String Theory Debates

This seems to be the month for string theory debates, with two a couple weeks ago in the UK involving Lee Smolin, and another featuring Lawrence Krauss and Brian Greene scheduled for next week in Washington D.C. The Washington Times has an article about this.

Smolin’s book has just appeared in the UK, and there have been lots of (very positive) reviews. See here, here, here, here, and here.

Besides talks (for a report on the one at Cambridge by a skeptical American physics student in England, see here), there were two debates. One featured Smolin, Philp Candelas, Simon Saunders and Frank Close and was held at Oxford; for a report, see here. It appears to have been a respectful and reasonable public airing of a few of the issues where string theorists and some of their critics disagree.

A couple days earlier though, a debate in London between Smolin and Mike Duff (also involving philospher Nancy Cartwright) had a very different nature. According to the report from one attendee, after Smolin started things out by arguing his case:

Smolin sat down. Duff stood up. It got nasty.

The trouble with physics, Duff began, is with people like Smolin…

Duff is described as “string theorist and man for whom, one imagines, the words ‘self’ and ‘doubt’ do not often rub shoulders”, and seemed to think it was a good idea to answer criticisms of string theory with vociferous ad hominem attacks. Lubos Motl and Clifford Johnson both found Duff’s behavior an excellent example for all string theorists, inspiring Clifford to write part VII of his extended attack on me, Smolin and our two books. He admitted somewhere around part V or VI that he actually hadn’t looked at the books and had no intention of doing so, and he’s pretty steadfast in that attitude. It never ceases to surprise me that people like Clifford don’t realize that, much as they may enjoy engaging in or listening to personal attacks on me and Smolin, this just doesn’t do a lot for the credibility of their field. String theorists often complain that Smolin portrays them as arrogantly dismissing any criticism, but they should realize that behavior like Duff’s doesn’t help them at all on this issue, quite the opposite.

Duff pretty obviously has a double standard for popular books about string theory. He’s quite capable of being polite, writing a very respectful review of Susskind’s The Cosmic Landscape for Physics World. His review of Smolin’s book in Nature Physics is something very different, much more like his performance at the debate. The review begins by misquoting Smolin, based upon something that was in the proof copy of the book he had (which the author hasn’t had a chance to look at), but was different in the published version. After the review, he had been informed about this, but still seemed to think it was a good idea to use this as ammunition in his personal attack on Smolin during the debate.

One of his main points was that it is ridiculous to claim that string theory has not made any progress since the 80s. Obviously there are some areas in which there has been progress in better understanding the theory, but, as far as the central issue, that of getting any predictions out of the idea of using strings to unify physics, it’s interesting to follow the link that someone with a waggish sense of humor at Nature put at the bottom of the page of Duff’s review. It’s a story from 1986 entitled Where Now With Superstrings?, and it reports on the views of string theorists at the time, roughly one year after the early developments that caused so much enthusiasm for string theory as a unified theory. The problem of too many vacua was something people were starting to worry about, but the feeling was that:

… another problem of non-uniqueness in superstring theory, the variety (thousands) of possible four-dimensional worlds it allows, is showing some signs of resolution.

The “progress” on this more than twenty years later is that instead of “thousands”, the number has moved up to the exponent, and we’ve now got the “Landscape” of 101000 or so possible four-dimensional worlds. Any “signs of resolution” of this are long vanished. Just as physicists are now waiting for the LHC next year, those of 1986 were waiting for the Tevatron to start up the next year, with Weinberg claiming that the mass range to be explored by the Tevatron was “a very plausible mass for them [superpartners] to have”. The reporter wrote that:

If the Tevatron sees no superparticles, supersymmetry will lose its value in the hierarchy problem, and hence half its motivation.

So, I guess Duff is right that it’s inaccurate to say that things haven’t changed with the prospects for string theory since 1986, since the situation now is a lot worse than it was then.

If you want to listen to the debate, audio is available on-line here, with a transcript to appear shortly. For another kind of audio showing what this is all about, see this posting from Sabine Hossenfelder.

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82 Responses to String Theory Debates

  1. M says:

    dear Andrea,

    have you read “The Library of Babel” by Borges?

