The theory of "six handshakes" was first put forward by Hungarian science fiction writer Frieds Carinti in 1929. In the short story "The Links of the Chain, " he argued that anyone in the world can be contacted through a chain of five intermediaries.
In 1960, this unusual hypothesis was experimentally tested by the American psychologist Stanley Milgrem, who found that on average there are 5, 2 people in the chain. Researchers from the Department of Sociology at Columbia University repeated Milgram's experiment using e-mail. They offered thousands of volunteers to "reach out" to 20 secret people, about whom only the main characteristics were reported: name, surname, occupation, place of residence, education. The first successful attempt was to determine the postal address of one of these "classified" in Siberia. A volunteer from Australia found the address of the Siberian "target" with just four messages!
The advent of computers and the Internet has greatly increased the chances of the six-handshake hypothesis becoming an immutable fact. The analysis by Microsoft experts of the data obtained during the month of communication of 242, 720, 596 users took two years. The volume of the studied data was about 4.5 terabytes. On this database, it was found that each of the 240 million users of the service could “reach” the other in an average of 6, 6 “steps”. Than the researchers mathematically proved the theory and common joke that after five people each of us is familiar with the Queen of England.
The University of Milan and social networking site Facebook also conducted a joint study of the theory of six handshakes, based on data from the social graph of Facebook. It was found that any two Facebook users are separated by 4, 74 levels of communication. For the USA, the number of links was 4, 37.
On the VKontakte social network, the application ("Chain of friends - the theory of six handshakes") allows you to search for dating chains between network users. Since the VKontakte audience is limited (Russia and the CIS countries), it is not possible to achieve the same results as described above - the chains are shorter (3-4 people). However, it is interesting that chains longer than 6 people practically do not occur, which indirectly confirms the original theory.