Books by Smolin, Lee

Smolin, Lee. Einstein's Unfinished Revolution. New York: Penguin Press, 2019. ISBN 978-1-59420-619-1.

In the closing years of the nineteenth century, one of those nagging little discrepancies vexing physicists was the behaviour of the photoelectric effect. Originally discovered in 1887, the phenomenon causes certain metals, when illuminated by light, to absorb the light and emit electrons. The perplexing point was that there was a minimum wavelength (colour of light) necessary for electron emission, and for longer wavelengths, no electrons would be emitted at all, regardless of the intensity of the beam of light. For example, a certain metal might emit electrons when illuminated by green, blue, violet, and ultraviolet light, with the intensity of electron emission proportional to the light intensity, but red or yellow light, regardless of how intense, would not result in a single electron being emitted.

This didn't make any sense. According to Maxwell's wave theory of light, which was almost universally accepted and had passed stringent experimental tests, the energy of light depended upon the amplitude of the wave (its intensity), not the wavelength (or, reciprocally, its frequency). And yet the photoelectric effect didn't behave that way—it appeared that whatever was causing the electrons to be emitted depended on the wavelength of the light, and what's more, there was a sharp cut-off below which no electrons would be emitted at all.

In 1905, in one of his “miracle year” papers, “On a Heuristic Viewpoint Concerning the Production and Transformation of Light”, Albert Einstein suggested a solution to the puzzle. He argued that light did not propagate as a wave at all, but rather in discrete particles, or “quanta”, later named “photons”, whose energy was proportional to the wavelength of the light. This neatly explained the behaviour of the photoelectric effect. Light with a wavelength longer than the cut-off point was transmitted by photons whose energy was too low to knock electrons out of metal they illuminated, while those above the threshold could liberate electrons. The intensity of the light was a measure of the number of photons in the beam, unrelated to the energy of the individual photons.

This paper became one of the cornerstones of the revolutionary theory of quantum mechanics, the complete working out of which occupied much of the twentieth century. Quantum mechanics underlies the standard model of particle physics, which is arguably the most thoroughly tested theory in the history of physics, with no experiment showing results which contradict its predictions since it was formulated in the 1970s. Quantum mechanics is necessary to explain the operation of the electronic and optoelectronic devices upon which our modern computing and communication infrastructure is built, and describes every aspect of physical chemistry.

But quantum mechanics is weird. Consider: if light consists of little particles, like bullets, then why when you shine a beam of light on a barrier with two slits do you get an interference pattern with bright and dark bands precisely as you get with, say, water waves? And if you send a single photon at a time and try to measure which slit it went through, you find it always went through one or the other, but then the interference pattern goes away. It seems like whether the photon behaves as a wave or a particle depends upon how you look at it. If you have an hour, here is grand master explainer Richard Feynman (who won his own Nobel Prize in 1965 for reconciling the quantum mechanical theory of light and the electron with Einstein's special relativity) exploring how profoundly weird the double slit experiment is.

Fundamentally, quantum mechanics seems to violate the principle of realism, which the author defines as follows.

The belief that there is an objective physical world whose properties are independent of what human beings know or which experiments we choose to do. Realists also believe that there is no obstacle in principle to our obtaining complete knowledge of this world.

This has been part of the scientific worldview since antiquity and yet quantum mechanics, confirmed by innumerable experiments, appears to indicate we must abandon it. Quantum mechanics says that what you observe depends on what you choose to measure; that there is an absolute limit upon the precision with which you can measure pairs of properties (for example position and momentum) set by the uncertainty principle; that it isn't possible to predict the outcome of experiments but only the probability among a variety of outcomes; and that particles which are widely separated in space and time but which have interacted in the past are entangled and display correlations which no classical mechanistic theory can explain—Einstein called the latter “spooky action at a distance”. Once again, all of these effects have been confirmed by precision experiments and are not fairy castles erected by theorists.

From the formulation of the modern quantum theory in the 1920s, often called the Copenhagen interpretation after the location of the institute where one of its architects, Neils Bohr, worked, a number of eminent physicists including Einstein and Louis de Broglie were deeply disturbed by its apparent jettisoning of the principle of realism in favour of what they considered a quasi-mystical view in which the act of “measurement” (whatever that means) caused a physical change (wave function collapse) in the state of a system. This seemed to imply that the photon, or electron, or anything else, did not have a physical position until it interacted with something else: until then it was just an immaterial wave function which filled all of space and (when squared) gave the probability of finding it at that location.

