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It seems to me that the use of string theory in calculations of strongly-interacting matter in condensed matter physics is an example of the theory being on the right track. And then there's the application of string theory to black holes. Have these quieted the skeptics? If not, what's the deal? Could a theory be used in making accurate calculations and still be wrong? Aren't the odds of that happening rather small?

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Which skeptics? – user1504 Jun 16 '12 at 14:25
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Yes, which ones? – user1504 Jun 16 '12 at 18:04
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I'm only at a senior undergraduate level, so I don't know much about this. But naively speaking, if a theory postulates something (say, like a set of axioms), and the consequences of these postulates correspond to reality, then it seems to me that the theory is better off for it. Although, I suppose there COULD be multiple theories that satisfy the criteria. (I'm being more philosophical than scientific.) Again, I'm not sure quite how string theory is used in the context of CMPhy. – Joebevo Jun 17 '12 at 11:13
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@Joebevo Well, the whole AdS/CMT (and generalizations of it) are not really physical predictions of string theory, where you start with strings and at low energies derive standard model and continue to lower energies and describe non-relativistic electrons and superconductivity. In physics there exist many examples of two theories which are dual to each other. One important example is holographic dualities (gravity is non-local in a certain sense). The applications of string theory to condensed matter physics is essentially purely mathematical, and takes advantage of this duality. – Heidar Jun 17 '12 at 18:08
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Its not really a physical consequence of string theory as such. So I don't think it says so much about the correctness of string theory as a theory of "everything". But it indicates once more that the theory seems quit consistent and attractive, indeed! But as I discussed in my answer, the whole AdS/CMT business seems to be far from being under control and so far is of very limited use. This will hopefully change. – Heidar Jun 17 '12 at 18:12
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I know very little about this field, so please don't take my answer too seriously.

My impression is that, its mainly string theorists who are excited about this line of research, condensed matter physicists are mostly skeptical (but many are following the field with interest). I guess the main reason is that these holographic calculations have not yet (as far as I know) given anything which is both new and impressive (from condensed matter perspective). But I have to add that, recently I have noticed papers using holographic methods with only conventional (and serious) condensed matter authors (say, this one). This might be a sign of slow acceptance by part of the condensed matter community...?

My impression is also that these holographic calculations are in no way under control (compared to the original Maldacena proposal) and relies on many layers of conjectures. Given a QFT, I don't think anybody knows how to systematically construct the gravitational dual. People just try to construct space times with the correct asymptotic symmetries (AdS, Lifshitz, Schroedinger, ...), try different matter configurations and then assume that the AdS/CFT dictonary is still valid. They only try to say certain generic things about a big class of QFT's, using holographic methods, rather than calculate precise quantities for a very specific QFT. But these tools have potential to become very useful for non-perturbative physics if they come under control in the future.

But whether string theory can make precise and useful calculations for condensed matter physics, won't say anything about how correct it is as a theory of quantum gravity (or "everything"), as you seem to imply. What application to black holes do you have in mind? Microscopic calculations of black hole entropy? These calculations show that string theory is consistent as a theory of gravity (there are many other impressive calculations of this sort). Only few people would disagree on the impressive consistency of string theory and no alternative theory has been as successful in this regard. But consistency is not enough to declare a theory as correct.

Which skeptics do you have in mind? People which are skeptic about usefulness of applications in condensed matter physics, or skeptics of string theory in general?

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