There are about 7.6 billion people on the planet, yet the theory runs that no two people need scan through a chain of more than six social connections before they find a common one. Back in 2008, Microsoft researchers decided to investigate how true this rather implausible-sounding theory really was. Using billions upon billions of electronic messages, they worked out that any two random people in the world really are apart by only six degrees of separation. Or, to be more precise, 6.6 degrees. After all, who doesn’t have 0.6 of a friend?