Carroll Overton Alley, Jr. (June 13, 1927 – February 24, 2016) was an American physicist. He served as the Principal Investigator on the Apollo Program's Lunar Laser Ranging Experiment, which significantly restricted the possible range of spatial variation of the strength of the gravitational interaction. Alley was a PhD student of Robert Henry Dicke. Alley’s goal was nothing less than understanding quantum mechanics, gravitation, and relativity. His lifelong research interests included experimental and theoretical questions about the foundations of gravitational and quantum physics. Alley developed some of the earliest important laboratory tests of Albert Einstein's theories of relativity. In recent years he became known for alternative theories of gravitation. He was a physics professor at University of Maryland, College Park, emeritus since 2008, until his death on 24 February 2016. Career details Professor C. O. Alley served as the first chairman of the Lunar Ranging Experiment team. He was the Principal Investigator (PI) for the Apollo 11 laser ranging retro-reflector (LR3) experiment, deployed on the moon by Neil Armstrong and Buzz Aldrin in 1969. In addition to the gravitational interaction results mentioned above, the experiment measured the orbit of the moon to centimeter accuracy—and still produces data to this day. For this work he was awarded the NASA Exceptional Scientific Achievement Award in 1973; was designated by the Maryland Academy of Sciences, for their 1976 Bicentennial Exhibit, as one of two outstanding 20th Century Scientists; and received an honorary Doctor of Science degree from the University of Richmond in 1978. Some additional accomplishments of Professor Alley, his graduate students, the Quantum Electronics Research and Lunar Ranging Experiment Teams, support staff, and numerous collaborators include: Surveyor 7 laser beam pointing tests in preparation for the Apollo 11 experiment and visual detection of laser beams from Earth, as well as subsequent lunar laser ranging on later Apollo missions Role in the commissioning of the Global Positioning System by contributing to the calculations that correct for time dilation in gravitational fields Conducting relativistic proper time experiments by flying caesium and rubidium atomic clocks in a Navy P3C aircraft over the Chesapeake Bay, to measure the effects of gravitational potential difference on their recorded proper times and comparing those times to ground clocks using short laser pulses Experiments in fundamental quantum mechanics with light quanta, including the first delayed-choice experiment in quantum mechanics First use of spontaneous parametric down conversion in quantum optics to