Kilogram Reference Losing Weight

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.""

Comments

The Kilogram is not losing weight

[allanc]

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.

Re:The Kilogram is not losing weight

[Volatar]

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

Re:The Kilogram is not losing weight

[Anonymous Coward]

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

Impressive.

Re:The Kilogram is not losing weight

[Meshach]

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

[Anonymous Coward]

> 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

[Chris Burke]

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

[hjf]

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

[Ferzerp]

hah.

at what temperature exactly?

Re:The Kilogram is not losing weight

[nwbvt]

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

[rm999]

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

[nwbvt]

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

[Bender0x7D1]

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 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

[snowgirl]

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

[pclminion]

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 for various proposals of how to do it.

Re:The Kilogram is not losing weight

[Anonymous Coward]

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

[TheRaven64]

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

[snowgirl]

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

[OrangeTide]

What percentage can have stable hydrogen and oxygen isotopes?

Re:The Kilogram is not losing weight

[BlueParrot]

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.

Re:The Kilogram is not losing weight

[E 99]

"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.

Re:The Kilogram is not losing weight

[SQLGuru]

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

Layne

Re:The Kilogram is not losing weight

[Ferzerp]

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

[Eternauta3k]

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...)

Yeah, cause that meridian is so different to the rest _

Re:The Kilogram is not losing weight

[suv4x4]

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.

One would think it'll still be a better reference than a chunk of rusty metal kept under lock.

The silicon sphere can be worked on in the mean time.

Not to mention you need a container to keep it in...

Right, let me think.. if your scales show weight X on empty container (never mind what it is) and it shows 1kg+X after you put in 100cm^3, then I guess your scales measures properly.

Re:The Kilogram is not losing weight

[Goglu]

We all expected this since the failed attempt to sabotage the Meter, in the 70s (http://en.wikipedia.org/wiki/Superdupont).

Re:The Kilogram is not losing weight

[CrimsonAvenger]

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.

No. The meter was originally defined as one ten-millionth of the distance from the North Pole to the Equator. Which isn't really too far off - less than one fifth of one percent.

Re:The Kilogram is not losing weight

[WilliamSChips]

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? Why use seconds for that anyways? A better idea would be to build things up from the Planck units.

Re:The Kilogram is not losing weight

[rm999]

I believe they used to define it by the most dense state of water at 1 atm. Of course this gets tricky, because pressure is defined using mass, which is currently ill-defined.

Regardless, IMO all SI definitions should be reproducible in a lab. Reference objects serve no real purpose other than producing a museum piece. A kilogram could be defined as some fixed number of some molecule - at that point, a lab could find a way to collect that number of molecules.

Re:The Kilogram is not losing weight

[compro01]

Similarly, a kilogram is a useful weight about the same size as a pound. What pound are you using? 1kg is equal to about 2 pounds where I come from.

Re:The Kilogram is not losing weight

[Entropius]

You could specify the density of water at $PRESSURE and at its maximum density (somewhere around 4 C). The only problem with doing this for high-precision measurements is: what is water? Some fraction of the hydrogen will be deuterium, and that'll throw off the density. What fraction of the hydrogen should be deuterium for "standard water"?

Re:The Kilogram is not losing weight

[Alien Being]

It is different. It scales the height of the collective French ego.

Re:The Kilogram is not losing weight

[Entropius]

In physics we talk about the masses of things from single atoms to galaxies.

In that range, 1 ~= 2

Re:The Kilogram is not losing weight

[CastrTroy]

That's ok, the British still use stone to weigh themselves.

Re:The Kilogram is not losing weight

[pipingguy]

Usually it's 14.7 psig (0 psia) @ 70 degrees F.

Re:The Kilogram is not losing weight

[azenpunk]

of course not, well not in the metric system. the kilogram still weighs the same number of newtons...but it's weighing less in pounds. i wonder what this will do to the famed columbian/english cocaine cartels?

Re:The Kilogram is not losing weight

[azenpunk]

we need to have a 'pendantic olympics'. the top prize would be a kick in the teeth. here goes my performance: water itself is not pure H2O, since the term water predates the knowledge of the chemical formula, however even the empirical formula for water comes out to H2O (assuming the only ions present are H3O+ {there's never really any naked protons in solution, top that!} and OH-, no sodium ions or chloride or anything like that). scores: 4.7, 4.6, 4.1, 1.6 (french judge), 4.4, 4.6 totaling: 24.0, er...23.99999999 if we're going by the metric standard.

Re:The Kilogram is not losing weight

[gardyloo]

My god! How can you have left out mention of isotopes and virtual particles? Maybe some mention of absolute zero? (since E~mc^2, if you add energy in the form of heat, the mass actually goes up). Geez.

Re:The Kilogram is not losing weight

[jmv]

It will be some mixture of H2O, H+ and O-- ions.

I really doubt you'll see O-- ions in water. H2O actually splits into H+ and OH- and the H+ often ends up (IIRC) forming an H3O+ ion.

Re:The Kilogram is not losing weight

[Watson Ladd]

No, we all *mass* the same. The kilogram is not a Newton.

Re:The Kilogram is not losing weight

[The One and Only]

There's currently a project (which was reported on Slashdot months ago) to make a new reference kilogram of a specific element and geometry. From that, they can define the kilogram as a certain number of atoms of a certain element.

Re:The Kilogram is not losing weight

[fractoid]

Gases are the liquid with varying density. <pedant>Actually, gases are a fluid, as are liquids. Gases are not liquids.</pedant> Also, as others have pointed out, water's density is invariant wrt. pressure, not temperature, otherwise there would be no convective currents in water. Water is densest at 4 degrees Centigrade and, due to some weirdness involving Van der Waal's force, actually gets less dense as it cools below that point.

Re:The Kilogram is not losing weight

[Guppy06]

"water is essentially invariant to pressure."

If "essentially" were good enough, we wouldn't be using platinum-iridium.

Re:The Kilogram is not losing weight

[Ticklemonster]

Oh no! It's man made global gravity loss!!! Quick, someone call Al! No weight, I mean wait, he'll never lose wait, I mean weight.

Re:The Kilogram is not losing weight

[Guppy06]

"You could specify the density of water at $PRESSURE and at its maximum density (somewhere around 4 C)."

Self-referential. Pressure is (force)/(length^2), or breaking it down further, (mass)/[(time^2)(length)]. This is why BIPM abandoned the "cubic deciliter of water" definition in favor of the current platinum-iridium artifact (less compressible, less affected by temperature, etc).

"The only problem with doing this for high-precision measurements is: what is water? Some fraction of the hydrogen will be deuterium, and that'll throw off the density. What fraction of the hydrogen should be deuterium for "standard water"?"

Not an issue, as the average rates of naturally occurring isotopes in the universe is already known (hence the non-integer masses in periodic tables). You'd have a greater problem establishing the purity of the water sample in question, at least if you insist on using it in its liquid state; they don't call it the "universal solvent" for nothing.

Re:The Kilogram is not losing weight

[jollyreaper]

That's one reason we are trying to make a perfect sphere to replace the reference kilogram. Then we will have a definition of the kilogram in terms of number of silicon atoms. Good luck on that. This reference bar is certainly worse than we've sphered.

Re:The Kilogram is not losing weight

[loshwomp]

we need to have a 'pendantic olympics'

Oooh, can I compete? I guess for starters I'll point out that the word you're looking for is 'pedantic'.

Re:The Kilogram is not losing weight

[neoform]

That must be it, the scientists that own the cube must have forgotten about the whole temperature dealy.

Re:The Kilogram is not losing weight

[Guppy06]

"We can't use water as a reference since the molecules in the water are constantly splitting into ions and reforming as molecules."

OK, exactly how far up your ass did you have to reach to pull that one out?

See, we have this thing called "The First Law of Thermodynamics." At the molecular scale, water molecules don't just decide to break up and go their own way willy-nilly, not the least because both elements involved (hydrogen and oxygen) really don't like being alone (the two hydrogen atoms can go off on their own merry way as a diatomic molecule, but the oxygen will be lonely). Breaking molecular bonds in water takes energy, otherwise cracking water to produce hydrogen would be more cost-effective than cracking methanol (the carbon atoms have a more independent personality and are better able to get over any rejection issues it might have).

Beyond that, even if the energy to crack an individual water molecule were as trivially small as you believe, the energy would have to come from somewhere. Cracking water is endothermic, but so is making it (oxygen atoms, at least, need to be pried apart against their will first, assuming they're not in some kinky threeway), but even if one of those two reactions was exothermic, the energy required to do one act must necessarily equal the energy released by the other, meaning a net change in energy, and a net change in the number of water molecules, of zero.

The real reasons we don't use water are:

1. Corrosiveness (which you already covered)
2. Compressibility (there is no such thing as an incompressible substance, but liquids are more susceptible than solids)
3. Thermal expansion (something else solids are less susceptible to)
4. Last, but not least: evaporation

"So it is essentially impossible to get 1000 cm^3 of "pure" water."

Very easy, actually; the problem is maintaining its purity after it cools down from superheated steam.

"That's one reason we are trying to make a perfect sphere to replace the reference kilogram. "

Actually, there are a number of different proposals. One involves fixing the Avogadro constant as you say, but the other involves basing mass in terms of an electrical current through a device called a watt balance, which would reverse the current relationship between mass and electric current.

Re:The Kilogram is not losing weight

[Anonymous Coward]

Just to be clear, since it's not obvious anyone has spelled it out: liquids, including water, do have a compressibility with respect to pressure. They are not invariant.

http://en.wikipedia.org/wiki/Water_(molecule)#Compressibility

Re:The Kilogram is not losing weight

[Guppy06]

"One would think it'll still be a better reference than a chunk of rusty metal kept under lock."

They tried that. But water evaporates, dissolves things, is grossly susceptible to thermal expansion, and is far more susceptible to compression by atmospheric pressure. And don't forget that anything that alters its density also alters its buoyancy in the atmosphere.

Far better to find a substance like platinum-iridium (or even stainless steel) that doesn't corrode appreciably over the course of decades. The "cubic decimeter of water" definition was precise enough until the world industrialized and precision was required for manufacturing.

"if your scales show weight X on empty container (never mind what it is)"

Uh, no, I very much mind what it is. I need to know the container's density in order to adjust for atmospheric buoyancy. Unless you want to try to measure this liquid water in a vacuum...

Re:The Kilogram is not losing weight

[camperdave]

Unless he wants to enter the jewelry dangling event.

Re:The Kilogram is not losing weight

[iocat]

This is why we need to continue to use the English system. The metric system seems all orderly, till you realize the core definitions are based on lame french stuff. In my world, a mile is a mile, based on my Nike+iPod telling me I have gone a mile (ideally backed up with Lance Armstrong or that English chick congratulating me). A yard is the distance between King George's nose and the tip of his finger. A foot is 12 inches. And a pound is what my scale tells me I have too many of.

Anyway, I measure most things in Smoots.

Re:The Kilogram is not losing weight

[fatmal]

we need to have a 'pendantic olympics'.

Actually, it would be 'Pedant Olympics'

Re:The Kilogram is not losing weight

[camperdave]

Silly Americans... Your pounds are defined in terms of the kilogram.

The international avoirdupois pound is equal to exactly 453.59237 grams. The definition of the international pound was agreed by the United States and countries of the Commonwealth of Nations in 1958.

Wikipedia

Re:The Kilogram is not losing weight

[Eiron]

Because a Newton is fruit and cake?

Re:The Kilogram is not losing weight

[g-san]

Good thing we don't use those meters to send space probes to Mars... oh wait.

Re:The Kilogram is not losing weight

[OakDragon]

See, we have this thing called "The First Law of Thermodynamics."

And in this house, we obey the laws of thermodynamics!

Re:The Kilogram is not losing weight

[amper]

we need to have a 'pendantic olympics'. the top prize would be a kick in the teeth....totaling: 24.0, er...23.99999999 if we're going by the metric standard.

Oh, for Dog's sake, *please* do not start up the 0.9999...=1 argument again!

Re:The Kilogram is not losing weight

[azenpunk]

no, i have a cold.

Re:The Kilogram is not losing weight

[bcat24]

Why not? It's always so much fun!

Re:The Kilogram is not losing weight

[shinghei]

Guys, chill out. Read the title...it's just a "prototype"!

Re:The Kilogram is not losing weight

[azenpunk]

the original plan for the eiffel tower was to use as a framework to cover with dirt, creating a large and very steep manmade hill on that meridian, adding 0.278 miles to the length of the meridian through paris. well, they are french after all.

Re:The Kilogram is not losing weight

[azenpunk]

4.3, 4.8, 5.1, 2.1 (frenchie again), 5.0 3.9

Re:The Kilogram is not losing weight

[zxsqkty]

Similarly, a kilogram is a useful weight about the same size as a pound.

1kg = 2.2lbs

Re:The Kilogram is not losing weight

[gomiam]

Remember this useless thing called pH, used for measuring acidity and basicity? You may remember that the neutral point is 7, the pH of pure water at 25 degrees Celsius, when the amounts of H3O+ and OH- are almost equal (yes, those ions exist even in pure liquid water). See this for more information. Thermodynamics is all right but some of its laws get quirky at sufficiently small distances.

Re:The Kilogram is not losing weight

[Detritus]

A major problem is that water is composed of a number of hydrogen and oxygen isotopes. The proportions of these isotopes varies depending on where you collect the water. While very useful for scientists, it means that the weight of a given volume of water is not a constant.

Re:The Kilogram is not losing weight

[poopdeville]

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.

This gets really hard to think about if you try to think about it in depth. It's defined to be 1 kg exactly. A unit of mass. But the Newton is a derived unit, linear in mass. So the reference kilogram isn't feeling less of a force from gravity.

On the other hand, the "amount of matter" in the reference kilogram has decreased. From which one can conclude that mass is not a measure of the amount of matter, but of something closely related. What does this mean for the law of conservation of mass?

Re:The Kilogram is not losing weight

[FrangoAssado]

Not an issue, as the average rates of naturally occurring isotopes in the universe is already known (hence the non-integer masses in periodic tables).

Just a small nitpick: that's not the only reason for non-integer masses in periodic tables. When neutrons and protons come together in an atom nucleus, their mass change, and a corresponding amount of energy (E=m*c^2) is released or absorbed. For example, while the atomic mass of Carbon-12 is 12, the atomic mass of Hydrogen-1 (only one proton) is a little over 1.

In effect, that's how nuclear bombs work: when the nucleus of an atom of plutonium breaks up, the mass of the resulting pieces is less than the mass of the original nucleus; the difference is released as radiation and heat.

Re:The Kilogram is not losing weight

[Guppy06]

"Thermodynamics is all right but some of its laws get quirky at sufficiently small distances."

Not the first law and certainly not at the scale of a cubic decimeter of water (meaning ~3 x 10^22 water molecules). Without a net change of energy in the water sample to or from an outside source, conservation of energy dictates that one endothermic dissociation of a molecule must be countered by one exothermic combination of a molecule elsewhere in the system. The reason pH has to be defined based on a fixed temperature to begin with is because of what "temperature" is: a measure of the average kinetic energy of the molecules involved. A change in the activity of the molecules in the water sample, a change in its temperature, would require a change of the energy in a water sample, at which point you'd be more concerned with thermal expansion. So long as the temperature is constant, so is the dissociation constant (the ratio of free ions to water molecules).

Re:The Kilogram is not losing weight

[or-switch]

Except that it doesn't matter if it varies or not. Standard Temperature and Pressure (STP) is well defined as 25 degrees C and 1 atmosphere of pressure. There can be precisely controlled. But people who work in the standards groups will always want a solid physical reference that doesn't (or at least shouldn't) vary. The guy overeacted when he said, "Oh no, this could have ramifications for everything including such things as power generation). I doubt a powerstation has any mass measuring system that is precise to 50 ug out of and object weighing 1000000000 ug. Except for the instruments at places like the national institute of standards, very little else has this kind of precision so until it loses something like a whole gram it isn't going ot have a practical consequence.

Re:The Kilogram is not losing weight

[Walt Dismal]

Actually, the present administration, with its superb sense of science, has based the kilogram on the value of the dollar. In simple terms, this means we will all soon be weightless.

Re:The Kilogram is not losing weight

[zippthorne]

Ok, but how would that change the mass

Re:The Kilogram is not losing weight

[Anonymous Coward]

The key point, of course, is that it is fundamnetaly different to the meridian at Greenwich.

Note that the French are fighting back, with the new requirement to call GMT UCT. Fight for real Greenwich Time!

Re:The Kilogram is not losing weight

[KiloByte]

Anyway, I measure most things in Smoots. Are you sure your reference artifact has remained exactly the same height after all these years?
And is he preserved well enough? What will happen to your definition when he dies? Are you going to pull a Lenin?

Re:The Kilogram is not losing weight

[johny42]

He meant (10 cm).