    String theory seems to be a similar story. If tomorrow you scan 10^200 string vacua, you can probably find one vacuum that fits all the physics we know, and you get a Nobel prize. If on sunday you finish the work scanning the 10^500 remaining vacua, you can find 10^300 more vacua that fit everything, and you get an igNobel prize.

  2. Mike C. says:


    You are not correct. These vacua only look like they’re 2+1 dimensional to large creatures like us. Tiny creatures, however (~1 micron), would see 3+1 dimensions, with one dimension wrapping around if they move along it far enough. Their physics—including gravity—is 3+1 dimensional and looks almost exactly the same as ours, all the way up to energies 20 times the Planck scale (when you start making black holes bigger than 20 microns) except for variations of all their coupling constants and masses. Read the paper to see why. So gravity is no more tractable for them than it is for us, and they still would have no explanation for the values of those coupling constants.

  3. Mike C. says:

    I must say that I’m a little bit disappointed with many of the commenters here. It seems like a lot of people here are making assertions and demands without having done their reading. People read the first two pages of a paper, for example, essentially just to find things that support their argument, and then start spouting things that aren’t true. A lot of the comments indicate that people don’t understand or haven’t read the relevant material. I’m feeling a lot of prejudice here. Can’t we all be a little more open minded?

  4. woit says:


    You’ve come here, posted 13 comments, full of sophistry about the landscape which you base on a 44 page paper, which you refuse to answer my questions about. You seem to expect me and others to drop what we are doing and go read this 44 page paper. Sorry, everything I heard about it indicates to me that my time would be better spent reading other papers. It’s not even the topic of this posting at all. This isn’t a general discussion forum where you can just appear, start going on about what interests you, and expect others to go out and spend their time thinking about what you want them to think about, unless you’ve got a lot more compelling argument.

  5. Brett says:

    I don’t think it’s especially interesting that there is a “landscape of vacua” in theories in which some of the space-time directions are compactified. I say “landscape of vacua”–in quotes–because at the quantum field theory level, the different compactifications correspond to different theories; the underlying space-time is an element of the definition of the field theory. In a quantum gravity theory, maybe these are different states of the same underlying theory, but the standard model is not a quantum theory of gravity.

    It’s no real surprise that by choosing different compactifications, one can get significantly different physics, because the compactifications themselves are ingredients in defining the theory. The parameter space of the theory includes the space of compactification manifolds. In order for these theories to be interesting physically, some additional conditions must be met; otherwise, we’re just adding extra free parameters. If there were any experimental indications that some of the dimensions of our universe were compact (either one of the four we see, compactified on a large scale or additional ones on small scales), this would be a very interesting subject. Or if having compact dimensions allowed a natural solution to some kind of hierarchy problem. Of course, there are various proposed “solutions” of such hierarchy problems using extra dimensions, but they are not natural. If we clean up a known hierarchy by introducing unnaturally sized extra dimensions, we haven’t solved anything, just moved the fine tuning into a new set of free parameters we’ve introduced just for that purpose.

    If we want to allow for the possibility that one of the four dimensions we see is actually compact, and that somewhere far away in the universe, the corresponding compactification scale is quite small, that’s fine. This introduces a new generalization of the standard model, and maybe it’s what the universe really looks like. But it’s very much like introducing a new sector of particles near the Planck scale, with new free parameters, but hardly any new predictions for feasible experiments.

  6. M says:

    Mike C., I don’t see what these tiny creatures can teach us. In the case of strings, 10^500 vacua come out because you start with fields with a few 10d Lorentz indices and compactify many dimensions. These ‘features’ are not present when you compactify the SM to 2+1 dimensions.

    Anyway I agree that theories with compactified dimensions tend to have many vacua, as discussed e.g. in the book by Smolin.

    The true problem is: can we get good physics from the big string landscape? If the best we can do is debating about tiny creatures, then better to move to biology.

  7. dan says:

    Hi Peter,

    you wrote “As long as you don’t know what non-perturbative string theory is, your arguments that “you can’t get that from string theory” are going to be dubious.”

    How do you feel about physicists pursuing a non-perturbative string theory as a frontier of HEP?


