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The Changing Definition Of 'Kilogram'

timothy posted more than 10 years ago | from the jenny-craig-kilograms dept.

Science 964

DrLudicrous writes "The NYTimes is reporting that the platinum-iridium standard mass for the kilogram is shedding at an appreciable rate -- at least compared to other reference masses. The Pt-Ir cylinder is kept in France, and measured annually, and the slight discrepancy is important because the kg is an SI base unit- thus other quantities such as the Volt are based on it. A new standard is being sought- the two frontrunners are counting the number of atoms in a perfectly spherical single crystal of silicon, and another technique uses a device known as the Watt balance."

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964 comments

metric system (-1, Flamebait)

Anonymous Coward | more than 10 years ago | (#6044675)

who gives a shit?

give me imperial measurements any day

Re:metric system (-1)

Neuropol (665537) | more than 10 years ago | (#6044679)

obviously not the US. :|

Re:metric system (0)

Anonymous Coward | more than 10 years ago | (#6044712)

Nope. We dont use Volts either. At least not the same kind of volt everyone else does, apparently. So, if the kilo is shedding causing them to recalibrate the volt, is my electric bill growing or is it shrinking? Answer that and I will tell you my opinion on the matter.

Kilogram? (5, Funny)

ihatewinXP (638000) | more than 10 years ago | (#6044681)

Hey I live in America you insensitive clod! (but then again I alawys want to know how much they are lifting on Strongman Competition).

Re:Kilogram? (5, Funny)

PhlegmMaster (596165) | more than 10 years ago | (#6044692)

Then maybe america should move out of the dark ages sometime.

Re:Kilogram? (0)

Anonymous Coward | more than 10 years ago | (#6044738)

God it must suck having to do all those conversions if you do science.

I doubt if they will ever shift.

Re:Kilogram? (1)

Gregg M (2076) | more than 10 years ago | (#6044844)

God it must suck having to do all those conversions if you do science.

We don't. Anyone in Science, in the US, uses metric. Like the rest of the world. It's the non-technical folk who don't use it.

I love to say Kilo-meter when they say Killa-matter.

Re:Kilogram? (1)

Gyorg_Lavode (520114) | more than 10 years ago | (#6044863)

Except machinists. All people working use metric, but when you have to build something you wind up in inches and mills.

Re:Kilogram? (0)

Anonymous Coward | more than 10 years ago | (#6044747)

Move out?? Hell, we're just starting to go deeper!

Thank you G.W.B!

Sigh.

Re:Kilogram? (5, Informative)

el-spectre (668104) | more than 10 years ago | (#6044760)

It's not a matter of dark ages, it's a matter of infrastructure... while not the largest country in the world (the US is probably third or fourth, I'm not sure), we have by far the most technological infrastructure. It is not feasible to change all that in a short period of time.

A friend is in construction, and guestimates that it will take over 100 years to replace all failing/obsolete tech with the versions in metric equivalents. It just does not make any economic sense to replace a set of, say, water pipes with the metric standard if the current ones will last 20 years. It'll have to be a gradual thing.

Just to be difficult, though, I'd mention that most construction is done in 'tenths of feet', even the surveying equipment is marked this way. Has nothing to do with the metric system, it just makes the math easier...

Re:Kilogram? (1)

Timesprout (579035) | more than 10 years ago | (#6044812)

guestimates that it will take over 100 years to replace all failing/obsolete tech And would those be earth years, saturnian, mercurian, dog, light ?

Re:Kilogram? (0)

BrokenHalo (565198) | more than 10 years ago | (#6044918)

guestimates that it will take over 100 years to replace all failing/obsolete tech with the versions in metric equivalents

I guess it will if they never get started.

I Agree - We should go metric (1)

ihatewinXP (638000) | more than 10 years ago | (#6044771)

-Then maybe america should move out of the dark ages sometime.-

But honestly its (the kilo) as arbitrtary as any other unit we have come up with to describe reality (red, one second, a kilometer) so why rewrite the bible as it were and change something like this?
I know the implications could be staggering, but why not chalk it up to having a leap year and other silly things about our units of measurment.

Re:I Agree - We should go metric (5, Funny)

Anonymous Coward | more than 10 years ago | (#6044851)

It's not the arbitrariness, but the fact that metric is a decimal system.

The only countries left that don't use metric are the US and Bhutan. Bhutan is a fundamentalist islamic country that doesn't even have any phones yet. I guess we can see what the US' technical level is.

Re:I Agree - We should go metric (0)

Anonymous Coward | more than 10 years ago | (#6044894)

Higher than the technical level of your country.

Re:I Agree - We should go metric (1)

PhlegmMaster (596165) | more than 10 years ago | (#6044896)

Because the metric system makes a bit more sense when using it (especially in the mathematical or scientific sense). It's easy to remember how many mm in a cm and how many cm in a m. Also the naming scheme is global and makes sense.

A leap year is just because somebody screwed up with time (which I personally think that if we could accept the 1.25 year year, then we'd be a lot better for it)

Re:Kilogram? (4, Funny)

Tumbleweed (3706) | more than 10 years ago | (#6044827)

> Then maybe america should move out of the dark ages sometime.

Yeah, tell it to the Queen.

Re:Kilogram? (1)

acidrain69 (632468) | more than 10 years ago | (#6044852)

I'm a stupid american, but doesn't the british system also use likes stones, or foot-lbs and other nonsense? Which queen are you talking about?

