Jacques’ blog has an interesting post about advising the young people in the field concerning whether they should be worried about the future of what topic they are working on before deciding to continue on it. I think that overall, his advice is excellent. It followed on from an earlier, related discussion and comments which made it seem that there is some stark choice to be made: You either work on something entirely because it is interesting (not worrying whether it is going to yield results reasonably rapidly or whether other people are working on it), or, you worry about whether it can produce results reasonably rapidly and whether others care about those results (not caring whether it is interesting to you the researcher). Funny how these things get framed in this way. Come on. It need not be one or the other. Clearly it’s a little bit of both. We have finite resources of time and money. Of course we also have to keep an eye on things other than just the pure physics goals of any given project. But we must do things in balance. Not all of one, nor all of the other. A bit of both. Compromise.
There. Having sorted that one out…No, you’re too kind. Stop applauding, please. It was no trouble, really…. I’d like to move on. There was another issue, which actually began all of this discussion. Should Strings 2005 have had a panel discussion considering the next Revolution in the field? (For those of you not in the field, I should tell you that string theory had two famous Revolutions in the field, roughly ten years apart, and so being a bit spoiled (and immature), we as a field get a bit scared when another ten years go by and we have not had another one.) Well, I sort of agree with Jacques that such an exercise -a set up with a panel of experts- should not be taken too seriously, but I don’t agree that it is in principle a waste of time. I was not there for the discussion and so don’t know the details. But in principle there is nothing whatsoever wrong with serious reflection and taking stock, but we must remember that the “experts” don’t know the answers either. This sort of taking stock exercise has happened regularly all through the history of the field, so why is it a priori a “wrong-headed” thing to do now?
In fact, one of the reasons I’ve been unhappy with the format of several Strings conferences is that there is no time set aside for reflection or discussion. I would argue that this is in fact more important that presenting increasingly glossy computer slides actually. We can just look at those on the web and not bother showing up to have them flashed before us if we can’t discuss them together. I suspect that this panel discussion was an attempt to rectify the situation and have some real spontaneous discussion. So maybe the thing to do as a member of the audience would have been to help shape the discussion at the time, had the format allowed. But I was not there, so can’t comment in detail if that was feasible (e.g. microphones in the audience, etc).
My own “advice” to the young string theorist. If you want to know what might well be the window to the next revolution, wait until you hear that Steve Shenker is giving a seminar. If in the first five minutes of the talk he says something like “I’m confused”, and begins to survey certain sets of results and try to synthesize them, pay full attention and take notes! I know of at least two times he’s done this and it has paid off big time. In my experience, Joe Polchinski is another person who’s been notably confused by the right things. Keep an eye on those guys’ confusions!
-cvj
July 19th, 2005 at 5:57 pm
We should blog about the usefulness of panel discussions, and then have a panel discussion about the usefulness of blogs. The need for substantive content will become progressively less pressing.
Okay, we certainly do a bad job at helping young people decide what to do. I’ve always been (like Clifford, I gather) very much against the two extremist schools of “do what seems popular to enhance your job prospects” and “do just what interests you, regardless of the prospects for further advancement it offers.” Hopefully, there is at least one topic lying in the intersection of what interests you and what interests other people. If not, perhaps you are in the wrong field.
But the panel discussion does address what young people would really want to know — what will be going on in the future, when they are in the thick of things? Sadly, it’s a documented fact that no panel has ever answered this question correctly.
Still, the panels serve a purpose. Get the wise heads up there and let them chatter, without powerpoint slides as crutch. Listen to their less polished thoughts, see what they are interested in. Don’t necessarily believe their predictions — it’s what they don’t say, or are clueless about, that might reveal something important.
July 19th, 2005 at 6:41 pm
At the risk of offending some of the conference organizers (who succeeded spectacularly with their back-of-the-name-tag schedule innovation), I didn’t meet a single person at the conference who, ahead of time, thought this panel was a good idea.
Perhaps I’m overly paranoid, but any more I’d rather say in e-mail if anyone cares (and they probably shouldn’t care what I think). One thing I definitely learned from sitting near the back in this conference is that a lot of people read blogs (and newspaper articles about Karl Rove).
On the subject of listening to Joe, his comments involved being puzzled about the nature of dualities, both string theoretical and, more interestingly from my perspective, field theoretical. It brought to mind, for me, the following question. Back when quantum mechanics was young, everyone knew that it made no sense mathematically, but we used it, got the right answers, and nobody cared. A few years later, the mathematicians cleaned it all up, and everyone could be happy. Now we’ve got quantum field theory which makes no sense mathematically, but we get the right answers, and, generally, we don’t care. The thing is, of course, that it’s been quite a while now, and the mathematicians haven’t managed to clean up after us. In fact, from my rather distant perspective, outside of a few theorems, constructive and axiomatic field theory have been spectacularly unfruitful (I’m sure I’ll now get corrected on this point.). So, the question is, is it possible that there’s something we’re missing about field theory? By this, I don’t mean that we should all go out and study rigorous field theory. Rather, I wonder if the fact that nobody’s made it all precise means that there’s something fundamental about the nature of the theory that we just don’t get.