In 1927, de Broglie proposed a pilot wave theory as a realist alternative to the Copenhagen interpretation. In the pilot wave theory there is a real particle, which has a definite position and momentum at all times. It is guided in its motion by a pilot wave which fills all of space and is defined by the medium through which it propagates. We cannot predict the exact outcome of measuring the particle because we cannot have infinitely precise knowledge of its initial position and momentum, but in principle these quantities exist and are real. There is no “measurement problem” because we always detect the particle, not the pilot wave which guides it. In its original formulation, the pilot wave theory exactly reproduced the predictions of the Copenhagen formulation, and hence was not a competing theory but rather an alternative interpretation of the equations of quantum mechanics. Many physicists who preferred to “shut up and calculate” considered interpretations a pointless exercise in phil-oss-o-phy, but de Broglie and Einstein placed great value on retaining the principle of realism as a cornerstone of theoretical physics. Lee Smolin sketches an alternative reality in which “all the bright, ambitious students flocked to Paris in the 1930s to follow de Broglie, and wrote textbooks on pilot wave theory, while Bohr became a footnote, disparaged for the obscurity of his unnecessary philosophy”. But that wasn't what happened: among those few physicists who pondered what the equations meant about how the world really works, the Copenhagen view remained dominant.

In the 1950s, independently, David Bohm invented a pilot wave theory which he developed into a complete theory of nonrelativistic quantum mechanics. To this day, a small community of “Bohmians” continue to explore the implications of his theory, working on extending it to be compatible with special relativity. From a philosophical standpoint the de Broglie-Bohm theory is unsatisfying in that it involves a pilot wave which guides a particle, but upon which the particle does not act. This is an “unmoved mover”, which all of our experience of physics argues does not exist. For example, Newton's third law of motion holds that every action has an equal and opposite reaction, and in Einstein's general relativity, spacetime tells mass-energy how to move while mass-energy tells spacetime how to curve. It seems odd that the pilot wave could be immune from influence of the particle it guides. A few physicists, such as Jack Sarfatti, have proposed “post-quantum” extensions to Bohm's theory in which there is back-reaction from the particle on the pilot wave, and argue that this phenomenon might be accessible to experimental tests which would distinguish post-quantum phenomena from the predictions of orthodox quantum mechanics. A few non-physicist crackpots have suggested these phenomena might even explain flying saucers.

Moving on from pilot wave theory, the author explores other attempts to create a realist interpretation of quantum mechanics: objective collapse of the wave function, as in the Penrose interpretation; the many worlds interpretation (which Smolin calls “magical realism”); and decoherence of the wavefunction due to interaction with the environment. He rejects all of them as unsatisfying, because they fail to address glaring lacunæ in quantum theory which are apparent from its very equations.

The twentieth century gave us two pillars of theoretical physics: quantum mechanics and general relativity—Einstein's geometric theory of gravitation. Both have been tested to great precision, but they are fundamentally incompatible with one another. Quantum mechanics describes the very small: elementary particles, atoms, and molecules. General relativity describes the very large: stars, planets, galaxies, black holes, and the universe as a whole. In the middle, where we live our lives, neither much affects the things we observe, which is why their predictions seem counter-intuitive to us. But when you try to put the two theories together, to create a theory of quantum gravity, the pieces don't fit. Quantum mechanics assumes there is a universal clock which ticks at the same rate everywhere in the universe. But general relativity tells us this isn't so: a simple experiment shows that a clock runs slower when it's in a gravitational field. Quantum mechanics says that it isn't possible to determine the position of a particle without its interacting with another particle, but general relativity requires the knowledge of precise positions of particles to determine how spacetime curves and governs the trajectories of other particles. There are a multitude of more gnarly and technical problems in what Stephen Hawking called “consummating the fiery marriage between quantum mechanics and general relativity”. In particular, the equations of quantum mechanics are linear, which means you can add together two valid solutions and get another valid solution, while general relativity is nonlinear, where trying to disentangle the relationships of parts of the systems quickly goes pear-shaped and many of the mathematical tools physicists use to understand systems (in particular, perturbation theory) blow up in their faces.