Re:Kilogram? (1)

PhlegmMaster (596165) | more than 10 years ago | (#6044911)

All countries, EXCEPT the US use the metric system. The UK made a change a few years ago (they also kinda outlawed the imperial system).

Re:Kilogram? (0)

Anonymous Coward | more than 10 years ago | (#6044877)

Then maybe america should move out of the dark ages sometime.

over my dead... elected officials.

Re:Kilogram? (1)

Saint Stephen (19450) | more than 10 years ago | (#6044916)

I love finding inconsitencies in the world.

Metric-lovers quip about decimal then measure time in sexagesimal following the Babylonians.

And Europeans laughing at fat Americans but smoke like chimneys.

[ducks]

Re:Kilogram? (3, Insightful)

LX.onesizebigger (323649) | more than 10 years ago | (#6044724)

And since the inf^H^Hmperior^H^Hal system is now defined in terms of the metric system (an inch is 2.54 cm), your strange units change as well.

Imperial Measures Grow on You. (0)

Anonymous Coward | more than 10 years ago | (#6044893)

You are right about the imperial system being defined in terms of SI. However I find that where I am familiar with both the imperial and metric measure, the imperial one is usually easier to understand.

No mystery why. The imperial is just one of the many systems that grew over centuries in europe and the world to measure things that ordinary people actually use. The metric system was made up by a few revolutionary frenchmen over a shortish period and held hostage to a fetish about the number 10. Over time it has been updated only for very technical reasons.

This is why English system is superior. (0)

Anonymous Coward | more than 10 years ago | (#6044761)

We don't have any fancy platinum masses to decay, just gets you a hogshead and a rod, and you're set!

Re:Kilogram? (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#6044775)

Even if you're in America and use British Imperial units, you're still in the minority. You see, America is a continent, not a country. Really, feel free to look it up in any world map, U.S. currency, or best of all, the document where the country got its name:

http://www.house.gov/Constitution/Constitution.h tm l

"We the People of the United States...do ordain and establish this Constitution for the United States of America."

If you'd like to look at some maps, here you go:
http://www.lib.utexas.edu/maps/americas.html

I mean, how could there be North, Central and South America when a country tries to call itself "America" all by itself? This is as silly as if France or Germany tried to call itself "Europe"... Not to mention that North America includes Canada and Mexico! (that's right people, Central America starts with Guatemala).

But I've digressed and gone off-topic enough, so mod me to oblivion.

Re:Kilogram? (0)

Anonymous Coward | more than 10 years ago | (#6044805)

Yeah, it's far better to say you're on a completely different continent than those yellow-skinned heathens to the east ("Hey, we're seperated by a mountain range...")

Re:Kilogram? (0)

Anonymous Coward | more than 10 years ago | (#6044874)

>You see, America is a continent, not a country.

How many times do we have to go over this.

North America is a continent.
South America is a continent.

America is a shortened version of United States of America.

This is very simple to understand, remember asking my dad when I was about 4 and it made perfect sense then. Even if you're 12 you should still be able to understand that.

Just like North Dakoda is a state, South Dakoda is a state, but a Dakoda is a member of the Siouan people.

North and South America together are refered to as "The Americas".

Re:Kilogram? (1)

marko123 (131635) | more than 10 years ago | (#6044914)

That would explain why americans "pound brews". If we "kilogrammed piss" though, we'd be gay. So we "sink" it instead. At least downunder.

Annually (1)

JJahn (657100) | more than 10 years ago | (#6044682)

Why exactly does it have to be measured annually, and why should I care if it detoritates? Anyone care to enlighten me?

Re:Annually (4, Informative)

sould (301844) | more than 10 years ago | (#6044839)

Why exactly does it have to be measured annually......Anyone care to enlighten me?

It doesn't exactly have to be measured. They just do that to check it's still right. Go read about the history of the Systeme International the NIST site [nist.gov] and the definition of a kilogram at the same place [nist.gov]


But essentially, its part of a way of ensuring that the measuring units Scientists use around the world are the same, not slightly different.

For instance, anyone around the world can reproduce (in a well equipped lab anyway) the definition for time (The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom).


There are only 7 base SI units (meter, kilogram, second, ampere, kelvin, and candela) from which many more units [abdn.ac.uk] are derived. Hence, if kilo is out/changing many of these are changing too.


and why should I care if it detoritates?


Presuming you're American, you would use feet, pounds, find metric too complicated, etc, etc - so probably wont care if it does.

The mystery unit? (1)

Midajo (654520) | more than 10 years ago | (#6044884)

There are only 7 base SI units (meter, kilogram, second, ampere, kelvin, and candela)

Sould, you're killing me! What's the seventh unit? Is it the mole?

yay! (1, Funny)

Anonymous Coward | more than 10 years ago | (#6044683)

Yay, I wiegh less!

However, I don't know by how much, since I don't live in bloody England.

Re:yay! (2, Informative)

sky_fire (109496) | more than 10 years ago | (#6044702)

actually since the kilo weighs less you weigh more because it takes more kilograms to equal your mass. :p

Re:yay! (1)

Millyways (262662) | more than 10 years ago | (#6044770)

Since when has England been the home of the metric system?

Last time I checked England and the US where pretty much the only countries not using it.

