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453 comments

alternate theories (5, Informative)

arun_s (877518) | more than 7 years ago | (#19517089)

I found some alternate theories that are also attempting to precisely measure the kilogram at everything2 [everything2.com] . They look pretty interesting, here's a small excerpt:

Superconducting levitation

This method works along essentially the same principles as the Watt Balance. In it, a superconductor of a known mass is placed within a superconducting coil. By running current through the coil, a magnetic field is generated that causes the superconducting mass to levitate. By levitating it at different positions and measuring the current required to do so, the magnetic flux can be calculated. Magnetic flux relates directly to Planck's constant, and because the force generated by the magnetically-induced levitation and the downward force of gravity must be equal, Planck's constant can thus be precisely related to the kilogram.

Hey wait, TFA skims over what they're going to do with the Silicon ball once its made. Again, from everything1:

X-ray interferometry is used to determine the distance between lattice planes in the silicon crystal, permitting physicists to determine, as closely as possible, the number of atoms in these spheres. Currently, a measurement accuracy of one part in 10^7 is possible, after considering all of the various sorts of error introduced in the process, but it is hoped that ten times this accuracy will be possible within five years.

Re:alternate theories (5, Insightful)

JanneM (7445) | more than 7 years ago | (#19517193)

This method works along essentially the same principles as the Watt Balance. In it, a superconductor of a known mass is placed within a superconducting coil.

If you have a lump of anything of a known mass, why bother with the rest?

Re:alternate theories (2, Insightful)

jimstapleton (999106) | more than 7 years ago | (#19517319)

maybe because you are using the lump of known mass to measure something else.

Duck Measurer: "I put a duck on one side of the scale, and use weights (lumps of known mass) on the other side to determine the mass of the duck."
Some Guy: "Umm, but you already know the mass of the weights, why are you bothering?"

Re:alternate theories (4, Insightful)

Delirium Tremens (214596) | more than 7 years ago | (#19517423)

You are confusing mass and weight.
Mass = how much matter there is in an object.
Weight = how much pull does a particular gravity (like Earth's g) has on that quantity of matter.

That's why you could be floating (weightless) in a space ship without having lost any of your fingers or other parts of your body (mass) ;-)

Re:alternate theories (5, Interesting)

jmv (93421) | more than 7 years ago | (#19517257)

I personally wouldn't put too much trust into a measurement that depends on gravitational acceleration for several reasons.
1) It means you can't move the setup somewhere else easily because gravity is location-dependent
2) Events like the 2004 tsunami has a slight (but measurable) effect on the Earth's rotation and hence on the acceleration (because of centrifugal force) ... and most importantly
3) Your measurement will (*literally*) depend on the phase of the moon (just like tides)

Re:alternate theories (1)

porpnorber (851345) | more than 7 years ago | (#19517259)

But wait! You say "the force generated by the magnetically-induced levitation and the downward force of gravity must be equal, Planck's constant can thus be precisely related to the kilogram," but that won't work. Force is measured in Newtons; you've just measured weight, not mass. In fact, this 'method' would give you different values depending on when and where you used it!

Or am I deeply confused?

"perfect" sphere (0, Redundant)

johnny cashed (590023) | more than 7 years ago | (#19517091)

Yeah, right, a perfect sphere. Ok, I'm sure it could be an improvement, but can you ever really get a perfect anything? (I'm talking about physical objects here)

Re:"perfect" sphere (3, Funny)

Rendo (918276) | more than 7 years ago | (#19517101)

Women are perfect, and they're physical objects. Or at least they've always told me that...

Re:"perfect" sphere (3, Funny)

Gorshkov (932507) | more than 7 years ago | (#19517149)

May God have mercy on your soul if you ever attempt to call a woman a physical object to her face.

Re:"perfect" sphere (5, Funny)

Anonymous Coward | more than 7 years ago | (#19517197)

>May God have mercy on your soul if you ever attempt to call a woman a physical object to her face.
Especially if he compares her to a perfect sphere.

Re:"perfect" sphere (5, Funny)

CommunistHamster (949406) | more than 7 years ago | (#19517285)

It makes the calculations simpler.

