Quantum Connection Could Revitalize Superstrings

Finally back from vacation, postings may appear somewhat more regularly…

Science journalist Tom Siegfried has been one of the most vociferous proponents of string theory for many, many years (see here), but even his faith seems like it might be failing as the decades roll on. His latest on the topic starts out:

Sometimes it’s nice to reflect nostalgically on the last couple of decades of the 20th century. You know, the era of Madonna and Duran Duran, Cheers and The X-Files, McGwire and Sosa, the Macarena, and superstring theory.

The article does try and mount an argument that string theory may not be moribund, with the hope for the future coming from a new paper by Bars and Rychkov entitled Is String Interaction the Origin of Quantum Mechanics?. The idea here seems to be that if you assume you somehow have a fully consistent string field theory, not based on quantum mechanics, then the occurrence in this theory of non-commutative phenomena would “explain” quantum mechanics. To me, this seems to deserve some sort of award for the most desperate attempt yet to justify string theory, but Siegfried is a fan, explaining:

For decades, explaining why nature observes the mysterious rules of quantum physics has perplexed physicists everywhere. Nobody could explain why those rules worked. The connection between string physics and the quantum math may now lead the way to an answer.

I’ll write more soon about those “mysterious rules of quantum physics”, but I just don’t see at all how string field theory (which supposedly is based on quantum mechanics…) makes anything about quantum mechanics less mysterious.

Siegfried of course is not just a fan of string theory, but also of the multiverse, so he ends with:

On top of all that, the string-quantum connection suggests an intriguing insight into the nature of reality. Quantum physics is notorious for implying the existence of multiple realities, as articulated in the “many worlds” interpretation of quantum mechanics. Superstring theory has also annoyed many physicists by forecasting the existence of a huge “landscape” of different vacuum states, essentially a multiverse comprising multiple universes with a wide range of physical properties (many not suitable for life, but at least one that is). If string interactions really are responsible for the rules of quantum physics, maybe there’s some connection between the multiple quantum realities and the superstring landscape. For fans of the late 20th century, it seems like an idea worth exploring.

One thing remarkable about this is that he has another piece that recently appeared, an interview with Katherine Freese, where he tries to convince her about the multiverse, but doesn’t get anywhere:

Theory predicts vastly more vacuum energy than the amount actually observed. Wouldn’t this huge disparity be explained if there are multiple universes, a multiverse, and each has a different density of vacuum energy? Then the reason we have a low amount in ours is because that’s the only way we could exist in it.

I don’t like that idea. A lot of people like it because of string theory. Originally people thought that string theory would give a unique solution to the vacuum-energy equations. But it turns out that in string theory there are maybe 10-to-the-500th different vacuum states. So the idea is that they’re all out there, but we have to live in one with a value of the cosmological constant close to the one we have. But I don’t like anthropic arguments. They rely on the fact that human life can only come to exist under certain conditions, so that of the many universes out there it’s not surprising we live in the one that supports our type of life. That’s not a good enough explanation for me. I feel there are physics problems that we have to answer, and we can answer them in this universe, in this piece of the universe we live in. I think it’s our job to try to do that, and it’s not good enough for me to give up on it and say, well, it has to have this value because otherwise we couldn’t exist. I think we can do better than that. I know, I’m old-fashioned.

Isn’t part of the question whether there is a multiverse or not? If you had really strong evidence that there is a multiverse, then the anthropic explanation becomes better motivated. Inflation, the rapid burst of expansion right after the Big Bang, supposedly can produce a multiverse by way of “eternal inflation.”

I do believe in inflation, so can inflation give you a multiverse or not? Because if it can, then I’m forced to consider this possibility. I recently wrote a paper with Will Kinney on this. We concluded that what we observe in the cosmic microwave background radiation is not giving rise to eternal inflation. So how do you know that ever happened?

Are the recent results on the cosmic microwave background from the BICEP2 experiment relevant to this issue?

If you take the BICEP data literally, which I’m not saying you should, you never have eternal inflation. So you don’t have to have eternal inflation, if you ask me. I was very happy about that.

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22 Responses to Quantum Connection Could Revitalize Superstrings

  1. comment says:

    It is unfortunate that Sigfried honed in on Bars’ paper and that Peter amplifies it for the purpose of painting string theorists as desperate and intellectually dishonest. No independent theorist would vouch for Bars’ claim to have derive quantum mechanics based on what has been demonstrated.

