Einstein's clocks, Poincarâe's maps : empires of time

In May 1905 Albert Einstein changed time forever; his theory of relativity had practical consequences that changed the world.

Only a century ago Europe had a huge number of local time zones and no proper system of synchronizing them.

This threatened chaos, particularly on the railways and communications.

Synchronized time was necessary to create timetables for passengers and stop trains from crashing as they hurtled in opposite directions along single tracks.Enter two revolutionary thinkers.

Henri Poincare, a member of the Paris Bureau of Longitude, realized that synchronized clocks would underpin further French conquests in Africa.

So a grid of telegraph cables was planned from France all the way down to colonial Senegal and onwards.

A Paris masterclock would transmit a telegraphic pulse with which all the clocks in Africa could synchronize.Meanwhile, working in the Bern patent office, Albert Einstein witnessed the stream of new inventions designed to synchronize the world's clocks.

This set him thinking and suggested the revolutionary conclusion that there was no such thing as "universal time" - it was just an illusion given by properly synchronized clocks.

Published when he was only 26, Einstein's special theory of relativity paper had profound consequences for the world.