Re:The Kilogram is not losing weight

[teh kurisu]

The problem with the definition of the kilogram is that it depends on a physical object in France.

The problem with the definition of the gallon is that it depends on which side of the Atlantic you are on.

Re:The Kilogram is not losing weight

[johny42]

(10 cm)^2. Sorry, I don't know why the ^2 sign didn't show up in my previous comment.

Re:The Kilogram is not losing weight

[Anonymous Coward]

(10cm)^3, just for the sake of oneupmanship

Re:The Kilogram is not losing weight

[thsths]

> A yard is the distance between King George's nose and the tip of his finger.

Wouldn't you have a rather hard time convincing King George to lift his arm?

Re:The Kilogram is not losing weight

[Bender Unit 22]

Ah, the comments here are a good example of why I prefer /. to digg. :D

Re:The Kilogram is not losing weight

[locofungus]

much as a pint of water weighs a pound (the world around, and takes 1 BTU to raise temperature by 1 degree F).

You've got a strange definition of world there.

On this side of the pond:
"A pint of water weighs a pound and a quarter"

I'm ashamed to have to say that it appears the majority of my countrymen would prefer to use "fundamental" units that have rhyming mnemonics rather than units that make all the calculations simple and consistent across the world.

http://news.bbc.co.uk/1/hi/uk/6637587.stm

Tim.

Re:The Kilogram is not losing weight

[Anonymous Coward]

It will affect the volume of the whole system. Once you think you have 1 litre of water, some recombinations occur, and your volume increases. This makes it hard to get (or define) exactly 1 litre of water.

Re:The Kilogram is not losing weight

[edittard]

Which metal? Lead, uranium, polonium ... well we can hope, can't we?

Re:The Kilogram is not losing weight

[Moderatbastard]

I don't know why the ^2 sign didn't show up

Maybe the system's smart enough to know the difference between area and volume?

Re:The Kilogram is not losing weight

[Kuad]

No, the real problem is that 1L of H20 is equal to one kilogram only at its most dense temperature (roughly 4C) and at one atmosphere of pressure. Which is where the problem lies - you need a standard kilogram in order to have units of pressure. A Pascal is 1N/m2, and 1N is 1kg.m/s2.

You can't define the kilogram in terms of a "standard" litre of water, because you need the kilogram defined in order to have the proper amount of water.

Re:The Kilogram is not losing weight

[jeffstar]

where are my mod points when i need them! use them or lose them my ass

Re:The Kilogram is not losing weight

[Moderatbastard]

It will be some mixture of H2O, H+ and O-- ions.

There are no 0-- ions in water. Or H+, for that matter. It's H30+ and OH-.

Re:The Kilogram is not losing weight

[Anonymous Coward]

The problem with the Imperial system is that the core definitions are based on lame English stuff like the foot being the length of 36 ears of barleycorn ignoring the fact that barleycorn has increased in size by 15%.

Re:The Kilogram is not losing weight

[Anonymous Coward]

> the English system

Please don't call it the "English" system. Here in England, we do most things in metric; and when we do use old units, most of them are not the same as the ones that you use. (Stones, yards, pints, gallons, cups....)

Re:The Kilogram is not losing weight

[gomiam]

Ermm... I'm just correcting your notion about water having no H3O+ and OH- ions while liquid. It has. No need to read anything else into it.

By the way, switching scales as it suits you is not a good debate method. You started talking about molecules here, not cubic decimeters of anything. And at the molecular level, Brownian movements can provide energy enough to break a few links. You said:

At the molecular scale, water molecules don't just decide to break up and go their own way willy-nilly...

At the molecular scale, some water molecules actually just break up because they got hit, moved and stretched in the right way, and no one bats an eye. And again, I'm not saying the post you answer to is right, because it isn't: not all water is breaking and recreating bonds. Just a tiny part of it.

Re:The Kilogram is not losing weight

[Bloke down the pub]

The question isn't about which system of measures is better, it's about whether a bunch of unelected bureaucrats have the right to interfere in other people's business.

If people, particularly the elderly, want to shop in units that they understand, why shouldn't they? Don't we believe in consumer choice? Half a litre of beer just doen't feel right. Trust me, I've made a study of these things.

From TFA:

We are trying to put ourselves forward as a modern country putting our imperial past in perspective, like slavery, and here we are glorifying one element of it
Roz Denny, UK Metric Association

Political correctness gone mad.

Re:The Kilogram is not losing weight

[RockDoctor]

I think you mean that the density of water is essentially invariant to pressure.
It very much fluctuates with temperature.

It (the density of water) fluctuates noticeably under industrially-used pressures too. It's not as big a variation as other common variations (e.g. changes due to gas bubbles going into true solution instead of just shrinking), but the compressibility of water is something that you have to pay attention to when interpreting the results of pressure tests of anything much above 10,000 psi, so it's normally included in the interpretation of any non-trivial pressure tests.
For example, you know :

• the approximate volume of your pressure vessel, and
• the pressure-volume relation for the whole system including flexible lines between pump and vessel.

So that you can calculate how much volume you expect to pump to test to $TEST-PRESSURE, you also need to correct for the compressibility of the water you use for the test.
If you

• pump much less before reaching $TEST-PRESSURE, then there's something wrong;
• much more, then something somewhere is leaking, or over-stretching and you need to continue the test to find the problem;
• pump the calculated volume to get to $TEST-PRESSURE but then need to continue pumping to maintain $TEST-PRESSURE, then you've got a leak;
• and if the volume you bleed-off on returning from $TEST-PRESSURE to ambient is less than you pumped, then you've pushed something beyond it's elastic limit and need to investigate.

Pressure testing isn't as simple as pressing your tyre gauge to the tyre valve.

Re:The Kilogram is not losing weight

[makapuf]

In fact IIRC the definition didn't refer to a specific meridian and neither equator because any country has its OWN meridian, addind to the universality of the definition (which has a main motive then).

Re:The Kilogram is not losing weight

[had3l]

Erm, no one was talking about actually getting 10 square centimeters of water, putting in a container and coming up with the kilogram.

If you can define that 10 square centimeters of water at X degrees and at X air pressure is equivalent to 1 kilogram, you can establish through a few simple calculations, how much is a kilogram, without ever having to weight anything.

Re:The Kilogram is not losing weight

[Ferzerp]

I agree, but I was just correcting the claim that temperature didn't affect water density. I was just pointing out they were thinking about pressure which really doesn't affect it much. But you are correct, it DOES affect it. and as others have said, pressure involves mass, so you could never, ever use something like that for setting a kg standard.

I was not advocating using water ;) That would be nuts.

Re:The Kilogram is not losing weight

[Mr. Underbridge]

There's currently a project (which was reported on Slashdot months ago) to make a new reference kilogram of a specific element and geometry. From that, they can define the kilogram as a certain number of atoms of a certain element.

Relativistic effects? Me no likey.

Re:The Kilogram is not losing weight

[Ferzerp]

Yes, it does.

but not like it does with temperature, and I was trying to just correct the original mistake :)

Re:The Kilogram is not losing weight

[pimpimpim]

The funny thing is, in Holland we call chemistry, physics, and math 'exact sciences' (exacte wetenschappen). Apart from math, this is quite far from the truth. Chemistry stops at the 3rd digit and physics is, as you say more a scaling science: if it is not ten times as big, it's the same.

Re:The Kilogram is not losing weight

[Chris Burke]

Since gravitational acceleration isn't changing either, we all weight the same too.

Re:The Kilogram is not losing weight

[Anonymous Coward]

See, we have this thing called "The First Law of Thermodynamics." At the molecular scale, water molecules don't just decide to break up and go their own way willy-nilly, not the least because both elements involved (hydrogen and oxygen) really don't like being alone (the two hydrogen atoms can go off on their own merry way as a diatomic molecule, but the oxygen will be lonely). Breaking molecular bonds in water takes energy,

Can someone please mod this fishy statement down? Not only does our friend here seem to think that we're talking about water dissociating into H2 and O2 rather than H3O+ and OH-, but it sounds like he'd be quite shocked to learn that the world is not sitting around at absolute zero! There's plenty of energy available at room temperature for all sorts of reactions to occur in small quantities. Remember that temperature only represents the _average_ kinetic energy of a system -- some small number of molecules will gain enough energy through interactions with other molecules (while other molecules lose energy, keeping the average intact) to undergo a reaction which is not spontaneous in general at room temperature.

Re:The Kilogram is not losing weight

[Chris Burke]

Man, don't give me that, going by the mods is why I made my pedantic reply when the OP was modded +1 Insightful.

Also your implication that fact correction is sometimes unnecessary goes against everything I've learned on /.

Re:The Kilogram is not losing weight

[superiority]

2H2O ==> H3O+ + OH-
H3O+ + OH- ==> 2H2O
The enthalpy change of the one reaction is the negative of the other, so there is no net change in energy. GP pulled it out of basic chemistry, not his ass.

Re:The Kilogram is not losing weight

[locofungus]

The "metric martyrs" got into trouble because they _refused_ to sell using metric units.

There's absolutely no problem about a butcher selling a "pound of steak" to someone who asks for it (although the receipt will have to show 454g).

But

"If people, particularly the young who have never been taught pounds and inches, want to shop in units that they understand, why shouldn't they?"

Is what the "metric martyrs" want to prevent.

Tim.

Re:The Kilogram is not losing weight

[superiority]

No, they define the kilogram. The kilogram is the base unit, but prefixes are applied to the derived unit 'gram', and a gram is defined as one thousandth of a kilogram. Although I believe you are correct in that when the metric system was created, the gram was the base unit of mass, based on the mass of water.

Re:The Kilogram is not losing weight

[Anonymous Coward]

H2O actually behaves as if it splits into H+ and OH- ...

Fixed that for you.

... and the H+ often ends up (IIRC) forming an H3O+ ion.

Maybe.

It turns out that water is pretty slippery stuff, and even though we know its empirical formula very well, we don't really know that much about its packing behavior under different conditions. The H3O+ ion is probably grossly oversimplified, as is OH- ion. Complexes like H9O4+ and H7O4- might be quite common, and might actually dominate the sample under some conditions.

Part of the problem is that water is a strong candidate for the Most Reactive Substance Ever Award. So much so that it is really quite hard to obtain a sample of pure water, and very hard to verify that a sample is pure, and extremely hard to store that sample in a way that assures its continued purity.

[While everything said above is true for any given value of truthiness, this post is also a candidate for the Pedantry Award].

Re:The Kilogram is not losing weight

[rkww]

> I think you meant 1 cubic decimeter

that is, a cube 10cm per side. 10x10x10 = 1000 cubic centimeters = 1 litre

The reference mass in Paris is notionally equivalent to the mass of a liter of water at it's maximum density. In fact due to errors in establishing the true maximum density it's out by about 25ppm.

If you define a kg as the reference mass in Paris, pure water at STP has a density of 0.998.23 g/cm3; seawater is around 1.025 g/cm3.

See wikipedia for more details.

Re:The Kilogram is not losing weight

[Anonymous Coward]

Just a suggestion: Perhaps the continental plate that the country (and I use that term loosely!) France is on could have moved upward a few centimeters since the last measurement. This should effect the distance to the centre of the Earth therefore, essentially effecting the measurement of the weight of the Kilo standard ever so slightly...

Haven't done the hard math to see if the amount of lift possible would be plausible to account for the loss...I'm at work and have actual "work things' to do...

Re:The Kilogram is not losing weight

[Anonymous Coward]

See, we have this thing called "The First Law of Thermodynamics." And in this house, we obey the laws of thermodynamics!

Except we fudge at the quantum level.

And for any quantity of water, we've got to include the fudge factor to model its behavior when something like NaCl is added. Water behaves as if a small fraction of it is always dissociated into its constituent ions.

Re:The Kilogram is not losing weight

[Mr2cents]

It will be some mixture of H2O, H+ and O-- ions. That should be: H+ and OH- ions. (H+ -> acid, like in HCl, OH- -> base, like in NaOH).

Re:The Kilogram is not losing weight

[otter42]

OK, exactly how far up your ass did you have to reach to pull that one out?

See, we have this thing called "The First Law of Thermodynamics." At the molecular scale, water molecules don't just decide to break up and go their own way willy-nilly, not the least because both elements involved (hydrogen and oxygen) really don't like being alone (the two hydrogen atoms can go off on their own merry way as a diatomic molecule, but the oxygen will be lonely). Breaking molecular bonds in water takes energy, otherwise cracking water to produce hydrogen would be more cost-effective than cracking methanol (the carbon atoms have a more independent personality and are better able to get over any rejection issues it might have).

Trolling hogwash. On a molecular scale, molecules of water most certainly do break up. It takes a certain amount of energy, of course, but that energy is freely provided by stray molecules that have much more free energy than the average. What you're claiming is akin to saying that evaporation doesn't exist when water isn't at 100C. It does exist, just not so much of it. There's no law of thermodynamics that says that pure water won't boil at 20Cat 1atm, it's just the statistical probability that shows that the odds are so astronomic we can effectively assume, for all intents and purposes, that it won't.

Don't apply macro thermodynamic laws to individual molecules. They only apply to systems. If you want to understand this better, I suggest studying statistical thermodynamics, which give a much better understanding. And as long as you're going to be wrong, you could at least be polite about it. Sheesh...

Re:The Kilogram is not losing weight

[Entropius]

... and as far as I can tell the math people don't even know what a "measurement" is.

Re:The Kilogram is not losing weight

[Anonymous Coward]

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

Does silicon have no different isotopes to make this definition vague?

Why can't we define mass unit as multiple rest mass of electron, or multiple of equivalent mass ( h/(lambda*C) ) of a single quant of "the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" (shamelessly copied from definition of a second)?

Re:The Kilogram is not losing weight

[smellsofbikes]

To be more precise, in 1866 the US officially designated the Metric System as a legal system for weights and measures in commerce -- the only system that Congress has ever approved (although it has tacitly approved the Imperal system) and the decision to base the Imperial system on the Metric System was made in 1893, known as the Mendenhall Order

Re:The Kilogram is not losing weight

[rk]

I don't get the love affair with the metric system for everything. For scientific and engineering computation, sure, it's great, and you can take the metric system from me when you pry my meter stick from my cold (293K at room temperature) dead (BP: 0 mmHg) hands.

For a lot of every day stuff, working in a system that only has the prime factors 2 and 5 between its units can be a real pain. A lot of the traditional units of measure have 3 in the prime factorization of their conversion factors and that makes many things easier to think about. I occasionally do woodworking projects and (for me anyway) it's a lot simpler to work in traditional units, largely because you can divide quickly. Example: I have a one yard board I want to hang five hooks on, evenly spaced. Where do the hooks go? Reflexively, in English units, I can say six inches apart. In metric, I have a one meter board I want to hang five hooks on, evenly spaced. Where do the hooks go? I had to think about it for a second or two before I arrived at ~167 mm. And I'm better than most at doing arithmetic in my head.

Re:The Kilogram is not losing weight

[kbielefe]

Of course government has a compelling interest in establishing standards of weight and measure. On the other hand, you make a very good point that there is little reason that a government can't maintain two different sets.

Sometimes, people have the impression that Americans don't use the metric system. Nothing could be further from the truth. Science, engineering, and medicine use the metric system extensively. However, our government seems to have caught on that humans might be able to use both systems for different purposes.

Even non-scientists here use the metric system when it is appropriate. For example, my wife keeps our kitchen scale set to grams, because that's how our daughter's medicine is measured. She also has no problem measuring in milliliters, and knows that a milliliter of water is the same as a cubic centimeter and weighs 1 gram.

On the other hand, she has no idea how many milliliters are in a teaspoon, even though she uses both units extensively. She has no need to know.

Re:The Kilogram is not losing weight

[Guppy06]

"(while other molecules lose energy, keeping the average intact)"

Exactly. If the amount of energy in a water sample is fixed, if the temperature is constant, then so is the number of dissociated water molecules within the water sample at any given time.

Re:The Kilogram is not losing weight

[nairnr]

Problem is you are using a example of something that is intrinsicly in your set of units. You want to subdivide a yard. And if you had something a meter long divided into 5 you would have them 20cm apart. Housing and construction is mostly imperial, but there is a suprising amount of metric. Last time I had a house built, the sizing was imperial, but all of the window sizes where metric.

Re:The Kilogram is not losing weight

[operagost]

I never have mod points when I need them.

Re:The Kilogram is not losing weight

[Guppy06]

"On a molecular scale, molecules of water most certainly do break up."

Not without interacting with something else (e. g. other water molecules).

"It takes a certain amount of energy, of course, but that energy is freely provided by stray molecules that have much more free energy than the average."

And those "stray" molecules lose energy in the process, maintaining a constant net energy in the system. As I pointed out in the next paragraph, with no change in energy in the system, the number of whole water molecules in your sample must necessarily be constant; they may not always be the same molecules, but the number is the same, maintaining a constant volume (absent all other factors).

