Six Degrees of Separation

Defination

The Six Degrees of Separation theory, also known as the Small World Phenomenon, contends that all people in the world are connected together through a chain of no more than six people. The theory is that there are only six degrees (or levels) of separation between you and everyone else in the world. This is the idea that everyone in the world can be reached through a short chain of social acquaintances. In other words, everyone in the world is separated from anyone else by no more than six degrees of separation, or simply speaking, six acquaintances or friend. A degree of separation is defined as an acquaintance or friend who separates you from someone else. As such, there is zero degree of separation between you and your immediate friends or acquaintances.

History

In 1967, the Harvard Social Psychologist Stanley Milgram sent out roughly 300 letters to randomly selected people in Omaha, Nebraska with the instruction to get the letter to a single "target" person in Boston using only personal contacts.

Milgram gave each "sender" some information about the target including name, location, and occupation, so that if the sender did not know the target, and it was extremely unlikely that they would, they could send the letter to someone whom they did know who they thought would be "closer" to the target. This began a chain of senders, with each member of the chain attempting to zero in on the target by sending the letter to someone else, may these people be a friend, a family member, a business associate, or a casual acquaintance.

Milgram's surprising finding was that for the 60 chains that eventually reached the target, the average number of steps in a chain was around six, a result that has entered folklore as the phrase "six degrees of separation."

While Milgram's first experiment suggests it is, other experiments have been less conclusive, and no experiment has been done to test the theory on a global scale.

Mathematics

We assume that a person only knows 50 other persons, and each of these 50 persons in turn know another 50 non-redundant persons (this assumption eradicates the possibility of duplication of persons with the first person). In this case, each of the 50 persons would then know another 50 non-redundant persons and so on up to six degrees.

This works out to be:
50x 50 x 50 x 50 x 50 x 50 = 15.63 x 1010 or about 15 to 16 billion persons!

If the current entire population of the whole world is only about 6 to 7 billion persons, then this computation would show that six degrees of separation is enough to cover the world's population.