Not Even Wrong

The Spring 2009 IAS newsletter is out, available online here. It includes the news that the IAS is stealing yet another physics faculty member from Harvard, with Matias Zaldarriaga moving there in the fall.

The cover story of the newsletter is called Feynman Diagrams and Beyond, and it starts with some history, emphasizing the role of the IAS’s Freeman Dyson. It goes on to describe recent work on the structure of gauge theory scattering amplitudes going on at the IAS, emphasizing recent work by IAS professor Arkani-Hamed and collaborators that uses twistor space techniques, as well as Maldacena’s work using AdS/CFT to relate such calculations to string theory. Arkani-Hamed (see related posting here) says he’s trying to find a direct formulation of the theory (not just the scattering amplitudes) in twistor space:

We have a lot of clues now, and I think there is a path towards a complete theory that will rewrite physics in a language that won’t have space-time in it but will explain these patterns.

and explains the relation to AdS/CFT as:

The AdS/CFT correspondence already tells us how to formulate physics in this way for negatively curved space-times; we are trying to figure out if there is some analog of that picture for describing scattering amplitudes in flat space. Since a sufficiently small portion of any space-time is flat, figuring out how to talk about the physics of flat space holographically will likely represent a real step forward in theoretical physics.

One IAS member who is also working in this area is Emil Bjerrum-Bohr, a great-grandson of Niels Bohr, and the newsletter has an article about him and the various members of the Bohr family who have been at the IAS at one point or another.

For one more piece of news related to Feynman diagrams, Zvi Bern et al. have a new paper out where they explicitly construct the four-loop four-particle amplitude, for N=8 supergravity, and show that it is ultraviolet finite in both 4 and 5d. This provides yet one more piece of evidence for the ultraviolet finiteness of N=8 supergravity. Remember all those claims made for string theory that it is the only way to tame the short-distance fluctuations of a quantum theory of gravity?

Update: One of the authors of the four-loop paper wrote to me with some comments about it, which he gave me permission to post here:

I just wanted to point out what I see as two of the interesting things with this calculation:

1) Honest four-loop QFT calculations in (massless) gauge and gravity theories are now possible, if not exactly trivial. This isn’t just “big fancy computers.” Sure, computers help with the book-keeping of the calculation, but no computer in the world could have accomplished this by naively marching through Feynman diagrams (just look at the size of the expression of 3-graviton Feynman rule in your favorite gauge, and do vertex counting on the number of distinct graph topologies). Rather, this is due to advances in understanding how to manipulate lower-loop and tree-level scattering amplitudes to get (complete) higher-loop scattering amplitudes.

To understand how powerful this is, consider the following: the construction of the four-loop four-point N=4 super-Yang-Mills amplitude required (as input) nothing more complicated than the Parke-Taylor expressions for MHV three-, four-, and five-gluon scattering amplitudes in four dimensions — not even requiring the (very nice) recursion relations for higher point trees mentioned in the IAS piece above. (Verification, of course, required more 🙂 ). If you’ve seen the Parke-Taylor expressions you’ll know how simple they are! The construction and verification of the four-loop N=8 supergravity amplitude requires only knowing the four-loop four-point N=4 super-Yang-Mills amplitude.

Even had we not gotten the nice result regarding the tame UV behavior, getting to the point where these types of calculations are doable is I think important in its own right, and possibly even more important in the long-run. I should probably point out that these types of approaches can and are being generalized to more physical theories, like the exciting high-multiplicity one-loop QCD work going on.

2) Maybe there’s a perturbatively finite (point-like) QFT of gravity in 4D. This is exciting as it suggests that QFT could be a more powerful framework for describing the universe than people have been giving it credit for recently. We do believe that, if it is perturbatively finite, it will be so due to some previously unrecognized symmetry or dynamical mechanism that once understood should greatly improve our understanding of gravity. There does seem to be some connection with the very good scaling behavior of tree-level pure-graviton amplitudes in theories related to Einstein-Hilbert gravity.

That being said, we really don’t have anything to say about its non-perturbative behavior. Really. Nothing at all. It absolutely could require non-perturbative completeness from string theory. It could already be non-perturbatively complete in a way that’s best described by a string theory in certain regimes (emergent string theory if you like). Maybe it only works with higher-dimensional invisi-pink elephants. I really don’t know; it’s not what we’re after right now. I certainly encourage people to consider working on non-perturbative N=8 questions if they’re curious!

