The scientific community is working on the replacement:
Known as the Avogadro Project, the plan is to bring together enough atoms of one substance – silicon – to make a kilo.
Attention has focused on silicon because:
- its characteristics are very well understood
- a single crystal of the right size can be grown
- its atomic structure is extremely uniform
- its widespread use in the computer industry means it can be obtained with relative ease at high purity and resonable cost.
A spherical shape was chosen because a sphere has no edges that might get damaged and only one dimension has to be measured in order to calculate its volume.
> A spherical shape was chosen because a sphere has no edges that might get damaged and only one dimension has to be measured in order to calculate its volume.
Surely every dimension needs to be checked, to ensure that it's a perfect sphere? (Which I assume is harder than checking a cuboid has six flat sides joined at right angles)
The Avogadro project isn't the only horse in this race. The electromechanical approach, known as a Watt balance, is underway in several national standards labs around the world.
For dieters, you're entirely correct. A lighter kilo makes the dieter have a greater mass when measured in kilograms.
> Besides, can't they recreate a "canonical kilo" with the required measurements?
This is the main point of the drive to redefine the kilogram. Right now, the IPK (the French kilogram) is the SI standard for the kilogram. Groups are working hard to redefine the kilo in terms of either Planck's constant or the Avogadro number. In order to do so, the experiments that measure one of those fundamental constants must be more reliable than the IPK.
They're very close, but absolute mass measurements of the required precision at the kilogram scale have never been done before.
If the kilo is getting lighter, it means that your mass in kilograms is going up! Better hit that treadmill before the meter starts shrinking and you need to run farther.
There is another competing proposal for solution that the article does not mention. It is define kilo as a specific number of Silicon-28 atoms, that have a well known mass. The laboratory with that proposal made the most perfect sphere ever, in attempt to allow measurements.
A side-benefit of this project (The Avogadro Project) is that there are a load of interesting things you can do with almost-pure Silicon-28, e.g. see http://www.nist.gov/pml/div684/enriched-silicon-project.cfm (and more besides: there was a really interesting paper I saw recently which irritatingly I can't find now)
I completely agree, It's time to start counting atoms/molecules of something (being careful with isotopes).
Integer numbers are very good for "perfect" (well, very good) abstract definitions.
And it would also really prolong the French Revolution spirit in the sense that this unit would become so universal that you don't need a physical reference anymore, like what we could achieve with the other base units (like second then meter).
"Weirdly, it’s not even known if the IPK is getting lighter, or if the national prototypes are getting heavier — but either way, something is causing these kilos to change weight, by around 50 micrograms every 100 years."
Well they COULD always do that thing with the water where they heat it to 4 degrees celcius and measure its volume and weight. Then they'd know which it is.
I often wonder why they don't make a set of scales with a electro magnet at one end that attracts one end of a balance and you place the weight on the other end and adjust the strength of the magnet until you get a balance and from there can measure out that same weight. Now would need very well pression made electro magnet and balance.
Though idealy the ability to measure out a fixed amout of atoms of element and wheigh that and work out the relationship of how many atoms of element X is needed for a kilo. Well until then it is one of the last area's of measurment that history still firmly has its teeth into.
Was nice TV show in the UK not long ago that covered the whole area of weights and measures from the science and history of them comming about. One of the better science shows.
"Deep underground in a vault beneath Paris lives the most important lump of metal in the world - Le Grand K. Created in the 19th century, it's the world's master kilogramme, the weight on which every other weight is based. But there is a problem with Le Grand K - it is losing weight. Professor Marcus du Sautoy explores the history of this strange object and the astonishing modern day race to replace it."
I'm not a physicist, but it's irritating to me that this article is using weight and mass interchangeably. I doubt they'd ever allow this, but the "simple" solution is to bring the weight aboard the ISS and capture its mass on an inertial balance.
Nobody can build a kilogram-scale inertial balance of sufficient absolute precision. If we knew how, we'd be doing it.
Also, the ISS is a tricky place to work for a precision measurement. It's electrically, seismically, and gravitationally noisy (and huge gradients). Precision gravitational measurements are generally carried out in dedicated spacecraft with careful attention to those concerns, if they can't be done on the ground.
Can somebody explain to me why an SI unit has the "kilo" prefix already in it, making other SI prefixes unusable with it?
1 kJ = 1000 standard units of energy.
1 kg = 1 unit of mass.
