Less Than Kilogram

0:28Hey, it's Latif. This is Radiolab. If you're leaving this holiday feeling like you need something concrete, something apolitical, something objective in this moment, this episode is for you. It's an episode we originally broadcast in 2014 about a project to make something everlasting, something that everyone everywhere could agree to follow. And we actually have kind of a dramatic update at the end. So stay tuned for that. Here you are, less than kilogram. Wait, you're listening. Okay. All right. Okay. All right. You're listening to Radiolab. Radiolab. From WNYC.

1:19Rewind. Hey, I'm Jad Ibumrad. I'm Robert Krulwich. This is Radiolab, the podcast. And this... I actually brought a list. Okay, let's why don't you share with me your list. Where is this thing? This is Andrew Moretz. He's a writer and editor at The New Yorker magazine. I might have gotten lost. Who occasionally pops onto our show. Maybe you were mugged by a... Ah, here it is. And he recently got obsessed with a... It's a list of measurements. Base units, they're called. There's their SI base units, the Systeme Internationale, you know. So let me do it this way. Have you ever wondered how long an inch is?

2:00I mean, exactly how long. I know. I just look at a ruler. Well, but how do you know that your ruler and my ruler do have the same amount of inch space or that someone in China, that their inches are inches, your inches, my inch? I haven't really thought about it, but I just assume that there's like a master inch somewhere. Bien sûr. I say it in French for a reason, which you'll feel 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.

2:31Okay. So when you go down the list of the système international des units. Here's what you get. A meter is a fraction of a second of the distance traveled by light in a vacuum. Okay. What? 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 a particular atom jiggle? Yeah. Wow. 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 2 times 10 to the negative 7th newtons per meter of length.

3:15I have no idea what that means. See, that's the thing. If you look at the actual definitions of any of these things, amp, 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 math, 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 is it what? Wait, what? Let me just take you back to the beginning of the story. Like, I must admit that I expected this story to be a lot more boring than I found.

4:07It'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 are 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.

4:44Or something is as far as I can throw a stone.

4:50So that would mean like say, okay, I'm going to build a farm here, and I'm going to do it three thorough 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 throw rocks away or it's ten throw rocks away. But, you know, there might be some built-in uncertainty there because if you ask Achilles, it could be two throw rocks away, but if you ask me, it would be like 78. You have nailed exactly the problem with the throw rock system.

5:27And 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?

6:07And I'd say, I have two yards. And you'd say, what's a yard? I'd say, it's this much. And the other guy would say, no, no, it's this much. And he would say, no, no, it's this much. And he would, no, no, it's this much. 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 hangry. They were hangry. They were very hangry. 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.

6:45But 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 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.

7:19Don'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. OK, 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.

8:04The 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. Liberté, fraternité, égalité. Exactly. They wanted something that would be eternal and unchanging for everybody, for all time.

8:46So 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, but we're going to go into this. 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...

9:31Is 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 do? 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, Lumivi. 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 Ca, as they call it.

10:12Lives 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'd die trying. Here's how it works. The international prototype is... Big Kahuna. 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 U.S. 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.

10:46Every 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 was 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.

11:24They took it out of its jars. They put it in a steam bath. Hit it with the steam. That rinses everything. Wait for it to dry. Then... They commence a 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 they put the grand K on the other. And the IPK, the Le Grand K, the one, is light.

11:59What? It's light. It doesn't. How many, how many, how much lighter is it than its sisters? Roughly the mass of a grain of sugar. Oh. Yeah. 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.

12:38Well, we think that. We think the big guy's 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. What's clear is we may have a slightly trippy situation here. We got a hunk of metal losing weight and yet because it is the standard.

13:08It 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 that it's like 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 an answer to that question after the break.

13:45Hey, I'm Lantiv Nasser. You're listening to Radiolab. Before the break, we learned that the international standard for a kilogram, which is a tiny platinum cylinder, is ever so slowly losing weight. A problem which our emeritus host, Robert Kralwich, and New Yorker writer, Andrew Morantz, went to Maryland to investigate. 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 he 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.

