- Person
- Steven Weinberg
- Lived
- 1933–2021
- Field
- Theoretical physics
- From
- American
The story
A good theory must make predictions that can be tested. Steven Weinberg's 1967 electroweak model made several bold ones. It required a then-unknown kind of weak interaction, called the neutral current, carried by a heavy neutral particle, the Z boson. In an ordinary weak interaction, such as beta decay, a charged W particle is exchanged and the particles involved change their identity. In a neutral-current interaction, the Z is exchanged and the particles keep their charge and identity, so the effect is far subtler to detect. The theory also implied the existence of another particle, the Higgs boson, through its mechanism for giving mass to the weak force carriers.
The tests came over the following decades. In 1973 physicists using the Gargamelle bubble chamber at CERN observed neutrino scattering events of exactly the kind the theory required, the first evidence of weak neutral currents and a key verification of electroweak unification. In 1978 experiments found the predicted amount of parity violation caused by the Z boson's mixing with electromagnetism.
The Nobel Prize awarded to Weinberg, Sheldon Glashow and Abdus Salam in 1979 specifically mentioned the prediction of the weak neutral current. A central parameter of the theory, the weak mixing angle, still bears his name as the Weinberg angle, and its measured value, slightly below 30 degrees, has been pinned down with great precision.
The W and Z particles themselves were detected in 1983 by the UA1 and UA2 experiments at CERN's converted Super Proton Synchrotron. Finally, after a search lasting some 40 years, the ATLAS and CMS experiments at the Large Hadron Collider announced the discovery of the Higgs boson on 4 July 2012.
Each discovery confirmed that the theory Weinberg had set out at the age of thirty-four described nature with remarkable accuracy. In 1999 Gerard 't Hooft and Martinus Veltman received their own Nobel Prize for proving that the electroweak theory is mathematically consistent, or renormalisable, completing the picture.
Why it matters
The confirmed predictions made the electroweak theory one of the most successful in science and guided the design of experiments at the world's largest particle accelerators.
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 unified two forces of nature in 3 pagesIn 1967 Steven Weinberg's three-page paper A Model of Leptons showed that electromagnetism and the weak nuclear force are two faces of one force, now among the most cited papers in 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 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 Wikipedia
- Neutral current Wikipedia
- Higgs boson 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.