More Hype On Its Way

The latest trend among prominent theorists seems to be the writing of popular books hyping the unsuccessful speculative ideas they have been working on. Two new examples of this have been pointed out by Lubos Motl over at sci.physics.strings.

Both of these books are due to appear at the beginning of next May. One, by Leonard Susskind of Stanford, is entitled An Introduction To Black Holes, Information And The String Theory Revolution: The Holographic Universe. The second, by Lisa Randall of Harvard is called Warped Passages : Unraveling the Mysteries of the Universe’s Hidden Dimensions.

Randall’s book presumably is not so much about string theory as about the idea that we live on a brane inside a higher dimensional space. As far as I can tell, there’s even less evidence for this idea than there is for string theory itself. I don’t know exactly what her attitude about string theory is, but at a public debate at the Museum of Natural History here in New York a few years ago, I remember that she scornfully dismissed the argument that string theory predicts gravity, saying something like “Yeah, it predicts ten-dimensional gravity.”

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44 Responses to More Hype On Its Way

  1. Chris Oakley says:

    Steven Hawking has already achieved notoriety as a gangsta rapper. As for Lubos’s band, if he changes the name of his newsgroup to alt.religion.strings instead of sci.physics.strings then I don’t mind playing the Sax for him (I’m a bit rusty, but I could brush up).

  2. Anonymous says:

    The physics community has spent the past half century or so basically living off the glory of having created the atomic bomb. A few farsighted physicists have recognized that this will not last forever and that physicist will have to find a new way to market themselves to the public: as entertainers! Steven Hawking’s greatest contribution to physics is in pioneering this transition. Susskind and Randall are the latest to hop on the bandwagon and show great promise for creating appealing public personaes. Lubos is well positioned to follow in their footsteps provided he develop some distinctive peronality “hook” that will resonate with the public. Perhaps he could take up dueling or wear an eye patch, or start a rock band with some Harvard postdocs.

  3. wino says:

    “Sorry that post came out pompous sounding. I just mean that folks don’t need to be “protected” from popularizations of speculative physics.”

    It is not a question of “protection” of the lay public from “speculative physics”; it is a matter of clearly distinguishing between speculative physics and physics. There are lots of beautiful ideas, which turn out not to have anything to do with reality; they are not physics.

    When one throws about about grandiose terms like the “Theory of Everything”, the impression is that it fully describes and explains the world in detail; no hint of speculation here. This is very different from say, electrodynamics, or the standard model, which are in some sense correct in a very detailed sense (precision measurements), (though that does not necessarily mean they explain all of condensed matter physics, biology or chemistry in detail, as practitioners in those fields will argue).

    Of course, I must reserve judgement on the books until I have read them. But the track record in recent times of what appears in popular science magazines (like Scientific American) about such subjects does not inspire much confidence.

  4. D R Lunsford says:

    Steve – once we had George Gamow. Now, we don’t.


  5. Steve Esser says:

    Sorry that post came out pompous sounding. I just mean that folks don’t need to be “protected” from popularizations of speculative physics.

  6. D R Lunsford says:

    C’mon Lubos. surely you know some good old time Bohemian insults! I feel like I just got flamed by Eddie Haskell.


  7. Steve Esser says:

    Gentlemen: let me defend the educated layperson’s ability to read popular accounts of developments in physics and draw reasonable conclusions about what is going on in the field. Greene’s books, for example, were clearly and I think honestly written — such that despite his admirable enthusiasm one could come the conclusion that the last 10 years of string/M-theory has been somewhat of a disappointment relative to previous high expectations.
    Here’s hoping talented physicists of all stripes endeavor to write good books for the lay audience.
    Regards, – Steve

  8. Lubos Motl says:

    Dear DRL, I am not surprised that your co-workers think that you don’t enjoy mental health. In fact, I agree with them. I hope that they will call a doctor to save you. 😉

  9. D R Lunsford says:

    Peter –

    Thanks a lot, I have coffee dribbling from my nose…

    “String theory is mathematical science fiction” – my coworkers are all wondering what I’m laughing about…the best comment of the decade to date…


  10. Thomas Larsson says:

    Lubos, a couple of days ago you frankly asserted that SUSY will be seen, and that I would have to stay in the restroom for the rest of my life. Evidently you get cold feet as soon as somebody calls your bluff. Oh well, its your credibility…

  11. Lubos Motl says:

    Thomas, certainly not.

