This is a quick update on the school. I’ve been trying to give the students some of the core concepts they need to help them understand what string theory is, how it works, and what you can do with it. Here’s the really odd thing about all this (and an explanation of the post title): While this is a school on Quantum Gravity, after talking with the students for a while one learns that in most cases the little they’ve heard about string theory is often essentially over 20 years out of date and almost always totally skewed to the negative, to the extent that many of them are under the impression that string theory has nothing to do with quantum gravity at all! It is totally bizarre, and I suspect it is largely a result of things that are said and passed around within their research community.. So there are a few students here and there who have some familiarity with strings, huddling together at times for warmth in a sea of miscommunication, misinformation, and strange preconceptions. Let me be the first to point out that the string community also tends to pass on its prejudices about other Quantum Gravity approaches to its students. But my goodness it does seems extreme to me that an approach that has so many clear benchmarks of success (at achieving goals that at least used to be key objectives) in quantum gravity is treated as an irrelevant backwater by the community that thinks of itself as the main practitioners of quantum gravity. Odd. Anyway, my main message is to try to clearly show that the basics are quite easy to grasp if a student has a decent education in Quantum Field Theory, so they can keep an open mind and my lectures will help them navigate the literature (and the other courses coming up) and then make up their own minds about research paths to follow.
It has to be said that the organizers have made a good effort to have a fair amount of string or string related material on the schedule. My only concern is that with so little time given to basic introduction of the ideas (my three lectures), and with so many preconceptions to surmount, only a limited number of non-string students will be paying attention by time the later material from other lecturers gets into full swing…
There is hope though. A good number of students who have never seen string theory before are telling me (with no prompting) that they are beginning to see how it works, and are asking questions about things they’ve been told elsewhere, allowing me to explain the actual facts, give examples, clarifications, and point to lots of juicy results in the literature. They’re also talking to each other, including some of the students who work on strings, informing each other of their respective approaches… and so maybe they are forming a community of a new generation of scholars that will be less embattled than the current generation seems to be…
-cvj
Well, I kind of did something like that 12 years ago when I was still a PhD student. As I tried to tell you on several occasions, one single calculation is telling different people many different things. You start from Polyakov, do your perturbative business around Minkowski, and arrive at an anomaly in first order (with the ricci action as effective action). To me, this says, you are starting with the wrong action since I have this ”intuition” or ”principle” if you would like to, that I should be able to work around ANY background. Nature allows us to do this, it is the very procedure by which we learn new physics, that we neglect some part and focus on quantizing a subsystem. Only string theory – in your interpretation – would tell us that this procedure is untenable ; and no, these constraints on the background have nothing to do with Einsteins theory of gravitation. So what this calculation told me was that we are in the same situation as perturbative quantum gravity, there diffeomorphism invariance forces you to include all possible action terms (with an infinite number of coupling constants) at least if you trust you perturbative calculations. There, this happens at second order, here it already happens at first order. I have no proof of this but it appeared to me that string theory ‘done properly’ (in my view) would lead us to the same situation. Quantum mechanics, conformal invariance and coordinate invariance would force us to. What I find a real shame is that most string theorists have not even contemplated this possibility and regard this constraining business as a virtue (that really boggles my mind)!! I still uphold the possibility that I am wrong, but someone should explain me then.
So, here you have now a personal motivation of a ”could be” morelia student why (amongst other reasons) I am not really knowing more of string theory beyond that.
To Kim, my education was in mathematical physics and relativity. If you want to know more about Isham’s view on this question I refer you to his articles on topos theory.
Concerning your previous comment about ‘nonperturbative’ effects in quantum field theory, I guess you are talking about instanton *approximations* and so on. In a very precise sense, that strategy is still perturbative
For example, CDT is genuinely non-perturbative, but there you are forced to make computer approximations at some cutoff scale.
Cheers,
John
I am always amused by this path of reasoning in comment threads like this. The key part of the game is to lay bets on how many steps a commenter will take to go from “I’ve no knowledge of your field”, to “what you’re all doing is wrong”, usually with little or no time spent looking at the literature.
Physicists rock.
-cvj
Well, I gave you PHYSICAL arguments why I believe certain results to point in the wrong direction and you chose not to respond to it, actually you admitted not even to have thought about it. So, at least the little bit I know of string theory, it appears I have looked at it from many more sides than you did.
And that is what counts !! Indeed physicsts rock, I remember very well how ‘t hooft could shoot virtually all appoaches to the cosmological constant problem in just 5 minutes without even doing a calculation 
haha
You’re quite brilliant, evidently. I bow to you. I’ve no idea why you waste your time and brilliance here with sluggards like me. You should be off doing wonderful brilliant things.
All the best (and thanks for the laughs).
-cvj