Question

Significance of time reversal operation in physics

Answer 1

The problem is that we don’t really understand what the violations of CP symmetry mean outside of the very specific circumstances inside a particle collider. So it’s far easier to say “laws of physics are time symmetric, except for a few weird and extremely unfamiliar cases” than to say “B mesons and neutral kaons decay slightly more in one direction that would be predicted by CP symmetry”.

I’d say that time asymmetry isn’t widely discussed because the weak force is rarely discussed. The strong force is discussed in widely popular terms like “quarks” and “gluons”; it’s has a compelling explanation in terms of the Eightfold Way. Perhaps that’s just a side effect of Murray Gell-Mann, who had a knack of making fundamental physics sound interesting.

The weak force, with its W and Z bosons and the plethora of mesons just doesn’t have the same ring. It doesn’t (directly) explain protons and electrons, the two things that people get in high school science classes. It hasn’t (yet) found its way into the popular imagination, and so it’s really hard to get traction with “particles you’ve never heard of doing things you don’t understand”.

You’d sure think that “a possible explanation to the origin of matter over antimatter, and maybe the universe itself” would be a pretty compelling story to tell… but right now, that’s about as far as the story goes. I do think that the weak force deserves to be a lot better known, but right now there’s just no good story to tell outside of the physics community. CP symmetry breaking is an incredible hint, but just a hint.

In studies of the Standard Model, I assure you that CP symmetry (and its equivalent, T symmetry) are fundamental elements that come up all the time. The Standard Model is, however, really only relevant to particle physics, and simply isn’t useful in physics textbooks until a level much further than most people ever get. It’s got a certain amount of traction in the popular imagination, but it’s completely opaque to me what parts of physics will stir people’s interest and which won’t.