Radiolab - ≤ kg

Episode Date: June 13, 2014

A plum-sized lump of metal takes us from the French Revolution to an underground bunker in Maryland as we try to weigh the way we weigh the world around us.

Wait, you're listening. Okay. All right. All right. You're listening to Radio Lab. Radio Lab. Shorts! From W. N. Y.

C. C? Yes. And NPR. Hey, I'm Chad. I boom run. I'm Robert Krollwitch. This is Radio Lab, the podcast.

And this? I actually brought a list. Okay. Let's want you to share with me your list. Where is this thing? This is Andrew Moran. He's a writer and editor at the New Yorker magazine. Oh, I might have gotten lost.

Who occasionally pops onto our show. Maybe you were mugged. Maybe. Ah, here it is. And he recently got obsessed with a list of measurements. Base units, they're called. There's, they're SI base units. The System International, you know.

So let me do it this way. Have you ever wondered how long an inch is? I'm exactly how long. I know. I just look at a ruler. Well, but how do you know that you're, ruler and my ruler do have the same amount of inch space or that someone in China, that their inches are inches, your inch is my inch.

I haven't really thought about a bit. I'm just assumed that there's like a master inch somewhere. Bien-sue. I say it in French for reason, which you'll feel it in a moment. That is what was on this list that Andrew was looking at. It's a list of standard measures for everything we have around how big something is, how far something is, how hot something is. It's all on this list.

Okay. So when you go down the list of the system. System International de Units. Here's what you get. A meter is a fraction of a second of the distance traveled by light in a vacuum. Okay. A second is how much radiation corresponds to the transition between two hyperfine levels of the ground state of the cesium 133 atom. That's the definition of a second?

How many times does that particular atom jiggle? Yeah. An ampere, which measures electric current. You know, an amp. is a constant current, which, if maintained in two straight parallel conductors of infinite length, would produce between these conductors a force equal to two times 10 to the negative 7th Newton's per meter of length. I have no idea what that means. See, that's the thing. If you look at the actual definitions, any of these things, am, meter, second,

whatever, you go. But there is one standard on the list that is unique for its simplicity. The definition of the standard unit of measurement that is a kilogram is... No man. No numbers. It is a thing. A particular thing? A plum-sized thing. It is the only thing we use to measure things. It's the last one standing.

The only physical standard left. Why is it the last? And why were there? Is it what? Wait, what? Let me just take you back to the beginning of the story. Like, I must admit that I expect Did this story to be a lot more boring that I found.

It's like an epic story. That is Latif Nasser, science historian, regular on our show. And he says, if you go all the way back to the very first farmers back in Mesopotamia. All of the earliest measurements were super intuitive. And he says a lot of them came from the body. As in that bunny is coming close to the net. How close, Dad? Two hands.

But it's not just like, because we think of like hands and feet, but it was also there so many other kinds of measurements like you, would say, oh, something is as far as, you know, my voice can carry. Something is as far as I can see sitting on the top of a camel. Or something is as far as I can throw a stone. So that would mean, like, say, okay, I'm going to build a farm here, and I'm going to do it three throw rocks across? Yeah, yeah.

The way I read about it was, like, travelers. Like, if you're a Saharan traveler, you know, and you need to know where the next watering hole is, that's kind of a life and death measurement. They would say it's, you know, three throwler rocks away or it's 10 throw rocks away. But, you know, there might be some built-in uncertainty there because if you ask Achilles, it could be two throw-a-rocks away, but if you asked me, it would be like 78. You have nailed exactly the problem with the throw-or-rock system. And these problems kind of came to a head

in the 1700s. It's the eve of the French Revolution. In a little town called Paris. It's a pretty cosmopolitan place, which means that people are coming from different places and they all have their own measures. Approximately 250,000 different units of measurement in regular use. 250,000. Every

commodity has its own measure, so you have grain, wine, oil, salt, hay, coal, wood, fabric, everything. And it's extraordinarily confusing. Not to mention, it's extraordinarily bad for trade. So if I came to you and I said, Monsieur, I have a bit of cloth. You would

say, how much cloth you got? And I say, I have two yards. And you say, what's a yard? I said, it's this much. And my other guy said, no, no, no, is this match? And I was, no, no, it's this match. And I said, no, it's this match. And you could see the... Frustrating. It was frustrating.

