The Official String Theory Web Site:--> Cosmology :--> The Big Bang :--> Quark and gluon confinement

Quarks and gluons are confined

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. The Universe has now expanded and cooled to the point where something incredible happens to the quarks and gluons that are popping around at high speed by themselves. They undergo an enormous Universe-wide phase transformation where all of the quarks and gluons in the Universe become confined together inside mesons such as the pi meson and baryons such as the proton and neutron. Prior to this era, protons and neutrons and mesons don't exist, there is just a hot soup of quarks and gluons in their place.
. Actually, to be honest, particle physicists have only measured quarks and gluons that are trapped inside baryons and mesons. Nobody has ever measured a quark or a gluon zipping around freely on its own. In the theory of quarks and gluons, called Quantum Chromodynamics (QCD for short), it is believed there is a phase transition at high temperature where quarks and gluons become deconfined and can and do zip around freely by themselves.
. The details of this deconfinement transition are still not well understood, even in the theory. However, judging by the past successes of theoretical particle physics in predicting phenomena that were later observed, it's probably a safe bet to say that as the Universe cooled to a temperature below the deconfinement temperature of QCD, quarks and gluons were no longer able to zip around on their own and became confined together into the mesons and baryons that produced the Universe we see today.

How old is the Universe? // Structure of the Universe // The Big Bang // Before the Big Bang? // What about string theory?

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