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

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!

Before reading this book I heard many positive reviews from my friends, and having finished it I'm not disappointed. Not only does it give a very interesting history of the ideas of unification in physics (I did my project work in the UK on the original Kaluza Klein Theory), but also gives a glimpse of the community doing the science. Belief in what you do is necessary to do a good job, but belief can also backfire and become blind. This is most likely what has happened to String theory, that has had unfortunate repercussions for alternative theroies such as loop quantum gravity, twistors, and other visionary ideas. On top of this, Smolin also rightly critizises Universities to encourage "standard" Science and discourage visionaries from positions and jobs. This is a much more serious development and is (among other things) an effect of Big Science as Just Any Job, subject to tests, evaluations, peers, making a career for tenure, etc. I see this in my own country where scientists with original ideas have a hard time surviving in a bureaucratic tangle of committies, evaluations, politically correct research grant applications and heavy teaching burdens. I think the most interesting research these days come from hightech companies, and independent research insititutes like the Perimeter Institute and Santa Fe Institute for non-linear science, to mention a few. If I was financially independent with more brains than I actually have, I would open an institute like that. The research topic? Building artificial minds and trying to understand human and animal intelligence and cognition. And having a lot of fun at work without red tape getting in your way, which is what science and exploring the world is really about.

Einstein's theory of Relativity is incomplete, much like Newton's Laws are incomplete. While the theory and laws work well within their set of assumptions, they start to diverge as conditions move outside their envelope of comfort. Newton's laws, while intuitive, have been proven to produce wrong answers at high speed and intense gravity. Einstein's theory shows great correspondence with experiment - up until the user tries to apply it to Black Holes, or correlate it with Quantum Mechanics, also a well regarded theory in it's own right.

The Standard Model can be used to investigate some of these areas, but it doesn't forge new ground. It produces answers when initial conditions are customized, but tells us little or nothing about why those initial conditions are what they are.

String Theory is supposed to address these problems, but it doesn't. String Theory is really a large number of theories, each with it's own set of initial conditions, leaving us no further along than the Standard Model. Any advances made using String Theory can be made other ways, sometimes with less effort.

There are 5 great, unsolved problems in physics today:
1) Combine general relativity and quantum theory into a single theory that can claim to be the complete theory of nature.
2) Resolve the problems in the foundations of quantum mechanics, either by making sense of the theory as it stands or by inventing a new theory that does make sense.
3) Determine whether or not the various particles and forces can be unified in a theory that explains them all as manifestations of a single, fundamental entity.
4) Explain how the values of the free constants in the standard model of particle physics are chosen in nature.
5) Explain dark matter and dark energy. Or, if they don't exist, determine how and why gravity is modified on large scales. More generally, explain why the constants of the standard model of cosmology, including the dark energy, have the values they do.

The author argues that while the people that study string theory are all very intelligent and hard working, there has been little or no progress in physics due to their efforts in the last 25 to 30 years. These string theory proponents are highly confident that they will find the answers they seek (the answers are always just around the corner), and they monopolize most of the talent and money in physics in the failing effort.

That is the trouble with physics.

The author is very persuasive and provides a lot of data and good arguments for his points in this book, but more importantly, he provides suggestions for avenues of inquiry by the professional physics society, why this is important for lay people who are the readers of this book, and what we lay people can do to help. His suggestions sound reasonable and doable. Some of the problem descriptions he makes are so well stated and universal that they apply to all features of life, not just physics, and the suggestions gain credence from the association.

The book is long and some of the arguments are so complete that the reader just wants the author to move on, but deep rooted problems need that kind of exposure to be heard and understood. Skimming, at those points, is recommended; you'll recognize them when you see them.