Not to be overly contrarian, but I wouldn’t characterize any of this as a blow against string theory, and I don’t think most string theorists see it as such. String theorists have, on the whole, been very supportive of this line of research (even if it might mean a small technical modification of certain sentences in the introduction of certain texts 🙂 ). Besides one of our collaborators (Radu) also being a practicing string-theorist, we’ve met with a lot of support from all sorts of people who appreciate calculation, and are honestly curious about the results. Besides, there have been very strong string-theorists actively working on understanding this from the string-side. In terms of community support, i.e. not just good individuals here and there, Zvi’s been invited to talk at Strings ’09, Lance talked at ’08, and I think Zvi talked at ’07 if I remember correctly.

I, of course, can’t help but flinch a little when people glibly say string theory is the only way to talk about gravity (which is manifestly wrong, e.g. the CFT side of the AdS/CFT *duality*). Most thoughtful string-theorists I’ve met who say something similar, however, are using it as a shorthand for a much more long-winded statement which is accurate. Namely they’re compressing a statement regarding the level of understanding we’ve gained about gravity and gauge theories and non-perturbative solutions through string-theoretic analysis, which we haven’t from anywhere else. As we can see by my comment here, there are perils to giving in to long-windiness, so I tend to refrain from giving them too hard a time about it. There is trouble of course when similar statements are mindlessly parroted by the thoughtless, but the thoughtless tend to generate grief generically in any case.

John Joseph M. Carrasco
http://www.physics.ucla.edu./~jjmc/

I’m afraid that most of you have already missed one event here in New York involving someone who blogs about high energy physics. This was Tommaso Dorigo’s visit this Sunday to New York for a few hours. Luckily for you, he blogs about it, with pictures, here. I’m quite pleased to have finally gotten a chance to meet him in person. My mother feels the same way.

There is something else though here in New York, next Monday, that you still haven’t missed. I’ll be talking and answering questions at an event organized by the Center for Inquiry, which will take place at the Brooklyn Society for Ethical Culture in Park Slope. More information about the event is available here.

Oswaldo Zapata is a young string theorist who recently got his Ph.D. in the subject in Rome. He recently wrote to me to tell me about some essays on the history of superstring theory that he has written, which he is starting to put up on a web-site he calls Spinning the Superweb. I’ll be interested to follow the rest of the essays. He has also posted the first of these on the arXiv.

Zapata’s history is largely concerned with the question of how string theory has achieved acceptance in certain circles despite its failure to satisfy the conventional criteria normally demanded of a successful scientific theory. Reading him, you might initially get the idea he is a string theory skeptic unhappy with what has happened:

From the previous examples we have learnt some important things about the development of string theory. Firstly, as research progresses in a given topic, an explicit reference to the unsolved problem tends to disappear from the literature. For instance, we saw how the quantization of gravity is considered by string theorists to be an accomplished task that does not deserve further study, or even a mention. Secondly, while research advances, the initial problem changes in such a way that it becomes increasingly difficult to unravel the convoluted relationship connecting the final problem to the original one. This was illustrated by our second example concerning string theory and the unification of the forces. Originally the idea was to extract the standard model from superstring theory, an investigation encouraged during the second half of the eighties by the promising results obtained from the heterotic string. Then, by the mid-nineties, the goal was to determine the unique vacuum of the mother of all the theories, the M-Theory. And, more recently, the focus was on the right “environment” of the anthropic solution. Things have changed, but the fundamental query remains unsolved: how do we get the standard model from string theory? With these examples we have learnt something else: this occurs while an “outward” discourse (from the “inside” to the “outside” of the professional community) proclaims that the theory has solved such problems. Indeed, in this movement disadvantages have been transmuted into virtues…

At first, a hypothesis is made, explaining openly its significance as well as its difficulties. At this stage no one is sure of the real value of the conjecture, however, it is interesting enough to drive a significant part of the physics community to devote itself to its development. Step by step “evidence” accumulates and after a while the string theory fact emerges. String theorists have created in this way their own nature: a supersymmetric world, a big bang with all the fundamental forces combined, a multi-dimensional universe, and so forth.

Zapata appears to be claiming there is such a thing as a “string theory fact”, which is somehow different than the usual scientific notion of “fact”, one that requires experimental confirmation.

