Construct · 1 fields · 3 citations

fine-structure constant: a standalone construct

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● anchor · a standalone constant Nearest construct by meaningRydberg constantcompare the meanings
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fine-structureconstant1 CONSTRUCTFine-structure αSOMMERFELD · 1/137

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Physics

The dimensionless constant setting the strength of the electromagnetic interaction

Arnold Sommerfeld introduced the fine-structure constant in 1916, in his relativistic extension of the Bohr model of the atom, where it first appeared as the ratio of the speed of an electron in the innermost hydrogen orbit to the speed of light and governed the small splitting, the fine structure, of atomic spectral lines. Written as the Greek letter alpha and equal to about 1/137, it is a pure number with no physical units: it combines the elementary charge, the speed of light, Planck's constant, and the electric constant into a single ratio that fixes how strongly electrically charged particles couple to light and to one another. Because it is dimensionless, its value is the same in every system of units and for every observer, which is why it serves as the standard measure of the strength of the electromagnetic interaction across atomic physics, quantum electrodynamics, and cosmology. Modern determinations, such as the atom-recoil measurement reported by Morel and colleagues in 2020 and the periodically adjusted CODATA recommended values, pin it down to better than one part in a billion, placing it among the most precisely known quantities in physics.[1][2][3]

Unit
A dimensionless (unitless) physical constant, approximately 1/137.036
Recovery means
Not applicable
Measured by
Determined from precision atom-recoil and electron magnetic-moment experiments and fixed periodically in the CODATA adjustment of the fundamental physical constants

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Nearby constructs

constant2 fields · 2 citationsjingle · one word, two constructsquantum4 fields · 7 citationsjingle · one word, four constructsRydberg constant1 fields · 4 citationsanchor · a standalone physical constant

References

  1. Sommerfeld, A. (1916). Zur Quantentheorie der Spektrallinien. Annalen der Physik, 356(17), 1–94. https://doi.org/10.1002/andp.19163561702
  2. Morel, L., Yao, Z., Cladé, P., & Guellati-Khélifa, S. (2020). Determination of the fine-structure constant with an accuracy of 81 parts per trillion. Nature, 588(7836), 61–65. https://doi.org/10.1038/s41586-020-2964-7
  3. Tiesinga, E., Mohr, P. J., Newell, D. B., & Taylor, B. N. (2021). CODATA recommended values of the fundamental physical constants: 2018. Reviews of Modern Physics, 93(2), 025010. https://doi.org/10.1103/RevModPhys.93.025010

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