Re:"perfect" sphere (1)

TapeCutter (624760) | more than 7 years ago | (#19517323)

Funniest comeback, eva!

Re:"perfect" sphere (3, Funny)

metlin (258108) | more than 7 years ago | (#19517401)

Would you rather a square? =)

Reminds me of a story - a friend had gotten a boob-job and we were all out for dinner one night. Another common friend of ours hadn't known this and the first time he saw her, he burst out - "You've grown three dimensionally!"

Re:"perfect" sphere (-1, Offtopic)

Anonymous Coward | more than 7 years ago | (#19517113)

but can you ever really get a perfect anything? (I'm talking about physical objects here)
Yes sure! I'm perfect! Only thing: you can't get it! Wuhahahah!

Re:"perfect" sphere (4, Insightful)

Aladrin (926209) | more than 7 years ago | (#19517115)

No, it's impossible. What they -really- mean is that it'll be perfect as far as we are able to measure it. And it has absolutely nothing to do with what is really important here: They are counting the atoms of silicon in a kilogram and will use that measurement as the basis for the kilogram, instead of some lump of metal in a vault.

The kilogram will not change, only a proposed scientific definition of it.

The sphere doesn't mean -anything- except that it'll weight exactly a kilogram and be amazingly round.

There's either a lot of media spin, or someone's attempt to get his work recognized and used. From what I can see, there's not a single soul that has dedicated to USING this new scientific definition, other than those directly involved with the project.

Re:"perfect" sphere (4, Informative)

ozmanjusri (601766) | more than 7 years ago | (#19517235)

There's either a lot of media spin, or someone's attempt to get his work recognized and used.

It's important enough for laboratories in Germany, Italy, Belgium, Japan, Australia and USA to invest a great deal of time and effort.

The spheres are being made by CSIRO's Centre for Precision Optics. They've been making precision spheres for research since the late '80s, and have all the recognition they need from anyone who has a clue.

Have a look here; http://www.tip.csiro.au/IMP/Optical/spheres.htm [csiro.au] . It might help you understand the project better.

Re:"perfect" sphere (1)

giorgiofr (887762) | more than 7 years ago | (#19517121)

Well, at the end of the day you can't build with physical objects, even as tiny as atoms, a perfectly spherical shape. So this point is moot anyway. They probably meant "more precise than ever created".

Re:"perfect" sphere (1)

Walzmyn (913748) | more than 7 years ago | (#19517133)

Hey c'mon. It's gotta be easier than flying to paris and going through security to get into that vault every time you want to weigh something.

Re:"perfect" sphere (2, Funny)

TapeCutter (624760) | more than 7 years ago | (#19517147)

"but can you ever really get a perfect anything?"

The whole notion of "silicon balls" sounds fake to me!

don't need to create it to define it (0)

Anonymous Coward | more than 7 years ago | (#19517095)

Look, I like advancing on the French as much as any Anglo-Saxon worth his meat, but if we know the mass of one atom of silicon, then we don't need to construct a "perfect sphere" of silicon atoms to redefine the kilogram; we can just say "it's defined as x atoms".

Re:don't need to create it to define it (4, Insightful)

setagllib (753300) | more than 7 years ago | (#19517173)

The point of having a physical object is that it can be used as a root for calibrating devices. From there you can calibrate more devices on each other. The further you get, the less likely you are to be precise, but the chances are pretty good that little deviations up and down will cancel out overall. But it's absolutely important to have an exact starting point, and a physical object is the only way to do that.

It's a lot easier to measure a large object than a small one and multiply it, since a small error will also multiply out. What I don't get is how they intend to build an exact number of atoms into the sphere. You would need some other exact measurement, like number of electrons for calculating precise electrolysis procedures.

Silicon has 14 electrons per atom (2, Informative)

tepples (727027) | more than 7 years ago | (#19517349)

What I don't get is how they intend to build an exact number of atoms into the sphere. You would need some other exact measurement, like number of electrons for calculating precise electrolysis procedures.
The number of electrons in a crystal equals the number of protons. But "silicon" is defined as the element with 14 protons per atom. So the number of electrons equals the number of atoms times 14.