Ultimately, Smolin argues, giving up realism means abandoning what science is all about: figuring out what is really going on. The incompatibility of quantum mechanics and general relativity provides clues that there may be a deeper theory to which both are approximations that work in certain domains (just as Newtonian mechanics is an approximation of special relativity which works when velocities are much less than the speed of light). Many people have tried and failed to “quantise general relativity”. Smolin suggests the problem is that quantum theory itself is incomplete: there is a deeper theory, a realistic one, to which our existing theory is only an approximation which works in the present universe where spacetime is nearly flat. He suggests that candidate theories must contain a number of fundamental principles. They must be background independent, like general relativity, and discard such concepts as fixed space and a universal clock, making both dynamic and defined based upon the components of a system. Everything must be relational: there is no absolute space or time; everything is defined in relation to something else. Everything must have a cause, and there must be a chain of causation for every event which traces back to its causes; these causes flow only in one direction. There is reciprocity: any object which acts upon another object is acted upon by that object. Finally, there is the “identity of indescernibles”: two objects which have exactly the same properties are the same object (this is a little tricky, but the idea is that if you cannot in some way distinguish two objects [for example, by their having different causes in their history], then they are the same object).

This argues that what we perceive, at the human scale and even in our particle physics experiments, as space and time are actually emergent properties of something deeper which was manifest in the early universe and in extreme conditions such as gravitational collapse to black holes, but hidden in the bland conditions which permit us to exist. Further, what we believe to be “laws” and “constants” may simply be precedents established by the universe as it tries to figure out how to handle novel circumstances. Just as complex systems like markets and evolution in ecosystems have rules that change based upon events within them, maybe the universe is “making it up as it goes along”, and in the early universe, far from today's near-equilibrium, wild and crazy things happened which may explain some of the puzzling properties of the universe we observe today.

This needn't forever remain in the realm of speculation. It is easy, for example, to synthesise a protein which has never existed before in the universe (it's an example of a combinatorial explosion). You might try, for example, to crystallise this novel protein and see how difficult it is, then try again later and see if the universe has learned how to do it. To be extra careful, do it first on the International Space Station and then in a lab on the Earth. I suggested this almost twenty years ago as a test of Rupert Sheldrake's theory of morphic resonance, but (although doubtless Smolin would shun me for associating his theory with that one), it might produce interesting results.

The book concludes with a very personal look at the challenges facing a working scientist who has concluded the paradigm accepted by the overwhelming majority of his or her peers is incomplete and cannot be remedied by incremental changes based upon the existing foundation. He notes:

There is no more reasonable bet than that our current knowledge is incomplete. In every era of the past our knowledge was incomplete; why should our period be any different? Certainly the puzzles we face are at least as formidable as any in the past. But almost nobody bets this way. This puzzles me.

Well, it doesn't puzzle me. Ever since I learned classical economics, I've always learned to look at the incentives in a system. When you regard academia today, there is huge risk and little reward to get out a new notebook, look at the first blank page, and strike out in an entirely new direction. Maybe if you were a twenty-something patent examiner in a small city in Switzerland in 1905 with no academic career or reputation at risk you might go back to first principles and overturn space, time, and the wave theory of light all in one year, but today's institutional structure makes it almost impossible for a young researcher (and revolutionary ideas usually come from the young) to strike out in a new direction. It is a blessing that we have deep thinkers such as Lee Smolin setting aside the easy path to retirement to ask these deep questions today.

Here is a lecture by the author at the Perimeter Institute about the topics discussed in the book. He concentrates mostly on the problems with quantum theory and not the speculative solutions discussed in the latter part of the book.

May 2019 

Unger, Roberto Mangabeira and Lee Smolin. The Singular Universe and the Reality of Time. Cambridge: Cambridge University Press, 2015. ISBN 978-1-107-07406-4.