Probably not, but if revolutions tend to come from neglected issues that people generally ignore, that certainly is one. And how, as Joe asked, would one go about proving S-duality in N=4 SYM anyways?
And, lastly, how ’bout a ‘Preview’ button?
July 19th, 2005 at 7:41 pm
Hi Aaron,
“is it possible that there’s something we’re missing about field theory?”
I’m very glad to see you’re asking that question. It seems to me a crucial one, and following up on it is where hopes for progress lie. One of the main reasons I’ve been on such an anti-string theory campaign is the attitude of string theorists that thinking about field theory is something completely understood, that only fools still think about it, real men do strings, etc…. It seems to me that this attitude has made it very hard for people to work seriously on QFT.
I think you’re exactly right that rigorous field theory isn’t the right thing to think about. There are probably some fundamental missing ideas in our understanding of QFT, and until we have them, we don’t know what the right thing is that we should be trying to make rigorous.
I keep intending to write up my own list of precise things about QFT that seem to me not properly understood, and I wish everyone else in the field would do this. It’s a potentially embarassing thing to do: other people will claim that your problem is that you just don’t understand QFT well enough if you do this.
I’m less happy with your historical analogy. There never was any real problem with mathematical rigor and QM. von Neumann, Weyl and others had no trouble quickly coming up with a rigorous version of QM and proving things about it. The fact that this has been infinitely harder for QFT does make one suspicious that we don’t have the right basic set of ideas.
Back on topic: trying to predict the future is generally not that fruitful, but panel discussions on this topic can be more or less useful depending on the participants, whether they really speak freely, and whether a field is at a point where there are real questions about its future. String theory these days is certainly at such a point. Was this discussion video or audio taped, so we’ll all get to hear what happened?
I certainly can tell that there was a lot of blog reading going on at this conference, my logs are full of connections from utoronto.edu, wireless and others.
July 19th, 2005 at 8:13 pm
Aaron asked:
So, the question is, is it possible that there’s something we’re missing about field theory?
Well, field theory led us all to believe that the cosmological constant had to be 10^n times larger than it is, didn’t it? So now we *know* that there is something spectacularly wrong about field theory, and that that something is related to cosmology. It’s pretty obvious what one should be thinking about.
Recently I was at a workshop in Canada [not in Toronto..] where somebody suggested that maybe the Universe violates the Null Energy Condition. The response surprised me: basically the participants came down on the hapless questioner like a ton of bricks. No! Impossible! Field theory tells us that that is out of the question! Yeah, just like it told us that the universe should be accelerating 10^n times as fast as it actually does……..
July 19th, 2005 at 10:20 pm
Why would they do something like that? It’s straightforward to come up with something that violates the NEC.
July 19th, 2005 at 10:44 pm
I’m guessing that the reference is to phantom dark energy, something that has w < -1 and therefore has an energy density that increases as the universe expands. Because, yeah, quantum field theory violates the NEC all the time.
July 20th, 2005 at 4:56 am
I do not quite agree that panel discussions have never been useful. The best counter example was last year’s post strings workshop at CERN. That meeting I enjoyed a lot mainly because of the discussions in the cafeteria and the (not really panel) discussion sessions. The best one was the one led by Hermann Verlinde on no particular topic which pretty soon was about stingy black holes and collideds (and blackholes in 2D string theory). Besides Juan Maldacena and Steve Giddings this session really took off once David Gross changed from making noises of discontet to actually entering the discussion. This was real fun and I think everybody learned a lot, not only about the relation of Steve’s work based on geometric cross sections to Gross-Mende scattering of the old days.
Somehow, there, everybody was in a really good mood and the discussion ended up really fruitful.
