Slashdot is powered by your submissions, so send in your scoop


Forgot your password?
United States Science

US Objects To the Kilogram 538

Velcroman1 writes "For 130 years, the kilogram has weighed precisely one kilogram. Hasn't it? The US government isn't so sure. The precise weight of the kilogram is based on a platinum-iridium cylinder manufactured 130 years ago; it's kept in a vault in France at the International Bureau of Weights and Measures. Forty of the units were manufactured at the time, to standardize the measure of weight. But due to material degradation and the effects of quantum physics, the weight of those blocks has changed over time. That's right, the kilogram no longer weighs 1 kilogram, according to the National Institute of Standards and Technology. And it's time to move to a different standard anyway. A proposed revision would remove the final connection to that physical bit of matter, said Ambler Thompson, a NIST scientist involved in the international effort. 'We get rid of the last artifact.'"
This discussion has been archived. No new comments can be posted.

US Objects To the Kilogram

Comments Filter:
  • by XanC ( 644172 ) on Friday October 29, 2010 @03:44PM (#34066696)

    Last I heard, nobody had come up with a way to define mass without referring to an artifact. It seems easy but they all turn out to be circular.

    • by FooAtWFU ( 699187 ) on Friday October 29, 2010 @03:48PM (#34066760) Homepage
      Well, you can try counting atoms. But apparently that turns out to be a royal pain.
      • by Tumbleweed ( 3706 ) * on Friday October 29, 2010 @04:36PM (#34067606)

        Well, you can try counting atoms. But apparently that turns out to be a royal pain.

        Or at least an Imperial pain. :)

      • by fermion ( 181285 ) on Friday October 29, 2010 @05:20PM (#34068208) Homepage Journal
        This is essentially what is happening [], and it has been going on for a few years.

        Essentially a sphere will be created of a specific isotope of silicon and a specific diameter. This sphere will have a known number of atoms. This is superior not only because of degradation of a physical standard, but also because it will be easier to create a standard from basic principles using appropriate lab equipment.

        The US is quite late in it's objection as the problem has been known and accepted for many years. TIme and distance is essentially measured with light, and only the kilogram still has a physical representation.

        It is probably a simple matter for the US to accept the new standard.

        • by Darth ( 29071 ) on Friday October 29, 2010 @06:03PM (#34068668) Homepage

          The Avogadro project (the thing in your link) has been going on since 2007.

          The NIST (the U.S. measurements standards body) provided an implementation of another possible solution to the problem in April of 2007.

          To say that the U.S. is just now objecting is inaccurate.

          To say that the U.S. is late in its objection ignores the fact that the U.S. has been working on the problem with international standards bodies for many years.

          What (unsurprisingly) the Fox News article gets wrong is that the NIST is not submitting a formal objection.
          The Consultative Committee for Units (one of the advisory groups for CIPM), of which the NIST is a member, has submitted a formal resolution to change the definition to the CIPM. The CIPM is about to submit that resolution to the CGPM, which is the international body that regulates these definitions.

    • by jdgeorge ( 18767 ) on Friday October 29, 2010 @03:50PM (#34066786)

      Aren't they just proposing removing the dependence on the 1 kilogram cylinders?

      From the article:

      Physicists may scoff at the thought people allowed to walk among the living who don't know what a Planck value is. But all you need to know is, they're using it to determine the mass of one mole of silicon atoms.

      From there on, they'll theoretically be able to deduce a perfect kilogram and it won't have anything to do with lumps of metal ever again. /quote

    • by Guspaz ( 556486 )

      The gram was originally defined in relation to a cubic centimetre of water (the temperature originally being 0 degrees, later 4 degrees). Then the IPK was made based on this.

      So, what's the problem here? Don't we have a fixed reference, the weight of a given volume of water at a given temperature? Why can't we re-calibrate from that?

      • by XanC ( 644172 )

        No, because the volume depends on pressure. Which has a mass component. Circular.

      • by LWATCDR ( 28044 )

        Here I have the soluition. 1 gram = the mass of 6.02x10^12 carbon=12 atoms /12 not weight since that can very with location and atmospheric conditions.

      • Re: (Score:3, Informative)

        by BlitzTech ( 1386589 )
        You have it backwards. The liter was originally defined as 1 kilogram of water at 4C and 760 mm Hg.

