People may have heard of the “six degrees of Kevin Bacon“, related to the idea of six degrees of separation, where it was posited that any Hollywood actor could be linked to Kevin Bacon by six or fewer relationships (e.g. by virtue of having shared co-stars, etc).  This theory of networks is fascinating in its own right, due to the uneven connectedness of nodes (people) within a given network.  Not to be outdone, scientists have their own “centre of the universe” and that person is Paul Erdös (1913-1996).  

Erdös published thousands of mathematical research papers – more than any other mathematician – and had literally hundreds of collaborators over the course of his career.  The “Erdös number”, as has been known since being coined in the 1960s, represents the distance between a given researcher and Paul Erdös, linked by co-authors on scientific works.  I have met a mathematician who has an Erdös number of 1 (Jeff Shallit, with whom I shared a panel at the Polaris sci-fi convention a couple of years ago), with whom it is now my goal in life to publish something.  For the moment, however, I believe that I have an Erdös number of 5:

Erdös->Graham->Cohen->Lawton->Thompson->Hassall

…via the following papers:

1. Erdos, P. & Graham, R.L. (1980) Old and new problems and results in combinatorial number theory“. L’Enseignement Mathématique 28: 30–44.
2. Chung, F.R.K, Cohen, J.E. & Graham, R.L. (1988) Pursuit-evasion games on graphs. Journal of Graph Theory 12(2):159-167.
3. Pimm, S.L., Lawton, J.H. & Cohen, J.E. (1991) Food web patterns and their consequences. Nature 350:669-674.
4. Lawton, J.H., Thompson, B. and Thompson, D. J. (1980), The effects of prey density on survival and growth of damselfly larvae. Ecological Entomology, 5: 39–51.
5. Hassall, C., Thompson, D.J., French, G.C. and Harvey, I.F. (2007), Historical changes in the phenology of British Odonata are related to climate. Global Change Biology, 13: 933–941.

What’s your Erdös number?

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Erdös photo by Kmhkmh