So we use a irrational number to define something? (0)

Anonymous Coward | more than 7 years ago | (#19517099)

Since we're injecting Pi into the definition of a standard, that makes the standard ultimately unmeasurable doesn't it?
I'd rather have a cube than a sphere.

Re:So we use a irrational number to define somethi (1)

tom17 (659054) | more than 7 years ago | (#19517243)

We have a LOT of Pi now don't we?

I don't know if we have enough now, but surely if we DO have enough pi that any errors in the count introduced from the inaccuracy of pi are significantly less than 1 atom, then it would be sufficient, oder?

Want pie now!

Re:So we use a irrational number to define somethi (1)

lachlan76 (770870) | more than 7 years ago | (#19517461)

No, we can just keep calculating it further and further until we get enough accuracy to get the correct number of atoms (since there will be an integer number of atoms, the inaccuracy will be lost in the rounding).

Re:So we use a irrational number to define somethi (1)

Goaway (82658) | more than 7 years ago | (#19517463)

Yes, the fact that we only know pi to a couple billion digits will certainly make this definition completely useless!

First of all (2, Insightful)

alx5000 (896642) | more than 7 years ago | (#19517105)

... no sphere made of atoms will ever be a perfect one.
Second, if that rusty lump in Paris defines what a kilogram is, in no way is this sphere gonna change that.

Re:First of all (4, Informative)

Corporate Troll (537873) | more than 7 years ago | (#19517179)

Second, if that rusty lump in Paris defines what a kilogram is, in no way is this sphere gonna change that.

That's wrong. The lump is not rusty, because the lump is platinum-iridium which is quite unreactive so that corrosion ("rust") won't affect the material. Corrosion alters the weight, you know.

Second, it can change the definition. The metre used to be a platinum rod in Paris, now it is defined in how much distance light does in a certain (very short) time. Here it will be that the kilogram will be defined as N silicium atoms. (Where N is a very large number) Scientists do not like definitions based on objects, they prefer definitions based on universal constants. All this could of course be read in the article....

Re:First of all (-1, Troll)

tsa (15680) | more than 7 years ago | (#19517305)

"Quite unreactive" means "non totally unreactive". So the thing in Paris is indeed a rusty lump. But silicon also reacts with water and oxygen to form a layer of silicon oxide on its surface. This will increase the weight of the sphere, making this sphere just as unreliable as the lump in Paris. I really don't get why we need this sphere. And why a Sphere?? The fact that it is round means that it introduces rounding errors. Why not make a shape based on the (diamond) crystal structure of silicon? That would make much more sense to me. The fact that the sphere has to be as spherical as inhumanly possible also puzzles me. It doesn't magically become insensitive to scratching once it's perfectly round.

All in all, this looks like a very expensive hobby to me. Not much scientific value in it.

Re:First of all (1)

jackb_guppy (204733) | more than 7 years ago | (#19517369)

Round makes the math easier, since they are not actually going to count the number of atoms. 4/3 pi() r^3

Re:First of all (1)

martinthebrit (565913) | more than 7 years ago | (#19517481)

"Quite unreactive" means "non totally unreactive".
Actually the word quite is an oddity in that it has two seemingly contradictory definitions. The most common meaning is "to an extent", as you have interpreted it. However I believe that the original meaning of the word was "absolutely, completely", commonly found in classic literature. Hence the original assertion that platinum/irridium alloy is unreactive was correct.

Re:First of all (1)

alx5000 (896642) | more than 7 years ago | (#19517329)

I knew about the metre, I knew about the rod. I just think it's stupid to try and make a silicon sphere, when you can just say (as you stated in your reply) that 1 kilogram is X silicium atoms. BTW, if scientists don't like definitions based on objects then I'll guess it does make quite a lot sense to define a kilogram with a silicon sphere...

Re:First of all (1)

jollyreaper (513215) | more than 7 years ago | (#19517479)

Second, if that rusty lump in Paris defines what a kilogram is, in no way is this sphere gonna change that.
Wow, what a great straight line. There's just so many opportunities, I feel like Quagmire in an adult entertainment store. Giggity-giggity!

"Rusty lump? Oh, I'm sure she can afford to go with actual silicone."

"Wow, did that come out in the cavity search?"

