You’ve possibly been following my efforts over here to discuss and explain the several weaknesses in Smolin’s and Woit’s arguments and positions, and why the current “string debate” is all an overblown (and media-fueled) fake controversy. (See for example the series of posts entitled “More Scenes From the Storm in a Teacup”, the last three especially, (links: I, II, III, IV, V, VI); use the search engine for other instances.)

I’ve no idea what the effect of these discussions has been. Woit recently said “my views haven’t changed at all”, and so has covered his ears and dug his heels in, while Smolin has written some sort of response on his website. I don’t hold out much hope for them, but I do hope that readers of these discussions can see that there’s been a fair amount of wool pulled over their eyes, to say the least.

What to do? What more to say? Whatever more I say, I cannot say it all any better than Joe Polchinski, a true master from whom we’ve all learned so much physics. Read his review in a guest post over on Cosmic Variance!


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30 Responses to Masterclass

  1. spyder says:

    What i still don’t fully understand are the underlying human factors involved. Professional jealousies, access to $$$, recognitions, acceptances–all these seem more or less to be involved in the stirring of the pointless debate; on the part of those who are not physicists per se–and some who are it seems?

  2. dark-matter says:

    For a fundamental physics theory of ‘everything’ that has been under intense development for almost 30 years, Joe Polchinski highly-considered response to Smolin & Woit is amazingly weak. Having so little results to brag about, it is a struggled technical defense. I find it amusing that he tried to defend the supposed criticism that string theory is not mathematically vigorous enough, when the criticism is exactly the opposite – too much math carrying the theory off to the deep end, the Landscape of Neverland. Nevertheless, it is so far the best defense for string theory from a recognized master. But as Woit implied, string theory needs only to present a single compelling and precise scientific prediction, even at near Planck scale (as long as the argument is sound), and the controversy will likely end. Such a response could be a one-liner, a link to the paper. Prof Polchinski did not. Instead, he basically plead for more patience. He offers no insight on what direction string theory should take, or what will likely be the next result or discovery. Is he stuck, like Witten?

    As for the sociology, one can do a test. Identify an unusually bright postdoc with an interest and completely open mind in theoretical HE physics. Give him/her $1M, and the opportunity to work at any of the top 30 universities or institutes in the world. But he/she must commit to work either on sting theory or any of the alternative theories of QG for 10 years. With the worry about income and institution removed, what will this person choose?

  3. Clifford says:

    The person will choose to work on the most promising avenues of investigation into the current problems that we wish to solve. The problem is that nobody seems to be offering the alternatives that Smolin and Woit seem to want these people to work on. Smolin and Woit certainly have not offered much. They’re busy on their campaigns to try to drag down the work of others rather than contributing something positve. When those promising alternatives come along, they will be worked on. Right now, the right way to do things is not for people to sit at the sidelines and snipe away at what is going on by writing misleading books about what they don’t like. People should get on board and do some research – like the rest of us are.

    It’s pretty simple really. And all been said several times before.


  4. a cornellian says:

    With all due respect, you seem to be making their point for them. “The problem is that nobody seems to be offering the alternatives that Smolin and Woit seem to want these people to work on.” seems to support the assertion that string theory has monopolised the theorist market. As to them not offering solutions, just because they can notice a problem does not mean they can solve it. For example everyone can see sectarianism is bad, but no one has a good solution yet.

    Did your own views change at all due to the discussions? If not, how are you so sure that the proverbial wool is over their eyes and not yours?

  5. Clifford says:

    “The problem is that nobody seems to be offering the alternatives that Smolin and Woit seem to want these people to work on.” seems to support the assertion that string theory has monopolised the theorist market.

    I don’t see how that follows. I’ve said it so very many times now:- We all just want the best tools for the job. We’re all looking. Someone comes along with a demonstrably better tool, and everybody will use it. While working on understanding the currently most promising-looking tool, nobody is stopping people from finding and presenting new tools. Some theorists do both in fact, and encourage their students to do so. Please read the very very many discussions of this point on the threads I pointed to.

