Halting the horrible kilogram shrink

The kilogram is a-shrinkin’ and ain’t nobody sure why. The problem is the way it is defined: the mass of a lump o’ metal stored in a vault in Paris. That’s no good cos a few atoms rub off each time it is picked up and others seem to fall off even when it ain’t picked up. In the last few years, it’s lost about the mass of a grain of sand.

Ain’t there a better way to define the kilogram? There sure is and shortage of em either. In November the world’s heavyweight experts are meeting in Paris to select the best definition by a vote or a toss of a coin or by some other method they ain’t told us about.

So between now and then expect to see plenty of elbowin’ n’ jostlin as the various definitions jockey for position. This week it’s the turn of Ronald “McDonald” Fox and Theodore “Over-the” Hill at Georgia Tech in Atlanta to pitch their definition.

They reckon that best way to define a kilogram is to fix the value of Avogadro’s constant, the number of atoms in 12 grams of carbon-12, at 84446886^3. That would make one gram exactly equal to the mass of 18 x 14074481^3 atoms of carbon-12.

It’s a good try but ain’t nobody gonna be happy with that definition. Why use carbon-12 and not silicon which is the current darling of most heavyweights in physics? And why rely on countin’ when you can define a kilogram in terms of its equivalent energy, thereby linking it via relativity to another fundamental: the Planck constant?

It’s all shapin up nicely for one helluva mudwrestle in Paris in November. All we need is a unit of hellraisin so we can work out the winner.

Ref: arxiv.org/abs/0709.2576: A Better Definition of the Kilogram

4 Responses to “Halting the horrible kilogram shrink”

  1. devicerandom says:

    And why rely on countin’ when you can define a kilogram in terms of its equivalent energy, thereby linking it via relativity to another fundamental: the Planck constant?

    Beautiful approach. The only problem I see is that counting is possible (by mean of crystallography etc.), while measuring annihilation energy is probably quite harder. You also can measure it for one or a few atoms, but then you need to multiply it for the number of atoms in a kilogram (not counting binding energy etc)… therefore, you still need counting, I guess.

  2. KFC says:

    Not if ya use a Watt balance, a kinda celebrity smackdown in which a kilogram comes up against the force generated by an electromagnetic field. That gives you a pretty good way to determine the mass of the kilogram via the energy of an equivalent em field. Them measurers and metrologists at NIST have been a-prodding and a-kicking kilograms in this way for some time now

  3. David Freid says:

    If you know the number of atoms which have disappeared from the kilogram as measured orginally, can’t you determine the “correct” number of atoms and define the kilogram as that number of atoms? Also, can’t you determine the “correct” weight of the kilogram by adding its present weight plus the weight of what has been lost?

  4. Zephir says:

    By Aether Wave Theory the kilogram shrinking is related to iridium prototype dilatation and it’s the result of space-time collapse during universe expansion.


    It’s a result of the compressibility of Aether foam and it can be explained by MOND theory as well. As such this phenomena is related to the Pioneer anomaly and other phenomena, including the changes of physical constants. Compare the Expanding Earth hyptohesis.