In 1926/ 1927 Heisenberg worked with Niels Bohr at the University of Copenhagen. In February 1927, while Bohr was on extended skiing holidays, he invented the uncertainty principle and published the paper “Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik”—“On the Visualizable Contents of the Quantum-theoretical Kinematics and Mechanics”.