On the WTN / They Might Be Giants / plasma thing ...
I've always been suspicious of anything being called "the fourth state of matter". I've even seen the vacuum described that way. If plasma really a distinct state in the same sense as solid liquid and vapour?
The conventional three states have definite state-like characteristics. They are distinct, and there is a transition between them at a particular temperature and pressure where any energy put in or taken out goes into the state change rather than increasing or decreasing the temperature (i.e. latent heat at the freezing or boiling points).
As far as I know, a substance does not entirely convert to plasma at a particular temperature and pressure, nor does the transition involve latent heat. If a plasma physicist out there disagrees about that I'd be happy to be corrected.
We normally think of a plasma state as happening to a gas, since the nuclei and electrons are moving about freely, only transferring energy between themselves by random collisions. But is it possible for a plasma to occur in a sort of liquid state (where particles are close enough together to slide past each other, but not so close as to be locked in place), or even a solid state (particles held in a fixed lattice, only able to vibrate around their current positions)? I'm think of places like deep in the sun (for liquid) or certain types of white dwarf or "diamond star" (very hot solid carbon).
If anything can be called a fourth state it's probably a supercritical fluid (i.e. a permanent gas rather than a condensible vapour). At least that occurs at specific temperatures and pressures, and it is distinct from solid, liquid and vapour in that the definitions of the states don't overlap.