    Yes, I do find myself changed as a result of discussions, otherwise there is really no point in having them. I am not so arrogant as to go into a discussion pre-determining the outcome in my mind. What have I learned? Most importantly, after you strip away all the junk, the key points of substance that Smolin and Woit have raised are ones about the structure of academic careers in general, and has nothing to do with string theory. It is a sad mistake that they made to start a poisonous discussion based on chariacaturing the work of many (creating a straw man) in order to then make it seem like “the problem”. What they should have done was -if they wanted to write books- written books about academeic careers, etc, and the struggle to bring new ideas to the fore while not polluting the knowledge base …. the checks and balances of academia can be frustrating. I have sympathy with that… but it serves a useful purpose. What should we replace it with, if at all? All good questions that they are right to raise. But science has proceeded well in this mode, and there is no evidence that string theory is somehow any different in the role it is playing in science from any other scientific endeavour at any other point in the history of science. So science goes on… string theory will probably come, last for a while (maybe even as a useful description of nature for some time) and the go, to be replaced by the next level , etc. etc.

    Their problem is that such books (on how to do academic careers and pursuits differently) do not sell as well as creating a fake controversy like the one that they did. I did not go into the discussions with such a point -which is an important one – as clearly made up in my mind. It came out of the discussions. It makes me even more sad that they chose to (and remain fixed on) this business of making it al string theory’s fault. And sadly, as you can see from all of the physics discussions that we’ve had….. their technical objections -when they are able to even phrase them at all- are full of holes. I (and others) tried hard in the discussions to hear and address those technical points, as Joe has done recenlty as well)…. it just all falls apart rather readily. So it leaves an interesting discussion about academia in general…. the whole stirng theory aspect is a sham. And a sad waste of time and a poisonous -for the whole field- sham as well.


  6. dark-matter says:


    Thanks for responding.

    “the key points of substance that Smolin and Woit have raised are ones about the structure of academic careers in general, and has nothing to do with string theory.”

    That’s your opinion. I beg to differ. Indeed, I know of many string theorists who recognized that ST has unjustly monopolized research not due to it being a promisingly correct science, but largely due to the way science has been conducted in the US. Little of such phenomenon occurs elsewhere. And that, not so much the lack of scientific result, is why there is a controversy among practitioners. On the other hand, it is the science side, the way so much of the speculations of ST are being sold to the general public as ‘amazing almost truth’, driven by business profits, that has created a substantial backlash in the interested-public and other non-experts.

    For sure, let’s all go back to doing science the honest way. The humble way. No more of the ‘only game in town’, ‘science must be redefined to fit ST’, ‘non-ST theorists are clearly dumb and wrong’ arrogance. [This is a general statement. Nothing personal. Indeed, you run a great blog and I respect you for that.]

  7. Clifford says:

    dark-matter:- Also discussed many times here is the issue of who is doing the overselling. Nobody denies that coverage of the sting theory idea can and has gotten out of hand and unbalanced from time to time. I’ve discussed it here and elsewhere a lot….. But to tar all people working in the same field with the same brush is overkill.

    To use a new and deliberately overhyped message to combat overhyping mistakes is not the way to proceed.

    Furthermore, the “only game in town” phrase (not one I choose to use myself) is not untrue. There are no well-developed alternatives. How should we find them? I do not know, but you don’t make progress in a field by getting everyone to just stop what they are doing and sit around and wait for a great idea. This is not how science works. And nobody is actively stopping new good ideas from coming forth, despite how many times this is claimed.

    Furthermore, the ’science must be redefined to fit ST’, ‘non-ST theorists are clearly dumb and wrong’ attitudes….. how many string theorists have you spoken to that actually have this attitude? This is what Woit and Smolin claim we all say.. it is just an exaggeration… a chariacature of who we are. We are not all the same. We are not the Borg. We are not taking all our orders from some single source and we are not even all working on string theory for the same reason, in fact.

    It is a much more diverse and open field than those two people are claiming.