Was this just an unfortunate historical accident? But if the too that much care to make a unit system that makes intuitive sense, why would they let in such an annoying exception? Why didnt they just make "gram" the standard unit or just made up another name?
The order of magnitude chosen to calibrate the metric on doesn't change the prefix magnitude.
1 kJ = 1000J
1 kg = 1000g
Adjusting prefixes puts the units on the order of magnitude where they are easy to write in typical domain problems. For a heat-capacity and heat-transfer problem, I might end up with J/kg or kJ/kg being convenient, while for expressing the specific energy of jet fuel, I'll use MJ/kg because it's 39.
In the case of the kg, I'll bet that 1g was simply too small for the tools of the time to make an accurate model that was reproducible to the desired accuracy. For all I know, the weights were die-cast from the same melt, and the effect of scratches gets reduced as the surface-area/volume ratio goes down.
Check out this veritasium video https://www.youtube.com/watch?v=ZMByI4s-D-Y - It goes into a little detail on how the kilogram got it's name, it is also very interesting in it's own right.
Other SI units can and obviously are used with it. Micrograms, milligrams, and grams are really commonly used. I'm not sure why they chose to do it this way, but it definitely doesn't really have any bearing on how it's used.
OK, here's a wacky theory about why this is happening: The article says that the kilogram copies are brought to Paris to be compared. Therefore the copies are undergoing significant acceleration (e.g., transported on airplanes or trains) while the original in Paris remains stationary.
From the stationary kilogram's point of view, all of the other kilograms had undergone relativistic mass increases during the time of their travel. Suppose a tiny amount of this mass increase is somehow actually retained when all the transported kilograms are brought to the same frame of reference (i.e., when the airplanes land in Paris).
The "mass" gained from motion is really just the extra energy. When the energy is removed from the point of view of the stationary kilogram, all the extra "mass" is gone too.
I'm not sure you're right, but I totally agree with the idea behind your idea, which seems to be that it's better to explain the difference rather than work around it.
From a coder's perspective, I'm looking at this like you can either identify the root cause and fix the system itself, or you can start putting in spaghetti code to fix it.
Now, if the system itself isn't behaving like you expected, it makes sense to me that there's something more fundamental going on that needs to be looked into. Why work around the problem when the problem itself could be telling you something very interesting and useful?
Since you use equations of relativity to calculate the mass increase, you could use the same equations to calculate the mass at rest and show that it doesn't increase.
well, you seems to be on to something. These other kilos are kept at different places that have different gravitation (no mentioning that they control for that) - thus different time. So 1 year for IPK in Paris isn't a precise 1 year for its copy in another place. So whatever changes happen to the kilos they happen a bit quicker for some and a bit slower for the others.
I always thought 1 litre of water equals 1 kilogram. And as we know how long 1m is from nature, why don't they use 10cm x 10cm x 10cm of water at a specified temperature as a prototype of kilogram?
It's third lightest---there's an outlier that's way lower. But, again just from eyeballing, it looks like there's two clusters, one that has tracked with the IPK and one that is now heavier than the IPK. Based only on that, it strikes me as more likely that some of the national copies have gained mass(/weight), due to storage conditions or whatever, while others have kept their same weight.
Of course this "doesn't matter" in that whatever the mechanism, it's still a problem for the science!
90% platinum and 10% iridium for its virtual immunity to oxidization, and because it’s extremely hard-wearing
well thats bollocks. Platinum is hilariously soft.
There are a few issues, one is radioactivity. There are radioactive impurities that as they decay loose weight. Second, its postulated that there is a build up of trace amounts of mercury on the IPK due to environmental factors.
thirdly, they are not cleaned anymore. they used to be cleaned with shammy leather.
Originally the meter was defined as the distance around the Earth, perpendicular to the equator, divided by 40 million. The French spent a while triangulating the French countryside from North to South to calculate the Earth's curvature. Unfortunately it was assumed that the earth was a prolate spheroid, when actually it is oblate. This is one of the reasons it was reformulated.
The East India Company triangulated most of the length of India, but it was tremendously expensive. http://en.wikipedia.org/wiki/Great_Trigonometric_Survey
It has always bugged me that scientists consider this obviously terrible kludge of a standardization method acceptable.
A civilizaton looking back 20,000 years from now and translating our scientific literature would be able to figure out what we meant by "second" by measuring the decay of a cesium 133 atom. But a kilogram (or any unit derived therefrom)? Sorry, the prototype is at the bottom of a crater. You can't miss it - it's the size of a whole golf ball, after all.
