http://www.sciencealert.com/our-units-of-measurement-are-finally-getting-an-upgrade
Our units of measurement are finally about to get an upgrade
The new metric system.
FIONA MACDONALD
3 NOV 2016
By the end of 2018, a kilogram will no longer exist as we know it, with
our standard units of measurement finally scheduled to get a much-needed
upgrade for the first time in more than 50 years.
Under the new proposal, all seven basic units of measurement - including
the second, the kilogram, and the metre - will be defined by constant
properties of nature, such as the speed of light, rather than by a value
thought up by a bunch of scientists. And it's going to make the world a
whole lot more accurate.
So what does that mean, exactly? While most of us simply think of a
kilogram as 1,000 grams, or 2.2 pounds, the reality is actually a lot more
complicated than that.
Right now, the mass of a kilogram is defined by a single physical object -
a solid chunk of 90 percent platinum and 10 percent iridiumthat's sitting
in a vault in France, known as the International Prototype Kilogram (IPK),
or 'Le Grand K' (a replica is pictured above).
There are replicas around the world, but if you want to get specific about
it, for something to weigh 1 kilogram, it has to weigh exactly the same
amount as that one piece of metal in Paris.
And the IPK isn't even constant. Despite how well-guarded it is, it's
subject to lose or gain atoms over time - just like any physical object -
and the IPK seems to have become slightly heavier over the years due to
surface contamination.
Researchers aren't too happy about that, because a lot of scientific
assumptions are based on the mass of a kilo staying the same, and of the
seven International System (SI) - or metric system - units currently in
play, it's the only one that's still defined by a physical object.
But that's finally about to change, with the International Committee for
Weight and Measurements proposing new formal definitions for the SI base
units, which are scheduled to be rolled out at the 26th General Conference
on Weights and Measures towards the end of 2018.
The last major overhaul of the metric system was in 1960, so it's been a
long time coming.
As a refresher, the seven base units of measurement are:
second
metre
kilogram
ampere
kelvin
mole
candela (the base unit of luminosity)
Every one of these except the kilogram is already defined by a natural
phenomenon (the metre was the last to be defined a physical metre bar,
which changed in 1960) but four units will be getting an upgrade, and the
other three will be tweaked under the new proposal.
Most dramatically, the kilogram will no longer be defined by the IPK.
The hold up has been that, in order for researchers to formally redefine
the kilo, they had to agree on the value of something called Planck's
constant, which relates to a particle's energy compared to its frequency.
And it's been surprisingly hard to measure - scientists have been trying
to come up with a value for the natural constant since the 1970s.
But in 2014, researchers finally reached an agreement on the value of
Planck's constant (although scientists have until July next year to
overthrow that value), which means we can hopefully get rid of the IPK for
good come 2018.
The other overhauls are to the ampere, kelvin, and mole.
The definition of the ampere - the unit used to measure electrical current
- is currently defined in a pretty impractical way.
An ampere is the current that, when flowing through two infinitely long,
infinitely thin wires that are placed exactly 1 metre apart, would produce
a certain amount of force.
But infinitely long and thin wires are impossible to produce, so no one
can actually test precisely what that value should be.
Under the new proposal, an ampere will basically be defined based on the
electrical charge of the electron and the proton - something that
scientists will actually be able to measure.
The kelvin and mole will also be redefined by linking them to the exact
values of the Boltzmann constant and the Avogadro constant, respectively.
Right now, the Kelvin is defined as the triple point of water - the
obscure point where water coexists as a liquid, gas, and solid.
You can see the proposed changes, with the old system on the left, and the
new proposal on the right:
Emilio Pisanty/Wikimedia
In the image above,Cis the speed of light (which will define a metre,Cs is
the tick of a caesium atom clock (which defines a second),his the Planck
constant (which will define a kilogram),NAis the Avogadro constant (which
will define a mole), Kcdis luminous efficacy (which will define a
candela), kBis the Boltzmann constant (which defines a kelvin), andeis the
elementary charge (which defines an ampere).
So what does all of this mean for us? To be honest, not much. We're
talking about tiny, tiny changes to the definitions of these values, so,
don't worry, you're not going to suddenly start weighing more or less
overnight come 2018.
But for scientists, it's a pretty huge deal - and has been called a "once
in a lifetime event".
"Theres this hairline crack in the foundation, and you cannot build your
building of physics on that foundation," Stephan Schlamminger of the US
National Institute of Standards and Technology, told Emily Conover from
Science News.
Basically we'll now be able to do better science, seeing as our units of
measurement will be based on the latest and best research.
"The new units will be based on the modern understanding of physics,
including the laws of quantum mechanics and Einsteins theory of special
relativity,"said Conover.
Once we have this change, it should be a while before we need to redefine
the values again.
In fact, the only thing that can threaten the new metric system
definitions is if we suddenly discover that the constants of nature - such
as the speed of light and Planck's constant - actually vary slightly
throughout the Universe.
Which, we don't want to freak you out, but a 2011 study hinted at.
Still, for now, the fundamental forces within the Universe are constant
and unchanging.
And until researchers can prove otherwise, they're still the best and most
reliable thing we have to define our units of measurement around - much
more reliable than a slab of metal in a French vault.
Bring on 2018.
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