The Ottawa Citizen today has an Op-Ed by string cosmologist Jim Cline, headlined The Big Idea That Won’t Die, with a subtitle “The fact that string theory is suddenly under attack only underscores its success as a path to a unified description of nature.” There’s a lot that it outrageous about this piece, beginning with the subtitle. Normally scientists don’t start going on about the success of their theories until they have some experimental evidence for them.
Most outrageous are Cline’s claims that Smolin’s book and mine are written in a “defamatory style”, and are “slandering” string theory. Since he gives no evidence for either of these claims, there’s not much to say about them except that they’re defamatory and slanderous.
Cline makes the standard claim that string theory should be accepted since it has legitimately triumphed in the marketplace of ideas, while clearly being rather upset about the success that critics of string theory have recently been having in this same marketplace. Somehow, overhyping string theory is a legitimate marketplace activity, pointing out its problems is not.
He makes many of the by now standard bogus claims about supposed predictions and tests of string theory. At some point I suppose I should write a FAQ about these, since the string theory hype machine keeps promoting these things in a less than honest way to a public that is not well-equipped to see through the hype. Here’s a pretty complete list of the bogus “predictions”
String theory predicts supersymmetry and extra dimensions. The LHC will test these predictions.
The problem is that there is no prediction of either the scale of supersymmetry breaking or the size of the extra dimensions; in string theory these could be anything. All we know is that the energy scales involved are at least a TeV or so, since otherwise we’d have seen these phenomena already. There’s no reason at all to expect the extra dimension scale to be observable at the LHC, even most string theorists think this is highly unlikely. There is a standard argument that the hierarchy problem could be explained by a low supersymmetry breaking scale, but this is already starting to be in conflict with the lack of any observations of effects of supersymmetry in precision electroweak measurements, and now string theorists seem very willing to say that supersymmetry may be broken at an unobservably high scale.
String theory predicts observable effects in the CMB or gravitational waves.
If you look into this, this is based on very specific cosmological scenarios such as brane inflation, and again string theory doesn’t tell you even what the energy scale of the supposed predictions is. Undoubtedly you can get “predictions” from specific models, once one chooses various parameters, but not observing these “predicted” effects would not show that string theory is wrong but just that a specific scenario is wrong, with many other possible ones still viable. There’s a new review article by Henry Tye where he claims that “string theory is confronting data and making predictions”, which isn’t true. It is only certain specific scenarios that he has in mind, he admits that other, equally plausible, scenarios (such as using not branes but moduli fields as the inflaton) make no predictions at all. For more about this, one can watch recent talks by Tye and Polchinski at the KITP.
The anthropic landscape predicts the value of the cosmological constant and will make other predictions.
The latest contribution to the anthropic landscape hype is from Raphael Bousso and is entitled Precision Cosmology and the Landscape. I’ve written many times about the problems with the cosmological constant “prediction”. Bousso claims that “there is every reason to hope that a set of 10^500 vacua will yield to statistical reasoning, allowing us to extract predictions”. He doesn’t give any justification at all for this, neglecting to mention arguments about the inherent computational intractability of this question, and the failure of the program to try and predict the answer to the one question that seemed most likely to be approachable: is the supersymmetry breaking scale low or high?
String theory makes predictions testable at RHIC.
There are lots of problems with this, but the main one is that the “string theory” involved is a different one than the one that is supposed to unify particle physics and quantum gravity.
Update: For more promotional material about string theory, you can buy a set of lectures by Jim Gates entitled Superstring Theory: The DNA of Reality. I haven’t seen the videos, but Gates is probably not indulging in the kind of claims about “predictions” of string theory being made by many others.
Update: A couple people have pointed out that a new paper has appeared pointing out that the one “prediction” of the landscape claimed by Susskind, that of the sign of the spatial curvature, isn’t sustainable. This issue was discussed here with Steve Hsu, who was blogging from a conference where Susskind made that claim, and wrote about it in more detail here. Hsu is one of the co-authors of the new paper.
Update: There’s a rather critical review of Lee Smolin’s book in this week’s Science magazine by Aaron Pierce entitled Teach the Controversy! Somehow I suspect Pierce did not write the headline, since he doesn’t seem to think much of opposition to string theory or that it is a good idea to encourage any dissent about it. In his review, he pretty much completely ignores the fact that string theory is supposed to be a unified theory, explaining the standard model as well as quantum gravity, discussing just the question of string theory as a theory of quantum gravity. This is rather odd since quantum gravity isn’t even Pierce’s specialty. I’m somewhat curious what he might think of my book, which is pretty much all about string theory’s failure as an idea about particle theory.