I am ingoring Enlands failed attempt to change over that has left them in their current state of using both sets of units.

My wife changes her definition... (5, Funny)

craenor (623901) | more than 10 years ago | (#6044684)

Everytime she steps on the scales...I would tell you what it was defined as last week, but kids may be reading this.

any mirrors? (1)

switched4OSX (668686) | more than 10 years ago | (#6044690)

Would have been nice to link to a site that doesn't require name, rank, serial number, and blood type to read.

Re:any mirrors? (1, Funny)

Anonymous Coward | more than 10 years ago | (#6044783)

Would have been nice to link to a site that doesn't require name, rank, serial number, and blood type to read.

Doncha mean Would have been nice to link to a site that doesn't require Bill Gates' name, rank, serial number, and blood type to read.?

That's why I like the pound (-1)

Anonymous Coward | more than 10 years ago | (#6044691)

It never changes, right?

Re:That's why I like the pound (1, Interesting)

krisp (59093) | more than 10 years ago | (#6044868)

A pound is a measure of weight. A kilogram is a measure of mass. here [nyu.edu]
is a page describing the difference between weight and mass.

But for those of us who don't like to click:
1) Mass is a measurement of the amount of matter something contains, while Weight is the measurement of the pull of gravity on an object.

damn french (0)

Anonymous Coward | more than 10 years ago | (#6044695)

you can't even trust them with a bar of lead!!

an excuse not to diet (4, Funny)

circletimessquare (444983) | more than 10 years ago | (#6044698)

i'm not gaining weight, the kilogram is losing mass... so really, i stay the same weight, and they need more units to weigh me ;-)

My pee smells... from asparagus? (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#6044710)

The weirdest thing happened to me tonight. I went out to a restaurant and had a dinner with a large helping of asparagus. Later, I took a piss, and it just reaked!! Is that smell from the asparagus? If so, what causes it?

Re:My pee smells... from asparagus? (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#6044721)

If so, what causes it?

Asparagus. Also, stay away from your semen.

Re:My pee smells... from asparagus? (0)

Anonymous Coward | more than 10 years ago | (#6044743)

Yes, it's the asparagus. There's a compound in it which causes your urine to smell badly.

The effect's well known to all those who enjoy water sports...

Re:My pee smells... from asparagus? (0)

Anonymous Coward | more than 10 years ago | (#6044885)

I've never exactly examined the smell of my pee but I live on a lake I do a lot of water skiing during the summer... What's this strange pee you speak of? I am confused. Befuddled. Dildo in my butt.

Surprise at no repeatable standard. (1, Redundant)

MtViewGuy (197597) | more than 10 years ago | (#6044711)

I'm surprised that no one has tried until now to create a standard for the kilogram that could be repeated easily like atomic measurement of the length of a meter and the computation of a second of time based on the resonance frequency of a caesium atom.

If they succeed, we can get a reference standard for a kilogram that can be easily generated for scientific research.

Re:Surprise at no repeatable standard. (1)

duncf (628065) | more than 10 years ago | (#6044786)

I'm surprised that no one has tried until now to create a standard for the kilogram that could be repeated easily like atomic measurement of the length of a meter and the computation of a second of time based on the resonance frequency of a caesium atom.

Did you read the article?

One reason the kilogram has lagged behind the other units is that there has been no immediate practical benefit to increasing its precision.

who cares? (-1, Flamebait)

joeszilagyi (635484) | more than 10 years ago | (#6044714)

Metric is a backwards system that doesn't make anywhere near as much sense as English standard.

Re:who cares? (0)

Anonymous Coward | more than 10 years ago | (#6044755)

Huh? The English aren't even using their own system now.

Solution? (4, Funny)

The_dev0 (520916) | more than 10 years ago | (#6044715)

Why couldn't they just take it down the shops and measure it against, say, 1kg of carrots or a kg of sugar?

Re:Solution? (1)

anonymous loser (58627) | more than 10 years ago | (#6044835)

I agree. They should just define "1 kilogram" as the weight of a 1-kilogram bag of sugar. Sorta like the jargon file's definition of recursion [science.uva.nl] .

Why not... (1, Funny)

Anonymous Coward | more than 10 years ago | (#6044717)

...just define a kilogram in terms of 'x' number of Joules. Since c is a defined constant, then this would give you a constant mass.

Re:Why not... (1)

krisp (59093) | more than 10 years ago | (#6044910)

As you can see [nist.gov] , the National Institute of Standards and Technology already has the joule-kilogram relationship calculated out and referenced as a "Fundamental Physics Constant"

Look here... (4, Informative)

switched4OSX (668686) | more than 10 years ago | (#6044725)

Here is a site that gives some reasons why the are thinking of replacing the standard: http://physics.nist.gov/News/TechBeat/9501beat.htm l. No registration necessary

Counting Si (5, Interesting)

brokenbeaker (267889) | more than 10 years ago | (#6044728)

The problem with the single crystal of silicon method, a few years ago, was that there were all these lattice vacany defects cropping up. The formation of such point vacancies is so entropically favoured that I don't think they can ever eliminate them...

Re:Counting Si (5, Funny)

porp (24384) | more than 10 years ago | (#6044806)

I think I can speak for everyone and say

HUH?

porp

Re:Counting Si (1, Troll)

pod (1103) | more than 10 years ago | (#6044905)

Probably something to do with the varience of a flux capacitor.

