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≤ kg

Friday, June 13, 2014 - 11:24 AM

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.

In this short, 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.


Patrick Abbott, Cyrille Foasso, Andrew Marantz, Latif Nasser and Jon Pratt


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Comments [65]

Steven from Denver, CO

How did they find the circumference of the Earth in the 1700's?

Sep. 25 2016 11:15 PM
Bonnie from Cincinnati, OH

I kind've like that I listened to 9 Volt Nirvana with people experimentally home testing changing the neurons of their brain and now I'm following it up with kg where the experts cannot "capriciously" change the weight of the known kg by one grain of sugar - because that would be madness compared to the level of the North Korean government.

Dec. 23 2015 09:39 AM
Bert from Belgium

Yes, nice interview with cool sound effects.
Keep up the good work

Nov. 26 2015 07:22 AM

What happened in 1989??

Oct. 05 2015 08:04 PM
Gertrude G. Goethe from chair

I love the fact that the United states units of measurement are completely different to the rest of the worlds standards. It really shows how incredibly desperate we are to stand out. I found it interesting, though that the overall standards were created around the fundamental truths of our planet, so that thy're all constant. Also, who doesn't love a good French Revolution? The Bourgeois. It also kinda show how our scientific developments sometimes begin with the simple things like crushing poverty and mass famine.

Jan. 26 2015 05:59 PM
Ossian Öhrström

Does anyone know the piece of music that starts at 22.56, the baroque-sounding music with trumpets?

Jan. 25 2015 03:56 AM
Emma from Boston

Interesting episode but I don't think there has ever been anything more irritating than trying to listen to the man define the units of measure and that incredibly shrill voice echoing him.

Jan. 15 2015 05:24 PM
Chad from Portland, OR, USA

What is the significance of requiring consensus among the teams of scientists up to eight decimal places as opposed to six, seven, nine, or thirteen? Six does seem pretty precise.

Nov. 23 2014 02:39 AM
Richard from australia

This problem still exists! When I stayed in New York I spent a lot of time in bars and ordered a lot of pints. Not for a long time did I realise that American pints are much smaller than Imperial Pints!

Nov. 18 2014 04:55 PM
Archimbold Hannibal

It is very interesting to know where the standard comes from. It is also very good to know that the physical standard is being moved out in exchange for a fundamental measurement. Having a physical standard can lead to many problems that would be horribly detrimental to our current system. Everything based on a Kilogram would then be somehow incorrect. With a fundamental standard. this cannot happen. The force will not change overtime, it will not loose mass, and it cannot be corrupted. A fundamental standard will ensure that things will run smoothly.

Nov. 03 2014 09:14 PM
Loreli E. Bond from Florida

This was so interesting because I have never though of what weigh actually is. I see it on many products, but never thought that the world must have a single standardized version of a "kilogram". It's crazy to see how some scientists are changing the standardized unit from something tangible to something expressed in words.

Nov. 03 2014 08:10 PM
Aldous T Chrinchton

I think it's crazy that this plum sized kilogram weight is the only physical measure we have to accurately measure a kilogram. That is insane that there used to be 250,000 different measurements.

Nov. 03 2014 07:58 PM
Alice H. Nash

I think this was a very interesting podcast. It brings up a lot of interesting things that people never think of. Like the ruler example at the beginning of the podcast, how do you know that an inch on my ruler is the same inch thats on your ruler? Or even where any of these units came from. It is amazing how these units have impacted businesses and the trade industry as a whole.

Nov. 03 2014 02:11 PM
Upton D. Wilder

I found this podcast very interesting. You never really think about how the first meter or kilogram was measured. Or how the standard units came in to being in general. I learned a lot from this podcast that I didn't know before. I never really thought how the creation of the SI units has impacted international trade and commerce and how without the SI units, international trade may not even exist. I didn't know that the creation of the SI units had coincided with the French Revolution either. All in all, I found this podcast captivating and enjoyable.

