Peter Bender OBITUARY

Peter Bender died April 20, 2024, at the age of 93. He was a calm, gentle and optimistic presence in our lives, and we miss him. Pete was born in NYC and grew up in Leonia, NJ. His passion for math and physics led him to pursue an undergraduate degree at Rutgers University, followed by travel to the Netherlands to study at Leiden University and work at the Kamerlingh Onnes Lab on a Fulbright grant. In Europe, he and his fiancé, Bernice Koettgen, who was studying in Germany, hiked, biked and rode the rails through the alpine countries. Pete returned to Princeton University to earn graduate degrees and lay the groundwork for a career that would blend rigorous experimental physics with theoretical insights. His work at the National Bureau of Standards (NBS) in Gaithersburg, MD initially focused on precision measurements and magnetic fields. Pete and family moved to Boulder in 1962 with the formation of the Joint Institute for Laboratory Astrophysics (JILA). JILA was created by combining an atomic physics group from NBS, now National Institute of Standards and Technology (NIST), with university researchers in a synergistic organization within the University of Colorado. Pete was a founding member, and JILA remained his intellectual home for the rest of his life. Pete’s career spanned many transformative science projects. He often pursued applications of precision measurements based on lasers, incubated in the fertile JILA environment with co-workers James Faller and Nobelist John Hall, and other members of the institute, supplemented by a constant stream of talented students and visiting scientists. In the 60’s and 70’s Pete was a central figure in the Lunar Laser Ranging Experiment in which Apollo 11, 14 and 15 astronauts put reflector arrays on the Moon for measuring the distance to the Moon with laser pulses to better than an inch. The results have had wide-ranging impacts on space science, geophysics, and fundamental tests of Einstein’s General Theory of Relativity. The measurements continue to the present, the last remaining part of the Apollo Moon Program. Lunar laser ranging spawned the now routine placement of reflectors on most spacecraft for precision tracking. In another novel endeavor, Pete promoted and refined the idea of measuring changes in a planet’s gravity field with a precision measurement of the separation between a pair of identical satellites in identical orbits. That distance reflects mass anomalies in the Earth below. The GRACE mission (Gravity Recovery and Climate Experiment) revolutionized remote sensing of the Earth, mapping changes in ice sheets, oceans, aquifers and the solid Earth. The concept was replicated in subsequent missions with Pete’s suggested improvements. One version, GRAIL, orbited the Moon, probing its interior density variation. Pete is best known for his seminal role in creating the Laser Interferometer Space Antenna concept, a space-borne gravitational-wave detector known as LISA. He assembled most of the critical ideas and identified the extraordinary science that could be done with three spacecraft 1.5 million miles apart, connected by laser beams. LISA, now the premier future mission of the European Space Agency, will detect extreme events involving black holes, neutron stars and white dwarfs through distortions of spacetime traveling from as far away as the earliest moments of the Big Bang. Pete was internationally acclaimed for both his contributions and his humble manner. Although he officially retired years ago, Pete worked into his 90s and was perpetually scientifically engaged with folks across the globe. They discussed laser interferometers, atmospheric physics, atomic clocks, black holes, binary stars, pulsars, analytic techniques, and numerical simulations. Pete’s colleagues remember his love for physics, rigorous scientific calculations, attention to technical detail, enthusiasm for new projects, his kindness, and his permanent positive attitude. Pete’s last excursion to campus in March was to hear a talk about black holes and the physics of gravity. Pete and Bernice were married for 65 years. They met at a dance at Rutgers, were engaged in tulip gardens in the Netherlands and were married in Leonia. They lived in Princeton and Bethesda before moving to Boulder. Boulder was a very good place to land, and hiking became a passion for the whole family. Pete was especially fond of glaciers, and Pete and Bernice enjoyed hut-to-hut backpacking in Norway, Switzerland, Austria and other destinations around the world. Bernice died in 2019. Pete is survived by his sister, Mary Ellen Bender, his children, Carol (Dave Karle), Paul (Cheryl), and Alan (Laurel), his grandchildren, Katherine Hermann (Owen Lewis), Joseph Bender, and Anna Wynfield (Ted), and his great granddaughter Finley. His children remember visiting observatories, watching lava flowing, and creating lava rocks with sticks in Hawaii. We climbed the cascade to Sky Pond, trekked up South Arapaho Peak, and summited Hallett and Longs Peaks. His grandchildren fondly remember walking the logs at Mills Lake, picnicking at Pawnee Pass, dodging hail on Mount Audubon, and watching clouds roll over Indian Peaks.