David Peat

58 From Certainty to Uncertaintysome elementary particles, such as neutrons and protons, are not elementaryin themselves but are composed of various combinations ofthree types of quark. The theory promised to simplify the nature ofmatter, until scientists discovered that there had to be more than threequarks and, in addition, other sorts of particles, called gluons, to holdthese quarks together.An alternative approach was to abandon the notion of particles asfundamental building blocks in favor of superstrings, extended stringlikeobjects whose various vibrations and rotations, quantized into aseries of energy levels, produce what looks like the elementary particles.The original concept was proposed in 1970 by Yoichiro Nambu,and then revived in a striking new form by John Schwarz and MichaelGreen in 1984. Soon the vast majority of elementary particle physicistswere working on what looked to be “The Theory of Everything.”Superstrings are incredibly tiny. Take the scale of distances betweenthe atomic world and ourselves and double it to get down to thesuperstrings. What’s more, superstrings don’t inhabit our everydayworld of three spatial dimensions but, in Schwarz and Green’s theory,live in a 15-dimensional subatomic realm. For a time superstrings appearedto be the way of unifying the multiplicity of the elementaryparticles, but then a series of technical problems began to surface.Rather than there being a unique theory of superstrings, there turnedout to be an infinite number of possible theories and there was noclear way of discerning which one was appropriate. Some physicistsfeel that these technical problems can be resolved (or have already beenresolved) and that superstrings still hold the promise of a definitivetheory of elementary matter. Others are more skeptical.So what has happened to the Greek dream, the desire to discoverthe fundamental principle out of which all reality is built? What of thenotion that matter cannot be divided indefinitely, but that at somepoint we will arrive at the fundamental building blocks of all matter?Fundamental SymmetriesIt begins to look as if the elementary particles themselves are not thefinal goal but rather the manifestation of underlying principles of sym-