The small-world phenomenon indicates that an individual can be connected with any other in the world through a limited number of personal acquaintances. This concept is often summarized by the phrase “six degrees of separation,” suggesting that any two people are, on average, separated by six social connections.

This was famously demonstrated by Stanley Milgram’s experiments in the 1960s, where letters were sent through acquaintances to reach a target person, revealing the short path lengths in social networks.

Applications

• Viral marketing, where messages spread quickly through social ties.
• Epidemiology, modeling how diseases travel through human contact networks.
• Innovation diffusion, showing how new ideas reach distant communities.

References

• Milgram, S. (1967). “The Small World Problem.” Psychology Today, 2(1), 60-67.
• Watts, D. J., & Strogatz, S. H. (1998). “Collective dynamics of ‘small-world’ networks.” Nature, 393(6684), 440-442.
• Travers, J., & Milgram, S. (1969). “An Experimental Study of the Small World Problem.” Sociometry, 32(4), 425-443.
• Barabási, A.-L. (2002). Linked: The New Science of Networks. Perseus Publishing.