    Please please read the earlier discussion threads (linked in the main post above)… I can’t say it all again. It is just too time consuming, and too depressing that nobody is listening it seems. It havs all been said many many times. Sorry if I sound a bit frustrated. I am trying to give a more complex and accurate picture of what is going on… this is harder to hear than a simple -oversimplified- good vs evil message that is being unfairly put out by Smolin and Woit. You are intelligent… take the time to look behind the hype.

    Thanks. And I appreciate your kind remarks about the blog. I hope you and others continue reading and contributing.

  8. Gina says:

    It is my turn now to disagree with Clifford:

    A) On the controversy

    The recent controversy and discussions on string theory have many facets and are quite interesting!

    People very rarely change their minds in scientific controversies of this nature. (Even on small details, this is quite amazing!) But the opportunity for reflections on some basic truths, practices and conventions is healthy and should be welcomed.

    Clifford’s implied statement that the controversy is worthless does not stand, e.g., in view of Polchinski’s brilliant and insightful review of Lee’s and Peter’s Books. (It is like stating a theorem in a paper in mathematics, and providing a counter example a few lines earlier.)

    Clifford’s name of the series of posts on this controversy “More scenes from the storm in a teacup” may look demeaning, but it need not. Fortunately, even if Clifford will reconsider his position (this will represent a rare event, as I said,) and will realize that the discussion and whole controversy have some merits, the name can be kept. Creating a full fledge storm in a cup of tea, will be a first rate achievement in experimental physics!!

    Science, and intellectual life in general, should not be afraid of opinions and ideas even if provocative and misguided, and “intellectual storms in teacups” may very well be an important part of what academia and science are about.

    B. On String theory and “alternatives”

    I do not think that there is remotely sufficient evidence to show that “string theory had failed” as Peter Woit’s claim. Smolin’s central claim is much weaker, according to him string theory did not succeed yet, and there are some concerns about specific results, as well as the whole endeavor. I think many string theorists (including you Clifford?) may agree to such a statement.

    One the other hand, it is possible that string theory will fail even without specific alternatives being offered. The attempt for grand unification failed 80 years ago, and it is logically possible that physics and mathematics will mature for a correct quantum gravity theory only 80 years from now.

    It is not Woit’s and Smolin’s job to provide “alternatives”. Looking skeptically at string theory’s various insights and results should be part of the string theory endeavor itself. This should be (and probably is) part of what string theorists routinely do.

  9. a cornellian says:

    grr, didn’t post when i thought it did

    responce to clifford’s responce to my comment-fair enough

    As a general question how does on inside a system find flaws in the system, in particular if the flaws are very deep in the system?

  10. Alejandro Rivero says:

    On alternatives: for what?

    I think the focus on quantum gravity is the wrong thing. Most people on the blogs are enthusiastic abour gravity, and even the string community has refocused on it. But it was about particles, about the constituent blocks of the matter and all this, remember? It was an experimental science, not a observational science.

    To “commit to work either on stRing theory or any of the alternative theories of QG” is a trap.

  11. rgb says:

    Do you deny that quantum gravity is one of the most (if not the most) conceptually important problems in physics today?

    Also I am not sure why you lay stress on the experimental vs observational science aspect.

  12. Alejandro Rivero says:

    I was only going to deny that string theory is one of the “alternative theories of QG”. The problem with string theory is that it distracts resources, and people, from other alternative theories… of particle physics. In the best case, it asks for reformulation, in stringy language, of theories not needing such formulation. Tell me how many pure relativists are working on the classification of the moduli space of M theory, or such. Tell me how many papers on solutions of the Einstein Hilbert action can you find between the works of Polchinski, Wittten, Green, etc before 1985.
    Having replaced particle physics, the cosmologists now use input from string theory where they were using, 20 years before, input from quantum field theory. But at the end they solve old good Einstein equations and such.

    What is amazing is that, even before of the book of Smolin, laymen perceived string theory as one “theory of QG”. That was really good propaganda on the side of stringers.


