Preposterous Universe

Thursday, July 08, 2004
Quality and quantity

A recent article by Amanda Schaffer in Slate is causing physicists to sit up and take notice (see comments at Gnostical Turpitude, Quark Soup, Not Even Wrong). The article is nominally about Brian Greene's standing in the physics community, although it doesn't really address that question. Brian, of course, is a well-known string theorist at Columbia, but celebrated more widely as the author of The Elegant Universe and The Fabric of the Cosmos, as well as host of a NOVA special on PBS.

The real focus of the Slate article is more about the style of string theory -- in the absence of detailed experimental results, are the criteria of beauty and mathematical coherence that string theorists rely on sufficient guides to doing effective physics? Interesting questions, about which I've previously promised to blog, but haven't gotten around to it yet. But what about the nominal question, of someone's standing as a physicist? It should come as no surprise that physicists, being the hard-nosed quantitative types that they are, have developed an extremely precise (and, often, wildly inaccurate) method for rating the worthiness of their colleagues, and implemented it as a web page to boot. It's the SPIRES high-energy physics literature database, which keeps track of what articles are citing, and being cited by, other articles in physics (or at least in high-energy physics, and increasingly astrophysics and related areas). Coupled with the availability of the papers themselves (in preprint form at arxiv.org or in published form at various online journals), the ease with which one can search through literature citations has become fantastically greater over the last ten years or so. No self-respecting physicist goes to an actual library any more, much less uses a Xerox machine.

But the real fun of SPIRES is to figure out how many citations your friends have (and thus, how good they are). For example, I have about 40 papers listed, with about 2000 total citations -- pretty good for an assistant professor, but by no means near the top of the list. I have no "renowned" papers (more than 500 citations), but I do have seven "famous" papers (more than 100 citations). Even that is a bit of a cheat, since two of those papers are review articles, which are cheap ways to rack up lots of citations. There are numerous caveats to this measure of one's quality -- different specialties have very different rates of citations, certain fields are not covered as well by SPIRES, it's very hard to appropriate credit in large collaborations, not to mention the obvious fact that having a lot of citations is not the same as being a good paper -- but it's just so easy and quantitative that the citation numbers from SPIRES have become very influential.

It's humbling to look at the citation records of the really influential people in high-energy physics. Big names in string theory do especially well in the citation game; string theorists just write a lot of papers. Cumrun Vafa at Harvard has five renowned papers and 58 famous ones; David Gross at KITP in Santa Barbara (who was an extremely successful field theorist long before he became an influential string theorist) has twelve renowned papers and 41 famous ones. In cosmology, Andrei Linde has three renowned papers and 39 famous ones; in particle phenomenology, Howard Georgi has eight renowned papers and 47 famous ones. These are just representative names; I haven't done any systematic searches for who has the most citations. Besides, everyone knows the answer: Ed Witten has an amazing 36 renowned papers and 99 famous ones. Both prolific (over 200 papers) and profound (over 200 citations per paper). Everyone else is just playing for second place.

Ideas on culture, science, politics.
Sean Carroll

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