"Biggest ben wa ball ever."

"That's not a rusty lump, that's my watch, you insensitive clod!"

Huh? (0)

CarpetShark (865376) | more than 7 years ago | (#19517111)

OK, someone's going to have to explain this for me. Why do we have to have an actual object to define a weight?

Re:Huh? (1)

Aladrin (926209) | more than 7 years ago | (#19517151)

Because it's 'scientific' that way. This is apparently someone's pet project and they are acting like the world has asked them to do it.

I'm not against the project, and I think it'll be nice to have a more scientific definition, but it doesn't change -anything-. A kg is still a kg. There is no scientific theory being used to create the 'perfect weight system' or anything like that. They are merely measuring what already exists and using it.

Re:Huh? (0, Flamebait)

Timesprout (579035) | more than 7 years ago | (#19517177)

You are correct. They should just use a single atom of unobtanium and keep it in a chamber where gravity is increased to the point that it weighs 1 Kg.

Re:Huh? (1, Informative)

EricWright (16803) | more than 7 years ago | (#19517263)

Mass is constant (assuming it is at rest), and has nothing to do with the force of gravity on an object. The mass times gravitational acceleration is the weight, often reported in lbs or Newtons. In other words, a kilogram here is a kilogram everywhere.

BTW, in the English measurement system, mass is measured in stones.

Re:Huh? (0, Redundant)

Englabenny (625607) | more than 7 years ago | (#19517283)

Um, that's the typical physical misunderstanding. A kilogram is a measure of mass, not weight. Thus we need this object as defining a kilogram comes from what an object is (mass), not what it seems to be (weight).

Re:Huh? (1)

TapeCutter (624760) | more than 7 years ago | (#19517221)

"Why do we have to have an actual object to define a weight?"

Kinda like asking: why do we need space to define distance? - The reason is that only physical objects posses mass (to be pedantic you also need the planet Earth to define weight).

Re:Huh? (1)

MichaelSmith (789609) | more than 7 years ago | (#19517351)

you also need the planet Earth to define weight

And at this level of precision the location of the measurement may be very important. I don't think you could take this sphere to a different latitude and get an accurate calibration.

Re:Huh? (4, Informative)

Yvanhoe (564877) | more than 7 years ago | (#19517339)

A lot of units can be defined using physical properties : a second is 9,192,631,770 periods of a precise physical reaction (transition between the two hyperfine levels of the ground state of the caesium-133 atom according to the wikipedia), a meter is the distance travelled by light in a 1/299,792,458 of a second and so one, Volts, Joules, etc... are defined this way. Mass, however, was not yet related to physics constants. So there is a "yardstick" for kilograms. A platinium cylinder was made a century ago, the closest we could get to what was considered a kilogram at this time and it was proclaimed "the exact measurement of a kilogram is the mass of this particular object". It is stored somewhere in Paris. I am sure that modern scientists will manage to conceive an experiment with a great precision to transform the kilogram unit into the abstraction it is supposed to be.

Re:Huh? (4, Informative)

dschuetz (10924) | more than 7 years ago | (#19517407)

OK, someone's going to have to explain this for me. Why do we have to have an actual object to define a weight?

You don't. That's just the way we've done it in the past. I read a really interesting article a couple months ago in American Scientist magazine called An Exact Value for Avogadro's Number [americanscientist.org] that addresses exactly this question. In the past, Avogadro's Number (6.02andchange x 10^23) was defined experimentally, based on the reference kilogram. These scientists propose reversing that -- defining the number absolutely, based on the number of atoms of a particular element that fit within a sphere of a certain size. It's sort of similar to what they're doing with the silicon sphere, but it's all done on paper, rather than by actually manufacturing an artifact.

The advantage of this, they say, is that the number will remain constant and not be affected over time as refinements in building and measuring such "reference kilograms" change the accepted mass of a kilogram. They make several other arguments, as well, but it's much better if you just read the article. :) It's also mentioned that a similar approach was taken to defining the meter, based on an absolute definition of the speed of light.
 

