Some time back we learned that arxiv.org, the physics e-print server that has largely superseded the role of traditional print journals, had taken a major step towards integration with the blogosphere, by introducing trackbacks. This mechanism allows blogs to leave a little link associated with the abstract of a paper on arxiv to which the blog post is referring; you can check out recent trackbacks here. It's a great idea, although not without some potential for abuse. Now Peter Woit reports that he has been told that arxiv will not accept trackbacks from his blog. Peter, of course, is most well-known for being a critic of string theory. In this he is not alone; the set of "critics of string theory" includes, in their various ways, people like Roger Penrose, Richard Feynman, Daniel Friedan, Lee Smolin, Gerard 't Hooft, Robert Laughlin, Howard Georgi, and Sheldon Glashow. The difference is that these people were all famous for something else before they became critics of string theory; in substance, however, I'm not sure that their critiques are all that different. Unfortunately, Peter has not been given an explicit reason why trackbacks from his blog have been banned, although his interactions with the arxiv have a long history. It's not hard to guess, of course; the moderators presumably feel that his criticisms have no merit and shouldn't be associated with individual paper abstracts. I think it's a serious mistake, for many reasons. On the one hand, I certainly don't think that scientists have any obligation to treat the opinions of complete crackpots with the same respect that they treat those of their colleagues; on a blog, for example, I see nothing wrong with banning comments from people who have nothing but noise to contribute yet feel compelled to keep contributing it. But trackbacks are just about the least intrusive form of communication on the internet, and the most easily ignored; I have never contemplated preventing trackbacks from anyone, and it would be hard for anyone to rise to the level of obnoxiousness necessary for me to do so. On the other hand, I don't think there is any sense in which Peter is a crackpot, even if I completely disagree with his ideas about string theory. He is a contrarian, to be sure, not falling in line with the majority view, but that's hardly the same thing. Admittedly, it can be difficult to articulate the difference between principled disagreement and complete nuttiness (the crackpot index is, despite being both funny and telling, not actually a very good guide), but we usually know it when we see it. Since I'm not a card-carrying string theorist, I can draw analogies with skeptics in my own field of cosmology. I've certainly been hard on folks who push alternative cosmologies (see here and here, for example). But there is definitely a spectrum. Perfectly respectable scientists from Roger Penrose to yours truly have suggested alternatives to cherished ideas like inflation, dark matter, and dark energy; nobody would argue that such ideas are cranky in any sense. Respectable scientists have even questioned whether the universe is accelerating, which is harder to believe but still worth taking seriously. Further down the skepticism scale, we run into folks that disbelieve in the Big Bang model itself. From my own reading of the evidence, there is absolutely no reason to take these people seriously; however, some of them have good track records as scientists, and it doesn't do much harm to let them state their opinions. In fact, you can sharpen your own understanding by demonstrating precisely why they are wrong, as Ned Wright has shown. Only at the very bottom of the scale do we find the true crackpots, who have come up with a model of the structure of spacetime that purportedly replaces relativity and looks suspiciously like it was put together with pipe cleaners and pieces of string. There is no reason to listen to them at all. On such a scale, I would put string skepticism of the sort Peter practices somewhere around skepticism about the acceleration of the universe. Maybe not what I believe, but a legitimate opinion to hold. And the standard for actually preventing someone from joining part of the scientific discourse, for example by leaving trackbacks at arxiv, should typically err on the side of inclusiveness; better to have too many voices in there than to exclude someone without good reason. So I think it's very unfortunate that trackbacks from Not Even Wrong have been excluded, and I hope the folks at arxiv will reconsider their decision. Of course, there is a huge difference between string theory and the standard cosmological model; the latter has been tested against data in numerous ways. String theory, as rich and compelling as it may be, is still a speculative idea at this point; it might very well be wrong. Losing sight of that possibility doesn't do us any good as scientists. Update:Jacques Distler provides some insight into the thinking of the arxiv advisory board.