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Fine-structure constant
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In physics, the fine-structure constant (usually denoted , the Greek letter alpha) is a fundamental physical constant, namely the electromagnetic coupling constant (characterizing the strength of the electromagnetic interaction.) The numerical value of is the same in all systems of units, because is a dimensionless quantity. Arnold Sommerfeld introduced the fine-structure constant in 1916.
Contents
Definition
Three equivalent definitions of in terms of other fundamental physical constants are
where
- is the elementary charge;
- is the reduced Planck constant;
- is the speed of light in vacuum;
- is the electric constant or permittivity of free space;
- is the magnetic constant or permeability of free space;
- is the Coulomb constant.
The 2014 CODATA recommended value for α is:
Fine structure constant
The current estimate of the fine-structure constant is
- (A003673).
Reciprocal of the fine structure constant
The current estimate of reciprocal of the fine-structure constant is
- (A005600)
with continued fraction
- (A082726).
See also
- A003673 Current estimate of decimal expansion of fine-structure constant alpha.
- A005600 Current estimate of decimal expansion of reciprocal of fine-structure constant alpha.
- A082726 Continued fraction expansion of current estimate for reciprocal of fine-structure constant alpha.
Notes
External links
- Quotes about the Fine Structure Constant
- James G. Gilson, Fine Structure Constant.
- The NIST Reference on Constants, Units, and Uncertainty, [1], 2014.