In his 2013 book Time Reborn (June 2013), Lee Smolin argued that, despite its extraordinary effectiveness in understanding the behaviour of isolated systems, what he calls the “Newtonian paradigm” is inadequate to discuss cosmology: the history and evolution of the universe as a whole. In this book, Smolin and philosopher Roberto Mangabeira Unger expand upon that observation and present the case that the current crisis in cosmology, with its appeal to multiple universes and mathematical structures which are unobservable, even in principle, is a consequence of the philosophical, scientific, and mathematical tools we've been employing since the dawn of science attempting to be used outside their domain of applicability, and that we must think differently when speaking of the universe as a whole, which contains all of its own causes and obeys no laws outside itself. The authors do not present their own theories to replace those of present-day cosmology (although they discuss the merits of several proposals), but rather describe their work as a “proposal in natural philosophy” which might guide investigators searching for those new theories.

In brief, the Newtonian paradigm is that the evolution of physical systems is described by differential equations which, given a set of initial conditions, permit calculating the evolution of a system in the future. Since the laws of physics at the microscopic level are reversible, given complete knowledge of the state of a system at a given time, its past can equally be determined. Quantum mechanics modifies this only in that rather than calculating the position and momentum of particles (or other observables), we calculate the deterministic evolution of the wave function which gives the probability of observing them in specific states in the future.

This paradigm divides physics into two components: laws (differential equations) and initial conditions (specification of the initial state of the system being observed). The laws themselves, although they allow calculating the evolution of the system in time, are themselves timeless: they do not change and are unaffected by the interaction of objects. But if the laws are timeless and not subject to back-reaction by the objects whose interaction they govern, where did they come from and where do they exist? While conceding that these aren't matters which working scientists spend much time thinking about, in the context of cosmology they post serious philosophical problems. If the universe all that is and contains all of its own causes, there is no place for laws which are outside the universe, cannot be acted upon by objects within it, and have no apparent cause.

Further, because mathematics has been so effective in expressing the laws of physics we've deduced from experiments and observations, many scientists have come to believe that mathematics can be a guide to exploring physics and cosmology: that some mathematical objects we have explored are, in a sense, homologous to the universe, and that learning more about the mathematics can be a guide to discoveries about reality.

One of the most fundamental discoveries in cosmology, which has happened within the lifetimes of many readers of this book, including me, is that the universe has a history. When I was a child, some scientists (a majority, as I recall) believed the universe was infinite and eternal, and that observers at any time in the past or future would observe, at the largest scales, pretty much the same thing. Others argued for an origin at a finite time in the past, with the early universe having a temperature and density much greater than at present—this theory was mocked as the “big bang”. Discovery of the cosmic background radiation and objects in the distant universe which did not at all resemble those we see nearby decisively decided this dispute in favour of the big bang, and recent precision measurements have allowed determination of when it happened and how the universe evolved subsequently.

If the universe has a finite age, this makes the idea of timeless laws even more difficult to accept. If the universe is eternal, one can accept that the laws we observe have always been that way and always will be. But if the universe had an origin we can observe, how did the laws get baked into the universe? What happened before the origin we observe? If every event has a cause, what was the cause of the big bang?

The authors argue that in cosmology—a theory encompassing the entire universe—a global privileged time must govern all events. Time flows not from some absolute clock as envisioned by Newtonian physics or the elastic time of special and general relativity, but from causality: every event has one or more causes, and these causes are unique. Depending upon their position and state of motion, observers will disagree about the durations measured by their own clocks, and on the order in which things at different positions in space occurred (the relativity of simultaneity), but they will always observe a given event to have the same cause(s), which precede it. This relational notion of time, they argue, is primordial, and space may be emergent from it.

Given this absolute and privileged notion of time (which many physicists would dispute, although the authors argue does not conflict with relativity), that time is defined by the causality of events which cause change in the universe, and that there is a single universe with nothing outside it and which contains all of its own causes, then is it not plausible to conclude that the “laws” of physics which we observe are not timeless laws somehow outside the universe or grounded in a Platonic mathematics beyond the universe, but rather have their own causes, within the universe, and are subject to change: just as there is no “unmoved mover”, there is no timeless law? The authors, particularly Smolin, suggest that just as we infer laws from observing regularities in the behaviour of systems within the universe when performing experiments in various circumstances, these laws emerge as the universe develops “habits” as interactions happen over and over. In the present cooled-down state of the universe, it's very much set in its ways, and since everything has happened innumerable times we observe the laws to be unchanging. But closer to the big bang or at extreme events in the subsequent universe, those habits haven't been established and true novelty can occur. (Indeed, simply by synthesising a protein with a hundred amino acids at random, you're almost certain to have created a molecule which has never existed before in the observable universe, and it may be harder to crystallise the first time than subsequently. This appears to be the case. This is my observation, not the authors'.)