    The matrix-like interaction of open strings is closely related to non-abelian gauge symmetry. So if open string field theory proves quantum mechanics, I think you could claim that Yang-Mills proves it as well. But, unfortunately, quantum mechanics is more than a noncommutative algebra.

    I recently attended a very interesting conference on string field theory in Trieste. Some new results include:

    1) A nonperturbative proof of background independence in open string theory. This result addresses a major point of criticism for string theory opponents.

    2) New constructions of spacetime actions which may provide a systematic underpinning for superstring perturbation theory. This is another “weak link” which is a major target of critics.

    3) Powerful numerical techniques for mapping the space of two-dimensional boundary conformal field theories and conformal defects, with potentially useful applications to condensed matter physics.

    It is aggravating that this real progress is ignored on this blog and elsewhere. Incidentally, Bars also gave a talk at the conference, but it is fair to say that his recent paper was not the focal point of excitement.

  2. Peter Woit says:

    First of all, I’m not painting anyone here as intellectually dishonest. The “string theory implies quantum mechanics” claim here isn’t being made underhandedly. It’s straightforward, but it’s just bizarre and nonsensical.
    As for “desperate” though, yes, I think this kind of thing reeks of desperation. I don’t think you can read Siegfried’s article as anything other than a desperate grasping at straws to avoid acknowledging the failures of the theoretical ideas he has been spending the last couple decades writing promotional books and articles about.

    I think your basic problem is not with me, but with the part of the string theory community which puts out nonsense like this and the journalists who are taken in by it.

  3. comment says:

    Itzak Bars is not “part of the string theory community.” He is an individual, and his views represent his alone.

    Of course I have a problem with you posting about this, since it further amplifies the significance of an obscure idea which is not indicative of trends even in a very specialized subfield of string theory. But I understand that your interest is generally painting string theory in a negative light, and further amplifying noise gives people the impression that the subject is vacuous.

    My purpose was simply to provide a different point of view and remind people that progress is being made on fundamental questions, even within this minor subfield.

    I noticed that you took no interest in the main results presented at the recent conference. If you thought about and took a critical view of this work, it might be a more interesting starting point for debate on merits and progress in the field.

  4. @comment

    links to these talks/abstracts/papers/results?

  5. R-bot says:

    Is Bars not part of the string theory community? What are you saying? If he is not, why he had been invited for that conference as a speaker? His personnel website even introduces himself as “My current interests include String Field Theory, and Two-Time Physics and Cosmology.” Even he has just a minor of minor-alone view on a certain small subject (like some others on that field), he himself believes he is one of string community, and even he was invited for a string conference.

    Anyway I partly agree with you on your point (no high light for recent developments on the field). But this posting is criticizig its media-hype part of it, so you guys point at different directions. Also, as you may have noticed from Strominger’s vision talk at Strings 2014, nobody even knows for what string community should head in the future and what exactly the theory is. So the main criticism point on that field from this site is still relevant and no critical recent developments to defense.

    @David Roberts,
    Maybe this one: http://www.sissa.it/tpp/activity/conferences/SFT2014

  6. Cathy Dupont says:


    Background independence is not an important argument against or for string theory. Established physics is not background independent at all. The requirement has been “invented” by loop quantum gravity people to discredit string theory, but that is unfair: background independence does not help in making a theory that fits with observations or one that makes predictions. Background independence is a red herring.

    The test of a theory is that it agrees with observations. And also your other two points are red herrings in this respect …

  7. comment says:

    @ R-bot

    Bars is certainly a member of the community, but he alone does not represent “part” in the sense of a non-infinitessimal fraction. This is the sense of “part” that I was referring to.

    I don’t want to denigrate Bars’ and Rychkov’s work. I am glad they are excited about something. Wild proposals can be fodder for interesting conversation and new ideas… but only if you have the right context. There is certainly a correct analogy between string interactions and some equations in quantum mechanics, but I don’t think this analogy means what it sounds like it means. But perhaps Bars and Rychkov can exploit it for interesting purposes.

