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Roundest Object In the World Created
holy_calamity writes "An international research group has created the most perfect spheres ever made, in a bid to pin down a definition of the kilogram. It should be possible to count exactly the number of atoms in one of the roughly 9cm silicon spheres to define the unit. Currently the kilogram is defined only by a 120-year-old lump of platinum in Paris, but its mass is changing relative to copies held elsewhere. Other SI units have more systematic definitions."
That's precisely what they are trying to do.
Onda Technology Institute
That is what they are doing. They are defining the kilogram as X silocon atoms.
You can define a kilogram in the number of atoms of X element, but you still need a physical object to calibrate your scales against. In this case, I believe they did it by number of silicon atoms. TFA says they went and milled a silicon sphere (purified to only Silicon-28) weighing as close to the current standard as they can get it. Next they're going to measure it (X-rays and the such) to find the density, spacing, and the such and end up getting a number of silicon atoms. This number will now BE the kilogram, and these spheres are going to be the new physical standards. They are suppose to be an improvement in that is it theoretically possible to recreate these spheres should anything happen to them (as we know the amount silicon needed), while it is not possible to recreate the current standards.
My other summary was a bit off, got the process a little backwards.
Ero-manga?
Ero-Manga is the proper term for what most clueless US fanboys call "Hentai Manga."
Specifically, he was pointing out that some Ero-Mangaka ("Hentai Artists") draw breasts as if they were morbidly huge helium filled balloons floating on top of a woman's chest.
All this in an attempt to state that you do not know what good breasts look at, having (apparently?) based your opinion on Japanese ero-manga anatomy.
All this in a completely-missing-the-point of the "Heh, Boobs are Round, Scientists are Horny" joke he was replying to.
... Wow, geeky of me, eh? I do however, wish to go on the record that I fully support scientific efforts to find/create the perfect breasts.
Well, it's sorta like this: a standard is only useful if you have some effective way to reproduce it or measure with it.
1. time. You can essentially just make a MASER, which means basically a cavity which resonates at that frequency. The nice part is that it can be tuned, and even continuously tuned, by just measuring the amplitude of the signal. When you've reached the maximum power, the thing is tuned to that frequency.
2. length. It's measured by Interferometry, so you have a meaningful way to transform a wavelength into any given distance.
At any rate, the transition for these two only happened when someone build a device which could actually measure one second or one metre that way.
3. mass. Well, that's the tricky one. Saying that you define a kilogram as one bazillion silicium atoms is useless unless you can somehow actually produce a lump with that many atoms. As long as we can't actually be sure how many atoms are in there, it would be a useless standard.
These guys claim to have been able to do just that: say with a high degree of confidence that, yep, their spheres contain exactly that many atoms. If they're right, then we're finally ready to move the kilo to that standard.
A polar bear is a cartesian bear after a coordinate transform.
Please don't go around trying to be witty against people who don't just live in Japan, but also speaks the language.
Ero-manga is what they call it. If I wanted to talk about hentai, the really creepy kind of mangas, I'd have called it that.
- These characters were randomly selected.
number of atoms = (volume * density) / mass of silicon atom
With the volume of a perfect sphere simply being
Pi*r^3 (I think)
It's also much much easier to test for the perfection of a sphere over any other geometric shape. All you do is spin it with slight axis rotation while a laser is pointed at it, and measure the distance.
Defective Logic
You can't calibrate a scale by telling it your theoretical model - at some point there actually has to be a physical thing.
Not a dupe - a follow-up.
The first article mentions only the weight loss of the original kilogram, the second article follows up on that mentioning a perfect sphere is going to be made. The current article follows up on that, announcing the actual creation of this sphere.
Now the fourth article in this series should be the announcement of the number of silicon-28 atoms needed to create exactly one kilogram.
On the other hand, isn't the exact mass of atoms known? Then it should be easy to say "this number of atoms is exactly one kilogram". The creation of the sphere being an exercise left to the reader.
If it isn't possible to consistently construct and measure the spheres (or some other object), then the a number of atoms isn't particularly more useful for calibration (which is the whole point) than the old standard.
Nerd rage is the funniest rage.
Because its 1 liter of pure h2o at 4 deg C -at the sea level-, (remember, pressure isn't the same at the top of a mountain than it is at the bottom...and it changes everything). It is also not universal... if the earth was to go boom, (and somehow live), we'd lose our reference.
That is in opposition to, let say, a meter, which is a fraction of the distance light travels in a specific amount of time. Fairly universal. (I beleive it USED to be a fraction of the earth's size... which was quite bad too).
It's not totally worthless, as the kilogram is the basis for just about all other SI units. It is the only unit that is not defined according to other units, or in relation to a natural property. Thus, its definition is arbitrary, and everybody must agree as to what a kilogram is before the unit has any value as a standard. There's a very nice explanation of the kilogram as a fundamental unit here:
http://en.wikipedia.org/wiki/Kilogram#Importance_of_the_kilogram
I hate printers.
The picture in the article shows the sphere being handled in what obviously isn't a cleanroom. Won't that mess up its surface?
I'm sure they don't cart the real ones around for press tours.
They are measuring the sphere using interferometry - not possible with a cube.
I'm not sure if you were being facetious or not when you were talking about pi being irrational, but its value is known to billions of decimal places. I doubt it will introduce any additional uncertainty.
Because you need a physical standard to compare. Mass of an macroscopic object is (mostly) measured by comparing it's gravitational force to the gravitational force of an etalon at a place where the same gravitational field strength is exerted on both objects. When you define a kilogram as the mass of $bignumber silicon-atoms, someone has to make the first etalon. Other etalons, like light of a specific wavelength for measurement of length and time, are easier to produce.
I think the reason why they made it a sphere is because a sphere is defined by one parameter only, its diameter. To make a perfect sphere all you need is to make sure it has exactly the same curvature everywhere. Now, let's see what it takes to make a perfect cube:
1) each of its six faces must be perfectly plane
2) each of its twelve edges must have exactly the same length
3) each of its twelve angles must be exactly ninety degrees
Just to illustrate how difficult this is, I once read this anecdote about Wernher von Braun: when going through his mechanical engineering course in Germany, one of the professors gave each student an irregular lump of iron. The assignment would be to create a cube, as perfect as possible, from that lump. The size of the resulting cube didn't matter but, naturally, if it was a very small cube it meant the student had a tough job getting it right.
(NSFW)
http://images.fok.nl/upload/050701_30560_howtodrawboobsfok.jpg
I am a physicist at the UK's National Physical Laboratory and I am involved in the redefinition of another unit - the unit of temperature. The work concerning the redefinition of the kilogram is >much more philosophically fraught and technically difficult. I understand many of the rather skeptical comments expressed here The current situation is unsatisfactory because the mass of the kilogram is changing, albeit by a small amount - a few micrograms in 1 kg - i.e. a few parts in 10^9. The aim of the work is to replace this artefact with (essentially) a procedure. Effort onne (using the silicon sphere) is essentially trying to build a link between a macroscopic mass, and the microscopic masses which we expect to be fixed. The other effort not mentioned here is called the watt balance which is a machine which can exhibit the same inertial mass as a kilogram - or any other weight. At the moment the two watt balances disagree with each other and they both disagree with the silicon sphere result. There is still a lot of work to do on both approaches. Incidentally, the reason is it is a sphere rather than a cube is because of edges. Edges are amazingly fragile, hence the sphere. ALl the best M