Yeah. And make it matters worse. In the 1780s, there was a famine. So there was a shortage of grain, and people were hungry and people were angry, which I am going to call that they were hangary.

They were hangary. They were very hangary. So the bakers at the time, they knew that if they raised the price of bread, like an angry mob would basically come and kill them. But they also knew that with no absolute standard, there was no way to be sure that what you were getting is what you were getting.

And so what they started doing was they started just lightening their bread loaves by just a little. So as the famine got worse, people would be waiting in longer and longer lines to pay the same amount of money for smaller and smaller and smaller loaves. So they were getting hangrier and hangrier. And so one of the things that people

are like crying out for is that they want standardized weights and measures. If I go to the bakery and I buy a loaf of bread, I want a whole loaf of bread. Don't short me on this. This is serious. Well, you know what happens next. The Bastille is stormed and the king is under house arrest and then under the guillotine. And as soon as the revolutionary government takes over, they say, all right. Okay, this is one of our first priorities. We are going to make a new standard. But not based on something arbitrary like a king.

This is the Enlightenment. Why don't we draw on some kind of totally different authority? The authority of nature. Of nature. Of nature. So, long story short, they took the circumference of the earth. They took a quarter of that circumference. Divided that by $10 million, and they got the meter.

The meter, they then divided. by 10, cubed it, filled the cube with water, took the mass of the water, minted a cylinder of metal with that mass, and voila, they created the world's first kilogram. The idea of this was, if we make this thing that is so beautiful and perfect and everybody can see it that way, then not only will France use it, but the whole world will use it, then goods and ideas can be exchanged everywhere by all people, and it will be beautiful and glorious. Fraternity, Egality. Exactly.

They wanted something that would be eternal and unchanging for everybody for all time. So now I guess you want to see it, no? Yeah. Okay. Okay, so it's in here. We ended up visiting the National Institute of Standards and Technology in Maryland. And this is where we'll be going in. This guy, Patrick Abbott, physicist, was our guide.

They took us three stories down into the bedrock of the... state of Maryland because they want things down here to be totally still. We've just gone through one double door. Here comes another double door. Then we stepped into this vault of a room and there it was. What we're looking at then is a glass jar with a little handle on top and then inside that is another glass jar with a little handle on top and inside that is the thing. The thing. It's kind of gorgeous really the shiniest little cylinder you've ever seen

very small and it looks very clean doesn't it too? Yeah it's almost hard to tell where the like Russian doll glass jar stops because it's so reflective this might be a crazy question but can we hold a kilogram? That's our producer Linlevi no

I'm just curious to know what it feels like we've been talking about it so much they are very careful with the kilogram and this isn't even really the real one, the original of the original of the original of the original. Le Grand Caas, as they call it. Lives in a basement in France.

You can't get anywhere near that one. I could. No, you couldn't. I could get all Tom Cruise on that. You die trying. Here's how it works. The international prototype is... Big Gajuna. That's the one used to calibrate six identical platinum cylinders. What they call witnesses,

or Tamois in French. Those witnesses are then used to calibrate another set of cylinders, which are then used to calibrate the US standards, which is what we saw, and that one is used to calibrate all kinds of things, the weight of your lemons, the scale in your bathroom. Green team, you lost 34 pounds. Every time somebody loses a pound on that TV show biggest loser, 5.87%.

You can actually trace that like a bloodline, if you will, or an unbroken chain, back to the international prototype kilogram, to a single object in a basement in France, the holy of holies that is the kilogram. But you're telling me that when something is weighed in the world, often it goes all the way back to this one hunk of metal. That's what I'm saying. Which is why the next part of the story is so disconcerting. What happened in 1989...

