Slashdot Mirror
Perfect Silicon Sphere to Redefine the Kilogram
MrCreosote writes "The Age reports optical specialists at CSIRO are helping create a new standard for the kilogram, based on a precise number of atoms in a perfect sphere of silicon. This will replace the International Prototype, a lump of metal alloy in a vault in Paris."
I found some alternate theories that are also attempting to precisely measure the kilogram at everything2. They look pretty interesting, here's a small excerpt:
Hey wait, TFA skims over what they're going to do with the Silicon ball once its made. Again, from everything1:
I can explain it for you, but I can't understand it for you.
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)
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".
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.
... 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.
My 0.02 cents
OK, someone's going to have to explain this for me. Why do we have to have an actual object to define a weight?
Not a dupe, but I have seen this at least twice on German TV and that was already quite some time ago.
Ok... now.. does it have to be a sphere at all, why not cube? Hey silicon spheres.. perfect for implants!
--------- Cheng Ee well well
is because they are embarrassed of the fact that a T-rex managed to steal the original one and now they need a replacement.
Monstar L
..but how can they make sure the new kilogram weighs a kilogram? :)
(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'
# cat
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.
thank God the internet isn't a human right.
Knowing the french, the Sphere is sorely needed. The french can't do anything right.
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?
.: Max Romantschuk
A perfect sphere, down to the atom, of 1 kg silicon would require pi to what precision?
Dan East
Better known as 318230.
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.
Jonathanjk.com
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!
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?
So say we all
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
That's a lotta light!
Vote monkeys into Congress. They are cheaper and more trustworthy.
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?
I rarely criticize things I don't care about.
Mother Horta is mighty pissed...
and semidesintegration time, will they update the number of atoms?
Just wondering.
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.
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.
C - the footgun of programming languages
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?
silicon spheres will define the standard ... will they be coming in pairs by any chance?
How many pounds is that?
Jenna Jameson do your part for science.
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..
Real men use pounds, anyway.
One horsepower is the power of the reference horse in an archive in Paris.
Swedish plasma phys. PhD student; MSc EE; knows maths, programming, electronics; finance interest; seeks opportunities
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).
Yes, the fact that we only know pi to a couple billion digits will certainly make this definition completely useless!
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.
I prefer Flambe as apposed flamebait.
Standards for weights, mass, distance or any other measure, are critical in the calibration of instruments. This calibration provide the means that to compare product specifications and research results.
? ttype=2&tid=6345/
This particular effort is a very interesting set of challenges. It requires the use of single isotope of silicon; calibrations for distance and roundness, and a sophisticated means to to count the atoms. This last step requires the silicon to be perfectly crystalline.
Measurement is itself a very interesting study bordering on metaphysics and philosophy. The desire to measure things has been at the heart of a lot of scientific investigation, economics and other areas of study. Ref "Abstract Measurement Theory" by Louis Narens https://mitpress.mit.edu/catalog/item/default.asp
"If all the American people want is security, let them live in prisons." Eisenhower
I can tell you right now how many silicon atoms are in a kilogram ((1000/28.086)*(6.02214179*10^23) = 2.1441792316456597593106886*10^25), should that number be arbitrarily changed at any point we are pretty much fucked.
So is this sphere going to be isotopically pure Silicon 28? (92.23% natural abundance) If not, then this idea is doubly retarded. Talk about government workers. Some people will go to any lengths to get government funding from the gullible and scientifically ignorant politicians.
The Avogadro Project!?!? Surely he is rolling over in his grave!
There are a number of ways to define the kilogram and Avogadro's Number according to physical constants, and this Aussie propsal is not one of them. In fact there are very strong arguments against using a sphere: http://www.americanscientist.org/template/AssetDe
Naturally, Avogadro's Number should be an integer.
http://physics.nist.gov/cgi-bin/cuu/Value?na
http://physics.nist.gov/News/TechBeat/9501beat.ht
http://www.nist.gov/public_affairs/newsfromnist_b
I do not trust this Australian approach at all.
