Steven Weinberg obituary | Particle physics

The American theoretical particle physicist Steven Weinberg, who died at the age of 88, was one of the leading figures of the 20th century in this field. In 1979, he won a Nobel Prize for his work uniting two of nature’s fundamental forces, which became a foundation of the Standard Model of particle physics, the theory that describes all known particles and fundamental forces in the universe. .

From Weinberg’s prodigious work – in research, in his technical and popular books on quantum field theory and cosmology, and in scientific commentary articles – his work demonstrating that the transmutation of elements by the weak nuclear force is fundamentally related to electromagnetism constituted a truly remarkable breakthrough.

Following Peter Higgs’ discovery in 1964 that fundamental particles can, in theory, gain mass through the “Higgs mechanism”, he, Weinberg and others tried to find examples where this mechanism is used in the nature. These attempts initially focused on the strong force that binds atomic nuclei, but no consistent correspondence emerged, until 1967, while on his way to work at MIT (the Massachusetts Institute of Technology), Weinberg had an inspired thought: they had implemented the right idea. , but to the wrong problem.

Instead of the strong force, Weinberg realized that the mechanism could apply to the weak nuclear force, manifested by radioactivity. As a bonus, Weinberg realized that thanks to this application, he could describe in a single mathematical diagram both the phenomena of electromagnetism and the form of radioactivity which is the key to the creation of elements in stars. This idea would become the basis of the current standard model of particles and forces.

A viable quantum field theory of electromagnetism – quantum electrodynamics (QED) – had been known since 1947. The key to its consistency was that the photon – the basic particle of electromagnetic radiation – is massless. Weinberg’s marriage of weak and electromagnetic forces required the existence of analogues of the photon. These “W and Z bosons” were later discovered and confirmed to be very massive, as Weinberg had predicted.

There was a problem, however: being massive, they apparently undermined the mathematical coherence of the theory. Weinberg conjectured, but was unable to prove, that if the W and Z gained their masses through the Higgs mechanism, his extension of QED would indeed be a viable quantum theory of two forces.

Initially his paper had little impact, with one prominent scientist later describing the response: “Rarely has such a great achievement been so widely ignored.” Then, in 1971, a young Dutch student, Gerard ‘t Hooft, proved the model to be a complete and viable theory, winning himself a Nobel Prize in 1999 for this feat.

With the demonstration that Weinberg had indeed constructed a coherent relativistic quantum theory of electromagnetic and weak force fields, the predictions of which were soon confirmed in a variety of experiments, his seminal paper quickly became the most cited in all of theoretical physics. Its implications were so profound that they determined the direction of high-energy particle physics during the last decades of the 20th century. In what was to prove to be of momentous importance, his papers drew attention to a cornerstone of his theoretical construction – the necessary role of the ‘Higgs boson’. The search for this particle would take four decades; its discovery in 2012 was the final piece in a structure whose architectural design owed much to the genius of Weinberg.

Born in New York, Steven was the son of Jewish immigrants, Eva (née Israel) and Frederick Weinberg, a court stenographer. Steven’s love for science began in childhood with the gift of a chemistry set. He attended Bronx Science High School, which produced eight Nobel laureates, including Weinberg’s contemporary Sheldon Glashow, whose freelance work led him to share the 1979 prize with Weinberg and Abdus Salam. He earned a bachelor’s degree at Cornell University in 1954, and that year married Louise Goldwasser, whom he had met while a student; she became a law professor. After a year at what is now the Niels Bohr Institute in Copenhagen, Weinberg returned to the United States and Princeton University, where he earned a doctorate (1957).

After two years at Columbia University and six at Berkeley, in 1966 Weinberg joined Harvard University, first as a lecturer, and from 1973 as a professor of physics. Early in his Harvard stint, Weinberg had a joint appointment at MIT, and it was while driving there in his red Camarro that he had his weak nuclear force epiphany.

In 1982 he moved to the University of Texas at Austin, where he spent the rest of his career. He never retired and continued teaching until the spring of that year.

For decades, Weinberg’s ideas outside of his 1967 paper inspired new lines of research. His work on “effective field theories” redefined the direction of work in quantum field theory and influenced attempts to find a viable quantum theory of gravity. He was one of the founders of the concept of “chiral perturbation theory” as a mathematical approach to understanding aspects of the strong nuclear force.

In addition to these seminal research contributions, Weinberg wrote an influential text on gravitation, a masterful three-volume set of textbooks on quantum field theory, and authored the popular best-selling cosmology book The First Three Minutes (1977).

In 1992 he published Dreams of a Final Theory, which has become a classic discourse on the goal of fundamental physics at the dawn of the 21st century.

In his later years he became an authoritative historian of science, his gravity and wisdom making him a respected commentator on science policy as well as social issues, and making him one of the most respected figures in science. world.

He is survived by his wife, Louise, whom he married in 1954, their daughter, Elizabeth, and one granddaughter.

Steven Weinberg, theoretical physicist, born May 3, 1933; passed away on July 23, 2021

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