Nov. 02 2014 08:25 AM
Sir Lancelot from Sparta

Interesting how the throw of a rock was enough to get us by, until the French revolution. However, it isn't much different than what they came up with to make the kilogram. The only upper hand it had on the throw of a rock measurement was how we got it (the circumference of the Earth/10,000 and some other mathematics mentioned). Yet, that was all that was needed to keep everyone on the same playing field. Although, the weight now keeps on changing from the original Kilogram, which leads me to believe our method to standardization of measurements is flawed. The solution is a theoretical standardization, rather than a physical standardization.

Oct. 20 2014 10:01 PM
Lorelei M. Coleridge

The effects highlighting the definitions at the beginning are creative but slightly disconcerting, but I think the other effects add interest. The historical reason for units of measure is fascinating, as well as how their definitions have changed since the times of the French Revolution, with the advancement of science. I would never have imagined that the original kilogram still exists or that there is such a systematic network of connections to it. However, it makes sense that the standard would lose mass over such a long time under varied circumstances. I'm glad that someone is working on defining it more fundamentally, and magnetism is probably more practical than the idea that popped into my head, defining the kilogram by a certain number of moles of some element.

Oct. 18 2014 05:32 PM
Joel Washere from Corvallis, OR

Wow. What a lot of people whining about the audio effects. I hope these duds will put down whatever stupid tools they use in their boring jobs and go to school for ten years and then spend another twenty working in a high tech metrics lab gaining experience. Then I hope they go on to make the worlds roundest tennis ball and win the Nobel Prize for doing it and then mail it to me here. If that actually happened I promise that I will give it to my dog.

Sep. 28 2014 12:50 PM

That woman's voice was so annoying!

Sep. 22 2014 03:42 PM
Robert from Raleigh, North Carolina, USA

I love this show, my wife does as well and I spend every minute that I'm in my car listening to one podcast or another. This one is a frequent player. I have a bit of an issue though with your normally very comprehensive reporting. There are a number of other proposals to solve the disparity in the weight difference. One, which makes probably a better Youtube video even is the Avogardo experiment. This is a proposal to use a specific number of Silicon atoms, which are presented as a pure block of Si which has been ground and polished into a sphere with amazing precision. One good video is this:

I think the one other item of note which wasn't mentioned is that this is the only SI "base" measurement which is actually a multiple of another measurement (1000 grams in a KG). Interesting that here, they don't have a "Le Grand G" or have redefined the SI standard to be the gram. I believe originally this was largely because the gram was too hard for anyone to actually accurately make, and since the original definition was "The mass of one cubic meter of water" (also adds in the question of water purity, but....), it was easier to stay with that through time. We now do have the precision to adequately and accurately define and make a SI gram standard, so maybe it's time to switch? (Maybe we could scrap the whole thing and just define a pound and go on with life, :) )

I would finally, like to answer one question I see in the posts here. The term being used is "Le Grand K" -- French which is almost literally -- "The (Huge/Important/Grand...) 'K'". While the question of "Le Gramme K" actually would make sense since this is the reference "KiloGRAMME", it's not what SI or CGPM/BIPM actually call it.

Sep. 18 2014 07:25 AM
Melissa G from America

One of the guys sounds like Neil Flynn.

Sep. 09 2014 04:56 PM
David W.

Roger - Australia from Queensland, Australia:

We in the U.S. are using "SI" units. Our National Institute of Standards has defined the pound as 0.453_592_37 kilograms since the 1950s. But, don't tell us Americans that. We'd freak out we found out that our American measurements were based upon some Frenchy system. After that, it's only a small step to sipping wine, wearing berets, and playing soccer.

Thomas Jefferson (the third President of the U.S.) tried to get the U.S. to adopt the metric system. Under his influence, we were the first country to adopt a decimal based currency (100 pennies to the dollar). Since currency was based upon the weight in precious metals. It made sense to use a decimal based unit of measure as our official unit of measure. Unfortunately, the French Revolution turned violent, and the metric system became synonymous with the guillotine.

Aug. 26 2014 02:07 PM
Brandon from Reno

What do they call the International Prototype of the Kilogram (IPK)? In the show they keep saying it, but I can't find it on Google or Wiki. "Le Gramme Ka"?