"Don't apply macro thermodynamic laws to individual molecules. They only apply to systems."

Don't pretend that energy isn't conserved when dealing with individual molecules. The First Law still applies even at quantum scales.

"And as long as you're going to be wrong, you could at least be polite about it."

The specific charge I was answering was that water was an improper mass standard due to dissociation, suggesting that the volume of a water sample at a constant temperature not only fluctuates because of it (it doesn't, as the dissociation constant is just that), but fluctuates beyond acceptable tolerances, implying it was of a similar to or greater than the scale of the change in density caused by solution. Four moderators thought this was correct (and none so far have found it incorrect), giving the parent a wider audience to spread this misinformation to. Being polite, respectful, civil, etc. does not get the attention required to correct such mistakes in the minds of others.

Now, my being "impolite" can introduce other problems that hinder understanding (your visceral reaction to one paragraph apparently prevented you from reading others), but I'm not going to apologize for my tone if it gets people going in the right direction towards a better understanding.

Re:The Kilogram is not losing weight

[ramk13]

""We can't use water as a reference since the molecules in the water are constantly splitting into ions and reforming as molecules."

OK, exactly how far up your ass did you have to reach to pull that one out?

See, we have this thing called "The First Law of Thermodynamics." At the molecular scale, water molecules don't just decide to break up and go their own way willy-nilly, not the least because both elements involved (hydrogen and oxygen) really don't like being alone (the two hydrogen atoms can go off on their own merry way as a diatomic molecule, but the oxygen will be lonely). Breaking molecular bonds in water takes energy, otherwise cracking water to produce hydrogen would be more cost-effective than cracking methanol (the carbon atoms have a more independent personality and are better able to get over any rejection issues it might have).

Beyond that, even if the energy to crack an individual water molecule were as trivially small as you believe, the energy would have to come from somewhere. Cracking water is endothermic, but so is making it (oxygen atoms, at least, need to be pried apart against their will first, assuming they're not in some kinky threeway), but even if one of those two reactions was exothermic, the energy required to do one act must necessarily equal the energy released by the other, meaning a net change in energy, and a net change in the number of water molecules, of zero."

First, I'm with you for the most part on your listing of reasons as to why water isn't a good reference standard, but there's no need to insult the OP, especially since he or she is not totally wrong.

Water molecules do 'just decide to break up and go their own way willy-nilly.' It's dynamic equilbrium:

H2O H+ + OH-

So the forward rate of dissociation is equal to the reverse rate of recombination at equilibrium. So at any given time there are tons of water molecules 'just' dissociating. You're right that the net rate of reaction as written is zero, which is why it's called equilibrium. But the reactions are still happening. You even sort of say this in the next paragraph.

Also two protons (not hydrogen atoms) can't go off and form their own hydrogen molecule, because they are missing something important...two electrons which are still hanging out with the two OH- ions. You can reduce the H+ to H(0) and then if those two H(0) are really close to each other (i.e. at the surface of a catalyst) or if there is a really high concentration of them, then they'll form hydrogen. The original poster's comment had nothing to do with 'cracking water' anyway, so I don't know why it was brought into the discussion.

Also it can't be that 'cracking water' and forming water are both endothermic reactions. If they are the reverse of each other, then the change in enthalpy of one is the negative change of enthalpy in the other. (Just as you say in your next sentence) Maybe you mean forming water has an activation energy which has to be overcome for the reaction to start? But that has nothing to do with the original poster's comment either.

Also you say the problem is maintaining the purity of water after it cools from steam. Well, isn't that the point?? Who cares about pure steam - it isn't water.

There's just no need to jump on the original poster about being wrong in a condescending tone, when in fact, he/she wasn't really that wrong and then follow that up with an explanation filled with inaccuracies. Bottom line is "molecules in the water are constantly splitting into ions and reforming as molecules." That's a fact.

Re:The Kilogram is not losing weight

[dedalus2000]

Well at least we can all agree on a pint... even if we then argue about it's volume.

Re:The Kilogram is not losing weight

[oopsdude]

You scare me a little, because of how knowledgeable you seem to a layman and yet how wrong you are. At the molecular scale, water molecules don't just decide to break up and go their own way willy-nilly... Yes, they do, and it's called equilibrium. This probably the most fundamental concept of high school chemistry. Water molecules continually break into H+ and OH- ions and reform themselves from those ions. You'll find that when perfect equilibrium is reached, the product of their molarities (that's the moles solute per liter solvent) is 10^-7. That's where we get the neutral pH 7 from. Look it up here. Fascinating stuff.

...not the least because both elements involved (hydrogen and oxygen) really don't like being alone (the two hydrogen atoms can go off on their own merry way as a diatomic molecule, but the oxygen will be lonely).

Please stop pretending to know what you're talking about; you clearly have no concept of even ionic bonding. Water would never split that way unless you run a hydrolysis reaction (running an electric current through the water). Water ALWAYS splits into H+ and OH- ions. Read that sentence again; it's important. They are IONIC BONDS. You seem to think they are covalent. When water dissociates (that means splits, see equilibrium above), those ions HAVE to stay in solution. H+ DOES NOT bond with another H+ to form H2. Neither does the oxygen.

Breaking molecular bonds in water takes energy

Really? Then why does salt dissolve in water? EQUILIBRIUM.

Cracking water is endothermic, but so is making it AARGH. Then water would not exist! The heat of formation is ALWAYS the opposite of the heat of decomposition. Please, I'm begging you, take a chemistry course. Your sophomore one does not count, but you obviously slept through it anyway.

and a net change in the number of water molecules, of zero. YES! Good job! That's perfect equilibrium. The grandparent had the right idea about equilibrium, although he failed to realize that since there is a net change of zero, the mass also does not change. Ions do not leave solution, nor does their mass magically disappear.

Corrosiveness

Mr. McGuire: I want to say one word to you. Just one word.
Benjamin: Yes, sir.
Mr. McGuire: Are you listening?
Benjamin: Yes, I am.
Mr. McGuire: Plastics.

Compressibility

This is a fundamental property of water - it is INCOMPRESSIBLE. See here. You know nothing about chemistry. Stop, stop, stop.

Last, but not least: evaporation

Last, but not least: sealed container.

Very easy, actually; the problem is maintaining its purity after it cools down from superheated steam.

Solutes dissolve MORE in superheated water.

I don't know who you are. I don't know much about you. But I do know that you know nothing about chemistry. I know this is /., but STOP. STOP. STOP. People might actually believe you.

Re:The Kilogram is not losing weight

[khallow]

The "pendantic gambit" wins again. For you sports fans who missed it, here's the strategy:

1. Player A dumps an utterly pendantic post. Misspell pendantic deliberately.

2. Player B comes around and notes "Hey, it's spelled p-e-d-a-n-t-i-c."

3. Player B gets kicked in teeth.

Re:The Kilogram is not losing weight

[Anonymous Coward]

pure water at STP has a density of 0.998.23 g/cm3
0.998.23 g/cm3, eh? That's one weird number? ;-)

Re:The Kilogram is not losing weight

[Anonymous Coward]

Why do you wish her such ill? Hasn't she already suffered enough at the hands of Paris Hilton (and also, whomever decided it would be a good idea to name a girl after a famously adulterous Greek man)

Re:The Kilogram is not losing weight

[snowgirl]

Although I believe you are correct in that when the metric system was created, the gram was the base unit of mass, based on the mass of water.

That's what I intended to say... that back when the metric system was created. I mean, I talked about how the meter was some simple factor of an earthen geometry... they obviously don't define it that way anymore!

And yes, now they use as the reference mass the kilogram... otherwise they wouldn't have the "true kilogram artifact" which is apparently losing weight.

Re:The Kilogram is not losing weight

[snowgirl]

<pedant>Actually, gases are a fluid, as are liquids. Gases are not liquids.</pedant>

DOH! :( I guess that's why you're supposed to code review everything. You're right, s/the liquid/the fluid/.

And thanks for the information that density of water changes with temperature... I guess that's why we switched to using mercury for thermometers, less variance of density.

And I know about the weird hydrogens separating and introducing a less dense mass. I think it's pretty beneficial to our world that Ice floats... if it didn't, wow... we'd have weird problems to deal with...

Re:The Kilogram is not losing weight

[ar1550]

totaling: 24.0, er...23.99999999 if we're going by the metric standard I thought the SI defined metric, not Intel...

Re:The Kilogram is not losing weight

[Anonymous Coward]

Gases are the liquid with varying density. I think you mean Gases are the fluid with varying density. But liquids and solids also change density with changes in temperature and pressure (though to a much lesser degree).

Re:The Kilogram is not losing weight

[turbidostato]

"This makes it hard to get (or define) exactly 1 litre of water."

Not really. We have two problems here: one of definition and a different one of an operational reference. If we can come up with a valid definition, we can go with a "good enough" operational reference in hopes that our operational reference will be made up better as needs arises.

I.E.: We can define a kilogram to be an exact number of particles of a common enough material (probably for practical purpouses "particles" become "atoms", maybe mollecules, and "material" becomes "element", but there's no practical limits not to stick with water). We know Hydrogen to be quite common and simple, so why just not take the Avogadro's number and define the gram to be (6.024x10^23)/2 mollecules of H2 (isotope H1)? Or else, since Hydrogen is quite active, use the lightest noble gas instead (so it becomes (6.024x10^23)/4 atoms of Helium-2).

Of course, you come then to the problem of taking apart exactly (6.024x10^23)/4 atoms where exactly all of them are Helium-2 isotopes (no, the fact that the atoms may decay with time is not a problem, as long as you can "build" another kilogram afresh at any moment), but then you go with the "good enough" operational reference: If you are unable to currently get anything better than, say, (6.024x10^(23+-2))/4 Helium-2 99.99% pure, it means that for any practical usage you don't need any better either. And you can build a better operational reference as the need arises while the definition is still constant.

Re:The Kilogram is not losing weight

[turbidostato]

"Yeah, cause that meridian is so different to the rest _"

Yes, they are different enough, and since the ones effectively making the measures were French, they started out from Paris and then going North and South. It started as a quite local project: just laying out a better map of France (by the French for the French), nothing chauvinist here, but then it "outscaled", so to say and, again, nothing chauvinist here (just look at the so many USA "chauvinisms" on technological affairs, from ASCII-7 to flying altitude measured in feet) just common output from being the one effectively making the things happen at the time: every developed metropolis was engaded by the XVIII century on measure problems for very practical reasons (cartography and navigation); of course, English had "point zero" at London or Greenwich, French on Paris or Spanish on Madrid, Cadiz or Canary Islands at different times. Since French were the strong ones on the base-10 metric system, we got metre or kilogram defined over something Paris-based; since the English went to be the strongest metropoly by the XIX century (and USA being its cultural son), you get cartography based on Greenwich and navigational measures being feet and nautical miles; since Spain just lost the race, you get nothing but siesta based on Madrid, Cadiz or Canary Islands.

Re:The Kilogram is not losing weight

[turbidostato]

"Apart from math, this is quite far from the truth."

I'd say *including* math, not except from it. Chemistry or Physics are sciencies, but not so "exact". And then, Math, while quite exact is not a true "science".

Re:The Kilogram is not losing weight

[turbidostato]

While you are somehow right with the metric system not admiting number 3 so easily, you forget you don't need to be so precise when not needed.

I live on a "metric society" and I can assure you we don't have problems. On the butcher you will ask for a kilogram, half a kilogram, 100 grams, 150 grams, 200 grams, a quarter (250g) or even a "quarter and a half" (which being 250+125=375 grams comes "near enough" to be one third of a kilogram for this kind of practical purpouses).

But regarding woodworking or any other trades, I really doubt you really do in practice what you say. I don't know of anybody on the trade that would really divide any piece of raw material by adding measures: you will always end up adding measure errors on the farest end. You always do it by proportions, so errors get evenly distributed (of course, your average carpenter, or butcher or whatever won't know that, but still will apply some practical recipy that "just works" that probably will be based upon the "even error distribution" principle).

So, going to your example, even if you wanted to hang three hooks on a four meter wall (that makes for a very easy measure of hooking at 1, 2 and 3 exact meters from the beginning) you won't go to one end of the wall, take one meter, hook, take another, hook, take another hook, and then discover your last hook it's clearly out of place, but you'd go to the middle point, hook, then the middle to the right, then the middle to the left and you'll end up better even just by eye-metering.

When dividing by three (or any other odd number) you will see most of the times that disregarding if measuring on decimal or imperial units, people will go using the Thales Principle (projecting a known lenght segment over the one to divide) or the fact than an hexagon's side is exactly the lenght of the radius of the circunscribing circle, or the fact that a twelve units long rope (whatever the units are) will make for you a perfect square angle and will give you 3, 4 and 5 units long segments for free.

All in all, I'm used to the metrical system and I can tell its advantages outweight by faaaaaaaaaaar any minimal problems .

Re:The Kilogram is not losing weight

[LWATCDR]

funny I thought it was exactly the mass of 6.02x10^26 hydrogen atoms.

Re:The Kilogram is not losing weight

[jmv]

It turns out that water is pretty slippery stuff

Agreed. Especially when frozen :-)

Re:The Kilogram is not losing weight

[nwbvt]

The kilogram doesn't define the concept of mass, it merely measures it (imperfectly). Same with the Newton and the concept of force. Thus the force of the Earth's gravity on the Kilogram is qualitatively different, even if our imperfect measurements are incapable of quantifying it.

Re:The Kilogram is not losing weight

[poopdeville]

The kilogram doesn't define the concept of mass, it merely measures it (imperfectly). Same with the Newton and the concept of force. Thus the force of the Earth's gravity on the Kilogram is qualitatively different, even if our imperfect measurements are incapable of quantifying it.

You're going to have a very hard time explaining how the latter logically follows from the former (justifying your use of "thus" above). You might want to go the route of saying that Newton's Law of Universal Gravitation applies, but there's no logical reason to think that the process that affected the prototype didn't affect the rest of the planet as well.

From the SI: "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram." Note that the prototype kilogram has mass of exactly, to infinite precision, 1.0... kg by definition.

Mass is conceptually understood as the quantity of matter in an object or system. If the prototype kilogram contains less matter now than before, either the kilogram is not a measure of mass, or mass is fundamentally misunderstood.

By the way, in the sense of "taking a measurement", the kilogram does not measure mass. Scales or accelerometers do. This is an important distinction. Don't conflate the notions.

Re:The Kilogram is not losing weight

[nwbvt]

"You're going to have a very hard time explaining how the latter logically follows from the former (justifying your use of "thus" above)."

Only if the person I am trying to explain it to has trouble differentiating between qualitative and quantitative differences.

And for the record, not every statement made in a discussion on /. has to be a fully formed logical syllogism, so arguing whether or not every statement made "logically follows" from the previous one just demonstrates an inability to apply logical thinking to real world arguments.

"Mass is conceptually understood as the quantity of matter in an object or system. If the prototype kilogram contains less matter now than before, either the kilogram is not a measure of mass, or mass is fundamentally misunderstood."

No, its certainly a measure of mass, just not necessarily as precise of a measure as we previously thought. Just like paces are a measure of distance, but not a very precise one.

And before you go on some mythical "mass is fundamentally misunderstood" argument, remember that the only way we know of this issue is that the weight of the official Kilogram has gone down compared to the average weight of several unofficial Kilogram prototypes. This is not some universal phenomenon we are seeing, it is merely that differences have come up between very similar structures kept under very similar conditions. Strange, yes, but we certainly don't have to rewrite the laws of physics to explain it.

"By the way, in the sense of "taking a measurement", the kilogram does not measure mass. Scales or accelerometers do. This is an important distinction. Don't conflate the notions."

No, scales don't measure mass, the scientists taking the measurements do. Give me a break. Mass is determined by comparing the mass of one object (yes, using a scale or accelerometer) to the official Kilogram. Thus it plays a very important role in the measurement, thus I do and will continue giving it credit for the measurement.

Re:The Kilogram is not losing weight

[Bloke down the pub]

No they don't. I mentioned consumer choice, if one shop sells in metric the people who want metric will go there. If another sells in imperial, those who prefer that will shop there instead. And there are probably more cooks using imperial units anyway, since anybody under 30 only eats takeaways or microwave ready-meals.

Re:The Kilogram is not losing weight

[Bloke down the pub]

people will go using the Thales Principle (projecting a known lenght segment over the one to divide) or the fact than an hexagon's side is exactly the lenght of the radius of the circunscribing circle, or the fact that a twelve units long rope (whatever the units are) will make for you a perfect square angle and will give you 3, 4 and 5 units long segments for free.

Or they just guess.

Re:The Kilogram is not losing weight

[turbidostato]

"Or they just guess."

Yeah, but I was talking about successful artisans. Obviously failed ones can and will try quite a lot of different methods. Somehow, I didn't take them into cosideration.

