Full Idea
The laws of nature are time-reversal invariant, with the small exception of the kaon (a type of sub-atomic particle)
Gist of Idea
The kaon does not seem to be time-reversal invariant, unlike the rest of nature
Source
Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 5.3.2)
Book Reference
Baron,S/Miller,K: 'Introduction to the Philosophy of Time' [Polity 2019], p.132
A Reaction
If that fact about the kaon were very secure indeed, then that would mean the collapse of the claims about the time-invariance of the laws. Since time-invariance is still routinely asserted, I assume it is not secure.