Editor’s note: This article was updated on 30 September with a new submission.
Theoretical physicist Steven Weinberg died on 23 July in Austin, Texas, at age 88.
Born on 3 May 1933 in New York City, Weinberg was in the same Bronx High School of Science graduating class as Sheldon Glashow, with whom he would later share the Nobel Prize. Weinberg received a bachelor’s degree from Cornell University in 1954 and a PhD from Princeton in 1957. He is best known for his 1967 paper, “A model of leptons,” that unifies the electromagnetic interaction, mediated by massless photons, and the weak nuclear force, conveyed by the massive W and Z bosons. For his work on electroweak theory, he was awarded the 1979 Nobel Prize in Physics, which he shared with Glashow and Abdus Salam. Weinberg’s other research touched on many areas, including effective field theories and cosmology.
Weinberg was also passionate about the history of science and communicating science to the public. His popular books include The First Three Minutes: A Modern View of the Origin of the Universe (1977) and To Explain the World: The Discovery of Modern Science (2015). “It is rare indeed that one can say of a book that no one’s library is truly complete without it,” Physics Today reviewer Robert March wrote of The First Three Minutes.
Rather than have one person write an obituary, we asked several of Weinberg’s colleagues to share remembrances. If you would like to share a story about Weinberg, please leave a comment below the article.
- Helen Quinn
- Mark Raizen
- John Preskill
- Raphael Flauger
- Gerald Gilbert
- Robert McNees
- Tsvi Piran and Remo Ruffini
Professor of Particle Physics and Astrophysics Emerita, SLAC National Accelerator Laboratory
I first met Steve in early 1971. Tom Appelquist, Joel Primack, and I had just completed the first one-loop calculation, for mu decay, in Steve’s “theory of leptons,” showing it was a finite correction to the leading order, an indication that the theory was possibly renormalizable. This was four years after he wrote the paper. It took ’t Hooft and Veltman’s dimensional regulation to make the calculation possible—before that no one knew how to regulate the infinities without destroying the gauge symmetries, to be able to check whether they cancel. Tom called Steve, who was then at MIT, to tell him our result. Steve was so delighted that he invited us all to his office to explain the details and then to his home to sip a glass of sherry to celebrate. I believe he had expected, but not yet been able to prove, as Ben Lee and Jean Zinn-Justin did so elegantly later that year, that his theory was renormalizable. Our calculation gave him the first real indication that this was true. From that day on, Steve was a mentor and an advocate for me.
When Steve moved from MIT to Harvard a year or so later, we also became collaborators. He instituted “group meetings” for the particle physics group, which then consisted of Steve, Shelly Glashow, and Sidney Coleman as full professors, Tom and me as junior faculty, Howard Georgi as a junior fellow, and Alvaro de Rújula and Enrico Poggio as postdocs. I should also include David Politzer and Eric Weinberg, who were then Sidney’s graduate students. What a joy it was to be in the middle of the ferment as the standard model took shape, working with this group of people! Ideas abounded, collaborations were fluid, and we were connected to the world, because everyone sent their preprints to Harvard and we all shared whatever any of us received.
Working with Steve taught me to think deeply and clearly to define the problem to be solved before launching into solutions. He also gave me a sense of the history of physics, because, even then, he was conscious of it and cared about how the work we were doing would play a role in it. When we were writing our paper with Howard on “the hierarchy of interactions,” I wrote up the calculation and Steve wrote a beautiful introduction that put the work in context. Unfortunately, I found I had to cut most of it, to fit the paper into the length constraints of Physical Review Letters. He accepted that, but not happily.
For the sake of history, I should say that Steve asked the question about whether and where the strong, weak, and electromagnetic coupling constants would merge, as needed for grand unification, at a group meeting, one that I missed for reasons I do not remember. David explained the problem to me a little later that afternoon. Howard and I talked a while about it and then went home and each of us did the calculation that night, coming back the next day with the exciting discovery that the answer was yes, to the level of accuracy we could then achieve. Steve again was delighted with the result, and we decided the three of us should write it up together.
