Strings for Dummies

Joe Lykken just finished giving a series of talks at the SLAC summer school, now entitled “String Theory for Physicists”. This was changed from the original title, “String Theory for Dummies” (still on the poster). Presumably somebody realized that the title could be taken the wrong way, giving the impression that string theorists think non-string theorists are stupid.

Lykken’s talks are actually unusual for this kind of exercise in expounding string theory to non-string theorists. They begin with a long list of the pros and cons of string theory. I’d disagree with him about some of the “pros” he lists, but it is remarkable that he gives a detailed discussion of the problems with string theory. I’ve never seen a string theorist do that before. During the last few months I’ve been sensing a definite change in the atmosphere surrounding string theory. String theorists are on the defensive, and many science journalists and members of the general public are starting to get the idea that there might be something funny going on. For the first time there was open pessimism and defensiveness expressed at the panel discussion at Strings 2005 and the recent New York Times article about it had a somewhat mocking tone.

There’s a posting at cosmicvariance.com by JoAnne Hewett about the panel discussion and Times article, and many comments, including some from yours truly. Jacques Distler proves that he thinks anyone who doesn’t agree with him about string theory is just ignorant (OK, maybe he just thinks that I’m the only one who is ignorant) with his trademark tactic when he’s on the losing side of an argument: take something perfectly accurate that your opponent writes, change the wording to something else that can be interpreted as inaccurate, then use this as evidence to back up a sneering put-down of your opponent. Jacques seemingly can’t help himself from doing this. For an all-time classic, check out his contribution to one of the first postings here, where he attacks me for saying that the standard model is a chiral gauge theory.

Unfortunately, Jacques isn’t the only string theorist who thinks that this is an intelligent way to behave. Besides another well-known string theory blogger I could mention, at one point I had a remarkable experience with an unknown “prominent string theorist” (I’m pretty sure it wasn’t Jacques) who was asked to referee something I’d written about string theory. This referee wrote a report saying that I was just so wrong it wasn’t worth explaining why, but that they would give one example. Their example was constructed by taking a sentence out of context, then changing a singular to a plural to allow the sentence to be construed as saying something inaccurate. Some string theorists seem to be willing to go to any lengths to preserve their belief that any criticism of the theory is based on ignorance. My impression is that a lot more criticism is coming their way, and it will be interesting to see how long they try and keep claiming that their critics are just dummies.

Update: Lubos Motl is back from vacation, with a posting about the Toronto panel discussion.

This entry was posted in Uncategorized. Bookmark the permalink.

39 Responses to Strings for Dummies

  1. Nigel Cook says:

    ‘String theorists are on the defensive, and many science journalists and members of the general public are starting to get the idea that there might be something funny going on.’

    Like a conspiracy of string theorists to put over stuff that would look like science fiction if it wasn’t so boring? There is little physics coverage because it is becoming so awful. There is a decline in physics A-level uptake in Britain, and a large number of university physics and maths departments have shut here.

    ‘Children lose interest … because a natural interest in the world around them has been replaced by an unnatural acceptance of the soundness of certain views, the correctness of particular opinions and the validity of specific claims.’ – David Lewis, You can teach your child intelligence, Book Club Associates, London, 1982, p. 258.

  2. cvj says:

    Peter,

    Respectfully, I must point out that you’re misrepresenting several things here, in this post and others. (You are of course entitled to do this because it is your blog). First: The fact that you have not seen a string theorist point out the problems with string theory does not mean that it does not take place quite regularly. Second: As was discussed over at Cosmicvariance on several threads which I know you’ve read, there are several string theorists all around the world working on many things other than the landscape and anthropic issues that you have made central to your argument that string theory is in a crisis. Third: You fail to point out that there is at least one example of a string theorist blogger (perhaps not as prominent as the others you mention) who has been extremely welcoming to you, your comments, and who has taken the time out to address some of your objections (and clear up some of your misconceptions). I refer to myself.

    Your comments here on your own blog seem to be constructed to perpetuate your preferred mythology that all string theorists are on the defensive, and that they are all arrogant and think that all non-string theorists are dummies. I know that you used the phrase “some string theorists” in some places, but it was somewhat lost in the overall thrust and tone of your post.

    In summary: There is a much wider program of activity in string theory than you seem to acknowledge, and a much wider range of motivations. There is a much wider range of temperaments of string theorists than you seem to allow for. Oh, and the theory is not in a crisis, and there is nothing “funny” going on, assuming that you mean “peculiar”.

    Finally, The New York Times’ attitude to a body of scientific activity cannot be used as evidence of anything, in view of the fact that even when they are supportive of something, they often get the content, emphasis, and overall point woefully wrong. (There are several articles on string theory which fit that description. It is, however, good that they at least try to cover this activity, I must add.)