14:25Hi, 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. Yeah. 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. I don't even know how to describe it. It looks like a wheel turned on its side. 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 and parts and then all these coiled up wires and just a stunning machine But it's all just for the benefit of the one One measurement 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 And usually you would set that up so that you would literally put kid on one side of the teeter-totter, kid on the other side of the teeter-totter.

15:37Now, you've been in a playground, so you know how this goes. But what they've done here is on one side of the teeter-totter, they've got the kilogram, like the ground K. That's kid number one. On the other side, instead of another kilogram, or kid two, will 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 gongka sitting on the other side.

16:10And 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 Watt Balance. 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... A little scale and everything. You can see I just disturbed the balance, and it's jiggling around a little.

16:52It'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, you'd say it prompts me mass on. Mass on. Yeah, I'm going to put the mass on. He pushes a button. All right, and...

17:17Wait, 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. He had taken a little metal weight. He 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.

17:55So if they're able to do that, does that mean that the Grand Cay'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 nu. 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 Planck's constant. Classical little Bohr 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.

18:28You got another lab, actually a couple of them that have their seesaws. You got a third lab that'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.

19:07The new definition of the kilogram, the kilogram is the SI unit of mass. Its magnitude is set by fixing the numerical value of the Planck constant to be equal to exactly 6.626069. 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 the minus 34, when it's expressed in the unit for action, joule seconds, which is a meter squared kilogram per second. Phew, that'll be such a simpler definition. Oh, yeah. No, you've... And what will happen to the grand K when the new definition goes into effect? Well, now, so this is the sad part.

19:49It looks like a church. We will see after the end. We have a church where the Foucault. The Grand Cay 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 Musée des Arts et Métiers in Paris. So this is the beginning. Cyril Fassot was our tour guide. Yeah, what is this? Un litre. He showed us the original litre. Or is it 0.8 litres? Wow, some early thermometers. There's one funny object here. One room he showed us, 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.

20:48to 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

21:05so while we were over here singing the praises of this object how beautiful it is to have something real you can hold in your hands There's a group of people for whom the kilogram situation was unacceptable. This is scandalous. For example, Bill Phillips here from the National Institute of Standards and Technology. He's speaking to a big gathering of people who care about this stuff. If this were the real kilogram that I was holding in my hands, the fingerprints that have been put onto this kilogram would increase the mass. But of course, it can't increase the mass because this is by definition a kilogram.

21:42That means all of you would lose weight. For the people in this room, the fact that we, in the 21st century, are basing our most finely tuned measurements on a hunk of metal cast in 1889? Now that's a situation that is clearly intolerable. After years of work, researchers figured out that new definition they were looking for. In 2018, representatives gathered together in France. Hello, on commence? And they voted to replace the physical kilogram with that abstract bit of math. South Africa. Yes. Aleman, Germany. Yes. Yes. Arabi, Saudite, Saudi Arabia. Yes. Thank you. Argentine, Argentina. The physical kilogram was relegated to the dustbin of history.

23:05Special thanks to Ari Adland and Eric Earlmother and also to Terry Quinn. We don't want to forget Richard Davis and Ken Alder, Bob Waters, Michael Paul, Michael Newman. 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. Hello, I'm Natalia and I'm from New York City. And here are the staff's credits. Radiolab was created by Jad Abumrad and is edited by Soren Wheeler. Lulu Miller and Latif Nasser are our wonderful co-hosts. Dylan Keefe is our director of sound design.

24:19Our staff includes Thanks for listening to Radiolab. Bye.

24:30Hi, my name is Michael Smith. I'm calling from Pennington, New Jersey. Leadership support for Radiolab's science programming is provided by the Gordon and Betty Moore Foundation, Science Sandbox, the Simons Foundation Initiative, and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.

24:54Thank you.