The kilo is losing weight, changing all of science
extremetech.com
extremetech.com
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.
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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)
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?
Then there's also that if the measurement changes, the results can become pretty bizarre. Say, you are on a diet for one month. At the start of the month, the kilo prototype weights 1 skg and at the end 1 ekg = 0.9 skg. You measure yourself at the start of the diet, and get that you weight 100 skg. You use some very precise diet-fu to draft a program that should see you losing 5 skg during the month. And lo and behold, you manage to stick to the program and loose exactly 5 skg.
But at the end of the month, when you measure yourself against the now-lighter prototype, you get that you now weight 106 ekg. So, you actually achieved your target and lost 5 kilos, but meanwhile ended up with 6 kilos more body mass than before the diet!
(Disclaimer: real changes in the prototype mass are of course way, way smaller.)
It's perfectly reasonable to have the opinion that wpietri advanced, and it's perfectly reasonable to raise it in this context. One could believe that for aesthetic reasons, or for political reasons, or other reasons, or a combination thereof. And I suggest that it's a higher caliber of comment than the mean HN comment, given that it suggests a source for deeper study of the commenter's opinion.
On the other hand, attempting to (tentatively) diagnose psychiatric disorders based on a single sentence on HN is completely implausible, totally insensitive (to actually ASD sufferers, I mean.. I'm sure wpietri can take it), totally oblivious to social context, and suggests that you might have a "stereotyped pattern of behaviour or interest".
Unless, of course, you have professional qualifications for such a (tentative) diagnosis, in which case I take it back.
The headline writer for the original article put in a joke. Xentronium, correctly, pointed out he appeared to get the joke backwards. Somebody else said, "it's just a joke", which is a thoughtless thing to say when you're trying to analyze why a joke does or doesn't work. If there's anywhere it's reasonable to nerd out on a nerdy joke, it's here.
So I pointed out a great source, written by experts in funny, explaining why getting to truth really matters in comedy. I am unable to fathom why you think that's a sign of a social disorder, let alone sufficient license to act like a dick.
> 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 you want to generate a kilogram to a certain precision (say, a part in 10^8) as a sum of a thousand well-measured grams, the grams need to be measured sqrt(1000) better (about a factor of 30). If you could multiply, you're fine, but since you're required to make (or measure) an actual kilo, you have to sum.
If we were to accept the multiplication method, it would be equivalent to restandardizing the SI upon the gram. That would be an okay thing to do, but to maintain continuity with past measurements (referenced to the IPK), we'd still have to make or measure an actual kilo, requiring precision sufficient to do the sum.
... is that _aluminum foil_ wrapped around a hose in one of the pictures ? I wrapped an unshielded 12 foot vga cable in aluminum foil once and it greatly (subjectively) improved the video quality.
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).
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
Except they'd have to measure its weight (mass), which is in... Kg...
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
"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."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.
Some nice discussion: http://physics.stackexchange.com/questions/29929/gravity-on-...
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.
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?
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.
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.
However all the standard prefixes still apply normally, ie you will have milligrams (mg) that are 1/1000000 of 1kg.
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?
I imagine that the possible deviations from General Relativity have been thoroughly mapped out and tested, where possible.
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?
> One litre of liquid water has a mass of almost exactly one kilogram
One of the leading proposals for the 2014 redefinition is very similar in spirit, though: defining Avagadro's number to be an actual number rather than a derived quantity (effectively this uses Carbon 12 as the mass standard).
Another proposal is to define Planck's constant. I can't comment on the measurability of this one, but it would probably make people studying atomic physics happy because they like to use units that set most common constants to one, and the redefinition would make more of these implicit factors of 1 defined, rather than measured quantities.
There's the Vienna Standard Mean Ocean Water[1][2] which accounts for differing isotopic compositions in different parts of the world.
There's been some competing attempts to the Standard Kilogram, including a pure silicon sphere of extremely precise physical dimensions (which we're good at), and using the lattice spacing to determine the number of atoms.
See the Avagadro Project[3]
[1] https://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Wat...
[2] The "Ocean" bit doesn't mean what you might expect. It's still fresh (non-saline) water.
[3] https://en.wikipedia.org/wiki/Avogadro_project#Avogadro_proj...
The even distribution suggests (to my eye) that this is as likely random as by some systematic effect.
Of course this "doesn't matter" in that whatever the mechanism, it's still a problem for the science!
wow, good spot, thanks :)
Although it could be a problem for science, somehow it's nice that we can get a sense of margin of error by this method.
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.
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.
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.
Like they're more exposed to chemical disturbance? Some form of tiny relativistic effect?
A kilogram is not a unit of weight, but a unit of mass.
Much less precise.
"The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second."
A second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.
The milligram weigh sets (1 milligram = 1000 microgram) are/were standard equipment in a chemistry lab (Now, if you are lucky, you get an electronic balance.) The smaller weights are only a small tin of 1 milligram. See the images in the middle of this page: http://www.ebay.com/itm/STAINLESS-STEEL-MILLIGRAM-WEIGHT-SET...
I found a microgram weight set in Internet. (But I haven’t seen any of them in real life) http://cn.mt.com/cn/zh/home/products/Laboratory_Weighing_Sol... . These weights are only a small piece of thin wire, and you must handle them with a special tool because the fingers are too dirty. The smaller weight is 50 micrograms, that is approximately the variation between the kilo prototypes.
Since it isn't done like that, I assume it isn't easy to find an Y which is both easy to measure exactly and to keep pure. (I have a smattering of organic chemistry but no inorganic, so any more opinions from me would be without value.)
Edit: Other people here talk about Si. We can keep that clean, at least (see electronics).
[1] http://www.theepochtimes.com/n2/images/stories/large/2011/03... [2] http://www.ptb.de/cms/en/themenrundgaenge/hueterindereinheit...
this surely can have a "losing weight" effect.