The Shrinking World

“In 1929, a Hungarian author named Frigyes Karinthy published a volume of short stories titled "Everything is Different." One of these pieces was titled "Chains," or "Chain-Links." The story investigated in abstract, conceptual, and fictional terms many of the problems that would captivate future generations of mathematicians, sociologists, and physicists within the field of network theory. In particular, Karinthy believed that the modern world was shrinking due to the ever-increasing connectedness of human beings. Due to technological advances in communications and travel, friendship networks could grow larger and span even greater distances. Karinthy posited that despite great physical distances between the globe's individuals, the growing density of human networks made the actual social distance far smaller.
As a result of this hypothesis, Karinthy's characters believed that any two individuals could be connected through at most five acquaintances. In his story, the characters create a game out of this notion. He writes:
A fascinating game grew out of this discussion. One of us suggested performing the following experiment to prove that the population of the Earth is closer together now than they have ever been before. We should select any person from the 1.5 billion inhabitants of the Earth—anyone, anywhere at all. He bet us that, using no more than five individuals, one of whom is a personal acquaintance, he could contact the selected individual using nothing except the network of personal acquaintances.
This idea both directly and indirectly influenced a great deal of early thought on social networks. Thus, Karinthy is often regarded as the originator of the notion of Six Degrees of Separation.” (From Wikipedia)