Lee Smolin has done a fair amount of string research over the years and written a bunch of string papers. His most recent contribution is http://arxiv.org/hep-th/0503140 A quantization of topological M theory I think this paper could be important and by itself could justify considering Smolin a string theorist even without his other string papers. Incidentally it has been cited by two other string theorists recently. Other Smolin work has also been cited by Dijkgraaf, Gukov, Neitzke, Vafa. In the 1990s Smolin was one of those who developed the idea of quantum gravity as a constrained topological field theory, an idea which (whether or not he is personally acknowledged for it) is now proving influential. But Smolin is not a string theory believer. Apparently this has the curious effect of excluding him from "the string community". In nonperturbative QG research the situation is somewhat different and faith seems less of a prerequisite for belonging to the community of scholars. One can contribute to the development of several QG theories without being a believer in any particular one. Anyway Smolin has noticed this distinction. some people do their work, or at least talk about it, as believers, and others don't. And he has written this letter on "cosmicvariance". --------quote smolin------ Lee Smolin on Aug 15th, 2005 at 9:01 am Dear Clifford, Thanks for your piece on the landscape, which I agree is in a certain sense a very sensible view. At the same time, your stance is deeply puzzling to me. I’d like to take this opportunity to explain why, because I believe this is the core of the disagreement between those who consider themselves “string theorists” and those who like myself, remain outside the “string community”, in spite of doing some technical reserach on string theory. You seem to reason from an unstated premise, which is that, whatever happens, string theory will turn out to be relevent for the description of nature. Even in your closing, when you contemplate different possibilities, including that string theory is just “The Next Theory” you don’t mention the possibility that string theory will just be not relevent for nature. This is also evident in the reasoning in your paragraph: “The idea began to arise that maybe not everything about our universe is fundamentally computable in string theory… I would go as far as to say that it is perfectly fine for us to accept that this might true about string theory while still remaining extremely enthusiastic about it, given its remarkable properties.” You don’t consider the possibility that nothing will be computable in string theory because it is not the right theory. There are two logically possible styles of reasoning about string theory. Method A: ASSUME 1) that there is a real non-perturbative theory behind all the approximate caclulations and 2) that it is relevent for nature. Then interpret various results, having to do with dualities, the landscape etc given these asumptions. Method B: Look for evidence that the two assumptions of method A are true. One evaluates results very differently, depending on whether one uses method A or method B. There is nothing wrong with using Method A from time to time, so long as the assumptions are made explicit, and the risks that are thereby taken on explicitly acknowledged. One can learn things that will turn out be true about the theory, if 1) is true, or about nature, if 2) is true. But one cannot do science only or even mostly by Method A, no matter how promsing an idea may seem. What I find disturbing in your essay, and in many conversations with string theorists is that they reason by Method A but they do not state expliclty their assumptions. This puts me often in the uncomfortable situation, when discussing with a string theorist, of having to add, “but there is one more possibility, the theory might be wrong.” Many of us who seem fated to remain outside the “string community” are there becase we approach string theory by method B. We may, as I do, work sometimes on technical problems in string theory, motivated by our hope that evidence be uncovered that will show us whether assumptionss 1) and 2) are true or not. This leads to a different evaluations of results. For example, from the point of view of Method B work aimed to demonstrate the assumptions, such as attempts to prove conjectures like finiteness or the different dualities, is more highly valued than it seems to be by people whose work seems to grounded on the assumption that those conjectures are true. I should emphasize that we are not being unfair here. Most of those who work on other approaches to quantum gravity and particle phsyics approach our own theories through method B. If you come to the loops05 meeting--and you are very sincerely invited--you will find that we are at least as hard on our own approaches as we are on string theory. Observing both communities, what I see is an overemphasis on self-criticism in the non-string communities, and too much reasoninng with method A in the string community. Nowhere is the difference stronger than in the evaluation of the landscape results. From the point of view of method A, we are just following the theory to see where it leads. Since we assume beforehand that the theory is right, this is a worthy project. But from the point of view of method B, the failure to come up with any method to make falsifiable predictions, coupled with the failure to find a fundamental, fully non-perturbative formulation of string theory, both after many years of work by many smart people, count as evidence against asssumptions 1) and 2). I myself am drawn to the ideas of string theory, and I would be happy if they turn out to be true. But I believe an objective scientist must appraoch an untested theory by Method B rather than by Method A. The reason is that reasoning by Method A can lead to a situation where a large group of people come to irrationally believe in the existence of a theory they can neither construct nor test. Another way to say this is that it is more scientific to work on problems, presented by nature, rather than theories. If we commit ourselves too strongly to theories before they are confirmed by having survived many attempts to falsify them, we risk wasting lots of time and careers on ideas that turn out, beautiful as they are, to be false. Another consequence of Method A seems to be a lack of interest in other directions. Someone, perhaps Moshe, said on a blog recently that if there were good results on quantum gravity people would get excited and work on them. If by “people” was meant “string theorists” this is just not the case. There have been a continuous stream of significant, non-trivial results on several background independent approaches to quantum gravity over the last 20 years and the community of people who works on such approaches is growing fast. But we see very few string theorists taking an active interest in any of these approaches. If you think I exaggerate the significance of the results, come to loops05, or look at recent papers by the speakers there. Or just talk to someone in the field. The problem is that if you reason from Method A, you are bound to over-evaluate results in string theory, and under-evaluate results in alternative approaches, because you are already committed to one view being right. Perhaps you think I am being unfair in characterizing your reasoning in terms of methd A. So let me pose a question, “What would make you give up string theory? Is there a theoretical result, an experimental discovery, or the lack of such, that woud make you put your considerable talents in other directions?” Lest you think this is unfair, I know the answer for myself, for each of the several theories I work on, and can happily answer the same question, if needed. Thanks, Lee ---end quote--- I would like to take a closer look at this letter of Smolin and some of the reaction to it on Cosmic Variance blog.