Taking ħ (the Planck constant divided by 2π), c (the speed of light), and e = ⁠ q e / 4π ε 0 ⁠ (the electromagnetic coupling constant i.e. a measure of the strength of the electromagnetic force (where q e is the absolute value of the electronic charge and ε ε 0 is the vacuum permittivity)) we can form a dimensionless quantity called the fine-structure constant : α α = e 2 ℏ ℏ c = q e 2 4 π π ε ε 0 ℏ ℏ c ≈ ≈ 1 137