    Finally finally, it would be nice to think that the courtesy we’ve shown you over at Cosmicvariance would result in you making an effort to paint a less narrow and bitter characterization of the valuable discussions that have taken place there. There were several people addressing points you’d made besides Jacques, some of them also active string theoriest with a valid point of view, who quietly explained things to you, and listened to what you had to say.

    Best,

    -cvj

  3. woit says:

    Hi Clifford,

    First of all, I was in no way referring to you in my complaints about string theory bloggers. You’re right that you’ve always been welcoming to me and willing to engage in very reasonable discussion on all issues. I appreciate that. I also should say that in many of my discussions at cosmic variance as well as in hundreds of private discussions over the years I’ve found the great majority of string theorists to be reasonable people willing to respectfully discuss issues we disagree about (and we often find we agree about more things than we would have expected). I take your point that I should acknowledge this more often.

    That said, until you came on the scene, the two most prominent string theory bloggers have been Jacques and Lubos, and the behavior of both of them is atrocious. I can forgive Lubos a lot, I too was once young and foolish, but Jacques is a middle-aged man and there is absolutely no excuse for the kind of bullying behavior he chooses to engage in. I’m not going to put up with it.

    While Jacques is one of relatively few string theorists who behaves this way, he’s not the only one who chooses to react to the problems of the subject by engaging in intellectually dishonest and bullying behavior. When I first posted an article criticizing string theory I got a lot of positive responses, a small number of highly hostile responses personally attacking me, and zero reasonable, intelligent reactions from professional string theorists. What most surprised me were how many people complimented me on my courage, saying they agreed with me, but didn’t dare say so publicly for fear of retribution. There’s a really ugly side to the way string theory has come to dominate particle theory, and the Jacques Distlers of the world are a big part of the story.

    As for whether the field is in crisis, that’s a matter of perspective, and is something on which I think we do fundamentally disagree. But I assure you that my perspective is not purely a personal one, I’ve found that many graduate students, postdocs and more senior people agree with me about this. A few years ago I found it wasn’t uncommon for string theorists I talked to to agree about this. They often felt the lack of new ideas or forward motion was reaching the point of crisis. More recently I’ve found an even larger number of people agreeing with me, with very many sharing my point of view that a sizable and increasing fraction of the string theory program has been taken over by research which is pseudo-science, not science. Looks to me like a crisis. By definition a crisis doesn’t last that long, so we’ll see what things look like in few years, and then may be able to evaluate which one of us was right.

  4. Urs Schreiber says:

    While I don’t know if it does any good to try to discuss it, I am wondering where you think your arguments were distorted.

    I had the feeling your comments received pretty good replies. Seems like you tried to argue that all valuable progress attributed to string theory is actually progress in field theory. It was pointed out that this is an odd point of view, and a pretty good analogy was given to illustrate this.

  5. Peter says:

    Hi Urs,

    I don’t have any problem with any of the replies I received to my comments except those from Jacques. I didn’t actually say that “all valuable progress attributed to string theory is actually progress in field theory”, but certainly anyone who felt that was what I was saying and wanted to challenge it was more than welcome. In response to some of the replies, to Aaron and to Clifford I explained in more detail what I meant to say. In particular I made the completely accurate and unobjectionable statement that topological string theory at a fixed genus is a QFT, and that the string theory sum over genera is not a QFT.

    Jacques then began attacking me, first putting the words “topological string theory is just 2D QFT” in my mouth and saying I was “flat-out wrong”. When I copied for him my earlier comment explicitly saying that it was only at fixed genus that it was a QFT, he then made an analogy with the QFT perturbation expansion and in that context again put the “topological string theory is just QFT” argument in my mouth, using it to proudly announce that I was “not a serious interlocutor”.

    At this point, I was pretty pissed off by Jacques’s endless tactic of trying to find some way of twisting words that I write so he can find an interpretation of them in which they say something incorrect, and use this to attack my professional competence. I’ve had to put up with a large amount of this offensive behavior from him (and others), and am really sick of it. I pointed out to him that his own argument was worded incorrectly (he wrote “precisely equivalent” when he meant “precisely analogous”), but that I wouldn’t accuse him of being ignorant about QFT based on this.

    His rsponse was quite offensive (hint, in case this ever happens to you: if you have a Ph.D. in particle theory and someone carefully explains to you what a Feynman diagram is, then asks for a response that they announce will be “diagnostic”, you’re being insulted), so much so that he himself tried to retract it as “needlessly inflammatory”.

    Undoubtedly that’s more detail than anyone wants, but that’s what my posting and comments to Clifford are referring to.

