In Memoriam
Geoffrey Foucar Chew
Professor of Physics, Emeritus
UC Berkeley
1924-2019
Geoffrey Chew, who pioneered the S-Matrix approach to understanding the strong nuclear force, passed away on April 12, 2019 at the age of 94. The youngest of four children, he was born on June 5, 1924 in Washington, D.C., where his father worked for the Department of Agriculture. In 1944, Chew obtained a B.S. degree in physics from George Washington University. George Gamow, one of his professors there, recognized Chew’s talent and recommended him for Edward Teller’s team on the Manhattan Project. At Los Alamos, Chew carried out calculations relating to Teller’s ideas for a hydrogen bomb, and he witnessed the test of the first fission bomb from a nearby mountain. His reminiscences of this period are available at http://manhattanprojectvoices.org/oral-histories/geoffrey-chews-interview.
In 1946, Chew began his Ph.D. studies under Teller at the University of Chicago, but soon Teller decided to leave Chicago in order to resume the development of the hydrogen bomb, and so he arranged for Enrico Fermi to take over the supervision of his two students. (The other one was Chew’s friend and collaborator Marvin L. Goldberger, who became a professor of theoretical physics at Princeton University and later President of Caltech and Director of the Institute for Advanced Study.) Chew received his Ph.D. degree in theoretical physics in 1948. He was fully devoted to science, and so he did not do any military work after the war.
Following his Ph.D., Chew served a year as a postdoctoral fellow at the Berkeley Radiation Laboratory (1948-49) and a year as a UC Berkeley assistant professor of physics (1949-50). During this period there were growing fears, or even hysteria, in the nation that scientists with Communist leanings had leaked atomic secrets to the Soviets. Berkeley became a target, because secret research had been carried out at the Radiation Laboratory (now called the Lawrence Berkeley National Laboratory). In March 1949, the UC Regents imposed the requirement that all university employees swear before a notary that they were not members of the Communist Party. This was vigorously discussed at weekly faculty meetings throughout the 1949-50 academic year. In June 1950, Chew and a number of others (including Robert Serber and Wolfgang Panofsky) resigned in protest. Chew was the first to resign in the entire university. The remaining 31 non-signers were fired in August 1950, even though none of them had been accused of Communist membership or sympathy.
Chew then moved to the University of Illinois at Urbana-Champaign, where he quickly ascended through the ranks, becoming a full professor of physics in 1955. Shortly after his 1950 arrival, he founded the Urbana branch of the Federation of American Scientists. In 1957, after the loyalty oath requirement had been rescinded and fired faculty had been rehired, he returned to UC Berkeley as a professor of physics, a position he held until his 1991 retirement.
After his return, Chew’s research flourished, especially during the decade of the 1960s, when he was doing some of the most exciting and influential theoretical particle physics in the world. The goal of his research was to develop an understanding of the strong nuclear force, which is the force that holds neutrons and protons together inside the nucleus of an atom, overcoming the electrical repulsion of the protons. Chew was a leader in these endeavors, and his ideas played a major role in shaping the future of theoretical particle physics.
However, the story took some surprising twists and turns.
A very successful quantum field theory of electromagnetic forces, called quantum electrodynamics (QED), had been achieved earlier. Its success hinges on the existence of a small dimensionless parameter, the fine structure constant, which is roughly 1/100. Extremely accurate results for physical quantities, such as the magnetic moment of the electron or the muon, are achieved by using perturbation theory to compute the first few terms in a power series expansion in this parameter. The strong nuclear force, on the other hand, has no such small parameters, so Chew argued that the strong nuclear force could not be described usefully by a quantum field theory.
Much of the important physical information of a quantum mechanical particle theory is contained in the amplitudes that describe all scattering processes, and these are encoded in a mathematical quantity called the S matrix. So, Chew proposed that instead of looking for a new quantum field theory, a better approach would be to determine the S matrix for all hadrons. (By definition, a hadron is a particle that experiences the strong nuclear force.) The hadronic S matrix must satisfy certain physical requirements. One of them, called unitarity, ensures that probabilities are positive and add up to one. Another, called analyticity, ensures that cause precedes effect. These are features of any sensible particle theory, so more than this is required to determine a specific theory. Chew proposed as additional requirements the bootstrap principle and Regge behavior. Roughly speaking, the bootstrap principle asserts that hadrons provide the forces that are responsible for their own existence. Regge behavior concerns relationships between the masses and the spins of hadrons. It also determines certain high energy properties of the theory. In particular, this picture implies that all hadrons are on an equal footing, a principle that Chew dubbed “nuclear democracy.”