Steve also played a crucial, though less visible, role in my other most-cited work, the proposed solution to the question of how the strong interactions maintain CP conservation (or at least have at most tiny CP-violating effects), despite the fact that CP is not a symmetry of the standard model theory. This work, that I did with Roberto Peccei, introduced what is now referred to as Peccei–Quinn symmetry. Roberto and I thought we had found an answer to the problem, though we were not confident we had it right. At the time both Steve and I were visitors in the Stanford physics department, where Roberto was an assistant professor, so of course the first person we went to talk with about our ideas was Steve. We barely began when something I said triggered Steve to explain to us how to think about CP violation and how phase redefinitions of fields can remove many complex phases in coupling constants, and thus remove apparent but not actual CP violation possibilities. His short lecture, for that is what it was, made it clear to me how we were confused. I said to Roberto, “Let’s go, we need to think about this.” We never got to the point of telling Steve our wrong ideas. The clarity of his explanation of how to think about the problem showed not only how we had gone wrong, but also what we had to think about to get to a real answer to the problem. (I have repeated that lecture to others many times, as CP violation in the weak interactions became the central theme of my work and of B factory experiments in later years.)
A second part of this story came soon after, but Steve was no longer at Stanford. Roberto and I published our theory, including the simplest model realization of the symmetry, without examining the phenomenology of that model. We feared the model would not survive that test, and indeed it was soon ruled out. We wanted to publish the general theory—the model was just the simplest case. We did not want to get bogged down finding a realistic model. However, we failed to notice an important general consequence of the symmetry, true for any model, namely that it predicts a pseudo-Goldstone boson, now known as the axion. Steve, and separately Frank Wilczek, noticed it and each published a brief paper on it. Frank was the one who gave it its name. Before publishing his paper, Steve called me. He asked whether I was aware of this property of the theory. My response was something like, “Well, of course, you are right, but no, I had not noticed it.” Steve said, “Well, in that case, I will publish it by myself.” I am sure he would have offered me and Roberto the chance to co-author his paper had I said, “Yes, we know.” That was the kind of gentlemanly scholar that he was.
One more story, again for the sake of history, which Steve cared about deeply. When Steve came to Harvard, he was taking the place of Julian Schwinger, who had left to go to UCLA. Julian had left a pair of shoes in the office in the Jefferson building at Harvard that Steve was the next to occupy. I think it was probably Shelly who made the joke that they were there to see if Steve could fill them! But that is not my story. The story occurs when Julian came back as a Loeb lecturer and to sit on the thesis oral of his last Harvard graduate student. Steve and I formed the rest of the committee. The student’s thesis was a calculation in Schwinger’s source theory, an alternate formulation of QED that Schwinger hoped would answer some then outstanding problems. The student (whose name I do not remember) had barely introduced himself and his calculation when Steve challenged him about the value of source theory when the calculation could have, and in fact had already, been done by traditional methods. Of course, Julian responded to defend his theory and his student. The next half hour became a debate between Steve and Julian on what makes a good theory, while the student stood silently at the blackboard. Eventually they agreed to disagree and let the student present his work.
I wished I had a tape recorder, because historians of science would love a record of that debate. To sum it up, as best I remember it, Steve argued that the best theory was one that was so well defined that it could be tested and possibly falsified by experiment, while Julian argued that the best theory was so flexible that it could evolve to accommodate new results. In other words, they were not quite talking the same language. What Julian meant by a new theory was a new formalism, whereas to Steve it meant a new specific instantiation of an already well-developed formalism. But it was fascinating to hear them argue about it.
By any measure Steve was a great physicist and also a great historian of physics. While he was reserved and very private as a person, he was also, in my experience, a great friend. I always knew I could count on him for advice and support, even when I had not spoken to him for years. His support was critical to my career.
Professor of Physics and Professor of Medicine, University of Texas at Austin
Steven Weinberg was a major influence in my life since we first met, when I came to graduate school to work with him almost 40 years ago. The irony is that I became an experimental physicist, and he always told me that “I saw the light.” Perhaps that was Steve’s kind way of telling me that I would have made a lousy theorist. Steve served as my co-adviser, then colleague at UT Austin, and became my close friend.