Re:The Kilogram is not losing weight

[Guppy06]

"Yes, they do, and it's called equilibrium."

The energy to dissociate a molecule must come from somewhere, in this case from interactions with other molecules. Parent post seemed to insist that this was both wholly spontaneous and inherently unpredictable.

"Mr. McGuire: Plastics."

First off, the adoption of the platinum-iridium as the mass standard predates the mass-production of plastics.

Secondly, something need not be solid to be dissolved in water. Heating a sample of tap water will liberate dissolved air, for example. Opening and depressurizing a bottle of carbonated water will liberate dissolved carbon dioxide, which brings me to my next point...

"This is a fundamental property of water - it is INCOMPRESSIBLE."

Simply because something is assumed to be incompressible for particular engineering purposes doesn't make it actually incompressible. Unless you'd like to try to explain how an incompressible medium can conduct sound.

"Last, but not least: sealed container."

Since your favorite word seems to be "equilibrium," you of all people should understand that such a sealed container will eventually contain some mixture of liquid water and water vapor.

"Solutes dissolve MORE in superheated water."

I said "steam." In the neighborhood of 1000 kelivn. Of the kind that went through turbines to power the computer you're reading this on, all with less than 30 parts per billion of solid contaminants in it.

Re:The Kilogram is not losing weight

[Bloke down the pub]

Yeah, but I was talking about successful artisans.

And sadly, I was talking about the ones on real life, here on the planet we call "Earth" - specifically, any part of the EU that's let the Polacks in.

Re:The Kilogram is not losing weight

[turbidostato]

"specifically, any part of the EU that's let the Polacks in."

Well, you can think whatever you feel about it, but I specifically know quite a big bunch of Polacks and they are pretty good artisans specially regarding wood arts.

Re:The Kilogram is not losing weight

[Bloke down the pub]

I specifically know quite a big bunch of Polacks and they are pretty good artisans specially regarding wood arts.

Then why are they working as plumbers?

Sublimation?

[Eustace Tilley]

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?

[snowgirl]

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. And it's the first thing that I thought of myself as well.

Re:sublimation?

[AJWM]

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.)

Re:Sublimation?

[Hatta]

You should read the topics of comments you reply to.

Re:Sublimation?

[megaditto]

You sound like somebody would would vote for Kodos...

Re:sublimation?

[momerath2003]

Alphas are on the order of 5 MeV, which means it would be putting out about 4E-4 W. That's tiny but still probably noticeable. (But 10000 uCi of radioactive material would very definitely be noticed.)

Re:Sublimation?

[Jarjarthejedi]

Read the comment titles? You must be new here...

Re:Sublimation?

[Criliric]

Hatta (162192) -------------- Apparently not :P

Re:Sublimation?

[Guppy06]

"Well, why wouldn't the copies' atoms be drifting off as well?"

They are, but not at identical rates.

Re:sublimation?

[markov_chain]

Could the material be decaying into a gas somehow? Like radon?

Or maybe the chunk is porous and has some heavy gasses trapped.

Re:Sublimation?

[Anonymous Coward]

Because its just as likely that some of the copies aren't kept as safe as the original, and collect a little dust or something, making the original seem lighter when in fact the copies are heavier.

Re:Sublimation?

[Anonymous Coward]

Well, why wouldn't the copies' atoms be drifting off as well?

Obviously, the reference bar is trying to get the hell out of France.

Re:Sublimation?

[snowgirl]

BAH! What a stupid idea...

When has the topic of a comment ever contained information that was meaningful or important? Or come to think of it, which article has ever done that as well?

(Yes, if I could retract comments, I would have retracted this one...)

Haha!

[Twisted64]

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

Re:Haha!

[ILuvRamen]

But what you do have in common is you're both potential terrorist targets lol. But seriously, if they stole or damaged all of the copies made, this article makes it sound like the entire US would collapse. That's just stupid. Count the number of damn atoms in it, write it down, and melt the stupid things. It's stupid to rely on them

Gravity failing!

[ruiner13]

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

Re:Gravity failing!

[JiffyPop]

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

Re:Gravity failing!

[Volatar]

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

No one mentioned mass :)

Re:Gravity failing!

[vigmeister]

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

Cheers!

General relativity

[DigiShaman]

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

[Provocateur]

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

Re:General relativity

[John Jamieson]

Yes, when they made this one, they made others as well.

Either this one has lost mass, or the other ones have gained mass to varying degrees.

Re:General relativity

[zippthorne]

I blame global warming, myself. If only the US had ratified Kyoto, this wouldn't be happening.

Governments have been doing this for years!

[dada21]

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...

Re:Governments have been doing this for years!

[compwizrd]

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!

[phoenixwade]

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!

[FudRucker]

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

Re:Governments have been doing this for years!

[WilliamSChips]

Sad thing is, this post is probably completely serious for dada21.

The metre must be shrinking then...

[flyingfsck]

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...

[Anonymous Coward]

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...

[LiquidCoooled]

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...

[Clay Pigeon -TPF-VS-]

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

Re:The metre must be shrinking then...

[Anonymous Coward]

Yes! My cock is growing longer by the second!

Re:The metre must be shrinking then...

[fractoid]

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 in a vacuum, so unless that changed, the metre hasn't either. Fixed. Otherwise, you'd have to pay 20% more for sheet glass because meters inside the glass would be shorter than meters outside the glass. :P

Re:The metre must be shrinking then...

[Oktober Sunset]

It was supposed to be, but the French were to impatient to measure it properly, and fucked it up. This combined with other fuck ups is why the kilogram is a block of metal in France. It was supposed to the mass of a litre of water under standard conditions, but it all went tits up.

Re:The metre must be shrinking then...

[Detritus]

That was the original idea. The distance of the Paris meridian between the equator and the North Pole was defined as 10,000 km.

Re:The metre must be shrinking then...

[canadian_right]

The meter has a long history and was in fact once defined as "one ten-millionth of the length of the Earth's meridian along a quadrant, that is the distance from the equator to the north pole". Then it was a number of standard wave lengths and not until 1983 that the meter was defined as how far light travels in a very short time. Wiki has a good article on the meter.

In a vacuum the speed of light is constant - even in a gravitational field as long as your are freely falling.

Re:The metre must be shrinking then...

[Basehart]

When I was a kid I thought a foot was the length of Julias Ceasars foot and a metre was the length of Napoleon Bonapartes foot. When I found out later that a metre was considerably longer than a foot I deducted that Napoleon must have had really long feet. I later found out that Napoleon was also a very short fellow which made my mental image even more ridiculous. To this day whenever I hear the name I think of this short guy with three foot long feet.

Re:The metre must be shrinking then...

[kars]

-Of course- we're all expanding! Haven't you heard of global warming??

Re:The metre must be shrinking then...

[iamacat]

You misunderstood the background. Napoleon was not a tall fellow, but he was a great lover.

Re:The metre must be shrinking then...

[edittard]

So the whole of Europe got their asses kicked ... by a hobbit?

Re:The metre must be shrinking then...

[somersault]

"The meter has a long history"

Your posting privileges have been revoked for 2 months, or until such time as you show the adequate remorse necessary to prove that you are sorry for such a shameless pun.

Re:The metre must be shrinking then...

[Anonymous Coward]

"Otherwise, you'd have to pay 20% more for sheet glass because meters inside the glass would be shorter than meters outside the glass."

Make that 44% more, since the relevant dimensions of a sheet of glass are length and width. But your point was great.

Re:The metre must be shrinking then...

[Da Fokka]

Even worse. A French hobbit.

Re:The metre must be shrinking then...

[Anonymous Coward]

Corsican, monsieur.

Re:The metre must be shrinking then...

[JonathanBoyd]

Wasn't he a Corsican?

Re:The metre must be shrinking then...

[Anonymous Coward]

Most. Redundant. Post. Ever.
(not including this one)

Re:The metre must be shrinking then...

[slapout]

The problem I've always had with that is it's so hard to measure the speed of light. I mean, come on, I just need to know how big my living room is so I can order new carpet.

Re:The metre must be shrinking then...

[aliquis]

But then we have E=MC^2, and if the energy in the universe is constant (in solid or other form) then the speed of light is related to the amount of mass and if everything is getting heavier the speed of light is droping!

And then the meter is getting smaller aswell, which explains why his middle region measures more of a meter today!

Re:The metre must be shrinking then...

[aliquis]

(Thought of course in that equation the energy isn't constant but C is and if the mass various so would E, but whatever =P)
(Also E isn't the total energi including that in solid form.)

Re:The metre must be shrinking then...

[tehcyder]

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.

I don't see why it's not just defined as "one of your pathetic so-called English yards, plus a tenth for good luck."

Re:The metre must be shrinking then...

[AdamWeeden]

but it all went tits up

In the water? I guess they do make good flotation devices!

Re:The metre must be shrinking then...

[AdamWeeden]

I don't see why it's not just defined as "one of your pathetic so-called English yards, plus a tenth for good luck." Did anyone else read this while imagining the French knight from Monty Python and the Holy Grail saying it? If not, I recommend it you silly English k-nnnnniggets!

Re:The metre must be shrinking then...

[Reziac]

My first thought was "local gravitational shift" but that wouldn't explain why units brought in from elsewhere are heavier; they should become lighter as they approach the anomaly.

[backs up, thinks up different crackpot theorum]

Okay, how about this one: maybe something in the local gravitational field is changing the way the root unit behaves with respect to gravity; IOW, it's become "less attractive" so masses less.

So they need a newly-minted unit to sit right next to the old one, and a long time to observe whether it changes in the same ways. In fact a line of 'em stretching across the continent would be useful to examine the scope of the shift.

Of course, it could just be aliens stealing atoms, one at a time, from places where they didn't think a few atoms would be missed.

Re:The metre must be shrinking then...

[Impy the Impiuos Imp]

> or until such time as you show the adequate remorse necessary

How do you define "adequate"? Sorry to be lawyerly here, but you can't leave it so vague. Do you have a metric?

Re:The metre must be shrinking then...

[skuzzlebutt]

Yeah, but don't worry about it...if this is a global phenonemon, you can safely increase your daily calorie intake by 50 micrograms every century or so! Maybe that's why vampires and elves are always so svelte...

Re:The metre must be shrinking then...

[Impy the Impiuos Imp]

Tallfellows and Great Lovers -- Slashdot readers love to play various fantasy races and classes like this in their "emporgs" when getting away from their mundane lives.

Re:The metre must be shrinking then...

[Impy the Impiuos Imp]

> Wasn't he a Corsican?

I've yet to see a Slashdot article that doesn't eventually mention Star Wars!

Who can forget their favorite passage, updated?

Darth Vader. Bipedal. The distance light travels in a vacuum in two 1/299,792,458ths of a second tall.

Re:The metre must be shrinking then...

[operagost]

Excuse me, but I think you mean 3.2808399 foot-long feet.

Re:The metre must be shrinking then...

[somersault]

That is up to the moderators of course! Best thing about despotism

Re:The metre must be shrinking then...

[Anonymous Coward]

If hobbits could take out Sauron, Europe didn't have a chance. Don't fuck with hobbits.

Re:The metre must be shrinking then...

[smoker2]

...that a metre was considerably longer than a foot I deducted that Napoleon must have had really long feet.

The word is deduced.
Deducted is what happens when they take tax from your wages.

Re:The metre must be shrinking then...

[IchBinEinPenguin]

So the whole of Europe got their asses kicked ... by a hobbit?

You're thinking of WWII, which was much later than Napoleon.

Re:The metre must be shrinking then...

[lefticus]

Completely off topic to your post, but answering your sig:

Who the f*** decided that sentences on the Internet shall no longer be formatted with two spaces after a period?!

I had this explained to me in the mid '90's by someone who was involved in printing. With variable width fonts, you are no longer supposed to use two spaces, the typeface is supposed to leave an adequate gap. Two spaces is left over from the days of typewriters.

Re:The metre must be shrinking then...

[ZSO]

[...] with three foot long feet.

I think your childhood self confused a meter with a yard.

Re:The metre must be shrinking then...

[ConceptJunkie]

"three foot long feet"?

Depending on where you put the hyphen, Napoleon might have had 15 toes.

Re:The metre must be shrinking then...

[Anonymous Coward]

"Light speed is not constant in a gravitational field"

Light speed *is* constant in a gravitational field. Lenght and time are not.

Re:The metre must be shrinking then...

[Headcase88]

You have no idea how funny this is to people who read at a threshold that hides your parent's comment but keeps yours intact. Reading your post first, and then revealing the parent post out of curiosity, funniest thing I've read on /. in a while.

Re:The metre must be shrinking then...

[zero_offset]

The irony, of course, is that his own post misses two opportunities to insert those critically important extra spaces...

Re:The metre must be shrinking then...

[Impy the Impiuos Imp]

1. I do insert them. Something along the downstream chain removes them, or refuses to display them.

2. I am aware of the reasoning.

3. The reasoning is faulty. Without an intelligent stream formatter, there's no way to tell the difference between a normal space after a period and the extra space useful for the eye between sentences.

4. In practice, text renderers are not intelligent, stream formatters. Hence they just use the built-in kerning for a period followed by a space, which is decidedly not the same as what is desirable for space between sentences. The kerning concept just can't handle it since it is limited to a pairwise table of characters with extra pixel spacing pads.

Yes, proportional fonts should have their own intra-sentence spacing definition a little wider than a normal space. I do not see that in actual practice; they just use the normal dot-followed-by-normal-space setup. I suppose if there's a beef here, it's that the choice is removed from me because of the auto-stripping of the extra space, while the system as a whole doesn't even bother to add any extra space, which completely misses the whole point.

tag this "dirtycopies"

[ozphx]

You know its true ;)

Re:tag this "dirtycopies"

[John Hasler]

Yes, it probably is. The copies get handled much more, after all. They are much more likely to have picked up contaminants.

Blah

[Anonymous Coward]

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

This must be the reason ....

[Anonymous Coward]

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

sublimation?

[benburned]

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

Has anyone checked Ebay?

[Anonymous Coward]

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

Kilogram Reference Losing Weight

[MrYotsuya]

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

[E 99]

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

[Trogre]

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

Re: Kilogram Reference Losing Weight

[Dunbal]

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

[Jeff DeMaagd]

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

Re: Kilogram Reference Losing Weight

[TheRaven64]

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

[Anonymous Coward]

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

[QuickFox]

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

Re: Kilogram Reference Losing Weight

[shawb]

That's trivial... all that has to happen is a fundamental change of the gravitational constant. I'll leave it as an exercise for the reader to work out just how that happens.

Re: Kilogram Reference Losing Weight

[swillden]

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

Really? Wow, that's even bigger news! The kilogram reference is losing mass but somehow maintaining weight!! Is this unexplained increase in the Earth's gravitational field localized or general? What strange phenomenon is increasing gravity by the precise amount required to offset the reduced mass?

This observation of yours is going to require us to rethink large parts of physics.

Re: Kilogram Reference Losing Weight

[suv4x4]

That's trivial... all that has to happen is a fundamental change of the gravitational constant. I'll leave it as an exercise for the reader to work out just how that happens.

We bomb the Moon so the falling pieces increase the mass of Earth and hence increasing the gravity pull?

Re: Kilogram Reference Losing Weight

[LadyLucky]

Only if you don't want an accurate number. The value of g does vary over the surface of the earth, owing to its non-spherical nature, local anomalies and so forth.

Re: Kilogram Reference Losing Weight

[Entropius]

It's a serious problem. I had a student ask me today how she was supposed to find the force of $SOMETHING when her little spring scale only read mass... (it had a scale in kg).

Re: Kilogram Reference Losing Weight

[Anonymous Coward]

We bomb the Moon so the falling pieces increase the mass of Earth and hence increasing the gravity pull?

Rumsfeld says there aren't any good targets on the moon. Now, Earth, THAT'S a target-rich environment. He suggests we bomb the hell out of Earth, instead. Show 'em we mean business.

Thomas Friedman agrees, saying "We were attacked because of this bubble, this group of humans, and humans come from Earth. We need to go in there, into that pale blue bubble, and go up to them and say: Hey! We know where you live, and you're not gonna get away with it. So you know what? Suck. On. This."

Re: Kilogram Reference Losing Weight

[BronsCon]

Because, at 1G, the gravity here on earth, it weighs 1 kilogram. It's losing mass, but is still the reference for what a kilogram weighs.

Re: Kilogram Reference Losing Weight

[Trogre]

Because that's what weight means in real life. The term has been hijacked by scientists so they can sound clever when they correct people for using the "wrong" term.

And don't get me started on centrifugal force.

Re: Kilogram Reference Losing Weight

[Trogre]

Yes, I capitalised both my quantities (g and m) in an attempt to make it a bit more readable. It obviously failed.

As a side-note, as I clicked 'submit' I thought to myself "I bet some smart-arsed physics nazi is going to dress me down for bad notation". Congratulations :)

Re: Kilogram Reference Losing Weight

[Anonymous Coward]

And don't get me started on centrifugal force.

