[haraldurt]

>The average distance between any two of Facebook’s 1.5 billion users is 4.74 edges. Sorry Kevin. With 1.5 billion users the whole graph can be explored within 5 hops.

Nitpicking here, but that does not follow. Starting from a random user and hopping 5 times in all directions you'd expect to explore about half of the graph.

[fnbr]

Your post is technically correct, but I think that you'd be likelier to explore more- say, 80% of the graph. I suspect that there are small pockets of extremely unconnected people which creates a long tail, distorting the mean.

[eggie]

Unless the data can somehow be shared how is anyone to know what the structure is? There is no point in speculating...

[cortesoft]

Yeah, I noticed that, too. Just because 4.74 is the average doesn't tell you enough to know how many people you will reach by exploring 5 hops. Also, they clearly are not including unconnected people in their calculation - there are lots of people who are probably unconnected to the general population. I know from when I used to work on facebook apps that I had a few accounts only connected to each other.