There are a few personal stories that illustrate the Steven Weinberg that I knew and loved. When he taught a class, he usually wrote a textbook based on his notes, and he was proud of the fact that he wrote everything himself, including all the equations in LaTeX. A few years ago, when Steve was working on a textbook about quantum mechanics, he asked me to explain to him everything about quantum entanglement. After a brief panic attack, I dug into the literature and spent time with him on this complex subject. One thing that always impressed me about Steve was how hard he worked. This may sound strange, since his brilliance goes without saying, but most people do not realize the hard work of carrying through detailed calculations and making predictions that can be tested.
On a personal level, we had regular lunches before the pandemic and were looking forward to renewing that tradition when things got better. Steve loved to drive and always insisted on driving on our outings. This was a somewhat nerve-wracking experience, and his car bore evidence of many small “incidents.” One day, returning from lunch, he drove up to the automatic entrance gate near our building. It did not respond, much to Steve’s annoyance. After several trials of backing up and approaching the gate, Steve suddenly started laughing, as he had taken [his wife] Louise’s car that day to work! Steven Weinberg is gone, but he lives on in our minds and hearts, and his legacy stands as one of the greatest theoretical physicists of all times.
Richard P. Feynman Professor of Theoretical Physics, Caltech
I first met Steve Weinberg in December 1974. My then fiancée (now my wife) Roberta and I were in Boston for the day and decided it would be fun to drop into the Harvard physics department, where I hoped to enter the PhD program the following fall. Finding Steve’s office door open, I impetuously barged in, explaining that I was a prospective student, and introduced him to Roberta. While in the act, I felt a surge of embarrassment—how will Weinberg react to my audacity? There was an awkward pause, until Steve smiled and said, “Oh, Louise and I did the same thing!” I relaxed, and we had a very friendly chat.
By the summer of 1981, I had completed my PhD under Steve’s supervision and was starting a junior faculty position at Harvard. I knew that my parents, who were visiting, would enjoy meeting Steve and Louise, so we all had dinner together in my backyard. Realizing how much it would please my parents, Steve made some kind remarks about me during dinner. But the most memorable moment was when we were discussing how to make ice cream, and Steve expressed puzzlement over why one adds salt to the ice-cream maker. My Dad, who was not a scientist, helpfully suggested, “Isn’t it to lower the melting point of the ice, so the ice cream will be cold enough to solidify?” “Of course!” Steve replied, slapping his forehead. “I never understood that before. Thank you!” And for the rest of his life, my Dad would relish the time he gave the great Steven Weinberg a physics lesson.
Associate Professor of Physics, University of California, San Diego
The impact of Steve’s long and productive career on theoretical physics can hardly be overstated. While most would count themselves lucky to have one important result named after them, there are many that carry Steve’s name: Weinberg’s soft graviton theorem, the Weinberg sum rules, the Weinberg operator, the Weinberg angle (which I have always heard him refer to as the weak mixing angle), the Weinberg–Witten theorem, the Lee–Weinberg bound, and so on. Then there are his countless groundbreaking contributions that do not carry his name, including the development of effective field theory and the unification of the electromagnetic and weak forces, for which he is most widely known and for which he shared the Nobel Prize in 1979. As if this were not enough, his influence extends well beyond the reach of his research papers. Many of us have learned intricate details from his textbooks, and his popular science books have shaped how many think about physics, and about science and its place in society more generally. Several of his books have been translated into numerous languages, now 23 for The First Three Minutes.
I first realized it was essentially impossible to summarize his contributions in just a few sentences when I was preparing to introduce him for a recent lecture at UC San Diego that I had invited him to. No matter how hard I tried, there was always another result that didn’t make the list that could very well be someone else’s main career achievement. So I will not attempt to summarize his contributions here either, and I will let his research papers, books, and awards speak for themselves. I will instead focus on one personal experience that highlights his personality, which cannot be guessed from his publication record.