    Now, for the major point, yes indeed I could deny it too. Note that you have been forced to stress “conceptually” because it is clear that it is not an urgent problem of mismatch with experiment or observation. But conceptually speaking, particle physics has a lot of problems in the queue too. The Higgs or its alternatives to explain why a massless theory contains massive particles. The rigorous definition of the renormalisation group method and why it is there at all. The question of the triplication of generations. Their masses. Not to mention a lot of technical issues.

    What was hoped, time ago, is that the issue of QG would be clarifyed in the way of clarifying the subatomic problems. This hope was fueled because the GUT scale, coming purely from elementary particle arguments, happened to be near of the Planck scale. That the renormalisation cutoffs also impose a microscopic scale was, for some people during some time. another hint of a future role of QG. That the N=8 spin 2 theory, aka supergravity, was related to D=11 supergravity and that this was the minimal dimension for the standard model group to act in extra dimensions, was another. And so on. String theory amplified these hopes when it was noticed that, besides a spin 2 theory, implied some compatibility with curved backgrouns, Einstein-like. But nobody was focusing in the conceptual problems of Quantum Gravity. People was focusing in the internal problems of Quantum Field Theory.

  13. Alejandro Rivero says:

    By the way, rgb, I failed to notice that your pseudonim also stresses, casual or intentionally, another interesting problem: what about SU(3)_c in the non-perturbative range?

  14. Clifford says:

    But nobody was focusing in the conceptual problems of Quantum Gravity. People was focusing in the internal problems of Quantum Field Theory.

    I think that several physicists will find themselves quite surprised to be included among the “nobody” you say was focusing on conceptualy problems of Quantum Gravity. Some that you may have heard of include Penrose, Hawking, Feynman and Wheeler… the list is very long.


  15. Alejandro Rivero says:

    Hmm, I am afraid that I do not master the art of condensing a long comment in the last phrase. Instead, that last phrase was intended only to culminate the discourse of the parragraph where it sits. To be clear, I do not believe that N=8 supergravity were a research on QG, it was a research on QFT that happened to use gravity. Hawking radiation, on the other side, was a research on General Relativity (on gravity) that happened to use quantum mechanics (or QFT).

    Of the people you mention, indeed I have been in seminars of the two former and also read papers of the two later ones. But I think we were discussing the turn towards string that happened around 1981-83, and the conceptual work of these people was well developed already before the uprising of string theory. A better thread of QG work could be to name Asthekar and his consequences, but I do not know if to qualify this work as more technical than conceptual. Hawking seems to follow closely the developments of string theory (sometimes he comes to check who is speaking in the weekly pizza seminar) and tries to relate it to serious gravity issues, but most time it seems to me about cosmology. Same feeling with this conformal no big bang that Penrose is propagandising this year. Perhaps Rovelli is the one to put in the list of actual, modern, research on conceptual quantum gravity. To build the list, that could be a good topic for a separate posting.

  16. rgb says:

    “I was only going to deny that string theory is one of the “alternative theories of QG”.”

    You really wanted to say that string theory should not be counted even as a possible approach to quantum gravity?

    “The problem with string theory is that it distracts resources, and people, from other alternative theories… of particle physics.”

    A string theorist could well say the same of particle physics, and an astrophysicist/solid-state physicist/bio-physicist could say that of all other fields as well. What good does that do anyone?

    “Note that you have been forced to stress “conceptuall” because it is clear that it is not an urgent problem of mismatch with experiment or observation.” If you are trying to say that one should only study problems where there are urgent mismatches with experiment/observation; I am not
    sure that particle physics fits the bill either. Apart from neutrino masses where are the urgent mismatches with the standard model?

    And let me make it clear, that I was not trying to say that there are no interesting problems in particle physics … far from it. My point was that present physics is based fundamentally on GR and QM. If the two are incompatible, our entire edifice comes crumbling down. Hence, it is imperative to address the foundational issue. So I do not see how you can deny the importance of this question.

    As for whether or not there were people thinking about quantum gravity, apart from the names already mentioned by Clifford, I would like to ask why does it matter? If some people inspired by particle physics ideas found string theory , which was also interesting for gravity, and wanted to look into it, is there a problem?

