Ordinary ice turns into water at zero degrees. And matter at nuclear density, quark-gluon plasma, undergoes something similar at about 155 MeV (roughly two trillion degrees). Only here, it's not a crystal lattice that melts, but the so-called quark condensate — the vacuum sea that gives particles their mass. Above this threshold, quarks become massless but remain confined in color singlets, as if tethered by gluonic strings.
In such a hot medium, pions, the lightest composite particles, begin to swell rapidly. The reason is the Pauli principle: thermal quarks fill all the low-energy levels, leaving no room for the condensate to form. Without the condensate, the pion has nothing to lean on, and its size grows. In the limit of zero quark mass, the pion becomes infinitely large. This is not a hypothesis but a direct consequence of current algebra.
Huge pions easily collide with each other — hence the collectivity observed in experiments: particles move as a single fluid with a very small mean free path. Lattice calculations confirm that above 3T_{ch}, pion peaks in correlators disappear — likely because the particle no longer fits in the simulation box.
In the chiral limit (when the quark mass is exactly zero), the pion becomes infinitely large, yet it remains a bound state, the gluonic string does not break.
In Vernor Vinge's novel "A Fire Upon the Deep," faster-than-light communication works through "zones of thought," where the properties of space change — much like temperature switches the regimes of the QCD vacuum.