Maxwell's equations in a vacuum describe a wave propagating at speed \(c\) as the interaction of electric field \(E\) and magnetic field \(B\): \(\nabla \cdot E = 0\), \(\nabla \times E = -\frac{\partial B}{\partial t}\), \(\nabla \cdot B = 0\), \(\nabla \times B = \frac{1}{c^2} \frac{\partial E}{\partial t}\).
![SearchOnMath](https://cdn-ak-scissors.b.st-hatena.com/image/square/3839a5cc22b601dc8737587514bdbf9f8d932086/height=288;version=1;width=512/https%3A%2F%2Fwww.searchonmath.com%2Fmeta-images%2Ffacebook-card.png)