Peter Woit, noted blogger and string-theory gadfly, has written a book about his objections to string theory: Not Even Wrong, to be published next year by Jonathan Cape.
Good. I completely disagree with Peter’s opinions about string theory, and think that his accusations that the Landscape is non-scientific are completely off the mark. But his objections are not crazy, and his dislike for the theory is grounded in an informed scientific judgement. (Sometimes more than others, but that’s a matter of personal opinion.)
The whole discussion is a nice contrast with the Intelligent Design mess. The fact is, we don’t know what is the correct theory that unifies particle physics with gravitation. String theory is far and away the leading candidate, but its status as leader is a reflection of the educated judgement of the experts, not any airtight evidence. This judgement comes from looking at various pieces of information — what we know about gravitation, and quantum mechanics, and particle physics, and the history of ideas in physics, and the mathematical structures underlying gauge theory and general relativity, as well as an intuitive feeling for what principles are most important and what clues most worth pursuing — and deciding which path toward progress is likely to be fruitful. When people like Peter (or Lee Smolin) read these tea leaves, they come to a different conclusion than most scientists in the field. But it’s healthy disagreement among professionals working at the edge of what we know and don’t know — not politically-motivated intervention from people who have no clue, just an agenda, and operate completely apart from the scientific mainstream. To people looking in from the outside, I hope an accurate picture comes across: there is a widespread feeling that string theory is the best hope for a quantum theory of gravity, but it’s not a settled issue, and we’re working in good faith on moving forward.
So I’m happy to see this side of the argument represented in the popular press, even if I disagree — we shouldn’t be afraid of the free market of ideas. If people don’t agree, they should explain the sources of their disagreement rationally. There is always the danger of misprepresentation of course, and in this case there is an obvious worry — that a spate of stories will appear about how string theory is in trouble, and a house built on sand, and so forth. That might be true, but certainly isn’t the impression I have from talking to string theorists. In any event, I hope that we defenders of the theory can stick to the high road, and welcome this intervention in the discussion of these important ideas.
Very interesting discussion here…
Clifford: a.f.a.i.k.? As far as I know? You may be carrying shorthand too far, but t.i.a.v.n.b.a. (this is a very nice blog anyway).
> I hope we’re all agreed that QFT is a useful box of physics tricks that is hard to motivate from rigourous mathematical perspectives alone.
Yes, therefore we are so happy that many high-precision experiments support it. 😎
Hi Clifford,
Thanks very much for your answer, but it does not address the claims made in the paper I referred you to, hep-th/0303185. My claim there 1) is mostly not about holding at the supergravity vrs the stringy level, 2) is not contradicted by the Berenstien, Maladacena, Nastase and followup results on pp waves, which were discussed and cited in my paper (ref 164) and 3) is also not contradicted by Gupser, Klebanov and Polyakov, which was likewise cited (ref 155) and discussed. It does concern “different strengths of the conjecture” which are allowed by present evidence, even at the “stringy level”. Given that only the strongest requires complete equivalence of the string and gauge theory, I hope you will agree that it matters very much which of them is true.
So before you get excited and call my remarks “harsh partisan criticism” I would very kindly ask you to please read what I actually wrote. And please, I am not making the claim that there is no AdS/CFT correspondence, and I am not being “partisan”. Nor is my understanding of this field “out of date or [based on] just wrong information.” I read the literature carefully (something not everyone does), I go to talks and conferences to keep up and I aim when I can to contribute constructively to research in string theory. I would hope that carefully parsing out the different possible conjectures consistent with present evidence would be seen as a useful contribution to research. In this case, I would insist that the point is not whether there is or is not piles of evideence for some form of a string/gauge duality. The point is precisely what is true about that duality.
In fact you seem to agree with my main point, as you say that there “will be no rigorous proofs of any strong-weak coupling dualities or others in that spirit until we find techniques that go well beyond the current formulations of the theory”. How can you assert this and not be interested in the question of which precise conjecture will turn out to be true? And, not to attack you personally, but to try to make here constructively a point I’ve been trying to make, when you call someone who studies the literature carefully and makes a constructive contribution based on it a “harsh partisan critic”, you are not showing evidence of an openness to a range of viewpoints within the field.