Re:Huh? (-1)

s31523 (926314) | more than 7 years ago | (#19517411)

Weight = Mass / Volume

If "they" can get an exact number of atoms (mass) into an exact, perfect sphere (volume), they will have the "gold" standard for a kilogram. That is why you need an object to define weight. Like, back in the day with a balance beam scale. Put something of known weight on the one side and then an unknown weight on the other side, once it balances you have identified its weight. This is the only use I can really see for this project, that is, getting all giddie when you throw the perfect silicone ball on a precision scale and see 1.000000 kg and the old ball reads 1.00001

yay!

Old news... (0, Offtopic)

Corporate Troll (537873) | more than 7 years ago | (#19517117)

Not a dupe, but I have seen this at least twice on German TV and that was already quite some time ago.

Re:Old news... (1)

allscan (1030606) | more than 7 years ago | (#19517185)

Of course you've already heard about this in the EU. Slashdot is a primarily US focused site, and as we all know the US is stuck with retarded imperial measurements. No wonder we lag behind the rest of the world in education, jobs, and I see now we've dropped in broadband penetration as well.

Re:Old news... (0)

Anonymous Coward | more than 7 years ago | (#19517295)

Hey, in the UK we have to deal with BOTH- at all times!
And you yanks got your 'imperial' measurements wrong at some point... I believe that you use 'US customary units', NOT Imperial, which is what we use. There are some differences.

Re:Old news... (1)

MichaelSmith (789609) | more than 7 years ago | (#19517331)

the US is stuck with retarded imperial measurements. No wonder we lag behind the rest of the world in education, jobs...

Its not hard to change. We did it in the early '70's here in Australia. That would have been the ideal time, right after the Apollo program ended with everybody upbeat about the future. It just takes a will to change.

This also affects the pound (3, Informative)

tepples (727027) | more than 7 years ago | (#19517391)

Of course you've already heard about this in the EU. Slashdot is a primarily US focused site, and as we all know the US is stuck with retarded imperial measurements.
A U.S. pound is defined as exactly 0.45359237 kg, just as a foot is exactly 0.3048 m. Therefore, any changes to the kilogram's definition also affect that of the pound.

Why silicon sphere? (1)

chengee (821396) | more than 7 years ago | (#19517119)

Ok... now.. does it have to be a sphere at all, why not cube? Hey silicon spheres.. perfect for implants!

Re:Why silicon sphere? (1)

Corporate Troll (537873) | more than 7 years ago | (#19517199)

Explained in the article: cubes have edges and due to that they are more prone to get damaged.

Oh, and Silicon != Silicone. I pity the woman with Silicon breast implants...

Of course, you were trying to be funny.... I know, I know, that's the sound of a joke going over my head.

Re:Why silicon sphere? (1)

KDR_11k (778916) | more than 7 years ago | (#19517451)

Silicon implants only seem bad until you realize how many transistors you can fit into them.

Re:Why silicon sphere? (0)

Anonymous Coward | more than 7 years ago | (#19517207)

RTFA and your question will be answered

Re:Why silicon sphere? (1)

dcsmith (137996) | more than 7 years ago | (#19517215)

I don't suppose pointing out that silicon the element and silicone the polymer are different will stop the impending flood of breast implant jokes, will it?

Re:Why silicon sphere? (1)

TapeCutter (624760) | more than 7 years ago | (#19517293)

"why not cube?"

Why not RTFA....oh wait..what am I saying...

The real reason they are changing it (3, Funny)

antifoidulus (807088) | more than 7 years ago | (#19517131)

is because they are embarrassed of the fact that a T-rex managed to steal [qwantz.com] the original one and now they need a replacement.

Re:The real reason they are changing it (1)

eclectro (227083) | more than 7 years ago | (#19517381)

Actually the real reason they are changing it is so the kilogram can have balls.

Ah yes... (4, Funny)

Nerdposeur (910128) | more than 7 years ago | (#19517137)

..but how can they make sure the new kilogram weighs a kilogram? :)

Re:Ah yes... (1)

Zaatxe (939368) | more than 7 years ago | (#19517223)

..but how can they make sure the new kilogram weighs a kilogram? :)

They put it on a scale, silly!

