Arnold Sommerfeld

Arnold Johannes Wilhelm Sommerfeld was born on 5 December 1868 in Germany and trained a generation that rewrote physics. He introduced the second quantum number (azimuthal) and the third (magnetic), filling in the architecture of the atom that Bohr had sketched. He gave the world the fine-structure constant and pioneered X-ray wave theory. As doctoral or postdoctoral advisor, he guided seven future Nobel laureates and at least 30 other physicists and chemists who became famous in their own right. He died on 26 April 1951, the teacher who made the revolution possible.