Re:Counting Si (1)

acidrain69 (632468) | more than 10 years ago | (#6044913)

I think he means that when someone tries to make a crystal of silicon, it's very hard to get it to form the same way as someone else's did, thus the "lattice", or configuration of atoms in a solid, wasn't the same. That measn that the quantity won't be the same, which means your standard measurement isn't standard.

I only went as far as Chem 1 for majors, so don't try to save the earth with this information.

A better solution... (-1, Flamebait)

Anonymous Coward | more than 10 years ago | (#6044732)

...would be to have Rob Malda take a dump on a balance, and call that a kilogram. Sure, it would have significantly more mass than the current standard, but at least you could count on a constant source. (Twice a day if you feed him enough Doritos.)

Reminds me of the changing definition of MegaByte (1)

basser (676211) | more than 10 years ago | (#6044742)

I don't know if this happens anywhere else in the world, but in Australia, 1MB = 1000kb for an ISP.. Tel$tra thinks 1MB=1000KB, but 1KB=1024B.. Go Figure...

Re:Reminds me of the changing definition of MegaBy (0)

Anonymous Coward | more than 10 years ago | (#6044756)

Well according to the latest SI and IEEE standards, 1 MB = 10^6 bytes, 1 MiB = 2^20 bytes
You'll find hard disk manufacturers use it too.

Re:Reminds me of the changing definition of MegaBy (1)

el-spectre (668104) | more than 10 years ago | (#6044794)

When I was in school, I was taught that the standard method was to measure megs in base 10 for transmission (1000000 bits/bytes), and base 2 for storage (1048576 bits/bytes).

Pain in the ass to have to do the conversion back and forth... 1/2 the class took days to 'get it'

No wonder I keep gaining weight... (2, Funny)

HaloZero (610207) | more than 10 years ago | (#6044744)

It's not my ass, it's just that the units are getting incrementally smaller. Ho ho! It's not me. *dances*

Damned inreliable measure standards. *shakes fist*

I don't get it.... (1)

elixx (242653) | more than 10 years ago | (#6044758)

Does this mean we have to upgrade the firmware in our scales every year?

How do they measure it? (4, Interesting)

LX.onesizebigger (323649) | more than 10 years ago | (#6044759)

My question is, how do they measure it? Using a non-decaying meter stick? How do you measure the definition of a measure?

Re:How do they measure it? (2, Informative)

BJH (11355) | more than 10 years ago | (#6044817)

A meter is the distance light travels in a certain fraction of a second. c is invariant no matter where you are, and a second is defined as a particular number of caesium atom vibrations, giving you a very precise basis for measurement of distance.

Re:How do they measure it? (0)

Redglare (626839) | more than 10 years ago | (#6044869)

>>c is invariant no matter where you are not quite. c is the speed of light in a vacuum.

Re:How do they measure it? (0)

Anonymous Coward | more than 10 years ago | (#6044891)

"c is the speed of light in a vacuum"
which is still invariant no matter where you are, duh!

crazy question (0)

Anonymous Coward | more than 10 years ago | (#6044769)

how exactly do they derive volts from kilograms?

Re:crazy question (1)

zeno_2 (518291) | more than 10 years ago | (#6044808)

Here [wa.gov.au] is the answer.

If your lazy heres a cut and paste:

The volt is a unit of electric potential, electromotive force or potential difference and is derived from the units of kilogram metre squared per ampere per second cubed ( kg.m2/A.s3 ). One volt is the electric potential that exists between two points on a conductor carrying one ampere and the power of one watt is used.

Re:crazy question (2, Informative)

Midajo (654520) | more than 10 years ago | (#6044816)

how exactly do they derive volts from kilograms?

A volt is 1 newton-meter per coulomb.
A newton is the force required to accelerate a 1 kilogram mass 1 meter per second, per second.
Most (all?) units of (metric) measurement are based on kilograms, meters, and seconds.

Filthy Whore (Text of Article) (4, Informative)

Midajo (654520) | more than 10 years ago | (#6044773)

Scientists Struggling to Make the Kilogram Right Again
By OTTO POHL


RAUNSCHWEIG, Germany -- In these girth-conscious times, even weight itself has weight issues. The kilogram is getting lighter, scientists say, sowing potential confusion over a range of scientific endeavor.

The kilogram is defined by a platinum-iridium cylinder, cast in England in 1889. No one knows why it is shedding weight, at least in comparison with other reference weights, but the change has spurred an international search for a more stable definition.

"It's certainly not helpful to have a standard that keeps changing," says Peter Becker, a scientist at the Federal Standards Laboratory here, an institution of 1,500 scientists dedicated entirely to improving the ability to measure things precisely.

Even the apparent change of 50 micrograms in the kilogram -- less than the weight of a grain of salt -- is enough to distort careful scientific calculations.

Dr. Becker is leading a team of international researchers seeking to redefine the kilogram as a number of atoms of a selected element. Other scientists, including researchers at the National Institute of Standards and Technology in Washington, are developing a competing technology to define the kilogram using a complex mechanism known as the watt balance.

The final recommendation will be made by the International Committee on Weights and Measures, a body created by international treaty in 1875. The agency guards the international reference kilogram and keeps it in a heavily guarded safe in a château outside Paris. It is visited once a year, under heavy security, by the only three people to have keys to the safe. The weight change has been noted on the occasions it has been removed for measurement.

