Here.

We're here.

Thank you very much for that.

Welcome and thank you for all attending
as you can see what the title is I'm

going to be talking about measuring
physics the metric system and

the Planck constant I'll explain all
that and base I want to get started that

there is going to be a new redefinition
there's been redefinitions of the better

system in the side over the last hundred
something years in its existence.

So this is not really big news.

But now they're talking about going though
the final definition redefinition is

talking about changing
the of the mass kilogram and

there were a lot of people who when
this was first proposed said we're not

going to do this until hell freezes
over or the B. I.P.M. freezes over.

Well that's where this is it's the B.
I.P.M. in Paris which is the national

laboratory and this is not too long ago
it froze over you might want to say.

And so people are now not so.

Against that the idea of changing
the redefining the color.

So my contents will start out I've
decided it into tour sort of two parts

one is ancient history ancient history
to your college students is any time

before you were born.

So the ancient history part goes up until
one thousand nine hundred ninety but

it does go back to about two hundred
years that the invention of the metric.

System the adoption of
the international system.

I'll be talking about the difference
between the base units and what lab star.

Units are that won't cover the whole
system but it'll cover a fair amount.

What's important.

Tonight and then I'll go into the plane
concept why it's important what is it

not everybody here who's a physics and
had third year head quantum mechanics you

may not even know what concert is I'll
try and explain as much as I can to

make it simple as I can how to measure
it in how they try to measure it nearly

one thousand hundreds and all the way
through the one thousand hundreds and then

people back in the day of our be heard in
the one thousand nine hundred they said

let's close the patent office because
everything has already been invented.

Science has done well there
were still quantum mechanic and

physics discoveries as late
as one nine hundred eighty.

So then when the second half or
so of the talks them up.

I'll talk about the modern history of way.

So let's start out the best idea for
all worlds somebody

who once said that it's the best idea
ever invented this or the world.

OK.
Russell Davies was talk about Dr Who but

the idea that the in the metric system.

Is meant to be the best for
all worlds meaning it standardized

the units so people could sell from one
city to another one country to another

Ultimately you might want to sell
in the future one world to another.

So what happed How did
the metric system in the US I

start really the metric
system pre-dates S.

which is the system International in
French or the international system.

So when I say yes I units
that's the formal adoption of

the bedrock system back in
the late seventies hundreds.

It was proposed in by scientists mostly
French and they come up with ideas for

standardizing things to world
level world constant standards.

The second was defined as one eighty six

thousand four hundred of us mean solar
day where that number come from sixty

seconds times sixty Minutes times
twenty four hours simple them or.

Royal observatories and.

That number relative regularly by watching
stars transit and things like that.

The meter they wanted something about.

Yeah long something convenient

because that's how people sold cloth
square something like that and

they said let's find something
that gives us a standard meter and

they came up the end they knew roughly
what their sick conference was said one

ten millionth of the earths circumstance
is about a convenient value and

then we can call it the meter and
now so they started out by saying

OK we have to measure that actually go
back to time just this is Davis Dava Sobel

wrote the book laundry Tud and
it was about the invention of the time

pieces that were then used in sailing
ships in the late sixty's and early

seventy nine hundreds and that's where a
lot of the time was already developed and

very sophisticated by the time
the metric system was being developed.

So then as I said they had to measure the
earth circumference in order to figure out

what meter absolutely was.

And here I'm going to define.

Make some kind of definitions we
have a definition of a standard and

then the realisation of a standard
meaning you're tying the definition

of the definition ties to some
what you think is a constant.

For the Earth's rotation.

It was thought the earth rotation two
hundred years ago was thought to be

absolute constant we know now it's not but
that's the way things go then.

Yes.
So the realisation ties some constant to

a an artifact.

And the artifact is a called it then it
transfers gets to be a transfer standard

that absolute normal person
can use here we have a copy of

the book notebook that was made
by machine and butter Brit.

Who made a survey from Paris
one went north to Dunkirk and

one went south to Barcelona and they
measured a segment of a larger Tud and

then from there they could calculate what
the earth circumference was and that

defined what a meter was and so then they
made a meter bar and said OK now this me.

Bar is what we call a metre
relative to the planet and

to distribute it not average the average
person couldn't actually go into Paris and

wasn't going to be allowed to touch
that precious meter bar so they put.

Meters out on the road they
measured they took big copies and

they put it out where people could
actually go up and say here's my meter.

It made it convenient so
that people wouldn't cheat.

Other other customers by making up.

Here's my meter Here's your meter.

The kilogram is another base unit.

And in seven hundred ninety nine they
wanted to say OK we want something that's

very convenient to lift and as a mass so

they decided to fight a defined the mass
of the leader as the temperature amount of

water in a leader at temperate melting
point of ice that later on quickly.

Proved not so repeatable and

if you have done physical chemistry or
chemistry you know that measuring water.

Depends on the purity and
a whole lot of stuff.

So they eventually said OK fine.

We're just going to take this particular
amount of mass and call it a kilogram and

they made a brass kilogram and
in an eight hundred eighty nine.

They actually said well
the brass is rusty and so

we need to make something
a little bit more durable and

they put took platinum radium and
made a kilogram and they.

And the definition then an adopted
was a kilogram is the unit of mass.

It is equal to the mass of the
international prototype of the kilogram

it's a very circular argument the kilogram
is a kilogram because we say it is this is

a picture of the composite picture of the
actual kilogram these are not vacuum but

covers they are just dust covers by law.

It has to be kept in air so
it is susceptible to contamination.

It's a little hard to figure out how big
a kilogram is if you've never seen one and

know what size it is so
I've got a picture that

there aren't really any parents here but
do you may have done it in the past.

Flat Stanley made a visit to my lab
once and so you can see health.

This is K eighty five the mike
the telegram that was used

in measuring the plane concent to.

And it's a eighty fifth copy of
the original kilogram and so

you can see there's my fingers how roughly
what the sizes it's relatively small.

This is also a kilogram of steel.

There are about one hundred kilograms
of platinum really in the world but

there are thousands and thousands of steel
plate kilograms and so alternately that's

what you want to measure is kilograms
whether it's steel copper aluminum gold.

So it can whatever.

In chemist those are mechanical base
units in chemistry you have the mole and

you can see the bowl is
just the amount of units.

It's the amount of substance as many
militant elementary into these there

are in a twelve gram
amount of carbon twelve.

