Steven Weinberg (; May 3, 1933 – July 23, 2021) was an American theoretical physicist. He was one of the main developers of the standard model of particle physics.
Weinberg held the Josey Regental Chair in Science at the University of Texas at Austin. His research on elementary particles and physical cosmology was honored with numerous prizes and awards. He shared the 1979 Nobel Prize in Physics with Abdus Salam and Sheldon Glashow for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles.
Weinberg also had an extensive career as a writer. His first textbook was Gravitation and Cosmology (1972). His three-volume series The Quantum Theory of Fields is considered a classic. He also wrote popular science, beginning with The First Three Minutes. He occasionally wrote articles on various subjects for The New York Review of Books and other periodicals.
Steven Weinberg was born on May 3, 1933, in New York City. His parents were Jewish; his father, Frederick, worked as a court stenographer, while his mother, Eva (née Israel), was a housewife who had immigrated from Germany.
In a posthumously published memoir, Weinberg wrote: "Whatever native intelligence and intellectual curiosity I may have, I owe to my parents, in particular, my father."
Weinberg first became interested in physics after inheriting a chemistry set from a cousin. His interest in chemistry led him to want to learn about quantum mechanics.
He found inspiration in popular science, particularly George Gamow and James Jeans. He graduated from Bronx High School of Science in 1950. In the same graduating class was Sheldon Glashow, whose research, independent of Weinberg's, resulted in their sharing the 1979 Nobel in physics with Abdus Salam. Weinberg, Glashow, and Gerald Feinberg were friends at the school, and Weinberg initially shared an apartment with Glashow when he started at Cornell University, but moved out due to Glashow's "devil-may-care irresponsibility".
In 1954, Weinberg received his bachelor's degree from Cornell University, where he majored in physics. There he resided at the Telluride House.
He started graduate studies at the Niels Bohr Institute in Copenhagen. After a year, Weinberg moved to Princeton University, where he earned his Ph.D. in physics in 1957, completing his dissertation, The Role of Strong Interactions in Decay Processes, under the supervision of Sam Treiman. He chose to complete his PhD very quickly after his wife grew bored in Princeton and moved back to New York, leaving him alone.
After completing his Ph.D., Weinberg worked as a postdoctoral researcher at Columbia University from 1957 to 1959 and then at the University of California, Berkeley. He was promoted to faculty at Berkeley in 1960. Weinberg researched the high-energy behavior of quantum field theory, symmetry breaking, pion scattering, infrared photons and quantum gravity. During this time he developed the approach to quantum field theory described in his book The Quantum Theory of Fields and started to write his textbook Gravitation and Cosmology, having taken up an interest in general relativity after the discovery of cosmic microwave background radiation.
Weinberg collaborated with Abdus Salam during a stay at Imperial College in the 1961-1962 academic year.
In 1966, Weinberg left Berkeley and accepted a lecturer position at Harvard. In 1967 he was a visiting professor at MIT, where he proposed his model of unification of electromagnetism and nuclear weak forces (such as those involved in beta-decay and kaon-decay), with the masses of the force-carriers of the weak part of the interaction explained by spontaneous symmetry breaking. One of its predictions was the existence of the Higgs boson. Weinberg's model, now known as the electroweak unification theory, had the same symmetry structure that Glashow proposed in 1961: both included the then-unknown weak interaction mechanism between leptons known as neutral current and mediated by the Z boson.
The 1973 experimental discovery of weak neutral currents that implied the Z boson's existence was one verification of the electroweak unification.
In 1979, after the 1978 discovery of the predicted amount of parity violation due to Z bosons' mixing with electromagnetic interactions, Weinberg was awarded the Nobel Prize in Physics with Glashow and Salam, who had independently proposed a theory of electroweak unification based on spontaneous symmetry breaking.
The 1967 paper in which Weinberg presented this theory is one of the most cited works in high-energy physics. It cited Higgs's name first, and it has been suggested that the paper's popularity is a reason the Higgs boson was named after Higgs rather than other scientists who also suggested the mechanism.
After his seminal 1967 work on the unification of weak and electromagnetic interactions, Weinberg worked in many aspects of particle physics, quantum field theory, gravity, supersymmetry, superstrings and cosmology. In the 1970s, Weinberg proposed a modification of the Standard Model that did not contain the Higgs boson. He also proposed a theory later known as technicolor, in which new strong interactions resolve the hierarchy problem.
Weinberg spent the summer of 1972 trying, without success, to work out the reasons for quark and lepton masses, and said that was the mystery he most wanted to see solved in his lifetime.
Weinberg became Eugene Higgins Professor of Physics at Harvard University in 1973, a post he held until 1983. In 1979 with his "folk theorem", he pioneered the modern view on the renormalization of quantum field theory that considers all quantum field theories effective field theories. This approach allowed the development of an effective theory of quantum gravity and other developments, and is a topic of considerable interest in current research.