Norman Ramsey Dies at 96; Work Led to the Atomic Clock
By Jascha Hoffman
New York Times, November 7, 2011, page A19
Norman F. Ramsey in 1989
Ramsey signing the atomic bomb that was dropped on Nagasaki, Japan in 1945.
“If you made a list of the most outstanding physicists of the 20th century, he’d be among the leaders,” said Leon M. Lederman, emeritus director of the Fermi National Accelerator Laboratory in Batavia, Ill., which Dr. Ramsey helped found.
Early in the 20th century, physicists began to decipher the structure of atoms from measurements of the wavelengths of light they released and absorbed, a method called atomic spectroscopy. In 1937, the physicist Isidor Isaac Rabi of Columbia University developed a means of studying atoms and molecules by sending a stream of them through rapidly alternating magnetic fields. As Dr. Rabi’s student at Columbia in the late 1930s, Dr. Ramsey worked to refine it.
In 1949, when he was at Harvard, Dr. Ramsey discovered a way to improve the technique’s accuracy: exposing the atoms and molecules to the magnetic fields only briefly as they entered and left the apparatus. His new approach — which Dr. Ramsey called the separated oscillatory fields method, but which is often simply referred to as the Ramsey method — is widely used today. Dr. Ramsey’s research helped lay the groundwork for nuclear magnetic resonance, whose applications include the M.R.I. technique now widely used for medical diagnosis. (Do his MRIs help diagnose elderly Japanese with radiation sickness from Nagasaki? -Michael Hoffman)
But the most immediate application of the Ramsey method has been in the development of highly accurate atomic clocks. Since 1967 it has been used to define the exact span of a second, not as a fraction of the time it takes Earth to revolve around the Sun, but as 9,192,631,770 radiation cycles of a cesium atom. In 1960, working with his student Daniel Kleppner, now an emeritus professor of physics at the Massachusetts Institute of Technology, Dr. Ramsey invented a different type of atomic clock, known as the hydrogen maser, whose remarkable stability has since been used to confirm the minute effects of gravity on time as predicted by Einstein’s theory of general relativity. Atomic clocks like the hydrogen maser are also used in the ground-based timing systems that track global positioning satellites. Dr. Ramsey did not anticipate that his laboratory technique would have such applications. “I didn’t even know there was a problem about clocks initially,” he said in a 1995 oral history interview. “My wristwatch was pretty good.”
Norman Foster Ramsey Jr. was born on Aug. 27, 1915, in Washington, the son of Minna Bauer Ramsey, a mathematics teacher, and Norman Foster Ramsey, an Army officer. After receiving his Ph.D. under Dr. Rabi at Columbia, he worked at the M.I.T. Radiation Laboratory and served as a radar consultant to the secretary of war.
In 1943 he went to Los Alamos, N.M., to work on the Manhattan Project, leading a team that helped assemble the bombs dropped on Hiroshima and Nagasaki, Japan (the Times has no other comment on his role in the atomic holocaust - Michael Hoffman).
After the war, he taught for nearly four decades at Harvard, mentoring scores of graduate students, many of whom went on to start their own research groups. Although he officially retired in 1986, he continued his work through his early 90s. In recent years, he collaborated with a team of British physicists to study the symmetry of the neutron, searching for evidence that it was not perfectly spherical. Dr. Ramsey presided over the founding of Fermilab and another major particle accelerator laboratory, the Brookhaven National Laboratory on Long Island, where he was the first head of the physics department in the 1940s. As the first science adviser to NATO, he initiated summer school programs to train European scientists. He led a National Research Council committee that concluded in 1982 that contrary to the findings of the House Select Committee on Assassinations, acoustical evidence did not support the existence of a second gunman in the assassination of President John F. Kennedy.
Dr. Ramsey had an athletic flair. He learned to ski in Norway in the 1930s. Later, he took up long-board surfing and ice sailing, and he traveled with his second wife, Ellie Welch Ramsey, from the Himalayas to Antarctica. After having a knee replaced in the 1980s, he continued to ski. Dr. Ramsey’s first wife, Elinor, died in 1983. In addition to his wife, he is survived by four daughters, Margaret Kasschau, Patricia Ramsey, Winifred Swarr and Janet Farrell; two stepchildren, Marguerite and Gerard Welch; eight grandchildren; and nine great-grandchildren.
Colleagues said Dr. Ramsey was a tall man with bright white hair who gestured energetically and walked briskly. “He had a messianic quality when talking about his work,” said Gerald Gabrielse, a physics professor at Harvard. William Phillips, a physicist at the University of Maryland, said Dr. Ramsey’s forceful presence and as his contributions “set the tone for a generation of physicists.”