The Holy Patron of String Theory and its Holy Grail

Science News is running a long interview with Murray Gell-Mann, who will be celebrating his 80th birthday tomorrow. Gell-Mann was arguably (Feynman is one who would argue..) the most influential figure in theoretical particle physics throughout the 1950s and 1960s. In the interview, he gives the standard story about the cosmological constant/supersymmetry/hierarchy problem, expecting superpartners to be accessible at the LHC design energy, although perhaps not at its initial energy of 3.5 TeV/beam. If superpartners don’t show up at 7 TeV/beam, he says:

Well, we’d have to see exactly how bad it is. I mean how high up you go and still don’t find anything and so on. But yes, one might have to discard this whole line of reasoning.

Gell-Mann describes himself as not a string theorist, but someone who thought it was promising and continues to do so, claiming:

I was a sort of patron of string theory — as a conservationist I set up a nature reserve for endangered superstring theorists at Caltech, and from 1972 to 1984 a lot of the work in string theory was done there.

He speculates about what is missing in string theory as follows:

I am puzzled by what seems to me the paucity of effort to find the underlying principle of superstring theory-based unified theory. Einstein didn’t just cobble together his general relativistic theory of gravitation. Instead he found the principle, which was general relativity, general invariance under change of coordinate system. Very deep result. And all that was necessary then to write down the equation was to contact Einstein’s classmate Marcel Grossmann, who knew about Riemannian geometry and ask him what was the equation, and he gave Einstein the formula. Once you find the principle, the theory is not that far behind. And that principle is in some sense a symmetry principle always.

Well, why isn’t there more effort on the part of theorists in this field to uncover that principle? Also, back in the days when the superstring theory was thought to be connected with hadrons rather than all the particles and all the forces, back in that day the underlying theory for hadrons was thought to be capable of being formulated as a bootstrap theory, where all the hadrons were made up of one another in a self-consistent bootstrap scheme. And that’s where superstring theory originated, in that bootstrap situation. Well, why not investigate that further? Why not look further into the notion of the bootstrap and see if there is some sort of modern symmetry principle that would underlie the superstring-based theory of all the forces and all the particles. Some modern equivalent of the bootstrap idea, perhaps related to something that they call modular invariance. Whenever I talk with wonderful brilliant people who work on this stuff, I ask what don’t you look more at the bootstrap and why don’t you look more at the underlying principle. . . .

Lubos Motl seems to have calmed down a bit recently, and his latest posting is about the Gell-Mann interview. He describes Gell-Mann as not just a patron of string theory, but a holy patron of string theory, with the comments quoted above “the holy word”. They inspire him as he continues to work a few hours a day towards finding the holy grail of string theory: some fundamental principle that defines the theory non-perturbatively.

Searches for such a principle go back at least 25 years, to 1984 and the explosion of interest in string theory as a unified theory. After the first efforts to base unification on a Calabi-Yau, it soon became clear that more was needed than string perturbation theory. Just one of many such attempts that I remember was that of Friedan/Shenker in 1986, who hoped that in some sense the moduli space of all Riemann surfaces would somehow carry a unique vector bundle with flat connection. There were many others.

Lubos entered the field ten years later, after discoveries about dualities had led to Witten’s conjecture of the existence of an “M-theory” that would reduce in various limits to the known string theories. At the time, the hot candidate for such a theory was something called Matrix theory, and Lubos made his reputation with work on this. His thinking these days grows out of the “M-theory” conjecture that he first started working on as an undergraduate 13 years ago, and probably reflects well the kind of speculative hopes that drove this area of research from the beginning:

It also seems extremely likely that some UV/IR links – modeled by the modular invariance in the context of perturbative closed strings – will be important for the formulation of the ultimate principle. Non-perturbatively, it seems obvious that such a link will have to constrain the black hole microstates, i.e. the generic high-mass particle species in any theory of quantum gravity. The spectrum and detailed structure of the black hole microstates must be linked to low-energy fields and all of their higher-order interactions. These conditions will admit a limited number of solutions that will coincide with the allowed configurations of string/M-theory.

Moreover, it’s conceivable that we won’t be able to work “fully on the worldsheet” or “fully in the spacetime”. I feel that the ultimate set of consistency rules for quantum gravity will work “simultaneously” for the generalized worldvolumes as well as spacetime. So I am spending a lot of time by attempts to import some lessons – and methods to derive or generate new degrees of freedom – from spacetimes to the worldvolumes, and vice versa.

Modular invariance, mutual locality of operators, Dirac quantization rules, similar conditions, and their generalizations play an important role. But it remains to be seen whether there is a concise, ultimate principle or set of principles, why it generalizes the conformal symmetry (and modular invariance) in the perturbative limit, and why it admits old perturbative solutions as well as new, non-perturbative solutions such as the 11-dimensional vacuum of M-theory.

