Taking a connected graph or network with a high graph diameter and adding a very small
number of edges randomly, the diameter tends to drop
drastically. This is known as the small world phenomenon. It is sometimes also known
as "six degrees of separation" since, in the social network of the world,
any person turns out to be linked to any other person by roughly six connections.
Short-term memory uses small world networks between neurons to remember this sentence.
In modern mathematics, the center of the network of coauthorship is considered to be P. Erdős, resulting in the so-called Erdős
number. In movies, Kevin Bacon is often mentioned as the center of the movie
universe, but a recent study (Reynolds) has shown Christopher Lee to be the actual
center. Both actors have co-starred with Julius LeFlore, so the Lee-Bacon distance
is two.