  6. Aaron Bergman says:

    I can’t help but find this:

    In particular I made the completely accurate and unobjectionable statement that topological string theory at a fixed genus is a QFT, and that the string theory sum over genera is not a QFT.

    disingenuous. The discussion at hand was whether there was anything beautiful in string theory learned in the last 20 years (or something along those lines.) I responded with AdS/CFT and the topological string. Your response was that AdS/CFT dealt with field theory dualities and that the topological string at a fixed genus was just a field theory. The former is, as Clifford pointed out, wrong. The latter may be technically correct, but if construed that way, completely nonresponsive to the point. Given the context, it’s fair to infer that you were attacking the topological string as being just field theory in disguise. Otherwise, why mention it?

  7. Remarkably thin-skinned, coming from someone who, in a single recent post referred to me as

    a) “completely delusional”
    b) engaged in “educational malpractice.”

    I, fortunately, am rather thick-skinned. So, please, don’t change your style just for me. Continue to inveigh away at what an evil, mean-spirited (and completely delusional) person I am.

    I gather you have a loyal following, who just lap that stuff up.

  8. Quantoken says:

    I am not interested to make a judgement whether anything Peter said is right or wrong. Because it doesn’t matter and doesn’t change the fact that SST has so far unable to explain a single damn thing in nature. And that so far as it is unable to do that, it is a complete failure, and people like Jacques etc are a complete waste in their invain efforts to pursuit a goal that is simply wrong.

    Lubos is OK. He some times behave a bit silly and a bit arrogant. But he is young and he does show evidence of intelligence some times, like on the matter of global warming. As for Jacques, I have lost every little bit of respect for him after this. Clearly he has zero IQ on matters unrelated to SST, and could not think for himself.

  9. Peter says:

    Aaron,
    This is beating a dead horse, but let me try one more time:

    First of all, you’ve changed what initially led to this exchange, which was Jacques’s claim that

    “string theory has turned out to be a vastly more beautiful and intricate subject than anyone suspected 20 years ago.”

    not

    “whether there was anything beautiful in string theory learned in the last 20 years.”

    These are two very different statements. By changing what this discussion was about you’re constructing a straw man argument I never made and don’t agree with and putting it in my mouth. It’s an annoying debating tactic which Jacques also loves to use, but at least you don’t then go on to personally insult me.

    I have no problem with the second statement, and recent work on the topological string is a good example of something beautiful coming out of string theory.

    The first statement however is simply delusional (the beautiful part, not the intricate part, the subject sure is complicated). 20 years ago there was a conjectural idea about how to use string theory to produce a TOE, and many people made many public claims that this was an extremely beautiful idea. 20 years of work have shown just the opposite. All attempts to get a TOE this way lead to hideously complicated constructions which don’t even work. As a TOE, which is the main way string theory has been and continues to be sold, the situation is the precise opposite of what Jacques said, with the theory vastly uglier than anyone suspected 20 years ago.

    Some beautiful things have come out of string theory, but many of them are purely 2d QFT. Examples of 2d QFT results that I have in mind are the mid-late 80s work on CFTs, and the early 90s work on mirror symmetry (which involved topological sigma models with a fixed genus of the world sheet, often genus zero). In recent years there have been two related classes of results that truly are string theoretical and that truly are beautiful. They both come out of the idea of a having a precise duality between a gauge theory and a string theory. To be more specific they are:

    1. AdS/CFT. Of course I’m well aware that this is a duality between a string theory and a QFT, not a duality between two QFTs. It was my mistake to try and make the debating point that often this duality is checked by doing a QFT (supergravity) calculation on the string theory side. My bad, that muddied the waters and is pretty much beside the point.

    2. Topological string theory: As I’ve repeatedly said, there are certainly very interesting mathematical results about the full topological string theory expansion, and this full expansion is not a QFT. Among the most impressive things I’ve seen of this kind are the Gopakumar-Vafa results, and, correct me if I’m wrong, but part of the story is that these also come out of the idea of looking for a string/gauge theory duality, in this case using Chern-Simons as the gauge theory.

    So, when I look at the beautiful mathematics coming out of the last 20 years of string theory research, two sorts of things seem to me the most striking: some older results that are purely 2d QFT, and some more recent results that are based on the idea of looking at precise string theory duals of a gauge theory QFT. From this perspective, what is interesting about string theory is not the idea that was initially used to sell it, that it could give the standard model QFT + supergravity as a low energy limit, but the fact that it can provide an alternate formulation of QFT.

