The kilogram has changed forever. Here’s why.
100 Comments


– I grew up in the United States, which means I used pounds and ounces to measure everything
that I used growing up except maybe soda bottles. – Right, and I grew up in the U.K. where I use the metric system
for pretty much everything and pounds are what I pay
for things in the store with. – So while we don’t really agree on a unit of measurement yet, there is one thing that everyone
should be familiar with, and that’s the kilogram. – Right, and not just
because it’s a superior unit of measurement or because it’s used pretty much everywhere in the world, but because it recently changed. (rhythmic drumming) – How much does a kilogram weigh? This is not a trick question. When the kilogram was first introduced as a unit of mass in the 18th century, it was decreed to be the absolute weight of a volume of pure
water equal to the cube of the 100th part of the meter. (Correction: the 10th part) Basically, one cubic
decimeter, or one liter. About this much. Anyway, the French scientist who came up with this definition soon discovered it was a little sloppy. The weight of the water changes depending on things like purity
and atmospheric pressure. So they’ve replaced that definition with something like this. For more than a hundred years, a metal artifact similar to
this has been the definition of the kilogram. The real one is made of platinum iridium and it’s called the
International Prototype Kilogram. Since 1889, it’s been
kept under lock and key in a vault on the outskirts of Paris. The Prototype Kilogram
has been a big deal. Think about it. If we didn’t have
reliable units of weight, how would countries trade? How would scientists repeat experiments and share their results? How could you trust a recipe or even your bathroom scales? That little chunk of metal is the foundation of the modern world. But recently, scientists
voted to get rid of it and they replaced it with
something far, far stranger. (rhythmic drumming) – Last month, I visited
the headquarters of the International Bureau of
Weights and Measures in France, the body that acts as the
guardian of the metric system and I watched as delegates
from 60 countries voted to retire the Prototype Kilogram. It was amazing to see. Each country standing
up to vote one by one and then the whole hall erupts into applause and congratulations. (applause) For some of the scientists there, it was the culmination
of a lifetime of work, slimming down the world’s
system of measurement so that all the definitions
now fit onto a single card. (contemplative music) – But before we get into that, let’s think about how
weights work in general. We know that the Prototype Kilogram and its successor define
standards of weights around the world, but
if you grab some scales and weigh out a kilogram of flour, how do those scales know
how much a kilogram weighs? Well, we called some scale
companies to find out. – [Phone Voice] Hello, how may I help you? – Can you tell me how you go
about calibrating your scales, how do you make sure
that they’re accurate? – [Cory] Here’s what we learned. Basically, a scales company like Escali buys calibration weights
to place on their scales and dial them in. A weight like this one was measured against an even more accurate kilogram, which itself might be measured against an even more accurate kilogram, all the way up the ladder of accuracy, until, in the U.S. anyways, it reaches the National Institute of
Standards and Technology. They have a couple of
very special artifacts: two of the 40 original weights that were measured directly against the International
Prototype Kilogram in 1889. – And they numbered them from one to 40 and they screwed one number up and they left out eight and
numbered it 41 by mistake. (laughs) Small little detail. – [Cory] That’s Stefan
Schlamminger, a physicist at NST. He says there was a global raffle for countries to get
the 40 original weights. – And the United States got
two: number four and number 20. – [Cory] Today there
are more than just 40. New ones are measured against a final, ultra-accurate stand-in for the IPK, called the Working Standard. – The Working Standard is basically used to calibrate now all
masses from all nations. – That’s how things used to work, but with the redefinition last month, instead of tracing weights
back to the Prototype Kilogram, there’s a new top boss. The kilogram is no longer a lump of metal, it’s a constant of nature. (godly chorus sings) The kilogram isn’t the first
unit to go through this change. In fact, it’s the last. The meter, for example, was once defined as one ten-millionth of the distance from the North Pole to the Equator, a length that was enshrined
in a physical artifact. Now, it’s defined as the
distance that light travels in a tiny fraction of a
second, about a 300 millionth. The kilogram, on the
other hand, is now tied to the smallest action that
can be made by a photon, which is essentially the smallest possible
physical action there is. It’s called Planck’s Constant and in order to tie mass to it, scientists had to create one of these, a Kibble Balance. It works like an
old-fashioned balance beam, but instead of weighing
one mass against another, it weighs one mass against
an electromagnetic force. This force can be measured
with extreme precision using Planck’s Constant and this will be the new
definition of the kilogram. – But look, there’s one question we’ve not talked about so far. Why? Why are we going to all this trouble? Well, when I spoke to the scientists at the big vote last month,
they gave me two reasons. First, accuracy. The problem with using a physical standard to define the kilogram is
that physical objects change. None of them last forever. And over the past few decades, the Prototype Kilogram
itself has lost mass. Not much, about 50 micrograms, or the weight of a human eyelash, but still, thanks to that huge chain of calibrations we traced, technically every kilogram
in the world ends up shifting by one eyelash weight. Not ideal. But more importantly, they
said it was about ideology. The Prototype Kilogram is based in France because it was created
during the French Revolution. This was a time when
revolutionaries were tearing down and reconstructing so
many of society’s norms. And that included
weights and measurements. They wanted to make units
that were consistent, that were fair to the
working man and woman. And that was shared between countries. They wanted to unite the world. Their motto was “Pour tous les temps, “pour tous les peuples, for
all time, for all people.” But if we define mass using a single Prototype
Kilogram locked away in a basement in France, then it can’t be for all
men and for all women. And if it changes when we measure it, it can’t be for all time. So the scientists say
by tying the kilogram to a constant of nature, we are, in a way, freeing it
from its physical constraints. We’re achieving the dream of the creators of the metric system, a journey that’s been
centuries in the making. – Planck’s Constant is something, it’s woven into the
fabric of the universe, so everybody can access it. And I think that opens a whole world. (claps) – [Man Offscreen] Um. – Ah. (claps) (laughs) (claps and laughs) Sorry I’ll stop laughing
when I do that eventually.

