Heisenberg Submits Matrix Mechanics Paper

Working in isolation on the North Sea island of Helgoland to escape hay fever, Werner Heisenberg develops a new quantum mechanics based purely on observable quantities (transition frequencies and intensities), abandoning unobservable electron orbits. His paper 'Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen' — submitted July 29, 1925 — marks the birth of modern quantum mechanics.