I first met Steve nearly 20 years ago as an exchange student at UT Austin. I was fortunate to go on to be his teaching assistant, his PhD student, his colleague, and his collaborator, and we kept in touch throughout. There are many memories of our interactions over the years that I treasure. The one I will highlight here occurred shortly after I had accepted an offer from UT Austin to rejoin his theory group, this time as an assistant professor. After the end of my first semester, my mom was diagnosed with a rare form of cancer, and my dad passed away unexpectedly just a few days after her diagnosis. I felt I had no choice but to go back home to help my mom with her surgery and subsequent recovery, but I was scheduled to teach a class on effective field theory. Without hesitation, Steve, already 82 years old at the time, offered to teach the course for me even though he was scheduled to teach his own course as well. Perhaps to the detriment of the students, and all of us, who would have cherished another set of lectures by Steve on effective field theory, I did not have to take him up on his offer, but I will always remember how self-evident it seemed to him that he should offer to teach my course.
Steve not only was exceptional at pursuing the quest to understand the universe but also succeeded as much as anyone in giving a point “to the universe by the way we live, by loving each other, by discovering things about nature, by creating works of art.”
MITRE Fellow, MITRE–Princeton
Steven Weinberg has had a profound influence on my life since I became his doctoral student many years ago in Austin. He served as a North Star to many physicists, providing through his work and behavior a role model to which many have aspired.
Underlying this was, of course, his exceptional brilliance, but there was much more to the story. I remember Steve telling me about his year spent at the Niels Bohr Institute (NBI) in Copenhagen at the very beginning of his graduate studies, prior to going to Princeton. In describing his daily commute to and from NBI, he always talked about “going to work every morning”—he never said it any other way—unlike many grad students who might have referred to “going to the office” or “going to the Institute.” Steve was an extraordinarily hard worker all his life, and this, as much as his natural brilliance, is what I will always remember.
Although many people were in awe of him, and some even intimidated by him, in fact Steve was always scrupulously fair and, in my experience, kind. Two reminiscences may serve to illustrate this. Once, one of Steve’s postdocs brought his small son to the ninth floor of the building at UT Austin where Steve’s Theory Group worked. The five-year-old boy ran around the hall and offices throughout the morning, and, at some point, Steve came in to work. The child had overheard our conversations in which Steve was prominently mentioned, and so when Steve appeared in person the small boy cheerfully shouted out, “Hey Weinberg!” Steve, towering over the small person, stopped, looked down with a smile, and said in a friendly and calm voice, “You can call me Steve.”
Another story: Steve used to have informal weekly meetings in his office with the Theory Group. These were his famous “brown bag” lunches, with Steve often eating his favorite moo shu pork purchased from the lunch cart on the street outside the building. As his just-accepted doctoral student, the time came for me to give the weekly, informal technical talk at the lunch. I gave my presentation, but I was quite nervous presenting in front of Steve in such a setting. After the talk was over, the group left Steve’s office as usual, but Steve motioned for me to wait. After everyone had left the office, he closed the door and told me, “You did great.” He had seen how nervous I was and simply wanted to provide a kind and helpful word.
Steven Weinberg was one of the most important physicists in history. Steve’s work will forever serve as a monument to his greatness as a scientist, but his guidance and kindness to his students should also be remembered forever.
Associate Professor of Physics, Loyola University Chicago
Others will talk about Steven Weinberg’s important contributions to physics, his impeccable sense for which developments would prove to be important, and the clarity of his writing. I just wanted to share a few memories about being a graduate student in his Theory Group at UT Austin, and some of the things I learned there.
Steve was funny, friendly, and genuinely interested in what the graduate students were up to. Most of us were a bit awestruck at first, and perhaps did not expect that this towering figure of our field would be so approachable. But he was always happy to answer a question or offer guidance—especially if it had to do with something he was excited about. I joined the group not long after the discovery of the accelerating Hubble expansion, so the thing he was most excited about at the time was cosmology. Once, when we were talking about the cosmic microwave background (this must have been around the time the Wilkinson Microwave Anisotropy Probe was launched), he leaned back in his chair and told me that the field was entering a “golden age,” like particle physics in the 1950s and 1960s, when new discoveries seemed to happen almost every week. There was always someone running down the hall, he remembered, shouting about a new particle that had been found, and they would have to get to work figuring out where and if it fit in with everything else. Another time, when we were talking about quintessence models, I asked a question about the anthropic estimate of the cosmological constant in his 1989 review paper. He laughed and said that people my age shouldn’t be thinking about those sorts of arguments, that we should “leave that to the old folks” and focus on finding an actual mechanism that produces a small vacuum energy.
