The Trouble With Physics: The Rise of String Theory, the Fall of a Science, And What Comes Next

This book is not a critique of string theory, and it is not a condemnation of string theorists. He makes this clear at several points throughout the book, but the amount of time he spends criticizing string theory has led some people to believe that this book is an "anti" book to balance the spate of "pro" string theory books. In reality, this is a book about science and the nature of science. This is clear in the acknowledgments, where Smolin describes how he originally wanted to write a book on the relationship of democracy and science and settled on applying this thesis in a particular situation- that of string theory. The book is absolutely fascinating the whole way through. Along the way, one gets lessons in physics without the advanced mathematics- but one can feel Smolin's passion for both. Quantum theory and the nature of quantum theory is explained well, and the underlying principles which appear to contradict relativity are illumined clearly.

What really makes this book, though, is Smolin's own deep understanding of scientific reasoning, both in its strengths and weaknesses. Smolin reveals to us a world far more open than we had ever imagined- he describes a great variety of solutions to the problem of quantum gravity, including his own personal favorite, quantum loop gravity. He describes the way that science changed in between Einstein and the present. In the early days of 20th century physics, the great physicists- Einstein, Bohr, Heisenberg- also had astute philosophical minds, and their trade was deep reflection on the underlying nature of reality. Physics served that greater project. After this period, however, physics entered into a more pragmatic stage, where the emphasis lay in ensuring that the equations worked out. Smolin makes clear that he is not criticizing this mode- indeed, he says that such pragmatism is needed in some periods. It produced the extremely successful standard model of particle physics. But we have now moved past such a need. For issues like quantum gravity, we need philosophical minds like Einstein and Bohr to fundamentally consider the nature of reality.

In the midst of all this, Smolin describes the rise of string theory- a potentially promising unification of the forces and particles which sees all of them as manifestations of vibrating strings. The problem with string theory is that what it does predict- supersymmetry, eleven dimensions, and so on- have no evidence. The other problem is that besides this, it doesn't make predictions. There are so many solutions to the equations of string theory that one can adjust the freely varying constants to save the theory from falsification. Smolin points to earlier theories in physics which suffered the same problems- most interestingly, the Kaluza-Klein model of electromagnetism, a mathematically beautiful theory which posited that just as gravitation described the four dimensions of spacetime, electromagnetism described a curled up fifth dimension. The difficulty with these concepts is that relativity is background independent. Instead of moving against a fixed spatial background, gravity describes the warps and curves of the space itself. The Kaluza-Klein model and string theory is background dependent- that is, in trying to reconcile relativity with quantum theory, it fails to integrate the most fundamental insight of the former.

Smolin argues that the funding going to string theory is taking away from other creative thinkers, and in exploring why, he refers to the philosopher of science Paul Feyerabend, who argued in "Against Method" that there wasn't a fixed scientific method. Instead, he proposed that science develops through "scientific anarchy" where different scientists pursue their hunches for different reasons. Smolin uses this to encourage reform of the tenure and peer-review system, which has benefits, but which is presently discouraging innovation. If one needs to be cited as much as possible in order to acquire tenure, then one won't work in a new, upstart project with only a few people working with you- because others who are uninterested won't cite you. Smolin is one of the few scientists who has a real, and not merely nominal, respect for philosophy and the philosophy of science. This is very refreshing.

One point was rather odd, however, and led me to roll my eyes several times. In various places throughout the book, Smolin will take a shot at intelligent design, using it as an example of "bad science." He doesn't critique it, but merely mentions it in passing. But the critique that Smolin levels at the scientific industry is exactly that which proponents of ID have leveled. Everything he said could be quoted verbatim by them. And shouldn't Feyerabend's principle of scientific anarchy allow proponents of ID to develop their research program in peace? This is the logical conclusion of everything that Smolin has argued, and the ritual denunciation of ID was irritating.

Regardless, this is a wonderful book, and I commend it to anybody who wants to understand physics, or science itself, more deeply.

This is the first book I have read by Lee Smolin and I found it to be quite enlightening. He begins by introducing us to what he refers to as the five great problems in physics. He notes that “any theory that claims to be a fundamental theory of nature must answer each one of them.” They relate to quantum gravity, problems in quantum mechanics, unification of forces and particles, the free constants in the standard model, and dark matter and dark energy.

He then discusses the quest for unification going back to the work of Herman Weyl, who invented the modern concept of unification which eventually led to string theory. We learn of the work of Nordstrom, Theodor Kaluza, Oskar Klein, and Hendrik Lorentz, and the early work on the concept of extra dimensions. This work set the stage for the science of unification of the four fundamental forces of nature – electromagnetism, weak force, strong force, and gravity. The difference in the forces today arises, as we learn, from spontaneous symmetry breaking. The idea of a grand unification sought to find a symmetry between the quarks (ruled by strong force) and leptons (ruled by electroweak force). This symmetry came to be known as SU(5). But it was soon learned that something call supersymmetry could provide a way to unify the bosons (force particles) and the fermions (matter particles). Then there is the quandary called the hierarchy problem – the wildly differing strengths of the forces and the large differences in the masses of the particles. We then learn that supersymmetry may be important to understand why the Higgs maintains the weight it has, which is 120 times the mass of a proton. This research lead to something called the MSSM or minimally supersymmetric standard model. Smolin breaks all this stuff down nicely in an understandable fashion.