    If we see supersymmetry, it will be a good circumstantial evidence that we are on the right track. It won’t really prove string theory – one can really think about SUSY independently of string theory; it will just increase the value of string theory’s stocks.

    If the LHC does not see supersymmetry, it will be a discouraging news, but it certainly won’t prove that string theory is wrong. First of all, SUSY can be broken at slightly (or much) higher energies than the LHC scale. Second of all, it is an open question whether there exists inherently non-supersymmetric backgrounds in string theory. The only fact is that SUSY is important for us to have a mathematical control over what happens in string theory.

    Moreover, it is still possible that the LHC will not see SUSY, but it will nevertheless PROVE string theory – by seeing the excited strings, and/or various detailed phenomena related to extra dimensions. Of course, an excited string mode is a more typically stringy phenomenon than SUSY itself.

  12. Thomas Larsson says:


    Would you state for the record that the discovery of superpartners, or not, is a lithmus test for string theory? If sparticles are discovered string theory is probably on the right track, but if no sparticle is found within five years after the LHC is commissioned, then string theory has been disproven?

    For the past 20 years, Witten has repeatedly stated that string theory makes one postdiction, gravity, and one prediction, supersymmetry. Are you willing to stand up and proclaim that if Witten’s single prediction fails at the LHC, then string theory has failed?

  13. wino says:

    I think the books that are being talked about here are not science fiction, they belong to the category of “scientific fiction” 🙂

    What the string theorists (posting here, and in general) do not understand/realize is that they are ultimately going to cause great damage to the public perception of what physicists/scientists do (non-string theorists, in particular) and what physics/science is all about. By lowering the bar on what constitutes “physics” to such an extent that it is not terribly important to do things testable in the foreseeable future, is to do great disservice to the testable theoretical work (verified and falsified) done in so many sub-fields. Forget Peter Woit, a layman (taxpayer) will ultimately wonder if there is any difference between string theory and theology. I know it is an unfair comparison, but it will be an increasingly harder case to make as the great claims being routinely made cannot be proven. By peddling “sexy” stuff, of course book sales will be good, but this will be at a cost in the future: damage to credibility of science. Then, we physicists will be under siege, not unlike the biologists these days.

    I have not seen the books, but I suspect they will
    convey the impression that these are verified and tested ideas and gloss over (or even mention) the obvious problems, such as the wide variety of outcomes from “unique string theory”. Even if they sell it as a really good piece of mathematical physics, it will be alright. But no, I suspect, it will be the pretentious and condescending “Theory of Everything”, the “final word” with “a few details” left to be worked out. This is in sharp contrast with popular books on QED or GSW model, or even pure mathematics (Wiles) which are much more intellectually honest.

  14. Lubo Motl says:

    Thomas Larsson, I have not read Lenny’s book, so how can I criticize it? This would probably be your approach to criticize books that you have not read. Anything that is connected – at least by some vague link (like the name of the author) – with string theory immediately becomes a target of your criticism, even though you have no idea what it actually is.

    This is the stupid, blinded, fundamentalist way to judge the world around – it is your way, Thomas and Peter. Sorry, but we’re at a slightly different level. I apologize, but this way of approaching reality is one of the main reasons why the two of you are viewed as morons and your opinions do not have much value.

    I suppose that Lenny will also write about the landscape, but my assumption is still that it will be mainly a book about holography and string theory and such, and because I know Lenny, I expect this book to be a good book. But I just can’t tell you before I see it, do you understand this point???

  15. Lubo Motl says:

    Chris Oakley, you misunderstood the identity of different people on this board. Peter Woit has been criticized by non-string-theoretical particle physicists, such as Matt, as well as by string theorists.

    It’s just the stupid belief of these hard core Woit believers that Peter Woit knows what he’s talking about. He has no idea where string theory is and what it is, but he also has no idea about current particle physics and its real tasks for the future.

