Carroll Alley
Carroll Overton Alley, Jr. (June 13, 1927 – February 24, 2016) was an American physicist who led important experiments in gravity and quantum physics. He was the Principal Investigator of the Lunar Laser Ranging Experiment from NASA’s Apollo program, which used laser measurements to track the Moon’s orbit with centimeter precision. This work helped limit how much gravity’s strength could vary in space and time, and the data from the Moon still contribute to science today.
Alley studied under Robert Dicke and focused his work on gravitation, relativity, and quantum mechanics. He helped develop early tests of Einstein’s theories of relativity and later explored alternative ideas about gravity, including a theory proposed by Huseyin Yilmaz. He believed that understanding gravity required complex, interactive calculations beyond Einstein’s equations.
Career and education: Alley earned a B.S. in mathematics and physics from the University of Richmond in 1948, then went on to Princeton University, where he earned an M.S. in 1952 and a Ph.D. in 1962. His Ph.D. work involved advancing atomic clock technology. He taught and did research at the University of Rochester (1960–1963) before joining the University of Maryland, College Park, in 1963, where he spent most of his career and became Professor Emeritus in 2008.
Awards and roles: Alley was the first chairman of the Lunar Ranging Experiment team and served as the PI for the LR3 laser retro-reflector on the Moon, deployed during Apollo 11 in 1969. He received the NASA Exceptional Scientific Achievement Award in 1973 and was honored by the Maryland Academy of Sciences in 1976. He also received an honorary Doctor of Science degree from the University of Richmond in 1978.
Personal life: Alley was born in Richmond, Virginia. He married Elizabeth Slack Delany Alley, and they had daughters Frances and Margaret. He remained active in gravitation research for his whole career and until his death in 2016.
This page was last edited on 3 February 2026, at 19:09 (CET).