Fine-structure constant

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The fine-structure constant α determines the strength of the electromagnetic interaction. The value is

This fundamental physical constant is dimensionless and has the same value in all units systems

where

    e Elementary charge

    ℏ Reduced Planck constant

    c Speed of light

    ε₀ Vacuum permittivity

The fine-structure constant was introduced by the German physicist Arnold Sommerfeld in 1916.