    Peter Woit does not really understand the hierarchy problem, which is pretty bad for a person who tries to write something about particle physics.

  16. Lubo Motl says:

    I have not answered these things – right now I’m on a modem. 😉

    Sorry, glueless, but your basic assumptions and understanding of the meaning of popular books is absolutely wrong.

    Popular books must ALWAYS be focused on the current cutting edge research and the future, otherwise they can’t really be popular and virtually no one will read them.

    You are also absolutely confused if you call the material of Brian Greene’s book “fringe science”. Fringe science means something absolutely different. Brian Greene describes the *mainstream* science, and it is just your personal problem if you have not been able to understand that string theory is mainstream.

    Other people raised a lot of totally ridiculous points that people are only writing popular books when their best years are over. Of course that some people can only afford to write a book that will be popular *after* they become famous, but it by no means implies that they cannot make other important discoveries in the future.

    I find your criticisms to be a complete misunderstanding of the role of science, its popularization, the interests of the readers, and the books themselves – and it seems as a waste of time (and cents for modem) 😉 to reply. It’s pretty clear that an average person with some common sense understands what drives the books and what’s important much better than you do – so try to ask average people on the street if you want to have at least a glimpse of an idea.


  17. JC says:

    My impression is that this place seems to resemble a “mob of kangaroos”, with very little order and a very fleeting loyalty of any sort. It resembles less like a cult with a “high priest” as its leader.

    If this was a political party of some sort, it would confirm the idea that “loyalty” cannot be “bought” but can only be “rented out” temporarily. (In a metaphorical sense, that is).

  18. Chris Oakley says:

    There are a number of posts earlier by String theorists attacking Peter’s real or perceived views on what needs to be done next in particle physics phenomenology. I feel that these miss the point. Any one of you could give your views on any subject at all, and anyone else could pick holes in it. This is part of the whole process. The thing that Peter is objecting to, and the reason for the title of the blog, supported by his so-called “loyal following” (which I am afraid, apart from agreement on the one issue, is in practise not likely to be much more loyal than a herd of cats) is the way in which the devotees of one highly speculative approach seem to have hi-jacked the subject, thereby, given the limited resources available overall, all but silencing new proposals that do not fall within the String theory umbrella. These critcisms are long overdue.

  19. Peter says:

    John Horgan has a nice description of string theory and the like as “science fiction in mathematical form”. Personally I have nothing against smoking dope, watching Star Trek and thinking about how cool all the multiple universes and extra dimensions are. But the reason I went into physics was that it was science, not science fiction.

    If people want to write books about things they think are cool, but not likely to be right, they should acknowledge that they are writing science fiction, not science. Right now, I think more and more people can’t tell the difference.

  20. Aaron says:

    Well, I disagree about the desert of books between Feynman and the present. There are plenty of books devoted to general relativity, cosmology and the standard model.

    You’d like books on TQFT, condensed matter and CFT, I see. Good luck selling those books. Hell, if anyone could write a popular book about TQFT, I’d be impressed. It’s the sexy stuff that sells.

    And really, I don’t understand this word ‘hype’. People aren’t writing these books to get more funding or anything like that. Many scientists really do like to share what they’re working on with other people. Hell, when I had a blog once upon a time, I wrote a long post on faster than light travel in physics. Has that been ‘vetted’? Is it likely to be right? Of course not. But, it’s cool stuff, and I thought it would be fun to share it.

    So, are braneworlds likely to be right? No. But are they cool? Yes. Could they make a good book? Definitely.

    Lighten up. Physics is supposed to be fun. People being excited about their work is a good thing.

  21. Bob McNees says:

    The notion that “Writing popular books is something physicists usually do when their most productive years are behind them” is absurd. There are a lot of very active scientists who, like Aaron points out, are excited about sharing the ideas they are working on. For the most part our work is supported by government agencies like the NSF or DOE. So the public thinks that fundamental science is a worthwhile endeavor and they’re willing to fund it. Some of us are grateful for that, and we’d like to explain what it is we’ve been doing.

    Also, I’d like to see you tell Lenny that his good years are behind him.

