The kilogram is getting smaller by Corina Ciubotaru

Here's something you don't hear every day: the kilogram is becoming lighter. All of the world's measurement units have prototypes but the kilogram's is the only one that hasn't yet adapted to our computerized society. It's still a tubular piece of 90% platinum â€" 10% iridium alloy that seems to be changing weight when compared to its six copies also held at the BIPM (Bureau International des Poids et Mesures) near Paris and it's unclear to scientists if the kilogram is becoming lighter or the copies are getting heavier. The prototypes have been created in the 1880's with the original still being held today as the unit against which all other national copies are measured. The 80 national copies are sent regularly for checking and these are the only moments when the original is taken out of its safe but it looks like all the cleaning and contamination that occurs every time it is used has lead to its decay. This alteration has no meaning to the general public, as the difference between the original and the average weight of the copies is only 50 micrograms. Still, scientists intend to replace the tube with a sphere made of Silicon-28 isotope crystal which will have a fixed mass. It is estimated that the number of silicon atoms that go into a kilo will be 10 to the power of 24. The problem has been on specialists' minds for years, as measurements in physics can not be truly exact when the measurement unit varies in weight.

related story: http://news.yahoo.com/s/ap/20070912/ap_on_re_eu/shrinking_kilogram;_ylt=ApiqUYHjYAqyE6tYk3X86BCs0NUE

by Corina Ciubotaru for PocketNews (http://pocketnews.tv)

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