Less Than Kilogram

Summary

Radiolab Episode Summary: "Less Than Kilogram"

Introduction

In the episode titled "Less Than Kilogram," Radiolab delves into the intricate world of measurement standards, focusing on the kilogram—the only SI unit still defined by a physical object. Hosted by Latif Nasser and featuring contributions from emeritus host Robert Krulwich and New Yorker writer Andrew Marantz, the episode explores the history, challenges, and eventual redefinition of the kilogram. Originally broadcast in 2014, the episode includes a dramatic update reflecting significant developments in the field.

Historical Context: The Birth of the Kilogram

Latif Nasser sets the stage by transporting listeners back to pre-revolutionary France, where the lack of standardized measurements hindered trade and caused widespread confusion. In Paris, approximately 250,000 different units of measurement were in use, varying by commodity and region. This inconsistency was particularly problematic during the 1780s famine, leading bakers to shortchange loaves of bread, exacerbating public unrest.

Latif Nasser (00:05:20):
"The earliest measurements were super intuitive. A lot of them came from the body—two hands, a foot, etc.—but there were also more abstract measures like throwing rocks to estimate distance."

The chaos of multiple measurement systems fueled the revolutionary desire for a unified, rational system. The newly formed revolutionary government sought to base measurements on natural phenomena, leading to the creation of the meter and, subsequently, the kilogram.

The Physical Kilogram: An Unchanging Standard

Robert Krulwich and Andrew Marantz introduce listeners to the International Prototype Kilogram (IPK), a platinum cylinder stored in France. This physical object became the universal standard for the kilogram, ensuring consistency in measurements worldwide. The IPK's role was pivotal in facilitating global trade and scientific research.

Andrew Marantz (00:04:00):
"A meter is a fraction of a second of the distance traveled by light in a vacuum. A kilogram is a particular thing, a plum-sized object."

The episode takes listeners on a virtual tour of the National Institute of Standards and Technology (NIST) in Maryland, where Robert Krulwich and Andrew Marantz examine the IPK and its meticulously maintained copies. These copies, known as "witnesses," are distributed globally to ensure uniformity in mass measurements.

Latif Nasser (00:09:15):
"The international prototype is the big kahuna. It's used to calibrate six identical platinum cylinders, the witnesses, which then calibrate another set of cylinders, and so on."

Challenges with the Prototype: Weight Loss and Uncertainty

The stability of the IPK has long been assumed, but in 1989, it was discovered that the prototype was losing mass. During a ceremonial weighing, the IPK was found to be slightly lighter than its witnesses, revealing the fragility of relying on a physical object for a universal standard.

Andrew Marantz (00:13:00):
"They put the IPK in a steam bath, dried it, and weighed it against the copies. It was lighter by about the mass of a grain of sugar."

This revelation sparked concern among metrologists, as even minor discrepancies could have significant implications for scientific research, manufacturing, and daily commerce. Theories ranged from physical degradation due to cleaning to potential outgassing of elements from the platinum cylinder.

Robert Krulwich (00:14:00):
"The international standard for weight was losing weight, and because it is the standard, everything else was unknowingly becoming inaccurate."

The Redefinition Process: From Physical to Abstract

Acknowledging the limitations of the IPK, the scientific community embarked on a mission to redefine the kilogram based on fundamental constants of nature. This shift aimed to eliminate reliance on a physical object, ensuring greater stability and universality.

John Pratt, NIST Physicist (00:21:38):
"The new definition of the kilogram is based on fixing the numerical value of the Planck constant to ensure consistency across all measurements."

The episode describes the complex process of achieving agreement among international laboratories using various methods, including the Watt balance and the counting of atoms. These techniques connect mass directly to quantum mechanical properties, anchoring the kilogram in the immutable laws of physics.

Latif Nasser (00:24:20):
"By fixing the Planck constant, we redefine the kilogram in terms of universal constants, detaching it from any single physical object."

Implications of the Redefinition: A New Era of Precision

The redefinition of the kilogram marks a significant milestone in metrology, providing unprecedented precision and stability. This change ensures that mass measurements remain consistent regardless of the physical condition of any prototype, fostering advancements in science and technology.

Latif Nasser (00:27:00):
"Replacing the physical kilogram with an abstract mathematical definition was a necessary evolution, ensuring that our measurements remain reliable and universal."

