- Person
- Steven Weinberg
- Lived
- 1933–2021
- Field
- Theoretical physics
- From
- American
The story
Physicists in the 1960s knew of four fundamental forces: gravity, electromagnetism, and the strong and weak nuclear forces. The weak force, responsible for some kinds of radioactive decay, seemed utterly different from electromagnetism. It acted only over tiny distances and was carried, theory suggested, by heavy particles, while electromagnetism is carried by massless photons. Earlier attempts to unite the two, by Sheldon Glashow in 1961 and by Abdus Salam and John Ward in 1964, had to break their symmetries by hand, and no one knew how to make such theories free of troublesome infinities.
Steven Weinberg came at the problem from another direction. Since 1965 he had been working on spontaneous symmetry breaking and its role in the strong interactions. In 1967, then a visiting professor at MIT, he realised that the same ideas applied to the weak and electromagnetic forces. He published a three-page paper in Physical Review Letters called A Model of Leptons. In it he showed how the two forces could be unified into a single electroweak force, with the difference between them arising because a field filling space gives mass to the carriers of the weak force, the W and Z particles, while leaving the photon massless. He estimated the masses of the W and Z and suggested that the theory would be renormalisable, meaning free of the infinities that plagued earlier attempts.
The paper attracted little notice at first. That changed in 1971, when Gerard 't Hooft proved that theories of this kind are indeed renormalisable. The same year, the physicist Helen Quinn and her colleagues completed the first detailed quantum correction in Weinberg's theory, and she later recalled how delighted he was when they told him. Experimental confirmation followed with the discovery of neutral currents at CERN in 1973 and of the W and Z particles in 1983.
Today, according to the Bulletin of the Atomic Scientists, the paper ranks among the most cited research papers in history. It is a cornerstone of the Standard Model of particle physics and earned Weinberg a share of the 1979 Nobel Prize.
Why it matters
Electroweak unification is a pillar of the Standard Model, the theory that describes all known particles and every force except gravity.
About Steven Weinberg
Physicist whose three-page 1967 paper unified electromagnetism and the weak nuclear force, a pillar of the Standard Model, and whose The First Three Minutes brought the Big Bang to millions.
More about Steven Weinberg
- Steven Weinberg changed how physicists view their theoriesIn 1979 Steven Weinberg's folk theorem launched the modern view that quantum field theories are effective theories, valid at particular energy scales, an idea now used across physics.
- Steven Weinberg helped predict the axionIn 1978 Steven Weinberg, and separately Frank Wilczek, realised that a proposed symmetry implied a new particle, the axion, now a leading candidate for the universe's dark matter.
- Steven Weinberg's theory predicted new particle processesSteven Weinberg's electroweak theory predicted a new kind of weak interaction, the neutral current, which was discovered in 1973, and the Higgs boson, found in 2012.
- Steven Weinberg explained the Big Bang to millionsSteven Weinberg's 1977 book The First Three Minutes explained to a wide public how physics can reconstruct the earliest moments of the universe, winning a science writing award.
- Steven Weinberg worked to curb nuclear dangersSteven Weinberg advised the US Arms Control and Disarmament Agency, wrote Glory and Terror on the nuclear danger, and served on the Bulletin of the Atomic Scientists' Board of Sponsors from 2009.
Sources
- Steven Weinberg, Nobel laureate in physics and Bulletin board member, dies at 88 Bulletin of the Atomic Scientists
- Steven Weinberg Wikipedia
- Electroweak interaction Wikipedia
Another act of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.