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.
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Another book attacking string theory appeared at about the same time: “Not even wrong”  by Peter Woit, Computer Administrator and Senior Lecturer in Discipline at Columbia University.
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.
In the version of events appearing on Peter Woit’s blog : “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.”
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.
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 .
See the letter by Deser, Lawrence and Schnitzer  to Scientific American for a welcome exception.
Without peer review and completely uncontaminated by any contact with a scientist.
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 . 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” . 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 .
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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.
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 , 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.
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Duff, M.J. String and M-Theory: Answering the Critics. Found Phys 43, 182–200 (2013). https://doi.org/10.1007/s10701-011-9618-4
- String theory