A significant fraction of the theoretical particle physics community worldwide joined Chew in attempting to describe hadron physics starting from these principles. In Berkeley, Chew supervised the research of approximately 10 graduate students at a time throughout the 1960s, and his colleague Stanley Mandelstam, whose research was closely related, advised a few more. This was rather similar to Oppenheimer’s group at Berkeley in the 1930s. However, unlike Oppenheimer, Chew was a very encouraging advisor. I had the good fortune of being one of Chew’s advisees in the middle of the decade.
An important milestone in Chew’s S matrix program was Gabriele Veneziano’s 1968 discovery that a certain simple mathematical function satisfies most of the requirements sketched above for the special case in which two particles scatter elastically. This was quickly generalized to the case of an arbitrary number of particles in a manner that is consistent with unitarity and analyticity. At first, this subject was called dual resonance theory. After a couple of years, when it was realized that these amplitudes describe the scattering of quantum states of one-dimensional objects, the subject became known as string theory. This was a very active field until about 1974, when the study of string theory came to a sudden halt. So, what happened?
Guided by the theoretical work of Gell-Mann at Caltech and the experimental results from Stanford, it became clear in the late 1960s and early 1970s that hadrons could be viewed as bound states of “quarks.” This led to the formulation of a new quantum field theory, called quantum chromodynamics (QCD), which is based on quarks and force-carrying particles called “gluons.” The case for the fundamental correctness of QCD became overwhelming in 1973, with the proof that QCD has a property called asymptotic freedom. One of the three people responsible for this proof (and a resulting Nobel Prize) was David Gross. David was also a Chew student in the mid-1960s. It is ironic that a Chew student was largely responsible for showing that quantum field theory works for the strong nuclear force! By 1973-74, there were many good reasons to stop working on string theory: a successful and convincing theory of hadrons (QCD) had been discovered, and string theory had severe problems as a theory of hadrons. Among the problems of the known string theories, as a theory of hadrons, was the fact that the spectrum of open strings (strings with ends) contains massless spin 1 particles, and the spectrum of closed strings (strings that are loops) contains a massless spin 2 particle (as well as other massless particles), whereas there are no massless hadrons.
In 1974, Joel Scherk and I proposed interpreting the massless spin 2 particle in the closed-string spectrum as a graviton, the quantum of gravity. Also, the massless spin 1 particles in the open-string spectrum could be interpreted as particles associated to Yang-Mills gauge fields, like those of the standard model. Specifically, this meant interpreting string theory as a unified quantum theory of all forces, including gravity. This interpretation required that the strings are 20 orders of magnitude smaller than hadrons. It took a decade for this idea to gain traction, but for the past 35 years it has been a very active and fruitful area of research. Geoffrey Chew deserves a great deal of credit for steering theoretical physics in this direction. He had identified the right principles. His only “mistake” was to focus on hadrons and the strong nuclear force, rather than on all particles and forces! There might be another string theory, yet to be discovered, that gives an equivalent dual description of QCD. This would imply that he was exactly correct.
Chew, himself, did not pursue string theory, even though he was very enthusiastic about it. Instead, he decided to explore cosmology. In 1998, talking about his current research, Chew wrote: “For the last decade, motivated by puzzles encountered during four earlier decades of activity in particle theory, I have been attempting to find a quantum model of the expanding universe that spans all the scales recognized so far by science.” He explored these ideas, with his customary enthusiasm, for the rest of life.
Chew served as chair of the Berkeley department of physics (1974-78) and dean of physical sciences (1986-93). He took sabbatical leaves at Churchill College, Cambridge University (1962-63), Princeton University (1970-71), and the University of Paris (1983-84). His awards and honors include election to the National Academy of Sciences (1962) and the American Academy of Arts and Sciences (1966), as well as the Hughes Prize of the American Physical Society (1962) and the Ernest Orlando Lawrence Award from the U.S. Atomic Energy Commission (1969).
He was also a very active participant in shared governance as a member of the Berkeley Division of the Academic Senate. He served as a member of Graduate Council (1961-62), Budget and Interdepartmental Relations (1966-68), and the Committee on Committees (1965-66 and 1980-81). He was a Berkeley representative to the systemwide Assembly of the Academic Senate, serving for a total of 10 years (1958-61, 1968-70, 1973-76, and 1981-83).
Geoffrey Chew’s first wife, Ruth, whom he had met as an undergraduate, passed away in 1971. He is survived by their twins, Beverly and Berkeley, as well as his second wife, Denyse, and their three children, Pierre, Jean-Francois, and Pauline.
