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fine structure constant

The fine structure constant measures the strength of the electromagnetic force that controls how charged elementary particles (such as electrons and photons) interact. Because the constant is nearly equal to 1/137, and because it is a dimensionless constant, some scientists have been led to wonder whether it has mathematical significance of its own, such as pi, the ratio of a circle's circumference to its diameter.

The fine structure constant can be derived from other constants as follows:

 = e2 (2ohc)-1

where e is the elementary charge, o is the permittivity of free space, h is Planck's constant, and c is the speed of light. The constant is also equal to the ratio of the velocity v1 of the electron in the hydrogen atom to c, the speed of light.

This was last updated in May 2008

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