From A Doughty Theorist: Strings Are Matching Their Promise

In theoretical physics, superstring theory is presently the most lively effort to formulate a quantum theory of gravity and to provide a unified field theory that explains the fundamental forces of nature. Superstring theory, in fact, has the capacity to make important predictions that can be verified by experiment. Its formulations lead directly to the particles known to be responsible for carrying the forces, and the formulations predict the existence of new particles, such as scalar bosons and supersymmetric particles, which may only be detectable at the proposed superconducting supercollider accelerator. Superstring theory is an exciting area of research. It dates back to the late 1960s, when theoretical physicists, motivated by knowledge of the particle spectrum established experimentally at that time, discovered that the different modes of oscillations of a massless relativistic string, a one-dimensional object, had many features in common with these particles, much in the same way that different modes on a violin string result in different notes. In addition, the theory offered the first successful framework for unifying gravity with the other three fundamental forces (weak, strong, and electromagnetic forces) because the string interactions, corresponding to the breaking or joining of strings, require the presence of gravity. Between 1976 and 1.984, however, there was less activity in string theory, partly because other models. such as field theories and finite temperature physics were advancing quickly. Many of us who where getting our degrees during the period had very little exposure to it. Then along came a key mathematical tool infinite-dimensional symmetiy algebras. The physicists who applied the algebras to the string theory discovered that the result was a new and more powerful type of symmetry Although there were still nine space dimensions in the string, four corre sponded to the observed dimension of space/time. The symmetry also explained the nature of the force laws of particle physics. What makes the resulting superstring theories so exciting is that they appear to live up. to their, earlier promise of providing answers to the fundamental questions that have puzzled physicists for years. The approach not only is the first to offer a theory of quantum gravity, it also goes beyond grand unified theories (which united the other three forces) in other ways. It predicts the number of families of quarks and leptons, and does not allow for an arbitrary appendage of particles. And because superstring theories are the first to require supersymmetry for their consistency, they are a new and interesting stepping off point for theories of the early universe (where supersymmetry may play a major role). Very impressive also is the relationship established by strings between the number of space-time dimensions in which we live (namely four) and the form of the force laws that govern our world. In some respects, superstring the- ories are indeed a departure from theories more closely tied to experiment. String models have not yet been worked out to the extent that they can tell experimentalists how to find the top quark, for example. But these theories incorporate in a novel and yet obvious way many of the known properties of the real world, while also offering a level of sophistication for searches into the unknown world far beyond the reach of today’s accelerators. Science progresses only if we have the courage to take certain leaps. Pioneers like Heisenberg, Schrödinger, and Bohr for example, opened up the world of quantum mechanics because they were willing to follow the revolutionary implications of experiments showing quantum jumps of the hydrogen atom. In fact, string theory is at a stage comparable to the early days of quantum mechanics. While it is true that the thread between theory and experiment is thinner for superstrings than it was for quantum mechanics, the thread still exists in the form of the link to the experimental evidence of the force laws. String theory is a breath of fresh air. By its already established successes, it has earned the right to occupy the attention of physicists. In addition, it has the potential to add significantly to our understanding of our world. Even if it turns out not to be the correct theory, it still has enabled us to calculate and investigate quantities such as gravitational scattering heretofore inaccessible to relativistic quantum physics. This is the way that science goes forward. There is very little sentiment in physics. If someone comes up wiih a more accessible theory that is faster to work out or more intuitively correct, there is no doubt that other scientists will pick it up. The best idea will win. Louise Dolan is an associate professor of physics at Rockefeller University

From A Doughty Theorist: Strings Are Matching Their Promise

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