        A liter is now officially defined as 1 cubic decimeter, which makes the comparison to water only approximate.
    • by Anonymous Coward on Friday October 29, 2010 @03:51PM (#34066808)

      Nah, it's actually pretty easy. You say something like "one kilogram is the mass equivalent of the energy of 3.40812408 gazillion photons with a wavelength of 550.9466543 nanometers." The meter is already defined in terms of speed of light and the second, and the second is defined in terms of the natural frequency of the caesium-133 atom. So in the end, everything is defined in terms of the speed of light and the caesium atom, with no artifacts needed.

      • Re: (Score:3, Insightful)

        by DerekLyons ( 302214 )

        If counting and weighing photons were so easy... you'd have a point. But it isn't. Pretty much every proposal for replacing the kilogram standard so far has either ended up in a circular definition, or required us to do something we don't actually know how to do.

    • by Zerth ( 26112 )

      Um, the electron-volt(eV)?

      I suppose you could use a reference electron, but any old electron will do.

      • by harrkev ( 623093 ) <[gro.ylimafnoslerrah] [ta] [dsmfk]> on Friday October 29, 2010 @04:14PM (#34067244) Homepage

        No. The reference electrons are specially-calibrated in the lab to meet the exacting standards of the measurements industry. If you start using sub-standard electrons, you get sub-standard measurements.

        I have personally seen the effects of creating matter using electrons with a charge of -0.93 instead of the usual -1. The matter that we were shipping had a net positive charge, so we had to include EXTRA electrons in the order so that the USP guy what not fatally electrocuted when he picked up the box. Do you have any idea how much those extra electrons cost my company?

        Please do not even get me started about cut-rate protons. What happens when heavy water is not quite so heavy? You don't even want to know.

    • Last I heard, nobody had come up with a way to define mass without referring to an artifact.

      There are several ways to define a KG using constants or atomic weights. []

      The trick is that you not only have to be able to define it, but measure it reliably and accurately.

      • by blair1q ( 305137 )

        The artifact system is not reliable and accurate, and certainly not easy to use. If you can't replicate the conditions of the definition in a remote lab, then the definition is bollocks. I mean, what if we lose these things?

        The right way to do this is to reverse the definition of Avogadro's number. Instead of "Avogadro's number is the number of C-12 atoms in 12 grams of C-12," you say "Avogadro's number is exactly 6.022141500000000000000000x10^24 and that number of C-12 atoms is 12 grams."

        Now anyone who

    • by Sir_Sri ( 199544 )

      You could use an integer number of some base element (hydrogen, helium, carbon 12 something like that). Sort of like time based on radiation emissions or the like. The problem is both precisely and accurately measuring it, and agreeing on what base element. The actual details are fairly simple, you probably want something with the minimum of unstable isotopes that occur in the minimum quantities possible. It's a matter then of finding something suitable (that you can either separate out the isotope easi

    • Re: (Score:3, Informative)

      by goodmanj ( 234846 )

      The goal is to use a single atom as the artifact. Atoms (of a specific isotope) are always *exactly* the same, so there's no concern about variations in the weight of the artifact over time.

      So all you've got to do is build an object with a mass as close to 1 kilogram as possible, precisely count the number of atoms it contains, and then make a definition like:

      "A Kilogram is defined as the mass of 5.018451 x 10^22 atoms of Carbon 12".

      The difficulty is precisely counting the number of atoms in a macroscopic

    • by kenj0418 ( 230916 ) on Friday October 29, 2010 @04:06PM (#34067070)

      Last I heard, nobody had come up with a way to define mass without referring to an artifact. It seems easy but they all turn out to be circular.

      kilogram: the amount of mass required to deflect a proton by X degrees at a distance of Y meters.

      I'm guessing X and/or Y would have to be quite small.

    • Question... (Score:3, Funny)

      by Joce640k ( 829181 )

      How does "America" define the pound...?

  • BASE16 (Score:5, Funny)

    by AmigaHeretic ( 991368 ) on Friday October 29, 2010 @03:45PM (#34066712) Journal
    Death to KILLograms!
    Ounces and pounds were way a head of the time and are becoming even more useful with the advent of computer systems and the common use of base16.

    16 ounces in a Pound is not just coincidence.

    F=15 ounces
    10 = a pound

    We can all agree, I am sure, it's easier to look at 89 and go, 8 pounds 9 ounces. With metric I have to keep moving the decimal place around and remember how many 0s there were in huge words like kilogram, milligram, centigram.
    • Re: (Score:2, Informative)

      by Yvan256 ( 722131 )

      Computers use base 2, humans use base 10.