    If you want to challenge any of the above, go right ahead, I’m happy to discuss it further. If instead you want to ignore this elaboration of my earliest comments and make complaints about them based upon a misinterpretation of what I was saying, I don’t really see the point of continuing.

  10. Peter says:

    Jacques,

    Because of your continual insults of me as professionally incompetent, at some point I stopped worrying about whether my references to you were sufficiently polite or not. Perhaps this was a mistake, I hear they have a saying down in Texas about what happens if you start wrestling with pigs.

    If you want to continue your tactic of trying to deal with my criticisms of string theory by making up things I haven’t said and using them to insult me and to try and convince people that I don’t know what I’m talking about, go right ahead. But it’s slimy, pathetic, bullying behavior and you should know better. It may help you maintain your delusions about string theory, but the obnoxious way you and Lubos behave in the face of criticism makes clear to most people how little of a legitimate case you have on your side of the argument.

  11. Well, then, you probably don’t care that we were referring to the Gopakumar-Vafa papers on the duality with M-theory (I,II) — a highly nonperturbative rewriting of the Topological String free energy (summed over genera) — rather than to large-N Open/Close Topological String duality.

    And, no, in the latter case, the Open String side only reduces to Chern-Simons theory in the special case of T^*S^3.

    Anyway, I had forgotten why I avoid responding to your attacks. Thanks for reminding me.

  12. Peter says:

    You know Jacques, I think this is a mania, and you should consider seeking professional help.

    Let’s look at this and see the trademark Distler behavior in action. Recall how it works: first ignore the points at issue, and pick out one sentence in which some sort of reference is made to a particular technical idea that he knows something about. Then go on to interpret that reference in a way that can’t be supported by the actual text, but that allows him to attack me as not knowing something that he knows.

    In this particular case, the the technical thing at issue is results of Gopakumar-Vafa, about which I said, in toto:

    “part of the story is that these also come out of the idea of looking for a string/gauge theory duality, in this case using Chern-Simons as the gauge theory”

    I wrote “part of the story” specifically because I was only referring to, well, part of the story, the part that Jacques properly recognized as large N Open/Closed Topological string duality, and in particular the special case of the cotangent bundle of the 3-sphere. Note that I was very careful to not be claiming that this was a complete description of all of the Gopakumar-Vafa results.

    It’s pretty tedious to have to spend time writing comments like this very carefully, since I know Jacques is going to be spending his time searching them for something he can use to attack me as an incompetent. The thing that most amazes me about Jacques is that he just can’t stop himself from doing this kind of thing. You’d think that once anyone had publicly made a fool of himself so many times this way they’d learn their lesson.

  13. I can’t resist point out that, in the same recent post in which you called me “completely delusional” and “[engaged in] educational malpractice,” you also complained that, “This is the first time I can think of that he has actually used my name, even if as an insult.”

    So much for my “continual insults” of you and/or your professional competence.

    Now, I really feel the need to shower off and stop responding to your … umh …. well-reasoned critiques.

  14. woit says:

    Sorry Jacques, you’ve won and caught me in an imprecision. For “used my name”, I meant “used my name in his blog”.

    Your mania for avoiding the point and desperately trying to find something inaccurate in what I write continues. Get help.

  15. Even though this has become a flame war, I would like to make a comment that I hope is recognized as a technical comment, not intended to attack anyone personally.

    It was Peter who wrote above:

    As a TOE, which is the main way string theory has been and continues to be sold, the situation is the precise opposite of what Jacques said, with the theory vastly uglier than anyone suspected 20 years ago.

    ‘As a TOE’ = ‘as concerns it’s quasi-realistic solutions found so far’, yes indeed. Nobody can deny that and as far as I can see nobody around here is denying that.

    The discussion over at cosmicvariance was however about the theory, not about any of its solutions (or about any way (anthropic or what not) to pick its solutions). This is a big difference. Newtonian mechanics is beautiful. Specifying the solution to some billard problem, say, in Newtonian Mechanics is generically not so.

    It seems to me that the argument here became heated because the distinction has been blurred between statements like

    There are many beautiful aspects to be discovered once certain CFTs are interpreted as describing strings propagating in certain target spaces.

    on the one hand side and

    Such interpretation has however so far not led to a nice derivation of the standard model.

    on the other side.

    I believe there is no disagreement on the truth of either of these two statements between Peter and anyone else. The whole point is that Peter feels that the truth of the second statement totally undermines the usefulness of the first statement, while many others feels that the truth of the first stament is ample indication that we can eventually remove the ‘so far’ from the second statement.

  16. Chris Oakley says:

    I believe there is no disagreement on the truth of either of these two statements between Peter and anyone else. The whole point is that Peter feels that the truth of the second statement totally undermines the usefulness of the first statement, while many others feels that the truth of the first stament is ample indication that we can eventually remove the ’so far’ from the second statement.

