The following glossary includes terms that are used in Student Text, Epoch Two in our Evolving Universe.

Anti-quarks ('an-ti-'kwork)
Anti-matter particles that have the same mass as quarks but have opposite and equal electric charges.

X particles ('eks 'pär-ti-k&ls)
The theoretical particles that are thought to have decayed into quarks and anti-quarks during the Second Epoch.

Big Bang ('big 'ba[ng])
A scientific model that predicts that the origin of the universe was a very hot, very dense plasma.