Of course, one of the most obvious testing grounds for such new sets of ideas is the exceptional U-duality group of M-theory on tori – i.e. the maximally supersymmetric supergravity. The exceptional groups are pretty and they must have a pretty cool explanation in terms of a structure we still don’t fully know.

Like Gell-Mann, Lubos expects the right theory to emerge not from choice of a specific set of dynamical degrees of freedom, but by a “bootstrap”: discovery of some sort of consistency conditions that uniquely pick out the right theory. The idea is that you don’t have to get to fundamental variables at the bottom of things to rest your theory on, but can by some other means “pick yourself up by your bootstraps”. Since this doesn’t work in real life, I’ve always wondered why its advocates didn’t pick a more convincing name…

Lubos ends his posting with:

I think that some kind of bootstrap is needed to determine what “M” and its structure of symmetries really is. Is there a third person in the world who cares about this possibly most important question of science? These core topics of string theory are currently understudied at least by two orders of magnitude.

The question of why so few string theorists work on this question is an interesting one. The M-theory conjecture drove string theory research for many years. My own suspicion is that the fact of the matter is that most string theorists have just given up on it. The AdS/CFT correspondence appears to give a non-perturbative definition of string theory in a particular background (in terms of a QFT), and string theorists are more interested in investigating that than in continuing the so-far futile search for “M-theory”. In addition, arguments of landscapeologists indicate that if you did find the conjectured “M-theory”, it might be a useless untestable “theory” that could explain just about anything.

Physicists with a sense of history also have another good reason to be suspicious of calls for a new “bootstrap” program. This idea was all the rage during the sixties, but ended up a dismal failure. The conjecture that some known powerful principles (analyticity, crossing, etc..) would have a unique solution satisfying them just turned out to be wrong as a way of understanding the strong interactions. There are lots of possible solutions, and finding the right theory requires identifying the correct one: an SU(3) gauge theory with a specific, very beautiful set of geometrical degrees of freedom. This theory remains poorly understood, and the project of better understanding it recently has revived some of the bootstrap ideas, but in the context of trying out a new choice of geometrical degrees of freedom (twistors). This is now the hot idea of the subject, but it’s no longer one that promises unification via string theory. I suspect Lubos will be increasingly lonely in the pursuit of the dream of his youth, as his colleagues mostly give up on it and move on.

This entry was posted in Uncategorized. Bookmark the permalink.

17 Responses to The Holy Patron of String Theory and its Holy Grail

  1. Phil says:

    your link on Lubos’ page refers to this page:

    So I don’t think that he’d calmed down….

  2. As a one time student of Lubology, I would say that there have always been two Lumos, the vengeful prophet and the insightful scientist – Dr. Lubos and Mr. Motl. Good Lumo writes nice biographies and elegant explanations all the while pondering the deep questions of physics. Evil Lumo is obsessed with his many enemies. One cheers for the good guy, but you have to know the other one is waiting with … whatever.

  3. Thomas Larsson says:

    “Just one of many such attempts that I remember was that of Friedan/Shenker in 1986, who hoped that in some sense the moduli space of all Riemann surfaces would somehow carry a unique vector bundle with flat connection.”

    I met Friedan in 1990, at a conference to which I travelled with a mathematician friend who was very excited about the Friedan/Shenker work. Friedan himself did not show any interest to discuss it though. He dismissed his work as “very abstract”, and it was clear that this was not meant in a positive way.

  4. Franz says:

    I can testify that Lubos has NOT calmed down. I have copies of very recent emails in which Lubos told an aquaintance (on Lubos’ posting about Gell-Mann’s interview) that “careful observations” show that the world has either 10 or 26 space-time dimensions and that whoever believes that space has 3 dimensions has a “lethal disease” and is full of “blinded religious dogmatism”. (I am not making this up.) Despite believing in 3 dimensions, my acquaintance does not seem offended, but he sure is astonished.

  5. CIP, I agree – Lubos gives the impression of having two personalities. I think it bothers him a bit if I bring this up when he starts talking foul in my blog. He mostly behaves with me now. Right, Lubos ?

    Recently, I have also found out that he drops the conversation if I threaten him physically. He was suggesting that my male organ is undersized, and I offered to pay him a visit and have him experience it, adding that he should prepare lots of Lube, shave carefully, and use little makeup. I think that was too much for him to handle, and he dropped off the thread.


  6. Peter Woit says:


    Now, now, this is supposed to be a PG rated blog, as well as one that firmly espouses non-violence (at least in the string wars).