It's a convenient number for
a kilogram for the mole and

there be a little bit more about this is
the constant is called of a god number and

here's a picture of our God.

Remember that metal kind of come up
a little bit later for fun and games.

Now they're also there's a base unit for
electricity.

It's call it that early on and
still is the ampere by definition

it's too long infinite wires very long.

They're infinite infinitely thin and
if you put one amp through both of them.

You get in there one meter apart you get
two times in the minus seven Newtons.

That's the definition a very nice and
convenient definition but I have not yet

seen an infinitely long infamy if in wire.

So it's hard to reproduce.

But there is a ring at the amp here for

about a seventy or eighty years
from one thousand eight hundred on

was the realisation you can wrap
wire in Sol annoyed coils and

it's a pretty close approximation to
be an infinite so that's what they did.

This is a picture of the Curtis
ampere which was in use at

one hundred thirty two M.B.
S. at the time.

Bureau of Standards.

It's relatively familiar there's
some soul annoyed down here there's

two of them they coupled to each other.

And it's connected to a mass
balance up at the top.

It's all it is you could generate
electromagnetic force and

you measure it against gravity and
mass standards up at the top.

The trick with it was you had to calculate

the the mutual inductance between
the coils which meant you had to measure

the dimensions of the wire the size of the
wire the spacing and you had to do this.

Pre interferometry days you had collet
calipers rulers not it was very

difficult the best they could ever do was
maybe ten parts per million accuracy which

was still doing pretty good but they only
did this once every ten years or so.

But the ampere does not have
a representation you can't buy an ampere.

From the store that just doesn't exist.

So it doesn't have a good represent rep
realization or transfer standard but

voltage does voltage you can buy
batteries that are standard voltages and

and a Western cell and
I'll show you this as a was used for

many decades as a voltage standard and
in another package you

can buy that represents
a electrical standard is resistor.

So.

In one thousand nine hundred three the V B
people in the electricity was just been

invented essentially and being used to
pass around you had to measure voltages.

So people needed a voltage standard and
they needed a battery and

when Edward Weston came up
with an idea that if you

mix these rather nasty
chemicals cadmium mercury and

things like that you could get a very
standard very quiet reasonably.

Temperature incented insensitive
chemical battery cell

it generated one hundred volts.

But they knew that not every
cell was exactly the same.

So the idea was if you.

But every National Laboratory had to have.

Voltage bank of voltage cells
that was their bolted standard.

It got adjusted then by these amperes.

Tests but only every so often and you had
to have something in the intervening ten

years or so between these and protests.

So levered laboratories used anywhere
from forty to over one hundred cells

thinking if the sticks.

If you take the average
of a number of cells.

That's going to give you a better number
than any one which could go up or

down or whatever.

It was an idea that made some sense but

in fact we'll find out that
that's not necessarily true.

Turns out Edward Weston also
invented mag and wire which was used

to create one almost resistors and.

Just like the voltage standard the
national laboratories used to banks of one

ohm standards in order to
generate to generate and

maintain a one ohm resistance standard.

But by then my going to go into it but
this was actually the OEM is calculated

through a calculable capacitor various
which is also very difficult thing but

not to mention that but it's there
are these are the electrical standard

the realisation electric
centers with a voltage on.

So just to summarize this first section
now we've gone through a quick summary

of the we've got the base units there
are seven of them not Devon mentioned

temperature and luminous intensity
because that doesn't apply for tonight.

But then secondary lab standard meant.

You'll see that voltage resistance and

eventually power electrical power comes
in in the future of the measurements.

So now we're going to talk about
plane constant and the need question.

It while the ampere is a unit
of charge is defined as

the amount of electrons which is.

Amperes.

Electrons per second is amperes.

Good question.

All the units are sort of derivative from
in some way from one unit originally they

wanted to base everything relative to the
meter but that just became impractical.

So exactly.

Obs good observation frequency or

timing comes into measurements on all the
other or most of the other references so

you could look at it as the primary
unit of the world is the second or

frequency and all the other ones
the measurements actually have to do

with measuring frequency so
that's a good question.

Make sense.

OK so now it basically ideas
Planck constant came along and

I mentioned how that isn't so if explained
where it could why it's important in

a centrally if you were watch the old Star
Trek You might remember that at one point

they were back in time in the day idea is
they had to measure things and they had to

work with equipment which is hardly far
ahead of stone knives and bear skins.

Well the early days of
measuring a point constant was

one thousand hundreds
that was a long time ago.

So let's apply a constant.

And Max Planck of

asked in the later half later parts of
later years of the eighteen hundreds.

Scientists knew that matter was.

You could chop down matter and

eventually you got stuck at a point where
you were so you couldn't chop it anymore.

It had an atom.

You don't nobody knew at the time knew
what an animal looked like they just knew

that was a fundamental
discrete part of matter.

Planck's asked the question wall of matter
is discrete what is energy is discrete.

And there was a problem at
the time where if you heated

something up it radiated in
different frequencies but

it didn't radiate at all frequencies and
so Planck used the statistics of.

To explain the radiating temperature
the amount of frequencies out of a certain

temperature blackbody radiation and
by using a kind of a fudge constant.

The H. is what he just called it
a constant he actually could reproduce and

explain why energy.

Why this black body radiation didn't
have infinite frequencies coming off it.

Here is an example of

what Also it means if electron
changes state from one energy

level to another it radiates
something photon a frequency.

If it's a small amount of energy.

It's a lower frequency which is red.

If it's a little bit more energy.

It's a higher frequency it's blue and

there's a bit in the next light I'll
explain a little bit more that.

At early on.

People just said all that
stuff playing constant is just

a fictitious little
mathematical made up thing.

Einstein came along and said well no there
is some logic to this that if light really

is a particle oriented and it's a photon
you can use it to explain another physics

phenomenon of the time the people didn't
understand the photoelectric effect.

There the idea is that the energy
of a photon equals the frequency

of the of the light times each.

Now these are pictures of
the old the younger Planck and

people don't necessarily notice
that this is the younger Einstein.

People now.

This is an older Planck and
here's the more familiar Einstein.

I don't know for the hair there try and

do the same pose whether that's
consistent in the history of physics.

I don't know.
So here's a quick clip of Planck primer.

If you think of a photon as a jump rope.

Lower less energy is
the jump rope is obsoleting

slower in the wavelength as longer.

