Wilczek again - at his best. I'm up to time-reversal symmetry ("T"), which works for Newton but not for the second law of thermodynamics. Wilczek is looking at K mesons.
A meson is an even number of quarks together; as opposed to the classic triple-threat of a nucleon. The mesons are rare in nature, and nowhere on Earth naturally. The K meson has a strange quark and is the lightest such hadron possible. It's unstable of course; it decays.
Anyway in 1964 James Cronin and, er, cronies found that the K meson decay follows an Arrow Of Time, as Discover put it as decade later. Apparently (I have no real clue how) the Standard Model will allow for this if there be quarks beyond strange (and charm). But, no more than that. Thus the bottom and top quarks were "born", posited anyway; which then got found during the 1990s.
Wilczek cites Helen Quinn that T-asymmetry depends on a quantum field which tends to zero over time. Lower field, T becomes more symmetric. Or so I read him.
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