Fine-structure constant

coupling constant for the electromagnetic interaction

The fine-structure constant, commonly denoted by α, is a dimensionless physical constant which characterizes the strength of the electromagnetic interaction between elementary charged particles. The value 1/α = 137.035999139±.000000031 has been determined by experiment.


  • We know what kind of a dance to do experimentally to measure this number very accurately, but we don't what kind of a dance to do on a computer to make this number come out—without putting it in secretly!
  • The theoretical determination of the fine structure constant is certainly the most important of the unsolved problems of modern physics. To reach it, we shall, presumably, have to pay with further revolutionary changes of the fundamental concepts of physics with a still farther digression from the concepts of the classical theories.
  • The title of my talk may seem a bit ambitious, but please note the plural “constants”. To calculate the fine structure constant, 1/137, we would need a realistic model of just about everything, and this we do not have. In this talk I want to return to the old question of what it is that determines gauge couplings in general, and try to prepare the ground for a future realistic calculation.

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