Centrifugal force is real, in a certain reference frame. If you are riding in a car and go around a sharp curve, you will be pushed towards the outside of the curve. That is centrifugal force.

In a different reference frame, centrifugal force does not exist. If a stationary* person watches that same car go around the same curve, they will see the car push against the car passenger, towards the inside of the curve. That is centripetal force.

*Yes, if you want to be pedantic a stationary person on the earth isn't really stationary, since the earth is rotating, moving around the sun, and the sun is moving, and the milky way is moving, etc. But a stationary person on earth is just in a particular reference frame that we call stationary.

Re: Kilogram Reference Losing Weight

[Anonymous Coward]

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

Yes, it's called the slug. Really, it's called the slug.

If you ever had to do science in slugs/pounds/feet/farenheit, you will appreciate the value of the metric system.

Re: Kilogram Reference Losing Weight

[marcansoft]

A beam balance will easily tell you the mass of an object no matter what planet you're on.

Re: Kilogram Reference Losing Weight

[Anonymous Coward]

Obligatory xkcd reference

Re: Kilogram Reference Losing Weight

[Anonymous Coward]

"Because that's what weight means in real life."

Okay, lets say you are a rocket scientist. And You have to make some calculations. And the spec sheet say 100 kilograms for a part. Now you need to calculate some forces. F = MA Hum, kilograms is mass (M) and lets say A = 9.8 m/s. And if that 100 kg was obtained by measurement on a scale and called kilograms because that is "real life" your results would be off by an order of magnitude.

Re: Kilogram Reference Losing Weight

[Nexx]

Yes, I capitalised both my quantities (g and m) in an attempt to make it a bit more readable. It obviously failed.

No, you made it wrong :P. As you most likely know, G stands for Gravitational Constant, while 1g is defined as the amount of gravitational acceleration at sea level on Earth.

Re: Kilogram Reference Losing Weight

[Nexx]

What strange phenomenon is increasing gravity by the precise amount required to offset the reduced mass?

I dunno, a rapid ground sinkage due to number of factors?

Re: Kilogram Reference Losing Weight

[amorsen]

A beam balance will easily tell you the mass of an object no matter what planet you're on.

Only if the reference object has the same density as the object to be measured.

Re: Kilogram Reference Losing Weight

[Mac Scientist]

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

It may only be accumulating mass more slowly than the copies, in which case the kilogram is increasing overall. There are a number of possible surface effects theorized. The artifact is mostly platinum, so there could be mercury absorption from air pollution, or catalytic breakdown of hydrocarbons and hydrogen absorption from the air or the cleaning process. There is some research being done by the mass standards groups, but no one wants to sacrifice their national standard to test the theories by destructive analysis of the surface of a hundred year old artifact.

Check out the latest Wikipedia entry on mass changes in the kilogram and proposed alternative standards. http://en.wikipedia.org/wiki/Kilogram. Just updated this week. Total coincidence.

Re: Kilogram Reference Losing Weight

[liquiddark]

Maybe the mass thief is lowering the reference weight by a small amount? Or just putting a heavy object vaguely "underneath". Gravity is a gradient field, after all.

Re: Kilogram Reference Losing Weight

[Anonymous Coward]

That make absolutely no sense. I am trying to figure out where and why the force is supposed to come into the calculations. You want a part that has a mass of 100kg, then you use a correctly calibrated set of scales that will display the weight in kg. Alternatively you could use a newton meter to measure the force of gravity on the mass and assuming you are on Earth you would be looking for a force of ~9800N. The two methods are essentially the same, just that the scales will only be correct where the gravitational strength is the same as where they have been calibrated for, and the newton meter will always be correct, but you need to know how the acceleration force gravity applies fot where you are using it.

If a rocket scientist can't understand how this works then I wouldn't want to be on or near any of his rockets.

Re: Kilogram Reference Losing Weight

[Anonymous Coward]

No it doesn't. I can't remember the technical terms to describe this, but consider a see-saw, you have a person of a known mass sitting on one end and a person of unknown mass gets on the other end, the second person is clearly heavier because he weighs his end down so he moves to half way between the end and the pivot, now the see-saw is evenly balanced and you now know the second person is twice the mass of the first person, and since you know the mass of the first person you can calculate the mass of the second person. This principle can be scaled up as far as you need assuming the beam has sufficient length to counter the difference in mass and the relative distances from the pivot can be measured accurately.

Re: Kilogram Reference Losing Weight

[amorsen]

If the second person happens to have the same density as the atmosphere and the first person has a higher density, the first person will measure as heaviest -- even if the first person has a mass of 1kg and the second a mass of 1000kg.

Re: Kilogram Reference Losing Weight

[identity0]

Actually, it could be losing weight thorugh changes in the local gravity because the earth has an uneven, moving core and mantle.

Relativity?

[vigmeister]

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?

[sanyasi]

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?

[vigmeister]

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?

[Ferzerp]

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)

Re:Relativity?

[exp(pi*sqrt(163))]

> due to the twin paradox (as applied to mass)?

Is that like the liar paradox (as applied to wombats)? You can't just take an effect, write "(as applied to X)" after it, and hope that somehow you've made something that makes sense.

Re:Relativity?

[lhaeh]

Not really, the difference in weight (50ug) is quite a bit. Correctly calibrated balances have no problem discerning between a few micrograms. The best balance I saw could go down to 0.1ug, and there are much better ones out there.

Re:Relativity?

[vigmeister]

Ok... so please explain to me why the twin paradox cannot be applied to mass (if the different masses are at different latitudes at the time of measurement). The effect may not explain the 50ug difference, but it happens.

Cheers!

Re:Relativity?

[exp(pi*sqrt(163))]

There is no twin paradox for mass. I've no idea where you got this idea from.

How much you age when you travel from event A to event B depends on the path you took to get there. This is known as the "twin paradox", though it's not actually a paradox. According to special (or general) relativity, your mass doesn't depend on the path you take. There is nothing anywhere in the theory of relativity that talks about such a dependency. There's no reason to expect masses at different latitudes to diverge in mass over time. There's nothing to explain. You've simply pulled an imaginary phenomenon out of nowhere.

In summary: your age (or "proper time") is a function of your path. Your mass isn't.

Re:Relativity?

[vigmeister]

Hmmm... sort of an intensive versus extensive argument. But given that the two masses are in different states (diff velocities/acceleration at different latitudes), there would be a difference wouldn't there?

Cheers!
--
Vig

Re:Relativity?

[vigmeister]

Sorry, not intensive versus extensive; I meant state variables and non-state vars
Cheers!

Re:Relativity?

[exp(pi*sqrt(163))]

I have to admit, the intensive/extensive distinction came to my mind too. It's not quite right, but it's on the right track.

Anyway, individual observers shouldn't see any change in any mass that they observe over a period of time that remains in the same location. In order to compare two different masses you need to bring them to a common location with common velocities, so again, you shouldn't see any difference, and no 'memory' exists, in their mass, of the path they took to bring them together. The only conceivable time when you might spot a difference is when you decide to measure that masses of two different objects moving at different velocities - but that's a tricky thing to do anyway, and I doubt anyone is doing that.

Mass?

[forsetti]

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?

[edwardpickman]

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?

[fm6]

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?

[patcpong]

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

Re:Mass?

[djmurdoch]

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?

[megaditto]

300 nanograms you mean?

Re:Mass?

[djmurdoch]

A nanogram is 10^(-9) grams. So 300 nanograms would be 3 parts in 10^7 of a gram, not of a kilogram.

I think I got the units right; I'm not so sure about the inverse square law.

Re:Mass?

[megaditto]

I think you are right... I keep forgetting that the Metric unit is 10^3 grams, not 1 gram! So all the powers operations must be done on 10^3, not on 1.

One more reason the Metric system is so confusing...

Re:Mass?

[rmessenger]

isn't a kilogram a measure of mass?
Yes, the kilogram is a measure of mass.

isn't it actually possible that the mass has remained constant, but the force of gravity has slightly changed in that locality?
No. The story isn't really "the kilogram is losing weight." The author is just an idiot. When scientists measure the mass of the reference mass, they use methods which completely eliminate contamination by gravitational fluctuations.

other reference masses in the same locality could be used for comparison
Have you ever used a balance..? [wikipedia.org]
The simple lab balance is a good example of a device that can measure mass regardless of fluctuations in gravitational acceleration. In fact, you could take a lab balance right from a high school classroom to the moon and it would measure mass just as accurately without modification.

Re:Mass?

[thegrassyknowl]

It's really very simple. The kilo is evaporating. Everyone knows that even ice in your freezer evaporates over time. The kilogram has been kept there for how many years? Over the last 18 it's lose 50 micrograms. That's not a lot really compared to its mass. It's just evaporated is all.

Re:Mass?

[fm6]

Don't need a hint. Just came back from Mass. Boy, was it heavy.

Re:Mass?

[Guppy06]

"And therefore, if its weight is changing, isn't it actually possible that the mass has remained constant"

If you're using an artifact as your standard of mass, realistically it means you're using a beam balance to compare other things to it, which means you are indeed measuring mass directly (unless the force of gravity is perceptibly different on different ends of the beam balance).

Re:Mass?

[bakuun]

I think you are right... I keep forgetting that the Metric unit is 10^3 grams, not 1 gram! So all the powers operations must be done on 10^3, not on 1.

The standard metric unit for weight isn't 1000 grams - it is 1 gram. Of course, the 'k' in kg stands for 10^3. Unfortunately, I believe the scientists made a mistake when deciding on the weight of 1 g - IMHO, the standard unit of measure should have been what 1 kg is now as it is a more convenient weight for what we handle in day-to-day life. It was a regrettable mistake with the effect that we mostly speak of "kilos" instead of grams. However, at least I believe that they got the meter and the litre right.

I love the SI system. Everything becomes so much easier :) Try calculating how many square inches there is in one square mile, and you'll get my point..

Re:Mass?

[tehcyder]

According to the back of this envelope here

You forgot to provide a link to your webcam.

DON'T WORRRY GUYS

[Anonymous Coward]

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

[iamacat]

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

[AvitarX]

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.

Re:More fundamental standards

[BlueParrot]

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.

Re:More fundamental standards

[Anonymous Coward]

Averagado's number = 6.023 * 10 ^ 23 (exact).
Mass of one mole of carbon atoms (naturally occurring isotopic mix) = 16 grams (exact).

From these two, we can get mass of kilogram from physical constants.
Unfortunately, the equation for determining naturally occurring isotopic mixes from other physical constants is not known.

Re:More fundamental standards

[Yunzil]

Averagado's number = 6.023 * 10 ^ 23 (exact).
Mass of one mole of carbon atoms (naturally occurring isotopic mix) = 16 grams (exact).

Yeah, but it's a pain in the ass to count them all. Especially when you get lost somewhere around 5.1789 X 10^21 and have to start all over again. >:(

Re:More fundamental standards

[Anonymous Coward]

There is a more fundamental basis for a system of measurement. Look at 'natural' units. See http://en.wikipedia.org/wiki/Planck_units

Re:More fundamental standards

[Puff of Logic]

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. It strikes me that we don't really need a kilogram to be the reference mass. Why not simply do it for a gram and bring the standard unit for mass into line with the rest of the metric units, instead of that annoying 10^3 measure we have now? Hell, why not make our reference mass a nanogram, or microgram, and then simply define our "standard mass" gram as x orders of magnitude above that?

Re:More fundamental standards

[iamacat]

However, as technology progresses, we can obtain more and more precise measurements. This is the opposite of the current situation with a chunk of metal that changes it's mass at measurable rate.

Re:More fundamental standards

[iamacat]

I don't know about more fundamental, but it doesn't appear more precise. As I understand, every hydrogen atom's mass is exactly the same as another ones.

Re:More fundamental standards

[Anonymous Coward]

Mod parent insightful!

BWAAAHAHAHAHAHAHAAA

Re:More fundamental standards

[Watson Ladd]

What about the energy of the hyperfine transition of cesium-133? Just fix $h$ and then you have an energy unit, hence a mass unit from $\frac{1}{2}mv^2$.

Re:More fundamental standards

[Anonymous Coward]

They are already working on it. The link also proves that this is very old news.

Re:More fundamental standards

[joker784]

It is actually quite amazing that modern physics seem to have real difficulties with mass and gravity. You should think that this was really well understood, but as I understand it none of the current sub-atomic elementary particles have any mass...and mass should come from a postulated Higgs particle (but this has so far not been possible to be verified or observed...CERN is preparing a big experiment next year to hopefully rectify this)....Amazing

obligatory...

[abes]

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

Re:obligatory...

[sharkey]

It's Oprah?

Re:obligatory...

[Anonymous Coward]

Most likely over Christmas vacation.

Re:obligatory...

[abb3w]

...and then gain some more, and then there will be a semidecigram cylinder sitting next to it while a lot of physicists get asked pointed and embarrassing questions.

Possible reason?

[robably]

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?

[Misanthrope]

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

Re:Possible reason?

[E 99]

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

Re:Possible reason?

[Anonymous Coward]

If there doing it right it shouldnt matter because a kilogram is mass not force. For example a kilo of cocaine is the same amount here on earth as it is on mars though I think the street value changes.

Re:Possible reason?

[shawnce]

The simplest way is to use a balance and since the two sides of the balance are in such close proximity to each other any variation of gravity would affect both masses being compared. More complex ways involve measurements of inertia of the masses when a known forces act on the mass.

Re:Possible reason?

[localman]

On a balance scale, not a force scale. It seems a trivial difference if gravity is always the same, but it's not. A spring loaded scale will read differently here and on the moon, while a balance scale will not. Kilograms are supposed to be measured using a balance scale. Though I see lots of force scales used to measure kilos anyways... they just calibrate them for earth gravity, which is reasonably constant. But I figure the folks doing this measurement are familiar enough to know all that :)

Cheers.

Re:Possible reason?

[francium de neobie]

You can apply a known force to the mass and see how much it accelerates.

Re:Possible reason?

[John Jamieson]

Sorry to pick on you, but you got modded high enough (why?) that I noticed your post. Reading through all the responses to this Kilo article I can only ask DOES ANYONE READ THE FREAKEN ARTICLE(that means moderators as well)????

The background is that back in the 1890's (or something) they made a bunch of identical Kilo cylinders and kept one as the master. Now this master weighs LESS than all the others because it now has less mass than the others to varying degrees.

The real question is ... Did the master weight loose mass or did the other gain it.

So no, it is NOT because of where they weighed it.

Re:Possible reason?

[Guppy06]

"Maybe it's because of where they weighed it - the strength of gravity is not the same all over the planet,"

It would matter only if your method of measuring weight is based on the amount of force gravity exerts on it (such as measuring the compression of a spring). Realistically, using an artifact mass means using a beam balance, which relies on measuring the relative difference in the forces on the opposite ends of the beam, rather than measuring the force in absolute terms.

Re:Possible reason?

[noidentity]

My god did they not have scales in your school? These things compare mass of two objects, thus they work no matter what the gravity is (as long as it's non-zero).

Re:Possible reason?

[White Flame]

due to the movement of the Earth's outer core

Time to build a drill-train out of unobtainium and fix it with nukes!

Re:Possible reason?

[Anonymous Coward]

and what do you put on the other side to measure the weight of the standard kilogram? How do you ensure each copy is being balanced against the same mass?

Re:Possible reason?

[Anonymous Coward]

Well, beam balance works fine as long as the gravity is the same at the ends of the beam. For example if the beam is 1 meter long, the gravity may change by 0.00000001% or so on the ends (rough calculation using the change from pole to the equator) or greater if there is some anomaly. That may be not good enough.

Re:Possible reason?

[mebollocks]

They said that its mass was decreasing, not that its weight was decreasing. Besides, I'm sure they calibrated their measuring device with that of a known mass before measuring.

Re:Possible reason?

[Guppy06]

"For example if the beam is 1 meter long, the gravity may change by 0.00000001% or so on the ends (rough calculation using the change from pole to the equator) or greater if there is some anomaly. That may be not good enough."

Then orient it so that it's east-to-west rather than north-to-south. Problem solved.

Re:Possible reason?

[cc1984_]

You can apply a known force to the mass and see how much it accelerates.
To measure an object's mass, you could find a (admittedly elusive) frictionless table, attach two springs either side of the object to be measured , of equal and known spring constant, and let it undergo simple harmonic motion, measure its periodicity and deduce the mass involved. If the apparatus is oscillating parallel to the surface of the earth, it will be unaffected by gravity, thus circumventing the problem of unknown gravitational fields.

Where are my...

[msauve]

mod points when I need them?

Oh come on

[polygamous coward]

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

The Faster We Go, The Rounder We Get

[Doc Ruby]

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 Faster We Go, The Rounder We Get

[SQLGuru]

I think someone is secretly going there and shooting it with a high powered laser and burning some of it away. It's probably those pesky sharks from the aquarium.