Among the other unusual aspects of the string theory story that Zapata recognizes is one that has often struck me. This is a subject so complicated that very few people actually understand what is going on, including many of the people working on it. As a result, overhyped claims in the popular media play a big role, with few people able to evaluate them properly:

In fact, string theory is so complex that experts are neither able to understand entirely the main developments nor to follow its rapid growth. In general, practitioners feel confident only in a specific subfield. People working on the AdS/CFT correspondence or twistor theory, for example, do not comprehend the whole area, even though they can be extremely competent when tackling the particular problems of the subfield. Because of this, paradoxically, those that have provided the evidence in support of superstrings do not fully grasp it. Many do not understand the AdS/CFT correspondence completely but they believe in it; it is a matter of fact. A fact in string theory is a shared belief that something is unquestionably true. What I will try to show here is that string theorists often base their beliefs on what they have seen proclaimed everywhere. This ubiquitous discourse includes technical seminars and articles, which I will call the in-in discourse, as well as popular speeches and books, the out-in discourse. Furthermore, I will try to convince the reader that string theorists start to internalize the rules of the game long before they become experts; by means of a discourse that embraces the whole society. I will dub this the out-out discourse when the information comes from non-experts, and the in-out discourse when it comes from professional physicists.

Zapata goes on to give a truly remarkable description of the sociology and psychology of how people get into string theory. Remember, this is coming from a young string theorist:

The discussion above suggests that many string theorists have begun their careers with a biased view of the subject. How they conceive the theory during their formative years depends crucially on previous contact with materials intended for the general public and, later on, on the systematic training given by senior members of the community. We have seen how these two stages in the education of future string theorists coincide at one point: they present new subjects as confirmations of the most fundamental claims of the theory. The theory has succeeded in: quantizing gravity and unifying all the fundamental forces of nature. In addition, it explains the thermodynamics of black holes and has also demonstrated a precise gravity/particle physics correspondence. This is what is taught. Even though young string theorists can feel sometimes uncomfortable with the weakness of some arguments, the challenge usually exceeds their skills. Moreover, in such a competitive field there is no time to digress by asking fundamental questions. When finally the young researcher becomes a full member, with many more resources at hand to tackle fundamental issues, it turns out that they are probably working on a specific topic with its own problems. And, not surprisingly, all these investigations assume the validity of the basic claims of the theory. The once controversial claims are no more questioned; they have been internalized as matters of fact. Eventually, the young researcher becomes an accomplished theoretician; it is now their turn to protect the theory and contribute fervently to the in-out discourse. This final step consolidates further the scientific fact and, very importantly, guarantees the reproduction of well-trained newcomers. This long and tortuous process of internalizing the rules of the game is sociological, but unavoidably also psychological. As I said above, a fact in string theory is a deep and sincere belief, and nobody can dispute certain issues without at the same time denying their own self.

With belief in string theory based on this sort of psychology, it’s not surprising that defending it from skeptics can’t be done with the usual sort of scientific discourse, but requires propagandistic techniques:

What I’ve described in this section is an alternative strategy of validation that string theorists have persistently employed in order to preserve what they consider a worthwhile field of research. The purpose of this is to protect the theory from attacks from defenders of contending models; attacks due in part to theoretical and experimental shortcomings. It is not an exaggeration to say that string theory uses propaganda, more or less as Galileo did in his times: ‘‘He uses psychological tricks in addition to whatever intellectual reasons he has to offer. These tricks are very successful: they lead him to victory.’’

Describing a New York Times article on the Maldacena conjecture, he writes:

This article, and many others of the same sort, reinforce, willingly or not, the social belief that superstring theory is ‘‘on the right track.’’ In this case, the circle of believers is expanded thanks to the participation of non expert actors: science writers and interested readers. This sympathetic environment, which will be illustrated further in the next essays, has been vital for the development of the theory. It must be mentioned that this out-out discourse does not originate independently from professional string theorists. In general, it simply reproduces the in-out discourse of the experts. I do not mean to suggest that string theory popularizers are scientifically illiterate, I just want to highlight that the substance of what they say reflects the opinion and enthusiasm of string theory specialists. In such an abstract area, things could not be any other way. As a consequence of this discourse, a favourable disposition regarding superstrings has permeated into the public domain. The lay public’s attitude functions as a support for the internal discourse. What is more, the layman’s view of superstrings is sometimes internalized by experts on the theory and then works as a reconfirmation of the old belief. To put it differently: the out-out discourse is not only oriented to popular audiences but towards experts as well; the out-out discourse is also an out-in discourse. Consequently, “non-pure” conceptions penetrate and modify the theoretical development of the field. I will call this the in-out-in process. Notice that unlike the in-out-•••-in process explained above, the in-out-in process only concerns the movement of ideas (of course, persons are also involved here, but not in the sociological sense meant before). In this way, with contributions from the in and the out, the creeping belief in the accomplishments of superstring theory is gradually confirmed…

