Physics Buzz has a nice article about Paul Erdos and the Erdos Number Project (mine is 6), which ends with a good question:
I for one, am wondering: who would be the Paul ErdÅs of the physics world?
It’s a tough question, complicated further by the existence of really gigantic collaborations in experimental high-energy physics, where author lists can run to hundreds of people. The 511 collaborators that Erdos can boast is more impressive in math than in some fields of physics.
For something really equivalent in spirit to Erdos, you would need to look for a physicist who had a long and distinguished career, and who worked in a wide range of fields, so that they might reasonably be connected to physicists in lots of different areas. These days, that would probably mean a theorist, as experimental skills in most fields are highly specialized, and you don’t get a lot of field-switching. Theoretical methods, though, are pretty similar in different fields, so you can get people who make contributions in, say, solid state physics and particle physics both.
I’m not sure who a good modern candidate would be. Within my own field of AMO physics, somebody like Peter Zoller or Paul Julienne might work, as they’ve done a little bit of everything. I don’t know if you could easily connect them to particle physics, though. Ed Witten is the dominant figure in high-energy theory (or so it seems from the outside), but I don’t know if he’s a prolific collaborator.
Going back a bit, I. I. Rabi is somebody who might work, as he did important work in both atomic and nuclear physics. A lot of his connections to people were more administrative in nature than the sort of thing that would lead to co-authorship. John Wheeler is another possibility.
It’s a tough question. So I’ll just throw it out there: If you were going to establish an Erdos-number equivalent for physics, who would you use?