Small world theory is based on the idea that two individuals will be connected through a series of intermediaries. In the 1960s, Stanley Milgram tested this theory by giving packages to one person with a particular destination, but they could not mail it directly to the second person. Instead, the first person had to mail it to someone they knew and the next person would do the same. Some packages made it to their destination and others didn’t. However, this experiment became the first quantitative evidence for the small world theory. The “six degrees of separation” (or less) also comes from the same idea, but attempts to quantify the number of intermediaries needed within a network. The small world sits in the middle between a more linear network (mostly connections to neighbors) and a random network (see image below) by having both connections to neighbors and random individuals.
Weak ties allow for more random connections within a network. For example, ties between immediate family in an area would likely form a cluster with strong ties. Everyone gets together to celebrate holidays and birthdays. However, a tie with an extended family member would be a weaker tie and bring in additional possibilities due to distance or alternate circumstances. There might be a family reunion at a vacation spot every four years where you meet second cousins or see a well-traveled retired aunt. While strong ties might have significance because they have greater influence over your day to day activities, these weaker connections create more possibility for variability within your egocentric network. Job opportunity is one often cited area where extended networks could be of benefit.
The small world theory makes the “big world” more approachable and less alone. In 2016, Facebook claimed that their network had three and a half degrees of separation! However, Facebook is not necessarily the most altruistic of organizations collecting big data posted by their users and on their users. Some researchers use the term “prosumer” to describe the phenomenon where users offer their work freely online, which allows the collecting website to profit. SNA and big data offer unprecedented opportunities from the abundance of information to understand networks. However, many ethnical questions will follow big data, such as whether individuals have given permission for the use of their information or whether giving permission once for the original use applies to all derivative uses for other research.
Finally, Kevin Bacon has been used as a frequent example for small world theory within the network of Hollywood. Most actors have connections through other actors who have costarred in a movie with Bacon. This has become a joke where people will name a star and try to figure out the shortest connection (see image above).