    See the following recent papers:
    http://arxiv.org/abs/1401.7980 about using string field theory to uncover the space of boundary conformal field theories and defects.
    http://arxiv.org/abs/1406.3021 for a proof of background independence.
    http://arxiv.org/abs/1403.0940 and http://arxiv.org/abs/1312.2948 for a new approach to the field theory of superstrings.
    I think these results are in fact relevant to some criticisms of string theory, though I doubt they would impress Peter much. Perhaps Strominger is not certain where the field should be heading, but he does not speak for me personally.

    @ Cathy Dupont

    One main focus of the conference was string field theory. This is a formal subject whose main motivation is trying to find the “right” definition of string theory. It has little to say about connecting Planck scale physics to measurements. If this is what you care about, then there is not much interesting to report from the conference.

    But I think recent work charting the space of BCFTs could easily have quantitative applications to measurements of real world physical systems. But this is really an application of certain technology developed in the context of string theory to another field. It has no implications for the viability of strings as a description of Planck scale physics.

  8. Curious Mayhem says:

    Plus, “eternal inflation” à la Linde is historically prior to and independent of string theory and the “landscape.” Linde’s eternally inflating background metric is a connected spacetime, not a collection of separate realities. The two ideas have nothing to do with each other. That aspect of the whole bandwagon (not just Siegfried) is intellectually dishonest.

    As Katy points out in the interview, it’s very difficult to get inflation to work in string theory. And the current evidence is unfavorable to all but a small subset of “string-inspired” cosmologies and inconsistent with “eternal inflation.” In fact, the current data suggest something pretty old-fashioned, a quantum universe tunneling to a false vacuum, setting up the initial conditions for inflation. A simple version of this is presented in Kolb & Turner’s textbook.

    As always, more and better data will winnow down the field of contenders. The exciting thing is, we’ll probably see this moment soon.

  9. Lee Smolin says:

    Dear Peter,

    For what its worth, can I mention that I wrote a paper in 2002 showing that quantum mechanics can be derived from a matrix formulation of string/M theory: arXiv:hep-th/0201031?

    Dear Cathy Dupont,

    Background independence is for sure a principle of “established physics”, it is the general principle behind both the diffeomorphism invariance of general relativity and the local gauge invariance of Yang-Mills theory. It can be tied directly to the experimental success of GR, QED and the standard model, for example the experiments which verify these theories are pure spin 2 and pure spin 1, respectively.

    Furthermore, it is funny that you think that background independence was ““invented” by loop quantum gravity people to discredit string theory”; the idea was rather invented by Einstein, Weyl and others early in the 20th century as part of the invention of GR and local gauge theory. Look up, for example, the history of the “hole argument” in Einstein’s work between 1911 and 1916, followed by Weyl’s invention of local gauge invariance in 1919.

    btw the two comments are related because the 2002 paper deriving QM from string/M theory was part of a series of papers proposing a cubic matrix model as an approach to a background independent formulation of string theory.


    Lee Smolin

  10. Arash says:


    It’s kind of old story by now, and I’m aware you’ve heard this question several times before, but wouldn’t you call AdS/CFT a background independent formulation of string theory in asymptotically AdS spaces? (Asymptotic boundary conditions are allowed in (“background independent”) classical GR on non-compact manifolds, right?)


    From what I’ve gathered, what you call `noise amplification’ is in a sense one of the main purposes of this blog; to amplify what insiders (and enthusiasts) of string theory consider insignificant, while they should probably take them seriously. I don’t think many of the readers of this blog would find any interest in reports on recent technical progress.

  11. Peter Woit says:

    Do you really consider trying to have the same old empty argument with Lee about “background independence” and AdS/CFT to be anything other than your own form of “noise amplification”?

    I suppose you’re right though that one of the purposes of this blog is to do something string theory enthusiasts consider insignificant, correct the outrageous hype in the media about string theory.

    By the way, I think you’d be very surprised to know who many of the readers of this blog are and what their interests are.

  12. Arash says:

    Point taken, Peter!

  13. @R-bot – thanks, but there’s a lot of abstracts linked to purely by the name of the speaker. I haven’t the inclination to go through all of them and try to find the talks that comment described.

  14. Chris W. says:

    As an amusing sidelight on the above, Bars and Rychkov very recently posted another paper entitled “Background Independent String Field Theory” (arXiv:1407.4699). The abstract ends with this sentence:

    A byproduct of our approach is an astonishing suggestion of the formalism: the roots of ordinary quantum mechanics may originate in the rules of non-commutative interactions in string theory.

