MS. REBECCA SHEIR
This next story on today's "Falling" show is about something that's falling kind of out of whack. It's the official kilogram of the United States, and yes, there is an official kilogram of the United States. It's a copy, actually, of a platinum iridium kilogram that's stored in France. But anyway, the copy, which you can find in Gaithersburg, Md, is used to calibrate everything from gas pumps to bathroom scales. But, as Sabri Ben-Achour explains, the weight of our official kilogram is ever so mysteriously changing.
MR. SABRI BEN-ACHOUR
So, back in the day, doing trade between countries was kind of tough at times.
I'll give you a very good deal, I'll give you ten smirdlaps (sp?) of spices for two gold pieces.
I don't know what a smirdlap is, but it sounds foreign and untrustworthy. So how about 15 what you call its of spice for three gold pieces?
You are trying to rip me off.
Well, it wasn't that simple at all, but still.
MR. PATRICK ABBOTT
You know, if you're measuring mass in smirdlaps and I'm measuring them in whatcha calls, then somehow, if you and I want to do business, then I have to know how many smirdlaps are in a whatcha call, to ensure fair trade.
That's physicist Patrick Abbott. In 1875, 17 nations got together and decided they needed a standard definition of weight and length so they could all follow the metric system reliably. They made a platinum iridium cylinder that was to be the standard, like the definition of the kilogram, for the planet. They kept the original in France, and then made official copies of it, and one of them is here. Well, just behind this door. And this other door. And a couple more doors.
Two bell jars, three panes of glass here, and if you want to start counting locks, normally four, five, six.
And then, it's usually in a safe.
Anything at all will change the mass. Anything on the surface.
It's metallic, silver looking, perfectly polished, and small -- just a little bigger than a golf ball.
It is a cylinder of platinum iridium, 90 percent platinum, 10 percent iridium, and it was made in approximately 1889.
This is the kilogram for the United States of America, kept behind lock and key at the National Institute of Standards and Technology in Gaithersburg. Every prescription you take, every pound of fruit you buy, every ounce of self-loathing you feel when they you at your scale is all calibrated to this piece of platinum iridium metal.
Everything that is sold, you know, this is sold by weight, is ultimately related to the kilograms, trillions of dollar industry.
But, there's a small problem.
It is changing.
The definition of the kilogram is changing. The original in France and the copies don't match anymore. The standard in France is losing mass, compared to the copies.
How is it possible that it could change?
It could be losing mass as a result of things coming out of it. For instance, gaseous impurities can diffuse out. No one really knows.
The point is, is that it's changing. Now, this change is not like by a whole lot.
Fifty micrograms over the last 100 years.
So like a grain of sand?
Grains of sand are actually pretty heavy. They would be on the order of hundreds micrograms.
Maybe a human hair? An eyelash?
No, that's a pretty -- eyelashes are pretty thick, actually. The smallest piece of dust you can see, it's about 17 micrograms.
OK, so we're talking a little less than three particles of dust.
Yes, yes, yes, over 100 years.
So, like, who cares?
MR. MARK RUEFANACHT
The drift in the kilogram becomes important to me because of the precision and the accuracy that's required for my particular laboratory.
Mark Ruefanacht calibrates scales for a living. He’s with Heusser-Neweigh and sometimes teaches at the National Institute of Standards and Technology.
In our particular laboratory, we definitely see those changes. We are always adjusting for the latest information from the calibrations that we receive from NIST, and in essence, there is some frustration because it always feels like we've got this moving target.
So that means he can't guarantee the measurement of super, teensy, tiny amounts.
We’re already seeing the need for measuring these smaller things in the biotechnologies and in the pharmaceutical worlds.
Pharmaceuticals already measure things out in pretty small quantities.
If you think about a pill that you take, often times there's only a few milligrams, or what we would say, a few grains of salt that are actually the active ingredient in each pill. The rest of it is just kind of starch or filler that helps us swallow down that active ingredient.
So what scientists in governments around the world are trying to do is get rid of the kilogram. Not the idea of the kilogram, but the piece of metal. So they're trying to tie the definition of the kilogram to something cosmically stable. So they're looking at something called Planck constant.
The Planck constant is a constant that arises out of quantum mechanics.
That's physicist Patrick Abbott again.
But that depends then on the electrical parameters, like the Josephson...
Look, it's just math, OK? It's a number relating light and energy.
It comes up over and over and over again in quantum mechanics.
They're also looking at something called Avogadro's constant. The point is, is that these things aren't going to change. And they've done this for a few other units, like a second is defined by the time taken for a certain number of changes in a cesium atom. Or a meter is related to how far light travels in a certain period of time. But for the kilogram, they can’t quite measure the physical constant that they need, the Planck constant, well enough for it to be worthy of being an international standard. So more and more countries are trying to get this right over the next few years.
Until then, those platinum iridium cylinders are the standard, even as they ever so slowly and mysteriously drift apart from one another. I'm Sabri Ben-Achour.
For pictures of the U.S. kilogram and more on its history, visit our website, metroconnection.org.
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