Stephen Matthew Barr is an American physicist who is a professor emeritus of physics at the University of Delaware. A member of its Bartol Research Institute, Barr does research in theoretical particle physics and cosmology. In 2011, he was elected Fellow of the American Physical Society, the citation reading "for original contributions to grand unified theories, CP violation, and baryogenesis."

Wikipedia. CC BY-SA 4.0. Updated Jan 24, 2026.