Einstein’s Clocks, Poincaré’s Maps

Peter Galison sets two problems side by side: Henri Poincaré coordinating longitude and time zones across the French empire, and Albert Einstein reading patent applications for clock-synchronising devices in Bern. Both men were working on what it means for two distant events to happen at the same moment. Galison shows relativity emerging not from pure abstraction but from the practical business of making clocks agree across a continent.