String models

Interview with Henry Tye, professor emeritus of physics at Cornell, and subsequently professor emeritus of physics at Hong Kong University of Science and Technology (HKUST), and currently, Researcher at the Jockey Club Institute for Advanced Study at HKUST. Tye provides a brief history of HKUST, and he offers his views on China’s long-term goals in high energy physics. He recounts his childhood in Hong Kong where his family fled from mainland China during the Communist revolution, and he explains the opportunities that led to his undergraduate admission to Caltech. Tye describes how discussions of the Vietnam War permeated his college experience, and he describes the influence of Gerry Neugebauer on his interest in physics but that cosmology was far from his considerations at that point. He discusses his decision to study at MIT, where Francis Low became his advisor, and how he worked closely with Gabriele Veneziano on the relationship between the Thirring model and bosonic string theory. Tye explains the excitement surrounding the “November Revolution” which was unfolding just as he arrived at the SLAC Theory Group in 1974. He describes the origins of his interests in cosmology, and the source of his collaboration with Alan Guth during his postdoctoral work at Cornell, where he pursued matter-antimatter asymmetry. Tye explains how this collaboration ultimately created the field of inflation and why this addresses fundamental cosmological problems associated with flatness and the horizon. He explains how and why the original theory of inflation was revised by Andrei Linde and Paul Steinhardt, among others, and why he developed a subsequent interest in cosmic superstrings and branes which he recognized would give a perfect model for inflation. Tye describes why he is optimistic that technological advances will make cosmic superstrings a testable proposition, and that collaborations including the Sloan Digital Sky Survey and LIGO/Virgo are positive steps in that direction. He bemoans the dearth of string theorists focused on phenomenological work and why he thinks string theory will solve the quantum gravity problem. Tye describes his decision to join the Cornell faculty, why his notions of a “string landscape” suggest philosophical implications, why the cosmic landscape is central for understanding the wavefunction of the universe, and why both the universe and all multiverses can begin from truly nothing. At the end of the interview, Tye discusses his recent interests on the cosmological constant problem, the KLT relation, and the observations and experiments that are most likely to push cosmology into new and exciting areas of discovery. 

Interview with Michael Dine, Professor of Physics at the University of California at Santa Cruz. Dine conveys his provisional excitement over the g-2 muon anomaly experiment at Fermilab and he recounts his childhood in Cincinnati. Dine discusses his undergraduate education at Johns Hopkins, his developing interests in physics, and the opportunity that led to his graduate research at Yale. He describes working under the supervision of Tom Appelquist and trying to understand the force between heavy quarks within quantum chromodynamics. Dine describes his earliest exposure to string theory and his decision to take a postdoctoral appointment at SLAC, where he worked with Jonathan Saperstein on the next order calculation of the total electron-positron cross section. He discusses Lenny Susskind’s work on Technicolor and his subsequent appointment at the Institute for Advanced Study, his close collaboration with Willy Fischler, and the excitement surrounding supersymmetry at the time. Dine describes the impact made by Ed Witten when he arrived in Princeton and he discusses the origins of axion-dark matter research. He discusses his first faculty position at City College in New York and his reaction to the “string revolution” of 1984 and AdS/CFT a few years later. Dine explains his decision to move to UC Santa Cruz and his burgeoning interest in cosmology, he reflects on when his research focused to physics beyond the Standard Model, and he explains why it is possible to decouple the expectation that supersymmetry must be detected at the LHC. He explains why string theory is making strides toward experimental verifiability, and he reflects on the utility of being a theorist. At the end of the interview, Dine emphasizes his optimism about the axion as a dark matter candidate and why the field is moving steadily toward a greater understanding of physics at both the largest and smallest scales.

