The guardians of the world's most important standards of weights and measures have turned to the weird universe of quantum physics to try to resolve a dilemma.
To the bafflement of scientists, a cylinder of metal sitting in a closely-guarded strongbox that is the global benchmark for the kilogram is changing mass.
The enigma doesn't affect anyone who wants to buy 500-milligramme tablets of aspirin, half a kilo of carrots or a 50,000-tonne cruise ship.
But it poses a hefty theoretical challenge to physicists, and complicates the work of labs which need ultra-precise, always-standard measurement. More...Yahoo news
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