In 1967, the social psychologist Stanley Milgram handed a packet to a random person in Omaha and asked them to get it to a stranger in Boston — but only by passing it to someone they knew on a first-name basis. On average, the packets that arrived had passed through just five intermediaries.
That experiment gave us the phrase "six degrees of separation," and it has held up remarkably well.
Why the world is small
The math behind it is elegant. Even if each person knows only a few hundred others, those circles overlap just enough that the whole graph stays tightly connected. A handful of well-connected people — the hubs — act as shortcuts across the network.
Here is the rough shape of it:
| Degree | Who you reach |
|---|---|
| 1 | Your direct friends |
| 2 | Friends of friends |
| 3 | A small city |
| 4 | A large region |
| 5 | Almost anyone worth reaching |
By the fifth degree, the reachable set is enormous — but the path is still short, and still made of real relationships.
From trivia to tool
For decades this was a fun party fact. What changed is that the graph of who-knows-whom is now something software can reason about. That lets us flip the question:
- Instead of "How far apart are two random people?"
- We ask "What is the shortest trusted path between you and the person you actually need?"
The breakthrough was not making the world smaller. It was learning to walk the short path on purpose.
The catch
A short path is only useful if every link is genuine. A graph full of fake or meaningless connections collapses the whole idea — suddenly everyone is one degree from everyone, and the distance stops meaning anything.
That is exactly the problem our trust chains are designed to solve.