Isidor Isaac Rabi

Isidor Isaac Rabi: The Grocer's Son Who Weighed the Nucleus

Near the end of his life, doctors examining Isidor Isaac Rabi slid him into a magnetic resonance imaging machine — a device that exists because of experiments he ran with molecular beams in a Columbia laboratory in the 1930s. "I saw myself in that machine," he said. "I never thought my work would come to this." He had spent five decades building instruments, laboratories, and institutions, most of which are still running.

Rymanów to Brownsville

He was born on 29 July 1898 in Rymanów, in Austro-Hungarian Galicia, to a Polish Orthodox Jewish family that carried him to America as an infant. They lived in a two-room apartment on the Lower East Side and spoke Yiddish at home; in 1907 they moved to Brownsville, Brooklyn, and ran a grocery store. His name was an accident of immigration: a school official heard "Izzy" and wrote down the formal equivalent, Isidor.

The break with tradition came early and cleanly. Having read about Copernicus and the heliocentric solar system, the boy announced his atheism to his parents in one line: "It's all very simple... Who needs God?" For his bar mitzvah he compromised by delivering a speech in Yiddish about the electric light.

Cornell, Columbia, and a Wandering Fellowship

He entered Cornell in 1916 as an electrical engineering student, switched to chemistry, and graduated in June 1919 with a senior thesis on the oxidation states of manganese. He returned to Columbia as a graduate chemist in 1922, drifted into physics, and took his doctorate in 1926 under Albert Wills with a thesis on the principal magnetic susceptibilities of crystals.

What made him was the two years that followed. As a Barnard Fellow, on $1,500, he went to Europe and worked in the presence of Erwin Schrödinger, Arnold Sommerfeld, Werner Heisenberg, Niels Bohr, Wolfgang Pauli and — decisively — Otto Stern in Hamburg. Stern's molecular beam technique became Rabi's life's work, but not in Stern's form.

The Method

Rabi's improvement was a piece of pure experimental elegance. Stern's method required awkward non-uniform magnetic fields; Rabi replaced them with uniform fields set at an angle, so that atoms were deflected like light passing through a prism. Less apparatus, greater accuracy.

Back at Columbia — where he joined the faculty in 1929 as a lecturer on $3,000 a year and became full professor in 1937 — he built the Molecular Beam Laboratory and, through the 1930s, developed with Gregory Breit the Breit–Rabi equation and measured the nuclear magnetic moments of sodium, lithium compounds, hydrogen and deuterium. Between 1937 and 1939, with Polykarp Kusch, Sidney Millman and Jerrold Zacharias, he perfected nuclear magnetic resonance: weak oscillating fields used to read the magnetic properties of nuclei. The results were startling. The proton's magnetic moment came out at 2.785 nuclear magnetons, not the predicted value of 1 — a discrepancy that theory had to be rebuilt to accommodate. The 1944 Nobel Prize in Physics followed, "for his resonance method for recording the magnetic properties of atomic nuclei."

Radar, Trinity, and the Refusal

In 1940 he joined the MIT Radiation Laboratory, becoming associate director and head of Division 4 in March 1942. He drove the development of three-centimetre magnetrons and, under Norman Ramsey, an advanced group that produced the first three-centimetre waveguide radar by May 1941 — the technology behind H2X bombing radars and high-resolution shipboard sets.

He consulted for the Manhattan Project but refused to move to Los Alamos. He and Robert Bacher persuaded Oppenheimer that the laboratory had to be run by civilians rather than the military, which shaped everything about how it worked. At Trinity in July 1945 he won the betting pool on the yield, predicting 18 kilotons against an actual 18.6.

In 1950 the General Advisory Committee unanimously opposed developing the hydrogen bomb; Rabi went further than most, joining Enrico Fermi in opposing it on moral as well as technical grounds. Truman overrode them. "I never forgive Truman for buckling under the pressure," Rabi said. "He simply did not understand what it was about." At Oppenheimer's 1954 security hearing he was the most withering defence witness: "We have an A-bomb and a whole series of it, and we have a whole series of super bombs, and what more do you want, mermaids?"

The Institution Builder

From 1945 to 1949 he chaired a Columbia physics department that contained two Nobel laureates and eleven future ones. In January 1947 he and Norman Ramsey completed a nine-university coalition that created Brookhaven National Laboratory. As a UNESCO delegate in 1950 he proposed regional international laboratories; meetings in Florence in 1952 produced CERN, and the congratulatory letters from Bohr, Heisenberg and Amaldi hung framed in his home office. He chaired the AEC's General Advisory Committee from 1952 to 1956 and the Science Advisory Committee from 1956 to 1957, and his counsel to Eisenhower during the Sputnik crisis in October 1957 produced the President's Science Advisory Committee as a permanent institution.

Why Isidor Is Called a Genius

The faculty on display is economy of experimental design — the ability to look at an apparatus and see the simpler machine hidden inside it. Stern's beams needed fields that were difficult to shape and control; Rabi's insight was that uniform fields, tilted, would do the same job with less hardware and more precision, which is the kind of idea that looks obvious once someone has had it and occurs to nobody beforehand. From that single simplification came the measurement of nuclear moments, the anomalous proton result that forced theorists to rethink the nucleus, a Nobel Prize, and eventually magnetic resonance imaging. A second and rarer talent was judgment about people and structures: he assembled a Columbia department that held thirteen laureates past and future, co-founded Brookhaven, talked CERN into existence, and institutionalised scientific advice inside the American presidency.

The counter-case has to be made, and he supplies most of it himself. He was, by common consent, a terrible teacher — Norman Ramsey called his lectures "pretty dreadful"; William Nierenberg said he was "simply an awful lecturer." His prize was for a method rather than a law; he uncovered no new principle of nature, and the imaging technology that made his work famous was realised by others decades later. And he held frankly discriminatory views about women in science, believing they could not be physicists: he never supervised a female doctoral or postdoctoral student. Whatever the word genius covers, it plainly does not cover being right about people in general.

Legacy

The honours ran from the Newcomb Cleveland Prize in 1939 and the Elliott Cresson Medal in 1942 through the Nobel in 1944, the Medal for Merit and Britain's King's Medal in 1948, officer of the French Legion of Honour in 1956, the Niels Bohr International Gold Medal and the Atoms for Peace Award in 1967, the Oersted Medal in 1982, the Public Welfare Medal in 1985 and the Vannevar Bush Award in 1986. Columbia made him its first University Professor in 1964. He retired from teaching in 1967 and died at his home on Riverside Drive on 11 January 1988. There is a road named for him at CERN, a scholars' programme at Columbia, and an MRI scanner in almost every hospital in the developed world.