    • Jesus people it was a joke as to the headline of the article, "US objects to Kilogram" and how we still insist on using the pound over the kilogram.

      Obviously base16 would be retardedly hard for every day measure for most people.

      How many pounds is FCA again grandma?
      • Re: (Score:3, Interesting)

        by John Hasler ( 414242 )

        > ...we still insist on using the pound over the kilogram.

        But we don't. The metric system has been legal for trade in the USA since 1866 and the official customary units have been based on it for almost as long. In 1975 it was official adopted by the Federal government for its use and in 1985 it was identified as the "preferred" system for trade. Most goods are labeled in both metric and customary units. It's just that, unlike other countries, the USA has not outlawed the use of customary units as we

    • The Chinese Suan Pan had 5 earth beads and 2 heaven on each rod, with each heaven bead being 5. You counted 1, 2, 3, 4, then zero'd the Earth and shifted a Heaven bead for 5; 6, 7, 8, 9, then zero'd and shifted a Heaven bead to make 10; then 11, 12, 13, 14, and then finally used that last Earth bead to make 5 + 10 = 15. Then 1 on the next rod meant 16. This is because there were 16 liang to 1 jin.
    • Sure. Please do the following calculation in your head (you can use your fingers too)

      Let's say a bag of wood weighs 8 pound 9 ounces, and you want to buy 3 bags. What is the total weight in pound and ounces?
      Versus, you have 8.9kg of wood, and you want to buy 3 bags, what is the total weight in kg?

      I am sure you'd be able to multiply in BASE16 if you are trained for it, and memorize the BASE16 multiplication table when you were a kid. But for the rest of us, BASE10 is what we learned and used to.

  • by walmass ( 67905 ) on Friday October 29, 2010 @03:48PM (#34066758)
    It clearly states this is an international effort, and the objection is not the the unit 'kilogram' but rather to using a decaying (however slowly) object as the reference mass.
  • by Imabug ( 2259 ) on Friday October 29, 2010 @03:48PM (#34066764) Homepage Journal

    seriously, this is pretty old. physicists working in metrology have been working to redefine the kilogram for at least the last few decades

  • by Anne_Nonymous ( 313852 ) on Friday October 29, 2010 @03:49PM (#34066772) Homepage Journal

    We have American pints and British pints; the imperial tone, the short ton, and the tonne; why not have an American kilogram and traditional kilogram as well? That should really simplify things for NASA/EUA coordination.

  • by Max Romantschuk ( 132276 ) <> on Friday October 29, 2010 @03:49PM (#34066776) Homepage

    Funnily enough I never ever think of a kilogram as the weight of some standard weight in a vault somewhere. The only way I ever think about the kilogram is the weight of one liter of water. Also comes in handy when I'm calculating how much liquids I can afford to buy when shopping groceries, given that I often go to the store on foot for the exercise and have to make sure I can manage the haul back.

    So, um, does this all really matter? In practice, that is.

  • Who cares? (Score:5, Funny)

    by tarsi210 ( 70325 ) <> on Friday October 29, 2010 @03:50PM (#34066784) Homepage Journal
    It's the US of A -- we don't use the kilogram anyway. Change it as you like.

    That being said, keep your filthy hands off my hogshead.
  • by Homburg ( 213427 ) on Friday October 29, 2010 @03:51PM (#34066802) Homepage

    "There is one thing of which one can say neither that it is one metre long, nor that it is not one metre long, and that is the standard metre in Paris." - Wittgenstein, Philosophical Investigations

  • about a decimal place in which the instuments available to most of us can't even touch (precicion-wise...) But by all means, carry on.
    • No, but every NIST-traceable instrument eventually gets back to those standards. Sure, there are a very small number (probably a dozen or so) weights directly calibrated against the original articles. But then those are used to calibrate a few hundred weights at metrology labs, which are used to calibrate weights for thousands of customers around the world. Each step introduces uncertainty, but uncertainty around a precise value can be accounted for. Uncertainty around the wrong value renders the instru

  • by countertrolling ( 1585477 ) on Friday October 29, 2010 @03:54PM (#34066856) Journal

    We're going to let the kilogram "float" and put it on the commodities market. It should triple the value of the gram

  • Why is the US objecting to a standard that it has not ever taken the time to actually use? Talk about anything in metric to most anyone from the US and they go "what's that in English?" Argh!!!!

