Questions and answers with Steven Weinberg

Steven Weinberg is a distinguished theorist whose research has covered a broad range of topics in quantum field theory, elementary particle physics, and cosmology. Along with Sheldon Glashow and Abdus Salam, he was awarded the 1979 Physics Nobel Prize for his contributions to the standard model of elementary particles. He is currently a physics and astronomy professor at the University of Texas at Austin.

Steven Weinberg Photo Credit: Matt Valentine

Weinberg was educated at Cornell University, the Niels Bohr Institute, and Princeton University and has taught and conducted research at Columbia University; the University of California, Berkeley; MIT; and Harvard University. He is also known as a skilled writer. For the general audience, he has written, among others, The First Three Minutes: A Modern View of the Origin of the Universe (updated edition, Basic Books, 1993) and Lake Views: This World and the Universe (Harvard University Press, 2010). For the physics student and practitioner, he has written the classic Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity (Wiley, 1972), the more recent Cosmology (Oxford University Press, 2008), and the three-volume Quantum Theory of Fields (Cambridge University Press, 1995, 1996, 2000).

His latest textbook is Lectures on Quantum Mechanics (Cambridge University Press, 2013), which sprang from a UT Austin course he has taught to first-year graduate students. Mark Srednicki’s Physics Today review , appearing this month, describes it as presenting the standard graduate-level material “with a high level of rigor and clarity and with numerous discussions of related physics not always found in other textbooks,” but also lacking in figures, which may “temper its appeal as a primary textbook, especially for students with limited preparation.” Weinberg responded to the latter issue and more when Physics Today approached him recently to discuss the book.

Weinberg: I have been teaching first-year graduate quantum mechanics off and on over the past decade. As always seems to happen when I teach a course several times, my lecture notes somehow turned into a book. Not surprisingly, therefore, this book is aimed at physics graduate students. But in some universities bright undergraduate physics majors take graduate courses, and it should be accessible to them too. I hope that working physicists may also find useful things in it.

Weinberg: In teaching quantum mechanics I usually assigned some book so that students would have a place to look up formulas. I found existing books pretty good pedagogically, but none of them covered just the topics that I wanted to cover, and not in the way I wanted to cover them. I give much more emphasis to symmetry principles than usual, and though I go into standard wave-mechanical calculations, I try also to present things like scattering theory more generally.

Weinberg: I’m not against figures where they really help. Cosmology is full of graphs that show the agreement between approximate and exact calculations or between calculations and observation. I just didn’t find any similar need for figures in this book. I suppose that I could have lightened up my discussion of communication in entangled systems by showing pictures of Alice and Bob, but what would this have clarified? Not bothering with unnecessary figures reduced both the time it took me to get the book done and its price.

Weinberg: Some very good theorists seem to be happy with an interpretation of quantum mechanics in which the wavefunction only serves to allow us to calculate the results of measurements. But the measuring apparatus and the physicist are presumably also governed by quantum mechanics, so ultimately we need interpretive postulates that do not distinguish apparatus or physicists from the rest of the world, and from which the usual postulates like the Born rule can be deduced. This effort seems to lead to something like a “many worlds” interpretation, which I find repellent. Alternatively, one can try to modify quantum mechanics so that the wavefunction does describe reality, and collapses stochastically and nonlinearly, but this seems to open up the possibility of instantaneous communication. I work on the interpretation of quantum mechanics from time to time, but have gotten nowhere.

Weinberg: I have two papers coming out in Physical Review Letters any day now, one on cosmology and one on hadron physics. I’m also just now finishing a book on the emergence of physics and astronomy from Thales to Newton.

Weinberg: For [that] history book I’ve been working on, I have been reading the works on optics by Ptolemy and Descartes. For our book group here in Austin, I’m reading The Burgess Boys (Random House, 2013) by Elizabeth Strout. For pleasure, I usually turn to general history. Right now, I’m reading Robert Massie’s book about Peter the Great (Peter the Great: His Life and World, Wings Books, 1991), and rereading [Thomas Babington] Macaulay’s classic, The History of England from the Accession of James II (Kessinger Publishing, 2003).