5.1. Recipes for the glue

We could imagine a state of matter in which a large number of quarks would find themselves at mean distances smaller than one fermi. This state would take the aspect of a quark sea where the individual particles would not be perpetually confined to the same (one or two) neighbours - as in a pion or in a nucleon - and where the gluons would be exchanged between a large number of quarks. Such a state is often called a glue.

How could we prepare such a glue? There are several possibilities. We could simply compress ordinary matter to densities larger than the nuclear density (density of matter in a nucleus; 3 × 10¹⁴ g/cm³). Then the nucleons start interpenetrating each other and the average distance between the quarks becomes less than one fermi. Or we could generate a very hot medium, where pairs of quarks and antiquarks would coexist and be numerous enough to find themselves at mean distances less than one fermi. Remembering that the population of relativistic particles in a heat bath (M < kT) increases with the cube of the temperature, one computes that the corresponding temperature should be of the order of several hundred MeV.