Not Even Wrong

Over at his web-site, Lubos has posted a letter to the Wall Street Journal from Barton Zwiebach. The letter seriously misrepresents the current state of string theory in several ways:

string theory is an extraordinarily precise and rigorous framework where facts can be proven beyond doubt and computations give unequivocal answers.

All that is needed to confirm string theory is finding one solution that describes our universe. All that is needed to rule out string theory is showing that no solution describes our universe. An answer must exist.

Zwiebach gives the impression that there are rigorously well-defined, “extraordinarily precise” equations that characterize string theory, and all that is needed now is to solve the technical problem of finding the solutions to these equations and seeing if one of them agrees with what we observe. This is simply not true. Since we don’t know what non-perturbative string theory is or what its equations are, all equations used by string theorists to generate solutions are not “extraordinarily precise”, but are explicitly approximations, often very crude ones, whose reliability is unknown. If you look at the debate over the landscape, you will find that not only do most string theorists not believe that the solutions involved are “facts [that] can be proven beyond doubt”, many of them believe these are not real solutions to the full unknown theory at all.

Even if one does believe in the rigorous nature of the landscape solutions, Zwiebach’s claim that all one has to do is examine them to see if they agree with nature is again highly misleading. If there are 10¹⁰⁰⁰ or more of these solutions, all evidence is that identifying which of them have desired properties (e.g. the correct CC) is an inherently computationally intractable problem. Even if one could do this, the class of solutions that agree with all known values of the parameters characterizing the standard model seems likely to be so large that no new testable predictions would be possible.

Zwiebach also claims:

String theory has explained, for example, why black holes have entropy and temperature.

This is what Hawking did back in 1974 with a semi-classical calculation. Any theory of quantum gravity should reproduce this. What string theory adds to Hawking’s calculation is a long story, but if we manage to observe a black hole any time soon and it behaves as Hawking predicted, he’s the one who is going to get a Nobel prize for explaining “why black holes have entropy and temperature”, not string theorists.

I had been wondering what the response from string theorists would be to the public dissemination of arguments from Smolin and me about string theory. The response seen here from Distler et. al. and Zwiebach is not at all what I expected. Most serious string theorists I talk to take the reasonable attitude that string theory is still so poorly understood that it cannot be confronted with experiment, even in principle. Many publicly say that we still don’t know what “string theory” is. Zwiebach seems to believe that there now exist “extraordinarily precise” equations, with solutions that will give “unequivocal answers”. Whether this is true is a well-defined question. All he has to do is explain what these equations are, and let’s see if the string theory community will really stand by this definition and let string theory be judged accordingly.

Finally, perhaps the most surprising aspect of Zwiebach’s letter is the form in which he has chosen to distribute it. I and many people have been wondering what Lubos Motl’s colleagues in Cambridge think of the way he is defending their subject. Now at least one of them has made clear that he is fine with this and willing to encourage it.

Update: The usual response from Lubos Motl/Bill O’Reilly: an endless rant about how stupid people who disagree with him are, completely ignoring the scientific questions at issue.

The lack of any serious (Lubos doesn’t count) response to my book from string theorists since its appearance in the UK a month or so ago has begun to surprise me a bit. I was also suprised at how weak the defense of string theory was that the Wall Street Journal’s Sharon Begley put in her recent article. It seems that she did talk to some string theorists, but couldn’t get much usable from them (one supposedly told her that the best argument for string theory was the anthropic landscape). Peskin’s argument that string theory’s biggest success is its “explanation” of the number of generations was evidently the best he could come up with, although it’s obviously very weak.

I’ve heard that the WSJ has gotten some correspondence about this, with Jacques Distler writing in to complain about the article. In one letter from him (also signed by his two collaborators), he claims that Smolin is wrong to say that string theory is not falsifiable, since Distler has a recent paper called Falsifiying String Theory Through WW Scattering.

This paper was discussed extensively here. You can make up your own mind about it, but it’s undeniable that the calculations in the paper don’t involve string theory at all (Distler’s two co-authors are not string theorists). Pretty amazing trick to show that a theory is falsifiable without actually using the theory at all.