  22. glueless says:

    Lubos and Aaron,

    You haven’t answered Peter’s seemingly
    obvious point, about the disproportionate
    number of books devoted to new-age physics
    written by current leading practitioners.
    To some extent this is a trend in all of
    academia (professors retaining literary
    agents hoping to cash in a la Schama or
    Norman Diamond), and the accelerated
    publication and funding cycles leading
    to excess hype.

    Here is an experiment you could try;
    certainly in the Boston area
    Lubos can check that the following is true:

    Go to a non-technical bookstore with a popular physics section. You will find that there are
    several books on material that is speculative,
    fringe, or simply unproven — written by current working theorists. e.g., Smolin on loop gravity,
    Greene on strings, Maguiejo on variable
    speed of light, and now the Susskind and Randall
    books. By contrast, there is LITTLE OR
    NOTHING available, let alone written by leaders
    in the field, about established but no less
    exciting subjects like the standard model, conformal field theory, quantum topology a la Atiyah and Witten, condensed matter theory,
    etc. The one such popularization I can remember is Lederman’s reminiscences published a few years ago. The math section had some books on knot
    theory that, in passing, mention TQFT, but that’s
    about it.

    There is a “big desert” of (non)publications
    between Feynman’s QED popularization, and
    the new-age books of Greene et al.

    It’s hardly a matter of self-appointed guardianship of the public or scientific morals.
    There is a general tendency to hype results
    (or theories without “results” in the
    ordinary sense of the word) before they
    are vetted in the traditional ways.

  23. Peter says:

    Hi Aaron,

    I think this is kind of repeating myself, but, no, I don’t think particle theorists should all be thinking about mathematical foundations and not trying to extend the standard model in some phenomenolgically useful way. The fact of the matter is that there isn’t much in the way of promising new ideas around, so people should do a wide range of different things, trying to come up with something new. But whatever they do, they should be honest with themselves and with others about the prospects for the ideas they are working on. Despite many years of work on large extra dimension scenarios, as far as I can tell there’s nothing even close to a compelling model of this kind and virtually no one I know of would be willing to bet any significant amount of money on the LHC turning up evidence for these scenarios.

  24. Anonymous says:

    Writing popular books is something physicists usually do when their most productive years are behind them. So I can understand Susskind, but Randall should still have a few good years left in her.

  25. Aaron says:

    Some people have proposed giving up on SUSY to solve the hierarchy problem and just using it to achieve unification of the couplings and maybe a dark matter candidates.

    Now, the motivation for this work was anthropic, but it’s important to say that it’s perfectly legitimate to consider it as a fine tuned model with definite predictions for what will happen at the LHC. I find the anthropic verbiage that accompanies a lot of this sort of work distasteful, but I don’t see why we shouldn’t look at fine tuned models that have experimental consequences.

    I share Matt’s astonishment that Peter would rather have the high energy physics community mucking around with the mathematical foundations of the standard model rather than trying to extend it in ways that have definite, observable consequences within the decade.

    As for writing of the books, if Peter wants to be the self-appointed guardian of the public interest, so be it, but might I suggest that maybe the reason people want to write books is that they are excited about their ideas and want to share them with the public?

    Well, that and money.

  26. D R Lunsford says:

    I have the perfect title:

    “Malice in Wonderland”

    “Being the story of a six-foot clueless scowl”

  27. JC says:


    Since you seem to like to write a lot, have you ever thought about writing a popular press book on string theory in the form of a personal autobiography?

  28. Thomas Larsson says:


    The experimental situation is often summarized as “Supersymmetry requires fine-tuning at the one percent level”. Has this any relevance to SUSY as a solution to the hierarchy problem?


    Earlier you have been quite critical about the Landscape and the Anthropic Principle. It seems like Susskind’s book is mainly about such ideas. Is there any reason why you promote it now?


    Another interesting energy scale is the cosmological constant (or CC^(1/4)) at about 10^(-3) eV, close to the estimated neutrino masses.

  29. Plato says:

    I wonder how they ever arrived at here? Maybe this is better?

