Kind: captions
Language: en
on November 16th representatives from
nearly 60 nations will be meeting in
versailles france to vote to change the
definition of a kilogram not only that
they will also be changing the
fundamental unit of temperature the
kelvin the unit for amount of substance
the mole and the unit for electric
current the ampere that is four of the
seven base SI units in one day and after
that all SI units will be based on
fundamental constants of nature and not
physical artifacts the kilogram is the
last base SI unit to be defined by a
physical object since 1799 one kilogram
has been defined as exactly the mass of
a single metal cylinder stored in Paris
it was swapped out once in 1889 but this
international prototype kilogram or big
k as its affectionately known has
problems
I mean weighing it with in theory
identical cylinders scientists have
found that their masses are diverging so
it doesn't even seem to maintain its
mass plus it's really hard to get access
to big K and that makes using this
definition really difficult so how do
you create a mass standard that will
never change and also be available to
everyone everywhere with the solution is
you set Planck's constant to have a
fixed exact value now I know that sounds
a little strange so bear with me for a
moment
I mean Planck's constant is best known
for relating the frequency of a photon a
particle of light to its energy but we
also know that energy and mass are
related through e equals mc-squared so
hopefully you can see how Planck's
constant is involved in mass but the
problem as it stands today as I'm
recording this video is that Planck's
constant has some uncertainty I mean we
know the value of Planck's constant to a
large number of decimal places but those
last couple of digits they're actually
uncertain what is certain is the mass of
that platinum-iridium cylinder stored in
a climate-controlled vault in a basement
in Paris it is exactly one kilogram
uncertainty so the solution is to flip
this on its head set Planck's constant
to have an exact fixed value and then
that cylinder in Paris will no longer be
exactly 1 kilogram I mean it'll be a
kilogram but not exactly the thing that
is now exact is Planck's constant which
determines how big a kilogram is but if
you're gonna fix the value of Planck's
constant well you better get that value
right so that it's consistent with all
of our current measurements and all of
the masses that exist in the world right
now and so for the last several years
scientists around the world have used
multiple different techniques to try to
measure Planck's constant as accurately
as they possibly can
one of the major methods was using a
watt balance where essentially they
balance the weight of a kilogram with
the force from an electromagnet if you
want more detail you should check out my
video on that topic scientists also
created arguably the roundest object in
the world made of one type of silicon
atoms these methods have been
complementary because now they're able
to compare all of their different
findings from physics and from this more
chemistry method of a vegard's constant
and determine what Planck's constant
really should be so if the vote goes
well the future definition of Planck's
constant will be that it is exactly this
number Planck's constant is fixed that
cylinder in Paris no longer exactly
equal to a kilogram but you can't
redefine the kilogram in isolation
because other base SI units depend on it
take the mole for example currently the
mole is defined as the amount of
substance that contains the same number
of particles as there are atoms in 12
grams of carbon-12
that's avocados constant and it depends
on what 12 grams is which depends on
what a kilogram is so again Avogadro's
constant currently has some uncertainty
but after the vote the plan is to fix
Avogadro's constant to be exactly this
number in such a way that it is in turn
consistent with the new definition of
Planck's constant there's a direct
relationship between Avogadro's constant
and Planck's constant likewise the
ampere will no longer depend on the
kilogram instead it will be defined
based on this newly fixed value for the
charge on an electron and the Kelvin
will be based on the newly fixed
boltzmann constant which relates the
temperature of a gas to the average
kinetic energy of the molecules and this
will be its exact value with no
uncertainties now will these new
definitions change anything well for
most people no I mean your food is still
going the way the same as are you and
temperature is still gonna work the same
way
you know everything basically stays the
same and that is as it should be the
point of this definition change is not
to shake things up but to keep things
consistent and reliable forever
all we're doing is removing the
dependence on a physical object which
theoretically at least makes it possible
for anyone anywhere to make incredibly
precise measurements now I should point
out that a volt will actually change by
about one part in ten million and
resistance will change by a little bit
less than that and that's because back
in 1990 the electrical metrologist
decided to stop updating their value of
effectively Planck's constant and just
keep the one they had in 1990 and there
was a benefit to that they didn't have
to update their definitions or their
instruments but now that we've realized
that Planck's constant is actually
slightly different than the 1990 value
because of better measurement techniques
well now the electrical metrologist will
have to change but that's a very tiny
change for a very tiny number of people
I think they'll be fine you know I've
been trying to ask myself the question
why am I so interested in this topic I
mean I made like four videos on it and
the reason is you know to me the world
and the universe is a big complicated
place and when we're actually able to
ascribe numbers to it it's like we are
resting some sort of order out of the
chaos that is our universe and that
is the beginning of our understanding of
the way things work you know
measurements are the foundation of
science they allow us to make
observations I think it's no surprise
that you know Kepler was really able to
figure out what was going on with the
planets that they were actually moving
in elliptical orbits once Tycho Brahe he
had made the most accurate measurements
of their positions that people had ever
made I mean I think that's no
coincidence and if you look at the
discovery of the Higgs boson at CERN or
the the detection of gravitational waves
these are in my view the pinnacle of
human achievement I think there are
orders of magnitude greater than the
achievements that then we make in
literature and art and fashion and I
don't say that to disparage those
disciplines I know that they're hard I
know they take a lot of human brain
power and I'm not saying scientists are
smarter but the tools that scientists
work with and the system in which they
work is what allows them to make such
great leaps because science builds on
itself in almost you know an
exponentially improving way and that to
me is why this is so important is
because it allows us to take our
measurements to the next level no longer
are we bound to physical objects I mean
face it up until now we've essentially
been doing a glorified version of
Indiana Jones now we are taking that
next leap to the abstraction that all of
our units are based on the way nature is
and the way the universe is we're no
longer tied to physical objects
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