Facebook and Twitter were born in 18th century Europe
From humble origins, graph theory is shaping our world
In the early 1700s, the good people of Königsberg in Prussia had a problem on their minds. There were seven bridges that crossed the river in that town, and the big question was: could a route be found that allowed someone to cross all seven bridges without crossing any one bridge more than once?
Why exactly this was a concern is lost to history. Perhaps there were tolls on the bridges and people were trying to find the cheapest way about town? Or perhaps they were scared or bored of bridges? In any case, the point is that Facebook and Twitter owe a lot to the man that solved this problem.
That man was the Swiss-born mathematician Leonhard Euler. Euler seized the problem of the Königsberg bridges with the relish that only a true mathematician could have for a problem like this. And like a true mathematician always does, he reduced it to its simplest form. This problem was not about bridges — it was about something much simpler. What it reduced to was this: can you draw this graph with a pencil without crossing the same line twice and without taking your pencil off the paper:
