Steven Weinberg, a theoretical physicist who discovered that two of the universe’s forces are really the same, for which he was awarded the Nobel Prize, and who helped lay the foundation for the development of the Standard Model, a theory that classifies all known elementary particles in the universe, making it one of the most important breakthroughs in physics in the 20th century, died Friday in a hospital in Austin, Texas. He was 88.
His daughter, Dr. Elizabeth Weinberg, confirmed the death but did not specify a cause.
Steven Weinberg’s stature in physics would be hard to overstate.
Although he had the respect, almost awe, of his colleagues for his scientific abilities and insights, he also possessed a rare ability among scientists to communicate and explain abstruse scientific ideas to the public. He was a sought-after speaker, and he wrote several popular books about science, notably “The First Three Minutes: A Modern View of the Origin of the Universe” (1977).
The work for which Dr. Weinberg was awarded the Nobel had a transformative impact on physics, in particular on the development of quantum mechanics, which tries to understand and explain what happens in the subatomic world.
There are four known forces in the universe: gravity; electromagnetism; the strong force, which binds the nuclei of atoms together; and the weak force, which causes radioactive decay. The first two forces have been known for centuries, but the other two were discovered only in the first two decades of the 20th century.
Over the next decades, physicists struggled to find a theory that would account for all the forces, or what Einstein called a theory of everything. Although there were significant discoveries, particularly of new particles with exotic names like quarks (the components of protons and neutrons in the nucleus) and leptons (which include electrons but also more esoteric particles called muons and taus), a unified theory or model remained elusive.
In 1967, Dr. Weinberg began using something called gauge theory to study the interactions in weak forces, which had not been successfully explained.
Gauge theory had been developed in the 19th century by James Clerk Maxwell, a British physicist, in his seminal work to explain electromagnetism. In the 1950s, it was used by Robert Mills and Chen Ning Yang, a Chinese American physicist, who later won the Nobel Prize, to understand strong-force interactions.
But Dr. Weinberg’s application of gauge theory to the weak force soon ran into a problem.
Electromagnetism is a force that acts at large distances, but the weak force acts only at very short distances — smaller than the nucleus of an atom. In electromagnetism, when two particles — say, electrons — collide, they exchange a massless neutral particle called a photon, which is also known as a gauge boson. If two particles collide because of the weak force, gauge theory requires — because of the short distances of the interaction — that the gauge bosons that are exchanged be massive and possibly electrically charged.
Fortunately, several years earlier, physicists had come up with a way to generate mass for gauge bosons called the Higgs Mechanism. It was named for Peter Higgs, a British physicist, and it predicted the existence of a previously unknown particle that is responsible for giving other particles their mass. The particle was given the name the Higgs boson, and its discovery, in 2012, brought Higgs and his colleague François Englert the 2013 Nobel Prize.
Using this new idea, Dr. Weinberg was able to create a model in which weak interactions produced massive, at least by atomic standards, gauge boson particles. He called them W and Z bosons.
His theory also predicted that in some collisions — for example, between two electrically neutral particles like a neutron and a neutrino — a neutral current, as opposed to a charged one, would be created, indicating that there had been an exchange of a Z boson.
Dr. Weinberg theorized that there was a link between the photon and the W and Z bosons, suggesting that they were created by the same force. The conclusion was that, at very high energy levels, the electromagnetic and weak forces were one and the same. It was a step on the path to the unified theory that physicists had been searching for.
Dr. Weinstein published his findings in 1967 in a groundbreaking paper, “A Model of Leptons,” in the journal Physical Review Letters. The article is one of the most cited research papers in history.
Working separately, Dr. Abdus Salam, a Pakistani theoretical physicist, came to the same conclusions. Their model became known as the Weinberg-Salam Theory. It was revolutionary, not only for proposing the unification of the electromagnetic and weak forces, but also for creating a classification system of masses and charges for all fundamental particles, thereby forming the basis of the Standard Model, which includes all the forces except gravity.
The existence of neutral current was confirmed experimentally in 1973, while it took another decade for the W and Z bosons to be verified, by Carlo Rubbia and Simon van der Meer at the CERN supercollider in Switzerland near Geneva. That work earned Rubbia and van der Meer the 1984 Nobel Prize.
Weinberg, Salam, and Dr. Sheldon Lee Glashow, a high school classmate of Dr. Weinberg who had resolved a critical problem with the Weinberg-Salam model, were jointly awarded the 1979 Nobel Prize “for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles.”
After learning that Dr. Weinberg had died, John Carlos Baez, a theoretical physicist at the University of California Riverside, wrote on Twitter: “For all the talk of unification, there are few examples. Newton unified terrestrial and celestial gravity — apples and planets. Maxwell unified electricity and magnetism. Weinberg, Glashow, and Salam unified electromagnetism and the weak force.”
Dr. Weinberg’s prodigious output went well beyond his contributions to the Standard Model.
In the mid-1960s, after the discovery of cosmic background radiation, the heat signature left over from the Big Bang at the beginning of the universe, Dr. Weinberg began studying cosmology, leading to his book “Gravitation and Cosmology” in 1972.
He was invited to give a talk on the subject at the undergraduate science center at Harvard University. During the lecture, Dr. Weinberg described the evolution of the universe in the first three minutes after the Big Bang, when things had cooled down enough for atomic nuclei to bond together. He then commented, “After that, nothing of any interest would happen in the history of the universe.”
The quip led a book publisher to engage Dr. Weinberg to write “The First Three Minutes,” which gained a wide readership and made cosmology a respectable field for physicists. In the book he described the Earth as “a tiny part of an overwhelmingly hostile universe” and famously, and grimly, concluded, “The more the universe seems comprehensible, the more it also seems pointless.”
He wrote many other books, including one on the history of science, “To Explain the World: The Discovery of Modern Science” (2015), and three volumes totaling 1,500 pages on quantum field theory, which merges classical physics, special relativity, and quantum mechanics. The series is widely regarded as the definitive text on the subject.
Dr. Willy Fischler, a theoretical physicist whom Dr. Weinberg recruited for the faculty of the University of Texas, in 1982, said Dr. Weinberg’s greatest work may have been in the development of effective field theory, which provides a mathematical method to use in relatively low-energy experiments to detect the effects of higher energy particles that cannot be seen or measured directly. Fischler called him the father of effective field theory.
Steven Weinberg was born in New York City on May 3, 1933, the only child of Frederick and Eva (Israel) Weinberg. His father was a court stenographer, his mother a homemaker.
As he told the Nobel Institute in a 2001 interview, he first became interested in science when a cousin who had been given a chemistry set passed it along to him. The cousin had decided to take up boxing instead.
He went to the Bronx High School of Science, where Glashow was among his classmates and friends. After graduating from Cornell University in 1954, he spent a year at the Institute for Theoretical Physics in Copenhagen, which was later renamed the Niels Bohr Institute, after the Nobel laureate. Dr. Weinberg returned to the United States in 1955 to work on his doctorate at Princeton University.
Dr. Weinberg worked at Columbia University until 1959 and then at the University of California Berkeley, until 1966, when he became a lecturer at Harvard and a visiting professor at the Massachusetts Institute of Technology until 1969. MIT then hired him, but he moved back to Harvard in 1973 to become the Higgins professor of physics, succeeding Julian Schwinger, who had won the Nobel Prize in 1965 for his contributions to the understanding of particle physics. Dr. Weinberg was also named the senior scientist at the Smithsonian Astrophysical Observatory in Cambridge.
Dr. Weinberg married Louise Goldwasser in 1954; they had met as undergraduates at Cornell. In 1980, Louise Weinberg joined the University of Texas as a law professor. For the next two years, the couple commuted back and forth from Cambridge as Dr. Weinberg wrapped up his work at Harvard. He joined his wife in Texas in 1982, becoming a professor of physics and astronomy, as he had been at Harvard.
As part of his move, Dr. Weinberg was allowed to create a high-level theoretical physics research group at the University of Texas and recruit professors for it. It has grown to include eight full professors and five assistant professors and is considered one of the leading centers of physics research in the United States.
Fischler said of Dr. Weinberg, “He had a knack to consider the important problems, but not only what was important, but what was solvable.”
Dr. Weinberg, who never retired, continued to teach until this spring.
He received many awards and accolades besides the Nobel, including the National Medal of Science in 1991 and the Benjamin Franklin Medal for Distinguished Achievement in Science in 2004.
In addition to his daughter, a medical doctor, and his wife, he leaves a granddaughter.
Dr. Weinberg opposed religion, believing that it undermined efforts to seek and discover truth. In “The First Three Minutes” he wrote, “Anything that we scientists can do to weaken the hold of religion should be done and may in the end be our greatest contribution to civilization.”
”There is no cosmic plan for us,” he said in his interview with the Nobel Institute. “We are not actors in a drama that has been written with us playing the starring role. There are laws — we are discovering those laws — but they are impersonal, they are cold.”
He added: “It is not an entirely happy view of human life. I think it is a tragic view, but that is not new to physicists. A tragic view of life has been expressed by so many poets — that we are here without purpose, trying to identify something that we care about.”