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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