  8. Peter Woit says:


    Finding a useful non-perturbative string theory is the big problem in string theory, and many people have worked on this over the last few decades and continue to do so. It would be great if there were progress on this, I just don’t see much recently.

  9. andrea says:


    the paper on standard model landscape is actually on standard model + general relativity landscape, so spacetime geometry is genuinely dynamical… that said, it goes neither here nor there as far as physics is concerned.


    i don’t get the rigidity argument: a single unit switch on one of the handles of the Rube Goldberg machine will generically lead to very large changes of the low energy physics (different number of flavours, or different gauge groups or planckian change in the CC). Nearby vacua don’t give nearby physics.
    If at least one vacuum is found which matches the physics we know, then one can make all sort of predictions: if they are verified we keep it and make other predictions, if not one is free to look for another one (typically very far away). No need to say that there may exist no vacuum with the right properties, but if Nature actually worked that way i’d be somehow disappointed, but i would not be shocked.

    I’ve been following this debate for a while, and some string theorists have way passed the line of a civil exchange of ideas, but aside from that, the string community rightfully shows off its achievements (overhyping is unavoidable in the free market of ideas) and attracts smart guys because it is a very fashionable subject. The only way to put an end to this fashion before it eventually dies out is to take a swim in the swampland and falsify it. Sort of a catch22…

  10. Peter Woit says:


    For the reasons I mentioned, I just don’t think the “swampland” has anything to do with actually falsifying string theory. If it did, maybe I would work on it… The string theory backgrounds people have most closely investigated are the ones that look most like the standard model, there are all sorts of these and absolutely no argument I am aware of that suggests the possibility of ruling out the standard model as a low energy effective theory for some string theory.

    I just don’t believe that we’re going to find a single specific background that matches the standard model (which would then predict other things). There are solid arguments that it is inherently impossible to even identify those backgrounds with the right CC, much less the right CC and everything else. If one figures out how to overcome this, it would have to be by being able to precisely figure out the implications of large classes of vacua at once. If one can do that, I don’t see why one won’t end up with a large number of vacua with the SM properties, not just one or a small number.

    In any case, given the current state of the theory, this kind of discussion is pretty much a theological one. I just don’t think one can deny that what is happening is a classic example of failure: simple models disagree with experiment, so you are forced to more complicated ones. These are designed to be so complicated that you can’t analyze them and confront them with experiment. Once this happens you are supposed to give up, not conduct philosophical arguments trying to justify continuing.

  11. Anon says:

    “You seem to expect me and others to drop what we are doing and go read this 44 page paper. Sorry, everything I heard about it indicates to me that my time would be better spent reading other papers.”

    And you complain that Clifford Johnson won’t read your book?

    “It’s not even the topic of this posting at all.”

    But you’ve devoted space in previous blog postings to trashing this paper that you haven’t read.

  12. Peter Woit says:


    Actually, I haven’t mentioned the Arkani-Hamed paper in any of my postings. You’re quite right that if I was writing a posting about it and not reading it, that would be reprehensible.

    What I have done is responded to various commenters here who have written in claiming that “Arkani-Hamed et. al. show that the SM has the same landscape problem as string theory” by telling them that, while I don’t know what is in the paper, that statement is obvious nonsense, and explained why. I’ve also asked them to back up what they were saying, telling me what the evidence for this claim was from the paper, but haven’t gotten an answer. Presumably this is because the paper doesn’t really make that claim.

    Again, there are lots of interesting things I don’t have time to learn about, so the properties of the SM compactified on very non-physical backgrounds just isn’t very high on the list.

    People write in here everyday with all sorts of claims based upon all sorts of misunderstandings, quoting lots of different papers. I’m not about to read them all, but will continue to point it out when people are spouting nonsense.

  13. Anon says:

    “while I don’t know what is in the paper, that statement is obvious nonsense, and explained why.”

    It seems to me that MikeC has both read and understood the paper.

    Aren’t you on pretty thin ice calling his account of what’s in it “sophistry” ? Especially, since it mirrors what previous commenters have said and which you have previously called “nonsense.”