The episode also touches upon the cultural and symbolic aspects of this transition, highlighting the departure from historical artifacts to abstract concepts. This shift signifies humanity's progress towards more advanced and reliable systems of measurement.

Conclusion and Update

"Less Than Kilogram" concludes by celebrating the successful redefinition of the kilogram, rendering the IPK a historical relic. The new definition, grounded in fundamental constants, promises a future of precise and consistent measurements across all scientific and commercial fields.

Latif Nasser (00:27:48):
"The physical kilogram has been relegated to the dustbin of history, replaced by a definition that reflects the true nature of the universe."

Notable Quotes

• Latif Nasser (00:05:20):
  "The earliest measurements were super intuitive. A lot of them came from the body—two hands, a foot, etc."

• Andrew Marantz (00:04:00):
  "A meter is a fraction of a second of the distance traveled by light in a vacuum. A kilogram is a particular thing, a plum-sized object."

• Robert Krulwich (00:14:00):
  "The international standard for weight was losing weight, and because it is the standard, everything else was unknowingly becoming inaccurate."

• John Pratt (00:21:38):
  "The new definition of the kilogram is based on fixing the numerical value of the Planck constant to ensure consistency across all measurements."

• Latif Nasser (00:27:00):
  "Replacing the physical kilogram with an abstract mathematical definition was a necessary evolution, ensuring that our measurements remain reliable and universal."

Final Thoughts

"Less Than Kilogram" masterfully blends history, science, and storytelling to illuminate the profound impact of standardized measurements on society. Through engaging discussions and expert insights, Radiolab underscores the importance of precision in our daily lives and scientific endeavors, celebrating the harmonious marriage of tradition and innovation that has shaped our understanding of the world.

Transcript

[Latif Nasser]

Radiolab is supported by Dell Shop Dell Technologies Black Friday event for their lowest prices of the year. The Future is on sale today with limited time deals on select PCs like the XPS 16 that accelerate AI with Intel Core Ultra processors. Black Friday is their biggest sale of the year and the best time to upgrade. But it's only here for a limited time. Shop [e-mail] deals that's Dell. Radiolab is brought to you by Progressive Insurance. Do you ever think about switching insurance companies to see if you could save some cash? Progressive makes it easy to see if you could save when you bundle your home and auto policies. Try [e-mail] Progressive Casualty Insurance Company and affiliates. Potential savings will vary. Not available in all states. Listener supported WNYC Studios hey, it's Latif. This is Radiolab. I'm thinking today, in the aftermath of American Thanksgiving, about all the people who got together with their families, sat down for a nice little meal, and then, oh, God, politics came up somehow, and they found there was just something they couldn't agree on. And you can't even reckon, how does this other person not even understand the basic facts of the situation? And so 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.

[Robert Krulwich]

Wait, you're listening. Okay. All right. Okay. All right. You're listening to Radiolab.

[Andrew Marantz]

Radiolab from wnyc.

[Robert Krulwich]

See?

[Molly Webster]

Rewind.

[Jad Abumrad]

Hey, I'm Jad Abumrad.

[Robert Krulwich]

I'm Robert Krulwich.

[Jad Abumrad]

This is Radiolab, the podcast.

[Robert Krulwich]

And this.

[Andrew Marantz]

I actually brought a list.

[Robert Krulwich]

Okay, why don't you share with me your list? Where is this thing? This is Andrew Morenz. He's a writer and editor at the New Yorker magazine.

[Andrew Marantz]

Oh, I might have gotten lost.

[Robert Krulwich]

Who occasionally pops onto our show?

[Andrew Marantz]

Maybe you were mugged by a. Ah, here it is.

[Robert Krulwich]

And he recently got obsessed with a. It's a list of measurements.

[Andrew Marantz]

Base units, they're called. They're SI. Base units. The Systeme Internationale, you know.

[Robert Krulwich]

So let me do it this way. Have you ever wondered how long an inch is? Exactly how long?

[Jad Abumrad]

I know, I just look at a ruler.

[Robert Krulwich]

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 inch is our inch, as your inch is my inch.

[Jad Abumrad]

I haven't really thought about it, but I just assume that there's like a master inch somewhere.

[Robert Krulwich]

Bien sur. I say it in French for a 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.

[Andrew Marantz]

Okay, so when you go down the list of the Systeme Internationale de Unites.

[Robert Krulwich]

Here'S what you get.

[Andrew Marantz]

A meter. A meter is a fraction of a second of the distance traveled by light in a vacuum.