"It's part ceremony and part obligation," Dr. Richard Davis, head of the mass section at the research arm of the international committee.

"You'd have to amend the treaty if you didn't do it this way."

That ceremony has become a little sorrowful as the guest of honor appears to be, on a microscopic level at least, wasting away.

The race is already well under way to determine a new standard, although at a measured pace, since creating reliable measurements is such painstaking work.

The kilogram is the only one of the seven base units of measurement that still retain its 19th-century definition. Over the years, scientists have redefined units like the meter (first based on the earth's circumference) and the second (conceived as a fraction of a day). The meter is now the distance light travels in one-299,792,458th of a second, and a second is the time it takes for a cesium atom to vibrate 9,192,631,770 times. Each can be measured with remarkable precision, and, equally important, can be reproduced anywhere.

The kilogram was conceived to be the mass of a liter of water, but accurately measuring a liter of water proved to be very difficult. Instead, an English goldsmith was hired to make a platinum-iridium cylinder that would be used to define the kilogram.

One reason the kilogram has lagged behind the other units is that there has been no immediate practical benefit to increasing its precision. Nonetheless, the drift in the kilogram's weight carries over to other measurements. The volt, for example, is defined in terms of the kilogram, so a stable kilogram definition will allow the volt to be tied more closely to the base units of measure.

A total of 80 copies of the reference kilogram have been created and distributed to signatories of the metric treaty. The sometimes colorful history of these small metal cylinders underscores how long the world has used the same definition of the kilogram.

Some of the metal plugs were issued to countries that later vanished, including Serbia and the Dutch East Indies. The Japanese had to surrender theirs after World War II. Germany has acquired several weights, including the one issued to Bavaria in 1889 and the one that belonged to East Germany.

To update the kilogram, Germany is working with scientists from countries including Australia, Italy and Japan to produce a perfectly round one-kilogram silicon crystal. The idea is that by knowing exactly what atoms are in the crystal, how far apart they are and the size of the ball, the number of atoms in the ball can be calculated. That number then becomes the definition of a kilogram.

To separate the three isotopes of silicon, Dr. Becker and his team are turning to old nuclear weapons factories from the Soviet Union, where centrifuges once used to produce highly enriched uranium are able to produce the required purity of silicon.

"We need so many nines," Dr. Becker said, and Soviet uranium processors are one of the only places to get them. "With the Russians, we're getting about four of them," or 99.99 percent pure silicon 28.

A test crystal has already been produced, and Dr. Arnold Nicolaus, another scientist at the German standards laboratory, is responsible for measuring whether it is perfectly round. He has measured the crystal in a half-million places to determine its shape.

It's probably the roundest item ever made by hand. "If the earth were this round, Mount Everest would be four meters tall," Dr. Nicolaus said. An intriguing characteristic of this smooth ball is that there is no way to tell whether it is spinning or at rest. Only if a grain of dust lands on the surface is there something for the eye to track.

Scientists from the United States, England, France and Switzerland say the challenge of calculating the precise number of atoms in a silicon crystal is too imprecise with today's technology so they are refining a technique to calculate the kilogram using voltage.

"Measuring energy is easier than counting atoms," said Dr. Richard Steiner, a scientist at the National Institute of Standards and Technology in Washington, who is leading the international project to create the watt scale.

In the last few weeks, he has reported that his experiments have yielded data that are close to what they need. "Now we're into the picayune, itsy-bitsy errors," he said, having recently corrected "totally ridiculous" errors of 100 parts per million.

The idea of the watt balance is to measure the electromagnetic force needed to balance a reference kilogram. As long as the gravitational field is precisely known for the location of the experiment, the mass on the scale can be related to power. (The gravitational field is a complicated calculation that needs among other things constantly updated changes in tidal forces.)

The definition of the kilogram would then be a measurement of that power or in terms of something that could be derived from it, like the mass of an electron. The experiment in Washington is occurring in a large three-story structure, but in spite of the complexity and circuitous route of calculating mass, Dr. Steiner says he is confident that his team will have persuasive data shortly.

"In the short term, I think we'll win," he said.

Dr. Davis, who is working closely with those making the final decision about the fate of the kilogram, says he is not so sure. "In terms of published results, the watt balance is closer of the two," he said. "But it's very hard to say which is better."

Many scientists believe that the most elegant way to define the kilogram is by counting out a kilo's worth of atoms of an element. A project is under way to test that with gold atoms. But the sheer number of atoms in a kilogram, a number with roughly 25 digits in it, makes that approach unfeasible for the foreseeable future.

For now, Dr. Davis is willing to set his sights lower in the error-prone world of superprecision measurements. "It would be nice," he said, "just to have two experiments in the world that agreed with each other."

To hell with Registration (0, Redundant)

jonman_d (465049) | more than 10 years ago | (#6044774)

May 27, 2003
Scientists Struggling to Make the Kilogram Right Again
By OTTO POHL

B RAUNSCHWEIG, Germany -- In these girth-conscious times, even weight itself has weight issues. The kilogram is getting lighter, scientists say, sowing potential confusion over a range of scientific endeavor.

The kilogram is defined by a platinum-iridium cylinder, cast in England in 1889. No one knows why it is shedding weight, at least in comparison with other reference weights, but the change has spurred an international search for a more stable definition.