100 thoughts on “The kilogram has changed forever. Here’s why.

  1. Correction: An eagle-eyed viewer pointed out a small error when we described the old definition of a kilogram. It should have been "the weight of water equal to the cube of a tenth part of the metre"…not "the hundredth part." Otherwise, you'd be getting a gram, not a kilogram. Good catch…and a good argument for the metric system!

  2. What is the UK guy on saying we use metric for everything? We weigh ourselves in stones and pounds we use Miles for distances and buy milk in pints. We also use the metric system for various things but that’s been a slow change across my life and I’m about the same age as that guy

  3. I argued it was a human invention about a year ago, and now they're tying it to a constant of nature. Thanks for the video!

  4. Another reason why EVERYONE LEFT BRITTAIN& FORMED AMERICA.THIS "video", explained NOTHING.no shock.keep patting yourselves on the back while rubbing one out.Damn. P.S.I STILL LOVE TYSON FURY. ELEMENTARY KID, PEACE OUT

  5. I personally haven't had a need to learn metric yet. For the few times I'm presented with something only listed in metric, I just ask my phone to convert the metric unit to something useful. Usually that's only when I'm traveling outside the US, but even then I often see friendly pounds, feet or gallons in small print next to metric.

  6. So they picked Planck constant as the new defining constant for kilogram because Le Grand K was such a loser.

  7. whats heavier
    a kilogram of steel?
    or a kilogram of feathers?
    obviously a kilogram of steel because steel is heavier than feathers

  8. It’s interesting how life progresses for with time for us I wonder how much does this accuracy effect and increase in our future of science achievements if any 👍🏻

  9. I don't know why but i am so touched watching all the scientist from all nations agreed about the definition and applaud 😭

  10. Hmmm… I wonder if there are implications to the gold standard ("sound money") vs MMT monetary ("fiat money") debate.

  11. Just to clarify, Americans do like the metric system, its just nobody wants to be the first one to make the switch.

  12. 300 million people's homes are gonna be underwater in a few decades and we're spending money on this.
    Let that sink in.

  13. The kilogram is the superior measure of mass. After all, it translates so neatly into useable measures for cooking and everyday life, and it did put an astronaut on the moon first.
    Oh, wait, yeah lol

  14. Good job, but why are all videos on this topic almost exactly the same? First, the new standards are yes, more accurate, but the other important consideration is universality. Now national standards organizations and science labs no longer have to base their accuracy by comparison to a physical object (and were labs using universal constants prior to the adoption of the new standard? I'll bet some were. Were they all using what became the standard, or were their different methods?) .
    Another thing none of these videos mention, except yours! is how practical kilograms (and grams) can be generated by anyone by following the original protocol. 10x10x10cm of Water. Yes temperature, air pressure, water purity are factors, but to weigh yourself, your luggage, your backpack, the food you're taking on a multi-day hike, or to immediately know the weight of the water you're carrying, all of these can be measured to reasonable and very practical degree using a bottle of water, a stick, a pencil and some string. ( btw a 2 liter soda bottle weighs about 50 grams) The meter however I find to be very elusive. Many of our smallest finger nails are roughly 1 cm wide, but I've never been able to develop even a 20 cm ruler that was reasonably accurate enough for any practical use. Ideology? The French Republic promoted the metric standard, but its work was started before the revolution. (with the Bourbon restoration did France reject any of the Metric system?) And it's not ideology, it's principle that is being applied with the new standards. And never forget to mention that all the measurement standards in the anti-Metric United States are based on metric measurements. It's why 1 inch equals exactly 2.5400000 cm, whatever my countrymen thought was an inch this was considered the most useful conversion from le metre. (I lived through the anti-metrication nonsense of the 1970s. Some of that nonsense would make an interesting video.)

