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Kilogram Reference Losing Weight

CowboyNeal posted more than 7 years ago | from the incredible-shrinking-alloys dept.

Math 546

doubleacr writes "Ran across a story on CNN that says the "118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight — if ever so slightly. Physicist Richard Davis of the International Bureau of Weights and Measures in Sevres, southwest of Paris, says the reference kilo appears to have lost 50 micrograms compared with the average of dozens of copies.""

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The Kilogram is not losing weight (5, Funny)

allanc (25681) | more than 7 years ago | (#20597031)

The Kilogram is defined in reference to the chunk of metal in Paris. It's the *definition* of the Kilogram.

Therefore, the Kilogram is not getting lighter.

We're all getting heavier.

The metre must be shrinking then... (5, Funny)

flyingfsck (986395) | more than 7 years ago | (#20597071)

Ah, so that explains the obesity epidemic, but my ever increasing middle indicates that the metre must also be shrinking at the same time.

Re:The metre must be shrinking then... (2, Informative)

Anonymous Coward | more than 7 years ago | (#20597207)

Ah, so that explains the obesity epidemic, but my ever increasing middle indicates that the metre must also be shrinking at the same time.

I'm sorry dude, but unlike the kilogram, the metre isn't defined based on an artifact but rather it is defined based on the speed of light, so unless that changed, the metre hasn't either.

Re:The metre must be shrinking then... (5, Interesting)

LiquidCoooled (634315) | more than 7 years ago | (#20597303)

Actually, that might be possible.
Light speed is not constant in a gravitational field, if some of the other posters are correct and the kilogram has changed because of a localised gravitational shift, then its possible that the definition of a metre could also have changed..

Re:The metre must be shrinking then... (1)

Clay Pigeon -TPF-VS- (624050) | more than 7 years ago | (#20597333)

I thought the meter was based on the dimensions of Terra.

Not any more (5, Informative)

benhocking (724439) | more than 7 years ago | (#20597399)

A meter is defined as the distance light travels in a vacuum in 1/299,792,458th of a second.

Re:Not any more (5, Funny)

flyingfsck (986395) | more than 7 years ago | (#20597543)

So time is speeding up then?

Re:The Kilogram is not losing weight (1)

Volatar (1099775) | more than 7 years ago | (#20597093)

That sure explains why I have been gaining weight but still look like a twig...

Re:The Kilogram is not losing weight (0)

Anonymous Coward | more than 7 years ago | (#20597185)

> That sure explains why I have been gaining weight but still look like a twig...

That's an easy one to fix. Just step off the centrifuge.

Problem is, as long as the kilogram itself is getting lighter, you're gaining mass.

Re:The Kilogram is not losing weight (0, Funny)

Anonymous Coward | more than 7 years ago | (#20597101)

Paris Hilton has a metal dildo that weighs exactly 1 kilogram?

Impressive.

Re:The Kilogram is not losing weight (3, Informative)

Meshach (578918) | more than 7 years ago | (#20597127)

I thought that originally the kilogram was defined in terms of water, the mass of 10 square cm of water. The meter is defined in terms of the speed of light so that gives an empirical way to define the kg independent of anything else. It would be interesting to see if it has changed relative to that measurement

Re:The Kilogram is not losing weight (4, Insightful)

hjf (703092) | more than 7 years ago | (#20597291)

I thought that originally the kilogram was defined in terms of water, the mass of 10 square cm of water.
I think you meant 1 cubic decimeter.

Re:The Kilogram is not losing weight (1)

Ferzerp (83619) | more than 7 years ago | (#20597293)

hah.

at what temperature exactly?

Re:The Kilogram is not losing weight (1, Informative)

snowgirl (978879) | more than 7 years ago | (#20597445)

The density of liquid water is essentially invariant relative to temperature. (Given minor fluxuations of entropic internal force.)

Gases are the liquid with varying density.

That being said, it's STP (standard temperature and pressure, or "Schiffkuhlschrank" ("refrigerator on a ship")).

Re:The Kilogram is not losing weight (4, Informative)

Ferzerp (83619) | more than 7 years ago | (#20597509)

I think you mean that the density of water is essentially invariant to pressure.