In this interview, David Zierler, Oral Historian for AIP, interviews Cumrun Vafa, Hollis Professor of Mathematicks and Natural Philosophy in the Department of Physics at Harvard. Vafa surveys the current state of the field in string theory, and he recounts his upbringing in Iran and his family’s goal for him to pursue education in the United States. He explains the opportunities that led to his acceptance to MIT, and his intellectual journey from being practical-minded in his study of economics and engineering, to his blossoming love for mathematics and physics. Vafa describes his early difficulties reconciling the formalism of math with the intuition he sensed pervaded concepts in physics, and he explains how this changed as a student of Ed Witten’s at Princeton. He describes his entrée into string theory at the time that Witten had committed himself to learning string theory, and he describes the evolution of the field from the first to the second “revolutions” from 1984 to 1994. Vafa describes his time as a junior fellow at Harvard and some of the tensions that existed in the physics department between senior faculty who were not interested in string theory, and the junior faculty who were. He explains the circumstances that led to his rapid tenure at Harvard and he describes the ideas that became his “Swampland” concept. Vafa discusses his collaborations with Andy Strominger on black holes and with Robert Brandenberger on string gas cosmology and his solo research on F-theory. He talks about the long-term prospects for a truer understanding of quantum gravity, and at the end of the interview, Vafa engages with critics and string theory, and delineates between those who are not interests themselves (which he understands and respects) and those who wish to make it more difficult for others to study string theory (which he finds problematic). Vafa acknowledges the current gap between string theory and experimental verification but asserts that this gap is a function of current technological limitations in observation, and not a shortcoming of string theory itself.

In this interview, David Zierler, Oral Historian for AIP, interviews Daniel Z. Freedman, Professor Emeritus of Applied Mathematics and Physics at MIT and long-term visiting professor at Stanford. Freedman explains his understanding of the term’s mathematical physics and physical mathematics, and he bemoans the broad decoupling of experiment and theory in physics. He recounts his upbringing in West Hartford, Connecticut, and he describes his undergraduate education at Wesleyan. Freedman describes his early attachment to theory and his graduate work at the University of Wisconsin, where he worked under the direction of Ray Sawyer on Regge poles. He discusses his postdoctoral research as a NATO fellow in Europe at CERN and Imperial College London, and he conveys the sense of excitement at the time about the weak and strong interactions. Freedman describes his appointment at UC Berkeley before joining the Institute for Advanced Study, and he explains the opportunity that led to his faculty job at Stony Brook. He reflects on his interactions with Yang and he narrates the origins of supersymmetry, and shortly after, the origins of supergravity. Freedman explains what is “super” in supergravity, supersymmetry, and super-space, and he describes why the reality of supersymmetry must be true even if we lack the tools to see it. He explains his decision to move to MIT, and he connects the arc from the 1984 string revolution to the discovery of AdS/CFT in 1997. Freedman describes winning the Dirac medal and subsequently the Breakthrough Prize, which he understood as confirmation in the community about the importance of supergravity. At the end of the interview, Freedman connects his work to larger questions in cosmology and astrophysics, he expresses surprise by the increasing centrality of mathematics to physics, he explains his early work on neutrino scattering and why after 40 years, his original intuition has been vindicated.

Interview with Robert H. Brandenberger, Canada Research Chair and professor of physics at McGill University. Brandenberger recounts his childhood in Switzerland as the son of organic chemists, and he describes his undergraduate education at the ETH Zurich in physics. He discusses his graduate research at Harvard to work under the direction of Arthur Jaffe, and he describes his first exposure to cosmic inflation. Brandenberger describes his postdoctoral appointment at the ITP in Santa Barbara where he worked with Neil Turok and Andreas Albrecht, and his subsequent postdoctoral work with Stephen Hawking at Cambridge. He explains his initial ideas on cosmic strings as an alternative to inflation and his encounters with Cumrun Vafa and Slava Mukhanov. Brandenberger describes the origins of string gas cosmology, its implications for a multiverse and how it was received among string theorists. He discusses his faculty appointment at Brown and he explains his decision to move to McGill where the opportunity to work with graduate students was stronger. Brandenberger surmises what string theory as a testable proposition would look like, and he reflects on some of the obvious philosophical implications of unknowability in the universe. He explains the difference between a toy model and a proper theory, and he conveys optimism that string gas cosmology will advance research on dark energy. At the end of the interview, Brandenberger reflects on the idea that string theory is "smarter than we are."

