Editing Arrow of time (section)

=== Particle physics (weak) arrow of time ===
{{Main|CP violation}}
Certain subatomic interactions involving the [[weak nuclear force]] violate the conservation of both [[Parity (physics)|parity]] and [[charge conjugation]], but only very rarely. An example is the [[kaon]] [[Particle decay|decay]].<ref>{{cite web|url=https://physicsworld.com/p/|title=Home|website=Physics World|date=11 March 2008}}</ref> According to the [[CPT symmetry|CPT theorem]], this means they should also be time-irreversible, and so establish an arrow of time. Such processes should be responsible for [[Baryogenesis|matter creation]] in the early universe.

That the combination of parity and charge conjugation is broken so rarely means that this arrow only "barely" points in one direction, setting it apart from the other arrows whose direction is much more obvious. This arrow had not been linked to any large-scale temporal behaviour until the work of [[Joan Vaccaro]], who showed that T violation could be responsible for conservation laws and dynamics.<ref>{{Cite journal|last=Vaccaro|first=Joan|date=2016|title=Quantum asymmetry between time and space|journal=Proceedings of the Royal Society A|doi=10.1098/rspa.2015.0670|pmid=26997899|pmc=4786044|volume=472|issue=2185|pages=20150670|arxiv = 1502.04012 |bibcode = 2016RSPSA.47250670V }}</ref>