"It's certainly not helpful to have a standard that keeps changing," says Peter Becker, a scientist at the Federal Standards Laboratory here, an institution of 1,500 scientists dedicated entirely to improving the ability to measure things precisely.

Even the apparent change of 50 micrograms in the kilogram -- less than the weight of a grain of salt -- is enough to distort careful scientific calculations.

Dr. Becker is leading a team of international researchers seeking to redefine the kilogram as a number of atoms of a selected element. Other scientists, including researchers at the National Institute of Standards and Technology in Washington, are developing a competing technology to define the kilogram using a complex mechanism known as the watt balance.

The final recommendation will be made by the International Committee on Weights and Measures, a body created by international treaty in 1875. The agency guards the international reference kilogram and keeps it in a heavily guarded safe in a château outside Paris. It is visited once a year, under heavy security, by the only three people to have keys to the safe. The weight change has been noted on the occasions it has been removed for measurement.

"It's part ceremony and part obligation," Dr. Richard Davis, head of the mass section at the research arm of the international committee.

"You'd have to amend the treaty if you didn't do it this way."

That ceremony has become a little sorrowful as the guest of honor appears to be, on a microscopic level at least, wasting away.

The race is already well under way to determine a new standard, although at a measured pace, since creating reliable measurements is such painstaking work.

The kilogram is the only one of the seven base units of measurement that still retain its 19th-century definition. Over the years, scientists have redefined units like the meter (first based on the earth's circumference) and the second (conceived as a fraction of a day). The meter is now the distance light travels in one-299,792,458th of a second, and a second is the time it takes for a cesium atom to vibrate 9,192,631,770 times. Each can be measured with remarkable precision, and, equally important, can be reproduced anywhere.

The kilogram was conceived to be the mass of a liter of water, but accurately measuring a liter of water proved to be very difficult. Instead, an English goldsmith was hired to make a platinum-iridium cylinder that would be used to define the kilogram.

One reason the kilogram has lagged behind the other units is that there has been no immediate practical benefit to increasing its precision. Nonetheless, the drift in the kilogram's weight carries over to other measurements. The volt, for example, is defined in terms of the kilogram, so a stable kilogram definition will allow the volt to be tied more closely to the base units of measure.

A total of 80 copies of the reference kilogram have been created and distributed to signatories of the metric treaty. The sometimes colorful history of these small metal cylinders underscores how long the world has used the same definition of the kilogram.

Some of the metal plugs were issued to countries that later vanished, including Serbia and the Dutch East Indies. The Japanese had to surrender theirs after World War II. Germany has acquired several weights, including the one issued to Bavaria in 1889 and the one that belonged to East Germany.

To update the kilogram, Germany is working with scientists from countries including Australia, Italy and Japan to produce a perfectly round one-kilogram silicon crystal. The idea is that by knowing exactly what atoms are in the crystal, how far apart they are and the size of the ball, the number of atoms in the ball can be calculated. That number then becomes the definition of a kilogram.

To separate the three isotopes of silicon, Dr. Becker and his team are turning to old nuclear weapons factories from the Soviet Union, where centrifuges once used to produce highly enriched uranium are able to produce the required purity of silicon.

"We need so many nines," Dr. Becker said, and Soviet uranium processors are one of the only places to get them. "With the Russians, we're getting about four of them," or 99.99 percent pure silicon 28.

A test crystal has already been produced, and Dr. Arnold Nicolaus, another scientist at the German standards laboratory, is responsible for measuring whether it is perfectly round. He has measured the crystal in a half-million places to determine its shape.

It's probably the roundest item ever made by hand. "If the earth were this round, Mount Everest would be four meters tall," Dr. Nicolaus said. An intriguing characteristic of this smooth ball is that there is no way to tell whether it is spinning or at rest. Only if a grain of dust lands on the surface is there something for the eye to track.

Scientists from the United States, England, France and Switzerland say the challenge of calculating the precise number of atoms in a silicon crystal is too imprecise with today's technology so they are refining a technique to calculate the kilogram using voltage.

"Measuring energy is easier than counting atoms," said Dr. Richard Steiner, a scientist at the National Institute of Standards and Technology in Washington, who is leading the international project to create the watt scale.

In the last few weeks, he has reported that his experiments have yielded data that are close to what they need. "Now we're into the picayune, itsy-bitsy errors," he said, having recently corrected "totally ridiculous" errors of 100 parts per million.

The idea of the watt balance is to measure the electromagnetic force needed to balance a reference kilogram. As long as the gravitational field is precisely known for the location of the experiment, the mass on the scale can be related to power. (The gravitational field is a complicated calculation that needs among other things constantly updated changes in tidal forces.)

The definition of the kilogram would then be a measurement of that power or in terms of something that could be derived from it, like the mass of an electron. The experiment in Washington is occurring in a large three-story structure, but in spite of the complexity and circuitous route of calculating mass, Dr. Steiner says he is confident that his team will have persuasive data shortly.

"In the short term, I think we'll win," he said.

Dr. Davis, who is working closely with those making the final decision about the fate of the kilogram, says he is not so sure. "In terms of published results, the watt balance is closer of the two," he said. "But it's very hard to say which is better."

