There’s a new popular book out this week by string theorist Michael Dine, This Way to the Universe, as well a a new Sean Carroll podcast interviewing him about the book and the state of particle theory research. According to Carroll, Dine represents the “insider view” of what is really going on in fundamental physics:
you’re getting what basically is the closest to a consensus view of what state particle theory and fundamental physics is right now.
Much of the book is a very conventional and straightforward attempt to explain modern particle theory/GR/cosmology to a general audience, featuring some explanations from Dine about specific attempts to go beyond the Standard Model that he has worked on. The last quarter or so of the book is about string theory and the multiverse. One odd thing about this is that the jacket copy is fraudulent, stating:
People assume string theory can never be tested, but Dine intrepidly explores how the theory might be investigated experimentally.
whereas there’s nothing like that in the book that I could find. Instead, on page 253 one finds about string theory
it’s not clear it’s right, or that it even makes definite predictions at all…
Many readers will know that string theory has been a lightning rod for criticism. In this chapter, we’ll understand why, on the one hand, the subject is so seductive, and on the other, its critics may have a point.
On page 295 there’s
In fact, the existence of states in string theory that really look similar to what we see around us is highly conjectural. This hasn’t stopped me nor my colleagues from writing many papers speculating on a stringy reality. Unfortunately, none of these papers can be said to be making a prediction from string theory. Typically the author likes one particular solution of string theory or another, and selects one feature that is distinctive and goes beyond the Standard Model. But apart from the arbitrariness of this choice, the author has closed his or her eyes to two huge problems with their proposal [the cosmological constant and, perhaps, supersymmetry breaking].
On the Carroll podcast, there’s this exchange (starting around 1:25):
MD: There are people who work actively trying to… On what they would call string phenomenology, but I think that at the moment, this is a hard topic and we just don’t understand well enough how in detail the theory could be related to nature… …strings are rather simple things, but the steps from there to things that look like the standard model, that look like general relativity, are pretty elaborate, and along the way, there are steps we don’t really understand…
SC: … Let me ask you how you respond to sort of the hardcore critics who might say something like this: In the 1980s, the first superstring revolution, people are going around saying like, yeah, we’re going to unify everything, we’re going to predict the mass of the electron and everything is going to be finished in 10 years. Then not only has string theory not made any predictions that you can test in an accelerator, but once we have the landscape of string theory, we’re saying that string theory is compatible with almost any set of particle physics you can have, and at that point, shouldn’t you just give up and move on to something else? It’s not a thing that’s going to give you any testable predictions at any point in the future.
MD: Well, I would basically say that that, all that is fair, but at some gut level, I don’t exactly agree. So first of all, I would say that in 1985, already, in this era of the first superstring revolution, Nathan Seiberg and I pointed out what has come to be known as the Dine-Seiberg problem, a very basic and fundamental obstacle to relating string theory to nature. And people have proposed possible solutions, some of which are interesting, but really, there’s… In the subsequent nearly 40 years, people have not put forward. So I’m on safe ground, I sort of took both sides of this issue.
SC: .. why not just give up if we think that string theory could predict anything at all given the landscape problem?
MD: Well, I think my own attitude is to sit somewhere on the fence, not to devote huge amounts of energy to it, but to allow string theory to inform my thinking about various kinds of issues.
Dine is referring here to the “Dine-Seiberg problem”, described in a 1985 paper with abstract
We argue that if the superstring is to describe our world, it is probably strongly coupled. Several other (unlikely) possibilities are discussed.
The paper is specifically about the effective potential for the dilaton, but the problem is generic and fundamental: you can’t get anything like the real world out of the perturbative superstring and you don’t know what strongly coupled string theory is (one can argue that AdS/CFT tells you what strongly coupled string theory is, but again, that looks nothing like the real world).
The really odd thing about Dine’s current comments about testability (besides that they contradict the jacket of his book) is that 15-20 years ago he was for a while one of the theorists most prominently making the case that string theory and the landscape could be tested. I wrote about this often here on the blog, see for instance here and here. The second of these postings is about a 2007 Physics Today article by Dine entitled
String theory in the era of the Large Hadron Collider that claimed:
A few years ago, there seemed little hope that string theory could make definitive statements about the physics of the LHC. The development of the landscape has radically altered that situation. An optimist can hope that theorists will soon understand enough about the landscape and its statistics to say that supersymmetry or large extra dimensions or technicolor will emerge as a prediction and to specify some detailed features.
The Physics Today piece was rather explicitly an answer to my criticisms of the string theory landscape as untestable pseudo-science, with a subtitle
The relationship between string theory and particle experiment is more complex than the caricature presented in the popular press and weblogs.
Fifteen years later, in this new book Dine says nothing about his earlier claims about testing string theory at the LHC, or that others clearly pointed out at the time what was wrong with them. He ends with this summary of the situation:
… one can adopt the landscape viewpoint, but then one has to acknowledge that, at this point in time, we have nothing like a complete theoretical framework in which to make any scientific investigation, and that there are facts hard to reconcile with this viewpoint. I, for one, find this quite unsettling.
His experience of the last fifteen years does not seem to have made him think any more charitably of string theory critics, who get this sneering description on page 269-70:
[they] view the subject with total disdain, often wearing their ignorance of even its most rudimentary aspects as a badge of honor.
One telling mistake in the book is its reference (page 117) to the “Clay Mathematics Institute of Peterborough, New Hampshire”, an indication of the all too typical theoretical physicist’s lack of knowledge of anything about mathematicians and the mathematics community.
Update: There’s an interesting conversation between Dine and Lisa Randall about the book and these issues, see here.