  30. Peter says:

    Hi Lubos,

    The Planck mass is not necessarily the fundamental mass scale governing quantum gravitational effects. This is only true if you assume that whatever physics is producing the coefficient in front of the low energy effective Einstein Hilbert action is some combination of one particular mass scale and some dimensionless numbers of order one. The large extra dimensions scenarios evade this, and you can imagine otherways of evading it. For instance the dimensionless numbers that enter into the calculation of the effective low energy theory may be exponentially small. I wouldn’t be entirely surprised if the fundamental scale at which quantum gravity became relevant was a TeV, but I don’t find the large extra dimension scenarios very convincing (they’re kind of ugly and they don’t predict anything).

    Believe it or not, I had heard somewhere that fermion masses came from Yukawa couplings to the Higgs…. My point was that we know that these dimensionless numbers (ignoring issues about neutrino masses) range in values over many orders of magnitude: the ratio of the electron mass to the top quark mass is about 2 x 10^-6. Given the experimental fact that such small dimensionless numbers occur in the theory, I’m not sure why one should take seriously issues like the “little hierarchy” problem of the Higgs VEV being 40 times smaller than one might expect.

  31. Lubos Motl says:

    Your point 2 is even more ridiculous, Peter. Writing cheap articles “string theory is bad” for some of your idiotic readers is a profession that you mastered well, but particle physics is something very different, it seems.

    The little hierarchy problem is a small artifact of the hierarchy problem that survives even if we solve the usual hierarchy problem in one of the standard ways.

    But why do I say that your comment 2 is ridiculous? Because you’re treating different masses as “mass scales”. They may be mass scales, but according to the Standard Model or derived theories, they’re not “fundamental mass scales” in any way. The electron mass is small because the Yukawa coupling of the electron with Higgs is a small *dimensionless* number.

    You’ve probably never heard of it, but in the standard model the masses are not fundamental parameters – they arise as the product of the Higgs vev and the Yukawa couplings.

    It’s just a dimensionless parameter that is small – one that can be perhaps extracted from string theory in the future (the intersecting brane models have the most natural explanation of the exponential smallness of the Yukawa couplings). But the only real *dimensionful* parameter in these masses is the electroweak scale, i.e. the Higgs vev.

    The neutrino masses are a bit more subtle, and the see-saw mechanism relating their size to the GUT scale (where the electroweak scale is in the middle) is the most reasonable description of their smallness.

    3. I am amazed how you’re already scared – we would say in the Czech Republic that you’ve been shitting to your pants 😉 – by the two new popular books. You have not even seen them yet, but you already know that they’re overhyped bad books. I think that all these morons who take your opinions about physics seriously must be incredibly stupid indeed because you are telling them quite explicitly that your opinions have nothing to do with reality – you judge books that you have not seen at all (not even the table of contents), and you are not even trying to hide it.

    The people are promoting extra dimensions, supersymmetry, and holography because they are the dominant ideas in the current research and the people interested in fundamental physics should know about it. If there were other major important ideas for particle physics beyond the Standard Model, ones unrelated to string theory, people would write about them in their books, too.

  32. Matt Reece says:

    By the way, I also will try to address your comments more later, but don’t have time at the moment. Just thought that a clear statement of the little hierarchy would help clarify that discussion.

  33. Lubos Motl says:

    Peter, note that almost every time the discussion becomes a little bit technical and concrete – and not just your permanent complaints “string theory is so evil, evil, evil” – your comments start to be a bit ridiculous.

    What does it mean “I don’t believe the hierarchy problem should be treated seriously?” You don’t need to have grand unification to realize that there’s something like the hierarchy problem. You can also work with the Planck scale.

    It’s the very logic of effective quantum field theory that it’s valid up to some energy scale, but not higher. If we want to say that a field theory is valid even at higher energies, we must explain how its parameters are protected.

    In the conventional quantum field theory approaches, the electroweak scale simply can’t be the ultimate fundamental scale of Nature because this would mean that physics of QFT breaks down here and we have nothing to replace it with.

    Even in the most low-energy gravity scenarios of string theory, we want to describe the accelerator physics with an effective field theory.