According to Pauline, in addition to thinking deeply about theoretical physics, which was his main passion, he “was an avid outdoor adventurer, taking us all on numerous camping and hiking trips to the beautiful landscapes this country has to offer,“ and “his curiosity about people, other cultures, and constantly learning new things never ceased.”
John H. Schwarz
2020
In 1946, Chew began his Ph.D. studies under Teller at the University of Chicago, but soon Teller decided to leave Chicago in order to resume the development of the hydrogen bomb, and so he arranged for Enrico Fermi to take over the supervision of his two students. (The other one was Chew’s friend and collaborator Marvin L. Goldberger, who became a professor of theoretical physics at Princeton University and later President of Caltech and Director of the Institute for Advanced Study.) Chew received his Ph.D. degree in theoretical physics in 1948. He was fully devoted to science, and so he did not do any military work after the war.
Following his Ph.D., Chew served a year as a postdoctoral fellow at the Berkeley Radiation Laboratory (1948-49) and a year as a UC Berkeley assistant professor of physics (1949-50). During this period there were growing fears, or even hysteria, in the nation that scientists with Communist leanings had leaked atomic secrets to the Soviets. Berkeley became a target, because secret research had been carried out at the Radiation Laboratory (now called the Lawrence Berkeley National Laboratory). In March 1949, the UC Regents imposed the requirement that all university employees swear before a notary that they were not members of the Communist Party. This was vigorously discussed at weekly faculty meetings throughout the 1949-50 academic year. In June 1950, Chew and a number of others (including Robert Serber and Wolfgang Panofsky) resigned in protest. Chew was the first to resign in the entire university. The remaining 31 non-signers were fired in August 1950, even though none of them had been accused of Communist membership or sympathy.
Chew then moved to the University of Illinois at Urbana-Champaign, where he quickly ascended through the ranks, becoming a full professor of physics in 1955. Shortly after his 1950 arrival, he founded the Urbana branch of the Federation of American Scientists. In 1957, after the loyalty oath requirement had been rescinded and fired faculty had been rehired, he returned to UC Berkeley as a professor of physics, a position he held until his 1991 retirement.
After his return, Chew’s research flourished, especially during the decade of the 1960s, when he was doing some of the most exciting and influential theoretical particle physics in the world. The goal of his research was to develop an understanding of the strong nuclear force, which is the force that holds neutrons and protons together inside the nucleus of an atom, overcoming the electrical repulsion of the protons. Chew was a leader in these endeavors, and his ideas played a major role in shaping the future of theoretical particle physics.
However, the story took some surprising twists and turns.
A very successful quantum field theory of electromagnetic forces, called quantum electrodynamics (QED), had been achieved earlier. Its success hinges on the existence of a small dimensionless parameter, the fine structure constant, which is roughly 1/100. Extremely accurate results for physical quantities, such as the magnetic moment of the electron or the muon, are achieved by using perturbation theory to compute the first few terms in a power series expansion in this parameter. The strong nuclear force, on the other hand, has no such small parameters, so Chew argued that the strong nuclear force could not be described usefully by a quantum field theory.
Much of the important physical information of a quantum mechanical particle theory is contained in the amplitudes that describe all scattering processes, and these are encoded in a mathematical quantity called the S matrix. So, Chew proposed that instead of looking for a new quantum field theory, a better approach would be to determine the S matrix for all hadrons. (By definition, a hadron is a particle that experiences the strong nuclear force.) The hadronic S matrix must satisfy certain physical requirements. One of them, called unitarity, ensures that probabilities are positive and add up to one. Another, called analyticity, ensures that cause precedes effect. These are features of any sensible particle theory, so more than this is required to determine a specific theory. Chew proposed as additional requirements the bootstrap principle and Regge behavior. Roughly speaking, the bootstrap principle asserts that hadrons provide the forces that are responsible for their own existence. Regge behavior concerns relationships between the masses and the spins of hadrons. It also determines certain high energy properties of the theory. In particular, this picture implies that all hadrons are on an equal footing, a principle that Chew dubbed “nuclear democracy.”
A significant fraction of the theoretical particle physics community worldwide joined Chew in attempting to describe hadron physics starting from these principles. In Berkeley, Chew supervised the research of approximately 10 graduate students at a time throughout the 1960s, and his colleague Stanley Mandelstam, whose research was closely related, advised a few more. This was rather similar to Oppenheimer’s group at Berkeley in the 1930s. However, unlike Oppenheimer, Chew was a very encouraging advisor. I had the good fortune of being one of Chew’s advisees in the middle of the decade.
