Falsifying String Theory: Not

Back in April a paper appeared on the arXiv from string theorist Jacques Distler and collaborators that made a rather outrageously overhyped claim to have found a way to “falsify string theory”. The paper was entitled Falsifying String Theory Through WW Scattering, and was discussed extensively here. After the Wall Street Journal published an article in June about the problems of string theory, Distler wrote them to complain that the article was incorrect, because he and his collaborators had shown that string theory was falsifiable.

I had heard that this paper was going to be refereed, and was wondering whether a referee would really let the authors get away with the outrageous claim of their title. Well, it appears that the answer is no. A new version of the paper is now on the arXiv, with a new title: Falsifying Models of New Physics via WW Scattering. The abstract, which originally claimed that violations of the bounds they described “would falsify string theory” has now been modified to no longer make this claim; the new language is “would falsify generic models of string theory”.

The paper has acquired a new co-author and been extensively rewritten. I’m assuming many of the changes were made to satisfy a referee. Besides changing the misleading, overhyped title, criticisms of earlier work embedded in one reference have been removed, and nine new references to earlier work have been added.

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29 Responses to Falsifying String Theory: Not

  1. optimist says:

    It sounds to me that any model from string theory should obey Lorentz Invariance, Unitarity and analyticity in S-matrix.

    So if one believes that these properies are essential for any realistic theory then this paper is tautology, giving potential overhyped claim to layman.

    But if one believes that nature could show strange behavior from the view point of conventional physics then string theory is indeed a falsifiable theory because string theory can not admit those kinds of strange behavior.

    The point is that how many people expect nature would not obey those properites. If the number is too small then it could be overhyped claim. If the number is not too small then it is a reasonable claim, I think.

  2. Who says:

    you mention the new co-author Rafael Porto.
    I see that Distler et al reference [22] is
    A relational solution to the problem of time in quantum mechanics and quantum gravity induces a fundamental mechanism for quantum decoherence
    Rodolfo Gambini, Rafael Porto, Jorge Pullin
    13 pages
    Journal-ref: New J.Phys. 6 (2004) 45

    “The use of a relational time in quantum mechanics is a framework in which one promotes to quantum operators all variables in a system, and later chooses one of the variables to operate like a “clock”. Conditional probabilities are computed for variables of the system to take certain values when the “clock” specifies a certain time. This framework is attractive in contexts where the assumption of usual quantum mechanics of the existence of an external, perfectly classical clock, appears unnatural, as in quantum cosmology. Until recently, there were problems with such constructions in ordinary quantum mechanics with additional difficulties in the context of constrained theories like general relativity. A scheme we recently introduced to consistently discretize general relativity removed such obstacles. Since the clock is now an object subject to quantum fluctuations, the resulting evolution in the time is not exactly unitary and pure states decohere into mixed states. Here we work out in detail the type of decoherence generated, and we find it to be of Lindblad type. This is attractive since it implies that one can have loss of coherence without violating the conservation of energy. We apply the framework to a simple cosmological model to illustrate how a quantitative estimate of the effect could be computed. For most quantum systems it appears to be too small to be observed, although certain macroscopic quantum systems could in the future provide a testing ground for experimental observation.”

    (P.W. the original post had a typo where it said WWW scattering instead of WW scattering, you may already have corrected it by the time I submit this comment.)

    Gambini and Pullin do a variant of non-string QG related to LQG. they and Porto have more recent papers than the one cited which discuss the minimal rate of decoherence that necessarily attends using real clocks.

  3. MathPhys says:

    I don’t say why the words ‘string theory’ show up there at all. They seem to be making very general statements that have nothing to do with strings.

  4. Chris Oakley says:

    the original post had a typo where it said WWW scattering instead of WW scattering

    I hope it is not too late … there may already be an entry on the Reference Frame on the lines of “Anti-Science Crackpot Unable To Tell The Difference Between The World-Wide Web And The W Boson”.

  5. SFB says:

    Who, I don’t know what the relational post has to do with the rest of the thread, but the paper is interesting. However if you look at what I had thought was at least implicit in quant-ph/0506228 the calculations in the paper you mentioned seem confused. I tried to tell people about this in the mid 90’s. Instead everybody ran with Rovelli’s better publicized version, which is fine, but the understanding is superficial and they make all these fun but philosophically unmotivated calculations.

    I have started writing yet another paper explaining the old ideas, one that I hope will clarify this situation once and for all. Physicists like to calculate, whether in a philosophical vacuum or not, and string theory is just an extreme form of this calculate-itus.