Weird. I read about this in an exam I took last week. It stated that the present standard kilogram is a mass of platinum and iridium kept at STP underground, and asked what factors might affect the mass of the standard kilogram when it is measured. I answered if any isotopes of platinum or iridium decay, or if the standard kilogram had a velocity close to the speed of light.
You are being very dense here.
TODAY: 1kg = the mass of the "rusty lump" in Paris. We don't know how many atoms of Ir and Pt the "rusty lump" have. So, if the "rusty lump" changes mass (and it changes with time because of being rustier all the time) AND because the "rusty lump" is used to calibrate scales all over the world, the kilogram is effectively changing with time. This is BAD.
WHAT THE GUYS ARE DOING: they are trying to make the most perfect silicon sphere possible that weights the same as the "rusty lump". Once they get to do that, they will count the atoms of silicon on the sphere, using interferometry. Suppose the # of atoms of the shpere is M.
WHAT WILL WE GOT THEN: 1kg = M atoms of silicon. This definition will never change, and if the silicon spheres rust or break or change weight by any circunstances, we make new ones with M atoms and we have a forever-constant definition of a kilogram. This is GOOD.
Got it? They did the a similar thing with the meter -- the original was a rod roughly 1m in size, then they did some measurements and said (*) "oh, one meter is the length that the light takes 1/299,792,458 of a second to go through in vacuum." and now they can do as many calibrating rods as needed, provided they make them the length that the light takes 1/299,792,458 of a second to go thru.
(*) actually the meter had an intermediate definition of "1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum", but the new definition has the advantage of setting the light speed at exactly 299,792,458 m/s.
It's better to be the foot on the boot than the face on the pavement. ~~ tkx Kadin2048
I'd prefer A non-perfect sphere of Silicone .
Nothing sucks like a Vax, nothing blows like a PowerMac G4
Defining mass buy by sherical objects is not new. The British Standard Apple has a mass of 102 grams. Thus under a standard gravity there is a force of 1 Newton.
As far as i can remember, in my physics or chemistry classes at school, 1Kg was always defined as a number of carbon-12 atoms... 1/12*1000*Na*atoms of C12. Looking it up on the net it seems to be project Avogrado. By the way first time i was given that definition at school was in the late 80's.
we don't know how many silicium atoms there are in one standard kilogram. The thing they are doing is to measure exactly that, so they can proclaim after: "1 kg is X silicium atoms."
It's better to be the foot on the boot than the face on the pavement. ~~ tkx Kadin2048
and it's not weight, is mass... but I digress... today, we do have an actual object defining what is 1kg of mass. We want to escape that, so we are doing the most perfect possible silicon sphere with 1kg of mass, we will count the number of silicon atoms on it, and we will proclaim that 1kg = the mass of X silicon atoms.
It's better to be the foot on the boot than the face on the pavement. ~~ tkx Kadin2048
duddeee...I want one of those spheres! that looks so cool!! If I played with it, would it lose silicon atoms?? how well do atoms in a crystal of silicon hold together??
Everyone, including the scientists are calling this 1 Kg object a "sphere", but nobody seems to realize that a sphere actually has no substantial volume to it. A sphere is just a concept (like a circle). What they are making is a BALL of silicon that weighs 1 Kg. A sphere can't weigh 1 Kg. Don't get me wrong, by describing a sphere, you are defining the radius and, therefore, you are describing a volume in 3 dimensions BUT you cannot call that physical ball of silicon a "sphere".
A new standard is needed because the "standard kilogram" held in France has been slowly losing mass, about 50 micrograms in the last 100 years, compared to other reference masses. It's not known how this has occurred.
2 7/023252
Wikipedia - Kilogram
http://en.wikipedia.org/wiki/Kilogram
Slashdot: The Changing Definition of 'Kilogram'
http://science.slashdot.org/article.pl?sid=03/05/
Paid Q&A/Research
.....I can't possibly be the only alpha geek out there who immediately associates a perfect silicon sphere with this:
http://www.dcs.gla.ac.uk/~hwloidl/htg-all.html
(see #48)
The problem with quotes on the internet, is that nobody bothers to check their veracity. -- Abraham Lincoln
"Zut alors! Pierre, le sphere parfait - ou est-ce que tu le placer?
