Herman Feshbach’s office at MIT was not far from mine, and so when I stumbled across the term “Feshbach resonance,” it was natural to turn to him for an explanation. The phenomenon that piqued my curiosity was reported in a paper on the spectroscopy of the negative hydrogen ion. This ion had seemed an unlikely subject for spectroscopy because it has only one bound state. Nevertheless, an elegant experiment in the mid-1970s by Howard C. Bryant’s group at Los Alamos revealed features in the photoionization spectrum, including a sharp line that the authors described as a Feshbach resonance. Hence my visit to Herman.
He was at his desk, happily smoking a cigar (this was quite a few years before smoking was banned). “Herman,” I asked, “can you tell me what a Feshbach resonance is?” He leaned back, puffed thoughtfully on his cigar for a few moments and finally said: “Beats...
