Transcripts

Metal Cylinder Holding Weight Of The World Mysteriously Changes

MS. REBECCA SHEIR

00:00:04
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

00:00:38
So, back in the day, doing trade between countries was kind of tough at times.

UNIDENTIFIED MAN

00:00:42
I'll give you a very good deal, I'll give you ten smirdlaps (sp?) of spices for two gold pieces.

UNIDENTIFIED WOMAN

00:00:49
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?

MAN

00:01:00
You are trying to rip me off.

BEN-ACHOUR

00:01:02
Well, it wasn't that simple at all, but still.

MR. PATRICK ABBOTT

00:01:04
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.

BEN-ACHOUR

00:01:20
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.

ABBOTT

00:01:50
Two bell jars, three panes of glass here, and if you want to start counting locks, normally four, five, six.

BEN-ACHOUR

00:01:59
And then, it's usually in a safe.

ABBOTT

00:02:02
Anything at all will change the mass. Anything on the surface.

BEN-ACHOUR

00:02:04
It's metallic, silver looking, perfectly polished, and small -- just a little bigger than a golf ball.

ABBOTT

00:02:10
It is a cylinder of platinum iridium, 90 percent platinum, 10 percent iridium, and it was made in approximately 1889.

BEN-ACHOUR

00:02:20
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.

ABBOTT

00:02:38
Everything that is sold, you know, this is sold by weight, is ultimately related to the kilograms, trillions of dollar industry.

BEN-ACHOUR

00:02:44
But, there's a small problem.

ABBOTT

00:02:47
It is changing.

BEN-ACHOUR

00:02:48
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.

BEN-ACHOUR

00:02:59
How is it possible that it could change?

ABBOTT

00:03:03
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.

BEN-ACHOUR

00:03:14
The point is, is that it's changing. Now, this change is not like by a whole lot.

ABBOTT

00:03:19
Fifty micrograms over the last 100 years.

BEN-ACHOUR

00:03:21
So like a grain of sand?

ABBOTT

00:03:23
Grains of sand are actually pretty heavy. They would be on the order of hundreds micrograms.

BEN-ACHOUR

00:03:28
Maybe a human hair? An eyelash?

ABBOTT

00:03:30
No, that's a pretty -- eyelashes are pretty thick, actually. The smallest piece of dust you can see, it's about 17 micrograms.

BEN-ACHOUR

00:03:40
OK, so we're talking a little less than three particles of dust.

ABBOTT

00:03:46
Yes, yes, yes, over 100 years.

BEN-ACHOUR

00:03:48
So, like, who cares?

MR. MARK RUEFANACHT

00:03:51
The drift in the kilogram becomes important to me because of the precision and the accuracy that's required for my particular laboratory.

BEN-ACHOUR

00:03:59
Mark Ruefanacht calibrates scales for a living. He’s with Heusser-Neweigh and sometimes teaches at the National Institute of Standards and Technology.

RUEFANACHT

00:04:05
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.

BEN-ACHOUR

00:04:23
So that means he can't guarantee the measurement of super, teensy, tiny amounts.

RUEFANACHT

00:04:27
We’re already seeing the need for measuring these smaller things in the biotechnologies and in the pharmaceutical worlds.

BEN-ACHOUR

00:04:34
Pharmaceuticals already measure things out in pretty small quantities.

RUEFANACHT

00:04:37
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.

BEN-ACHOUR

00:04:51
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.

ABBOTT

00:05:07
The Planck constant is a constant that arises out of quantum mechanics.

BEN-ACHOUR

00:05:11
That's physicist Patrick Abbott again.

ABBOTT

00:05:13
But that depends then on the electrical parameters, like the Josephson...

BEN-ACHOUR

00:05:17
Look, it's just math, OK? It's a number relating light and energy.

ABBOTT

00:05:23
It comes up over and over and over again in quantum mechanics.

BEN-ACHOUR

00:05:26
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.

BEN-ACHOUR

00:05:56
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.

SHEIR

00:06:08
For pictures of the U.S. kilogram and more on its history, visit our website, metroconnection.org.
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