"C'etait sur le table, Jean-Claude"
"Merde, il avait roller sous le sofa encore!"
----------------------------------- My Other Sig Is Hilarious -----------------------------------
I wonder why they use a sphere. To me it seems more logical to use a silicon crystal of known dimensions. Crystals are guaranteed to have integer number of atom planes whereas sphere is somewhat diffuse on the edges.
I mean, come on, would you Australians to define scientific standards? I won't!
For starters, those guys believe the South is on the top and North is at the bottom of the maps! I feel upside down just thinking of it. And on which side of the road are they driving already? North or south? See: you cannot trust those guys!
Second, the issue with "the" current "reference" in Paris (there are three cylinders in fact) is that is loses atoms sometimes, so its mass diminishes. I mean it is still The Kilogramme but the kilogramme is not what it was some years ago when the grass was greener and the boys were nice and, hum! Anyway, how would that be different with yet another physical object? Wouldn't it lose some random atoms from time to time?
Third, it is well known that international standards are defined in Paris: the internationnal skirts lenght association, the general contest of retreat speed and the cheese-smelling index are all defined in my city and everybody agrees with that. M. Sarkozy has just battled staunchly with M. Puttin to assert our rights on those essential fields.
Finally, I suspect that the kilogramme may be re-defined in October 2007 in Paris (http://fr.wikipedia.org/wiki/Kilogramme): a meeting of the Bureau Internationnal des Poids et Mesures (BIPM, Internationnal Weights and Measures Bureau in French) is scheduled this year.
Best kisses from Earth.
I am not Remy Mouton, unfortunately: http://remy.mouton.free.fr/art/
Cajun cook and comedian Justin Wilson told of a Cajun who sent his son to college. When the boy came home for spring break, the dad asked him "what ya larn in that college, boy?"
The son thought for a minute and said "pi R square".
The fathar had a fit. "Pie aren't square, pie are round. Cornbread are square!"
is going to be a crystal ball? Woo hoo!
Pffft! Metric system!
The King had it right all along...
C = 1'/ns
the speed of light = 0.983571056 feet per nanosecond
I'm sure we can come up with something similar for pounds and fahrenheit eventually.
Nouvelles de jeux et technologies en français. TC
Estimating the diameter of the spehere in the picture to around 12 cm and assuming the final spehere is the same approximate size: If the final sphere was magnified to the size of the earth, it would have surface variation of 9.5 cm in altitude. Pretty slick - although I bet that within a week at least one american will find a way to trip and sue them into oblivion.
...or, if the person watching the standard kilogram of precious metal is Jewish.
"MR. GOLDSTEIN!!! For the LAST TIME, it was NEVER the standard '374 grams'!!"
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.
Currently the kilogram is defined by the "lump in paris". As some the previous posters already pointed out this is a Bad Thing (tm).
Better would be to say the kilogram is the mass of n atoms of y. Problem is: how many atoms has one kg of y?
Actually you have to count them, and one good way to count it is to use a crystal with a well understood structure.
You simply grow a near perfect crystal, measure the size and you can calculate the number of atoms. That's what they build these silicon (=crystal) spheres for.
Now they just have to get the precision at least as good as the current definition (which means they have to be 10 times as precise), so noone will not notice the switch of the two definitions, and we don't need that "lump" in paris anymore.
Worse - you can't touch the Sphere of One-ness with anything.
... in a vacuum chamber ... at the bottom of a flight of stairs, in a disused lavatory with a sign on the door reading "prendre garde du léopard."
Q: May I put my greasy paws on it?
A: No. Fingerprints will alter the mass in a measureable way.
Q: White gloves?
A: Abrasive.
Q: Use a special cradle that's machined to exactly the same radius profile such that you won't scratch or deform the Sphere of One-ness?
A: Nope. That'll result in a molecular interference fit. You'll never get the two pieces apart.