And if you do it faster.

It's a higher frequency and
has more energy that's why the queen does

a very efficient slow wave to save
her energy versus Granny Clampett for

the hill bit the Beverly Hillbillies wave
like that she would get tired very fast.

A lot of energy.

So that's where that's why gamma rays
have more energy then go down X.

rays ultraviolet visible goes down.

They have less energy longer frequency
lower frequencies longer wavelengths

simple hopefully.

So now that people understood
that there was a possibility

of that to this plane constant and
energy and actually work.

Millikan of Milliken all drop fame said
hey this is a great way to actually

measure fundamental constants Millikan I
just measured the electron charge.

So he said a let's measure
some more stuff and so

they wanted to measure Planck constant.

Well in the photo electric effect the way
it works is you being lights on a metal

and electrons will pop off that metal and
if you then create an electric circuit.

The electrons will create a currents
that you can measure if you then apply

a voltage that will stop those electrons
when they stop the elect the current goes

to zero and you can plot the voltage to
frequency that gives a line and that gives

you a ratio of H. to easy now to get age
you have to plug in a value for easy.

So Bill can said well I just
measured the electron charge.

Let's plug in my value and
we get eight and he did and

it came up with some numbers and
everybody was doing that later on they

proved on back in the thirty's and
forty's late twenty's and thirty's.

They actually made some
fancier measurements using X.

rays electron beam diffraction
with rule gradients and

they came up with in the values for
electron charge

which are independent of Millikan's that
was significant because now if you look at

the numbers that were getting measured
early in the one thousand hundreds.

They had a lot of uncertainty.

Let me quickly explain that
uncertainty in a measurement of this

kind you take the statistic still average
of the numbers you actually measure and.

Becomes the random or Taipei uncertainty.

Then you say well I've got corrections or
I've got unknowns and that becomes

an extra and certainly an example is if
you know that you can run a seven minute

jog a seven minute mile without any
wind and then you go out on a windy day.

How long how long how long is going
to take you if you're running

with the wind or against the wind.

Well that's an unknown factor.

So that's going to change your that's
going to your systematic error in how you

want to measure how far you are running or
how long it takes you to run a mile.

So that's where these error
bars come in but notice.

In one thousand thirteen Millikan actually
made of took to put together a table

of fundamental constants and specifically
the Planck constant plotted here.

ANNIE.

It was the first known table.

That is now continued to this day and

it's now called the code data
betterment of fundamental constants.

And at the time they were achieving
a tenth of a percent or less for

the uncertainty for the plane constant.

But in one nine hundred forty using
the new values derived from X.

rays an electron beans
noticed the difference.

Boom.

About a three tenths of a percent
jump in these guys were claiming

a third of that or less for
the uncertainties opes you don't want to

see somebody underestimating
their Certainly that badly.

So let's call in a C.S.I. Planck
investigation team constants in the SRI.

The early measure of the already
further electric measurements of H.

a very elegant combine the known values.

But everybody used Millikan's value for

the electron charge the elect the X.
rays and there were men who were X.

rays and a beam guys were measuring an
independent value for electron charge and

the ratio of the electron to the mass of
charge electrons the mass the electron.

And they were getting that it's
an independent value from the oil.

Experiment they were
getting a different value.

So what happened in the forty's
it was finally solved

that they looked back at
what Millikan had used.

And Milliken did a good job at
crit measuring the electron charge

from his old job experiment but he in
turn use somebody else's Unst value for

the air viscosity and
the Airbus cost of the value

was actually reported as having
an uncertainty of about two percent.

So it actually was off but
he ignored that two percent.

So what.

When they analyzed this they found that
people were getting way too low and

uncertainties and then you get you
make a measurement later on and

the change numbers change.

They realize that the primitives and

simple statistics of the time
wasn't handling the data right.

So what they actually lead to
newer statistical methods and

ways to combine data with uncertainties
and that's been that's been used today.

So now we're going back and saying OK
that all the thing was Expect was already

measured in one thousand eight hundred.

Well no there were two new measurements

discoveries made in physics one hundred
two in one thousand nine hundred.

This is one my favorite from an old
movie and if you've ever seen for

Been planet but it's a great comment
because it says I bet any quantum mechanic

in the service would give the rest of his
life to fool around with this gadget.

Well quantum mechanics is where all
this stuff comes from and to have

a guy being called a quantum mechanic
is a common in joke with car mechanics.

So in one hundred sixty two.

Brian Josephson as a in his he was
even a post-doc I think this was part

of his grad school.

He was looking into super
conducting devices.

And he looked at it in a superconductor
they had just recently found

that superconductors the electricity going
through something like yours is not just

one electron but the electrons are paired
so they come in pairs of two electrons.

It creates a way function it's
quantum mechanics it's way beyond

what I want to get into.

But he looked at this as
kind of a one dimensional.

What if you have a break in
that super going to circuit.

And then you shine microwave radiation
at the beam that's got bang that is

magnetic field and that can then get
the electron pairs going back and

forth back and forth back and
forth across that gap.

It's sort of a precursor
of what they call now.

Quantum Teleportation back then they call
it tunneling same different same thing.

Joseph and realize that even though
all the electrons will go back and

forth across that gap.

They will see it they it goes.

They go back and
forth as it's a different there and

yet they do see it as a weird typical
quantum mechanical type of thing.

The result is that you can get

in on an I.V.
curve didn't show up if you plot the I.V.

curve of this device you get
the super current going through but

then if you had higher current you get
a constant velocity a constant voltage.

That depends on the frequency
of the microwave radiation and

if you go up higher.

You get another step.

Another house step and so that's the
equation for that also affect some quantum

number and step number times frequency and
the what he came up

with was the ratio is age over to
the to be in the couple electrons.

Very quickly than just
kind of show it to you but

I'll bench of this a bit later that turned
into Eventually the definition in the use

the realization of the voltage standard.

So they got away from
the standard cells and

they started using this just in effect.

This is the modern day Johnson effect is
an array of about seventy thousand or

more junctions with microwaves
piped in and it generates

up to ten volts each four verses each
It's all cells actually generating.

One hundred few hundred Microvolt or

millivolt at most a few
one of Michael's having.

But taken out generate up to
ten volts to create static.

Here's a picture of Brian Johnson when he
was younger and here's a little bit older.

