...For Some Definition of Physical Reality

There's a press release dated a week or two ago from Leiden University headlined "Physical reality of string theory demonstrated," in an apparent bid to make Peter Woit's head explode. The release itself is really pretty awful, with poorly explained and irrelevant pictures, and a really confusing description of what this is really about (in part because English was not the first language of the person writing it, I suspect). You have to go down to the third paragraph to find a sort-of explanation of what this is about:

Electrons can form a special kind of state, a so-called quantum critical state, that plays a role in high-temperature super-conductivity. Super-conductivity at high temperatures has long been a 'hot issue' in physics. In super-conductivity, discovered by Heike Kamerlingh Onnes in Leiden, electrons can zoom through a material without meeting any resistance. In the first instance, this only seemed possible at very low temperatures close to absolute zero, but more and more examples are coming up where it also occurs at higher temperatures. So far, nobody has managed to explain high temperature super-conductivity. Zaanen: 'It has always been assumed that once you understand this quantum-critical state, you can also understand high temperature super-conductivity. But, although the experiments produced a lot of information, we hadn't the faintest idea of how to describe this phenomenon.' String theory now offers a solution.

The upshot is that they've shown that the "AdS/CFT correspondence" that is the biggest thing to come out of string theory in the last several years can be used to describe the properties of electrons inside a superconductor near the critical temperature. They have not explained the physical mechanism of high-temperature superconductivity or anything as revolutionary as that. They've used a mathematical relationship to transform a problem that nobody knows how to solve into a different problem that people who aren't me know how to solve. This was originally developed for looking at the interior of nuclei, where you have vast numbers of quarks and gluons and so on interacting with each other via the strong nuclear force, but the current work applies it to the interior of a superconductor, where you have vast numbers of electrons interacting with each other vie the electromagnetic force.

It's an interesting result-- how important it really is for understanding high-temperature superconductivity, it's hard for me to say, but it merited publication in Science, so it's pretty significant. Does it demonstrate the physical reality of string theory? My take on that is pretty similar to something Sean wrote a while back:

To be clear, we wouldn't be learning much about quantum gravity if we observed Hawking phonons from dumb holes. The underlying physics is still that of atoms (and, in this case, a Bose-Einstein condensate), not that of general relativity.

He's talking about a different situation, an experiment in which people use a Bose-Einstein Condensate to construct something that is mathematically equivalent to a black hole (in that sound waves are unable to escape from it in the same way that light waves are unable to escape a black hole). The same basic argument seems to me to apply to the Leiden result, though: the underlying physics of superconductors is still that of electrons and ions and electromagnetic interactions, not quarks and gluons and the strong nuclear force, let alone 11-dimensional vibrating strings.

This is an important result for confirming the validity of the mathematical techniques used in string theory. It doesn't tell us anything about the status of string theory as a theory of quantum gravity, or a unified theory of particle physics, though.