Speed of information

Nowadays, we say that the speed of information is the speed of light. That is justified by the rôle of the speed of light in relativity, in which it is the speed of causation. But it is also justified by the use of electromagnetic waves to transmit information between people.

It was not always so. It took much longer for information to travel in the past.

A day’s journey in pre-modern literature, including the Bible, ancient geographers and ethnographers such as Herodotus, is a measurement of distance. In the Bible, it is not precisely defined; the distance has been estimated from 32 to 40 kilometers (20–25 miles). Wikipedia

A critical fact in the world of 1801 was that nothing moved faster than the speed of a horse. No human being, no manufactured item, no bushel of wheat . . . no letter, no information, no idea, order, or instruction of any kind moved faster. Nothing ever had moved any faster.  Stephen E. Ambrose, Undaunted Courage (Simon & Schuster, 1996), p. 52.

The book A Farewell to Alms includes a table showing how long it took for news of sig­nif­i­cant events to reach London. Faster speeds resulted from the in­ven­tion and de­ploy­ment of the telegraph by 1880:

Speed of Information Travel to London, 1798-1914
EventYearDistance (miles)Days until reportSpeed (mph)
Battle of the Nile17982073621.4
Battle of Trafalgar18051100172.7
Earthquake, Kutch, India181941181531.1
Treaty of Nanking18425597842.8
Charge of the Light Brigade, Crimea18541646174.0
Indian Mutiny, Delhi Massacre18574176463.8
Treaty of TienSin (China)18585140822.6
Assassination of Lincoln186536741312
Assassination of Archduke Maximilian, Mexico186755451219
Assassination of Alexander II, St. Petersburg188113090.46119
Nobi Earthquake, Japan189159161246