Frank Wilczek is visiting Rice for two days this week, and is giving two talks. I was fortunate enough to have lunch with him. He's amazingly smart, and extremely versatile. You really don't run into too many people who are conversant on the highest levels of high energy theory (hey, the guy did win a Nobel for asymptotic freedom) and also on the highest levels of condensed matter (he's very interested in non-Abelian statistics and topological quantum numbers in condensed matter systems). His first talk, a public (named) lecture entitled "The Universe is a strange place," was this afternoon. As you might expect from someone as adept at writing physics for a general audience, Wilczek gave a very clear presentation that surveyed modern high energy physics. He discussed ideas relevant from QCD - that most of the mass of nucleons comes from the energy balled up in their constituent quarks and gluons rather than from the rest mass of the quarks. He also emphasized strongly the idea that quarks and other fundamental particles are simply organized, long-lived excitations of underlying quantum fields that are always fluctuating on short time scales (h/mc^2) and length scales (10^-13 cm for nucleons). I hadn't appreciated before that after fixing only three masses (e.g., the K, pi, and b-bbar mesons) lattice QCD nails all the other hadron masses. He talked briefly about dark matter and dark energy, and explained his reasoning for liking supersymmetry. In his words, either the beautiful ideas of supersymmetry are right, leading to unification of the running strong, electroweak, and gravitational couplings, with testable consequences in the form of superpartners detectable at the LHC; or, Nature is cruelly teasing us.
At the very end an audience member asked his opinion on string theory. Wilczek said that string theory was not, properly, a theory - it was not a well-defined set of equations with real predictive solutions (as in QCD). While recognizing the value of aesthetics and symmetry, he clearly understands that the real test of theory is experiment, not intrinsic beauty. (Cue Lubos denouncing Wilczek in 5, 4, 3, ....). He went on to say that it was a collection of very interesting ideas, that it may one day get to an actually predictive form, and that there were only a small number of approaches out there for treating quantum gravity.