Interview with Michael Green, Lucasian Professor Emeritus at Cambridge University and visiting professor at Queen Mary University. He recounts his childhood in London as the child of secular Jewish parents who immigrated to London just before World War II. Green discusses his early interests in physics and the opportunities that led to his enrollment at Cambridge, and he conveys Geoff Chew’s influence with his ideas on S-matrix and bootstrap theory, which informed his thesis research on hadronic interactions. He narrates the founding ideas that led to string theory and how the work on dual models became transformed into string theory. Green describes his postdoctoral work at the Institute for Advanced Study and his interactions with Veneziano. He explains his decision to return to Cambridge and the importance of the CERN theory group for his research, and he narrates the origins of his collaborations with John Schwarz. Green connects string theory to the ideas that led to supergravity, and he explains why he does not like the term “revolution” in relation to advances in string theory to explain what was happening between 1981-1984. He explains the meaning of the pronoun “super” in relation to string theory, and he conveys his disappointment that supersymmetry has yet to be observed. Green describes the importance of AdS/CFT and his contributions to the origins of D-branes with Joe Polchinski. He discusses his increasing reliance on computers for understanding aspects of AdS/CFT correspondence. Green reflects on winning the Breakthrough Prize, and the supposed aspirational recognition on working to unify the forces which are not yet unified, and he discusses the generational de-coupling of string theory education from particle physics. He provides sociological perspective in response to the impatience that certain physicists have expressed regarding string theory. At the end of the interview, Green ponders the future relationship between string theory and quantum computing, and he describes the field as an intellectual adventure which makes it difficult to predict the significance of these changes.

Interview with Edward Witten, Charles Simonyi Professor in the School of Natural Sciences at the Institute for Advanced Study. Witten discusses his current interests in quantum information theory in gravity, and he recounts his childhood in Baltimore and the influence of his father Louis Witten, who is a physicist. He describes his undergraduate education at Brandeis, where he majored in history, a brief stint working for the McGovern campaign, and a false start in graduate school to study economics before landing at Princeton to study first applied mathematics and then theoretical particle physics with David Gross. He describes the significance of deep inelastic scattering in the emergence of QCD and his earliest exposure to the ideas that would develop into string theory. Witten describes his postdoctoral appointment at Harvard to work with Steve Weinberg, Sidney Coleman, Shelly Glashow, and Howard Georgi. He discusses t’ Hooft’s success at solving the U(1) problem and his early work in supersymmetry by the time he joined the faculty at Princeton. Witten narrates the string revolution of 1984 and the early optimism that string theory would be able to describe the real world. He describes his involvement in topological quantum field theories and he explains his decision to move to the Institute from Princeton. Witten discusses his work with Nati Seiberg on N=2 super Yang Mills in four dimensions, the origins of M-theory in the 1994 string revolution, and the impact of Juan Maldacena’s work on AdS/CFT. He describes his collaboration with Seiberg on noncommutative geometry, his interest in the Langlands program, and the role of axions in string theory. Witten conveys the sense of optimism when the LHC turned on and the significance of Khovanov homology and Morse theory. He explains the need to revisit perturbative superstring theory and the possibility that the g-2 muon anomaly experiment at Fermilab will lead to new physics. At the end of the interview, Witten reflects on how little has been seen at the LHC after the Higgs discovery, and he expresses hope that string/M-theory and quantum gravity make meaningful contact during his lifetime.