Many scientists believe that the most elegant way to define the kilogram is by counting out a kilo's worth of atoms of an element. A project is under way to test that with gold atoms. But the sheer number of atoms in a kilogram, a number with roughly 25 digits in it, makes that approach unfeasible for the foreseeable future.

For now, Dr. Davis is willing to set his sights lower in the error-prone world of superprecision measurements. "It would be nice," he said, "just to have two experiments in the world that agreed with each other."

so (0)

Anonymous Coward | more than 10 years ago | (#6044781)

the thing is shrinking, right? so they come up one year to measure its mass again.

"what's the mass there?"
"0.999999 kg"
"the mass is a fraction of itself?"
"yeah i guess so"
"ok then, so we shall redefine the kg to be an infinitely small mass"
"tres bien!"
"oui"

and instantly the volt follows, causing electrical havok worldwide.

Hey, what's the /archive trick (0, Offtopic)

Spodie! (675056) | more than 10 years ago | (#6044788)

to get around NY Times registration?

Re:Hey, what's the /archive trick (0)

Anonymous Coward | more than 10 years ago | (#6044906)

Replace "www." with "archives." and there's no registration needed.

Posted as an AC so I'm not karma whoring.

reproducibility (5, Insightful)

nthomas (10354) | more than 10 years ago | (#6044793)

Although it was mentioned in the article, I think it should be emphasized that the SI definition of the kilogram, unlike their definitions of the meter and second, cannot be reproduced -- or rather, reproduced exactly. This is quite important, as it is neccessary for the standards governing body in each country to have a very precise reference weight of their own.

Since there is only one reference object for the kilogram, everything else is just a copy -- and even if it is a first generation copy, errors are bound to creep in.

The redefinition of the kg is long overdue, mad props to the scientists working on this.

obligatory.... (4, Funny)

SandmanWAIX (674838) | more than 10 years ago | (#6044801)

nah .. they should throw out the whole kilogram concept and weigh everything according to a "library of congress". eg. that woman weighes 2.36 libraries of congress.

Best units of measure (4, Interesting)

Alien54 (180860) | more than 10 years ago | (#6044813)

I sort of like the idea of a universal unit of measure.

One nominee that is amusing is to have the basic unit of distance based on the speed of light.

One light nanosecond = roughly 11.1 inches, kinda close to a foot.

I remember how Grace Hooper used to pass out wires that were that long, just to make the point.

Any other nominees?

Please Splain Something to Me? (1)

fidget42 (538823) | more than 10 years ago | (#6044822)

The volt, for example, is defined in terms of the kilogram...
Does anyone know how the volt is related to the kilogram? Enquiring minds want to know.

Re:Please Splain Something to Me? (4, Informative)

Yosho (135835) | more than 10 years ago | (#6044848)

The unit of "volt" can also be expressed as m^2kgs^-3A^-1.

Re:Please Splain Something to Me? (1)

HybridTheory (551364) | more than 10 years ago | (#6044865)

" The volt (symbolized V) is the Standard International (SI) unit of electric potential or electromotive force. A potential of one volt appears across a resistance of one ohm when a current of one ampere flows through that resistance. Reduced to SI base units, 1 V = 1 kg times m2 times s-3 times A-1 (kilogram meter squared per second cubed per ampere)."

From here Volt Definition [techtarget.com] first link returned on google.

Can someone help me convert here?? (5, Funny)

Helpadingoatemybaby (629248) | more than 10 years ago | (#6044832)

give me imperial measurements any day

Darn right! After all, it's easy enough to convert fortnights to stone with a Mayan calendar.

We're going to in the future eventually. It's inevitable.

I know it's 60 firesticks per 100 Watts, and 3000 Volts per staticy tomcat, but it might just be easier if we all just jumped in and switched to metric 144%.

I mean picture doing 100 on the highway! Wouldn't that be great? And dozens of future Mars landers would actually land on Mars, instead of digging ideal tree planting holes and landscaping future martian neighbourhoods. ("Zyphod! Incoming! It's the Americans!")

No more two sets of wrenches and lost sockets! Now you can have one set of sockets with half the sockets missing, instead of two sets of sockets with half the sockets missing. And no more asking for an 5mm and trying to make a 1 3/4" fit, rounding off the edges and carving a perfect turkey slice off your hand and gushing gallons of blood. It would be litres, which is less.

And you get to tell women that you, sir, are endowed with twenty-two centimeters of man!

Of course, the loss of the 25 cent piece will be a negative, since we'll have to pay for everything in dimes. But it's worth it dammit.

Seriously, we all know this is going to happen. When are we on board? Are we that stubborn?

I can't believe (-1, Troll)

MoThugz (560556) | more than 10 years ago | (#6044843)

...that some people actually gives a rat's ass on what the current kilogram is based upon. It's 1000 grams. Take the weight of whatever base item they're are using, and multiply it by a thousand.

And what's wrong with using the present scales available on the market... don't tell me that the manufacturers actually brought their designers to this place and actually weigh it on their prototypes!

Re:Millenium Project Up an Running (1)

CanadaDave (544515) | more than 10 years ago | (#6044855)

How can counting the number of silicon atoms in a perfectly spherical crystal of silicon be exact? First of all, how can you make a perfect sphere of silicon. If there want to do it this way wouldn't it make sense to use something inherently spherical like a Buckeyball?


And why is this sample in France deteriorating anyways? Don't they keep it in a vacuum (purged periodically with Helium)?