It very much fluctuates with temperature.

Re:The Kilogram is not losing weight (1)

OrangeTide (124937) | more than 7 years ago | (#20597457)

What percentage can have stable hydrogen and oxygen isotopes?

Re:The Kilogram is not losing weight (1)

nwbvt (768631) | more than 7 years ago | (#20597299)

Yeah, it changed some time ago. The new definition was adopted in 1889. Hence the line in the summary "Ran across a story on CNN that says the '118-year-old cylinder that is the international prototype for the metric mass...'"

Re:The Kilogram is not losing weight (1)

rm999 (775449) | more than 7 years ago | (#20597309)

Yeah, I don't understand why we need a reference weight. We have a definition of a meter, and we have water everywhere. Why didn't stick with that definition?

My guess is that the French created a reference weight because they knew they would be the only ones who would have it - i.e. for pride. But it's such a useless definition because:
A. it only gets weighed once every ~20 years - it can't be used as a reference
B. Every time it's weighed we realize it's changed mass. in 1980 they claimed it gained weight.

The density of water probably hasn't changed in the last billion years. Why can't we stick with that as a definition?

Re:The Kilogram is not losing weight (4, Informative)

TheRaven64 (641858) | more than 7 years ago | (#20597425)

The density of water changes when you vary the temperature or pressure, so you'd need an accurate measure of distance, temperature, and pressure in order to get your 1Kg of water.

Re:The Kilogram is not losing weight (5, Informative)

Bender0x7D1 (536254) | more than 7 years ago | (#20597371)

I thought that originally the kilogram was defined in terms of water, the mass of 10 square cm of water.

We can't use water as a reference since the molecules in the water are constantly splitting into ions and reforming as molecules. So it is essentially impossible to get 1000 cm^3 of "pure" water. It will be some mixture of H2O, H+ and O-- ions. Also, it would be incredibly hard to prevent other molecules from being disolved in the water. A few stray molecules hitting the surface will ruin your reference mass. Not to mention you need a container to keep it in...

The meter is defined in terms of the speed of light so that gives an empirical way to define the kg independent of anything else.

As mentioned above, we could measure a 1000 cm^3 volume, but we couldn't guarantee the purity of the water in that volume.

That's one reason we are trying to make a perfect sphere [slashdot.org] to replace the reference kilogram. Then we will have a definition of the kilogram in terms of number of silicon atoms.

Re:The Kilogram is not losing weight (1)

snowgirl (978879) | more than 7 years ago | (#20597391)

They don't really define the kilogram, but rather the gram itself. The gram was setup to be the mass of one cubic centimeter of water at STP. The meter was original defined such that the diameter or radius of the earth at GMT would be a simple power of ten of the meter. Of course, their measurements were even less accurate than the ancient greeks, so the meter was defined poorly as to the intent of the purpose.

Later the meter was refactored to be a specific value of the speed of light, (namely, we can no longer measure the speed of light any better, but rather can only better determine the meter. As the inch is defined as 2.54cm, the idea that one could measure the speed of light in feet any better is also incorrect.)

Over time, all of the base units have been rederived from the original derivations to the modern day derivations, except the kilogram. I don't exactly know why...

Re:The Kilogram is not losing weight (3, Informative)

Anonymous Coward | more than 7 years ago | (#20597407)

The meter was originally 1/10,000,000 of the distance between the equator and the North Pole along the meridian running through Paris. (No chauvinism there...) Someone made up a brass reference. Later, the meter spent some time as the distance between a couple of scratches on a platinum-iridium bar. Then we tried a fwe wavelengths of cesium, then krypton-86. Eventually, we adopted a definition for a similar length based on c.

You don't think anyone would really pick a number like 1 / 299,792,458 if they got to start from scratch, do you? Why not 1/300,000,000, just to make the calculations easier? Or, since powers of ten are supposed to be so vital to the system, why not 1/ 10,000,000, or 1/100,000,000?

Ultimately the meter is as long as it is because it's about a yard long, and that's a useful length for measuring on a human scale. It's not "scientific" at all.

