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Theoretical physicist James D. “BJ” Bjorken, a professor emeritus at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University whose work helped understand the structure of matter at a fundamental level, died Aug. 6 in Redwood City. He was 90.
Bjorken was widely known for inventing “Bjorken scaling,” a concept in particle physics that helps to explain how particles like protons and neutrons behave when observed closely, especially at high energies. SLAC theoretical physicist Michael Peskin described this as a pivotal moment in particle physics.
Born on June 22, 1934, Bjorken grew up in Park Ridge, Illinois, where he developed an early interest in math and chemistry. He earned his bachelor’s degree from MIT, majoring in physics. Later, he attended Stanford University for his Ph.D and stayed on as a postdoctoral researcher for several years.
He was one of several MIT physicists, including his advisor Sidney Drell and future SLAC director and Nobel laureate Burton Richter, who were attracted to Stanford’s new research facilities, including an early linear accelerator used to study protons and neutrons. The physicists wanted to understand the core secrets of matter.
A decade later, these experiments moved to SLAC, where the Accelerator allowed scientists to study matter at higher energy levels. At the time, theorists suggested that protons and neutrons were made up of smaller particles, but no one had yet figured out how to prove the existence of these particles.
In the late 1960s and early 1970s, Bjorken’s experiments confirmed that protons are made up of fundamental particles called quarks. His discovery was recognized with the Wolf Prize in physics and the 2015 High Energy and Particle Physics Prize of the European Physical Society. He was also honored for his contributions to developing the theory of the “strong force,” which controls the interactions between quarks within protons and neutrons.
In 2017, he shared the Robert R. Wilson Prize for his work at Fermilab, where he developed theories that sharpened the focus of particle beams in various accelerators by addressing key challenges related to their intensity and precision.
“What made him a great physicist was he thought differently from other people,” said Lance Dixon, a theoretical physicist at SLAC and Stanford.
Bjorken divided his time between homes in Woodside and Driggs, Idaho, passionately pursuing many interests outside physics, from mountain climbing, skiing, cycling and windsurfing to listening to classical music.
He would drive long distances to attend an opera in Chicago or unexpectedly visit a fellow physicist’s office for deep conversations on topics like general relativity, dark matter, and dark energy.
“I’ve found the most efficient way to test ideas and get hard criticism is one-on-one conversation with people who know more than I do,” he said.
Family members said Bjorken continued to amuse himself with physics until his very last days. “He was surrounded by physics equations and thoughts,” said his daughter, Johanna Bjorken. “It was truly what he loved – and yet it was just one dimension of the many things he loved.”
Bjorken is survived by his daughters Johanna Bjorken of Brooklyn, New York and Eliza B. Davies of San Carlos, California; stepchildren Peter Nauenberg of Crystal Bay, Nevada, and Maria James of San Leandro, California; and nine grandchildren. He was preceded in death by his wife Joan G. Bjorken (1983) and granddaughter Nova Joan Adan (2024).
At Bjorken’s request, there will be no formal services or a memorial.
