Six degrees of separation is the theory that anyone on the planet can be connected to any other person on the planet through a chain of acquaintances that has no more than five intermediaries.

• 你和地球上任何一个陌生人之间所间隔的人不会超过五个，也就是说，最多通过六个人你就能够认识任何一个陌生人。这就是六度空间理论。