So ultimately, they're building a very precise bauble that no one will ever be allowed to touch. I suspect that bouncing photons off the surface may displace an atom or two, so they'll keep it in a dark room
0.454 kg is defined as exactly 1 pound. ;)
we would be completly metric for year now if Reagan hadn't killed it. Yet another reason to pee on his grave.
The Kruger Dunning explains most post on
This example of the quantising effect of a superconducting ring is given early in Carver Mead's fairly straightforward text, Collective Electrodynamics.
Wikileaks, no DNS
I know this is kind of weird...but I've always fantasized abotu sneaking into that vault in Paris and filing a little bit off the kilogram mass standard. And maybe just trimming down the end of the meter stick a bit. On some level I feel like if you could do this, the world would be plunged into chaos within a few weeks.
Please don't hurt the Horta!
I swear, those guys down there weigh my kilos short every time.
(since there will be an integer number of atoms, the inaccuracy will be lost in the rounding)
:D
We split the atom years and years ago, so thats not a problem; we'll just have a load of half/quarter/eigth atoms around the edge. In fact, there's probably a load of spare atom parts lying around somewhere that could be used for just such a purpose!
There IS NO exact Kg. Its only defined to a value with a limited number of digits.
Lets say the current kg is exact on 9 digits.
If you have any new definition, which has more digits (for example 22, as in the number of silicon atoms in one kg), it wont be the same number.
Of course its not, as its more accurate.
The new definition will be a NEW value for the kg, which is more precise, and within the uncertaincy of the old definition.
Thats the same way like when they changed the meter. It actually shrunk a few parts of Angström during the redefinition, but it didnt matter, as it wasnt reproducable to that extend before.
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
Does it look and feel like the real thing? /Sili-what? oh.
*slight crashing sound*
The point of this is to figure out the exact number of atoms in 1KG. Even if the sphere gets damaged, they should theoretically be able to check it for the number of atoms or just grow another using the same procedure.
They should be careful with this thing. I heard that if you go inside it, it will give you the ability to manifest your thoughts into reality! Usually situations like that just end up with giant squids attacking your underwater science labs.
Eek!
If they redefine the kilogram, what happens to coefficients that rely on kilograms? For example, for the equation for Universal Gravitational Energy [G=(coefficient)(m1xm2)/d^2)], is the coefficient going to change?
WARNING: 1 kibigram = 1024 grams
I've seen a number of perfect spheres of silicone, and they typically come in pairs.
As the silicon has a cace-centered cubic crystal structure, a sphere could not be the perfect shape.
Maybe Computers will never be as intelligent as Humans.
For sure they won't ever become so stupid. [VR-1988]
The weight has been defined upon a lump of platinum since 19th century. ... weight so it depends upon that lump.
Atomic weight is
They will count the number of atoms in the sphere and will multiply it by the atomic weight of silicon.
The weight of the silicon ball will be correct if and only if is will weight the same as the platinum lump, not just because the number of atoms has been precisely defined.
I would prefer to stay with the platinum lump: less hassle!
Maybe Computers will never be as intelligent as Humans.
For sure they won't ever become so stupid. [VR-1988]
expecting something Tiffany Towers related. now_those_are perfect silicone spheres.
oh marmalade.
When you see the flash you count 'till there is the thunder.
When you take the number you counted and devide it by the distant of the thunder; you know exactly how fast you have counted.
If you mod this up, your slashdot background will turn into a beautiful sunset!
Haha. Love the Douglas Adams reference. Such a lead-in, too!
Seriously, though, photons of anywhere near visible frequencies won't displace the atoms; light bouncing is almost always a purely electronic transition thing. And if this thing is ultrapure silicon, atoms are NOT going to want to displace. No worries there.
Oops... umm..
Boss, I think I just dropped the.. perfect sphere...
All I know is that thing would make one hell of a bitchin paperweight. I totally want one.