  15. lun says:

    I do not think that what you call “background independence” is the same as what General Relativity people call background independence.

    Correct me if Im wrong, but Maccaferri et al give a recipe to construct a solution in another background given a solution in a certain background. “Background independence” means that these two solutions are in some sense locally indistinguishable for a given observer. Maccaferri et all did not prove this.
    Or am I wrong?

  16. Bill Radley says:

    A comment for Comment:

    The point is that Siegfried did promote the Bars paper, and that makes it news for a blog about unjustified string+ theory hype. Of course there are better ideas out there, from all sides of the argument, but the point, as ever here, is that they are losing out – in terms of public and media attention, funding, and serious scientific attention – to an increasingly questionable consensus. Some development from string theory may of course still turn out to have a deep contribution to make to our understanding of the universe. But what would be useful for all of us would be for its proponents to refrain from describing tentative, partial, speculative,ultraspecific or unproven abstract results as key insights into the nature of the universe.

  17. Peter Woit says:

    Bill Radley,

    There are always going to be people making dubious claims for their speculative ideas. Their sensible colleagues will just ignore them. The question is what to do when the press picks these things up. For random speculation that no one is paying attention to, probably best to just ignore such press stories unless they get widely spread.

    Dubious claims of the specific “I’ve found the answer to the problems of string theory!” variety are a common subclass though, and the fact that they get press attention has a lot to do with the long history of resistance by string theorists to any public acknowledgement of failure. For decades now there has been little to no willingness of string theorists to complain to those hyping the theory. They do seem to be willing to complain to me though…

  18. srp says:

    “The good ideas, the ones that eventually find their way into the textbooks, are out there, all right–but they are out on the shelf surrounded by all kinds of junk, which is packaged by its authors as attractively as possible and, of course, is never clearly labeled ‘junk.’ It’s not that people are out to fool you. They may be just confused or mistaken. Or, more commonly, they are doing work that is correct, in the sense of not containing errors, but not useful for progress. The work is too speculative or too safe; it loses contact with reality or remains narrowly earthbound.”

    One of my favorite quotations, from Frank Wilczek and Betsy Devine’s Longing For the Harmonies. It applies in many fields besides physics.

  19. Titus Weisstein says:

    The origin of quantum mechanics was stated by the old masters, like Werner Heisenberg and Niels Bohr: quantum mechanics follows from the existence of hbar. That is why Heisenberg used to wear a golden tie needle with hbar on it in the second half of his life. Just hbar.

    Stating that quantum mechanics follows from string theory would mean that string theory can explain why hbar exists.

    But string theory does nothing of the sort. Nor does loop quantum gravity. Therefore, proponents of both camps are just making wind.

    Putting yourself above Heisenberg and Bohr in this issue puts you in a bad light…

  20. Lee Smolin says:

    Dear Titus,

    No one is putting themselves above Bohr and Heisenberg, far from it, but that doesn’t mean we can’t make efforts to understand questions they left unresolved.

    I agree that LQG does not explain either quantum theory or the value of hbar, it is entirely an application of conventional quantization to GR. But in the work I mention I give a derivation of QM from a particular limit of a matrix model for string theory, to be precise the bosonic part of the BFSS model. There, in hep-th/0201031 I do give an explicit formula for hbar in terms of the parameters of the matrix model, it is eq 109.



  21. Georg Zwiebel says:


    formula 109 relates hbar to several other parameters that are unknown, unmeasured and whose existence is unconfirmed. And even time appears in it.

    Speculations and fantasies are ok. But you are not really convinced that this is an explanation of hbar, or are you?

  22. Lee Smolin says:

    Dear Georg,

    This is a model, not a theory. It serves as an existence proof of several ideas I think are worth exploring further. Among them 1) non-local hidden variable theories exist which reproduce Schrodinger quantum mechanics for an N body system, 2) there may be a simultaneous solution of the measurement problem of quantum foundations, unification and quantum gravity, and 3) hbar may indeed be a function of physical coupling constants and the number of degrees of freedom of that unified theory.

    btw t is not time, it is temperature, scaled by a power of the size of the matrices and some coupling constants. See eq 47.



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