Your concern is at the heart of the effort to redefine the kilo. Everyone wants to link it to fundamental constants. The trouble is that the IPK is still more reliable than our measurements of Planck's constant and Avogadro's number.
The meter was an artifact until measurements of the speed of light surpassed the prototype. The situation here is the same.
If the world ended and all of the distributed artifacts were lost, you could use existing measurements of fundamental constants to redefine the kilo at slightly worse precision.
[+] [-] velodrome|12 years ago|reply
Known as the Avogadro Project, the plan is to bring together enough atoms of one substance – silicon – to make a kilo.
Attention has focused on silicon because:
- its characteristics are very well understood
- a single crystal of the right size can be grown
- its atomic structure is extremely uniform
- its widespread use in the computer industry means it can be obtained with relative ease at high purity and resonable cost.
A spherical shape was chosen because a sphere has no edges that might get damaged and only one dimension has to be measured in order to calculate its volume.
---
http://www.csiro.au/content/ps35k
http://www.youtube.com/watch?v=ZMByI4s-D-Y
[+] [-] Shish2k|12 years ago|reply
Surely every dimension needs to be checked, to ensure that it's a perfect sphere? (Which I assume is harder than checking a cuboid has six flat sides joined at right angles)
[+] [-] ISL|12 years ago|reply
[+] [-] xentronium|12 years ago|reply
How is this good news for dieters? New kilo is lighter than old one, thus making all new measurements bigger in absolute numbers.
Besides, can't they recreate a "canonical kilo" with the required measurements?
[+] [-] ISL|12 years ago|reply
> Besides, can't they recreate a "canonical kilo" with the required measurements?
This is the main point of the drive to redefine the kilogram. Right now, the IPK (the French kilogram) is the SI standard for the kilogram. Groups are working hard to redefine the kilo in terms of either Planck's constant or the Avogadro number. In order to do so, the experiments that measure one of those fundamental constants must be more reliable than the IPK.
They're very close, but absolute mass measurements of the required precision at the kilogram scale have never been done before.
[+] [-] martin-adams|12 years ago|reply
[+] [-] hughes|12 years ago|reply
[+] [-] thejosh|12 years ago|reply
[+] [-] speeder|12 years ago|reply
[+] [-] Osmium|12 years ago|reply
[+] [-] ArikBe|12 years ago|reply
https://www.youtube.com/watch?v=ZMByI4s-D-Y
[+] [-] nraynaud|12 years ago|reply
And it would also really prolong the French Revolution spirit in the sense that this unit would become so universal that you don't need a physical reference anymore, like what we could achieve with the other base units (like second then meter).
[+] [-] EGreg|12 years ago|reply
Well they COULD always do that thing with the water where they heat it to 4 degrees celcius and measure its volume and weight. Then they'd know which it is.
That said, there's a nice video on this: http://youtube.com/watch?v=ZMByI4s-D-Y
[+] [-] yetanotherphd|12 years ago|reply
[+] [-] xenophonf|12 years ago|reply
[+] [-] fragsworth|12 years ago|reply
Except they'd have to measure its weight (mass), which is in... Kg...
[+] [-] unknown|12 years ago|reply
[deleted]
[+] [-] Zenst|12 years ago|reply
Though idealy the ability to measure out a fixed amout of atoms of element and wheigh that and work out the relationship of how many atoms of element X is needed for a kilo. Well until then it is one of the last area's of measurment that history still firmly has its teeth into.
Was nice TV show in the UK not long ago that covered the whole area of weights and measures from the science and history of them comming about. One of the better science shows.
http://www.bbc.co.uk/programmes/b02xgf5d
[+] [-] rmrfrmrf|12 years ago|reply
[+] [-] ISL|12 years ago|reply
Also, the ISS is a tricky place to work for a precision measurement. It's electrically, seismically, and gravitationally noisy (and huge gradients). Precision gravitational measurements are generally carried out in dedicated spacecraft with careful attention to those concerns, if they can't be done on the ground.
[+] [-] clubhi|12 years ago|reply
[+] [-] jamesjguthrie|12 years ago|reply
The article doesn't mention mass at all and it is true that if a stationary object is losing mass it is also losing weight.
[+] [-] muuh-gnu|12 years ago|reply
1 kJ = 1000 standard units of energy.
