Universe Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! ==== Hadrons ==== {{Main|Hadron}} A hadron is a [[composite particle]] made of [[quark]]s [[bound state|held together]] by the [[strong force]]. Hadrons are categorized into two families: [[baryon]]s (such as [[proton]]s and [[neutron]]s) made of three quarks, and [[meson]]s (such as [[pion]]s) made of one quark and one [[antiparticle|antiquark]]. Of the hadrons, protons are stable, and neutrons bound within atomic nuclei are stable. Other hadrons are unstable under ordinary conditions and are thus insignificant constituents of the modern universe.<ref name=Allday2002/>{{rp|118–123}} From approximately 10<sup>−6</sup> seconds after the [[Big Bang]], during a period known as the [[hadron epoch]], the temperature of the universe had fallen sufficiently to allow quarks to bind together into hadrons, and the mass of the universe was dominated by [[hadron]]s. Initially, the temperature was high enough to allow the formation of hadron–anti-hadron pairs, which kept matter and antimatter in [[thermal equilibrium]]. However, as the temperature of the universe continued to fall, hadron–anti-hadron pairs were no longer produced. Most of the hadrons and anti-hadrons were then eliminated in particle–antiparticle [[annihilation]] reactions, leaving a small residual of hadrons by the time the universe was about one second old.<ref name=Allday2002>{{cite book|last1=Allday|first1=Jonathan|title=Quarks, Leptons and the Big Bang|date=2002|publisher=IOP Publishing|isbn=978-0-7503-0806-9|edition=2nd}}</ref>{{rp|244–266}} Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here. You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Christianpedia:Copyrights for details). Do not submit copyrighted work without permission! Cancel Editing help (opens in new window) Discuss this page