I heard this morning the news that Steven Weinberg passed away yesterday at the age of 88. He was arguably the dominant figure in theoretical particle physics during its period of great success from the late sixties to the early eighties. In particular, his 1967 work on unification of the weak and electromagnetic interactions was a huge breakthrough, and remains to this day at the center of the Standard Model, our best understanding of fundamental physics.

During the years 1975-79 when I was a student at Harvard, I believe the hallway where Weinberg, Glashow and Coleman had offices close together was the greatest concentration of the world’s major figures driving the field of particle theory, with Weinberg seen as the most prominent of the three. From what I recall, in a meeting one of the graduate students (Eddie Farhi?) referred to “Shelly, Sidney and Weinberg”, indicating the way Weinberg was a special case even in that group. I had the great fortune to attend not only Coleman’s QFT course, but also a course by Weinberg on the quantization of gauge theory.

Weinberg was the author of an influential text on general relativity, as well as a masterful three-volume set of textbooks on QFT. The second volume roughly corresponds to the course I took from him, and the third is about supersymmetry. While most QFT books cover the basics in much the same way, Weinberg’s first volume is a quite different, original and highly influential take on the subject. It’s not easy going, but the details are all there and his point of view is an important one. When you hear Nima Arkani-Hamed preaching about the right way to understand how QFT comes out uniquely as the only sensible way to combine special relativity and quantum mechanics, he’s often referring specifically to what you’ll find in that first volume.

Besides his technical work, Weinberg also did a huge amount of writing of the highest quality about physics and science in general for wider audiences. An early example is his 1977 The Search for Unity: Notes for a History of Quantum Field Theory (a copy is here). His 1992 Dreams of a Final Theory is perhaps the best statement anywhere of the goal of fundamental physical theory during the 20th century. His large collection of pieces written for the *The New York Review of Books* covers a wide variety of topics and all are well worth reading.

At the time of the 1984 “First Superstring Revolution”, Weinberg joined in and worked on string theory for a while, but after a few years turned to cosmology. In early 2002 he was one of several people I wrote to about the current state of string theory, and here’s what I heard back from him:

I share your disappointment about the lack of contact so far of string theory with nature, but I can’t see that anyone else (including those studying topological nontrivialities in gauge theories) is doing much better. I thinks that some theorists should go on pushing as hard as they can on string theory, and others should do something else, but it is not easy to see what. I have myself voted with my feet (if that is the appropriate organ here) and switched entirely to work in cosmology, which is as exciting now as particle physics was in the 1960s and 1970s. I wouldn’t criticize anyone for their choices: it’s a tough time for fundamental physics.

A couple years after that time, Weinberg’s 1987 “prediction” of the cosmological constant became the main argument for the string theory multiverse. This “prediction” was essentially the observation that if you have a theory in which all values of the cosmological constant are equally likely, and put this together with the “anthropic” constraint that only for some range will galaxy formation give what seem to be the conditions for life, then you expect a non-zero CC of very roughly the size later found. I’ve argued ad nauseam here that this can’t be used as a significant argument for string theory in its landscape incarnation. One way to see the problem is to notice that my own theory of the CC (which is that I have no idea what determines it, so any value is as likely as any other) is exactly equivalent to the string landscape theory of the CC (in which you don’t know either the measure on the space of possible vacua, or even what this space is, so you assume all CC equally likely). One place where Weinberg wrote about this issue is his essay Living in the Multiverse, which I wrote about here (the sad story of misinterpretation of a comment of mine there is told here).

Weinberg’s death yesterday, taking away from us the dominant figure of the period of particle theory’s greatest success is both a significant loss and marks the end of an era. His 2002 remark that “it’s a tough time” is even more true today.

**Update**: Scott Aaronson writes about Weinberg here, especially about getting to know him during the last part of his life.

**Update**: For Arkani-Hamed on Weinberg, see here.

**Update**: Glashow writes about Weinberg here.

Weinberg was the last of the physics giants who produced fundamental theories validated by experiments. After half a century his Standard Model still holds, so maybe now is the fist time in physics history without scientific giants.

A tribute to him from one Astrophysics colleague who had recently joined UT Austin

https://twitter.com/MBKplus/status/1418972769509855236

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His last book “Foundations of Modern Physics came out a few months ago. From the preface:

“This book treats such a broad range of topics that it is impossible to go very far into any of them. Certainly its treatment of quantum mechanics, statistical mechanics, transport theory, nuclear physics, and quantum ﬁeld theory is no substitute for graduate-level courses on these topics, any one of which would occupy at least a whole year. This book presents what I think, in an ideal world, the ambitious physics student would already know when he or she enters graduate school. At least, it is what I wish that I had known when I entered graduate school.”

Does anybody have an opinion about how well he succeeded?

