In 1929, Frigyes Karinthy wrote a short story suggesting that everyone is connected to everyone else by six or seven degrees of separation.

In 1967, the Harvard social psychologist Stanley Milgram, inspired by the story, set out to test the idea.

He sent packages with folders of instructions to 160 random people living in Omaha, asking them to forward the package to a friend or acquaintance who they thought would bring the package closer to a certain stockbroker in Boston. At each step, each recipient was only allowed to forward their package to someone they knew personally on a first-name basis.

Remarkably, the first return package too just four days to reach its destination, with only two intermediate acquaintances in between. Overall, the acquaintance chains had between two and ten middle-men between the beginning and end points. The median length was five middle-men.

Or, in other words, six degrees of separation.

But it took another two decades for Duncan Watts & Steven Strogatz to begin to build the mathematics to describe the ‘small-world networks‘ that connect us all.

In this episode, we ask Samuel Hansen — Math (not Maths) raconteur, podcaster and storyteller — what this means for social networks, predicting the spread of disease, Kevin Bacon, and why our friends are more popular than we are.