    Not proven, I’m afraid. Just because something is “beautiful” (a very subjective thing anyway) it does not that mean that it is likely to be right. This obsession with mathematical beauty has led precisely nowhere, and it is high time that you people stopped pretending that what you do has more than a passing resemblance to physics.

    You can fool all of the people some of the time, etc.

  17. Quantoken says:

    Jacques:

    You clearly do not know anything you talk about. Are you really sure you have READ the Vafa paper carefully? I think you have NOT! To show how ignorant you are, please tell me, without go a read that paper again, exactly how many equations have occured and exactly how many pages that paper contains. You can’t answer that without cheating, can you?

    The point I want to make is the technicality details are totally un-interesting and unimportant. The important thing is even if you memorize everything Vafa ever published and down to the detail of page numbers and word counts, you are still a complete idiot and not knowing what you are talking about. The whole SST business is completely meaningless except it could be otherwise interesting to a few paid nerds like your kind. Clearly SST is unable to make any prediction so it belong to a category worse even than astrology, which at least makes predictions, right or wrong.

    Have you figured out which end of yours emit the kind noxious smell that contributed greatly to global warming, Jacques? I never thought that’s an important detail to know but you clearly had a different opinion.

  18. Aaron Bergman says:

    “string theory has turned out to be a vastly more beautiful and intricate subject than anyone suspected 20 years ago.?

    not

    “whether there was anything beautiful in string theory learned in the last 20 years.?

    I’m sorry, but there is almost no difference in the plain wording of these statements besides the word ‘vastly’. That you choose to interpret the former one as somehow implying that the use of string theory towards finding a realistic vacuum (and things along those lines) has become more beautiful is bizarre. It’s just not there in the sentence. At the risk of putting words in Jacques’s mouth, the sentence means precisely what it says, that string theory, as a subject, has turned out to be more beautiful and intricate, again, as a subject, that anyone suspected 20 years ago. The proliferation of candidate vacua in the past few years does little to negate this statement.

    From this perspective, what is interesting about string theory is not the idea that was initially used to sell it, that it could give the standard model QFT + supergravity as a low energy limit, but the fact that it can provide an alternate formulation of QFT.

    Nobody has said, Peter, that the vast areas of beauty are all part of the idea that was initially used to sell it (although many of these new understandings hav gone into the constructions of vacua.) You’re so fixated on this point that you cannot respond to the actual words that people are writing.

    And, you’re still wrong on the topological string. You can carefully word your statements as much as you like; you’re still using them to support your conclusion:

    So, when I look at the beautiful mathematics coming out of the last 20 years of string theory research, two sorts of things seem to me the most striking: some older results that are purely 2d QFT, and some more recent results that are based on the idea of looking at precise string theory duals of a gauge theory QFT.

    Now, when someone points out that your statements don’t actually support this conclusion, by pointing out that they involve things beyond field theory and field/string dualities, you appeal to your careful wording. In other words, you claim to be aware of the fact that your statements, precisely parsed, do not support your conclusion. Given your claims to greater knowledge, your careful wordings come across as simply deceptive.

  19. JKG says:

    Hi,

    On his first slide Lykken says „string theory is a consistent theory of quantum gravity?. Lee Smolin uses to stress that there is no proof that string theory is renormalizable to all orders, so this statement seems to be not exactly correct, but I have even more naïve question. Namely could anybody explain, what are the arguments that string theory is (contains) a theory of gravity, and not merely just a theory of spin 2 field moving on some backgrounds. Could one derive equivalence principle from strings? Is it possible to derive Newtonian potential (with some corrections perhaps) for point mass(es)?

    Thanks

    JKG

  20. Aaron Bergman says:

    One can find the consistent backgrounds on which one can do string perturbation theory. It turns out that these backgrounds are exactly those that satisfy the Einstein field equations (plus higher order corrections). String perturbation theory also gives rise to a spin 2 field, ie, perturbative gravity, and this contains the Newtonian potential.

  21. Chris Oakley says:

    Aaron,

    This was the question:

    Could one derive equivalence principle from strings? Is it possible to derive Newtonian potential (with some corrections perhaps) for point mass(es)?

    Your answer seems to be “we hope so” rather than “yes”. For some of us, this is not good enough.

  22. Aaron Bergman says:

    In what way does my answer seem to be “we hope so”? The equivalence principle (for various definitions thereof) fails for strings, but this isn’t a big deal. As I said, you can compute perturbative gravity and show that any background has to satisfy the EFEs. What more do you want?

