Edward Mills Purcell

Edward Mills Purcell was born in Taylorville, Illinois in 1912 and studied electrical engineering at Purdue before switching to physics at Harvard, where he took his Ph.D. under John Van Vleck in 1938. The Second World War pulled him into the MIT Radiation Laboratory, where he led the development of microwave radar receivers and absorbed the techniques for manipulating radiofrequency electromagnetic fields that would shape the rest of his career.

In 1946, back at Harvard, Purcell and his colleagues Robert Pound and Henry Torrey observed nuclear magnetic resonance in solid paraffin — protons in a sample precessing in a static magnetic field and absorbing energy from a resonant radiofrequency pulse. Felix Bloch at Stanford independently observed the same effect in liquids. They shared the 1952 Nobel Prize in Physics. NMR has since become one of the most productive experimental tools in all of science: the foundation of NMR spectroscopy for chemistry, of magnetic resonance imaging in medicine, and of precision magnetometry.

Purcell's other enduring contribution to the physics culture is a 1977 lecture at the American Institute of Physics titled Life at Low Reynolds Number. In it he explained — with clarity, charm, and a cartoon of a hypothetical 'one-hinge swimmer' — why the Navier-Stokes equations become time-reversible in the creeping-flow limit, why reciprocal motion cannot produce net displacement at low Reynolds number (the scallop theorem), and why every motile bacterium on Earth uses a rotating helical flagellum rather than a paddle.