    The fundamental scale where notions of geometry break down is the Planck scale. You can just calculate where the quantum corrections to gravity become of order 1 – and you will get the Planck scale, which is about 10^19 GeV. You don’t need to assume anything special about supersymmetry or unification – the question “where gravity gets strongly coupled” is a totally meaningful basic question, and it has the usual answer “the Planck scale”.

    The extra large dimensions scenarios are those in which gravity gets strongly coupled earlier or much earlier – i.e. at lower energy scales. But at any rate, there is a huge numerical ratio between the Planck scale and the electroweak scale, and this ratio must agree with whatever scientific theory you use, and it is a nontrivial constraint especially for natural theories.

    A solution of the hierarchy problem is the same thing as understanding some details behind the electroweak symmetry breaking – you don’t seem to appreciate that it is the same thing. Right, in the Standard Model we don’t understand at least something about the electroweak breaking, e.g. why the Higgs (if it’s elementary) remains light, and this is why we study the hierarchy problem.

    It is impossible for a physicist to present no solution of the hierarchy problem, and simultaneously say that it is not a problem. It’s only possible for an anti-physics terrorist, not for a scientist. 😉

  34. Matt Reece says:

    You say:

    “I’m not so sure either that there’s a “little hierachy” problem either. We’ve got mass scales of all sorts going from neutrino masses to a wide range of lepton and quark masses, and also the strong interaction scale and the electroweak symmetry breaking scale. It’s not clear to me that the way to think about any of this is that there is one underlying scale and then try to understand why some things occur at much lower mass.”

    I don’t see how you address the little hierarchy here. Simply stated, these are known facts:

    – the Higgs vev is 246 GeV, setting the electroweak symmetry breaking scale.
    – precision measurements of electroweak observables or four-fermion couplings generally put the scale of new physics at > 5 – 15 TeV.

    Taking an effective field theory viewpoint, one must write down all operators allowed by symmetries, and the coefficients of these determine the energy scales at which new physics must enter. *Even restricting to operators consistent with SM symmetries*, experiments suggest they are suppressed by scales of 5 – 10 TeV.

    I don’t see how one can avoid the conclusion that either there is finely tuned physics associated with EWSB, or there is some mechanism that stabilizes the Higgs mass enough to solve this “little hierarchy.” (Granted, the fine tuning implied here is *much* less than that implied by assuming a GUT, but it’s there, and the experimental evidence here is much stronger.)

  35. Peter says:

    Hi Matt,

    Unfortunately I only have a few moments to respond to what you wrote right now, sorry, it deserves more. A few quick comments:

    1. You’re right, I don’t believe the “hierarchy” problem should be taken as seriously as it is, not until we have better evidence for the existence of a GUT scale. The significance of the radiative instability of the Higgs mass is highly unclear, it is just one of many indications that we don’t really understand electroweak symmetry breaking.

    2. I’m not so sure either that there’s a “little hierachy” problem either. We’ve got mass scales of all sorts going from neutrino masses to a wide range of lepton and quark masses, and also the strong interaction scale and the electroweak symmetry breaking scale. It’s not clear to me that the way to think about any of this is that there is one underlying scale and then try to understand why some things occur at much lower mass.

    3. My comment about extra dimensions was in the context of the news that Lisa Randall has written a popular book on the subject. I agree that some of the things you mention may be worth investigation by someone, but that doesn’t mean anybody should be writing a book for a popular audience about how great these ideas are. The popular literature on string theory is virtually uniformly full of highly overhyped and misleadingly optimistic portrayals of string theory. I think these do a huge disservice to real progress in physics, and the Susskind and Randall books sound to me like they will be more of the same. Physicists have got to get a lot more honest with the public and with themselves about what the prospects are for most of the ideas they are working on. People who want to should go ahead and study complicated, ugly models involving supersymmetry, extra dimensions or whatever. They may very well end up learning something important that will give insight into the electroweak symmetry breaking problem. But they shouldn’t promote this work to the public until they have something a lot more convincing and solid than what they’ve got now.

  36. Matt Reece says:

    I should clarify that I don’t mean to say that the original Randall-Sundrum model is very much like technicolor, but some RS-type models are. But the original RS model still does involve coupling the SM to some CFT. The 4D way of thinking about generating these exponential hierarchies is through some large anomalous dimensions. Some of Matt Strassler’s papers along these lines are interesting. I really think that Randall-Sundrum models and AdS/CFT are very powerful tools for studying field theory.