Similarly, a kilogram is a useful weight about the same size as a pound. It happens to be about the mass 10 cm cubed of water, much as a pint of water weighs a pound (the world around, and takes 1 BTU to raise temperature by 1 degree F). Later they made a reference standard for this fairly arbitrary amount of mass.

Re:The Kilogram is not losing weight (2, Insightful)

Chris Burke (6130) | more than 7 years ago | (#20597227)

Weight is a property independent of the units you measure it with.

The object which defines the Kilogram is getting lighter (the fact that it is getting lighter is independent of this object's role in defining the Kilogram), ergo the definition of Kilogram is getting lighter. We all weight the same, we'll just use a slightly bigger number to describe how heavy we are.

Re:The Kilogram is not losing weight (2, Funny)

E++99 (880734) | more than 7 years ago | (#20597473)

"Humor. It is a difficult concept. It is not logical."

Nevertheless, the moderation system of this forum may serve to alert you to the utilization of humor, as posts utilizing it are often accompanied by a "Funny" indicator. In such cases, correction of fact can generally be assumed unnecessary, as said facts will likely have been intentionally misstated as a means of producing said humor.

The Faster We Go, The Rounder We Get (3, Interesting)

Doc Ruby (173196) | more than 7 years ago | (#20597265)

By Relativity, we must all be accelerating. How much more energy in the universe does 1:1E9 extra mass represent? Since that's probably more than in the equivalent 50ug, there's probably mass missing from all over the place.

Who's converting our extra mass to energy? This great criminal must be found before we all blueshift past the event horizon!

Or, this is just the greatest museum heist Paris has ever seen.

Re:The Kilogram is not losing weight (1)

nwbvt (768631) | more than 7 years ago | (#20597347)

It doesn't weigh fewer kilograms, that is certainly true. But the force of the Earth's gravity on the object (what most people refer to as 'weight') appears to have changed. Which most likely is because of reduction in the mass of the object. So it is lighter.

Re:The Kilogram is not losing weight (1)

pclminion (145572) | more than 7 years ago | (#20597405)

True, but due to exactly these sorts of variations in the IPK's mass, it has been proposed that the kilogram be redefined in terms of fundamental constants, in a way that can be replicated anywhere in the universe -- similar to how the meter has been redefined ("delineated," actually) to be equal to some exact number of wavelengths of a certain kind of coherent radiation.

See the Wikipedia entry [wikipedia.org] for various proposals of how to do it.

Re:The Kilogram is not losing weight (1)

BlueParrot (965239) | more than 7 years ago | (#20597461)

similar to how the meter has been redefined ("delineated," actually) to be equal to some exact number of wavelengths of a certain kind of coherent radiation.
These days the definition of the meter is that the speed of light in vacuum is 299,792,458m/s , exactly. The meter is defined as whatever length gives exactly this value for the speed of light.

I am finally able to answer the dreaded question.. (5, Funny)

this great guy (922511) | more than 7 years ago | (#20597417)

The wife: Don't you think I am gaining weight ?
Me: No honey, it's just the kilogram that is getting lighter.

Re:The Kilogram is not losing weight (1)

SQLGuru (980662) | more than 7 years ago | (#20597483)

We're all getting heavier.
Speak for yourself. We obnoxious Americans still weigh ourselves in pounds.

Layne

The Pound must be picking it up (1)

flyingfsck (986395) | more than 7 years ago | (#20597567)

Well, have you looked at the Dollar/Pound exchange rate lately? The Pound must be getting heavier...

Sublimation? (3, Interesting)

Eustace Tilley (23991) | more than 7 years ago | (#20597041)

Could it be a few atoms drifting off in the vapor? Well, why wouldn't the copies' atoms be drifting off as well?

Re:Sublimation? (1, Funny)

snowgirl (978879) | more than 7 years ago | (#20597243)

Could it be a few atoms drifting off in the vapor? Well, why wouldn't the copies' atoms be drifting off as well?


This is called sublimation [wikipedia.org] . And it's the first thing that I thought of myself as well.

Re:Sublimation? (1)

Hatta (162192) | more than 7 years ago | (#20597547)

You should read the topics of comments you reply to.

Haha! (0, Offtopic)

Twisted64 (837490) | more than 7 years ago | (#20597051)

So am I! But thankfully I'm not used as a reliable reference weight.