Re:Ah yes... (1)

Zaatxe (939368) | more than 7 years ago | (#19517281)

..but how can they make sure the new kilogram weighs a kilogram? :)

Actually the kilogram is a unit of mass, not weight. We say "it weights X kilograms", but we should really say "it weights under Earth's surface gravity the same as X kilograms". But of course we don't say that. We don't even say kilogram, we usually say "kilo", which means only "a thousand"!!

Re:Ah yes... (1)

Jamu (852752) | more than 7 years ago | (#19517335)

Weigh it against the old kilogram.

Re:Ah yes... (1)

tepples (727027) | more than 7 years ago | (#19517373)

but how can they make sure the new kilogram weighs a kilogram?
By putting it on an extremely precise balance against a carefully made copy of the Sevres kilo.

Re:Ah yes... (4, Informative)

at0mjack (953726) | more than 7 years ago | (#19517435)

They don't. The idea isn't to make the new sphere weigh a kilogram. The idea is to redefine the kilogram in terms of the weight of an atom of silicon (i.e. 602383623523895723945743 atoms of Si-14 weigh exactly 14 grams). The idea of the ultrapure and ultraround Si sphere is that (a) you can measure the lattice spacing of the Si atoms in it using x-ray crystallography, so you know how far apart the Si atoms are, and (b) you can measure the diameter of your ultraround sphere very accurately, so you can calculate its volume very accurately. Given these two, you can calculate with very small error bars how many atoms of Si there are in the sphere, and given the definition of the kg in terms of how many atoms of Si make up a kg you can calculate exactly how much the sphere weighs.

You can then stick it on your balance that needs calibrating, and twiddle the dials until the balance thinks that the sphere weighs the same as the calculated weight.

Si for silicon? (1)

zblach (977591) | more than 7 years ago | (#19517153)

(1 000 / 28.09) * 6.02 * (10^23) = 2.14311143 × 10^25

Why does redefining 1 kilogram to be one kilogram important? or is SI an abbreviation for silicon?

And funny how a silicon 'sphere' is to be the 'roundest object ever'

Re:Si for silicon? (1)

Timesprout (579035) | more than 7 years ago | (#19517253)

They want to redefine it because for some reason the International Prototype in Paris is slowly getting lighter over time (apparently its 50 micro grams lighter now). So they looking for something a little more constant and based on scientific principles in the same way they redefined the metre from a platinum rod to the distance travelled by light in absolute vacuum in 1/299,792,458 of a second.

I always thought that (3, Insightful)

oliverthered (187439) | more than 7 years ago | (#19517161)

A kilogram was equal to 1000 millilitres of water and that 1000 millilitres of water would fit into a space 10cm cubed.

If they've already defined the metre using constants, isn't something like this the best way of defining a kilogram.

Re:I always thought that (1)

tomstdenis (446163) | more than 7 years ago | (#19517303)

Shhh it's a make work project. We were taught [in Canada] that 1g = 1ml = 1cm^3.

Tom

Re:I always thought that (1)

WillAdams (45638) | more than 7 years ago | (#19517337)

One problem with that is the density of water varies w/ the temperature (it's this characteristic which makes life on earth possible --- water gets more dense as it approaches the freezing point, then less dense when it freezes), so the definition has to include a temperature &c.

William

Re:I always thought that (1)

Nimey (114278) | more than 7 years ago | (#19517383)

I'm pretty sure that STP (standard temperature & pressure) is implied.

...except according to Wackypedia, various standards bodies don't agree [wikipedia.org] on STP:

Re:I always thought that (1)

at0mjack (953726) | more than 7 years ago | (#19517489)

More to the point, you can't measure temperature accurately enough (it's a statistical property, not a fundamental one). The best thermometers get errors of a few ppm at STP: a few ppm error is absolutely useless for a kilogram standard.

A cold one. (1)

iknownuttin (1099999) | more than 7 years ago | (#19517485)

One problem with that is the density of water varies w/ the temperature (it's this characteristic which makes life on earth possible --- water gets more dense as it approaches the freezing point, then less dense when it freezes), so the definition has to include a temperature &c.

That's why you use beer. I liter of cold beer will be one kilo. Actually you add one sip to compensate for the bubbles which as as a salt and therefore increase the density.