Aug. 15 2014 12:44 AM
singertriboscience from 22302

To the 'keepers of standards,' it's not just about accuracy or about stuff, it's about precision and universality. Measurements must be accurate but also precise (more significant figures). I hope that the lay audience could appreciate the creativity of physicists in finding physical processes capable of ever-more precise values of standards. Hopefully, someday we'll learn empirically what we believe to be true: that physics here is the same as physics everywhere in the universe. ET: are you listening??

Aug. 10 2014 02:27 PM
James from Australia

'Those effects aren't just gimmicks. They serve a communication purpose. And this is why I love Radiolab.'

I found it hard to comprehend what they were saying due to it. I'd say that's a failure.

Aug. 08 2014 02:07 AM

I usually enjoy the computerized voice overlay effect, but its use during the scientist's revised definition of the kilogram obfuscated what he was saying, making it incredibly difficult to understand. Not the best moment for a show that takes pains to effectively communicate science to public.

Jul. 30 2014 03:34 PM
Trevor Post from Florida

I thought the voice effect on the standard units was a fun and effective touch, as a counterpoint to the negative feedback I'm seeing here. It made me think of Glados from the Portal series. People are often quick to point out what they dislike but are less inclined to offer praise when they expect a good/great product/service. Thank you Radiolab, for being awesome.

Jul. 14 2014 02:07 PM
Andre from Seattle, WA

I would also like to comment on the voices, noises, sounds, whatever you want to call them. They do make it difficult for me to understand what is being said, as I have problems picking voices out of the clutter. I am absolutely useless at a party and just tend to avoid them since I can't understand what people are saying. I will admit your bits and pieces aren't nearly as bad as some radio shows where they multiple hosts and they talk on top of each other. Great piece in any case.

Jul. 10 2014 05:13 PM
ArvVee from Toronto, Canada

Hang on... so French mathematicians made their original "kilogram" starting with a linear measure, the meter (which they then cubed). And a meter was one ten-millionth of a quarter of the earth's circumference.

What unit of measure did they use to find the earth's circumference? For that matter, what METHOD did they use to measure the earth's circumference?

Jul. 06 2014 01:52 AM
fartboi from fartland

at around 11:00 there is a shrill operatic voice that hurt my ears while listening on headphones at a normal volume. please don't

Jul. 04 2014 11:39 PM
Jean from Rochester, NY

Hey nice samples from the Swingle Singers in the soundtrack. For fellow fans - their 1964 Jazz Sebastian Bach albumn is available on CD.

Jun. 26 2014 11:33 PM
dov from Adelaide, Ozlandia

As I have come to expect, the content of this show was both insightful and amusing.
That's pretty much a given these days. I would, however, like to add my 2¢ regarding the sound design.
Listen not to the nay-sayers, J & R, the operatic singer and the repeated overlay of formulas worked brilliantly for me.
Great show; keep up the good work.

Jun. 26 2014 09:29 AM
Amaro from Brazil

There are also other researches trying to re-write the deffinition of a Kilogram, like the "Avogadro Project" for instance. I just think that you should have touched the subject and spoken about the other researches

Jun. 24 2014 01:08 PM
Rebecca from Lake Tahoe

Bach Fugue no. 2 in C minor from the Well-Tempered Clavier!

Jun. 23 2014 08:35 PM
Yanik from Brooklyn, NY

Hey guys, you say in the story that the French create the KG by taking one ten-millionth of a quarter of the earth's circumference ('the meter'), cubing it, filling it with water, taking the mass of the water and then creating a metal cylinder with the same mass. Given that this procedure should yield the same mass every time it is invoked, the fact that the original unit of measurement 'lost weight' shouldn't have been a cause for panic (or even necessitated the use of the 'magnetic force' measurement) since anyone could simply reproduce the initial process that forged the first kg, producing the exact same mass as before.
Is there something wrong with my logic? Please email me, as I'm curious to know!

Jun. 23 2014 01:48 AM

Ben Vernia, a straight-edge is easy to make. Make two sides parallel (it's easy to gauge that with a caliper) and lay it first on one edge then the other on a flat surface. When no light gets underneath in either position, the surface is flat and the straightedge is straight, killing two birds with one stone. There are methods like this for creating all measuring instruments; they don't derive their accuracy from some "original perfect" instrument created by God.

