Many string theorists seem to have decided to react to the criticisms of string theory that have recently been getting a lot of attention by going to the press with claims to have experimental tests of string theory that can be performed in the very near future.
The latest of these claims has nothing at all to do with the aspect of string theory that has come under criticism, its failure as a unified theory of gravity and particle physics, but instead involves the conjectural use of string theory as an approximation method in QCD. The main problem with this idea so far is that it involves not QCD but a related theory (N=4 supersymmetric Yang-Mills), and it is very unclear exactly what the relation is between the calculation and the real world. For some earlier comments about this, see here. John Baez also has a summary, and the Backreaction blog of Sabine Hossenfelder and Stefan Scherer has a very extensive explanation here.
Last week the AIP Physics News site carried a story entitled String Theory Explains RHIC Jet Suppression, which dealt with recent work by Hong Liu, Krishna Rajagopal and Urs Wiedemann concerning the jet quenching parameter, which describes how charmed quarks move through a quark-gluon plasma. In the AIP story, Rajagopal claims that their calculation “agrees closely with the experimentally observed value”, and that other related calculations “make a specific testable prediction using string theory.” This story was picked up by Scientific American, which has a story by JR Minkel. According to Scientific American, “trying to fit the QCD-like theory to reality makes the results only semi-precise, Rajagopal says,” alluding to the problem of doing the calculation in the wrong theory. Maldacena is quoted about this as follows:
It’s like saying you are trying to study water, but instead you are studying alcohol… We certainly know it’s not the correct theory, but maybe it behaves in the same way.
Theorist Ulrich Heinz is even more skeptical:
Even if any of the numbers worked out by accident, I don’t think it would validate the approach… If they predict the color of an apple, and somebody looks at a pear and finds it has the same color, would you say that the prediction was correct?
Other recent claims by Shiu et al. and Distler et al. to be able to make predictions using the string theory approach to unifying physics are covered in the latest issue of Plus magazine, in a story entitled Stringent Tests. According to this story
It seems that string theory, so far the strongest contender for a physical “theory of everything”, may soon be put to the test for the first time. Two separate teams of physicists have just published work describing how to compare the theory’s predictions with reality….
Neither of the two new tests will be capable of verifying string theory once and for all. If the results concur with its predictions, then this is just some further evidence for its correctness, not absolute proof. But the tests’ ability to falsify string theory, or at least certain aspects of it, means that a philosophical barrier has been overcome.