The family moved almost every year to follow his military placements, including an assignment to Pearl Harbor prior to World War II.
[1] In the 1950s and 60s, Reppy was active on Ragged Mountain in Connecticut where he collaborated on many first ascents and on publishing an area guidebook with Sam Streibert.
Reppy has said his earliest interest in rock climbing as a very young teenager was related to the re-opening of small open-pit mica mines in eastern Connecticut during World War II in response to increased war-time demand for electronics materials.
[3] As physics professor at Cornell University, he studies quantum properties of superfluids with an emphasis on boundary conditions and phase transitions in systems of reduced dimensionality.
Reppy's research group has close associations with David M. Lee and Robert C. Richardson also of Cornell, who shared the 1996 Nobel Prize in Physics with Douglas D. Osheroff for discoveries related to super fluidity in helium-3 ice.
Lee, in his Nobel Prize speech, credited Reppy's "extraordinary technical ingenuity" in experiments leading to the discovery.
Bose–Einstein condensation was predicted in 1924, and was seen decades ago in liquid helium, according to Ketterle, who acknowledged a controversial earlier claim by Reppy.
Reppy studied an exception: tiny amounts of helium trapped in nanometer-sized pores of a spongelike glass called Vycor.
Separately, work from Cornell physics laboratories has been used to test a theory of cosmic strings, hypothetical objects, which may have been important in the formation of galaxies, and may have arisen through "phase transitions" in a fraction of a second after the Big Bang.