# UT Austin’s Steven Weinberg wins $3M Special Breakthrough Prize in Fundamental Physics

The Selection Committee of the Breakthrough Prize in Fundamental Physics today announced a $3 million Special Breakthrough Prize in Fundamental Physics for Steven Weinberg, commending his “continuous leadership in fundamental physics, with broad impact across particle physics, gravity and cosmology, and for communicating science to a wider audience.”

Weinberg, a professor at the University of Texas at Austin, will be recognized at the Breakthrough Prize ceremony, along with the annual winners of the Breakthrough Prizes in Life Sciences, Mathematics and Fundamental Physics. As a result of the COVID-19 pandemic, this year’s ceremony has been postponed until March 2021.

Juan Maldacena, the chair of the Selection Committee, said, “Steven Weinberg has developed many of the key theoretical tools that we use for the description of nature at a fundamental level.”

“Steven Weinberg is one of the key architects of the Standard Model, one of the most successful physical theories ever,” said Yuri Milner, one of the founders of the Breakthrough Prizes. “He also provided deep insights across the range of subjects in fundamental physics.”

Symmetry Breaking and the Standard Model

There are four known fundamental forces of nature: electromagnetism, the strong and weak nuclear forces, and gravity. Early in his career, Weinberg made important contributions to understanding the dynamics of the strong nuclear force, as well as to “soft theorems” that describe electromagnetic and gravitational interactions with very low energy or momentum.

But his single greatest contribution was to the genesis of the Standard Model of particle physics—the description of three of the forces (electromagnetism and the two nuclear forces) in terms of quantum field theory. In 1967, Weinberg was the first to show that the notion of spontaneous gauge symmetry breaking could be applied to the weak nuclear force. Symmetry breaking is the idea that what appear as disparate phenomena are actually manifestations of an underlying unity, which when tipped past a critical point is “broken” into a non-symmetric state. Weinberg’s theory unified the weak force with electromagnetism, showing that they are manifestations of a single phenomenon. The currently accepted hypothesis is that the “electroweak” symmetry was broken within the first second after the big bang, after which electromagnetism and the weak force were two separate forces.

Other researchers, including in particular Sheldon Glashow, who had been Weinberg’s classmate at the Bronx High School of Science in 1950s, had proposed a theory of the weak nuclear force—the force responsible for radioactive decay—in which it is mediated by a massive particle, today called the W boson. However, this theory had some mathematical problems, preventing accurate quantum computations. Weinberg’s theory would eventually turn out to avoid these problems. Once the weak neutral current was discovered, Weinberg’s theory accurately predicted the masses of the W and Z bosons, which were discovered at CERN in the 1980s.

Moreover, Weinberg’s theory predicted the existence of a new particle, the Higgs particle.

Peter Higgs and other researchers had investigated what are now called Higgs fields in their work on the strong interactions. It was Weinberg who understood that these ideas should be applied to the weak interactions instead, and who predicted a weakly interacting Higgs particle—the particle which was eventually discovered at CERN in 2012. Moreover, it was Weinberg who used gauge symmetry breaking to account for the masses of elementary fermions, such as electrons. Later this idea was extended to quarks. Weinberg’s success in applying nonabelian gauge theory to understand the weak interactions had an enormous influence on the effort to understand the strong nuclear force, and thus to the construction of the full Standard Model as it is today.

A similar proposal concerning the electroweak interactions was independently made by Abdus Salam. Weinberg, Glashow and Salam shared the Nobel Prize in 1979.

Other work

While his contribution to the genesis of the Standard Model has undoubtedly been Weinberg’s greatest single achievement, he has made numerous other significant contributions to fundamental physics, and would be a recognized leader in the field even if he had not made this particular contribution.

These include a fundamental calculation, with Howard Georgi and Helen Quinn, extrapolating from the known particle forces to estimate the energy scale at which a unification of all particle interactions—including the strong nuclear force and gravity—might occur. This computation has been highly influential. Weinberg had the very simple yet fundamental idea that some of the approximate symmetries appearing in particles and spacetime are low-energy “accidents” that follow from the structure of the Standard Model. This way of thinking had a partial confirmation in later discoveries about neutrinos, and an apparent exception to it was a motivation for the prediction of the axion, a leading candidate for dark matter that Weinberg (and, independently, Frank Wilczek) proposed in 1977.

In cosmology, among other insights he was one of the first to seriously study quantum field theory at high temperature, and he was perhaps the first to fully understand the physics involved in the spontaneous production of baryons (the building blocks of atomic nuclei), in particular the fact that this effect is proportional to the expansion rate of the Universe. This proved essential in the development of the theory of cosmic inflation—the most widely accepted current theory of the early Universe, to which Weinberg has also been an important contributor. One of his most provocative ideas has concerned the extreme smallness of the cosmological constant—the energy density of empty space, which is the leading candidate for the dark energy causing the Universe’s expansion to accelerate. At a time when, observationally, the cosmological constant appeared to be precisely zero, Weinberg argued that a very small but nonzero cosmological constant would be naturally expected in an “anthropic” view of the Universe. In this view, the cosmos extends far beyond what we see, with different elementary particles and forces in different regions. We inevitably live where the expansion of the Universe is not too violent, because elsewhere any complex structure would be ripped apart. This view, though it remains speculative, received dramatic support a little over 20 years ago when it was discovered that the expansion of the Universe is indeed accelerating.

Books

As well as being one of the most important and productive physicists of his generation, Weinberg has been a major influence on succeeding generations through his teaching and his meticulously written textbooks. Numerous physicists, including some of the greatest working today, have learned General Relativity, cosmology and quantum field theory from these works, which include Gravitation and Cosmology, Cosmology and The Quantum Theory of Fields. His latest technical book is Lectures on Astrophysics.

Alongside his scientific books and articles, he has also written bestselling popular books, which explain the deepest ideas in science with exceptional clarity and readability. They include The First Three Minutes, Dreams of a Final Theory, and his recent To Explain the World, a fresh account of the history of science.

Science advocacy

For decades, Weinberg has been a highly visible public spokesman for science and rationality. In his articles, especially for the New York Review of Books, he has communicated to the public not only the profound ideas of theoretical physics, but the importance of the scientific worldview and the broader meaning of science in human culture.

Weinberg’s 1993 testimony before the United States Congress in support of the Superconducting Super Collider is an iconic defense of the societal worth of fundamental science not just for technological progress but for the intrinsic value of the pursuit of knowledge.

2020 Special Breakthrough Prize in Fundamental Physics

Steven Weinberg

The University of Texas at Austin

Citation: For continuous leadership in fundamental physics, with broad impact across particle physics, gravity and cosmology, and for communicating science to a wider audience.

Special Breakthrough Prize in Fundamental Physics