Science (and maths) is a small world. We even study this fact via Erdös numbers. The Erdös number of a scientist is the number of links between him or herself and the well-known and very prolific mathematician Paul Erdös. Each link is a paper. My Erdös number is 4, because I have published a scientific paper with someone with a number of 3, who has published with someone with a number of 2, who has published with someone with a number of 1. Someone with an Erdös number of 1 has worked directly with Erdös himself. Erdös is chosen as he is the mathematician published more scientific papers than anyone else in history.
The same idea works in films, where all actors have a Bacon number. It also works for other scientists. Inspired by a discussion over coffee we found that I have a Stevenson number of 4, and an Al-Khalili number of 5. The number of 4 is because I have written a paper with another Surrey academic, Joe Keddie, who has worked with Tony Clough who has worked with Paddy Regan, who was worked with Paul Stevenson. Paul has the enviably low Feynmann number of 3 as his PhD supervisor, Strayer worked with a guy called Baranger, who worked with Richard Feynman. My Feynman number is bigger but almost all scientists are connected to each other as we have all worked with someone who has worked with someone, etc. Science is a collaborative enterprise.