Now whether this hair
thing is got to do with

Einstein everybody trying to copy
Einstein I don't know again.

So then one nine hundred eighty.

Everybody thinks we're still
done now we're still not done

in one thousand eighty calls on Clinton.

Instead of can view in Ajo a junction of
the travels of electrons in one dimension.

He says well there's a elect ideal gas
if you put if you pin electrons in a two

dimension put them in a magnetic field
they'll go around in circles and

I don't explain it too much but
there you get if you generate if you ramp

the current through measure
the voltage across the device

you get constant steps which
are constant in resistance.

So it became a resistance standard and

the ratio in the sequel the equation.

He came up with and
proved right was the you get steps and

it's proportional to age over eastward.

So here are two new ways to
measure Planck's constant relative

to electronic charge and some people do
never hardly change as they get older.

So maybe it isn't just
this Einstein here that.

So now we have the up in the one nine
hundred eighty S. the significance of

adopting these two new systems was they
went from standard cells in all means to

electronic standards the Johnson effect
drastically reduced the uncertainty.

These are the older.

These are the original ones that
I showed you a way down here.

These are newer values and
notice how By the time you adopt

the Johnson effect the uncertainty it's
really small and then you get up here.

The uncertainties of applying
also the the quantum

all effect the uncertainties for
measuring H. really decrease fat.

Rapidly.

It's very nice.

So we're pretty much done with
a boat half or so the talk and

now we get into the modern history here.

Now I'm going to talk about
how plane constant where we've

been measuring it kind of independently
turns out there is still a better way of

measuring it directly and
that's what's comes out of the balance.

There's going to be a bit of math involved
but it's relatively simple math so

don't don't don't don't worry about it so
far yet.

Then after of explaining that math kind
of have a little bit of an early talking

about there is something about
the I P K That quantum kilogram standard

that isn't quite right.

So how we then use the quantum standard
of age of a god or comes into this and

then we can MIT we can talk about how
that relates to the platinum kilogram.

If I have time and
I think you do the middle of a technical

description of how to balance and how what
are they actually do the experiment and

it certainly still a pretty hard
thing to do but it can be done.

There's who's who and actually who's
doing it the finish up with the latest

most recent results and see maybe
there are more discrepancies involved.

And then I'll go full circle and talk
about the side coming of a nation so to

build a better Bell strap people will come
to your door so to better each and beyond.

There is the next section here.

Finally we come up with a way to

measure plane constant directly
in one thousand nine hundred six.

Codes on Barry Taylor the P.T.B.

in Germany Perry Taylor and a bit M.B.A.'s
and others put two and two together and

they said let's look at electric
power from the Josephine equation.

You've got voltage squared.

Is this function of
the Jo Cinequest equation.

Frequency H. over to E. Square.

Resistance voltage over all just squared
of resistance as electrical power

you throw in the van cleansing.

Equation quantum Hall Effect and

what you get is you notice the E.'s
squared cancel you get a bunch of quantum

numbers you get a frequency squared which
you can measure pretty very accurately.

And what's left over one
of the H.'s cancel and

you get each other for
no other fundamental constants.

It's a direct measurement.

If you can directly if you can
measure power in terms of the side so

that was the new goal let's measure power.

Turns out people were already doing
this without realizing the ramifications

of measuring power of the that
original ampere balance.

I mentioned is essential in
electric motor you met you.

It's you have a balance beam
which you can see in that picture

you have a magnetic field.

You have an induction coil and
you can generate a force all on that

coil to balance off a mass
a test mass of some sort.

You can do reversals you need
a half mass on the other side.

That's a kind of a technical point but

that's essentially the ampere balance is a
electric motor you're measuring the force

of gravity on the mass and the amount
of current you put into the coil.

Brian kibble from England said
well that's the electric motor.

What if you generate what if you
use it as an electric generator and

you move that induction coil up and down.

That is fair day's law you generate
voltage and you have to measure

the velocity and it made a huge
difference in measuring plane constant.

So for an electric motor you have
the force equals some current times

of magnetic field times the length of the
wire within the magnetic field there's a.

Geometry factor their electric generator
you're measuring the voltage generated

at the VOs of the of the coil times
that magnetic field in the length of

the wire and that geometry factor in their
you take that value divided by that value.

Look what happens that complicated.

B. L. in beautiful inductance which they
used to have to measure with micrometers

and rulers and things only drops out you
gain about a factor of one thousand or

more in resolution by not having
to dimension measure that be over.

L..
Now you rearrange the variables in from

fundamental physics one hundred one.

You might recognize free
Force times voltage for

signs of a LA city is mechanical power.

And that's directly because
of mechanical units.

That's time length and mass.

That's Sybase units.

Voltage times current if you had any
electrical were engineering yet.

That's electrical power and
that's what ninety.

And so if they want balance
equation then is force

times it's a mechanical power divided
by electric power power is power.

So there shouldn't be any difference
between mechanical power and

electric power but there is this
wanton ninety and woke a way to tick.

What is this what ninety what is this
ninety units what does that mean.

In one thousand actually
even earlier in one

thousand seventy two when they switched
from the standard cells in the bank

in the ampere balances that measured them
they switched into the jobs in effect.

But different countries adopted
a value for each over to over to E.

and different countries had different
banks of cells so they said well my cell

voltage is right and the United States
said that in France and NO myself.

It is right in England said to myself and
in.

Germany in its country kind of adopted a
different value for H. over to E. because

they wanted their cells to be the right
ones that didn't work because over time.

Everybody's cells were different.

It wasn't standardized in one nine hundred
ninety the world got together made a ton

of measurements and they said OK
let's fix the values for the H.

over each over to E. and H. over easy and
we'll sign a constant for them.

K J ninety.

R K ninety and everybody will adopt them
and never in one thousand nine hundred

everybody did that meant they joined
which had been assigned earlier in the.

Century atomic clocks which now define
the second by the transition level

cesium and
laser length which had been assigned.

That didn't still come up right.

Speed of light that should be lambda so
my little try to change it earlier.

Well it still didn't work.

Let the stats equation for the wavelength
of light times the frequency

of light equals the speed of
light same way for sound.

So that now you have four different
quantum mechanical electronic methods for

measuring base units.

What happened in one nine hundred ninety
was kind of interesting that join

your first January first
one hundred ninety.

This was the big the voltage standard bank
of the United States and on January first.