Layne

Re:The Faster We Go, The Rounder We Get

[Oktober Sunset]

It's stubborn Americans, secretly sabotaging it, this way they have a new excuse to sticking to their crazy old fashioned system.

Re:The Faster We Go, The Rounder We Get

[Anonymous Coward]

You're laughing, but in reality, the pound is defined by the kilogram reference!

Re:The Faster We Go, The Rounder We Get

[iwein]

It has been staring us in the face the whole time: "50 micrograms is roughly equivalent to the weight of a fingerprint."

The reference hasn't changed, the copies have. There must be some guy putting fingerprints on them...

Re:The Faster We Go, The Rounder We Get

[Anonymous Coward]

I read somewhere that the mass loss is due to osmium. The standard is made of platinum-iridium; osmium is chemically related and is found in the same ores. While platinum and iridium are very inert, osmium will react with air at room temperature to form a volatile oxide that then evaporates away.

And from the Wikipedia article, it appears possible that someone may have just forgotten to clean the replicas.

amusing background

[cinnamon colbert]

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

[MavEtJu]

It's kg, not Kg.

Re:amusing background

[SkyFalling]

Clean it? If they're letting it get dirty so that it'd need cleaning, they've got some bigger problems than aging staff. How do you clean something like this without abrading away some of the mass? It's not like you can just spray it down with Windex and give it a wipe.

Then the problem becomes...

[msauve]

which type of hydrogen atom - African or European?

Re:Then the problem becomes...

[SkyFalling]

Mauve.

Re:Then the problem becomes...

[WilliamSChips]

Man, this coulda been so good a joke too... I think you mean: "What type of atom, protium or deuterium?"

vapor pressure

[cjanota]

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

[Trifthen]

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?

[r_jensen11]

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.

Re:Losing mass or weight?

[Colin Smith]

radioactive impurities.

Re:Losing mass or weight?

[Anonymous Coward]

Everyone is thinking too hard here. First off, who can expect whatever scale or balance it has been sitting on x number of years to still retain the same reading. Whats that you say. They've been remeasuring it over and over again on different balances? So they've been handling it all this time, measuring it over and over again. Well no wonder it lost a measly 50mcg by now from all that handling.

The problem is that it is in France

[fishthegeek]

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

[Anonymous Coward]

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!

Re:Inertia

[Dr Fro]

How would you define a unit of force without starting with a given amount of mass?

Re:Inertia

[yo_tuco]

"m=f/a"

Significant figures! If a = acceleration due to gravity, how accurate do you know that, I wonder? If you only know it to, say, 6 significant figures, you will not know the change in mass anymore accurate than that no matter how accurate you know the force.

Re:Inertia

[Guppy06]

They're working on it.

Re:Inertia

[Anonymous Coward]

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

A Newton second^2 per meter is a kilogram: http://en.wikipedia.org/wiki/Newton.

Original article

[Toinou]

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. 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....

[prxp]

...the newest French diet!

Stop cleaning it!

[eknagy]

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?

[Trifthen]

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?

Mmmkay...

[TofuDog]

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.

Not any more

[benhocking]

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

Re:Not any more

[flyingfsck]

So time is speeding up then?

Re:Not any more

[ArsonSmith]

Ok, I got a flash light and a dirt devil. Anyone have a watch? Preferably with a seconds hand. Lets check how accurate this is.

Re:Not any more

[Nullav]

I got a flash light and a dirt devil. Anyone have a watch?

Not particularly. I'm not sure about the flashlight, but you might want to take out the spring first.

Re:Not any more

[Anonymous Coward]

I'll bite: why 1/299,792,458?

Re:Not any more

[Nullav]

The same reason a second is currently defined as 9,192,631,770 oscillations of a Cesium-133 atom and the Kilogram is defined as some crazyass cylinder of stuff; it's necessary to have a reference for any measure, so writings from decades ago still make sense.

Re:Not any more

[Cardcaptor_RLH85]

The meter is defined as the distance light (in a vacuum) travels in 1/299,792,458th of one second because light travels 299,792,458 meters per second as classically defined so they just reversed it and made it the standard. Just like the second is defined as "...the duration of exactly 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom at a temperature of 0 K." from http://en.wikipedia.org/wiki/SI_base_unit/ In fact the Kilogram is the only SI base unit still defined by a physical object.

Re:Not any more

[drsmithy]

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

True, but it's still *based* on the dimensions of Earth - "retconning" it into somewhat more universal units won't change that ;).

Re:Not any more

[Anonymous Coward]

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

You just defined the meter in terms of the second. This begs the question, as under the International System of Units, the second is currently defined as 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 caesium-133 atom.

----
Shamelessly ripped from Wikipedia.

Re:Not any more

[SorcererX]

Not quite, according to wikipedia "the second is currently defined as 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 caesium-133 atom."

Re:Not any more

[Anonymous Coward]

Sir, you are suggesting caesium is responsible for obesity. I find that rather hard to believe.

Re:Not any more

[BobPaul]

This begs the question, as under the International System of Units, the second is currently defined as 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 caesium-133 atom. You forgot the question that is begged.

Re:Not any more

[PhysicsPhil]

Not quite, according to wikipedia "the second is currently defined as 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 caesium-133 atom."

Your quote must be from an outdated wikipedia article. The current article gives the correct definition (the distance travelled by light in a vaccum in 1/299 792 458 of a second), which has been in place since 1983.

Re:Not any more

[iago-vL]

FYI, he was defining a second, and you're defining a meter.

Re:Not any more

[djasbestos]

Can't they just pick a round number? Like five billion orbits of an electron around a hydrogen atom?

Re:Not any more

[xYoni69x]

No.

http://en.wikipedia.org/wiki/Beg_the_question

Re:Not any more

[Gnavpot]

FYI, he was defining a second, and you're defining a meter.

It must be pretty embarrassing to have the user name "PhysicsPhil" when you make a mistake like that.

Re:Not any more

[BigAssRat]

I give you kudos on this post...I am currently cleaning my monitor from the Dr Pepper that was just sprayed all over it. That was DAMN FUNNY!

Re:Not any more

[Anonymous Coward]

Kinda like a religious person naming their avatar "CuriousJoe".

Re:Not any more

[operagost]

Clearly, the kilogram reference should be constructed of cesium-133. This will remove all ambiguity.

Re:Not any more

[Jorgandar]

Ok...

So how long is a second? :)

Re:Not any more

[BobPaul]

Interesting. I've only ever heard that phrase used in the incorrect "modern" form. Thanks for that one.

Regardless, the AC's comment is still incorrect as defining a meter in terms of seconds is not a fallacy. A second is defined by the time taken for a certain atom at a certain temp to vibrate a certain number of times. A meter is then defined as the distance light travels in a vacuum in a certain number of seconds. This is simply an A->B, B->C situation.

Re:Not any more

[turbidostato]

"I'll bite: why 1/299,792,458?"

Because by the time these light-based definitions came to live we already "knew" what a metre or a second was, and the IBWM just "made up" the number that just fitted.

For the meter case (you probably already know it) it started from being 1/10^7 the lenght of the quadrant of the meridian crossing Paris to the lenght between to marks on a bar in Paris. Using this unit, the speed of light in vacuum was stablished to be 299.792.458 m/s, so by the time they decided to change the definition seeking that basic SI units were based upon natural "artifacts" as much as possible, considering 'c' to be a universal constant, it just made sense that the "new" metre and the old one lenght's were the same, so there you come with the current "funny" number.

That being send, probably it would have been good for the sanity of the new generations to "round it up" to 1/300.000.000 of the distance the light travels in a second instead of this wacky number.

I am finally able to answer the dreaded question..

[this great guy]

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

Re:Did they really expect a permanently stable mas

[pclminion]

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.

Call us when you're using Newtons, and we'll talk.

[Valdrax]

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

And how do you suppose they measure mass?...

[msauve]

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?

Radioactive decay?

[pclminion]

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

Re:Radioactive decay?

[treeves]

I thought that too, but what are the other several kilogram standards made of? Not the same thing I suppose.
Perhaps oxidation is causing weight gains in the others.
I'd like to know what was the standard deviation of all the other masses over time.

Re:Radioactive decay?

[Colin Smith]

That's what I reckon it'll be.

They are slowly whittling it down to a pound.

[Schmapdi]

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

Re:They are slowly whittling it down to a pound.

[Anonymous Coward]

Will not happen. A pound was defined as 0.45359237 kilograms in 1958.

Re:They are slowly whittling it down to a pound.

[Anonymous Coward]

Hum, pound = force = weight != mass. Maybe the definitions is the "weight" of X kilograms at some reference location or one pound-mass = 0.45359237 kilograms.

Great Scott!

[cashman73]

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

Re:Great Scott!

[Pfhorrest]

I thought Doc Brown said things were supposed to get heavier in the future! Oh wait, sorry,. . . that was Marty McFly! If the defining standard of the kilogram gets lighter, then everything else will be measured as heavier by that standard. So yes, this is pretty heavy stuff we're dealing with.

I like the US customary system

[OrangeTide]

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!"

Re:I like the US customary system

[John Hasler]

"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!"

Your car is burning 63 gallons every eighth of a mile. And you like it. Ok...

Re:I like the US customary system

[camperdave]

Wow! That's three times worse mileage than the crawler transporters that NASA uses get.

Re:I like the US customary system

[Carewolf]

Your car is burning 63 gallons every eighth of a mile. And you like it. Ok...

Yeah, it has better fuel effiency than my other car

Re:Did they really expect a permanently stable mas

[patcpong]

They knew about quantum tunneling/cosmic rays in 1889?

Before making announcements of this nature...

[Anonymous Coward]

...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.

Re:Before making announcements of this nature...

[aeve]

How about: the other reference copies aren't quite so tightly guarded and occasionally pick up a fingerprint?

Re:Before making announcements of this nature...

[Anonymous Coward]

I don't know - if they are going to bother shipping in all these kilos, you'd think they'd at least compare them to each other as well...

The Pound must be picking it up

[flyingfsck]

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

have they extrapolated

[Anonymous Coward]

to determine when the world will end? Somebody should tell the Chicago Cubs they'd better make a move soon.

hmmmm

[Anonymous Coward]

Date: September 16, 62002

Location: God's Court

"God": My angels, we have a problem. The Universe we created 6000 years ago is about to die.

"Angel 1": Holy shit dude, you suck. You were supposed to create the universe for eternity. This is like, what the fifth time?

"Angel 2": What are the humans figuring it out again?

"God": Well, frankly, yes. A few are close, again. They keep learning as we expected, but we didn't account for how fast they would learn. All these exponentials. As you all know, the fabric of their reality only works as long as no consciousness figures out how I did it. Once they do, we are morally obligated to treat them as alive.

"Angel 1": Can't we just fuck with them again? You know, turn off a few suns or create another particle or something?

"God": (Sighing deeply) We don't have much choice. We have to do something sublte, yet significant... Bob, would you go ahead and start changing how mass is calculated. Make it something that will be hard to find.

Angel 2 smiles, and turns around to his machine, and starts typing furiously...


sudo cp /var/lib/reality/core/constants/MassCalulator.rb /tmp/MassCalulator.rb.orig
sudo emacs /var/lib/reality/core/constants/MassCalulator.rb
sudo /usr/sbin/reload_constants.rb


The screens shift slightly, a few numbers flutter

"Angel 2": It is done, Joe.

"Angel 1": Hey, who wants to grab a beer?

--
My future is coming on;think twice, that's my only advice;Tóg do chroísa. Tar trí na stoirmeacha.

Re:hmmmm

[religious freak]

Great post, AC!

Re:hmmmm

[Anonymous Coward]

clearly fabricated. Angels are old school. They all use vi.

Re:hmmmm

[jagdish]

Posted AC to avoid the Wrath (TM) pf god?

Re:hmmmm

[mnot]

Typical developers, using a program where a config file would do. I bet God used a consultant.

Re:hmmmm

[biraneto]

Neo: Whoa, deja vu. Trinity: What did you just say? Neo: Nothing, I just had a little deja vu.

Re:hmmmm

[Guppy06]

Blasphemy! God would be using ed!

Re:hmmmm

[thegoofeedude]

The universe was written in Lisp, you insensitive clod!

Re:hmmmm

[Anonymous Coward]

Date: September 16, 62002

Location: God's Court

"God": My angels, we have a problem. The Universe we created 6000 years ago is about to die.

I see even assholes don't know how to do math. By the way, the joke is on you anyway considering God has already caused various constants to change throughout the age of the universe. Just when we think we are smarter than God He goes and changes things.

Re:hmmmm

[Anonymous Coward]

Those two numbers were not typos. It appears you just didn't get it.

--the op ac

The point was that the simulation for our world, being run by root ^H^H^H God, is happening in the very far future, like 60K years ahead of our current technology. The 6000 is a comic head-nod to the religious whackos who have at times said with a straight face that our world really is 6000 years old, but if this is a simulation - how would you ever know? and what would years mean in a simulation anyway? What I did was take the 6000 and put it into the context of the timeframe of the people running the simulation. Maybe our *simulation* has been running that long!

Why would you label a funny Ac (me) an asshole? Most labels are unhelpful judgements, and support violence. I suggest you read Nonviolent Communication by Marshall Rosenberg. Rethink your life.

Re:hmmmm

[Comatose51]

*.rb? You must think we live in a perfect and elegant world.

Re:hmmmm

[Anonymous Coward]

Or an incomprehensible, highly magical one rife with hidden side effects. Wait a minute......

Re:hmmmm

[Anonymous Coward]

> If you can read this... 01110101 00100000 01110010 00100000 01100001 00100000 01101110 01100101 01110010 01100100

Am not!

Re:hmmmm

[IdeaMan]

u r 2

Re:hmmmm

[againjj]

Fool! God would use vi!

Re:hmmmm

[RzUpAnmsCwrds]

sudo cp /var/lib/reality/core/constants/MassCalulator.rb /tmp/MassCalulator.rb.orig
sudo emacs /var/lib/reality/core/constants/MassCalulator.rb
sudo /usr/sbin/reload_constants.rb

No wonder the universe is so screwy. It's coded in Ruby. Maybe next time they'll use a proper language like Java.

Re:hmmmm

[drDugan]

Well, just the physical constants are in Ruby. They could modify themselves at runtime.

See, Buffalos and Elephants and Tigers - they are all in Java.

Nightmares, worries, and scary stories - C++.

The wind and the stars and the sea - Smalltalk.

We did memories and mathmatics in Erlang.

But the best of all, love dreams and courage, those are straight Lisp.

Proof of non-biological evolution!

[Max Littlemore]

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

This is almost true, although it's 1000 cubic cm or 1 litre rather than 10 square cms. Mathematics, however, has evolved.

10 cubic cm can be described as the volume of a cube with ten cm per side, or 10 x 10 x 10 = 1000 cm3. At least that's how it was. These days, multiplication has mutated slightly, so 10 x 10 is now 99.9999994482 +/- 0.0000000002. This means that the mass of a litre of water has indeed changed slightly, while the standard kilogram remains correct. In fact, the mass of a litre of water is now subtly different depending on the shape of its container, an effect which is more evident with larger containers. A 50 litre cube of water without handles is indeed heavier than a 50 litre flexible bag with a nice long handle attached to a harness.

While this doesn't currently pose any major problems, I for one pity the engineers when cartesian geometry evolves opposable thumbs.

Re:Proof of non-biological evolution!

[Clith]

10 cubic cm can be described as the volume of a cube with ten cm per side

Actually, a cube with 10cm per side would be "10 cm cubed", not "10 cubic cm".

Re:Did they really expect a permanently stable mas

[pclminion]

As if those were the only way the thing could change mass?

I have just the opposite problem!

[JohnnyGTO]

And its not measured in micrograms :-(

Bogus story, I think

[fm6]

This entire story (which has appeared on a lot of general news sites, but no science news sites) is probably just a case of a reporter misunderstanding something a scientist said. According to the UK NPL site, fluctuations in the physical objects used to define fundamental metric units has always been a problem. Back when they were created, the ideal material for them seemed to be a hard, dense iridium-platinum alloy. This turned out to be a nasty mistake: the alloy is slightly radioactive, which means that some of its mass flies off into space all the time. No mystery there.

This is why most fundamental units are now based on natural constants. For example, the meter used to be the distance between two notches on a platinum-iridium stick. (Before that, it was defined as 1 ten-millionth of a line that goes from the equator to the north pole; except they miscalculated the length of the line!) Now it's based on how far light travels in some tiny amount of time. But there's no consensus as to the best way to get rid of the physical kilogram.

In other words, all we have here is a clueless reporter trying to fill up a slow news day.