Changing the definition of kilogram (-1, Offtopic)

Anonymous Coward | more than 10 years ago | (#6044867)

Once upon a time whilst strolling in a park near my house...I asked a geek "Do you have a girlfriend?". He responded with a very puzzled look. "A girlfriend?," he mused, "Who is the developer?". I chuckled and told him this was not an open source project. He then became slightly angry and told me "Are you trying to insult me? Only the best geeks use open source only!". I reassured him I was well aware of his integrity as a geek (white skin, clumsy, pants that are too short, lack of daily shower, etc), but a girlfriend is a female who to a male (most oftenly a male) has an intimate friendship. He gave me a very confused look. "I have never heard of such a thing.. this.. g-g-irlfriend?" He asked me, sounding very baffled. "I have heard of friends before, those pets other people have. But what is this thing you say.. Grill?". "Girl," I corrected. Then I asked him to sit down on a bench nearby so I could explain it too him, the poor, helpless thing. I told him that for human beings to reproduce, sexual intercourse must occur between a male and a female. "Perhaps you hear the trolls mention a thing called "pussy" on slashdot?". The geek burst into laughter, "Haha, you have been browsing at -1 lately, haven't you? You know that is just troll talk. Those silly trolls never have anything intelligent to say." My face turned serious. "My dear geek, are you not aware of the female population amongst you? Do you not stare in the street and want to hump a post when you pass by a hot, slim, gorgeous looking chick with a firm bust and well sculpted ass?". The geek immediately began to appear as if we was having a nervous breakdown. His glasses began to fog up and he took them off to wipe them with this linux embroidered shirt, "I think I know what you are talking about. Those things are icky. They have cooties. Get away from me!" I felt offended. "Nonsense, I pleaded! Pussy is a beautiful thing. A sacred thing." The geek would not listen and he began to cry. "STOP IT!! You are EVIL!!" He then skipped off. I walked back to my house quite sad. Why don't they listen to me I asked myself? When I got home my girlfriend opened the door. She was wearing short-shorts and a sports bra. She had been doing the thigh master for the past 30 minutes and was sweating. I could see her dark nipples underneath her slightly damp bra. Oh god I could fuck her to the moon and back. I could smell her horniness the second I took my shoes off. I chased her, both of us laughing, to our bedroom [THE FOLLOWING has been censored for the well-being of Geeks].... Six hours later, finally satisfied a little, I sat up and noticed that same Geek hiding in the trees. He had been watching us the entire time. I swear his penis had to have been the size of a fucking horse cock (not bad for a geek, i might add), and he appeared as if he had gone into a state of shock. I could see cum stains forming near the bulge of his pant zipper. I thought to myself. There is one geek, finally brought into the real world.

Why is it losing mass? (0)

Anonymous Coward | more than 10 years ago | (#6044879)

I wonder why the standard is decaying. Seems like it would be one of three things:
1) sublimation
2) radioactive decay
3) desorption of surface films

Sublimation being metal atoms going directly from the solid to the gaseous state. Metals have extremely low vapor pressures, but maybe after 100+ years enough metal has evaporated to make a difference.

Radioactive decay could be from trace impurities of radioactive elements in the standard.

Finally, perhaps the original standard had a film of something adsorbed to its surface, and that film is slowly desorbing.

Dust? Fingerprints? (1)

rebelcool (247749) | more than 10 years ago | (#6044882)

I always thought it was odd the kilo was based on a metal bar. Unless the bar is perfectly clean - no dust, and no fingerprints - you will face weight discrepancies from year to year.

Basically you would have to keep the bar in a hermetically sealed vacuum where it couldn't accumulate any dust or outgassing from its container. This is probably why its 'losing' weight. Perhaps it had some fingerprints or other smudges on it that have eventually evaporated away.

One Kilogram's Worth (0)

Anonymous Coward | more than 10 years ago | (#6044887)

Many scientists believe that the most elegant way to define the kilogram is by counting out a kilo's worth of atoms of an element.

Like duh. How else would you do it?

I wonder if the new guy is wiping the kg too hard (2, Interesting)

Anonymous Coward | more than 10 years ago | (#6044889)

There used to be a custodian of the kilogram whose job it was to wipe the dust and oxidation off the mass with a chamois before it was used. It had to be done just right-too little pressure and the kg would have some stuff left on it and weigh more. He retired a few years back, so i wonder how it's done now. Also, apparently there had to always be two people to handle the kg, one to carry and another to catch it.

That's easy! (3, Funny)

sprprsnmn (619113) | more than 10 years ago | (#6044898)

One kilogram is equal to the weight of 1/256th of a VW beetle! Simple as that! Silly French.

Why not use diamond? (4, Interesting)

Jeremy Erwin (2054) | more than 10 years ago | (#6044899)

Is there any physical reason (other than that small matter of cost ) that crafting a new kilogram (or more likely, gram) out of diamond would not be an ideal solution?

BTW, theNational Physical Institute [npl.co.uk] has a FAQ on its Pl-Ir standard kilo.

Go back to the old method!!! (1)

jericho4.0 (565125) | more than 10 years ago | (#6044907)

I personly like the old idea, that a Kg is one liter of water, one liter = 10Cm^3. The article mentioned this was discarded because of the dificulty of working with water. Still, it has a lot of elegance, and links nicley with the concept of temurature.
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