In the year and a half, roughly, that I've been operating this blog, I haven't yet talked about string theory. Actually, I can think of at least one instance where I've referred to string theory, only to say that we should ignore it at that point.
In one of my very first entries (March 18, 2005), I linked to this diagram of the components of matter at ever-decreasing scales: ordinary matter, molecules, atoms, and sub-atomic particles. I then noted that:
Actually, the figure depicts one additional set of entities down the smallness scale, called "strings;" string theory is very controversial, so for now we'll stop at sub-atomic particles.
In my March and April 2005 postings (see month-by-month archives on the right-hand side of the page, midway down) I talked about a variety of sub-atomic particles, both matter particles (e.g., electrons, quarks) and force-carrying particles (e.g., photons, gluons).
The basic idea of string theory, stated simply then, is that these particles themselves are made out of incredibly small strings, or as Brian Greene sometimes refers to them, "tiny filaments of energy" that behave like strings. As Greene elaborates on pp. 346-347 of his book, The Fabric of the Cosmos:
...the wealth of particle species simply reflects the different vibrational patterns that a string can execute. It's just like what happens with more familiar strings like those on a violin or cello. A cello string can vibrate in many different ways, and we hear each pattern as a different musical note... A [physics] string vibrating in one particular pattern might have the properties of an electron, while a string vibrating in a different pattern might have the properties of an up-quark...
OK, so I've now introduced string theory. Now seems like a good time to do so, with books, media articles (most recently in Time Magazine), and blogs bringing string theory to the general public with seemingly unprecedented volume and vigor.
Also, the current schedule calls for the Large Hadron Collider (LHC), the latest and most energetic experimental particle physics facility, to open in November 2007, a little over a year from now (although the full phase-in to the major experiments, never mind the results of them, will take at least several months beyond the opening of the collider).
I don't believe anyone expects direct evidence of strings to be found at the LHC, but some phenomena that bear more indirectly on string theory could be found.
For all these reasons, the focus of my postings over the next year will generally fall into three categories: additional key issues in string theory; related topics such as supersymmetry and extra dimensions; and the workings of particle accelerators and colliders.
Discussion of all of these issues in a single blog posting is impractical, so I'll have to "string you along."