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Summary

The fine-structure constant, commonly denoted by α (the Greek letter alpha), is a fundamental physical constant which quantifies the strength of the electromagnetic interaction between elementary charged particles. It is defined as the square of the completely screened charge, that is, the value observed at infinite distance or in the limit of zero momentum transfer.
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Summary
In physics, the fine-structure constant, also known as the Sommerfeld constant, commonly denoted by α (the Greek letter alpha), is a fundamental physical constant which quantifies the strength of the electromagnetic interaction between elementary charged particles.

Fine-structure constant - Wikipedia
wikipedia.org

Numerically, the fine-structure constant, denoted by the Greek letter α (alpha), comes very close to the ratio 1/137. It commonly appears in formulas governing light and matter. “It’s like in…

Quanta Magazine
quantamagazine.org

In fine structure …a dimensionless constant called the fine-structure constant . This constant is given by the equation α = ke 2 /hc, where k is Coulomb’s constant , e is the…

Fine-structure constant | physics | Britannica
britannica.com