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Steven Weinberg: a legend is lost

Physics World September 2021

Physics World

 
News & Analysis Physics World  September 2021

Steven Weinberg: a legend is lost

By unifying the electromagnetic and weak forces, Steven Weinberg was vital to the formation of the Standard Model of particle physics. Michael Banks looks back at a giant of theoretical physics 

Particle pioneer Steven Weinberg, who has died aged 88, carried out work in the 1960s that became a cornerstone of the Standard Model of particle physics. (Courtesy: CERN/Maximilien Brice)

The US physicist Steven Weinberg, who shared the 1979 Nobel Prize for Physics for his theoretical contributions to the Standard Model of particle physics, died on 23 July aged 88. In the 1960s Weinberg’s work was instrumental in understanding the weak interaction in particle physics, which is best known for its role in nuclear decay. He shared the 1979 Nobel prize equally with Sheldon Glashow and Abdus Salam.

Born in New York on 3 May 1933, Weinberg attended the Bronx High School of Science, which has seen seven former pupils go on to win physics Nobels. In 1954 Weinberg received a degree in physics from Cornell University and after a year at the Institute for Theoretical Physics in Copenhagen (now the Niels Bohr Institute), he returned to the US to compete his PhD at Cornell University, graduating in 1957.

After a stint at Columbia University, in 1959 Weinberg went to the University of California, Berkeley, before heading to Harvard University in 1966. A year later, Weinberg became a visiting professor at the Massachusetts Institute of Technology where he carried out much of his pioneering work in unifying the weak and electromagnetic interaction. 

In 1967, at the age of 34, Weinberg published his groundbreaking work. Titled “A model of leptons” and barely three pages long, it became a cornerstone of the Standard Model of particle physics – and one of the most highly cited papers in physics. The work predicted the existence of the W and Z bosons, which carry the electroweak force, and also theorized that “weak neutral currents” dictated how elementary particles interact with one another.

Working independently to Weinberg, Glashow (who was in the same year group as Weinberg at the Bronx High School) and Salam made their own contributions to the model, which later became known as the Salam–Weinberg theory. However, at the time it was not taken seriously by some physicists because it seemed impossible to subject the theory to the usual “renormalization” procedure. This meant it generated infinite and therefore meaningless expressions, so it seemed impossible to perform accurate calculations with it.

That particular issue was overcome in 1972 when the Dutch physicists Martinus Veltman and Gerardus ‘t Hooft showed how to carry out this renormalization and used their theory to make precise calculations of particle properties. A year later physicists working at the CERN particle-physics lab near Geneva announced the discovery of weak neutral currents – interactions that are governed by the Z boson. In 1979 Glashow, Salam and Weinberg were awarded the Nobel Prize for Physics “for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including, inter alia, the prediction of the weak neutral current”. The W and Z particles were then detected for the first time in 1983 at CERN. 

In 1973 Weinberg returned to Harvard while also taking up a position at the Smithsonian Astrophysical Observatory. In 1982 he moved to the University of Texas at Austin, where he was to spend the rest of his career. Weinberg worked in many areas of physics throughout his life, one of which was cosmology – an interest that he developed in the 1960s. Weinberg published numerous books including the popular-science account The First Three Minutes (1977), which told the story of the origin of the universe as well as Dreams of a Final Theory (1993), in which he wrote about his belief that physics was on the verge of discovering a theory that would unite physics.

One of his last books – To Explain the World: the Discovery of Modern Science (2015) – examined the history of physics from the ancient Greeks to the present day. It was criticized by some science historians and philosophers given that it judged the past from the standpoint of the present – known as “Whig interpretation”. Weinberg knew that this would ruffle feathers, but defended taking such a perspective (see ‘The wonder of Weinberg).

“An immeasurable loss” 

Weinberg was the recipient of numerous prizes including the US National Medal of Science in 1991 and the Benjamin Franklin Medal for Distinguished Achievement in Science in 2004. Last year, he received a Special Breakthrough Prize in Fundamental Physics – and with it $3m – for his contributions to physics.

Steven Weinberg was one of the most accomplished scientists of our age and an eloquent spokesperson for the scientific worldview

John Preskill from the California Institute of Technology, who was Weinberg’s PhD student at Harvard, says his death is an “immeasurable loss”. “[Weinberg was] one of the most accomplished scientists of our age, and a particularly eloquent spokesperson for the scientific worldview,” adds Preskill. “[He] remained intellectually active to the end.”

Jay Hartzell, president of the University of Texas at Austin, noted in a statement that Weinberg’s work “unlocked the mysteries” of the universe that has “enriched” our concept and understanding of nature. “From his students to science enthusiasts, from astrophysicists to public decision makers, he made an enormous difference in our understanding. In short, he changed the world.”