  14. Tim says:


    You quot a reporter from the event:

    “The trouble with physics, Duff began, is with people like Smolin…”

    This posting of yours demonstrates very well that you are no different than the bad journalists and popular science reporters that you often complain about. This whole blog is full of misquotations and misinterpretation like the one above just as there are loads of misquotation and misinterpretation in bad populer science papers. I hope this will convince you and the audience here that what you are doing is not science but bad popular scientific journalism.

    If you would have cared to check your facts — indeed a minimal requirement for any journalist — you would have found that what Michael Duff has said is the following:

    “The trouble with physics, ladies and gentlemen, is that there is not one Lee Smolin but two.”

    Michael Duff went on explaining that the speaker before him — Lee Smolin — presented arguments which are perfectly fine and one can only agree with them. On the other hand his book is not of this nature but has rather many inaccuracies and went on explaining what he disliked in the book. Hence his opening sentence “there is not one Lee Smolin but two”, which in the light of true facts becomes something completely different than what you quoted in your posting. The mp3 audio from the event is available to everyone including good and bad popular science writers but of course only the good ones will take the initiative to actually check it.

    Here it is: and it was avaiable at the time of your posting.

    Now I’m sure you will be ready to explain us all that your blog consists of hundreds of postings and so few have misquotations and misinterpretations such as the one above so everything is okay. Just the same argument any journalist or popular science magazine would pull when confronted with lies and distortion in their magazines “oooh, we have been publishing thousands of articles in the last 20 years and it’s actually a proof of our high standards that only a couple of articles are completely false” and of course they would not be discomfortable with pulling the same argument over and over again and no matter how many times they are caught they would still continue to publish their magazine because that is what they live on.

    The same behaviour that one can observe in the attitude of corrupt politicians. Although they might know they are not telling the truth and they know that they will continue to be distorting events but they have no other choice because that is what they live on and they are not couregous to say “okay, I’ve been caught too many times, it’s time to stop and actually look for a real job”.

    Best regards,

  15. Tim says:

    Oh, and I forgot the always winning argument “some of my opponents were telling bigger lies than me so why should I resign?”


  16. Chris Oakley says:

    “The trouble with physics, ladies and gentlemen, is that there is not one Lee Smolin but two.”

    Or there could be just one Lee Smolin, the illusion of two being a result of lensing by galactic-scale superstrings.

  17. Peter Woit says:


    What I put in quotes is not a misquotation. It is an explicit quote from the report by someone who was there that I linked to. It does not purport to be a direct quote of what Duff said. It is a direct quote of how that person chose to characterize what Duff said. It reflects precisely how that person interpreted what he was hearing Duff say.

    If you can point to a legitimate misquotation, even one, anywhere in the thousands of pages I’ve written here, please do so. Otherwise you should not make the kinds of accusations you are making. The one you mention was completely accurate, and included reference to the source it came from, so people could determine for themselves its reliability. Sure, they can also listen to the audio file, which I also linked to, and judge for themselves whether that report was accurate.

  18. Peter Woit says:


    For about the 10th time, what I called sophistry is the claim that “the SM has the same landscape problem as string theory”. I explained repeatedly here and elsewhere why that claim is sophistry and nonsense.

  19. Tim says:


    I think we are getting into a problem in linguistics. The statement “your posting contains a misquotation and is hence misleading” holds. I did not say that you quote someone inaccurately, indeed, you quote the bad reporter accurately. The bad reporter on the other hand does misquote Michael Duff and hence your posting does contain a misquotation.

    A good journalist certainly does not want to quote people saying misleading statements without clarifying that the person just quoted was indeed saying something misleading because if he did so he would himself be misleading his audience.

    This is just what has happen in your case, you uncritically have taken over a quotation from someone that is very misleading and even insulting to a third person. You did not research the subject of your post although you have known full well that the quotation you quote will put a third person into an embarrassing light.

    It is indeed the duty of every good journalist to give an impartial view, give the chance to anyone attacked by any of his quoted respondents to defend him/herself and check whether his sources are accurate or not. Failure to do so due to the fact that the respondents and other sources of his article are supportive of his preconception results in poor, biased, partial and activism oriented journalism something that is very far from a professional stand point.

    In simple terms: repeating a lie (although accurately giving the source) without actually checking it and commenting on its untruefulness is called: propagating lies.