1 kg = 1 unit of mass.
Was this just an unfortunate historical accident? But if the too that much care to make a unit system that makes intuitive sense, why would they let in such an annoying exception? Why didnt they just make "gram" the standard unit or just made up another name?
[+] [-] knappador|12 years ago|reply
1 kJ = 1000J 1 kg = 1000g
Adjusting prefixes puts the units on the order of magnitude where they are easy to write in typical domain problems. For a heat-capacity and heat-transfer problem, I might end up with J/kg or kJ/kg being convenient, while for expressing the specific energy of jet fuel, I'll use MJ/kg because it's 39.
In the case of the kg, I'll bet that 1g was simply too small for the tools of the time to make an accurate model that was reproducible to the desired accuracy. For all I know, the weights were die-cast from the same melt, and the effect of scratches gets reduced as the surface-area/volume ratio goes down.
[+] [-] EdiX|12 years ago|reply
However all the standard prefixes still apply normally, ie you will have milligrams (mg) that are 1/1000000 of 1kg.
[+] [-] JamieLewis|12 years ago|reply
[+] [-] stormbrew|12 years ago|reply
[+] [-] samatman|12 years ago|reply
Therefore, a better gramme could be established by weighing a kilogramme and dividing by 1000.
This is also why an STP ml of water (used to) weigh a gramme, btw.
[+] [-] cantrevealname|12 years ago|reply
From the stationary kilogram's point of view, all of the other kilograms had undergone relativistic mass increases during the time of their travel. Suppose a tiny amount of this mass increase is somehow actually retained when all the transported kilograms are brought to the same frame of reference (i.e., when the airplanes land in Paris).
What's a simple way to disprove this idea?
[+] [-] sp332|12 years ago|reply
[+] [-] yetanotherphd|12 years ago|reply
I imagine that the possible deviations from General Relativity have been thoroughly mapped out and tested, where possible.
[+] [-] jasonkolb|12 years ago|reply
From a coder's perspective, I'm looking at this like you can either identify the root cause and fix the system itself, or you can start putting in spaghetti code to fix it.
Now, if the system itself isn't behaving like you expected, it makes sense to me that there's something more fundamental going on that needs to be looked into. Why work around the problem when the problem itself could be telling you something very interesting and useful?
[+] [-] mtdewcmu|12 years ago|reply
[+] [-] VladRussian2|12 years ago|reply
[+] [-] legierski|12 years ago|reply
[+] [-] ronaldx|12 years ago|reply
The even distribution suggests (to my eye) that this is as likely random as by some systematic effect.
[+] [-] blahedo|12 years ago|reply
Of course this "doesn't matter" in that whatever the mechanism, it's still a problem for the science!
[+] [-] KaiserPro|12 years ago|reply
well thats bollocks. Platinum is hilariously soft.
There are a few issues, one is radioactivity. There are radioactive impurities that as they decay loose weight. Second, its postulated that there is a build up of trace amounts of mercury on the IPK due to environmental factors.
thirdly, they are not cleaned anymore. they used to be cleaned with shammy leather.
[+] [-] CoryG89|12 years ago|reply
[+] [-] smcl|12 years ago|reply
[+] [-] NAFV_P|12 years ago|reply
[+] [-] mistercow|12 years ago|reply
A civilizaton looking back 20,000 years from now and translating our scientific literature would be able to figure out what we meant by "second" by measuring the decay of a cesium 133 atom. But a kilogram (or any unit derived therefrom)? Sorry, the prototype is at the bottom of a crater. You can't miss it - it's the size of a whole golf ball, after all.
[+] [-] ISL|12 years ago|reply
The meter was an artifact until measurements of the speed of light surpassed the prototype. The situation here is the same.
If the world ended and all of the distributed artifacts were lost, you could use existing measurements of fundamental constants to redefine the kilo at slightly worse precision.
[+] [-] scott_s|12 years ago|reply
[+] [-] alan|12 years ago|reply
Like they're more exposed to chemical disturbance? Some form of tiny relativistic effect?
[+] [-] scotchmi_st|12 years ago|reply
[+] [-] kunai|12 years ago|reply
[+] [-] leeoniya|12 years ago|reply
http://www.wired.com/magazine/2011/09/ff_kilogram/all/1
[+] [-] harigov|12 years ago|reply
[+] [-] unknown|12 years ago|reply
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