July 20th, 2005 at 6:31 am
Yes, that is *exactly* the type of discussion I want to see more of at the big meetings. Like I said, there’s no room made for discussion in the big meetings. It is too easy just to schedule a bunch of seminar-type slots, since its neat and tidy. Getting people to talk in a more free-form way about the issues is rather like herding cats, but maybe it is not impossible to at least get *some* discussion. We claim to be the smartest people on the planet so how come we’re so backward in this regard? And Aaron and Peter, I am in complete agreement with you about the several unturned stones we have in the field. And while I really enjoy your digs at the field, Peter, please make sure that you’re not condemning the whole exercise because of the way it has been marketed by many of its practicioners. The problem with string theory is that the field has progressed by following the line of least resistance, and we’ve many tasty and juicy fruits from this sort of labour, and so we’ve been spoiled. We work on some aspect of it because it is yielding results. This should still happen, of course. Why would you *not* follow something that is yielding results in some direction? What happens though is that we as a field forget that we made certain choices at an early stage, and it falls out of our folklore; we forget to tell our young people that some of those choices were maybe not physically the only good things to do, but just the easiest things to do at the time. Some of those choices should be re-examined from time to time. We should always remind the younger people what these choices were, and not to take everything as Gospel. Also, Peter, I think that you’ll find that most honest and mature string theorists are fully aware that there is a lot to learn about field theory and that there is nothing “un-macho” about worrying about issues there. In fact, I would go as far as to say that anyone who thinks that field theory is “sorted” has not been awake to everything that has been happening in both non-perturbative string theory *and* field theory for the last decade at least! So in this case, do shoot the messengers if you want to (metaphorically speaking!!), but know that the message that string theory has something fundamental to teach us about Nature is still not as obviously wrong as you seem to imply from time to time.
I must say that I do enjoy reading several of your posts, and in that regard, I like to remind myself: “What does not kill us will make us strong”.
-cvj
July 20th, 2005 at 7:53 am
Hi Clifford,
I’m very glad that you’ve decided to participate in this weblog. Without naming any names, much of the public face of string theory in recent years has consisted of people who are either uncritical over-enthusiasts and/or intent on personal attacks on anyone who has anything critical to say about what is going on. On the other hand, almost all seasoned string theorists I meet or know personally have much more moderate and reasonable views, and in discussions with them I generally find we agree about most things.
Often our disagreements come down just to a different point of view on the prospects for someone coming up with the new ideas that the field desperately needs. They point out to me that if a really good new idea emerges, string theorists will be glad to work on it, even if it doesn’t involve strings. I point out that this is unlikely to happen unless good young people are encouraged to try new things that don’t fit into the program that string theorists have pursued for the past twenty years. We both then look longingly in Witten’s direction, hoping he’ll come up with something that will save us all, then sigh and say “maybe after 2008 when the LHC results start coming in….”
July 20th, 2005 at 11:38 am
Speaking of lines of least resistance, I see an old argument brewing here, and the interesting point pushed aside. It is clear to me that QFT is not a finished subject, even in the last year there was enormous progress in perturbative (!) QFT. It would be nice if people who have thought about it come up with examples of interesting difficulties of field theory, maybe we can learn something we don’t already know.
July 20th, 2005 at 12:49 pm
Hi Moshe, Welcome, and also to Robert and Aaron and Jack (I should have said so earlier). You’re very correct of course. Why not discuss it? Maybe there are others lurking who can point up some of their favourite things. For what it’s worth, and by way of amplification of the point you’ve made (and because there are non-experts listening), I’ll say that the work that has been happening in both string theory and field theory, perturbative or non-perturbative, has led us to realize that the key tools that we have used to formulate and calculate with are clearly not in any sense fundamental in determining what the theory “is”. We saw it very clearly non-perturbatively with dualities such as S-duality and its cousins in field theory, and very spectacularly with strong/weak coupling dualities in string theory, which relate completely different theories, often in spacetimes of different dimensions. The weak form AdS/CFT (connecting gravity in 5D to strongly coupled gauge theory in 4D) combined these things into a clean and stunning example, and droe the point further home: The Lagrangian and Feynman diagrams don’t tell you the whole story. But in retrospect it was already beginning to be apparent perturbatively in gauge theory, because of the huge redundancy that exists there in formulating computations in terms of Feynman diagrams, (and further, the philosophy of effective field theory and RG flow was itself suggestive). But with the program of computing in these completely new ways given by the twistor program using spectacularly fewer diagrams, etc, the perturbative reliance on Feynman diagrams as a “definition” of what field theory is also seems very shaky. These are interesting times. But I know that you know all that….but this maybe gets the ball rolling…..
-cvj
July 20th, 2005 at 2:58 pm
“It is clear to me that QFT is not a finished subject, even in the last year there was enormous progress in perturbative (!) QFT.”
Moshe, link to some representative papers, please!
July 20th, 2005 at 3:09 pm
I assume Moshe’s referring to the twistor stuff, starting with Witten’s paper and following with various papers by some subset of Volovich, Spradlin and Roiban, the collected works of Freddy Cachazo, and the stuff by Dixon et al.
And probably plenty more than that. You can also check out Freddy’s slides at Strings 05.
July 20th, 2005 at 3:12 pm
Arun- nice lectures are at hep-th/0504194, for a new calculation in pure QCD using these methods look at hep-ph/0507005.
