Editing Physical constant (section)

== Dimensionless physical constants ==
Any [[ratio]] between physical constants of the same dimensions results in a [[dimensionless physical constant]], for example, the [[proton-to-electron mass ratio]]. The [[fine-structure constant]] ''α'', introduced by [[Arnold Sommerfeld]], is the best known dimensionless fundamental physical constant. It is the value of the [[elementary charge]] squared expressed in [[Planck units]]. This value has become a standard example when discussing the derivability or non-derivability of physical constants.