Throughout a lifetime we have the **chance to meet hundreds of people**. The first friendships from school, the passage to higher studies, the **coworkers or friendships arisen in various ways** they are forming our nucleus of friendships during our life. Now, in this age interconnected with the **Internet era relationships are even greater**.

Regarding how many people we can meet in life, the **Six Degree Theory** establishes the possibility of contacting **any of the more than 7.7 billion people around the world using up to five contacts**. This theory is already more than 90 years old and was formulated by the writer of Hungarian origin **Frigyes Karinthy in her story Chains**.

### Six Degree Theory

Is it possible to prove it? It is something that large entities such as **Facebook and IBM**, and some experts consider that, in this massively interconnected world, **it is possible to reduce from the initial six degrees to four**. The addressee, who would be the last link in the chain, also enters these six degrees.

Before the advent of the internet and social networks, the theory was that **each person knows, on average, about 50 or 100 people** (family, friends, acquaintances …). This figure, with the rise of new technologies, has grown. Continuing with the theory and taking from **refer a total of 100 friends, each of them will have another 100**: with just two degrees (friends and friends of friends) you can already contact **10,000 people**.

The third degree represents a significant jump in the number of people to contact: the 10,000 previous contacts each know 100 people, resulting in one million. From there to **100 million in the fourth level, 10,000 million (exceeding the total of terrestrial inhabitants)** in the fifth one billion people in the sixth and last level.

### Theory shortcomings

But of course it also has some weak points. The first of these is the assumption that each person knows **100 different people from the rest of family and friends**, something impossible to put into practice, because **there are many that are common**. But since a billion people are reached in total and there are not so many inhabitants on Earth, **eliminating mutual friends could continue within the stipulated figure**.

Another aspect to keep in mind is that **most people have more than 100 contacts**, and these relationships do not stay local, but reach a global level. Furthermore, it is possible that **some member of the chain refuses to search for their contacts**, so it would be impossible to implement.

### The IBM and MIT attempt

The theory did not emerge until the 20th century, when **began to globalize the world with the train, ships, airplanes or the telephone**, which allowed the fact of being able to connect with people from the farthest corners of the planet. Before it would have been a utopia. Karinthy, in her story *Chains* make a bet with his friends: he could **relate to any of the 1,500 million inhabitants of that time (1930)** with just five contacts.

“I know a friend who is a tennis fan, who knows a person who **plays tennis with the director of an international tournament who meets the King of Sweden, a tennis fan, and who also meets the last Nobel Prize in Literature**, because he has given him the award. So I could contact the Nobel Prize for Literature, “he said.

Years later, in the 50s, the academic **Ithiel de Sola Pool, from the Massachusetts Institute of Technology (MIT), and the mathematician Manfred Kochen, from IBM**, they tried to demonstrate this theory using computers of their time. However, after several years in which **the mathematical equations did not find a solution**, they left it. The variables were many: an indeterminate number of people who **do not have known, or have very few, populations that are isolated**, or the influence that a person has to be more or less known.

### Four degrees instead of six?

The increase in connectivity thanks to the internet has made many bet on **four degrees instead of six. One of those who bet on this alternative is Facebook**. Mark Zuckerberg’s social network tried to prove the theory in 2011 through his study Anatomy of Facebook. In it, I connect the friends of the 721 million users at that time (10% of the world’s population) to see how they connected with each other: **99.5% of them connected with just five degrees of separation**.

Later, in 2016 and with a database of 1,600 million users, the degrees of connection dropped to 4.5. For its part, **University of Milan** carried out a similar study on other social networks: **degrees of separation were 4.67 on Twitter and 3 on LinkedIn**.

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How many people do you know around the planet? This is how the theory of the six degrees of separation works