It originated from the chain letter experiment of understanding interpersonal network conducted by Stanley milgram, a psychology professor at Harvard University, in 1967, and found that the average interval between people and any stranger would not exceed 6. In other words, you can know any stranger through six people.

The six-degree separation theory expresses an important concept: any two strangers can always have an inevitable connection or relationship through certain contact methods. In other words, more new relationships can be developed by passing on friends between friends.

Extended data:

1 and the development of six-degree separation theory;

1998, Duncan Watts, a young scholar who teaches in the sociology department of Columbia University, and Strogatz, a mathematician who is the tutor of his doctoral thesis, put forward the "small world network", that is, the W-S small world network model.

In this model, they think that many networks in the real world can neither be completely regular closed-loop networks nor completely random decentralized networks, and the "small world model" is in between.

2. Small-world network has the characteristics of "high network aggregation" and "low average path";

Aggregation means that if individuals have common friends, then two individuals are more likely to become friends.

"Low average path" means that two people can get in touch through a relatively short intermediate connection.