Name: The Science of Six Degrees of Separation
Uploaded: 2020-03-28T18:36:08.000Z
Duration: 9 min 23 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

I have a friend named Sammy who back in the early 2000s wrote some code for his MySpace

And what the code did was anybody who visited his page would have his picture and a tag

line that said, “Sammy is my hero,” copied over to their homepage.

And that was a bit of fun for a while, but Sammy wanted more.

And so he tweaked his code so that no only the picture and the tag line were copied over,

In just nine hours he had reached 480 accounts.

And in just over 18 hours he had hit a million accounts, which was a full 1/35th of all the

So in a panic, he tried to delete his page.

And when he was successful he actually took down the whole of MySpace with it.

He was arrested and convicted of computer hacking and ordered not to touch a computer

But I think what this story really tells us is just how connected we all are.

Imagine you have 44 friends and each one of those friends has 44 friends who are not also

And each of them has an additional 44 friends, each of whom has 44 friends who again has

Then in a chain of just six steps you would be connected to 44 to the sixth or 7.26 billion

people, more than are alive on earth today.

And we have contemplated how closely connected we area since long before MySpace even existed.

Back in 1929 a Hungarian author and poet named Frigyes Karinthy wrote a short story called

And in it, one of the characters challengers the others to find another person on earth

that he cannot connect himself to through fewer than five intermediaries.

This is the origin of six degrees of separation.

If the theory is correct, it means that you would be connected to the Queen or Tom Cruise

What about this shop owner or the Mongolian sheep herder?

What the theory really means is that any two people picked at random from anywhere on the

earth would be connected by just six steps.

The idea remained just fiction until in the 1960s a Harvard psychologist, Stanley Milgram,

He called it the small world experiment after that phenomenon where you are at a party,

you meet a stranger and you find out that you have a friend in common and you remark:

What he did was he sent out 300 packages to people both in Boston and in Nebraska.

Now what he wanted those people to do was try to send their package to a target person

in Boston, but they weren’t allowed to send it directly to him.

They had to send it to someone they knew on a first name basis who they thought had a

better chance of knowing the target and they could forward it on in the same way.

Now, as you might expect, most of the packages never made it, but 64 did and the average

So now six degrees of separation had experimental confirmation.

If you look more closely at Milgram’s sample, you will find that of the 300 people, 100

were located in Boston, the actual city where the target lived.

Another 100 were stockbrokers, which was the same profession as the target.

So only 100 people lived in a different state and had a different job.

And of them only 18 of their packages made it to the target.

So we are talking about a sample size of 18 is all the evidence there was for six degrees

So experimental evidence was tough to come by.

But a decade earlier, a mathematician named Paul Erdos had tried to work out the theoretical

But he didn’t have any information on the structure of real social networks, so he decided

to work on networks where the connections between nodes were all completely random.

And we can actually simulate a network like this using buttons and thread where we just

What Erdos found is that when the number of links per node is small, the network is fragmented.

Pick up any button and few others will come with it.

But once you exceed an average of one connection per node, the behavior the network changes

They almost all link up forming a giant cluster.

Now if you pick up any button almost all of the rest will come with it.

This change happens rapidly and it resembles a phase transition in physics.

Now you could call this a small world network, since the path between any two buttons is

The thing about random networks is that they are naturally small world networks, because

you are just as likely to be connected to someone here in Manila as you are to someone

But obviously a random network doesn't represent real life very well.

So what do real world networks look like?

Well, for that, we need to go to the empirical data.

In 1994 a couple of college kids invented a game called six degrees of Kevin Bacon in

which you try to connect any actor to Kevin Bacon through just six steps through his costars.

Now a couple of sociology researchers got access to their database of a quarter million

actors and they analyzed the network and what they found was that it was a small world network,

meaning between any two actors there were only a very small number of steps.

And that is very similar to a random network.

But unlike a random network, the actor network also showed a high degree of clustering, that

is, they often worked together in small groups.

So how do you get both this grouping behavior, a high degree of clustering, and the short

Well, to figure this out they looked at two different extremes.

Now if you connect them at random you get the same outcome as Erdos, short paths between

Now consider connecting up the nodes only with their nearest two neighbors on each side.

Now clustering is high, but path lengths are long for two nodes picked at random.

But what if you take this set up and rewire just a small number of connections randomly.

What you find is that the path length drops rapidly, but clustering still remains high.

So the key to modeling real social networks is to have a lot of clustering behavior—that

is, your friends are also friends with each other—but also to have a few random acquaintances.

And the importance of those acquaintances can’t be overstated.

There was a researcher named Granovetter in the 1970s who published a paper called “The

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