Aleksandr Lyapunov

Aleksandr Mikhailovich Lyapunov was born in Yaroslavl in 1857 and grew up in a family of mathematicians and astronomers. At St. Petersburg University he became the closest student of Pafnuty Chebyshev, and his 1892 doctoral thesis — The General Problem of the Stability of Motion — created a discipline.

Before Lyapunov, 'stability' had meant different things to different mechanicians; after him it meant one thing, defined rigorously by what is now called a Lyapunov function, and the exponential rate at which nearby trajectories separated could be made a precise numerical quantity, the Lyapunov exponent. He worked mostly on the shapes of rotating equilibrium figures of fluids, an old problem of Newton's that connects to the structure of stars and planets, and he extended probability theory with a sharp version of the central limit theorem.

He taught in Kharkov and St. Petersburg, was elected to the Academy of Sciences in 1901, and lived the quiet life of a nineteenth-century Russian professor. The Russian Civil War found him living in Odessa in 1918. When his wife died of tuberculosis in October of that year, he shot himself that same day; he lingered three more days before dying. His mathematics has outlived two empires and one superpower.