World’s Roundest Object!

Can I hold it? Only if you promise to be really, really careful. I promise I will be so incredibly careful.
I will be incredibly careful with it. I promise. So, it’s slippery, be careful.
Alright, are we ready? I’m about to touch a 1kg sphere of silicon-28
atoms. There are about 2.15×10^25 of them. It feels absolutely incredible. Wow, that
is amazing. Besides its creators, I am one of only a handful
of people ever to hold this sphere. The raw material used to make it was worth
1 million Euros but now that it has been so precisely sculpted — How much is that worth? It’s priceless. … This you are looking at
now is the roundest object in the world. How can you say for sure it’s the roundest
object? I mean the Earth is pretty round, isn’t it?
If this was the Earth… If this were the Earth then the highest mountain
to the lowest valley would be… about 14m apart. That is shocking. That is shockingly round. But why would you invest one million Euros
and thousands of man-hours perfecting a pure, polished silicon sphere? Well the answer is grave. Or rather ‘grave’
as it would have been pronounced in the original French. You see the grave was the original name for
the base unit of mass in the metric system, which became the Systeme International d’unites
or SI units. In 1793, a commision which included notable scientist and aristocrat Antoine Lavoisier,
defined the base unit of mass as the weight of a cubic decimeter of water at the melting
temperature of ice — essentially just a litre of ice water. The name grave came from the
Latin gravitas, meaning weight. But it wasn’t to last. It sounded too similar
to the aristocratic title ‘graf’ — which is the equivalent of an earl or a count. And
with the French revolution in full swing with the rallying cry of equality for all, you
couldn’t exactly have one unit nobler than the others. At this Lavoisier lost his head,
literally, not because he helped devise one of the greatest systems of measurement of
all time, but because he was collecting taxes as a nobleman. So things really were grave. The new republican government believed a grave
would be too big for the things they wanted to measure anyway and and so they settled
on the gramme, which was just a thousandth of the grave. But soon they realized that a gram was too
small and so they returned to the grave, but since they couldn’t call it that, they invented
the kilogram — a thousand grams. And that is why out of the seven base SI units, the
kilogram is the only one to have a prefix in its name. In 1799 the kilogram definition was refined
to be the mass of a litre of water at 4 degrees Celcius — the temperature at which it is
densest. But water itself is obviously not the most sensible thing to use as a mass standard.
So a pure platinum cylinder was created to have the same mass as the water definition
and it was declared Kilogram of the Archives. Now it’s important to note at this point the
kilogram is no longer tied to the mass of a volume of water — the kilogram of the archives
is by definition THE kilogram. 90 years later, in 1889 the kilogram was upgraded
to a platinum-iridium alloy cylinder. Now it was much harder than the original but was
otherwise basically identical. And to this day, it remains the definition of the kilogram.
It is officially called the International Prototype Kilogram, though it’s affectionately
known as Le Grand K — or Big K. Oh, and it’s about this big… It is the only thing in the entire universe
with a mass of exactly one kilogram because it IS the kilogram. It is also the only SI
unit that is still defined by a physical object. It sits under three bell jars, next to six
sister kilograms, in a climate-controlled vault locked by three independently controlled
keys, in the basement of the International Bureau of Weights and Measures on the outskirts
of Paris. Now if you were able to break into the vault
and tamper with Big K, you would be changing the definition of the kilogram, a definition
on which many of our measurements rely, and so you would throw the world into chaos! Well
no, not actually– but how would anyone ever know if the mass of Big K changed? Well when it was first created, 40 identical
replicas were also made. Well they weren’t quite identical – they had a mass which was
slightly different to Big K but those offsets were recorded. Now these replicas were sent
out to countries around the world to serve as their national standards. In 1948 the kilograms were reunited for a
weigh-in. And this is when the problems started. Because even though all the cylinders were
made of the same alloy and stored under virtually the same conditions, their masses had diverged
over time. The mass of Big K wasn’t even the same as the six sister cylinders stored with
it. And to make matters worse when they were brought together again forty years later,
their masses had further diverged, up to about 50 micrograms – that’s about the weight of
a fingerprint. But fingerprints were not the culprits since the kilograms were carefully
washed before their weigh-ins. So some physical process must have actually
