Daniel Kleppner, Physicist Who Brought Precision to GPS, Dies at 92

New York Times

2 days ago

Daniel Kleppner, an experimental physicist who helped to develop an atomic clock that became an essential part of global positioning systems, or GPS, and who also helped to discover a rare fundamental state of matter predicted by Albert Einstein and his fellow theoretical physicist Satyendra Nath Bose, died on June 16 in Palo Alto, Calif. He was 92.
His wife, Beatrice, confirmed the death. She said he collapsed while visiting their daughter, Sofie Kleppner, and her son, Darwin, who was graduating from high school.
It was in the mid-1950s, while he was doing a fellowship at the University of Cambridge in England, that Dr. Kleppner learned something surprising: It was possible, a tutor told him, to build a clock precise enough to detect the effects of gravity on time. Curious, he went in search of more information and read Norman Ramsey's 1953 book 'Nuclear Moments.'
After his fellowship, he went on to do graduate work at Harvard University, where he discovered that Dr. Ramsey was on the faculty. He immediately applied for Dr. Ramsey's research group and was accepted.
Dr. Ramsey would eventually share the 1989 Nobel Prize in Physics for research he had done in the 1940s, when he discovered a way to measure the frequencies of electromagnetic radiation absorbed by atoms and molecules. His experimental technique laid the groundwork for nuclear magnetic resonance, a precursor to the M.R.I. technology used in medicine today.
The atoms of each element vibrate at a unique frequency, like the signature call of a bird. Dr. Ramsey's work made it possible for scientists to build what is known as an atomic clock — a device that measures those vibrations, using the information to keep incredibly precise time. (The official measure of a second, for example, is 9,192,631,770 oscillations of a cesium atom.)
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