Prof. Emeritus Dietrich Müller, a renowned experimental physicist at the University of Chicago who spent half a century building instruments to study energetic particles from space called cosmic rays, died Dec. 22 at the age of 85.
Müller helped build experiments that took data during space shuttle flights and aboard balloons circling above the Arctic and Antarctic, measuring energetic particles called cosmic rays that zip through our solar system from elsewhere in the galaxy. These experiments revealed new information about cosmic rays, which offer a window into the stars and astrophysical phenomena around us, as well as the fundamental makeup of the universe. For example, one of Müller’s instruments collected some of the first evidence that there are more positrons in the galaxy than predicted—a mystery which has continued to puzzle scientists for decades.
“Dietrich was a renowned cosmic ray experimentalist with a gift for devising innovative instrumentation,” said Prof. Scott Wakely, Müller’s friend and colleague for many years. “He was legendary for asking exactly the question you should have been thinking about, but weren’t.”
“With him goes an era,” said longtime colleague Michael Turner, the Bruce V. and Diana M. Rauner Distinguished Service Professor Emeritus at UChicago.
Born in Leipzig, Germany in 1936, Müller received degrees in physics at the Universities of Leipzig and Bonn in Germany. After receiving his Ph.D., he arrived at the Enrico Fermi Institute at UChicago in 1968 as a research associate and joined the Department of Physics in 1970 as an assistant professor. He would remain a member of the UChicago community for more than 50 years.
Müller joined an extraordinary group of physicists at the University of Chicago studying cosmic rays—a source of great scientific excitement. These extraterrestrial particles arrive at Earth as messengers from all sorts of interesting events and places, including from the sun as well as supernovae and powerful stars elsewhere in the galaxy.
Cosmic rays can reveal hints about everything from dark matter to how elements are made. “They are this extraordinary source of information,” said Turner. “We can’t travel around the universe, but we can get these samples of material that have traveled here from elsewhere in the galaxy and beyond.”
In his early years, Müller worked with Prof. Peter Meyer on an experiment affectionately nicknamed the “Chicago Egg,” a large instrument that flew aboard the Challenger space shuttle. It was a difficult project, as Müller himself would later recall: “The shuttle was still in development, and NASA imposed new requirements almost daily; the type of detector we were trying to build was entirely new and not proven before.” Nonetheless, the Egg successfully made direct observations of high-energy cosmic rays at energies beyond the reach of most detectors.