Radiolab - Less Than Kilogram

Less Than Kilogram

Nov 29, 2024 - 24m 56s

In today’s story, which originally aired in 2014, we meet a very special cylinder. It's the gold standard (or, in this case, the platinum-iridium standard) for measuring mass. For decades it's been coddled and cared for and treated like a tiny king. But, as we learn from writer Andrew Marantz, things change—even things that were specifically designed to stay the same.

Special thanks to Ken Alder, Ari Adland, Eric Perlmutter, Terry Quinn and Richard Davis.And to the musical group, His Majestys Sagbutts & Cornetts, for the use of their song “Horses and Hounds.”We have some exciting news! In the “Zoozve” episode, Radiolab named its first-ever quasi-moon, and now it's your turn! Radiolab has teamed up with The International Astronomical Union to launch a global naming contest for one of Earth’s quasi-moons. This is your chance to make your mark on the heavens. Vote on your favorites soon, check here for details: https://radiolab.org/moonSign-up for our newsletter!! It includes short essays, recommendations, and details about other ways to interact with the show. Sign up (https://radiolab.org/newsletter)!

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AI-Generated

The Politics of Conversation

In the wake of Thanksgiving, Latif Nasser reflects on the divisive nature of family discussions, particularly around politics. He introduces the episode's main theme of seeking something objective and universal amidst discord—the discussion about the kilogram, an enduring standard that everyone can agree upon.

The Mystery of Measurement

The episode delves into the history and significance of measurement systems, with Andrew Marantz exploring the SI base units. The discussion focuses on how measurements have evolved from intuitive, body-based measures to standardized units, culminating in the concept of the kilogram as a singular, precise standard.

The Quest for a Universal Standard

The narrative reveals the dramatic journey of measurement from chaos during the French Revolution, where over 250,000 units were in use, to the establishment of the meter and kilogram based on natural phenomena. The episode discusses how these standards aimed to unite commerce, science, and everyday life.

The Grand K and Its Decline

Listeners are taken into the vault housing the international prototype kilogram, described as the last physical standard. However, tensions arise as the Grand K is discovered to be losing weight. This revelation poses significant questions about the integrity of this measurement standard and leads to the quest for a new definition of the kilogram.

Redefining the Kilogram

As the narrative unfolds, it becomes evident that researchers are working on redefining the kilogram based on fundamental physical constants rather than a physical object. The episode ends with the exciting conclusion that in 2018, a new definition was adopted, transitioning away from the Grand K and marking a new era in measurement.

- The kilogram, once considered an unquestioned standard, has faced challenges related to its physical integrity.
- The evolution of measurement reflects historical contexts, particularly significant moments of societal change, such as the French Revolution.
- The shift from a physical kilogram to an abstract mathematical definition represents a major advancement in science.
- Engaging storytelling and expert insights can make complex scientific ideas accessible to a broad audience.
- Understanding the concept of standards can inspire listeners to appreciate the systems that underpin our everyday existence.

Transcription

This is Radio Lab.

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 like how does 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 ever lasting, 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.

Graham.

You're listening to Radio Lab from WNYC.

Hey, I'm Jadipum Ron.

I'm Robert Kroelich.

This is Radio Lab, the podcast.

And this actually brought a list.

Okay.

Where is this thing?

This is Andrew Moritz.

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 by a...

Ah, here it is.

And he recently got obsessed with a list of measurements.

Base units, they're called.

There's their SI base units.

The system international, you know.

So let me do this way.

Have you ever wondered how long an inch is?

That's 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 a bit.

I'm just assuming that there's like a master inch somewhere?

Me, I see.

I say it in French for a reason in which I feel at the 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 International, the Units, here's what you get a meter 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 Newton's per meter of length.

I have no idea what that means.

Gee, that's the thing.

If you look at the actual definitions, 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 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 one?

And why would there...

is it...

what?

wait what?

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

Like I must admit that I I expected this story to be a lot more boring than I found.

It's like an epic story.

It's true.

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-thrower 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 three-thrower rocks away or it's ten-thrower rocks away.

But, you know, that there might be some built-in uncertainty there, because if you ask Like Achilles, it could be two through a Roxway, but he asked me, it would be like 78.

You have nailed exactly the problem with the Thriller 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 uses.

250,000 every commodity has its own measure so you have green, wine, oil, salt, hay, whore, 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 say this year I have a bit of cloth you would say how much cloth you got and I'd say I have two yards and say what's a yard?

I said, it's this match, and the other guy said, no, no, it's this match, it was, no, no, it's this match, no, it's this match, and you could see the...

Frustrating.

It was frustrating.

Yeah.

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.

They were hangry.

very angry.

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 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 best deal 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, 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.

Beauty, fraternit\u00e9, egalit\u00e9.

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 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 gonna go in this guy Patrick Abbott physicist was our guide they took us three stories down into the bid rock 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 the 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, brush-and-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, Limevi.

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.

