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Math Science

Kilogram Reference Losing Weight 546

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

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  • by allanc (25681) on Thursday September 13, 2007 @07:53PM (#20597031) Homepage
    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.
    • by flyingfsck (986395) on Thursday September 13, 2007 @07:56PM (#20597071)
      Ah, so that explains the obesity epidemic, but my ever increasing middle indicates that the metre must also be shrinking at the same time.
    • by Meshach (578918) on Thursday September 13, 2007 @08:00PM (#20597127)
      I thought that originally the kilogram was defined in terms of water, the mass of 10 square cm of water. The meter is defined in terms of the speed of light so that gives an empirical way to define the kg independent of anything else. It would be interesting to see if it has changed relative to that measurement
      • by hjf (703092) on Thursday September 13, 2007 @08:13PM (#20597291) Homepage

        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.
      • by Bender0x7D1 (536254) on Thursday September 13, 2007 @08:17PM (#20597371)

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

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

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

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

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

        • by azenpunk (1080949) on Thursday September 13, 2007 @10:00PM (#20598255)
          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.
        • by jmv (93421) on Thursday September 13, 2007 @10:07PM (#20598305) Homepage
          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 [wikipedia.org].
        • by EmbeddedJanitor (597831) on Thursday September 13, 2007 @10:11PM (#20598343)
          Who cares if it loses weight. It just must not lose mass. kg is a unit of **mass**, not weight.

        • by jollyreaper (513215) on Thursday September 13, 2007 @10:55PM (#20598669)

          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.
        • by Guppy06 (410832) on Thursday September 13, 2007 @11:11PM (#20598791)
          "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 [wikipedia.org], which would reverse the current relationship between mass and electric current.
      • Re: (Score:3, Informative)

        by 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
        • by Eternauta3k (680157) on Thursday September 13, 2007 @08:40PM (#20597593) Homepage Journal

          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: (Score:3, Informative)

            by makapuf (412290) *
            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: (Score:3, Insightful)

          by locofungus (179280)
          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 [bbc.co.uk]

          Tim.
      • 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

    • Re: (Score:3, Insightful)

      by Chris Burke (6130)
      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.
    • by Doc Ruby (173196) on Thursday September 13, 2007 @08:10PM (#20597265) Homepage Journal
      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.
      • by SQLGuru (980662)
        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
    • by this great guy (922511) on Thursday September 13, 2007 @08:20PM (#20597417)
      The wife: Don't you think I am gaining weight ?
      Me: No honey, it's just the kilogram that is getting lighter.
  • Sublimation? (Score:4, Interesting)

    by Eustace Tilley (23991) <6wdasttjcc@snkmail.com> on Thursday September 13, 2007 @07:54PM (#20597041) Journal
    Could it be a few atoms drifting off in the vapor? Well, why wouldn't the copies' atoms be drifting off as well?
    • Re: (Score:2, Funny)

      by snowgirl (978879) *

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


      This is called sublimation [wikipedia.org]. And it's the first thing that I thought of myself as well.
    • Re: (Score:3, Insightful)

      by Guppy06 (410832)
      "Well, why wouldn't the copies' atoms be drifting off as well?"

      They are, but not at identical rates.
  • Oh no, perhaps gravity is weakening, which is causing all the earthquakes in the indonesian fault lines! EVERYBODY PANIC!!!
  • 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?
  • by dada21 (163177) <adam.dada@gmail.com> on Thursday September 13, 2007 @07:56PM (#20597067) Homepage Journal
    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...
  • by Anonymous Coward
    ... why Americans use ounce-feet (or something) instead.
  • by Anonymous Coward
    How much on the black market for a microgram off the ole standard?
  • by MrYotsuya (27522) on Thursday September 13, 2007 @07:59PM (#20597119)
    It's not losing weight, it's losing mass!. The kilogram is not a measure of weight, but mass. Silly pound-centric editors :p
  • 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!
  • Mass? (Score:2, Interesting)

    by forsetti (158019)
    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: (Score:3, Interesting)

      by edwardpickman (965122)
      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
      • Re:Mass? (Score:4, Insightful)

        by djmurdoch (306849) on Thursday September 13, 2007 @08:33PM (#20597541)
        I doubt there's any equipment sensitive enough to detect weight difference in an object that was moved several feet but there is a change.

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

        Unless I was off by a few orders of magnitude...
  • by iamacat (583406) on Thursday September 13, 2007 @08:03PM (#20597163)
    I am surprised that they are not using more fundamental standards, like the mass of a hydrogen atom. After all, too many things can happen to a chunk of metal - evaporation, oxidation, radioactive decay.
    • by AvitarX (172628) <meNO@SPAMbrandywinehundred.org> on Thursday September 13, 2007 @08:10PM (#20597259) Journal
      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.
  • by abes (82351) on Thursday September 13, 2007 @08:06PM (#20597193) Homepage
    but don't worry, it will regain the weight after a couple of months.
  • Possible reason? (Score:5, Interesting)

    by robably (1044462) on Thursday September 13, 2007 @08:06PM (#20597201) Journal
    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.
  • Original article (Score:4, Informative)

    by Toinou (1059440) on Thursday September 13, 2007 @08:17PM (#20597367)
    The study comes from the BIPM ( international bureau for weights and measures) , and here is the original article : http://www.bipm.org/en/scientific/mass/verifications.html [bipm.org]. In fact it seems to be very old news since the study is carried every 40 years and the last one was in 1992, according to the BIPM :

    On three occasions, roughly 40 years apart, the mass of the official copies, the national prototypes and the working standards of the BIPM have been compared with the mass of the international prototype. [...] the last of these occasions (1988-1992) [...]
  • hmmmm (Score:5, Funny)

    by Anonymous Coward on Thursday September 13, 2007 @08:40PM (#20597585)
    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.
  • Bogus story, I think (Score:5, Informative)

    by fm6 (162816) on Thursday September 13, 2007 @08:50PM (#20597685) Homepage Journal
    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 [npl.co.uk], 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.
  • by commodoresloat (172735) * on Thursday September 13, 2007 @09:06PM (#20597857)
    Proof at last that the imperial system of weights and measures is superior to that silly "metric" fad....
  • by AllTheGoodNamesWereT (546114) on Thursday September 13, 2007 @09:32PM (#20598041)
    This was in the news in mid-2003. On June 3 of that year, the Los Angeles Times [latimes.com] 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.
  • by Entropius (188861) on Thursday September 13, 2007 @09:33PM (#20598043)
    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.

  • by neomage86 (690331) on Thursday September 13, 2007 @09:38PM (#20598063)
    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.
  • by drfireman (101623) <<dan> <at> <kimberg.com>> on Thursday September 13, 2007 @09:54PM (#20598209) Homepage
    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.
  • by pipingguy (566974) * on Thursday September 13, 2007 @09:55PM (#20598221) Homepage
    I just want to know what a klingongram is; a measure of mass or a method of communication.
  • by Nefarious Wheel (628136) * on Thursday September 13, 2007 @11:01PM (#20598717) Journal
    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...
  • by Tablizer (95088) on Friday September 14, 2007 @12:48AM (#20599463) Homepage Journal
    ...an Al Gore film about this someday.
  • The funniest part (Score:4, Interesting)

    by aepervius (535155) on Friday September 14, 2007 @01:35AM (#20599771)
    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: (Score:3, Funny)

      by Just Some Guy (3352)

      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.

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