According to Maxwell's electromagnetic theory, the velocity of electromagnetic waves (light) in a vacuum is a fundamental constant determined by the electric and magnetic properties of free space. The relation is given by: $c = \frac{1}{\sqrt{\mu_0 \varepsilon_0}}$ where $\mu_0$ is the permeability of free space and $\varepsilon_0$ is the permittivity of free space . This relation unites electromagnetism with optics.