Introducing social networks

In the late 1960s, the famous psychologist Stanley Milgram decided to investigate the small-world concept, which states that the entire world is connected through short chains of acquaintances. Performing an ingenious experiment, Milgram asked a few hundred people from various locations to get a letter to a stranger in Boston. The participants were given information about the target recipient and instructed to send the letter to someone they knew that would more likely know that individual. The following person in the chain had to repeat the same task and send the letter to someone even closer. When Milgram examined the letters that reached the target, he realized they had changed hands about six times on average. The result demonstrated that, on average, any two individuals in the US are separated by five connections, known by the phrase six degrees of separation.

Although this outcome can be debated for many reasons, it paved the way for similar experiments...