An important milestone in Chew’s S matrix program was Gabriele Veneziano’s 1968 discovery that a certain simple mathematical function satisfies most of the requirements sketched above for the special case in which two particles scatter elastically. This was quickly generalized to the case of an arbitrary number of particles in a manner that is consistent with unitarity and analyticity. At first, this subject was called dual resonance theory. After a couple of years, when it was realized that these amplitudes describe the scattering of quantum states of one-dimensional objects, the subject became known as string theory. This was a very active field until about 1974, when the study of string theory came to a sudden halt. So, what happened?
Guided by the theoretical work of Gell-Mann at Caltech and the experimental results from Stanford, it became clear in the late 1960s and early 1970s that hadrons could be viewed as bound states of “quarks.” This led to the formulation of a new quantum field theory, called quantum chromodynamics (QCD), which is based on quarks and force-carrying particles called “gluons.” The case for the fundamental correctness of QCD became overwhelming in 1973, with the proof that QCD has a property called asymptotic freedom. One of the three people responsible for this proof (and a resulting Nobel Prize) was David Gross. David was also a Chew student in the mid-1960s. It is ironic that a Chew student was largely responsible for showing that quantum field theory works for the strong nuclear force! By 1973-74, there were many good reasons to stop working on string theory: a successful and convincing theory of hadrons (QCD) had been discovered, and string theory had severe problems as a theory of hadrons. Among the problems of the known string theories, as a theory of hadrons, was the fact that the spectrum of open strings (strings with ends) contains massless spin 1 particles, and the spectrum of closed strings (strings that are loops) contains a massless spin 2 particle (as well as other massless particles), whereas there are no massless hadrons.
In 1974, Joel Scherk and I proposed interpreting the massless spin 2 particle in the closed-string spectrum as a graviton, the quantum of gravity. Also, the massless spin 1 particles in the open-string spectrum could be interpreted as particles associated to Yang-Mills gauge fields, like those of the standard model. Specifically, this meant interpreting string theory as a unified quantum theory of all forces, including gravity. This interpretation required that the strings are 20 orders of magnitude smaller than hadrons. It took a decade for this idea to gain traction, but for the past 35 years it has been a very active and fruitful area of research. Geoffrey Chew deserves a great deal of credit for steering theoretical physics in this direction. He had identified the right principles. His only “mistake” was to focus on hadrons and the strong nuclear force, rather than on all particles and forces! There might be another string theory, yet to be discovered, that gives an equivalent dual description of QCD. This would imply that he was exactly correct.
Chew, himself, did not pursue string theory, even though he was very enthusiastic about it. Instead, he decided to explore cosmology. In 1998, talking about his current research, Chew wrote: “For the last decade, motivated by puzzles encountered during four earlier decades of activity in particle theory, I have been attempting to find a quantum model of the expanding universe that spans all the scales recognized so far by science.” He explored these ideas, with his customary enthusiasm, for the rest of life.
Chew served as chair of the Berkeley department of physics (1974-78) and dean of physical sciences (1986-93). He took sabbatical leaves at Churchill College, Cambridge University (1962-63), Princeton University (1970-71), and the University of Paris (1983-84). His awards and honors include election to the National Academy of Sciences (1962) and the American Academy of Arts and Sciences (1966), as well as the Hughes Prize of the American Physical Society (1962) and the Ernest Orlando Lawrence Award from the U.S. Atomic Energy Commission (1969).
He was also a very active participant in shared governance as a member of the Berkeley Division of the Academic Senate. He served as a member of Graduate Council (1961-62), Budget and Interdepartmental Relations (1966-68), and the Committee on Committees (1965-66 and 1980-81). He was a Berkeley representative to the systemwide Assembly of the Academic Senate, serving for a total of 10 years (1958-61, 1968-70, 1973-76, and 1981-83).
Geoffrey Chew’s first wife, Ruth, whom he had met as an undergraduate, passed away in 1971. He is survived by their twins, Beverly and Berkeley, as well as his second wife, Denyse, and their three children, Pierre, Jean-Francois, and Pauline.
According to Pauline, in addition to thinking deeply about theoretical physics, which was his main passion, he “was an avid outdoor adventurer, taking us all on numerous camping and hiking trips to the beautiful landscapes this country has to offer,“ and “his curiosity about people, other cultures, and constantly learning new things never ceased.”
John H. Schwarz
2020
