The Fermi-Pasta-Ulam (FPU) problem is named after the numerical experiments first performed by Enrico Fermi, John Pasta, and Stanislaw Ulam in the summer of 1953 on the Los Alamos MANIAC computer, one of the first electronic computers. They wanted to understand how a one-dimensional crystal evolves toward thermal equilibrium by simulating a chain of particles coupled by spring-like forces that included quadratic and cubic interactions. It was assumed that these nonlinear terms would cause the system to "thermalize" by redistributing energy from an initial mode into many other modes. In other words, an initial mode of vibration would quickly become more or less random.

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