It is sad news that Weinberg is not with us anymore but I cannot agree with Alessandro Strumia that “Weinberg was the last of the physics giants who produced fundamental theories validated by experiments…so maybe now is the fi(r)st time in physics history without scientific giants.” Please be reminded that C. N. Yang and T. D. Lee still are healthily living.

@Ricardo: I wrote the following review on one of my piazza sites a few weeks ago. I am currently half way through the book, and I am enjoying the book, although I am familiar with most of the content already. As I indicated below it is more of a review book, than a teaching book.

Steven Weinberg had come out with a new book: Foundations of Modern Physics. I have read the first 2 chapters, and scanned the rest of the book – the book is a short 300 pages and the hardcover is about $40. The level of the book is intermediate to advanced undergraduate.

I often encounter online students who have taken several of the MIT physics MOOC’s but often feel that they either lack some background, or don’t see what they have learned (especially in the QM sequence) and how it will be applied. To many of these students my advice is usually to read the Feynman Lectures on physics, to get the big picture and for more background in QM prerequisite physics, and/or find a good textbook on modern physics.

When I was in college almost half a century ago, I remember using Leighton’s classic book Principles of Modern Physics 1959 (about 700 pages in length), and suggest students try and find a more recent book covering roughly the same material – I haven’t seen one, so let me know if you have. There seem to be many freshman/sophomore level books covering modern physics, but I don’t think these are sufficient.

Weinberg’s book is less of a textbook (while there are 25 problems at the end of the book, there are no exercises at the end of chapters, and no worked out examples). It is written in Weinberg style, few pictures or diagrams, unusual symbols ($m_1$ for the atomic mass unit, usual notation is u), nice but sometimes terse arguments, and excellent content with interesting historical asides. The math level is low at the beginning (algebra – elementary calculus), and rises a little with the level of the material, but not nearly as difficult as his graduate level books.

There are seven chapters in the book:

Early Atomic Theory

Thermodynamics and Kinetic Theory

Early Quantum Theory

Relativity

Quantum Mechanics

Nuclear Physics

Quantum Field Theory

So the coverage is exactly what a student should be looking for in a modern physics book (perhaps astrophysics and cosmology are left out, because Weinberg just published a set of lectures on astrophysics, and has a whole book on Cosmology). The book seems more of a review or plug holes in background, and less of a teaching masterpiece.

I recommend that students looking for a book on this type of material take a look at the book and see if it is for them. I think students who are taking or have finished the MITx 8.04-8.06 sequence might find the book worthwhile as a review and also as filling out some material, and get a preview of quantum field theory as well.

Steven Weinberg – a great, highly creative physicist and wonderfully involved teacher of fundamental physics who shaped my own education in quantum field theory and cosmology during essential steps. I’ll miss him and his sober views very much.

Dear Wei, thank you, let me try to explain better. Historians like to choose a somehow arbitrary moment to symbolise a gradual change. If the change I mentioned will really happen, I expect they will choose this moment.

Alessandro, Glashow is still around, isn’t he? So not quite the last. As a sophomore, I attended a talk by GSW when they were here in Stockholm to collect their Nobel prize, and I understood absolutely nothing.

Btw. I learned from Lubos that Miguel Virasoro has passed away as well.

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I was working at Cambridge University Press in 1995 when the first volume of his “Quantum Theory of Fields” was released. I recall speaking briefly with him on the phone about something trivial like distributing review copies, and picking up a copy of the book that had been delivered to our office. I read the first page and then put it back down—it was just a *bit* over my head…

My PhD thesis was a measurement of the Weinberg angle (sin^2\theta_W) using polarized electrons at the SLAC linear collider. Some people insisted the W stood for Weak but I always held it is W for Weinberg. I read and reread his paper A Model of Leptons many times until I could reproduce it at my defense. I wish all theory papers were as clear and understandable.

Miguel Virasoro died the same day

Amitabha: From what I understand the “Weinberg” angle was first introduced by Glashow.

Shantanu, that is funny because I was told to call it Weak Mixing Angle (and not Weinberg angle) after I gave this talk at Harvard. Glashow was in the room but he was not the one who made that comment. I made the correction with a marker on my transparencies right there. This was a while ago, but I also vaguely remember some chatter about “well if this is right it means the higgs is light”. We were, and it was.

Amitabha: This is also mentioned on Peter’s blog https://www.math.columbia.edu/~woit/wordpress/?p=17

I have also heard this mentioned in many HEP seminars I attended as a grad student.

Dreams of a Final Theory is available on Audible. It’s read by Weinberg himself. It’s written for a general audience, so even untutored but interested readers like me can understand it.

That is sad news, but it was a long life well-lived. He was an authentic giant. His book on GR is still my favorite (tied with that of Fock) and I was lucky to learn the subject in detail mostly from that. Agree also about QTF II. I wish we had made more progress in his last years for him to enjoy and contribute to. RIP.

-drl