In physics, the fine-structure constant, also known as the Sommerfeld constant, commonly denoted by α, is a fundamental physical constant which quantifies the strength of the electromagnetic interaction between elementary charged particles.

Arnold Johannes Wilhelm Sommerfeld, was a German theoretical physicist who pioneered developments in atomic and quantum physics, and also educated and mentored many students for the new era of theoretical physics. He served as doctoral supervisor and postdoc supervisor to seven Nobel Prize winners and supervised at least 30 other famous physicists and chemists. Only J. J. Thomson's record of mentorship offers a comparable list of high-achieving students.