Cosmological constants

Interview with Savas Dimopoulos, Professor of Physics at Stanford University. The interview begins with Dimopoulos reflecting on how the pandemic has affected his research, and he gives his initial impressions on the g-2 muon anomaly experiment at Fermilab. He discusses the push and pull between theory and experimentation when searching for physics beyond the Standard Model. Dimopoulos then recounts his early childhood in Turkey, where his family was part of the Greek minority. Due to ethnic tensions, he fled with his family to Athens as refugees. Dimopoulos remembers his early exposure to math and physics and being torn between the two. He describes moving to the US at age 18 for his undergraduate studies at University of Houston. Dimopoulos then recounts his inclination toward theory and his acceptance at University of Chicago to pursue his graduate studies under Yoichiro Nambu. He discusses his post-doctoral appointment at Columbia which then led to an offer from Stanford. He explains his research in baryogenesis and technicolor, as well as his brief time at Harvard with Howard Georgi. Dimopoulos talks about his return to Stanford, his work at CERN, and his research on large extra dimensions with Dvali and Arkani-Hamed. He concludes the interview with predictions for the future of physics beyond the Standard Model.

Interview with Robert M. Wald, Charles H. Swift Distinguished Service Professor of Physics at the University of Chicago, where he also has appointments with the Kadanoff Center and the Kavli Institute for Cosmological Physics. Wald recounts his childhood in New York, he describes the tragedy of losing his parents in an airplane crash when he very young, and he explains the ongoing legacy of his father Abraham Wald who was a prominent professor of statistics at Columbia. He describes his high school education at Stuyvesant and his decision to pursue a physics degree at Columbia, where he became close with Alan Sachs, who supervised him at Nevis Laboratory. Wald explains his decision to focus on general relativity for graduate school and his interest in working with John Wheeler at Princeton. He describes the excitement surrounding recent advances in approaching astrophysics through relativity, the significance of the discovery of pulsars and the field of black hole uniqueness, and he discusses his postdoctoral research with Charles Misner at the University of Maryland. Wald describes the impact of Saul Teukolsky’s discovery of a variable Weyl tensor component that satisfied a decoupled equation, and he explains the circumstances leading to his faculty position at Chicago, where he was motivated to work with Bob Geroch. He reflects on the experience writing Space, Time, and Gravity, the advances in black hole collapse research, and he explains why he felt the field needed another textbook which motivated him to write General Relativity. Wald discusses his work on the Hawking Effect and his long-term interest in quantum field theory, and he explains the influence of Chandrasekhar on his research. He describes his contributions to the LIGO collaboration, and he explains what is significant about the Event Horizon Telescope’s ability to capture an image of a black hole. Wald explains the state of gravitational radiation research and the accelerating universe, he prognosticates on what advances might allow for a unification of gravity and the Standard Model, and he explains why dark energy is apparently a cosmological constant. At the end of the interview, Wald discusses his recent work on the gravitational memory effect and, looking to the future, he explains his interest to continue working to understand the S-matrix in quantum electrodynamics.

Interview with Steven Weinberg, Jack S. Josey-Welch Foundation Chair in Science and Regental Professor at the University of Texas at Austin. The focus of the interview is on how and when Weinberg became interested in cosmology, and how he defines it as a distinct discipline from astronomy and astrophysics. Weinberg explains that between the intensity of interest in particle physics in the 1950s and the speculative nature of cosmology, he had neither the interest nor the outlet to pursue cosmology in a rigorous way. He discusses some of the theoretical and experimental limitations at the time that kept cosmology in a largely “mystical” realm, and why the discovery of the microwave background by Penzias and Wilson “changed everything.” Weinberg explains what new questions can be considered as a result of evidence for a hot early universe, and he discusses when he first became interested in the formation of galaxies. He describes why the cosmological constant has bothered him for a long time, and he traces this problem back to Einstein and what Weinberg considers Einstein’s incorrect approach to his own theory. Contrasting his own experience as a graduate student, he cites John Preskill as his first student to pursue cosmology, and he explains that while his interests in particle physics and cosmology are generally separate, he always looks for intersecting research opportunities, which is well represented in the relevance of beta decay physics in the first three minutes of the universe. At the end of the interview, Weinberg surveys the value and problems associated with the term “Big Bang,” and he reflects on his career-long effort not to be dogmatic in his views on cosmology.

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.