There are two obvious problems with the claim in the title of the paper, the first is that when one says a theory is falsifiable, one is talking about the characteristic predictions of the theory, and that’s not what the paper is about. The second is that “string theory” is an ill-defined term, and many versions of “string theory” don’t satisfy the assumptions of the paper (one of the co-authors admits this in the comment section). To fudge his way around this, in the letter to the WSJ, Distler refers to “the canonical definition of string theory” as opposed to “string theory”, although he provides no reference to what this is. Putting “canonical definition” and “string theory” into Google doesn’t turn up anything relevant.

It will be interesting to see if a referee can be found who will go along with allowing the “falsifiying string theory” claim. Most physicists, string theorist and not, that I’ve talked to about this think it’s way out of bounds. It seems to me pretty amazing that Distler would choose to take this case to the Wall Street Journal.

We’ll also see if the WSJ publishes the letter, if not I’ve asked one of the co-authors if they’ll let me publish it here.

I could certainly do a better job of defending string theory than the people Begley talked to. The strongest argument string theorists have is clearly the one that they have “the most promising approach to quantum gravity”. The problem with this is that there are plenty of people who disagree, especially those who do LQG. This is the reason that Distler has been on an anti-LQG campaign throughout the blogosphere recently. His latest posting is about this, with comment section featuring the always incoherent Lubos Motl, and the trademark Distlerian sarcastic sneering at people he disagrees with, e.g. the following comment on a paper by Thomas Thiemann:

I suppose that it is only Thomas’s natural modesty that prevented him from submitting this paper for the Clay prize.

In the first comment, someone quotes from my book something I have to say about the issue being discussed in this posting. For the record, I’m no expert on LQG, and can’t judge exactly how close they are to having a fully satisfactory quantum gravity theory, but my impression is that what they are doing is a more promising approach to quantum gravity than string theory, and the fact that they are convincing more people about this is what is getting Distler and others very worked up. I also don’t think either LQG or string theory has made any headway on the problems of the standard model, although several orders of magnitude more effort have gone into the string theory approach.

Since Distler has a whole posting and ongoing discussion in his comment section about this and I’m no expert, if you want to discuss LQG, its problems and prospects, or comparisons to string theory, please do it there, not here.

Today’s Wall Street Journal has an article by Sharon Begley entitled Has String Theory Tied Up Better Ideas In Field of Physics? (sorry, subscription required for on-line version). The summary of the article goes

After two decades in which string theory has been the doyenne of best-seller lists and the dominant paradigm in particle physics, some critics say it may be tying up better ideas.

and in some sense it covers for the public in simplified form the discussion going on over at Cosmic Variance at the moment. It quotes Lee Smolin and me as critics, with Mike Peskin as the only defender of string theory. Peskin acknowledges the compactification problem, and then makes only a strikingly weak argument for string theory: that it can claim some success because it explains the number of generations. This “explanation” in terms of the topology of the Calabi-Yau is no explanation at all, since you can get any value for this number you want. I don’t see how changing the parametrization of your ignorance from that of a single natural number to that of the topology of a Calabi-Yau is any improvement.

I assume that any moment now Lubos will be producing a rant comparing Sharon Begley to one sort of animal or another.

There’s also a long review of Not Even Wrong from John Walker over at his blog called Fourmilog. He does a good job of laying out the controversial argument of the book, and we seem to be mostly in agreement, although I don’t share his conviction that government funding is a major source of the problem.

Update: I just heard that official publication date in the US is September 8, although books should be for sale a bit earlier than this. Lubos has a posting about the WSJ article, less of a rant than some of his recent ones. He has restored his anti- Sean Carroll screed, which was a classic that many people were sorry to see suppressed.

Update: A commenter points out that the WSJ article is available on-line here. There’s also a mention at Slashdot. The extensive discussion there is heavily anti-string theory which is an interesting sign of the times, but also convinces me that the idea of moderating this kind of discussion by having participants vote on which comments are worthwhile just doesn’t work at all.

Update: There’s commentary on this from science writer David Appell here, who pretty much gets the situation right.

Over at Cosmic Variance Sean Carroll has a posting about The String Theory Backlash. Probably best if anyone who wants to discuss it do so over there, so I’ll turn off comments here.

Update: More about this here.

Update: The posting in the last link (which was an impressive anti-Sean Carroll rant) is now gone, presumably because many of the author’s colleagues finally realized something had to be done, and wrote in to his blog telling him that he “must be on crack”, and had “completely jumped the shark”.