    Interesting to see from Lubos’s latest comments on his posting that he’s upset not only about me and Smolin, but about the recent behavior of the powers that be in particle theory:

    “This is about forces that have penetrated almost everywhere into the “official” scheme of things. This is about the Chamberlainian attitude of the physicists who actually know what the truth is. It is about the drivers that lead people, especially the young ones, to decide about their “focus” and “excitement” which is so rarely real these days. All these things are wrong and I don’t want to be a part of it.”

    Particle theory is in a sad way these days, and, as usual, I suspect that Lubos and I agree about more things than most people realize…

  7. TomK says:

    Would it be a good idea to place a short warning within this posting to warn future readers what will happen when they follow that particular link?

  8. Franz says:

    Peter, as you cited already, in the fast comment section on his posting on Gell-Mann, Lubos criticizes the patrons of physics: “it is about the drivers that lead people, especially the young ones, to decide about their “focus” and “excitement” which is so rarely real these days.”

    At the beginning of that comment section he behaves in exactly the way that he criticizes: he writes incorrect and offensive statements about a researcher and his unification attempt. I am really shocked by this double standard. Lubos turns out to behave in exactly the same way as the people he criticizes.

    Let us hope that Gell-Mann’s proposed search for an underlying principle will be undertaken by more people. Lubos narcissistic personality disorder will prevent him to find any such principle. We need professional scientists to achieve it, people who are focused and determined.

  9. big vlad says:

    I am really shocked by this:

    “I am really shocked by this double standard. Lubos turns out to behave in exactly the same way as the people he criticizes.”

  10. Tim vB says:

    concerning Lubos: One basic rule of psychology is that what you dislike most with other people are your own biggest faults.
    BTW: Since it seems that Lubos doesn’t know: Gell-Man took the name quark from the novel “Finnegan’s Wake” by James Joyce,
    but Joyce himself did probably hear the word during his stay in Austria, it is a common German word meaning “curd cheese”.

  11. Dave Miller says:

    Peter wrote:
    > Particle theory is in a sad way these days, and, as usual, I suspect that Lubos and I agree about more things than most people realize…

    I’ve always suspected that. Lubos comes from that Central European milieu where, in print, you take no prisoners, but I’ve always suspected that you guys might actually have a pleasant dinner together (if you’re ever in Sacramento at the same time, you have a standing invitation).

    I took a freshman course on particle physics from John Schwarz, who I thought was a truly nice guy, during the early days of string theory (too early for John to tell us frosh about it). I think Gell-Mann does deserve credit for “protecting” what was, after all, an interesting idea – even if it later became a fad.

    I’ve always had this nagging suspicion myself that there is some underlying geometric-style symmetry behind all of the string/post-string math. Maybe Gell-Mann, Lubos, and I are all still blinded from our youth by having learned about how Einstein worked out GR.

    Or, maybe, Lubos will actually stumble upon something.

    Dave Miller in Sacramento

  12. chris says:

    but Joyce himself did probably hear the word during his stay in Austria, it is a common German word meaning “curd cheese”.

    i don’t think he heard that in Austria, since it’s called “Topfen” there, not quark 🙂 afaik, he read a grocers ad “Musterquark fuer 3 Mark” and transformed it into “3 quarks for muster mark”.

  13. Tim vB says:

    Hi Chris,
    I stand corrected, so the ad was a German one, since the currency in Autria would have been Schilling, not Mark, right?
    Anyway, Murray Gell-Man was looking for a name for some mysterious entity and ended up with the name of a milk product, which is an anecdote worth telling in every class on QFT 🙂

  14. Chris Oakley says:

    According to this you’re all wrong about quarks as “three quarks for muster Mark” refers to derisory squawks directed against King Mark, the Cornish king whose bride – the Irish Princess Iseult (or Isolda) – turned out to be far more interested in Tristram (or Tristan), one of his knights, than the king himself. One of my ambitions is to make a movie of Wagner’s version of this legend (his opera Tristan und Isolde) but as I have just turned 50, and have yet to make any movies, it is looking ever less likely.

    BTW: perhaps the only thing I agree with Jacques Distler about is that giving air time to Lubos or to comments about him is a Bad Thing. Can I propose a similar policy here?

  15. Kea says:

    They serve quark cake at some mountain restaurants in the Bernese Oberland in Switzerland … and maybe further afield, but I’m not sure.

  16. Marcus says:

    Yes, deliciously rich, with butter and higg-yolks.

  17. Parts of string theory will survive and be testable. It is basically the quantization of the classical Einstein-Cartan localization of the 10-parameter Poincare group + supersymmetry. I am on way to Trinity College, Cambridge and will elaborate on this another time. Agreed on the MPD of Lubos who has a webpage from Rutgers that he is a transexual ET – humorous of course. If Lubos did not exist I would have had to invent him as a larger-than-life character in a Pynchon or Borges story. 🙂

Comments are closed.