I read Usenet for the articles.
yuo have a sphere that is exceedingly round. They been very careful to make certain it is very precise but to calculate the volume of the sphere don't you depend on a transcendental number call Pi that can be calculated out to so many places but hasn't an end so you're end result for the volume of the thing is going the depend on how namy digits of Pi you decide to bring into the equation. How many digits along do you need to go to reach the point where one more digit of pi results in one half an atom's worth of volume?
This is the most perfect crystal ball ever! We can see the future better than ever before!
Consciousness is an illusion caused by an excess of self consciousness.
... which weighs 1 Kg. But, alas, the new weight of Kg has been introduced yesterday, so I am afraid that the 1 Kg will now cost you 20% more.
;=)
Yes, you heard that right: for the new Kg is 20% more than the old one ! Don't you just love redefining the metric system ?
Slashdot: stuff for news, nerds that matter, matter for news, stuff that nerd
Figure out how many atoms of carbon-12 are really in a kilogram, and fix Avagadro's number accordingly so 1 mole of carbon 12 had a mass of exactly 12 kilograms.
Use as many significant digits as you need so the current "standard" kilogram is within the margin of measurement error and zero-fill the rest of the number.
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
> bringing the kilogram into line with other base units such as the metre and the second, which are all defined by physical constants...
One cubic centemeter of H2O is one gram, right? If a "metre" is based on a physical constant and a gram can be derived from it using a physical constant (the mass of water), what's the point of playing with the disco ball thingy?
... I've ever seen is a Horta egg.
Research shows that 67% of those who use the term "research shows", are just making shit up.
Personally, I think years of waiting for the right material and special grinding is a waste of money... I could of pointed them in the right direction if they only had asked. Here, looking for YOUR OWN silicon sphere:
P ACE-HI-TECH-BALL-2-D_W0QQitemZ260110751261QQihZ016 QQcategoryZ3225QQrdZ1QQssPageNameZWD1VQQcmdZViewIt em
:)
http://cgi.ebay.com/Siaz-SILICON-CRYSTAL-SPHERE-S
PS.. This is not my auction, I just KNEW it must exist on ebay if someone needed it.
--- Relax, that mass muderer is just trying to reduce our carbon footprint, one fetus at a time...
Molecular interference fit? I should say something smarmy about people who do a poor job at feigning knowledge and expertise, but since there's no Wikipedia article on the phenomenon I'll let it slide. What you are talking about is optical contacting, and has nothing to do with molecular interference. (I'm not even sure what that means in this context.)
It's not a perfect sphere. If you zoom in really really close, it's got the jaggies.
"It's the height of ridiculousness to say for those 9 lines you get hundreds of millions."
that's all I'm going to do when I convert it anyway.
I'm glad to hear they're making progress on it, this is something I've been looking forward to for a while. ... Yes, really. =) No, I'm not being sarcastic... =(
Slightly OT: Just read up on metric/imperial systems recently, apparently the only ones still really using Imperial are the US, Burma, and Liberia. Oh yeah that's a great crowd... Maybe, once the new measure passes muster, we can finally extricate ourselves from the "axis of incompetence". Or we could go on trying to figure out how many king's big toes are in a furlong...
I use Windows... like a two dollar wh.. why don't I just go ahead and not finish that sentence.
The picture shows a beautiful shot of the perfect silicon sphere. Out of curiosity, I looked very closly at the scene reflected by it's surface, thinking perhaps I might get a glimpse of the photographer. However, he was nowhere to be seen.
Then I got to thinking - it should be easy to reconstruct the scene that is portrayed in the reflection from the surface of the sphere. All that is needed is to cut out the image of the silicon sphere and paste onto the surface of a three dimensional sphere. Then we could rotate it this way and that and look around the scientist's lab. So I did this - using a software simulation. I cut out the silicon sphere from the article's photo, and used it as a texture on a spherical 3D mesh, and added a little code to rotate it back and forth so that I could look around the scientist's lab. Guess what - there is no sign of the photographer! What we see is a very messy lab, with a closed door on the right. There are florescent fixtures on the ceiling that are currently turned off. There is a large window at the end of the room. I do believe that the ceiling, though it meets the left wall at the usual 90 degree angle, curves down to the wall at the right - a very unusual space, as if it was crammed into to an attic. At the extreme right of the room I believe we see a curtain hastily thrown over whatever would have been on the right side of the view. If the photographer is in the room, as he must be, I think he must be kneeling to the left of the window about three-quarters of the way back, and using a telephoto lens.
