Editing Atom (section)

==== Exotic matter ====
{{Main|1=Exotic matter}}

Each particle of matter has a corresponding [[antimatter]] particle with the opposite electrical charge. Thus, the [[positron]] is a positively charged [[antielectron]] and the [[antiproton]] is a negatively charged equivalent of a [[proton]]. When a matter and corresponding antimatter particle meet, they annihilate each other. Because of this, along with an imbalance between the number of matter and antimatter particles, the latter are rare in the universe. The first causes of this imbalance are not yet fully understood, although theories of [[baryogenesis]] may offer an explanation. As a result, no antimatter atoms have been discovered in nature.<ref name=koppes1999 /><ref name=cromie20010816 /> In 1996, the antimatter counterpart of the hydrogen atom ([[antihydrogen]]) was synthesized at the [[CERN]] laboratory in [[Geneva]].<ref name=nature419_6906_439 /><ref name=BBC20021030 />

Other [[exotic atom]]s have been created by replacing one of the protons, neutrons or electrons with other particles that have the same charge. For example, an electron can be replaced by a more massive [[muon]], forming a [[muonic atom]]. These types of atoms can be used to test fundamental predictions of physics.<ref name=ns1728_77 /><ref name=psT112_1_20 /><ref name=ripin1998 />