Is Light Matter?

[Ziggurat]

Is the Sun the best analogy for the quark-gluon plasma? I tend to think of a neutron star as one atom. Did the quark-gluon plasma of the nascent universe have a lot of unoccupied states or few? (it's still mostly semantics though)

Best analogy? Maybe not. But it's closer than a neutron star, because there would indeed have been lots of unoccupied states. It wouldn't have been close to a degenerate fermi liquid.

Of course, neutron stars aren't expected to completely fit the one-atom picture either. At the surface, there isn't enough pressure to bind lone neutrons together, so the crust is probably made of ordinary matter. If you were to strip the crust, the exposed top layer of neutrons would decay into protons and electrons (since it would no longer have sufficient pressure to bind it together), and form a new ordinary-matter crust.