Re:I always thought that (5, Informative)

at0mjack (953726) | more than 7 years ago | (#19517377)

The main problem with this as a definition is that water expands and contracts with temperature. So, if you wanted to define the kilogram in terms of a volume of water, you need to specify the temperature at which you are making the measurement. Temperature isn't something you can measure with very high precision (parts per million or parts per billion), so you end up with unavoidably large errors. As a result this is useless as a basic standard, the essence of which is that you should be able to repeat the standard measurement and get the same answer to N decimal places.

Knowing the french, the Sphere is sorely needed (0)

Anonymous Coward | more than 7 years ago | (#19517171)



Knowing the french, the Sphere is sorely needed. The french can't do anything right.

What's it useful for? (3, Interesting)

Max Romantschuk (132276) | more than 7 years ago | (#19517175)

Except for the challenges of making one, what's it useful for? You can't use it to calibrate anything, the wear and tear caused by the friction of handling would eventually change it's mass and defy it's purpose. Is the actual "finished product" good for anything else than sitting in another vault somewhere?

Re:What's it useful for? (2, Interesting)

meringuoid (568297) | more than 7 years ago | (#19517299)

Except for the challenges of making one, what's it useful for? You can't use it to calibrate anything, the wear and tear caused by the friction of handling would eventually change it's mass and defy it's purpose.

It's hierarchical. You use the standard kilogram to calibrate other, slightly less exalted standard kilograms. So the one kept in London and the one in New York and the one in Tokyo get calibrated against the one in Paris. Then you calibrate actual working weights against those.

Calibration of reference weights (1)

Lonewolf666 (259450) | more than 7 years ago | (#19517355)

I guess it would be used to calibrate a (limited by wear and tear, yes) number of "second generation" reference weights. Which would obviously not be quite as accurate, but still good enough to serve as reference to calibrate commercially weights and weighing machines.

The great advantage of this approach is that you can reproduce the original reference weight if necessary, while the loss of the current prototype would mean a much bigger problem.

Re:What's it useful for? (3, Informative)

dargaud (518470) | more than 7 years ago | (#19517357)

You can't use it to calibrate anything, the wear and tear caused by the friction of handling would eventually change it's mass and defy it's purpose.
Yes you can. The problem with the current reference weight is that it cannot be reproduced. Here you have a definition: this volume (4/3.Pi.R^3) contains such an amount of Si atoms. We define their individual mass and we define the whole sphere to be one kilo, ergo we can build another one. Just like defining the meter as a distance covered by light, here it's the weight of a given number of atoms.

Okay geeks... (3, Funny)

Dan East (318230) | more than 7 years ago | (#19517219)

A perfect sphere, down to the atom, of 1 kg silicon would require pi to what precision?

Dan East

Re:Okay geeks... (1)

EricWright (16803) | more than 7 years ago | (#19517279)

By definition, a "perfect" sphere would require pi to infinite precision. Let me know when you've got that figured out.

Measurements (1)

emj (15659) | more than 7 years ago | (#19517417)

an atom might have an diameter of about 0.1 nm, they say they have a perfect sphere which is just 35nm from being perfect, what ever that means. So you don't need that many positions of PI at all..

Re:Okay geeks... (1)

tepples (727027) | more than 7 years ago | (#19517419)

A perfect sphere, down to the atom, of 1 kg silicon would require pi to what precision?
Avogadro's number, the number of atoms in 0.012 kg of carbon-12 is 6.022 * 10^23. So you'd need about 25 digits for 1 kg of silicon. But there are several times that many digits in the pi song [ytmnd.com] .

Re:Okay geeks... (1)

gawdonblue (996454) | more than 7 years ago | (#19517443)

Blasphemer! Pi equals 3.000000000000000000000000000000000000000000 plus a whole lot more of them round things.

You can find more information at the Creation Museum or BIBLE://I Kings 7:23/

Labyrinth props (1)

CrackedButter (646746) | more than 7 years ago | (#19517225)

Didn't David Bowie have a few of these the institute could borrow instead of making new ones? Just keep them away from baby sitters.

What about the pound? (1)

Zaatxe (939368) | more than 7 years ago | (#19517251)

I've lived all my life in countries that use the metric system, so I have to ask... does the pound have an "official reference" like the kilogram?

