"Stanley Milgram in his famous paper challenged people to route postcards to a fixed recipient by passing them only through direct acquaintances. The average length of the path of the postcards layed between 4.6 and 6.1, depending on the sample of people chosen. We report the results of the first world-scale social-network graph-distance computations, using the entire Facebook network of active users (721 million users, 69 billion friendship links). The average distance we observe is 4.74, showing that the world is even smaller than we expected. We study the distance distribution of Facebook and of some interesting geographic subgraphs, looking also at their evolution over time. The networks we are able to explore are almost two orders of magnitude larger than those analysed in the previous literature. We report detailed statistical metadata showing that our measurements (which rely on probabilistic algorithms) are very accurate." Background, https://www.facebook.com/notes... - Adriano