What is the 6-degree separation theory and how exactly does it work?

It's the ideal theory for the Internet age, but it's over 90 years old. The Six Degrees of Separation Theory has been attempted several times. Is it valid? What's the use?

Around 7.7 billion people live in the world. Is there a possibility to contact any of them, using a maximum of five contacts? Today, with the Internet, it seems relatively likely. But almost 100 years ago it was just a sci-fi idea.

The Six Degrees of Separation theory | HackerEarth Blog

The Theory of the Six Degrees of Separation was first formulated by the Hungarian writer Frigyes Karinthy in his short story Cadenas, published in 1930, although that name was adopted in the 1960s. A theory that was initially considered indemonstrable, but which was rescued from oblivion with the rise of the Internet.

From Facebook to IBM they have tried to prove it, with different results. Today the world is so interconnected that some experts believe it can be reduced from six to four degrees.

Six degrees of separation - Wikipedia

An interconnected world?
The Six Degrees of Separation Theory states that it is possible to contact anyone on the planet, using a maximum of five intermediaries. Six, if you count the recipient. That's why it's called Six Degrees of Separation.

Part of the idea that each person knows on average about 50 or 100 people, counting family, friends, acquaintances, etc. Now with the Internet, this number has grown, but before social media, that was about the average.

Suppose a person has 100 acquaintances. Each of them knows 100 other people, so with only two degrees of contacts (your friends and friends of your friends), you can contact 100x100 x, 10,000 people.

Those 10,000 people know another 100 each, so the next grade covers 1,000,000 people. If everyone knows another 100, we have 100 million, and on a fifth level, 10 billion people, more than 7.7 billion people on Earth. The sixth and final grade would cover 1 billion people or a billion people.

Of course, you will soon have seen the first weakness of the theory: it assumes that each person knows 100 others who are completely different from those of other family and friends. In practice, this is impossible because family and friends have many acquaintances in common. But because the theory reaches a billion people and on Earth lives far fewer people, even if we eliminate common friends we could still be within that figure.

Teoría de los seis grados de separación

It all started in a story
The Six Degrees of Separation Theory could only be formulated in a globalized world. That's why it didn't come until the 20th century when the train, ships, and planes, or the phone, already allowed people from all over the planet to be connected. It was an unthinkable theory for a philosopher from Ancient Greece or a thinker from the Middle Ages because then it took months to travel the world, and contacts were very limited.

In this tale, the protagonist proposes a bet to his friends: he could relate to any of the 1.5 billion inhabitants of the planet (the population in 1930) using only five individuals.

Friends were proposing characters to him, and the protagonist got to link everyone to reasoning such as "I know a friend who is a tennis fan, who meets a person who plays tennis with the director of an international tournament who meets the King of Sweden, a tennis fan, and who also knows the latest Nobel Prize in Literature because he has given him the prize. So I could contact the Nobel Prize in Literature."

This idea, in 1930, was demonstrable and was considered only a fantastic theory, typical of the tale in which he was born.

Teoría de los seis grados de separación

The flaws of the theory
Although it is a fascinating concept and many experts believe that, thanks to the Internet, it will end up becoming reality, as a theory it has some gaps.

The first one we have already seen: it is assumed that each acquaintance knows completely different people, although friends and family often have many acquaintances in common.

The second is that for the six degrees of separation to work, everyone has to be willing to collaborate. But in real life, some members of the chain can refuse to look for their contacts.

Finally, even if such contact is possible, it does not mean that it can occur. You may be able to get to Donald Trump with only 5 contacts, but I'm unlikely to want to talk to you...

Despite these difficulties, many people have tried to prove the theory.

Six Degrees of Kevin Bacon (with a Graph Database) - The Flerlage Twins:  Analytics, Data Visualization, and Tableau

IBM and MIT enter the game
In the 1950s, Ithiel of Sola Pool of the Massachusetts Institute of Technology and Manfred Kochen of IBM used computers of the time to try to demonstrate this theory mathematically.

But after years of attempts with different mathematical equations they did not find the solution, since the variables are many: it is not known how many lonely people who do not have known, or very few, there are in the world, how many isolated populations, what influence a person has more or less famous, etc.

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