Is that according to Andrew, the folks who take care of the official kilogram? The Big K... They took it out of its jars. They put it in a steam bath. Hit it with a steam that rinses everything. Wait for it to dry. Then... They commence a certain...

ceremonial weighing. Right. How do you weigh the thing that is the standard of weight? Well, you weigh it against the copies. Like the U.S. copy, for example, so they get one of those, and they put it on one side of the scale,

and then they put the Grand Cay on the other. And the IPK, the grandk, the one, is light. What? It's light. It doesn't... How many, how much lighter is it than its sisters? Roughly the mass of a grain of sugar.

Oh. Yeah. So... Is that gigantic? It's measurable. Wait, how do they know that it was light and not that the other ones were heavier? Right. Well, they didn't.

So they used the second sister copy. Still light. And the third sister copy. Still light. And the fourth and fifth and sixth. In comes the man from Germany. Light. In comes the man from Canada.

Light. In comes the man from Spain. Light. Which led them to the troubling possibility that the international standard for weight was losing weight. Well, we think that. We think the big guy. the problem. As far as how it lost that weight, really no one knows. One possibility is it got cleaned too much and maybe some of it got scraped away. Although it's disputed whether cleaning it more would

make it lose weight or gain weight. The other theory is outgassing. Like maybe a little hydrogen is seeping out of the metal. And then there was one thing I read that said foul play cannot be ruled out. Well see, I was thinking maybe the Taliban. Well, it's clear as we may have a slightly trippy situation here. We got a hunk of metal losing weight. And yet because it is the standard, It still weighs exactly a kilogram. Right? If the definition of a kilogram is the mass of the international prototype kilogram, whatever happens when you put that thing on the scale, that's a kilogram.

You can't do that. And then everything else in the world is wrong. No, you can't. It's ridiculous. That doesn't sit right. That's like something that like the North Korean government would do. Just be like, no more cash. Like that, we can't just go around capriciously doing stuff like that.

All right. So if the standard of weight is, as you're saying, losing weight, so how do you fix that? Well, I'm getting zero cell phone reception down here. That means we're really deep. When we were down in that underground room in Maryland, we met a guy who has some thoughts about this. Oh, there we is. Okay. His name's John Pratt. I'm the leader of the Fundamental Electrical Measurements Group at the National Institute of Standards and Technology.

Hi, John. John walked us through even more high security doors, and then we walked into this. Oh, my God. Amazing room. It's big. It is big. About three stories tall. And it's made of, it's like a silver room. It has a silver gray floor.

It has silver shiny walls. And your hair is on the silvery side. Very much so. You probably wouldn't be allowed in here if you were a redhead. No. No. I don't even know how to describe it. It looks like a wheel turned on its side with...

The thing itself looked sort of just like a massive round metal cauldron or like a big metal pot. But then there are all these weird little gizmos. parts and then all these coiled up wires and... It's just a stunning machine. But it's all just for the benefit of the one... The one measurement. The one kilogram. Yep.

Because inside that giant cauldron there is an extremely, extremely sensitive... Balance. An equal arm balance. Which is basically like a seesaw. Or a teeter totter. And usually you would set that up so that you would literally put kit on one side of the teeter-totter, kit on the other side of the teeter-totter. Now, you've been in a plet-totter. Now, you've been in a playground, so you know how this goes.

But what they've done here is on one side of the titter-totter, they've got the kilogram, like the grandk, that's kid number one. On the other side, instead of another kilogram, or kid two? We'll have a highly variable magnet. Now, here's the thing. The magnet won't be touching that side of the scale. It'll be exerting a force, an invisible force on that side. It'll produce a force, and we could use that to hold the balance still.

And the force it takes to hold up the balance, That, of course, is the same as the weight of the Gonca sitting on the other side. And if you can convert that force into a number that everybody agrees to, voila! You have just redefined the kilogram. You have wrenched it from the world of things, and it's become attached to the fundamental forces of the universe. Yep.