Gravity failing! (1)

ruiner13 (527499) | more than 7 years ago | (#20597055)

Oh no, perhaps gravity is weakening, which is causing all the earthquakes in the indonesian fault lines! EVERYBODY PANIC!!!

Re:Gravity failing! (1)

JiffyPop (318506) | more than 7 years ago | (#20597137)

Mass does not depend upon the acceleration it is placed under...

Re:Gravity failing! (1)

Volatar (1099775) | more than 7 years ago | (#20597173)

The story however, is titled: " Kilogram Reference Losing Weight"

No one mentioned mass :)

Re:Gravity failing! (1)

vigmeister (1112659) | more than 7 years ago | (#20597183)

Really? Read my other post below for the answer :)

Cheers!

General relativity (1)

DigiShaman (671371) | more than 7 years ago | (#20597059)

Might have something to do with the universe always in a state of change? Do we have any other 100+ year prototype weights to confirm?

Re:General relativity (1)

Provocateur (133110) | more than 7 years ago | (#20597553)

We do, but most of them have declined to comment on this development. Some would blame envy at their "former friend's" makeover.

Governments have been doing this for years! (4, Funny)

dada21 (163177) | more than 7 years ago | (#20597067)

If you look over history, governments have taken metals that were supposed to be a certain weight, and mysteriously removed weight from them and still called the weight the same thing.

Look at the standard weight known as the "dollar" (thaler). It used to be the equivalent of 1/20th of an ounce of gold. Then it was 1/35th of an ounce of gold. Last month that same dollar weight standard was 1/650th of an ounce of gold, and today I believe it is 1/711th of an ounce of gold.

The Roman Empire leaders also had mysteriously disappearing weights... Their Denarius lost over 99% of its official weight over just a few hundred years.

It is definitely a mystery...

Where are my... (1)

msauve (701917) | more than 7 years ago | (#20597211)

mod points when I need them?

Re:Governments have been doing this for years! (1)

compwizrd (166184) | more than 7 years ago | (#20597311)

Most governments had a clever idea to get around that problem though.

I believe it was 1933 the US Gov't went off the gold standard.

Re:Governments have been doing this for years! (1)

phoenixwade (997892) | more than 7 years ago | (#20597443)

Most governments had a clever idea to get around that problem though.

I believe it was 1933 the US Gov't went off the gold standard.
Really? I thought it was Inflation..... But then I saw the article that was having a problem with inflation and some string......

(yes, It is a joke, even if someone with mod points doesn't get it)

Re:Governments have been doing this for years! (1)

FudRucker (866063) | more than 7 years ago | (#20597529)

one monday in 1929 there was some really bad inflation...

tag this "dirtycopies" (1)

ozphx (1061292) | more than 7 years ago | (#20597073)

You know its true ;)

Blah (0)

Anonymous Coward | more than 7 years ago | (#20597079)

Here in Kentucky, we measure 10 hectaires to the hogshead and that's how wes like it.

This must be the reason .... (2, Funny)

Anonymous Coward | more than 7 years ago | (#20597087)

... why Americans use ounce-feet (or something) instead.

I like the US customary system (2, Funny)

OrangeTide (124937) | more than 7 years ago | (#20597507)

foot-pounds and even inch-pounds. It's so neat.

"The metric system is the tool of the devil! My car gets forty rods to the hogshead, and that's the way I likes it!"

sublimation? (1)

benburned (1091769) | more than 7 years ago | (#20597097)

can that material undergo sublimation? I don't think that could possibly be the cause though

Re:sublimation? (1)

AJWM (19027) | more than 7 years ago | (#20597263)

No, but if it has a small fraction of radioisotope components they could be decaying and the mass loss be mostly e.g. alpha particles.

Although I suspect that the radioactivity to account for that much mass loss would make the block rather warm. (Haven't done the math -- 50 ug of alpha would be about 1.3*10^18 particles? Over 110 years (110*365*24*60*60 seconds, about 3.47*10^9, so 3.7*10^8 alphas/second. I'd have to go look up the typical energy of an alpha decay, and right now dinner's calling.)

