Metric Flux: A “Constant” Dilemma

As a girl with a hard-on for science, I am a cheerleader for the metric system. Naturally. Base 10 all the way, baby.

The current iteration of ye olde metric system is the International System of Units (SI). See, back in the 19th century, use of the metric system was sloppy and uncoordinated according to the rigorous dictates of science. While the scientists were all using a system in base 10, there was no consensus on what the fundamental units for each quantity were. Everyone was using kilograms, but there was no definitive chunk of mass out there that was the kilogram. Depending on the scientific discipline, some of the fundamental units… wavered a bit.

And so, in the 20th century, it was decided that we were going to rationalize the system of measurement, which eventually led to the 1960 birth of SI. But, who decided this? The General Conference on Weights and Measure (CGPM- the acronym, like that of SI, comes from the French name), that’s who. These badass motherfuckers are one of three bodies in charge of overseeing the metric system. They’re like monks charged with watching over an ancient relic so that a dark prophecy can’t come true. Except, unlike the monks who invariably fail, the CGPM is actually doing its job.

Oh snap.

The CGPM has done a lot in the history of the metric system. They are the ones who decide what units are needed and define them. Made up of delegates from its 55 member states and 34 associate states (and yes, despite being the retarded cousin of the measurement world, even the USA is a member state), they meet once every four years in Paris. Unsurprisingly, the CGPM is notoriously slow and bureaucratic.

Now, even before the SI came about, scientists were aware of the need for universal standards in fundamental units. That’s why the very first meeting of the CGPM in 1889 defined precisely what the kilogram was and crafted the international prototype kilogram (IPK), a platinum-iridium (god, I’m never going to be able to talk about iridium again without thinking of this fucking song) cylinder kept at the International Bureau of Weights and Measures in France. Dozens of exact copies were made and distributed around the world. And so, we had a perfect definition of the kilogram.

Or so we thought.

Horror of horrors, in 1949, we discovered that all those supposedly perfect same-mass cylinders had masses that were drifting apart from one another. Upon checking again in 1989… we found the problem hadn’t just gone away (no shit, right?). The average difference was about 50 micrograms (the mass of a grain of fine salt), which might not seem like much to you, but holy shit, that’s a big deal for scienceland. Remember, the science requires incredibly precise measurements. Hell, one of the biggest criticisms of that FTL neutrinos experiment right now is that their measurements might have been off by infinitesimally small amounts.

Anyway, with drifting IPK values, we were back in the same goddamn boat as before the SI was implemented. We had multiple base standards floating around.


So, the CGPM has had to rethink its standards. If the kilogram is fucked, so is the mole. And this isn’t the only problem with the system. The kelvin is defined by the property of water in a certain state, which makes precise measurements at very high or low temperatures impossible. Oh, and the ampere? Yeah, its definition is so fucking impractical that scientists actually ignore the SI definition and turn to a definition based in quantum processes instead.

That means four of the seven units are all fucked up (the candela can wait). There just has to be a neater way to define them.

And there is!

It has been proposed that we take those four troublemakers and tie them to some of the fundamental constants of the universe. For the kilogram, Planck’s constant. For the mole, the Avogadro constant. The kelvin would get Boltzmann’s constant, and the ampere would get the elementary charge carried by one proton or electron.

Here it is in handy chart form!

Sounds magical (or, rather, sounds scientific, which is more badass than magic, anyway… also, it’s real), but proposing an idea and having the CGPM actually okay it are two different things. Because the CGPM meets so infrequently and is slower than a bale of turtles1  slogging through a pool of peanut butter.

The intrepid reformers had their work cut out for them, as they had to convince the conservative elements within the CGPM that the changes were necessary. They brought up the fact that, back in the day, the meter was defined by a scratch on a metal bar and the second was related to the rotation of the Earth. But these are not precise enough for some of the most useful measures of time and distance today, such as the use of satellites for GPS.

The final presentation was on October 17. A mere ten minutes in length, the future of the SI rode on the outcome of the vote on the proposition (well, that and five days of behind-the-scenes talks and lobbying).

The result?

The CGPM has backed the proposed changes. Unanimously.

Now, the new system won’t go into place yet. It has to pass another CGPM vote… four years from now. But if it does, we’re looking at historic change.

1 Fun Fact: My very first memory of going to the public library and actually using it for research (back before I had ready access to the interwebs) was to finish a school assignment where I had to list the group names for various animals. Why they can’t all just be herds is fucking beyond me.

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