[Robert Krulwich]

Okay, What?

[Andrew Marantz]

A second is how much radiation corresponds to the transition between two hyperfine levels of the ground state of the cesium 133 atom.

[Jad Abumrad]

That's the definition of a second.

[Robert Krulwich]

How many times does a particular atom jiggle?

[Andrew Marantz]

Yeah.

[Robert Krulwich]

Wow.

[Andrew Marantz]

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. I have no idea what that means.

[Robert Krulwich]

See, that's the thing. If you look at the actual definitions of any of these things, AM, meter, second, whatever you go. But there is one standard on the list that is unique for its simplicity.

[Andrew Marantz]

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.

[Robert Krulwich]

It is the only thing we use to measure things. It's the last one standing, the only physical standard left.

[Jad Abumrad]

Why is it the last? And why were there? Is it.

[Robert Krulwich]

What?

[Jad Abumrad]

Wait, what?

[Robert Krulwich]

Let me just take you back to the beginning of the story.

[Latif Nasser]

Like, I must admit that I expected this story to be a lot more boring than I found. It's like an epic story. It's really.

[Robert Krulwich]

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.

[Latif Nasser]

Earliest measurements were super intuitive.

[Robert Krulwich]

And he says a lot of them.

[Latif Nasser]

Came from the body.

[Robert Krulwich]

As in that bunny is coming close to the net. How close, dad?

[Latif Nasser]

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. Or that 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.

[Robert Krulwich]

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.

[Latif Nasser]

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. Yeah, they would say it's, you know, three thrower rocks away, or it's 10 thrower rocks away.

[Robert Krulwich]

But you know that there might be some built in uncertainty there. Because if you ask Achilles, yeah, it could be two throw rocks away, but if you ask me, it would be like 78.

[Latif Nasser]

You have nailed exactly the problem with the throw a rock system.

[Robert Krulwich]

And these problems kind of came to a head in the 1700s.

[Latif Nasser]

It's the Eve of the French Revolution.

[Robert Krulwich]

In a little town called Paris.

[Latif Nasser]

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.

[Robert Krulwich]

250.

[Latif Nasser]

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.

[Robert Krulwich]

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'd say, I have two yards. And you say, what's a yard? I said, it's this much. And the other guy would say, no, no, it's this much. Then I said, no, no, it's this much. And I would, no, no, it's this much. And you could see that.

[Jad Abumrad]

Frustrating.

[Robert Krulwich]

It was frustrating, yeah.

[Latif Nasser]

And making 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 they were hangry.

[Robert Krulwich]

They were hangry.

[Latif Nasser]

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.

[Robert Krulwich]

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.

[Latif Nasser]

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. Don't short me on this. This is serious.

[Robert Krulwich]

Well, you know what happens next?

[Latif Nasser]

The Bastille is stormed and the king is under house arrest. And then under the guillotine.

[Robert Krulwich]

And as soon as the revolutionary government takes over, they say, all right, okay.

[Latif Nasser]

This is one of our first priorities. We are going to make a new.

[Robert Krulwich]

Standard, but not based on something arbitrary like a king. This is the Enlightenment.

[Latif Nasser]

Why don't we draw on some kind of totally different authority? The authority of nature.

[Robert Krulwich]

Of nature.

[Latif Nasser]

Of nature.

[Robert Krulwich]

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.

[Latif Nasser]

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, glorious.

[Robert Krulwich]

Liberty, fraternity, egalite.

[Latif Nasser]

Exactly. They wanted something, something that would be eternal and unchanging for everybody for all time.

[Robert Krulwich]

So now, I guess you want to see it. No. Yeah. Okay.

[Jad Abumrad]

Okay.

[Robert Krulwich]

So it's in here. We ended up visiting the National Institute of Standards and Technology in Maryland.

[Latif Nasser]

And this is where we'll be going.

[Robert Krulwich]

In, but we're going to go into 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, to you?

[Andrew Marantz]

Yeah. It's almost hard to tell where the, like, Russian doll glass jar stops because it's so reflective.

[Molly Webster]

This might be a crazy question, but can we hold a kilogram?

[Jad Abumrad]

That's our producer, Lynn Levy.

[Robert Krulwich]

No.

[Molly Webster]

I'm Just curious to know what it feels like. We've been talking about it so much.

[Robert Krulwich]

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.

[Andrew Marantz]

Le Grand Ca, as they call it.