Has anyone checked Ebay? (2, Funny)

Anonymous Coward | more than 7 years ago | (#20597109)

How much on the black market for a microgram off the ole standard?

Kilogram Reference Losing Weight (5, Informative)

MrYotsuya (27522) | more than 7 years ago | (#20597119)

It's not losing weight, it's losing mass!. The kilogram is not a measure of weight, but mass. Silly pound-centric editors :p

Re: Kilogram Reference Losing Weight (0)

E++99 (880734) | more than 7 years ago | (#20597315)

It's not losing weight, it's losing mass!

And how exactly is it managing to lose mass without losing weight?

Re: Kilogram Reference Losing Weight (1)

Trogre (513942) | more than 7 years ago | (#20597335)

It's losing both. Keeping G constant, it is losing both mass (M) and weight (=MxG).

Re: Kilogram Reference Losing Weight (1)

TheRaven64 (641858) | more than 7 years ago | (#20597455)

I think you mean g, not G. Altering G will also alter the weight of the mass, but in quite a different way.

Re: Kilogram Reference Losing Weight (0)

Anonymous Coward | more than 7 years ago | (#20597523)

OT but why does everyone say something weights X kilograms when we all know weight = (mass) * (acceleration of gravity)? I guess kilograms-force is what people really mean with very few knowing that because of the abused use of kilograms to mean weight.

Re: Kilogram Reference Losing Weight (1, Funny)

QuickFox (311231) | more than 7 years ago | (#20597563)

Keeping G constant,
It's in France. Are you sure you can trust the French to do that?

Re: Kilogram Reference Losing Weight (1)

Dunbal (464142) | more than 7 years ago | (#20597427)

It's not losing weight, it's losing mass!. The kilogram is not a measure of weight, but mass. Silly pound-centric editors :p

      However if you are putting it on a scale to weigh it, you are measuring weight. On earth, weight = mass. Of course you could measure the mass through the density equation or a number of other means, but the simplest method is to weigh it.

Re: Kilogram Reference Losing Weight (1)

Jeff DeMaagd (2015) | more than 7 years ago | (#20597447)

There does exist a pound mass, but it's rarely used.

Call us when you're using Newtons, and we'll talk. (1, Troll)

Valdrax (32670) | more than 7 years ago | (#20597465)

The kilogram is not a measure of weight, but mass. Silly pound-centric editors :p

Dear Metric Using Countries,

Please call us back when the majority of your citizens are measuring their weight in Newtons instead of Kilograms, and we'll consider addressing your charge of Pound-related bias.

Sincerely,
The People of the United States of America

Relativity? (1)

vigmeister (1112659) | more than 7 years ago | (#20597133)

If the copies were at different locations, wouldn't they have been travelling at different accelerations and speeds for long enough to have the Paris one be relatively 'losing weight' due to the twin paradox (as applied to mass)?

Cheers!

Re:Relativity? (2, Informative)

sanyasi (900484) | more than 7 years ago | (#20597251)

Thats not relativity. The twin paradox wont degrade the mass over time. It would make it 'younger' according to the situation you described, but not lighter.

Re:Relativity? (1)

vigmeister (1112659) | more than 7 years ago | (#20597429)

I'd say it would unless all the blocks are measured in Paris ... maybe 50 micrograms is too much, but if all the calibration did not take place at the same place as the place of origin of the blocks, there might be a discrepancy unless we used the same measuring equipment in the same place.

Cheers!

Re:Relativity? (1)

Ferzerp (83619) | more than 7 years ago | (#20597433)

This *could* be possible I suppose, but not really how you think (I think).

I'm going to assume they are kept under a glass in a vacuum. If we suppose the glass sublimates in to the vacuum somehow, and then the glass is absorbed by the hunk of metal... The travel would make the travelling ones slightly older, and they would have had more time to absorb.

Or more likely, they have to remove the protection to measure the items and since the standard probably is measured less often, it is less contaminated. (This has nothing to do with your post)

Mass? (1, Interesting)

forsetti (158019) | more than 7 years ago | (#20597141)

High school physics was a while back for me now, but technically, isn't a kilogram a measure of mass? And therefore, if its weight is changing, isn't it actually possible that the mass has remained constant, but the force of gravity has slightly changed in that locality? Of course, other reference masses in the same locality could be used for comparison to determine gravitational fluctuations ... but how does one account for that?

