About

Gordon Baym is a Research Professor and the George and Ann Fisher Professor in Engineering Emeritus at the University of Illinois, with additional titles as Professor of Physics Emeritus and affiliated with the Center for Advanced Study. He received his bachelor's degree in physics from Cornell University in 1956, his A.M. in mathematics from Harvard in 1957, and his Ph.D. in physics from Harvard in 1960. He joined the Department of Physics at the University of Illinois as an assistant professor in 1963. Professor Baym has been a major leader in the study of matter under extreme conditions in astrophysics and nuclear physics, making original, seminal contributions to our understanding of neutron stars, relativistic effects in nuclear physics, condensed matter physics, quantum fluids, and Bose-Einstein condensates. His work is characterized by a superb melding of basic theoretical physics concepts across condensed matter, nuclear, and elementary particle physics. He pioneered the application of field-theory methods in quantum condensed matter systems and has elucidated the nuclear physics of neutron star crusts, structure, and formation in supernovae explosions. His studies of the deep interiors of neutron stars have been seminal, addressing the fundamental nature of pion condensed states, quark matter, and the quark-gluon plasma. Professor Baym has also been an advocate for laboratory experiments on matter under extreme conditions, playing a leadership role in the international effort to use ultrarelativistic heavy-ion collisions to test these phenomena, notably contributing to the establishment of the relativistic heavy ion collider (RHIC) project at Brookhaven National Laboratory. His contributions extend to the physics of ultrarelativistic heavy-ion collisions, condensed matter physics, and Bose-Einstein condensed atomic systems. He is the author of influential textbooks and monographs, and has maintained a lifelong interest in the history of physics. Recognized for his exceptional achievements, he is a member of the National Academy of Sciences and the American Philosophical Society, and received the Hans A. Bethe Prize in 2002 for his synthesis of fundamental concepts in matter at extreme conditions.

Research topics

• Physics
• Computer Science
• Algorithm
• Nuclear physics
• Quantum mechanics
• Particle physics

Selected publications

• Resolution of the hyperfine puzzle and its significance for two fermion Dirac atoms

  ArXiv.org · 2026-01-05

  articleOpen access1st authorCorresponding

  The hyperfine interaction in the ground state of a hydrogen atom of assumed radius $R$ is proportional to $-1/R^3$, raising the question of why the hyperfine interaction does not lead to collapse of hydrogen, or positronium. We approach the problem in terms of a minimax variational calculation based on the exact Gordon solution of the Dirac equation for the hydrogen atom ground state. The full Dirac treatment leads to the result that in an assumed variational state of size $R$, when $R$ minimizes the total energy the magnetic moment of the electron assumes its usual value, $e\hbar/2mc$, but when $R<\hbar/mc$, the effective electron magnetic moment becomes essentially $eR/2$, softening the hyperfine interaction and eliminating an energy minumum at small $R$. The magnetic moment of the proton is similarly suppressed, and the hyperfine interaction of a small size atom becomes bounded by the kinetic energy, thus assuring stability. We extend the Dirac variational calculation to positronium where we find simple results for the ground state energy and hyperfiine interaction, and then extend this variational calculation to Coulombic atoms of two fermions of arbitrary masses. This paper also lays out a framework for treating diquarks as relativistic Coulombic systems, in the presence of color electric and magnetic interactions.

  PublisherOA PDF

• Resolution of the hyperfine puzzle and its significance for two fermion Dirac atoms

  arXiv (Cornell University) · 2026-01-05

  preprintOpen access1st authorCorresponding

  The hyperfine interaction in the ground state of a hydrogen atom of assumed radius $R$ is proportional to $-1/R^3$, raising the question of why the hyperfine interaction does not lead to collapse of hydrogen, or positronium. We approach the problem in terms of a minimax variational calculation based on the exact Gordon solution of the Dirac equation for the hydrogen atom ground state. The full Dirac treatment leads to the result that in an assumed variational state of size $R$, when $R$ minimizes the total energy the magnetic moment of the electron assumes its usual value, $e\hbar/2mc$, but when $R&lt;\hbar/mc$, the effective electron magnetic moment becomes essentially $eR/2$, softening the hyperfine interaction and eliminating an energy minumum at small $R$. The magnetic moment of the proton is similarly suppressed, and the hyperfine interaction of a small size atom becomes bounded by the kinetic energy, thus assuring stability. We extend the Dirac variational calculation to positronium where we find simple results for the ground state energy and hyperfiine interaction, and then extend this variational calculation to Coulombic atoms of two fermions of arbitrary masses. This paper also lays out a framework for treating diquarks as relativistic Coulombic systems, in the presence of color electric and magnetic interactions.

