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Leon Cooper, who has died aged 94, helped to resolve an issue that had stumped most of the best minds in twentieth-century physics. Along with his colleagues John Bardeen and Robert Schrieffer, he deciphered the dance of electrons that causes superconductivity, or the sudden drop in electrical resistance skilled by sure supplies, reminiscent of mercury, after they attain temperatures only some levels above absolute zero. This phenomenon has since served to generate, for instance, the very excessive magnetic fields wanted to function know-how reminiscent of magnetic resonance imaging physique scanners. The Bardeen–Cooper–Schrieffer (BCS) idea of superconductivity received them the Nobel Prize in Physics in 1972.
Having labored out one of many hardest issues in physics, Cooper turned his consideration to neuroscience. Along with his graduate college students Elie Bienenstock and Paul Munro, he developed a mannequin — inevitably dubbed the Bienenstock–Cooper–Munro (BCM) idea to reflect the BCS idea — of adjustments within the energy of the neuronal connections within the mind as people study.
His pioneering theoretical work on neural networks locations him within the firm of different physicists reminiscent of John Hopfield and Geoffrey Hinton — winners of the 2024 Nobel Prize in Physics who developed algorithms that would symbolize the method of studying in a mannequin of a really small quantity of mind tissue.
Cooper (initially Kupchik) was born in New York Metropolis, the son of Jewish immigrants from Belarus and Poland. After his mom died, he and his sister spent a part of their childhood in care. In 1947, he graduated from the Bronx Excessive Faculty of Science, which has produced six different Nobel laureates in physics. He then studied physics at Columbia College, New York Metropolis, finishing a PhD in 1954.
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He joined the Institute of Superior Research in Princeton, New Jersey, for a 12 months, earlier than Bardeen recruited him to the College of Illinois at Champaign–Urbana, to work collectively on issues of condensed-matter idea and particularly on superconductivity. “The lengthy and really imposing checklist of physicists (amongst them [Niels] Bohr, [Werner] Heisenberg and [Richard] Feynman) who had tried or had been making an attempt their hand at superconductivity ought to have given me pause,” recalled Cooper in a later memoir. Feynman had even stated that anybody making an attempt to sort out superconductivity would quickly uncover that they had been “too silly to resolve the issue”.
Superconductivity was first noticed in 1911, however by the mid-Nineteen Fifties it was nonetheless unknown how electrons may stream seemingly with out restrict in supercooled mercury. Some prompt that new physics — an undiscovered form of particle, for instance — is likely to be wanted to account for the phenomenon. Working for greater than a 12 months with each theoretical instrument at his disposal, Cooper proposed that faint vibrations in lattices of atoms at low temperatures prompted electrons to pair up as an alternative of repelling each other. All of those ‘Cooper pairs’ may in flip function as a single entity and move via the lattice unopposed.
Mathematical evaluation by Schrieffer supported the speculation, which Bardeen refined. Their paper prompted a sensation (J. Bardeen et al. Phys. Rev. 108, 1175; 1957); it was subsequently confirmed by experiment. The identical phenomenon additionally underlies the efficiency of extra just lately found ‘high-temperature superconductors’, which attain a resistance-free state at as much as 100 levels above absolute zero. “The nice factor that Bardeen, Cooper and Schrieffer confirmed was that no new particles or forces needed to be launched to know superconductivity,” wrote Steven Weinberg, a theoretical physicist who received the Nobel Prize in Physics in 1979.
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In 1958, Cooper moved to Brown College in Windfall, Rhode Island, the place he remained for the remainder of his working life. In 1974, he based the Institute for Mind and Neural Methods there, recruiting a staff to analysis the connectivity underlying cognitive perform. The group constructed on the work of pioneers reminiscent of mind researchers Warren McCulloch and Walter Pitts of the College of Illinois at Chicago, who had printed a mathematical mannequin of a neural community in 1943 (W. S. McCulloch and W. Pitts, Bull. Math. Biophys. 5, 115–133; 1943), and of the Canadian psychologist Donald Hebb, whose 1949 e book The Group of Conduct proposed that, if neurons repeatedly fireplace — that’s, ship electrical alerts — to the physique and mind on the similar time, the synapses between them turn into stronger.
The BCM idea, printed in 1982, addressed how particular cells within the visible cortex turn into selective for sure stimuli, reminiscent of an edge at a selected angle, relying on earlier visible expertise. It proposed that, the extra typically incoming alerts activated a neuron, the upper the brink for its activation would turn into, and vice-versa. This sliding threshold has the impact of stabilizing the responsiveness of the neuron, making it both roughly energetic. Cooper’s purpose was to mannequin how dwelling brains work, and the BCM idea has stood the take a look at of time. It has additionally performed an element within the growth of machine studying. Cooper and his collaborators went on to use insights from machine studying to many different fields, reminiscent of sonar detection.
Though he formally retired in 2014, Cooper by no means misplaced his curiosity. That 12 months, he printed a set of essays, Science and Human Expertise, based mostly on his full of life curiosity in physics, neuroscience, philosophy and the way these fields interacted with one another. He argued that science emerged from a uniquely human want to elucidate the world that surrounds us, and that creativeness was an important a part of the method. “Our creativeness is marvellously free,” he wrote, “able to any juxtaposition, unbounded by logic or expertise.”
Competing Pursuits
The creator declares no competing pursuits.
