Particle physicist Martin Moses Block was born on 29 November 1925 in Newark, New Jersey, and died in Los Angeles on 22 July 2016 after a brief illness. His career was distinguished not only by many contributions but also by longevity: His first paper was published in September 1949, and his most recent in June 2016, 67 years later. Block really had two careers in physics: first, as an experimentalist, until he went emeritus in 1996, and second, as a theorist, carried out from home in his beloved Aspen, Colorado. He was active in the Aspen Center for Physics and was responsible for founding the center’s enduring Aspen Winter Physics Conference series.
Block received his BS in 1947, MA in 1948, and PhD, under William Havens, in 1952, all from Columbia University, where he also helped design the magnets for the Nevis cyclotron. As a young professor at Duke University, he contributed the revolutionary notion that parity wasn’t conserved in weak interactions. While rooming with Richard Feynman at the Rochester Conference on High Energy Physics in 1956, he’d hatched the idea as a way to resolve the so-called tau–theta paradox: two otherwise identical particles that decayed into different parity states and thus were believed to be distinct. Feynman recounted the story in his 1985 memoir, Surely You’re Joking, Mr. Feynman! Adventures of a Curious Character (W. W. Norton, page 247):
I was sharing a room with a guy named Martin Block, an experimenter. And one evening he said to me, ”Why are you guys so insistent on this parity rule? Maybe the tau and theta are the same particle. What would be the consequences if the parity rule were wrong?”
I thought a minute and said, ”It would mean that nature’s laws are different for the right hand and the left hand, that there’s a way to define the right hand by physical phenomena. I don’t know that that’s so terrible, though there must be some bad consequences of that, but I don’t know. Why don’t you ask the experts tomorrow?”
He said, ”No, they won’t listen to me. You ask.”
So the next day, at the meeting … I got up and said, ”I’m asking this question for Martin Block: What would be the consequences if the parity rule was wrong?”
Murray Gell-Mann often teased me about this, saying I didn’t have the nerve to ask the question for myself. But that’s not the reason. I thought it might very well be an important idea.
Important, indeed! The 1957 Nobel Prize in Physics went to Tsung-Dao Lee and Chen-Ning Yang for their theoretical analysis of the process. But it was not shared by Chien-Shiung Wu for her 1956 experimental demonstration of parity violation in the beta decay of cobalt-60 nuclei, nor was Block’s contribution acknowledged at the time. The episode was recounted in a bit of rueful doggerel by physicist Erich Harth (Physics Today, August 1991, page 91).
At Duke, Block developed the first liquid-helium bubble chamber and used it to study the properties of several newly discovered particles. He left Duke in 1961 for Northwestern University, where he served on the faculty for the remainder of his experimental career. He codiscovered the eta meson, and he probed particles at ever-higher energies by using heavy-liquid bubble chambers and, eventually, modern counter detectors. His work took him to accelerators all over the world, with extended stints at Fermilab, CERN, and Lawrence Berkeley, Brookhaven, and Argonne National Laboratories.
Block’s lifelong passion for the mountains, especially for downhill skiing and fly-fishing, eventually took him to Aspen, where he joined the Aspen Center for Physics in its nascent years. He purchased a family home there in 1964, and he spent many vacations in Aspen until he left Northwestern to spend full time in Colorado. At that point he took up a second career in theoretical and computational physics.
A central focus of his later work was on the forward-scattering amplitudes of hadron collisions, particularly at the highest energies available at the most powerful modern accelerators as well as from cosmic rays. He sought to understand scattering structure and, specifically, why the proton–proton interaction cross section grows with the square of the logarithm of the energy. After toying with models inspired by quantum chromodynamics, Block realized that the experimental data had become sufficiently precise to make a model-independent prediction of the asymptotic behavior of the cross section. His work anticipated quantitatively the measurements eventually performed at the Large Hadron Collider at CERN. In one of his final papers, he showed that the data demonstrate convincingly that both the proton–proton and antiproton–proton scattering amplitudes asymptotically approach those of a so-called black disk, presumably as a consequence of gluon saturation.
Martin Block remained productive up until the end, when he and collaborators were revising drafts of his latest manuscript. He was, his friends and colleagues agree, quite a character, and something of a force of nature.