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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.
http://science.slashdot.org/article.pl?sid=07/09/13/2234236
http://science.slashdot.org/article.pl?sid=07/06/15/0541230
Government cannot make man richer, but it can make him poorer. - Ludwig von Mises
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.
Crystal growth is often spherical. And very controlled crystal growth is a method to get a very uniform object without (many) defects.
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.
I've never really understood the problem with creating a more stringent definition of the kilogram.
Others have pointed out that they are doing more or less what you advocate, but let me address the more general issue.
Remember that the definitions for the fundamental units are intended, above all, to be *practical*. In other words, the goal is to make the definition as easy as possible for a competent scientist/engineer anywhere in the world to reproduce in order to calibrate some instrument. All the fundamental units have been defined this way, except one: the kilogram.
There are numerous ways they could define a kilogram, but they all suffer either from the non-portability problem (e.g., using a unique artifact, which no one has access to), or the expensive, difficult device problem. Counting the number of atoms in a perfect sphere is not exactly a simple engineering problem. But it's the best anyone has come up with so far.
Sometimes it's best to just let stupid people be stupid.
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.
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).
Easy. At some point in time some people decided to base the US system on the metric system. There was a time of course when the US system was standalone, but then came a situation when these people had to refine this system and they made the choice to base it on the metric one.
Adventure, Romance, MAD SCIENCE!
Quote:
In the United States, the (avoirdupois) pound as a unit of mass has been officially defined in terms of the kilogram since the Mendenhall Order of 1893.
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.
I was pointing out why you go through the physical process. If you can't use it to produce a calibration mass that is superior to the current system *today*, then it isn't particularly useful to switch over to it (but it would be at the point that the calibration masses become superior).
Nerd rage is the funniest rage.
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.
You do realize that, in the real world, these perfect spheres are, most likely, impossible to produce in large quantities. And, even if they do figure out how to mass-produce them, they'll wear out very quickly. They're made of silicon, for God's sake. Sand. Abrasive.
Something like this is useful in a laboratory setting, but useless in the real world. You have to strive to create the best tolerances with the materials you have, but lower-friction bearings are unlikely to result from perfect spheres. There'll be uses, don't get me wrong, but most of those uses will probably be in very high-precision test equipment, sensors for spacecraft, etc. Replacing all the bearings in, say, my car with ones using perfect spheres would probably increase the efficiency only negligibly. Other factors, such as aerodynamics, weight reduction, efficiency of the engine in producing power, etc. would give much greater efficiency gains, without the exacting precision necessary to create spheres that are perfect on an atomic level. So yeah, it's cool, but it isn't likely to find it's way into 'green' technology, since the precision required to produce then doesn't justify the efficiency gains. So please, before you toss the green buzzword onto everything, stop for a moment and think "Will ball bearings that are perfect spheres, on an atomic level, really matter in a manufacturing process that deals with tolerances of thousandths of inches? Nope."
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.
I hope someone with more knowledge than I do answers, but I'll try to give my best answer, from the understanding I've gleaned so far from my Engineering Physics courses at the University I'm attending. . .
I think, at an atomic level, atoms don't actually touch. When they get close enough, I think the internal atomic forces cause them to repel each other based upon field-forces (field forces are things like magnetism, or gravity, where no contact is required for things to act upon each other), or, for some elements, start sharing electrons and form lattices/grids of evenly spaced atoms (and, again, the grid spacing is determined by a balancing of repelling and attracting field forces, I think). This is definitely an area of physics I want to learn more about, and like I said, I hope someone who truly knows the answer will comment, but that's my best answer.
(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
Actually, "eromanga" is a plain japanese word and not any kind of neologism. It just means "porn manga".
"Hentai", however, is a western neologism that is not used in Japanese.
This answer is mostly correct, but it should be noted that the primary force that keeps atoms apart is the electromagnetic force. At large distances an atom appears neutral being made up of an equal number of positive and negative charges. However since the negative charges (i.e. electrons) are on the outside and the positive charges are on the inside (i.e. protons), when atoms get close to each other the repulsive force between the negative charges is over a shorter distance and is thus stronger than the canceling out attractive force between the positive and negative charges. (Disclaimer: This ignores quantum effects which paint a slightly different picture.)
Two silicon atoms that are in the same sphere will be sharing a metallic (?) bond which means they will be sharing electrons. Silicons atoms in different spheres won't be sharing electrons.
Finally, I suspect that the two spheres will deform slightly where they touch so more than one atom will be "touching". It would look about like if you were push two rubber balls together, except the physics might be totally different (I am not a rubber expert).
Dan Gilbert did this experiment - its described his book Stumbling on Happiness. Here is the NYtimes article. In this video, he describes the theory of Choice Paralysis
The theory in short means we all think that "Breasts of my wife GREAT! All others suck! " (except Tina Fey.. and Natalie Portman and.. Penelope Cruz)