I also agree with your main message that people should not criticize ignorantly and that we should get on with research as that is the only way to find out what is true. But I do think that carefully and critically setting out the range of possible outcomes of that research is an important part of succeeding at that research. In a case like this, where there are several distinct conjectures all consistent with present evidence, it helps to be aware of that fact, as different strategies may be required to attempt to prove different versions of the conjecture. Furthermore logic dictates that only the weakest conjecture consistent with the present evidence can be considered to be supported by that evidence.
Here is one reason it matters. There are as well different forms of the holographic conjecture (see hep-th/000305 for a review of them). It matters for which version of holography is realized in string theory which version of the AdS/CFT conjecture is true. Some people use the strong form of the AdS/CFT conjecture to argue for a strong form of holography, one that would exclude bouncing black hole singularities and baby universes. Since there is evidence in non-perturbative quantum gravity calculations for elimination of black hole singularities there is a possible contradiction here with the strong form of AdS/CFT. But there is no contradiction with a weaker form, such as Witten’s conformal induction conjecture, as that only requires that certain observables (those that can be measured from infinity) of the string theory are represented in expectation values of the gauge theory. This is, by the way, why the talk of Liu at the Toronto string conference was so interesting, because it was an indication that the gauge theory might be able to probe what happens to the singularity.
If someone just believes that the strong form of AdS/CFT is true, they may miss the possibility that string theory could lead to baby universes. So what you believe about open problems does determine the direcction of research you are willing to pursue. This is why I believe it is important to have careful, critical discussion within a field, and to have a field be friendly to the widest range of views consistent with the actual results.
Thanks,
Lee
Clifford, you continue to provide a nice framework for discussion here. Thanks
While one might not want to be the barometer, it does allow for a point of view to materialize(nurturing the creation of ideas). For others, to come through and watch this process.
How would one move constructively from what has been offered? The next step?
Since Peter Woit mentioned me, I might as well run my impressions by the string theorists and others here. As I said on David Bacon’s blog, I’m not a string theorist, in fact I will probably never be a string theorist, but string theory does look interesting to me.
I also haven’t read Peter Woit’s book, of course, but I did read physics/0102051. An excerpt:
The way that I read this is “I view gauge field theory as an intellectual pinnacle, therefore I don’t want string theory to surpass it.” I realize that this is harsh, but am I really wrong?
Another excerpt:
It smacks of professional jealousy, if you ask me. Moreover, the idea that we need to save the children from string theory is surely offensive. Somehow I doubt that the string theory job market is so easy compared to the rest of physics. In light of passages like this, I don’t really know what Sean means when he says that it’s a healthy disagreement.
Lee,
I was talking about partisan criticism in other contexts, not this particular discussion of AdS/CFT. Anyway, I’d like to point out that I did say in a preface to my remarks that if I misunderstood what you were getting at, then I apologize for any negative characterization. So, I seem to have misunderstood what you’re getting at, and so I apologize.
So since the points I made seem to be irrelevant to what you’re getting at, I’ll step back and let someone else have a go at addressing your concerns. I’m not seeing the two sharp forms of the conjecture that you’re seeing. Moreover, you may well be as up to date on things as I am, possibly more, in which case I may be of no use to you whatsoever.
Cheers,
-cvj
Greg,
From our previous discussion you clearly have no interest at all in my actual views, instead you adopt the pathetic tactic I’ve become all too familiar with from string theory fanatics of making up idiotic interpretations of what I write instead of even bothering to try and understand what I have to say. No, I don’t think anything like “I view gauge field theory as an intellectual pinnacle, therefore I don’t want string theory to surpass it” and never have said anything like that. I do think gauge field theory is very deep mathematics and physics. It is not a pinnacle but something we need to better understand and ultimately surpass. I recommended to you to take a look at hep-th/0206135 but I doubt you’ve bothered. It contains a detailed speculative outline of mathematical ideas that I think surpass those of gauge field theory and which I personally think are a promising way forwards to better understand the standard model QFT and find a way to improve on it. Maybe I’m wrong, but if you want to argue with my views on mathematics and physics, that paper is what you have to argue with, not some stupid statement you make up.