It suddenly dropped by exactly nine point
two four to six for parts per million.

Didn't it was in an accident and
physics changed the unit changed.

So as you measured it one
day it had a voltage and

as in the next day at a different
voltage because they adjusted the units.

It happens it happened in
one nine hundred ninety.

It actually happened throughout the
century is just that there were small and

nobody noticed it.

While this was fairly big they
all was actually adjusted to

at a smaller level but
that's the way it works so

periodically the system has
been tweaked so change innit.

In the future isn't anything really new.

What happened this time.

Basically I don't have to worry
about it it just happened.

But ultimately the whole point was better
to Benjamin better Benjamin techniques

occurred in the eighty's where there were
better absolute gold measurements quantum

Hall matured Joelson got very mature and
people were starting to measure

the WATT And so if they went from back
in the late sixty's to make an ampere

measure the last emperor measurements ever
made had about a five million certainty.

Now measure people were
making sub part per million.

And certainly regularly so
it was really impressive change.

So now we go back to actually
comparing the power units and

here's where the question comes in
again here's the last of the math.

Those fundamental constants which
are assigned they are now used worldwide.

Regardless of what is squared
to erase every square to matter

people use those constant or
fixed numbers.

We already know from those from the other
question that we can get each other for

in terms of the what
side in the what ninety.

We have this other balance equation
that says they have to be equal.

We combine that and you get what's
called the watt balance equation.

It's a mechanical power versus
electrical power in ninety

units one thousand nine hundred units with
the fundamental constants used and you get

planes concent are actually the nice thing
the interesting thing about this equation.

Is you don't care what
those numbers really

are as long as you make those measurements
in terms of those measurements.

You can sit there.

These in turn.

You can make this one and
you would still get H..

But now your voltage would be something
totally different than whatever you

normally think it is.

The question is now though this
is tying math in all these

other constants that are fixed with
electronic quantum mechanical systems and

they're measuring Planck's Constant
what happens or what do you what.

If the mass which isn't in a fundamental
isn't a base electronic unit.

What if that's really changing
when one of it's not constant.

So now we get up into the section of
the talk about the kilogram the I P K

back in the Apollo thirteen.

This is typical in the Now this is what
people are saying we have a problem.

I P K The kilogram is the last
of the artifact standards.

It's as I mentioned it's defined by a
search in a circular argument that itself.

In one thousand nine hundred
nine forty copies were made and

they were all measured relative to each
other and one was chosen as matching

the original brass kilogram said
That's our kilogram and all the rest.

We know what they are so
we know the difference.

In forty snotty forty six after World War
two They took them all back to Paris.

They all measured them again
looks another oops all

the standards which were thought to
back then were going to last for

ten thousand years as
a state as a mass standard.

There are varying by twenty five or so.

Up to fifty in the scatter
is fifty parts per billion.

Well then in one thousand
nine hundred eighty S.

They took them back to
Paris they measured again.

And it scattering even more.

OK now what mention remember I mentioned
that they were initially think thought

that standard cells if you average them
was a better number that the driftwood but

the plus and minus and
they would stay true.

So people initially said well if
the average of these other copies.

Are drifting higher then maybe we
should take the average of them and

that's really what the kilogram is doing.

And wrong because they're all
the same chemistry are the facts

will age still change
somehow the question is.

The they are there are copies
that are distributed to

National Laboratories worldwide they can.

Taken out of the vault more than
once every thirty or forty years so

they see the atmosphere more often
they're going to get contaminated more.

And if they're getting ten million more
more than likely everything is drifting.

And so that's really what it looks like.

All the masses are probably increasing.

But you can see from this graph.

They all would measure exactly the same
you can't tell by measuring artifacts

against artifacts what the total drift is
you have to have an outside measurement.

There's a nice solution to this.

In one respect what if you could what you
can do is since we know we can measure

Planck constant with a lot balance.

We then use Planck's original

formula that's energy is relative to
planes constant time some frequency.

No I've just explained this to you.

So you might remember this from
early in a lecture whether

you even had any math or not.

Almost everybody in the world knows

equals MC squared the Einstein's
Special Relativity equation.

So now you take the Planck quantum
Quezon the Einstein equation and

you equate ease and
what you get is a mass can be measured

by against some frequency that
question earlier on where it said

frequency is part of other
units here it is again and

the constants in our planes Hansen in the
speed of light speed of light is already

defined we define plane constant and now
we have a very simple relation to measure

masses at relative to a frequency and
against its final constants.

There is an alternative the Avogadro
number there is a joint effort

international effort to count the atoms in
the silicon Spears and that becomes that

counts as number anyway and

there is a relation between planes
constant and of a god is number with

a lot of other fundamental constants
involved the experimental C.

is a defined number but
these other constants are measured.

But there.

Measured at very far in excess excess

lower uncertainty than of a god or
plain consonances So

the limiting factor of the insert is
in the eye of a god your measure.

Trouble is this is a hard measurement.

Eight different national labs measure
about six different variables in order to

get that I've got your number and plus
their duplicate so not one lab is only

one variables only conducted by one lab so
it's a lot of measurements.

They are only now using to enhance
twenty twentieth's fears because

originally they were using natural silicon
natural silicon has a contamination

of about two percent of other isotopes
which is part of the equation for

coming up with the Godhra number.

And it was so
they actually got about seven or

eight years ago now they had these
unemployed Russian scientists who could no

longer make use in their centrifuges
to make your enrich uranium for

atomic bombs but they actually got hired
to put silicon into their centrifuges

to come up with an enhanced silicon and
they made two spheres out of it.

So they now are measuring two
spears all these variables but

they only get one value.

It's a good value but it's only one.

So now we get a kind of a summarizing
here we've got various ways

of mention of measuring Planck constant
it's an essentially an energy measurement.

Against frequency.

And so it's a fairly easy
easier way to doing it or

you can measure the silicon
agogic crystals.

It's a more dramatic measurement.

It's counting the atoms in the circuit.

It is mass but it's hard very hard and
you don't do it very often.

Either way you have a potential
solution to the I pick a drift but

it's still not easy.

It's hard work to be done and
there's no magic way out.

And here's of a god goddess picture
somebody noticed that maybe

if you could wave a magic wand and
you might be able to come out with it.

Well no it doesn't work but the magic why.

And could be by a magical creature
who looks a lot like God Joe.

