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A Greek alpha for a pure number near one over one hundred and thirty-seven.
Also known as: Alpha constant, Sommerfeld constant
The fine-structure constant is a pure number, about one part in one hundred and thirty-seven, measuring the strength of the electromagnetic interaction. Being dimensionless it has the same value in every system of units, which is why it is one of the few constants a physicist quotes as a number rather than as a measurement.
Denotes the dimensionless coupling constant of electromagnetism, approximately one divided by one hundred and thirty-seven.
Contexts: Laboratory
Has no units, so its value is the same in every system of measurement, which makes it a genuine property of nature rather than of a measuring convention.
Contexts: Laboratory
A lowercase Greek letter of a single looping stroke crossing itself once.