This Way to the Universe

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.

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9 Responses to This Way to the Universe

  1. Jim Given says:

    Logicians have very unflattering terms for those who want to have things both ways.

  2. DrDave says:

    I think one thing that we are seeing is string theory folded into mainstream science books, generally favorable to ST but appearing to be a wider overview (which they can be, of course) without any real attempt to present any evidence to the contrary. And what we aren’t seeing is the exactly the same sort of book but with a real critical appraisal of ST. A very practical way to monopolize the shelfspace of ideas.

  3. Sabine says:

    In all fairness the “predictions” for the LHC (be that from string phenomenology or other BSM physics) had little to do with the theories per se and all with the added requirement of “naturalness” that Dine has written about a lot. I’m still waiting to see a particle physicist admit that they were wrong to think that naturalness is a scientific criterion on which one can base predictions.

    (And that they almost all believed this naturalness stuff is why one should be very skeptical of “consensus views”…)

  4. Andreas Karch says:

    Naturalness is a property of quantum field theory that is well established mathematical fact and has been experimentally proven in many instances. Certain quantities in a quantum field theory are sensitive to the short distance details (for example scalar masses). Having a light scalar requires fine tuning. We can test these ideas in quantum field theories where we know the exact short distance physics — that is in condensed matter systems. There the underlying microscopic theory is a lattice of nuclei and electrons. We know “the theory of everything” as far as materials are concerned. At long distances, quantum field theory is the right description. To see light scalars, you need to fine tune microscopic parameters. A typical example is the order parameter near a phase transition. That is a light scalar, but you need to tune near the critical point for it to appear in the low energy QFT. Usually it is pushed up to high energies, that is the UV cutoff set by the lattice. On the other hand, light fermions are natural. The Fermi liquid describing most metals does not need to be fine tuned (let’s forget about superconductivity for now, this requires a well understood but more subtle discussion). Landau’s theory of phase transitions as well as Landau’s theory of Fermi liquids is just the idea of naturalness spelled out. These are very powerful and scientifically proven theories. So no one is going to give up on naturalness as a property of quantum field theory ever — since it is true and it works.

    Now applying naturalness to particle physics is of course a guess. No one had any right to demand that it has to apply there. But it’s an appealing idea. If at the microscopic level we have many choices for the fundamental parameters (as we do for a condensed matter system), you could expect that we live at a “generic” point in this parameter space. Of course we don’t know if this is in fact so as we haven’t established the microscopic theory in that case. But unlike model building based on completely random guesses, naturalness basically makes this one assumption and then asks what the consequences would be. And the consequence is that you would need a mechanism to keep the Higgs mass light. And all known mechanisms to do that would leave extra light particles behind. The fact that we didn’t find any of these new particles in retrospect makes it look like naturalness was not the right idea to pursue. But to claim it was a bad idea to check out is something few physicist will ever agree. It’s a simple to state and well motivated principle and one was able to test it.

  5. Peter Woit says:

    Andreas Karch/Sabine Hossenfelder,

    I don’t want to start up yet another discussion of “naturalness” here, but as blog owner will just repeat my usual argument that the sensitivity of scalars to short distance physics only causes a fine-tuning problem for people who are pushing a theory with complicated new degrees of freedom at exponentially short distances. If you try to fix a problem caused by a bad theory at unobservably short distances by invoking more bad theory at the electroweak scale, it’s not surprising the LHC tells you this doesn’t happen.

    Dine makes the usual comments about naturalness and fine-tuning, but there’s no serious discussion in his book. In the end, the failure of “naturalness” arguments for new physics at the electroweak scale gets used in the conventional way by Dine, as an argument for the anthropic landscape. The main point about this I think is just that if your argument leads you to untestable pseudo-science, you’ve proved that it’s not a good scientific argument.

  6. eigenmoore says:

    That’s why I like the book ‘Why String Theory?’ from Joseph Conlon, he has a entire chapter titled something like ‘Experimental Evidence for String Theory’ and it’s just full blank page!

  7. Peter Woit says:

    Dine has done much the same thing: in the text of the book he explicitly admits there’s no way to make predictions using string theory and explains why.

    His innovation is to do this, then have the publisher put on the cover of the book promotional material claiming that inside it contains an explanation of how string theory will be investigated experimentally.

  8. Lee Smolin says:

    Dear Peter,

    I was sorry to read that quote of Dine’s as I’ve always found him openminded. But, in the spirit of being not even wrong, here is a test: Jay Armas has edited a collection of “Conversations on quantum gravity” including researchers of diverse points of view.

    Let’s assign to each researcher a +1 for every mention of an approach not their own which is objective ie checkable and correct, a -1 for every objective but false statement about another approach and a -2 for every statement evaluating an approach, theirs or not, that has no objective meaning by which it could be checked. I haven’t done this-anyone want to try it?

  9. Peter Woit says:

    To be fair to Dine, the full quote contrasts extremists: those “who view string theory as a sort of holy grail” to others who “view the subject with total disdain, often wearing their ignorance of even its most rudimentary aspects as a badge of honor” I’m assuming he’d put you as in neither category (not sure about me though…).

    Exactly because Dine is otherwise very mild-mannered and willing to admit that critics might be right (to the point of even claiming to be on both sides of the argument) that this sentence stands out in the book. Those like Dine who publicly joined the string wars on what I would claim was the losing side (see his Physics Today piece), as open-minded as they may be, may still be nursing wounds from that era.

    I agree with your implicit point that in the Armas volume the difference between the way string theorists and non-string theorists discuss the problems of various approaches is rather striking.

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