I don't know if it's going
to work a lot but we'll see.

So now that we have a die deal of changing

the what changing the kilogram by
betting that Planck's constant.

I'm going to through I'm
doing OK on time but

I'm going to zip through
this little bit faster.

Everything's going to change because now
we're going to measure the plank constant

order to moderate Kilgour I'm
speaking of Perry Potter.

This is a quote from Goblet of Fire.

Everything's going to change.

Here's how a kilogram balance works.

You have to have a magnetic
field at NIST we have a super

going to console annoyed you have a coil.

Built in in the field and
you can weigh against it.

You can move it.

It's kind of.

Sit there similar things involved
in all the standards and all or

all the different projects
involved in the world.

I'll show you those eventually to kind of.

That's most of the laboratories

use permanent magnets near is
just an idea of how it works.

You've got a permanent Samarium Cobalt
magnet this is for the new disk design.

They're opposite poles.

It's in a mate it's in a iron yoke.

So the magnetic field isn't closed and
here's an air gap where that coil will

fit and you can see it's
a relatively uniform field in there.

So there's two different ways
of generating magnetic field.

Here's how I want balance works.

This is essential.

How the empirical and swerved you have
the magnetic field you have a coil you put

a const a counter mass on a force
generates about five Newtons and

it balances the mass then
you put your test mass on.

Reverse the current balance the mass and

that's how you get your you
measure the current you measure of

the force by measuring the mass
times gravity is you have to make

gravity measurements separate itself but
again gravity measurements as met length.

And time quantum those are the quantum
systems so a commercial gravity meter

is pretty is expensive but it's actually
spec two parts in ten of the nine.

And certainly so they're pretty good.

This is just an interesting picture
of going back to two thousand and

four during crib Christmas
two thousand and

four I was measuring the current
over the course of the.

Holidays and what normally is a very quiet
current all of a sudden got very noisy.

December twenty fifth two thousand and
four was a this was about twenty minutes

after the earthquake hit the earthquake
hit some Ochoa twenty minutes later

the seismic waves are all over
the planet and we saw it.

So we have a really from
not only do we have a great

measurement of playing Skansen.

But we have a seismic
girth way to take it.

If you move the balance.

This is the electric motor
part electric generator part.

You just take the masses off
you move the coil up and

down you measure the velocity and
then you measure

the electric the voltage and
you get the other half of the equation.

It's fairly simple.

It's either way whether you work it
with the superconducting coil or

anything else it works fine.

This just shows it's a little
more complicated than that.

This is the curve the magnetic
field isn't source uniform but

the actual noise is a fair amount of noise
about half of percent of noise but this is

these are not on the same scale that's
actually noise that noise cancels and

the left over the variation in the field
is about one hundred forty people.

We may care in the actual noise left
over when you cancel the voltage and

velocity you have to measure
them simultaneously.

It actually gets the noise
down quite a bit.

But.

We weigh at a specific point and
that value has to be known to partner.

So there's a whole fancy protocol I
came up with for analyzing that and

we can actually do that.

Here's an example shows
you can actually do that.

The blue is the force current
mode the electrical mode

the red is the Volokh city mode and

the magnetic field actually varies quite a
bit over the course of today measurement.

But then you take the ratio to get rid
of that magnetic field structure and

what you end up here is
these dark blue dots and

you can see there's a little bit of
a gap here there's another gap here.

That's this high peak here high peak here.

Remember I measure against gravity gravity
does change per day lunar and solar

tides used to calculate those at that
light blue line you subtract them out.

You get the pink left over the standard
deviation of that today run

is about sixteen parts per billion.

So that's really pretty good.

So in spite of being a lot of noise.

We can make measurements
now that are that random

error on a good day is down at the ten
to twenty parts per billion level.

So now that we have a science of today
means the technology of tomorrow.

This is a real quick scan
of who's who in measuring.

The things until all I'm going to
show you here is typical equipment.

Pictures but just showing you that they're
all roughly the same you've got a lever

arm of the test mass.

There's a magnet here in the coil
is inside here this is what is the.

Metaphysical laboratory
in London the N.P.L.

built this back in the eighty's and then
they decided they weren't going to run it

anymore because it didn't make any
profit so they sold it to Canada.

So no Canada National Research Council in
Canada is actually running that system.

Here's the newest version.

It's got the solenoid the coil
the magnetic so annoyed.

It's all in a vacuum chamber.

And here's that there is test math.

We use a wheel instead of a lever arm
same thing we have an auction coils

Bangit sores notice here
there's a meter indicator.

This is all about a four to
five meter tall experiment.

It's very tall the biggest in the world.

As opposed to the maddest measurement
laboratory in Bern Switzerland.

It's the smallest in the world
that sits on a tabletop.

And again you have a lever arms.

You have the magnet is actually here
it's kind of a vertical magnet.

And they use a little force scale at
the top to actually make the measurement.

For the force it works and
they've actually it works just fine.

Kind of an intermediate is Ellen E.
and Paris.

They have slightly different geometry but

it's essentially identifiable as the same
they have the magnet is down in here it's

an enclosed that permanent magnet
enclosure the coil drops inside it.

The flexure are the the the lever arms are
actually three different flexure points.

So the whole thing actually goes up and
down to maintain a vertical motion.

It's actually it hasn't been running yet
fully but they're assembling it now.

Paris is doing again something similar.

They have test masses this is
their prototype what they want

to do is actually measure
things simultaneously.

If it works.

It'll be a nice even better measurement
if it doesn't they can always do and

separately.

There are two different laboratories
are trying something a little bit

more novel in New Zealand.

They're exploring an AC voltage technique.

A small tabletop version.

That's uses an upright upright
hydraulic pressure balance and

then they can oscillate the pressure
up and down by a very small amount and

at the maximum slope of
the sine wave that's.

That can be going fast enough to generate
a lot of older so it doesn't have to go on

that high a frequency but in a sine
wave it's going pretty fast and they

can only have to move it up and down a few
tenths of a milk few millimeters or so.

So they're working on that.

Trouble is they also since
they're generate an AC wave.

They may see reference and
that really doesn't exist or

they'll actually it's being worked on.

A slightly different version of the ampere
balances being worked on in China

where they're actually it's a color
the jewel balance they're not going to

move the coil.

And measure the velocity they're going to
measure using modern techniques they're

going to measure electrically the mutual
inductance and then go to the place where

they know where the what they
think is the mutual duct and.