  17. Plato says:

    Lee Smolin himself classified the “three Roads to quantum gravity” by including string theory.

    Quantum Gravity (n): the synthesis of the quantum theory of particles with the General Relativistic theory of gravitation, expected to be relevant at the Planck scale.

    I do not know by definition if it could be written any different today? But it forced one to think of GR in quantum realistic ways. This forced the thinking then to include astrophysics and the move to think of cosmology in different ways as well. Even in face of the contradictions between the two?

    This is known as the Planck mass, after Max Planck, who noted in 1900 that some such mass would appear naturally in any attempt to combine his quantum theory with the theory of gravitation. The Planck mass is roughly the energy at which the gravitational force between particles becomes stronger than the electroweak or the strong forces. In order to avoid an inconsistency between quantum mechanics and general relativity, some new features must enter physics at some energy at or below 1019 proton masses. (Weinberg 1981, p. 71).

    I think it would be good to trace this thinking back as well and show this developmental thinking in todays world. It seems to have become clouded by the different arguments.

  18. Gina says:

    Dear Lee, Thanks for your interesting comments. Let me try to move ahead with my critique.

    A) The scientific evaluation of ST:

    (We discussed points 3-5 here are 1 and 2.)

    1. Asserting that there was no progress on the five major problems of Chapter 1 is incorrect or at least very problematic.

    Perhaps Lee’s assertion can best be seen through Penrose’s words on the back cover:

    “… so his claim that string theory is responsible for the lack of real progress in fundamental physics for the past quarter century carries considerable weight.”

    (Note that Penrose attributes to Lee an even stronger statement. That ST is not only responsible to its own alleged failure but also to the lack of progress in other areas of physics! I will not discuss it.)

    In my opinion the claim of “no real progress” should be rejected.

    The first question is, of course, what “real progress” means.

    Here is an example: Richard Hamilton proposed in the early 80’s a program to solve the Poincare conjecture. Judging at the year 1992 did Hamilton’s program represented at that time “real progress” towards the solution of the Poincare conjecture?

    In hindsight the answer is of course yes, Pereleman’s proof relies on Hamilton’s program.

    I was told that most experts were quite pessimistic in 1992. Of course, some people thought that the Poincare conjecture may very well be false. Even if true, it was not clear if Hamilton’s program is a good avenue towards a solution and even if this is the case if the technical problems can be overcome.

    My definition for “real progress” requires that the theory in question have a substantial chance for making or contributing to a definite progress. By this rule, I will attribute “real progress” mark to Hamilton’s program judged in 1992 (regardless of the turn of events later on)as well as to ST judged now.

    We discussed earlier the interesting question how to test partial progress of a theory. Here are some possibilities, non of which is ideal.

    a) To evaluate the likelihood that the theory will achieve its goals.

    b) To evaluate the contributions of the theory CONDITIONED on the assumption that it will fail to achieve its central goal.

    c) to compare the likelihood of the theory to achieve its goals compared to current alternatives.

    Criterions a) and c) are very subjective and are influenced by hypes and by crusades a la Woit. Criterion b) is sort of nice but is based on gloomy worst-case scenario. I am not aware of any current tentative theory that is more successful than ST in terms of criterion b).

    I am not sure that Lee’s assertion (in Penrose’ words)of “no real progress in three decades concerning the fundamental problems of physics” is fair, also in connection with other items, say the unexplained dark mass/dark energy where the collected evidence is quite new.

    2. (Even ignoring 1.) Interpretation of the lack of progress or the small progress in answering the five major problems as a definite failure is very problematic.

    Large parts of theoretical physics (as ST and LQG) are becoming more remote from empirics and more mathematical. Theories are tested to a large extent by their internal integrity and consistency and not by experiments. The times scales we are familiar with in the area of mathematics may be more appropriate to appreciate progress. For mathematical major problems three decades are “too short to call”.

  19. Gina says:

    B) Pluralism

    (This is a continuation of my critique on Smolin’s book from teacup IV; I continued it here by mistake, but it make sense as this post is to some extent a continuation of teacup IV.)