[Robert Krulwich]

Lives in a basement in France. You can't get anywhere near that one.

[Jad Abumrad]

I could.

[Robert Krulwich]

No, you couldn't.

[Jad Abumrad]

I could get old Tom Cruise on that.

[Robert Krulwich]

You die trying. Here's how it works. The international prototype is the big gahuna. That's the one used to calibrate six identical platinum cylinders, what they call witnesses.

[Latif Nasser]

Or tamois in French.

[Robert Krulwich]

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.

[Jad Abumrad]

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?

[Robert Krulwich]

That's what I'm saying. Which is why the next part of the story is so disconcerting.

[Andrew Marantz]

What happened in 1989 is that according.

[Robert Krulwich]

To Andrew, the folks who take care of the official kilogram, the big K, they took it out of its jars.

[Andrew Marantz]

They put it in a steam bath.

[Latif Nasser]

Hit it with the steam that rinses.

[Andrew Marantz]

Everything, wait for it to dry, then.

[Robert Krulwich]

They commence a ceremonial weighing.

[Andrew Marantz]

Right.

[Robert Krulwich]

Well, how do you weigh the thing that is the standard of weight?

[Andrew Marantz]

Well, you weigh it against the copies.

[Robert Krulwich]

Like the US 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 Queue on the other.

[Andrew Marantz]

And the ipk, the Le Grand Car, the one is light. What?

[Robert Krulwich]

It's light.

[Andrew Marantz]

It doesn't.

[Robert Krulwich]

How many? How many? How much lighter is it than its sisters?

[Andrew Marantz]

Roughly the mass of a grain of sugar. Oh, yeah.

[Robert Krulwich]

Is that gigantic?

[Andrew Marantz]

It's measurable.

[Jad Abumrad]

Wait, how do they know that it was light and not that the other ones were heavier?

[Andrew Marantz]

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.

[Robert Krulwich]

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.

[Latif Nasser]

Well, we think that. We think the big guy's the problem.

[Andrew Marantz]

As far as how it lost that weight. Really, no one knows.

[Robert Krulwich]

One possibility is it got cleaned too much, and maybe some of it got scraped away.

[Andrew Marantz]

Although it's disputed whether cleaning it more would make it lose weight or gain weight. The other theory is outgassing.

[Robert Krulwich]

Like maybe a little hydrogen is seeping out of the metal.

[Andrew Marantz]

And then there was one thing I read that said foul play cannot be ruled out.

[Robert Krulwich]

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.

[Andrew Marantz]

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.

[Robert Krulwich]

No, you can't do that.

[Andrew Marantz]

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.

[Jad Abumrad]

All right, so if the standard of weight is, as you're saying, losing weight, so how do you fix that?

[Latif Nasser]

An answer to that question after the break.

[Molly Webster]

My name is Molly Webster, and I'm the senior correspondent at Radiolab. I host some episodes. I do like series, but mostly I'm just doing a lot of reporting. And so my job is to just basically get, like, mini master's degrees. Every week that I work on the show, I've got a mini master's in butterflies. The moon, strange organs, thymus, placenta, black holes. Oh, smoke, for sure. Covid. I'm going to give myself a whole PhD for that. Maybe a postdoc in, like, sex development and biology. There are, like, some honorary degrees that happen sometimes in two hours, depending on the time pressure. I like to sort of rack up my mini degrees because I feel like we all specialize and we all have our little corners of the world, but most people just don't have time to leave those corners. And so I think one of the great things about the show and my job is that we get to bring people into all of these spaces that might never be open to them, just based on logistics, just based on time, and we're able to do this because of you. Radiolab exists thanks to the ears and minds and generosity of our listeners. Your support allows us to keep expanding my world and your world and the worlds of people that you'll never meet. If you like what we do and getting these mini Masters with us, the best way to support the show is to become a member of the Lab. When you join the Lab, you not only support the entire show and the work we make, but you also get access to members only perks and benefits like ad free listening, bonus content, our full archive merch. Such good merch and so much more. So become a member so we can all get our little mini Master's degrees and go out into the world and talk about science and humans and just understand this big crazy universe that we live in. To join go to radiolab.org join.

