John Hopfield

American physicist at Princeton University, earlier at the California Institute of Technology (Caltech). After work in solid-state physics and biophysics, including the theory of kinetic proofreading (1974), he introduced the Hopfield networkHopfield network, n.: A network of on–off units, all connected to one another, that stores patterns as stable states. Given a partial or noisy pattern, it settles into the closest stored one, like recalling a memory from a hint. (1982): a recurrent network of binary units with symmetric connections whose dynamics always lower an energy function, so that stored patterns become stable states and a partial or noisy input settles into the nearest stored memory. By linking neural computation to the statistical physics of spin glasses, the work drew physicists into neural-network research and, with Geoffrey HintonGeoffrey Hinton, prop. n.: A British-Canadian scientist whose decades of persistent work on brain-inspired neural networks laid the foundations of modern AI; often called a 'godfather of AI', he now warns publicly about its dangers.'s Boltzmann machineBoltzmann machine, n.: A network of randomly flipping on–off units, including hidden ones, that learns the statistical patterns in its training data and can then produce new examples like them., prepared the ground for energy-based modelsenergy-based model, n.: A model that scores how well things fit together by giving each possibility an 'energy': low for plausible combinations, high for implausible ones, like a ball settling into the lowest valleys.; with David Tank he applied such networks to optimization problems such as the traveling-salesman problem (1985). He helped found Caltech's Computation and Neural Systems program. He shared the 2024 Nobel Prize in Physics with Hinton, the committee crediting the pair with the discoveries on which today's neural-network learning was built (see Nobel Prizes for AINobel Prizes for AI, phr.: The two 2024 Nobel Prizes, in physics and chemistry, that honored artificial intelligence research for the first time, recognizing neural-network pioneers and the protein-structure system AlphaFold.).