1837 Mintwood Pl NW, Washington, DC 20009 - COOPERSTOWN - Robert Waldo Ellsworth, an accomplished scientist who brought his love of physics to everything from the study of subatomic particles to the toys he built for his children, died on Aug. 6. He was 89.

Born in 1937 in Cooperstown, Bob was the second of three children. His mother, Dorris, was a teacher, and his father, Waldo, an artist. He graduated from Yale in 1960 with a degree in physics and later completed postdoctoral studies at the University of Washington and UC Berkeley in particle physics. He moved to DC in 1968 to teach at the University of Maryland and later became a faculty member at George Mason University, where he spent his career.

His work in particle physics and cosmology helped advance human understanding of core principles of the physical world. In the 1990s, he worked alongside an international team at the Super-Kamiokande observatory to prove that 'ghostly' subatomic particles known as neutrinos have mass—a landmark discovery that solved one of the biggest cosmic questions of our time.

Bob was an active member of the Adams Morgan community who served for many years as vice president of the Kalorama Citizens Association. He was a fierce advocate for maintaining the historic buildings and green spaces that gave the neighborhood its charm.

He retired from teaching in 2016 but continued to do research at the University of Maryland. He happily spent his final years living in his home on Mintwood Place, reading newspapers and magazines and graciously offering his home to those who were passing through or needed a place to stay. His kindness, curiosity, and generosity will be greatly missed.