The theory of rotational Brownian motion allows one to calculate the net result of these two competing effects, and to predict how the permittivity of a dielectric material depends on the strength and frequency of the imposed electric field.
Rotational Brownian motion was first discussed by Peter Debye,[1] who applied Albert Einstein's theory of translational Brownian motion to the rotation of molecules having permanent electric dipoles.
Debye ignored inertial effects and assumed that the molecules were spherical, with an intrinsic, fixed dipole moment.
This is not observed; instead, the absorption tends toward a maximum and then declines with increasing frequency.
These are computationally very difficult problems and rotational Brownian motion is a topic of much current research interest.