  23. woit says:

    Hi Urs,

    I’m glad to have someone commenting here who seems interested in having a reasonable discussion. A couple comments of my own:

    First of all, it’s not so clear in this case what is “the theory” and what is “the solutions to the theory”, so the ugliness of the latter is not irrelevant to the question of the beauty of the former. To discuss the issue of the beauty of “the theory” that is supposed to be a TOE we have to first agree about what “the theory” is. If you want to very precisely tell me what “the theory” is, we can try and have a discussion about its aesthetic properties, positive and negative.

    Secondly, about the two statements you give, I’m not completely happy with your formulation of either one. In the first statement, you need to specify precisely what CFTs and what target spaces you’re talking about before I’ll sign on. I’ll happily agree with this statement if we’re talking about the topological string and target spaces where string theory has led to calculations of the full sum over genera. But I suspect you have in mind other CFTs and other target spaces. Your second statement is misleading: not only hasn’t work on string theory led to a “nice” derivation of the standard model, it hasn’t led to any derivation of the standard model, nice or not nice.

  24. JKG says:

    Hi Aaron,

    You say

    “String perturbation theory also gives rise to a spin 2 field, ie, perturbative gravity, and this contains the Newtonian potential”

    I understand that you compute entirely within string theory the scattering of two particles mediated by graviton, go to the static limit and get Newtonian potential. This sounds reasonable. Is it then obvious that from the first principles it follows that the relevant charge is to be mass (inertial one because you do not have anything else to start with), or you just put it by hand, somehow? In the first case you would have more-or-less the equivalence principle.

    Thanks

    JKG

  25. Aaron Bergman says:

    The violation of the equivalence principle comes from the fact that string theory really gives dilaton-gravity.

  26. woit says:

    Hi Aaron,

    First of all, look at what you are doing in defending Jacques’s statement. You argue:

    “the sentence means precisely what it says, that string theory, as a subject, has turned out to be more beautiful and intricate, again, as a subject, that anyone suspected 20 years ago.”

    I don’t have any problem with your changing “string theory” to “string theory, as a subject” (it actually doesn’t clarify the tricky point of what “string theory” refers to), but the “vastly” you decided to drop is a big part of the problem.

    In standard use of the English language the two questions of

    whether string theory is “vastly more beautiful … than anyone suspected 20 years ago”

    and

    “whether there was anything beautiful in string theory learned in the last 20 years.?

    are quite different and have very different truth values. To make the second one true you just need to demonstrate one beautiful thing about string theory learned in the last 20 years, and there are plenty of candidates.

    To make the first one true, you have to first understand what people thought about the beauty of string theory 20 years ago. Note that Jacques didn’t just say that string theory is more beautiful than the average string theorist thought, he says that it is “more beautiful than anyone suspected” back then, so you have to identify the maximal amount of beauty that any string theorist suspected the theory might have back in 1985.

    I have a bit of an advantage over you here in that I was there, spending lots of time talking to people and going to talks about string theory. Unlike many people who have problems with string theory, my problem is not that I object to being guided by mathematical beauty, especially when you don’t have experimental results to help you. Many people at the time were going on about the beauty of string theory and I was having trouble seeing this. The quantization of the string never seemed to me a beautiful business (and still doesn’t). Part of what people generally seemed to mean about the beauty of the theory was the way anomaly cancellation conditions picked out 10d and a gauge group like SO(32) or E8xE8, together with the way conformal invariance picked out approximately Calabi-Yau spaces among all possible 6d spaces. Some people were quite taken with the beauty of the geometry of these Calabi-Yau complex threefolds. Algebraic geometry is a beautiful subject.

    So, 20 years ago, at least some practicioners would have claimed that string theory was a very beautiful subject, with one of their arguments being the beauty of the Calabi-Yau condition in picking out an attractive class of algebraic varieties, one of which would soon explain all of particle physics to us. Fast forwarding 20 years, much of this “beauty” has collapsed, as it has become clear that to get anything that looks like physics, you can’t just use a Calabi-Yau, but have to add in all sorts of ugly, complicated and poorly understood structure.

    Sure, some beautiful things have been discovered about parts of string theory having nothing to do with its use as a TOE, but I still think you have to be delusional to think that these are “vastly” more beautiful than the maximalist claims of beauty for the theory that were being made back in 1985.

    Perhaps like Urs you’re also of the opinion that one can consistently claim that the ugliness problems of string theory come just from its solutions, not the theory itself. If so, see my response to him about this.

    As for the rest of your comment, you seem to be objecting to my conclusion describing what, to me, are the most beautiful things coming out of work on string theory: things coming from 2d QFT and things that come from the discovery of various string/gauge theory dualities. That was a personal statement describing my aesthetic reaction to those things I have learned about by following research in string theory. No I don’t claim to understand everything going on in string theory, and if you know of something you find significantly more beautiful than the things I mentioned and want to tell me about them, I’d be happy to learn something.

