Einstein’s Clocks, Poincaré’s Maps

by Peter Galison

This is an absolutely brilliant investigation into two related discoveries that deal with how you define what is simultaneous. Poincaré helped us get to the notion of time zones and longitude in the 19th century. Einstein was working as a patent clerk in 1905, and Galison’s wonderful research shows how he was looking at a lot of applications for ways to synchronise clocks. They tended to require sending a light or radio signal between two distant clocks, and this helped inform Einstein’s thought experiments that led to his special theory of relativity.