And that way then they can avoid the very
complicated waveform analysis that you

have you get when you move the the coil.

So now we go to getting down to
the point is there a problem.

Yes there may be.

This is kind of a summary of the current
results on a very gross scale.

You can see over one hundred years the
uncertainty has been gradually decreasing.

And this was the early era was
the photoelectric measurement era.

Then it turned into the X.
ray era the Jolson junction era.

Now we have the water era and

the Green Line is sort of an average
of what the modern values are.

So low as blow up those numbers and
so where we are now.

Well for the Georgia Tech people
we're almost done with this talk.

These are the other ways that
they used to use to measure.

Base in directly measure plane constant
you can see the uncertainties are fairly

large these are all the plank the white
balance summers so well the take those.

Blow them up and look at where they
stand now centrally from the eight

hundred eighty nine hundred eighty S.
there was a nice agreement between amp.

And NIST then N.P.L.
made another measurement and they shifted.

Actually if you go back here.

The original days of using

natural silicon the Avogadro people
came up with a really different value.

They found an error in their measurement
and so then they reconnected it and

that's now.

This is the corrected value and

so it actually much more
agreed with the other values.

Nowadays though people are getting
slightly different menace came

out with a very result in two thousand and
eleven with large uncertainty they kind of

agreeable you can see these lines are kind
of just randomly not so randomly drawn in.

But we're getting roughly two sets
of values the oldness values and

the newer in our C. and some.

More recently of a God Your numbers are
sort of fitting in unofficial I can tell

you that the newer NIST value is sort
of fitting more in the middle too so

the values are starting to converge.

That's good news.

So just to kind of summarize
we've got values the people

are actually can Cordie now about
thirty parts per billion uncertainties.

Which is actually very good.

The difference is those two lines
are about three hundred parts per billion

difference which it far
exceeds that thirty.

Per billion uncertainty.

So clearly there's a discrepancy
there's a problem but

they're getting it's getting less.

The massed artifact now
his showing more wear and

more uncertainty than they thought so
there is now a scheduled a new mass.

Kilogram although the nations the world
are going to be sending those original

killer and back to Paris and
they're going to be remembered.

So basically what we're doing now is we're
waiting for there's some new values come

out new designs investigating prototypes
South Korea's actually going to start

their own so
as young Kirk said in the Star Trek.

I don't believe in no wins.

Ariel's So let's make it one last time.

Let's redefine everything.

Currently if we took the the last
code data values for

the fundamental constants which
was true thousand and ten and

we redefined every Well the current values
as they are know now the mass being

an artifact self defined is exact
the uncertainties on Planck in of a god or

roughly forty four they for
the two thousand and ten evaluation.

They were forty four the more
recent values are about thirty of

the actual values but the CO data
value averages the differences and so

they're actually have
a higher uncertainty.

If that new technique of average
Gene different values with

different uncertainties.

Comes out right.

So you can see all these are number
all the constants are have a certain

uncertainty new notch permeability
in dielectric vacuum are exact lets

the redefinition will take
some future Co data value and

redefine the S.I. the metric
system in terms of the constants

what that will do is it will make
the artifact standard noisier the norm and

more uncertain but all these constants
will be defined they will be exact.

The mass of the with the best of
the electron has a little bit of

an uncertainty because it's got alpha
measurements in it which is a constant

it's calculated and measured that has a
little bit of an uncertainty but it's much

smaller and certainly the problem then
lies in you because these are defined

under the present system they'll have
a small uncertainty but it's pretty small.

But notice that's a good thing having.

Constants that are all exact and
having standards that are much better.

So if you redefine it it's a win win for
centuries to come.

But what does that mean for
industry and commerce were.

Still going to have those seven basic
units in answering commerce will

still measure against
those you basic units.

They'll In fact won't necessarily
have current they'll be measured

against the Joe some fact
in quantum Hall effect but

it doesn't really matter in history
will have those however you read

hidden behind this little fear
is the fundamental constants.

So these values will now be tied
to fundamental constants and

it will be a much more you know
these with you on the planet varies.

The road the circumstance of
the earth varies more and

more than I ever thought
two hundred years ago.

As far as we know except on
the order of billion years

these fundamental constants don't change.

What does that mean for industry and
commerce which is what we

really care about ultimately they're
not going to see any difference.

They're going to be behind this
wall of the front of the base units

the fundamental measure metrology
lab's this N.P.L. Canada.

Wherever they'll worry about these
fundamental constants Commerce and

Industry will be on
the other side of Wall.

Everything will be hunky dory.

So you have seven base units still but

now based on constants the fixed
value of the constants will be

not only valid on a place of the earth but
any star in the galaxy.

You have the fundamental
constants are all based on.

They all that they relate realisation

systems will relate to
the constants it's great.

So eventually it enters
the exact energy conversions.

So a lot of this stuff is in my
history in progress on the accurate

measurements of plain constant and
as James Kirk said Are we done I'm done.

And he questions.

Thank you for time.

Questions.

Can you still find the meter
inscriptions in the streets of Paris.

I took that picture just
a couple years ago.

Yes there are a few Is
there still a few left.

Quantum Electrodynamics figure and
you have this.

Part you know the magnetic moment.

Measurement electro magnetic moment
measurement is that competitive is.

Joseph's and his dirt physics I mean
the only one it's in the mental physics.

I'm not all that familiar with
all the derivative constants and

other measurements.

Because they're trying to preserve things
relative to that those original base

units that sort of the red
definition as applies now.

There probably are some other fundamental
constants that maybe better but

you can't have too many concepts because
then it gets redundant and so if the plane

constant is a simple thing that applies
to the mass faulty gene resistance.

You start throwing in other constants
they have a relation in physics

to other variables and
it gets a little bit complicated so

it's possible that the measurements are
better but it gets in conflict with other.

Fundamental constants I
think just one question.

There you showed at the end the standards
that the industry is going to be using.

Are based on constants which are going to
be defined and those are behind a screen.

But they're going to be as we're
going to be done in the constants.

I don't quite understand why
that leads to stability.

Is sensually once they redefine
technically once they redefine

the constants.

Work won't be done to measure
the constants but the car.

Instance will be used to
measure the standards and.

The presumption is in the air
as there have been changes

in the past they were fairly large changes
ten parts per million one and a half.