Interview with Sylvester James Gates, Jr., Ford Foundation Professor of Physics and Director of the Theoretical Physics Center at Brown University. Gates discusses his preparations to lead the APS and the value of his service for PCAST for this new role. Gates recounts his family heritage and he discusses his father’s military service and the death of his mother. He explains how his family navigated racist challenges during his upbringing in El Paso and then in Orlando and how he navigated his own intellectual abilities in school. Gates explains his interest in physics in high school and the opportunities that led to his admission at MIT for his undergraduate work. He recounts the many mentors who made a positive impression on him and he explains his realization that his specialty would be at the boundary between math and physics. Gates describes his earliest interactions with string theory and he explains his decision to remain at MIT for his graduate work to work with Jim Young on supersymmetry. He paints a broader picture of supergravity research at this time and the rising importance of computers for this work. Gates describes his postdoctoral research at Harvard as a Junior Fellow, where he worked closely with Warren Siegel, and he describes his decision to join the faculty at MIT after a subsequent postdoctoral position at Caltech. He addresses Shelly Glashow’s criticism of string theory, and he explains his decision to leave MIT for a faculty position at the University of Maryland. Gates reflects on his teaching and mentoring career at Maryland, he describes his time at Howard University, and he discusses the broader issue of diversity in physics and AIP’s TEAM-UP Report. He describes his more recent interests in graph theory and the broader effort to unify gravity with the other forces. Gates reflects on how he became an advisor to President Obama for PCAST and how he worked with John Holdren to translate reports into policy changes. He explains his decision to go emeritus at Maryland and to take a new position at Brown, and why joining the Watson Institute was an attractive part of the offer. Gates reflects on assuming leadership at APS during the twin crises of Covid and racial strife, he surveys the state of string theory and high energy physics, and he explains why supersymmetry might offer a path to understanding dark matter. At the end of the interview, Jim conveys his hope that his work in math will yield deep insights into nature, and he considers the possibility of pursuing an autobiographical project.

Interview with Albert Schwarz, Distinguished Professor of Mathematics Emeritus at UC Davis. Schwarz discusses his current interests in pursuing a geometric approach to quantum theory, and he recounts his family origins in Russia and Eastern Europe and their travails under Stalin’s oppression. He describes his early interests in math and his education at the Ivanovo Pedagogical Institute under the guidance of Professor Efremovich, who guided him in the new field of geometric group theory. Schwarz discusses his graduate research at Moscow University, where he focused on the homology of the space of closed curves and on the topology of the space of Fredholm maps during his postgraduate work. He explains the impact of Polyakov’s and t’Hooft’s work on magnetic monopoles and gauge fields in the 1970s, and he describes his contributions to instanton research. Schwarz recounts his earliest exposure to string theory and his subsequent work on supergravity, and he explains the opportunities and considerations that allowed him to emigrate to the United States. He discusses his initial contacts with Ed Witten and his appointment at the Institute for Advanced Study and his job offer at Davis. Schwarz explains his interest in Batalin-Vilkovisky formalism and his appreciation of the value in relating non-commutative geometry to string theory and M-theory. He describes why a geometric approach to quantum theory de-emphasizes the differences between classical and quantum mechanics. At the end of the interview, Schwarz reflects on some of the life lessons he learned from the difficulties of his youth, how his background gives him a uniquely Russian approach to math and physics, and he explains a duality in string theory where it does not currently explain reality but that ultimately, the “right” physics will arise from it.

Interview with Pierre Ramond, Distinguished Professor of Physics at the University of Florida. Ramond recounts childhood in Paris, he describes his family’s experiences during World War II, and he explains that opportunities that led to his education in electrical engineering at the New Jersey Institute of Technology. He discusses his graduate degree in physics at Syracuse University to focus on general relativity and his first exposure to the earliest iterations of string theory. Ramond describes his work at Fermilab on Veneziano modelling, his postdoctoral research at Yale, and his subsequent work at Los Alamos. He describes Gell-Mann’s interest in grand unified theories and the influence of Ken Wilson. Ramond explains the excitement regarding the muon anomaly experiment at Fermilab, and he narrates his decision to join the faculty at the University of Florida. He explains how the department’s stature has risen over the past forty years, and he reflects on his involvement with the superstring revolution in 1984. Ramond describes the difference between effective and fundamental theories in particle physics and he conveys the productive intellectual ferment at the annual Aspen conferences. He describes his service work on the faculty senate and he describes his leadership position at the APS during the discovery of the Higgs. Ramond explains why he thinks supersymmetry would have been detected at a completed SSC and he reflects on receiving the Dirac medal in 2020. At the end of the interview, he discusses Einstein’s misgivings on quantum mechanics, he imagines how string theory might be testable, and he explains why he remains interested in CP violation.