Re:What about the pound? (1)

thefirelane (586885) | more than 7 years ago | (#19517287)

I've lived all my life in countries that use the metric system, so I have to ask... does the pound have an "official reference" like the kilogram? Yes, it is one of those Kilogram weights, cut into a piece about 45.359237% smaller

Re:What about the pound? (1)

EricWright (16803) | more than 7 years ago | (#19517307)

The pound is a weight (mass times acceleration due to gravity). There is no standard because weight is not a fundamental dimension of measurement. I have no idea if there is an "official stone".

Re:What about the pound? (1)

marka (32447) | more than 7 years ago | (#19517429)

Indeed it has. The same one, in fact.
A pound is defined to be exactly 0.454 kg.

Re:What about the pound? (0)

Anonymous Coward | more than 7 years ago | (#19517473)

Should be 0.45359237 kg.

Why a Sphere (0)

Anonymous Coward | more than 7 years ago | (#19517255)

For all units of measure, we can communicate them in words. For distance, we use a wavelength of a certain pure type of light. For time, we use the oscilation of a certain element. For mass, we use a lump of metal. The difference is that if we wanted to (and were able to) have a conversation with an alien species, we could tell them about speed, distance, time, and every other term in physics. But, we would have to load the International Prototyle on a rocket and send it to them to convey mass.

Now for the sphere, a previous poster wanted to know why a sphere. Two reasons. First, from the article, it has no edges to be damaged. Second, you know all about it if you know the substance and the diameter. The creation of the sphere is merely a means of ascertaining the dimension needed to define mass in words. Once that is done, the sphere itself will be little use except as a curiosity.

-cliff

Optical kilogram? (1)

bryan1945 (301828) | more than 7 years ago | (#19517269)

That's a lotta light!

isotopes (1)

ArbitraryConstant (763964) | more than 7 years ago | (#19517301)

How do they account for different isotopes? Or do they just get a sphere that weighs the same as N many atoms of pure silicon 28 would weigh?

Meanwhile (0)

Anonymous Coward | more than 7 years ago | (#19517325)

Mother Horta is mighty pissed...

FaiL`zors!? (-1, Offtopic)

Anonymous Coward | more than 7 years ago | (#19517327)

go find something Prospects are at times. From aal parties it's good manners

Nuclear decay (1)

pfortuny (857713) | more than 7 years ago | (#19517333)

and semidesintegration time, will they update the number of atoms?

Just wondering.

This is about measuring the Paris kilo (5, Informative)

femto (459605) | more than 7 years ago | (#19517353)

The CSIRO project is about determining how many silicon atoms are equivalent in mass to the current standard kilogram. Once that number is established the actual kilogram in Paris is redundant. If it gets lost or destroyed we can reconstruct the kilogram by counting out 'n' silicon atoms. It also means anyone can construct their own kilogram by counting out 'n' silicon atoms, without having to go to Paris to do a comparison.

It is a separate (but related) project to figure out the second part of the project: how to easily count out 'n' silicon atoms, so creating a universally available standard. One way might be to make a silicon sphere, like the CSIRO, but most people don't have the ability to do that.

Perfectly spherical...? (0)

Anonymous Coward | more than 7 years ago | (#19517363)

From TFA, "A spherical shape was chosen for the project because it has no edges that might be damaged..."

That's all fine and good, but for God's sake don't drop it! Without having bothered to Google it, how malleable is silicon?

perfect, well-rounded, bouncy (5, Funny)

siddesu (698447) | more than 7 years ago | (#19517387)

silicon spheres will define the standard ... will they be coming in pairs by any chance?

KG? (0)

Anonymous Coward | more than 7 years ago | (#19517389)

How many pounds is that?

Insert random breast implant joke here. (2, Funny)

JDark (512354) | more than 7 years ago | (#19517409)

Jenna Jameson do your part for science.

Who cares? (0)

Anonymous Coward | more than 7 years ago | (#19517439)

Real men use pounds, anyway.

SI horsepower (5, Funny)

Bromskloss (750445) | more than 7 years ago | (#19517449)

One horsepower is the power of the reference horse in an archive in Paris.

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