changed the mass of the cylinders, but how that exactly works remains a matter of speculation.
One this is for certain, the mass of a platinum-iridium cylinder is not stable over time. And this
is a big problem. You can’t have a unit which changes its value.
And the fallout isn’t limited to measurements of mass since of the seven base SI units,
four of them depend on the mass of the kilogram, not to mention all the derived units like
Newtons, Joules, Volts and Watts. At this point those of you in countries that
have not adopted the metric system–yes I’m speaking to you Liberia, Burma, and the US–you
may be feeling rather smug that your unit of mass, the avoirdupois pound, is no longer
defined by a physical object. No, instead it is defined as precisely 0.45359237 kilograms. Sucked in. So clearly something needs to be done to eliminate
the kilogram’s dependence on a physical object and this is where the silicon sphere comes
in, but how exactly does that help? Here you have a physical object and it’s beautiful
but you know it’s still a physical object. You’re trying to get away from that.
We’re trying to get away from the physical object but what we’re doing with this particular
object is counting how many atoms are in there. You can’t actually count how many are in there
can you? You can’t count how many are in there but
you can calculate how many are in there because this material is silicon, there’s no voids
or dislocations. So this is like a perfect crystal of silicon.
That’s right. Not only is it pure silicon, it contains only
one isotope of silicon, silicon-28, and that explains why the original material was so
expensive. And why a sphere?
Well, a sphere is a pretty simple object. If you know the diameter of the sphere you
can characterise the entire dimension of the object.
Well that explains why the sphere has to be the roundest object ever created, but how
do you actually make something that round? We actually start with an oversized sphere.
So it was about two millimetres larger in diameter and then we just grind it progressively
finer and finer using abrasive. It’s actually massaging atoms. You’re down at that level
of trying to control the shape of an object down at the atomic level.
But making the sphere is only half the battle, then you need to accurately measure its diameter.
The diameter is actually measured via a laser. So you’re actually measuring having the sphere
in the centre of a cavity and a laser is hitting both sides and you’re actually measuring the
gap. By knowing the diameter you can determine
its volume. And since the atom spacing in silicon is known to high precision, you can
the calculate how many atoms make up the sphere. This allows you to redefine Avogadro’s constant.
At the moment, Avogadro’s constant is defined based on the kilogram. It is equal to the
number of atoms in twelve grams of carbon 12. But using this approach, the number of
silicon atoms in the sphere would be used to fix Avogadro’s constant, which would then
define the kilogram. So even if the silicon spheres were lost or
damaged, it would have no effect on the definition of the kilogram because it would be defined
not by a physical object but by a concept. You would like to see the official definition
of the kilogram say “a kilogram is the mass of 2.15×10^25 silicon-28 atoms”
Yes. Is it – is it going to happen?
There’s a likelihood, a high likelihood that it’s going to happen.
But there is another approach to redefining the kilogram which involves fixing Planck’s
constant and it’s done using something called a Watt Balance. These two approaches are complimentary.
Each one provides a check on the other, and if they show good agreement and are able to
bring their uncertainties down to about twenty micrograms they may redefine the kilogram
as early as 2014. And then the kilogram finally will be an unchanging unit, no longer defined
by a physical object in the basement vault of some place in Paris.
Now if the kilogram was originally intended to be the mass of a litre of water at its
densest temperature then how well did we do? Well if you look at a litre of water at nearly
four degrees Celcius it has a mass of 999.975 grams. So I guess you could look at this two
ways. On the one hand you could say the kilogram is slightly heavier than it should be, but
on the other hand 214 years ago, scientists were able to create an artifact that was correct
within the margin of error of a grain of rice. Now that is truly remarkable. Now if you want
to hear more about the Watt Balance, let me know in the comments and I will see what I
can do. It does seem to be the frontrunner in terms of redefining the kilogram, so we
will have to wait and see what happens. One last thing, I should point out that it took
an international collaboration of scientists to create the silicon sphere but don’t you
think that the scientist who originally conceived of silicon as an element should receive some
of the credit. Well in 1787, that was none other than Antoine Lavoisier. So he’s been
involved in the definition of a kilogram from start to finish or from cradle to grave.