[Latif Nasser]

Radiolab is supported by Lumen, the world's first handheld metabolic coach that measures your metabolism through your breath. And on the app it lets you know if you're burning fat or carbs and gives you tailored guidance to improve your nutrition, workouts, sleep and even stress management. All you have to do is breathe into your lumen first thing in the morning and you'll know what's going on with your metabolism, whether you're burning mostly fats or carbs. Then Lumen gives you a personalized nutrition plan for that day based on your measurements. You can also breathe into it before or after workouts or meals so you know exactly what's going on in your body in real time. And Lumen will give you tips to keep you on top of your health game. So if you want to stay on track with your health this holiday season, go to Lumen Me Radiolab to get 15% off your Lumen, that is L U M E N M E Radiolab for 15% off your purchase. Radiolab is brought to you by Progressive Insurance. Do you ever find yourself playing the budgeting game? Well, with the Name youe Price tool from Progressive, you can find options that fit your budget and potentially lower your bills. Try [e-mail] Progressive Casualty Insurance Company and affiliates Price and coverage match limited by state law. Not available in all states.

[Robert Krulwich]

Planet Money helps you understand the economy.

[Molly Webster]

We find the people at the center of the story.

[Robert Krulwich]

Garbage in New York that was like a controlled substance. We show you how money influences everything. Tell me what you like by telling.

[John Pratt]

Me how you spend your money.

[Molly Webster]

And we dig until we get answers.

[Andrew Marantz]

I had a bad feeling you're gonna bring that up.

[Robert Krulwich]

Planet Money finds out all you have to do is listen the Planet Money podcast from npr.

[Latif Nasser]

Hey, I'm lativnasar. 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 Krulwich and New Yorker writer Andrew Marantz went to Maryland to investigate.

[Andrew Marantz]

Well, I'm getting zero cell phone reception down here. That means we're really deep.

[Robert Krulwich]

When we were down in that underground room in Maryland, we met a guy who has some thoughts about this. Oh, there he is.

[John Pratt]

Okay.

[Robert Krulwich]

His name's John Pratt.

[John Pratt]

I'm the leader of the Fundamental Electrical Measurements Group at the National Institute of Standards and Technology.

[Robert Krulwich]

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. 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.

[John Pratt]

Very much so.

[Robert Krulwich]

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.

[Andrew Marantz]

Its side with the thing itself looked sort of just like a. 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 it's just a stunning machine. But it's all just for the benefit of the one.

[John Pratt]

The one measure.

[Andrew Marantz]

The one kilogram.

[John Pratt]

Yep.

[Robert Krulwich]

Because inside that giant cauldron, there is an extremely, extremely sensitive balance, an equal arm balance, which is basically like a.

[John Pratt]

Seesaw or a teeter totter. 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.

[Robert Krulwich]

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 teeter totter, they've got the kilogram, like the ground K, that's kid number one. On the other side, that of another.

[John Pratt]

Kilogram, or kid two, we'll have a highly variable magnet.

[Robert Krulwich]

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.

[John Pratt]

It'll produce a force, and we could use that to hold the balance still.

[Robert Krulwich]

And the force it takes to hold up the balance, that of course, is the same as the weight of the Gonka sitting on. 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.

[John Pratt]

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.

[Robert Krulwich]

Okay.

[John Pratt]

If I can fire it up.

[Jad Abumrad]

Lego Lego 1.

[Robert Krulwich]

Well, see, the big one was being tested or something, so they took us over to look at the little one.

[John Pratt]

Okay.

[Robert Krulwich]

So we have a little scale and everything.

[John Pratt]

You can see I just disturbed the balance and it's, you know, jiggling around a little. It's free floating.

[Robert Krulwich]

Okay, so you're now going with your tweezers and you're plucking a itty bitty. Yep.

[John Pratt]

Two gram mass.

[Robert Krulwich]

He puts this tiny little thimble thing on the balance and now it's going to. He says, levitate.

[John Pratt]

Now it, see, it prompts me. Mass on.

[Robert Krulwich]

Mass on.

[John Pratt]

Yeah, I'm gonna put the mass on.

[Robert Krulwich]

He pushes a button.

[John Pratt]

All right. And.

[Latif Nasser]

Wait.

[Andrew Marantz]

But when do we see the levitation?

[John Pratt]

That was it.

[Robert Krulwich]

I didn't. I missed it. Do it again. It was floating.

[John Pratt]

It is floating. Sitting on the balance.

[Robert Krulwich]

Okay, it's not floating.

[John Pratt]

That is floating. Does it fall to Earth?