  15. In murika we pay bills with dollar bills. LOL. I likes the metric system and old English where nice means fool and gay doesn't mean queer.
    Paying in lbs does sound more correct than paying with dollar bills.
    However after this video, I hate kilogram measurement even more now LOL.

  16. its all lies.. heres why they want the kilo gram and meters etc.. there finite smaller.. see lbs and feet are to broad and companies and people who sell things based on weight and or ship things think they are loosing money by making things super acurate they can increase rates… and scam us little people… like power companies now have digital meters… before you had analog worked fine companies realized they wanted more money so they found out on start up a fridge uses 6 amps then drops to 1 amp after 30 seconds the analog just measures the constant flow.. of power.. so they can lie and make up they need a digital to find out how much start up power you use.. meaning that 6 amps for 30 seconds they charge you that then when it goes to 1 amp your paying for 1 amp.. so cpmanies are captureing the little start up of machines washers and driers.. its pretty fucked up.. so they make an extra 5 cents per kilowat.. same thing with the weights and meassures thing they realized they can tape into smaller numbers and be more precise now they can charge if you fucking breath on the item and spit was left behind..

    no scientist create anything to benifit man any more folks.. they do it to benifit them self the institution that made it makes millions off the pattent and its not just handed over.. the polio vacine was givin away by a scientist that said this needs to stop he didnt want any reconition… yet handed it over and we all but cured it unless some idiot licks the poop hands of the last guy who still has it on this earth… lol so with that said fucking wash your hands before you eat people geesh.. after that companies big pharma realized they could profit from suffering so lets not cure lets stave off till that person dies… this is why suicied is illgal think about it your a money sack even if your in jail for life someone institution makes thousands per month off your suffering and you … this earth should be freee and open but since people are greedy and greed and doubt entered mans heart it will never change.. my dick is bigger than yours attitude and inflation omg dont get me started on that inflation is a way to make sure we cant afford things ie uncle sam wants his power back he gave us 500 years ago the middle class he wants poor and rich only why power… to control… anyway that the truth this world sucks and its only going to get worse.. be thankful you only live in it for alittle time

  17. oh and america will never adopt this shit why cuz we hate the world we hate the uk we wanted to be diffrent.. so thats why.. and its to engrained in us our system i wont start having a break out card just to figure out how much fuel i put in my car fuck that but i bet they force it on us in 10 years how by just swapping over and teaching our kids in school first and fuck the adults mentality people we need to take back the earth paradise was handed to us.. and we fucked it all up polluted it and raped it of resources all for greed all for money or pussy etc.. we could be like star trek all live in piece no money etc and by now wed be out in sapce and talking to aliens but greed has horded technology and horded knowledge and horded further advancements

  18. To clear things up for any of the uneducated ignoramuses out there who think America is dumb for not switching over entirely to the SI system of measurement:
    Many scientists and engineers in the U.S. prefer measuring weights in pounds rather than kilograms and temperature in Fahrenheit rather than Celsius because the English units are more precise than the Metric units for the same number of significant digit. When measuring smaller weights, the gram is preferred over the ounce because it is more precise, and so on.

  19. I’m in the UK and we use imperial and metric. A town is miles away, I’m 6ft, but that’s 30cm long and this is 7 meters.

  20. Metric is so much easier to use since it's based on 10. We in the USA think it's sooo hard to have to use it because we are not raised on it and the FPS (Foot-Pound-Second) system is so very ingrained in us. If we had been raised in the metric system and someone tried to get us to convert to the FPS system, we would think they were crazy. And we would be right. It's an ad-hoc system based on arbitrary standards.

    The one thing that would have been nice though is if the founder(s) of the metric system standards had made the meter to the same standard as the yard. They could have. All they would have had to do is adjust the millimeter slightly to make it all work out. That, at least, would have made the conversion of distance much easier to do in your head. But they didn't consult me, so here we are.

  21. Nah British people are of the firm belief that people should be measured in feet inches pounds and stones. And we more or less gave up the yard but you'll have to grasp the mile from our cold dead hands.

  22. That is actually so damn cool, to have the weights and measures tied to natural phenomena rather than physical objects. That's actually mind blowing!

  23. The good thing about being a drug addict in America is you finally get to learn the metric system! Oh, we learn real fast — as long as there's something tangible in it for us.

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