  27. Aaron Bergman says:

    Again, you miss the point. Our understanding of string theory has expanded. Expanded vastly, even. And, there has been a whole lot of beauty in those new areas that have been discovered. These are areas and directions that no one suspected back when string theory first became popular. As best I can tell, you don’t disagree with any of these facts. Nonetheless, you seem so obsessed with the vacuum situation that you automatically interpret the statement that the field is vastly more beautiful as referring to that. Did the people in the early 80s suspect AdS/CFT? Did they suspect mirror symmetry? Did they suspect dualities? I could go on. Are these ugly ideas? You’re attacking as ‘delusional’ statements that nobody has made.

    As for the rest of your comment, you seem to be objecting to my conclusion describing what, to me, are the most beautiful things coming out of work on string theory

    I was objecting to your implication that various areas of beauty I mentioned were, in fact, just field theory and not string theory. You’re welcome to find beauty whereever you care to look. What I dislike is when you misrepresent the facts of a situation (even when carefully worded to be technically correct) in order to score cheap points.

  28. Peter says:

    Aaron,

    You’re just repeating yourself and showing no signs of even bothering to read anything I write. You’re continuing to go on about how I’m claiming that certain subjects are just field theory, long after I’ve repeatedly wasted a lot of my time acknowledging that some of these subjects are definitely string theory, not QFT and trying to be precise about which is which. I’ll take your lack of response to my last question as at least indicating that we’re in agreement that the most beautiful things to come out of string theory are various ideas about 2d QFT, and various examples of string/gauge theory duality.

    You seem to agree that what I’m saying is technically correct, but you find it a misrepresentation of the “facts” of the situation. What’s going on is that I have a very different interpretation of the significance of and lessons learned from a lot of the undeniable advances achieved in work on string theory over the last 20 years. If you want to argue against it, you’re welcome to do so and we might both learn something. But you first have to at least read what I write and pay some attention to it.

  29. Aaron Bergman says:

    One would naively expect that the effective potential strengthens at short distances due to the extra dimensions appearing; Do you know a quantitative estimate for the deviation from Newton and would experimental evidence that the potential actually weakens (relative to Newton) be a hint that string theory is wrong?

    I don’t know of any way to explain it with what we currently know about string theory (or field theory, for that matter.) Is it a hint that string theory is wrong? I don’t feel that we understand string theory well enough to say. That’s one of the reasons I’m not particularly enthusiastic about the attempts to do string phenomenology these days.

    It would, however, pretty much rule out all the large extra dimension scenarios that I know of.

    Peter,

    George Bush never actually said outright that Saddam Hussein and Al Qaeda were linked, but he damn well implied it. That’s the feeling I get from your argument here. Your careful wordings seem tactical and designed to give a wrong impression while remaining technically correct.

    I’ve already mentioned what I find most beautiful these days: AdS/CFT and the topological string. In fact, it’s exactly a subject on the intersection of those two that is frustrating me right now.

  30. Aaron Bergman says:

    No. String theory is the only known consistent quantization of a gravitational theory in more than three dimensions. There are plenty of different theories of gravitation. We know that the vanilla perturbative string gives supergravity in ten dimensions. Compactifications of this give gravity in lower dimensions.

    The theory is not well-developed enough to be falsifiable (to my knowledge) by anything less than a probe of the Planck scale.

  31. Gordon says:

    Aaron,

    You may always regulate gravity in the same way string theory is,
    when you take the low-energy limit. The GR theory is sensible, and
    even models string theory. What do you expect string theory to
    be at scales below the Planck scale? You are not going to see all
    of the states, but rather some theory that we call gravity (which
    is regulated the particular way).

  32. Peter says:

    Hi Aaron,

    If you’re concerned about people who use wording designed to give the wrong impression, check out hep-th/0508034 by Michael Douglas, which just came out and which I just started looking at.

    “we begin with compactification of the heterotic string on a three-complex dimensional Calabi-Yau manifold. This was the first construction which led convincingly to the Standard Model”

    And, by the way, referring to string theory as giving a “consistent” quantization of gravity, somewhat strains the conventional meaning of the word “consistent”.

    If I’m behaving like George Bush, some others have to be compared to the Iraqi information minister.

  33. Michael Sanford says:

    Dr. Woit and Dr. Distler,

    For the most part, I enjoy reading the differing opinions found on this blog. I have learned some interesting things as well. However, this flame war between the two of you is unprofessional. It does not put either of you in a good light. It is obvious that neither of you are going to agree on the subject of String Theory or about each other personally. So, can you two take the high road and agree to disagree?

