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Monday, 2 August 2021

Steven Weinberg (1933-2021): The world of physics has lost a giant

 The scientific community will long remember a man whose impact on modern physics is almost unmatched

The world is poorer today.” That is how a colleague put it in an email as news of the death of one of the towering figures of 20th-century science began to circulate in the physics community. Steven Weinberg won the Nobel Prize in 1979, along with Sheldon Glashow and Abdus Salam, for their independent contributions to a theory that successfully unified two of the four forces of nature—Maxwell’s theory of electromagnetism and the Weak Force responsible for the processes that power the Sun—into a single “Electroweak” model. 

This was the first step in developing what is now known as the Standard Model of particle physics, a wildly successful theoretical framework that has met the test of experiment for over 50 years, and which describes three of the four known forces in ways that are consistent with the stringent underlying constraints imposed by nature due to relativity and quantum mechanics. As far as we can tell, the model successfully allows us to understand and correctly predict essentially all phenomena underlying everything we can see, from the inner workings of stars to the fundamental behaviour of subatomic particles inside atoms and molecules. 

If this were Weinberg’s only contribution to science and to the world at large, it would be worth commemorating, but his influence was far broader. His published articles ranged over many different fields of physics, and touched on every major development in fundamental physics for the last half of the 20th century, from Grand Unification to String Theory. Beyond this, he reached the wider public through seminal popular writing, gaining wide attention first for his slim bestselling volume The First Three Minutes, published in 1977, which described our then-current understanding of the earliest moments of the Big Bang. It is testimony not just to his expertise but to his wisdom in choice of topics that this book is still essentially as current now as it was then.

While Weinberg’s name is perhaps not as widely known as that of some physicists, such as the late Stephen Hawking, his impact on the development of modern physics is almost unmatched. He rarely issued wild speculations, so that whenever a paper by Weinberg appeared one could be assured there was substance. And even when he did speculate, it provided a firm groundwork for new ideas—such as when in 1987, based on anthropic arguments regarding  the requirements for life to have evolved in our universe, he argued that perhaps one would expect a very small (but non-zero) value of Einstein’s mysterious “cosmological constant,” or what is essentially now called “Dark Energy,” that results in a force that now dominates the expanse of the universe. A dozen years later, observers measured a phenomenon with a value corresponding to Weinberg’s speculations. The astronomers won the Nobel Prize in 2011.

But even all of this doesn’t fully capture the impact Weinberg had. When I was doing my PhD at MIT and later had a position at Harvard, many of the young physicists there, and later throughout the world, referred to Weinberg as “Big Steve.” The name came not because of flashy ideas that would surprise and delight, as his remarkable Harvard colleagues Sheldon Glashow and Sidney Coleman would produce from time to time. Rather, we viewed him as a giant steamroller, bringing a towering set of technical skills, a laser-like focus and inexhaustible energy to tackling any problem he was working on. 

This is one of the reasons Weinberg had so few students: it was simply hard to keep up with him. My friend Lawrence Hall, who was his student at Harvard at the time, told me he never would have been able to finish his PhD if Weinberg hadn’t won the Nobel Prize that year, temporarily distracting him from working on a problem he had suggested Hall work on. At the time, even though I was at MIT, I had taken almost all my graduate courses from Weinberg, so I felt comfortable asking him if he would supervise me on a problem. With his blunt honesty he agreed, but said that the problem he thought I should work on would probably not interest me and moreover, if a good Harvard student approached him he would feel obliged to suggest the same problem to them. I didn’t like the odds, so I demurred.

Nevertheless, while he was fully aware of his towering impact on the younger generation of physicists, all hierarchical dominance dropped if he was interested in a problem. Again, I remember how bowled over I was when as a lowly graduate student, Weinberg phoned me up one night because he had heard I was working on something he had become interested in. He invited me over to his house the next day, where like an intellectual vacuum cleaner he sucked all the knowledge out of me. I was flattered and amazed. Other students I knew had had the same experience, and same reaction.

Weinberg was also perhaps one of the true physics “scholars,” at least among physicists still working at the forefront of the discipline. He had encyclopedic knowledge and deep interest in ideas, especially in history, and I tend to think of him as the conscience of the field. If he made pronouncements about ideas and discoveries they were bound to be worth taking seriously. His popular books are also serious academic resources, and his textbooks are unequalled.

The fact that he took time to write for the public also influenced an entire generation. In my own case, it emboldened me to consider doing the same, and while I was at Harvard Weinberg was kind enough to introduce me to his publisher, Martin Kessler, at Basic Books, who eventually convinced me to write my own first popular book. In a field where figures like Carl Sagan had been discounted for their interest in popularisation, the fact that a Nobel Prize-winner like Weinberg was doing it legitimised the activity. I tend to think that many among the subsequent physics popularisers, including Hawking and Brian Greene, who had also been a student at Harvard, owe him a debt of gratitude.

While focusing on understanding and explaining scientific issues, Weinberg periodically made provocative statements about societal issues when he felt it important to do so. In spite of his work with JASON, the scientific group that advised the Department of Defense, he was a passionate activist for sensible nuclear disarmament. He was also an outspoken atheist. As he put it, “Science doesn’t make it impossible to believe in God, it just makes it possible not to believe in God.” As a leading scientist of Jewish descent, he was a passionate defender of the State of Israel.

For almost all physicists of my generation, Weinberg was a role model and mentor. For me, he was also a teacher, a colleague, and eventually a friend. He had a wry sense of humour, and he agreed to contribute a blooper to my book The Physics of Star Trek, where he said the biggest mistake was the split infinitive, “To Boldy Go.” And while he could be intimidating, and often was, he was given to surprisingly warm acts of friendship. When I was going through a difficult time in the media a few years ago, he wrote me a letter of confidence and support, based on what he said he knew of me from our friendship over many years. Coming from someone else it may have seemed like a kind and simple gesture. From Big Steve, it remains one of my most treasured possessions. 

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