Illuminating the Cosmos with Brilliance: Remembering JILA Fellow James E. Faller

The JILA and NIST communities are recently saddened by the passing of physicist James “Jim” E. Faller. Faller was a visionary whose scientific contributions have contributed to our understanding of the universe. Faller’s work as a JILA Fellow spanned over 50 years (since 1972), and he remained actively engaged in the scientific research process, serving as NIST QPD Division Chief for a time. With heavy hearts, we bid farewell to a brilliant mind, a passionate explorer, and a respected member of the scientific community.

Early Life and Research

Born in 1934, Jim Faller possessed an insatiable curiosity and an unwavering dedication to unraveling the mysteries of the cosmos. From a young age, his thirst for knowledge propelled him on a life-long journey that left an indelible mark on physics. This drive led him to become a respected physicist.

Faller arrived at JILA in December 1962 as a postdoctoral researcher working with JILA Fellow Pete Bender. Before his arrival, Faller came up with the original idea for a lunar laser-ranging experiment when he was a graduate student at Princeton University, working with Robert H. Dicke.  The ranging experiment would help scientists understand how far away the Moon was from Earth and allow them to track the Moon’s orbit better. Faller’s idea led to a laser retroreflector package designed by Faller (at JILA), placed on the Moon in 1969 by the Apollo 11 astronauts.  “Jim is the person, first in the world, who developed a converging procedure for polishing the 3 prism-faces of the corner cubes to the near-diffraction-limited accuracy needed as Lunar Ranging Reflectors,” explained JILA Fellow John “Jan” Hall, a Nobel laureate. “This first-ever capability was developed in collaboration with the son of one of famous Optical Physicist A. A. Michelson's collaborators, Bud Pearson, who ran a precision optics shop in Boulder in the 1970s.” 

According to JILA and NIST Fellow Judah Levine, a colleague of Faller’s, Faller had built a telescope to measure the reflected signal from the Moon. “It was a monster thing,” Levine stated. “It filled a whole room.” The telescope once sat in the first floor of JILA’s B-wing, until it was eventually shipped to the Mauna Kea Observatory on top of Hawaii’s Haleakala volcano. Currently, measurements of retroreflectors at three Apollo landing sites are carried out roughly every three days, with sensitivity in recent years of a few centimeters for the Earth-Moon distance. 

During his career at JILA, Faller strongly advocated for the institute. “He was passionate about JILA and the future of JILA,” elaborated JILA and NIST Fellow Eric Cornell, a Nobel Laureate. “He was a strong advocate for hiring Debbie Jin [a leading researcher in ultracold physics].” As a JILA Fellow, Faller collaborated closely with Hall and shared JILA's massive underground spectroscopy laboratory for more than two decades. Their collaborations and friendly competitions enhanced the research done by both groups.

Faller’s passion for JILA also helped him become a well-respected collaborator for other JILA Fellows. “He had a great sense of the qualitative understanding of a lot of physics, especially classical mechanics,” added Cornell. “I remember talking to him about the design of an experiment and him having good suggestions.” Levine agreed that Faller’s most significant contribution to JILA was having “super clever mechanical designs,” Levine elaborated. “He had an eye for mechanics, which really drove his experiments.” Like Cornell, Levine also asked Faller for suggestions on his own research, specifically for mechanical advice. Faller’s passion for mechanics also made its way into JILA’s instrument shop. Cornell explained: “He was a big advocate for the instrument shop. I think part of it is because he admired those guys for building and designing things.” 

Faller’s Work on LISA (Laser Interferometer Space Antenna)

As a physicist, Faller was also interested early in the possibility of gravitational wave measurements in space at minute frequencies in the milli-Hertz range.  Such signals come from massive black holes throughout the universe and are too low of frequencies to be detectable by ground-based gravitational wave detectors.  In 1981, Faller and Bender made the first suggestion of the preliminary mission design for a mission now called the Laser Interferometer Space Antenna (LISA), which has been widely studied since then.  In the last 5 years, LISA has been under concentrated study by the European Space Agency as a flight candidate for launch in 2035, and a designation as an official flight mission is expected shortly.  NASA is also considering making a major contribution to the flight’s hardware and to the scientific studies during the LISA mission.

Faller’s Work on Gravity Precision

With the help of his students, postdocs, and collaborators, Faller was also a leader in designing and applying highly accurate absolute gravimeters.  These instruments are now used at many sites worldwide to monitor minor variations in Earth’s gravitational acceleration due to local mass distribution changes.  For example, small motions of magma streams way below the earth's surface in volcanic active areas can be studied.  And, when slip occurs on the lower parts of fault systems, the measured gravitational changes at the surface can help understand the amplitude and the geometry of the displacements.  Changes smaller than 10 parts in a billion in gravitational acceleration can be measured in a few minutes.
Other experiments by Faller continue to be utilized by researchers today. As JILA and NIST Fellow Jun Ye elaborated: “Jim and his postdoc Harold Parks invested a long effort in making a precise measurement of the gravitational constant G in the basement of JILA. Their experimental apparatus was unique and clever. Their experimental value for big G disagrees by 6 parts in 105 from the others, and some of them agree with each other but some disagree by about the same amount with the opposite sign. So, an accurate determination of big G beyond 5 digits still remains elusive, and Jim often reminded us that this served as a strong motivation for continued experimental development for the measurement of this fundamental constant of nature.” 

Awards and Recognition

Throughout his career, Faller's work garnered numerous accolades and earned him the respect of his peers. His groundbreaking research was recognized with prestigious awards, including the Joseph F. Keithley Award (2001), the Federal Laboratory Consortium Technology Transfer Award (1992), the Department of Commerce Gold Medal (1990), NASA Group Achievement Award (1973), the NASA Exceptional Scientific Achievement Medal (1973), Alfred P. Sloan Fellowship (1972-1973), National Bureau of Standards Precision Measurement Award (1970), and the Arnold O. Beckman Award of the Instrument Society of America (1970). He was elected a Fellow of OPTICA (formerly Optical Society of America) in 2020. These honors stand as a testament to his contributions and impact on the scientific community.

Faller the Mentor

Yet, in addition to his scientific achievements, Faller remained passionate about mentoring individual scientitsts. “When I first arrived at JILA, I always felt like Jim was looking out for me,” stated Cornell. “I felt that he took a real interest in my research and wanted to see it flourish, even when I was a very young professor.” Faller was known for his willingness to mentor aspiring scientists and enthusiasm for sharing knowledge. Faller's generosity and passion for science inspired countless young minds to pursue their own scientific dreams and continue pushing the boundaries of human understanding. “He saw JILA as more than just a bunch of research groups,” Levine stated. “He saw the institute as really being bigger than that.” 

Beyond his scientific pursuits, Faller was also an accomplished musician, playing the recorder, French Horn, and other instruments. 

Please add your memories of Jim to this memorial page: https://jila.colorado.edu/form/james-e-faller-memorial-stories-

Written by Kenna Hughes-Castleberry, JILA Science Communicator 

Read Jim Faller's Physics Today obituary here: https://pubs.aip.org/physicstoday/online/43069