    (The canonical reference for anyone who wants to start to read about some of this is probably the paper “Holography and Phenomenology” by Nima Arkani-Hamed, Massimo Porrati, and Lisa Randall, hep-th/0012148.)

  37. Matt Reece says:


    Now, if you ask most of the people who work on extra dimensions in particle physics whether they believe there’s good evidence for whatever model they’re working on, they will say no, of course not. We don’t believe that we can construct the *right* theory of physics up to 10 TeV or so at the moment, but when the LHC turns on we’ll start getting all sorts of evidence pointing toward that theory. Either we can do nothing in the meantime, or we can try to start understanding the space of possible answers. And extra-dimensional theories are powerful tools for building new *effective* field theories valid up to several TeV. It’s up to you whether you take the five-dimensional character seriously, but it gives us an alternative weakly coupled description where we can calculate things that are not calculable in the four-dimensional description. Extra dimensional thinking has also led to the idea of “deconstruction,” which is another useful tool for studying four-dimensional field theories.

    While I would expect some of your blog’s readers to object to the idea of building effective field theories valid up to some energy scale, since many of them seem not to believe in renormalization, I would think you understand field theory well enough to know that this is a sensible approach. Instead you seem to want to critique both the top-down approach of string theory *and* the bottom-up approach of particle theory. That doesn’t leave much.

    I really think you misunderstand the attitude of many of us who study various sorts of theories. Even if our universe is not supersymmetric, or does not have large extra dimensions, that doesn’t make studying these models worthless. In the past five years alone I think our appreciation of possible physics we could see at the LHC has grown vastly. People will be a lot more cautious about calling interesting events SUSY now, I think, because we realize that there are other realistic models, like little Higgs models or extra-dimensional models, that can give you the same sorts of results.

    One can make this sort of argument not just for extra-dimensional theories but for SUSY as well. Even if there is no SUSY at low energies, you can’t dismiss work like Seiberg’s discovery of dualities between different SUSY QCD theories. This is important stuff about the qualitative behavior of field theories, which we don’t understand well at all. The non-SUSY case is just really hard, though, while SUSY gives powerful constraints that make things easier to study.

    I think at this point many of us working in particle theory take a pragmatic view. There are many possibilities for what can happen beyond the TeV scale, and sitting around thinking hard about what we already know just isn’t enough to tell us what they are. Only experiment will settle that. But we want to get some idea of the possibilities, and this is what we’re doing, with any tool we can find. Some of the models are ugly, some are implausible, but from an *effective field theory* point of view what we’re really doing is looking at the different sorts of completions of the Standard Model up to the scale of several TeV that can alleviate the problems in the SM (like the hierarchy problem).

    I have some sympathy for your viewpoint that the mathematical structure of the SM is interesting. I like geometry. If I weren’t doing physics, I would probably be doing geometry or topology of some sort. But I don’t think that thinking about these issues is going to be especially helpful for understanding particle physics at the TeV scale. (How do you see the hierarchy problem geometrically? It’s inherently quantum, not classical. If you have a nice geometric version of it, great, I’d love to hear it, but I’m doubtful.) I think most particle theorists are taking a very pragmatic approach that will hopefully give us all the insights we need to start interpreting the LHC data when it turns on.

    In short, I don’t think your attacks on the state of particle theory are justified, and I wish you would at least get a better sense of what’s going on and what the attitudes of particle theorists are before you start caricaturing us as being convinced that extra dimensions will be discovered at the LHC, or some such nonsense.


  38. Matt Reece says:


    I find this post a little ridiculous. In the past you’ve said (something like) that you think that electroweak symmetry breaking is the central problem in particle physics today. Well, many of us who are working in particle theory agree with you. And I expect Lisa Randall is one of them.

    You say about “the idea that we live on a brane inside a higher dimensional space” that “there’s even less evidence for this idea than there is for string theory itself.” I think this indicates that you’re missing the point, and further that you’re rather out of touch with the particle physics community.

