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The Trouble With Physics; Lee Smolin

In The Trouble with Physics, Lee Smolin presents numerous thoughtful comments on controversial ideas about science, and a well reasoned critique of string theory. The book is sure to be interesting to anyone enthusiastic about physics or the history and philosophy of science. Smolin argues that there is something wrong with the way we have been studying fundamental physics for the last few decades. The Trouble with Physics is divided into four parts.

On The Shoulders of Giants

In the first part of the book, Smolin notes that there were giant steps in our understanding of the laws of nature every twenty-five years from 1780 to 1980. Between 1780 and 1805, Antoine Lavoisier’s experiments firmly established the law of conservation of mass. Between 1805 and 1830, scientists discovered Coulomb’s law, conceived of matter as made of indivisible atoms, established the conservation of energy, and used the wave theory of light to explain interference and diffraction. Between 1830 and 1855, Michael Faraday introduced the idea of electric and magnetic fields. Between 1855 and 1880, physics gained Maxwell’s equations and the description of light as an electromagnetic wave, the kinetic theory of gases, and the idea of entropy. Between 1880 and 1905, scientists discovered X-rays and electrons – the first known subatomic particles – and successfully described blackbody radiation by assuming that energy comes in discrete bundles. Between 1905 and 1930, Einstein alone explained Brownian motion and the photoelectric effect and invented special and general relativity. Meanwhile, various scientists developed quantum mechanics, and learned that the universe is expanding. Between 1930 and 1955, physicists combined quantum mechanics with special relativity, discovered a host of subatomic particles, and proposed that all attractions in the universe are combinations of just four fundamental forces. Between 1955 and 1981, physicists created the standard model of particle physics, explained how black holes can emit radiation, and developed successful models of cosmology. For two hundred years, our understanding of the laws of nature improved explosively!

A Long Way to a Theory of Everything

However, Smolin contends that from the 1980s to the present, we have witnessed no significant leaps in fundamental physics. We have discovered that neutrinos have mass, and that the observable matter and energy in the universe do not account for the observed expansion of the universe. Physicists have applied what we know to explaining, for instance, the properties of materials and how biological systems function. We have put our knowledge to use, and we have observed some unexplained phenomena, but we do not know appreciably more about the laws of the universe than we did in the 1970s. The reason for this is not that there is not very much left to learn; Smolin identifies five great problems in theoretical physics:

(1) Combining general relativity and quantum theory into a single, complete theory of nature;
(2) Resolving the foundational problems in quantum mechanics – that is, finding a description of reality that does not depend on what we choose to measure;
(3) Finding a theory that explains all the various particles and forces as manifestations of a single entity;
(4) Explaining how the values of various arbitrary constants in particle physics are chosen in nature;
(5) Explaining dark matter and dark energy, or modifying our theory of gravity to explain the expansion of the universe without them.

There is clearly much more to learn about fundamental physics! In the rest of the first part of the book, Smolin describes attempts to unify the four fundamental forces into one theory of everything that take us to the present rut in physics.

Elegant Ideas, Questionable Science

In the second part of the book, Smolin provides a history of string theory. He explains the basic ideas of string theory, and argues that its description of the universe are motivated by neither experiment nor observation, but by mathematical elegance. Moreover, he asserts that the few predictions made by the myriad different versions of string theory cannot be tested, either in principle or in practice. This runs contrary to centuries of science based on rejecting ideas that make predictions contrary to what we observe in reality. Smolin cites remarks that demonstrate that some proponents of string theory advocate an entirely new philosophy of science that accommodates string theory as valid science.

In the third part of the book, Smolin discusses some competing theories, and highlights that they make predictions that can be tested by experiments that are possible with current technology, in keeping with the methods that have successfully advanced knowledge since the scientific revolution.

The Trouble with the Establishment

In the fourth part of the book, Smolin expresses concern with about the scientific establishment. He argues that the establishment’s over-investment in string theory is harmful to the rest of physics. The problem is not simply that we continue to pursue a line of inquiry that has not proved fruitful. It is that we are pursuing it at the expense of other approaches. Any scientific program requires scientists and funding. Smolin argues that string theory has taken more than its fair share of both of these resources. Students feel pressured to go into string theory out of fear that they will not be able to get research grants if they commit to a less popular program. Smolin believes that it is never wise to take one approach, no matter how successful, at the cost of excluding all others. For if the program’s key ideas were rejected because they disagreed with some observation, as any scientific idea could be, we would have to begin again from nothing. It is always worth having multiple perspectives on the same phenomenon.

Smolin argues one step further that string theory has not even been shown to be a particularly successful or promising approach. It only addresses two of Smolin’s five problems: Unifying general relativity and quantum theory, and unifying the particles and forces of nature as manifestations of microscopic, vibrating strings in multiple dimensions. String theory does not address the fundamental strangeness of quantum mechanics or the nature of dark matter, and it introduces additional arbitrary constants without explaining how the values of any of the constants of particle physics are determined. Not only does it address only two of five fundamental questions; it has failed to answer them in a manner consistent with the methodology of science. The achievement of string theory is mathematical elegance, not agreement with experiment or observation. Worse yet, Smolin cites conversations he has had with string theorists demonstrating that some of them do not recognize that many of the elegant claims of string theory are in fact based on unproven conjectures

From this perspective, investing in string theory at the expense of other approaches seems frankly ill advised: It has failed to make predictions that can be borne out by experiment, and its mathematical elegance is overestimated. It is no wonder that our understanding of the laws of nature has not advanced appreciably in the last quarter of a century: The establishment has focused on one program of questionable merit.