I can explain a bit more about the paragraph you quote since you’re a trained mathematician and should more easily than most physicists be able to see what I’m getting at if you’re willing to pay attention. I just spent a year teaching our graduate geometry class here at Columbia. There wasn’t a textbook, but during the first semester I was largely following Kobayshi and Nomizu, volume I. I share their point of view that perhaps the most fundamental construction in geometry is that of a connection on a principal bundle (aka a gauge field), and the implications of this idea takes up most of the book.
During the second semester I first covered aspects of Riemannian, symplectic, Kahler and spin geometry. In some sense spin geometry is the most fundamental, since you can build arbitrary sorts of tensors out of spinors, while you can’t construct spinors out of tensors. Finally, in the last part of the course, I was discussing Hodge theory and the various sorts of geometrically defined elliptic complexes that make up the basic examples that motivated the Atiyah-Singer index theorem. In this story, the fundamental role is played by the Dirac operator.
You may have a different point of view on differential geometry, but I think the one I took in the course is a very modern and very powerful one. It followed excellent texts by mathematicians who developed these ideas for purely mathematical reasons, especially Kobayashi and Nomizu’s book, as well as the more recent book on Spin Geometry by Lawson and Michelson. This point of view puts connections, spinors and the Dirac operator in central roles in modern geometry, and I happen to think it is a very deep and amazing fact that the same constructs are among the fundamental constructs of the standard model.
The story of the geometry behind string theory is a complicated one, but for the part of string theory which is well-understood the main parts of the construction involve Riemann surfaces, which are truly fundamental mathematical objects, but also complex Calabi-Yau 3-folds, which really aren’t. Calabi-Yaus are mathematically quite specialized and complicated gadgets, which before string theory few mathematicians took an interest in. No one was teaching about them in first year graduate geometry classes (and if they are now, it would be a bit perverse). The perturbative string theory philosophy for getting the standard model is that the things I was talking about in my graduate geometry course are not fundamental, but what is fundamental is the superstring (a mathematically quite complicated and non-obvious construction) and the Calabi-Yau (also a mathematically rather complicated construction). The connections=gauge fields of my graduate course are not fundamental in this picture, but only dominate in the low-energy limit.
We suffer from having no experimental guidance at all about how to get beyond the standard model. Personally my point of view is that in such a circumstance the best thing to do is to remember that deep mathematics and deep physics have traditionally gone hand in hand. The mathematical structures of the standard model are about the deepest ones we know of in the modern approach to geometry. Those of the superstring and Calabi-Yau aren’t. This seems to me to be evidence that the superstring idea of how to get beyond the standard model is misguided from the point of view of mathematical aesthetics. The fact that it has utterly failed to lead to a framework in which one can make predictions about the real world seems to me to confirm the argument from aesthetics that it is the wrong way to go.
String theorists like Clifford will reasonably object that, for such an aesthetic argument, what is really important is not the approximate perturbative string theory, but the unknown non-perturbative theory they suspect exists, and for which they have unearthed all sorts of tantalizing evidence, including relations to the gauge field theories I am taking as fundamental. Maybe he’s right and there is some more wonderful underlying thing to be found which involves depths of fundamental physical and mathematical beauty still unkonwn, with the geometry from my graduate course only coming out in some limit. No one has actually produced this yet, and I’m skeptical of its existence. Or more accurately, I think there are still unknown very deep mathematical and physical structures to be found, I just believe they will be closer to the ones of the standard model than to the ones of string theory found so far.
About the second part of your comments, again you’re making up something I didn’t say. I never said “the string theory job market is so easy compared to the rest of physics”. What I said is that the particle theory job market in general is a brutal one, and this is very true. String theorist or not, it is very difficult to get a permanent job in this business. If you want to have any real chance at it at all, you need to be working in what is perceived as a really active area of research where a lot is happening. In practice these days, that means your chances, while slim, are best if you’re doing string theory, phenomenology, or cosmology (best if you can do all at once!). If you happen to believe that string theory is misguided, but also believe that sophisticated mathematics is the thing needed for progress in particle theory, you’re pretty much completely out of luck. I don’t know what physics department these days is going to hire you. If, like me, you believe that our best hope for progress is smart, ambitious young people working on mathematically sophisticated ideas about how to extend the standard model, you would find this current job market problematic.
