In addition to the controversy over proposed extra dimensions (discussed in my previous posting), a second line of argument voiced by string theory critics involves what some have called the "disconnect" between string theory and traditional empirical research.
In an interview done with the PBS show NOVA in conjunction with the network's documentary on "The Elegant Universe," Nobel laureate Sheldon Glashow critiques this aspect of string theory in several quotes:
It's called superstring theory and it is, so far as I can see, totally divorced from experiment or observation. If not totally divorced, pretty well divorced...
No experiment can ever check up what's going on at the distances that are being studied. No observation can relate to these tiny distances or high energies...
[String theory] gives a quantum theory of gravity that appears to be consistent but doesn't make any other predictions. That is to say, there ain't no experiment that could be done nor is there any observation that could be made that would say, "You guys are wrong." The theory is safe, permanently safe. I ask you, is that a theory of physics or a philosophy?...
Two subthemes from Glashow's quotes are thus the seeming impossibility (now and for as long as many people can envision) of studying strings in traditional particle accelerators, and the lack of falsifiable predictions on the part of string theorists. The remainder of today's posting will focus on the first of these problems, with the second to be addressed in a later entry.
The basic idea in string theory is that each of the known particles in physics (e.g., an electron, a gluon) is distinguished by its own "signature" pattern of string vibrations (see the quotes from Brian Greene's book The Fabric of the Cosmos that I included in this earlier posting).
These strings are thought to be extremely small ("...so small that a direct observation would be tantamount to reading the text on this page from a distance of 100 light-years...", Greene, p. 352). Further, extremely high energy collisions are needed to jolt these tiny strings into their various vibrational patterns. However, as Greene acknowledges, current accelerators are "far too feeble to excite any but string theory's most placid vibrational patterns" (p. 358).
Elaborating on the same thing, a December 7, 2004 New York Times article by Dennis Overbye on string theory notes that:
Strings are generally presumed to be so small that "stringy" effects should show up only when particles are smashed together at prohibitive energies, roughly 10^19 [10 raised to the 19th power] billion electron volts. That is orders of magnitude beyond the capability of any particle accelerator that will ever be built on earth.
Fear not, seems to be Greene's attitude: "While we may never have technology capable of seeing strings directly, the history of science is replete with theories that were tested experimentally through indirect means" (p. 352).