  PublisherDOI

• Macroscopic neutrinoless double beta decay: Long range quantum coherence

  Nuclear Physics B · 2025-02-05

  articleOpen access1st author

  We re-introduce, in light of our modern understanding of neutrinos, the concept of “macroscopic neutrinoless double beta decay” (MDBD) for Majorana neutrinos. In this process an antineutrino produced by a nucleus undergoing beta decay, X → Y + e − + ν ¯ e , is absorbed as a neutrino by another identical X nucleus via the inverse beta decay reaction, ν e + X → e − + Y . The distinct signature of MDBD is that the total kinetic energy of the two electrons equals twice the endpoint energy of single beta decay. The amplitude for MDBD, a coherent sum over the contribution of different mass states of the intermediate neutrinos, reflects quantum coherence over macroscopic distances, and is a new macroscopic quantum effect. We evaluate the rate of MDBD for a macroscopic sample of “ X ” material, e.g., tritium, acting both as the source and the target. The accidental background for MDBD originating from two separate single beta decays, which contains two final state neutrinos, can be readily rejected by measuring the energy of the detected two electrons. We discuss the similarities and differences between the MDBD and conventional neutrinoless double beta decay. While MDBD is clearly not a viable replacement for traditional 0 ν DBD experiments, analysis of the concept of MDBD offers new perspectives on the physics of neutrinoless double beta decays.

  PublisherDOI

• Generalized Beth--Uhlenbeck entropy formula from the $Φ-$derivable approach

  ArXiv.org · 2025-12-03

  preprintOpen accessSenior author

  We derive a generalized Beth-Uhlenbeck formula for the entropy of a dense fermion system with strong two-particle correlations, including scattering states and bound states. We work within the $Φ-$derivable approach to the thermodynamic potential. The formula takes the form of an energy-momentum integral over a statistical distribution function times a unique spectral density. In the near mass-shell limit, the spectral density reduces, contrary to naïve expectations, not to a Lorentzian but rather to a "squared Lorentzian" shape. The relation of the Beth-Uhlenbeck formula to the $Φ$-derivable approach is exact at the two-loop level for $Φ$. The formalism we develop, which extends the Beth-Uhlenbeck approach beyond the low-density limit, includes Mott dissociation of bound states, in accordance with Levinson's theorem, and the self-consistent back reaction of correlations in the fermion propagation. We discuss applications to further systems, such as quark matter and nuclear matter.

  PublisherOA PDFDOI

• Understanding the puzzle of angular momentum conservation in beta decay and related processes

  Proceedings of the National Academy of Sciences · 2024-11-19

  articleOpen access1st authorCorresponding

  We ask the question of how angular momentum is conserved in electroweak interaction processes. To introduce the problem with a minimum of mathematics, we first raise the same issue in elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon, and note its presence in scattering of a fully relativistic spin-1/2 particle by a central potential. We then consider inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus. While both the incident neutrino and final electron spins are antiparallel to their momenta, the final spin is in a different direction than that of the neutrino-an apparent change of angular momentum. However, prior to measurement of the final particle, in all these cases angular momentum is indeed conserved. The apparent nonconservation of angular momentum arises in the quantum measurement process in which the measuring apparatus does not have an initially well-defined angular momentum, but is localized in the outside world. We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens, enabling physically transparent derivations of angular and helicity distributions in these reactions.

  PublisherOA PDFDOI

• Understanding the puzzle of angular momentum conservation in beta decay and related processes

  arXiv (Cornell University) · 2024-05-23

  preprintOpen access1st authorCorresponding

  We ask the question of how angular momentum is conserved in electroweak interaction processes. To introduce the problem with a minimum of mathematics, we first raise the same issue in elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon, and note its presence in scattering of a fully relativistic spin-1/2 particle by a central potential. We then consider inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus. While both the incident neutrino and final electron spins are antiparallel to their momenta, the final spin is in a different direction than that of the neutrino -- an apparent change of angular momentum. However, prior to measurement of the final particle, in all these cases angular momentum is indeed conserved, The apparent non-conservation of angular momentum arises in the quantum measurement process in which the measuring apparatus does not have an initially well-defined angular momentum, but is localized in the outside world. We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens, enabling physically transparent derivations of angular and helicity distributions in these reactions.

