Posted: Jan 19, 2018 11:25 am
On the question of conservation laws and symmetries, it is true that, in particle physics, there is only conservation when there is symmetry, but no particle events have been shown to be irrreversible. Unfortunately, it is usually entirely impractical to experimentally examine such things as particle decays in reverse, because of the requirememt to converge specific combinations of particles. Irreversibility occurs in bulk physics, but this is because of heat generation. Heat (and temperature and entropy) is a phenomenon restricted to bulk physics, as oppsed to particle physcis.