May 23, 2005

May 22

"Game over", or revival of (S) Matrix Theories

Current blog discussions remind me of the good old 1960's when (perturbative) field theory was considered useless in dealing with the hadronic interactions. A fundamentally different candidate theory, based on agreeable mathematical concepts like analyticity and unitarity, and called the

, or bootstrap theory or nuclear democracy, was advocated vigorously by many prominent physicists. Soon, during the next decade field theory took its position back in the form of Yang-Mills theories where new type of particles, quarks and yet to be discovered scalars, play central role.

Today, doubt is cast over the by now traditional theories, the Standard Model, by the string theory camp for one. This new theory does not overthrow the old, rather it gives it as a low energy limit. Quantum gravity is the major issue. It seems as if mathematical elegance is again used as a method for searching new physical theory and the strings and branes are the new kind of "particles", though they have no experimental support like the quark model had even in its early form in hadron spectroscopy.

My way of thinking is that instead of one or two we, in principle, have many candidate theories including deterministic (April 27, 2005), condensed matter-like, Loop Quantum Gravity, string/M/K (or as one opponents call it, " non-predictive", (May 18 and back) and Noncommutative Geometry theories. Some of them are mutually exclusive (or disfavored), some not. Historically, string theory came about from the S-matrix (Veneziano) theory, so it seems like matrices are looking for a second chance to beat field theory, with the name S-matrix now replaced by just M or Matrix. And "nuclear democracy" being replaced by "brane democracy". - For amusing historical notes on matrices in physics in the 1920's, read this (May 9).

Among the problems in string/M theory are the vacuum and the singularities in Big Bang. They are discussed by Lubos Motl (May 15 and 16, 2005), based mainly on talks in the Conference at Columbia on May 13. Lubos Motl continues his analysis of landscapes' nature on May 21: it's infinite ... "Frankly speaking, the number of vacua has always been infinite." He discusses the stabilization of moduli, referring to a recent paper on Type IIA Moduli Stabilization, with comments from the authors, DeWolfe & al. (who quote for help Florence Nightingale - not Nightengale ;-) ), concluding that stabilization works in the case studied. (It is not widely known that FL was well trained in math, too!)