Further, not only may the laws change, but entirely new kinds of change may occur: change itself can change. For example, on Earth, change was initially governed entirely by the laws of physics and chemistry (with chemistry ultimately based upon physics). But with the emergence of life, change began to be driven by evolution which, while at the molecular level was ultimately based upon chemistry, created structures which equilibrium chemistry never could, and dramatically changed the physical environment of the planet. This was not just change, but a novel kind of change. If it happened here, in our own recent (in cosmological time) history, why should we assume other novel kinds of change did not emerge in the early universe, or will not continue to manifest themselves in the future?

This is a very difficult and somewhat odd book. It is written in two parts, each by one of the co-authors, largely independent of one another. There is a twenty page appendix in which the authors discuss their disagreements with one another, some of which are fundamental. I found Unger's part tedious, repetitive, and embodying all of things I dislike about academic philosophers. He has some important things to say, but I found that slogging through almost 350 pages of it was like watching somebody beat a moose to death with an aluminium baseball bat: I believe a good editor, or even a mediocre one, could have cut this to 50 pages without losing anything and making the argument more clearly than trying to dig it out of this blizzard of words. Lee Smolin is one of the most lucid communicators among present-day research scientists, and his part is clear, well-argued, and a delight to read; it's just that you have to slog through the swamp to get there.

While suggesting we may have been thinking about cosmology all wrong, this is not a book which suggests either an immediate theoretical or experimental programme to explore these new ideas. Instead, it intends to plant the seed that, apart from time and causality, everything may be emergent, and that when we think about the early universe we cannot rely upon the fixed framework of our cooled-down universe with its regularities. Some of this is obvious and non-controversial: before there were atoms, there was no periodic table of the elements. But was there a time before there was conservation of energy, or before locality?

September 2015 

Smolin, Lee. Time Reborn. New York: Houghton Mifflin, 2013. ISBN 978-0-547-51172-6.

Early in his career, the author received some unorthodox career advice from Richard Feynman. Feynman noted that in physics, as in all sciences, there were a large number of things that most professional scientists believed which nobody had been able to prove or demonstrate experimentally. Feynman's insight was that, when considering one of these problems as an area to investigate, there were two ways to approach it. The first was to try to do what everybody had failed previously to accomplish. This, he said, was extremely difficult and unlikely to succeed, since it assumes you're either smarter than everybody who has tried before or have some unique insight which eluded them. The other path is to assume that the failure of numerous brilliant people might indicate that what they were trying to demonstrate was, in fact, wrong, and that it might be wiser for the ambitious scientist to search for evidence to the contrary.

Based upon the author's previous work and publications, I picked up this book expecting a discussion of the problem of time in quantum gravity. What I found was something breathtakingly more ambitious. In essence, the author argues that when it comes to cosmology: the physics of the universe as a whole, physicists have been doing it wrong for centuries, and that what he calls the “Newtonian paradigm” must be replaced with one in which time is fundamental in order to stop speaking nonsense.

The equations of general relativity, especially when formulated in attempts to create a quantum theory of gravitation, seem to suggest that our perception of time is an illusion: we live in a timeless block universe, in which our consciousness can be thought of as a cursor moving through a fixed, deterministic spacetime. In general relativity, the rate of perceived flow of time depends upon one's state of motion and the amount of mass-energy in the vicinity of the observer, so it makes no sense to talk about any kind of global time co-ordinate. Quantum mechanics, on the other hand, assumes there is a global clock, external to the system and unaffected by it, which governs the evolution of the wave function. These views are completely incompatible—hence the problem of time in quantum gravity.