100 thoughts on “World’s Roundest Object!

  1. Hi Ve
    A grate fan of you Channel here:

    the silense between [10:11] and [10:27]
    as i recall and i remembered it, you verry slight brieflie touch the subject about info of cigarettes containing about the ingredients like suger and radioactive material (something ?)

    Quick question…
    – why is it scilenced out?
    – where can i find your Ve vision about this topic

    Thank you

  2. is it possible that the Earth's rotational speed has something to do with the weight differences ?
    meteors known and unknown slamming Earth can possibly be a reason ?
    also weather in the past 40 some year's may have caused some degree of change in it's weight ?
    do you think or wonder if we brought a giant Dinosaur from a million years ago to the present , would the dinasaur be able to stand and walk normal like it did back then or do you think it would flop to the ground due to it's emence weight and the Earth spinning slower than it did millions of years ago ? the Mayans predicted the end of the Earth 2012 , they gazed and studied the stars as we do a tv screen.
    for thousands of years (?)
    in 1994 the planet Jupiter was hit by a comet that left a hole 3/4 the size of our planet . the Mayans maybe predicted that the comet was headed for us , they were only 22 years off .
    lucky for us Jupitor blocked the comet saving us from an extinction level event , like in that movie ? 🤔

  3. (Preparing for a massive wave of hate)
    I genuinely believe that the imperial system is more useful than the metric. Allow me to explain.

    1. The units are of a more practical size for measuring things. Decimals are not required for measuring the height of an average-ish human, which is what I and many other people are measuring the most often. Having to resort to either decimals or centimeters before reaching the number 2 gets a little annoying sometimes.

    2. Being able to convert centimeters to meters to kilometers and so on very rarely comes in handy. It does not help to know that someone who is 1.8 meters tall is also 1,800 millimeters, or 0.0018 kilometers. It is not essential to know how many inches tall someone is to know how many feet tall they are. Almost everyone who uses the imperial system measures their height in feet. When there is a partial foot of space left after all the exact feet have been covered, the remaining height is measured in inches. The metric system is very similar, just substitute feet for meters and inches for centimeters in the last 2 sentences.

    3. Advocates of the metric system are a bit hypocritical when they say something like this: "The imperial system is so inconsistent! 12 inches a foot, 3 feet a yard, 5280 feet a mile, it makes no sense!". While it is true that the metric system goes up or down by a power of ten each time you increase or decrease the size of a unit, many of these units are basically never used. I can't recall the last time I remember someone using a decagram or hectometer. So you essentially have a system that goes like this: Ten millimeters a centimeter, a hundred centimeters a meter, a thousand meters a kilometer. Any units in between these three are rarely used, just as there are units in the imperial system that are almost never used, such as hogsheads or cords.

    4. If having your units easily convertible to each other is just that much better, why don't we do the same for measurements of time? Why not ten seconds a minute, ten minutes an hour, ten hours a day, and so on? If the units in the imperial system were actually difficult to convert to each other, as advocates of the metric system often say, then very few people would know how long an hour or week is. Obviously this is not true, as basically everyone on the planet learns the globally accepted system of measurements for time before graduating preschool.

  4. Hi Derek – when you picked up that ball of silicon 28 you probably brushed off a couple of atoms…. But okay, like you told us to expect, on the 20th May 2019 the kilogram was redefined on the basis of Planck's constant – yeeee!