Re:Mass? (2, Interesting)

edwardpickman (965122) | more than 7 years ago | (#20597323)

Technically if the table was higher the weight would be less. The mass is constant but weight is more of an interaction with the Earth's gravity. The higher you go the lower the gravity. The effect is enough to change time measurements on high mountains or high flying aircraft. I doubt there's any equipment sensitive enough to detect weight difference in an object that was moved several feet but there is a change. The shape of the earth is in flux so it's not impossible that that affected it. Gravity isn't even uniform over the surface so a measurement at a 100' above sea level in one location may not be the same at a 100' in another location. The ground would have changed height over a 100 years as well. More than likely it was either a measurement error or handling and gentle wiping of the object would be enough to cause the error. Far more likely than changes in gravity.

Re:Mass? (3, Insightful)

djmurdoch (306849) | more than 7 years ago | (#20597541)

I doubt there's any equipment sensitive enough to detect weight difference in an object that was moved several feet but there is a change.

According to the back of this envelope here, the weight change from raising a kilogram by one metre would be
about equivalent to reducing its mass by about 3 parts in 10^7, i.e. 300 micrograms. The article says the measured loss was around 50 micrograms. So I guess there is equivalent sensitive enough to measure that.

Unless I was off by a few orders of magnitude...

Re:Mass? (1)

fm6 (162816) | more than 7 years ago | (#20597411)

High school physics was a while back for me now, but technically, isn't a kilogram a measure of mass?
So far, this story has appeared only in the popular press, whose readers aren't expected to know what mass is.

Re:Mass? (1)

patcpong (952524) | more than 7 years ago | (#20597477)

So you're saying the masses don't know what mass is? (hint: say it out loud).

DON'T WORRRY GUYS (0)

Anonymous Coward | more than 7 years ago | (#20597143)

I have a replacement... 1.. 2.. 3.. 4.. 5.., shit, 1.. 2.. 3.. 4.. what was Avagrodos number again?!? 1.. 2...3.. 4.. 5.. 6..

More fundamental standards (2, Informative)

iamacat (583406) | more than 7 years ago | (#20597163)

I am surprised that they are not using more fundamental standards, like the mass of a hydrogen atom. After all, too many things can happen to a chunk of metal - evaporation, oxidation, radioactive decay.

Re:More fundamental standards (3, Informative)

AvitarX (172628) | more than 7 years ago | (#20597259)

I read an article about this.

It is apparently really hard to get the right amount of atoms reliably and constantly. This is why mass is still using a reference while time and length have ways to reproduce them in a lab (I believe it is measuring the speed of light, and the waves coming ff some substance that is heated up).

There is some work being done making spheres with a silicone chrystal structure, but the margin of error is a few hundred atoms (molecules?), and they wanted it down to around 50. This was a few years ago, things may have changed.

Then the problem becomes... (1)

msauve (701917) | more than 7 years ago | (#20597279)

which type of hydrogen atom - African or European?

Re:More fundamental standards (1)

BlueParrot (965239) | more than 7 years ago | (#20597355)

I am surprised that they are not using more fundamental standards, like the mass of a hydrogen atom. After all, too many things can happen to a chunk of metal - evaporation, oxidation, radioactive decay.
Considerable work is going into creating an atomic definition of the kilogram, the problem is that so far nobody has actually been able to measure atomic weights with high enough accuracy to actually beat the old definition. The problem mainly arises because there are so many atoms in a kilogram. You basically need to estimate the number of atoms in a Kg which is no easy task. 1 gram of hydrogen contains about 6*10^23 atoms, which is a rather huge number, making it tricky to get an accurate enough figure. So essentially, the answer to your question is that, no, at the moment the prototype is the most accurate way to define a Kg. If you can create a device with better accuracy you are probably in for a Nobel price.

obligatory... (4, Funny)

abes (82351) | more than 7 years ago | (#20597193)

but don't worry, it will regain the weight after a couple of months.

