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The Helmut W. Baer Lecture

The Helmut W. Baer Lecture  is a special colloquium supported by family and friends in honor of Dr. Helmut Baer. Dr. Baer's career in physics began with his work at the University of Michigan where he was awarded a doctorate in nuclear physics in 1967. He published over 100 articles that cover a range of physics topics including nuclear physics and pion interactions. Dr. Baer was named a Fellow of the American Physical Society in March of 1989, and to his delight enjoyed countless opportunities over the years to talk about physics at universities and conferences internationally. Dr. Baer set the highest personal standards for himself and his research. This lecture is held approximately every two years.

The 2023 Helmut W. Baer Lecture in Physics

George M. Fuller


George M. Fuller
Distinguished Professor of Physics (University of California, San Diego)

Wednesday, February 8, 2023
3:00 PM

340 West Hall



Lecture Title: The Insidious Neutrinos, Entropy, and Gravitational Collapse:
what we learn about neutrinos, beyond standard model physics, and the creation of the elements, from the collapse of massive stars

Abstract: The weakest forces of nature team up to engineer the demise of massive stars, compact objects, and maybe the odd causal horizon volume in the very early universe.

Stars make a Faustian bargain with gravitation and the weak interaction: Energy generation and, hence, promise of a longer life, in exchange for changing composition and the seemingly innocent loss of a little entropy through neutrino emission. It is a good deal for lower-mass stars like the sun. But the price proves to be too high for stars with masses in excess of ~ 8 solar masses, where the neutrino emission-induced loss of entropy and the nonlinear nature of gravitation combine with the weak interaction and exotic nuclear physics to cause collapse of the cores of these stars to neutron stars or black holes. Stars with masses in excess of ~ 100 solar masses likewise are vulnerable to instability because so much of their pressure support comes from radiation.

In fact, the nonlinear nature of gravitation means that self-gravitating systems get into trouble whenever their pressure support involves particles moving near light speed. Such objects are, in the words of my late research mentor, “Trembling on the verge of instability.”

That means that very subtle influences, from known, standard model weak interaction processes, but perhaps also from new, beyond-standard-model physics, can figure in the evolution of these objects. Collapse to neutron stars or black holes is the inevitable outcome, but clues about how these murders were committed may be found in nucleosynthesis (especially of the heaviest nuclei) and in the spectrum of remnant masses.

We will discuss how frontier issues in elementary particle physics, especially those involving the mysterious and ghostlike neutrinos, could figure prominently in what happens in these gravitational collapse events and their aftermath.


George Fuller is Distinguished Professor of Physics at the University of California, San Diego, and the Director of the Center for Astrophysics and Space Sciences (CASS) there. He received his undergraduate degree and PhD in physics from the California Institute of Technology in 1976 and 1981, respectively. His PhD advisor at Caltech was Professor William A. Fowler. Subsequently, Fuller went to the University of Chicago, where he was a Robert R. McCormick Fellow 1981-83, a postdoctoral Visiting Research Astrophysicist at UC Santa Cruz/Lick Observatory from 1983-84, a Research Assistant Professor at the (old) Institute for Nuclear Theory, University of Washington 1985-86, and then a staff member in the IGPP astrophysics group at Lawrence Livermore National Laboratory 1986-1988. He came to UCSD as an Associate Professor in 1988. He is a Fellow of the American Physical Society. He is a recipient of the Hans A. Bethe Prize in 2013.

Fuller's work has revolved around the interplay of the weak interaction, nuclei, and gravitation in the cosmos. The recent focus of his work has been on neutrino physics, in particular the role of neutrino mass and flavor mixing in the early universe and in core-collapse supernovae, the synthesis of the light and heavy nuclei, and cosmology.