    I look forward to more spirited (but polite) discussion here.

  34. Gavin says:

    Peter,

    I’ve been following your comments on several threads, and just want to make sure I understand. I would welcome any corrections.

    QFT makes a ton of predictions about all sorts of low energy experiments once you pick the particle content, masses and couplings. There are many choices you can make, but there are some restrictions, the most obvious being that the theory has to be renormalizable and anomaly free. We actually have a set of particles and couplings, the standard model, which matches very well with experiment, and the theory is renormalizable and anomaly free. All very nice.

    The only bad news is gravity, which is not renormalizable. Based on our current understanding of QFT, gravity should be left out. Opps.

    String theory looks like QFT at low energies, so if we could find a “standard vacuum” that gives the right particle content and interactions, then string theory would be as good as QFT, although needlessly complicated. There is one advantage, however, which is that string theory predicts gravity where QFT recoils.

    If we lived in ten dimensions, then we could do a lot better. With only a handful of string theories to chose from, it would be pretty exciting if the low energy spectrum matched the massless modes of one of the string theories. If the spectrum was different, then string theory would be out.

    Living in four dimensions means there are tons of vacuums, so practically anything is possible. This makes it hard to see how string theory is any better than QFT.

    Am I on track with this?

    Gavin

  35. Aaron Bergman says:

    Wolfgang, do something about your wrapping, please. There’s a preview right below the entry box.

    By the way, does anybody understand why and how M-theory compactifies to 4D ? And also why this compactification “stops? at small distances? (Roger Penrose raises this question in his book. )

    The better question to ask is, why do four dimensions become large, not why do however many become small. Everything was small at one point if you believe in the big bang, after all. Is there a definite answer to this question? No. There are plenty of attempts at answering it (Brandenberger-Vafa being the most famous, probably), but nothing is close to definite. It’s an open problem. There are lots of them. I don’t understand the second question.

    If I understand Gordon’s comments as being against the idea that you can get too many funky modifications to gravity in the IR, my response is that string theory has surprised us in the past and will probably do so again in the future. Given that there already are weird linkages between the UV and the IR in the theory, I’m not comfortable making definite pronouncements about anything.

    For Peter, I’m not here to defend Douglas (whose philosophy on landscapy things I generally disagree with). The statement does seem weasely to me. I’ll stand by ‘consistent’, however, unless you can point out anything inconsistent in string theory. Goedel’s theorem, of course, tells us that anything consistent must be incomplete and string theory certainly is that.

    (joke)

  36. Nigel Cook says:

    Gavin: string theory doesn’t ‘predict’ gravity. General relativity is testable, string theory isn’t. Eddington in his 1920 book Space Time and Gravitation counted 200 other speculative theories for gravity. None made testable quantitative predictions, so none were really science. If they don’t make testable predictions, they are crackpot. Witten in Physics Today, April 1996, claimed that string theory ‘predicts gravity’ which is extremely misleading, as Penrose points out in The Road to Reality. This is the real crime of string theory, these distortions of the facts. They make it heavy going for everyone trying things outside string theory.

  37. Arun says:

    Something that Peter Woit wrote, about not trusting mathematical beauty to be a guide to the world, resonated with something I just read by biologist Sean B. Carroll. The context is how structure arises, and in particular varoius regular patterns arise, in a biological organism that starts off from a single cell.

    For several decades, mathematicians and computer scientists were drawn to the periodic patterns of body segmentation, zebra stripes and seashell markings. Heavily influenced by a 1952 paper by the genius Alan Turing (a founder of computer science who helped crack the German Enigma code in World War II), “The Chemical Basis of Morphogenesis”, many theoreticians sought to explain how periodic patterns could be organized across entire large structures. While the math and models are beautiful, none of this theory has been borne out by the discoveries of the last twenty years. The mathematicians never envisioned that modular genetic switches held the key to pattern formation, or that the periodic patterns we see are actually the composite of numerous individual elements.”

    (From “Endless Forms Most Beautiful : The new science of Evo Devo”.)

    Not precisely on the topic of string theory, but I hope relevant nonetheless.

  38. woit says:

    Hi Gavin,

    “Am I on track with this?”

    In a word, yes. However, one important difference between the standard model and string theory is that in the standard model case we have a non-perturbative formulation of the theory (although there is an interesting caveat about chiral gauge couplings), whereas there is no workable non-perturbative formulation of string theory that includes the standard model as a limit.

  39. Aaron Bergman says:

    I don’t have Penrose’s book, so I can’t comment.

Comments are closed.