The Arxiv is the server where most physics papers that come out are sent and are available for free download. It is an indespensable tool for the professional physicist, at least in the areas more related to high energy physics. Last year, the Arxiv advisory board decided to enable trackbacks on arxiv papers. This means that when going to the arxiv webpage for a paper where the title, authors, abstract and other details are filed, there would also appear a list of links to blogs that had linked to that paper.
One can see immediately advantages in this decision: it makes easier discussion between physicists, enabling the authors or others to see easily what other people are saying about any paper. But there are also obvious problems: a lot of blogs and other informal websites that might use the service are run by people who are not professional physicists, many of them even by crackpots, and the Arxiv board was concerned that enabling links from the arxiv to these pages would seem an endorsment of them, and also make unacceptably high the "noise to signal ratio" for the people that wanted serious, high quality discussion. In short, they decided they needed a filtering criterion to decide which blogs they would accept trackbacks from and which not. The criterion they decided was that to be considered "acceptable" a blogger would have to be an "active researcher", who regularly posts new papers in the arxiv. This decision, however, was not made public, presumably because of fear of loud complaints from people "left out". The system was started, and some people just found they could get trackbacks and some people found they didn't
Among those who found they didn't was Peter Woit. His blog, Not Even Wrong, is dedicated mostly to high energy physics and the mathematics related to it, with special emphasis on string theory. Woit has a very negative view of string theory and has declared in several occasions that it is, or at least it is rapidly becoming, a pseudo-science. Naturally, his opinions are strongly opposed by string theorists, many of which consider him little better than an ordinary crackpot. This is clearly not the case: Woit has a permanent position at Columbia University, has many publications on high energy physics, and has taught several courses on the subject. His opinions on string theory may be wrong or foolish, but he certainly is no crackpot. However in the past years he has published very little and has actually only two papers on the Arxiv. On these ground his blog was not considered fit to get trackbacks, even though it is one of the most read by the physics community and though it has been host to many long and high-quality discussions on string theory, loop quantum gravity and other issues in fundamental physics.
Woit thought at first that there was some technical problem responsible for him not getting trackbacks, but after many unsuccessful tries to communicate with the arxiv board and inquire what the problem was, he began to feel censored. A part of the reason for this is that string theorist Jacques Distler is a member of the board. Woit suspected that Distler was deliberately "supressing" his criticism of string-theoretical papers. Last week, Woit finally heard confirmation that trackbacs from his blog were deliberately not allowed. Still not knowing the reason for this, Woit sent a protesting letter to the arxiv board and posted it in his blog
Things started to move after that. Sean Carroll posted at Cosmic Variance supporting Woit. It was in the comments to that post that a former memeber of the arxiv board made public for first time the "active researcher" criterion, adding the words "That excludes Peter, who likes to discuss physics, but is not a researcher. It also excludes lots of other people, although I can’t remember anyone else’s name coming up. I’m not going to hazard a guess as to the role that existence of Peter’s blog played in settling on this standard." The following day Jacques Distler posted in his blog on the subject, explaining how the criterion was set and asking for possible suggestions for a better one, but refusing to discuss specifically Woit's case. Many people came into the discussion afterwards; for a variety of opinions, see Lubos Motl (who predictably defends Distler and is as insulting to Woit as usual), Chad Orzel (who criticizes the "active researcher" criterion; also here) and Georg von Hippel (who gives a fairly impartial summary). And, of course, the follow-up from Peter Woit himself
Now, what are my opinions on all this story?
First: It an obvious exageration to call it censorship, since Peter Woit can write everything he wants in his own blog, and is allowed to submit papers to the arxiv. The is no "inalienable right" to get trackbacks. The anti-string-theory crowd that is infesting comment sections in blogs making accusations of censorship is laughable.
Second: However it does seem that the criterion and the way it was interpreted (Woit himself claims to be an "active researcher" who happens to publish little) were devised on purpose to exclude Not Even Wrong from the list of "acceptable" blogs, and that this is related to Distler thinking Woit's views are of little or none scientific value. After all, there are not so many physics-related blogs that are very well known and which are in need of a carefully designed criterion (because they are not either 100% respectable like the String Coffee Table or John Baez's This Week's Finds, or 100% crackpotish like many I won't link to). The commentetor at Cosmic Variance implied that Peter Woit's case was explicitly discussed by the deciding comitee.
Third: In this case, it is inexcusable that the concsious decision was made to exclude Not Even Wrong. Regaldless of the merit of Woit's criticism of string theory, his posts are scientifically informed and give rise to interesting discussions, in which lots of well-known physicists have participated. Just to pick an example, when he commented on a paper by John Baez a long and valuable discussion followed, in which Baez himself participated. A criterion that would exclude this discussion from being trackbacked is obviously ill-designed.
Fourth: It was clearly a wrong decision to not make public the criterion immediately, giving rise to so much speculation and talk of censorship.
Fifth: The criterion itself is much too subjective to be of value. As many have asked, how many papers are needed to qualify as an active researcher? Is a graduate student who has published only a couple of papers an active researcher? (Am I?) Why not make "having a position at a physics or mathematics department" the criterion? (relaxing it to include graduate students if more inclusiveness is wanted). This is much more objective and leaves out all or almost all the crackpots.
Sixth: Is this matter really so important to justify all the electronic ink wasted on it? (Including the one in this post).