Steven Weinberg. Photo: CERN
In the passing away of Prof Steven Weinberg on July 23, 2021, the world has lost much more than just a Nobel laureate recognised for some specific contributions to science. Weinberg was an intellectual in the true sense of the word, with a wide range of interests that went well beyond physics.
Quite apart from his path-breaking research articles in physics, his erudite commentaries on a wide spectrum of other subjects, ranging from the history and nature of science to religion, have appeared in literary magazines like the New York Review of Books.
In eulogising any outstanding person, it is important to also identify the individuals and institutions that nourished his development. Weinberg was born on May 3, 1933, in New York, the city that has given the world so many outstanding scientists and scholars. Further, he went to “Bronx Science “, the nickname for the Bronx High School of Science, which has the distinction of being able to count seven Nobel laureates in physics among its alumni. In particular Sheldon Glashow, who was to share the Nobel Prize with Weinberg thirty years later, was his classmate.
(This is reminiscent of an even more extraordinary group of scientists – the Hungary-born Theodore von Kármán, John von Neumann, Leó Szilárd, Edward Teller and Eugene Wigner. All five of them attended the same high school and technical university in Budapest before migrating to the US and having an extraordinary impact on their profession and on world events. They were nicknamed ‘The Martians’, for what else could explain this sudden outbreak of superlative brilliance at one place?)
From New York city, Weinberg went on to Cornell University to get his undergraduate degree in 1954. This was followed by a stint at the Institute for Theoretical Physics in Copenhagen (founded by Neils Bohr, the father of quantum theory), as part of his postgraduate education. He returned to the US and worked on his doctoral work under Prof Sam Treiman at Princeton University, earning his PhD in 1957. (Prof Treiman, apart from his own celebrated work on elementary-particle theory, was a great mentor of graduate students at Princeton).
When he died, Weinberg was rightly hailed as the doyen of elementary particle physics. He not only directly contributed to some of its most fundamental developments, but could also ride astride, well into his eighties, the constantly changing and increasingly complex mathematical formulations of that subject.
He generously shared his deep understanding of vast areas of theoretical physics through his lectures in summer schools and his classic textbooks, including one on gravitation and cosmology and another on quantum field theory. A whole generation of cosmologists and particle physicists has been brought up on these books.
Weinberg was a very good communicator. Different realms of science communication call for different forms of pedagogical skill. Weinberg excelled at all of them. In the category of ‘popular science’ books, Weinberg’s The First Three Minutes (1977), which simplified for the benefit of the layman the story of how the universe came into being, became a global success, comparable to (and in my view, even better than) Stephen Hawking’s A Brief History of Time (1988). Weinberg’s numerous commentaries and reviews in the New York Review of Books were of another category, still addressed to the lay public, but of a more erudite class.
In contrast, explaining in clear mathematical detail the intricacies of sophisticated theoretical formulations to advanced research scholars is an altogether different matter. Weinberg has repeatedly been doing that too, with his textbooks mentioned above as well as his published lecture notes at various summer schools.
My first acquaintance with Weinberg’s depth of understanding and clarity of presentation came in the mid-1960s, when I was trying to enlarge my own domain of research to include elementary particle physics in addition to nuclear theory. Towards that end, I remember poring over the published notes of Weinberg’s superb lectures delivered at the 1964 Brandeis Summer Institute in Theoretical Physics (Prentice Hall, 1965).
In that same summer school, Weinberg had actually given two series of detailed lectures on two altogether different topics. One was on the quantum theory of massless particles and the other on the scattering theory of many particle systems. I still have a well-thumbed copy of those notes on my bookshelf.
Let me take a stab at conveying the importance of the work which earned him the Nobel Prize in 1979, along with Professors Abdus Salam and Sheldon Glashow.
By the mid-20th century, science had established that the apparently infinite variety of forces that objects in the universe seem to exert on other objects, whether it is by the horse pulling a cart, or a cricket bat hitting a ball, or the ball slowing down due to friction as it travels on the ground, or Earth being held captive by the sun, are all actually some combinations of just four fundamental forces.
Two of them, the force of gravity and the electromagnetic force, are familiar to us in day-to-day life. The other two are the so-called “strong” forces , which bind the nuclei of all atoms, and the “weak” forces which govern the decay of unstable atomic nuclei. (One would have thought that particle physicists would have found suitably impressive technical names for these forces instead of calling them ”strong” and “weak”, but they were too busy trying to understand the forces to worry about giving them better names!)
That the seemingly myriad varieties of forces at play in nature are just some combinations of these four fundamental forces offers a huge simplification in understanding nature – just as the fact that all objects in the universe are made of only 90-odd elements enables us, at least in principle, to deduce the chemical behaviour of any object from knowing its elemental composition.
But physicists are a perennially dissatisfied lot when it comes to further unification. So a massive effort had been on since the mid-20th century to combine at least some of these four distinct fundamental forces into some common structure. Weinberg, Salam and Glashow, each in his own way, made theoretical advances which led to a unified formulation encompassing two of those four fundamental forces, namely, the electromagnetic forces with the so-called “weak” interactions. As a by-product, the theory also predicted the existence of new elementary particles, all of which were subsequently detected in experiments.
Although this theory was popularly called the Weinberg model when he first published it in 1967, Weinberg was not a “model builder”. As he once told colleagues over lunch, “I am not a model builder. In my life, I have built only one model”.
Of course building models is important in all branches of science including, most recently, in analysing the COVID-19 pandemic or climate change. In physics, too, all theories in some sense do attempt to model nature. Unfortunately, there are lots of people who build a model a day and “run it up the flagpole to see if anyone salutes”, as the expression goes. But at the highest levels of theoretical physics, special respect is accorded to a theory arrived at inexorably from experimental facts rather than by trial and error.
I had the privilege of overlapping with Prof Weinberg in the fall of 1979 during my sabbatical at Harvard, where his office was just across the corridor from the one assigned to me. And right next to Weinberg’s office was that of Prof Sheldon Glashow, who was also at Harvard then. Furthermore, their joint Nobel Prize with Salam was also announced at that time. It was most interesting for me, as a visitor from India accustomed to people doing somersaults at the mention of the word ‘Nobel’, to observe from close the relatively sober manner in which the announcement was received and celebrated at Harvard.
Glashow, when he needed a break from his work, would occasionally wander into my office, ready with some wisecrack, sometimes at the expense of Weinberg (they were after all classmates in school!). But not so Weinberg, who was a more serious man. The group would often go for lunch at a nearby cafeteria, and whenever Weinberg could join us, his interventions were always learned and precise. He was very widely read and had strong opinions on many matters outside physics as well, which he took no pains to hide. In particular, he strongly disapproved of religion – all religions. He has reportedly said:
“Religion is an insult to humanity. With or without religion, you would have good people doing good things and evil people doing evil things. But for good people to do evil things, that takes religion.”
I dread to think of what today’s Twitterati would do with that comment!
Outstanding scientists are rare. But rarer still are people like Steven Weinberg, who combined their scientific creativity with such commitment to communicating their science to the rest of us at various levels. The world was very fortunate in having such a man and is now a poorer place without him.
R. Rajaraman is emeritus professor, Jawaharlal Nehru University, New Delhi.