[Robert Krulwich]

That's a different idea. Levitation. Now, 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.

[Jad Abumrad]

So if they're able to do that, does that mean that the Grand Cay's reign is. Is it done?

[Robert Krulwich]

Not yet, no. Because first of all, you have to get straight with a lot of math.

[John Pratt]

MC squared equals H nu. Work backwards.

[Robert Krulwich]

You got to divide by E and then by M, measure the B field.

[John Pratt]

Let's go.

[Robert Krulwich]

And then you get your amperes and your watts and your Planck's constant classical.

[John Pratt]

Bohr model of atoms and stuff.

[Robert Krulwich]

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 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.

[John Pratt]

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 Planck constant to be equal to exactly 6.626069. And we have X's because we haven't all agreed with the final.

[Andrew Marantz]

Those are the missing decimals.

[John Pratt]

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.

[Robert Krulwich]

Phew.

[Andrew Marantz]

That'll be such a simpler definition.

[John Pratt]

Oh, yeah. No, you.

[Jad Abumrad]

And what will happen to the grand K when the new definition goes into effect?

[Robert Krulwich]

Well, so this is the sad part. Looks like a church. We will see after the end, the church where the Foucault, the Grand Quai, 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 Musee des Arts et Metiers in Paris. So this is the beginning, was our tour guide. Yeah, what is this? He showed us the original liter, some early thermometers. There's one funny 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.

[Jad Abumrad]

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. It's a little uncomfortable.

[Latif Nasser]

So 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.

[Robert Krulwich]

This is scandalous.

[Latif Nasser]

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.

[Robert Krulwich]

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. That means all of you would lose weight.

[Latif Nasser]

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.

[Robert Krulwich]

Hello. En commence.

[Latif Nasser]

And they voted to replace the physical kilogram with that abstract bit of math.

[Robert Krulwich]

South Africa. Yes. Alamang. Germany. Yes. Arabi. Saudi. Saudi Arabia. Yes. Thank you. Argentine? Argentina.

[Latif Nasser]

The physical kilogram was relegated to the dustbin of history.

[Robert Krulwich]

Australia. Australia. Otrich. Austria. Belgic. Belgium. Brazil. Brazil. Yes. Thank you. Special thanks to Ari Adland and Eric Carlmother. And also to Terry Quinn. We don't want to forget Richard Davis and Ken Older, Bob Waters, Michael Baum, Michael Newman.

[Jad Abumrad]

And finally, thank you to our math angel soprano Melissa Hughes.

[Robert Krulwich]

Very weird to sing my own name.

[Jad Abumrad]

Also, big props to reporter Andrew Marantz, Latif Nasser and our producer Lynn Levy.

[Robert Krulwich]

Hello, I'm Natalia and I'm from New York City. And here are the staff 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. Our staff includes Simon Adler, Jeremy Bloom, Becca Bressler, W. Harry Fortuna, David Gable, Maria Pascutieres, Sindhu Nyanam Sambandan, Matt Kilty, Rebecca Lacks, Annie McEwen, Alex Neeson, Sara Khari, Sarah Sandbach, Anissa Viza, Arianne Wack, Pat Walters and Molly Webster. Our fact checkers are Diane Kelly, Emily Krieger and Natalie Middleton. Thanks for listening to Radiolab. Bye. Hi, my name is Michael Smith. I'm calling from Pennington, New Jersey. Leadership support for Radiolab Science programming is provided by the Gordon and Betty Moore Foundation Science Sandbox, a Simons foundation initiative, and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.

[Latif Nasser]

The kind of burgers you get today.

[Robert Krulwich]

Tells you a lot about yourself.

[Latif Nasser]

You're either someone who settles for sad.

[Robert Krulwich]

Same old same old burgers, or you're.

[Latif Nasser]

At a Carl's Jr obsessed with a tangy OG Western bacon cheeseburger, demanding a house made guacamole.

[John Pratt]

Loaded guac bacon.

[Latif Nasser]

Fired up for the insanely hot El Diablo? Or craving a classic Charbold Famous Star? Give in to your flavor cravings.

[Robert Krulwich]

Get your mouth to Carl's Jr. Big Burger. Good Burger.

[Latif Nasser]

This is the sound of your ride.

[Robert Krulwich]

Home with dad after he caught you vaping. Awkward, isn't it? Most vapes contain seriously addictive levels of nicotine and disappointment. Know the real cost of vapes brought to you by the fda?