But the author argues that “timelessness” has its roots much deeper in the history and intellectual structure of physics. When one uses Newtonian mechanics to write down a differential equation which describes the path of a ball thrown upward, one is reducing a process which would otherwise require enumerating a list of positions and times to a timeless relationship which is valid over the entire trajectory. Time appears in the equation simply as a label which causes it to emit the position at that moment. The equation of motion, and, more importantly, the laws of motion which allow us to write it down for this particular case, are entirely timeless: they affect the object but are not affected by it, and they appear to be specified outside the system.

This, when you dare to step back and think about it, is distinctly odd. Where did these laws come from? Well, in Newton's day and in much of the history of science since, most scientists would say they were prescribed by a benevolent Creator. (My own view that they were put into the simulation by the 13 year old superkid who created it in order to win the Science Fair with the most interesting result, generating the maximum complexity, is isomorphic to this explanation.) Now, when you're analysing a system “in a box”, it makes perfect sense to assume the laws originate from outside and are fixed; after all, we can compare experiments run in different boxes and convince ourselves that the same laws obtain regardless of symmetries such as translation, orientation, or boost. But note that once we try to generalise this to the entire universe, as we must in cosmology, we run into a philosophical speed bump of singularity scale. Now we cannot escape the question of where the laws came from. If they're from inside the universe, then there must have been some dynamical process which created them. If they're outside the universe, they must have had to be imposed by some process which is external to the universe, which makes no sense if you define the universe as all there is.

Smolin suggests that laws exist within our universe, and that they evolve in an absolute time, which is primordial. There is no unmoved mover: the evolution of the universe (and the possibility that universes give birth to other universes) drives the evolution of the laws of physics. Perhaps the probabilistic results we observe in quantum mechanical processes are not built-in ahead of time and prescribed by timeless laws outside the universe, but rather a random choice from the results of previous similar measurements. This “principle of precedence”, which is remarkably similar to that of English common law, perfectly reproduces the results of most tests of quantum mechanics, but may be testable by precision experiments where circumstances never before created in the universe are measured, for example in quantum computing. (I am certain Prof. Smolin would advocate for my being beheaded were I to point out the similarity of this hypothesis with Rupert Sheldrake's concept of morphic resonance; some years ago I suggested to Dr Sheldrake a protein crystallisation experiment on the International Space Station to test this theory; it is real science, but to this date nobody has done it. Few wish to risk their careers testing what “everybody knows”.)

This is one those books you'll need to think about after you've read it, then after some time, re-read to get the most out of it. A collection of online appendices expand upon topics discussed in the book. An hour-long video discussion of the ideas in the book by the author and the intellectual path which led him to them is available.

June 2013 

Smolin, Lee. The Trouble with Physics. New York: Houghton Mifflin, 2006. ISBN 0-618-55105-0.

The first forty years of the twentieth century saw a revolution in fundamental physics: special and general relativity changed our perception of space, time, matter, energy, and gravitation; quantum theory explained all of chemistry while wiping away the clockwork determinism of classical mechanics and replacing it with a deeply mysterious theory which yields fantastically precise predictions yet nobody really understands at its deepest levels; and the structure of the atom was elucidated, along with important clues to the mysteries of the nucleus. In the large, the universe was found to be enormously larger than expected and expanding—a dynamic arena which some suspected might have an origin and a future vastly different than its present state.

The next forty years worked out the structure and interactions of the particles and forces which constitute matter and govern its interactions, resulting in a standard model of particle physics with precisely defined theories which predicted all of the myriad phenomena observed in particle accelerators and in the highest energy events in the heavens. The universe was found to have originated in a big bang no more distant than three times the age of the Earth, and the birth cry of the universe had been detected by radio telescopes.

And then? Unexpected by almost all practitioners of high energy particle physics, which had become an enterprise larger by far than all of science at the start of the century, progress stopped. Since the wrapping up of the standard model around 1975, experiments have simply confirmed its predictions (with the exception of the discovery of neutrino oscillations and consequent mass, but that can be accommodated within the standard model without changing its structure), and no theoretical prediction of phenomena beyond the standard model has been confirmed experimentally.