Whatever the guestimate
now is if they changed.

Planck's constant in the voltage relative

to what we are measuring now there
would be roughly a hundred fifty P.P.

B. change in the voltage compared to
the one nine hundred ninety which was

ten parts per billion that's an order
of magnitude down the anticipation

is there might be some tweaking
in the far distant future but

it's going to be at
the parts per billion or

ten parts per billion level which
industry cannot see industry

does not want to make any more changes and
in fact you wouldn't necessarily have to.

Because industry won't care and so whether
they make any future changes decades from

now it won't affect anything
except the National Labs who.

Who are worried about it.

Industry.

Unless they have their
own quantum standard.

And they have to type in a number
which is the conversion factor.

They won't care either because
they will absolutely see anything.

It's kind of within the noise.

So presumably by redefining things.

There will be no more
large changes as the mass.

In fact that's why there's an interest
in changing fairly soon to

get rid of the artifact standard because
electrical standards are getting better.

Then parts in ten of the eight.

But the uncertainty in the mass is
increasing beyond parts intended the SO

as the mass gets a more uncertain
voltage uncertainties electrical

uncertainties are decreasing.

And so in the future.

We don't change that now we're going to
have to really crank in a change and so

if we do it now.

It kind of maintains where we are now for

it which is of a few parts into
the eighth and certainly maybe

decade couple decades somebody will
come up with a new quantum discovery and

they can make some better numbers but
at least for the forseeable future.

There won't be any more changes
beyond the part of the eighth or

few pay part of these levels.

OK.

Anything else is

there a good example we can keep
in mind like from industry like if

there was a substantial change like
how we would see that manifest and

something sort of every day or
how like a corporation or

something like Intel what change that
have to make to accommodate that.

It's a it's a tricky
question to answer because

industry now can kind of make
adjustments for changes.

They still use artifact Vala standards for
the most part.

Zener references standard ohms
transfer standards sed kits some

fancier corporations have their own Joseph
X S M So they make the old voted voltage.

The quantum all effect
is way too complicated.

So industry doesn't have generally
doesn't have theirs so they do transfer

standards which means their transfer
standards their lab standard will change.

But then they get it
calibrated against NIST or

against calibration laboratory
periodic Lee and then the adjusted and

if they're smart about it they can track
it in time and so they can predict it.

So they are even though their laboratory
standard is changing their day

to cicadas they're sophisticated enough
to apply a linear drift correction and.

And so it works fine.

If all of a sudden.

The V. unit changed considerably.

Which one is like what happened
in one nine hundred ninety.

There was a booklet sent out all over the
world at least all over the United States

explaining how to handle it and it was
that estimated that in one nine hundred

ninety four a large change of
ten part per million maybe

twenty five or so laboratories would
have to even worry about it and

make a change to their bank of standards.

The rest of the laboratories
might notice it but

then they would be kind of
fixed up in the next hell.

Gratian most of the industries
never even pay attention.

There were the hundred parts per
million or worse level of testing.

Nowadays if it were a ten part per
million change five hundred or

so laboratories would notice it.

But a tenth of a proper change.

We're going back to the ten or
twenty that might notice it.

So and it's moment mostly those
laboratories that make electronic

instruments and Agilent fluke
things like that but they know

enough to there where of how to make those
changes so they wouldn't care they would

not like having to go into the computer
into just a constant in their program but

that's all it would take as for
people who might actually

need these phenomenally accurate voltages
and electronics and things like that.

Again all we can argue is that.

One.

If you transfer a standard you lose some
uncertainty every time you transfer it.

So if you have to go from NIST
to a calibration laboratory

to a primary laboratory
a company to your slab floor.

That's a four times for
the fourth and loss of uncertainty.

That's why the National Standards
have to have such high and

certainly low in certain levels because
industry then by the time they get it.

There's a lot more uncertainty
in the transfers and

why they also might need it is
they use it for quality control.

If they're making a ten million
part production line you want

all the references measuring those
the quality of that ten million parts.

Of production line statistic supply and
you need to be good.

You need to be measuring the quality
of that to a part in a million or

part in ten million or
you start rejecting components.

So there is a certain argument
there where you need good numbers

in order to do quality
control the military might.

The military is demand the best of
the uncertainty that we can provide.

And they don't tell us why.

So there's something in there that they
may actually have instruments that they

need that quality but they're not going to
tell us what they are but we don't know.

OK question

back in a day when they were
using brass male correct that

the you can still buy brass weights
you would only buy a brass weight.

If you're only worried
about a tenth of a percent

because it's a hell of a lot
cheaper than even a steel weight.

And the going rate for a platinum
Meridia mass which is only machined.

The mention this at the morning meeting.

It cost roughly thirty thousand
dollars staff in mechanics

time at the be eight pm to make a new
platinum really platinum Iridium copy.

About seven or
eight years ago the going rate for

the materials was about thirty thousand
twenty thousand dollars of platinum.

Now it's sixty fifty or sixty thousand
dollars it costs almost one hundred

thousand dollars to make a platinum
mass there are really good masses but

it's just getting way too expensive so
people want to use cheaper masses

in the in the what balance you can
throw in a brass mass steel mass

platinum mass silicon mass you
can measure pretty much anything

half kilogram one kilogram two kilograms
and you get fairly good accuracy.

So that's why that will
probably be adopted

is that it has the potential of
having a measurement a wide range

of different kinds of masses
different values of masses.

And it fund it.

It's there it's that fundamental
realisation of tying

it to fundamental constants that makes it
a broad thing like the voltage standards.

The original cells were
only one A one eight volts.

Plus are usually plus a little bit and
that was it so

you had to deal with one
zero one eight volts.

Nowadays with the Planck ons with the
modern voltage stand just in standards.

You can measure anything from one cell
couple hundred Microvolt up to ten volts

the bigger range allows you more
accuracy over a larger range.

It's a big advantage play the white
balance will solve that problem.

There are other problems with measuring
masses and comparing them with buoyancy

and things like that one hundred fifty
years ago they will be cared for

was cheap and
people could buy brasses brass masses and

long as you were cheating the customer
by a factor of two people were happy.

So that's when but ultimately science
got more accurate and they needed

better standards and so they went from
brass to platinum which are really only

circulated between the science
laboratories any last questions.

Well.

All right let's think our speaker
one more time and thank you for

coming to say this in front.