  5. What about the ambient pressure? Does it changes the sphere size? And what about the laser measurement of the sphere? How reliable is it, really? Cause I saw it spinning and, since it spins to measure, it must have perfect components measurements that forms the mmachine's mechanism so it can be perfect. I see lots of flaws. Even the gravitational earth's pull could change the sphere's measures in one or another axis. I think it's an impossible task to have a perfect definition of a kilogram because it simply won't ever be a constant.

  6. I think this pure silicon object is polished by "Okamoto" in Yokohama in Japan.
    I have nerver met the engineer who polished this.
    But I heard this object was finished by hand polish in the last process from the sales of them.

  7. When he picked it up I wish he would of freaked out like Morty did when he walked on Rick's perfectly level floor.

  8. The kilagram cyinder units could absurbing cosmic rays from the sun that can penetrate through the cylinder absorb it . To see which one got heavyer or which took in more cosmic rays relative to location on Earth.

  9. Once you pick it up you stop and say "oh it's kinda heavy, how much does it weigh again?"
    Then you get their face on camera and BREAK THE INTERNET! lol

  10. 20 May 2019

    The kilogram is defined in terms of three fundamental physical constants: The speed of light c, a specific atomic transition frequency ΔνCs, and the Planck constant h. The formal definition is:

    The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs.[2][4]

    This definition makes the kilogram consistent with the older definitions: the mass remains almost exactly the same as the mass of a litre of water.

  11. My weed guy will tell you all you need to know about kilos man. He know his [email protected] people. So spending all these Euros on a round shiny ball is a waste.
    He can even make a kee "look" round dude! With his nothing but his sticky hands…


  12. So if this sphere were the Earth then the highest mountain to the lowest valley would be… about 14 meters apart. Pfft. Not impressed. I was thinking she was gonna say the difference the highest and lowest points would be about .14mm not 14 meters. I make snowballs smoother than that. LOL

  13. Hang on.. is no one going to talk about how the mass of identical objects changed over time.. it's not as if they were radioactive.. so wth is going on??

  14. The most spherical man-made objects are the fused quartz gyroscopic rotors onboard the Gravity Probe B Spacecraft operated by NASA and Stanford University. Their average departure from mathematically perfect sphericity is only 1.8⋅10−71.8⋅10−7 of their diameter.

  15. Kilogram : *defines avogrado's constant*
    Avogrado's constant: UNO reverse card
    Kilogram: now defined by avogrado's constant

  16. Erreur la révolution française n'a profité aucunement au peuple,bon visionnage.

  17. Wooow I watched this when it first came out. I'm now starting college and I thank the youtubers such as veritasium, steve mould and the king of random for my interest in science. I've had learning disabilities my whole life and I passed science with higher than 2 C's. Thankyou for inspiring me to learn

  18. My nipple is perfectly oblong maybe the amount of hairs on nipple to the 12th power divided by pi +7.29 to the 3rd power can equal a deep fried rat at whataburger?

  19. it's round, but i think the nature can outtake that out, it's make a clear since why we need a uniform wight, but it also a meth.

  20. Warning: don't watch this video right after seeing the movie "Phantasm".

  21. I'm a CPA, and I can't tell you how many atoms are in the sphere, but I can tell you EXACTLY what it cost. Accounting triumphs over science!!!

  22. Are u telling me every object that I have seen in my entire life wasn’t even round ?? Damn I thought they were round but I started checking on every round object which I can find & figured I was wrong cuz they’re all squares and shapeless.. heahea🤪🤪🤪
    Pls tell me if I am exit


  24. I believe she said that the sphere is so round that if it was scaled up to the size of the Earth the difference between the highest and lowest point would be about 14 meters. The gyroscopes built for the Gravity Probe B satellite were rounder. At the time of their manufacture, the gyroscopes were the most nearly spherical objects ever made.Approximately the size of ping pong balls, they were perfectly round to within forty atoms (less than 10 nm). If one of these spheres were scaled to the size of the Earth, the distance from tallest mountains to the deepest ocean trench would measure only 2.4 m.

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