    That said, I am compelled to agree with the reasons for the change... hopefully the new value is close enough to the old that not too much should require updating (I'm thinking the most likely candidates for updates are books in astrophysics).

  • ...given the bulk of the population doesn't even know what metric is and that they measure distances in football field lengths.

    Not quite as retarded as calculating weight in stones, but it`s only a foot away from that.

  • by MConlon ( 246624 ) on Friday October 29, 2010 @04:03PM (#34067014)

    Newton is a weight. The summary (and the Fox article) are incorrect, while the NIST article correctly refers to the reference mass.


  • by starseeker ( 141897 ) on Friday October 29, 2010 @04:04PM (#34067036) Homepage

    and misses the point. The variability of the kilogram standard is a scientific and engineering concern, not a political one.

    Wikipedia discusses the issue: []

    In a nutshell - in order to create 1 kilogram physical standard masses, you have to first know what a kilogram IS. The physical standards referred to in the article do not appear to have retained constant mass over time. You can't define a constant based on something that is variable, so the current masses are (as I understand it) acknowledged to be an inadequate basis for the definition of the unit. The problem arises when you try to pick something to define it with that is both stable (i.e. a fundamental property of the natural laws of the universe) and practical (can actually create one to use as a practical mass standard against which you can prepare working standards.)

    From articles that have popped up about this over the years, my guess is they will have to pick something as a basis and then work on various practical techniques to get as close to that ideal as possible - the question is what specifically to pick. N Carbon atoms? N Si atoms? What are the pros and cons when trying to physically create something that represents those numbers? How stable will a standard created according to a chosen standard be over time? (I.e., how often to we have to make new master standards? It's an important question - obviously the existing masses were not chosen with the expectation that their mass would vary with time, so how do we know to trust a given solution?)

    So it's not the US objecting to the kilogram as a unit, but rather concern over the methods used to DEFINE the unit. That's something quite rational, not specific to the USA, and of scientific interest. Editors, how about changing the title to "US to Propose New Method of Defining a Standard Kilogram" instead?

    • Re: (Score:3, Insightful)

      by goodmanj ( 234846 )

      This is Fox News. From their perspective, *all* concerns are political concerns.

      Global warming, economic policy, genetic engineering, epidemiology: all of these are relevant to Fox News (and MSNBC etc) only for their impact on the great battle between conservatism and liberalism.

  • by david.given ( 6740 ) <dg AT cowlark DOT com> on Friday October 29, 2010 @05:34PM (#34068360) Homepage Journal

    Oddly enough, back in about 1780, the US was desperate to switch to the new metric standard that was being developed by France.

    The reason why the US didn't go for it was the definition of the metre. Benjamin Franklin, who was a pretty good scientist when he wasn't being distracted by all this political nonsense, was unhappy with the French definition, which was a certain ratio of the Earth's circumference. The trouble with this is that not only is it practically unmeasurable, but it's not even a knowable value, as it changes depending on what you consider to be the Earth's surface. Franklin was aware that industry can always use as much precision as it can get. Events bore him out as the first metre artifact made turned out to be out by 0.2mm.

    Instead he advocated an alternate definition based on the swing of a pendulum of a fixed period. This was a knowable value; it could be theoretically calculated to as much precision as your definition of the second. As the second was at the time was based on the length of the average solar day it could be determined as precisely as you could build your telescopes, it was a much more useful definition.

    Unfortunately for complicated political reasons France was unwilling to go with this (possibly because their arch enemies, the British, were also considering a pendulum-based definition), so Franklin decided to stay with home-grown units rather than adopting the new metric system.

    So if Franklin had been just a little bit more convincing when addressing the committees in Paris, the US might have been one of the driving forces of metricisation, and maybe my web browser would have the word 'metre' in its spellchecker dictionary.

    • Re: (Score:3, Informative)

      by geekoid ( 135745 )

      we were very close to converting. Reagan killed that, because he need to make it look like he was cutting spending. Fucking douche.

  • by Tanuki64 ( 989726 ) on Friday October 29, 2010 @07:38PM (#34069548)
    If Americans want to redefine the kilogram it most likely means that in the next step they try to get royalties whenever someone weighs something.

Never say you know a man until you have divided an inheritance with him.