As for your idea that I’m suffering from professional jealousy, let me point out you don’t know the first thing about me personally, and as far as I know we have never met. If you knew anything about me, you would know that, far from being bitter and disappointed in my career, I feel quite the opposite. When I went into particle theory I assumed that I’d most likely end up struggling to get a job involving too much teaching at a not so great educational institution in some place I really didn’t want to live. Instead I’ve ended up very happily with a permanent position living in my favorite city in the world, part of a great mathematics department with wonderful colleagues I enjoy learning from and interacting with and who have treated me exceedingly well. In recent years I’ve been able to teach pretty much whatever I felt like and have learned a great deal from this. I’ll also point out that due to a clever choice of parents and dumb luck in the real estate market I am financially extremely well off. I could quit my job tomorrow and never work again if I felt like it. I do what I do every day because I love it, not because I have to. Few people in life have been blessed with the good luck I have.
Your comparison of my criticism of string theory to the Intelligent Design criticism of evolution and conviction that my only motivation is unwillingness to learn string theory are both massively stupid and deeply disgraceful. You should be ashamed of yourself. I really don’t understand what it is about string theory that leads people to behave in this way.
No, I did look at hep-th/0206135. Sections 1-6 are a competent summary of a grab bag of interesting mathematics. Sections 8 and 9 are a competent (I suppose) outline of quantum field theory in 1 and 2 dimensions. Sections 7 and 10 are some speculative remarks that I don’t understand. (Maybe someone else here can help me out?) Finally section 11 is a denunciation of string theory and supersymmetry, a short version of physics/0102051.
In regard to the above remarks, the words “deep” and “beautiful” are often euphemisms for “math that I learned”, while words like “complicated” and “gadgets” are often euphemisms for “math that I don’t want to learn”. A lot of people talk this way. It is a plausible interpretation of the above comments, because otherwise I would have no idea why Riemann surfaces are “truly fundamental” while superstrings are “quite complicated and non-obvious”. I don’t see that passing from Riemann surfaces to super-Riemann surfaces is a great leap, much less a downward plunge.
Greg,
Let’s see, you don’t understand string theory and you don’t understand my speculative ideas, but you feel quite comfortable attacking me anyway. Isn’t there something wrong with this picture?
You still seem to suffer from this obsession that my objection to superstring theory is that “I don’t want to learn” it. I suspect I know far more about the construction of the superstring and Calabi-Yaus than you ever will. Unless you have some actual evidence that my views are based on not wanting to learn something, you should stop making this kind of offensive personal argument.
Any discussion of what is “deep” or “beautiful” mathematics suffers from the problem of “de gustibus…”, but your comments lead me to strongly suspect you don’t understand the construction of the superstring (there’s much more to it than passing from Riemann to super-Riemann).
I spent some time with Polchinski (or rather, his textbook) to better learn what a superstring is. I am not sure that discussions in blog comments are intellectually healthy, but reading Polchinski certainly is.
In the simplest definition, the ordinary bosonic string is not even as complicated as a Riemann surface. It’s really just a topological surface, and its action functional is just its area as a submanifold of spacetime. This is equivalent to the Polyakov functional for a conformal surface. As I said, whether or not it is “deep” depends on whether or not you want to learn it. Certainly some mathematicians have seen before, because in mathematics, the same two functionals are familiar as the Plateau problem. In some treatments of the Plateau problem, the Nambu-Goto action is called “area” (duh), while the Polyakov action is called “energy”.
Is a superstring anything more than a superconformal surface? If it’s a Type II superstring, not really. Admittedly consistent Type I superstrings and heterotic strings have some decorations that seem ad hoc to naive little me. (For example, that Type I superstrings have to be open and have SO(32) Chan-Paton decorations.) But the action for the Type II superstring (either IIA or IIB) seems like a natural superization of the action for the bosonic string, which is either nothing more than or not even as much as a conformal surface.
So if you think that conformal surfaces are beautiful but Type II superstrings are ugly, that’s like saying that Audrey Hepburn is beautiful but Eliza Doolittle is ugly. You might say that if you don’t want to learn about Eliza Doolittle.
