Fermi–Pasta–Ulam–Tsingou RecurrencePluck a string that is a chain of beads on springs, but make the springs very slightly stiffer when stretched. Common sense says the energy will scatter into all the higher notes and blur into heat. Instead it sloshs between a few low notes and then — astonishingly — almost all of it flows back into the original pluck.Fermi, Pasta, Ulam and Mary Tsingou ran this on the MANIAC computer in 1953, expecting thermalisation. The near-perfect return launched the study of solitons and chaos: weak nonlinearity does not always mix.