Visualisation of the early universe. This image depicts particles in the quark-gluon \soup\" which existed less than one millionth of a second after the Big Bang. Quarks are shown in red, green and blue; anti-quarks are cyan magenta and yellow. Other colours are gluons. The grey particles are electrons and electroweak force bosons. Gluons are the carriers of the strong nuclear force, but at the high energy density of the universe at this time (a million billion degrees temperature), quarks would not have been confined by the force. As the universe continued to expand, and the temperature dropped, the quarks were able to combine into baryons such as protons and neutrons."