Hi Clifford,
Thank you for kind remarks, they are very much appreciated. They illustrates one reason you are respected widely not only inside the string community, but outside of it as well. I am happy also to acknowledge that the main points you have been arguing for are correct: there are critics of string theory who are not as informed as they should be, and they do under estimate the breadth and variety of views and approaches within the string community.
But I would ask to impose just a bit more on your hospitality here to say something I think is terribly important, that exchanges on this and other blogs have illustrated. Let us call the range of views that can be heard from people who live in the string community R. My observation is that, however wide this is, it is a proper subset of another set P, which is the possible range of views that could reasonably be taken on various issues, which are as well supported by the evidence from calculations and from nature as are the views in R. I will call the views in P but outside R, O. I also observe that among those who are considered outsiders by string theorists, there are some who are in fact familiar with many of the technical details, and who could, and in some cases do, contribute research to string theory. Let me call such people the “competent outsiders”. Now here is what I think is so important:
-One draws different conclusions about the possible futures for string theory, given views in O than in R. Thus, it matters a lot for physics, which views are correct. The importance of the competent outsiders is that they sometimes hold views in O.
-Occasionally a view is moved from O to R. One illustration of this was the significance of 11 dimensional supergravity and the 11d supermembrane for string theory, which was moved from O to R in 95. Another example is the view that the connection between string theory and nature will involve a landscape of equally possible theories rather than a unique, single theory, which was moved from O to R in the last few years. In these and other cases there were competent outsiders who had been insisting on the importance of these views, that were not listened to by insiders.
-These examples illustrate the importance of O, as it can have a big effect on the direction of research when a view is moved from O to R.
-Nevertheless, at any one time, insiders are often not aware of the views currently in O or, if they are, they do not accord them much interest. Even when a view is moved from O to R, some insiders think of it as a new invention and do not appreciate that the view has been held for some time by competent outsiders.
-There remain views in O that may still turn out to be important. Among these I would put the fact that there are a range of possible versions of the AdS/CFT conjecture allowed by the evidence and the view that string theory cannot succeed unless a truly background independent formulation is found.
So, while I agree that the breadth of views in R, held by insiders is sometimes unappreciated, I hope you can appreciate that some outsiders have a valid point when they remark that the range of views allowed by the evidence is wider than that usually heard within the string community.
These stories raise several questions for me, that I am thinking about as I try to write a kind of intellectcual history of the subject. First, wouldn’t it have been better if the views I mentioned that moved from O to R had been all the time included within the range of views discussed and considered by insiders? Does this imply that progress would be faster if the range of views considered seriously by string theorists were broadened?
There are also some general questions about how science works. Is the situation I’ve described common, or is it special to string theory? Is R always narrower than P, and why? Is there commonly a class of competent outsiders? Related to this, why is R at any one time narrower than P? And why are insiders sometimes not aware of, or dismissive of views in O? Are strong divisions between research programs, such as we see between the different approaches to quantum gravity, generally good or bad for the progress of science?
Thanks,
Lee
Greg,
“the ordinary bosonic string is not even as complicated as a Riemann surface. It’s really just a topological surface…”
“Is a superstring anything more than a superconformal surface? If it’s a Type II superstring, not really.”
Well, I no longer suspect that you don’t know what a superstring is, now I’m sure. From what you wrote, you don’t even seem to know what a bosonic string is. What you’ve written is pretty confused, but for one thing you don’t seem to be aware that the subject is about quantized, not classical strings, and there’s a lot more to them than writing down an action functional.
Whatever time you’ve spent with Polchinski, it seems to have left you with:
1. Not much of an idea about what either a string or superstring actually is.
2. The conviction that, even though some constructions appear ad hoc to you, they really aren’t for some unknown reason.
3. An incredibly ignorant and arrogant attitude, using the small amount of misinformation you’ve picked up to justify personally attacking people people who actually understand things you don’t as “unwilling to learn”.
Reading Polchinski doesn’t seem to have been an intellectually healthy experience for you, quite the opposite.
I’ve had some bizarre exchanges with string theory partisans over the years, but this one really takes the cake.
From being an O, it is important that the physics is brought into perspective with R, yet how would such an adventourous mind of those in O appeal to the strict formulations in R?
The people in O had to have some understanding as Lee states, of the concepts formulated by the degrees lead too, by seeing such Physics correlations of R in O?
