The weight is over: will kilograms get an upgrade? – Science Weekly podcast

On 16 November, scientists vote on whether to update the way we measure the kilogram. This week, Ian Sample investigates the history of the metric system, and finds out how universal constants might now make it more robust

On 16 November, scientists will vote on whether or not to update the way we measure the kilogram and three other base units. Currently the kilogram is defined by a cylinder of platinum-iridium, locked in a vault in a suburb of Paris. But few have access to it, and the international copies are ever so slightly shifting their weight relative to it.

The hope now is to move away from this unstable, physical artefact and instead base our definition of mass on a fundamental constant of nature - Planck's constant. If this goes through, the whole metric system will for the first time be derivable from natural phenomena.