  6. Chris W. says:


    At some point you may have encountered an anecdote about Einstein’s exasperation with a certain theorist, which Einstein expressed by the remark “the man can calculate, but he can’t think.” I believe I came across it in a book published during the centennial year of Einstein’s birth (1979).

  7. Crimson says:

    I think there must be a confusion. Well, my confusion anyways. I just checked hep-ph/0604255 out of
    curiosity, and I can only find version 3. I cannot find the v4 you link to and discuss in your comment. None of the changes you mention are there in v3.

  8. Crimson says:

    Ok, now v4 is actually there….

  9. Who says:

    Crimson, try

    You say
    **I think there must be a confusion. Well, my confusion anyways. I just checked hep-ph/0604255 out of
    curiosity, and I can only find version 3. I cannot find the v4 you link to and discuss in your comment. None of the changes you mention are there in v3.**

    it sounds like you just used the first link Peter gave and not the second

  10. Benni says:

    Lubos Motl has a new blog entry on this:
    He calls Peter a nutcase….

  11. Jimbo says:

    I would strongly suggest that anybody who has seen Lubos’ most recent rant, would agree that he is totally out-of-control, foul-mouthed, and should be severely disciplined by Harvard for utterly unprofessional behavior. He is beyond doubt, academia’s best approximation to a human pit-bull, and should be de-clawed & neutered.

  12. Tony Smith says:

    Benni refers to a new blog entry by Lubos Motl.
    In it, Lubos Motl says in part:
    “… Lorentz symmetry breaking, breaking of unitarity, locality, rotational invariance … can’t be embedded in string theory …”,
    and concludes that string theory is falsifiable because any one of those things, if shown experimentally, would therefore falsify string theory.

    Lubos Motl goes on to say, in part:
    “… String theory … has fixed Lagrangians and quantitatively accurate and rigorous formulae … it predicts various masses and cross sections. Moreover, it has no continuous non-dynamical adjustable parameters.
    On the other hand, it has a large discrete set of classical solutions – possible universes. The number of them that have a chance to be compatible with the basic features of reality is probably finite.
    Each of them accurately predicts the values of the usual quantities used in quantum field theory – masses and couplings. …”.

    Note that Lubos Motl does NOT show EVEN ONE example of a string theory solution that makes such predictions that are consistent with the experimental observations of the Standard Model.

    Further, Lubos Motl goes on to say:
    “… given the obvious progress and unique results with the supersymmetric vacua, we are confident that an answer to these questions exists in the non-supersymmetric case and it will be unique just like it was in the supersymmetric cases. …”.

    Back in 2004, acting as a sci.physics.strings moderator, Lubos Motl said:

    “… “String theory” is a shorthand for “superstring theory” …”

    His statement was made in the context of his opposition to my (non-supersymmetric) string version of my physics model that I put on the web as CERN-CDS-EXT-2004-031 as an example of a physically realistic (although non-supersymmetric) string theory.

    Perhaps Lubos Motl has realized that the smart money is betting that the LHC will rule out the type of supersymmetry upon which “superstring theory” relies,
    is now hyping non-supersymmetric string theory as a way to preserve the Bureaucratic Empire of SuperString Theory.

    Even though my CERN-CDS-EXT-2004-031 could be seen as at least one concrete example of a realistic string theory,
    something that Lubos Motl and his ilk have been unable to come up with themselves,
    it is my guess that his hatred of me (he describes me as a “moronic crackpot”) will outweigh his desire to exhibit it as such an example.

    Tony Smith

  13. Vogelsang says:

    Wasn’t it the observational discovery of the acceleration of the Universe’s expansion that has led String Theory to its current sorry state of confusion? If so, it would be fair to say that it was Astronomers who showed that String Theory is not phenomenologically viable. That, in turn, would explain why Lubos hates Astronomy to such an irrational extreme.

  14. TheGraduate says:

    John C. Mather and George F. Smoot are our newest Nobel prize winners in physics!

  15. Stefan says:

    Lubos has written something on this topic [string theory falsifiability, or lack thereof] on his blog. As may be expected, it’s the usual rant with semi-relevant and -valid technical points and arguments to give his post the requisite scholarly-authoratative lustre. All in all, I think he did a fairly decent job.

    Moving on to other topics:


    Please help me!! [… or atleast help me to help myself!] make some sense of the Amazonian labyrinth that is hep textbook titles at Amazon.com [no pun intended : – )]. I feel like Bush ; – ) in the White House when I surf through Amazon[.com] trying to figure out EXACTLY *which* titles are the best buys.

