String and M-Theory: Answering the Critics

An Erratum to this article was published on 22 December 2012


Using as a springboard a three-way debate between theoretical physicist Lee Smolin, philosopher of science Nancy Cartwright and myself, I address in layman’s terms the issues of why we need a unified theory of the fundamental interactions and why, in my opinion, string and M-theory currently offer the best hope. The focus will be on responding more generally to the various criticisms. I also describe the diverse application of string/M-theory techniques to other branches of physics and mathematics which render the whole enterprise worthwhile whether or not “a theory of everything” is forthcoming.

This is a preview of subscription content, access via your institution.


  1. 1.

    Another book attacking string theory appeared at about the same time: “Not even wrong” [32] by Peter Woit, Computer Administrator and Senior Lecturer in Discipline at Columbia University.

  2. 2.

    Here in the UK, commentators expressed delight at the news that the Treasury, up until recently the only government department not to have a chief scientific advisor, has finally appointed one. Few seemed bothered that his Ph.D. is in economics.

  3. 3.

    In the version of events appearing on Peter Woit’s blog [33]: “Smolin sat down. Duff stood up. It got nasty. The trouble with physics, Duff began, is with people like Smolin”. Just to set the record straight, what I actually said was: “The trouble with physics, Ladies and Gentlemen, is that there is not one Lee Smolin but two. On the one hand, there is the reasonable Lee Smolin who has just spoken to you, and with whom I hope to share a drink later this evening… . Unfortunately for physics… there is the Lee Smolin who wrote this book… . And this Lee Smolin is far from reasonable”. When someone who had read the transcript pointed this out, Woit responded: “It does not purport to be a direct quote of what Duff said. It is a direct quote of how that person chose to characterize what Duff said. It reflects precisely how that person interpreted what he was hearing Duff say.”

  4. 4.

    In the debate I quoted from the version of the book I was sent to review by the journal Nature Physics: “I think of myself as a seer”, but this did not appear in the published version. My apologies to Lee.

  5. 5.

    I do not share Lubos Motl’s extreme views on politics, global warming, and sometimes not even string theory. However, he occasionally has some good physics summaries, including a recent one giving a nice history of the triumphs of unification [26].

  6. 6.

    See the letter by Deser, Lawrence and Schnitzer [4] to Scientific American for a welcome exception.

  7. 7.

    Without peer review and completely uncontaminated by any contact with a scientist.

  8. 8.

    Since falsifiability of string theory is the single issue of Peter Woit’s “single-issue protest group”, his blog has had a running commentary on the black-hole/qubit correspondence, which may be summarised as (1) It’s wrong (2) It’s trivial (3) Mathematicians thought of it first. These comments are in keeping with Woit’s unerring gift for inaccuracy. For example, he wrongly credits me with having told author Ian McEwan about the Bagger-Lambert-Gustavsson model in M-theory, which he then proceeds to criticise [34]. Commenting on a recent BBC documentary about claims of faster-than-light neutrinos, he refers to “… trademark hype from string theorist Mike Duff about how string theory could explain this” [35]. In fact I said that, although superluminal travel is in principle possible in the “braneworld” picture of string theory, in my opinion this was NOT the explanation for the claims [12].


  1. 1.

    Andre, M.: Dubious success. In: Research EU, the magazine of the European research area, June 2009

  2. 2.

    Borsten, L., Dahanayake, D., Duff, M.J., Marrani, A., Rubens, W.: Four-qubit entanglement from string theory. Phys. Rev. Lett. 105, 100507 (2010). arXiv:1005.4915 [hep-th]

    MathSciNet  ADS  Article  Google Scholar 

  3. 3.

    Cartwright, N.:

  4. 4.

    Deser, S., Lawrence, A., Schnitzer, H.J.: Disagreeing on everything. Sci. Am., 8 April 2011.

  5. 5.

    Distler, J., Garibaldi, S.: There is no “theory of everything” inside E8. J. Math. Phys. 298, 419–436 (2010).

    MathSciNet  ADS  MATH  Google Scholar 

  6. 6.

    Duff, M., Sutton, C.: The membrane at the end of the universe. New Sci. 118, 67 (1988)

    Google Scholar 

  7. 7.

    Duff, M.J.: Not the standard superstring review. In: Zichichi, A. (ed.) Proceedings: The Superworld II: Proceedings. Subnuclear Series, vol. 25, pp. 11–564. Plenum, New York (1990)

    Google Scholar 

  8. 8.

    Duff, M.: The theory formerly known as strings. Sci. Am. 278, 64 (1998)

    Article  Google Scholar 

  9. 9.

    Duff, M.J.: Flatland modulo 8. In: The world in eleven-dimensions: a tribute to Oskar Klein. ArXiv:hep-th/0111237

  10. 10.

    Duff, M.: Theory of everything. New Sci. 210, i–viii (2011)

    Google Scholar 

  11. 11.

    Duff, M.:

  12. 12.

    Duff, M.: Faster than the speed of light.

  13. 13.

    Durrani, M.: And the winner is… . Physics World Blog, 24 March 2011.

  14. 14.

    Geometry is all: A shape could describe the cosmos and all it contains, 22 Nov 2007.

  15. 15.

