Tomorrow’s Tech Treepowered by Astra

Sensors & Measurement · Recorded milestone

Metre defined by light

Recorded year1983

The metre is redefined by the speed of light, measured with lasers.

Explore this milestone on the interactive map

Built on

Atomic clockRecorded · 1955requires
Integrated circuitRecorded · 1958requires
International System of UnitsRecorded · 1960enables
LaserRecorded · 1960enables

Led to

SI redefined on constantsRecorded · 2019enables

Sources & evidence

Additional source

Dataset updated 2026-10-18. This individual record has not been separately re-reviewed.