    If anyone else wants to assist me, by all means send a ‘yes’ reply and I will provide access to my ‘To Purchse Now’ Wish List to you.


  16. Who says:

    we could be entering a new stage of the game.
    maybe stringery CAN be falsified as a fundamental picture of nature
    and yet not falsified as an EFFECTIVE theory, permitting calculations.

    one can have an effective theory which one knows is wrong, but which provides good approximate calculations.

    so far one cannot calculate anything from stringery so one cannot check if it is a useful effective theory.

    but at least one can imagine being able to show that it is fundamentally incorrect as a picture of nature. I think this is the direction that Distler et al paper is going:

    Distler et al begins to persuade us that stringery might actually be falsifiable in a certain PHILOSOPHICAL way by general reasoning like, for example, this:

    Gambini Porto Pullin showed on general grounds that realistically speaking time-evolution cannot be unitary. It is only approximately unitiary. There is a certain minimum necessary rate of decoherence.

    Perhaps the most accessible paper is not the one which Distler et al cite but these more recent ones:
    Relational physics with real rods and clocks and the measurement problem of quantum mechanics
    Rodolfo Gambini, Jorge Pullin
    19 pages

    “The use of real clocks and measuring rods in quantum mechanics implies a natural loss of unitarity in the description of the theory. We briefly review this point and then discuss the implications it has for the measurement problem in quantum mechanics. The intrinsic loss of coherence allows to circumvent some of the usual objections to the measurement process as due to environmental decoherence.”

    Fundamental decoherence from quantum gravity: a pedagogical review
    Rodolfo Gambini, Rafael Porto, Jorge Pullin
    9 pages

    We present a discussion of the fundamental loss of unitarity that appears in quantum mechanics due to the use of a physical apparatus to measure time. This induces a decoherence effect that is independent of any interaction with the environment and appears in addition to any usual environmental decoherence. The discussion is framed self consistently and aimed to general physicists. We derive the modified Schroedinger equation that arises in quantum mechanics with real clocks and discuss the theoretical and potential experimental implications of this process of decoherence.”

    Relational physics, using realistic clocks instead of presumed absolute time, is primarily an invention of Carlo Rovelli (that is, from the standpoint of Jacques Distler, the devil) and it has been most actively developed by Gambini, Pullin and by Distler’s new co-author Rafael Porto.

    Based on general arguments of Gambine et al, it is a NO BRAINER that string is falsifiable. Indeed it is already falsified as a fundamental picture of how nature is. So Distler wins the argument that it is falsifiable, right? String cannot be right because it assumes time evolution is unitary.

    Conceivably also beginning next year one might be able to show that string cannot be a correct picture because it lacks the very slight energy-dependence of the speed of light appearing in other post-string QG theories—something that may be observed by the GLAST.

    But these are very tiny effects which would in any case only falsify string as a fundamental theory. If it could be made to produce numbers, then it could still be tested as an effective theory. In this context I think Distler et al paper can be seen as a kind of shifting, which could be called progress.

    It is why I made comment about the paper’s reference [22] earlier, with the abstract of the 2004 Gambini Porto Pullin paper. I think Rafael Porto could be a big help to Distler, if he is disposed to listen to reason 🙂

    please excuse the rank speculativeness of this comment 🙂

  17. Garbage says:

    I think the paper didnt change its goals at all, indeed it made them broader!
    I think the new version has effectively new results for WW scattering, which was unclear in the old version, and was discussed here as far as I recall. A violation of the new given bounds, in the absense of a light Higgs, will still falsify string theory in all of the forms currently known, or uknown if they obey the S matrix constraints discussed in the paper. One could argue that M theory (whatever that is) could get around this bounds but I pretty much doubt it if the latter desires any reality check. Even though experimentally speaking it is extremly unlikely the bounds will be violated, or the existence of a heavy Higgs for that matter, the idea remains appealing and deserves further study…

  18. Clark says:

    You may be interested by Burton Richter’s Reference Frame in the October Physics Today: Theory in particle physics: Theological speculation versus practical knowledge
    “…String theory was born roughly 25 years ago, and the landscape concept is the latest twist in its evolution. Although string theory needed 10 dimensions in order to work, the prospect of a unique solution to its equations, one that allowed the unification of gravity and quantum mechanics, was enormously attractive. Regrettably, it was not to be. Solutions expanded as it was realized that string theory had more than one variant and expanded still further when it was also realized that as 3-dimensional space can support membranes as well as lines, 10-dimensional space can support multidimensional objects (branes) as well as strings. Today, there seems to be nearly an infinity of solutions, each with different values of fundamental parameters, and no relations among them. The ensemble of all these universes is known as the landscape… What we have is a large number of very good people trying to make something more than philosophy out of string theory. Some, perhaps most, of the attempts do not contribute even if they are formally correct….”
    Richter ^

