Fine structure constant α
This is a dimensionless constant, represented with the symbol α (alpha), and it relates together the electric charge, the vacuum permittivity, and the speed of light.
The equation is as follows:
The impedance of free space is Zo = 1/(εoc) = 2αh/e2, with electric constant εo (also called vacuum permittivity), the speed of light in the vacuum c, and the fine structure constant α = e2/(2εohc), with elementary charge e [coulombs], Planck constant h, and c as before. All these are generally considered physical constants, i.e. are fixed values for the universe.
One example of how this relationship may be used is as follows. Given the electric charge, and the vacuum permittivity, then the alpha equation may be used to explain why the speed of light has the value it does. The equation may be rearranged into other equivalent forms.
What is the physical meaning of the fine structure constant?
This is a more difficult question, especially when coupled with the question, Why does alpha take the value it does? This is something of a mystery.
We believe we can answer some parts of this question. In a recent paper of the Cordus theory it has been proposed that both the vacuum permittivity and the speed of light are dependent variables, and situationally specific. It is proposed that εo represents the density of the discrete forces in the fabric, and thus depends on the spatial distribution of mass within the universe. Thus the electric constant is recast as an emergent property of the fabric, and hence of matter.
From this perspective α is a measure of the transmission efficacy of the fabric, i.e. it determines the relationship between the electric constant of the vacuum fabric, and the speed of propagation c through the fabric.
This is consistent with the observation that α appears wherever electrical forces and propagation of fields occur, and this includes cases such as electron bonding.
The reason the speed of light is limited to a certain finite value is explained by this theory as a consequence of the fabric density creating a temporal impedance. Thus denser fabric results in a slower speed of light, and this is consistent with time dilation, and optical refraction generally. In the Cordus theory the speed of light in turn is determined by the density of the fabric discrete forces and is therefore locally consistent and relativistic, but ultimately dependent on the past history of matter density in the locally available universe. Thus the vacuum (fabric) has a finite speed of light, despite an instantaneous communication across the fibril of the particule. This Cordus theory is consistent with the known impedance of free space though comes at it from a novel direction.
The implications are the electric constant of free space is not actually constant, but rather depends on the fabric density, hence on the spatial distribution of matter. The fabric density also determines the speed of light in the situation, and α is the factor that relates the two for this universe. It would appear to be a factor set at genesis of the universe.
Pons, D. J. (2015). Inner process of Photon emission and absorption. Applied Physics Research, 7(4 ), 14-26. doi:http://dx.doi.org/10.5539/apr.v7n4p24