27 August 1915, Washington (USA) - 4 November 2011, Boston (USA)
He began his engineering studies at Columbia University (New York, USA), but became interested in mathematics and switched to this specialty. Finally, he was already interested in physics by the time he received his degree in 1935.
He was awarded the Kellett Fellowship to study physics at the famous Cavendish Laboratory (UK) with Lord Rutherford, where he obtained his PhD in 1940.
He met important scientists who were driving forces in atomic physics such as Maurice Goldhaber, Edward Appleton, Max Born, Edward Bullard, James Chadwick, John Cockcroft, Paul Dirac, Arthur Eddington, Ralph Fowler, Mark Oliphant, and J.J. Thomson.
Ramsey wrote a final paper for Goldhaber on magnetic moments and returned to Columbia where he began his doctoral thesis under the supervision of Isidor Isaac Rabi, sparking his interest in molecular beams. Rabi (Nobel Prize in Physics in 1944) pioneered the development of a method for measuring the magnetic properties of atomic nuclei. This period was extremely important for the progress of nuclear technology as a whole, but in the case of Rabi's experiment, as in many others aimed at measuring very short times, his discoveries went beyond the nuclear field and served as the basis for the important developments that atomic and molecular physics have undergone since the 1970s.
Rabi himself applied his magnetic resonance technique to the study of atomic structure and its characteristic frequencies, but it was Ramsey who made a decisive contribution to its practical application. He introduced an improvement based on the use of two separate fields that induce atomic oscillations in two different regions which, when interfering with each other, provide an image of very high resolution. In other words, the application of these external fields allows us to read the oscillation frequencies of atoms and transform them into images or precise witnesses of the passage of time.
Ramsey together with Rabi's team (Jerome Kellogg, Polykarp Kusch, Sidney Millman, and Jerrold Zacharias) led them to invent molecular beam resonance spectroscopy, and together with Rabi and Jerrold Zacharias, they shared the discovery that the deuteron was a magnetic quadruple. This meant that the atomic nucleus was not spherical, as previously thought.
In 1940, he accepted a teaching position at the University of Illinois, but World War II intervened and, in September of that year, the British Tizard Mission brought several new technologies to the United States, including a cavity magnetron, a high-powered device that generates microwaves using the interaction of a stream of electrons with a magnetic field, which promised to revolutionise radar.
Alfred Lee Loomis established the Radiation Laboratory at the Massachusetts Institute of Technology (MIT) to develop this technology. Ramsey was one of the scientists recruited by Rabi for this work as a group leader.
At the end of the war, Ramsey returned to Columbia as a professor and researcher. Rabi and Ramsey picked up where they left off before the war with their experiments to measure the fundamental properties of atoms and molecules using molecular beams. Ramsey and his first graduate student, William Nierenberg, measured nuclear magnetic dipole moments and electric quadrupoles. With Rabi, he helped establish Brookhaven National Laboratory.
In 1946, he became the first head of the Physics Department at Columbia University. He became a fellow at the Carnegie Institution in Washington DC, where he studied neutron-proton and proton-helium scattering and, from 1947, was Professor of Physics at Harvard University. There he carried out precise magnetic resonance experiments with molecular beams. However, the accuracy of the measurements depended on the uniformity of the magnetic field, and Ramsey found that it was difficult to create sufficiently uniform magnetic fields. In 1949, he developed the separate oscillatory field method as a means of achieving the accuracy he wanted.
Ramsey and his PhD student Daniel Kleppener developed the atomic hydrogen maser, seeking to increase the precision with which they could measure the hyperfine separations of atomic hydrogen, deuterium and tritium, and to investigate how much the hyperfine structure was affected by external magnetic and electric fields.
During the 1950s, he held positions in government and international agencies such as NATO and the United States Atomic Energy Commission.
In 1989, he shared the Nobel Prize with Hans Georg Dehmelt and Wolfgang Paul, for their method of separate oscillatory fields, which made the development of the atomic clock possible. Curiously, he had already retired in 1986.
n collaboration with the Laue-Langevin Institute, Ramsey also worked on applying similar methods to neutron beams, measuring the neutron's magnetic moment and finding a limit to its electric dipole moment.
As president of the Universities Research Association during the 1960s, he was involved in the design and construction of the US Department of Energy (DOE) Fermilab in Batavia, Illinois, and held positions in government and international agencies such as NATO and the United States Atomic Energy Commission.
The two most important technological applications based on his discoveries are nuclear magnetic resonance and the atomic clock. The former has become a major medical diagnostic technique, now commonly used in traumatology, but which in combination with other tomography scans is providing images of brain dynamics that promise important advances in the early detection of degenerative brain diseases; the latter led to the development of the caesium atomic clock, which in 1967 was adopted as a standard of time measurement.
Although the image of a scientist obsessed with discovering the essential properties of matter and their practical applications perfectly defines Ramsey's personality, his biography has a lesser-known extra-scientific aspect: his courageous confrontation of Senator McCarthy's witch-hunt during the 1950s. Ramsey was one of the few prominent researchers to testify on behalf of several colleagues accused of communism. ‘It was all against people's rights,’ he declared.
In 2004, he signed a letter along with 47 other Nobel laureates endorsing John Kerry for US president as someone who would ‘restore science to its proper place in government’.
He also headed a 1982 National Research Council committee that concluded that, contrary to the findings of the House Select Committee on Assassinations, the acoustic evidence did not indicate the presence of a second gunman in the assassination of President John F. Kennedy.
In addition to the Nobel Prize in Physics, Ramsey received several awards, including the Ernest Orlando Lawrence Award (1960), the Davisson-Germer Award (1974), the IEEE Medal of Honor (1984), the Rabi Award (1985), the Rumford Premium Award (1985), the Compton Medal (1986), the Oersted Medal and the National Medal of Science (1988) and the Golden Plate Award of the American Academy of Achievement (1990).