What went wrong? Well, we certainly haven't reached the End of Science or even the End of Physics, because the theories which govern phenomena in the very small and very large—quantum mechanics and general relativity—are fundamentally incompatible with one another and produce nonsensical or infinite results when you attempt to perform calculations in the domain—known to exist from astronomical observations—where both must apply. Even a calculation as seemingly straightforward as estimating the energy of empty space yields a result which is 120 orders of magnitude greater than experiment shows it to be: perhaps the most embarrassing prediction in the history of science.

In the first chapter of this tour de force, physicist Lee Smolin poses “The Five Great Problems in Theoretical Physics”, all of which are just as mysterious today as they were thirty-five years ago. Subsequent chapters explore the origin and nature of these problems, and how it came to be, despite unprecedented levels of funding for theoretical and experimental physics, that we seem to be getting nowhere in resolving any of these fundamental enigmas.

This prolonged dry spell in high energy physics has seen the emergence of string theory (or superstring theory, or M-theory, or whatever they're calling it this year) as the dominant research program in fundamental physics. At the outset, there were a number of excellent reasons to believe that string theory pointed the way to a grand unification of all of the forces and particles of physics, and might answer many, if not all, of the Great Problems. This motivated many very bright people, including the author (who, although most identified with loop quantum gravity research, has published in string theory as well) to pursue this direction. What is difficult for an outsider to comprehend, however, is how a theoretical program which, after thirty-five years of intensive effort, has yet to make a single prediction testable by a plausible experiment; has failed to predict any of the major scientific surprises that have occurred over those years such as the accelerating expansion of the universe and the apparent variation in the fine structure constant; that does not even now exist in a well-defined mathematical form; and has not been rigorously proved to be a finite theory; has established itself as a virtual intellectual monopoly in the academy, forcing aspiring young theorists to work in string theory if they are to have any hope of finding a job, receiving grants, or obtaining tenure.

It is this phenomenon, not string theory itself, which, in the author's opinion, is the real “Trouble with Physics”. He considers string theory as quite possibly providing clues (though not the complete solution) to the great problems, and finds much to admire in many practitioners of this research. But monoculture is as damaging in academia as in agriculture, and when it becomes deeply entrenched in research institutions, squeezes out other approaches of equal or greater merit. He draws the distinction between “craftspeople”, who are good at performing calculations, filling in blanks, and extending an existing framework, and “seers”, who make the great intellectual leaps which create entirely new frameworks. After thirty-five years with no testable result, there are plenty of reasons to suspect a new framework is needed, yet our institutions select out those most likely to discover them, or force them to spend their most intellectually creative years doing tedious string theory calculations at the behest of their elders.

In the final chapters, Smolin looks at how academic science actually works today: how hiring and tenure decisions are made, how grant applications are evaluated, and the difficult career choices young physicists must make to work within this system. When reading this, the word “Gosplan” (Госпла́н) kept flashing through my mind, for the process he describes resembles nothing so much as central planning in a command economy: a small group of senior people, distant from the facts on the ground and the cutting edge of intellectual progress, trying to direct a grand effort in the interest of “efficiency”. But the lesson of more than a century of failed socialist experiments is that, in the timeless words of Rocket J. Squirrel, “that trick never works”—the decisions inevitably come down on the side of risk aversion, and are often influenced by cronyism and toadying to figures in authority. The concept of managing risk and reward by building a diversified portfolio of low and high risk placements which is second nature to managers of venture capital funds and industrial research and development laboratories appears to be totally absent in academic science, which is supposed to be working on the most difficult and fundamental questions. Central planning works abysmally for cement and steel manufacturing; how likely is it to spark the next scientific revolution?

There is much more to ponder: why string theory, as presently defined, cannot possibly be a complete theory which subsumes general relativity; hints from experiments which point to new physics beyond string theory; stories of other mathematically beautiful theories (such as SU(5) grand unification) which experiment showed to be dead wrong; and a candid view of the troubling groupthink, appeal to authority, and intellectual arrogance of some members of the string theory community. As with all of Smolin's writing, this is a joy to read, and you get the sense that he's telling you the straight story, as honestly as he can, not trying to sell you something. If you're interested in these issues, you'll probably also want to read Leonard Susskind's pro-string The Cosmic Landscape (March 2006) and Peter Woit's sceptical Not Even Wrong (June 2006).

September 2006