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.