Steven Weinberg

Abstract Photograph of Steven Weinberg. When Steven Weinberg began his research career, he worked on quantum field theories. For much of the community, the problems of divergences seemed to show these were a dead end. By the time of his passing in July 2021, his point of view had become the zeitgeist of the field and Weinberg widely regarded as its leading scientist. By that date, Steven Weinberg was arguably the greatest living theoretical physicist. He was awarded the Nobel Prize in Physics in 1979 for the unification of the electromagnetic and weak interactions. The electroweak unification of Glashow, Weinberg and Salam belongs to the same level of achievement as those of Newton, Maxwell and Einstein. The discovery of the electroweak theory can, however, be argued not to be his most lasting scientific legacy. Weinberg taught us that what one really does is to uncover the outermost layer of the onion of knowledge. Although not new in itself, what was new was the development of tools, effective field theories, that systematized how to extract information one layer at a time. The great conceptual simplicity of these tools allows predictions to be made where they were not previously possible. They also pointed to a fruitful way forward in long-standing problems, such as reconciling quantum mechanics with gravity, whose ultimate resolution is not yet settled. Besides having an extremely prolific research career extending over eight decades, he reached a much wider audience. His eight classic textbooks are widely acknowledged as standard references in each of their different fields. His award-winning popular science books were bestsellers, engagingly explaining the intricacies of cosmology and elementary particle physics to lay audiences. As a public figure, he used this platform to become an advocate for science, justice and critical thinking. This often spawned a controversial dialogue with social scientists and others about the very nature of scientific knowledge and of the role of religion in society. His essays on these subjects reveal a refreshing common sense laced with a sharp wit and a gift for the pithy phrase.