    6. The issue of plurality should be studied from a wider perspective.

    There are many scientific areas where there is a dominant theory and a number of competing approaches. I do not think what we observed in other areas is much different than what is seen here. This was a point raised also by Clifford. What is missing to me in the book, in the context of Lee’s call for pluralism in high energy physics, is some more information on other areas of theoretical physics. Lee referred to it in in of his remarks above (teacup IV) asserting that in many areas of theoretical physics there are grand projects which where the progress is partial and we have some difficulties to asses it. (Of course, pluralism is an interesting issue in more general contexts: when it should be encouraged, when it should be tolerated, and when it should be suppressed.)

    7. Lee overlooks (or neglects) a more serious concern about plurality in the high energy physics community which is potentially problematic to his other claims, though.)

    For somebody looking from the outside, like myself,(especially with a conservative point of view) the unusual thing about string theory is not that we do not see even more revolutionary theories, like those suggested by Lee, but that string theory became so dominant in high energy physics on the expense of more traditional approaches.

    Aren’t there any interesting research areas closer to QED/QCD/ the standard model? Isn’t there too much emphasis on fundamental problems? and not enough effort to identify interesting “second line” problems based on progress already achieved on fundamental problems?

    Perhaps the belief is that string theory will eventually solve such problems as well?

    8. It is strongly implied by Lee but not explained that it is not reasonable that string theory and drastically different quantum gravity approaches will develop separately. E.g., that string theorists should be on top of development in LQG. As a matter of fact, it seems quite reasonable that (,e.g.,) ST and LQG will develop separately.

    The two (or more) approaches for quantum gravity are overall quite “orthogonal”, and I do not see any scientific reason for a “unification”. Of course some awareness of what is going on with the “competitors” can be useful. And from time to time a joint conference is not a bad idea. But for achieving the goal of “quicker scientific progress” letting these two approaches (and even others) work in separation looks very reasonable, maybe it is a healthier approach. There is no strong scientific reason to unite the communities. Are there social reasons?

  20. Alejandro Rivero says:

    rgb, yes I really can not deny the importance of the mismatch between gravity and quatum mechanics.. But I still hope that this mistmatch will solve itself, either from the solution of some extant problem in cosmology and general relativity, or by the solution of some extant problem in particles or quantum field theory. Because there is still such possiblity, I still do not see it as one of the more important actual problems. It could be a future important problem, and we could know already if it is a problem or now, had we put more effort into QFT than into string-inspired mathematics.

    As for string theory being a QG theory, you should ask, “what inputs do string theory takes from General Relativity”. None. It is not that string theory is “particle inspired”; the fact is that it is a theory developed from and for particle phenomenology. Yeah, it is true they raised the bets by looking for spin 2 particles, but this barely qualifies as input from GR. The fact is that you need an even spin for a boson to be attractive between equal charges, so pure field theory already tells yoy that for equal mass to attract then must use either a spin 0 or a spin 2 (And I am not sure, but I believe there is even some problem about massless spin 0 for gauge forces). So I find suspicius that a theory not needing input from GR can solve the problem of QG. Yes I know it implies the Einstein equations, but it is mostly a geometrical consequence; the wordsheet is a two dimensional object, and Einstein-Hilber action is about a two dimensional object too, the curvature. As a QG theoretist told me some monhts ago, “there are not many two-dimensional objects”.

    About QG and QM, I asked time ago: for what radius of its circular orbit will a particle, orbiting around the (weak) newtonian field of a point mass M, sweep a Planck unit of area in a Planck unit of time?

  21. Lee Smolin says:

    Dear Clifford,

    I am sorry I had not noticed this thread, but I would like to take some exception to your “The problem is that nobody seems to be offering the alternatives that Smolin and Woit seem to want these people to work on. Smolin and Woit certainly have not offered much. They’re busy on their campaigns to try to drag down the work of others rather than contributing something positive….”

