In spring 2021, the brilliant theoretical physicist Steven Weinberg sat down virtually with my colleague Andrew Strominger as part of a series of book talks I’ve been organizing at the independently run Harvard Book Store. The two spoke about popular books Weinberg had written, including The First Three Minutes: A Modern View of the Origin of the Universe (rev. ed., 1993), To Explain the World: The Discovery of Modern Science (2015), and Third Thoughts (2018).
During my discussions with Weinberg in preparation for the talk, he mentioned that he had a new textbook coming out, but we worried that discussing a pedagogical work might be too dry for a public-facing event. We were wrong. Foundations of Modern Physics, published shortly before Weinberg’s death last summer, is a beautiful book that synthesizes the first two years of undergraduate physics and takes the reader on a historical journey up through the discovery of quantum field theory in the mid 20th century.
Steven Weinberg in front of a blackboard at the American Physical Society’s annual meeting in February 1977.
Steven Weinberg in front of a blackboard at the American Physical Society’s annual meeting in February 1977.
The book is a result of Weinberg teaching an upper-level physics course at the University of Texas at Austin called Modern Physics and Introduction to Thermodynamics. Weinberg’s colleague, Roy Schwitters, had taught that course for many years, but Schwitters never found a textbook that covered all the relevant material. When Schwitters retired, Weinberg asked to teach the course so that he could write a textbook for it, and Foundations of Modern Physics is the result.
The course was aimed at undergraduates who had already taken the introductory physics sequence through quantum mechanics. Weinberg began writing the textbook by supplementing a review of material the students had already learned with real applications and back-of-the-envelope or dimensional arguments. Structuring the book topically, he divided it into seven chapters: one each on early atomic theory, thermodynamics and kinetic theory, early quantum theory, relativity, quantum mechanics, nuclear physics, and quantum field theory.
Whereas many textbooks forgo historical notes, Weinberg delights the reader by adding terse yet apt context to the physical concepts he introduces. In fact, those notes are so well placed that I got a better sense of the flow of ideas in physics over time than ever before. The book goes over some introductory concepts before synthesizing an array of undergraduate-level ideas. The slim 300-page volume includes just enough material to make the book appealing and readable, but far too much, I think, for it to be used as a textbook for a one-semester course.
Weinberg’s writing reads less like a textbook and more like a story—although, to be sure, he includes many substantial derivations. Along with equations, he shows a clear interest in how physicists measure things. It is as if he is imagining what students might be puzzled by and then solves those problems.
For instance, when introducing Coulomb’s law, Weinberg notes that the French physicist could not measure charge directly with the equipment available to him in the 18th century. Instead, he noticed that if he touched a charged body to a similarly sized uncharged body of the same material, both the charge of the first body and the force between the two bodies were reduced by a factor of two. And when discussing the discovery of the electron, Weinberg mentions the brilliant air pump developed by Heinrich Geissler that made the discovery possible.
As an experimentalist, I am used to first looking at diagrams and data plots, and I was initially surprised that few figures were included in the book. I thought they might have added something to the clarity of the discussion. But when I reread a descriptive passage I had not at first been able to visualize, I found that Weinberg’s prose was impressively vivid. I could see fine without any figures.
Although it passes as a textbook, Foundations of Modern Physics is many things. It is a way for physicists to review what they have learned early in their studies and to think physically about what they know. It is also a source of relevant historical details and instruction for readers about topics and facts they weren’t previously familiar with. Although I have picked up a bit of nuclear physics here and there over the years, I never studied it in a class. So I read that portion of the book as if I were an undergraduate student encountering the material on nuclear physics in an academic setting for the first time, and I was very pleased.
But is this a textbook for undergraduates or incoming graduate students? It could be—if it is used carefully. It is certainly appropriate for advanced graduate students and faculty, who will be delighted and inspired to use it when teaching many introductory courses. I read the book slowly and episodically: Just 10 pages at a time provided enough for a week’s worth of thinking. I will certainly use the parts about elementary-particle physics when I next teach that course. And I already included things I learned from the book when I taught premeds this past spring.
Of course, everyone will want to have Foundations of Modern Physics on their bookshelf. There is always something new to be found in it, and—similar to having a conversation about physics with Weinberg—there is never a dull moment when reading it.
Melissa Franklin is the Mallinckrodt Professor of Physics at Harvard University. She is an experimental particle physicist whose research focuses on the search for long-lived particles and physics beyond the standard model.