    Editorial, Hawking’s faith in M-theory. New Sci. 207, 5 (2010)

  16. 16.

    Gibbs, P.:

  17. 17.

    Grayling, A.C.: Bad vibrations. New Humanist 122(2) (2007).

  18. 18.

    Hanlon, M.: Is big physics peddling science pornography? New Sci. 197, 22 (2008).

    Article  Google Scholar 

  19. 19.

    Highfield, R.: Surfer dude stuns physicists with theory of everything. The Daily Telegraph, Wednesday 29 June 2007.

  20. 20.

    Highfield, R.: Surfer dude’s theory of everything: the magic of Garrett Lisi. The Daily Telegraph, Wednesday 10 November 2009.

  21. 21.

    Hughes, C.: Labour peer warns of crisis in science. The Independent, 24 January 2001.

  22. 22.

    Johnston, H.: The theory of everything on a T-shirt. Physics World Blog, 19 January 2011.

  23. 23.

    Garrett Lisi, A.: An exceptionally simple theory of everything.

  24. 24.

    Garrett Lisi, A., Owen Weatherall, J.: A geometric theory of everything. Sci. Am. 303, 54–61 (2010). Deep down, the particles and forces of the universe are a manifestation of exquisite geometry by A. Garrett Lisi

    Article  Google Scholar 

  25. 25.

    Maldacena, J.: The illusion of gravity. Sci. Am. 293, 56 (2005)

    ADS  Article  Google Scholar 

  26. 26.

    Motl, L.: Unification as a source of certainty. The Reference Frame, 23 June 2011.

  27. 27.

    Ritchie, H.: The string that has science tied up in knots. The Mail on Sunday, 25 February 2007

  28. 28.

    Smolin, L.: The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and what Comes Next. Houghton Mifflin, Boston (2006)

    Google Scholar 

  29. 29.

    Smolin, L.:

  30. 30.

    ’t Hooft, G.:

  31. 31.

    Wallace-Wells, B.: Surfing the universe: An academic dropout and the search for a Theory of Everything, Benjamin Wallace-Wells, 21 July 2008.

  32. 32.

    Woit, P.: Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law. Basic Books, New York (2006)

    Google Scholar 

  33. 33.

    Woit, P.: String theory debates. Not Even Wrong, 22 March 2007.

  34. 34.

    Woit, P.: Solar. Not Even Wrong, 5 April 2010.

  35. 35.

    Woit, P.: Faster than light. Not Even Wrong, 19 October 2010.

Download references


I am grateful to Phil Gibbs for useful discussions. The author is supported in part by the STFC under rolling Grant No. ST/G000743/1.

Author information



Corresponding author

Correspondence to M. J. Duff.

Appendix: FAQ

Appendix: FAQ

Q. Is your falsifiable prediction of 31 ways to entangle four qubits really a test of string theory? Some physicists, including Shelly Glashow (Nobel Laureate), Edward Witten (Fields Medalist) and Jim Gates (member of the President’s Council of Advisors on Science and Technology), have been quoted as saying it isn’t.

A. Shelly and Edward both told me later they were responding to the journalist’s question of whether it is test of string theory as a “theory of everything”, to which they gave the same answer I gave: “No”. I said it is a test of string theory’s ability to make statements about quantum information theory; in that particular paper we had nothing to say about particle physics, cosmology or a theory of everything. Jim’s objection was that it is not, in any case, a test of string theory itself but of supergravity (which is conventionally regarded as the low energy limit of string theory but which could, in principle, be regarded as a theory in its own right). This is an interesting point that Jim and I are still debating, but one that was lost in the media coverage.Footnote 8

Q. But an Imperial College press release carried a headline “New study suggests researchers can now test the ‘theory of everything’ ”. Isn’t this an example of string theory hype your critics are complaining about?

A. That was admittedly unfortunate. Members of the Imperial media team I dealt with were very professional and sensitive to avoiding such hype. Consequently, I approved a version of the press release quoting me as saying:

  • “This will not be proof that string theory is the right “theory of everything” that is being sought by cosmologists and particle physicists. However, it will be very important to theoreticians because it will demonstrate whether or not string theory works, even if its application is in an unexpected and unrelated area of physics.”

The contradictory “theory of everything” headline was added by someone else in the media team, without my knowledge or consent. Then all hell broke loose on the blogosphere.

Q. Criticism of string theory is not confined to Lee Smolin, Peter Woit and the blogosphere. Nobel Laureates Shelly Glashow and Gerard ’t Hooft, for example, have also raised objections.

A. I have the greatest respect for both of them, and if they could come up with a better way of reconciling gravity and quantum mechanics, I would gladly give up string theory and work on theirs. Actually ’t Hooft seems to have softened his stance [30], saying “… it is now possible to describe at least some members of the black hole family using string theory with multidimensional membranes, called D-branes, added to it … . String theory is just an instrument to do calculations in regions of a theory that are otherwise inaccessible.” I take this as an endorsement of the view expressed in Sect. 5 that the whole enterprise is worthwhile whether or not “a theory of everything” is forthcoming.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Duff, M.J. String and M-Theory: Answering the Critics. Found Phys 43, 182–200 (2013).

Download citation


  • String theory
  • M-theory