    First, you never answered my post on a previous thread of yours listing six major results within the last few years in non-string approaches to quantum gravity. Please do not continue to assert that no alternative is being offered when there is a lot of good recent work on alternative approaches. No one is requiring you or anyone to work on them, but when you state publically that there is no alternative you take on the responsibility to investigate claims to the contrary.

    I would like though to put this more positively, would you like an invitation to the next international Loop quantum gravity meeting, this next June, so you can come and see for yourself what is going on and why people in this area are so optimistic these days? Please look at You can see that, as we always do, one of the topics to be covered is string theory, perhaps you could propose you give a talk to this conference so you can also educate us.

    Finally, as to what I am busy with, please note that since finalizing the text of TTWP this past Spring I have posted 4 research papers on four different topics, with several more papers in the pipeline to be posted soon. This was on top of a major paper this spring showing how LQG automatically contains chiral matter. In fact, I am turning down many invitations connected with my book so I can concentrate on doing physics. For the same reason, I don’t get to these blogs as often as I would like, but I am pleased that most discussions on them are now pretty constructive.



  22. rgb says:


    “yes I really can not deny the importance of the mismatch between gravity and quatum mechanics.” I am glad we can agree on stuff .
    “… will solve itself, either from the solution of some extant problem in cosmology and general relativity”.
    I am not sure what you mean by this. Are you saying that perhaps one will have to modify our understanding of classical gravity (maybe with a new action) as more and more data from cosmology/astrophysics comes in, and then perhaps there will be no mismatch? That would definitely be cool …but do you have something specific in mind?
    I am also confused when you say: “what inputs do string theory takes from General Relativity”. I thought a fundamental theory should not take any inputs, but give GR in appropriate limits; much in the same way that Special Relativity kinematics reduces to non relativistic kinematics in the appropriate limit. Are you saying this because in string theory, one does not quantize the Einstein-Hilbert action, but rather two dimensional CFTs? I don’t see why that is a bad thing. Naturally, it would be hard for anyone to dream this up when thinking about quantizing GR; which is perhaps why historically it was not dreamed up by people working on quantum gravity, but arrived at from a particle physics viewpoint. But once someone dreamed it up, and recognized its importance, I see no reason to throw it out. BTW, you seem to suggest that the Einstein Equations follow simply because the worldsheet is 2D … but that would imply that one could get Einstein equations without demanding conformal invariance.

  23. Alejandro Rivero says:

    I am thinking both in data and in theoretical analysis. From the side of QFT, perhaps even the theoretical analysis will prove more important than data. But no, I am sorry I have not specifics in mind. One could mention the excitation a couple years ago about highly energetic cosmic rays. But really Gravity is not my field of experience.

    The issue of the inputs: when you think of GR, you think of a series of inputs: diffeomorfism invariance, compatibility with Minkowski, compatibility with Newtonian gravity etc… Same when you think of Gauge QFT. I was pointing out that the development of string theory does not worry a lot about the kind of inputs GR worries. It mainly starts from QFT ideas and it arrives to an output that happens to coincide with GR. But look for instance all the discussion they keep about background independence; it is so troublesome because it is not in the inputs of string theory.

    Have you taken ten minutes to think and answer the riddle in the last three lines of my previous post? Please try it. I find it is very iluminating, in order to start to think about relationships between gravity and quantum mechanics.

  24. nc says:


    See 9 Dec 2006 New Scientist p53 for how these problems still occur widely in science: Barry Marshall showed that bacteria cause duodenal ulcers and most gastric ulcers in 1984 met with the same kind of unhelpful response until widely accepted in 1997 (he won a Nobel Prize in 2005):

    We published our results … and waited for the sparks to fly. … gastroenterologists thought they already knew the cause of ulcers, and there were very effective treatments which acted by reducing stomach acid – though they weren’t a cure …

    Many people built careers on researching ulcers, but they were barking up the wrong tree. … If people don’t have an investment in the existing paradigm, they are free to invent a new one. There is a lot of inertia in research. People running major research projects can’t suddenly change tack and move the whole lab into another area. … If you know nothing about a subject, and someone comes up with an idea, you can’t tell whether the person is crazy or not. … It was very easy for them to stick with the old treatments. I was annoyed about the level of opposition to our theory, and that people were not testing it …

