Zwiebach Letter to the WSJ

Over at his web-site, Lubos has posted a letter to the Wall Street Journal from Barton Zwiebach. The letter seriously misrepresents the current state of string theory in several ways:

string theory is an extraordinarily precise and rigorous framework where facts can be proven beyond doubt and computations give unequivocal answers.

All that is needed to confirm string theory is finding one solution that describes our universe. All that is needed to rule out string theory is showing that no solution describes our universe. An answer must exist.

Zwiebach gives the impression that there are rigorously well-defined, “extraordinarily precise” equations that characterize string theory, and all that is needed now is to solve the technical problem of finding the solutions to these equations and seeing if one of them agrees with what we observe. This is simply not true. Since we don’t know what non-perturbative string theory is or what its equations are, all equations used by string theorists to generate solutions are not “extraordinarily precise”, but are explicitly approximations, often very crude ones, whose reliability is unknown. If you look at the debate over the landscape, you will find that not only do most string theorists not believe that the solutions involved are “facts [that] can be proven beyond doubt”, many of them believe these are not real solutions to the full unknown theory at all.

Even if one does believe in the rigorous nature of the landscape solutions, Zwiebach’s claim that all one has to do is examine them to see if they agree with nature is again highly misleading. If there are 101000 or more of these solutions, all evidence is that identifying which of them have desired properties (e.g. the correct CC) is an inherently computationally intractable problem. Even if one could do this, the class of solutions that agree with all known values of the parameters characterizing the standard model seems likely to be so large that no new testable predictions would be possible.

Zwiebach also claims:

String theory has explained, for example, why black holes have entropy and temperature.

This is what Hawking did back in 1974 with a semi-classical calculation. Any theory of quantum gravity should reproduce this. What string theory adds to Hawking’s calculation is a long story, but if we manage to observe a black hole any time soon and it behaves as Hawking predicted, he’s the one who is going to get a Nobel prize for explaining “why black holes have entropy and temperature”, not string theorists.

I had been wondering what the response from string theorists would be to the public dissemination of arguments from Smolin and me about string theory. The response seen here from Distler et. al. and Zwiebach is not at all what I expected. Most serious string theorists I talk to take the reasonable attitude that string theory is still so poorly understood that it cannot be confronted with experiment, even in principle. Many publicly say that we still don’t know what “string theory” is. Zwiebach seems to believe that there now exist “extraordinarily precise” equations, with solutions that will give “unequivocal answers”. Whether this is true is a well-defined question. All he has to do is explain what these equations are, and let’s see if the string theory community will really stand by this definition and let string theory be judged accordingly.

Finally, perhaps the most surprising aspect of Zwiebach’s letter is the form in which he has chosen to distribute it. I and many people have been wondering what Lubos Motl’s colleagues in Cambridge think of the way he is defending their subject. Now at least one of them has made clear that he is fine with this and willing to encourage it.

Update: The usual response from Lubos Motl/Bill O’Reilly: an endless rant about how stupid people who disagree with him are, completely ignoring the scientific questions at issue.

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59 Responses to Zwiebach Letter to the WSJ

  1. Roy says:

    “What Hawking showed was that there is a reason black holes have entropy and temperature, completely independent of the microscopic description. This explains these two facts, you don’t need to know the microscopic definition.”
    I must admit don’t know the technical details of string theoretic calculation of microstates, but isn’t that the entire point of thermodynamics and stat. mech? For example, most of undergraduate thermal physics can be done without stat. mech by somehow guessing or physically arguing for a equation of state or the some potential function, but the stat. mech approach is superior because it actually derives everything from first principles. Of course stat. mech is not certainly limited only to providing proofs for thermodynamic equations– it has infinitely many more interesting applications and ideas and I do not know whether the string theoretic approach has similar advantages and I think Borun is claiming(and perhaps quite correctly) that string theory provides a better framework for the understanding of the black hole entropy calculation(Borun, please correct me if I am wrong here)
    If string theory has managed to derive a semi-classical result that is widely believed to be true– and managed to calculate the microstates correctly– isn’t that a strong point for the credibility of string theory?
    May be you had further objections to Borun’s claim, or in general this string theory result, based on technical points that I do not understand and in that case it will be nice if you would explain why you think that string approach is not satisfactory in this case.