Lagong Ka, 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 the Gouna.

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 trains 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, 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, and 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 ceremonial way.

Right.

How do you weigh the thing that is the standard of weight?

Well, you weigh it against the copies.

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 K on the other.

And the the IPK, the legoon ka, the one, is light.

What?

It's light.

How many, how many, how much is it lighter 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 and the third sister copy Still light and the fourth and fifth and sixth Incomes the man from Germany, light incomes the man from Canada, light incomes 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 guys 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?

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.

It 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?

I'd answer to that question after the break.

My name is Molly Webster and I'm the Senior Correspondent at Radio Lab.

My job is to just basically get like mini-masters degrees every week that I work on the show.

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Hey, I'm Lative Nasr, you're listening to Radio Lab.

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 Krollwich and New Yorker writer, Andrew Morance, went to Maryland to investigate.

Well, I'm getting zero cell phone reception down here.

That means we're really deep.

Well, 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.

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 very much so you probably wouldn't be allowed any if you're a redhead 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 like a massive Round metal cauldron or like 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.

The one measure.

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 kid on one side of the teeter totter, kid on the other side of the teeter 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 teeter totter, they've got the kilogram, like the grand k, that's kid number one.

On the other side, that 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 of the gongko sitting on the other side.

And if you can convert that force into a number that everybody agrees to, 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 wanna see that happen?

Yeah, right now I can show you this with our Lego version of the Wad Balance.

If I can fire it up.

Lego Lego one.

Well, see they're the big one was being tested or something so they took us over to look at the little one Okay, so we have have a little scale everything you can see that I just disturbed the balance and it's you know Chiklin 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 grandmas.

He puts this tiny little thimble thing on the balance and now it's going to he says levitate No, it seems he props me a mass on mass on yeah, I'm gonna put the mass on he pushes a button all right and 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 It's not floating, that's just floating.

Does it fall to earth?

That's a different idea.

The 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.

Now 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?

Nah, yeah, no.

Because first of all, you have to get straight with a lot of math.

MC squared equals H new, work backwards.

You got to divide by E and then by M.

Measure the B field.

Woo! Let's go.

And then you get your Ampere's and your Watts and your Planck's constant.

Classical 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 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, there, 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 Planck constant to be equal to Exactly.

6.62669 and we have X's because we haven't all agreed what the final Those are the missing decimal those are the missing decimal places times 10 the minus 34 when it's expressed in the unit for actions dual seconds, which is A meter squared kilogram per second whoo.

That'll be such a simpler definition.

Oh, yeah No, you And what will happen to the Grand K when the new definition goes into effect?

Well, so this is the sad part.

You have it, for example?

Looks like a church.

You will see after the church wherever...

Of course.

The Grand K may eventually end up in a place like this.

For so many standards have gone to die.

This is the Muse des Arts et M\u00e9tiers \u00e0 Paris in Paris.

So this is the beginning?

So Il Faso is our tour guide.

What is this?

A litre.

He showed us the original litre.

Wow.

Some early thermometers.

There is an object, perhaps, a hydraulic.

A room, he showed us the original.

I think it was the Parisian meters.

When 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, so imagine like the thing, the grand thing being in this place.

It's sort of like seeing the Pope in shorts or something.

It makes me a little so uncomfortable.

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.

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.

That means all of you would lose weight.

For the people in this room, the fact that we in the 21st century or 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 and they voted to replace the physical kilogram with that abstract bit of math.

South Africa.

Yes.

The physical kilogram was relegated to the dustbin of history.

Australia, Australia, Australia, Belgium, Brazil, Brazil, Brazil, thank you, Bulgaria, Thank you to our math angel, soprano, very weird to sing my own name.

Also big props to reporter Andrew Morantz, Latifnosser, and our producer then Levy.

Hello, I'm Natalia and I'm from New York City, and here are the staff's credits.

Radio Lab was created by Chad Abumrod and is edited by Soaring Wheeler.

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Our staff includes Simon Adler, Jeremy Bloom, Becca Pressler, W.

Harry Fortuna, David Gable, Maria Pascotieras, Sindu Nyanem Sambandan, Matt Kilti, Rebecca Lacks, Annie McEwan, Alex Nason, Sarah Carrey, Sarah Sandback, Vanessa Vica, Aryan Lack, Pat Walters, and Molly Webster.

Our fact checkers are Diane Kelly, Emily Krieger, and Natalie Middleton.

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Take a listen wherever you get your podcasts.","created_at":"2024-11-29T16:02:58.000000Z","updated_at":"2025-07-15T08:09:11.000000Z","requested_by":[2],"status":"completed","delay_time":null,"worker_id":null,"job_id":null,"execution_time":null,"runpod_job_id":null,"error_message":null,"completed_at":null,"word_level_timestamps":null,"claimed_at":null,"embedding_claimed_at":"2025-07-15 08:09:11","embedding_worker_id":"macbook-air-worker-1"}

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