(Also, the "world's roundest object" is at the CSIRO/NMI site just 4km from here - they have one of the duplicate 1kg standards there. The video shows the young project manager, not the older bloke who actually made it round. The world is running out of his kind of person)

Jun. 22 2014 07:36 PM
Ben Vernia

As a weekend woodworker, I've sometimes thought that there must be a genealogy of tools - particularly straight edges. In order to create a straight edge, you must use some tool that itself has a straight or flat edge. You could create the edge of a wooden ruler, for example, but you would probably use a hand plane to do it. The base of the plane, which defines the straightness of the ruler edge, was in turn created by another, earlier tool with a straight or flat surface. If you knew the provenance of each tool in turn, you could find some very ancient tool from which modern tools descend.

Jun. 21 2014 09:42 PM
James AG

I really loved the scoring on this one.

Jun. 20 2014 01:55 PM
Jose from Singapore

I actually liked the playfulness of the female voice while they were reciting the definitions. I think the point of those segments weren't to tell you exactly what the definition are but to give you an impression how technical and otherwordly they are. Compared to, say, the intuitive though imprecise measures of, say, a stone throw's away.

Those effects aren't just gimmicks. They serve a communication purpose. And this is why I love Radiolab.

Jun. 19 2014 10:20 PM
Brett Johnson

For the setting the new standard for KG, how do they account for the differences in gravity depending on where you are in the world?

Jun. 19 2014 04:56 PM
Mike Henry

I love Radiolab.
Let me rephrase: I love the *content* I hear on Radiolab. But I have never in my life heard a more over-produced program. The random echoes for emphasis (that then loop underneath the actual VO for the next 10 or 15 seconds), the goofy sound effects, and — most irritating — the tendency they have for interjecting the sudden screech of an operatic alto at four times the decibels of the quiet talking that immediately preceded it! You should try listening to your own show on some earbuds, then decide if that's a pleasant experience.

I get it. You guys are cool, and edgy, and unique. Good. Fine. But can you just dial it down a couple of notches?

And why am I posting this comment on this particular episode? What set me off unfortunately happened at the opening of the program (which truly affected my ability to enjoy the rest of the show), when, as the standards for various weights and measures were being read aloud, the producers thought it might be awesome to have an excruciatingly annoying female munchkin voice at 2-times speed repeat it, about two beats behind the actual human voice. Holy cow, that was irritating!

Otherwise, fine work (truly)! Just please, a little less vigor from- and a little less caffeine for your audio production staff.

Jun. 19 2014 12:22 PM
Will from Seattle

Has no one heard of a stone's throw away?
"Throw a rock"..?

Jun. 19 2014 11:53 AM
Joe Holm

What about using one mole of some element? If we found out that one mole of calcium was a kilogram, could we use that as a standard?

Jun. 19 2014 08:04 AM
Just a Random Physicist

The reason why "The Mass of one Litre of Water at four degrees Celsius and one atmosphere of pressure" definition doesn't work is because it relies on a unit of pressure, the atmosphere, because the density, and therefore mass, of water changes with pressure. And because pressure is defined as force over area, and force as *mass* times acceleration, you would have a circular definition. And that just doesn't work.

Jun. 19 2014 05:32 AM
Life from Mars

Brad, I was confused about the definition too, because I also thought it was based on a given volume of water. Based on wikipedia I think the initial definition was 1kg=the mass of one liter of water at 4 degrees C, but I'm assuming for ease of measurement, they made a metal one. And it so happened that the metal one was slightly off from the actual defined kg, but since that was the standard, then the definition of kg changed. I do wish they had clarified this point in the podcast, but still thoroughly enjoyed listening!

Jun. 18 2014 03:56 PM
Solomon from Ohio

Minority Report

Jun. 18 2014 02:31 PM
Saranya Phadungruengkij from Thailand

It will be better if this podcast is translated into alphabet or article ,too. Because I can't listen by android.

Thank you.

Jun. 18 2014 01:45 PM
Solomon from Ohio

I was more distracted by trying to place the singing, from what movie was it taken?? I just cant place it.

Jun. 18 2014 10:45 AM

I second the comment about the singing of the measurement definitions. As an ADD person, it was completely crazy-making.