You've grasped the gist of it. You want to see that happen right now? I can show you this with our Lego version of the Wad balance. Okay. If I can fire it up. Lego? Lego one? Well, see, the big one was being tested or something,

so they took us over to look at the little one. Okay, so we have... Had a little scale and everything. You can see, I just disturbed the balance, and it's, you know, jiggling around a little... It's free floating. Okay, so you're now going with your tweezers and you're plucking a itty-bitty...

Yep, two-gram mass. He puts this tiny little thimble thing on the balance, and now it's going to... He says, levitate. Now, it's... See, it prompts me mass on. Mass on. Yeah, I'm gonna put the mass on.

He pushes a button. All right. And. Wait, but when do we see the levitation? That was it? I didn't, I missed it. Do it again. It was floating?

It is floating sitting on the balance. That's not floating. That is floating. Does it fall to Earth? That's a different idea of levitation. No, the truth is that once I finally figured out what this guy was doing, it was actually sort of cool. actually sort of cool. He had taken a little metal weight. He'd put it on one side of the scale. And on the other side of the scale, it was just empty. But yet, the thing didn't tip over because the

empty side actually had a magnetic force equivalent to the metal, holding it just perfectly still. So if they're able to do that, does that mean that the Grand K's reign is done? Not yet. No, because first of all, you have to get straight with a lot of math. MC squared equals H-new, work backwards. You've got to divide by E and then by M. Measure the B field. Woo, let's go. And then you get your amperes and your watts and your planks constant. Classic little bore model of atoms and stuff.

Anyway, it is actually way more complicated this whole thing than I frankly will ever understand. But here's where we are at. You got all these different teams around the world. You got John's team in Maryland with his seesaw. You got another lab. Actually, a couple of them that have their seesaws. You've got a third lab.

It's literally counting the atoms. They're all doing experiments, comparing numbers, trying to get the numbers to agree so that by whatever route, everybody agrees on exactly what a kilogram is. Right now, they're close. They're in agreement out to about six decimal places, and that's not good enough.

They want the numbers to agree out to eight decimal places. But if they can do that, then, and only then will the Grand K be no more. Yeah. Because instead of defining the kilogram as whatever is equal to the Grand K, now you have a new. definition. The new definition of the kilogram. The kilogram is the SI unit of mass. Its magnitude is set by fixing the numerical value of the plant constants be equal to exactly 6.626.069. And we have X's because

we haven't all agreed what the final... Those are the missing decimals. Those are the missing decimal places times 10 to minus 34. When it's expressed in the unit for action, joules seconds, which is a meter squared kilogram per second. That'll be such a simpler definition. Oh, yeah. And what will happen to the Grand K when the new definition goes into effect? Well, now, so this is the sad part.

It looks like a church. You will see after the end. The church where the Foucault. The Grand K may eventually end up in a place like this. That's a big deal. Where so many standards have gone to die. This is the Musees of Arts and Metier in Paris. So this is the beginning.

Zeril Faso is our tour guide. Yeah, what is this? A litre. He showed us the original liter. Or so is it 0.8. Wow, some early thermometers. There's one object here. One room, he showed us the original.

I think it was the Parisian meter. So in Paris, this was the infallible, the absolute standard. From 1801, I think. It's in a wooden box with a velvet. packing and it's got silk ribbons at either end and it's just a very beautiful looking silver rod. Oh, to imagine like the thing, the grand thing being in this place. Sort of like seeing the Pope in shorts or something.

It makes me a little uncomfortable. Special thanks to Ari Adland and Eric Earl Mother and also to Terry Quinn. We don't want to forget. Richard Davis and Penn Alder and finally Thank you to our math angel

soprano Melissa Hughes Very weird to sing my own name Also big props to reporter Andrew Morantz Latif Nasser and our producer Lynn Levy

And oh oh oh oh oh Also You should go to RadioLab.org Not only to support the show By clicking the support button but also to check out a collaboration video

that we did with Henry Reich from Minute Physics You can see it at RadioLab.org or also YouTube.com slash minute physics. Yet another meditation on what things or unthings are all about. I'm Chad I boomrod. I'm Robert Krollwich.

Thanks for listening.