The journal Foundations of Physics has been promising a special issue on “Forty Years of String Theory: Reflecting on the Foundations” for quite a while now, with a contribution first appearing back when it really was 40 years since the beginnings (more like 43 now). The final contribution has now appeared, an introductory essay by the editors (’t Hooft, Erik Verlinde, Sebastian de Haro and Dennis Dieks).
The overall tone of the collection is one of defensive promotion of the subject. The fact that string theory’s massively overhyped claims to give a unified theory of particle physics have led to miserable failure is mostly completely ignored. From the introductory essay one would never guess that string theory was ever supposed to have something to do with explaining the Standard Model of particle physics and that there were hopes that it would find some sort of vindication at the LHC, perhaps via the discovery of SUSY (the LHC is not even mentioned in this essay). String theory is presented purely as a theory of quantum gravity that has led to new insights in mathematics and had various other applications through the dualities it has uncovered. It’s main shortcoming is described as
the lack of directly testable experimental predictions that would signal ‘string physics’
which seems to me intentionally misleading, implying that string theory makes indirectly testable predictions. The problem with string theory is that it makes no predictions about anything, not that it only makes indirectly testable ones.
Three of the eleven articles in the collection are described as representing critics of string theory. The first, from Carlo Rovelli, does do a good job of explaining many of the problems of string theory. Lee Smolin’s contribution is not much about string theory, but more an examination of the general issue of the “Landscape problem”, comparing a range of different theories in which the laws of physics are different outside our observable universe.
’t Hooft’s On the Foundations of Superstring theory calls for more attention to the lack of any fundamental description that tells us what string theory really “is”, taking the point of view:
we conjecture that the “true theory” is something totally different from superstring theory (and certainly also different from gravitating quantum field theories), but that string theory may approximate the truth to various degrees of accuracy in one or several of its compactified realizations, just as it does for some condensed matter systems and QCD.
He ends with an argument (which he notes is “one where only few readers will follow me”) that one problem with string theory is that it uses the conventional quantum formalism, which he feels is flawed, needing replacement by an “emergent” version of quantum mechanics. For more about the sort of thing he has in mind, see here.
Two articles by philosophers of science, Dean Rickles and Richard Dawid address the question of how to evaluate a supposedly scientific theory that, like string theory, makes no experimentally testable predictions. Both pieces seem to me to suffer from a rather uncritical attitude towards various forms of string theory hype. For Rickles, the dominance of string theory can be justified by its “mathematical fertility”, for Dawid the justification is “the assessment of scientific underdetermination” (roughly, there aren’t any other good ideas). That it has led to some interesting mathematics and that there’s not a lot of good alternative ideas out there are perhaps the two best arguments for pursuing string theory, but in both cases the situation is far more complicated than string theory advocates would have one believe.
The articles by string theorists (Balasubramanian, Giddings, Gubser. Martinec, Susskind and Duff) have a range of interesting things to say, sometimes amidst large dollops of string theory hype. Almost all evade serious discussion of string theory’s failure to say anything about the Standard Model (although Susskind argues, a la Multiverse, that this a positive feature of string theory). Giddings perhaps makes the most serious criticism of string theory in the entire volume, discussing its problems as a theory of quantum gravity, where other authors see a big success and the theory’s main selling point.
The article by Duff is by far the most bizarre thing in the volume, and I wrote about it extensively a year ago here. As Duff sees it, the problem is just that critics of string theory are misguided and misinformed. He includes a three page denunciation of Garrett Lisi which has nothing to do with string theory, characterizes the major recent research directions in string theory as fluid mechanics and the black hole/qubit correspondence, and has an appendix about the press release Imperial College put out making absurd claims that he had finally figured out how to make predictions from string theory (see here). The editors of the volume seem to be rather defensive about publishing such a thing, noting
Needless to say that the opinions expressed in this paper are entirely the author’s own and that it is not our intent to spark new popular or otherwise heated discussions.
but justifying it as
we are happy to include this paper in our special issue as addressing questions that are important not only to scientists but also to the wider public, which was among our initial intents.
and ending with
We warmly recommend Duff’s very readable and playful contribution.
Nothing about Duff’s piece struck me as “playful”, but that the editors see it as some sort of joke would explain why they thought it worth publishing.
Update: Over at The Browser, Steven Gubser recommends that people should read The Elegant Universe and four string theory textbooks. Asked about the “no predictions problem”, Gubser does his best to mislead, claiming the situation is just like that with QED that Feynman got the Nobel Prize for. As for SUSY, if the LHC finds it, that’s evidence for string theory, if not, no problem. There’s the old favorite “the LHC might produce microscopic black holes”. About whether string theory makes testable predictions about the heavy ion physics the LHC is studying
String theory might predict that such and such number is one, and the experiment might say well it’s about two, but it could instead be one. That’s the kind of accuracy with which things can typically be done.
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