Smolin carefully explains all the problems associated with the current understanding we have. For instance, the MSSM adds 105 free, adjustable constants to the already existing 20 of the standard model. In addition, we really don’t know why the particles have the values they have as they are determined experimentally. He notes that by 1974, “a background dependent approach to combining general relativity with quantum theory did not make sense.” We are then introduced to the next great thing: supergravity – could this provide the long sought answer? At the time of the writing of this book, Smolin felt that no one really understood what supersymmetry really meant.

But a revolution was brewing in the name of a concept called string theory. Was this finally the answer to unification? Smolin explains the early history of the theory – how it required twenty-five dimensions, tachyons (particles that traveled faster than light), massless particles, and the omission of fermions. These problems were solved eventually and much progress was made on the theory. String theory came to provide an impressive list of accomplishments: unification of elementary particles, gauge fields, gravitons, and unification of bosons and fermions.

A second revolution occurred around 1995. Here we are introduced to the concept of dualities – two different ways of looking at the same phenomenon. These dualities provided “relationships” between the five superstring theories that existed. These five theories became part of something called M-theory. Joseph Polchinski discovered that string theory was not just a theory of strings; he entertained the notion that other objects lived in the ten-dimensional spacetime. These objects came to be called D-branes. New relationships were discovered: between string and gauge theories and between branes and black holes. Smolin notes that “Our understanding expanded greatly following a set of fascinating, unprecedented results.” He realizes unfortunately that though M-theory remained a tantalizing conjecture and it was tempting to believe it, “it is not really a theory – it is a conjecture about a theory we would love to believe in.”

In 1998, it was discovered that the expansion of the universe was accelerating. This required something called a positive cosmological constant – something string theory failed to predict. A crucial breakthrough occurred in 2003 by a group of scientists from Stanford. The problem now was that there were ten to the 500th power possible theories – yikes! As Smolin remarks, “If an attempt to construct a unique theory of nature leads instead to ten to the 500th power theories, that approach has been reduced to absurdity.” So it seems the string theorists are now ready to accept that there is a landscape containing a large number of theories. The history of science has seen many promising theories fail; could this be such a case, Smolin wonders. Particularly, if we find that supersymmetry, higher dimensions, or unification of the forces does not exist, then string theory would prove to be false. Perhaps, as Smolin posits, somebody in the future will formulate a string theory which will uniquely lead to the standard model of particle physics, will be background-independent, and will function in our three-dimensional non-supersymmetric world.

Smolin now moves beyond string theory to discuss some very interesting phenomena. There is an interesting property of something called the cosmological constant which is referred to as the scale R. Combining this with a constant of nature gives us the speed of light squared divided by R. This is a special acceleration value that seems to be related to dark matter and the acceleration of stars found in galaxies; it is called Milgrom’s law, and it may have important consequences for Newton’s law of gravitation. Then there is the additional acceleration affecting the Pioneers 10 and 11 spacecraft pulling them toward the sun. In addition, something called the GZK prediction may even indicate a breakdown in special relativity at extreme energies – all fascinating stuff. There is some discussion about something called doubly special relativity II or DSR II. In this version of relativity, photons that have more energy travel faster; thus shortly after the big bang, when you had tremendous energy levels, light traveled much faster that it does today. This variable-speed-of-light theory is called Gravity’s Rainbow. Could this lead to the long sought quantum theory of gravity? Only time will tell.

Smolin now gets into the sociology of the string theory community. He notes the fierce competition for places in research universities today, lamenting the difficulty for a creative person wanting to pursue their own research program to secure some kind of academic position. He wonders why “string theory, in spite of a dearth of experimental predictions, has monopolized the resources available to advance fundamental physics, thus choking off the investigation of equally promising alternative approaches.” This leads him to list seven unusual aspects of the string theory community, such as tremendous self-confidence, a sense of identification with the group, tendency to believe results because they are widely accepted and so on. This segues into a necessary discussion of what is science. He notes that science has succeeded because of “a community that is defined and maintained by adherence to a shared ethic.” He refers to the scientific community in the terms “ethical community” and “imaginative community” and proceeds to define these terms. Scientific progress can be slowed by orthodoxy and fashion; but as long as we have those who are willing to pursue competing ideas, it cannot not be stopped completely.

Part of what tends to stifle innovative research is the fact that “you cannot get tenure in science at a U.S. research university if you haven’t been successful in getting grants, and you can’t get hired unless there is a likelihood that you will get grants.” Smolin sees as a solution the creation of small foundations that search out independent-minded seers who are working on their own approaches to theoretical problems, noting that the Royal Society in the United Kingdom has such a program. It has jump-started the careers of several scientists who now hold important positions in their fields. It seems like we need a better system to produce the breakthrough developments that will move us forward in our quest to understand the universe we live in. Will we solve the five great problems in physics? Only time will tell; I hope so!

A fascinating work of deconstruction, describing how theoretical physicists have wandered afield over the past thirty years piling untested and indeed unfalsifiable speculation upon speculation into a towering edifice of all but metaphysical hypotheses with little to show for all the effort and expense at the end. Smolin ably sets up his premise in the first chapter, defining the five major problems confronting theoretical physics, but then (probably inevitably) goes into such detail valiantly trying to describe in words what is really only comprehensible in mathematical terms that in the first half of the book the reader may find it difficult to see the forest for the trees. Also relevant and of interest are the snippets of autobiography Smolin provides. Definitely worth a read, but don't be disappointed if, as a non-physicist or non mathematician, you fail to follow all the technicalities.