  20. Anon says:

    “For about the 10th time, what I called sophistry is…”

    You accused MikeC of engaging in “sophistry” when all he has done is (accurately) recount what is in Arkani-Hamed et al’s paper.

    That’s pretty much the same thing as accusing Arkani-Hamed et al of engaging in “sophistry.”

    But you’d never do that … because you haven’t read their paper. Right?

  21. Q says:

    ‘In simple terms: repeating a lie (although accurately giving the source) without actually checking it and commenting on its untruefulness is called: propagating lies.’ – Tim,

    Tim, you’ve just contradicted yourself. You earlier stated that you want Peter’s quote to be corrected to Duff’s lying claim to the effect there are two Lee Smolins!

    If you want quotes to not include lies, then it would be impossible to quote much said by some defenders of string theory.

    For example, is the following quote a lie, because string theory predicts unobserved gravitons (instead of really predicting real gravity):

    ‘String theory has the remarkable property of predicting gravity.’ – Dr Edward Witten, M-theory originator, Physics Today, April 1996.

    Should I ‘correct’ Witten’s remark when I quote it, so I’m not propagating lies myself. Say to something like:

    ‘String theory has the stupid property of predicting unseen gravitons and nothing checkable about gravity.’ – Dr Edward Witten, M-theory originator, Physics Today, April 1996.

    Would that make things nice and accurate in your view? 😉

  22. Tim says:


    Thank you for taking time to respond. No, that would not be accurate. The following would, if I suppose that you think that the quote from Witten is wrong:

    ” ‘String theory has the remarkable property of predicting gravity.’ – the above quote is from Dr Edward Witten, M-theory originator and has appeared in Physics Today, April 1996. I don’t agree with Dr Witten’s opinion for this and this reason.”

    In order for everyone to understand, the professional way for Peter to write his posting would have been this:

    According to the report from one attendee, after Smolin started things out by arguing his case:

    Smolin sat down. Duff stood up. It got nasty.

    The trouble with physics, Duff began, is with people like Smolin…

    Now it turns out that I have checked what Duff said and the reported quoted is above is in fact lying, because Duff said

    “The trouble with physics, ladies and gentlemen, is that there is not one Lee Smolin but two.”

    My opinion is however that Duff is wrong in saying the above because of this and this reason.

    Is it clear now?

    If not let me give another example. I’m living in Germany so let’s imagine I hang posters all over Berlin with the following content “Jews are killing Christian babies – see: Protocols of the Elders of Zion”. Am I quoting accurately? Sure I am. Can people check the facts? Sure they can and they will find exactly what I am stating, namely that if they look up the Protocols of the Elders of Zion, they will find the quote I chose to post. Am I propagating lies? Sure I am. Is it impossible to quote from the Protocols of the Elders of Zion? Sure it isn’t, all I need to do is make clear that it is a forgery something along the lines: “Jews are killing Christian babies – as can be read in the well known forgery Protocols of the Elders of Zion which nobody takes seriously in a civilized country”

    I’m going to so much detail because I still believe that people like Peter can be convinced to change track and do somthing useful for the physics community instead of propagating lies and becoming irrelavant laughing stocks.


  23. Peter Woit says:

    Anon (and why is it that all you guys are anonymous, anyway?)

    For about the 11th time, the claim that “the SM has the same landscape problem as string theory” is sophistry, see earlier iterations for the explanation why. It’s sophistry whoever is making it, but the ones I know about are the ones writing in anonymously to my blog.


    In the quote I repeated, Duff’s words are not in quotes and it is pretty clear that the person who wrote it is not giving a transcription of what Duff actually said, but the impression it left him with. He makes clear that is what he is reporting, and he explains why. Listening to what actually happened I think one can understand why this person had that impression of Duff’s remarks.

    I’m extremely careful in what I quote here. If something is in italics or quotation marks, it is an accurate quote from a source that has been indicated, and I have taken trouble to make sure that it is accurate and not taken out of context. In this case, what I wrote starts with “According to..”, and explicitly gives the source. Everything I wrote is completely accurate.