He was also interested in what we were doing outside of physics, what we were reading and listening to, or if we’d seen any good performances. We had informal lunchtime seminars every week where Theory Group faculty, postdocs, and graduate students would get together, and someone would give a talk about whatever they were working on at the time. Steve usually showed up early and would chat with the grad students while looking at the day’s newspaper. One time my officemate and I were talking about the books we were reading. Steve, who had been marking up a draft of a paper, set down his pen and asked if either of us had read Paul Bowles’s The Sheltering Sky. It was, in his opinion, the greatest novel written in the English language, and we should really read it sometime. We both bought copies that afternoon.
As a group member, I gave my share of talks at those informal lunchtime meetings. They were usually held in another building, and Steve was always very generous with feedback and advice on the walk back to our offices. These conversations really clarified for me what I was supposed to be doing when I talked about physics, and some of the habits I picked up during that time turned out to be just as useful for teaching classes and writing papers. I would usually sketch out my talk, try to anticipate Steve’s questions, and then rewrite those parts (or sometimes the whole talk) so that he didn’t need to ask them. This probably started because I was terrified of not having a good answer. But it ended up being a useful way to assess whether I was really explaining the physics, rather than just describing it. This is a distinction we often heard Steve make. There are a few places in his writing where he more or less says it in those terms, and it definitely came through in the questions he asked and the advice he gave. I think this question—Are you describing the physics, or are you explaining it?—is always buzzing around in the back of my head when I prepare a lecture or a new paper.
As a group member, I was officially a “research associate,” which meant that I didn’t have to work as a TA. But since I was always talking to him about cosmology, Steve thought I might be interested in grading his graduate class and maybe even reading some early drafts of a new book that he was starting to write. (Yes and yes.) A few weeks before I left Austin for my first postdoc, we briefly met to discuss a student who had taken a grade of “incomplete” in the course that spring. The student completed their work over the summer, and I had graded the assignments. I just needed to give Steve the papers so he could finalize everything. I am calling him Steve here, but back then I always addressed him as Dr. Weinberg. Even after four years in his research group, as a freshly minted PhD about to start a new postdoctoral position, I couldn’t bring myself to go for the first name. We went over the papers, sorted out the final grade, and he thanked me for making time to help right before my move. I said, “It’s no problem, Dr. Weinberg” and got up to leave. As I gathered my things he laughed and said, “You know, you’re allowed to call me Steve.”
Schwartzman Chair for Theoretical Physics, Racah Institute of Physics, The Hebrew University of Jerusalem
Director, International Centre for Relativistic Astrophysics Network, Pescara, Italy
The Marcel Grossmann Award of the Sixteenth Marcel Grossmann meeting (MG16) was presented by Roy Kerr to Steven Weinberg on 5 July, just a few days before Steven passed away. The motivation of the award read, “for unwavering support for the MG meetings since their inception, a true companion in the search for the deeper meaning of Einstein’s great theory.” Particular mention was given to the forceful action of Steven, as well as Yuval Ne’eman, to request the official presence of Israeli scientists at the MG3 meeting in Shanghai in 1982.
This was successful, and Israeli scientists participated in this first truly international scientific meeting held in China. The following year, Steven established the Jerusalem Winter School for Theoretical Physics, which is held annually at the Israel Institute for Advanced Studies at the Hebrew University of Jerusalem. Steven, who served 10 years as the school’s first director, attracted the finest lectures and students to Jerusalem. Most leaders in the field have been participants in the School. With great dedication, Steven turned the School into one of the best in the world.
We were fortunate to have been able to express to Steven our gratitude for forcefully promoting these worldwide collaborations.