Is “Strings” a Dud Theory?

The beauty and elegance of superstring theory lies in the hopes and dreams of its practitioners, hopes and dreams that are vanishing as every year it becomes more and more unlikely that they are ever to be realized. Superstring theorists would like to believe that some day a simple equation, beautiful physical idea, or fundamental symmetry principle will be found that will explain the intricate structure they have been studying, the present situation of the field is that no such thing is actually in sight despite more than twenty years of effort looking for it. (Peter Woit, Not even wrong, 2006, pp. 262-262)

Many scientists believe that answers to these questions are tied up with some of the deepest unsolved problems in physics. A thirty-year old framework known as string theory promises new insights and offers hope that answers to at least some of these puzzles may be on the horizon. (Edward Witten, Universe on a String)

Although there was a great deal of upbeat feeling about the string theory particularly when Witten formulated his M-theory in 1995, nothing of any great consequence has occurred since then. String theories, including the M-theory, have not made much progress toward their avowed goal of unifying the fundamental forces. One of the co-founders of the original string concept, Leonard Susskind, wrote in the epilogue of his book, The Cosmic Landscape, that was published in 2006, “I often joke that if the best theories are the ones with the minimum number of defining equations and principles, String Theory is by far the best – no one has ever found even a single defining equation or principle! String theory gives every indication of being a very elegant mathematical structure with a degree of consistency far beyond any other physical theory. But nobody knows what its defining rules are, nor does anyone know what the basic ‘building blocks’ are.”

Several new books have recently been published on string theory criticizing it and some supporting it. There are three books which I had access to. I have already quoted above from one of them. The title of another is “Not Even Wrong” written by Peter Woit who is “a lecturer in the mathematics department of Columbia University. He graduated from Harvard University in 1979 and has a Ph.D. in theoretical physics from Princeton University.” The subtitle of his book is “The Failure of String Theory and the Search for Unity in Physical Law.” In his chapter on “Is Superstring Theory Science,” he wrote, “More than twenty years of intensive research by the thousands of the best scientists in the world producing tens of thousands of scientific papers has not led to a single testable experimental prediction of the theory. This unprecedented situation leads one to ask whether one can really describe the superstring theory research as scientific research in the field of physics.” But the string theorists rebut with a degree of credibility that the theory does produce testable predictions but our present equipment cannot test them. In the future, the theory may be vindicated, they proclaim. See Ed. Witten’s comments on this issue later on.

In the concluding chapter of his book, Woit wrote, “The failure of the superstring theory program must be recognized and lessons learned from this failure before there can be much hope of moving forward… Much of the argument of this book has been of a very negative nature, criticizing the superstring theory program as a failed and over-hyped project.”

The title of the third book is “The Trouble with Physics,” 2006, written by Lee Smolin who has a Ph.D. in physics from Harvard, taught at Yale and Pennsylvania universities and helped found “the innovative Perimeter Institute.” He has previously written “The Life of the Cosmos” and “Three Roads to Quantum Gravity.” In the introduction of his last book (The Trouble…), he wrote, “String theory rests on several key conjectures, for which there is some evidence but no proof. Even worse, after all the scientific labor expended in its study, we still do not know whether there is a complete and coherent theory that can even go by the name ‘string theory’” These are harsh words indeed but the inadequacy of the string theory is such that even some of its strong proponents recognize it. Another book that was published in 2006 is “The Fabric of the Cosmos” by Brian Greene, the author of “The Elegant Universe.” Quoting from Greene’s book, Lee Smolin wrote, “Even today, more than three decades after the initial articulation, most string practitioners believe we still don’t have a comprehensive answer to the rudimentary question, What is String Theory?” Quoting from David Gross, a Nobel laureate for his work on the standard model who has become an aggressive and ‘formidable champion’ of string theory, Lee Smolin wrote, “We don’t know what we are talking about… The state of physics today is like it was when we were mystified by radioactivity… They were missing something absolutely fundamental. We are missing perhaps something as profound as they were back then.”

If string theory is so deficient, one may ask: Is there any other alternative theory that can unify quantum mechanics with general relativity? Lee Smolin wrote in his book, “One prominent string theorist, Joseph Polchinski, of the Kavli Institute at UC Santa Barbara, was asked not long ago to give a talk on ‘Alternatives to String Theory.’ His first reaction, he said, was that this was silly. There are no alternatives…All good ideas are part of string theory.”

