The S matrix of e--e scattering has the structure of a projection operator
that projects incoming separable product states onto entangled two-electron
states. In this projection operator the empirical value of the fine-structure
constant alpha acts as a normalization factor. When the structure of the
two-particle state space is known, a theoretical value of the normalization
factor can be calculated. For an irreducible two-particle representation of the
Poincare group, the calculated normalization factor matches Wyler's
semi-empirical formula for the fine-structure constant alpha. The empirical
value of alpha, therefore, provides experimental evidence that the state space
of two interacting electrons belongs to an irreducible two-particle
representation of the Poincare group.Comment: 12 pages, minor change