I have made available the exe that I created on my web site so that you may take a look for yourself. The code is a hasty adaptation of Microsoft's DX3D mesh tutorial "Tut_06Meshes" from the DxSDK 9.0, which is also included. You can get the zip package here. Perhaps you could modify the code to produce an even better view, but unfortunately, the resolution of the original image is really too low to get much out of it. It was a lot of fun doing this, and if you come up with a better result than me I would like to hear from you.
But a sphere is round, so how do you keep it from rolling off the scale when you are trying to weigh it?
n/t
This is the best explanation in this whole discussion.
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
because
In other words they want to show off their skillz and know some RA or post doc is going to be messing with it.
Which is really useful I mean knowing the solids never expand or contract with temperature.
If someone is passing you on the right, you are an asshole for driving in the wrong lane.
So, just because you can't find something on Wikipedia you're willing to impugn someone's knowledge and intellectual honesty?
Incidentally, Wikipedia does have an entry for "interference fit". You incorrectly parsed "molecular interference fit" as "molecular interference fit" rather than "molecular interference fit."
For the record I have no idea whether such a phenomenon actually exists but it sounds plausible enough to me that I'm not going to denounce it without doing more than a Wikipedia search.
I know a guy that could get them a perfect kilo, seriously, this guy used to eyeball perfect quarter ounces with one eye closed !
Wanna fight ? Bend over, stick your head up your ass, and fight for air.
...my fellow countrymen will never accept the kilogram as a unit of measure until it is redefined as being equal to 16 oz.
At the risk of being pedantic, where did you put your referential, and why?
Rethinking email
All the other basic measurement units where redefined this way at the XX century. Only the kilogram is a troublemaker.
Rethinking email
IAAM (I am a machinist), and interference fit is a common term/practice in machining, and is as the wikipedia entry describes.
There are varying degrees of interference that are often specified by the engineer's drawings - often it is enough to "press fit" two parts together by a hammer or hydraulic means, while a particularily tight fit might involve a torch or an oven on the part containing the hole and a freezer on the shaft being put through the hole.
Sometimes cutting tools will have an interference fit into the toolholder using an oven, if ultra precise concentricity is required for a milling operation. (when collets or chucks have too much runout)
Article title: "Perfect silicon sphere to redefine the kilogram!"
Slashdot summary: "This will replace the International Prototype!"
Actual content of article: "...could help pave the way..."
Some day. Maybe. Unless one of the other alternatives (watt balance, ion counting, etc) is chosen.
Stop worrying about the risks of nuclear power and start worrying about the risks of not using nuclear power.
You make a great point about the use of water creating a circular reference (honestly, that was brilliant!), but don't discount the meter reference. Believe it or not, that standard was chosen because it made it easy to reproduce. Further (if I recall correctly), since the meter and the second are both related to the light emission properties of cesium, a competent physicist should be able to inexpensively reproduce either or both with things he already has around the lab. A sample of cesium, a handful of electronics no more complex than a microwave transmitter, an interferometer for the meter, and a mass spectrometer* for the second would do the job. Simple to understand, reproducible with techniques already in common practice (interferometry and mass spectroscopy), inexpensive to build - really, it's a much better standard than it seems at first reading.
*For the standards cognoscenti in the audience, I know that modern second standards don't use mass spectrometers. It would do the job, though, and most physicists have access to one in a pinch.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
In orbir you ARE weightless. Just as you are in a free-falling elevator.
But you have mass. And this will transpose into weight when you, ummm.. decelerate at the bottom of the shaft.
- Ze Laws ov Termodynamics? BAH!
Kelvin vas a fool!
Mit Hydrogen + Pinoqachole ve can break zes laws anytime!