Possible reason? (4, Interesting)

robably (1044462) | more than 7 years ago | (#20597201)

Maybe it's because of where they weighed it - the strength of gravity is not the same all over the planet, and I'm guessing it can change in one place over time due to the movement of the Earth's outer core and give a different result.

Re:Possible reason? (1)

Misanthrope (49269) | more than 7 years ago | (#20597241)

Sorry to beat a dead horse, but it's a measurement of mass not weight. Where it's measured shouldn't matter.

And how do you suppose they measure mass?... (1)

msauve (701917) | more than 7 years ago | (#20597489)

Other than by accellerating it, and measuring the resulting force? And what better way to do that, than by using gravitational "accelleration?" Under uniform gravity, identical masses will have the same weight.

In response to the grandparent, they article states that the discrepancy was discovered by comparing ("comparison with other cylinders shipped in periodically from around the world."), implying that the masses were measured contemporaneously, at the same place. Is there any way to transfer absolute (non-referenced) mass measurements between places, if you can't count atoms precisely?

Re:Possible reason? (1)

E++99 (880734) | more than 7 years ago | (#20597533)

If they're not weighing it, how are they measuring its mass?

Oh come on (1)

polygamous coward (1127507) | more than 7 years ago | (#20597223)

This is obviously proof that God exsits, or maybe UFO's, or maybe I'll get laid someday.

amusing background (1)

cinnamon colbert (732724) | more than 7 years ago | (#20597273)

a few years ago, there was a story about international reference stds, and how the Kg was the only one that relied on unique object - by comparison, the second and distance are defined by fundamental propertys of atoms; in principal anyone can build an atomic clock and measure time for themselves, though of course in practice it aint easy
anyway, there are whole conferences devoted to what is going to happen to the entire legal scale of weights when this block of iridium in paris is no good

now for the amusing part: every now and then, you actually have to take the Kg out of its special chamber and compare it to a secondary std. There was this old guy in paris who was the only person in the world who could clean the Kg without changing its weight (you can measure a delta )
maybe this guy died

Re:amusing background (1)

MavEtJu (241979) | more than 7 years ago | (#20597491)

It's kg, not Kg.

vapor pressure (1)

cjanota (936004) | more than 7 years ago | (#20597281)

Even solids loose mass through vapor. Excited atoms on the surface can leave the material into the atmosphere. I assume that they have thought of that and accounted for it though. This probably cannot account for the fact that the sample is loosing mass relative to the others, but they could all be loosing a little bit of mass because of this.

Re:vapor pressure (1)

Trifthen (40989) | more than 7 years ago | (#20597535)

Exactly this. There's also the issue of quantum effects such as tunneling and other strange behavior. Most people don't know about vapor pressure, though. Zoom into any material far enough, and there are little swirls and eddies of turbulence where the border between the solid and the atmosphere are not clearly defined. Being a metal, the standard weight will also have an "electron sea" casually cascading over its surface, which could also be steadily lost. Even in a vacuum chamber, the mass could react on a quantum level with the surface it rests on, or the chamber itself.

Then of course, can they be sure the material they made the mass from doesn't have an imperceptibly small half-life? Even reacting with the rare passing neutrino can radiate alpha, beta, or gamma radiation in immeasurable quantities unless they've also surrounded the storage chamber with fairly advanced detectors.

Of course, There is no such thing as a stable mass--though they may be surprised by the amount of mass lost through various possible mechanisms. 50-micrograms is relatively quite a bit.

Of course, since the original mass was created 118 years ago, it's possible they couldn't have created it with the sheer amount of accuracy available today. Unless they have a chart of the "weight loss," I'm willing to apply Occam's razor and assume the original was merely miscast by 50-micrograms.

Losing mass or weight? (1)

r_jensen11 (598210) | more than 7 years ago | (#20597337)

If it's losing weight, there could be a number of explainations. Some include a smaller force of gravity pulling on it, some magnetism partially levitating it, etc. If it's losing mass, then there's only three real explainations: either erosion, chemical transformations (e.g. oxidation,) or theft.

The problem is that it is in France (1)

fishthegeek (943099) | more than 7 years ago | (#20597345)

When all you have is wine, cheese, and snails its obvious why it is losing weight. Everyone knows that if you want something to GAIN weight you should move it to America! Three Double Whoppers with Cheese a day is what it really needs to get that weight back!