    Again, I am not trying to be confrontational or arrogant here– I would genuinely like to know your objections .

  2. Arun says:

    Is it true that the extremal string blackhole has the right Bekenstein entropy, but has no energy to radiate because it is a minimal energy state of the string? i.e., where the exact calculation is possible, we have the entropy but not the Hawking radiation? Are non-radiating black holes a prediction of string theory?

  3. scott says:


    I doubt that joe doesn’t understand that “the credibility of an argument and the credibility of a person are two quite different things” However he thinks, and with good reason, that WSJ not being a qualified expert, will likely simply look at his credentials instead of spending an employees time contacting other experts to see if they think the argument itself is credible. Apparrently regard the WSJ in a much higher regard then Joe. I think Joe’s appraisal of how the WSJ would determine credibility to be more realistic.

    However there is another possibility that they will simply not publish it because they don’t think the issue is worth the space regardless of credibility. Or as you point out because they publish some other string theorist’s responce.

  4. scott says:

    Apparrently regard the WSJ in a much higher regard then Joe. I think Joe’s appraisal of how the WSJ would determine credibility to be more realistic.

    um this should say something like:

    Apparrently you regard the WSJ in a much higher regard then Joe. I think Joe’s appraisal of how the WSJ would determine credibility to be the more realistic one.

    there is some other sentences with bad grammer but they are( I think) still understandable.

  5. scott says:

    and of course even in my correction the grammar is still f’ed up.

  6. Arun says:

    One may also ask how the ordinary matter from which any black hole in our universe is assembled turns into the highly wound-up string + brane state in the string blackholes.

    If this is not known, then the result really is that the exotic string matter that makes up a string blackhole has the correct number of microscopic states to produce the Bekenstein entropy. I agree it is an impressive result, in that we cannot yet count the microscopic states in any other framework. There are some scenarios in string theory that gravitationally are blackholes and where microscopic states can be counted; but presumably there are many scenarios (e.g., with everyday matter) where microscopic states cannot be counted, and one has to demonstrate this doesn’t matter, the count of microscopic states remains the same.

    Presumably molecules interacting like billiard balls, or with van der Waals forces or with any of a large set of force laws produce the right thermodynamics, and thus thermodynamics sets only a weak constraint on how molecules may interact.

  7. woit says:

    Yes, it certainly is a point in favor of string theory if it can provide a microscopic definition. I was not arguing with that, all I was doing was pointing out that you don’t need the microscopic definition to know what the entropy and temperature of a black hole will be, Hawking already told us that long ago. It’s also true that string theory arguments do not provide such a microscopic definition for physical black holes, which Zwiebach neglects to mention.

  8. D R Lunsford says:

    RE Motl’s latest rant –

    Motl is doing classic Jungian shadow projection, just like O’Reilly does. Obviously he is insecure in his own understanding, and this is why he does not argue facts, only opinions – he doesn’t have facts to argue with, nor the grounding in history to draw correct inferences. (Compare O’Reilly’s claim that Germans were massacred by American GIs at Malmedy.) Effective shadow projectors often rise to prominence – only to have their crippling flaw publically exposed. This is some kind of healing process in the projector’s divided psyche.


  9. Torbjörn Larsson says:

    “Everyone seems to believe that the recent paper by Acharya and Douglas “shows” finiteness, when, if you look at it, you’ll see that they are just making conjectures.”

    I took it they were pretty solid results, and that they confined the number of string vacua. Thank’s for supplying the missing reference!

    “And no, even with the kind of finiteness that Acharya and Douglas conjecture, the words “computationally tractable” definitely don’t apply in this case.”

    I found by Denef and Douglas that argued that “such problems are typically NP hard”. That is different yes, they are computationally intractable.

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