Redefining the kilogram: units, measurement and the new SI
It’s hard to believe that the kilogram is still based on a lump of metal in a vault in Paris. But that looks set to change this month as part of a wider overhaul of SI units. This is the subject of our cover story by science writer Benjamin Skuse. Elsewhere in this special issue, Helen Margolis from the UK’s National Physical Laboratory tells you all you need to know about optical clocks, while Stephen Ornes guides you through “smoots”, “garns” and other weird and wonderful units that usually go under the radar.
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