THE TROUBLE WITH PHYSICS. The rise of string theory, the fall of a science and what comes next. By Lee Smolin. 416pp. Penguin. Paperback, Pounds 8.99. - 978 0
14 101835 5. US: Mariner Books. $15.95. - 978 0 618 91868 3.
In his critical examination of string theory, The Trouble with Physics, Lee Smolin has launched a controversial attack on those working on the dominant model in theoretical physics. He accuses string theorists of racism, sexism, arrogance, ignorance, messianism and, worst of all, of wasting their time on a theory that hasn't delivered.
Smolin begins by setting out the five major problems confronting theoretical physicists at the beginning of the twenty-first century, problems that seem to indicate that a radically new type of theory is required. According to Smolin, these problems constitute the unfinished business of the twentieth century's revolution in theoretical physics, begun by Albert Einstein with his twin discovery of general relativity and quantum mechanics. These two theories divide the world into two regions. General relativity is a theory of the very big, which describes how matter bends space and time. Quantum mechanics is a theory of the very small, which describes how matter and energy are split up into tiny chunks. In their separate realms, each has been extremely successful, but they are totally incompatible. The first problem facing twenty-first-century physics is to combine gravity and quantum mechanics into a single theory which can explain phenomena that are both big and small.
The foundations of quantum mechanics are Smolin's second problem. He believes that quantum theory's refusal to describe nature beyond what is observed leaves it as an incomplete description of reality, and that any solution to the other problems will require a "sensible" replacement for quantum mechanics, despite the steady drip of experimental results placing ever stricter limits on just how "sensible" such a replacement can be. Smolin's third problem is to determine whether the four forces of nature (gravity, electromagnetism and the strong and weak nuclear forces) can be explained as aspects of a single, underlying entity - though, again, it is gravity that is causing the trouble.
The masses of the particles and the strengths of the forces that act between them form the fourth of Smolin's unanswered questions. A theory that could explain why quarks and leptons come in families, or why gravity is so much weaker than the other forces, would have much to recommend it. His fifth and final puzzle comes from recent results in cosmology, and appears at first sight to be unrelated to the other four; but the indications that all the types of particle found on earth seem to make up only 4 per cent of the matter density of the universe may turn out to be an important clue.
Smolin then sets off on a historical tour of scientific revolutions, drawing out "lessons for would-be unifiers" along the way: "mathematical beauty can be misleading"; "when someone proposes the right unification, the implications become obvious very quickly"; "a real revolution often requires that several new proposals for unification come together to support one another". The story of the century since Einstein is mapped out in failed attempts at unifications - Kaluza-Klein theory, quantum gravity, SU(5) grand unification. Each time, the same moral is drawn out. For a unification to be successful, it must draw together things that seem to be different, and at the same time explain why they appear at first glance to be distinct.
The stage is now set for Smolin's presentation of string theory, which he does with the clarity and enthusiasm of one who has spent years working in the field. The basic idea of superstring theory is to replace the unphysical, zero-dimensional point particles of the standard model of particle physics with tiny, vibrating strings. The vibrations of the strings - the notes they are playing - provide the different types of particles we see in the standard model. The ways they can break and join together provide the different forces that act between them. The attractions of this manoeuvre are considerable. It solves the third and fourth of Smolin's five major problems at a stroke: all the forces, all the particles in the standard model, are just strings wobbling.
