October 06, 2006

Zeitgeist String Era

Bert Schroer has written a very interesting essay (the kind I've been hoping to write some day ;) String theory and the  crisis in particle physics. A historical overview of quantum theory is also given, back from the 1920's. Making use of the clarity of style of the author I give a few quotes of his text as a warm-up for a potential reader.  Mainly from the introduction, to avoid mentioning any names of people involved ;).

"For the present particle theorist to be successful it is not sufficient to propose an interesting idea via written publication and oral presentation, but he also should try to build or find a community around this idea. The best protection of a theoretical proposal against profound criticism and thus securing its longtime survival is to be able to create a community around it. If such a situation can be maintained over a sufficiently long time it develops a life of its own because no member of the community wants to find himself in a situation where he has spend the most productive years on a failed project. In such a situation intellectual honesty gives way to an ever increasing unwillingness and finally a loss of critical abilities as a result of self-delusion."

"I would like to argue that these developments have been looming in string theory for a long time and the recent anthropic manifesto [1] (L. Susskind, The Cosmic Landscape: String Theory and the Illusion of Intelligent Design) (which apparently led to a schism within the string community) is only the extreme tip of an iceberg. Since there has been ample criticism of this anthropic viewpoint (even within the string theory community), my critical essay will be directed to the metaphoric aspect by which string theory has deepened the post standard model crisis of particle physics. Since in my view the continuation of the present path could jeopardize the future research of fundamental physics for many generations, the style of presentation will occasionally be somewhat polemic."

"An age old problem of QFT which resisted all attempts to solve it is the problem of existence of models i.e. whether there really exist a QFT behind the Lagrangian name and perturbative expressions. Since there are convincing arguments that perturbative series do not converge (they are at best asymptotic expressions) this is a very serious and (for realistic models) unsolved problems. The problem that particle physics most successful theory of QED is also its mathematically most fragile has not gone away. In this sense QFT has a very precarious status very different from any other area of physics in particular from QM. This is very annoying and in order to not to undermine the confidence of newcomers in QFT the prescribed terminology is to simply use the word ”defined” or ”exists” in case some consistency arguments (usually related in some way to perturbation theory) have been checked."

"These problems become even worse in theories as string theory (which in the eyes of string protagonists are supposed to supersede QFT). In this case one faces in addition to the existence problem the conceptual difficulty of not having been able to extract characterizing principles from ad hoc recipes. Unlike in renormalizable QFT there exists up to date no n-th order proof that string theory is free of renormalization parameters."

"Since there was no operator formalism in which the underlying ideas (invariance, unitarity, crossing, maximal analyticity) could have been implemented,  the problem of constructing a crossing symmetric, unitary, maximally analytic S-matrix was ill-formulated. Tinkering with properties of Beta functions and their representation in terms of Gamma functions, Veneziano was able to construct the first model for an apparent crossing symmetric elastic scattering amplitude. His proposal did not satisfy unitarity, but the realization that his on-shell prescription allowed an auxiliary field theoretic description in terms of a (off-shell) two-dimensional conformal field operators theory and that it also admitted an auxiliary presentation in terms of the canonical quantization of a classical relativistic Nambu-Goto string Lagrangian contributed significantly to its theoretical attraction. It also nourished the hope that the model can be unitarized in a later stage. Its main popularity it however enjoyed among strong interaction phenomenologists who actually (for reasons which nowadays hardly anybody remembers) liked the idea of satisfying crossing already with infinite towers of intermediate particle states, duality = crossing among with (infinitly many) one-particle without the participations without the participation of the multi-particle scattering continua as would be required for an S-matrix coming from QFT. In conjunction with the phenomenological use of ideas of Regge poles, the emerging trajectory pictures (mass versus spin) had a certain phenomenological charm, and although infinite particle towers cause some field theoretic headache, there was no reason to reject it as a phenomenological proposal which captures some aspects of strong interactions and to worry about those conceptual problems later."

"But this never happened; the dual model became a phenomenological orphan and after its string-theoretic completion, by the time it was presented as a TOE (this time including gravity), the conceptual problem behind the crossing-duality relation was forgotten, and a chance to understand something about conceptual relations of string theory to QFT was (presumably permanently) lost. Particle physics these days is generally not done by individuals but by members of big groups, and when these big caravans have passed by a problem, it will remain in the desert. A reinvestigation (naturally with improved mathematical tool and grater conceptual insight) could be detrimental to the career of somebody who does not enjoy the security of a community."

"In its new string theoretical setting its old phenomenological flaw of containing a spin=2 particle was converted into the ”virtue” of the presence of a graviton. The new message was the suggestion that string theory (as a result of the presence of spin two and the apparent absence of perturbative ultraviolet divergencies) should be given the status of a fundamental theory at an energy scale of the gravitational Planck mass ∼ 10^19 GeV i.e. as a true theory of everything (TOE), including gravity. Keeping in mind that the frontiers of fundamental theoretical physics (and in particular of particle physics) are by their very nature a quite speculative subject, one should not be surprised about the highly speculative radical aspects of this proposals; we know from history that some of our most successful theories originated as speculative conjectures. What is however worrisome about this episode is rather its uncritical reception. After all there is no precedent in the history of physics of a phenomenologically conceived idea for laboratory energies to became miraculously transmuted into a theory of everything by just sliding the energy scale upward through 15 orders of magnitudes and changing the terminology without a change in its mathematical-conceptual setting."

Finally, from Conclusions:
"In this essay I emphasized that, as recent progress already forshadows, the issue of QG will not be decided in an Armargeddon between ST and LQG, but QFT will enter as a forceful player once it has conceptually solidified the ground from where exploratory jumps into the blue yonder including a return ticket can be undertaken."

"The problem is not that there are no other games in town, but rather that there are no bright young players who take the risk of jeopardizing their career by learning and expanding the sophisticated rules for playing other games."

By the way, I wrote my (modest) thesis on five point Veneziano phenomenology.
Now, probably back to break (due to ailing health).