    On the other hand, you choose to make the accusation “This whole blog is full of misquotations and misinterpretation” and are not able to give any evidence of this. I think you have no evidence for this, and for you to make that kind of accusation is dishonest.

  24. The man says:


    You often mention that *most* string theorists are reasonable and the type of string theory partisans that (often anonymously) post here are a strong minority.

    After seeing the sampling of anonymous posts here, and at Clifford’s, I’m beginning to doubt that. Where’s the evidence the most string theorists don’t behave like this?

  25. Anon says:

    “For about the 11th time, the claim that ‘the SM has the same landscape problem as string theory’ is sophistry,…”

    Nowhere in his comments here does MikeC use the phrase “landscape problem.” Nor does the phrase appear anywhere in Arkani Hamed et al’s paper.

    And yet you accused MikeC of engaging in sophistry.

    As far as I can tell, he has given an accurate rendition of what’s in the paper. So, if anything, you are accusing Arkani Hamed et al of sophistry.

    Which might be OK if you had read their paper.

  26. Aaron Bergman says:

    At the risk of being annoyingly socratic, let’s say that there was susy at 100 TeV. Would you say that this ameliorates the fine tuning in the Higgs mass?

  27. Mike C. says:

    I’m a little disappointed. I visited this blog, and saw that there was a mention of the landscape in the original blog posting. I was curious if the folks here had seen the recent work showing that the Standard Model has a landscape of a very similar form to that found in string theory, consisting of a continuum of lower-dimensional vacua. I pointed out a recent paper on the subject, which demonstrated the existence of these physically inequivalent vacua, and showed that they are perfectly acceptable solutions to the Standard Model + gravity with interpolations to our 3+1 dimensional vacuum. The paper also had the upshot of showing that any theory that contains the Standard Model must contain this landscape of 2+1 dimensional vacua, since their existence depends only on low-energy physics, and in particular, any theory containing the Standard Model has a landscape, by definition of what the word landscape means.

    Instead Peter has repeatedly called me a “sophist” and people have told me that they can’t be bothered even to look at the paper and clearly aren’t even reading my posts. Well, fine. Perhaps I’m a sophist. But Peter, you’re a dick.

    I’ve got better things to do with my time too. Perhaps one day you guys will stop just for a moment and question your assumptions and prejudices. More likely, you’re too confident in your ideology. I feel sorry for you.


  28. Jean-Paul says:

    I looked at the paper on 2+1 landscape. It deals with another nonsense extension of SM. Nonsense in, nonsense out.

  29. woit says:


    Maybe it’s just late at night, but I can’t even tell what point you are trying to make, or how what you are asking is responsive to my last comment here (is it?). I think it has been quite a few iterations since any substantive new point was made by either of us.


    I spent a lot of time trying to have a discussion with you, involving 13 comments here by you on my blog. You completely refused to address the points I made in response to you or answer the questions I asked you about the argument you were making, instead just endlessly repeating yourself and insulting me.

    The Man,

    On days like this, I must say that it becomes hard to maintain the point of view that most string theorists are reasonable. I still choose to believe that there’s a silent majority out there, and the anonymous commenters don’t reflect the behavior of most string theorists. My experience dealing personally with string theorists is very different. Only on very rare occasions have I run into unreasonable behavior in personal interaction. Anonymous blog comments unfortunately I think encourage this. You can behave like a complete jerk at no personal cost to yourself or your reputation by hiding behind anonymity. That’s why people generally choose to do this.

  30. Aaron Bergman says:

    I’m just trying to understand how your philosophy applies to the case of another fine-tuned parameter.

  31. a says:

    dear Mike C., I read the section about “The SM landscape” and I confirm that the landscape exists only in the title: what they find is one 2+1d vacuum with one light scalar. A honest landscape is much bigger.

  32. Peter Woit says:


    It seems to me you keep ignoring the point I’m making (you don’t have to agree with it, you just have to acknowledge that it’s there), and trying to discuss something else.

    As for the hierarchy problem, it’s different, but the existence of a physically measureable 100 Gev or so SSYM breaking scale is also relevant. In the hierarchy case it’s a feature (you’re trying to use supersymmetry to explain why the Higgs is around 100 GeV), in the CC case it’s a bug because it’s the wrong scale.

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