Originally, I thought of calling this article “Is String Theory Dead?” but then I realized that it is very much alive and kicking because there are so many prominent mathematicians and physicists working on this theory in the hope that they would achieve their goal one day. String theory is criticized by its critics mainly because they claim that it doesn’t make any testable predictions. The few predictions that it does make are the ones which other existing theories had already made. So in their opinion, string theory is not scientific in the usual Popperian sense because it cannot be falsified. Empirical verification is the key point. If this is so obvious to the critics, why are string theorists so oblivious of it? Actually, it is not as simple as that. The string theorists believe the theory is testable but we do not have the right kind of equipment yet for this purpose.

Shedding light on this point, Brian Greene whom Lee Smolin quoted in his book as seen above, wrote in his article, “The Universe on a String”, in The New York Times (October 20, 2006), “We understand string theory much better now than we did 20 years ago. We’ve developed powerful techniques of mathematical analysis that have improved the accuracy of its calculations and provided invaluable insights into the theory’s logical structure. Even so, researchers worldwide are still working toward an exact and tractable formulation of the theory’s equations. And without that final formulation in hand, the kind of detailed definitive predictions that would subject the theory to comprehensive experimental vetting remain beyond our reach,”

Another point of criticism is the requirement of ten or eleven dimensions that the theory needs. The critics believe that ten or eleven dimensional universe is unrealistic. Also, the method of compactification of the extra dimensions creates some serious doubts. Each method of compactification gives a new theory and a new universe. There are almost infinite versions of the string theory. Nobody knows which one of these (or any of these) is the right one.

Yet another criticism that is leveled at the string theory is that it is not “background-independent” meaning that it is based on a fixed geometry of the space. Einstein’s theory of general relativity showed that the space geometry is dynamic and changing in time. “this is a basic discovery and cannot be reversed, so any further theory must incorporate it,” asserted Lee Smolin. He continued, “String theory doesn’t, so if string theory is valid, there must lie behind it a more fundamental theory – one that is background-independent.”

Again, it is sometimes mentioned that Einstein’s theory of relativity was not immediately tested and verified. Here the difference is that Einstein’s theory made some very important predictions which guided the scientists how to test the theory. For example, the theory predicted that light rays are bent in the vicinity of massive stars; also predicted black holes and that the universe is constantly expanding, among many others. All these predictions have come true. On the other hand, string theory doesn’t make predictions which can be tested. Strong proponents of string theory believe that it does. These predictions are however such that cannot be tested at present because we don’t have the right equipment to do so.

Towards the end of his article, Greene wrote, “I have worked on string theory for more than 20 years because I believe it provides the most powerful framework for constructing the long-sought unified theory. Nonetheless, should an inconsistency be found, or should future studies reveal an insuperable barrier to making contact with experimental data, or should new discoveries reveal a superior approach, I’d change my research focus, and I have little doubt that most string theorists would too. But this hasn’t happened.”

One of the strongest supporters of string theory is Edward Witten, “a mathematical physicist at the Institute for Advanced Study in Princeton, New Jersey. Witten has been awarded everything from a McArthur ‘genius grant’ to the Fields Medal, the highest honor in the world of mathematics.” Answering a question regarding the testability of string theory, he observed, “One very important aspect of string theory is definitely testable. That was the prediction of supersymmetry, which emerged from string theory in the early ‘70s. Experimentalists are still trying to test it. It hasn’t been proved that supersymmetry is right. But there is a very precise relationship among the interaction rates of different kinds of particles which follows from supersymmetry and which has been tested successfully. Because of that and a variety of other clues, many physicists do suspect that our present is the decade when supersymmetry will be discovered. Supersymmetry is a very big prediction; it would be interesting to delve into history and try to see any theory that ever made as big a prediction,” (http://www.pbs.org/wgbh/nova/elegant/view-witten.html).

Theory tells us that there are “superpartners” for every elementary particle that has the same electric charge but differs in other properties such as spin.” It will become possible to check the existence of these superpartners using the high energy Large Hadron Collider (LHC) which is presently under construction near Geneva. Its completion is expected in 2007/2008.

Before closing this article, I quote again from Greene’s article. He wrote, “To be sure, no one successful experiment would establish that string theory is right, but neither would the failure of all such experiments prove the theory wrong. If the accelerator experiments fail to turn up anything, it could be that we need more powerful machines; if the astronomical observations fail to turn up anything, it could mean the effects are too small to be seen. The bottom line is that it’s hard to test a theory that not only taxes the capacity of today’s technology, but is also still very much under development.”

So the story of string theory is still unfolding. The theory is not dead although many consider it a dud theory. It took three hundred years to find the proof of Fermat’s Last Theorem. Let us hope that the unification theory wouldn’t take that long.