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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.
... 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
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.
"If you make people think they're thinking, they'll love you; But if you really make them think, they'll hate you." - DM
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? :)
"but can you ever really get a perfect anything?"
The whole notion of "silicon balls" sounds fake to me!
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
May God have mercy on your soul if you ever attempt to call a woman a physical object to her face.
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.
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.
Sam ty sig.
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
>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.
A perfect sphere, down to the atom, of 1 kg silicon would require pi to what precision?
Dan East
Better known as 318230.
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. It might help you understand the project better.
"I've got more toys than Teruhisa Kitahara."
It makes the calculations simpler.
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.
The Wise adapts himself to the world. The Fool adapts the world to himself. Therefore, all progress depends on the Fool.
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.
silicon spheres will define the standard ... will they be coming in pairs by any chance?
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!"
OK, someone's going to have to explain this for me. Why do we have to have an actual object to define a weight?
:) It's also mentioned that a similar approach was taken to defining the meter, based on an absolute definition of the speed of light.
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 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.
Jenna Jameson do your part for science.
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
Ok, people are giving snarky answers here, but I'll try to give you a more straight answer.
The only way we have to keep a standard unit is to have an object with that unit and call that the standard. Let's say you were building some sort of a scale that would measure weight in kilograms; you'd have to calibrate it first. This means that you'd have to find an existing weight that was one kilogram, put it on the scale, and mark that this weight is a kilogram. But then how do you find a 1 kilogram weight? You have to measure it on some scale that's already calibrated correctly. This chain continues, and has to end somewhere.
So the two questions I anticipate are:
To answer the first question, a scale would be harder to maintain accurately. It could break, and calibrations don't hold forever. You'd have to re-calibrate it every so often, and how do you do that without an object known to be exactly 1kg?
The answer to the second question (which I imagine might have been your question all along) is a little more complicated. Let's imagine that we have no exact 1kg object stored anywhere that we use as the standard. So one guy in a lab is using an iron ball as his 1kg weight, calibrating scales with it, and selling scales to others. The iron ball slowly rusts over time, and the weight of the ball changes a little. Someone takes one of the scales calibrated with the rusty balls and does the same thing, but this time with his own hunk of iron, but the environmental conditions in this guy's lab aren't as controlled, and he tends to get water condensation on his iron ball, meaning it rusts faster and each calibration varies depending on how much water has collected.
Now, imagine it keeps on like this for 75 years, with different guys selling scales, getting their original measure from someone else, and then using their less-than-perfect means to continue calibrating and making scales. After 75 years, there are some drastically different "kilograms" floating around I buy a scale, measure out 1 kilogram, take it to a different scale and get 1.5 kilograms, while another says .75 kilograms. In this case, who's kilogram is "correct"? When the issue was raised, people would say, "Oh, if only we had a standard "kilogram" to compare them to!"
And so we have someone keep a physical reference object under very controlled conditions and of materials that will prevent corrosion or other corruption to the material.
Yes, there are standard Imperial weights and measures. I seem to recall that one set are on display at the Tower of London. However, the pound now seems to be legally defined as 0.453 592 37 kilogram.
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.
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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
The kg is a unit of mass, not weight.
I am not a crackpot.
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 have moved from metric countries to the US, and have actually researched that issue. Turns out, that the US is implicitly metric!!! The "Customary US Units of Measurement" are defined by relating them to metric base units, e.g. 1 yd = 3 ft = 36 in = 36 in * 2.54 cm/in = 91.44 cm. Weights are similarly defined. The "implicit conversion" is based on bills passed in the early 70's
-- Cave quid dicis, quando, et cui
Actually, a pound is sometimes both a mass and a weight. It's one of the stupider quirks of the customary system. When the distinction is important and not obvious from the context, pounds mass (lbm) or pounds force (lbf) is specified. The "conversion" between the two involves a constant, usually written as g-sub-c.
lbf = lbm * (accel due to gravity) / g-sub-c
constant = 32.174 lbm*ft*s^-2*lbf^-1
That way, one lbm weighs very close to 1 lbf.
http://en.wikipedia.org/wiki/Pound-force
I'd prefer A non-perfect sphere of Silicone .
Nothing sucks like a Vax, nothing blows like a PowerMac G4
No, it's widely accepted as a necessary step towards being able to define the unit of mass in terms of a specific number of carbon 12 atoms. Look, it would be a lot better for this discussion if you made the effort to learn what the project was for.
Just because you personally don't understand it doesn't make it "media spin" or otherwise redundant. There's more information here http://www.npl.co.uk/mass/avogadro.html, including an FAQ which might clear up some of your misconceptions.
"I've got more toys than Teruhisa Kitahara."
Wrong what we are trying to do is count the number of Si atoms in a sphere so we can say sphere X has a mass of Y, and then use the sphere to calibrate other masses. We already have a number for how many silicon atoms in a kilogram, and once we can count atoms precisely enough that preexisting number will be fixed.
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
The real purpose of the project is to produce a reproducable standard. If something was to happen to the lump of metal that currently defines a kilogram, there is no reliable way to reproduce it. You can make another lump of metal and weigh it, but even the most precise scale we have been calibrated back to the original lump of metal plus or minus the error of the machine. The problem is that the errors are cumulative. If we have to replace the lump of metal several times, it will be less and less precise. If however we can base the weight on a physical constant, then we can use that physical constant to calibrate future scales on. There will be errors based on the precision of the machine, but they are no longer cumulative. If you build a more precise machine, you get a more precise measurement.
"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 remember a small magazine (called Science Digest, IIRC) I read in the mid 80's. It was short little science articles, probably a couple hundred words each (at most)...not unlike RSS feeds today, perhaps.
One article was about scientists making the most perfect sphere to date out of some crystal. It was measured to be so perfectly round that if you scaled it up to the size of the earth, it's highest peak would be 12 feet higher than it's lowest point.
I'm sure the technology for this thing has improved a lot in 20 years.
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/
A friend with a boob job? This is Slashdot so you're obviously not talking about a female (I'll ignore the "her" and assume it's a typo.). Who got the boob job? Is his name Robert Paulson?
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.
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
Does it look and feel like the real thing? /Sili-what? oh.
*slight crashing sound*
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?
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.
The 'special crystal which took three years to grow in Russia' that the article writes about is made of pure silicon-28 precisely to get around this objection.
I think the concern is that samples of silicon from different sources (consider, for example, 'depleted silicon' from the scrapyard of the Russian isotope-enrichment facility) might have different isotope distributions at the 10^-7 level, whilst good laser enrichment can ensure a really very constant isotope distribution.
And you are you going to determine if you have x atoms? It will take a long time to count them out. That is the point of this project: to create an object, the sphere, whose number of atoms is known as precisely as possible. If it is a perfect sphere, its volume is precisely known. And if the crystal spacing of silicon is known (which it is, very well), then you have a very precisely known number of silicon atoms. This means that you have a macro-scale object, suitable for use in a balance or equivalent, whose mass is known in terms of unique natural substance rather than an arbitrary lump.
Consciousness is an illusion caused by an excess of self consciousness.
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.