The effects of these kinds of comments on the theory are two-fold. On one side they create a favourable background for the theory to develop, on the other they send a clear message to string theorists that they are doing right, that nature is really as they think it is. I must confess that this hypothesis is hard to prove. However this is what the next essays try to do. Before moving on to these more detailed discussions, I would like to observe something that a string theorist would be unlike to deny: when a newspaper says that colleagues at Harvard are dancing ‘‘La Maldacena,’’ they feel more confident about their own results. Something similar occurred when David Gross was honoured with the Nobel Prize for physics in 2004. My experience was that the general mood among string theorists was very optimistic. They felt that this award was somehow recognition of their own efforts in string theory. Evidence in support of this claim is varied: from technical seminars to public speeches, and from published articles to forwarded emails.

All in all, Zapata does an excellent job of explaing why string theory has been the subject of such a long-term relentless campaign of hype and propaganda, one that continues to this day.

In his essay, he concentrates on the story of AdS/CFT, the one place that string theory has had some real success. As part of this, he engages in some propaganda himself, quoting me out of context in a misleading way. When I wrote in my book about string theory as a “failed project”, I was referring to its failure as an idea about unification, not describing AdS/CFT as a failure.

All in all, Zapata’s essay is something quite remarkable: a view from the inside of what things look like to someone who is both a true believer, as well as a clear-eyed observer of how string theory has gotten to where it is today. I suspect though that his history is already starting to be out-of-date, with the same phenomena that he describes looking very different to the rest of the world. Most physicists have begun to lose patience with the hype and propaganda surrounding string theory, and want nothing to do with a supposedly scientific subject full of true believers acting on a new and non-standard concept of what is a scientific fact and what isn’t.

The latest Woody Allen film, Whatever Works, was shown recently at the Tribeca Film Festival. I missed it there, but it looks like I’ll have to see it when it comes out in theaters later this year. It features the conventional Woody Allen theme of a gorgeous young woman falling in love with a misanthropic Manhattanite old enough to be her grandfather. But this time, the Woody Allen character is a string theorist. Here’s part of the plot summary:

A former Columbia Professor and self-proclaimed genius who came close to winning a Nobel Prize for Quantum Mechanics, Boris fancies himself the only one who fully comprehends the meaningless of all human aspirations, and the pitch-black chaos of the universe….

Boris once had a picture-perfect life. A world-renowned physicist teaching String Theory at Columbia, he was married to Jessica (Carolyn McCormick), a brilliant and beautiful, rich woman, and lived in an opulent uptown apartment. But Boris’s good fortune didn’t alleviate his perpetual feelings of despair, and one night, in the midst of an argument with Jessica, he leapt out the window. To his great disappointment, he landed on a canopy and survived. Afterwards, he divorced Jessica and moved downtown.

One night, Boris is about to enter his apartment when he is approached by a young runaway, Melody St. Ann Celestine (Evan Rachel Wood), who begs to be let into his apartment….

Edward Witten has been visiting CERN this past academic year, and it seems that besides continuing to work on things related to geometric Langlands (see his recent talk at Atiyah80), he also has been returning to his roots as a phenomenologist, and taking a wide interest in a range of phenomenological questions being discussed at CERN.

Next week CERN will be hosting a workshop on New Opportunities in the Physics Landscape at CERN, to discuss experiments at CERN over the next 5-10 years that are NOT directly related to the LHC. Witten will open the workshop with a talk on Perspectives in the Physics Landscape away from the Energy Frontier, and his slides are already available. He comments on a variety of topics, including CMB measurements relevant to inflation, neutrino masses and mixings, proton decay, CP violation and axions, and dark matter candidates. All in all, it’s a quite comprehensive survey of how possible non-LHC results might address beyond Standard Model physics questions, mostly from the point of view of the now conventional speculative framework of Supersymmetry/GUTs/String theory.