In that same vein, your "mix tape" goodie is a nightmare for introverts, who are easily overwhelmed by too much simultaneous stimuli. This is one of those ideas that sounds better in your head.

Jun. 17 2014 10:14 PM
gc from nj

Great story but the woman singing was really distracting, I get artistic liberty but I was really trying to hear and understand the definitions.

Jun. 17 2014 08:29 PM

What where those podcasts mentioned during the direct donation portion of the podcast? I thought I heard "Byline Earned" and "Brainpickings", but I can't find anything called "Byline Earned".


Jun. 17 2014 05:15 PM
Roger - Australia from Queensland, Australia

The elephant in the room here is why all the reverential worship in this American podcast of SI Units, when Americans stubbornly refuse to use SI units? Ditch your silly pounds, miles,inches and Fahrenheit and get with the 21st Century and the rest of the world community! Everyone else made the change - why not you?

Jun. 17 2014 05:13 PM

Mass and weight are not the same thing. You use them interchangeably in the story which is quite disconcerting for a physicist. Other than that, great story.

Jun. 17 2014 04:14 PM
Brad from San Diego, CA

1kg is supposed to be equal to the mass of 1L of water at 4 degrees C, right?

What am I missing?

Jun. 17 2014 02:53 PM

One of my favorite family stories is of unconventional measurements - I was reminded of it by the description of throwing a stone to measure distance. In the 1950s my two great great aunts, who had spent their lives working as missionaries in China, moved to Taos, NM. The old woman who sold them land in the Taos canyon measured plots of land by how far she could walk before her cigarette burned down. A charming measurement that caused my dad headaches when he eventually inherited the land and had to determine propert lines.

Jun. 17 2014 01:16 PM
Jared Van Leeuwen from Monroe, WA

A Kilogram isn't a measurement of weight, it's the measurement of mass. An object is the same number of kilograms that it is on the Moon as it is on the Earth, even though the attraction to the large body due to gravity is different. Different places on Earth will have very tiny variations on how much gravity is affecting that area verses others.

Jun. 17 2014 11:51 AM

Does anyone know about Dinosaur Comics? 1. They're brilliant and 2. This very topic was covered (in much less detail, but in an amusing way nonetheless) on January 12, 2007:

Jun. 17 2014 07:56 AM
Risto from Austin, TX

C0br4 from Honduras:

The music sounds to me like the Swingle Singers

Not sure what song/s though. I have many of their albums on vinyl that I found at a thrift store and fell in love with! Check them out. Even if it's not them on the show you will very much enjoy them (especially the older works)!

Jun. 16 2014 07:05 PM
C0br4 from Honduras

Does anyone know the music used in this episode? I'm dying to hear it 500 times

Jun. 16 2014 01:56 PM
Frank from Yakima

The Veritasiun podcast is this same subject not long ago.

Jun. 16 2014 01:10 PM
Chris from Sweden

So after listening for like 200 times I finally understood the name of the museum. Here's the link for everyone else interestedée_des_Arts_et_Métiers

Jun. 16 2014 03:33 AM
nino from behind you

Damnit somebody else beat me to it but yeah "World's Roundest Object" by Veritasium:

Jun. 15 2014 04:55 PM
Steffen from Germany

PLs added other Payment options. Im from Germany and the most here dont have Creditcards. E.G. Paypal.

Jun. 15 2014 02:57 PM
Adrian Carmona from Puerto La Cruz, Venezuela

Greetings from Venezuela awesome people!!!
I've been a fan of you for a long time! But this is the first time that I'm compele to give an input;
I just want to point that you didn't talk about the other form to substitute the "Big K" and I don't know how you missed...
You can find on youtube an excellent video from "VERITASIUM" about (and you can search it by this title)
I hope you can find it interesting as I do!
Love the show!

Jun. 14 2014 01:47 PM
Margo from Seattle, WA

Donated! Always wanted to but forgot and finally got a new job so it's a lot easier to contribute to something I love so much~ Excited to also be receiving a mix tape

Jun. 13 2014 06:27 PM

I have finally donated. I hope the mix tape uses music from the show. I have found so much great music listening to this show

Jun. 13 2014 04:28 PM

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