Re:Bogus story, I think

[KillerBob]

1KG = 1L of pure (distilled) water = 1 cubic decimeter (1000 cubic centimeters)

When talking about pure DHMO that is. When you start mixing in salts (as is found in our drinking water), it messes up the density of water, which messes up the measurement, if only slightly.

Re:Bogus story, I think

[ookabooka]

Yes, but at what temperature/pressure? Both of these things affect the density of water as well. I'm assuming its STP or 25C and 1atm. Then again, how exactly do you go about measuring that...

Re:Bogus story, I think

[Petrushka]

It isn't bogus, the story is accurate, and you are the clueless one. (See? Other people can throw around gratuitous insults for no reason too.) Variations in the weight (and, obviously, mass) of the kilogramme prototype have been well-known and studied for decades. Here are some previous Slashdot stories that have covered this and related topics: here, here, and here. Personally, I find it interesting to note that while the kilogramme is losing weight now, it seems that in the early 90s it was gaining weight.

Re:Bogus story, I think

[Toinou]

fluctuations in the physical objects used to define fundamental metric units has always been a problem The most famous example is the definition of the second. Until 1671 everybody thought that the gravity was constant on earth, so with a meter defined as a fraction of a meridian, the second was equal to the period of a one meter long pendulum. Everybody was very disapointed to learn that the gravity was not the same in Paris and in Cayenne (French Guyana).
So, until 1967 the second was based on the mean length of a day.
In fact, it is so complicated to properly define a measure that, during the french revolution, they took the old measures and renamed it. So the meter is based on the toise de Paris. However, at that time, the main problem was building the simplest system possible, and they did achieve it.

Re:Bogus story, I think

[Anonymous Coward]

But there's no consensus as to the best way to get rid of the physical kilogram.

You mean I can't just break into that vault and use a blowtorch?

Re:Bogus story, I think

[fm6]

That's the original definition of a kilogram. It's been abandoned. Apparently it's hard to guarantee that water has consistent density.

Re:Bogus story, I think

[Toinou]

It is clearly completely bogus and outdated according to the BIPM :
-data are 15 years old
-the kilogram is losing weight since the beginning (circa 1890)
Furthermore the article seems to say that using an object as a standard is bad. This is false, and the reverse is quite true. Until atomic clock, the second was very difficult to mesure, due to an absence of a concrete standard. The meter was defined by the speed of light in the sixties.
And it IS possible to define a kilogramm without an object, but it is imprecise, despite a huge effort in research.
And funnily, in french, the place where the BIPM is not situated in a chateau but in a "pavillon".
What I think is that a reporter wanted to spend a few days in Paris. His superiors did not notice that the BIPM had a very well documented web site, and did not see that they have been fooled. Fortunately, there is a lot of international institutions in Paris, so this reporter can still have some nice holidays. Next week :"Water stress tends to occur where individual rights and liberties are limited...." (from UNESCO which have its headquarters in the wealthiest quarter of Paris).

Re:Bogus story, I think

[fm6]

My insults are never gratuitous. For example: you're an idiot because your "correction" of what I said says the same thing I said.

Re:Bogus story, I think

[darkmeridian]

"But there's no consensus as to the best way to get rid of the physical kilogram."

New technology may be able to help. By growing silicon crystals in a near-perfect lattice, and being able to form an almost perfect spheres in this silicon lattice, and therefore being able to figure out how many silicon atoms there are in the sphere, scientists want to redefine the kilogram as a precise number of silicon atoms. Then anybody who can count out that number of silicon atoms (or a known fraction thereof) can have their own reference mass without going to Paris.

Re:Call us when you're using Newtons, and we'll ta

[tftp]

People measure their mass, which just happens to be proportional to their weight at any given point in space. The proof of that is in the units that they get their readings in. Newton and gram are SI units of force and mass. There is no contradiction.

Expanding universe?

[Roadkills-R-Us]

I've often wondered whether the expanding universe would affect perceived mass and/or weight...

Re:Expanding universe?

[exp(pi*sqrt(163))]

> I've often wondered whether the expanding universe would affect perceived mass and/or weight...

Why do you expect the expansion of the universe to somehow affect our perceptions?

Screw the SI system...

[Anonymous Coward]

All these problems with units & standards could be sorted once and for all if we simply define everything using the "Furlong/Firkin/Fortnight" system (http://en.wikipedia.org/wiki/FFF_System). This has some nice convenient measures for everyday things. For example :

• 1 centifirkin is slightly less than 1 pound (.90202)
• 1 millifortnight is equal to about 20 minutes.
• 1 decafurlong is about 2.01168 kilometers.
• The speed of light is approximately 1.8 terafurlongs per fortnight

Practical for both general public and scientists!

Eat that, Eurotrash!!

[commodoresloat]

Proof at last that the imperial system of weights and measures is superior to that silly "metric" fad....

Re:Eat that, Eurotrash!!

[Anonymous Coward]

Eurotrash? Try the entire world except the US, Myanmar, and Liberia.

Re:Eat that, Eurotrash!!

[Anonymous Coward]

> Proof at last that the imperial system of weights and measures is superior to that silly "metric" fad....

Except that the customary measures (both british and yankee system) are OFFICIALLY defined in terms of metric units and have been for several decades! There is no such thing as a supermaster pound etalon kept inside multiple vacuum jars somewhere, it is just 0,452blahblah part of the prototype kilo's weight kept in Paris.

Therefore any problem with SI units affects the anglosaxons as well.

Re:Eat that, Eurotrash!!

[Quill_28]

It is a joke people. And I thought it was funny.
Why dissect a joke?

Almost everyone I know in America is not crazy about the "English" system.
But we have grown up with it, especially Fahrenheit and miles.
We are getting better knowing how much a liter is or how long a cm is, but not Celsius and Kilometers.

Unit of force

[SkyFalling]

If you think the kilogram is in bad shape, consider the dire fate of the Newton (the SI unit of force, a.k.a. weight). Newton's been decomposing for centuries -- there's no way he weighs the same as he used to!

Re:Unit of force

[Guppy06]

"Newton's been decomposing for centuries"

Could be worse: he could be Ohm.

Better standard than a chunk of metal.

[Neanderthal Ninny]

I remember a very long time ago the other standards like distance and time were defined by very archaic standards like scratches on a long bar for distance and fraction 1/86 400 of the mean solar day for time. Now we use more advance technology to define these measurement but one has remained the same, mass. So we need to use some better standard than a chunk of metal to define mass so like the other people we should use an non-varying and stable standard for this like how many moles of C12 (carbon 12) which is stable.

Re:Better standard than a chunk of metal.

[Anonymous Coward]

Too bad the mole is based on the kilogram. 1 mole = number of C12 in 12 grams. (Avogadro's "constant", about 6.02214179x10^23)
 
So, to solve this we just need to use number of C12 atoms per kilo.. about 5.01845149167x10^25 atoms. Or we could use weed or coke.

Idea!

[Atario]

How about the mass of a hydrogen atom (a regular single-electron, single-proton one) times some massive number? Wouldn't that work as well as the cesium-wavelength-times-a-massive-number standard for length?

Re:Idea!

[fm6]

Don't ask me, I have trouble measuring coffee.

Re:Idea!

[elFarto the 2nd]

Length is c (speed of light) divided by some large number. Caesium is used for time.

Regards
elFarto

lb

[starrsoft]

And here I thought from reading the headline that we were finally starting to win the imperial/metric war!

E=m.c^2

[femto]

Since E=m.c^2, wouldn't the mass of "N" silicon atoms (or of any particle that generates a gravitational or electric field) depend on the configuration of those atoms and their energy states. Yes, it is a tiny uncertainty, but might it be significant?

Re:E=m.c^2

[starrsoft]

E=m.c^2 is wrong. You don't want to concatenate m and c^2.

Re:E=m.c^2

[Guppy06]

"E=mc^2"

This means it would take a (comparatively) whopping 1.49241789 * 10^-10 J to change the mass by 1.66053886 * 10^-27 kg, a difference of 17 zeros.

"depend on the configuration of those atoms and their energy states."

Long story short, we call that "temperature."

Re:E=m.c^2

[femto]

I didn't make it clear that my comment was in the context of counting atoms as a mass standard, not in relation to the fifty microgram change in the current kilogram. For example, take the mass of "n" isolated silicon atoms. Now form chemical bonds between them. How much energy is in those bonds, and what is the mass equivalent of that energy? Is it comparable to the precision of the standard? If so it will have to be accounted for.

The latent heat of vapourisation of Si is 13700J/g
Thus at a rough guess the energy in the bonds for 1kg of solid Si is 13.7MJ
Now m = E/c^2 = 13.7MJ/(3*10^8m/s)^2 = 1.52*10^-10kg. = 0.15ug.
So the mass equivalent of the bonds in 1kg of Si around 0.15ug.

It seems reasonable that a kilogram could be measured with a precision of ten decimal places, so in the worst case of no bonds vs. bonds the energy of the bonds would seem to be significant in a mass definition. In practise it might be a more subtle rearrangement of the bonds, with a lower energy differential, but for high precision comparisons it might still be a significant contributor to the the mass of 1kg of silicon.

50 micrograms is just the right weight

[Provocateur]

Put a warning label weighing 50 micrograms that says:

WARNING: Measurements are approximate

Problem solved.

Re:50 micrograms is just the right weight

[Toinou]

Sure, the weight of about 1500 bilions of hydrogen atoms is such a huge imprecision comparing to 50 micrograms.

Re:50 micrograms is just the right weight

[Anonymous Coward]

2000 years later, the original kilogram with its 29 weight adjusting stickers, including the famous "Measurements are approximate", the "cowboy neal for world president" and the "this standard is the property of the klingon empire" is still the standard for humanity.
Some random dude says:
"Hey if we used another reference to find out this standard's been changing all this time, why don't we just use the reference as the new standard?"
to which his coworker said:
"Ah shut up and keep shinning these balheks! We ain't paid to think."

It's pretty bad...

[Anonymous Coward]

It's pretty bad, when weight loses weight... yet, the already-overweight population just gains more weight.

The Ultimate Weapon of Mass Destruction?

[AllTheGoodNamesWereT]

This was in the news in mid-2003. On June 3 of that year, the Los Angeles Times ran a very funny column by Crispin Sartwell ("Crispin Sartwell teaches philosophy at the Maryland Institute College of Art") titled "Kilo Crisis Could Bring Down the Universe," which is unfortunately no longer available for free on their website. Here's an excerpt:

The kilogram is defined as the weight of the standard cylinder, whatever it may be. It is logically impossible for the kilo cylinder to lose or gain weight, at least within the metric system of measurement, because it is itself the standard by which all weights must be judged.

Thus it is impossible to "discover" that the cylinder has lost weight. The instruments by which the cylinder is weighed are wrong because the cylinder itself, by definition, is always right. Indeed, it is possible that the rest of the material in the universe, including the silicon atom, has become slightly heavier. But it is not possible that the weight of that cylinder has changed.

[....]

Now one suspects that in the long run the kilogram cylinder will continue to shed atoms. By my calculations (or rather, those of my wife, who can do stuff like multiply), at a rate of 50 micrograms per century, the cylinder will disappear entirely in 200 billion years.

Then the kilogram itself will disappear, which entails that all objects will weigh an infinite number of kilograms: Any given feather or dust mote will be infinitely heavy. And, at that point, the universe will collapse under the influence of infinite gravity into a disk about the size of a lentil, inhaling everything into a dimensional wormhole. And that will suck, with infinite force and acceleration.

In other words, that standard kilo platinum-iridium cylinder is the smoking gun, the ultimate weapon of mass destruction.

Re:The Ultimate Weapon of Mass Destruction?

[shadowbearer]

  Ultimate Weapon of Mass Distinction?

SB

Re:The Ultimate Weapon of Mass Destruction?

[nametaken]

The real sick part of all this is that some part of me really wants to accidentally knock a big chip out of that cylinder just to throw everyone for a loop.

Re:The Ultimate Weapon of Mass Destruction?

[Bloke down the pub]

That would be too obvious. Just file it down a smidgen.

Why don't we just do again what we did for the m?

[Entropius]

A while back the meter was defined artificially, by some marks on a post.

Then someone got the idea to peg it to another unit. Time and space are related, and the conversion between them is the speed of light. So the solution to the problem was to adopt a precise definition of c, thus defining the meter in terms of the second (defined elsewhere) and the speed of light (a constant).

Couldn't we peg the kilogram to either the meter or the second as well, using another fundamental constant as the conversion. Planck's constant is the obvious one. Here's a clunky definition:

Define the joule to be "The energy difference between two states which interfere with a frequency of 1.50919067 × 10^33 cycles per second" or "6.626068 × 10^-34 joule is the energy difference between two states which interfere with a frequency of 1 cycle per second." What is a second? That's defined empirically, based on a transition in cesium. Or you could define a joule as some fraction of the energy carried by a photon with such-and-such wavelength, or however you want to do it.

Now you've got the joule, the meter, and the second defined. The second is the only empirical one; the other two are defined in reference to it and two fundamental constants of the universe, h and c.

Then you define the kilogram as that mass which, when moving at a speed of 2N meters per second, has a kinetic energy of N joules, in the limit of small N (to dodge the relativistic correction). Or you could calculate the relativistic correction at 2 meters per second and put it into the definition.

They should redefine a kilogram

[neomage86]

in terms of planck mass. The planck constants are (to the best of our current knowledge) invariant since they are all based off universal constants (like the speed of light or the gravitational constant).

The planck mass is defined as the mass for which the Schwarzschild radius is equal to the Compton wavelength over Pi.

The Schwarzchild radius is 2Gm/c^2, while the Compton wavelength = h/mc = 2*pi * dirac's constant/(mc). (I'll refer to dirac's constant as d, since I don't know how to type the proper character).

Setting the two equal yields 2Gm/c^2 = 2d/mc => m= sqrt(dc/G). Then, we could define 1 kg as 45940892.447777 planck masses. The only thing's we're assuming as constant are the speed of light, the universal gravitational constant, and planck's constant.

Re:They should redefine a kilogram

[Falladir]

I'm pretty sure that the reason this hasn't been done is that G is not known precisely enough. It's an ironic state of affairs: of all the universal constants, G was the first to be identified (by which I mean that its significance was understood) and measured, and remains the least precisely known.

Re:They should redefine a kilogram

[aeve]

I agree, redefine...but it seems easier to redefine it by fixing Avogadro's number and then saying that the mass of one mole of C12 divided by 12 equals one gram.

Maybe to a physicist/mathematician it seems inelegant to base the definition of mass on an arbitrary number (Avogadro's) rather than on a physical constant. But are we absolutely, positively sure that physical constants are constant throughout the space-time continuum and that we've got them exactly right?

It's been shamed into losing weight.

[langelgjm]

I think if you had a bunch of people staring at you all day long worrying about your weight, you'd try and lose a little too!

Smaller Kilo - Smaller Package

[Zakias]

I tell you truthfully:

If my cylinder was locked in a cold dark vault for 118 years there would definitely be some shrinkage -- why is this so surprising? Especially if it's French like me!! :-)

Wonderful news!

[LynnwoodRooster]

Lose a few thousand more micrograms, and my BMI will be PERFECT!

obvious ploy by us government

[drfireman]

Shave a little off the kilogram reference, everyone who measures their weight in kilos gains a little. US residents are largely unaffected, and it helps squelch stories about the American obesity epidemic. I'll bet if you turn the Secretary of Health and Human Services upside-down, 50 micrograms of metal shavings drops right to the floor.

Dyslexics Untie

[pipingguy]

I just want to know what a klingongram is; a measure of mass or a method of communication.

Re:Dyslexics Untie

[Rod Beauvex]

Klingongram for Captain Kirk, doo dah doo dah!

Re:Dyslexics Untie

[Farmer Tim]

A klingongram? "Say it with bat'leths."

Re:Dyslexics Untie

[azenpunk]

michael dorn shows up on your doorstep in full makeup singing a telegram and tap dancing. (works been slow, and he's still got a mortgage on his mig15 {no really, look it up}.)

Not a problem

[Anonymous Coward]

This is not a problem. The unit of measure in the metric system, the metre, is defined in terms of speed of light (so it can even measure relativistic distances). Why bother mentioning it? Well in the metric system, a decimeter is 1/10 of a meter. 1 decimeter cubed is called a liter. Now when you fill a 1 liter container (1 dm^3) with pure *pure* water, it weighs exactly (actually by definition) 1 kilogram. Now on this planet we call earth, all you need to do is find *somewhere* 1/1000 of a cubic meter of water (or 1 liter) and somehow make sure that this mysterious 'water' is pure, and it will (by definition) weigh 1 kilogram. Good luck!

How would they know

[Brad1138]

If the object that defines the mass of a kilogram is showing less massive, isn't it possible that whatever they are using to weigh it needs to be calibrated by said object? They said that the "missing" mass is equivalent to the mass of a finger print. Maybe it was cleaning day and someone cleaned of an old fingerprint?

