http://www-conf.slac.stanford.edu/ssi/2005/lec_notes/Lykken1/default.htm Every year Stanford SLAC has a summer institute. This summer Fermilab Joe Lykken is giving a series of talks called "String Theory for physicists". His first 7 slides summarize what he thinks are the stringy goods and bads. In case anyone might want to discuss, question them, clarify, I will transcribe the list. The slides are handwritten--so in case the list is interesting to anyone here at PF, it may be useful to have it copied out. The rest of this post is a transcription of Lykken's list: "good/bad news about string theory" ==== Good: String theory is a consistent theory of quantum gravity. Bad: It's really a generator of an infinite number of mostly disconnected theories of quantum gravity, each around a different ground state. No background independent truely off-shell formulation of string theory is known (yet). ==== Good: String theory is unique. i.e. there is only one distinct consistent theory of "fundamental" strings Bad: It has an infinite number of continuously connected ground states plus a google of discrete ones. There appears to be no vacuum selection principle, other than the stability of supersymmetric vacua, which gives the wrong answer. ==== Good: String theory gives you chiral gauge theories, with big gauge groups, for free + complicated flavor structure at low energies is mapped into the geometry of extra dimensions Bad: Doesn't like to give the Standard Model as the low energy theory. A "typical" string compactification is either much simpler (with more SUSY and bigger gauge groups) or much more complicated (lots of extra exotic matter extra U(1) gauge groups etc) ==== Good: String theory predicts supersymmetry and extra dimensions of space Bad: It's happy to hide them both up at the Planck scale ==== Good: No length or energy scales are put in by hand; all scales should be determined dynamically Bad: Appears to be too many (hundreds!) scalar fields (moduli) with too much SUSY to get determined dynamically; may be forced to appeal to cosmic initial conditions (the Landscape) ==== Good: String theory gives a microphysical description of (at least some) black holes, resolves their singularities Bad: Doesn't seem to resolve the singularity of the Big Bang (good for inflation, though) ==== Good: Lots of powerful dualities including weak <--> strong coupling dualities and short <--> long distance dualities Bad: Can't tell what are the "fundamental" degrees of freedom. String theory not necessarily a theory of strings ==== Good: Unification of all the forces is almost for free, may need an (interesting) extra dimensional assist Bad: In our most realistic string constructions so far, SU(3)C, SU(2)W, and U(1)Y have essentially nothing to do with each other: related to different features of complicated D-brane setups ==== Good: AdS/CFT duality shows that 10 dim. String theory in a certain background is equivalent to a 4 dim. gauge theory!! Use this e.g. to show that RHIC QCD physics maps onto quantum gravity/black holes. Bad: Add more confusion: can't tell an extra dimension apart from technicolor ==== Good: We are starting to use string theory to learn tricks for perturbative QCD, understanding the QCD strings, etc. Bad: The QCD community was already doing fine, thank you.