Thanks for the reply, Clifford, I agree with everything you say. I should say welcome as well- it is already clear that one has no chance of getting anything done at the face of 5 (!) of you guys…
July 21st, 2005 at 7:11 am
I think the reason one might think that some are convinced that there are no field theory questions left and all is just strings (and friends) is this very succesfull approach of the last decade to reformulate field theory questions in terms of branes and then use geometry (of one kind or the other) to attack these problems. A lot of mileage has been gained this way but this of course does not mean that these are not intrinsic field theory questions and that not all questions can be approached this way.
As nobody else starts I’ll take the lead to list a couple of field theory questions: And I start with a non-field theory question: Is gravity just a field theory? I.e. is there really an intrinsic difference between gravity and ordinary field theories or is it just another field theory with spin 2 fields and a large gauge invariance. People often take it for granted that there is some special magic with gravity but I am not yet convinced this is the case. For example these peopl e point out that it is remarkabel that AdS/CFT connects a field theory with a gravitational theory. But it seems one could also come up with similar purely field theoretic examples. Maybe you are going to say that gravity has holography but in that case please define holography precisely and explain why this cannot be a property of a field theory.
There are of course millions of questions to understand theories without susy and non-holomorphic properties of N=1 theories beyond the first couple of orders of pertubation theory, confinement being just one of them.
I think what is not such an interesting question (and I believe even many of the more formal people agree) is to show that there are interesting field theories in the mathematical sense (e.g. Whiteman or Haag-Kastler axioms): My understanding is that the only examples where this has been worked out are free theories and rational CFTs in 2D but I think nobody has doubts that 4D gauge theories (maybe supersymmetric) fulfill these (or some reasonably adopted) axioms: You could start from the lattice (once you solved the problem of having chiral fermions and susy in this case) and then attempt to prove that the continuum limit exists and has nice properties (covariance, locality, positivity). Technically, this is a very very hard problem but I doubt that anybody believes that there serious problems there.
I have the impression that there are a lot of interesting things still to be learned from the connection between field theories and topology (and these might again have brane interpretations) but maybe Peter can comment on this.
Please comment and continue!
July 21st, 2005 at 12:40 pm
Robert:
Gravity is a fine classical field theory, but it is easy to see it cannot be treated as a QFT, since it cannot be renormalized. Just try to calculate almost anything with the usual formalism of QFT, you’ll get nonsense.
If you redefine what you mean by either gravity or QFT, all bets are off.
There are less mechanical ways to state the problem, for example the lack of decoupling in gravity. Decoupling is at the heart of properly defining QFT via RNG flows etc., but in gravity heavy objects cannot be treated as “fast” variables a la Born-Oppenheimer, because they are simultaneously strongly coupled, exactly because they are massive.
One issue in QFT which may be interesting is its applications to highly dynamical situations, such as non-equilibrium processes. I have a feeling that a lot of the Lorentzian issues one encounters in string theory lately will already be manifested there, and there is probably a useful body of knowledge out there.
July 22nd, 2005 at 4:33 am
I should have said “gravity might be like any other power non-renormalizable field theory”. Luckily, in particle physics we usually don’t have to deal with those as the bad terms are nearly zero by RG flow.
July 22nd, 2005 at 6:35 am
[...] In view of the varying opinion about the state of string theory, regarded by some as the last, best hope for fundamental physics (going to get myself into trouble there), discussed wonderfully and I hope continually on this very blog (e.g. here and here), it might be worth sitting back and letting the pod do its thing, and tell us the future. [...]
July 23rd, 2005 at 6:41 pm
[...] Well, a number of things did come up as interesting and fun to try, and the following is one of them. I’ve already said on this blog that our particular field (string theory and related topics) could do with more ways of having discussion, both general and specific. We have already accelerated the primary way in which we exchange research results (revolutionizing scientific publishing in the process) by establishing the Archive (see writing about this by Paul Ginsparg), and it undeniably helped drive the field’s rapid developments in the middle 90s while also democratising it by enabling serious papers from the traditional large and famous institutions to be seen on everybody’s computer screen right alongside the serious papers from smaller less well known institutions, often within minutes or hours of the completion of the work. [...]
August 2nd, 2005 at 7:52 pm
[...] We have already heard about the panel discussion on the Next Revolution in String Theory at Strings 2005 from Clifford and Jacques. Today, it made the New York Times. It shouldn’t be a surprise that the NYT had a slightly different spin. The NYT paid some homage to the concept that by their nature revolutions can’t be predicted. Progress in science occurs when scientists work on questions that puzzle them rather than when they try to guess which questions might have the biggest payoff. Most of the NYT article was devoted to The Vote. [...]