EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY
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Robert Vivian Pound (born 1919), Canadian-US physicist, carrying out a famous experiment in 1960 that confirmed a prediction of Einstein's General Relativity. Pound is at the top of a tower at Harvard University, and is communicating by telephone with Glen Rebka in the basement. They are using crystals to emit and absorb gamma radiation over the vertical distance of 22.5 metres. Einstein's theory had predicted that radiation changes in frequency as it travels through a gravitational field. The effect is tiny, but by clever experimental design and accurate measurements, Pound and Rebka were able, by 1964, to verify the slight shift in frequency.
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