String Theory: Physics or Theology?

Victor J. Stenger

For Reality Check in December, 2006 Skeptical Briefs.

Draft of Tuesday, October 24, 2006 12:49 PM. For comment only. Do not copy, quote or distribute.

 

For three decades now, elementary particle physics has found itself in a situation unprecedented in the history of science. It has been blessed by a theory called the standard model of particles and forces that agrees with every measurement ever made in any physics laboratory to this day. Furthermore, the standard model has provided the physical foundation for the development of a highly successful model of cosmology, as that once very speculative field has grown into one of enormous observational and theoretical sophistication. We can now describe the basic physics of the observable universe back to when it was only a trillionth of a second old.

       To most physicists, however, the success of the standard model has been far from a blessing. A whole generation of experimentalists have tried and failed to find some empirical anomaly that would point in the direction of the physics that surely lies beyond the standard model, and science without anomaly is no fun. They have worked hard and made important new discoveries, such as neutrino mass, but these have been trimmings to the model rather than paradigm shifts.

Despite its empirical success, the standard model is far from a complete theory. For one, it does not include gravitational phenomena, which have remained successfully described for three generations now by Einstein's theory of general relativity. Second, the standard model contains over twenty parameters, such as the masses of most particles and the strengths of the forces, which must be determined by experiment.

The ingredients of the standard model include a spectrum of elementary particles—quarks, leptons, and gauge bosons—and a mathematical description of how they interact with one another. All of familiar atomic matter is composed of just three particles: the u-quark, d-quark, and electron. The electromagnetic interaction is unified with the weak nuclear interaction while the strong nuclear interaction is separate but of the same basic form. They are described by what are called gauge theories. Gauge invariance, or gauge symmetry is a generalization of the notion that the laws of physics cannot depend on any specific point of view, an idea that goes back to Copernicus.

Soon after the development of the standard model, many attempts were made to apply gauge symmetry beyond the standard model and unify the strong and electroweak interactions in what were called Grand Unified Theories (GUTs). The simplest of these theories made a profound prediction that was within reach of experiments with existing technology: the proton should decay with a mean lifetime of about 1030 years. In the eighties, immense tanks of highly purified water, placed deep underground to minimize cosmic ray background, were used to search for the telltale light that would signal proton decay. None saw any signal, though some continue the search with the lower limit now at about 1033 years. The largest of these continuing experiments, Super-Kamiokande in Japan, which I worked on before retiring in 2000, has made other important discoveries, notably the observation in 1998 that neutrinos have mass.

The simplest GUT, however, was falsified, and no other versions made any predictions that were immediately testable. In the meantime, the GUT approach was largely abandoned in favor of another idea, super string theory. The great attraction of string theory was that it provided a natural place for gravity to be included in a fully unified scheme, holding out the promise of perhaps turning into what was grandly termed by some as the TOE: the Theory of Everything.

I am sure the reader is well familiar with the media hype that has projected string theory into the consciousness of anyone who pays even the slightest attention to developments in science. But, more important, a whole generation of young physicists, with a few exceptions, have devoted themselves to the study of a theory, or set of theories, that utilizes some of the most esoteric mathematical techniques known.

String theory, which now goes by a more general name, m-theory, has had a number of what aficionados claim have been major breakthroughs. Those of us not versed in the mathematics have to take their word for it. For the non-expert, none of the scores of popular books and TV specials on the subject give much insight into what these breakthroughs may be.

Actually there is one breakthrough that we mere mortals can understand. It has been proven (they do a lot of proving in string theory) that there is not just one string theory but at least 10500 different theories. In a recent book The Cosmic Landscape, pioneer string theorist Leonard Susskind views this not with alarm but with delight. He suggests it provides for a "landscape" of possible universes that may exist in reality and thus provide the basis for the so-called anthropic principle in which our universe contains just the values of physical constants needed to make our kind of life possible. There are 10500 universes and we are in the one suited for us.

All very exciting, but some physicists are beginning to lose patience—especially at the huge expenditure of talent on this single line of thought that has yet to come even close to providing any testable physics, even in principle. In Physics Today, Nobel laureate Burt Richter writes, "Much of what currently passes as the most advanced theory looks to be more like theological speculation." Two new books by experts, The Trouble with Physics: The Rise of String Theory, The Fall of Science, and What Comes Next by Lee Smolin and Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law by Peter Woit describe what they see are the problems with the string approach and why they think it is heading for a dead end. Furthermore, alternatives have been proposed for going beyond the standard mode, although none can claim any more success.

In the meantime, some philosophers of science are being to ponder the possibility that there might never be a theory of everything—at least one from which all the fundamental principles and parameters of physics are calculable from a single universal principle. Perhaps this is the way the universe is, described by models that maintain certain basic symmetries while other symmetries are broken spontaneously. The universe looks very much like the universe you would expect if it came from nothing as a product of symmetry and chance.


Vic Stenger's latest book, The Comprehensible Cosmos: Where Do the Laws of Physics Come from, is now on the market. His next book, God: The Failed Hypothesis. How Science Shows that God Does Not Exist should be out in early 2007.