Sound and Fury

Signifying nothing

yotta, zetta, exa, peta, tera, giga, mega… kilo?

with 9 comments

All SI prefixes that are positive powers of 10^3 end in an “a” except “kilo-” I propose we change it to “kila-” because it won’t really make a difference to how people talk; a kilagram and a kilogram would be pronounced similarly by most people. What about people talking about “a kilo of rice” or whatever? Well, “kilo” can be adopted as a non-SI measure of weight much like “pound” or “ounce.”

Similarly, all SI prefixes that are positive powers of 10^-3 (or negative powers of 10^3) end in an “o” except “milli-” We should change that to “millo-” again with little or no need to alter how we talk.

Surely the Système International d’Unités is all about consistency. This is a a huge oversight on their part. Also, having a kilo, or kilagram, in Paris which is what we use to define what a kg is is quite unsatisfactory. If you want to know how long a second is, you look it up on wikipedia:

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 can get an atom of caesium 133 and do it yourself. With that measurement in place you can find out how long a metre is:

The metre is the length of the path travelled by light in vacuum during a time interval of 1299,792,458 of a second. It follows that the speed of light in vacuum is exactly 299,792,458 metres per second.

You can procure a light source and a vacuum and find out how big a metre is.

But the kilagram, not so. If you want to know how big a kilo is, you have to go to Paris and weigh something against the International Prototype Kilogram. And while we’re at it, why does the SI unit have a prefix. That’s annoying too! I’m glad there are at least proposed future definitions. I don’t know if I’ve got my physics all backwards here, but here is perhaps another approach: Define a kilagram to be the mass a proton has when accelerated to speed X. Since distance and time are both well defined without recourse to an artefact like the IPK, this would put the kilo on the same level as them. This is an impractical definition, but no more impractical than counting osscilations in a caesium atom to measure a second or the proposed “counting atoms of carbon” approach to defining the kilagram.

Here’s a good quiz question: what do Liberia, Myanmar and the US have in common? They are the only 3 countries that have not adopted SI units as their primary method of measurement.

How cool is it that I can copy/paste text from wikipedia into wordpress and all the links automagically still work. That is really neat. Is that wordpress’ doing? Or wikipedia’s? Or firefox’s? Or Ubuntu’s? Whoever is responsible, you are now my heroes!


Written by Seamus

July 3, 2008 at 12:25 pm

Posted in annoying, random, science

9 Responses

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  1. […] was thinking a bit more about my complaint about the kilo. I was wondering whether you could define a kilo in terms of the weight of a certain volume of a […]

  2. i’m glad i know i’m not the only person that this kind of thing bothers. People ask me questions about these things a lot because i’m the resident scientist, but the almost don’t believe me when they ask abuot grams and kil[a]grams that the definition based off this little block in france


    July 10, 2008 at 8:28 pm

  3. let’s paint all the walls in the world grey for consistancy’s sake too. ;)


    July 11, 2008 at 1:51 am

  4. Mass is calculated based apon a Meter (metre) which was defined in the whole vacuum and light test.

    Take a block which is 1/10 of a meter in height width and depth, fill it with pure water (H20) at 25 degrees C. And it will weigh Exactly 1 Kg. Or, take one cubic centimeter (one cc) of water, at 25 degrees C. And it will weigh exactly one gram.


    December 30, 2008 at 6:02 pm

    • While true, technically speaking this isn’t how the kilo is defined. Maybe it should be. Presumably this coincidence of measurements was deliberate, but strangely the institute in charge of these things didn’t see fit to make what you describe as definitional as to what a kilo should be. Perhaps they felt that it wasn’t accurate enough – temperature measurements can only be so accurate. Remember temperature is just thermodynamical shorthand for mean kinetic energy of the particles, so there are fundamental limits below which temperature doesn’t mean anything. Perhaps these concerns preclude your method from being accurate enough for the instute…


      January 17, 2009 at 3:40 pm

      • Dear Nerds,

        You know too much about too little…
        The metro was defined (200 years ago) based on the length of the Earth Meridian.
        It is no coincidence that one degree of latitude corresponds to 100Km.
        Obviously, the unit of weight is the Gram and the Kilogram is a multiple of it.
        It is no coincidence that it corresponds to 1cm3 of water.

        200 years ago it was a great progress compared to how England and the US measurement standards.

        One must not forget that (thanks to Hitler) many great scientists (and also artists) came to America after the war making it a significant scientific country.

        Before that, English, French, Italian, German, French and even Russian scientists discovered everything significant.

        You don’t need to go to Paris (actually, Sevres) to measure anything according to the International System.

        You can just go to an american store and buy a measuring device built according to the International Standard.

        However, if you prefer to use sub-atomic particles to do your measurements, the same way there are subsequent definitions of length based on micro-wave radiation there are also definitions of weight based on the mass of the Proton or Electron (if you think a Proton is not small enough).

        You can also measure everything in Inches or Pounds and later convert to International Standards.

        However, if you are a scientist, you can also refuse to convert and publish your work in Burma and Liberia.

        Good Luck!


        November 20, 2009 at 8:12 pm

      • Do your research. The SI base unit of mass is the Kilogram. Not the gram.

        The point of the post was simply to point out that this is weird. I’m not claiming that I am incapable of measuring something to near enough a kilo. The point is that it is strange that a kilo is defined in such an archaic way: while the metre is defined in terms of an experiment I can in principle repeat, the kilogram is not.

        I doubt there is such a thing as knowing too much about something. And don’t tell me my range of knowledge isn’t broad enough.


        December 7, 2009 at 5:05 pm

  5. Could you explain better? Maybe a same temperature could implicate a different radiation spectrum, and that is why it could implicate a different molecular asset hence a different specific volume?
    Cannot we ask directly that damned Institute of Weights? I suspect it is just a matter of French grandeur!
    Thanks for this interesting matter.


    June 7, 2009 at 2:30 pm

  6. Some one, for instance Fabio Marchesi, a light expert engineer (who’s site is, believe that light speed can change…
    Whenever it should happen, what would do the Institute of Measurements? Have they considered this hypotesis?


    June 7, 2009 at 3:12 pm

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