Hypothesis

Imagine a graph, the peaks of which are all people on earth, and the ribs are acquaintances. If two people are familiar, there is a rib between the corresponding peaks. The hypothesis of six degrees of distance suggests that between any two vertices there is a path no longer than six edges.

The author of the hypothesis is Stanley Milgram, who conducted an interesting experiment in 1967. He wrote several hundred letters to two addressees from Boston and distributed them to random people from two American states. People had to send letters to their friends who live as close as possible to the addressees. Only one fifth of the letters reached the addressees. These letters went through an average of six intermediaries. Unfortunately, the result of the experiment can be equally considered as a failure, and a confirmation of the theory.

More about the popularization of the hypothesis and experiments can be found in the English wikipedia en.wikipedia.org/wiki/Six_degrees_of_separation .

Social networks

What is a social network? This is a subgraph of the graph described above. No more sending letters. The database of any social network contains all the necessary information for the experiment. Habr suggests us to watch the list of friends of the second circle. Do not you wonder how many people are on the third round? And on the sixth?
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Conclusion

Why did I write this topic? Because I want to interest the authors and owners of social networks. And I want to know the results of such experiments.

PS By the way, on the title page of my circle there is a mention of this hypothesis.