QED [quantum electrodynamics] reduces ... "all of chemistry and most of physics," to one basic interaction, the fundamental coupling of a photon to electric charge. The strength of this coupling remains, however, as a pure number, the so-called fine-structure constant, which is a parameter of QED that QED itself is powerless to predict.
Frank Wilczek, Longing for the Harmonies: Themes and Variations from Modern Physics
fine-structure-constant, physics, quantum-physics