Falsifiability and Predictivity

GLENDOWER I can call spirits from the vasty deep.

HOTSPUR Why, so can I, or so can any man;
But will they come when you do call for them?

.....................Henry IV, Part I, Act III, Scene I

If string theory turns out to be right, string theorists will turn out to be the greatest heroes in the history of science.

.....................The Trouble With Physics, by Lee Smolin

One of the knocks against string theory is the Popperian idea that a good scientific idea should be falsifiable - it should predict something new that can be tested by experiment. My favorite string theorist has a long post up about falsifiability in physics and string theory. I don't know much about string theory, but, unfortunately, one doesn't need to know much to know that a lot of what he says is crap. Some examples:

In all of its [string theory's] known formalisms, it has fixed Lagrangians and quantitatively accurate and rigorous formulae just like renormalizable quantum field theories. Again, it predicts various masses and cross sections.

One of his commenters asks about the mass predictions, and Lubos replies:

the spectrum of masses depends on the vacuum. For example, in all maximally-dimensional vacua of superstring theory at zero coupling, the spectrum of masses of closed string states is

sqrt(2n / alpha')

where "n" is an integer and alpha' is a characteristic dimensionful constant of string theory.

One small detail he omits. For n=0, all masses are zero. For n>0, all masses are Planck scale - 17 or so orders of magnitude larger than any known particle mass.

Another quote:

Although string theory predicts many new phenomena whose details are not uniquely known, it also implies that many old principles are exactly valid. If string theory is correct, the superposition principle of quantum mechanics, Lorentz invariance, unitarity, crossing symmetry, equivalence principle etc. are valid to much higher accuracy than the accuracy with which they have been tested as of 2006.

I suppose string theory can take some sort of credit for crossing symmetry, since it was the inspiration for string theory. All the others, except for one, are familiar components of twentieth century physics used in all physics. String theory implies them only in the trivial sense that a brick house implies bricks. The exception is the equivalence principle. Motl knows, or at least should know, that the scalar fields of string theory explicitly violate the equivalence principle. Witten has even suggested violations of the equivalence principle (if found) as potential evidence for string theory.

Lubos, and Barton Zwiebach, whom he cites, point out that string theory could be falsified by finding all of its solutions (somewhere between 10^350 and infinitely many) and showing that none of them replicated our world. The silliness of this notion has some merit as humor, but is irrelevant to science.

If string theory is to become part of real physics, it will need to start making some unambiguous predictions about the real world that can be tested, not just in the infinite imaginable future, but sometime soon. That day isn't here yet, and pitiful attempts to obscure that fact only invite ridicule.