Today a colleague and I had a heated debate over whether, when an external electric field is applied across a dielectric, the molecules in the dielectric actually move/rotate (flip to align with the electric field) in any way or whether they stay fixed in place and only the electron density is redistributed.
I believe I remember being taught in school that polar molecules will align themselves with the electric field, and that the rotational inertia (or maybe friction?) of the molecules is what causes the dielectric to "slowly" become polarized over time, with some time constant.
My colleague however completely refuted that idea, saying that the molecules don't actually move it is only the electron density that is redistributed.
The "molecules-flipping" explanation seems very much based on classical-mechanics and so I wouldn't be surprised if quantum-mechanics has something else to say about this.
If my old school-explanation is correct (I.e. that polar molecules flip to align with the electric field) then does that also happen when the dielectric is a single crystalline solid? or when the dielectric is a polycrystalline?
I am sure that the answer is out there but I wasn't able to find it, perhaps because I don't know the right words to search for. Sorry for wasting your time if this is a stupid question, but I appreciate any answers that can further my understanding.