    Do you agree that there is a hierarchy problem? OK, so you’re skeptical of GUTs. Fair enough. But there is certainly at least a little hierarchy problem. There’s good *experimental evidence* for this. The Higgs mass is radiatively unstable, so either you must accept the distasteful idea that it is finely-tuned (some phenomenologists have been thinking along those lines) or you must start looking for explanations of the little hierarchy. One of the simplest is supersymmetry, but you don’t like this idea. OK, again, fair enough, it involves predicting a plethora of new phenomena we haven’t seen yet.

    So, what are other ways of solving the hierarchy problem? One of the oldest ones (going back to Susskind and Weinberg in 1979, although some people had thought along these lines before) is that it is dynamically broken through technicolor. Unfortunately it’s very hard to build a model of technicolor without lots of difficulty satisfying electroweak precision measurements, or flavor problems.

    Lisa Randall and Raman Sundrum gave us a very nice alternative solution to the hierarchy problem, namely that it comes from warped space. But, because of Maldacena’s AdS/CFT duality (which again, you’ve admitted is one of the most compelling reasons to study string theory), this is really just another type of technicolor! Again there are difficulties with electroweak precision measurements and flavor, but they take on a different character in the 5d picture, and some of us are thinking about both how to solve them and how they relate to older technicolor ideas.

    [let me break this off here and continue in another]

  39. Peter says:

    Hi Lubos,

    I think the Billy Cottrell story deserves more prominent display, so I’ll post something in a minute about it. Thanks for pointing it out!

  40. Lubos Motl says:

    You know, Lisa’s book has a lot about string theory, too – especially D-branes and their history, relations to p-branes, and so forth.

    Sure, I will ask her what she exactly thinks about string theory’s prediction of gravity.

    Incidentally, Peter, string theory was proved to be physics in the courthouse – a trial about SUVs ;-), read,1413,206~22097~2541722,00.html

    I think that it’s OK to promote idas, even those not well-established ones, as long as you honestly say that they’re not proved, and as long as you describe honestly how much your viewpoint is shared by other scientists.

    Such books are written in the people interested in physics – which does not just mean the boring proved physics from the textbooks, but also the current cutting-edge and future physics!

  41. Peter says:

    Hi Lubos,

    Thanks for the more detailed description of Randall’s book. But I still think there is something wrong with writing books for a popular audience promoting speculative ideas for which there is no experimental evidence.

    I don’t think I misinterpreted what she had to say about the “string theory predicts gravity” argument, but she’s your colleague, so perhaps you could ask her yourself and report back.

  42. plato says:


    To remain dimensionally connected, it should be Line Hook and Sinker? Hopefully my blog will update by the time one looks, as a title should appear when being looked at, as such.

    Sorry Lubos for following your posts, it just seems that when I am ready I find you had already done so.

    The Comments about Lisa Randall seemed to say the same thing to me.

    What exactly is the hierarchy problem? was a legitmate question?

  43. Lubos Motl says:

    Lisa Randall is a phenomenologist, the most cited high energy physicist in the last 5 years, and a string-theory-friendly phenomenologist.

    I don’t think that the sentence “Yes, string theory predicts ten-dimensional gravity” was her dismissal of string theory’s predictions of the low-energy spectrum. You might have misunderstood her answer.

    Her book is very advanced and it covers all the things that the laymen interested in particle physics should know – the hierarchy problem and proposals to solve it, with the emphasis on supersymmetry and extra dimensions in particular.

    Of course, the book will be too difficult for your fans who always say “Yes Yes Mr. Woit” on your pages – like the moron signed “JC” before me. Don’t you think that something is wrong with the things you write, Peter, if you attract this type of people?

    I don’t know if the book will be an easy reading for yourself, Peter, but I am sure that her book is a must read for all non-professionals genuinely interested in particle physics – not just string theory – and in fact, it’s useful for professionals, too. It’s been useful for me.

    It’s a book that goes beyond all popular books on particle physics published so far – and it has many witty metaphors in it, too.

    I have not read Lenny’s book yet.

  44. JC says:

    Is this “advocacy” (via popular press books) a sign of desperation amongst gravity/string theorists? Or is there something deeper going on here?

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