Now such historical correlations and derivatives of string/M theory needed the valuation of R to develope views in O. Although R is strictly mathematical(?) the generalization moved to concept developement arising from R, moved O to consider such physics correlations. They had to go hand in hand, and reval the precipice of change such a model might institue in how we percieve in O.
I hope this makes sense.:)
Yes, I know that string theory is a quantum theory. Although I would only be a beginning student of string theory, I do know quantum mechanics. In quantum mechanics, you don’t really quantize objects, you quantize their dynamics. Also, since quantum mechanics is true, all dynamics in the universe are quantized. So a string in string theory is not logically any more or less quantum than a shoelace. Of course its dynamics are much more quantum, but only because it’s much smaller.
Well, you could call the fermionic part of a superstring inherently quantum, in the sense that fermionic fields are inherently quantum. But you could also call fermionic fields “anti-classical” rather than quantum, given that bosonic fields (absent quantum dynamics) are classical.
Moreover, there really isn’t any more to quantum mechanics than “writing down” an action, or more precisely, solving it. The laws of perturbative superstring theory really are just a superization of the area functional, as in the Plateau problem. (Granted, the usual Plateau problem is in Euclidean space, but I can excuse physicists for preferring Minkowski space.) All of the complicated stuff comes from trying to solve the dynamics of this simple action. It seems that some people are confusing laws with solutions in this business.
When I said that some constructions seemed ad hoc, I was careful to explain that I wasn’t referring to type II superstrings, which don’t seem at all ad hoc to me. As for the other three superstring theories, they don’t seem very ad hoc at first glance, just more than zero. One side of them that certainly isn’t ad hoc is that they are chosen for their logical consistency.
I admit that I don’t really know string theory, but on the other hand no string theorist has disputed my comments.
Finally, Peter, I got the idea that you don’t want to learn string theory from your own words, not from any string theorist. If you don’t like that inference, then you have misrepresented yourself.
Greg,
You’re just parading a truly massive amount of ignorance and making it crystal clear that you have no idea of what you are talking about here. From statements like
“there really isn’t any more to quantum mechanics than “writing down” an action, or more precisely, solving it”
you make clear that you not only don’t understand string theory, you also don’t understand quantum mechanics.
The idea that “I don’t want to learn string theory” is something you made up for yourself out of arrogance and ignorance. On Dave Bacon’s blog I wrote:
“I have a Ph.D. in particle theory from Princeton, and have devoted much of the last twenty years to learning as much as I can about the subject, including a great deal of string theory. Arguably I’ve spent far too much of these twenty years trying to learn about string theory, instead of spendng my time on something more fruitful.”
Let me repeat this in simpler terms: I have had about the best high-level training in particle theory you can get in this world, and then have spent twenty years professionally working in this area, including spending a sizable fraction of that time learning about string theory. You admit you don’t know much about the subject, and make this clear with everything you write. And yet, you are willing to attack my competence to discuss this subject. What is wrong with you? What is wrong with this subject that its partisans behave like this?
Peter, Greg. Chill Dudes! Or take it outside. Not in my house, ok?
🙂
-cvj
Clifford,
Hey, it’s not me who’s coming into your place and launching personal attacks on anyone. I’m getting the impression that the way much of the string theory community intends to deal with my arguments is to not answer them, but to engage in personal, ad hominem attacks on my competence. If that’s not something you want to be part of, you might want to consider telling people who do this they’re out of line. Otherwise, they’ll hear from me….
Peter,
You have every right to defend yourself, and you’ve done so (and quite well). I don’t think anyone is under any illusions….. so now I think you can safely move on.
Honor is restored on both sides….. let’s call a truce. Then we can all come back and fight the good fight another day. 😉
Cheers,
-cvj
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thanks Pete its so nice to hear that somebody is still trying to find new ways to find out what we may never know …..but in every different idea the seed of truth may be sowed. i hope n pray that men such as yourself are reading your interview in Discover this month ……and starting to THINK…..thanks fer yer time rock on dude!
P.S> tell Clifford hes an ass. the guy argues fer a whole page and then tries to make up?…..camon cliff you may be surprised when CERN comes on line in 2007…..we may all thank Peter for being the voice of reason….we just dont know yet fer sure …do you cliff?
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