  19. Tony Smith says:

    Clark mentions Burton Richter’s Reference Frame article in October 2006 Physics Today.
    In that article, Richter also discusses supersymmetry, saying:
    “… If, for example, the Higgs mass is quadratically divergent, invent supersymmetry to make it only logarithmically divergent and to keep it small. The price of this invention is 124 new constants, which I always thought was too high a price to pay … a conceptual nicety was accompanied by an explosion in arbitrary parameters. However, the conceptual nicety, matching every fermion with a boson to cancel troublesome divergences in the theory, was attractive to many …
    The Large Hadron Collider at CERN will start taking data in 2008 and we will know in a couple of years if there is anything supersymmetric there. If nothing is found, the “natural” theory of supersymmetry will be gone. …”.

    Richter’s present-day view of supersymmetry is consistent with what he said 6 years ago in hep-ex/0001012 :
    “… supersymmetry … was introduced to stabilize the Higgs mass which is quadratically divergent in the standard model and only logarithmically divergent in the supersymmetric variants of the standard model. Supersymmetry does reduce to the standard model at “low” energies, but it also introduces 80 real and 44 complex constants. The theorists who are fans of supersymmetry are groping for variants that reduce these 124 new constants to a handful. If the supersymmetric successor to the standard model cannot reduce the total number of constants, it would seem to me to be a step backwards rather than an advance.
    To the experimenters I would say that supersymmetry is a pure “social construct” with no supporting evidence despite many years of effort. It is okay to continue looking for supersymmetry as long as it doesn’t seriously interfere with real work (top, Higgs, neutrinos, etc.). …”.

    As I mentioned in comment 12. above, it seems that now even Lubos Motl seems to ahve lost his blind faith in the validity of supersymmetry,
    possibly because he realizes that it is likely that the LHC will not find supersymmetry,
    and that, as Richter said, “… the “natural” theory of supersymmetry will be gone. …”.

    With respect to the LHC, it may be worthwhile to quote some excerpts from Richter’s hep-ex/0001012 :

    “… LHC … experiments are huge and the sociology will be complex.
    Beware of too many boards and committees … a bureaucratic overlay to the science with committees that decide on the trigger, data analysis procedures, error analysis, speakers, paper publications, etc.
    The participating scientists are imprisoned by golden bars of consensus….”.

    Tony Smith

  20. Stefan says:

    Hello to All:

    I am currently nearing the end of Ch. 31 of Penrose’s mega-tome-mini-encyclopedia – ‘The Road to Reality’. Chapter 31 is especially fun and informative as it relates to his views on ‘strings’, ‘supersymmetry’, and ‘extra dimensions’.

    I am hoping to start a lively discussion forum of interested individuals at my newly-started blog: ‘Space-Time-Matter’ [http://faustscorner.blogspot.com]. Interested readers are welcome to share their thoughts on the text.


    p.s. I haven’t started posting on the topic yet; that will be tomorrow. (I have other things to do today.)

  21. Anonymous Coward Michael says:

    Hey Peter,

    how’s your own research coming? We are still waiting for you to explain to us all the subtleties of the BRST formalism. Surely you must be about to finish up your long awaited paper, right!?

  22. kramnik says:

    I’d just like to mention this paper hep-th/0610043 (and no I’m not one of the authors). It seems to be suggesting that N=8 super gravity might not be as plagued by infinities as first thought, which leaves the door open to a quantum field theory of gravity.

    Any opinions?

  23. Peter Woit says:

    Garbage appears to be a sock-puppet…

    I urge everyone who feels the need to discuss Lubos Motl’s rants here to keep in mind John Baez’s excellent advice that while it is difficult to ignore Lubos, it always repays the effort. I suspect John would have the same advice about Lubos’s fan Michael.

  24. Who says:

    [b]Garbage appears to be a sock-puppet…[/b]

    in that case I reckon Distler odds-on favorite
    for the puppeteer.

  25. woit says:


    No, your guess is wrong.

  26. Garbage says:

    Woit & Who appear to be not even Wrong….;p


  27. Stefan says:

    Dear Friends,

    I have posted my first entry at my very own site: ‘Space-Time-Matter’.

    Please make my site a success, by:

    a) visiting it (thought this was obvious, but you never can tell these days);
    b) leaving a helpful commentary.

    Thank you.


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