Henry Bennie recently travelled to Paris with the UK kilogram to witness the historic redefinition vote. His trip was captured by BBC's Inside Science

Almost 130 years after the kilogram was first defined by the IPK (international prototype kilogram) - a precise metal weight held in a vault in Paris - scientists have voted to update the metric system and retire the IPK. 

In order for the redefinition to be ratified, the General Conference on Weights and Measures met in Paris on 16 November where member states had to vote unanimously to use Planck's constant. 

"Metrologists from across the world have just voted to update the metric system. With the redefinition of the kilogram, alongside the units for temperature, electrical current and amount of substance. For the first time, we now have a measurement system defined by fundamental constants of the universe and not physical artefacts made by humans."

Imperial's Henry Bennie was given privileged access to this process, travelling with the UK's own kilogram from the National Physical Laboratory in London to the Bureau international des poids et mesures (BIPM) in Paris for the vote.

His report, commissioned by BBC Radio 4, can be listened to at:

https://www.bbc.co.uk/programmes/m00017wq (from about 12 mins)

Henry is an alumnus of the MSc in Science Communication and former Horizons student.