Still traveling, but will be back soon. This week’s bogus “test of string theory” is described in a NASA press release about three satellite-based experiments that would look for violations of the equivalence principle. From the press release:
…it [a violation of the equivalence principle] could provide the first real evidence for string theory. String theory elegantly explains fundamental particles as different vibrations of infinitesimal strings, and in doing so solves many lingering problems of modern physics… The equivalence principle could offer one way to test string theory…
“Some variants of string theory predict the existence of a very weak force that would make gravity slightly different depending on an object’s composition,” says [Clifford] Will. “Finding a variation in gravity for different materials wouldn’t immediately prove that string theory is correct, but it would give the theory a dose of supporting evidence.”
…string theory makes a range of predictions about how strong this new force would be, so it’s possible that the effect would be too small for even these space-borne instruments to detect.
Does string theory predict violations of the equivalence principle? From a posting on Lubos Motl’s blog:
In reality, it will probably be impossible to falsify string theory because string theory is probably correct and you can’t ever falsify correct theories. But if string theory were wrong, there would be thousands of ways to falsify it, even in the very near future. 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.
If you believe that string theory is wrong, just prove any of the theories predicting all the bizarre phenomena like Lorentz symmetry breaking, breaking of unitarity, locality, rotational invariance, and so on. I think that all these things are badly motivated – but it’s mostly because I know that it seems that they can’t be embedded in string theory. If you don’t believe string theory, you should believe that anything can occur and every new test of Lorentz invariance has a potential to falsify special relativity. Every new test has a potential to falsify the equivalence principle. And there are dozens of such examples. Without string theory, all these laws are approximate accidental laws and symmetries. I assure you that string theory will pass every new test of this type and its foes will always lose. String theory allows us to redefine what proposals about new physics are reasonable and what proposals are not, even without the exact knowledge of the vacuum.
I guess it’s all right that I don’t have time to comment on this, since no comment seems necessary…