    The mainstream needn’t worry about being scientific and considering revolutionary ideas contrary to M-theory’s beautiful “fact” that the 10-d superstring universe is a brane on 11-d supergravity. Since the people in string theory are not the kind of people who demand non-ad hoc evidence before investing years in speculations, I don’t think any evidence will swing them. Francis Bacon insisted that a theory be both built on foundations with evidence, and also tested:

    A fruitful natural philosophy has a double scale or ladder ascendant and descendant; ascending from experiments to axioms and descending from axioms to the invention of new experiments. – Novum Organum.

    This would allow LGQ to be built as a bridge between path integrals and general relativity.

  25. Clifford says:

    Alejandro Rivero: – Pardon me for being rude, but I have to say that 90% of what you are saying about research in string theory, field theory and general relativity is just misleading and wrong. There are several good textbooks and reviews on the subject, showing how they all fit together, and how the subjects all work hand in hand and inform one another. The casual reader should know this, and so I’m pointing it out.


  26. Clifford says:


    The issue is one of promising alternatives, as I’ve said many times. And we’ve all discussed the ideas you’ve talked about before in several places. I was simply explaining why a lot of people work on strings… it seems to be the most well-developed of the ideas out there, and there is a ton more to do. Its dominance is mostly about the physics and not sociology. It simply is a very powerful tool, and people like it for pragmatic reasons. Yes, it may turn out to be that we’re barking up the wrong tree, but you work with what you can until you learn why it is not the right thing, or until something better gets developed. We are not close to either situation yet, as far as we know. Physics. Not sociology. That is what this should be about. Nobody is saying that people should be ignoring the other topics you mentioned… and people are free to work on them. I said nothing to the contrary.


  27. Alejandro Rivero says:

    Do not worry about being rude if it is as you see it. It is amazing how the same books can tell different histories to different people. I have been one whole week reading old papers on supersymmetry and supergravity, from standard collections. Previous week I run over a good bunch of the papers of Witten before of 1985. And a lot of dual models from the 1970 have crossed my table during the last month. Plus some mathematics papers on string theory. It is true that I do not check most of the work on strings related to cosmology, but I am under the impression that all this work is post-1985, am I wrong here?

    Or perhaps it is really a literature mismatch. I am speaking mainly from the sources between 1970-1984, ie untile the first superstring revolution. And my comments, the casual reader must be alerted, were based mainly of this reading. But I think I was clear in this point, and at least once above I have told explicitly “Before 1985”.

    30 December 1985 is the date of publication of “Strings in background fields”, and 1 April 1991 is Witten’s “String theory and black holes”. During this period string theory begins its involvement with GR and cosmology, do yoy agree?

    Thinking about, this could explain some of the disagreement between parties about the sucess of string theory. Counting from 1985 and looking at black holes, etc, the results have been pretty decent in 20 years. Counting from 1974, or even from the first dual models, and looking at particle theory, the view is more depressing.

  28. Gina says:

    Dear Clifford,

    You said

    “…it seems to be the most well-developed of the ideas out there, and there is a ton more to do”


    “Yes, it may turn out to be that we’re barking up the wrong tree, but you work with what you can until you learn why it is not the right thing, or until something better gets developed.”

    These sounds very reasonable positions. However two questions come to mind:

    1) How, precisely or vaguely, it may turn out that you are barking the wrong tree? After all, the tree is not barking back (no experimental evidence exists), so what possible hypothetical scenarios do you see for learning it is not the right thing?

    2) For sure, after three decades of extensive research string theory is the most well-developed idea out there. Do you think a fresh not-yet-developed alternative (which at the end may turn out to be better) may have a chance to be seriously considered?

  29. Clifford says:

    1) You develop the theory to a point where it is confronted with experiment and observation. You do the experiment/observations. When they rule it out you move on. Standard process of doing science. No different than any other.

    2) Yes.


  30. nc says:

    ‘When they rule it out you move on.’

    Move on? Or move back! 😉