The Trouble with Physics: the Rise of String Theory, the Fall of a Science, and What Comes Next
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Book Review The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next Reviewed by Brent Deschamp The Trouble with Physics: The Rise of String it stands or by inventing a new theory Theory, the Fall of a Science, and What Comes that does make sense. Next Lee Smolin Problem 3: Determine whether or not Houghton Mifflin Company, 2006 the various particles and forces can be US$26.00, 392 pages unified in a theory that explains them ISBN 0-618-55105-0 all as the manifestation of a single, fundamental entity. The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next Problem 4: Explain how the values is a book about the history of physics from Coper- of the free constants in the standard nicus forward. It is also a book that discusses the model of particle physics take on the current state of physics research, particularly the values they do in nature. dominion that string theory holds over the field. The author covers many diverse topics, and, while Problem 5: Explain dark matter and the title singles out string theory, this is a book dark energy, or if they don’t exist, de- about much more. termine how and why gravity is modi- Smolin starts with the five great unanswered fied on large scales. problems in physics today. I replicate them here Smolin goes into some detail about each prob- as they appear in Chapter 1: lem, and with this background he walks the reader through the amazing advances in physics since Problem 1: Combine general relativity Copernicus. His tour is guided by the idea that and quantum theory into a single the- physicists seek to unify both theories and objects ory that can claim to be the complete in an attempt to come to a better, and one hopes theory of nature (known as quantum simpler, understanding of the universe. Along the gravity). way Smolin spends almost as much time on the ideas that failed as on those that have survived. Problem 2: Resolve the problems in the His reasons become clear later on, but at this point foundations of quantum mechanics, in the book this emphasis shows the path great either by making sense of the theory as minds with great ideas have traveled to bring us to modern physics. Brent Deschamp is professor of mathematics at California He begins with two failures. The first is that State Polytechnic University, Pomona. His email address sound and light are instances of the same phe- is [email protected]. nomenon, which led to the invention of aether, 990 NOTICES OF THE AMS VOLUME 54, NUMBER 8 the substance through which sound and light were restriction that they minimize the surface area of supposedly transmitted. He moves on to planetary the tubes they sweep out over time. motion and the theory of circles circling circles, or String theory unifies all particles and all forces, epicycles, and he even spends time talking about it connects to symmetry though the existence of Kepler’s theory that the orbits of the five known gauge fields, it unifies the quantum and relativity, planets were related to the five Platonic solids. and it reduces twenty basic free variables in the With each theory he shows how it was disproved standard model to one variable in string theory. So as experiment and evidence began to show oth- from the beginning it had great potential in that erwise. it helped deal with two of the great problems in He then shows some of the great unifications: physics (1 and 3). Newton’s unification of motion and rest; Bruno’s String theory, unfortunately, first existed as unification that the sun and stars are the same hundreds of versions of the same theory, though thing; Faraday and the understanding that forces it was eventually whittled down to only five. At and fields are the same; Maxwell’s unification of this point a revolution took place in the theory electricity and magnetism; and Einstein’s double when Edward Witten gave a talk unifying all five unifications, of space and time in special relativity, theories into a coherent theory, which he called and acceleration and gravity in general relativity. M-Theory. The presentation of these concepts is intended for To listen to string theorists talk to the public it a general audience. Still, it is done in a manner so appears as if M-Theory is a solid, existent theory, that for those of us who understand the concepts but Smolin points out that what Witten did is not these descriptions are not boring. create a new theory but to point out some of the Among the interesting side notes Smolin pres- features such a theory would have to have. This ents during this discussion is a hypothesis that explanation was, to me personally, a great shock arose after the unification of electricity and mag- since I had always believed M-Theory was a com- plete theory. Smolin points out other aspects of netism: it suggested magnetic lines might be string theory where public perception does not knotted in various ways and that each knot might match reality. be associated with a particular atom. Knowing if The author also stumbles at this point in his one knot was the same as another was suddenly usual careful descriptions for the general public. of great interest. The theory was wrong, but it led He talks a great deal about “higher-order terms” to the establishment of knot theory as a branch of while never defining them. My assumption, given mathematics. The book is filled with such intrigu- his vague description of the mathematics, is that ing side notes, and it is clear Smolin knows a great he is trying to talk about convergence of series deal about the history of physics. solutions. Given my own confusion, I can only won- Throughout these discussions Smolin points out der at what a general audience might make of the that each unification not only led to a better under- following: He states that for string theory to work standing but also raised new questions—questions the higher-order terms need to be finite and that no one could have foreseen before the unification. their sum needs to be finite, too. It has been shown Each of these led to testable hypotheses, and in that the first two terms in the sum are finite, and that way the validity and usefulness of each theory many in string theory assumed the rest had been was measured. shown to be finite as well. Smolin digs into the past Smolin ends the first section of the book by de- papers on the subject and reveals this has not actu- scribing the state of physics at the dawn of string ally been done in general, but in only one special theory. This includes a nice discussion of basic case. Everyone, including Smolin, had assumed it quantum theory, symmetry and spontaneous sym- had been done in general, so a key foundation of metry breaking, along with the gauge principle and string theory seems to be incomplete. the current search for the Higgs boson. He again Smolin’s other great complaint with string delves into incorrect theories such as SU(5) and the theory is that it is background-dependent, in other unsuccessful search for proton decay. His point is words, to begin with a theory of strings one first that experiments in physics show the correctness/ fixes the background space in which the strings incorrectness of theories. He also spends several live. Relativity, which string theory supposedly chapters discussing supersymmetry, cosmology, unifies with the quantum, rests on the theory supergravity, and quantum gravity theories. that space is not fixed, and so any theory that Smolin now turns to string theory. He describes fixes space would not be consistent with other, how it began as an ignored idea and slowly ex- accepted, theories. panded into the theory that has dominated particle Further chapters look into the extra dimensions physics for the last twenty years. He does a good that seem to come with string theory, the advent of job of explaining the idea that everything is com- branes, string theory and black holes, cosmological posed of small vibrating strings and that strings constants, dark energy, the anthropic principle, propagate through time according to the simple and the relationship between supersymmetry and SEPTEMBER 2007 NOTICES OF THE AMS 991 string theory. The final score is that string theory his field. But again, this doesn’t mean he dislikes has potential for resolving Problem 3, it has made string theory. progress on Problem 1, but it has failed when it How then, does Smolin really feel? comes to the other problems. His point is this: he likes string theory, he’s For this reason Smolin concludes string theory, worked in string theory, it’s come up with some as the next great theory in physics, has failed. He good ideas, but it simply cannot be “the only game also continuously reminds the reader that string in town”. The theory has its limitations, and he theory has never produced results that are experi- feels the physics community is deluding itself by mentally verifiable or falsifiable. The theory stands thinking string theory by itself is going to answer outside the realm of experiment, and so as a theory the big questions. of the universe it lacks testability and cannot be Smolin sees the problem two-fold: seriously considered as a theory for physics.