, however, the kilogram finally got a non-circular redefinition in terms of the Planck constant. We also got new definitions of the kelvin, ampere, and mole in terms of natural constants.

Happy Retirement

It’s often said that the important things in life can’t be measured, such as the value of freedom, affection, kindness, and contentment – or for that matter hate, meanness, and anguish. This might not be entirely true. One frequently can determine a cash value of something like stress or some aspect of freedom by seeing how much money a person will demand to suffer the former or surrender the latter. There may well be an exact number. However, there is little doubt that such measurements are subjective: your dollar figure will be different from mine, whereas your kilogram is exactly the same as mine. The new definitions don’t much impinge on my daily routine. I won’t be buying a cesium atomic clock to tell time; I’ll continue to rely on my $11 watch even though I need to adjust the hands a little every couple of months. Nor will I be calculating my mass from scratch in terms of the Planck constant; I’ll step on my bathroom scale, which is probably off by 1% or so. Nonetheless, it’s nice to know those things in principle can be done. In a largely subjective and all too often polarized world, it is reassuring that some things, at least, are objective.

Lord of The Lost – The Measure of All Things