Inertia (0)

Anonymous Coward | more than 7 years ago | (#20597349)

Shouldn't we just measure things based upon how much momentum/inertia they have? apply so and so a force, see how fast it accelerates. Or is that how they've measured the mass to have decreased

Some basic physics:

f = ma

so:

m = f/a

Maybe I'll stop measuring in either pounds or kilograms. Newton/ms^2's ftw!

Original article (4, Informative)

Toinou (1059440) | more than 7 years ago | (#20597367)

The study comes from the BIPM ( international bureau for weights and measures) , and here is the original article : http://www.bipm.org/en/scientific/mass/verifications.html [bipm.org] . In fact it seems to be very old news since the study is carried every 40 years and the last one was in 1992, according to the BIPM :

On three occasions, roughly 40 years apart, the mass of the official copies, the national prototypes and the working standards of the BIPM have been compared with the mass of the international prototype. [...] the last of these occasions (1988-1992) [...]

behold.... (1)

prxp (1023979) | more than 7 years ago | (#20597369)

...the newest French diet [amazon.com] !

Stop cleaning it! (2, Funny)

eknagy (1056622) | more than 7 years ago | (#20597387)

If that old lady who plugs that vacuum cleaner into the UPS every day at 05:00 would stop cleaning it, there would be no such problems with gravity!

Did they really expect a permanently stable mass? (1)

Trifthen (40989) | more than 7 years ago | (#20597393)

Quantum tunneling. Or, unless the material is 100% physically inert and kept in a 100% vacuum chamber with no other possible reactants (it's not), mass will be lost or gained. Next?

Re:Did they really expect a permanently stable mas (1)

pclminion (145572) | more than 7 years ago | (#20597453)

Quantum tunneling. Or, unless the material is 100% physically inert and kept in a 100% vacuum chamber with no other possible reactants (it's not), mass will be lost or gained. Next?

Even if you did that, there are still reasons it could change mass. A cosmic ray could strike the mass and eject a certain number of atoms from it, for instance.

I don't think anyone EXPECTED that it would remain absolutely constant, but it's the best they could do at the time.

Re:Did they really expect a permanently stable mas (1)

patcpong (952524) | more than 7 years ago | (#20597517)

They knew about quantum tunneling/cosmic rays in 1889?

Mmmkay... (2, Funny)

TofuDog (735357) | more than 7 years ago | (#20597397)

You need to drop at least 250 micrograms to really experience the magnitude of the kilogram, man... Wow, Mr. Mackie, Drugs -are- bad. It's not just reference mass lost -Where is my mind? -you thieving Pixies. woooo-oooooh.

Radioactive decay? (1)

pclminion (145572) | more than 7 years ago | (#20597493)

Surely among all those platinum and iridium atoms, there are a few which are unstable isotopes. As those decay, that could change the mass.

They are slowly whittling it down to a pound. (1)

Schmapdi (840038) | more than 7 years ago | (#20597499)

It will save us from having to do all sorts of difficult conversions down the line.

Great Scott! (1)

cashman73 (855518) | more than 7 years ago | (#20597505)

I thought Doc Brown said things were supposed to get heavier in the future! Oh wait, sorry,. . . that was Marty McFly!

Before making announcements of this nature... (0)

Anonymous Coward | more than 7 years ago | (#20597545)

...double check that you haven't accidentally mistaken Nicole Ritchie for your international prototype for metric mass. They weigh about the same, but one is significantly duller and less interesting than a featureless chunk of metal.

Okay, in seriousness...

the reference kilo appears to have lost 50 micrograms compared with the average of dozens of copies.

Of all the world's kilograms, only the one in Sevres really counts. It is kept in a triple-locked safe at a chateau and rarely sees the light of day -- mostly for comparison with other cylinders shipped in periodically from around the world.

If the only interaction with the reference kilo is comparisons to copies, and the reference kilo undergoes the comparison "dozens of times" more than the copies, then I would suggest that the comparison makes them all slightly lighter, and it only shows up on the reference kilo because the reference kilo will be compared with each copy, whereas the copies will only be compared with the reference kilo.

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