Milgram's experiment
Milgram (1967) and Travers and Milgram (1969) asked people to pass a letter to a Boston stranger via acquaintances; completed chains averaged about five intermediaries.
The Watts–Strogatz model
Watts and Strogatz (1998) showed a few random links shorten path lengths sharply while clustering stays high. Such ties act like weak ties bridging structural holes; Kleinberg (2000) analysed how short paths are found.
Later work
Dodds and colleagues (2003) replicated it by email, Backstrom and colleagues (2012) measured about four degrees on Facebook, and Uzzi and Spiro (2005) linked small worlds to creativity, informing social capital research.
FAQ
- What is a small-world network in simple terms?
- Mostly local clusters, but a few long ties connect anyone in a few steps.
- Is it really six steps?
- It is a rough average; Facebook measured about four.
Sources reviewed: 2026-10-26
References
- Milgram, S. (1967). The small world problem. Psychology Today, 1(1), 61–67. The original experiment.
- Travers, J., & Milgram, S. (1969). An experimental study of the small world problem. Sociometry, 32(4), 425–443. Academic report of the experiment.
- Watts, D. J., & Strogatz, S. H. (1998). Collective dynamics of 'small-world' networks. Nature, 393(6684), 440–442. The formal model.
- Kleinberg, J. M. (2000). Navigation in a small world. Nature, 406(6798), 845. How short paths are found.
- Dodds, P. S., Muhamad, R., & Watts, D. J. (2003). An experimental study of search in global social networks. Science, 301(5634), 827–829. Global email replication.
- Uzzi, B., & Spiro, J. (2005). Collaboration and creativity: The small world problem. American Journal of Sociology, 111(2), 447–504. Small worlds and creativity.
- Backstrom, L., Boldi, P., Rosa, M., Ugander, J., & Vigna, S. (2012). Four degrees of separation. In Proceedings of the 4th Annual ACM Web Science Conference (pp. 33–42). Facebook-scale distances.