Re:Why don't we just do again what we did for the

[HoserHead]

Couldn't you just use E=mc^2 to derive the kilogram from the joule?

It must not lose mass!

[EmbeddedJanitor]

Who cares if it loses weight. It just must not lose mass. kg is a unit of **mass**, not weight.

Re:It must not lose mass!

[ArsonSmith]

I don't think you understand the gravity of the situation.

Re:It must not lose mass!

[CowboyBob500]

I can't believe I got this far down the page before anyone mentioned that it's a unit of mass and not weight.

Bob

Re:It must not lose mass!

[Anonymous Coward]

Of course it is 9.81 N/kg. Oh crap, kg again!

Re:Why don't we just do again what we did for the

[Entropius]

That'd be another way to do it once you get the joule, sure.

Excuse me?

[WheelDweller]

If "THE kilogram" is changing it's weight/density/frebosity, then isn't the _need_ for an exact kilogram lessened? If you can detect such slight changes and call them authorative, why not make a dozen of them identical, and pass'em around the nations?

"This is George Washington's hammer. Sure, it's had 12 new heads and 9 new handles, but it's *still* his hammer." :>

What's a kilogram between friends, anyway?

Re:What do you expect from France?

[Farmer Tim]

They can't do anything right except make wine and surrendor.

Obviously "surrender" isn't even in your dictionary...

Reading is Fundamental!

[coaxial]

Bogus story, I think. This entire story (which has appeared on a lot of general news sites, but no science news sites) is probably just a case of a reporter misunderstanding something a scientist said. Wow with the background of a layperson that could take the time to google up the UK NPL site, but not be bothered to read the linked article, I'm waiting with baited breath for your expert hypothesis! Please, continue!

According to the UK NPL site, fluctuations in the physical objects used to define fundamental metric units has always been a problem. Back when they were created, the ideal material for them seemed to be a hard, dense iridium-platinum alloy. This turned out to be a nasty mistake: the alloy is slightly radioactive, which means that some of its mass flies off into space all the time. No mystery there. Now let's go the article, and in particular the quote from Richard Davis, physicist with the International Bureau of Weights and Measures in Sevres France.

The mystery is that [the reference kilo and the dozens of copies] were all made of the same material, and many were made at the same time and kept under the same conditions, and yet the masses among them are slowly drifting apart. We don't really have a good hypothesis for it.

Certainly sounds like a misquote and everything is well understood to me! Kudos fm6! Kudos!

Re:Reading is Fundamental!

[fm6]

Will you please stop pretending to he all these different people? It's very tiresome.

it's a quote

[Kreigaffe]

attention poster!

You require more classic Simpsons intake.

Don't break the seal, please...

[Nefarious Wheel]

I remember hearing some years back about a graduated set of calibrated weights sent to Kennedy Space Center -- very expensive, environment-controlled copies calibrated against the standard in Paris. The set arrived in good condition, but the quartermaster who received them had instructions affix an identification plate to all inbound goods received, and complained that some of the smaller weights had turned out to be too small to drill and rivet...

Re:Why don't we just do again what we did for the

[Anonymous Coward]

-or-, and I'm just throwing this out there, we could find ourselves a nice block of iridium, and say "Hey. that thar hunk o'metal be the definitive kilogram.".

There. Now which solution was easier?

Re:Why don't we just do again what we did for the

[Entropius]

If we did physics because it was easy we'd be art history majors.

I have a watch.

[lheal]

But it only goes up to 12.

Man, the people who figured this stuff out must have been really smart.

Re:I have a watch.

[somersault]

Yeah they just made up weird standards to confuse us after they'd sorted out the whole year thing. The people who invented time - the french - actually have watches that go up to a nice round 100, and have 1000 days every year. That's why a lot of europeans can be caught napping in our afternoons, or having more than 3 meals per 'day'. I can't say any more at this juncture.

Re:I have a watch.

[thegux]

My watch goes up to eleven!

The real culprits...

[kidcharles]

This is clearly the work of International Metric Mass Prototype Gnomes. 1. Collect platinum/iridium alloy. 2. ???? 3. Profit!

Re:Why don't we just do again what we did for the

[zackeller]

Or just call it 10cm^2 of water.

Re:Call us when you're using Newtons, and we'll ta

[plover]

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

Rear Peephole of the Unix Tates of Ammonium,

Wii are using Newtons, butt wood prefer Palm Pilates.

Sincerely,
Matrix Using Counties

Re:Why don't we just do again what we did for the

[zackeller]

Or 10cm^3 of water, whichever is more existent.

Moles of carbon 12....

[Joce640k]

My chemistry teacher told me that one mole of Carbon 12 weighed exactly twelve grams so why are we still fiddling around with chunks of metal?

Maybe I just need more sleep

[SaidinUnleashed]

But did anyone else read "The Klingongram is Losing Weight"?

Oh no!

[belg4mit]

The protons are decaying! "Longer than the expected life of the universe," my ass.

Re:The metre? Hey, Swan-..

[Anonymous Coward]

You oughta see MY tattoo!

Can you spell "Saskatchewan"?

This explains it!

[Anonymous Coward]

1. Kg definition losing mass.
2. ???
3. GLOBAL WARMING!!!!

Not alot

[Joebert]

I bet the dust on my nose hairs weights more than 50 micrograms.

I predict...

[Tablizer]

...an Al Gore film about this someday.

The Iridium Diet

[yeranalyst]

I'm quite sure that loss of mass has something to do with Hawking radiation and quantum tunnelling. He was probably thinking about where the standard was at the same time he was measuring its mass. This is a common error.

Re:Why don't we just do again what we did for the

[ChrisMaple]

The properties needed for a reference are utility, stability and ease of measurement. It's fairly easy (haha) to measure both the time and the distance of so many cycles of radiation from cesium, at least in principle. Both time and distance have a great deal of utility as very accurate standards. I suspect the utility of a mass standard is much better than the utility of an energy standard, and it is much easier to duplicate. Furthermore, I don't think that energy can be measured as easily as mass (provided that there's a reference mass to measure against). Thus, the standard should be a certain number of atoms of a material that is as chemically and radiologically inert as possible, and that does not normally exist in a variety of isotopes. "Anyone" could recreate the standard by counting out the prescribed number of atoms.

Or is it...

[MadnessASAP]

If it's the official reference wait then technically that doesn't mean that its weighing less kilos everything else is weighing more kilos. (Not the usage of the word kilos rather then mass)

Re:Or is it...

[MadnessASAP]

Oh jeez... Must remember to proof read when taking Tylenol 3

If it's the official reference weight then technically doesn't that mean it's the opposite and everything is weighing more kilos? (Not the usage of the word kilos rather then mass)

Re:Moles of carbon 12....

[Detritus]

How do you obtain a mole of Carbon 12? Carbon has a bunch of isotopes, two of which are stable. Then you have the problem of how to count the atoms.

The funniest part

[aepervius]

Is that the pouind is defined as 1/2.2 Kg. In other word the two last country of earth resisting the introduction of SI, are using SI as reference.... It might be old news for many here, but I can't stop laughing at the irony.

Re:The funniest part

[Just Some Guy]

It might be old news for many here, but I can't stop laughing at the irony.

If that's an unceasing chucklefest for you, then I'm pretty sure you need to get out more.

Re:The funniest part

[Nivag064]

Actually an imperial pound weight is equivalent of 2.2046Kg under a standard acceleration of 1 g (note that 'g' is defined as 9.80665 m/s^2 [m: metre, s: second], however the Earth's gravity varies depending on where you are on the Earth (but always much less than 5%).

So who will recalibrate all those scales ...

[The Sith Lord]

... sounds like a PITA ...

Maybe...

[Greyfox]

They just didn't measure it very well to begin with. Why not just define it as a bunch of atoms of something-or-other and be done with it? Actually, do Hydrogen, just because it'd be really funny to watch someone try to work with the reference weights...

Re:Maybe...

[Dunbal]

Then a kilogram is 1000 moles of Hydrogen, or 6.023 x 10^27 Hydrogen atoms.

Re:Maybe...

[Dunbal]

me, it's been a while - maybe I should look up avogadro's number before hitting submit. 6.022 x 10^26 atoms is 1000 moles

Anyone check with the cleaning crew?

[HollowSky]

Bet the damn thing is wiped down every night. A slow sanding by terrycloth...

Metallophagic bacteria?

[Aelcyx]

Aren't there bacteria that eat anything? Perhaps it is oxidizing the metal and it's becoming gaseous and escaping through the vacuum jars somehow? If this one in Sevres is more famous, it was probably touched more and could have been transmitted by someone somehow.

Kind of a long shot, but first thing I thought of.

that's good news!

[buttle2000]

Now I can give up my diet. :)

news?

[Anonymous Coward]

this isn't news is it? isn't this why they're growing a new Kg down under?

Oh great...

[Anonymous Coward]

Now _I_ have the same mental image too.

MOD PARENT DOWN

[Anonymous Coward]

o-- IONS?! WTF?!!?! Go learn chemistry, idiot & idiot moderators!!!

Imperial reference units?

[testerus]

Excuse my ignorance, but what reference units does the imperial system use?

Re:Imperial reference units?

[cnettel]

The only reference is conversion into S.I. by well-defined constants, and then trusting the S.I. references.

triple point

[Anonymous Coward]

i think its defined at the triple point. http://en.wikipedia.org/wiki/Triple_point

isotopes

[Anonymous Coward]

to ensure that the isotopes are in a standard ratio

http://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water

Ask the cleaning lady

[Bombur]

118 years of polishing should be enough to lose some weight.

Herbal medicine!

[kbahey]

Yes, indeed. The herbal weight loss pills are working!

News for nerds.

[salmiak]

Stuff that matters?

c^2 is pretty big

[Anonymous Coward]

so you'd need to be able to measure mass change VERY accurately. And that's a problem because the best reference would be Avogadro's number of C12 (not C13 or C14) atoms. But Avogadro's number is HUGE. We can't sit about and count carbon atoms for even a miniscule fraction of that number. And in bulk, you need to have length and purity of object accurate and keep re-measuring both to make sure it hasn't changed. The errors this make could swamp any calculation since errors in MASS change are multiplied c*c times for energy under this definition.

6" height difference = 50ug/kg

[redelm]

Do the math. If the platform/building/Paris is 6 inches further away from the Earth's center of gravitation, that makes for 50 ug/kg less gravitational force.

There may be some effect of magma density and or local buildings.

If we are being pedantic

[marcosdumay]

Ok you'll find the H3O+ ion... But you must also take into acount the H5O2+, H7O3+ and H9O4+ ions. As there will be H3O2-, H5O3-, H7O4- and H9O5-. Not counting other rarer complexes.

Also, as a previous poster pointed out, you should take the several isotopes. But not virtual particles, they add no further mass.

Re:If we are being pedantic

[azenpunk]

i didn't think you could make a fourier series out of water.

Spektrum der Wissenschaft

[Anonymous Coward]

There was a really great 7-page article on the kilogram standard and how they're trying to make a perfect sphere of silicon-28 to create a perfect standard in the June issue of the German language Spektrum der Wissenschaft (spectrum of science). You can download the pdf here: http://www.wissenschaft-online.de/artikel/874646

Losing weight...

[ekimminau]

I think it must be sweating it off due to global warming.

Re:The Kilogram is not losing mass

[Anonymous Coward]

Perhaps the kilogram is not loosing mass. Perhaps the earths gravitational field has decreased as a result of launching a load of stuff into space - therefore decreasing the earth's MASS and decreasing the kilograms WEIGHT.

Woohoo no more dieting!!!!

[DigitalReverend]

Readjusting for the loss I am now considered physically fit.

English System Definitions

[goodben]

Nowadays the English system is defined in terms of the metric system: for instance an inch is defined as exactly 2.54 cm, pounds are defined in terms of kilograms, etc.

That doesn't work

[Anonymous Coward]

A kilogram could be defined as some fixed number of some molecule - at that point, a lab could find a way to collect that number of molecules.

I tried this. It doesn't work. I always end up being off by one molecule. Very fustrating!

Re:Call us when you're using Newtons, and we'll ta

[Valdrax]

Wow. Three troll mods after one funny mod for pointing out the hypocrisy of claiming that calling kilograms a unit of weight implies US pound-bias when everyone else in the world measures their weight in kilograms?

Yeesh. I doubt we had THAT tough of a crowd here last night. Someone had an axe to grind.

Smoots?

[uberjoe]

Next you are going to say that your car gets 40 rods to the hogshead, and thats the way you likes it!

Re:Smoots?

[Ka0s_EricRat]

Jeez, and I though I got bad gas mileage. 40 rods to the hogshead is 504 miles to the gallon, on my side of the Atlantic anyway.

Re:Smoots?

[Carnildo]

Jeez, and I though I got bad gas mileage. 40 rods to the hogshead is 504 miles to the gallon, on my side of the Atlantic anyway.

How big's your gallon, rod, mile, and hogshead? Over here, 40 rods to the hogshead converts to a decidedly unfavorable fuel economy of 1186 square millimeters.

What?

[geekmansworld]

Damn you Jenny Craig! DAMN YOOOUUU!!!!

I don't get it

[Kookus]

I don't get how you can weigh anything and expect that weight to not change. Is the moon in the exact same spot? Is all of the materials under your feet in the exact same spot as well as the material throughout the world? Where are we in relationship to the sun?

There's so much mass that affects gravity that has to be accounted for that it seems pointless to try an weigh things to such precise measurements.

This is old news

[The_mad_linguist]

Not that I'm surprised, but I saw this a few years ago.

Using ed...

[White Yeti]

...and programming in Whitespace.

God runs Linux?

[acomj]

and BASH shell.
and has a sense of humor*.

Now its all making sense.

(*Dilbert)

Definition of water

[againjj]

You could specify the density of water at $PRESSURE and at its maximum density (somewhere around 4 C). The only problem with doing this for high-precision measurements is: what is water? Some fraction of the hydrogen will be deuterium, and that'll throw off the density. What fraction of the hydrogen should be deuterium for "standard water"?

Wikipedia defines what water is: http://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water

This is a job for...

[Anonymous Coward]

Aquaman!

Did you even take chemistry?????

[tempest69]

OK, exactly how far up your ass did you have to reach to pull that one out? See, we have this thing called "The First Law of Thermodynamics." At the molecular scale, water molecules don't just decide to break up and go their own way willy-nilly, not the least because both elements involved (hydrogen and oxygen) really don't like being alone (the two hydrogen atoms can go off on their own merry way as a diatomic molecule, but the oxygen will be lonely). Breaking molecular bonds in water takes energy, otherwise cracking water to produce hydrogen would be more cost-effective than cracking methanol (the carbon atoms have a more independent personality and are better able to get over any rejection issues it might have). Beyond that, even if the energy to crack an individual water molecule were as trivially small as you believe, the energy would have to come from somewhere. Cracking water is endothermic, but so is making it (oxygen atoms, at least, need to be pried apart against their will first, assuming they're not in some kinky threeway), but even if one of those two reactions was exothermic, the energy required to do one act must necessarily equal the energy released by the other, meaning a net change in energy, and a net change in the number of water molecules, of zero. The real reasons we don't use water are: Corrosiveness (which you already covered) Compressibility (there is no such thing as an incompressible substance, but liquids are more susceptible than solids) Thermal expansion (something else solids are less susceptible to) Last, but not least: evaporation

"So it is essentially impossible to get 1000 cm^3 of "pure" water."

the PH of "pure" water is 10 exp -7

that means that under normal conditions there is one ten millionth concentration of hydronium molecules. H3O+

this number increases with temperature.

protons jump in water fantastically well. This is why you can acidify standing water much faster than a dye will propagate.

Storm

Channling the Far Side...

[The Raven]

Bob knew that licking the reference weight was wrong, but his willpower was weak.

Fatsoes

[Nicolay77]

No, actually as both dollar and kilogram will lose value you will then weight much more kilograms.

So you will be very fat :P

Re:Fatsoes

[Walt Dismal]

Ah yes. I see you went to the London School of Economics and Physics. Bang on! (Actually, the shrinking kilogram is caused by global warming. The shrinking dollar is caused by rank stupidity and greed.)

Weight & Mass

[Zagra]

I found the original article unbelievably used the terms 'Weight' and 'Mass' to describe the same phenomenon - almost in the same breath! 'Mass' is surely used to describe a given quantity of matter while 'Weight' is used to describe the property of a given 'Mass' in a particular gravitic field. If the gravitic field varies then the 'Weight' will vary - the 'Mass' stays the same. If the original article meant that the 'Mass' is changing, then we have a problem in all fields of science and measurement, albeit only 50 parts per 1,000,000,000. If the term 'Weight' was intended then this can easily be explained by a local change in the gravitic field by long term movement of the Earths core, magma or other geological phenomena which may change the localised density under the Earths crust thereby reducing (or increasing) the localised field of gravity.