# Dirac equation

The Dirac equation in natural units is : $(iD-m) \Psi =0$. In this equation, $i$ is the imaginary unit, $D$ is the Dirac operator, which describes the way the electron moves in space and time, $m$ is the rest mass of the electron, and $\Psi$ is the electron’s wavefunction, which describes the electron’s state.
There are many different ways of writing it down: above is the simplest. It is considered so important, it has been engraved onto the floor of Westminster Abbey.