  PublisherOA PDFDOI

• Macroscopic neutrinoless double beta decay: long range quantum coherence

  arXiv (Cornell University) · 2024-03-05 · 1 citations

  preprintOpen access1st authorCorresponding

  We re-introduce, in light of our modern understanding of neutrinos, the concept of ``macroscopic neutrinoless double beta decay" (MDBD) for Majorana neutrinos. In this process an antineutrino produced by a nucleus undergoing beta decay, $X\to Y + e^- + \bar ν_e$, is absorbed as a neutrino by another identical $X$ nucleus via the inverse beta decay reaction, $ν_e + X \to e^-+Y$. The distinct signature of MDBD is that the total kinetic energy of the two electrons equals twice the endpoint energy of single beta decay. The amplitude for MDBD, a coherent sum over the contribution of different mass states of the intermediate neutrinos, reflects quantum coherence over macroscopic distances, and is a new macroscopic quantum effect. We evaluate the rate of MDBD for a macroscopic sample of ``$X$" material, e.g., tritium, acting both as the source and the target. The accidental background for MDBD originating from two separate single beta decays, which contains two final state neutrinos, can be readily rejected by measuring the energy of the detected two electrons. We discuss the similarities and differences between the MDBD and conventional neutrinoless double beta decay.

  PublisherOA PDFDOI

• Implication of Helicity Modifications of Primordial Neutrinos on Their Detection

  2022-12-26 · 1 citations

  articleOpen accessSenior author
  PublisherDOI

• Ben Mottelson: Codeveloper of the unified theory of the structure and dynamics of atomic nuclei

  Proceedings of the National Academy of Sciences · 2022-09-28

  articleOpen access1st authorCorresponding

  Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans the biological, physical, and social sciences.

  PublisherOA PDFDOI

• Long Range Plan: Dense matter theory for heavy-ion collisions and neutron stars

  arXiv (Cornell University) · 2022-11-04 · 18 citations

  preprintOpen access

  Since the release of the 2015 Long Range Plan in Nuclear Physics, major events have occurred that reshaped our understanding of quantum chromodynamics (QCD) and nuclear matter at large densities, in and out of equilibrium. The US nuclear community has an opportunity to capitalize on advances in astrophysical observations and nuclear experiments and engage in an interdisciplinary effort in the theory of dense baryonic matter that connects low- and high-energy nuclear physics, astrophysics, gravitational waves physics, and data science

  PublisherOA PDFDOI

Recent grants

• Microscopic Theory of Many-Particle Systems

  NSF · $770k · 2007–2011

• Properties of Condensed Matter Systems and Field Theories (Materials Research)

  NSF · $460k · 1982–1985

• Theoretical Nuclear Physics

  NSF · $870k · 1998–2002

• Theoretical Nuclear Physics

  NSF · $950k · 1995–1998

• Theoretical Nuclear Physics: A Group Proposal

  NSF · $901k · 2004–2008

Frequent coauthors

• C. J. Pethick

  161 shared

• Tetsuo Hatsuda

  66 shared

• Jean-Paul Blaizot

  Commissariat à l'Énergie Atomique et aux Énergies Alternatives

  48 shared

• Toru Kojo

  29 shared

• Philip D. Powell

  Lawrence Livermore National Laboratory

  26 shared

• Markus Holzmann

  Graz University of Technology

  24 shared

• Naoki Yamamoto

  Kagoshima University

  23 shared

• C. J. Pethick

  University of Illinois Urbana-Champaign

  18 shared

Education

• Ph.D., Electrical Engineering

  University of Illinois at Urbana-Champaign

  1985

• M.S., Electrical Engineering

  University of Illinois at Urbana-Champaign

  1981

• B.S., Electrical Engineering

  University of Illinois at Urbana-Champaign

  1979

Awards & honors

• APS Medal for Exceptional Achievement in Research, 2021
• Lars Onsager Prize, American Physical Society, 2008
• Hans A. Bethe Prize, APS (2002)
• Alfred P. Sloan Foundation Research Fellow (1965-1967)
• University Scholar (1987-1990)