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US Objects To the Kilogram

Posted by Soulskill on from the weighty-subjects dept.

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.'"

9 of 538 comments (clear)

  1. Get rid of the artifact? by XanC · · Score: 3, Interesting

    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.

    1. Re:Get rid of the artifact? by jdgeorge · · Score: 5, Interesting

      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

    2. Re:Get rid of the artifact? by Anonymous Coward · · Score: 5, Interesting

      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.

    3. Re:Get rid of the artifact? by kenj0418 · · Score: 4, Interesting

      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.

    4. Re:Get rid of the artifact? by Abcd1234 · · Score: 3, Interesting

      But you know that it depends on the actual structure of the silicon crystal how much X silicon atoms weigh?

      No, I don't know that at all. Please to explain.

  2. Re:Weight a minute... by XanC · · Score: 4, Interesting

    Because this prototypical kilogram is what the definition of the pound is currently based on.

  3. old, and not just the US by Imabug · · Score: 5, Interesting

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

    --
    "For I am a Bear of Very Little Brain, and Long Words Bother Me"
  4. Speaking as a metric man by Max+Romantschuk · · Score: 3, Interesting

    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.

    --
    .: Max Romantschuk :: http://max.romantschuk.fi/
  5. Re:The difficulty of standard artifacts by goodmanj · · Score: 4, Interesting

    Very clever, Mr. Wittgenstein. Unfortunately shortly after you died we defined the meter in terms of the speed light travels in a certain amount of time, and abandoned the Paris standard meter. So one thing can be said for sure: the Paris standard meter is definitely *NOT* one meter long."